Sample records for regional angular unconformity
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Blodgett, Robert B.; Sralla, Bryan
2008-01-01
A major angular unconformity separates carbonates and shales of the Upper Triassic Kamishak Formation from an underlying unnamed sequence of Permian agglomerate, volcaniclastic rocks (sandstone), and limestone near Puale Bay on the Alaska Peninsula. For the first time, we photographically document the angular unconformity in outcrop, as clearly exposed in a seacliff ~1.3 mi (2.1 km) west of Cape Kekurnoi in the Karluk C?4 and C?5 1:63,360-scale quadrangles. This unconformity is also documented by examination of core chips, ditch cuttings, and (or) open-hole electrical logs in two deep oil-and-gas-exploration wells (Humble Oil & Refining Co.?s Bear Creek No. 1 and Standard Oil Co. of California?s Grammer No. 1) drilled along the Alaska Peninsula southwest of Puale Bay. A third well (Richfield Oil Corp.?s Wide Bay Unit No. 1), south of and structurally on trend with the other two wells, probed deeply into the Paleozoic basement, but Triassic strata are absent, owing to either a major unconformity or a large fault. Here we briefly review current and newly acquired data on Permian and Triassic rocks of the Puale Bay-Becharof Lake-Wide Bay area on the basis of an examination of surface and subsurface materials. The resulting reinterpretation of the Permian and Triassic stratigraphy has important economic ramifications for oil and gas exploration on the Alaska Peninsula and in the Cook Inlet basin. We also present a history of petroleum exploration targeting Upper Triassic reservoirs in the region.
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Cambrian Sauk transgression in the Grand Canyon region redefined by detrital zircons
NASA Astrophysics Data System (ADS)
Karlstrom, Karl; Hagadorn, James; Gehrels, George; Matthews, William; Schmitz, Mark; Madronich, Lauren; Mulder, Jacob; Pecha, Mark; Giesler, Dominique; Crossey, Laura
2018-06-01
The Sauk transgression was one of the most dramatic global marine transgressions in Earth history. It is recorded by deposition of predominantly Cambrian non-marine to shallow marine sheet sandstones unconformably above basement rocks far into the interiors of many continents. Here we use dating of detrital zircons sampled from above and below the Great Unconformity in the Grand Canyon region to bracket the timing of the Sauk transgression at this classic location. We find that the Sixtymile Formation, long considered a Precambrian unit beneath the Great Unconformity, has maximum depositional ages that get younger up-section from 527 to 509 million years old. The unit contains angular unconformities and soft-sediment deformation that record a previously unknown period of intracratonic faulting and epeirogeny spanning four Cambrian stages. The overlying Tapeats Sandstone has youngest detrital zircon ages of 505 to 501 million years old. When linked to calibrated trilobite zone ages of greater than 500 million years old, these age constraints show that the marine transgression across a greater than 300-km-wide cratonic region took place during an interval 505 to 500 million years ago—more recently and more rapidly than previously thought. We redefine this onlap as the main Sauk transgression in the region. Mechanisms for this rapid flooding of the continent include thermal subsidence following the final breakup of Rodinia, combined with abrupt global eustatic changes driven by climate and/or mantle buoyancy modifications.
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Paleozoic and Mesozoic deformations in the central Sierra Nevada, California
Nokleberg, Warren J.; Kistler, Ronald Wayne
1980-01-01
Analysis of structural and stratigraphic data indicates that several periods of regional deformation, consisting of combined folding, faulting, cataclasis, and regional metamorphism, occurred throughout the central Sierra Nevada during Paleozoic and Mesozoic time. The oldest regional deformation occurred alono northward trends during the Devonian and Mississippian periods in most roof pendants containing lower Paleozoic metasedimentary rocks at the center and along the crest of the range. This deformation is expressed in some roof pendants by an angular unconformity separating older thrice-deformed from younger twice-deformed Paleozoic metasedimentary rocks. The first Mesozoic deformation, which consisted of uplift and erosion and was accompanied by the onset of Andean-type volcanism during the Permian and Triassic, is expressed by an angular unconformity in several roof pendants from the Saddlebag Lake to the Mount Morrison areas. This unconformity is defined by Permian and Triassic andesitic to rhyolitic metavolcanic rocks unconformably overlying more intensely deformed Pennsylvanian, Permian(?), and older metasedimentary rocks. A later regional deformation occurred during the Triassic along N. 20?_30? W. trends in Permian and Triassic metavolcanic rocks of the Saddlebag Lake and Mount Dana roof pendants, in upper Paleozoic rocks of the Pine Creek roof pendant, and in the Calaveras Formation of the western metamorphic belt; the roof pendants are crosscut by Upper Triassic granitic rocks of the Lee Vining intrusive epoch. A still later period of Early and Middle Jurassic regional deformation occurred along N. 30?-60? E. trends in upper Paleozoic rocks of the Calaveras Formation of the western metamorphic belt. A further period of deformation was the Late Jurassic Nevadan orogeny, which occurred along N. 20?_40? W. trends in Upper Jurassic rocks of the western metamorphic belt that are crosscut by Upper Jurassic granitic rocks of the Yosemite intrusive epoch. Structures of similar age occur in intensely deformed oceanic-lithospheric and syntectonic plutonic rocks of the lower Kings River area, in Jurassic metavolcanic rocks of the Ritter Range roof pendant, and in Triassic metasedimentary rocks of the Mineral King roof pendant. The final Mesozoic deformation occurred along N. 50?-80? W. trends in both high-country roof pendants and the lower Kings River area; structures of this generation are crosscut by relatively undeformed Upper Cretaceous granitic rocks of the Cathedral Range intrusive epoch.
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Nature and significance of Austin-Taylor unconformity on western margin of east Texas basin
DOE Office of Scientific and Technical Information (OSTI.GOV)
Surles, M.A. Jr.
1984-04-01
The Taylor Marl unconformably overlies the Austin Chalk on the western margin of the East Texas basin. Along this contact, up to 275 ft (84 m) of upper Austin is missing in the Waco area and up to 450 ft (137 m) in Bell County. However, the Austin Chalk appears to have been more-or-less uniformly deposited throughout the study area. Apparently regional uplift caused a regression that terminated Austin deposition and was related to the erosion of the upper Chalk. While the unconformity is areally extensive, slightly angular, and accounts for a relatively long period of time, the mechanism ofmore » erosion that caused the unconformity is still uncertain. Erosion was terminated by the deposition of the lower Taylor Marl. Taylor A, the lowermost subdivision of the lower Taylor, was deposited in a near-shore environment that was highly variable. Of particular interest is the relationship of this unconformity to structure and probably to oil occurrence in the Austin Chalk in McLennan and Falls Counties. Major Austin fracturing, which apparently does not extend into the Taylor in Falls County, clearly indicates that structure in the Chalk, at least in part, antedates Taylor deposition. Oil occurrence in the Chalk is clearly related to fracturing and probably is localized by post-Austin-pre-Taylor fracture systems.« less
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Regional stratigraphic framework of the Lisburne Group of ANWR
DOE Office of Scientific and Technical Information (OSTI.GOV)
Watts, K.F.; Carlson, R.C.; Harris, A.G.
1995-05-01
The Carboniferous Lisburne Group, a major carbonate platform succession, is widely exposed in the Brooks Range and forms an extensive hydrocarbon target in the subsurface of the North Slope of Alaska. Gradationally beneath carbonates of the Lisburne Group, terrigenous sediments of the Mississippian Endicott Group (conglomerate and sandstone of the Kekiktuk Formation overlain by the Kayak Shale) were derived from local and northern (Ellesmerian) source areas. Locally, at the Endicott-Lisburne transition, sandy limestones of the Itkilyariak Formation record another phase of siliciclastic influx that lies above and/or is a lateral equivalent of the Kayak Shale and Lisburne Group in areasmore » adjacent to paleotopographic highs. This siliciclastic to carbonate transition represents a major transgressive succession that onlaps northward over the sub-Mississippian unconformity, a regional angular unconformity and sequence boundary in northern Alaska. The age and nature of onlap depend upon the paleotopography of the underlying sub-Mississippian rocks and regional passive margin subsidence. The Lisburne Group is a thick succession of carbonate rocks subdivided into the Alapah Limestone and overlying Wahoo Limestone, both having informal members.« less
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Houseknecht, David W.; Craddock, William H.; Lease, Richard O.
2016-02-12
Shallow cores collected in the 1980s on the Chukchi Shelf of western Arctic Alaska sampled pre-Cenozoic strata whose presence, age, and character are poorly known across the region. Five cores from the Herald Arch foreland contain Cenomanian to Coniacian strata, as documented by biostratigraphy, geochronology, and thermochronology. Shallow seismic reflection data collected during the 1970s and 1980s show that these Upper Cretaceous strata are truncated near the seafloor by subtle angular unconformities, including the Paleogene mid-Brookian unconformity in one core and the Pliocene-Pleistocene unconformity in four cores. Sedimentary structures and lithofacies suggest that Upper Cretaceous strata were deposited in a low accommodation setting that ranged from low-lying coastal plain (nonmarine) to muddy, shallow-marine environments near shore. These observations, together with sparse evidence from the adjacent western North Slope, suggest that Upper Cretaceous strata likely were deposited across all of Arctic Alaska.A sixth core from the Herald Arch contains lower Toarcian marine strata, indicated by biostratigraphy, truncated by a Neogene or younger unconformity. These Lower Jurassic strata evidently were deposited south of the arch, buried structurally to high levels of thermal maturity during the Early Cretaceous, and uplifted on the Herald thrust-fault system during the mid to Late Cretaceous. These interpretations are based on regional stratigraphy and apatite fission-track data reported in a complementary report and are corroborated by the presence of recycled palynomorphs of Early Jurassic age and high thermal maturity found in Upper Cretaceous strata in two of the foreland cores. This dataset provides evidence that uplift and exhumation of the Herald thrust belt provided sediment to the foreland during the Late Cretaceous.
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Pennsylvanian-Permian tectonism in the Great Basin: The Dry Mountain trough and related basins
DOE Office of Scientific and Technical Information (OSTI.GOV)
Snyder, W.S.; Spinosa, C.; Gallegos, D.M.
1991-02-01
Pennsylvanian-Permian tectonism affected the continental margin of western North America from the Yukon to the Mojave Desert. Specific signatures of this tectonism include local angular unconformities, regional disconformities, renewed outpouring of clastic debris from a reactivated Antler and related highlands, and development of deeper water basins with anoxic sediments deposited below wave base. The basins formed include Ishbel trough (Canada), the Wood River basin (Idaho), Cassia basin, Ferguson trough, Dry Mountain trough (all Nevada), and unnamed basins in Death Valley-Mojave Desert region. The Dry Mountain trough (DMT) was initiated during early Wolfcampian and received up to 1,200 m of sedimentmore » by the late Leonardian. The lower contact is a regional unconformity with the Ely Limestone, or locally with the Diamond Peak or Vinini formations. Thus, following a period of localized regional uplift that destroyed the Ely basin, portions of the uplifted and exposed shelf subsided creating the Dry Mountain trough. Evidence suggesting a tectonic origin for the DMT includes (1) high subsidence rates (60-140 m/m.y.); (2) renewed influx of coarse clastic debris from the Antler highlands: (3) possible pre-Early Permian folding, thrusting, and tilting within the highlands; and (4) differential subsidence within the Dry Mountain trough, suggesting the existence of independent fault blocks.« less
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NASA Astrophysics Data System (ADS)
McNabb, James C.; Dorsey, Rebecca J.; Housen, Bernard A.; Dimitroff, Cassidy W.; Messé, Graham T.
2017-11-01
A thick section of Pliocene-Pleistocene nonmarine sedimentary rocks exposed in the Mecca Hills, California, provides a record of fault-zone evolution along the Coachella Valley segment of the San Andreas fault (SAF). Geologic mapping, measured sections, detailed sedimentology, and paleomagnetic data document a 3-5 Myr history of deformation and sedimentation in this area. SW-side down offset on the Painted Canyon fault (PCF) starting 3.7 Ma resulted in deposition of the Mecca Conglomerate southwest of the fault. The lower member of the Palm Spring Formation accumulated across the PCF from 3.0 to 2.6 Ma during regional subsidence. SW-side up slip on the PCF and related transpressive deformation from 2.6 to 2.3 Ma created a time-transgressive angular unconformity between the lower and upper members of the Palm Spring Formation. The upper member accumulated in discrete fault-bounded depocenters until initiation of modern deformation, uplift, and basin inversion starting at 0.7 Ma. Some spatially restricted deposits can be attributed to the evolution of fault-zone geometric complexities. However, the deformation events at ca. 2.6 Ma and 0.7 Ma are recorded regionally along 80 km of the SAF through Coachella Valley, covering an area much larger than mapped fault-zone irregularities, and thus require regional explanations. We therefore conclude that late Cenozoic deformation and sedimentation along the SAF in Coachella Valley has been controlled by a combination of regional tectonic drivers and local deformation due to dextral slip through fault-zone complexities. We further propose a kinematic link between the 2.6-2.3 Ma angular unconformity and a previously documented but poorly dated reorganization of plate-boundary faults in the northern Gulf of California at 3.3-2.0 Ma. This analysis highlights the potential for high-precision chronologies in deformed terrestrial deposits to provide improved understanding of local- to regional-scale structural controls on basin formation and deformation along an active transform margin.
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NASA Astrophysics Data System (ADS)
Carpentier, Cédric; Hadouth, Suhail; Bouaziz, Samir; Lathuilière, Bernard; Rubino, Jean-Loup
2016-05-01
Aims of this paper are to propose a geodynamic and sequential framework for the late Triassic and early Jurassic of and south Tunisia and to evidence the impact of local tectonics on the stratigraphic architecture. Facies of the Upper Triassic to Lower Jurassic of Southern Tunisia have been interpreted in terms of depositional environments. A sequential framework and correlation schemes are proposed for outcrops and subsurface transects. Nineteen middle frequency sequences inserted in three and a half low frequency transgression/regression cycles were evidenced. Despite some datation uncertainties and the unknown durations of Lower Jurassic cycles, middle frequency sequences appear to be controlled by eustasy. In contrast the tectonics acted as an important control on low frequency cycles. The Carnian flooding was certainly favored by the last stages of a rifting episode which started during the Permian. The regression accompanied by the formation of stacked angular unconformities and the deposition of lowstand deposits during the late Carnian and Norian occured during the uplift and tilting of the northern basin margins. The transpressional activity of the Jeffara fault system generated the uplift of the Tebaga of Medenine high from the late Carnian and led to the Rhaetian regional angular Sidi Stout Unconformity. Facies analysis and well-log correlations permitted to evidence that Rhaetian to Lower Jurassic Messaoudi dolomites correspond to brecciated dolomites present on the Sidi Stout unconformity in the North Dahar area. The Early-cimmerian compressional event is a possible origin for the global uplift of the northern African margin and Western Europe during the late Carnian and the Norian. During the Rhaetian and the early Jurassic a new episode of normal faulting occured during the third low frequency flooding. This tectonosedimentary evolution ranges within the general geodynamic framework of the north Gondwana margin controlled by the opening of both Neotethys and Atlantic oceans.
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NASA Astrophysics Data System (ADS)
Gulick, S. P. S.; Fernandez-Vasquez, R. A.; Frederick, B.; Saustrup, S., Sr.; Domack, E. W.; Lavoie, C.; Shevenell, A.; Blankenship, D. D.; Leventer, A.
2014-12-01
In 2014, the R/V Nathaniel B. Palmer (NBP1402) sailed to a virtually unexplored continental shelf along the Sabrina Coast, East Antarctica. The shelf contains the sedimentary record of environmental and ice volume changes within the Aurora Subglacial Basin (ASB), which is presently occupied by ~7 m sea level-rise equivalent of ice. We acquired 750 km of high-resolution seismic data proximal to the Reynolds Trough and Moscow University Ice Shelf glacial systems west of the Dalton Ice Tongue using dual 45/45 cu. in. G.I. guns and a 24 ch. streamer with 3.125 m groups providing a vertical resolution of ~3 m simultaneously with CHIRP data. These are the first images of this margin acquired and show a remarkable set of sequence stratigraphic transitions. Crystalline basement is at the seafloor landward and buried seaward with a transition to smoother reflection interface. Reflective sedimentary strata overlie the basement, dip seaward, and are capped by a landward-dipping regional angular unconformity. Above this are a series of transparent seismic facies that, along with the middle to outer shelf seafloor, dip landward towards a shelf-oblique glacial trough. The older, seaward-dipping strata include a deeper series of units that display at least three stratal architectures interpreted to be shelf deltas implying a pre-glacial, fluvial environment within the drainage basin. Above these sequences, the seismic facies transition to surfaces exhibiting significant erosion, small u-shaped valleys, and channel fill sequences, all of which are reminiscent of temperate glacial features. We interpret these sequences as including sub-ice tunnel valleys and grounding zone wedges with interspersed non-glacial to pro-glacial deposits. Increasing glaciogenic facies upsection suggests a gradual fluvial to glacial transition and increasing glacial extent with time. The subsequent transition to ice sheets is marked by erosion to basement landward and the angular unconformity seaward. The unconformity is overlain by glacial diamict, representing an incomplete record of cold-based glaciations after the ASB became ice-filled. Correlations with cores collected above and below the unconformity and deltaic unit should allow us to determine the ages of these transitions from fluvial to polythermal to ice sheets in East Antarctica.
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Fridrich, Christopher J.; Thompson, Ren A.
2011-01-01
The Death Valley region, of southeast California and southwest Nevada, is distinct relative to adjacent regions in its structural style and resulting topography, as well as in the timing of basin-range extension. Cenozoic basin-fill strata, ranging in age from greater than or equal to 40 to approximately 2 million years are common within mountain-range uplifts in this region. The tectonic fragmentation and local uplift of these abandoned basin-fills indicate a multistage history of basin-range tectonism. Additionally, the oldest of these strata record an earlier, pre-basin-range interval of weak extension that formed broad shallow basins that trapped sediments, without forming basin-range topography. The Cenozoic basin-fill strata record distinct stratigraphic breaks that regionally cluster into tight age ranges, constrained by well-dated interbedded volcanic units. Many of these stratigraphic breaks are long recognized formation boundaries. Most are angular unconformities that coincide with abrupt changes in depositional environment. Deposits that bound these unconformities indicate they are weakly diachronous; they span about 1 to 2 million years and generally decrease in age to the west within individual basins and regionally, across basin boundaries. Across these unconformities, major changes are found in the distribution and provenance of basin-fill strata, and in patterns of internal facies. These features indicate rapid, regionally coordinated changes in strain patterns defined by major active basin-bounding faults, coincident with step-wise migrations of the belt of active basin-range tectonism. The regionally correlative unconformities thus record short intervals of radical tectonic change, here termed "tectonic reorganizations." The intervening, longer (about 3- to 5-million-year) interval of gradual, monotonic evolution in the locus and style of tectonism are called "tectonic stages." The belt of active tectonism in the Death Valley region has abruptly stepped westward during three successive tectonic reorganizations that intervened between four stages of basin-range tectonism, the youngest of which is ongoing. These three tectonic reorganizations also intervened between four stages of volcanic activity, each of which has been distinct in the compositions of magmas erupted, in eruption rates, and in the locus of volcanic activity—which has stepped progressively westward, in close coordination with the step-wise migrations in the locus of basin-range extension. The timing of the Cenozoic tectonic reorganizations in the Death Valley region correlates closely with the documented timing of episodic reorganizations of the boundary between the Pacific and North American plates, to the west and southwest. This supports models that explain the widely distributed transtensional tectonism in southwestern North America since approximately 40 million years ago as resulting from traction imposed by the adjacent, divergent Pacific plate.
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NASA Astrophysics Data System (ADS)
Andrés-Martínez, Miguel; Pérez-Gussinyé, Marta; Armitage, John; Morgan, Jason P.
2017-04-01
Rifting is a regional process which results in thinning of the crust over hundreds of kilometres. However, basins where deposition takes place could have different subsidence histories due to local graben-bounding fault kinetics. A change in the rift dynamics often results in a displacement of the basin depocenters, with subsequent erosion of old sediments and later deposition, creating an unconformity. Unconformities of regional character are typically studied to unveil the overall rift deformation history, and major ones separating syn- and post-kinematic sediments are often associated with break-up of the continental crust. However, evolution of the basement deformation is typically challenging to study since reflection images are usually diffuse at these depths and boreholes are typically scarce, which complicates the dating of the sediments overlying the basement. Consequently, relating the deformation styles and rift evolution to unconformities is not straight forward. We use numerical models in order to approach the meaning of regional unconformities and to study the sedimentation patterns under different modes of extension. Our models solve 2D Stokes flow for rocks treated as non-Newtonian bodies, together with heat conservation equation. Viscosities and densities depend on temperatures. Elasticity and plasticity are plugged-in in the mechanical formulation. We also use strain softening to simulate faulting and shear zones. The top boundary is a free-surface so that tectonics result in topography. Additionally, we update this topography every time step using a sediment transport model, and we store information about depositional times, paleo-depths and erosional events. These models allow for the recovery of the basement deformation during rift evolution simultaneously to the recovery of sedimentation history. Here, we run models with different crustal rheologies to reproduce different extensional modes. This allows us to contrast sedimentation patterns and unconformities under variable kinetic scenarios, from regional to faulted-block scales. We find that unconformities are generally associated to a change in the locus of extension. In models with intermediate-strength crust, sequential faulting takes place, so that only one fault is active at a time and occur in the hanging wall of the previous fault, resulting in asymmetric conjugate margins. In this case a major unconformity separates syn- and post-kinematic sediments. Both syn- and post-kinematic sediments young oceanwards and the unconformity dates the time in which extension abandons the area in favour of new faults forming oceanwards. Models with weaker crusts display extension along a wide region, with overprinting of different faulting phases. Eventually, deformation localizes in a narrow region due to cooling, and crustal break-up occurs. In this case, a first set of unconformities separates different phases of faulting inside the syn-kinematic sediments, and later unconformities separate syn-kinematic and post-kinematic sediments, dating the time at which extension localizes. We also find that unconformities date the crustal break-up only when they develop in the vicinity of the break-up locus. This stresses on that terms such as syn- and post-rift sediments and break-up unconformity should be handled carefully when seismic interpretation is done, and also provides support for unconformities as rifting story-tellers.
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NASA Astrophysics Data System (ADS)
Ilhan, I.; Coakley, B.
2016-12-01
A stratigraphic framework for offshore northwest of Alaska has been developed from multi-channel seismic reflection data and direct seismic-well ties to the late 80's Crackerjack and Popcorn exploration wells along the late Cretaceous middle Brookian unconformity. This unconformity is characterized by downlap, onlap, and bi-directional onlap of the overlying upper Brookian strata in high accommodation, and erosional incision of the underlying lower Brookian strata in low accommodation. This surface links multiple basins across the southwestern Chukchi Borderland, Arctic Ocean. The lower Brookian strata are characterized by pinch out basin geometry in which parallel-continuous reflectors show north-northeasterly progressive onlap of the younger strata onto a lower Cretaceous unconformity. These strata are subdivided into Aptian-Albian and Upper Cretaceous sections along a middle Cretaceous unconformity. The north-northeasterly thinning-by-onlap is consistent across hundreds of kilometers along the southwestern Chukchi Borderland. While this suggests a south-southwesterly regional source of sediment and transport from the Early Cretaceous Arctic Alaska-Chukotka orogens, pre-Brookian clinoform strata, underlying the lower Cretaceous unconformity angularly, have been observed for the first time in southeastern margin of the Chukchi Abyssal Plain. This suggests a change in sediment source and transport direction between the pre-Brookian and the lower Brookian strata. Although the mechanism for the accommodation is not well understood, we interpret the pre-Brookian strata as passive-margin slope deposits due to the fact that we have not observed any evidence for upper crustal tectonic deformation or syn-tectonic "growth" strata in the area. Thus, this implies that depositional history of the southwestern Chukchi Borderland post-dates the accommodation. This interpretation puts a new substantial constrain on the pre-Valanginian clockwise rotation of the Chukchi Borderland away from the East Siberian continental shelf, associated with the antecedent counter-clockwise rotation of the Arctic Alaska-Chukotka microplate away from the Canadian Arctic Islands and extensional deformation of the Amerasia Basin.
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Seismic stratigraphy of the Mianwali and Bannu depressions, north-western Indus foreland basin
NASA Astrophysics Data System (ADS)
Farid, Asam; Khalid, Perveiz; Ali, Muhammad Y.; Iqbal, Muhammad Asim; Jadoon, Khan Zaib
2017-11-01
Regional seismic reflection profiles, deep exploratory wells, and outcrop data have been used to study the structure and stratigraphic architecture of the Mianwali and Bannu depressions, north-western Indus foreland basin. Synthetic seismograms have been used to identify and tie the seismic horizons to the well data. Nine mappable seismic sequences are identified within the passive and active margin sediments. In general, the Mianwali and Bannu depressions deepens towards north due to the flexure generated by the loading and southward shifting of the thrust sheets of the North-western Himalayan Fold and Thrust Belt. The seismic profiles show a classic wedge shaped foreland basin with a prominent angular unconformity which clearly differentiates the active and passive margin sediments. The onlap patterns in the Late Cretaceous sediments suggest the initial onset of foreland basin formation when the Indian Plate collided with Eurasian Plate. As the collision progressed, the lithospheric flexure caused an uplift along the flexural bulge which resulted in onlaps within the Paleocene and Eocene sequences. The tectonic activity reached to its maximum during Oligocene with the formation of a prominent unconformity, which caused extensive erosion that increases towards the flexural bulge.
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Tosdal, R.M.; Stone, P.
1994-01-01
A previously unrecognized angular unconformity divides the Jurassic and Cretaceous McCoy Mountains Formation into a lower and an upper unit in the Dome Rock Mountains and Livingston Hills of western Arizona. The intraformation unconformity in the McCoy Mountains Formation developed where rocks of the lower unit were deformed adjacent to the southern margin of the Maria fold and thrust belt. The upper unit of the formation is interpreted as a foreland-basin deposit that was shed southward from the actively rising and deforming fold and thrust belt. The apparent absence of an equivalent unconformity in the McCoy Mountains Formation in adjacent California is presumably a consequence of the observed westward divergence of the outcrop belt from the fold and thrust belt. Tectonic burial beneath the north-vergent Mule Mountains thrust system in the latest Late Cretaceous (~70 Ma) marked the end of Mesozoic contractile deformation in the area. -from Authors
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DOE Office of Scientific and Technical Information (OSTI.GOV)
Hicks, J.F.; Tauxe, L.
1992-01-01
A west-east chronostratigraphic correlation has been made of the latest Cretaceous sediments of northern Wyoming. Five sections from Jackson Hole to Red Bird have been dated magnetostratigraphically (C34N-C26R) and radiometrically (81-68 Ma), and integrated with the ammonite biostratigraphy of the Niobrara and Pierre Shale. Four major sequence surfaces have been identified in section and the time missing within the unconformities has been measured and traced laterally. These bounding unconformities define six alloformations. The lowest straddles the C34N/C33R chronic boundary and contains the Cody, Telegraph Creek and Eagle Fms. The second ranges from the mid- to upper part of C33N ofmore » C32R and contains the Claggett and Judith River/Mesaverde Fms. The third (C32R ) is the Teapot Sandstone Member of the Mesaverde Fm. The fourth extends from the lower to upper part of C32N or to mid-C31R and includes the Bearpaw Shale and Meeteetse Fm. The fifth extends from C31N to C30N or C29N and includes the Harebell and Lance Fms. The base of the uppermost alloformation has been identified within C26R in the uppermost alloformation has been identified within C26R in the lowermost Fort Union. The unconformable surfaces are angular adjacent to the Sevier Thrust Belt but form paraconformities or hiatuses in the marine units to the east. The unconformities are eustatically controlled throughout the Campanian, but become tectonically driven in the Maastrichtian with the onset of rapid foredeep subsidence in Jackson Hole, and forebulge uplift in the Bighorn and Wind River Basin region which correlates exactly to the rapid regression of the Bearpaw Sea from the area in the range of Baculites clinolobatus.« less
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Kolata, Dennis R.; Huff, W.D.; Bergstrom, Stig M.
1998-01-01
Stratal patterns of the Middle Ordovician Hagan K-bentonite complex and associated rocks show that the Black River-Trenton unconformity in the North American midcontinent formed through the complex interplay of eustasy, sediment accumulation rates, siliciclastic influx, bathymetry, seawater chemistry, and perhaps local tectonic uplift. The unconformity is diachronous and is an amalgamated surface that resulted from local late Turinian lowstand exposure followed by regional early Chatfieldian transgressive drowning and sediment starvation. The duration of the unconformity is greatest in southern Wisconsin, northern Illinois, and northern Indiana, where the Deicke and Millbrig K-bentonite Beds converge at the unconformity. On the basis of published isotopic ages for the Deicke and Millbrig beds, it is possible that in these regions erosion and non-deposition spanned a period of as much as 3.2 m.y. Two broad coeval depositional settings are recognized within the North American midcontinent during early Chatfieldian time. 1) An inner shelf, subtidal facies of fossiliferous shale (Spechts Ferry Shale Member and Ion Shale Member of the Decorah Formation) and argillaceous lime mudstone and skeletal wackestone (Guttenberg and Kings Lake Limestone Members) extended from the Canadian shield and Transcontinental arch southeastward through Minnesota, Wisconsin, Iowa, and Missouri. 2) A seaward, relatively deep subtidal, sediment-starved, middle shelf extended eastward from the Mississippi Valley region to the Taconian foreland basins in the central and southern Appalachians and southward through the pericratonic Arkoma and Black Warrior basins. In the inner shelf region, the Black River-Trenton unconformity is a composite of at least two prominent hardground omission surfaces, one at the top of the Castlewood and Carimona Limestone Members and the other at the top of the Guttenberg and Kings Lake Limestone Members, both merging to a single surface in the middle shelf region. The inner and middle shelves redeveloped later in approximately the same regions during Devonian and Mississippian time.
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NASA Astrophysics Data System (ADS)
Cipollari, Paola; Cosentino, Domenico
1995-12-01
This paper shows the results obtained from an integrated study (geology, biostratigraphy and geochemistry) carried out on the Miocene edimentary deposits in Central Italy in order to define the timing of the sedimentary basin evolution. This paper deals also with the causes of the unconformities recorded in these basins. In the Miocene deposits of the Latina Valley and the Ernici-Simbruini Mts. several unconformities which distinguish different stratigraphic sequences have been recognized (D 0, D 1, D 2 D 3 and D 4). For each unconformity a general description together with a geodynamical significance is provided. In particular, D 0 unconformity appears to be related to a regional tectonic event (Adria-Europe collision). As a consequence, the Adria lithosphere folded and the area underwent a regional erosive event. D 1, D 2 and D 3 unconformities have had a more local tectonic control since they represent the stratigraphic record of the migration of the Apennines thrust belt/foredeep system. D 1 and D 2 unconformities are related to the late Tortonian foredeep stage, whereas D 3 is linked to the early Messinian piggy-back stage. Moreover, the D 4 unconformity, which took place during the Messinian piggy-back stage, is strictly linked to the sea-level drop of the Messinian salinity crisis. In this paper the genesis and evolution of a late Tortonian foreland basin is also stressed (Latina Valley foredeep basin). Finally, taking into account sequence boundaries, nannofossil biostratigraphy and geochemistry isotopic data, a comparison with the curve of the 3rd order of the relative coastal onlap (Haq et al., 1988) has been attempted in order to distinguish the unconformities controlled either by tectonic or eustatic processes.
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NASA Astrophysics Data System (ADS)
Song, Ying; Stepashko, Andrei; Liu, Keyu; He, Qingkun; Shen, Chuanbo; Shi, Bingjie; Ren, Jianye
2018-03-01
The classic lithosphere-stretching model predicts that the post-rift evolution of extensional basin should be exclusively controlled by decaying thermal subsidence. However, the stratigraphy of the Songliao Basin in northeastern China shows that the post-rift evolution was punctuated by multiple episodes of uplift and exhumation events, commonly attributed to the response to regional tectonic events, including the far-field compression from plate margins. Three prominent tectonostratigraphic post-rift unconformities are recognized in the Late Cretaceous strata of the basin: T11, T03, and T02. The subsequent Cenozoic history is less constrained due to the incomplete record of younger deposits. In this paper, we utilize detrital apatite fission track (AFT) thermochronology to unravel the enigmatic timing and origin of post-rift unconformities. Relating the AFT results to the unconformities and other geological data, we conclude that in the post-rift stage, the basin experienced a multiepisodic tectonic evolution with four distinct cooling and exhumation events. The thermal history and age pattern document the timing of the unconformities in the Cretaceous succession: the T11 unconformity at 88-86 Ma, the T03 unconformity at 79-75 Ma, and the T02 unconformity at 65-50 Ma. A previously unrecognized Oligocene unconformity is also defined by a 32-24 Ma cooling event. Tectonically, all the cooling episodes were regional, controlled by plate boundary stresses. We propose that Pacific dynamics influenced the wider part of eastern Asia during the Late Cretaceous until Cenozoic, whereas the far-field effects of the Neo-Tethys subduction and collision processes became another tectonic driver in the later Cenozoic.
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NASA Astrophysics Data System (ADS)
Markwitz, Vanessa; Porwal, Alok; Campbell McCuaig, T.; Kreuzer, Oliver P.
2010-05-01
Uranium deposits are usually classified based on the characteristics of their host rocks and geological environments (Dahlkamp, 1993; OECD/NEA Red Book and IAEA, 2000; Cuney, 2009). The traditional unconformity-related deposit types are the most economical deposits in the world, with the highest grades amongst all uranium deposit types. In order to predict undiscovered uranium deposits, there is a need to understand the spatial association of uranium mineralization with structures and unconformities. Hydrothermal uranium deposits develop by uranium enriched fluids from source rocks, transported along permeable pathways to their depositional environment. Unconformities are not only separating competent from incompetent sequences, but provide the physico-chemical gradient in the depositional environment. They acted as important fluid flow pathways for uranium to migrate not only for surface-derived oxygenated fluids, but also for high oxidized metamorphic and magmatic fluids, dominated by their geological environment in which the unconformities occur. We have carried out comprehensive empirical spatial analyses of various types of uranium deposits in Australia, and first results indicate that there is a strong spatial correlation between unconformities and uranium deposits, not only for traditional unconformity-related deposits but also for other styles. As a start we analysed uranium deposits in Queensland and in particular Proterozoic metasomatic-related deposits in the Mount Isa Inlier and Late Carboniferous to Early Permian volcanic-hosted uranium occurrences in Georgetown and Charters Towers Regions show strong spatial associations with contemporary and older unconformities. The Georgetown Inlier in northern Queensland consists of a diverse range of rocks, including Proterozoic and early Palaeozoic metamorphic rocks and granites and late Palaeozoic volcanic rocks and related granites. Uranium-molybdenum (+/- fluorine) mineralization in the Georgetown inlier varies from strata- to structure-bound and occurs above regional unconformities. The Proterozoic basins in the Mount Isa Inlier rest unconformably on Palaeoproterozoic basement accompanied by volcanic and igneous rocks, which were deformed and metamorphosed in the Mesoproterozoic. Uranium occurrences in the Western Succession of Mount Isa are either hosted in clastic metasediments or mafic volcanics that belong to the Palaeoproterozoic Eastern Creek Volcanics. Uranium and vanadium mineralization occur in metasomatised and hematite-magnetite-carbonate alteration zones, bounded by major faults and regional unconformities. The results of this study highlight the importance of unconformities in uranium minerals systems as possible fluid pathways and/or surfaces of physico-chemical contrast that could have facilitated the precipitation of uranium, not only in classical unconformity style uranium deposits but in several other styles of uranium mineralization as well. References Cuney, M., 2009. The extreme diversity of uranium deposits. Mineralium Deposita, 44, 3-9. Dahlkamp, F. J., 1993. Uranium ore deposits. Springer, Berlin, p 460. OECD / NEA Red Book & IAEA, 2000. Uranium 1999: Resources, Production and Demand. OECD Nuclear Energy Agency and International Atomic Energy Agency, Paris.
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NASA Astrophysics Data System (ADS)
Sorlien, C. C.; Luyendyk, B. P.; Wilson, D. S.; Decesari, R. C.; Bartek, L. R.; Diebold, J. B.
2006-12-01
The extent of the West Antarctic ice sheet during mid-Cenozoic time is controversial and important to climate models. High-resolution multichannel seismic reflection data were acquired using the RVIB Palmer along the edge of the Ross Ice Shelf across the Eastern Basin of Ross Sea, in an area where calving of the ice shelf has exposed seafloor that has not been accessible to marine geophysics in several decades. A sub-basin in the far southeast corner of Ross Sea contains a succession of sediment-filled troughs, each capped by an unconformity. These troughs range between 2 and 20 km across, are 100 to 150 m-deep, with the narrower ones bounded by flat-topped ridges interpreted as moraines. We interpret the troughs interval to slightly predate 25 Ma. Reflections just 100 m below the troughs interval can be directly correlated to near DSDP270 where they underlie strata dated at ~25 Ma. A deeper stack of prograding sequences associated with a flat- topped ridge are interpreted as pre-25 Ma, possibly early Oligocene, deltas formed adjacent to the grounding line of a glacier, and the flat-topped ridge to be a moraine. The shallowest of the stack of unconformities capping the broad troughs can be projected across a basement ridge on trend with Roosevelt Island to a regional angular unconformity ("Red"), present across 70 km to deep sedimentary Eastern Basin. This unconformity represents about 1 km of missing stratigraphic section, is smooth and level, and splits into several major sequence boundaries within deep Eastern Basin. The second shallowest of these boundaries is dated about 14 Ma at DSDP-270. We interpret this unconformity to be cut by regional thick, grounded ice at depths several hundred meters below sea level. Pre-25 Ma strata show evidence of narrow erosional troughs and reflective mounds or ridges on the west flank of the basement ridge, but such features are not present in southern deep Eastern Basin near the ice shelf edge. This is evidence that the troughs were carved by glaciers issuing from distant highlands of Marie Byrd Land and not from East Antarctica. Late Oligocene through mid Miocene and younger prograding and unconformities farther north in Eastern Basin indicate grounded ice there. One possible interpretation is that "Red" was cut by thick, grounded ice that affected all of the Eastern Ross Sea paleo-shelf, while the pre-25 Ma glaciers affected only the area proximal to Marie Byrd Land. Late Oligocene glaciation on the outer shelf above deep Eastern Basin may have been sourced from East Antarctica and/or Central High. Evidence for pre-25 Ma glaciation proximal to Marie Byrd Land, combined with evidence for Oligocene ice caps at widely-separated localities of West Antarctica, allow the interpretation that portions of the West Antarctic Ice Sheet developed during Oligocene time. The broad troughs and the stack of prograding sequences may be related to dynamic ice caps and sea level falls in mid Oligocene and earliest Oligocene time. The Middle Miocene Red unconformity may be related to development of polar (cold-base) ice sheets. Oligocene glaciation implies that Marie Byrd Land and eastern Ross Sea have subsided from higher elevation due to cooling after late Cretaceous crustal thinning.
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NASA Astrophysics Data System (ADS)
Cao, R.; Knapp, J. H.
2016-12-01
Integration of new 2-D seismic reflection profile with existing wells and potential field data from southeastern Georgia, USA provide exciting discovery of a new stratigraphic unit associated with the post-rift phase of the South Georgia Rift (SGR) basins. These data document an apparent reversal of rift basin asymmetry across the Warner Robins Transfer Zone, and the apparent presence of a new sub-horizontal stratigraphic unit (informally named the Hazlehurst Formation) which overlies with angular unconformity an inferred Triassic rift basin (Valdosta Basin), and sits below the regional Coastal Plain unconformity. Triassic rifting of the supercontinent Pangea left behind numerous extensional basins on what is now the eastern North American margin. The SGR is thought to be the most regionally extensive and best preserved of these basins, which were capped by thick basalt -flows of the Central Atlantic Magmatic Province (CAMP) and later buried beneath the Cretaceous and younger Coastal Plain section. Because it is buried beneath the Coastal Plain, the SGR is only known through relatively sparse drilling and geophysical methods. With these new seismic data acquired in 2013 near Hazlehurst, Georgia, we are able to put more constraints into the tectonic history of the basin. We test several hypotheses related to the SGR: (1) the "Transfer Zone" had to exist to transmit extensional strain between rift sub-basins with reverse polarities; (2) the newly identified sub-horizontal stratigraphic interval ("Hazlehurst Formation"), with a possible Jurassic age may represent a post-rift phase of regional subsidence; (3) the extent of this new unit appears to cover most of the coastal plain from eastern Mississippi to South Carolina. The result of this study suggests the previous inferred extent of the might need revision.
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NASA Astrophysics Data System (ADS)
Ridgway, K. D.; Witmer, J. W.; Enkelmann, E.; Plafker, G.; Brennan, P. R.
2011-12-01
Over 5 km of Neogene sedimentary strata are well exposed in the Chugach-St. Elias Ranges within the southern Alaska syntaxis. This syntaxis forms where the Pacific-North America plate boundary changes from the northwest-trending Queen Charlotte-Fairweather transform system to the southwest-trending Alaska-Aleutian subduction zone. Active collision and subduction of the buoyant Yakutat microplate in the syntaxis results in a wide collisional zone defined by active mountain belts, extensive glaciation, and thick packages of synorogenic strata. New stratigraphic and U-Th/He thermochronologic data from Neogene synorogenic strata, named the Yakataga and Redwood Formations, provide insights on collisional tectonics, glacial erosion, and sediment transport, deposition, burial, and exhumation from the onshore Chugach and St. Elias Ranges to the exposed accretionary prism of the Aleutian trench. Stratigraphic analyses show that along the southeastern part of the syntaxis, Neogene strata are characterized by deposition in braid delta, shallow marine, and glaciomarine slope apron depositional systems that resulted in construction of a broad continental shelf. In the central part of the syntaxis, marine shelf and upper slope environments deposited thick-bedded sandstone and mudstone in a thrust belt/foreland basin system. Along the southwestern part of the syntaxis, Neogene strata were deposited in a regional submarine fan system that filled the easternmost part of the Aleutian trench. Geologic mapping of the contact between the Yakataga Formation and underlying strata along the syntaxis document an angular unconformity with maximum stratigraphic separation (> 5 km) in the central part of the syntaxis. Along strike, this unconformity becomes conformable along both the southwestern and southeastern parts of the syntaxis. The regional angular unconformity and facies transitions both point to the importance of the central part of the syntaxis in the generation and distribution of synorogenic sediment. Apatite and zircon U-Th/He thermochronologic data from granitoid and gneissic clasts in conglomerate suggest that Neogene sediments were buried no deeper than ~2 km in the central and southeastern parts of the syntaxis, and that burial temperatures did not exceed ~40-45°C. In contrast, Neogene sediment deposited by submarine fans in the Aleutian trench along the southwestern part of the syntaxis were buried at depths of 5 to 7.5 km and reached temperatures between ~120-160°C. These strata were subsequently exhumed as the trench fill was incorporated into the growing accretionary prism. Collectively, our data show that the first-order sediment pathway along a glaciated syntaxis is dynamically linked to tectonic uplift, focused glacial erosion, deposition of thick packages of glacial marine sediment, and rapid exhumation along thrust belts and accretionary prisms.
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Vannucchi, P.; Scholl, D. W.; Meschede, M.; McDougall-Reid, K.
2001-01-01
The convergent margin off the Pacific coast of the Nicoya Peninsula of Costa Rica exhibits evidence for subduction erosion caused by the underthrusting Cocos plate. Critical evidence for efficacy of this process was recovered at the Ocean Drilling Program (ODP) drilling Site 1042 (Leg 170), positioned ???7 km landward of the Middle America trench axis off the Nicoya Peninsula. The primary drilling objective at this site was to identify the age and origin of a regionally extensive and prominent seismic discontinuity, the so-called base-of-slope sediment (BOSS) horizon or surface. The BOSS horizon, which can be traced landward from near the trench to the Nicoya coastal area and parallel to it for hundreds of kilometers, separates a low-velocity (??? 2.0-2.5 km s-1) sequence of slope sediment, from an underlying sequence of much higher-velocity (> 4-4.5 km s-1) rock. Site 1042 reached the acoustically defined BOSS horizon at a below sea level depth of ??? 3900 m and yielded a carbonate-cemented calcarenitic breccia of early-middle Miocene age. Sedimentological, geochemical, paleontological, and cement paragenesis data document that the breccia accumulated in a shallow water depositional environment. On the basis of coastal exposures, the BOSS horizon, as a margin-wide geologic interface, can be temporally and lithostratigraphically correlated to a regional angular unconformity. This unconformity, known as the Mal Pais unconformity, separates Neogene and younger shelf-to-littoral beds from the underlying mafic units of the Mesozoic Nicoya Complex and Cretaceous and early Tertiary sedimentary sequences. At Site 1042 it is inferred that tectonism caused the vertical subsidence of the early Neogene breccia from a shallow to a deep water setting. The Mal Pais unconformity of the BOSS horizon thus connects the rock fabric of the outermost part of margin to that of coastal Nicoya and implies that in the early Neogene the Nicoya shelf extended seaward to near the present trench axis. This circumstance requires that the early Neogene trench axis was at least 50 km seaward of where it is now located. The long-term effects of subduction erosion, similar to those described for the scientifically drilled Japan, Tonga, and Peru margins, best account for offshore and onshore evidence for a post-Paleogene history of crustal thinning and landward trench migration of Costa Rica's Pacific margin. During the past 16-17 Myr the calculated mass removal and landward migration rates are 34-36 km3 Myr-1 km-1 of margin, and 3 km Myr-1, respectively. These values are similar to those found for other Pacific margins dominated by nonaccretionary subduction zone processes.
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DOE Office of Scientific and Technical Information (OSTI.GOV)
Odland, S.K.; Gardner, M.H.; Gustason, E.R.
1986-08-01
It has long been known that an unconformity plays a critical role in trapping oil in the Muddy Sandstone in the Powder River basin, but opinions have varied as to exactly where in the section that unconformity is located. Their work indicates that there are, in fact, two unconformities associated with the Muddy in the northern part of the basin. The older of these occurs on top of the Skull Creek Shale, whereas the younger is largely intraformational. In places, the younger unconformity has truncated the older one. It is the younger unconformity that is responsible for creating favorable settingsmore » for stratigraphic entrapment of oil. Two types of unconformity-related oil traps result from fluvial downcutting into and through the strand-plain sandstones of the oldest member of the Muddy during a major sea level drop. In cases where the unconformity cuts through the Muddy into the underlying Skull Creek Shale, permeable valley-fill sediments, deposited during the Muddy transgression, are juxtaposed against the impermeable Skull Creek Shale along the valley walls. Where valleys are oriented roughly perpendicular to regional structure, as at Kitty field, the updip portion of the valley wall can form a permeability barrier to the fluvial reservoir sandstones of the adjacent valley fill. In cases where the unconformity is intraformational, such as at Amos Draw field, early diagenetic clay, associated with the weathered horizon directly beneath the unconformity, can create a seal on top of the strand-plain sandstones of the oldest member of the Muddy.« less
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A 3-D morphometric analysis of erosional features in a contourite drift from offshore SE Brazil
NASA Astrophysics Data System (ADS)
Alves, Tiago M.
2010-12-01
A contourite drift from offshore Brazil is mapped in detail and investigated using state-of-the-art 3-D seismic data. The aim was to review the relevance of erosional features in contourite drifts accumulated on continental slopes. Topographically confined by growing salt diapirs, the mapped contourite ridge is limited by two erosional features, a contourite moat and a turbidite channel, showing multiple slide scars on it flanks. Associated with the latter features are thick accumulations of high-amplitude strata, probably comprising sandy/silty sediment of Miocene to Holocene age. The erosional unconformities are mostly observed in a region averaging 3.75km away from the axes of a channel and a moat, whose deposits interfinger with continuous strata in central parts of the contourite drift. The multiple unconformities observed are mostly related to slide scars and local erosion on the flanks of the drift. This work demonstrates that the existence of widespread unconformities within contourite drifts on continental slopes: (1) may not be as prominent as often documented, (2) are often diachronic and interfinger with correlative hiatuses or aggraded strata in axial regions of contourite drifts. Although less widespread than regional, or ocean-scale unconformities, these diachronous features result in significant hiatuses within contourite drifts and are, therefore, potentially mappable as relevant (regional-scale) unconformities on 2-D/3-D seismic data. Thus, without a full 3-D morphometric analysis of contourite drifts, significant errors may occur when estimating major changes in the dynamics of principal geostrophic currents based on single-site core data, or on direct correlations between stratigraphic surfaces of distinct contourite bodies.
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The stratigraphy of the Steep Rock Group, N.W. Ontario, with evidence of a major unconformity
NASA Technical Reports Server (NTRS)
Wilks, M. E.; Nisbet, E. G.
1986-01-01
The Steep Rock Group is exposed 6 km north of Atikokan, 200 km west of Thunder Bay. It is situated on the southern margin of the Wabigoon Belt of the Archaean Superior Province, N. W. Ontario. Reinvestigation of the geology of the Group has shown that the Group lies unconformably on the Tonalite Complex to the east. This unconformity has been previously suspected, from regional and ine mapping but no conclusive outcrop evidence for its existence has as yet been published. The strike of the group, comprised of Basal Conglomerate, Carbonate Member, Ore Zone and Ashrock is generally north-northwest dipping steeply to the southwest. Of the 7 contacts between the Steep Rock Group and the Tonalite Complex, 3 expose the unconformity (The Headland, S. Roberts Pit, Trueman Point), and 4 are faulted. These three outcrops demonstrate unequivocally that the Steep Rock group was laid down unconformably on the underlying Tonalite Complex, which is circa 3 Ga old.
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Racheboeuf, Patrick R.; Moore, Thomas E.; Blodgett, Robert B.
2004-01-01
Newly discovered fossil localities in coarse-grained deposits of the Pennsylvanian and Permian Antler overlap assemblage in the southern Shoshone Range, north-central Nevada have yielded a low-diversity assemblage consisting chiefly of a new species of chonetoidean brachiopod: Dyoros (Lissosia) nevadaensis nov. sp. The subgenus Dyoros (Lissosia), is known from Leonardian and lower Guadalupian strata in North America, mainly in Texas. The coarse-grained lithology of the host strata, their unconformable relation on deformed lower Paleozoic rocks, and the Leonardian and(or) lower Guadalupian age indicated by Dyoros (Lissosia) provide evidence that host strata are younger than strata of the Antler overlap assemblage in nearby areas of the southern Shoshone Range and suggest that an unconformity of local extent may be present within the overlap assemblage. The fossil age ranges and lithologic data suggest that the host strata may be correlative with the Guadalupian Edna Mountain Formation, an unconformity-bounded unit that forms the upper part of the Antler sequence in the Battle Mountain area to the north. This correlation suggests that the unconformity beneath these strata may have regional extent in north-central Nevada. The origin of the inferred regional unconformity is unknown and may have resulted from relative changes of sea level or regional extensional or contractional tectonism in the area of the former Antler highlands, which forms the substrate for the Antler overlap assemblage. ?? 2004 Elsevier SAS. All rights reserved.
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DOE Office of Scientific and Technical Information (OSTI.GOV)
Hertig, S.P.; Tye, R.S.; Coffield, D.Q.
1991-08-01
Paleozoic to Lower Mesozoic strata of the southeastern Algerian Tassili are traditionally subdivided by regionally extensive unconformities such as the Pan African, Taconic, Caledonian, and Hercynian. Using outcrop data from southeastern Algeria, this classic approach is modified by reinterpreting the genesis of these unconformities and rock sequences. Five prominent sequences, defined within the Paleozoic and lower Mesozoic section, usually consist of a succession of lowstand, transgressive, and highstand system tracts separated by sequence boundaries or transgressive surfaces. The Pan-African, Taconic, Caledonian, and Hercynian unconformities are sequence boundaries. Important sequence boundaries also occur within the Ordovician and Silurian sections. These sequencesmore » correlate with subsurface data in the Illizi basin and provide a framework for renewed exploration in the subsurface of the Algerian Sahara, where more than 30 billion bbl of recoverable oil and oil equivalent have been generated and trapped.« less
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NASA Astrophysics Data System (ADS)
Wu, Lin; Guan, Shuwei; Zhang, Shuichang; Yang, Haijun; Jin, Jiuqiang; Zhang, Xiaodan; Zhang, Chunyu
2018-06-01
The Tarim Craton is overlain by thick Neoproterozoic sedimentary successions in rift tectonic setting. This study examines the latest outcrop, seismic, and drilling core data with the objective of investigating the regional stratigraphy to deeply recognize the evolution of rifting in the craton. Cryogenian to Lower Ediacaran successions are mainly composed of clastic rocks with thicknesses of 2000-3000 m, and the Upper Ediacaran successions are composed of carbonate rocks with thicknesses of 500-800 m. The rift basins and stratigraphic zones are divided into northern and southern parts by a central paleo-uplift. The northern rift basin extends through the northern Tarim Craton in an E-W direction with two depocenters (Aksu and Kuruktag). The southern rift basin is oriented NE-SW. There are three or four phases of tillites in the northern zone, while there are two in the southern zone. Given the north-south difference of the stratigraphic framework, the northern rift basin initiated at ca. 740 Ma and the southern rift basin initiated at ca. 780 Ma. During the Cryogenian and Ediacaran, the northern and southern rift basins were separated by the central paleo-uplift, finally connecting with each other in the early Cambrian. Tectonic deformation in the Late Ediacaran led to the formation of a parallel unconformity in the rift basins and an angular unconformity in the central paleo-uplift. The Neoproterozoic rift basins continued to affect the distribution of Lower Cambrian hydrocarbon source rocks. The north-south distribution and evolution of the rift basins in the Tarim Craton have implications for reconstructions of the Rodinia supercontinent.
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NASA Astrophysics Data System (ADS)
Wise, James M.; Noble, Donald C.; Zanetti, Kathleen A.; Spell, Terry L.
2008-12-01
In the Ayacucho basin of central Perú the regional Quechua II contractional deformation is bracketed by 40Ar/ 39Ar isotopic age determinations to a maximum duration of about 300,000 years, and probably less than 150,000 years, centered on 8.7 Ma. The strongly deformed Huanta Formation beneath the Quechua II angular unconformity was deposited during a period of extension that began before 9.05 ± 0.05 Ma. Deposition of a thick succession of alluvial fan deposits interbedded with flows of basaltic andesite in the Tingrayoc Member continued up to about 8.76 ± 0.05 Ma with the later part of the sedimentary record reflected by lacustrine deposits of the Mayocc Member. The upper limit on contractional deformation is constrained by an age of 8.64 ± 0.05 Ma on a unit of tuff near the base of the Puchcas volcanics, which in places was deposited upon near-vertical beds of the Huanta Formation. The Ayacucho Formation was deposited, locally unconformably, upon the Puchcas volcanics beginning slightly before 7.65 ± 0.10 Ma. Extended periods of neutral to tensional stress interrupted by rapid well-developed pulses of contractional deformation demonstrate the episodic behavior of Andean orogeny in Perú. The very short duration for the Quechua II event implies that driving forces for episodic deformation may be related to coupling along the orogen boundaries and strain accumulation and release mechanisms in the continental crust instead of much longer-term variations in the configuration of converging plates.
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Seismic stratigraphy and late Quaternary shelf history, south-central Monterey Bay, California
Chin, J.L.; Clifton, H.E.; Mullins, H.T.
1988-01-01
The south-central Monterey Bay shelf is a high-energy, wave-dominated, tectonically active coastal region on the central California continental margin. A prominent feature of this shelf is a sediment lobe off the mouth of the Salinas River that has surface expression. High-resolution seismic-reflection profiles reveal that an angular unconformity (Quaternary?) underlies the entire shelf and separates undeformed strata above it from deformed strata below it. The Salinas River lobe is a convex bulge on the shelf covering an area of approximately 72 km2 in water depths from 10 to 90 m. It reaches a maximum thickness of 35 m about 2.5 km seaward of the river mouth and thins in all directions away from this point. Adjacent shelf areas are characterized by only a thin (2 to 5 m thick) and uniform veneer of sediment. Acoustic stratigraphy of the lobe is complex and is characterized by at least three unconformity-bounded depositional sequences. Acoustically, these sequences are relatively well bedded. Acoustic foresets occur within the intermediate sequence and dip seaward at 0.7?? to 2.0??. Comparison with sedimentary sequences in uplifted onshore Pleistocene marine-terrace deposits of the Monterey Bay area, which were presumably formed in a similar setting under similar processes, suggests that a general interpretation can be formulated for seismic stratigraphic patterns. Depositional sequences are interpreted to represent shallowing-upwards progradational sequences of marine to nonmarine coastal deposits formed during interglacial highstands and/or during early stages of falling sea level. Acoustic foresets within the intermediate sequence are evidence of seaward progradation. Acoustic unconformities that separate depositional sequences are interpreted as having formed largely by shoreface planation and may be the only record of the intervening transgressions. The internal stratigraphy of the Salinas River lobe thus suggests that at least several late Quaternary regressions and transgressions may be recorded under the present shelf. This record may represent the last major eustatic cycle of sea level, an interval not observed in uplifted onshore Pleistocene marine terraces. ?? 1988.
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NASA Astrophysics Data System (ADS)
Ma, Anlin; Hu, Xiumian; Garzanti, Eduardo; Han, Zhong; Lai, Wen
2017-07-01
The Mesozoic stratigraphic record of the southern Qiangtang basin in central Tibet records the evolution and closure of the Bangong-Nujiang ocean to the south. The Jurassic succession includes Toarcian-Aalenian shallow-marine limestones (Quse Formation), Aalenian-Bajocian feldspatho-litho-quartzose to feldspatho-quartzo-lithic sandstones (shallow-marine Sewa Formation and deep-sea Gaaco Formation), and Bathonian outer platform to shoal limestones (Buqu Formation). This succession is truncated by an angular unconformity, overlain by upper Bathonian to lower Callovian fan-delta conglomerates and litho-quartzose to quartzo-lithic sandstones (Biluoco Formation) and Callovian shoal to outer platform limestones (Suowa Formation). Sandstone petrography coupled with detrital-zircon U-Pb and Hf isotope analysis indicate that the Sewa and Gaaco formations contain intermediate to felsic volcanic detritus and youngest detrital zircons (183-170 Ma) with ɛHf(t) ranging widely from +13 to -25, pointing to continental-arc provenance from igneous rocks with mixed mantle and continental-crust contributions. An arc-trench system thus developed toward the end of the Early Jurassic, with the southern Qiangtang basin representing the fore-arc basin. Above the angular unconformity, the Biluoco Formation documents a change to dominant sedimentary detritus including old detrital zircons (mainly >500 Ma ages in the lower part of the unit) with age spectra similar to those from Paleozoic strata in the central Qiangtang area. A major tectonic event with intense folding and thrusting thus took place in late Bathonian time (166 ± 1 Ma), when the Qiangtang block collided with another microcontinental block possibly the Lhasa block.
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NASA Astrophysics Data System (ADS)
del Papa, Cecilia E.; Petrinovic, Ivan A.
2017-01-01
The Conglomerado Los Patos is a coarse-grained clastic unit that crops out irregularly in the San Antonio de los Cobres Valley in the Puna, Northwestern Argentina. It covers different units of the Cretaceous-Paleogene Salta Group by means of an angular unconformity and, in turn, is overlaid in angular unconformity by the Viscachayoc Ignimbrite (13 ± 0.3 Ma) or by late Miocene tuffs. Three lithofacies have been identified in the Corte Blanco locality; 1) Bouldery matrix-supported conglomerate (Gmm); 2) Clast-supported conglomerate (Gch) and 3) Imbricated clast-supported conglomerate (Gci). The stratigraphic pattern displays a general fining upward trend. The sedimentary facies association suggests gravitational flow processes and sedimentation in alluvial fan settings, from proximal to medial fan positions, together with a slope decrease upsection. Provenance studies reveal sediments sourced from Precambrian to Ordovician units located to the southwest, except for volcanic clasts in the Gmm facies that shows U/Pb age of 14.5 ± 0.5 Ma. This new age represents the maximum depositional age for the Conglomerado Los Patos, and it documents that deposition took place simultaneously during a period of increased tectonic and volcanic activity in the area. The structural analysis of the San Antonio de los Cobres Valley and the available thermochronological ages, indicate active N-S main thrusts and NW-SE transpressive and locally normal faults during the middle Miocene. In this context, we interpret the Conglomerado Los Patos to represent sedimentation in a small, extensional and short-lived basin associated with the compressional Andean setting.
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Deformation style of the Mesozoic sedimentary rocks in southern Thailand
NASA Astrophysics Data System (ADS)
Kanjanapayont, Pitsanupong
2014-10-01
Mesozoic sedimentary rocks in southern Thailand are widespread from NNE-SSW and N-S in Chumphon and Trang provinces. The Mesozoic stratigraphic units are the marine Triassic Sai Bon Formation and the non-marine Jurassic-Cretaceous Thung Yai Group, the latter subdivided into Khlong Min, Lam Thap, Sam Chom, and Phun Phin Formations. These units overlie Permian carbonate rocks with an angular unconformity, and are overlain unconformably by Cenozoic units and the Quaternary sediments. The Mesozoic rocks have been folded to form two huge first-ordered syncline or synclinoria, the Chumphon and Surat Thani-Krabi-Trang synclinoria. These synclinoria are elongated in NNE-SSW to N-S direction, and incorporate asymmetric lower-order parasitic folds. The folds have moderately to steeply dipping eastward limbs and more gently dipping westward limbs. These folds were transected by brittle fractures in four major directions. These geologic structures indicate WNW-ESE to E-W contraction with top-to-the-east simple shear at some time before the deposition of the Cenozoic sedimentary units. No major deformation has affected the rocks subsequently, apart from the formation of the fault-controlled Cenozoic basins.
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Structure and kinematics of a major tectonic contact, Michipicoten greenstone belt, Ontario
NASA Technical Reports Server (NTRS)
Mcgill, George E.
1992-01-01
The Michipicoten greenstone belt, Ontario, experienced a complex history of folding, faulting, and fabric development. Near Wawa, a major east-west contact, here named the Steep Hill Falls (SHF) contact, extends entirely across the belt. The SHF contact is both an angular unconformity and a fault and is interpreted to be a regionally significant tectonic contact separating distinct northern and southern terranes, both of which include volcanic rocks of probable island-arc origin. The amount of horizontal transport involved in bringing the two terranes together along the SHF contact is not known. Mapping and structural analysis suggest that regionally significant horizontal displacements took place, with movement vectors that changed with time. Early faults, folds, and fabrics imply north-south to northeast-southwest (with respect to present directions) convergence, with a vergence reversal occurring during this complex event. The most likely models infer early south vergence and later north vergence. Transecting the earliest structures are younger (but still Archean) northeast-striking steep cleavages with associated upright folds that may relate to northwest-southeast assembly of the Superior Province craton. The craton assembly event thus involved a transport direction at a high angle to that inferred for the earlier assembly of the Michipicoten greenstone belt.
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Lomonosov Ridge, Arctic Ocean: New MCS Data for the Definition of Targets for Scientific Drilling
NASA Astrophysics Data System (ADS)
Kristoffersen, Y.; Coakley, B.; Hall, J. K.
2001-12-01
The 1500 km long and 50-150 km wide Lomonosov Ridge rises more than 3000 m above the adjacent abyssal plains, separating the Mesozoic-aged Amerasian basin from the Cenozoic-Recent Eurasian basin. Multichannel seismic reflection data collected from icebreakers on four cruises together with swath bathymetry and high resolution chirp sonar data collected by nuclear submarines across the central ridge show a cap of hemipelagic drape (c. 450 m thick) on top of normal faulted and peneplained sedimentary sequences, the remnants of the Mesozoic Barents margin, which pre-dates the opening of the Eurasian Basin. A new multichannel seismic survey to augment the site survey data base for ODP proposal 533 was carried out on the Lomonosov Ridge under difficult ice conditions in late July 2001 from the Swedish icebreaker Oden. The primary objectives of ODP Proposal 533 are to obtain continuous paleoceanographic records for most of the Cenozoic from the hemipelagic sequence and to sample the underlying passive margin sequence below the regional unconformity, which would provide the first direct constraints on the early tectonic history of the ridge. Of particular interest is the extent of mass wasting along the ridge perimeter. This regional unconformity offers an opportunity for implementing a strategy of offset shallow drill holes to obtain a complete hemi-pelagic section as well as to penetrate the regional unconformity. The new data, which will, in conjunction with the existing MCS data base, provide the first 3-D control on the passive margin structures and overlying unconformity, will be presented.
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Tertiary stratigraphy and basin evolution, southern Sabah (Malaysian Borneo)
NASA Astrophysics Data System (ADS)
Balaguru, Allagu; Nichols, Gary
2004-08-01
New mapping and dating of strata in the southern part of the Central Sabah Basin in northern Borneo has made it possible to revise the lithostratigraphy and chronostratigraphy of the area. The recognition in the field of an Early Miocene regional unconformity, which may be equivalent to the Deep Regional Unconformity recognised offshore, has allowed the development of a stratigraphic framework of groups and formations, which correspond to stages in the sedimentary basin development of the area. Below the Early Miocene unconformity lies ophiolitic basement, which is overlain by an accretionary complex of Eocene age and a late Paleogene deep water succession which formed in a fore-arc basin. The late Paleogene deposits underwent syn-depositional deformation, including the development of extensive melanges, all of which can be demonstrated to lie below the unconformity in this area. Some localised limestone deposition occurred during a period of uplift and erosion in the Early Miocene, following which there was an influx of clastic sediments deposited in delta and pro-deltaic environments in the Middle Miocene. These deltaic to shallow marine deposits are now recognised as forming two coarsening-upward successions, mapped as the Tanjong and Kapilit Formations. The total thickness of these two formations in the Central Sabah Basin amounts to 6000 m, only half of the previous estimates, although the total stratigraphic thickness of Cenozoic clastic strata in Sabah may be more than 20,000 m.
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NASA Astrophysics Data System (ADS)
Poselov, Viktor; Kireev, Artem; Smirnov, Oleg; Butsenko, Viktor; Zholondz, Sergey; Savin, Vasily
2016-04-01
Massive amount of multichannel seismic (MCS) data were obtained by Russian High Arct ic expeditions "Arctica-2011", "Acrtica-2012" and "Arctica-2014". More than 40 MCS lines are located in the Amerasian basin and help to substantiate the seismic stratigraphy model of its sedimentary cover. The proposed seismic stratigraphy model was successively determined for the Cenozoic and pre-Cenozoic parts of the sedimentary section and was based on correlation of the Russian MCS data and seismic data documented by boreholes. Cenozoic part of the sedimentary cover is based on correlation of the Russian MCS data and AWI91090 section calibrated by ACEX-2004 boreholes on the Lomonosov Ridge. Two major unconformities are traced. The upper regional unconformity (RU) is associated with a major pre-Miocene hiatus. Another major hiatus is recorded in the borehole section between the Campanian and the Upper Paleocene units. It is recognized as the post-Campanian unconformity (pCU) in the seismic sections. Formation of the regional unconformities is associated with a fundamental change in depositional environment. Formation of RU was initiated by opening of the Fram Strait gateway at the Paleogene/Neogene boundary. Post-Campanian unconformity is linked with the initial stage of the Eurasian Basin opening between the Cretaceous and the Paleogene. Cenozoic sedimentary units are continuously traced from the East-Siberian and Chukchi sea shelves across the transit zone to the Amerasian basin. Paleogene unit (between pCU and RU) is formed under the neritic depositional environment and it is characterized by an extremely small thickness on the Lomonosov Ridge (less than 200 m), on the Mendeleev Rise and in the Podvodnikov Basin (not more than 300-400 m). Neogene unit (above RU) consists of hemipelagic deposits and occupies the essential part of thickness of the Cenozoic section in Podvodnikov and Makarov Basins. Interval velocities in the Paleogene unit vary within 2.8-3.2 km/s, in the Neogene unit they vary within 1.8-2.7 km/s. Pre-Cenozoic part of the sedimentary cover is based on tracing major unconformities from boreholes on the Chukchi shelf (Crackerjack, Klondike, Popcorn) to the North-Chuckchi Trough and further to the Mendeleev Rise as well as to the Vilkitsky Trough and the adjacent Podvodnikov Basin. Three regional unconformities are correlated: Jurassic (JU - top of the Upper Ellesmerian unit), Lower Cretaceous (LCU) and Brookian (BU - base of the Lower Brookian unit). Above the acoustic basement the pre-Cenozoic section is mainly represented by terrigenous units. Two major unconformities: RU and pCU are allocated on all MCS lines intersecting the Mendeleev Rise along its entire extent. BU is traced nearly everywhere along the rise excepting certain acoustic basement highs. All unconformities are also traced from the Mendeleev Rise to the continental structure of the Chuckchi Borderland. Sedimentary sequence between pCU and JU which underlies deposits of the Upper Ellesmerian unit is recorded as a synrift unit of the entire area of the Podvodnikov Basin. MCS data show a natural prolongation of the sedimentary cover from the shelf to the Podvodnikov Basin without any breaks and tectonic movements. Interval velocities in the Upper Cretaceous unit (between pCU and BU) vary within 3.2-3.9 km/s, in the pre-Upper Cretaceous units (between BU and the acoustic basement) vary within 4.1-4.8 km/s.
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DOE Office of Scientific and Technical Information (OSTI.GOV)
Phillips, S.; Hewlett, J.S.; Bazeley, W.J.M.
1996-01-01
Tectonic evolution of the southern San Joaquin basin exerted a fundamental control on Cenozoic sequence boundary development, reservoir, source and seal facies distribution, and hydrocarbon trap development. Spatial and temporal variations in Tertiary sequence architecture across the basin reflect differences in eastside versus westside basin-margin geometries and deformation histories. Deposition of Tertiary sequences initiated in a forearc basin setting, bounded on the east by a ramp-margin adjacent to the eroded Sierran arc complex and on the west by the imbricated accretionary wedge of the Coast Ranges thrust. The major stages of Cenozoic basin evolution are: (1) Episodic compressional folding andmore » thrusting associated with oblique convergence of the Farallon and North American plates (Late Cretaceous to Oligocene), (2) localized folding and onset of basin subsidence related to Pacific Plate reorganization, microplate formation and rotation (Oligocene to Early Miocene), (3) transtensional faulting, folding basin subsidence associated with initiation of the San Andreas transform and continued microplate rotation (Micocene to Pliocene), and (4) compressional folding, extensional and strike- slip faulting related to evolution of the Pacific-North American transform boundary (Plio- Pleistocene). Complex stratigraphic relationships within Eocene to Middle Miocene rocks provide examples of tectonic influences on sequence architecture. These include development of: (1) Tectonically enhanced sequence boundaries (Early Eocene base Domengine unconformity) and local mid-sequence angular unconformities, (2) westside-derived syntectonic [open quotes]lowstand[close quotes] systems (Yokut/Turitella Silt wedge and Leda Sand/Cymric/Salt Creek wedge), (3) regional seals associated with subsidence-related transgressions (Round Mountain Silt), and (4) combination traps formed by structural inversion of distal lowstand delta reservoirs (e.g. Coalinga East Extension field).« less
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DOE Office of Scientific and Technical Information (OSTI.GOV)
Phillips, S.; Hewlett, J.S.; Bazeley, W.J.M.
1996-12-31
Tectonic evolution of the southern San Joaquin basin exerted a fundamental control on Cenozoic sequence boundary development, reservoir, source and seal facies distribution, and hydrocarbon trap development. Spatial and temporal variations in Tertiary sequence architecture across the basin reflect differences in eastside versus westside basin-margin geometries and deformation histories. Deposition of Tertiary sequences initiated in a forearc basin setting, bounded on the east by a ramp-margin adjacent to the eroded Sierran arc complex and on the west by the imbricated accretionary wedge of the Coast Ranges thrust. The major stages of Cenozoic basin evolution are: (1) Episodic compressional folding andmore » thrusting associated with oblique convergence of the Farallon and North American plates (Late Cretaceous to Oligocene), (2) localized folding and onset of basin subsidence related to Pacific Plate reorganization, microplate formation and rotation (Oligocene to Early Miocene), (3) transtensional faulting, folding basin subsidence associated with initiation of the San Andreas transform and continued microplate rotation (Micocene to Pliocene), and (4) compressional folding, extensional and strike- slip faulting related to evolution of the Pacific-North American transform boundary (Plio- Pleistocene). Complex stratigraphic relationships within Eocene to Middle Miocene rocks provide examples of tectonic influences on sequence architecture. These include development of: (1) Tectonically enhanced sequence boundaries (Early Eocene base Domengine unconformity) and local mid-sequence angular unconformities, (2) westside-derived syntectonic {open_quotes}lowstand{close_quotes} systems (Yokut/Turitella Silt wedge and Leda Sand/Cymric/Salt Creek wedge), (3) regional seals associated with subsidence-related transgressions (Round Mountain Silt), and (4) combination traps formed by structural inversion of distal lowstand delta reservoirs (e.g. Coalinga East Extension field).« less
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Molenaar, C.M.; Cobban, W.A.; Merewether, E.A.; Pillmore, C.L.; Wolfe, D.G.; Holbrook, J.M.
2002-01-01
Sedimentary rocks of Cretaceous age along Transect DD'' in eastern Arizona, northern New Mexico, southern Colorado, and western Oklahoma consist mainly of sandstone, siltstone, shale, limestone, and bentonite. They accumulated as sediments in continental, nearshore marine, and offshore marine environments on the west side of a north-trending epicontinental sea. The rocks record intermittent deposition and erosion as well as regional and local subsidence and uplift possibly beginning in Aptian time (about 121-112 Ma) and occurring in Albian through Maastrichtian time (about 112-65.4 Ma). Most of the Lower Cretaceous (Berriasian through Aptian, 142-112 Ma) in this transect is represented by a basal unconformity. The Cretaceous rocks and unconformities along the transect are depicted on the attached lithostratigraphic cross sections (sheets 1 and 2); one extending from the Mogollon Rim in eastern Arizona to Pagosa Springs in southwestern Colorado and the other from Pagosa Springs, Colorado, to Kenton in western Oklahoma. The same rocks and unconformities are also represented on the attached chronostratigraphic profile (sheet 3), which was prepared mainly from surface and subsurface data shown on the lithostratigraphic cross sections.
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Rift-drift transition in the Dangerous Grounds, South China Sea
NASA Astrophysics Data System (ADS)
Peng, Xi; Shen, Chuanbo; Mei, Lianfu; Zhao, Zhigang; Xie, Xiaojun
2018-04-01
The South China Sea (SCS) has a long record of rifting before and after subsequent seafloor spreading, affecting the wide continent of the Dangerous Grounds, and its scissor-shape opening manner results in the rifting structures that vary along this margin. Some 2000 km of regional multichannel seismic data combined with borehole and dredge data are interpreted to analyze the multistage rifting process, structural architecture and dynamic evolution across the entire Dangerous Grounds. Key sequence boundaries above the Cenozoic basement are identified and classified into the breakup unconformity and the rift end unconformity, which consist of the rift-related unconformities. Reflector T70 in the east of the Dangerous Grounds represents the breakup unconformity, which is likely corresponding to the spreading of the East Subbasin. T60 formed on the top of carbonate platform is time equivalent to the spreading of the Southwest Subbasin, marking the breakup unconformity of the central Dangerous Grounds. The termination of the spreading of the SCS is manifested by the rift end unconformity of T50 in the southwest and the final rift occurring in the northwest of the Dangerous Grounds is postponed to the rift end unconformity of T40. On the basis of the stratigraphic and structural analysis, distinct segments in the structural architecture of the syn-rift units and the ages of rift-drift transition show obvious change from the proximal zone to the distal zone. Three domains, which are the Reed Bank-Palawan Rift domain, the Dangerous Grounds Central Detachment domain and Nam Con Son Exhumation domain, reflect the propagation of the margin rifting developed initially by grabens formed by high angle faults, then large half-grabens controlled by listric faults and detachments and finally rotated fault blocks in the hyper-extended upper crust associated with missing lower crust or exhumed mantle revealing a migration and stepwise rifting process in the south margin of the SCS.
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Neogene stratigraphy and Andean geodynamics of southern Ecuador
NASA Astrophysics Data System (ADS)
Hungerbühler, Dominik; Steinmann, Michael; Winkler, Wilfried; Seward, Diane; Egüez, Arturo; Peterson, Dawn E.; Helg, Urs; Hammer, Cliff
2002-01-01
The present paper reviews Tertiary volcanic and sedimentary formations in the Inter-Andean region of southern Ecuador (between 2°S and 4°20'S) in order to develop a geodynamic model of the region. The formations occur in the southern shallow prolongation of the Inter-Andean Valley between the Cordillera Real to the east, and the Cordillera Occidental and Amotape-Tahuín Provinces to the west. One hundred fifty zircon fission-track analyses has established a detailed chronostratigraphy for the sedimentary and volcanic formations and several small intrusions. The Paleogene to early Miocene formations are dominated by intermediate and acidic volcanic and pyroclastic rocks. In addition, relics of Eocene continental sedimentary series have been identified. The Neogene sedimentary series lie unconformably on deformed and eroded metamorphic, sedimentary and volcanic formations. They were deposited in two stages, which are separated by a major unconformity dated at ≈10-9 Ma. (1) During the middle and early late Miocene (≈15-10 Ma) marginal marine deltaic, lagoonal, lacustrine and fluvial environments prevailed, which we group under the heading "Pacific Coastal sequences". They presumably covered a greater surface area in southern Ecuador than their present occurrence in small topographic depressions. We suggest that they were deposited in the shallow marine Cuenca and Loja Embayments. Deposition in a marginal marine environment is also supported by the occurrence of brackish water ostracods and other fauna. (2) Above the regional (angular) unconformity, the coastal facies are overlain by late Miocene (≈9-5 Ma) continental alluvial fan and fluvial facies which are in turn covered by mainly airborne volcanic material. They represent the "Intermontane sequences" of the basins of Cuenca, Girón-Santa Isabel, Nabón, Loja and Malacatos-Vilcabamba. Sedimentologic and stratigraphic results are used to discuss the tectonic setting of Neogene sedimentation in the forearc and arc domain of the Ecuadorian subduction system. During the Pacific Coastal stage, northward displacement of the coastal forearc block along the Calacali-Pallatanga fault zone has driven crustal collapse in the Inter-Andean region. As a result, extensional subsidence drove the eastward ingression of shallow seas into the Cuenca and Loja Embayments from the Manabí and Progreso Basins to the west. Tectonic inversion in the forearc area during the early late Miocene (at ≈9.5 Ma) reflects the initiation of W-E oriented compression and uplift in the Inter-Andean region and the establishment of smaller Intermontane stage basins, which host the continental sequences. Coeval topographic rise of the Cordillera Occidental is indicated by the onset of clastic input from the west. The small Intermontane Basin of Nabón (≈8.5-7.9 Ma) formed during the period of maximum compression. The present data prove that the Neogene Andean forearc and arc area in southern Ecuador was a site of important but variable tectonic activity, which was presumably driven by the collision and coupling of the Carnegie Ridge with the Ecuadorian margin since ≈15-9 Ma.
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Geology and evolution of the Northern Kara Sea Shelf
DOE Office of Scientific and Technical Information (OSTI.GOV)
Vinogradov, A.
1991-08-01
The interpretation of regional multichannel seismic reflection profiles collected during 1988-1987 yields the following features of the geology of the Northern Kara Sea Shelf (NKSS). Two regional deep sedimentary basins are clearly distinguished within the NKSS. They have rather complex inner structures and contain sediments 14.0-16.0 km thick. The basin are separated from each other by a relatively narrow, linear zone of basement high which extends from Uedineniya Island on the south to Vize Island on the north, where basement depth is 1.5-4.0 km. The sedimentary sections of the basins are composed of four lithological-stratigraphical sequences separated by unconformities whichmore » correlate well with regional unconformities in adjacent land areas. The initial stages of sedimentary basin development within the NKSS date back to the late Riphean-Vendian; probably they were associated with intracontinental rifting, when up to 4 km of sediments were deposited. During the most of the Phanerozoic, regional subsidence dominated; however, the rates of subsidence were different in the western and in the eastern basins, and varied in time for each basin. The subsidence was interrupted for relatively short periods when the region was affected by uplifts and erosion which resulted in formation of regional unconformities. The seismic data gave no evidence of Caledonian or any other Phanerozoic folding within the NKSS, which is in contrast with widespread assumptions. The results show that the geological structure and evolution of the NKSS differ greatly from those of adjacent Barents and Southern Kara Sea shelves.« less
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DOE Office of Scientific and Technical Information (OSTI.GOV)
Fritsche, A.E.; Hanna, F.M.
1985-04-01
Three large, isolated exposures of a light-gray, coarse-grained, thick-bedded sandstone unit occur in the northern San Rafael Mountains of Santa Barbara County, California. These rocks are moderately fossiliferous and contain Vertipecten bowersi, Amussiopecten vanvlecki, Aequipecten andersoni, Otrea howelli, shark teeth, whale bones, and regular echinoid spines. The fossils indicate that the sandstone unit, although previously reported as upper(.) Miocene, correlates best with the lower Miocene Vaqueros Formation. This unit was deposited in angular unconformity on a Cretaceous, greenish-gray turbidite sequence of interbedded sandstone and shale, and onlaps the unconformity erosion surface from west to east, the unit being thicker inmore » the west and older at its base. The underlying Cretaceous sandstone beds are well indurated, and during the eastward transgression of the early Miocene sea, they resisted wave erosion and stood as seastacks offshore of the advancing coastline, thus creating a very irregular topographic surface upon which the Vaqueros Formation was deposited. Some seastacks were as much as 4 m tall, as indicated by inliers of Cretaceous rock surrounded by 4-m thick sections of the Vaqueros Formation.« less
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NASA Astrophysics Data System (ADS)
Akgün, Funda; Sözbilir, Hasan
The study, explains stratigraphy of the Oligo-Miocene molasse around the Denizli province (SW Anatolia), based on the palynology which is also supported by the detailed mapping and correlation of the measured sections from the coal-bearing sequences of the molasse deposits. For this purpose, two huge depressions named as the Kale-Tavas molasse and Denizli molasse basins were examined. The Kale-Tavas molasse deposits has a basal unconformity with the underlying pre-Oligocene basement and begins with the Chattian Karadere and Mortuma formations which are covered unconformably by the Aquitanian Yenidere formation. An angular unconformity between the Chattian and the Burdigalian is only observed in the middle part of the basin, around Kale. In the Tavas section, the Aquitanian and the Burdigalian are absent. The Denizli molasse is characterized by Chattian-Aquitanian sequence consisting of distinctive sedimentary facies, alluvial fan and deltaic-shallow marine deposits with carbonate patch reefs. Palynostratigraphic studies, which have given the Chattian age, have been carried out from the coal lenses of alluvial fan and delta plain deposits. In addition to the palynological determinations, coral and foraminiferal content of the carbonate patch reefs which rest conformably on the coal-bearing sequences have yielded the Chattian-Aquitanian age. Two different palynomorph associations have been determined from the molasse deposits. The first palynomorph association which is established in the samples from the Sağdere and Mortuma formations, corresponds to the Chattian age, whilst the second is of the Aquitanian age. The Late Oligocene-Early Miocene which is claimed as the time of N-S-extensional tectonics in western Turkey, is related to the depositional time of the molasse sequences in the study area. Thus, the molasse is older than the basal deposits of the Gediz and Büyük Menderes grabens.
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NASA Astrophysics Data System (ADS)
Morley, C. K.
2016-04-01
The distribution of unconformities and end of Cenozoic rifting events in the South China Seas (SCS) reflects both the modes of rift development, and the effects of driving mechanisms. Continental rifting began in the eastern basins during the Paleocene, and propagated westwards to the Vietnam basin margin in the Late Eocene. Continental breakup around 32-28 Ma caused a regional reduction or cessation in extensional activity, particularly affecting basins furthest from the spreading centre. Basins in the slope and deepwater area north of the spreading centre exhibit reduced fault activity until 21-20 Ma. Propagation of oceanic crust westwards between ∼25 and 23 Ma, and termination of seafloor spreading sometime between 20.5 and 16 Ma affected fault activity in the Qiongdongnan, and Nam Con Song basins. In the Phu Khanh Basin and South, in the Dangerous Grounds area, extension continued until about 16 Ma, ending at the Red Unconformity. The end of seafloor spreading around 20.5 Ma reflects loss of extensional driving force as thinned continental crust entered the NW Borneo subduction zone. Controversially, a key component of the driving force maybe attributed to slab-pull. A transitional period of about 5-7 my between the onset of subduction of continental crust, and final jamming of the subduction zone (Deep Regional Unconformity, DRU) is inferred. The last pulse of extension was focussed in the western SCS, and terminated around 10.5 Ma. Detailed understanding of proto South China Seas development remains uncertain and controversial.
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Quantitative palaeodrainage analysis in the Pleistocene of the Po Plain (Italy)
NASA Astrophysics Data System (ADS)
Vezzoli, G.; Garzanti, E.; Sciunnach, D.
2009-04-01
During the Pleistocene, Po Plain deposits recorded repeated waxing and waning of Alpine ice caps, and thus provide an excellent opportunity to investigate the interactions between pronounced climatic fluctuations and background tectonic activity (Scardia et al., 2006), resulting in frequent changes of drainage patterns. A high-resolution Pleistocene stratigraphy, with a complete sedimentological, paleontological, petrographic-mineralogical, magneto-stratigraphic, and seismic data base, was recently obtained from eleven continuous cores drilled in the Lombardy Po Plain north of the Po River (ENI and Regione Lombardia, 2002). In the present study we focus on two cores in the proximal (Cilavegna) and distal plain (Pianengo), which best exemplify the drastic change in sedimentary systems and drainage patterns associated with the onset of major Pleistocene glaciations in the Alps (˜870ky; Muttoni et al., 2003). This climatic event is recorded by a regional unconformity (named R-unconformity by Muttoni et al., 2003), traced all across the Po Basin and encountered at -81 m depth in the Pianengo Core and at -98 m depth in the Cilavegna Core. The Cilavegna Core consists of metamorphiclastic floodplain sediments, capped by the R-unconformity and overlain by quartzofeldspathic braidplain deposits. The Pianengo Core consists of metamorphiclastic deltaic to floodpain sediments, capped by the R-unconformity and overlain by alluvial-fan gravels rich in carbonate pebbles; another unconformity at -39 m depth is overlain by metamorphiclastic braidplain deposits. Our quantitative approach to paleodrainage analysis is based on comprehensive information obtained from modern settings (Garzanti et al., 2004; 2006). End-member modelling and similarity analysis allows us to objectively compare detrital modes from modern and ancient deposits, and to reconstruct the evolution of sediment pathways through geologic time (Vezzoli and Garzanti 2009). The Cilavegna Core documents stepwise south-westward shifts of major tributaries draining the axial belt. The Pianengo Core records the rapid southward progradation of transverse alluvial fans fed locally from the Southern Alps, followed by progressive establishment of the modern Adda river system. Evolving drainage patterns and river avulsions represent a major cause of compositional change in foreland-basin deposits. Lateral shifts of river courses, commonly associated with unconformities and favoured by an increase in the ratio between sediment fluxes and subsidence, provide crucial information on tectonic or climatic events, and should be given full consideration in provenance studies. ENI and Regione Lombardia. 2002. Geologia degli acquiferi padani della Regione Lombardia. Firenze, Società Elaborazioni Cartografiche s.r.l., 130 p. Muttoni G., Carcano C., Garzanti E., Ghielmi M., Piccin A., Pini R., Rogledi S., and Sciunnach D. 2003. Onset of major Pleistocene glaciations in the Alps. Geology, 31, 989-992. Scardia G., Muttoni G., and Sciunnach D. 2006. Subsurface magnetostratigraphy of Pleistocene sediments from the Po Plain (Italy): constraints on rates of sedimentation and rock uplift. Geological Society of America Bulletin, 118, 1299-1312. Vezzoli G. and Garzanti E. 2009. Tracking paleodrainage in foreland-basin sequences. Journal of Geology, In press.
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McCloy, C.; Ingle, J.C.; Barron, J.A.
1988-01-01
Foraminifera and diatoms have been analyzed from an upper Miocene through Pleistocene(?) sequence of marine sediments exposed on Maria Madre Island, largest of the Tre??s Marias Islands off the Pacific coast of Mexico. The Neogene stratigraphic sequence exposed on Maria Madre Island includes a mid-Miocene(?) non-marine and/or shallow marine sandstone unconformably overlain by a lower upper Miocene to uppermost Miocene upper to middle bathyal laminated and massive diatomite, mudstone, and siltstone unit. This unit is unconformably overlain by lower Pliocene middle to lower bathyal sandstones and siltstones which, in turn, are unconformably overlain by upper Pliocene through Pleistocene(?) upper bathyal to upper middle bathyal foraminiferal limestones and siltstones. These beds are unconformably capped by Pleistocene terrace deposits. Basement rocks on the island include Cretaceous granite and granodiorite, and Tertiary(?) andesites and rhyolites. The upper Miocene diatomaceous unit contains a low diversity foraminiferal fauna dominated by species of Bolivina indicating low oxygen conditions in the proto-Gulf Maria Madre basin. The diatomaceous unit grades into a mudstone that contains a latest Miocene upper to middle bathyal biofacies characterized by Baggina californica and Uvigerina hootsi along with displaced neritic taxa. An angular unconformity separates the upper Miocene middle bathyal sediments from overlying lower Pliocene siltstones and mudstones that contain a middle to lower bathyal biofacies and abundant planktonic species including Neogloboquadrina acostaensis and Pulleniatina primalis indicating an early Pliocene age. Significantly, this Pliocene unit contains common occurrences of benthic species restricted to Miocene sediments in California including Bulimina uvigerinaformis. Pliocene to Pleistocene(?) foraminiferal limestones and siltstones characterize submarine bank accumulations formed during uplift of the Tre??s Marias Island area, and include abundant planktonic foraminifera such as Pulleniatina obliquiloculata and Neogloboquadrina duterteri. Common benthic foraminifera in this unit are indicative of upper bathyal water depths. The Neogene depositional history recorded on Maria Madre Island involves an early late Miocene subsidence event marking formation of the Tre??s Marias Basin with relatively undiluted diatomaceous sediment deposited in a low oxygen setting. Subsidence and deepening of the basin continued into the early Pliocene along with rapid deposition of terrigenous clastics. Uplift of the basinal sequence began in late Pliocene time accompanied by deposition of upper Pliocene-Pleistocene foraminiferal limestones on a rising submarine bank. Continued episodic uplift of the Neogene deposits brought the island above sea level by late Pleistocene time. ?? 1988.
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Sedimentary Evolution of Marginal Ganga Foreland Basin during the Late Pleistocene
NASA Astrophysics Data System (ADS)
Ghosh, R.; Srivastava, P.; Shukla, U. K.
2017-12-01
Ganga foreland basin, an asymmetrical basin, was formed as result of plate-plate collision during middle Miocene. A major thrust event occurred during 500 ka when upper Siwalik sediments were uplifted and the modern Ganga foreland basin shifted towards craton, making a more wide and deep basin. The more distal part of this basin, south of axial river Yamuna, records fluvial sedimentary packages that helps to understand dynamics of peripheral bulge during the late Quaternary. Sedimentary architecture in conjunction with chemical index of alteration (CIA), paleocurrent direction and optically stimulated dating (OSL) from 19 stratigraphic sections helped reconstructing the variations in depositional environments vis-à-vis climate change and peripheral bulge tectonics. Three major units (i) paleosol; (ii) cratonic gravel; (iii) interfluve succession were identified. The lower unit-I showing CIA values close to 70-80 and micro-morphological features of moderately well-developed pedogenic unit that shows development of calcrete, rhizoliths, and mineralized organic matter in abundance. This is a regional paleosols unit and OSL age bracketed 200 ka. This is unconformably overlain by unit-II, a channelized gravel composed of sub-angular to sub-rounded clasts of granite, quartz, quartzite, limestone and calcrete. The gravel have low CIA value up to 55, rich in vertebrate fossil assemblages and mean paleocurrent vector direction is NE, which suggesting deposition by a fan of a river draining craton into foreland. This unit is dated between 100 ka and 54 ka. The top unit-III, interfluve succession of 10-15 m thick is composed of dark and light bands of sheet like deposit of silty clay to clayey silt comprises sand lenses of red to grey color and displaying top most OSL age is 12 ka. The basal mature paleosol signifies a humid climate developed under low subsidence rate at >100 ka. After a hiatus represented by pedogenic surface deposition of unit-II (gravel) suggests uplift and increased relief in the peripheral bulge region resulting into large flux of coarse sediments from craton. This was accompanied by humid climate and braided rivers forming a craton derived north propagating fans. Similar depositional setup at the base Siwalik is termed as peripheral bulge unconformity.
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The subsurface geology of the Florida-Hatteras shelf, slope, and inner Blake Plateau
Paull, Charles K.; Dillon, William P.
1979-01-01
The structure and stratigraphy of the Florida-Hatteras Slope and inner Blake Plateau was studied by means of 4,780 km of single-channel air gun seismic reflection profiles. Control for the seismic stratigraphy is provided by correlating reflecting units and paleontologically dated stratigraphic units identified in offshore wells and dredge hauls. Many Tertiary unconformities exist, and major regional unconformities at the end of the Oligocene and in the late Paleocene are mapped. Reflecting surfaces believed to represent the tops of the Cretaceous, Paleocene, and Oligocene extend throughout the region. Upper Cretaceous (pre-Maastrichtian) rocks on the southeastern side of the Carolina Platform form a large seaward-facing progradational wedge. The Upper Cretaceous rocks in the Southeast Georgia Embayment, are seismically transparent and on the inner Blake Plateau are cut by numerous small faults, perhaps due to compaction. Within the survey area relatively flat-lying Maastrichtian and Paleocene strata show no evidence that a feature similar to the present Florida-Hatteras Slope existed at the beginning of the Tertiary. Late Paleocene erosion, related to the initiation of the Gulf Stream flow, probably developed this regional unconformity. Eocene and Oligocene sediments landward of the present Gulf Stream form a thick sequence of seaward-dipping progradational beds. A seaward progradational wedge of Miocene to Holocene age covers a regionally traceable unconformity, which separates the Oligocene from the Miocene sediments. Under and seaward of the present Gulf Stream, the Eocene and younger sediment supply was much smaller and the buildup is comparatively insignificant. The difference in accumulation rates in the Eocene and younger sediments, landward and seaward of the Gulf Stream, is responsible for the Florida-Hatteras Slope. Tertiary isopach maps suggest that there is a well developed triangular depocenter under the shelf. The edges of the depocenter correspond with magnetic anomalies and it is suggested that the depocenter is related to differential subsidence during the Tertiary across older crustal structures. The Eocene and Oligocene units contain the aquifer onshore, and the aquifer probably remains in these units offshore. With this assumption the potential aquifer has been identified and traced under the shelf and slope.
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Johnson, G.H.; Kruse, S.E.; Vaughn, A.W.; Lucey, J.K.; Hobbs, C. H.; Powars, D.S.
1998-01-01
Upper Cenozoic strata covering the Chesapeake Bay impact structure in southeastern Virginia record intermittent differential movement around its buried rim. Miocene strata in a graben detected by seismic surveys on the York River exhibit variable thickness and are deformed above the creater rim. Fan-like interformational and intraformational angular unconformities within Pliocene-Pleistocene strata, which strike parallel to the crater rim and dip 2-3?? away from the crater center, indicate that deformation and deposition were synchronous. Concentric, large-scale crossbedded, bioclastics and bodies of Pliocene age within ~20km of the buried crater rim formed on offshore shoals, presumably as subsiding listric slump blocks rotated near the crater rim.
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Dynamic Passage of Topography Beneath the Southern Costa Rica Forearc seen with Seismic Stratigraphy
NASA Astrophysics Data System (ADS)
Edwards, J. H.; Kluesner, J. W.; Silver, E. A.
2014-12-01
3D seismic reflection data (CRISP) collected across the southern Costa Rica margin reveals that a thick, deforming sedimentary wedge underlies the younger slope sediments (Silver et al., this meeting). The older wedge material and younger slope sediments are separated by a high-amplitude regional unconformity. Seismic stratigraphy of the sedimentary strata overlying this regional unconformity reflects a dynamic deformation history of the margin. The younger slope sediments contain series of more localized unconformities, separating sedimentary units as thick as 1 km that reveal a dynamically changing set of inverted, overlapping basins. The geometry of these overlapping, inverted basins indicate sequential uplift events. The direction of basin thickening varies upsection, and these basins are cut by both thrust and normal faults and are deformed by folding. Structural development appears to be controlled by relief on the subducting plate interface, which induces uplift and subsidence and thereby controls the pattern of erosion and deposition. We interpret the evolution of these inverted stratigraphic packages as forming from subducting topography. Correlating these seismic-stratigraphic packages to recent drilling based on preliminary magnetostratigraphy from IODP site U1413 (Expedition 344 Scientists, 2013), allows us to date the passage of the subducting plate topography beginning ~2 Ma.
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In Review (Geology): Alpine Landscape Evolution Dominated by Cirque Retreat
NASA Technical Reports Server (NTRS)
Oskin, Michael; Burbank, Doug
2005-01-01
Despite the abundance in alpine terrain of glacially dissected landscapes, the magnitude and geometry of glacial erosion can rarely be defined. In the eastern Kyrgyz Range, a widespread unconformity exhumed as a geomorphic surface provides a regional datum with which to calibrate erosion. As tectonically driven surface uplift has progressively pushed this surface into the zone of ice accumulation, glacial erosion has overprinted the landscape. With as little as 500 m of incision into rocks underlying the unconformity, distinctive glacial valleys display their deepest incision adjacent to cirque headwalls. The expansion of north-facing glacial cirques at the expense of south-facing valleys has driven the drainage divide southwards at rates up to 2 to 3 times the rate of valley incision. Existing ice-flux-based glacial erosion rules incompletely model expansion of glacial valleys via cirque retreat into the low-gradient unconformity remnants. Local processes that either directly sap cirque headwalls or inhibit erosion down-glacier appear to control, at least initially, alpine landscape evolution.
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Timing, distribution, amount, and style of Cenozoic extension in the northern Great Basin
Henry, Christopher D.; McGrew, Allen J.; Colgan, Joseph P.; Snoke, Arthur W.; Brueseke, Matthew E.
2011-01-01
This field trip examines contrasting lines of evidence bearing on the timing and structural style of Cenozoic (and perhaps late Mesozoic) extensional deformation in northeastern Nevada. Studies of metamorphic core complexes in this region report extension beginning in the early Cenozoic or even Late Cretaceous, peaking in the Eocene and Oligocene, and being largely over before the onset of “modern” Basin and Range extension in the middle Miocene. In contrast, studies based on low-temperature thermochronology and geologic mapping of Eocene and Miocene volcanic and sedimentary deposits report only minor, localized extension in the Eocene, no extension at all in the Oligocene and early Miocene, and major, regional extension in the middle Miocene. A wealth of thermochronologic and thermobarometric data indicate that the Ruby Mountains–East Humboldt Range metamorphic core complex (RMEH) underwent ~170 °C of cooling and 4 kbar of decompression between ca. 85 and ca. 50 Ma, and another 450 °C cooling and 4–5 kbar decompression between ca. 50 and ca. 21 Ma. These data require ~30 km of exhumation in at least two episodes, accommodated at least in part by Eocene to early Miocene displacement on the major west-dipping mylonitic zone and detachment fault bounding the RMEH on the west (the mylonitic zone may also have been active during an earlier phase of crustal extension). Meanwhile, Eocene paleovalleys containing 45–40 Ma ash-flow tuffs drained eastward from northern Nevada to the Uinta Basin in Utah, and continuity of these paleovalleys and infilling tuffs across the region indicate little, if any deformation by faults during their deposition. Pre–45 Ma deformation is less constrained, but the absence of Cenozoic sedimentary deposits and mappable normal faults older than 45 Ma is also consistent with only minor (if any) brittle deformation. The presence of ≤1 km of late Eocene sedimentary—especially lacustrine—deposits and a low-angle angular unconformity between ca. 40 and 38 Ma rocks attest to an episode of normal faulting at ca. 40 Ma. Arguably the greatest conundrum is how much extension occurred between ca. 35 and 17 Ma. Major exhumation of the RMEH is interpreted to have taken place in the late Oligocene and early Miocene, but rocks of any kind deposited during this interval are scarce in northeastern Nevada and absent in the vicinity of the RMEH itself. In most places, no angular unconformity is present between late Eocene and middle Miocene rocks, indicating little or no tilting between the late Eocene and middle Miocene. Opinions among authors of this report differ, however, as to whether this indicates no extension during the same time interval. The one locality where Oligocene deposits have been documented is Copper Basin, where Oligocene (32.5–29.5 Ma) conglomerates are ~500 m thick. The contact between Oligocene and Eocene rocks in Copper Basin is conformable, and the rocks are uniformly tilted ~25° NW, opposite to a normal fault system dipping ~35° SE. Middle Miocene rhyolite (ca. 16 Ma) rests nonconformably on the metamorphosed lower plate of this fault system and appears to rest on the tilted upper-plate rocks with angular unconformity, but the contact is not physically exposed. Different authors of this report interpret geologic relations in Copper Basin to indicate either (1) significant episodes of extension in the Eocene, Oligocene, and middle Miocene or (2) minor extension in the Eocene, uncertainty about the Oligocene, and major extension in the middle Miocene. An episode of major middle Miocene extension beginning at ca. 16–17 Ma is indicated by thick (up to 5 km) accumulations of sedimentary deposits in half-graben basins over most of northern Nevada, tilting and fanning of dips in the synextensional sedimentary deposits, and apatite fission-track and (U-Th)/He data from the southern Ruby Mountains and other ranges that indicate rapid middle Miocene cooling through near-surface temperatures (~120–40 °C). Opinions among authors of this report differ as to whether this period of extension was merely the last step in a long history of extensional faulting dating back at least to the Eocene, or whether it accounts for most of the Cenozoic deformation in northeastern Nevada. Since 10–12 Ma, extension appears to have slowed greatly and been accommodated by high-angle, relatively wide-spaced normal faults that give topographic form to the modern ranges. Despite the low present-day rate of extension, normal faults are active and have generated damaging earthquakes as recently as 2008.
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Martian crater degradation by eolian processes: Analogy with the Rio Cuarto Crater Field, Argentina
NASA Technical Reports Server (NTRS)
Grant, J. A.; Schultz, P. H.
1993-01-01
Numerous degraded and rimless craters occur across broad areas of the Martian surface that are mantled by thick, unconformable deposits. These regions include Arabia, Mesogaea, Electris, Tempe, the interior and surface to the northwest of Isidis Basin, southern Ismenius Lacus, and the polar layered terrains. Occurrence of the deposits and low regional thermal inertias indicate that at least some accumulated fine-grained sediment (effective particle diameters of 0.1-0.5 mm or coarse silt to medium sand) to a thickness of 100's to 1000's of meters. Most unconformable deposits experienced some eolian modification that may be recent in some locales. Despite the presence of these deposits, simple eolian deposition appears incapable of creating the numerous degraded and rimless craters occurring within their limits. Nevertheless, terrestrial analyses of the Rio Cuario craters formed into loessoid deposits demonstrates that eolian redistribution of fine-grained sediment in and around craters produces degraded morphologies that are analogous to some found in mantled regions on Mars.
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NASA Astrophysics Data System (ADS)
Horn, B. L. D.; Melo, T. M.; Schultz, C. L.; Philipp, R. P.; Kloss, H. P.; Goldberg, K.
2014-11-01
The Santacruzodon assemblage zone was originally defined as a vertebrate fossil assemblage composed basically of non-mammalian cynodonts found in Santa Cruz do Sul and Venâncio Aires municipalities in Southern Brazil. This assemblage zone was positioned at the top of the Sequence I, in the Triassic Santa Maria Supersequence, Paraná Basin. However, the Santacruzodon assemblage zone does not occur across the entire area of the Santa Maria Supersequence. Based on new paleontological, structural and sedimentological data, we propose the existence of a new third-order sequence (Santa Cruz Sequence) between Sequences I and II in the Santa Maria Supersequence. Satellite image analysis was used to identify regional, NW- and NE-oriented lineaments that limit the occurrence zone. Outcrop data allowed the identification of a regional, angular unconformity that bounds the new sequence. The faunal content allowed the correlation of the new Santa Cruz Sequence with Madagascar's Isalo II fauna, corresponding to the Ladinian (Middle Triassic). New names were suggested for the sequences in the Santa Maria Supersequence, since the Santa Cruz Sequence was deposited between the former Sequences I and II. This unit was deposited or preserved exclusively on the hanging wall of normal faults, being absent from the adjacent structural blocks.
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Geology and Ore Deposits of the Uncompahgre (Ouray) Mining District, Southwestern Colorado
Burbank, Wilbur Swett; Luedke, Robert G.
