Sample records for stratigraphy sedimentology age

  1. Relationships among sedimentology, stratigraphy, and diagenesis in the Proterozoic Thelon Basin, Nunavut, Canada: implications for

    E-print Network

    Hiatt, Eric E.

    Relationships among sedimentology, stratigraphy, and diagenesis in the Proterozoic Thelon Basin and paragenetic relationships vary systematically with sedimentology and stratigraphy of the Thelon and provide. Keywords: Diagenesis; Sedimentology; Thelon; Sequence stratigraphy; Hydrostratigraphy 0375-6742/03/$ - see

  2. The Early Aptian of Aralar (northern Spain): stratigraphy, sedimentology, ammonite biozonation, and OAE1

    E-print Network

    Gilli, Adrian

    The Early Aptian of Aralar (northern Spain): stratigraphy, sedimentology, ammonite biozonation Stratigraphy Ammonite biozonation TOC Oceanic Anoxic Event 1 a b s t r a c t The stratigraphy, sedimentology. The sedimentology indicates general deposition in a shallow marine environment, corresponding to mixed siliciclastic

  3. Sedimentology and sequence stratigraphy of reefs and carbonate platforms

    SciTech Connect

    Schlager, W. (Free Univ., Amsterdam (NL))

    1992-01-01

    Classical sequence stratigraphy has been developed primarily from siliciclastic systems. Application of the concept to carbonates has not been as straightforward as was originally expected even though the basic tenets of sequence stratigraphy are supposed to be applicable to all depositional systems. Rather than force carbonate platforms into the straightjacket of a concept derived from another sediment family, this course takes a different tack. It starts out from the premise that sequence stratigraphy is a modern and sophisticated version of lithostratigraphy and as such is a sedimentologic concept. More sedimentology into sequence stratigraphy is the motto of the course and the red line that runs through the chapter of this book. The cook sets out with a review of sedimentologic in reference to petroleum deposits principles governing the large-scale anatomy of reefs and platforms. It then looks at sequences an systems tracts from a sedimentologic point of view, assesses the differences between siliciclastics and carbonates in their response to sea level, evaluates processes that compete with sea level for control on carbonate sequences, and finally presents a set of guidelines for application of sequence stratigraphy to reefs and carbonate platforms.

  4. Reading and Abstracting Journal Articles in Sedimentology and Stratigraphy.

    ERIC Educational Resources Information Center

    Conrad, Susan Howes

    1991-01-01

    An assignment centered on reading journal articles and writing abstracts is an effective way to improve student reading and writing skills in sedimentology and stratigraphy laboratories. Each student reads two articles and writes informative abstracts from the author's point of view. (PR)

  5. Sedimentology and sequence stratigraphy of the Sturgeon Lake field, Alberta

    SciTech Connect

    Mederos, S.M. [Maraven, S.A., Caracas (Venezuela); Moslow, T.F. [Univ. of Alberta, Edmonton (Canada)

    1996-08-01

    This study examines the sedimentology, sequence stratigraphy and reservoir characterization of the Lower Triassic Montney Formation in the Sturgeon Lake field located in west-central Alberta. The Montney Formation is grouped into two facies associations. Facies Association 1 is a siliciclastic upward-coarsening sequence deposited by storm, current and wave processes and is interpreted as a low energy progradational lower shoreface. Facies Association 2 is a carbonate shallowing upward sequence deposited in a wave dominated progradational shoreface. The contact between Facies Association 1 and 2 is marked by a major change in lithology and is erosive. Palynological analyses reveal two missing palynologic subzones between Facies Association 1 and Facies Association 2 suggesting a period of erosion and/or nondeposition. The boundary between the two facies association is defined as a sequence boundary which stratigraphically divides the Montney Formation into two sequences in the study area. The Lower Montney sequence is composed of eight retrogradational, aggradational and progradational parasequences and represent the Transgressive and the High-stand System Tract. The Upper Montney sequence is composed only of one parasequence and represents the Transgressive System Tract. The Sturgeon Lake Field has two types of reservoir with respect to lithology, porosity, permeability and geometry. The best reservoir facies is a brachiopod wackestone-packstone with permeabilities up to 8 Darcys. Siliciclastic reservoirs consist of very fine grained sandstones with permeabilities of 132 md when fractured.

  6. Integrated Field Project in Structural Geology and Sedimentology/Stratigraphy

    NSDL National Science Digital Library

    Lawrence Malinconico

    The field project described in the Big Horn Basin is a capstone experience for our innovative full-year course sequence that combines two geologic disciplines traditionally taught separately (in "silos") sedimentology/stratigraphy and structural geology. We feel that a holistic approach that combines an understanding of the processes involved in both disciplines allows students to more easily develop the geologic history of an area from collected field data. The result is a two-semester course sequence that integrates the concepts of the two disciplines through a full year of study. While we have more than ten different field projects during the year, these are simply "snapshots" that allow the student to only see a piece of the geologic puzzle. These exercises do develop skills that the student will use in the capstone experience the geologic synthesis of a specific region currently the Sheep Mountain region of the Big Horn Basin. The field-mapping project in the Big Horn Basin is followed by five weeks of sequenced work that allows each student to synthesize a complete geologic (sedimetologic and structural) history of the region. This includes the construction of a geologic map and cross-sections, understanding the depositional history (including environments of deposition), the syn- or post-depositional deformation of the region and an attempt to put the local geologic history into the context of regional deformation and tectonics. We believe that by integrating the disciplines into the two-semester sequence capped with the field mapping and synthesis better prepares students to "think like a geologist".

  7. Sedimentology, stratigraphy, and glacier dynamics, western Scottish Highlands

    E-print Network

    with deposits formed in contemporary glaciated environments. These new data are subsequently appraised in terms the warming climate and increasing precipitation. These new palaeoglaciological and palaeoenvironmental Weichselian; Younger Dryas; British Ice Sheet; Stratigraphy; Glacier dynamics; Palaeoglaciology; Scotland

  8. Contribution of logging data to sedimentology and stratigraphy. [Electrofacies

    SciTech Connect

    Serra, O.; Abbott, H.T.

    1982-02-01

    A technique has been developed using multivariate analysis of logging data to give a high-resolution sedimentological description of any sequence of formations. The number of different logs and their range allow determination of many of the physical characteristics of the rock. The definition of a lithofacies has been extended by introducing the concept of an electrofacies, constructed on the basis of all the logging data at any depth interval. Each logging datum is considered a descriptor for purposes of establishing electrofacies in a logged interval. Once established, electrofacies then can be correlated with actual geologic facies, if the logged interval has been cored. 23 refs.

  9. Carboniferous clastic-wedge stratigraphy, sedimentology, and foreland basin evolution: Black Warrior basin, Alabama and Mississippi

    SciTech Connect

    Hines, R.A.

    1986-05-01

    Carboniferous clastic-wedge stratigraphy and sedimentology in the Black Warrior basin of Alabama and Mississippi indicate deposition in an evolving foreland basin flanking the Appalachian-Ouachita fold-thrust belt. The strata reflect specific responses to foreland basin subsidence, orogenic activity, sediment supply, and dispersal systems. Definition of the regional stratigraphy of the clastic wedge provides for interpretation of the foreland basin subsidence history by enabling quantitative reconstruction of regional compaction and subsidence profiles. Comparison of the interpreted subsidence history with model profiles of foreland basin subsidence (predicted from loading and flexure of continental lithosphere) allows evaluation of mechanical models in terms of observed clastic-wedge sedimentology and stratigraphy. Mechanical modeling of foreland basin subsidence predicts formation of a flexural bulge that migrates cratonward ahead of the subsiding foreland basin during loading. In the Black Warrior basin, local stratigraphic thins, pinch-outs, and areas of marine-reworked sediments suggest migration of the flexural bulge. Comparison of flexural bulge migration with thermal maturation history allows evaluation of timing of stratigraphic trapping mechanisms with respect to onset of hydrocarbon generation.

  10. Preservation of exceptional vertebrate assemblages in Middle Permian fluviolacustrine mudstones of Kotel'nich, Russia: stratigraphy, sedimentology,

    E-print Network

    Benton, Michael

    of Kotel'nich, Russia: stratigraphy, sedimentology, and taphonomy Michael J. Benton a, , Andrew J. Newell b Region 610000, Russia d School of Geography, Earth and Environmental Sciences, University of Plymouth Profsoyuznaya 123, Moscow 117997, Russia a b s t r a c ta r t i c l e i n f o Article history: Received 2 July

  11. Stratigraphy and sedimentology of the upper Proterozoic Kingston Peak Formation, Panamint Range, eastern California

    NASA Astrophysics Data System (ADS)

    Miller, J. M. G.

    The Kingston Peak Formation was deposited under glacial conditions with contemporaneous volcanism and tectonic activity. Sedimentation in the Panamint Range was on the continental shelf and locally terrestrial. Two ice advances are recorded with associated sea level fluctuations. Striated stones and dropstones in the formation east of Death Valley support this interpretation. Data were collected during mapping of parts of the Manly Peak and Telescope Peak quadrangles; eight stratigraphic sections between Goler Wash and Wildrose Canyon were measured and sedimentologic observations were made in intervening areas and east of Death Valley. Interbedded pillow basalt demonstrates subaqueous volcanism. Overlying laminated limestone marks a transgression. Succeeding interbedded limestone, graded graywacke and siltstone double in thickness over a few kilometers demonstrates local subsidence and renewed terrigenous input. Trough cross laminated arkosic sandstone overlain by diamicite, with a locally erosive base, represent glaciofluvial deposits and lodgement till recording the second ice advance. The stratigraphy and thickness of the formation are variable across the Death Valley region and alternative correlation schemes exist. A coherent stratigraphy among ranges southeast of Death Valley supports severe Cenozoic extension, but elsewhere constraints on palinspastic reconstructions are restricted by stratigraphic variation. Deposition was in local basins with nearby source areas during incipient continental rifting.

  12. Sedimentology and sequence stratigraphy of Lower Shihezi Formation in Shenguhao area, northern Ordos basin, China

    NASA Astrophysics Data System (ADS)

    Chen, Lin; Lu, Yongchao; Lin, Zi

    2015-04-01

    The structural location of Shenguhao area locates at the transition zone of Yimeng uplift and Yishan slope of northern Ordos basin, China. The study area is in erosion condition until Late Carboniferous and has deposited Taiyuan Formation (C2t), Shanxi Formation (P1s), Lower Shihezi Formation (P1x), Upper Shihezi Formation (P2s) and Shiqianfeng Formation (P2sh) in succession during Late Paleozoic, which mainly develops transition facies and alluvial plain facies. The fluvial sandstone of Lower Shihezi Formation is the major target layer of gas exploration and development in this area. This study is based on the interpretation of 38 wells and 113 sesmic reflection profiles. Three significant lithofacies were identified with sedimentological analysis of cores from the Shenguhao area: fluvial conglomerates, fluvial sandstone and floodplain mudstone, which represent fluvial depositional environment. Based on sequence stratigraphy methodology, well log patterns and lithofacies analysis, Lower Shihezi Formation can be divided into four depositional sequence cycles (1-4) bounded by fluvial scouring erosional surfaces. Each sequence succession shows the trend of base level rising and overall performs fining-upward feature, which characterized by coarsening-upward lower to upper fluvial sandstone and floodplain mudstone. In ascending order, sequence 1 records the transition from the underlying braided river delta plain fine-grained sediments of Shanxi Formation into the overlying fluvial sandstone of Lower Shihezi Formation and develops scouring erosional unconformity at the base, representing a regression. Sequence 1 consists of a package of progradting thick layer of amalgamated fluvial sandstone at the lower part passing into aggrading thin layer of floodplain mudstone at the upper part, suggesting that accommodation growing rate is gradually greater than deposition supply rate under the background of base level gradual increase. Sequence 2 and 3 record similar stratigraphic stacking patterns with sequence 1, but the upper part floodplain mudstone of sequence 2 and 3 is thicker than sequence 1. Sequence 4 mainly contains several single isolated fluvial sandstones and thick layer extensive over-bank deposits or floodplain mudstones, which mainly develops aggradational stratigraphic stacking pattern, suggesting that sediments accumulate during high accommodation. The lower part coarse-grained fluvial sandstone of each sequence was interpreted as sediments of lowstand system tract; the upper part fine-grained floodplain mudstone was interpreted as sediments of transgressive system tract. The stratigraphic architecture patterns reflect that the uplifting rate of base level indicates the increasing trend from the early stage of Lower Shihezi Formation to the late stage. Channel style exhibits evolution from a thick layer multi-phase amalgamated to more solitary. Floodplain mudstone gradual tends to be more development, suggesting that accommodation inclines to be much higher. The thickness of each sequence shows uniform variable laterally, indicating that there are small influence of structure movement on sediments accumulation. The characters of sedimentary evolution under the sequence stratigraphic framework imply that sequence development and evolution is mainly controlled by sea level change.

  13. Sedimentology and stratigraphy of a tidal sand bank in the southern North Sea

    Microsoft Academic Search

    Alain Trentesaux; Ad Stolk; Serge Berné

    1999-01-01

    A set of 125 vibrocores collected on the basis of a dense grid of high and very high resolution seismic coverage over a tidal sand bank (the Middelkerke Bank) provides a unique opportunity to reconstruct the stratigraphy and sedimentary facies succession of such a large tidal sand body. Five sedimentary facies are distinguished. They range from clay to pebble and

  14. Stratigraphy, sedimentology, chronology and palaeohydrology of Quaternary lacustrine deposits at Madigan Gulf, Lake Eyre, south Australia

    Microsoft Academic Search

    J. W. Magee; J. M. Bowler; G. H. Miller; D. L. G. Williams

    1995-01-01

    Madigan Gulf is a large bay at the southern end of Lake Eyre North, a major ephemerally flooded playa in arid central Australia at the southwestern margin of a vast (1,300,000 km2) internal drainage basin. The stratigraphy and chronology of the Quaternary sequence in the gulf is described from 8 cores and a cliff exposure at the gulf margin. A

  15. High-resolution seismic stratigraphy and its sedimentological interpretation on the Amazon continental shelf

    Microsoft Academic Search

    Clark R. Alexander; Charles A. Nittrouer; David J. Demaster

    1986-01-01

    Seismic profiles (3.5 kHz) from over 6000 km of shiptrack and piston cores from 26 stations were examined to evaluate the seismic-stratigraphic framework of the Amazon subaqueous delta. Acoustic reflectors in the seismic profiles were related to sedimentological and acoustic properties in piston-core sediment. Grain size in cores from the Amazon shelf correlates well with seismic velocity and saturated bulk

  16. Integration of sequence stratigraphy and process sedimentology: Miocene Rincon and Topanga Formations, Santa Barbara basin near Point Mugu, California

    SciTech Connect

    Jordan, D.W.; Marquard, R.S. (ARCO Oil and Gas Co., Plano, TX (USA))

    1990-05-01

    The Miocene Rincan and Topanga formations exposed at Point Mugu comprise over 1,200 ft of interbedded sandstones, siltstones, claystones, and clay shales that were deposited in a tectonically active marine basin adjacent to the present Santa Monica Mountains. Integration of sequence stratigraphic interpretation techniques and process sedimentology demonstrates that this section originated as shelfal deposits during sea level rise that were cut by a submarine canyon during subsequent sea level lowstand. The base of the sequence contains a bioturbated silty sandstone indicative of a transgressive deposit within the sequence stratigraphic framework. Upsection, dark clay shales of a condensed section contain fish fragments and sponge progradational highstand shelf sandstones. An erosional surface flooring a deep-water canyon cuts the highstand deposits and marks a sequence boundary. Within the submarine canyon fill, deep-water deposits represent at least two episodes of sediment gravity flows. A predominantly deformed lower section is cut by an erosional surface (another sequence boundary ) overlain by undeformed strata. The deformed section was caused by slumping of a canyon wall within a slope environment and deposition of high-density turbidites and debris flows. The undeformed section contains Bouma sequences, graded beds, dish structures, and biogenic structures. Interstratified bed-thinning and bed-thickening sequences suggest minor progradational events and small feeder channels within the undeformed section. These relationships demonstrate that not all sequences comprising deep-water deposits can be easily assigned to facies, such as channels and lobes, based on vertical and lateral profiles. This integration of sequence stratigraphy and sedimentology has assisted in understanding the vertical and lateral heterogeneities present within exploration and production areas in the adjacent Santa Barbara Channel.

  17. Basin Evolution and Exhumation of the Xigaze Forearc, Southern Tibet: Insight from Sedimentology, Stratigraphy, and Geo-Thermochronology

    NASA Astrophysics Data System (ADS)

    Orme, D. A.; Carrapa, B.; Abbey, A. L.; Kapp, P. A.; Ding, L.

    2012-12-01

    Forearc basins are important data archives for understanding continental dynamics because they preserve the tectono-erosional record of continental margins before collision. This study focuses on the Cretaceous-Eocene Xigaze forearc basin in southern Tibet, which is exposed along ~600 km of the Indus-Yarlung Suture Zone between the Indian craton to the south and the Asian Lhasa terrane to the north. From late Cretaceous to early Cenozoic time, subduction of Neo-Tethyan oceanic crust beneath the southern margin of Asia accommodated the northward motion of the Indian craton and formed the Xigaze forearc basin. Following collision with India in the early Cenozoic, the basin transitioned from predominantly marine to non-marine sedimentation and was subsequently uplifted to a mean elevation of 5000 m. How this transition occurred remains unresolved. This study's overall objective is to decipher forearc-basin and Indo-Asia continental-margin development from field sedimentology and stratigraphy, and detrital geo-thermochronology. We present new stratigraphic sections, totaling 8 km thick, from a previously unexplored ~60 km segment of the Xigaze forearc, ~50 km north-northwest of Saga. These sections are quite different from those known farther east. Sedimentary facies of mid-Cretaceous to early Eocene deposits indicate a shoaling-upward trend consistent with other ancient forearc basins (e.g., Great Valley forearc, California). Middle to late Cretaceous deposits indicate a variety of facies and depositional environments along strike in the study area. Facies include distal marine turbidites, shelf limestones, estuarine siliciclastics, and brown paleosols. In contrast, Eocene depositional environments are transitional from nearshore marine to pericontinental. Facies consist of dirty limestones, packstones, and wackestones, interbedded with terrigenous conglomerates and red-green paleosols. Eocene fauna include abundant foraminifera such as Nummulites-Discocyclina and Miscellanea-Daviesina. The along-strike variability of the Cretaceous strata suggests that, prior to collision, the diverse and irregular paleogeography of Asia's southern margin greatly influenced the three-dimensional nature and distribution of time-equivalent facies. In order to determine the timing of exhumation of Xigaze forearc strata, we utilize zircon (U-Th)/He thermochronology coupled with U-Pb geochronology. Preliminary U-Pb detrital geochronology indicates that the primary source of forearc detritus is the Gangdese magmatic arc which was active from ~150 Ma to 50 Ma. Preliminary double-dated (U-Th/He and U-Pb) zircon crystals from eight samples in ~80 Ma deposits suggest basin exhumation from 30 to 10 Ma. This time span corresponds to ages determined independently for movements occurring along the basin-bounding Great Counter Thrust system. Therefore, we postulate that this fault system was responsible for erosional exhumation of the Xigaze forearc.

  18. The Mud Hills, Mojave Desert, California: Structure, stratigraphy and sedimentology of a rapidly extended terrane

    SciTech Connect

    Ingersoll, R.V.; Devaney, K.A.; Geslin, J.K.; Cavazza, W.; Diamond, D.S.; Jagiello, K.J.; Marsaglia, K.M.; Paylor, E.D. II; Short, P.F. (Univ. of California, Los Angeles, CA (United States). Dept. of Earth and Space Sciences)

    1993-04-01

    The Mud Hills exposes synorogenic breccia (Mud Hills Fm.) deposited during the final stages of crustal extension of the upper plate above the Waterman Hills detachment (20--18 Ma). Previous workers have misinterpreted fault contacts as stratigraphic contacts, and have developed intricate pseudostratigraphy to explain their observations. The authors' detailed mapping, combined with stratigraphic and sedimentologic data, documents that the volcaniclastic Pickhandle Fm. is conformably overlain by the plutoniclastic Mud Hills Fm., with no interfingering. Repetition of these south-dipping lithologic units is due to imbricate, north-dipping listric faults. These relations are demonstrated by the systematic northward v''ing of fault contacts and southward v''ing of stratigraphic contacts. Stratigraphic dip decreases upsection, which is consistent with incremental rotation of basinal strata simultaneously with deposition. Most of the Mud Hills Fm. consists of rock-avalanche breccia and megabreccia derived from granodiorite, which is identical to basement exposed beneath the Pickhandle and Jackhammer Fms. to the north. The Mud Hills Fm. was derived from now-buried granodiorite of a stranded upper-plate block to the south, as demonstrated by northward paleocurrents, facies relations and the presence of fine-grained units close to the presumed master fault (as is typical of half-graben sedimentation). Unconformably overlying the Mud Hills Fm. is the Owl Conglomerate (Barstow Fm.), which has mixed provenance with southward paleocurrents; the Owl Conglomerate was derived from residual highlands after extension ceased. Integration of structural, stratigraphic and sedimentologic information is essential for correct reconstruction of highly extended terranes.

  19. Stratigraphy, Sedimentology, and Depositional History of Gas Hydrate Bearing Sediments Along the Eastern Continental Margin of India and in the Andaman Accretionary Wedge: Results from NGHP Expedition 01

    NASA Astrophysics Data System (ADS)

    Johnson, J. E.; Giosan, L.; Rose, K.; Fraschetti, J.; Nghp Expedition 1, S.

    2007-12-01

    An international ocean drilling effort led by the Indian National Gas Hydrate Research Program (NGHP) and the U.S. Geological Survey to study gas hydrates along the Indian continental margins was completed during the summer of 2006. Drill and core sites documented the presence of gas hydrate along the eastern continental margin of India in the Krishna-Godavari (K-G) and Mahanadi basins, and in the Andaman wedge near Little Andaman Island. 2-D and 3-D seismic data provide the high-resolution structural and stratigraphic context for each of the drill sites. These data combined with detailed lithologic descriptions, multi-sensor core logger (MSCL) measurements, and logging while drilling (LWD) data characterize the sedimentology of the recovered cores and of the in situ stratigraphy at each site. In the K-G basin slope environment, sedimentological description and interpretation of the cores collected from seven sites (up to 300 mbsf) reveals a Quaternary history of sedimentation dominated by dark grey to black colored nannofossil bearing to rich clay and silty clay deposition, likely sourced from the nearby Krishna and Godavari Rivers. Silt to fine sand turbidites (1-5 cm thick) also occur throughout the section as well as visible terrestrial organic material. Foraminifera and coccoliths occur throughout the records but are highly diluted by the terrigenous constituents. Authigenic carbonates, present in fine grained bands and as micronodules (less than 1 cm) to large nodules (greater than 5 cm) are particularly abundant throughout most of recovered stratigraphy and are consistent with the recovery and presence of gas hydrate and other indicators of gas hydrate throughout this region. Sediments recovered from the two sites drilled in the Mahanadi basin to the north are biogenic-rich (foraminifera, coccoliths, diatoms, and radiolaria) clays to oozes and void of turbidites. A volcanic ash bed near the top of the section and volcanic glass bearing intervals deeper in the section are also present. Based on initial biostratigraphy, the age of the recovered sediments spans Late Miocene to recent at these sites. Authigenic carbonates are rare throughout the section and there was less gas hydrate recovered at these sites. At the single site drilled in the Andaman wedge, a long record (nearly 700 m) of carbonate and biosiliceous clays and oozes, punctuated by abundant volcanic ashes, was recovered. Initial biostratigraphy here also suggests a late Miocene to recent record. An extremely deep BSR (610 mbsf) indicates a thick zone of potential gas hydrate stability at this site; gas hydrate was recovered throughout this interval and often associated with volcanic ash beds. Post-cruise XRD, XRF, organic and inorganic carbon, and other geochemical measurements will help to further characterize the stratigraphy at all of these sites.

  20. Stratigraphy, sedimentology and paleontology of lower Eocene San Jose formation, central San Juan basin, New Mexico

    SciTech Connect

    Lucas, S.G.; Smith, L.N. (New Mexico Museum of Natural History, Albuquerque (USA))

    1989-09-01

    The lower Eocene San Jose Formation in the central portion of the San Juan basin (Gobernador-Vigas Canyon area) consists of the Cuba Mesa, Regina, Llaves, and Tapicitos Members. Well log data indicate that, from its 100-m thickness, the Cuba Mesa Member thins toward the basin center and pinches out to the northeast by lat. 36{degree}40'N, long. 107{degree}19'W. The Regina Member has the most extensive outcrops in the central basin, and it decreases in sandstone/mud rock ratio to the north. The Llaves and Tapicitos Members occur only at the highest elevations, are thin due to erosion, and are not mappable as separate units. Well log data and 1,275 m of measured stratigraphic section in the Regina, Llaves, and Tapicitos Members indicate these strata are composed of approximately 35% medium to coarse-grained sandstone and 65% fine-grained sandstone and mud rock. Sedimentology and sediment-dispersal patterns indicate deposition by generally south-flowing streams that had sources to the northwest, northeast, and east. Low-sinuosity, sand-bedded, braided( ) streams shifted laterally across about 1 km-wide channel belts to produce sheet sandstones that are prominent throughout the San Jose Formation. Subtle levees separated channel environments from floodplain and local lacustrine areas. Avulsion relocated channels periodically to areas on the floodplain, resulting in the typically disconnected sheet sandstones within muddy overbank deposits of the Regina Member.

  1. Sedimentology and stratigraphy of tidal sand ridges southwest Florida inner shelf

    SciTech Connect

    Davis, R.A. Jr.; Klay, J.; Jewell, P. (Univ. of South Florida, Tampa (United States))

    1993-01-01

    Detailed investigation of linear shelf sand ridges located off the southwest coast of Florida shows them to be tide-dominated sand bodies. These ridges are remarkably similar to the large sand ridges of the North Sea, and they have abundant apparent analogs in the stratigraphic record, many of which are important petroleum producers. The Florida ridges are asymmetric in profile, about 10 km long, 1 km wide, with relief of 3-4 m with the adjacent sea bed. Extensive tidal current monitoring, sediment distribution patterns and side scan sonar surveys permit characterizing their morphodynamics. Tidal currents show distinct bidirectional patterns with speeds up to 70 cm/s. There is slight flood-dominance, and currents show much higher velocities in the troughs as compared to the crests of the ridges. Megaripples and sand waves are widespread and migrate obliquely across the ridges at opposite directions on the gentle and steep side of the ridge. Shallow, high-resolution seismic data and 39 vibracores din the area of the ridges show a consistent sequence characterized by three ascending Holocene lithofacies: (1) muddy quartz sand with limestone clasts; (2) bioturbated muddy shelly quartz sand; and (3) well-sorted, cross-stratified quartz sand that characterizes the sand ridges themselves. Each of the tidal sand ridges displays a coarsening-upward sequence of fine, well-sorted sand. Small-scale, multidirectional, cross stratification dominates the stratigraphy of the cores in this facies, but megaripple cross stratification is also present. All data indicate that these tidal ridges are good modern analogs for many of the shelf sand bodies in the ancient record, especially the Mesozoic of the mid-continent area.

  2. Sedimentology, stratigraphy, and micropalaeontology of the Upper Triassic reefal series in Eastern Sulawesi (Indonesia)

    Microsoft Academic Search

    Rossana Martini; Daniel Vachard; Louisette Zaninetti; Simonetta Cirilli; Jean-Jacques Cornée; Bernard Lathuilière; Michel Villeneuve

    1997-01-01

    An Upper Triassic (Upper Norian-Rhaetian) carbonate complex, composed of open marine to reefal deposits, has been investigated for the first time in Eastern Sulawesi. The age is based on the occurrence of benthic foraminifera, and also of the Upper Sevatian to Rhaetian conodont Misikella posthernsteini Kozur and Mock. Palynological assemblages contain Upper Triassic-Lower Jurassic palynomorphs. The scleractinian coral Retiophyllia seranica

  3. Sedimentology and petroleum geology

    SciTech Connect

    Bjorlykke, K.O. (Oslo Univ. (Norway))

    1989-01-01

    This book presents an introduction to sedimentology as well as petroleum geology. It integrates both subjects, which are closely related but mostly treated separately. The author covers the basic aspects of sedimentology, sedimentary geochemistry and diagenesis. Principles of stratigraphy, seismic stratigraphy and basin modelling forms the base for the part on petroleum geology. Subjects discussed include the composition of kerogen and hydrocarbons, theories of migration and trapping of hydrocarbons and properties of reservoir rocks. Introductions to well logging and production geology are given.

  4. Sedimentology and stratigraphy of Cenozoic deposits in the Ka??zman-Tuzluca Basin, northeastern Turkey

    NASA Astrophysics Data System (ADS)

    Varol, Baki; ?en, ?evket; Ayy?ld?z, Turhan; Sözeri, Koray; Karaka?, Zehra; Métais, Grégoire

    2015-06-01

    The Ka??zman-Tuzluca Basin is located in the northeastern Anatolia, to the east of the intersection point (near Karl?ova) of the major North and East Anatolian Fault systems. This intermontane basin displays a thick sequence (over 2000 m) of mostly terrestrial deposits represented by repetitive alternations of the lake and fluvial environments ranging from ?Late Eocene/Oligocene to Middle/? Late Miocene. A marine incursion only mappable in the southeastern margin of the basin deposited limestones and sandy limestones rich in marine mollusks and nummulites, in particular N. fichteli that constrain an Early Oligocene age for this marine unit (Ka?an Fm). The terrestrial basin-fill deposits show different thicknesses throughout the basin due to irregular bottom topography and tectonic configuration of the basin margins. The thickest deposits were accumulated along the different margins of the basin, which received high quantities of siliciclastics from meandering river, alluvial and coastal fans, fan delta/Gilbert-type delta and wave-worked fluvial delta. Climate changes have also driven the development of lake environments during distinct depositional periods. Siliciclastic-dominated overfilled lakes (Hal?k??lak and K?z?lkaya formations) and chemical-dominated underfilled lakes (Turabi and Tuzluca formations) were formed. They have been also classified as "Newark-type" and "Fundy-type" lakes, respectively. Fluvial systems evolved from high-energy meandering rivers deposited under humid climate (Güngören Formation) to low-energy meandering rivers resulted from arid and semiarid climates (Çincavat Formation). The transitional intervals from ephemeral river-dry mudflat (Çincavat Formation) to saline pan/lake (Tuzluca Formation) indicate wadi-sand flat-playa fluvial systems. The chronostratigraphic constrains of the entire sequence remain poor and so far solely based on vertebrate fossil assemblages. The evaporitic Tuzluca Formation would be Middle Miocene in age due to its stratigraphic position over the Çincavat Formation.

  5. Name: _____________________________________ Sedimentology & Stratigraphy

    E-print Network

    Wilson, Mark A.

    (just one). Please include a labeled map-view diagram (as viewed from the air) showing the wind.0 gm/cm3) d = grain diameter g = gravitational constant (981 cm/sec2) µ = fluid viscosity (water is 0 length, such as depth = fluid density (water is 1.0 gm/cm3) µ = fluid viscosity (water is 0.01 gm

  6. University of Minnesota: Sedimentology Group

    NSDL National Science Digital Library

    The sedimentology group at the University of Minnesota presents its research in earthscape processes at this website. Visitors can find out about the goals, results, and publications of three main research areas: experimental stratigraphy and landscape evolution, theoretical sedimentology and stratigraphy, and river dynamics. The site offers downloads for many of the group's publications. Visitors discover the latest sedimentology-related news. While the links Useful Things and Links do not contain information at this time, users can still learn about the work of sedimentologists at this website.

  7. Constraining the sedimentology and stratigraphy of submarine intraslope lobe deposits using exhumed examples from the Karoo Basin, South Africa

    NASA Astrophysics Data System (ADS)

    Spychala, Y. T.; Hodgson, D. M.; Flint, S. S.; Mountney, N. P.

    2015-06-01

    Intraslope lobe deposits provide a process record of the infill of accommodation on submarine slopes and their recognition enables the accurate reconstruction of the stratigraphic evolution of submarine slope systems. Extensive exposures of discrete sand-prone packages in Units D/E and E, Fort Brown Formation, Karoo Basin, South Africa, permit analysis of the sedimentology and stacking patterns of three intraslope lobe complexes and their palaeogeographic reconstruction via bed-scale analysis and physical correlation of key stratal surfaces. The sand-prone packages comprise tabular, aggradationally to slightly compensationally stacked lobe deposits with constituent facies associations that can be attributed to lobe axis, lobe off-axis, lobe-fringe and distal lobe-fringe environments. Locally, intraslope lobe deposits are incised by low aspect ratio channels that mark basinward progradation of the deepwater system. The origin of accommodation on the slope for lobe deposition is interpreted to be due to differential compaction or healing of scars from mass wasting processes. The stacking patterns and sedimentary facies arrangement identified in this study are distinct from those of more commonly recognized basin-floor lobe deposits, thereby enabling the establishment of recognition criteria for intraslope lobe deposits in other less well exposed and studied fine-grained systems. Compared to basin floor lobes, intraslope lobes are smaller in volume, influenced by higher degrees of confinement, and tend to show aggradational stacking patterns.

  8. Stratigraphy and sedimentology of pre-late Wisconsin catastrophic glacial flood sediments, western Walla Walla Valley, Washington

    SciTech Connect

    Robertson, J.L.; Spencer, P.K. (Whitman College, Walla Walla, WA (United States). Geology Dept.)

    1993-04-01

    The Cummins Bridge site in the western Walla Walla Valley exhibits clear evidence for pre-late Wisconsin catastrophic glacial flooding. The section consists of an unstratified, poorly sorted diamict with angular basaltic clasts in a matrix of sand and silt, and a large number of well-rounded clasts of exotic lithology in the coarse fraction, gradationally overlain by a coarse, angular gravel that is matrix poor and exotic-free; this unit grades upward into a matrix-rich diamict with a well-developed caliche in the upper portion. Above this is a sand and silt unit showing vague cross-stratification, lamination, and graded beds; this unit may represent local temporary ponding of the ancestral drainage. Overlying this on a pronounced erosional surface are rhythmically stratified sand-to-salt beds assigned to the late Wisconsin Toughet Beds. The section is capped by a thin bed of Holocene loess. Stratigraphic and sedimentologic criteria suggest that the lowermost units represent an indirect record of catastrophic glacial flooding. Flood sediments were deposited on an adjacent topographic high and subsequently mass-wasted via mudflow into their present position. Normal fluvial processes alternated with mass-wasting events to concentrate the angular, matrix-poor basaltic gravel. The lower diamict shows characteristics similar to documented pre-late Wisconsin catastrophic flood sediments at a nearby site, including rounded exotic clasts, angular basaltic clasts, lack of stratification, and poor sorting. The two sites may represent the same pre-late Wisconsin flood event.

  9. Stratigraphy and Isotope Ages of Lunar Geologic Units: Chronological Standard for the Inner Solar System

    Microsoft Academic Search

    D. Stöffler; G. Ryder

    2001-01-01

    The absolute ages of cratered surfaces in the inner solar system, including Mars, are derived by extrapolation from the impact flux curve for the Moon which has been calibrated on the basis of absolute ages of lunar samples. We reevaluate the lunar flux curve using isotope ages of lunar samples and the latest views on the lunar stratigraphy and the

  10. Sedimentology and Stratigraphy Architecture of the late Pleistocene-Holocene Succession of the Gargaresh Formation, Subratah Basin, NW Libya

    NASA Astrophysics Data System (ADS)

    Hlal, Osama; Bennur, Sami

    2014-05-01

    Gargaresh Formation outcrops is comprises the outcrops between the Misurata (N32o22'18'' E15o12'03'') to the Tripoli(N32o 51'10'' E13o 03'22'') areas is represented by prominent carbonate aeolianite exposed in extensive outcrops along the NW Libyan shoreline. Gargaresh Formation outcrops comprises two Members an upper Kaam Member of Aeolian origin and a lower Karrot Member of marine origin. The study of the Gargaresh Formation can provide useful information on reconstructions of Late Pleistocene-Holocene history of NW Libya and new insights on palaeogeography. It is forming low ridges and cliffs along the coastline of NW Libya and occurs as cliffs continuously attached to the sea tide, and occasionally interrupted by broad wadis or deep-cut embayment. The Gargaresh Formation sediments are dominated by calcarenites with skeletal marine fauna and non-skeletal grains of lithoclasts, aggregate, with oolites. In addition, these rocks are characterized by very well aeolian controlling factors represented by wind blown sediments such as large scale cross lamination (aeolianite) . The majority of palaeocurrent direction was to SE, on the other hand the dune migration was SE also. The sediments of Gargaresh Formation outcrops from Misurata to Tripoli NW Libya mostly allochthonous except the paleosols red-brown unit. Most of its fossils are thanatoconoses. Gargaresh Formation sediments shows that the original aragonite composition of pelecypoda and gastropods fragments are mostly preserved, but partly transformed into granular calcite as pendulous (meniscus) cement texture in response to meteoric fresh-water. Keywords: Sedimentology; Stratigraphic architecture; Aeolian origin; marine origin; Calcarenites; Late Pleistocene-Holocene

  11. Taconic foreland basin evolution: Sedimentology and cement stratigraphy of the Black River Group limestones in the Champlain Basin

    SciTech Connect

    Bechtel, S.C.; Mehrtens, C.J. (Univ. of Vermont, Burlington, VT (United States). Geology Dept.)

    1993-03-01

    The Black River Group (Middle Ordovician, Mohawkian Series) limestones in the Champlain Basin record the transition between the shallow deposits of the underlying Chazy Group limestones and the shale-limestone couplets of the overlying Trenton Group which record rapid deepening of the foreland basin. The Black River Group was deposited in a subsiding foreland basin during the early stages of the Taconic Orogeny. Syn-depositional block faulting as a result of thrust loading has been demonstrated to affect Chazy and Trenton Group deposition. Abrupt lithofacies changes within the Black River Group record the dynamic bathymetry present in the Champlain Basin during its deposition. The Black River Group helps refine the timing of extensional block faulting during the Taconic Orogeny. The Black River Group in the Champlain Basin is a relatively thin unit, approximately 80 feet thick at Crown Point, New York. Exposures between Crown Point, NY and South Hero Island, VT record deposition of the Black River Group limestones in a protected lagoonal environment, with an evolving fringing pellet shoal barrier complex. Eight lithofacies are defined, grading from a basal sandstone and/or a sandy dolomite, to a micrite to biomicrite, to an intra-pelsparite of a shoal environment. Intraclast horizons and broken, rounded marine allochems suggest the influence of storm activity as a modifier of depositional history. Rapid deepenings into the normal marine subtidal environment, as well as micro-karst textures and fossil beach rock exposures are interpreted to represent sudden bas level changes, possibly from syndepositional block fault movement. Although dynamic bathymetry influences the stratigraphy within the Black River Group, a macro-scale deepening upwards on a formation scale is present, representing subsidence of the foreland basin.

  12. Ages and stratigraphy of mare basalts in Oceanus Procellarum, Mare Nubium, Mare Cognitum, and Mare Insularum

    E-print Network

    Head III, James William

    Ages and stratigraphy of mare basalts in Oceanus Procellarum, Mare Nubium, Mare Cognitum, and Mare July 2003. [1] Accurate estimates of mare basalt ages are necessary to place constraints on the duration and the flux of lunar volcanism as well as on the petrogenesis of lunar mare basalts

  13. Origin and paleoclimatic significance of late Quaternary loess in Nebraska: Evidence from stratigraphy, chronology, sedimentology, and geochemistry

    USGS Publications Warehouse

    Muhs, Daniel R.; Bettis, E. Arthur, III; Aleinikoff, John N.; McGeehin, John P.; Beann, Jossh; Skipp, Gary; Marshall, Brian D.; Roberts, Helen M.; Johnson, William C.; Benton, Rachel

    2008-01-01

    Loess is one of the most extensive surficial geologic deposits in midcontinental North America, particularly in the central Great Plains region of Nebraska. Last-glacial-age loess (Peoria Loess) reaches its greatest known thickness in the world in this area. New stratigraphic, geochronologic, mineralogic, and geochemical data yield information about the age and provenance of Peoria Loess, as well as evaluation of recent climate models. Sixteen new radiocarbon ages and recently acquired optically stimulated luminescence ages indicate that Peoria Loess deposition in Nebraska occurred between ca. 25,000 cal yr B.P. and ca. 13,000 cal yr B.P. After ca. 13,000 cal yr B.P. a period of pedogenesis began, represented by the dark, prominent Brady Soil. At some localities, further loess deposition was minimal. At other localities, sometime after ca. 11,000 cal yr B.P., there were additional episodes of loess deposition (Bignell Loess) intermittently throughout the Holocene. The spatial variability of particle size abundances in Peoria Loess shows a northwest-to-southeast fining in Nebraska, consistent with maps of previous workers that show a northwest-to-southeast thinning of loess. These observations indicate that paleowinds that deposited the loess were from the west or northwest and that the source or sources of Peoria Loess lay to the west or northwest. New mineralogical and geochemical data indicate that the most important sources of loess were likely Tertiary siltstones of the White River and Arikaree Groups, silt facies of Pliocene eolian sediments, and small contributions from Pierre Shale. It is likely that fine-grained silts were transported episodically through the Nebraska Sand Hills from Tertiary and Cretaceous bedrock sources to the north, in agreement with a model presented recently. The identification of Tertiary siltstones and silts as the primary sources of loess is consistent with isotopic data presented in a companion paper. Contributions of glaciogenic silt from the Platte and Missouri Rivers were limited to loess zones close to the valleys of those drainages. An earlier computer-based model of global dust generation during the last glacial period did not identify the Great Plains of North America as a significant source of nonglaciogenic eolian silt. However, a refined version of this model does simulate this region as a significant non-glacial dust source during the last glacial period, in good agreement with the results presented here.

  14. Sedimentology and petroleum geology

    SciTech Connect

    Bjorlykke, K.

    1989-01-01

    In this introduction to sedimentology and petroleum geology the subjects, which are closely related but mostly treated separately, are integrated. The first part covers the basic aspects of sedimentology, sedimentary geochemistry and diagenesis, including brief discussions of flow in rivers and channels, types of sediment transport, lake and river deposits, deltas (river-dominated, tide-dominated, and wave-dominated) and the water budget. Principles of stratigraphy, seismic stratigraphy and basin modeling form the basis for the last part on petroleum geology. Here subjects include the composition of kerogen and hydrocarbons, theories of migration and trapping of hydrocarbons and properties of reservoir rocks. Finally, short introductions to well logging and production geology are given.

  15. Mars north polar deposits: stratigraphy, age, and geodynamical response

    USGS Publications Warehouse

    Phillips, R.J.; Zuber, M.T.; Smrekar, S.E.; Mellon, M.T.; Head, J.W.; Tanaka, K.L.; Putzig, N.E.; Milkovich, S.M.; Campbell, B.A.; Plaut, J.J.; Safaeinili, A.; Seu, R.; Biccari, D.; Carter, L.M.; Picardi, G.; Orosei, R.; Surdas, Mohit P.; Heggy, E.; Zurek, R.W.; Egan, A.F.; Giacomoni, E.; Russo, F.; Cutigni, M.; Pettinelli, E.; Holt, J.W.; Leuschen, C.J.; Marinangeli, L.

    2008-01-01

    The Shallow Radar (SHARAD) on the Mars Reconnaissance Orbiter has imaged the internal stratigraphy of the north polar layered deposits of Mars. Radar reflections within the deposits reveal a laterally continuous deposition of layers, which typically consist of four packets of finely spaced reflectors separated by homogeneous interpacket regions of nearly pure ice. The packet/interpacket structure can be explained by approximately million-year periodicities in Mars' obliquity or orbital eccentricity. The observed ???100-meter maximum deflection of the underlying substrate in response to the ice load implies that the present-day thickness of an equilibrium elastic lithosphere is greater than 300 kilometers. Alternatively, the response to the load may be in a transient state controlled by mantle viscosity. Both scenarios probably require that Mars has a subchondritic abundance of heat-producing elements.

  16. Lunar impact basins: Stratigraphy, sequence and ages from superposed impact crater populations measured from Lunar Orbiter Laser Altimeter (LOLA) data

    E-print Network

    Fassett, C. I.

    Impact basin formation is a fundamental process in the evolution of the Moon and records the history of impactors in the early solar system. In order to assess the stratigraphy, sequence, and ages of impact basins and the ...

  17. Initial sedimentology, geocronology and oxygen isotope stratigraphy of a new core from Pretty Lake, Indiana: Exploring Midwestern hydroclimate during the last 2000 years

    NASA Astrophysics Data System (ADS)

    Albert, A.; Bird, B. W.; Gilhooly, W., III; Stamps, L. G.; Rudloff, O. M.; Steinman, B. A.; Lowell, T. V.

    2014-12-01

    Isotope-based hydroclimate records from the mid-continental United States that span the late Holocene with sub-decadal resolution are rare. As a result, the relationship between temperature and hydroclimate for this region is not well constrained. Pollen-based temperature reconstructions from North America suggest that the Medieval Climate Anomaly (MCA; 650 to 1050 CE) was warmer than the Little Ice Age (LIA; 1550 to 1850 CE), but that both were cooler than the current warm period (CWP; last 100 years). It has further been suggested that much of the mid-continental US experienced drought during the MCA and pluvial conditions during the LIA. This is supported by modern correlations between seasonal temperatures and precipitation, which are anti-correlated for much of the Midwest; however, for portions of the continental core, which includes the study region, the opposite relationship exists between temperature and precipitation (i.e., warmer is wetter and colder is drier). Within the context of this and previous paleoclimate work in the Midwest, including at Pretty Lake, we present initial geochronology, sedimentology and oxygen isotopic results from a new 12 m composite core from Pretty Lake, a 25 m deep kettle lake in LaGrange County, northeastern Indiana. Here we focus on the last 2000 years of the 16,000-year record in order to explore hydroclimate variability in response to temperature anomalies during the MCA and LIA. Pretty Lake is well suited for this type of investigation because the closed surface hydrology of the lake basin renders it sensitive to evaporation. This is reflected in oxygen isotope (?18O) measurements of surface waters from the lake, which show that it is approximately 4‰ higher than meteoric precipitation and the surface waters of nearby, hydrologically-open Martin Lake. High-resolution down core ?18O measurements, therefore hold tremendous potential for reconstructing regional hydroclimate during the last 2000 years, particularly when combined with isotopic records of local precipitation and modeling approaches.

  18. Stratigraphy, sedimentology and diagenetic evolution of the Lapur Sandstone in northern Kenya: Implications for oil exploration of the Meso-Cenozoic Turkana depression

    NASA Astrophysics Data System (ADS)

    Tiercelin, Jean-Jacques; Potdevin, Jean-Luc; Thuo, Peter Kinyua; Abdelfettah, Yassine; Schuster, Mathieu; Bourquin, Sylvie; Bellon, Hervé; Clément, Jean-Philippe; Guillou, Hervé; Nalpas, Thierry; Ruffet, Gilles

    2012-08-01

    The northern Turkana region of northwestern Kenya forms the intersection between two major rift systems in Africa, the Cretaceous-Paleogene Central African Rift System (CARS), and the eastern arm of the Paleogene-Present East African Rift System (EARS). The southern Sudanese oil-rich rift basins form part of the CARS, and their extension into the Anza Rift in northeastern Kenya makes the area of northern Turkana an important target for oil exploration. Limited past exploration activity in the area leaves the study of surface outcrops as the main avenue for understanding the reservoir potential of the fluvial deposits of these rift systems. The outcrops of these potential reservoirs, collectively referred to as "Turkana Grits" in the past, are represented on the western side of Lake Turkana by the Lapur Sandstone in the north, and by other grit formations in the central and southern parts of the basin. Isotopic age determinations on the basal parts of the "Turkana Volcanics" that overlie the Lapur Sandstone have enabled the precise dating of the upper parts of the LS at between 35 and 37 Ma, while the lower part of the formation near the contact with the underlying Precambrian basement is estimated as Upper Cretaceous (Turonian-early Campanian), based on the discovery of dinosaur and other reptilian fauna. Detailed lithological logging, coupled with subsequent petrographic and sedimentological studies, have enabled the determination of the depositional environments and the diagenetic evolution of the Lapur Sandstone. The basal and uppermost parts of the formation are interpreted as distal alluvial fan environments possibly connected to the last stages of rifting characterizing the Central African Rift System. The middle part of the Lapur Sandstone corresponds to a wide braided fluvial system that can be compared to fluvial episodes of Late Cretaceous age in the Sudan region, associated to major palaeogeographical changes in northern Africa. The nearly abrupt disappearance of the Lapur upper fan system relates to the deposition of the "Turkana Volcanics" from Late Eocene, possibly as a consequence of the emplacement of the Afar Plume at 45-35 Ma. In terms of diagenesis, the main cement material at the base of the Lapur Sandstone is calcite, whereas at the middle of the formation, hematite becomes the dominant cement, and at the topmost section, kaolin cement dominates. The diagenetic evolution of the sandstones has been favourable to the retention of adequate primary intergranular porosity and the creation of secondary intragranular dissolution porosity, mainly through feldspar dissolution, and thus preserving the reservoir potential of the Lapur Sandstone. The reservoir characteristics, such as the porosity and cementation style, of the Lapur Sandstone are comparable to those of the fluvial sandstone reservoirs of the southern Sudan oil fields and this should positively contribute to the overall petroleum potential of the northern Turkana region. Though the northern Turkana area has remained largely unexplored, it is hoped that the demonstration of the presence of reasonably good reservoir quality sandstones in the Lapur Sandstone will serve to encourage further interest in hydrocarbon exploration in the Turkana area.

  19. Principles of lake sedimentology

    SciTech Connect

    Janasson, L.

    1983-01-01

    This book presents a comprehensive outline on the basic sedimentological principles for lakes, and focuses on environmental aspects and matters related to lake management and control-on lake ecology rather than lake geology. This is a guide for those who plan, perform and evaluate lake sedimentological investigations. Contents abridged: Lake types and sediment types. Sedimentation in lakes and water dynamics. Lake bottom dynamics. Sediment dynamics and sediment age. Sediments in aquatic pollution control programmes. Subject index.

  20. Edgar_Answers to student questions 414.pdf Student questions: Lauren Edgar colloquium on "Martian Sedimentology as Revealed by the

    E-print Network

    Rhoads, James

    Sedimentology as Revealed by the Curiosity Rover" 3/26/14 Question 1: How are the studies that you've done of the same kinds of instruments to investigate the sedimentology and stratigraphy at each landing site

  1. BGS School of Field Geology An introduction to Sequence Stratigraphy

    E-print Network

    Stratigraphy in the field.The course also provides the opportunity to gain experience of clastic sedimentology stratigraphic approaches to the division of rock successions, sedimentology of Cretaceous alluvial to marine siliciclastic rocks, sedimentology of Permian to Cretaceous alluvial, red bed successions, including palaeosols

  2. Reservoir sedimentology

    SciTech Connect

    Tillman, R.W.; Weber, K.J.

    1987-01-01

    Collection of papers focuses on sedimentology of siliclastic sandstone and carbonate reservoirs. Shows how detailed sedimentologic descriptions, when combined with engineering and other subsurface geologic techniques, yield reservoir models useful for reservoir management during field development and secondary and tertiary EOR. Sections cover marine sandstone and carbonate reservoirs; shoreline, deltaic, and fluvial reservoirs; and eolian reservoirs. References follow each paper.

  3. Evaporite sedimentology

    SciTech Connect

    Warren, J.K.

    1989-01-01

    The purpose of this book is to introduce the sedimentology of evaporites and to demonstrate how sedimentological principles can be applied to ancient evaporites. It includes chapter on: Sabkhas; marine and continental; Shallow water evaporites: lakes, salinas and platforms; and deep water evaporites.

  4. Integrating Facies Analysis, Terrestrial Sequence Stratigraphy, and the First Detrital Zircon (U-Pb) Ages of the Twist Gulch Formation, Utah, USA: Constraining Paleogeography and

    E-print Network

    Seamons, Kent E.

    Integrating Facies Analysis, Terrestrial Sequence Stratigraphy, and the First Detrital Zircon (U Zircon (U- Pb) Ages of the Twist Gulch Formation, Utah, USA: Constraining Paleogeography stratigraphy, and detrital zircon (U-Pb) ages to improve paleogeographic reconstructions as well as identify

  5. Stratigraphy and age of the Cappadocia ignimbrites, Turkey: reconciling field constraints with paleontologic,

    E-print Network

    with paleontologic, radiochronologic, geochemical and paleomagnetic data J.-L. Le Penneca, , A. Temelb , J Valibaba Tepe ignimbrite. Keywords: ignimbrite; geochronology; paleontology; stratigraphy; rock magnetism

  6. A re-evaluation of the stratigraphy and sedimentology of the Day Point Formation (Chazy Group): A new look at old reefs

    SciTech Connect

    Falkenberg, J.; Mehrtens, C.J. (Vermont Univ., Burlington, VT (United States). Dept. of Geology)

    1993-03-01

    The Day Point Formation (Chazy Group, Middle Ordovician) outcrops in the Champlain Valley of New York and Vermont. The stratigraphy of the Day Point Formation is complex, containing lithologic sequences that are unique at different localities around the Champlain Valley. The formation exhibits complex lateral interfingering of seven lithofacies: (1) Highly bioturbated sandstone with symmetrical and bifurcating ripples. (2) Bioturbated, brachiopod rich, wackestone facies. (3) Planar cross-bedded, interlayered sand and sandy packstone. (4) Interlayered sand and shale grading into sand and limestone layers. (5) Grainstone which, at some localities, contains mound-shaped bryozoan reefs, at other localities thin non-reefal sheet-like layers are present. The grainstone also has planar laminated and cross stratified beds. (6) Fine-grained, calcareous sandstone with planar and herringbone cross bedding, which in places contains small bryozoan reefs and thin sheet-reefs. (7) Planar cross bedded packstone containing bryozoan reefs and thin sheet-like non-reefal layers. The thin reefal layers are found where the mound-shaped reefs are absent. The sand units are found only in the lower portion of the Day Point Formation. The bryozoan reefs and non-reefal layers are associated with the sand beds in the lower portion of the Day Point Formation, and either live within the sand or on top of it. The bryozoans that form the non-reefal layers, found in the limestones, are contained within thin layers of sand. In contrast, no sand is found in the upper section of the Day Point Formation, yet the bryozoan reefs flourish.

  7. STRATIGRAPHY OF COUNTER-POINT-BAR AND EDDY-ACCRETION DEPOSITS IN LOW-ENERGY MEANDER BELTS OF THE PEACE-ATHABASCA

    E-print Network

    Sedimentologic Solutions, 2104 3rd Avenue NW, Calgary, AB, T2N 0K4, Canada DALE A. LECKIE, AND MILOVAN FUSTIC 801 little research attention, and their stratigraphy and sedimentology is poorly understood in modern-point-bar deposits (CPBD) (Smith et al., 2009). Smith et al. (2009) examined the stratigraphy, sedimentology

  8. AGE AND ORIGIN OF THE CHICXULUB IMPACTAND SANDSTONE COMPLEX, BRAZOS RIVER, TEXAS: EVIDENCE FROM LITHOSTRATIGRAPHY AND

    E-print Network

    Keller, Gerta

    LITHOSTRATIGRAPHY AND SEDIMENTOLOGY THIERRY ADATTE Geological and Paleontological Institute, Anthropole, CH-1015 on the lithology, sedimentology, mineralogy, and biostratigraphy of upper Maastrichtian to lower Danian boundary, sedimentology, sequence stratigraphy, mineralogy, organic matter, sea level, depositional environment, incised

  9. Analytical sedimentology

    SciTech Connect

    Lewis, D.W. (Univ. of Canterbury, Christchurch (New Zealand). Dept. of Geology); McConchie, D.M. (Southern Cross Univ., New South Wales (Australia). Centre for Coastal Management)

    1994-01-01

    Both a self instruction manual and a cookbook'' guide to field and laboratory analytical procedures, this book provides an essential reference for non-specialists. With a minimum of mathematics and virtually no theory, it introduces practitioners to easy, inexpensive options for sample collection and preparation, data acquisition, analytic protocols, result interpretation and verification techniques. This step-by-step guide considers the advantages and limitations of different procedures, discusses safety and troubleshooting, and explains support skills like mapping, photography and report writing. It also offers managers, off-site engineers and others using sediments data a quick course in commissioning studies and making the most of the reports. This manual will answer the growing needs of practitioners in the field, either alone or accompanied by Practical Sedimentology, which surveys the science of sedimentology and provides a basic overview of the principles behind the applications.

  10. Stratigraphy and sedimentology of the Niger Delta

    NASA Astrophysics Data System (ADS)

    Reijers, T. J. A.

    2011-09-01

    During the Cenozoic, until the Middle Miocene, the Niger Delta grew through pulses of sedimentation over an oceanward-dipping continental basement into the Gulf of Guinea; thereafter progradation took place over a landward-dipping oceanic basement. A 12,000 m thick succession of overall regressive, offlapping sediments resulted that is composed of three diachronous siliciclastic units: the deep-marine pro-delta Akata Group, the shallow-marine delta-front Agbada Group and the continental, delta-top Benin Group. Regionally, sediment dispersal was controlled by marine transgressive/regressive cycles related to eustatic sea-level changes with varying duration. Differential subsidence locally influenced sediment accumulation. Collectively, these controls resulted in eleven chronostratigraphically confined delta-wide mega-sequences with considerable internal lithological variation. The various sea-level cycles were in or out of phase with each other and with local subsidence, and interfered with each other and thus influenced the depositional processes. At the high inflection points of the long-term eustatic sea-level curve, floodings took place that resulted in delta-wide shale markers. At the low inflection points, erosional channels were formed that are often associated, downdip, with turbidites in low-stand sediments (LSTs). The megasequences contain regional transgressive claystone units (TST) followed by a range of heterogeneous fine-to-coarse progradational or aggradational siliciclastic (para)sequence sets formed during sea-level high-stand (HST). An updated biostratigraphic scheme for the Niger Delta is presented. It also updates a sedimentation model that takes into consideration local and delta-wide effects of sea-level cyclicity and delta tectonics. Megasequences were formed over time intervals of ~5 Ma within individual accurate megastructures that laterally linked into depobelts. The megasequences form the time-stratigraphic frame of the delta and are the backbone for the new delta-wide lithostratigraphy proposed here. Such a new lithostratigraphy is badly needed, in particular because of the vigorous new activity in the offshore part of the Niger Delta (not covered in this contribution). There, as well as in the onshore part of the delta, the traditional lithostratigraphic subdivision of the Cenozoic Niger Delta section into three formations is insufficient for optimum stratigraphic application; moreover, the various informal subdivisions that have been proposed over time are inconsistent.

  11. Kandik basin stratigraphy, sedimentology, and structure

    SciTech Connect

    Wiley, T.J.; Howell, D.G.; Kauffman-Linam, L.; Boundy-Sanders, S.; Murray, R.W.; Jones, D.L.

    1987-05-01

    East-central Alaska's Kandik basin is a structural remnant of a larger Permian to Cretaceous basin. Permian shallow-water Tahkandit Limestone and Step Conglomerate at the base of the sequence rest unconformably on Paleozoic chert-pebble conglomerate, siliceous shale, and limestone. These Permian rocks are overlain by Triassic to Lower Cretaceous open-ocean Glenn Shale, which grades upward into Lower Cretaceous (Valanginian) hummocky cross-bedded (outer shelf to upper slope) Keenan Quartzite. The quartzite grades upward into fine-grained north-northeast-flowing turbidites of the Biederman Argillite (undated). East-northeast-flowing pebbly turbidites of the Kathul Graywacke (undated) overlie Biederman strata. Locally, Cretaceous (Albian and younger) through Paleogene nonmarine rocks unconformably overlie the Kandik basin sequence. The Mesozoic part of the sequence is similar to that of Manley basin, northwest Yukon Territory, and much of the North Slope. East-directed flow for Kandik basin strata may require paleogeographic reconstructions involving local to large-scale palinspastic rotations or a western source of chert detritus. Deformation of the Mesozoic sequence in Kandik basin west of the US-Canada border shows northwest-southeast shortening. Shaly units are tightly folded with well-developed cleavage striking northeast. Strikes of beds swing from northeast to east in the extreme southwestern part of the basin, suggesting clockwise rotation. Thrust faults, reverse faults, and fold axes trend east to northeast; normal faults trend northwest. These relations are all consistent with, and probably are closely related to, right slip on the west-northwest-trending Tintina fault.

  12. Mars Stratigraphy Mission

    NASA Technical Reports Server (NTRS)

    Budney, C. J.; Miller, S. L.; Cutts, J. A.

    2000-01-01

    The Mars Stratigraphy Mission lands a rover on the surface of Mars which descends down a cliff in Valles Marineris to study the stratigraphy. The rover carries a unique complement of instruments to analyze and age-date materials encountered during descent past 2 km of strata. The science objective for the Mars Stratigraphy Mission is to identify the geologic history of the layered deposits in the Valles Marineris region of Mars. This includes constraining the time interval for formation of these deposits by measuring the ages of various layers and determining the origin of the deposits (volcanic or sedimentary) by measuring their composition and imaging their morphology.

  13. Ninth international congress on Carboniferous stratigraphy and geology. Proceedings, volume 3. Neuvieme congres international de stratigraphie et de geologie du Carbonifere. Compte rendu, volume 3

    SciTech Connect

    Geldsetzer, H.H.J.; Nassichuk, W.W.; Belt, E.S.; Macqueen, R.W.

    1984-01-01

    Papers were presented on the Carboniferous stratigraphy of the Atlantic Coast basins, on paleogeography and paleotectonics and on sedimentology and geochemistry. A total of 14 papers concerning coal have been abstracted separately. Papers are in English or in French.

  14. The role of U-Pb ages of detrital zircons in sedimentology-An alarming case study for the impact of sampling for provenance interpretation

    NASA Astrophysics Data System (ADS)

    Zimmermann, Udo; Andersen, Tom; Madland, Merete Vadla; Larsen, Ingrid Skipenes

    2015-05-01

    U-Pb ages on detrital zircons are often utilised for stratigraphic and paleogeographic interpretations and correlation. Sampling is carried out in such a way that the samples are representative for a formation, and then used for provenance identification and/or defining a maximum time limit for deposition. Is it possible that sedimentological factors and sampling would influence the results? This is perhaps an obvious consideration for sedimentologists, but is in many studies treated as a secondary concern or even not mentioned. U-Pb LA-ICP-MS analysis on detrital zircons from two samples of Cambrian age (Herrería Formation, Cantabrian Mountains, Spain) revealed very different provenance signatures at the base and top of the formation. Both successions have been deposited in a shallow marine environment, are lithologically comparable (arenites, feldspathic arenites, siltstone, shales intercalated with marls and dolomite) and differ only slightly in age. Nearly 80% of all detrital zircons (n = 152; discordance ? 10) at the base of the formation are younger than 650 Ma. Detrital zircons older than 1.0 Ga amount to only 10% (n = 16) of the entire population. In contrast, only around 32% of all detrital zircons from the top of the formation (n = 123; discordance ? 10) are younger than 650 Ma while more than 16% are Archean and nearly 50% Paleoproterozoic. This implies a fundamental change in provenance, with a shift from Neoproterozoic to Paleoproterozoic (1.9-2.2 Ga) aged sediment sources. Consequently, changes of sediment transport systems have had an extremely profound impact on the provenance of the formation. Therefore, when correlating sedimentary rocks, interpreting source rocks and modelling paleogeography from U-Pb ages of detrital zircons, sedimentological parameters are possibly paramount and these need to be at least discussed before any interpretation is made.

  15. Cambrian Stratigraphy

    NSDL National Science Digital Library

    This site describes in detail the stratigraphy of the Cambrian period, starting approximately 545 million years ago and ending about 490 million years ago. It was one of the most important and dramatic periods because the lower boundary of the Cambrian is not only the beginning of a new system, but also the start of the Paleozoic and the Phanerozoic. Also the Early Cambrian saw the extremely rapid diversification of multicellular animals, the Cambrian Explosion, which determined the animal evolution and is indirectly responsible for present-day life. The site defines both the bottom and the top of the Cambrian layers and also provides a list of type sections with corresponding dates. Two charts are provided. One shows the changes in age assignments from 1982 to 1998 and another shows a time line for the Vendian and the Cambrian. The site also includes a section on isotopic studies and paleomagnetism of Cambrian strata.

  16. Carbon isotope stratigraphy, magnetostratigraphy, and 40Ar/39Ar age of the Cretaceous South Atlantic coast, Namibe Basin, Angola

    NASA Astrophysics Data System (ADS)

    Strganac, Christopher; Salminen, Johanna; Jacobs, Louis L.; Polcyn, Michael J.; Ferguson, Kurt M.; Mateus, Octávio; Schulp, Anne S.; Morais, Maria Luísa; Tavares, Tatiana da Silva; Gonçalves, António Olímpio

    2014-11-01

    We present the ?13C and paleomagnetic stratigraphy for marine strata at the coast of southern Angola, anchored by an intercalated basalt with a whole rock 40Ar/39Ar radiometric age of 84.6 ± 1.5 Ma, being consistent with both invertebrate and vertebrate biostratigraphy. This is the first African stable carbon isotope record correlated to significant events in the global carbon record spanning the Late Cenomanian to Early Maastrichtian. A positive ?3‰ excursion seen in bivalve shells below the basalt indicates the Cenomanian-Turonian Boundary Event at 93.9 Ma, during Oceanic Anoxic Event 2. Additional excursions above the basalt are correlated to patterns globally, including a negative ?3‰ excursion near the top of the section interpreted as part of the Campanian-Maastrichtian Boundary Events. The age of the basalt ties the studied Bentiaba section to a pulse of Late Cretaceous magmatic activity around the South Atlantic and significant tectonic activity, including rotation, of the African continent.

  17. sup 40 Ar/ sup 39 Ar age calibration of the litho- and paleomagnetic stratigraphies of the Ngorora Formation, Kenya

    SciTech Connect

    Deino, A.; Drake, R. (Institute of Human Origins, Berkeley, CA (USA)); Tauxe, L. (Scripps Institute of Oceanography, La Jolla, CA (USA)); Monaghan, M. (Univ. of Chicago, IL (USA))

    1990-07-01

    Precise eruptive ages have been determined by the laser-fusion, single-crystal {sup 40}Ar/{sup 39}Ar method for juvenile volcanic feldspars from reworked and contaminated volcaniclastic rocks of the middle Miocene Ngorora Formation, Kenya Rift Valley. These ages range from 13.06 Ma at the base to 10.51 Ma toward the top of the type section near Kabarsero. Correlation of the local paleomagnetic stratigraphies with the geomagnetic reversal time scale yields magnetochronologic age estimates that are younger than the isotopic ages by an average of 0.18 Ma. Much of the discrepancy can be eliminated if an inferred change in sea-floor spreading rate occurred at 13 Ma or earlier, rather than at 10.42 Ma as previously suggested. Sedimentation rates at Kabarsero calculated from the {sup 40}Ar/{sup 39}Ar results decrease from initial values of {approximately}25 cm/1,000 yr to {approximately}5 cm/1,000 yr toward the top of the section. The initial rapid sedimentation rates characterize the first 0.1 to 0.3 m.y. following emplacement of the underlying, voluminous, basin-filling Tiim Phonolites, indicating that the Baringo Basin at this time may not have existed as a rift valley created by extensional tectonics, but instead may have been a subsidence feature formed in response to removal of large volumes of magma from the lithosphere. A premolar tentatively identified as Proconsul sp. indet. found in the Ngorora Formation near the village of Bartabwa has been dated at {approximately}12.42 Ma, representing perhaps the last known occurrence of this genus in the fossil record.

  18. Sedimentology, weathering, age and geomorphological significance of Tertiary sediments on the far south coast of New South Wales

    Microsoft Academic Search

    J. F. Nott; R. W. Young; M. Idnurm

    1991-01-01

    The age of the NSW coastal lowland from Tuross to the Victorian border can now be shown to be at least mid?Tertiary. By this time the coastal plain had twice been partially blanketed by terrestrial sediments. Palaeomagnetic determinations on the more recent of these sedimentary accumulations, the Long Beach Formation, reveal a minimum depositional age of Early Miocene. Eustatic influences

  19. Nonmarine stratigraphy of latest Cretaceous and early Tertiary age, southwestern New Mexico

    SciTech Connect

    Lawton, T.F.; Mack, G.H.; Lucas, S.G.; Kietzke, K.K. (New Mexico State Univ., Las Cruces (USA))

    1989-09-01

    Recent fossil collections from nonmarine strata at localities in southwestern New Mexico indicate that the Ringbone formation, as originally defined, comprises units separated by a major hiatus that is represented in the field by an angular unconformity. The lower unit has yielded (NMMNH locality 298) two anterior caudal vertebral centra, morphologically and metrically indistinguishable from those of the Late Cretaceous tyrannosaurids Albertosaurus and Daspletosaurus. These dinosaur fossils establish a late Campanian or Maastrichtian age for the unit, indicating its equivalence with the McRae Formation of south-central New Mexico and the Fort Crittenden Formation of southeastern Arizona. The unit is composed of approximately 1,000 m of sedimentary-clast conglomerate, arkose, volcanic litharenite, and gray shale; it thus appears to contain detritus from several different source areas. The younger unit has yielded a low-diversity ostracod fauna of Paleocene to early Eocene age. Diagnostic taxa from the assemblage include Pseudoeocypris pagei and Cypridea arvadensis. The age of this fauna suggests equivalence with the Love Ranch and Lobo Formations of southern New Mexico. The unit consists of approximately 350 m of interbedded red siltstone and boulder conglomerate derived from Lower Cretaceous strata overlain by a sequence of laminated shale and subordinate sandstone with a preserved thickness of 150 m.

  20. Lunar Impact Basins: Stratigraphy, Sequence and Ages from Superposed Impact Crater Populations Measured from Lunar Orbiter Laser Altimeter (LOLA) Data

    NASA Technical Reports Server (NTRS)

    Fassett, C. I.; Head, J. W.; Kadish, S. J.; Mazarico, E.; Neumann, G. A.; Smith, D. E.; Zuber, M. T.

    2012-01-01

    Impact basin formation is a fundamental process in the evolution of the Moon and records the history of impactors in the early solar system. In order to assess the stratigraphy, sequence, and ages of impact basins and the impactor population as a function of time, we have used topography from the Lunar Orbiter Laser Altimeter (LOLA) on the Lunar Reconnaissance Orbiter (LRO) to measure the superposed impact crater size-frequency distributions for 30 lunar basins (D = 300 km). These data generally support the widely used Wilhelms sequence of lunar basins, although we find significantly higher densities of superposed craters on many lunar basins than derived by Wilhelms (50% higher densities). Our data also provide new insight into the timing of the transition between distinct crater populations characteristic of ancient and young lunar terrains. The transition from a lunar impact flux dominated by Population 1 to Population 2 occurred before the mid-Nectarian. This is before the end of the period of rapid cratering, and potentially before the end of the hypothesized Late Heavy Bombardment. LOLA-derived crater densities also suggest that many Pre-Nectarian basins, such as South Pole-Aitken, have been cratered to saturation equilibrium. Finally, both crater counts and stratigraphic observations based on LOLA data are applicable to specific basin stratigraphic problems of interest; for example, using these data, we suggest that Serenitatis is older than Nectaris, and Humboldtianum is younger than Crisium. Sample return missions to specific basins can anchor these measurements to a Pre-Imbrian absolute chronology.

  1. Age, Stratigraphy, and Correlations of the Late Neogene Purisima Formation, Central California Coast Ranges

    USGS Publications Warehouse

    Powell, Charles L.; Barron, John A.; Sarna-Wojcicki, Andrei M.; Clark, Joseph C.; Perry, Frank A.; Brabb, Earl E.; Fleck, Robert J.

    2007-01-01

    The Purisima Formation is an important upper Miocene and Pliocene stratigraphic unit in central California, cropping out from the coast at Point Reyes north of San Francisco to more extensive exposures in the Santa Cruz Mountains to the south. The fine-grained rocks in the lower parts of the Purisima Formation record a latest Miocene transgressive event, whereas the middle and upper parts of the formation consist of increasingly clastic-rich siltstones and sandstones resulting from uplift of adjacent coastal regions and the Sierra Nevada during Pliocene transgressive and regressive sea-level events. Exposures of the Purisima occur in three different, fault-bounded, structural blocks - the Santa Cruz, Pigeon Point, and Point Reyes tectonic blocks - that complicate correlations and regional age assignments. We summarize and compare published and new biostratigraphic and geochronologic data for various exposures of the Purisima Formation on the basis of mollusks, diatoms, radiometric dating, magnetostratigraphy, tephrochronology, and strontium isotope dating. On the basis of these data, we conclude that the Purisima Formation ranges in age from the latest Miocene (about 7 Ma) to the late Pliocene (about 2.6 Ma). The Purisima Formation of Santa Cruz County, exposed in the sea cliffs from Santa Cruz to Rio del Mar, is here designated a supplementary reference section because it is the most complete and well studied Purisima section in central California.

  2. OSL age and stratigraphy of the Strauss sand sheet in New Mexico, USA

    NASA Astrophysics Data System (ADS)

    Hall, Stephen A.; Goble, Ronald J.

    2015-07-01

    The Strauss sand sheet occurs in south-central New Mexico, USA, and northern Chihuahua, Mexico, covering an area of about 4740 km2. Its chronology is determined by 19 OSL ages. The sand sheet formed primarily during three phases of eolian deflation and deposition, each phase with a separate sand source and under different climatic and environmental circumstances. The first phase of eolian sedimentation occurred 45 to 15 ka with the deposition of unit 1. The sand source for the first phase was beach-related features along the eastern shoreline of pluvial Lake Palomas in Mexico. The glacial-age climate was cool, wet, and windy because of the southern path of the jet stream at that time. After 15 ka, with the onset of warmer conditions of the Bølling-Allerød, the shutting down of the Palomas sand source, and wet conditions of the Younger Dryas, the sand sheet stabilized with weak soil development in unit 1. By 11 ka, the climate shifted to Holocene drying conditions and the second phase of sand accumulation began, forming unit 2; the sand source was the local deflation of the previously deposited unit 1 sand. The sand sheet stabilized again by 1.9 ka with slightly wetter late Holocene climate; a weak soil formed in unit 2 sand. About A.D. 1500 and extending to about A.D. 1850 or later, an A horizon formed on the sand sheet, probably in response to a desert grassland vegetation during the period of wet climate of the Little Ice Age. In an anthropogenic third phase of eolian activity, after A.D. 1850, the vegetation was likely disturbed by overgrazing; and the unit 2 and A horizon (unit 3) sands were deflated, resulting in the deposition of a thin layer of massive eolian sand (unit 4) across the sand sheet. By about A.D. 1900 mesquite shrubs had increased in abundance; and deflated sand, largely from unit 2, began to accumulate around the shrubs, forming coppice dunes (unit 5). Mesquite coppice dunes continued to increase in number and volume during the twentieth century and at present dominate most of the sand sheet. This third phase of eolian deflation-deposition is ongoing today.

  3. Evidencing syn-sedimentary volcanism in volcaniclastic series using coupled sedimentological and geochronological (U-Pb/zircon) analyses

    NASA Astrophysics Data System (ADS)

    Rossignol, Camille; Poujol, Marc; Bourquin, Sylvie; Dabard, Marie-Pierre; Hallot, Erwan; Nalpas, Thierry

    2015-04-01

    Volcaniclastic sediments, often under-studied, constitute an important part of the global sedimentary record, both in marine and continental environments. These sediments are of particular importance in order to constrain the age of sedimentation, particularly in series where interbedded lava flow are absent. Volcaniclastics sediments are also used in order to constrain the duration of the volcanic activity and to link volcanism with a specific geodynamic context. To demonstrate that volcanism and sedimentation were contemporaneous in a given basin, it is crucial to determine to which extent volcaniclasts present in the volcaniclastic sediments have been reworked. However, this determination is notoriously difficult. As a case study, we characterized the Triassic volcaniclastic series from the Luang Prabang Basin, Laos, using coupled sedimentological and geochronological analyses. Sedimentological and petrographical analyses show a wild range of depositional environments (alluvial fan, braided river and alluvial plain) and evidence for reworking of the volcaniclastics in each of the corresponding deposits. U-Pb geochronology conducted on zircon grains extracted from the volcaniclastic samples of known stratigraphic position indicates that the maximum depositional ages get younger together with the sedimentary succession. This good correlation between absolute ages and stratigraphy demonstrates that, despite evidences of reworking, the volcaniclasts were produced, at least to some extent, contemporaneously with sedimentation. Then, in this specific example, the uncertainties obtained from the U-Pb ages can be used to indicate the 'reworking time scale', defined as the difference between the age of volcaniclast production and the depositional age of its host strata. Short reworking time scales, of ca. 1 Ma, one order of magnitude smaller than the total duration of the sedimentary record reveal that volcanism and sedimentation were contemporaneous. The use of coupled sedimentological and geochronological analyses may thus allow to determine the duration of volcanic activity even in the absence of volcanic deposits. Constraining the reworking time scales is useful to describe volcaniclastics deposits in which the volcaniclasts were reworked.

  4. Tertiary tectonic and sedimentological evolution of the South Carpathians foredeep: tectonic vs eustatic control

    Microsoft Academic Search

    T. Rab?gia; L. Ma

    1999-01-01

    A detailed seismic sequence stratigraphy study based on a dense network of seismic profiles is integrated with structural observations from interpreted geological sections to derive a tectonic and sedimentological model for the Miocene–Pliocene evolution of the South Carpathians foredeep (Getic Depression). Following Paleogene and older orogenic phases, the first tectonic event which affected the studied area was characterised by Early

  5. Practical sedimentology, Second edition

    SciTech Connect

    Lewis, D.W. (Univ. of Canterbury, Christchurch (New Zealand). Dept. of Geology); McConchie, D.M. (Southern Cross Univ., New South Wales (Australia). Centre for Coastal Management)

    1994-01-01

    This book is for technical professionals in mineral exploration, environmental management, agriculture or forestry, this new edition takes an interdisciplinary approach to provide a lively and detailed overview of practical sedimentology. Emphasizing application over theory, the text is streamlined for comprehension, and it features many summary tables and graphs. The ideal companion to Analytical Sedimentology, this volume updates both methodology and applications, incorporates software information and extensively covers new technical developments. Specifically designed for students and cross-functional practitioners, it requires minimal geological background.

  6. Stratigraphy and structure of coalbed methane reservoirs in the United States: an overview

    USGS Publications Warehouse

    Pashin, J.C.

    1998-01-01

    Stratigraphy and geologic structure determine the shape, continuity and permeability of coal and are therefore critical considerations for designing exploration and production strategies for coalbed methane. Coal in the United states is dominantly of Pennsylvanian, Cretaceous and Tertiary age, and to date, more than 90% of the coalbed methane produced is from Pennsylvanian and cretaceous strata of the Black Warrior and San Juan Basins. Investigations of these basins establish that sequence stratigraphy is a promising approach for regional characterization of coalbed methane reservoirs. Local stratigraphic variation within these strata is the product of sedimentologic and tectonic processes and is a consideration for selecting completion zones. Coalbed methane production in the United States is mainly from foreland and intermontane basins containing diverse compression and extensional structures. Balanced structural models can be used to construct and validate cross sections as well as to quantify layer-parallel strain and predict the distribution of fractures. Folds and faults influence gas and water production in diverse ways. However, interwell heterogeneity related to fractures and shear structures makes the performance of individual wells difficult to predict.Stratigraphy and geologic structure determine the shape, continuity and permeability of coal and are therefore critical considerations for designing exploration and production strategies for coalbed methane. Coal in the United States is dominantly of Pennsylvanian, Cretaceous and Tertiary age, and to date, more than 90% of the coalbed methane produced is from Pennsylvanian and Cretaceous strata of the Black Warrior and San Juan Basins. Investigations of these basins establish that sequence stratigraphy is a promising approach for regional characterization of coalbed methane reservoirs. Local stratigraphic variation within these strata is the product of sedimentologic and tectonic processes and is a consideration for selecting completion zones. Coalbed methane production in the United States is mainly from foreland and intermontane basins containing diverse compressional and extensional structures. Balanced structural models can be used to construct and validate cross sections as well as to quantify layer-parallel strain and predict the distribution of fractures. Folds and faults influence gas and water production in diverse ways. However, interwell heterogeneity related to fractures and shear structures makes the performance of individual wells difficult to predict.

