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Sample records for stratigraphy sedimentology age

  1. 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)

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

    SciTech Connect

    Mederos, S.M.; Moslow, T.F.

    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.

  3. Stratigraphy and sedimentology of the Upper Cretaceous to Paleogene Kilwa Group, southern coastal Tanzania

    NASA Astrophysics Data System (ADS)

    Nicholas, Christopher J.; Pearson, Paul N.; Bown, Paul R.; Jones, Tom Dunkley; Huber, Brian T.; Karega, Amina; Lees, Jackie A.; McMillan, Ian K.; O'Halloran, Aoife; Singano, Joyce M.; Wade, Bridget S.

    2006-08-01

    The geology of southern coastal Tanzania has remained poorly understood since the first comments on its stratigraphy were made over 100 years ago. However, new field surveys combined with shallow drilling along the coast between Kilwa and Lindi are beginning to resolve the depositional history and structural evolution of this region over the past 85 Ma. Here we present the first attempt to synthesize the results of these studies to provide a coherent sedimentological, litho- and sequence stratigraphic framework, including new geological maps, for the Upper Cretaceous and Paleogene of the coastal zone. Santonian to Oligocene sediments crop out along a broad coastal belt south of the Rufiji River from the Kilwa peninsula to Lindi Creek in southern Tanzania. During ˜55 Ma, over 1 km of a broadly homogeneous, mid to outer shelf clay-dominated succession was deposited across the passive margin, which we define here as the Kilwa Group. This lies disconformably across the shelf on Albian marls and is itself unconformably overlain by shallow water Miocene clays and more recent limestones, sands and gravels. Four formations can be identified within the Kilwa Group on the basis of characteristic secondary lithologies and facies, described here for the first time; the Nangurukuru, Kivinje, Masoko and Pande Formations. These formations include conformable stratigraphic intervals through both the Paleocene-Eocene and Eocene-Oligocene boundaries. Within the Kilwa Group, 12 sequence stratigraphic cycles can be identified at present, demonstrating relatively uniform and continual subsidence across the margin from Santonian to Early Oligocene time. A further major bounding surface is present between the Upper Cretaceous and Paleogene, but this may become partly conformable in the Lindi area. Although the principal lithology in all formations is clay or claystone, there are more permeable intervals containing pervasive coarser siliciclastic sediments and these have yielded traces of crude oil which is likely to have migrated from lower in the succession. The Kilwa Group thus also provides important new evidence for petroleum play development in the southern coastal zone.

  4. 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.

  5. Sedimentology, stratigraphy, and extinctions during the Cretaceous-Paleogene transition at Bug Creek, Montana

    SciTech Connect

    Fastovsky, D.E.; Dott, R.H. Jr.

    1986-04-01

    Bug Creek Valley, the source of an unusual and controversial Cretaceous-Paleogene coincidence of mammals, dinosaurs, pollen, and iridium, exemplifies the importance of depositional process in the reconstruction of evolutionary events. Five sedimentary facies are recognized at Bug Creek: a cross-stratified sandstone, a green and purple siltstone, a lateral accretionary sandstone, a coal, and a variegated siltstone. Repeated fluvial channeling restricts the accuracy of lateral correlations, and the relationship of the fossil assemblage to the presumed Cretaceous-Paleogene boundary cannot be established. Sedimentologically, the Cretaceous-Paleogene transition is represented here by Cretaceous meandering channels that gave way initially to Paleogene swamp deposition. 13 references, 4 figures.

  6. Stratigraphy and sedimentology of the K/T boundary deposit in Haiti

    NASA Technical Reports Server (NTRS)

    Carey, S.; Sigurdsson, H.; Dhondt, S.; Espindola, J. M.

    1993-01-01

    The K/T boundary sequence is exposed in uplifted carbonate sediments of the southwest peninsula of Haiti. It is found at 15 localities within the Beloc formation, a sequence of limestone and marls interpreted as a monoclinal nappe structure thrust to the north. This tectonic deformation has affected the K/T boundary deposit to varying degrees. In some cases the less competent K/T deposit has acted as a slip plane leading to extensive shearing of the boundary layer, as well as duplication of the section. The presence of glassy tektites, shocked quartz, and an Ir anomaly directly link the deposit to a bolide impact. Stratigraphic and sedimentological features of the tripartite sequence indicate that it was formed by deposition from ballistic fallout of coarse tektites, emplacement of particle gravity flows and fine grained fallout of widely dispersed impact ejecta.

  7. 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. . 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.

  8. Stratigraphy, sedimentology, paleontology, and paleomagnetism of Pliocene-early Pleistocene lacustrine deposits in two cores from western Utah

    USGS Publications Warehouse

    Thompson, R.S.; Oviatt, Charles G.; Roberts, A.P.; Buchner, J.; Kelsey, R.; Bracht, C.J.; Forester, R.M.; Bradbury, J.P.

    1995-01-01

    The paleoclimatic history of western Utah is being investigated as part of the USGS Global Change and Climate History Program studies of long-term climatic changes in the western United States. The initial objective of the study is to document the environmental conditions during the mid-Pliocene period of warmer-than-modern global climates (the focus of the USGS Pliocene Research, Interpretation, and Synoptic Mapping [PRISM] project). The investigation also seeks to determine how and when these conditions gave way to the late Quaternary pattern of climatic variations (in which short periods of very moist climates have been separated by long periods of arid conditions). This is a collaborative project involving specialists from the USGS, Kansas State University, and the University of California-Davis in paleontology (Thompson, Buchner, Forester, Bradbury), stratigraphy and sedimentology (Oviatt, Kelsey, Bracht), and paleomagnetism and environmental magnetism (Roberts). The data presented herein represent preliminary findings of the analyses of two cores of Pliocene and early Pleistocene sediments from the eastern Great Basin.

  9. Stratigraphy, sedimentology and tectonic evolution of the Upper Cretaceous/Paleogene succession in north Eastern Desert, Egypt

    NASA Astrophysics Data System (ADS)

    El Ayyat, Abdalla M.; Obaidalla, Nageh A.

    2013-05-01

    The stratigraphy, sedimentology and syn-depositional tectonic events (SdTEs) of the Upper Cretaceous/Paleogene (K-P) succession at four localities in north Eastern Desert (NED) of Egypt have been studied. These localities are distributed from south-southwest to north-northeast at Gebel Millaha, at North Wadi Qena, at Wadi El Dakhal, and at Saint Paul Monastery. Lithostratigraphically, four rock units have been recorded: Sudr Formation (Campanian-Maastrichtian); Dakhla Formation (Danian-Selandian); Tarawan Formation (Selandian-Thanetian) and Esna Formation (Thanetian-Ypresian). These rock units are not completely represented all over the study area because some of them are absent at certain sites and others have variable thicknesses. Biostratigrapgically, 18 planktonic foraminiferal zones have been recorded. These are in stratigraphic order: Globotruncana ventricosa Zone (Campanian); Gansserina gansseri, Contusotruncana contusa, Recimguembelina fructicosa, Pseudohastigerina hariaensis, Pseudohastigerina palpebra and Plummerita hantkenenoides zones (Maastrichtian); Praemurica incostans, Praemurica uncinata, Morozovella angulata and Praemurica carinata/Igorina albeari zones (Danian); Igorina albeari, Globanomanlina pseudomenradii/Parasubbotina variospira, Acarinina subsphaerica, Acarinina soldadoensis/Globanomanlina pseudomenardii and Morozovella velascoensis zones (Selandian/Thantian); and Acarinina sibaiyaensis, Pseudohastigerina wilcoxensis/Morozovella velascoensis zones (earliest Ypresian). Sedimentologically, four sedimentary facies belts forming southwest gently-dipping slope to basin transect have been detected. They include tidal flats, outer shelf, slumped continental slope and open marine hemipelagic facies. This transect can be subdivided into a stable basin plain plus outer shelf in the extreme southwestern parts; and an unstable slope shelf platform in the northeastern parts. The unstable slope shelf platform is characterized by open marine hemipelagic, fine-grained limestones and fine siliciclastic shales (Sudr, Dakhla, Tarawan and Esna formations). The northeastern parts are marked by little contents of planktonic foraminifera and dolomitized, slumped carbonates, intercalated with basinal facies. Tectonically, four remarkable syn-depositional tectonic events (SdTEs) controlled the evolution of the studied succession. These events took place strongly within the Campanian-Ypresian time interval and were still active till Late Eocene. These events took place at: the Santonian/Campanian (S/C) boundary; the Campanian/Maastrichtian (C/M) boundary; the Cretaceous/Paleogene (K/P) boundary; and the Middle Paleocene-Early Eocene interval. These tectonic events are four pronounced phases in the tectonic history of the Syrian Arc System (SAS), the collision of the Afro-Arabian and Eurasian plates as well as the closure of the Tethys Sea.

  10. Stratigraphy and surface ages on Iapetus

    NASA Astrophysics Data System (ADS)

    Schmedemann, N.; Denk, T.; Wagner, R.; Neukum, G.

    2007-08-01

    Introduction: The examination of the geologic history of Iapetus is a major goal of the Cassini imaging experiment (ISS). Crater counting for the determination of model ages is a powerful tool to understand stratigraphic relationships between different terrain units (e.g., Neukum 1983, Neukum et al. 1998). In the case of Iapetus (Porco et al. 2005), the situation is unusual because this moon has a very large semi-major axis, resulting in unusually low relative velocities of planetocentric impactors. Nevertheless, the surface of Iapetus is heavily cratered, indicating a rather old surface. The shapes of the measured crater-size frequency distributions follow very closely the distribution of Earth's moon (after correction for the different impact conditions) (Neukum et al. 2006), justifying its usage here for model age determinations. Castillo-Rogez et al. (2007) suggest that the formation of Iapetus has occurred very precisely between 4.5622 and 4.5647 Ga ago. Assuming it took roughly 100 Ma for formation of a rigid surface which is able to hold the cratering record, absolute surface (model) ages can be calibrated to these boundary conditions. Stratigraphy: At the time of this writing, four different surface areas were investigated so far for stratigraphic comparison: 1. A small part of the ridge near 96°W longitude; 2. an "average" dark terrain sample north of the ridge; 3. the "landslide" crater (diameter ˜ 120 km; 6°N/36°W) in the south western part of a huge basin, and its surroundings; 4. a large, 420 km diameter basin on the leading side of Iapetus (34°N, 80°W). Following the models of Castillo-Rogez and Neukum, an age of 4.4 Ga is expected for the oldest parts of Iapetus' surface, which is actually found at the equatorial ridge and on the "average" terrain north of the ridge. The "landslide crater" and the landslide partly covering the crater and a neighboring area in the northwest are a few hundred million years younger (˜4.1 Ga). Thus, the idea that the impact event might have triggered the landslide is consistent with the data. The surroundings of the "landslide crater" are covered by its ejecta blankets to different degrees. Further away from the crater, the ejecta blanket is thinner, and the former underlying surface (especially the larger craters) is still visible. This results in a mixed age from the blanket and the former surface. The model age of the investigated basin on the leading side of Iapetus is 4.3 Ga. The crater statistics of the outer part of the basin, which is characterised by multiple ring structures, shows evidence of surviving of larger craters in the course of basin formation. References: Castillo-Rogez J.C., D.L. Matson, C. Sotin, T.V. Johnson, J.I. Lunine, P.C. Thomas (2007): Iapetus' Geophysics: Rotation Rate, Shape, and Equatorial Ridge, Icarus, doi:10.1016/j.icarus.2007.02.018 Neukum, G. (1983): Meteoritenbombardement und Datierung planetarer Oberflächen, Habilitation Dissertation for Faculty Membership, Ludwig-Maximilians Univ. München, Munich, Germany, 186 pp. Neukum, G., R. Wagner, U. Wolf, B.A. Ivanov, J.W. Head, R. T. Pappalardo, J.E. Klemaszewski, R. Greeley, M.J.S. Belton, and Galileo SSI Team (1998): Cratering chronology in the Jovian system and derivation of absolute ages, Lunar Planet. Sci. Conf. 29th, abstr. No. 1742 [CD-Rom] Neukum, G.; Wagner, R.; Wolf, U.; Denk, T. (2006): The Cratering Record and Cratering Chronologies of the Saturnian Satellites and the Origin of Impactors: Results from Cassini ISS Data, European Planetary Science Congress 2006. Berlin, Germany, 18 - 22 September 2006., p.610 Porco, C.C., et al. (2005): Cassini Imaging Science: Initial Results on Phoebe and Iapetus, Science 307, 1237-1242.

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

    SciTech Connect

    Davis, R.A. Jr.; Klay, J.; Jewell, P. )

    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.

  12. The Grayling Fingers region of Michigan: soils, sedimentology, stratigraphy and geomorphic development

    NASA Astrophysics Data System (ADS)

    Schaetzl, Randall J.; Weisenborn, Beth N.

    2004-08-01

    This paper provides data on the landforms, soils, and sediments within a unique northern Michigan landscape known as the Grayling Fingers, and evaluates these data to develop various scenarios for the geomorphic development of this region. Composed of several large, flat-topped ridges that trend N-S, the physiography of the "Fingers" resembles a hand. Previously interpreted as "remnant moraines", the Grayling Fingers are actually a Pleistocene constructional landscape that was later deeply incised by glacial meltwater. The sediments that comprise the Fingers form a generally planar assemblage, with thick (>100 m), sandy glacial outwash forming the lowest unit. Above the outwash are several meters of till that is remarkably similar in texture to the outwash below; thus, the region is best described as an incised ground moraine. Finally, a thin silty "cap" is preserved on the flattest, most stable uplands. This sediment package and the physiography of the Fingers are suggestive of geomorphic processes not previously envisioned for Michigan. Although precise dates are lacking, we nonetheless present possible sequences of geomorphic/sedimentologic processes for the Fingers. This area was probably a topographic high prior to the advance of marine isotope stage 2 (Woodfordian) ice. Much of the glacial outwash in the Fingers is probably associated with a stagnant, early Woodfordian ice margin, implying that this interlobate area remained ice-free and ice-marginal for long periods during stage 2. Woodfordian ice eventually covered the region and deposited 5-10 m of sandy basal till over the proglacial outwash plain. Small stream valleys on the outwash surface were palimpsested onto the till surface as the ice retreated, as kettle chains and as dry, upland valleys. The larger of these valleys were so deeply incised by meltwater that they formed the large, through-flowing Finger valleys. The silt cap that occupies stable uplands was probably imported into the region, while still glaciated. The Fingers region, a col on the ice surface, could have acted as a collection basin for silts brought in as loess or in superglacial meltwater. This sediment was let down as the ice melted and preserved only on certain geomorphically stable and fluvially isolated locations. This study demonstrates that the impact of Woodfordian ice in this region was mostly erosional, and suggests that Mississippi Valley loess may have indirectly impacted this region.

  13. Sedimentology and sequence stratigraphy of the Lower Jurassic Kayenta Formation, Colorado Plateau, United States

    NASA Astrophysics Data System (ADS)

    Sanabria, Diego Ignacio

    2001-07-01

    Detailed outcrop analysis of the Lower Jurassic Kayenta Formation provides the basis for the formulation of a new sequence stratigraphic model for arid to semi-arid continental deposits and the generation of a comprehensive set of sedimentologic criteria for the recognition of ephemeral stream deposits. Criteria for the recognition of ephemeral deposits in the ancient record were divided into three categories according to the scale of the feature being considered. The first category takes into account sedimentary structures commonly found in the record of ephemeral stream deposits including hyperconcentrated and debris flow deposits, planar parallel bedding, sigmoidal cross-bedding, hummocky cross-bedding, climbing ripple lamination, scour-and-fill structures, convolute bedding, overturned cross-bedding, ball-and-pillow structures, pocket structures, pillars, mud curls, flaser lamination, algal lamination, termite nests, and vertebrate tracks. The second category is concerned with the mesoscale facies architecture of ephemeral stream deposits and includes waning flow successions, bedform climb, downstream accretion, terminal wadi splays, and channel-fill successions indicating catastrophic flooding. At the large-scale facies architecture level, the third category, ephemeral stream deposits are commonly arranged in depositional units characterized by a downstream decrease in grain size and scale of sedimentary structures resulting from deposition in terminal fan systems. Outcrops of the Kayenta Formation and its transition to the Navajo Sandstone along the Vermilion and Echo Cliffs of Northern Arizona indicate that wet/dry climatic cyclicity exerted a major control on regional facies architecture. Two scales of wet/dry climatic cyclicity can be recognized in northern Arizona. Three sequence sets composed of rocks accumulated under predominantly dry or wet conditions are the expression of long-term climatic cyclicity. Short-term climatic cyclicity, on the other hand, is represented by high-frequency sequences composed of eolian or ephemeral fluvial deposits overlain by perennial fluvial sediments. Increased evapotranspiration rates, depressed water tables, and accumulation of eolian or ephemeral fluvial deposits characterize the dry portion of these cycles. The wet part of the cycles is marked by an increase in precipitation and the establishment of perennial fluvial systems and lacustrine basins. This depositional model constitutes a valuable tool for correlation of similar deposits in the subsurface.