2008-01-01
The Uncompahgre mining district, part of the Ouray mining district, includes an area of about 15 square miles (mi2) on the northwestern flank of the San Juan Mountains in southwestern Colorado from which ores of gold, silver, copper, lead, and zinc have had a gross value of $14 to 15 million. Bedrock within the district ranges in age from Proterozoic to Cenozoic. The oldest or basement rocks, the Uncompahgre Formation of Proterozoic age, consist of metamorphic quartzite and slate and are exposed in a small erosional window in the southern part of the district. Overlying those rocks with a profound angular unconformity are Paleozoic marine sedimentary rocks consisting mostly of limestones and dolomites and some shale and sandstone that are assigned to the Elbert Formation and Ouray Limestone, both of Devonian age, and the Leadville Limestone of Mississippian age. These units are, in turn, overlain by rocks of marine transitional to continental origin that are assigned to the Molas and Hermosa Formations of Pennsylvanian age and the Cutler Formation of Permian age; these three formations are composed predominantly of conglomerates, sandstones, and shales that contain interbedded fossiliferous limestones within the lower two-thirds of the sequence. The overlying Mesozoic strata rest also on a pronounced angular unconformity upon the Paleozoic section. This thick Mesozoic section, of which much of the upper part was eroded before the region was covered by rocks of Tertiary age, consists of the Dolores Formation of Triassic age, the Entrada Sandstone, Wanakah Formation, and Morrison Formation all of Jurassic age, and the Dakota Sandstone and Mancos Shale of Cretaceous age. These strata dominantly consist of shales, mudstones, and sandstones and minor limestones, breccias, and conglomerates. In early Tertiary time the region was beveled by erosion and then covered by a thick deposit of volcanic rocks of mid-Tertiary age. These volcanic rocks, assigned to the San Juan Formation, are chiefly tuff breccias of intermediate composition, which were deposited as extensive volcaniclastic aprons around volcanic centers to the east and south of the area. The Ouray area, in general, exhibits the typical effects of a minimum of three major uplifts of the ancestral San Juan Mountains. The earliest of these uplifts, with accompanying deformation and erosion, occurred within the Proterozoic, and the other two occurred at the close, respectively, of the Paleozoic and Mesozoic. The last event, known as the Laramide orogeny, locally was accompanied by extensive intrusion of igneous rocks of dominantly intermediate composition. Domal uplifts of the ancestral mountains resulted in peripheral monoclinal folds, plunging anticlines radial to the central core of the mountain mass, faults, and minor folds. The principal ore deposits of the Uncompahgre district were associated with crosscutting and laccolithic intrusions of porphyritic granodiorite formed during the Laramide (Late Cretaceous to early Tertiary) orogeny. The ores were deposited chiefly in the Paleozoic and Mesozoic sedimentary strata having an aggregate thickness of about 4,500 feet (ft) and occur beneath the early Tertiary unconformity, which in places truncated some of the uppermost deposits. A few ore deposits of late Tertiary age occur also in the sedimentary rocks near the southern margin of the district, but are restricted mostly to the overlying volcanic rocks. Ore deposits in the Uncompahgre district range from low-grade, contact-metamorphic through pyritic base-metal bodies containing silver and gold tellurides and native gold to silver-bearing lead-zinc deposits, and are zoned about the center of intrusive activity, a stock in an area referred to as The Blowout. Ore deposition within the Uncompahgre district was largely controlled by structural trends and axes of uplift established mainly in the late Paleozoic phase of deformation, but also in part by structural lin
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NASA Technical Reports Server (NTRS)
Grant, J. A.; Schultz, P. H.
1987-01-01
A large area in the Electris region of Mars is (or once was) covered by an unconformable and etched deposit. Although interpreted as lava filling volcano-tectonic depressions or fluvial deposits filling large degraded craters, more recent work has shown the deposit is more likely the result of air-fall deposition. Crater densities on both the surface of the deposit and on exhumed, underlying ridged plains indicate that the deposit was emplaced and eroded over a relatively short time. These crater statistics also demonstate that the relative age of the Electris deposit is similar to those obtained for other unconformable deposits, thereby suggesting they may be related.
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NASA Astrophysics Data System (ADS)
Ilao, Kimberly A.; Morley, Christopher K.; Aurelio, Mario A.
2018-04-01
The Pagasa Wedge is a poorly imaged deepwater orogenic wedge that has been variously interpreted as representing an accretionary prism, a former accretionary prism modified by thrusting onto a thinned continental margin, and a gravity-driven fold-thrust belt. This study, using 2D and 3D seismic data, together with well information indicates that at least the external part of the wedge is dominantly composed of mass transport complexes, capped by syn-kinematic sediments that have thrusts and normal faults superimposed upon them. Drilling shows that despite stratigraphic repetition of Eocene Middle Miocene units, there is stratigraphic omission of Oligocene and Early Miocene units. This absence suggests that mass transport processes have introduced the Eocene section into the wedge rather than tectonic thrusting. The accretionary prism stage (Oligocene) of the Central Palawan Ophiolite history appears to be marked by predominantly north-vergent deformation. The Deep Regional Unconformity (∼17 Ma) likely indicates the approximate time when obduction ceased in Palawan. The Pagasa Wedge is a late-stage product of the convergence history that was active in its final phase sometime above the top of the Nido Limestone (∼16 Ma) and the base of the Tabon Limestone in the Aboabo-A1X well (∼9 Ma). The top of the wedge is traditionally associated with the Middle Miocene Unconformity (MMU), However the presence of multiple unconformities, diachronous formation tops, local tectonic unconformities and regional diachronous events (e.g. migrating forebulges) all suggest simply giving a single age (or assigning a single unconformity, such as the MMU as defining the top of the Pagasa Wedge is inappropriate. The overall NE-SW trend of the wedge, and the dominant NW transport of structures within the wedge diverge from the more northerly transport direction determined from outcrops in Palawan, and also from the Nido Limestone in the SW part of the Pagasa Wedge. Possibly this NW transport direction is more related to gravity-driven structures responding to uplift of NE-SW Dangerous Grounds margin during the Middle Miocene (related to slab breakoff?) than it is to thrusting rooted in a plate boundary. The final modification of the wedge occurred when the effects of compression deformation on the wedge had largely ended, but gravity processes (in particular mass transport and normal faulting) still operated.
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Sedimentary Cover of the Central Arctic
NASA Astrophysics Data System (ADS)
Kireev, Artem; Poselov, Viktor; Butsenko, Viktor; Smirnov, Oleg
2017-04-01
Partial revised Submission of the Russian Federation for establishment of the OLCS (outer limit of the continental shelf) in the Arctic Ocean is made to include in the extended continental shelf of the Russian Federation, in accordance with article 76 of the Convention, the seabed and its subsoil in the central Arctic Ocean which is natural prolongation of the Russian land territory. To submit partial revised Submission in 2016, in 2005 - 2014 the Russian organizations carried out a wide range of geophysical studies, so that today over 23000 km of MCS lines, over hundreds of wide-angle reflection/refraction seismic sonobuoy soundings and 4000 km of deep seismic sounding are accomplished. All of these MCS and seismic soundings data were used to establish the seismic stratigraphy model of the Arctic region. Stratigraphy model of the sedimentary cover was successively determined for the Cenozoic and pre-Cenozoic parts of the section and was based on correlation of the Russian MCS data and seismic data documented by existing boreholes. Interpretation of the Cenozoic part of the sedimentary cover was based on correlation of the Russian MCS data and AWI91090 section calibrated by ACEX-2004 boreholes on the Lomonosov Ridge for Amerasia basin and by correlation of onlap contacts onto oceanic crust with defined magnetic anomalies for Eurasia basin, while interpretation of the Pre-Cenozoic part of the sedimentary cover was based on correlation with MCS and boreholes data from Chukchi sea shelf. Six main unconformities were traced: regional unconformity (RU), Eocene unconformity (EoU) (for Eurasia basin only), post-Campanian unconformity (pCU), Brookian (BU - base of the Lower Brookian unit), Lower Cretaceous (LCU) and Jurassic (JU - top of the Upper Ellesmerian unit). The final step in our research was to estimate the total thickness of the sedimentary cover of the Arctic Ocean and adjacent Eurasian shelf using top of acoustic basement correlation data and bathymetry data. Structural prolongation of the shallow shelf into deep-water could be observed on this sedimentary map.
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Ettensohn, F.R.; Pashin, J.C.
1997-01-01
The Devonian-Carboniferous transition on Laurussia was a time of diverse geologic activity associated with the assembly of Pangea, including episodes of Late Devonian glacial-eustatic lowstand and active orogeny on four margins. Six widespread unconformities are present in the Devonian-Carboniferous (Mississippian) interval on southern parts of Laurussia. We suggest that attention to the timing and plan of the unconformities may provide ways of discerning tectonic and climatic controls on their respective origins. Indeed, unconformities generated by pure eustasy are ideally of interregional extent, whereas unconformities generated by tectonism reflect more local factors associated with the evolution of sedimentary basins. Each of the six unconformities analyzed provides evidence for concurrent eustasy and tectonism. Glaciation was apparently the dominant factor driving the development of unconformities during the latest Devonian. During the Early Carboniferous, however, the volume of glacial ice available to drive eustasy was limited and, at times, tectonism may have been the source of a subordinate eustatic signal. Development of unconformities in southern Laurussia appear to be local manifestations of tectonic and climatic processes associated with supercontinent assembly. Thus, the time may be at hand for construction of a new global stratigraphic paradigm that is based on the plate tectonic supercycle affecting continentality and climate.
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Murray, B.; Koutnik, M.; Byrne, S.; Soderblom, L.; Herkenhoff, K.; Tanaka, K.L.
2001-01-01
We have examined the local base of the south polar layered deposits (SPLD) exposed in the bounding scarp near 72??-74??S, 215??- 230??W where there is a clear unconformable contact with older units. Sections of layering up to a kilometer thick were examined along the bounding scarp, permitting an estimate of the thinnest individual layers yet reported in the SPLD. Rhythmic layering is also present locally, suggesting a similarly rhythmic variation in environmental conditions and a recorded climate signal at least in some SPLD strata. Locally, angular unconformities may be present, as has been reported for the north polar layered deposits (NPLD) and may likewise imply intervals of subaerial erosion in the SPLD. The outcropping layers display a broad range of weathering styles and may reflect more diverse conditions of depositions, erosion, and diagenesis than might have been expected from simple aeolian depostion modulated only by astronomically driven climatic fluctuations. An unexpected finding of our study is the presence of locally abundant small pits close to the bounding scarp. These quasi-circular, negative, rimless features probably originated as impact craters and were modified to varying degrees by local endogenic processes, as well as locally variable blanketing. A nominal exposure age for the most heavily cratered region in our study area is about 2 million years, and the crater statistics appear consistent with those for the overall SPLD, although there are large uncertainties in the absolute ages implied by the crater size-frequency statistics, as in all martian crater ages. Another new finding is the presence of mass wasting features along the steepest portion of the retreating bounding scarp as well as a number of examples of brittle fracture, consistent with large-scale slumping along the bounding scarp and probably also ancient basal sliding. Both subhorizontal and high angle faults appear to be exposed in the bounding scarp, but the dips of the faults are poorly constrained. These fractures, along with the relatively undeformed layers between them, suggest to us that whatever horizontal motion may have taken place outward from the central cap region was accomplished by ancient basal sliding rather than large-scale glacial-like flow or ice migration by differential ablation, as proposed recently for the northern permanent cap and underlying NPLD. We have also obtained the, first direct estimate of the regional dip of the SPLD, around 2-3* outward (northward) in one area. ?? 2001 Elsevier Science.
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NASA Astrophysics Data System (ADS)
Dkhaili, Noomen; Bey, Saloua; El Abed, Mahmoud; Gasmi, Mohamed; Inoubli, Mohamed Hedi
2015-09-01
An integrated study of available seismic and calibrated wells has been conducted in order to ascertain the structural development and petroleum potential of the Cretaceous Formations of the Western Gulf of Gabes. This study has resulted in an understanding of the controls of deep seated Tethyan tectonic lineaments by analysis of the Cretaceous deposits distribution. Three main unconformities have been identified in this area, unconformity U1 between the Jurassic and Cretaceous series, unconformity U2 separating Early from Late Cretaceous and known as the Austrian unconformity and the major unconformity U3 separating Cretaceous from Tertiary series. The seismic analysis and interpretation have confirmed the existence of several features dominated by an NE-SW extensive tectonic regime evidenced by deep listric faults, asymmetric horst and graben and tilted blocks structures. Indeed, the structural mapping of these unconformities, displays the presence of dominant NW-SE fault system (N140 to N160) bounding a large number of moderate sized basins. A strong inversion event related to the unconformity U3 can be demonstrated by the mapping of the unconformities consequence of the succession of several tectonic manifestations during the Cretaceous and post-Cretaceous periods. These tectonic events have resulted in the development of structural and stratigraphic traps further to the porosity and permeability enhancement of Cretaceous reservoirs.
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Blake, B.M.; Beuthin, J.D.
2008-01-01
A prominent unconformity, present across shallow shelf areas of the Euramerican paleoequatorial basins, is used to demark the boundary between the Mississippian and Pennsylvanian subsystems. This unconformity, the mid-Carboniferous eustatic event, is generally attributed to a major glacio-eustatic sea-level fall. Although a Mississippian-Pennsylvanian unconformity is recognized throughout most of the Appalachian region, the record of the mid-Carboniferous eustatic event in the structurally deepest part of the basin has been controversial. Based on early reports that suggested the most complete Pennsylvanian section was present in southern West Virginia, various conceptual depositional models postulated continuous sedimentation between the youngest Mississippian Bluestone Formation and the oldest Penn-sylvanian Pocahontas Formation. In contrast, tabular-erosion models envisioned axial drainage systems that evolved in response to changing basin dynamics. These models predicted a Mississippian-Pennsylvanian unconformity. All these models suffered from a lack of biostratigraphic control. The presence of a sub-Pocahontas paleovalley, herein named the Lashmeet paleovalley, has been confirmed in southern West Virginia. The Lashmeet paleovalley was incised over 35 m into Bluestone strata and filled by lithic sands derived from the Appalachian orogen to the northeast and east. The polygenetic Green Valley paleosol complex marks the Bluestone-Pocahontas contact on associated interfluves. Together, these features indicate a substantial period of subaerial exposure and argue strongly in favor of a Mississippian-Pennsylvanian unconformity. Paleontologic data from the Bluestone Formation, including marine invertebrates and conodonts from the marine Bramwell Member and paleofloral data, support a late, but not latest, Arnsbergian age assignment. Marine fossils are not known from the Pocahontas Formation, but macrofloral and palynomorph taxa support a Langsettian age for most of the Poca-hontas. The biostratigraphic, sedimentologic, and paleogeographic data support the presence of an early Pennsylvanian (middle to late Namurian) disconformity in the Appalachian Basin that corresponds to the mid-Carboniferous eustatic event. ?? 2008 Geological Society of America.
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NASA Astrophysics Data System (ADS)
Vandenburg, Colby J.; Janecke, Susanne U.; McIntosh, William C.
1998-12-01
The Horse Prairie basin of southwestern Montana is a complex, east-dipping half-graben that contains three angular unconformity-bounded sequences of Tertiary sedimentary rocks overlying middle Eocene volcanic rocks. New mapping of the basin and its hanging wall indicate that five temporally and geometrically distinct phases of normal faulting and at least three generations of fault-related extensional folding affected the area during the late Mesozoic (?) to Cenozoic. All of these phases of extension are evident over regional or cordilleran-scale domains. The extension direction has rotated ˜90° four times in the Horse Prairie area resulting in a complex three-dimensional strain field with ≫60% east-west and >25% north-south bulk extension. Extensional folds with axes at high angles to the associated normal fault record most of the three-dimensional strain during individual phases of extension (phases 3a, 3b, and 4). Cross-cutting relationships between normal faults and Tertiary volcanic and sedimentary rocks constrain the ages of each distinct phase of deformation and show that extension continued episodically for more than 50 My. Gravitational collapse of the Sevier fold and thrust belt was the ultimate cause of most of the extension.
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Analysis of some seismic expressions of Big Injun sandstone and its adjacent interval
DOE Office of Scientific and Technical Information (OSTI.GOV)
Xiangdong, Zou; Wilson, T.A.; Donaldson, A.C.
1991-08-01
The Big Injun sandstone is an important oil and gas reservoir in western West Virginia. The pre-Greenbrier unconformity has complicated correlations, and hydrocarbon explorationists commonly have misidentified the Big Injun in the absence of a regional stratigraphic study. Paleogeologic maps on this unconformity show the West Virginia dome, with the Price/Pocono units truncated resulting in pinch-outs of different sandstones against the overlying Big Lime (Greenbrier Limestone). Drillers have named the first sandstone below the Big Lime as Big Injun, and miscorrelated the real Big Injun with Squaw, upper Weir, and even the Berea sandstone. In this report, an 8-mi (13-km)more » seismic section extending from Kanawha to Clay counties was interpreted. The study area is near the pinch-out of the Big Injun sandstone. A stratigraphic cross section was constructed from gamma-ray logs for comparison with the seismic interpretation. The modeling and interpretation of the seismic section recognized the relief on the unconformity and the ability to determine facies changes, too. Both geophysical wireline and seismic data can be used for detailed stratigraphic analysis within the Granny Creek oil field of Clay and Roane countries.« less
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Geologic framework of lower Cook Inlet, Alaska
Fisher, M.A.; Magoon, L.B.
1978-01-01
Three seismic reflectors are present throughout the lower Cook Inlet basin and can be correlated with onshore geologic features. The reflections come from unconformities at the base of the Tertiary sequence, at the base of Upper Cretaceous rocks, and near the base of Upper Jurassic strata. A contour map of the deepest horizon shows that Mesozoic rocks are formed into a northeast-trending syncline. Along the southeast flank of the basin, the northwest-dipping Mesozoic rocks are truncated at the base of Tertiary rocks. The Augustine-Seldovia arch trends across the basin axis between Augustine Island and Seldovia. Tertiary rocks thin onto the arch from the north and south. Numerous anticlines, smaller in structural relief and breadth than the Augustine-Seldovia arch, trend northeast parallel with the basin, and intersect the arch at oblique angles. The stratigraphic record shows four cycles of sedimentation and tectonism that are bounded by three regional unconformities in lower Cook Inlet and by four thrust faults and the modern Benioff zone in flysch rocks of the Kenai Peninsula and the Gulf of Alaska. The four cycles of sedimentation are, from oldest to youngest, the early Mesozoic, late Mesozoic, early Cenozoic, and late Cenozoic. Data on organic geochemistry of the rocks from one well suggest that Middle Jurassic strata may be a source of hydrocarbons. Seismic data show that structural traps are formed by northeast-trending anticlines and by structures formed at the intersections of these anticlines with the transbasin arch. Stratigraphic traps may be formed beneath the unconformity at the base of Tertiary strata and beneath unconformities within Mesozoic strata.
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Poag, C. Wylie; Ward, Lauck W.
1993-01-01
Publication of Volumes 93 and 95 ('The New Jersey Transect') of the Deep Sea Drilling Project's Initial Reports completed a major phase of geological and geophysical research along the middle segment of the U. S. Atlantic continental margin. Relying heavily on data from these and related published records, we have integrated outcrop, borehole, and seismic-reflection data from this large area (500,000 km^2 ) to define the regional allostratigraphic framework for Upper Cretaceous and Cenozoic sedimentary rocks. The framework consists of 12 alloformations, which record the Late Cretaceous and Cenozoic depositional history of the contiguous Baltimore Canyon trough (including its onshore margin) and Hatteras basin (northern part). We propose stratotype sections for each alloformation and present a regional allostratigraphic reference section, which crosses these basins from the inner edge of the coastal plain to the inner edge of the abyssal plain. Selected supplementary reference sections on the coastal plain allow observation of the alloformations and their bounding unconformities in outcrop. Our analyses show that sediment supply and its initial dispersal on the middle segment of the U. S. Atlantic margin have been governed, in large part, by hinterland tectonism and subsequently have been modified by paleoclimate, sea-level changes, and oceanic current systems. Notable events in the Late Cretaceous to Holocene sedimentary evolution of this margin include (1) development of continental-rise depocenters in the northern part of the Hatteras basin during the Late Cretaceous; (2) the appear ance of a dual shelf-edge system, a marked decline in siliciclastic sediment accumulation rates, and widespread acceleration of carbonate production during high sea levels of the Paleogene; (3) rapid deposition and progradation of thick terrigenous delta complexes and development of abyssal depocenters during the middle Miocene to Quaternary interval; and (4) deep incision of the shelf edge by submarine canyons, especially during the Pleistocene. Massive downslope gravity flows have dominated both the depositional and erosional history of the middle segment of the U. S. Atlantic Continental Slope and Rise during most of the last 84 million years. The importance of periodic widespread erosion is recorded by well-documented unconformities, many of which can be traced from coastal-plain outcrops to coreholes on the continental slope and lower continental rise. These unconformities form the boundaries of the 12 allostratigraphic units we formally propose herein. Seven of the unconformities correlate with supercycle boundaries (sequence boundaries) that characterize the Exxon sequence-stratigraphy model.
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Arctic Ocean Sedimentary Cover Structure, Based on 2D MCS Seismic Data.
NASA Astrophysics Data System (ADS)
Kireev, A.; Kaminsky, V.; Poselov, V.; Poselova, L.; Kaminsky, D.
2016-12-01
In 2016 the Russian Federation has submitted its partial revised Submission for establishment of the OLCS (outer limit of the continental shelf) in the Arctic Ocean. In order to prepare the Submission, in 2005 - 2014 the Russian organizations carried out a wide range of geological and geophysical studies, so that today over 23000 km of MCS lines and 4000 km of deep seismic sounding are accomplished. For correct time/depth conversion of seismic sections obtained with a short streamer in difficult ice conditions wide-angle reflection/refraction seismic sonobuoy soundings were used. All of these seismic data were used to refine the stratigraphy model, to identify sedimentary complexes and to estimate the total thickness of the sedimentary cover. Seismic stratigraphy model was successively determined for the Cenozoic and pre-Cenozoic parts of the sedimentary section and was based on correlation of the Russian MCS data and seismic data documented by boreholes. Cenozoic part of the sedimentary cover is based on correlation of the Russian MCS data and AWI91090 section calibrated by ACEX-2004 boreholes on the Lomonosov Ridge for Amerasia basin and by correlation of onlap contacts onto oceanic crust with defined magnetic anomalies for Eurasia basin. Pre-Cenozoic part of the sedimentary cover is based on tracing major unconformities from boreholes on the Chukchi shelf (Crackerjack, Klondike, Popcorn) to the North-Chuckchi Trough and further to the Mendeleev Rise as well as to the Vilkitsky Trough and the adjacent Podvodnikov Basin. Six main unconformities were traced: regional unconformity (RU), Eocene unconformity (EoU) (for Eurasia basin only), post-Campanian unconformity (pCU), Brookian (BU - base of the Lower Brookian unit), Lower Cretaceous (LCU) and Jurassic (JU - top of the Upper Ellesmerian unit). The final step in our research was to generalize all seismic surveys (top of acoustic basement correlation data) and bathymetry data in the sedimentary cover thickness map of the Arctic Ocean and adjacent Eurasian shelf, on which the structural prolongation of the shallow shelf into deep-water is obviously seen.
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Large fluctuations of shallow seas in low-lying Southeast Asia driven by mantle flow
NASA Astrophysics Data System (ADS)
Zahirovic, Sabin; Flament, Nicolas; Dietmar Müller, R.; Seton, Maria; Gurnis, Michael
2016-09-01
The Sundaland continental promontory, as the core of Southeast Asia, is one of the lowest lying continental regions, with half of the continental area presently inundated by a shallow sea. The role of mantle convection in driving long-wavelength topography and vertical motion of the lithosphere in this region has often been ignored when interpreting regional stratigraphy, including a widespread Late Cretaceous-Eocene unconformity, despite a consensus that Southeast Asia is presently situated over a large-amplitude dynamic topography low resulting from long-term post-Pangea subduction. We use forward numerical models to link mantle flow with surface tectonics and compare predicted trends of dynamic topography with eustasy and regional paleogeography to determine the influence of mantle convection on regional basin histories. A Late Cretaceous collision of Gondwana-derived terranes with Sundaland choked the active margin, leading to slab breakoff and a ˜10-15 Myr-long subduction hiatus. A subduction hiatus likely resulted in several hundred meters of dynamic uplift and emergence of Sundaland between ˜80 and 60 Ma and may explain the absence of a Late Cretaceous-Eocene sedimentary record. Renewed subduction from ˜60 Ma reinitiated dynamic subsidence of Sundaland, leading to submergence from ˜40 Ma despite falling long-term global sea levels. Our results highlight a complete "down-up-down" dynamic topography cycle experienced by Sundaland, with transient dynamic topography manifesting as a major regional unconformity in sedimentary basins.
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Composition and stable-isotope geochemistry of natural gases from Kansas, Midcontinent, U.S.A.
Jenden, P.D.; Newell, K.D.; Kaplan, I.R.; Watney, W.L.
1988-01-01
More than 28??1012 ft.3 (79??1010 m3) of natural gas and 5.3??109 bbl (8.4??108 m3) of oil have been produced in Kansas, U.S.A., from Paleozoic carbonate and sandstone reservoirs on structural uplifts and shallow embayments along the northern margin of the Anadarko basin. A heavily-explored, geologically well-characterized state, Kansas is an excellent place to study hydrocarbon migration and to test geochemical models for the origin of natural gases. Immature to marginally-mature rocks of eastern Kansas (Cherokee and Forest City basins) produce mixed microbial and thermogenic gases. Gases in this region have wetness = 0.03-51%, methane ??13C = -65 to -43??? and methane ??D = -260 to -150???. Gases from central and western Kansas (Nemaha uplift to Hugoton embayment) are entirely thermogenic and have wetness =4-51%, methane ??13C = -48 to -39??? and methane ??D = -195 to -140???. Ethane and propane ??13C-values throughout Kansas vary from -38 to -28??? and from -35 to -24???, respectively. Mature thermogenic gas (generated from source rocks in southwestern Kansas and the Anadarko basin with 1.0% ??? Ro ??? 1.4%) is recognized throughout the state. Lateral migration into shallow reservoirs on the Central Kansas and northern Nemaha uplifts and in the Cherokee basin probably occurred along basal Pennsylvanian conglomerates and weathered Lower Paleozoic carbonates at the regional sub-Pennsylvanian unconformity. Early thermogenic gas (generated by local source rocks with Ro ??? 0.7%) is recognized in isolated fields in the Salina and Forest City basins, in Ordovician reservoirs beneath the sub-Pennsylvanian unconformity in the Cherokee basin, and in reservoirs generally above the unconformity in the Cherokee and Sedgwick basins, the eastern Central Kansas uplift and the Hugoton embayment. ?? 1988.
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NASA Astrophysics Data System (ADS)
Gillespie, Janice M.; Heller, Paul L.
1995-08-01
Subsidence analysis and geometry of Jurassic-Cretaceous foreland strata in northwestern Montana and southern Alberta and British Columbia suggest that loading by the fold-thrust belt in Canada began as much as 40 m.y. earlier than in Montana. In Canada, early foreland basin deposits are Late Jurassic age, thicken rapidly westward, and are restricted to a narrow belt within 30 km of the thrust belt. In western Montana, contemporaneous deposits are widespread and do not increase markedly in thickness toward the thrust belt. The unconformity overlying these deposits also changes from Canada, where it is angular, to a disconformity in western Montana near Great Falls. Between these two areas, foreland geometry is transitional over a distance of <250 km. Beyond the transition zone, early foreland basin geometries are broadly consistent, showing Late Jurassic foreland subsidence in southern Canada and Early Cretaceous initial subsidence in the United States.
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NASA Astrophysics Data System (ADS)
Qin, Yu; Feng, Qiao; Chen, Gang; Chen, Yan; Zou, Kaizhen; Liu, Qian; Jiao, Qianqian; Zhou, Dingwu; Pan, Lihui; Gao, Jindong
2018-05-01
The Maoniushan Formation in the northern part of the North Qaidam Orogen (NQO), NW China, contains key information on a Paleozoic change in tectonic setting of the NQO from compression to extension. Here, new zircon U-Pb, petrological, and sedimentological data for the lower molasse sequence of the Maoniushan Formation are used to constrain the timing of this tectonic transition. Detrital zircons yield U-Pb ages of 3.3-0.4 Ga with major populations at 0.53-0.4, 1.0-0.56, 2.5-1.0, and 3.3-2.5 Ga. The maximum depositional age of the Maoniushan Formation is well constrained by a youngest detrital zircon age of ∼409 Ma. Comparing these dates with geochronological data for the region indicates that Proterozoic-Paleozoic zircons were derived mainly from the NQO as well as the Oulongbuluk and Qaidam blocks, whereas Archean zircons were probably derived from the Oulongbuluk Block and the Tarim Craton. The ∼924, ∼463, and ∼439 Ma tectonothermal events recorded in this region indicate that the NQO was involved in the early Neoproterozoic assembly of Rodinia and early Paleozoic microcontinental convergence. A regional angular unconformity between Devonian and pre-Devonian strata within the NQO suggests a period of strong mountain building between the Oulongbuluk and Qaidam blocks during the Silurian, whereas an Early Devonian post-orogenic molasse, evidence of extensional collapse, and Middle to Late Devonian bimodal volcanic rocks and Carboniferous marine carbonate rocks clearly reflect long-lived tectonic extension. Based on these results and the regional geology, we suggest that the Devonian volcano-sedimentary rocks within the NQO were formed in a post-orogenic extensional setting similar to that of the East Kunlun Orogen, indicating that a major tectonic transition from compression to extension in these two orogens probably commenced in the Early Devonian.
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NASA Astrophysics Data System (ADS)
Song, Insun; Chang, Chandong
2017-05-01
This paper presents a complete set of in situ stress calculations for depths of 200-1400 meters below seafloor at Integrated Ocean Drilling Program (IODP) Site C0002, near the seaward margin of the Kumano fore-arc basin, offshore from southwest Japan. The vertical stress component was obtained by integrating bulk density calculations from moisture and density logging data, and the two horizontal components were stochastically optimized by minimizing misfits between a probabilistic model and measured breakout widths for every 30 m vertical segment of the wellbore. Our stochastic optimization process reveals that the in situ stress regime is decoupled across an unconformity between an accretionary complex and the overlying Kumano fore-arc basin. The stress condition above the unconformity is close to the critical condition for normal faulting, while below the unconformity the geologic system is stable in a normal to strike-slip fault stress regime. The critical state of stress demonstrates that the tectonic evolution of the sedimentary system has been achieved mainly by the regionally continuous action of a major out-of-sequence thrust fault during sedimentation in the fore-arc basin. The stable stress condition in the accretionary prism is interpreted to have resulted from mechanical decoupling by the accommodation of large displacement along the megasplay fault.
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NASA Technical Reports Server (NTRS)
Brockmann, C. E. (Principal Investigator); Ayllon, R. B.
1973-01-01
The author has identified the following significant results. Using ERTS-1 imagery, it is possible to delimit great lithological units, folds, lineaments, faults, and in lesser degree unconformities. In the morphological aspect, the images show clearly the relief necessary for geological interpretation. The ERTS-1 images are important for the preparation of the geological and tectonic map of Bolivia, on a 1:1 million scale, if conventional methods of work are used as a base.
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Thermal Ion Upwelling in the High-Altitude Ionosphere
1990-01-01
hard sphere collisions) while Vst is the momentum transfer collision frequency between all the other species t and a single s species particle. For... angular dimensions of day side entrance region off of Od degrees towards evening Od angular dimensions of day side entrance region off of 0d...degrees towards morning + angular dimensions of night side exit region off of on towards degrees On degre morning On angular dimensions of night side exit
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Hill, Jenna C.; Brothers, Daniel S.; Craig, Bradley K.; ten Brink, Uri S.; Chaytor, Jason D.; Flores, Claudia
2017-01-01
Multiple styles of failure, ranging from densely spaced, mass transport driven canyons to the large, slab-type slope failure of the Currituck Slide, characterize adjacent sections of the central U.S. Atlantic margin that appear to be defined by variations in geologic framework. Here we use regionally extensive, deep penetration multichannel seismic (MCS) profiles to reconstruct the influence of the antecedent margin physiography on sediment accumulation along the central U.S. Atlantic continental shelf-edge, slope, and uppermost rise from the Miocene to Present. These data are combined with high-resolution sparker MCS reflection profiles and multibeam bathymetry data across the Currituck Slide Complex. Pre-Neogene allostratigraphic horizons beneath the slope are generally characterized by low gradients and convex downslope profiles. This is followed by the development of thick, prograded deltaic clinoforms during the middle Miocene. Along-strike variations in morphology of a regional unconformity at the top of this middle Miocene unit appear to have set the stage for differing styles of mass transport along the margin. Areas north and south of the Currituck Slide are characterized by oblique margin morphology, defined by an angular shelf-edge and a relatively steep (> 8°), concave slope profile. Upper slope sediment bypass, closely spaced submarine canyons, and small, localized landslides confined to canyon heads and sidewalls characterize these sectors of the margin. In contrast, the Currituck region is defined by a sigmoidal geometry, with a rounded shelf-edge rollover and gentler slope gradient (< 6°). Thick (> 800 m), regionally continuous stratified slope deposits suggest the low gradient Currituck region was a primary depocenter for fluvial inputs during multiple sea level lowstands. These results imply that the rounded, gentle slope physiography developed during the middle Miocene allowed for a relatively high rate of subsequent sediment accumulation, thus providing a mechanism for compaction–induced overpressure that preconditioned the Currituck region for failure. Detailed examination of the regional geological framework illustrates the importance of both sediment supply and antecedent slope physiography in the development of large, potentially unstable depocenters along passive margins.
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Drowning unconformities: Palaeoenvironmental significance and involvement of global processes
NASA Astrophysics Data System (ADS)
Godet, Alexis
2013-07-01
Drowning unconformities are stratigraphic key surfaces in the history of carbonate platforms. They mostly consist in the deposition of deep marine facies on top of shallow marine limestones. Although large-scale depositional geometries mimic lowstand systems track architecture, these sedimentary turnovers are developed in relation with major sea level rise, inducing an increase in the rate of creation of accommodation space that outpaces the capacity of carbonate to keep up. This so-called paradox of carbonate platform drowning implies that parameters other than purely eustatic fluctuations are involved in the demise of shallow marine ecosystems. Worldwide and at different times during Earth history, in-depth studies of drowning unconformities revealed that changes in nutrient input, clastic delivery, temperature, or a combination of them may be responsible for a decrease in light penetration in the water column and the progressive suffocation and poisoning of photosynthetic carbonate producers. The examination of such case examples from various stratigraphic intervals and palaeogeographical settings thus helps in identifying and hierarchizing potential triggering mechanisms for drowning unconformities. This is complemented by new data from Early Cretaceous successions from the Helvetic Alps. During this time period, the Helvetic carbonate platform developed along the northern Tethyan margin using both photozoan and heterozoan communities. Phases of healthy production were interrupted by several drowning episodes. The latter are marked in the sedimentary record by condensation and associated phosphogenesis and glauconitisation. From the earliest Valanginian to the early to late Barremian, three drowning unconformities reflect the intermittent installation of a more humid climate and subsequent enhanced trophic conditions, which first induced a switch from photozoan to heterozoan communities and then to long-lasting drowning phases. The latter encompass several sea level rise and fall cycles, and may be linked to strengthened upwelling currents. With the return to more oligotrophic conditions during the late Barremian, photozoan, Urgonian-type communities took up again. Their development has been abruptly stopped at the end of the early Aptian by a major emersion phase. The subsequent drowning is documented in various peritethyan areas. This initial crisis is followed by three other drowning phases that ultimately led to the replacement of shallow ecosystems by a deeper marine sedimentation in the Cenomanian. This long-term trend in the evolution of the Helvetic carbonate platform and of other peritethyan ecosystems may have been driven by more global phenomena. In particular, the progressive opening of the northern and equatorial Atlantic may have impacted sea level by creating new oceanic basins. The emplacement of submarine volcanic plateaus may have triggered sea level rise and fertilized deep oceanic waters through hydrothermal processes. Drowning unconformities thus record the interplay of local with long-term processes, and constitute regional sedimentary archives of global phenomena.
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Paleobathymetric Reconstruction of Ross Sea: seismic data processing and regional reflectors mapping
NASA Astrophysics Data System (ADS)
Olivo, Elisabetta; De Santis, Laura; Wardell, Nigel; Geletti, Riccardo; Busetti, Martina; Sauli, Chiara; Bergamasco, Andrea; Colleoni, Florence; Vanzella, Walter; Sorlien, Christopher; Wilson, Doug; De Conto, Robert; Powell, Ross; Bart, Phil; Luyendyk, Bruce
2017-04-01
PURPOSE: New maps of some major unconformities of the Ross Sea have been reconstructed, by using seismic data grids, combined with the acoustic velocities from previous works, from new and reprocessed seismic profiles. This work is carried out with the support of PNRA and in the frame of the bilateral Italy-USA project GLAISS (Global Sea Level Rise & Antarctic Ice Sheet Stability predictions), funded by the Ministry of Foreign Affairs. Paleobathymetric maps of 30, 14 and 4 million years ago, three 'key moments' for the glacial history of the Antarctic Ice Sheet, coinciding with global climatic changes. The paleobathymetric maps will then be used for numeric simulations focused on the width and thickness of the Ross Sea Ice Sheet. PRELIMINARY RESULTS: The first step was to create TWT maps of three main unconformity (RSU6, RSU4, and RSU2) of Ross Sea, revisiting and updating the ANTOSTRAT maps, through the interpretation of sedimentary bodies and erosional features, used to infer active or old processes along the slope, we identified the main seismic unconformities. We used the HIS Kingdom academic license. The different groups contribution was on the analysis of the Eastern Ross Sea continental slope and rise (OGS), of the Central Basin (KOPRI) of the western and central Ross Sea (Univ. of Santa Barbara and OGS), where new drill sites and seismic profiles were collected after the publication of the ANTOSTRAT maps. Than we joined our interpretation with previous interpretations. We examined previous processing of several seismic lines and all the old acoustic velocity analysis. In addiction we reprocessed some lines in order to have a higher data coverage. Then, combining the TWT maps of the unconformity with the old and new speed data we created new depth maps of the study area. The new depth maps will then be used for reconstructing the paleobathymetry of the Ross Sea by applying backstripping technique.
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Edwards, L.E.; Bybell, L.M.; Gohn, G.S.; Frederiksen, N.O.
1997-01-01
Pregnall No. 1, a 346-ft-deep corehole in northern Dorchester County, South Carolina, recovered sediments of late Paleocene, middle and late Eocene, and late Oligocene age. The core bottomed in the Chicora Member of the Williamsburg Formation (Black Mingo Group) of late Paleocene age (calcareous nannofossil Zones NP 7/8 (?) and NP 9). The Chicora (346 to 258 ft depth) consists of two contrasting lithologic units, a lower siliciclastic section of terrigenous sand, silt, and clay, and an upper carbonate section of moldic pelecypod limestone. The Chicora is overlain unconformably by the middle Eocene Moultrie Member of the Santee Limestone (Orangeburg Group). The Moultrie (258.0 to 189.4 ft) consists primarily of bryozoan-pelecypod-peloid packstones and grainstones, which are assigned to calcareous nannofossil Zone NP 16. Unconformably above the Moultrie are the locally shelly, microfossiliferous limestones of the Cross Member of the Santee Limestone (Orangeburg Group), which are assigned to middle Eocene Zone NP 17 and upper Eocene Zone NP 18. The Cross Member (189.4 to 90.9 ft) is unconformably overlain by a very thin, basal section of the upper Eocene Harleyville Formation (Cooper Group). The thin Harleyville section consists of fossiliferous limestone, primarily pelecypod-foraminifer-peloid packstones (90.9 to 85.8 ft), and is assigned to Zone NP 18, although samples from thicker Harleyville sections in the region typically are assigned to upper Eocene Zone NP 19/20. The Harleyville is overlain unconformably by the upper Oligocene Ashley Formation (Cooper Group). The Ashley Formation (85.8 to 30.0 ft) consists of a relatively homogeneous section of calcareous, microfossiliferous, silty and sandy clays assigned to Zones NP 24 and NP 25 (?). Neogene and (or) Quaternary deposits present in the upper 30 ft of the Pregnall section are assigned provisionally to an unnamed unit (30 to 22 ft) and to the Waccamaw Formation(?)(22 to 0 ft).
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Poag, C. Wylie; Reynolds, Leslie A.; Mazzullo, James M.; Keigwin, Loyd D.
1985-01-01
Sediment samples taken at close intervals across four major unconformities (middle Miocene/upper Miocene, lower Oligocene/upper Oligocene, lower Eocene/upper Eocene, lower Paleocene/upper Paleocene) at DSDP-IPOD Site 548, Goban Spur, reveal that coeval biostratigraphic gaps, sediment discontinuities, and seismic unconformities coincide with postulated low stands of sea level. Foraminiferal, lithic, and isotopic analyses demonstrate that environments began to shift prior to periods of marine erosion, and that sedimentation resumed in the form of turbidites derived from nearby upper-slope sources. The unconformities appear to have developed where a water-mass boundary intersected the continental slope, rhythmically crossing the drill site in concert with sea-level rise and fall.
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NASA Astrophysics Data System (ADS)
Davy, B. W.; Henrys, S. A.; Wilson, T. J.; Fielding, C. R.; Levy, R. H.; Andrill Mis-Science Team
2010-12-01
ROSSMAP aims to produce a new series of digital seismic stratigraphic and structural maps for the Ross Sea region, and develop reconstructions of past sedimentary volumes and paleo-bathymetry that will be used in numerical models to help identify tectonic and climate feedbacks. In particular, ROSSMAP will define targets for future drilling initiatives in the Ross Sea region, and provide a legacy of web-based electronic databases that will be available to other researcher. Interpretation in the Victoria Land Basin (VLB) has focused on establishing links to new and existing drill holes. Several regional seismic reflectors were mapped throughout the southern portion of the Victoria Land Basin (VLB) and are tied to the ANDRILL McMurdo Sound drill cores. The age of one prominent reflector (Ri - red, correlative with RSU-2) is 4.7-4.3 Ma based on a tie to AND-1B and extensively mapped in the VLB. Mapping, together with quantitative biostratigraphic correlation techniques, indicates that the red reflector is associated with relative sea-level fall resulting from ice-sheet growth and/or local tectonic uplift. Correlative sediments preserved in AND-1B indicate regional climatic warmth, which suggests that the red reflector is more likely related to a tectonic event. Furthermore, the onset of sediment accumulation at CIROS-2 post-dates 4.5 Ma, suggesting that local subsidence and creation of accommodation space began at this time. Two other stratigraphic horizons (Rh and Rg) have been extensively mapped where seismic data image above the seafloor multiple. Reflector Rh (dark green and correlative with RSU-4a marks a basin-wide unconformity. Near the western margin of the Victoria Land Basin, this horizon is a marked angular discordance with angularity increasing westward. In AND-1B Rh is correlated with the base of a ~180-m-thick interval of late Miocene-early Pliocene, pyrite-cemented, high-velocity volcanic sandstone and mudstone. Volcanic rocks in a tongue extending from beneath White Island have been mapped at the dark green horizon in ROSSMAP seismic data data. If a new maximum age for White Island of 7.6 Ma is adopted, then this provides an approximate estimate for the age of Rh. Rg (light green and correlative with RSU-5) is a regionally extensive discontinuity correlated with the base of a 150-m-thick, high-velocity (3000 ms-1) interval of diamictite cycles in AND-1B and the base of a similarly thick diamictite dominated sequences in AND-2A. In AND-1B, 40Ar/39Ar dates on ashes beneath Rg indicate that this discontinuity is <13.8 Ma. In regional mapping Rg marks the onset of renewed rifting (Terror Rift) in the VLB but also may coincide with major global cooling associated with Mi3 event.
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Jurassic through Oligocene paleogeography of the Santa Maria basin area, California
DOE Office of Scientific and Technical Information (OSTI.GOV)
Fritsche, A.E.; Yamashiro, D.A.
1991-02-01
Compilation from published reports indicates that the paleogeographic history of the Santa Maria basin area of California (west of the Sur-Nacimiento fault and north of the Santa Ynez Fault) began in the Early Jurassic in an area for to the south with the creation of a spreading-center ophiolite sequence. As the ophiolite rocks moved relatively away from the spreading center, they were covered by Lower Jurassic through Lower Cretaceous basin plain and prograding outer continental margin deposits. During this time, right-lateral movement along faults that were located to the east was transporting the area relatively northward toward its present location.more » A mild tectonic event in the middle of the Cretaceous caused formation of a parallel unconformity. Renewed subsidence in the Late Cretaceous brought deposition in trench, slope, sandy submarine fan, shelf, and ultimately in the eastern part of the area, delta and fluvial environments. During the ensuing Laramide orogeny, significant deformation raised the entire area above sea level and erosion created a major angular unconformity. During the early Tertiary, most of the Santa Maria basin area remained elevated as a forearc highland. The present-day east-west-trending area south of the Santa Ynez River fault was at the time oriented north-south. During the Eocene, this portion of the area was submerged and became a forearc basin that was located to the east of the forearc ridge that served as a source of sediment. The basin filled through the Eocene and Oligocene with submarine fan, sloe, shelf, coastal, and finally fluvial deposits. In the medial Miocene, these forearc basin rocks were rotated clockwise into their present position along the southern margin of the basin and the upper Tertiary Santa maria basin was formed.« less
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NASA Astrophysics Data System (ADS)
Mora, J. Alejandro; Oncken, Onno; Le Breton, Eline; Ibánez-Mejia, Mauricio; Faccenna, Claudio; Veloza, Gabriel; Vélez, Vickye; de Freitas, Mario; Mesa, Andrés.
2017-11-01
Collision with and subduction of an oceanic plateau is a rare and transient process that usually leaves an indirect imprint only. Through a tectonostratigraphic analysis of pre-Oligocene sequences in the San Jacinto fold belt of northern Colombia, we show the Late Cretaceous to Eocene tectonic evolution of northwestern South America upon collision and ongoing subduction with the Caribbean Plate. We linked the deposition of four fore-arc basin sequences to specific collision/subduction stages and related their bounding unconformities to major tectonic episodes. The Upper Cretaceous Cansona sequence was deposited in a marine fore-arc setting in which the Caribbean Plate was being subducted beneath northwestern South America, producing contemporaneous magmatism in the present-day Lower Magdalena Valley basin. Coeval strike-slip faulting by the Romeral wrench fault system accommodated right-lateral displacement due to oblique convergence. In latest Cretaceous times, the Caribbean Plateau collided with South America marking a change to more terrestrially influenced marine environments characteristic of the upper Paleocene to lower Eocene San Cayetano sequence, also deposited in a fore-arc setting with an active volcanic arc. A lower to middle Eocene angular unconformity at the top of the San Cayetano sequence, the termination of the activity of the Romeral Fault System, and the cessation of arc magmatism are interpreted to indicate the onset of low-angle subduction of the thick and buoyant Caribbean Plateau beneath South America, which occurred between 56 and 43 Ma. Flat subduction of the plateau has continued to the present and would be the main cause of amagmatic post-Eocene deposition.
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Evolution of the continental margin of southern Spain and the Alboran Sea
Dillon, William P.; Robb, James M.; Greene, H. Gary; Lucena, Juan Carlos
1980-01-01
Seismic reflection profiles and magnetic intensity measurements were collected across the southern continental margin of Spain and the Alboran basin between Spain and Africa. Correlation of the distinct seismic stratigraphy observed in the profiles to stratigraphic information obtained from cores at Deep Sea Drilling Project site 121 allows effective dating of tectonic events. The Alboran Sea basin occupies a zone of motion between the African and Iberian lithospheric plates that probably began to form by extension in late Miocene time (Tortonian). At the end of Miocene time (end of Messinian) profiles show that an angular unconformity was cut, and then the strata were block faulted before subsequent deposition. The erosion of the unconformity probably resulted from lowering of Mediterranean sea level by evaporation when the previous channel between the Mediterranean and Atlantic was closed. Continued extension probably caused the block faulting and, eventually the opening of the present channel to the Atlantic through the Strait of Gibraltar and the reflooding of the Mediterranean. Minor tectonic movements at the end of Calabrian time (early Pleistocene) apparently resulted in minor faulting, extensive transgression in southeastern Spain, and major changes in the sedimentary environment of the Alboran basin. Active faulting observed at five locations on seismic profiles seems to form a NNE zone of transcurrent movement across the Alboran Sea. This inferred fault trend is coincident with some bathymetric, magnetic and seismicity trends and colinear with active faults that have been mapped on-shore in Morocco and Spain. The faults were probably caused by stresses related to plate movements, and their direction was modified by inherited fractures in the lithosphere that floors the Alboran Sea.
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NASA Astrophysics Data System (ADS)
Zhu, Chuanqing; Hu, Shengbiao; Qiu, Nansheng; Jiang, Qiang; Rao, Song; Liu, Shuai
2018-01-01
The Middle-Late Permian Emeishan Large Igneous Province (ELIP) in southwestern China represents a classic example of a mantle plume origin. To constrain the thermal regime of the ELIP and contemporaneous magmatic activity in the northeastern Sichuan Basin, maximum paleotemperature profiles of deep boreholes were reconstructed using vitrinite reflectance (Ro) and apatite fission track data. Two heating patterns were identified: (1) heating of the overlying lithosphere by magma storage regions and/or magmatic activity related to the mantle plume, which resulted in a relatively strong geothermal field and (2) direct heating of country rock by stock or basalt. Borehole Ro data and reconstructed maximum paleotemperature profiles near the ELIP exhibit abrupt tectonothermal unconformities between the Middle and Late Permian. The profiles in the lower subsections (i.e., pre-Middle Permian) exhibited significantly higher gradients than those in the upper subsections. Distal to the basalt province, high paleo-geotemperatures (hereafter, paleotemperatures) were inferred, despite deformation of the paleogeothermal curve due to deep faults and igneous rocks within the boreholes. In contrast, Ro profiles from boreholes without igneous rocks (i.e., Late Permian) contained no break at the unconformity. Paleotemperature gradients of the upper and the lower subsections and erosion at the Middle/Late Permian unconformity revealed variations in the thermal regime. The inferred spatial distribution of the paleothermal regime and the erosion magnitudes record the magmatic and tectonic-thermal response to the Emeishan mantle plume.
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Paull, C.K.; Twichell, D.C.; Spiess, Fred N.; Curray, Joseph R.
1991-01-01
An unconformity of 100 m.yr magnitude continues to form on the western edge of the Florida-Bahama Platform, near 26??N, where distal Mississippi Fan sediments are progressively burying the Florida Escarpment. Multiple perspectives of the developing unconformity's morphology are revealed using available technologies including GLORIA images of the entire platform's edge, Seabeam bathymetric contours, and Deep-Tow's high resolution side-scan data calibrated with bottom photographs. The structure and stratigraphy of the buried escarpment and the associated unconformity are resolved by airgun, sparker, and Deep-Tow's 4 kHz seismic reflection data; we summarize the morphological data on the exposed part of the unconformity and the sedimentary deposits accumulating in the basin above the unconformity. The exposed cliff face is composed of a staircase of bedding-plane terraces which are developed along joint planes. The terraces extend 100-1000 m along the escarpment's face, and the intervening vertical walls are up to 100 m high. The jointed morphology of this Mesozoic limestone cliff apparently reflects erosional exposure of its interior anatomy rather than its accretionary shape. The change in slope between the platform face and the abyssal plain is very abrupt. In places along the contact between the escarpment and fan sediments, reduced chemical-charged brine seeps occur, which locally cause carbonate dissolution and precipitation, sulfide mineralization, and the deposition of a fossiliferous and organic carbon-rich lens associated with chemosynthetic communities. These seep deposits and escarpment-derived megabreccias intercalate with basinal sediments that overlie the unconformity. Because surface seismic reflection data do not produce images of the escarpment's face that closely reflect the exposed escarpment's morphology, they must also be of limited value in characterizing the surface of similar steeply dipping buried escarpments. Thus, the downslope extent of the heavily eroded platform edge is unclear.
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Eagle Mountain Mine: geology of the former Kaiser Steel Operation in Riverside County, California
Force, Eric R.
2001-01-01
Iron ore replaces a variety of host rocks along the two unconformities, forming massive to globular bodies, and its mineralogy correlates with deuteric alteration features, not anhydrous skarn. Its pyrite contains as much as 3% cobalt. Iron was only one of five elements that showed mobility in this region on a scale that suggests basic crustal processes. The others in probable order of flux magnitude are silica, magnesium, sodium, and potassium, to form regionally distributed “vitreous quartzite”, dolomite, and secondary feldspars, respectively.
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Cenozoic stratigraphy of the Sahara, Northern Africa
Swezey, Christopher S.
2009-01-01
This paper presents an overview of the Cenozoic stratigraphic record in the Sahara, and shows that the strata display some remarkably similar characteristics across much of the region. In fact, some lithologies of certain ages are exceptionally widespread and persistent, and many of the changes from one lithology to another appear to have been relatively synchronous across the Sahara. The general stratigraphic succession is that of a transition from early Cenozoic carbonate strata to late Cenozoic siliciclastic strata. This transition in lithology coincides with a long-term eustatic fall in sea level since the middle Cretaceous and with a global climate transition from a Late Cretaceous–Early Eocene “warm mode” to a Late Eocene–Quaternary “cool mode”. Much of the shorter-term stratigraphic variability in the Sahara (and even the regional unconformities) also can be correlated with specific changes in sea level, climate, and tectonic activity during the Cenozoic. Specifically, Paleocene and Eocene carbonate strata and phosphate are suggestive of a warm and humid climate, whereas latest Eocene evaporitic strata (and an end-Eocene regional unconformity) are correlated with a eustatic fall in sea level, the build-up of ice in Antarctica, and the appearance of relatively arid climates in the Sahara. The absence of Oligocene strata throughout much of the Sahara is attributed to the effects of generally low eustatic sea level during the Oligocene and tectonic uplift in certain areas during the Late Eocene and Oligocene. Miocene sandstone and conglomerate are attributed to the effects of continued tectonic uplift around the Sahara, generally low eustatic sea level, and enough rainfall to support the development of extensive fluvial systems. Middle–Upper Miocene carbonate strata accumulated in northern Libya in response to a eustatic rise in sea level, whereas Upper Miocene mudstone accumulated along the south side of the Atlas Mountains because uplift of the mountains blocked fluvial access to the Mediterranean Sea. Uppermost Miocene evaporites (and an end-Miocene regional unconformity) in the northern Sahara are correlated with the Messinian desiccation of the Mediterranean Sea. Abundant and widespread Pliocene paleosols are attributed to the onset of relatively arid climate conditions and (or) greater variability of climate conditions, and the appearance of persistent and widespread eolian sediments in the Sahara is coincident with the major glaciation in the northern hemisphere during the Pliocene.
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Gutman, Shawn; Kim, Daniel; Tarafder, Solaiman; Velez, Sergio; Jeong, Julia; Lee, Chang H
2018-02-01
To determine the regionally variant quality of collagen alignment in human TMJ discs and its statistical correlation with viscoelastic properties. For quantitative analysis of the quality of collagen alignment, horizontal sections of human TMJ discs with Pricrosirius Red staining were imaged under circularly polarized microscopy. Mean angle and angular deviation of collagen fibers in each region were analyzed using a well-established automated image-processing for angular gradient. Instantaneous and relaxation moduli of each disc region were measured under stress-relaxation test both in tensile and compression. Then Spearman correlation analysis was performed between the angular deviation and the moduli. To understand the effect of glycosaminoglycans on the correlation, TMJ disc samples were treated by chondroitinase ABC (C-ABC). Our imaging processing analysis showed the region-variant direction of collagen alignment, consistently with previous findings. Interestingly, the quality of collagen alignment, not only the directions, was significantly different in between the regions. The angular deviation of fiber alignment in the anterior and intermediate regions were significantly smaller than the posterior region. Medial and lateral regions showed significantly bigger angular deviation than all the other regions. The regionally variant angular deviation values showed statistically significant correlation with the tensile instantaneous modulus and the relaxation modulus, partially dependent on C-ABC treatment. Our findings suggest the region-variant degree of collagen fiber alignment is likely attributed to the heterogeneous viscoelastic properties of TMJ disc that may have significant implications in development of regenerative therapy for TMJ disc. Copyright © 2017 Elsevier Ltd. All rights reserved.
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Chukchi Borderland | Crustal Complex of the Amerasia Basin, Arctic Ocean
NASA Astrophysics Data System (ADS)
Ilhan, I.; Coakley, B.; Houseknecht, D. W.
2017-12-01
In the Arctic Ocean, Chukchi Borderland separates the North Chukchi shelf and Toll deep basins to the west and Canada deep basin to the east. Existing plate reconstructions have attempted to restore this north-striking, fragments of the continental crust to all margins of the Amerasia Basin based on sparse geologic and geophysical measurements. Regional multi-channel seismic reflection and potential field geophysics, and geologic data indicate it is a high standing continental block, requiring special accommodation to create a restorable model of the formation of the Amerasia Basin. The Borderland is composed of the Chukchi Plateau, Northwind Basin, and Northwind Ridge divided by mostly north striking normal faults. These offset the basement and bound a sequence of syn-tectonic sediments. Equivalent strata are, locally, uplifted, deformed and eroded. Seaward dipping reflectors (SDRs) are observed in the juncture between the North Chukchi, Toll basins, and southern Chukchi Plateau underlying a regional angular unconformity. This reveals that this rifted margin was associated with volcanism. An inferred condensed section, which is believed to be Hauterivian-Aptian in age, synchronous with the composite pebble shale and gamma-ray zone of the Alaska North Slope forms the basal sediments in the North Chukchi Basin. Approximately 15 km of post-rift strata onlap the condensed section, SDRs and, in part, the wedge sequence on the Chukchi Plateau from west to east, thinning to the north. These post-Aptian sediments imply that the rifted margin subsided no later than the earliest Cretaceous, providing a plausible time constraint for the inferred pre-Cretaceous rifting in this region. The recognition of SDRs and Hauterivian—Aptian condensed section, and continuity of the Early—Late Cretaceous post-rift strata along the margins of the Borderland, strike variations of the normal faults, absence of observable deformation along the Northwind Escarpment substantially constrain tectonic models proposed for tectonic development of the Amerasia Basin. Models that require significant relative motion between the Chukchi Shelf and Borderland since the Early Cretaceous are precluded by these observations.
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NASA Astrophysics Data System (ADS)
Vaught-Mijares, R. M.; Hillman, A. L.; Abbott, M. B.; Werne, J. P.; Arkush, E.
2017-12-01
Drought and flood events are thought to have shaped the ways in which Andean societies have adapted to life in the Titicaca Basin region, particularly with regard to land use practices and settlement patterns. This study examines a small lake in the region, Laguna Orurillo. Water isotopes suggest that the lake primarily loses water through evaporation, making it hydrologically sensitive. In 2015, a 3.4 m overlapping sediment record was collected and inspected for evidence of shallow water facies and erosional unconformities to reconstruct paleohydrology. Sediment core chronology was established using 7 AMS radiocarbon dates and 210Pb dating and indicates that the core spans 5000 years. Additional sediment core measurements include magnetic susceptibility, bulk density, organic/carbonate content, and XRD. Results show a pronounced change in sediment composition from brittle, angular salt deposits to massive calcareous silt and clay around 5000 years BP. Multiple transitions from clay to sand show potential lake level depressions at 1540, 2090, and 2230, yr BP that are supported by a drastic increase in carbonate composition from 2760-1600 yr BP. Additional shallow-water periods may be reflected in the presence of rip-up clasts from 4000 to 3000 yr BP. These early interpretations align well with existing hydrologic records from Lake Titicaca. In order to develop a more detailed climate and land use record, isotope analyses of authigenic carbonate minerals using δ13C and δ18O and leaf waxes using δD are being developed. Ultimately, this record will be linked with records from nearby Lagunas Arapa and Umayo. Additional proxies for human population such as fecal 5β-stanols and proximal anthropologic surveys will be synthesized to contribute to a regional understanding of Holocene climate variability and human demography in the Peruvian Altiplano.
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Evidence for changes in the angular velocity of the surface regions of the sun and stars
NASA Technical Reports Server (NTRS)
1972-01-01
A round table discussion of problems of solar and stellar spindown and theory is presented. Observational evidence of the angular momentum of the solar wind is included, emphasizing changes in the angular velocity of the surface regions of the sun and stars.
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The Middle Ordovician Knox unconformity in the Black Warrior Basin
Dwyer, Gary S.; Repetski, John E.
2012-01-01
Based on conodont biostratigraphy from four cores and from a previous study on cuttings from a nearby well, the unconformity is middle Whiterockian in age and likely spans most or all of the Histiodella holodentata Biozone.
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The three-dimensional angular widths of CMEs and their relations to the source regions
NASA Astrophysics Data System (ADS)
Zhao, X.; Feng, X. S.
2017-12-01
The angular width of a coronal mass ejection (CME) is an important factor to determine whether the corresponding interplanetary CME (ICME) and its preceding shock will reach our Earth. However, very few studies are involved to study the decisive factors of the CME's angular width. In this study, we use the three-dimensional (3D) angular width of CMEs obtained from the Graduated Cylindrical Shell (GCS) model based on observations of Solar Terrestrial Relations Observatory (STEREO) to study the relations between the CME's 3D width and characteristics of the CME's source region. We find that for the CMEs produced by active regions (ARs), the CME width has some correlations with the AR's area and flux, but these correlations are not strong. The magnetic flux contained in the CME seems to come from only part of the AR's total flux. For the CMEs produced by flare regions, the correlations between the CME angular width and the flare region's area and flux are strong. The magnetic flux within those CMEs seems to totally (even not enough) come from the flare region. Our findings prefer to support that the CME's 3D angular width can be generally estimated based on observations of Solar Dynamics Observatory (SDO) for its source region instead of the observations from coronagraphs onboard Solar and Heliospheric Observatory (SOHO) and STEREO.
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Percolation of diagenetic fluids in the Archaean basement of the Franceville basin
NASA Astrophysics Data System (ADS)
Mouélé, Idalina Moubiya; Dudoignon, Patrick; Albani, Abderrazak El; Cuney, Michel; Boiron, Marie-Christine; Gauthier-Lafaye, François
2014-01-01
The Palaeoproterozoic Franceville basin, Gabon, is mainly known for its high-grade uranium deposits, which are the only ones known to act as natural nuclear fission reactors. Previous work in the Kiéné region investigated the nature of the fluids responsible for these natural nuclear reactors. The present work focuses on the top of the Archaean granitic basement, specifically, to identify and date the successive alteration events that affected this basement just below the unconformity separating it from the Palaeoproterozoic basin. Core from four drill holes crosscutting the basin-basement unconformity have been studied. Dating is based on U-Pb isotopic analyses performed on monazite. The origin of fluids is discussed from the study of fluid inclusion planes (FIP) in quartz from basement granitoids. From the deepest part of the drill holes to the unconformable boundary with the basin, propylitic alteration assemblages are progressively replaced by illite and locally by a phengite + Fe chlorite ± Fe oxide assemblage. Illitic alteration is particularly strong along the sediment-granitoid contact and is associated with quartz dissolution. It was followed by calcite and anhydrite precipitation as fracture fillings. U-Pb isotopic dating outlines three successive events: a 3.0-2.9-Ga primary magmatic event, a 2.6-Ga propylitic alteration and a late 1.9-Ga diagenetic event. Fluid inclusion microthermometry suggests the circulation of three types of fluids: (1) a Na-Ca-rich diagenetic brine, (2) a moderately saline (diagenetic + meteoric) fluid, and (3) a low-salinity fluid of probable meteoric origin. These fluids are similar to those previously identified within the overlying sedimentary rocks of the Franceville basin. Overall, the data collected in this study show that the Proterozoic-Archaean unconformity has operated as a major flow corridor for fluids circulation, around 1.9 Ga. highly saline diagenetic brines; hydrocarbon-rich fluids derived from organic matter-rich formations; a low-salinity fluid likely of meteoric origin migrating through the granitic basement; mineralizing fluids resulting from the mixing of fluids 1 and 3; high-temperature fluids resulting from the natural nuclear reactor environment (Mathieu et al., 2000). The present paper attempts to characterize the succession of alteration events that have affected the top of the basement below the Palaeoproterozoic sediment unconformity. Are these alterations related to early post-magmatic to hydrothermal events, to palaeoweathering, or to late infiltration of diagenetic brines from the overlying basin? Our study, carried out on drill core samples from Kiéné, is supported by petrographic investigation, new fluid inclusion data and U-Pb geochronology on monazite.
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NASA Astrophysics Data System (ADS)
Novak, Andrej; Šmuc, Andrej
2016-04-01
The Planica-Tamar valley is located in the Julian Alps in north-west Slovenia. The Planica-Tamar valley represents typical mountain glacial valley bounded by steep, mainly carbonate cliffs with some glacial deposits still preserved. The valley is currently being filled with numerous Holocene sediments deposited by rock falls, landslides, mass gravity flows and fluvial flows. These deposits are forming active or inactive interfingering talus slopes, alluvial and debris-flow fans, all of them with a complex history of sedimentation and erosion forming unconformity bounded sedimentary units. In order to make a thorough analysis of these deposits a detailed geomorphological map in a scale of 1:10 000 has been made. Six different types of sedimentary deposits were defined and mapped. These are moraines, lacustrine sediments, fluvio-glacial deposits, talus slopes, debris fans and alluvial fans. Other mapped features also include shape of ravines, their depths, ridges and direction of sedimentary flow. Additionally areas of active, semi-active and inactive sedimentation were marked. Moraines forms a ridge in the bottom of the valleys and are composed of unconsolidated, poorly sorted, subangular grains ranging from clay size to a few cubic meters big blocks. Lacustrine sediments are represented by laminated well sorted sand and silt, while fluvio-glacial deposits are composed of washed out subrounded sands and gravels. Talus slope deposits are characterised by clast-supported poorly sorted very angular gravel. Debris flow fans are represented by extremely poorly sorted matrix-supported gravels with grain size ranging from clay to few cubic meters big blocks. Alluvial fans are composed by variety of sedimentary textures. Sediments at the fan apex are clast-supported poorly sorted very angular gravels with up to a few cubic meters big block. In the middle part of the fan the sieve deposits are common, while in the distal parts a few centimeters thick layers of sand and moderately sorted clast or sandy matrix-supported angular gravels occur. In cross-sections of alluvial fans distinct palaeosoil horizons are present indicating longer inactivity of that part of the fan. The geomorphological map forms a base for further research and thorough analysis of Quaternary deposits in order to reconstruct the Holocene dynamic of triggering and sedimentation of different types of slope deposits and relate them to base rock geology, tectonic and local/regional climate events. Key words: geomorphological mapping, Holocene slope deposits, alluvial fans, debris fans, Alpine geomorphology.
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The Middle Jurassic Entrada Sandstone near Gallup, New Mexico
Robertson, J.F.; O'Sullivan, R. B.
2001-01-01
Near Gallup, New Mexico, the Middle Jurassic Entrada Sandstone consists of, in ascending order, the Iyanbito Member, the Rehoboth Member, and an upper sandstone member. The Rehoboth Member is named herein to replace the middle siltstone member, with a type section located 26 km east of Gallup. The Iyanbito Member has been erroneously equated with the Wingate Sandstone of northeast Arizona, and the Rehoboth Member has been miscorrelated with the Dewey Bridge Member of the Entrada in Utah. The Dewey Bridge is an older unit that does not extend into New Mexico. The Iyanbito Member, east of Gallup, overlies the J-2 unconformity and the eroded tops of the Owl Rock and Petrified Forest Members of the Chinle Formation. The Wingate Sandstone of the Lower Jurassic Glen Canyon Group overlies the J-0 unconformity and the underlying Rock Point Member (topmost unit) of the Chinle Formation in northeast Arizona. Both the Wingate Sandstone and the Rock Point Member are missing east of Gallup below the J-2 unconformity. Similarly, the Wingate is missing southwest of Gallup, near Lupton, Arizona, but the Rock Point Member is present and underlies the Iyanbito from Zuni northward to Toadlena, New Mexico. The Wingate and other formations of the Glen Canyon Group thin and wedge out southward and eastward in northeast Arizona. The J-2 unconformity truncates the Wingate Sandstone and the underlying J-0 unconformity, 5 km north of Toadlena.
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North polar region of Mars: imaging results from viking 2.
Cutts, J A; Blasius, K R; Briggs, G A; Carr, M H; Greeley, R; Masursky, H
1976-12-11
During October 1976, the Viking 2 orbiter acquired approximately 700 high-resolution images of the north polar region of Mars. These images confirm the existence at the north pole of extensive layered deposits largely covered over with deposits of perennial ice. An unconformity within the layered deposits suggests a complex history of climate change during their time of deposition. A pole-girdling accumulation of dunes composed of very dark materials is revealed for the first time by the Viking cameras. The entire region is devoid of fresh impact craters. Rapid rates of erosion or deposition are implied. A scenario for polar geological evolution, involving two types of climate change, is proposed.
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Tectonics versus eustatic control on supersequences of the Zagros Mountains of Iran
NASA Astrophysics Data System (ADS)
Heydari, Ezat
2008-04-01
At least 12 km of strata ranging in age from the latest Precambrian to the Recent are exposed in the Zagros Mountains of Iran. This sedimentary cover is characterized by distinct stratal packages separated by major unconformities forming twelve supersequences. They are informally named as: (1) Late Precambrian - Cambrian Hakhamanesh Supersequence, (2) Ordovician Kourosh Supersequence, (3) Silurian Camboojiyeh Supersequence, (4) Devonian Darioush Supersequence, (5) Mississippian - Pennsylvanian Khashayar Supersequence, (6) Permian - Triassic Ashk Supersequence, (7) Jurassic Farhad Supersequence, (8) Early Cretaceous Mehrdad Supersequence, (9) Late Cretaceous Ardavan Supersequence, (10) Paleocene - Oligocene Sassan Supersequence, (11) Oligocene - Miocene Ardeshir Supersequence, and (12) Miocene - Pleistocene Shapour Supersequence. These supersequences and their correlatives in neighboring areas have been used to infer tectonic events. The dominant interpretation has been that local or regional epeirogenic movements were responsible for the formation of these supersequences. Unconformities are considered as indications that epeirogenic movements associated with tectonic events affected the area. The present investigation provides an alternative to the established view of the Phanerozoic supersequences of the Zagros Mountains. A good correlation exists between the lithofacies of supersequences in the Zagros Mountains and the second-order eustatic sea-level changes. Deposition of deep-water, marine shales occurred during periods of eustatic sea-level rise. Platform-wide unconformities coincided with eustatic sea-level lows. In fact, supersequences of the Zagros Mountains are nearly identical to those described from the North American Craton and the Russian Platform suggesting that these stratal packages are global. These observations suggest that supersequences of the Zagros Mountains formed by second order eustatic sea-level changes and not by local or regional epeirogenic movements. Although tectonic events did not produce supersequences of the Zagros Mountains, they influenced regional lithofacies patterns through the formation of intrashelf depressions such as the Hormoz Salt Basin during the Precambrian and the Dezful Embayment and the Lorestan Basin during the Mesozoic. Tectonic events also affected sedimentation during the Tertiary collision of Arabia and the Central Iran microplate through uplift, erosion, and the formation of the Zagros Foreland Basin. The results of this investigation necessitate a re-evaluation of the role and the significance of pre-Tertiary tectonic events commonly used to interpret the geological evolution of the Zagros Mountains.
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Model for dolomite formation in northwest Florida
Cooper, C.R.; Tindall, J.A.
1994-01-01
Petrographic methods are used to examine the nature of the Floridan post-Oligocene unconformity and diagenetic responses in the associated carbonate units. The study addresses the depositional environment and the character of sediments associated with the unconformity, types and timing of diagenetic changes, and mode of dolomitization for the Suwannee Limestone dolomites and basal Hawthorn Group dolosilts. The purpose of the study is to determine if the original texture of geologic materials is preserved more frequently in rocks deposited in a supratidal environment in the uppermost Floridan carbonates, to examine possible sources of magnesium for the dolomitization that has occurred in the Floridan aquifer, and to determine the chemical environment of dolomite formation. On the basis of lithology, the tri-county study area can be divided into two regions; one in which the uppermost Floridan carbonate is calcareous or locally silicified, and one in which the aquifer system is capped with dolomite. Lateral interfingering between the two regions is apparent, and it is inferred that the boundary between the limestone and dolomite represents a geochemical boundary between a mixed marine and freshwater environment and a subaerially exposed freshwater environment. Where dolomite has replaced the uppermost Suwannee Limestone, the dolomite is overlain by a thin unit of dolosilt. The predominant source of magnesium for the dolomitization that occurred in the study area is probably seawater. ?? 1994.
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Strike-slip faulting at Thebes Gap, Missouri and Illinois; implications for New Madrid tectonism
Harrison, Richard W.; Schultz, Art
1994-01-01
Numerous NNE and NE striking strike-slip faults and associated normal faults, folds, and transtensional grabens occur in the Thebes Gap area of Missouri and Illinois. These structures developed along the northwestern margin of the buried Reelfoot rift of Precambrian-Cambrian age at the northern edge of the Mississippi embayment. They have had a long-lived and complex structural history. This is an area of recent moderate seismicity, approximately 45 km north of the New Madrid seismic zone. Stratigraphic evidence suggests that these faults were active during the Middle Ordovician. They were subsequently reactivated between the Early Devonian and Late Cretaceous, probably in response to both the Acadian and Ouachita orogenies. Deformation during this period was characterized by strongly faulted and folded Ordovician through Devonian rocks. In places, these deformed rocks are overlain with angular unconformity by undeformed Cretaceous strata. Fault motion is interpreted as dominantly strike slip. A still younger period of reactivation involved Late Cretaceous and Cenozoic formations as young as the Miocene or Pliocene Mounds Gravel. These formations have experienced both minor high-angle normal faulting and subsequent major, right-lateral strike-slip faulting. En echelon north-south folds, ENE striking normal faults, regional fracture patterns, and drag folds indicate the right-lateral motion for this major episode of faulting which predates deposition of Quaternary loess. Several nondefinitive lines of evidence suggest Quaternary faulting. Similar fault orientations and kinematics, as well as recent seismicity and proximity, clearly suggest a structural relationship between deformation at Thebes Gap and tectonism associated with the New Madrid area.
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Seismic stratigraphy of sedimentary cover in the southern Amerasia Basin between 140E and 170W
NASA Astrophysics Data System (ADS)
Poselov, V.; Butsenko, V.; Kaminskiy, V.; Kireev, A.; Grikurov, G.
2013-12-01
Seismic reflection data (MCS) acquired by Russian expeditions in 2007, 2009, 2011 and 2012 are correlated with earlier Polarstern (AWI-91090) and US (78AR_808) lines calibrated by drilling on the Lomonosov Ridge (LR) and in the Chukchi Sea (ACEX hole and POPCORN well, respectively). In the absence of direct intersections between those and Russian lines, the correlation is based on analysis of wave fields. Main seismic horizons and their intervening units are traced throughout the entire study area. The uppermost unconformity in both holes is related to pre-Miocene depositional hiatus at the base of essentially hemipelagic unit. Specific wave characteristics of both the unconformity and overlying sediments are persistently recorded on seismic lines. Hemipelagic drape is typically relatively thin (few hundred meters) but may thicken to ~1,500-2,000 m in some deepwater basins. Another major depositional hiatus spanning ~20 Ma is interpreted in the ACEX hole between the lowermost drilled Campanian and Upper Paleocene units. On seismic records it is recognized as post-Campanian unconformity (pCU) traced along the length of the near-Siberia segment of LR and in deep shelf/margin sedimentary basins of the East Siberian and western Chukchi Seas. Farther east pCU correlates with Mid-Brookian unconformity (MBU) separating the Lower and Upper Brookian terrigenous sequences. In Popcorn well the Upper Brookian is about 1,300 m thick; on the Russian margin a comparable thickness of equivalent Upper Paleocene-Eocene units sandwiched between pCU and pre-Miocene unconformity is observed only in structural lows. Older cover units on the Russian East Arctic margin are not sampled by drilling. Among them only one displays particular wave field features clearly comparable to those observed in the carbonate-dominated Carboniferous-Permian Lisburne Group (LG) of the US Chukchi Sea. This marker sequence is confidently recognized on seismic sections in the North Chukchi Trough (NCT) and the Vilkitsky Basin as relatively thick (1,500-3,000 m) unit whose much thinner (~300 m) continuation can also be traced over the southern Mendeleev Rise. A thick (~5000 m) well stratified sedimentary pile mapped in NCT between LG-type unit and the acoustic basement is likely to represent a counterpart of the D3-C1 base of the Lower Ellesmerian Sequence. Like in the US Chukchi Sea, the latter is also truncated here by Permian(?) unconformity and buried under 5,000-7,000 m of inferred Late Permian to Early Cretaceous strata probably corresponding to Upper Ellesmerian, 'Rift' and Lower Brookian Sequences and separated by respective (presumably Jurassic and Early Cretaceous) unconformities. The thickness of pre-Cenozoic units in NCT and the relief of intervening unconformities are highly variable suggesting syndepositional rifting.
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NASA Astrophysics Data System (ADS)
Zhang, Feng-Qi; Chen, Han-Lin; Batt, Geoffrey E.; Dilek, Yildirim; A, Min-Na; Sun, Ming-Dao; Yang, Shu-Feng; Meng, Qi-An; Zhao, Xue-Qin
2015-12-01
The age spectra obtained from 505 spots of detrital zircon U-Pb ages of five representative sandstone samples from the Sanjiang Basin in NE China point to a significant change in its provenance during the Coniacian-Santonian. The predominant detrital source for the Sanjiang Basin during the early Cretaceous was the Zhangguangcai Range magmatic belt and Jiamusi Block along its western and southern periphery, whereas it changed in the late Cretaceous to its eastern periphery. The timing of these inferred changes in the detrital source regions and drainage patterns nearly coincide with the age of a regional unconformity in and across the basin. The time interval of non-deposition and unconformity development was coeval with a transitional period between an extensional tectonic regime in the early Cretaceous and a contractional deformation episode in the late Cretaceous. The Sanjiang Basin evolved during this time window from a backarc to a foreland basin. The migration of the coastal orogenic belt and the fold and thrust belt development farther inland during the late Cretaceous marked the onset of regional-scale shortening and surface uplift in the upper plate of a flat (or very shallow-dipping) subduction zone. The stratigraphic record, the detrital source and geochronology of the basinal strata, and the internal structure of the Sanjiang Basin present, therefore, an important record of a tectonic switch in the nature of continental margin evolution of Northeast Asia during the late Mesozoic.
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NASA Astrophysics Data System (ADS)
Trobec, Ana; Šmuc, Andrej; Poglajen, Sašo; Vrabec, Marko
2016-04-01
The youngest seafloor sediments of the Gulf of Trieste (Northern Adriatic) are represented by an up to several 100 meters thick succession of Pliocene to Quaternary continental and shallow-marine deposits recording numerous transgressive-regressive cycles. These sediments are separated from older lithologies (mainly Eocene flysch) by an erosional unconformity. Previous geophysical campaigns conducted in the Italian part of the Gulf of Trieste revealed a complex undulating morphology of the unconformity characterised by numerous morphological steps in the flysch appearing between 40 and 200 m below sea level. From correlation with onshore well data from the Friuli and Veneto area it is assumed that the highest system of these unconformities located at approximately 40 mbsl represents a marine abrasion platform formed during the MIS 5 period sea-level highstand. We present the first observations of these abrasion platforms in the Bay of Koper in the southern (Slovenian) part of the Gulf of Trieste. A series of perpendicular sub-bottom sonar profiles with a spacing of 250-500 meters was acquired in the Bay of Koper between 2009 and 2012 with the Innomar parametric sediment echo sounder SES-2000. Along the northern coast of the bay several acoustic facies were resolved, including the top erosional unconformity surface of the flysch. On this surface we located platforms at 35 ms (platform A), 40 ms (platform B) and 50 ms (platform C) of two-way-travel time. The top of abrasion platform B coincides with the top of a sediment progradational wedge which overlies abrasion platform C. No progradational wedge is developed at the top of platform A. Due to signal attenuation and multiples sub-bottom profiles could not be interpreted below 53 ms TWT time. We used a sound velocity of 1650 m/s for the time to depth conversion, which places the platforms at the depth of 28, 33 and 41 mbsl, respectively. Assuming that the abrasion platforms are a remnant of the MIS 5 highstand, this implies an average subsidence rate of the area between 0.28 and 0.38 mm/year, which agrees with previously published data for the Gulf of Trieste. This new dataset demonstrates that the Bay of Koper was connected to the Adriatic Sea approximately 125.000 ky ago during the MIS 5 sea-level highstand. Together with marine abrasion platforms and well data previously documented in the northeastern part of the Gulf of Trieste and well data from the northwestern part of the gulf our data corroborates the long-term subsidence of the Northern Adriatic region.
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DOE Office of Scientific and Technical Information (OSTI.GOV)
McDonald, T.A.; Tabor, E.; Marzolf, J.E.
1994-04-01
Regional stratigraphic relations in southern Illinois suggest a major unconformity near the top of the St. Genevieve Limestone. Large exposures below the unconformity within the Anna quarries display a retrogradational parasequence-stacking pattern. Eight to 12 m-thick parasequences comprise thinning-upward marine bioclastic wackestone overlain by oolitic and bioclastic thickening-upward eolian( ) grainstone. An eolian origin for the bioclastic grainstones is supported by large scale cross stratification (0.5 to 2 m-thick sets), reworked character of rounded, coated bioclasts, and preserved duneforms. At the quarries, the unconformity is directly overlain by mudstones and sandstones. Thinning-upward mudstones interbedded with very thin (1 to 3more » cm thick) intraclastic packstone tempestites crop out in a roadcut about 500 m NE of the quarries. Small-scale ripples and absence of trace fossils in lower mudstone units suggest an estuarine or lagoonal, brackish-waver environment. The trace fossil Conostichus and horizontal burrows appear abruptly in the upper, thin mudstone units. Highly bioturbated green and red shales overlying a 1 to 4 m-thick covered interval in a roadcut 610 m farther north are interbedded with tidally deposited, medium- to coarse-grained, bioclastic grainstones. The shale-draped, medium cross-bedded grainstones document ten or more tidal bundles. The cross-bedded grainstone is overlain by wavy- to flaser-bedded very fine-grained sandstone suggestive of sand flat origin. These sandstones are overlain by the Aux Vases Sandstone. Numerous low-angle bounding surfaces within the Aux Vases enclose low-angle, wedge-planar cross-bedding. A single irregular surface coated by a few centimeters of poorly sorted unstratified sandstone defines a ravinement surface near the base of the Aux Vases Sandstone.« less
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NASA Astrophysics Data System (ADS)
Kamiya, N.; Yamamoto, Y.; Takemura, T.
2015-12-01
Since forearc-basin evolve associated with development of the accretionary prisms, their geologic structures have clues to understanding the tectonic processes associated with plate subduction. We found a major difference in paleo-geothermal structure and consolidation states between the unconformity in the forearc basin in the Boso Peninsula, central Japan. The geology of the Boso Peninsula, central Japan is divided into three parts; Early Miocene and Late Miocene accretionary prisms in the southern part, the Hayama-Mineoka tectonic belt mainly composed of ophiolite in the middle part, and post-Middle Miocene forearc basin in the northern part. Sediments in the forearc basin are composed of 15-3Ma Miura Group and 3-0.6Ma Kazusa Group. Boundary of the two groups is the Kurotaki Unconformity formed about 3Ma, when convergent direction of the Philippine Sea Plate has been changed (Takahashi, 2006). Vitrinite reflectance (Ro) analyses were conducted and revealed that major variation of paleo-maximum temperature between the Miura and Kazusa groups. The maximum paleo-temperature in the Miura Group is estimated as 70-95˚C, whereas in the lower part of the Kazusa Group is less than 10-35˚C. Given 20˚C/km (Sakai et al, 2011) paleo-geothermal gradient, approximately 2000 m uplifting/erosion of the Miura Group is expected when the unconformity formed. To verify the amount of this uplifting/erosion, we are performing consolidation test of mudstone. [Reference] Takahashi, M., 2006, Tectonic Development of the Japanese Islands Controlled by Philippine Sea Plate Motion, Journal of Geography, 115, 116-123. Sakai R., Munakata M., Kimura H., Ichikawa Y., and Nakamura M., 2011, Study on Validation Method of Regional Groundwater Flow Model : Case Study for Boso Peninsula, JAEA-research 2010(66), 1-20, 1-2.
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Church, Jessica A.; Balota, David A.; Petersen, Steven E.; Schlaggar, Bradley L.
2010-01-01
In a previous study of single word reading, regions in the left supramarginal gyrus and left angular gyrus showed positive BOLD activity in children but significantly less activity in adults for high-frequency words. This developmental decrease may reflect decreased reliance on phonological processing for familiar stimuli in adults. Therefore, in the present study, variables thought to influence phonological demand (string length and lexicality) were manipulated. Length and lexicality effects in the brain were explored using both ROI and whole-brain approaches. In the ROI analysis, the supramarginal and angular regions from the previous study were applied to this study. The supramarginal region showed a significant positive effect of length, consistent with a role in phonological processing, whereas the angular region showed only negative deflections from baseline with a strong effect of lexicality and other weaker effects. At the whole-brain level, varying effects of length and lexicality and their interactions were observed in 85 regions throughout the brain. The application of hierarchical clustering analysis to the BOLD time course data derived from these regions revealed seven clusters, with potentially revealing anatomical locations. Of note, a left angular gyrus region was the sole constituent of one cluster. Taken together, these findings in adult readers (1) provide support for a widespread set of brain regions affected by lexical variables, (2) corroborate a role for phonological processing in the left supramarginal gyrus, and (3) do not support a strong role for phonological processing in the left angular gyrus. PMID:20433237
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Correlation between Angular Widths of CMEs and Characteristics of Their Source Regions
DOE Office of Scientific and Technical Information (OSTI.GOV)
Zhao, X. H.; Feng, X. S.; Feng, H. Q.
The angular width of a coronal mass ejection (CME) is an important factor in determining whether the corresponding interplanetary CME (ICME) and its preceding shock will reach Earth. However, there have been very few studies of the decisive factors of the CME’s angular width. In this study, we use the three-dimensional (3D) angular width of CMEs obtained from the Graduated Cylindrical Shell model based on observations of Solar Terrestrial Relations Observatory ( STEREO ) to study the relations between the CME’s 3D width and characteristics of the CME’s source region. We find that for the CMEs produced by active regionsmore » (ARs), the CME width has some correlations with the AR’s area and flux, but these correlations are not strong. The magnetic flux contained in the CME seems to come from only part of the AR’s total flux. For the CMEs produced by flare regions, the correlations between the CME angular width and the flare region’s area and flux are strong. The magnetic flux within those CMEs seems to come from the whole flare region or even from a larger region than the flare. Our findings show that the CME’s 3D angular width can be generally estimated based on observations of Solar Dynamics Observatory for the CME’s source region instead of the observations from coronagraphs on board the Solar and Heliospheric Observatory and STEREO if the two foot points of the CME stay in the same places with no expansion of the CME in the transverse direction until reaching Earth.« less
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Houseknecht, David W.; Connors, Christopher D.
2015-01-01
Oil-prone source rocks, reservoir-quality sandstone, migration pathways, and structural closure are linked intimately across the Jurassic unconformity, which reflects inversion. Thus, all these key petroleum systems elements were in place when Triassic source rocks entered the oil generation window during Cretaceous–Cenozoic stratigraphic burial.
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Ruda, Mitchell C [Tucson, AZ; Greynolds, Alan W [Tucson, AZ; Stuhlinger, Tilman W [Tucson, AZ
2009-07-14
One or more disc-shaped angular shear plates each include a region thereon having a thickness that varies with a nonlinear function. For the case of two such shear plates, they are positioned in a facing relationship and rotated relative to each other. Light passing through the variable thickness regions in the angular plates is refracted. By properly timing the relative rotation of the plates and by the use of an appropriate polynomial function for the thickness of the shear plate, light passing therethrough can be focused at variable positions.
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NASA Astrophysics Data System (ADS)
Cheng, Xiaogan; Chen, Hanlin; Lin, Xiubin; Yang, Shufeng; Chen, Shenqiang; Zhang, Fenfen; Li, Kang; Liu, Zelin
2016-12-01
The Pamir region, located to the northwest of the Tibetan Plateau, provides important information that can aid the understanding of the plateau's tectonic evolution. Here we present new findings on the deformation geometry and timing of the Wupoer thrust belt at the northeastern margin of Pamir. Field investigations and interpretations of seismic profiles indicate that the eastern portion of the Wupoer thrust belt is dominated by an underlying foreland basin and an overlying piggy-back basin. A regional unconformity occurs between the Pliocene (N2) and the underlying Miocene (N1) or Paleogene (Pg) strata associated with two other local unconformities between Lower Pleistocene (Q1) and N2 and between Middle Pleistocene (Q2-4) and Q1 strata. Results of structural restorations suggest that compressional deformation was initiated during the latest Miocene to earliest Pliocene, contributing a total shortening magnitude of 48.6 km with a total shortening rate of 48.12%, most of which occurred in the period from the latest Miocene to earliest Pliocene. These results, combined with previous studies on the Kongur and Tarshkorgan extensional system, suggest an interesting picture of strong piedmont compressional thrusting activity concurrent with interorogen extensional rifting. Combining these results with previously published work on the lithospheric architecture of the Pamir, we propose that gravitational collapse drove the formation of simultaneous extensional and compressional structures with a weak, ductile middle crustal layer acting as a décollement along which both the extensional and compressional faults merged.
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Sedimentary evolution of the Pliocene and Pleistocene Ebro margin, northeastern Spain
Alonso, B.; Field, M.E.; Gardner, J.V.; Maldonado, A.
1990-01-01
The Pliocene and Pleistocene deposits of the Spanish Ebro margin overlie a regional unconformity and contain a major disconformity. These unconformities, named Reflector M and Reflector G, mark the bases of two seismic sequences. Except for close to the upper boundary where a few small channel deposits are recognized, the lower sequence lacks channels. The upper sequence contains nine channel-levee complexes as well as base-of-slope aprons that represent the proximal part of the Valencia turbidite system. Diverse geometries and variations in seismic units distinguish shelf, slope, base-of-slope and basin-floor facies. Four events characterize the late Miocene to Pleistocene evolution of the Ebro margin: (a) formation of a paleodrainage system and an extensive erosion-to-depositional surface during the latest Miocene (Messinian), (b) deposition of hemipelagic units during the early Pliocene, (c) development of canyons during the late Pliocene to early Pleistocene, and (d) deposition of slope wedges, channel-levee complexes, and base-of-slope aprons alternating with hemipelagic deposition during the Pleistocene. Sea-level fluctuations influenced the evolution of the sedimentary sequences of the Ebro margin, but the major control was the sediment supply from the Ebro River. ?? 1990.
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DOE Office of Scientific and Technical Information (OSTI.GOV)
Lane, H.R.; Frye, M.W.; Couples, G.D.
1992-01-01
Biothems are regional wedge- or lens-shaped bodies of strata that are bounded shelfward or cratonward by paleontologically recognizable unconformities; generally thicken on marine shelves, where they are typically conformable with underlying and overlying biothems; are commonly thinner or represent starved sequences further basinward; and in their most basinward extent, are either bounded by biostratigraphically recognizable unconformities or are conformable with underlying and overlying biothems. As recognized to date, biothems have a logical distribution of faunal and floral components, as well as facies groupings that represent internally consistent and logical sequences of depositional environments. A west-to-east transect within the North Americanmore » Mississippian System which extends from the Basin and Range Province, across the Transcontinental Arch (TA), into the Anadarko Basin, was constructed to demonstrate the regional distribution and tectono-stratigraphic significance of biothems relative to the axis of the TA. The relationships portrayed on the transect, tied to an understanding of North American Mississippian paleogeography, imply that biothems deposited during relative highstand events on one flank of the TA are time-equivalent to biothems deposited during relative lowstand events on the opposite flank of the TA. This distribution is interpreted to have been controlled by intraplate tectonic events that formed piano key basins along the flanks of the TA. The spatial patterns of these basins are not consistent with published models of basin evolution. A further conclusion is that the lack of coincident, transgressive or regressive Mississippian biothems on either flank of the TA suggests that it is inadvisable to impose the Mississippi Valley-derived eustasy curve on western flank depositional sequences.« less
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DOE Office of Scientific and Technical Information (OSTI.GOV)
Cullen, A.B.; Pigott, J.D.
1990-06-01
The present-day North New Guinea basin is a Plio-Pleistocene successor basin that formed subsequent to accretion of the Finisterre volcanic arc to the Australian Plate. The Ramu, Sepik, and Piore infrabasins formed in a forearc setting relative to the continental Maramuni magmatic arc. The evolution of these infrabasins was strongly influenced by accretion of the composite Torricelli-Prince Alexander terrane to the Australian Plate. Regional reflection seismic data and tectonic subsidence-subsidence rate calculations for seven wells drilled in the North New Guinea basin reveal a complex history. The timing and magnitude of subsidence and changes in subsidence rates differ between eachmore » of the Miocene infrabasins. A diachronous middle to late Miocene unconformity generally truncates infrabasin sequences. The Nopan No. 1 in the Sepik basin, however, has a complete middle Miocene to Pleistocene sedimentary record. This well records late Miocene negative subsidence rates documenting that the Nopan anticline grew as erosion occurred elsewhere in the region. This circumstance suggests that the major, sequence-bounding unconformity results from regional uplift and deformation, rather than changes in global sea level. The Plio-Pleistocene evolution of the North New Guinea basin has two profound implications regarding hydrocarbon exploration. First, the late Pliocene structural inversion of parts of the basin hinders stratigraphic and facies correlation inferred from the present setting. The recognition of basin inversion is particularly important in the Piore basin for predicting the distribution of potential reservoir facies in the Miocene carbonates. Second, the subsidence data suggest that although potential source rocks may be thermally within the oil window, these rocks may not have had sufficient time to mature owing to their recent burial.« less
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Hansley, Paula L.; Johnson, Ronald C.
1980-01-01
This report presents preliminary results of a mineralogic and diagenetic study of some low-permeability sandstones from measured surface sections and cores obtained from drill holes in the Piceance Creek Basin of northwestern Colorado. A documentation of the mineralogy and diagenetic history will aid in the exploration for natural gas and in the development of recovery technology in these low-permability sandstones. These sandstones are in the nonmarine upper part of the Mesaverde Formation (or Group) of Late Cretaceous age and are separated from overlying lower Tertiary rocks by a major regional unconformity. Attention is focused on the sandstone units of the Ohio Creek Member, which directly underlies the unconformity; however, comparisons between the mineralogy of the Ohio Creek strata and that of the underlying sandstone units are made whenever possible. The Ohio Creek is a member of the Hunter Canyon Formation (Mesaverde Group) in the southwestern part of the basin, and the Mesaverde Formation in the southern and central parts of the basin. The detrital mineralogy is fairly constant throughout all of these nonrnarine Cretaceous sandstone units; however, in the southeastern part of the basin, there is an increase in percentage of feldspar, quartzite, and igneous rock fragments in sandstones of the Ohio Creek Member directly underlying the unconformity. In the southwestern part of the basin, sandstones of the Ohio Creek Member are very weathered and are almost-entirely comprised of quartz, chert, and kaolinite. A complex diagenetic history, partly related to the overlying unconformity, appears to be responsible for transforming these sandstones into potential gas reservoirs. The general diagenetic sequence for the entire Upper Cretaceous interval studied is interpreted to be (early to late): early(?) calcite cement, chlorite, quartz overgrowths, calcite cement, secondary porosity, analcime (surface only), kaolinite and illite, and late carbonate cements. Authigenic high-iron chlorite, which occurs on grain rims and in pore throats, is primarily responsible for the low-permeability of the subsurface sandstones of the Ohio Creek Member in the center of the basin. Kaolinite is the most abundant pore-filling authigenic clay in these sandstones, from the southwestern part of the basin and is responsible for their distinctive white-weathering color in outcrop. In the sandstones below the Ohio Creek Member, however, chlorite and kaolinite occur locally, and authigenic calcite and illite are more abundant. The occurrence and distribution of secondary porosity is one of the most important aspects of the diagenetic history of these sandstones. It is present as moldic intra- and intergranular porosity, as well as microporosity among authigenic clay pariicles. Although present locally in most sandstone units, secondary porosity is particularly common in the uppermost sandstone units and is interpreted to have formed primarily asa result ofweathering during the time represented by the Cretaceous-Tertiary unconformity.
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Church, Jessica A; Balota, David A; Petersen, Steven E; Schlaggar, Bradley L
2011-06-01
In a previous study of single word reading, regions in the left supramarginal gyrus and left angular gyrus showed positive BOLD activity in children but significantly less activity in adults for high-frequency words [Church, J. A., Coalson, R. S., Lugar, H. M., Petersen, S. E., & Schlaggar, B. L. A developmental fMRI study of reading and repetition reveals changes in phonological and visual mechanisms over age. Cerebral Cortex, 18, 2054-2065, 2008]. This developmental decrease may reflect decreased reliance on phonological processing for familiar stimuli in adults. Therefore, in the present study, variables thought to influence phonological demand (string length and lexicality) were manipulated. Length and lexicality effects in the brain were explored using both ROI and whole-brain approaches. In the ROI analysis, the supramarginal and angular regions from the previous study were applied to this study. The supramarginal region showed a significant positive effect of length, consistent with a role in phonological processing, whereas the angular region showed only negative deflections from baseline with a strong effect of lexicality and other weaker effects. At the whole-brain level, varying effects of length and lexicality and their interactions were observed in 85 regions throughout the brain. The application of hierarchical clustering analysis to the BOLD time course data derived from these regions revealed seven clusters, with potentially revealing anatomical locations. Of note, a left angular gyrus region was the sole constituent of one cluster. Taken together, these findings in adult readers (1) provide support for a widespread set of brain regions affected by lexical variables, (2) corroborate a role for phonological processing in the left supramarginal gyrus, and (3) do not support a strong role for phonological processing in the left angular gyrus.
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NASA Technical Reports Server (NTRS)
Lapalme, Caitlin M.; Fortier, Daniel; Pollard, Wayne; Lacelle, Denis; Davila, Alfonso; McKay, Christopher P.
2017-01-01
The cryostratigraphy of permafrost in ultraxerous environments is poorly known. In this study, icy permafrost cores from University Valley (McMurdo Dry Valleys, Antarctica) were analyzed for sediment properties, ground-ice content, types and distribution of cryostructures, and presence of unconformities. No active layer exists in the valley, but the ice table, a sublimation unconformity, ranges from 0 to 60 cm depth. The sediments are characterized as a medium sand, which classifies them as low to non-frost susceptible. Computed tomography (CT) scan images of the icy permafrost cores revealed composite cryostructures that included the structureless, porous visible, suspended and crustal types. These cryostructures were observed irrespective of ground-ice origin (vapour deposited and freezing of snow meltwater), suggesting that the type and distribution of cryostructures could not be used as a proxy to infer the mode of emplacement of ground ice. Volumetric ice content derived from the CT scan images underestimated measured volumetric ice content, but approached measured excess ice content. A palaeo-sublimation unconformity could not be detected from a change in cryostructures, but could be inferred from an increase in ice content at the maximum predicted ice table depth. This study highlights some of the unique ground-ice processes and cryostructures in ultraxerous environments.
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Southwest USA Exhumation History Recorded Below the Great Unconformity
NASA Astrophysics Data System (ADS)
Heizler, M. T.; Karlstrom, K. E.
2002-05-01
The Southwestern USA Precambrian terranes preserve a long and variable exhumation history that can be tracked using thermochronological methods. This exhumation history is controlled on two interrelated scales. At first order, it is recognized that 1.7 to 1.4 Ga mid-crustal (10 km, 2-4 kbar) rocks were ultimately exhumed and reside below unconformities of variable age. In Arizona, Mesoproterozoic Apache Group and Neoproterozoic Supergroup sedimentary rocks lie directly on basement and thus indicate exhumation of some regions relatively soon following the 1.4 Ga events. In the Rocky Mountains of Colorado and the Rio Grande rift uplifts of New Mexico, basement is generally overlain by Cambrian to Mississippian strata. The unconformities are useful markers of net exhumation; however do not reveal a time-integrated path. Using published, and hundreds of new 40Ar/39Ar analyses of hornblende, muscovite, biotite and K-feldspar, and a growing U/Pb accessory mineral thermochronology database, we are extracting exhumation information with great detail. The thermochronological data continue to support the claim that relatively low net exhumation occurred following 1.7 to 1.6 Ga accretion of volcanic arc terranes to the southern margin of Laurentia. Mid-crustal (2-4 kbar) rocks stabilized soon after accretion, whereas in some regions like the Upper Granite Gorge, Grand Canyon deeper (6 kbar) metamorphic terranes decompressed to 3 kbar before stabilization. The cooling history of these mid-crustal rocks post 1.65 Ga remains somewhat unknown. Overall slow-cooling models (550 \\deg C to 300 \\deg C from 1.7 to 1.4 Ga) require high geothermal gradients in order to maintain 10 km deep rocks at high temperatures for 100's of Ma. Alternatively, isobaric cooling models to more normal geothermal gradients (i.e. 25 \\deg C/km) at ca. 1.65 Ga require later (1.4 Ga) thermal pulses and/or Mesoproterozoic vertical displacements to explain highly discordant thermochronological data. Either model supports relatively normal crustal thickness during 1.8-1.6 Ga arc accretion. In the Grand Canyon, cooling and exhumation are recorded at 1.4 Ga and 1.25 Ga. 1.4 Ga tectonism is shown by a sharp contrast in mica ages (1.4 vs. 1.6 Ga) across the 96-mile shear zone. The 1.25 Ga denudation is required by 1.25-1.30 Ga K-feldspar argon ages from basement that is unconformably overlain by a 1253 Ma volcanic ash horizon in the Unkar Group sediments. Arizona transition zone rocks of similar metamorphic pressure yield highly variable argon ages and indicate that small differences in exposed paleodepth can yield significantly different data. This is supported by cooling ages that systematically decrease with increase in paleodepth in the Gold Butte block, NV. Combined, the thermochronological data from the SW USA record a complex exhumation history that is characterized by discrete block uplift superimposed on an overall billion year erosional history that brings mid-crustal rocks to the surface a variable times.
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Low-btu gas in the US Midcontinent: A challenge for geologists and engineers
Newell, K. David; Bhattacharya, Saibal; Sears, M. Scott
2009-01-01
Several low-btu gas plays can be defined by mapping gas quality by geological horizon in the Midcontinent. Some of the more inviting plays include Permian strata west of the Central Kansas uplift and on the eastern flank of Hugoton field and Mississippi chat and other pays that subcrop beneath (and directly overlie) the basal Pennsylvanian angular unconformity at the southern end of the Central Kansas uplift. Successful development of these plays will require the cooperation of reservoir geologists and process engineers so that the gas can be economically upgraded and sold at a nominal pipeline quality of 950 btu/scf or greater. Nitrogen is the major noncombustible contaminant in these gas fields, and various processes can be utilized to separate it from the hydrocarbon gases. Helium, which is usually found in percentages corresponding to nitrogen, is a possible ancillary sales product in this region. Its separation from the nitrogen, of course, requires additional processing. The engineering solution for low-btu gas depends on the rates, volumes, and chemistry of the gas needing upgrading. Cryogenic methods of nitrogen removal are classically used for larger feed volumes, but smaller feed volumes characteristic of isolated, low-pressure gas fields can now be handled by available small-scale PSA technologies. Operations of these PSA plants are now downscaled for upgrading stripper well gas production. Any nitrogen separation process should be sized, within reason, to match the anticipated flow rate. If the reservoir rock surprises to the upside, the modularity of the upgrading units is critical, for they can be stacked to meet higher volumes. If a reservoir disappoints (and some will), modularity allows the asset to be moved to another site without breaking the bank.
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NASA Astrophysics Data System (ADS)
Yusufoğlu, H.
2013-04-01
The Elbistan Basin in the east-Central Anatolia is an intramontane structural depression in the interior part of the Anatolide-Tauride Platform. The Neogene fill in and around Elbistan Basin develops above the Upper Devonian to lower Tertiary basement and comprises two units separated by an angular unconformity: (1) intensely folded and faulted Miocene shallow marine to terrestrial and lacustrine sediments and (2) nearly flat-lying lignite-bearing lacustrine (lower unit) and fluvial (upper unit) deposits of Plio-Quaternary Ahmetçik Formation. The former is composed of Lower-Middle Miocene Salyan, Middle-upper Middle Miocene Gövdelidağ and Upper Miocene Karamağara formations whereas the latter one is the infill of the basin itself in the present configuration of the Elbistan Basin. The basin is bound by normal faults with a minor strike-slip component. It commenced as an intramontane pull-apart basin and developed as a natural response to Early Pliocene tectonic escape-related strike-slip faulting subsequent to post-collisional intracontinental compressional tectonics during which Miocene sediments were intensely deformed. The Early Pliocene time therefore marks a dramatic changeover in tectonic regime and is interpreted as the beginning of the ongoing last tectonic evolution and deformation style in the region unlike to previous views that it commenced before that time. Consequently, the Elbistan Basin is a unique structural depression that equates the extensional strike-slip regime in east-Central Anatolia throughout the context of the neotectonical framework of Turkey across progressive collision of Arabia with Eurasia. Its Pliocene and younger history differs from and contrasts with that of the surrounding pre-Pliocene basins such as Karamağara Basin, on which it has been structurally superimposed.
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NASA Astrophysics Data System (ADS)
Gale, J.; Steckler, M. S.; Sousa, D.; Seeber, L.; Goodbred, S. L., Jr.; Ferguson, E. K.
2014-12-01
The Ganges-Brahmaputra Delta abuts the Indo-Burman Arc on the east. Subduction of the thick delta strata has generated a large subaerial accretionary prism, up to 250 km wide, with multiple ranges of anticlines composed of the folded and faulted delta sediments. As the wedge has grown, the exposed anticlines have become subject to erosion by the rivers draining the Himalaya, a local Indo-Burman drainage network, and coastal processes. Multiple lines of geophysical, geologic, and geomorphologic evidence indicate anticline truncation as a result of interaction with the rivers of the delta and sea level. Seismic lines, geologic mapping, and geomorphology reveal truncated anticlines with angular unconformities that have been arched due to continued growth of the anticline. Buried, truncated anticlines have been identified by seismic lines, tube well logs, and resistivity measurements. The truncation of these anticlines also appears to provide a pathway for high-As Holocene groundwater into the generally low-As Pleistocene groundwater. Overall, the distribution of anticline erosion and elevation in the fold belt appears to be consistent with glacial-interglacial changes in river behavior in the delta. The anticline crests are eroded during sea level highstands as rivers and the coastline sweep across the region, and excavated by local drainage during lowstands. With continued growth, the anticlines are uplifted above the delta and "survive" as topographic features. As a result, the maximum elevations of the anticlines are clustered in a pattern suggesting continued growth since their last glacial highstand truncation. An uplift rate is calculated from this paced truncation and growth that is consistent with other measurements of Indo-Burman wedge advance. This rate, combined with the proposed method of truncation, give further evidence of dynamic fluvial changes in the delta between glacial and interglacial times.