  7. Corrigendum Corrigendum to "Sedimentology, stratigraphy, and glacier dynamics,

    E-print Network

    to weakly stratified, some centimeter to decimeter-scale pods, lenses and beds of silt and sand Massive to weakly stratified, some laterally persistent partings of silt and fine sand Massive, never stratified Matrix material Sand Silt and sand Silt and clay Silt and sand Coarse sand and fine gravel Coarse sand

  8. Recent Trends and Advances in Sedimentology.

    ERIC Educational Resources Information Center

    Suttner, Lee J.

    1979-01-01

    Briefly surveys recent trends and developments in sedimentology. Includes Clastic sedimentary petrology, petrology of argillaceous rocks, terrigenous depositional environments, and chemical sedimentology. (MA)

  9. Sedimentology and depositional environments of part of the Walden Creek Group, central east Tennessee

    SciTech Connect

    Lewis, R.F. III (Louisiana State Univ., Baton Rouge, LA (United States). Dept. of Geology and Geophysics); Miller, J.M.G. (Vanderbilt Univ., Nashville, TN (United States). Dept. of Geology)

    1993-03-01

    Recent questions concerning the age of the Walden Creek Group (WCG), Ocoee Supergroup have increased interest in the depositional history of these rocks. This study focuses on the sedimentology and local stratigraphy of rocks in exposures of the lithologically diverse late Precambrian and/or lower Paleozoic WCG occurring within the Kinzel Springs and Wear Cove quadrangles. Units exposed in the structurally complex Alleghenian thrust setting include the Licklog, Shields, and Wilhite formations. These rocks are divided into twelve lithofacies composed of shale, siltstone, sandstone, conglomerate and carbonate rock. The lithofacies are grouped into seven facies associations indicating deposition below storm wave base in a deep-water, probably marine, environment. Within the study area, rocks of the Wilhite Formation represent deposition in basin plain, lower slope, slope, base of slope, and sandy channel environments. Rocks of the Shields Formation are coarse channel and related overbank deposits of the inner to middle parts of a deep water fan environment. The Licklog Formation contains rocks deposited as lobe and outer-fan or fan-fringe deposits in a middle- to lower-fan environment. These formations can be placed within a single depositional system composed of a submarine slope transitional with a basin plain, and of proximal channels and distal lobes in a sand-rich submarine fan system. Inferred depositional components (associations) compare well with general models of deep-water deposits associated with high gradient fan-delta-fed margins. The basin was bounded by an uplifted, most likely block faulted, margin composed of crystalline basement located to the northwest. Local sedimentologic and stratigraphic relationships suggest an overall progradational sequence during the deposition of these rocks.

  10. Global stratigraphy. [of planet Mars

    NASA Technical Reports Server (NTRS)

    Tanaka, Kenneth L.; Scott, David H.; Greeley, Ronald

    1992-01-01

    Attention is given to recent major advances in the definition and documentation of Martian stratigraphy and geology. Mariner 9 provided the images for the first global geologic mapping program, resulting in the recognition of the major geologic processes that have operated on the planet, and in the definition of the three major chronostratigraphic divisions: the Noachian, Hesperian, and Amazonian Systems. Viking Orbiter images permitted the recognition of additional geologic units and the formal naming of many formations. Epochs are assigned absolute ages based on the densities of superposed craters and crater-flux models. Recommendations are made with regard to future areas of study, namely, crustal stratigraphy and structure, the highland-lowland boundary, the Tharsis Rise, Valles Marineris, channels and valley networks, and possible Martian oceans, lakes, and ponds.

  11. Middle Stone Age stratigraphy and excavations at Die Kelders Cave 1 (Western Cape Province, South Africa): the 1992, 1993, and 1995 field seasons.

    PubMed

    Marean, C W; Goldberg, P; Avery, G; Grine, F E; Klein, R G

    2000-01-01

    Die Kelders Cave 1, first excavated under the direction of Franz Schweitzer in 1969-1973, was re-excavated between 1992 and 1995 by a combined team from the South African Museum, SUNY at Stony Brook, and Stanford University. These renewed excavations enlarged the artefactual and faunal samples from the inadequately sampled and less intensively excavated lower Middle Stone Age (MSA) layers, increased our understanding of the complex site formation processes within the cave, enlarged the hominid sample from the MSA deposits, and generated ESR, TL, and OSL dates for the MSA layers. Importantly, these new excavations dramatically improved our comprehension of the vertical and lateral characteristics of the MSA stratigraphy. Surface plotting of the MSA layers has led to the identification of at least two major zones of subsidence that significantly warped the layers, draping some along the eroding surface contours of major blocks of fallen limestone roof rock. A third zone of subsidence is probably present in the older excavations. Dramatic roof falls of very large limestone blocks occurred at least twice-once in the middle of Layer 4/5 where the roof blocks were only slightly weathered after collapse, and at the top of Layer 6 where the blocks weathered heavily after collapse, producing a zone of decomposed rock around the blocks. Many of the sandy strata are cut by small and localized faults and slippages. All of the strata documented by Schweitzer's excavations are present throughout the exposed area to the west of his excavated area, where many of them thicken and become more complex. Layer 6, the thickest MSA layer, becomes less diagenetically altered and compressed to the west. PMID:10627396

  12. Assistant or Associate Professor in Sedimentology

    E-print Network

    Assistant or Associate Professor in Sedimentology The Department of Earth Sciences (DES), Mineral for a tenure-track Assistant or Associate Professor position in Sedimentology to begin in July 2015. We seek an innovative individual with excellent teaching and research skills in sedimentology. Expertise in Precambrian

  13. Stratigraphy and structural geology

    NASA Technical Reports Server (NTRS)

    Carr, M. H.; Wilhelms, D. E.; Greeley, R.; Guest, J. E.

    1976-01-01

    The immediate goal of stratigraphy and structural geology is to reduce the enormous complexity of a planetary surface to comprehensible proportions by dividing the near-surface rocks into units and mapping their distribution and attitude.

  14. Lithofacies, palynofacies, and sequence stratigraphy of Palaeogene strata in Southeastern Nigeria

    Microsoft Academic Search

    Francisca E. Oboh-Ikuenobe; Chuks G. Obi; Carlos A. Jaramillo

    2005-01-01

    Integrated sedimentologic, macrofossil, trace fossil, and palynofacies data from Paleocene-Middle Eocene outcrops document a comprehensive sequence stratigraphy in the Anambra Basin\\/Afikpo Syncline complex of southeastern Nigeria. Four lithofacies associations occur: (1) lithofacies association I is characterized by fluvial channel and\\/or tidally influenced fluvial channel sediments; (2) lithofacies association II (Glossifungites and Skolithos ichnofacies) is estuarine and\\/or proximal lagoonal in origin;

  15. The USGS Bedform Sedimentology Site

    NSDL National Science Digital Library

    The USGS Bedform Sedimentology Site offers materials that are companions to the book: Cross-Bedding, Bedforms, and Paleocurrents, by D. M. Rubin of the USGS Pacific Science Center. Visitors can read an online version of the book, read about bedform initiation, view QuickTime and MPEG movies of bedforms and cross-bedding, download bedform simulation software, and find out how to identify low-dimensional deterministic systems (chaos) in time series or spatial patterns.

  16. A consistent magnetic polarity stratigraphy of late Neogene to Quaternary fluvial sediments from the Heidelberg Basin (Germany): A new time frame for the Plio-Pleistocene palaeoclimatic evolution of the Rhine Basin

    NASA Astrophysics Data System (ADS)

    Scheidt, Stephanie; Hambach, Ulrich; Rolf, Christian

    2015-04-01

    This work presents the results of a magnetostratigraphic survey performed on 1150 m of core material from three sites within the Heidelberg Basin. The cores intersect one of the thickest continuous accumulations of Plio-Pleistocene fluvial sediments in western Central Europe. The resultant magnetic polarity stratigraphy includes every Quaternary polarity chron, thereby providing constant age constraint down to the Gauss-Matuyama Boundary (2.58 Ma). Older deposits cannot be unequivocally dated; instead, various age-depth models are discussed. We base our chronostratigraphic interpretation of the successions tentatively on three assumptions. A) The accommodation was almost constant over time. B) Hiatuses in the duration of subchrons (on the order of 0.2 Myr) may occur, and the actual step-like age-depth relationship is best depicted as a smooth curve with almost constant slope. C) Long chrons and subchrons have a higher preservation potential than shorter polarity intervals. The stratigraphic scenarios with the highest probability - based upon our three assumptions - lead to minimum ages of > 5.235 Ma and > 4.187 Ma for the oldest parts of the Viernheim and Heidelberg cores, respectively. Consequently, this study provides the first consistent magnetic polarity stratigraphy for quasi-continuous sequences of late Neogene to Quaternary fluvial sediments in the Rhine Basin and generally in western central Europe. This methodologically independent chronostratigraphy supplies an urgently required temporal model for on-going tectonic and sedimentological studies and the reconstruction of the palaeoclimate since the Pliocene in this part of Europe.

  17. Tectonic sequence stratigraphy, Early Permian Dry Mountain trough, east-central Nevada

    SciTech Connect

    Snyder, W.S.; Gallegos, D.M.; Spinosa, C. (Boise State Univ., ID (United States)); Schwarz, D.L. (Univ. of Iowa, Iowa City (United States))

    1991-06-01

    The Early Permian Dry Mountain trough (DMT) of east-central Nevada is one of several tectonic basins and associated uplifts that developed along the continenetal margin during the latest Pennsylvanian-Early Permian Dry Mountain tectonic phase. The sequence stratigraphy reflects a combination of eustatic sea level changes and tectonic uplift or subsidence. Fewer than one to only a few million years separate the development of sequence boundaries within the DMT. At this scale, differences among published eustasy curves preclude their use as definitive tools to identify eustatically controlled sequence boundaries. Nevertheless, available data indicate several pulses of tectonism affected sedimentation within the DMT. The authors are attempting to develop criteria to distinguish tectonic from eustatic sequence boundaries. Detailed biostratigraphic data are required to provide an independent check on the correlation of sequence boundaries between measured sections. For example, the same age boundary may reflect tectonic uplift in one part of the basin and subsidence in another. The uplift may or may not result in subaerial exposure and erosion. For those boundaries that do not result from subaerial exposure, lithofacies and biofacies analyses are required to infer relative uplift (water depth decrease) or subsidence (water depth increase). There are inherent resolution limitations in both the paleontologic and sedimentologic methodologies. These limitations, combined with those of eustasy curves, dictate the preliminary nature of their results.

  18. Sedimentology and paleoenvironment from the Maar Lac du Bouchet for the last climatic cycle, 0-120,000 years (Massif Central, France)

    Microsoft Academic Search

    Elisabeth Truze; Kerry Kelts

    1993-01-01

    This paper summarizes sedimentological and geochemical studies from seven cores taken from the Bouchet crater lake, France.\\u000a It includes studies of water and soils from the drainage basin. The sedimentary record is subdivided into 14 distinct sedimentary\\u000a units, which comprise different combinations of 8 recurring lithofacies. The lithostratigraphic results are correlated with\\u000a prior information from magnetic-, pollen-, diatom-, and chrono-stratigraphy

  19. Snow Pit Stratigraphy

    NSDL National Science Digital Library

    Stephan Custer

    The student understands that snow leads to avalanches, but is often very inexperienced in the observation of the snow pack. This exercise provides the opportunity to learn about snow stratigraphy, observation, and measurement from a detailed observational perspective. The students work in small groups in 3-6 pits (depends on the class size). By working on a transect from the trees out into the opening, they discover (usually) that the snow depth is different and that the descriptions in the pits differ as one proceeds out from the trees into the opening. (Different stratigraphic units, different thickness, different temperature, different density, different crystals.)

  20. Simplifying the stratigraphy of time

    NASA Astrophysics Data System (ADS)

    Zalasiewicz, Jan; Smith, Alan; Brenchley, Patrick; Evans, Jane; Knox, Robert; Riley, Nicholas; Gale, Andrew; Gregory, F. John; Rushton, Adrian; Gibbard, Philip; Hesselbo, Stephen; Marshall, John; Oates, Michael; Rawson, Peter; Trewin, Nigel

    2004-01-01

    We propose ending the distinction between the dual stratigraphic terminology of time-rock units (of chronostratigraphy) and geologic time units (of geochronology). The long-held, but widely misunderstood, distinction between these two essentially parallel time scales in stratigraphy has been rendered unnecessary by the widespread adoption of the global stratotype sections and points (GSSP—golden spike) principle in defining intervals of geologic time within rock strata. We consider that the most appropriate name for this stratigraphic discipline is “chronostratigraphy,” which would allow “geochronology” to revert to its mainstream and original meaning of numerical age dating. This in turn makes the little-used formal term “geochronometry” redundant. The terms “eonothem,” “erathem,” “system,” “series,” and “stage” would become redundant, in favor of “eon,” “era,” “period,” “epoch” and (disputably) “age.” Our favored geologic time units may be qualified by “early” and “late,” but not by “lower” and “upper.” These suggested changes should simplify stratigraphic practice, encompass both stratified and nonstratified rocks, and help geologic understanding, while retaining precision of meaning.

  1. Ages and stratigraphy of lunar mare basalts in Mare Frigoris and other nearside maria based on crater size-frequency distribution measurements

    NASA Astrophysics Data System (ADS)

    Hiesinger, H.; Head, J. W.; Wolf, U.; Jaumann, R.; Neukum, G.

    2010-03-01

    We report on ages derived from impact crater counts for exposed mare basalt units in the northern part of the lunar nearside hemisphere (Mare Frigoris), the eastern and northeastern part of the nearside hemisphere (Lacus Temporis, Joliot, Hubble, Goddard, Mare Marginis, and Mare Smythii), the central part of the nearside hemisphere (Palus Putredinis, Mare Vaporum, and Sinus Medii), and the southwestern part of the nearside hemisphere (Grimaldi, Crüger, Rocca A, Lacus Aestatis, and Schickard). In Mare Frigoris, we dated 37 basalt units, showing ages from 2.61 to 3.77 Gyr, with most units being formed in the late Imbrian period between 3.4 and 3.8 Gyr ago. In Mare Vaporum we dated six spectrally homogeneous units that show model ages of 3.10 to 3.61 Gyr. Our model ages of basalts in Mare Marginis range from 3.38 to 3.88 Gyr and are mostly older than basalts in Mare Smythii (3.14-3.48 Gyr). The model ages of four units in Sinus Medii indicate that the basalts in this region formed 3.63 to 3.79 Gyr ago. We find an excellent agreement of our crater size-frequency model ages of the Palus Putredinis area, which contains the Apollo 15 landing site, with the radiometric ages of Apollo 15 samples. According to our crater counts, basalts in Palus Putredinis are 3.34 Gyr old and this compares favorably with the radiometric ages of 3.30-3.35 Gyr of the olivine-normative and quartz-normative basalts of the Apollo 15 landing site. Lacus Aestatis is a small irregular-shaped mare patch in the southwestern nearside and shows an Imbrian age of 3.50 Gyr; basalts in Lacus Temporis in the northeastern nearside formed between 3.62 and 3.74 Gyr ago and are, therefore, older than the basalts in Lacus Aestatis. We found that basalts in craters of the southwestern nearside (Schickard, Grimaldi, Crüger, and Rocca A) are also mostly younger than basalts in craters of the northeastern nearside (Hubble, Joliot, and Goddard). While basalt ages vary between 3.16 and 3.75 Gyr in the southwest, basalts in the northeast are 3.60-3.79 Gyr old. These results confirm and extend the general distribution of ages of mare basalt volcanism and further underline the predominance of older mare basalt ages in the eastern and southern nearside and in patches of mare peripheral to the larger maria, in contrast to the younger basalt ages on the western nearside (Oceanus Procellarum).

  2. Proceedings, 1983 symposium on surface mining, hydrology, sedimentology, and reclamation

    SciTech Connect

    Graves, D.H. (ed.)

    1983-12-01

    Papers were presented on the following topics: mining technology; hydrology; sedimentology; reclamation; surface mining technology and policy; poster presentations; phosphate and arid land reclamation; reclamation special applications; and hydrology-sedimentology special applications. 45 papers have been abstracted separately.

  3. Ages and stratigraphy of lunar mare basalts in Mare Frigoris and other nearside maria based on crater size-frequency distribution measurements

    Microsoft Academic Search

    H. Hiesinger; J. W. Head III; U. Wolf; R. Jaumann; G. Neukum

    2010-01-01

    We report on ages derived from impact crater counts for exposed mare basalt units in the northern part of the lunar nearside hemisphere (Mare Frigoris), the eastern and northeastern part of the nearside hemisphere (Lacus Temporis, Joliot, Hubble, Goddard, Mare Marginis, and Mare Smythii), the central part of the nearside hemisphere (Palus Putredinis, Mare Vaporum, and Sinus Medii), and the

  4. Lithostratigraphy, petrography, biostratigraphy, and strontium-isotope stratigraphy of the surficial aquifer system of western Collier County, Florida

    USGS Publications Warehouse

    Edwards, L.E.; Weedman, S.D.; Simmons, R.; Scott, T.M.; Brewster-Wingard, G. L.; Ishman, S.E.; Carlin, N.M.

    1998-01-01

    In 1996, seven cores were recovered in western Collier County, southwestern Florida, to acquire subsurface geologic and hydrologic data to support ground-water modeling efforts. This report presents the lithostratigraphy, X-ray diffraction analyses, petrography, biostratigraphy, and strontium-isotope stratigraphy of these cores. The oldest unit encountered in the study cores is an unnamed formation that is late Miocene. At least four depositional sequences are present within this formation. Calculated age of the formation, based on strontium-isotope stratigraphy, ranges from 9.5 to 5.7 Ma (million years ago). An unconformity within this formation that represents a hiatus of at least 2 million years is indicated in the Old Pump Road core. In two cores, Collier-Seminole and Old Pump Road, the uppermost sediments of the unnamed formation are not dated by strontium isotopes, and, based on the fossils present, these sediments could be as young as Pliocene. In another core (Fakahatchee Strand-Ranger Station), the upper part of the unnamed formation is dated by mollusks as Pliocene. The Tamiami Formation overlies the unnamed formation throughout the study area and is represented by the Ochopee Limestone Member. The unit is Pliocene and probably includes the interval of time near the early/late Pliocene boundary. Strontium-isotope analysis indicates an early Pliocene age (calculated ages range from 5.1 to 3.5 Ma), but the margin of error includes the latest Miocene and the late Pliocene. The dinocyst assemblages in the Ochopee typically are not age-diagnostic, but, near the base of the unit in the Collier-Seminole, Jones Grade, and Fakahatchee Strand State Forest cores, they indicate an age of late Miocene or Pliocene. The molluscan assemblages indicate a Pliocene age for the Ochopee, and a distinctive assemblage of Carditimera arata and Chione cortinaria in several of the cores specifically indicates an age near the early/late Pliocene boundary. Undifferentiated sands overlie the Pliocene limestones in two cores in the southern part of the study area. Artificial fill occurs at the top of most of the cores. The hydrologic confining units penetrated by these cores are different in different parts of the study area. To the west, a hard tightly cemented dolostone forms the first major confining unit below the water table. In the eastern part of the study area, confinement is more difficult to determine. A tightly cemented sandstone, much younger than the dolostones to the west and probably not laterally connected to them, forms a slight confining unit in one core. Thick zones of poorly sorted muddy unconsolidated sands form a slight confining unit in other cores; these probably are not correlative to either the sandstone or the dolostones to the west. The age and sedimentologic observations suggest a complex compartmentalization of the surficial aquifer system in southwestern Florida. The calibrations of dinocyst and molluscan occurrences with strontium-isotope stratigraphy allows us to expand and document the reported ranges of many taxa. This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards or with the North American Stratigraphic Code. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

  5. Lunar Crustal Stratigraphy

    NASA Astrophysics Data System (ADS)

    McCallum, I. S.; O'Brien, H. E.

    1996-03-01

    Intense bombardment during the first 600 Ma of lunar history has rendered the task of reconstructing the stratigraphy of the lunar crust especially difficult. On a planetary scale, the distribution of lithologies around multi-ringed basins coupled with orbital geochemical data reveal that the lunar crust is heterogeneous both laterally and vertically. Ejecta from the large multi-ringed basins is exclusively of crustal origin since twenty five years of lunar sample study have failed to identify any unequivocal mantle samples. Given the most recent determination of crustal thickness, this implies an upper limit to the depth of excavation of around 60 km. In the younger multi-ringed basins (Orientale and Imbrium), the occurrence of anorthosites in inner rings is consistent with an anorthositic upper crust (Al2O3 = 26-28 wt.%). On the other hand, basin impact melts, most notably the low-K Fra Mauro (LKFM) composition associated with the Imbrium and Serenitatis basins, are distinctly more mafic with a composition corresponding to norite (Al2O3 ~ 20 wt.%). Cratering models suggest that such melts are generated at the lower to middle crustal depths (30 to 60 km). The paucity of unequivocal deep-seated crystalline plutonic rocks is also consistent with cratering models which suggest that unmelted rock fragments in ejecta blankets are most likely derived from the upper part of the crust. Consequently, the possibility exists that no crystalline lunar samples from deeper that ~30 km are present in the returned sample collection.

  6. Impact of sea level rise don the sedimentology and stratigraphy of estuarine systems

    SciTech Connect

    Ward, L.G.; Kearney, M.S.

    1988-02-01

    Drowned-river valley estuaries are characteristic features of trailing-edge continental margins, as exemplified by the US Atlantic Coast. During marine transgressions, the classic cycle of estuarine development is one of the initial submergence and subsequent infilling, with the latter stages marked by extensive accumulations of fine-grained sediments in expanding marshes, deltas, and floodplains. Seismic surveys, vibracoring, and radiocarbon dating in the estuarine tributaries in middle Chesapeake Bay (the largest estuary along the Atlantic Coast) indicate that thick accumulations (> 25 m) of organic-rich fine-grained sediments have been deposited since the middle Holocene. However, studies of recent accretion rates (based on pollen and radionuclide analyses) suggest the marshes, which represent a near-end member of the estuarine depositional sequence, may no longer be accumulating significant volumes of sediment. Relatively rapid crustal subsidence plus eustatic sea level rise produces a local submergence of /approximately/4 mm/yr. Although marsh accretion rates in the upper eustarine tributaries approach 1 cm/yr, marsh accretion rates in the middle and lower reaches are significantly less (< 2 mm/yr) than submergence. Here, numerous marshes are converting to open water as they become increasingly flooded by the tides. This change in depositional regime is also reflected in the carbon content (decreasing) and grain size (coarsening) of the marsh sediments and tidal channel migrations. In the coming decades, the rate of the world sea level rise is projected to increase significantly. This acceleration in the global eustatic trend together with lower sediment inputs from surrounding watersheds may reverse the historic trend of estuarine infilling.

  7. Impact of sea level rise on the sedimentology and stratigraphy of estuarine systems

    SciTech Connect

    Ward, R.F.; Kearney, M.S.

    1988-01-01

    Drowned-river valley estuaries are characteristic features of trailing-edge continental margins, as exemplified by the United States Atlantic Coast. During marine transgressions, the classic cycle of estuarine development is one of initial submergence and subsequent infilling, with the latter stages marked by extensive accumulations of fine-grained sediments in expanding marshes, deltas, and floodplains. Seismic surveys, vibracoring, and radiocarbon dating in the estuarine tributaries in middle Chesapeake Bay (The largest estuary along the Atlantic Coast), indicate that thick accumulations (>25 m) of organic-rich fine-grained sediments have been deposited since the middle Holocene. However, studies of recent accretion rate (based on pollen and radionuclide analyses) suggest the marshes, which represent a near-end member of the estuarine depositional sequence, may no longer be accumulating significant volumes of sediment. Relatively rapid crustal subsidence plus eustatic sea level rise produces a local submergence of approx. 4 mm/yr. Although marsh accretion rates in the upper estuarine tributaries approach 1 cm/yr, marsh accretion rates in the middle and lower reaches are significantly less (<2 mm/yr) than submergence. Here, numerous marshes are converting to open water as they become increasingly flooded by the tides. This change in depositional regime is also reflected in the carbon content (decreasing) and grain size (coarsening) of the marsh sediments and tidal channel migrations. In the coming decades, the rate of the world sea level rise is projected to increase significantly. This acceleration in the global eustatic trend together with lower sediment inputs from surrounding watersheds may reverse the historic trend of estuarine infilling.

  8. Neogene stratigraphy and sedimentology in eastern Azerbaijan: Outcrop observations and subsurface implications

    SciTech Connect

    Ali-zade, A.A.; Guliyev, I.S.; Ateava, E.Z. [GIA, Baku (Azerbaijan)] [and others

    1995-08-01

    The largely Pliocene Productive Series of eastern Azerbaijan contains about 26 billion barrels oil equivalent. It is well exposed in outcrops on the Apsheron Peninsula which a joint team from the GIA and the BP and Statoil Alliance have described. Detailed biostratigraphic and petrographic studies have subsequently been carried out. Productive Series deposition was initiated by a dramatic relative sea-level fall which left the South Caspian an isolated basin fed by deeply incised precursors to the modern Volga, Amu Darya, and Kura rivers. Five facies associations have been recognised within the Productive Series at outcrop, encompassing a range of palaeoenvironments from alluvial braided river sandstones and conglomerates to delta-front siltstones and mudstones. The facies associations suggest a river-dominated, braid delta. Four idealised reservoir models can be recognised: fluvial, delta-plain, proximal delta-front and distal delta-front. Each has distinct grain-size and shale distributions. Studies of nearby oilfields suggest that these models form useful subsurface analogues. Flow simulation models suggest that each reservoir type has dramatically different performance. Productive Series sediments are typically loosely cemented and smectite rich, which may result in clay swelling and sand control problems. Localised reduction in reservoir quality is caused by fault-associated calcite cements. Proximal facies of the upper Productive Series contain porosity occluding gypsum cements. Palynology and nannopalaeontology have been applied to the Neogene sediments of Azerbaijan for almost the first time, and have given encouraging results, at least in terms of a broad biozonation. Micropaleontological analyses have also provided useful palaeoenvironmental data.

  9. Oligocene Hackberry Formation of southwest Louisiana: Sequence stratigraphy, sedimentology, and hydrocarbon potential

    SciTech Connect

    Cossey, S.P.J.; Jacobs, R.E. (BP Exploration, Houston, TX (United States))

    1992-05-01

    The Oligocene Hackberry sequence was deposited in a slope environment consisting of an irregular, updip slide scar, a rotational slide zone up to 4 mi (6.5 km) wide, and a downdip region more than 20 mi (32 km) wide where meandering submarine channels deposited thick turbiditic sands. The shelf margin slides probably began during the late stage of a relative fall in sea level and prior to a maximum flood event in the middle Oligocene. The slides probably were caused by a combination of salt withdrawal and an unstable shelf edge. The play has produced more than 374 million bbl of oil equivalent (BOE) up to December 1988. The first fields were discovered in structural/stratigraphic traps on the updip flanks of the salt domes, where channels were forced to meander around paleobathymetric highs. Other fields are located in the paleobathymetric lows many miles downdip of the salt domes. Statistical analysis of field data shows that 41 fields with more than 1 million BOE each and with a total estimated ultimate recovery of 117 million BOE remain to be discovered in the play. Interpretation in southwestern Louisiana has shown that new reserves could be discovered in three potential reservoir sands: (1) lower Frio shelf-edge sands preserved in large slide blocks, (2) onlapping, sandy 'fill sequences' restricted to the lows between slide blocks, and (3) meandering, dip-oriented, sandy channel complexes less than 4,500 ft (1,400 m) wide. These three sandstones cannot be distinguished unless dipmeter, seismic, and paleontologic data are used in combination.

  10. Sedimentology and stratigraphy of the Queen Formation, Millard Field, Pecos County, Texas 

    E-print Network

    Williams, Matt Brian

    1984-01-01

    , originally as gypsum, in a subaqueous environment (Lang, 1937; Sarg, 1977; Crawford and Dunham, 1982). The sabkha model analogous to what is now found on the Persian Gulf Sabkha (Curtis et al, 1963; Butler, 1969; Kinsman, 1969), proposes deposition... OOOO 0 2 10 q 8 JE f D] ~, , P C'+c I 1 gf ~ [--'K ~%8%~ , ( 16 This anhydrite texture and crystal arrangement occurs as a secondary feature both in the Persian Gulf sabkha (Shearman, 1966, Butler, 1969) and in shallow subaqueous setting...

  11. Sedimentology and Holocene stratigraphy of a carbonate mangrove buildup, Twin Cays, Belize, Central America

    E-print Network

    Bond, Gregor Benton

    1988-01-01

    the total length of the tube. The modified tube was then attached to a winch system bolted onto one of the tripod's legs. At the bottom of the irrigation tube was a core catcher designed to allow easy pene- tration of the sediment. and maximum retention... in Belfze, Central America. This was accomplished by analyzing 19 sediment vibracores and 132 surface samples collected from the mangrove island and surrounding shelf lagoon. Present-day lagoonal microenvironments were defined by size fequency data...

  12. The morphology, stratigraphy and sedimentology of the Carstairs esker, Scotland, U.K.

    NASA Astrophysics Data System (ADS)

    Thomas, G. S. P.; Montague, E.

    The series of ridges, mounds and basins around Carstairs have been variously interpreted as recessional moraines, kames, sub- or en-glacial eskers or as landforms developed in response to supraglacial outwash fan sediments deposited on stagnant ice. This paper argues that the ridges are eskers. They formed in an interlobate sediment sink between the uncoupling margins of Highland and Southern Upland ice during Devensian deglaciation. This conclusion is based on geomorphological mapping, lithofacies and palaeocurrent analysis, and borehole interpretation. An extensive lake system developed between the two ice margins and was fed by a major sub-glacial conduit flowing towards the NE. This conduit initially exited into the lake subaqueously to form a prominent single esker ridge across the lake floor. On downwasting, the feeding conduit emerged onto the surface of the ice to form a complex supraglacial outwash sandur. During periods of catastrophic flow, large channels cut through the sandur surface into underlying ice. These channels filled with coarse gravel which, on abandonment and further downwasting, were topographically inverted to form a series of sub-parallel, slightly sinuous ridges giving the appearance of braiding. During lower flow extensive finer-grained supraglacial sandur sedimentation took place on the periphery of these ridges and this passed down-current across the ice margin into fan-deltas feeding into the expanding ice-front lake.

  13. Sequence stratigraphy, sedimentology, and hydrocarbon potential in the North-Eastern part of the Pannonian Basin

    SciTech Connect

    Lazar, O.R.; Corbeanu, R.; Vasiliu, G. [Institute for Research and Technology, Prahova (Romania)] [and others

    1995-08-01

    The Pannonian basin lies within the Alpine mountain belts of east-central Europe. Deformation of the Pannonian region occurred during the final stage of thrusting and folding in the outer part of the Carpathians. The result was a system of several smaller individual basins separated by relatively shallow basement blocks. The {open_quotes}North-eastern part of the Pannonian basin{close_quotes} represents one of these individual basins. Over the basement, the Neogene sedimentation started with continental or marine transgressive beds followed by shallow-marine shales and marls with sandy intercalations. Several stratigraphic sequences were separated within the succession of sedimentary deposits using the seismic, paleontologic, and well-log data. These sequences with their hydrocarbon significance are largely described in the paper.

  14. Stratigraphy and sedimentology of a dry to wet eolian depositional system, Burns formation, Meridiani Planum, Mars

    Microsoft Academic Search

    J. P. Grotzinger; R. E. Arvidson; J. F. Bell III; W. Calvin; B. C. Clark; D. A. Fike; M. Golombek; R. Greeley; A. Haldemann; K. E. Herkenhoff; B. L. Jolliff; A. H. Knoll; M. Malin; S. M. McLennan; T. Parker; L. Soderblom; J. N. Sohl-Dickstein; S. W. Squyres; N. J. Tosca; W. A. Watters

    2005-01-01

    Outcrop exposures of sedimentary rocks at the Opportunity landing site (Meridiani Planum) form a set of genetically related strata defined here informally as the Burns formation. This formation can be subdivided into lower, middle, and upper units which, respectively, represent eolian dune, eolian sand sheet, and mixed eolian sand sheet and interdune facies associations. Collectively, these three units are at

  15. Sedimentology, stratigraphy, and depositional environment of the Crystal Geyser Dinosaur Quarry, east-central Utah

    USGS Publications Warehouse

    Suarez, M.B.; Suarez, C.A.; Kirkland, J.I.; Gonzalez, Luis A.; Grandstaff, D.E.; Terry, D.O., Jr.

    2007-01-01

    The Crystal Geyser Dinosaur Quarry, near Green River, Utah, is located at the base of the Lower Cretaceous (Barremian) Yellow Cat Member of the Cedar Mountain Formation. The quarry preserves a nearly monospecific accumulation of a new basal therizinosauroid, Falcarius utahensis. We used field descriptions and petrographic analysis to determine the depositional environment and development of the quarry strata. Results of these analyses suggest that the quarry represents multiple episodes of bone accumulation buried by spring and overbank flood deposits. Evidence for these previously undescribed spring deposits includes calcite macroscopic structures within the quarry strata - such as pisolites and travertine fragments - and calcite micromorphologies - including radial-fibrous, feather, and scandulitic dendrite morphologies and tufa clasts. At least two episodes of bone incorporation are preserved in the quarry based on their stratigraphic position and lithologic associations. The unique depositional setting in and around the Crystal Geyser Dinosaur Quarry appears to have been favorable for the preservation of vertebrate fossils and provides insight into early Cretaceous environments in North America. Copyright ?? 2007, SEPM (Society for Sedimentary Geology).

  16. STRATIGRAPHY AND SEDIMENTOLOGY OF THE UPPER JURASSIC MORRISON FORMATION, DILLON, MONTANA

    Microsoft Academic Search

    JON J. SMITH; STEPHEN T. HASIOTIS; WILLIAM J. FRITZ

    2006-01-01

    Abstract—Red, purple and gray-green mudrocks near Dillon, Montana, have been mapped traditionally as the Up- per Jurassic Morrison Formation. There are very few studies of the Mesozoic strata in this area and questions exist as to whether this unit actually is the Morrison Formation, or whether it is similarly variegated mudrocks of other formations at nearly the same stratigraphic interval.

  17. Sedimentology and stratigraphy of the Queen Formation, Millard Field, Pecos County, Texas

    E-print Network

    Williams, Matt Brian

    1984-01-01

    , 1982. Production in the Queen Formation is from two zones, the Queen A, which is at a depth of 1500 to 2000 ft in the field and the Queen C, which is not penetrated by all wells, between 1600 and 2200 ft (Fig. 9, p. 25). The producing zones... grained sandstone matrix, base of section has parallel, continuous, even lamina- tions 0'-10', abrupt basal contact. 48 Tenneco Holmes 44 (Dueen Formation) continued DEPTH THICKNESS (?) DESCRIPTION 1548 Sandstone: dark gray to gray-green; very fine...

  18. Sedimentology: Recent developments and applied aspects

    SciTech Connect

    Brenchley, P.J.

    1985-01-01

    This book reflects some of the developments which have occurred in sedimentology during the last two decades. It identifies problems of concern to sedimentologists. Topics covered include the following: loose-boundary hydraulics and fluid mechanics: selected advances since 1961; clastic facies models and facies analysis; recent shelf clastic sediments; deep-sea clastics; deep-sea pelagic sediments and palaeo-oceanography; facies analysis of volcaniclastic sediments; shallow-marine carbonate facies and facies models; diagenesis of shallow-marine carbonates; clastic diagenesis; sedimentary ore deposits; role of clastic sedimentology in the exploration and production of oil and gas in the North Sea; and carbonate facies analysis in the exploration for hydrocarbons: a case-study from the Cretaceous in the Middle East.

  19. Sequence stratigraphy: A personal history of lows and highs

    SciTech Connect

    Sangree, J.B.; Mitchum, R.M. III

    1995-12-31

    We have been privileged to observe and to participate in the development of sequence stratigraphy over the last forty years. We have been mainly laborers in the vineyard, rather than vintners, but in a way this is our own story. We can only present it as a personal view of the history of the subject. Sequence stratigraphy has several roots and each has its own history. Sequence stratigraphy is an attempt to find practical physical applications for the ideas of chronostratigraphy, ideas that stretch back at least into the early nineteen hundreds. Another basic root is the concept of cyclic patterns of onlap of coastal facies sediments onto the continents. This abstraction includes the idea that many of these longer term cycles may be synchronous on an intercontinental basis, at least within the limitations of current biostratigraphic age dates. A third root lies unexpectedly in the parallelism of seismic reflections an chronostratigraphic surfaces. Initially this notion meet with resistance and skepticism, but it has proved a sturdy tool in the development of our understanding of regional time-stratigraphy. Finally, and most controversially, is the notion that many cycles of continental onlap owe their origin to rise and fall of worldwide sea level. The nature and causes of eustasy look as though they will be debated into the next millennium, but the physical evidence for cyclic changes in sea level relative to the continent is now well fixed.

  20. Workshop on quantitative dynamic stratigraphy

    SciTech Connect

    Cross, T.A.

    1988-04-01

    This document discusses the development of quantitative simulation models for the investigation of geologic systems. The selection of variables, model verification, evaluation, and future directions in quantitative dynamic stratigraphy (QDS) models are detailed. Interdisciplinary applications, integration, implementation, and transfer of QDS are also discussed. (FI)

  1. Amino acid racemization analysis (AAR) as a successful tool for dating Holocene coastal sediments: Stratigraphy of a barrier island spit (Southern Sylt/North Sea)

    NASA Astrophysics Data System (ADS)

    Tillmann, Tanja; Ziehe, Daniel

    2014-05-01

    Dating of Holocene sediments in shallow coastal areas of the German North Sea by conventional techniques is commonly problematic. In particular the marine reservoir effect of radiocarbon means that radiocarbon dating cannot be applied to sediments younger than about 400 years. Amino acid racemization dating (AAR) is a viable alternative for dating young sediments. The method is based on the determination of ratios of D and L amino acid enantiomers in organic matrices of biogenic carbonates. In this study we use AAR as a tool for dating Holocene barrier islands sediments. Based on an AAR derived chronological framework we develop a model of barrier spit accretion which describes the interaction between extreme events, fair weather coastal processes and sedimentary development that constrains the major episodes of barrier island evolution. The stratigraphy was defined using ground-penetrating radar (GPR) surveys complemented by sedimentological coring data. The stratigraphy is then conceptualised in a AAR chronostratigraphic framework to define a chronological order and allow the development of a stratigraphic model of the evolution of Southern Sylt. The AAR data provide high temporal resolution and have been used for dating stages of barrier spit accretion. The time lines are marked as storm surge generated erosion unconformities in the stratigraphic profile. Individual shells and shell fragments of Cerastoderma edule, Mya arenaria, Mytilus edulis and Scrobicularia plana have been accumulated by short-term storm events as shell layers associated with the erosion unconformities and have been dated by AAR. Time lines reveal that the barrier spit accretion occurred episodically, and is dependant on the provided rate of sand delivery. The general trend is that sequences young to the. South. The AAR derived time lines have been verified and correlated by historic maps and sea charts. It is apparent that spit enlargement at this site increased significantly during the Middle Ages (1593 - 1794) and was coupled with several intensive storm surges in this period. The findings indicate that when combined with GRR stratigraphy AAR provides useful results of high accuracy for dating stages of barrier spit progradation.

  2. First Year Sedimentological Characteristics and Morphological Evolution of an Artificial Berm at Fort Myers Beach, Florida

    E-print Network

    US Army Corps of Engineers

    First Year Sedimentological Characteristics and Morphological Evolution of an Artificial Berm Methods and Data Analysis 29 Results and Discussion 34 Sedimentological Characteristics of the Artificial Project Area 45 Control Area Northwest of Berm 47 Discussion of Sedimentological Characteristics 49

  3. Combining sedimentological, trace metal (Mn, Mo) and molecular evidence for reconstructing past water-column

    E-print Network

    Wehrli, Bernhard

    Combining sedimentological, trace metal (Mn, Mo) and molecular evidence for reconstructing past online 22 June 2013 Abstract Here, we present sedimentological, trace metal, and molecular evidence underscores the value of combining sedimentological, geochemical, and microbiological approaches

  4. Linking sedimentological, stratigraphic and diagenetic processes to understand unconventional reservoirs: the Upper Jurassic Vaca

    E-print Network

    Henderson, Gideon

    Linking sedimentological, stratigraphic and diagenetic processes to understand unconventional as to the scale of sedimentological variability within mudstone successions, and how related diagenetic alteration by Profs Taylor and Flint, to document the scale of sedimentological and diagenetic variability

  5. Les ongulés d'Atapuerca. Stratigraphie et biogéographie

    Microsoft Academic Search

    Jan van der Made

    2001-01-01

    The Ungulates from Atapuerca: Stratigraphy and Biogeography. The Sierra de Atapuerca, near Burgos (Spain), has various fissure fillings that yielded fossil animals, including fossil man, and archaeological remains, of late Early Pleistocene to Holocene age.Level TD6 in the locality Gran Dolina, which contained the type material of Homo antecessor as well as archaeological objects, and levels TDW4 and TDE5 yielded

  6. The stratigraphy of mass extinction

    NASA Astrophysics Data System (ADS)

    Holland, Steven

    2015-04-01

    The discovery of the end-Cretaceous bolide impact and the recognition of mass extinctions through taxonomic compendia triggered keen interest in the stratigraphic pattern of species extinctions. A principal question has been whether patterns of fossil occurrence indicate gradual, stepwise, pulsed, or instantaneous extinction. Based on principles of sequence stratigraphy, marine ecology, and evolution, numerical models of fossil occurrences in stratigraphic sections indicate that the last occurrence of fossils does not generally indicate the time of extinction but is instead controlled by stratigraphic architecture. These models have been confirmed in multiple field studies from different sedimentary basins of different ages. These models identify several distinct processes controlling the last occurrence of fossils. Anything that lowers the probability of collection of a species, such as peak abundance or environmental tolerance, causes the last occurrence to be shifted backward in time relative to the time of extinction. Sequence-bounding subaerial unconformities generally also force the last occurrence backward in time, except in the case of reworking, which may place fossil remains in rocks younger than the time of extinction. Unconformities also cause last occurrences of multiple species to be clustered as a result of the hiatus. Surfaces of abrupt facies change, such as flooding surfaces and surfaces of forced regression, also cause last occurrences to be clustered, with such clustering reflecting the environmental preferences of species. Stratigraphic condensation can also cause clustering of last occurrences. All of these surfaces - subaerial unconformities, flooding surfaces, surfaces of forced regression, and condensed horizons - have highly predictable positions with depositional sequences. Thus, it is the normal expectation that last occurrences should be clustered in the fossil record, that these clusters should occur in stratigraphically predictable positions, and that these clusters arise even when extinction rates are constant through time. Many interpretations of the tempo of extinction based on stratigraphic patterns of last occurrences need to be reinterpreted in light of the sequence stratigraphic record. In particular, double-pulsed extinctions are a common result of prolonged elevated extinction, with clusters of last occurrences produced by subaerial unconformities, flooding surfaces surfaces of forced regression, and condensed horizons.

  7. Lithostratigraphy, geophysics, biostratigraphy, and strontium-isotope stratigraphy of the surficial aquifer system of eastern Collier County and northern Monroe County, Florida

    USGS Publications Warehouse

    Weedman, S.D.; Paillet, F.L.; Edwards, L.E.; Simmons, K.R.; Scott, T.M.; Wardlaw, B.R.; Reese, R.S.; Blair, J.L.

    1999-01-01

    In 1997, ten cores were drilled in eastern Collier County and northern Monroe County, within the limits of the Big Cypress National Preserve. These cores represent a continuation of the study of seven cores in western Collier County begun in 1996 and reported in Weedman and others (1997) and Edwards and others (1998). This joint U.S. Geological Survey and Florida Geological Survey project is designed to acquire subsurface geologic and hydrologic data in southwest Florida to extend current ground-water models, thereby expanding the utility of these models for land and water management. In this report we describe the lithostratigraphy, geophysical logging, sedimentological analysis, dinocyst biostratigraphy, and strontium-isotope stratigraphy of these ten cores. The three geophysical logs (natural gamma-ray, induction conductivity, and neutron porosity) assumed to be related to formation lithology and water quality show that a number of clay-rich zones are present in all of the boreholes, and that pore-water conductivity increases with depth. The clay-rich zones are confirmed by visual examination of core material and sedimentological analysis. The relative transmissivity calculated at 10-foot-thick intervals shows that in six of the boreholes, high values are associated with the shallow aquifer in the 0-40 ft interval. Two of the boreholes (the most northerly and the most easterly) showed relatively higher values of transmissivity in permeable zones at or somewhat below 100 ft in depth. Core geology and logs indicate that the deeper aquifers are not more permeable than similar deeper zones in the other boreholes, but rather that the shallow aquifer appears to be less permeable in these two coreholes. The Arcadia (?) Formation was only penetrated in the deepest core where it is late Miocene in age. The Peace River Formation was penetrated in all but the two westernmost cores. It yields a late Miocene age, based on both dinocysts and strontium-isotope stratigraphy. The top is an irregular surface. Age and stratigraphic relations suggest that the upper part of the Peace River and lower part of the unnamed formation are at least partially equivalent laterally. The unnamed formation was recovered in every core. It is thinnest in the northernmost core and thickest to the west. Ages calculated from strontium isotopes range from 6.9 to 4.6 million years ago (late Miocene to early Pliocene). The top of the unnamed formation is deepest to the north and it becomes shallower to the southwest. The Tamiami Formation also was recovered in every core and consistently yields early Pliocene ages; it yields late Pliocene ages near the top in two cores. The age and lateral relations strongly suggest that the lower part of the Tamiami Formation and the upper part of the unnamed formation are lateral facies of each other. The Fort Thompson (?) Formation, Miami Limestone, and undifferentiated siliciclastic sediments and limestone at the very top of the cores were not dated.

  8. Integrating sequence stratigraphy and rock-physics to interpret seismic amplitudes and predict reservoir quality

    NASA Astrophysics Data System (ADS)

    Dutta, Tanima

    This dissertation focuses on the link between seismic amplitudes and reservoir properties. Prediction of reservoir properties, such as sorting, sand/shale ratio, and cement-volume from seismic amplitudes improves by integrating knowledge from multiple disciplines. The key contribution of this dissertation is to improve the prediction of reservoir properties by integrating sequence stratigraphy and rock physics. Sequence stratigraphy has been successfully used for qualitative interpretation of seismic amplitudes to predict reservoir properties. Rock physics modeling allows quantitative interpretation of seismic amplitudes. However, often there is uncertainty about selecting geologically appropriate rock physics model and its input parameters, away from the wells. In the present dissertation, we exploit the predictive power of sequence stratigraphy to extract the spatial trends of sedimentological parameters that control seismic amplitudes. These spatial trends of sedimentological parameters can serve as valuable constraints in rock physics modeling, especially away from the wells. Consequently, rock physics modeling, integrated with the trends from sequence stratigraphy, become useful for interpreting observed seismic amplitudes away from the wells in terms of underlying sedimentological parameters. We illustrate this methodology using a comprehensive dataset from channelized turbidite systems, deposited in minibasin settings in the offshore Equatorial Guinea, West Africa. First, we present a practical recipe for using closed-form expressions of effective medium models to predict seismic velocities in unconsolidated sandstones. We use an effective medium model that combines perfectly rough and smooth grains (the extended Walton model), and use that model to derive coordination number, porosity, and pressure relations for P and S wave velocities from experimental data. Our recipe provides reasonable fits to other experimental and borehole data, and specifically improves the predictions of shear wave velocities. In addition, we provide empirical relations on normal compaction depth trends of porosity, velocities, and VP/VS ratio for shale and clean sands in shallow, supra-salt sediments in the Gulf of Mexico. Next, we identify probable spatial trends of sand/shale ratio and sorting as predicted by the conventional sequence stratigraphic model in minibasin settings (spill-and-fill model). These spatial trends are evaluated using well data from offshore West Africa, and the same well data are used to calibrate rock physics models (modified soft-sand model) that provide links between P-impedance and quartz/clay ratio, and sorting. The spatial increase in sand/shale ratio and sorting corresponds to an overall increase in P-impedance, and AVO intercept and gradient. The results are used as a guide to interpret sedimentological parameters from seismic attributes, away from the well locations. We present a quantitative link between carbonate cement and seismic attributes by combining stratigraphie cycles and the rock physics model (modified differential effective medium model). The variation in carbonate cement volume in West Africa can be linked with two distinct stratigraphic cycles: the coarsening-upward cycles and the fining-upward cycles. Cemented sandstones associated with these cycles exhibit distinct signatures on P-impedance vs. porosity and AVO intercept vs. gradient crossplots. These observations are important for assessing reservoir properties in the West Africa as well as in other analogous depositional environments. Finally, we investigate the relationship between seismic velocities and time temperature index (TTI) using basin and petroleum system modeling at Rio Muni basin, West Africa. We find that both VP and VS increase exponentially with TTI. The results can be applied to predict TTI, and thereby thermal maturity, from observed velocities.

  9. Simplifying the stratigraphy of time

    Microsoft Academic Search

    Jan Zalasiewicz; Alan Smith; Patrick Brenchley; Jane Evans; Robert Knox; Nicholas Riley; Andrew Gale; F. John Gregory; Adrian Rushton; Philip Gibbard; Stephen Hesselbo; John Marshall; Michael Oates; Peter Rawson; Nigel Trewin

    2004-01-01

    We propose ending the distinction between the dual stratigraphic terminology of time-rock units (of chronostratigraphy) and geologic time units (of geochronology). The long-held, but widely misunderstood, distinction between these two essentially parallel time scales in stratigraphy has been rendered unnecessary by the widespread adoption of the global stratotype sections and points (GSSP---golden spike) principle in defining intervals of geologic time

  10. Mesozoic-Cenozoic sequence stratigraphy of European basins

    SciTech Connect

    Vail, P.R. (Rice Univ., Houston, TX (United States)); Jacquin, T. (Ecole des Mines de Paris, Paris (France))

    1993-09-01

    The preliminary results of the project, [open quotes]Mesozoic-Cenozoic Sequence Stratigraphy of European Basins[close quotes] (introduced at a seminar in Dijon, France, on May 18-20, 1992), show that the Mesozoic-Cenozoic stratigraphic succession of western Europe can be subdivided into a series of transgressive-regressive facies cycles (second order, 3-50 m.y.) and related to tectonic events by subsidence analysis and regional geology. The distribution of the second-order cycles are shown on a series of transects that extend from the Mediterranean to the North Sea. Where possible, each transgressive-regressive phase has been subdivided into a series of higher frequency sequence cycles (third order, 0.5-3 m.y.). These sequence cycles are identified in regions with good outcrops and biostratigraphic control. The sequence stratigraphy interpretation of these outcrop sections provides documentation for the age and distribution of the second- and third-order stratigraphic cycles of western Europe. Subsurface seismic and well data from the North Sea Basin, Paris basin, and the Mediterranean area are interpreted in terms of sequence stratigraphy and correlated to the outcrop reference sections. Chronobiostratigraphy and numerical ages are based on a series of new charts made especially for this project that show the latest correlation of the biostratigraphic zones for both microfossils and macrofossils across Europe. The charts also include a numerical time scale that reconciles the differences between existing time scales.

  11. Sedimentological analysis using geophysical well logs

    SciTech Connect

    Izotova, T.S. (Ukrainian State Geological Research Institute, Kiev (Ukraine))

    1993-09-01

    The application of geophysical well logs in sedimentology and stratigraphic prospecting holds great promise in solving a number of geological problems. A suite of logs provides data on a wide range of rock properties: vertical and lateral variation of resistivity, natural polarization, natural and induced radioactivity, shear strength, and acoustic properties. Each of these properties is controlled by the depositional environment of the sediments and their later diagenesis. The attention of geologists and geophysicists is drawn to new techniques in the interpretation of geophysical well logs for exploration, appraisal, and development of oil and gas fields. The relationship between geophysical logs and depositional environments is explored. Bulk composition, rock structure, and texture and facies variation can be quantified by electric log parameters. Also, the possibility of using logs to demonstrate long- and short-period sedimentary cycles is demonstrated. Methods of sedimentological analysis using geophysical well logs are demonstrated. The importance of a genetic approach in the interpretation of geological sequences and paleogeological reconstructions is emphasized using examples taken from oil and gas prospecting operations in the Ukraine.

  12. CAMBRIAN STRATIGRAPHY AND PALEONTOLOGY OF NORTHERN ARIZONA AND SOUTHERN NEVADA

    E-print Network

    Mateo, Jill M.

    #12;CAMBRIAN STRATIGRAPHY AND PALEONTOLOGY OF NORTHERN ARIZONA AND SOUTHERN NEVADA THE 16TH FIELD. A., and Foster, J. R., (editors), 2011, Cambrian Stratigraphy and Paleontology of Northern Arizona Stratigraphy and Paleontology of Northern Arizona and Southern Nevada REGIONAL SETTING AND GENERAL STRATIGRAPHY

  13. Sedimentology and taphonomy of the upper Karoo-equivalent Mpandi Formation in the Tuli Basin of Zimbabwe, with a new 40Ar/ 39Ar age for the Tuli basalts

    NASA Astrophysics Data System (ADS)

    Rogers, Raymond R.; Rogers, Kristina Curry; Munyikwa, Darlington; Terry, Rebecca C.; Singer, Bradley S.

    2004-10-01

    Karoo-equivalent rocks in the Tuli Basin of Zimbabwe are described, with a focus on the dinosaur-bearing Mpandi Formation, which correlates with the Elliot Formation (Late Triassic-Early Jurassic) in the main Karoo Basin. Isolated exposures of the Mpandi Formation along the banks of the Limpopo River consist of red silty claystones and siltstones that preserve root traces, small carbonate nodules, and hematite-coated prosauropod bones. These fine-grained facies accumulated on an ancient semi-arid floodplain. Widespread exposures of quartz-rich sandstone and siltstone representing the upper Mpandi Formation crop out on Sentinel Ranch. These strata preserve carbonate concretions and silicified root casts, and exhibit cross-bedding indicative of deposition via traction currents, presumably in stream channels. Prosauropod fossils are also preserved in the Sentinel Ranch exposures, with one particularly noteworthy site characterized by a nearly complete and articulated Massospondylus individual. An unconformity caps the Mpandi Formation in the study area, and this stratigraphically significant surface rests on a laterally-continuous zone of pervasive silicification interpreted as a silcrete. Morphologic, petrographic, and geochemical data indicate that the Mpandi silcrete formed by intensive leaching near the ground surface during prolonged hiatus. Chert clasts eroded from the silcrete are intercalated at the base of the overlying Samkoto Formation (equivalent to the Clarens Formation in the main Karoo Basin), which in turn is overlain by the Tuli basalts. These basalts, which are part of the Karoo Igneous Province, yield a new 40Ar/ 39Ar plateau age of 186.3 ± 1.2 Ma.

  14. Large-scale River Channel Shifts on the Western Indo-Gangetic Plains and their implications for the Bronze-age Harappan Civilisation Settlement Patterns

    NASA Astrophysics Data System (ADS)

    Gupta, S.; Sinha, R.; Mason, P.; Yadav, G.; Singh, A.; Carter, A.; Murrey, A.

    2009-12-01

    The distribution of settlements in ancient societies is commonly linked to the courses of large river systems. The Bronze Age Harappan civilisation (4800-3500BP) is no exception with the major sites of Harappa and Mohenjo-Daro located along the Indus river system. However, the largest collection of Harappan archaeological sites are associated with the postulated surface trace of a large palaeo-river channel in the drainage divide tract between the Ganges and Indus river systems, where no major river currently flows. It has been proposed that this palaeo-channel was occupied by a major river sourced in the Himalaya, and that this river provided water resources to sustain the extensive Harappan sites located along its ancient course. The abrupt abandonment of urban centres here at ~3500 BP has been explained as a consequence of river diversion, although alternative explanations for cultural decline have also been entertained. These hypotheses have remained untested because the stratigraphy and chronology of the postulated palaeochannel has never been determined. We use a combination of satellite image analysis, subsurface geophysical analysis and sediment coring to analyse the large-scale planform geometry, and detailed sedimentary and stratigraphic nature of the postulated palaeochannel in NW India. In particular we focus our analysis on a tract of the proposed channel adjacent to the major Harappan urban centre of Kalibangan in Rajastan State. We find that the surface trace of a postulated palaeochannel on satellite imagery is confirmed by subsurface geophysical investigation and detailed coring. In this presentation we will describe the remotely sensed character of the palaeochannel on satellite imagery, and the detailed stratigraphy and sedimentology based on resistivity investigations and sedimentological analysis of the cores. We will consider how changes in the course of the palaeochannel may have influenced settlement patterns of the Harappan civilisation in present day NW India.

  15. Sequence stratigraphy, basin dynamics, and petroleum geology of the Miocene from eastern Tunisia

    Microsoft Academic Search

    M. Bedir; S. Tlig; C. Bobier

    1996-01-01

    On the eastern margin of Tunisia, Miocene limestones, marl, and siliciclastic deposits crop out poorly and are lacking in age-diagnostic faunal content. The biostratigraphic and lithostratigraphic subdivisions of these series are not clearly defined. A regional study of subsurface sequences of this margin (Cap Bon, Gulf of Hammamet, and Sahel) by means of sequence stratigraphy and subsurface structural analyses permits

  16. Stratigraphy and structure of coalbed methane reservoirs in the United States: An overview

    Microsoft Academic Search

    Jack C Pashin

    1998-01-01

    Stratigraphy and geologic structure determine the shape, continuity and permeability of coal and are therefore critical considerations for designing exploration and production strategies for coalbed methane. Coal in the United States is dominantly of Pennsylvanian, Cretaceous and Tertiary age, and to date, more than 90% of the coalbed methane produced is from Pennsylvanian and Cretaceous strata of the Black Warrior

  17. Sedimentology by satellite: Space age approach to the coastal zone

    SciTech Connect

    Doyle, L.J.; McGarry, G.

    1988-08-01

    Satellites such as LANDSAT (EOSAT) and SPOT, with a variety of spectral configurations, combined with computer interpretive systems will allow us to synoptically evaluate coastal systems at relatively short intervals. Resolution of satellite images measured in meters dictates concentration on large-scale changes and fluxes. In areas of relatively clear water, such as the Mediterranean Sea or the eastern Gulf of Mexico, some satellite spectra will allow us to map below the sea surface and hence determine how the innermost shelf changes with time. To illustrate these points, we studied the barrier island system of the central west Florida coastline (USA) before and after the 1985 hurricane season. Two major storms impacted this region during that period. By computer overlaying before and after images, we were able to map changes in the barrier islands and to quantify acreage gained and lost. We were also able to detect and map changes in the submarine portions of the system, especially in the ebb and flood tidal deltas associated with inlets. The third dimension can be added by surveying the submarine features with high-resolution geophysics. Applications of this kind hold the promise of a new era in investigating beach/barrier islands and their relationship with the inner continental shelf.

  18. Sedimentology by satellite: Space age approach to the coastal zone

    Microsoft Academic Search

    L. J. Doyle; G. McGarry

    1988-01-01

    Satellites such as LANDSAT (EOSAT) and SPOT, with a variety of spectral configurations, combined with computer interpretive systems will allow us to synoptically evaluate coastal systems at relatively short intervals. Resolution of satellite images measured in meters dictates concentration on large-scale changes and fluxes. In areas of relatively clear water, such as the Mediterranean Sea or the eastern Gulf of

  19. Fluvial-deltaic sedimentation and stratigraphy of the ferron sandstone

    USGS Publications Warehouse

    Anderson, P.B.; Chidsey, T.C., Jr.; Ryer, T.A.

    1997-01-01

    East-central Utah has world-class outcrops of dominantly fluvial-deltaic Turonian to Coniacian aged strata deposited in the Cretaceous foreland basin. The Ferron Sandstone Member of the Mancos Shale records the influences of both tidal and wave energy on fluvial-dominated deltas on the western margin of the Cretaceous western interior seaway. Revisions of the stratigraphy are proposed for the Ferron Sandstone. Facies representing a variety of environments of deposition are well exposed, including delta-front, strandline, marginal marine, and coastal-plain. Some of these facies are described in detail for use in petroleum reservoir characterization and include permeability structure.

  20. Sequence stratigraphy, paleoclimate, and tectonics of coal-bearing strata

    SciTech Connect

    Jack C. Pashin; Robert A. Gastaldo (eds.)

    2004-07-15

    The origin of coal-bearing strata has been debated vigorously for more than a century, and with the emergence of coalbed methane as a major energy resource and the possibility of sequestering greenhouse gas in coal, this debate has never been more relevant. This volume contains 10 chapters on coal-bearing strata of Carboniferous through Tertiary age and is based on a special session that was held at an AAPG Annual Meeting in New Orleans. Contributors have employed a multitude of approaches ranging from basin analysis to plant taphonomy to support a variety of views on the sequence stratigraphy, paleoclimate, and tectonics of coal-bearing strata.

  1. Paleozoic cratonal/miogeoclinal stratigraphy in the western Mojave Desert

    SciTech Connect

    Martin, M.W.; Walker, J.D. (Univ. of Kansas, Lawrence (United States))

    1991-02-01

    Detailed mapping of metasedimentary rocks by many workers in the western Mojave Desert, California, has revealed Paleozoic lithologies of cratonal/miogeoclinal affinity. These exposures are metamorphosed, highly strained, and dismembered, and sit as roof pendants to Mesozoic and Tertiary intrusive rocks. In most outcrops no diagnosis fossils are preserved. Age correlation of these units is based, therefore, solely on similarities to lithologic packages outside the region. Despite the complex tectonic history this area has suffered since the late Paleozoic paleogeographic elements trend southwest into the region from where they are last clearly defined near the California-Nevada border. Dolomitic and calcitic marbles, quartzites, and biotite schists make up a major part of the stratigraphy in many areas. The stratigraphy and lithology of these units strongly suggest that they are correlative with late Precambrian-Cambrian units in the Death Valley region. Possible Ordovician and Devonian marbles also are present within some sections; at least one locality contains stromatoporoids of probable Devonian age. Calcite marbles tentatively correlated with lithologically similar Permian units in the Death Valley area are also represented and appear to be depositionally overlain by Mesozoic( ) shallow-marine and are-derived clastic rocks. Although the western Mojave Desert region has experienced compressional, transcurrent, and extensional deformation since late Paleozoic, our current understanding and restoration of this deformation history does not significantly alter the general southwest Paleozoic paleogeographic trends known to exist farther east.

  2. Sedimentology of coastal chevron deposits - tsunamigenic versus aeolian origin

    NASA Astrophysics Data System (ADS)

    Garcia Garcia, A.; Spiske, M.; Tsukamoto, S.; Schmidt, V.

    2012-12-01

    The genesis of v-shaped coastal chevrons is currently controversially discussed. So far, chevrons are only described regarding their morphology, but not in terms of their origin. Two possible origins of chevrons are proposed: both aeolian transport and tsunami inundation are discussed as depositing processes. We present initial results of a detailed sedimentological survey of Holocene coastal chevrons from the American and Australian west coasts. The chevrons were measured and levelled using a differential GPS system. Large scale internal structures were recorded by ground penetrating radar imaging. Trenches were dug for sampling and analyzing small scale internal structures. The sediment samples were used for the analysis of grain-size distributions, mineral composition and content of marine microorganisms. Additional samples were taken for optically stimulated luminescence (OSL) and radiocarbon dating. Furthermore, we took reference samples from beaches, cliffs and rivers, which could act as potential sediment sources for the surveyed chevrons. Tsunami deposits are commonly polymodal, exhibit a grain-size decrease and tend to show better sorting in landward direction. Such trends are not present in the surveyed chevrons. Most samples are well to moderately well sorted and unimodal. The OSL ages decrease in transport direction and indicate a long term generation process, such as dune migration, rather than a short term event like a tsunami. This fact is additionally underlined by land snails found in different stratigraphic levels within the Australian chevrons. Furthermore, the occurrence of intercalated soil horizons implies a change of stable and active migration phases. The initial results of this study point out to an aoelian origin of coastal chevrons and do not support the previously supposed thesis of a tsunamigenic origin.

  3. Seismic stratigraphy of the Bahamas

    SciTech Connect

    Ladd, J.W.; Sheridan, R.E.

    1987-06-01

    Seismic reflection profiles from the Straits of Florida, Northwest Providence Channel, Tongue of the Ocean, and Exuma Sound reveal a seismic stratigraphy characterized by a series of prograding Upper Cretaceous and Tertiary seismic sequences with seismic velocities generally less than 4 km/sec overlying a Lower Cretaceous section of low-amplitude reflections which are more nearly horizontal than the overlying prograding clinoforms and have seismic velocities greater than 5 km/sec. The prograding units are detrital shallow-water carbonates shed from nearby carbonate banks into deep intrabank basins that were established in the Late Cretaceous. The Lower Cretaceous units are probably shallow-water carbonate banks that were drowned in the middle Cretaceous but which, during the Early Cretaceous, extended from Florida throughout the Bahamas region. The seismic reflection profiles reveal a sharp angular unconformity at 5-sec two-way traveltime in northwest Tongue of the Ocean, suggesting a rift-drift unconformity and deposition on thinned continental crust. No such unconformity is seen in central and southeast Tongue of the Ocean or in Exuma Sound, suggesting that these areas are built on oceanic crust.

  4. Sequence stratigraphy - a historical perspective

    SciTech Connect

    Weimer, R.J. (Colorado School of Mines, Golden, CO (United States))

    1993-09-01

    Sequence stratigraphy was originally defined by Sloss as the study of genetically related strata that are bounded by unconformities. A sequence was regarded as a lithostratigraphic unit. The definition has been expanded to [open quotes]bounded by unconformities of their correlative conformities[close quotes] and a sequence was changes to a chronostratigraphic unit. In petroleum exploration within shelf areas of foreland and continental margin basins and cratonic basins, two types of unconformities are particularly important, both related to sea level changes. The first type of unconformity, a subaerially exposed lowstand surface of erosion (LSE, sequence boundary), is caused by relative sea level lowering. The boundary is recognized by incised paleovalleys, paleosols, and missing facies. The second type of unconformity is a transgressive surface of erosion (TSE, sometimes called a ravinement surface), and occurs where shoreface erosion moves over coastal plain deposits during a relative sea level rise. Examples of subtle stratigraphic traps in siliciclastic rocks associated with unconformities are discussed for the Lower Pennsylvanian strata of the mid-continent region. Also reviewed are the problems of applying the new sequence stratigraphic terminology in relation to established terminology.

  5. Author's personal copy Reverse engineering mother nature --Shale sedimentology from an

    E-print Network

    Polly, David

    Author's personal copy Review Reverse engineering mother nature -- Shale sedimentology from of the sedimentology of shales can take a variety of forms. At its simplest one can experiment with suspensions conducted by hydraulic engineers, the transfer of that knowledge to sedimentology is hampered by the fact

  6. Mid-Holocene strengthening of the Southern Westerlies in South America --Sedimentological evidences from

    E-print Network

    Gilli, Adrian

    Mid-Holocene strengthening of the Southern Westerlies in South America -- Sedimentological layers, a composite sedimentological record of almost 25 m was established covering the last ~16,000 cal yr. Sedimentological and petrophysical analysis of the cores revealed the establishment of a dominant

  7. CAMBRIAN STRATIGRAPHY AND PALEONTOLOGY OF NORTHERN ARIZONA AND SOUTHERN NEVADA

    E-print Network

    Mateo, Jill M.

    #12;CAMBRIAN STRATIGRAPHY AND PALEONTOLOGY OF NORTHERN ARIZONA AND SOUTHERN NEVADA THE 16TH FIELD. A., and Foster, J. R., (editors), 2011, Cambrian Stratigraphy and Paleontology of Northern Arizona! software ( National Geographic, 2002). 236 #12;Cambrian Stratigraphy and Paleontology of Northern Arizona

  8. CAMBRIAN STRATIGRAPHY AND PALEONTOLOGY OF NORTHERN ARIZONA AND SOUTHERN NEVADA

    E-print Network

    Mateo, Jill M.

    #12;CAMBRIAN STRATIGRAPHY AND PALEONTOLOGY OF NORTHERN ARIZONA AND SOUTHERN NEVADA THE 16TH FIELD. A., and Foster, J. R., (editors), 2011, Cambrian Stratigraphy and Paleontology of Northern Arizona and Southern Nevada: Museum of Northern Arizona Bulletin 67, 321 p. #12;Cambrian Stratigraphy and Paleontology

  9. The Baja California peninsula borderland: structural and sedimentological characteristics

    Microsoft Academic Search

    Enrique H. Nava-Sánchez; Donn S. Gorsline; Adolfo Molina-Cruz

    2001-01-01

    Structural and sedimentological data from three oceanographic cruises define the peninsular margin of the Gulf of California as a borderland similar to the California Continental Borderland. Bathymetric and high resolution seismic profiles show some active normal faults with a lateral strike slip component, which are parallel and oblique at low angle to the peninsular coast, and delimit horst and graben

  10. 1981 symposium on surface-mining hydrology, sedimentology, and reclamation

    SciTech Connect

    Graves, D.H. (ed.)

    1981-01-01

    Papers presented at the symposium are included in this volume. Discussions are presented under the following headings: reclamation; special applications; hydrology; sewage sludge application; sedimentology; and wildlife and recreation. The proceedings contains 80 papers, 74 of which are abstracted separately for inclusion in the Energy Data Base. (DMC)

  11. Sedimentology of coal and coal-bearing sequences

    SciTech Connect

    Rahmani, R.A.; Flores, R.M.

    1985-01-01

    Papers on all aspects of coal sedimentology are presented. The emphasis of the book is on coal depositional environments and facies models, and the main topics covered are coal environments, composition and geochemistry, facies models of associated clastic rocks, applications of facies models to coal mining, and sedimentary tectonics of coal basins.

  12. Sedimentology and geochemistry of saline lakes of the Great Plains

    Microsoft Academic Search

    W. M. Last; T. H. Schweyen

    1983-01-01

    Southern Saskatchewan and portions of adjacent Alberta, North Dakota and Montana are occupied by hundreds of saline and hypersaline lakes ranging in size from small prairie potholes (less than 1 km2) to relatively large bodies of water (greater than 300 km2). From a sedimentological perspective, distinction must be made between two basic types of saline lakes: playas and perennial lakes.

  13. Sedimentological study of sandy and shaly deposits (Beglia Formation) in Cap Bon area

    SciTech Connect

    Mahjoub, M.N.; Khessibi, M.

    1988-08-01

    Sedimentological study of sandy and shaly deposits of the Beglia formation has been made in Cap Bon (northeast of Tunisia) to define a sedimentological and paleogeographical model which could be extrapolated into the Gulf of Hammamet. The main results follow. (1) The Beglia formation is serravalian in age and has a migratory deltaic complex facies which includes river and marine affinities (flood plain and tidal). (2) Three intervals within the Beglia have been studied in detail and indicate a northwest-southeast depositional trend which the authors consider the main direction of the middle Miocene detrital deposits in northeastern Tunisia. (3) The fine and well-sorted sandstones which extend up to hectometric and kilometric size, observed in outcrop, are the distal zones of the migratory fans and bars. (4) These sandstone bodies, because of their relative small size within their deltaic model, do not extend to the Gulf of Hammamet. The sandstones offshore have produced hydrocarbons in several areas. They are the distal equivalent of the poorly sorted and coarse channel deposits studied in the outcrops.

  14. Sequence stratigraphy and sedimentology of the late Triassic TAG-I (Blocks 401\\/402, Berkine Basin, Algeria)

    Microsoft Academic Search

    P. Turner; D. Pilling; D. Walker; J. Exton; J. Binnie; N. Sabaou

    2001-01-01

    The Berkine Basin is an intra- or pericratonic basin that developed during the Middle to Late Triassic on the margin of the Saharan platform. The basin lies to the east of the north–south trending Hassi Messaoud Ridge which separates it from the Oued Mya Basin to the west. These Algerian basins lie to the south and east of the network

  15. Sedimentology and stratigraphy of the Palisades, Lower Comanche, and Arroyo Grande areas of the Colorado River Corridor, Grand Canyon, Arizona

    USGS Publications Warehouse

    Draut, Amy E.; Rubin, David M.; Dierker, Jennifer L.; Fairley, Helen C.; Griffiths, Ronald E.; Hazel, Joseph E., Jr.; Hunter, Ralph E.; Kohl, Keith; Leap, Lisa M.; Nials, Fred L.; Topping, David J.; Yeatts, Michael

    2005-01-01

    This report analyzes various depositional environments in three archaeologically significant areas of the Colorado River corridor in Grand Canyon. Archaeological features are built on and buried by fluvial, aeolian, and locally derived sediment, representing a complex interaction between geologic and cultural history. These analyses provide a basis for determining the potential influence of Glen Canyon Dam operations on selected archaeological sites and thus for guiding dam operations in order to facilitate preservation of cultural resources. This report presents initial results of a joint effort between geologists and archaeologists to evaluate the significance of various depositional processes and environments in the prehistoric formation and modern preservation of archaeological sites along the Colorado River corridor in Grand Canyon National Park. Stratigraphic investigations of the Palisades, Lower Comanche, and Arroyo Grande areas of Grand Canyon yield detailed information regarding the sedimentary history at these locations. Reconstruction of past depositional settings is critical to a thorough understanding of the geomorphic and stratigraphic evolution of these three archaeologically significant areas. This examination of past sedimentary environments allows the relative significance of fluvial, aeolian, debris-fan, and slope-wash sedimentary deposits to be identified at each site. In general the proportion of fluvial sediment (number and thickness of flood deposits) is shown to decrease away from the river, and locally derived sediment becomes more significant. Flood sequences often occur as 'couplets' that contain a fluvial deposit overlain by an interflood unit that reflects reworking of fluvial sediment at the land surface by wind and local runoff. Archaeological features are built on and buried by sediment of various depositional environments, implying a complex interaction between geologic and cultural history. Such field analysis, which combines geological and archaeological information and techniques, can provide a basis for future determination of the effects of Glen Canyon Dam operations on selected areas of the river corridor. This knowledge is essential to the development of preservation strategies for cultural resources in Grand Canyon.

  16. Continental, brackish and marine carbonates from the Lower Cretaceous of Kolone–Barbariga (Istria, Croatia): stratigraphy, sedimentology and geochemistry

    Microsoft Academic Search

    Michela Dini; Giorgio Tunis; Sandro Venturini

    1998-01-01

    During the Early Cretaceous, wide areas of the Dinaric–Adriatic Carbonate Platform emerged for long periods. The Hauterivian–Barremian carbonates from Kolone–Barbariga show a few typical examples of lacustrine facies with dinosaur bones and brackish\\/palustrine facies. The sequence of the platform is made for the most part by subtidal and intertidal limestones. The bone levels are located in a large depression few

  17. Sedimentology and sequence stratigraphy of paralic and shallow marine Upper Jurassic sandstones in the northern Danish Central Graben

    Microsoft Academic Search

    Peter N. Johannessen

    Paralic and shallow marine sandstones were deposited in the Danish Central Graben during Late Jurassic rifting when half-grabens were developed and the overall eustatic sea level rose. During the Kimmeridgian, an extensive plateau area consisting of the Heno Plateau and the Gertrud Plateau was situated between two highs, the Mandal High to the north, and the combined Inge and Mads

  18. Rudist formations in mixed siliciclastic-carbonate depositional environments, Upper Cretaceous, Austria: stratigraphy, sedimentology, and models of development

    Microsoft Academic Search

    Diethard Sanders; Josep Maria Pons

    1999-01-01

    The upper Turonian to lower Campanian succession (Lower Gosau Subgroup) of the Northern Calcareous Alps, Austria, provides a model for the development of rudist formations on wave-dominated, mixed siliciclastic-carbonate shelves that were situated on top of an accretionary wedge. The rudist formations are present either within parasequences or in non-cyclic transgressive successions, and include (a) skeletal mounds up to about

  19. The orbital record in stratigraphy

    NASA Technical Reports Server (NTRS)

    Fischer, Alfred G.

    1992-01-01

    Orbital signals are being discovered in pre-Pleistocene sediments. Due to their hierarchical nature these cycle patterns are complex, and the imprecision of geochronology generally makes the assignment of stratigraphic cycles to specific orbital cycles uncertain, but in sequences such as the limnic Newark Group under study by Olsen and pelagic Cretaceous sequence worked on by our Italo-American group the relative frequencies yield a definitive match to the Milankovitch hierarchy. Due to the multiple ways in which climate impinges on depositional systems, the orbital signals are recorded in a multiplicity of parameters, and affect different sedimentary facies in different ways. In platform carbonates, for example, the chief effect is via sea-level variations (possibly tied to fluctuating ice volume), resulting in cycles of emergence and submergence. In limnic systems it finds its most dramatic expression in alternations of lake and playa conditions. Biogenic pelagic oozes such as chalks and the limestones derived from them display variations in the carbonate supplied by planktonic organisms such as coccolithophores and foraminifera, and also record variations in the aeration of bottom waters. Whereas early studies of stratigraphic cyclicity relied mainly on bedding variations visible in the field, present studies are supplementing these with instrumental scans of geochemical, paleontological, and geophysical parameters which yield quantitative curves amenable to time-series analysis; such analysis is, however, limited by problems of distorted time-scales. My own work has been largely concentrated on pelagic systems. In these, the sensitivity of pelagic organisms to climatic-oceanic changes, combined with the sensitivity of botton life to changes in oxygen availability (commonly much more restricted in the Past than now) has left cyclic patterns related to orbital forcing. These systems are further attractive because (1) they tend to offer depositional continuity, and (2) presence of abundant microfossils yields close ties to geochronology. A tantalizing possibility that stratigraphy may yield a record of orbital signals unrelated to climate has turned up in magnetic studies of our Cretaceous core. Magnetic secular variations here carry a strong 39 ka periodicity, corresponding to the theoretical obliquity period of that time - Does the obliquity cycle perhaps have some direct influence on the magnetic field?

  20. Ice Sheet Stratigraphy Can Constrain Basal Slip

    NASA Astrophysics Data System (ADS)

    Wolovick, M.; Creyts, T. T.; Buck, W. R.; Bell, R. E.

    2014-12-01

    Basal slip is an important component of ice sheet mass flux and dynamics. Basal slip varies over time due to variations in basal temperature, water pressure, and sediment cover. All of these factors can create coherent patterns of basal slip that migrate over time. Our knowledge of the spatial variability in basal slip comes from inversions of driving stress, ice thickness, and surface velocity, but these inversions contain no information about temporal variability. We do not know if the patterns in slip revealed by those inversions move over time. While englacial stratigraphy has classically been used to constrain surface accumulation and geothermal flux, it is also sensitive to horizontal gradients in basal slip. Here we show that englacial stratigraphy can constrain the velocity of basal slip patterns. Englacial stratigraphy responds strongly to patterns of basal slip that move downstream over time close to the ice sheet velocity. In previous work, we used a thermomechanical model to discover that thermally controlled slip patterns migrate downstream and create stratigraphic structures, but we were unable to directly control the pattern velocity, as that arose naturally out of the model physics. Here, we use a kinematic flowline model that allows us to directly control pattern velocity, and thus is applicable to a wide variety of slip mechanisms in addition to basal temperature. We find that the largest and most intricate stratigraphic structures develop when the pattern moves at the column-average ice velocity. Patterns that move slower than the column-average ice velocity produce overturned stratigraphy in the lower part of the ice sheet, while patterns moving at the column-average eventually cause the entire ice sheet to overturn if they persist long enough. Based on these forward models, we develop an interpretive guide for deducing moving patterns in basal slip from ice sheet internal layers. Ice sheet internal stratigraphy represents a potentially vast untapped source of information on basal sliding.