  14. 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.

  15. High resolution seismic stratigraphy and sedimentological signature of the Late Quaternary deposits in the northern Western Basin (Ross Sea, Antarctica)

    NASA Astrophysics Data System (ADS)

    Corradi, N.; Finocchiaro, F.; Ivaldi, R.; Melis, R.; Pittà, A.

    2003-04-01

    The northern Western Basin is a sector of the continental shelf of the Western Ross Sea that is considered to be the natural northward extension of the Drygalski Basin by many authors. The literature provides a general model of the evolution of the basin and the recent papers propose a seismic stratigraphy for the post-Miocene sedimentation. However, the sedimentary processes during the Late Quaternary and, in particular, the Last Glacial Maximum (LGM) are still little understood (Brambati et al., 2001). In this paper we present the preliminary results of the very high-resolution seismic surveys (Sub Bottom Profiler, Huntec Deep Tow Boomer and Sparker) and their calibration with the sediment samples collected during the three Marine Geology Campaigns of the PNRA (XIII, XIV and XVII), with the scientific objective of the research to investigate the role of the East Antarctic Ice Sheet (EAIS) in the morphogenesis and deposition of the Late Quaternary sedimentary series.

  16. 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.

  17. Late Quaternary stratigraphy, sedimentology, and geochemistry of an underfilled lake basin in the Puna (north-west Argentina)

    USGS Publications Warehouse

    McGlue, Michael M.; Cohen, Andrew S.; Ellis, Geoffrey S.; Kowler, Andrew L.

    2013-01-01

    Depositional models of ancient lakes in thin-skinned retroarc foreland basins rarely benefit from appropriate Quaternary analogues. To address this, we present new stratigraphic, sedimentological and geochemical analyses of four radiocarbon-dated sediment cores from the Pozuelos Basin (PB; northwest Argentina) that capture the evolution of this low-accommodation Puna basin over the past ca. 43 cal kyr. Strata from the PB are interpreted as accumulations of a highly variable, underfilled lake system represented by lake-plain/littoral, profundal, palustrine, saline lake and playa facies associations. The vertical stacking of facies is asymmetric, with transgressive and thin organic-rich highstand deposits underlying thicker, organic-poor regressive deposits. The major controls on depositional architecture and basin palaeogeography are tectonics and climate. Accommodation space was derived from piggyback basin-forming flexural subsidence and Miocene-Quaternary normal faulting associated with incorporation of the basin into the Andean hinterland. Sediment and water supply was modulated by variability in the South American summer monsoon, and perennial lake deposits correlate in time with several well-known late Pleistocene wet periods on the Altiplano/Puna plateau. Our results shed new light on lake expansion–contraction dynamics in the PB in particular and provide a deeper understanding of Puna basin lakes in general.

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

    SciTech Connect

    Robertson, J.L.; Spencer, P.K. . 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.

  19. 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.

  20. Sedimentology and stratigraphy of Cenozoic deposits in the Kağızman-Tuzluca Basin, northeastern Turkey

    NASA Astrophysics Data System (ADS)

    Varol, Baki; Şen, Şevket; Ayyıldız, Turhan; Sözeri, Koray; Karakaş, Zehra; Métais, Grégoire

    2016-01-01

    The Kağızman-Tuzluca Basin is located in the northeastern Anatolia, to the east of the intersection point (near Karlıova) 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 (Kağan 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 (Halıkışlak and Kızılkaya 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.

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

    PubMed

    Phillips, Roger J; Zuber, Maria T; Smrekar, Suzanne E; Mellon, Michael T; Head, James W; Tanaka, Kenneth L; Putzig, Nathaniel E; Milkovich, Sarah M; Campbell, Bruce A; Plaut, Jeffrey J; Safaeinili, Ali; Seu, Roberto; Biccari, Daniela; Carter, Lynn M; Picardi, Giovanni; Orosei, Roberto; Mohit, P Surdas; Heggy, Essam; Zurek, Richard W; Egan, Anthony F; Giacomoni, Emanuele; Russo, Federica; Cutigni, Marco; Pettinelli, Elena; Holt, John W; Leuschen, Carl J; Marinangeli, Lucia

    2008-05-30

    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 approximately 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. PMID:18483402

  2. 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.

  3. 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.

  4. Identifying Fracture Types and Relative Ages Using Fluid Inclusion Stratigraphy

    SciTech Connect

    Dilley, Lorie M.; Norman, David; Owens, Lara

    2008-06-30

    Enhanced Geothermal Systems (EGS) are designed to recover heat from the subsurface by mechanically creating fractures in subsurface rocks. Understanding the life cycle of a fracture in a geothermal system is fundamental to the development of techniques for creating fractures. Recognizing the stage of a fracture, whether it is currently open and transmitting fluids; if it recently has closed; or if it is an ancient fracture would assist in targeting areas for further fracture stimulation. Identifying dense fracture areas as well as large open fractures from small fracture systems will also assist in fracture stimulation selection. Geothermal systems are constantly generating fractures, and fluids and gases passing through rocks in these systems leave small fluid and gas samples trapped in healed microfractures. Fluid inclusions trapped in minerals as the fractures heal are characteristic of the fluids that formed them, and this signature can be seen in fluid inclusion gas analysis. Our hypothesis is that fractures over their life cycle have different chemical signatures that we can see in fluid inclusion gas analysis and by using the new method of fluid inclusion stratigraphy (FIS) the different stages of fractures, along with an estimate of fracture size can be identified during the well drilling process. We have shown with this study that it is possible to identify fracture locations using FIS and that different fractures have different chemical signatures however that signature is somewhat dependent upon rock type. Open, active fractures correlate with increase concentrations of CO2, N2, Ar, and to a lesser extent H2O. These fractures would be targets for further enhancement. The usefulness of this method is that it is low cost alternative to current well logging techniques and can be done as a well is being drilled.

  5. Tethyan and German Triassic stratigraphy, correlation and numerical ages

    NASA Astrophysics Data System (ADS)

    Kozur, Heinz W.; Bachmann, Gerhard H.

    2010-05-01

    The correlation of the Germanic Triassic with the Tethyan Triassic is well constrained biostratigraphically. However, radiometric data are lacking and have to be imported for numerical calibration of litho- and chronostratigraphic units. These imported data can be extended to intervals without primary numerical data by astronomical calibration with Milankovitch cycles that are well recognisable in continental lake deposits of the Germanic Triassic, and correlated back to the marine realm. Such cross-correlation is a powerful method for improving numerical stage ages in the marine realm. The calculations of numerical ages for the Germanic Lower and Middle Triassic by astronomical calibration are remarkably close to the subsequently published most recent radiometric data of different authors. For the Lower Triassic, up to the base of the Anisian, the 252.5 ± 0.3 Ma for the basal I. isarcica Zone at Meishan (Mundil et al., 2001) was taken as a reference value. On this base, Kozur (2003) calculated a numerical age of 252.6 Ma for the Permian-Triassic boundary, which age was later confirmed with new radiometric data by Mundil et al. (2004). Bachmann & Kozur (2004) correlated the base of the Stammen Beds (= base Thuringian Chirotherium Sandstone) with the Anisian base and calculated for this boundary 247 Ma. Lehrmann et al. (2006) used high-precision single zircon data for determination of the Anisian base at 247.2 Ma. In the mainly marine Germanic Middle Triassic the radiometric data from the Tethyan Middle Triassic can be used after marine biostratigraphic correlation. Both the older (late Illyrian and Ladinian) and newer radiometric data (early and middle Anisian) fit well with the ages calculated by astronomical calibration. The greatest problems are in the Upper Triassic, where very few radiometric data are known. At present there are mutually exclusive ages that have been proposed for the Carnian-Norian boundary, each based on radiometric dates. These conflicting data have produced a "short Norian model" and a "long Norian model." In the SW USA, there are several new radiometric data from which approximately 218 Ma can be calculated for the Norian base (Irmis & Mundil, 2008, and J. Ramezani, CPCP Meeting Albuquerque, May 2009). This value is close to the 216.5 Ma of the Norian base by Gradstein et al. (2004) and Ogg et al. (2008). From these data a duration of the Norian of 10.5-12 myrs results (short Norian model). Such contradicts, however, the 230.91 ± 0.33 Ma for the late early Tuvalian (Furin et al., 2006) and a corrected age of 231.4 Ma for the Tuvalian Adamanian LVF of Ishigualasto, Argentina (Irmis & Mundil, 2008) which would require a minimum duration of the Tuvalian of 14-15.5 myrs. The Tuvalian substage would then be longer than the entire Norian, which seems very improbable. The long Norian model of Gallet et al. (2003) placed the Norian base at ~227 Ma in the lower Stockton Formation of the Newark Basin and estimated the duration of the Norian as ~25 myrs. According to biostratigraphic data this Norian base lies within the middle Tuvalian, and the duration of the Norian is too long. Bachmann & Kozur (2004) and Kozur & Weems (2007) placed the Norian base between 223 to 226 Ma and assumed a Norian duration of 17-20 myrs. These data fit well with the Tuvalian radiometric ages (Lagonegro Basin, Furin et al., 2006; Ishigualasto, Irmis & Mundil, 2008), and with the basal Norian age of 225 ± 3 Ma from Alaska (Gehrels et al., 1987).

  6. 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.

  7. 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.

  8. Till stratigraphy and sedimentology at the margins of terrestrially terminating ice streams: case study of the western Canadian prairies and high plains

    NASA Astrophysics Data System (ADS)

    Evans, David J. A.; Hiemstra, John F.; Boston, Clare M.; Leighton, Iain; Cofaigh, Colm Ó.; Rea, Brice R.

    2012-07-01

    Complex glacigenic sediment sequences arranged in large arcuate assemblages and demarcating the lobate termini of fast ice flow corridors in western Canada represent the terrestrial equivalents of the trough-mouth fans of the marine palaeo-ice stream record. Intensive sedimentological and stratigraphic investigations at a regional scale are employed in the interpretation of thick units or sequences of diamicton and two depositional scenarios are proposed. First, glacier-marginal till thickening and the stacking of till wedges takes place in areas where an ice stream margin was stationary for short periods of time. Stacks of subglacial traction tills potentially record annual sub-marginal incremental thickening at ice stream margins especially in areas where densely spaced recessional push moraines appear to record seasonal climatic forcing. Second, proglacial lake and valley infilling with glacilacustrine rhythmites and mass flow diamictons is associated with the advection of sub-marginal till into preglacial bedrock depressions and records ice stream marginal oscillations and debris influx into discontinuous proglacial lakes, which act as subaqueous sediment sinks for materials that would otherwise have been used to construct sub-marginal till wedges and moraines. Glacial overriding modifies the deposits produced in both scenarios through deformation and the dislocation and entrainment of bedrock and sediment rafts at the margins of bedrock valley walls, resulting in the widespread development of glacitectonites and megablocks. The occurrence of the thickest deposits as preglacial valley fills may be significant in groundwater siphoning away from subglacial deforming layers and the promotion of sticky spots.

  9. Sedimentology and Sequence Stratigraphy of the Lower Cretaceous Fortress Mountain and Torok Formations Exposed Along the Siksikpuk River, North-Central Alaska

    USGS Publications Warehouse

    Houseknecht, David W.; Schenk, Christopher J.; Wartes, Marwan A.

    2007-01-01

    An exposure of the Lower Cretaceous Fortress Mountain and Torok Formations along the Siksikpuk River in north-central Alaska provides a rare opportunity to observe the stratigraphic contact between these two formations and to interpret the depositional facies and sequence stratigraphy of the exposed strata. The Fortress Mountain Formation at the base of the measured section includes braided-fluvial and coastal-plain facies deposited in a lowstand-systems tract, and an overlying succession of mostly shallow marine facies deposited in the basal part of a transgressive-systems tract. The overlying Torok Formation includes a thick, upward-deepening succession of marine-shelf to marine-slope facies deposited in the upper part of the transgressive-systems tract. The upper part of the section includes marine-slope and incised-slope-channel turbidite deposits of the Torok Formation, interpreted as a highstand-systems tract. Consideration of the balance between accommodation and sediment flux inferred from the sequence-stratigraphic analysis suggests that both tectonics and eustasy may have influenced deposition of the lowstand-systems and transgressive-systems tracts. In contrast, the highstand-systems tract may have been primarily influenced by progradation of a regional sediment-dispersal system and by subsidence induced by sediment loading.

  10. 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. . 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.

  11. K-Ar ages and magnetic stratigraphy of a hotspot-induced, fast grown oceanic island: El Hierro, Canary Islands

    NASA Astrophysics Data System (ADS)

    Guillou, H.; Carracedo, J. C.; Torrado, F. Pérez; Badiola, E. Rodriguez

    1996-09-01

    The combined use of accurate radiometric dating and magnetic stratigraphy can be applied to define the main stages of the building of oceanic volcanic islands. This method has been successfully applied on the island of El Hierro, the westernmost island of the Canaries Archipelago. For the emerged part of this island, built in the last 1.2 Ma, magnetic stratigraphy and mapping show the presence of four consecutive subchrons. K-Ar dating of eighteen samples in stratigraphic sequences using an unspiked technique produced ages consistent with the general volcanic stratigraphy. The ages show that the magnetic polarity zones correlate to the upper part of the Matuyama and to the Brunhes chrons. The Jaramillo normal polarity subchron of the upper part of the Matuyama reverse polarity Chron is recorded in one of the lava sequences. The lower limit of this event is constrained by two ages of 1.04 ± 0.02 Ma and one of 1.05 ± 0.02 Ma, close to the value deduced from the astronomically tuned magnetic polarity time scale (APTS). The volcanic history can be summarised by two consecutive main basaltic volcanic edifices: the El Tinor, active during the upper part of the Matuyama Chron and the El Golfo edifice, constructed during the Brunhes Chron.

  12. 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.

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

    NASA Astrophysics Data System (ADS)

    Stöffler, D.; Ryder, G.

    2001-04-01

    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 principles of relative and absolute age dating of geologic surface units of the Moon. The geological setting of the Apollo and Luna landing areas are described as far as they are relevant for this reevaluation. We derive the following best estimates for the ages of the multi-ring basins and their related ejecta blankets and present alternative ages for the basin events (in parentheses): 3.92 +/- 0.03 Gyr (or 3.85 +/- 0.05 Gyr) for Nectaris, 3.89 +/- 0.02 Gyr (or 3.84 +/- 0.04 Gyr) for Crisium, 3.89 +/- 0.01 Gyr (or 3.87 +/- 0.03 Gyr) for Serenitatis, and 3.85 +/- 0.02 Gyr (or 3.77 +/- 0.02 Gyr) for Imbrium. Our best estimates for the ages of the mare landing areas are: 3.80 +/- 0.02 Gyr for Apollo 11 (old surface), 3.75 +/- 0.01 Gyr for Apollo 17, 3.58 +/- 0.01 Gyr for Apollo 11 (young surface), 3.41 +/- 0.04 Gyr for Luna 16, 3.30 +/- 0.02 Gyr for Apollo 15, 3.22 +/- 0.02 Gyr for Luna 24, and 3.15 +/- 0.04 Gyr for Apollo 12. The ages of Eratosthenian and Copernican craters remain: ~ 2.1 (?) Gyr (Autolycus), 800 +/- 15 Myr (Copernicus), 109 +/- 4 Myr (Tycho), 50.3 +/- 0.8 (North Ray crater, Apollo 16), and 25.1 +/- 1.2 (Cone crater, Apollo 14). When plotted against the crater densities of the relevant lunar surface units, these data result in a revised lunar impact flux curve which differs from the previously used flux curve in the following respects: (1) The ages of the stratigraphically most critical impact basins are notably younger, (2) the uncertainty of the calibration curve is decreased, especially in the age range from about 4.0 to 3.0 Gyr, (3) any curve for ages older than 3.95 Gyr (upper age limit of the Nectaris ejecta blanket) is abandoned because crater frequencies measured on such surface formations cannot be correlated with absolute ages obtained on lunar samples. Therefore, the impact flux curve for this pre-Nectarian time remains unknown. The new calibration curve for lunar crater retention ages less than about 3.9 Gyr provides an updated standard reference for the inner solar system bodies including Mars.