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Le Dantec, Nicolas; Hogarth, Leah J.; Driscoll, Neal W.; Babcock, Jeffrey M.; Barnhardt, Walter A.; Schwab, William C.
2010-01-01
CHIRP seismic and swath bathymetry data acquired offshore La Jolla, California provide an unprecedented three-dimensional view of the La Jolla and Scripps submarine canyons. Shore-parallel patterns of tectonic deformation appear to control nearshore sediment thickness and distribution around the canyons. These shore-parallel patterns allow the impact of local tectonic deformation to be separated from the influence of eustatic sea-level fluctuations. Based on stratal geometry and acoustic character, we identify a prominent angular unconformity inferred to be the transgressive surface and three sedimentary sequences: an acoustically laminated estuarine unit deposited during early transgression, an infilling or “healing-phase” unit formed during the transgression, and an upper transparent unit. Beneath the transgressive surface, steeply dipping reflectors with several dip reversals record faulting and folding along the La Jolla margin. Scripps Canyon is located at the crest of an antiform, where the rocks are fractured and more susceptible to erosion. La Jolla Canyon is located along the northern strand of the Rose Canyon Fault Zone, which separates Cretaceous lithified rocks to the south from poorly cemented Eocene sands and gravels to the north. Isopach and structure contour maps of the three sedimentary units reveal how their thicknesses and spatial distributions relate to regional tectonic deformation. For example, the estuarine unit is predominantly deposited along the edges of the canyons in paleotopographic lows that may have been inlets along barrier beaches during the Holocene sea-level rise. The distribution of the infilling unit is controlled by pre-existing relief that records tectonic deformation and erosional processes. The thickness and distribution of the upper transparent unit are controlled by long-wavelength, tectonically induced relief on the transgressive surface and hydrodynamics.
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NASA Astrophysics Data System (ADS)
Sundell, K. E.; Saylor, J.; Lapen, T. J.; Styron, R. H.; Villarreal, D. P.; Usnayo Perales, W. P.; Cárdenas, J.
2017-12-01
Stratigraphy of the Peruvian Altiplano contains valuable information salient to debated geodynamic processes active during the Cenozoic construction of the Andean Plateau. Central to this discussion is the relative timing, location, and magnitude of basin subsidence and surface uplift; however, records of these processes are limited in the Andean Plateau of southern Peru. We measured 6200 m of non-marine clastic stratigraphy in the northernmost Altiplano, characterized through lithofacies and paleocurrent analysis, conglomerate clast counts, sandstone petrography, and detrital zircon U-Pb geochronology. We employ a host of new quantitative detrital zircon techniques including multidimensional scaling, mixture modeling, and quantification of zircon roundness. Results consistently show sediment sourcing from the Western Cordillera and/or western Altiplano, despite close proximity to the modern Eastern Cordillera. Sediment accumulation rates based on new detrital zircon U-Pb maximum depositional ages define an upward-convex, Paleogene subsidence profile with rates increasing from 36 m/Myr to >150 m/Myr. These rates are consistent with deposition and northeastward migration of a Paleogene flexural foreland basin system, which requires coeval lithospheric loading in the Western Cordillera and/or western Altiplano and relative subsidence in the location of the modern Eastern Cordillera. Transition to hinterland basin deposition is marked by a latest Oligocene to middle Miocene angular unconformity. Following this transition, sediment accumulation rates increase to >800 m/Myr during the late Miocene, consistent with strike-slip-induced subsidence, likely under Airy isostatic support. Results in the context of the greater Andean Plateau highlight along-strike variability in rates and timing of deposition in a regionally-contiguous foreland basin system extending from southern Peru to northwest Argentina, and support models of cyclical orogenic processes.
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A Role for the Left Angular Gyrus in Episodic Simulation and Memory.
Thakral, Preston P; Madore, Kevin P; Schacter, Daniel L
2017-08-23
Functional magnetic resonance imaging (fMRI) studies indicate that episodic simulation (i.e., imagining specific future experiences) and episodic memory (i.e., remembering specific past experiences) are associated with enhanced activity in a common set of neural regions referred to as the core network. This network comprises the hippocampus, medial prefrontal cortex, and left angular gyrus, among other regions. Because fMRI data are correlational, it is unknown whether activity increases in core network regions are critical for episodic simulation and episodic memory. In the current study, we used MRI-guided transcranial magnetic stimulation (TMS) to assess whether temporary disruption of the left angular gyrus would impair both episodic simulation and memory (16 participants, 10 females). Relative to TMS to a control site (vertex), disruption of the left angular gyrus significantly reduced the number of internal (i.e., episodic) details produced during the simulation and memory tasks, with a concomitant increase in external detail production (i.e., semantic, repetitive, or off-topic information), reflected by a significant detail by TMS site interaction. Difficulty in the simulation and memory tasks also increased after TMS to the left angular gyrus relative to the vertex. In contrast, performance in a nonepisodic control task did not differ statistically as a function of TMS site (i.e., number of free associates produced or difficulty in performing the free associate task). Together, these results are the first to demonstrate that the left angular gyrus is critical for both episodic simulation and episodic memory. SIGNIFICANCE STATEMENT Humans have the ability to imagine future episodes (i.e., episodic simulation) and remember episodes from the past (i.e., episodic memory). A wealth of neuroimaging studies have revealed that these abilities are associated with enhanced activity in a core network of neural regions, including the hippocampus, medial prefrontal cortex, and left angular gyrus. However, neuroimaging data are correlational and do not tell us whether core regions support critical processes for simulation and memory. In the current study, we used transcranial magnetic stimulation and demonstrated that temporary disruption of the left angular gyrus leads to impairments in simulation and memory. The present study provides the first causal evidence to indicate that this region is critical for these fundamental abilities. Copyright © 2017 the authors 0270-6474/17/378142-08$15.00/0.
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A Role for the Left Angular Gyrus in Episodic Simulation and Memory
2017-01-01
Functional magnetic resonance imaging (fMRI) studies indicate that episodic simulation (i.e., imagining specific future experiences) and episodic memory (i.e., remembering specific past experiences) are associated with enhanced activity in a common set of neural regions referred to as the core network. This network comprises the hippocampus, medial prefrontal cortex, and left angular gyrus, among other regions. Because fMRI data are correlational, it is unknown whether activity increases in core network regions are critical for episodic simulation and episodic memory. In the current study, we used MRI-guided transcranial magnetic stimulation (TMS) to assess whether temporary disruption of the left angular gyrus would impair both episodic simulation and memory (16 participants, 10 females). Relative to TMS to a control site (vertex), disruption of the left angular gyrus significantly reduced the number of internal (i.e., episodic) details produced during the simulation and memory tasks, with a concomitant increase in external detail production (i.e., semantic, repetitive, or off-topic information), reflected by a significant detail by TMS site interaction. Difficulty in the simulation and memory tasks also increased after TMS to the left angular gyrus relative to the vertex. In contrast, performance in a nonepisodic control task did not differ statistically as a function of TMS site (i.e., number of free associates produced or difficulty in performing the free associate task). Together, these results are the first to demonstrate that the left angular gyrus is critical for both episodic simulation and episodic memory. SIGNIFICANCE STATEMENT Humans have the ability to imagine future episodes (i.e., episodic simulation) and remember episodes from the past (i.e., episodic memory). A wealth of neuroimaging studies have revealed that these abilities are associated with enhanced activity in a core network of neural regions, including the hippocampus, medial prefrontal cortex, and left angular gyrus. However, neuroimaging data are correlational and do not tell us whether core regions support critical processes for simulation and memory. In the current study, we used transcranial magnetic stimulation and demonstrated that temporary disruption of the left angular gyrus leads to impairments in simulation and memory. The present study provides the first causal evidence to indicate that this region is critical for these fundamental abilities. PMID:28733357
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Pipiringos, G.N.; O'Sullivan, Robert Brett
1978-01-01
The Triassic and Jurassic rocks in Western Interior United States contain nine unconformities each of which was destroyed to some extent by a younger unconformity. Regardless of extent, all are useful for correlation of rock sequences in areas where fossils or age dates are lacking. The purpose of this report is to call attention to the presence, significance, and value for correlation of these unconformities. The Triassic unconformities are designated from oldest to youngest, Tr-1, Tr-2, and Tr-3; the Jurassic ones similarly are designated J-0, J-l, J-2, J-3, J-4, and J-5. Of these, the J-2 surface is the best preserved and most widespread. It extends throughout the Western Interior and truncates the older unconformities in different parts of this area. Consequently, the J-2 surface is discussed and illustrated in much more detail than the others. Identification of these unconformities throughout large areas where their presence hitherto had been unknown results in some new unexpected correlations and conclusions. Principal among these are: (1) The Red Draw Member of the Jelm Formation of southeastern Wyoming equals the lower part of the Crow Mountain Sandstone of central Wyoming. The Sips Creek Member of the Jelm Formation of southeastern Wyoming equals the upper part of the Crow Mountain Sandstone of central Wyoming and the Gartra Member of the Chinle Formation in the Uinta Mountains of northeastern Utah and northwestern Colorado. The Chinle Formation of the Colorado Plateau and the Uinta Mountains equals the upper part of the Crow Mountain plus the Popo Agie Formation of central Wyoming. (2) The Nugget Sandstone of northern Utah and southwestern Wyoming approximately equals the Glen Canyon Group of the Colorado Plateau. The Temple Cap Sandstone of southwestern Utah equals the Gypsum Spring Formation and the Gypsum Spring Member of the Twin Creek Limestone of Wyoming and the Nesson Formation of Nordquist in the subsurface of the Williston basin. The Sawtooth and Piper Formations at their type sections in Montana and the lower parts of the Twin Creek Limestone (including only the Sliderock, Rich, and Boundary Ridge Members) in western Wyoming and of the Carmel Formation in the Colorado Plateau, at their respective type localities, are equivalent, but none of these correlate with any part of the Gypsum Spring Formation of Wyoming. The Curtis Formation at its type locality in the San Rafael Swell, Utah, equals only the lower part of the Curtis Formation of the Uinta Mountains. The upper part of the Curtis in the Uinta Mountains and the Redwater Shale Member of the Sundance Formation of Wyoming and South Dakota are equivalent. Estimates of the length of time in millions of years (m.y.) required for uplift and erosion of an unconformity range from less than 1 to as much as 10 m.y.; the average is about 1.8 m.y. if the extremes in time are excluded. The length of time for burial of the surfaces by transgression ranges from less than 1 to about 10 m.y.; the average is less than 1 m.y. if the extremes in time are disregarded.
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NASA Astrophysics Data System (ADS)
Getz, Joseph Edward
The Middleton Place Summerville Seismic Zone (MPSSZ) near Summerville, South Carolina was the site of renewed extensive investigation, beginning in the 1970's, for the source of the 1886 Charleston earthquake. Reactivation of faults associated with a putative fault-bounded Triassic rift basin through analysis of seismic reflection, seismic refraction, and well data has since become the favored interpretation for the source of MPSSZ seismicity. Critical to this interpretation is the association of continental redbed sedimentary rocks with Triassic basins identified throughout the North American Atlantic margin. Reanalysis of 18 seismic reflection profiles and 25 seismic refraction profiles within the MPSSZ suggests that the red beds found here are a thin, sub-horizontal, regionally extensive, generally unbroken subsurface stratigraphic sequence distinct from the sedimentary architecture observed in analog Triassic rift systems. In addition, this sequence appears to unconformably overly a structural depression (the Jedberg basin) previously interpreted as a Triassic rift basin in the vicinity of the MPSSZ. In addition to the geometries observed on seismic reflection profiles, seismic refraction velocities ranging from 4.2 to 6.1 km/s can be correlated with (1) Jurassic basalt flows, (2) the newly proposed Summerville Formation, and (3) the Basement (B) sequences respectively. The current study maps the Summerville red bed section and its bounding reflectors. In addition to mapping the regional extent of the newly proposed Summerville Formation, refraction velocities and changes in reflection character, the lateral extent of the basalt flows can be changed to a more localized flow rather than a regionally extensive flow of which was previously thought. Reanalysis of data in the MPSSZ suggests that the area may not be part of the Triassic South Georgia Rift system due to the sub-horizontal geometry of the red bed reflections, the apparent lack of faulting, and their regional extent.
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NASA Astrophysics Data System (ADS)
Batezelli, Alessandro; Ladeira, Francisco Sergio Bernardes
2016-01-01
With the breakup of the supercontinent Gondwana, the South American Plate has undergone an intense process of tectonic restructuring that led to the genesis of the interior basins that encompassed continental sedimentary sequences. The Brazilian Bauru, Sanfranciscana and Parecis basins during Late Cretaceous have had their evolution linked to this process of structuring and therefore have very similar sedimentary characteristics. The purpose of this study is to establish a detailed understanding of alluvial sedimentary processes and architecture within a stratigraphic sequence framework using the concept of the stratigraphic base level or the ratio between the accommodation space and sediment supply. The integration of the stratigraphic and facies data contributed to defining the stratigraphic architecture of the Bauru, Sanfranciscana and Parecis Basins, supporting a model for continental sequences that depicts qualitative changes in the sedimentation rate (S) and accommodation space (A) that occurred during the Cretaceous. This study discusses the origin of the unconformity surfaces (K-0, K-1 and K-1A) that separate Sequences 1, 2A and 2B and the sedimentary characteristics of the Bauru, Sanfranciscana and Parecis Basins from the Aptian to the Maastrichtian, comparing the results with other Cretaceous Brazilian basins. The lower Cretaceous Sequence 1 (Caiuá and Areado groups) is interpreted as a low-accommodation systems tract compound by fluvial and aeolian systems. The upper Cretaceous lacustrine, braided river-dominated alluvial fan and aeolian systems display characteristics of the evolution from high-to low-accommodation systems tracts (Sequences 2A and 2B). Unconformity K-0 is related to the origin of the Bauru Basin itself in the Early Cretaceous. In Sanfranciscana and Parecis basins, the unconformity K-0 marks the contact between aeolian deposits from Lower Cretaceous and Upper Cretaceous alluvial systems (Sequences 1 and 2). Unconformity K-1, which was generated in the Late Cretaceous, is related to an increase of the A/S ratio, whereas Unconformity K-1A is the result of the decrease in the A/S ratio. Unconformity K-1A bound Sequence 2A (lacustrine and fluvial systems) and Sequence 2B (alluvial deposits) in Bauru Basin whereas in the Sanfranciscana and Parecis basins this unconformity marks the transition from alluvial system to aeolian system (Sequences 2A and 2B). Changes in depositional style in both basins correspond to two distinct tectonic moments occurring within the South American plate. The first associated with post-volcanic thermal subsidence of the Early Cretaceous (Serra Geral and Tapirapuã volcanismos), and the second moment associated with the uplift occurred in the Late Cretaceous (Alto Paranaíba, Vilhena and Serra Formosa Arcs).
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The Angular Momentum of Baryons and Dark Matter Halos Revisited
NASA Technical Reports Server (NTRS)
Kimm, Taysun; Devriendt, Julien; Slyz, Adrianne; Pichon, Christophe; Kassin, Susan A.; Dubois, Yohan
2011-01-01
Recent theoretical studies have shown that galaxies at high redshift are fed by cold, dense gas filaments, suggesting angular momentum transport by gas differs from that by dark matter. Revisiting this issue using high-resolution cosmological hydrodynamics simulations with adaptive-mesh refinement (AMR), we find that at the time of accretion, gas and dark matter do carry a similar amount of specific angular momentum, but that it is systematically higher than that of the dark matter halo as a whole. At high redshift, freshly accreted gas rapidly streams into the central region of the halo, directly depositing this large amount of angular momentum within a sphere of radius r = 0.1R(sub vir). In contrast, dark matter particles pass through the central region unscathed, and a fraction of them ends up populating the outer regions of the halo (r/R(sub vir) > 0.1), redistributing angular momentum in the process. As a result, large-scale motions of the cosmic web have to be considered as the origin of gas angular momentum rather than its virialised dark matter halo host. This generic result holds for halos of all masses at all redshifts, as radiative cooling ensures that a significant fraction of baryons remain trapped at the centre of the halos. Despite this injection of angular momentum enriched gas, we predict an amount for stellar discs which is in fair agreement with observations at z=0. This arises because the total specific angular momentum of the baryons (gas and stars) remains close to that of dark matter halos. Indeed, our simulations indicate that any differential loss of angular momentum amplitude between the two components is minor even though dark matter halos continuously lose between half and two-thirds of their specific angular momentum modulus as they evolve. In light of our results, a substantial revision of the standard theory of disc formation seems to be required. We propose a new scenario where gas efficiently carries the angular momentum generated by large-scale structure motions deep inside dark matter halos, redistributing it only in the vicinity of the disc.
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NASA Astrophysics Data System (ADS)
Popovs, K.; Saks, T.; Ukass, J.; Jatnieks, J.
2012-04-01
Interpretation of geological structures in 3D geological models is a relatively new research topic that is already standardized in many geological branches. Due to its wide practical application, these models are indispensable and become one of the dominant interpretation methods in reducing geological uncertainties in many geology fields. Traditionally, geological concepts complement quantitative as much as qualitative data to obtain a model deemed acceptable, however, available data very often is insufficient and modeling methods primarily focus on spatial data but geological history usually is mostly neglected for the modeling of large sedimentary basins. A need to better integrate the long and often complex geological history and geological knowledge into modeling procedure is very acute to gain geological insight and improve the quality of geological models. During this research, 3D geological model of the Baltic basin (BB) was created. Because of its complex regional geological setting - wide range of the data sources with multiple scales, resolution and density as well as its various source formats, the study area provides a challenge for the 3D geological modeling. In order to create 3D regional geometrical model for the study area algorithmic genetic approach for model geometry reconstruction was applied. The genetic approach is based on the assumption that post-depositional deformation produce no significant change in sedimentary strata volume, assuming that the strata thickness and its length in a cross sectional plane remains unchanged except as a result of erosion. Assuming that the tectonic deformation occurred in sequential cycles and subsequent tectonic stage strata is separated by regional unconformity as is the case of the BB, there is an opportunity for algorithmic approach in reconstructing these conditions by sequentially reconstructing the layer original thickness. Layer thicknesses were sliced along fault lines, where applicable layer thickness was adjusted by taking into account amount of erosion by the presence of the regional unconformities. Borehole data and structural maps of some surfaces were used in creating geological model of the BB. Used approach allowed creating geologically sound geometric model. At first borehole logs were used to reconstruct initial thicknesses of different strata in every tectonic stage, where topography of each strata was obtained sequentially summing thickness to the initial reference surface from structural maps. Thereby each layer reflects the topography and amount of slip along the fault of the overlying layer. Overlying tectonic cycle sequence is implemented into the model structure by using unconformity surface as an initial reference surface. Applied techniques made possible reliably reconstructing and predicting in areas of sparse data layer surface geometry, its thickness distribution and evaluating displacements along the fault planes. Overall results indicate that the used approach has a good potential in development of regional geological models for the sedimentary basins and is valid for spatial interpretation of geological structures, subordinating this process to geological evolution prerequisites. This study is supported by the European Social Fund project No. 2009/0212/1DP/1.1.1.2.0/09/APIA/VIAA/060.
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NASA Astrophysics Data System (ADS)
Charrier, Reynaldo; Wyss, AndréR.; Flynn, John J.; Swisher, Carl C.; Norell, Mark A.; Zapatta, Franyo; McKenna, Malcolm C.; Novacek, Michael J.
1996-11-01
New geologic, paleontologic and isotopic geochronometric results from the Termas del Flaco region in the upper Tinguiririca River valley in central Chile demand considerable revision of the accepted geotectonic history of the Andean Main Range in this region. A diverse, transitional Eocene-Oligocene aged, land-mammal fauna was recovered from several sites in volcaniclastic sediments of the Coya-Machalí (=Abanico) Formation. Major results of our study include: 1) The 1000 + m thick studied deposits, previously attributed to the Cretaceous Colimapu Formation, belong to the Coya-Machalí (=Abanico) Formation. Radioisotopic data from levels immediately above (31.5 Ma) and below (37.S Ma) the fossiliferous horizon indicate a latest Eocene to early Oligocene age for the basal part of the formation and the fauna contained in it. 2) The fossiliferous unit rests with slight angular offset on different Mesozoic units: "Brownish-red Clastic Unit" (BRCU) and Baños del Flaco Formation; in a limited area it also overlies a white tuff dated at 104 Ma. 3) The contacts just discussed (none of which is attributable to faulting), demonstrate the existence of two, or possibly three, unconformities in the region. 4) Sedimentological criteria argue against reference of the BRCU to the Colimapu Formation, and imply correlation of the former unit to basal levels with in the late Cretaceous Neuquén Group of western Argentina. 5) The Coya-Machalí Formation, previously viewed as representing the western volcanic equivalent of Riográndico Supercycle deposits of western Argentino, is likely coeval to much younger units in that region such as the Agua de la Piedra Formation. 6) Paleomagnetic results from the fossil producing horizon indicate about 20 ° of post-early Oligocene, counterclockwise rotation. 7) Fossil mammals from the Coya-Machalí Formation near Termas del Flaco represent a distinct biochronologic interval not heretofore clearly recognized from elsewhere on the continent. This new fauna helps fill the long recognized post-?middle Eocene, pre-late Oligocene faunal hiatus between the Mustersan and Deseadan South American Land Mammal Ages (SALMA). In addition, it records the earliest known presence of rodents in South America and otherwise differs strongly from the enigmatic Divisaderan SALMA.
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Klotsko, Shannon; Driscoll, Neal W.; Kent, Graham; Brothers, Daniel
2016-01-01
New high-resolution CHIRP seismic data acquired offshore San Onofre, southern California reveal that shelf sediment distribution and thickness are primarily controlled by eustatic sea level rise and sediment supply. Throughout the majority of the study region, a prominent abrasion platform and associated shoreline cutoff are observed in the subsurface from ~ 72 to 53 m below present sea level. These erosional features appear to have formed between Melt Water Pulse 1A and Melt Water Pulse 1B, when the rate of sea-level rise was lower. There are three distinct sedimentary units mapped above a regional angular unconformity interpreted to be the Holocene transgressive surface in the seismic data. Unit I, the deepest unit, is interpreted as a lag deposit that infills a topographic low associated with an abrasion platform. Unit I thins seaward by downlap and pinches out landward against the shoreline cutoff. Unit II is a mid-shelf lag deposit formed from shallower eroded material and thins seaward by downlap and landward by onlap. The youngest, Unit III, is interpreted to represent modern sediment deposition. Faults in the study area do not appear to offset the transgressive surface. The Newport Inglewood/Rose Canyon fault system is active in other regions to the south (e.g., La Jolla) where it offsets the transgressive surface and creates seafloor relief. Several shoals observed along the transgressive surface could record minor deformation due to fault activity in the study area. Nevertheless, our preferred interpretation is that the shoals are regions more resistant to erosion during marine transgression. The Cristianitos fault zone also causes a shoaling of the transgressive surface. This may be from resistant antecedent topography due to an early phase of compression on the fault. The Cristianitos fault zone was previously defined as a down-to-the-north normal fault, but the folding and faulting architecture imaged in the CHIRP data are more consistent with a strike-slip fault with a down-to-the-northwest dip-slip component. A third area of shoaling is observed off of San Mateo and San Onofre creeks. This shoaling has a constructional component and could be a relict delta or beach structure. (C) 2015 Elsevier B.V. All rights reserved.
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NASA Astrophysics Data System (ADS)
Shepherd, Tom J.; Bouch, Jon E.; Gunn, Andrew G.; McKervey, John A.; Naden, Jonathan; Scrivener, Richard C.; Styles, Michael T.; Large, Duncan E.
2005-07-01
An integrated mineralogical-geochemical study of unconformity-related Au-Pd occurrences within and around the Permo Triassic basins of southwest England, UK, has confirmed the importance of low temperature (86±13°C), hydrothermal carbonate veins as hosts for the mineralisation. Fluid inclusion data for the carbonate gangue, supported by stable isotope (13C and 18O) and radiogenic (87Sr/86Sr) data, have identified three principal fluids: (1) a reducing calcic brine [>25 wt% salinity, <0.5 NaCl/(NaCl+CaCl2)] originating in the sub-unconformity basement and an expression of advanced mineral fluid interaction; (2) an oxidising sodic brine [~16 wt% salinity, >0.9 NaCl/(NaCl+CaCl2)] originating in the post-unconformity red beds under evaporitic conditions, and (3) an oxygenated, low salinity groundwater (<3 wt% salinity). The sodic brine is reasoned to be the parent metalliferous fluid and to have acquired its enrichment in Au and Pd by the leaching of immature sediments and intra-rift volcanic rocks within the local Permo Triassic basins. Metal precipitation is linked to the destabilisation of Au and Pd chloride complexes by either mixing with calcic brines, dilution by groundwaters or interaction with reduced lithologies. This explains the diversity of mineralised settings below and above the unconformity and their affinity with red bed brines. The paucity of sulphide minerals, the development of selenides (as ore minerals and as mineral inclusion in gold grains), the presence of rhodochrosite and manganoan calcites (up to 2.5 wt% Mn in calcite) and the co-precipitation of hematite and manganese oxides are consistent with the overall high oxidation state of the ore fluids. A genetic model is proposed linking Permo Triassic red beds, the mixing of oxidising and reducing brines, and the development of unconformity-related precious metal mineralisation. Comparison with other European Permo Triassic basins reveals striking similarities in geological setting, mineralogy and geochemistry with Au, Au-Pd and selenide occurrences in Germany (Tilkerode, Korbach-Goldhausen), Poland (Lubin) and the Czech Republic (Svoboda nad Úpou and Stupná). Though the known Au-Pd occurrences are sub-economic, several predictive criteria are proposed for further exploration.
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NASA Astrophysics Data System (ADS)
Lobo, F. J.; García, M.; Luján, M.; Mendes, I.; Reguera, M. I.; Van Rooij, D.
2018-02-01
The main aim of this study is to explore the spatial patterns of the shelf-scale erosional unconformity related to the last glacial maximum (LGM), particularly in terms of the role of underlying geology and the presumed primary influence of sea-level changes. This involved a detailed mapping of the most recent and widespread erosional shelf surface in a sector of the northern margin of the Gulf of Cádiz (northeast Atlantic Ocean) located adjacent to a major fluvial source. A dense network of high-resolution seismic profiles collected in the 1990s and 2013 off the Guadiana River revealed two distinct geomorphological domains on the LGM shelf-scale subaerial surface. The outer domain exhibits a widespread occurrence of erosional truncations, with a rugged, erosional pattern over the most distal shelf setting that evolves landward into a planar unconformity. The inner domain is more extensive and is characterized by the common occurrence of highly reflective, localized mounded seismic facies that laterally evolve into an irregular surface and in places may develop a channelized morphology. Significant fluvial incision is limited to a major straight valley and a secondary distributary channel. A distinct partition of the lowstand surface is documented, and attributed to a well-marked lithological change. A coarse-grained inner shelf comprises underlying lithified coastal deposits, whereas a fine-grained outer shelf is regarded as the uppermost expression of regressive prodeltaic wedges. The influence of regional indurated surfaces is also expressed in (1) the pattern of erosion, this being more patchy on the inner shelf due to lateral changes of erodibility, whereas on the outer shelf it shows laterally continuous bands, owing to different modes of transgressive ravinement; (2) the spatial and temporal variability of fluvial incision. Inner shelf armoring by indurated deposits prevents reoccupation of previously incised valleys.
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NASA Astrophysics Data System (ADS)
Breitfeld, H. Tim; Hall, Robert; Galin, Thomson; BouDagher-Fadel, Marcelle K.
2018-07-01
The Kuching Zone in West Sarawak consists of two different sedimentary basins, the Kayan and Ketungau Basins. The sedimentary successions in the basins are part of the Kuching Supergroup that extends into Kalimantan. The uppermost Cretaceous (Maastrichtian) to Lower Eocene Kayan Group forms the sedimentary deposits directly above a major unconformity, the Pedawan Unconformity, which marks the cessation of subduction-related magmatism beneath SW Borneo and the Schwaner Mountains, due to termination of the Paleo-Pacific subduction. The successions consist of the Kayan and Penrissen Sandstones and are dominated by fluvial channels, alluvial fans and floodplain deposits with some deltaic to tidally-influenced sections in the Kayan Sandstone. In the late Early or early Middle Eocene, sedimentation in this basin ceased and a new basin, the Ketungau Basin, developed to the east. This change is marked by the Kayan Unconformity. Sedimentation resumed in the Middle Eocene (Lutetian) with the marginal marine, tidal to deltaic Ngili Sandstone and Silantek Formation. Upsequence, the Silantek Formation is dominated by floodplain and subsidiary fluvial deposits. The Bako-Mintu Sandstone, a potential lateral equivalent of the Silantek Formation, is formed of major fluvial channels. The top of the Ketungau Group in West Sarawak is formed by the fluvially-dominated Tutoop Sandstone. This shows a transition of the Ketungau Group in time towards terrestrial/fluvially-dominated deposits. Paleocurrent measurements show river systems were complex, but reveal a dominant southern source. This suggests uplift of southern Borneo initiated in the region of the present-day Schwaner Mountains from the latest Cretaceous onwards. Additional sources were local sources in the West Borneo province, Mesozoic melanges to the east and potentially the Malay Peninsula. The Ketungau Group also includes reworked deposits of the Kayan Group. The sediments of the Kuching Supergroup are predominantly horizontal or dip with low angles and form large open synclines. Steep dips are usually restricted to faults, such as the Lupar Line.
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On the shelf resonances of the Gulf of Carpentaria and the Arafura Sea
NASA Astrophysics Data System (ADS)
Webb, D. J.
2012-09-01
A numerical model is used to investigate the resonances of the Gulf of Carpentaria and the Arafura Sea, and the additional insights that come from extending the analysis into the complex angular velocity plane. When the model is forced at the shelf edge with physically realistic real values of the angular velocity, the response functions at points within the region show maxima and other behaviour which imply that resonances are involved but provide little additional information. The study is then extended to complex angular velocities, and the results then show a clear pattern of gravity wave and Rossby wave like resonances. The properties of the resonances are investigated and used to reinterpret the response at real values of angular velocity. It is found that in some regions the response is dominated by modes trapped between the shelf edge and the coast or between opposing coastlines. In other regions the resonances show cooperative behaviour, possibly indicating the importance of other physical processes.
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Giant angular dependence of electromagnetic induced transparency in THz metamaterials
NASA Astrophysics Data System (ADS)
Liu, Changji; Huang, Yuanyuan; Yao, Zehan; Yu, Leilei; Jin, Yanping; Xu, Xinlong
2018-02-01
The giant electromagnetic induced transparency (EIT) phenomenon is observed in symmetrical metamaterials with angular dependence in the THz region. This is due to the asymmetrical electromagnetic field distribution on the surface of the metamaterials, which induces asymmetric current distribution. Blueshift with the increase of the unit cell period has been observed, which is due to the unusual electromagnetic interaction between units at oblique incidence. This EIT demonstrates an angular dependent high Q-factor, which is sensitive to the dielectric environment. The angle-induced EIT effect could pave the way for future tunable sensing applications in the THz region.
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Study of the mode of angular velocity damping for a spacecraft at non-standard situation
NASA Astrophysics Data System (ADS)
Davydov, A. A.; Sazonov, V. V.
2012-07-01
Non-standard situation on a spacecraft (Earth's satellite) is considered, when there are no measurements of the spacecraft's angular velocity component relative to one of its body axes. Angular velocity measurements are used in controlling spacecraft's attitude motion by means of flywheels. The arising problem is to study the operation of standard control algorithms in the absence of some necessary measurements. In this work this problem is solved for the algorithm ensuring the damping of spacecraft's angular velocity. Such a damping is shown to be possible not for all initial conditions of motion. In the general case one of two possible final modes is realized, each described by stable steady-state solutions of the equations of motion. In one of them, the spacecraft's angular velocity component relative to the axis, for which the measurements are absent, is nonzero. The estimates of the regions of attraction are obtained for these steady-state solutions by numerical calculations. A simple technique is suggested that allows one to eliminate the initial conditions of the angular velocity damping mode from the attraction region of an undesirable solution. Several realizations of this mode that have taken place are reconstructed. This reconstruction was carried out using approximations of telemetry values of the angular velocity components and the total angular momentum of flywheels, obtained at the non-standard situation, by solutions of the equations of spacecraft's rotational motion.
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NASA Astrophysics Data System (ADS)
Hamahashi, M.; Screaton, E.; Tanikawa, W.; Hashimoto, Y.; Martin, K. M.; Saito, S.; Kimura, G.
2015-12-01
The Costa Rica subduction zone offshore Osa Peninsula is known as an erosive margin with active seismicity and the subduction of the Cocos Ridge. One of the major unknowns in this margin is the nature of the unconformity at the base of the slope sediments in the upper plate and the high velocity materials below. To investigate the geologic processes across the unconformity, we examined the consolidation state and mineral assemblages of the sediments at the mid-slope Site 1380 drilled during IODP Expedition 344 by conducting microstructural observation, particle size analysis, X-ray fluorescence/diffraction analysis and resistivity measurement. The general compaction trend is controlled primarily by grain-size sorting and the physical property transition is likely caused by massive sediment removal under normal fault regime, thickness of which range between ~600-850 m determined from the composite porosity-depth curve. Across the unconformity between the late Pliocene~late Pleistocene silty clay (Unit 1) and late Pliocene~early Pleistocene clayey siltstone (Unit 2), the mineral/element components of the sediments is marked by the transitions in zeolite compositions; Unit 1 consists of laumontite and heulandite, whereas below the unconformity, Unit 2 sediments contain analcime, laumontite, and heulandite, but laumontite become less abundant at lower depth. The experienced temperature of the sediments in Unit 2 is estimated to have reached between ~86 and 122℃ as inferred from analcime burial diagenesis. This may correspond with the greater depth range prior to mass movement and normal faulting. The initial analcime burial diagenetic zone was likely cut off by the sediment removal across the unconformity, and later overprinted by high temperature fluid along the boundary forming laumontite and heulandite in the vicinity. These results illustrate that ridge subduction has substantial potential to cause mass movement, an extensional stress regime, and fluid flow from depth.
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Early Mesozoic history and petroleum potential of formations in Wyoming and northern Utah
DOE Office of Scientific and Technical Information (OSTI.GOV)
Picard, M.D.
1993-08-01
During the Triassic and Jurassic, over what is now Wyoming and northern Utah, roughly equal amounts of sediment were being deposited in continental settings-lake, stream, and eolian-and in shallow-marine or deltaic-plain settings-delta, beach, marsh, tidal flat, and shallow shelf. Clastic rocks dominate. In order of decreasing abundance, the rocks are fine-grained clastics (siltstone, claystone, mudstone), sandstone, carbonates, evaporites, and claystone- and carbonate-pebble conglomerate. Approximately four-fifths of the succession contains red beds or variegated layers-purple, maroon, lavender, olive, green. Unconformities bound Jurassic formations in Wyoming-Nugget, Gypsum Spring, Sundance, and Morrison. Unconformities also bound the continental Upper Triassic section-unnamed red bed unit,more » Jelm, Popo Agie-separating it from the underlying shallow-marine formations-Dinwoody, Red Peak, Alcova, Crow Mountain. Within the marine sequence, an unconformity occurs at the top of the Alcova and, quite likely, shorter periods of erosion took place at the top and below the base of the sandy faces that underlies the Alcova. The postulate duration of the principal unconformities totals about 18 m.y., at least one-sixth of early Mesozoic time. The bulk of the remaining 80-100 m.y. may be represented by a large number of smaller unconformities. For the lower Mesozoic, as for most stratigraphic intervals, a few beds contain the story of what has taken place during the abyss of geologic time. Like other places in the world where evaporites occur in the Triassic, the Wyoming section produces little crude oil. No significant sequence in the early Mesozoic shows source-bed characteristics. The Crow Mountain Sandstone contains the best reservoirs. The Lower( ) Jurassic Nugget Sandstone produces the most oil and gas in the thrust belt of southwestern Wyoming and northern Utah. Cretaceous claystones below the thrusts contain the source beds.« less
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Investigation of a Major Stratigraphic Unconformity with the Curiosity Rover
NASA Astrophysics Data System (ADS)
Lewis, K. W.; Grotzinger, J. P.; Gupta, S.; Rubin, D. M.
2015-12-01
Since its departure from the plains of Aeolis Palus, the Curiosity rover has traversed through a number of new geologic units at the base of Mount Sharp in Gale crater. These have included both units inferred to comprise the lower strata of Mount Sharp itself, along with units that appear to superpose Mount Sharp. Over the last 100 sols, Curiosity has documented several occurrences of a stratigraphic contact between fine-grained mudstones of the Murray Formation, and coarser sandstones of the overlying Stimson Unit. Detailed mapping from both orbital and rover image and topographic data suggests an unconformable relationship between the two units. From orbit, inferred exposures of the unconformity span at least several tens of meters, climbing up the lowermost slopes of Mount Sharp. Although the absolute timing of the two units is poorly constrained, this unconformity between likely represents a geologically significant gap in time. Deposition of the overlying Stimson Unit is inferred to post-date the large-scale erosion of Mount Sharp, likely requiring late stage aqueous interaction in the lithification of the Stimson Unit. From the rover, stereo imaging reveals the small-scale topography preserved at the Murray-Stimson contact, and allows the determination of bedding geometries within the units. Where laminations are expressed, the basal Mount Sharp rocks exhibit planar stratification at low angles to horizontal. In contrast, the coarser-grained Stimson Unit exhibits large-scale cross stratification. Three dimensional bedding geometry within this unit indicates a predominant southward transport direction uphill towards Mount Sharp. The observation of rounded calcium sulfate clasts in the lowermost Stimson Unit, interpreted to be reworked veins from the underlying Murray formation, supports the interpretation of an erosional unconformity. Investigations at the boundary between these two distinct units present a unique opportunity to probe the long-term environmental history of the Gale crater basin.
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Structure, stratigraphy, and eruption dynamics of a young tuff ring: Hanauma Bay, O'ahu, Hawai'i
NASA Astrophysics Data System (ADS)
Rottas, K. M.; Houghton, B. F.
2012-09-01
The Hanauma Bay-Koko Head complex is one of several young volcanic landforms along the Koko fissure, in southeastern O'ahu. The Hanauma Bay region of the complex comprises two nested tuff rings, inner and outer Hanauma Bay, and multiple smaller vents. The internal structure of the inner tuff ring, well exposed due to subsequent breaching by the ocean and wave erosion, indicates that it formed during a minimum of five distinct phases of deposition that produced five mappable units. Significant inward collapses generated major unconformities that separate the units exposed in the inner wall. The planes of failure are cut by narrow steep-walled, locally overhung channels and gullies, suggesting that the collapse events were each followed by short time breaks during which the deposits were eroded by rainfall runoff. Within each pyroclastic unit, there are many local slump scars and unconformities, suggesting that minor instability of the inner wall was a near-constant feature. From bedding sags and surge bed forms, it is apparent that the vent shifted at least twice during tuff ring growth. Ballistic blocks in the youngest unit indicate that the eruption overlapped in time with a separate eruption to the north, most likely to be that of the Kahauloa tuff ring 880 m away.
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Poppe, Lawrence J.; Oldale, Robert N.; Foster, David S.; Smith, Shepard M.
2012-01-01
High-resolution seismic-reflection profiles collected across pro-glacial outwash deposits adjacent to the circa 18 ka b.p. Orient Point–Fishers Island end moraine segment in westernmost Block Island Sound reveal extensive deformation. A rhythmic seismic facies indicates the host outwash deposits are composed of fine-grained glaciolacustrine sediments. The deformation is variably brittle and ductile, but predominantly compressive in nature. Brittle deformation includes reverse faults and thrust faults that strike parallel to the moraine, and thrust sheets that extend from beneath the moraine. Ductile deformation includes folded sediments that overlie undisturbed deposits, showing that they are not drape features. Other seismic evidence for compression along the ice front consists of undisturbed glaciolacustrine strata that dip back toward and underneath the moraine, and angular unconformities on the sea floor where deformed sediments extend above the surrounding undisturbed correlative strata. Together, these ice-marginal glaciotectonic features indicate that the Orient Point–Fishers Island moraine marks a significant readvance of the Laurentide ice sheet, consistent with existing knowledge for neighboring coeval moraines, and not simply a stillstand as previously reported.
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Geldon, Arthur L.
2003-01-01
The geology of the Paleozoic rocks in the Upper Colorado River Basin in Arizona, Colorado, New Mexico, Utah, and Wyoming, was studied as part of the U.S. Geological Survey's Regional Aquifer-System Analysis Program to provide support for hydrogeological interpretations. The study area is segmented by numerous uplifts and basins caused by folding and faulting that have recurred repeatedly from Precambrian to Cenozoic time. Paleozoic rocks in the study area are 0-18,000 feet thick. They are underlain by Precambrian igneous, metamorphic, and sedimentary rocks and are overlain in most of the area by Triassic formations composed mostly of shale. The overlying Mesozoic and Tertiary rocks are 0-27,000 feet thick. All Paleozoic systems except the Silurian are represented in the region. The Paleozoic rocks are divisible into 11 hydrogeologic units. The basal hydrogeologic unit consisting of Paleozoic rocks, the Flathead aquifer, predominantly is composed of Lower to Upper Cambrian sandstone and quartzite. The aquifer is 0-800 feet thick and is overlain gradationally to unconformably by formations of Cambrian to Mississippian age. The Gros Ventre confining unit consists of Middle to Upper Cambrian shale with subordinate carbonate rocks and sandstone. The confining unit is 0-1,100 feet thick and is overlain gradationally to unconformably by formations of Cambrian to Mississippian age. The Bighom aquifer consists of Middle Cambrian to Upper Ordovician limestone and dolomite with subordinate shale and sandstone. The aquifer is 0-3,000 feet thick and is overlain unconformably by Devonian and Mississipplan rocks. The Elbert-Parting confining unit consists of Lower Devonian to Lower Mississippian limestone, dolomite, sandstone, quartzite, shale, and anhydrite. It is 0-700 feet thick and is overlain conformably to unconformably by Upper Devonian and Mississippian rocks. The Madison aquifer consists of two zones of distinctly different lithology. The lower (Redwall-Leadville) zone is 0-2,500 feet thick and is composed almost entirely of Upper Devonian to Upper Mississippian limestone, dolomite, and chert. The overlying (Darwin-Humbug) zone is 0-800 feet thick and consists of Upper Mississippian limestone, dolomite, sandstone, shale, gypsum, and solution breccia. The Madison aquifer is overlain conformably by Upper Mississippian and Pennsylvanian rocks. The Madison aquifer in most areas is overlain by Upper Mississippian to Middle Pennsylvanian rocks of the Four Comers confining unit. The lower part of this confining unit, the Belden-Molas subunit, consists of as much as 4,300 feet of shale with subordinate carbonate rocks, sandstone, and minor gypsum. The upper part of the confining unit, the Paradox-Eagle Valley subunit, in most places consists of as much as 9,700 feet of interbedded limestone, dolomite, shale, sandstone, gypsum, anhydrite, and halite. Locally, the evaporitic rocks are deformed into diapirs as much as 15,000 feet thick. The Four Corners confining unit is overlain gradationally to disconformably by Pennsylvanian rocks. The uppermost Paleozoic rocks comprise the Canyonlands aquifer, which is composed of three zones with distinctly different lithologies. The basal (Cutler-Maroon) zone consists of as much as 16,500 feet of Lower Pennsylvanian to Lower Permian sandstone, conglomerate, shale, limestone, dolomite, and gypsum. The middle (Weber-De Chelly) zone consists of as much as 4,000 feet of Middle Pennsylvanian to Lower Permian quartz sandstone with minor carbonate rocks and shale. The upper (Park City-State Bridge) zone consists of as much as 800 feet of Lower to Upper Permian limestone, dolomite, shale, sandstone, phosphorite, chert, and gypsum. The Canyonlands aquifer is overlain disconformably to unconformably by formations of Triassic and Jurassic age.
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On the study of angular velocity in mass asymmetry nuclei
NASA Astrophysics Data System (ADS)
Kaur, Kamaldeep; Kumar, Suneel
2018-05-01
Using isospin-dependent quantum molecular dynamics (IQMD) model, the role of angular velocity (Wy) has been explored by changing the mass asymmetric content of the colliding nuclei at the incident energy of 50 MeV/nucleon for centrality 0.25
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Stratigraphy of Aeolis Dorsa, Mars: Stratigraphic context of the great river deposits
NASA Astrophysics Data System (ADS)
Kite, Edwin S.; Howard, Alan D.; Lucas, Antoine S.; Armstrong, John C.; Aharonson, Oded; Lamb, Michael P.
2015-06-01
Unraveling the stratigraphic record is the key to understanding ancient climate and past climate changes on Mars (Grotzinger, J. et al. [2011]. Astrobiology 11, 77-87). Stratigraphic records of river deposits hold particular promise because rain or snowmelt must exceed infiltration plus evaporation to allow sediment transport by rivers. Therefore, river deposits when placed in stratigraphic order could constrain the number, magnitudes, and durations of the wettest (and presumably most habitable) climates in Mars history. We use crosscutting relationships to establish the stratigraphic context of river and alluvial-fan deposits in the Aeolis Dorsa sedimentary basin, 10°E of Gale crater. At Aeolis Dorsa, wind erosion has exhumed a stratigraphic section of sedimentary rocks consisting of at least four unconformity-bounded rock packages, recording three or more distinct episodes of surface runoff. Early deposits (>700 m thick) are embayed by river deposits (>400 m thick), which are in turn unconformably draped by fan-shaped deposits (<100 m thick) which we interpret as alluvial fans. Yardang-forming layered deposits (>900 m thick) unconformably drape all previous deposits. River deposits embay a dissected landscape formed of sedimentary rock. The river deposits are eroding out of at least two distinguishable units. There is evidence for pulses of erosion during the interval of river deposition. The total interval spanned by river deposits is >(1 × 106-2 × 107) yr, and this is extended if we include alluvial-fan deposits. Alluvial-fan deposits unconformably postdate thrust faults which crosscut the river deposits. This relationship suggests a relatively dry interval of >4 × 107 yr after the river deposits formed and before the fan-shaped deposits formed, based on probability arguments. Yardang-forming layered deposits unconformably postdate all of the earlier deposits. They contain rhythmite and their induration suggests a damp or wet (near-) surface environment. The time gap between the end of river deposition and the onset of yardang-forming layered deposits is constrained to >1 × 108 yr by the high density of impact craters embedded at the unconformity. The time gap between the end of alluvial-fan deposition and the onset of yardang-forming layered deposits was at least long enough for wind-induced saltation abrasion to erode 20-30 m into the alluvial-fan deposits. We correlate the yardang-forming layered deposits to the upper layers of Gale crater's mound (Mt. Sharp/Aeolis Mons), and the fan-shaped deposits to Peace Vallis fan in Gale crater. Alternations between periods of low mean obliquity and periods of high mean obliquity may have modulated erosion-deposition cycling in Aeolis. This is consistent with the results from an ensemble of simulations of Solar System orbital evolution and the resulting history of the obliquity of Mars. 57 of our 61 simulations produce one or more intervals of continuously low mean Mars obliquity that are long enough to match our Aeolis Dorsa unconformity data.
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NASA Astrophysics Data System (ADS)
Djouder, Hocine; Lüning, Sebastian; Da Silva, Anne-Christine; Abdallah, Hussein; Boulvain, Frédéric
2018-06-01
The economic potential for unconventional shale oil and gas production in the Silurian of the Berkine - Ghadames and Illizi basins (BGI) in south-eastern Algeria has been recently confirmed through exploration drilling. The aim of the present paper attempts a better understanding of the Intra-Tassilian depression within the entire Silurian of the Tassili n'Ajjer plateau. The continuous deposits of the Silurian are exposed at the southern margin of the prolific BGI basins, in the Tassili n'Ajjer plateau, offering the chance to understand the sedimentology, ichnology, and to present a detailed sequence stratigraphy framework for the region. The 410 m-thick clastic Silurian sedimentary strata are subdivided into three formations in the context of sequence stratigraphy, namely: (i) the Oued Imihrou Fm. (Llandoverian) overlain by (ii) the Atafaïtafa Fm. (late Llandoverian to Wenlockian), and (iii) the Oued Tifernine Fm. (late Wenlockian to Pridolian). These can be also distinguished across the entire investigated area and laterally traceable over kilometers. Clear cyclic stacking patterns are identified within the four studied sections showing progressively a general trend of thickening- and coarsening-upward, over a complete 2nd-order megasequence (SIL-1 MS). This transgressive-regressive succession suggests deltaic progradation, shallowing and basin infilling as evidenced by numerous diagnostic sedimentary features and trace fossils, largely from eastern-to western-Tassili plateau. Indeed, the wealth of outcrop data in the Silurian siliciclastic succession enables us to distinct thirteen facies (facies A-M), ranging from shallow-to marginal-marine facies, and in turn, grouped into six facies associations (FA1-FA6). The lowermost part of the succession, which is the most prolific sources of hydrocarbons in North Africa, consists of thick organic-rich graptolite-yielding black 'hot' shales and 'lean' shales with sparse bioturbation with small Thalassinoides belonging to the distal Cruziana ichnofacies. In contrast, the uppermost part of the Silurian deposits becomes progressively coarser and fluvial in response to the progradation of the North African Akakus deltaic system, during regional sea level fall and uplifting of the region. These progradational deposits exhibit well-preserved trace fossils with moderate to high degree of bioturbation, such as Skolithos or the so-called "Tigillites" pipe-rock, Cruziana isp., Rusophycus isp., Monocraterion isp., and Syringomorpha. The SIL-1 MS is bounded by a post-glacial latest Hirnantian unconformity on the basal (SB1), as confirmed by the moderately diverse early Silurian graptolite faunas, and by the Caledonian unconformity on the top (SB7). Each of the three formations of SIL-1 MS reveals two major 3rd-order progradational sequences, commonly delineated by discontinuity surfaces (in ascending order, SB1 to SB7), and in turn, these six sequences (i.e. Si-1 to Si-6) are subdivided into at least ten shorter-term cycles. The regional extent of each unconformity is directly linked to significant facies changes and to inflection points on the global sea level curve.
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NASA Technical Reports Server (NTRS)
Heubeck, C.; Lowe, D. R.
1994-01-01
The 3.22-3.10 Ga old Moodies Group, uppermost unit of the Swaziland Supergroup in the Barberton Greenstone Belt (BGB), is the oldest exposed, well-preserved quartz-rich sedimentary sequence on earth. It is preserved in structurally separate blocks in a heavily deformed fold-and-thrust belt. North of the Inyoka Fault, Moodies strata reach up to 3700 m in thickness. Detailed mapping, correlation of measured sections, and systematic analysis of paleocurrents show that the lower Moodies Group north of the Inyoka Fault forms a deepening- and fining-upward sequence from a basal alluvial conglomerate through braided fluvial, tidal, and deltaic sandstones to offshore sandy shelf deposits. The basal conglomerate and overlying fluvial facies were derived from the north and include abundant detritus eroded from underlying Fig Tree Group dacitic volcanic rocks. Shoreline-parallel transport and extensive reworking dominate overlying deltaic, tidal, and marine facies. The lithologies and arrangement of Moodies Group facies, sandstone petrology, the unconformable relationship between Moodies strata and older deformed rocks, presence of at least one syndepositional normal fault, and presence of basaltic flow rocks and airfall fall tuffs interbedded with the terrestrial strata collectively suggest that the lower Moodies Group was deposited in one or more intramontane basins in an extensional setting. Thinner Moodies sections south of the Inyoka Fault, generally less than 1000 m thick, may be correlative with the basal Moodies Group north of the Inyoka Fault and were probably deposited in separate basins. A northerly derived, southward-thinning fan-delta conglomerate in the upper part of the Moodies Group in the central BGB overlies lower strata with an angular unconformity. This and associated upper Moodies conglomerates mark the beginning of basin shortening by south- to southeast-directed thrust faulting along the northern margin of the BGB and suggest that the upper Moodies Group was deposited in a foreland basin. Timing, orientation, and style of shortening suggest that this deformation eventually incorporated most of the BGB into a major fold-and-thrust belt.
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Valles Marineris Basin Beds: a Complex Story
NASA Technical Reports Server (NTRS)
Lucchitta, B. K.
1985-01-01
High resolution stereoimages of the central Valles Marineris enabled detailed geologic mapping on Ophir and Candor Chasmata. Abundant light colored deposits, both layered and massive, fill the chasmata in this region. Units within these deposits were identified by their erosional characteristics and superposition and cross cutting relations. The Valles Marineris beds reflect a history of repeated faulting, volcanic eruptions, and deposition and erosion, resulting in stratigraphic sequences with several unconformities. Because of the preponderance of apparent volcanic deposits inside the troughs, the chasmata may not be simple grabens, but rather giant volcano tectonic depressions. Major events in chasmata development are examined.
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Stratigraphy and sedimentology of the Upper Cretaceous (Campanian) Anacacho Limestone, Texas, USA
Swezey, C.S.; Sullivan, E.C.
2004-01-01
The Upper Cretaceous Anacacho Limestone is exposed in outcrops between the cities of San Antonio and Del Rio, Texas. A detailed study of four outcrops (Blanco Creek section, Sabinal River section, Seco Creek section, Hondo Creek section) shows that the Anacacho Limestone rests on the Upson Clay (which contains fauna of early Campanian age) and is overlain by the Corsicana Marl (which contains fauna of early Maastrichtian age). An unconformity within the Anacacho Limestone is used herein to separate the limestone into a lower member and an upper member. The lower Anacacho member contains fauna of early Campanian age, whereas the upper Anacacho member contains fauna of middle Campanian age. The lower Anacacho member consists predominantly of wackestones to packstones, which are overlain by packstones to grainstones capped by the unconformity. This unconformity is interpreted as a marine flooding surface, delineating a transition from carbonate grainstones deposited in shallow water (<30 m depth) to a chalk deposited in deeper water. Above the unconformity, the upper Anacacho member is characterized by a chalk, overlain by wackestones and packstones. The uppermost section of the Anacacho Limestone consists of packstones and grainstones with abundant and diverse fossils. Most of the Anacacho Limestone developed in relatively shallow water (<50 m depth) leeward of a large carbonate build-up (possibly a rudistid reef) that now comprises the Anacacho Mountains. The environment, however, was open to marine water throughout deposition of the Anacacho Limestone. ?? 2004 Elsevier Ltd. All rights reserved.
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Geology of Badlands National Park: a preliminary report
Stoffer, Philip W.
2003-01-01
Badlands National Park is host to perhaps the most scenic geology and landscape features in the Western Interior region of the United States. Ongoing erosion that forms the "badlands" exposes ancient sedimentary strata of Late Cretaceous through Oligocene age. Quaternary erosional and depositional processes are responsible for most of the modern landscape features in the park and surrounding region. This report provides a basic overview of the park geology The discussions presented within include both well-established concepts and theories and new, preliminary data and interpretations. Much emphasis is placed on presenting information about the oldest and least studied rocks in the park (particularly the Late Cretaceous and earliest Tertiary deposits that underlie the White River beds throughout the park region). Rock formations and selected fossils they contain are described. Faults, folds, unconformities, and other geologic structures in the North Unit of the park are illustrated, including features associated with the Sage Creek anticline and fault system.
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New geological data of New Siberian Archipelago
NASA Astrophysics Data System (ADS)
Sobolev, Nikolay; Petrov, Evgeniy
2014-05-01
The area of New Siberian Archipelago (NSA) encompasses different tectonic blocks is a clue for reconstruction of geological structure and geodynamic evolution of East Arctic. According to palaeomagnetic study two parts of the archipelago - Bennett and Anjou Islands formed a single continental block at least from the Early Palaeozoic. Isotope dating of De Long Islands igneous and sedimentary rocks suggests Neoproterozoic (Baikalian) age of its basement. The De Long platform sedimentary cover may be subdivided into two complexes: (1) intermediate of PZ-J variously deformed and metamorphosed rocks and (2) K-KZ of weakly lithified sediments. The former complex comprises the Cambrian riftogenic volcanic-clastic member which overlain by Cambrian-Ordovician turbiditic sequence, deposited on a continental margin. This Lower Palaeozoic complex is unconformably overlain by Early Cretaceous (K-Ar age of c.120 Ma) basalts with HALIP petrochemical affinities. In Anjou Islands the intermediate sedimentary complex encompasses the lower Ordovician -Lower Carboniferous sequence of shallow-marine limestone and subordinate dolomite, mudstone and sandstone that bear fossils characteristic of the Siberian biogeographic province. The upper Mid Carboniferous - Jurassic part is dominated by shallow-marine clastic sediments, mainly clays. The K-KZ complex rests upon the lower one with angular unconformity and consists mainly of coal-bearing clastic sediments with rhyolite lavas and tuffs in the bottom (117-110 Ma by K-Ar) while the complexe's upper part contains intraplate alkalic basalt and Neogene-Quaternary limburgite. The De-Long-Anjou block's features of geology and evolution resemble those of Wrangel Island located some 1000 km eastward. The Laptev Sea shelf outcrops in intrashelf rises (Belkovsky and Stolbovoy Islands) where its geology and structure may be observed directly. On Belkovsky Island non-dislocated Oligocene-Miocene sedimentary cover of littoral-marine coal-bearing unconformably overlies folded basement. The latter encompasses two sedimentary units: the Middle Devonian shallow-marine carbonate and Late-Devonian-Permian olistostrome - flysch deposited in transitional environment from carbonate platform to passive margin. Dating of detrital zircons suggests the Siberian Platform and Taimyr-Severnaya Zemlya areas as the most possible provenance. The magmatic activity on Belkovsky Island resulted in formation of Early Triassic gabbro-dolerite similar to the Siberian Platform traps. Proximity of Belkovsky Island to the north of Verkhoyansk foldbelt allows continuation of the latter into the Laptev Sea shelf. The geology of Bolshoy Lyakhovsky Island is discrepant from the rest of the NSA. In the south of Bolshoy Lyakhovsky Island the ophiolite crops complex out: it is composed of tectonic melange of serpentinized peridotite, bandedf gabbro, pillow-basalt, and pelagic sediments (black shales and cherts). All the rocks underwent epidot - amphibolite, glaucophane and greenschist facies metamorphism. The ophiolite is intruded by various in composition igneous massifs - from gabbro-diorite to leuco-granite, which occurred at 110-120 Ma. The Bolshoy Lyakhovsky Island structure is thought to be a westerly continuation of the South Anui suture of Chukchi.
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NASA Astrophysics Data System (ADS)
Sarti, Giovanni; Bertocchini, Federico; Chiesura, Guido; Bini, Monica; Cascella, Antonio; Ribolini, Adriano; Patacca, Etta; Casacchia, Claudia
2014-05-01
The volcanic island of Santiago de Cape Verde was the first stop of Darwin during his circumnavigation on board of the Beagle vessel (1832). The exploration of Santiago played a fundamental role in the growth of his interest for geology. During the three weeks spent on the island, Darwin had the opportunity of doing many pioneering and insightful observations around the morphology and structure of the basaltic platforms. He was also very impressed by a white fossiliferous layer. This horizon, few meters thick, is sandwiched in between two black volcanic units and outcrops extensively along the coastal cliff in the southern part of Santiago. Darwin rightly identified the marine depositional origin of the white layer (Darwin's old beach) observing that the same fossilized shells and algae were still living in the beaches of the island. In 2008, 2009 and 2102 under the auspices of the scientific project "Darwin at Santiago de Cape Verde Island" three expeditions have been performed on the footsteps of Darwin. The firsts two missions have been focused on the mapping and characterization of the basaltic units while the third has exclusively dealt with the facies analysis of the white sedimentary layer. The main goal of this study is to revisit, by a modern sedimentological, stratigraphical, and geomorphological point of view, the white old beach sequence described by Darwin in 1832. The first results display a very complex and fascinating geological history, largely grasped by the observations of Darwin, driven by the interplay among volcanic, tectonic and sea level changes factors. The old beach sequence (likely Pleistocene in age) is composed of two main transgressive depositional units separated by an angular erosional unconformity. This is a first important new topic enriching the Darwin's observations. The unconformity is well exposed along the small Quail island cliff, located about 1 km seaward of the Praia harbour. The unconformity divides sandy fossil-rich deposits, characterized by the abundance of Oyster colony and Turritella, from a white limestone/sandstone layer that commonly shows at its base accumulation of rodholits (the "Nulliporae" of Darwin). This obviously implies that a significant chronological hiatus is recorded in the section. As a whole the white limestone/sandstone layer is organized in a fining and deepening upward sequence that is abruptly truncated by a subaerial basalt unit in the Eastern side of the Praia Harbour and by a subaqueous pillows lava unit to the West. In addition the limestone/sandstone layer outcrops patchily at different quotes, from more than 30 m above sea level down to plunge below the sea. Ours study highlights how the white sedimentary layer, that so much aroused the curiosity of Darwin, records more than one depositional event. At least the position of four palaeoshores can be identified, evidencing how the island undergone to several phases of relative sea-level variations driven by eustatic and/ or tectonic factors.
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Stromatolites at ~3,500 Myr and a greenstone-granite unconformity in the Zimbabwean Archaean
NASA Astrophysics Data System (ADS)
Orpen, J. L.; Wilson, J. F.
1981-05-01
Two controversial areas of geological endeavour are the establishment of the antiquity of life and the tectonic setting of greenstone sequences. We record here the recent discoveries in the Fort Victoria greenstone belt of stromatolites in limestones assigned to ~3,500 Myr (minimum age) Sebakwian Group rocks of the Rhodesian Archaean Craton within Zimbabwe, and a nearby outcrop of a thin sedimentary formation, basal to a thick ~2,700 Myr volcanic pile, resting with definite unconformity on ~3,500 Myr Mushandike Granite.
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NASA Astrophysics Data System (ADS)
Horton, B. K.; Gillis, R. J.; Mann, P.
2009-12-01
Although large-magnitude extension in the Woodlark Rift of eastern Papua New Guinea (PNG) and the D’Entrecasteaux Islands has been addressed through previous research on the late Cenozoic structure and cooling history of metamorphic domes, few studies have evaluated the exhumational record contained within adjacent sedimentary basins. Onshore exposures of Neogene basin fill in PNG along the northern flank of the Papuan peninsula (east of the Dayman metamorphic dome and west-southwest of the domes of the D’Entrecasteaux Islands) provide a record of basin evolution prior to and during growth of the active spreading center that defines the boundary between the Australian plate and Woodlark microplate. Along the northern margin of the Papuan peninsula, a collection of lithofacies associations consisting of sandstone and subordinate conglomerate and mudstone represent deposition in bottomset, foreset, and topset subenvironments in a series of marine Gilbert-type deltas. Internal angular unconformities within the basin-fill succession indicate slope instability likely related to syndepositional deformation. This deformation is attributed to principally down-to-the north motion along extensional and strike-slip structures bordering the northern margin of Papuan peninsula, notably the ESE-striking Goodenough fault zone. Small-scale folding is interpreted as the product of late Miocene to Quaternary fault-related folding in an extensional setting, although we cannot rule out possible contraction coeval with significant collision-related shortening on the southern flank of the Papuan peninsula within the south-directed Papuan fold-thrust belt. Differences in sandstone petrographic results for the northern margin of the Papuan peninsula and the smaller Vogel peninsula suggest a multiphase history of basin evolution, with early Neogene subsidence of uncertain origin and late Neogene subsidence linked to regional extension. The timing of basin evolution will be assessed through pending chronological analyses based on marine microfossils and 40Ar/39Ar geochronology. These results will define the timing of basin evolution and related exhumation, allowing direct comparison with the structural record of cooling in metamorphic domes of the region.
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Bouma, Arnold H.; Feeley, Mary H.; Kindinger, Jack G.; Stelting, Charles E.; Hilde, Thomas W.C.
1981-01-01
A high-resolution seismic reflection survey was conducted in a small area of the upper Louisiana Continental Slope known as Green Canyon Area. This area includes tracts 427, 428, 471, 472, 515, and 516, that will be offered for sale in March 1982 as part of Lease Sale 67.The sea floor of this region is, slightly hummocky and is underlain by salt diapirs that are mantled by early Tertiary shale. Most of the shale is overlain by younger Tertiary and Quaternary deposits, although locally some of the shale protrudes the sea floor. Because of proximity to older Mississippi River sources, the sediments are thick. The sediment cover shows an abundance of geologic phenomena such as horsts, grabens, growth faults, normal faults, and consolidation faults, zones with distinct and indistinct parallel reflections, semi-transparent zones, distorted zones, and angular unconformities.The major feature of this region is a N-S linear zone of uplifted and intruded sedimentary deposits formed due to diapiric intrusion.Small scale graben development over the crest of the structure can be attributed to extension and collapse. Large scale undulations of reflections well off the flanks of the uplifted structure suggest sediment creep and slumping. Dipping of parallel reflections show block faulting and tilting.Air gun (5 and 40 cubic inch) records reveal at least five major sequences that show masked onlap and slumping in their lower parts grading into more distinct parallel reflections in their upper parts. Such sequences can be related to local uplift and sea level changes. Minisparker records of this area show similar sequences but on a smaller scale. The distinct parallel reflections often onlap the diapir flanks. The highly reflective parts of these sequences may represent turbidite-type deposition, possibly at times of lower sea level. The acoustically more transparent parts of each sequence may represent deposits containing primarily hemipelagic and pelagic sediment.A complex ridge system is present along the west side of the area and distinct parallel reflections onlap onto this structure primarily from the east. Much of this deposition may be ascribed to sedimentation within a submarine canyon whose position is controlled by this ridge.
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Quaternary Geologic Framework of the St. Clair River between Michigan and Ontario, Canada
Foster, David S.; Denny, Jane F.
2009-01-01
Concern about the effect of geomorphic changes in the St. Clair River on water levels in the Upper Great Lakes resulted in the need for information on the geologic framework of the river. A geophysical survey of the Upper St. Clair River between Port Huron, MI, and Sarnia, Ontario, Canada, was conducted to determine the Quaternary geologic framework of the region. Previously available and new sediment samples and photographic and video data support the interpretation of the seismic stratigraphy and surficial geology. Three seismic stratigraphic units and two unconformities were identified. Glacial drift, consisting of interbedded till and glaciolacustrine deposits, overlies shale. Glaciofluvial and modern fluvial processes have eroded the glacial drift. Glaciofluvial, glaciolacustrine, fluvial, and lacustrine deposits overlie this unconformity. Seismic facies were interpreted to identify areas where these geologic facies exist; however, in the absence of distinct boundaries between facies, these deposits were mapped as one undifferentiated unit. This unit is thickest in the northernmost 3 kilometers of the river, where it consists of relatively coarse-grained fluvial, reworked glaciofluvial, and possibly glaciofluvial deposits. To the south, this coarse-grained unit thins or is absent. The undifferentiated unit comprises most of the surficial deposits in the northernmost river area. Some areas of glacial drift, predominantly till, are exposed at the lake and riverbed. The shale is not exposed anywhere in the region. Geophysical surveys at sites downriver, together with the results of previous studies, indicate that the geologic framework is similar to that in the northernmost river area except for the absence or reduced thickness of the coarse-grained fluvial deposits. Instead, glacial drift is exposed at the riverbed or is covered by a veneer of sediment. This information on the substrate is important for ongoing sediment transport studies.
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Oil-bearing sediments of Gondwana glaciation in Oman
DOE Office of Scientific and Technical Information (OSTI.GOV)
Levell, B.K.; Braakman, J.H.; Rutten, K.W.
1988-07-01
More than 3.5 billion bbl of oil in place have so far been discovered in reservoirs of the Al Khlata Formation of the Permian-Carboniferous lower Haushi Group in south Oman. Glacially striated pavements and boulders in exposures at Al Khlata in east-central Oman confirmed previous interpretations that the formation is, at least partly, of glacial origin. Core and wireline-log data from some 500 wells that penetrate the formation show that glacial facies are widespread in the subsurface. Shales with varvelike laminations and dropstones are present in two main layers, which extend over the larger part of south Oman and aremore » perhaps the most diagnostic facies. Diamictites are also widespread, and some, which can be correlated as sheets over thousands of square kilometers, are interpreted as true tillites. Other diamictites are interbedded with shales with varvelike laminations or unbedded siltstones and are interpreted as subaqueous glacial deposits. Ten sedimentary facies have been described in cores and outcrops. An important result of this study is a formal scheme to interpret these facies from wireline logs using quantitative analysis of density and neutron logs and qualitative information from other logs. Lateral facies relationships are complicated by syndepositional salt withdrawal and dissolution, paleorelief on the basal unconformity, and intraformational unconformities beneath regionally extensive tillites. At least three glacial phases can be recognized: an early phase, represented only by erosional remnants of diamictites, and two later phases, the last of which extended over the whole of Oman south of the Oman Mountains. Deglaciation is represented by a regional shale bed sharply overlying the diamictite sheet of this last glaciation. 19 figures, 1 table.« less
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Geologic Map of the Albuquerque 30' x 60' Quadrangle, North-Central New Mexico
Williams, Paul L.; Cole, James C.
2007-01-01
The Albuquerque 30' x 60' quadrangle spans the Rio Grande rift between the Colorado Plateau and Great Plains geologic provinces, and includes parts of the Basin and Range and Southern Rocky Mountain physiographic provinces. Geologic units exposed in the quadrangle range in age from Early Proterozoic schist and granite to modern river alluvium. The principal geologic features of the area, however, chiefly reflect contractional folding and thrusting of the Late Cretaceous Laramide orogeny and the Neogene extension of the Rio Grande rift. Significant parts of the history of the rift in this region are displayed and documented by the geology exposed in the Albuquerque quadrangle. Post-Laramide erosion, beginning at about 60 Ma, is recorded by the Diamond Tail and Galisteo Formations (upper Paleocene and Eocene) that are preserved in the Hagan Basin and around the uplifted margins of the younger Rio Grande rift. Intermediate volcaniclastic deposits of the Espinaso Formation (upper Eocene and Oligocene) were shed in and around the contemporaneous volcanic-intrusive complexes of the Ortiz porphyry belt in the northeastern part of the quadrangle. The earliest fluvial sediments attributed to extension in the Rio Grande rift in this area are the Tanos and Blackshare Formations (upper Oligocene and Miocene) in the Hagan Basin, which indicate extension was underway by 25 Ma. Farther west, the oldest rift-filling sediments are eolian sand and interdune silty deposits of the Zia Formation (lower to middle Miocene). Major extension occurred during the Miocene, but subsidence and sedimentation were highly irregular from place to place. Parts of three rift sub-basins are known within the Albuquerque quadrangle, each basin locally as deep as about 14,000 ft, separated by less-extended zones (structural horsts) where the rift fill is much thinner. The geometry of these early, deep rift sub-basins suggests the primary extension direction was oriented northeast-southwest. Significant local folding and uplift within the complex rift seems to have occurred in the late Miocene, accompanied by erosion and recycling of earlier rift-fill sediments. This deformation may reflect clockwise reorientation of the primary extension direction to its Pliocene and current east-west alignment. Late Miocene and early Pliocene uplift and erosion were widespread in the region, as indicated by channeled and local angular unconformities at the bases of all Pliocene units, especially prominent along basin margins. These Pliocene fluvial and alluvial deposits (Ceja and Ancha Formations and Tuerto Gravel) and the upper part of the Cochiti Formation are all conspicuously coarser grained than the Miocene beds they cover, particularly near source areas along the margins of the rift. These observations together indicate that the regional streams flowed at much greater discharge than the Miocene streams and that the Pliocene onset of cooler, wetter climate worldwide was the most likely cause. Despite these higher discharge conditions, it appears there was no Pliocene trunk stream through the rift valley because the youngest Pliocene beds in the basin center are largely fine grained sand, pebbly sand, and sandy silt. No Pliocene cobble-gravel deposits, or thick crossbed sets indicative of major stream discharge, have been documented in the basin center. Considerable evidence indicates significant erosion began in late Pliocene time, coincident with and following eruption of abundant basalt from several local centers at about 2.7-2.6 Ma. The onset of central valley erosion marks the initiation of the first through-flowing, high-energy trunk stream (the 'ancestral' Rio Grande), which most likely was caused by integration of drainage southward through the Socorro region. No upper Pliocene fluvial deposits have been identified in the valley center; rather, a significant unconformity separates beds with medial (or earliest late) Blancan fauna (older than about 2.2 Ma) from
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The Paleotethys suture in Central Iran
NASA Astrophysics Data System (ADS)
Bagheri, S.; Stampfli, G. M.
2003-04-01
The Triassic rocks of the Nakhlak area have been used to justify the hypothesis of the rotation of the Central-East Iranian microplate, mainly based on paleomagnetic data. Davoudzadeh and his coworkers (1981) pointed out the existing contrast between the Nakhlakh succession and the time-equivalent lithostratigraphic units exposed in the surrounding regions and compared them with the Triassic rocks of the Aghdarband area on the southern edge of the Turan plate. We recently gathered evidences that this part of central Iran effectively belongs to the Northern Iranian Paleo-Tethys suture zone and related Variscan terrains of the Turan plate. This is the case for the northwestern part of central Iran, where the Anarak-Khur belt (Anarak schists and their thick Cretaceous-Paleocene sedimentary cover) presents all the elements of an orogenic zone such as dismembered ophiolites and silisiclastics, calcareous and volcanic cover which has been deformed and metamorphosed. This belt is separated to the northwest from the Alborz microcontinent by the Great Kavir fault and Cretaceous ophiolite mélanges. To the southeast it is bounded by the Biabanak fault and serpentinites and the Biabanak block, part of the central-east Iranian plate. The later zone is formed by Proterozoic metamorphic basement and marine sedimentary cover, nearly continuous from the Ordovician to the Triassic, at the uppermost part upper Triassic-lower Jurassic bauxites and silisiclastics are observed. Excepted the Ordovician angular unconformities and the boundary between lower Jurassic and younger layers, this sequence displays no significant main unconformities and can be attributed to the Cimmerian super-terrain. Thus, this sequences represents the classical evolution of the southern Paleo-Tethys passive margin, as found in the Alborz microcontinent or the Band-e Bayan zone of Afghanistan and is the witness of large scale duplication of the Paleo-Tethys suture zone through major Alpine strike-slip faults. Within the Anarak-Khur belt limit and to the northeast of the Nakhlak succession, the area of Godar-e Siah of Jandaq, remnants of the Eurasian active margin are found, represented by: 1- A lower Paleozoic to upper Devonian unit consisting mainly of metamorphosed rocks including ophiolitic rocks, pelagic sediments, flysch-like deposits and shallow-water limestones of Devonian age belonging to the Anarak and Kabudan areas. Folding and thrusting was pre-Carboniferous and all geochronological dating based on K/Ar for the Anarak and Kaboudan schists placed this metamorphic event between middle Devonian and Visean. 2- the main part of the lower Carboniferous unit consists of a volcano-sedimentary complex with intercalations of limestone containing Coral, Brachiopod and Foraminiferas. Pyroclastic deposits are followed by continental red beds containing a great variety of grain types, such as hypabyssal to several types of granitoid rock fragments derived from the arc, accompanied by pebbles of chert, fossiliferous carbonate and serpentinite recycled from the accretionary complex, pointing to a fore-arc environment of deposition. 3- The middle Carboniferous to Permian unit consists of coarse littoral conglomerate and sandstones derived from ophiolitic to felsic material with some platform limestones. They represent the final infill of the fore-arc basin and rest unconformably on both the metamorphites and Lower Carboniferous units. These tectono-stratigraphic units are similar to the western Hindu Kush sequences of Afghanistan and Tuarkyr in Turkmenistan and belong to the northern active margin of Paleo-Tethys. Therefore, the Anarak-Khur belt was part of the Variscan terranes located along this margin. Volcano-sedimentary strata with Conodont-bearing limestones of Permian to Triassic age have been found in direct contact with the Biabanak fault which, therefore, is most likely following and reactivating the Paleo-Tethys suture zone.
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Digital depth horizon compilations of the Alaskan North Slope and adjacent Arctic regions
Saltus, Richard W.; Bird, Kenneth J.
2003-01-01
Data have been digitized and combined to create four detailed depth horizon grids spanning the Alaskan North Slope and adjacent offshore areas. These map horizon compilations were created to aid in petroleum system modeling and related studies. Topography/bathymetry is extracted from a recent Arctic compilation of global onshore DEM and satellite altimetry and ship soundings offshore. The Lower Cretaceous Unconformity (LCU), the top of the Triassic Shublik Formation, and the pre-Carboniferous acoustic basement horizon grids are created from numerous seismic studies, drill hole information, and interpolation. These horizons were selected because they mark critical times in the geologic evolution of the region as it relates to petroleum. The various horizons clearly show the major tectonic elements of this region including the Brooks Range, Colville Trough, Barrow Arch, Hanna Trough, Chukchi Platform, Nuwuk Basin, Kaktovik Basin, and Canada Basin. The gridded data are available in a variety of data formats for use in regional studies.
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NASA Astrophysics Data System (ADS)
Çifçi, Günay; Barın, Burcu; Okay, Seda; Dondurur, Derman; Sorlien, Christopher; Suc, Jean-Pierre; Lericolais, Gilles
2015-04-01
The Messinian Salinity Crisis widely accepted as one of the most interesting events concerning the Mediterranean marine environment in the earth's geological history. Late Miocene tectonic changes in Mediterranean-Atlantic connectivity caused this huge event. The Sea of Marmara region has been improperly considered as a gateway between the Paratethys and Mediterranean since the Middle Miocene. However, it is a very important location for paleoclimatic research including the sea level change associated with the Messinian Salinity Crisis. Although considerable work has been carried out on the Messinian Salinity Crisis, very little has been reported on the status of the Marmara Sea during the Messinian. The case study includes the southern shelf and North İmrali Basin of the Marmara Sea, which is in the region located from the Çanakkale Strait (Dardanelles) to İmralı Island. The structural and stratigraphic interpretation were carried out using high resolution multi-channel seismic reflection (MCS) data which were collected with the facilities of Seismic Laboratory (SeisLab) in the Institute of Marine Sciences and Technology and R/V K. Piri Reis belonging to Dokuz Eylül University under the frame of several projects including TUBİTAK-NSF. Seismic profiles acquired in southern shelf of the Marmara Sea suggest that Messinian fluvial erosion has occurred at the base of all the main sub-basins. The southern shoreline has provided well-preserved evidence of Messinian fluvial erosion followed by the post-crisis marine reflooding. Interpretation is focused on the nature of erosion related to this acoustic basement and to a major angular unconformity that may merge with it. The basement and erosionalsurface are interpreted in the Çanakkale outletandon the southern shelf of the Sea of Marmara. A buried East-West to NW-SE channel cut into acoustic basement that may belong to the Messinian period was interpreted on the MCS data. For instance, based on interpretation of these data, the channel could come into existence at the Messinian. The Messinian Salinity Crisis has significantly affected the Çanakkale and Marmara region, and the Black Sea. In the Marmara domain, the Messinian fluvial network interpreted onland is to be drawnoffshore. Also these data are implying that fault activity associated with the majority of the subsidence and sedimentation in the Sea of Marmara transtensional basin commenced after the Messinian Salinity Crisis.
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NASA Astrophysics Data System (ADS)
Kergaravat, Charlie; Ribes, Charlotte; Darnault, Romain; Callot, Jean-Paul; Ringenbach, Jean-Claude
2017-04-01
The aim of this study is to present the influence of regional shortening on the evolution of a minibasin province and the associated foldbelt geometry based on a natural example, the Sivas Basin, then compared to a physical experiment. The Sivas Basin in the Central Anatolian Plateau (Turkey) is a foreland fold-and-thrust belt, displaying in the central part a typical wall and basin province characterized by spectacularly exposed minibasins, separated by continuous steep-flanked walls and diapirs over a large area (45x25 km). The advance of the orogenic wedge is expressed within the second generation of minibasins by a shortening-induced squeezing of diapirs. Network of walls and diapirs evolve form polygonal to linear pattern probably induced by the squeezing of pre-existing evaporite walls and diapirs, separating linear primary minibasins. From base to top of secondary minibasins, halokinetic structures seem to evolve from small-scale objects along diapir flanks, showing hook and wedges halokinetic sequences, to large stratigraphic wedging, megaflap and salt sheets. Minibasins show progressively more linear shape at right angle to the regional shortening and present angular unconformities along salt structures related to the rejuvenation of pre-existing salt diapirs and walls probably encouraged by the shortening tectonic regime. The advance of the fold-and-thrust belts during the minibasins emplacement is mainly expressed during the late stage of minibasins development by a complex polygonal network of small- and intermediate-scale tectonic objects: (1) squeezed evaporite walls and diapirs, sometimes thrusted forming oblique or vertical welds, (2) allochthonous evaporite sheets, (3) thrusts and strike-slip faults recording translation and rotation of minibasins about vertical axis. Some minibasins are also tilted, with up to vertical position, associated with both the salt expulsion during minibasins sinking, recorded by large stratigraphic wedge, and the late thrust faults developments. The influence of the regional shortening deformation seems to be effective when the majority of the evaporite is remobilized toward the foreland. Results of scaled physical experiments, where continuous shortening is applied during minibasins emplacement, closely match with the deformation patterns observed in the Sivas minibasins. Shortening induce deformations such as translation of minibasins basinward, strike-slip fault zones along minibasin margin, rejuvenation of silicon walls and diapirs, emergence of silicon glaciers and rotation of minibasins along vertical and horizontal axis.
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NASA Astrophysics Data System (ADS)
Neel, B.; Hagedorn, B.; Xu, X.; Walker, J. C.
2016-12-01
Groundwater flow in the East Newport Mesa has not been extensively studied due to the lack of sufficiently deep production or monitoring wells in the area. In this study, a conceptual hydrogeologic model of the area is developed to characterize lateral and vertical flow patterns between the shallow-most semi-perched, semi-confined aquifer and the underlying regional, potable, confined aquifer. Groundwaters from 12 newly constructed monitoring wells throughout the region, screened at depths ranging from 6.5 to 110 meters below ground surface were sampled and analyzed once for 222Rn, 14C, 13C, 18O, and 2H, and one year quarterly for major ion composition. Additionally, water levels in each well were monitored weekly and adjacent surface waters were analyzed once for 222Rn activity. Geochemical analysis and groundwater level trends were used to test against a model developed based on correlation of downhole logs and known regional geologic structure from basin-wide reports. Major ion analysis revealed endmember groundwaters of NaHCO3, CaHCO3, and NaCl character, and others that fall along endmember mixing lines, while time-series data show that groundwaters in the shallow eastern-most portion of the mesa varied up to 20% in Ca:Na ratio throughout the year. 13C values range from -26.3 to -12.4‰, while 14C age dates range from 485 to 10,280 years before present, and in some cases show an age-inversion, where waters of younger apparent age lie below those of older. Groundwaters sampled throughout the mesa showed 222Rn values ranging from 8 to 1,501 pCi/L. A primary feature of the preliminary conceptual model is the presence of an aquifer mergence zone, i.e., an angular or erosional unconformity in which the intervening aquitard between the two zones is eroded away, thus hydraulically joining the two aquifers. Mixing patterns inferred by major ion data and asymptotic decay of 14C support the existence of a mergence zone and also highlight a potential seasonal intrusion of seawater from the Upper Newport Back Bay into the mesa. This conceptual model will potentially serve as the foundation for a numerical flow model, and related contaminant transport model, with implications for managing and protecting drinking water production wells in the Orange County Groundwater Basin.
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NASA Astrophysics Data System (ADS)
Edwards, J. H.; Kluesner, J. W.; Silver, E. A.
2015-12-01
3D seismic reflection data (CRISP) collected across the southern Costa Rica forearc reveals broad, survey-wide erosional events in the upper ~1 km of slope sediments in the mid-slope to outer shelf. The upper 0-280 m of continuous, weakly deformed sediments, designated by IODP Expedition 344 as structural domain I, is bounded by a major erosional event, (CRISP-U1, dated near 1 Ma), suggesting wave-plain erosion from the present shelf break out to 25 km seaward, to a present-day water depth of 900-1300 m. The eastern toe of its surface is characterized by a large drainage system, likely including submarine channels that eroded to depths >1500 m below present-day water depth. CRISP-U1 is variably uplifted by a series of fault propagation folds and cut by an intersecting array of normal faults. Another, major erosional event, (CRISP-M1, approximately 2 Ma) extended from the outer shelf to the mid slope and removed 500-1000 m of material. Overlying CRISP-M1 is up to 1 km of sediments that are more deformed by fault propagation folds, back thrusts, and intersecting arrays of normal faults. Unconformities with smaller areal extent are variably found in these overlying sediments across the mid-slope to outer shelf, at present-day water depths >220 m. Below CRISP-M1, sediments are more densely deformed and also contain major unconformities that extend survey-wide. Both unconformities, CRISP-U1 and CRISP-M1, are encountered in well U1413 and are demarcated by major benthic foraminifera assemblage changes at 149 mbsf and ~504 mbsf (Harris et al., 2013, Proceeding of the IODP, Volume 344).CRISP-M1 is likely correlative to the major sediment facies and benthic foraminifera assemblage change found in U1379 at ~880 mbsf (Vannuchi et al., 2013). The unconformities and intersecting array of normal faults may demarcate the passing of topography on the downgoing Cocos plate, episodically lifting and then subsiding the Costa Rica margin, with amplitudes up to about 1 km.
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NASA Astrophysics Data System (ADS)
Pek, A. A.; Malkovsky, V. I.
2017-05-01
In the global production of uranium, 18% belong to the unconformity-type Canadian deposits localized in the Athabasca Basin. These deposits, which are unique in terms of their ore quality, were primarily studied by Canadian and French scientists. They have elaborated the diagenetic-hydrothermal hypothesis of ore formation, which suggests that (1) the deposits were formed within a sedimentary basin near an unconformity surface dividing the folded Archean-Proterozoic metamorphic basement and a gently dipping sedimentary cover, which is not affected by metamorphism; (2) the spatial accommodation of the deposits is controlled by the rejuvenated faults in the basement at their exit into the overlying sedimentary sequence; the ore bodies are localized above and below the unconformity surface; (3) the occurrence of graphite-bearing rocks is an important factor in controlling the local structural mineralization; (4) the ore bodies are the products of uranium precipitation on a reducing barrier. The mechanism that drives the circulation of ore-forming hydrothermal solutions has remained one of the main unclear questions in the general genetic concept. The ore was deposited above the surface of the unconformity due to the upflow discharge of the solution from the fault zones into the overlying conglomerate and sandstone. The ore formation below this surface is a result of the downflow migration of the solutions along the fault zones from sandstone into the basement rocks. A thermal convective system with the conjugated convection cells in the basement and sedimentary fill of the basin may be a possible explanation of why the hydrotherms circulate in the opposite directions. The results of our computations in the model setting of the free thermal convection of fluids are consistent with the conceptual reasoning about the conditions of the formation of unique uranium deposits in the Athabasca Basin. The calculated rates of the focused solution circulation through the fault zones in the upflow and downflow branches of a convection cell allow us to evaluate the time of ore formation up to the first hundreds of thousands years.
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NASA Astrophysics Data System (ADS)
Breitfeld, H. T.; Hennig, J.; BouDagher-Fadel, M.; Hall, R.
2017-12-01
The offshore Sarawak Basin NW of North Sarawak is a major hydrocarbon province in SE Asia. A very thick sedimentary sequence of Oligocene to ?Early Miocene age, named Cycle 1, is an important hydrocarbon source and reservoir. Despite numerous wells the stratigraphy and tectonic history is not very well understood. The Nyalau Formation of onshore North Sarawak is the supposed equivalent of the offshore Cycle 1 sequence. The Nyalau Formation is a thick sedimentary sequence of mainly tidal to deltaic deposits. The formation is dominated by well-bedded sandstone-mudstone alternations and thicker sandstones with abundant bioturbation. The sandstones are predominantly arenaceous. Various lithic fragments and feldspar indicate multiple sources and fresh input from igneous and metamorphic rocks. Interbedded thin limestone beds and marls yielded Early Miocene foraminifera for the upper part of the succession. Zircons separated from the sandstones yielded mainly Cretaceous and Triassic ages. The Triassic is the dominant age population. The Nyalau Formation conformably overlies the Buan Shale and the Tatau Formation, and in places unconformably overlies the Belaga Formation. The Belaga Formation is part of the Rajang Group that represents remnants of a large submarine fan deposited in the Late Cretaceous to Eocene in Central Sarawak. In contrast to the Nyalau Formation, the majority of zircons from the Rajang Group have Cretaceous ages. This marks an important change in provenance at the major unconformity separating the Belaga and Nyalau Formations. This unconformity was previously interpreted as the result of an orogeny in the Late Eocene. However, there is no evidence for a subduction or collision event at this time in Sarawak. We interpret it to mark plate reorganisation in the Middle Eocene and name it the Rajang Unconformity. Borneo is the principal source of Cretaceous zircons which were derived from the Schwaner Mountains and West Sarawak. The dominant Triassic zircon age population in the Nyalau Formation indicates either major input from the Malay Peninsula (Malay-Thai Tin belt) or Indochina (SE Vietnam). It also suggests that Borneo supplied little or no sediment to Sarawak in the Oligocene to Early Miocene.
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Vibrational excitation of triatomic molecules near the shape resonance region
NASA Astrophysics Data System (ADS)
Ishijima, Y.; Ohkawa, M.; Hoshino, M.; Campbell, L.; Brunger, M. J.; Tanaka, H.
2012-11-01
In this study we have measured angular distributions of differential cross sections (DCS) for vibrational excitation and superelastic scattering from vibrationally excited N2O. The results are analyzed and interpreted using the angular correlation theory by Read.
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NASA Astrophysics Data System (ADS)
Martz, Pierre; Cathelineau, Michel; Mercadier, Julien; Boiron, Marie-Christine; Jaguin, Justine; Tarantola, Alexandre; Demacon, Mickael; Gerbeaud, Olivier; Quirt, David; Doney, Amber; Ledru, Patrick
2017-12-01
Graphitic shear zones are spatially associated with unconformity-related uranium deposits that are located around the unconformity between the strata of the Paleo- to Mesoproterozoic Athabasca Basin (Saskatchewan, Canada) and its underlying Archean to Paleoproterozoic basement. The present study focuses on basement-hosted ductile-brittle graphitic shear zones near the Cigar Lake U deposit, one of the largest unconformity-related U deposits. The goal of the study is to decipher the pre-Athabasca Basin fluid migration history recorded within such structures and its potential role on the formation of such exceptional deposit. Dominantly C-O-H(-N) metamorphic fluids have been trapped in Fluid Inclusion Planes (FIPs) in magmatic quartz within ductile-brittle graphitic shear zones active during retrograde metamorphism associated with the formation of the Wollaston-Mudjatik Transition Zone (WMTZ) between ca. 1805 and 1720 Ma. Such fluids show a compositional evolution along the retrograde path, from a dense and pure CO2 fluid during the earliest stages, through a lower density CO2 ± CH4-N2 (± H2O) fluid and, finally, to a very low density CH4-N2 fluid. Statistical study of the orientation, distribution, proportion, and chemical characterization of the FIPs shows that: i) CO2 (δ13CCO2 around - 9‰ PDB) from decarbonation reactions and/or partial water-metamorphic graphite equilibrium initially migrated regionally and pervasively under lithostatic conditions at about 500 to 800 °C and 150 to 300 MPa. Such P-T conditions attest to a high geothermal gradient of around 60 to 90 °C/km, probably related to rapid exhumation of the basement or a large-scale heat source. ii) Later brittle reactivation of the shear zone at around 450 °C and 25-50 MPa favored circulation of CO2-CH4-N2(± H2O) fluids in equilibrium with metamorphic graphite (δ13CCO2 around - 14‰) under hydrostatic conditions and only within the shear zones. Cooling of these fluids and the water uptake linked to fluid-basement rock reactions led to the precipitation at around 450 °C of poorly-crystallized hydrothermal graphite. This graphite presents isotopic (δ13C - 30 to - 26‰ PDB) and morphological differences from the high-T metamorphic graphite (> 600 °C, - 29 to - 20‰ δ13C) derived from metamorphism of C-rich sedimentary material. The brittle structural reactivation and the related fluid migration and graphite precipitation were specifically focused within the shear zones and related damage zones. The brittle reactivation produced major changes in the petro-physical, mineralogical, and chemical characteristics of the structures and their damage zones. It especially increased the fracture paleoporosity and rock weakness toward the fault cores. These major late metamorphic modifications of the graphitic shear zones were likely key parameters favoring the enhanced reactivity of these basement zones under tectonic stress following deposition of the Athabasca Basin, and so controlled basinal brine movement at the basin/basement interface related to the formation of the unconformity-related uranium deposits. This relationship consequently readily explains the specific spatial relationships between unconformity-related U deposits and the ductile-brittle graphitic shear zones.
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NASA Astrophysics Data System (ADS)
Brault, N.; Bourquin, S.; Guillocheau, F.; Dabard, M.-P.; Bonnet, S.; Courville, P.; Estéoule-Choux, J.; Stepanoff, F.
2004-01-01
The Mio-Pliocene in Western Europe is a period of major climatic and tectonic change with important topographic consequences. The aim of this paper is to reconstruct these topographic changes (based on sedimentological analysis and sequence stratigraphy) for the Armorican Massif (western France) and to discuss their significance. The Mio-Pliocene sands of the Armorican Massif (Red Sands) are mainly preserved in paleovalleys and are characterized by extensive fluvial sheetflood deposits with low-preservation and by-pass facies. This sedimentological study shows that the Red Sands correspond to three main sedimentary environments: fluvial (alluvial fan, low-sinuosity rivers and braided rivers), estuarine and some rare open marine deposits (marine bioclastic sands: "faluns" of French authors). Two orders of sequences have been correlated across Brittany with one or two minor A/ S cycles comprised within the retrogradational trend of a major cycle. The unconformity at the base of the lower cycle is more marked than the unconformity observed at the top, which corresponds to a re-incision of the paleovalley network. A comparison of the results of the sequence stratigraphy analysis with eustatic variations and tectonic events during the Mio-Pliocene allows (1) to discuss their influence on the evolution of the Armorican Massif and (2) to compare the stratigraphic record with other west-European basins. The unconformity observed at the base of the first minor cycle may be attributed to Serravallian-Tortonian tectonic activity and/or eustatic fall, and the unconformity of the second minor cycle may be attributed to Late Tortonian-Early Messinian tectonic activity. The earlier unconformity is coeval with the development of a "smooth" paleovalley network compared to the jagged present-day relief. A single episode of Mio-Pliocene deformation recorded in Brittany may be dated as Zanclean, thus explaining the lack of the maximum flooding surface except in isolated areas. From this study, five paleogeographic maps were drawn up also indicating paleocurrent directions: three maps for the lower cycle (Tortonian retrogradational trend, Late Tortonian to Early Messinian maximum flooding surface and Messinian progradational trend) and two for the upper cycle (Pliocene retrogradational trend and Piacenzian maximum flooding surface). These maps show (1) the variations of paleocurrent directions during the Mio-Pliocene, (2) the extent of estuarine environments during the maximum flooding intervals and (3) a paleodrainage watershed oriented NNW-SSE following the regional Quessoy/Nort-sur-Erdre Fault during the retrogradational trend of the upper cycle and possibly during the progradational trend of the lower cycle. The present-day morphology of the Armorican Massif is characterized by (1) incised valleys and jagged topography, in contrast with the "smooth" morphology described for Mio-Pliocene times and (2) a main East-West drainage watershed, located to the north, separating rivers flowing towards the English Channel from rivers flowing towards the Atlantic Ocean. The Mio-Pliocene/Pleistocene paleotopographic changes seem to be controlled by climatic effects. These can be related to the change in runoff associated with warmer and wetter conditions during the Mio-Pliocene, which control the river discharge and lead to the development of extensive fluvial sheetflood deposits. Tectonic or eustatic factors exert a second-order control.
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NASA Astrophysics Data System (ADS)
Bjerrum, Christian J.; Dorsey, Rebecca J.
1995-08-01
An electronic supplement of this material may be obtained on a diskette or Anonymous FTP from KOSMOS.AGU.ORG. (LOGIN to AGU's FTP account using ANONYMOUS as the username and GUEST as the password. Go to the right directory by typing CD APEND. Type LS to see what files are available. Type GET and the name of the file to get it. Finally, type EXIT to leave the system.) (Paper 95TC01448, Tectonic controls on deposition of Middle Jurassic strata in a retroarc foreland basin, Utah-Idaho trough, western interior, United States, Christian J. Bjerrum and Rebecca J. Dorsey). Diskette may be ordered from American Geophysical Union, 2000 Florida Avenue, N. W., Washington, DC 20009; $15.00. Payment must accompany order. A thick succession of Jurassic nonmarine and marine sedimentary rocks is exposed in a large area from northern Arizona to eastern Idaho and western Wyoming. These sediments accumulated in the Utah-Idaho trough, a deep elongate cratonal basin whose origin has recently been debated. Detailed stratigraphic analysis, subsidence analysis, and first-order flexural modeling of these deposits (this study) provide new insights into the timing and mechanisms of subsidence in the Utah-Idaho trough. Lower and Middle Jurassic strata are divided into six unconformity-bounded sequences. In contrast to the overall uniform thickness of Lower Jurassic sequences (1 and 2), Middle Jurassic strata (sequences 3 through 6) consist of distinctly westward thickening sedimentary packages in which basal shallow marine deposits onlap eastward onto bounding unconformities. Basal strata of sequences 3 through 6 pass upward into widespread progradational continental deposits that are truncated progressively toward the east (cratonward) by the next unconformity. Decompacted total subsidence curves show that the rate of subsidence in most sections increased sharply at the end of sequence 2 time (J-2 unconformity; ˜170 Ma). This is interpreted to record the onset of Middle Jurassic deposition in the distal part of a retroarc foreland basin. The unconformities and distinctive stratal geometries may have formed in response to forebulge migration caused by episodic thrusting in the Cordilleran orogen to the west. First-order flexural modeling was carried out to test the hypothesis of flexural subsidence in the Utah-Idaho trough. Trial-and-error comparisons produce a close match between decompacted stratigraphic profiles and model deflection profiles. The best fit is obtained using an infinite elastic plate (D = 1 × 1024 Nm), a moderate load topography, elevated base level, and an overfilled basin. Using recently published tectonic reconstructions for Nevada and Utah, we find close spatial agreement between a large Middle Jurassic fold-thrust belt and the supracrustal load inferred from model simulations. Our integrated basin analysis thus supports the interpretation of some previous studies that the Middle Jurassic Utah-Idaho trough was a retroarc foreland basin that formed east of a belt of regional contractile deformation and crustal thickening in western and central Nevada and southeastern California. Late Jurassic extension and normal faulting in northeastern Nevada may have been related to gravitational collapse of overthickened crust in the Cordilleran orogen. This coincides with a period of slowed subsidence in the Utah-Idaho trough that began at about 157 Ma.
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On the Shelf Resonances of the Gulf of Carpentaria and the Arafura Sea
NASA Astrophysics Data System (ADS)
Webb, D. J.
2012-02-01
A numerical model is used to investigate the resonances of the Gulf of Carpentaria and the Arafura Sea. The model is forced at the shelf edge, first with physically realistic real values of angular velocity. The response functions at points within the region show maxima and other behaviour which imply that resonances are involved but it is difficult to be more specific. The study is then extended to complex angular velocities and the results then show a clear pattern of gravity wave and Rossby wave like resonances. The properties of the resonances are investigated and used to reinterpret the responses at real values of angular velocity. It is found that in some regions the response is dominated by modes trapped between the shelf edge and the coast or between opposing coastlines. In other regions the resonances show cooperative behaviour, possibly indicating the importance of other physical processes.
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Large-scale retreat and advance of shallow seas in Southeast Asia driven by mantle flow
NASA Astrophysics Data System (ADS)
Zahirovic, Sabin; Flament, Nicolas; Dietmar Müller, R.; Seton, Maria; Gurnis, Michael
2016-04-01
The Indonesian islands and surrounding region represent one of the most submerged, low-lying continental areas on Earth. Almost half of this region, known as Sundaland, is presently inundated by a shallow sea. The role of mantle convection in driving long-wavelength topography and vertical motion of the lithosphere in this region has largely been ignored when interpreting regional stratigraphic sections, despite a consensus that Southeast Asia presently situated on a "dynamic topography low" resulting from long-term post-Pangea subduction. However, dynamic topography is typically described as a temporally and spatially transient process, implying that Sundaland may have experienced significant vertical motions in the geological past, and thus must be considered when interpreting relative sea level changes and the paleogeographic indicators of advancing and retreating shallow seas. Although the present-day low regional elevation has been attributed to the massive volume of oceanic slabs sinking in the mantle beneath Southeast Asia, a Late Cretaceous to Eocene regional unconformity indicates that shallow seas retreated following regional flooding during the mid-Cretaceous sea level highstand. During the Eocene, less than one fifth of Sundaland was submerged, despite global sea level being ~200 m higher than at present. The regional nature of the switch from marine to terrestrial environments, that is out-of-sync with eustatic sea levels, suggests that broad mantle-driven dynamic uplift may have led to the emergence of Sundaland in the Late Cretaceous and Paleocene. We use numerical forward modelling of plate tectonics and mantle convection, and compare the predicted trends of dynamic topography with evidence from regional paleogeography and eustasy to determine the extent to which mantle-driven vertical motions of the lithosphere have influenced regional basin histories in Southeast Asia. A Late Cretaceous collision of Gondwana-derived terranes with Sundaland choked the active margin, leading to slab breakoff and a weakened mantle down-welling acting on the overriding plate, which resulted in regional dynamic uplift and emergence from a ~10-15 Myr-long subduction hiatus along the Sunda active margin. This explains the absence of sediment deposition across Sundaland and the emergence of Sundaland between ~80-60 Ma. Renewed subduction from ~60 Ma reinitiated dynamic subsidence of Sundaland, leading to submergence from ~40 Ma despite falling long-term global sea levels. Our results highlight a complete 'down-up-down' dynamic topography cycle experienced by Sundaland over 100 million years, with the transience of topography revealed in sedimentary basin stratigraphy punctuated with regional unconformities. Subduction-driven mantle convection models are now able to transform the geological record of basins into a dynamic surface history, enabling a deeper understanding of mechanisms that control landscape evolution across spatial and temporal scales.
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NASA Astrophysics Data System (ADS)
Bromley, Michael
1992-09-01
Outliers of Navajo Sandstone (Lower Jurassic Glen Canyon Group) form low paleohills east of the main body of the Formation in the Salt Anticline region of southwestern Colorado. The paleohills consist of interdune deposits which developed topographic inversion during erosion of the Jurassic J-2 unconformity owing to a tough shell of early cemented sandstones and cherty limestones. The interdune deposits accumulated over playa mudstones of the Kayenta Formation which formed in a structural low between the Uncompahgre Uplift and the Paradox Valley salt anticline. Open-framework textures indicate the early formation of quartz or chert cement in sandstone beds immediately above the impermeable playa mudstones. The mudstones enhanced the subsequent formation of wet interdune deposits keeping groundwater near the surface. Microcrystalline quartz cements and fresh feldspars suggest that groundwater was alkaline. A source of alkalinity may have been eolian dust carried from emergent Pennsylvanian evaporite intrusions upwind of the playa deposits. The high specific surface of siliceous and evaporite dusts combined with shallow groundwater and high evaporation rates resulted in the rapid formation of quartzitic silcrete crusts above the playa mudstone aquacludes. As these early silcretes were buried, the impermeable mudstone foundations beneath them continued to serve as aquacludes. The inclined potentiometric surface of perched water tables above the isolated aquacludes intersected the land surface at progressively higher levels as the mudstone lenses were buried. Groundwater moving laterally from above the aquacludes carried dissolved material towards the inclined water tables at their margins. This mobilized material was redeposited as early cement where the capillary fringe intersected the land surface. As the land surface aggraded vertically, the zone of cement formation migrated laterally in response of a change of the relative positions of the land surface and an inclined perched water table. The final products of this process were topographic remnants of Navajo Sandstone with a resistant rind of cemented material enclosing a core of leached, compacted and friable sandstones. Erosion of the J-2 unconformity left the cemented rind in relief while removing all material around it. The resulting hills survived the onlap of the Middle Jurassic Entrada Formation, leaving considerable relief beneath the unconformity.