  1. Seismo and sequence stratigraphy of Cenozoic units of the Morondava Basin, offshore western Madagascar

    NASA Astrophysics Data System (ADS)

    Kaufmann, Dirk; Stollhofen, Harald; Klimke, Jennifer; Franke, Dieter

    2015-04-01

    The N-S trending Morondava Basin extends in width from western onshore Madagascar over about 350 km westwards to the offshore Davie Ridge in the Mozambique Channel. Although basin formation was initiated during Karoo times, the main basin evolution took place during Jurassic rifting and subsequent drifting until middle Cretaceous as a result of Gondwana breakup (Geiger et al., 2004). Contemporaneous to the separation of India and Madagascar widespread flood basalts were emplaced during the late Cretaceous (Storey et al., 1995). Present knowledge of the Morondava Basin is mainly based on outcrop studies, seismic surveys and borehole information (e.g. Geiger et al., 2004), gathered in western onshore Madagascar, although the fast majority of the basin, including its depocenter is located offshore in the Mozambique Channel, now at up to 3,500 m water depth. Almost all of the recent offshore studies of the Morondava Basin rely on industrial data but up to date publications of exploration results are generally rare and mostly anonymized. Our study aims to extend knowledge, particularly on the offshore seismic and sequence stratigraphy of the Morondava Basin. A key question is also to test the proposed tectonic stability of the Davie Ridge over the last 40 Ma. For this purpose 12 seismic profiles and bathymetric data, acquired in early 2014 by RV SONNE, are interpreted. Most of the profiles cover the distal deep marine areas of the northern Morondava Basin between the Davie Ridge and the shelf break of Madagascar. Top Cretaceous, Top Eocene, Top Oligocene, the Middle Miocene Unconformity and the Base Pliocene, are mapped as major seismic marker horizons. Especially shelf and slope sedimentary units are important resources to reconstruct the tectonostratigraphic basin evolution. At the continental slope diffuse to chaotic seismic pattern of Miocene and younger age are identified which are subdivided by laterally continuous, high frequency reflectors with a higher impedance contrast. Bounded by the Base Tertiary and the Base Pliocene these units can be used to develop and verify a sequence stratigraphic approach for the Cenozoic in the Morondava Basin. Prelimary results indicate that the major sedimentation at the continental slope moved after Early Pliocene significantly landwards. In general the thickness of post-Pliocene units increases to the east. Work in progress encompasses the application of seismo and sequence stratigraphic concept for Mesozoic sedimentary units and a correlation with other, potentially time-equivalent, basins in the area, such as the Mandawa Basin in northern Mozambique. References Geiger, M., Clark, D.N., und Mette, W., 2004, Reappraisal of the timing of the break-up of Gondwana based on sedimentological und seismic evidence from the Morondava Basin, SW Madagascar: Journal of African Earth Sciences, v. 38, p. 363-381. Storey, M., Mahoney, J. J., Saunders, A. D., Duncan, R. A., Kelley, S. P., und Coffin, M. F., 1995, Timing of Hot Spot--Related Volcanism und the Breakup of Madagascar und India: Science, v. 267, no. 5199, p. 852-855.

  2. Testing the limits of high-resolution whole-rock ?13Ccarb stratigraphy

    NASA Astrophysics Data System (ADS)

    McLaughlin, P.; Emsbo, P.; Brett, C.; Hurth, M.; Sell, B. K.; Johnson, C. A.

    2014-12-01

    Uncertainty about the effects of "diagenetic noise" on primary ?13Ccarb signals has been a principal obstacle in interpreting whole-rock ?13Ccarb stratigraphy. We have evaluated the fidelity of the whole-rock ?13Ccarb signal through a high-resolution sampling of correlative marine Paleozoic sections in North America and Europe across facies transitions spanning pure limestone to calcareous black shale and sandstone. Sections altered by metosomatic (diagenetic and hydrothermal) processes were specifically targeted for comparison with pristine unaltered sections. Precise stratigraphic correlations were confirmed using bentonite fingerprinting/dating, Sr-isotope stratigraphy, and whole-rock XRF chemistry. Our results demonstrate that whole-rock ?13Ccarb is an extraordinarily robust signal of global marine ?13C compositions. Correlative sections show strikingly similar ?13Ccarb values and patterns regardless of location, facies and rock type. Closely spaced successions of pristine limestone show highly reproducible ?13Ccarb profiles. Remarkably, ?13Ccarb trends cut across zones of alteration with no offset, and sections completely replaced by diagenetic/hydrothermal dolomite produce the same ?13Ccarb profiles as their unaltered counterparts. Our study confirms that whole-rock ?13Ccarb is an unprecedented chronostratigraphic tool. Our high-resolution approach identified abrupt offsets in ?13Ccarb profiles that correspond with unconformity horizons (supported by sedimentologic features) that can be correlated throughout different basins around the globe. A systematic covariation between shallowing-deepening trends and ?13Ccarb demonstrates its primary origin. The fidelity of the high-resolution record provides previously unattainable fine-scale temporal correlation - a resolution that, ultimately, will be required to fully understand the processes that fractionate the global carbon reservoir and have led to its overarching control on Earths evolution.

  3. Stratigraphy and structure of the Williams Creek area, Hinsdale, Mineral, and Archuleta counties, Colorado

    E-print Network

    Moore, George Edwards

    1964-01-01

    rocks and the granite are unconformably overlain by the Entrada Sandstone of Late Jurassic age. MESOZOIC ROCKS The Mesozoic units cropping out in the Williams Creek area are widespread in the Four Corners region. In Table 2, the stratigraphic... Vegetation Land Use . PHYSIOGRAPHY Topography Drainage . STRATIGRAPHY General Statement . Precambrian Rocks Uncompahgre Formation Eolus Granite Mesozoic Rocks Jurassic System Entrada Formation. Wanakah Formation Pony Express Member Middle...

  4. Sedimentology: general introduction and definitions : fluvial sediment and channel morphology

    USGS Publications Warehouse

    Wolff, Roger G.; Benedict, Paul C.

    1964-01-01

    Sedimentology, the study of sedimentary rocks and the processes by which they are formed, includes and is related to a large number of phenomena. Sedimentology includes the five fundamental processes defined by the term sediaentation --weathering, erosion, transportation, deposition and diagenesis. Sedimentology shares with geomorphology the study of the surface features of the earth. Sedimentology also shares with hydrology the study of river.--channels. River channels are formed in part or in total as a result of flowing water and sediment transport, commonly called the "work of the rivers." This survey of published literature was made to aid in arriving at definitions which would be acceptable to, and representative of, a majority of professional personnel actively engaged in laboratory and field investigations related to the "work of the river." The definitions in this list are intended to explain the terms used in studies of fluvial sediment and channel morphology. No set of definitions can expect universal acceptance, however, i t is hoped that this compilation will be considered a summary and synthesis of present and past usage and that it will serve as a starting point for future usage. Multiple references are cited from textbooks, glossaries and dictionaries, scientific journals and u.s. Government publications. To obtain a mutual understanding and enhance precision, many of the proposed definitions are a composite of those selected from papers or reports covering research studies and field investigations. A draft of this glossary has been reviewed by a group of interested personnel. The results of this review have been carefully considered and the originally-suggested definitions have been revised accordingly, resulting in the present compilation. R. G. Wolff, with the help of Mrs. v. Blatcher, carried out the literature search and compilation of terms and the review results. Paul c. Benedict approved or composed the definitions as presented in this report.

  5. Jurassic sequence stratigraphy of the eastern Gulf Coastal Plain: Applications to hydrocarbon exploration

    SciTech Connect

    Tew, B.H.; Mancini, E.A.; Mink, R.M. (Geological Survey of Alabama, Tuscaloosa (United States))

    1991-03-01

    Based on regional stratigraphic and sedimentologic data, three unconformity-bounded depositional sequences associated with cycles of relative sea-level change and coastal onlap are recognized for Jurassic strata in the eastern Gulf Coastal Plain area. These sequences are designated, in ascending order, the LZAGC (Lower Zuni A Gulf Coast)-3.1, the LZAGC-4.1, and the LZAGC-4.2 sequences and include Callovian through Kimmeridgian Stage strata. An understanding of the relationship of Jurassic reservoirs to sequence stratigraphy can serve as an aid to hydrocarbon exploration in the eastern gulf area. The most extensive and productive Jurassic hydrocarbon reservoirs in the study area occur within the progradational, regressive highstand deposits of the LZAGC-3.1 and LZAGC-4.1 depositional sequences. For example, the majority of Norphlet sandstone reservoirs in the onshore and offshore Alabama area are interpreted to have accumulated in eolian dune, interdune, and wadi (fluvial) depositional environments, which occurred in association with the highstand regressive system of the LZAGC-3.1 sequence. The most important Smackover reservoirs generally consist of partially to completely dolomitized ooid and peloid packstones and grainstones in the upper portion of the unit. These reservoirs occur in subtidal to supratidal, shoaling-upward carbonate mudstone to grainstone cycles in the highstand regressive system of the LZAGC-4.1 sequence. In addition, minor reservoirs that are discontinuous and not well developed are associated with the shelf margin and transgressive systems of the LZAGC-4.1.

  6. GEOBULLETIN GeoBulletin is distributed weekly, by E-mail. Contributions are requested!

    E-print Network

    Carlson, Anders

    in sedimentology and stratigraphy, and geological mapping. Currently I am studying geology for the academic year interested in sedimentology and stratigraphy at Miami and have since taken additional courses at Trinity including sedimentology and stratigraphy, sedimentary petrology, and paleontology, paleoecology

  7. The Sedimentology and Alluvial Architecture of a Fluvial Braid Bars: the influence of scale and variability

    NASA Astrophysics Data System (ADS)

    Parsons, Daniel; Ashworth, Phillip; Sambrook Smith, Gregory; Best, Jim; Lunt, Ian; Orfeo, Oscar

    2015-04-01

    The influence of flow regime and scale on the sedimentology of river systems is largely unquantified. This paper presents results from ~ 30 km of ground penetrating radar (GPR) data from a mid-channel bar in the sixth largest river in the world, the Río Paraná, Argentina. The GPR profiles, with depth of penetration up to 12 m below the bar surface, allow a detailed quantification of substrate sedimentology of a large sandy braid bar ~ 3 km long by ~ 1 km wide on a grid with a 200 to 400 m spacing. Two facies were found to dominate the sedimentary architecture of the bar. The principal facies (~ 83% of total facies) comprises trough and planar cross-strata related to the migration of dunes, with the thickness of the cross-strata decreasing towards the bar surface. The second significant facies (~ 15%) is high-angle (generally 10-20°) strata that typically form by accretion at the bar margins or bartail. Clay drapes (< 2%) and cross-bar channels (< 1%) are shown to constitute only a minor part of the deposits. The paper compares these Río Paraná GPR surveys with other GPR studies of sandy braid bars from a range of different size river, that include the South Saskatchewan, Wisconsin, and Jamuna rivers. The dominance of dune deposits is ubiquitous to all rivers, with each also possessing a significant proportion of large-scale high-angle strata. However, two differences were found to exist between the deposits of these rivers: (1) the compound-bar deposits of smaller rivers contained greater proportions of the fills of cross-bar channels, which suggests a potential role for discharge variability as a factor in shaping the alluvial architecture through its impact on the frequency of sediment reworking over the bar tops, and, (2) the thickness of large-scale, high-angle sets decreases with the age of the bar, which suggests that the deposits of older bars may provide more useful geometrical analogues for interpreting ancient successions, than smaller transient, or recent, bar forms that have undergone only limited modification. The paper discusses the issue of flow variability in terms of both scale and the influences of tropical monsoonal signals on the sedimentology of the world's largest river systems.

  8. Sedimentology, Lithostratigraphy and Depositional History of the Laetoli Area

    Microsoft Academic Search

    Peter Ditchfield; Terry Harrison

    \\u000a A review of the stratigraphy and paleoenvironmental context of the main sedimentary units that outcrop at Laetoli is presented\\u000a here, with a primary focus on the Upper Laetolil Beds. The lithological sequences at many of the numbered paleontological\\u000a localities, as designated by Leakey (1987a), are described and sedimentary logs for many of these localities are presented.\\u000a The litho-facies as described

  9. Stratigraphy and paleontology of upper Pleistocene deposits in the interandean depression, northern Ecuador

    NASA Astrophysics Data System (ADS)

    Ficcarelli, G.; Azzaroli, A.; Borselli, V.; Coltorti, M.; Dramis, F.; Fejfar, O.; Hirtz, A.; Torre, D.

    1992-10-01

    In the Interandean Depression of northern Ecuador (Carchi Province), more than 50 m of pyroclastic and windblown deposits (Cangahua Formation) were deposited during the cold phases of the Quaternary, interrupted many times by the development of evolved paleosoils during interstadials. The deposition occurred during downcutting if the plateau and covered existing morphologic irregularities. The upper part of the Cangahua Formation includes three fossiliferous horizons that contain fauna of Lujanian Mammal Age. On the basis of geomorphologic, sedimentologic, and paleontologic evidence, the upper part of the Cangahua is referred to the latest Pleistocene. After this, a renewed phase of downcutting began, reflecting early Holocene climatic amelioration.

  10. Chicxulub Post-Impact Sedimentary Sequence: Integrated Borehole Paleogene Carbonate Stratigraphy

    NASA Astrophysics Data System (ADS)

    Fucugauchi, J. U.; Perez-Cruz, L. L.; Escobar-Sanchez, E.; Ortega-Nieto, A.; Velasco-Villarreal, M.

    2014-12-01

    The Chicxulub crater was formed by a bolide impact on the southern Gulf of Mexico at ~66 Ma ago that marked the Cretaceous/Paleogene (K/Pg) boundary, represented worldwide by the ejecta layer. The K/Pg boundary layer with its global distribution provides a high resolution marker, allowing high precision stratigraphic analyses in marine and continental sequences. Following crater formation, sedimentation re-established in the carbonate platform, filling the basin. Crater is located half on-land and half offshore, with the crater floor covered by sediments with variable thickness up to about 1 km. The target, impact and post-impact sequences have been drilled and cored, providing samples for stratigraphic, petrographic and physical-chemical laboratory studies. The post-impact stratigraphy has been analyzed in several studies at proximal, intermediate and distal outcrops and in the crater boreholes, using e.g., radiometric dating, micropaleontology, paleomagnetism, and strontium and stable isotope geochemistry. Emphasis has been given on the impact breccias-carbonates contact and the basal Paleocene sequence. Here we re-analyze the available data, revisiting the stratigraphy for the Santa Elena, Tekax, Peto and Yaxcopoil-1 boreholes using newly constructed detailed lithostratigraphic columns in the continuously cored boreholes. Additionally we extend the study to the Paleogene sequence in the Santa Elena and Yaxcopoil-1 boreholes using bulk carbon and oxygen isotopes, magnetic polarity, XRF core geochemistry and magnetic susceptibility stratigraphy. Results spanning chrons c29 to c24 constrain the K/Pg boundary, c29r-c29n polarity reversal and the Paleocene-Eocene thermal maximum, providing high resolution records. The basal Paleocene gap and age differences in an integrated stratigraphy are discussed and correlated to the GPTS scale and IODP marine isotope records. The extent and characteristics of crater structure and target/cover sediments have been imaged with terrestrial, marine and aerogeophysical surveys. We use the marine seismic sections for correlation of the geophysical logs and borehole stratigraphy, allowing lateral correlation across the crater and further constraining the sequence stratigraphy, platform evolution and impact effects.

  11. Lake Geneva Holocene delta seismic stratigraphy S11 High-resolution seismic stratigraphy of an Holocene lacustrine delta in

    E-print Network

    Gilli, Adrian

    Lake Geneva Holocene delta seismic stratigraphy S11 High-resolution seismic stratigraphy of an Holocene lacustrine delta in western Lake Geneva (Switzerland) IRA BASTER1, 2, STÃ?PHANIE GIRARDCLOS1, 3, ANDRÃ? PUGIN1, 4 & WALTER WILDI1 Key words: lacustrine delta, western Lake Geneva, Holocene, seismic

  12. Part II of manuscript submitted to Sedimentology, May, 2006 Unraveling the conundrum of river response to rising sea level from

    E-print Network

    Parker, Gary

    Part II of manuscript submitted to Sedimentology, May, 2006 1 Unraveling the conundrum of river to Sedimentology, May, 2006 2 deltas is adapted to describe the response of the Fly-Strickland River system, Papua of manuscript submitted to Sedimentology, May, 2006 3 Pleistocene-Holocene eustatic sea level rise of some 120 m

  13. Late-Quaternary morpho-sedimentology and submarine mass movements of the Betsiamites area, Lower St. Lawrence Estuary, Quebec, Canada

    E-print Network

    St-Ong, Guillaume

    Late-Quaternary morpho-sedimentology and submarine mass movements of the Betsiamites area, Lower St 2008 Accepted 4 March 2008 Keywords: submarine mass movements morpho-sedimentology multibeam bathymetry the submarine morpho-sedimentology of an area of 500 km2 with focus on the consequences of four mass movement

  14. Sedimentology of Seismo-Turbidites off the Cascadia and Northern California Active Tectonic Continental Margins, Northwest Pacific Ocean

    E-print Network

    Goldfinger, Chris

    ÔØ Å ÒÙ× Ö ÔØ Sedimentology of Seismo-Turbidites off the Cascadia and Northern California Active, Goldfinger, Chris, Escutia, Carlota, Sedimentology of Seismo-Turbidites off the Cascadia and Northern Cal ACCEPTED MANUSCRIPT 1 Sedimentology of Seismo-Turbidites off the Cascadia and Northern California Active

  15. Part I of Manuscript submitted to Sedimentology, May, 2006 Unraveling the conundrum of river response to rising sea level

    E-print Network

    Parker, Gary

    Part I of Manuscript submitted to Sedimentology, May, 2006 1 Unraveling the conundrum of river of Manuscript submitted to Sedimentology, May, 2006 2 Fly-Strickland River system, Papua New Guinea to Holocene of Manuscript submitted to Sedimentology, May, 2006 3 Mississippi River was able to resist drowning due to sea

  16. Sedimentological evidence for debris-flow formation of Martian gullies

    NASA Astrophysics Data System (ADS)

    de Haas, Tjalling; Hauber, Ernst; Ventra, Dario; Conway, Susan; Kleinhans, Maarten

    2015-04-01

    Gullies are among the youngest landforms formed by liquid water on Mars, and therefore of critical importance in resolving the planet's recent hydrologic and climatic history. The key to estimating the amount of liquid water involved in gully formation is their formative mechanism. Water-free sediment flows, debris flows and fluvial flows, which all require very different amounts of liquid water, contributed to gully formation but their abundance and effectiveness differs greatly between sites. We show that many gullies dominantly formed by debris flows, based on sedimentological analysis of outcrops in gully-fans rather than surficial debris-flow features, which are often degraded beyond recognition by weathering and wind erosion or masked by ice-dust mantling. This resolves the controversy between previously published morphometric analyses implying debris-flow formation and observations of modified fan surfaces often interpreted to have formed by fluvial flows. Furthermore, it shows that deriving formative processes on gullies from surface characteristics can be highly misleading, which should therefore be inferred from multiple approaches, including sedimentological outcrop and morphometric analyses.

  17. Probable age of Autolycus and calibration of lunar stratigraphy

    SciTech Connect

    Ryder, G. (Lunar and Planetary Institute, Houston, TX (USA)); Bogard, D. (NASA-Johnson Space Center, Houston, TX (USA)); Garrison, D. (Lockheed ESC, Houston, TX (USA))

    1991-02-01

    {sup 39}Ar-{sup 40}Ar analyses of three petrographically distinct, shocked Apollo 15 KREEP (i.e., high K, rare earth element, P, and other trace element contents) basalt samples demonstrate that a major impact event affected all three samples at about 2.1 Ga. The Copernican System craters Aristillus and Autolycus are to the north; a ray from one of them crosses the landing site and had been suggested prior to the Apollo 15 mission as a source of material that could be used to date these craters. Autolycus, the older of the two, is in a particularly appropriate terrain and is the most likely source of the 2.1 Ga heating and delivery event. With this calibration point, and if Autolycus really is a Copernican crater, the Copernican System lasted twice as long as has previously been suggested. Furthermore, the Moon was not subjected to a constant cratering rate over the past 3 b.y.; the average rate in the preceding Eratosthenian must have been twice that in the Copernican.

  18. New insights into Wellington Harbours' tectonic settings from marine geophysical and sedimentological data

    NASA Astrophysics Data System (ADS)

    Woelz, Susi; Nodder, Scott; Barnes, Philip; Orpin, Alan

    2015-04-01

    After the experience of several damaging coastal earthquakes in New Zealand in the last three years, the importance of locating and characterising the earthquake potential of active faults close to urban areas has become more obvious, especially when cities lie in complex tectonic settings as it is the case for Wellington. To assess the earthquake and tsunami potential and the associated hazard posed by such faults, it is necessary to characterise fault geometry, slip rate, earthquake history and earthquake potential. In the marine environment, we have the advantage that faults can be assessed cross-sectionally through the application of high-resolution geophysical data without having to excavate trenches across the active fault trace. We present new marine data from Wellington Harbour that helps to characterise three faults; the Wellington Fault at Kaiwharawhara, the Evans Bay Fault, and a newly discovered fault off Oriental Bay, informally referred to as the Mount Victoria Fault. New marine geophysical data has better delineated the location and characteristics of these faults. High-resolution multi-beam bathymetric data (50 cm grid-cell size), covering the entire Wellington Harbour, were also used to determine the occurrence of seafloor scarps associated with surface ruptures on the faults. Sediment cores from either side of the Wellington Fault off Kaiwharawhara Stream, in about 17.5 m water depth, provide insight into the late Quaternary-Holocene stratigraphy and age of sediments that have been deformed by activity on the faults delineated in Wellington Harbour. The stratigraphy reveals details of the post-glacial marine flooding of the harbour that occurred about 10,000 years ago.

  19. Fluvial responses to climate and sea-level change: a review and look forward

    E-print Network

    Törnqvist, Torbjörn E.

    stratigraphic, sedimentological and geochronological frameworks in a variety of continental interior sedimentology, Quaternary geology, sea-level change, sequence stratigraphy. Sedimentology (2000), 47 (Suppl. 1

  20. Fluvial landscapes - human societies interactions during the last 2000 years: the Middle Loire River and its embanking since the Middle Ages (France)

    NASA Astrophysics Data System (ADS)

    Castanet, Cyril; Carcaud, Nathalie

    2015-04-01

    This research deals with the study of fluvial landscapes, heavily and precociously transformed by societies (fluvial anthroposystems). It aims to characterize i), fluvial responses to climate, environmental and anthropogenic changes ii), history of hydraulical constructions relative to rivers iii), history of fluvial origin risks and their management - (Program: AGES Ancient Geomorphological EvolutionS of the Loire River hydrosystem). The Middle Loire River valley in the Val d'Orléans was strongly and precociously occupied, particularly during historical periods. Hydrosedimentary flows are there irregular. The river dykes were built during the Middle Ages (dykes named turcies) and the Modern Period, but ages and localizations of the oldest dykes were not precisely known. A systemic and multi-scaled approach aimed to characterize i), palaeo-hydrographical, -hydrological and -hydraulical evolutions of the Loire River, fluvial risks (palaeo-hazards and -vulnerabilities) and their management. It is based on an integrated approach, in and out archaeological sites: morpho-stratigraphy, sedimentology, geophysics, geochemistry, geomatics, geochronology, archaeology. Spatio-temporal variability of fluvial hazards is characterized. A model of the Loire River fluvial activity is developed: multicentennial scale variability, with higher fluvial activity episodes during the Gallo-Roman period, IX-XIth centuries and LIA. Fluvial patterns changes are indentified. Settlement dynamics and hydraulical constructions of the valley are specified. We establish the ages and localizations of the oldest discovered dikes of the Middle Loire River: after the Late Antiquity and before the end of the Early Middle Ages (2 dated dykes), between Bou and Orléans cities. During historical periods, we suggest 2 main thresholds concerning socio-environmental interactions: the first one during the Early Middle Ages (turcies: small scattered dykes), the second during the Modern Period (levees: high quasi-continuous dykes).

  1. Mesozoic stratigraphy of northwestern Australian and northern Himalayan margins

    SciTech Connect

    Ogg, J.; Kopaskamerkel, D.C.

    1989-03-01

    The Mesozoic stratigraphies of the Himalayan margin, the Argo abyssal plain, and the Exmouth Plateau exhibit marked contrasts in their sedimentation histories. The sedimentary sequence on the northeastern Exmouth Plateau off Australia includes a Carnian to Rhaetian sequence of fluviodeltaic and marine clastics and carbonates, capped by a shallowing-upward sequence of platform carbonates overlain, with a major unconformity, by marine Aptian sediments deposited during rapid subsidence of the plateau. Argo abyssal plain basement is overlain by red-brown, bioturbated, inoceramid-rich quartzose claystones, bentonites, and quartz siltstones, dated by radiolarians and benthic foraminifera as lowest Cretaceous. This is overlain by red and green claystones and nannofossil chalks. The basal age indicates that sea-floor spreading began in the earliest Cretaceous, not Oxfordian as had been thought. In the Thakkola region of Nepal, uppermost Triassic through Lower Jurassic shelf and carbonate platform facies are capped by a ferruginous oolite deposit of latest Bathonian to earliest Callovian age. Sedimentation resumed in the middle Oxfordian with deposition of Berriasian( ) deep-water black organic-rich mud. Following a valanginian regression and progradation of terrigenous clastics, Aptian black shales were deposited. In geological studies of the northwestern Australian margin, the ubiquitous hiatus within the Callovian-Oxfordian has been termed the breakup unconformity. Existence of a similar-aged hiatus in the Himalayas on a margin which formed during the late Paleozoic, absence of any Jurassic on the Exmouth Plateau, and the apparent initiation of spreading in the Argo basin during the earliest Cretaceous suggest that this widespread unconformity is not associated with a continental breakup in these regions.

  2. Osmium isotope stratigraphy of a marine ferromanganese crust

    USGS Publications Warehouse

    Klemm, V.; Levasseur, S.; Frank, M.; Hein, J.R.; Halliday, A.N.

    2005-01-01

    Ferromanganese crusts provide records of long term change in ocean circulation and continental weathering. However, calibrating their age prior to 10 Ma has been entirely based on empirical growth rate models using Co concentrations, which have inherently large uncertainties and fail to detect hiatuses and erosional events. We present a new method for dating these crusts by measuring their osmium (Os) isotope record and matching it to the well-known marine Os isotope evolution of the past 80 Ma. The well-characterised crust CD29-2 from the central Pacific, was believed to define a record of paleooceanographic change from 50 Ma. Previous growth rate estimates based on the Co method are consistent with the new Os isotope stratigraphy but the dating was grossly inaccurate due to long hiatuses that are now detectable. The new chronology shows that it in fact started growing prior to 70 Ma in the late Cretaceous and stopped growing or was eroded between 13.5 and 47 Ma. With this new technique it is now possible to exploit the full potential of the oceanographic and climatic records stored in Fe-Mn crusts. ?? 2005 Elsevier B.V. All rights reserved.

  3. LITHOEVENTS -OOLITES IN EVENT STRATIGRAPHY Paper No. 18-0

    E-print Network

    Calner, Mikael

    for noncommercial purposes advancing science and education, including classroom use, providing all reproductions Meeting (April 3­5, 2002) Session No. 18--Booth# 33 Stratigraphy (Posters) Heritage Hall: East 8:00 AM-12

  4. Shallow Subsurface Stratigraphy of the Wetumpka Impact Structure, Alabama USA

    NASA Astrophysics Data System (ADS)

    King, D. T.; Ormo, J.; Petruny, L.; Markin, J. K.; Tabares Rodenas, P.; Johnson, R. C.; Neathery, T. L.

    2012-09-01

    Wetumpka impact structure is a small, marine target feature on the Coastal Plain of Alabama. Eight core holes have been drilled in Wetumpka and the resulting shallow subsurface stratigraphy is presented in summary here.

  5. Seismic stratigraphy and structure of the Progreso Basin, Ecuador 

    E-print Network

    Goyes Arroyo, Patricio

    1987-01-01

    SEISMIC STRATIGRAPHY AND STRUCTURE OF THE PROGRESO BASIN, ECUADOR A Thesis by PATRICIO GOYES ARROYO Submitted to the Graduate College of Texas A&M University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE May... 1987 Major Subject: Oceanography SEISMIC STRATIGRAPHY AND STRUCTURE OF THE PROGRESO BASIN, ECUADOR A Thesis by PATRICIO GOYES ARROYO Approved as to style and content, by: Joe . 'atmns (Chairman) ornas '. . ' de (Member) i ram . ager...

  6. Sequential stratigraphy of Jurassic and Cretaceous in the central Saudi Arabian platform

    SciTech Connect

    Le Nindre, Y.M.; Manivit, J.; Vaslet, D. (Bureau de Recherches Geologiques et Minieres, Orleans (France)); Manivit, H. (Bureau de Recherches Geologiques et Minieres, Orleans (France) Univ. Pierre et Marie Curie, Paris (France))

    1991-08-01

    Depositional sequences and system tracts in the Jurassic and Cretaceous sedimentary rocks of the Central Saudi Arabian platform have been established on the basis of precise lithofacies analysis, detailed sedimentologic interpretation, and accurate age determination by ammonites, nautoli, brachipods, echinoids, and nannoflora. A eustatic depositional model integrated with accepted worldwide sequential stratigraphic data is proposed, and appears to correlate fairly well with the 1988 global sea level chart by Haq and others, particularly for the Lower and Middle Jurassic and the Middle and Upper Cretaceous. Ages determined by accurate biostratigraphic data enable time correlations to be made with third-order eustatic cycles from Vail's 1988 global chart. Eustatic changes therefore appear to be the main factors of sedimentary control during the Jurassic and Cretaceous on the Arabian platform.

  7. Sedimentology and origin of source rocks in the Tertiary Niger delta

    SciTech Connect

    Bustin, R.M.

    1988-08-01

    Organic matter in Tertiary strata of the Niger delta is mainly a mixture of types II and III, has a high pristane/phytane ratio (> 1.0), and is composed of the macerals vitrinite and minor liptinite. The main palynofacies are structured woody material, cuticles, pollen, spores, and opaque and minor amorphous organic matter. The distribution and abundance of the organic matter reflects the age and sedimentology of the strata. There is a progressive decline in mean total organic carbon (TOC) content from upper Eocene (2.2% TOC) to Pliocene strata (0.90% TOC) and an associated general decrease in hydrogen index (HI) and pristane/phytane ratio. The decrease in TOC and HI in younger strata mainly reflects increased dilution of a nearly constant supply of terrestrial organic matter associated with the generally higher sedimentation rates of younger strata. The low pristane/phytane ratio of younger strata may reflect less oxidizing depositional conditions. No rich source rocks occur in the Niger delta and, as conventionally measured, the strata have little or no oil generating potential. The poor quality of the source rocks has been compensated for by their greater volume and excellent migration routes. The Niger delta type of source rock - although an end member in terms of general source rock composition - appears to be relatively typical of Tertiary deltas.

  8. Geomorphological and sedimentological evidences in the Western Massif of Picos de Europa since the Last Glaciation

    NASA Astrophysics Data System (ADS)

    Ruiz-Fernández, Jesus; Oliva, Marc; Cruces, Anabela; Lopes, Vera; Conceição Freitas, Maria; García-Hernández, Cristina; Nieuwendam, Alexandre; López-Sáez, José Antonio; Gallinar, David; Geraldes, Miguel

    2015-04-01

    The Western Massif of Picos de Europa includes some of the highest peaks of the Cantabrian Mountains. However, the environmental evolution in this massif since the Last Glaciation is still poorly understood. This research provides a new geochronological approach to the sequence of environmental events occurred here since the maximum expansion of glaciers during the last Pleistocene glaciation. The distribution of the glacial landforms suggests four main stages regarding the environmental evolution in the massif: maximum glacial advance, phase of second maximum glacial expansion, Late Glacial and Little Ice Age. A 5.4-m long sedimentological section retrieved from the kame terrace of Belbín, in a mid-height area of the massif, complements the geomorphological interpretation and provides a continuous paleoenvironmental sequence from this area since the Last Glaciation until nowadays. This section suggests that the maximum glacial expansion occurred at a minimum age of 37.2 ka cal BP, significantly prior to the global Last Glacial Maximum. Subsequently, a new glacial expansion occurred around 18.7-22.5 ka cal BP. The melting of the glaciers after this phase generated a shallow lake in the Belbín depression. Lake sediments do not reveal the occurrence of a cold stage during the Late Glacial, whilst, at higher locations, moraine complexes were formed suggesting a glacier readvance. The terrestrification of this lake started at 8 ka cal BP, when Belbín changed to a peaty environment. At 5 ka cal BP human occupation started at the high lands of the massif according to the existence of charcoal particles in the section. The presence of moraines in the highest northern cirques evidences the last phase with formation of small glaciers in the Western Massif of Picos de Europa, corresponding to the Little Ice Age cold event. Since then, the warming climate has led to the melting of these glaciers.

  9. Sediment transport processes and their resulting stratigraphy: informing science and society

    NASA Astrophysics Data System (ADS)

    Nittrouer, J. A.

    2013-12-01

    Sediment transport physically shapes planetary surfaces by producing patterns of erosion and deposition, with the relative magnitudes of geomorphic actions varying according to environmental conditions. Where sediment fills accommodation space and generates accumulation, a stratigraphic archive develops that potentially harbors a trove of information documenting dynamic conditions during the periods of sediment production, transport and deposition. By investigating the stratigraphic record, it is possible to describe changes in surface environments, as well as hypothesize about the development of regional tectonic and climate regimes. Ultimately, information contained within the stratigraphic record is critical for evaluating the geological history of terrestrial planets. The enigma of stratigraphy, however, is that sediment deposition is finicky, there is no uninterrupted record, and while deposits may reflect only a brief temporal window, they may still be used to infer about conditions that encompass much longer periods of time. Consider a case where meter-scale dune foresets, deposited in a matter of minutes to hours, are in contact with sediments above and below that reflect entirely different depositional circumstances and are separated in time by a hiatus of thousands or perhaps millions of years. To effectively unlock the scientific trove bound in stratigraphy, it is first necessary to identify where such unconformities exist and the conditions that lead to their development. This challenge is made much simpler through scientific advances in understanding sediment transport processes -- the examination of how fluid and solids interact under modern conditions -- because this is precisely where sediment patterns first emerge to produce accumulation that builds a stratigraphic record. By advancing an understanding of process-based sedimentology, it is possible to enhance diagnostic evaluations of the stratigraphic record. Fortunately, over the past several decades, there have been numerous scientific advances pertaining to the coupling of sediment transport and hydrodynamics. This research has produced new theory about how sediments accumulating in many unique environments shape the stratigraphic record. Recent studies have taken advantage of novel methods for acquiring observational data, which in turn have been used to advance numerical modeling schemes as well as experimental designs. As an example, consider fluvial deltas: here, hydrodynamics are constantly evolving over space and time. Patterns of sediment deposition and erosion (from dune to delta-lobe scales), resolved using high-resolution 3-D acoustic data, are used as input data to construct models that further show how channel dynamics (e.g., avulsions) and kinematics (e.g., lateral migration) evolve due to sediment and hydrodynamic coupling. This information is used to propose new theories of delta stratigraphy, which are then tested by examining ancient fluvial-delta systems. Finally, research efforts evaluating modern sediment-transport and depositional processes offer significant benefits to society. For example, fluvial deltas are heavily relied upon for societal welfare and yet are among the most dynamic landscapes on Earth's surface. Therefore, research examining the evolution of these landscapes not only advances basic science, but also doubles as an exercise in applied geomorphology.

  10. 50 years of snow stratigraphy observations

    NASA Astrophysics Data System (ADS)

    Johansson, C.; Pohjola, V.; Jonasson, C.; Challagan, T. V.

    2012-04-01

    With start in autumn 1961 the Abisko Scientific Research Station (ASRS) located in the Swedish sub Arctic has performed snow stratigraphy observations, resulting in a unique 50 year long time series of data. The data set contains grain size, snow layer hardness, grain compactness and snow layer dryness, observed every second week during the winter season. In general snow and snow cover are important factors for the global radiation budget, and the earth's climate. On a more local scale the layered snowpack creates a relatively mild microclimate for Arctic plants and animals, and it also determines the water content of the snowpack (snow water equivalent) important for e.g. hydrological applications. Analysis of the snow stratigraphy data, divided into three consecutive time periods, show that there has been a change in the last time period. The variable most affected is the snow layer hardness, which shows an increase in hardness of the snowpack. The number of observations with a very hard snow layer/ice at ground level increased three-fold between the first two time periods and the last time period. The thickness of the bottom layer in the snowpack is also highly affected. There has been a 60% increase in layers thinner than 10 cm in the last time period, resulting in a mean reduction in the thickness of the bottom layer from 14 cm to 11 cm. Hence the living conditions for plants and animals at the ground surface have been highly changed. The changes in the snowpack are correlated to an increased mean winter air temperature. Thus, continued increasing, or temperatures within the same ranges as in the last time period, is likely to create harder snow condition in the future. These changes are likely to affect animals that live under the snow such as lemmings and voles or animals that graze sub-Arctic vegetation in winter (e.g. reindeer that would potentially require increased supplementary feeding that incurs financial costs to Sami reindeer herders). Any decrease in lemmings and vole populations is likely to have cascading effects on biodiversity, particularly predators such as arctic foxes and snowy owls.

  11. Stratigraphy and Leonardian F'usulinid Paleontology in Central Pequop Mountains,

    E-print Network

    Seamons, Kent E.

    Stratigraphy and Leonardian F'usulinid Paleontology in Central Pequop Mountains, Elko County ......................Systematic paleontology 110 General statement ............................ 110 ..............Genus

  12. Geomorphology, facies architecture, and high-resolution, non-marine sequence stratigraphy in avulsion deposits, Cumberland Marshes, Saskatchewan

    USGS Publications Warehouse

    Farrell, K.M.

    2001-01-01

    This paper demonstrates field relationships between landforms, facies, and high-resolution sequences in avulsion deposits. It defines the building blocks of a prograding avulsion sequence from a high-resolution sequence stratigraphy perspective, proposes concepts in non-marine sequence stratigraphy and flood basin evolution, and defines the continental equivalent to a parasequence. The geomorphic features investigated include a distributary channel and its levee, the Stage I crevasse splay of Smith et al. (Sedimentology, vol. 36 (1989) 1), and the local backswamp. Levees and splays have been poorly studied in the past, and three-dimensional (3D) studies are rare. In this study, stratigraphy is defined from the finest scale upward and facies are mapped in 3D. Genetically related successions are identified by defining a hierarchy of bounding surfaces. The genesis, architecture, geometry, and connectivity of facies are explored in 3D. The approach used here reveals that avulsion deposits are comparable in process, landform, facies, bounding surfaces, and scale to interdistributary bayfill, i.e. delta lobe deposits. Even a simple Stage I splay is a complex landform, composed of several geomorphic components, several facies and many depositional events. As in bayfill, an alluvial ridge forms as the feeder crevasse and its levees advance basinward through their own distributary mouth bar deposits to form a Stage I splay. This produces a shoestring-shaped concentration of disconnected sandbodies that is flanked by wings of heterolithic strata, that join beneath the terminal mouth bar. The proposed results challenge current paradigms. Defining a crevasse splay as a discrete sandbody potentially ignores 70% of the landform's volume. An individual sandbody is likely only a small part of a crevasse splay complex. The thickest sandbody is a terminal, channel associated feature, not a sheet that thins in the direction of propagation. The three stage model of splay evolution proposed by Smith et al. (Sedimentology, vol. 36 (1989) 1) is revised to include facies and geometries consistent with a bayfill model. By analogy with delta lobes, the avulsion sequence is a parasequence, provided that its definition is modified to be independent from sea level. In non-marine settings, facies contacts at the tops of regional peats, coals, and paleosols are analogous to marine flooding surfaces. A parasequence is redefined here as a relatively conformable succession of genetically related strata or landforms that is bounded by regional flooding surfaces or their correlative surfaces. This broader definition incorporates the concept of landscape evolution between regional flooding surfaces in a variety of depositional settings. With respect to landscape evolution, accommodation space has three spatial dimensions - vertical (x), lateral (y), and down-the-basin (z). A flood basin fills in as landforms vertically (x) and laterally accrete (y), and prograde down-the-basin (z). Vertical aggradation is limited by the elevation of maximum flood stage (local base level). Differential tectonism and geomorphology control the slope of the flood basin floor and the direction of landscape evolution. These processes produce parasequences that include inclined stratal surfaces and oriented, stacked macroforms (clinoforms) that show the magnitude and direction of landscape evolution. ?? 2001 Elsevier Science B.V. All rights reserved.

  13. Hauptdolomit (Norian) — stratigraphy, paleogeography and diagenesis

    NASA Astrophysics Data System (ADS)

    Fruth, I.; Scherreiks, R.

    1982-06-01

    Geochemical and carbonate petrographical methods were coordinated in facies investigations and environmental reevaluations, related to the Hauptdolomit (Hd.) = main doimite formation (±Norian) of the Northern Calcareous Alps. It is practical to distinguish eight, environmentally controlled, facies units (1-8) and three geochemical groups (I-III). Superimposed upon the environment pattern (tidal complex, lagoonal complex, barrier bar and shoal complex) is a predictable (geochemical) dolomitization and non-carbonate distribution. The vertical and lateral facies associations, their waxing and waning in the geologic columns, allow paleogeographic reconstructions. Especially important are clayey, ±bituminous facies, commonly known as "Seefeld facies", which are interpreted to be of mainly intertidal to very shallow near-shore, rather than of deep-water, origin. Threefold stratigraphy can be substantiated and is found to be practicable for the Hd. formation in a large part of the Northern Calcareous Alps. In an attempt to explain some of the phenomena associated with dolomitization in the Hd. formation, a model of anaerobic dolomitization has been considered, outlining steps of early diagenetic dolomitization.

  14. Foraminiferal stratigraphy of Ranikot (Paleocene) of Pakistan

    SciTech Connect

    Kureshy, A.A.

    1983-03-01

    The sedimentary deposits of Pakistan are divided into three distinct basins: the Lower Indus basin, the Upper Indus basin, and the Baluchistan basin. The Lower Indus basin is further divided into two parts; the northern part is the Sulaiman Province, and the southern part is known as Kirthar Province. The tertiary stratigraphy of Kirthar Province is conspicuous for its characteristic lithostratigraphic units. The Paleocene deposits of Kirthar Province are designated as Ranikot Group. The Ranikot Group was divided by Cheema et al in 1977 into three distinct lithostratigraphic units: the Khadro formation (Cardita beaumonti beds), Bara formation (Lower Ranikot), and Lakhra formation (Upper Ranikot). The Khadro and Lakhra formations are marine, characterized by foraminiferal assemblages. The characteristic planktonic forms are: Globigerina triloculinoides Plummer, Globorotalia pseudobulloids (Plummer), G. compressa (Plummer), G. valascoensis (Cushman), and G. pseudomenardii Bolli. The diagnostic forms of larger foraminifera are: Nummulites nuttalli Davies, Miscellanea (d'Archiac and Haime), Kathina major Smout, and Lockartia conditii (Nuttall). The planktonic foraminifera were assigned to Globorotali trinidadensis, G. pseudomenardii, and G. velasoensis zones of Kureshy in 1977, and larger foraminifera were assigned to Nummulities nuttalli zones of Kureshy in 1978.

  15. Jurassic stratigraphy of the Wiggins Arch, Mississippi

    SciTech Connect

    Rhodes, J.A.; Maxwell, G.B. (Mobil Oil Company, Houston, TX (United States))

    1993-09-01

    Mobil and Shell jointly explored the Wiggins arch area in southern Mississippi from 1985 to 1991. The effort concentrated on the Jurassic Norphlet and Smackover formations. Two wells were drilled into Paleozoic crystalline rocks and one well into the Pine Hill formation. Two of these wells were located on the southern side of the Wiggins arch and provide significant data for interpreting Jurassic stratigraphy. The Mobil No. 1 U.S.A. well encountered a complete Jurassic section, but with some significantly different facies than those encountered by wells to the north. A granite wash section is the equivalent to the Frisco City formation previously only found 100 mi to the north-northeast. All 300 ft of Smackover is crystalline dolomite. The Norphlet section is entirely granite wash. The Pine Hill anhydrite is unusually thick and interpreted to be equivalent to the Louann Salt. Correlations to other wells on the Wiggins arch, particularly the Conoco No. 1 Higgins, indicate that the Jurassic can be divided into three transgressive events separated by the Norphlet/Pine Hill and Frisco City/Buckner regressive events.

  16. Defining the Lateglacial stratigraphy in the Eastern-Alps using gravitational and glacial sedimentation sequences.

    NASA Astrophysics Data System (ADS)

    Günther Bichler, Mathias; Reindl, Martin; Reitner, Jürgen M.; Ivy-Ochs, Susan

    2015-04-01

    Traditional Alpine Lateglacial stratigraphy rests upon morphostratigraphic characteristics of glacial deposits (e.g. end moraines) which were defined in isolated type localities in different valleys. Thus, a "type valley" with spatial succession documenting the chronology of the whole Lateglacial glacier dynamic is missing. The so far used framework is overwhelmingly based on non-continuous erosional remnants mostly lacking sequences showing super-imposition. Hence absolutely dated (SED, 14C) Lateglacial to Holocene landforms are mostly not verified by an associating relative stratigraphy. Here we present the results of ongoing detailed geological and geomorphological mapping of Quaternary sediments and dating of related relevant depositional sequences in the inner-alpine part of the Eastern Alps. These allow us to constrain a general model of past glacier and mass movement dynamics from the termination of the LGM to the Holocene. To back up this model we show field examples of the neighbouring Hüttwinkl-valley and Gastein-valley, two typically northward trending valleys on the northern flank of the Hohe Tauern Range in the province of Salzburg, Austria. The head of the Hüttwinkl-valley reveals a succession of different landscape-forming events (glacial advances, glacial retreats and mass movements) since the Last Glacial Maximum (LGM), which enable us to reconstruct a local Lateglacial to Holocene stratigraphy based on unconformity-bounded sediment bodies. We dated the sediment-bodies of this super-imposed succession (two landslides bracketing a till cover of a dominant glacial stadial) with 10Be and in additon with 14C to augment the ages gained by exposure dating. With this very well dated Lateglacial depositional sequence as a reference we show how Quaternary features and sediments of neighbouring valleys fit into the assumed general model of landscape evolution since the LGM.

  17. ELASTIC-WAVEFIELD SEISMIC STRATIGRAPHY: A NEW SEISMIC IMAGING TECHNOLOGY

    SciTech Connect

    Bob A. Hardage

    2004-05-06

    The focus of elastic-wavefield seismic stratigraphy research shifted from onshore prospects to marine environments during this report period. Four-component ocean-bottom-cable (4-C OBC) seismic data acquired in water depths of 2400 to 2500 feet across Green Canyon Block 237 in the Gulf of Mexico were processed and analyzed. The P-P and P-SV images of strata immediately below the seafloor exhibit amazing differences in P-P and P-SV seismic facies. These data may be one of the classic examples of the basic concepts of elastic-wavefield seismic stratigraphy.

  18. Annual layers in polar firn detected by Borehole Optical Stratigraphy

    NASA Astrophysics Data System (ADS)

    Hawley, Robert L.; Waddington, Edwin D.; Alley, Richard B.; Taylor, Kendrick C.

    2003-08-01

    We have developed a system called Borehole Optical Stratigraphy which can detect annual layers in boreholes in polar firn. Borehole Optical Stratigraphy consists of a downhole camera package and post-processing routines, which allow us to measure the intensity of light emitted from an on-board source and returned from the borehole wall. We manually identify the annual layers in this optical signal. We used this system at Siple Dome, Antarctica, in the 2001-2002 austral summer season. Our results agree well with counts of annual layers detected with two different methods in an ice core recovered 50 meters from our borehole.

  19. What can I do with this major? AREAS EMPLOYERS

    E-print Network

    Berdichevsky, Victor

    Energy Sources) Stratigraphy Sedimentology Structural Geology Geophysics Geochemistry Economic Geology. #12;STRATEGIESEMPLOYERSAREAS (Geology, Page 2) ENVIRONMENTAL GEOLOGY GEOLOGIC MAPPING Sedimentology. Structural Geology Stratigraphy Sedimentology Remote Sensing Federal government agencies: US Geological

  20. Stable isotope stratigraphy of the shallow marine early Quaternary of Noordwijk, North Sea Basin.

    NASA Astrophysics Data System (ADS)

    Noorbergen, Lars J.; Lourens, Lucas J.; Munsterman, Dirk K.; Verreussel, Roel M. C. H.

    2015-04-01

    The North sea area is a classical region of Early Quaternary stratigraphy, comprising many investigations in both the terrestrial and marine realm. Several investigations suggested the imprint of early Quaternary glacial - interglacial cycles in the sedimentary archive. Complementary integration of these studies is however hampered due to scarcity of independent age control. Moreover, a counterintuitive relation between lithology and glacial - interglacial sea level fluctuation is further complicating palaeo-environmental interpretations. In order to tackle above problems an independent high resolution chronology is essential. Here, a high-resolution benthic stable isotope record is presented of shallow marine sediments from borehole Noordwijk covering the early Quaternary. Based on isotope value and pattern similarities, we calibrate our ?18O record of Noordwijk to the global LR04 reference stack [1]. The resultant high-resolution isotope chronology is providing important insights on regional stratigraphy. The time control is further used for correlating additional on- and offshore North Sea boreholes in order to create a regional interpretation of environmental and sedimentary changes. [1] Lisiecki, L.E., Raymo, M.E.A., (2005). Pliocene-Pleistocene stack of 57 globally distributed benthic d18O records. Paleoceanography, 20.

  1. Sedimentology of Martian Gravels from Mardi Twilight Imaging: Techniques

    NASA Technical Reports Server (NTRS)

    Garvin, James B.; Malin, Michael C.; Minitti, M. E.

    2014-01-01

    Quantitative sedimentologic analysis of gravel surfaces dominated by pebble-sized clasts has been employed in an effort to untangle aspects of the provenance of surface sediments on Mars using Curiosity's MARDI nadir-viewing camera operated at twilight Images have been systematically acquired since sol 310 providing a representative sample of gravel-covered surfaces since the rover departed the Shaler region. The MARDI Twilight imaging dataset offers approximately 1 millimeter spatial resolution (slightly out of focus) for patches beneath the rover that cover just under 1 m2 in area, under illumination that makes clast size and inter-clast spacing analysis relatively straightforward using semi- automated codes developed for use with nadir images. Twilight images are utilized for these analyses in order to reduce light scattering off dust deposited on the front MARDI lens element during the terminal stages of Curiosity's entry, descent and landing. Such scattering is worse when imaging bright, directly-illuminated surfaces; twilight imaging times yield diffusely-illuminated surfaces that improve the clarity of the resulting MARDI product. Twilight images are obtained between 10-30 minutes after local sunset, governed by the timing of the end of the no-heat window for the camera. Techniques were also utilized to examine data terrestrial locations (the Kau Desert in Hawaii and near Askja Caldera in Iceland). Methods employed include log hyperbolic size distribution (LHD) analysis and Delauney Triangulation (DT) inter-clast spacing analysis. This work extends the initial results reported in Yingst et al., that covered the initial landing zone, to the Rapid-Transit Route (RTR) towards Mount Sharp.

  2. Implications of sedimentological studies for environmental pollution assessment and management: Examples from fluvial systems in North Queensland and Western Australia

    Microsoft Academic Search

    Bradley D Eyre; David M McConchie

    1993-01-01

    Sedimentology is of increasing importance in environmental research, particularly environmental pollution studies, where past trends in environmental processes need to be combined with data on present conditions to predict likely future changes—the past and present as a key to the future. Two examples are used to illustrate the role of sedimentology in assessing the influence of major processes on the

  3. Overdeeping and stratigraphy of a typical Alpine foreland glacier

    NASA Astrophysics Data System (ADS)

    Salcher, Bernhard; Reinhard, Starnberger; Götz, Joachim

    2015-04-01

    The Northern Alpine Foreland was repeatedly covered by massive piedmont glaciers during Quaternary peak glacial periods. Remnants of the Salzach foreland glacier (Austria/Germany) represent the easternmost of a series of piedmont glaciers entering the Foreland by major Alpine valleys reaching far into the Alpine Molasse. The area of the former Salzach foreland glacier (SFG) marks a unique place as remnants of at least 4 glacial maxima meet an abundant geodatabase including information on the digital topography and the internal built up of glacial deposits derived from outcrops and several hundreds of drillings. During the LGM, it covered an area of more than 1000 km² and was even more extensive during older peak glacial periods. The lack of absolute ages as well as systemic investigation of the internal built up did so far impede the reconstruction on its dynamics. Here we aim to bring more light into the erosional and depositional history of a typical north Alpine piedmont glacier, the SFG, by analyzing drill log data, field outcrops, topography and the depositional ages of sediments. We focus on the proximal (axial) and distal parts of the SFG lobe. Some of the major unresolved questions regarding the Quaternary evolution of the major Alpine foreland glaciers are: Is the glacial erosion of Miocene bedrock the consequence of one glacial cycle or does it rather reflect successive erosional events during each glacial period? What is the spatial variability and potential depth of erosion? What is the structure and internal built up these deposits? The intent of this study is not to answer these questions in detail but to deliver important constraints: Our results indicate that more than 300- 400 m of bedrock were eroded during an early peak glacial period (such as antepenultimate glacial period or even earlier). Erosion was rather uniform across the lobe with larger values only occurring in the center (axis) of the glacier. Accumulation of more than 100 m of deposits occurred later, potentially during the antepenultimate and penultimate glacial maximum (MIS 6). Deposits suggest a characteristic stratigraphy of glaciofluvial sediments and basal tills, with the lithofacies of fluvial sediments varying from the proximal to distal lobe parts. The general impact of the LGM (MIS2) seems to be minor.

  4. Large-scale River Channel Shifts on the Western Indo-Gangetic Plains and their implications for the Bronze-age Harappan Civilisation Settlement Patterns

    NASA Astrophysics Data System (ADS)

    Gupta, S.; Singh, A.; Sinha, R.; Thomsen, K.; Murray, A. S.; Carter, A.; Mark, D. F.; Buylaert, J.; Mason, P.; Ferrat, M.

    2011-12-01

    The distribution of settlements in ancient societies is commonly linked to the courses of large river systems. The Bronze Age Harappan civilisation (4800-3500BP) is no exception with the major sites of Harappa and Mohenjo-Daro located along the Indus river system. However, the largest collection of Harappan archaeological sites are associated with the postulated surface trace of a large paleo-river channel in the drainage divide tract between the Ganges and Indus river systems, where no major river currently flows. It has been proposed that this paleo-channel was occupied by a major river sourced in the Himalaya, and that this river provided water resources to sustain the extensive Harappan sites located along its ancient course. The abrupt abandonment of urban centres here at ~3500 BP has been explained as a consequence of river diversion, although alternative explanations for cultural decline have also been entertained. These hypotheses have remained untested because the stratigraphy and chronology of the postulated paleochannel has never been determined. Here we investigate the evolution of these paleodrainage systems using a combination of satellite image analysis, subsurface geophysical analysis and sediment coring to analyse the large-scale planform geometry, and detailed sedimentary and stratigraphic nature of the postulated paleochannel in NW India. We focus our analysis on tracts of the proposed channel that lie adjacent to major Harappan urban centres in NW India, such as the site of Kalibngan in Rajastan. We find that the postulated surface trace of the paleochannel on satellite imagery is is confirmed by subsurface geophysical investigation and detailed coring. The sedimentology and stratigraphy of multiple cores taken at several transects along the trace of the paleochannel shows the evolution of the fluvial system. We determine the provenance of the fluvial channels using U-Pb dating of detrital zircons and Ar-Ar dating of detrital muscovites. These detrital minerals can be fingerprinted with potential source areas in the Himalaya using modern river sands and bedrock ages to constrain sediment sources. We use optically stimulated luminescence dating to develop age models for the cores. These data are combined to reconstruct the spatial and temporal evolution of this paleo-river and consider its influence on settlement patterns of the Harappan civilization in NW India.

  5. Evolution of Ganges-Brahmaputra western delta plain: Clues from sedimentology and carbon isotopes

    NASA Astrophysics Data System (ADS)

    Sarkar, A.; Sengupta, S.; McArthur, J. M.; Ravenscroft, P.; Bera, M. K.; Bhushan, Ravi; Samanta, A.; Agrawal, S.

    2009-12-01

    Sedimentology, carbon isotope and sequence stratigraphic analysis of subsurface sediments from western part of Ganges-Brahmaputra (GB) delta plain shows that a Late Quaternary marine clay and fluvial channel-overbank sediments of MIS 5 and 3 highstands are traceable below the Holocene strata. During the Last Glacial Maximum (LGM) sea-level lowering of >100 m produced a regional unconformity (type 1), represented by palaeosols and incised valley. C4 vegetation expanded on exposed lowstand surface in an ambient dry glacial climate. At ˜9 ka transgression inundated the lowstand surface pushing the coastline and mangrove front ˜100 km inland. Simultaneous intensification of monsoon and very high sediment discharge (˜4-8 times than modern) caused a rapid aggradation of both floodplain and estuarine valley fill deposits between 8 and 7 ka. The Hoogli River remaining along its present drainage possibly acted as the main conduit for transgression and sediment discharge that was subsequently abandoned. C3 vegetation dominated the delta plain during this time. From 7 ka onward progradation of delta plain started and continued till recent. This period experienced a mixed C3-C4 vegetation with localized mangroves in the mid-Holocene to dominant return of C4 vegetation in the late Holocene period. The study indicates that while the initiation of western part of GB delta occurred at least 1 ka earlier than the global mean delta formation age, the progradation started at ˜7 ka, at least 2 ka earlier than thought before. The terrestrial vegetation change was modulated by changes in depositional environment, specific ecological niches and climate rather than pCO 2.

  6. Geometric and sedimentologic characteristic of Mid-Miocene lowstand reservoir sandstones, offshore northwest Java, Indonesia

    SciTech Connect

    Lowry, P.; Kusumanegara, Y.; Warman, S. (ARCO Indonesia, Jakarta (Indonesia))

    1996-01-01

    Numerous reservoirs in the Upper Cibulakan Formation (Mid-Miocene) of the Offshore Northwest Java shelf occur in sharp-based sandbodies that range from less than 1 m up to 10 m in thickness. Well-log derived net-sand isopach and seismic amplitude maps of these sandbodies depict elongate features, that are 1-2 km wide and 5-8 km long. The orientation of the longest axis of these sandbodies is predominantly north-south. Conventional cores reveal that these sandbodies are burrowed to completely bioturbated sandstones. Common trace fossils associated with these sandbodies include Ophiomorpha, Teichichnus and Thalassinoides. The lower contact of these sands is typically sharp and is commonly associated with a Glossifungites surface and siderite mud clasts. Overlying and underlying mudstones are relatively devoid of burrowing. Benthonic foraminifera assemblages within these mudstones indicate inner to outer neritic conditions in a relatively restricted marine setting. The upper contact of these sandstones is gradational over a 0.5 to 1m interval. Sandbodies of the same age and similar facies were observed in outcrops in onshore west Java. Here, they can be observed to pinch out over a distance of 500 m. The lower bounding contact appears discordant with underlying interbedded sandstones and mudstones. Several of the sandstones contain abundant accumulations of the large, open marine, benthonic foraminifera Cycloclypeus and Lepidocyclina. Occasionally the concentration of these large foraminifera form limestones within the sharp-based sandbodies. These bioclastic deposits commonly exhibit planar-tabular and trough cross-stratification. The sandbodies are interpreted as having been emplaced during relative falls in sea-level within a large Mid-Miocene embayment. Our understanding of their geometry and sedimentologic characteristics is leading to a more effective exploitation strategy for these sandbodies in the Offshore Northwest Java area.

  7. Sedimentologic and biostratigraphic implications for early Eocene lacustrine systems, eastern Great Basin, Nevada

    SciTech Connect

    Dubiel, R.F.; Potter, C.J.; Snee, L.W. (Geological Survey, Denver, CO (United States)); Good, S.C. (State Univ. Coll., Cortland, NY (United States))

    1993-04-01

    A multidisciplinary study integrating sedimentology, molluscan paleontology and paleoecology, structural and geologic mapping, and [sup 40]Ar/[sup 39]Ar dating of volcanic flows indicates the White Sage Formation north of the Deep Creek Range on the NV-UT border was deposited during the early Eocene in marginal-lacustrine, lacustrine, freshwater-marsh, and minor terrestrial settings. Sedimentary facies include wave-reworked, locally derived Paleozoic carbonate-clast basal conglomerates in contact with bedrock; carbonate tufa mounds; organic-rich mudstones; and laminated to medium-bedded carbonates. The wave-reworked conglomerate implies a broad lake with considerable fetch to generate large waves, but one with only small drainage basins with sharp relief to supply the locally-derived clasts. There is a striking lack of any fluvial, deltaic, or alluvial-fan deposits that would indicate development of substantial drainage areas. The large tufa mounds indicate a high-wave-energy shoaling environment with stable substrate and topography. The profusion of lacustrine carbonates indicates dominantly chemical- or biochemical-induced deposition in a carbonate-saturated lake. The aquatic molluscan fauna indicates shallow, quiet lacustrine conditions with emergent vegetation. The limpets inhabited areas of rooted aquatic vegetation, and the terrestrial gastropods indicate marshes adjacent to the lacustrine system. The molluscan assemblage constrains the age of the White Sage as early Eocene, indicating a lacustrine system equivalent to the Sheep Pass Formation and to outcrops near Illipah, NV that have similar facies and molluscan faunas and that also lack significant fluvial, deltaic, or alluvial fan deposits. The data are consistent with a model wherein the White Sage, Sheep Pass, and Illipah carbonates were deposited in a large lake superimposed on preexisting topography with low relief and little or no syndepositional extension.

  8. Geometric and sedimentologic characteristic of Mid-Miocene lowstand reservoir sandstones, offshore northwest Java, Indonesia

    SciTech Connect

    Lowry, P.; Kusumanegara, Y.; Warman, S. [ARCO Indonesia, Jakarta (Indonesia)

    1996-12-31

    Numerous reservoirs in the Upper Cibulakan Formation (Mid-Miocene) of the Offshore Northwest Java shelf occur in sharp-based sandbodies that range from less than 1 m up to 10 m in thickness. Well-log derived net-sand isopach and seismic amplitude maps of these sandbodies depict elongate features, that are 1-2 km wide and 5-8 km long. The orientation of the longest axis of these sandbodies is predominantly north-south. Conventional cores reveal that these sandbodies are burrowed to completely bioturbated sandstones. Common trace fossils associated with these sandbodies include Ophiomorpha, Teichichnus and Thalassinoides. The lower contact of these sands is typically sharp and is commonly associated with a Glossifungites surface and siderite mud clasts. Overlying and underlying mudstones are relatively devoid of burrowing. Benthonic foraminifera assemblages within these mudstones indicate inner to outer neritic conditions in a relatively restricted marine setting. The upper contact of these sandstones is gradational over a 0.5 to 1m interval. Sandbodies of the same age and similar facies were observed in outcrops in onshore west Java. Here, they can be observed to pinch out over a distance of 500 m. The lower bounding contact appears discordant with underlying interbedded sandstones and mudstones. Several of the sandstones contain abundant accumulations of the large, open marine, benthonic foraminifera Cycloclypeus and Lepidocyclina. Occasionally the concentration of these large foraminifera form limestones within the sharp-based sandbodies. These bioclastic deposits commonly exhibit planar-tabular and trough cross-stratification. The sandbodies are interpreted as having been emplaced during relative falls in sea-level within a large Mid-Miocene embayment. Our understanding of their geometry and sedimentologic characteristics is leading to a more effective exploitation strategy for these sandbodies in the Offshore Northwest Java area.

  9. Workshop on quantitative dynamic stratigraphy. Final conference report

    SciTech Connect

    Cross, T.A.

    1988-04-01

    This document discusses the development of quantitative simulation models for the investigation of geologic systems. The selection of variables, model verification, evaluation, and future directions in quantitative dynamic stratigraphy (QDS) models are detailed. Interdisciplinary applications, integration, implementation, and transfer of QDS are also discussed. (FI)

  10. Perspective on the sequence stratigraphy of continental strata

    Microsoft Academic Search

    K. W. Shanley; P. J. McCabe

    1994-01-01

    This report is the result of a working group on continental sequence stratigraphy that was set up at the 1991 NUNA conference in Banff, Canada. To data, sequence stratigraphic concepts have been applied mainly to the marine realm, but unconformity-bounded units have long been recognized in nonmarine strata. Successful application of sequence stratigraphic concepts to continental strata requires careful consideration

  11. The volcanic stratigraphy and petrogenesis of the Oman ophiolite complex

    Microsoft Academic Search

    T. Alabaster; J. A. Pearce; J. Malpas

    1982-01-01

    The volcanic stratigraphy and trace element geochemistry of the Oman ophiolite complex indicate a multistage magmatic origin comprising: (1) magmatism due to sea-floor spreading in a marginal basin; (2) magmatism associated with discrete submarine volcanic centres or seamounts; (3) magmatism associated with crustal uplift and rifting; and (4) magmatism associated with continent-arc collision.

  12. Stratigraphy and sedimentation in the Mediterranean Ridge diapiric belt

    Microsoft Academic Search

    M. B. Cita; E. Erba; R. Lucchi; M. Pott; R. van der Meer; L. Nieto

    1996-01-01

    Two basic sediment types are recorded in the Mediterranean Ridge diapiric belt: the host sediment and the mud breccia. The host sediment consists of hemipelagic marl as dominant lithology, associated with sapropels and tephras as minor isochronous lithologies. A high resolution stratigraphy, which allows much more detailed and precise correlations than those based on biostratigraphy (essentially calcareous nannofossils) is applicable

  13. Revision of the late Pleistocene stratigraphy of Bermuda

    Microsoft Academic Search

    Paul J. Hearty

    2002-01-01

    The Quaternary stratigraphy of Bermuda is one of the world's most complete sedimentary records of interglacial highstands, representing at least the past million years. Yet in terms of the last interglacial (Rocky Bay Formation), marine isotope substage (MIS) 5e, only scanty deposits are preserved. In contrast, MIS 7, generally regarded as a diminutive interglaciation, exposes widespread emergent subtidal deposits of

  14. Glacioeustatic fluctuation: The mechanism linking stable isotope events and sequence stratigraphy from the early Oligocene to middle Miocene

    SciTech Connect

    Abreu, V. (Petrobras and Rice Univ., Houston, TX (United States)); Haddad, G. (Rice Univ., Houston, TX (United States))

    1996-01-01

    One of the most difficult challenges of sequence stratigraphy is the establishment of synchronism between events observed in widely-separated basins. Problems arise because the resolution of the best stratigraphic methods is not good enough to establish the synchronism of similar-aged events on a global scale. Unless a common mechanism affecting global eustasy is assumed, such as variations in the ice volume, there is no a priori reason to expect that sequences of similar age in widely-separated basins are indeed synchronous. The stable oxygen isotope composition of marine carbonates is a proxy for sea level which has been underutilized in sequence stratigraphy. Identification of isotope events is based on d[sup 18]O data from DSDP and ODP sites 522, 529, 563, 608, and 747 drilled in the Atlantic and Indian oceans. These records were used to define Oligocene and Miocene oxygen isotope zones. In addition, we present isotope data from PETROBRAS Well A drilled in the Campos Basin (Brazil). Ages of isotope events correspond well with the ages of sequence boundaries and maximum flooding surfaces. Because of the good correlation between the isotope and sequence stratigraphic records, we reconfirm that ice-volume change is the common mechanism driving sea-level fluctuations from the Oligocene to present.

  15. Glacioeustatic fluctuation: The mechanism linking stable isotope events and sequence stratigraphy from the early Oligocene to middle Miocene

    SciTech Connect

    Abreu, V. [Petrobras and Rice Univ., Houston, TX (United States); Haddad, G. [Rice Univ., Houston, TX (United States)

    1996-12-31

    One of the most difficult challenges of sequence stratigraphy is the establishment of synchronism between events observed in widely-separated basins. Problems arise because the resolution of the best stratigraphic methods is not good enough to establish the synchronism of similar-aged events on a global scale. Unless a common mechanism affecting global eustasy is assumed, such as variations in the ice volume, there is no a priori reason to expect that sequences of similar age in widely-separated basins are indeed synchronous. The stable oxygen isotope composition of marine carbonates is a proxy for sea level which has been underutilized in sequence stratigraphy. Identification of isotope events is based on d{sup 18}O data from DSDP and ODP sites 522, 529, 563, 608, and 747 drilled in the Atlantic and Indian oceans. These records were used to define Oligocene and Miocene oxygen isotope zones. In addition, we present isotope data from PETROBRAS Well A drilled in the Campos Basin (Brazil). Ages of isotope events correspond well with the ages of sequence boundaries and maximum flooding surfaces. Because of the good correlation between the isotope and sequence stratigraphic records, we reconfirm that ice-volume change is the common mechanism driving sea-level fluctuations from the Oligocene to present.

  16. Sedimentological Evidence For The Last Interglacial (Sensu Lato) From El'gygytgyn Crater Lake

    NASA Astrophysics Data System (ADS)

    Apfelbaum, M. A.; Brigham-Grette, J.; Asikainen, C.

    2002-12-01

    During May of 1998 a 13.0 m sediment core was retrieved from El'gygytgyn Crater Lake, located 100 km north of the Arctic Circle in northeast Siberia. The lake was formed by a 3.6 million year old meteorite impact, which generated a crater roughly 20 km in diameter. Geochronological age models of sediments from this core suggest that the upper 6.5 meters of the core represents ~150 ky of paleoenvironmental change from northeast Siberia (Nowaczyk et al., in press). The magnetic susceptibility record from the 1998 core shows a strong pattern of correlation with the Greenland Ice Sheet stable isotope record (GISP2) in the upper 6.0 meters of the core where significant age control exists, based upon optically stimulated luminescence ages (Forman and Pierson, unpublished data), magnetic events (Nowaczyk et al., in press), and significant shifts in pollen (Lozhkin et al., 2001). The marine isotopic stages derived from SPECMAP have been correlated to the magnetic susceptibility record of the 1998 core. Much of the current terrestrial study of marine isotopic stage 5 (MIS 5) and the Last Interglacial (LI, substage 5e) are confined to a few distinct long continental records predominately in Europe. The research presented here summarizes the LI signal from a key Arctic location. The climate signal contained within the sediments of the LI are particularly important, as the extensive length of the sediment record may provide a high resolution archive of interglacial climate patterns for comparison with the Holocene. As a result, a sedimentological record has been constructed for the interval spanning the LI. The core is almost entirely composed of silt and clay (25-85% silt and 20-75% clay) with a few intervals containing sand. Moreover, no significant correlation between grain size and magnetic susceptibility exists, as is the case in many lacustrine environments. Clay mineralogy analyses using x-ray diffraction show that the abundance of chlorite increases during colder periods within the upper 200 cm of the core, representing roughly the last 40ka (Asikainen, in progress). This work has been expanded to include the interstadial/stadial substages of MIS 4-6. The behavior of illite-smectite and chlorite during MIS 5 suggests that the warm/wet conditions associated with interglacials may not be as pronounced at high latitudes. An additional gravity core was recovered in 2000 and used for comparison with the LI sediments obtained in 1998. Detailed grain size measurements also yielded no significant correlation with magnetic susceptibilty. A high-resolution archive of petrographic thin sections has recently been constructed to explore changes on a much finer scale.

  17. The stratigraphy and palaeoenvironment of the Bathonian "Great Oolite Group" of Woodeaton Quarry, Oxfordshire.

    NASA Astrophysics Data System (ADS)

    Guthrie, Ronald; Stukins, Stephen; Raub, Tim

    2014-05-01

    Woodeaton Quarry, Oxfordshire, represents the most continuously exposed section of the Upper Bathonian 'Great Oolite Group' in the United Kingdom. Like most of the British Bathonian, it is lacking in reliable ammonite zonation from which to define a chronostratigraphy. The sedimentology of the succession can be broken up into two broad facies types: A clay rich, brackish lagoonal environment with intermixed freshwater-influenced flora and fauna; A marginal marine calcareous succession of an oolitic nature with periodic mud-drape intervals. The marginal marine depositional setting, the completeness of the Upper Bathonian stratigraphy and lack of biostratigraphically important macrofauna has motivated this study into the micropalaeontology of Woodeaton. The primary aims of this study are to use foraminifera and ostracods to reconstruct the palaeoenvironments and to refine the biostratigraphy of the Upper Bathonian. The studied succession commences at the top of the Taynton Limestone Formation, which fines upwards into the clay-rich Rutland Formation. Several species of marine ostracods known from the Mid-Upper Bathonian are recovered from the base of the Rutland Formation, such as Praeschuleridea confossa and Angliaecytherldea calvata, as well as fragments of fish scales and elasmobranch teeth. Freshwater influence is evident further up the Rutland Formation where freshwater charophytes, nested bivalves and ostracods of the genus Bisulcocypris have been found. The progression from the Rutland Formation's marine base into the freshwater influenced clays is clear from the varied micropalaeontological fauna. A return to marine conditions in the overlying White Limestone Formation can be observed through the increasing number of benthic foraminiferal taxa - with Spirillina and Lenticulina the most abundant - compared to the Rutland Formation. Within the Shipton and Ardley Members there are also indicative marine ostracod taxa present (including Acanthocythere spiniscutulata and Terquemula robusta). The upper part of the section exposes the Bladon Member that displays a relative shallowing within the fimbriatus-waltoni beds preserving a number of in situ rootlets and exogenous carbonised logs. This unit contains a mixed assemblage of marine species of ostracods (e.g. Fossaterquemula blakeana) and foraminifera (e.g. Lenticulina tricarinella) in association with freshwater ostracod taxa such as Timiriasevia sp. The succession at Woodeaton Quarry of Upper Bathonian carbonates exhibits microfaunal assemblages that can be viewed as direct proxies to the palaeoenvironment. The assemblages of ostracods and foraminifera indicate marine conditions prevailed in the basal Rutland Formation before the evolution of a freshwater environment. A return to a marine dominated environment with freshwater fluctuations occurs throughout the White Limestone Formation. It is through the high-resolution micropalaeontological study that palaeoenvironmental analysis can be refined in the marginal marine settings of the Upper Bathonian in Oxfordshire.

  18. An evaluation of the Early Cretaceous of Spitsbergen: new insights into stratigraphy and palaeoclimate

    NASA Astrophysics Data System (ADS)

    Vickers, Madeleine; Price, Gregory; FitzPatrick, Meriel; Watkinson, Matthew; Jerrett, Rhodri

    2015-04-01

    During the Early Cretaceous, Spitsbergen was located at a palaeolatitude of ~60°N. Abundant fossil wood derived from conifer forests, dinosaur trackways, enigmatic deposits such as glendonite horizons and rare outsized clasts, and stable isotope data from the Early Cretaceous formations of Spitsbergen suggest that the climate at that time was much more dynamic than the traditional view of "invariant greenhouse" conditions on Earth. The purpose of this study is to test the veracity of using such proxies as climate indicators, and to evaluate the climatic character of Arctic Svalbard during the Early Cretaceous. To these ends, the sedimentological and sequence stratigraphic context of glendonites and outsized clasts within the Rurikfjellet, Helvetiafjellet and Carolinefjellet formations are being documented. This is being achieved through high resolution sedimentary logging (bed-scale) of the Early Cretaceous succession at multiple locations, documentation of glendonites, outsized clasts, together with sampling (every < 0.5m) for stable isotope analysis, in order to constrain and elucidate the nature of environmental and possible climatic variations during this time. The Early Cretaceous succession at Festningen is 750m thick and is considered to have been deposited between the Berriasian and late Aptian/early Albian. The basal Rurikfjellet Formation comprises a normally regressive water to wave/storm dominated shoreface. A forced regression (expressed as a regional unconformity) marks the base of the overlying Helvetiafjellet Formation. The Helvetiafjellet and overlying Carolinefjellet Formation represent a strongly aggradational, weakly transgressive succession characterised by delta plain deposits, containing abundant terrestrial woody material and with ornithopod footprints, passing upward into deep water mudstones and rare storm beds. Abundant glendonites occur within the shoreface deposits of the upper Rurikfjellet Formation, and in the Carolinefjellet Formation. The expanded nature of the sedimentary deposits in the Carolinefjellet Formation suggest high subsidence rates and high sedimentation rates, implying that the main signature here is that of higher rates of tectonic subsidence, rather than a eustatic control possibly evident in the lower part of the succession. Stable isotope results from the Valanginian - Barremian part of the succession (the upper Rurikfjellet and Helvetiafjellet formations) are also be presented. These data are being used to both improve the resolution of dating of the succession (carbon-isotope stratigraphy), and to shed light on how global perturbations in the carbon cycle, particularly during the Valanginian, may have been expressed in the northern high latitudes. This study aims to improve our understanding of the global climatic and sequence stratigraphic context in which these rocks were deposited.

  19. New insight into the sedimentology and stratigraphy of the Dur At Talah tidal-fluvial transition sequence (Eocene-Oligocene, Sirt Basin, Libya)

    NASA Astrophysics Data System (ADS)

    Abouessa, Ashour; Pelletier, Jonathan; Duringer, Philippe; Schuster, Mathieu; Schaeffer, Philippe; Métais, Eddy; Benammi, Mouloud; Salem, Mustafa; Hlal, Osama; Brunet, Michel; Jaeger, Jean-Jacques; Rubino, Jean-Loup

    2012-04-01

    The Dur At Talah escarpment is exposed in the Abu Tumayam Trough at the southern part of the Sirt Basin, central Libya. The cliff (˜145 m high and ˜150 km long) is oriented along an E-W axis and faces southward. Only a few field studies have been previously carried out in this area, and these were mainly focused on the succession's famous vertebrate fossil-content. The reconstruction of the depositional environments, which is the purpose of this paper, remained poorly documented. In this study, the uppermost Eocene rock succession composing the Dur At Talah escarpment is divided into two stratigraphic units: the New Idam Unit at the base composed of highly bioturbated fine sand/claystone alternations, and the Sarir Unit at the top dominated by medium to very coarse grading sometimes to microconglomeratic sandstones. This complete succession is built up of shallow marine (New Idam Unit) to fluvial (upper part of Sarir Unit) deposits passing through a "marine/fluvial" transition zone (lower Sarir Unit). The stratigraphic succession suggests a global regressive trend. The marine part of the New Idam Unit is dominated by deposits attributed to tidal depositional environments including tidal flat, tidal channel and tidal bars as well as biostroms of oyster shells at the base of the unit. The lower part of the Sarir Unit appears to be deposited in a fluvial influenced, tide-dominated environment. The upper part of the Sarir Unit, made of coarse-grained to microconglomeratic sandstones interbedded with paleosoil horizons, is interpreted as being fluvial.

  20. Stratigraphy, sedimentology, and ichnology of the Late Pennsylvanian Glenshaw Formation (Lower Conemaugh Group), southern Dunkard basin, Ohio-Kentucky-West Virginia

    SciTech Connect

    Martino, R.L. (Marshall Univ., Huntington, WV (United States). Dept. of Geology)

    1994-03-01

    Facies analysis of outcrops of the Glenshaw Formation was carried out at 45 localities over a 761 sq. km area. The glenshaw Formation is 61--76 m thick in the study area. Four marine units (Lower Brush Creek, Upper Brush Creek, Cambridge , and Ames) occur which contain invertebrate body fossils and/or trace fossils including Teichichnus, Rhizocorallium, Aulichnites, Paleophycus, Lockeia, and Curvolithus. Alluvial channel-fills contain internal features that reflect deposition in high sinuosity suspended or mixed load rivers. Paleocurrent data (N = 77) are broadly dispersed with a mean azimuth of 335 degrees. Overbank facies have yielded trackways from giant arthropods and Eryopoid amphibians (Limnopus). There are fewer marine units in the glenshaw than toward the north and west which has made direct detailed correlation of much of the formation problematic. The coal beds and marine units used previous stratigraphic studies may be extended through the recognition of non-coal-bearing paleosols and marine-influenced intervals distinguished by facies relations, and sedimentary and biogenic structures. Nine laterally persistent, paleosol-bounded packages occur which are comparable to allocyclic T-R units reported by Busch and Rollins (1984) from Pennsylvania and Ohio. Alternating episodes of soil formation and alluvial aggradation may reflect updip coastal plain responses to low stand incision of drainage lines and sediment bypassing followed by aggradation of alluvial systems in response to rising sea level. Climate changes may also have played a role in sediment flux.