  14. Sedimentological and micromorphological investigation on the fill of the Bronze age wooden pool at Noceto La Torretta (northern Italy)

    NASA Astrophysics Data System (ADS)

    Zerboni, Andrea; Cremaschi, Mauro

    2010-05-01

    A recent excavation at Noceto La Torretta (Parma, northern Italy) revealed an exceptional archaeological structure, composed of a wooden pool, quadrangular in shape, about 12 x 6 m, up to 4 m deep. Since the beginning the pool appears as an unicum in the Prehistory of Europe (Bernabò Brea and Cremaschi, 2009); furthermore, it represents an important naturalistic and environmental archive and the sedimentary infilling undergone to sedimentological and micromorphological analyses. The Noceto La Torretta site is placed on the hydrographic left side of the Taro river, on the northernmost fringe of the Pleistocene Apennine terraces. On the basis of pottery type it is possible to attribute the structure to the Terramare culture (beginning of the advanced phase of the Middle Bronze Age, second half of XV century a.C.). Six radiocarbon dates are available up to now, and, once calibrated, they put the building and activity of the wooden pool between 1420 and 1320 cal. years BP. On the basis of sedimentological and micromorphological analyses (Cremaschi et al., 2009) the stratigraphic sequence could be divided into four groups of units. A) Upper deposits, silty and sandy sediments deposited by colluviation in shallow water, interlayered by charcoal and diatom rich layers. B) Organic deposits, formed in deeper and anoxic water. C) Gyttja in a sandy-silty matrix; three main facies are present: pair of organic and inorganic laminae (O/I), poorly laminated gyttja, anoxic and clastic layers. D) basal deposits. Considering the short time of the deposition inside the pool and the recurrent sedimentary facies, a seasonal control in sedimentation should be inferred. The gyttja-rich laminae should indicate the summer season, with intense biological activity inside and outside the pool, promoting a strong production of organics, while the anoxic and clastic layers are possibly related to the winter season (without production of organic matter). Finally, the O/I laminae represent the rain seasons (spring/autumn), marked by intense sheet-erosion of the banks of the pool. References Bernabò Brea, M., Cremaschi, M., 2009. La vasca di Noceto La Torretta. Acqua e civiltà nell'età del Bronzo. Università degli Studi di Milano e Skirà, Milano. Cremaschi, M., Ferrari, P., Salvioni, M., Zerboni, A., 2009. Il riempimento della vasca e della fossa. In: Bernabò Brea M., Cremaschi M. (Eds.), La vasca di Noceto La Torretta. Acqua e civiltà nell'età del Bronzo. Università degli Studi di Milano e Skirà, Milano, pp. 112-120.

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

    NASA Astrophysics Data System (ADS)

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

    2003-07-01

    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 and their relationship to the thermal evolution of the Moon. We performed new crater size-frequency distribution measurements in order to investigate the stratigraphy of mare basalts in Oceanus Procellarum and related regions such as Mare Nubium, Mare Cognitum, and Mare Insularum. We used high-resolution Clementine color data to define 86 spectrally homogeneous units within these basins, which were then dated with crater counts on Lunar Orbiter IV images. Our crater size-frequency distribution measurements define mineralogical and spectral surface units and offer significant improvements in accuracy over previous analyses. Our data show that volcanism in the investigated region was active over a long period of time from ~3.93 to 1.2 b.y., a total of ~2.7 b.y. Volumetrically, most of the basalts erupted in the Late Imbrian Period between ~3.3 and 3.7 b.y., and we see evidence that numerous units have been resurfaced. During the Eratosthenian Period, significantly less basalt was erupted. Depending on the absolute model ages that one can assign to the lunar chronostratigraphic systems, five units might be of Copernican age. Younger basalts are generally exposed in the center of the investigated area, that is, closer to the volcanic centers of the Aristarchus Plateau and Marius Hills. Older basalts occur preferentially along the northwestern margin of Oceanus Procellarum and in the southeastern regions of the studied area, i.e., in Mare Cognitum and Mare Nubium. Combining the new data with our previously measured ages for basalts in Mare Imbrium, Serenitatis, Tranquillitatis, Humorum, Australe, and Humboldtianum, we find that the period of active volcanism on the Moon lasted ~2.8 b.y., from ~4 b.y. to ~1.2 b.y. On the basis of the basalts dated so far, which do not yet include the potentially young basalts of Mare Smythii [e.g., Schultz and Spudis, 1983], we conclude that Oceanus Procellarum not only exhibits the widest range of ages of all investigated basins but probably also is the location of some of the youngest basalts on the lunar surface.

  16. The Cambrian to Devonian odyssey of the Brabant Massif within Avalonia: A review with new zircon ages, geochemistry, Sm-Nd isotopes, stratigraphy and palaeogeography

    NASA Astrophysics Data System (ADS)

    Linnemann, Ulf; Herbosch, Alain; Liégeois, Jean-Paul; Pin, Christian; Gärtner, Andreas; Hofmann, Mandy

    2012-05-01

    This study provides an up-to-date and comprehensive review of the Early Palaeozoic evolution of the Brabant Massif belonging to the Anglo-Brabant Deformation Belt. Situated at the southeastern side of Avalonia microplate, it is the only well-known part of the northern passive margin of the Rheic Ocean. The Cambrian-Silurian sedimentary pile is > 13 km thick, with > 9 km for the Cambrian only. The unraveling of this continuous registration reflects the successive rifting and drifting of Avalonia from the Gondwana mainland, followed by soft-collisional processes with Baltica and finally the formation of Laurussia. Based on recently established detailed stratigraphy, sedimentology and basin development, on U-Pb LA-ICP-MS analyses of igneous and detrital zircon grains along with geochemical data including Sm-Nd isotopes, a new geodynamic and palaeogeographic evolution is proposed. Brabant Megasequence 1 (lower Cambrian to lowermost Ordovician, > 9 km thick) represents an embayment of the peri-Gondwanan rift from which the Rheic Ocean has evolved. Detrital zircon ages demonstrate that the Brabant is a typical peri-Gondwanan terrane with a major Pan-African (Neoproterozoic age) and a mixed West African and Amazonian source (Palaeoproterozoic, Archaean and some Mesoproterozoic age). The transition towards the Avalonia drifting is marked by an unconformity and a short volcanic episode. The northward drift of Avalonia towards Baltica is recorded by the Megasequence 2 (Middle to Upper Ordovician, 1.3 km thick). The source for Mesoproterozoic zircons vanished, as the result of the Rheic Ocean opening and the isolation from Amazonian sources. The transition to Megasequence 3 is marked by a drastic change in palaeobathymetry and an important (sub)volcanic episode during a tectonic instability period (460-430 Ma), reflecting the Avalonia-Baltica soft docking as also shown by the reappearance of Mesoproterozoic detrital zircons, typical of Baltica. Unradiogenic Nd isotope signature (ɛNd - 4/- 5) and TDM model ages (1.3-1.7 Ga) for Brabant magmatic rocks indicate an old recycled component. Megasequence 3 (uppermost Ordovician to lowermost Devonian; > 3.5 km thick) includes the onset of a Silurian foreland basin that reflects the tectonic inversion of the core of the massif (Brabantian orogeny) in response to the Baltica-Avalonia-Laurentia collision. Finally, the comparison with the strikingly similar Cambrian successions of the Harlech Dome (Wales, Avalonia) and the Meguma terrane (Nova Scotia, peri-Gondwana) allows the construction of a new Early Cambrian palaeogeographic model for the whole Avalonia microplate, in which the Meguma terrane is included.

  17. 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.

  18. 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.

  19. Fracture and mechanical stratigraphy for Mississippian-Pennsylvanian age carbonates, Ozark Dome, NW Arkansas

    NASA Astrophysics Data System (ADS)

    Peppers, M.; Burberry, C. M.

    2014-12-01

    Identifying natural fracture patterns in an area gives a detailed look into the local tectonic history. Comparing those fractures to the mechanical properties of the rocks provides key insights into predicting fractures in the subsurface. The Ozark Dome is an ideal study area for fracture research due to multiple fracturing events resulting from the multi-stage deformation Ouachita Orogeny during the late Paleozoic. This study used field observations of lithology and fracture attributes over ~10 outcrops in the Mississppian-Pennsylvanian (360-298 ma) carbonate sequence of the Ozark Plateau. Outcrops were chosen having excellent lithological exposure up the sequence from the Boone to Atoka formations and with 3D representations of the fracture patterns. In all, the area investigated covered nearly 60 square miles. Fracture attributes collected included fracture intensity, length, and abutting relationships; and rock hardness data collected from a Schmidt Hammer. Data was analyzed using programs such as Stereonet and MOVE structural software that generated rose diagrams, structural cross sections, and products. Initial results indicate 4 main fracture orientations that resulted from at least 3 discrete phases of deformation during the Miss-Penn. Initial results also indicate that the present-day mechanical stratigraphy is not the same one that existed during the deformation phases. Work done at the Tiger Blvd. outcrops showed at least 2 distinct mechanical units. Fractures observed at the outcrop did not respect mechanical bed boundaries, and showed no relationship to the differences in mechanical properties observed. This study will aid in the interpretation of fractures in regards to mechanical stratigraphy, which allows for a better understanding of subsurface fracture prediction in carbonate sequences worldwide. Finally, the fracture work here will also help in elucidating the tectonic history of the field area during the Mississippian and Pennsylvanian.

  20. 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.

  1. 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 δ13C 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.

  2. 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. ); Tauxe, L. ); Monaghan, M. )

    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.

  3. Ochoan (upper Permian) stratigraphy and age determinations, southeastern New Mexico and west Texas

    SciTech Connect

    Lucas, S.G. ); Anderson, O.R. )

    1994-03-01

    Upper Permian strata, which are the stratotype of the Ochoan State (Series), have an extensive subsurface distribution and limited outcrop area in southeastern New Mexico and west Texas. The oldest strata are alternating laminae of anhydrite and calcite of the Castile Formation and are as much as 700 m thick. The closely related and overlying Salado Formation is a much as 600 m thick and is mostly halite and argillaceous halite with minor anhydrite. The overlying Rustler Formation is as much as 150 m thick and consists of anhydrite, red silty shale and magnesian limestone. Overlying red beds are the Quartermaster Formation (Dewey Lake Formation is a synonym, as is the term Pierce Canyon red beds), which is as much as 106 m thick and consist of fine sandstones, siltstones, and minor gypsum. The Castile rests disconformably on the Capitanian (middle Permian) Lamar Limestone Member of the Bell Canyon Formation and its equivalent, the Tansill Formation of the Artesia Group. Counting of Castile-Salado laminae and their posited relationship to astronomical cycles suggests that Castile-Salado deposition took only 200,000-300,000 yr. Limited assemblages of brachiopods and conodonts from the Rustler Formation indicate a Late Permian age, but are no more precise age indicators. A small assemblage of bivalves, K-Ar ages and magnetostratigraphy indicate a late Permian age for the Quartermaster Formation. There is no evidence to support a Triassic age assignment for the Quarter-master; it is disconformably overlain by the Upper Triassic (Carnian) Chinle group. Most workers us the Ochoan as a Late Permian Stage-Age, although its typical strata generally lack good age indicators and may represent relatively short and sporadic intervals of the Late Permian. We prefer recognition of the Ochoan as a lithostratigraphic unit (group) without regional or global geochronologial significance.

  4. 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. )

    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.

  5. Constraints on the age of the Great Sand Dunes, Colorado, from subsurface stratigraphy and OSL dates

    USGS Publications Warehouse

    Madole, Richard F.; Mahan, Shannon; Romig, Joe H.; Havens, Jeremy C.

    2013-01-01

    The age of the Great Sand Dunes has been debated for nearly 150 yr. Seven ages ranging from Miocene to late Holocene have been proposed for them. This paper presents new information—chiefly subsurface stratigraphic data, OSL dates, and geomorphic evidence—that indicates that the Great Sand Dunes began to form in the latter part of the middle Pleistocene. The dunes overlie a thick wedge of piedmont-slope deposits, which in turn overlies sediment of Lake Alamosa, a paleolake that began to drain about 440 ka. The wedge of piedmont-slope deposits extends westward for at least 23 km and is as much as 60 m thick at a distance of 10 km from the Sangre de Cristo Range. Ostracodes from one well indicate that the eastern shoreline of Lake Alamosa extended to within 4.3 km of where the Great Sand Dunes eventually formed. The time represented by the wedge of piedmont-slope deposits is not known exactly, but the wedge post-dates 440 ka and was in place prior to 130 ka because by then the dunes overlying it were sufficiently close and tall enough to obstruct streams draining from the Sangre de Cristo Range.

  6. 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.

  7. A history of glacial stratigraphy in China

    NASA Astrophysics Data System (ADS)

    Derbyshire, Edward

    Glacial stratigraphy had a late start in China, and it fell to Li Szeguang, an outstanding geologist with a little experience of the European Alps, to inject a systematic approach into the study of Chinese Pleistocene glacial stratigraphy starting in the early 1920s. Several diamictons in low latitude mountains of E. China were attributed to glaciation. A formal stratigraphy had to await his detailed and long term studies of the Lushan (29°30'N) on which he based a three-fold sequence of Poyang (Gunz correlate), Da Gu (= Mindel) and Lushan (Riss). A Dali (Würm) glaciation was added on the basis of evidence from Yunnan Province. Based on much morphological and erosional evidence as well as an assumption of glacial provenance for the widespread bouldery clays, and despite early critical reviews, this work became the dominant hypothesis in Chinese glacial stratigraphy for over 50 years. Echoes of it still remain in the literature, despite mounting sedimentological evidence that the diamictons are weathered debris flow and alluvial accumulations (with some thin, high-level solifluction earths). Increasingly, glacial stratigraphy is now being based on the glaciated west of China from Yunnan to western Xinjiang and it is here that the definitive glacial stratigraphy will be established. At least four glaciations arealready authenticated in many localities in this vast region, although the resolution of this stratigraphy may never match that of the classic loess stratigraphy of Shaanxi and the yet-to-be studied stratigraphy of the thick lacustrine successions in the high desert basins of the west.

  8. 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.

  9. 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.

  10. Messinian events: new constraints from sedimentological investigations and new 40Ar/ 39Ar ages in the Melilla-Nador Basin (Morocco)

    NASA Astrophysics Data System (ADS)

    Cornée, J. J.; Roger, S.; Münch, P.; Saint Martin, J. P.; Féraud, G.; Conesa, G.; Pestrea-Saint Martin, S.

    2002-07-01

    New 40Ar/ 39Ar ages obtained both from within a platform and from the adjacent basin allow, through the extension of a previous argon dataset, the establishment of a chronological framework for the Messinian carbonate complex of Melilla (Morocco). In the platform, prograding bioclastic deposits began around 6.87±0.02 Ma, whereas the youngest preserved deposits are 5.77±0.04 Ma old. The southern part of the basin was uplifted and emergent prior to 6.23±0.03 Ma. The Tortonian/Messinian and the Messinian/Pliocene boundaries have not yet been identified in the Melilla region. Durations of the prograding bioclastic deposits (ca. 410 ka), the prograding Porites reefs (ca. 360 ka) and the preserved part of the terminal carbonate complex (TCC) (ca. 330 ka) can be estimated. Sedimentological and geochronological investigations do not indicate any major subaerial unconformity nor any major time gap. If a major sea level fall did exist during Messinian times, it developed after 5.77±0.04 Ma. Chronological correlations show that the onset of the Sorbas gypsum deposition (Southern Spain), considered as the marker of the Messinian Salinity Crisis onset, is contemporaneous with aggrading Porites reef building of the terminal carbonate complex of Melilla. A major paleoceanographic change in the marginal areas of the Mediterranean, with the cessation of upwelling systems, could be partly coeval with the onset of the Messinian Salinity Crisis.