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NASA Astrophysics Data System (ADS)
Barnes, Christopher; Schneider, David; Majka, Jaroslaw
2016-04-01
Svalbard, the northwestern sub-aerial exposure of the Barents Shelf, offers significant insight into the geodynamics of the High Arctic. The tectonics and sedimentation on Svalbard from the Late Mesozoic through Cenozoic can be attributed to two Large Igneous Provinces: the High Arctic Large Igneous Province (HALIP; 130-90 Ma) and the North Atlantic Large Igneous Province (NAIP; 62-55 Ma). The relationship between the HALIP and the tectonics of the High Arctic remains somewhat unclear, whereas the NAIP is directly linked to opening of the North Atlantic Ocean. This study attempts to establish links between the HALIP and geodynamics of the High Arctic, and reveals the far-field tectonic consequences of the NAIP on Svalbard and the High Arctic. We focus on the Southwestern Caledonian Basement Terrane of Svalbard, characterized by the West Spitsbergen Fold and Thrust Belt, formed during the Eurekan Orogeny (c. 55-33 Ma). Crystalline basement was sampled from four regions (Prins Karls Forland, Oscar II Land, Wedel Jarlsberg Land, and Sørkapp Land) for the purpose of zircon and apatite (U-Th)/He thermochronometry which allows for resolution of thermal events below 200°C. We forward model our datasets using HeFTy software to produce temperature-time histories for each of these regions, and compare these thermal models with Svalbard stratigraphy to resolve the geodynamics of Svalbard from the Late Mesozoic through Cenozoic. The Cretaceous stratigraphy of Svalbard is characterized by a short-lived Mid-Cretaceous sub-aerial unconformity (c. 129 Ma) and a significant Late Cretaceous unconformity (c. 105-65 Ma). Our thermal models reveal a Mid-Cretaceous heating event, suggesting an increasing geothermal gradient coeval with development of the first unconformity. This may indicate that short-lived domal-uplift, related to the arrival of the HALIP plume, was a primary control on Svalbard tectonics and sedimentary deposition throughout the Mid-Cretaceous. Late Cretaceous cooling (85-65 Ma), coeval with development of the Late Cretaceous unconformity, is indicative of moderate uplift on Svalbard during this time. We interpret this as rift-flank uplift, related to opening in the Lincoln Sea north of Svalbard. Given the location of the HALIP plume on the southern Alpha Ridge, we suggest that HALIP emplacement contributed to a stress-field facilitating rifting in the Lincoln Sea (a precursor to rifting of the southern Eurasian Basin; c. 56 Ma). A change in paleoflow direction of Svalbard sediments from Paleogene NNE-sourced to Eocene W-sourced sediments denotes a change from HALIP-influenced to NAIP-influenced tectonics and sedimentation on Svalbard. An Eocene heating event (55-40 Ma) is the result of tectonic burial via overthrusting during the Eurekan Orogeny, providing the western sediment source. Eurekan tectonism on Svalbard is the result of the northward movement of the Greenland microplate, a consequence of spreading in the North Atlantic Ocean. The most recent cooling event (40-20 Ma) is primarily attributed to rift-flank uplift resulting from northward propagation of the North Atlantic Ocean and opening of the Fram Strait. Low-temperature (U-Th)/He low-temperature thermochronometry allow us to document shallow crustal processes that, which are linked to Large Igneous Provinces and other mantle dynamics.
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Ryder, R.T.; Burruss, R.C.; Hatch, J.R.
1998-01-01
Nearly 600 million bbl of oil (MMBO) and 1 to 1.5 trillion ft3 (tcf) of gas have been produced from Cambrian and Ordovician reservoirs (carbonate and sandstone) in the Ohio part of the Appalachian basin and on adjoining arches in Ohio, Indiana, and Ontario, Canada. Most of the oil and gas is concentrated in the giant Lima-Indiana field on the Findlay and Kankakee arches and in small fields distributed along the Knox unconformity. Based on new geochemical analyses of oils, potential source rocks, bitumen extracts, and previously published geochemical data, we conclude that the oils in both groups of fields originated from Middle and Upper Ordovician blcak shale (Utica and Antes shales) in the Appalachian basin. Moroever, we suggest that approximately 300 MMBO and many trillions of cubic feet of gas in the Lower Silurian Clinton sands of eastern Ohio originated in the same source rocks. Oils from the Cambrian and Ordovician reservoirs have similar saturated hydrocarbon compositions, biomarker distributions, and carbon isotope signatures. Regional variations in the oils are attributed to differences in thermal maturation rather than to differences in source. Total organic carbon content, genetic potential, regional extent, and bitument extract geochemistry identify the balck shale of the Utica and Antes shales as the most plausible source of the oils. Other Cambrian and Ordovician shale and carbonate units, such as the Wells Creek formation, which rests on the Knox unconformity, and the Rome Formation and Conasauga Group in the Rome trough, are considered to be only local petroleum sources. Tmax, CAI, and pyrolysis yields from drill-hole cuttings and core indicate that the Utica Shale in eastern and central Ohio is mature with respect to oil generation. Burial, thermal, and hydrocarbon-generation history models suggest that much of the oil was generated from the Utica-Antes source in the late Paleozoic during the Alleghanian orogeny. A pervasive fracture network controlled by basement tectonics aided in the distribution of oil from the source to the trap. This fracture network permitted oil to move laterally and stratigraphically downsection through eastward-dipping, impermeable carbonate sequences to carrier zones such as the Middle Ordovician Knox unconformity, and to reservoirs such as porous dolomite in the Middle Ordovician Trenton Limestone in the Lima-Indiana field. Some of the oil and gas from the Utica-Antes source escaped vertically through a partially fractured, leaky Upper Ordovician shale seal into widespread Lower Silurian sandstone reservoirs.Nearly 600 million bbl of oil (MMBO) and 1 to 1.5 trillion ft3 (tcf) of gas have been produced from Cambrian and Ordovician reservoirs (carbonate and sandstone) in the Ohio part of the Appalachian basin and on adjoining arches in Ohio, Indiana, and Ontario, Canada. Most of the oil and gas is concentrated in the giant Lima-Indiana field on the Findlay and Kankakee arches and in small fields distributed along the Knox unconformity. Based on new geochemical analyses of oils, potential source rocks, bitumen extracts, and previously published geochemical data, we conclude that the oils in both groups of fields originated from Middle and Upper Ordovician black shale (Utica and Antes shales) in the Appalachian basin. Moreover, we suggest that approximately 300 MMBO and many trillions of cubic feet of gas in the Lower Silurian Clinton sands of eastern Ohio originated in these same source rocks.
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Coherence Volume of an Optical Wave Field with Broad Frequency and Angular Spectra
NASA Astrophysics Data System (ADS)
Lyakin, D. V.; Mysina, N. Yu.; Ryabukho, V. P.
2018-03-01
We consider the sizes of a region in a three-dimensional space in which an optical wave field excites mutually coherent perturbations. We discuss the conditions under which the length of this region along the direction of propagation of the wave field and, correspondingly, its volume are determined either by the width of the frequency spectrum of the field or by the width of its angular spectrum, or by the parameters of these spectra simultaneously. We obtain expressions for estimating extremely small values of the coherence volume of the fields with a broad frequency spectrum and an extremely broad angular spectrum. Using the notion of instantaneous speckle-modulation of the wave field, we give a physical interpretation to the occurrence of a limited coherence volume of the field. The length of the spatiotemporal coherence region in which mutually coherent perturbations occur at different times is determined. The coherence volume of a wave field that illuminates an object in high-resolution microscopy with frequency broadband light is considered. The conditions for the dominant influence of the angular or frequency spectra on the longitudinal length of the coherence region are given, and the conditions for the influence of the frequency spectrum width on the transverse coherence of the wave field are examined. We show that, when using fields with broad and ultrabroad spectra in high-resolution microscopy, this influence should be taken into account.
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Form features provide a cue to the angular velocity of rotating objects
Blair, Christopher David; Goold, Jessica; Killebrew, Kyle; Caplovitz, Gideon Paul
2013-01-01
As an object rotates, each location on the object moves with an instantaneous linear velocity dependent upon its distance from the center of rotation, while the object as a whole rotates with a fixed angular velocity. Does the perceived rotational speed of an object correspond to its angular velocity, linear velocities, or some combination of the two? We had observers perform relative speed judgments of different sized objects, as changing the size of an object changes the linear velocity of each location on the object’s surface, while maintaining the object’s angular velocity. We found that the larger a given object is, the faster it is perceived to rotate. However, the observed relationships between size and perceived speed cannot be accounted for simply by size-related changes in linear velocity. Further, the degree to which size influences perceived rotational speed depends on the shape of the object. Specifically, perceived rotational speeds of objects with corners or regions of high contour curvature were less affected by size. The results suggest distinct contour features, such as corners or regions of high or discontinuous contour curvature, provide cues to the angular velocity of a rotating object. PMID:23750970
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Form features provide a cue to the angular velocity of rotating objects.
Blair, Christopher David; Goold, Jessica; Killebrew, Kyle; Caplovitz, Gideon Paul
2014-02-01
As an object rotates, each location on the object moves with an instantaneous linear velocity, dependent upon its distance from the center of rotation, whereas the object as a whole rotates with a fixed angular velocity. Does the perceived rotational speed of an object correspond to its angular velocity, linear velocities, or some combination of the two? We had observers perform relative speed judgments of different-sized objects, as changing the size of an object changes the linear velocity of each location on the object's surface, while maintaining the object's angular velocity. We found that the larger a given object is, the faster it is perceived to rotate. However, the observed relationships between size and perceived speed cannot be accounted for simply by size-related changes in linear velocity. Further, the degree to which size influences perceived rotational speed depends on the shape of the object. Specifically, perceived rotational speeds of objects with corners or regions of high-contour curvature were less affected by size. The results suggest distinct contour features, such as corners or regions of high or discontinuous contour curvature, provide cues to the angular velocity of a rotating object. PsycINFO Database Record (c) 2014 APA, all rights reserved.
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Narrowband Angular Reflectance Properties of the Alkali Flats at White Sands, New Mexico
NASA Technical Reports Server (NTRS)
Whitlock, Charles H.; LeCroy, Stuart R.; Wheeler, Robert J.
1994-01-01
Results from helicopter measurements of the angular properties of surface reflectance for the alkali flats regions of the White Sands Missile Range are presented for the wavelength interval of 0.4 to 0.85 microns. This work was performed to allow accurate radiative transfer calculations over the region. Detailed tables and interpolation equations are given that permit other investigators to perform satellite calibrations over the alkali flats site. The effects of wavelength and soil moisture on narrowband angular reflectance are also investigated. Although there is a spectral variation in surface albedo, there is little spectral effect in Anisotropic Factor except in the forward scattering peak at solar zenith angles greater than 60 deg. The magnitude of the forward-scattering peak is also sensitive to soil moisture, with wet conditions causing a larger peak. The significance of this result is that angular reflectance properties at the center of the alkali flats usually will be different than those at the flats edge because moisture differences typically exist.
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Realism on the rocks: Novel success and James Hutton's theory of the earth.
Rossetter, Thomas
2018-02-01
In this paper, I introduce a new historical case study into the scientific realism debate. During the late-eighteenth century, the Scottish natural philosopher James Hutton made two important successful novel predictions. The first concerned granitic veins intruding from granite masses into strata. The second concerned what geologists now term "angular unconformities": older sections of strata overlain by younger sections, the two resting at different angles, the former typically more inclined than the latter. These predictions, I argue, are potentially problematic for selective scientific realism in that constituents of Hutton's theory that would not be considered even approximately true today played various roles in generating them. The aim here is not to provide a full philosophical analysis but to introduce the case into the debate by detailing the history and showing why, at least prima facie, it presents a problem for selective realism. First, I explicate Hutton's theory. I then give an account of Hutton's predictions and their confirmations. Next, I explain why these predictions are relevant to the realism debate. Finally, I consider which constituents of Hutton's theory are, according to current beliefs, true (or approximately true), which are not (even approximately) true, and which were responsible for these successes. Copyright © 2017 The Author. Published by Elsevier Ltd.. All rights reserved.
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Aliasing Detection and Reduction Scheme on Angularly Undersampled Light Fields.
Xiao, Zhaolin; Wang, Qing; Zhou, Guoqing; Yu, Jingyi
2017-05-01
When using plenoptic camera for digital refocusing, angular undersampling can cause severe (angular) aliasing artifacts. Previous approaches have focused on avoiding aliasing by pre-processing the acquired light field via prefiltering, demosaicing, reparameterization, and so on. In this paper, we present a different solution that first detects and then removes angular aliasing at the light field refocusing stage. Different from previous frequency domain aliasing analysis, we carry out a spatial domain analysis to reveal whether the angular aliasing would occur and uncover where in the image it would occur. The spatial analysis also facilitates easy separation of the aliasing versus non-aliasing regions and angular aliasing removal. Experiments on both synthetic scene and real light field data sets (camera array and Lytro camera) demonstrate that our approach has a number of advantages over the classical prefiltering and depth-dependent light field rendering techniques.
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DOE Office of Scientific and Technical Information (OSTI.GOV)
Zhang, Wenkun; Zhang, Hanming; Li, Lei
2016-08-15
X-ray computed tomography (CT) is a powerful and common inspection technique used for the industrial non-destructive testing. However, large-sized and heavily absorbing objects cause the formation of artifacts because of either the lack of specimen penetration in specific directions or the acquisition of data from only a limited angular range of views. Although the sparse optimization-based methods, such as the total variation (TV) minimization method, can suppress artifacts to some extent, reconstructing the images such that they converge to accurate values remains difficult because of the deficiency in continuous angular data and inconsistency in the projections. To address this problem,more » we use the idea of regional enhancement of the true values and suppression of the illusory artifacts outside the region to develop an efficient iterative algorithm. This algorithm is based on the combination of regional enhancement of the true values and TV minimization for the limited angular reconstruction. In this algorithm, the segmentation approach is introduced to distinguish the regions of different image knowledge and generate the support mask of the image. A new regularization term, which contains the support knowledge to enhance the true values of the image, is incorporated into the objective function. Then, the proposed optimization model is solved by variable splitting and the alternating direction method efficiently. A compensation approach is also designed to extract useful information from the initial projections and thus reduce false segmentation result and correct the segmentation support and the segmented image. The results obtained from comparing both simulation studies and real CT data set reconstructions indicate that the proposed algorithm generates a more accurate image than do the other reconstruction methods. The experimental results show that this algorithm can produce high-quality reconstructed images for the limited angular reconstruction and suppress the illusory artifacts caused by the deficiency in valid data.« less
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NASA Astrophysics Data System (ADS)
Zhang, Wenkun; Zhang, Hanming; Li, Lei; Wang, Linyuan; Cai, Ailong; Li, Zhongguo; Yan, Bin
2016-08-01
X-ray computed tomography (CT) is a powerful and common inspection technique used for the industrial non-destructive testing. However, large-sized and heavily absorbing objects cause the formation of artifacts because of either the lack of specimen penetration in specific directions or the acquisition of data from only a limited angular range of views. Although the sparse optimization-based methods, such as the total variation (TV) minimization method, can suppress artifacts to some extent, reconstructing the images such that they converge to accurate values remains difficult because of the deficiency in continuous angular data and inconsistency in the projections. To address this problem, we use the idea of regional enhancement of the true values and suppression of the illusory artifacts outside the region to develop an efficient iterative algorithm. This algorithm is based on the combination of regional enhancement of the true values and TV minimization for the limited angular reconstruction. In this algorithm, the segmentation approach is introduced to distinguish the regions of different image knowledge and generate the support mask of the image. A new regularization term, which contains the support knowledge to enhance the true values of the image, is incorporated into the objective function. Then, the proposed optimization model is solved by variable splitting and the alternating direction method efficiently. A compensation approach is also designed to extract useful information from the initial projections and thus reduce false segmentation result and correct the segmentation support and the segmented image. The results obtained from comparing both simulation studies and real CT data set reconstructions indicate that the proposed algorithm generates a more accurate image than do the other reconstruction methods. The experimental results show that this algorithm can produce high-quality reconstructed images for the limited angular reconstruction and suppress the illusory artifacts caused by the deficiency in valid data.
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NASA Astrophysics Data System (ADS)
Holford, S. P.; Green, P. F.; Hillis, R. R.; Duddy, I. R.; Turner, J. P.; Stoker, M. S.
2008-12-01
The magma-rich NE Atlantic passive margin provides a superb natural laboratory for studying vertical motions associated with continental rifting and the rift-drift transition. Here we present an extensive apatite fission-track analysis (AFTA) database from the British Isles which we combine with a detailed stratigraphic framework for the Cretaceous-Cenozoic sedimentary record of the NE Atlantic margin to constrain the uplift history along and inboard of this margin during the past 120 Myr. We show that the British Isles experienced a series of uplift episodes which began between 120 and 115 Ma, 65 and 55 Ma, 40 and 25 Ma and 20 and 15 Ma, respectively. Each episode is of regional extent (~100,000 sq km) and represents a major period of exhumation involving removal of up to 1 km or more of section. These uplift episodes can be correlated with a number of major tectonic unconformities recognised within the sedimentary succession of the NE Atlantic margin, suggesting that the margin was also affected by these uplift episodes. Anomalous syn- and post-rift uplift along this margin have been interpreted in terms of permanent and/or transient movements controlled by the Iceland plume, but neither the timing nor distribution of the uplift episodes, with the exception of the 65 to 55 Ma episode, supports a first-order control by plume activity on vertical motions. Each uplift episode correlates closely with key deformation events at adjacent plate boundaries, suggesting a causative link, and we examine the ways in which plate boundary forces can account for the observed uplift episodes. Similar km-scale uplift events are revealed by thermochronological studies in other magma-rich and magma-poor continental margins, e.g. SE Australia, South Africa, Brazil. The low angle unconformities which result from these regional episodes of km-scale burial and subsequent uplift are often incorrectly interpreted as representing periods of non-deposition and tectonic stability. Similar considerations have also led to an erroneous view of the post-rift stability of many continental margins. Our results indicate that km-scale regional uplift has affected many regions previously interpreted as areas of long-term stability, and that plate boundary deformation exerts the primary control on such episodes.
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NASA Astrophysics Data System (ADS)
Smith, M. E.; Cassel, E. J.; Jicha, B. R.; Singer, B. S.; Carroll, A.
2014-12-01
Numerical and conceptual models of flat-slab rollback predict broad initial dynamic subsidence above the slab hinge then uplift and volcanism triggered by the advection of asthenosphere beneath the overriding plate. These predicted surface effects provide a viable but largely untested explanation for lake basin formation in Cordilleran-type orogenies. We argue that the hydrologic closure of both the foreland (early Eocene) and hinterland (late Eocene) of the North American Cordillera were caused by a trenchward-migrating wave of dynamic and thermal topography resulting from progressive removal of the Farallon flat-slab. Two major episodes of hydrologic drainage closure are recorded by Eocene terrestrial strata in the western United States. The first occurred in the retroarc foreland during the early Eocene, and resulted in the deposition of the Green River Fm. The second occurred in the hinterland during the late Eocene and resulted in accumulation of the Elko Fm. In both regions, lake strata overlie fluvial strata and become progressively more evaporative up-section, and are overlain by volcaniclastic strata. Both successions were then truncated by regional unconformities that extend until the Oligocene. We interpret these stratigraphic successions to record trenchward propagation of a regional topographic wave, caused by slab rollback. Migration of the slab-hinge initially caused dynamic subsidence and initiation of lacustrine deposition. Regional surface uplift followed, and was associated with scattered volcanism. Uplift promoted formation of endorheic basins and ultimately the development of regional unconformities. The height of the uplift can be roughly approximated by the preserved thickness of lacustrine and other nonmarine deposits at both locations (0.2-1.0 km). The 40Ar/39Ar and U-Pb geochronology of Green River Fm ash beds indicate that this surface topographic wave migrated trenchward (SW) across the foreland from 53 to 47 Ma at a velocity of ~6 cm/yr. Single crystal sanidine 40Ar/39Ar ages for ash beds within the Elko Fm indicate hydrologic ponding from 43 to 38 Ma. The 4 myr gap between Green River and Elko Fm deposition may represent the time required for the rollback wave to transit the steep eastern slope of the Sevier fold-thrust belt.
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Stratigraphy of the Neogene Sahabi units in the Sirt Basin, northeast Libya
NASA Astrophysics Data System (ADS)
El-Shawaihdi, M. H.; Mozley, P. S.; Boaz, N. T.; Salloum, F.; Pavlakis, P.; Muftah, A.; Triantaphyllou, M.
2016-06-01
A revision of the nomenclature of lithostratigraphic units of Neogene strata at As Sahabi, northeast Libya, is presented, based on new fieldwork conducted during 2006-2008. The Sahabi units are correlated across the Ajdabya Sheet (NH 34-6) in northeastern Libya. Major conclusions are: (1) Miocene (Langhian through Messinian) strata are predominantly carbonate and should be referred to as formation "M"; (2) A local unconformity of Miocene (early Messinian) age overlies strata of the formation "M"; (3) This unconformity is overlain by Messinian gypsiferous sand and mud (formerly formation "P" and partially member "T"), which are designated as the "lower member" (gypsiferous) of the Sahabi Formation; (4) The "lower member" is overlain by sand and mud of late Messinian age (formerly partially member "T" and members "U1", "UD", and "U2") in a generally fining-upwards sequence, and are designated as the "upper member" (non-gypsiferous) of the Sahabi Formation; (5) The latest Miocene sand and mud of the "upper member" are capped by an unconformity that is correlated with the regression and desiccation of the Mediterranean Sea during the Messinian Salinity Crisis and with Eosahabi Channel cutting; (6) The unconformity is overlain by Pliocene medium, coarse, and pebbly sands, which are referred to as the Qarat Weddah Formation (formerly Garet Uedda Formation); (7) The Pliocene sands of Qarat Weddah Formation are overlain by carbonate soil (calcrete) of Late Pliocene age, which is referred to as formation "Z" (formerly member "Z"). The major outcome of this study is a revised stratigraphic description and nomenclature of the Sahabi units that helps to provide a formal and unified context for understanding paleontological discoveries in northeastern Libya, which will serve to facilitate a broader correlation of the Sahabi units with their equivalents elsewhere in Africa and in Europe and Asia.
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NASA Astrophysics Data System (ADS)
Sierro, Francisco J.; Ledesma, Santiago; A: Flores, Jose; Garcia-Castellanos, Daniel; Hernandez-Molina, Javier
2014-05-01
The Miocene Pliocene boundary is associated in the Mediterranean to a major flooding of Atlantic water that terminated with the Messinian salinity crisis. In many seismic profiles all over the Mediterranean margins this event is linked to an erosion surface that separates the Messinian evaporitic units from the overlying open marine Pliocene sediments. This unconformity originally identified as reflector "M" can be traced to the deep basins as a paraconformity / local erosional surface that has been usually named as Horizon M. This erosive surface in Mediterranean continental margins has been linked to a pronounced drawdown of base level triggered during the Messinian. In consequence, this unconformity should be only expressed in the Mediterranean. However, a significant unconformity has been recognized in the Guadalquivir basin and in the Gulf of Cadiz in the Atlantic side of Iberia that is identified as a Messinian canyon deepening towards the Atlantic. Recently, the cyclostratigraphic and biostratigraphic analyses of various logs recovered by different oil and gas exploration companies over the last decades allowed us to accurately date this major discontinuity in the Guadalquivir basin and the Gulf of Cadiz, as well as to compare sedimentary cycles in the Atlantic with those of the Mediterranean. The astronomical tuning of these cycles unambiguously links this discontinuity in the Atlantic with the Miocene Pliocene boundary, raising important questions about the origin of this major event. We explore the potential origins for this discontinuity, including the tectonic vertical motions of the Betic-Guadalquivir system, or the presence of a seaway undergoing intense bottom-current circulation between the Mediterranean and the Atlantic.
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DOE Office of Scientific and Technical Information (OSTI.GOV)
Handford, C.R.
Exploration is increasingly dependent upon obtaining credible stratigraphic interpretations of seismic data. With respect to carbonate platforms, two of the most important seismic-imaging and interpretation problems are (1) distinguishing between lowstand unconformities and drowning unconformities, and (2) recognizing paleokarst reservoirs. Lowstand unconformities vs. drowning unconformities. Many contend that onlapping wedges of strata above sequence boundaries but below the previous shelf break comprise the lowstand systems tract. An alternative view is that onlapping wedges do not record sea level falls, but instead chronicle sea level rises and platform demise. A Mississippian carbonate ramp exposed along the southern margin of North Americamore » is flanked by a siliciclastic lowstand wedge and overlain by a drowning succession of black shales. This dual history of lowstand exposure and drowning formed two baselap surfaces, which lie so close to each other on the shelf that seismic dissemination is almost impossible. The paradox is that although the ramp was terminated by drowning, the visible seismic baselap was due to low-stand exposure. Numerous large fields around the world produce from carbonate reservoirs with a moderate to strong paleokarst overprint. Their discoveries, however, were structurally driven and rarely based upon predrill knowledge of paleokarst systems. In fact, there has been little effort to determine how to recognize paleocave systems in seismic reflection data. To narrow this gap, the sedimentary fill and stratal geometries of modern cave systems were examined and modeled seismically. The models show a passage from continuous reflections in the undisturbed country rock to discontinuous reflections inclined toward the cavern core. Velocity pull-ups and pull-downs are significant where velocity and density contrasts between the country rock and collapsed chamber are important.« less
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NASA Astrophysics Data System (ADS)
Wang, W. B.; Gozali, Richard; Nguyen, Thien An; Alfano, R. R.
2015-03-01
Light scattering and transmission of optical Laguerre Gaussian (LG) vortex beams with different orbital angular momentum (OAM) states in turbid scattering media were investigated in comparison with Gaussian (G) beam. The scattering media used in the experiments consist of various sizes and concentrations of latex beads in water solutions. The LG beams were generated using a spatial light modulator in reflection mode. The ballistic transmissions of LG and G beams were measured with different ratios of thickness of samples (z) to scattering mean free path (ls) of the turbid media, z/ls. The results show that in the ballistic region where z/ls is small, the LG and G beams show no significant difference, while in the diffusive region where z/ls is large, LG beams show higher transmission than Gaussian beam. In the diffusive region, the LG beams with higher orbital angular momentum L values show higher transmission than the beams with lower L values. The transition points from ballistic to diffusive regions for different scattering media were studied and determined.
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NASA Astrophysics Data System (ADS)
Steenberg, L.; Gruber, B.; Boroughs, S.; Wolff, J.
2015-12-01
The Brown's Creek rhyolite (BCR), ~70 km south of Boise, Idaho, erupted during a period of widespread rhyolitic volcanism in southwestern Idaho during the middle Miocene. However, the Brown's Creek unit has several characteristics that are unusual relative to near contemporaneous units in the Central Snake Rive Plain (CSRP) and units in the Western Snake River Plain (WSRP). The BCR can contain up to 40% phenocrysts, with some feldspar and quartz crystals in excess of 2 cm in diameter. A proximal vent location is particularly well exposed in the BCR, and appears as an elongated topographic "dome" with pervasive, chaotic and steep flow banding, ramp structures, and breccias. Evidence of dome building activity is also represented by a matrix supported deposit of ash and poorly sorted, angular, rhyolite clasts up to boulder size; which crops out in a small area near the vent. The BCR is among numerous units in the CSRP and WSRP that show evidence of interaction with ancient Lake Idaho (e.g. silicification, opalized zones, pepperites, etc), but the unconformity with the sedimentary rocks of the lake and its feeder streams, is extremely well preserved in the Brown's Creek rhyolite. Geochemically, the Brown's Creek rhyolite shows greater compositional variation in comparison to other individual units in the region. This variation (e.g. Ba/Sr and Zr/Nb) may be a result of variable crystal cargo in hand samples, but could potentially represent a zoned magma body, which is also extremely rare in the CSRP or WSRP. A limited number of samples have trace element concentrations/ratios (e.g. Rb, U, and Th) that may indicate the presence of a second unit underlying the dominant outcrops of BCR, but Nb/Ta ratios are relatively invariant across the entire BCR suite; if there are two units in the BCR, their sources are the same or very similar.
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Seismic stratigraphy, tectonics and depositional history in the Halk el Menzel region, NE Tunisia
NASA Astrophysics Data System (ADS)
Sebei, Kawthar; Inoubli, Mohamed Hédi; Boussiga, Haïfa; Tlig, Said; Alouani, Rabah; Boujamaoui, Mustapha
2007-01-01
In the Halk el Menzel area, the proximal- to pelagic platform transition and related tectonic events during the Upper Cretaceous-Lower Miocene have not been taken into adequate consideration. The integrated interpretation of outcrop and subsurface data help define a seismic stratigraphic model and clarify the geodynamic evolution of the Halk el Menzel block. The sedimentary column comprises marls and limestones of the Campanian to Upper Eocene, overlain by Oligocene to Lower Miocene aged siliciclastics and carbonates. Well to well correlations show sedimentary sequences vary considerably in lithofacies and thicknesses over short distances with remarkable gaps. The comparison of sedimentary sequences cut by borehole and seismic stratigraphic modelling as well help define ten third order depositional sequences (S1-S10). Sequences S1 through S6 (Campanian-Paleocene) are mainly characterized by oblique to sigmoid configurations with prograding sedimentary structures, whereas, sequences S7-S10 (Ypresian to Middle Miocene) are organized in shallow water deposits with marked clinoform ramp geometry. Sedimentary discontinuities developed at sequence boundaries are thought to indicate widespread fall in relative sea level. Angular unconformities record a transpressive tectonic regime that operated from the Campanian to Upper Eocene. The geometry of sequences with reduced thicknesses, differential dipping of internal seismic reflections and associated normal faulting located westerly in the area, draw attention to a depositional sedimentary system developed on a gentle slope evolving from a tectonically driven steepening towards the Northwest. The seismic profiles help delimit normal faulting control environments of deposition. In contrast, reef build-ups in the Eastern parts occupy paleohighs NE-SW in strike with bordering Upper Maastrichtian-Ypresian seismic facies onlapping Upper Cretaceous counterparts. During the Middle-Upper Eocene, transpressive stress caused reactivation of faults from normal to reverse play. This has culminated in propagation folds located to the west; whereas, the eastern part of the block has suffered progressive subsidence. Transgressive carbonate depositional sequences have predominated during the Middle Miocene and have sealed pre-existing tectonic structures.
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Wilch, T.I.; McIntosh, W.C.
2007-01-01
Ar geochronology of seven eroded monogenetic volcanoes near the Hobbs Coast, Marie Byrd Land, West Antarctica provide proxy records of WAIS paleo-ice-levels in Miocene-Pliocene times. Interpretations, based on lithofacies analysis, indicate whether the volcanoes erupted below, near, or above the level of the ice sheet. Our interpretations differ significantly from previous interpretations as they highlight the abundant evidence for ice-volcano interactions at emergent paleoenvironments but limited evidence of higher-than-present syn-eruptive ice-levels. Evidence for subglacial volcanic paleoenvironments is limited to Kennel Peak, a ~8 Ma volcano where a pillow lava sequence extending 25 m above current ice level overlies an inferred glacial till and unconformity. A major complication in the Hobbs Coast region is that the volcanism occurred on interfluves between regions of fast-flowing ice. Such a setting precludes establishing precise regional paleo-ice-levels although the presence or absence of ice at times of eruptions can be inferred.
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Newburg-South Westhope oil fields, North Dakota
DOE Office of Scientific and Technical Information (OSTI.GOV)
Marafi, H.
1972-01-01
The Newburg and South Westhope oil fields, located in Bottineau County, North Dak., in the NE. part of the Williston Basin, are excellent examples of stratigraphic traps, although structural elements are involved in trapping of the accumulations. The oil is produced from 2 adjacent zones separated by a major unconformity, and they are considered to be a common reservoir. The productive units are the ''Ratcliffe'' interval of the Mississippian Charles Formation and the Saude Member of the Triassic Spearfish Formation. Post-Paleozoic migration of the oil is indicated because, even though the Ratcliffe was exposed to considerable erosion, it is productivemore » at the unconformity.« less
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Montgomery, P.; Farr, M.R.; Franseen, E.K.; Goldstein, R.H.
2001-01-01
A high-resolution chronostratigraphy has been developed for Miocene shallow-water carbonate strata in the Cabo de Gata region of SE Spain for evaluation of local, regional and global factors that controlled platform architecture prior to and during the Messinian salinity crisis. Paleomagnetic data were collected from strata at three localities. Mean natural remanent magnetization (NRM) ranges between 1.53 ?? 10-8 and 5.2 ?? 10-3 Am2/kg. Incremental thermal and alternating field demagnetization isolated the characteristic remanent magnetization (ChRM). Rock magnetic studies show that the dominant magnetic mineral is magnetite, but mixtures of magnetite and hematite occur. A composite chronostratigraphy was derived from five stratigraphic sections. Regional stratigraphic data, biostratigraphic data, and an 40Ar/39Ar date of 8.5 ?? 0.1 Ma, for an interbedded volcanic flow, place the strata in geomagnetic polarity Chrons C4r to C3r. Sequence-stratigraphic and diagenetic evidence indicate a major unconformity at the base of depositional sequence (DS)3 that contains a prograding reef complex, suggesting that approximately 250 000 yr of record (Subchrons C3Br.2r to 3Br.1r) are missing near the Messinian-Tortonian boundary. Correlation to the GPTS shows that the studied strata represent five third- to fourth-order DSs. Basal units are temperate to subtropical ramps (DS1A, DS1B, DS2); these are overlain by subtropical to tropical reefal platforms (DS3), which are capped by subtropical to tropical cyclic carbonates (Terminal Carbonate Complex, TCC). Correlation of the Cabo de Gata record to the Melilla area of Morocco, and the Sorbas basin of Spain indicate that early - Late Tortonian ramp strata from these areas are partially time-equivalent. Similar strata are extensively developed in the Western Mediterranean and likely were influenced by a cool climate or influx of nutrients during an overall rise in global sea-level. After ramp deposition, a sequence boundary (SB3) in Cabo de Gata correlates with a sequence boundary in Morocco and a published third-order eustatic fall suggesting at least a partial eustatic control for the sequence boundary. Coral reefs began to develop earlier in Cabo de Gata than at Melilla or Sorbas, arguing for local factors affecting this major environmental transition. Later Messinian reefs (DS3) from all areas are time-equivalent, suggesting a regional or global control on their formation. Some Halimeda-rich horizons in the Western Mediterranean are not time-equivalent event strata as hypothesized by others. Correlation of the relative sea-level curve for the fringing reef complex (DS3) with a published eustatic curve suggests at least a partial third-order global eustatic control for the highstand part of the sequence. Downstepping DS3 reefs and initial subaerial exposure of earlier DS3 reef strata approximately correlate with initiation of a series of subaerial unconformities in the South Pacific. The longer-term relative fall in sea-level during DS3 downstepping reef progradation does not correlate with a published third-order eustatic fall. Eustatic sea-level fluctuations may have been associated with initiation of the Mediterranean Messinian salinity crisis, but the longer-term fall may have been linked to tectonic uplift in the Mediterranean region. Widespread distribution of 'TCC-style' cycles of approximately the same age suggests a regional (Western Mediterranean) or global control on sea-level change responsible for TCC cycles. In addition, four subaerial exposure-capped TCC cycles may correlate with similar subaerial unconformities in the South Pacific, suggesting at least a partial eustatic control on TCC cyclicity. The high rates of relative sea-level change needed to generate a minimum of 25-30 m sea-level changes associated with each cycle are consistent with glacio-eustacy along with rapid evaporitic drawdown in the Mediterranean. ?? 2001 Elsevier Science B.V. All rights reserved.
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Jade, Sridevi; Shrungeshwara, T S; Kumar, Kireet; Choudhury, Pallabee; Dumka, Rakesh K; Bhu, Harsh
2017-09-12
We estimate a new angular velocity for the India plate and contemporary deformation rates in the plate interior and along its seismically active margins from Global Positioning System (GPS) measurements from 1996 to 2015 at 70 continuous and 3 episodic stations. A new India-ITRF2008 angular velocity is estimated from 30 GPS sites, which include stations from western and eastern regions of the plate interior that were unrepresented or only sparsely sampled in previous studies. Our newly estimated India-ITRF2008 Euler pole is located significantly closer to the plate with ~3% higher angular velocity than all previous estimates and thus predicts more rapid variations in rates and directions along the plate boundaries. The 30 India plate GPS site velocities are well fit by the new angular velocity, with north and east RMS misfits of only 0.8 and 0.9 mm/yr, respectively. India fixed velocities suggest an approximate of 1-2 mm/yr intra-plate deformation that might be concentrated along regional dislocations, faults in Peninsular India, Kachchh and Indo-Gangetic plain. Relative to our newly-defined India plate frame of reference, the newly estimated velocities for 43 other GPS sites along the plate margins give insights into active deformation along India's seismically active northern and eastern boundaries.
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Angular distribution of γ rays from neutron-induced compound states of 140La
NASA Astrophysics Data System (ADS)
Okudaira, T.; Takada, S.; Hirota, K.; Kimura, A.; Kitaguchi, M.; Koga, J.; Nagamoto, K.; Nakao, T.; Okada, A.; Sakai, K.; Shimizu, H. M.; Yamamoto, T.; Yoshioka, T.
2018-03-01
The angular distribution of individual γ rays, emitted from a neutron-induced compound-nuclear state via radiative capture reaction of 139La(n ,γ ) has been studied as a function of incident neutron energy in the epithermal region by using germanium detectors. An asymmetry ALH was defined as (NL-NH) /(NL+NH) , where NL and NH are integrals of low- and high-energy region of a neutron resonance respectively, and we found that ALH has the angular dependence of (A cosθγ+B ) , where θγ is the emitted angle of γ rays, with A =-0.3881 ±0.0236 and B =-0.0747 ±0.0105 in 0.74 eV p -wave resonance. This angular distribution was analyzed within the framework of interference between s - and p -wave amplitudes in the entrance channel to the compound-nuclear state, and it is interpreted as the value of the partial p -wave neutron width corresponding to the total angular momentum of the incident neutron combined with the weak matrix element, in the context of the mechanism of enhanced parity-violating effects. Additionally, we use the result to quantify the possible enhancement of the breaking of time-reversal invariance in the vicinity of the p -wave resonance.
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NASA Astrophysics Data System (ADS)
Ukstins, Ingrid A.; Renne, Paul R.; Wolfenden, Ellen; Baker, Joel; Ayalew, Dereje; Menzies, Martin
2002-05-01
40Ar/ 39Ar dating of mineral separates and whole-rock samples of rhyolitic ignimbrites and basaltic lavas from the pre- and syn-rift flood volcanic units of northern Ethiopia provides a temporal link between the Ethiopian and Yemen conjugate rifted volcanic margins. Sixteen new 40Ar/ 39Ar dates confirm that basaltic flood volcanism in Ethiopia was contemporaneous with flood volcanism on the conjugate margin in Yemen. The new data also establish that flood volcanism initiated prior to 30.9 Ma in Ethiopia and may predate initiation of similar magmatic activity in Yemen by ˜0.2-2.0 Myr. Rhyolitic volcanism in Ethiopia commenced at 30.2 Ma, contemporaneous with the first rhyolitic ignimbrite unit in Yemen at ˜30 Ma. Accurate and precise 40Ar/ 39Ar dates on initial rhyolitic ignimbrite eruptions suggest that silicic flood volcanism in Afro-Arabia post-dates the Oligocene Oi2 global cooling event, ruling out a causative link between these explosive silicic eruptions (with individual volumes ≥200 km 3) and climatic cooling which produced the first major expansion of the Antarctic ice sheets. Ethiopian volcanism shows a progressive and systematic younging from north to south along the escarpment and parallel to the rifted margin, from pre-rift flood volcanics in the north to syn-rift northern Main Ethiopian Rift volcanism in the south. A dramatic decrease in volcanic activity in Ethiopia between 25 and 20 Ma correlates with a prominent break-up unconformity in Yemen (26-19 Ma), both of which mark the transition from pre- to syn-rift volcanism (˜25-26 Ma) triggered by the separation of Africa and Arabia. The architecture of the Ethiopian margin is characterized by accumulation and preservation of syn-rift volcanism, while the Yemen margin was shaped by denudational unloading and magmatic starvation as the Arabian plate rifted away from the Afar plume. A second magmatic hiatus and angular unconformity in the northern Main Ethiopian Rift is evident at 10.6-3.2 Ma, and is also observed throughout the Arabian plate in Jordanian, Saudi Arabian and Yemeni intraplate volcanic fields and is possibly linked to tectonic re-organization and initiation of sea floor spreading in the Gulf of Aden and the Red Sea at 10 and 5 Ma, respectively.
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NASA Astrophysics Data System (ADS)
Andrews-Speed, C. P.
1986-07-01
The structurally defined Mporokoso Basin contains up to 5000 m of continental and marine clastic sediments and minor silicic volcanics which together form the Mporokoso Group. These rocks overlie unconformably a basement of silicic-intermediate igneous rocks and accumulated within the interval 1830-1130 Ma. This sedimentological study was restricted to the eastern end of the basin and was part of an assessment of the potential for palaeoplacer gold in the Mporokoso Group. At the base of the Mporokoso Group, the Mbala Formation consists of 1000-1500 m of purple sandstones and conglomerates deposited in a braided-stream system overlain by 500-1000 m of mature quartz arenites deposited in a tidal marine setting. A general coarsening-upward trend exists within the fluvial sediments. Sandy, distal braided-stream facies passes upwards into more proximal conglomeratic facies. In proximal sections, poorly sorted conglomerates form the top of the coarsening-up sequence which is 500-700 m thick. The overlying fluvial sediments fine upwards. The tidal marine sandstones at the top of the Mbala Formation resulted from reworking of fluvial sediments during a marine transgression. Well-exposed sections with fluvial conglomerates were studied in detail. Individual conglomerate bodies form sheets extending for hundreds of metres downstream and at least one hundred metres across stream, with little sign of deep scouring or channelling. They are generally matrix-supported. The whole fluvial sequence is characterised by a paucity of mud or silt. These conglomerates were deposited by large velocity, sheet flows of water which transported a bed-load of pebbles and sand. Most fine material settling out from suspension was eroded by the next flow. The great lateral and vertical extent and the uniformity of the fluvial sediments suggest that the sediments accumulated over an unconfined alluvial plain and that the tectonic evolution of the source area was relatively continuous and not episodic. These features are characteristic of other Proterozoic fluvial sequences. There are no distinctly channelised fluvial conglomerates nor angular unconformities within the fluvial sequence, both of which would have been potential sites for economic gold concentrations. Reworking of the fluvial sands during the marine transgression may have concentrated gold locally within the marine sandstones.
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NASA Astrophysics Data System (ADS)
Mtelela, Cassy; Roberts, Eric M.; Hilbert-Wolf, Hannah L.; Downie, Robert; Hendrix, Marc S.; O'Connor, Patrick M.; Stevens, Nancy J.
2017-05-01
This paper presents a detailed sedimentologic investigation of a newly identified, fossiliferous Late Neogene sedimentary succession in the Rukwa Rift Basin, southwestern Tanzania. This synrift deposit is a rare and significant new example of a fossiliferous succession of this age in the Western Branch of East Africa Rift System. The unit, informally termed the lower Lake Beds succession, is late Miocene to Pliocene in age based on cross-cutting relationships, preliminary biostratigraphy, and U-Pb geochronology. An angular unconformity separates the lower Lake Beds from underlying Cretaceous and Oligocene strata. Deposition was controlled by rapid generation of accommodation space and increased sediment supply associated with late Cenozoic tectonic reactivation of the Rukwa Rift and synchronous initiation of the Rungwe Volcanic Centre. The lower Lake Beds, which have thus far only been identified in three localities throughout the Rukwa Rift Basin, are characterized by two discrete lithologic members (herein A and B). The lower Member A is a volcanic-rich succession composed mostly of devitrified volcanic tuffs, and volcaniclastic mudstones and sandstones with minor conglomerates. The upper Member B is a siliciclastic-dominated succession of conglomerates, sandstones, mudstones and minor volcanic tuffs. Detailed facies analysis of the lower Lake Beds reveals various distinctive depositional environments that can be grouped into three categories: 1) alluvial fan; 2) fluvial channel; and 3) flood basin environments, characterized by volcanoclastic-filled lakes and ponds, abandoned channel-fills and pedogenically modified floodplains. Member A represents a shallow lacustrine setting filled by tuffaceous sediments, which grade up into a system of alluvial fans and high-energy, proximal gravel-bed braided rivers. An unconformity marks the contact between the two members. Member B shows an upward transition from a high-energy, gravel-bed braided river system to a sandy braided river system with increasingly abundant floodplain deposits and well-developed paleosols. Vertebrate fossils are sparse in member A, but common in member B, preserved both within pedogenic soil horizons and as isolated elements and microsites within fluvial channel facies associations. Faunal remains include fishes, turtles and crocodylians, along with well-preserved mammal cranial and post-cranial remains. In addition, freshwater gastropod shells are locally present in member A and continental trace fossils, including abundant fossilized termite nests, are present in both members.
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Revolution evolution: tracing angular momentum during star and planetary system formation
NASA Astrophysics Data System (ADS)
Davies, Claire Louise
2015-04-01
Stars form via the gravitational collapse of molecular clouds during which time the protostellar object contracts by over seven orders of magnitude. If all the angular momentum present in the natal cloud was conserved during collapse, stars would approach rotational velocities rapid enough to tear themselves apart within just a few Myr. In contrast to this, observations of pre-main sequence rotation rates are relatively slow (∼ 1 - 15 days) indicating that significant quantities of angular momentum must be removed from the star. I use observations of fully convective pre-main sequence stars in two well-studied, nearby regions of star formation (namely the Orion Nebula Cluster and Taurus-Auriga) to determine the removal rate of stellar angular momentum. I find the accretion disc-hosting stars to be rotating at a slower rate and contain less specific angular momentum than the disc-less stars. I interpret this as indicating a period of accretion disc-regulated angular momentum evolution followed by near-constant rotational evolution following disc dispersal. Furthermore, assuming that the age spread inferred from the Hertzsprung-Russell diagram constructed for the star forming region is real, I find that the removal rate of angular momentum during the accretion-disc hosting phase to be more rapid than that expected from simple disc-locking theory whereby contraction occurs at a fixed rotation period. This indicates a more efficient process of angular momentum removal must operate, most likely in the form of an accretion-driven stellar wind or outflow emanating from the star-disc interaction. The initial circumstellar envelope that surrounds a protostellar object during the earliest stages of star formation is rotationally flattened into a disc as the star contracts. An effective viscosity, present within the disc, enables the disc to evolve: mass accretes inwards through the disc and onto the star while momentum migrates outwards, forcing the outer regions of the disc to expand. I used spatially resolved submillimetre detections of the dust and gas components of protoplanetary discs, gathered from the literature, to measure the radial extent of discs around low-mass pre-main sequence stars of ∼ 1-10 Myr and probe their viscous evolution. I find no clear observational evidence for the radial expansion of the dust component. However, I find tentative evidence for the expansion ofthe gas component. This suggests that the evolution of the gas and dust components of protoplanetary discs are likely governed by different astrophysical processes. Observations of jets and outflows emanating from protostars and pre-main sequence stars highlight that it may also be possible to remove angular momentum from the circumstellar material. Using the sample of spatially resolved protoplanetary discs, I find no evidence for angular momentum removal during disc evolution. I also use the spatially resolved debris discs from the Submillimetre Common-User Bolometer Array-2 Observations of Nearby Stars survey to constrain the amount of angular momentum retained within planetary systems. This sample is compared to the protoplanetary disc angular momenta and to the angular momentum contained within pre-stellar cores. I find that significant quantities of angular momentum must be removed during disc formation and disc dispersal. This likely occurs via magnetic braking during the formation of the disc, via the launching of a disc or photo-evaporative wind, and/or via ejection of planetary material following dynamical interactions.
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NASA Technical Reports Server (NTRS)
Dennis, Brian; Li, Mary; Skinner, Gerald
2013-01-01
X-ray optics were fabricated with the capability of imaging solar x-ray sources with better than 0.1 arcsecond angular resolution, over an order of magnitude finer than is currently possible. Such images would provide a new window into the little-understood energy release and particle acceleration regions in solar flares. They constitute one of the most promising ways to probe these regions in the solar atmosphere with the sensitivity and angular resolution needed to better understand the physical processes involved. A circular slit structure with widths as fine as 0.85 micron etched in a silicon wafer 8 microns thick forms a phase zone plate version of a Fresnel lens capable of focusing approx. =.6 keV x-rays. The focal length of the 3-cm diameter lenses is 100 microns, and the angular resolution capability is better than 0.1 arcsecond. Such phase zone plates were fabricated in Goddard fs Detector Development Lab. (DDL) and tested at the Goddard 600-microns x-ray test facility. The test data verified that the desired angular resolution and throughput efficiency were achieved.
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Holocene paleoclimatic evidence and sedimentation rates from a core in southwestern Lake Michigan
Colman, Steven M.; Jones, Glenn A.; Forester, R.M.; Foster, D.S.
1990-01-01
Preliminary results of a multidisciplinary study of cores in southwestern Lake Michigan suggest that the materials in these cores can be interpreted in terms of both isostatically and climatically induced changes in lake level. Ostracodes and mollusks are well preserved in the Holocene sediments, and they provide paleolimnologic and paleoclimatic data, as well as biogenic carbonate for stable-isotope studies and radiocarbon dating. Pollen and diatom preservation in the cores is poor, which prevents comparison with regional vegetation records. New accelerator-mass spectrometer 14C ages, from both carbon and carbonate fractions, provide basin-wide correlations and appear to resolve the longstanding problem of anomalously old ages that result from detrital organic matter in Great Lakes sediments. Several cores contain a distinct unconformity associated with the abrupt fall in lake level that occurred about 10.3 ka when the isostatically depressed North Bay outlet was uncovered by the retreating Laurentide Ice Sheet. Below the unconformity, ostracode assemblages imply deep, cold water with very low total dissolved solids (TDS), and bivalves have ?? 18O (PDB) values as light as - 10 per mil. Samples from just above the unconformity contain littoral to sublittoral ostracode species that imply warmer, higher-TDS (though still dilute) water than that inferred below the unconformity. Above this zone, another interval with ?? 18O values more negative than - 10 occurs. The isotopic data suggest that two influxes of cold, isotopically light meltwater from Laurentide ice entered the lake, one shortly before 10.3 ka and the other about 9 ka. These influxes were separated by a period during which the lake was warmer, shallower, but still very low in dissolved solids. One or both of the meltwater influxes may be related to discharge from Lake Agassiz into the Great Lakes. Sedimentation rates appear to have been constant from about 10 ka to 5 ka. Bivalve shells formed between about 8 and 5 ka have ?? 18O values that range from-2.3 to-3.3 per mil and appear to decrease toward the end of the interval. The ostracode assemblages and the stable isotopes suggest changes that are climatically controlled, including fluctuating water levels and increasing dissolved solids, although the water remained relatively dilute (TDS < 300 mg/l). A dramatic decrease in sedimentation rates occurred at about 5 ka, about the time of the peak of the Nippissing high lake stage. This decrease in sedimentation rate may be associated with a large increase in effective wave base as the lake approached its present size and fetch. A dramatic reduction in ostracode and mollusk abundances during the late Holocene is probably due to this decrease in sedimentation rates, which would result in increased carbonate dissolution. Ostracode productivity may also have declined due to a reduction in bottom-water oxygen caused by increased epilimnion algal productivity.
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Influence of angular acceleration-deceleration pulse shapes on regional brain strains.
Yoganandan, Narayan; Li, Jianrong; Zhang, Jiangyue; Pintar, Frank A; Gennarelli, Thomas A
2008-07-19
Recognizing the association of angular loading with brain injuries and inconsistency in previous studies in the application of the biphasic loads to animal, physical, and experimental models, the present study examined the role of the acceleration-deceleration pulse shapes on region-specific strains. An experimentally validated two-dimensional finite element model representing the adult male human head was used. The model simulated the skull and falx as a linear elastic material, cerebrospinal fluid as a hydrodynamic material, and cerebrum as a linear viscoelastic material. The angular loading matrix consisted coronal plane rotation about a center of rotation that was acceleration-only (4.5 ms duration, 7.8 krad/s/s peak), deceleration-only (20 ms, 1.4 krad/s/s peak), acceleration-deceleration, and deceleration-acceleration pulses. Both biphasic pulses had peaks separated by intervals ranging from 0 to 25 ms. Principal strains were determined at the corpus callosum, base of the postcentral sulcus, and cerebral cortex of the parietal lobe. The cerebrum was divided into 17 regions and peak values of average maximum principal strains were determined. In all simulations, the corpus callosum responded with the highest strains. Strains were the least under all simulations in the lower parietal lobes. In all regions peak strains were the same for both monophase pulses suggesting that the angular velocity may be a better metric than peak acceleration or deceleration. In contrast, for the biphasic pulse, peak strains were region- and pulse-shape specific. Peak values were lower in both biphasic pulses when there was no time separation between the pulses than the corresponding monophase pulse. Increasing separation time intervals increased strains, albeit non-uniformly. Acceleration followed by deceleration pulse produced greater strains in all regions than the other form of biphasic pulse. Thus, pulse shape appears to have an effect on regional strains in the brain.
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NASA Astrophysics Data System (ADS)
Weissbrod, T.; Perath, I.
A systematic study of the Precambrian and Paleozoic-Mesozoic clastic sequences (Nubian Sandstone) in Israel and Sinai, and a comparative analysis of its stratigraphy in neighbouring countries, has shown that besides the conventional criteria of subdivision (lithology, field appearance, photogeological features, fossil content), additional criteria can be applied, which singly or in mutual conjuction enable the recognition of widespread units and boundaries. These criteria show lateral constancy, and recurrence of a similar vertical sequence over great distances, and are therefore acceptable for the identification of synchronous, region-wide sedimentary units (and consequently, major unconformities). They also enable, once the units are established, to identify detached (not in situ) samples, samples from isolated or discontinous outcrops, borehole material or archive material. The following rock properties were tested and found to be usefuls in stratigraphic interpretation, throughout large distribution areas of the clastic sequence: Landscape, which is basically the response of a particular textural-chemic al aggregate to atmospheric weathering. Characteristic outcrop feature — styles of roundness or massivity, fissuring or fliatin, slope profile, bedding — express a basic uniformity of these platform-type clastics. Colors are often stratigraphically constant over hundreds of kilometers, through various climates and topographies, and express some intrinsic unity of the rock bodies. Grain size and sorting, when cross-plotted, enable to differentiate existing unit. The method requires the analysis of representative numbers of samples. Vertical trends of median grain size and sorting show reversals, typically across unconformities. Feldstar content diminishes from 15-50% in Precambrian-Paleozoic rocks to a mere 5% or less in Mesozoic sandstones — a distinctive regionwide time trend. Dominance of certain feldstar types characterizes Precambrian and Paleozoic units. Clay minerals, though subordinate, characterize certain units. Illite is usually the dominant clay mineral in the Precambrain-Paleozoic sediments, showing different degress of crystallization in different units. Kaolinite is the main, often the only clay mineral in Mesozoic units. Heavy minerals, whose species spectra reflect on parent rock and provenance terrain and whose differential response to degradation points to the sedimentary history of the deposit, show certain vertical regularities, such as the abrupt disappearance of species or whole assemblages at certain levels, indicating unconformities. Trace metals, which in places reach ore concentrations (e.g. copper), are often extensive, though of well-defined vertical distribution. They express adsorptive capacity of specific widespread lithologies, enabling the discrimination of units. Even though each of these criteria is not always by itself diagnostic, they may in conjuction with one or more other criteria amount to a petrographic fingerprint that enables fairly accurate identification of the age interval of the unit, and its relation both to the regional and the local stratigraphic sequence.
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NASA Astrophysics Data System (ADS)
Chen, Zhonghong; Zha, Ming; Liu, Keyu; Zhang, Yueqian; Yang, Disheng; Tang, Yong; Wu, Kongyou; Chen, Yong
2016-09-01
The Kebai Fault zone of the West Junggar Basin in northwestern China is a unique region to gain insights on the formation of large-scale petroleum reservoirs in volcanic rocks of the western Central Asian Orogenic Belt. Carboniferous volcanic rocks are widespread in the Kebai Fault zone and consist of basalt, basaltic andesite, andesite, tuff, volcanic breccia, sandy conglomerate and metamorphic rocks. The volcanic oil reservoirs are characterized by multiple sources and multi-stage charge and filling history, characteristic of a complex petroleum system. Geochemical analysis of the reservoir oil, hydrocarbon inclusions and source rocks associated with these volcanic rocks was conducted to better constrain the oil source, the petroleum filling history, and the dominant mechanisms controlling the petroleum accumulation. Reservoir oil geochemistry indicates that the oil contained in the Carboniferous volcanic rocks of the Kebai Fault zone is a mixture. The oil is primarily derived from the source rock of the Permian Fengcheng Formation (P1f), and secondarily from the Permian Lower Wuerhe Formation (P2w). Compared with the P2w source rock, P1f exhibits lower values of C19 TT/C23 TT, C19+20TT/ΣTT, Ts/(Ts + Tm) and ααα-20R sterane C27/C28 ratios but higher values of TT C23/C21, HHI, gammacerane/αβ C30 hopane, hopane (20S) C34/C33, C29ββ/(ββ + αα), and C29 20S/(20S + 20R) ratios. Three major stages of oil charge occurred in the Carboniferous, in the Middle Triassic, Late Triassic to Early Jurassic, and in the Middle Jurassic to Late Jurassic periods, respectively. Most of the oil charged during the first stage was lost, while moderately and highly mature oils were generated and accumulated during the second and third stages. Oil migration and accumulation in the large-scale stratigraphic reservoir was primarily controlled by the top Carboniferous unconformity with better porosity and high oil enrichment developed near the unconformity. Secondary dissolution pores and fractures are the two major reservoir storage-space types in the reservoirs. Structural highs and reservoirs near the unconformity are two favorable oil accumulation places. The recognition of the large-scale Carboniferous volcanic reservoirs in the Kebai Fault zone and understanding of the associated petroleum accumulation mechanisms provide new insights for exploring various types of volcanic reservoir plays in old volcanic provinces, and will undoubtedly encourage future oil and gas exploration of deeper strata in the region and basins elsewhere with similar settings.
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Yin, Anmin; Wang, Xiaochen; Glorieux, Christ; Yang, Quan; Dong, Feng; He, Fei; Wang, Yanlong; Sermeus, Jan; Van der Donck, Tom; Shu, Xuedao
2017-07-01
A photoacoustic, laser ultrasonics based approach in an Impulsive Stimulated Scattering (ISS) implementation was used to investigate the texture in polycrystalline metal plates. The angular dependence of the 'polycrystalline' surface acoustic wave (SAW) velocity measured along regions containing many grains was experimentally determined and compared with simulated results that were based on the angular dependence of the 'single grain' SAW velocity within single grains and the grain orientation distribution. The polycrystalline SAW velocities turn out to vary with texture. The SAW velocities and their angular variations for {110} texture were found to be larger than that the ones for {111} texture or the strong γ fiber texture. The SAW velocities for {001} texture were larger than for {111} texture, but with almost the same angular dependence. The results infer the feasibility to apply angular SAW angular dispersion measurements by laser ultrasonics for on-line texture monitoring. Copyright © 2017 Elsevier B.V. All rights reserved.
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The Cretaceous-Tertiary boundary interval in Badlands National Park, South Dakota
Stoffer, Philip W.; Messina, Paula; Chamberlain, John A.; Terry, Dennis O.
2001-01-01
A marine K-T boundary interval has been identified throughout the Badlands National Park region of South Dakota. Data from marine sediments suggest that deposits from two asteroid impacts (one close, one far away) may be preserved in the Badlands. These impact-generated deposits may represent late Maestrichtian events or possibly the terminal K-T event. Interpretation is supported by paleontological correlation, sequence stratigraphy, magnetostratigraphy, and strontium isotope geochronology. This research is founded on nearly a decade of NPS approved field work in Badlands National Park and a foundation of previously published data and interpretations. The K-T boundary occurs within or near the base of a stratigraphic interval referred to as the "Interior Zone." We interpret the stratigraphy of the Interior Zone as a series of distinct, recognizable lithologic members and units from oldest to youngest, an upper weathered interval of the Elk Butte Member of the Pierre Shale (early late Maestrichtian), a complete (albeit condensed) interval of Fox Hill Formation, a pedogenically altered K-T Boundary "Disturbed Zone," and a generally unresolved sequence of marine to marginal marine units ranging in age from possibly latest Maestrichtian to late Paleocene (the "Yellow Mounds"), that underlie a basal red clay unit (the late Eocene overbank channel facies of the Chamberlain Pass Formation at the base of the White River Group). Within this sequence is a series of unconformities that all display some degree of subaerial weathering and erosion. The dating of marine fossils above and below these unconformities are in line with generally accepted global sea-level changes recognized for the late Campanian through early Eocene. Within the greater framework of regional geology, these findings support that the Western Interior Seaway and subsequent Cannonball Seaway were dependently linked to the changing base-level controlled by sea-level of the global ocean through the Gulf of Mexico and possibly the Arctic Ocean. The variation of facies preserved in Late Cretaceous strata in the Badlands National Park area were in part controlled by local or regional tectonic blocks that were either rising or sinking contemporaneous with deposition.
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NASA Astrophysics Data System (ADS)
Wilson, Gary S.; Levy, Richard H.; Naish, Tim R.; Powell, Ross D.; Florindo, Fabio; Ohneiser, Christian; Sagnotti, Leonardo; Winter, Diane M.; Cody, Rosemary; Henrys, Stuart; Ross, Jake; Krissek, Larry; Niessen, Frank; Pompillio, Massimo; Scherer, Reed; Alloway, Brent V.; Barrett, Peter J.; Brachfeld, Stefanie; Browne, Greg; Carter, Lionel; Cowan, Ellen; Crampton, James; DeConto, Robert M.; Dunbar, Gavin; Dunbar, Nelia; Dunbar, Robert; von Eynatten, Hilmar; Gebhardt, Catalina; Giorgetti, Giovanna; Graham, Ian; Hannah, Mike; Hansaraj, Dhiresh; Harwood, David M.; Hinnov, Linda; Jarrard, Richard D.; Joseph, Leah; Kominz, Michelle; Kuhn, Gerhard; Kyle, Philip; Läufer, Andreas; McIntosh, William C.; McKay, Robert; Maffioli, Paola; Magens, Diana; Millan, Christina; Monien, Donata; Morin, Roger; Paulsen, Timothy; Persico, Davide; Pollard, David; Raine, J. Ian; Riesselman, Christina; Sandroni, Sonia; Schmitt, Doug; Sjunneskog, Charlotte; Strong, C. Percy; Talarico, Franco; Taviani, Marco; Villa, Giuliana; Vogel, Stefan; Wilch, Tom; Williams, Trevor; Wilson, Terry J.; Wise, Sherwood
2012-10-01
Stratigraphic drilling from the McMurdo Ice Shelf in the 2006/2007 austral summer recovered a 1284.87 m sedimentary succession from beneath the sea floor. Key age data for the core include magnetic polarity stratigraphy for the entire succession, diatom biostratigraphy for the upper 600 m and 40Ar/39Ar ages for in-situ volcanic deposits as well as reworked volcanic clasts. A vertical seismic profile for the drill hole allows correlation between the drill hole and a regional seismic network and inference of age constraint by correlation with well-dated regional volcanic events through direct recognition of interlayered volcanic deposits as well as by inference from flexural loading of pre-existing strata. The combined age model implies relatively rapid (1 m/2-5 ky) accumulation of sediment punctuated by hiatuses, which account for approximately 50% of the record. Three of the longer hiatuses coincide with basin-wide seismic reflectors and, along with two thick volcanic intervals, they subdivide the succession into seven chronostratigraphic intervals with characteristic facies: The base of the cored succession (1275-1220 mbsf) comprises middle Miocene volcaniclastic sandstone dated at approx 13.5 Ma by several reworked volcanic clasts; A late-Miocene sub-polar orbitally controlled glacial-interglacial succession (1220-760 mbsf) bounded by two unconformities correlated with basin-wide reflectors associated with early development of the terror rift; A late Miocene volcanigenic succession (760-596 mbsf) terminating with a ~ 1 my hiatus at 596.35 mbsf which spans the Miocene-Pliocene boundary and is not recognised in regional seismic data; An early Pliocene obliquity-controlled alternating diamictite and diatomite glacial-interglacial succession (590-440 mbsf), separated from; A late Pliocene obliquity-controlled alternating diamictite and diatomite glacial-interglacial succession (440-150 mbsf) by a 750 ky unconformity interpreted to represent a major sequence boundary at other locations; An early Pleistocene interbedded volcanic, diamictite and diatomite succession (150-80 mbsf), and; A late Pleistocene glacigene succession (80-0 mbsf) comprising diamictite dominated sedimentary cycles deposited in a polar environment.
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NASA Astrophysics Data System (ADS)
Voigt, Joana R. C.; Hamilton, Christopher W.
2018-07-01
The Elysium Volcanic Province consists of numerous overlapping flow units and may include the youngest lava flows on Mars. However, it is possible that these volcanic units have been modified or overprinted by aqueous processes. Understanding the timing of the igneous and aqueous events in this region is therefore essential for constraining the geological and environmental history of Mars during the Amazonian Period. We investigate the geologic evolution of Eastern Elysium Planitia to determine the relationship between major units, with the support of a geological map and chronological constraints from crater size-frequency distributions. We also evaluate the hypothesized origin of these units via volcanic, fluvial, and/or fluvioglacial processes using a detailed facies-mapping approach. The study area includes the Eastern Cerberus Fossae, Rahway Valles, and Marte Vallis. The surficial deposits in Rahway Valles were formerly interpreted to be modified by fluvial and fluvioglacial processes. However, our facies map reveals that the surface of Eastern Elysium Planitia includes nineteen morphologically distinct regions (i.e., facies), which are interpreted to be the products of flood lava volcanism, including: ´a´ā, pāhoehoe, and transitional lava flow types. In contrast to previous studies, which determined that Rahway Valles and Marte Vallis consist of two distinct geologic units with Middle to Late Amazonian ages, the results of this work show that the region was resurfaced by at least two volcanic flows with much younger ages of 20.0 Ma and 8.8 Ma. Furthermore, by coupling results of our geologic and facies mapping with chronological constraints as well as subsurface information provided by Shallow Radar reflectors, we show that there is an erosional unconformity located between the two youngest lava flow units in Marte Vallis. We interpret that this unconformity was generated by a catastrophic aqueous flooding event that occurred only 8.8 - 20.0 Ma ago. This implies alternating episodes of volcanism and aqueous flooding that have continued into the geologically recent past on Mars, and may again occur within Elysium Planitia.
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The Sedimentary Architecture of the Hatton Basin from New 2D Seismic Reflection and Gravity Data
NASA Astrophysics Data System (ADS)
Bérdi, L.; Prada, M.; O'Reilly, B.; Haughton, P.; Shannon, P.; Martínez-Loriente, S.
2017-12-01
The Hatton Basin is located at the western European Atlantic Margin, approximately 600 km west of Scotland and Ireland. It is bounded by the Rockall Bank to the east and by the Hatton High to the west. Little is known about its structure and evolution within the context of the North Atlantic opening. Here we present a preliminary interpretation of the large-scale sedimentary structure of the Hatton basin from new 2D regional long-streamer seismic reflection data and DSDP information. Gravity data and previous knowledge on the crustal structure of the basin are used to investigate its formation processes.First interpretations of the seismic data suggest the presence of three megasequences referred to as Ha (Early Pliocene to Holocene), Hb (Late Eocene to Late Miocene) and Hc (Paleocene to middle Eocene), which are bounded by regional unconformities C10 (intra-Early Pliocene), C30 (intra-Late Eocene) and C40 (base Cenozoic) respectively. The C20 (intra-Early Miocene) surface is absent in the basin but is locally identified to the south of the study area. The mapped regional reflectors are recognized throughout the European North Atlantic.Below the Cenozoic succession, the presence of Mesozoic and/or older rocks in the basin is proposed based on the seismic character of the reflectors and the apparent rotated fault blocks. In the lowest Cenozoic megasequence (Hc), a prograding sedimentary wedge system was identified at the basin margins that implies a relative sea level fall during this period. In Late Paleocene‒Early Eocene times, the basin was affected by extensive magmatism that resulted in the emplacement of volcanic intrusives and extrusives of basaltic origin. The deposition of megasequence Hb was controlled by strong bottom current activity as a consequence of rapid subsidence and deep marine conditions. The transition from sequence Hb to Ha is marked by the C10 unconformity, which records the late Cenozoic uplift and erosion of Ireland and Britain. Megasequence Ha is locally eroded and is characterized by contourite, debris flow and mass transport deposits. This publication has emanated from research supported in part by a research grant from Science Foundation Ireland (SFI) under Grant Number 13/RC/2092 and co-funded under the European Regional Development Fund and by PIPCO RSG and its member companies.
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Elman, Jeremy A; Cohn-Sheehy, Brendan I; Shimamura, Arthur P
2013-03-01
In fMRI analyses, the posterior parietal cortex (PPC) is particularly active during the successful retrieval of episodic memory. To delineate the neural correlates of episodic retrieval more succinctly, we compared retrieval of recently learned spatial locations (photographs of buildings) with retrieval of previously familiar locations (photographs of familiar campus buildings). Episodic retrieval of recently learned locations activated a circumscribed region within the ventral PPC (anterior angular gyrus and adjacent regions in the supramarginal gyrus) as well as medial PPC regions (posterior cingulated gyrus and posterior precuneus). Retrieval of familiar locations activated more posterior regions in the ventral PPC (posterior angular gyrus, LOC) and more anterior regions in the medial PPC (anterior precuneus and retrosplenial cortex). These dissociable effects define more precisely PPC regions involved in the retrieval of recent, contextually bound information as opposed to regions involved in other processes, such as visual imagery, scene reconstruction, and self-referential processing. Copyright © 2012 Elsevier Ltd. All rights reserved.
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Levi-Civita cylinders with fractional angular deficit
NASA Astrophysics Data System (ADS)
Krisch, J. P.; Glass, E. N.
2011-05-01
The angular deficit factor in the Levi-Civita vacuum metric has been parametrized using a Riemann-Liouville fractional integral. This introduces a new parameter into the general relativistic cylinder description, the fractional index α. When the fractional index is continued into the negative α region, new behavior is found in the Gott-Hiscock cylinder and in an Israel shell.
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NASA Astrophysics Data System (ADS)
Amadori, Chiara; Toscani, Giovanni; Ghielmi, Manlio; Maesano, Francesco Emanuele; D'Ambrogi, Chiara; Lombardi, Stefano; Milanesi, Riccardo; Panara, Yuri; Di Giulio, Andrea
2017-04-01
The Pliocene-Pleistocene tectonic and sedimentary evolution of the eastern Po Plain and northern Adriatic Foreland Basin (PPAF) (extended ca. 35,000 km2) was the consequence of severe Northern Apennine compressional activity and climate-driven eustatic changes. According with the 2D seismic interpretation, facies analysis and sequence stratigraphy approach by Ghielmi et al. (2013 and references therein), these tectono-eustatic phases generated six basin-scale unconformities referred as Base Pliocene (PL1), Intra-Zanclean (PL2), Intra-Piacenzian (PL3), Gelasian (PL4), Base Calabrian (PS1) and Late Calabrian (PS2). We present a basin-wide detailed 3D model of the PPAF region, derived from the interpretation of these unconformities in a dense network of seismic lines (ca. 6,000 km) correlated with more than 200 well stratigraphies (courtesy of ENI E&P). The initial 3D time-model has been time-to-depth converted using the 3D velocity model created with Vel-IO 3D, a tool for 3D depth conversions and then validated and integrated with depth domain dataset from bibliography and well log. Resultant isobath and isopach maps are produced to inspect step-by-step the basin paleogeographic evolution; it occurred through alternating stages of simple and fragmented foredeeps. Changes in the basin geometry through time, from the inner sector located in the Emilia-Romagna Apennines to the outermost region (Veneto and northern Adriatic Sea), were marked by repeated phases of outward migration of two large deep depocenters located in front of Emilia arcs on the west, and in front of Ferrara-Romagna thrusts on the east. During late Pliocene-early Pleistocene, the inner side of the Emilia-Romagna arcs evolved into an elongated deep thrust-top basin due to a strong foredeep fragmentation then, an overall tectono-stratigraphic analysis shows also a decreasing trend of tectonic intensity of the Northern Apennine since Pleistocene until present.
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NASA Astrophysics Data System (ADS)
Lazzez, Marzouk; Zouaghi, Taher; Ben Youssef, Mohamed
2008-08-01
A multidisciplinary study concerning Aptian and Albian deposits is reported from petroleum wells and the exposed section. The biostratigraphic and sedimentological analysis defined four sedimentary units. Well-logging signals' analysis allows us to refine the record resolution on Aptian series and reveals, in the Djeffara field, a transgressive system tract (TST) and a highstand system tract (HST). Exceptionally, the first sequence (S1) in the Mareth 1 well and the fifth sequence in the two wells Mareth 1 and Gourine 1 reveal the lower-stand system tract (LST). The unconformities characterized by the absence of Upper Aptian (Clansayesian) and Lower to Middle Albian deposits signed by a significant gamma-ray reduction. The Middle and Upper Albian is represented by only one deposit sequence (S6) in Mareth 1. Towards the south, in the Gourine well, two deposit sequences were identified (S6 and S7); to specify the Aptian and Albian evolution of the deposit sequences, a tentative correlation has been established between the Chotts and Djeffara areas. This correlation allows us to characterize the sedimentary unconformities related to the tectonics and eustatic events. The Chotts and the Djeffara deposition areas were developed, characterized by an irregular subsidence and separated by the Tebaga Medenine high area. The Aptian-Albian subsidence platform of southern Tunisia may be considered as a block diagram of environmental deposit with regressive and transgressive trends, showing the impact of tectonic deformations on the palaeogeographic evolution of southeastern Tunisia during the Austrian phase. This study also must be replaced within regional structural patterns that may explain both the sequential and sedimentological evolution of the area. Deformations regionally identified are integrated in the more general context of both Tethyan and Atlantic areas related to the drift of the African platform.
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RadioAstron Maser Observations: a Record in Angular Resolution
NASA Astrophysics Data System (ADS)
Sobolev, A. M.; Shakhvorostova, N. N.; Alakoz, A. V.; Baan, W. A.; RadioAstron Maser Team
2017-06-01
Extremely long baselines of the space-ground interferometer RadioAstron allow to achieve ultra-high angular resolutions. The possibility of detection of a maser emission with resolutions about tens of micro-arcseconds was arguable before successful experiments reported in this paper. We present the results of the maser survey obtained by RadioAstron during first 5 years of operation. Extremely high angular resolution of 11 microarcseconds have been achieved in observations of the megamaser galaxy NGC 4258. For the galaxy at the distance about 7 Mpc this corresponds to linear resolution around 80 AU. Very compact features with angular sizes about 20 micro-arcseconds have been detected in star-forming regions of our Galaxy. Corresponding linear sizes are about 5-10 millions of kilometers.
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Tsang, Sharon M H; Szeto, Grace P Y; Lee, Raymond Y W
2013-07-01
Research on the kinematics and inter-regional coordination of movements between the cervical and thoracic spines in motion adds to our understanding of the performance and interplay of these spinal regions. The purpose of this study was to examine the effects of chronic neck pain on the three-dimensional kinematics and coordination of the cervical and thoracic spines during active movements of the neck. Three-dimensional spinal kinematics and movement coordination between the cervical, upper thoracic, and lower thoracic spines were examined by electromagnetic motion sensors in thirty-four individuals with chronic neck pain and thirty-four age- and gender-matched asymptomatic subjects. All subjects performed a set of free active neck movements in three anatomical planes in sitting position and at their own pace. Spinal kinematic variables (angular displacement, velocity, and acceleration) of the three defined regions, and movement coordination between regions were determined and compared between the two groups. Subjects with chronic neck pain exhibited significantly decreased cervical angular velocity and acceleration of neck movement. Cross-correlation analysis revealed consistently lower degrees of coordination between the cervical and upper thoracic spines in the neck pain group. The loss of coordination was most apparent in angular velocity and acceleration of the spine. Assessment of the range of motion of the neck is not sufficient to reveal movement dysfunctions in chronic neck pain subjects. Evaluation of angular velocity and acceleration and movement coordination should be included to help develop clinical intervention strategies to promote restoration of differential kinematics and movement coordination. Copyright © 2013 Elsevier Ltd. All rights reserved.
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NASA Astrophysics Data System (ADS)
Pushkarev, A. B.; Kovalev, Y. Y.
2015-10-01
We have measured the angular sizes of radio cores of active galactic nuclei (AGNs) and analysed their sky distributions and frequency dependences to study synchrotron opacity in AGN jets and the strength of angular broadening in the interstellar medium. We have used archival very long baseline interferometry (VLBI) data of more than 3000 compact extragalactic radio sources observed at frequencies, ν, from 2 to 43 GHz to measure the observed angular size of VLBI cores. We have found a significant increase in the angular sizes of the extragalactic sources seen through the Galactic plane (|b| ≲ 10°) at 2, 5 and 8 GHz, about one-third of which show significant scattering. These sources are mainly detected in directions to the Galactic bar, the Cygnus region and a region with galactic longitudes 220° ≲ l ≲ 260° (the Fitzgerald window). The strength of interstellar scattering of the AGNs is found to correlate with the Galactic Hα intensity, free-electron density and Galactic rotation measure. The dependence of scattering strengths on source redshift is insignificant, suggesting that the dominant scattering screens are located in our Galaxy. The observed angular size of Sgr A* is found to be the largest among thousands of AGNs observed over the sky; we discuss possible reasons for this strange result. Excluding extragalactic radio sources with significant scattering, we find that the angular size of opaque cores in AGNs scales typically as ν-1, confirming predictions of a conical synchrotron jet model with equipartition.
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NASA Astrophysics Data System (ADS)
López-Gamundí, O. R.; Rossello, E. A.
1993-04-01
The Devonian-Carboniferous contact in southern South America, characterized by a sharp unconformity, has been related to the Late Devonian-Early Carboniferous Eo-Hercynian orogeny. The Calingasta-Uspallata basin of western Argentina and the Sauce-Grande basin (Ventana Foldbelt) of eastern Argentina have been selected to characterize this unconformity. The Eo-Hercynian movements were accompanied in western Argentina by igneous activity related to a Late Devonian—Early Carboniferous magmatic arc mainly exposed today along the Andean Cordillera. This magmatic activity is partly reflected also in eastern Argentina (Ventana Foldbelt), where isotopic dates suggest a thermal event also related to the intrusions present to the west in the North Patagonian Massif and Sierras Pampeanas. The scarcity of Lower Carboniferous deposits in the stratigraphic record of southern South America suggests that the Early Carboniferous was a time interval dominated by uplift and erosion followed by widespread subsidence during the Middle and Late Carboniferous. The origin of the Eo-Hercynian orogeny can be linked with the convergence between the Arequipa Massif, and its southern extension, and the South American continent. Its effects are best represented along the ‘Palaeo-Pacific’ margin, although distant effects are discernible in the cratonic areas of eastern South America.
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Network representations of angular regions for electromagnetic scattering
2017-01-01
Network modeling in electromagnetics is an effective technique in treating scattering problems by canonical and complex structures. Geometries constituted of angular regions (wedges) together with planar layers can now be approached with the Generalized Wiener-Hopf Technique supported by network representation in spectral domain. Even if the network representations in spectral planes are of great importance by themselves, the aim of this paper is to present a theoretical base and a general procedure for the formulation of complex scattering problems using network representation for the Generalized Wiener Hopf Technique starting basically from the wave equation. In particular while the spectral network representations are relatively well known for planar layers, the network modelling for an angular region requires a new theory that will be developed in this paper. With this theory we complete the formulation of a network methodology whose effectiveness is demonstrated by the application to a complex scattering problem with practical solutions given in terms of GTD/UTD diffraction coefficients and total far fields for engineering applications. The methodology can be applied to other physics fields. PMID:28817573
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Low-energy Auger electron diffraction: influence of multiple scattering and angular momentum
NASA Astrophysics Data System (ADS)
Chassé, A.; Niebergall, L.; Kucherenko, Yu.
2002-04-01
The angular dependence of Auger electrons excited from single-crystal surfaces is treated theoretically within a multiple-scattering cluster model taking into account the full Auger transition matrix elements. In particular the model has been used to discuss the influence of multiple scattering and angular momentum of the Auger electron wave on Auger electron diffraction (AED) patterns in the region of low kinetic energies. Theoretical results of AED patterns are shown and discussed in detail for Cu(0 0 1) and Ni(0 0 1) surfaces, respectively. Even though Cu and Ni are very similar in their electronic and scattering properties recently strong differences have been found in AED patterns measured in the low-energy region. It is shown that the differences may be caused to superposition of different electron diffraction effects in an energy-integrated experiment. A good agreement between available experimental and theoretical results has been achieved.
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Development of a High Angular Resolution Diffusion Imaging Human Brain Template
Varentsova, Anna; Zhang, Shengwei; Arfanakis, Konstantinos
2014-01-01
Brain diffusion templates contain rich information about the microstructure of the brain, and are used as references in spatial normalization or in the development of brain atlases. The accuracy of diffusion templates constructed based on the diffusion tensor (DT) model is limited in regions with complex neuronal micro-architecture. High angular resolution diffusion imaging (HARDI) overcomes limitations of the DT model and is capable of resolving intravoxel heterogeneity. However, when HARDI is combined with multiple-shot sequences to minimize image artifacts, the scan time becomes inappropriate for human brain imaging. In this work, an artifact-free HARDI template of the human brain was developed from low angular resolution multiple-shot diffusion data. The resulting HARDI template was produced in ICBM-152 space based on Turboprop diffusion data, was shown to resolve complex neuronal micro-architecture in regions with intravoxel heterogeneity, and contained fiber orientation information consistent with known human brain anatomy. PMID:24440528
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Angular default mode network connectivity across working memory load.
Vatansever, D; Manktelow, A E; Sahakian, B J; Menon, D K; Stamatakis, E A
2017-01-01
Initially identified during no-task, baseline conditions, it has now been suggested that the default mode network (DMN) engages during a variety of working memory paradigms through its flexible interactions with other large-scale brain networks. Nevertheless, its contribution to whole-brain connectivity dynamics across increasing working memory load has not been explicitly assessed. The aim of our study was to determine which DMN hubs relate to working memory task performance during an fMRI-based n-back paradigm with parametric increases in difficulty. Using a voxel-wise metric, termed the intrinsic connectivity contrast (ICC), we found that the bilateral angular gyri (core DMN hubs) displayed the greatest change in global connectivity across three levels of n-back task load. Subsequent seed-based functional connectivity analysis revealed that the angular DMN regions robustly interact with other large-scale brain networks, suggesting a potential involvement in the global integration of information. Further support for this hypothesis comes from the significant correlations we found between angular gyri connectivity and reaction times to correct responses. The implication from our study is that the DMN is actively involved during the n-back task and thus plays an important role related to working memory, with its core angular regions contributing to the changes in global brain connectivity in response to increasing environmental demands. Hum Brain Mapp 38:41-52, 2017. © 2016 Wiley Periodicals, Inc. © 2016 Wiley Periodicals, Inc.
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Shallow seismic reflection profiles and geological structure in the Benton Hills, southeast Missouri
Palmer, J.R.; Hoffman, D.; Stephenson, W.J.; Odum, J.K.; Williams, R.A.
1997-01-01
During late May and early June of 1993, we conducted two shallow, high-resolution seismic reflection surveys (Mini-Sosie method) across the southern escarpment of the Benton Hills segment of Crowleys Ridge. The reflection profiles imaged numerous post-late Cretaceous faults and folds. We believe these faults may represent a significant earthquake source zone. The stratigraphy of the Benton Hills consists of a thin, less than about 130 m, sequence of mostly unconsolidated Cretaceous, Tertiary and Quaternary sediments which unconformably overlie a much thicker section of Paleozoic carbonate rocks. The survey did not resolve reflectors within the upper 75-100 ms of two-way travel time (about 60-100 m), which would include all of the Tertiary and Quaternary and most of the Cretaceous. However, the Paleozoic-Cretaceous unconformity (Pz) produced an excellent reflection, and, locally a shallower reflector within the Cretaceous (K) was resolved. No coherent reflections below about 200 ms of two-way travel time were identified. Numerous faults and folds, which clearly offset the Paleozoic-Cretaceous unconformity reflector, were imaged on both seismic reflection profiles. Many structures imaged by the reflection data are coincident with the surface mapped locations of faults within the Cretaceous and Tertiary succession. Two locations show important structures that are clearly complex fault zones. The English Hill fault zone, striking N30??-35??E, is present along Line 1 and is important because earlier workers indicated it has Pleistocene Loess faulted against Eocene sands. The Commerce fault zone striking N50??E, overlies a major regional basement geophysical lineament, and is present on both seismic lines at the southern margin of the escarpment. The fault zones imaged by these surveys are 30 km from the area of intense microseismicity in the New Madrid seismic zone (NMSZ). If these are northeast and north-northeast oriented fault zones like those at Thebes Gap they are favorably oriented in the modern stress field to be reactivated as right-lateral strike slip faults. Currently, earthquake hazards assessments are most dependent upon historical seismicity, and there are little geological data available to evaluate the earthquake potential of fault zones outside of the NMSZ. We anticipate that future studies will provide evidence that seismicity has migrated between fault zones well beyond the middle Mississippi Valley. The potential earthquake hazards represented by faults outside the NMSZ may be significant.
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NASA Astrophysics Data System (ADS)
Martin-Banda, Raquel; Insua-Arevalo, Juan Miguel; Garcia-Mayordomo, Julian
2017-04-01
Many studies have dealt with the calculation of fault-propagation fold growth rates considering a variety of kinematics models, from limb rotation to hinge migration models. In most cases, the different geometrical and numeric growth models are based on horizontal pre-growth strata architecture and a constant known slip rate. Here, we present the estimation of the vertical slip rate of the NE Segment of the Carrascoy Fault (SE Iberian Peninsula) from the geometrical modeling of a progressive unconformity developed on alluvial fan sediments with a high depositional slope. The NE Segment of the Carrascoy Fault is a left-lateral strike slip fault with reverse component belonging to the Eastern Betic Shear Zone, a major structure that accommodates most of the convergence between Iberian and Nubian tectonics plates in Southern Spain. The proximity of this major fault to the city of Murcia encourages the importance of carrying out paleosismological studies in order to determinate the Quaternary slip rate of the fault, a key geological parameter for seismic hazard calculations. This segment is formed by a narrow fault zone that articulates abruptly the northern edge of the Carrascoy Range with the Guadalentin Depression through high slope, short alluvial fans Upper-Middle Pleistocene in age. An outcrop in a quarry at the foot of this front reveals a progressive unconformity developed on these alluvial fan deposits, showing the important reverse component of the fault. The architecture of this unconformity is marked by well-developed calcretes on the top some of the alluvial deposits. We have determined the age of several of these calcretes by the Uranium-series disequilibrium dating method. The results obtained are consistent with recent published studies on the SW segment of the Carrascoy Fault that together with offset canals observed at a few locations suggest a net slip rate close to 1 m/ka.
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From Head to Sword: The Clustering Properties of Stars in Orion
NASA Astrophysics Data System (ADS)
Gomez, Mercedes; Lada, Charles J.
1998-04-01
We investigate the structure in the spatial distributions of optically selected samples of young stars in the Head (lambda Orionis) and in the Sword (Orion A) regions of the constellation of Orion with the aid of stellar surface density maps and the two-point angular correlation function. The distributions of young stars in both regions are found to be nonrandom and highly clustered. Stellar surface density maps reveal three distinct clusters in the lambda Ori region. The two-point correlation function displays significant features at angular scales that correspond to the radii and separations of the three clusters identified in the surface density maps. Most young stars in the lambda Ori region (~80%) are presently found within these three clusters, consistent with the idea that the majority of young stars in this region were formed in dense protostellar clusters that have significantly expanded since their formation. Over a scale of ~0.05d-0.5d the correlation function is well described by a single power law that increases smoothly with decreasing angular scale. This suggests that, within the clusters, the stars either are themselves hierarchically clustered or have a volume density distribution that falls steeply with radius. The relative lack of Hα emission-line stars in the one cluster in this region that contains OB stars suggests a timescale for emission-line activity of less than 4 Myr around late-type stars in the cluster and may indicate that the lifetimes of protoplanetary disks around young stellar objects are reduced in clusters containing O stars. The spatial distribution of young stars in the Orion A region is considerably more complex. The angular correlation function of the OB stars (which are mostly foreground to the Orion A molecular cloud) is very similar to that of the Hα stars (which are located mostly within the molecular cloud) and significantly different from that of the young stars in the lambda Ori region. This suggests that, although spatially separated, both populations in the Orion A region may have originated from a similar fragmentation process. Stellar surface density maps and modeling of the angular correlation function suggest that somewhat less than half of the OB and Hα stars in the Orion A cloud are presently within well-defined stellar clusters. Although all the OB stars could have originated in rich clusters, a significant fraction of the Hα stars appear to have formed outside such clusters in a more spatially dispersed manner. The close similarity of the angular correlation functions of the OB and Hα stars toward the molecular cloud, in conjunction with the earlier indications of a relatively high star formation rate and high gas pressure in this cloud, is consistent with the idea that older, foreground OB stars triggered the current episode of star formation in the Orion A cloud. One of the OB clusters (Upper Sword) that is foreground to the cloud does not appear to be associated with any of the clusterings of emission-line stars, again suggesting a timescale (<4 Myr) for emission-line activity and disk lifetimes around late-type stars born in OB clusters.
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NASA Astrophysics Data System (ADS)
Barrett, Samuel; Starnberger, Reinhard; Spötl, Christoph; Brauer, Achim; Tjallingii, Rik; Dulski, Peter; Abfalterer, Christof
2015-04-01
The sequence of pre-LGM lacustrine sediments at Baumkirchen (Austria) provides a key record in Alpine Quaternary stratigraphy. These sediments from within the boundary of the Alps potentially provide unique insights into the regional paleoclimate. Recent drilling revealed at least ~250m (the base was not reached) of almost entirely mm- to cm-scale lacustrine sediments. The laminated sediments are comprised of alternations between clayey silt and event layers of medium silt to fine sand. The sequence is interrupted only by a short section of gravel supported in an unlaminated clay-rich matrix. Optically stimulated luminescence dating identifies two distinct sequences: the upper sequence spanning mid-late Marine Isotope Stage (MIS) 3 (~33 to ~45 ka BP), agreeing with existing calibrated radiocarbon ages, and the lower section dating to MIS 4 (~59 to ~73 ka BP). Whether the hiatus is an erosional unconformity, or if the sequences represent two separate lake phases is unclear. Although the precise location of the hiatus is hard to identify, the gravel-rich section lies at the very top of the lower sequence. Pebbles in these gravels are largely angular and contain a significant proportion of non-local, regional lithologies. Such gravels are absent in the remainder of the entire 250 m-thick sequence and hence suggest a unique event rather than e.g. an interfingering local delta gravel foresets with the basin sediments. The gravels are therefore likely to be ice-rafted debris from icebergs from nearby glaciers calving into the lake. This therefore represents the first sedimentological evidence of a MIS 4 ice advance in the Eastern Alps. X-ray fluorescence analysis (ITRAX core scanning) of event layers indicates a strong change in the geochemical composition from generally K, Zr and Ti-rich layers in the upper sequence to mainly Ca and/or Si-rich layers in the lower sequence. X-ray diffraction analysis shows the Ca and Si signals to be controlled by carbonate (both calcite and dolomite) and quartz, respectively. This suggests a change in dominant sediment source and may indicate a change in catchment or paleolake configuration, re-raising the long outstanding question of how the lake or lakes were dammed.
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Early neogene history of the central American arc from Bocas del Toro, western Panama
Coates, Anthony G.; Aubry, Marie-Pierre; Berggren, William A.; Collins, Laurel S.; Kunk, Michael J.
2003-01-01
A newly discovered sequence of lower to middle Miocene rocks from the eastern Bocas del Toro archipelago, western Panama, reveals the timing and environment of the earliest stages in the rise of the Isthmus of Panama in this region. Two new formations, the Punta Alegre Formation (lower Miocene, Aquitanian to Burdigalian) and the Valiente Formation (middle Miocene, Langhian to Serravallian), are here named and formally described. The Punta Alegre Formation contains a diagnostic microfauna of benthic and planktic foraminifera and calcareous nannofossils that indicate deposition in a 2000-m-deep pre-isthmian neotropical ocean from as old as 21.5–18.3 Ma. Its lithology varies from silty mudstone to muddy foraminiferal ooze with rare thin microturbidite layers near the top. The Valiente Formation, which ranges in age from 16.4 to ca. 12.0 Ma, lies with slight angular unconformity on the Punta Alegre Formation and consists of five lithofacies: (1) columnar basalt and flow breccia, (2) pyroclastic deposits, (3) coarse-grained volcaniclastic deposits, (4) coral-reef limestone with diverse large coral colonies, and (5) marine debris-flow deposits and microturbidites. These lithofacies are interpreted to indicate that after ca. 16 Ma a volcanic arc developed in the region of Bocas del Toro and that by ca. 12 Ma an extensively emergent archipelago of volcanic islands had formed. 39Ar/40Ar dating of basalt flows associated with the fossiliferous sedimentary rocks in the upper part of the Valiente Formation strongly confirms the ages derived from planktic foraminifera and nannofossils. Paleobathymetric analysis of the two new formations in the Valiente Peninsula and Popa Island, in the Bocas del Toro archipelago, shows a general shallowing from lower- through upper-bathyal to upper-neritic and emergent laharic and fluviatile deposits from ca. 19 to 12 Ma. The overlying nonconformable Bocas del Toro Group contains a lower transgressive sequence ranging from basal nearshore sandstone to upper-bathyal mudstone (ca. 8.1–5.3 Ma) and an upper regressive sequence (5.3–3.5 Ma). A similar paleobathymetric pattern is observed from the Gatun to Chagres Formations (12–6 Ma) in the Panama Canal Basin area and in the Uscari, Rio Banana, Quebrada Chocolate, and Moin Formations (8–1.7 Ma) in the southern Limón Basin of Costa Rica.
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Atmospheric Science Data Center
2013-04-16
... of the region and can be used to understand the geophysical environment. The top panel shows the region from MISR's downward-looking ... angular reflectance properties help explain the geophysical environment. project: MISR category: gallery ...
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NASA Technical Reports Server (NTRS)
Joy, M.; Bilbro, J.; Elsner, R.; Jones, W.; Kolodziejczak, J.; Petruzzo, J.; ODell, S.; Weisskopf, M.
1997-01-01
The next generation of orbiting x-ray observatories will require high angular resolution telescopes that have an order of magnitude greater collecting area in the 0.1-10 keV spectral region than those currently under construction, but with a much lower weight and cost per unit area. Replicated Wolter-I x-ray optics have the potential to meet this requirement. The currently demonstrated capabilities of replicated Wolter-I optics will be described, and a development plan for creating lightweight, high angular resolution, large effective area x-ray telescopes will be presented.
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Long lasting paleolandscapes stability of the French Massif Central during the Mesozoic
NASA Astrophysics Data System (ADS)
Ricordel-Prognon, C.; Thiry, M.; Theveniaut, H.; Lagroix, F.
2009-04-01
Regional geodynamical evolution is mainly constrained by the sedimentary record in the basins. Usually, little is known about geodynamics of the peripheral areas and even less on the evolution of the basement areas. Continental unconformities are essential to estimate erosion rates of basement and to model the crustal dynamics that control subsidence of surrounding sedimentary basins but also uplift and erosion on their edges. Dating such unconformities has always been the stumbling block while it is a prerequisite to constrain geodynamical models. Paleomagnetism has been proven as a suitable tool to date ferrugineous paleoweathering features. The method has been applied to paleoweathering occurrences resting on the Massif Central crystalline basement as well as to paleoweathering features affecting the crystalline basement itself. The remanence measurements were obtained at the Paleomagnetic Laboratory of the Institut Physique du Globe de Paris and data analyses were carried out using PaleoMac 5 software (Cogné, 2003). Relative dating of the paleoweathering profiles have been acquired by comparing the recorded paleomagnetic poles from the analysed samples to the apparent polar wandering path of the Eurasian plate (Edel et Duringer, 1997 ; Besse and Courtillot, 2003). Thick red kaolinitic formations rest locally on the Massif Central basement. They are generally bounded by the Tertiary grabens and buried by the Oligocene formations. Thus these azoic red formations have classically been ascribed to the "Siderolithic" formations of Eocene-Oligocene age. They show many pedogenic features (termites burrows, illuviation and hydromorphic features and nodules) and strong relationships with paleolandscape organisation (leaned against fault scarps, infilling paleovalleys, etc.). Macro and micromorphological arrangements show that these formations are in situ paleosols. Paleomagnetic ages range from 160 Ma (Late Jurassic) in the centre of the Massif Central to 140 Ma (Early Cretaceous) in the northern parts of the massif (Ricordel et al., 2005; Ricordel, 2007;). These new ages, fairly older than the expected ones, bring considerable changes in the palaeogeographic evolution of the Massif Central during Mesozoic and Cenozoic. Basement rocks (granites, gneiss, rhyolites and even Permo-Carboniferous sediments) show often pinkish facies throughout the Massif Central. It has been shown that these pink facies are albitised (mainly pseudomorphic replacement of the primary plagioclases into albite and alteration of the biotite into chlorite) (Schmitt, 1992; Parcerisa et al., 2009). These albitised facies are arranged in a clear succession against (?) the Triassic unconformity that gives significant constraints about their development in relation with the Triassic palaeosurface. Secondary albite and chlorite contain minute hematite inclusions, which have been dated, using paleomagnetism, to be Triassic in age (245 Ma) (Ricordel et al., 2007). Given that the alterations are of the same age as the unconformity, it then follows that the albitised facies be related to the Triassic palaeosurface and be used to track back the Triassic palaeosurface through wide crystalline areas, even far away from the Mesozoic cover. Palaeomagnetic analyses allowed dating a large range of paleoweathering features for which no objective datings were previously available. Spatial and temporal distributions of the paleoweathering features and related unconformities provide key arguments to unravel the geodynamic evolution of the Massif Central. Triassic, Late Jurassic and Tertiary unconformities are superimposed on large areas of the Massif Centrall. This implies very little erosion of the crystalline basement since Triassic time, as shown by the widespread preservation of the Triassic albitized facies. Since the red kaolinitic paleosols of Late Jurassic/Early Cretaceous age rest directly on the basement rocks, large areas of the Massif Central were uncovered at this period, and more importantly no Jurassic cover was preserved (if such a cover was even deposited?) on the massif. Consequently, the Massif Central probably never did support an important (more than 500 m) sedimentary cover during the Mesozoic. These paleosurface ages provide important constraints to crustal dynamics modeling. Identification and dating of the successive continental unconformities are evidence for long lasting continental evolution and landscape stability of large areas of the Massif Central during the Mesozoic. The alternative hypothesis was that the Massif Central was subsidizing during Mesozoic time and covered with a 2,000 m thick sedimentary series, which was fairly quickly eroded during early Tertiary (Barbarand et al., 2001). In the future, making substantial progress in paleoweathering profiles dating, especially in the scope of improving time resolution, will allow attempting efficient correlation between the continental records and the diverse processes involved in their development (eustatism, climate, global and regional tectonics). Moreover, progress in dating paleoweathering features and continental azoic deposits, will allow to develop a "continental stratigraphy" of climatic and geomorphological events and to establish a mass balances between weathering/erosion weathering/erosion on land and deposition in basins. References Barbarand J., Lucazeau F., Pagel M., Séranne M., 2001, Burial and exhumation history of the south-eastern Massif Central (France) constrained by apatite fission track thermochronology. Tectonophysics, 335, 3-4, p. 275-290. Besse, J., Courtillot, V., 2003. Apparent true polar wander and the geometry of the geomagnetic field over the last 200 Myr: Correction: Journal of Geophysical Research, 108, p. 2300. Cogné, J.P., 2003. PaleoMac: a MacintoshTM application for treating paleomagnetic data and making plate reconstructions. Geochemistry Geophysics Geosystems, 4 (1), 1007. Edel J.B., Duringer P., 1997, The apparent polar wander path of the European plate in Upper Triassic-Lower Jurassic times and the Liassic intraplate fracturing of the Pangea : New palaeomagnetic constraints from NW France and SW Germany. Geophysical Journal International 128 (2), 331-344. Parcerisa D., Thiry M., Schmitt J.-M., 2009, Albitization related to the Triassic unconformity in igneous rocks of the Morvan Massif (France), International Journal of Earth Sciences, DOI: 10.1007/s00531-008-0405-1 Ricordel C, Parcerisa D, Thiry M, Moreau M-G, Gómez-Gras D (2007) Triassic magnetic overprints related to albitization in granites from the Morvan massif (France). Palaeogeogr Palaeoclimatol Palaeoecol 251: 268-282 Ricordel C. (2007) - Datations par paléomagnétisme des paléoaltérations du Massif central et de ses bordures : implications géodynamiques. Thèse Ecole Nat. Sup. Des Mines de Paris, Paris, 172 p. Ricordel C., Thiry M., Moreau M.-G., Théveniaut H. (2005) Paleomagnetic datings on "Siderolithic" paleoweathering profiles along French Massif Central. European Geosciences Union, Vienne, Autriche, 24-29 avril, Geophysical Research Abstracts, vol. 7, 06631, 6 p. Schmitt J.M. (1992) Triassic albitization in southern France: an unusual mineralogical record from a major continental paleosurface In: Schmitt JM, Gall Q (eds). Mineralogical and geochemical records of paleoweathering. Paris, ENSMP, Mem Sci Terre 18, pp 115-131
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Mechanisms underlying the perceived angular velocity of a rigidly rotating object.
Caplovitz, G P; Hsieh, P-J; Tse, P U
2006-09-01
The perceived angular velocity of an ellipse undergoing a constant rate of rotation will vary as its aspect ratio is changed. Specifically, a "fat" ellipse with a low aspect ratio will in general be perceived to rotate more slowly than a "thin" ellipse with a higher aspect ratio. Here we investigate this illusory underestimation of angular velocity in the domain where ellipses appear to be rotating rigidly. We characterize the relationship between aspect ratio and perceived angular velocity under luminance and non-luminance-defined conditions. The data are consistent with two hypotheses concerning the construction of rotational motion percepts. The first hypothesis is that perceived angular velocity is determined by low-level component-motion (i.e., motion-energy) signals computed along the ellipse's contour. The second hypothesis is that relative maxima of positive contour curvature are treated as non-component, form-based "trackable features" (TFs) that contribute to the visual system's construction of the motion percept. Our data suggest that perceived angular velocity is driven largely by component signals, but is modulated by the motion signals of trackable features, such as corners and regions of high contour curvature.
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Transverse angular momentum in topological photonic crystals
NASA Astrophysics Data System (ADS)
Deng, Wei-Min; Chen, Xiao-Dong; Zhao, Fu-Li; Dong, Jian-Wen
2018-01-01
Engineering local angular momentum of structured light fields in real space enables applications in many fields, in particular, the realization of unidirectional robust transport in topological photonic crystals with a non-trivial Berry vortex in momentum space. Here, we show transverse angular momentum modes in silicon topological photonic crystals when considering transverse electric polarization. Excited by a chiral external source with either transverse spin angular momentum or transverse phase vortex, robust light flow propagating along opposite directions is observed in several kinds of sharp-turn interfaces between two topologically-distinct silicon photonic crystals. A transverse orbital angular momentum mode with alternating phase vortex exists at the boundary of two such photonic crystals. In addition, unidirectional transport is robust to the working frequency even when the ring size or location of the pseudo-spin source varies in a certain range, leading to the superiority of the broadband photonic device. These findings enable one to make use of transverse angular momentum, a kind of degree of freedom, to achieve unidirectional robust transport in the telecom region and other potential applications in integrated photonic circuits, such as on-chip robust delay lines.
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NASA Technical Reports Server (NTRS)
Glikson, A. Y.
1986-01-01
The distribution patterns of mafic-ultramafic xenoliths within Archaean orthogneiss terrain furnish an essential key for the elucidation of granite-greenstone relations. Most greenstone belts constitute mega-xenoliths rather than primary basin structures. Transition along strike and across strike between stratigraphically low greenstone sequences and xenolith chains demonstrate their contemporaneity. These terrains represent least deformed cratonic islands within an otherwise penetratively foliated deformed gneiss-greenstone crust. Whereas early greenstone sequences are invariably intruded by tonalitic/trondhjemitic/granodioritic gneisses, stratigraphically higher successions may locally overlap older gneiss terrains and their entrained xenoliths unconformably. The contiguity of xenolith patterns suggests their derivation as relics of regional mafic-ultramafic volcanic crustal units and places limits on horizontal movements between individual crustal blocks.
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U.s. Geological survey core drilling on the atlantic shelf.
Hathaway, J C; Poag, C W; Valentine, P C; Manheim, F T; Kohout, F A; Bothner, M H; Miller, R E; Schultz, D M; Sangrey, D A
1979-11-02
The first broad program of scientific shallow drilling on the U.S. Atlantic continental shelf has delineated rocks of Pleistocene to Late Cretaceous age, including phosphoritic Miocene strata, widespread Eocene carbonate deposits that serve as reflective seismic markers, and several regional unconformities. Two sites, off Maryland and New Jersey, showed light hydrocarbon gases having affinity to mature petroleum. Pore fluid studies showed that relatively fresh to brackish water occurs beneath much of the Atlantic continental shelf, whereas increases in salinity off Georgla and beneath the Florida-Hatteras slope suggest buried evaporitic strata. The sediment cores showed engineering properties that range from good foundation strength to a potential for severe loss of strength through interaction between sediments and man-made structures.
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Ring structure in the HII region of NGC 5930
NASA Astrophysics Data System (ADS)
Su, Bu-Mei; Mutel, R. L.; Zhang, Fu-Jing; Li, Yong-Sheng
1992-03-01
Radio continuous observations of the barred spiral galaxy NGC5930 at 2- and 3.6-cm wavelengths have been carried out with the VLA. It has been found that at 2 cm the HII region appears to be a ring structure on which hot spots are distributed. The outer angular diameter of the ring is 2.2 arcsec, and the inner angular diameter - 0.3 arcsec. The center is a hole from which no radio emission has been detected. The electron density in the HII region is 80 - 90 cu cm, and its mass is 10 exp 7 solar mass units. In NGC 5930 there is very strong infrared radiation. The infrared luminosity is 10 exp 6 times larger than the radio luminosity. There is a steep Balmer attenuation. This is a region where a star is being formed violently.