  1. Stratigraphie et paléontologie (plantes, vertébrés) de la série paralique Albien terminal–Cénomanien basal de Tonnay-Charente (Charente-Maritime, France)

    Microsoft Academic Search

    Didier Néraudeau; Romain Vullo; Bernard Gomez; Vincent Perrichot; Blaise Videt

    2005-01-01

    Stratigraphy and palaeontology (plants, vertebrates) of the paralic deposits from the Uppermost Albian–Lower Cenomanian of Tonnay-Charente (Charente-Maritime, France). The Tonnay-Charente area (Charente-Maritime, southwestern France) contains several sand and clay exploitations of Uppermost Albian and Lower Cenomanian ages. These sediments have been deposited in a coastal area where plant remains, amber, and aquatic or terrestrial vertebrates were trapped. The two last

  2. Stratigraphy, petrology, and structure of the Pingston terrane, Mount Hayes C-5 and C-6 quadrangles, eastern Alaska Range, Alaska

    NASA Astrophysics Data System (ADS)

    Nokleberg, W. J.; Schwab, C. E.; Miyaoka, R. T.; Buhrmaster, C. L.

    Recent field, petrologic, and structural studies of the Pingston terrane in the Mount Hayes C-5 and C-6 quandrangles reveal that in this area the terrane: (1) has a highly distinctive stratigraphy, age, petrology (relict textures, relict minerals, and metamorphic facies), and structure; and (2) differs markedly from that described in previous studies. These more recent studies indicate that the major rock types, in order of decreasing abundance, are meta-andesite, metadacite and metarhyodacite flows and (or) tuff, metabasalt, metagabbro, metavolcanic graywacke, metagray-wacke, metasiltstone, metaquartzite or metachert, and very sparse marble. The general petrography of the major rock units in the Pingston terrane is given.

  3. Acoustic stratigraphy and hydrothermal activity within Epi Submarine Caldera, Vanuatu, New Hebrides Arc

    USGS Publications Warehouse

    Greene, H. Gary; Exon, N.F.

    1988-01-01

    Geological and geophysical surveys of active submarine volcanoes offshore and southeast of Epi Island, Vanuatu, New Hebrides Arc, have delineated details of the structure and acoustic stratigraphy of three volcanic cones. These submarine cones, named Epia, Epib, and Epic, are aligned east-west and spaced 3.5 km apart on the rim of a submerged caldera. At least three acoustic sequences, of presumed Quaternary age, can be identified on single-channel seismic-reflection profiles. Rocks dredged from these cones include basalt, dacite, and cognate gabbroic inclusions with magmatic affinities similar to those of the Karua (an active submarine volcano off the southeastern tip of Epi) lavas. ?? 1988 Springer-Verlag New York Inc.

  4. Stratigraphy and paleoenvironment of the Danish Eocene Azolla event

    NASA Astrophysics Data System (ADS)

    Heilmann-Clausen, Claus; Beyer, Claus; Snowball, Ian

    2010-05-01

    Spores (massulae and megaspores) of the freshwater fern Azolla are recorded in several Danish Eocene outcrops and boreholes. The Azolla-bearing interval is 0.5 - ca. 3 m thick and occurs within the L2 Bed, a unit in the lower part of the hemipelagic, bathyal Lillebælt Clay Formation deposited in the central and eastern parts of the North Sea Basin. Intervals of organic-rich clay, usually including two distinctive, black sapropels, are present in the lower part of Bed L2, indicating a generally reduced oxygen content in the bottom waters during this time, with at least two episodes of severe, basinwide stagnation. The oxygen-deficit points to reduced circulation and/or enhanced marine productivity in the North Sea Basin. Azolla occurs in the upper part of this mainly organic-rich interval. The frequency of Azolla spores relative to marine dinoflagellate cysts fluctuates within the interval. The Azolla interval has previously been correlated to levels near the Ypresian/Lutetian transition in Belgium, based on dinoflagellate stratigraphy. Calibration of a new magnetostratigraphic study of the lower Lillebælt Clay with the dinoflagellate biostratigraphy suggests that Bed L2 spans the upper part of Chron 22r, C22n and lower part of C21r. The Azolla pulse spans the upper part of C22n and lowermost part of C21r. The combined bio-magnetostratigraphy from Denmark allows a detailed comparison with published data from the northern part of the Norwegian-Greenland Sea (ODP Hole 913B). The correlation confirms earlier assumptions, which were based on biostratigraphy alone, that the marine Azolla pulse in the two areas, and therefore probably over the whole Norwegian-Greenland Sea - North Sea region, is of the same age. An ongoing palynological study of the L2 Bed has so far revealed no indication for freshwater episodes or brackish waters in the basin during the Azolla pulse, except perhaps for Azolla itself. It is, therefore, suggested that the Azolla spores were transported to the sea by rivers from swamps and lakes in coastal areas of surrounding landmasses. Azolla habitats may have existed in Fennosarmatia 200-400 km away. It is noteworthy that the Azolla pulse coincided with a major, apparently eustatic, sea-level fall or the slow subsequent transgression, during which widespread swamps may have formed in the coastal areas. The combination of a low sea-level and a warm, humid climate may have led to increased productivity, both in Azolla-swamps and in the adjacent marine waters. This may explain the presence of organic-rich marine clays with Azolla spores.

  5. Experimental observation of magnetosome chain collapse in magnetotactic bacteria: Sedimentological, paleomagnetic,

    E-print Network

    their ability to preserve NRM in sediments. As the genomes of two magnetotactic bacteria contain severalExperimental observation of magnetosome chain collapse in magnetotactic bacteria: Sedimentological Magnetotactic bacteria precipitate intracellular crystals of single-domain magnetite (Fe3O4) and/or greigite (Fe

  6. The Cretaceous/ Tertiary boundary: sedimentology and micropalaeontology at El Mulato section, NE Mexico

    E-print Network

    Royer, Dana

    The Cretaceous/ Tertiary boundary: sedimentology and micropalaeontology at El Mulato section, NE-8109, USA Introduction Numerous researchers have focused investigations on Cretaceous / Tertiary (K / T and therefore formation over a long period of time. Bolide impact is also the most widely accepted explanation

  7. Sedimentological characteristics and 3-D internal architecture of washover deposits from Hurricanes Frances, Ivan, and Jeanne

    Microsoft Academic Search

    Mark H Horwitz

    2008-01-01

    Extensive overwash occurred along Florida's Atlantic and northern Gulf facing barrier islands during the passages of Hurricanes Frances, Ivan, and Jeanne in 2004. These high-energy storm events provided a unique opportunity to study the spatial depositional patterns and internal sedimentary architecture of fresh washover deposits resulting from inundation to collision regime overwash events. Sedimentological characteristics and 3-D internal architecture of

  8. DALHOUSIE UNIVERSITY, DEPARTMENT OF EARTH SCIENCES Assistant Professor -Geophysics, Sedimentology, or Geochemistry

    E-print Network

    Brownstone, Rob

    DALHOUSIE UNIVERSITY, DEPARTMENT OF EARTH SCIENCES Assistant Professor - Geophysics, Sedimentology, or Geochemistry The Department of Earth Sciences at Dalhousie University invites applications for a faculty research projects. Essential qualifications include a Ph.D. in Earth Sciences or closely related field

  9. Paleozoic Sedimentary Basins and Volcanic-Arc Systems of Southern Mongolia: New Stratigraphic and Sedimentologic Constraints

    Microsoft Academic Search

    Melissa A. Lamb; Gombosuren Badarch

    1997-01-01

    Paleozoic rocks of southern Mongolia record an important part of the tectonic growth and amalgamation of central Asia, but have not been studied closely because of their remote location. New stratigraphic and sedimentologic data from 17 localities help constrain previous geological models and strongly suggest tectonic activity throughout much of the Paleozoic, with deposition occurring predominantly within basins associated with

  10. Limnology, sedimentology, and hydrology of a jökulhlaup into a meromictic High Arctic lake1

    Microsoft Academic Search

    Ted Lewis; Pierre Francus; Raymond S. Bradley

    A large ice-dammed lake drained catastrophically into Lake Tuborg, Ellesmere Island, beginning on 25 July 2003. Limnological, sedimentological, and hydrological parameters were recorded before, during, and after this event. For several weeks prior to the jökulhlaup, water overtopped the ice-dammed lake and flowed into Lake Tuborg's fresh- water basin. A shallow sill separates the freshwater basin from a larger, deeper

  11. Morphological and sedimentological responses of streams to human impact in the southern Blue Ridge Mountains, USA

    Microsoft Academic Search

    Katie Price; David S. Leigh

    2006-01-01

    Morphological and sedimentological responses of streams to basin-scale impact have been well documented for intensively agricultural or urban areas. Sensitivity thresholds of streams to modest levels of disturbance, however, are not well understood. This study addresses the influence of forest conversion on streams of the southern Blue Ridge Mountains, a region that has received little attention with respect to human

  12. Stratigraphy and optically stimulated luminescence (OSL) dating of a Quaternary sequence along the Dong Nai River, southern Vietnam

    NASA Astrophysics Data System (ADS)

    Kitazawa, Toshiyuki; Nakagawa, Takahiro; Hashimoto, Tetsuo; Tateishi, Masaaki

    2006-10-01

    The pre-Holocene Cenozoic sequence outcrops in the terrestrial part of the eastern margin of the Mekong Basin. However, the stratigraphy of the sequence is still unclear. Its detailed stratigraphy and chronology were therefore studied along the Dong Nai River, southern Vietnam, and the lithofacies and the relations among the formations were investigated from the outcrops. The ages of the deposits were determined by using optically stimulated luminescence (OSL) dating. The Ba Mieu Formation was deposited about 176±52 ka during marine isotope stage (MIS) 7-6. The Thu Duc Formation was deposited about 97±27 ka during MIS 5. Both the Ba Mieu and Thu Duc formations are composed of fluvial and tidally influenced coastal deposits. The newly proposed Nhon Trach Formation was originally an eolian (blanket) deposit, but it has been partly reworked by fluvial processes. The Nhon Trach Formation was deposited about 10.9±4.7 ka, in the last part of the Pleistocene to the beginning of the Holocene. The OSL ages for the Ba Mieu, Thu Duc, and Nhon Trach formations are younger than the ages previously assigned to these formations.

  13. Sr-isotope stratigraphy of the Upper Jurassic of central Portugal (Lusitanian Basin) based on oyster shells

    NASA Astrophysics Data System (ADS)

    Schneider, Simon; Fürsich, Franz T.; Werner, Winfried

    2009-12-01

    Strontium isotope stratigraphy was performed on oyster shells from the Late Jurassic of the Lusitanian Basin (central Portugal). This represents the first approach to obtain numerical ages for these strata. The new chronostratigraphic data provide a more precise age determination of several units. After a basin-wide hiatus sedimentation in the Late Jurassic is proven in the Cabo Mondego and Cabaços formations to resume as early as the Middle Oxfordian. The Alcobaça formation can be placed in the latest Late Oxfordian to Late Kimmeridgian, while data from the upper part of the Abadia Formation indicate an Early to Late Kimmeridgian age. The Farta Pao formation ranges from the latest Kimmeridgian to the latest Tithonian. The largely synchronous Sobral, Arranhó I, and Arranhó II members are overlain by the late Early to Late Tithonian Freixial Member. The brief, local carbonate incursion of the Arranhó I member marks the Kimmeridgian-Tithonian boundary. Oysters are shown once more to be suitable for strontium isotope studies. Their calcitic shells are often unaffected by diagenesis. In particular for marginal marine Jurassic and Cretaceous strata, where belemnites are usually absent, oysters may serve as a valuable tool for isotope stratigraphy.

  14. The deglaciation in Picos de Europa (area of Enol Glacier) based on geomorphological and sedimentological studies

    NASA Astrophysics Data System (ADS)

    Ruiz-Fernández, Jesus; Oliva, Marc; García, Cristina

    2013-04-01

    The chronology for the deglaciation in the Cantabrian Range is still poorly understood. Several papers have proposed a maximum advance well before the LGM (Jiménez and Farias, 2002; Moreno et al. 2010; Serrano et al. 2012). The Western massif of Picos de Europa held a ice field of 50 km2. In this communication we present two cores collected in two glacial depressions in the frontal area of Enol Glacier that allow reconstructing the environment since the deglaciation of the massif. The first core (5.6 m long) was collected in the kame terrace of Belbin. This terrace was dammed by a lateral moraine corresponding to the phase of maximum expansion of Enol Glacier. Three clear layers are observed: the basal 2.5 m consists of grey clay with small gravel limestones; the second is 2 m thick and is composed of grey clays; the upper 1.1 m shows several paleosoils with abundant organic matter and charcoals. The based was dated at 14,810 ± 70 yr BP. This age represents a minimum age for the maximum expansion of Enol Glacier. The second core was collected in the glaciokarst depression of Vega del Bricial, located within a moraine complex corresponding to LGM. The core is 8 m long and looks very homogeneous. It consists of a succession of organic layers and slope deposits. Two radiocarbon dates were performed on the sediments at 8 and 2.8 m depth, resulting in 9,690 ± 260 and 3,420 ± 95 yr BP, respectively. Based on sedimentological and geomorphological evidences, we propose a chronology for the environmental changes occurred in this massif since the last glacial period. References Jiménez, M. and Farias, P., 2002. New radiometric and geomorphologic evidences of a Last Glacial Maximum older than 18 ka in SW European mountains: the example of Redes Natural Park (Cantabrian Mountains, NW Spain). Geodinamica Acta, 15, 93-101. Moreno, A., Valero, B. L., Jiménez, M., Domínguez, M. J., Mata, M. P., Navas, A., González, P., Stoll, H., Farias, P., Morellón, M., Corella, J. P. and Rico, M., 2010. The last deglaciation in the Picos de Europa National Park (Cantabrian Mountains, Northern Spain). Journal of Quaternary Science, 25 (7), 1076-1091. Serrano, E., González-Trueba, J. J. and González-García, M., 2012. Mountain glaciation and paleoclimate reconstruction in the Picos de Europa (Iberian Peninsula, SW Europe). Quaternary Research, 78, 303-314.

  15. Volcaniclastic stratigraphy of Gede volcano in West Java

    NASA Astrophysics Data System (ADS)

    Belousov, A.; Belousova, M.; Zaennudin, A.; Prambada, O.

    2012-12-01

    Gede volcano (2958 m a.s.l.) and the adjacent Pangrango volcano (3019 m a.s.l.) form large (base diameter 35 km) volcanic massif 60 km south of Jakarta. While Pangrango has no recorded eruptions, Gede is one of the most active volcanoes in Indonesia: eruptions were reported 26 times starting from 1747 (Petroeschevsky 1943; van Bemmelen 1949). Historic eruptions were mildly explosive (Vulcanian) with at least one lava flow. Modern activity of the volcano includes persistent solfataric activity in the summit crater and periodic seismic swarms - in 1990, 1991, 1992, 1995, 1996, 1997, 2000, 2010, and 2012 (CVGHM). Lands around the Gede-Pangrango massif are densely populated with villages up to 1500-2000 m a.s.l. Higher, the volcano is covered by rain forest of the Gede-Pangrango Natural Park, which is visited every day by numerous tourists who camp in the summit area. We report the results of the detailed reinvestigation of volcaniclastic stratigraphy of Gede volcano. This work has allowed us to obtain 24 new radiocarbon dates for the area. As a result the timing and character of activity of Gede in Holocene has been revealed. The edifice of Gede volcano consists of main stratocone (Gumuruh) with 1.8 km-wide summit caldera; intra-caldera lava cone (Gede proper) with a 900 m wide summit crater, having 2 breaches toward N-NE; and intra-crater infill (lava dome/flow capped with 3 small craters surrounded by pyroclastic aprons). The Gumuruh edifice, composed mostly of lava flows, comprises more than 90% of the total volume of the volcano. Deep weathering of rocks and thick (2-4 m) red laterite soil covering Gumuruh indicates its very old age. Attempts to get 14C dates in 4 different locations of Gumuruh (including a large debris avalanche deposit on its SE foot) provided ages older than 45,000 years - beyond the limit for 14C dating. Outside the summit caldera, notable volumes of fresh, 14C datable volcaniclastic deposits were found only in the NNE sector of the volcano where they form a fan below the breached summit crater. The fan is composed of pyroclastic flows (PFs) and lahars of Holocene age that were deposited in 4 major stages: ~ 10 000 BP - voluminous PF of black scoria; ~ 4000 BP - two PFs of mingled grey/black scoria; ~ 1200 BP - multiple voluminous PFs strongly enriched by accidental material; ~ 1000 BP - a small scale debris avalanche (breaching of the crater wall) followed by small scale PFs of black scoria. The intra-crater lava dome/flow was erupted in 1840 (Petroeschevsky, 1943). Three small craters on the top of the lava dome were formed by multiple post-1840 small-scale phreatomagmatic eruptions. Ejected pyroclasts are lithic hydrothermally altered material containing a few breadcrust bombs. The Holocene eruptive history of Gede indicates that the volcano can produce moderately strong (VEI 3-4) explosive eruptions and send PFs and lahars onto the NE foot of the volcano.

  16. Cenozoic stratigraphy of the northern Sakhalin shelf

    NASA Astrophysics Data System (ADS)

    Zharov, A. E.; Mitrofanova, L. I.; Tuzov, V. P.

    2013-09-01

    The analysis of diatom, palynofloral, and benthic foraminiferal assemblages made it possible to substantiate the age of Cenozoic sections recovered by wells on the northern and northeastern Sakhalin shelf. Biostratigraphic materials, lithological properties of stratigraphic units, and standard logs served as the basis for developing the first stratigraphic correlation scale of Cenozoic sequences on the Sakhalin shelf.

  17. Changes in Colorado Subalpine Fen Peat Stratigraphy and Humification During the Holocene

    NASA Astrophysics Data System (ADS)

    Sullivan, D. G.

    2013-12-01

    This project focuses on the record of peat stratigraphy and decomposition preserved in cores taken from minerotrophic peatlands in Colorado. Subalpine peatlands in the Colorado Rocky Mountains and in the Colorado Plateau cover only about 2% of the state's land area, yet these wetlands provide important wildlife habitat and ecosystem services. The peatlands in Colorado are fens, and, while summer precipitation contributes to the local hydrology, the fens are only found in locations where winter snowpack persists long enough into the summers to maintain sufficiently high water tables to preserve the peat. We hypothesized that changes in summer precipitation and winter snowpack through the Holocene would be evident in the degree of peat humification and stratigraphy. We were interested in determining how warmer summer conditions early in the Holocene influenced precipitation, particularly summer monsoons, and thus, groundwater. In addition, our research using lake sediment cores in the region indicates that sediment organic content may fluctuate with paleotemperature. We sought to determine whether fens likewise preserve evidence of relatively low magnitude temperature changes, including those associated with the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA). Since fens persist in the region only under marginal conditions, they are very sensitive to fluctuations in climate and consequent hydrological responses. Nine fens were sampled in the study. Fen stratigraphy was studied at all of the sites. Humification analysis and bulk density and organic content determinations were conducted at one-centimeter intervals on cores from four of the fens. Core chronology was established using radiocarbon dating. Our results suggest that warmer summers in the early Holocene led to earlier snowmelt at lower elevations. Fens located near the lower margins of the subalpine zone (<3100 m elevation) ceased to accumulate peat during this period, changing to alluvial depositional environments, only returning to peat accumulation when cooler/moister conditions reestablished. This stratigraphic change is similar to that found by other researchers working in the Sierra Nevada, California. Higher elevation fens in Colorado persisted as peatlands throughout the Holocene, but warmer periods produced higher rates of peat accumulation and greater humification during these intervals. Peat humifiation and stratigraphic analyses indicate that the subalpine fens in Colorado preserve a sensitive record of Holocene climate change and ecohydrological conditions. Our results suggest that warmer summers over the next century will likely result in earlier snowmelt and the potential loss of lower elevation fens, and changes in peat accumulation in higher elevation fens in the subalpine zone. These changes will have significant impacts on water quality and hydrology in Colorado.

  18. Structural geology and sedimentology of the Sermat Quartzites, Strandja Massif, NW Turkey

    NASA Astrophysics Data System (ADS)

    Yaz?c?, Müge; Natal'in, Boris A.

    2015-04-01

    The Strandja Massif, NW Turkey, is the eastern continuation of the Rhodope Massif in Bulgaria. The massif is generally correlated with the Hercynian orogenic belt that was later modified by the Cimmerian orogeny. The basement of the massif is composed by various kinds of gneisses and schists, which are intruded by the metagranites. In the studied area, the Cambrian K-feldspar metagranites are unconformably overlain by metaclastics, where both units have fault contacts with volcano-sedimentary rocks. The metagranite intrusions yield Carboniferous U-Pb zircon ages (Natal'in et al., 2012a). All of them constitute the basement of the Strandja Massif. Cambrian age of metagranites and their subduction related nature as well as the subduction related nature of the Carboniferous igneous rocks suggest a prolong evolution of the Strandja Massif (Natal'in et al., 2012a). The Cambrian metagranites are unconformably overlain by a metasedimetary cover unit, which is known in the literature as the ?ermat Quartzite of presumably Permo-Triassic age (Ça?layan and Yurtsever, 1998). In the studied region, detrital zircons extracted from quartzites show that their depositional age is not younger than the Ordovician (Natal'in et al., 2012a). The basement of the Strandja Massif is subjected to the epidote-amphibolite-greenschist facies of metamorphism and high strain deformation in the late Jurassic - early Cretaceous times. The ?ermat Quartzite forms a transgressive sequence, which starts with metaconglomerates, metasandstones and grades up to quartz-sericite schists. The thickness of bedding changes from thin to medium with parallel bedding planes, containing lens-shaped bodies of massive quartzites. The late Jurassic - early Cretaceous foliation (S1) is generally parallel to the primary bedding plane. Foliations and lineations consistently dip to the northeast and kinematic indicators suggest a tectonic transport in the same direction. High strain in the ?ermat Quartzite prevented the preservation of sedimentary structures such as flute casts and cross-beddings, which can be used to determine the sedimentary environments of the ?ermat Basin. Nevertheless, all available relicts indicate the transportation of sediments from a source area in the south. If the ?ermat Quartzites is Ordovician age, they can be correlated with the Ordovician rocks of the Istanbul Zone, which is interpreted as a south-facing passive continental margin. Sedimentological framework of the ?ermat Quartzites contradicts this correlation. Further studies of the region are necessary in order to determine the connection between the Strandja Massif and the Istanbul Zone. Keywords: Hercynian orogeny, Cimmerides, Strandja Massif, ?stanbul Zone, Sedimentary Basin, Turkey References Ça?layan, M. A. & Yurtsever, A., 1998, Geological map of Turkey at 1:100000 scale, no. 20, 21, 22, 23, Burgaz-A3, Edirne-B2 and -B3, Burgaz A4, and K?rklareli-B4-B5-B6 and -C6 sheets, Mineral Research and Exploration Institute (MTA) of Turkey publications (in Turkish with English abstract). Natal'in, B., Sunal, G., Zhiqing, Y. & Gün, E., 2012a, Late Paleozoic subduction-accretion orogeny in the eastern part of the Turkish Strandja Massif (Vize - K?y?köy region), in Kocbay, A., Esat, K., and Hasancebi, N., eds., 65th Geological Congress of Turkey. Abstracts Book: Ankara, Chamber of Geological Engineers, p. 454-455 Natal'in, B., Sunal, G., Sat?r, M. & Toraman, E., 2012, Tectonics of the Strandja Massif, NW Turkey: History of a Long-Lived Arc at the Northern Margin of Palaeo-Tethys: Turkish Journal of Earth Sciences, v. 21, p. 755-798.

  19. Integrating radar stratigraphy with high resolution visible stratigraphy of the north polar layered deposits, Mars

    NASA Astrophysics Data System (ADS)

    Christian, S.; Holt, J. W.; Byrne, S.; Fishbaugh, K. E.

    2013-11-01

    Shallow Radar (SHARAD) on board NASA’s Mars Reconnaissance Orbiter has successfully detected tens of reflectors in the subsurface of the north polar layered deposits (NPLD) of Mars. Radar reflections are hypothesized to originate from the same material interfaces that result in visible layering. As a first step towards verifying this assumption, this study uses signal analyses and geometric comparisons to quantitatively examine the relationship between reflectors and visible layers exposed in an NPLD outcrop. To understand subsurface structures and reflector geometry, reflector surfaces have been gridded in three dimensions, taking into account the influence of surface slopes to obtain accurate subsurface geometries. These geometries reveal reflector dips that are consistent with optical layer slopes. Distance-elevation profiling of subsurface reflectors and visible layer boundaries reveals that reflectors and layers demonstrate similar topography, verifying that reflectors represent paleosurfaces of the deposit. Statistical and frequency-domain analyses of the separation distances between successive layers and successive reflectors confirms the agreement of radar reflector spacing with characteristic spacing of certain visible layers. Direct elevation comparisons between individual reflectors and discrete optical layers, while necessary for a one-to-one correlation, are complicated by variations in subsurface structure that exist between the outcrop and the SHARAD observations, as inferred from subsurface mapping. Although these complications have prevented a unique correlation, a genetic link between radar reflectors and visible layers has been confirmed, validating the assumption that radar reflectors can be used as geometric proxies for visible stratigraphy. Furthermore, the techniques for conducting a stratigraphic integration have been generalized and improved so that the integration can be undertaken at additional locations.

  20. Different sedimentological and thermal evolution of three north-pyrenean basins during their set-up

    NASA Astrophysics Data System (ADS)

    Chelalou, Roman; Nalpas, Thierry; Bousquet, Romain; Lahfid, Abdeltif

    2015-04-01

    The Pyrenean belt is resulting in the inversion of several lower Cretaceous basins, separating the Iberia micro-plate from the Eurasia plate. The eat-west oriented basins are well known for their high-temperature metamorphism synchronous of the last deposits during Aptian-Albian times. For the first time, we present a combined sedimentological and thermal study of three north pyrenean basins (Boucheville, St Paul-de-Fenouillet and Bas-Agly). With the help of detailed stratigraphic logs of each basin, we propose restored cross-sections for the whole area. North-south sections across Boucheville and St Paul-de-Fenouillet basins show that theses basins have large asymmetrical structure. The Boucheville basin is a large anticline bordered by two isoclinal syncline highly skewed, while the St Paul-de-Fenouillet one is a unique syncline. Detailed sedimentalogical observations show common features for these basins: deposits of white limestones and breccias during the Jurassic time following by black sandstones with a calcareous matrix of lower Cretaceous age. On one hand, Jurassic limestones were deposited on a shelf environment and their thickness is homogeneous all over each basin. On the other hand, sandstones deposits seem to occur at greater depths during the Albian time and are displaying asymmetrical north-south variation of their thickness. The quantification of the temperature overprint occurred in the basin was done using the graphitisation of the carbonaceous material, and was measured by RAMAN spectroscopy (Lahfid et al. 2010). Despite their similar deposits, the mapping of the temperature-peak inside the three basins show contrasted thermal evolution. Then we document a lower temperature overprint around 150-200?C in the northern basin {St Paul-de-Fenouillet) while the highest overprint up to 600?C has been reached in the southern basin (Boucheville) in which diopside - scapolite and also probably olivine are occurring. These three north-pyrenean basin turn out to be good places where to study the evolution of passive margin analogue and also to be a good example where the sediments were metamorphosed during the basin set up.

  1. Clear Lake sediments: anthropogenic changes in physical sedimentology and magnetic response.

    PubMed

    Osleger, David A; Zierenberg, Robert A; Suchanek, Thomas H; Stoner, Joseph S; Morgan, Sally; Adam, David P

    2008-12-01

    We analyzed the sedimentological characteristics and magnetic properties of cores from the three basins of Clear Lake, California, USA, to assess the depositional response to a series of land use changes that occurred in the watershed over the 20th century. Results indicate that distinct and abrupt shifts in particle size, magnetic concentration/mineralogy, and redox conditions occur concurrently with a variety of ecological and chemical changes in lake bed sediments. This coincidence of events occurred around 1927, a datum determined by an abrupt increase in total mercury (Hg) in Clear Lake cores and the known initiation of open-pit Hg mining at the Sulphur Bank Mercury Mine, confirmed by 210Pb dating. Ages below the 1927 horizon were determined by accelerator mass spectrometry on 14C of coarse organic debris. Calculated sedimentation rates below the 1927 datum are approximately 1 mm/yr, whereas rates from 1927 to 2000 are up to an order of magnitude higher, with averages of approximately 3.5-19 mm/yr. In both the Oaks and Upper Arms, the post-1927 co-occurrence of abrupt shifts in magnetic signatures with color differences indicative of changing redox conditions is interpreted to reflect a more oxygenated diagenetic regime and rapid burial of sediment below the depth of sulfate diffusion. Post-1927 in the Oaks Arm, grain size exhibits a gradual coarsening-upward pattern that we attribute to the input of mechanically deposited waste rock related to open-pit mining activities at the mine. In contrast, grain size in the Upper Arm exhibits a gradational fining-upward after 1927 that we interpret as human-induced erosion of fine-grained soils and chemically weathered rocks of the Franciscan Assemblage by heavy earthmoving equipment associated with a road- and home-building boom, exacerbated by stream channel mining and wetlands destruction. The flux of fine-grained sediment into the Upper Arm increased the nutrient load to the lake, and that in turn catalyzed profuse cyanobacterial blooms through the 20th century. The resulting organic biomass, in combination with the increased inorganic sediment supply, contributed to the abrupt increase in sedimentation rate after 1927. PMID:19475928

  2. SIMON FRASER The Applied Research in Ichnology and Sedimentology (ARISE) Group (www.sfu.ca/arise) in the Department of

    E-print Network

    Dashtgard, Shahin

    SIMON FRASER UNIVERSITY The Applied Research in Ichnology and Sedimentology (ARISE) Group (www.sfu.ca/arise) in the Department of Earth Sciences (www.sfu.ca/earth-sciences) at Simon Fraser University (SFU) is seeking

  3. Three-dimensional sedimentary architecture of Quaternary deposits; a case study of environmental sedimentology (Bam, Iran)

    Microsoft Academic Search

    K. Rezaei; B. Guest; A. Friedrich; F. Fayazi; M. Nakhaei; H. Bakhtiari; L. Nouri

    2009-01-01

    Detailed 3-D analysis of the sedimentary structure and stratigraphy of these deposits allows for an accurate understand of sedimentary model of basin. This paper presents a case study in Bam (SE Iran) reconstructing the 3-D distribution of fluvial sediments based on a high resolution, process-orientated sedimentary facies classification and lithostratigraphy. We investigated the mean grain size with vertical and horizontal

  4. Stratigraphy of Atlantic coastal margin of United States north of Cape Hatteras; brief survey

    USGS Publications Warehouse

    Perry, W.J.; Minard, J.P.; Weed, E.G.A.; Robbins, E.I.; Rhodehamel, E.C.

    1975-01-01

    A synthesis of studies of sea-floor outcrops of the sedimentary wedge beneath the northeastern United States continental shelf and slope and a reassessment of coastal plain Mesozoic stratigraphy, particularly of the coastal margin, provide insight for estimating the oil and gas potential and provide geologic control for marine seismic investigations of the Atlantic continental margin. The oldest strata known to crop out on the continental slope are late Campanian in age. The Cretaceous-Tertiary contact along the slope ranges from a water depth of 0.6 to 1.5 km south of Georges Bank to 1.8 km in Hudson Canyon. Few samples are available from Tertiary and Late Cretaceous outcrops along the slope. Sediments of the Potomac Group, chiefly of Early Cretaceous age, constitute a major deltaic sequence in the emerged coastal plain. This thick sequence lies under coastal Virginia, Maryland, Delaware, southeastern New Jersey, and the adjacent continental shelf. Marine sands associated with this deltaic sequence may be present seaward under the outer continental shelf. South of the Norfolk arch, under coastal North Carolina, carbonate rocks interfinger with Lower Cretaceous clastic strata. From all available data, Mesozoic correlations in coastal wells between coastal Virginia and Long Island have been revised. The Upper-Lower Cretaceous boundary is placed at the transition between Albian and Cenomanian floras. Potential hydrocarbon source beds are present along the coast in the subsurface sediments of Cretaceous age. Potential reservoir sandstones are abundant in this sequence.

  5. A carbon isotopic and sedimentological record of the latest Devonian (Famennian) from the Western U.S. and Germany

    USGS Publications Warehouse

    Myrow, P.M.; Strauss, J.V.; Creveling, J.R.; Sicard, K.R.; Ripperdan, R.; Sandberg, C.A.; Hartenfels, S.

    2011-01-01

    New carbon isotopic data from upper Famennian deposits in the western United States reveal two previously unrecognized major positive isotopic excursions. The first is an abrupt ~. 3??? positive excursion, herein referred to as ALFIE (A Late Famennian Isotopic Excursion), recorded in two sections of the Pinyon Peak Limestone of north-central Utah. Integration of detailed chemostratigraphic and biostratigraphic data suggests that ALFIE is the Laurentian record of the Dasberg Event, which has been linked to transgression in Europe and Morocco. Sedimentological data from the Chaffee Group of western Colorado also record transgression at a similar biostratigraphic position, with a shift from restricted to open-marine lithofacies. ALFIE is not evident in chemostratigraphic data from age-equivalent strata in Germany studied herein and in southern Europe, either because it is a uniquely North American phenomenon, or because the German sections are too condensed relative to those in Laurentia. A second positive carbon isotopic excursion from the upper Chaffee Group of Colorado is recorded in transgressive strata deposited directly above a previously unrecognized paleokarst interval. The age of this excursion, and the duration of the associated paleokarst hiatus, are not well constrained, although the events occurred sometime after the Late Famennian Middle expansa Zone. The high positive values recorded in this excursion are consistent with those associated with the youngest Famennian Middle to Late praesulcata Hangenberg Isotopic Excursion in Europe, the isotopic expression of the Hangenberg Event, which included mass extinction, widespread black shale deposition, and a glacio-eustatic fall and rise. If correct, this would considerably revise the age of the Upper Chaffee Group strata of western Colorado. ?? 2011 Elsevier B.V.

  6. PermophilesInternational Commission on Stratigraphy International Union of Geological Sciences

    E-print Network

    Newsletter of the Subcommission on Permian Stratigraphy Number 53 ISSN 1684-5927 June 2009 Includes The Upper Permian and Lower Triassic of Iran (p. 2). Photo by Shuzhong Shen. Right: The Lower Permian Charles M. Henderson Report of the field trip of the Permian stratigraphy in central and eastern Iran 2

  7. A martian case study of segmenting images automatically for granulometry and sedimentology, Part 2: Assessment

    NASA Astrophysics Data System (ADS)

    Karunatillake, Suniti; McLennan, Scott M.; Herkenhoff, Kenneth E.; Husch, Jonathan M.; Hardgrove, Craig; Skok, J. R.

    2014-02-01

    In a companion work, we bridge the gap between mature segmentation software used in terrestrial sedimentology and emergent planetary segmentation with an original algorithm optimized to segment whole images from the Microscopic Imager (MI) of the Mars Exploration Rovers (MER). In this work, we compare its semi-automated outcome with manual photoanalyses using unconsolidated sediment at Gusev and Meridiani Planum sites for geologic context. On average, our code and manual segmentation converge to within ?10% in the number and total area of identified grains in a pseudo-random, single blind comparison of 50 samples. Unlike manual segmentation, it also locates finer grains in an image with internal consistency, enabling robust comparisons across geologic contexts. When implemented in Mathematica-8, the algorithm segments an entire MI image within minutes, surpassing the extent and speed possible with manual segmentation by about a factor of ten. These results indicate that our algorithm enables not only new sedimentological insight from the MER MI data, but also detailed sedimentology with the Mars Science Laboratory’s Mars Hand Lens Instrument.

  8. Sedimentological evolution in an UASB treating SYNTHES, a new representative synthetic sewage, at low loading rates.

    PubMed

    Aiyuk, Sunny; Verstraete, Willy

    2004-07-01

    The changes in the sedimentological attributes of the sludge bed in an upflow anaerobic sludge blanket (UASB) reactor fed with a low-strength wastewater mimicking raw domestic sewage were assessed in this study. The reactor was inoculated with 250 ml of granular sludge from a full-scale UASB reactor. The organic loading rate (OLR) varied from 1 to 2 g COD/ld. During the half-year long study, the reactor was operated at hydraulic retention times (HRTs) of 4.8 and 10 h, at 33 degrees C. Sludge sedimentology showed that the original granular sludge experienced serious instability and disintegration, leading to a much finer final grain assemblage, mainly due to substrate transfer limitation and cell starvation at the interior of larger granules. With time, the size uniformity tended to decrease, sphericity tended to increase, the skewness of the granule size distribution became negative, and the kurtosis became peaked and leptokurtic. In spite of the observed size reduction, reactor efficiency increased to a CODtotal removal of 96%. Biomass (sludge) yield was 0.012 g VS/g COD removed. The CH4 content of the biogas was high (up to 96%). This study thus highlights the treatment of a new type of wastewater with the deployment of the UASB reactor. It also reports the evolutionary trend of the biomass particle size distribution, making reference to a classic sedimentological appraisal. PMID:15062822

  9. The "Continental Intercalaire" of southern Tunisia: Stratigraphy, paleontology, and paleoecology

    NASA Astrophysics Data System (ADS)

    Fanti, Federico; Contessi, Michela; Franchi, Fulvio

    2012-09-01

    The "Continental Intercalaire" deposits of southern Tunisia preserve one of the most diverse Early Cretaceous vertebrate fauna from Africa, consisting of elasmobranchs, actinopterygians, sarcopterygians, turtles, crocodyliforms, pterosaurs, and non-avian dinosaurs. Vertebrate remains representative of both marine and fluvial environments have been historically referred to a specific bonebed within the Chenini Member, which crops out extensively in the Tataouine region. A stratigraphic revision of the mainly siliciclastic deposits of the Douiret and the Aïn El Guettar formations in the area based on new sedimentological and paleontological data is presented. Data collected indicate the presence of multiple fossil-bearing strata encompassing the stratigraphic interval from the Berriasian to the Albian and document faunal variation through time as well as major environmental and climatic changes. Detailed sedimentological analysis combined with biostratigraphic correlation performed at a basin scale indicate lateral facies variability within each formation as a result of tectonically and climatically driven zonations within the Tataouine Basin in the Early Cretaceous. Furthermore, proposed stratigraphic correlations indicate that vertebrate remains previously referred to the fluvial Chenini Member (and in particular theropod and sauropod dinosaurs) are instead representative of a transgressive deposit which mark the base of the overlying Oum ed Diab Member.

  10. Petroacoustic Modelling of Heterolithic Sandstone Reservoirs: A Novel Approach to Gassmann Modelling Incorporating Sedimentological Constraints and NMR Porosity data

    NASA Astrophysics Data System (ADS)

    Matthews, S.; Lovell, M.; Davies, S. J.; Pritchard, T.; Sirju, C.; Abdelkarim, A.

    2012-12-01

    Heterolithic or 'shaly' sandstone reservoirs constitute a significant proportion of hydrocarbon resources. Petroacoustic models (a combination of petrophysics and rock physics) enhance the ability to extract reservoir properties from seismic data, providing a connection between seismic and fine-scale rock properties. By incorporating sedimentological observations these models can be better constrained and improved. Petroacoustic modelling is complicated by the unpredictable effects of clay minerals and clay-sized particles on geophysical properties. Such effects are responsible for erroneous results when models developed for "clean" reservoirs - such as Gassmann's equation (Gassmann, 1951) - are applied to heterolithic sandstone reservoirs. Gassmann's equation is arguably the most popular petroacoustic modelling technique in the hydrocarbon industry and is used to model elastic effects of changing reservoir fluid saturations. Successful implementation of Gassmann's equation requires well-constrained drained rock frame properties, which in heterolithic sandstones are heavily influenced by reservoir sedimentology, particularly clay distribution. The prevalent approach to categorising clay distribution is based on the Thomas - Stieber model (Thomas & Stieber, 1975), this approach is inconsistent with current understanding of 'shaly sand' sedimentology and omits properties such as sorting and grain size. The novel approach presented here demonstrates that characterising reservoir sedimentology constitutes an important modelling phase. As well as incorporating sedimentological constraints, this novel approach also aims to improve drained frame moduli estimates through more careful consideration of Gassmann's model assumptions and limitations. A key assumption of Gassmann's equation is a pore space in total communication with movable fluids. This assumption is often violated by conventional applications in heterolithic sandstone reservoirs where effective porosity, which includes a capillary bound water porosity component, is used. The novel approach attempts to better address this assumption through incorporation of NMR porosity data which distinguishes between bound water and free (movable) fluid components of porosity. The simplistic approach to heterolithic sandstone sedimentology, with poor linkage between petrophysical and sedimentological analyses and ignorance of model caveats, compounds petroacoustic modelling issues. This research uses a single well dataset comprising a log suite including NMR and OBMI data, together with extensive core data including core-NMR, SEM images and detailed sedimentological analysis. Integration of log and core data enables better insight to the key sedimentological properties influencing reservoir elastic properties. This approach improves understanding of key sedimentological properties affecting acoustic propagation in heterolithic sandstones and in turn provides better models for describing these important reservoirs. This contributes to enhanced seismic data interpretation of reservoir properties, including fluid saturations, during exploration and development phases.

  11. The INTIMATE event stratigraphy of the last glacial period

    NASA Astrophysics Data System (ADS)

    Olander Rasmussen, Sune; Svensson, Anders

    2015-04-01

    The North Atlantic INTIMATE (INtegration of Ice-core, MArine and TErrestrial records) group has previously recommended an Event Stratigraphy approach for the synchronisation of records of the Last Termination using the Greenland ice core records as the regional stratotypes. A key element of these protocols has been the formal definition of numbered Greenland Stadials (GS) and Greenland Interstadials (GI) within the past glacial period as the Greenland expressions of the characteristic Dansgaard-Oeschger events that represent cold and warm phases of the North Atlantic region, respectively. Using a recent synchronization of the NGRIP, GRIP, and GISP2 ice cores that allows the parallel analysis of all three records on a common time scale, we here present an extension of the GS/GI stratigraphic template to the entire glacial period. In addition to the well-known sequence of Dansgaard-Oeschger events that were first defined and numbered in the ice core records more than two decades ago, a number of short-lived climatic oscillations have been identified in the three synchronized records. Some of these events have been observed in other studies, but we here propose a consistent scheme for discriminating and naming all the significant climatic events of the last glacial period that are represented in the Greenland ice cores. In addition to presenting the updated event stratigraphy, we make a series of recommendations on how to refer to these periods in a way that promotes unambiguous comparison and correlation between different proxy records, providing a more secure basis for investigating the dynamics and fundamental causes of these climatic perturbations. The work presented is a part of a newly published paper in an INTIMATE special issue of Quaternary Science Reviews: Rasmussen et al., 'A stratigraphic framework for abrupt climatic changes during the Last Glacial period based on three synchronized Greenland ice-core records: refining and extending the INTIMATE event stratigraphy', Quaternary Science Reviews, vol. 106, p. 14-24, 2014.

  12. The Georgia Embayment continental shelf: stratigraphy of a submergence.

    USGS Publications Warehouse

    Pilkey, O.H.; Blackwelder, B. W.; Knebel, H. J.; Ayers, M.W.

    1981-01-01

    The Holocene-Pleistocene sediment veneer is thin, generally less than 4m thick. Lagoon sediments deposited during the last regression or the Holocene transgression occur in patches on the inner and central shelf. During each transgression or submergence, the surficial sand sheet is recharged with a new biogenic carbonate fraction along with the addition of small amounts of clastic sediments derived from 'overrun' estuaries and erosion of underlying Tertiary sediments. The stratigraphy based on the vibracores supports the concept of cross-shelf migration of the shore face-barrier island systems in response to rising sea level. -from Authors

  13. Stratigraphy and Observations of Nepthys Mons Quadrangle (V54), Venus

    NASA Technical Reports Server (NTRS)

    Bridges, N. T.

    2001-01-01

    Initial mapping has begun in Venus' Nepthys Mons Quadrangle (V54, 300-330 deg. E, 25-50 deg. S). Major research areas addressed are how the styles of volcanism and tectonism have changed with time, the evolution of shield volcanoes, the evolution of coronae, the characteristics of plains volcanism, and what these observations tell us about the general geologic history of Venus. Reported here is a preliminary general stratigraphy and several intriguing findings. Additional information is contained in the original extended abstract.

  14. The Department of Geology at Wayne State University consists of five full-time faculty and five

    E-print Network

    VandeVord, Pamela

    (Geochemistry and Geophysics), Jeffrey Howard (Sedimentology), Larry Lemke (Hydrogeology), and Ed van Hees conduct research in the general areas of Sedimentology, Stratigraphy, Soil Science, Hydrogeology

  15. The Department of Geology at Wayne State University consists of five full-time faculty and five

    E-print Network

    Baskaran, Mark

    (Geochemistry and Geophysics), Jeffrey Howard (Sedimentology), Larry Lemke (Hydrogeology), and Ed van Hees faculty are conducting research in the general areas of Sedimentology, Stratigraphy, Soil Science

  16. Program of Study Research Facilities

    E-print Network

    Thomas, Andrew

    state-of-the-art stable isotope laboratory, climatology laboratory, sedimentology laboratory, geological geology, quaternary stratigraphy, and sedimentology. Harold W. Borns, Jr., Ph.D. (Boston University, 1959

  17. Cosmogenic dating of rock avalanches constraining Quaternary stratigraphy and regional neotectonics in the Argentine Central Andes (32° S)

    NASA Astrophysics Data System (ADS)

    Moreiras, Stella M.; Hermanns, Reginald L.; Fauqué, Luis

    2015-03-01

    This paper provides a comprehensive review of the chronostratigraphy of six rock avalanches clustered in the northern extreme of the Cordon del Plata range. These rock avalanches are stratigraphically related to Pleistocene glacial drifts and valley-fill deposits documenting the regional neotectonic activity. We used cosmogenic dating (TCN) to directly date block surfaces of rock-avalanche deposits, as well as optically stimulated luminescence dating (OSL) of paleo-lakes dammed by these rock avalanches. Our new direct dates (17 TCN and 4 OSL) determine the Middle-to-Late Pleistocene age of these collapses. These are in contrast to the previously established chronostratigraphy based on relative dating techniques, paleontological context, and tephrochronology. These new data help to redefine the geomorphological evolution of the Mendoza River valley. Especially, the new data indicate that the glacial stratigraphy earlier proposed must be reconsidered. We redefine this stratigraphy as far as possible with our data and discuss the data in relation with other recently published results. However, it becomes clear that the glacial history of the Mendoza valley has to be studied anew by using modern dating techniques. In addition, our data suggest that the Carrera Fault system bounding the valleys of the Cordillera del Plata has been active more recently than proposed earlier.

  18. Sequence stratigraphy, basin dynamics, and petroleum geology of the Miocene from eastern Tunisia

    SciTech Connect

    Bedir, M. [Campus Universitaire, Tunis (Tunisia)]|[Unite des Ressources Naturelles et Environnement, Hammam-Lif (Tunisia); Tlig, S. [Campus Universitaire, Tunis (Tunisia); Bobier, C. [Universite Bordeaux, Talence (France)] [and others

    1996-01-01

    On the eastern margin of Tunisia, Miocene limestones, marl, and siliciclastic deposits crop out poorly and are lacking in age-diagnostic faunal content. The biostratigraphic and lithostratigraphic subdivisions of these series are not clearly defined. A regional study of subsurface sequences of this margin (Cap Bon, Gulf of Hammamet, and Sahel) by means of sequence stratigraphy and subsurface structural analyses permits the identification of seven third-order sedimentary sequences of inferred Langhian to Messinian age, the boundaries of which are characterized by downlap and onlap/toplap relationships. These sequences include turbidites, sands, and sandstones deposited in connection with eustatic sea level changes and tectonic movements of east-west and south-north deep-seated faults due to the Alpine and Atlassic paroxysm. Stratal sequences are organized around Miocene syndepositional grabens, half-grabens, platforms, and folds occurring inside and outside of regional tectonic corridors. The geodynamic evolution of Miocene basins has led to the deposition of turbiditic black argillaceous source rocks, and sandstone and carbonate reservoirs that present new Miocene petroleum targets. The basin subsidence in response to the Alpine/Atlassic orogeny has permitted the maturation of Miocene source rocks, oil generation, and the formation of oil traps, stratigraphic pinch-outs, and structural enclosures on the flanks of folds and on the borders of grabens.

  19. The Middle to Upper Paleolithic transition: dating, stratigraphy, and isochronous markers.

    PubMed

    Blockley, S P E; Ramsey, C Bronk; Higham, T F G

    2008-11-01

    Accurate and precise dating is vital to our understanding of the Middle to Upper Paleolithic transition. There are, however, a number of uncertainties in the chronologies currently available for this period. We attempt to examine these uncertainties by utilizing a number of recent developments in the field. These include: the precise dating of the Campanian Ignimbrite (CI) tephra by 40Ar/39Ar; the tracing of this tephra to a number of deposits that are radiocarbon dated; the publication of revised radiocarbon calibration data for the period, showing a much better convergence with other available data than during the recent IntCal comparison; and a layer-counted ice-core chronology extending beyond 40,000cal BP. Our data comparisons suggest that a reasonable overall convergence between calibrated radiocarbon ages and calendar dates is possible using the new curves. Additionally, we suggest that charcoal-based radiocarbon ages, as well as bone-based radiocarbon determinations, require cautious interpretation in this period. Potentially, these issues extend far beyond the sites in this study and should be of serious concern to archaeologists studying the Middle to Upper Paleolithic. We conclude by outlining a strategy for moving the science forward by a closer integration of archaeology, chronology, and stratigraphy. PMID:18926557

  20. Sequence stratigraphy and 3-D seismic imaging in low-accommodation basins

    SciTech Connect

    Hardage, B.A.; Carr, D.L.; Hamilton, D.S.; Simmons, J.L. Jr. [Univ. of Texas, Austin, TX (United States)

    1996-12-31

    Pennsylvanian-age rocks in several areas of the Midcontinent of the United States were deposited in low-accommodation basinal settings. Many sequences in these low-accommodation environments exhibit severe lateral heterogeneity because they have been extensively reworked by repeated transgressions and regressions. Consequently, the distinctive geometries of relic depositional features tend to be distorted or totally destroyed, in contrast to such geometries in high-accommodation basins where depositional topography, once buried, is rarely exposed to erosional processes. Our objective is to show how these thin and obscure low-accommodation sequences can be identified in well control and interpreted in 3-D seismic data volumes. Numerous, deep-rooted karst-collapse zones affected the areal continuity of many sequences in some Midcontinent basins. We combine sequence stratigraphy with 3-D seismic imaging to document that many of these karst-collapse zones originate at deep Ellenburger (?) levels and then extend vertically for a distance of 2,000 ft (600 m) or more into Pennsylvanian-age rocks. We also offer evidence that properly chosen seismic attributes, calculated in thin, accurately defined seismic time windows that correspond to log-defined sequences, show compartmented reservoir facies in low-accommodation basins.

  1. Sequence stratigraphy and 3-D seismic imaging in low-accommodation basins

    SciTech Connect

    Hardage, B.A.; Carr, D.L.; Hamilton, D.S.; Simmons, J.L. Jr. (Univ. of Texas, Austin, TX (United States))

    1996-01-01

    Pennsylvanian-age rocks in several areas of the Midcontinent of the United States were deposited in low-accommodation basinal settings. Many sequences in these low-accommodation environments exhibit severe lateral heterogeneity because they have been extensively reworked by repeated transgressions and regressions. Consequently, the distinctive geometries of relic depositional features tend to be distorted or totally destroyed, in contrast to such geometries in high-accommodation basins where depositional topography, once buried, is rarely exposed to erosional processes. Our objective is to show how these thin and obscure low-accommodation sequences can be identified in well control and interpreted in 3-D seismic data volumes. Numerous, deep-rooted karst-collapse zones affected the areal continuity of many sequences in some Midcontinent basins. We combine sequence stratigraphy with 3-D seismic imaging to document that many of these karst-collapse zones originate at deep Ellenburger ( ) levels and then extend vertically for a distance of 2,000 ft (600 m) or more into Pennsylvanian-age rocks. We also offer evidence that properly chosen seismic attributes, calculated in thin, accurately defined seismic time windows that correspond to log-defined sequences, show compartmented reservoir facies in low-accommodation basins.

  2. Strontium-isotope stratigraphy of Enewetak Atoll

    USGS Publications Warehouse

    Ludwig, K. R.; Halley, Robert B.; Simmons, Kathleen R.; Peterman, Zell E.

    1988-01-01

    87Sr/86Sr ratios determined for samples from a 350 m core of Neogene lagoonal, shallow-water limestones from Enewetak Atoll display a remarkably informative trend. Like the recently published data for Deep Sea Drilling Project (DSDP) carbonates, 87Sr/86Sr at Enewetak increases monotonically but not smoothly from the early Miocene to the Pleistocene. The data show intervals of little or no change in 87Sr/86Sr, punctuated by sharp transitions to lower values toward greater core depths. The sharp transitions correlate with observed solution disconformities caused by periods of subaerial erosion, whereas the intervals of little or no change in 87Sr/86Sr correspond to intervals of rapid accumulation of shallow-water carbonate sediments. When converted to numerical ages using the published DSDP 590B trend, the best-resolved time breaks are at 282 m (12.3 to 18.2 Ma missing) and 121.6 m (3.0 to 5.3 Ma missing) below the lagoon floor. At Enewetak, Sr isotopes offer a stratigraphic resolution for these shallow-marine Neogene carbonates comparable to that of nannofossil zonation in deep-sea carbonates (0.3-3 m.y.). In addition, the correlation of times of Sr-isotope breaks at Enewetak with times of rapid Sr-isotope change in the DSDP 590B samples confirms the importance off sea-level changes in the evolution of global-marine Sr isotopes and shows that the Sr-isotope response to sea-level falls is rapid.

  3. Hierarchal Genetic Stratigraphy: A Framework for Paleoceanography

    NASA Astrophysics Data System (ADS)

    Busch, R. M.; West, R. R.

    1987-04-01

    A detailed, genetic stratigraphic framework for paleoceanographic studies can be derived by describing, correlating, interpreting, and predicting stratigraphic sequences relative to a hierarchy of their constituent time-stratigraphic transgressive-regressive units ("T-R units"). T-R unit hierarchies are defined and correlated using lithostratigraphic and paleoecologic data, but correlations can be enhanced or "checked" (tested to confirm or deny) with objective biostratigraphic, magnetostratigraphic, or chemostratigraphic data. Such chronostratigraphies can then be bracketed by radiometric ages, so that average periodicities for T-R units can be calculated and a hierarchal geochronology derived. T-R units are inferred to be the net depositional result of eustatic cycles of sea level change and can be differentiated from autocyclic deepening-shallowing units because the latter are noncorrelative intrabasinally. Boundaries between T-R units are conformable or unconformable "genetic surfaces" of two types: transgressive surfaces and "climate change surfaces". The latter are useful for correlating minor transgressive phases through nonmarine intervals, thereby deriving information linking paleoclimatic and paleoceanographic processes. Permo-Carboniferous sequences can be analyzed relative to a hierarchy of six scales of genetic T-R units having periodicities of 225-300 m.y. (first order), 20-90 m.y. (second order), 7-13 m.y. (third-order), 0.6-3.6 m.y. (fourth order), 300-500 × 10³ years (fifth order), and 50-130 × 10³ years or less (sixth-order). Paleogeographic maps for the time of maximum transgression ("transgressive apex") of successive fifth-order T-R units (5-25 m thick) in the Glenshaw Formation (Upper Pennsylvanian, Northern Appalachian Basin) delineate delta lobes, embayments, islands, and linear seaways. Relative extent of marine inundation on the fifth-order maps was used to delineate fourth-order T-R units, and the fourth-order T-R units constitute the transgressive half of a third-order T-R unit. This third-, fourth-, and fifth-order hierarchy is correlated more than 1200 km (750 miles) to the Western Interior "Basin," and is confirmed with limited objective biostratigraphy.

  4. Perspective on the sequence stratigraphy of continental strata

    SciTech Connect

    Shanley, K.W. (Shell Development Company, Houston, TX (United States)); McCabe, P.J. (Geological Survey, Denver, CO (United States))

    1994-04-01

    This report is the result of a working group on continental sequence stratigraphy that was set up at the 1991 NUNA conference in Banff, Canada. To data, sequence stratigraphic concepts have been applied mainly to the marine realm, but unconformity-bounded units have long been recognized in nonmarine strata. Successful application of sequence stratigraphic concepts to continental strata requires careful consideration of controls on base level and sediment supply. As with shallow marine environments, relative sea level can be considered as the stratigraphic as well as the geomorphic base level for coastal nonmarine settings. Farther inland, stratigraphic base level, which determines accomodation space, is more complex and takes various forms, such as the graded profile for fluvial strata, groundwater tables for some eolian strata, and lake level for some intermontane sediments. Sediment supply is also generally a more complex variable for nonmarine environments than in the marine realm because of the proximity to the source area. The influence of climate and tectonism on sediment supply can clearly be seen in many continental sediments. Although in its infancy, sequence stratigraphy concepts have been applied to a wide variety of continental settings in attempts to explain variations in facies architecture. Future advances in this field promise tools for more precise correlation of nonmarine strata and better prediction of the location and geometry of facies from a limited knowledge of the stratigraphic relationships within a basin. This would be useful in the exploration for fluvial and eolian sandstone reservoirs and coalbeds. 135 refs., 13 figs.

  5. Quantitative stratigraphy of snow resolved by high-resolution penetrometry

    NASA Astrophysics Data System (ADS)

    Proksch, Martin; Reuter, Benjamin; Schneebeli, Martin; Löwe, Henning

    2014-05-01

    Precise measurements of snow structural parameters are essential to understand and model snow physical processes. Snow metamorphism, mass and energy balance of snow, radiative properties or the snowpack stability with respect to avalanche formation, all these processes depend on the snow structural parameters and the stratigraphy of the snowpack. However, most snow measurements are limited in spatial and temporal resolution and by extensive measurement times. For this reason, we developed a statistical model to derive three major snow structural parameters, density, correlation length and specific surface area (SSA) solely from a portable, high-resolution penetrometer. We demonstrate the potential of the method by a transect through Alpine snow in the Wannengrat study site, Davos, Switzerland. The two-dimensional plot of the transect reveals the depositional and metamorphic events. The results for the density are compared to independent density measurements from snow profiles. Based on these data, we are able to give a more complete interpretation of the snow stratigraphy and the underlying physical processes.

  6. Evaluation of the structure and stratigraphy over Richton Dome, Mississippi

    SciTech Connect

    Werner, M.L.

    1986-05-01

    The structure and stratigraphy over Richton Salt Dome, Mississippi, have been evaluated from 70 borings that were completed to various depths above the dome. Seven lithologic units have been identified and tentatively correlated with the regional Tertiary stratigraphy. Structure-contour and thickness maps of the units show the effects of dome growth from Eocene through early Pliocene time. Growth of the salt stock from late Oligocene through early Pliocene is estimated to have averaged 0.6 to 2.6 centimeters (0.2 to 1.1 inches) per 1000 years. No dome growth has occurred since the early Pliocene. The late Oligocene to early Pliocene strata over and adjacent to the dome reflect arching over the entire salt stock; some additional arching over individual centers may represent pre-Quaternary differential movement in the salt stock. The lithology and structure of the caprock at the Richton Salt Dome indicate that the caprock probably was completely formed by late Oligocene. In late Oligocene, the caprock was fractured by arching and altered by gypsum veining. Since late Oligocene, there are no indications of significant hydrologic connections through the caprock - that is, there are no indications of dissolution collapse or further anhydrite caprock accumulation. This structural and stratigraphic analysis provides insights on dome growth history, dome geometry, and neardome hydrostratigraphy that will aid in planning site characterization field activities, including an exploratory shaft, and in the conceptual design of a high-level waste (HLW) repository.

  7. Fluctuating Mesozoic and Cenozoic sea levels and implications for stratigraphy

    SciTech Connect

    Haq, B.U. (National Science Foundation, Washington, DC (USA))

    1988-12-01

    Sequence stratigraphy encompasses depositional models of genetically related packages of sediments deposited during various phases of cycle of sea level change, i.e., from a lowstand to highstand to the subsequent lowstand. The application of these models to marine outcrops around the world and to subsurface data led to the construction of Mesozoic-Cenozoic sea level curves with greater event resolution than the earlier curves based on seismic data alone. Construction of these better resolution curves begins with an outline of the principles of sequence-stratigraphic analysis and the reconstruction of the history of sea level change from outcrop and subsurface data for the past 250 Ma. Examples of marine sections from North America, Europe, and Asia can be used to illustrate sequence analysis of outcrop data and the integration of chronostratigraphy with sea level history. Also important are the implications of sequence-stratigraphic methodology and the new cycle charts to various disciplines of stratigraphy, environmental reconstruction, and basin analysis. The relationship of unconformities along the continental margins to hiatuses and dissolution surfaces in the deep basins must also be explored, as well as the relevance of sequence-stratigraphic methodology to biofacies and source rock prediction.

  8. Preliminary Model Results of Beach Profile Dynamics with Stratigraphy

    NASA Astrophysics Data System (ADS)

    Reniers, A. J.; Koktas, M.; Gallagher, E. L.; Wadman, H. M.; Brodie, K. L.; Johnson, B. D.; McNinch, J.

    2014-12-01

    The presence of spatial variation in grain size within the surf and swash zone is often ignored in numerical modeling whereas Upon closer inspection, a broad range of grain sizes is visible on a beach. This could potentially lead to a significant mismatch between predictions and observations of profile evolution given the strong sensitivity of sediment transport formulae to the grain size. To explore this in more detail, numerical simulations with XBeach have been performed to simulate the observations of changes in beach profile and stratigraphy within the swash zone at Duck, NC, under a range of wave and tidal conditions (see presentations by Wadman et al., and Gallagher et al. for complementary information on the observations at this conference). The research focus is to establish the morphodynamic response to the sediment dynamics at short and longer time scales in the presence of stratigraphy. A better understanding of the mechanisms and subsequently improved modeling will provide more accurate predictions of the morphodynamic response of the beach during moderate and extreme conditions. It will also help in the interpretation of sediment layering of the beach to relate to past extreme storms on geological time scales.

  9. Late Holocene isotopic and sedimentologic records contained in carbonate lagoonal cores, northern Little Bahama Bank 

    E-print Network

    Canova, Judy Lynn

    1988-01-01

    of species selection. On the other hand, there is evidence that, due to the presence of chlorophyte symbionts, ~i may exhibit vital effect (Wefer and Berger 1980; Wefer et al. 1981) as do many benthonic foraminifera with symbionts (Vinot..., the isotope stratigraphies of the cores show no apparent relationship to sea-level rise. However, microenvironmental variation in the shallower lagoons had a significant effect on the isotopic composition of the benthic foraminifera ~r' 8ftgtt)ffftt8...

  10. Pleistocene calcretes from eastern Tunisia: The stratigraphy, the microstructure and the environmental significance

    NASA Astrophysics Data System (ADS)

    Gallala, Wissem; Gaied, Mohamed Essghaïer; Essefi, Elhoucine; Montacer, Mabrouk

    2010-10-01

    This paper is meant to study the stratigraphy, the mineralogy, the microstructure and the geochemistry of Pleistocene calcretes from eastern Tunisia in order to infer the environmental factors intervening in their formation. Samples of eight profiles of Pleistocene calcretes from eastern Tunisia were examined on the basis of a variety of techniques including Optical Microscopy (OM), Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), chemical analysis and Atomic Absorption Spectrophotometer (AAS) techniques. Then, the obtained data underwent a statistical analysis on the basis of Factor Analysis (FA) and Principal Component Analysis (PCA). On the basis of field missions, five different horizons have been differentiated from bottom to top of all profiles: nodular, powdery, massive Brecciated and laminar horizon. The mineralogical study shows two minerals categories inversely proportional: calcite and (quartz and the clay). It shows also shows that Palygorskite is the dominant clay mineral. The escarpment edge is capped by a limestone containing fibrous palygorskite. Finally, superficial calcrete are described: a brecciated horizon which occurs in pockets on the plateau surface. This study about eastern Tunisia revealed the occurrence of successive cycles of calcretisation. Pedogenesis, water table oscillation, sedimentogenesis and stromatogenesis are the intervening factors in the calcretisation process. During the Pleistocene, they interfered with each other according to the climatic pulsations. From the studied case, it may be noticed that the formation of each calcrete horizon is the result of a dominating process that takes place during a distinguishable stage. In the first stage, the pedogenic process is developed by palygorskite formation including authigenic replacement or formation from a precursor mineral, neoformation from the breakdown products of such minerals or neoformation from suitable solutions. In the second stage, the powdery horizon is formed in the slope of the distal zone which presents a drained environment. In the third stage, several diagenetic processes (cementing, compaction, dissolution...) contribute to the formation of the laminar and massive horizon. Since it is exposed to dryness for a long period, the massive horizon is harder and more compact. In the fourth stage, the banding of light-dark in the laminar horizons reflects a dry-wet season alternation seasons. Dark beds are formed by the stromatolitic cover were developed during the wet season, whereas light beds were developed in an extremely arid climate argued by the presence of the detrital grains. In the fifth stage, the brecciated horizon, which occupies the channels, is formed by well rolled concretions, which present a dismantling material of Early and Middle Pleistocene calcretes after the Post-Villafranchian compressive phase. Thus, calcretisation seems to have been controlled by periods of uplift and stability of the slope, given that calcrete formation might be inhibited by the activation of the sedimentation of colluvial materials as a consequence of the tectonic activity. We also suggest that groundwater and biological activity may play a significant role in the development of pedogenic, sedimentological and polygenetic calcrete cycles within the same sedimentary basin. The alternation of dry and wet climatic periods may be responsible for the calcrete genesis.

  11. Sedimentologic and stratigraphic constraints on emplacement of the Star Kimberlite, east-central Saskatchewan

    NASA Astrophysics Data System (ADS)

    Zonneveld, John-Paul; Kjarsgaard, Bruce A.; Harvey, Shawn E.; Heaman, Larry M.; McNeil, David H.; Marcia, Kirsten Y.

    2004-09-01

    Diamond-bearing kimberlites in the Fort à la Corne region, east-central Saskatchewan, consist primarily of extra-crater pyroclastic deposits which are interstratified with Lower Cretaceous (Albian and Cenomanian) marine, marginal marine and continental sediments. Approximately 70 individual kimberlite occurrences have been documented. The Star Kimberlite, occurring at the southeastern end of the main Fort à la Corne trend, has been identified as being of economic interest, and is characterized by an excellent drill core database. Integration of multi-disciplinary data-sets has helped to refine and resolve models for emplacement of the Star Kimberlite. Detailed core logging has provided the foundation for sedimentological and volcanological studies and for construction of a regionally consistent stratigraphic and architectural framework for the kimberlite complex. Micropaleontologic and biostratigraphic analysis of selected sedimentary rocks, and U-Pb perovskite geochronology on kimberlite samples have been integrated to define periods of kimberlite emplacement. Radiometric age determination and micropaleontologic evidence support the hypothesis that multiple kimberlite eruptive phases occurred at Star. The oldest kimberlite in the Star body erupted during deposition of the predominantly continental strata of the lower Mannville Group (Cantuar Formation). Kimberlites within the Cantuar Formation include terrestrial airfall deposits as well as fluvially transported kimberlitic sandstone and conglomerate. Successive eruptive events occurred contemporaneous with deposition of the marginal marine upper Mannville Group (Pense Formation). Kimberlites within the Pense Formation consist primarily of terrestrial airfall deposits. Fine- to medium-grained cross-stratified kimberlitic (olivine-dominated) sandstone in this interval reflects reworking of airfall deposits during a regional marine transgression. The location of the source feeder vents of the Cantuar and Pense kimberlite deposits has not been identified. The youngest and volumetrically most significant eruptive events associated with the Star Kimberlite occur within the predominantly marine Lower Colorado Group (Joli Fou and Viking Formations). Kimberlite beds, which occur at several horizons within these units, consist of subaerial and marine fall deposits, the latter commonly exhibiting evidence of wave-reworking. Black shale-encased resedimented kimberlite beds, likely deposited as subaqueous debris flows and turbidites, are particularly common in the Lower Colorado Group. During its multi-eruptive history, the Star Kimberlite body is interpreted to have evolved from a feeder vent and overlying positive-relief tephra ring, into a tephra cone. Initial early Joli Fou volcanism resulted in formation of a feeder vent (˜200 m diameter) and tephra ring. Subsequent eruptions, dominated by subaerial deposits, partly infilled the crater and constructed a tephra cone. A late Joli Fou eruption formed a small (˜70 m diameter) feeder pipe slightly offset to the NW of the early Joli Fou feeder vent. Deposits from this event further infilled the crater, and were deposited on top of early Joli Fou kimberlite (proximal to the vent) and sediments of the Joli Fou Formation (distal to the vent). The shape of the tephra cone was modified during multiple marine transgression and regression cycles coeval with deposition of the Lower Colorado Group, resulting in wave-reworked kimberlite sand along the fringes of the cone and kimberlitic event deposits (tempestites, turbidites, debris flows) in more distal settings.

  12. Uranium-series ages of marine terraces, La Paz Peninsula, Baja California Sur, Mexico

    Microsoft Academic Search

    L. Sirkin; B. J. Szabo; G. A. Padilla; S. A. Pedrin; E. R. Diaz

    1990-01-01

    Uranium-series dating of coral samples from raised marine terrace deposits between 1.5 and 10 m above sea level in the La Paz Peninsula area, Baja California Sur, yielded ages between 123 ka and 138 ka that are in agreement with previously reported results. The stratigraphy and ages of marine units near the El Coyote Arroyo indicate the presence of two

  13. Sedimentological Investigations of the Martian Surface using the Mars 2001 Robotic Arm Camera and MECA Optical Microscope

    NASA Technical Reports Server (NTRS)

    Rice, J. W., Jr.; Smith, P. H.; Marshall, J. R.

    1999-01-01

    The first microscopic sedimentological studies of the Martian surface will commence with the landing of the Mars Polar Lander (MPL) December 3, 1999. The Robotic Arm Camera (RAC) has a resolution of 25 um/p which will permit detailed micromorphological analysis of surface and subsurface materials. The Robotic Ann will be able to dig up to 50 cm below the surface. The walls of the trench will also be inspected by RAC to look for evidence of stratigraphic and / or sedimentological relationships. The 2001 Mars Lander will build upon and expand the sedimentological research begun by the RAC on MPL. This will be accomplished by: (1) Macroscopic (dm to cm): Descent Imager, Pancam, RAC; (2) Microscopic (mm to um RAC, MECA Optical Microscope (Figure 2), AFM This paper will focus on investigations that can be conducted by the RAC and MECA Optical Microscope.

  14. Intrusive origin of the Sudbury Igneous Complex: Structural and sedimentological evidence

    NASA Technical Reports Server (NTRS)

    Cowan, E. J.; Schwerdtner, W. M.

    1992-01-01

    In recent years, many geoscientists have come to believe that the Sudbury event was exogenic rather than endogenic. Critical to a recent exogenic hypothesis is the impact melt origin of the Sudbury Igneous Complex (SIC). Such origin implies that the SIC was emplaced before deposition of the Whitewater Group, in contrast to origins in which the SIC postdates the lithification of the Onaping Formation. Structural and sedimentological evidence is summarized herein that supports an intrusion of the SIC after lithification of all Whitewater Group strata, and conflicts with the hypothesis advanced by other researchers.

  15. Stable organic carbon isotope stratigraphy across Oceanic Anoxic Event 2 of Demerara Rise, western tropical Atlantic

    NASA Astrophysics Data System (ADS)

    Erbacher, Jochen; Friedrich, Oliver; Wilson, Paul A.; Birch, Heather; Mutterlose, JöRg

    2005-06-01

    Ocean Drilling Program (ODP) Leg 207 recovered expanded sections of organic-carbon-rich laminated shales on Demerara Rise (western tropical Atlantic). High-resolution organic carbon isotope and total organic carbon (TOC) records are presented, which span the Cenomanian-Turonian boundary interval (CTBI), including the Oceanic Anoxic Event (OAE) 2, from four sites oriented along a NW striking depth transect. These records represent the first high-resolution carbon isotope records across OAE 2 from the South American margin of the tropical Atlantic. Due to the scarcity of age significant fossils, the main purpose of this study was to develop a detailed carbon isotope stratigraphy in order to correlate the CTBI across the depth transect and to tie this to biostratigraphically well-defined sections in the Western Interior Basin (Pueblo, USA), boreal shelf seas (Eastbourne, England), and western Tethys (Oued Mellegue, Tunisia). All four sections studied document a 6‰ increase of ?13Corg values at the base of the CTBI, which is followed by an interval of elevated ?13Corg values and a subsequent decrease. Our results supply an important stratigraphic base for subsequent paleoceanographic studies on Late Cenomanian to Early Turonian sediments from Demerara Rise and elsewhere.

  16. The role of sequence stratigraphy in 3-D characterization of carbonate reservoirs

    SciTech Connect

    Tinker, S.W.; Brondos, M.D.; Brinton, L. [Marathon Oil Co., Littleton, CO (United States)

    1996-12-31

    The product of 3-D reservoir characterization is a 3-D reservoir model. The integrity of the 3-D reservoir model is largely a function of the stratigraphic framework. Interpreting the correct stratigraphic framework for a subsurface reservoir is the most difficult and creative part of the 3-D modeling process. Sequence- and seismic-stratigraphic interpretation provide the best stratigraphic framework for 3-D reservoir modeling. Depositional sequences are comprised of many petrophysically-distinct lithofacies regions. If each lithofacies region was uniform and homogeneous, it would be reasonable to use a lithofacies ({open_quote}layer-cake{close_quote}) framework interpretation to distribute data in a 3-D model. However, lithofacies are typically time- transgressive, and often internally heterogeneous because geologic processes such as siliciclastic sediment deposition, sediment bypass, hardground formation, variable diagenesis, and facies shifts occur along depositional time surfaces on carbonate platforms. Therefore, a sequence stratigraphic framework interpretation, in which stratal geometries are honored, is better for controlling the distribution of petrophysical data in 3-D. The role that sequence stratigraphy plays in the 3-D characterization of carbonate reservoirs will be presented using two outcrop and four subsurface studies from the Paleozoic. The outcrop examples illustrate the important distinction between lithostratigraphic and sequence stratigraphic correlation, and the subsurface examples illustrate the process of quantification, integration, reduction, and analysis of geological, petrophysical, seismic, and engineering data. The concepts and techniques can be applied to carbonate reservoirs of any age.

  17. The role of sequence stratigraphy in 3-D characterization of carbonate reservoirs

    SciTech Connect

    Tinker, S.W.; Brondos, M.D.; Brinton, L. (Marathon Oil Co., Littleton, CO (United States))

    1996-01-01

    The product of 3-D reservoir characterization is a 3-D reservoir model. The integrity of the 3-D reservoir model is largely a function of the stratigraphic framework. Interpreting the correct stratigraphic framework for a subsurface reservoir is the most difficult and creative part of the 3-D modeling process. Sequence- and seismic-stratigraphic interpretation provide the best stratigraphic framework for 3-D reservoir modeling. Depositional sequences are comprised of many petrophysically-distinct lithofacies regions. If each lithofacies region was uniform and homogeneous, it would be reasonable to use a lithofacies ([open quote]layer-cake[close quote]) framework interpretation to distribute data in a 3-D model. However, lithofacies are typically time- transgressive, and often internally heterogeneous because geologic processes such as siliciclastic sediment deposition, sediment bypass, hardground formation, variable diagenesis, and facies shifts occur along depositional time surfaces on carbonate platforms. Therefore, a sequence stratigraphic framework interpretation, in which stratal geometries are honored, is better for controlling the distribution of petrophysical data in 3-D. The role that sequence stratigraphy plays in the 3-D characterization of carbonate reservoirs will be presented using two outcrop and four subsurface studies from the Paleozoic. The outcrop examples illustrate the important distinction between lithostratigraphic and sequence stratigraphic correlation, and the subsurface examples illustrate the process of quantification, integration, reduction, and analysis of geological, petrophysical, seismic, and engineering data. The concepts and techniques can be applied to carbonate reservoirs of any age.

  18. Knob fields in the Terra Cimmeria/Terra Sirenum region of Mars: Stratigraphy, mineralogy and morphology

    NASA Astrophysics Data System (ADS)

    Wendt, Lorenz; Bishop, Janice L.; Neukum, Gerhard

    2013-07-01

    We investigate the stratigraphy, morphology and mineralogy of five major knob fields in the region between Terra Cimmeria and Terra Sirenum on Mars based on HRSC, CTX, MOC and HiRISE imagery together with hyperspectral data from CRISM. The knob fields comprise Ariadnes Colles, Atlantis Chaos and Gorgonum Chaos and further, unnamed fields of mounds. They have been mapped in previous studies as Hesperian or Amazonian units and are located within the shoreline of the proposed "Eridania lake", the putative source of Ma'adim Vallis. The mounds contain Mg/Fe-bearing phyllosilicates and locally Al-rich phyllosilicates. Our geological mapping shows that the knob fields have a late Noachian age, which indicates later phyllosilicate formation than typically observed on Mars. The knob fields formed by alteration of the "Electris deposit", an airfall deposit possibly rich in basaltic glass (Grant, J.A., Schultz, P.H. [1990]. Icarus 84, 166-195), in local depressions, possibly in the Eridania lake. The spectroscopic detection of phyllosilicates here may indicate that liquid water persisted longer in this region than elsewhere on Mars. The knob fields are embayed by the Hesperian ridged plains. Numerous valleys carve into the ridged plains and document that the aqueous history of this region continued into the Hesperian and Amazonian. The study area is traversed by the Sirenum Fossae. These graben appear to post-date the aqueous activity in the study area except in the Gorgonum basin, where a lake developed after their formation.

  19. Lithofacies, palynofacies, and sequence stratigraphy of Palaeogene strata in Southeastern Nigeria

    E-print Network

    Bermingham, Eldredge

    Lithofacies, palynofacies, and sequence stratigraphy of Palaeogene strata in Southeastern Nigeria lithofacies asso- ciations occur: (1) lithofacies association I is characterized by fluvial channel and/or tidally influenced fluvial channel sediments; (2) lithofacies association II (Glossifungites and Skolithos

  20. Radiogenic isotopes: systematics and applications to earth surface processes and chemical stratigraphy

    E-print Network

    Banner, Jay L.

    Radiogenic isotopes: systematics and applications to earth surface processes and chemical Accepted 23 June 2003 Abstract Radiogenic isotopes have wide application to chemical stratigraphy briefly reviews the principles of radiogenic isotope geochemistry and the distribution of a number

  1. CARBON ISOTOPE STRATIGRAPHY AND DIAGENESIS OF PENNSYLVANIAN (DESMOINESIAN-MISSOURIAN) CARBONATES IN EAST-CENTRAL IDAHO 

    E-print Network

    Wood, Stephanie

    2011-05-10

    Carbon isotope stratigraphy of carbonate sediments is instrumental in examining major perturbations in the global carbon cycle and in correlating strata. However, the primary isotopic signal recorded in these sediments can vary with depositional...

  2. Stratigraphy and Hydrologic Conditions in the HSDP II Borehole: Implications for Ocean Island Stability

    NASA Astrophysics Data System (ADS)

    Thomas, D. M.

    2005-12-01

    The Hawaii Scientific Drilling Project has recently extended the HSDP II borehole to a depth of 3340 m. The borehole has been (nearly) continuously cored from the surface and provides a uniquely detailed record of the subsurface stratigraphy and hydrology of an ocean island volcano. The first kilometer of the stratigraphic section is dominated by subaerial pahoehoe and a`a lava flows along with rare soil and ash intervals and confirms subsidence of this portion of Hawaii Island by more than 1 km. The next kilometer of section comprises hyaloclastites (fragmental lavas that have been formed by interaction of lava flows with shallow seawater) that have undergone progressive induration with age and depth. Temperature surveys show a low temperature gradient in the first 500 m of this interval, consistent with high rates of fluid circulation, whereas the bottom-most 500 m shows a conductive temperature gradient with minimal circulation. At 1980 m, the first interval of pillow lavas was encountered and, from this depth to bottom-hole, the section consisted of alternating intervals of multiple pillow units inter-layered with progressively thinner hyaloclastite intervals. Throughout this section, the pillow units were found to be highly fractured with variable amounts of fracture filling secondary minerals whereas the hyaloclastites were fully indurated with clays and zeolites filling the pores of the compacted primary fragmental deposits. The complex stratigraphy hosts an equally complex hydrologic system. The surface basal freshwater lens gives way to seawater saturated rocks within a few tens of meters of the surface. However, the interface between Mauna Loa and Mauna Kea rocks at 300 m depth, shows a second 150 m thick freshwater layer beneath a soil and ash horizon that marks this interface. This is underlain by a cold circulating seawater system that is gradually choked off by induration of the hyaloclastites at depths below 1500 m. Temperature and pressure spikes at the pillow intervals below 2000 m show, however, that the fractured pillow layers are serving as water bearing formations. Wellhead pressure measurements show that artesian pressures within these formations exceed local hydrostatic pressure by more than 10 bars and fluid compositions indicate that these are confined aquifers that are isolated from the ocean and are in communication with surface freshwater systems. These findings suggest that the fresh ground water system within ocean island volcanoes may be substantially larger than has been generally recognized and that atypical hydrostatic pressures, arising from intense rainfall events or long-term climatic changes, could propagate to substantial depths within ocean island volcanoes and contribute to edifice instability.