  11. Stratigraphy, age and environments of the late Miocene Mpesida Beds, Tugen Hills, Kenya.

    PubMed

    Kingston, John D; Fine Jacobs, Bonnie; Hill, Andrew; Deino, Alan

    2002-01-01

    Interpretations of faunal assemblages from the late Miocene Mpesida Beds in the Tugen Hills of the Central Kenyan Rift Valley have figured prominently in discussions of faunal turnover and establishment of the modern East African communities. These faunal changes have important implications for the divergence of the human lineage from the African apes ca. 8-5 Ma. While fossil material recovered from the Mpesida Beds has traditionally been analyzed collectively, accumulating evidence indicates that Mpesida facies span the 7-6 Ma interval and are scattered more than 25 km along the eastern flanks of the Tugen Hills. Stratigraphic distinctions between Mpesida facies and younger sediments in the sequence, such as the Lukeino Formation, are not yet fully resolved, further complicating temporal assessments and stratigraphic context of Mpesida facies. These issues are discussed with specific reference to exposures of Mpesida facies at Rurmoch, where large fossil tree fragments were swept up in an ancient ash flow. Preserved anatomical features of the fossil wood as well as estimated tree heights suggest a wet, lowland rainforest in this portion of the rift valley. Stable isotopic analyses of fossil enamel and paleosol components indicate the presence of more open habitats locally. Overlying air-fall tuffs and epiclastic debris, possibly associated with the ash flow, have yielded an assemblage of vertebrate fossils including two teeth belonging to one of the earliest colombines of typical body size known from Africa, after the rather small Microcolobus. Single-crystal, laser-fusion,(40)Ar/(39)Ar dates from a capping trachyte flow as well as tuffs just below the lava contact indicate an age of greater than 6.37 Ma for the fossil material. PMID:11795970

  12. Subsurface stratigraphy and geochemistry of late Quaternary evaporites, Searles Lake, California, with a section on radiocarbon ages of stratigraphic units

    USGS Publications Warehouse

    Smith, George I.; Stuiver, Minze

    1979-01-01

    Searles Lake is a dry salt pan, about 100 km 2 in area, that lies on the floor of Searles Valley, in the desert of southeast California. Several salt bodies of late Quaternary age lie beneath the surface, mostly composed of sodium and potassium carbonate, sulfate, chloride, and borate minerals. Mud layers separate the salt bodies, which contain interstitial brine that is the source of large quantities of industrial chemicals. The value of annual production from the deposit exceeds $30 million; total production to date exceeds $1 billion. The salts and muds were deposited during Pleistocene and Holocene times by a series of large lakes (200 m maximum depth, 1,000 km 2 maximum area) that fluctuated in size in response to climatic change. Salts were deposited during major dry (interpluvial) episodes, muds during wet (pluvial) episodes that correlate with glacial advances in other parts of North America and the world. Data based on cores from the deposit are used in this paper to establish the stratigraphy of the deposit, the chemical and mineral compositions of successive units, and the total quantities of components contained by them. These parameters are then used to determine the geochemical evolution of the sedimentary layers. The results provide a refined basis for reconstructing the limnology of Searles Lake and the regional climate during late Quaternary time. Six main stratigraphic units were distinguished and informally named earlier on the basis of their dominant composition: Unit Typical thickness 14C age, uncorrected (in meters) (years B.P.) Overburden Mud 7 0 to >3,500 Upper Salt 15 >3,500 to 10,500 Parting Mud 4 10,500 to 24,000 Lower Salt 12 24,000 to 32,500 Bottom Mud 30 32,500 to 130,000 Mixed Layer 200+ > 130,000 (The age of 130,000 years for the Mixed Layer is based on extrapolated sedimentation rates.) The Lower Salt is subdivided into seven salt units (S-l to S-7) and six mud units (M-2 to M-7), the Mixed Layer into six units (A to F). For each salt unit, the areal extent, volume, shape, mineralogy, and chemical composition of the solids and brines have been determined; for each mud unit (which originally extended over much of the basin), the shape and volume within a standard area, and the mineralogy, have been determined. The bulk compositions (brines plus salts) of the combined Lower Salt units S-l to S-5 and units S-6 and S-7, and the Upper Salt, were determined so that the total quantities and ratios of ions in the initial brines could be reconstructed. The 74 published HC dates on Searles Lake core samples from all but the oldest unit are supplemented by 14 new dates (determined by Minze Stuiver) on the Lower Salt. Most of the age control comes from dates based on disseminated organic carbon; two dates are on wood; dates on carbonate minerals are less reliable. Although the probable disequilibrium between the carbon in the lake and atmosphere (because of contamination, slow equilibrium rates, and other factors) causes disseminated carbon dates to be an estimated 500-2,500 years 'too old,' the ages of the major and minor units are relatively well established. The list above indicates rounded and uncorrected ages for the contacts of major units. The age of the only salt bed in the Lower Salt which indicates desiccation (S-5) is about 28,000 years. The average uncorrected sedimentation rate in the Parting Mud is 4

  13. Characterizing avulsion stratigraphy in ancient alluvial deposits

    NASA Astrophysics Data System (ADS)

    Jones, H. L.; Hajek, E. A.

    2007-11-01

    Guidelines for identifying ancient avulsion deposits were set forth by Kraus and Wells [Kraus, M.J., Wells, T.M., 1999. Recognizing avulsion deposits in the ancient stratigraphical record. In: Smith, N.D., Rogers, J. (Eds.), Fluvial Sedimentology VI, Special Publication of the International Association of Sedimentologists, vol. 28, pp. 251-268], building on the study by Smith et al. [Smith, N.D., Cross, T.A., Dufficy, J.P., Clough, S.R., 1989. Anatomy of an avulsion. Sedimentology 36, 1-23] of the modern Saskatchewan River system (Cumberland Marshes, central Canada), and serve to characterize avulsion depositional sequences in the ancient Willwood and Fort Union Formations (Paleogene, Bighorn Basin, NW Wyoming, USA). We recognize, however, that the model is not universally applicable to avulsion-dominated successions, specifically systems which lack defining "heterolithic avulsion deposits", set forth by Kraus and Wells [Kraus, M.J., Wells, T.M., 1999. Recognizing avulsion deposits in the ancient stratigraphical record. In: Smith, N.D., Rogers, J. (Eds.), Fluvial Sedimentology VI, Special Publication of the International Association of Sedimentologists, vol. 28, pp. 251-268]. Observations in several fluvial intervals suggest that the avulsion stratigraphy outlined by Kraus and Wells [Kraus, M.J., Wells, T.M., 1999. Recognizing avulsion deposits in the ancient stratigraphical record. In: Smith, N.D., Rogers, J. (Eds.), Fluvial Sedimentology VI, Special Publication of the International Association of Sedimentologists, vol. 28, pp. 251-268] represents one category of avulsion stratigraphy found in the rock record, but does not capture the nature of avulsion deposits everywhere. Based on observations (using measured sections, outcrop photo-panels, and aerial photographs) in the Willwood Formation (Eocene, Wyoming) and Ferris Formation (Cretaceous/Paleogene, Wyoming), we present two end-member categories of avulsion stratigraphy in ancient deposits; stratigraphically abrupt, when a main paleochannel is stratigraphically juxtaposed directly atop floodplain/overbank deposits, and stratigraphically transitional, where crevasse splays and other non-floodplain/-overbank deposits stratigraphically precede a main paleochannel. This characterization provides a broader, more inclusive way to recognize and describe avulsion stratigraphy in ancient deposits and may be an important factor to consider when modeling connectivity in fluvial reservoirs. Furthermore, our observations show that one type of avulsion channel stratigraphy may prevail over another within an ancient basin, suggesting that system-wide factors such as splay-proneness or avulsion style (i.e. aggradational, incisional, etc.; [Slingerland, R., Smith, N.D., 2004. River avulsions and their deposits. Annual Review of Earth and Planetary Sciences 32, 257-285]) may be primary controls on the type of avulsion stratigraphy deposited and preserved in ancient basin-fills.

  14. Late Quaternary sedimentological and climate changes at Lake Bosumtwi Ghana: new constraints from laminae analysis and radiocarbon age modeling

    USGS Publications Warehouse

    Shanahan, Timothy M.; Beck, J. Warren; Overpeck, Jonathan T.; McKay, Nicholas P.; Pigati, Jeffrey S.; Peck, John A.; Scholz, Christopher A.; Heil, Clifford W., Jr.; King, John W.

    2012-01-01

    The Lake Bosumtwi sediment record represents one of the longest and highest-resolution terrestrial records of paleoclimate change available from sub-Saharan Africa. Here we report a new sediment age model framework for the last ~ 45 cal kyr of sedimentation using a combination of high-resolution radiocarbon dating, Bayesian age-depth modeling and lamination counting. Our results highlight the practical limits of these methods for reducing age model uncertainties and suggest that even with very high sampling densities, radiocarbon uncertainties of at least a few hundred years are unavoidable. Age model uncertainties are smallest during the Holocene (205 yr) and the glacial (360 yr) but are large at the base of the record (1660 yr), due to a combination of decreasing sample density, larger calibration uncertainties and increases in radiocarbon age scatter. For portions of the chronology older than ~ 35 cal kyr, additional considerations, such as the use of a low-blank graphitization system and more rigorous sample pretreatment were necessary to generate a reliable age depth model because of the incorporation of small amounts of younger carbon. A comparison of radiocarbon age model results and lamination counts over the time interval ~ 15–30 cal kyr agree with an overall discrepancy of ~ 10% and display similar changes in sedimentation rate, supporting the annual nature of sediment laminations in the early part of the record. Changes in sedimentation rates reconstructed from the age-depth model indicate that intervals of enhanced sediment delivery occurred at 16–19, 24 and 29–31 cal kyr, broadly synchronous with reconstructed drought episodes elsewhere in northern West Africa and potentially, with changes in Atlantic meridional heat transport during North Atlantic Heinrich events. These data suggest that millennial-scale drought events in the West African monsoon region were latitudinally extensive, reaching within several hundred kilometers of the Guinea coast. This is inconsistent with a simple southward shift in the mean position of the monsoon rainbelt, and requires changes in moisture convergence as a result of either a reduction in the moisture content of the tropical rainbelt, decreased convection, or both.

  15. Age constraints, sedimentology, and tectonics from a well bedded sequence of Feuerstätter Sandstein south of Balderschwang, Allgäu Alps, Bavaria

    NASA Astrophysics Data System (ADS)

    Blaha, Ulrich; Scholz, Herbert; Rochow, Henning v.; Lebsanft, Frans

    2014-05-01

    The majority of the outcrops of the alpine Feuerstätter Sandstein in southwestern Bavaria and Vorarlberg (Austria) suggests rather massive, homogeneous, more or less glauconite-containing sandstone bodies than well bedded sequences. Normally, the up to 50 m thick Feuerstätter Sandstein formation is characterized by the absence of datable material, massive brittle tectonic deformation and recent mass movements. In contrast, an unusually well bedded sequence of Feuerstätter Sandstein is exposed in the Lappach valley south of the village of Balderschwang, lining the border between Bavaria and Vorarlberg. This specific sandstone succession contains several thin marly intercalations from which samples have been collected recently. Calcareous nannoplancton dating of these marl samples provides an upper Middle-Eocene depositional age which is the youngest age reported for the Feuerstätter Sandstein. The sequence of the quartz sandstone of the Lappach succession including the marly layers is tectonically undisturbed. The beds dip northwards, steeply inclined at the bottom (85°) and moderately in the uppermost part (40°) of the sequence. The sandstone beds of the main part of the complex reveal mostly layers which are 0.1 to 0.7 m thick. In contrast, the uppermost beds exposed within the sequence show an increasing thickness of 2.5 to 4.5 m. A variety of different sedimentary structures occur in individual beds of the lower part: graded bedding, varying grain sizes, different amounts of glauconite, local occurrence of feldspar clasts, fine lamination and N-S striking channel structures at the bottom of certain sandstone layers. Within the uppermost exposed particularly thick and poorly to unsorted deposits of the sequence coarser grain sizes occur, containing even small quartz pebbles. The continuous development from the well bedded and fine grained basal layers towards the massive and coarser grained sandstone deposits at the top suggests sedimentation from a distal to a proximal position in a submarine fan, reflecting an increase of energy within the deposits. Sedimentary structures and northwards inclined beds suggest sediment transport from south to north. Additionally, a syn-sedimentary northward tilting of the base of the sedimentary succession during deposition cannot be excluded. Origin of the deposited sands is most likely a diversified coastal realm providing sand material of various stages of maturity and composition. Among instabilities of sand masses near the coast, frequent seismic activities can be assumed to have triggered the individual events of deposition observed in the Lappach valley sandstone succession, most likely driven by actively prograding tectonic nappes in the south.

  16. Lithofacies, Age, and Sequence Stratigraphy of the Carboniferous Lisburne Group in the Skimo Creek Area, Central Brooks Range

    USGS Publications Warehouse

    Dumoulin, Julie A.; Whalen, Michael T.; Harris, Anita G.

    2008-01-01

    The Lisburne Group, a mainly Carboniferous carbonate succession that is widely distributed across northern Alaska, contains notable amounts of oil and gas at Prudhoe Bay. Detailed studies of the Lisburne in the Skimo Creek area, central Brooks Range, delineate its lithofacies, age, conodont biofacies, depositional environments, and sequence stratigraphy and provide new data on its hydrocarbon source-rock and reservoir potential, as well as its thermal history, in this area. We have studied the Lisburne Group in two thrust sheets of the Endicott Mountains allochthon, herein called the Skimo and Tiglukpuk thrust sheets. The southern, Skimo Creek section, which is >900 m thick, is composed largely of even-bedded to nodular lime mudstone and wackestone intercalated with intervals of thin- to thick-bedded bioclastic packstone and grainstone. Some parts of the section are partially to completely dolomitized and (or) replaced by chert. A distinctive, 30-m-thick zone of black, organic-rich shale, lime mudstone, and phosphorite is exposed 170 m below the top of the Lisburne. The uppermost 40 m of section is also distinctive and made up of dark shale, lime mudstone, spiculite, and glauconitic grainstone. The northern, Tiglukpuk Creek section, which is similar to the Skimo Creek section but only ~760 m thick, includes more packstone and grainstone and less organic-rich shale. Analyses of conodonts and foraminifers indicate that both sections range in age from late Early Mississippian (Osagean) through Early Pennsylvanian (early Morrowan) and document a hiatus of at least 15 m.y. at the contact between the Lisburne and the overlying Siksikpuk Formation. No evidence of subaerial exposure was observed along this contact, which may represent a submarine erosional surface. Lithofacies and biofacies imply that the Lisburne Group in the study area was deposited mainly in midramp to outer-ramp settings. Deepest water strata are mud rich and formed below storm or fair-weather wave base on the outer ramp to outer midramp; shallowest facies are storm, sand-wave, and shoal deposits of the inner midramp to inner ramp. A relatively diverse, open-marine fauna occurs throughout much of the Lisburne in the study area, but some beds also contain clasts typical of more restricted, shallow-water environments that were likely transported seaward by storms and currents. Radiolarians are abundant in the shale and phosphorite unit at Skimo Creek and also occur in equivalent strata at Tiglukpuk Creek; high gamma-ray response and elevated total organic-carbon contents (max 5?8 weight percent) also characterize this unit at Skimo Creek. Lithologic, faunal, and geochemical data all suggest that these rocks formed mainly in an outer-ramp to basinal setting with low sedimentation rates, high productivity, and poorly oxygenated bottom water. Shale and mudstone at the top of the Lisburne Group accumulated in a similarly sediment starved, mainly outer ramp environment but lack comparable evidence for high nutrient and low oxygen levels during deposition. Vertical shifts in rock types and faunas delineate numerous parasequences and six probable third-order sequences in the study area; the same sequences are also recognized in the Lisburne Group to the east. Transgressive-system tracts in these sequences generally fine upward, whereas highstand-system tracts coarsen upward. Sequences in the Tiglukpuk Creek section are mostly thinner, contain thinner and more numerous parasequences, and accumulated in somewhat shallower settings than those in the Skimo Creek section. These differences reflect the more seaward position and, thus, increased accommodation space of the Skimo Creek section relative to the Tiglukpuk Creek section during deposition. Organic-rich calcareous shale in the shale and phosphorite unit has a cumulative thickness of at least 15 m and a lateral extent of >50 km; this lithology is the best potential hydrocarbon source rock in the Lisburne Group

  17. 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.

  18. Stratigraphy of small shield volcanoes on Venus: Criteria for determining stratigraphic relationships and assessment of relative age and temporal abundance

    NASA Astrophysics Data System (ADS)

    Ivanov, Mikhail A.; Head, James W.