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Angular momentum of dwarf galaxies
NASA Astrophysics Data System (ADS)
Kurapati, Sushma; Chengalur, Jayaram N.; Pustilnik, Simon; Kamphuis, Peter
2018-05-01
Mass and specific angular momentum are two fundamental physical parameters of galaxies. We present measurements of the baryonic mass and specific angular momentum of 11 void dwarf galaxies derived from neutral hydrogen (HI) synthesis data. Rotation curves were measured using 3D and 2D tilted ring fitting routines, and the derived curves generally overlap within the error bars, except in the central regions where, as expected, the 3D routines give steeper curves. The specific angular momentum of void dwarfs is found to be high compared to an extrapolation of the trends seen for higher mass bulge-less spirals, but comparable to that of other dwarf irregular galaxies that lie outside of voids. As such, our data show no evidence for a dependence of the specific angular momentum on the large scale environment. Combining our data with the data from the literature, we find a baryonic threshold of ˜109.1 M⊙ for this increase in specific angular momentum. Interestingly, this threshold is very similar to the mass threshold below which the galaxy discs start to become systematically thicker. This provides qualitative support to the suggestion that the thickening of the discs, as well as the increase in specific angular momentum, are both results of a common physical mechanism, such as feedback from star formation. Quantitatively, however, the amount of star formation observed in our dwarfs appears insufficient to produce the observed increase in specific angular momentum. It is hence likely that other processes, such as cold accretion of high angular momentum gas, also play a role in increasing the specific angular momentum.
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Exceptional marine sand bodies in the Paleozoic of Oklahoma
DOE Office of Scientific and Technical Information (OSTI.GOV)
Fritz, R.D.; Kuykendall, M.D.; Hooker, E.O.
Of the wide variety of sandstone reservoirs in Oklahoma, the most unusual types of sand bodies are present in the Atokan Spiro Sandstone, Devonian Misener Sandstone, and Morrowan lower Morrow Sandstone. The common factors are that upon correlation and mapping these units are channel-like (fluvial-deltaic) in geometry, but from petrographic evidence are quartz-rich shallow-marine units, with the exclusion of intraclastic and diagenetic constituents. Stratigraphic mapping of the Spiro Sandstone of the Arkoma basin indicates two types of sand bodies: channel and sheet. The marine channel-like deposits, 10-150 ft thick, probably were deposited on a paleosurface produced by a pre-Atokan unconformity.more » Examination of cores and outcrop indicate that both the channel and sheet Spiro sands contain shallow-marine fossils, limestones, peloidal chamosite, burrows, and bioturbation, all indicative of a shallow-marine setting. The Misener Sandstone of north-central Oklahoma ranges from 10 to 100 ft thick with sharp boundaries. It was deposited in pre-Frisco/Woodford eroded paleochannels. Core evidence for shallow-marine deposition is glauconite, phosphatic fossils and clasts, burrows, and bioturbation. These were probably deposited in an embayed, estuary-like environment. The lower Morrow Sandstone of the Anadarko basin is similar in geometry, except that the sand bodies are multistoried and multilateral and do not appear to be associated with a regional unconformity. The lower Morrow sandstones, usually 30-60 ft thick. commonly are elongated and deposited parallel to the shoreline. Deposition is inferred to be shallow-marine from marine fossils and glauconite.« less
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Poag, C.W.; Commeau, J.A.
1995-01-01
The Paleocene to Middle Miocene sedimentary fill of the southwestern Salisbury Embayment contains a fragmental depositional record, interrupted by numerous local diastems and regional unconformities. Using planktic foraminiferal biostratigraphy, 15 unconformity-bounded depositional units have been identified, assigned to six formations and seven alloformations previously recognized in the embayment. The units correlate with second- and third-order sequences of the Exxon sequence stratigraphy model, and include transgressive and highstand systems tracts. Alloformation, formation, and sequence boundaries are marked by abrupt, scoured, burrowed, erosional surfaces, which display lag deposits, biostratigraphic gaps, and intense reworking of microfossils above and below the boundaries.Paleocene deposits represent the upper parts of upper Pleocene Biochronozones P4 and P5, and rest uncomformably on Cretaceous sedimentary beds of various ages (Maastrichtian to Albian). Lower Eocene deposits represent parts of Biochronozones P6 and P9. Middle Eocene strata represent mainly parts of Biochronozones P11, P12, and P14. Upper Eocene sediments include parts of Biochronozones P15, P16, and P17. Oligocene deposits encompass parts of Biochronozones. N4b to N7 undifferentiated, P21a, and, perhaps, N4a. Lower Miocene deposits encompass parts of Biochronozones N4b to N7 undifferentiated. Middle Miocene strata represent mainly parts of Biochronorones N8, N9, and N10.Nine plates of scanning electron micrographs illustrate the principal planktic foraminifera used to establish the biostratigraphic framework. Two new informal formine of Praeterenuitella praegemma Li, 1987, are introduced.
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Overlapping inflow events as catalysts for supermassive black hole growth
NASA Astrophysics Data System (ADS)
Carmona-Loaiza, Juan M.; Colpi, Monica; Dotti, Massimo; Valdarnini, Riccardo
2014-02-01
One of the greatest issues in modelling black hole fuelling is our lack of understanding of the processes by which gas loses angular momentum and falls from galactic scales down to the nuclear region where an accretion disc forms, subsequently guiding the inflow of gas down to the black hole horizon. It is feared that gas at larger scales might still retain enough angular momentum and settle into a larger scale disc with very low or no inflow to form or replenish the inner accretion disc (on ˜0.01 pc scales). In this paper we report on hydrodynamical simulations of rotating infalling gas shells impacting at different angles on to a pre-existing, primitive large-scale (˜10 pc) disc around a supermassive black hole. The aim is to explore how the interaction between the shell and the disc redistributes the angular momentum on scales close to the black hole's sphere of influence. Angular momentum redistribution via hydrodynamical shocks leads to inflows of gas across the inner boundary, enhancing the inflow rate by more than 2-3 orders of magnitude. In all cases, the gas inflow rate across the inner parsec is higher than in the absence of the interaction, and the orientation of the angular momentum of the flow in the region changes with time due to gas mixing. Warped discs or nested misaligned rings form depending on the angular momentum content of the infalling shell relative to the disc. In the cases in which the shell falls in near counter-rotation, part of the resulting flows settle into an inner dense disc which becomes more susceptible to mass transfer.
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USDA-ARS?s Scientific Manuscript database
Rust, Anthracnose, and angular leaf spot are major diseases of common bean in the world and most particularly in the Americas and Africa, which are the largest common bean production regions of the world. The Mesoamerican black-seeded cultivar Ouro Negro is unusual in that it has resistance to all t...
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NASA Astrophysics Data System (ADS)
Sheldon, Dane P. H.
Seismic stratigraphy, sedimentology, lithostratigraphy, downhole geophysical logging, mineralogy, and palynology were used to study and interpret the upper 70 meters of the inner continental shelf sediments within a proposed wind farm site located approximately two to three nautical miles to the southeast of Block Island, Rhode Island. Core samples and downhole logging collected from borings drilled for geotechnical purposes at proposed wind turbine sites along with seismic surveys in the surrounding area provide the data for this study. Cretaceous coastal plain sediments that consist of non-marine to marine sand, silt, and clay are found overlying bedrock at a contact depth beyond the sampling depth of this study. The upper Cretaceous sediments sampled in borings are correlated with the Magothy/Matawan formations described regionally from New Jersey to Nantucket. An unconformity formed through sub-aerial, fluvial, marine, and glacial erosion marks the upper strata of the Cretaceous sediments separating them from the overlying deposits. The majority of Quaternary deposits overlying the unconformity represent the advance, pulsing, and retreat of the Laurentide ice sheet that reached its southern terminus in the area of Block Island approximately 25,000 to 21,000 years before present. The sequence consists of a basal glacial till overlain by sediments deposited by meltwater environments ranging from deltaic to proglacial lakefloor. A late Pleistocene to early Holocene unconformity marks the top of the glacial sequence and was formed after glacial retreat through fluvial and subaerial erosion/deposition. Overlying the glacial sequence are sediments deposited during the late Pleistocene and Holocene consisting of interbedded gravel, sand, silt, and clay. Sampling of these sediments was limited and surficial reflectors in seismic profiles were masked due to a hard bottom return. However, two depositional periods are interpreted as representing fluvial and estuarine/marine environments respectively. One sample recovered at five meters contained shell fragments within a gray fine to coarse sand possibly representing a shallow estuarine to marine environment. A coarse near surface deposit described but not recovered in all borings may represent a transgressive unconformity and resulting lag deposit however due to lack of sampling and seismic resolution in the upper 5 meters, the nature of this deposit is merely speculation. In areas where depth to the glacial surface increased, sediments ranging from sand to fine-grained silt and clay were encountered in borings. In summary, the upper 70 meters of the inner continental shelf section within the study site consists of unconsolidated sediments spanning three major depositional periods. Sediments derived from glacial activity represent the bulk of samples collected. The glacial sequences represent various depositional environments, although most samples are interpreted to be the product of glacial meltwater deposition with distribution determined by source as well as highs and lows present in the antecedent topography. Finely laminated (varved) sediment to the south of Block Island indicates the presence of proglacial lakes in the area during the time of glacial retreat. Overlying sediments represent environments ranging from fluvial to marine.
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NASA Astrophysics Data System (ADS)
Black, C. J.; Whitesides, A. S.; Anderson, J. L.; Culbert, K. N.; Vandeveer, M.; Cox, I. V.; Cardamone, J.; Torrez, G.; Quirk, M.; Memeti, V.; Cao, W.; Paterson, S. R.
2010-12-01
Field mapping in the Northern Ritter Range pendant, central Sierra Nevada reveals four different lithotectonic units. Unit 1, east of Gem Lake, consists of Paleozoic passive margin metasedimentary rocks. Unit 2 lies unconformably above and west and is composed of Late Triassic to Middle Jurassic rhyolitic to andesitic, clast-rich, metavolcanic rocks that are typically massive, thick bedded, relatively homogeneous. Breccias and millimeter sized plagioclase phenocrysts are common in these beds. Unit 3 west of and structurally higher than unit 2 and is composed of thinly bedded metavolcanic and metasedimentary rocks of same age. Unit 2 and Unit 3 both steeply dipping and NW striking bedding and bedding parallel foliations. Unit 4 is composed of less deformed, Cretaceous, rhyolitic to andesitic breccias and rare volcaniclastic units that are west of and unconformably above unit 3. All units are now separated by faults. The Cretaceous dextral, oblique Gem Lake shear zone reactivated the uncomformity between units 1 and 2. West of the shear zone, both the shearing and strain intensity gradually decrease, the later from >60% to 40% shortening. Unit 2 and 3 are separated by a thrust fault, with local pseudotachelite now overprinted by ductile deformation. Unit 3 and 4 are now juxtaposed along a deformed unconformity west of which strain decreases to shortening values > 30%. These host rocks are intruded by granitic to dioritic plutons preserving a wide range of internal characteristics and emplacement styles. The oldest pluton is the 100 Ma Rush Creek Granodiorite, which intruded into unit 2. The Kuna Crest (KC, 94.6 Ma), the Waugh Lake (WL, 93.6 Ma), and the Thousand Island Lake leucogranodiorites (TIL) (~94 Ma) all intrude into the unit 3. The TIL cut the unconformity between units 3 and 4. The WL pluton is possibly cut by movement between units 2 and 3. The typically NW striking steeply dipping bedding in host rock units is dramatically deflected to EW orientations along the SW margin of the KC lobe. Within the nearby WL Granodiorite, hundreds of andesitic host rock blocks, some up to hundred meter lengths suggest that stoping was an important emplacement process. Migmatitic zones occur along several pluton margins. Our observations are consistent with aspects of the Tobisch et al. (2000) paper suggesting early brittle thrusting led to rotation of beds to steep dips. However our results indicate that beds were already at near vertical dips prior to ductile shortening and well before pluton emplacement. And although regional downward flow of extrusive volcanics has certainly occurred we see evidence against previous suggestions that this downward flow was localized in pluton aureoles as plutons typically cut discordantly across already steeply dipping beds and in turn are deformed by the younger ductile deformation. Although ductile shortening may play a minor role in rotation of beds, much of the ductile deformation had to occur after beds were steeply dipping as the 100-93.5 m.y. plutons have fabrics that are continuous with ductile deformation in the host rocks.
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Petroleum geology of Cook Inlet basin - an exploration model
Magoon, L.B.; Claypool, G.E.
1981-01-01
Oil exploration commenced onshore adjacent to lower Cook Inlet on the Iniskin Peninsula in 1900, shifted with considerable success to upper Cook Inlet from 1957 through 1965, then returned to lower Cook Inlet in 1977 with the COST well and Federal OCS sale. Lower Cook Inlet COST No. 1 well, drilled to a total depth of 3,775.6 m, penetrated basinwide unconformities at the tops of Upper Cretaceous, Lower Cretaceous, and Upper Jurassic strata at 797.1, 1,540.8, and 2,112.3 m, respectively. Sandstone of potential reservoir quality is present in the Cretaceous and lower Tertiary rocks. All siltstones and shales analyzed are low (0 to 0.5 wt. %) in oil-prone organic matter, and only coals are high in humic organic matter. At total depth, vitrinite readings reached a maximum ave age reflectance of 0.65. Several indications of hydrocarbons were present. Oil analyses suggest that oils from the major fields of the Cook Inlet region, most of which produce from the Tertiary Hemlock Conglomerate, have a common source. More detailed work on stable carbon isotope ratios and the distribution of gasoline-range and heavy (C12+) hydrocarbons confirms this genetic relation among the major fields. In addition, oils from Jurassic rocks under the Iniskin Peninsula and from the Hemlock Conglomerate at the southwestern tip of the Kenai lowland are members of the same or a very similar oil family. The Middle Jurassic strata of the Iniskin Peninsula are moderately rich in organic carbon (0.5 to 1.5 wt. %) and yield shows of oil and of gas in wells and in surface seeps. Extractable hydrocarbons from this strata are similar in chemi al and isotopic composition to the Cook Inlet oils. Organic matter in Cretaceous and Tertiary rocks is thermally immature in all wells analyzed. Oil reservoirs in the major producing fields are of Tertiary age and unconformably overlie Jurassic rocks; the pre-Tertiary unconformity may be significant in exploration for new oil reserves. The unconformable relation between reservoir rocks and likely Middle Jurassic source rocks also implies a delay in the generation and expulsion of oil from Jurassic until late Tertiary when localized basin subsidence and thick sedimentary fill brought older, deeper rocks to the temperature required for petroleum generation. Reservoir porosities, crude oil properties, the type of oil field traps, and the tectonic framework of the oil fields on the west flank of the basin provide evidence used to reconstruct an oil migration route. The route is inferred to commence deep in the truncated Middle Jur ssic rocks and pass through the porous West Foreland Formation in the McArthur River field area to a stratigraphic trap in the Oligocene Hemlock Conglomerate and the Oligocene part of the Tyonek Formation at the end of Miocene time. Pliocene deformation shut off this route and created localized structural traps, into which the oil moved by secondary migration to form the Middle Ground Shoal, McArthur River, and Trading Bay oil fields. Oil generation continued into the Pliocene, but this higher API gravity oil migrated along a different route to the Granite Point field.
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Radiation physics and modelling for off-nadir satellite-sensing of non-Lambertian surfaces
NASA Technical Reports Server (NTRS)
Gerstl, S. A.; Simmer, C.
1986-01-01
The primary objective of this paper is to provide a deeper understanding of the physics of satellite remote-sensing when off-nadir observations are considered. Emphasis is placed on the analysis and modeling of atmospheric effects and the radiative transfer of non-Lambertian surface reflectance characteristics from ground-level to satellite locations. The relative importance of spectral, spatial, angular, and temporal reflectance characteristics for satellite-sensed identification of vegetation types in the visible and near-infrared wavelength regions is evaluated. The highest identification value is attributed to angular reflectance signatures. Using radiative transfer calculations to evaluate the atmospheric effects on angular reflectance distributions of vegetation surfaces, atmosphere-invariant angular reflectance features such as the 'hot spot' and the 'persistent valley' are identified. A new atmospheric correction formalism for complete angular reflectance distributions is described. A sample calculation demonstrates that a highly non-Lambertian measured surface reflectance distribution can be retrieved from simulated satellite data in the visible and near infrared to within about 20 percent accuracy for almost all view directions up to 60 deg off-nadir. Thus the high value of angular surface reflectance characteristics (the 'angular signature') for satellite-sensed feature identification is confirmed, which provides a scientific basis for future off-nadir satellite observations.
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NASA Astrophysics Data System (ADS)
Sugimura, Kazuyuki; Hosokawa, Takashi; Yajima, Hidenobu; Inayoshi, Kohei; Omukai, Kazuyuki
2018-05-01
Accretion on to seed black holes (BHs) is believed to play a crucial role in formation of supermassive BHs observed at high-redshift (z > 6). Here, we investigate the combined effect of gas angular momentum and radiation feedback on the accretion flow, by performing 2D axially symmetric radiation hydrodynamics simulations that solve the flow structure across the Bondi radius and the outer part of the accretion disc simultaneously. The accreting gas with finite angular momentum forms a rotationally-supported disc inside the Bondi radius, where the accretion proceeds by the angular momentum transport due to assumed α-type viscosity. We find that the interplay of radiation and angular momentum significantly suppresses accretion even if the radiative feedback is weakened in an equatorial shadowing region. The accretion rate is O(α) ˜ O(0.01 - 0.1) times the Bondi value, where α is the viscosity parameter. By developing an analytical model, we show that such a great reduction of the accretion rate persists unless the angular momentum is so small that the corresponding centrifugal radius is ≲ 0.04 times the Bondi radius. We argue that BHs are hard to grow quickly via rapid mass accretion considering the angular momentum barrier presented in this paper.
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Satellite angular velocity estimation based on star images and optical flow techniques.
Fasano, Giancarmine; Rufino, Giancarlo; Accardo, Domenico; Grassi, Michele
2013-09-25
An optical flow-based technique is proposed to estimate spacecraft angular velocity based on sequences of star-field images. It does not require star identification and can be thus used to also deliver angular rate information when attitude determination is not possible, as during platform de tumbling or slewing. Region-based optical flow calculation is carried out on successive star images preprocessed to remove background. Sensor calibration parameters, Poisson equation, and a least-squares method are then used to estimate the angular velocity vector components in the sensor rotating frame. A theoretical error budget is developed to estimate the expected angular rate accuracy as a function of camera parameters and star distribution in the field of view. The effectiveness of the proposed technique is tested by using star field scenes generated by a hardware-in-the-loop testing facility and acquired by a commercial-off-the shelf camera sensor. Simulated cases comprise rotations at different rates. Experimental results are presented which are consistent with theoretical estimates. In particular, very accurate angular velocity estimates are generated at lower slew rates, while in all cases the achievable accuracy in the estimation of the angular velocity component along boresight is about one order of magnitude worse than the other two components.
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Satellite Angular Velocity Estimation Based on Star Images and Optical Flow Techniques
Fasano, Giancarmine; Rufino, Giancarlo; Accardo, Domenico; Grassi, Michele
2013-01-01
An optical flow-based technique is proposed to estimate spacecraft angular velocity based on sequences of star-field images. It does not require star identification and can be thus used to also deliver angular rate information when attitude determination is not possible, as during platform de tumbling or slewing. Region-based optical flow calculation is carried out on successive star images preprocessed to remove background. Sensor calibration parameters, Poisson equation, and a least-squares method are then used to estimate the angular velocity vector components in the sensor rotating frame. A theoretical error budget is developed to estimate the expected angular rate accuracy as a function of camera parameters and star distribution in the field of view. The effectiveness of the proposed technique is tested by using star field scenes generated by a hardware-in-the-loop testing facility and acquired by a commercial-off-the shelf camera sensor. Simulated cases comprise rotations at different rates. Experimental results are presented which are consistent with theoretical estimates. In particular, very accurate angular velocity estimates are generated at lower slew rates, while in all cases the achievable accuracy in the estimation of the angular velocity component along boresight is about one order of magnitude worse than the other two components. PMID:24072023
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Assunção, Wirley Gonçalves; Gomes, Erica Alves; Rocha, Eduardo Passos; Delben, Juliana Aparecida
2011-01-01
Three-dimensional finite element analysis was used to evaluate the effect of vertical and angular misfit in three-piece implant-supported screw-retained fixed prostheses on the biomechanical response in the peri-implant bone, implants, and prosthetic components. Four three-dimensional models were fabricated to represent a right posterior mandibular section with one implant in the region of the second premolar (2PM) and another in the region of the second molar (2M). The implants were splinted by a three-piece implant-supported metal-ceramic prosthesis and differed according to the type of misfit, as represented by four different models: Control = prosthesis with complete fit to the implants; UAM (unilateral angular misfit) = prosthesis presenting unilateral angular misfit of 100 μm in the mesial region of the 2M; UVM (unilateral vertical misfit) = prosthesis presenting unilateral vertical misfit of 100 μm in the mesial region of the 2M; and TVM (total vertical misfit) = prosthesis presenting total vertical misfit of 100 μm in the platform of the framework in the 2M. A vertical load of 400 N was distributed and applied on 12 centric points by the software Ansys, ie, a vertical load of 150 N was applied to each molar in the prosthesis and a vertical load of 100 N was applied at the 2PM. The stress values and distribution in peri-implant bone tissue were similar for all groups. The models with misfit exhibited different distribution patterns and increased stress magnitude in comparison to the control. The highest stress values in group UAM were observed in the implant body and retention screw. The groups UVM and TVM exhibited high stress values in the platform of the framework and the implant hexagon, respectively. The three types of misfit influenced the magnitude and distribution of stresses. The influence of misfit on peri-implant bone tissue was modest. Each type of misfit increased the stress values in different regions of the system.
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DOE Office of Scientific and Technical Information (OSTI.GOV)
Lovekin, J.R.; Odland, S.K.; Quartarone, T.S. Gardner, M.H.
1986-08-01
Stratigraphic traps account for most of the oil produced from the Muddy Sandstone in the northern Powder River basin. Two categories of traps exist. The first trap type is the result of lateral and vertical facies changes. Reservoir facies include tidal channels, point bars, bayhead deltas, barrier islands, and strand-plain sandstones; trapping facies include bay-fill and estuarine sediments, mud-filled tidal channels, and flood-plain deposits. The second of the two categories of traps results from an unconformity that juxtaposes permeable and impermeable sediments of quite different ages. Structural and diagenetic factors often modify and locally enhance reservoir quality within both categoriesmore » of stratigraphic traps. The various types of traps are demonstrated by studies of six field areas: (1) barrier-island sandstones, sealed updip by back-barrier shales, produce at Ute and Kitty fields; (2) tidal channels produce at Collums and Kitty fields; (3) bayhead deltas, encased in estuarine sediments, form traps at Oedekoven and Kitty fields; (4) fluvial point-bar sandstones form traps at Oedekoven, Store, and Kitty fields; (5) unconformity-related traps exist where Muddy fluvial valley-fill sediments lap out against impermeable valley walls of Skull Creek Shale on the updip side at Store, Oedekoven, and Kitty fields; and (6) the clay-rich weathered zone, directly beneath an intraformational unconformity, forms the seal to the reservoirs at Amos Draw field.« less
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Restoring the spatial resolution of refocus images on 4D light field
NASA Astrophysics Data System (ADS)
Lim, JaeGuyn; Park, ByungKwan; Kang, JooYoung; Lee, SeongDeok
2010-01-01
This paper presents the method for generating a refocus image with restored spatial resolution on a plenoptic camera, which functions controlling the depth of field after capturing one image unlike a traditional camera. It is generally known that the camera captures 4D light field (angular and spatial information of light) within a limited 2D sensor and results in reducing 2D spatial resolution due to inevitable 2D angular data. That's the reason why a refocus image is composed of a low spatial resolution compared with 2D sensor. However, it has recently been known that angular data contain sub-pixel spatial information such that the spatial resolution of 4D light field can be increased. We exploit the fact for improving the spatial resolution of a refocus image. We have experimentally scrutinized that the spatial information is different according to the depth of objects from a camera. So, from the selection of refocused regions (corresponding depth), we use corresponding pre-estimated sub-pixel spatial information for reconstructing spatial resolution of the regions. Meanwhile other regions maintain out-of-focus. Our experimental results show the effect of this proposed method compared to existing method.
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SCATTERING OF NEUTRONS BY $alpha$-PARTICLES AT 14.1 Mev
DOE Office of Scientific and Technical Information (OSTI.GOV)
Fasoli, U.; Zago, G.
1963-12-01
The angular distribution of 14.1-Mev neutrons elastically scattered by alpha particles was measured by observing the alpha recoils in a helium-filled cloud chamber. The results are in satisfactory agreement with those previously obtained by others. Inspection of the small-angle region of the measured distribution shows that phase shifts of orbital angular momentum higher than L = 1 are not negligible, although, according to the present experiment, quantitative information on D-waves turns out to be somewhat elusive. The azimuthal angular distribution agrees well with the value P = 0.02 of the neutron beam polarization, as measured by Perkins. (auth)
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Moon-based visibility analysis for the observation of “The Belt and Road”
NASA Astrophysics Data System (ADS)
REN, Yuanzhen; GUO, Huadong; LIU, Guang; YE, Hanlin; DING, Yixing; RUAN, Zhixing; LV, Mingyang
2016-11-01
Aiming at promoting the economic prosperity and regional economic cooperation, the “Silk Road Economic Belt” and the “21st Century Maritime Silk Road” (hereinafter referred to as the Belt and Road) was raised. To get a better understanding of “the Belt and Road” whole region, considering the large-scale characteristic, the Moon platform is a good choice. In this paper, the ephemeris is taken as data source and the positions and attitudes of Sun, Earth and Moon are obtained based on the reference systems transformation. Then we construct a simplified observation model and calculate the spatial and angular visibility of the Moon platform for “the Belt and Road” region. It turns out that Moon-based observation of this region shows a good performance of spatial visibility and variable angular visibility, indicating the Moon being a new potential platform for large-scale Earth observation.
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Iwahashi, Toshihiko; Ogawa, Makoto; Hosokawa, Kiyohito; Kato, Chieri; Inohara, Hidenori
2016-11-01
To assess the angular velocity between the vocal folds just before the compression phase of throat clearing (TC) using high-speed digital imaging (HSDI) of the larynx. Twenty normal healthy adults (13 males and seven females) were enrolled in the study. Each participant underwent transnasal laryngo-fiberscopy, and was asked to perform weak/strong TC followed by a comfortable, sustained vowel phonation while recording an HSDI movie (4000 frames/s) of the larynx. Using a motion analysis, the changes in the vocal fold angle and angular velocity during vocal fold adduction were assessed. Subsequently, we calculated the average angular velocities in the ranges of 100-80%, 80-20%, and 20-0% from all of the angular changes. The motion analysis demonstrated that the changes in the angular velocity resulted in polynomial-like and sigmoid curves during TC and vowel phonation, respectively. The angular velocities during weak TC were significantly higher in the 20-0%, 80-20%, and 100-80% regions (in order); the 80-20% angular velocity in vocal fold adduction during phonation was highest. The 20-0% angular velocity during strong TC was more than twofold higher than 20-0% angular velocity during phonation. The present results confirmed that the closing motions of the vocal folds accelerate throughout the precompression closing phase of a TC episode, and decelerate just before the impact between the vocal folds at the onset of phonation, suggesting that the vocal fold velocity generated by TC is sufficient to damage the laryngeal tissues. Copyright © 2016 The Voice Foundation. Published by Elsevier Inc. All rights reserved.
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Development of a high angular resolution diffusion imaging human brain template.
Varentsova, Anna; Zhang, Shengwei; Arfanakis, Konstantinos
2014-05-01
Brain diffusion templates contain rich information about the microstructure of the brain, and are used as references in spatial normalization or in the development of brain atlases. The accuracy of diffusion templates constructed based on the diffusion tensor (DT) model is limited in regions with complex neuronal micro-architecture. High angular resolution diffusion imaging (HARDI) overcomes limitations of the DT model and is capable of resolving intravoxel heterogeneity. However, when HARDI is combined with multiple-shot sequences to minimize image artifacts, the scan time becomes inappropriate for human brain imaging. In this work, an artifact-free HARDI template of the human brain was developed from low angular resolution multiple-shot diffusion data. The resulting HARDI template was produced in ICBM-152 space based on Turboprop diffusion data, was shown to resolve complex neuronal micro-architecture in regions with intravoxel heterogeneity, and contained fiber orientation information consistent with known human brain anatomy. Copyright © 2014 Elsevier Inc. All rights reserved.
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Formation of the Shelf-edge Cretaceous-Tertiary contact off the southeastern U.S. Coast
Poppe, L.J.; Hathaway, J.C.; Hall, R.E.; Commeau, R.F.
1986-01-01
Submarine erosion, associated with changes in position of the proto-Gulf Stream, was the dominant mechanism controlling the formation of the Cretaceous-Tertiary unconformity in AMCOR borehole 6004. Paleontologic evidence indicates that this unconformity, which is marked by a gravelly-sand enriched in glauconitic and phosphoritic concretions, represents a hiatus of about 7 m.y. Both Cretaceous and Paleocene sediments contain middle-outer neritic foraminiferal assemblages that become more diverse with distance from the contact. Of the elemental abundances measured, Al, Ba, Co, Fe, Ga, K, Mg/Ca, Mo, Ni, P, Sr/Ca, V, Y, and Zn show a strong positive correlation with proximity to the contact, probably as a result of the concentration of authigenic and heavy minerals present as lag sediments on the erosion surface. ?? 1986.
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DOE Office of Scientific and Technical Information (OSTI.GOV)
Witzke, B.J.
1993-03-01
Four large-scale (2--8 Ma) T-R sedimentary sequences of M. Ord. age (late Chaz.-Sherm.) were delimited by Witzke Kolata (1980) in the Iowa area, each bounded by local to regional unconformity/disconformity surfaces. These encompass both siliciclastic and carbonate intervals, in ascending order: (1) St. Peter-Glenwood fms., (2) Platteville Fm., (3) Decorah Fm., (4) Dunleith/upper Decorah fms. Finer-scale resolution of depth-related depositional features has led to regional recognition of smaller-scale shallowing-upward cyclicity contained within each large-scale sequence. Such smaller-scale cyclicity encompasses stratigraphic intervals of 1--10 m thickness, with estimated durations of 0.5--1.5 Ma. The St. Peter Sandst. has long been regarded asmore » a classic transgressive sheet sand. However, four discrete shallowing-upward packages characterize the St. Peter-Glenwood interval regionally (IA, MN, NB, KS), including western facies displaying coarsening-upward sandstone packages with condensed conodont-rich brown shale and phosphatic sediments in their lower part (local oolitic ironstone), commonly above pyritic hardgrounds. Regional continuity of small-scale cyclic patterns in M. Ord. strata of the Iowa area may suggest eustatic controls; this can be tested through inter-regional comparisons.« less
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NASA Astrophysics Data System (ADS)
Smith, W. H.; Grall, C.; Sorlien, C. C.; Steckler, M. S.; Okay, S.; Cormier, M. H.; Seeber, L.; Cifci, G.; Dondurur, D.
2016-12-01
The submerged section of the North Anatolian Fault in the Sea of Marmara, which corresponds to the dextral plate boundary between Eurasia and Anatolia, poses strong hazard for earthquakes and subsequent submarine landslides and tsunamis in the vicinity of the highly populated region of Istanbul. Most of the right-lateral slip is accommodated by the Northern Branch of the North Anatolian Fault (NAF-N), which crosses the central part of the Sea of Marmara and is capable of an earthquake with a magnitude greater than 7. However, both the geology and the geodesy suggest that the NAF-N accommodates only 3/4 of the total slip between the plates. The deformation mechanisms for the rest of the strain (slip distributed on secondary faults, strain partitioning, and diffuse deformation) remains unexplained. Other fault systems, primarily south of the NAF-N, are shown to be important regarding the tectonic evolution of the Sea of Marmara. However, the activity of these peripheral fault systems as well as their relationships with the NAF-N need to be further constrained. For this purpose, a dense dataset of 2D geophysical images (high-resolution seismic reflection data, sparker reflection, CHIRP sub-bottom profiling), as well as multibeam bathymetry, have been acquired in 2008, 2010, 2013 and 2014 during TAMAM and SOMAR cruises, primarily in the southern shelf of the Sea of Marmara. The 15-20 km-wide southern shelf ledge is relatively flat and mostly shallower than 90 m. In this shallow marine region, we have been able to image the detailed stratigraphic record associated with the 125 ka and younger glacio-eustatic cycles and, notably, to identify paleo-shorelines at water depths shallower than 100 m. Several erosional unconformities, laterally correlative to low-stand deltas have been regionally linked to the stratigraphic boundaries previously defined for the last 130-540 ka. While the present-day shelf is relatively flat, a shallow ridge separates the inner and outer parts of the shelf. This ridge exhibits erosional unconformities, and a set of transtensive faults are mapped along its length. We show that parts of these faults were active during the last 540 ka. By estimating fault slip and folding rates along these structures, we estimate the deformation that they accommodated over this time-frame.
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NASA Astrophysics Data System (ADS)
Japsen, Peter; Green, Paul F.; Bonow, Johan M.; Chalmers, James A.
2016-04-01
We have undertaken a regional study of the thermo-tectonic development of East Greenland (68-75°N; Bonow et al. 2014; Japsen et al. 2014) and of southern Norway (58-64°N) based on integration of apatite fission-track analysis (AFTA), stratigraphic landscape analysis and the geological record onshore and offshore. Volcanic and sedimentary rocks accumulated on the subsiding, East Greenland margin during and following breakup and then began to be exhumed during late Eocene uplift that preceded a major, early Oligocene plate reorganization in the NE Atlantic. The Norwegian margin also experienced Eocene subsidence and burial; there are hemipelagic, deep-marine sediments of Eocene age along the coast of southern Norway. End-Eocene uplift of the NW European margin led to the formation of a major unconformity along the entire margin and to progradation of clastic wedges from Norway towards the south. Our AFTA data from East Greenland and southern Norway reveal a long history of Mesozoic burial and exhumation across the region, with a number of broadly synchronous events being recorded on both margins. AFTA data from East Greenland show clear evidence for uplift at the Eocene-Oligocene transition whereas the data from Norway do not resolve any effects of exhumation related to this event. AFTA data from the East Greenland margin show evidence of two Neogene events of uplift and incision of the in the late Miocene and Pliocene whereas results from southern Norway define Neogene uplift and erosion which began in the early Miocene. A Pliocene uplift phase in southern Norway is evident from the stratigraphic landscape analysis and from the sedimentary sequences offshore. In East Greenland, a late Eocene phase of uplift led to formation of a regional erosion surface near sea level (the Upper Planation Surface, UPS). Uplift of the UPS in the late Miocene led to formation of the Lower Planation Surface (LPS) by incision below the uplifted UPS, and a Pliocene phase led to incision of valleys and fjords below the uplifted LPS, leaving mountain peaks reaching 3.7 km above sea level. In southern Norway (as also in southern Sweden), the sub-horizontal Palaeic surfaces truncate the tilted, sub-Mesozoic erosion surface along the coasts. Lidmar-Bergström et al. (2013) used this relationship to conclude that the Palaeic relief is of Cenozoic age. In Greenland, definition of the chronology of events benefits from the availability of AFTA data from boreholes onshore where the plateau surfaces truncate Palaeogene basalts, and thus make it possible to date formation of these surfaces and correlate them with offshore unconformities. In Norway, the absence of post-rift rocks onshore precludes such integrated analysis. However, the presence of offshore unconformities, coupled with similar onshore landscapes and Cenozoic cooling history suggest a similar overall style of evolution. The similarities between the two margins lead us to us suggest that these margins developed in broadly similar fashion, and that the mountains of Norway also reached their present elevation long after Atlantic breakup. Bonow, Japsen, Nielsen 2014. Global and Planetary Change 116. Japsen, Green, Bonow, Nielsen, Chalmers 2014. Global and Planetary Change 116. Lidmar-Bergström, Bonow, Japsen 2013. Global and Planetary Change 100.
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Englund, K.J.; Thomas, R.E.
1997-01-01
Two contrasting concepts specifying the age and duration of the hiatus resulting from a mid-Carboniferous eustatic event in the eastern United States are based on different evidence. The original model indicated that the hiatus is at an unconformity in cratonic areas that was assumed to coincide with the Mississippian-Pennsylvanian boundary at the contact between the Mississippian Bluestone Formation and the Pennsylvanian Pocahontas Formation in the Appalachian foreland basin. This concept was adhered to exclusively until 1969 and continues to reappear in reports dealing with global correlations and division of the Carboniferous into the Mississippian and Pennsylvanian Systems. This division is at a major eustatic event that supposedly occurred at about 330 Ma in scattered parts of the world, including the Appalachian basin. An alternative concept, fully supported by geologic mapping and biostratigraphic studies, indicates that the unconformity and associated hiatus are much younger because they originate in the Appalachian foreland basin in the lower part (upper Namurian) of the Lower Pennsylvanian New River Formation, about 260 m above the Mississippian-Pennsylvanian boundary. The duration of this hiatus increases in a northwesterly direction onto the cratonic shelf because the unconformity progressively truncated the underlying Lower Pennsylvanian and Upper Mississippian successions. The westward onlap of Pennsylvanian strata onto the eroded surface resulted in a hiatus from the Early Mississippian (Tournaisian) to the Middle Pennsylvanian (Westphalian B). The systemic boundary, which is in a depositional continuous sequence of strata in the Appalachian foreland basin, was correlated biostratigraphically by Pfefferkorn and Gillespie in 1982 with Gothan's "Florensprung" (floral break) described in 1913 at the Namurian A-B boundary in the Upper Silesian basin. An intra-Namurian erosive event was noted also in the Upper Silesian basin by Havlena, who reported in 1982 that an intra-Namurian erosive contact occurs well above the Florensprung. The origin of the Florensprung in depositional continuous strata has been attributed to tectonism, environment, or climate. However, spherules found in depositional continuous strata near the Mississippian-Pennsylvanian boundary in the Appalachian basin indicate that the effect of an asteroid impact may be the underlying cause for the biodiversity noted at the systemic boundary.
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Physical experience enhances science learning.
Kontra, Carly; Lyons, Daniel J; Fischer, Susan M; Beilock, Sian L
2015-06-01
Three laboratory experiments involving students' behavior and brain imaging and one randomized field experiment in a college physics class explored the importance of physical experience in science learning. We reasoned that students' understanding of science concepts such as torque and angular momentum is aided by activation of sensorimotor brain systems that add kinetic detail and meaning to students' thinking. We tested whether physical experience with angular momentum increases involvement of sensorimotor brain systems during students' subsequent reasoning and whether this involvement aids their understanding. The physical experience, a brief exposure to forces associated with angular momentum, significantly improved quiz scores. Moreover, improved performance was explained by activation of sensorimotor brain regions when students later reasoned about angular momentum. This finding specifies a mechanism underlying the value of physical experience in science education and leads the way for classroom practices in which experience with the physical world is an integral part of learning. © The Author(s) 2015.
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Angland, P.; Haberberger, D.; Ivancic, S. T.; ...
2017-10-30
Here, a new method of analysis for angular filter refractometry images was developed to characterize laser-produced, long-scale-length plasmas using an annealing algorithm to iterative converge upon a solution. Angular filter refractometry (AFR) is a novel technique used to characterize the density pro files of laser-produced, long-scale-length plasmas. A synthetic AFR image is constructed by a user-defined density profile described by eight parameters, and the algorithm systematically alters the parameters until the comparison is optimized. The optimization and statistical uncertainty calculation is based on a minimization of themore » $$\\chi$$2 test statistic. The algorithm was successfully applied to experimental data of plasma expanding from a flat, laser-irradiated target, resulting in average uncertainty in the density profile of 5-10% in the region of interest.« less
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DOE Office of Scientific and Technical Information (OSTI.GOV)
Khachatryan, Vardan; et al.
2011-03-01
A measurement of the angular correlations between beauty and anti-beauty hadrons (B B-bar) produced in pp collisions at a centre-of-mass energy of 7 TeV at the CERN LHC is presented, probing for the first time the region of small angular separation. The B hadrons are identified by the presence of displaced secondary vertices from their decays. The B hadron angular separation is reconstructed from the decay vertices and the primary-interaction vertex. The differential B B-bar production cross section, measured from a data sample collected by CMS and corresponding to an integrated luminosity of 3.1 inverse picobarns, shows that a sizablemore » fraction of the B B-bar pairs are produced with small opening angles. These studies provide a test of QCD and further insight into the dynamics of b b-bar production.« less
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Fractional Fourier transform of Lorentz-Gauss vortex beams
NASA Astrophysics Data System (ADS)
Zhou, GuoQuan; Wang, XiaoGang; Chu, XiuXiang
2013-08-01
An analytical expression for a Lorentz-Gauss vortex beam passing through a fractional Fourier transform (FRFT) system is derived. The influences of the order of the FRFT and the topological charge on the normalized intensity distribution, the phase distribution, and the orbital angular momentum density of a Lorentz-Gauss vortex beam in the FRFT plane are examined. The order of the FRFT controls the beam spot size, the orientation of the beam spot, the spiral direction of the phase distribution, the spatial orientation of the two peaks in the orbital angular momentum density distribution, and the magnitude of the orbital angular momentum density. The increase of the topological charge not only results in the dark-hollow region becoming large, but also brings about detail changes in the beam profile. The spatial orientation of the two peaks in the orbital angular momentum density distribution and the phase distribution also depend on the topological charge.
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DOE Office of Scientific and Technical Information (OSTI.GOV)
Angland, P.; Haberberger, D.; Ivancic, S. T.
Here, a new method of analysis for angular filter refractometry images was developed to characterize laser-produced, long-scale-length plasmas using an annealing algorithm to iterative converge upon a solution. Angular filter refractometry (AFR) is a novel technique used to characterize the density pro files of laser-produced, long-scale-length plasmas. A synthetic AFR image is constructed by a user-defined density profile described by eight parameters, and the algorithm systematically alters the parameters until the comparison is optimized. The optimization and statistical uncertainty calculation is based on a minimization of themore » $$\\chi$$2 test statistic. The algorithm was successfully applied to experimental data of plasma expanding from a flat, laser-irradiated target, resulting in average uncertainty in the density profile of 5-10% in the region of interest.« less
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Oliveira, Abinael B; Bakke, Knut
2016-06-01
The behaviour of a neutral particle (atom, molecule) with an induced electric dipole moment in a region with a uniform effective magnetic field under the influence of the Kratzer potential (Kratzer 1920 Z. Phys. 3 , 289-307. (doi:10.1007/BF01327754)), and rotating effects is analysed. It is shown that the degeneracy of the Landau-type levels is broken and the angular frequency of the system acquires a new contribution that stems from the rotation effects. Moreover, in the search for bound state solutions, it is shown that the possible values of this angular frequency of the system are determined by the quantum numbers associated with the radial modes and the angular momentum, the angular velocity of the rotating frame and by the parameters associated with the Kratzer potential.
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NASA Astrophysics Data System (ADS)
He, Shaoming; Wang, Jiang; Wang, Wei
2017-12-01
This paper proposes a new composite guidance law to intercept manoeuvring targets without line-of-sight (LOS) angular rate information in the presence of autopilot lag. The presented formulation is obtained via a combination of homogeneous theory and sliding mode control approach. Different from some existing observers, the proposed homogeneous observer can estimate the lumped uncertainty and the LOS angular rate in an integrated manner. To reject the mismatched lumped uncertainty in the integrated guidance and autopilot system, a sliding surface, which consists of the system states and the estimated states, is proposed and a robust guidance law is then synthesised. Stability analysis shows that the LOS angular rate can be stabilised in a small region around zero asymptotically and the upper bound can be lowered by appropriate parameter choice. Numerical simulations with some comparisons are carried out to demonstrate the superiority of the proposed method.
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Angular Momentum Transport in Turbulent Flow between Independently Rotating Cylinders
DOE Office of Scientific and Technical Information (OSTI.GOV)
Paoletti, M. S.; Lathrop, D. P.; Institute for Physical Science and Technology, University of Maryland, College Park, Maryland 20742
2011-01-14
We present measurements of the angular momentum flux (torque) in Taylor-Couette flow of water between independently rotating cylinders for all regions of the ({Omega}{sub 1}, {Omega}{sub 2}) parameter space at high Reynolds numbers, where {Omega}{sub 1} ({Omega}{sub 2}) is the inner (outer) cylinder angular velocity. We find that the Rossby number Ro=({Omega}{sub 1}-{Omega}{sub 2})/{Omega}{sub 2} fully determines the state and torque G as compared to G(Ro={infinity}){identical_to}G{sub {infinity}.} The ratio G/G{sub {infinity}} is a linear function of Ro{sup -1} in four sections of the parameter space. For flows with radially increasing angular momentum, our measured torques greatly exceed those of previousmore » experiments [Ji et al., Nature (London), 444, 343 (2006)], but agree with the analysis of Richard and Zahn [Astron. Astrophys. 347, 734 (1999)].« less
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NASA Astrophysics Data System (ADS)
Worthington, L. L.; Gulick, S. P.; Ridgway, K. R.; Jaeger, J. M.; Cowan, E. A.; Slagle, A. L.; Forwick, M.
2013-12-01
The offshore St. Elias fold-thrust belt records the complex interaction between collisional tectonics and glacial climate variability, providing insight for models of orogenesis and the evolution of glacial depocenters. Ongoing collision of the Yakutat (YAK) microplate with North America (NA) has driven orogenesis of the St. Elias Mountains and the advance of the offshore deformation front to the southeast. Glacial erosion and deposition have provided sediment that constructed the upper continental shelf, much of which has been reincorporated into the orogenic wedge through offshore faulting and folding. We integrate core and downhole logging data from IODP Expedition 341 (Sites U1420 and U1421) drilled on the Yakutat shelf and slope with high-resolution and regional seismic profiles to investigate the coupled structural and stratigraphic evolution of the St. Elias margin. Site U1420 lies on the Yakutat shelf within the Bering Trough, a shelf-crossing trough that is within primary depocenter for Bering Glacier sediments. The sub-seafloor architecture of the Bering Trough region is defined by a regional unconformity that marks the first glacial advance to the shelf edge. Below the unconformity, the shelf is constructed by multiple aggradational packages that are likely a series of pro-glacial outer shelf/slope fans. Two faults underlie the glacial packages and have been rendered inactive as the depositional environment has evolved, while faulting elsewhere on the shelf has initiated. Site U1421 lies on the current continental slope, within the backlimb of an active thrust that forms part of the modern YAK-NA deformation front. At each of these sites, we recovered glacigenic diamict (at depths up to ~1015 m at Site U1420), all of which is younger than 0.781 Ma. Preliminary age models for the Bering Trough region indicate that the entire outer shelf and shelf edge environment have been built since the Mid-Pleistocene Transition (MPT), and is possibly even younger. In stark contrast to previous interpretations, the shelf environment, in addition to the proximal deep-sea fan system, appears to be a primary glacial depocenter since the MPT, with an average accumulation rate >1.3 mm/yr. Additionally, initiation of active deformation away from the Bering Trough depocenter likely occurred since ~1 Ma. These observations suggest that possible tectonic reorganization due to mass redistribution by glacial processes occurs at time scales on the order of 100kyr-1Myr. It follows that the St. Elias orogenic system may be more sensitive to glacial-interglacial cycles than previously recognized.
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Disentangling the Dynamical Mechanisms for Cluster Galaxy Evolution
2008-02-01
reversible energy and angular momentum exchange between the density wave and the disk matter and the outward transport of these exchanged energy and angular...elapsed time for a smaller z as well. Yet the argument should hold no matter what observation epoch one uses, as long as one concentrates to the regions... matter (CDM) paradigm, galaxy mergers are the preferred means of morphological evolution of galaxies in clusters (see, e.g., Kauffmann 1995). Even though
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Angular Superresolution for a Scanning Antenna with Simulated Complex Scatterer-Type Targets
2002-05-01
Approved for public release; distribution unlimited. The Scan- MUSIC (MUltiple SIgnal Classification), or SMUSIC, algorithm was developed by the Millimeter...with the use of a single rotatable sensor scanning in an angular region of interest. This algorithm has been adapted and extended from the MUSIC ...simulation. Abstract ii iii Contents 1. Introduction 1 2. Extension of the MUSIC Algorithm for Scanning Antenna 2 2.1 Subvector Averaging Method
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The formation of sharp edges in planetary rings by nearby satellites
NASA Astrophysics Data System (ADS)
Borderies, N.; Goldreich, P.; Tremaine, S.
1989-08-01
Equations are derived which govern the shapes of the perturbed streamlines near the 'sharp edge' boundaries between regions of high and low planetary ring optical depth; these are maintained by the shepherd satellites, which transfer angular momentum to and from ring particles. The results obtained by these equations' solution with a simple numerical model, whose parameters resemble those of the Encke division, are found to faithfully reproduce the sharp edges bounding the division; they imply that the ring thickness in the unperturbed regions far from the edges is of the order of 10 m, and that the angle-averaged surface density varies on a much shorter radial length scale than that over which the satellite torque is applied. This feature's relationship to the local reversal of angular momentum viscous transport, in the most strongly perturbed regions, is demonstrated.
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The formation of sharp edges in planetary rings by nearby satellites
NASA Technical Reports Server (NTRS)
Borderies, Nicole; Goldreich, Peter; Tremaine, Scott
1989-01-01
Equations are derived which govern the shapes of the perturbed streamlines near the 'sharp edge' boundaries between regions of high and low planetary ring optical depth; these are maintained by the shepherd satellites, which transfer angular momentum to and from ring particles. The results obtained by these equations' solution with a simple numerical model, whose parameters resemble those of the Encke division, are found to faithfully reproduce the sharp edges bounding the division; they imply that the ring thickness in the unperturbed regions far from the edges is of the order of 10 m, and that the angle-averaged surface density varies on a much shorter radial length scale than that over which the satellite torque is applied. This feature's relationship to the local reversal of angular momentum viscous transport, in the most strongly perturbed regions, is demonstrated.
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NASA Astrophysics Data System (ADS)
Bouzekraoui, Hicham; Barakat, Ahmed; El Youssi, Mohammed; El Khalki, Yahia; Hafid, Abdelatif; Mouaddine, Atika
2016-04-01
Central High-Atlas mountain in the centre of Morocco, contains an exceptional geodiversity. Some geomorphological and geological objects of it are included and protected recently by the World Heritage list. The valley of Aït Bou Oulli is located in the heart of the Moroccan central High-Atlas, whose height is 4068 m in Ighil M'goun and 3800 m in Rat Mountain. The mountain areas are characterized by higher geodiversity in comparison with other areas. The valley possesses a geological and geomorphological heritage which is very rich, much diversified and exceptional landscapes of high mountains. It is part of geopark M'Goun; the valley attracts a number of tourists every year. However, this number remains restricted because of the lack of the tools of promotion, valuation and mediation of this geoheritage. Moreover, the touristic infrastructure is modest. Regarding this situation, the geotouristic map appears as a tool of promotion of the geotourism and diversification of the regional and national tourist product. This work aims at elaborating new maps of geomorphosites, cultural sites, and geomonuments in high Mountain landscapes of the valley, suggested in geotourism circuits. The first results reveal the low exploitation of the geodiversity of this valley-oasis: the spectacular waterfalls, water sources, canyons, glacial cirques and U-shaped valleys, superficial karstic forms (sinkholes and swallow-holes), high-Atlas peaks and cliffs, spectacular scree slopes, badlands landscapes, fairy chimneys, and the geological history dating back to the Paleozoic and angular unconformity. In addition, the valley has diverse tangible cultural heritage spanning hundreds of years such as the enigmatic rock engravings (dating from 2000 to 3000 years), troglodyte caves and terraced agriculture landscapes, geomonuments (old cooperative storage, Kasbah, traditional water mills) and the architecture of the villages. It has also an intangible cultural heritage such as folklore. This cultural heritage, however, remains low valued. This richness was the object of 3 geodidactic and geotouristic circuits and itineraries that will be proposed at the end of this work. Keywords: geomorphosites, geoheritage, cultural heritage, circuits, geotouristic map, geotourism.
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NASA Astrophysics Data System (ADS)
Marliyani, G. I.; Arrowsmith, R.; Helmi, H.
2015-12-01
Instrumental and historical records of earthquakes, supplemented by paleoeseismic constraints can help reveal the earthquake potential of an area. The Pasuruan fault is a high angle normal fault with prominent youthful scarps cutting young deltaic sediments in the north coast of East Java, Indonesia and may pose significant hazard to the densely populated region. This fault has not been considered a significant structure, and mapped as a lineament with no sense of motion. Information regarding past earthquakes along this fault is not available. The fault is well defined both in the imagery and in the field as a ~13km long, 2-50m-high scarp. Open and filled fractures and natural exposures of the south-dipping fault plane indicate normal sense of motion. We excavated two fault-perpendicular trenches across a relay ramp identified during our surface mapping. Evidence for past earthquakes (documented in both trenches) includes upward fault termination with associated fissure fills, colluvial wedges and scarp-derived debris, folding, and angular unconformities. The ages of the events are constrained by 23 radiocarbon dates on detrital charcoal. We calibrated the dates using IntCal13 and used Oxcal to build the age model of the events. Our preliminary age model indicates that since 2006±134 B.C., there has been at least five ground rupturing earthquakes along the fault. The oldest event identified in the trench however, is not well-dated. Our modeled 95th percentile ranges of the next four earlier earthquakes (and their mean) are A.D. 1762-1850 (1806), A.D. 1646-1770 (1708), A.D. 1078-1648 (1363), and A.D. 726-1092 (909), yielding a rough recurrence rate of 302±63 yrs. These new data imply that Pasuruan fault is more active than previously thought. Additional well-dated earthquakes are necessary to build a solid earthquake recurrence model. Rupture along the whole section implies a minimum earthquake magnitude of 6.3, considering 13km as the minimum surface rupture length.
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NASA Astrophysics Data System (ADS)
Nabawy, Bassem S.; El Sharawy, Mohamed S.
2015-12-01
The Middle Miocene Belayim Formation is one of the most prolific formations in the Southern Gulf of Suez. It consists of four members; two members are evaporitic (Baba and Feiran) and the other two members are prospective, mostly clastics (Hammam Faraun and Sidri). The hydrocarbon potential and depositional environment of Hammam Faraun Member, the target of the present study, have been studied in 11 wells distributed in the southern province of the Gulf of Suez. The traditional well log data, as well as the Spectral Gamma-Ray logs 'SGR' and dipmeter data were used to evaluate the petrophysical properties and distribution of the Hammam Faraun Member in the Southern Gulf of Suez. It varies greatly in thickness with the greatest thicknesses in GS 365 (372 ft) and GS 373 (430 ft) fields in the central parts and the thinnest at the basin margins of the studied area at GH376 (65 ft) and Ras El Bahar (67.5 ft) fields. It is composed of clastic rocks, mainly shales and sometimes reef carbonates. The very good petrophysical properties of the studied sequence indicate a good reservoir in some fields with good to very good porosity (13.5 ≤ ∅ ≤ 25.0%). The shale volume of this reservoir sequence is less than 33% and the water saturation is less than 42.3%, while the net-pay thickness is up to 58 ft. The SGR and Pe logs indicate that, the studied rocks were deposited mostly in lagoonal to shallow marine environments, with illite and montmorillonite as dominant clay minerals. The dipmeter data obtained in some wells indicate slightly tilted beds, mostly less than 20° with an overall dip direction towards the SW, which represents the regional dip in the Southern Gulf of Suez. Based on dipmeter data, two major angular unconformities can be detected; one at the top of the sequence, separating it from the overlying South Gharib evaporates, and another one at the base of the sequence, separating it from the underlying Feiran Member.
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Tectonic signatures on active margins
NASA Astrophysics Data System (ADS)
Hogarth, Leah Jolynn
High-resolution Compressed High-Intensity Radar Pulse (CHIRP) surveys offshore of La Jolla in southern California and the Eel River in northern California provide the opportunity to investigate the role of tectonics in the formation of stratigraphic architecture and margin morphology. Both study sites are characterized by shore-parallel tectonic deformation, which is largely observed in the structure of the prominent angular unconformity interpreted as the transgressive surface. Based on stratal geometry and acoustic character, we identify three sedimentary sequences offshore of La Jolla: an acoustically laminated estuarine unit deposited during early transgression, an infilling or "healing-phase" unit formed during the transgression, and an upper transparent unit. The estuarine unit is confined to the canyon edges in what may have been embayments during the last sea-level rise. The healing-phase unit appears to infill rough areas on the transgressive surface that may be related to relict fault structures. The upper transparent unit is largely controlled by long-wavelength tectonic deformation due to the Rose Canyon Fault. This unit is also characterized by a mid-shelf (˜40 m water depth) thickness high, which is likely a result of hydrodynamic forces and sediment grain size. On the Eel margin, we observe three distinct facies: a seaward-thinning unit truncated by the transgressive surface, a healing-phase unit confined to the edges of a broad structural high, and a highly laminated upper unit. The seaward-thinning wedge of sediment below the transgressive surface is marked by a number of channels that we interpret as distributary channels based on their morphology. Regional divergence of the sequence boundary and transgressive surface with up to ˜8 m of sediment preserved across the interfluves suggests the formation of subaerial accommodation during the lowstand. The healing-phase, much like that in southern California, appears to infill rough areas in the transgressive surface. Reflectors within the laminated upper unit exhibit divergence towards the Eel River Syncline, which suggests that deposition in the syncline is syntectonic. The transgressive surface is offset across the Eureka Anticline indicating deformation has occurred since ˜10 ka. The relief observed along the transgressive surface is consistent with deformation rates measured onshore.
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NASA Astrophysics Data System (ADS)
Kelly, M. J.; Bladon, A.; Clarke, S.; Najman, Y.; Copley, A.; Kloppenburg, A.
2015-12-01
The Barmer Basin, situated within the West Indian Rift System, is an intra-cratonic rift basin produced during Gondwana break-up. Despite being a prominent oil and gas province, the structural evolution and context of the rift within northwest India remains poorly understood. Substantial subsurface datasets acquired during hydrocarbon exploration provide an unrivalled tool to investigate the tectonic evolution of the Barmer Basin rift and northwest India during India-Asia collision. Here we present a structural analysis using seismic datasets to investigate Barmer Basin evolution and place findings within the context of northwest India development. Present day rift structural architectures result from superposition of two non-coaxial extensional events; an early mid-Cretaceous rift-oblique event (NW-SE), followed by a main Paleocene rifting phase (NE-SW). Three phases of fault reactivation follow rifting: A transpressive, Late Paleocene inversion along localised E-W and NNE-SSW-trending faults; a widespread Late Paleocene-Early Eocene inversion and Late Miocene-Present Day transpressive strike-slip faulting along NW-SE-trending faults and isolated inversion structures. A major Late Eocene-Miocene unconformity in the basin is also identified, approximately coeval with those identified within the Himalayan foreland basin, suggesting a common cause related to India-Asia collision, and calling into question previous explanations that are not compatible with spatial extension of the unconformity beyond the foreland basin. Although, relatively poorly age constrained, extensional and compressional events within the Barmer Basin can be correlated with regional tectonic processes including the fragmentation of Gondwana, the rapid migration of the Greater Indian continent, to subsequent collision with Asia. New insights into the Barmer Basin development have important implications not only for ongoing hydrocarbon exploration but the temporal evolution of northwest India.
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Volcano-tectonic evolution of the Castle Mountains: 22 to 14 MA
DOE Office of Scientific and Technical Information (OSTI.GOV)
Capps, R.C.
1993-04-01
The alkali-calcic Castle Mountains Volcanic rocks (CMV) are host to major gold mineralization. They are located about 100 km south of Las Vegas, Nevada and are on the boundary between the Basin and Range Province and Colorado River extensional corridor (35[degree]18 minutes 45 seconds N, 115[degree]05 minutes 10 seconds W). New data show the following chronology. 22 Ma. A regional rhyolite ash-flow tuff, the Castle Mountain Tuff member, was deposited on a Proterozoic-Paleozoic basement of low relief. <22 Ma - > 17 Ma. Normal faulting (N30--60[degree]W, 60--65[degree]NE) formed half-grabens. Latite and basalt flows, minor ash-flow tuffs, lahars and sediments (Jacksmore » Well member - JW) were deposited unconformably. JW magmas are enriched in light REE compared to the younger CMV. <17 Ma to 15.5 Ma. Oxidizing upper portions (796 C) of a shallowly emplaced silicic melt erupted to form the high-silica rhyolite dome complexes and intrusives (Linder Peak member - LP) of the NNE-striking Castle Mountains. NW-striking transverse structures caused discontinuities in strike direction of the subvolcanic intrusive and domes and helped form a synvolcanic depression. During a hiatus in volcanism, early Hart Peak member (HP) sediments were deposited marginal to the Castle Mountains. Major gold mineralization and widespread hydrothermal alteration occurred at about 15.5 Ma. 16 Ma to 14 Ma. Early HP volcaniclastic sediments, rhyolite pyroclastic-surge tuff, and basaltic flows, were deposited during late hydrothermal alteration and then fractured and displaced by NNE-striking normal faults, especially in the eastern and northeastern CMV. < 14 Ma. Tectonically significant flat-lying boulder conglomerate and unconformably overlying, largely andesitic flows fill depressions in the Castle Mountains and the Piute Range to the east.« less
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NASA Astrophysics Data System (ADS)
Soares, Emílio Alberto Amaral; D'Apolito, Carlos; Jaramillo, Carlos; Harrington, Guy; Caputo, Mario Vicente; Barbosa, Rogério Oliveira; Bonora dos Santos, Eneas; Dino, Rodolfo; Gonçalves, Alexandra Dias
2017-11-01
The Amazonas fluvial system originates in the Andes and runs ca. 6700 km to the Atlantic Ocean, having as the main affluent the Negro River (second largest in water volume). The Amazonas transcontinental system has been dated to the late Miocene, but the timing of origin and evolutionary processes of its tributaries are still poorly understood. Negro River alluvial deposits have been dated to the middle to late Pleistocene. Recently, we studied a number of boreholes drilled for the building of a bridge at the lower course of the Negro River. A thin (centimetric) sedimentary deposit was found, laterally continuous for about 1800 m, unconformably overlaying middle Miocene strata and unconformably overlain by younger Quaternary deposits. This deposit consists predominantly of brownish-gray sandstones cemented by siderite and with subordinate mudstone and conglomerate beds. Palynological, granulometric, textural and mineralogical data suggest that the initial Negro River aggradation took place in the deep incised valley under anoxic conditions and subsequently along the floodplain, with efficient transport of mixed origin particles (Andean and Amazonic). Angiosperm leaves, wood and pollen are indicative of a tropical continental palaeoenvironment. A well preserved palynoflora that includes Alnipollenites verus, Grimsdalea magnaclavata and Paleosantalaceaepites cingulatus suggests a late Pliocene to early Pleistocene (Piacenzian to Gelasian) age for this unit, which was an age yet unrecorded in the Amazon Basin. These results indicate that by the late Pliocene-early Pleistocene, large scale river activity was occurring in Central Amazonia linking this region with the Andean headwaters, and therefore incompatible with Central Amazonia barriers like the Purus arch.
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Contributions to the stratigraphy of southwestern Colorado
Cross, Whitman; Larsen, E.S.
1915-01-01
In the course of field work of the United States Geological Survey in the San Juan region of Colorado observations have been made in the last three seasons that considerably extend our knowledge of the great stratigraphic break below the La Plata sandstone, which is currently assumed to be of Jurassic age. The new data pertain partly to the relations existing in the Gunnison Valley, north of the San Juan Mountains, where the unconformity marking this break was already known at certain places, and partly to the conditions in the Piedra Valley, on the south side of the mountains, where the unconformity had not before been noted. The Piedra Valley is of special interest, and it seems well to call attention to the relations observed even though they were examined only in a reconnaissance. The first part of this paper is devoted to the evidence of the overlap of the La Plata sandstone; the second to the stratigraphic relations in the Piedra Valley. The section of sedimentary formations in Piedra Canyon is of much interest because none of the pre-La Plata formations are known east of this locality on the south side of the San Juan Mountains. Most of these formations exhibit a notably different facies where they reappear from beneath the overlying beds at their nearest exposures in New Mexico, southeast of the Piedra Valley. It is believed that the character of the formations in the Piedra section should be recorded for the benefit of geologists who may be studying the Paleozoic and Mesozoic rocks of New Mexico, and accordingly the second part of the paper presents details of the structure and the stratigraphic section of Piedra Valley.
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NASA Astrophysics Data System (ADS)
Hall, T.; Wilson, T. J.; Henrys, S.; Speece, M. A.
2016-12-01
The interplay of tectonics and climate is recorded in the sedimentary strata within Victoria Land Basin, McMurdo Sound, Antarctica. Patterns of Cenozoic sedimentation are documented from interpretation of seismic reflection profiles calibrated by drillhole data in McMurdo Sound, and these patterns provide enhanced constraints on the evolution of the coupled Transantarctic Mountains-West Antarctic Rift System and on ice sheet advance/retreat through multiple climate cycles. The research focuses on shifts from warm based to cold based ice sheets through the variable climate and ice sheet conditions that characterized the early to middle Miocene. The study seeks to test the view that cold based ice sheets in arid, polar deserts minimally erode the landscape by calculating sediment volumes for critical climatic intervals. Revised seismic mapping through McMurdo Sound has been completed, utilizing the seismic stratigraphic framework first established by Fielding et al. (2006) and new reflectors marking unconformities identified from the AND-2A core (Levy et al., 2016). Reflector age constraints are derived by tying surfaces to the Cape Roberts Project, CIROS-1, and AND-2A drillholes. Seismic facies coupled with AND-2A core provenance information provides insight into depositional mechanisms and ice sheet behavior. Seismic facies transitions occur across the major unconformity surfaces in the AND-2A core. Sediment volume calculations for subareas within McMurdo Sound where reflectors are most continuous indicate substantial decreases in preserved sediment volume between the Oligocene and Early Miocene sequences, and between the early and mid-Miocene sequences. Sediment volumes, used in combination with an ice sheet model in a backstacking procedure, provide constraints on landscape modification and further understanding of how landscapes erode under warm and cold based ice sheet regimes.
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Context of ancient aqueous environments on Mars from in situ geologic mapping at Endeavour Crater
Crumpler, L.S.; Arvidson, R. E.; Bell, J.; Clark, B. C.; Cohen, B. A.; Farrand, W. H.; Gellert, Ralf; Golombek, M.; Grant, J. A.; Guinness, E.; Herkenhoff, Kenneth E.; Johnson, J. R.; Jolliff, B.; Ming, D. W.; Mittlefehldt, D. W.; Parker, T.; Rice, J. W.; Squyres, S. W.; Sullivan, R.; Yen, A. S.
2015-01-01
Using the Mars Exploration Rover Opportunity, we have compiled one of the first field geologic maps on Mars while traversing the Noachian terrain along the rim of the 22 km diameter Endeavour Crater (Latitude −2°16′33″, Longitude −5°10′51″). In situ mapping of the petrographic, elemental, structural, and stratigraphic characteristics of outcrops and rocks distinguishes four mappable bedrock lithologic units. Three of these rock units predate the surrounding Burns formation sulfate-rich sandstones and one, the Matijevic Formation, represents conditions on early Mars predating the formation of Endeavour Crater. The stratigraphy assembled from these observations includes several geologic unconformities. The differences in lithologic units across these unconformities record changes in the character and intensity of the Martian aqueous environment over geologic time. Water circulated through fractures in the oldest rocks over periods long enough that texturally and elementally significant alteration occurred in fracture walls. These oldest pre-Endeavour rocks and their network of mineralized and altered fractures were preserved by burial beneath impact ejecta and were subsequently exhumed and exposed. The alteration along joints in the oldest rocks and the mineralized veins and concentrations of trace metals in overlying lithologic units is direct evidence that copious volumes of mineralized and/or hydrothermal fluids circulated through the early Martian crust. The wide range in intensity of structural and chemical modification from outcrop to outcrop along the crater rim shows that the ejecta of large (>8 km in diameter) impact craters is complex. These results imply that geologic complexity is to be anticipated in other areas of Mars where cratering has been a fundamental process in the local and regional geology and mineralogy.
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NASA Astrophysics Data System (ADS)
Bhattacharya, R.; Liberty, L. M.; Almeida, R. V.; Hubbard, J.
2016-12-01
We explore the structural and depositional evolution of the Stevenson Basin, Gulf of Alaska from a dense network of 2-D marine seismic profiles that span the Gulf of Alaska continental margin. The grid of 71 seismic profiles was acquired as part of a 1975 Mineral Management Services (MMS) exploration project to assess basin architecture along the Alaska continental shelf. We obtained unmigrated and stacked seismic profiles in TIFF format. We converted the data to SEGY format and migrated each profile. Within the Stevenson Basin, we identify key seismic horizons, including the regional Eocene-Miocene unconformity, that provide insights into its depositional and structural history. Using these observations combined with stacking velocities, sonic logs from wells, and refraction velocities from the Edge profile of Ye et al. (1997), we develop a local 3D velocity model that we use to depth-convert the seismic reflection profiles. By using ties to >2.5 km deep exploration wells, we note the Stevenson Basin is one of many Eocene and younger depocenters that span the forearc between Kodiak and Prince William Sound. Well logs and seismic data suggest basal strata consist of Eocene sediments than are unconformably overlain by Neogene and younger strata. Faults that breach the sea floor suggest active deformation within and at the bounds of this basin, including on new faults that do not follow any pre-existing structural trends. This assessment is consistent with slip models that place tsunamigenic faults that ruptured during the 1964 Great Alaska earthquake in the vicinity of the basin. The catalog of faults, their slip history and the depositional evolution of the Stevenson Basin, all suggest that the basin evolution may be controlled by heterogeneities along the incoming plate.
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Structure, stratigraphy, and eruption chronology of the Hanauma Bay Tuff Ring, Oahu, Hawaii
NASA Astrophysics Data System (ADS)
Rottas, K. M.; Houghton, B. F.
2010-12-01
The Hanauma Bay-Koko Head Complex is one of several volcanic landforms along the Koko fissure, in southeastern Oahu, that formed during rejuvenated volcanism. The Hanauma Bay region of the complex is comprised of two nested tuff rings. The internal structure of the inner tuff ring is well exposed due to subsequent breaching and wave erosion and is described in detail here for the first time. The inner tuff ring is currently believed to have formed during a single eruption episode. However, field observations, detailed photography, structural mapping in both the vertical and horizontal planes, extensive measurements of bedding attitudes, and stratigraphic analysis suggest that there were a minimum of five distinct intervals of deposition, which also blanketed the deposits of the outer tuff ring with ejecta. These intervals of sedimentation were separated by significant collapses, generating major unconformities that cross the inner wall of the inner ring. The planes of failure are marked by smaller steep-walled channels and gullies, eroded by rainfall-induced runoff and suggesting the failures were each followed by short time breaks with erosion. Within each pyroclastic sequence there are also smaller slump scars and local unconformities. The inner tuff ring was predominately formed by pyroclastic surges, although the beds of Phase 3 are primarily fall deposits. From ballistic trajectories and bedding features, it is apparent that the eruption locus shifted a minimum of two times during tuff ring growth. Ballistic blocks in the final Phase 5 indicate that the Hanauma Bay eruption was contemporaneous with a separate eruption to the north, most likely that of the Kahauloa tuff ring 880 meters away.
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Carbonate mound development in contrasting settings on the Irish margin
NASA Astrophysics Data System (ADS)
van der Land, Cees; Eisele, Markus; Mienis, Furu; de Haas, Henk; Hebbeln, Dierk; Reijmer, John J. G.; van Weering, Tjeerd C. E.
2014-01-01
Cold-water coral carbonate mounds, formed by framework building cold-water corals, are found in several mound provinces on the Irish margin. Differences in cold-water coral mound development rates and sediment composition between mounds at the southwest Rockall Trough margin and the Galway Mound in the Porcupine Seabight are investigated. Variations in sediment composition in the two mound provinces are related to the local environmental conditions and sediment sources. Mound accumulation rates are possibly higher at the Galway Mound probably due to a higher influx of hemipelagic fine grained non-carbonate sediments. In both cold-water coral mound areas, mound growth has been continuous for the last ca 11,000 years, before this period several hiatuses and unconformities exist in the mound record. The most recent unconformity can be correlated across multiple mounds and mound provinces at the Irish margin on the basis of apparent age. On the southwest Rockall Trough margin these hiatuses/unconformities are associated with post-depositional aragonite dissolution in, and lithification of, certain intervals, while at Galway Mound no lithification occurs. This study revealed that the influx and types of material transported to cold-water coral mounds may have a direct impact on the carbonate mound accumulation rate and on post-depositional processes. Significantly, the Logachev Mounds on the SW Rockall Trough margin accumulate slower but, because they contain lithified layers, are less susceptible to erosion. This net effect may account for their larger size compared to the Belgica Mounds.
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DOE Office of Scientific and Technical Information (OSTI.GOV)
Nibbelink, K.A.; Sorgenfrei, M.C.; Rice, D.E.
Yombo field in the Congo is sourced from the lacustrine shales of the presalt rift stage and produces from the Albian and Cenomanian, postsalt, Sendji carbonate and Tchala Sandstone. The Yombo prospect exploration model included an upper Sendji stratigraphic trap with two components and a structural nose. The buried hill component of the trap is formed by topographic relief on the reservoir below the top Sendji unconformity. The lower Sendji slump blocks provide a high on which the upper Sendji grainstone shoal facies develop. Both depositional relief and erosion during the top Sendji unconformity contribute to the topography. An isochronmore » thick in the overlying Tchala valley-fill sediments defined a drainage pattern on the unconformity around the buried hill of the underlying upper Sendji. The facies change component is formed by the pinch-out of the grainstone shoal reservoir facies into porous, but impermeable lagoonal dolomite interbedded with anhydrite and shale. Capillary pressure measurements on the 16% porosity, 0.1 md permeability lagoonal dolomite, along with pore throat radius and buoyancy calculations, demonstrated this facies could trap a significant column of low-gravity oil at shallow depth. The Tchala Sandstone contains several separate hydrocarbon accumulations. A stratigraphic trap in the lower Tchala is formed by marine and tidal channel sandstones pinching out into lagoonal shales. The nearshore marine sandstones of the upper Tchala contain additional hydrocarbons in structural and stratigraphic traps. The stratigraphic pinch-out that cross the Yombo nose trap a significant hydrocarbon accumulation, even though the four-way structural closure is relatively small.« less
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Faulting at Thebes Gap, Mo. -Ill. : Implications for New Madrid tectonism
DOE Office of Scientific and Technical Information (OSTI.GOV)
Harrison, R.W.; Schultz, A.P.
1992-01-01
Recent geologic mapping in the Thebes Gap area has identified numerous NNE- and NE-striking faults having a long-lived and complex structural history. The faults are located in an area of moderate recent seismicity at the northern margin of the Mississippi embayment, approximately 45 km north of the New Madrid seismic zone. Earliest deformation occurred along dextral strike-slip faults constrained as post-Devonian and pre-Cretaceous. Uplift and erosion of all Carboniferous strata suggest that this faulting is related to development of the Pascola arch (Ouachita orogeny). This early deformation is characterized by strongly faulted and folded Ordovician through Devonian rocks overlain inmore » places with angular unconformity by undeformed Cretaceous strata. Elsewhere, younger deformation involves Paleozoic, Cretaceous, Paleocene, and Eocene formations. These units have experienced both minor high-angle normal faulting and major, dextral strike-slip faulting. Quaternary-Tertiary Mounds Gravel is also involved in the latest episode of strike-slip deformation. Enechelon north-south folds, antithetic R[prime] shears, and drag folds indicate right-lateral motion. Characteristic positive and negative flower structures are commonly revealed in cross section. Right-stepping fault strands have produced pull-apart basins where Ordovician, Silurian, Devonian, Cretaceous, and Tertiary units are downdropped several hundreds of meters and occur in chaotic orientations. Similar fault orientations and kinematics, as well as recent seismicity and close proximity, clearly suggest a structural relationship between deformation at Thebes Gap and tectonism associated with the New Madrid area.« less
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Structural and sedimentary evolution of the Malay Basin
DOE Office of Scientific and Technical Information (OSTI.GOV)
Ismail, M.T.; Rudolph, K.W.; Abdullah, S.A.
1994-07-01
The Malay Basin is a back-arc basin that formed via Eocene ( ) through Oligocene extension. This early extensional episode is characterized by large east-west and northwest-southeast-trending normal fault systems with associated block rotation. Extensional subbasins are filled with a thick succession of alluvial and fluvial sediments that show increasing lacustrine influence toward the central basin dep. In the early Miocene, the basin entered a passive sag phase in which depositional relief decreased, and there is the first evidence of widespread marine influence. Lower Miocene sediments consist of cyclic offshore marine, tidal-estuarine, and coastal plain fluvial sediments with very widemore » facies tracts. The middle Miocene is dominated by increasing compressional inversion, in which preexisting extensional lows were folded into east-west anticlines. This compression continues well into the Pliocene-Pleistocene, especially in the northwest portion of the basin and is accompanied by an increase in basin-wide subsidence. There is significant thinning over the crest of the growing anticlines and an angular unconformity near the top of the middle Miocene in the southeast portion of the basin. Middle Miocene sedimentary facies are similar to those seen in the lower Miocene, but are influenced by the contemporaneous compressional folding and normal faulting. Based on this study, there is no evidence of through-going wrench-fault deformation in the Malay Basin. Instead, localized strike-slip faulting is a subsidiary phenomenon associated with the extensional and compressional tectonic episodes.« less
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NASA Astrophysics Data System (ADS)
Fan, Jian-Jun; Li, Cai; Wang, Ming; Xie, Chao-Ming
2018-01-01
When and how the Bangong-Nujiang Tethyan Ocean closed is a highly controversial subject. In this paper, we present a detailed study and review of the Cretaceous ophiolites, ocean islands, and flysch deposits in the middle and western segments of the Bangong-Nujiang suture zone (BNSZ), and the Cretaceous volcanic rocks, late Mesozoic sediments, and unconformities within the BNSZ and surrounding areas. Our aim was to reconstruct the spatial-temporal patterns of the closing of the middle and western segments of the Bangong-Nujiang Tethyan Ocean. Our conclusion is that the closure of the ocean started during the Late Jurassic and was mainly complete by the end of the Early Cretaceous. The closure of the ocean involved both "longitudinal diachronous closure" from north to south and "transverse diachronous closure" from east to west. The spatial-temporal patterns of the closure process can be summarized as follows: the development of the Bangong-Nujiang Tethyan oceanic lithosphere and its subduction started before the Late Jurassic; after the Late Jurassic, the ocean began to close because of the compressional regime surrounding the BNSZ; along the northern margin of the Bangong-Nujiang Tethyan Ocean, collisions involving the arcs, back-arc basins, and marginal basins of a multi-arc basin system first took place during the Late Jurassic-early Early Cretaceous, resulting in regional uplift and the regional unconformity along the northern margin of the ocean and in the Southern Qiangtang Terrane on the northern side of the ocean. However, the closure of the Bangong-Nujiang Tethyan Ocean cannot be attributed to these arc-arc and arc-continent collisions, because subduction and the development of the Bangong-Nujiang Tethyan oceanic lithosphere continued until the late Early Cretaceous. The gradual closure of the middle and western segments of Bangong-Nujiang Tethyan Ocean was diachronous from east to west, starting in the east in the middle Early Cretaceous, and being mainly complete by the end of the Early Cretaceous. The BNSZ and its surrounding areas underwent orogenic uplift during the Late Cretaceous.
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NASA Astrophysics Data System (ADS)
Smith, M. E.; Cassel, E. J.; Canada, A.; Jicha, B.; Singer, B. S.
2015-12-01
Eastern Nevada lay east of the Cordilleran continental divide and experienced continental drainage ponding during the Eocene Epoch. Though recognized for nearly a century, lake deposits of the Elko Formation have yet to be placed in a regional chronostratigraphic context, due primarily to Neogene extension and a paucity of radioisotopic ages. New geochronology is essential for creating robust reconstructions of paleogeography and paloeohydrology from scattered surviving outcrops, and for assessing competing tectonic interpretations for lake basin formation and evolution. New single crystal sanidine 40Ar/39Ar ages for 21 ash beds collected from the Elko Formation and contemporaneous fluvial deposits indicate that lacustrine deposition occurred locally as early as ca. 48.7 Ma, coeval with deposition of the Bridgerian portion of the lacustrine Sheep Pass Formation to the south. Lake Elko's most expansive phase occurred between ca. 44.0 and 40.5 Ma, resulting in regional overlap of lacustrine strata atop fluvial strata. Based on lithofacies and lithofacies stacking patterns, an up-section transition from overfilled to balanced-fill conditions occurred at ca. 41.3 Ma. This transition led to increasing salinity and lake level variations that formed a prominent 1-4 meter-scale depositional cyclicity characteristic of partly closed lakes that periodically dropped below their sill elevation. The stromatolitic uppermost Elko Formation records proximal volcanism, including several welded ignimbrites, and is overlain by an unconformity of >10 m.y. duration. Initial ponding, the shift to balanced fill conditions, voluminous siliceous volcanism, and subsequent unconformity are interpreted to reflect the progressive NE to SW advance of 500-900 m of topographic uplift and volcanism resulting from rollback of the Farallon slab. 40Ar/39Ar ages for ash beds at five individual locations suggest that a single ignimbrite, likely the Tuff of Nelson Creek, was deposited across a ~10,000 km2 area of NE NV at 40.45 ± 0.08 Ma, near the end of Elko Formation accumulation. Within this bed, the hydrogen isotope composition of glass hydration waters vary systematically according to paleo-landscape position, recording a 102 ± 20‰ increase in δD values for glasses deposited in lacustrine versus fluvial environments.
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NASA Astrophysics Data System (ADS)
Karaaǧaç, Serdal; Koral, Hayrettin
2017-04-01
This study investigates stratigraphy and structural features in the Cenozoic sedimentary sequence of the fold-thrust belt of the Nallıhan-Ankara region, located to the north of the İzmir-Ankara-Erzincan Suture Zone. Permian-Triassic age marble intercalated with schist-phyllites, the upper Jurassic-lower Cretaceous age limestone and the upper Cretaceous age sandstone-shale alternation compose the basement in the study area. These rocks are unconformably overlain by the Cenozoic age terrestrial sedimentary and volcanic units. The Cenozoic stratigraphy begins with the Paleocene-Eocene age coal-bearing, at times, volcanic intercalated conglomerate-sandstone-mudstone alternation of alluvial-fluvial origins (Aksaklar Formation) and the tuff intercalated with lacustrine limestone, bituminous limestone (Kabalar Formation). These units are conformably overlain by the Eocene age basalt-andesite and pyroclastic rocks (Meyildere volcanics). The Paleocene-Eocene aged units are unconformably overlain by the conglomerate-sandstone-mudstone-marl of a lower-middle Miocene lacustrine environment (Hançili Formation). The terrestrial conglomerate-sandstone alternation (Örencik Formation) is the youngest unit in the Cenozoic stratigraphy, and is assumed to be of Pliocene age based its stratigraphic position on older units. Field study shows existence of both folds and faults in the sedimentary cover. Stereographic projections of bedding measured in the field shows N25W/45NW and N60W/4SE-oriented fold axes in the Paleocene-Eocene age units. There are also N76W/12SE and N88E/8NE-oriented folds. The difference in fold-axis orientations suggests that some folds may have been rotated in blocks bound by faults during the post-Paleocene/Eocene period. Whereas, the lower-middle Miocene units manifest N88W/13SE-oriented fold axes. It is thus proposed that the observed difference in the azimuth of fold axes represent two different folding phases, one with NE-SW and the other with N-S directed axis of compression. Open folds with E-W orientation seem to be structural elements developed during the last phase of the deformation.
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Banham, Steve G.; Gupta, Sanjeev; Rubin, David M.; Watkins, Jessica A.; Sumner, Dawn Y.; Edgett, Kenneth S.; Grotzinger, John P.; Lewis, Kevin W.; Edgar, Lauren; Stack, Kathryn M.; Barnes, Robert; Bell, Jame F. III; Day, Mackenzie D.; Ewing, Ryan C.; Lapotre, Mathieu G.A.; Stein, Nathan T.; Rivera-Hernandez, Frances; Vasavada, Ashwin R.
2018-01-01
Reconstruction of the palaeoenvironmental context of Martian sedimentary rocks is central to studies of ancient Martian habitability and regional palaeoclimate history. This paper reports the analysis of a distinct aeolian deposit preserved in Gale crater, Mars, and evaluates its palaeomorphology, the processes responsible for its deposition, and its implications for Gale crater geological history and regional palaeoclimate. Whilst exploring the sedimentary succession cropping out on the northern flank of Aeolis Mons, Gale crater, the Mars Science Laboratory rover Curiosity encountered a decametre‐thick sandstone succession, named the Stimson formation, unconformably overlying lacustrine deposits of the Murray formation. The sandstone contains sand grains characterized by high roundness and sphericity, and cross‐bedding on the order of 1 m in thickness, separated by sub‐horizontal bounding surfaces traceable for tens of metres across outcrops. The cross‐beds are composed of uniform thickness cross‐laminations interpreted as wind‐ripple strata. Cross‐sets are separated by sub‐horizontal bounding surfaces traceable for tens of metres across outcrops that are interpreted as dune migration surfaces. Grain characteristics and presence of wind‐ripple strata indicate deposition of the Stimson formation by aeolian processes. The absence of features characteristic of damp or wet aeolian sediment accumulation indicate deposition in a dry aeolian system. Reconstruction of the palaeogeomorphology suggests that the Stimson dune field was composed largely of simple sinuous crescentic dunes with a height of ca10 m, and wavelengths of ca 150 m, with local development of complex dunes. Analysis of cross‐strata dip‐azimuths indicates that the general dune migration direction and hence net sediment transport was towards the north‐east. The juxtaposition of a dry aeolian system unconformably above the lacustrine Murray formation represents starkly contrasting palaeoenvironmental and palaeoclimatic conditions. Stratigraphic relationships indicate that this transition records a significant break in time, with the Stimson formation being deposited after the Murray formation and stratigraphically higher Mount Sharp group rocks had been buried, lithified and subsequently eroded.
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Toroidal rotation and ion heating during neutral beam injection in PBX-M
NASA Astrophysics Data System (ADS)
Asakura, N.; Fonck, R. J.; Jaehnig, K. P.; Kaye, S. M.; LeBlanc, B.; Okabayashi, M.
1993-08-01
Determination of the profiles of the ion temperature and the plasma toroidal rotation has been accomplished by charge exchange recombination spectroscopy in PBX-M. The angular momentum and the thermal ion energy transport have been studied mainly during the H mode phase of a high βp discharge (Ip approx 330 kA, 3.5 × 1019 <= ne <= 6.5 × 1019 m-3) having different heating beam configurations (combination of two perpendicular and two tangential neutral beam injections, abbreviated as 2 perp. NBI and 2 parall. NBI). The toroidal rotation velocity Vphi rises substantially in the region of r/a >= 0.5 after the L-H transition, and the Vphi profile (peakedness) is more highly dependent on the beam configuration than the Ti profile. The angular momentum confinement time varies from 147 ms (rigid rotation for 2 perp. NBI) to 39 ms (viscous rotation for 2 parall. NBI). In contrast, the thermal energy confinement time is 44-48 ms and is almost independent of the configuration. The transport analysis shows that the radial angular momentum diffusion is caused mainly by the viscous losses and that the angular momentum diffusivity χphi is reduced substantially in the outer minor radius region during the 2 perp. NBI H mode. The neoclassical friction effect between the bulk ions and the impurities may influence the χphi profiles locally, where the ion temperature gradient is steep
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NASA Astrophysics Data System (ADS)
Brookfield, Michael E.; Hashmat, Ajruddin
2001-10-01
The North Afghan platform has a pre-Jurassic basement unconformably overlain by a Jurassic to Paleogene oil- and gas-bearing sedimentary rock platform cover, unconformably overlain by Neogene syn- and post-orogenic continental clastics. The pre-Jurassic basement has four units: (1) An ?Ordovician to Lower Devonian passive margin succession developed on oceanic crust. (2) An Upper Devonian to Lower Carboniferous (Tournaisian) magmatic arc succession developed on the passive margin. (3) A Lower Carboniferous (?Visean) to Permian rift-passive margin succession. (4) A Triassic continental magmatic arc succession. The Mesozoic-Palaeogene cover has three units: (1) A ?Late Triassic to Middle Jurassic rift succession is dominated by variable continental clastics. Thick, coarse, lenticular coal-bearing clastics were deposited by braided and meandering streams in linear grabens, while bauxites formed on the adjacent horsts. (2) A Middle to Upper Jurassic transgressive-regressive succession consists of mixed continental and marine Bathonian to Lower Kimmeridgian clastics and carbonates overlain by regressive Upper Kimmeridgian-Tithonian evaporite-bearing clastics. (3) A Cretaceous succession consists of Lower Cretaceous red beds with evaporites, resting unconformably on Jurassic and older deposits, overlain (usually unconformably) by Cenomanian to Maastrichtian shallow marine limestones, which form a fairly uniform transgressive succession across most of Afghanistan. (4) A Palaeogene succession rests on the Upper Cretaceous limestones, with a minor break marked by bauxite in places. Thin Palaeocene to Upper Eocene limestones with gypsum are overlain by thin conglomerates, which pass up into shales with a restricted brackish-water ?Upper Oligocene-?Lower Miocene marine fauna. The Neogene succession consists of a variable thickness of coarse continental sediments derived from the rising Pamir mountains and adjacent ranges. Almost all the deformation of the North Afghan platform began in the Miocene. Oil and gas traps are mainly in Upper Jurassic carbonates and Lower Cretaceous sandstones across the entire North Afghan block. Upper Jurassic carbonate traps, sealed by evaporites, occur mainly north of the southern limit of the Upper Jurassic salt. Lower Cretaceous traps consist of fine-grained continental sandstones, sealed by Aptian-Albian shales and siltstones. Upper Cretaceous-Palaeocene carbonates, sealed by Palaeogene shales are the main traps along the northern edge of the platform and in the Tajik basin. Almost all the traps are broad anticlines related to Neogene wrench faulting, in this respect, like similar traps along the San Andreas fault. Hydrocarbon sources are in the Mesozoic section. The Lower-Middle Jurassic continental coal-bearing beds provide about 75% of the hydrocarbons; the Callovian-Oxfordian provides about 10%; the Neocomian a meagre 1%, and the Aptian-Albian about 14%. The coal-bearing source rocks decrease very markedly in thickness southwards cross the North Afghan platform. Much of the hydrocarbon generation probably occurred during the Late Cretaceous-Paleogene and migrated to structural traps during Neogene deformation. Since no regional structural dip aids southward hydrocarbon migration, and since the traps are all structural and somewhat small, then there is little chance of very large petroleum fields on the platform. Nevertheless, further studies of the North Afghan platform should be rewarding because: (a) the traps of strike-slip belts are difficult to find without detailed exploration; (b) the troubles of the last 20 years mean that almost no exploration has been done; and, (c) conditions may soon become more favorable. There should be ample potential for oil, and particularly gas, discoveries especially in the northern and western parts of the North Afghan platform.
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Investigation of Nuclear Structure and Quasi-Discrete Features in 150,152Sm via the (p,t) Reaction
NASA Astrophysics Data System (ADS)
Humby, Peter James Charnall
The (p,t) reaction was used to identify new levels and gamma-ray transitions in 150,152Sm utilising the particle-gamma and particle-gamma-gamma coincidence techniques. The experiment was performed using the STARLiTeR array located at the Cyclotron Institute of Texas A&M University. The relative partial cross sections for the observed levels, angle averaged between 34 and 58 degrees, were measured. A narrow peak-like structure was observed between 2.3-3.0 MeV excitation energy, in between the region of strongly populated discrete states at low energy and the high energy continuum region. In 150Sm, 39(4)% of the strength of the peak-like structure could be accounted for by the observed discrete states, which compares to a value of 93(15)% for 152Sm. The orbital angular-momentum transfer was probed by comparison of the experimental angular distributions to those calculated using the DWBA theory. The experimental angular distributions for the population of the peak-like structures are very similar in the two reactions, and significantly different to both the angular distribution of the background under the structures, and to the distribution obtained from the nearby continuum region at higher excitation energy. Post irradiation, the half-lives of isomeric states in 152Eu, populated in the 154Sm(p,3n) reaction, were obtained by measuring the decrease in intensity of the gamma rays emitted in the decay of these long lived levels. The half-life of the Jpi = 8- isomer 152m2Eu was measured to be 95.8(4) min, which is a factor of 2.5 reduction in uncertainty compared to the previous literature value of 96(1) min.
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Reconnaissance study of late quaternary faulting along cerro GoDen fault zone, western Puerto Rico
Mann, P.; Prentice, C.S.; Hippolyte, J.-C.; Grindlay, N.R.; Abrams, L.J.; Lao-Davila, D.
2005-01-01
The Cerro GoDen fault zone is associated with a curvilinear, continuous, and prominent topographic lineament in western Puerto Rico. The fault varies in strike from northwest to west. In its westernmost section, the fault is ???500 m south of an abrupt, curvilinear mountain front separating the 270- to 361-m-high La CaDena De San Francisco range from the Rio A??asco alluvial valley. The Quaternary fault of the A??asco Valley is in alignment with the bedrock fault mapped by D. McIntyre (1971) in the Central La Plata quadrangle sheet east of A??asco Valley. Previous workers have postulated that the Cerro GoDen fault zone continues southeast from the A??asco Valley and merges with the Great Southern Puerto Rico fault zone of south-central Puerto Rico. West of the A??asco Valley, the fault continues offshore into the Mona Passage (Caribbean Sea) where it is characterized by offsets of seafloor sediments estimated to be of late Quaternary age. Using both 1:18,500 scale air photographs taken in 1936 and 1:40,000 scale photographs taken by the U.S. Department of Agriculture in 1986, we iDentified geomorphic features suggestive of Quaternary fault movement in the A??asco Valley, including aligned and Deflected drainages, apparently offset terrace risers, and mountain-facing scarps. Many of these features suggest right-lateral displacement. Mapping of Paleogene bedrock units in the uplifted La CaDena range adjacent to the Cerro GoDen fault zone reveals the main tectonic events that have culminated in late Quaternary normal-oblique displacement across the Cerro GoDen fault. Cretaceous to Eocene rocks of the La CaDena range exhibit large folds with wavelengths of several kms. The orientation of folds and analysis of fault striations within the folds indicate that the folds formed by northeast-southwest shorTening in present-day geographic coordinates. The age of Deformation is well constrained as late Eocene-early Oligocene by an angular unconformity separating folDed, Deep-marine middle Eocene rocks from transgressive, shallow-marine rocks of middle-upper Oligocene age. Rocks of middle Oligocene-early Pliocene age above unconformity are gently folDed about the roughly east-west-trending Puerto Rico-Virgin Islands arch, which is well expressed in the geomorphology of western Puerto Rico. Arching appears ongoing because onshore and offshore late Quaternary oblique-slip faults closely parallel the complexly Deformed crest of the arch and appear to be related to exTensional strains focused in the crest of the arch. We estimate ???4 km of vertical throw on the Cerro GoDen fault based on the position of the carbonate cap north of the fault in the La CaDena De San Francisco and its position south of the fault inferred from seismic reflection data in Mayaguez Bay. Based on these observations, our interpretation of the kinematics and history of the Cerro GoDen fault zone incluDes two major phases of motion: (1) Eocene northeast-southwest shorTening possibly accompanied by left-lateral shearing as Determined by previous workers on the Great Southern Puerto Rico fault zone; and (2) post-early Pliocene regional arching of Puerto Rico accompanied by normal offset and right-lateral shear along faults flanking the crest of the arch. The second phase of Deformation accompanied east-west opening of the Mona rift and is inferred to continue to the present day. ?? 2005 Geological Society of America.
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NASA Astrophysics Data System (ADS)
Lehnert, O.; Calner, M.; Ahlberg, P.; Harper, D. A.
2012-04-01
Several prominent palaeokarst surfaces have recently been detected in the Cambro-Ordovician sedimentary succession of Sweden. The oldest palaeokarst was found in autumn 2011 in Västergötland. An irregular palaeokarst cave with a breccia fill yielding large, angular Orsten clasts in a dark mud- to wackestone matrix is exposed beneath a karstic surface in the Cambrian Alum Shale Formation at Kakeled Quarry, Kinnekulle. The karstic surface occurs near the top of the Kakeled Limestone Bed that ranges from the upper Agnostus pisiformis into the Ctenopyge tumida Zone. The base of the cave is more than 1.4 m below this unconformity. A mass occurrence of Orusia lenticularis, a shallow-water brachiopod originally settling on hard substrates, in the karst pockets reflects deposition of the conglomeratic cover in extremely shallow marine environments. We interpret the widespread Orusia occurrences together with a brecciated or conglomeratic interval above an irregular surface in various Swedish locations as evidence for transgression after a major regression, regionally exposing the sea-floors of the Alum Shale Basin. A slightly younger karst surface is exposed in Tomten Quarry at Torbjörntorp, Västergötland. This resembles "Schrattenkalk" in the quarry wall but rock slabs cut vertical and parallel to bedding display a karren system, which reconstructed in 3D resembles "Napfkarren" or cockling features. Trilobites of the Ctenopyge bisulcata and C. linnarssoni zones have been recovered from the orsten bed just below the base of a 1-2 cm thick and irregular glauconitic packstone layer of the Bjørkåsholmen Formation (upper P. deltifer conodont Zone). The huge stratigraphic gap comprises the six uppermost trilobite zones of the Furongian plus most of the Tremadocian. Darriwilian conodonts with reworked older material within a limestone bed slightly above the glauconitic packstone point to yet another substantial gap in the succession. In the new Tingskullen core from northeastern Öland a karstic surface with grikes and evidence of repeated exposure occurs on the top of the upper Djupvik Formation (equivalent to the Bjørkåsholmen Formation). This palaeokarst is covered by the Töyen Formation and represents erosion and karstification during the global Ceratopyge Regressive Event (CRE). Higher up in the Ordovician of Öland, the lower Dapingian Blommiga Bladet hardground complex (Flowery Sheet) preserves karst morphologies. It can be correlated by means of the typical large borings of Gastrochaenolites oelandicus across most of Baltoscandia, including the Siljan district (new observations). An unconformity has recently been identified on top of the Skagen Formation in the Röstånga core from Scania (Skåne). This surface yield solution features possibly of subaerial origin and correlates with a conglomerate at the upper boundary of the same formation in the Borenshult core (Östergötland). Lastly, a prominent, basin-wide palaeokarst horizon in the Upper Ordovician Slandrom Limestone has been recently documented in detail. The multiple karst horizons in the Cambro-Silurian of Sweden imply subaerial exposure, and even locally soil-forming processes, during major regressions. Their preservation implies rapid burial and transgression. The common evidence for palaeokarst together with other sedimentary and biotic proxies of extremely shallow-water, challenge earlier models favouring a stable and deep basin.
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NASA Astrophysics Data System (ADS)
Wińska, Małgorzata; Nastula, Jolanta; Kołaczek, Barbara
2016-02-01
The impact of continental hydrological loading from land water, snow and ice on polar motion excitation, calculated as hydrological angular momentum (HAM), is difficult to estimate, and not as much is known about it as about atmospheric angular momentum (AAM) and oceanic angular momentum (OAM). In this paper, regional hydrological excitations to polar motion are investigated using monthly terrestrial water storage data derived from the Gravity Recovery and Climate Experiment (GRACE) mission and from the five models of land hydrology. The results show that the areas where the variance shows large variability are similar for the different models of land hydrology and for the GRACE data. Areas which have a small amplitude on the maps make an important contribution to the global hydrological excitation function of polar motion. The comparison of geodetic residuals and global hydrological excitation functions of polar motion shows that none of the hydrological excitation has enough energy to significantly improve the agreement between the observed geodetic excitation and geophysical ones.
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Photoelectron angular distributions from rotationally resolved autoionizing states of N 2
Chartrand, A. M.; McCormack, E. F.; Jacovella, U.; ...
2017-12-08
The single-photon, photoelectron-photoion coincidence spectrum of N 2 has been recorded at high (~1.5 cm -1) resolution in the region between the N 2 + X 2Σ g +, v + = 0 and 1 ionization thresholds by using a double imaging spectrometer and intense vacuum-ultraviolet light from the Synchrotron SOLEIL. This approach provides the relative photoionization cross section, the photoelectron energy distribution, and the photoelectron angular distribution as a function of photon energy. The region of interest contains autoionizing valence states, vibrationally autoionizing Rydberg states converging to vibrationally excited levels of the N 2 + X 2Σ g +more » ground state, and electronically autoionizing states converging to the N 2 + A 2Π and B 2Σ u + states. The wavelength resolution is sufficient to resolve rotational structure in the autoionizing states, but the electron energy resolution is insufficient to resolve rotational structure in the photoion spectrum. Here, a simplified approach based on multichannel quantum defect theory is used to predict the photoelectron angular distribution parameters, β, and the results are in reasonably good agreement with experiment.« less
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Nanofocusing of structured light for quadrupolar light-matter interactions.
Sakai, Kyosuke; Yamamoto, Takeaki; Sasaki, Keiji
2018-05-17
The spatial structure of an electromagnetic field can determine the characteristics of light-matter interactions. A strong gradient of light in the near field can excite dipole-forbidden atomic transitions, e.g., electric quadrupole transitions, which are rarely observed under plane-wave far-field illumination. Structured light with a higher-order orbital angular momentum state may also modulate the selection rules in which an atom can absorb two quanta of angular momentum: one from the spin and another from the spatial structure of the beam. Here, we numerically demonstrate a strong focusing of structured light with a higher-order orbital angular momentum state in the near field. A quadrupole field was confined within a gap region of several tens of nanometres in a plasmonic tetramer structure. A plasmonic crystal surrounding the tetramer structure provides a robust antenna effect, where the incident structured light can be strongly coupled to the quadrupole field in the gap region with a larger alignment tolerance. The proposed system is expected to provide a platform for light-matter interactions with strong multipolar effects.
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NASA Technical Reports Server (NTRS)
Tosdal, R. M.; Sherrod, D. R.
1985-01-01
The geometry of Miocene extensional deformation, which changes along a 120 km-long, northeast-trending transect from the southestern Chocolate Mountains, southeastern California, to the Trigo and southern Dome Rock Mountains, southwestern Arizona is discussed. Based upon regional differences in the structural response to extension and estimated extensional strain, the transet can be divided into three northwesterly-trending structural domains. From southwest to northeast, these domains are: (1) southestern Chocolate-southernmost Trigo Mountains; (2) central to northern Trigo Mountains; and (3) Trigo Peaks-southern Dome Rock Mountains. All structures formed during the deformation are brittle in style; fault rocks are composed of gouge, cohesive gouge, and local microbreccia. In each structural domain, exposed lithologic units are composed of Mesozoic crystalline rocks unconformably overlain by Oligocene to Early Miocene volcanic and minor interbedded sedimentary rocks. Breccia, conglomerate, and sandstone deposited synchronously with regional extension locally overlie the volcanic rocks. Extensional deformation largely postdated the main phase of volcanic activity, but rare rhyolitic tuff and flows interbedded with the syndeformational clastic rocks suggest that deformation began during the waning stages of valcanism. K-Ar isotopic ages indicate that deformation occurred in Miocene time, between about 22 and m.y. ago.
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Pratt, Thomas L.; Holmes, Mark; Schweig, Eugene S.; Gomberg, Joan S.; Cowan, Hugh A.
2003-01-01
High-resolution seismic reflection profiles from Limo??n Bay, Republic of Panama, were acquired as part of a seismic hazard investigation of the northern Panama Canal region. The seismic profiles image gently west and northwest dipping strata of upper Miocene Gatu??n Formation, unconformably overlain by a thin (<20 m) sequence of Holocene muds. Numerous faults, which have northeast trends where they can be correlated between seismic profiles, break the upper Miocene strata. Some of the faults have normal displacement, but on many faults, the amount and type of displacement cannot be determined. The age of displacement is constrained to be Late Miocene or younger, and regional geologic considerations suggest Pliocene movement. The faults may be part of a more extensive set of north- to northeast-trending faults and fractures in the canal region of central Panama. Low topography and the faults in the canal area may be the result of the modern regional stress field, bending of the Isthmus of Panama, shearing in eastern Panama, or minor deformation of the Panama Block above the Caribbean subduction zone. For seismic hazard analysis of the northern canal area, these faults led us to include a source zone of shallow faults proximal to northern canal facilities. ?? 2003 Elsevier B.V. All rights reserved.
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DOE Office of Scientific and Technical Information (OSTI.GOV)
Hayakawa, T.; Ogata, K.; Miyamoto, S.
The M1 strengths (or level density of 1{sup +} states) are of importance for estimation of interaction strengths between neutrinos and nuclei for the study of the supernova neutrino-process. In 1957, Agodi predicted theoretically angular distribution of neutrons emitted from states excited via dipole transitions with linearly polarized gamma-ray beam at the polar angle of θ=90° should be followed by a simple function, a + b cos(2φ), where φ, is azimuthal angel. However, this theoretical prediction has not been verified over the wide mass region except for light nuclei as deuteron. We have measured neutron angular distributions with (polarized gamma,more » n) reactions on Au, Nal, and Cu. We have verified the Agodi's prediction for the first time over the wide mass region. This suggests that (polarized gamma, n) reactions may be useful tools to study M1 strengths in giant resonance regions.« less
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Spacecraft angular velocity estimation algorithm for star tracker based on optical flow techniques
NASA Astrophysics Data System (ADS)
Tang, Yujie; Li, Jian; Wang, Gangyi
2018-02-01
An integrated navigation system often uses the traditional gyro and star tracker for high precision navigation with the shortcomings of large volume, heavy weight and high-cost. With the development of autonomous navigation for deep space and small spacecraft, star tracker has been gradually used for attitude calculation and angular velocity measurement directly. At the same time, with the dynamic imaging requirements of remote sensing satellites and other imaging satellites, how to measure the angular velocity in the dynamic situation to improve the accuracy of the star tracker is the hotspot of future research. We propose the approach to measure angular rate with a nongyro and improve the dynamic performance of the star tracker. First, the star extraction algorithm based on morphology is used to extract the star region, and the stars in the two images are matched according to the method of angular distance voting. The calculation of the displacement of the star image is measured by the improved optical flow method. Finally, the triaxial angular velocity of the star tracker is calculated by the star vector using the least squares method. The method has the advantages of fast matching speed, strong antinoise ability, and good dynamic performance. The triaxial angular velocity of star tracker can be obtained accurately with these methods. So, the star tracker can achieve better tracking performance and dynamic attitude positioning accuracy to lay a good foundation for the wide application of various satellites and complex space missions.