  3. Postglacial transgressive stratigraphy of the Durban continental shelf, South Africa

    NASA Astrophysics Data System (ADS)

    Green, Andrew; Salzmann, Leslee; Cooper, Andrew

    2014-05-01

    This paper examines the geomorphology and seismic stratigraphy of the high-energy KwaZulu-Natal shelf offshore Durban, South Africa. Particular attention is paid to a laterally persistent (30 km) Holocene submerged shoreline located at 60 m water depth. Five major seismic units are identified (Units 1-5). Unit 1 comprises a series of infilled incised valleys that formed during the sea level lowering towards the Last Glacial Maximum. Unit 2 comprises a calcarenite core that forms the -60 m postglacial barrier complex. Unit 3 comprises lake-lagoon depressions in the back-barrier that formed simultaneously with the barrier system. These are backed to landward by several relict parabolic dunes preserved in Unit 2. Several relict weathering features (Unit 4) are associated with the barrier and reflect similar processes observed in contemporary aeolianite/beachrock outcrops on the adjacent coastline. These are draped by a thin veneer of post-transgressive Holocene sediment that caps the shelf stratigraphy (Unit 5). The development of the barrier and associated features occurred during a period of stillstand or slowstand associated with the Younger Dryas Cold Period (~12.7-11.6 Ka BP). Shoreline preservation in such a high-energy environment is considered unlikely as a result of the intense ravinement processes experienced during shoreline translation, coupled with the relatively low gradient setting of the KwaZulu-Natal shelf. The preservation of both the 100 m and 60 m shorelines was fostered by overstepping of the paleo-landscape, whereby preservation was promoted by a particularly rapid phase of relative sea-level rise associated with meltwater pulse 1B. This was further aided by early subtropical diagenesis during stillstand.

  4. Structure and stratigraphy of Dungeness Arch, and western Malvinas basin, offshore Tierra Del Fuego, Argentina 

    E-print Network

    Kalkan, Fercan Engin

    1989-01-01

    STRUCTURE AND STRATIGRAPHY OF DUNGENESS ARCH) AND WESTERN MALVINAS BASIN, OFFSHORE TIERRA DEL FUEGO, ARGENTINA A Thesis by FERCAN ENGIN KALKAN Submitted to the Office of Graduate Studies of Texas AkM University in partial fulfillment... of the requirements for the degree of MASTER OF SCIENCE August 1989 Major Subject: Geophysics STRUCTURE AND STRATIGRAPHY OF THE DUNGENESS ARCH, AND WESTERN MALVINAS BASIN, OFFSHORE TIERRA DEL FUEGO, ARGENTINA A Thesis by FERCAN ENGIN KALKAN Approved...

  5. Seismic stratigraphy and structure of the Barter Island sector of the Western Beaufort Sea 

    E-print Network

    Coffman, Jeffrey Dale

    1988-01-01

    SEISMIC STRATIGRAPHY AND STRUCTURE OF THE BARTER ISLAND SECTOR OF THE WESTERN BEAUFORT SEA A Thesis by JEFFERY DALE COFFMAN Submitted to the Graduate College of Texas A&M University in partial fulfillment of the requirement for the degree... of MASTER OF SCIENCE August 1988 Major Subject: Geophysics SEISMIC STRATIGRAPHY AND STRUCTURE OF THE BARTER ISLAND SECTOR OF THE UESTERN BEAUFORT SEA A Thesis by JEFFERY DALE COFFMAN Approved as to style and content by: t ~g, Robert McCabe (Co...

  6. The effect of stratigraphy and soil plasticity on the settlement characteristics of reclaimed surface mined land 

    E-print Network

    Rangel, Jorge Enrique

    1979-01-01

    THE EFFECT OF STRATIGRAPHY AND SOIL PLASTICITY ON THE SETTLEMENT CHARACTERISTICS OF FECLAIMED SURFACE MINED I~D A Thesis GORGE ENRIQUE RANGEL Submitted to the Graduate College of Texas ASM University in partial fulfillment of the regni ement... by (Chairman of Committee) (Membe") Member) (Head Department) ABSTRACT THE EFFECT OF STRATIGRAPHY AND SOIL PLASTICITY ON THE SETTLEHEN CHARACTERISTICS OF RECLAIMED SURFACE HINED LAND (December, 1979) Jorge Enrique Rangel, Geophysical Engineer Central...

  7. EARTHSCIENCESwww.earthsciences.osu.edu S C H O O L O F

    E-print Network

    Kubatko, Laura S.

    Earth Sci 4502 Stratigraphy and Sedimentology 4 Earth Sci 1121 & 1122 b) Complete at least one of the following courses: Earth Sci 501 Paleontology 5 Earth Sci 502 Stratigraphy and Sedimentology 5 Earth Sci 550

  8. The aeolian sedimentary system in the northern Qilian Shan and Hexi Corridor (N-China) - geomorphologic, sedimentologic and climatic drivers

    NASA Astrophysics Data System (ADS)

    Nottebaum, Veit; Lehmkuhl, Frank; Stauch, Georg

    2015-04-01

    The formation of aeolian deposits depends on the influence of climatic factors but also on non-climatic controls, such as local geomorphological setting and tectonic activity. Unravelling the environmental history needs a careful consideration of a set of sections to capture spatial variability and a detailed investigation of depositing processes and chronology. Along the northern margin of the Qilian Shan mountain range 22 OSL-dated loess and aeolian sand sections and additional surface samples reveal the interactions between climatic, geomorphologic and sedimentologic factors. Thin loess covers (~1-2 m) occur in elevations of 2000 to 3800 m asl, which were mainly accumulated during the Holocene. End-member modelling of loess grain size data exhibits three dominant aeolian transport pathways representing local transport from fluvial storages, dust storm contribution and background dust deposition. Their relative contributions show a clear dependence on geomorphological setting, and additionally, synchronous trends throughout the Holocene. Their relative changes allow conclusions about Holocene environmental conditions. Discontinuous archives (aeolian sand, lacustrine, and alluvial deposition) in the lower forelands of the Qilian Shan show a distinct spatial pattern contrasting western and eastern forelands. The comparison of OSL ages exhibits high sediment accumulation (~2 m/ka) in the drier western part during the Late Glacial, while the lack of Holocene ages indicates sediment discharge / deflation. In contrast, moister areas in the eastern foreland yield scattered Holocene ages. This indicates high sediment dynamics, benefiting from fluvial reworking and thus provided sediment availability. Fluvial sediment supply plays an important role in sediment recycling. Meanwhile, western forelands lack efficient sand sources and fluvial reworking agents. The study exemplifies the complex sedimentary systems acting along mountain to foreland transects which often host sedimentary palaeoenvironmental archives. Sand availability, vegetation cover, the presence (or absence) of perennial fluvial activity and potential tectonic activity followed by rapid discharge of sediment have to be thoroughly evaluated when interpreting aeolian palaeoenvironmental archives. Conclusions drawn from these loess and aeolian sand sections are used to set up a model of aeolian transport and deposition in this environmentally sensitive (semi-) arid region.

  9. Proposition curve: A tool for reservoir modeling and for improvement of sedimentological interpretations

    SciTech Connect

    Ravenne, C. (Institut Francais du Petrole, Rueil-Malmaison (France)); Galli, A.

    1993-02-01

    The IFP and Center of Geostatistics of Paris School of Mines have been working on reservoir characterization modeling since 1986. Emphasis has been placed upon the acquisition of geological data from outcrops and definition of the pertinent parameters that can be quantified which will constrain the simulations. It has been demonstrated that detailed sequence and cyclostratigraphy studies are necessary in order to provide the boundaries of the reservoir units, horizontal reference level used for computations, and a sequential ordering of lithofacies. Mathematical tools have also been created. Two quantitative parameters of primary importance for modeling are proportion curves of lithofacies and variograms. In the development of an accurate reservoir model, two points should be emphasized. (1) The quality of the preliminary sedimentological study is often inadequate for a quantitative modeling and limited data creates correlation problems. (2) Proportion curves are very powerful for refining the sedimentological interpretation and/or testing different hypotheses of correlation. These points will be illustrated with proportion curves computed mainly in fluvial or fluvial to deltaic environment from both outcrop analogs and subsurface field data.

  10. Sedimentologic and tectonic patterns in Dead Sea rift and their application to hydrocarbon exploration

    SciTech Connect

    Eshet, Y.; Robbins, E.I.

    1986-05-01

    The Dead Sea rift was produced primarily by sinistral strike-slip movement that offset many prominent geologic features along its 600-km length, from the Red Sea to the Lebanon Mountains. Unique structural patterns such as pull-apart basins arranged en echelon show that east-west extension and compression also occurred. The sedimentologic history includes deposits of Miocene lacustrine and continental clastic sediments, Pliocene lagoonal evaporites from a marine tongue, and Pleistocene peat in the north with various clastic and chemical sediments derived from narrow, closed lakes in the south. The southern sediments were penetrated by the rising Sedom salt diapir. Recent sedimentologic features include alluvial fans along the rift margins that are being dissected during the winter by runoff. At the eastern rift margin, sands are being offset by active faults. The Dead Sea, a remnant of an earlier lake, is halite saturated and is precipitating carbonates, sulfates, and halite. Tar sands and asphalt seeps in marginal outcrops, oil and gas shows in cores, and the huge Sedom salt body have attracted hydrocarbon exploration to the Dead Sea area. Hydrocarbons may originate from (1) Senonian oil shales that occur both east and west of the rift, or (2) older (Permian-Triassic.) reservoirs that have undergone hydrologic changes brought on by rift-valley formation. An exploration model is being tested to evaluate the possibility of oil being generated by deep circulation of heavy, organic matter-rich brines along fault boundaries.

  11. Late Quaternary Provenance and Flow Regime Reconstruction through Sedimentologic and Geochemical Evidence from the Bering/Chukchi Seas

    NASA Astrophysics Data System (ADS)

    Pelto, B. M.; Brigham-Grette, J.; Kocis, J. J.; Petsch, S.

    2013-12-01

    The last 20 kyr have been marked by great changes in the Arctic, as the Laurentide Ice Sheet melted and led to the submergence of the Bering Land Bridge and the re-opening of the Bering Strait (BS). The BS is a narrow connection (about 85 km wide) between the Arctic and Pacific Oceans averaging less than 50 m in depth, with present-day flow of seawater northward through the BS, from the Pacific to the Arctic. This flow is of vital importance to global ocean circulation through its role in formation and stability of North Atlantic Deep Water (NADW). An open BS is believed to speed dispersal of North Atlantic freshwater anomalies, both by keeping thermohaline circulation strong, and through reversals of flow through the BS when the North Atlantic is hosed with freshwater. When the BS is closed, these anomalies cannot efficiently dissipate and thermohaline circulation is weakened, which is considered a factor in climate perturbations outside of orbital forcing. Given the period of flux and transition in the Arctic following the Last Glacial Maximum (LGM), the paleoceanographic history of the Bering and Chukchi Seas post-LGM, is important to an understanding of Arctic Ocean circulation, and consequent climate impacts. Today the Arctic is in a period of rapid change, multi-year sea ice is disappearing, and the continuation of climatic stability of the Holocene appears to be at an end. Comprehension of the functioning of the Arctic as a dynamic system is essential to predict future response of the system to change, such as seawater salinity-density changes, lowered sea and land albedo, and rising temperatures. Changes in BS throughflow intensity and direction during deglaciation and submergence of the Bering Land Bridge are proposed and supported in modeling simulations, and are thought to occur during millennial-scale climate changes. We have conducted a coupled sedimentological and geochemical investigation of a suite of marine sediment cores from the Bering and Chukchi Seas. Elemental, isotopic, and grain size shifts correspond to changes in sediment routing, identifying changes in the magnitude and direction of throughflow in the BS. Major and trace element geochemistry spanning the past ~30 kyr was derived using an ITRAX XRF core scanner. Age control is well established by previous studies for a majority of the cores, primarily radiocarbon dates on diatoms. Elemental XRF data indicate significant change during the Bølling-Allerød warming around 15 kyr, and the opening of the BS at 11 kyr. During both of these periods there is a drop in Ti, Fe, K, and Ba with a corresponding rise in Cl, Ca, and Br. These data, in concert with the other sedimentologic data, infer shifts in paleo-flow conditions and sediment provenance during this time period. A key goal is the identification of how variations in geochemical properties correspond to bulk biogeochemical or biomarker variability, in comparison to sea ice proxies. The data being collected will add to a growing understanding of the Arctic as a dynamic system and answer questions concerning the post-glacial and Holocene evolution of changes that took place across the marine portion of the Bering Land Bridge.

  12. From Grains to Basin: An Example of a Project-Based Sedimentology Exercise

    NSDL National Science Digital Library

    Frederika Harmsen

    To prepare for this project, students have gained familiarity with thin-section preparation and the use of analytical equipment such as the XRD. The students have also learnt how to measure and interpret paleocurrent data. They have read background articles on the basin of study. In the field, students learn how to measure a stratigraphic section and the application of Walther's Law. The goal is to combine the skills acquired earlier in the class to interpret the stratigraphy, facies, depositional history and paleogeography of an outcrop in the field. This exercise also links sedimentation and tectonics.

  13. Magnetic Stratigraphy and Relative Paleointensity from IODP Site U1313 from 2.4-6 Ma

    NASA Astrophysics Data System (ADS)

    Evans, H. F.; Acton, G. D.; Guyodo, Y.; Channell, J. E.; Ohno, M.; Kanamatsu, T.

    2006-12-01

    IODP Expedition 306 to the North Atlantic drilled three sites in the Spring of 2005 including Site U1313 which is a re-occupation of DSDP Site 607. A complete spliced composite section was obtained down to 300 mcd (meters composite depth) from 4 holes drilled at the site. U-channel samples were collected for the upper ~280 meters of the section. The 2.4-6 Ma interval has produced a magnetic reversal stratigraphy that defines all the subchrons of the Gauss and Gilbert chrons. The Gauss and Gilbert chrons are ~ 45 meters and ~100 meters thick respectively and have mean sedimentation rates of 4.5 cm/kyr. The sediments carry a weak low- coercivity magnetization most likely carried by magnetite. In the upper part of the section (0-130 mcd) the sediments show a cyclic alternation between nannofossil oozes and silty-clay nannofossil ooze. The light nannofossil oozes represent interglacials while the darker silty clay nannofossil oozes represent the glacials. The sediment in the lower part of the section (130-300 mcd) consists of white nannofossil oozes. The volume magnetic susceptibility, although very weak when measured on the u-channel samples, is reproducible as demonstrated by replicate measurements. Natural gamma data collected shipboard on the whole core and magnetic susceptibility from u-channel samples can be correlated to a benthic oxygen isotope stack. The resulting age model based on this correlation and the reversal chronology is applied to the normalized remanence record between 2.4 and 4 Ma. Three relative paleointensity proxies have been calculated: NRM/ARM, NRM/IRM and the slope of NRM/ARM-acquisition. Consistency among the three proxies and acceptable correlation to Pacific records of the same age implies that the site has yielded useful a paleointensity record for the Gauss and Gilbert chrons.

  14. Sedimentology of the Moosebar Tongue and Bounding Strata, Lower Cretaceous Blairmore Group, South-Central Foothills, Alberta

    Microsoft Academic Search

    David R. Taylor

    1981-01-01

    This thesis provides detailed sedimentological descriptions and generalized interpretations of depositional environments within the Lower Cretaceous Blairmore Group of Alberta. In earliest Blairmore time (Hauterivian - Barremian ?), uplift to the west resulted in a period of extensive pedimentation and deposition of coarse clastics of the Cadomin Formation. Paleogeographic reconstructions indicate that a series of humid-climate alluvial fans to the

  15. Late-Quaternary morpho-sedimentology and submarine mass movements of the Betsiamites area, Lower St. Lawrence Estuary, Quebec, Canada

    E-print Network

    Long, Bernard

    Late-Quaternary morpho-sedimentology and submarine mass movements of the Betsiamites area, Lower St 2008 Accepted 4 March 2008 Available online xxxx Keywords: submarine mass movements morpho submarine geomorphology was revealed from multibeam bathymetry and seismic reflection surveys conducted

  16. Comparative Analysis of Biogeographic, Sedimentologic and Paleomagnetic Data and the Geodynamics of Terranes of Northeast Asia in Late Permian

    Microsoft Academic Search

    A. Biakov; E. Kolosev

    2004-01-01

    We present the first consistent model of the relative locations of the most important tectonic structures in Northeast of Asia for Late Paleozoic time. This model is based on comparative analysis of paleomagnetic, sedimentologic and biogeographic data. Results of research by the authors and critically reviewed data of the other researchers are used. The current paleomagnetic data for Permian rocks

  17. Sedimentology, dating and palaeoclimatic interpretation of A 76.3 ka record from Lago Grande di Monticchio, southern Italy

    Microsoft Academic Search

    Bernd Zolitschka; Jörg F. W. Negendank

    1996-01-01

    Detailed sedimentological and microstratigraphical investigations of lacustrine sediments from Lago Grande di Monticchio (southern Italy) provide a time scale based on rates of sedimentation obtained from annual laminations. Although not annually laminated throughout, a time scale covering the last 76.3 ka is available by interpolation of sedimentation rates. Results of this chronology agree with radiocarbon dates, and with ArAr dates

  18. Stratigraphy and paleogeography of the Cretaceous in Arabian Peninsula

    SciTech Connect

    Alsharhan, A.S.; Nairn, A.E.M.

    1986-05-01

    The Cretaceous of the Arabian Peninsula is divided into three major units by regional unconformities: Lower Cretaceous Thamama Group (Berriasian-middle Aptian), middle Cretaceous Wasia Group (Albian-Turonian), and Upper Cretaceous Aruma Group (Coniacian-Maestrichtian). The profusion of named stratigraphic units in the area reflects not only the lithologic variation resulting from facies changes, but also terminologies adopted by different companies. The authors provide a stratigraphic nomenclature defining standard type sections and indicate synonymies, which follow the recommendation of 10th Geological Liaison Meeting and hence are acceptable to operators in the area. The sedimentologic history of the area was presented in a series of paleogeographic maps, which they relate to the regional tectonic framework. The maps show a predominantly carbonate shelf ramp bordering a land area to the north and west. The principal change in depositional environment occurs during the Upper Cretaceous, as a result of tectonic activity. Less significant changes are attributed to eustatic sea level fluctuations, on which tilting caused by tectonic movement may be superposed during the Lower and middle Cretaceous. The major producing horizons lie below the regional unconformities; secondary porosity in the shelf reefal buildups was developed during subaerial exposure in the Shuaiba Formation (early-middle Aptian), in the Mishrif Formation (late Cenomanian), and in the Simsima Formation (Maestrichtian).

  19. Geoscience Curriculum Environmental Geoscience track Directed Electives: take one from each category

    E-print Network

    Carlson, Anders

    Introduction to Geologic Structures (Fall) 4 GEOSCI 430 Sedimentology and Stratigraphy 3 GEOSCI 204 Geologic 3 GEOSCI 375 Principles of Geochemistry 3 GEOSCI 430 Sedimentology and Stratigraphy 3 Geobiology: GEOSCI 411 Energy Resources 3 GEOSCI 431 Sedimentology and Stratigraphy Lab 1 GEOSCI 455 Structural

  20. Geological Sciences 330 Fall 2007 Sedimentary Geology

    E-print Network

    . Principles of sedimentology and stratigraphy. 4th edition. Prentice Hall, Upper Saddle River, NJ. 662 pp: Principles of Stratigraphy and Sedimentology (1) Week 2 10 Sept Sedimentary Particles: Weathering (13, 15 & 16) 28 Nov Integrated Stratigraphy and Sedimentology Lab 10: Well-log Interpretation Week 14

  1. New Geoscience Curriculum Environmental Geoscience track Directed Electives: take one from each category

    E-print Network

    Sheridan, Jennifer

    GEOSCI 430 Sedimentology and Stratigraphy 3 GEOSCI 204 Geologic Evolution of the Earth 4 GEOSCI 627 Sedimentology and Stratigraphy 3 Geobiology GEOSCI 455 Structural Geology 4 GEOSCI 304 Geobiology 3 Geoscience as a Public Problem 3 Required: GEOSCI 411 Energy Resources 3 GEOSCI 431 Sedimentology and Stratigraphy Lab 1

  2. Xavier Janson Professional Summary

    E-print Network

    Yang, Zong-Liang

    . Carbonates sedimentology and sequence stratigraphy. B. Petrophysics of carbonate. C. Seismic signature). Reservoir Characterization Research Laboratory (RCRL). C. Researcher, Sedimentology Department, Elf Record, 2009 - 2012 Associate Editor, Sedimentology, International Association of Sedimentologists, 2008

  3. DESCRIPTIONS/STRATEGIES What can I do with this major?

    E-print Network

    New Hampshire, University of

    Sedimentology StructuralGeology Geophysics EconomicGeology Geomorphology Paleontology Fossil Energy Geologists. Minerals MiningGeology Mineralogy Geochemistry EconomicGeology Paleontology Stratigraphy Sedimentology) LANDSCAPE EnvironmentalGeology Sedimentology Hydrology Geomagnetism Earth Surface Dynamics Coastal & Marine

  4. DESCRIPTIONS/STRATEGIES What can I do with this degree?

    E-print Network

    Kaminsky, Werner

    Sedimentology StructuralGeology Geophysics EconomicGeology Geomorphology Paleontology Fossil Energy Geologists. Minerals MiningGeology Mineralogy Geochemistry EconomicGeology Paleontology Stratigraphy Sedimentology) LANDSCAPE EnvironmentalGeology Sedimentology Hydrology Geomagnetism Earth Surface Dynamics Coastal & Marine

  5. GEOBULLETIN GeoBulletin is distributed weekly, by E-mail. Contributions are requested!

    E-print Network

    Carlson, Anders

    /Geography at the Johann Wolfgang Goethe-University Frankfurt invites applications · Assistant Professor, Sedimentology for a faculty position in Geophysics, Sedimentology, or Geochemistry · Post-doc in experimental petrology - U geochemistry, low-temperature geochemistry, mineralogy, paleoclimatology, sedimentology and stratigraphy

  6. Preliminary Sequence stratigraphy framework of the SW part of the Actopan Platform, Lower Cretaceous, Hidalgo, Mexico

    NASA Astrophysics Data System (ADS)

    Abascal, G.; Murillo-Muñeton, G.

    2013-05-01

    The oldest sedimentary rocks in what is known as the Actopan Platform, in the State of Hidalgo, Mexico, are superbly exposed toward the southwestern part of such platform. A detailed stratigraphic/sedimentologic study was carried out to a 623 m-thick section; this study was focused to establish a sequence stratigraphic framework. The base of the section consists of a Lower Cretaceous 6223-m thick, mixed siliciclastic-carbonate sedimentary succession that has been named Santuario Formation. The terrigenous facies of this unit correspond to red beds that consist of shales, sandstones y few conglomerates deposited under continental conditions (fluvial). White and yellowish sandstones, possibly deposited by deltaic systems, occur in minor amounts. A tuff layer is found in its lower part. The carbonate facies of the Santuario Formation consist mainly of skeletal mudstones/wackestones de bioclastos-peloides and subordinate quantities of sandy dolostones, skeletal packstones/grainstones and rudist (requeniids) boundstones. The middle and upper parts of the studied stratigraphic section correspond to an essentially carbonate succession that in known as El Abra Formation. This unit is comprised of the following facies: skeletal mudstones/wackestones, skeletal packstones/grainstone, and minor rudist (requeniid and Chondrodonta) boundstones and cryptalgal laminites deposited in shallow subtidal lagoon to tidal flat conditions. At this location, a "Middle" Cretaceous age (Albian-Cenomanian) has been assigned to the El Abra Formation. However, the common presence of the benthic foraminifer Chofatella decipiens Schlumberger in these facies indicates that their age extends, at least, to the Lower Cretaceous (Barremian). This age was confirmed with the dating of zircons in tuff deposited in the base section. The carbonate facies of the Santuario Formation stack forming fifth-order subtidal cycles or parasequences. While the carbonate facies of the El Abra Formation also stack forming subtidal and peritidal cycles. In turn, the fifth order cycles also stack forming fourth-order high frequency sequences. These sequences in the Santuario Formation are distinguished by the presence in their bases of the red beds interpreted as their lowstand systems tracts.

  7. The Relationship between Dynamic Topography and Sequence Stratigraphy

    NASA Astrophysics Data System (ADS)

    White, N. J.

    2014-12-01

    An evolving pattern of convective circulation within the mantle generates and maintains dynamic topography which is some fraction of observed topography. Spatial variations of dynamic topography are easy to measure within the oceanic realm and it is possible to exploit inventories of seismic reflection and wide-angle data to determine the dynamic topography of the oldest oceanic lithosphere that abuts passive continental margins. Results show that oceanic lithosphere has dynamic topographic anomalies of +/- 1 km with wavelengths of 500-1000 km. These substantial anomalies intersect coastal shelves and so it is expected that the development of these anomalies has affected sequence stratigraphic architecture in important ways. A series of examples will be used to illustrate how sequence stratigraphy can be profoundly influenced by changing patterns of dynamic topography. First, along the West African margin a set of dynamic topographic domes intersect the shelf edge. Onshore, the Neogene growth of these domes is recorded by emergent terraces and by drainage patterns. Offshore, an Oligo-Miocene switch from aggradation to progradation together with a series of younger disconformities have modified stratigraphic architecture along the shelf. Secondly, along the Northwest Shelf of Australia there is evidence for 700 m of dynamic drawdown of the oldest oceanic floor. Regional mapping and backstripping of clinoformal geometries within a Miocene carbonate reef complex shows that there is a dramatic switch from progradation to aggradation which cannot be attributed to glacio-eustatic variations. Instead, this switch appears to reflect growth of dynamic drawdown within the mantle. Finally, the Icelandic plume has controlled vertical motions along fringing North Atlantic margins over the last 60 Ma. Thanks to the intersecting mid-oceanic ridge, there is independent evidence that the temperature structure of this plume has fluctuated through time. These fluctuations are recorded within the detailed sequence stratigraphy of the margins where a series of ephemeral terrestrial landscapes have been mapped. Stratigraphic architecture appears to be an important repository of details about transient convective circulation which are otherwise difficult to obtain.

  8. Tracing time in the ocean: a brief review of chronological constraints (60-8 kyr) on North Atlantic marine event-based stratigraphies

    NASA Astrophysics Data System (ADS)

    Austin, William E. N.; Hibbert, Fiona D.

    2012-03-01

    Well-resolved event-based stratigraphies in marine sediments spanning a significant portion of the last glacial period (60-8 kyr) provide a unique opportunity for time-stratigraphic correlation in the North Atlantic region. Here, we review the current methods available to chronologically constrain these event-based stratigraphies, highlighting, in particular, the value of tephrochronology as an independent tool to validate correlations between records. While the INTIMATE protocols (Lowe et al., 2008; Blockley et al., 2011) are equally applicable to marine and terrestrial records, spatially and temporally variable marine radiocarbon reservoir age effects (MREs) provide a challenge to using marine radiocarbon in the former as an independent chronostratigraphic tool. Despite the inherent uncertainties associated with 'tuning', we conclude that the mid-points of the common abrupt warming transitions associated with the well-defined, millennial-scale climate oscillations (the Dansgaard-Oeschger (D/O) cycles) observed in the oxygen isotopes of the Greenland ice cores and North Atlantic sea surface temperature (SST) records currently provide the most robust correlation tie-points from which to derive age control. In this invited INTIMATE special issue article we propose a new protocol for establishing marine event-based chronostratigraphies in the North Atlantic region and focus on areas of chronological potential in palaeoceanographic research.

  9. Soil sedimentology at Gusev Crater from Columbia Memorial Station to Winter Haven

    USGS Publications Warehouse

    Cabrol, N.A.; Herkenhoff, K.E.; Greeley, R.; Grin, E.A.; Schroder, C.; d'Uston, C.; Weitz, C.; Yingst, R.A.; Cohen, B.A.; Moore, J.; Knudson, A.; Franklin, B.; Anderson, R.C.; Li, R.

    2008-01-01

    A total of 3140 individual particles were examined in 31 soils along Spirit's traverse. Their size, shape, and texture were quantified and classified. They represent a unique record of 3 years of sedimentologic exploration from landing to sol 1085 covering the Plains Unit to Winter Haven where Spirit spent the Martian winter of 2006. Samples in the Plains Unit and Columbia Hills appear as reflecting contrasting textural domains. One is heterogeneous, with a continuum of angular-to-round particles of fine sand to pebble sizes that are generally dust covered and locally cemented in place. The second shows the effect of a dominant and ongoing dynamic aeolian process that redistributes a uniform population of medium-size sand. The texture of particles observed in the samples at Gusev Crater results from volcanic, aeolian, impact, and water-related processes. Copyright 2008 by the American Geophysical Union.

  10. First ERTS-1 results in southeastern France: Geology, sedimentology, pollution at sea

    NASA Technical Reports Server (NTRS)

    Fontanel, A.; Guillemot, J.; Guy, M.

    1973-01-01

    Results obtained by four ERTS projects in southeastern France are summarized. With regard to geology, ERTS photos of Western Alps are very useful for tectonic interpretation because large features are clearly visible on these photographs even though they are often hidden by small complicated structures if studied on large scale documents. The 18-day repetition coverage was not obtained, and time-varying sedimentological surveys were impossible. Nevertheless, it was possible to delineate the variations of the shorelines in the Rhone Delta for a period covering the least 8,000 years. Some instances of industries discharging pollutant products at sea were detected, as well as very large anomalies of unknown origin. Some examples of coherent optical processing have been made in order to bring out tectonic features in the Alps mountains.

  11. Sedimentology of the Sbaa oil reservoir in the Timimoun basin (S. Algeria)

    SciTech Connect

    Mehadi, Z. (Institute des Hydrocarbures et de la Chimique, Boumerdes (Algeria))

    1990-05-01

    In 1980 oil was discovered in the Timimoun portion of the Sbaa depression in Southern Algeria. Until that time this basin had produced only dry gas. Since the 1980 oil discovery, several wells have been drilled. Data acquired from these wells were analyzed and are presented in this study. The oil reservoir is located within a sandstone interval of the Sbaa formation which has an average thickness of 75 m. The Sbaa lies between the Tournaisian (Lower Carboniferous) silts and the Strunian (uppermost Devonian) shales and sandstones. The sedimentological study reveals that the Sbaa formation contains bimodal facies consisting of coarse siltstones and fine sandstones. The sequence has been attributed to a deltaic environment developed in the central part of the Ahnet basin. The sources of the associated fluvial system are from the surrounding In-Semmen, Tinessourine, and Arak-Foum-Belrem paleohighs. Thermoluminescence indicates the provenance for the Sbaa sands was the crystalline basement Cambrian and Ordovician sections.

  12. Sedimentological data indicate greater range of water depths for Costistricklandia lirata in the Southern Appalachians

    SciTech Connect

    Bolton, J.C. (Univ. of Tennessee, Knoxville (USA))

    1990-08-01

    Two distinct horizons of the pentamerid brachiopod Costistricklandia lirata occur in the upper part of the Red Mountain Formation (Lower Silurian) in northern Alabama. Stratigraphic and sedimentologic characteristics of the rocks associated with the brachiopods suggest water depths of 15-150 m during times of low rates of terrigenous influx. Costistricklandid assemblages from the lower horizon are composed of extremely large individuals in association with a diverse population of large corals. They are interpreted to have lived in a protected environment. In an overlying horizon, costistricklandids occur in growth position at the base of a thick siliciclastic interval. These brachiopods lived in a storm-dominated environment and were buried in situ by the rapid influx of sediment associated with a passing storm.

  13. Acoustic stratigraphy of Bear Lake, Utah-Idaho: late Quaternary sedimentation patterns in a simple half-graben

    USGS Publications Warehouse

    Colman, Steven M.

    2006-01-01

    A 277-km network of high-resolution seismic-reflection profiles, supplemented with a sidescan-sonar mosaic of the lake floor, was collected in Bear Lake, Utah–Idaho, in order to explore the sedimentary framework of the lake's paleoclimate record. The acoustic stratigraphy is tied to a 120 m deep, continuously cored drill hole in the lake. Based on the age model for the drill core, the oldest continuously mapped acoustic reflector in the data set has an age of about 100 ka, although older sediments were locally imaged. The acoustic stratigraphy of the sediments below the lake indicates that the basin developed primarily as a simple half-graben, with a steep normal-fault margin on the east and a flexural margin on the west. As expected for a basin controlled by a listric master fault, seismic reflections steepen and diverge toward the fault, bounding eastward-thickening sediment wedges. Secondary normal faults west of the master fault were imaged beneath the lake and many of these faults show progressively increasing offset with depth and age. Several faults cut the youngest sediments in the lake as well as the modern lake floor. The relative simplicity of the sedimentary sequence is interrupted in the northwestern part of the basin by a unit that is interpreted as a large (4 × 10 km) paleodelta of the Bear River. The delta overlies a horizon with an age of about 97 ka, outcrops at the lake floor and is onlapped by much of the uppermost sequence of lake sediments. A feature interpreted as a wave-cut bench occurs in many places on the western side of the lake. The base of this bench occurs at a depth (22–24 m) similar to that (20–25 m) of the distal surface of the paleodelta. Pinch-outs of sedimentary units are common in relatively shallow water on the gentle western margin of the basin and little Holocene sediment has accumulated in water depths of less than 30 m. On the steep eastern margin of the basin, sediments commonly onlap the hanging wall of the East Bear Lake Fault. However, no major erosional or depositional features suggestive of shoreline processes were observed on acoustic profiles in water deeper than about 20–25 m.

  14. Tectonic features on Saturns satellites Dione and Rhea: Morphology and stratigraphy derived from Cassini ISS images

    NASA Astrophysics Data System (ADS)

    Wagner, R. J.; Neukum, G.; Stephan, K.; Giese, B.; Roatsch, T.; Wolf, U.; Porco, C. C.

    2009-04-01

    Introduction: The second- and fourth-largest satellites of Saturn, Rhea (1528 km in diameter) and Dione (1124 km), harbor old, densely cratered surfaces but also show evidence of resurfacing through tectonism in the images taken by the two ISS cameras aboard the Cassini spacecraft since July 2004. On Dione, tectonic features are more widespread than on Rhea implying that geologic activity has been going on for a longer time, whereas on Rhea tectonic activity may have ceased early in its history. The tectonic inventory of both satellites incorporates (a) troughs (graben), (b) scarps, (c) ridges, (d) lineaments, and (e) plateaus on Dione. Procedure: In this paper we focus on the stratigraphic sequence of events which created these tectonic landforms, independent of specific stress origins which are the topic of further work. Our investigation is based on the global ISS image coverage at regional (150 - 500 m/pxl), and, for selected target areas, at high-resolution scale (< 50 m/pxl). Relative ages of tectonic landforms are constrained by (1) cross-cutting relationships, (2) by their degree of degradation, (3) and by their superimposed crater frequency. On Dione, the image resolutions are sufficient to examine stratigraphic relationships between tectonic features while on Rhea the areas affected by tectonism could not yet be observed so far at regional or high resolution. Stratigraphy: On both satellites, densely cratered plains are the dominant geologic units with inferred high ages of ~ 3 - 4.2 Gyr from cratering chronology models. Degraded, densely cratered graben in the high northern and southern latitudes on Dione were formed early in its history. On Rhea, ridges seen in stereo data also appear to be rather old features. Troughs and graben on Rhea's trailing hemisphere could be old, but further regional- and high-resolution imaging is needed for detailed investigations. On Dione's trailing hemisphere, a stratigraphic sequence of horsts, graben and scarps has been derived by mutual crosscutting and truncation. Three age groups can be observed: (1) Clusium and Carthage Fossae are the oldest, truncated by (2) Eurotas and Palatine Chasmata which in turn were truncated by (3) Padua Chasmata representing the youngest set of troughs. Time and duration of tectonic activity on the two satellites is difficult to determine because of uncertainties in cratering chronology models. In the Eurotas Chasmata region, for example, cratering models suggest either older tectonism of about ~ 3 Gyr, or even younger events of about ~ 1 Gyr. No age determinations of tectonic events on Rhea have been made so far due to lack of sufficient image coverage.

  15. Large-scale cement stratigraphy in cavern porosity, Mallorca, Spain

    SciTech Connect

    Pomar, L.

    1989-03-01

    Rapid precipitation of carbonate cements occurs at the air-water interface in the zone of mixed fresh and marine waters in karstic caverns near the coast of Mallorca, Spain,. These cements, which have been precipitating at least since the middle Pleistocene, occur as fibrous calcite, rhombic calcite, and fibrous aragonite, which have accumulated in superimposed bands reaching total thicknesses of a few centimeters to a few meters. Calcite overgrown on aragonite without evidence of aragonite dissolution is common, although in some places the calcite shows later dissolution. Recent fibrous calcite with rapid rates of growth is precipitated in the few-decimenters-thick zone of tidal fluctuation (atmospheric pressure tides). Carbon-14 dating of these cements gives growth rates of 72.5 mm/1000 years. Extensive coatings of these cements extend 55 m vertically, from 40 m above to 15 m below the water table. Uranium-thorium and SER dating of some of the coatings shows that the cycles of precipitation recorded in the cements over the least 700,000 years are on the order of 100,000 years (Milankovich cyclicity). Precipitation of these cements occurred in the upper phreatic zone, whose position was tied to sea level changes during the Pleistocene-Holocene. The stratigraphy of these cements therefore provides an excellent record of late Quaternary sea level history in the western Mediterranean.

  16. Stratigraphy of the Jurassic system in northern Egypt

    SciTech Connect

    Keeley, M.L.; Shaw, D.; Forbes, G.A.

    1988-08-01

    A regional synthesis is presented of the stratigraphy of Jurassic strata in Egypt north of 30/degree/N, based on the study of about 80 wells and outcrops from northeastern Egypt. Almost all fossil groups have been investigated for biostratigraphic control. Published work on ammonite faunas from Gebel el Maghara (north Sinai) is integrated with extensive original work on palynofloras (and, to a lesser extent, ostracod/foraminiferal faunas) recovered from marine rocks in the subsurface. The recovery of rich dinocyst assemblages enables the recognition of a ten-fold zonation scheme, largely within the Middle-Late Jurassic sedimentary package. The upper limit of this package is marked by the Cimmerian erosional event; strata younger than Oxfordian are rarely preserved. Only east of 30/degree/E is significant sedimentation known to have occurred immediately prior to the major early Bajocian transgressive event. Thereafter mean sea level rose steadily. The Lower Triassic-Lower Jurassic sedimentary package is poorly understood, largely the result of scanty and ambiguous stratigraphic evidence. However, regional correlations suggest that only very thin earliest Jurassic (Hettangian ) clastic deposition succeeded a sequence of Upper Triassic carbonates and evaporites (Wadi en Natrun Formation) in the north. Arising from these studies is a standard lithostratigraphical scheme. The upper sedimentary package, the Gebel el Maghara Group, comprises three formations (Masajid, Khatatba, and Inmar) and seven members; new units are defined and old units redefined.

  17. Layering stratigraphy of eastern Coprates and northern Capri Chasmata, Mars

    NASA Astrophysics Data System (ADS)

    Beyer, Ross A.; McEwen, Alfred S.

    2005-12-01

    Distinct competent layers are observed in the slopes of eastern Coprates Chasma, part of the Valles Marineris system on Mars. Our observations indicate that the stratigraphy of Coprates Chasma consists of alternating thin strong layers and thicker sequences of relatively weak layers. The strong, competent layers maintain steeper slopes and play a major role in controlling the overall shape and geomorphology of the chasmata slopes. The topmost competent layer in this area is well preserved and easy to identify in outcrops on the northern rim of Coprates Chasma less than 100 m below the southern Ophir Planum surface. The volume of the topmost emplaced layer is at least 70 km 3 and may be greater than 2100 km 3 if the unit underlies most of Ophir Planum. The broad extent of this layer allows us to measure elevation offsets within the north rim of the chasma and in a freestanding massif within Coprates Chasma where the layer is also observed. Rim outcrop morphology and elevation differences between Ophir and Aurorae Plana may be indicative of the easternmost extent of the topmost competent layer. These observations allow an insight into the depositional processes that formed the stratigraphic stack into which this portion of the Valles Marineris is carved, and they present a picture of some of the last volcanic activity in this area. Furthermore, the elevation offsets within the layer are evidence of significant subsidence of the massif and surrounding material.

  18. Yucatán subsurface stratigraphy: Implications and constraints for the Chicxulub impact

    NASA Astrophysics Data System (ADS)

    Ward, W. C.; Keller, G.; Stinnesbeck, W.; Adatte, T.

    1995-10-01

    Much of the discussion about the effects of an end-of-Cretaceous impact by a large extraterrestrial body in northwestern Yucatán has been done in the context of limited and partly erroneous published data on the Mesozoic stratigraphy of that area. Reexamination of cores and geophysical logs taken in several Pemex wells has produced improved lithologic and biostratigraphic correlation of the Jurassic to Maastrichtian section across the northern Yucatán peninsula. These data suggest that major disturbance of strata by an impact would have been confined to within about 100 km of the proposed impact center near Chicxulub. The only unusual lithologic unit is polymict breccia, which apparently was penetrated at or near the top of the Cretaceous section in all the deep wells of northern Yucatán. This breccia in Pemex wells Yucatán 1, 2, 4, 5A, and 6 is composed predominantly of detrital dolomite, limestone, and anhydrite clasts set in dolomitized carbonate mud matrix, which contains upper Maastrichtian foraminifers. These constituents, mixed with fragments of altered glass or melt rock, shocked quartz and feldspar, and basement rock, suggest an impact as the most likely origin for the breccia. The timing of brecciation is poorly constrained by biostratigraphic data. There is some evidence, however, that the breccia unit is overlain by about 18 m of uppermost Maastrichtian marls, suggesting an impact before the Cretaceous-Tertiary boundary. In addition, there may have been more than one episode of breccia deposition.

  19. Evidence of Late Cenozoic uplift and climate change in the stratigraphy of the Macquarie River valley, New South Wales

    Microsoft Academic Search

    K. M. Tomkins; P. P. Hesse

    2004-01-01

    The stratigraphy of the alluvial sediments filling the Macquarie River valley, New South Wales, was investigated to test models of landscape evolution of the rifted margin Eastern Highlands of Australia. In the neighbouring Lachlan River valley, the stratigraphy of Neogene sediments has been incorporated into a model proposing denudation and episodic passive (denudational isostatic) uplift of the highlands throughout the

  20. Comparison of Soil and Stratigraphy Structures in Similar Landforms at Selected Sites in the Amargosa River Valley, California

    Microsoft Academic Search

    F. I. Aldridge; M. M. Schultz; C. L. Bracco; M. R. Doyle

    Soils and stratigraphy were recorded at selected sites and specific landforms along the Amargosa River near Tecopa, CA. Data were collated to compare sites for similarity of near-surface stratigraphy, as part of a larger study to support runoff modeling of the Amargosa Basin. Studied sites showed little correlation. Data is discussed and suggestions made for possible future study designs that

  1. Extended stratigraphy, palynology and depositional environments record the initiation of the Himalayan Gyirong Basin (Neogene China)

    E-print Network

    Utrecht, Universiteit

    the complex relationships between climate change and tectonism, particularly in the Late Cenozoic period Himalayas Neogene Sedimentology Palynology Climate change Tectonism a b s t r a c t Here we report new-currents was associated with a deciduous coniferous and broad-leaved mixed forest that suggests an increase in climate

  2. Late Quaternary stratigraphy and sedimentation patterns in the western Arctic Ocean

    USGS Publications Warehouse

    Polyak, L.; Bischof, J.; Ortiz, J.D.; Darby, D.A.; Channell, J.E.T.; Xuan, C.; Kaufman, D.S.; Lovlie, R.; Schneider, D.A.; Eberl, D.D.; Adler, R.E.; Council, E.A.

    2009-01-01

    Sediment cores from the western Arctic Ocean obtained on the 2005 HOTRAX and some earlier expeditions have been analyzed to develop a stratigraphic correlation from the Alaskan Chukchi margin to the Northwind and Mendeleev-Alpha ridges. The correlation was primarily based on terrigenous sediment composition that is not affected by diagenetic processes as strongly as the biogenic component, and paleomagnetic inclination records. Chronostratigraphic control was provided by 14C dating and amino-acid racemization ages, as well as correlation to earlier established Arctic Ocean stratigraphies. Distribution of sedimentary units across the western Arctic indicates that sedimentation rates decrease from tens of centimeters per kyr on the Alaskan margin to a few centimeters on the southern ends of Northwind and Mendeleev ridges and just a few millimeters on the ridges in the interior of the Amerasia basin. This sedimentation pattern suggests that Late Quaternary sediment transport and deposition, except for turbidites at the basin bottom, were generally controlled by ice concentration (and thus melt-out rate) and transportation distance from sources, with local variances related to subsurface currents. In the long term, most sediment was probably delivered to the core sites by icebergs during glacial periods, with a significant contribution from sea ice. During glacial maxima very fine-grained sediment was deposited with sedimentation rates greatly reduced away from the margins to a hiatus of several kyr duration as shown for the Last Glacial Maximum. This sedimentary environment was possibly related to a very solid ice cover and reduced melt-out over a large part of the western Arctic Ocean.

  3. Sequence stratigraphy of a Mesozoic carbonate platform-to-basin system in western Sicily

    NASA Astrophysics Data System (ADS)

    Basilone, Luca

    2009-09-01

    Sequence stratigraphic studies of the Triassic through Paleogene carbonate successions of platform, slope and basin in western Sicily (Palermo and Termini Imerese Mountains) have identified a sedimentary cyclicity mostly caused by relative oscillations of sea level. The stratigraphic successions of the Imerese and Panormide palaeogeographic domains of the southern Tethyan continental margin were studied with physical-stratigraphy and facies analysis to reconstruct the sedimentary evolution of this platform-to-basin system. The Imerese Basin is characterized by a carbonate and siliceous-calcareous succession, 1200-1400m thick, Late Triassic to Eocene in age. The strata display a typical example of a carbonate platform margin, characterized by resedimented facies with progradational stacking patterns. The Panormide Carbonate Platform is characterized by a carbonate succession, 1000-1200 m thick, Late Triassic to Late Eocene, mostly consisting of shallow-water facies with periodic subaerial exposure. The cyclic arrangement has been obtained by the study of the stratigraphic signatures (unconformities, facies sequences, erosional surfaces and stratal geometries) found in the slope successions. The recognized pattern has been compared with coeval facies of the shelf. This correlation provided evidence of sedimentary evolution, influenced by progradation and backstepping of the shelf deposits. The stratigraphic architecture of the platform-to-basin system is characterized by four major transgressive/regressive cycles during the late Triassic to late Eocene. These cycles, framed in a chronostratigraphic chart, allows the correlation of the investigated shelf-to-basin system with the geological evolution of the African continental margin during the Mesozoic, showing tectono-eustatic cycles. The first cycle, encompassing the late Triassic to early Jurassic, appears to be related to the late syn-rift stage of the continental margin evolution. The following three cycles, spanning from the Jurassic to Eocene, can be related to the post-rift evolution and to thermal subsidence changes.

  4. Depositional sequence analysis and sedimentologic modeling for improved prediction of Pennsylvanian reservoirs (Annex 1)

    SciTech Connect

    Watney, W.L.

    1992-01-01

    Interdisciplinary studies of the Upper Pennsylvanian Lansing and Kansas City groups have been undertaken in order to improve the geologic characterization of petroleum reservoirs and to develop a quantitative understanding of the processes responsible for formation of associated depositional sequences. To this end, concepts and methods of sequence stratigraphy are being used to define and interpret the three-dimensional depositional framework of the Kansas City Group. The investigation includes characterization of reservoir rocks in oil fields in western Kansas, description of analog equivalents in near-surface and surface sites in southeastern Kansas, and construction of regional structural and stratigraphic framework to link the site specific studies. Geologic inverse and simulation models are being developed to integrate quantitative estimates of controls on sedimentation to produce reconstructions of reservoir-bearing strata in an attempt to enhance our ability to predict reservoir characteristics.

  5. High-resolution palaeoecological and sedimentological records as a tool for understanding pre- and protohistoric settlement and land-use systems in Sandy Flanders (NW Belgium)

    NASA Astrophysics Data System (ADS)

    Court-Picon, Mona; Polfliet, Tim; Serbruyns, Lynn; de Smedt, Phillippe; Zwertvaegher, Ann; Bats, Machteld; de Reu, Jeroen; Werbrouck, Ilke; Verniers, Jacques; Crombe, Philippe

    2010-05-01

    The area of Sandy Flanders, situated between the North Sea coast and the lower course of the Scheldt River in NW Belgium, is a relatively flat and low-lying area situated at the southern limit of the lowland cover sand region of the NW European plain. During the Late Pleniglacial and the Late Glacial, numerous, generally small but elongated sand dunes, shallow lakes and wet depressions were formed. During the last three decades intense archaeological prospection has taken place in this region, which is now one of the most intensively surveyed areas of NW Europe. This has led to the production of archaeological distribution maps, which show a distinct pattern regarding the temporal and spatial distribution of these archaeological sites. Some areas with a presumed high ecological value, such as the large but shallow Late Glacial fossil lake of the Moevaart Depressie (ca. 15km long and 2,5km wide), seem to have been attractive settlement locations in Prehistory, given the high amount of close-lying sites along its borders and on the cover sand ridge on its northern border. Habitation however seems to have ‘moved' in time, and is completely absent in Protohistory and even the Roman Period. During the Late Glacial and Holocene the landscape in the Belgian area of Sandy Flanders was subjected to major changes due to climatic fluctuations, and besides human factors, environmental conditions such as topography, soil, vegetation, but also hydrology and climate, may have influenced settlement conditions throughout time and played a role in this change in site location and the occupational history of the region. In this light an inter-disciplinary project 'Prehistoric settlement and land-use systems in Sandy Flanders (NW Belgium): a diachronic and geoarchaeological approach' (GOA project, UGent), involving archaeology, geography, palaeoecology, sedimentology and geophysical survey, has been undertaken. The study of both "empty" and densely inhabited areas is ongoing and aims at analyzing the settlement dynamics of the area of Sandy Flanders in terms of environmental potentials (theory of "wandering farmsteads") and the human impact ("enculturation") on the landscape. Likewise, we seek to investigate the reasons why other areas, which were inhabited in previous periods (e.g. the Moervaart area) were apparently not attractive anymore from the Metal Ages onwards. Indeed, to determine the suitability of a certain land type for a certain activity, it is necessary to understand the different types of land use (hunting-gathering, farming, …), the soil characteristics and the environment at different time intervals. During a large field campaign, a 70m long trench was dug through the deepest part of the former Moervaart lake, revealing alternating layers of (organic) lake marl and peat(y clay) indicating warmer/colder and drier/wetter phases. In addition, 15 mechanical corings have been made at four different locations within the depression, in large palaeochannels that cross the palaeolake, and on its borders. Both trench and corings were extensively sampled for palaeoenvironmental and sedimentological analyses and for OSL and 14C-dating. We present here the first results of the palaeoecological (mainly palynology, but also plant macroremains, charcoal, diatoms, ostracods, mollusks, beetles and Chironomideae) and sedimentological (water content, LOI, magnetic susceptibility, gamma-density) approaches, which provide new insights in the palaeolandscape evolution of this area during the Late Glacial and the early Holocene, in order to evaluate in detail how and to which degree this evolution determined the pre- and protohistoric occupation and exploitation within Sandy Flanders. Furthermore, significant emphasis is placed on the impact of prehistoric populations on both regional and local landscapes.

  6. Stratigraphy, Structure, and Ore Deposits of the Southern Limb of the Midcontinent Rift System

    NSDL National Science Digital Library

    T. Bornhorst

    This site features an overview of the Midcontinent Rift system of North America, an area that extends for more than 2000 km northeasterly from Kansas, through the Lake Superior region, and then southeasterly through lower Michigan. This summary of the stratigraphy, structure, and mineralization of rift rocks provides an overview of the geologic history in northern Wisconsin and upper Michigan. Separate sections describe the tectonic history and structural features of the area, the stratigraphy of volcanic and sedimentary deposits, and the mineralization that produced rich copper and silver deposits. Information is supported by numerous citations while maps and diagrams help illustrate the concepts.

  7. Nonmarine stratigraphy of latest Cretaceous and early Tertiary age, southwestern New Mexico

    Microsoft Academic Search

    T. F. Lawton; G. H. Mack; S. G. Lucas; K. K. Kietzke

    1989-01-01

    Recent fossil collections from nonmarine strata at localities in southwestern New Mexico indicate that the Ringbone formation, as originally defined, comprises units separated by a major hiatus that is represented in the field by an angular unconformity. The lower unit has yielded (NMMNH locality 298) two anterior caudal vertebral centra, morphologically and metrically indistinguishable from those of the Late Cretaceous

  8. Phyllosilicate Stratigraphy near Mawrth Vallis, Mars: New Insights from Topography

    NASA Astrophysics Data System (ADS)

    Wray, James; Squyres, S. W.; Ehlmann, B. L.; Mustard, J. F.; Kirk, R. L.

    2007-10-01

    Phyllosilicate minerals were first identified on Mars by the OMEGA spectrometer on board Mars Express [1,2]. On Earth, these minerals form most commonly through prolonged interactions between rock and water, so their presence on Mars may have significant implications for the planet's aqueous history. In finely layered outcrops surrounding the ancient outflow channel Mawrth Vallis, OMEGA found two compositionally distinct types of phyllosilicates. With the higher-resolution view afforded by CRISM and HiRISE on the Mars Reconnaissance Orbiter, we find that these different minerals occur in distinct stratigraphic horizons, implying changing environmental conditions and/or a variable source of sediment for this location during the Noachian era. A layered unit containing Al-rich phyllosilicates overlies the most extensive of at least two units rich in Fe/Mg-phyllosilicates; in places, these are separated by another unit containing hydrated material of unknown mineralogy. All units are fractured into blocks ranging from decimeters to over a hundred meters across, and the morphology and scale of fractures correlates with the compositional stratigraphy. The lateral continuity of these stratigraphic units over scales exceeding 100 km and the uniformity (at CRISM resolution) of hydrated mineral signatures within each unit suggest that alteration occurred prior to sedimentary emplacement at this site. We use topographic data from HiRISE and the High Resolution Stereo Camera on Mars Express to aid in regional stratigraphic correlations and improve our understanding of the three-dimensional geometries of the phyllosilicate-rich layers. The layer geometries provide constraints on the timing of sedimentary deposition in Mawrth Vallis. [1] Bibring, J.-P. et al. (2005) Science 307, 1576-1581. [2] Poulet, F. et al. (2005) Nature 438, 623-627.

  9. Late Holocene development of a Norwegian alpine alluvial fan affected by proximal glacier variations, episodic distal undercutting, and colluvial activity

    Microsoft Academic Search

    Lindsey J. McEwen; Geraint Owen; John A. Matthews; John F. Hiemstra

    2011-01-01

    The late-Holocene, especially post-Little Ice Age, evolution of Nystølen alluvial fan, Langedalen, Jostedalsbreen region, southern Norway, is investigated using a combination of evidence from surface morphology, recent aerial photography, lichenometric dating, hydrological reconstruction, stratigraphy, and sedimentology. The fan is of predominantly fluvial origin, but it was effectively influenced by variations in the extent of the Nystølsbreen glacier, which advanced onto

  10. Early Triassic magnetic polarity time scale—integration of magnetostratigraphy, ammonite zonation and sequence stratigraphy from stratotype sections (Canadian Arctic Archipelago)

    NASA Astrophysics Data System (ADS)

    Ogg, James G.; Steiner, Maureen B.

    1991-10-01

    Stratotypes defining the stages of the Early Triassic (Griesbachian, Dienerian, Smithian and Spathian) are located on Ellesmere and Axel Heiberg islands in the northern Canadian Arctic. Ammonite-rich horizons are within a clastic outer shelf-to-slope facies of thick progradational wedges of mudstones and siltstones. Three sections were sampled for magnetostratigraphy and interpreted for transgressive and regressive pulses of sedimentation. Using the ammonite zonation as a guide, the transgressive-regressive cycles and magnetostratigraphies have been correlated among the sections and to the published Triassic sequence stratigraphy time scale, thus enabling definition of the magnetic polarity pattern for the upper Griesbachian to Smithian stages in multiple sections. The magnetic polarity and associated sequence stratigraphy pattern for the lower Griesbachian and for the Spathian were derived from single sections. The Griesbachian and Dienerian stages each have two pairs of normal- and reversed-polarity chrons; the Smithian is predominantly of normal polarity, and the Spathian is predominantly of reversed polarity. This magnetic polarity time scale may help to resolve age correlations of North American redbed facies and to define the Permian-Triassic boundary. After correction for variable structural orientations, the mean directions of magnetization from the three sites converge at 296° declination, 57° inclination ( k = 60, ? 95 = 16.5° ; equivalent pole = 41°N, 161°E; paleolatitude = 38°N), which is consistent with the pole derived from nearby Early Permian volcanics and supports a postulated post-Early Triassic, pre-Tertiary counterclockwise rotation of this region with respect to cratonic North America.

  11. Sedimentological control on the clay mineral distribution in the marine and non-marine Palaeogene deposits of Mallorca (Western Mediterranean)

    Microsoft Academic Search

    M. Ingles; E. Ramos-Guerrero

    1995-01-01

    During the Middle Eocene-Oligocene a marine and non-marine succession, about 1000 m thick, was deposited on Mallorca. Palaeoenvironmental interpretation of these deposits was obtained from sedimentological and palaeontological data in earlier studies.The non-marine environments recorded are: alluvial, fluvial (channel and flood plain deposits) and lacustrine (prevailing terrigenous, organic-rich or carbonate sedimentation). Marine environments are represented by littoral and shelf deposits.

  12. Sedimentological, archeological and historical evidences of paleoclimatic changes during the holocene in the lagoon of Venice (Italy)

    SciTech Connect

    Bonardi, M.; Canal, E.; Cavazzoni, S. [Istituto per lo Studio della Dinamica delle Grandi Masse, Venezia (Italy)] [and others

    1997-12-31

    Sedimentological investigations and archeological and historical information have allowed to correlate paleoenvironmental and coastline variations, in the Lagoon of Venice, to climatic changes during the Holocene. In particular, we report the results of a detailed study of Holocene sediments, from salt marshes and small islands, taken above and below a level with well dated archeological findings that gave a good indication of the mean sea level.

  13. Petrology, diagnosis, and sedimentology of oil reservoirs in Upper Cretaceous Shannon Sandstone Beds, Powder River basin, Wyoming

    SciTech Connect

    Hansley, P.L.; Whitney, C.G.

    1990-01-01

    This paper reports on a study of the petrology of the Shannon Sandstone Member that indicates diagenetic alterations of outcrop and near-surface sandstones cannot be used to predict the diagenesis of deeply buried sandstones. Textural relations show that oil migrated to reservoirs late in the postdepositional history of the Shannon. Petrologic and sedimentologic data suggest that an alternative depositional model (for example, a nearshore rather than mid-shelf setting) should be considered for the Shannon.

  14. Sedimentology, Petrography and Microfacies of the Paleogene Carbonate Sequence - Yaxcopoil-1 Borehole (Chicxulub, Yucatan)

    NASA Astrophysics Data System (ADS)

    Escobar-Sanchez, E.; Fucugauchi, J. U.

    2013-05-01

    Chicxulub crater is one the three largest known impact craters on Earth, formed 66 Ma-old, with multi-ring basin morphology. Crater is located in northwestern Yucatan, southern Gulf of Mexico, with rim diameter of 200 km and crater center at Chicxulub Perto in the coastline. It is buried beneath the carbonate and evaporitic Cenozoic sequence. Study of the structure requires geophysics and drilling, with several boreholes drilled in the peninsula. The Yaxcopoil-1 borehole was drilled south of Merida, about 62 km from center, as part of the Chicxulub Scientific Drilling Program. One of the main objectives was to determine the role of the Chicxulub impact event in the K/Pg mass extinction and boundary events. We present a sedimentological and petrological study of the carbonate sequence in the interval from 404 m to 792 m overlying the K/Pg boundary. The well reached a depth of 1510.6 m. In this interval, we identified twelve units marked by different lithological and sedimentological changes, and supplemented by thin section analysis. Facies are composed mainly of marls, argillaceous, limestones, dolomitized limestones, calcareous breccias and calcarenites with shales thin beds. From the microfacies study we observed several major changes in the microfacies. From bottom of the sequence several textural changes cyclic from mudstone to bioclastic planktic foraminiferal wackestone, bioclastic packstone and some bioclastic grainstone. Two textures dominated in the calcareous sequence: bioclastic wackestone and packstone microfacies. From the microfacies study, we derived inferences on stable environmental conditions. We observed benthic and planktic foraminiferal layers. The benthic foraminifera strongly depend on environmental parameters, such as nutrient supply or oxygenation of the sea bottom water in the Paleocene and Eocene. Changes suggest occurrence of a progradational event, with a relative increase in sea level very slowly, with the sediment enough to overcome the elevation. In the last meters of Unit 2 (778-772 m), a series of thin layers of marl and calcareous shale interbedded with wackestone are interpreted as a transgressive event. In the first few meters of Unit 3 provides greater energy currents causing variations in the grain size. Petrographic observations show that planktonic and benthic facies are arranged as intermittent flows in parts of the unit, which points to flow currents. Predominance of coarse-grained facies rich in carbonates possibly indicates a prograding event into deep areas. In the sequence several possible changes in sea level are recorded, especially from Unit 5 to 8 Unit, where a possible limit between the Paleocene and Eocene is located between Unit 6 and Unit 7, at about 660 m. Biostratigraphy was obtained by zones corresponding to P4 and P5. In Unit 8 contains the first record of turbidite or storm deposits outer shelf environments that could be related to platform progradation. The Paleocene-Eocene thermal maximum represents a period of global warming and sea level rise. The sedimentological and micropaleontological changes may be correlated with the faunal turnover in the Gulf of Mexico, providing a complementary tool for biostratigraphic inferences.

  15. Sedimentology and diagenesis of misoa C-2 reservoir, VLE-305/326 area, block V, Lamar Field, Maracaibe Lake, Venezuela

    SciTech Connect

    Cabrera de Casas, L.; Chacartegui, F. (Maraven S.A., Caracas (Venezuela))

    1993-02-01

    The main purpose of this study was to characterize the Upper Eocene C-2 reservoir using sedimentological, petrophysical and biostratigraphic parameters. The reservoir quality was evaluated by defining its physical attributes, geometry, areal distribution and orientation, from facies analysis of sedimentary units identified in core samples. In evaluating the sedimentary features of the Misoa C-2 reservoir in VLE 305/326 area, Block V, Lamar Field, Maracaibo Lake, 2,000' of cores from five wells (named VLe-339, VLE-720, VLE -723, VLe-754, LPG-1211) were analyzed. The sedimentary sequence studied represents upper-middle deltaic plain deposits with no marine influence. These deposits were identified as interdistributary channels, crevasse splays and interdistributary bays deposited in a northward prograding system. Seven sedimentary facies were defined from the physical, chemical and biological features observed in all cores. These facies were petrophysically and petrographically characterized then grouped in six sedimentary units which were then correlated over the entire area. One hundred well logs were correlated using sedimentological criteria. Finally, four flow units were identified in the reservoir using the sedimentological parameters, petrophysical data and production behavior. A surface trend analysis program utilizing thickness values resulted in contours, trends, residuals and isometry maps of each unit with a generalized southwest-northeast trend orientation. It was determined that facies distribution in the units controls the reservoir quality. These results are the main input into reservoir simulation. An accurate reservoir modeling is needed to prepare for optimizing secondary oil recovery.

  16. The sedimentology of a palaeo ice stream bed: an in-depth analysis of the Wielkopolska (Poland) MSGL field

    NASA Astrophysics Data System (ADS)

    Spagnolo, Matteo; Phillips, Emrys; Piotrowski, Jan A.; Rea, Brice; Carr, Simon; Ely, Jeremy; Ribolini, Adriano; Szuman, Izabela

    2015-04-01

    Ice streams are fast flowing (up to 1000s m per year) corridors of ice within ice sheets. They are the main arteries through which ice sheets lose mass, accounting for up to 90% of Antarctic discharge. Ice streams are also dynamic and can widen, migrate or shut down on decadal timescales. One of the key controlling factors on ice stream behaviour is the interaction with a soft sedimentary bed, but the exact mechanism of this interaction is far from known or well understood. Studies on the sedimentology of ice stream bed are challenging in present-day glaciated regions or in offshore palaeo-settings. However, some good examples of onshore and 'relatively' easy-to-access palaeo ice stream beds do exist. In Europe, one of these settings is in Poland, near the town of Poznan, in the Wielkopolska region. Mega-Scale Glacial Lineations (MSGLs), the characterising landform signature of ice stream beds, have been investigated using state of the art sedimentological techniques. These include, extensive investigation of multiple trenches excavated along the crests and flanks of MSGL and ground penetrating radar profiling of large sections of the MSGL field. Micro-sedimentological characterisation via thin sections, AMS and CT scans, as well as various lab analyses, including granulometry and mineralogy were also undertaken. Results indicate a homogeneous facies (to >3m), across all depths and locations within the palaeo ice stream bed. This has profound implications on the formation of MSGLs and the dynamics of ice stream flow.

  17. Preliminary Investigation of Linkages Between Arctic Pingos and Subsurface Stratigraphy

    NASA Astrophysics Data System (ADS)

    Casavant, R.; Skirvin, S.; Patel, C.; Burr, D.

    2008-12-01

    This NASA-SETI supported study investigates the distribution of pingos (elliptically-shaped ice-rich topographic mounds) across 2300 square kilometers of the central coastal plain of Arctic Alaska in relation to the shallow geological framework that exists immediately beneath them. Pingos in the central North Slope of Alaska are classified as being of the closed or hydrostatic type. Their genesis is often assigned to freezing and cryogenic uplift of near-surface saturated thaw lake sediments that are exposed as lakes are drained and/or become choked with sediments. Although thaw lakes appear rather ubiquitous across the study area, pingos do not. Pingo distributions can be categorized as either clusters of elements or as relatively dispersed. Spatial statistical analysis reveals that pingo distribution is non-random and clustered. The analysis also took into account that pingo distribution is a function of preferential preservation between modern rivers channels that cross the study area. Pingo distributions and frequency were tested in relation to the location and type of stratigraphic and sedimentological features that characterized the shallow subsurface across the study area. Subsurface interpretation was derived mostly from oil well wireline logs. Gamma ray logs for more than 160 wells were used to define, correlate and assess the connectivity and conductivity of shallow and near-surface stratigraphic units between wells. Assessed also were major facies changes and the type and locations of subsurface structures such as major basement-to-surface faults and folds. The surface and near-surface truncation and subcropping of tilted, alternating units of permeable coarse-grained and confining fine- grained units were also mapped in relation to pingo locations. Preliminary and intriguing findings will be presented which contribute to the hypothesis that pingo genesis, location, and variations in morphology could be, in part, linked to a well-documented and active subsurface geohydrologic system. This system is characterized by multiple stacked hydrocarbon-, saline- and freshwater-rich reservoirs. Processes include fault reactivation and basin subsidence that drive episodic basin expulsion, and upward migration and mixing of deep basin and phreatic fluids along basin margins. Endpoints of the system include demonstrable gas hydrates deposits that occur below and within the permafrost, and documented seepage of hydrocarbons and groundwater at the surface. Our hypothesis entertains the idea that closed pingos might also be endpoints of the petroluem system as basin and phreatic fluids migrate vertically within a thick and leaky permafrost interval along faults and tilted reservoir sand-rich units, which intersect and differentially charge frozen near-surface sedimentary units. Future field-based sampling and geophysical studies may shed additional light on this model's application for pingo genesis and resource exploration on Mars.

  18. Quaternary deposits and soil formation in the Aragón Pyrenees (Spain) - First results from sedimentological studies

    NASA Astrophysics Data System (ADS)

    Hirsch, Florian; Raab, Thomas; Schuhart, Stefan

    2010-05-01

    Within the scope of the research project Post LGM Pedogenesis and Geomorphodynamics in the Aragón Pyrenees funded by the DFG (Az RA 931/3-1) late Quaternary glacial, periglacial, fluvial and anthropogenic sediments are used to reconstruct the palaeoenvironment. The two research areas Gállego Valley and Aragón Valley are located in Aragón about 50 km northwest of Huesca which is a type region for Pleistocene glaciation in the Central Spanish Pyrenees. Our reconstruction of the paleoenvironment is based on a first soil mapping along catenas and the facies differentiation of the sediments. Sedimentological analyses are performed by a measurement of macrofabrics, clast roundness, lithology and followed in the laboratory by grain size and chemical analyses. Preliminary results indicate that beside the glacial also periglacial morphodynamics play a major role for the formation of the soils present in the area. Moreover, we have hints for human impacts on the soil landscape as in several profiles periglacial and glacial sediments are superimposed by colluvial sediments which we interpret as a correlative sediment of soil erosion on the slopes. The pedostratigraphy is characterized by horizontal and vertical small scale heterogeneity which also results in varying stages of pedogenesis. Sedimentological analyses show that in the unglaciated backslopes periglacial slope deposits (PSD) consisting of a Lower and an Upper Head are present. The coarse fraction (> 2 mm) of the PSDs in the unglaciated area is limited to autochthon or parautochthon material. The Upper Head clearly differs from the Lower Head and tills by higher amounts of fine material (< 2 mm) which is interpreted as a result of the eolian genesis typically mentioned for this type of PSD. Upper Heads are mainly found on sheltered sites (old forest stands) indicating the frequent erosion caused by anthropogenic land-use. On these sheltered sites luvisols are developed. Lower Heads are characterized by only a small amount of fine material and a high amount of angular clasts, whose a-axes are parallel to the slope direction. Therefore the Lower Heads are more resistant to erosion induced by anthropogenic land-use. On the exposed Lower Heads leptosols are the dominant soil type indicating a short time for soil formation. Formerly glaciated areas on the footslopes and on the valley floors are characterized by diamictic and allochthon sediments consisting solely of angular to sub-rounded clasts orientated parallel to the direction of the former glacier movement. These properties are characteristic for subglacial environments and lodgement processes. Soils on the glacigenic sediments are reddish and form cambic horizons. Anthropogenic superimposing is common on the tills with truncated profiles and colluvisols.

  19. Structure and seismic stratigraphy of deep Tertiary basins in the northern Aegean Sea

    NASA Astrophysics Data System (ADS)

    Beniest, Anouk; Brun, Jean-Pierre; Smit, Jeroen; Deschamps, Rémy; Hamon, Youri; Crombez, Vincent; Gorini, Christian

    2015-04-01

    Whereas active basin formation in the Aegean Sea is illustrated by seafloor bathymetry, the sedimentary and tectonic history of Tertiary basins is poorly known as existing offshore industrial seismic and well-log data are not easily accessible. We studied the evolution of the northern Aegean Sea with a focus on the North Aegean Trough and the Northern Skyros Basin, which are amongst the deepest basins of the northern Aegean domain. Structural and seismic stratigraphic interpretation of a 2D seismic dataset retrieved in the 1970's is combined with the well-investigated records of the onshore deep basins of northern Greece and Western Turkey. A general seismic signature chart was established using onshore basin stratigraphy and poorly-constrained well data. The studied domain shows two sharp unconformities that correspond to the Eocene-Oligocene transition and the Miocene-Pliocene shift, respectively. These transitions were then used as pillars for a more detailed structural and seismic stratigraphic interpretation. A NW-SE trending seismic line that cross-cuts the southern part of the NE-SW-trending North Aegean Through displays the main features that are observed in the area: 1) an overall basin geometry that is rather symmetrical; 2) pre-Pliocene units affected by steep normal faults; 3) a rather constant thickness of Oligocene sediments that define a depocenter with an apparent NW-SE orientation; 4) an ablation of Miocene sediments by erosion, likely related to the Messinian Salinity Crises (MSC); (5) thick deltaic/turbiditic deposits in the NE-SW oriented central through of Neogene age; 6) trans-tensional growth patterns in Pliocene and Quaternary sediments that combine NE-SW steeply dipping fault zones, more likely corresponding to strike-slip corridors, and E-W-trending normal faults. The evidence listed above suggest that, in the northern Aegean Sea, (1) extension started at the latest during the Late Eocene/Early Oligocene (data quality does not allow for a more precise age, nor does it excludes a mid-Eocene onset of extension as in the nearby located Rhodope Massif) and (2) sedimentation has been almost continuous from Late Eocene to present-day, however with a short interruption and even local erosion, during the Late Miocene. This tectono-sedimentary history is discussed in the frame of the Aegean extension, driven only by slab rollback from Middle Eocene to Middle Miocene and by the interaction between slab rollback and Anatolia extrusion since Middle Miocene.

  20. Magnetic and sequence stratigraphy of redeposited Upper Cretaceous limestones in the Montagna della Maiella, Abruzzi, Italy

    NASA Astrophysics Data System (ADS)

    Lampert, S. A.; Lowrie, W.; Hirt, A. M.; Bernoulli, D.; Mutti, M.

    1997-07-01

    The carbonate platform margin of the Montagna della Maiella in the Abruzzi region of central Italy has a complex history of sedimentation, consisting of aggradational and progradational episodes along the shelf margin and pelagic deposition in the basin. A paleomagnetic study at 12 regionally distributed limestone sites of late Cretaceous to Miocene age in the Maiella anticline was unable to define stable magnetic directions at most sites, largely due to the weakness of the magnetizations. At the few usable sites inclinations agreed with reference values based on an African polar wander path. Declinations were inconsistent, indicating local tectonic rotations. Both normal and reversed polarities were preserved at some sites. A magnetostratigraphic section, consisting of 280 samples spaced at 1-1.5 m intervals, was sampled along a profile in the Valle delle Tre Grotte, near the village of Pennapiedimonte. Sequence stratigraphy, based on two-dimensional analysis of outcrops, formed the stratigraphic framework for the magnetostratigraphic study. Rock magnetic analyses showed that magnetite is the dominant ferromagnetic mineral in the limestones. Both alternating field and thermal demagnetization were satisfactory in defining two main components in the weak magnetizations. A component with low coercivity, low unblocking temperature and normal polarity was close in direction to the present axial dipole field direction at the site. A higher coercivity, higher unblocking temperature component with both polarities was interpreted as the characteristic remanent magnetization (ChRM). Although the mean directions of samples with normal and reversed polarity are not exactly antipodal, a stratigraphic sequence of magnetozones is very clearly defined. The Pennapiedimonte magnetostratigraphy correlates well with late Cretaceous Chrons C30r to C34n in the established polarity timescale; numerical ages can thus be allocated to the reversals. Correlation to the Gubbio section allows paleontological dates for the reversal sequence to be inferred. The correlations allow more precise dating of formational and sequence boundaries and a better evaluation of stratigraphic hiatuses. In particular, the boundary between the Tre Grotte Formation (Supersequence 1, Turonian to middle Campanian) and the Orfento Formation (Supersequence 2, upper Campanian to upper Maastrichtian) is shown to be associated with a significant hiatus, spanning most of the middle Campanian G. ventricosa zone. Likewise, the absence of Chron C29r at the top of the Orfento Formation (SS2) documents non-deposition during the latest Maastrichtian or

  1. A re-appraisal of the stratigraphy and volcanology of the Cerro Galán volcanic system, NW Argentina

    USGS Publications Warehouse

    Folkes, Christopher B.; Wright, Heather M.; Cas, Ray A.F.; de Silva, Shanaka L.; Lesti, Chiara; Viramonte, Jose G.

    2011-01-01

    From detailed fieldwork and biotite 40Ar/39Ar dating correlated with paleomagnetic analyses of lithic clasts, we present a revision of the stratigraphy, areal extent and volume estimates of ignimbrites in the Cerro Galán volcanic complex. We find evidence for nine distinct outflow ignimbrites, including two newly identified ignimbrites in the Toconquis Group (the Pitas and Vega Ignimbrites). Toconquis Group Ignimbrites (~5.60–4.51 Ma biotite ages) have been discovered to the southwest and north of the caldera, increasing their spatial extents from previous estimates. Previously thought to be contemporaneous, we distinguish the Real Grande Ignimbrite (4.68?±?0.07 Ma biotite age) from the Cueva Negra Ignimbrite (3.77?±?0.08 Ma biotite age). The form and collapse processes of the Cerro Galán caldera are also reassessed. Based on re-interpretation of the margins of the caldera, we find evidence for a fault-bounded trapdoor collapse hinged along a regional N-S fault on the eastern side of the caldera and accommodated on a N-S fault on the western caldera margin. The collapsed area defines a roughly isosceles trapezoid shape elongated E-W and with maximum dimensions 27?×?16 km. The Cerro Galán Ignimbrite (CGI; 2.08?±?0.02 Ma sanidine age) outflow sheet extends to 40 km in all directions from the inferred structural margins, with a maximum runout distance of ~80 km to the north of the caldera. New deposit volume estimates confirm an increase in eruptive volume through time, wherein the Toconquis Group Ignimbrites increase in volume from the ~10 km3 Lower Merihuaca Ignimbrite to a maximum of ~390 km3 (Dense Rock Equivalent; DRE) with the Real Grande Ignimbrite. The climactic CGI has a revised volume of ~630 km3 (DRE), approximately two thirds of the commonly quoted value.

  2. Stratigraphy of a proposed wind farm site southeast of Block Island: Utilization of borehole samples, downhole logging, and seismic profiles

    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.

  3. The Cretaceous Paleogene (K P) boundary at Brazos, Texas: Sequence stratigraphy, depositional events and the Chicxulub impact

    NASA Astrophysics Data System (ADS)

    Schulte, Peter; Speijer, Robert; Mai, Hartmut; Kontny, Agnes

    2006-02-01

    Two cores from Brazos, Texas, spanning the Cretaceous-Paleogene (K-P) boundary, are investigated by a multidisciplinary approach aiming at unraveling environmental changes and sequence stratigraphic setting. In addition, the sedimentology of the K-P event deposit and its correlation with the K-P boundary is studied. Foraminifera and nannofossil stratigraphy indicates that both cores include a latest Maastrichtian (Zone CF1-CF2) and earliest Danian (P0, P? and P1a) shale sequence with a sandy and Chicxulub ejecta-bearing event deposit at the K-P boundary; a hiatus of unknown duration may be present by the unconformable base of the event deposit. Planktic foraminifera as well as calcareous nannofossil abundance and diversity both decline abruptly above the event deposit (K-P mass extinction), whereas benthic foraminifera show a pronounced faunal change but no mass extinction. Mineralogical and geochemical proxies suggest that-except for the sandwiched K-P event deposit-no facies change took place across the K-P boundary and no evidence for adverse an- or dysoxic sedimentary conditions following the Chicxulub impact was observed. Therefore, the interval bracketing the K-P event deposit is considered as highstand systems tract. Increased coarse detritus input and low planktic/benthic (P/B) foraminifera ratios during the earliest Paleocene (P0 and P?) both suggest an increased coastal proximity or relative sea-level lowering, although the K-P mass extinction of planktic foraminifera might have influenced the P/B ratios as well. Consequently, the sandy shales of the early Paleocene are considered as late regressive highstand or as lowstand deposit. During P1a, shales assigned as transgressive systems tract overlie a pyrite- and glauconite-rich bioturbated transgressive surface or type-2-sequence boundary. The smectite-dominated clay assemblage, with minor illite, kaolinite and chlorite indicates semiarid-humid climates with no obvious shifts across the K-P boundary. The magnetic susceptibility signature during the Maastrichtian reveals a subtle cyclic (or rhythmic) pattern, whereas a high-amplitude cyclic pattern is present during the early Danian. The K-P event deposit shows a succession of high-energetic debris flows and turbidites derived from multiple source areas, followed by a period of decreasing current energy. Deposition was likely triggered by multiple tsunami or tempestites followed by a prolonged period of reworking and settling. The Chicxulub ejecta at the base of the K-P event deposit consists of Mg-rich smectite-as well as Fe-Mg-rich chlorite-spherules. Their mineralogical composition points to target rocks of mafic to intermediate composition, presumably situated in the northwestern sector of the Chicxulub impact structure. Besides these silicic phases, the most prominent ejecta components are limestone clasts, accretionary carbonate clasts, and microspar, suggesting that the Texas area received ejecta also from shallow, carbonate-rich lithologies at the impact site on the Yucatán carbonate platform. The excellent correlation of Chicxulub ejecta at Brazos with ejecta found in the K-P boundary layer worldwide - along with the associated mass extinction - provides no evidence that Chicxulub predated the K-P boundary and allows for unequivocal positioning of the K-P boundary at the event deposit.