    2004-10-01

    Small volcanic edifices, shields with a diameter less than about 20 km, are common and sometimes very abundant features on the plains of Venus. Typically, they form tight or loose clusters of features known as shield fields. Small shields are interpreted to be formed due to small-scale eruptions through numerous and distinct sources, a mode of formation apparently significantly different from the mechanism thought to be responsible for the emplacement of the vast regional plains of Venus. Did the eruption style of small shields occur repeatedly throughout the visible part of the geologic record of Venus? Or was this style more concentrated in a specific epoch or epochs of geologic history? Do the clusters of shields represent localized development of sources over a thermal anomaly such as a plume, or do they represent exposures or kipukas of a more regional unit or units? A major step toward answering these questions is an understanding of small shield stratigraphy. Multiple criteria have been developed to assess the stratigraphic relationships of individual small shields and that of shield fields with the adjacent units. In our analysis, we expanded and developed the previous criteria and added detailed criteria to describe specific patterns of deformation within shield fields, cross-cutting, and embayment relationships between shield fields and surrounding units. We also used secondary characteristics of shield fields such as radar albedo difference, changes in shield density and size, etc. In our study, we applied these criteria and analyzed in detail stratigraphic relationships of shield fields in a random sample of features (64 fields) and in the global geotraverse along 30°N (77 fields). The total number of analyzed shield fields (141) represents about 22% of the general population of these features catalogued by Crumpler and Aubele [2000]. The majority of the fields (98, or ~69%) predate emplacement of material of vast regional plains with wrinkle ridges. Fifteen fields (~11%) appear to be synchronous with regional plains, and eleven fields (~8%) postdate the plains. Nine fields (~6%) display ambiguous relationships with regional plains and their relative age is uncertain, and eight fields (~6%) represent unclear cases when fields are covered by crater-related materials or by young lava flows or are not in contact with regional plains. The results of our study provide evidence for a distinct change of volcanic style from the mode of formation of globally abundant small shields to the mode of emplacement of vast regional plains in many areas on Venus. This systematic change of volcanic style appears to be inconsistent with the ``nondirectional'' or quasi steady state character of the geologic record of Venus. Although individual small shields were formed throughout the majority of the visible geologic history of Venus, in the syn- and postregional plains time the small-shields style of volcanism was significantly reduced in abundance. The shield fields that predate regional plains do not display a strong tendency to form a single group or a few groups and can be found virtually in all places on Venus. We interpret this observation to mean that these shield fields were globally distributed before the emplacement of regional plains. This interpretation means that the shield fields embayed by regional plains represent exposures of a specific, globally widespread unit, shield plains (psh). In contrast, shield fields that postdate regional plains occur preferentially in the Beta-Atla-Themis region on Venus, well known for its concentration of relatively young volcanic and tectonic activity. The spatial association of relatively young fields with the large centers of young volcanism suggests a genetic link of these fields with the formation and development of the large-scale volcanic centers. The abrupt decrease of the number of shields that postdate the formation of shield plains (psh) strongly suggests a major change of the style of volcanism following their emplacement as a globally distributed unit.

  19. Sedimentology of the Pennsylvanian and Permian Strathearn Formation, Northern Carlin Trend, Nevada; with a section on microfossil controls on the age of the Strathearn Formation

    USGS Publications Warehouse

    Berger, Vladimir I.; Singer, Donald A.; Theodore, Ted G.; Harris, Anita G.; Stevens, Calvin H.

    2001-01-01

    Two framework-supported, poorly bedded conglomerate units of the middle Upper Pennsylvanian and middle Lower Permian Strathearn Formation belonging to the overlap assemblage of the Antler orogen are prominent in the northern Carlin trend. These horizons stratigraphically and temporally bracket thrust emplacement of a major allochthonous thrust plate of mainly quartzarenite of the Ordovician Vinini Formation. Lithologic and shape-ratio data from approximately 4,200 pebbles and cobbles at 17 sites as well as biostratigraphic data in the Strathearn, and their geologic implications, are included in this report. Conodont biofacies throughout the Strathearn Formation are normal marine and suggest middle shelf or deeper depositional environments. The conglomerate units roughly are similar in that they contain only chert and quartzarenite pebbles, but they differ in compositional proportions of the two lithologies. The relative proportion of quartzarenite pebbles increases sixfold in the middle Lower Permian upper conglomerate unit versus its content in the middle Upper Pennsylvanian lower unit, whereas chert pebbles predominate in both units. Various roundness categories of chert pebbles in both conglomerate units of the Strathearn show that the equant pebble class (B/A) = 1 clearly is represented strongly even in the subangular category, the lowest roundness categories for the pebbles. Thus, development of equant pebbles cannot be ascribed totally to a rounding process during predeposition transport. The equant character of many pebbles might, in part, be an original feature inherited from pre-erosion rock fractures and (or) bedding that control overall form of the fragments prior to their release to the transport environment. The allochthon of the Coyote thrust has been thrust above the lower conglomerate unit of the Strathearn during a regionally extensive contractional event in the late Paleozoic. The middle Lower Permian upper conglomerate unit, highest unit recognized in the Strathearn Formation, as well as similarly-aged dolomitic siltstone, onlap directly onto quartzarenite that comprises the allochthon of the Coyote thrust. The conglomerate units thus represent submarine fanglomerates whose quartz grains and quartzarenite fragments of variable roundness and shape were derived from a sedimentologically restored largely southeastward advancing late Paleozoic allochthonous lobe of mostly quartzarenite of the Ordovician Vinini Formation. Chert fragments in the conglomerates probably were derived mostly from Devonian Slaven Chert, including a widespread thick melange unit of the Slaven in the footwall of the Coyote thrust. Some chert pebbles may have been derived from the Ordovician Vinini Formation.

  20. First Clarkforkian equivalent Land Mammal Age in the latest Paleocene basal Sparnacian facies of Europe: fauna, flora, paleoenvironment and (bio)stratigraphy.

    PubMed

    Smith, Thierry; Quesnel, Florence; De Plöeg, Gaël; De Franceschi, Dario; Métais, Grégoire; De Bast, Eric; Solé, Floréal; Folie, Annelise; Boura, Anaïs; Claude, Julien; Dupuis, Christian; Gagnaison, Cyril; Iakovleva, Alina; Martin, Jeremy; Maubert, François; Prieur, Judicaël; Roche, Emile; Storme, Jean-Yves; Thomas, Romain; Tong, Haiyan; Yans, Johan; Buffetaut, Eric

    2014-01-01

    The Paleocene-Eocene Thermal Maximum (PETM) is correlated with the first occurrences of earliest modern mammals in the Northern Hemisphere. The latest Paleocene Clarkforkian North American Land Mammal Age, that has yielded rodents and carnivorans, is the only exception to this rule. However, until now no pre-PETM localities have yielded modern mammals in Europe or Asia. We report the first Clarkforkian equivalent Land Mammal Age in the latest Paleocene deposits of the basal Sparnacian facies at Rivecourt, in the north-central part of the Paris Basin. The new terrestrial vertebrate and macroflora assemblages are analyzed through a multidisciplinary study including sedimentologic, stratigraphic, isotopic, and palynological aspects in order to reconstruct the paleoenvironment and to evaluate biochronologic and paleogeographic implications. The mammals are moderately diverse and not abundant, contrary to turtles and champsosaurs. The macroflora is exceptional in preservation and diversity with numerous angiosperms represented by flowers, fruits, seeds and wood preserved as lignite material, revealing an abundance of Arecaceae, Betulaceae, Icacinaceae, Menispermaceae, Vitaceae and probably Cornaceae. Results indicate a Late Paleocene age based on carbon isotope data, palynology and vertebrate occurrences such as the choristoderan Champsosaurus, the arctocyonid Arctocyon, and the plesiadapid Plesiadapis tricuspidens. However, several mammal species compare better with the earliest Eocene. Among these, the particular louisinid Teilhardimys musculus, also recorded from the latest Paleocene of the Spanish Pyrenees, suggests a younger age than the typical MP6 reference level. Nevertheless, the most important aspect of the Rivecourt fauna is the presence of dental remains of a rodent and a "miacid" carnivoran, attesting to the presence of two modern mammalian orders in the latest Paleocene of Europe. Interestingly, these two groups are also the only modern groups recorded from the latest Paleocene of North America, making Rivecourt the first direct equivalent to the Clarkforkian Land Mammal Age outside of North America. PMID:24489703

  1. First Clarkforkian Equivalent Land Mammal Age in the Latest Paleocene Basal Sparnacian Facies of Europe: Fauna, Flora, Paleoenvironment and (Bio)stratigraphy

    PubMed Central

    Smith, Thierry; Quesnel, Florence; De Plöeg, Gaël; De Franceschi, Dario; Métais, Grégoire; De Bast, Eric; Solé, Floréal; Folie, Annelise; Boura, Anaïs; Claude, Julien; Dupuis, Christian; Gagnaison, Cyril; Iakovleva, Alina; Martin, Jeremy; Maubert, François; Prieur, Judicaël; Roche, Emile; Storme, Jean-Yves; Thomas, Romain; Tong, Haiyan; Yans, Johan; Buffetaut, Eric

    2014-01-01

    The Paleocene-Eocene Thermal Maximum (PETM) is correlated with the first occurrences of earliest modern mammals in the Northern Hemisphere. The latest Paleocene Clarkforkian North American Land Mammal Age, that has yielded rodents and carnivorans, is the only exception to this rule. However, until now no pre-PETM localities have yielded modern mammals in Europe or Asia. We report the first Clarkforkian equivalent Land Mammal Age in the latest Paleocene deposits of the basal Sparnacian facies at Rivecourt, in the north-central part of the Paris Basin. The new terrestrial vertebrate and macroflora assemblages are analyzed through a multidisciplinary study including sedimentologic, stratigraphic, isotopic, and palynological aspects in order to reconstruct the paleoenvironment and to evaluate biochronologic and paleogeographic implications. The mammals are moderately diverse and not abundant, contrary to turtles and champsosaurs. The macroflora is exceptional in preservation and diversity with numerous angiosperms represented by flowers, fruits, seeds and wood preserved as lignite material, revealing an abundance of Arecaceae, Betulaceae, Icacinaceae, Menispermaceae, Vitaceae and probably Cornaceae. Results indicate a Late Paleocene age based on carbon isotope data, palynology and vertebrate occurrences such as the choristoderan Champsosaurus, the arctocyonid Arctocyon, and the plesiadapid Plesiadapis tricuspidens. However, several mammal species compare better with the earliest Eocene. Among these, the particular louisinid Teilhardimys musculus, also recorded from the latest Paleocene of the Spanish Pyrenees, suggests a younger age than the typical MP6 reference level. Nevertheless, the most important aspect of the Rivecourt fauna is the presence of dental remains of a rodent and a “miacid” carnivoran, attesting to the presence of two modern mammalian orders in the latest Paleocene of Europe. Interestingly, these two groups are also the only modern groups recorded from the latest Paleocene of North America, making Rivecourt the first direct equivalent to the Clarkforkian Land Mammal Age outside of North America. PMID:24489703

  2. 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)

  3. Stratigraphy of the Anthropocene

    NASA Astrophysics Data System (ADS)

    Zalasiewicz, J.; Williams, M.; Haywood, A.; Kerr, A. C.; Pearson, P.; Smith, A.; Barry, T. L.; Coe, A.; Bown, P. R.; Brenchley, P.; Gale, A.; Gibbard, P.; Gregory, F. J.; Hounslow, M.; Knox, R.; Powell, J.; Waters, C.; Marshall, J.; Oates, M.; Rawson, P.; Stone, P.

    2008-12-01

    The Anthropocene is an informal unit that has recently been introduced to refer to the current interval of anthropogenic global environmental change. It is being increasingly adopted in the scientific literature, and has also attracted widespread public interest in emphasizing the scale of contemporary environmental perturbation. An argument may therefore be put forward for its eventual formalization. Such formalization would be the responsibility of the International Commission on Stratigraphy (ICS) and would be preceded by formation of an Anthropocene Working Group, best attached to the Subcommission on Quaternary Stratigraphy. Consideration of evidence for and against formalization would take several years, and would enter novel territory for such discussions. This might include assessment of ongoing environmental change in the context of the near-present and earlier stratigraphic record, and likely also forward-modelling (of sea level, ocean/atmospheric chemistry, biotic composition and so on). Consideration of an effective boundary needs also be made, including whether it should be linked to a Global Stratigraphic Section and Point (GSSP) or Global Stratigraphic Standard Age (GSSA), and also of the hierarchical scale of the unit. We here ask the ICS to establish an Anthropocene Working Group, without prejudice to the eventual outcome. As in past determinations of formal chronostratigraphic boundaries, focussing scientific debate on this question would provide valuable data and insights to both the geological and wider scientific communities

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

    SciTech Connect

    Lewis, R.F. III . Dept. of Geology and Geophysics); Miller, J.M.G. . 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.

  5. 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.

  6. Stratigraphy, age, and depositional setting of the Miocene Barstow Formation at Harvard Hill, central Mojave Desert, California

    USGS Publications Warehouse

    Leslie, Shannon R.; Miller, David M.; Wooden, Joseph L.; Vazquez, Jorge A.

    2010-01-01

    New detailed geologic mapping and geochronology of the Barstow Formation at Harvard Hill, 30 km east of Barstow, CA, help to constrain Miocene paleogeography and tectonics of the central Mojave Desert. A northern strand of the Quaternary ENE-striking, sinistral Manix fault divides the Barstow Formation at Harvard Hill into two distinct lithologic assemblages. Strata north of the fault consist of: a green rhyolitic tuff, informally named the Shamrock tuff; lacustrine sandstone; partially silicified thin-bedded to massive limestone; and alluvial sandstone to pebble conglomerate. Strata south of the fault consist of: lacustrine siltstone and sandstone; a rhyolitic tuff dated at 19.1 Ma (U-Pb); rock-avalanche breccia deposits; partially silicified well-bedded to massive limestone; and alluvial sandstone and conglomerate. Our U-Pb zircon dating of the Shamrock tuff by SHRIMP-RG yields a peak probability age of 18.7 ± 0.1 Ma. Distinctive outcrop characteristics, mineralogy, remanent magnetization, and zircon geochemistry (Th/U) suggest that the Shamrock tuff represents a lacustrine facies of the regionally extensive Peach Spring Tuff (PST). Here we compare zircon age and geochemical analyses from the Shamrock tuff with those of the PST at Stoddard Wash and provide new insight into the age of zircon crystallization in the PST rhyolite. Results of our field studies show that Miocene strata at Harvard Hill mostly accumulated in a lacustrine environment, although depositional environments varied from a relatively deep lake to a very shallow lake or even onshore setting. Rock-avalanche breccias and alluvial deposits near the base of the exposed section indicate proximity to a steep basin margin and detrital studies suggest a southern source for coarse-grained deposits; therefore, we may infer a southern basin-margin setting at Harvard Hill during the early Miocene. Our geochronology demonstrates that deposition of the Barstow Formation at Harvard Hill extended from before ~19.1 Ma until well after ~18.7 Ma, similar to timing of Barstow Formation lake deposition in the Calico Mountains but at least 3 million years older than comparable lacustrine facies in the Mud Hills type section. These observations are consistent with either of two paleogeographic models: westward transgression of lacustrine environments within a single large basin, or sequential development of geographically distinct eastern and western sub-basins.

  7. Timing of amalgamation of the Alxa Block and the North China Block: Constraints based on detrital zircon U-Pb ages and sedimentologic and structural evidence

    NASA Astrophysics Data System (ADS)

    Zhang, Jin; Zhang, Beihang; Zhao, Heng

    2016-02-01

    Detrital zircon LA-ICP-MS U-Pb ages of the Paleozoic strata in the southeastern Alxa Block indicate that the primary provenance did not change between the Devonian and the Early Carboniferous. Except for a sample from the Cambrian strata, the Early Paleozoic North Qilian Orogenic Belt may have been a major source of Paleozoic sediments in the study area. The main source of Lower-Middle Devonian sediments was the Early Paleozoic North Qilian Orogenic Belt. The source of the Upper Devonian sediments was the Alxa Block, while the North China Block was a minor contributor. The deformation of the Cambrian and Devonian Systems in the southeastern Alxa Block indicates that a strong east-west compression event occurred in the study area before the Early Carboniferous. The paleocurrents of the Upper Devonian in the southeastern Alxa Block indicate that the source was located to the north and was not the North Qilian Orogenic Belt to the south. Moreover, the deposition of the Upper Devonian in the southeastern Alxa Block was a response to a strong deformation event that occurred along the eastern boundary of the Alxa Block during the Late Devonian and Early Carboniferous. The North China Block became the primary source during the Early Carboniferous, and the Alxa Block was a minor source. A regional stratigraphic comparison also indicates that similar depositional environments were present until the Carboniferous and Permian on the Alxa Block and North China Block. All of these data indicate that amalgamation of the Alxa Block and the North China Block occurred between the Late Devonian and the Early Carboniferous.