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Kulesza, Joel A.; Solomon, Clell J.; Kiedrowski, Brian C.
2018-01-02
This paper presents a new method for performing angular biasing in Monte Carlo radiation transport codes using arbitrary convex polyhedra to define regions of interest toward which to project particles (DXTRAN regions). The method is derived and is implemented using axis-aligned right parallelepipeds (AARPPs) and arbitrary convex polyhedra. Attention is also paid to possible numerical complications and areas for future refinement. A series of test problems are executed with void, purely absorbing, purely scattering, and 50% absorbing/50% scattering materials. For all test problems tally results using AARPP and polyhedral DXTRAN regions agree with analog and/or spherical DXTRAN results within statisticalmore » uncertainties. In cases with significant scattering the figure of merit (FOM) using AARPP or polyhedral DXTRAN regions is lower than with spherical regions despite the ability to closely fit the tally region. This is because spherical DXTRAN processing is computationally less expensive than AARPP or polyhedral DXTRAN processing. Thus, it is recommended that the speed of spherical regions be considered versus the ability to closely fit the tally region with an AARPP or arbitrary polyhedral region. It is also recommended that short calculations be made prior to final calculations to compare the FOM for the various DXTRAN geometries because of the influence of the scattering behavior.« less
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Generation and Sustainment of Plasma Rotation by ICRF Heating
NASA Astrophysics Data System (ADS)
Perkins, F. W.
2000-10-01
When tokamak plasmas are heated by the fundamental minority ion-cyclotron process, they are observed to rotate toroidally, even though this heating process introduces negligable angular momentum. This work proposes and evaluates a physics mechanism which resolves this apparent conflict. The argument has two elements. First, it is assumed that angular momentum transport is governed by a diffusion equation with a v_tor = 0 boundary condition at the plasma surface and a torque-density source. When the source consists of separated regions of positive and negative torque density, a finite central rotation velocity results, even though the volume integrated torque density - the angular momentum input - vanishes. Secondly, ions energized by the ICRF process can generate separated regions of positive and negative torque density. Heating increases their banana widths which leads to radial energetic-particle transport that must be balanced by neutralizing radial currents and a j_rB_pR torque density in the bulk plasma. Additional, comparable torque density results from collisional transfer of mechanical angular momentum from energetic particles to the bulk plasma and particle loss through banana particles impacting the wall. Monte-Carlo calculations utilizing the ORBIT code evaluate all sources of torque density and rigorously assure that no net angular momentum is introduced. Two models of ICRF heating, diffusive and instantaneous, give similar results. When the resonance location is on the LFS, the calculated rotation has the magnitude, profile, and co-current sense of Alcator C-Mod observations. For HFS resonance locations, the model predicts counter-current rotation. Scans of rotational profiles vs. resonance location, initial energy, particle loss, pitch, and qm will be presented as will the location of the velocity shear layer its scaling to a reactor.
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A systematic investigation of the (α, 2nγ) reaction on medium-heavy nuclei
NASA Astrophysics Data System (ADS)
Fields, C. A.; De Boer, F. W. N.; Ristinen, R. A.; Smith, P. A.; Sugarbaker, E.
1982-03-01
Exclusive neutron spectra and angular distributions have been measured for 28-35 MeV (α, 2nγ) reactions on various nuclei in the 80 ≦ A ≦ 210 region. Pre-equilibrium processes dominate the 35 MeV (α, 2nγ) reaction mechanism in much of this region. Analysis of systematic variation in the neutron spectrum parameters shows that the reaction mechanism is strongly correlated with the target neutron excess parameter ( N- Z/ A. Analysis of the γ-decay of the entry states shows that well-defined incident angular momentum windows exist for the pre-etjuilibrium (α, 2nγ) reaction. These features are discussed in terms of various models for the reaction mechanism.
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On the Variation of Eta with Energy in the 100-1000 ev Region
DOE R&D Accomplishments Database
Wigner, E. P.
1949-11-01
Fluctuations in the fission yield in the 100- to 1000-ev region led to an investigation of the influencing variables. Changes in fission width from level to level and higher angular momentum phenomena are seen as possible explanations. (D.E.B.)
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NASA Astrophysics Data System (ADS)
Hougardy, Devin D.
The history of glacial Lake Agassiz is complex and has intrigued researchers for over a century. Over the course of its ˜5,000 year existence, the size, shape, and location of Lake Agassiz changed dramatically depending on the location of the southern margin of the Laurentide Ice Sheet (LIS), the location and elevation of outflow channels, and differential isostatic rebound. Some of the best-preserved sequences of Lake Agassiz sediments are found in remnant lake basins where erosional processes are less pronounced than in adjacent higher-elevation regions. Lake of the Woods (LOTW), Minnesota, is among the largest of the Lake Agassiz remnant lakes and is an ideal location for Lake Agassiz sediment accumulation. High-resolution seismic-reflection (CHIRP) data collected from the southern basin of LOTW reveal up to 28 m of stratified lacustrine sediment deposited on top of glacial diamicton and bedrock. Five seismic units (SU A-E) were identified and described based on their reflection character, reflection configuration, and external geometries. Three prominent erosional unconformities (UNCF 1-3) underlie the upper three seismic units and indicate that deposition at LOTW was interrupted by a series of relatively large fluctuations in lake level. The lowermost unconformity (UNCF-1) truncates uniformly draped reflections within SU-B at the margins of the basin, where as much as four meters of sediment were eroded. The drop in lake level is interpreted to be contemporaneous with the onset of the low-stand Moorhead phase of Lake Agassiz identified from subaerial deposits in the Red River Valley, Rainy River basin, and Lake Winnipeg. A rise in lake level, indicated by onlapping reflections within SU-C onto UNCF-1, shifted the wave base outwards and as much as 11 m of sediment were deposited (SU-C) in the middle of the basin before a second drop, and subsequent rise, in lake level resulted in the formation of UNCF-2. Reflections in the lower part of SU-D onlap onto UNCF-2 only near the margins of the basin, suggesting that water occupied much of the middle of the southern basin after lake level drawdown. The reflection character and configuration of SU-C and SU-D are genetically different indicating that the depositional environment had changed following the formation of UNCF-2. Piston-type sediment cores collected from the southern basin of LOTW at depths that correspond to the middle of SU-D contain high amounts of organic material and charcoal fragments and sediment that are probably not related to Lake Agassiz. Instead, they were likely deposited during a transitional phase between when Lake Agassiz left the LOTW basin (UNCF-2) and inundation of LOTW from the northern basin due to differential isostatic rebound (UNCF-3). All sediment cores collected from the southern basin of LOTW record the uppermost unconformity, analogous in depth to UNCF-3 in the seismic images, which separates modern sediments from mid to late-Holocene sediments. The lithology of sediments below this unconformity varies across the basin from gray clay to laminated silt and clay. Radiocarbon ages from two peat layers immediately below the unconformity indicate that subaerial conditions had existed prior to the formation of UNCF-1, at about 7.75 ka cal BP. The timing correlates well with other lakes in the upper Midwest that record a prolonged dry climate during the mid-Holocene. UNCF-3 is planar and erosional across the entire survey area but erosion is greatest in the northern part of the basin as the result of a southward transgressing wave base driven by differential isostatic rebound. Deposition in the southern basin probably resumed around 3.3 ka cal BP, though no radiocarbon dates were collected directly above UNCF-3. The lithology of sediment above UNCF-3 is highly uniform across the basin and represents modern sedimentation. Late-Holocene sedimentation rates were calculated at about 0.9 mm year-1 and are roughly double the sedimentation rates in the NW Angle basin, suggesting that erosion of the southern shoreline contributes significantly to deposition in the southern basin.
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Digital database of microfossil localities in Alameda and Contra Costa Counties, California
McDougall, Kristin; Block, Debra L.
2014-01-01
The eastern San Francisco Bay region (Contra Costa and Alameda Counties, California) is a geologically complex area divided by faults into a suite of tectonic blocks. Each block contains a unique stratigraphic sequence of Tertiary sediments that in most blocks unconformably overlie Mesozoic sediments. Age and environmental interpretations based on analysis of microfossil assemblages are key factors in interpreting geologic history, structure, and correlation of each block. Much of this data, however, is distributed in unpublished internal reports and memos, and is generally unavailable to the geologic community. In this report the U.S. Geological Survey microfossil data from the Tertiary sediments of Alameda and Contra Costa counties are analyzed and presented in a digital database, which provides a user-friendly summary of the micropaleontologic data, locality information, and biostratigraphic and ecologic interpretations.
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Paleomagnetic evidence for rapid vertical-axis rotation in the Peruvian Cordillera ca. 8 Ma
NASA Astrophysics Data System (ADS)
Rousse, Sonia; Gilder, Stuart; Farber, Daniel; McNulty, Brendan; Torres, Victor R.
2002-01-01
Paleomagnetic results from 31 Neogene sites in the Peruvian Andes yield primary magnetizations, as demonstrated by positive fold and reversal tests. Strata dated as 18 9 Ma record a significant counterclockwise rotation (-11° ± 5°), whereas unconformably overlying younger strata (7 6 Ma) are not rotated. The age of rotation thus is between 9 and 7 Ma, a period that coincides with the widespread Quechua 2 deformation phase. Moreover, eight independent studies on 107 9 Ma rocks from Peru between 9°S and 15°S reveal similar and significant rotations (-15° ± 6°). This suggests that the region rotated during a 2 m.y. period of deformation ca. 8 Ma, when the Andes underwent rapid uplift and important deformation commenced in the Subandean zone.
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Stratigraphic development and hydrothermal activity in the central western Cascade Range, Oregon
DOE Office of Scientific and Technical Information (OSTI.GOV)
Cummings, M.L.; Bull, M.K.; Pollock, J.M.
1990-11-10
Two volcanic sequences bounded by erosional unconformities compose the stratigraphy of the North Santiam mining district, Western Cascade Range, Oregon. Diorite, grandodiorite, and leucocratic quartz porphyry dikes, stocks, and sills intrude the breccias, flows, and tuffs of a volcanic center in the older Sardine Formation. Tourmaline-bearing breccia pipes are associated with the porphyritic granodiorite intrusions. An erosional unconformity separates the Sardine Formation from the overlying Elk Lake formation. The alteration patterns in the two formations are consistent with the development of hydrothermal systems during the eruption of each formation. However, the development of the two hydrothermal systems is separated bymore » a period of erosion of the older volcanic pile. Early formation of mineralization that resembles porphyry copper deposits occurred within the Sardine Formation, and later, after eruption of the Elk Lake formation, epithermal veins and alteration developed along faults, fractures, and the margins of dikes in the Sardine Formation.« less
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Diagenetic silica enrichment and late-stage groundwater activity in Gale crater, Mars
Frydenvang, Jens; Gasda, Patrick J.; Hurowitz, Joel A.; Grotzinger, John P.; Wiens, Roger C.; Newsom, Horton E.; Edgett, Ken S.; Watkins, Jessica; Bridges, John C.; Maurice, Sylvestre; Fisk, Martin R.; Johnson, Jeffrey R.; Rapin, William; Stein, Nathan; Clegg, Sam M.; Schwenzer, S. P.; Bedford, C.; Edwards, P.; Mangold, Nicolas; Cousin, Agnes; Anderson, Ryan; Payre, Valerie; Vaniman, David; Blake, David; Lanza, Nina L.; Gupta, Sanjeev; Van Beek, Jason; Sautter, Violaine; Meslin, Pierre-Yves; Rice, Melissa; Milliken, Ralf; Gellert, Ralf; Thompson, Lucy; Clark, Ben C.; Sumner, Dawn Y.; Fraeman, Abigail A.; Kinch, Kjartan M; Madsen, Morten B.; Mitofranov, Igor; Jun, Insoo; Calef, Fred J.; Vasavada, Ashwin R.
2017-01-01
Diagenetic silica enrichment in fracture-associated halos that crosscut lacustrine and unconformably overlying aeolian sedimentary bedrock is observed on the lower north slope of Aeolis Mons in Gale crater, Mars. The diagenetic silica enrichment is colocated with detrital silica enrichment observed in the lacustrine bedrock yet extends into a considerably younger, unconformably draping aeolian sandstone, implying that diagenetic silica enrichment postdates the detrital silica enrichment. A causal connection between the detrital and diagenetic silica enrichment implies that water was present in the subsurface of Gale crater long after deposition of the lacustrine sediments and that it mobilized detrital amorphous silica and precipitated it along fractures in the overlying bedrock. Although absolute timing is uncertain, the observed diagenesis likely represents some of the most recent groundwater activity in Gale crater and suggests that the timescale of potential habitability extended considerably beyond the time that the lacustrine sediments of Aeolis Mons were deposited.
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Aaij, R.; Adeva, B.; Adinolfi, M.; ...
2016-12-01
Here, measurements of the differential branching fraction and angular moments of the decay B 0 → K +π - μ + μ - in the K +π - invariant mass range 1330 < m(K +π -) < 1530 MeV/c 2 are presented. Proton-proton collision data are used, corresponding to an integrated luminosity of 3 fb -1 collected by the LHCb experiment. Differential branching fraction measurements are reported in five bins of the invariant mass squared of the dimuon system, q 2, between 0.1 and 8.0 GeV 2/c 4. For the first time, an angular analysis sensitive to the S-, P-more » and D-wave contributions of this rare decay is performed. The set of 40 normalised angular moments describing the decay is presented for the q 2 range 1.1-6.0 GeV 2/c 4.« less
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Peter, Humby; Simon, Anna; Beausang, C. W.; ...
2016-01-01
New levels and γ-ray transitions were identified in 150,152Sm utilizing the (p,t) reaction and particle-γ coincidence data. A large, peak-like structure observed between 2.3–3.0 MeV in excitation energy in the triton energy spectra was also investigated. The orbital angular-momentum transfer was probed by comparing the experimental angular distributions of the outgoing tritons to calculated distorted wave Born approximation curves. The angular distributions of the outgoing tritons populating the peak-like structure are remarkably similar in the two reactions and are significantly different from the angular distributions associated with the nearby continuum region. Relative partial cross sections for the observed levels, anglemore » averaged between 34 and 58 degrees, were measured. In 150Sm, 39(4)% of the strength of the peak-like structure could be accounted for by the observed discrete states. This compares with a value of 93(15)% for 152Sm« less
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DOE Office of Scientific and Technical Information (OSTI.GOV)
Peter, Humby; Simon, Anna; Beausang, C. W.
New levels and γ-ray transitions were identified in 150,152Sm utilizing the (p,t) reaction and particle-γ coincidence data. A large, peak-like structure observed between 2.3–3.0 MeV in excitation energy in the triton energy spectra was also investigated. The orbital angular-momentum transfer was probed by comparing the experimental angular distributions of the outgoing tritons to calculated distorted wave Born approximation curves. The angular distributions of the outgoing tritons populating the peak-like structure are remarkably similar in the two reactions and are significantly different from the angular distributions associated with the nearby continuum region. Relative partial cross sections for the observed levels, anglemore » averaged between 34 and 58 degrees, were measured. In 150Sm, 39(4)% of the strength of the peak-like structure could be accounted for by the observed discrete states. This compares with a value of 93(15)% for 152Sm« less
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DOE Office of Scientific and Technical Information (OSTI.GOV)
Aaij, R.; Adeva, B.; Adinolfi, M.
Here, measurements of the differential branching fraction and angular moments of the decay B 0 → K +π - μ + μ - in the K +π - invariant mass range 1330 < m(K +π -) < 1530 MeV/c 2 are presented. Proton-proton collision data are used, corresponding to an integrated luminosity of 3 fb -1 collected by the LHCb experiment. Differential branching fraction measurements are reported in five bins of the invariant mass squared of the dimuon system, q 2, between 0.1 and 8.0 GeV 2/c 4. For the first time, an angular analysis sensitive to the S-, P-more » and D-wave contributions of this rare decay is performed. The set of 40 normalised angular moments describing the decay is presented for the q 2 range 1.1-6.0 GeV 2/c 4.« less
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Mahato, Niladri Kumar
2011-12-01
The talus and the calcaneus share the bulk of load transmitted from the leg to the skeleton of the foot. The present study analyses the inter-relationship between the superior articular surface and the angular dimensions of the talus with the morphology of the sustentaculum tali. Identification of possible relationships between different angular parameters of the talus morphology and the sustentaculum tali in context of load transmission through the foot. One articular surface and three angular parameters at the junction of the head and the body were measured from dried human talar bones. Corresponding calcaneal samples were measured for four dimensions at the sustentaculum tali. Correlation and regression statistical values between parameters were worked out and analysed. Several parameters within the talus demonstrated significant correlations amongst themselves. The neck vertical angle showed a strong correlation with the articulating surface area below the head of the talus. The inter-relationship between articular and angular parameters within the talus demonstrates strong correlation for certain parameters. Data presented in the study may be helpful to adjust calcaneal and talar screw placement techniques, prosthesis designing and bio-mechanical studies at this important region. Copyright © 2011 Elsevier Ltd. All rights reserved.
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High energy gamma-ray astronomy observations of Geminga with the VERITAS array
NASA Astrophysics Data System (ADS)
Finnegan, Gary Marvin
The closest known supernova remnant and pulsar is Geminga. The Geminga pulsar is the first pulsar to have ever been detected initially by gamma rays and the first pulsar in a class of radio-quiet pulsars. In 2007, the Milagro collaboration detected a large angularly extended (˜ 2.6°) emission of high energy gamma rays (˜ 20 TeV ) that was positionally coincident with Geminga. The Very Energetic Radiation Imaging Telescope Array System (VERITAS) is a ground- based observatory with four imaging Cherenkov telescopes with an energy range between 100 GeV to more than 30 TeV. The imaging Cherenkov telescopes detect the Cherenkov light from charged particles in electromagnetic air showers initiated by high energy particles such as gamma rays and cosmic rays. Most gamma-ray sources detected by VERITAS are point like sources, which have an angular extension smaller than the angular resolution of the telescopes (˜ 0.1°). For a point source, the background noise can be measured in the same field of view (FOV) as the source. For an angularly extended object, such as Geminga, an external FOV from the source region must be used to estimate the background noise, to avoid contamination from the extended source region. In this dissertation, I describe a new analysis procedure that is designed to increase the observation sensitivity of angularly extended objects like Geminga. I apply this procedure to a known extended gamma-ray source, Boomerang, as well as Geminga. The results indicate the detection of very high energy emission from the Geminga region at the level of 4% of the Crab nebula with a weighted average spectral index of -2.8 ± 0.2. A possible extension less than one degree wide is shown. This detection, however, awaits a confirmation by the VERITAS collaboration. The luminosity of the Geminga extended source, the Vela Nebula, and the Crab nebula was calculated for energies greater than 1 TeV. The data suggest that older pulsars, such as Geminga and Vela, convert the spin-down power of the pulsar more efficiently to TeV energies than a younger pulsar such as the Crab pulsar.
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Stratigraphic comparison of six oil fields (WV) producing from Big Injun sandstones
DOE Office of Scientific and Technical Information (OSTI.GOV)
Zou, X.; Donaldson, A.C.
1993-08-01
Clustered within western West Virginia, six oil fields produce from the lower Mississippian Big Injun sandstones, and three more oil fields also supplement this production either from underlying Squaw or Weir sandstones. Shales separate these sandstones that occur stratigraphically between the Sunbury Shale (maximum flooding surface) and pre-Greenbrier unconformity (maximum regressive erosional surface), and represent highstand regressive deposits associated with the postorogenic phase of foreland basin accumulation. Stratigraphic studies show two Big Injun sandstones. The upper sandstone, called the Maccrady Big Injun, is separated from the lower Price/Pocono Big Injun sandstone by red shales. Both Big Injun sandstones consist ofmore » fine-grained river-mouth bars capped by coarse-grained river-channel deposits. Although the six fields are within three adjacent counties, Maccrady Big Injun sandstones of Blue Creek (Kanawha) and Rock Creek (Roane) fields are younger and were deposited by a different fluvial-deltaic system than the Price/Pocono Big Injun sandstones of Granny Creek (Clay), Tariff (Roane) Clendenin (Clay), and Pond Fork (Kanawha) fields. Upper Weir sandstones are thick, narrow north-trending belts underlying Pond Fork and Blue Creek fields, with properties suggesting wave-dominated shoreline deposits. Allocycles spanning separate drainage systems indicate eustasy. Postorogenic flexural adjustments probably explain stacked sandstone belts with superposed paleovalleys of overlying unconformities (pre-Greenbrier, Pottsville), particularly where aligned along or parallel basement structures of Rome trough or West Virginia dome. Initially, differential subsidence or uplift during sedimentation influenced the position, geometry, trend, and distribution patterns of these reservoir sandstone, then influenced their preserved condition during erosion of pre-Greenbrier unconformity.« less
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DOE Office of Scientific and Technical Information (OSTI.GOV)
Wingard, G.L.; Edwards, L.E.; McCartan, L.
1993-03-01
Preliminary analysis of paleontologic and isotopic data from 15 coreholes, integrated with the lithostratigraphic framework, has revealed three chronostratigraphic depositional units in the subsurface of the Arcadia and Sarasota 30 [times] 60-minute quadrangles, in the southern Florida peninsula. (1) An upper Oligocene depositional unit unconformably overlies the lower Oligocene Suwannee Formation and has been dated by using [sup 87]Sr/[sup 86]Sr values and molluscs. (2) A lower and middle Miocene depositional unit has been dated on the basis of [sup 87]Sr/[sup 86]Sr values, molluscs, and dinoflagellates. The upper boundary of this unit is marked by the top of the Venice Claymore » in the western part of the study area. (3) A Pliocene and Pleistocene depositional unit, dated on the basis of [sup 87]Sr/[sup 86]Sr values, molluscs, dinoflagellates, foraminifera, ostracodes, and pollen, unconformably overlies the lower and middle Miocene beds; this unconformity represents approximately a 13-million-year gap in the record. The Pliocene and Pleistocene unit is seen in the surficial deposits of the Caloosahatchee, Tamiami, Bermont, and Fort Thompson Formations. The interpretation of Florida's geologic history is hampered by the interfingering of onlap/offlap cycles from two coastlines, a unique situation in southeastern coastal plain geology. In addition, a complex diagenetic history, mixing of carbonate and siliciclastic regimes, and lack of surface exposures make interpretation of the stratigraphic sequences difficult. The chronostratigraphic depositional units identified cut across lithofacies boundaries and allow correlation across the Florida peninsula, thus leading to the development of coherent, well-defined lithostratigraphic units.« less
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NASA Astrophysics Data System (ADS)
Stoch, B.; Anthonissen, C. J.; McCall, M.-J.; Basson, I. J.; Deacon, J.; Cloete, E.; Botha, J.; Britz, J.; Strydom, M.; Nel, D.; Bester, M.
2017-12-01
The Sishen deposit is one of the largest iron ore concentrations in current production. Hematite mineralization occurs along a strike length of 14 km, with a width of 3.2 km and a maximum vertical extent of 400 m below the original surface. The 986-Mt reserve incorporates a suite of individual orebodies, beneath a locally preserved tectonized unconformity, with a wide range of geometries, depths, and orientations. Fully constrained, implicit 3D modeling of the entire mining volume (> 70 km3), was undertaken to the original, pre-mining topography. The model incorporates 5287 mapping points and > 21,000 drillholes and provides exceptional insight into the original configuration of ore and its relationship to contacts, unconformities, and structures in the enclosing country rock. The bulk of ore occurs to the west of a strike-extensive, partially inverted normal fault (Sloep Fault), within an asymmetrical synclinal structure on its western flank. This linear, N-S distribution of deep, thick ore is punctuated by palaeosinkholes, wherein base-of-ore dips of greater than 45°, are concentrically arranged. Localized ore volumes also occur along faults and in fault-bounded, downthrown blocks, to the north of NW-SE- and NE-SW-trending strike-slip faults that show relatively minor uplift to the south, probably due to the Lomanian Namaqua-Natal Orogeny. The revised model demonstrates the proximity of ore to a tectonized unconformity and highlights the structural control on ore volumes, implying that Fe mineralization at Sishen cannot be exclusively attributed to supergene enrichment and concentric palaeosinkhole formation.
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Widespread effects of middle Mississippian deformation in the Great Basin of western North America
Trexler, J.H.; Cashman, P.H.; Cole, J.C.; Snyder, W.S.; Tosdal, R.M.; Davydov, V.I.
2003-01-01
Stratigraphic analyses in central and eastern Nevada reveal the importance of a deformation event in middle Mississippian time that caused widespread deformation, uplift, and erosion. It occurred between middle Osagean and late Meramecian time and resulted in deposition of both synorogenic and postorogenic sediments. The deformation resulted in east-west shortening, expressed as east-vergent folding and east-directed thrusting; it involved sedimentary rocks of the Antler foredeep as well as strata associated with the Roberts Mountains allochthon. A latest Meramecian to early Chesterian unconformity, with correlative conformable lithofacies changes, postdates this deformation and occurs throughout Nevada. A tectonic highland-created in the middle Mississippian and lasting into the Pennsylvanian and centered in the area west and southwest of Carlin, Nevada- shed sediments eastward across the Antler foreland, burying the unconformity. Postorogenic strata are late Meramecian to early Chesterian at the base and are widespread throughout the Great Basin. The tectonism therefore occurred 20 to 30 m.y. after inception of the Late Devonian Antler orogeny, significantly extending the time span of this orogeny or representing a generally unrecognized orogenic event in the Paleozoic evolution of western North America. We propose a revised stratigraphic nomenclature for Mississippian strata in Nevada, based on detailed age control and the recognition of unconformities. This approach resolves the ambiguity of some stratigraphic names and emphasizes genetic relationships within the upper Paleozoic section. We take advantage of better stratigraphic understanding to propose two new stratigraphic units for southern and eastern Nevada: the middle Mississippian Gap Wash and Late Mississippian Captain Jack Formations.
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NASA Astrophysics Data System (ADS)
Lan, Qing; Yan, Yi; Huang, Chi-Yue; Clift, Peter D.; Li, Xuejie; Chen, Wenhuang; Zhang, Xingchang; Yu, Mengming
2014-09-01
The Cenozoic in East Asia is marked by major changes in tectonics, landscapes, and river systems, although the timing and nature of such changes remains disputed. We investigate the geochemistry and neodymium isotope character of Cenozoic mudstones spanning the breakup unconformity in the Western Foothills of Taiwan in order to constrain erosion and drainage development in southern China during the opening of the South China Sea. The La/Lu, Eu/Eu*, Th/Sc, Th/La, Cr/Th, and ɛNd values in these rocks show an abrupt change between ˜31 and 25 Ma. Generally the higher ɛNd values in sediments deposited prior to 31 Ma indicate erosion from Phanerozoic granitic sources exposed in coastal South China, whereas the lower ɛNd values suggest that the main sources had evolved to inland southern China by ˜25 Ma. The SHRIMP U-Pb ages of zircons from a tuff, together with biostratigraphy data constrain the breakup unconformity to be between ˜39 and 33 Ma, suggesting that the seafloor spreading in the South China Sea commenced before ˜33 Ma. This is significantly older than most of the oceanic crust preserved in the deeper part of the basin. Diachronous westward younging of the breakup unconformities and provenance changes of basins are consistent with seafloor spreading propagating from east to west. Initial spreading of the South China Sea prior to ˜33 Ma corresponds to tectonic adjustment in East Asia, including extrusion of the Indochina block and the rotation and eastward retreat of the subducting Pacific Plate.
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Smosna, R.; Bruner, K.R.; Riley, R.A.
2005-01-01
A karst-unconformity play at the top of the Ordovician Beekmantown Dolomite is judged to have great petroleum potential in Ohio and adjacent states; wells have high ultimate reserves and large areas remain untested. To better understand the origin, development, and distribution of Beekmantown porosity, we conducted a petrologic-stratigraphic study of cores and thin sections from 15 oil and gas wells. The massive dolomite, characterized by a hypidiotopic-idiotopic texture, formed by the replacement of stacked peritidal carbonate cycles. Secondary porosity occurs at two scales: (1) mesoscopic - breccia porosity, solution-enlarged fractures, large vugs, and caverns, and (2) microscopic - intercrystalline, intracrystalline, molds, small vugs, and microfractures. Mesoscopic pores (providing the major storage capacity in this reservoir) were produced by intrastratal solution and collapse of carbonate layers, whereas microscopic pores (connecting the larger pores) generally formed by the leaching of individual carbonate grains and crystals. Most pore types developed during periods of subaerial exposure across the carbonate bank, tied to either the numerous, though brief falls of relative sea level during Beekmantown deposition or more importantly the prolonged Knox unconformity at the close of sedimentation. The distribution of reservoir-quality porosity is quite heterogeneous, being confined vertically to a zone immediately below the unconformity and best developed laterally beneath buried hills and noses of this erosion surface. The inferred, shallow flow of ground water in the Beekmantown karst, primarily below topographic highs and above a diagenetic base level close to the water table, led to this irregular distribution of porosity.
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Tectonic implications of facies patterns, Lower Permian Dry Mountain trough, east-central Nevada
DOE Office of Scientific and Technical Information (OSTI.GOV)
Gallegos, D.M.; Snyder, W.S.; Spinosa, C.
1991-02-01
Paleozoic tectonism is indicated by a study of a west-east facies analysis transect across the northern portion of the Lower Permian Dry Mountain trough (DMT). In an attempt to characterize the Early Permian basin-filling sequences, three broadly recognizable facies packages have been identified across the DMT: the western margin facies and the central basin facies of the DMT and an eastern shelf facies. In the western margin facies of the basin, pulses of tectonic activity are recorded at McCloud Spring in the Sulphur Springs Range. Here, shallow open-marine carbonate overlies eroded Vinini Formation and, in turn, is unconformably overlain bymore » basinal marine carbonate. An unconformity also marks the contact with the overriding prograding coarse clastic facies. These abrupt transitions suggest the sediments were deposited in a tectonically active area where they preservation of Waltherian sequences is unlikely to occur. Similarly abrupt transitions are evident in the western part of the central basin facies. At Portuguese Springs n the Diamond Range, a thin basal marine conglomerate delineates Lower Permian sedimentation over the Pennsylvanian Ely Formation. Coarsening-upward basinal carbonate strata of pelagic, hemipelagic, and turbidite components overlie the basal conglomerate. this progression of sediments is unconformably overlain by a subaerial sequence of coarse clastic deposits. Within the eastern part of the central basin facies in the Maverick Spring Range, the Lower Permian sediments are open-marine siltstone, wackestone, packstone, and grainstone. The sediments are assigned to a gradually sloping ramp, indicating the effects of tectonism on this margin of the basin were subdued.« less
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Angular analysis of the B 0 → K *0 μ + μ - decay using 3 fb-1 of integrated luminosity
NASA Astrophysics Data System (ADS)
Aaij, R.; Abellán Beteta, C.; Adeva, B.; Adinolfi, M.; Affolder, A.; Ajaltouni, Z.; Akar, S.; Albrecht, J.; Alessio, F.; Alexander, M.; Ali, S.; Alkhazov, G.; Alvarez Cartelle, P.; Alves, A. A.; Amato, S.; Amerio, S.; Amhis, Y.; An, L.; Anderlini, L.; Andreassi, G.; Andreotti, M.; Andrews, J. E.; Appleby, R. B.; Aquines Gutierrez, O.; Archilli, F.; d'Argent, P.; Artamonov, A.; Artuso, M.; Aslanides, E.; Auriemma, G.; Baalouch, M.; Bachmann, S.; Back, J. J.; Badalov, A.; Baesso, C.; Baldini, W.; Barlow, R. J.; Barschel, C.; Barsuk, S.; Barter, W.; Batozskaya, V.; Battista, V.; Bay, A.; Beaucourt, L.; Beddow, J.; Bedeschi, F.; Bediaga, I.; Bel, L. J.; Bellee, V.; Belloli, N.; Belyaev, I.; Ben-Haim, E.; Bencivenni, G.; Benson, S.; Benton, J.; Berezhnoy, A.; Bernet, R.; Bertolin, A.; Bettler, M.-O.; van Beuzekom, M.; Bifani, S.; Billoir, P.; Bird, T.; Birnkraut, A.; Bizzeti, A.; Blake, T.; Blanc, F.; Blouw, J.; Blusk, S.; Bocci, V.; Bondar, A.; Bondar, N.; Bonivento, W.; Borghi, S.; Borisyak, M.; Borsato, M.; Bowcock, T. J. V.; Bowen, E.; Bozzi, C.; Braun, S.; Britsch, M.; Britton, T.; Brodzicka, J.; Brook, N. H.; Buchanan, E.; Burr, C.; Bursche, A.; Buytaert, J.; Cadeddu, S.; Calabrese, R.; Calvi, M.; Calvo Gomez, M.; Campana, P.; Campora Perez, D.; Capriotti, L.; Carbone, A.; Carboni, G.; Cardinale, R.; Cardini, A.; Carniti, P.; Carson, L.; Carvalho Akiba, K.; Casse, G.; Cassina, L.; Castillo Garcia, L.; Cattaneo, M.; Cauet, Ch.; Cavallero, G.; Cenci, R.; Charles, M.; Charpentier, Ph.; Chefdeville, M.; Chen, S.; Cheung, S.-F.; Chiapolini, N.; Chrzaszcz, M.; Cid Vidal, X.; Ciezarek, G.; Clarke, P. E. L.; Clemencic, M.; Cliff, H. V.; Closier, J.; Coco, V.; Cogan, J.; Cogneras, E.; Cogoni, V.; Cojocariu, L.; Collazuol, G.; Collins, P.; Comerma-Montells, A.; Contu, A.; Cook, A.; Coombes, M.; Coquereau, S.; Corti, G.; Corvo, M.; Couturier, B.; Cowan, G. A.; Craik, D. C.; Crocombe, A.; Cruz Torres, M.; Cunliffe, S.; Currie, R.; D'Ambrosio, C.; Dall'Occo, E.; Dalseno, J.; David, P. N. Y.; Davis, A.; De Aguiar Francisco, O.; De Bruyn, K.; De Capua, S.; De Cian, M.; De Miranda, J. M.; De Paula, L.; De Simone, P.; Dean, C.-T.; Decamp, D.; Deckenhoff, M.; Del Buono, L.; Déléage, N.; Demmer, M.; Derkach, D.; Deschamps, O.; Dettori, F.; Dey, B.; Di Canto, A.; Di Ruscio, F.; Dijkstra, H.; Donleavy, S.; Dordei, F.; Dorigo, M.; Dosil Suárez, A.; Dovbnya, A.; Dreimanis, K.; Dufour, L.; Dujany, G.; Dungs, K.; Durante, P.; Dzhelyadin, R.; Dziurda, A.; Dzyuba, A.; Easo, S.; Egede, U.; Egorychev, V.; Eidelman, S.; Eisenhardt, S.; Eitschberger, U.; Ekelhof, R.; Eklund, L.; El Rifai, I.; Elsasser, Ch.; Ely, S.; Esen, S.; Evans, H. M.; Evans, T.; Fabianska, M.; Falabella, A.; Färber, C.; Farley, N.; Farry, S.; Fay, R.; Ferguson, D.; Fernandez Albor, V.; Ferrari, F.; Ferreira Rodrigues, F.; Ferro-Luzzi, M.; Filippov, S.; Fiore, M.; Fiorini, M.; Firlej, M.; Fitzpatrick, C.; Fiutowski, T.; Fleuret, F.; Fohl, K.; Fol, P.; Fontana, M.; Fontanelli, F.; Forshaw, D. C.; Forty, R.; Frank, M.; Frei, C.; Frosini, M.; Fu, J.; Furfaro, E.; Gallas Torreira, A.; Galli, D.; Gallorini, S.; Gambetta, S.; Gandelman, M.; Gandini, P.; Gao, Y.; García Pardiñas, J.; Garra Tico, J.; Garrido, L.; Gascon, D.; Gaspar, C.; Gauld, R.; Gavardi, L.; Gazzoni, G.; Gerick, D.; Gersabeck, E.; Gersabeck, M.; Gershon, T.; Ghez, Ph.; Gianì, S.; Gibson, V.; Girard, O. G.; Giubega, L.; Gligorov, V. V.; Göbel, C.; Golubkov, D.; Golutvin, A.; Gomes, A.; Gotti, C.; Grabalosa Gándara, M.; Graciani Diaz, R.; Granado Cardoso, L. A.; Graugés, E.; Graverini, E.; Graziani, G.; Grecu, A.; Greening, E.; Griffith, P.; Grillo, L.; Grünberg, O.; Gui, B.; Gushchin, E.; Guz, Yu.; Gys, T.; Hadavizadeh, T.; Hadjivasiliou, C.; Haefeli, G.; Haen, C.; Haines, S. C.; Hall, S.; Hamilton, B.; Han, X.; Hansmann-Menzemer, S.; Harnew, N.; Harnew, S. T.; Harrison, J.; He, J.; Head, T.; Heijne, V.; Heister, A.; Hennessy, K.; Henrard, P.; Henry, L.; Hernando Morata, J. A.; van Herwijnen, E.; Heß, M.; Hicheur, A.; Hill, D.; Hoballah, M.; Hombach, C.; Hulsbergen, W.; Humair, T.; Hushchyn, M.; Hussain, N.; Hutchcroft, D.; Hynds, D.; Idzik, M.; Ilten, P.; Jacobsson, R.; Jaeger, A.; Jalocha, J.; Jans, E.; Jawahery, A.; John, M.; Johnson, D.; Jones, C. R.; Joram, C.; Jost, B.; Jurik, N.; Kandybei, S.; Kanso, W.; Karacson, M.; Karbach, T. M.; Karodia, S.; Kecke, M.; Kelsey, M.; Kenyon, I. R.; Kenzie, M.; Ketel, T.; Khairullin, E.; Khanji, B.; Khurewathanakul, C.; Kirn, T.; Klaver, S.; Klimaszewski, K.; Kochebina, O.; Kolpin, M.; Komarov, I.; Koopman, R. F.; Koppenburg, P.; Kozeiha, M.; Kravchuk, L.; Kreplin, K.; Kreps, M.; Krokovny, P.; Kruse, F.; Krzemien, W.; Kucewicz, W.; Kucharczyk, M.; Kudryavtsev, V.; Kuonen, A. K.; Kurek, K.; Kvaratskheliya, T.; Lacarrere, D.; Lafferty, G.; Lai, A.; Lambert, D.; Lanfranchi, G.; Langenbruch, C.; Langhans, B.; Latham, T.; Lazzeroni, C.; Le Gac, R.; van Leerdam, J.; Lees, J.-P.; Lefèvre, R.; Leflat, A.; Lefrançois, J.; Lemos Cid, E.; Leroy, O.; Lesiak, T.; Leverington, B.; Li, Y.; Likhomanenko, T.; Liles, M.; Lindner, R.; Linn, C.; Lionetto, F.; Liu, B.; Liu, X.; Loh, D.; Longstaff, I.; Lopes, J. H.; Lucchesi, D.; Lucio Martinez, M.; Luo, H.; Lupato, A.; Luppi, E.; Lupton, O.; Lusiani, A.; Machefert, F.; Maciuc, F.; Maev, O.; Maguire, K.; Malde, S.; Malinin, A.; Manca, G.; Mancinelli, G.; Manning, P.; Mapelli, A.; Maratas, J.; Marchand, J. F.; Marconi, U.; Marin Benito, C.; Marino, P.; Marks, J.; Martellotti, G.; Martin, M.; Martinelli, M.; Martinez Santos, D.; Martinez Vidal, F.; Martins Tostes, D.; Massacrier, L. M.; Massafferri, A.; Matev, R.; Mathad, A.; Mathe, Z.; Matteuzzi, C.; Mauri, A.; Maurin, B.; Mazurov, A.; McCann, M.; McCarthy, J.; McNab, A.; McNulty, R.; Meadows, B.; Meier, F.; Meissner, M.; Melnychuk, D.; Merk, M.; Michielin, E.; Milanes, D. A.; Minard, M.-N.; Mitzel, D. S.; Molina Rodriguez, J.; Monroy, I. A.; Monteil, S.; Morandin, M.; Morawski, P.; Mordà, A.; Morello, M. J.; Moron, J.; Morris, A. B.; Mountain, R.; Muheim, F.; Müller, D.; Müller, J.; Müller, K.; Müller, V.; Mussini, M.; Muster, B.; Naik, P.; Nakada, T.; Nandakumar, R.; Nandi, A.; Nasteva, I.; Needham, M.; Neri, N.; Neubert, S.; Neufeld, N.; Neuner, M.; Nguyen, A. D.; Nguyen, T. D.; Nguyen-Mau, C.; Niess, V.; Niet, R.; Nikitin, N.; Nikodem, T.; Novoselov, A.; O'Hanlon, D. P.; Oblakowska-Mucha, A.; Obraztsov, V.; Ogilvy, S.; Okhrimenko, O.; Oldeman, R.; Onderwater, C. J. G.; Osorio Rodrigues, B.; Otalora Goicochea, J. M.; Otto, A.; Owen, P.; Oyanguren, A.; Palano, A.; Palombo, F.; Palutan, M.; Panman, J.; Papanestis, A.; Pappagallo, M.; Pappalardo, L. L.; Pappenheimer, C.; Parker, W.; Parkes, C.; Passaleva, G.; Patel, G. D.; Patel, M.; Patrignani, C.; Pearce, A.; Pellegrino, A.; Penso, G.; Pepe Altarelli, M.; Perazzini, S.; Perret, P.; Pescatore, L.; Petridis, K.; Petrolini, A.; Petruzzo, M.; Picatoste Olloqui, E.; Pietrzyk, B.; Pikies, M.; Pinci, D.; Pistone, A.; Piucci, A.; Playfer, S.; Plo Casasus, M.; Poikela, T.; Polci, F.; Poluektov, A.; Polyakov, I.; Polycarpo, E.; Popov, A.; Popov, D.; Popovici, B.; Potterat, C.; Price, E.; Price, J. D.; Prisciandaro, J.; Pritchard, A.; Prouve, C.; Pugatch, V.; Puig Navarro, A.; Punzi, G.; Qian, W.; Quagliani, R.; Rachwal, B.; Rademacker, J. H.; Rama, M.; Ramos Pernas, M.; Rangel, M. S.; Raniuk, I.; Rauschmayr, N.; Raven, G.; Redi, F.; Reichert, S.; dos Reis, A. C.; Renaudin, V.; Ricciardi, S.; Richards, S.; Rihl, M.; Rinnert, K.; Rives Molina, V.; Robbe, P.; Rodrigues, A. B.; Rodrigues, E.; Rodriguez Lopez, J. A.; Rodriguez Perez, P.; Roiser, S.; Romanovsky, V.; Romero Vidal, A.; Ronayne, J. W.; Rotondo, M.; Ruf, T.; Ruiz Valls, P.; Saborido Silva, J. J.; Sagidova, N.; Saitta, B.; Salustino Guimaraes, V.; Sanchez Mayordomo, C.; Sanmartin Sedes, B.; Santacesaria, R.; Santamarina Rios, C.; Santimaria, M.; Santovetti, E.; Sarti, A.; Satriano, C.; Satta, A.; Saunders, D. M.; Savrina, D.; Schael, S.; Schiller, M.; Schindler, H.; Schlupp, M.; Schmelling, M.; Schmelzer, T.; Schmidt, B.; Schneider, O.; Schopper, A.; Schubiger, M.; Schune, M.-H.; Schwemmer, R.; Sciascia, B.; Sciubba, A.; Semennikov, A.; Sergi, A.; Serra, N.; Serrano, J.; Sestini, L.; Seyfert, P.; Shapkin, M.; Shapoval, I.; Shcheglov, Y.; Shears, T.; Shekhtman, L.; Shevchenko, V.; Shires, A.; Siddi, B. G.; Silva Coutinho, R.; Silva de Oliveira, L.; Simi, G.; Sirendi, M.; Skidmore, N.; Skwarnicki, T.; Smith, E.; Smith, E.; Smith, I. T.; Smith, J.; Smith, M.; Snoek, H.; Sokoloff, M. D.; Soler, F. J. P.; Soomro, F.; Souza, D.; Souza De Paula, B.; Spaan, B.; Spradlin, P.; Sridharan, S.; Stagni, F.; Stahl, M.; Stahl, S.; Stefkova, S.; Steinkamp, O.; Stenyakin, O.; Stevenson, S.; Stoica, S.; Stone, S.; Storaci, B.; Stracka, S.; Straticiuc, M.; Straumann, U.; Sun, L.; Sutcliffe, W.; Swientek, K.; Swientek, S.; Syropoulos, V.; Szczekowski, M.; Szumlak, T.; T'Jampens, S.; Tayduganov, A.; Tekampe, T.; Tellarini, G.; Teubert, F.; Thomas, C.; Thomas, E.; van Tilburg, J.; Tisserand, V.; Tobin, M.; Todd, J.; Tolk, S.; Tomassetti, L.; Tonelli, D.; Topp-Joergensen, S.; Torr, N.; Tournefier, E.; Tourneur, S.; Trabelsi, K.; Traill, M.; Tran, M. T.; Tresch, M.; Trisovic, A.; Tsaregorodtsev, A.; Tsopelas, P.; Tuning, N.; Ukleja, A.; Ustyuzhanin, A.; Uwer, U.; Vacca, C.; Vagnoni, V.; Valenti, G.; Vallier, A.; Vazquez Gomez, R.; Vazquez Regueiro, P.; Vázquez Sierra, C.; Vecchi, S.; van Veghel, M.; Velthuis, J. J.; Veltri, M.; Veneziano, G.; Vesterinen, M.; Viaud, B.; Vieira, D.; Vieites Diaz, M.; Vilasis-Cardona, X.; Volkov, V.; Vollhardt, A.; Voong, D.; Vorobyev, A.; Vorobyev, V.; Voß, C.; de Vries, J. A.; Waldi, R.; Wallace, C.; Wallace, R.; Walsh, J.; Wang, J.; Ward, D. R.; Watson, N. K.; Websdale, D.; Weiden, A.; Whitehead, M.; Wicht, J.; Wilkinson, G.; Wilkinson, M.; Williams, M.; Williams, M. P.; Williams, M.; Williams, T.; Wilson, F. F.; Wimberley, J.; Wishahi, J.; Wislicki, W.; Witek, M.; Wormser, G.; Wotton, S. A.; Wraight, K.; Wright, S.; Wyllie, K.; Xie, Y.; Xu, Z.; Yang, Z.; Yu, J.; Yuan, X.; Yushchenko, O.; Zangoli, M.; Zavertyaev, M.; Zhang, L.; Zhang, Y.; Zhelezov, A.; Zhokhov, A.; Zhong, L.; Zhukov, V.; Zucchelli, S.
2016-02-01
An angular analysis of the B 0 → K *0(→ K + π -) μ + μ - decay is presented. The dataset corresponds to an integrated luminosity of 3.0 fb-1 of pp collision data collected at the LHCb experiment. The complete angular information from the decay is used to determine CP-averaged observables and CP asymmetries, taking account of possible contamination from decays with the K + π - system in an S-wave configuration. The angular observables and their correlations are reported in bins of q 2, the invariant mass squared of the dimuon system. The observables are determined both from an unbinned maximum likelihood fit and by using the principal moments of the angular distribution. In addition, by fitting for q 2-dependent decay amplitudes in the region 1.1 < q 2 < 6.0 GeV2/ c 4, the zero-crossing points of several angular observables are computed. A global fit is performed to the complete set of CP-averaged observables obtained from the maximum likelihood fit. This fit indicates differences with predictions based on the Standard Model at the level of 3.4 standard deviations. These differences could be explained by contributions from physics beyond the Standard Model, or by an unexpectedly large hadronic effect that is not accounted for in the Standard Model predictions. [Figure not available: see fulltext.
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Griffith, H Randall; Stewart, Christopher C; Stoeckel, Luke E; Okonkwo, Ozioma C; den Hollander, Jan A; Martin, Roy C; Belue, Katherine; Copeland, Jacquelynn N; Harrell, Lindy E; Brockington, John C; Clark, David G; Marson, Daniel C
2010-02-01
To better understand how brain atrophy in amnestic mild cognitive impairment (MCI) as measured using magnetic resonance imaging (MRI) volumetrics could affect instrumental activities of daily living (IADLs) such as financial abilities. Controlled, matched-sample, cross-sectional analysis regressing MRI volumetrics with financial performance measures. University medical and research center. Thirty-eight people with MCI and 28 older adult controls. MRI volumetric measurement of the hippocampi, angular gyri, precunei, and medial frontal lobes. Participants also completed neuropsychological tests and the Financial Capacity Instrument (FCI). Correlations were performed between FCI scores and MRI volumes in the group with MCI. People with MCI performed significantly below controls on the FCI and had significantly smaller hippocampi. Among people with MCI, performance on the FCI was moderately correlated with angular gyri and precunei volumes. Regression models demonstrated that angular gyrus volumes were predictive of FCI scores. Tests of mediation showed that measures of arithmetic and possibly attention partially mediated the relationship between angular gyrus volume and FCI score. Impaired financial abilities in amnestic MCI correspond with volume of the angular gyri as mediated by arithmetic knowledge. The findings suggest that early neuropathology within the lateral parietal region in MCI leads to a breakdown of cognitive abilities that affect everyday financial skills. The findings have implications for diagnosis and clinical care of people with MCI and AD.
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Angular analysis of the B o → K *oμ +μ – decay using 3 fb –1 of integrated luminosity
Aaij, R.; Abellán Beteta, C.; Adeva, B.; ...
2016-02-16
An angular analysis of the B o → K *o (→ K +π –)μ +μ – decay is presented. The dataset corresponds to an integrated luminosity of 3.0 fb –1 of pp collision data collected at the LHCb experiment. The complete angular information from the decay is used to determine CP-averaged observables and CP asymmetries, taking account of possible contamination from decays with the K +π – system in an S-wave configuration. The angular observables and their correlations are reported in bins of q 2, the invariant mass squared of the dimuon system. The observables are determined both from anmore » unbinned maximum likelihood fit and by using the principal moments of the angular distribution. In addition, by fitting for q 2 -dependent decay amplitudes in the region 1.1 < q 2 < 6.0 GeV 2/c 4, the zero-crossing points of several angular observables are computed. A global fit is performed to the complete set of CP-averaged observables obtained from the maximum likelihood fit. This fit indicates differences with predictions based on the Standard Model at the level of 3.4 standard deviations. These differences could be explained by contributions from physics beyond the Standard Model, or by an unexpectedly large hadronic effect that is not accounted for in the Standard Model predictions.« less
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Techniques for High-contrast Imaging in Multi-star Systems. II. Multi-star Wavefront Control
NASA Astrophysics Data System (ADS)
Sirbu, D.; Thomas, S.; Belikov, R.; Bendek, E.
2017-11-01
Direct imaging of exoplanets represents a challenge for astronomical instrumentation due to the high-contrast ratio and small angular separation between the host star and the faint planet. Multi-star systems pose additional challenges for coronagraphic instruments due to the diffraction and aberration leakage caused by companion stars. Consequently, many scientifically valuable multi-star systems are excluded from direct imaging target lists for exoplanet surveys and characterization missions. Multi-star Wavefront Control (MSWC) is a technique that uses a coronagraphic instrument’s deformable mirror (DM) to create high-contrast regions in the focal plane in the presence of multiple stars. MSWC uses “non-redundant” modes on the DM to independently control speckles from each star in the dark zone. Our previous paper also introduced the Super-Nyquist wavefront control technique, which uses a diffraction grating to generate high-contrast regions beyond the Nyquist limit (nominal region correctable by the DM). These two techniques can be combined as MSWC-s to generate high-contrast regions for multi-star systems at wide (Super-Nyquist) angular separations, while MSWC-0 refers to close (Sub-Nyquist) angular separations. As a case study, a high-contrast wavefront control simulation that applies these techniques shows that the habitable region of the Alpha Centauri system can be imaged with a small aperture at 8× {10}-9 mean raw contrast in 10% broadband light in one-sided dark holes from 1.6-5.5 λ/D. Another case study using a larger 2.4 m aperture telescope such as the Wide-Field Infrared Survey Telescope uses these techniques to image the habitable zone of Alpha Centauri at 3.2× {10}-9 mean raw contrast in monochromatic light.
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Single crystal metal wedges for surface acoustic wave propagation
Fisher, E.S.
1980-05-09
An ultrasonic testing device has been developed to evaluate flaws and inhomogeneities in the near-surface region of a test material. A metal single crystal wedge is used to generate high frequency Rayleigh surface waves in the test material surface by conversion of a slow velocity, bulk acoustic mode in the wedge into a Rayleigh wave at the metal-wedge test material interface. Particular classes of metals have been found to provide the bulk acoustic modes necessary for production of a surface wave with extremely high frequency and angular collimation. The high frequency allows flaws and inhomogeneities to be examined with greater resolution. The high degree of angular collimation for the outgoing ultrasonic beam permits precision angular location of flaws and inhomogeneities in the test material surface.
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Single crystal metal wedges for surface acoustic wave propagation
Fisher, Edward S.
1982-01-01
An ultrasonic testing device has been developed to evaluate flaws and inhomogeneities in the near-surface region of a test material. A metal single crystal wedge is used to generate high frequency Rayleigh surface waves in the test material surface by conversion of a slow velocity, bulk acoustic mode in the wedge into a Rayleigh wave at the metal-wedge test material interface. Particular classes of metals have been found to provide the bulk acoustic modes necessary for production of a surface wave with extremely high frequency and angular collimation. The high frequency allows flaws and inhomogeneities to be examined with greater resolution. The high degree of angular collimation for the outgoing ultrasonic beam permits precision angular location of flaws and inhomogeneities in the test material surface.
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Magnetoresistance effect in (La, Sr)MnO3 bicrystalline films.
Alejandro, G; Steren, L B; Pastoriza, H; Vega, D; Granada, M; Sánchez, J C Rojas; Sirena, M; Alascio, B
2010-09-01
The angular dependence of the magnetoresistance effect has been measured on bicrystalline La(0.75)Sr(0.25)MnO(3) films. The measurements have been performed on an electronically lithographed Wheatstone bridge. The study of the angular dependence of both the magnetoresistance and the resistance of single-crystalline and grain-boundary regions of the samples allowed us to isolate two contributions of low-field magnetoresistance in manganites. One of them is associated with the spin-orbit effect, i.e. the anisotropic magnetoresistance of ferromagnetic compounds, and the other one is related to spin-disorder regions at the grain boundary. Complementary x-ray diffraction, ferromagnetic resonance and low temperature magnetization experiments contribute to the characterization of the magnetic anisotropy of the samples and the general comprehension of the problem.
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A Classroom Demonstration of Thermohaline Circulation.
ERIC Educational Resources Information Center
Dudley, Walter C.
1984-01-01
Density-driven deep circulation is important in influencing geologic processes ranging from the dissolution of biogenic siliceous and calcareous sediments to the formation of erosional unconformities. A technique for dynamically demonstrating this process using an aquarium to enhance student understanding is described. (BC)
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NASA Astrophysics Data System (ADS)
Wang, Jin; Li, Haoxu; Zhang, Xiaofeng; Wu, Rangzhong
2017-05-01
Indoor positioning using visible light communication has become a topic of intensive research in recent years. Because the normal of the receiver always deviates from that of the transmitter in application, the positioning systems which require that the normal of the receiver be aligned with that of the transmitter have large positioning errors. Some algorithms take the angular vibrations into account; nevertheless, these positioning algorithms cannot meet the requirement of high accuracy or low complexity. A visible light positioning algorithm combined with angular vibration compensation is proposed. The angle information from the accelerometer or other angle acquisition devices is used to calculate the angle of incidence even when the receiver is not horizontal. Meanwhile, a received signal strength technique with high accuracy is employed to determine the location. Moreover, an eight-light-emitting-diode (LED) system model is provided to improve the accuracy. The simulation results show that the proposed system can achieve a low positioning error with low complexity, and the eight-LED system exhibits improved performance. Furthermore, trust region-based positioning is proposed to determine three-dimensional locations and achieves high accuracy in both the horizontal and the vertical components.
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NASA Astrophysics Data System (ADS)
Lees, J. P.; Poireau, V.; Prencipe, E.; Tisserand, V.; Garra Tico, J.; Grauges, E.; Martinelli, M.; Milanes, D. A.; Palano, A.; Pappagallo, M.; Eigen, G.; Stugu, B.; Sun, L.; Brown, D. N.; Kerth, L. T.; Kolomensky, Yu. G.; Lynch, G.; Koch, H.; Schroeder, T.; Asgeirsson, D. J.; Hearty, C.; Mattison, T. S.; McKenna, J. A.; Khan, A.; Blinov, V. E.; Buzykaev, A. R.; Druzhinin, V. P.; Golubev, V. B.; Kravchenko, E. A.; Onuchin, A. P.; Serednyakov, S. I.; Skovpen, Yu. I.; Solodov, E. P.; Todyshev, K. Yu.; Yushkov, A. N.; Bondioli, M.; Curry, S.; Kirkby, D.; Lankford, A. J.; Mandelkern, M.; Stoker, D. P.; Atmacan, H.; Gary, J. W.; Liu, F.; Long, O.; Vitug, G. M.; Campagnari, C.; Hong, T. M.; Kovalskyi, D.; Richman, J. D.; West, C. A.; Eisner, A. M.; Kroseberg, J.; Lockman, W. S.; Martinez, A. J.; Schalk, T.; Schumm, B. A.; Seiden, A.; Cheng, C. H.; Doll, D. A.; Echenard, B.; Flood, K. T.; Hitlin, D. G.; Ongmongkolkul, P.; Porter, F. C.; Rakitin, A. Y.; Andreassen, R.; Dubrovin, M. S.; Meadows, B. T.; Sokoloff, M. D.; Bloom, P. C.; Ford, W. T.; Gaz, A.; Nagel, M.; Nauenberg, U.; Smith, J. G.; Wagner, S. R.; Ayad, R.; Toki, W. H.; Spaan, B.; Kobel, M. J.; Schubert, K. R.; Schwierz, R.; Bernard, D.; Verderi, M.; Clark, P. J.; Playfer, S.; Watson, J. E.; Bettoni, D.; Bozzi, C.; Calabrese, R.; Cibinetto, G.; Fioravanti, E.; Garzia, I.; Luppi, E.; Munerato, M.; Negrini, M.; Piemontese, L.; Baldini-Ferroli, R.; Calcaterra, A.; de Sangro, R.; Finocchiaro, G.; Nicolaci, M.; Pacetti, S.; Patteri, P.; Peruzzi, I. M.; Piccolo, M.; Rama, M.; Zallo, A.; Contri, R.; Guido, E.; Lo Vetere, M.; Monge, M. R.; Passaggio, S.; Patrignani, C.; Robutti, E.; Bhuyan, B.; Prasad, V.; Lee, C. L.; Morii, M.; Edwards, A. J.; Adametz, A.; Marks, J.; Uwer, U.; Bernlochner, F. U.; Ebert, M.; Lacker, H. M.; Lueck, T.; Dauncey, P. D.; Tibbetts, M.; Behera, P. K.; Mallik, U.; Chen, C.; Cochran, J.; Crawley, H. B.; Meyer, W. T.; Prell, S.; Rosenberg, E. I.; Rubin, A. E.; Gritsan, A. V.; Guo, Z. J.; Arnaud, N.; Davier, M.; Derkach, D.; Grosdidier, G.; Le Diberder, F.; Lutz, A. M.; Malaescu, B.; Roudeau, P.; Schune, M. H.; Stocchi, A.; Wormser, G.; Lange, D. J.; Wright, D. M.; Bingham, I.; Chavez, C. A.; Coleman, J. P.; Fry, J. R.; Gabathuler, E.; Hutchcroft, D. E.; Payne, D. J.; Touramanis, C.; Bevan, A. J.; di Lodovico, F.; Sacco, R.; Sigamani, M.; Cowan, G.; Paramesvaran, S.; Brown, D. N.; Davis, C. L.; Denig, A. G.; Fritsch, M.; Gradl, W.; Hafner, A.; Alwyn, K. E.; Bailey, D.; Barlow, R. J.; Jackson, G.; Lafferty, G. D.; Cenci, R.; Hamilton, B.; Jawahery, A.; Roberts, D. A.; Simi, G.; Dallapiccola, C.; Salvati, E.; Cowan, R.; Dujmic, D.; Sciolla, G.; Lindemann, D.; Patel, P. M.; Robertson, S. H.; Schram, M.; Biassoni, P.; Lazzaro, A.; Lombardo, V.; Palombo, F.; Stracka, S.; Cremaldi, L.; Godang, R.; Kroeger, R.; Sonnek, P.; Summers, D. J.; Nguyen, X.; Taras, P.; de Nardo, G.; Monorchio, D.; Onorato, G.; Sciacca, C.; Raven, G.; Snoek, H. L.; Jessop, C. P.; Knoepfel, K. J.; Losecco, J. M.; Wang, W. F.; Honscheid, K.; Kass, R.; Brau, J.; Frey, R.; Sinev, N. B.; Strom, D.; Torrence, E.; Feltresi, E.; Gagliardi, N.; Margoni, M.; Morandin, M.; Posocco, M.; Rotondo, M.; Simonetto, F.; Stroili, R.; Ben-Haim, E.; Bomben, M.; Bonneaud, G. R.; Briand, H.; Calderini, G.; Chauveau, J.; Hamon, O.; Leruste, Ph.; Marchiori, G.; Ocariz, J.; Sitt, S.; Biasini, M.; Manoni, E.; Rossi, A.; Angelini, C.; Batignani, G.; Bettarini, S.; Carpinelli, M.; Casarosa, G.; Cervelli, A.; Forti, F.; Giorgi, M. A.; Lusiani, A.; Neri, N.; Oberhof, B.; Paoloni, E.; Perez, A.; Rizzo, G.; Walsh, J. J.; Lopes Pegna, D.; Lu, C.; Olsen, J.; Smith, A. J. S.; Telnov, A. V.; Anulli, F.; Cavoto, G.; Faccini, R.; Ferrarotto, F.; Ferroni, F.; Gaspero, M.; Li Gioi, L.; Mazzoni, M. A.; Piredda, G.; Bünger, C.; Hartmann, T.; Leddig, T.; Schröder, H.; Waldi, R.; Adye, T.; Olaiya, E. O.; Wilson, F. F.; Emery, S.; Hamel de Monchenault, G.; Vasseur, G.; Yèche, Ch.; Aston, D.; Bard, D. J.; Bartoldus, R.; Benitez, J. F.; Cartaro, C.; Convery, M. R.; Dorfan, J.; Dubois-Felsmann, G. P.; Dunwoodie, W.; Field, R. C.; Franco Sevilla, M.; Fulsom, B. G.; Gabareen, A. M.; Graham, M. T.; Grenier, P.; Hast, C.; Innes, W. R.; Kelsey, M. H.; Kim, H.; Kim, P.; Kocian, M. L.; Leith, D. W. G. S.; Lewis, P.; Li, S.; Lindquist, B.; Luitz, S.; Luth, V.; Lynch, H. L.; Macfarlane, D. B.; Muller, D. R.; Neal, H.; Nelson, S.; Ofte, I.; Perl, M.; Pulliam, T.; Ratcliff, B. N.; Roodman, A.; Salnikov, A. A.; Santoro, V.; Schindler, R. H.; Snyder, A.; Su, D.; Sullivan, M. K.; Va'Vra, J.; Wagner, A. P.; Weaver, M.; Wisniewski, W. J.; Wittgen, M.; Wright, D. H.; Wulsin, H. W.; Yarritu, A. K.; Young, C. C.; Ziegler, V.; Park, W.; Purohit, M. V.; White, R. M.; Wilson, J. R.; Randle-Conde, A.; Sekula, S. J.; Bellis, M.; Burchat, P. R.; Miyashita, T. S.; Alam, M. S.; Ernst, J. A.; Gorodeisky, R.; Guttman, N.; Peimer, D. R.; Soffer, A.; Lund, P.; Spanier, S. M.; Eckmann, R.; Ritchie, J. L.; Ruland, A. M.; Schilling, C. J.; Schwitters, R. F.; Wray, B. C.; Izen, J. M.; Lou, X. C.; Bianchi, F.; Gamba, D.; Lanceri, L.; Vitale, L.; Lopez-March, N.; Martinez-Vidal, F.; Oyanguren, A.; Ahmed, H.; Albert, J.; Banerjee, Sw.; Choi, H. H. F.; King, G. J.; Kowalewski, R.; Lewczuk, M. J.; Lindsay, C.; Nugent, I. M.; Roney, J. M.; Sobie, R. J.; Gershon, T. J.; Harrison, P. F.; Latham, T. E.; Puccio, E. M. T.; Band, H. R.; Dasu, S.; Pan, Y.; Prepost, R.; Vuosalo, C. O.; Wu, S. L.
2011-07-01
We present branching fraction and CP asymmetry measurements as well as angular studies of B→ϕϕK decays using 464×106 BB¯ events collected by the BABAR experiment. The branching fractions are measured in the ϕϕ invariant mass range below the ηc resonance (mϕϕ<2.85GeV). We find B(B+→ϕϕK+)=(5.6±0.5±0.3)×10-6 and B(B0→ϕϕK0)=(4.5±0.8±0.3)×10-6, where the first uncertainty is statistical and the second systematic. The measured direct CP asymmetries for the B± decays are ACP=-0.10±0.08±0.02 below the ηc threshold (mϕϕ<2.85GeV) and ACP=0.09±0.10±0.02 in the ηc resonance region (mϕϕ in [2.94, 3.02] GeV). Angular distributions are consistent with JP=0- in the ηc resonance region and favor JP=0+ below the ηc resonance.
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NASA Technical Reports Server (NTRS)
Tauber, Jan A.; Tielens, A. G. G. M.; Meixner, Margaret; Foldsmith, Paul F.
1994-01-01
We present observations of the molecular component of the Orion Bar, a prototypical Photodissociation Region (PDR) illuminated by the Trapezium cluster. The high angular resolution (6 sec-10 sec) that we have achieved by combining single-dish and interferometric observations has allowed us to examine in detail the spatial and kinematic morphology of this region and to estimate the physical characteristics of the molecular gas it contains. Our observations indicate that this PDR can be essentially described as a homogeneously distributed slab of moderately dense material (approximately 5 x 10(exp 4)/cu cm), in which are embedded a small number of dense (greater than 10(exp 6)/cu cm) clumps. The latter play little or no role in determining the thickness and kinetic temperature structure of this PDR. This observational picture is largely supported by PDR model calculations for this region, which we describe in detail in this work. We also find our model predictions of the intensities of a variety of atomic and molecular lines to be in good general agreement with a number of previous observations.
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Techniques for High Contrast Imaging in Multi-Star Systems II: Multi-Star Wavefront Control
NASA Technical Reports Server (NTRS)
Sirbu, D.; Thomas, S.; Belikov, R.
2017-01-01
Direct imaging of exoplanets represents a challenge for astronomical instrumentation due to the high-contrast ratio and small angular separation between the host star and the faint planet. Multi-star systems pose additional challenges for coronagraphic instruments because of the diffraction and aberration leakage introduced by the additional stars, and as a result are not planned to be on direct imaging target lists. Multi-star wavefront control (MSWC) is a technique that uses a coronagraphic instrument's deformable mirror (DM) to create high-contrast regions in the focal plane in the presence of multiple stars. Our previous paper introduced the Super-Nyquist Wavefront Control (SNWC) technique that uses a diffraction grating to enable the DM to generate high-contrast regions beyond the nominal controllable region. These two techniques can be combined to generate high-contrast regions for multi-star systems at any angular separations. As a case study, a high-contrast wavefront control (WC) simulation that applies these techniques shows that the habitable region of the Alpha Centauri system can be imaged reaching 8 times 10(exp -9) mean contrast in 10 percent broadband light in one-sided dark holes from 1.6-5.5 lambda (wavelength) divided by D (distance).
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A new model-independent approach for finding the arrival direction of an extensive air shower
DOE Office of Scientific and Technical Information (OSTI.GOV)
Hedayati, H. Kh., E-mail: hedayati@kntu.ac.ir
2016-11-01
A new accurate method for reconstructing the arrival direction of an extensive air shower (EAS) is described. Compared to existing methods, it is not subject to minimization of a function and, therefore, is fast and stable. This method also does not need to know detailed curvature or thickness structure of an EAS. It can have angular resolution of about 1 degree for a typical surface array in central regions. Also, it has better angular resolution than other methods in the marginal area of arrays.
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NASA Astrophysics Data System (ADS)
Rogatko, Marek
2014-02-01
Mass, angular momentum, and charge inequalities for axisymmetric maximal time-symmetric initial data invariant under an action of U(1) group, in Einstein-Maxwell-axion-dilaton gravity being the low-energy limit of the heterotic string theory, is established. We assume that a data set with two asymptotically flat regions is given on a smooth simply connected manifold. We also pay attention to the area momentum charge inequalities for a closed orientable two-dimensional spacelike surface embedded in the spacetime of the considered theory.
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MIPS - The Multiband Imaging Photometer for SIRTF. [Multiband Imaging Photometer for SIRTF
NASA Technical Reports Server (NTRS)
Rieke, G. H.; Lada, C.; Lebofsky, M.; Low, F.; Strittmatter, P.; Young, E.; Arens, J.; Beichman, C.; Gautier, T. N.; Werner, M.
1986-01-01
The Multiband Imaging Photometer for SIRTF (MIPS) is to be designed to reach as closely as possible the fundamental sensitivity and angular resolution limits for SIRTF over the 3 to 700 micron spectral region. It will use high performance photoconductive detectors from 3 to 200 micron with integrating JFET amplifiers. From 200 to 700 microns, the MIPS will use a bolometer cooled by an adiabatic demagnetization refrigerator. Over much of its operating range, the MIPS will make possible observations at and beyond the conventional Rayleigh diffraction limit of angular resolution.
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MIPS - The Multiband Imaging Photometer for SIRTF
NASA Technical Reports Server (NTRS)
Rieke, G. H.; Lada, C.; Lebofsky, M.; Low, F.; Strittmatter, P.; Young, E.; Beichman, C.; Gautier, T. N.; Mould, J.; Werner, M.
1986-01-01
The Multiband Imaging Photometer System (MIPS) for SIRTF is to be designed to reach as closely as possible the fundamental sensitivity and angular resolution limits for SIRTF over the 3 to 700 microns spectral region. It will use high performance photoconductive detectors from 3 to 200 microns with integrating JFET amplifiers. From 200 to 700 microns, the MIPS will use a bolometer cooled by an adiabatic demagnetization refrigerator. Over much of its operating range, the MIPS will make possible observations at and beyond the conventional Rayleigh diffraction limit of angular resolution.
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Euclidean perspective on the unfolding of azurin: angular correlations
NASA Astrophysics Data System (ADS)
Warren, Jeffrey J.; Gray, Harry B.; Winkler, Jay R.; Kozak, John J.
2013-12-01
The geometrical model introduced previously by the authors has been extended quantitatively to document changes in angular correlations between and among residues as azurin unfolds. In the early stages of denaturation, these changes are found to be more pronounced than changes in the spatial displacement of residues, a result that is also found for residues acting in concert, viz., α-helices, β-sheet residues and residues in 'turning regions.' Our analysis leads to a picture of the large-scale motion of the polypeptide chain as azurin denatures. Flanking a central 'ribbon' of residues whose orientation remains essentially invariant, we find that in the early stages of unfolding, left- and right-hand 'wings' adjacent to this stationary scaffolding pivot counterclockwise, while smaller regions on opposing ends of the β-barrel pivot clockwise. As spatial constraints characterising the native state are further relaxed, our calculations show that some regions reverse their orientational motion, reflecting the enhanced flexibility of the polypeptide chain in the denatured state.
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NASA Technical Reports Server (NTRS)
Hoffman, P. F.
1986-01-01
A prograding (direction unspecified) trench-arc system is favored as a simple yet comprehensive model for crustal generation in a 250,000 sq km granite-greenstone terrain. The model accounts for the evolutionary sequence of volcanism, sedimentation, deformation, metamorphism and plutonism, observed througout the Slave province. Both unconformable (trench inner slope) and subconformable (trench outer slope) relations between the volcanics and overlying turbidities; and the existence of relatively minor amounts of pre-greenstone basement (microcontinents) and syn-greenstone plutons (accreted arc roots) are explained. Predictions include: a varaiable gap between greenstone volcanism and trench turbidite sedimentation (accompanied by minor volcanism) and systematic regional variations in age span of volcanism and plutonism. Implications of the model will be illustrated with reference to a 1:1 million scale geological map of the Slave Province (and its bounding 1.0 Ga orogens).
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Wiseman, S.M.; Arvidson, R. E.; Andrews-Hanna, J. C.; Clark, R.N.; Lanza, N.L.; des Marais, D.; Marzo, G.A.; Morris, R.V.; Murchie, S.L.; Newsom, Horton E.; Noe Dobrea, E.Z.; Ollila, A.M.; Poulet, F.; Roush, T.L.; Seelos, F.P.; Swayze, G.A.
2008-01-01
Orbital topographic, image, and spectral data show that sulfate- and hematite-bearing plains deposits similar to those explored by the MER rover Opportunity unconformably overlie the northeastern portion of the 160 km in diameter Miyamoto crater. Crater floor materials exhumed to the west of the contact exhibit CRISM and OMEGA NIR spectral signatures consistent with the presence of Fe/Mg-rich smectite phyllosilicates. Based on superposition relationships, the phyllosilicate-bearing deposits formed either in-situ or were deposited on the floor of Miyamoto crater prior to the formation of the sulfate-rich plains unit. These findings support the hypothesis that neutral pH aqueous conditions transitioned to a ground-water driven acid sulfate system in the Sinus Meridiani region. The presence of both phyllosilicate and sulfate- and hematite-bearing deposits within Miyamoto crater make it an attractive site for exploration by future rover missions. Copyright 2008 by the American Geophysical Union.
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Structural and Sequence Stratigraphic Analysis of the Onshore Nile Delta, Egypt.
NASA Astrophysics Data System (ADS)
Barakat, Moataz; Dominik, Wilhelm
2010-05-01
The Nile Delta is considered the earliest known delta in the world. It was already described by Herodotus in the 5th Century AC. Nowadays; the Nile Delta is an emerging giant gas province in the Middle East with proven gas reserves which have more than doubled in size in the last years. The Nile Delta basin contains a thick sedimentary sequence inferred to extend from Jurassic to recent time. Structural styles and depositional environments varied during this period. Facies architecture and sequence stratigraphy of the Nile Delta are resolved using seismic stratigraphy based on (2D seismic lines) including synthetic seismograms and tying in well log data. Synthetic seismograms were constructed using sonic and density logs. The combination of structural interpretation and sequence stratigraphy of the development of the basin was resolved. Seven chrono-stratigraphic boundaries have been identified and correlated on seismic and well log data. Several unconformity boundaries also identified on seismic lines range from angular to disconformity type. Furthermore, time structure maps, velocity maps, depth structure maps as well as Isopach maps were constructed using seismic lines and log data. Several structural features were identified: normal faults, growth faults, listric faults, secondary antithetic faults and large rotated fault blocks of manly Miocene age. In some cases minor rollover structures could be identified. Sedimentary features such as paleo-channels were distinctively recognized. Typical Sequence stratigraphic features such as incised valley, clinoforms, topsets, offlaps and onlaps are identified and traced on the seismic lines allowing a good insight into sequence stratigraphic history of the Nile Delta most especially in the Miocene to Pliocene clastic sedimentary succession.
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NASA Astrophysics Data System (ADS)
Karpov, Yury; Stoupakova, Antonina; Suslova, Anna; Agasheva, Mariia
2017-04-01
The East Siberian Sea basin (ESSB) one of the most unexplored part of the Russian Arctic shelf, extending for over 1000 km from New Siberian Islands archipelago to Wrangel Island. This region is considered as a region with probable high petroleum potential. Within the ESSB several phases of orogeny are recognized [1]: Elsmerian orogeny in Early Devonian, Early Brooks orogeny in Early Cretaceous, Late Brooks orogeny in Late Cretaceous. Two generations of the basins could be outlined. Both of these generations are controlled by the basement domains [1]: Paleozoic (post-Devonian) to Mesozoic basins preserved north of the Late Mesozoic frontal thrusts; Aptian-Albian to Quaternary basins, postdating the Verkhoyansk-Brookian orogeny, and evolving mainly over the New-Siberian-Chukchi Fold Belt. Basin is filled with siliclastic sediments and in the deepest depocentres sediments thickness exceeds 8-10 km in average. Seismic data was interpreted using methods of seismic stratigraphy. Finally, main seismic horizons were indicated and each horizon follows regional stratigraphic unconformities: mBU - in base of Cenozoic, BU - in base of Upper Cretaceous, LCU - in base of Cretaceous, JU - in middle of Jurassic, F - in top of Basement. In ESSB, we can identify Permian, Triassic, Jurassic, Cretaceous, Paleogene and Neogene seismic stratigraphy complexes. Perspective structures, investigated in ESSB were founded out by comparing seismogeological cross-sections with explored analogs in other onshore and offshore basins [2, 3, 4]. The majority of structures could be connected with stratigraphic and fault traps. The most perspective prospects are probably connected with grabens and depressions, where thickness of sediments exceed 10 km. Reservoirs in ESSB are proposed by regional geological explorations on New Siberian Islands Archipelago and Wrangel Island. Potential seals are predominantly assigned to Jurassic and Cretaceous periods. Thick clinoform units of various geometry and trajectories were found in Southern part of ESSB. These clinoform sequences could be formed as a result of significant subsidence followed by rapid sedimentary influx. All possible perspective structures were mapped on tectonic scheme of basin. References: [1] Drachev S.S., Malyshev N.A. and Nikishin A.M., 2010 Tectonic history and petroleum geology of the Russian Arctic Shelves: an overview. Petroleum Geology Conference series, 7, 591-619. [2] Spencer A.M., Embry A.F., Gautier D.L., Stoupakova A.V. and Sorensen K., 2011 An overview of the petroleum geology of the Arctic, Geological Society Memoirs, 35, 1-15. [3] Stoupakova A., Kirykhina T., Suslova A., Kirykhina N., Sautkin R. and Bordunov S., 2012 Structure, hydrocarbon prospects of the Russian Western arctic shelf. AAPG Arctic technology conference. Manuscript. Electronic version. AAPG Houston, USA. [4] Verzhbitsky V.E., Sokolov, S.D., Tuchkova M.I., Frantzen E.M., Little A., Lobkovsky L.I., 2012 The South Chukchi Sedimentary Basin (Chukchi Sea, Russian Arctic): Age, Structural Pattern, and Hydrocarbon Potential in D. Gao, ed., Tectonics and sedimentation: Implications for petroleum systems: AAPG Memoir, 100, 267-290.
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Eckstein, Martin; Yang, Chung-Hsin; Frassetto, Fabio; Poletto, Luca; Sansone, Giuseppe; Vrakking, Marc J J; Kornilov, Oleg
2016-04-22
Autoionizing Rydberg states of molecular N_{2} are studied using time-, energy-, and angular-resolved photoelectron spectroscopy. A femtosecond extreme ultraviolet pulse with a photon energy of 17.5 eV excites the resonance and a subsequent IR pulse ionizes the molecule before the autoionization takes place. The angular-resolved photoelectron spectra depend on pump-probe time delay and allow for the distinguishing of two electronic states contributing to the resonance. The lifetime of one of the contributions is determined to be 14±1 fs, while the lifetime of the other appears to be significantly shorter than the time resolution of the experiment. These observations suggest that the Rydberg states in this energy region are influenced by the effect of interference stabilization and merge into a complex resonance.
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Recent advances in the cretaceous stratigraphy of Korea
NASA Astrophysics Data System (ADS)
Chang, Ki-Hong; Suzuki, Kazuhiro; Park, Sun-Ok; Ishida, Keisuke; Uno, Koji
2003-06-01
A subrounded, accidental, zircon grain from a rhyolite sample of the Oknyobong Formation has shown an U-Pb CHIME isochron age, 187 Ma, implying its derivation from a Jurassic felsic igneous rock. Such a lower limit of the geologic age of the Oknyobong Formation, combined with its pre-Kyongsang upper limit, constrains that the Oknyobong Formation belongs to the Jasong Synthem (Late Jurassic-early Early Cretaceous) typified in North Korea. The Jaeryonggang Movement terminated the deposition of the Jasong Synthem and caused a shift of the depocenter from North Korea to the Kyongsang Basin, Southeast Korea. The Cretaceous-Paleocene Kyongsang Supergroup of the Kyongsang Basin is the stratotype of the Kyongsang Synthem, an unconformity-bounded unit in the Korean Peninsula. The unconformity at the base of the Yuchon Volcanic Group is a local expression of the interregionally recognizable mid-Albian tectonism; it subdivides the Kyongsang Synthem into the Lower Kyongsang Subsynthem (Barremian-Early Albian) and the Upper Kyongsang Subsynthem (Late Albian-Paleocene). The latter is unconformably overlain by Eocene and younger strata. The Late Permian to Early Jurassic radiolarian fossils from the chert pebbles of the Kumidong and the Kisadong conglomerates of the Aptian-Early Albian Hayang Group of the Kyongsang Basin are equivalent with those of the cherts that constitute the Jurassic accretionary prisms in Japan, the provenance of the chert pebbles in the Kyongsang Basin. Bimodal volcanisms throughout the history of the Kyongsang Basin is exemplified by the felsic Kusandong Tuff erupted abruptly and briefly in the Late Aptian when semi-coeval volcanisms were of intermediate and mafic compositions. The mean paleomagnetic direction shown by the Kusandong Tuff is in good agreement with the Early Cretaceous directions known from North China, South China and Siberia Blocks.
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DOE Office of Scientific and Technical Information (OSTI.GOV)
Harak, B. A. de; Bartschat, K.; Martin, N. L. S.
Angular distribution and spectral (e,2e) measurements are reported for the helium autoionizing levels (2s{sup 2}){sup 1}S, (2p{sup 2}){sup 1}D, and (2s2p){sup 1}P. A special out-of-plane geometry is used where the ejected electrons are emitted in a plane perpendicular to the scattered electron direction. The kinematics are chosen so that this plane contains the momentum-transfer direction. While the recoil peak almost vanishes in the angular distribution for direct ionization, it remains significant for the autoionizing levels and exhibits a characteristic shape for each orbital angular momentum L=0,1,2. A second-order model in the projectile-target interaction correctly reproduces the observed magnitudes of themore » recoil peaks, but is a factor of 2 too large in the central out-of-plane region. Observed (e,2e) energy spectra for the three resonances over the full angular range are well reproduced by the second-order calculation. Calculations using a first-order model fail to reproduce both the magnitudes of the recoil peaks and the spectral line profiles.« less
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Particle dynamics around time conformal regular black holes via Noether symmetries
NASA Astrophysics Data System (ADS)
Jawad, Abdul; Umair Shahzad, M.
The time conformal regular black hole (RBH) solutions which are admitting the time conformal factor e𝜖g(t), where g(t) is an arbitrary function of time and 𝜖 is the perturbation parameter are being considered. The approximate Noether symmetries technique is being used for finding the function g(t) which leads to t α. The dynamics of particles around RBHs are also being discussed through symmetry generators which provide approximate energy as well as angular momentum of the particles. In addition, we analyze the motion of neutral and charged particles around two well known RBHs such as charged RBH using Fermi-Dirac distribution and Kehagias-Sftesos asymptotically flat RBH. We obtain the innermost stable circular orbit and corresponding approximate energy and angular momentum. The behavior of effective potential, effective force and escape velocity of the particles in the presence/absence of magnetic field for different values of angular momentum near horizons are also being analyzed. The stable and unstable regions of particle near horizons due to the effect of angular momentum and magnetic field are also explained.
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Photoelectron imaging of autoionizing states of xenon: Effect of external electric fields
DOE Office of Scientific and Technical Information (OSTI.GOV)
Shubert, V. Alvin; Pratt, Stephen T.
Velocity map photoelectron imaging was used to study the photoelectron angular distributions of autoionizing Stark states of atomic xenon excited just below the Xe{sup +} {sup 2} P{sub 1/2}{sup o} threshold at fields ranging from 50 to 700 V/cm. Two-color, two-photon resonant, three-photon excitation via the 6p{sup '}[1/2]{sub 0} level was used to probe the region of interest. The wavelength scans show a similar evolution of structure to that observed in single-photon excitation [Ernst et al., Phys. Rev. A 37, 4172 (1988)]. The photoelectron angular distributions following autoionization of the Stark states provide information on the decay of excited statesmore » in electron fields. In the present experiments, the large autoionization width of the ({sup 2} P{sub 1/2}{sup o})nd[3/2]{sub 1}{sup o} series dominates the decay processes, and thus controls the angular distributions. However, the angular distributions of the Stark states also indicate the presence of other decay channels contributing to the decay of these states.« less
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DOE Office of Scientific and Technical Information (OSTI.GOV)
Garraffo, Cecilia; Drake, Jeremy J.; Cohen, Ofer
Rotation evolution of late-type stars is dominated by magnetic braking and the underlying factors that control this angular momentum loss are important for the study of stellar spin-down. In this work, we study angular momentum loss as a function of two different aspects of magnetic activity using a calibrated Alfvén wave-driven magnetohydrodynamic wind model: the strengths of magnetic spots and their distribution in latitude. By driving the model using solar and modified solar surface magnetograms, we show that the topology of the field arising from the net interaction of both small-scale and large-scale field is important for spin-down rates andmore » that angular momentum loss is not a simple function of large scale magnetic field strength. We find that changing the latitude of magnetic spots can modify mass and angular momentum loss rates by a factor of two. The general effect that causes these differences is the closing down of large-scale open field at mid- and high-latitudes by the addition of the small-scale field. These effects might give rise to modulation of mass and angular momentum loss through stellar cycles, and present a problem for ab initio attempts to predict stellar spin-down based on wind models. For all the magnetogram cases considered here, from dipoles to various spotted distributions, we find that angular momentum loss is dominated by the mass loss at mid-latitudes. The spin-down torque applied by magnetized winds therefore acts at specific latitudes and is not evenly distributed over the stellar surface, though this aspect is unlikely to be important for understanding spin-down and surface flows on stars.« less
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Ethington, Raymond L.; Repetski, John E.; Derby, James R.
2012-01-01
The oldest formation that crops out in the region is the Jefferson City Dolomite, which may be present in outcrops along incised river valleys near the Missouri-Arkansas border. Rare fossil gastropods, bivalves, brachiopods, conodonts, and trilobites permit correlation of the Cotter through Powell Dolomites with Ibexian strata elsewhere in Laurentia. Conodonts in the Black Rock Limestone Member of the Smithville Formation and the upper part of the Powell Dolomite confirm regional relationships that have been suggested for these units; those of the Black Rock Limestone Member are consistent with deposition under more open marine conditions than existed when older and younger units were forming. Brachiopods and conodonts from the overlying Everton Formation assist in interpreting complex facies within that formation and its correlation to equivalent rocks elsewhere. The youngest conodonts in the Everton Formation provide an age limit for the Sauk-Tippecanoe unconformity near the southern extremity of the great American carbonate bank. The correlation to coeval strata in the Ouachita Mountains of central Arkansas and in the Arbuckle Mountains of Oklahoma and to rocks penetrated in wells drilled in the Reelfoot rift basin has been improved greatly in recent years by integration of biostratigraphic data with lithologic information.
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Relative sea level changes during the Cretaceous in Israel
DOE Office of Scientific and Technical Information (OSTI.GOV)
Flexer, A.; Rosenfeld, A.; Lipson-Benitah, S.
1986-11-01
Detailed lithologic, microfaunal, and biometric investigations, using relative abundances, diversity indexes, and duration charts of ostracods and foraminifera, allowed the recognition of sea level changes during the Cretaceous of Israel. Three major transgressive-regressive sedimentation cycles occur on the northwest margins of the Arabian craton. These cycles are the Neocomian-Aptian, which is mostly terrigenous sediments; the Albian-Turonian, which is basin marls and platform carbonates; and the Senonian, which is uniform marly chalks. The cycles are separated by two major regional unconformities, the Aptian-Albian and Turonian-Coniacian boundaries. The sedimentary cycles are related to regional tectonic and volcanic events and eustatic changes. Themore » paleodepth curve illustrates the gradual sea level rise, reaching its maximum during the Late Cretaceous, with conspicuous advances during the late Aptian, late Albian-Cenomanian, early Turonian, early Santonian, and early Campanian. Major lowstands occur at the Aptian-Albian, Cenomanian-Turonian, Turonian-Coniacian, and Campanian-Maastrichtian boundaries. This model for Israel agrees well with other regional and global sea level fluctuations. Four anoxic events (black shales) accompanying transgressions correspond to the Cretaceous oceanic record. They hypothesize the presence of mature oil shales in the present-day eastern Mediterranean basin close to allochthonous reef blocks detached from the Cretaceous platform. 11 figures.« less
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USDA-ARS?s Scientific Manuscript database
Multi-angle remote sensing has been proved useful for mapping vegetation community types in desert regions. Based on Multi-angle Imaging Spectro-Radiometer (MISR) multi-angular images, this study compares roles played by Bidirectional Reflectance Distribution Function (BRDF) model parameters with th...
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Extraction of space-charge-dominated ion beams from an ECR ion source: Theory and simulation
NASA Astrophysics Data System (ADS)
Alton, G. D.; Bilheux, H.
2004-05-01
Extraction of high quality space-charge-dominated ion beams from plasma ion sources constitutes an optimization problem centered about finding an optimal concave plasma emission boundary that minimizes half-angular divergence for a given charge state, independent of the presence or lack thereof of a magnetic field in the extraction region. The curvature of the emission boundary acts to converge/diverge the low velocity beam during extraction. Beams of highest quality are extracted whenever the half-angular divergence, ω, is minimized. Under minimum half-angular divergence conditions, the plasma emission boundary has an optimum curvature and the perveance, P, current density, j+ext, and extraction gap, d, have optimum values for a given charge state, q. Optimum values for each of the independent variables (P, j+ext and d) are found to be in close agreement with those derived from elementary analytical theory for extraction with a simple two-electrode extraction system, independent of the presence of a magnetic field. The magnetic field only increases the emittances of beams through additional aberrational effects caused by increased angular divergences through coupling of the longitudinal to the transverse velocity components of particles as they pass though the mirror region of the electron cyclotron resonance (ECR) ion source. This article reviews the underlying theory of elementary extraction optics and presents results derived from simulation studies of extraction of space-charge dominated heavy-ion beams of varying mass, charge state, and intensity from an ECR ion source with emphasis on magnetic field induced effects.
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Initial angular momentum and flow in high energy nuclear collisions
NASA Astrophysics Data System (ADS)
Fries, Rainer J.; Chen, Guangyao; Somanathan, Sidharth
2018-03-01
We study the transfer of angular momentum in high energy nuclear collisions from the colliding nuclei to the region around midrapidity, using the classical approximation of the color glass condensate (CGC) picture. We find that the angular momentum shortly after the collision (up to times ˜1 /Qs , where Qs is the saturation scale) is carried by the "β -type" flow of the initial classical gluon field, introduced by some of us earlier. βi˜μ1∇iμ2-μ2∇iμ1 (i =1 ,2 ) describes the rapidity-odd transverse energy flow and emerges from Gauss's law for gluon fields. Here μ1 and μ2 are the averaged color charge fluctuation densities in the two nuclei, respectively. Interestingly, strong coupling calculations using anti-de Sitter/conformal field theory (AdS/CFT) techniques also find an energy flow term featuring this particular combination of nuclear densities. In classical CGC the order of magnitude of the initial angular momentum per rapidity in the reaction plane, at a time 1 /Qs , is |d L2/d η |≈ RAQs-3ɛ¯0/2 at midrapidity, where RA is the nuclear radius, and ɛ¯0 is the average initial energy density. This result emerges as a cancellation between a vortex of energy flow in the reaction plane aligned with the total angular momentum, and energy shear flow opposed to it. We discuss in detail the process of matching classical Yang-Mills results to fluid dynamics. We will argue that dissipative corrections should not be discarded to ensure that macroscopic conservation laws, e.g., for angular momentum, hold. Viscous fluid dynamics tends to dissipate the shear flow contribution that carries angular momentum in boost-invariant fluid systems. This leads to small residual angular momentum around midrapidity at late times for collisions at high energies.
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Che Hasan, Rozaimi; Ierodiaconou, Daniel; Laurenson, Laurie; Schimel, Alexandre
2014-01-01
Multibeam echosounders (MBES) are increasingly becoming the tool of choice for marine habitat mapping applications. In turn, the rapid expansion of habitat mapping studies has resulted in a need for automated classification techniques to efficiently map benthic habitats, assess confidence in model outputs, and evaluate the importance of variables driving the patterns observed. The benthic habitat characterisation process often involves the analysis of MBES bathymetry, backscatter mosaic or angular response with observation data providing ground truth. However, studies that make use of the full range of MBES outputs within a single classification process are limited. We present an approach that integrates backscatter angular response with MBES bathymetry, backscatter mosaic and their derivatives in a classification process using a Random Forests (RF) machine-learning algorithm to predict the distribution of benthic biological habitats. This approach includes a method of deriving statistical features from backscatter angular response curves created from MBES data collated within homogeneous regions of a backscatter mosaic. Using the RF algorithm we assess the relative importance of each variable in order to optimise the classification process and simplify models applied. The results showed that the inclusion of the angular response features in the classification process improved the accuracy of the final habitat maps from 88.5% to 93.6%. The RF algorithm identified bathymetry and the angular response mean as the two most important predictors. However, the highest classification rates were only obtained after incorporating additional features derived from bathymetry and the backscatter mosaic. The angular response features were found to be more important to the classification process compared to the backscatter mosaic features. This analysis indicates that integrating angular response information with bathymetry and the backscatter mosaic, along with their derivatives, constitutes an important improvement for studying the distribution of benthic habitats, which is necessary for effective marine spatial planning and resource management. PMID:24824155
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NASA Technical Reports Server (NTRS)
Balaban, Carey D.; McGee, David M.; Zhou, Jianxun; Scudder, Charles A.
2002-01-01
The caudal aspect of the parabrachial (PBN) and Kolliker-Fuse (KF) nuclei receive vestibular nuclear and visceral afferent information and are connected reciprocally with the spinal cord, hypothalamus, amygdala, and limbic cortex. Hence, they may be important sites of vestibulo-visceral integration, particularly for the development of affective responses to gravitoinertial challenges. Extracellular recordings were made from caudal PBN cells in three alert, adult female Macaca nemestrina through an implanted chamber. Sinusoidal and position trapezoid angular whole body rotation was delivered in yaw, roll, pitch, and vertical semicircular canal planes. Sites were confirmed histologically. Units that responded during rotation were located in lateral and medial PBN and KF caudal to the trochlear nerve at sites that were confirmed anatomically to receive superior vestibular nucleus afferents. Responses to whole-body angular rotation were modeled as a sum of three signals: angular velocity, a leaky integration of angular velocity, and vertical position. All neurons displayed angular velocity and integrated angular velocity sensitivity, but only 60% of the neurons were position-sensitive. These responses to vertical rotation could display symmetric, asymmetric, or fully rectified cosinusoidal spatial tuning about a best orientation in different cells. The spatial properties of velocity and integrated velocity and position responses were independent for all position-sensitive neurons; the angular velocity and integrated angular velocity signals showed independent spatial tuning in the position-insensitive neurons. Individual units showed one of three different orientations of their excitatory axis of velocity rotation sensitivity: vertical-plane-only responses, positive elevation responses (vertical plane plus ipsilateral yaw), and negative elevation axis responses (vertical plane plus negative yaw). The interactions between the velocity and integrated velocity components also produced variations in the temporal pattern of responses as a function of rotation direction. These findings are consistent with the hypothesis that a vestibulorecipient region of the PBN and KF integrates signals from the vestibular nuclei and relay information about changes in whole-body orientation to pathways that produce homeostatic and affective responses.
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NASA Astrophysics Data System (ADS)
Cabral, Alexandre Raphael; Ließmann, Wilfried; Lehmann, Bernd
2015-10-01
At Roter Bär, a former underground mine in the polymetallic deposits of St. Andreasberg in the middle-Harz vein district, Germany, native gold and palladium minerals occur very locally in clausthalite-hematite pockets of few millimetres across in carbonate veinlets. The native gold is a Au-Ag intermetallic compound and the palladium minerals are characterised as mertieite-II [Pd8(Sb,As)3] and empirical PdCuBiSe3 with some S. The latter coexists with bohdanowiczite (AgBiSe2), a mineral that is stable below 120 °C. The geological setting of Roter Bär, underneath a post-Variscan unconformity, and its hematite-selenide-gold association suggest that oxidising hydrothermal brines of low temperature were instrumental to the Au-Pd mineralisation. The Roter Bär Au-Pd mineralisation can be explained by Permo-Triassic, red-bed-derived brines in the context of post-Variscan, unconformity-related fluid overprint.
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Sequence stratigraphic control on prolific HC reservoir development, Southwest Iran
Lasemi, Y.; Kondroud, K.N.
2008-01-01
An important carbonate formation in the Persian Gulf and the onshore oil fields of Southwest Iran is the Lowermost Cretaceous Fahliyan formation. The formation in Darkhowain field consists of unconformity-bounded depositional sequences containing prolific hydrocarbon reservoirs of contrasting origin. Located in the high stand systems tract (HST) of the lower sequence encompassing over 200m of oil column are the most prolific reservoir. Another reservoir is over 80m thick consisting of shallowing-upward cycles that are best developed within the transgressive systems tract of the upper sequence. Vertical facies distribution and their paleobathymetry and geophysical log signatures of the Fahliyan formation in the Darkhowain platform reveal the presence of two unconformity-bounded depositional sequences in Vail et al., Van Wagoner et al., and Sarg. The Fahliyan formation mainly consists of platform carbonates composed of restricted bioclastic lime mudstone to packstone of the platform interior, Lithocodium boundstone or ooid-intraclast-bioclast grainstone of the high energy platform margin and the bioclast packstone to lime mudstone related to the off-platform setting.
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Is the Cameron River greenstone belt allochthonous?
NASA Technical Reports Server (NTRS)
Kusky, T. M.
1986-01-01
Many tectonic models for the Slave Province, N.W.T., Canada, and for Archean granite - greenstone terranes in general, are implicitly dependent on the assumption that greenstone belt lithologies rest unconformably upon older gneissic basement. Other models require originally large separations between gneissic terranes and greenstone belts. A key question relating to the tectonics of greenstone belts is therefore the original spatial relationship between the volcanic assemblages and presumed-basement gneisses, and how this relationship has been modified by subsequent deformation. What remains unclear in these examples is the significance of the so-called later faulting of the greenstone - gneiss contacts. Where unconformities between gneisses and overlying sediments are indisputable, such as at Point Lake, the significance of faults which occur below the base of the volcanic succession also needs to be evaluated. As part of an on-going investigation aimed at answering these and other questions, the extremely well-exposed Cameron River Greenstone Belt and the Sleepy Dragon Metamorphic Complex in the vicinity of Webb Lake and Sleepy Dragon Lake was mapped.
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ANOMALOUS MICROWAVE EMISSION IN H ii REGIONS: IS IT REALLY ANOMALOUS? THE CASE OF RCW 49
DOE Office of Scientific and Technical Information (OSTI.GOV)
Paladini, Roberta; Ingallinera, Adriano; Agliozzo, Claudia
2015-11-01
The detection of an excess of emission at microwave frequencies with respect to the predicted free–free emission has been reported for several Galactic H ii regions. Here, we investigate the case of RCW 49, for which the Cosmic Background Imager tentatively (∼3σ) detected Anomalous Microwave Emission (AME) at 31 GHz on angular scales of 7′. Using the Australia Telescope Compact Array, we carried out a multi-frequency (5, 19, and 34 GHz) continuum study of the region, complemented by observations of the H109α radio recombination line. The analysis shows that: (1) the spatial correlation between the microwave and IR emission persistsmore » on angular scales from 3.′4 to 0.″4, although the degree of the correlation slightly decreases at higher frequencies and on smaller angular scales; (2) the spectral indices between 1.4 and 5 GHz are globally in agreement with optically thin free–free emission, however, ∼30% of these are positive and much greater than −0.1, consistent with a stellar wind scenario; and (3) no major evidence for inverted free–free radiation is found, indicating that this is likely not the cause of the Anomalous Emission in RCW 49. Although our results cannot rule out the spinning dust hypothesis to explain the tentative detection of AME in RCW 49, they emphasize the complexity of astronomical sources that are very well known and studied, such as H ii regions, and suggest that, at least in these objects, the reported excess of emission might be ascribed to alternative mechanisms such as stellar winds and shocks.« less
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Van Ettinger-Veenstra, Helene; McAllister, Anita; Lundberg, Peter; Karlsson, Thomas; Engström, Maria
2016-01-01
This study investigates the relation between individual language ability and neural semantic processing abilities. Our aim was to explore whether high-level language ability would correlate to decreased activation in language-specific regions or rather increased activation in supporting language regions during processing of sentences. Moreover, we were interested if observed neural activation patterns are modulated by semantic incongruency similarly to previously observed changes upon syntactic congruency modulation. We investigated 27 healthy adults with a sentence reading task-which tapped language comprehension and inference, and modulated sentence congruency-employing functional magnetic resonance imaging (fMRI). We assessed the relation between neural activation, congruency modulation, and test performance on a high-level language ability assessment with multiple regression analysis. Our results showed increased activation in the left-hemispheric angular gyrus extending to the temporal lobe related to high language ability. This effect was independent of semantic congruency, and no significant relation between language ability and incongruency modulation was observed. Furthermore, there was a significant increase of activation in the inferior frontal gyrus (IFG) bilaterally when the sentences were incongruent, indicating that processing incongruent sentences was more demanding than processing congruent sentences and required increased activation in language regions. The correlation of high-level language ability with increased rather than decreased activation in the left angular gyrus, a region specific for language processing, is opposed to what the neural efficiency hypothesis would predict. We can conclude that no evidence is found for an interaction between semantic congruency related brain activation and high-level language performance, even though the semantic incongruent condition shows to be more demanding and evoking more neural activation.
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Enabling Super-Nyquist Wavefront Control on WFIRST
NASA Astrophysics Data System (ADS)
Bendek, Eduardo; Belikov, Ruslan; Sirbu, Dan; Shaklan, Stuart B.; Eldorado Riggs, A. J.
2018-01-01
A large fraction of sun-like stars is contained in Binary systems. Within 10pc there are 70 FGK stars from which, 43 belong to a multi-star system, and 28 of them have companion leak that is greater than 1e-9 contrast assuming typical Hubble-quality space optics. Currently, those binary stars are not included in the WFIRST-CGI target list, but they could be observed if high-contrast imaging around binary star systems using WFIRST is possible, increasing by 70% the number of possible FGK targets for the mission. The Multi-Star Wavefront Control (MSWC) algorithm can be used to suppress the companion star leakage. If the targets have angular separations larger than the Nyquist controllable region of the Deformable Mirror the MSWC must operate in its Super-Nyquist (SN) mode. This mode requires a target star replica within the SN region in order to provide the energy, and coherent light necessary to null speckles at SN angular separations. For the case of WFIRST, about half of the targets that can be observed using MSWC have angular separations larger than the Nyquist controllable region of the 48x48 actuator Deformable Mirror (DM) to be used. Here, we discuss multiple alternatives to generate those PSF replicas with minimal or no impact to the WFIRST Coronagraph instrument such as 1) the addition of a movable diffractive pupil mounted of the Shape Pupil wheel. 2) Design of a modified Shape Pupil design able to create a dark zone and at the same time diffract a small fraction of the starlight on the SN region. 3) Predict the minimum residual quilting on Xinetics DM that would allow observing a given target.
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Van Ettinger-Veenstra, Helene; McAllister, Anita; Lundberg, Peter; Karlsson, Thomas; Engström, Maria
2016-01-01
This study investigates the relation between individual language ability and neural semantic processing abilities. Our aim was to explore whether high-level language ability would correlate to decreased activation in language-specific regions or rather increased activation in supporting language regions during processing of sentences. Moreover, we were interested if observed neural activation patterns are modulated by semantic incongruency similarly to previously observed changes upon syntactic congruency modulation. We investigated 27 healthy adults with a sentence reading task—which tapped language comprehension and inference, and modulated sentence congruency—employing functional magnetic resonance imaging (fMRI). We assessed the relation between neural activation, congruency modulation, and test performance on a high-level language ability assessment with multiple regression analysis. Our results showed increased activation in the left-hemispheric angular gyrus extending to the temporal lobe related to high language ability. This effect was independent of semantic congruency, and no significant relation between language ability and incongruency modulation was observed. Furthermore, there was a significant increase of activation in the inferior frontal gyrus (IFG) bilaterally when the sentences were incongruent, indicating that processing incongruent sentences was more demanding than processing congruent sentences and required increased activation in language regions. The correlation of high-level language ability with increased rather than decreased activation in the left angular gyrus, a region specific for language processing, is opposed to what the neural efficiency hypothesis would predict. We can conclude that no evidence is found for an interaction between semantic congruency related brain activation and high-level language performance, even though the semantic incongruent condition shows to be more demanding and evoking more neural activation. PMID:27014040
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Lindsey, David A.