  4. Equivalent hydraulic conductivity of an experimental stratigraphy: Implications for basin-scale flow

    E-print Network

    Gable, Carl W.

    Equivalent hydraulic conductivity of an experimental stratigraphy: Implications for basin-scale groundwater flow models are the estimation of representative hydraulic conductivity for the model units. In this study, high-resolution, fully heterogeneous basin-scale hydraulic conductivity map is generated

  5. Pleistocene calcretes from eastern Tunisia: The stratigraphy, the microstructure and the environmental significance

    Microsoft Academic Search

    Wissem Gallala; Mohamed Essghaïer Gaied; Elhoucine Essefi; Mabrouk Montacer

    2010-01-01

    This paper is meant to study the stratigraphy, the mineralogy, the microstructure and the geochemistry of Pleistocene calcretes from eastern Tunisia in order to infer the environmental factors intervening in their formation.Samples of eight profiles of Pleistocene calcretes from eastern Tunisia were examined on the basis of a variety of techniques including Optical Microscopy (OM), Scanning Electron Microscopy (SEM), X-ray

  6. Quaternary seismic stratigraphy and paleoenvironments on the continental shelf of the East China Sea

    Microsoft Academic Search

    Zhen-Xia Liu; Serge Berne; Yoshiki Saito; G. Lericolais; T. Marsset

    2000-01-01

    Paleoenvironments and stratigraphy have been interpreted from 4380 km of seismic profiling collected during a geological and geophysical cruise on the continental shelf of the East China Sea (ECS) undertaken in 1996. The geophysical data are correlated with a borehole situated on the outer shelf obtained by Shanghai Marine Geology Bureau, indicating that six seismic units have been preserved since

  7. Long-period orbital control on middle Miocene global cooling: Integrated stratigraphy and astronomical tuning

    E-print Network

    Utrecht, Universiteit

    Long-period orbital control on middle Miocene global cooling: Integrated stratigraphy in the middle Miocene global cooling (13.82 Ma ± 0.03) coincides with minimum eccentricity values associated Paleogene and Neogene. The stepwise character of the middle Miocene cooling event appears to be controlled

  8. PermophilesInternational Commission on Stratigraphy International Union of Geological Sciences

    E-print Network

    Newsletter of the Subcommission on Permian Stratigraphy Number 51 ISSN 1684-5927 June 2008 #12;Contents Notes ..................................................................................................................................1 Charles M. Henderson Report: Resolution of the reported Upper Permian conodont occurrences from. Henderson,A. Nicora, R. Rettori, L. Carabelli New data about the Permian section and fusulinids

  9. Foraminifera, sequence stratigraphy and regional correlation; an example from the uppermost Albian of Southern England

    Microsoft Academic Search

    Malcolm B. Hart

    2000-01-01

    While the general principles of sequence stratigraphy are well-established, the detailed distribution of fossils within sequences is less well known. Emery & Myers (1996) indicate that the most distinctive palaeontological information comes from the Maximum Flooding Surface where diverse assemblages, often dominated by planktonic taxa, are characteristic. The palaeontological features of a number of sequences in the uppermost Albian of

  10. Structure and stratigraphy of Home Plate from the Spirit Mars Exploration Rover

    E-print Network

    Grotzinger, John P.

    Structure and stratigraphy of Home Plate from the Spirit Mars Exploration Rover Kevin W. Lewis,1 November 2008. [1] Home Plate is a layered plateau observed by the Mars Exploration Rover Spirit Rover, J. Geophys. Res., 113, E12S36, doi:10.1029/2007JE003025. 1. Introduction [2] The Mars Exploration

  11. Magnetic polarity stratigraphy and paleolatitude of the Triassic^Jurassic Blomidon Formation in the Fundy basin

    E-print Network

    Olsen, Paul E.

    Magnetic polarity stratigraphy and paleolatitude of the Triassic^Jurassic Blomidon Formation] characterized the Triassic as perhaps the most arid period of the Phanerozoic, citing evidence for widespread,5] and the apparent expan- sion of deserts in the Triassic and Early Jurassic to an extent not since repeated [6

  12. Contaminant Stratigraphy of the Ballville Reservoir, Sandusky River, NW Ohio: Implications for Dam Removal

    E-print Network

    Gottgens, Hans

    Contaminant Stratigraphy of the Ballville Reservoir, Sandusky River, NW Ohio: Implications for Dam Green, Ohio 43403 ABSTRACT. The Ballville Dam (Sandusky River) is one of the major structures in the Lake Erie water- shed, impounding 1.7 million m3 of water and sediment. Removal of the dam would open

  13. Application of MASW technology to identification of tidal flat stratigraphy and its geoenvironmental interpretation

    Microsoft Academic Search

    Yoichi Watabe; Shinji Sassa

    2008-01-01

    Intertidal flats are key elements in marine environments; they consist of regions with rich bioactivity and also contribute to water purification. Recently, it has been demonstrated that benthic activities in intertidal flats are closely related to geoenvironmental characteristics. The purpose of this study is to investigate the tidal flat stratigraphy which should be strongly affected by the geoenvironmental characteristics. We

  14. Stratigraphy and Hydrologic Conditions at the Brookhaven National Laboratory and Vicinity,

    E-print Network

    Stratigraphy and Hydrologic Conditions at the Brookhaven National Laboratory and Vicinity, Suffolk in cooperation with the Brookhaven National Laboratory and the U.S. Department of Energy #12;Cover Photo: View of Brookhaven National Laboratory, March 1997, showing developed area near center of site, sewage treatment

  15. Effects of global eustatic sea level variations and tectonism on stratigraphy of Iraq

    Microsoft Academic Search

    S. L. Gawarecki; S. Schamel

    1986-01-01

    The stratigraphy of Iraq is marked by complex vertical and lateral facies sequences controlled predominantly by two factors: (1) eustatic sea level variations, and (2) tectonic movements. Analysis of the sedimentary cycles provides a framework for evaluating the relative economic importance of transgressive versus regressive facies within the Iraq stratigraphic succession. Most reservoir rocks, principally reefal and neritic limestones and

  16. Stratigraphy of small shield volcanoes on Venus: Criteria for determining stratigraphic relationships and assessment of relative

    E-print Network

    Head III, James William

    Stratigraphy of small shield volcanoes on Venus: Criteria for determining stratigraphic than about 20 km, are common and sometimes very abundant features on the plains of Venus. Typically plains of Venus. Did the eruption style of small shields occur repeatedly throughout the visible part

  17. High-Resolution Sequence Stratigraphy in the Lower Member of Es2 in Shanghe Oilfield

    Microsoft Academic Search

    Lihua Gao; Zuozhen Han; Xiangqing Yu; Naijie Chi; Zhen Qin; Chao Han

    2011-01-01

    By using high resolution sequence stratigraphy theory and technique, chronostratigraphic sequence framework is established and finely compared, 3 medium term base level cycles and 46 short term base level cycles are outlined of the lower member of the Es2 in Shanghe Oilfield. According to coring data, logging, drilling and other experimental analysis data, the main depositional environments in the study

  18. Seismic stratigraphy of the Adare Trough area, Antarctica Joanne M. Whittaker , R. Dietmar Mller

    E-print Network

    Müller, Dietmar

    Seismic stratigraphy of the Adare Trough area, Antarctica Joanne M. Whittaker , R. Dietmar Müller May 2006; accepted 17 May 2006 Abstract The Adare Trough, located 100 km NE of Cape Adare, Antarctica, is the extinct third arm of a Tertiary spreading ridge that separated East from West Antarctica. We use seismic

  19. Sequence stratigraphy and facies associations of Falher units C and D, lower Cretaceous, Alberta Basin, Canada

    Microsoft Academic Search

    J. E. Casas; R. G. Walker

    1996-01-01

    The Lower Cretaceous Falher Member (Spirit River Formation) in the Deep Basin of Alberta is composed of 5 units (A-E) comprising the reservoir of the giant Elmworth gas field. Using high resolution sequence stratigraphy, 333 well logs and 65 cores were integrated to understand the evolution of Falher C and D in the study area. Five major faces associations were

  20. Instruments and Methods Contact spectroscopy for determination of stratigraphy of snow

    E-print Network

    California at Santa Barbara, University of

    albedo and microwave emission. Measurements of the spectral reflectance of the snow-pit surface are made-size stratigraphy using a hand lens to provide modeling constraints for microwave radiative transfer models (D. Accurate detection of snow grain size is particularly important for modeling applications where snow grain

  1. Hydrology, morphology and sedimentology of the Campos continental margin, offshore Brazil

    NASA Astrophysics Data System (ADS)

    Viana, A. R.; Faugeres, J. C.; Kowsmann, R. O.; Lima, J. A. M.; Caddah, L. F. G.; Rizzo, J. G.

    1998-01-01

    Slope sand deposits have accumulated from at least the Neogene to the Present on the southeastern Brazilian continental margin (Campos Basin area). This region shows sand accumulations concentrated on the upper portion and on the base of the continental slope with a middle to lower slope bypass zone. A synthesis of preliminary results, supported by recent cores, high-resolution geophysical surveys, geotechnical investigations and environmental research, is presented and permits a prelitrunary analysis of the sedimentological mechanisms operational in this area. These point toward a temporal and spatial multiscale set of phenomena responsible for sand deposits. At any sea-level stand these deposits are dependent on: (1) a suitable sediment source; (2) offshelf transport mechanisms; (3) a morphostructural and hydrodynamic context responsible for the deposition of these sands in the upper portion of continental slopes. The proposed scenario of depositional processes concerns: (1) a set of hydrological processes such as surface currents and counter-currents, waves, tides and eddies with sufficient energy to form submarine sand dune fields at the outer shelf; (2) the offshelf export of this sediment under a combined action of spillover, internal waves, eddies 'seafloor polishing effect' and gravity processes (turbidity currents); and (3) the slope sand deposits and their distribution controlled by the action of contour currents, mass movements and the morphological context, such as canyons, gullies or scarps.

  2. Variation in sedimentology and architecture of Eocene alluvial strata, Wind River and Washakie basins, Wyoming

    SciTech Connect

    Patterson, P.E.; Larson, E.E. (Univ. of Colorado, Boulder (United States))

    1991-03-01

    Eocene continental, alluvial strata of the Wind River Formation (Wind River Basin) and the Cathedral Bluffs Member of the Wasatch Formation (Washakie basin) provide two examples of Laramide intermontane basin aggradation. These alluvial sediments primarily represent overbank flood deposits marginal to channel complexes. Their sedimentology and architecture, although grossly similar, appear to vary somewhat with proximity to Laramide uplifts. In both cases, repetitive sedimentation on the floodplain produced a succession of depositional couplets, each composed of a light-gray sand overlain by a red clay-rich silt or sand. The lower sands are tabular bodies that, near their distal margins, taper discernibly. They commonly display planar and ripple-drift laminations. Upper clay-rich layers, which are laminated, are also generally tabular. Those floodplain strata depositional proximal to Laramide uplifts show little evidence of scouring prior to deposition of the next, overlying couplet. Most of these sedimentary layers, therefore, are laterally continuous (up to 2 km). This alluvial architecture results in relatively uniform porosity laterally within depositional units but variable porosity stratigraphically through the sequence. In contrast, alluvial sediments deposited farther from the Laramide uplifts have undergone sporadic incision (either during rising flood stage or subsequently) followed by aggradation. As a result, many of these floodplain couplets are discontinuous laterally and, hence, exhibit large-scale lateral variability in porosity. Both alluvial sequences have undergone similar types and extents of burial diagenesis.

  3. Sedimentology and petroleum occurrence, Schoolhouse Member, Maroon Formation (Lower Permian), northwestern Colorado

    SciTech Connect

    Johnson, S.Y.; Schenk, C.J.; Anders, D.L.; Tuttle, M.L. (Geological Survey, Denver, CO (USA))

    1990-02-01

    The Lower Permian Schoolhouse Member of the Maroon Formation (formerly considered the Schoolhouse Tongue of the Weber Sandstone) forms a partly exhumed petroleum reservoir in the Eagle basin of northwestern Colorado. The Schoolhouse consists mainly of yellowish gray to gray, low-angle to parallel bedded, very fine to fine-grained sandstone of eolian sand-sheet origin; interbedded fluvial deposits are present in most sections. The sand-sheet deposits of the Schoolhouse Member are sedimentologically and petrologically similar to those in the underlying red beds of the main body of the Maroon Formation, and the Schoolhouse is considered the uppermost sand sheet in the Maroon depositional sequence. The bleached and oil-stained Schoolhouse member is distinguished from the underlying Maroon red beds on the basis of its diagenetic history, which is related to regional hydrocarbon migration and development of secondary porosity. Geological and geochemical data suggest that Schoolhouse Member oils have upper Paleozoic sources, including the intrabasinal Belden Formation. 13 figs., 1 tab.

  4. A paleoclimate record with tephrochronological age control for the last glacial-interglacial cycle from Lake Ohrid, Albania and Macedonia

    Microsoft Academic Search

    Hendrik Vogel; Bernd Wagner; Giovanni Zanchetta; Roberto Sulpizio; Peter Rosén

    2010-01-01

    Lake Ohrid is probably of Pliocene age, and the oldest extant lake in Europe. In this study climatic and environmental changes\\u000a during the last glacial-interglacial cycle are reconstructed using lithological, sedimentological, geochemical and physical\\u000a proxy analysis of a 15-m-long sediment succession from Lake Ohrid. A chronological framework is derived from tephrochronology\\u000a and radiocarbon dating, which yields a basal age of

  5. Sorting out meandering and braiding: discriminating formative conditions and stratigraphy

    NASA Astrophysics Data System (ADS)

    Kleinhans, M. G.; van de Lageweg, W. I.; Schuurman, F.; Van Dijk, W. M.

    2011-12-01

    For various river channel patterns, the necessary formative conditions differ, but how is not entirely understood. Furthermore, not only the morphology and dynamics differ, but also the resulting stratigraphy differs, of which understanding is required to infer past environmental conditions and predict reservoir behaviour. Our objective is to identify the necessary and sufficient conditions for forming dynamic meandering and braided rivers. We reproduced both patterns experimentally and with a physics-based numerical model, and produced synthetic stratification from bed elevation maps and control lacquer peels for the experiments. Experimental meandering was produced using a mixture of poorly sorted sediment and silt-sized silica flour and a transversely moving inflow boundary. Braiding was produced in exactly the same conditions but without the silica flour. These experiments represent gravel-bed rivers in nature, where both experimental meandering and braiding channels were close to the transition between the types. Onset meandering was also produced in the numerical model (Delft3D) with a similar transversely moving inflow boundary, whilst braided rivers formed with fixed inflow or some noise on the transverse discharge distribution at the inflow boundary. The silica flour deposited on crevasse splays and in chute channels, forming new floodplain. This caused much less chute cutoffs and stronger banks. The resulting meandering river formed multiple sets of scroll bars forming pointbars, overlain by splays and floodplain. The braided river, in contrast, showed mid-channel bars and multiple active channels, faster and more haphazard bar and channel migration, and frequent chute cutoffs. Apart from the floodplain, stratification in meandering rivers consisted of sigmoidally stratified units formed by scroll bars and channel fills, usually formed after chute cutoff. Braided rivers had similar units but much smaller and more. In both cases the highest preservation potential is in the deepest channels. We conclude that some floodplain-filling sediment or vegetation is required for meandering to prevent chute cutoffs to lead to weak braiding, but, more importantly, that some dynamics are required at the upstream boundary, where periodic perturbation causes meandering whilst stochastic perturbation causes braiding. Furthermore, morphology and stratification in braided gravel-bed rivers have much smaller morphological and stratigraphic units relative to average channel width than the meandering rivers, even though active bar dimensions are comparable.

  6. Reconstruction of the sedimentological environment and paleo-tsunami events offshore Jisr Az-Zarka (central Israel)

    NASA Astrophysics Data System (ADS)

    Tyuleneva, Natalia; Braun, Yael; Suchkov, Igor; Ben-Avraham, Zvi; Goodman-Tchernov, Beverly

    2015-04-01

    Previous research shows that cores retrieved offshore central Israel (Caesarea) have anomalous sedimentary sequences that correspond to at least three tsunami events. Identification of the tsunami horizons was carried out by quantifying the presence of a wide range of characteristics described in modern and paleotsunami analogs. In this study, a sediment core (219cm) was obtained from 15.3 m water depth, some 1.5 km to the south-west of the Crocodile River mouth, offshore the village of Jisr Az-Zarka, and ~4 km north of Caesarea. The core was sampled at 1 cm intervals for grain size and micropaleontological analyses. XRD and XRF analyses were also performed at coarser resolution. The aim of the study was to correlate anomalous layers in the core with previously identified tsunami layers off Caesarea and to test whether their expression differs, given the impact of the river runoff and land material input. An additional aim was to study the inter-event sediments to determine broader environmental changes. This is uniquely possible here because the maximum age of the deposits (<6yBP) and depth of the collection area negate the presence of sea-level change influence; and this portion of the coastline is considered tectonically quiet for at least 2000 years; thereby negating two possible effects on the sedimentological signatures. In this new core two tsunami horizons corresponding with known Caesarea events (~1200 yBP, perhaps 749 AD earthquake; and ~3500 yBP 'Santorini eruption') were recognized, and, one previously unidentified event, dated by 14C to 5.6-6 ka, was discerned as well. The Nile River has been the dominant and most stable source of terrigenous components in the study area, such as siliciclastic quartz for the sand fraction and smectite - for the clays. Thus, the prevailing marine settings are dominated by these two mineralogical components. XRD analysis of nine intervals in the core determined the following clay minerals: smectite, hydromica (illite), chlorite and kaolinite. Normal marine settings are characterized by the stable relative ratios between these minerals, while the contribution from the surrounding landmass here can be detected by increase of illite and smectite. The Santorini tsunami layer is characterized by an increment of high illite content (2.5 fold increase relative to the average content of this mineral in the core). The earliest tsunami interval is characterized by distinct increases of titanium and zirconium concentrations according to XRF analysis. New results from this study suggest that (1) relative to other tsunami events, the Santorini eruption-age tsunami waves caused more input of terrestrial material onto the upper shelf, as indicated by the content of illite; (2) the oldest tsunami event is characterized by a significant content of titanium and zirconium elements, which are the constituents of such minerals as rutile and zircon. This is probably the result of processes of concentration of heavy minerals; (3) the increment of smectite content found downcore, which lacks tsunamigenic indicators, between 4.5 and 3.5 ky, is attributed to increased input from the land and larger river runoff, possibly the result of a more humid climate.

  7. The International Subcommission on Stratigraphic Classification of the International Commission on Stratigraphy: The Knowledge

    NASA Astrophysics Data System (ADS)

    Pratt, Brian

    2014-05-01

    The International Subcommission on Stratigraphic Classification (ISSC) was born in 1955 as an effort to promote awareness of stratigraphic principles and encourage worldwide standardization of stratigraphic approaches and terminology. The first major achievement of ISSC was the 1976 publication of the International Stratigraphic Guide. It was revised in 1994, with an abridged version appearing in 1999. These documents achieved their goals magnificently: cited innumerable times and forming the core of many national stratigraphic codes. As the discipline has evolved, particularly from technological advances and ocean drilling, new tools and methodologies have been developed and these have led to ever finer resolution of geological time and ever more exact correlation of stratigraphic units and events, thereby enhancing the understanding of the genesis of the geological record. Under the leadership of M. B. Cita, ISSC embarked in 2002 on a renewed initiative to disseminate to the global geological community these newer developments, and ultimately incorporate them into a third edition of the Guide. To this aim, traditional and new branches of stratigraphy are being treated: chemostratigraphy, cyclostratigraphy, magnetostratigraphy, lithostratigraphy, sequence stratigraphy, biostratigraphy, and chronostratigraphy. An open-access review paper is dedicated to each and published in Newsletters on Stratigraphy. The next edition of the Guide will be inclusive of all branches of stratigraphy and also embrace igneous and metamorphic rocks. It is envisaged that a textbook on stratigraphy based on these papers and the revised Guide could prove a timely contribution, especially to younger generations of practitioners, and aid global communication and understanding of stratigraphic principles and methods.

  8. The Afragola settlement near Vesuvius, Italy: The destruction and abandonment of a Bronze Age village revealed by archaeology, volcanology and rock-magnetism

    NASA Astrophysics Data System (ADS)

    Di Vito, Mauro A.; Zanella, Elena; Gurioli, Lucia; Lanza, Roberto; Sulpizio, Roberto; Bishop, Jim; Tema, Evdokia; Boenzi, Giuliana; Laforgia, Elena

    2009-01-01

    Public works in progress in the Campanian plain north of Somma-Vesuvius recently encountered the remains of a prehistoric settlement close to the town of Afragola. Rescue excavations brought to light a Bronze Age village partially destroyed and buried by pyroclastic density currents (PDCs) of the Vesuvian Pomici di Avellino eruption (3.8 14C ka BP) and subsequently sealed by alluvial deposits. Volcanological and rock-magnetic investigations supplemented the excavations. Careful comparison between volcanological and archaeological stratigraphies led to an understanding of the timing of the damage the buildings suffered when they were struck by a series of PDCs. The first engulfed the village, located some 14 km to the north of the inferred vent, and penetrated into the dwellings without causing major damage. The buildings were able to withstand the weak dynamic pressure of the currents and deviate their path, as shown by the magnetic fabric analyses. Some later collapsed under the load of the deposits piled up by successive currents. Stepwise demagnetization of the thermal remanent magnetization (TRM) carried by potsherds embedded in the deposits yields deposition temperatures in the order of 260-320 °C, fully consistent with those derived from pottery and lithic fragments from other distal and proximal sites. The fairly uniform temperature of the deposits is here ascribed to the lack of pervasive air entrainment into the currents. This, in turn, resulted from the lack of major topographical obstacles along the flat plain. The coupling of structural damage and sedimentological analyses indicates that the currents were not destructive in the Afragola area, but TRM data indicate they were still hot enough to cause death or severe injury to humans and animals. The successful escape of the entire population is apparent from the lack of human remains and from thousands of human footprints on the surface of the deposits left by the first PDCs. People were thus able to walk barefoot across the already emplaced deposits and escape the subsequent PDCs. The rapid cooling of the deposits was probably due to both their thinness and heat dissipation due to condensation of water vapour released in the mixture by magma-water interaction.

  9. A review of Arbuckle Group strata in Kansas from a sedimentologic perspective: Insights for future research from past and recent studies

    USGS Publications Warehouse

    Franseen, E.K.

    2000-01-01

    Arbuckle Group and equivalent-age rocks (Cambrian and Lower Ordovician) represent an important record of sediment deposition in the history of the North American continent and they contain important accumulations of hydrocarbons (oil and gas) and base metal deposits. This is true for Kansas as well where Arbuckle strata account for approximately 40% of the volume of produced petroleum and known reserves. However, in comparison to their counterparts in other areas, such as the Ellenburger and Knox, Arbuckle rocks in Kansas remain relatively understudied, especially with respect to sedimentology and diagenesis. The Arbuckle is present in the subsurface in most of Kansas and is absent only in areas of northeastern and northwestern Kansas, and over ancient uplifts and buried Precambrian highs. Arbuckle rocks thicken from north to south and are up to 1,390 feet in the southeastern corner of Kansas. Arbuckle Group and equivalent-age rocks from Kansas and surrounding areas are similar, consisting of platform deposits dominated by ramp-type subtidal to peritidal carbonates (mostly dolomitized) which can be subdivided into cycles, less than 0.5 m to 40 m thick, based on facies type and depositional patterns. Recent studies from central Kansas show that major depositional facies consist of coarse-grained packstones/ grainstones, fine-grained packstones/wackestones/mudstones, stromatolites-thrombolites, intraclastic conglomerate and breccia, and shale. In addition, secondary features include dolomitization, breccia, fracture, and conglomerate related to early subaerial exposure and later karst, burial or structural processes, silicification, and local mineralization. Arbuckle and equivalent strata in the Midcontinent were affected by prolonged subaerial exposure that began immediately after Arbuckle deposition, forming the sub-Tippecanoe to sub-Absaroka unconformity. Favorable reservoir qualities generally are thought to be related directly to basement structural elements and karstic features from the post-Arbuckle subaerial exposure event. Although most production in Kansas is from the top of the Arbuckle, some early and recent studies indicate that the Arbuckle is not a simple homogeneous reservoir, that complex vertical and lateral heterogeneities exist including both nonporous and porous horizons in the formation, and that high probability exist of locating additional oil with improved reservoir characterization. Although fracture and vuggy porosity contribute importantly to the production of Arbuckle strata, recent observations indicate a significant amount of porosity (about 50%) in many cores is controlled by depositional facies and dolomitization. Studies of Arbuckle and equivalent-age strata from other areas indicate that Arbuckle strata and diagenetic processes are complex and that porosity/permeability patterns are related to a number of processes. These studies underscore the importance of continued study of Arbuckle rocks in Kansas for improved reservoir characterization. Ongoing and future geologic studies of Arbuckle rocks in Kansas are being directed toward: (1) Continued sedimentologic, stratigraphic, and sequence stratigraphic analyses incorporating core, well log, and seismic data; (2) petrophysical studies. Initial studies indicate that core plug petrophysical properties are controlled by matrix grain size and that upscalling from plug to whole-core and drill-stem test data can identify and quantify the relative contribution of karstic, fracture and matrix porosity and permeability: (3) Regional and local structural analyses and mapping of the upper Arbuckle surface to provide more details on the contribution of structural features and karst paleogeomorphology to reservoir character; and (4) diagenetic and geochemical studies focusing especially on the timing of, and processes associated with, dolomitization and karstification events and their contributions to creating or occluding porosity.

  10. Seismic stratigraphy of the Tyrrhenian Sea (western Mediterranean Sea) based on ODP leg results: Consequences for the basin evolution

    SciTech Connect

    Mascle, J.; Rehault, J.

    1988-08-01

    A revision of the seismic stratigraphy of the Tyrrehenian Sea is based on detailed calibrations between a dense network of single-channel seismic reflection lines, about 2,000 km of recent multichannel seismic profiles, and the seven sites drilled within the Tyrrhenian in 1986 during the Ocean Drilling Program Leg 107. These correlations substantiate that the basin has been submitted to a succession of short-lived rifting episodes progressively shifting toward the southeast and leading to the local creation of discrete oceanic crust floored basins. Most of the Tyr-rhenian basins and margins have been created in a very short time (between 8 and 2 m.y. in age) and are much younger than previously anticipated. Rifting processes have been acting on a very heterogeneous continental basement (including several suture zones); drifting has created small oceanic subbasins also floored by a very heterogeneous magmatic basement (including serpentinized peridotites). The hypothesis of an asymmetric evolution facilitated by one or several crustal detachment fault systems and driven by geodynamic mechanisms of the bordering collision/subduction is considered.

  11. 3-D seismic evidence of the effects of carbonate karst collapse on overlying clastic stratigraphy and reservoir compartmentalization

    SciTech Connect

    Hardage, B.A.; Carr, D.L.; Simmons, J.L. Jr.; Jons, R.A. [Univ. of Texas, Austin, TX (United States). Bureau of Economic Geology] [Univ. of Texas, Austin, TX (United States). Bureau of Economic Geology; Lancaster, D.E. [S.A. Holditch and Associates, Inc., College Station, TX (United States)] [S.A. Holditch and Associates, Inc., College Station, TX (United States); Elphick, R.Y. [Scientific Software Intercomp, Denver, CO (United States)] [Scientific Software Intercomp, Denver, CO (United States); Pendleton, V.M. [Integrity Geophysics, Austin, TX (United States)] [Integrity Geophysics, Austin, TX (United States)

    1996-09-01

    A multidisciplinary team, composed of stratigraphers, petrophysicists, reservoir engineers, and geophysicists, studied a portion of Boonsville gas field in the Fort Worth Basin of north-central Texas to determine how modern techniques can be combined to understand the mechanisms by which fluvio-deltaic depositional processes create reservoir compartmentalization in a low- to moderate-accommodation basin. An extensive database involving well logs, cores, production, and pressure data from more than 200 wells, 26 mi{sup 2} of 3-D seismic data, vertical seismic profiles, and checkshots was assembled to support this investigation. The authors found the most important geologic influence on stratigraphy and reservoir compartmentalization in this basin to be the existence of numerous karst collapse chimneys over the area covered. These near-vertical karst collapses originated in, or near, the deep Ordovician-age Ellenburger carbonate section and created vertical chimneys extending as high as 2,500 ft above their point of origin, causing significant disruptions in the overlying clastic strata.

  12. Seismic and sequence stratigraphy of the eastern Porcupine Basin Supervisors: Professor Patrick Shannon and Professor David Naylor

    E-print Network

    Seismic and sequence stratigraphy of the eastern Porcupine Basin Supervisors: Professor Patrick successions of the eastern Porcupine Basin, offshore Ireland. These strata represent the deposits sandstones in the Porcupine Basin Supervisors: Dr Shane Tyrrell and Professor Patrick Shannon Contact: shane

  13. Deciphering the Geochronological Framework of Serbian Loess Using Amino Acid Stratigraphy

    NASA Astrophysics Data System (ADS)

    Oches, E. A.; Machalett, B.; McCoy, W. D.; Markovic, S.

    2010-12-01

    Serbian loess deposits preserve the most widespread, semi-continuous terrestrial records of glacial-interglacial climate variability in Europe. The sedimentary deposition, distribution, and thickness of loess in SE Europe are closely linked with major fluvial systems draining the continental interior. During glacial periods, under predominantly cold, semiarid climatic conditions, the extensive floodplain of the middle and lower Danube River was exposed to aeolian deflation, resulting in the accumulation of loess deposits up to 50 m thickness on adjacent fluvial terraces. The geomorphic setting of these loess formations, however, made them vulnerable to fluvial erosion and reworking, resulting in unconformities that may not be visually recognized in sedimentary sequences. Such unconformities, often of unknown duration and spatial extent, confound regional chronostratigraphic and paleoclimatic interpretations. Amino acid racemisation (AAR) geochronology, although primarily a relative dating method, offers an independent assessment of numerical age estimates when results are at or near their methodological limits and can assist in the chronostratigraphic evaluation of loess units beyond the applicable range of numerical dating methods. In this study we present the first comprehensive aminostratigraphic results measured on fossil gastropod shells of the genera Pupilla, Helicopsis, and Vallonia from the loess series at Stari Slankamen and Mosorin/Dukatar (Titel Plateau) in Vojvodina, Serbia, in order to verify the chronostratigraphic position of the upper stratigraphic units and to establish a reliable correlation between older loess-paleosol couplets. Given the interpreted stratigraphic continuity and the high sedimentation rates at Mosorin/Dukatar, we established this site as a chronostratigraphic reference for correlation with the long-studied loess profile Stari Slankamen, where at least two unconformities have led to ambiguous paleoclimatic and stratigraphic interpretation in previous studies. AAR analyses allow us to establish an independent chronostratigraphic framework for Serbian loess sequences correlated with marine oxygen-isotope stages 16-2. The results demonstrate the vast potential of amino acid stratigraphy to identify and constrain the extent, continuity, and duration of erosional discontinuities in long sedimentary sequences, such as those at Stari Slankamen. Ultimately, these results contribute to the development of a robust regional chronostratigraphic framework in support of paleoclimate reconstructions from high-resolution proxies, such as grain-size data, toward an improved understanding of the paleoenvironmental dynamics of SE Europe in an intra-hemispheric context.

  14. Ground-Water Salinity and Isotope Stratigraphy of North Carolina's Outer Banks

    NASA Astrophysics Data System (ADS)

    Bratton, J. F.; Thieler, E. R.; Hoffman, C. W.; Brooks, R. W.

    2002-12-01

    As part of a larger investigation of the geologic framework of the North Carolina coast, ground-water and sediment samples were collected and analyzed for salinity and ?13C of total organic carbon (TOC). Salinity was measured on samples from eight borings (depths up to 56 m), located between Kitty Hawk and Nags Head, to determine the thickness of the barrier island's fresh-water lens, and to examine stratigraphic control on freshwater-saltwater boundaries. ?13C was measured to establish the origin of organic matter (OM) preserved in the sediments. Results indicate that ground-water salinity is strongly correlated with stratigraphy based on core descriptions and downhole gamma logs. The subsurface fresh-water lens is 3-30 m thick across the study region (20 km). The thickness of the fresh-saline transition at depth is also highly variable (<2 m to 15 m). At three of four deep coring locations (\\>38 m), a zone of fresher water exists beneath an intermediate saline zone. The maximum salinity of water in the saline zone is typically around 27 ppt, but in one location a brine (45 ppt) is present. Based on preliminary ?13C-TOC data, most OM in the cores appears to be derived from mixed terrestrial (?13C \\approx -26 permil VPDB) and marine (?13C \\approx -20 permil) sources. Two cores show a clear trend from more terrestrial OM at depth toward more marine OM with a component of salt-marsh material (?13C \\approx -13 to -15 permil) near the surface. Sharp upcore transitions from terrestrial to mixed, or mixed to salt-marsh OM may indicate either unconformities, marine incursions associated with rapid sea-level rise events, or opening of inlets. Such transitions are present in one core at a depth of 20 m (14C age = 23.7 cal ka), and in two other cores at 33 to 36 m (10.6 cal ka). The study showed that filled paleo-valleys and paleo-tidal inlets under the modern barrier are serving as conduits for both salt-water migration and sub-estuarine transport of fresh water from the mainland. Channel fills contain OM from a variety of distinct coastal paleoenvironments.

  15. MOSAIC: An organic geochemical and sedimentological database for marine surface sediments

    NASA Astrophysics Data System (ADS)

    Tavagna, Maria Luisa; Usman, Muhammed; De Avelar, Silvania; Eglinton, Timothy

    2015-04-01

    Modern ocean sediments serve as the interface between the biosphere and the geosphere, play a key role in biogeochemical cycles and provide a window on how contemporary processes are written into the sedimentary record. Research over past decades has resulted in a wealth of information on the content and composition of organic matter in marine sediments, with ever-more sophisticated techniques continuing to yield information of greater detail and as an accelerating pace. However, there has been no attempt to synthesize this wealth of information. We are establishing a new database that incorporates information relevant to local, regional and global-scale assessment of the content, source and fate of organic materials accumulating in contemporary marine sediments. In the MOSAIC (Modern Ocean Sediment Archive and Inventory of Carbon) database, particular emphasis is placed on molecular and isotopic information, coupled with relevant contextual information (e.g., sedimentological properties) relevant to elucidating factors that influence the efficiency and nature of organic matter burial. The main features of MOSAIC include: (i) Emphasis on continental margin sediments as major loci of carbon burial, and as the interface between terrestrial and oceanic realms; (ii) Bulk to molecular-level organic geochemical properties and parameters, including concentration and isotopic compositions; (iii) Inclusion of extensive contextual data regarding the depositional setting, in particular with respect to sedimentological and redox characteristics. The ultimate goal is to create an open-access instrument, available on the web, to be utilized for research and education by the international community who can both contribute to, and interrogate the database. The submission will be accomplished by means of a pre-configured table available on the MOSAIC webpage. The information on the filled tables will be checked and eventually imported, via the Structural Query Language (SQL), into MOSAIC. MOSAIC is programmed with PostgreSQL, an open-source database management system. In order to locate geographically the data, each element/datum is associated to a latitude, longitude and depth, facilitating creation of a geospatial database which can be easily interfaced to a Geographic Information System (GIS). In order to make the database broadly accessible, a HTML-PHP language-based website will ultimately be created and linked to the database. Consulting the website will allow for both data visualization as well as export of data in txt format for utilization with common software solutions (e.g. ODV, Excel, Matlab, Python, Word, PPT, Illustrator…). In this very early stage, MOSAIC presently contains approximately 10000 analyses conducted on more than 1800 samples which were collected from over 1600 different geographical locations around the world. Through participation of the international research community, MOSAIC will rapidly develop into a rich archive and versatile tool for investigation of distribution and composition of organic matter accumulating in seafloor sediments. The present contribution will outline the structure of MOSAIC, provide examples of data output, and solicit feedback on desirable features to be included in the database and associated software tools.

  16. Upper Devonian vertebrate taphonomy and sedimentology from the Klunas fossil site, Tervete Formation, Latvia

    NASA Astrophysics Data System (ADS)

    Vasiļkova, J.; Lukševi?s, E.; Stinkulis, Ä.¢.; Zupinš, I.

    2012-04-01

    The deposits of the Tervete Formation, Famennian Stage of Latvia, comprising weakly cemented sandstone and sand intercalated with dolomitic marls, siltstone and clay, have been traditionally interpreted as having formed in a shallow, rather restricted sea with lowered salinity. During seven field seasons the excavations took place in the south-western part of Latvia, at the Klunas site, and resulted in extensive palaeontological and sedimentological data. The taphonomical analysis has been performed, having evaluated the size, sorting, orientation of the fossils, articulation and skeletal preservation as well as the degree of fragmentation and abrasion. The sedimentological analysis involved interpretation of sedimentary structures, palaeocurrent direction reconstruction, grain-size analysis and approximate water depth calculations. The vertebrate assemblage of the Klunas site represents all known taxa of the Sparnene Regional Stage of the Baltic Devonian, comprising placoderms Bothriolepis ornata Eichwald, B. jani Lukševi?s, Phyllolepis tolli Vasiliauskas, Dunkleosteus sp. and Chelyophorus sp., sarcopterygians Holoptychius nobilissimus Agassiz, Platycephalichthys skuenicus Vorobyeva, Cryptolepis sp., Conchodus sp., Glyptopomus ? sp., "Strunius" ? sp., and Dipterus sp., as well as an undetermined actinopterygian. Placoderms Bothriolepis ornata and B. jani dominate the assemblage. The fossils are represented in the main by fully disarticulated placoderm plates and plate fragments, sarcopterygian scales and teeth, rarely bones of the head and shoulder girdle, and acanthodian spines and scales. The characteristic feature is the great amount of fragmentary remains several times exceeding the number of intact bones. The horizontal distribution of the bones over the studied area is not homogenous, distinct zones of increased or decreased density of fossils can be traced. Zones of the increased density usually contain many elements of various sizes, whereas zones of the decreased density might be subdivided into two types: 1, with limited number of large bones; 2, with scattered relatively small scales or fragments. The shape and size of zones of increased density of fossils slightly resemble that of subaqueous dunes. Within the Klunas fossil site three taphonomically distinct oryctocoenoses can be traced, differing in the compactness of accumulation, size, disarticulation and fragmentation of bones and showing various degree of mixing of repeatedly buried and very fresh, partially articulated material. Analysis of similarities and differences between these oryctocoenoses demonstrates that all are sedimentary concentrations and have to be assessed as allochtonous assemblages. However, despite these differences, the 1st and the 3rd oryctocoenoses, which have been formed as vertebrate bone accumulations on the bottom of an erosional channel, have much in common contrary to the 2nd oryctocoenosis, which exemplifies the lens of fossil bearing cross-stratified sandstone formed in subaqueous dunes. The concentrations of vertebrate remains have been formed under the influence of fluvial and tidal processes in the shallow water environment, most probably deltaic or estuarine settings. It has been found also that elongated placoderm and sarcopterygian bones might be better indicators of the palaeoflow direction in comparison with very elongated, but dense acanthodian spines or sarcopterygian teeth.

  17. Sedimentological control on Mn, and other trace elements, in groundwater of the Bengal delta.

    PubMed

    McArthur, J M; Sikdar, P K; Nath, B; Grassineau, N; Marshall, J D; Banerjee, D M

    2012-01-17

    To reveal what controls the concentration and distribution of possibly hazardous (Mn, U, Se, Cd, Bi, Pb) and nonhazardous (Fe, V, Mo, PO(4)) trace elements in groundwater of the Bengal delta, we mapped their concentrations in shallow groundwater (<60 mbgl) across 102 km(2) of West Bengal. Only Mn is a potential threat to health, with 55% of well water exceeding 0.3 mg/L, the current Indian limit for drinking water in the absence of an alternate source, and 75% exceeding the desirable limit of 0.1 mg/L. Concentrations of V are <3 ?g/L. Concentrations of U, Se, Pb, Ni, Bi, and Cd, are below WHO guideline values. The distributions of Fe, Mn, As, V, Mo, U, PO(4), and ?(18)O in groundwater reflect subsurface sedimentology and sources of water. Areas of less negative ?(18)O reveal recharge by sources of evaporated water. Concentrations of Fe, As, Mo, and PO(4) are high in palaeo-channel groundwaters and low in palaeo-interfluvial groundwaters. Concentrations of U, V, and Mn, are low in palaeo-channel groundwaters and high in palaeo-interfluvial groundwaters. Concentrations of Fe and Mn are highest (18 and 6 mg/L respectively) at dual reduction-fronts that form strip interfaces at depth around the edges of palaeo-interfluvial aquifers. The fronts form as focused recharge carries dissolved organic carbon into the aquifer margins, which comprise brown, iron-oxide bearing, sand. At the Mn-reduction front, concentrations of V and Mo reach peak concentrations of 3 ?g/L. At the Fe-reduction front, concentrations of PO(4) and As reach concentrations 3 mg/L and 150 ?g/L respectively. Many groundwaters contain >10 mg/L of Cl, showing that they are contaminated by Cl of anthropogenic origin and that organic matter from in situ sanitation may contribute to driving reduction. PMID:22148466

  18. Sedimentology and paleogeography of the Natih carbonate platform in the Oman mountains

    SciTech Connect

    Philip, J.M. (Univ. Aix-Marseille I, Marseille (France)); Borgomano, J.R.; Al Maskiry, S. (Petroleum Development Oman, Muscat (Oman))

    1993-09-01

    Field study of the Natih Formation in the Jebel Akhdar and the Oman foothills allows us to establish a new stratigraphical and sedimentological model of this important hydrocarbon reservoir unit. Thanks to the study of rudists and the discovery of ammonites, a new precisions can be given to the chronostratigraphy of the Natih Formation. It was especially demonstrated by the presence of Hippuritids (rudists) that the top of the Natih Formation matches the Cenomanian/Turonian boundary and corresponds to either rudist-rich layers or hard grounds and condensed levels. The stratigraphical correlations between several outcrop section allow one to establish a conceptual sequence stratigraphic model which can be compared to the subsurface by using the Natih subdivisions [open quotes]A to G.[close quotes] The recognition of sequence boundaries, maximum flooding surfaces, and system tracts might help to understand the seismo-stratigraphic expression of the Natih interval in the subsurface. Furthermore, this sequence stratigraphic model clearly illustrates the interfingering of the carbonate reservoir intervals and the organic-rich units (Fitri Mb) at the top of the Natih Formation. We also have identified a clear zonation from deeper marine to shallow-marine carbonate deposits, the most significant of which are the rudistid facies. They form banks, thickets, and biostroms and do not constitute anomalous build ups such as bioherms. Good leaching potentials generally are related to these rudistid facies, especially when they are very rich in skeletal aragonite from the Caprinids shells. Significant primary porosity may be related also to the Hippuritid skeletal cavities at the top of the Natih. Reservoir potentials can be enhanced if these Caprinid-rich intervals are related to exposure surfaces such as the top Natih E and the top Natih A.

  19. Morphology and sedimentology of a central Brazos River point bar, Boxley Bend, Brazos County, Texas

    SciTech Connect

    Connolly, W.M.; Mazzullo, J.

    1986-09-01

    A reconnaissance of Brazos River point bars reveals great variety in their morphology and sedimentology, owing to the complex interaction of climate, local hydrography, and local sediment sources. This paper presents the first in a series of studies of point bars of the Brazos River and concentrates on the Boxley Bend point bar near Snook, Texas. The summer morphology of the point bar is complex, consisting of an upper and lower tier separated by a scarp but connected by a central ramp. The surfaces of the lower tier and ramp display numerous large gravel bars and shallow scour pools as well as low-amplitude sand waves, ripples, and current lineations. In cross section, the lower tier and ramp are characterized by (1) trough cross-bedded, medium to fine sand produced by megaripple migration during floods; (2) massive gravel beds, the product of formation and migration of gravel bars during floods; and (3) fine rippled sand and clay drapes formed during falling flood. The surface of the upper tier displays ripple-laminated eolian sand and deflation deposits of mud clasts. In cross section, the upper tier is characterized by thick beds of horizontally stratified fine sand. During the winter, the entire surface of the point bar is covered by large (2 m high) transverse bars separated by deep scour troughs. Transverse bars migrate into the troughs to produce a sequence of fine sand with backflow ripple cross-stratification overlain by thick beds of tabular cross-bedded medium sand. The transverse bars appear to be transitory features with little net effect on sedimentation, because they are removed from the surface of the point bar by summertime.

  20. Changing sedimentary environment during the Late Quaternary: Sedimentological and isotopic evidence from the distal Bengal Fan

    NASA Astrophysics Data System (ADS)

    Kessarkar, Pratima M.; Rao, V. Purnachandra; Ahmad, S. M.; Patil, S. K.; Anil Kumar, A.; Anil Babu, G.; Chakraborty, Sukalyan; Soundar Rajan, R.

    2005-09-01

    The sediments recovered from two gravity cores of the lower and distal Bengal Fan were investigated for sedimentological properties and Sr-Nd isotopes. Each core exhibits two distinct units, the lower unit 2 and upper unit 1 sediments. The unit 2 sediments are predominantly olive black/grey in colour with abundant finer silt-size fractions, low organic carbon and CaCO 3, quartz and mica in the coarse fraction, dominant illite and chlorite in the <2 ?m fraction and uniform rock-magnetic properties. Biogenic constituents are extremely rare or restricted to the lower part of unit 2. The unit 1 sediments, on the other hand, are moderate brown/yellowish brown in colour with intermittent thin dark-coloured sediment layers. Higher clay, organic carbon, CaCO 3, and biogenic constituents in the coarse fraction, and enriched smectite and kaolinite in the <2 ?m fraction are typical. Magnetic susceptibility values are higher and correlate well with acid-insoluble residue content. Higher Rb, Sr, Sm and Nd concentrations, 87Sr/ 86Sr ratios and more radiogenic ? values are characteristic for unit 2 sediments compared to unit 1 in both the cores. The unit 2 sediments represent Pleistocene hemiturbidites, older than 13 14C kyr BP with their source from the northern Bay of Bengal (NBOB), derived from the Himalayas and transported by the Ganges-Brahmaputra (G-B) River system. Unit 1 sediments are calcareous pelagic sediments, which started depositing ˜12 14C kyr BP, with its clastic sediments derived from the Himalayas and SE Indian/Sri Lankan margins. The change in lithofacies from unit 2 to unit 1 suggests that the sediment deposition by turbidity current activity ceased in the distal Bengal Fan at ˜12 14C kyr BP, perhaps because of the rapid rise in sea-level during the melt water pulse 1A and Holocene.

  1. Subtle traps prediction using sequence stratigraphy and 3D seismic technology: A case study from Qikou depression in Huanghua basin

    Microsoft Academic Search

    Ning-bo Mao; Ta-gen Dai; Sheng-lin Peng

    2005-01-01

    Forecasting subtle traps by sequence stratigraphy and 3D seismic data is a sensitive topic in hydrocarbon exploration. Research\\u000a on subtle traps by geophysical data is the most popular and difficult. Based on the sufficiently drilling data, log data,\\u000a core data and 3D seismic data, sediment sequence of Qikou depression, Huanghua basin was partitioned by using sequence stratigraphy\\u000a theory. Each sediment

  2. Improved method for correlating late Pleistocene/Holocene records from the Bering Sea: application of a biosiliceous/geochemical stratigraphy

    USGS Publications Warehouse

    Morley, J.J.; Robinson, S.W.

    1986-01-01

    The combination of high-resolution siliceous biostratigraphy and radiocarbon dating provides a mechanism for detailed assessment of the depositional history in late Pleistocene sediments from the Bering Sea where average accumulation rates are uncharacteristically high compared to rates calculated for most other ocean basins. Vital to the development of this stratigraphy was the recognition that the abundance pattern of the radiolarian species Cycladophora davisiana in Bering Sea cores is quite similar to this species' previously correlated abundance curve in a late Pleistocene/Holocene record from the northwest Pacific. Comparison of this high-resolution stratigraphy with other recently developed floral and lithologic stratigraphies for late Pleistocene Bering Sea sediments shows that the various stratigraphies do not always yield identical results when applied to a particular sediment sequence. With this new stratigraphy based upon a combination of siliceous microfaunal abundance patterns and radiocarbon dating, one can identify reworking, discontinuities and other interruptions in the depositional sequence more precisely than with previously devised stratigraphies, thereby improving the correlation techniques for comparison of late Pleistocene/Holocene records from this marginal sea. ?? 1986.

  3. The Late Holocene Stratigraphy of an Inlet-Dominated Barrier Island, Pea Island, North Carolina.

    NASA Astrophysics Data System (ADS)

    Smith, C. G.; Ames, D.; Corbett, D. R.; Culver, S.; Mallinson, D.; Riggs, S. R.; Vance, D.

    2002-12-01

    Sedimentological, foraminiferal, geochemical, and geophysical data sets as well as aerial photographs have been used to investigate the natural processes (inlet dynamics, ocean/estuarine washover, and sea-level change) responsible for the late Holocene units preserved in the barrier island subsurface at Pea Island National Wildlife Refuge. Historic nautical charts indicate that three inlets characterized Pea Island between early European exploration (1590) and the late 19th century; aerial photographs show New Inlet open in 1932 and 1940. Vibracores (up to 5.5 m) collected along three transects across Pea Island extend our knowledge of the geological evolution of this region to pre-historic times. The section in the longest core (PI01S6) consists of four fining-upwards depositional sequences. The basal unit of each sequence is a bedded, medium to fine, clean quartz sand with increasing concentrations of organic matter (3-4 % detrital and 5-7 % in situ Spartina alterniflora roots) or irregular mud clasts (2-5 cm) to spherical mud balls (1-2 cm) up core. The clean sand units have so far proven to be barren of foraminifera except for a shelly unit at ca. 220 cm below MSL. The foraminiferal assemblage in this unit is of open shelf character (Elphidium excavatum, Hanzawaia strattoni, and Buccella inusitata). A 14C age on a disarticulated Chione cancellata valve from this unit is cal. 930+/-60 BP. The sand grades into a gray, tight mud in the first two sequences and into an inter-laminated mud and in situ peat in the third sequence. The peat contains leaf fragments and rhizomes of the marsh plants Juncus roemarianus, Spartina cynosuroides, and/or Phragmites spp. The peat and muddy sand units contain marsh foraminifera (Trochammina spp., Miliammina fusca, Arenoparrella mexicana), which are also found in modern marsh deposits. A peat sample from the third fining upward sequence (the only one to grade into a true peat) has a 14C age of cal. 395+/-35 BP, cal. 295+/-35 BP, or cal 180+/-40 BP. The four fining-upwards sequences have sharp erosional basal contacts. These deposits appear to reflect back-barrier processes including sequential deposition of flood-tide delta sands and/or sound sands adjacent to marshes. The shelly sands, containing open shelf foraminiferal assemblages, represent oceanic overwash, inlet deposits, or open embayment sands deposited behind a laterally extensive breach in the barrier island. The sequences are capped by the deposits of modern environments that include algal flats, tidal creeks, high and low marshes, back-barrier berms, overwash fans, and aeolian dunes. Several of the modern environments became covered with marsh vegetation after the construction of barrier dune ridges in the late 1930?s.

  4. Sedimentology and sequence stratigraphy of a Tithonian-Valanginian carbonate ramp (Vaca Muerta Formation): A misunderstood exceptional source rock in the Southern Mendoza area of the Neuquén Basin, Argentina

    NASA Astrophysics Data System (ADS)

    Kietzmann, Diego A.; Palma, Ricardo M.; Riccardi, Alberto C.; Martín-Chivelet, Javier; López-Gómez, José

    2014-04-01

    The Vaca Muerta Formation (early Tithonian-early Valanginian) is a rhythmic succession of marls and limestones, cropping out in the Neuquén Basin, west-central Argentina. This lithostratigraphic unit was traditionally interpreted as basinal to slope deposits. Detailed facies analysis allows to differentiate seven facies associations, representing basinal to middle ramp facies of a homoclinal ramp system prograding westward from the eastern margin, and slope facies attributed to a distally steepened ramp system that progrades eastward from the Andean volcanic arc in the west. Two sequence hierarchies are recognized: five third order depositional sequences, and fifteen fourth order high-frequency sequences. Fluctuations in organic matter content within the Vaca Muerta Formation suggest relationship with depositional sequences, finding the highest values associated with transgressive system tracts. This work represents an important advance in the understanding of the sedimentary and stratigraphic evolution of this exceptional unconventional reservoir. Our sequence stratigraphic approach contributes to the understanding of the relationship between organic matter, facies, and sea-level changes.

  5. A Laminated Carbonate Record of Late Holocene Mid-Continental Hydroclimate: Geochemical and Sedimentological Results from Martin Lake, LaGrange County, Indiana

    NASA Astrophysics Data System (ADS)

    Stamps, L. G.; Bird, B. W.; Gilhooly, W., III

    2014-12-01

    Paleoclimate records from the mid-continental United States that span the Holocene with sub-decadal resolution are rare. This is especially true for geochemical records that capture the isotopic composition of precipitation or local precipitation/evaporation balances. As a result, many questions remain about the hydrologic expression of abrupt climate events in this region that today is one of the world's largest agricultural centers. Here, we present sedimentological, geochemical, and chronological data spanning the last 3,000 years from a set of sediment cores from Martin Lake in northeastern Indiana. Today, this kettle lake is hydrologically open with persistent water column stratification and bottom water anoxia. Radiometric dating shows that the lake formed at approximately 16,000 cal yr BP and continuously accumulated sediment thereafter. We focus here on developing a stable isotope record of the late Holocene at decadal resolution to provide a detailed view of precipitation isotopic variability during this time. The Midwest has been influenced by changes in atmospheric circulation patterns throughout the late Holocene, leading to climate events like the Little Ice Age and Medieval Climate Anomaly, which significantly changed temperature and precipitation regimes. The isotopic composition of precipitation in the Midwest has been shown to be heavily influenced by the source of atmospheric moisture as mediated by the Pacific North American mode of atmospheric variability that in turn affects the position of the Polar Front Jetstream. Using high-resolution stable isotope measurements and ultimately climate modeling, we seek to reconstruct the isotopic expression of late Holocene climate events in the mid continental United States and assess the possible relationship with these dominant modes of atmospheric variability. Future work includes extending this reconstruction through the Holocene and increasing the temporal resolution of the data.

  6. Seismic stratigraphy and the evolutionary history of Shatsky Plateau

    E-print Network

    Chen, Yu-Hsin

    1984-01-01

    . They are separated by a strong reflector(Ka), the top of which correlates to Late Albian age material in DSDP Site 307 to the south and Barremian age material in Site 304 to the north(Larson, Moberly et al. , 1975) . Line drawing interpretations of three.... They are conformable with the reflector Ka in most places. Based on samples from Site 51 of DSDP leg 6(Fischer, Heezen et al. , 1971) and Site 303 of DSDP Leg 32(Larson, Moberly et al. , 1975) this sequence consists of diatom-radiolarian ooze and radiolarian...

  7. Modeling of the Sedimentary Interbedded Basalt Stratigraphy for the Idaho National Laboratory Probabilistic Seismic Hazard Analysis

    SciTech Connect

    Suzette Payne

    2006-04-01

    This report summarizes how the effects of the sedimentary interbedded basalt stratigraphy were modeled in the probabilistic seismic hazard analysis (PSHA) of the Idaho National Laboratory (INL). Drill holes indicate the bedrock beneath INL facilities is composed of about 1.1 km of alternating layers of basalt rock and loosely consolidated sediments. Alternating layers of hard rock and “soft” loose sediments tend to attenuate seismic energy greater than uniform rock due to scattering and damping. The INL PSHA incorporated the effects of the sedimentary interbedded basalt stratigraphy by developing site-specific shear (S) wave velocity profiles. The profiles were used in the PSHA to model the near-surface site response by developing site-specific stochastic attenuation relationships.

  8. Combining Seismic Geomorphology and Physical Sedimentology to Resolve Depositional Processes within Submarine Channel Bends

    NASA Astrophysics Data System (ADS)

    Fernandes, A. M.; Mohrig, D.; Petter, A. L.; Steel, R. J.; Henriksen, S.

    2012-12-01

    Turbidity currents display exaggerated super-elevation at the outer banks of channel bends because they have low excess densities relative to the ambient sea-water. Low-velocity zones form where flows separate from the inner banks of bends. Depositional processes associated with the development of bank-attached bars in these flow-separation zones are evaluated using: a) measurements of geometries of bank-attached bars and their positions along channel curvature from two buried submarine channels, imaged in a high-resolution seismic data-set from the continental margin of West Africa, and b) detailed measurements of bed geometry, sedimentary structures and grain-sizes of a bank-attached bar in an exposed submarine channel complex from the Permian Brushy Canyon Formation, in west Texas. The 226 bar surfaces mapped in the seismic volume have high median slopes (10-11 degrees), occupy less than 30% of channel width, and are associated with weak channel incision and small amounts of lateral migration equal to less that 70% of a channel width. The mapped bank-attached bar outcrop shows a 17m-thick set of steeply inclined (median dip=10 degrees) fine-grained sandstone beds. Sub- to super-critically climbing ripple-lamination is abundant with paleo-transport oriented at 20-120 degrees relative to the dip azimuths of interpreted bar surfaces. Sedimentary structures, grain-size distributions and paleo-transport reconstructions from deposits in the bar and those filling the main channel reveal that this bar was constructed from fully-suspended sediment. These observations suggest that bank-attached bars constructed from fully-suspended sediment in submarine channels have been under-recognized on passive continental margins thus far. This data also defines the connection between the large scale morphologies of depositional elements, the processes responsible for their construction and the fine-scale attributes of the resulting stratigraphy.

  9. Effects of sediment mixing and benthic algal production on fossil pigment stratigraphies

    Microsoft Academic Search

    P. R. Leavitt; S. R. Carpenter

    1989-01-01

    Effects of sediment mixing and benthic algal production on fossil pigment profiles were quantified by fine-interval analysis of cores in a transect across the basin of Paul Lake, MI. Annually resolved profiles (1957–1986) of carotenoids and chlorophyll a from varved sediments at deepwater (15 m) sites were compared to fine-interval (2.5–3.5 mm) stratigraphies from sites with increasing sediment mixing and

  10. Stratigraphy and paleogeography of the Ediacaran Doushantuo Formation (ca. 635–551 Ma) in South China

    Microsoft Academic Search

    Ganqing Jiang; Xiaoying Shi; Shihong Zhang; Yue Wang; Shuhai Xiao

    2011-01-01

    The Ediacaran Doushantuo Formation (ca. 635–551Ma) in South China contains exceptionally well-preserved fossils of multicellular eukaryotes including early animals, and it is one of the most intensively investigated Ediacaran units in the world. Various stratigraphic methods including litho-, chemo-, bio-, and sequence-stratigraphy have been applied to establish a stratigraphic framework for the Doushantuo Formation, but so far regional correlation across

  11. Improved Quaternary North Atlantic stratigraphy using relative paleointensity (RPI), oxygen isotopes, and magnetic excursions (Invited)

    NASA Astrophysics Data System (ADS)

    Channell, J. E.

    2013-12-01

    Improving the resolution of Quaternary marine stratigraphy is one of the major challenges in paleoceanography. IODP Expedition 303/306, and ODP Legs 162 and 172, have yielded multiple high-resolution records (mean sedimentation rates in the 7-20 cm/kyr range) of relative paleointensity (RPI) that are accompanied by oxygen isotope data and extend through much of the Quaternary. Tandem fit of RPI and oxygen isotope data to calibrated templates (LR04 and PISO), using the Match protocol, yields largely consistent stratigraphies, implying that both RPI and oxygen isotope data are dominated by regional/global signals. Based on the recent geomagnetic field, RPI can be expected to be a global signal (i.e. dominated by the axial dipole field) when recorded at sedimentation rates less than several decimeters/kyr. Magnetic susceptibility, on the other hand, is a local/regional lithologic signal, and therefore less useful for long-distance correlation. Magnetic excursions are directional phenomena and, when adequately recorded, are manifest as paired reversals in which the virtual geomagnetic poles (VGPs) reach high latitudes in the opposite hemisphere, and they occupy minima in RPI records. Reversed VGPs imply that excursions are attributable to the main axial dipole, and therefore provide global stratigraphy. The so-called Iceland Basin excursion is recorded at many IODP/ODP sites and lies at the MIS 6/7 boundary at ~188 ka, with a duration of 2-3 kyr. Other excursions in the Brunhes chron are less commonly recorded because their duration (perhaps <~1 kyr) requires sedimentation rates >20 cm/kyr to be adequately recorded. On the other hand, several excursions within the Matuyama Chron are more commonly recorded in North Atlantic drift sediments due to relatively elevated durations. With some notable exceptions (e.g. Iberian Margin), high quality RPI records from North Atlantic sediments, together with magnetic excursions, can be used in tandem with oxygen isotope data to strengthen Quaternary (North Atlantic) stratigraphy.

  12. Seismic stratigraphy and structure of the Barter Island sector of the Western Beaufort Sea

    E-print Network

    Coffman, Jeffrey Dale

    1988-01-01

    -Chair of Committee) 1)i liam B yant (Co-Chair of Committee) Davis Fahlqu st (Member) Earl Hoskins (Head of Department) August 1988 111 ABSTRACT Seismic Stratigraphy and Structure of the Barter Island Sector of the Western Beaufort Sea. (August 1988) Jeffery... of the oldest sequence is unclear. Mapping of these sequences indicates that two structural uplifts increased the deposition of Tertiary sediments in Barter and Demarcation subbasins. Demarcation Ridge acted as a barrier to sediments which created...

  13. Integrated stratigraphy and astrochronology of the Messinian GSSP at Oued Akrech (Atlantic Morocco)

    Microsoft Academic Search

    F. J. Hilgen; L. Bissoli; S. Iaccarino; W. Krijgsman; R. Meijer; A. Negri; G. Villa

    2000-01-01

    A much improved high-resolution integrated stratigraphy (calcareous plankton biostratigraphy, magnetostratigraphy, cyclostratigraphy) is presented for the classic section of Oued Akrech (Atlantic Morocco) straddling the Tortonian–Messinian boundary. Magnetobiostratigraphic correlations with time-equivalent and astronomically dated sections in the Mediterranean indicate that cyclic alternations of indurated light beige coloured marls and softer, more clayey and reddish coloured marls are dominantly precession-controlled. Characteristic sedimentary

  14. The stratigraphy and palaeontology of the Upper Weald Clay (Barremian) at Smokejacks Brickworks, Ockley, Surrey, England

    Microsoft Academic Search

    Andrew J. Ross; Elizabeth Cook

    1995-01-01

    The stratigraphy of the Weald Clay of Surrey is summarized. The Hauterivian\\/Barremian boundary is shown to correspond closely to the Lower Weald Clay\\/Upper Weald Clay boundary, which lies at the base of BGS (British Geological Survey) Bed 3a and is close to the Ewhurst\\/Capel ostracod faunicycle boundary. Detailed sections of the sediments exposed in the pit at Smokejacks Brickworks are

  15. Snow stratigraphy over a uniform depositional surface: spatial variability and measurement tools

    Microsoft Academic Search

    Joel T Harper; John H Bradford

    2003-01-01

    Instrumentation and methods for measuring snow properties are compared in an investigation of millimeter- to meter-scale stratigraphy in a snowpack not influenced by topography, vegetation, or a warm and variable ground surface. Field measurements were conducted within a 20×20×2 m plot at Pika Glacier, Alaska. The snow was characterized by more than 600 point measurements of density, stratigraphic mapping in

  16. Lower Cretaceous turbiditic sediments from the Rif chain (Northern Marocco) — palynology, stratigraphy and palaeogeographic setting

    Microsoft Academic Search

    Alfred A. Gübeli; Peter A. Hochuli; Walter Wildi

    1984-01-01

    Zusammenfassung  Von den afrikanischen und Alboran-Kontinentalrändern der westlichen Tethys (Externe Domäne und Flyschdecken im Rif, Nordmarokko) werden terrigene turbiditische Tiefseesedimente von Unterkreidealter beschrieben (Palynologie, Stratigraphie, Sedimentologie und paläogeographischer Rahmen).Während der Unterkreide finden sich terrigene turbiditische Tiefseeablagerungen in zwei verschiedenen paläogeographischen Räumen des Südteils der westlichen Tethys:? \\u000aIm Nordteil der Externen Domäne (Ketama-Einheit des Rif) werden Wechsellagerungen von Areniten und Peliten als

  17. Stratigraphy of Oceanus Procellarum basalts - Sources and styles of emplacement

    NASA Technical Reports Server (NTRS)

    Whitford-Stark, J. L.; Head, J. W., III

    1980-01-01

    The basaltic fill of Oceanus Procellarum has been formally subdivided into four lithostratigraphic formations: The Repsold Formation, the Telemann Formation, the Hermann Formation, and the Sharp Formation. The Repsold Formation is composed of high-Ti basalts and pyroclastic deposits with an estimated age of 3.75 + or - 0.05 b.y. and an estimated volume of about 2.1 x 10 to the 5th cu km. This is overlain by the Telemann Formation composed of very low-Ti basalts and pyroclastic deposits with an estimated age of 3.6 + or - 0.2 b.y. and a volume of 4.2 x 10 to the 5th cu km. The Hermann Formation, composed of intermediate basalts with an estimated age of 3.3 + or - 0.3 b.y., represents the next youngest unit with an estimated volume of 2.2 x 10 to the 5th cu km. The youngest materials in Procellarum are the medium-to-high-Ti basalts comprising the Sharp Formation with an estimated age of 2.7 + or - 0.7 b.y. and a volume of 1.8 x 10 to the 4th cu km.

  18. The Cretaceous stratigraphy of the Western Cordillera Oriental, Columbia

    SciTech Connect

    Allen, R.B.; Alfonso, C.A.; Ressetar, R.; Salazar, A. (Univ. of South Carolina, Columbia (United States)); Ballesteros, I.; Cardozo, E.; Laverde, F.; Ramirez, C. (Hocol-Shell, Cartegena (Colombia)); Moreno, J.M. (Universidad Nacional de Colombia, Bogota (Colombia)); Rubiano, J.; Sarmiento, L. (Instituto Colombiano de Petroleos, Bucaramanga (Colombia))

    1993-02-01

    During 1987 and 1988, a major field project sponsored by Tenneco was undertaken along the west flank of the Cordillera Oriental of Colombia between Alpujarra (between the Neiva and Girardot Sub-Basins) and the Middle Magdalena Basin (Cimitarra area). An important result of this study was the documentation of pronounced regional variation in the age, thickness, and facies of the Cretaceous section. The maximum thickness estimated was 7 km for the Bogota-Villeta section, with ages as old as Berriasian. This section can be divided into 4 or 5 depositional sequences. A clastic source to the west or southwest is indicated for the lower sequence 1 (and 2 ), an eastern source dominated sequences 3 and 4, and eastern and western sources supplied the upper sequence. Toward the north the section thins to an estimated 3-5 km but still ranges in age throughout the Cretaceous. Southward, on the other hand, the Cretaceous thins to about 2 km and is restricted to Aptian-Albian and younger ages. The variations in ages, facies, and thickness are consistent with recent models of the evolution of the Cretaceous basin. During the Neocomian, the Bogata area formed the main depocenter of the basin and was characterized by restricted facies and turbidites, suggesting steep, possibly faulted basin margins. Facies to the north, near the Middle Magdalena Basin, indicate shallower water, possibly a platform. By the end of the Early Cretaceous, expansion of the marine basin out of the central Cordillera Oriental and regionally more constant facies indicate the onset of dominantly thermal subsidence. The end of the Cretaceous was marked by regression and asymmetric clastic input from east and west of the basin.

  19. Hydrocarbon potential, organic matter diagenesis, sedimentology, and paleoenvironment of upper Mesozoic dark shales, northern Himalayas and Argo abyssal plain

    SciTech Connect

    Thurow, J.; Gibling, M.

    1989-03-01

    The Late Jurassic was a time favorable for the deposition of black shale-type sediments in shallow environments as known from circum-North Atlantic basins, North Sea, and Himalayan Tethys regions. Locally these shales have excellent hydrocarbon source potential. The site of the Spiti shales in the Thakkola region of north-central Nepal provides the opportunity to study a long-term (Oxfordian-Tithonian) stable, shallow, and oxygen-depleted environment. Strata with calcareous benthic communities show that the environment was not anoxic. Organic geochemical and sedimentological analyses on the Spiti shales (Oxfordian-Valanginian) were done to understand the hydrocarbon potential, organic matter diagenesis, sedimentology, and paleoenvironment of this sequence. The depositional environment changed, driven by tectono-eustatic and climatic events, from an open shelf (approximately 250 m) with low amounts of detrital input and rich macrofossil communities to an extremely shallow, partly continental environment with intercalations of quartzose channel fill, silty shales, rare lumachelle layers, and coal seams. Paleocurrents suggest a north-facing continental margin bordering the Tethys Sea. The organic matter changed from marine (Jurassic) to terrestrial in the Cretaceous. Analysis of coeval strata, deposited in the deep-marine environment off the northern Indian shelf (contiguous with the present-day Argo abyssal plain), demonstrates the changing shallow to deep-water hydrocarbon potential. It reflects the more advanced organic matter maturation of the onshore material due to Himalayan tectonics and allows tracing the transport of the organic matter.

  20. Mid-Holocene strengthening of the Southern Westerlies in South America — Sedimentological evidences from Lago Cardiel, Argentina (49°S)

    NASA Astrophysics Data System (ADS)

    Gilli, Adrian; Ariztegui, Daniel; Anselmetti, Flavio S.; McKenzie, Judith A.; Markgraf, Vera; Hajdas, Irka; McCulloch, Robert D.

    2005-11-01

    The paleoclimatic evolution of southern South America is characterized to a large extent by the behavior (strength and latitudinal position) of the storm tracks of the Southern Westerlies. Our study site, Lago Cardiel (49°S), lies within the modern influence of the Southern Westerlies and, therefore, is ideally located to track the past migrations of these storm tracks. With a coring strategy taking into account the lateral differences in sedimentation and an excellent core-to-core correlation using tephra layers, a composite sedimentological record of almost 25 m was established covering the last ˜16,000 cal yr. Sedimentological and petrophysical analysis of the cores revealed the establishment of a dominant lake current since 6800 cal yr BP leading to a drift deposition, which is especially well-expressed in the sedimentary record by an increase in magnetic susceptibility values. As this pattern of currents is most likely induced by wind activity, we propose that the observed increase in magnetic susceptibility documents an intensification of the westerly storm tracks. This intensification occurred slightly earlier than previously suggested based on palynological evidence. The strengthening in the Southern Westerlies during the mid-Holocene is most likely caused by an increase in the temperature gradient as a result of enhanced influence and/or southward migration of the Southeast Pacific anticyclone and a larger Antarctic sea-ice extent.

  1. A ground penetrating radar survey to assist the sedimentologic and geomorphologic interpretation of washover fans in NW Australia.

    NASA Astrophysics Data System (ADS)

    Leopold, Matthias; Callow, Nik; May, Simon Matthias

    2015-04-01

    The NW Australian coast is prone to both tropical cyclones and tsunamis which can generate extreme wave events in this region. Along the W coast of the Exmouth Gulf, distinct lobate washover fans consist of shell debris and sand layers and exhibit delta-type sedimentation patterns. Using ground penetrating radar (GPR) and unmanned aerial vehicle survey (UAV) techniques helps in a first step to locate important geomorphic points of interest for later sedimentologic, pedologic and chronologic studies. UAV surveys developed a detailed 3D surface model (cm resolution) which helps to better understand the extent and the general pattern of the geomorphic forms. A subsequent GPR survey using a bi-static 250 MHz antenna with a Mala CU-II in a continuous mode generated multiple transects which could be further interpreted. Coarse sandy-gravelly washover fan-matrix sits on top of clayey pan sediments which provide an excellent sedimentologic contrast for GPR surveys. Multiple delta like structures representing single wave activities, erosion channels and their backfill structures as well as several palaeosols could be identified in the GPR images. This information is now used in a subsequent chrono-stratigraphic approach for a final geomorphic interpretation.

  2. Sedimentological dynamics of the Orlovat loess-paleosol sequence (Northern Serbia) show both local and regional paleoenvironmental fluctuations

    NASA Astrophysics Data System (ADS)

    Obreht, Igor; Zeeden, Christian; Eckmeier, Eileen; Schulte, Philipp; Hambach, Ulrich; Timar-Gabor, Alida; Lehmkuhl, Frank

    2015-04-01

    The last glacial cycle as recorded in the Orlovat loess section (Northern Serbia) gives insight into both local and regional paleoenvironmental conditions. The Orlovat section is a unique section in the Carpathian Basin and it is characterized by irregularities in sedimentology, magnetic susceptibility, geochemistry and other paleoproxies. Therefore the local conditions need to be understood before making claims on a regional scale. Especially the grain size distribution indicates that the Orlovat site was influenced by specific paleoenvironmental conditions. Relatively coarse grained sand was delivered during interglacials, probably from the Deliblato sands by the Košava wind. However, commonly applied methods such as grain size and rock magnetic investigations could not explain the unique situation during the MIS 3, where a paleosol is missing. Therefore, for the first time in the studies of the region, we applied high resolution X-ray fluorescence analysis to trace the changing source areas of sediment material during the Last Glacial. These changes in the provenance of the sediment might be associated with stronger river activities and erosion. This study highlights the importance of a sedimentological understanding for a reliable paleoenvironmental evaluation.

  3. Sedimentologic, Chemical, and Isotopic Constraints on the Anthropogenic Influence on Chilika Lake, India

    NASA Astrophysics Data System (ADS)

    Vennemann, T. W.; Decrouy, L.; Ecuyer, M.; Delavy, K.; Lange, P.; Rastogi, G.; Pattnaik, A.; Suar, M.

    2014-12-01

    Chilika Lake, the largest Asian lagoon on the east coast of India, has a surface area of 1160 km2 or about 900 km2, respectively for the wet, monsoon vs. dry winter-spring season. The average depth is only about 1.2 m. It is separated from the Bay of Bengal by a 100 m to 1.5 km wide sand bar of about 30 km length, separating the outer channel that connects the lagoon naturally to the sea. Long-shore development of this sand bar as of the Late Holocene increasingly isolated the lagoon from the sea, until final closure in 1992. Given the population increase in the catchment and according changes in land use policies, agricultural practices, and water resource management, Chilika Lake has been subjected to increasing anthropogenic influence. As a consequence the unique biodiversity and also primary production within the lagoon decreased, while eutrophication and siltation increased. As a counter-initiative it was decided to artificially open the lagoon to the sea by dredging. To help trace and quantify the anthropologic effects on Chilika Lake, a combined sedimentologic, chemical, and isotopic study of the lagoon and its sediments was is in progress. First results from a campaign during the monsoon season suggest that the large gradients in salinity, sediment and nutrient input, as well as primary productivity within the lagoon are controlled by variable fluxes of water, sediment, and nutrients from the three separate catchments to the lagoon. Trends in changes of salinity, H- and O-isotope compositions of waters, but also of concentrations and C- and/or N-isotope compositions of the dissolved inorganic carbon (DIC), particulate organic matter (POM), and aquatic plants indicate that mixing in the lagoon occurs between new freshwater inputs and evaporated water within the basin itself. Except for the outer channel, mixing with seawater is limited. In contrast, the C-isotope composition of the organic matter in the sediments either suggests a higher overall proportion of "marine" or of estuarine-derived POM during the past. The latter may be important during the dry season, coupling salinity increase to the changes in DIC and POM carbon isotope compositions. The salinity-DIC-H-, O-, C-isotope compositions of water are compatible with evaporation as the main driver for salinity increase, rather than admixtures with seawater.

  4. Rare earth and trace elements of fossil vertebrate bioapatite as palaeoenvironmental and sedimentological proxies

    NASA Astrophysics Data System (ADS)

    Žigait?, Živil?; Fadel, Alexandre; Pérez-Huerta, Alberto; Jeffries, Teresa

    2015-04-01

    Rare earth (REE) and trace element compositions of fossil vertebrate dental microremains have been studied in Silurian and Devonian vertebrate dental scales and spines in-situ, using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Samples were selected from the well-known Silurian bone beds of Vesiku and Ohesaare in Saaremaa island of Estonia, and a number of Lower Devonian localities from Spitsbergen (Svalbard), Andrée Land group. Biomineral preservation was assessed using spot semi-quantitative elemental chemistry (SEM-EDS) and electron back-scatter difractometry (EBSD) for cristallinity imaging. The obtained PAAS shale-normalised REE concentrations were evaluated using basic geochemical calculations and quantifications. The REE patterns from the Lower Devonian vertebrate apatite from Andrée Land, Spitsbergen (Wood Bay and Grey Hœk formations) did not show any recognisable taxon-specific behavior, but had rather well expressed differences of REE compositions related to biomineral structure and sedimentary settings, suggesting REE instead to reflect burial environments and sedimentological history. The Eu anomaly recorded in two of the studied localities but not in the other indicate different taphonomic conditions and palaeoenvironment, while La/Sm, La/Yb ratios sugeest considerable influence of terrestrial freshwater during the early diagenesis. The La/Yb and La/Sm plots also agree with the average REE concentrations, reflecting domination of the adsoption over substitution as principal REE uptake mechanism in the fossils which had significantly lower overall REE concentrations, and vice versa. Vesiku (Homerian, Wenlock) microremains yielded very uniform REE patterns with slightly lower overall REE concentrations in enameloid than in dentine, with strong enrichment in middle REE and depletion in heavy REE. Negative Europium (Eu) anomaly was pronounced in all the profiles, but Cerium (Ce) anomalies were not detected suggesting possible suboxic to anoxic conditions of the bottom and pore waters during the formation of Vesiku bone bed. In Ohesaare (Pridoli), the REE compositions were nearly identical across all the morphotypes and histologies of acanthodian microremains showing flat REE patterns with slight depletion in HREE. There were no visible enrichment in MREE, indicating relatively good preservation of original bioapatite and likely absence of any pronounced fractionated REE incorporation during later stages of diagenesis. The shale normalised (La/Yb)SN and (La/Sm)SN REE ratio compilations showed addsorption as dominating REE uptake mechanism across all the studied microfossils. The absence of well-defined Ce anomaly suggest oxic palaeoseawater conditions, which agrees with existing interpretations of Ohesaare sequence as high-energy shoal and regressive open ocean sedimentary environment.

  5. Sedimentology and paleoenvironments of the Las Chacritas carbonate paleolake, Cañadón Asfalto Formation (Jurassic), Patagonia, Argentina

    NASA Astrophysics Data System (ADS)

    Cabaleri, Nora G.; Benavente, Cecilia A.