  8. Workshop on the Martian Northern Plains: Sedimentological, Periglacial, and Paleoclimatic Evolution

    NASA Technical Reports Server (NTRS)

    Kargel, Jeffrey S. (Editor); Moore, Jeffrey (Editor); Parker, Timothy (Editor)

    1993-01-01

    Papers that have been accepted for presentation at the Workshop on the Martian Northern Plains: Sedimentological, Periglacial, and Paleoclimatic Evolution, on 12-14 Aug. 1993 in Fairbanks, Alaska are included. Topics covered include: hydrological consequences of ponded water on Mars; morphological and morphometric studies of impact craters in the Northern Plains of Mars; a wet-geology and cold-climate Mars model: punctuation of a slow dynamics approach to equilibrium; the distribution of ground ice on Mars; and stratigraphy of the Martian Northern Plains.

  9. Volcanic stratigraphy of a high-altitude Mammuthus columbi (Tlacotenco, Sierra Chichinautzin), Central México

    NASA Astrophysics Data System (ADS)

    Guilbaud, Marie-Noelle; Arana-Salinas, Lilia; Siebe, Claus; Barba-Pingarrón, Luis Alberto; Ortiz, Agustín

    2015-03-01

    The discovery of a near complete skeleton of Mammuthus columbi in a cornfield located on the northern slopes of the Sierra Chichinautzin volcanic field south of Mexico City sparked the interest of the scientific and public community. Although remains of this species of mammoth are frequently discovered in central Mexico, this new find is at the southernmost and highest (ca. 2770 m asl) location yet within the Mexico Basin. In addition, the bones were found embedded in dark volcanic ash, raising the possibility of a relationship between the death of the animal and explosive activity at a neighboring scoria cone, as the site is located <10 km from several young volcanoes. Stratigraphic, sedimentological, geochemical, and geochronological studies were conducted at the discovery site and within a 5-km radius to determine the tephra stratigraphy in the area and constrain the source of the " mammoth ash" and the age and taphonomy of the fossil remains. Results show that the mammoth was buried after death by stream-flows (dilute lahars) that were triggered by torrential rain that remobilized loose scoriaceous ash ejected by the San Miguel cone some time after its eruption ca. 17,000 BP.

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

    SciTech Connect

    Snyder, W.S.; Gallegos, D.M.; Spinosa, C. ); Schwarz, D.L. )

    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.

  11. Mineralogical Stratigraphy of Ganges Chasma, Mars

    NASA Astrophysics Data System (ADS)

    Cull-Hearth, Selby; Clark, M. Caroline

    2015-11-01

    Mars’ Valles Marineris canyon system reveals a several-kilometer deep stratigraphies sequence that extends thousands of kilometers; this sequence thus represents a unique opportunity to explore millions of years of volcanic and aqueous activity in this region of Mars. Of particular interest to the study of both volcanic and aqueous processes is Ganges Chasma, which lies on the northeastern boundary of the Valles Marineris canyon system on Mars. The canyon likely opened during the Late Noachian to Early Hesperian, modifying previously emplaced Noachian-aged volcanic plains. During formation, volcanic activity from the nearby Tharsis shield complex emplaced olivine-rich dikes throughout the region. After formation, sulfate-bearing Interior Layered Deposits (ILDs) were emplaced in Ganges and many other chasmata throughout the Valles Marineris system. Today, Ganges reveals a complex stratigraphy, including wide-spread olivine-rich sands, hydrated minerals on the plateaus surrounding the canyon, and a central sulfate-rich ILD. Here, we present updated stratigraphies of Ganges Chasma, using new data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), and synthesizing it with previous data sets. Olivine sands are traced back to source outcrops on the canyon floor, and new outcrops of hydrated minerals on the surrounding plateau are identified and mapped. Recently reported spectroscopic signatures of ankerite and smectite in the chasm are assessed, and new olivine-rich outcrops identified and mapped. Understanding the stratigraphy of Ganges Chasma will help us compare stratigraphies among the chasmata of the Valles Marineris, further building our understanding of the geologic history of this large region of Mars.

  12. A luminescence dating study of the sediment stratigraphy of the Lajia Ruins in the upper Yellow River valley, China

    NASA Astrophysics Data System (ADS)

    Zhang, Yuzhu; Huang, Chun Chang; Pang, Jiangli; Zhou, Yali; Zha, Xiaochun; Wang, Longsheng; Zhou, Liang; Guo, Yongqiang; Wang, Leibin

    2014-06-01

    Pedo-sedimentological fieldwork were carried out in the Lajia Ruins within the Guanting Basin along the upper Yellow River valley. In the eolian loess-soil sections on the second river terrace in the Lajia Ruins, we find that the land of the Qijia Culture (4.20-3.95 ka BP) are fractured by several sets of earthquake fissures. A conglomerated red clay covers the ground of the Qijia Culture and also fills in the earthquake fissures. The clay was deposited by enormous mudflows in association with catastrophic earthquakes and rainstorms. The aim of this study is to provide a luminescence chronology of the sediment stratigraphy of the Lajia Ruins. Eight samples were taken from an eolian loess-soil section (Xialajia section) in the ruins for optically stimulated luminescence (OSL) dating. The OSL ages are in stratigraphic order and range from (31.94 ± 1.99) ka to (0.76 ± 0.02) ka. Combined OSL and 14C ages with additional stratigraphic correlations, a chronological framework is established. We conclude that: (1) the second terrace of the upper part of Yellow River formed 35.00 ka ago, which was followed by the accumulation of the eolian loess-soil section; and (2) the eolian loess-soil section is composed of the Malan Loess of the late last glacial (MIS-2) and Holocene loess-soil sequences.

  13. 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.

  14. 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).

  15. Continental margin sedimentation: from sediment transport to sequence stratigraphy

    USGS Publications Warehouse

    Nittrouer, Charles A., (Edited By); Austin, James A.; Field, Michael E.; Kravitz, Joseph H.; Syvitski, James P.M.; Wiberg, Patricia L.

    2007-01-01

    This volume on continental margin sedimentation brings together an expert editorial and contributor team to create a state-of-the-art resource. Taking a global perspective, the book spans a range of timescales and content, ranging from how oceans transport particles, to how thick rock sequences are formed on continental margins. - Summarizes and integrates our understanding of sedimentary processes and strata associated with fluvial dispersal systems on continental shelves and slopes - Explores timescales ranging from particle transport at one extreme, to deep burial at the other - Insights are presented for margins in general, and with focus on a tectonically active margin (northern California) and a passive margin (New Jersey), enabling detailed examination of the intricate relationships between a wide suite of sedimentary processes and their preserved stratigraphy - Includes observational studies which document the processes and strata found on particular margins, in addition to numerical models and laboratory experimentation, which provide a quantitative basis for extrapolation in time and space of insights about continental-margin sedimentation - Provides a research resource for scientists studying modern and ancient margins, and an educational text for advanced students in sedimentology and stratigraphy

  16. High resolution sequence stratigraphy of Scythian-early Anisian continental deposits of east of Paris basin: Applications to gas storage

    SciTech Connect

    Roselyne, F.; Guillocheau, F.; Wicquart, E.

    1995-08-01

    Continental facies of Scythian-early Anisian age (Buntsandstein) of East of the Paris Basin form the underground gas storage reservoir exploited by Gaz de France in the area of Nancy (east of France). An accurate sedimentological study and the application of Genetic Stratigraphy principles lead to the understanding of the deposition of fluvial, which form the reservoirs, and to the reconstruction of their geometries. The subsurface data are calibrated on outcrops. Three types of fluvial systems (braided, sinuous to straight and anastomosed) are defined. A special focus on anastomosed channels permits to differentiate a proximal and a distal facies. Study of laterally continuous outcrops induces recurrent cycles of thickness, velocity and time variations (few tens to hundred ka). These correspond to the highest frequence stratigraphic units, i.e. parasequences or genetic units. Maximum of channel and levee presentation occurs during base-level rise: base-level fall is characterised by amalgamation of sets, by-pass and erosion. This method is applied to subsurface data by an accurate calibration of well logs on cores. Thus the electric expression of genetic units corresponding to different environments is determined as well as the expression of base-level variations. The correlation of these units using stacking pattern method leads to a very fine subdivision of reservoir between timelines. Different orders of depositional sequences are pointed out, resulting in reservoir geometry characterization and permeability barrier distribution.

  17. 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.

  18. New high precision U-Pb ages for the Vinchina Formation: Implications for the stratigraphy of the Bermejo Andean foreland basin (La Rioja province, western Argentina)

    NASA Astrophysics Data System (ADS)

    Ciccioli, P. L.; Limarino, C. O.; Friedman, R.; Marenssi, S. A.

    2014-12-01

    The Vinchina Formation is one of the thickest Cenozoic units related to the Andean orogeny in Argentina totaling more than 5100 m in thickness. Different ages, from Eocene to latest Miocene, have been postulated for this red-bed succession based on fission track, magnetostratigraphy and whole rock isotopic analyses. Two new high precision U-Pb zircon ages are reported herein for this unit. A maximum U-Pb age of 15.6 ± 0.4 Ma was obtained from detritic zircons collected from a thick tuffaceous interval of the Lower Member of the Vinchina Formation at La Cueva (Precordillera), while a depositional U-Pb age of 9.24 ± 0.034 Ma was derived from volcanic zircons collected from a thin tuff bed in the Upper Member at Quebrada de Los Pozuelos (Northwestern Sierras Pampeanas). At La Cueva, the Vinchina Formation unconformably overlies eolian sandstones of the Vallecito Formation and was divided into four units representing 1) deposits of high-sinuosity ephemeral rivers associated with 2) a playa-lake passing upwards to 3) low-sinuosity sandy ephemeral rivers and finally, 4) a gravelly-sandy braided plain. The tuffaceous level corresponding to unit 1 is located 280 m above the base of the formation. At Quebrada de Los Pozuelos, the Vinchina Formation unconformably overlies the Vallecito Formation and is covered by a deeply incised surface at the base of the Toro Negro Formation. We divided the Vinchina Formation into four units. Unit 1 represents sedimentation in shallow fluvial channels with sandy to muddy floodplains. Units 2 and 3 record sedimentation in braided, meandering and anastomosing rivers. Finally unit 4 represents deposition in braided and wandering fluvial systems. The sampled tuff is located within unit 4 at ˜3470 m above the base of the formation. The new ages indicate that the bulk of the Vinchina Formation is Miocene in age but they do not preclude a longer time span for the sedimentation of the whole unit. Ages of the sampled volcanic zircons match an important episode of volcanism recorded in the Cerro Las Tórtolas Formation, located ˜90 km to the west in the Andean Cordillera, but also the upper tuff could be related to the late Miocene Puna volcanism. Comparison of the new ages with previous chronological data suggests coetaneous sedimentation along different depocenters of the Bermejo basin (e.g., Vinchina and Talampaya depocenters in Western Sierras Pampeanas and La Troya depocenter and Huaco-Mogna sections in Precordillera) and strenghten the need for correlation among them. In addition the age of 15.6 ± 0.4 Ma constrains the end of the severe arid conditions recorded in the Sierras Pampeanas and Precordillera region.

  19. Sedimentology of polar carbonate systems

    NASA Astrophysics Data System (ADS)

    Frank, T. D.; James, N. P.

    2013-12-01

    The key attributes, processes, and products associated with carbonate accumulation and diagenesis at tropical and temperate latitudes are well known. Comparatively little work has concentrated on carbonate deposition at the coldest end of the depositional spectrum, the polar shelves. Such deposits are not abundant, but they have the potential to provide unique insights into paleoceanographic and paleoclimatic conditions in regions of the planet that are arguably the most sensitive to global change. We examined skeletal assemblages, facies, stratigraphy, petrography, geochemistry, and diagenesis of Quaternary deposits from the Ross Sea, Antarctica and Permian counterparts from Gondwana (now eastern Australia). These modern and ancient polar carbonate factories possess several unique characteristics that set them apart from better-known systems of the temperate and tropical latitudes. All production is biogenic and there are no significant calcareous phototrophs. Carbonate communities are not capable of building rigid frameworks, and thus their deposits are prone to winnowing and reworking by waves and bottom currents. The seawater, although frigid, is isothermal, and thus deep-water benthic communities can exist near the surface. Carbonate saturation, which is at or below solubility for both aragonite and high-Mg calcite, plays a key role in determining the dominant mineralogy of benthos as well as the preservation potential of skeletal debris. As many taxa precipitate low-Mg calcite in isotopic equilibrium, deposits have potential to provide geochemical proxy information for use in paleoceanographic and paleoclimatic reconstructions. More than any other type of carbonate system, the slow biogenic carbonate production and accumulation in cold waters is achieved firstly by arresting siliciclastic sedimentation and secondly by increasing nutrient availability. Thus, carbonate deposition may occur during the coldest of times, such as during glacial advance when terrigenous clastics are sequestered inboard and invigorated ocean circulation enhances upwelling. Radiocarbon data from Quaternary deposits in the Ross Sea indicate that short windows of accumulation during favorable conditions are followed by longer intervals of non-productivity, during which skeletal debris undergoes dissolution and infestation by endolithic borers, carbonate sediments are reworked by bottom currents, and glacigene siliciclastic facies are deposited. Similar patterns are evident in Permian deposits. We interpret the post-carbonate depositional periods as not only due to increased terrigenous input but also dramatically reduced trophic resources. The foregoing hypothesis is at odds with most current thinking about carbonate deposition and points to an evolving paradigm within which polar carbonate deposition is dramatically different than that in temperate and tropical settings.

  20. Ground-penetrating radar and its use in sedimentology: principles, problems and progress

    NASA Astrophysics Data System (ADS)

    Neal, Adrian

    2004-08-01

    Ground-penetrating radar (GPR, also referred to as ground-probing radar, surface-penetrating radar, subsurface radar, georadar or impulse radar) is a noninvasive geophysical technique that detects electrical discontinuities in the shallow subsurface (<50 m). It does this by generation, transmission, propagation, reflection and reception of discrete pulses of high-frequency (MHz) electromagnetic energy. During the 1980s radar systems became commercially available, but it was not until the mid-1990s that sedimentary geologists and others began to widely exploit the technique. During the last decade numerous sedimentological studies have used GPR to reconstruct past depositional environments and the nature of sedimentary processes in a variety of environmental settings; to aid hydrogeological investigations, including groundwater reservoir characterisation, and to assist in hydrocarbon reservoir analogue studies. This is because in correctly processed radar profiles, and at the resolution of a survey, primary reflections usually parallel primary depositional structure. Despite the wide use of GPR, a number of fundamental problems remain in its application to sedimentary research. In particular, there are a wide range of approaches to the processing of radar data and interpretation techniques used on the final subsurface images vary widely, with little consensus over a common methodology. This review attempts to illustrate that methods for the collection, processing and interpretation of radar data are intimately linked and that thorough understanding of the nature, limitations and implications of each step is required if realistic sedimentological data are to be generated. In order to extract the maximum amount of meaningful information, the user must understand the scientific principles that underlie the technique, the effects of the data collection regime employed, the implications of the technique's finite resolution and depth of penetration, the nature and causes of reflections unrelated to primary sedimentary structure, and the appropriateness of each processing step with respect to the overall aim of the study. Following suitable processing, a radar stratigraphy approach to reflection profile interpretation should be adopted. New or modified terminologies and techniques to define a radar stratigraphy are also recommended, in order to make the interpretation process more transparent and to avoid confusion with related methodologies such as seismic stratigraphy and sequence stratigraphy. The full potential of GPR in sedimentary research will only be realised if more thorough and systematic approaches to data collection, processing and interpretation are adopted.

  1. Isothermal plateau fission-track age for a paleomagnetic excursion in the Mamaku Ignimbrite, New Zealand, and implication for late Quaternary stratigraphy

    NASA Astrophysics Data System (ADS)

    Shane, Phil; Black, Tasha; Westgate, John

    1994-08-01

    Mamaku Ignimbrite, the youngest of the large, welded ignimbrite sheet-forming eruptions from the Taupo Volcanic Zone in New Zealand, is dated at 230 +/- 12 ka by the isothermal plateau fission-track (ITPFT) method on glass. This age is older and more precise than that indicated by previous studies, requiring the revision of loess/paleosol coverbed chronologies. The eruption occurred during a paleomagnetic excursion allowing the ignimbrite to be easily distinguished from other eruptive events by paleomagnetic methods. This excursion is one of the few such events recorded in igneous rocks in the Southern Hemisphere, may be widely recorded in New Zealand, and is now temporally well constrained.