1982-01-01
The Thomas Range and northern Drum Mountains have a history of volcanism, faulting, and mineralization that began about 42 m.y. (million years) ago. Volcanic activity and mineralization in the area can be divided into three stages according to the time-related occurrence of rock types, trace-element associations, and chemical composition of mineral deposits. Compositions of volcanic rocks changed abruptly from rhyodacite-quartz latite (42-39 m.y. ago) to rhyolite (38-32 m.y. ago) to alkali rhyolite (21 and 6-7 m.y. ago); these stages correspond to periods of chalcophile and siderophile metal mineralization, no mineralization(?), and lithophile metal mineralization, respectively. Angular unconformities record episodes of cauldron collapse and block faulting between the stages of volcanic activity and mineralization. The youngest angular unconformity formed between 21 and 7 m.y. ago during basin-and-range faulting. Early rhyodacite-quartz latite volcanism from composite volcanoes and fissures produced flows, breccias, and ash-flow tuff of the Drum Mountains Rhyodacite and Mt. Laird Tuff. Eruption of the Mt. Laird Tuff about 39 m.y. ago from an area north of Joy townsite was accompanied by collapse of the Thomas caldera. Part of the roof of the magma chamber did not collapse, or the magma was resurgent, as is indicated by porphyry dikes and plugs in the Drum Mountains. Chalcophile and siderophile metal mineralization, resulting in deposits of copper, gold, and manganese, accompanied early volcanism. Te middle stage of volcanic activity was characterized by explosive eruption of rhyolitic ash-flow tuffs and collapse of the Dugway Valley cauldron. Eruption of the Joy Tuff 38 m.y. ago was accompanied by subsidence of this cauldron and was followed by collapse and sliding of Paleozoic rocks from the west wall of the cauldron. Landslides in The Dell were covered by the Dell Tuff, erupted 32 m.y. ago from an unknown source to the east. An ash flow of the Needles Range(?) Formation was erupted 30-31 m.y. ago from an unknown source. Mineralization probably did not occur during the rhyolitic stage of volcanism. The last stage of volcanism was contemporaneous with basin-and-range faulting and was characterized by explosive eruption of ash and pumice, forming stratified tuff, and by quiet eruption of alkali rhyolite as viscous flows and domes. The first episode of alkali rhyolite volcanism deposited the beryllium tuff and porphyritic rhyolite members of the Spor Mountain Formation 21 m.y. ago. After a period of block faulting, the stratified tuff and alkali rhyolite of the Topaz Mountain Rhyolite were erupted 6-7 m.y. ago along faults and fault intersections. Erosion of Spor Mountain, as well as explosive eruptions through dolomite, provided abundant dolomite detritus to the beryllium tuff member. The alkali rhyolite of both formations is fluorine rich, as is evident from abundant topaz, and contains anomalous amounts of lithophile metals. Alkali rhyolite volcanism was accompanied by lithophile metal mineralization which deposited fluorite, beryllium, and uranium. The structure of the area is dominated by the Thomas caldera and the younger Dugway Valley cauldron, which is nested within the Thomas caldera; the Thomas caldera is surrounded by a rim of Paleozoic rocks at Spor Mountain and Paleozoic to Precambrian rocks in the Drum Mountains. The Joy fault and Dell fault system mark the ring-fracture zone of the Thomas caldera. These structural features began to form about 39 m.y. ago during eruption of the Mt. Laird Tuff and caldera subsidence. The Dugway Valley cauldron sank along a series of steplike normal faults southeast of Topaz Mountain in response to collapse of the magma chamber of the Joy Tuff. Caldera structure was modified by block faulting between 21 and 7 m.y. ago, the time of widespread extensional faulting in the Basin and Range Province. Vents erupted alkali rhyolite 6-7 m.y. ago along basin-and-range faults.
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NASA Astrophysics Data System (ADS)
Wilch, T. I.; McIntosh, W. C.; Panter, K. S.; Dunbar, N. W.; Smellie, J.; Fargo, A. J.; Ross, J. I.; Antibus, J. V.; Scanlan, M. K.
2011-12-01
Minna Bluff, a 45km long, 5km wide Late Miocene alkaline volcanic peninsula that extends SE into the Ross Ice Shelf, is a major obstruction to ice flow from the south into the McMurdo Sound region. Interpretations of the abundant paleoclimate and glacial history archives, including the ANDRILL records, need to account for the effects of paleogeography on past ice-flow configurations and sediment transport. Mapping and 40Ar/39Ar dating of volcanic sequences indicate that Minna Bluff was constructed between 12 and 4 Ma. The volcanic complex first emerged as an isolated island in the Ross Sea at about 12 Ma. The edifice, here named Minna Hook Island, was constructed between 12 and 8 Ma. During this first stage of growth, regional ice was able to flow through a ~40 km gap between the island and mainland. The second stage of volcanism built the main arm of Minna Bluff, now called McIntosh Cliffs, between 8 and 4 Ma. The second stage resulted in the eruption of exclusively subaerial cinder cones and lava flows. By approximately 5 Ma the peninsula had fully emerged above sea level, fully obstructing ice flow. Evidence for volcano-ice interaction is common in Minna Hook stratigraphic sequences. Well exposed cliff sections exhibit alternations between rocks erupted in subaerial and subaqueous conditions; these sequences are interpreted to represent syneruptive interactions between lava flows and glacial ice and provide evidence for periodic glaciations between 12 and 8 Ma. The lack of coherent horizontal passage zones between subglacial and subaerial lithofacies and the alternating nature of the deposits suggest that the eruptions did not occur in a large stable ice sheet but instead occurred in a more ephemeral local ice cap or rapidly drained ice sheet. At least two widespread, undulating glacial unconformities mantled by glacial and fluvial sediments are exposed near the base of the Minna Hook sequences. These unconformities record broad scale Antarctic Ice Sheet events between 10.46 and 10.31 Ma and between 9.81 and 9.46 Ma. The older of these widespread glaciations may correspond to Miocene Isotope Event 6 (Mi6), identified in marine sediment records. Eruptions and glacial overriding events at Minna Bluff occurred over the same time interval as sedimentation at the Andrill MIS and SMS core sites.
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New Tertiary stratigraphy for the Florida Keys and southern peninsula of Florida
Cunningham, K.J.; McNeill, D.F.; Guertin, L.A.; Ciesielski, P.F.; Scott, T.M.; De Verteuil, L.
1998-01-01
Seven lithologic formations, ranging in age from Oligocene to Pleistocene, were recently penetrated by core holes in southernmost Florida. From bottom to top, they are the early Oligocene Suwannee Limestone; late-early Oligocene-to-Miocene Arcadia Formation, basal Hawthorn Group; late Miocene Peace River Formation, upper Hawthorn Group; newly proposed late Miocene-to-Pliocene Long Key and Stock Island Formations; and Pleistocene Key Largo and Miami Limestones. The rocks of the Suwannee Limestone form a third-order sequence. Although the entire thickness was not penetrated, 96 m of Suwannee core from one well contains at least 50 vertically stacked, exposure-capped limestone cycles, presumably related to rapid eustatic fluctuations while experiencing tropical to subtropical conditions. The Arcadia Formation is a composite sequence containing four high-frequency sequences composed of multiple vertically stacked carbonate cycles. Most cycles do not show evidence of subaerial exposure and were deposited under more temperate conditions, relative to the Suwannee Limestone. The Arcadia Formation in southernmost Florida is bounded by regional unconformities representing third-order sequence boundaries. Post-Arcadia transgression produced a major backstepping of sediment accumulation above the upper sequence boundary of the Arcadia Formation. The Peace River Formation, composed of diatomaceous mudstones, has been identified only beneath the Florida peninsula and is not present beneath the Florida Keys. Deposition occurred during marine transgressive to high-stand conditions and a local phosphatization event (recorded in northeast Florida). The transgression is possibly related to a global rise in sea level, which resulted in upwelling of relatively cooler, relatively nutrient-rich water masses onto the Florida Platform. It is proposed that the absence of Peace River sediments beneath the Keys is due to sediment bypass of the upper surface of the Arcadia, a result of sediment sweeping by an ancestral Florida current. During late Miocene to Pliocene time in the Florida Keys, siliciclastics of the Long Key Formation and fine-grained carbonates of the Stock Island Formation prograded toward the southern edge of the Florida Platform and downlapped onto the regional unconformity at the top of the Arcadia. Shallow-marine Pleistocene limestones (Key Largo and Miami Limestones), deposited during tropical to subtropical conditions, drape over accretionary successions of the Long Key and Stock Island Formations.
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Geology of the Cupsuptic quadrangle, Maine
Harwood, David S.
1966-01-01
The Cupsuptic quadrangle, in west-central Maine, lies in a relatively narrow belt of pre-Silurian rocks extending from the Connecticut River valley across northern New Hampshire to north-central Maine. The Albee Formation, composed of green, purple, and black phyllite with interbedded-quartzite, is exposed in the core of a regional anticlinorium overlain to the southeast by greenstone of the Oquossoc Formation which in turn is overlain by black slate of the Kamankeag Formation. In the northern part of the quadrangle the Albee Formation is overlain by black slate, feldspathic graywacke, and minor greenstone of the Dixville Formation. The Kamankeag Formation is dated as 1-ate Middle Ordovician by graptolites (zone 12) found near the base of the unit. The Dixville Formation is correlated with the Kamankeag Formation and Oquossoc Formation and is considered to be Middle Ordovician. The Albee Formation is considered to be Middle to Lower Ordovician from correlations with similar rocks in northeastern and southwestern Vermont. The Oquossoc and Kamankeag Formations are correlated with the Amonoosuc and Partridge Formations of northern New Hampshire. The pre-Silurian rocks are unconformably overlain by unnamed rocks of Silurian age in the southeast, west-central, and northwest ninths of the quadrangle. The basal Silurian units are boulder to cobble polymict conglomerate and quartz-pebble conglomerate of late Lower Silurian (Upper Llandovery) age. The overlying rocks are either well-bedded slate and quartzite, silty limestone, or arenaceous limestone. Thearenaceous limestone contains Upper Silurian (Lower Ludlow) brachiopods. The stratified rocks have been intruded by three stocks of biotite-muscovite quartz monzonite, a large body of metadiorite and associated serpentinite, smaller bodies of gabbro, granodiorite, and intrusive felsite, as well as numerous diabase and quartz monzonite dikes. The metadiorite and serpentinite, and possibly the gabbro and granodiorite are Late Ordovician in age. The quartz monzonite is considered to be Late Devonian. Five tectonic events are inferred from the structural features in the area. The earliest was a period of folding producing tightly-appressed, northeast-trending folds in the rocks of pre-Silurian age. In the second stage the folded pre-Silurian rocks were uplifted, eroded, and truncated to produce a major unconformity between the Middle Ordovician and Lower Silurian rocks. These events constitute the Taconic orogeny. The third tectonic event was a period of folding, probably of Middle Devonian age, that warped the unconformity and overlying rocks into open, gently-plunging, east-trending folds. This period of folding undoubtedly changed the attitude of the early folds in the pre-Silurian units but it did not produce any recognizable, cross-cutting planar features in the older rocks. The fourth tectonic event was a period of igneous intrusion that locally deformed the northeast-trending folds in the pre-Silurian rocks into a macroscopic drag fold plunging at 80 degrees in a direction S.10?w. A north-trending, subvertical slip cleavage was produced locally during this period of Late Devonian (?) deformation. A period of faulting, possibly of Triassic age, dislocated some of the earlier features. The rocks are in the chlorite zone of regional metamorphism, but have been contact metamorphosed to sillimanite-bearing hornfels adjacent to the quartz monzonite stocks. The chemical changes in chlorite, biotite, garnet, cordierite, and muscovite in the chlorite, biotite, andalusite, and sillimanite zones have been-studied by optical and x-ray methods and by partial chemical analyses. The progressive changes in mineral assemblages have been graphically portrayed on quaternary diagrams and ternary projections.
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A Green Bank Telescope Survey of Large Galactic H II Regions
NASA Astrophysics Data System (ADS)
Anderson, L. D.; Armentrout, W. P.; Luisi, Matteo; Bania, T. M.; Balser, Dana S.; Wenger, Trey V.
2018-02-01
As part of our ongoing H II Region Discovery Survey (HRDS), we report the Green Bank Telescope detection of 148 new angularly large Galactic H II regions in radio recombination line (RRL) emission. Our targets are located at a declination of δ > -45^\\circ , which corresponds to 266^\\circ > {\\ell }> -20^\\circ at b=0^\\circ . All sources were selected from the Wide-field Infrared Survey Explorer Catalog of Galactic H II Regions, and have infrared angular diameters ≥slant 260\\prime\\prime . The Galactic distribution of these “large” H II regions is similar to that of the previously known sample of Galactic H II regions. The large H II region RRL line width and peak line intensity distributions are skewed toward lower values, compared with that of previous HRDS surveys. We discover seven sources with extremely narrow RRLs < 10 {km} {{{s}}}-1. If half the line width is due to turbulence, these seven sources have thermal plasma temperatures < 1100 {{K}}. These temperatures are lower than any measured for Galactic H II regions, and the narrow-line components may arise instead from partially ionized zones in the H II region photodissociation regions. We discover G039.515+00.511, one of the most luminous H II regions in the Galaxy. We also detect the RRL emission from three H II regions with diameters > 100 {pc}, making them some of the physically largest known H II regions in the Galaxy. This survey completes the HRDS H II region census in the Northern sky, where we have discovered 887 H II regions and more than doubled the size of the previously known census of Galactic H II regions.
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MISR Level 2 Aerosol and Land Versioning
Atmospheric Science Data Center
2017-10-11
... surfaces was changed: instead of using a surface contrast threshold, a new test is used which is based on a weighted mean equivalent reflectance threshold. A regional angular correlation screening test was added to aerosol ...
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NASA Astrophysics Data System (ADS)
Poh, Jonathan; Yamato, Philippe; Gapais, Denis; Duretz, Thibault; Ledru, Patrick
2017-04-01
The formation of the architecture of the main cratons of the Canadian Shield has been debated over the past three decades. Understanding the role of tangential Vs. vertical tectonics in the Rae craton is of great interest as the role of inherited structure is fundamental for the subsequent drainage of fluids and the formation of high to ultra-high grade unconformity-type uranium deposits. These deposits are located in the vicinity of the intersection between the unconformity at the base of the Paleoproterozoic Athabasca sedimentary basin (1.75-1.5 Ga) and the graphite-rich metasediments of the Wollaston-Mudjatik transition zone, one of the main fault system of the Rae Craton related to the Trans-Hudson orogeny (1.82-1.78 Ga). A new tectonic model, Pop-down tectonics, was proposed as the primary driving process to concentrate supracrustal materials, strains, fluid transfers and metal transport in permeability enhanced deformation zones. The sub-vertical structural patterns with regional horizontal shortening seen in the tectonic model appear to be consistent with field evidences and has the potential for sustaining strong fluid-rock interactions. In the light of previous analogue modelling studies, we test the viability of the Pop-down tectonics model in a thermo-mechanical framework. The numerical experiments are based on a series of 2D visco-elasto-plastic thermo-mechanical models. We employ various thermal and rheological parameters derived from laboratory experiments. The geometry, thermicity and kinematics of the models are further constrained by applying existing geophysical and geological data. We impose a fixed upper mantle temperature of 1330 °C and a thin crust ranging from 30 - 40 km. The outcome of the models will provide insights into the mechanical processes controlling the deformation of hot lithospheres in convergent settings.
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NASA Astrophysics Data System (ADS)
Mathieu, Jordan; Turner, Elizabeth C.; Rainbird, Robert H.
2017-04-01
Paleokarst is most commonly expressed as subtle stratigraphic surfaces rather than large void systems penetrating deeply into the paleo-subsurface. In contrast, a regional Precambrian-Cambrian unconformity on Victoria Island (NWT, Canada), is associated with exceptional exposure of large, intact Cambrian paleocaverns (100 m diameter; tens of m high). The paleocaves are distributed along a paleo-horizontal plane, and an associated gryke network is present in the 30-60 m of Neoproterozoic dolostone between cave rooves and the base of overlying Cambrian sandstone; both are filled by Cambrian sandstone. The formation and preservation of such karst features require aggressive dissolution along a stable paleo-water-table shortly before transgression and deposition of shallow-marine sand over the dolostone. During the transgression, the karst network acted as a conduit for flowing groundwater that was discharged through overlying, unconsolidated Cambrian shallow-marine sand, producing water-escape structures (sand volcanoes and their conduits). The conduits are preserved as cylindrical remnants of the sand volcanoes' feeder pipes. Sediment fluidisation was probably caused by variations in the hydraulic-head gradient in a meteoric lens near the Cambrian coastline under a tropical climate with abundant, probably seasonally variable rainfall that caused pulses in subsurface fluid flow. Spatial distribution of the paleocaves and sand volcanoes suggests their formation on the southeast side of a recently faulted horst of Proterozoic carbonate bedrock that formed a nearshore island during early Cambrian sea-level rise. Fluidisation structures such as those reported here have generally been difficult to interpret owing to a lack of data on the fluid hydraulics of the underlying aquifer. This is the first report linking the hydraulics of a well-characterised paleokarst to development of fluid-escape structures. Such structures are widely known from sandstones overlying the sub-Cambrian unconformity around the circumference of Laurentia.
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NASA Astrophysics Data System (ADS)
Sauermilch, Isabel; Whittaker, Joanne; Totterdell, Jennifer; Jokat, Wilfried
2017-04-01
The sedimentary stratigraphy along the conjugate Australian-Antarctic continental margins provide insights into their tectonic evolution as well as changes in paleoceanographic conditions in the Southern Ocean. A comprehensive network of multichannel seismic reflection data as well as geological information from drill cores have been used to interpret the stratigraphic evolution of these margins. However, a number of alternative seismic interpretations exist for the Antarctic side, particularly due to sparse drill core information. A prominent high-amplitude reflector observed along the margin, extending from the continental shelf to the foot-of-slope, is at the centre of debate. Recently, two major hiatuses (from 33.6 - 47.9 Ma and 51.06 - 51.9 Ma) were recovered by the IODP drill core U1356A offshore Wilkes Land and correlated to this prominent reflector. Previous seismic stratigraphic investigations interpreted this structure as an erosional unconformity and proposed different events as a possible cause for this formation, including first arrival of the continental glaciation at the coast at about 34 Ma, increase in spreading rate between Australia and Antarctica at about 45 Ma and drastic global sea level drop of 70 m at about 43 Ma. However, such a large-scale erosion must consequently lead to a re-deposition of a significantly large amount of sediment somewhere along the margins, but, to date, no such deposition is observed in the seismic reflection data. Here, we present an alternative seismo-stratigraphic interpretation based on correlation to the sedimentary structures along the Australian margin. We argue that the prominent unconformity is formed due to non-deposition of sediment between 47.8 and 33.6 Ma. The sedimentary units underlying this unconformity show strong similarities in structure, seismic characteristics and variation along the margin with sequences that are partly exposed to the seafloor at the foot of the Australian slope. On the Australian flank, the age of these exposed sediment sequences ranges from 65 Ma to 45 Ma. Low to no sedimentation from 45 Ma to the present-day offshore Australia has been interpreted to explain the exposure of these old sediment units. We propose that non-deposition occurred along both margins from 45 Ma, until large-scale glacial deposition started at 33.6 Ma along the Antarctic margin. Using our new interpretation, we create paleo-bathymetric reconstructions using the software BALPAL at 83 Ma, 65 Ma and 45 Ma. The resulting paleo-bathymetric maps provide essential information, e.g. for paleo-oceanographic and -climatic investigations in the Southern Ocean.
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The South China - Indochina collision: a perspective from sedimentary basins analysis
NASA Astrophysics Data System (ADS)
Rossignol, Camille; Bourquin, Sylvie; Hallot, Erwan; Poujol, Marc; Roger, Françoise; Dabard, Marie-Pierre; Martini, Rossana; Villeneuve, Michel; Cornée, Jean-Jacques; Peyrotty, Giovan
2017-04-01
Sedimentary basins, through the sedimentary successions and the nature of the deposits, reflect the geology of the area from which the sediments were derived and thus provide valuable record of hinterland tectonism. As the collision between the South China and the Indochina blocks (i.e., the Indosinian orogeny) is still the object of a number of controversies regarding, for instance, its timing and the polarity of the subduction, the sedimentary basins associated with this mountain belt are likely to provide clues to reconstruct its geodynamic evolution. However, both the Sam Nua Basin (located to the south of the inner zones of the Indosinian orogeny and the Song Ma ophiolites) and the Song Da Basin (located to the north of the inner zones), northern Vietnam, are still lacking important information regarding the depositional environments and the ages of the main formations that they contain. Using sedimentological and dating analyses (foraminifers biostratigraphy and U-Pb dating on detrital zircon), we provide a new stratigraphic framework for these basins and propose a geodynamic evolution of the present-day northern Vietnam. During the Early Triassic, the Sam Nua Basin was mainly supplied by volcaniclastic sediments originating from an active volcanic activity. Geochemical investigations, combined with sedimentological and structural analyses, support an arc-related setting for this magmatism. This magmatic arc resulted from the subduction of a south dipping oceanic slab that once separated the South China from the Indochina blocks. During the Middle to the Late Triassic, the Sam Nua Basin underwent erosion that lead to the formation of a major unconformity, termed the Indosinian unconformity. This unconformity is interpreted to result from the erosion of the Indosinian mountain belt, built after the continental collision between the South China and the Indochina blocks. Later, during the Late Triassic, the Sam Nua Basin experienced the deposition of very coarse material, emplaced under continental setting and representing the product of the erosion of the Indosinian mountain belt. To the North, the Song Da Basin is characterized by strongly diachronous deposits over a basal unconformity developed at the expense of volcanic and volcaniclastic deposits related to the Emeishan Large Igneous Province. The sedimentary succession indicates a foreland setting during the Early to the Middle Triassic, which contrasts with the commonly assumed rift setting for these sediments. Thus, the Song Da Basin documents the formation of the Indosinian thrust belt, located immediately to the South of the basin.
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Assessing the duration of drowning episodes during the Early Cretaceous
NASA Astrophysics Data System (ADS)
Godet, A.; Föllmi, K. B.
2013-12-01
Drowning unconformities are stratigraphic key surfaces in the history of carbonate platforms. They mostly consist in the deposition of deep marine facies on top of shallow marine limestones. Although large-scale depositional geometries mimic lowstand systems track architecture, these sedimentary turnovers are developed in relation with major sea level rise, inducing an increase in the rate of creation of accommodation space that outpaces the capacity of carbonate to keep up. This so-called paradox of carbonate platform drowning implies that other parameters than purely eustatic fluctuations are involved in the demise of shallow marine ecosystems. Worldwide and at different time during Earth history, in-depth studies of drowning unconformities revealed that changes in nutrient input, clastic delivery, temperature, or a combination of them may be responsible for a decrease in light penetration in the water column and the progressive suffocation and poisoning of photosynthetic carbonate producers. The examination of such case examples from various stratigraphic intervals and palaeogeographical settings thus helps in identifying and hierarchizing potential triggering mechanisms for drowning unconformities. This is complemented by new data from Early Cretaceous successions from the Helvetic Alps. During this time period, the Helvetic carbonate platform developed along the northern Tethyan margin using both photozoan and heterozoan communities. Phases of healthy production were interrupted by several drowning episodes. The latter are marked in the sedimentary record by condensation and associated phosphogenesis and glauconitisation. From the earliest Valanginian to the early to late Barremian, three drowning unconformities reflect the intermittent installation of a more humid climate and subsequent enhanced trophic conditions, which first induced a switch from photozoan to heterozoan communities and then to long-lasting drowning phases. The latter encompass several sea level rise and fall cycles, and may be linked to strengthened upwelling currents. Moreover during the late Hauterivian - early Barremian time period, the correlation of platform carbonates with basinal sediments, by means of bio-, chemo- and sequence stratigraphy, allows to estimate the duration of a drowning episode. With the return to more oligotrophic conditions during the late Barremian, photozoan, Urgonian-type communities took up again. Their development has been abruptly stopped at the end of the early Aptian by a major emersion phase. The subsequent drowning is documented in various peritethyan areas. This initial crisis is followed by three other drowning phases that ultimately led to the replacement of shallow ecosystems by a deeper marine sedimentation in the Cenomanian. This long-term trend in the evolution of the Helvetic carbonate platform and of other peritethyan ecosystems may have been driven by more global phenomena.
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2.9-1.9 Ga paleoalterations of Archean granitic basement of the Franceville basin (Gabon)
NASA Astrophysics Data System (ADS)
Mouélé, Idalina Moubiya; Dudoignon, Patrick; El Albani, Abderrazak; Meunier, Alain; Boulvais, Philippe; Gauthier-Lafaye, François; Paquette, Jean-Louis; Martin, Hervé; Cuney, Michel
2014-09-01
The Archean granitoids in the Kiéné area, Gabon, are overlained by the Paleoproterozoic sediments of the Franceville basin (2.1 Ga). The basin is known for its high-grade uranium deposits among which some have been forming natural nuclear fission reactors. Most of the studies were dedicated to the FA-FB Paleoproterozoic sediments hosting these uranium deposits. Little is known on the Archean basement itself and specifically on the hydrous alteration events it experienced before and after the sediment deposition. The present work is focused on their petrographical, mineralogical and geochemical characterization. Dating the successive alteration events has been attempted on altered monazite crystals. Rocks in different alteration states have been sampled from eight drill cores crosscutting the Archean - Paleoproterozoic unconformity. The Archean granitoids observed in the deepest levels exhibit typical petrographical features of a propylitic alteration while they are intensely illitized up to the unconformity. The propylitic alteration is mainly pervasive but the original texture of the granitoïds is conserved in spite of the formation of new minerals: Mg-chlorite, allanite and epidote forming a typical paragenesis. The illitic alteration is much more invasive near the unconformity. The illitization process leads to the replacement of feldspars and the corrosion of quartz crysals by an illitic matrix while the ferromagnesian minerals are pseudomorphosed by a Fe-chlorite + phengite + hematite assemblage. The final fluid-rock interaction step is marked by fissural deposits of calcite and anhydrite. The δ13C isotopic data show that the fissural carbonates precipitated from diagenetic fluids enriched carbon products deriving from the maturation of organic matter. The U-Pb isotopic analyzes performed on monazite crystals have dated three distinct events: 3.0-2.9 Ga (magmatic), 2.6 Ga (propylitic alteration) and 1.9 Ga (diagenetic illitization). The calculation of geochemical mass balances suggests that the water-rock ratio during the propylitic alteration event was weak. On the contrary, it was much higher during the overprinted illitization which is characterized by an intense leaching of Na, Ca, Mg, Sr, REE and an enrichment in K, Rb,Cs. Neither the petrographic features nor the geochemical data militate for an Archean weathering event (paleosol). In the present case, diagenetic fluids have percolated from the unconformity into the basement where they overprinted the illitization processes upon the previously propylitized rocks. These fluids were probably oxidant as they are also responsible of the U mobilization which led to the formation of the ore deposits close to the FA-FB interface.
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Quasi-local gravitational angular momentum and centre of mass from generalised Witten equations
NASA Astrophysics Data System (ADS)
Wieland, Wolfgang
2017-03-01
Witten's proof for the positivity of the ADM mass gives a definition of energy in terms of three-surface spinors. In this paper, we give a generalisation for the remaining six Poincaré charges at spacelike infinity, which are the angular momentum and centre of mass. The construction improves on certain three-surface spinor equations introduced by Shaw. We solve these equations asymptotically obtaining the ten Poincaré charges as integrals over the Nester-Witten two-form. We point out that the defining differential equations can be extended to three-surfaces of arbitrary signature and we study them on the entire boundary of a compact four-dimensional region of spacetime. The resulting quasi-local expressions for energy and angular momentum are integrals over a two-dimensional cross-section of the boundary. For any two consecutive such cross-sections, conservation laws are derived that determine the influx (outflow) of matter and gravitational radiation.
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Angular velocity integration in a fly heading circuit.
Turner-Evans, Daniel; Wegener, Stephanie; Rouault, Hervé; Franconville, Romain; Wolff, Tanya; Seelig, Johannes D; Druckmann, Shaul; Jayaraman, Vivek
2017-05-22
Many animals maintain an internal representation of their heading as they move through their surroundings. Such a compass representation was recently discovered in a neural population in the Drosophila melanogaster central complex, a brain region implicated in spatial navigation. Here, we use two-photon calcium imaging and electrophysiology in head-fixed walking flies to identify a different neural population that conjunctively encodes heading and angular velocity, and is excited selectively by turns in either the clockwise or counterclockwise direction. We show how these mirror-symmetric turn responses combine with the neurons' connectivity to the compass neurons to create an elegant mechanism for updating the fly's heading representation when the animal turns in darkness. This mechanism, which employs recurrent loops with an angular shift, bears a resemblance to those proposed in theoretical models for rodent head direction cells. Our results provide a striking example of structure matching function for a broadly relevant computation.
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X-ray diving in the center of Sh2-129: looking for the driving source of Ou4
NASA Astrophysics Data System (ADS)
Grosso, Nicolas
2012-10-01
The outflow phenomenon is associated both with the early and the last phase of the stellar evolution. Recently, a unique bipolar outflow with an angular size of 1.2 degrees was discovered in the blister HII region Sh2-129. Ou4, nicknamed "The Giant Squid", is to our knowledge the bipolar outflow with the largest angular size ever found. We propose joint XMM-Newton/EPIC (35 ks) and Chandra/HRC-I (16 ks) observations to look for the driving source of Ou4 and to clarify the nature of this object.
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Variations in atmospheric angular momentum and the length of day
NASA Technical Reports Server (NTRS)
Rosen, R. D.; Salstein, D. A.
1982-01-01
Six years of twice daily global analyses were used to create and study a lengthy time series of high temporal resolution angular momentum values. Changes in these atmospheric values were compared to independently determined charges in the rotation rate of the solid Earth. Finally, the atmospheric data was examined in more detail to determine the time and space scales on which variations in momentum occur within the atmosphere and which regions are contributing most to the changes found in the global integral. The data and techniques used to derive the time series of momentum values are described.
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Neural foundations to moral reasoning and antisocial behavior
Yang, Yaling
2006-01-01
A common feature of the antisocial, rule-breaking behavior that is central to criminal, violent and psychopathic individuals is the failure to follow moral guidelines. This review summarizes key findings from brain imaging research on both antisocial behavior and moral reasoning, and integrates these findings into a neural moral model of antisocial behavior. Key areas found to be functionally or structurally impaired in antisocial populations include dorsal and ventral regions of the prefrontal cortex (PFC), amygdala, hippocampus, angular gyrus, anterior cingulate and temporal cortex. Regions most commonly activated in moral judgment tasks consist of the polar/medial and ventral PFC, amygdala, angular gyrus and posterior cingulate. It is hypothesized that the rule-breaking behavior common to antisocial, violent and psychopathic individuals is in part due to impairments in some of the structures (dorsal and ventral PFC, amygdala and angular gyrus) subserving moral cognition and emotion. Impairments to the emotional component that comprises the feeling of what is moral is viewed as the primary deficit in antisocials, although some disruption to the cognitive and cognitive-emotional components of morality (particularly self-referential thinking and emotion regulation) cannot be ruled out. While this neurobiological predisposition is likely only one of several biosocial processes involved in the etiology of antisocial behavior, it raises significant moral issues for the legal system and neuroethics. PMID:18985107
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Leung, Mei-Kei; Chan, Chetwyn C H; Yin, Jing; Lee, Chack-Fan; So, Kwok-Fai; Lee, Tatia M C
2013-01-01
Previous voxel-based morphometry (VBM) studies have revealed that meditation is associated with structural brain changes in regions underlying cognitive processes that are required for attention or mindfulness during meditation. This VBM study examined brain changes related to the practice of an emotion-oriented meditation: loving-kindness meditation (LKM). A 3 T magnetic resonance imaging (MRI) scanner captured images of the brain structures of 25 men, 10 of whom had practiced LKM in the Theravada tradition for at least 5 years. Compared with novices, more gray matter volume was detected in the right angular and posterior parahippocampal gyri in LKM experts. The right angular gyrus has not been previously reported to have structural differences associated with meditation, and its specific role in mind and cognitive empathy theory suggests the uniqueness of this finding for LKM practice. These regions are important for affective regulation associated with empathic response, anxiety and mood. At the same time, gray matter volume in the left temporal lobe in the LKM experts appeared to be greater, an observation that has also been reported in previous MRI meditation studies on meditation styles other than LKM. Overall, the findings of our study suggest that experience in LKM may influence brain structures associated with affective regulation.
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Pion single and double charge exchange in the resonance region: Dynamical corrections
NASA Astrophysics Data System (ADS)
Johnson, Mikkel B.; Siciliano, E. R.
1983-04-01
We consider pion-nucleus elastic scattering and single- and double-charge-exchange scattering to isobaric analog states near the (3,3) resonance within an isospin invariant framework. We extend previous theories by introducing terms into the optical potential U that are quadratic in density and consistent with isospin invariance of the strong interaction. We study the sensitivity of single and double charge exchange angular distributions to parameters of the second-order potential both numerically, by integrating the Klein-Gordon equation, and analytically, by using semiclassical approximations that explicate the dependence of the exact numerical results to the parameters of U. The magnitude and shape of double charge exchange angular distributions are more sensitive to the isotensor term in U than has been hitherto appreciated. An examination of recent experimental data shows that puzzles in the shape of the 18O(π+, π-)18Ne angular distribution at 164 MeV and in the A dependence of the forward double charge exchange scattering on 18O, 26Mg, 42Ca, and 48Ca at the same energy may be resolved by adding an isotensor term in U. NUCLEAR REACTIONS Scattering theory for elastic, single-, and double-charge-exchange scattering to IAS in the region of the P33 resonance. Second-order effects on charge-exchange calculations of σ(A, θ).
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Geology of the Lake Mary quadrangle, Iron County, Michigan
Bayley, Richard W.
1959-01-01
The Lake Mary quadrangle is in eastern Iron County, in the west part of the Upper Peninsula of Michigan. The quadrangle is underlain by Lower and Middle Precambrian rocks, formerly designated Archean and Algonkian rocks, and is extensively covered by Pleistocene glacial deposits. A few Upper Precambrian (Keweenawan) diabase dikes and two remnants of sandstone and dolomite of early Paleozoic age are also found in the area. The major structural feature is the Holmes Lake anticline, the axis of which strikes northwest through the northeast part of the quadrangle. Most of the quadrangle, therefore, is underlain by rock of the west limb of the anticline. To the northwest along the fold axis, the Holmes Lake anticline is separated from the Amasa oval by a saddle of transverse folds in the vicinity of Michigamme Mountain in the Kiernan quadrangle. The Lower Precambrian rocks are represented by the Dickinson group and by porphyritic red granite whose relation to the Dickinson group is uncertain, but which may be older. The rocks of the Dickinson group are chiefly green to black metavolcanic schist and red felsite, some of the latter metarhyolite. The dark schist is commonly magnetic. The Dickinson group underlies the core area of the Holmes Lake anticline, which is flanked by steeply dipping Middle Precambrian formations of the Animikie series. A major unconformity separates the Lower Precambrian rocks from the overlying Middle Precambrian rocks. In ascending order the formations of the Middle Precambrian are the Randville dolomite, the Hemlock formation, which includes the Mansfield iron-bearing slate member, and the Michigamme slate. An unconformity occurs between the Hemlock formation and Michigamme slate. The post-Hemlock unconformity is thought to be represented in the Lake Mary quadrangle by the absence of iron-formation of the Amasa formation, which is known to lie between the Hemlock and the Michigamme to the northwest of the Lake Mary quadrangle in the Crystal Falls quadrangle. Post-Hemlock erosion may account also for the absence of iron-formation of the Fence River formation on the east limb of the Holmes Lake anticline within the Lake Mary quadrangle. The Randville dolomite is not exposed and is known only from diamond drilling in the northeast part of the area where it occurs in the east and west limbs of the Holmes Lake anticline. The formation has a maximum thickness of about 2,100 feet; this includes a lower arkosic phase, some of which is quartz pebble conglomerate, a medial dolomitic phase, and an upper slate phase. The triad is gradational. Included within the formation are a few beds of chloritic schist thought to be of volcanic origin. An unconformity between the Randville and the succeeding Hemlock is not indicated in the quadrangle, but is probably present. The Hemlock formation is best exposed in the northwest and south-central parts of the area. The apparent thickness of the formation is 10,000- 17,000 feet. It is composed mainly of mafic metavolcanic rocks and intercalated slate and iron-formation. In the north part of the quadrangle the volcanic rocks are greenstone, which includes altered basaltic flow rocks, volcanic breccia, tuff, and slate. Pillow structures are common in the metabasalt. It is not certain if any Hemlock rocks are present in the east limb of the Holmes Lake anticline. In the south part of the quadrangle, the rocks of the Hemlock are chiefly chlorite and hornblende schist and hornfels. Pyroxene hornfels is sparingly present. At least two sedimentary slate belts are included in the Hemlock formation. One of these, the Mansfield iron-bearing slate member, includes in its upper part an altered chert-siderite iron-formation 30 to over 150 feet thick from which iron ore has been mined at the Mansfield location. The position of the iron-bearing rocks has been determined magnetically, and past explorations for iron ore are discussed. Though probably; unconformable, the contact between the Hemlock and the Michigamme formations appears conformable. The Michigamme slate consists of at least 4,000 feet of interbedded mica schist and granulite, the altered equivalents of the slate and graywacke characteristic of the Michigamme in adjacent areas. The Michigamme rocks are best exposed in the south part of the quadrangle in the vicinity of Peavy Pond. Two periods of regional metamorphism have resulted in the alteration of almost all of the rocks of the quadrangle. The Lower Precambrian rocks underwent at least one period of metamorphism, uplift, and erosion before the deposition of the Randville dolomite. After the deposition of the Michigamme slate, a post-Middle Precambrian period of regional metamorphism occurred with attending deformation and igneous intrusion. The grade of metamorphism rises toward the south in the area. The rocks in the northern two-thirds of the quadrangle are representative of greenschist facies of regional metamorphism, whereas the rocks in the southern onethird of the quadrangle are representative of the albite-epidote-amphibolite, the amphibolite, and the pyroxene hornfels facies, the metamorphic node centering about the intrusive Peavy Pond complex in the Peavy Pond area. The Precambrian sedimentary and volcanic rocks are cut by intrusive igneous rocks of different types and several different ages. Gabbroic sills and dikes invaded the Hemlock rocks at some time after the Hemlock was deposited and before the post-Middle Precambrian orogeny and metamorphism. Some contact metamorphism attended the intrusion of the major sills. One of the sills, the West Kiernan sill, is well differentiated. A syntectonic igneous body, composed of gabbro and minor ultramafic parts and fringed with intermediate and felsic differentiates and hybrids, the Peavy; Pond complex, was intruded into the Hemlock and Michigamme formations during the post-Middle Precambrian orogeny. The complex is situated in the Peavy Pond area at the crest of the regional metamorphic node. Contact-altered sedimentary and volcanic rocks margin the complex. The effects of regional metamorphism have been superposed on the contact metamorphic rocks peripheral to the complex and on the igneous rocks of the complex as well. The mafic augite-bearing rocks of the complex emplaced early in the orogeny were deformed by granulation at the peak of the deformation and subsequently metamorphosed to hornblende rocks. Some of the intermediate and felsic rocks of the complex were foliated by the deformation, while the more fluid, felsic parts of the complex were intruded under orogenic stress and crystallized after the peak of deformation. The deformation culminated in major faulting during which the formations were dislocated, and some of the granite of the complex was extremely brecciated. A few diabase dikes, probably of Keweenawan age, have intruded the deformed and altered Animikie rocks. The only known metallic resource is iron ore. The Mansfield mine produced 1¥2 million tons of high-grade iron ore between the years 1890 and 1913. Sporadic exploration since 1913 has failed to reveal other ore deposits of economic importance.
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ERIC Educational Resources Information Center
Wilson, Michael Jason
2009-01-01
This dissertation studies clouds over the polar regions using the Multi-angle Imaging SpectroRadiometer (MISR) on-board EOS-Terra. Historically, low thin clouds have been problematic for satellite detection, because these clouds have similar brightness and temperature properties to the surface they overlay. However, the oblique angles of MISR…
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NASA Astrophysics Data System (ADS)
Gogacz, A.; Hall, J.; Cifci, G.; Yasar, D.; Kucuk, M.; Yaltirak, C.; Aksu, A.
2009-05-01
The Antalya Basin is one of a series of basins that sweep along the Cyprus Arc in the forearc region between the (formerly) volcanic Tauride Mountains on Turkey in the north and the subduction zone and associated suture between the African plate and the Aegean-Anatolian microplate in the eastern Mediterranean, south of Cyprus. Miocene contraction occurs widely on southwest verging thrusts. Pliocene-Quaternary structures vary from extension/transtension in the northeast, adjacent to the Turkish coastline, to transpression in the southwest, farther offshore. All these structures are truncated at the northwest end of the Antalya Basin by a broad zone of NNE-SSW-trending transverse structure that appears to represent a prolongation of the extreme easterly transform end of the Hellenic arc. Our mapping suggests that this broad zone links the Hellenic Arc with the Isparta Angle in southern Turkey, which we suggest is an earlier location of the junction of Hellenic and Cyprus Arcs: the junction migrated to the southwest over time, as the Hellenic Arc rolled back. The Turkish coastline turns from parallel to the Antalya Basin structures in the east to a N-S orientation, cutting across the trend of the Antalya Basin. The Antalya Complex and the Bey Dağları Mountains provide a spectacular backdrop to this edge of the offshore basin. Somewhere offshore lies the structural termination of the Antalya Basin. In 2001, we acquired around 400 km of high-resolution multi-channel seismic reflection data across the western end of the Antalya Basin to explore the nature of the termination, which we call the Bey Dağları lineament. We present a selection of the seismic profiles with interpretation of the nature and Neogene history of the lineament. Landward of the N-S-trending coastline, ophiolites of the Antalya Complex are exposed in a series of westerly-verging thrust slivers that extend to the carbonate sequences of the Bey Dağları Mountains. Our seismic data indicate that N-S trending west- and east-verging thrusts define a transpressional continental margin. The shelf is underlain by a prominent angular unconformity between overlying shallow-dipping Pliocene-Quaternary sediments and underlying, easterly- dipping ?Miocene sediments.
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NASA Astrophysics Data System (ADS)
Chae, S.; Hong, J.; Jung, S.; Ree, J.
2011-12-01
The Silurian Hoedongri Formation of the Taebaeksan Basin of South Korea has been used as a key unit to the correlation of tectonic provinces of East Asia since the South China craton (or Yangtz block) contains Silurian-Devonian sequences as well as Cambrian-Ordovician ones in the Paleozoic basins while the North China craton (or Sino-Korea block) is devoid of Silurian-Devonian sequences. In the Biryongdong area near the type locality of the Hoedongri Formation, it has been reported that the gray limestone of the Hoedongri Formation unconformably overlies brownish gray limestone of the Ordovician Haengmae Formation. However, our detailed examination on the Biryongdong section reveals that both of the brownish gray and gray limestones are mylonitic marbles with the boundary between the two units being a healed fault breccia zone (~ 12 m thick). The main difference of the two units is that repeated cycles of plastic deformation and fracturing occurred in the underlying brownish gray marble ('Haengmae') while the gray marble ('Hoedongri') deformed mainly by intracrystalline plasticity. The mylonitic foliation strikes NW with a low to moderate dip angle (20-60°) to NE. The ridge-in-groove type lineation on foliation surface trends NNW. The shape-preferred foliation of elongated calcite grains are oblique to the mylonitic foliation defined by layers with a grain-size variation, indicating a top-to-the-SSE shear sense. The mylonitic marble consists of elongated remnant grains (80-120 μm) with deformation twins and dynamically recrystallized matrix grains (10-40 μm). Grain boundaries and twin boundaries are lobate or wavy, indicating dynamic boundary migration. Some layers of the gray mylonitic marble are composed entirely of larger (80-120 μm) elongated calcite grains. In the brownish gray mylonitic marble unit, layers of brittle fracturing overprinting mylonitic foliation occur. In some of these layers, fragments (several cm - tens of cm) of the mylonitic marble are angular to subangular with coarse calcite fillings between the fragments. In other layers, mylonitic marble fragments are elongated with matrix foliation wrapping around them. These features suggest repeated cycles of plastic deformation and fracturing. Tectonic significance of this shear zone (at least 90 m thick) is not clear at present, and the regional extent and absolute age constraint of the shear zone should be clarified.
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NASA Astrophysics Data System (ADS)
Wiemer, D.; Schrank, C. E.; Murphy, D. T.
2014-12-01
We present a detailed lithostratigraphic and structural analysis of the Archean Doolena Gap greenstone belt to shed light on the tectonic evolution of the EPT. The study area is divided into four structural domains: i) marginal orthogneisses of the MGC (Muccan Granitoid Complex), ii) a dominantly mafic mylonitic shear zone (South Muccan Shear Zone, SMSZ) enveloping the MGC, iii) a Central Fold Belt of dominantly mafic greenschists (CFB), and iv) a lower greenschist- to sub-greenschist southern domain. Toward the dome margin, abrupt increases in deformation intensity occur across domain boundaries. Domain boundaries and intra-domain shear zones are marked by significant carbonate +/- quartz alteration and high-strain non-coaxial deformation with dome-up kinematics. The southern domain comprises pillow basalts of the Mount Ada Formation (MAF), conformably overlain by clastic sediments and minor pillow basalts of the Duffer Formation (DF). The MAF and DF are overlain by an up to 1km thick package of quartzite (Strelley Pool Formation) across an angular unconformity. Isoclinal folds (F2) within the CFB to the North deform an early foliation (S1) within dominantly mafic schists and associated carbonate veins. F2 folds are preserved within lozenges that are parallel to the axial planes of F2 folds in a regional E-W trending foliation (S2) and to the SMSZ. Lozenges are often bound by zones of significant carbonate alteration. The lozenges are folded recumbently (F3), with sub-vertical fold axes pointing towards the dome. The F3 axes are parallel to mineral stretching lineations on S2 indicating dome-up movement. The entire belt is cut by late NE-SW-striking faults that exhibit dominantly brittle deformation in the southern domain but ductile drag folding (F4) in the CFB. Therefore, the southern domain must have overlain the CFB during this D4 event. We propose a protracted structural history of the greenstone belt where successive deformation events relate to the episodic emplacement of the MGC. We demonstrate that the greenstone keel is mainly characterised by an anastomosing shear zone network, induced by hydro-chemical weakening of mafic schists. This implies that previous estimates of stratigraphic thickness are significantly overestimated.
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NASA Astrophysics Data System (ADS)
Sluijs, A.; van Roij, L.; Harrington, G. J.; Schouten, S.; Sessa, J. A.; LeVay, L. J.; Reichart, G.-J.; Slomp, C. P.
2014-07-01
The Paleocene-Eocene Thermal Maximum (PETM, ~ 56 Ma) was a ~ 200 kyr episode of global warming, associated with massive injections of 13C-depleted carbon into the ocean-atmosphere system. Although climate change during the PETM is relatively well constrained, effects on marine oxygen concentrations and nutrient cycling remain largely unclear. We identify the PETM in a sediment core from the US margin of the Gulf of Mexico. Biomarker-based paleotemperature proxies (methylation of branched tetraether-cyclization of branched tetraether (MBT-CBT) and TEX86) indicate that continental air and sea surface temperatures warmed from 27-29 to ~ 35 °C, although variations in the relative abundances of terrestrial and marine biomarkers may have influenced these estimates. Vegetation changes, as recorded from pollen assemblages, support this warming. The PETM is bracketed by two unconformities. It overlies Paleocene silt- and mudstones and is rich in angular (thus in situ produced; autochthonous) glauconite grains, which indicate sedimentary condensation. A drop in the relative abundance of terrestrial organic matter and changes in the dinoflagellate cyst assemblages suggest that rising sea level shifted the deposition of terrigenous material landward. This is consistent with previous findings of eustatic sea level rise during the PETM. Regionally, the attribution of the glauconite-rich unit to the PETM implicates the dating of a primate fossil, argued to represent the oldest North American specimen on record. The biomarker isorenieratene within the PETM indicates that euxinic photic zone conditions developed, likely seasonally, along the Gulf Coastal Plain. A global data compilation indicates that O2 concentrations dropped in all ocean basins in response to warming, hydrological change, and carbon cycle feedbacks. This culminated in (seasonal) anoxia along many continental margins, analogous to modern trends. Seafloor deoxygenation and widespread (seasonal) anoxia likely caused phosphorus regeneration from suboxic and anoxic sediments. We argue that this fueled shelf eutrophication, as widely recorded from microfossil studies, increasing organic carbon burial along many continental margins as a negative feedback to carbon input and global warming. If properly quantified with future work, the PETM offers the opportunity to assess the biogeochemical effects of enhanced phosphorus regeneration, as well as the timescales on which this feedback operates in view of modern and future ocean deoxygenation.
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NASA Astrophysics Data System (ADS)
El Harfi, A.; Lang, J.; Salomon, J.; Chellai, E. H.
2001-06-01
Cenozoic continental sedimentary deposits of the Southern Atlas named "Imerhane Group" crop out (a) in the Ouarzazate foreland basin between the Precambrian basement of the Anti Atlas and the uplifted limestone dominated High Atlas, and (b) in the Aït Kandoula and Aït Seddrat nappes where Jurassic strata detached from the basement have been thrust southwards over the Ouarzazate Basin. New biostratigraphic and geochronological data constraining the final Eocene marine regression, the characterization of the new "Aït Ouglif Detrital Formation" presumed to be of Oligocene age, and the new stratigraphic division proposed for the Continental Imerhane Group clarify the major tectonogenetic alpidic movements of the Central High Atlas Range. Four continental formations are identified at regional scale. Their emplacement was governed principally by tectonic but also by eustatic controls. The Hadida and Aït Arbi formations (Upper Eocene) record the major Paleogene regression. They are composed of margino-littoral facies (coastal sabkhas and fluviatile systems) and reflect incipient erosion of the underlying strata and renewed fluvial drainage. The Aït Ouglif Formation (presumed Oligocene) had not been characterized before. It frequently overlies all earlier formations with an angular unconformity. It includes siliciclastic alluvial deposits and is composed predominantly of numerous thin fining-upward cycles. The Aït Kandoula Formation (Miocene-Pliocene) is discordant, extensive, and represents a thick coarsening-upward megasequence. It is composed of palustro-lacustrine deposits in a context of alluvial plain with localized sabkhas, giving way to alluvial fans and fluviatile environments. The Upper Conglomeratic Formation (Quaternary) is the trace of a vast conglomeratic pediment, forming an alluvial plain and terraces. The second and third formations correspond to two megasequences engendered by the uplift of the Central High Atlas in two major compressive phases during late Oligocene and Miocene-Pliocene times. These two geodynamic events were separated by a tectonically calm phase, materialized by palustro-lacustrine sedimentation (Görler et al. 1988). Tectono-sedimentary analysis of the two megasequences shows that the basin structure and depositional processes were controlled by the compressive tectonic context generated by the collision of North Africa and Iberia in Tertiary times (Jacobshagen et al. 1988). The Quaternary Formation was apparently controlled by a tectonic continuum and by climatic variations.
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Hydrodynamical Modeling of Large Circumstellar Disks
NASA Astrophysics Data System (ADS)
Kurfürst, P.; Krtǐcka, J.
2016-11-01
Direct centrifugal ejection from a critically or near-critically rotating surface forms a gaseous equatorial decretion disk. Anomalous viscosity provides the efficient mechanism for transporting the angular momentum outwards. The outer part of the disk can extend up to a very large distance from the parent star. We study the evolution of density, radial and azimuthal velocity, and angular momentum loss rate of equatorial decretion disks out to very distant regions. We investigate how the physical characteristics of the disk depend on the distribution of temperature and viscosity. We also study the magnetorotational instability, which is considered to be the origin of anomalous viscosity in outflowing disks. We use analytical calculations to study the stability of outflowing disks submerged to the magnetic field. At large radii the instability disappears in the region where the disk orbital velocity is roughly equal to the sound speed. Therefore, the disk sonic radius can be roughly considered as an outer disk radius.
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Aab, A; Abreu, P; Aglietta, M; Ahn, E J; Samarai, I Al; Albuquerque, I F M; Allekotte, I; Allen, J; Allison, P; Almela, A; Castillo, J Alvarez; Alvarez-Muñiz, J; Batista, R Alves; Ambrosio, M; Aminaei, A; Anchordoqui, L; Andringa, S; Aramo, C; Aranda, V M; Arqueros, F; Asorey, H; Assis, P; Aublin, J; Ave, M; Avenier, M; Avila, G; Awal, N; Badescu, A M; Barber, K B; Bäuml, J; Baus, C; Beatty, J J; Becker, K H; Bellido, J A; Berat, C; Bertaina, M E; Bertou, X; Biermann, P L; Billoir, P; Blaess, S; Blanco, M; Bleve, C; Blümer, H; Boháčová, M; Boncioli, D; Bonifazi, C; Bonino, R; Borodai, N; Brack, J; Brancus, I; Bridgeman, A; Brogueira, P; Brown, W C; Buchholz, P; Bueno, A; Buitink, S; Buscemi, M; Caballero-Mora, K S; Caccianiga, B; Caccianiga, L; Candusso, M; Caramete, L; Caruso, R; Castellina, A; Cataldi, G; Cazon, L; Cester, R; Chavez, A G; Chiavassa, A; Chinellato, J A; Chudoba, J; Cilmo, M; Clay, R W; Cocciolo, G; Colalillo, R; Coleman, A; Collica, L; Coluccia, M R; Conceição, R; Contreras, F; Cooper, M J; Cordier, A; Coutu, S; Covault, C E; Cronin, J; Curutiu, A; Dallier, R; Daniel, B; Dasso, S; Daumiller, K; Dawson, B R; Almeida, R M de; Domenico, M De; Jong, S J de; Neto, J R T de Mello; Mitri, I De; Oliveira, J de; Souza, V de; Peral, L Del; Deligny, O; Dembinski, H; Dhital, N; Giulio, C Di; Matteo, A Di; Diaz, J C; Castro, M L Díaz; Diogo, F; Dobrigkeit, C; Docters, W; D'Olivo, J C; Dorofeev, A; Hasankiadeh, Q Dorosti; Dova, M T; Ebr, J; Engel, R; Erdmann, M; Erfani, M; Escobar, C O; Espadanal, J; Etchegoyen, A; Luis, P Facal San; Falcke, H; Fang, K; Farrar, G; Fauth, A C; Fazzini, N; Ferguson, A P; Fernandes, M; Fick, B; Figueira, J M; Filevich, A; Filipčič, A; Fox, B D; Fratu, O; Fröhlich, U; Fuchs, B; Fujii, T; Gaior, R; García, B; Roca, S T Garcia; Garcia-Gamez, D; Garcia-Pinto, D; Garilli, G; Bravo, A Gascon; Gate, F; Gemmeke, H; Ghia, P L; Giaccari, U; Giammarchi, M; Giller, M; Glaser, C; Glass, H; Berisso, M Gómez; Vitale, P F Gómez; Gonçalves, P; Gonzalez, J G; González, N; Gookin, B; Gordon, J; Gorgi, A; Gorham, P; Gouffon, P; Grebe, S; Griffith, N; Grillo, A F; Grubb, T D; Guarino, F; Guedes, G P; Hampel, M R; Hansen, P; Harari, D; Harrison, T A; Hartmann, S; Harton, J L; Haungs, A; Hebbeker, T; Heck, D; Heimann, P; Herve, A E; Hill, G C; Hojvat, C; Hollon, N; Holt, E; Homola, P; Hörandel, J R; Horvath, P; Hrabovský, M; Huber, D; Huege, T; Insolia, A; Isar, P G; Jandt, I; Jansen, S; Jarne, C; Josebachuili, M; Kääpä, A; Kambeitz, O; Kampert, K H; Kasper, P; Katkov, I; Kégl, B; Keilhauer, B; Keivani, A; Kemp, E; Kieckhafer, R M; Klages, H O; Kleifges, M; Kleinfeller, J; Krause, R; Krohm, N; Krömer, O; Kruppke-Hansen, D; Kuempel, D; Kunka, N; LaHurd, D; Latronico, L; Lauer, R; Lauscher, M; Lautridou, P; Coz, S Le; Leão, M S A B; Lebrun, D; Lebrun, P; Oliveira, M A Leigui de; Letessier-Selvon, A; Lhenry-Yvon, I; Link, K; López, R; Agüera, A Lopez; Louedec, K; Bahilo, J Lozano; Lu, L; Lucero, A; Ludwig, M; Malacari, M; Maldera, S; Mallamaci, M; Maller, J; Mandat, D; Mantsch, P; Mariazzi, A G; Marin, V; Mariş, I C; Marsella, G; Martello, D; Martin, L; Martinez, H; Bravo, O Martínez; Martraire, D; Meza, J J Masías; Mathes, H J; Mathys, S; Matthews, J; Matthews, J A J; Matthiae, G; Maurel, D; Maurizio, D; Mayotte, E; Mazur, P O; Medina, C; Medina-Tanco, G; Meissner, R; Melissas, M; Melo, D; Menshikov, A; Messina, S; Meyhandan, R; Mićanović, S; Micheletti, M I; Middendorf, L; Minaya, I A; Miramonti, L; Mitrica, B; Molina-Bueno, L; Mollerach, S; Monasor, M; Ragaigne, D Monnier; Montanet, F; Morello, C; Mostafá, M; Moura, C A; Muller, M A; Müller, G; Müller, S; Münchmeyer, M; Mussa, R; Navarra, G; Navas, S; Necesal, P; Nellen, L; Nelles, A; Neuser, J; Nguyen, P; Niechciol, M; Niemietz, L; Niggemann, T; Nitz, D; Nosek, D; Novotny, V; Nožka, L; Ochilo, L; Olinto, A; Oliveira, M; Pacheco, N; Selmi-Dei, D Pakk; Palatka, M; Pallotta, J; Palmieri, N; Papenbreer, P; Parente, G; Parra, A; Paul, T; Pech, M; Pȩkala, J; Pelayo, R; Pepe, I M; Perrone, L; Petermann, E; Peters, C; Petrera, S; Petrov, Y; Phuntsok, J; Piegaia, R; Pierog, T; Pieroni, P; Pimenta, M; Pirronello, V; Platino, M; Plum, M; Porcelli, A; Porowski, C; Prado, R R; Privitera, P; Prouza, M; Purrello, V; Quel, E J; Querchfeld, S; Quinn, S; Rautenberg, J; Ravel, O; Ravignani, D; Revenu, B; Ridky, J; Riggi, S; Risse, M; Ristori, P; Rizi, V; Carvalho, W Rodrigues de; Cabo, I Rodriguez; Fernandez, G Rodriguez; Rojo, J Rodriguez; Rodríguez-Frías, M D; Rogozin, D; Ros, G; Rosado, J; Rossler, T; Roth, M; Roulet, E; Rovero, A C; Saffi, S J; Saftoiu, A; Salamida, F; Salazar, H; Saleh, A; Greus, F Salesa; Salina, G; Sánchez, F; Sanchez-Lucas, P; Santo, C E; Santos, E; Santos, E M; Sarazin, F; Sarkar, B; Sarmento, R; Sato, R; Scharf, N; Scherini, V; Schieler, H; Schiffer, P; Schmidt, D; Schröder, F G; Scholten, O; Schoorlemmer, H; Schovánek, P; Schulz, A; Schulz, J; Schumacher, J; Sciutto, S J; Segreto, A; Settimo, M; Shadkam, A; Shellard, R C; Sidelnik, I; Sigl, G; Sima, O; Kowski, A Śmiał; Šmída, R; Snow, G R; Sommers, P; Sorokin, J; Squartini, R; Srivastava, Y N; Stanič, S; Stapleton, J; Stasielak, J; Stephan, M; Stutz, A; Suarez, F; Suomijärvi, T; Supanitsky, A D; Sutherland, M S; Swain, J; Szadkowski, Z; Szuba, M; Taborda, O A; Tapia, A; Tartare, M; Tepe, A; Theodoro, V M; Timmermans, C; Peixoto, C J Todero; Toma, G; Tomankova, L; Tomé, B; Tonachini, A; Elipe, G Torralba; Machado, D Torres; Travnicek, P; Trovato, E; Tueros, M; Ulrich, R; Unger, M; Urban, M; Galicia, J F Valdés; Valiño, I; Valore, L; Aar, G van; Bodegom, P van; Berg, A M van den; Velzen, S van; Vliet, A van; Varela, E; Vargas Cárdenas, B; Varner, G; Vázquez, J R; Vázquez, R A; Veberič, D; Verzi, V; Vicha, J; Videla, M; Villaseñor, L; Vlcek, B; Vorobiov, S; Wahlberg, H; Wainberg, O; Walz, D; Watson, A A; Weber, M; Weidenhaupt, K; Weindl, A; Werner, F; Widom, A; Wiencke, L; Wilczyńska, B; Wilczyński, H; Will, M; Williams, C; Winchen, T; Wittkowski, D; Wundheiler, B; Wykes, S; Yamamoto, T; Yapici, T; Yuan, G; Yushkov, A; Zamorano, B; Zas, E; Zavrtanik, D; Zavrtanik, M; Zaw, I; Zepeda, A; Zhou, J; Zhu, Y; Silva, M Zimbres; Ziolkowski, M; Zuccarello, F
Energy-dependent patterns in the arrival directions of cosmic rays are searched for using data of the Pierre Auger Observatory. We investigate local regions around the highest-energy cosmic rays with [Formula: see text] eV by analyzing cosmic rays with energies above [Formula: see text] eV arriving within an angular separation of approximately 15[Formula: see text]. We characterize the energy distributions inside these regions by two independent methods, one searching for angular dependence of energy-energy correlations and one searching for collimation of energy along the local system of principal axes of the energy distribution. No significant patterns are found with this analysis. The comparison of these measurements with astrophysical scenarios can therefore be used to obtain constraints on related model parameters such as strength of cosmic-ray deflection and density of point sources.
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All-fiber orbital angular momentum mode generation and transmission system
NASA Astrophysics Data System (ADS)
Heng, Xiaobo; Gan, Jiulin; Zhang, Zhishen; Qian, Qi; Xu, Shanhui; Yang, Zhongmin
2017-11-01
We proposed and demonstrated an all-fiber system for generating and transmitting orbital angular momentum (OAM) mode light. A specially designed multi-core fiber (MCF) was used to endow with guide modes different phase change and two tapered transition regions were used for providing low-loss interfaces between different fiber structures. By arranging the refractive index distribution among the multi-cores and controlling the length of MCF, which essentially change the phase difference between the neighboring cores, OAM modes with different topological charge l can be generated selectively. Through two tapered transition regions, the non-OAM mode light can be effectively injected into the MCF and the generated OAM mode light can be easily launched into OAM mode supporting fiber for long distance and high purity transmission. Such an all-fiber OAM mode generation and transmission system owns the merits of flexibility, compactness, portability, and would have practical application value in OAM optical fiber communication systems.
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Aab, Alexander
2015-06-20
Energy-dependent patterns in the arrival directions of cosmic rays are searched for using data of the Pierre Auger Observatory. We investigate local regions around the highest-energy cosmic rays with E ≥ 6×10 19 eV by analyzing cosmic rays with energies above E ≥ 5×10 18 eV arriving within an angular separation of approximately 15°. We characterize the energy distributions inside these regions by two independent methods, one searching for angular dependence of energy-energy correlations and one searching for collimation of energy along the local system of principal axes of the energy distribution. No significant patterns are found with this analysis.more » As a result, the comparison of these measurements with astrophysical scenarios can therefore be used to obtain constraints on related model parameters such as strength of cosmic-ray deflection and density of point sources.« less
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Active Structures in the Georgia Basin, NW Washington State, USA, and SW British Columbia, Canada
NASA Astrophysics Data System (ADS)
Polivka, P.; Riedel, M.; Pratt, T. L.
2013-12-01
The Georgia basin is a local depression in the Cascadia forearc straddling the USA-Canadian border that hosts Canada's largest west coast population. The basin contains late Pleistocene and Holocene sediments overlying a thick sequence of Eocene and Cretaceous sedimentary rocks and is currently experiencing N-S shortening. Tectonic structures capable of accommodating this N-S shortening are recognized in Oregon and Washington; however, none have been identified in southwest Canada despite multiple independent geodetic studies indicating that shortening continues further north. This conflict of observed shortening over a region without recognized active structures suggests that seismic hazard may be underestimated in Canada. We combine multiple seismic reflection surveys and multibeam bathymetry with published geophysical data and on-shore mapping to identify active structures and assess seismic hazard. Reflection datasets span the USA-CA border and include those from the deep 1998 Seismic Hazards Investigations of Puget Sound (SHIPS), high resolution 2002 SHIPS, localized sparker, and deep industry lines. These data are augmented by digitized paper records of past reflection surveys. The 1998 SHIPS and industry lines show strong reflections of folded and faulted Cretaceous and Eocene sedimentary bedrock to 5 km depth. Shallow sediment deformation is imaged on the 2002 SHIPS and sparker lines. Combining these profiles, bathymetry, and surficial bedrock mapping in a 3-D interpretation program facilitated the correlation of features across multiple 2-D seismic lines, allowing us to interpret four new regional stratigraphic and tectonic characteristics. (1) The 1997 ML4.6 Gabriola Island earthquake was a north-side up thrust event occurring 30 km west of Vancouver at ~3.5 km depth. The event was previously correlated with a zone of low coherence on the SHIPS 1998 line. We reprocessed the line and imaged distinct reflector terminations. A generally E-W strike is interpreted from regional bedrock fault trends and shallow sediment deformation imaged on the 2002 SHIPS lines. (2) Kelsey et al. (2012, JGR) identified three subparallel NW-striking faults in NW Washington. We use the industry lines to constrain the subsurface geometries of these faults to >4 km depth. (3) Interpreting on-shore mapping, bathymetric bedrock ridges, and intersecting deep seismic profiles, we conclude that the E-K boundary is an angular unconformity across and along the length of the basin. (4) We correlate kinks in bathymetric bedrock ridges with bedrock folds on the intersecting SHIPS 1998 profile to re-interpret previously identified NE-trending 'secondary faults' as blind and broken-through fault-propagation folds. These faults are orthogonal to the subduction margin and collectively deemed the Vancouver Fold and Thrust Belt. The Gabriola Island earthquake indicates that the fault system is active, and likely accommodates at least part of the strain measured on GPS networks but not accounted for in previous tectonic models.
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Potter, C.J.; Drahovzal, James A.; Sargent, M.L.; McBride, J.H.
1997-01-01
Four high-quality seismic reflection profiles through the southern Illinois Basin, totaling 245 km in length, provide an excellent regional subsurface stratigraphic and structural framework for evaluation of seismic risk, hydrocarbon occurrence, and other regional geologic studies. These data provide extensive subsurface information on the geometry of the intersection of the Cambrian Reelfoot and Rough Creek rifts, on extensive Proterozoic reflection sequences, and on structures (including the Fluorspar Area Fault Complex and Hicks Dome) that underlie a transitional area between the well-defined New Madrid seismic zone (to the southwest) and a more diffuse area of seismicity in the southern Illinois Basin. Our principal interpretations from these data are listed here in order of geologic age, from oldest to youngest: 1. Prominent Proterozoic layering, possibly equivalent to Proterozoic (???1 Ga) Middle Run Formation clastic strata and underlying (1.3-1.5 Ga) volcanic rocks of the East Continent rift basin, has been strongly deformed, probably as part of the Grenville foreland fold and thrust belt. 2. A well-defined angular unconformity is seen in many places between Proterozoic and Cambrian strata; a post-Grenville Proterozoic sequence is also apparent locally, directly beneath the base of the Cambrian. 3. We infer a major reversal in Cambrian rift polarity (accommodation zone) in the Rough Creek Graben in western Kentucky. 4. Seismic facies analysis suggests the presence of basin-floor fan complexes at and near the base of the Cambrian interval and within parts of a Proterozoic post-Grenville sequence in several parts of the Rough Creek Graben. 5. There is an abrupt pinchout of the Mount Simon Sandstone against crystalline basement beneath the Dale Dome (near the Texaco no. 1 Cuppy well, Hamilton County) in southeastern Illinois, and a more gradual Mount Simon pinchout to the southeast. 6. Where crossed by the seismic reflection line in southeast Illinois, some faults in the Wabash Valley Fault System produce discrete offset in Ordovician and younger strata only; one of the Wabash Valley faults cuts the top of the Precambrian on this seismic profile. 7. The data show clear evidence of late Paleozoic reverse faulting along both boundaries of the Rough Creek Graben in western Kentucky, although significant unreactivated Cambrian rift-bounding faults are also preserved. 8. Chaotic reflection patterns in the lower and middle Paleozoic strata near Hicks Dome, southern Illinois, are related to a combination of intrusive brecciation, intense faulting, and alteration of carbonate strata by acidic mineralizing fluids, all of which occurred in the Permian. 9. Late Paleozoic(?) reverse faulting is interpreted on one flank of the Rock Creek Graben, southern Illinois. 10. Permian and Mesozoic(?) extensional faulting is clearly imaged in the Fluorspar Area Fault Complex; neotectonic studies suggest that these structures were reactivated in the Quaternary.
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Sestieri, Carlo; Corbetta, Maurizio; Romani, Gian Luca; Shulman, Gordon L.
2011-01-01
The default mode network (DMN) is often considered a functionally homogeneous system that is broadly associated with internally directed cognition (e.g. episodic memory, theory of mind, self-evaluation). However, few studies have examined how this network interacts with other networks during putative “default” processes such as episodic memory retrieval. Using fMRI, we investigated the topography and response profile of human parietal regions inside and outside the DMN, independently defined using task-evoked deactivations and resting state functional connectivity, during episodic memory retrieval. Memory retrieval activated posterior nodes of the DMN, particularly the angular gyrus, but also more anterior and dorsal parietal regions that were anatomically separate from the DMN. The two sets of parietal regions showed different resting-state functional connectivity and response profiles. During memory retrieval, responses in DMN regions peaked sooner than non-DMN regions, which in turn showed responses that were sustained until a final memory judgment was reached. Moreover, a parahippocampal region that showed strong resting-state connectivity with parietal DMN regions also exhibited a pattern of task-evoked activity similar to that exhibited by DMN regions. These results suggest that DMN parietal regions directly supported memory retrieval, whereas non-DMN parietal regions were more involved in post-retrieval processes such as memory-based decision making. Finally, a robust functional dissociation within the DMN was observed. While angular gyrus and posterior cingulate/precuneus were significantly activated during memory retrieval, an anterior DMN node in medial prefrontal cortex was strongly deactivated. This latter finding demonstrates functional heterogeneity rather than homogeneity within the DMN during episodic memory retrieval. PMID:21430142
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Sestieri, Carlo; Corbetta, Maurizio; Romani, Gian Luca; Shulman, Gordon L
2011-03-23
The default mode network (DMN) is often considered a functionally homogeneous system that is broadly associated with internally directed cognition (e.g., episodic memory, theory of mind, self-evaluation). However, few studies have examined how this network interacts with other networks during putative "default" processes such as episodic memory retrieval. Using functional magnetic resonance imaging, we investigated the topography and response profile of human parietal regions inside and outside the DMN, independently defined using task-evoked deactivations and resting-state functional connectivity, during episodic memory retrieval. Memory retrieval activated posterior nodes of the DMN, particularly the angular gyrus, but also more anterior and dorsal parietal regions that were anatomically separate from the DMN. The two sets of parietal regions showed different resting-state functional connectivity and response profiles. During memory retrieval, responses in DMN regions peaked sooner than non-DMN regions, which in turn showed responses that were sustained until a final memory judgment was reached. Moreover, a parahippocampal region that showed strong resting-state connectivity with parietal DMN regions also exhibited a pattern of task-evoked activity similar to that exhibited by DMN regions. These results suggest that DMN parietal regions directly supported memory retrieval, whereas non-DMN parietal regions were more involved in postretrieval processes such as memory-based decision making. Finally, a robust functional dissociation within the DMN was observed. Whereas angular gyrus and posterior cingulate/precuneus were significantly activated during memory retrieval, an anterior DMN node in medial prefrontal cortex was strongly deactivated. This latter finding demonstrates functional heterogeneity rather than homogeneity within the DMN during episodic memory retrieval.
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NASA Astrophysics Data System (ADS)
Geuna, Silvana E.; Somoza, Rubén; Vizán, Haroldo; Figari, Eduardo G.; Rinaldi, Carlos A.
2000-08-01
A paleomagnetic study in Jurassic and Cretaceous rocks from the Cañadón Asfalto basin, central Patagonia, indicates the occurrence of about 25-30° clockwise rotation in Upper Jurassic-lowermost Cretaceous rocks, whereas the overlying mid-Cretaceous rocks do not show evidence of rotation. This constrains the tectonic rotation to be related to a major regional unconformity in Patagonia, which in turn seems to be close in time with the early opening of the South Atlantic Ocean. The sense and probably the timing of this rotation are similar to those of other paleomagnetically detected rotations in different areas of southwestern Gondwana, suggesting a possible relationship between these and major tectonic processes related with fragmentation of the supercontinent. On the other hand, the mid-Cretaceous rocks in the region yield a paleopole located at Lat. 87° South, Long. 159° East, A95=3.8°. This pole position is consistent with coeval high-quality paleopoles of other plates when transferred to South American coordinates, implying it is an accurate determination of the Aptian (circa 116 Ma) geomagnetic field in South America.
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Gbara, Ali; Heiland, Max; Schmelzle, Rainer; Blake, Felix
2008-04-01
Following open reduction, internal fixation of fractures of the mandible is predominantly achieved using plates and screws. Today, a multitude of osteosynthesis systems are available on the market. One therapy modality, primarily developed for orthopaedic surgery, is using angular stable osteosynthesis plate systems. The dominating principle of these is the bond between screw and plate following insertion. This principle of an "internal fixateur" results in a more stable fixation of the fragments associated with less compression of the bone surfaces. A new multidirectional osteosynthesis system (TiFix=Smartlock, Hamburg - Germany) was modified to fit the maxillofacial region and compared with four other well established osteosynthesis systems developed by Mondial, Medicon, Synthes, Leibinger-Stryker, one of these (Unilock by Synthes) being also angular stable. The resistance to deformation in varying directions was investigated following fixation in four different materials. The TiFix system proved more resistant to deformation even when mounted with fewer screws than the non-angular stable systems. This system results in greater stability even when fewer screws are used. For the clinician this means smaller access incisions, less soft tissue trauma, better aesthetic results, decreased duration of operation and a reduction of costs.
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2015-01-01
al. (2014), and of the Large Magellanic Cloud (LMC) Tarantula Nebula region by Sana et al. (2013b), demonstrate that the binary frequency may be »70...Monte-Carlo method to fit spectroscopic results for a large sample of O-type stars in the Tarantula Nebula region of the LMC, and they find a best fit
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New insights into the earliest Quaternary environments in the Central North Sea from 3D seismic
NASA Astrophysics Data System (ADS)
Lamb, Rachel; Huuse, Mads; Stewart, Margaret; Brocklehurst, Simon H.
2014-05-01
In the past the transition between an unconformable surface in the south to a conformable horizon towards the north has made identification and mapping the base-Quaternary in the central North Sea difficult (Sejrup et al 1991; Gatliff et al 1994). However recent integration of biostratigraphy, pollen analysis, paleomagnetism and amino acid analysis in the Dutch and Danish sectors (Rasmussen et al 2005; Kuhlmann et al 2006) has allowed greater confidence in the correlation to the region 3D seismic datasets and thus has allowed the base-Quaternary to be mapped across the entire basin. The base-Quaternary has been mapped using the PGS MegaSurvey dataset from wells in the Danish Sector along the initially unconformable horizon and down the delta front into the more conformable basin giving a high degree of confidence in the horizon pick. The revised base-Quaternary surface reaches a depth of 1248 ms TWT with an elongate basin shape which is significantly deeper than the traditionally mapped surface. Using RMS amplitudes and other seismic attributes the revised base-Quaternary has been investigated along the horizon and in time slice to interpret the environments of the earliest Quaternary prior to the onset of glaciation. Combined with analysis of aligned elongate furrows over 10 km long, 100 m wide and 100 m deep suggest a deep marine environment in an almost enclosed basin with persistent strong NW-SE bottom currents in the deepest parts. Pockmarks were formed by the escape of shallow gas on the sides of a small delta in the eastern part of the basin. The progradation of large deltas from both the north and south into the basin make up the majority of the deposition of sediment into the basin. Key Words: base-Quaternary; seismic interpretation; paleoenvironments References: Gatliff, R.W, Richards, P.C, Smith, K, Graham, C.C, McCormac, M, Smith, N.J.P, Long, D, Cameron, T.D.J, Evans, D, Stevenson, A.G, Bulat, J, Ritchie, J.D, (1994) 'United Kingdom offshore regional report: the geology of the central North Sea.' London: HMSO for the British Geological Survey Kuhlmann, G., Langereis C.G., Munsterman, D., van Leeuwen, R.-J., Verreussel, R., Meulenkamp, J.E., Wong, Th.E., 2006 'Intergrated chronostratigraphy of the Pliocene-Pliestocene interval and its relation to the regional stratigraphical stages in the Southern North Sea region' Netherlands Journal of Geosciences 85(1), 29-45 Rasmussen, E.A., Vejb?k O.V., Bidstrup, T., Piasecki, S., Dybkj?r, K., 2005 'Late Cenozoic depositional history of the Danish North Sea Basin: implications for the petroleum systems in the Kraka, Halfdan, Siri and Nini fields', Petroleum Geology Conference series 6, 1347-1358 Sejrup, H.P., Aareseth, I., Haflidason, H., 1991 'The Quaternary succession in the northern North Sea' Marine Geology 101 103-111
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Conditions for achieving ideal and Lambertian symmetrical solar concentrators.
Luque, A; Lorenzo, E
1982-10-15
In this paper we are concerned with symmetrical bidimensional concentrators, and we prove that for a given source's angular extension a curve exists that divides the plane into two regions. No ideal concentrator can be found with its edges on the outer region and no Lambertian concentrator can be found with its edges on the inner region. A consequence of this theorem is that a concentrator is forced to cast some of the incident energy outside the collector to ensure its obtaining the maximum power.
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Examination of the low-energy enhancement of the γ -ray strength function of Fe 56
Jones, M. D.; Macchiavelli, A. O.; Wiedeking, M.; ...
2018-02-22
A model-independent technique was used to determine the γ-ray strength function (γSF) of 56Fe down to γ-ray energies less than 1 MeV for the first time with GRETINA using the (p,p') reaction at 16 MeV. No difference was observed in the energy dependence of the γSF built on 2 + and 4 + final states, supporting the Brink hypothesis. In addition, angular distribution and polarization measurements were performed. The angular distributions are consistent with dipole radiation. In conclusion, the polarization results show a small bias towards magnetic character in the region of the enhancement.
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Examination of the low-energy enhancement of the γ -ray strength function of 56Fe
NASA Astrophysics Data System (ADS)
Jones, M. D.; Macchiavelli, A. O.; Wiedeking, M.; Bernstein, L. A.; Crawford, H. L.; Campbell, C. M.; Clark, R. M.; Cromaz, M.; Fallon, P.; Lee, I. Y.; Salathe, M.; Wiens, A.; Ayangeakaa, A. D.; Bleuel, D. L.; Bottoni, S.; Carpenter, M. P.; Davids, H. M.; Elson, J.; Görgen, A.; Guttormsen, M.; Janssens, R. V. F.; Kinnison, J. E.; Kirsch, L.; Larsen, A. C.; Lauritsen, T.; Reviol, W.; Sarantites, D. G.; Siem, S.; Voinov, A. V.; Zhu, S.
2018-02-01
A model-independent technique was used to determine the γ -ray strength function (γ SF ) of 56Fe down to γ -ray energies less than 1 MeV for the first time with GRETINA using the (p ,p') reaction at 16 MeV. No difference was observed in the energy dependence of the γ SF built on 2+ and 4+ final states, supporting the Brink hypothesis. In addition, angular distribution and polarization measurements were performed. The angular distributions are consistent with dipole radiation. The polarization results show a small bias towards magnetic character in the region of the enhancement.
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NASA Astrophysics Data System (ADS)
Gorelik, V. S.; Yashin, M. M.; Pudovkin, A. V.; Vodchits, A. I.
2017-11-01
The article considers optical properties (transmission and reflection) of one-dimensional photonic crystals based on mesoporous anodic aluminum oxide, with periods of crystal lattices 188 and 194 nm. A comparison of the experimentally measured reflection spectrum in the spectral region of the first stop-zone with the theoretical dependence obtained from the dispersion relation for one-dimensional photonic crystal is carried out. The angular dependence of the first stop-zone spectral positions of one-dimensional photonic crystal is established. The authors analyze the possibility of applications of mesoporous one-dimensional photonic crystals based on aluminum oxide as the selective narrowband filters and mirrors.
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Examination of the low-energy enhancement of the γ -ray strength function of Fe 56
DOE Office of Scientific and Technical Information (OSTI.GOV)
Jones, M. D.; Macchiavelli, A. O.; Wiedeking, M.
A model-independent technique was used to determine the γ-ray strength function (γSF) of 56Fe down to γ-ray energies less than 1 MeV for the first time with GRETINA using the (p,p') reaction at 16 MeV. No difference was observed in the energy dependence of the γSF built on 2 + and 4 + final states, supporting the Brink hypothesis. In addition, angular distribution and polarization measurements were performed. The angular distributions are consistent with dipole radiation. In conclusion, the polarization results show a small bias towards magnetic character in the region of the enhancement.
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DOE R&D Accomplishments Database
Ade, P.; Balbi, A.; Bock, J.; Borrill, J.; Boscaleri, A.; de Bernardis, P.; Ferreira, P. G.; Hanany, S.; Hristov, V. V.; Jaffe, A. H.; Lange, A. E.; Lee, A. T.; Mauskopf, P. D.; Netterfield, C. B.; Oh, S.; Pascale, E.; Rabii, B.; Richards, P. L.; Smoot, G. F.; Stompor, R.; Winant,C. D.; Wu, J. H. P.
2005-06-04
We present a map and an angular power spectrum of the anisotropy of the cosmic microwave background (CMB) from the first flight of MAXIMA. MAXIMA is a balloon-borne experiment with an array of 16 bolometric photometers operated at 100 mK. MAXIMA observed a 124 deg{sup 2} region of the sky with 10' resolution at frequencies of 150, 240 and 410 GHz. The data were calibrated using in-flight measurements of the CMB dipole anisotropy. A map of the CMB anisotropy was produced from three 150 and one 240 GHz photometer without need for foreground subtractions.
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Transport in a magnetic field modulated graphene superlattice.
Li, Yu-Xian
2010-01-13
Using the transfer matrix method, we study the transport properties through a magnetic field modulated graphene superlattice. It is found that the electrostatic barrier, the magnetic vector potential, and the number of wells in a superlattice modify the transmission remarkably. The angular dependent transmission is blocked by the magnetic vector potential because of the appearance of the evanescent states at certain incident angles, and the region of Klein tunneling shifts to the left. The angularly averaged conductivities exhibit oscillatory behavior. The magnitude and period of oscillation depend sensitively on the height of the electrostatic barrier, the number of wells, and the strength of the modulated magnetic field.
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Spatial biostratigraphy of NW Pakistan
NASA Astrophysics Data System (ADS)
Shafique, Naseer Ahmed
2001-07-01
Mesozoic to Cenozoic biostratigraphy of NW Pakistan has been conducted in order to document the temporal and spatial relationship between different marine strata with the help of remote sensing and Geographic Information Systems (GIS). These relationships were then used to help distinguish different tectonostratigraphic units in the Waziristan and the Kurram areas located at the northwestern margin of the Indo-Pakistani craton. Extensive biostratigraphic work in the Waziristan and Kurram areas enabled to distinguish five tectonostratigraphic units and two significant unconformities in the study area. Different foraminiferal zones from Early Jurassic to Middle Eocenewere developed, although due to random samples these zones are not continuous in the sedimentary record. However continuous biozonation from the Late Paleocene P4 to the Early Eocene P9 (Bolli, 1985) biozone was observed. It is observed that the Santonian stage is generally missing in the sedimentary sequence, and it is only found in the olistoliths. This implies that during the Campanian stage there was instability in the shelf due to ophiolite obduction, which caused the displacement of the Santonian strata. The absence of Early Paleocene (Zone P1--P3) microfauna is suggested by rapid subsidence of the NW Indian shelf beginning in the early Paleocene. Moreover, index fossils for the Palpha, P1a, b, c, d, P2 and P3 biozones are absent in the melange of the Thal area suggesting regional uplift during the Paleocene. The presence of Planorotalites pseudomenardii P4 zone microfauna above the unconformable Upper Cretaceous Kahi melange strata suggest the India-Asia collision age between 58 Ma--56 Ma. Foraminiferal biostratigraphy of upper Cretaceous olistoliths was conducted from the Mughal Kot gorge, Baluchistan, Pakistan in order to reveal the depositional history of Late Santonian aged (Dicarinella asymmetrica zone) olistoliths and associated upper Cretaceous to early Tertiary Indo-Pakistani shelf strata. These olistoliths are embedded in uppermost Campanian strata of the Mughal Kot Formation. Similar olistostromes are found at approximately the same stratigraphic level across a broad region of NW Pakistan. These olistostromes are similar in age to radiometrically constrained deformation in the Zhob and Waziristan ophiolites 50 and 90 km to the west and northwest respectively and may record incipient underthrusting of the NW Indo Pakistani craton beneath oceanic crust now in Waziristan and northern Baluchistan. This Campanian event precedes stratigraphically constrained Paleocene and Early Eocene deformation in Parachinar, Orakzai and the Attock-Cherat Ranges, which is interpreted as the collision of NW Indo-Pakistan with Asia and the Kabul Block. A turbiditic depositional environment of the Mughal Kot Formation was developed due to the regional collapse of the NW Indo-Pakistani shelf margin during the Late Campanian (G. calcarata zone ˜80--74 Ma), possibly as a result of ophiolite obduction as the Indo-Pakistani plate moved beneath Tethyan oceanic crust.
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Sedimentology and tectonics of the collision complex in the east arm of Sulawesi Indonesia
NASA Astrophysics Data System (ADS)
Simandjuntak, Tohap Oculair
An imbricated Mesozoic to Palaeogene continental margin sequence is juxtaposed with ophiolitic rocks in the East Arm of Sulawesi, Indonesia. The two tectonic terranes are bounded by the Batui Thrust and Balantak Fault System, which are considered to be the surface expression of the collision zone between the Banggai-Sula Platform and the Eastern Sulawesi Ophiolite Belt. The collision complex contains three distinctive sedimentary sequences : 1) Triassic-Palaeogene continental margin sediments, ii) Cretaceous pelagic sediments and iii) Neogene coarse clastic sediments and volcanogenic turbidites. (i) Late Triassic Lemo Beds consisting largely of carbonate-slope deposits and subsidiary clastics including quartz-rich lithic sandstones and lensoidal pebbly mudstone and conglomeratic breccia. The hemipelagic limestones are rich in micro-fossils. Some beds of the limestone contain bivalves and ammonites, including Misolia, which typifies the Triassic-Jurassic sequence of eastern Indonesia. The Jurassic Kapali Beds are dominated by quartzose arenites containing significant amounts of plant remains and lumps of coal. The Late Jurassic sediments consist of neritic carbonate deposits (Nambo Beds and Sinsidik Beds) containing ammonites and belemnites, including Belemnopsis uhligi Stevens, of Late Jurassic age. The Jurassic sediments are overlain unconformably by Late Cretaceous Luok Beds which are predominantly calcilutite with chert nodules rich in microfossils. The Luok Beds are unconformably overlain by the Palaeogene Salodik Limestones which consist of carbonate platform sediments rich in both benthic and planktonic foraminifera of Eocene to Early Miocene age. These sediments were deposited on the continental margin of the Banggai-Sula Platform. (ii) Deep-sea sediments (Boba Beds) consist largely of chert and subsidiary calcilutite rich in radiolaria of Cretaceous age. These rocks are part of an ophiolite suite. (iii) Coarse clastic sediments (Kolo Beds and Biak Conglomerates) are typical post-orogenic clastic rocks deposited on top of the collision complex. They are composed of material derived from both the continental margin sequence and ophiolite suite. Volcanogenic Lonsuit Turbidites occur in the northern part of the East Arm in Poh Head and unconformably overlie the ophiolite suite. Late Miocene to Pliocene planktonic foraminifera occur in the intercalated marlstone and marly sandstone beds within these rocks. The collision zone is marked by the occurrence of Kolokolo Melange, which contain exotic fragments detached from both the ophiolite suite and the continental margin sequence and a matrix of calcareous mudstone and marlstone rich in planktonic foraminifera of late Middle Miocene to Pliocene age. The melange is believed to have been formed during and after the collision of the Banggai-Sula Platform with the Eastern Sulawesi Ophiolite Belt. Hence, the collision event took place in Middle Miocene time. The occurrence of at least three terraces of Quaternary coraline reefs on the south coast of the East Arm of Sulawesi testifies to the rapid uplift of the region. Seismic data suggest that the collision might still be in progress at the present time.
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NASA Astrophysics Data System (ADS)
Hemmi, R.; Yoshida, S.; Nemoto, Y.; Kotake, N.
2010-12-01
The early-to-middle Holocene outcrops of Izu-Oshima island, 100 km SSW of Tokyo, comprise sand- to gravel-size pyroclasts, and exhibit undulating layered structures, with each wavelet typically measuring 5-10 m high. These outcrops were traditionally interpreted as exemplary subaerial "ash-fall" deposits in volcanology textbooks (e.g. Schmincke 2006). Our detailed sedimentological analyses, however, have revealed that it is of pyroclastic density-current origin, the majority of which formed in shallow-marine settings. The present study focuses on the outcrops along the western coast of the Island, where the three-dimensional architecture of the outcrops is superbly exposed, and the existing archaeological framework provides a reliable chronostratigraphic control. The outcrops contain abundant compound bedforms, where small bedforms (dunes/antidunes) occur within the larger bedforms. The compound bedforms exhibit four-fold hierarchy (ranks 1 to 4), and bedforms for each scale display dominantly upstream-accreting geometry. The largest scale (Rank 1) of these bedforms show wavy parallel-bedding geometry (each wavelet typically measuring 5-10 m high and 50-100 m wide). We interpreted the large-scale architecture as sediment waves (gigantic antidunes) similar to the one reported from the shallow-marine deposits associated with AD 79 Mt. Vesuvius eruptions (Milia et al. 2008). Moreover, we have identified crustacean burrows and other trace fossils indicative of a nearshore shallow-marine environment. The pervasive occurrence of these fossils throughout the outcrops and abundant water-escape structures also suggests their subaqueous origin. On the other hand, evidence of subaerial deposition (e.g., paleosols and rootlets) or subaerial reworking (e.g., lahar) is absent, except for some spots on several regional unconformities that divide 10’s-m-thick sediment-wave deposits. On some of these unconformities, ribbon- to fan-shaped lava and/or ancient human-dwelling sites (5.0-7.5 ka) are locally present. These observations suggest that the deposition of the pyroclastic and lava flow occurred near the coastline, with rapid fluctuations of relative sea level. Earlier workers suggested that these outcrops were “subaerial ash-fall” deposits, with each dm-thick layer representing a small eruption that occurred at about 150-year interval from 20 ka to 5 ka, with the total number of eruptions reaching or possibly exceeding 100 (Tazawa 1980). However, we suggest that these layers form several 10’s-m-thick unconformity-bounded units (sediment waves). Together with the abundant shallow-marine trace fossils, we believe that these outcrops are of subaqueous pyroclastic-flow origin, recording less frequent but much bigger catastrophic eruptions than previously thought. Without recognizing the stratal packaging patterns on the 2-D/3-D vertical cross-sections, these outcrops can easily be mistaken for ash-fall deposits, and the magnitude of eruptions can be vastly underestimated.
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NASA Astrophysics Data System (ADS)
Guallini, Luca; Rossi, Angelo Pio; Forget, François; Marinangeli, Lucia; Lauro, Sebastian Emanuel; Pettinelli, Elena; Seu, Roberto; Thomas, Nicolas
2018-07-01
The Mars South Polar Layered Deposits (SPLD) are the result of depositional and erosional events, which are marked by different stratigraphic sequences and erosional surfaces. To unambiguously define the stratigraphic units at regional scale, we mapped the SPLD on the basis of observed discontinuities (i.e., unconformities, correlative discontinuities and conformities), as commonly done in terrestrial modern stratigraphy. This methodology is defined as "Discontinuity-Bounded Units" or allostratigraphy, and is complemented by geomorphological mapping. Our study focuses on Promethei Lingula (PL) and uses both high-resolution images (CTX, HiRISE) and radargrams (SHARAD) to combine surface and sub-surface observations and obtain a 3D geological reconstruction of the SPLD. One regional discontinuity (named AUR1) was defined within the studied stratigraphic succession and is exposed in several non-contiguous outcrops around PL as well as observed at depth within the ice sheet. This is the primary contact between two major depositional sequences, showing a different texture at CTX resolution. The lower sequence is characterized mainly by a "ridge and trough" morphology (Ridge and Trough Sequence; RTS) and the upper sequence shows mainly by a "stair-stepped" morphology (Stair-Stepped Sequence; SSS). On the basis of the observations, we defined two regional "discontinuity-bounded" units in PL, respectively coinciding with RTS and SSS sequences. Our stratigraphic reconstruction provides new hints on the major scale events that shaped this region. Oscillations in Martian axial obliquity could have controlled local climate conditions in the past, affecting the PL geological record.
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2006-09-01
Richardson, in review). Figure 1 shows the lithostratigraphic setting for Eocene through Miocene strata, and the occurrence of hydrostratigraphic units of...basal Haw- thorn unit lies unconformably on lithologies informally called “ Eocene limestones,” which consist of Suwannee Limestone, Ocala Limestone
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Ten metre global sea-level change associated with South Atlantic Aptian salt deposition
NASA Technical Reports Server (NTRS)
Burke, Kevin; Sengor, A. M. Celal
1988-01-01
Catastrophic filling of the kind of subsea-level depression commonly formed during ocean opening and ocean closing is the only mechanism, other than glacial eustacy, capable of rapidly lowering sea level. Aptian evaporites overlying oceanic crust on both sides of the South Atlantic between the Walvis Ridge and the Niger Delta were deposited in such a basin by repeated spilling of ocean water. The final flooding of the South Atlantic north of the Walvis Ridge extracted about 14 x 10 to the 8th cu km of sea water from the world ocean and effected about 10 m of sea-level lowering. It is speculated that the middle Aptian unconformity, which is one of the more prominent world-wide unconformities, is associated with this sea-level drop of about 10 m. A corollary of this interpretation is that if the catastrophic sea-level lowerings during the Mesozoic era had amplitudes substantially greater than 10 m, then a glacial mechanism to explain them would seem inescapable although the stratigraphic record has not yet yielded any evidence of such glaciation.
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The Jurassic section along McElmo Canyon in southwestern Colorado
O'Sullivan, Robert B.
1997-01-01
In McElmo Canyon, Jurassic rocks are 1500-1600 ft thick. Lower Jurassic rocks of the Glen Canyon Group include (in ascending order) Wingate Sandstone, Kayenta Formation and Navajo Sandstone. Middle Jurassic rocks are represented by the San Rafael Group, which includes the Entrada Sandstone and overlying Wanakah Formation. Upper Jurassic rocks comprise the Junction Creek Sandstone overlain by the Morrison Formation. The Burro Canyon Formation, generally considered to be Lower Cretaceous, may be Late Jurassic in the McElmo Canyon area and is discussed with the Jurassic. The Upper Triassic Chinle Formation in the subsurface underlies, and the Upper Cretaceous Dakota Sandstone overlies, the Jurassic section. An unconformity is present at the base of the Glen Canyon Group (J-0), at the base of the San Rafael Group (J-2), and at the base of the Junction Creek Sandstone (J-5). Another unconformity of Cretaceous age is at the base of the Dakota Sandstone. Most of the Jurassic rocks consist of fluviatile, lacustrine and eolian deposits. The basal part of the Entrada Sandstone and the Wanakah Formation may be of marginal marine origin.
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DOE Office of Scientific and Technical Information (OSTI.GOV)
Hendrix, E.D.
1993-04-01
The Soledad Basin (central Transverse Ranges, CA) contains the first recognized example of mid-Tertiary detachment-faulting west of the San Andreas fault. Displacements along the Pelona detachment fault and syn-extensional upper-plate sedimentation occurred between [approximately] 26--18 Ma, resulting in deposition of at least 4 separate lithogenetic sequences (LS) which record distinct phases of crustal response to extension. The 1st LS (lower Vasquez Fm.) predates syn-extensional volcanism and records initial basin subsidence along small, discontinuous faults. The 2nd LS (middle Vasquez Fm.) consists of both volcanic and sedimentary strata and signals simultaneous onset of magmatism and initial development of a well-defined networkmore » of high-angle, upper-plate normal faults, creating 2 separate sub-basins. Resulting alluvial fans were non-entrenched, implying that subsidence rates, and thus vertical displacement rates on high-angle faults, equaled or exceeded an estimated average sedimentation rate of 1.4 mm/yr. The 3rd LS (upper Vasquez Fm.) reflects transition to a single, well-integrated depositional basin characterized by streamflood sedimentation. This suggests an enlarged drainage basin and a decrease in subsidence rate relative to sedimentation rate, triggered possibly by uplift of the detachment lower-plate. The 4th LS (Tick Canyon Fm.) lies with angular unconformity above the 3rd LS and contains the 1st clasts eroded from the detachment lower plate. Detachment faulting in the Soledad basin appears to involve, in part, reactivation of structural zones of weakness along the Vincent thrust. Preliminary reconstructions of Soledad extension imply 25--30 km of displacement along the Pelona detachment fault system at an averaged slip rate of 3.6--4.3 mm/yr.« less
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NASA Astrophysics Data System (ADS)
Priest, George R.; Hladky, Frank R.; Mertzman, Stanley A.; Murray, Robert B.; Wiley, Thomas J.
2013-08-01
geologic mapping of the Klamath Falls-Keno area revealed the complex relationship between subduction, crustal extension, and magmatic composition of the southern Oregon Cascade volcanic arc. Volcanism in the study area at 7-4 Ma consisted of calc-alkaline basaltic andesite and andesite lava flowing over a relatively flat landscape. Local angular unconformities are evidence that Basin and Range extension began at by at least 4 Ma and continues today with fault blocks tilting at a long-term rate of 2°/Ma to 3°/Ma. Minimum NW-SE extension is 1.5 km over 28 km ( 5%). High-alumina olivine tholeiite (HAOT) or low-K, low-Ti transitional high-alumina olivine tholeiite (LKLT) erupted within and adjacent to the back edge of the calc-alkaline arc as the edge receded westward at a rate of 10 km/Ma at 2.7-0.45 Ma. The volcanic front migrated east much slower than the back arc migrated west: 0 km/Ma for 6-0.4 Ma calc-alkaline rocks; 0.7 km/Ma, if 6 Ma HAOT-LKLT is included; and 1 km/Ma, if highly differentiated 17-30 Ma volcanic rocks of the early Western Cascades are included. Declining convergence probably decreased asthenospheric corner flow, decreasing width of calc-alkaline and HAOT-LKLT volcanism and the associated heat flow anomaly, the margins of which focused on Basin and Range extension and leakage of HAOT-LKLT magma to the surface. This declining corner flow combined with steepening slab dip shifted the back arc west. Compensation of extension by volcanic intrusion and extrusion allowed growth of imposing range-front fault scarps only behind the trailing edge of the shrinking arc.
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DOE Office of Scientific and Technical Information (OSTI.GOV)
Kokogian, D.A.; Vasquez, J.R.
1996-01-01
The project objectives were to define the upside potential and identified drilling locations, both for exploratory and development wells, in Loma Negra-Nl-Huincul old fields, inactive due to pressure depletion Fields are located in Dorsal de Huincul area (Huincul Range) which is a highly complex structure associated with a major transtensive-transpressive wrench system. Several angular unconformities are very noticeable, having eroded hundreds of meters of the stratigraphic column. Study was focused on the fluvial-deltaic sediments of the Cuyo Group (Bajocian-Bathonian), the main productive levels in the area. An understanding of the stratigraphic units, visible at outcrop, seismic and well scales, providedmore » the appropriated framework for the analysis. Seismic facies, detailed log and core analysis allowed us to generate paleogeographic maps and predict the reservoir distribution into each individual stratigraphic unit, Fluvial channels, overbank, crevasses splay, mouth-bar, interdistributary and delta front facies were recognized. Finally, the integrated model was compared and adjusted with the outcrop data. As a result of this study, exploratory and development wells were proposed, being all of them productive either gas or oil. Several of the new drilled wells found new productive horizons with original reservoir pressure, proving the presence of different tanks predicted by the model. This fact encourages the evaluation of the whole adjacent areas. Summing up, this integrated approach using the best outputs of the geology and geophysics in subsurface as well as in surface has been proved as a powerful tool to explore and reactivate a very mature area.« less
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DOE Office of Scientific and Technical Information (OSTI.GOV)
Kokogian, D.A.; Vasquez, J.R.
1996-12-31
The project objectives were to define the upside potential and identified drilling locations, both for exploratory and development wells, in Loma Negra-Nl-Huincul old fields, inactive due to pressure depletion Fields are located in Dorsal de Huincul area (Huincul Range) which is a highly complex structure associated with a major transtensive-transpressive wrench system. Several angular unconformities are very noticeable, having eroded hundreds of meters of the stratigraphic column. Study was focused on the fluvial-deltaic sediments of the Cuyo Group (Bajocian-Bathonian), the main productive levels in the area. An understanding of the stratigraphic units, visible at outcrop, seismic and well scales, providedmore » the appropriated framework for the analysis. Seismic facies, detailed log and core analysis allowed us to generate paleogeographic maps and predict the reservoir distribution into each individual stratigraphic unit, Fluvial channels, overbank, crevasses splay, mouth-bar, interdistributary and delta front facies were recognized. Finally, the integrated model was compared and adjusted with the outcrop data. As a result of this study, exploratory and development wells were proposed, being all of them productive either gas or oil. Several of the new drilled wells found new productive horizons with original reservoir pressure, proving the presence of different tanks predicted by the model. This fact encourages the evaluation of the whole adjacent areas. Summing up, this integrated approach using the best outputs of the geology and geophysics in subsurface as well as in surface has been proved as a powerful tool to explore and reactivate a very mature area.« less
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Lithologies of the basement complex (Devonian and older) in the National Petroleum Reserve - Alaska
Dumoulin, Julie A.; Houseknecht, David W.
2001-01-01
Rocks of the basement complex (Devonian and older) were encountered in at least 30 exploratory wells in the northern part of the NPRA. Fine-grained, variably deformed sedimentary rocks deposited in a slope or basinal setting predominate and include varicolored (mainly red and green) argillite in the Simpson area, dark argillite and chert near Barrow, and widespread gray argillite. Chitinozoans of Middle-Late Ordovician and Silurian age occur in the dark argillite and chert unit. Sponge spicules and radiolarians establish a Phanerozoic age for the varicolored and gray argillite units, both of which contain local interbeds of chert-rich sandstone and silt-stone. Conglomerate and sandstone, also chert-rich but interbedded with mudstone and coal and of Early-Middle Devonian age, occur in the Topagoruk area; these strata formed in a fluvial environment. At East Teshekpuk, granite of probable Devonian age was penetrated. Brecciated, quartz-veined rock of uncertain protolith that may be part of the basement complex was encountered in the Ikpikpuk well. Seismic data indicate that angular unconformities truncate all sedimentary units of the basement complex in NPRA. Rocks correlative in age and lithofacies with the dark argillite and chert unit occur in the subsurface near Prudhoe Bay. Other argillite units in NPRA have similarities to basement rocks in the subsurface adjacent to ANWR and the Ordovician-Silurian Iviagik Group at Cape Lisburne, but lack the interbedded limestones found in the ANWR strata, and are less metamorphosed than, and compositionally distinct from, the Iviagik. The Topagoruk conglomerate and the East Teshekpuk granite resemble the Ulungarat formation and the Okpilak batholith, respectively, in the northeastern Brooks Range.
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Wang, Song; Wang, Fei; Liao, Zhenhua; Wang, Qingliang; Liu, Yuhong; Liu, Weiqiang
2015-10-01
A ball-on-socket contact configuration was designed to simulate an artificial cervical disk in structure. UHMWPE (ultra high molecular weight polyethylene) hot pressed by powders and Ti6Al4V alloy were selected as the material combination of ball and socket. The socket surface was coated by a ~500 nm C-DLC (carbon ion implantation-diamond like carbon) mixed layer to improve its surface nano hardness and wear resistance. The torsional fretting wear behavior of the ball-on-socket model was tested at different angular displacements under 25% bovine serum lubrication with an axial force of 100 N to obtain more realistic results with that in vivo. The fretting running regimes and wear damage characteristics as well as wear mechanisms for both ball and socket were studied based on 2D (two dimension) optical microscope, SEM (scanning electron microscope) and 3D (three dimension) profiles. With the increase of angular displacement amplitude from 1° to 7°, three types of T-θ (Torsional torque-angular displacement amplitude) curves (i.e., linear, elliptical and parallelogram loops) corresponding to running regimes of PSR (partial slip regime), MR (mixed regime) and SR (slip regime) were observed and analyzed. Both the central region and the edge zone of the ball and socket were damaged. The worn surfaces were characterized by wear scratches and wear debris. In addition, more severe wear damage and more wear debris appeared on the central region of the socket at higher angular displacement amplitude. The dominant damage mechanism was a mix of surface scratch, adhesive wear and abrasive wear for the UHMWPE ball while that for the coated socket was abrasive wear by PE particles and some polishing and rolling process on the raised overgrown DLC grains. The frictional kinetic behavior, wear type, damage region and damage mechanism for the ball-on-socket model revealed significant differences with those of a ball-on-flat contact while showing better consistency with that of in vitro cervical prosthesis simulations according to the literature. Copyright © 2015. Published by Elsevier B.V.
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Multiple Scattering Effects on Pulse Propagation in Optically Turbid Media.