    2013-02-01

    The Las Chacritas Member is the lower part of the Cañadón Asfalto Formation (Jurassic). The unit is a completely continental limestone succession with volcanic contributions that were deposited during the development of the Cañadón Asfalto Rift Basin (Chubut province, Patagonia, Argentina). A detailed sedimentological analysis was performed in the Fossati depocenter to determine the paleoenvironments that developed in the context of this rift. The Las Chacritas Member represents a carbonate paleolake system with ramp-shaped margins associated with wetlands that were eventually affected by subaerial exposure and pedogenesis. This process is represented by three main subenvironments: a) a lacustrine setting sensu stricto (lacustrine limestone facies association), represented by Mudstones/Wackestones containing porifera spicules (F1), Intraclastic packstones (F6) and Tabular stromatolites (F10) in which deposition and diagenesis were entirely subaqueous; b) a palustrine setting (palustrine limestone facies association) containing Microbial Mudstones (F2), Intraclastic sandy packstone with ostracode remains (F3), Oncolitic packstone (F5), Brecciated limestone (F7) and Nodular-Mottled limestone (F8) representing shallow marginal areas affected by groundwater fluctuations and minor subaerial exposure; and c) a pedogenic paleoenvironment (pedogenic limestone facies association) including Intraclastic limestone (F4) and Packstones containing Microcodium (F9) facies displaying the major features of subaerial exposure, pedogenic diagenesis and the development of paleosols. The fluvial-palustrine-lacustrine succession shows a general shallow upward trend in which contraction-expansion cycles are represented (delimited by exposure and surface erosion). The variations in the successive formations reflect the responses to fluctuations in a combination of two major controls, the tectonic and local climatic variables. The predominance of the palustrine facies associations was determined by its accommodation space as well as the local climate conditions. The variations in the lacustrine limestone facies associations reflect differential patterns of subsidence within the sub-basin. The diagnostic features of the palustrine limestone facies associations (organic matter (OM) content, microinvertebrate fauna, abundant mud cracks, brecciation, presence of evaporitic minerals) frame the sub-basin in a climatic context intermediate between arid and subhumid conditions.

  6. Biogeomorphological influence of slope processes and sedimentology on vascular talus vegetation in the southern Cascades, California

    NASA Astrophysics Data System (ADS)

    Pérez, Francisco L.

    2012-02-01

    The vascular vegetation of alpine talus slopes between 2035 and 3095 m altitude was studied at Lassen Volcanic National Park (California) in the Cascade Range. Taluses show a diverse flora, with 79 plant species; growth forms include coniferous trees, shrubs, suffrutices, herbs, graminoids, and ferns. Spatial patterns of plant distribution were studied along 40 point-intercept transects. Plant cover was low (0-32.7%) on all slopes, spatially variable, and showed no consistent trends. Sedimentological characteristics were determined by photosieving next to 1500 plants; this census indicated preferential plant growth on blocks and cobbles, with 43.2% and 23.3% of the plants growing on these stones, respectively; fewer specimens were rooted on pebbles (13%) or on stone-free gravel areas (20.5%). Growth forms displayed different substrate preferences: 92.5% of the shrubs and 83% of the suffrutices colonized blocks or cobbles, but only 57.2% of the herbs and 59.8% of the graminoids grew on large stones. Plants are associated with large clasts because (1) coarse talus is more stable than fine sediment areas, which are more frequently disturbed by various geomorphic processes, and (2) large stones help conserve substrate water beneath them while moisture quickly evaporates from fine debris. Root patterns were studied for 30 plant species; 10 specimens for each species were excavated and inspected, and several root growth ratios calculated. All species exhibited pronounced root asymmetry, as roots for most plants grew upslope from their shoot base. For 23 species, all specimens had 100% of their roots growing upslope; for the other 7 species, 92.2-99.3% of below-ground biomass extended uphill. This uneven root distribution is ascribed to continual substrate instability and resulting talus shift; as cascading debris progressively buries roots and stems, plants are gradually pushed and/or stretched downhill. Various disturbance events affect root development. Slope erosion following rubble removal often exposes plant roots. Debris deposition can completely bury plants; some may survive sedimentation, producing new shoots that grow through accumulated debris. Shrubs may propagate by layering, as adventitious roots develop along buried stems; or produce new clones along their roots. Slope processes may damage and transport plant pieces downhill; some species can sprout from severed, displaced root or stem fragments. Vegetation interacts with several geomorphic processes, including debris flows, grain flows, rockfall, snow avalanches, frost creep, and runoff. Larger plants may alter local patterns of debris movement and deposition, damming cascading debris on their upslope side and deflecting sediments laterally to plant margins, where they form narrow elongated stone stripes.

  7. Systems tracts sedimentology in the lagoon of Mayotte associated with the Holocene transgression

    NASA Astrophysics Data System (ADS)

    Zinke, J.; Reijmer, J. J. G.; Thomassin, B. A.

    2003-08-01

    Twelve gravity cores from various settings within the Mayotte barrier reef-lagoon complex were studied to determine the sedimentology of the sequence stratigraphic systems tracts that formed during the Holocene transgression. Our studies focussed on the determination of physical, chemical, mineralogical and biological parameters of the sediments from specific systems tracts. These parameters determine the thickness and facies of each systems tracts and are controlled by the rate and amplitude of sea-level rise, lagoonal topography and environmental changes. The lowstand systems tract (LST) (before 11.5 ka BP) comprises ferralitic or organic-rich paleosoils in the proximal and middle lagoon and karstified Pleistocene reefal carbonates in the distal lagoon. The transgressive systems tract (TST) (11.5-7 ka BP) consists of a lower terrigenous and an upper mixed terrigenous-carbonate or carbonate-dominated unit. Locally, mangrove muds were deposited. The highstand systems tract (HST) can be divided into an early highstand (eHST) (7-1 ka BP) and a late highstand systems tract (lHST) (after 1 ka BP). In the proximal lagoonal wedge, the early highstand systems tract consists of terrigenous or mixed terrigenous-carbonate muds to sandy muds. In the middle lagoon, it shows carbonate mud to sandy mud and carbonate gravel to reefal carbonates in the distal lagoons. Terrigenous muds dominate the late highstand systems tract in the proximal lagoonal wedge. In the mid-lagoonal plain, mixed terrigenous-carbonate or carbonate mud to sandy mud dominates, while carbonate gravel to reefal carbonate prevails in the distal lagoon. For the last 9 ka, sedimentation in the lagoon of Mayotte has been spatially divided into a proximal terrigenous and a distal, carbonate-dominated province. Maximum carbonate concentrations between 4 and 1 ka BP coincide with the time of maximum solar insolation. After 1 ka BP, a general decrease in carbonate concentrations can be observed. This coincides with increased terrigenous sediment input, which results from a reduction in accommodation space and to some extent is of anthropogenic origin.

  8. Coral Patch seamount (NE Atlantic) - a sedimentological and megafaunal reconnaissance based on video and hydroacoustic surveys

    NASA Astrophysics Data System (ADS)

    Wienberg, C.; Wintersteller, P.; Beuck, L.; Hebbeln, D.

    2013-05-01

    The present study provides new knowledge about the so far largely unexplored Coral Patch seamount which is located in the NE Atlantic Ocean half-way between the Iberian Peninsula and Madeira. For the first time a detailed hydroacoustic mapping (MBES) in conjunction with video surveys (ROV, camera sled) were performed to describe the sedimentological and biological characteristics of this sub-elliptical ENE-WSW elongated seamount. Video observations were restricted to the southwestern summit area of Coral Patch seamount (water depth: 560-760 m) and revealed that this part of the summit is dominated by exposed hard substrate, whereas soft sediment is just a minor substrate component. Although exposed hardgrounds are dominant for this summit area and, thus, offer suitable habitat for settlement by benthic organisms, the benthic megafauna shows rather scarce occurrence. In particular, scleractinian framework-building cold-water corals are apparently rare with very few isolated and small-sized live occurrences of the species Lophelia pertusa and Madrepora oculata. In contrast, dead coral framework and coral rubble are more frequent pointing to a higher abundance of cold-water corals on Coral Patch during the recent past. This is even supported by the observation of fishing lines that got entangled with rather fresh-looking coral frameworks. Overall, long lines and various species of commercially important fish were frequently observed emphasising the potential of Coral Patch as an important target for fisheries that may have impacted the entire benthic community. Hydroacoustic seabed classification covered the entire summit of Coral Patch and its northern and southern flanks (water depth: 560-2660 m) and revealed extended areas dominated by mixed and soft sediments at the northern flank and to a minor degree at its easternmost summit and southern flank. Nevertheless, these data also predict most of the summit area to be dominated by exposed bedrock which would offer suitable habitat for benthic organisms. By comparing the locally restricted video observations and the broad-scale monitoring of a much larger and deeper seafloor area as derived by hydroacoustic seabed classification, it becomes obvious that habitat information obtained by in situ sampling may provide a rather scattered pattern about the entire seamount ecosystem. Solely with a combination of both methods, a satisfactory approach to describe the diverse characteristics of a seamount ecosystem can be derived which is in turn indispensable for future scientific monitoring campaigns as well as management and conservation purposes.

  9. Coral Patch seamount (NE Atlantic) - a sedimentological and macrofaunal reconnaissance based on video and hydroacoustic surveys

    NASA Astrophysics Data System (ADS)

    Wienberg, C.; Wintersteller, P.; Beuck, L.; Hebbeln, D.

    2012-12-01

    The present study provides new knowledge about the so far largely unexplored Coral Patch seamount which is located in the NE Atlantic Ocean half-way between the Iberian Peninsula and Madeira. For the first time a detailed hydroacoustic mapping (MBES) in conjunction with video surveys (ROV, camera sled) were performed to describe the sedimentological and biological characteristics of this sub-elliptical ENE-WSW elongated seamount. Video observations were restricted to the south-western summit area of Coral Patch seamount (area: ~ 8 km2, water depth: 560-760 m) and revealed that this part of the summit is dominated by exposed hard substrate, whereas soft sediment is just a minor substrate component. Although exposed hardgrounds are dominant for this summit area, and thus, offer suitable habitat for settlement by benthic organisms, the macrofauna shows rather low abundance and diversity. In particular, scleractinian framework-building cold-water corals are apparently rare with very few isolated and small-sized live occurrences of the species Lophelia pertusa and Madrepora oculata. In contrast, dead coral framework and coral rubble are more frequent pointing to a higher abundance of cold-water corals on Coral Patch during the recent past. This is even supported by the observation of fishing lines that got entangled with rather fresh-looking coral frameworks. Overall, long lines and various species of commercially important fish were frequently observed emphasising the potential of Coral Patch as an important target for fisheries that may have impacted the entire benthic community. Hydroacoustic seabed classification covered the entire summit of Coral Patch and its northern and southern flanks (area: 560 km2; water depth: 560-2660 m) and revealed extended areas dominated by mixed and soft sediments at the northern flank and to a minor degree at its easternmost summit and southern flank. Nevertheless, also these data predict most of the summit area to be dominated by exposed bedrock which would offer suitable habitat for benthic organisms. By comparing the locally restricted video observations and the broad-scale monitoring of a much larger and deeper seafloor area as derived by hydroacoustic seabed classification, it becomes obvious that habitat information obtained by in situ sampling may provide a rather scattered pattern about the entire seamount ecosystem. Solely with a combination of both methods, a satisfactory approach to describe the diverse characteristics of a seamount ecosystem can be derived which is in turn indispensable for future scientific monitoring campaigns as well as management and conservation purposes.

  10. Stratigraphy and depositional environments of the upper Pleistocene Chemehuevi Formation along the lower Colorado River

    USGS Publications Warehouse

    Malmon, Daniel V.; Howard, Keith A.; House, P. Kyle; Lundstrom, Scott C.; Pearthree, Philip A.; Sarna-Wojcicki, Andrei M.; Wan, Elmira; Wahl, David B.

    2011-01-01

    The Chemehuevi Formation forms a conspicuous, widespread, and correlative set of nonmarine sediments lining the valleys of the Colorado River and several of its larger tributaries in the Basin and Range geologic province. These sediments have been examined by geologists since J. S. Newberry visited the region in 1857 and are widely cited in the geologic literature; however their origin remains unresolved and their stratigraphic context has been confused by inconsistent nomenclature and by conflicting interpretations of their origin. This is one of the most prominent stratigraphic units along the river below the Grand Canyon, and the formation records an important event or set of events in the history of the Colorado River. Here we summarize what is known about these deposits throughout their range, present new stratigraphic, sedimentologic, topographic, and tephrochronologic data, and formally define them as a lithostratigraphic unit. The Chemehuevi Formation consists primarily of a bluff-forming mud facies, consisting of gypsum-bearing, horizontally bedded sand, silt, and clay, and a slope-forming sand facies containing poorly bedded, well sorted, quartz rich sand and scattered gravel. The sedimentary characteristics and fossil assemblages of the two facies types suggest that they were deposited in flood plain and channel environments, respectively. In addition to these two primary facies, we identify three other mappable facies in the formation: a thick-bedded rhythmite facies, now drowned by Lake Mead; a valley-margin facies containing abundant locally derived sediment; and several tributary facies consisting of mixed fluvial and lacustrine deposits in the lower parts of major tributary valleys. Observations from the subsurface and at outcrops near the elevation of the modern flood plain suggest that the formation also contains a regional basal gravel member. Surveys of numerous outcrops using high-precision GPS demonstrate that although the sand facies commonly overlies the mud facies where the two are found together, contacts between the two occur over a range in elevation, and as a consequence, the sand and mud facies are similarly distributed both horizontally and vertically throughout the valley. Collectively, the outcrops of the formation lie below a smooth elevation envelope that slopes 50 percent more steeply than the historic (pre-Hoover Dam) valley, from nearly 150 m above the historic flood plain near the mouth of the Grand Canyon to less than 30 m above the flood plain at the head of the flood plain near Yuma, Arizona. The steepness of the valley at the peak of aggradation probably represents a depositional slope. Layers of fine grained volcanic tephra have been found below and within the Chemehuevi Formation at five widely separated sites, one of which is now submerged beneath Lake Mead. Major element geochemistry of glass shards from the four accessible tephra sites were analyzed. Three of the sampled tephra layers are interbedded within the Chemehuevi Formation, and a fourth tephra conformably underlies the formation. The three interbedded tephra layers are similar enough to one another that they are probably from the same eruptive unit, hereafter referred to as the Monkey Rock tephra bed. The other sample, which locally underlies the formation, is similar enough to the Monkey Rock tephra bed to suggest it is from the same volcanic source area; however, it may not be from the same eruption, and thus may not be the same age. On the basis of the stratigraphic contexts of chemically similar tephra layers found elsewhere in the Basin and Range, we suspect that the source area is the Mammoth Mountain dome complex in Long Valley, east-central California. Two samples of proximal Mammoth Mountain pumice were analyzed and produced geochemical signatures similar to all four of the Chemehuevi Formation tephra, supporting Mammoth Mountain as a possible source area. The Mammoth Mountain volcanic center produced eruptions between about 111±2 and 57±2 ka and was most active in the later part of this time

  11. Mars - Stratigraphy and gravimetry of Olympus Mons and its aureole

    NASA Astrophysics Data System (ADS)

    Hiller, K. H.; Neukum, G. P. O.; Janle, P.; Guest, J. E.; Lopes, R. M. C.

    1982-11-01

    The relative ages of the major geologic units on and around Olympus Mons are considered, together with an interpretation of the gravity anomaly found for this area. The crater data for this investigation have been acquired and interpreted according to the method outlined by Neukum and Hiller (1981). After careful geological mapping, craters clearly identified as impacts are measured and counted. Crater frequency values per sq km for craters greater than or equal to 1 km ('crater retention ages') are read from the individual counts by fitting the Martian cumulative crater production size-frequency distribution to the individual counts. In addition to age dating, the problem of the origin and nature of the aureole materials using gravity data is addressed. This is done by determining whether the line-of-sight gravity extending from Olympus Mons to the northwestern part of the aureole can be explained by the aureole masses alone or whether additional high-density intrusive masses must be assumed in the aureola area.

  12. Glacial stratigraphy of Stough Creek Basin, Wind River Range, Wyoming

    NASA Astrophysics Data System (ADS)

    Dahms, Dennis E.

    2002-01-01

    Multiparameter relative-age (RA) techniques identify four post-Pinedale morphostratigraphic units in each of three cirque valleys tributary to Stough Creek Basin, Wind River Range, WY. Soil development, lichenometry, boulder weathering characteristics, and the geomorphic relations among morphostratigraphic units indicate glacial deposits here correspond to the sequence previously described in the Temple Lake valley [Arct. Alp. Res. 6 (1974) 301]. Cirque deposits in Stough Creek Basin correspond to the Temple Lake, Alice Lake, Black Joe, and Gannett Peak alloformations [GSA Abs. Prog. 32 (2000) A-16]. 10Be ages from moraine boulders and polished-striated bedrock [Assoc. Am. Geogr. Annu. Mtg. Abs. (2000) 155] support recent numeric age estimates from Temple Lake and Titcomb Basin that indicate the Temple Lake Alloformation corresponds to the Younger Dryas climate episode [Geogr. Phys. Quat. 41 (1987) 397; Geology 23 (1995) 877; Science 268 (1995) 1329; GSA Abs. Prog. 31 (1999) A-56]. Soils described from Pinedale recessional deposits here represent the first systematic description of Pinedale alpine deposits in the WRR.

  13. Time-stratigraphic reconstruction and integration of paleopedologic, sedimentologic, and biotic events (Willwood Formation, Lower Eocene, northwest Wyoming, USA)

    USGS Publications Warehouse

    Bown, T.M.; Kraus, M.J.

    1993-01-01

    An empirically-based model is advanced using paleosol maturities to estimate the relative geologic time separating any stratigraphic levels within the lower Eocene Willwood Formation. The reviewed Willwood time stratigraphy from this analysis helps evaluate the nature, tempo, and possible causes of three major episodes of mammalian appearance and disappearance. These faunal events are directly correlated with certain apects of paleosol evolution in the Willwood Formation. That evolution is tied directly to climatic changes and to varying sediment accumulation rates in response to tectonism. -from Authors

  14. Sedimentological discontinuties as chances for enhancing process-based palaeo-environmental reconstruction

    NASA Astrophysics Data System (ADS)

    Hartmann, Kai; Lockot, Gregori; Wünnemann, Bernd; Ramisch, Arne; Diekmann, Bernhard; Yan, Dada

    2014-05-01

    Morpho-stratigraphic approaches in the field of palaeoenvironmental reconstruction are time consuming, have a low temporal resolution and the problem of equifinality in terms of processes or simply the reputation of fuzziness. Nevertheless, investigations of seemingly continuous archives such as lake sediments are more effective if climate driven catchment signals are considered. Lake level data sets provide valuable indices for modelling the palaeoclimatic history and feedback-mechanisms on regional, supra-regional or even hemispherical scales. However, they are frequently used without considering the role of sediment trapping, signal buffering and random events (tectonic, mass-movements, etc.) along related sediment cascades. Moreover, dating inversions, record gaps and unlikely high or low SARs are considered as archive-internal disturbances or simply measurement errors which have to be smoothed by increasingly sophisticated tools of statistics or simply eliminated. This poster examines the value of such discontinuities and random events within continuous lake record for deciphering catchment-wide feedbacks/responses and their related processes. Our first example shows the influence of lake level changes and permafrost uplift on the reservoir effect of Lake Heihai, Northern Tibetan Plateau. A drop in lake level induced the reworking of sediment sequences, which is not identifiable by disturbances of the stratighraphy. This problem only becomes apparent, if several on-shore sediment records and at least two lake cores are compared. Several lake records from Hala Lake, Qilian Mountains, northeastern Tibetan Plateau confirm highly diverse stratigraphies and sediment properties, thus underpinning the necessity of data comparison from different locations (within the lake) for a reliable reconstruction of climate-driven hydrological variations within a lake-catchment system. A third example from a large endorheic foreland basin of the Tibetan Plateau (Ejina Basin also known as Gaxun Nur B.) shows that only a large set of well dated sediment records with overlapping time frame lead to an understanding of the underlying sedimentation processes. The information of sedimentation variance derived from a cored sediment record is punctual. Only the spatial relation and geomorphological context provide insights into a larger set of interrelated processes and thus ensure spatially reliable reconstructions of climate-induced hydrography. Finally we show that a single record without considering the geomorphological process ensemble will provide less resolution or greater fuzziness than a geomorphological archive. Only the combination of more than one core from a "final" sink, an unbiased analyses of different proxy sets and at least a well dated morphostratigraphy may lead to a reliable process-based reconstruction of palaeo-environmental (-climate) variance.

  15. Ages, rare-earth element enrichment, and petrogenesis of tholeiitic and alkalic basalts from Kahoolawe Island, Hawaii

    Microsoft Academic Search

    R. V. Fodor; F. A. Frey; G. R. Bauer; D. A. Clague

    1992-01-01

    Kahoolawe Island, Hawaii (18×11 km), is a basaltic shield volcano with caldera-filling lavas, seven identified postshield vents, and at least two occurrences of apparent rejuvenated-stage eruptive. We examined 42 samples that represent all stages of Kahoolawe volcano stratigraphy for their petrography, whole-rock major-and trace-element contents, mineral compositions, and K-Ar ages. The two oldest shield samples have an average age of

  16. Floodplain deposits, channel changes and riverbank stratigraphy of the Mekong River area at the 14th-Century city of Chiang Saen, Northern Thailand

    NASA Astrophysics Data System (ADS)

    Wood, Spencer H.; Ziegler, Alan D.; Bundarnsin, Tharaporn

    2008-10-01

    Riverbank stratigraphy and paleochannel patterns of the Mekong River at Chiang Saen provide a geoarchaeological framework to explore for evidence of Neolithic, Bronze-age, AD 5th Century Yonok and AD 14-16th Century Lan Na Cultures. Typical bank stratigraphy charted on the Thailand side is imbricate cobble gravel overlain by 5-10 m of reddish-brown sandy silt. The silt section is composed chiefly of 1/2 to 2-m thick layers of massive silt without paleosols interpreted as near-channel floodplain and gently-inclined levee deposits laid down by episodic, infrequent, large floods. The surface soil is dark-brown clay loam (< 1-m thick) with abundant brick fragments, pottery shards and charcoal of Lan Na time. Brick ruins of 14-16th Century Buddhist temples are crumbling into the river at Chiang Saen Noi, and formerly did so at Chiang Saen until banks were stabilized by rock walls. Bank retreat from river erosion has been > 20 m since Lan Na time, and has exposed a silt-filled moat. A radiocarbon age of 1475 cal yr AD was obtained from charcoal at the bottom of the moat, beneath 5.6 m of silt. Lag material from erosion of the silt banks contains Neolithic and Bronze Age artifacts out of stratigraphic context, as well as ceramics and bricks of Lan Na age. These artifacts as well Neolithic artifacts obtained from a 1972 excavation near the mouth of the Kham River indicate long human habitation of this riverbank area. In northern Thailand the Mekong is mostly in a bedrock canyon, but shifting topography along the active strike-slip Mae Chan fault has formed the upstream 2-5-km wide floodplain at Chiang Saen, and downstream has diverted the river into a broad S-shaped loop in the otherwise straight course of the river. A 1.7-Ma basalt within the bedrock channel 45-km downstream of Chiang Saen indicates little vertical incision by the river. Satellite images show former channels in the Chiang Saen area, meander-point-bar scrolls (radii of curvature > 1.2 km), and floodplain edges as arcuate cuts of similar curvature into the saprolite-mantled bedrock hills These features indicate channel avulsion occurred by meander loop cutoff in the past. Brick Buddhist monuments of the 14th-16th Century were built upon the floodplain with meander features on the Thai and Laos side of the river, indicating that these meandering channel features and the broader floodplain are mostly older than 600 years.

  17. Sequence stratigraphy and the world sea-level curve: The 2005 Benjamin Franklin Medal in Earth and Environmental Science awarded to Peter R. Vail

    Microsoft Academic Search

    William E. Bonini; Robert D. Varrin; John Van Wagoner

    2006-01-01

    During the mid-1960s, Peter R. Vail at Exxon Production Research Co. led a group working with the new, greatly improved generation of multifold seismic reflection data being shot along the continental margins of the world. The work of this group, inspired by Vail, brought the worlds of stratigraphy and seismic interpretation together in developing the original concepts of seismic stratigraphy.Later

  18. Geology and stratigraphy of forearc basin sediments in Hokkaido, Japan: Cretaceous environmental events on the north-west Pacific margin

    Microsoft Academic Search

    Reishi Takashima; Fumihisa Kawabe; Hiroshi Nishi; Kazuyoshi Moriya; Ryoji Wani; Hisao Ando

    2004-01-01

    Litho-, bio-, and chemostratigraphy of the Cretaceous forearc basin sediments exposed in Hokkaido, northern Japan allow a synthesis of the faunal, sedimentological, and environmental history of the north-west Pacific margin. Although the succession, named the Yezo Group, has yielded an abundant record of mid- to late Cretaceous invertebrates, monotonous lithologies of sandstone and mudstone, showing occasional lateral facies changes, have

  19. Luminescence dating of Middle Stone Age deposits at Die Kelders.

    PubMed

    Feathers, J K; Bush, D A

    2000-01-01

    Luminescence dating of sediments has not been used extensively for dating Middle Stone Age deposits in South Africa, despite its potential for contributing to a poorly dated record. Such deposits at Die Kelders cave, on the southern South African coast, consist of narrow bands of occupation debris separated by thicker layers of aeolian sands containing much less evidence of occupation. Homogeneous, aeolian sediments are usually considered ideal for luminescence dating. Here we report luminescence analyses of five samples from these sands that demonstrate sufficient bleaching prior to burial to validate dating and that yield ages of about 60-70 ka, in agreement with other evidence from sedimentology, archaeology and electron spin resonance. Lack of significant differences in the ages suggests the deposits accumulated fairly rapidly during the early part of the Last Glaciation. PMID:10627398

  20. Eo-Ulrichian to Neo-Ulrichian views: The renaissance of "layer-cake stratigraphy"

    USGS Publications Warehouse

    Brett, Carlton E.; McLaughlin, P.I.; Baird, G.C.

    2007-01-01

    Classical notions of "layer-cake stratigraphy" have been denigrated as representing an antiquated "Neptunian" view of the geologic record with the American paleontologist-stratigrapher E.O. Ulrich vilified as its quintessential advocate. Some of the extreme "layer-cake" interpretations of E.O. Ulrich are demonstrably incorrect, especially where applied in marginal marine and terrestrial settings. However, close scrutiny of Ulrich's work suggests that the bulk was correct and demonstrated considerable insight for the time. Subsequent development of facies concepts revolutionized geologists' view of time-space relationships in stratigraphy, but rather than focusing on facies patterns within the established stratigraphic (layer-cake) frameworks many geologists in North America came to view strata as parts of diachronous facies mosaics. Recent advances in the development of event and sequence stratigraphic paradigms are beginning to swing the pendulum back the other way. Possible causes of "layer-cake" patterns are numerous and varied, including: (1) parallelism of depositional strike and outcrop belts, especially in foreland basins, (2) very widespread environmental belts developed in low-relief cratonic areas, (3) time-averaging homogenizes facies to a limited extent, resulting in a very subtle signature of lateral change, (4) condensed beds (hardgrounds, bone beds, ironstones, etc.) often form in responses to extrabasinal forces, thus they cross-cut facies, and (5) large events (i.e. hurricanes, floods, tsunamis, eruptions, etc.) are "over represented" in the rock record. A revised ("Neo-Ulrichian") layer-cake paradigm carries many of the original correct empirical observations of pattern, noted by Ulrich, recast in terms of event and sequence stratigraphy.

  1. High-Frequency Allogenic Forcings on the Holocene Stratigraphy of Santa Monica Basin, California (Invited)

    NASA Astrophysics Data System (ADS)

    Romans, B.; Covault, J. A.; Fildani, A.

    2009-12-01

    Investigations of stratigraphy from natural systems commonly relate depositional sequences to allogenic forcings lasting tens to hundreds of thousands of years or more, whereas stratigraphic products from shorter time scales have been linked to autogenic processes. In this study we use a stratigraphic framework constrained by radiocarbon dates integrated with high-resolution seismic-reflection data from the Holocene Santa Monica Basin, offshore California, to evaluate allogenic and autogenic controls at millennial scales. The depositional history from 7 ka to present indicates that the recurrence interval for large turbidity-current events is relatively constant (300-360 yr), but the volume of sediment deposited on the fan and in the basin plain increased by a factor of two over this period. Moreover, the amount of sand per event on the basin plain during the same interval increased by a factor of seven. Maps of sediment distribution derived from correlation of seismic-reflection profiles indicate that this trend cannot be attributed exclusively to autogenic processes (e.g., progradation of depocenters). The observed variability in sediment accumulation rates is thus largely controlled by interacting allogenic factors, including: (1) increased discharge of Santa Clara River as a result of increased magnitude and frequency of El Niño-Southern Oscillation (ENSO) events from ~2 ka to present and (2), an apparent change in routing of coarse-grained sediment within the staging area at ~3 ka (i.e., from direct river input to indirect, littoral cell input into Hueneme submarine canyon. Therefore, the basinal stratigraphy records variability of sediment routing pathways in the staging area superimposed on the more fundamental signal of fluctuating climatic conditions. Results of this study demonstrate that bed-scale stratigraphic patterns are controlled by high-frequency allogenic forcings, which highlights the need to reconsider interpretations of stratigraphy from purely autogenic forcings.

  2. Apollo 16 stratigraphy - The ANT hills, the Cayley Plains, and a pre-Imbrian regolith

    NASA Technical Reports Server (NTRS)

    Taylor, G. J.; Drake, M. J.; Hallam, M. E.; Marvin, U. B.; Wood, J. A.

    1973-01-01

    A total of 645 particles in the 1 to 2 mm size range has been classified in the Apollo 16 soil samples 60602,3, 61242,7, 66042,4, 67602,13, and 69942,13. Five major categories of lithic fragments recognized in these samples include (1) an anorthositic/noritic/troctolitic, or ANT suite, (2) light-matrix breccias, (3) poikiloblastic noritic/anorthositic fragments, (4) spinel-troctolites, and (5) feldspathic basalts. The petrography and phase chemistry of the lithic fragments are discussed along with results of the fragment census and the stratigraphy of the Apollo 16 site.

  3. The Significance of Stratigraphy and Lithology in Landform Development in Washington County, Oklahoma

    NSDL National Science Digital Library

    This winning entry in the museum's Young Naturalist Awards 1999 by Katie, a 15 year old student from Oklahoma, takes a look at the development of Washington County, Oklahoma. Katie's essay has a field-journal focus and explains stratigraphy and lithology, two of the main factors controlling the shape of the land in her county. She provides an overview of the six different formations in the Skiatook Group and the five different formations that outcrop in the Bartlesville area. There are descriptions of the many rock samples she took for this study.

  4. Hyperspectral Analysis of Paleoseismic Trench Stratigraphy: Toward Improving the Recognition and Documentation of Past Earthquakes

    NASA Astrophysics Data System (ADS)

    Ragona, D. E.; Minster, B.; Fialko, Y.; Rockwell, T.

    2003-12-01

    We are conducting a pilot project to use hyperspectral imagery to assist in the recognition and documentation of paleoseismic events in trench exposures. Recent advances in hyperspectral imagery suggest that stratigraphy can be analyzed in much the same way as Aviris imagery of Earth's surface. In principle, hyperspectral images may be able to elucidate and record otherwise-poor stratigraphy in some exposures, thereby improving the information that can be gleaned from a paleoseismic site. This technique may also eliminate some problems in interpretation of the earthquake history of a site by illuminating details of the stratigraphy and structure that are not apparent to the human eye, such as unique unit correlations across complicated fault ruptures. The trench site chosen for this study is located at Hog Lake in the Anza seismic gap along the San Jacinto Fault in southern California. The site was selected because of its detailed, well defined stratigraphy. The method adopted was to obtain a 50 cm side square matrix of samples that could be used to generate a low-resolution image of the sampled area, in the sense that each sample represents a single pixel. The samples were collected 2.5 cm apart in a square matrix of 20x20 samples. Each of the 400 samples collected are stored into PVC or metallic cylinders of 3/4" or 1/2" diameter. All samples were spectrally analyzed at JPL using a FieldSpec Pro instrument that measure radiation in the 350-2,500 nm wavelength window. Five measurements of each sample were performed, along with measurements of the radiation reflected by a reference surface (Spectralon), under natural light and clear sky conditions. The data obtained was then processed to obtain reflectance spectra for all samples. Principal Component Analysis was used to create a pixilated image from the three dominant components. That image shows promising similarity with the standard digital picture of the sampled trench wall. However, large random measurement errors created problems in some samples when we tried to separate classes of different materials. We are currently working on the identification of the source of noise to either correct the data or to improve the experimental procedure. Our current preliminary results show that the hyperspectral data can discriminate between different lithologies for those samples that provide consistent spectrums with high signal to noise ratio Whole spectrum comparisons yielded better results than single absorption features identification.

  5. Stratigraphy of the unsaturated zone and uppermost part of the Snake River Plain aquifer at test area north, Idaho National Engineering Laboratory, Idaho

    SciTech Connect

    Anderson, S.R.; Bowers, B.

    1995-06-01

    A complex sequence of basalt flows and sedimentary interbeds underlies Test Area North (TAN) at the Idaho National Engineering Laboratory in eastern Idaho. Wells drilled to depths of at least 500 feet penetrate 10 basalt-flow groups and 5 to 10 sedimentary interbeds that range in age from about 940,000 to 1.4 million years. Each basalt-flow group consists of one or more basalt flows from a brief, single or compound eruption. All basalt flows of each group erupted from the same vent, and have similar ages, paleomagnetic properties, potassium contents, and natural-gamma emissions. Sedimentary interbeds consist of fluvial, lacustrine, and eolian deposits of clay, silt, sand, and gravel that accumulated for hundreds to hundreds of thousands of years during periods of volcanic quiescence. Basalt and sediment are elevated by hundreds of feet with respect to rocks of equivalent age south and cast of the area, a relation that is attributed to past uplift at TAN. Basalt and sediment are unsaturated to a depth of about 200 feet below land surface. Rocks below this depth are saturated and make up the Snake River Plain aquifer. The effective base of the aquifer is at a depth of 885 feet below land surface. Detailed stratigraphic relations for the lowermost part of the aquifer in the depth interval from 500 to 885 feet were not determined because of insufficient data. The stratigraphy of basalt-flow groups and sedimentary interbeds in the upper 500 feet of the unsaturated zone and aquifer was determined from natural-gamma logs, lithologic logs, and well cores. Basalt cores were evaluated for potassium-argon ages, paleomagnetic properties, petrographic characteristics, and chemical composition. Stratigraphic control was provided by differences in ages, paleomagnetic properties, potassium content, and natural-gamma emissions of basalt-flow groups and sedimentary interbeds.

  6. Late Cenozoic tephrochronology, stratigraphy, geomorphology, and neotectonics of the Western Black Mountains Piedmont, Death Valley, California: Implications for the spatial and temporal evolution of the Death Valley fault zone

    NASA Astrophysics Data System (ADS)

    Knott, Jeffrey Rayburn

    This study presents the first detailed tephrochronologic study of the central Death Valley area by correlation of a Nomlaki-like tuff (>3.35 Ma), tuffs of the Mesquite Spring family (3.1 -- 3.35 Ma), a tuff of the lower Glass Mountain family (1.86 -- 2.06 Ma), and tephra layers from the upper Glass Mountain family (0.8 -- 1.2 Ma), the Bishop ash bed (0.76 Ma), the Lava Creek B ash bed (~0.66 Ma), and the Dibekulewe ash bed (~0.51 Ma). Correlation of these tuffs and tephra layers provides the first reliable numeric-age stratigraphy for late Cenozoic alluvial fan and lacustrine deposits for Death Valley and resulted in the naming of the informal early to middle Pleistocene Mormon Ploint formation. Using the numeric-age stratigraphy, the Death Valley fault zone (DVFZ) is interpreted to have progressively stepped basinward since the late Pliocene at Mormon Point and Copper Canyon. The Mormon Point turtleback or low-angle normal fault is shown to have unequivocal late Quaternary slip at its present low angle dip. Tectonic geomorphic analysis indicates that the (DVFZ) is composed of five geomorphic segments with the most persistent segment boundaries being the en-echelon step at Mormon Point and the bedrock salient at Artists Drive. Subsequent geomorphic studies resulting from the numeric-age stratigraphy and structural relations include application of Gilberts field criteria to the benches at Mormon Point indicating that the upper bench is a lacustrine strandline and the remaining topographically-lower benches are fault scarps across the 160--185 ka lake abrasion platform. In addition, the first known application of cosmogenic 10Be and 26Al exposure dating to a rock avalanche complex south of Badwater yielded an age of 29.5 +/- 1.9 ka for the younger avalanche. The 28 meter offset of the older avalanche may be interpreted as post-160--185 ka yielding a 0.1 mm/year slip rate, or post-29.5 +/- 1.9 ka yielding a maximum slip rate of 0.9 nun/year for the DVFZ. A consequence of these studies is the hypothesis that the turtleback or low-angle normal faults represent a thermally-warped detachment fault related to the Black Mountains igneous complex and do not conform with the present domino or a rolling-hinge models of low-angle normal fault development.

  7. High resolution seismic stratigraphy of Tampa Bay, Florida

    SciTech Connect

    Tihansky, A.B.; Hine, A.C.; Locker, S.D.; Doyle, L.D. (Univ. of South Florida, St. Petersburg, FL (United States). Dept. of Marine Science)

    1993-03-01

    Tampa Bay is one of two large embayments that interrupt the broad, regional nature of the carbonate ramp of the west coast of the Florida carbonate platform. It is believed to have formed as a result of preferential dissolution of the Cenozoic limestones beneath it. Highly reactive freshwater systems became hydrologically focused in the bay region as the surface and groundwater systems established themselves during sea-level lowstands. This weakening of the underlying limestone resulted in extensive karstification, including warping, subsidence, sinkhole and spring formation. Over 120 miles of high resolution seismic reflection data were collected within Tampa Bay. This record has been tied into 170 core borings taken from within the bay. This investigation has found three major seismic stratigraphic sequences beneath the bay. The lowermost sequence is probably of Miocene age. Its surface is highly irregular due to erosion and dissolution and exhibits a great deal of vertical relief as well as gentler undulations or warping. Much of the middle sequence consists of low angle clinoforms that gently downlap and fill in the underlying karst features. The uppermost sequence is a discontinuous unit comprised of horizontal to low angle clinoforms that are local in their extent. The recent drainage and sedimentation patterns within the bay area are related to the underlying structure controlled by the Miocene karst activity.

  8. Holocene climate change inferred from stratigraphy and OSL chronology of aeolian sediments in the Qaidam Basin, northeastern Qinghai-Tibetan Plateau

    NASA Astrophysics Data System (ADS)

    Yu, LuPeng; Lai, ZhongPing

    2014-05-01

    Paleoclimatic reconstruction based on aeolian sediments in the eastern Qaidam Basin (QB) has been hindered by the limited chronological data. Here we present 61 Optically Stimulated Luminescence (OSL) ages. On the basis of these OSL ages and the lithologic stratigraphy, we propose the ‘effective moisture index (EMI)' for aeolian sediments to reconstruct the effective moisture change. Based on the EMI from twelve sections, the effective moisture change, moisture sources and relevant mechanisms for paleoclimatic change in the eastern QB are discussed. The results indicate that (1) aeolian deposition started at least before 12.4 ± 0.7 ka during the deglaciation, the paleosols developed at the early and mid-Holocene, and aeolian sand and loess accumulated at mid- and late Holocene; (2) effective moisture history was: hyper-arid at 12.8-11.6 ka, humid and variable at 11.6-8.3 ka, moderately humid and stable at 8.3-3.5 ka, and increasingly arid at 3.5-0 ka; (3) the effective moisture change was mainly controlled by the Asian summer monsoon (ASM), which mainly followed the change of Northern Hemispheric summer insolation, and the westerlies strengthened and increased the aridity in the QB when the ASM shrank.

  9. Stratigraphy and compositional evolution of Cinder Cone, a composite monogenetic cone in Lassen Volcanic National Park, California

    NASA Astrophysics Data System (ADS)

    Clynne, M. A.

    2011-12-01

    Cinder Cone, in Lassen Volcanic National Park, has received considerable attention in the literature since its description by Harkness (1875) and Diller (1891) and has provoked considerable controversy concerning its age and eruptive history (e.g. Finch and Anderson, 1930; Finch, 1937). Geologic mapping of the composite cinder cone, an extensive tephra blanket, and 5 lava flows determined the eruptive sequence stratigraphy (Clynne and Muffler, 2010), and tree-ring chronology dated the eruption as 1666 C.E. (Sheppard et al., 2008). Tephra, divided into 3 units by Heiken (1978), accounts for 20% of the 0.36 km3 total volume of the eruption. The lava field consists of 5 block lava flows: Old Bench (OB), Painted Dunes (PD) 1 and 2, and Fantastic Lava Beds (FL) 1 and 2. Magnesian olivine containing inclusions of chromian spinel is the most abundant phenocryst, followed by plagioclase and sparse augite. Xenocrystic quartz is ubiquitous. Three types of inclusions are present: 1) sparse, mostly melted, inclusions of granitic rocks derived from Sierran basement, 2) abundant single crystals of quartz derived from granitic rocks and multicrystalline inclusions of metamorphic quartz from veins, and 3) rare magmatic enclaves of olivine basalt with quenched textures. The tephra and OB, PD, and FL lithologies are olivine basaltic andesite to andesite with subtle differences. Analyses of tephra from a measured section document the compositional evolution of Cinder Cone eruption. Unit 1 tephra contains 55.5% SiO2, 7.9% MgO, and 1.25% K2O. Initial unit 2 tephra contains 54.8% SiO2, 8.2% MgO, and 1.2% K2O. Unit 2 tephra becomes increasing more mafic up section to 53.8% SiO2, 9.0% MgO, and 1.0% K2O and then rapidly more felsic to 56.3% SiO2, 8.0% MgO, and 1.3% K2O. Initial unit 3 tephra contains 58.0% SiO2, 7.5% MgO, and 1.6% K2O but becomes more mafic to 55.0% SiO2, 7.5% MgO, and 1.2% K2O up section. The OB flow and the early PD 1 flow are equivalent in composition to the early unit 2 tephra, and the subsequent late PD 1 flow and PD 2 flows mimic late unit 2 tephra. FL 1 and 2 flows are compositionally equivalent to early and late unit 3 tephra, respectively. A mostly destroyed remnant cinder cone has unit 2 tephra composition, and Cinder Cone has unit 3 composition. The complex compositional variation at Cinder Cone, superficially a monogenetic volcano, is ascribed to the combined effects of fractional crystallization and assimilation and concurrent recharge of the system by a new mafic magma. Variation of the early magmas can be modeled by fractional crystallization and assimilation of granitic xenoliths. The reversal of compositional variation near the unit 2-3 boundary and subsequent decrease in SiO2 can be modeled by mixing with a new mafic magma having the composition of the quenched basaltic enclaves. Details of the mineral compositions are consistent with the stratigraphy and bulk compositional evolution.

  10. Genetic stratigraphy of key demographic events in Arabia.

    PubMed

    Fernandes, Verónica; Triska, Petr; Pereira, Joana B; Alshamali, Farida; Rito, Teresa; Machado, Alison; Fajkošová, Zuzana; Cavadas, Bruno; ?erný, Viktor; Soares, Pedro; Richards, Martin B; Pereira, Luísa

    2015-01-01

    At the crossroads between Africa and Eurasia, Arabia is necessarily a melting pot, its peoples enriched by successive gene flow over the generations. Estimating the timing and impact of these multiple migrations are important steps in reconstructing the key demographic events in the human history. However, current methods based on genome-wide information identify admixture events inefficiently, tending to estimate only the more recent ages, as here in the case of admixture events across the Red Sea (~8-37 generations for African input into Arabia, and 30-90 generations for "back-to-Africa" migrations). An mtDNA-based founder analysis, corroborated by detailed analysis of the whole-mtDNA genome, affords an alternative means by which to identify, date and quantify multiple migration events at greater time depths, across the full range of modern human history, albeit for the maternal line of descent only. In Arabia, this approach enables us to infer several major pulses of dispersal between the Near East and Arabia, most likely via the Gulf corridor. Although some relict lineages survive in Arabia from the time of the out-of-Africa dispersal, 60 ka, the major episodes in the peopling of the Peninsula took place from north to south in the Late Glacial and, to a lesser extent, the immediate post-glacial/Neolithic. Exchanges across the Red Sea were mainly due to the Arab slave trade and maritime dominance (from ~2.5 ka to very recent times), but had already begun by the early Holocene, fuelled by the establishment of maritime networks since ~8 ka. The main "back-to-Africa" migrations, again undetected by genome-wide dating analyses, occurred in the Late Glacial period for introductions into eastern Africa, whilst the Neolithic was more significant for migrations towards North Africa. PMID:25738654

  11. Stratigraphy of the Grande Savane Ignimbrite Sequence, Dominica, Lesser Antilles

    NASA Astrophysics Data System (ADS)

    Schneider, S.; Smith, A. L.; Deuerling, K.; Killingsworth, N.; Daly, G.

    2007-12-01

    The island of Dominica, located in the central part of the Lesser Antilles island arc has eight potentially active volcanoes. One of these, Morne Diablotins, is a composite stratovolcano with several superimposed stratigraphic sequences ranging in age from Pliocene (4-2 Ma) to "Younger" Pleistocene (<1.8 Ma). The most recent major eruptive activity from this volcano was a series of Plinian eruptions that produced ignimbrites that gave dates of >22,000 and >40,000 years B.P. The ignimbrite sequences form four flow fans that reached both the east and west coasts of the island. One of these flow fans, the Grande Savane, on the west coast of the island, also extends off-shore for a distance of at least 14 km as a distinctive submarine fan. Stratigraphical studies of the on- shore deposits that make up this fan indicate an older sequence of block and ash flow deposits, within which occurs a distinctive vulcanian fall deposit. These are overlain, with no evidence of an intervening paleosol, by a sequence of ignimbrites containing welded horizons (ranging in thickness from around 4 m to 16m). The lack of fall deposits beneath the ignimbrites suggest they may have been formed by instantaneous continuous collapse of the eruption column. This whole succession is overlain by a series of planar and dune bedded pumiceous surge deposits with interbedded pumiceous lapilli fall and ash fall deposits, that extend laterally outside of the main area of ignimbrite deposition. Beds within this upper sequence often contain accretionary lapilli and gas cavities suggesting magma-water interaction. The youngest deposits from Morne Diablotins appear to be valley- fill deposits of both ignimbrite and block and ash flow. A comparison of the of the Grande Savane pyroclastic sequence with the Pointe Ronde (west coast) and Londonderry (east coast) pyroclastic flow fans will provide information on the eruptive history of this major Plinian episode.

  12. Reconstructing paleoenvironment in the west-tethyan continental domain at the Late Permian and Early Triassic from sedimentological and palaeobotanical data

    NASA Astrophysics Data System (ADS)

    Bercovici, Antoine; Bourquin, Sylvie; Broutin, Jean; Diez, José B.

    2010-05-01

    The final buildup of Pangea at the end of the Palaeozoic led to the formation of massive landmass unrivaled in later times. On a climatic perspective, the end of the Carboniferous ice age opened into a period of progressive warming, creating vast arid regions on land. The lower Triassic is the culmination of this trend, and represents a period where land vegetation is scarce or non-existent. The following work presents the palaeogeographical evolution of the north-western tethyan terrestrial domain (currently most of western Europe), re-evaluated by a sedimentological and palaeobotanical (megafloras and palynofloras) combined approach. Preservation condition required for fossilization is a limit for dating the upper Permian and lower Triassic sedimentary sequences. As the general climate underwent a major warming phase, the use of fossils as biostratigraphical and palaeoenvironmental tools becomes limited. In these conditions, sedimentary proxies linked to climate can be used instead as valuable correlation tools in continental sections. During the Early Permian, continental sedimentation was limited in a series of isolated endoreic basins, in between differences in preservation and floral assemblages can be observed. This partitionning, at the scale of western Europe, is mainly driven by the Variscan topography. However, the general evolution of Permian flora in the western tethyan domain is still linked at the first order to the global warming event. The general aridification of climates on Pangea led to profound modifications of floras long before the Permian/Triassic biotic crisis. In all sedimentary basins of the north-western tethyan domain, with the exception of the Germanic Basin, the Permian/Triassic transition is characterized by a lack of sedimentary deposition of variable time. This period of no record is associated with: (1) an angular uncomformity of increasing angle towards the axis of the Variscan range, (2) important sedimentary flux at the re-initiation of sedimentation during the Triassic, (3) periods of sedimentation stops indicated by palaeosols, (4) a switch in palaeocurrent direction for fluvial systems between the Permian and the Triassic and, (5) by sedimentary transit and bypass during the lower Triassic. All these observations imply the existence of a still active Variscan range, modifying palaeoclimatic conditions and controlling sedimentation in the end-Permian sedimentary basins of western Europe.

  13. Start-Up Meeting Mudrock Systems Research Laboratory

    E-print Network

    Texas at Austin, University of

    Ford (Cretaceous) sedimentology, stratigraphy, and geochemistry: Ruppel, Nance, Harbour 2:05 PM Sedimentology and geochemistry of the Jurassic Haynesville/Bossier system: Ursula Hammes. 2:30 PM Wilcox

  14. IU GEOLOGICAL SCIENCES graduate handbook appendices

    E-print Network

    Polly, David

    -7994 G524a pdpolly Geol Sci Professor LisaPratt Biogeochemistry,Sedimentology/ Stratigraphy 5-9203 MSBII Research Scientist Erika Elswick Geochemistry,Sedimentology, SedimentaryOreDeposits 5-2493 MSBII428

  15. Wednesday, March 14, 2007 MARS SEDIMENTS AND GEOCHEMISTRY: VIEW FROM THE SURFACE

    E-print Network

    Rathbun, Julie A.

    Golombek M. Parker T. Squyres S. W. Sullivan R. Structure and Sedimentology of the Western Margin of Erebus Crater, Meridiani Planum, Mars [#2235] The structure, stratigraphy and sedimentology of two outcrops

  16. Cenomanian Turonian facies and sequence stratigraphy, Bahloul Formation, Tunisia

    NASA Astrophysics Data System (ADS)

    Zagrarni, Mohamed Faouzi; Negra, Mohamed Hédi; Hanini, Amine

    2008-02-01

    The Cenomanian-Turonian Bahloul Formation in Tunisia consists of well-bedded dark grey limestones, with common local intercalations of marls and argillaceous limestones. In the Oued Bahloul section, the Bahloul Formation (28 m in thickness) directly overlies a massive bed (4 m), consisting of conglomeratic sandy limestone showing an incised base. In terms of sequences, the Oued Bahloul section shows that the Bahloul Formation is composed of deepening upward metric cycles, each comprising three units. Each cycle starts with a laminated dark grey limestone, progressively changing to argillaceous limestone, and terminates with bioturbated marls containing microfauna of the Whiteinella archaeocretacea biozone. This deepening upward cycle package, constituting the Bahloul Formation, is interpreted to be the expression of a transgressive interval directly overlying, in the Oued Bahloul area, a shelf margin wedge formed by the conglomeratic limestones. The transgressive interval ends with a maximum flooding surface (mfs) included within the filaments-rich facies. This mfs represents the upper boundary of the Bahloul Formation, which is directly overlain by a marly unit, the Annaba Member of the Kef Formation, assigned to the Helvetoglobotruncana helvetica biozone, indicating an early Turonian age. The filament event is one of four biosedimentary event horizons identified within the late Cenomanian-early Turonian interval in the Oued Bahloul section. From base to top, these four event horizons correspond to (1) the extinction of Rotalipora, (2) the Heterohelix shift, (3) the Whiteinella proliferation, and (4) the filament event. These events are recognized also in other areas in Tunisia and abroad, and we identify them here within sections preferentially located on the platform (to the south), in the basin (to the north) and especially within the transitional platform-basin environments (in Central Tunisia). Toward the SW, in Jebel Bireno, the Bahloul Formation is thinner (6 m) than in Oued Bahloul and wholly carbonate, and it was deposited in relatively shallower conditions (probably in an outer platform environment). In fact, organic-rich facies constituting the Bahloul Formation change to the south to open platform facies, in which planktonic microfauna are associated with benthonic foraminifera and rudists. However, toward the north (in the Bazina area, for example), the Bahloul facies changes to basinal marls rich in ammonites and planktonic foraminifera. Isotope analyses show that the main ?13C positive excursions coincide with transgressive and maximum flooding surfaces. The latter are commonly used in regional and global correlations.

  17. Magnetic stratigraphy and biostratigraphy of the Piacenzian (Upper Pliocene) at Monte San Nicola (Sicily)

    SciTech Connect

    Channell, J.E.T.; Sprovieri, R.; Di Stefano, E.

    1985-01-01

    During the Neogene, the Mediterranean was a rather unique biogeographic province. For this reason, first and last occurrences of Neogene species recorded in the Mediterranean region may not be synchronous with those recorded in the open oceans. This has important implications as most of the Neogene stage boundaries are defined on the basis of Mediterranean type sections. The most direct way to determine the relative timing of Mediterranean and open ocean datums is through correlation with the polarity time scale. Such correlations are not available for the Mediterranean Pliocene. The Trubi pelagic limestones and Monte narbone marls which characterize the SicilianPliocene are not ideal for magnetic stratigraphy due to weak remnant intensities and an ubiquitous normal polarity overprint. However, at Monte San Nicola, a magnetic stratigraphy has been resolved by stepwise demagnetization in small temperature increments. The upper and lower bounds of the Gauss Epoch, and the Mammoth and Kaena polarity events can be correlated to well defined planktonic foraminiferal and calcareous nannofossil datums. Hence the synchronism of these datums between the Mediterranean and the open ocean can be tested. The most notable discrepancy is in the last occurrence of G. margaritae which occurs at the base of the Gauss in most open marine sections, but is found at the top of the Gilbert at Monte San Nicola.

  18. Stratigraphy, geomorphology, geochemistry and hazard implications of the Nejapa Volcanic Field, western Managua, Nicaragua

    NASA Astrophysics Data System (ADS)

    Avellán, Denis Ramón; Macías, José Luis; Pardo, Natalia; Scolamacchia, Teresa; Rodriguez, Dionisio

    2012-02-01

    The Nejapa Volcanic Field (NVF) is located on the western outskirts of Managua, Nicaragua. It consists of at least 30 volcanic structures emplaced along the N-S Nejapa fault, which represents the western active edge of the Managua Graben. The study area covers the central and southern parts of the volcanic field. We document the basic geomorphology, stratigraphy, chemistry and evolution of 17 monogenetic volcanic structures: Ticomo (A, B, C, D and E); Altos de Ticomo; Nejapa; San Patricio; Nejapa-Norte; Motastepe; El Hormigón; La Embajada; Asososca; Satélite; Refinería; and Cuesta El Plomo (A and B). Stratigraphy aided by radiocarbon dating suggests that 23 eruptions have occurred in the area during the past ~ 34,000 years. Fifteen of these eruptions originated in the volcanic field between ~ 28,500 and 2,130 yr BP with recurrence intervals varying from 400 to 7,000 yr. Most of these eruptions were phreatomagmatic with minor strombolian and fissural lava flow events. A future eruption along the fault might be of a phreatomagmatic type posing a serious threat to the more than 500,000 inhabitants in western Managua.

  19. Gold placer and Quaternary stratigraphy of the Jabal Mokhyat area, southern Najd Province, Kingdom of Saudi Arabia

    USGS Publications Warehouse

    Schmidt, D.L.; Puffett, W.P.; Campbell, W.L.; Al-Koulak, Z. H.

    1981-01-01

    An ancient gold placer at Jabal Mokhyat (lat 20?12.2'N., long 43?28'E.), about 90 km east of Qalat Bishah in the southern Najd Province, Kingdom of Saudi Arabia, was studied in 1973. Seven hundred and twenty-eight samples in 25 measured sections were collected along trenches and pits 2.5 m in depth and 2,600 m in total length. Alluvium was thicker than the excavation depth along about 50 percent of the trench length. The average gold content was 4.4 mg per m3, and the highest grade trench contained 40 mg gold per m 3. Because fine particulate gold is rare in the alluvium, a few large particles, 1 to 5 mm in diameter, greatly affected the sampling results. The ancient placer diggings are in small headwater wadis distributed over a 30-km 2 area, and the total dug area is about 1.2 km2. The placer produced an estimated 50 kg of gold and was worked about 2,600 + 250 years ago. The potential for a present-day placer operation is small. The gold is sparsely distributed in locally derived, flood-deposited, immature gravels throughout a stratigraphic section that consists of 1) calichified, saprolitic bedrock of Precambrian age; 2) basal, intensely calichified, saprolitic gravel (0-3 m thick) of Pleistocene age; 3) disconformable, slightly consolidated gravel and sand (0-1 m thick) of late Pleistocene age containing sparse, disseminated caliche; 4) firm loessic silt (0-1 m thick) of early Holocene age; and 5) loose sand and gravel (0.3-1 m thick) of late Holocene age. The loessic silt accumulated during the Holocene pluvial. The top of the loessic silt unit is dated at about 6,000 years B.P. by using charcoal from hearths of ancient man. Following the Holocene pluvial, the climate became arid, and extreme desiccation resulted in abundant eolian sand that progressively diluted the late Holocene gravels. The remnants of the pre-Holocene stratigraphy suggest similar climatic cycles during the Pleistocene. Abundant, sparsely mineralized, gold-bearing quartz veins (0-1 m wide) were the source of the placer gold. These late Proterozoic veins have hydrothermally altered wall-rock zones (1-5 m wide). The veins are dispersed over an area of 50 km 2. Though many veins were prospected in ancient times and some were slightly worked, only the Mokhyat ancient mine, located on a quartz-vein zone 30 m wide by 200 m long, was extensively worked. The quartz contains chalcopyrite, galena, sphalerite, tetrahedrite, an unidentified bismuth mineral, and small amounts of dispersed gold. The fissure quartz veins lie at the complexly splayed, terminal end of a small northwest-trending Najd fault that elsewhere along strike has ii km of left-lateral displacement. Most large veins are in north-trending vertical fractures where the stresses were distributed along an older, north-trending structural grain in andesitic greenstone terrane. Subhorizontal fracture sets contain conspicuous, well-developed gold-bearing quartz veins and associated alteration zones. These attest to the shallowness and youthfulness of mineralization during latest Precambrian time. Late Precambrian granitic plutons (625-600 m.y. old) had been deeply eroded before the gold minerals were emplaced; hence, the gold is not related to granitic plutonism. Abundant, widely distributed diabasic dikes associated with the Najd faulting event of latest Precambrian age were probably the heat source for the hydrothermal convection system and possibly the source of the gold.

  20. Excursions and Paleointensity: integration of magnetic and oxygen isotope stratigraphies

    NASA Astrophysics Data System (ADS)

    Channell, J. E.

    2008-12-01

    Although the study of magnetic excursions began 40 years ago, the documentation of magnetic excursions has gained strength in the last 10 years ago with increased and improved recovery of high sedimentation rate records from the deep sea. Artifacts of remanence acquisition and coring deformation have led to numerous spurious "excursions" being added to the excursion inventory. This is particularly true for the Arctic oceans where lack of traditional stratigraphic tools leads to a high degree of freedom in the correlation and labeling of "excursions", and new data implicate authigenic greigite as the carrier of "excursional" remanence in some Arctic cores. Nonetheless, magnetic excursions with durations of a few kyr, are characteristic of the Brunhes and Matuyama chrons with about 7 excursions now firmly established in each polarity chron. The better quality (least smoothed) excursion records exhibit close to 180 degrees of directional change, and are globally manifest, implying that excursions should be considered as short-lived polarity chrons or "microchrons". As excursions are certainly not unique to the Brunhes and Matuyama chrons, we might expect at least 5 excursions for each 1 Myr of reversal history or more than 300 during the Cenozoic, thereby putting them at odds with a Poisson distribution of chron durations, implying that excursions are not part of a continuum of geomagnetic behavior with polarity chrons. The fact that excursion duration tends to lie close to estimates for the magnetic diffusion time of the inner core favors the model of Gubbins (1999) in which outer core reversal must perpetuate long enough (the uncommon case) for diffusion through the inner core to lead to long-lived field reversal. A new stack of relative paleointensity (RPI) data for the last 1.5 Myr utilizes 11 records, mainly from the North Atlantic but also including records from the South Atlantic and Pacific oceans. IODP Site 1308 from the North Atlantic (re-drill of DSDP Site 609) is used as the correlation target as it possesses both high quality benthic oxygen isotope and RPI records over the entire 1.5 Myr interval. The stack differs from previous stacks in that it utilizes only RPI records that have accompanying oxygen isotope data. The Match protocol of Lisiecki and Lisiecki (2002) is used to simultaneous optimize the correlation of RPI and accompanying isotope records thereby reducing the degree of freedom associated with correlation of RPI (or isotope) records alone. The resulting oxygen isotope stack has comparable resolution to the LR04 stack, and the RPI stack provides a useful reference template, with improved definition of 10,000-yr scale features relative to earlier stacks. Power at orbital periods that has been detected in many RPI records is virtually absent in the stack, supporting the contention that orbital power in RPI records is due to lithologic contamination of some individual records. In this new stack, excursions and reversals occupy times of low geomagnetic paleointensity, indeed, all the more extreme RPI minima correspond to ages of adequately documented excursions or reversals implying that geomagnetic intensity has a threshold that triggers both excursions and reversals. The coupling of RPI and oxygen isotope records, and the recognition of RPI minima that feature excursions, provides a new template for global stratigraphic correlation that promises not only to improve stratigraphic resolution, into the realm of interest for the study of "abrupt" climate change, but also to liberate (benthic) oxygen isotope data from their chronological role and allow their regional environmental characteristics to be fully utilized.

  1. Submersible study of mud volcanoes seaward of the Barbados accretionary wedge: sedimentology, structure and rheology

    Microsoft Academic Search

    Sophie Lance; Pierre Henry; Xavier Le Pichon; Siegfried Lallemant; Hervé Chamley; Frauke Rostek; Jean-Claude Faugères; Eliane Gonthier; Karine Olu

    1998-01-01

    In 1992, the Nautile went to a mud volcano field located east of the Barbados accretionary wedge near 13 ° 50N. Using nannofossil analysis on cores, we determined the sedimentation rate, and provided a new estimation of the age of the mud volcanoes (750,000 years for the oldest one). Six structures have been explored with the submersible Nautile, and manifestations

  2. Revised stratigraphy and reinterpretation of the Miocene Pohang basinfill, SE Korea: sequence development in response to tectonism and eustasy in a back-arc basin margin

    NASA Astrophysics Data System (ADS)

    Sohn, Y. K.; Rhee, C. W.; Shon, H.

    2001-09-01

    The Miocene Pohang Basin is a pull-apart basin formed along the eastern continental margin of Korea (ECMK) during the back-arc opening of the East Sea (Sea of Japan). The basin is filled by more than 1 km thick, nonmarine to deep-marine strata. These strata show extreme vertical and lateral lithofacies changes and have caused decades-long controversies on their nature and stratigraphy. Previous sedimentological studies suggest that the basinfill was deposited by a series of contemporaneously developed depositional systems, including fan delta, prodelta, slope apron, and basin plain. Detailed mapping and magnetotelluric surveying show, however, that the basinfill is composed of several packages of strata (sequences) that are bounded by distinct and laterally persistent stratigraphic discontinuities (sequence boundaries). This suggests that the depositional systems in the Pohang Basin developed sequentially rather than contemporaneously. Six packages of strata are identified in the basin: a nonmarine to shallow marine (transgressive) sequence (Sequence 1), a Gilbert-type-delta conglomerate (Sequence 2), and alternations of submarine conglomerates and hemipelagic mudstones (Sequences 3-6). The conglomerates and hemipelagic mudstones of the latter four sequences are interpreted to represent lowstand depositional systems (slope apron, submarine fan, and high-gradient delta) and condensed intervals, respectively. Compilation of geochronologic, paleomagnetic, and biostratigraphic data suggests that Sequence 1 formed during the gradual subsidence of the ECMK prior to 17 Ma, whereas Sequence 2 formed in response to abrupt downfaulting of the Pohang Basin at about 17 Ma. Both sequences are interpreted to have developed in response to the early Miocene back-arc-opening tectonism of the East Sea. On the other hand, Sequences 3-6 formed between 17 and about 10.5 Ma. The Pohang Basin was subject to only minor tectonism during this period and could record global sea-level fluctuations. We suggest that the four alternations of conglomerates (lowstand systems) and hemipelagic mudstones (condensed intervals) resulted most probably from the 3rd-order glacioeustatic cycles during the middle Miocene. This finding implies that the signatures of global sea-level fluctuations can be deciphered from a tectonically active sedimentary basin if the timing of regional tectonic development is well constrained, and the global sea-level chart of Haq et al. ( Haq, B.W., Hardenbol, J., Vail, P.R., 1987, Chronology of fluctuating sea levels since the Triassic. Science 235, 1156-1167; Haq, B.U., Hardenbol, J., Vail, P.R., 1988. Mesozoic and Cenozoic chronostratigraphy and eustatic cycles. In: Wilgus, C.K., Hastings, B.S., Posamentier, H., Van Wagoner, J., Ross, C.A., Kendall, C.G.S.C. (Eds.), Sea-Level Changes: an Integrated Approach: Soc. Econ. Paleont. Mineral. Spec. Publ. 42, pp. 71-108) may serve as a guide to basinfill interpretation even in tectonically active sedimentary basins.

  3. Integrated stratigraphy of the Early Miocene lacustrine deposits of Pag Island (SW Croatia): Palaeovegetation and environmental changes in the

    E-print Network

    Utrecht, Universiteit

    Integrated stratigraphy of the Early Miocene lacustrine deposits of Pag Island (SW Croatia Orbital forcing Long-lived lakes Dinaride Lake System Early Miocene Croatia An integrated stratigraphic and that it corresponds to the Burdigalian Stage of the Early Miocene, and the regional Karpatian Stage of the Central

  4. Stratigraphy and Subaerial Exposure of Late Quaternary Tidal Deposits in Haenam Bay, Korea (South-eastern Yellow Sea)

    Microsoft Academic Search

    Y. A. Park; D. I. Lim; B. K. Khim; J. Y. Choi; S. J. Doh

    1998-01-01

    Late Quaternary stratigraphy of the coastal deposits in Haenam Bay, south-western coast of Korea (south-eastern Yellow Sea) consists of two depositional units: a Holocene intertidal deposit (Unit I), and an underlying Late Pleistocene tidal deposit (Unit II), both of which are distinguished by distinct unconformity. The yellowish colour and more consolidated and oxidized nature are characteristics of the sediments in

  5. Seismic stratigraphy, buried beach ridges and contourite drifts: the Late Quaternary history of the closed Lago Cardiel basin,

    E-print Network

    Gilli, Adrian

    of the closed Lago Cardiel basin, Argentina (49°S) ADRIAN GILLI1 *, FLAVIO S. ANSELMETTI*, DANIEL ARIZTEGUI stratigraphic analysis of a closed lake basin, Lago Cardiel, in southernmost South America are reported. Very with the formation of beach ridges preserved in the lake stratigraphy on the floor of the modern Lago Cardiel at four

  6. Reconstructions of western Ross Sea palaeo-ice-stream grounding zones from high-resolution acoustic stratigraphy

    E-print Network

    Howat, Ian M.

    with Oxygen Isotope Stage 2 (Hilfinger 1995; Domack et al. 1999). Acoustic profiles, swath bathymetry and coreReconstructions of western Ross Sea palaeo-ice-stream grounding zones from high-resolution acoustic of western Ross Sea palaeo-ice-stream ground- ing zones from high-resolution acoustic stratigraphy. Boreas 32

  7. Apparent polar wander and reversal stratigraphy of the Palaeo-Mesoproterozoic southeastern McArthur Basin, Australia

    Microsoft Academic Search

    M. Idnurm; J. W. Giddings; K. A. Plumb

    1995-01-01

    Approximately 1800 samples from volcanic, clastic and carbonate sequences of the southeastern McArthur Basin in northern Australia were analysed palaeomagnetically to define in detail the Australian apparent polar wander path (APWP) for a period centred at ? 1670 Ma and to develop a Proterozoic reversal stratigraphy for correlation and dating. Twelve palaeomagnetic poles are interpreted as primary, including two that

  8. High-Resolution Carbon Isotope Stratigraphy, Pennsylvanian Snaky Canyon Formation, East-Central Idaho: Implications for Regional and Global Correlations

    E-print Network

    Jolley, Casey

    2012-07-16

    Nearly 550 samples of fine grained carbonates, collected every 0.5 to 1.0 m from the Bloom Member of the Snaky Canyon Formation at Gallagher Peak, Idaho, were analyzed to determine the high-resolution carbon isotope stratigraphy. To constrain...

  9. Sequence Stratigraphy of the Dakota Sandstone, Eastern San Juan Basin, New Mexico, and its Relationship to Reservoir Compartmentalization

    SciTech Connect

    Varney, Peter J.

    2002-04-23

    This research established the Dakota-outcrop sequence stratigraphy in part of the eastern San Juan Basin, New Mexico, and relates reservoir quality lithologies in depositional sequences to structure and reservoir compartmentalization in the South Lindrith Field area. The result was a predictive tool that will help guide further exploration and development.

  10. Cosmogenic nuclide age constraints on Middle Stone Age lithics from Niassa, Mozambique

    NASA Astrophysics Data System (ADS)

    Mercader, Julio; Gosse, John C.; Bennett, Tim; Hidy, Alan J.; Rood, Dylan H.

    2012-07-01

    The late phases of the Middle Stone Age (MSA) in the East African Rift System (EARS) are known for their evolutionary shifts and association with bottlenecks, transcontinental expansion, and climatic fluctuations. The chronology of MSA sites contemporaneous with these eco-demographic upheavals is uncertain because of the scarcity of datable sites and the poor understanding of their depositional and erosional histories. We apply terrestrial cosmogenic nuclide dating in a stratigraphic section with a complex exposure history to the study of the Luchamange Beds, a widespread sedimentological unit underlying MSA sites from the shores of Lake Niassa (Mozambican EARS). We use an innovative approach, which may be applicable elsewhere, to calculate their age using a Monte Carlo-based Bayesian model that links depth profiles of 26Al and 10Be, and uses other geomorphic and cosmogenic nuclide age constraints on episodic erosion and burial. The age of the basal Luchamange Beds is 42 + 77/-15 ka, and the MSA occupation on top is 29 + 3/-11 ka. These dates suggest temporal overlap between MSA and the earliest Later Stone Age and diversity in cultural manifestations at the end of the MSA.

  11. Comparative Analysis of Biogeographic, Sedimentologic and Paleomagnetic Data and the Geodynamics of Terranes of Northeast Asia in Late Permian

    NASA Astrophysics Data System (ADS)

    Biakov, A.; Kolosev, E.

    2004-12-01

    We present the first consistent model of the relative locations of the most important tectonic structures in Northeast of Asia for Late Paleozoic time. This model is based on comparative analysis of paleomagnetic, sedimentologic and biogeographic data. Results of research by the authors and critically reviewed data of the other researchers are used. The current paleomagnetic data for Permian rocks from the Northeast region still remain scanty and are practically non-existent for some tectonic structures such as the Okhotsk microcontinent. Nevertheless we believe that it can be shown that there was no major (thousands of kilometers) horizontal motion between the separate tectonic blocks of Yana-Kolyma fold-and-thrust area, at least starting Middle Paleozoic. In paleogeographic terms Northeast Asia in the Permian represented a system of marine basins of various types. Okhotsk microcontinent was outboard from the Siberian craton to the southeast (present day coordinates). A system of deepwater marginal type marine basins lay to the east of the Siberian craton. The Koni-Taigonos volcanic arc was along the south edge, and. its erosion products formed deepwater fore-arc basins. Significant differences between the Permian bivalve communities on the Omolon microcontinent and contemporary communities of Verkhoyansk indicate the existence of the deepwater Ayan-Yuryakh trough basin. The strata of the latter are characterized as thick (up to 7 km) flysch deposits plus thick diamictites. Paleobiogeographic studies show that major biogeographic units can be clearly distinguished in the Verkhoyansk-Okhotsk on one side and Kolyma-Omolon biochores on the other, which can be currently ranked as sub regions. Verkhoyansk-Okhotsk sub region includes Verkhoyansk epicontinental sea shelf and the Okhotsk microcontinent shelf. These can be further subdivided into a number of provinces. The Kolyma-Omolon sub region includes continental shelves of the Omolon, Omulevka, Prykolyma microcontinents and the Koni-Taigonos arc. The degree of diversity of these two biochores is so great that it requires separate development and indicates the existence of a major biogeographical barrier during the Permian. The distinctions between the Verkhoyansk-Okhotsk and Kolyma-Omolon sub regions are found througout the whole Permian and over other faunal groups such as brachiopods and ammonites as well as over the rest of bivalve taxons. Multiple use of biogeographic, sedimentologic and paleomagnetic materials including new original data on sedimentology and paleomagnetism allowed a model of the relative positions of the basic tectonic structures of Verkhoyansk-Kolyma fold-and-thrust area in the second half of the Permian. . These studies have been supported by the Russian Foundation for Basic Research, grant N 03-05-96012-Arctic and Far East Branch Russian Academy of Sciences, Grant N 04-3-A-08-014.

  12. Workshop on Techtonic Evolution of Greenstone Belts

    NASA Technical Reports Server (NTRS)

    Dewit, M. J. (editor); Ashwal, Lewis D. (editor)

    1986-01-01

    Topics addressed include: greenstone belt externalities; boundaries; rock terranes; synthesis and destiny; tectonic evolution; rock components and structure; sedimentology; stratigraphy; volcanism; metamorphism; and geophysics.

  13. Imaging the water column using sediment echosounder, ADCP and multibeam echosounder - new possibilities for sedimentological, biological and oceanographic studies

    NASA Astrophysics Data System (ADS)

    Preu, B.; Spiess, V.; Schwenk, T.; Haberkern, J.; Bergmann, F.; Max, L.; Iversen, M.; Fischer, G.; Hanebuth, T.; Krastel, S.; Hernández-Molina, F.; Schneider, R. R.

    2011-12-01

    Detection and characterization of nepheloid layers, which are often bound to water mass interfaces, and benthic boundary layers are today mostly restricted to sampling and optical measurements allowing quantification of particles at one single location. However, spatial analysis of the lateral variability of suspension clouds would offer remarkable new insight into the dynamics of large scale marine sediment dispersal systems. The understanding of along-slope and down-slope sedimentary processes and their deposits could be significantly improved by mapping of particle layers. Additionally, mapping of particle clouds in time and space would allow inferring on plankton concentrations and their migration in the water column, which would improve the understanding of the biological pump. Whereas spatial measurements using sampling and optical methods are time intensive and therefore, hard to accomplish, new developments in hull-mounted high-resolution hydro-acoustic instruments allow to store and process acoustic data, imaging the water column and thereby offer an easy and time saving alternative. We will present preliminary results of an integrated acoustic approach to image and analyze nepheloid layers and comparable particle clouds. We collected multiple hydro-acoustic data sets including 18 kHz echosounder (PARASOUND) and both 38 and 75 kHz ADCP (RD INSTRUMENTS) data in current controlled and high accumulating sedimentary regimes. Additionally, multibeam echosounder measurements including water column imaging were carried out using the new EM 122 (KONGSBERG). First, we present data off SE-Africa linking the oceanographic and sedimentological framework, in particular the impact of a lee eddy in the source region of the Agulhas Current on contouritic deposits. Secondly, data collected off Mauritania are used to determine the sensitivity of 18, 38 and 75 kHz to particle sizes in relation to optical estimated concentrations. Further, the vertical plankton migration is analyzed during day and night cycles. Thirdly, we show water column data recorded off Galicia using the EM122 multibeam echosounder and will present preliminary estimations on data quality and potential for further analysis. Similar studies are conducted using data collected off northern Argentina/Uruguay and in the Gulf of Cadiz. We will present an overview about all studies to demonstrate that nepheloid layers are frequently triggered and distributed along water mass interfaces due to density contrasts and associated processes (internal waves, tidals, etc). Indirect detection by hydro-acoustic methods would open a new important research field for decoding variability of waters masses and offer new tools for future multidisciplinary research enhancing our understanding of sedimentological, biological and oceanographic processes.

  14. Sedimentology and permeability architecture of Atokan Valley-fill natural gas reservoirs, Boonsville Field, north-central Texas

    SciTech Connect

    Burn, M.J.; Carr, D.L. [Univ. of Texas, Austin, TX (United States); Stuede, J. [Scientific Measurement Systems, Inc., Austin, TX (United States)

    1994-09-01

    The Boonsville {open_quotes}Bend Conglomerate{close_quotes} gas field in Jack and Wise counties comprises numerous thin (10-20 ft) conglomerate sandstone reservoirs within an approximately 1000-ft-thick section of Atokan strata. Reservoir sandstone bodies commonly overlie sequence-boundary unconformities and exhibit overall upward-fining grain-size trends. Many represent incised valleyfill deposits that accumulated during postunconformity baselevel rise. This stratal architecture is repeated at several levels throughout the Bend Conglomerate, suggesting that sediment accumulation occurred in a moderate-to low-accommodation setting and that base level fluctuated frequently. The reservoir units were deposited by low-sinuosity fluvial processes, causing a hierarchy of bed forms and grain-avalanche bar-front processes to produce complex grain-size variations. Permeability distribution is primarily controlled by depositional factors but may also be affected by secondary porosity created by the selective dissolution of chert clasts. High-permeability zones (up to 2.8 darcys) are characterized by macroscopic vugs comprised of clast-shaped moldic voids (up to 5 mm in diameter). Tight (low-permeability) zones are heavily cemented by silica, calcite, dolomite, and ankerite and siderite cements. Minipermeameter, x-radiograph, and petrographic studies and facies analysis conducted on cores from two Bend Conglomerate reservoirs illustrate the hierarchy of sedimentological and diagenetic controls on permeability architecture.

  15. Sedimentology and permeability architecture of Atokan Valley-Fill natural gas reservoirs, Boonsville Field, North-Central Texas

    SciTech Connect

    Burn, M.J.; Carr, D.L. [Univ. of Texas, Austin, TX (United States); Stuede, J. [Scientific Measurement Systems, Inc., Austin, TX (United States)

    1994-12-31

    The Boonsville {open_quotes}Bend Conglomerate{close_quotes} gas field in Jack and Wise Counties comprises numerous thin (10-20 ft) conglomeratic sandstone reservoirs within an approximately 1,000-ft-thick section of Atokan strata. Reservoir sandstone bodies commonly overlie sequence-boundary unconformities and exhibit overall upward-fining grain-size trends. Many represent incised valley-fill deposits that accumulated during postunconformity base-level rise. This stratal architectures is repeated at several levels throughout the Bend Conglomerate, suggesting that sediment accumulation occurred in a moderate- to low-accommodation setting and that base level fluctuated frequently. The reservoir units were deposited by low-sinuosity fluvial processes, causing a hierarchy of bed forms and grain-avalanche bar-front processes to produce complex grain-size variations. Permeability distribution is primarily controlled by depositional factors but may also be affected by secondary porosity created by the selective dissolution of chert clasts. High-permeability zones ({approximately}2.8 darcys) are characterized by macroscopic vugs composed of clast-shaped moldic voids ({approximately}5 mm in diameter). Tight (low-permeability) zones are heavily cemented by silica, calcite, dolomite, and ankerite and siderate cements. Minipermeameter, x-radiography, and petrographic studies and facies analysis conducted on cores from two Bend Conglomerate reservoirs (Threshold Development Company, I.G. Yates 33, and OXY U.S.A. Sealy {open_quotes}C{close_quotes} 2) illustrate the hierarchy of sedimentological and diagenetic controls on permeability architecture.

  16. Stratigraphy and hydrologic conditions at the Brookhaven National Laboratory and vicinity, Suffolk County, New York, 1994-97

    USGS Publications Warehouse

    Scorca, Michael P.; Dorsch, William R.; Paquette, Douglas E.