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

    SciTech Connect

    Ali-zade, A.A.; Guliyev, I.S.; Ateava, E.Z.

    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.

  3. Sedimentology and genetic stratigraphy of Dean and Spraberry Formations (Permian), Midland basin, Texas

    SciTech Connect

    Handford, C.R.

    1981-09-01

    The Spraberry trend of west Texas, once known as the world's largest uneconomic oil field, will undoubtedly become an increasingly important objective for the development of enhanced oil recovery techniques in fine-grained, low-permeability, low-pressure reservoirs. As the trend expands, facies and stratigraphic data should be integrated into exploration strategies. The Spraberry and Dean Formations may be divided into three genetic sequences, each consisting of several hundred feet of interbedded shale and carbonate overlain by a roughly equal amount of sandstone and siltstone. These sequences record episodes of shelf-margin progradation, deep-water resedimentation of shelf-derived carbonate debris, followed by influxes of terrigenous clastics into the basin by way of feeder channels or submarine canyons, and suspension settling of fine-grained sediment from the water column. Four lithofacies comprise the terrigenous clastics of the Spraberry and Dean Fomations: (1) cross-laminated, massive, and parallel-laminated sandstone, (2) laminated siltstone, (3) bioturbated siltstone, and (4) black, organic-rich shale. Carbonate lithofacies occur mostly in the form of thin-bedded turbidites, slump, and debris-flow deposits. Terrigenous clastic rocks display facies sequences, isopach patterns, and sedimentary structures suggestive of deposition from turbidity currents, and long-lived saline density underflow and interflow currents. Clastic isopach patterns reflect an overall southward thinning of clastics in the Midland basin. Channelized flow and suspension settling were responsible for the formation of elongate fan-shaped accumulations of clastic sediments.

  4. Stratigraphy, sedimentology, and structural style of the Wilson Island Group, Northwest Territories

    SciTech Connect

    Johnson, B.J.

    1985-01-01

    The lower Proterozoic Wilson Island Group is exposed in a NE-trending belt in the East Arm of Great Slave Lake, Northwest Territories. The lower part of the 6 km thick succession outcrops on Wilson Island and adjacent islands, south of the McDonald-Wilson fault. Deposition of intercalated basalt flows, felsic flows and related intrusions, volcaniclastics, and braided alluvial arkose and conglomerate occurred in a tectonically active basin, probably a continental rift. Overlying the volcanic assemblage is a debris flow paraconglomerate, which grades vertically into fluvial to marginal marine or lacustrine arkose and dolostone. Several km further east, and north of the McDonald-Wilson fault, similar arkoses and dolostones are overlain by fine-grained subarkose, argillaceous siltstone, quartz granulestone, and concretionary dolomitic ironstone. These lithologies represent mixed fluvial, tidal flat, and shallow water facies. The remainder of the section consists of arkosic arenite/mudstone cycles (turbidites.), gradational upward into laminated mudstone with minor intercalated basalt. Rocks of the Wilson Island Group have been metamorphosed in greenschist to lower amphibolite facies, and deformed into eastward- to northeastward-plunging folds. Folds in the lower part of the section are open, whereas the finer-grained sediments of the upper part are isoclinally folded. These structures have been dissected by dextral transcurrent faults of the McDonald fault system.

  5. The sequence stratigraphy, sedimentology, and economic importance of evaporite carbonate transitions: a review

    NASA Astrophysics Data System (ADS)

    Sarg, J. F.

    2001-04-01

    World-class hydrocarbon accumulations occur in many ancient evaporite-related basins. Seals and traps of such accumulations are, in many cases, controlled by the stratigraphic distribution of carbonate-evaporite facies transitions. Evaporites may occur in each of the systems tracts within depositional sequences. Thick evaporite successions are best developed during sea level lowstands due to evaporative drawdown. Type 1 lowstand evaporite systems are characterized by thick wedges that fill basin centers, and onlap basin margins. Very thick successions (i.e. saline giants) represent 2nd-order supersequence set (20-50 m.y.) lowstand systems that cap basin fills, and provide the ultimate top seals for the hydrocarbons contained within such basins. Where slope carbonate buildups occur, lowstand evaporites that onlap and overlap these buildups show a lateral facies mosaic directly related to the paleo-relief of the buildups. This facies mosaic, as exemplified in the Silurian of the Michigan basin, ranges from nodular mosaic anhydrite of supratidal sabkha origin deposited over the crests of the buildups, to downslope subaqueous facies of bedded massive/mosaic anhydrite and allochthonous dolomite-anhydrite breccias. Facies transitions near the updip onlap edges of evaporite wedges can provide lateral seals to hydrocarbons. Porous dolomites at the updip edges of lowstand evaporites will trap hydrocarbons where they onlap nonporous platform slope deposits. The Desert Creek Member of the Paradox Formation illustrates this transition. On the margins of the giant Aneth oil field in southeastern Utah, separate downdip oil pools have accumulated where dolomudstones and dolowackestones with microcrystalline porosity onlap the underlying highstand platform slope. Where lowstand carbonate units exist in arid basins, the updip facies change from carbonates to evaporite-rich facies can also provide traps for hydrocarbons. The change from porous dolomites composed of high-energy, shallow water grainstones and packstones to nonporous evaporitic lagoonal dolomite and sabkha anhydrite occurs in the Upper Permian San Andres/Grayburg sequences of the Permian basin. This facies change provides the trap for secondary oil pools on the basinward flanks of fields that are productive from highstand facies identical to the lowstand dolograinstones. Type 2 lowstand systems, like the Smackover Limestone of the Gulf of Mexico, show a similar relationship. Commonly, these evaporite systems are a facies mosaic of salina and sabkha evaporites admixed with wadi siliciclastics. They overlie and seal highstand carbonate platforms containing reservoir facies of shoalwater nonskeletal and skeletal grainstones. Further basinward these evaporites change facies into similar porous platform facies, and contain separate hydrocarbon traps. Transgressions in arid settings over underfilled platforms (e.g. Zechstein (Permian) of Europe; Ferry Lake Anhydrite (Cretaceous), Gulf of Mexico) can result in deposition of alternating cyclic carbonates and evaporites in broad, shallow subaqueous hypersaline environments. Evaporites include bedded and palmate gypsum layers. Mudstones and wackestones are deposited in mesosaline, shallow subtidal to low intertidal environments during periodic flooding of the platform interior. Highstand systems tracts are characterized by thick successions of m-scale, brining upward parasequences in platform interior settings. The Seven Rivers Formation (Guadalupian) of the Permian basin typifies this transition. An intertonguing of carbonate and sulfates is interpreted to occur in a broad, shallow subaqueous hypersaline shelf lagoon behind the main restricting shelf-edge carbonate complex. Underlying paleodepositional highs appear to control the position of the initial facies transition. Periodic flooding of the shelf interior results in widespread carbonate deposition comprised of mesosaline, skeletal-poor peloid dolowackestones/mudstones. Progressive restriction due to active carbonate deposition and/or an environment of net evaporation causes bri

  6. Stratigraphy and sedimentology of ledge sandstone in Arctic National Wildlife Refuge northeastern Alaska

    SciTech Connect

    Cloft, H.S.

    1983-03-01

    Data collected from four measured sections of the Ledge Sandstone member of the Ivishak Formation are presented. These sections are located in the Arctic National Wildlife Refuge (ANWR) in northeastern Alaska. The Ledge Sandstone is the time equivalent of the Ivishak sandstones that form the reservoir in the Prudhoe Bay field, east of the study area. The ANWR region is of interest for oil and gas exploration owing to the numerous oil seeps on the coastal plain and surficial expression of possible subsurface antiforms. The Ledge Sandstone in ANWR consists primarily of a massive, thickly bedded, very fine to fine-grained, well-sorted quartz sandstone. The thick sandstones are separated by thin siltstone intervals ranging from less than an inch to several feet in thickness. Although the thicker siltstones appear laterally continuous, the thinner beds generally are lenticular over short distances (10 to 20 ft; 3 to 6 m). Cementation of the siltstone appears sporadic, varying laterally and vertically within the unit. Burrowing is extensive in the siltstone intervals. Typically, burrowing cannot be detected in the sandstones because of the obliteration by lithification and diagenetic processes. Fossils are sparse throughout the unit, even in the poorly lithified silts. These data are consistent with a shallow marine environment, within wave base. This contrasts with the nonmarine conglomerates and sandstones of Prudhoe Bay. Time-equivalent units to the south and west consist primarily of cherts and shales of probable deep marine origin, with some arkosic sandstones dolomites occuring in NPRA. Thus a paloshoreline is probably located somewha north of the measured sections.

  7. Seismo-turbidite Sedimentology: Implications for Active Tectonic Margin Stratigraphy and Sediment Facies Patterns

    NASA Astrophysics Data System (ADS)

    Nelson, C. H.; Goldfinger, C.; Gutierrez Pastor, J.; Polonia, A.; Van Daele, M. E.

    2014-12-01

    Earthquakes generate mass transport deposits (MTDs); megaturbidites (MTD overlain by coeval turbidite); multi-pulsed, stacked, and mud homogenite seismo-turbidites; tsunamites; and seiche deposits. The strongest (Mw 9) earthquake shaking signatures appear to create multi-pulsed individual turbidites, where the number and character of multiple coarse-grained pulses for correlative turbidites generally remain constant both upstream and downstream in different channel systems. Multiple turbidite pulses, that correlate with multiple ruptures shown in seismograms of historic earthquakes (e.g. Chile 1960, Sumatra 2004 and Japan 2011), support this hypothesis. The weaker (Mw = or < 8) (e.g. northern California San Andreas) earthquakes generate dominantly upstream simple fining-up (uni-pulsed) turbidites in single tributary canyons and channels; however, downstream stacked turbidites result from synchronously triggered multiple turbidity currents that deposit in channels below confluences of the tributaries. Proven tsunamites, which result from tsunami waves sweeping onshore and shallow water debris into deeper water, are a fine-grained turbidite cap over other seismo-turbidites. In contrast, MTDs and seismo-turbidites result from slope failures. Multiple great earthquakes cause seismic strengthening of slope sediment, which results in minor MTDs in basin floor turbidite system deposits (e.g. maximum run-out distances of MTDs across basin floors along active margins are up to an order of magnitude less than on passive margins). In contrast, the MTDs and turbidites are equally intermixed in turbidite systems of passive margins (e.g. Gulf of Mexico). In confined basin settings, earthquake triggering results in a common facies pattern of coeval megaturbidites in proximal settings, thick stacked turbidites downstream, and ponded muddy homogenite turbidites in basin or sub-basin centers, sometimes with a cap of seiche deposits showing bi-directional flow patterns.

  8. 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).

  9. The Heidelberg Basin Drilling Project - Sedimentology and Stratigraphy of the Quaternary succession

    NASA Astrophysics Data System (ADS)

    Ellwanger, Dietrich; Gabriel, Gerald; Hahne, Jürgen; Hoselmann, Christian; Menzies, John; Simon, Theo; Weidenfeller, Michael; Wielandt-Schuster, Ulrike

    2010-05-01

    Within the context of the Heidelberg Basin Drilling Project (Gabriel et al. 2008), a detailed sediment succession is presented here based upon deep drillings taken at Heidelberg UniNord and Mannheim Käfertal. Sediment structures, and micromorphological and pollen analyses were conducted and used to reconsider some of the climate transitions within the lower Pleistocene. A new and novel scenario is postulated regarding the preservation of Quaternary sediment packages within the Cenozoic Graben environment of the Heidelberg basin. The palynological evidence comprises the periods of warm climate of the Holsteinian (mainly Abies (fir), some Fagus (beech), Pterocarya & Azolla); the Cromerian (Pinus-Picea-QM (pine-spruce-QM)); the Bavelian (Abies, Tsuga (hemlock fir), QM & phases of increased NAP including Pinus); the Waalian (Abies, Tsuga, QM); and the Tiglian (Fagus & early Pleistocene taxa especially Sciadopytis, downward increasing Tertiary taxa). The sediment package was studied both macroscopically and microscopically. Both techniques provide evidence of fluvial, lacustrine and mass movement sedimentary processes. Some include evidence of periglacial processes (silt droplets within fine grained sands indicative of frozen ground conditions). The periglacial structures are often, not always, accompanied by pollen spectra dominated by pine and NAP. E.g. the Tiglian part of the succession shows periglacial sediment structures at its base and top but not in its middle sections. I.e. it appears not as a series of warm and cold phases but rather as a constant warm period with warm-cold-alternations at its bottom and top. All results illustrate sediment preservation in the Heidelberg basin almost throughout the Quaternary. This may be due to tectonic subsidence, but also to compaction by sediment loading of underlying fine sediments (Oligocene to Quaternary) leading to incomplete but virtually continuous sediment preservation (Tanner et al. 2009). References Gabriel, G., Ellwanger, D., Hoselmann, C. & Weidenfeller, M. (2008): The Heidelberg Basin Drilling Project. - Eiszeitalter u. Gegenwart (Quaternary Science Journal), 57, 3-4, 253-260, Hannover. Tanner, D.C., Martini, N., Buness, H. & Krawczyk, C.M. (2009): The 3D Geometry of the Quaternary and Tertiary strata in the Heidelberg Basin, as defined by reflection seismics. - DGG Tagung, Dresden, 30.9-02.10.09, Schriftenreihe der Deutschen Gesellschaft für Geowissenschaften, 63, 58.

  10. Sedimentology and stratigraphy of the Kanayut Conglomerate, central Brooks Range, Alaska; report of 1980 field season

    USGS Publications Warehouse

    Nilsen, T.H.; Moore, T.E.; Balin, D.F.; Johnson, S.Y.

    1982-01-01

    The Upper Devonian Kanayut Conglomerate crops out along the crest of the Brooks Range of northern Alaska for a distance of almost 1000 km. It ranges in thickness from 2600 m in the Atigun River area to 700 m south of Anaktuvuk Pass and has been subdivided into four regionally persistent members: (a) the basal sandstone member, consisting of marine sandstone and shale with some conglomerate; (b) the lower shale member, consisting of nonmarine quartzite, conglomerate and shale; (c) the middle conglomerate member, consisting of nonmarine pebble and cobble conglomerate and quartzite; and (d) the Stuver Member, consisting of nonmarine sandstone and shale. The Kanayut conformably overlies the Upper Devonian marine Hunt Fork Shale and is conformably overlain by the Mississippian marine Kayak Shale. The Kanayut is wholly allochthonous and has probably been transported northward on a series of thrust plates. The basal sandstone member of the Kanayut Conglomerate, which overlies prodelta turbidites of the Hunt Fork Shale, contains marginal-marine coarsening-upward channel-mouth bar sequences. It is conformably overlain by the lower shale member. Measured sections of the nonmarine members of the Kanayut show that the lower shale member ranges in thickness from 120 m to 1115 m and consists of fining-upward cycles interpreted to have been deposited by meandering streams on a broad floodplain. These cycles contain, in ascending order, channelized basal conglomerate, trough cross-stratified sandstone, and ripple-marked siltstone. The cycles are interpreted to be channel and point-bar deposits. Individual cycles average about 10 m in thickness and are separated by intervals of black, brown or maroon floodplain shale deposits. These typically contain thin coarsening-upward units that probably represent prograding levee sequences and irregular and ungraded sandstone bodies interpreted to be crevasse-splay deposits. In the Okokmilaga River area, the lower shale member contains a distinctive coarse-grained unit which is burrowed and interpreted to represent a widespread marine incursion. The middle conglomerate member, which ranges in thickness from 155 m to 525 m, consists of braidplain deposits. It contains fining-upward couplets of conglomerate and parallel-stratified or cross-stratified sandstone that average 2-7 m in thickness. The couplets record deposition in channels and on bars of braided streams. The middle conglomerate member contains the largest clasts, little or no shale, and represents the maximum progradation of nonmarine sedimentation in the Kanayut depositional system. The Stuver Member consists of fining-upward cycles that resemble those of the lower shale member. It ranges in thickness from 160 m to 1400 m and grades upward into tidal and marginal-marine deposits of the Kayak Shale. Conglomerate in the Kanayut is compositionally very mature, averaging 82 percent white, gray, black or red chert clasts, 14 percent vein quartz clasts, 3 percent quartzite clasts, and less than I percent other lithologies, mainly argillite. Although red chert is locally abundant in the Shainin Lake-Galbraith Lake area, there is little variation in conglomerate composition in the Kanayut, suggesting derivation from a single major source terrane.