NASA Astrophysics Data System (ADS)
Joelson, Bradley David
The effects of multiple scattering in a optically turbid media is examined for an impulse solution to the radiative transfer equation for a variety of geometries and phase functions. In regions where the complexities of the phase function proved too cumbersome for analytic methods Monte Carlo techniques were developed to describe the entire scalar radiance distribution. The determination of a general spread function is strongly dependent on geometry and particular regions where limits can be placed on the variables of the problem. Hence, the general spread function is first simplified by considering optical regions which reduce the complexity of the variable dependence. First, in the small-angle limit we calculate some contracted spread functions along with their moments and then use Monte Carlo techniques to establish the limitations imposed by the small-angle approximation in planar geometry. The point spread function (PSF) for a spherical geometry is calculated for the full angular spread in the forward direction of ocean waters using Monte Carlo methods in the optically thin and moderate depths and analytic methods in the diffusion domain. The angular dependence of the PSF for various ocean waters is examined for a range of optical parameters. The analytic method used in the diffusion calculation is justified by examining the angular dependence of the radiance of a impulse solution in a planar geometry for a prolongated Henyey-Greenstein phase function of asymmetry factor approximately equal to that of the ocean phase functions. The Legendre moments of the radiance are examined in order to examine the viability of the diffusion approximation which assumes a linearly anisotropic angular distribution for the radiance. A realistic lidar calculation is performed for a variety of ocean waters to determine the effects of multiple scattering on the determination of the speed of sound by using the range gated frequency spectrum of the lidar signal. It is shown that the optical properties of the ocean help to ensure single scatter form for the frequency spectra of the lidar signal. This spectra can then be used to compute the speed of sound and backscatter probability.
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The angular momentum of cosmological coronae and the inside-out growth of spiral galaxies
NASA Astrophysics Data System (ADS)
Pezzulli, Gabriele; Fraternali, Filippo; Binney, James
2017-05-01
Massive and diffuse haloes of hot gas (coronae) are important intermediaries between cosmology and galaxy evolution, storing mass and angular momentum acquired from the cosmic web until eventual accretion on to star-forming discs. We introduce a method to reconstruct the rotation of a galactic corona, based on its angular momentum distribution (AMD). This allows us to investigate in what conditions the angular momentum acquired from tidal torques can be transferred to star-forming discs and explain observed galaxy-scale processes, such as inside-out growth and the build-up of abundance gradients. We find that a simple model of an isothermal corona with a temperature slightly smaller than virial and a cosmologically motivated AMD is in good agreement with galaxy evolution requirements, supporting hot-mode accretion as a viable driver for the evolution of spiral galaxies in a cosmological context. We predict moderately sub-centrifugal rotation close to the disc and slow rotation close to the virial radius. Motivated by the observation that the Milky Way has a relatively hot corona (T ≃ 2 × 106 K), we also explore models with a temperature larger than virial. To be able to drive inside-out growth, these models must be significantly affected by feedback, either mechanical (ejection of low angular momentum material) or thermal (heating of the central regions). However, the agreement with galaxy evolution constraints becomes, in these cases, only marginal, suggesting that our first and simpler model may apply to a larger fraction of galaxy evolution history.
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NASA Technical Reports Server (NTRS)
Moore, Ron; Falconer, David; Sterling, Alphonse
2008-01-01
We present evidence supporting the view that, while many flares are produced by a confined magnetic explosion that does not produce a CME, every CME is produced by an ejective magnetic explosion that also produces a flare. The evidence is that the observed heliocentric angular width of the full-blown CME plasmoid in the outer corona (at 3 to 20 solar radii) is about that predicted by the standard model for CME production, from the amount of magnetic flux covered by the co-produced flare arcade. In the standard model, sheared and twisted sigmoidal field in the core of an initially closed magnetic arcade erupts. As it erupts, tether-cutting reconnection, starting between the legs of the erupting sigmoid and continuing between the merging stretched legs of the enveloping arcade, simultaneously produces a growing flare arcade and unleashes the erupting sigmoid and arcade to become the low-beta plasmoid (magnetic bubble) that becomes the CME. The flare arcade is the downward product of the reconnection and the CME plasmoid is the upward product. The unleashed, expanding CME plasmoid is propelled into the outer corona and solar wind by its own magnetic field pushing on the surrounding field in the inner and outer corona. This tether-cutting scenario predicts that the amount of magnetic flux in the full-blown CME plasmoid nearly equals that covered by the full-grown flare arcade. This equality predicts (1) the field strength in the flare region from the ratio of the angular width of the CME in the outer corona to angular width of the full-grown flare arcade, and (2) an upper bound on the angular width of the CME in the outer corona from the total magnetic flux in the active region from which the CME explodes. We show that these predictions are fulfilled by observed CMEs. This agreement validates the standard model. The model explains (1) why most CMEs have much greater angular widths than their co-produced flares, and (2) why the radial path of a CME in the outer corona can be laterally far offset from the co-produced flare.
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NASA Astrophysics Data System (ADS)
Kluska, Jacques; Kraus, Stefan; Davies, Claire L.; Harries, Tim; Willson, Matthew; Monnier, John D.; Aarnio, Alicia; Baron, Fabien; Millan-Gabet, Rafael; Ten Brummelaar, Theo; Che, Xiao; Hinkley, Sasha; Preibisch, Thomas; Sturmann, Judit; Sturmann, Laszlo; Touhami, Yamina
2018-03-01
High angular resolution observations of young stellar objects are required to study the inner astronomical units of protoplanetary disks in which the majority of planets form. As they evolve, gaps open up in the inner disk regions and the disks are fully dispersed within ∼10 Myr. MWC 614 is a pretransitional object with a ∼10 au radius gap. We present a set of high angular resolution observations of this object including SPHERE/ZIMPOL polarimetric and coronagraphic images in the visible, Keck/NIRC2 near-infrared (NIR) aperture masking observations, and Very Large Telescope Interferometer (AMBER, MIDI, and PIONIER) and Center for High Angular Resolution Astronomy (CLASSIC and CLIMB) long-baseline interferometry at infrared wavelengths. We find that all the observations are compatible with an inclined disk (i ∼ 55° at a position angle of ∼20°–30°). The mid-infrared data set confirms that the disk inner rim is at 12.3 ± 0.4 au from the central star. We determined an upper mass limit of 0.34 M ⊙ for a companion inside the cavity. Within the cavity, the NIR emission, usually associated with the dust sublimation region, is unusually extended (∼10 au, 30 times larger than the theoretical sublimation radius) and indicates a high dust temperature (T ∼ 1800 K). As a possible result of companion-induced dust segregation, quantum heated dust grains could explain the extended NIR emission with this high temperature. Our observations confirm the peculiar state of this object where the inner disk has already been accreted onto the star, exposing small particles inside the cavity to direct stellar radiation. Based on observations made with the Keck observatory (NASA program ID N104N2) and with ESO telescopes at the Paranal Observatory (ESO program IDs 073.C-0720, 077.C-0226, 077.C-0521, 083.C-0984, 087.C-0498(A), 190.C-0963, 095.C-0883) and with the Center for High Angular Resolution Astronomy observatory.
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Sims, Jordyn A; Kapse, Kushal; Glynn, Peter; Sandberg, Chaleece; Tripodis, Yorghos; Kiran, Swathi
2016-04-01
Recovery from aphasia, loss of language following a cerebrovascular incident (stroke), is a complex process involving both left and right hemispheric regions. In our study, we analyzed the relationships between semantic processing behavioral data, lesion size and location, and percent signal change from functional magnetic resonance imaging (fMRI) data. This study included 14 persons with aphasia in the chronic stage of recovery (six or more months post stroke), along with normal controls, who performed semantic processing tasks of determining whether a written semantic feature matched a picture or whether two written words were related. Using region of interest (ROI) analysis, we found that left inferior frontal gyrus pars opercularis and pars triangularis, despite significant damage, were the only regions to correlate with behavioral accuracy. Additionally, bilateral frontal regions including superior frontal gyrus, middle frontal gyrus, and anterior cingulate appear to serve as an assistive network in the case of damage to traditional language regions that include inferior frontal gyrus, middle temporal gyrus, supramarginal gyrus, and angular gyrus. Right hemisphere posterior regions including right middle temporal gyrus, right supramarginal gyrus, and right angular gyrus are engaged in the case of extensive damage to left hemisphere language regions. Additionally, right inferior frontal gyrus pars orbitalis is presumed to serve a monitoring function. These results reinforce the importance of the left hemisphere in language processing in aphasia, and provide a framework for the relative importance of left and right language regions in the brain. Copyright © 2016 Elsevier Ltd. All rights reserved.
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Effective star tracking method based on optical flow analysis for star trackers.
Sun, Ting; Xing, Fei; Wang, Xiaochu; Li, Jin; Wei, Minsong; You, Zheng
2016-12-20
Benefiting from rapid development of imaging sensor technology, modern optical technology, and a high-speed computing chip, the star tracker's accuracy, dynamic performance, and update rate have been greatly improved with low power consumption and miniature size. The star tracker is currently one of the most competitive attitude measurement sensors. However, due to restrictions of the optical imaging system, difficulties still exist in moving star spot detection and star tracking when in special motion conditions. An effective star tracking method based on optical flow analysis for star trackers is proposed in this paper. Spot-based optical flow, based on a gray gradient between two adjacent star images, is analyzed to distinguish the star spot region and obtain an accurate star spot position so that the star tracking can keep continuous under high dynamic conditions. The obtained star vectors and extended Kalman filter (EKF) are then combined to conduct an angular velocity estimation to ensure region prediction of the star spot; this can be combined with the optical flow analysis result. Experiment results show that the method proposed in this paper has advantages in conditions of large angular velocity and large angular acceleration, despite the presence of noise. Higher functional density and better performance can be achieved; thus, the star tracker can be more widely applied in small satellites, remote sensing, and other complex space missions.
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Uddin, Lucina Q; Supekar, Kaustubh; Amin, Hitha; Rykhlevskaia, Elena; Nguyen, Daniel A; Greicius, Michael D; Menon, Vinod
2010-11-01
The inferior parietal lobule (IPL) of the human brain is a heterogeneous region involved in visuospatial attention, memory, and mathematical cognition. Detailed description of connectivity profiles of subdivisions within the IPL is critical for accurate interpretation of functional neuroimaging studies involving this region. We separately examined functional and structural connectivity of the angular gyrus (AG) and the intraparietal sulcus (IPS) using probabilistic cytoarchitectonic maps. Regions-of-interest (ROIs) included anterior and posterior AG subregions (PGa, PGp) and 3 IPS subregions (hIP2, hIP1, and hIP3). Resting-state functional connectivity analyses showed that PGa was more strongly linked to basal ganglia, ventral premotor areas, and ventrolateral prefrontal cortex, while PGp was more strongly connected with ventromedial prefrontal cortex, posterior cingulate, and hippocampus-regions comprising the default mode network. The anterior-most IPS ROIs, hIP2 and hIP1, were linked with ventral premotor and middle frontal gyrus, while the posterior-most IPS ROI, hIP3, showed connectivity with extrastriate visual areas. In addition, hIP1 was connected with the insula. Tractography using diffusion tensor imaging revealed structural connectivity between most of these functionally connected regions. Our findings provide evidence for functional heterogeneity of cytoarchitectonically defined subdivisions within IPL and offer a novel framework for synthesis and interpretation of the task-related activations and deactivations involving the IPL during cognition.
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Supekar, Kaustubh; Amin, Hitha; Rykhlevskaia, Elena; Nguyen, Daniel A.; Greicius, Michael D.; Menon, Vinod
2010-01-01
The inferior parietal lobule (IPL) of the human brain is a heterogeneous region involved in visuospatial attention, memory, and mathematical cognition. Detailed description of connectivity profiles of subdivisions within the IPL is critical for accurate interpretation of functional neuroimaging studies involving this region. We separately examined functional and structural connectivity of the angular gyrus (AG) and the intraparietal sulcus (IPS) using probabilistic cytoarchitectonic maps. Regions-of-interest (ROIs) included anterior and posterior AG subregions (PGa, PGp) and 3 IPS subregions (hIP2, hIP1, and hIP3). Resting-state functional connectivity analyses showed that PGa was more strongly linked to basal ganglia, ventral premotor areas, and ventrolateral prefrontal cortex, while PGp was more strongly connected with ventromedial prefrontal cortex, posterior cingulate, and hippocampus—regions comprising the default mode network. The anterior-most IPS ROIs, hIP2 and hIP1, were linked with ventral premotor and middle frontal gyrus, while the posterior-most IPS ROI, hIP3, showed connectivity with extrastriate visual areas. In addition, hIP1 was connected with the insula. Tractography using diffusion tensor imaging revealed structural connectivity between most of these functionally connected regions. Our findings provide evidence for functional heterogeneity of cytoarchitectonically defined subdivisions within IPL and offer a novel framework for synthesis and interpretation of the task-related activations and deactivations involving the IPL during cognition. PMID:20154013
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DOE Office of Scientific and Technical Information (OSTI.GOV)
Harvey, E.W.
Study of late Pleistocene-age sediments near the mouth of the Mad River revealed a sequence of nearshore marine and shallow bay deposits. This sequence, bounded by unconformities, is informally named the Mouth of Mad unit. The Mouth of mad unit can be divided into four distinct depositional facies at the study site. The lowest facies are the Nearshore Sand and Estuarine Mud, which lie unconformably on a paleosol. The sand facies grades upward into a high-energy, interbedded Nearshore Sand and Gravel facies containing storm and rip-channel deposits. Above the sand and gravel is a Strand-Plain Sand facies. This sand ismore » overlain by a laterally variable sequence of shell-rich Bay facies. The bay deposits can be further divided into five subfacies: (1) a Bioturbated Sand; (2) a Lower Tidal Flat Mud; (3) a Mixed Sand and Mud; (4) an oyster-rich Bay Mud; and (5) an Upper Tidal Flat Mud. The bay sequence is overlain unconformably by younger late Pleistocene-age marine terrace deposits. The depositional environments represented by these facies progress from a shoreline estuary to nearshore deposits, above storm wave base, and slowly back to shoreline and finally shallow bay conditions. The Mouth of Mad unit represents a transgressive-regressive sequence, involving the development of a protective spit. The uppermost mud within the Mouth of Mad unit has been dated, using thermoluminescence age estimation, at 176 [+-] 33 ka, placing it in the late Pleistocene. The Mouth of Mad unit appears to be younger than the fossiliferous deposits at Elk Head, Crannell Junction, Trinidad Head, Moonstone Beach, and the Falor Formation near Maple Creek, and possibly time equivalent with gravel deposits exposed at the western end of School Road in McKinleyville.« less
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Titov, V N
2016-01-01
The phylogenetic processes continue to proceed in Homo Sapiens. At the very early stages ofphylogenesis, the ancient Archaea that formed mitochondria under symbiotic interaction with later bacterial cells conjointly formed yet another system. In this system, there are no cells' absorption of glucose if it is possible to absorb fatty acids from intercellular medium in the form of unesterfied fatty acids or ketonic bodies--metabolites of fatty acids. This is caused by objectively existed conditions and subsequent availability of substrates at the stages ofphylogenesis: acetate, ketonic bodies, fatty acids and only later glucose. The phylogenetically late insulin used after billions years the same dependencies at formation of regulation ofmetabolism offatty acids and cells' absorption of glucose. In order that syndrome ofresistance ceased to exist as afoundation of metabolic pandemic Homo Sapiens has to understand the following. After successful function ofArchaea+bacterial cells and considered by biology action of insulin for the third time in phylogenesis and using biological function of intelligence the content ofphylogenetically earlier palmitic saturated fatty acid infood can't to exceed possibilities of phylogenetically late lipoproteins to transfer it in intercellular medium and blood and cells to absorb it. It is supposed that at early stages of phylogenesis biological function of intelligence is primarily formed to bring into line "unconformities" of regulation of metabolism against the background of seeming relative biological "perfection". These unconformities were subsequently and separately formed at the level of cells in paracrin regulated cenosises of cells and organs and at the level of organism. The prevention of resistance to insulin basically requires biological function of intelligence, principle of self-restraint, bringing into line multiple desires of Homo Sapiens with much less extensive biological possibilities. The "unconformities" of regulation of metabolism in vivo are etiological factors of all metabolic pandemics including atherosclerosis, metabolic arterial hypertension, obesity and metabolic syndrome Tertiannondatum.
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NASA Astrophysics Data System (ADS)
DeLucia, M. S.; Marshak, S.; Guenthner, W.; Anders, A. M.; Thomson, S. N.
2016-12-01
The Ozark Plateau is an uplift in the cratonic platform of Midcontinent United States. In the northeast corner of the plateau (the St. Francois Mountains), Precambrian basement of 1.47 Ga granite and rhyolite crops out. These rocks are overlain, at the Great Unconformity, by Paleozoic strata, defining the map pattern of the Ozark Dome. Strata thicken substantially eastward into the Illinois Basin, so that there is over 7 km of structural relief across the boundary between the Illinois Basin and the Ozark Dome at the level of the Great Unconformity. Multiple unconformities in the Paleozoic section indicates that the crest of the Ozark Dome was at or above sea level several times during the Paleozoic. Key questions about the Plateau remain. For example: (1) Did the 1.47 Ga basement remain at upper-crustal depths since its formation, or was it buried deeply and later exhumed? (2) Has the plateau remained high since the Paleozoic or has it undergone post-Paleozoic uplift? Results from new zircon (U-Th)/He thermochronology indicate that the 1.47 Ga granites were exhumed significantly in the Neoproterozoic (about 750Ma), after the Rodinia supercontinent assembly. Fission-track dates (Brown, 2005) and (U-Th)/He apatite dates (Flowers and Kelley, 2011; Zhang et al., 2012; and new results) hint that some post-Paleozoic exhumation has occurred. Analysis of a high-resolution DEM of the Ozark Plateau supports this proposal; bedrock-incising streams occur throughout the plateau (locally producing incised meanders), and strath terraces can be identified. The rate of uplift, however, must be relatively slow, for drainages do not display knick points, and drainage networks display mature profiles. Given these constraints, we propose that the lithospheric architecture that distinguished the Ozark Dome from the Illinois Basin became established in the Neoproterozoic, and that the Ozark Plateau has been maintained isostatically by subsequent slow exhumation.
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NASA Astrophysics Data System (ADS)
Calabozo, Fernando M.; Strelin, Jorge A.; Orihashi, Yuji; Sumino, Hirochika; Keller, Randall A.
2015-05-01
We present here the results of detailed mapping, lithofacies analysis and stratigraphy of the Neogene James Ross Island Volcanic Group (Antarctic Peninsula) in the Cerro Santa Marta area (northwest of James Ross Island), in order to give constraints on the evolution of a glaciated volcanic island. Our field results included recognition and interpretation of seventeen volcanic and glacial lithofacies, together with their vertical and lateral arrangements, supported by four new unspiked K-Ar ages. This allowed us to conclude that the construction of the volcanic pile in this area took place during two main eruptive stages (Eruptive Stages 1 and 2), separated from the Cretaceous bedrock and from each other by two major glacial unconformities (U1 and U2). The U1 unconformity is related to Antarctic Peninsula Ice sheet expansion during the late Miocene (before 6.2 Ma) and deposition of glacial lithofacies in a glaciomarine setting. Following this glacial advance, Eruptive Stage 1 (6.2-4.6 Ma) volcanism started with subaerial extrusion of lava flows from an unrecognized vent north of the study area, with eruptions later fed from vent/s centered at Cerro Santa Marta volcano, where cinder cone deposits and a volcanic conduit/lava lake are preserved. These lava flows fed an extensive (> 7 km long) hyaloclastite delta system that was probably emplaced in a shallow marine environment. A second unconformity (U2) was related to expansion of a local ice cap, centered on James Ross Island, which truncated all the eruptive units of Eruptive Stage 1. Concomitant with glacier advance, renewed volcanic activity (Eruptive Stage 2) started after 4.6 Ma and volcanic products were fed again by Cerro Santa Marta vents. We infer that glaciovolcanic eruptions occurred under a moderately thin (~ 300 m) glacier, in good agreement with previous estimates of paleo-ice thickness for the James Ross Island area during the Pliocene.
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NASA Astrophysics Data System (ADS)
Michels, A.; Johnson, L.; Niemi, T. M.
2017-12-01
Plio-Quaternary sediments of the Tirabuzón, Infierno, and Santa Rosalía formations record syntectonic deposition in the Santa Rosalía basin—an oblique-rift-margin basin along the Gulf of California in Baja California Sur, Mexico. These deposits unconformably overlie the upper Miocene, Cu-Zn-Co-Mn-rich Boleo Formation. The Mesa Soledad outcrops, exposed on the Minera Boleo mine property, show interfingering of marine and terrestrial deposits of the three formations along the inland margin of the basin in an area that has not previously been studied. Faults that cut the Pliocene section of the mesa are mostly steeply-dipping, NW- and NE-striking faults with normal displacement determined from stratigraphic offset and steep plunge in striations. Two stratigraphic sections were measured on either side of one of these high-angle, NW-striking fault that has a normal throw of 26 m. Our analyses of sediment grain size, fossil assemblages, and sedimentary petrography indicate a mismatch of the stratigraphic units across the fault and suggest a component of strike slip. North of the fault, poorly-sorted, well-rounded, fluvial gravels from the Pliocene-aged, Tirabuzón Formation unconformably underlie fossiliferous marine deposits from the late-Pliocene to Pleistocene? -aged Infierno Formation. South of the fault, marine deposits of the Tirabuzón Formation grade upward into imbricated, clast-supported beach gravel, and finally into non-marine conglomerates. The absence of the Infierno Formation on the southern side of the fault suggests the deposits were either eroded unevenly due to uplift or laterally displaced by strike-slip movement. Fossiliferous sandstones and conglomerates of the Santa Rosalía Formation unconformably cap the entire outcrop and show no displacement from faulting. The Santa Rosalía Formation is overlain by the 1.4 Ma La Reforma ignimbrite (Schmidt 2006), indicating that the style of deformation of the basin changed at approximately this time.
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The roles of organic matter in the formation of uranium deposits in sedimentary rocks
Spirakis, C.S.
1996-01-01
Because reduced uranium species have a much smaller solubility than oxidized uranium species and because of the strong association of organic matter (a powerful reductant) with many uranium ores, reduction has long been considered to be the precipitation mechanism for many types of uranium deposits. Organic matter may also be involved in the alterations in and around tabular uranium deposits, including dolomite precipitation, formation of silicified layers, iron-titanium oxide destruction, dissolution of quartz grains, and precipitation of clay minerals. The diagenetic processes that produced these alterations also consumed organic matter. Consequently, those tabular deposits that underwent the more advanced stages of diagenesis, including methanogenesis and organic acid generation, display the greatest range of alterations and contain the smallest amount of organic matter. Because of certain similarities between tabular uranium deposits and Precambrian unconformity-related deposits, some of the same processes might have been involved in the genesis of Precambrian unconformity-related deposits. Hydrologic studies place important constraints on genetic models of various types of uranium deposits. In roll-front deposits, oxidized waters carried uranium to reductants (organic matter and pyrite derived from sulfate reduction by organic matter). After these reductants were oxidized at any point in the host sandstone, uranium minerals were reoxidized and transported further down the flow path to react with additional reductants. In this manner, the uranium ore migrated through the sandstone at a rate slower than the mineralizing ground water. In the case of tabular uranium deposits, the recharge of surface water into the ground water during flooding of lakes carried soluble humic material to the water table or to an interface where humate precipitated in tabular layers. These humate layers then established the chemical conditions for mineralization and related alterations. In the case of Precambrian unconformity-related deposits, free thermal convection in the thick sandstones overlying the basement rocks carried uranium to concentrations of organic matter in the basement rocks.
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Nowroozi, B. N.; Brainerd, E. L.
2012-01-01
Unlike mammalian, disc-shaped intervertebral joints (IVJs), the IVJs in fishes are biconid structures, filled with fluid and thought to act as hydrostatic hinge joints during swimming. However, it remains unclear which IVJ structures are dominant in mechanical resistance to forces in fishes, and whether variation in these tissues might impact the function of the vertebral column along its length. Here, we measured the dynamic mechanical behaviour of IVJs from striped bass, Morone saxatilis. During lateral bending, angular stiffness was significantly lower in the caudal and cervical regions, relative to the abdominal region. The neutral zone, defined as the range of motion (ROM) at bending moments less than 0.001 Nm, was longer in the caudal relative to the abdominal IVJs. Hysteresis was 30–40% in all regions, suggesting that IVJs may play a role in energy dissipation during swimming. Cutting the vertical septum had no statistically significant effect, but cutting the encapsulating tissues caused a sharp decline in angular stiffness and a substantial increase in ROM and hysteresis. We conclude that stiffness decreases and ROM increases from cranial to caudal in striped bass, and that the encapsulating tissues play a prominent role in mechanical variation along the length of the vertebral column. PMID:22552920
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Nowroozi, B N; Brainerd, E L
2012-10-07
Unlike mammalian, disc-shaped intervertebral joints (IVJs), the IVJs in fishes are biconid structures, filled with fluid and thought to act as hydrostatic hinge joints during swimming. However, it remains unclear which IVJ structures are dominant in mechanical resistance to forces in fishes, and whether variation in these tissues might impact the function of the vertebral column along its length. Here, we measured the dynamic mechanical behaviour of IVJs from striped bass, Morone saxatilis. During lateral bending, angular stiffness was significantly lower in the caudal and cervical regions, relative to the abdominal region. The neutral zone, defined as the range of motion (ROM) at bending moments less than 0.001 Nm, was longer in the caudal relative to the abdominal IVJs. Hysteresis was 30-40% in all regions, suggesting that IVJs may play a role in energy dissipation during swimming. Cutting the vertical septum had no statistically significant effect, but cutting the encapsulating tissues caused a sharp decline in angular stiffness and a substantial increase in ROM and hysteresis. We conclude that stiffness decreases and ROM increases from cranial to caudal in striped bass, and that the encapsulating tissues play a prominent role in mechanical variation along the length of the vertebral column.
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Enhancing the Damping Behavior of Dilute Zn-0.3Al Alloy by Equal Channel Angular Pressing
NASA Astrophysics Data System (ADS)
Demirtas, M.; Atli, K. C.; Yanar, H.; Purcek, G.
2017-06-01
The effect of grain size on the damping capacity of a dilute Zn-0.3Al alloy was investigated. It was found that there was a critical strain value (≈1 × 10-4) below and above which damping of Zn-0.3Al showed dynamic and static/dynamic hysteresis behavior, respectively. In the dynamic hysteresis region, damping resulted from viscous sliding of phase/grain boundaries, and decreasing grain size increased the damping capacity. While the quenched sample with 100 to 250 µm grain size showed very limited damping capacity with a loss factor tanδ of less than 0.007, decreasing grain size down to 2 µm by equal channel angular pressing (ECAP) increased tanδ to 0.100 in this region. Dynamic recrystallization due to microplasticity at the sample surface was proposed as the damping mechanism for the first time in the region where the alloy showed the combined aspects of dynamic and static hysteresis damping. In this region, tanδ increased with increasing strain amplitude, and ECAPed sample showed a tanδ value of 0.256 at a strain amplitude of 2 × 10-3, the highest recorded so far in the damping capacity-related studies on ZA alloys.
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OT2_pbjerkel_1: Herschel observations of the shocked gas in HH54
NASA Astrophysics Data System (ADS)
Bjerkeli, P.
2011-09-01
A shock that can be studied in detail, using a very limited amount of Herschel time, is the Herbig-Haro object HH54 located in the nearby Chamaeleon II cloud at a distance of 180 pc. The shocked region has an angular extent of roughly 30'' and is not contaminated with emission from other nearby objects. The gas, traced by H2O and CO, emits radiation predominantly in the far-infrared regime. For that reason, this program can only be executed using the instruments aboard the Herschel Space Observatory. We propose spectroscopy of rotational H2O and CO transitions, falling in the wavelength range covered by SPIRE and PACS. These observations will allow us to stratify the shocked region in different physical/kinematical components. We will also improve our understanding of the mechanisms responsible for water production and destruction. Given the relatively large angular extent of the region, we will determine the types of shock responsible for the emission in different positions along the shocked surface. We also propose HIFI observations of selected CO and H2O transitions. A bullet feature has previously been observed in several CO line profiles. Using HIFI, we will constrain the origin and physical properties of the region responsible for this emission.
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Vortex Chain in a Resonantly Pumped Polariton Superfluid
Boulier, T.; Terças, H.; Solnyshkov, D. D.; Glorieux, Q.; Giacobino, E.; Malpuech, G.; Bramati, A.
2015-01-01
Exciton-polaritons are light-matter mixed states interacting via their exciton fraction. They can be excited, manipulated, and detected using all the versatile techniques of modern optics. An exciton-polariton gas is therefore a unique platform to study out-of-equilibrium interacting quantum fluids. In this work, we report the formation of a ring-shaped array of same sign vortices after injection of angular momentum in a polariton superfluid. The angular momentum is injected by a ℓ = 8 Laguerre-Gauss beam. In the linear regime, a spiral interference pattern containing phase defects is visible. In the nonlinear (superfluid) regime, the interference disappears and eight vortices appear, minimizing the energy while conserving the quantized angular momentum. The radial position of the vortices evolves in the region between the two pumps as a function of the density. Hydrodynamic instabilities resulting in the spontaneous nucleation of vortex-antivortex pairs when the system size is sufficiently large confirm that the vortices are not constrained by interference when nonlinearities dominate the system. PMID:25784592
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DOE Office of Scientific and Technical Information (OSTI.GOV)
Dasgupta, Basudeb; Sen, Manibrata; Mirizzi, Alessandro, E-mail: bdasgupta@theory.tifr.res.in, E-mail: alessandro.mirizzi@ba.infn.it, E-mail: manibrata.sen@gmail.com
2017-02-01
It has been recently pointed out that neutrino fluxes from a supernova can show substantial flavor conversions almost immediately above the core. Using linear stability analyses and numerical solutions of the fully nonlinear equations of motion, we perform a detailed study of these fast conversions , focussing on the region just above the supernova core. We carefully specify the instabilities for evolution in space or time, and find that neutrinos travelling towards the core make fast conversions more generic, i.e., possible for a wider range of flux ratios and angular asymmetries that produce a crossing between the zenith-angle spectra ofmore » ν {sub e} and ν-bar {sub e} . Using fluxes and angular distributions predicted by supernova simulations, we find that fast conversions can occur within tens of nanoseconds, only a few meters away from the putative neutrinospheres. If these fast flavor conversions indeed take place, they would have important implications for the supernova explosion mechanism and nucleosynthesis.« less
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Angular velocity integration in a fly heading circuit
Turner-Evans, Daniel; Wegener, Stephanie; Rouault, Hervé; Franconville, Romain; Wolff, Tanya; Seelig, Johannes D; Druckmann, Shaul; Jayaraman, Vivek
2017-01-01
Many animals maintain an internal representation of their heading as they move through their surroundings. Such a compass representation was recently discovered in a neural population in the Drosophila melanogaster central complex, a brain region implicated in spatial navigation. Here, we use two-photon calcium imaging and electrophysiology in head-fixed walking flies to identify a different neural population that conjunctively encodes heading and angular velocity, and is excited selectively by turns in either the clockwise or counterclockwise direction. We show how these mirror-symmetric turn responses combine with the neurons’ connectivity to the compass neurons to create an elegant mechanism for updating the fly’s heading representation when the animal turns in darkness. This mechanism, which employs recurrent loops with an angular shift, bears a resemblance to those proposed in theoretical models for rodent head direction cells. Our results provide a striking example of structure matching function for a broadly relevant computation. DOI: http://dx.doi.org/10.7554/eLife.23496.001 PMID:28530551
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Relativistic low angular momentum accretion: long time evolution of hydrodynamical inviscid flows
NASA Astrophysics Data System (ADS)
Mach, Patryk; Piróg, Michał; Font, José A.
2018-05-01
We investigate relativistic low angular momentum accretion of inviscid perfect fluid onto a Schwarzschild black hole. The simulations are performed with a general-relativistic, high-resolution (second-order), shock-capturing, hydrodynamical numerical code. We use horizon-penetrating Eddington–Finkelstein coordinates to remove inaccuracies in regions of strong gravity near the black hole horizon and show the expected convergence of the code with the Michel solution and stationary Fishbone–Moncrief toroids. We recover, in the framework of relativistic hydrodynamics, the qualitative behavior known from previous Newtonian studies that used a Bondi background flow in a pseudo-relativistic gravitational potential with a latitude-dependent angular momentum at the outer boundary. Our models exhibit characteristic ‘turbulent’ behavior and the attained accretion rates are lower than those of the Bondi–Michel radial flow. For sufficiently low values of the asymptotic sound speed, geometrically thick tori form in the equatorial plane surrounding the black hole horizon while accretion takes place mainly through the poles.
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Buffler, Richard T.; Watkins, Joel S.; Dillon, William P.
1979-01-01
The sedimentary section is divided into three major seismic intervals. The intervals are separated by unconformities and can be mapped regionally. The oldest interval ranges in age from Early Cretaceous through middle Late Cretaceous, although it may contain Jurassic rocks where it thickens beneath the Blake Plateau. It probably consists of continental to nearshore clastic rocks where it onlaps basement and grades seaward to a restricted carbonate platform facies (dolomite-evaporite). The middle interval (Upper Cretaceous) is characterized by prograding clinoforms interpreted as open marine slope deposits. This interval represents a Late Cretaceous shift of the carbonate shelf margin from the Blake Escarpment shoreward to about its present location, probably due to a combination of co tinued subsidence, an overall Late Cretaceous rise in sea level, and strong currents across the Blake Plateau. The youngest (Cenozoic) interval represents a continued seaward progradation of the continental shelf and slope. Cenozoic sedimentation on the Blake Plateau was much abbreviated owing mainly to strong currents.
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NASA Technical Reports Server (NTRS)
Rice, Melissa S.; Gupta, Sanjeev; Bell, James F., III; Warner, Nicholas H.
2011-01-01
Eberswalde crater was selected as a candidate landing site for the Mars Science Laboratory (MSL) mission based on the presence of a fan-shaped sedimentary deposit interpreted as a delta. We have identified and mapped five other candidate fluvio -deltaic systems in the crater, using images and digital terrain models (DTMs) derived from the Mars Reconnaissance Orbiter (MRO) High Resolution Imaging Science Experiment (HiRISE) and Context Camera (CTX). All of these systems consist of the same three stratigraphic units: (1) an upper layered unit, conformable with (2) a subpolygonally fractured unit, unconformably overlying (3) a pitted unit. We have also mapped a system of NNE-trending scarps interpreted as dip-slip faults that pre-date the fluvial -lacustrine deposits. The post-impact regional faulting may have generated the large-scale topography within the crater, which consists of a Western Basin, an Eastern Basin, and a central high. This topography subsequently provided depositional sinks for sediment entering the crater and controlled the geomorphic pattern of delta development.
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DOE Office of Scientific and Technical Information (OSTI.GOV)
Maughan, E.K.
Pennsylvanian sedimentary rocks in the northern Rocky Mountains and in the northern Great Plains of the United States were deposited primarily on a broad marine shelf between the North American craton and the late Paleozoic continental margin in Idaho and adjacent states. The Lower Pennsylvanian (Morrowan) Tyler Formation comprises detrital sediments and some limestone beds in Montana and North Dakota that were deposited along an eastward-transgressing marine shoreline after regional uplift, warping, and faulting had resulted in an erosional unconformity on top of Mississippian strata. The Lower Pennsylvanian shoreline finally extended onto the cratonic interior in eastern North Dakota. Initialmore » Tyler sediments were deposited as a deltaic and fluviolacustrine complex succeeded by littoral deposits as the Early Pennsylvanian shoreline transgressed eastward across the shelf. The Tyler Formation is subdivided into the Stonehouse Canyon Member at the base, the Bear Gulch Member, and the Cameron Creek Member at the top.« less
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Ojima, Shiro; Matsuba-Kurita, Hiroko; Dan, Ippeita; Tsuzuki, Daisuke; Katura, Takusige; Hagiwara, Hiroko
2011-01-01
A large-scale study of 484 elementary school children (6–10 years) performing word repetition tasks in their native language (L1-Japanese) and a second language (L2-English) was conducted using functional near-infrared spectroscopy. Three factors presumably associated with cortical activation, language (L1/L2), word frequency (high/low), and hemisphere (left/right), were investigated. L1 words elicited significantly greater brain activation than L2 words, regardless of semantic knowledge, particularly in the superior/middle temporal and inferior parietal regions (angular/supramarginal gyri). The greater L1-elicited activation in these regions suggests that they are phonological loci, reflecting processes tuned to the phonology of the native language, while phonologically unfamiliar L2 words were processed like nonword auditory stimuli. The activation was bilateral in the auditory and superior/middle temporal regions. Hemispheric asymmetry was observed in the inferior frontal region (right dominant), and in the inferior parietal region with interactions: low-frequency words elicited more right-hemispheric activation (particularly in the supramarginal gyrus), while high-frequency words elicited more left-hemispheric activation (particularly in the angular gyrus). The present results reveal the strong involvement of a bilateral language network in children’s brains depending more on right-hemispheric processing while acquiring unfamiliar/low-frequency words. A right-to-left shift in laterality should occur in the inferior parietal region, as lexical knowledge increases irrespective of language. PMID:21350046
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Sugiura, Lisa; Ojima, Shiro; Matsuba-Kurita, Hiroko; Dan, Ippeita; Tsuzuki, Daisuke; Katura, Takusige; Hagiwara, Hiroko
2011-10-01
A large-scale study of 484 elementary school children (6-10 years) performing word repetition tasks in their native language (L1-Japanese) and a second language (L2-English) was conducted using functional near-infrared spectroscopy. Three factors presumably associated with cortical activation, language (L1/L2), word frequency (high/low), and hemisphere (left/right), were investigated. L1 words elicited significantly greater brain activation than L2 words, regardless of semantic knowledge, particularly in the superior/middle temporal and inferior parietal regions (angular/supramarginal gyri). The greater L1-elicited activation in these regions suggests that they are phonological loci, reflecting processes tuned to the phonology of the native language, while phonologically unfamiliar L2 words were processed like nonword auditory stimuli. The activation was bilateral in the auditory and superior/middle temporal regions. Hemispheric asymmetry was observed in the inferior frontal region (right dominant), and in the inferior parietal region with interactions: low-frequency words elicited more right-hemispheric activation (particularly in the supramarginal gyrus), while high-frequency words elicited more left-hemispheric activation (particularly in the angular gyrus). The present results reveal the strong involvement of a bilateral language network in children's brains depending more on right-hemispheric processing while acquiring unfamiliar/low-frequency words. A right-to-left shift in laterality should occur in the inferior parietal region, as lexical knowledge increases irrespective of language.
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The Width of a Solar Coronal Mass Ejection and the Source of the Driving Magnetic Explosion
NASA Technical Reports Server (NTRS)
Moore, Ronald L.; Sterling, Alphonse C.; Suess, Steven T.
2007-01-01
We show that the strength of the magnetic field in the area covered by the flare arcade following a CME-producing ejective solar eruption can be estimated from the final angular width of the CME in the outer corona and the final angular width of the flare arcade. We assume (1) the flux-rope plasmoid ejected from the flare site becomes the interior of the CME plasmoid, (2) in the outer corona (R greater than 2R(sub Sun)) the CME is roughly a spherical plasmoid with legs shaped like a light bulb, and (3) beyond some height in or below the outer corona the CME plasmoid is in lateral pressure balance with the surrounding magnetic field. The strength of the nearly radial magnetic field in the outer corona is estimated from the radial component of the interplanetary magnetic field measured by Ulysses. We apply this model to three well-observed CMEs that exploded from flare regions of extremely different size and magnetic setting. One of these CMEs is an over-and-out CME that exploded from a laterally far offset compact ejective flare. In each event, the estimated source-region field strength is appropriate for the magnetic setting of the flare. This agreement (1) indicates that CMEs are propelled by the magnetic field of the CME plasmoid pushing against the surrounding magnetic field, (2) supports the magnetic-arch-blowout scenario for over-and-out CMEs, and (3) shows that a CME s final angular width in the outer corona can be estimated from the amount of magnetic flux covered by the source-region flare arcade.
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Shen, Yuedi; Yao, Jiashu; Jiang, Xueyan; Zhang, Lei; Xu, Luoyi; Feng, Rui; Cai, Liqiang; Liu, Jing; Wang, Jinhui; Chen, Wei
2015-08-01
Accumulating evidence suggests that early improvement after two-week antidepressant treatment is predictive of later outcomes of patients with major depressive disorder (MDD); however, whether this early improvement is associated with baseline neural architecture remains largely unknown. Utilizing resting-state functional MRI data and graph-based network approaches, this study calculated voxel-wise degree centrality maps for 24 MDD patients at baseline and linked them with changes in the Hamilton Rating Scale for Depression (HAMD) scores after two weeks of medication. Six clusters exhibited significant correlations of their baseline degree centrality with treatment-induced HAMD changes for the patients, which were mainly categorized into the posterior default-mode network (i.e., the left precuneus, supramarginal gyrus, middle temporal gyrus, and right angular gyrus) and frontal regions. Receiver operating characteristic curve and logistic regression analyses convergently revealed excellent performance of these regions in discriminating the early improvement status for the patients, especially the angular gyrus (sensitivity and specificity of 100%). Moreover, the angular gyrus was identified as the optimal regressor as determined by stepwise regression. Interestingly, these regions possessed higher centrality than others in the brain (P < 10(-3)) although they were not the most highly connected hubs. Finally, we demonstrate a high reproducibility of our findings across several factors (e.g., threshold choice, anatomical distance, and temporal cutting) in our analyses. Together, these preliminary exploratory analyses demonstrate the potential of neuroimaging-based network analysis in predicting the early therapeutic improvement of MDD patients and have important implications in guiding earlier personalized therapeutic regimens for possible treatment-refractory depression. © 2015 Wiley Periodicals, Inc.
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Akalin, Zerrin Fidan; Ozkan, Yasemin Kulak; Ekerim, Ahmet
2013-01-01
The effects of implant angulation, impression material, and variation in width of the arch curvature on transfer models were evaluated. Three edentulous maxillary epoxy resin models were fabricated, and six internal-connection implant analogs were placed in different locations and different angulations in each model. In the first model, implants were positioned in the canine, first premolar, and first molar regions, and all analogs were positioned parallel to each other and perpendicular to the horizontal crestal plane (parallel model). In the second model, analogs were positioned in same regions (canine, first premolar, and first molar), but three of them were positioned with 10-degree buccal angulations (versus the horizontal crestal plane) (angular model). In the third model, analogs were inserted in the lateral incisor, canine, and second molar regions and parallel to each other (wide-arch model). Eighteen impressions of each model were made with each of the three materials--condensation silicone, polyvinyl siloxane, and polyether--and impressions were poured and kept at room temperature for 24 hours. They were then observed under a toolmaker's microscope, with epoxy resin models of each group used as references. Distance deformations between implants in each model in the x- and y-axes were recorded separately. Implant angulation deformations were recorded in the x-z plane. Statistical evaluations were performed with analysis of variance and the least significant difference post hoc test. Angular model measurements showed the greatest deformation values (P < .05). All impression materials showed deformation, and the polyether impression models showed statistically significantly less deformation in angular measurements (P < .05). The models with implants placed parallel to each other exhibited greater accuracy than a model with implants placed at angles to each other.
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Sweetkind, D.S.; Dickerson, R.P.; Blakely, R.J.; Denning, Paul
2001-01-01
This report presents a network of 28 geologic cross sections that portray subsurface geologic relations within the Death Valley regional ground-water system, a ground-water basin that encompasses a 3? x 3? area (approximately 70,000 km2) in southern Nevada and eastern California. The cross sections transect that part of the southern Great Basin that includes Death Valley, the Nevada Test Site, and the potential high-level nuclear waste underground repository at Yucca Mountain. The specific geometric relationships portrayed on the cross sections are discussed in the context of four general sub-regions that have stratigraphic similarities and general consistency of structural style: (1) the Nevada Test Site vicinity; (2) the Spring Mountains, Pahrump Valley and Amargosa Desert region; (3) the Death Valley region; and (4) the area east of the Nevada Test Site. The subsurface geologic interpretations portrayed on the cross sections are based on an integration of existing geologic maps, measured stratigraphic sections, published cross sections, well data, and geophysical data and interpretations. The estimated top of pre-Cenozoic rocks in the cross sections is based on inversion of gravity data, but the deeper parts of the sections are based on geologic conceptual models and are more speculative. The region transected by the cross sections includes part of the southern Basin and Range Province, the northwest-trending Walker Lane belt, the Death Valley region, and the northern Mojave Desert. The region is structurally complex, where a locally thick Tertiary volcanic and sedimentary section unconformably overlies previously deformed Proterozoic through Paleozoic rocks. All of these rocks have been deformed by complex Neogene ex-tensional normal and strike-slip faults. These cross sections form a three-dimensional network that portrays the interpreted stratigraphic and structural relations in the region; the sections form part of the geologic framework that will be incorporated in a complex numerical model of ground-water flow in the Death Valley region.
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The Cosmology Large Angular Scale Surveyor
NASA Technical Reports Server (NTRS)
Harrington, Kathleen; Marriage, Tobias; Ali, Aamir; Appel, John; Bennett, Charles; Boone, Fletcher; Brewer, Michael; Chan, Manwei; Chuss, David T.; Colazo, Felipe;
2016-01-01
The Cosmology Large Angular Scale Surveyor (CLASS) is a four telescope array designed to characterize relic primordial gravitational waves from inflation and the optical depth to reionization through a measurement of the polarized cosmic microwave background (CMB) on the largest angular scales. The frequencies of the four CLASS telescopes, one at 38 GHz, two at 93 GHz, and one dichroic system at 145217 GHz, are chosen to avoid spectral regions of high atmospheric emission and span the minimum of the polarized Galactic foregrounds: synchrotron emission at lower frequencies and dust emission at higher frequencies. Low-noise transition edge sensor detectors and a rapid front-end polarization modulator provide a unique combination of high sensitivity, stability, and control of systematics. The CLASS site, at 5200 m in the Chilean Atacama desert, allows for daily mapping of up to 70% of the sky and enables the characterization of CMB polarization at the largest angular scales. Using this combination of a broad frequency range, large sky coverage, control over systematics, and high sensitivity, CLASS will observe the reionization and recombination peaks of the CMB E- and B-mode power spectra. CLASS will make a cosmic variance limited measurement of the optical depth to reionization and will measure or place upper limits on the tensor-to-scalar ratio, r, down to a level of 0.01 (95% C.L.).
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Angular photogrammetric comparison of the soft-tissue facial profile of Kenyans and Chinese.
Wamalwa, Peter; Amisi, Stella Kabarika; Wang, Yunji; Chen, Song
2011-05-01
The purpose of this study was to determine the average angular dimensions that define the normal soft-tissue facial profiles of black Kenyans and Chinese and compare them with each other and with values proposed for whites. Standardized facial profile photographs, taken in natural head position, of 177 black Kenyans and 156 Chinese with normal occlusion and well-balanced faces were analyzed for 12 angular parameters. Two-sample t-tests were used to determine sex and racial differences. Kenyan and Chinese averages were compared with proposed white values using 1-sample t-tests. Eight parameters in Kenyans and 7 in Chinese showed sex differences. All angles, except for facial convexity, nasal dorsum, and inferior facial height, were different between Kenyans and Chinese. Kenyan and Chinese averages for all parameters were different from proposed white average, except for facial convexity. Nasolabial and mentolabial angles showed large individual variability and racial differences. The study demonstrated many differences in average angular measurements of the facial profiles of black Kenyans, Chinese, and white standards. Orthodontists, maxillofacial and plastic surgeons, and other clinicians working in the craniofacial region should bear these in mind when setting aesthetic treatment goals for patients of different races. Mean values from this study can be used for comparison with similar records of subjects with same ethnicity.
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RadioAstron Science Program Five Years after Launch: Main Science Results
NASA Astrophysics Data System (ADS)
Kardashev, N. S.; Alakoz, A. V.; Andrianov, A. S.; Artyukhov, M. I.; Baan, W.; Babyshkin, V. E.; Bartel, N.; Bayandina, O. S.; Val'tts, I. E.; Voitsik, P. A.; Vorobyov, A. Z.; Gwinn, C.; Gomez, J. L.; Giovannini, G.; Jauncey, D.; Johnson, M.; Imai, H.; Kovalev, Y. Y.; Kurtz, S. E.; Lisakov, M. M.; Lobanov, A. P.; Molodtsov, V. A.; Novikov, B. S.; Pogodin, A. V.; Popov, M. V.; Privesenzev, A. S.; Rudnitski, A. G.; Rudnitski, G. M.; Savolainen, T.; Smirnova, T. V.; Sobolev, A. M.; Soglasnov, V. A.; Sokolovsky, K. V.; Filippova, E. N.; Khartov, V. V.; Churikova, M. E.; Shirshakov, A. E.; Shishov, V. I.; Edwards, P.
2017-12-01
The RadioAstron ground-space interferometer provides the highest angular resolution achieved now in astronomy. The detection of interferometric fringes from quasars with this angular resolution on baselines of 100-200 thousand km suggests the brightness temperatures which exceed the Compton limit by two orders of magnitude. Polarimetric measurements on ground-space baselines have revealed fine structure testifying to recollimation shocks on scales of 100-250 μas and a helical magnetic field near the base of radio emission in BL Lacertae. Substructure within a the scattering disk of pulsar emission on interferometer baselines (from 60000 to 250000 km) was discovered. This substructure is produced by action of the interstellar interferometer with an effective baseline of about 1 AU and the effective angular resolution of better than 1 μas. Diameters of scattering disks were measured for several pulsars, and distances to diffusing screens were evaluated. The ground-space observations of sources of the maser radiation in lines of water and hydroxyl have shown that the maser sources in star-forming regions remain unresolved on baselines, which considerably exceed the Earth diameter. These very compact and bright features with angular sizes of about 20-60 μas correspond to linear sizes of about 5-10 million km (several solar diameters).
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The cosmic web and the orientation of angular momenta
NASA Astrophysics Data System (ADS)
Libeskind, Noam I.; Hoffman, Yehuda; Knebe, Alexander; Steinmetz, Matthias; Gottlöber, Stefan; Metuki, Ofer; Yepes, Gustavo
2012-03-01
We use a 64 h-1 Mpc dark-matter-only cosmological simulation to examine the large-scale orientation of haloes and substructures with respect to the cosmic web. A web classification scheme based on the velocity shear tensor is used to assign to each halo in the simulation a web type: knot, filament, sheet or void. Using ˜106 haloes that span ˜3 orders of magnitude in mass, the orientation of the halo's spin and the orbital angular momentum of subhaloes with respect to the eigenvectors of the shear tensor is examined. We find that the orbital angular momentum of subhaloes tends to align with the intermediate eigenvector of the velocity shear tensor for all haloes in knots, filaments and sheets. This result indicates that the kinematics of substructures located deep within the virialized regions of a halo is determined by its infall which in turn is determined by the large-scale velocity shear, a surprising result given the virialized nature of haloes. The non-random nature of subhalo accretion is thus imprinted on the angular momentum measured at z= 0. We also find that the haloes' spin axis is aligned with the third eigenvector of the velocity shear tensor in filaments and sheets: the halo spin axis points along filaments and lies in the plane of cosmic sheets.
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Observations of H II regions around Zeta OPH and other O-B stars
NASA Astrophysics Data System (ADS)
Shestakova, L. I.; Kutirev, A. S.; Ataev, A. Sh.
1988-01-01
A Fabry-Perot spectrometer was used to measure the emission intensities in H-beta near Zeta Oph, Alpha Vir, Alpha Cam, and HD 188209. The spectrometer sensitivity is 0.2 rayleighs, the intensity measurement accuracy is 20 percent. Ionization zone boundaries are determined for Zeta Oph and Alpha Vir; the angular diameters of both regions are about 15 deg. The contour of the H II region near Zeta Oph on the level of the double background in the southwest does not close; instead, it expands again and incorporates the region associated with the B-association II Sco.
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Johnson, Ronald C.
2007-01-01
Detailed measured sections and regional stratigraphic cross sections are used to reconstruct facies maps and interpret paleogeographic settings for the interval from the base of Upper Cretaceous Mesaverde Formation to top of lower member of the Paleocene Fort Union Formation in the Wind River Basin, Wyoming. The Mesaverde Formation spans the time during which the Upper Cretaceous seaway retreated eastward out of central Wyoming in Campanian time and the initial stages of the Lewis transgression in earliest Maastrichtian time. This retreat stalled for a considerable period of time during deposition of the lower part of the Mesaverde, creating a thick buildup of marginal marine sandstones and coaly coastal plain deposits across the western part of the basin. The Lewis sea transgressed into the northeast part of Wind River Basin, beginning in early Maastrichtian time during deposition of the Teapot Sandstone Member of the Mesaverde Formation. The Meeteetse Formation, which overlies the Teapot, was deposited in a poorly-drained coastal plain setting southwest of the Lewis seaway. The Lewis seaway, at maximum transgression, covered much of the northeast half of the Wind River Basin area but was clearly deflected around the present site of the Wind River Range, southwest of the basin, providing the first direct evidence of Laramide uplift on that range. Uplift of the Wind River Range continued during deposition of the overlying Maastrichtian Lance Formation. The Granite Mountains south of the basin also became a positive feature during this time. A rapidly subsiding trough during the Maastrichtian time formed near the presentday trough of the Wind River Basin in which more than 6,000 feet of Lance was deposited. The development of this trough appears to have begun before the adjacent Owl Creek Mountains to the north started to rise; however, a muddy facies in the upper part of Lance in the deep subsurface, just to the south, might be interpreted to indicate that the Cretaceous Cody Shale was being eroded off a rising Owl Creek Mountains in latest Cretaceous time. The Paleocene Fort Union Formation unconformably overlies older units but with only slight angular discordance around much of the margins of the Wind River Basin. Pre-Fort Union erosion was most pronounced toward the Wind River Range to the southwest, where the Fort Union ultimately overlies strata as old as the upper part of the Cretaceous Cody Shale. The unconformity appears to die out toward the basin center. Coal-forming mires developed throughout the western part of the basin near the beginning of the Paleocene. River systems entering the basin from the Wind River Range to the southwest and the Granite Mountains to the south produced areas of sandy fluvial deposition along mountain fronts. A major river system appears to have entered the basin from about the same spot along the Wind River Range throughout much of the Paleocene, probably because it became incised and could not migrate laterally. The muddy floodplain facies that developed along the deep basin trough during latest Cretaceous time, expanded during the early part of the Paleocene. Coal-forming mires that characterize part of the lower Fort Union Formation reached maximum extent near the beginning of the late Paleocene and just prior to the initial transgression of Lake Waltman. From the time of initial flooding, Lake Waltman expanded rapidly, drowning the coal-forming mires in the central part of the basin and spreading to near basin margins. Outcrop studies along the south margin of the basin document that once maximum transgression was reached, the lake was rapidly pushed basinward and replaced by fluvial environments.
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NASA Astrophysics Data System (ADS)
Karlsson, Nanna B.; Holt, John W.; Hindmarsh, Richard C. A.; Choudhary, Prateek
2010-05-01
The North Polar Layered Deposits (NPLD) is one of the largest reservoirs of surface water on Mars and, via an active exchange of water vapour with the atmosphere, it plays an important role in the Martian climate. The impact of ice flow on the overall shape of the NPLD is still widely debated. A study by Winebrenner et al. (2008) found evidence for relict flow lines in the southernmost part of the NPLD called Gemina Lingula (GL). Other studies have concluded that the upper part of the NPLD shows no evidence of flow (Fishbaugh and Hvidberg, 2006) and that surface mass balance alone can produce the topography (Greve et al., 2004 and Greve and Mahajan, 2005) . This paper presents results from an analysis of radar data from the SHARAD (SHallow RADar) instrument on board NASA's Mars Reconnaissance Orbiter. The SHARAD instrument operates with a 20MHz centre frequency and a 10MHz bandwidth and one of its primary mission goals is to map the state and distribution of water on Mars. For more details on the SHARAD instrument please refer to Seu et al. (2007). In the SHARAD data we identified and mapped six internal horizons from over 80 radar lines retrieved over GL. All horizons were easily identifiable in the majority of the data and were on average present in over 80% of the radar data considered. The observed layers were then compared to modelled layers from a 3D ice flow model. The model uses a smoothed surface topography, where troughs and scarps have been filled in, and assumes that the shape and the mass balance of the NPLD are constant in time. The shape of the internal layers are then calculated as they would appear in a flowing ice cap given those parameters. More information on the model can be found in Hindmarsh et al. (2009). The overall fit between modelled and observed layers is reasonably good, but the goodness of the fit varies both between the different horizons and the different regions of GL. Horizons in the upper part of the ice fit less well than horizons in the lower part. The upper horizons also generally achieve a better fit in the western part of GL while the fit for the lower horizons has a less distinct geographical variation. These differences could indicate a time gap in the deposition of the layers and may be explained by the existence of an angular unconformity previously identified within GL (Holt and Safaeinili, 2009). It is possible that the lower layers experienced a significantly different history than the upper, and/or that the geometry of the upper layers is primarily the result of draping the unconformity surface which is an elongated dome. Only taking into account individual layer geometry, our comparison between modelled and observed internal layering indicates that it is possible that ice flow has influenced the shape of NPLD. However, if this is the case GL must have extended farther to the southeast, or alternatively the accumulation pattern must have been significantly different to what is assumed in the model. Fishbaugh and Hvidberg. Journal of Geophysical Research, 111, 2006. Greve et al. Planetary and Space Science, 52, p. 775-787, 2004. Greve and Mahajan. Icarus, 174, p. 475-485, 2005. Hindmarsh et al. Annals of Glaciology, 50, 130140, 2009. Holt and Safaeinili. LPSC XXXX, # 1721, 2009. Phillips et al. Science, 320, 1182, 2008. Putzig et al. Icarus, 204, p. 443-457, 2009. Seu et al. Journal of Geophysical Research, 112, 2007. Winebrenner et al. Icarus, 195, p. 90-105, 2008.
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NASA Astrophysics Data System (ADS)
Matias, J.; Mescia, F.; Ramon, M.; Virto, J.
2012-04-01
We present a complete and optimal set of observables for the exclusive 4-body overline B meson decay {overline B_d} to {overline {text{K}}^{{*0}}} (→ Kπ) ℓ + ℓ -in the low dilepton mass region, that contains a maximal number of clean observables. This basis of observables is built in a systematic way. We show that all the previously defined observables and any observable that one can construct, can be expressed as a function of this basis. This set of observables contains all the information that can be extracted from the angular distribution in the cleanest possible way. We provide explicit expressions for the full and the uniangular distributions in terms of this basis. The conclusions presented here can be easily extended to the large- q 2 region. We study the sensitivity of the observables to right-handed currents and scalars. Finally, we present for the first time all the symmetries of the full distribution including massive terms and scalar contributions.
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Slantwise convection on fluid planets: Interpreting convective adjustment from Juno observations
NASA Astrophysics Data System (ADS)
O'Neill, M. E.; Kaspi, Y.; Galanti, E.
2016-12-01
NASA's Juno mission provides unprecedented microwave measurements that pierce Jupiter's weather layer and image the transition to an adiabatic fluid below. This region is expected to be highly turbulent and complex, but to date most models use the moist-to-dry transition as a simple boundary. We present simple theoretical arguments and GCM results to argue that columnar convection is important even in the relatively thin boundary layer, particularly in the equatorial region. We first demonstrate how surface cooling can lead to very horizontal parcel paths, using a simple parcel model. Next we show the impact of this horizontal motion on angular momentum flux in a high-resolution Jovian model. The GCM is a state-of-the-art modification of the MITgcm, with deep geometry, compressibility and interactive two-stream radiation. We show that slantwise convection primarily mixes fluid along columnar surfaces of angular momentum, and discuss the impacts this should have on lapse rate interpretation of both the Galileo probe sounding and the Juno microwave observations.
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NASA Technical Reports Server (NTRS)
Gorenstein, P.; Perlman, D.; Parsignault, D.; Burns, R.
1979-01-01
A sealed position sensitive proportional counter filled with two atmospheres of 95% xenon and 5% methane, and containing a drift region of 24 atm cm, has operated in a stable manner for many months. The detector contains G-10 frames to support the anode and cathode wires. The detector was sealed successfully by a combination of vacuum baking the G-10 frames at 150 C for two weeks followed by assembly into the detector in an environment of dry nitrogen, and the use of passive internal getters. The counter is intended for use with a circumferential cylindrical collimator. Together they provide a very broad field of view detection system with the ability to locate cosmic hard X-ray and soft gamma ray sources to an angular precision of a minute of arc. A set of instruments based on this principle have been proposed for satellites to detect and precisely locate cosmic gamma ray bursts.
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NASA Astrophysics Data System (ADS)
Adlarson, P.; Augustyniak, W.; Bardan, W.; Bashkanov, M.; Bergmann, F. S.; Berłowski, M.; Bondar, A.; Büscher, M.; Calén, H.; Ciepał, I.; Clement, H.; Czerwiński, E.; Demmich, K.; Engels, R.; Erven, A.; Erven, W.; Eyrich, W.; Fedorets, P.; Föhl, K.; Fransson, K.; Goldenbaum, F.; Goswami, A.; Grigoryev, K.; Gullström, C.-O.; Heijkenskjöld, L.; Hejny, V.; Hüsken, N.; Jarczyk, L.; Johansson, T.; Kamys, B.; Kemmerling, G.; Khatri, G.; Khoukaz, A.; Khreptak, A.; Kirillov, D. A.; Kistryn, S.; Kleines, H.; Kłos, B.; Krzemień, W.; Kulessa, P.; Kupść, A.; Kuzmin, A.; Lalwani, K.; Lersch, D.; Lorentz, B.; Magiera, A.; Maier, R.; Marciniewski, P.; Mariański, B.; Morsch, H.-P.; Moskal, P.; Ohm, H.; Parol, W.; Perez del Rio, E.; Piskunov, N. M.; Prasuhn, D.; Pszczel, D.; Pysz, K.; Pyszniak, A.; Ritman, J.; Roy, A.; Rudy, Z.; Rundel, O.; Sawant, S.; Schadmand, S.; Schätti-Ozerianska, I.; Sefzick, T.; Serdyuk, V.; Shwartz, B.; Sitterberg, K.; Skorodko, T.; Skurzok, M.; Smyrski, J.; Sopov, V.; Stassen, R.; Stepaniak, J.; Stephan, E.; Sterzenbach, G.; Stockhorst, H.; Ströher, H.; Szczurek, A.; Trzciński, A.; Wolke, M.; Wrońska, A.; Wüstner, P.; Yamamoto, A.; Zabierowski, J.; Zieliński, M. J.; Złomańczuk, J.; Żuprański, P.; Żurek, M.; Wilkin, C.; WASA-at-COSY Collaboration
2018-07-01
New data on both total and differential cross sections of the production of η mesons in proton-deuteron fusion to 3He η in the excess energy region 13.6MeV ≤Qη ≤ 80.9MeV are presented. These data have been obtained with the WASA-at-COSY detector setup located at the Forschungszentrum Jülich, using a proton beam at 15 different beam momenta between pp = 1.60GeV / c and pp = 1.74GeV / c. While significant structure of the total cross section is observed in the energy region 20MeV ≲Qη ≲ 60MeV, a previously reported sharp variation around Qη ≈ 50MeV cannot be confirmed. Angular distributions show the typical forward-peaking that was noted earlier. For the first time, it is possible to study the development of these angular distributions with rising excess energy over a wide interval.
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The Large Deployable Reflector (LDR) report of the Science Coordination Group
NASA Technical Reports Server (NTRS)
1986-01-01
The Large Deployable Reflector (LDR) is a telescope designed to carry out high-angular resolution, high-sensitivity observations at far-infrared and submillimeter wavelengths. The scientific rationale for the LDR is discussed in light of the recent Infrared Astronomical Satellite (IRAS) and Kuiper Airborne Observatory (KAO) results and the several new ground-based observatories planned for the late 1980s. The importance of high sensitivity and high angular resolution observations from space in the submillimeter region is stressed. The scientific and technical problems of using the LDR in a light bucket mode at approx. less than 5 microns and in designing the LDR as an unfilled aperture with subarcsecond resolution are also discussed. The need for an aperture as large as 20 m is established, along with the requirements of beam-shape stability, spatial chopping, thermal control, and surface figure stability. The instrument complement required to cover the wavelength-spectral resolution region of interest to the LDR is defined.
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The formation of the planetary system
NASA Astrophysics Data System (ADS)
Tscharnuter, W. M.
1984-12-01
The basic ideas concerning solar system formation were developed by Kant (1755) and Laplace (1796) whose starting point was the so-called nebular hypothesis. The great advantage of the nebular hypothesis is that many regularities, e.g. prograde motions of all planets and asteroids in almost coplanar orbits, can be explained. Observations in the radio and infrared region strongly support the nebular hypothesis provided that the angular momentum problem can be solved in some way. Three possibilities are listed: (1) magnetic fields via Alfvén waves which can transport angular momentum from the contracting cloud fragment into the external medium, (2) turbulent friction, (3) gravitational torques exerted by high amplitude spiral or bar-like density waves in the nebula.
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Results on angular distributions of thermal dileptons in nuclear collisions
NASA Astrophysics Data System (ADS)
Usai, Gianluca; NA60 Collaboration
2009-11-01
The NA60 experiment at the CERN SPS has studied dimuon production in 158 AGeV In-In collisions. The strong pair excess above the known sources found in the mass region 0.2
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First Results on Angular Distributions of Thermal Dileptons in Nuclear Collisions
NASA Astrophysics Data System (ADS)
Arnaldi, R.; Banicz, K.; Castor, J.; Chaurand, B.; Cicalò, C.; Colla, A.; Cortese, P.; Damjanovic, S.; David, A.; de Falco, A.; Devaux, A.; Ducroux, L.; En'Yo, H.; Fargeix, J.; Ferretti, A.; Floris, M.; Förster, A.; Force, P.; Guettet, N.; Guichard, A.; Gulkanian, H.; Heuser, J. M.; Keil, M.; Kluberg, L.; Lourenço, C.; Lozano, J.; Manso, F.; Martins, P.; Masoni, A.; Neves, A.; Ohnishi, H.; Oppedisano, C.; Parracho, P.; Pillot, P.; Poghosyan, T.; Puddu, G.; Radermacher, E.; Ramalhete, P.; Rosinsky, P.; Scomparin, E.; Seixas, J.; Serci, S.; Shahoyan, R.; Sonderegger, P.; Specht, H. J.; Tieulent, R.; Usai, G.; Veenhof, R.; Wöhri, H. K.
2009-06-01
The NA60 experiment at the CERN Super Proton Synchrotron has studied dimuon production in 158AGeV In-In collisions. The strong excess of pairs above the known sources found in the complete mass region 0.2
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Star-Forming Regions in Orion as a Dust Evolution Laboratory
NASA Astrophysics Data System (ADS)
Wiebe, D.; Murga, M.; Sivkova, E.
2017-06-01
Star-forming regions (SFR) represent a convenient opportunity to study various processes related both to dust growth and to dust destruction. While extragalactic SFRs allow considering these processes in a wide range of metallicities, UV field intensities, etc., the Orion star-forming complex opens up a possibility to observe dust evolution with an unprecedented angular resolution. We review various observations related to dust evolution in some most prominent Orion regions, paying special attention to organic dust evolution, and introduce a new model of organic dust evolution.
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NASA Astrophysics Data System (ADS)
Derder, M. E. M.; Maouche, S.; Liégeois, J. P.; Henry, B.; Amenna, M.; Ouabadi, A.; Bellon, H.; Bruguier, O.; Bayou, B.; Bestandji, R.; Nouar, O.; Bouabdallah, H.; Ayache, M.; Beddiaf, M.
2016-03-01
Intraplate deformation is most often linked to major stress applied on plate margins. When such intraplate events are accompanied by magmatism, the use of several dating methods integrated within a multidisciplinary approach can bring constraints on the age, nature and source mobilized for generating the magma and in turn on the nature of the intraplate deformation. This study focuses on the large gabbro Arrikine sill (35 km in extension) emplaced within the Silurian sediments of the western margin of the Murzuq cratonic basin in southeastern Algeria. Its emplacement is dated during the early Devonian (415-400 Ma) through the determination of a reliable paleomagnetic pole by comparison with the Gondwana Apparent Polar Wander Path (APWP). This age can be correlated with deep phreatic eruptions before Pragian time thought to be at the origin of sand injections and associated circular structures in Algeria and Libya. For the sill, the K-Ar age of 325.6 ± 7.7 Ma is related to a K-rich aplitic phase that has K-enriched by more than 20% the Devonian gabbro. Laser-ICP-MS U-Pb method dates only inherited zircons mostly at c. 2030 Ma with additional ages at c. 2700 Ma and younger ones in the 766-598 Ma age range. The Arrikine sill is a high-Ti alkaline gabbro having the geochemical composition of a hawaiite akin to several intraplate continental and oceanic provinces, including the contemporaneous Aïr ring complexes province in Niger, but also to the Mauna Loa volcano in Hawaii. This peculiar composition akin to that of the contemporaneous Aïr province is in agreement with a lower Devonian age for the Arrikine sill. The lower Devonian Arrikine sill emplacement is related to a "Caledonian" transtensive reactivation of the western metacratonic boundary of the Murzuq craton. This event also generated in the Saharan platform the so-called "Caledonian unconformity" of regional extension, the Aïr ring complexes and magmatic rocks that produced sand injections. It could be related to rifting of the Hun terranes that occurred at the plate margin to the north (Stampfli and Borel, 2002, Blackey, 2008 and references therein). The mid-Carboniferous (c. 326 Ma) reactivation corresponds to Variscan compression on NW Africa generating aplitic fluids, but also to the major "Hercynian unconformity" of regional extension. The generation of the Arrikine magma is attributed to partial melting through adiabatic pressure release of uprising asthenosphere along tectonically reactivated mega-shear zones, here bordering the relictual Murzuq craton enclosed in the Saharan metacraton.
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Schaben field, Kansas: Improving performance in a Mississippian shallow-shelf carbonate
Montgomery, S.L.; Franseen, E.K.; Bhattacharya, S.; Gerlach, P.; Byrnes, A.; Guy, W.; Carr, T.R.
2000-01-01
Schaben field (Kansas), located along the northeastern shelf of the Hugoton embayment, produces from Mississippian carbonates in erosional highs immediately beneath a regional unconformity. Production comes from depths of around 4400 ft (1342 m) in partially dolomitized shelf deposits. A detailed reservoir characterization/simulation study, recently performed as part of a Department of Energy Reservoir Class Oil Field Demonstration Project, has led to important revision in explanations for observed patterns of production. Cores recovered from three new data wells identify three main facies: Spicule-rich wackestone-packstone, echinoderm wackestone/packstone/grainstone, and dolomitic mudstone-wackestone. Reservoir quality is highest in spicule-rich wackestone/packstones but is subject to a very high degree of vertical heterogeneity due to facies interbedding, silification, and variable natural fracturing. The oil reservoir is underlain by an active aquifer, which helps maintain reservoir pressure but supports significant water production. Reservoir simulation, using public-domain, PC-based software, suggests that infill drilling is an efficient approach to enhanced recovery. Recent drilling directed by simulation results has shown considerable success in improving field production rates. Results from the Schaben field demonstration project are likely to have wide application for independent oil and exploration companies in western Kansas.Schaben field (Kansas), located along the northeastern shelf of the Hugoton embayment, produces from Mississippian carbonates in erosional highs immediately beneath a regional unconformity. Production comes from depths of around 4400 ft (1342 m) in partially dolomitized shelf deposits. A detailed reservoir characterization/simulation study, recently performed as part of a Department of Energy Reservoir Class Oil Field Demonstration Project, has led to important revision in explanations for observed patterns of production. Cores recovered from three new data wells identify three main facies: spicule-rich wackestone-packstone, echinoderm wackestone/packstone/grainstone, and dolomitic mudstone-wackestone. Reservoir quality is highest in spicule-rich wackestone/packstones but is subject to a very high degree of vertical heterogeneity due to facies interbedding, silification, and variable natural fracturing. The oil reservoir is underlain by an active aquifer, which helps maintain reservoir pressure but supports significant water production. Reservoir simulation, using public-domain, PC-based software, suggests that infill drilling is an efficient approach to enhanced recovery. Recent drilling directed by simulation results has shown considerable success in improving field production rates. Results from the Schaben field demonstration project are likely to have wide application for independent oil and exploration companies in western Kansas.
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Methods for rapidly processing angular masks of next-generation galaxy surveys
NASA Astrophysics Data System (ADS)
Swanson, M. E. C.; Tegmark, Max; Hamilton, Andrew J. S.; Hill, J. Colin
2008-07-01
As galaxy surveys become larger and more complex, keeping track of the completeness, magnitude limit and other survey parameters as a function of direction on the sky becomes an increasingly challenging computational task. For example, typical angular masks of the Sloan Digital Sky Survey contain about N = 300000 distinct spherical polygons. Managing masks with such large numbers of polygons becomes intractably slow, particularly for tasks that run in time with a naive algorithm, such as finding which polygons overlap each other. Here we present a `divide-and-conquer' solution to this challenge: we first split the angular mask into pre-defined regions called `pixels', such that each polygon is in only one pixel, and then perform further computations, such as checking for overlap, on the polygons within each pixel separately. This reduces tasks to , and also reduces the important task of determining in which polygon(s) a point on the sky lies from to , resulting in significant computational speedup. Additionally, we present a method to efficiently convert any angular mask to and from the popular HEALPIX format. This method can be generically applied to convert to and from any desired spherical pixelization. We have implemented these techniques in a new version of the MANGLE software package, which is freely available at http://space.mit.edu/home/tegmark/mangle/, along with complete documentation and example applications. These new methods should prove quite useful to the astronomical community, and since MANGLE is a generic tool for managing angular masks on a sphere, it has the potential to benefit terrestrial mapmaking applications as well.
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DOE Office of Scientific and Technical Information (OSTI.GOV)
Richers, Sherwood; Nagakura, Hiroki; Ott, Christian D.
The mechanism driving core-collapse supernovae is sensitive to the interplay between matter and neutrino radiation. However, neutrino radiation transport is very difficult to simulate, and several radiation transport methods of varying levels of approximation are available. We carefully compare for the first time in multiple spatial dimensions the discrete ordinates (DO) code of Nagakura, Yamada, and Sumiyoshi and the Monte Carlo (MC) code Sedonu, under the assumptions of a static fluid background, flat spacetime, elastic scattering, and full special relativity. We find remarkably good agreement in all spectral, angular, and fluid interaction quantities, lending confidence to both methods. The DOmore » method excels in determining the heating and cooling rates in the optically thick region. The MC method predicts sharper angular features due to the effectively infinite angular resolution, but struggles to drive down noise in quantities where subtractive cancellation is prevalent, such as the net gain in the protoneutron star and off-diagonal components of the Eddington tensor. We also find that errors in the angular moments of the distribution functions induced by neglecting velocity dependence are subdominant to those from limited momentum-space resolution. We briefly compare directly computed second angular moments to those predicted by popular algebraic two-moment closures, and we find that the errors from the approximate closures are comparable to the difference between the DO and MC methods. Included in this work is an improved Sedonu code, which now implements a fully special relativistic, time-independent version of the grid-agnostic MC random walk approximation.« less
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Richers, Sherwood; Nagakura, Hiroki; Ott, Christian D.; ...
2017-10-03
The mechanism driving core-collapse supernovae is sensitive to the interplay between matter and neutrino radiation. However, neutrino radiation transport is very difficult to simulate, and several radiation transport methods of varying levels of approximation are available. In this paper, we carefully compare for the first time in multiple spatial dimensions the discrete ordinates (DO) code of Nagakura, Yamada, and Sumiyoshi and the Monte Carlo (MC) code Sedonu, under the assumptions of a static fluid background, flat spacetime, elastic scattering, and full special relativity. We find remarkably good agreement in all spectral, angular, and fluid interaction quantities, lending confidence to bothmore » methods. The DO method excels in determining the heating and cooling rates in the optically thick region. The MC method predicts sharper angular features due to the effectively infinite angular resolution, but struggles to drive down noise in quantities where subtractive cancellation is prevalent, such as the net gain in the protoneutron star and off-diagonal components of the Eddington tensor. We also find that errors in the angular moments of the distribution functions induced by neglecting velocity dependence are subdominant to those from limited momentum-space resolution. We briefly compare directly computed second angular moments to those predicted by popular algebraic two-moment closures, and we find that the errors from the approximate closures are comparable to the difference between the DO and MC methods. Finally, included in this work is an improved Sedonu code, which now implements a fully special relativistic, time-independent version of the grid-agnostic MC random walk approximation.« less
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DOE Office of Scientific and Technical Information (OSTI.GOV)
Richers, Sherwood; Nagakura, Hiroki; Ott, Christian D.
The mechanism driving core-collapse supernovae is sensitive to the interplay between matter and neutrino radiation. However, neutrino radiation transport is very difficult to simulate, and several radiation transport methods of varying levels of approximation are available. In this paper, we carefully compare for the first time in multiple spatial dimensions the discrete ordinates (DO) code of Nagakura, Yamada, and Sumiyoshi and the Monte Carlo (MC) code Sedonu, under the assumptions of a static fluid background, flat spacetime, elastic scattering, and full special relativity. We find remarkably good agreement in all spectral, angular, and fluid interaction quantities, lending confidence to bothmore » methods. The DO method excels in determining the heating and cooling rates in the optically thick region. The MC method predicts sharper angular features due to the effectively infinite angular resolution, but struggles to drive down noise in quantities where subtractive cancellation is prevalent, such as the net gain in the protoneutron star and off-diagonal components of the Eddington tensor. We also find that errors in the angular moments of the distribution functions induced by neglecting velocity dependence are subdominant to those from limited momentum-space resolution. We briefly compare directly computed second angular moments to those predicted by popular algebraic two-moment closures, and we find that the errors from the approximate closures are comparable to the difference between the DO and MC methods. Finally, included in this work is an improved Sedonu code, which now implements a fully special relativistic, time-independent version of the grid-agnostic MC random walk approximation.« less
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Precise predictions for the angular coefficients in Z-boson production at the LHC
NASA Astrophysics Data System (ADS)
Gauld, R.; Gehrmann-De Ridder, A.; Gehrmann, T.; Glover, E. W. N.; Huss, A.
2017-11-01
The angular distributions of lepton pairs in the Drell-Yan process can provide rich information on the underlying QCD production mechanisms. These dynamics can be parameterised in terms of a set of frame dependent angular coefficients, A i=0,…,7, which depend on the invariant mass, transverse momentum, and rapidity of the lepton pair. Motivated by recent measurements of these coefficients by ATLAS and CMS, and in particular by the apparent violation of the Lam-Tung relation A 0 - A 2 = 0, we perform a precision study of the angular coefficients at O({α}s^3) in perturbative QCD. We make predic-tions relevant for pp collisions at √{s}=8 TeV, and perform comparisons with the available ATLAS and CMS data as well as providing predictions for a prospective measurement at LHCb. To expose the violation of the Lam-Tung relationship we propose a new observable ΔLT = 1 - A 2 /A 0 that is more sensitive to the dynamics in the region where A 0 and A 2 are both small. We find that the O({α}s^3) corrections have an important impact on the p T,Z distributions for several of the angular coefficients, and are essential to provide an adequate description of the data. The compatibility of the available ATLAS and CMS data is reassessed by performing a partial χ 2 test with respect to the central theoretical prediction which shows that χ 2 /N data is significantly reduced by going from O({α}s^2) to O({α}s^3).
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Angular dependence of the nanoDot OSL dosimeter.
Kerns, James R; Kry, Stephen F; Sahoo, Narayan; Followill, David S; Ibbott, Geoffrey S
2011-07-01
Optically stimulated luminescent detectors (OSLDs) are quickly gaining popularity as passive dosimeters, with applications in medicine for linac output calibration verification, brachytherapy source verification, treatment plan quality assurance, and clinical dose measurements. With such wide applications, these dosimeters must be characterized for numerous factors affecting their response. The most abundant commercial OSLD is the InLight/OSL system from Landauer, Inc. The purpose of this study was to examine the angular dependence of the nanoDot dosimeter, which is part of the InLight system. Relative dosimeter response data were taken at several angles in 6 and 18 MV photon beams, as well as a clinical proton beam. These measurements were done within a phantom at a depth beyond the build-up region. To verify the observed angular dependence, additional measurements were conducted as well as Monte Carlo simulations in MCNPX. When irradiated with the incident photon beams parallel to the plane of the dosimeter, the nanoDot response was 4% lower at 6 MV and 3% lower at 18 MV than the response when irradiated with the incident beam normal to the plane of the dosimeter. Monte Carlo simulations at 6 MV showed similar results to the experimental values. Examination of the results in Monte Carlo suggests the cause as partial volume irradiation. In a clinical proton beam, no angular dependence was found. A nontrivial angular response of this OSLD was observed in photon beams. This factor may need to be accounted for when evaluating doses from photon beams incident from a variety of directions.
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Angular dependence of the nanoDot OSL dosimeter
DOE Office of Scientific and Technical Information (OSTI.GOV)
Kerns, James R.; Kry, Stephen F.; Sahoo, Narayan
Purpose: Optically stimulated luminescent detectors (OSLDs) are quickly gaining popularity as passive dosimeters, with applications in medicine for linac output calibration verification, brachytherapy source verification, treatment plan quality assurance, and clinical dose measurements. With such wide applications, these dosimeters must be characterized for numerous factors affecting their response. The most abundant commercial OSLD is the InLight/OSL system from Landauer, Inc. The purpose of this study was to examine the angular dependence of the nanoDot dosimeter, which is part of the InLight system. Methods: Relative dosimeter response data were taken at several angles in 6 and 18 MV photon beams, asmore » well as a clinical proton beam. These measurements were done within a phantom at a depth beyond the build-up region. To verify the observed angular dependence, additional measurements were conducted as well as Monte Carlo simulations in MCNPX. Results: When irradiated with the incident photon beams parallel to the plane of the dosimeter, the nanoDot response was 4% lower at 6 MV and 3% lower at 18 MV than the response when irradiated with the incident beam normal to the plane of the dosimeter. Monte Carlo simulations at 6 MV showed similar results to the experimental values. Examination of the results in Monte Carlo suggests the cause as partial volume irradiation. In a clinical proton beam, no angular dependence was found. Conclusions: A nontrivial angular response of this OSLD was observed in photon beams. This factor may need to be accounted for when evaluating doses from photon beams incident from a variety of directions.« less
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Angular dependence of the nanoDot OSL dosimeter
Kerns, James R.; Kry, Stephen F.; Sahoo, Narayan; Followill, David S.; Ibbott, Geoffrey S.
2011-01-01
Purpose: Optically stimulated luminescent detectors (OSLDs) are quickly gaining popularity as passive dosimeters, with applications in medicine for linac output calibration verification, brachytherapy source verification, treatment plan quality assurance, and clinical dose measurements. With such wide applications, these dosimeters must be characterized for numerous factors affecting their response. The most abundant commercial OSLD is the InLight∕OSL system from Landauer, Inc. The purpose of this study was to examine the angular dependence of the nanoDot dosimeter, which is part of the InLight system.Methods: Relative dosimeter response data were taken at several angles in 6 and 18 MV photon beams, as well as a clinical proton beam. These measurements were done within a phantom at a depth beyond the build-up region. To verify the observed angular dependence, additional measurements were conducted as well as Monte Carlo simulations in MCNPX.Results: When irradiated with the incident photon beams parallel to the plane of the dosimeter, the nanoDot response was 4% lower at 6 MV and 3% lower at 18 MV than the response when irradiated with the incident beam normal to the plane of the dosimeter. Monte Carlo simulations at 6 MV showed similar results to the experimental values. Examination of the results in Monte Carlo suggests the cause as partial volume irradiation. In a clinical proton beam, no angular dependence was found.Conclusions: A nontrivial angular response of this OSLD was observed in photon beams. This factor may need to be accounted for when evaluating doses from photon beams incident from a variety of directions. PMID:21858992
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Evidence for Cluster to Cluster Variations in Low-mass Stellar Rotational Evolution
NASA Astrophysics Data System (ADS)
Coker, Carl T.; Pinsonneault, Marc; Terndrup, Donald M.
2016-12-01
The concordance model for angular momentum evolution postulates that star-forming regions and clusters are an evolutionary sequence that can be modeled with assumptions about protostar-disk coupling, angular momentum loss from magnetized winds that saturates in a mass-dependent fashion at high rotation rates, and core-envelope decoupling for solar analogs. We test this approach by combining established data with the large h Per data set from the MONITOR project and new low-mass Pleiades data. We confirm prior results that young low-mass stars can be used to test star-disk coupling and angular momentum loss independent of the treatment of internal angular momentum transport. For slow rotators, we confirm the need for star-disk interactions to evolve the ONC to older systems, using h Per (age 13 Myr) as our natural post-disk case. There is no evidence for extremely long-lived disks as an alternative to core-envelope decoupling. However, our wind models cannot evolve rapid rotators from h Per to older systems consistently, and we find that this result is robust with respect to the choice of angular momentum loss prescription. We outline two possible solutions: either there is cosmic variance in the distribution of stellar rotation rates in different clusters or there are substantially enhanced torques in low-mass rapid rotators. We favor the former explanation and discuss observational tests that could be used to distinguish them. If the distribution of initial conditions depends on environment, models that test parameters by assuming a universal underlying distribution of initial conditions will need to be re-evaluated.
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NASA Astrophysics Data System (ADS)
Richers, Sherwood; Nagakura, Hiroki; Ott, Christian D.; Dolence, Joshua; Sumiyoshi, Kohsuke; Yamada, Shoichi
2017-10-01
The mechanism driving core-collapse supernovae is sensitive to the interplay between matter and neutrino radiation. However, neutrino radiation transport is very difficult to simulate, and several radiation transport methods of varying levels of approximation are available. We carefully compare for the first time in multiple spatial dimensions the discrete ordinates (DO) code of Nagakura, Yamada, and Sumiyoshi and the Monte Carlo (MC) code Sedonu, under the assumptions of a static fluid background, flat spacetime, elastic scattering, and full special relativity. We find remarkably good agreement in all spectral, angular, and fluid interaction quantities, lending confidence to both methods. The DO method excels in determining the heating and cooling rates in the optically thick region. The MC method predicts sharper angular features due to the effectively infinite angular resolution, but struggles to drive down noise in quantities where subtractive cancellation is prevalent, such as the net gain in the protoneutron star and off-diagonal components of the Eddington tensor. We also find that errors in the angular moments of the distribution functions induced by neglecting velocity dependence are subdominant to those from limited momentum-space resolution. We briefly compare directly computed second angular moments to those predicted by popular algebraic two-moment closures, and we find that the errors from the approximate closures are comparable to the difference between the DO and MC methods. Included in this work is an improved Sedonu code, which now implements a fully special relativistic, time-independent version of the grid-agnostic MC random walk approximation.
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Photoionization of rare gas clusters
NASA Astrophysics Data System (ADS)
Zhang, Huaizhen
This thesis concentrates on the study of photoionization of van der Waals clusters with different cluster sizes. The goal of the experimental investigation is to understand the electronic structure of van der Waals clusters and the electronic dynamics. These studies are fundamental to understand the interaction between UV-X rays and clusters. The experiments were performed at the Advanced Light Source at Lawrence Berkeley National Laboratory. The experimental method employs angle-resolved time-of-flight photoelectron spectrometry, one of the most powerful methods for probing the electronic structure of atoms, molecules, clusters and solids. The van der Waals cluster photoionization studies are focused on probing the evolution of the photoelectron angular distribution parameter as a function of photon energy and cluster size. The angular distribution has been known to be a sensitive probe of the electronic structure in atoms and molecules. However, it has not been used in the case of van der Waals clusters. We carried out outer-valence levels, inner-valence levels and core-levels cluster photoionization experiments. Specifically, this work reports on the first quantitative measurements of the angular distribution parameters of rare gas clusters as a function of average cluster sizes. Our findings for xenon clusters is that the overall photon-energy-dependent behavior of the photoelectrons from the clusters is very similar to that of the corresponding free atoms. However, distinct differences in the angular distribution point at cluster-size-dependent effects were found. For krypton clusters, in the photon energy range where atomic photoelectrons have a high angular anisotropy, our measurements show considerably more isotropic angular distributions for the cluster photoelectrons, especially right above the 3d and 4p thresholds. For the valence electrons, a surprising difference between the two spin-orbit components was found. For argon clusters, we found that the angular distribution parameter values of the two-spin-orbit components from Ar 2p clusters are slightly different. When comparing the beta values for Ar between atoms and clusters, we found different results between Ar 3s atoms and clusters, and between Ar 3p atoms and clusters. Argon cluster resonance from surface and bulk were also measured. Furthermore, the angular distribution parameters of Ar cluster photoelectrons and Ar atom photoelectrons in the 3s → np ionization region were obtained.
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Glacioeustasy, meteoric diagenesis, and the carbon cycle during the Middle Carboniferous
NASA Astrophysics Data System (ADS)
Dyer, Blake; Maloof, Adam C.; Higgins, John A.
2015-10-01
Middle Carboniferous carbonates in the western U.S. have undergone Pleistocene Bahamas-style meteoric diagenesis that may be associated with expanding late Paleozoic ice sheets. Fourteen stratigraphic sections from carbonate platforms illustrate the regional distribution and variable intensity of physical and chemical diagenesis just below the Middle Carboniferous unconformity. These sections contain top-negative carbon isotope excursions that terminate in regional exposure surfaces that are associated with some combination of karst towers, desiccation cracks, fabric destructive recrystallization, or extensive root systems. The timing of the diagenesis is synchronous with similarly scaled top-negative carbon isotope excursions observed by others in England, Kazakhstan, and China. The mass flux of negative carbon required to generate similar isotopic profiles across the areal extent of Middle Carboniferous platform carbonates is a significant component of the global carbon cycle. We present a simple carbon box model to illustrate that the δ13C of dissolved inorganic carbon in the ocean could be elevated by ˜1.4‰ as isotopically light carbon from the weathering of terrestrial organic matter reacts with exposed platforms before reaching the ocean and atmosphere. These results represent an improvement on global biogeochemical models that have struggled to provide a congruent solution to the high δ13C of the late Paleozoic icehouse.
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Geology and insolation-driven climatic history of Amazonian north polar materials on Mars
Tanaka, K.L.
2005-01-01
Mariner 9 and Viking spacecraft images revealed that the polar regions of Mars, like those of Earth, record the planet's climate history. However, fundamental uncertainties regarding the materials, features, ages and processes constituting the geologic record remained. Recently acquired Mars Orbiter Laser Altimeter data and Mars Orbiter Camera high-resolution images from the Mars Global Surveyor spacecraft and moderately high-resolution Thermal Emission Imaging System visible images from the Mars Odyssey spacecraft permit more comprehensive geologic and climatic analyses. Here I map and show the history of geologic materials and features in the north polar region that span the Amazonian period (???3.0 Gyr ago to present). Erosion and redeposition of putative circumpolar mud volcano deposits (formed by eruption of liquefied, fine-grained material) led to the formation of an Early Amazonian polar plateau consisting of dark layered materials. Crater ejecta superposed on pedestals indicate that a thin mantle was present during most of the Amazonian, suggesting generally higher obliquity and insolation conditions at the poles than at present. Brighter polar layered deposits rest unconformably on the dark layers and formed mainly during lower obliquity over the past 4-5 Myr (ref. 20). Finally, the uppermost layers post-date the latest downtrend in obliquity <20,000 years ago. ?? 2005 Nature Publishing Group.
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Biostratigraphic interpretation for the cyclic sedimentation in northwestern Libya
DOE Office of Scientific and Technical Information (OSTI.GOV)
Tekbali, A.O.; Cornell, W.C.
1993-02-01
Mesozoic sediments in western Libya are best exposed along the Jabal Nafusah escarpment. This northeast-southwest trending structure overlooks the Al Jifarah plain and extends more than 300 km westward to connect with a T-shaped anticlinorium in Algeria and Tunisia. The Al Aziziyan fault (normal, north side down) parallels the northern edge of the escarpment and marks its initial position. Alternate deposition of marine and continental sediments began in the Triassic before the formation of a major monocline in the Late Jurassic-Early Cretaceous time. Subsequent epiorogenic movements and isostatic adjustments initiated a westward sloping shelf along the southern edge of themore » Tethys. As a result, the eastern and central regions of western Libya were subjected to severe erosion and coalescing of unconformities towards the topographic highs, prior to the deposition of the overstepping Kiklah Formation. Geometrical and physical interpretation of the Mesozoic sediments in the region, combined with paleogeographic reconstruction indicate that the post-Hercynian epiorogenic adjustments and fluctuations of the Tethys resulted in local cyclic sedimentation. Accurate age assessment of the boundaries between the Jurassic-Early Cretaceous facies in northwestern Libya can be carried out on the basis of microfloral and faunal distribution and makes possible correlation of aquifers and probable oil-bearing sequences in western Libya.« less
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Geology and insolation-driven climatic history of Amazonian north polar materials on Mars.
Tanaka, Kenneth L
2005-10-13
Mariner 9 and Viking spacecraft images revealed that the polar regions of Mars, like those of Earth, record the planet's climate history. However, fundamental uncertainties regarding the materials, features, ages and processes constituting the geologic record remained. Recently acquired Mars Orbiter Laser Altimeter data and Mars Orbiter Camera high-resolution images from the Mars Global Surveyor spacecraft and moderately high-resolution Thermal Emission Imaging System visible images from the Mars Odyssey spacecraft permit more comprehensive geologic and climatic analyses. Here I map and show the history of geologic materials and features in the north polar region that span the Amazonian period (approximately 3.0 Gyr ago to present). Erosion and redeposition of putative circumpolar mud volcano deposits (formed by eruption of liquefied, fine-grained material) led to the formation of an Early Amazonian polar plateau consisting of dark layered materials. Crater ejecta superposed on pedestals indicate that a thin mantle was present during most of the Amazonian, suggesting generally higher obliquity and insolation conditions at the poles than at present. Brighter polar layered deposits rest unconformably on the dark layers and formed mainly during lower obliquity over the past 4-5 Myr (ref. 20). Finally, the uppermost layers post-date the latest downtrend in obliquity <20,000 years ago.
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The Yilgarn Craton western Australia: A tectonic synthesis
NASA Technical Reports Server (NTRS)
Fripp, R. E. P.
1986-01-01
The Yilgarn Craton in Western Australia is one of the larger contiguous preserved Archaean crustal fragments, with an area of about 650,000 square kilometres. Of this, by area, about 70% is granitoid and 30% greenstone. The Craton is defined by the Darling Fault on its western margin, by Proterozoic deformation belts on its southern and northwestern margins, and by unconformable younger sediments on its eastern and northeastern margins. A regional geotectonic synthesis at a scale of 1:500,000 is being prepared. This is based largely upon the 1:250,000 scale mapping of the Geological Survey of Western Australia together with interpretation using geophysical data, mainly airborne magnetic surveys. On a regional basis the granitoids are classied as pre-, syn- and post-tectonic with respect to greenstone belt deformation. The post-tectonic granitoids yield Rb-Sr isochrons of about 2.6 b.y., close to Rb-Sr ages for the greenstones themselves which are up to about 2.8 b.y. old, although data for the latter is sparse. Contacts between earlier granitoids and greenstones which are not obscured by the post-tectonic granitoids are most commonly tectonic contacts, intensely deformed and with mylonitic fabrics. The general concensus however is that there is a pre-tectonic, pre-greenhouse sialic gneiss preserved in places. A discussion follows.
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McKeown, N.K.; Bishop, J.L.; Noe Dobrea, E.Z.; Ehlmann, B.L.; Parente, M.; Mustard, J.F.; Murchie, S.L.; Swayze, G.A.; Bibring, J.-P.; Silver, E.A.
2009-01-01
Mawrth Vallis contains one of the largest exposures of phyllosilicates on Mars. Nontronite, montmorillonite, kaolinite, and hydrated silica have been identified throughout the region using data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM). In addition, saponite has been identified in one observation within a crater. These individual minerals are identified and distinguished by features at 1.38-1.42, ???1.91, and 2.17-2.41 ??m. There are two main phyllosilicate units in the Mawrth Vallis region. The lowermost unit is nontronite bearing, unconformably overlain by an Al-phyllosilicate unit containing montmorillonite plus hydrated silica, with a thin layer of kaolinite plus hydrated silica at the top of the unit. These two units are draped by a spectrally unremarkable capping unit. Smectites generally form in neutral to alkaline environments, while kaolinite and hydrated silica typically form in slightly acidic conditions; thus, the observed phyllosilicates may reflect a change in aqueous chemistry. Spectra retrieved near the boundary between the nontronite and Al-phyllosilicate units exhibit a strong positive slope from 1 to 2 ??m, likely from a ferrous component within the rock. This ferrous component indicates either rapid deposition in an oxidizing environment or reducing conditions. Formation of each of the phyllosilicate minerals identified requires liquid water, thus indicating a regional wet period in the Noachian when these units formed. The two main phyllosilicate units may be extensive layers of altered volcanic ash. Other potential formational processes include sediment deposition into a marine or lacustrine basin or pedogenesis. Copyright 2009 by the American Geophysical Union.
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C 3, A Command-line Catalog Cross-match Tool for Large Astrophysical Catalogs
NASA Astrophysics Data System (ADS)
Riccio, Giuseppe; Brescia, Massimo; Cavuoti, Stefano; Mercurio, Amata; di Giorgio, Anna Maria; Molinari, Sergio
2017-02-01
Modern Astrophysics is based on multi-wavelength data organized into large and heterogeneous catalogs. Hence, the need for efficient, reliable and scalable catalog cross-matching methods plays a crucial role in the era of the petabyte scale. Furthermore, multi-band data have often very different angular resolution, requiring the highest generality of cross-matching features, mainly in terms of region shape and resolution. In this work we present C 3 (Command-line Catalog Cross-match), a multi-platform application designed to efficiently cross-match massive catalogs. It is based on a multi-core parallel processing paradigm and conceived to be executed as a stand-alone command-line process or integrated within any generic data reduction/analysis pipeline, providing the maximum flexibility to the end-user, in terms of portability, parameter configuration, catalog formats, angular resolution, region shapes, coordinate units and cross-matching types. Using real data, extracted from public surveys, we discuss the cross-matching capabilities and computing time efficiency also through a direct comparison with some publicly available tools, chosen among the most used within the community, and representative of different interface paradigms. We verified that the C 3 tool has excellent capabilities to perform an efficient and reliable cross-matching between large data sets. Although the elliptical cross-match and the parametric handling of angular orientation and offset are known concepts in the astrophysical context, their availability in the presented command-line tool makes C 3 competitive in the context of public astronomical tools.
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NASA Astrophysics Data System (ADS)
Liu, Jiafu; McInnes, Colin R.
2018-03-01
This paper considers utilizing solar radiation pressure (SRP) to actively control the surface shape of a reflector consisting of a rigid hoop and slack membrane with embedded reflectivity control devices. The full nonlinear static partial differential governing equations for a reflector with negligible elastic deformations are established for the circumferential, radial and transverse directions respectively, in which the SRP force with ideal/non-perfect models, the centripetal force caused by the rotation of the reflector and the internal stresses are considered. The inverse problem is then formulated by assuming that the required surface shape is known, and then the governing algebraic-differential equations used to determine the required surface reflectivity, together with the internal stresses where are presented accordingly. The validity of the approach is verified by comparing the results in this paper with corresponding published results as benchmarks. The feasible regions of the angular velocity and Sun angle for a paraboloidal reflector with an invariant radius and focal length (case 1), and the achievable focal lengths with a specific angular velocity and Sun angle (case 2) are presented for two SRP models respectively, both by considering the constraints on the reflectivity and internal stresses. It is then found that the feasible region is toward a larger angular velocity and Sun angle when using the non-perfect SRP model, compared with the ideal one in case 1. The angular velocity of the spinning reflector should be within a certain range to make the required reflectivity profiles within a practical range, i.e., [0, 0.88], as indicated from prior NASA solar sail studies. In case 2, it is found that the smallest achievable focal length of the reflector with the non-perfect SRP model is smaller than that with the ideal SRP model. It is also found that the stress level is extremely low for all cases considered and that the typical real material strength available for the reflector is sufficient to withstand these internal stresses.
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NASA Astrophysics Data System (ADS)
Ridgway, K.; Trop, J. M.; Finzel, E.; Brennan, P. R.; Gilbert, H. J.; Flesch, L. M.
2015-12-01
Studies the past decade have fundamentally changed our perspective on the Mesozoic and Cenozoic tectonic configuration of Alaska. New concepts include: 1) A link exists between Mesozoic collisional zones, Cenozoic strike-slip fault systems, and active deformation that is related to lithospheric heterogeneities that remain over geologic timescales. The location of the active Denali fault and high topography, for example, is within a Mesozoic collisional zone. Rheological differences between juxtaposed crustal blocks and crustal thickening in this zone have had a significant influence on deformation and exhumation in south-central Alaska. In general, the original configuration of the collisional zone appears to set the boundary conditions for long-term and active deformation. 2) Subduction of a spreading ridge has significantly modified the convergent margin of southern Alaska. Paleocene-Eocene ridge subduction resulted in surface uplift, unconformity development and changes in deposystems in the forearc region, and magmatism that extended from the paleotrench to the retroarc region. 3) Oligocene to Recent shallow subduction of an oceanic plateau has markedly reconfigured the upper plate of the southern Alaska convergent margin. This ongoing process has prompted growth of some of the largest mountain ranges on Earth, exhumation of the forearc and backarc regions above the subducted slab, development of a regional gap in arc magmatism above the subducted slab as well as slab-edge magmatism, and displacement on the Denali fault system. In the light of these new tectonic concepts for Alaska, we will discuss targets of opportunity for future integrated geologic and geophysical studies. These targets include regional strike-slip fault systems, the newly recognized Bering plate, and the role of spreading ridge and oceanic plateau subduction on the location and pace of exhumation, sedimentary basin development, and magmatism in the upper plate.
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Multiscalar approach to archaeological site formation at GaJj17, East Turkana, Kenya
NASA Astrophysics Data System (ADS)
Murray, B. M.; Ranhorn, K. L.; Colarossi, D.; Mavuso, S. S.; Dogandžić, T.; Ziegler, M. J.; Warren, S. L.; Braun, D. R.; Harris, J. W. K.
2017-12-01
Kenya's East Turkana region hosts a rich PlioPleistocene record of fossils, archaeological artifacts, and sedimentary features whose chronostratigraphic histories are often obscured by landscape changes from erosional events and tectonic activity. The Middle Stone Age (MSA) record of the Koobi Fora Formation (KF Fm.) has particularly been subjected to this complex depositional history, making it a sparse unit and, consequently, widely understudied. Stratigraphically located in between the maximum capping unconformity of the KF Fm.'s Chari tuff ( 1.39 Ma) and that of the Galana Boi Fm. ( 10 ka), the unit provides a unique window into understanding the Late Pleistocene of the region. The MSA surface scatters at archaeological site GaJj17 prompted further study into the site's age and depositional chronology. The GaJj17 ridge is locally distinguished by its cap of Late Pleistocene sands overlying strata containing tuffs likely of the Upper Burgi (2.0-1.87 Ma) or KBS (1.87-1.56 Ma) members. To investigate whether GaJj17's preservation is due to tectonic deformation, a broader scale examination of the structural geology was conducted through surveys and aerial imagery. Regions of deformation were identified and mapped to establish the geological history of the locality. Resultant observations and elevation data offer insight into regional faults at the root of prolonged structural alterations which have facilitated the unique preservation of MSA materials. Through a multiscalar approach it is possible to understand both the formation of GaJj17 and the underlying processes behind preservation and destruction in the changing landscape of the Turkana basin, enabling future identification of archaeological sites through proxies of elevation, regional stratigraphy, and fault mapping. This research was supported by IRES grants 1358178 and 1358200 from the U.S. National Science Foundation.
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Cambrian-lower Middle Ordovician passive carbonate margin, southern Appalachians: Chapter 14
Read, J. Fred; Repetski, John E.
2012-01-01
The southern Appalachian part of the Cambrian–Ordovician passive margin succession of the great American carbonate bank extends from the Lower Cambrian to the lower Middle Ordovician, is as much as 3.5 km (2.2 mi) thick, and has long-term subsidence rates exceeding 5 cm (2 in.)/k.y. Subsiding depocenters separated by arches controlled sediment thickness. The succession consists of five supersequences, each of which contains several third-order sequences, and numerous meter-scale parasequences. Siliciclastic-prone supersequence 1 (Lower Cambrian Chilhowee Group fluvial rift clastics grading up into shelf siliciclastics) underlies the passive margin carbonates. Supersequence 2 consists of the Lower Cambrian Shady Dolomite–Rome-Waynesboro Formations. This is a shallowing-upward ramp succession of thinly bedded to nodular lime mudstones up into carbonate mud-mound facies, overlain by lowstand quartzose carbonates, and then a rimmed shelf succession capped by highly cyclic regressive carbonates and red beds (Rome-Waynesboro Formations). Foreslope facies include megabreccias, grainstone, and thin-bedded carbonate turbidites and deep-water rhythmites. Supersequence 3 rests on a major unconformity and consists of a Middle Cambrian differentiated rimmed shelf carbonate with highly cyclic facies (Elbrook Formation) extending in from the rim and passing via an oolitic ramp into a large structurally controlled intrashelf basin (Conasauga Shale). Filling of the intrashelf basin caused widespread deposition of thin quartz sandstones at the base of supersequence 4, overlain by widespread cyclic carbonates (Upper Cambrian lower Knox Group Copper Ridge Dolomite in the south; Conococheague Formation in the north). Supersequence 5 (Lower Ordovician upper Knox in the south; Lower to Middle Ordovician Beekmantown Group in the north) has a basal quartz sandstone-prone unit, overlain by cyclic ramp carbonates, that grade downdip into thrombolite grainstone and then storm-deposited deep-ramp carbonates. Passive margin deposition was terminated by arc-continent collision when the shelf was uplifted over a peripheral bulge while global sea levels were falling, resulting in the major 0- to 10-m.y. Knox–Beekmantown unconformity. The supersequences and sequences appear to relate to regionally traceable eustatic sea level cycles on which were superimposed high-frequency Milankovitch sea level cycles that formed the parasequences under global greenhouse conditions.