    1999-01-01

    Brookhaven National Laboratory (BNL) has installed many test borings as part of an effort to delineate the extent of ground-water contamination at the site. In 1994, the U.S. Geological Survey began a study in cooperation with BNL to define the stratigraphy in the 28-square-mile area encompassing BNL, and to monitor ground-water levels in the 300 squaremile area of central Suffolk County that surrounds BNL. The uppermost geologic units at BNL are of Pleistocene age. These sediments are underlain unconformably by the Matawan Group-Magothy Formation, undifferentiated (referred to as the Magothy Formation), of Cretaceous age, which typically consists of light- to dark-gray, variably sorted sand interbedded with light- to dark-gray clay layers; it also contains beds of grayish-brown to brownish-gray sand. Bed thicknesses differ substantially within each boring and tend to be laterally discontinuous as a result of their terrestrial deltaic depositional environment, although a prominent clay unit, referred to as the ?grayish-brown clay? in this report, was encountered at many borings. Pollen-sample analyses confirm that this unit is of Cretaceous age and is the uppermost unit of Cretaceous sediments in several parts of the study area. The upper surface of the Cretaceous deposits is irregular within the 28-square-mile study area and has relief of about 120 feet. Several prominent channels and ridges in the surface are aligned generally northwest-southeast. The Cretaceous surface beneath BNL is characterized more by local erosional features than by the regional cuesta shape that was suggested by previous authors. The overlying Pleistocene-aged units include (1) a sand layer overlain by the Gardiners Clay, (2) the Gardiners Clay, and (3) upper Pleistocene deposits, which include the Upton unit, glacial outwash, glaciolacustrine deposits, and terminal moraine deposits. The sand unit below the Gardiners Clay was the first Pleistocene unit to be deposited atop the irregular surface of the Cretaceous deposits in this area. The Gardiners Clay was deposited during a major rise in sea level as the sea encroached into parts of the present-day BNL study area. The shallow part of the upper Pleistocene deposits generally consists of light-brown sand and gravel but overlies green to grayish-green, variably sorted sand, silt, and clay at altitudes of 50 to 70 feet below sea level in some parts of the study area. This lower part of the upper Pleistocene deposits in the study area was referred to by previous investigators as the unidentified unit and has been designated as the Upton unit in this report. The discharge of ground water to the Peconic and Carmans Rivers locally affects the water-table configuration. The main ground-water divide on Long Island is about 0.5 miles north of the site; a secondary divide originates near the start of flow of the Peconic River and extends east-southeastward toward the South Fork. The water-table configuration on the BNL site is affected by pumping from supply wells and remediation wells, by infiltration of the water through recharge basins, by discharge from the sewage-treatment plant, and by local near-surface clay units. The horizontal hydraulic gradient at BNL typically is 0.001 foot per foot but can steepen near recharge basins and pumping wells. Vertical flow gradients within the upper Pleistocene deposits (upper glacial aquifer) were as large as 0.007 foot per foot (downward) in the northern part of BNL and were negligible in the southern part. Downward vertical gradients between the lower part of the upper glacial aquifer and the upper part of the Magothy Formation (Magothy aquifer) were about 0.018 foot per foot throughout the site.

  17. Seismic stratigraphy of the East Antarctic margin: a record of Cenozoic environmental changes

    NASA Astrophysics Data System (ADS)

    Leychenkov, German; Guseva, Julia

    2010-05-01

    We have analyzed more than 120000 km of MCS sections collected on the East Antarctic margin (EAM) from 7E to 142E to correlate seismic stratigraphy with Antarctic glacial history predicted from drilling data and deep-sea proxy records, and to estimate what sort of information about ice sheet behavior and paleoceanographic conditions is contained in seismic records. Most of analyzed MCS lines are located on the continental rise and only the Prydz Bay (PB) shelf was studied in details. Five mayor horizons numbered up-section from "1" to "5" are identified in sedimentary cover of deep water EAM (continental rise). Horizon "1" and "2" are correlated with asynchronous Gondwana breakup and early post-breakup events, respectively; horizons "3", "4" and "5" are proposed to be isochronous surfaces related to Late Cenozoic paleoenvironmental transitions. The distinguishing feature of EAM sedimentary cover is the clear upward change in reflection pattern across horizons "3" and "4" that separates a lower sedimentary unit with mostly parallel reflectors from an upper one consisting of variety of acoustic facies typical of active down-slope and along slope processes. This change is associated with the arrival of the ice sheet to the Antarctic margin and significant increase in sedimentary input to deep water regions. Major results of our study are following: 1) Widespread development of channel-levee systems and other facies related to mass-wasting on the EAM is observed above horizon "4" and this interface is proposed to mark continental-scale Antarctic glaciation in the Early Oligocene. However, earliest signs of active down-slope processes are revealed on the Wilkes Land margin (WLM) above horizon "3" and we infer that this margin was glaciated first, probably in the Late Eocene. Under the temperate climate condition debris was delivered to the slope and rise by glaciers (which flowed from central Antarctica via Aurora Subglacial Basin) and abundant melt-water. The rate of sedimentation (debris flux to the deep-water area) on the western WLM during the Late Eocene was anomalous. Some other parts of EAM show evidence of fluvial deposition and contourite drifts development at this time. During the Oligocene the rate of sedimentation on EAM was changeable ranging from 30 to 100 m/m.y. implying that ice sheet dynamics were not uniform over the space. 2) Horizon "5" is well defined on the margin between 35E and 100E where it denotes wider development of channel/levee systems and contourite drifts, and less distinctive on the other part of the EAM. The age of horizon "5" is estimated to be about 24 Ma. The rate of Oligocene glacial marine sedimentation on the continental rise is calculated to be 40-60 m/m.y. but it is twice as much off western PB and on western WLM. 3) The rate of sedimentation during the Early-Middle Miocene was 80-100 m/m.y. off PB and on the western WLM and a little less on the other part of EAM. At about Middle Miocene, sedimentation rates on the continental rise decreased dramatically. Shelf progradation was active but depocenters began to shift landward from the continental rise. During post-Early Pliocene time, rates of sedimentations on the rise are minimal and focused mostly on the continental slopes; shelves show local aggradation (shelf banks), erosion, trough-mouth fans (locally) and progradation. 4) Thickness of syn-glacial sediments on EAM averages 1.2-1.5 km but off PB and on western WLM it amounts to 2.5 km. These areas correlate with places where present-day ice discharge is highest. The correlation points to high sediment (and ice) flux in the same areas from the Early Oligocene to the Middle Miocene. Structure of buried and modern submarine channels in a post-Early Oligocene strata and their evolution through time are different along the EAM and depend mostly on activity of down-slope currents and turbidite flows.

  18. Multiple Episodes of Recent Gully Activity Indicated by Gully Fan Stratigraphy in Eastern Promethei Terra, Mars.

    NASA Astrophysics Data System (ADS)

    Schon, S.; Head, J.; Fassett, C.

    2008-09-01

    Introduction Gullies are considered among the youngest geomorphic features on Mars based upon their stratigraphic relationships, superposition on steep slopes and distinctive morphology in unconsolidated sediment. Multiple formation hypotheses have been proposed, which can be divided into three broad classes: entirely dry mechanisms (e.g., [1,2]), wet mechanisms invoking groundwater or ground ice (e.g., [3,4]) and wet mechanisms invoking surficial meltwater (e.g., [5,6,7,8]). It has been difficult to differentiate between these hypotheses based upon past observations and it remains possible that gullies are polygenetic landforms. This study presents stratigraphic relationships in the depositional fan of a crater wall gully system that suggest: (1) multiple episodes of alluvial fan-style deposition, (2) very recent depositional activity that is younger than a newly recognized rayed crater, and (3) surficial snowmelt as the most likely source of these multiple episodes of recent gully activity. Gully-Fan Stratigraphy In Eastern Promethei Terra an ~5 km-diameter crater is observed with a well-developed gully system (Fig. 1) and several smaller gullies in its northnortheast wall. The large gully system (composed of a small western gully and larger eastern gully) shows evidence for incision into the crater wall country rock and has multiple contributory sub-alcoves and channels. The depositional fan associated with this gully system is bounded on its western side by a small arcuate ridge swell that is not observed on the eastern side of the fan. This ridge is interpreted as a moraine-like structure that may have bounded a glacially-formed depression into which the fan is deposited [8]. Similar depressions with bounding ridges are commonly observed in this latitude band (~30-50°S) in association with deeply incised gully alcoves [9,10,11]. This gully fan is composed of multiple lobes with distinct lobe contacts, incised channels, and cut-andfill deposits - all features similar to those seen in terrestrial alluvial fans [12,13]. The western portion of the fan is contained within the depression, while the younger eastern portion overlies and obscures any potential evidence of the ridge structure. A very striking and unusual feature of this gully fan is the large number of superposed impact craters; due to their density and similar diameter, we interpret these to be secondary craters from a large nearby primary impact crater. The depositional lobes of the fan can be divided into two groups: 1) those that predate the secondary crater population and 2) younger lobes that are superposed on the secondary craters. Numerous secondary craters (~1-25 m-diameter) superpose the lowermost stratigraphic lobe (Fig. 1, A), while at least three younger lobes (Fig. 1, C1, D1, and D2) directly superpose the cratered lobe. The emplacement date of these secondaries provides a robust maximum age for the youngest lobes of this fan, and therefore the most recent fluvial activity of the gully. Most gullies either have no superposed impact craters [3,7] or are too small to date with any certainty using crater counts [14]. Therefore, locating and dating the parent impact crater of these secondaries is critical to constrain the chronology and origin of gully systems. Rayed-Crater Source of the Secondary Craters Regional reconnaissance for the origin of the secondary craters led to the discovery of a previously unidentified rayed crater complex (consisting of an ~18 km-diameter outer crater and an ~7 km-diameter inner crater) approximately 175 km southwest of the gully system. Distinctive rays are observed in THEMIS nighttime thermal inertia data, but are not observable as albedo contrasts in THEMIS visible data, consistent with other identifications of young rayed craters on Mars [15,16]. The rims of both craters are distinct and consistent with the morphology of very young impact craters on Mars. The inner crater has a greater depth to diameter ratio than the outer crater (0.121 compared to 0.073), consistent with young Martian craters [17]. Both the ou

  19. K/T boundary stratigraphy: Evidence for multiple impacts and a possible comet stream

    NASA Technical Reports Server (NTRS)

    Shoemaker, E. M.; Izett, G. A.

    1992-01-01

    A critical set of observations bearing on the K/T boundary events were obtained from several dozen sites in western North America. Thin strata at and adjacent to the K/T boundary are locally preserved in association with coal beds at these sites. The strata were laid down in local shallow basins that were either intermittently flooded or occupied by very shallow ponds. Detailed examination of the stratigraphy at numerous sites led to the recognition of two distinct strata at the boundary. From the time that the two strata were first recognized, E.M. Shoemaker has maintained that they record two impact events. We report some of the evidence that supports this conclusion.

  20. Learning how to use resistivity soundings for interpretation of subsurface stratigraphy

    NSDL National Science Digital Library

    Remke Van Dam

    Students will be presented with a problem; that is to determine the general characteristics (stratigraphy, water table depth) of a heterogeneous deposit (glacial till south of the MSU campus or proglacial sediments south of Ludington, MI) using electrical resistivity methods. The project consists of three separate activities: 1) use laboratory experiments to measure the relationship between soil water content and electrical resistivity for different soil samples obtained from the sites (2-3 samples per group), 2) use simple modeling software to calculate the resistivity response for simple geological models, based on information from well logs and the results of the laboratory measurements, and 3) design (min-max a-spacing and stepsize, based on the forward modeling results), execute, and analyze a field sounding experiment. Results will be summarized in a report and presented in class. Uses geophysics to solve problems in other fields

  1. Lower Silurian stratigraphy and brachiopods of the Chingiz range, eastern Kazakhstan

    NASA Astrophysics Data System (ADS)

    Nikitina, O. I.; Nikitin, I. F.; Olenicheva, M. A.; Palets, L. M.

    2015-05-01

    New data on the stratigraphy and faunal assemblages of the Lower Silurian of the Chingiz region are presented. Owing to the discovery of Ruddanian brachiopods in the basal Alpeis Formation, the position of the Ordovician-Silurian boundary has been revised. The stratigraphic range of the Alpeis Formation has been revised to correspond to the range of the Alpeis Horizon in the stratotype and is limited to the beds with the brachiopod Eospirifer cinghizicus and the beds with the graptolites of the Coronograptus gregarius Zone. Beds with Pentamerus longiseptatus of the Donenzhal Horizon are assigned to the Zhumak Formation. A new Ruddanian brachiopod assemblage (ten species) is recognized in the lower part of the beds with E. cinghizicus.

  2. Life on the Edge: Holocene Tephra Stratigraphy of Tanginak Anchorage, Sitkalidak Island, Kodiak Archipelago, Alaska

    NASA Astrophysics Data System (ADS)

    Mahrt, E.; Bourgeois, J.; Fitzhugh, J. B.

    2004-12-01

    Geologic hazards associated with volcanism in the North Pacific have profound if usually temporary effects on the environment and human populations. Ash falls associated with these events are often preserved across large areas providing time specific markers. In the past century, volcanic activity and its effects in the North Pacific have been recorded, but much of the Holocene volcanic record in the Alaskan region is still being investigated. The Kodiak Archipelago, while not volcanic itself, is located near both Aleutian and Alaskan peninsula volcanoes. However, little has been published about the Holocene tephrochronology of the Kodiak region. This study focuses on the area around Tanginak Spring Site (KOD481). Located on Sitkalidak Island it is the earliest known human occupation in the Kodiak archipelago. We are documenting Holocene environmental changes on Sitkalidak Island and relating these changes to the archaeological record. As part of this work, we will establish a local tephrochronology using stratigraphy and geochemistry which will allow us to better correlate sedimentary changes across large areas as well as study human interaction with ashfall events. Herein we report a preliminary tephrochronology in peat excavations on Sitkalidak Island dating back to the earliest Holocene. Dates are radiocarbon years BP on peat directly below tephra. Marker tephra present in our reference sections are Katmai 1912, light gray (historic?), medium gray (3370), medium gray (3720), beige 1 (4340), apricot (5390), beige 3 (6790), black (9280), and white (11,520). Geochemical and petrographic analysis will help to determine with which volcanic events these tephra are associated. Establishing a local tephrochronology is important not only for local correlation but also to ascertain the tephra stratigraphy of the Kodiak Archipelago and beyond. The frequency of tephra in Tanginak Anchorage sections suggests that tephra will be a very useful stratigraphic tool in this region.

  3. A review of the stratigraphy and sedimentary environments of the Karoo-aged basins of Southern Africa

    NASA Astrophysics Data System (ADS)

    Smith, R. M. H.; Eriksson, P. G.; Botha, W. J.

    1993-02-01

    The Karoo Basin of South Africa was one of several contemporaneous intracratonic basins in southwestern Gondwana that became active in the Permo-Carboniferous (280 Ma) and continued to accumulate sediments until the earliest Jurassic, 100 million years later. At their maximum areal extent, during the early Permian, these basins covered some 4.5 million km 2. The present outcrop area of Karoo rocks in southern Africa is about 300 000 km 2 with a maximum thickness of some 8000 m. The economic importance of these sediments lies in the vast reserves of coal within the Ecca Group rocks of northern and eastern Transvaal and Natal, South Africa. Large reserves of sandstone-hosted uranium and molybdenum have been proven within the Beaufort Group rocks of the southern Karoo trough, although they are not mineable in the present market conditions. Palaeoenvironmental analysis of the major stratigraphic units of the Karoo succession in South Africa demonstrates the changes in depositional style caused by regional and localized tectonism within the basin. These depocentres were influenced by a progressive aridification of climate which was primarily caused by the northward drift of southwestern Gondwana out of a polar climate and accentuated by the meteoric drying effect of the surrounding land masses. Changing palaeoenvironments clearly influenced the rate and direction of vertebrate evolution in southern Gondwana as evidenced by the numerous reptile fossils, including dinosaurs, which are found in the Karoo strata of South Africa, Lesotho, Namibia and Zimbabwe. During the Late Carboniferous the southern part of Gondwana migrated over the South Pole resulting in a major ice sheet over the early Karoo basin and surrounding highlands. Glacial sedimentation in upland valleys and on the lowland shelf resulted in the Dwyka Formation at the base of the Karoo Sequence. After glaciation, an extensive shallow sea covered the gently subsiding shelf, fed by large volumes of meltwater. Marine clays and muds accumulated under cool climatic conditions (Lower Ecca Group) including the distinctive Mesosaurus-bearing carbonaceous shales of the Whitehill Formation. Subduction of the palaeo-Pacific plate reslted in an extensive chain of mountains which deformed and later truncated the southern rim of the main Karoo Basin. Material derived from these "Gondwanide" mountains as well as from the granitic uplands to the north-east, accumulated in large deltas that prograded into the Ecca sea (Upper Ecca Group). The relatively cool and humid climate promoted thick accumulations of peat on the fluvial and delta plains which now constitute the major coal reserves of southern Africa. As the prograding deltas coalesced, fluvio-lacustrine sediments of the Beaufort Group were laid down on broad gently subsiding alluvial plains. The climate by this time (Late Permian) had warmed to become semi-arid with highly seasonal rainfall. Vegetation alongside the meander belts and semi-permanent lakes supported a diverse reptilian fauna dominated by therapsids or "mammal-like reptiles". Pulses of uplift in the southern source areas combined with possible orographic effects resulted in the progadation of two coarse-grained alluvial fans into the central parts of the basin (Katberg Sandstone Member and Molteno Formation). In the upper Karoo Sequence, progressive aridification and tectonic deformation of the basin through the late Triassic and early Jurassic led to the accumulation, in four separate depositories, of "redbeds" which are interpreted as fluvial and flood-fan, playa and dune complexes (Elliot Formation). This eventually gave way to westerly wind-dominated sedimentation that choked the remaining depositories with fine-grained dune sand. The interdune areas were damp and occasionally flooded and provided a habitat for small dinosaurs and the earliest mammals. During this time (Early Jurassic), basinwide volcanic activity began as a precursor to the break-up of Gondwana in the late Jurassic and continued until the early Cretaceous. This

  4. Stratigraphy and age of Karoo basalts of Lesotho and implications for correlations within the Karoo igneous province

    NASA Astrophysics Data System (ADS)

    Marsh, J. S.; Hooper, P. R.; Rehacek, J.; Duncan, R. A.; Duncan, A. R.

    The Lesotho remnant contains the type succession for Karoo low-Ti basalts of central southern Africa. The 40Ar/39Ar dating indicates that the sequence was emplaced within a very short period at about 180 Ma and consists of a monotonous pile of compound basalt lava flows which lacks significant palaeosols and persistent sedimentary intercalations. We have used geochemistry to establish a stratigraphic subdivision of the lava pile. Thin units of basalt flows, the Moshesh's Ford, Golden Gate, Sani, Roma, Letele, and Wonderkop units, with diverse geochemical character and restricted geographical distribution, are present at the base of the succession. These are overlain by extensive units of compositionally more uniform basalt, the Mafika Lisiu, Maloti, Senqu and Mothae units, which build the bulk of the sequence. A single palaeomagnetic polarity reversal occurs within the lower third of the basalt succession and is consistently located within the Mafika Lisiu unit. This and the persistent and relatively uniform thickness of the stratigraphic units suggest that the pile was constructed in a uniform manner by eruption of basalt onto a generally planar surface from a widespread plexus of dykes. The stratigraphic sequence in Lesotho closely resembles that in the thinner sequence of low-Ti basalts of the Springbok Flats remnant, some 400 km to the north. A thin unit of high-Ti basalt within the upper part of the Springbok Flats sequence can be correlated with the thick high-Ti basalt suite along the rift-related Lebombo structure on the eastern margin of the Karoo province. This is the first established correlation between these two important outcrops of Karoo volcanic rocks and demonstrates that the low-Ti basalts of Lesotho and the cratonic interior are the approximate time equivalents of the lower part of the Lebombo sequence. This conclusion has important implications for models for the origin of the Karoo flood basalt province.

  5. Molecular-isotopic stratigraphy of long-chain n-alkanes in Lake Baikal Holocene and glacial age sediments

    Microsoft Academic Search

    David Brincat; Keita Yamada; Ryoshi Ishiwatari; Hitoshi Uemura; Hiroshi Naraoka

    2000-01-01

    The molecular distribution and the carbon-isotopic composition (?13C) of n-alkanes extracted from a Lake Baikal core spanning the last 20 kyr of sediment accumulation have been investigated. A terrestrial origin has been inferred for the odd carbon-numbered long-chain (>C27) n-alkanes, on the basis of the observed high CPI27-33 values (range: 8.7–10.8) typical of n-alkanes derived from leaf waxes of higher

  6. U-Pb provenance ages of shocked zircons from the K-T boundary, Raton Basin, Colorado

    NASA Technical Reports Server (NTRS)

    Premo, W. R.; Izett, G. A.

    1993-01-01

    U-Pb isotopic systematics from analyses of single zircons identify at least two provenance ages, approximately 575 Ma and approximately 330 Ma, for zircons from the impact layer of the K-T boundary, Raton Basin, Colorado. These data are a preliminary confirmation of results reported from the same layer. The zircon provenance ages provide a unique signature for identification of the source crater since igneous rocks of these ages (or sedimentary rocks derived from them) must characterize part of the impact stratigraphy.

  7. Petrographical, palynological, and sedimentological aspects regarding the genesis of Palaeogene lignites near Alexandroupolis, Thrace, Greece

    SciTech Connect

    Antoniadis, P.; Kaouras, G.; Khanaqa, P.; Riegel, W.; Gentzis, T. [CDX Canada Co, Calgary, AB (Canada)

    2006-01-21

    Several minor lignite deposits of Palaeogene (Eocene to Oligocene) age occur in the vicinity of Alexandroupolis, Thrace, northern Greece. A few, rather thin seams were mined in the past by small private operations for local use. Coal samples have been collected from old mine dumps and outcrops around abandoned mine posts to be studied by means of maceral analysis at high magnification. The groundwater and vegetation index are calculated from the maceral composition and used to draw conclusions concerning the environment of deposition. In addition, block samples of coal cut perpendicular to bedding were studied at intermediate magnification and underfluorescence, thus revealing some interesting bedding features as well as well-preserved plant organisms. The coals are characteristically finely laminated and highly gelified. Palynological preparations have thus far yielded only poorly preserved palynomorph assemblages, rather low in diversity and dominated by fern spores. This fern dominance is rather unusual: however, it is compatible with the occurrence of fertile fern fronds observed in petrographic coal sections. Accompanying clastic sediments exhibit cyclic fining-upward sequences at a scale averaging about 1 m in vertical extent. Grain sizes range from small gravel to clay and silt. In some cases, siltstones in the roof of coal seams include abundant plant fragments showing parallel venation. The evidence presented from various sources suggests a rather unstable fluvial environment and a generally high water table on the flood plain for the formation of these lignites.

  8. Sedimentological and geochronological evidences of anthropogenic impacts on river basins in the Northern Latium coastal area (Italy)

    NASA Astrophysics Data System (ADS)

    Piazzolla, Daniele; Paladini de Mendoza, Francesco; Scanu, Sergio; Marcelli, Marco

    2015-04-01

    In this work we aimed to compare sedimentological and geochronological data from three sediment core samples (MIG50, MRT50, and GRT50) taken in the Northern Latium (Italy) coastal area, at -50 m depth, to data regarding rainfall, river flows and the land use in the three most important hydrographic basins (Mignone, Marta and Fiora) and in the coastal area. Different trends of sediment mass accumulation rate (MAR) are detected in the three cores: a strongly increasing trend was identified in MIG50 and MRT50 cores while GRT50 doesn't show significant variation. Data from the sedimentological analysis of GRT50 core identify a progressive decrease in the sandy component, which declined from about 30% to the current level of 7% over the last 36 years, while MRT50 and MIG50 cores (mainly composed by pelitic fraction > 95%) showed slight variations of textural ratio between silt and clay. According to the general decrease of pluviometric trend observed in Italy, related to teleconnection pattern tendency (NAO), the statistical analysis of rain identified significative decrease only in the Fiora river basin, whereas in the other two locations the decrease was not as significant. Regarding the Fiora river flow, a significative decreasing trend of average flow is detected, while the flood regime remained unaffected over the past 30 years. The analysis of the land use shows that the human activities are increased of 6-10% over the available time steps (1990 - 2006) in Fiora and Mignone river basins, while the Marta river basin has a strong human impact since 1990 highligting more than 80% of artificial soil covering. The largest variation is observed on the Fiora basin (10%) where the antrhopic activities have expanded to an area of about 85 Km2. Moreover, in the last ten years a large beach nourishment in 2004 (570000 m3) and dredging activities in the early second half of 2000s (1000000 m3 moved) were performed in Marina di Tarquinia beach and in front of the Torrevaldaliga coal-fired power plant respectively. The land use change and human intervention on the riverbeds, detected on the Fiora river basin over the last 30 years, could have produced the textural variation observed in the GRT50 core sample, while the absence of the flood regime variation justify the observed MAR values. The results of this work revealed that variations caused by the working of fluvial processes have affected the water runoff of the Fiora river, and that the consequent decrease in sand production was testified by the recession of beaches in the coastal area between Tarquinia and Montalto di Castro which led to the nourishment that affected the MAR evolution in the coastal area. The changes observed in the MAR of MRT50 and MIG50 show temporal agreement with the beach nourishment and the dredging activities respectively.

  9. Depositional Environments and Sequence Stratigraphy of the Lower Cretaceous Dakota Sandstone in the Ridgway Area, Southwestern Colorado

    E-print Network

    Serradji, Hayet

    2008-01-30

    B. S., Algerian Petroleum Institute, Boumerdes, Algeria, 2005. Submitted to the graduate program in Geology and to the Graduate Faculty of the University of Kansas In partial fulfillment of the requirements for the degree of Master... Depositional Environments and Sequence Stratigraphy of the Lower Cretaceous Dakota Sandstone in the Ridgway Area, Southwestern Colorado By C2007 Hayet Serradji B.S., University of Science and Technology Houari Boumediane, Algeria, 2002...

  10. THE GEOLOGY OF ELEUTHERA ISLAND, BAHAMAS: A ROSETTA STONE OF QUATERNARY STRATIGRAPHY AND SEA-LEVEL HISTORY

    Microsoft Academic Search

    PAUL J. HEARTY

    1998-01-01

    A 5-km stretch of coastline in north Eleuthera reveals a long and detailed stratigraphy that includes all known surficial limestone units in the Bahamas, and supplements the record with several previously unrecognized ones. Eight paleosol-bounded limestone parasequences comprise at least six interglacial periods. The lithostratigraphy demonstrates cyclicity at several frequencies (105, 104 (20–40ka), and 103years) and displays a variety of

  11. Analysing the origin of the Upper Cretaceous ?Lower Tertiary Rio Capim semi flint (Pará State, Brazil) under a sedimentologic perspective

    NASA Astrophysics Data System (ADS)

    Rossetti, Dilce de Fatima; Santos, Antônio Emídio de Araújo dos

    2006-04-01

    The Rio Capim kaolin, one of the largest kaolin reserves in the world currently under exploration, is typified by a lower and an upper unit represented of a soft, well-structured kaolin and a semi-flint kaolin, respectively, the latter term been applied here for a flint-like fire clay consisting of indurated kaolinite, which develops no plasticity when ground up. The latter is characterized by its elevated hardness and massive nature, which has been preliminarily attributed to stronger weathering relative to the underlying soft kaolin. Despite the overall massive aspect, a detailed sedimentologic investigation of freshly exposed sections along open mines revealed a variety of structures in the semi-flint kaolin that are attributed to primary sedimentary features. The features include channel like forms having distinct lags of quartz sandstones at their bottoms. These deposits intergrade with strata displaying a series of inclined lines, defining lobed bodies that are locally highlighted by distinctively soft, massive mud layers. The lobes are internally truncated by undulating surfaces attributed to wave erosion. The features described in this work are related to deposition of the semi-flint kaolin unit in either distributary channels and mouth bar or tidal inlet and tidal delta areas associated with deltaic or wave-dominated estuarine settings, respectively. The recognition of these deposits in the semi-flint unit has large implications to analyze its composition, which must have primarily included sand grain sizes, at least in the case of the lobed strata. The apparent muddy nature of the semi-flint kaolin might be due, at least in part, to post depositional modification of a sandy unit composed most likely by grains of previously formed kaolinite derived from reworking of the underlying soft kaolin unit.

  12. Trace fossils and sedimentology of a Late Cretaceous Progradational Barrier Island sequence: Bearpaw and Horseshoe Canyon Formations, Dorothy, Alberta

    SciTech Connect

    Saunders, T.D.; Pemberton, A.G.; Ranger, M.J. (Univ. of Alberta, Edmonton (Canada))

    1990-05-01

    A well-exposed example of a regressive barrier island succession crops out in the Alberta badlands along the Red Deer River Valley. In the most landward (northwestern) corner of the study area, only shallow-water and subaerial deposits are represented and are dominated by tidal inlet related facies. Seaward (southeast), water depth increases and the succession is typified by open-marine beach to offshore-related facies arranged in coarsening-upward progradational sequence. Detailed sedimentologic and ichnologic analyses of this sequence have allowed for its division into three distinct environmental zones (lower, middle, and upper). The lower zone comprises a laterally diverse assemblage of storm-influenced, lower shoreface through offshore deposits. Outcrop in the northeast is dominated by thick beds of hummocky and/or swaley cross-stratified storm sand. In the southeast, storm events have only minor influence. This lower zone contains a wide diversity of well-preserved trace fossils whose distribution appears to have been influenced by gradients in wave energy, bottom stagnation, and the interplay of storm and fair-weather processes. The middle zone records deposition across an upper shoreface environment. Here, horizontal to low-angle bedding predominates, with interspersed sets of small- and large-scale cross-bedding increasing toward the top. A characteristic feature of the upper part of this zone is the lack of biogenic structures suggesting deposition in an exposed high-energy surf zone. The upper zone records intertidal to supratidal progradation of the shoreline complex. Planar-laminated sandstone forms a distinct foreshore interval above which rhizoliths and organic material become increasingly abundant, marking transition to the backshore. A significant feature of this zone is the occurrence of an intensely bioturbated interval toward the top of the foreshore.

  13. Filling the temporal gap in Plio-Pleistocene sedimentological records from the southern Afar Depression, Ethiopia

    NASA Astrophysics Data System (ADS)

    Dimaggio, E.; Arrowsmith, R.; Reed, K.; Campisano, C. J.

    2009-12-01

    The structural development of the Afar Depression controls sedimentary basin architecture and thus directly influences the spatial and temporal pattern of depositional environments. Over the past 5 Myr these processes, in addition to climate variations and volcanic eruptions, influenced the composition and variation of early human habitats and their record is preserved in the sediment record of synchronous rift basins. Here we present results from field investigations at Geraru located within the Ledi-Geraru field site, part of the greater Hadar sedimentary basin in the Afar region of Ethiopia. We aim to characterize local basin structure and expand and refine interpretations of the complex Plio-Pleistocene history of local and regional-scale landscape change during a time of critical importance for understanding hominin evolution. We mapped Geraru geology (1:7000), measured stratigraphic sections, and sampled 20 tephra deposits for absolute age dating (40Ar/39Ar) and for compositional studies and correlation using glass shard chemistry. We mapped over 16 km2 and identified lacustrine to fluvial sediments that are well-exposed along NW-SE to NE-SW trending faulted basalt hills that offset sediment blocks up to ~30 m. Although stratigraphic sections are not continuous, faulting relationships and marker beds suggest that at least 65m of strata are accessible. The lower ~40m of sediments are lacustrine deposits indicated by finely laminated silts and clays, two <2m thick diatomite layers, and gastropod shells. Conformably overlying them, we found ~25m of coarse fluvial sands and gravels that are locally cross-bedded and contain fossils of terrestrial fauna. Compositional results of glass shards from 4 tephra samples indicate that they not chemically similar to tephras from the Hadar (ca. 3.8-2.9 Ma) or Busidima (ca. 2.7-0.16 Ma) Formations. One tephra sample collected from the central portion of the stratigraphic section yielded a plateau age of 2.814 ± 0.017 Ma (more dates are being processed). Based on our preliminary stratigraphic interpretation and mapping, and review of notes from early workers in the region, Geraru strata likely represent depositional environments ca. 2.9-2.7 Ma. Other observations that support deposition at Geraru at that time include glass chemistry correlation and sedimentation patterns. Elsewhere in the Awash region, sediments spanning ca. 2.9-2.7 Ma are scarcely documented due to a period of non-deposition and erosion. Therefore, we are re-assessing structural models of basin geometry that indicate basin-wide reorganization near 2.9 Ma because models infer that the paleolandscape was erosional at that time (evidenced by an unconformity surface) rather than depositional (as suggested by strata at Geraru) - implying that Geraru may have been in a separate basin. Our work demonstrates that the sedimentary sequences at Geraru provide access to an important depositional record with good geochronological controls. It corresponds to important changes in regional tectonics and local basin configuration, climate patterns, and diversification and adaptive shifts in hominins.

  14. Sedimentological, geomorphological and dynamic context of debris-mantled glaciers, Mount Everest (Sagarmatha) region, Nepal

    NASA Astrophysics Data System (ADS)

    Hambrey, Michael J.; Quincey, Duncan J.; Glasser, Neil F.; Reynolds, John M.; Richardson, Shaun J.; Clemmens, Samuel

    2009-06-01

    This paper presents the sediment, landform and dynamic context of four avalanche-fed valley glaciers (Khumbu, Imja, Lhotse and Chukhung) in the Mount Everest (Sagarmatha) region of Nepal. All four glaciers have a mantle of debris dominated by sandy boulder-gravel that suppresses melting to an increasing degree towards the snout, leading to a progressive reduction in the overall slope of their longitudinal profile. Prominent lateral-terminal moraine complexes, also comprising sandy bouldergravel, enclose the glaciers. These terminal moraines originally grew by accretion of multiple sedimentary facies of basal glacial and supraglacial origin, probably by folding and thrusting when the glaciers were more dynamic during the Little Ice Age. The four glaciers are in various stages of recession, and demonstrate a range of scenarios from down-wasting of the glacier tongue, through morainedammed lake development, to post-moraine-dam breaching. Khumbu Glacier is at the earliest stage of supraglacial pond formation and shows no sign yet of developing a major lake, although one is likely to develop behind its >250 m high composite terminal moraine. Imja Glacier terminates in a substantial body of water behind a partially ice-cored moraine dam (as determined from geophysical surveys), but morphologically appears unlikely to be an immediate threat. Chukhung Glacier already has a breached moraine and a connected debris fan, and therefore no longer poses a threat. Lhotse Glacier has an inclined, free-draining tongue that precludes hazardous lake development. From the data assembled, a conceptual model, applicable to other Himalayan glaciers, is proposed to explain the development of large, lateral-terminal moraine complexes and associated potentially hazardous moraine dams. - 2008 Elsevier Ltd. All rights reserved .

  15. Sedimentological, geomorphological and dynamic context of debris-mantled glaciers, Mount Everest (Sagarmatha) region, Nepal

    NASA Astrophysics Data System (ADS)

    Hambrey, Michael J.; Quincey, Duncan J.; Glasser, Neil F.; Reynolds, John M.; Richardson, Shaun J.; Clemmens, Samuel

    2008-12-01

    This paper presents the sediment, landform and dynamic context of four avalanche-fed valley glaciers (Khumbu, Imja, Lhotse and Chukhung) in the Mount Everest (Sagarmatha) region of Nepal. All four glaciers have a mantle of debris dominated by sandy boulder-gravel that suppresses melting to an increasing degree towards the snout, leading to a progressive reduction in the overall slope of their longitudinal profile. Prominent lateral-terminal moraine complexes, also comprising sandy boulder-gravel, enclose the glaciers. These terminal moraines originally grew by accretion of multiple sedimentary facies of basal glacial and supraglacial origin, probably by folding and thrusting when the glaciers were more dynamic during the Little Ice Age. The four glaciers are in various stages of recession, and demonstrate a range of scenarios from down-wasting of the glacier tongue, through moraine-dammed lake development, to post-moraine-dam breaching. Khumbu Glacier is at the earliest stage of supraglacial pond formation and shows no sign yet of developing a major lake, although one is likely to develop behind its >250 m high composite terminal moraine. Imja Glacier terminates in a substantial body of water behind a partially ice-cored moraine dam (as determined from geophysical surveys), but morphologically appears unlikely to be an immediate threat. Chukhung Glacier already has a breached moraine and a connected debris fan, and therefore no longer poses a threat. Lhotse Glacier has an inclined, free-draining tongue that precludes hazardous lake development. From the data assembled, a conceptual model, applicable to other Himalayan glaciers, is proposed to explain the development of large, lateral-terminal moraine complexes and associated potentially hazardous moraine dams.

  16. Three-dimensional model of reference thermal/mechanical and hydrological stratigraphy at Yucca Mountain, southern Nevada

    SciTech Connect

    Ortiz, T.S.; Williams, R.L.; Nimick, F.B.; Whittet, B.C.; South, D.L.

    1985-10-01

    The Nevada Nuclear Waste Storage Investigations (NNWSI) project is currently examining the feasibility of constructing a nuclear waste repository in the tuffs beneath Yucca Mountain. A three-dimensional model of the thermal/mechanical and hydrological reference stratigraphy at Yucca Mountain has been developed for use in performance assessment and repository design studies involving material properties data. The reference stratigraphy defines units with distinct thermal, physical, mechanical, and hydrological properties. The model is a collection of surface representations, each surface representing the base of a particular unit. The reliability of the model was evaluated by comparing the generated surfaces, existing geologic maps and cross sections, drill hole data, and geologic interpolation. Interpolation of surfaces between drill holes by the model closely matches the existing information. The top of a zone containing prevalent zeolite is defined and superimposed on the reference stratigraphy. Interpretation of the geometric relations between the zeolitic and thermal/mechanical and hydrological surfaces indicates that the zeolitic zone was established before the major portion of local fault displacement took place; however, faulting and zeolitization may have been partly concurrent. The thickness of the proposed repository host rock, the devitrified, relatively lithophysal-poor, moderately to densely welded portion of the Topopah Spring Member of the Paintbrush Tuff, was evaluated and varies from 400 to 800 ft in the repository area. The distance from the repository to groundwater level was estimated to vary from 700 to 1400 ft. 13 figs., 1 tab.

  17. Cretaceous sequence stratigraphy of the Northern South American Passive Margin: Implications for tectonic evolution

    SciTech Connect

    Kauffman, E.G.; Villamil, T.; Johnson, C.C. (Univ. of Colorado, Boulder, CO (United States))

    1993-02-01

    The passive margin of northern South America, from Colombia to northeastern Venezuela, was relatively stable through the Cretaceous and only broadly affected by the entry of the Caribbean Plate into the Protocaribbean Basin. This region offers a unique opportunity to test the relative effects of global sealevel change, autocyclic sedimentologic processed, and regional tectonics in shaping the stratigraphic record of Cretaceous passive margins. High-resolution stratigraphic studies of Colombia and Venezuela have established a precise system of regional chronology and correlation with resolution <1 Ma (50-500 ka for the middle Cretaceous). This allows precise separation of allocyclic and autocyclic controls on facies development. This new chronology integrates assemblage zone biostratigraphy with event/cycle chronostratigraphy. Newly measured Cretaceous sections in Venezuela and throughout Colombia are calibrated to this new chronology, and sequence stratigraphic units independently defined to the third-order of resolution. Graphic correlation of all sections is used to identify sequences with regional stratigraphic expression, and those which correlate to sequence stratigraphic standards of North America, Europe and the global cycles of Hag et al. (1988). 50-60 percent of the stratigraphic sequences across the South American passive margin correlate to other continents and to the global sequence stratigraphic standard, reflecting strong eustatic influence on Cretaceous sedimentation across northern South America. The remaining sequences in this region reflect tectonic modification of the passive margin and autocyclic sedimentary processes.

  18. Stratigraphy and depositional history, Bone Spring Formation, Lea County, New Mexico

    SciTech Connect

    Mazzullo, L.J. (Nearburg Producing Co., Dallas, TX (USA))

    1987-02-01

    The Bone Spring formation of the northern Delaware basin in southeastern New Mexico produces oil in Lea County from foreshelf detrital carbonate facies, such as in Scharb field. Production there comes from several intervals. Stratigraphic correlations between the various Bone Springs units and equivalent Leonardian facies of the Northwest shelf in Lea County suggest that the Bone Spring is correlative to the Yeso Formation of the Northwest shelf. The shelf facies there are divided into lower, middle, and upper Yeso. The upper part of what has generally been considered to be Wolfcamp in some areas, beneath the lowermost Bone Spring sandstone, is inferred to be lower Leonardian (lower Yeso) throughout the area studied. A model is proposed for the sedimentologic and reservoir evolution of the Bone Spring Formation in Lea County. Permian-Pennsylvanian tectonic activity provided the initial substrate for the development of a high-energy shelf edge in early Yeso time. In early middle Yeso time, the basin filled with sediments of the 3rd and 2nd Bone Spring units, and the shelf to basin transition was more subtle. As the basin subsided with infilling, a high-energy shelf edge again developed in late middle Yeso time. With continued basin infilling by 1st Bone Springs facies, the shelf to basin transition again evolved into a more subtle feature. Continued basin subsidence caused infilling by a thick sequence of upper Yeso carbonate, which was capped by progradational shelf carbonates of the upper Yeso.

  19. Aging gauge

    DOEpatents

    Betts, Robert E. (Huntsville, AL); Crawford, John F. (Huntsville, AL)

    1989-01-01

    An aging gauge comprising a container having a fixed or a variable sized t opening with a cap which can be opened to control the sublimation rate of a thermally sublimational material contained within the container. In use, the aging gauge is stored with an item to determine total heat the item is subjected to and also the maximum temperature to which the item has been exposed. The aging gauge container contains a thermally sublimational material such as naphthalene or similar material which has a low sublimation rate over the temperature range from about 70.degree. F. to about 160.degree. F. The aging products determined by analyses of a like item aged along with the aging gauge for which the sublimation amount is determined is employed to establish a calibration curve for future aging evaluation. The aging gauge is provided with a means for determining the maximum temperature exposure (i.e., a thermally indicating material which gives an irreversible color change, Thermocolor pigment). Because of the relationship of doubling reaction rates for increases of 10.degree. C., equivalency of item used in accelerated aging evaluation can be obtained by referring to a calibration curve depicting storage temperature on the abscissa scale and multiplier on the ordinate scale.

  20. AGING GAUGE

    DOEpatents

    Betts, Robert E.; Crawford, John F.

    1989-04-04

    An aging gauge comprising a container having a fixed or a variable sized t opening with a cap which can be opened to control the sublimation rate of a thermally sublimational material contained within the container. In use, the aging gauge is stored with an item to determine total heat the item is subjected to and also the maximum temperature to which the item has been exposed. The aging gauge container contains a thermally sublimational material such as naphthalene or similar material which has a low sublimation rate over the temperature range from about 70.degree. F. to about 160.degree. F. The aging products determined by analyses of a like item aged along with the aging gauge for which the sublimation amount is determined is employed to establish a calibration curve for future aging evaluation. The aging gauge is provided with a means for determining the maximum temperature exposure (i.e., a thermally indicating material which gives an irreversible color change, Thermocolor pigment). Because of the relationship of doubling reaction rates for increases of 10.degree. C., equivalency of item used in accelerated aging evaluation can be obtained by referring to a calibration curve depicting storage temperature on the abscissa scale and multiplier on the ordinate scale.

  1. Layer-cake vs. fruit-cake stratigraphy of megadune-related snows of East Antarctica

    NASA Astrophysics Data System (ADS)

    Wise, D. U.; Cianfarra, P.; Salvini, F.

    2009-12-01

    Published models of snow deposits of the East Antarctic Plateau visualize km-scale snow stripes in scattered megadune fields as actively-forming stratigraphic zones growing through later Holocene time in parallel with other patches and zones of more normal snow and ice, in effect a stratigraphy of lumps scattered like fruit-cake “goodies.” An alternate four-unit layer-cake model seems more appropriate based on superposition relationships in satellite images. In this model the oldest unit (#1) contains upslope-climbing, relic megadune sets and cosets of pseudo-beds beneath the striped surfaces. This unit is transitional upward into unit #2, divisible into several facies: a) abandoned megadune plains or wind-swept snow regs to use a sand desert term, b) sudden appearance of high topographic relief “Duke of York” dunes from the children’s song of the Grand Old Duke’s soldiers abandoned “neither up nor down,” c) extensions of megadune snow stripes growing into downslope-migrating, lobate dunes, and d) downslope-migrating sheets of coalesced, mostly lobate dune forms, commonly lineated on regional scales. Unit #3 is a pile of snow blankets, transverse and longitudinal dunes that commonly form snow ergs, another sand desert term. This unit is semi-transparent to radar as indicted by near-surface trends and patterns on Modis images disappearing on radar images to show clearly defined unit #2 facies patterns for the same area. These three stratigraphic units appear analogous to an abbreviated form of the aqueous Bouma sequence of fining upward turbiditic beds that pass from upper flow regime (UFR), upstream-climbing antidunes through transitional units into lower flow regime (LFR), downstream-migrating dunes. If megadunes are UFR, very rapid deposition necessitated massive supplies of moisture-rich air available only from open water in the Ross and Weddell Seas or across narrow winter ice shelves of the Southern Ocean, a climate much warmer than present. The most likely candidate is 5-8 ka BP when C14 dates indicate penguins roosted around the Ross Sea and abundant organic carbon disappeared from marine cores at 5 ka. Freezing of these local sources initiated transition into unit #2 and the start of unit #3’s LFR conditions with more chemical-free, colder, less recrystallized and hence more radar-transparent snows. Deposited locally across all these is unit #4, a modern deposit of scattered patches of 100-200-m wavelength longitudinal dunes reported at surface sites as aligned sastrugi, features combining sintered snow deposition and wind erosion. At the two major megadune core-sample sites, satellite images show unit #4 rests on reg surfaces of unit #2 whereas unit #3 separates them in immediately adjacent areas. This indicates a previously unrecognized time gap or unconformity must exist in these cores, invalidating past interpretations of active, modern megadunes derived by simple downward extrapolation of young dates and snow accumulation rates. Instead, satellite images and these ice cores suggest megadunes are inactive relics of a past climate, part of a layer-cake stratigraphy topped with a final anthropogenic icing, an alternative to the currently favored fruit-cake stratigraphy.

  2. A Sedimentological Multi-Proxy Study of Late Holocene Climate Change in Southern Patagonia

    NASA Astrophysics Data System (ADS)

    Hutchinson, E. C.; Leroy, S. L.; Dunbar, R. B.

    2014-12-01

    The southern hemisphere westerlies force and respond to circulation and heat exchange with the Southern Ocean, which in turn plays a large role in global climate change. Southern Patagonia is the only significant land mass in the path of the southern westerlies, so it is an ideal location to examine variability of this wind system and its relation to regional and global climate. Precipitation and wind strength exhibit a strong positive correlation, and we take advantage of this relationship to use a paleoclimate archive to probe past changes in the wind field. We examined a 3.6m long sediment core from Lago Sarmiento (51.06?S, 72.91?W) in Torres del Paine National Park, Chile, for indicators of past environmental change. Here we present a high resolution, multi-proxy record of regional paleoclimate that includes physical, biological, and chemical data sets. We measured magnetic susceptibility, weight percent organic carbon and nitrogen, ?13C of bulk sediment, and weight percent carbonate of the core. These results provide information about precipitation, relative wind strength, volcanic activity, and biological productivity in and around Lago Sarmiento over the past 4,000 years. Our age model for the core is based in part on tephrochronology. We identified three tephras, or volcanic ashes, in the core at 68-71, 110-112, and 284-286cm that are supported visually and with magnetic susceptibility measurements. Analysis of the C:N ratio of the Lago Sarmiento core demonstrates a long-term increase in the deposition of terrestrial organic matter in Lago Sarmiento over time, perhaps indicating a change from grassland to woodland due to increased precipitation. The largest excursions in the C:N ratio occur at 20, 53, 139-140, 225-226, and 252cm. The average ?13C of organic carbon is -24.81‰, and large decreases occur at 9, 45, 180, 245-246, and 252-253cm, which could indicate overturning events in the lake. The average weight percent carbonate is 18%, with large decreases at 69-70, 98-111, 284-285, and 334-337cm, which we interpret as decreases in lake productivity. These results encompass new knowledge about the paleoclimate patterns in and around Lago Sarmiento and have significant implications for climate change, human health, and environmental policy.

  3. Multiple working hypotheses for the formation of compositional stratigraphy on Mars: Insights from the Mawrth Vallis region

    NASA Astrophysics Data System (ADS)

    Michalski, Joseph R.; Niles, P. B.; Cuadros, J.; Baldridge, A. M.

    2013-09-01

    A unique aspect of martian geology is the presence of similar compositional stratigraphy observed in many locations throughout the surface. Where the Al-rich and Fe/Mg-rich clay minerals occur together, aluminous clays typically overly layered ferromagnesian clays, possibly indicating that precipitation-driven leaching occurred in a warmer, wetter climate. Sulfates generally occurring stratigraphically above clays could be relics of a global environmental shift between clay-forming and sulfate forming epochs. These compositional relationships speak to an important aspect of the martian geosystem that is yet poorly understood. We synthesized recent ideas to produce several working hypotheses for the formation of compositional stratigraphy on Mars and tested the hypotheses on well-exposed sulfate- and clay-bearing rocks found in the Mawrth Vallis region. In the Mawrth Vallis area, interpretations of compositional stratigraphy are strongly constrained by the fact that the sulfates and clays occur within a friable unit (probably loessite or tephra) that was deposited unconformably onto cratered terrain of fundamentally different character. Within the friable unit, the presence of aluminous clays over ferromagnesian clays might represent evidence for leaching associated with rainfall, but the presence of montmorillonite, beidellite, and sulfates argue against intense leaching as a dominant process. We suggest that ice/snow-mediated chemical weathering of dust could produce a deposit consistent with the observations through hydrolysis reactions facilitated by acidic, briny solutions within the icy dust deposit. Slow downward transport of Mg2+ and possibly Fe2+ in these solutions could potentially have produced the crude compositional stratigraphy, but regional scale leaching of basaltic bedrock by rainfall is unlikely to explain the observations. Because both clays and sulfates are found within draping, friable sedimentary deposits that occur at a range of elevations, formation of the alteration minerals by upwelling groundwater is implausible. The locations where compositional stratigraphy is observed may not be relics of a global environmental change, but rather they cold represent the locations where significant deposits of snow/ice and dust/ash once existed.

  4. Geochemical and Sedimentological Records of Late Quaternary Climate Change, Lake Tanganyika, Tropical East Africa

    NASA Astrophysics Data System (ADS)

    Felton, A. A.; Russell, J. M.; Cohen, A. S.; Baker, M. E.; McGlue, M. M.; Lezzar, K. E.

    2005-12-01

    We have analyzed piston core records from Lake Tanganyika (western Tanzania, East African Rift Valley) to investigate possible signals of tropical paleoclimate change during the Late Quaternary. Long paleoclimate records from East Africa are of importance for understanding climatic processes such as the role of solar variability in regulating tropical climates at Milankovitch time scales, and the relationship between abrupt climate changes, migration of Intertropical Convergence Zone, and regional climate variability (Nicholson, 2000). However, records of pre-Holocene climate variability from tropical African lakes (>25ka) are still quite rare. Long records from Lake Tanganyika are of particular interest given the lake's antiquity and its demonstrated potential for producing high resolution (frequently annually laminated) sedimentary records (Cohen et al., 1993). We analyzed physical properties, grain size, total organic carbon, major, minor and trace element variability, and biogenic silica data for a 7.75 m core from the Kalya slope and horst region of central Lake Tanganyika at 640m water depth. Nine 14C dates provide an age model for the core, which spans ~62 cal kyr. Elemental concentrations preserved in Lake Tanganyika sediments record variability in deposition and runoff into the lake basin. Under conditions of rapid erosion, exposure and rapid weathering of bedrock has been shown to generate high concentrations of original silicate minerals enriched in soluble cations such as sodium and potassium, elements that are also biologically conservative. Prior to 40ka cal yr. core sediments are characterized by high magnetic susceptibility, intermediate levels of organic carbon, low to intermediate levels of biogenic silica, and fine grain size, indicative of relatively high precipitation. There is a profound decrease in magnetic susceptibility, a decrease in organic carbon and an increase in grain size at 40ka cal yr, which persists until ~16ka cal yr. Seismic reflection profiles demonstrate the existence of paleodeltas at ~360m below modern lake level that may have formed during this period, although it is unclear whether this deposit represents a Late Quaternary (OIS 2) or earlier (OIS 6) event. Maximum aridity occurred at about 20-20.5ka cal yr, consist with earlier interpretations of lake lowstands (Gasse et al., 1989, Scholz et al., 1997). The late Pleistocene and earliest Holocene sediments in our record are characterized by generally rising magnetic susceptibility, declining organic carbon and biogenic silica, and finer grain size. However during this period there are marked fluctuations in magnetic susceptibility and biogenic silica at millennial time-scales. These indicate intervals of fluctuating precipitation, productivity, and possibly windiness and are particularly prominent during the Pleistocene-Holocene transition. Massive clays, rising magnetic susceptibility, low biogenic silica and low organic carbon mark the early Holocene, indicative of increased rainfall during a regionally wet interval. These sediments are capped by a laminated ooze, indicative of drier conditions and a more stratified water body.

  5. Palaeogegraphic and palaeotopography evolution of the chinese Tien Shan during the Mesozoic : a sedimentological synthesis

    NASA Astrophysics Data System (ADS)

    Heilbronn, Gloria; Jolivet, Marc; Robin, Cécile; Barrier, Laurie; Bourquin, Sylvie; Jia, Yingying; Fu, Bihong

    2014-05-01

    The Tian Shan is one of the main ranges of Central Asia Orogenic Belt. The Tertiary deformation is driven by the India-Asia collision stress field. However, the deformation appears localised along inherited tectonic structures formed during the Palaeozoic - Early Mesozoic history of the range (e.g. Jolivet et al., 2010). Our aim is to reconstruct the pre-Tertiary history of relief building in the Chinese Tian Shan. We use the sedimentary facies, sediment provenances and paleocurrent directions of the exposed Mesozoic sections in the northern and southern piedmonts and inside the range. This will be used to understand the long-term reactivation pattern of the main inherited structures and to assess their influence on the localisation and propagation of the deformation. We first established 6 complete reference sections spanning from the Upper Triassic to the Palaeogene. These sections are interpreted in terms of sedimentary facies, palaeoenvironments and prograding-retrograding sequences. The correlation of these 6 sections allows us to propose some palaeogeographic maps for the middle Jurassic, the upper Jurassic - lower Cretaceous transition, the upper Cretaceous and the late Cretaceous - Paleogene transition. The dismantling of reliefs associated to the late-paleozoic range stops in the upper Trias. The Jurassic is characterised by a low tectonic activity and results in a general planation phase of the Tian Shan area. The supposed low relief is possibly associated to local activity of normal faults : this is attested by alluvial fan deposits on the internal sections, as well as paleocurrent directions to the North in the northern foothills and to the south in the southern foothills. These faults could belong to pull apart basins opening in a transtensive tectonic régime, under a humid climate, what is testified by numerous organic matter layers. The upper Jurassic - lower Cretaceous transition is characterized by a huge conglomeratic event at the scale of all the northern foothills, associated with some eolian deposits certified a arid climat at this period. We propose that alluvial fans are the result of the erosion of relatively small and local reliefs, caused by normal faults. This interpretation is in contradiction with all hypothesis of the literature supporting compressional tectonic and reactivation of the range during the Upper Jurassic. Nevertheless it fits to the interpretation of low thermochronology data. During the Upper Cretaceous, the widespread occurrence of alluvial fans indicates the ongoing erosion of a local positive topography in the Tian Shan area. A significant late Lower - early Upper Cretaceous unconformity is observable in the S-Junggar, N-Tarim and Turfan Basins (Hendrix et al., 1992). It is confirmed by low temperature thermochronology data that show a "major" late Lower Cretaceous unroofing event near Kuqa on the southern foothills (Dumitru et al., 2001) and some late Lower to early Upper Cretaceous exhumation ages within the range (Jolivet et al., 2010). This marks the onset of a new exhumation phase that goes on during the Upper Cretaceous and seems to stop after a peak in the late Upper Cretaceous. Following the Upper Cretaceous inversion episode, a tectonic quiet period characterises the late Upper Cretaceous - Early Paleogene and enables the formation of a widespread calcrete.

  6. Middle Age.

    ERIC Educational Resources Information Center

    Owen, Roger, Ed.

    Problems of middle age are explored by contributors from a variety of backgrounds, academic disciplines, and experiences in this book, which was associated with a BBC television series broadcast in Autumn 1967. The book is divided into sections on the middle aged personality, body (health hazards), mental powers (ability and retraining in…

  7. Late Miocene - Early Pliocene Stratigraphy and Paleoceanography of the South Atlantic and Southwest Pacific Oceans: A Synthesis

    NASA Astrophysics Data System (ADS)

    Hodell, David A.; Kennett, James P.

    1986-09-01

    The stratigraphy and paleoceanography of the late Miocene and early Pliocene have been examined at six sites in the South Atlantic and southwest Pacific oceans: Deep Sea Drilling Project (DSDP) sites 284, 516A, 519, 588, and 590 and two piston cores from Chain cruise 115. A consistent stratigraphy was developed among sites using graphic correlation, which resulted in age models for all sites that are tied to the revised paleomagnetic time scale of Berggren et al. (1985). Applying these chronologies, we assessed latitudinal and interocean contrasts in the stratigraphic ranges of late Miocene-early Pliocene planktonic foraminiferal and nanno - fossil datums. Salient stratigraphic results include (1) The last appearance datum (LAD) of Globoquadrina dehiscens is a late Miocene (˜6.4 Ma) event in the subtropics and is not useful for the placement of the Miocene/Pliocene (M/P) boundary in this biogeographic province. (2) The first appearance datum (FAD) of Globorotalia crassaformis occurred at ˜5.1 Ma in the South Atlantic near the M/P boundary, suggesting that Gr. crassaformis may have first evolved in the South Atlantic and later migrated to other regions. (3) In the southwest Pacific, the FADs of Gr. margaritae (5.97 Ma), Gr. puncticulata (5.09 Ma), and Gr. crassaformis (4.87 Ma) are significantly time transgressive between temperate and warm subtropical regions. Time lags of ˜1.0 m.y. were required for these species to adapt to physical and/or biotic conditions peripheral to their endemic biogeographic provinces. (4) Between the subtropics of the South Atlantic and southwest Pacific, many planktonic foraminiferal datums (FAD of Dentogloboquadrina altispira, Gr. cibaoensis, Gr. conomiozea, Gr. margaritae, and Gq. dehiscens and LAD of Gr. cibaoensis) markedly depart from the correlation suggested by magnetostratigraphy, indicating that these datum levels are unreliable for correlation between these ocean basins. (5) In contrast, available calcareous nannofossil datum levels fall on or near the paleomagnetic correlation line, indicating synchroneity of events within the subtropics. (6) Biostratigraphic, magnetic, and 87Sr/86Sr correlation between sites 588 and 519 and the M/P neostratotype at Capo Rossello, Sicily, suggests that the base of the Zanclean stratotype occurs at 5.1-5.0 Ma in the lower reversed subchron of the Gilbert, about 2-3 × 105 years above the Gilbert/Chron 5 boundary. Oxygen isotopic results from DSDP sites 284, 519, and CH115 piston cores confirm a prolonged benthic ?18O increase in the latest Miocene between ˜5.6 and 5.0 Ma, as originally proposed by Shackleton and Kennett (1975). At DSDP site 588, the benthic ?18O record in the latest Miocene is marked by high-frequency fluctuations with amplitude variations of ˜0.5‰, and a long-period wavelength component of ˜400,000 years. Maximum ?18O values, however, occurred during the late Miocene (Kapitean Stage) between 5.5 and 5.1 Ma. The late Miocene ?18O changes resulted from mid- and high-latitude cooling and pulses of ice sheet expansion and contraction. Glacial events were most intense during the latest Miocene (Kapitean Stage), and occurred at 5.50-5.35 Ma and at 5.10 Ma. Glacial events are estimated to have lowered sea level by ˜40 to 60 m and contributed to the isolation and desiccation of the Mediterranean Basin during the late Messinian. Interglacial conditions prevailed at 5.2 Ma and between 5.0 and 4.1 Ma ihe early Pliocene. The beginning of the Pliocene was marked by changes in many proxy climatic indicators at all sites, suggesting a prolonged interval of warm, interglacial conditions between 5.0 and 4.1 Ma during the earliest Pliocene. Supplementary tables are available with entire article onmicrofiche. Order from American Geophysical Union, 2000Florida Avenue, N.W., Washington, DC 20009. DocumentP86-001; $2.50. Payment must accompany order.

  8. Chronostratigraphy and Sedimentology of the Marmara Sea Over the Last 40 kyrs

    NASA Astrophysics Data System (ADS)

    Çagatay, M. N.

    2003-04-01

    The Marmara Sea (MS) is a transitional basin between Mediterranean and Black Seas. It is connected with these neighbouring seas via the straits of Çanakkale (Dardanelles) and Istanbul (Bosphorus), having present sill depths of 65 and 35m, respectively. The MS Basin consists of ca. 1250-m three deep basins and <10 km-wide shelf in the north and 45-km wide southern shelf and -400 m Imrali Platform in the south. The deep basins are separated from each other by -450 to -600 m pressure ridges. The MS has a two-layer water stratification and a flow system with a halocline/oxycline at a depth of about 20 m, which separates the lower water layer of Mediterranean origin ( ~ 36 per mil) from the upper layer of Black Sea origin ( ~ 22 per mil). Based on the fossil content and C-14 datings, the sedimentary section in cores from near the shelf edge and pressure highs can be divided into essentially three stratigraphic units, covering the last 40 kyr: the upper marine, the middle lacustrine and the lower brackish(?) marine (Unit 3) units. Unit 1 is more than 1-m thick gray green to olive geen, locally laminated mud with two sapropelic layers having higher than 1.5 wt pct organic carbon. This unit contains marine (Mediterranean) fossils, such as foraminifera, molluscs, echinoderms and fish bones, all of which indicate that it was deposited after the transgression of the MS by the Mediterranean waters at about 12 kyr BP. On the northern shelf this unit is mainly represented by bioherms consisting of euryhaline molluscs, serpulids, corals and benthic forams, which developed soon after the marine inundation of the MS. Based on radiocarbon dating, the upper and lower sapropelic layers in Unit 1 were deposited during 4.75-3.2 and 10.6-6.4 kyr BP, respectively. The lower sapropel layer is broadly contemporaneous with the S1 sapropel of the Eastern Mediterranean and Aegean Seas. The presence of the upper sapropelic layer is marked on the southern shelf, but less distinct in the deeper water parts. The predominance of benthic foraminiferal species in the sapropelic layers, such as Bulimina aculeata, Brizalina spatulata, Cassudilina crassa and Hyalinea baltica, indicates dysoxic to suboxic oxygen conditions and high organic flux in the bottom waters. Unit 2 is locally laminated, iron monosulfide banded, gray to dark gray mud, with freshwater ostracods and Neoeuxinian Black Sea molluscs. The faunal content of Unit 2 shows that it was deposited during fresh/brackish water (salinitiy: <6 per mil) lacustrine phase of the MS during from ca. 35 ky to 12 kyr BP, covering late part of MIS 3 (marine isotope stage 3) and MIS 2. During the deposition of this unit the water level was at -85 m, and the shelf areas were subareally exposed or occupied by small isolated lakes. Unit 2 includes a rhyodacitic ash layer, correlated with the 18 kyr BP (calibr. age: 22 kyr BP) Y-2 ash-layer of Santorini origin. The lower Unit 3 contains some marine molluscs and benthic foraminifers, which indicate at least a weak Mediterranean marine incursion during the early part of MIS 3. The deep basins are characterized by alternation of normal hemipelagic sedimentation with turbidite-homogenite (T-H) units. The latter units consists of a thin (<5 cm) sand layer with erosional lower contact at the base and a relatively thick, homogeneous mud layer at the top, and are mostly deposited during seismic events. As a result, the deep basins are characterized by very high (>1 m/kyr) and variable sedimentation rates that vary with the morphotectonics and glacio-eustatic water-level changes (i.e., lacustrine vs. marine periods). The rates are the highest in the deepest, tectonically subsiding parts of the basins, and more than three times higher for the low-stand lacustrine period (Unit 2) than those for the high-stand marine period (Unit 1). Sedimentation rates on the southern shelf during the Holocene vary from higher than 0.5 m/kyr on the inner shelf to about 0.2 m/kyr on the outer shelf and the shelf margin. On the Imrali Plateau, it is 0.1-0.3 m/kyr during the Holo

  9. Pliocene anisotropy of magnetic susceptibility (AMS) and diatom stratigraphy from the Wilkes Land margin

    NASA Astrophysics Data System (ADS)

    Sugisaki, S.; Iwai, M.; Tauxe, L.; van de Flierdt, T.; Cook, C.; Jimenez-Espejo, F.; Passchier, S.; Roehl, U.; González, J.; Escutia, C.

    2012-12-01

    During IODP Expedition 318, Sites U1359 and U1361 were drilled on the continental rise offshore the Wilkes subglacial basin to reconstruct the stability of the East Antarctic Ice Sheet (EAIS) during Neogene warm periods, such as the late Miocene and the early Pliocene. As the drilled core has complex story of compaction, erosion (thus hiatuses), and possibly artificial disturbance, identifying these is important for reconstructing paleoenvironments. Anisotropy of magnetic susceptibility (AMS) is sensitive to lithological changes and differential compaction. At site U1359, highly anisotropic layers correspond with lithologic boundaries and hiatuses. In places, it appeared that the degree of anisotropy was controlled by the presence or absence of diatoms. Here we present a detailed study of the relationships between sediment compaction based on AMS fabric and variations in diatom taxa and magnetic mineralogy. There is clear correlation between degree of anisotropy and moisture content; where moisture content is high, the layer is more isotropic, and vice versa. Moreover, the anisotropic layers correspond to layers with abundant fibrous diatom taxa (e.g, Thalassionema nitzschioides). In contrast, the more isotropic layers are dominated by the Pennate diatom taxa (e.g, Rouxia spp.). There are also strong rock magnetic indications for changes in the sources of the magnetic minerals. We will describe our AMS and diatom stratigraphy to 1) characterize sediments compaction with diatom taxa variation and 2) detect the source of magnetic mineralogy throughout Pliocene.

  10. 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.

  11. Construction and maintenance of the ganges-brahmaputra-meghna delta: linking process, morphology, and stratigraphy.

    PubMed

    Wilson, Carol A; Goodbred, Steven L

    2015-01-01

    We present a review of the processes, morphology, and stratigraphy of the Ganges-Brahmaputra-Meghna delta (GBMD), including insights gained from detailed elevation data. The review shows that the GBMD is best characterized as a composite system, with different regions having morphologic and stratigraphic attributes of an upland fluvial fan delta; a lowland, backwater-reach delta; a downdrift tidal delta plain; and an offshore subaqueous-delta clinoform. These distinct areas of upland and lowland fluvial reaches and tidal dominance vary in time and space, and we distinguish late-Holocene phases of delta construction, maintenance, and decline similar to delta-lobe cycling in other systems. The overall stability of the GBMD landform, relative to many deltas, reflects the efficient, widespread dispersal of sediment by the large monsoon discharge and high-energy tides that affect this region. However, we do identify portions of the delta that are in decline and losing elevation relative to sea level owing to insufficient sediment delivery. These areas, some of which are well inland of the coast, represent those most at risk to the continued effect of sea-level rise. PMID:25251271

  12. Rapid Measurements of Snow Stratigraphy Using A Portable Penetration Field Instrument

    NASA Astrophysics Data System (ADS)

    Foster, Robert; Louge, Michel; Clifford, Kelly; Decker, Rand

    We describe a new field-portable tool for avalanche forecasting and hydrology that can rapidly generate stratigraphic profiles of density, permittivity and temperature through the snow pack. This penetration instrument consists of a wedged capacitance tip mounted at the end of a pole and a mechanical depth gauge. By appropriate place- ment of its reference, guard and sensor conductive surfaces, the instrument sheds hor- izontal electric field lines resolving horizontal snow layers of 2.5mm thickness. The probe was tested under realistically cold conditions at the mountain resort of Alta near Salt Lake City, Utah. There, it recorded the stratigraphy of the real and imaginary parts of the dielectric constant at 3.9kHz and the temperature through a typical winter snow pack. The portable electronics was carried in a small backpack and the depth was recorded using a rotary digital encoder in frictional contact with the pole. The profiles were automatically acquired on a hand-held Personal Digital Assistant. Using independent calibrations, measurements of the real part provided an accurate profile of density later confirmed by the conventional excavation of a detailed snow cover profile. The ratio of the imaginary and real permittivities also revealed the signature of individual snow layers that could be identified in the excavation.

  13. Application of sequence stratigraphy to Neritic sediments of the Niger delta

    SciTech Connect

    McHargue, T.; Diedjomahor, J.; Arowolo, I.; Hobbet, R.; Onyia, V. (Chevron Nigeria Limited, Lagos (Nigeria))

    1993-09-01

    Sequence stratigraphy is an approach to correlation that emphasizes regional unconformities as the basis for subdividing sediments into time-equivalent packages called sequences. In Chevron's acreage in the northwestern Niger delta, three-dimensional (3-D) seismic data have been used to map each sequence-bounding unconformity based on the presence of a submarine canyon near the paleoshelf edge. Erosion lateral to each canyon is slight or even absent. Useful criteria for recognizing sequence boundaries in 3-D seismic data in neritic sediments of the niger delta are (1) truncation of underlying reflections, (2) drape, dip discordance, or onlap of younger reflections over topography on the sequence boundary, (3) contrast in seismic attributes across the sequence boundary, and (4) termination of faults at the sequence boundary. Published criteria for recognizing sequence boundaries from logs and paleontological data are being adaped to the Niger delta, where high-frequency fourth-order sequences are strongly developed. Identifying and mapping sequence boundaries is beneficial because sequence boundaries (1) may form truncation traps where shales of the younger sequence overlie truncated sands of the older sequence, (2) assist correlations across faults, (3) subdivide the section into units of genetically related sediments, and (4) provide an objective basis for regional correlations.

  14. Refined stratigraphy of the Middle Permian Abrahamskraal Formation (Beaufort Group) in the southern Karoo Basin

    NASA Astrophysics Data System (ADS)

    Jirah, Sifelani; Rubidge, Bruce S.

    2014-12-01

    Fluvially deposited rocks of the Abrahamskraal Formation of the lower Beaufort Group in the South African Karoo record sediment deposition during the Middle Permian, the earliest terrestrial environment of Gondwana. A rich diversity of fossil tetrapods from this Formation provides a unique opportunity for understanding Middle Permian biodiversity changes in Gondwanan terrestrial ecosystems, but this is dependent on the existence of a robust stratigraphic framework that has been hampered by lack of lateral continuity of lithological markers combined with structural complexities relating to formation of the Cape Fold Belt. Because the Abrahamskraal Formation covers a large geographic area of the main Karoo Basin previous stratigraphic studies have been undertaken over large areas. This study combines geology and palaeontology to refine the stratigraphy of the Abrahamskraal Formation in a part of the southwestern Karoo Basin and revealed mappable lithological units with lateral continuity throughout the study area. The measured stratigraphic section manifests a total thickness of 2565 m for the Formation (the thickest occurrence of the Abrahamskraal Formation in the Beaufort Group). For the first time stratigraphic ranges of biostratigraphically important Middle Permian index taxa which have restricted stratigraphic ranges have been determined and, apart from dicynodonts, include the parareptile Eunotosaurus and the biarmosuchid therapsid Hipposaurus. The Abrahamskraal Formation comprises a 1104 m thick basal Eodicynodon Assemblage Zone, overlain by a 1441 m thick Tapinocephalus Assemblage Zone whose upper limit is 20 m below the Poortjie Member of the Teekloof Formation.

  15. Sedimentological Records of Organic Matter Accumulation in the Inshore Region of the Fly River Clinoform (Papua New Guinea)

    NASA Astrophysics Data System (ADS)

    Gisewhite, R.; Goni, M. A.; Clinton, R.; Monacci, N.; McKay, M.; Crockett, J.; Nittrouer, C.

    2004-12-01

    Thirteen kasten cores collected from the northeast and southwest regions of the clinoform topset off the Fly River Delta and from the Umuda Channel were selected for elemental (organic carbon, nitrogen), mineral surface area (SA), stable isotope (d13C and d15N) and biomarker (lignin phenols) analyses. The depth of the cores ranged from 30 to over 250 cm and represent variable periods of depositional history. The average organic carbon content (OC) of sediments ranged from 0.6 to 2 wt. percent, depending on the site location. The highest OC levels were observed in the northeast region off the Fly River Delta, while the lowest levels were found in cores located in the southern offshore region. Average molar organic carbon:nitrogen ratios ranged from 10 to 18, with the lowest C/N ratios found in the sites located to the south of the delta. Average d13C and nitrogen d15N signatures ranged from -26 to -25 per mil and from 1.4 to 2.5 per mil, respectively. Average OC/SA ratios for the sediments in these cores ranged from 0.4 to 1.7 mg C/m2, with the lowest values measured in samples from the Umuda Channel and the most distal site in the northeast region of the topset. Overall, these compositions indicate organic matter accumulation in all these sites is dominated by the burial of terrigenous derived soil organic matter. Down core peaks in C/N and OC/SA ratios indicate the presence of discrete layers enriched in vascular plant detritus. Low OC/SA ratios indicative of extensive decay were only measured in selected sites and in specific horizons. In contrast, most samples were characterized by "normal" organic carbon loadings that are consistent with the active burial and effective preservation of terrigenous organic matter in this region of the Fly River Delta and clinoform. There is little evidence for the preservation of marine-derived organic matter in these deposits. These data will be further interpreted in the context of additional sedimentological data (X-rays, grain size, radioisotope activities).

  16. Sedimentology and Carbon Isotope in Lower Tertiary Sediments of Rajasthan:Implication to Post Paleocene/Eocene Thermal Maximum Event

    NASA Astrophysics Data System (ADS)

    Samanta, A.; Sarkar, A.; Bera, M.

    2008-12-01

    The Paleocene-Eocene thermal maxima (PETM; ~55 My.), identified as the most abrupt and transient climatic events in Cenozoic era, associated with pronounced warming of ocean and atmosphere, change in ocean chemistry, and perturbation of global carbon cycle. Catastrophic (~5° -6° C) rise in the deep sea temperature and oxygen deficiency might cause 30-50% extinction of benthic foraminifera, increase in sea surface temperature by ~8° C at high latitude (lesser amount towards equator) affected the planktonic biota, and this global warming event led to a pulse of speciation or migration of mammal. PETM is characterized by a prominent drop in carbon isotope values by ~3-4 per mil in both marine and terrestrial sediments in less than 10 ka. The source and triggering mechanism of PETM event are still raging debate. Input of massive amount of greenhouse gas from the dissociation of 13C poor methane hydrate from the continental slop as well as from the terrestrial biosphere is currently the most acceptable explanation for the warming and the negative carbon isotope excursion (CIE). Like other catastrophic events the post-PETM recovery was gradual. Interestingly, ?13C of both carbonate and organic matter shifted towards positive during the recovery period possibly as a combined effect of increased organic burial and silicate weathering. Compared to most studied PETM and post-PETM sections of subtropical to high latitudes, data for equatorial regions and marginal marine are scanty. The marginal marine are important as the effect of silicate weathering or increased burial of shallow marine organic matter will be more pronounced here. The lower Tertiary marginal marine successions of Rajasthan (Akli formation; Giral lignite mine) (paleolatitude ~5° S) shed light on the PETM and post-PETM events and the response of the events on equatorial marginal marine environment. Sedimentological studies suggest that the Akli formation was deposited in a lagoonal environment occasionally inundated by marine incursions. High resolution ?13C Bulk organic matter profile in these lignitic beds and its comparison with the oceanic foraminiferal carbonate ?13C profile reveals that the upper part of the Akli formation was deposited during Early Eocene or recovery phase of PETM. This inference is also supported by the presence of larger benthic foraminifera Nummulites burdigalensis (~52My) in the sand beds. The preliminary data (presence of lignites and C/N Values) suggest that substantial organic carbon burial in shallow seas world over could have been responsible for atmospheric CO2 reduction and enriched ?13C values during the early Eocene period.

  17. A magnetostratigraphic study of the sediments of the Ridge Basin, southern California and its tectonic and sedimentologic implications

    NASA Astrophysics Data System (ADS)

    Ensley, Ross A.; Verosub, Kenneth L.

    1982-06-01

    A magnetic polarity zonation has been established for the upper Castaic Formation and lower Ridge Route and Peace Valley Formations of the Ridge Basin of the central Transverse Ranges of southern California. The zonation is based on the analysis of over 1900 samples from 669 sites in the 5800 m thick sedimentary sequence. Rock magnetic studies provide evidence that the carrier of the primary remanence is magnetite and that the magnetization was acquired at or shortly after deposition of the sediment. Although many samples contain a secondary, normal overprint, systematic analysis of the changes in direction upon demagnetization leads to an accurate determination of the original polarity. Thirteen polarity intervals are recognized. On the basis of biostratigraphic constraints imposed by a marine invertebrate faunaat the base of the sequence and a terrestrial vertebrate fauna at the top, the magnetic polarity zonation can be correlated to the magnetic polarity time scale. The studied interval extends from the Epoch 5/Epoch 6 boundary to the middle of Epoch 8. Polarity changes within the studied interval represent chronostratigraphic horizons which can be used to analyze tectonic and sedimentologic processes which are recorded in the sediments of the Ridge Basin. The locus of the tectonic activity within the basin has been dated as occurring on the Clearwater fault from 8.1 to 7.8 m.y. ago, on the Liebre faultfrom 7.3 to 6.1 m.y. ago and on the North Liebre fault from 6.0 to 5.0 m.y. ago. During this entire period of time, the San Gabriel fault on the western margin of the basin was continuously active, and a period of particularly vigorous activity has been dated at 7.3 to 7.0 m.y. The mean declinations of samples from the normal magnetozones provide no evidence for the existence of a major rotation of the Ridge Basin subsequent to about 8.5 m.y. ago. Sedimentation rates for interbedded sandstone and shale units within the basin have been separately determined as 0.2 m/1000 years and 3.0 m/1000 years, respectively. The water content of certain deformed structures within the sequence has been determined to have been 35% and 40% at the time of deformation.

  18. Sedimentological and Stable Isotope Changes at the Messinian-Pliocene Boundary Along a West to East Mediterranean Transect.

    NASA Astrophysics Data System (ADS)

    Pierre, C.; Rouchy, J.; Blanc-Valleron, M.

    2001-12-01

    During Messinian times, the whole Mediterranean area was submitted to evaporitic conditions which ended by the "Lago-Mare" brackish episode before the reset of open marine conditions in the early Pliocene. These major paleoceanographic changes resulted from regional tectonic reorganizations and global climate changes at this critical time interval, both acting to modify drastically the physiography and the hydrological budget of the Mediterranean basins. There exist outcropping sections and a few deep-sea ODP cores which contain the complete and continuous sedimentary sequence of the Messinian-Pliocene boundary (MPB), making it possible to follow the paleoenvironmental changes at a high resolution scale. We compare here sedimentological and carbonate stable isotope records on three sections for which a high- resolution sampling was applied to the 2 meters thick interval including the MPB. In the Vera section from South Spain, there is no clear change in the carbonate content of the silty clay succession when crossing the MPB. The oxygen and carbon isotopic compositions of calcite both increase by 1 permil across a 40 cm-thick interval which corresponds to the Messinian-Pliocene transition. At ODP Site 968 from the eastern Levantine basin, there is an important sedimentary change between Messinian brown silty clays containing about 20 percent of carbonate and Pliocene gray nannofossil ooze which carbonate content averages 60 percent. Across this 10 cm-thick transitional interval, the oxygen and carbon isotopic compositions of bulk calcite both increase by 4.5 permil. In the Pissouri section from Cyprus, the uppermost Messinian reddish to brown marls with paleosoils are overlain by white Pliocene marls. The carbonate content increases from 20 percent to reach 60 percent across a 40 cm-thick transitional interval. Within this interval corresponding to the MPB, the oxygen and carbon isotopic compositions increase by 4 permil and 2 permil respectively. These results indicate that the MPB is recorded everywhere from W to E Mediterranean by significant and sharp increases in the oxygen and carbon isotopic compositions, which indicate that the early Pliocene marine flooding of the Mediterranean basins was a very abrupt event.

  19. The Sedimentology of Pyroclastic Flow Lift-Off: The 18 May 1980 Mt. St. Helens Singe Zone Deposit