  11. Sedimentology and sequence stratigraphy of upper Pleistocene carbonates of southeastern Barbardos, West Indies

    SciTech Connect

    Humphrey, J.D.; Kimbell, T.N. )

    1990-11-01

    Upper Pleistocene reef-associated carbonates of southeastern Barbados have been studied in outcrop and core. Reef terraces, formed during glacio-eustatic sea level highstands and subsequently uplifted, are characterized by thick and areally extensive sequences of allochthonous and autochthonous fore-reef calcarenites. Depositional textures are primarily packstones, and grainstones, wackestones, and coral floatstones are volumetrically less significant. Sediments are coarse- to fine-grained reef-derived allochems and micrite, and autochthonous benthic foraminifera and coralline red algae. Rates of sediment accumulation of fore-reef calcarenites range from about 1 to 4 m/1,000 yr. Although of relatively small scale, the carbonate terraces of southeastern Barbados provide excellent analogs for sequence stratigraphic concepts in carbonate settings. The terraces are primarily highstand systems tract deposits separated by type 1 unconformities. These highstand deposits are characterized by reef development and the progradation of fore-reef calcarenites. Extensive fore-reef deposits resulted from mechanical erosion of the reef framework on this high-energy, windward coastline. Type 1 unconformities are characterized by thin caliche layers developed during lowstand subaerial exposure. Thin basal transgressive systems tract deposits are characterized by incorporation of extraformational clasts derived from the underlying sequence during sea level rise. Slope-front erosion, vertical shift in the position of freshwater lens, and shift in the position of coastal onlap are all consequences of the interplay between eustasy and tectonics. These effects and the development of facies geometries on Barbados are primarily controlled by the glacio-eustatic component, inasmuch as rates of eustatic changes of sea level are at least two orders of magnitude greater than the maximum average rates of tectonic uplift. 12 figs.

  12. Sedimentology, stratigraphy and tectonics of evolving wedge-top depozone: Ariano Basin, southern Apennines, Italy

    NASA Astrophysics Data System (ADS)

    Ciarcia, Sabatino; Vitale, Stefano

    2013-05-01

    The late Zanclean wedge-top Ariano Basin, located in the external sector of the southern Apennines, was initially characterized by alluvial and fan-delta environments and successively, southward of the Benevento-Buonalbergo fault, by a gradual drowning with coastal and alluvial plains evolving to shelf and marine coastal settings, respectively. Basin evolution continued with a synsedimentary uplift of different sectors resulting in variations in the drainage pattern and basin shape, and ultimately leading to complete basin closure and transition to continental depositional environments. Early Pliocene paleogeography, prior to the Ariano Basin activity, is due to regional subsidence and subsequent differential uplifts that resulted from geodynamic processes related to both the downgoing Apulian slab and the allochthonous orogenic wedge. Slab break off and the migration of a tear in the southeastward Apulian slab occurred, producing a strong subsidence in the external sectors of the southern Apennines recorded by the development of the Ariano Basin. Subsequently out-of-sequence synsedimentary thrusting, related to thin-skinned tectonics, occurred in the allochthonous units and unconformably overlying wedge-top basin deposits, producing northeastward migration of the main depocenters in the Ariano Basin. Finally renewed thrusting, related to the inversion of pre-existing normal faults located in the buried Apulian Platform and enhanced by regional uplift, affected the whole tectonic and sedimentary pile, as recorded by deformation of the overlying Pliocene deposits.

  13. 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.

  14. Sedimentology of gas-bearing Devonian shales of the Appalachian Basin

    SciTech Connect

    Potter, P.E.; Maynard, J.B.; Pryor, W.A.

    1981-01-01

    The Eastern Gas Shales Project (1976-1981) of the US DOE has generated a large amount of information on Devonian shale, especially in the western and central parts of the Appalachian Basin (Morgantown Energy Technology Center, 1980). This report summarizes this information, emphasizing the sedimentology of the shales and how it is related to gas, oil, and uranium. This information is reported in a series of statements each followed by a brief summary of supporting evidence or discussion and, where interpretations differ from our own, we include them. We believe this format is the most efficient way to learn about the gas-bearing Devonian shales of the Appalachian Basin and have organized our statements as follows: paleogeography and basin analysis; lithology and internal stratigraphy; paleontology; mineralogy, petrology, and chemistry; and gas, oil, and uranium.

  15. Correlation between high resolution sequence stratigraphy and mechanical stratigraphy for enhanced fracture characteristic prediction

    NASA Astrophysics Data System (ADS)

    Al Kharusi, Laiyyan M.

    Sequence stratigraphy relates changes in vertical and lateral facies distribution to relative changes in sea level. These relative changes in carbonates effect early diagenesis, types of pores, cementation and dissolution patterns. As a result, in carbonates, relative changes in sea level significantly impact the lithology, porosity, diagenesis, bed and bounding surfaces which are all factors that control fracture patterns. This study explores these relationships by integrating stratigraphy with fracture analysis and petrophysical properties. A special focus is given to the relationship between mechanical boundaries and sequence stratigraphic boundaries in three different settings: (1) Mississippian strata in Sheep Mountain Anticline, Wyoming, (2) Mississippian limestones in St. Louis, Missouri, and (3) Pennsylvanian limestones intermixed with elastics in the Paradox Basin, Utah. The analysis of these sections demonstrate that a fracture hierarchy exists in relation to the sequence stratigraphic hierarchy. The majority of fractures (80%) terminate at genetic unit boundaries or the internal flooding surface that separates the transgressive from regressive hemicycle. Fractures (20%) that do not terminate at genetic unit boundaries or their internal flooding surface terminate at lower order sequence stratigraphic boundaries or their internal flooding surfaces. Secondly, the fracture spacing relates well to bed thickness in mechanical units no greater than 0.5m in thickness but with increasing bed thickness a scatter from the linear trend is observed. In the Paradox Basin the influence of strain on fracture density is illustrated by two sections measured in different strain regimes. The folded strata at Raplee Anticline has higher fracture densities than the flat-lying beds at the Honaker Trail. Cemented low porosity rocks in the Paradox Basin do not show a correlation between fracture pattern and porosity. However velocity and rock stiffness moduli's display a slight correlation to fracture spacing. Furthermore, bed thickness is found to be only one factor in determining fracture density but with increasing strain, internal bedforms and rock petrophysical heterogeneities influence fracture density patterns. This study illustrates how integrating sedimentologic and sequence stratigraphic interpretations with data on structural kinematics can lead to refined predictive understanding of fracture attributes.

  16. 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)

  17. Stratigraphy of the crater Copernicus

    NASA Technical Reports Server (NTRS)

    Paquette, R.

    1984-01-01

    The stratigraphy of copernicus based on its olivine absorption bands is presented. Earth based spectral data are used to develop models that also employ cratering mechanics to devise theories for Copernican geomorphology. General geologic information, spectral information, upper and lower stratigraphic units and a chart for model comparison are included in the stratigraphic analysis.

  18. 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.

  19. 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.

  20. Relative paleointensity (RPI) and oxygen isotope stratigraphy at IODP Site U1308: North Atlantic RPI stack for 1.2-2.2 Ma (NARPI-2200) and age of the Olduvai Subchron

    NASA Astrophysics Data System (ADS)

    Channell, J. E. T.; Hodell, D. A.; Curtis, J. H.

    2016-01-01

    Integrated Ocean Drilling Program (IODP) Site U1308 (49°53‧N, 24°14‧W; water depth 3871 m) provides a record of relative paleointensity (RPI) and benthic stable isotope stratigraphy back to 3.2 Ma. The record since 1.5 Ma was published previously, and here we present the interval from 1.5 Ma to 3.2 Ma (Early Pleistocene-Late Pliocene). The benthic oxygen isotope record in this interval is correlated to Marine Isotope Stage (MIS) 51 to KM2, with an apparent hiatus that removed part of the interval spanning MIS 104-G2 (2.6-2.65 Ma), at the Gauss-Matuyama boundary. The mean sedimentation rate for the 1.5-3.2 Ma period is 8.5 cm/kyr. The age model was built by correlation of the benthic oxygen isotope record to a global stack (LR04). Apart from the expected polarity reversals, three magnetic excursions are recorded: Punaruu in MIS 31/32 at 1092 ka, Gilsa in MIS 54/55 at 1584 ka, and a newly recognized excursion labeled Porcupine (after the nearby Porcupine Abyssal Plain) in MIS G6/G7 at 2737 ka. The ages of polarity reversals at Site U1308, on the LR04 time scale, are consistent with the current geomagnetic polarity timescale (GPTS) with the exception of the base of the Olduvai Subchron that occurred in MIS 73, corresponding to 1925 ka on the LR04 time scale, 25 kyr younger than in the current GPTS. The RPI record at Site U1308 is calibrated using the oxygen isotope age model, and combined with four other North Atlantic records to obtain a North Atlantic RPI stack for 1.2-2.2 Ma (NARPI-2200) that is compared with published RPI stacks: Epapis, Sint-2000 and PADM2M. For 2.2-3.2 Ma, the Site U1308 RPI record is compared with a RPI record from North Atlantic IODP Site U1314, and with the Pacific Epapis stack. The mean sedimentation rates of the North Atlantic sites in NARPI-2200 are greater (by about an order of magnitude) than most of the records incorporated in other stacks. The comparison of Epapis and NARPI-2200 yields an apparent lag for NARPI-2200 relative to Epapis, attributed the Epapis age model constructed by correlation of magnetic concentration parameters (a proxy for carbonate percentage) to a calibrated oxygen isotope record. The long RPI record from Site U1308 yields a very similar mean value for the Brunhes and Matuyama virtual axial dipole moments (7.05 × 1022 Am2), implying no polarity bias in the strength of the main geomagnetic dipole, in contrast to interpretations from Sint-2000 and PADM2M. The results strengthen the case that RPI can be used to improve global stratigraphic correlation for sites with mean sedimentation rates up to several decimeters/kyr.

  1. 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.

  2. Sedimentological characterization of braided and meandering fluvial reservoirs: Prediction of size and heterogeneity

    SciTech Connect

    Davies, D.K. ); Vargas, J. )

    1993-02-01

    Fluvial reservoirs host significant volumes of hydrocarbons. They comprise a significant reserve base in areas and formations as diverse as the San Jorge Basin, Argentina, the Lagunillas Formation, Venezuela, and Cano Limon Field, Colombia. Effective development and reservoir management required detailed sedimentological characterization because fluvial reservoirs, irrespective of age and geographic location, are characterized by considerable variability in geometry and internal heterogeneity. This paper presents models of braided and meandering reservoirs in selected Tertiary and Cretaceous fields of South and North America, based on sedimentological characterization using conventional cores and wireline logs. Fieldwide (macro-scale) and inter-well (meso-scale) heterogeneity is determined through detailed evaluation of facies distribution, particularly the distribution and maturity of paleosol horizons (e.g. calcretes). Within a given reservoir, micro-scale variations in porosity, permeability and saturation are fundamentally related to depositional environment. Effective permeability to hydrocarbons varies with environment and bedding style. The size of meandering and braided channel reservoirs is predicted using empirical geological equations. Predicted dimensions are compared with the independent results of reservoir simulation analysis for the same sand bodies. Engineering and sedimentological predictions of reservoir size and heterogeneity are similar, particularly in reservoirs where median permeability to hydrocarbons is > 1 md. The size and heterogeneity of productive channel reservoirs can be predicted at an early stage in field development is channel style and channel depth are known. Determination of these two fundamental parameters required sedimentological characterization at the macro-, meso-, and micro-scale using wireline logs and cores.

  3. Lower Cretaceous nannofossil stratigraphy of the Great Valley sequence

    SciTech Connect

    Bralower, T.J. )

    1990-05-01

    The calcareous nannofossil stratigraphy of four sections in the Great Valley Sequence of the Sacramento Valley, California, has been investigated in detail. These sections include Grindstone and Stony Creeks (Glenn County) and McCarty Creek and the Vestal Road segment of Dry Creek (both in Tehama County). The ages of the sections investigated, which have independently been studied by ammonite, pelecypod, and radiolaria biostratigraphers, range from Berriasian to Albian. Nannofossils occur rarely in these sediments and are restricted largely to mudstone deposited in the most distal portions of turbiditic sequences. Approximately 5% of the samples collected are nannofossiliferous. Assemblages contain some elements of Boreal floras but are dominated by Tethyan taxa. These assemblages are more directly comparable to those of stratotype sequences in Europe than are the other fossil groups, but the ages given are generally similar. However, two major discrepancies do exist. The results of this study indicate that the pelecypod, Buchia aff. B. okensis zone is Berriasian in age, not Tithonian as previously believed and the B. pacifica zone is not entirely Valanginian but partly Berriasian. Nannofossil data provide useful age calibrations for ammonite stratigraphy. The stratigraphy obtained supports structural interpretations based upon Buchia, in particular that the Paskenta fault zone remained active throughout the Early Cretaceous. The study illustrates that nannofossil biostratigraphy can be effectively used to date sediments deposited in convergent margin settings.

  4. 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.

  5. The Pleistocene hominid site of Ternifine, Algeria: New results on the environment, age, and human industries

    NASA Astrophysics Data System (ADS)

    Geraads, Denis; Hublin, Jean-Jacques; Jaeger, Jean-Jacques; Tong, Haiyan; Sen, Sevket; Toubeau, Philippe

    1986-05-01

    A new multidisciplinary research program, started in 1981, provided new data on the stratigraphy, fauna, and human industries, as well as the first results on paleomagnetism and sedimentology, for the Ternifine site in Algeria, which yielded the earliest hominid remains known in North Africa. The fossils were deposited in a swamp or lake surrounded by a very open, dry environment. The lake was fed by artesian springs that raised the underlying Miocene sands. Although nothing suggests a camp or butchery site, we discovered the first undisputable bone artifact in this site, the earliest known in this part of Africa. According to paleontological data, 700,000 yr B.P. is a likely age for the Ternifine deposits, which is consistent with the paleomagnetic results.

  6. Paleocene stratigraphy in Egypt

    NASA Astrophysics Data System (ADS)

    Farouk, Sherif

    2016-01-01

    The Egyptian Paleocene is widely distributed with vertical and lateral facies changes geographically separated and subject to different tectonic and sedimentary regimes. Five coeval facies associations of the Paleocene outcrops are identified and named from south to north: Garra El-Arbain, Nile Valley, Farafra, Sinai, and Southern Galala. Ten Paleocene third-order depositional sequences (Ds Da1 to Ds Th9) are tentatively distinguished in Egypt. These are bounded at their base and top by ten sequence boundaries (Eg.Da-1, Eg.Da-2, Eg.Da-3, Eg.Da-4, Eg.Da-5, Eg.Da-6, Eg.Se-7, Eg.Th.-8, Eg.Th.-9, and Eg.Eo-10). The relative ages and correlation of the Paleocene depositional sequences are based on planktonic foraminiferal biostratigraphy. Comparison of identified Paleocene sequences in and outside Egypt are referred to eustatic sea-level changes and partly to regional tectonics events, which have caused hiatuses of variable durations and different configurations of Paleocene sedimentary regimes from place to place.

  7. Sedimentological techniques applied to the hydrology of the Atlantic coastal plain in South Carolina and Georgia near the Savannah River Site

    SciTech Connect

    Falls, F.W. ); Baum, J.S. ); Edwards, L.E. )

    1994-03-01

    Potential for migration of contaminants in ground water under the Savannah River from South Carolina into Georgia near the US Department of Energy (DOE) Savannah River Site (SRS). The SRS is located in the inner Atlantic Coastal Plain of South Carolina and is underlain by 200 to more than 300 meters of permeable, unconsolidated to poorly consolidated sediments of Cretaceous and Tertiary age. The US Geological Survey, in cooperation with the US Department of Energy and the Georgia Department of Natural Resources, is evaluating ground-water flow through the Coastal Plain sediments in the area. Preliminary hydrologic studies conducted to provide the data needed for digital modeling of the ground-water flow system identified the need for more extensive investigation into the influence of the geologic complexities on that flow system. The Coastal Plain physiographic province in South Carolina and Georgia is comprised of a complex wedge of fluvial, deltaic, and marine sedimentary deposits locally modified by faulting. Several techniques commonly used in petroleum basin analysis (sequence stratigraphy, biostratigraphy, detailed core description, and geophysical well log analysis), were used together with water-level measurements, aquifer-test data, and geochemical data to identify six regional aquifers. Hydraulic conductivity distribution maps within each of these aquifers were constructed using textural analysis of core materials, aquifer test data, and depositional system reconstruction. Sedimentological techniques were used to improve understanding of the depositional system and the ground-water flow system dynamics, and to help focus research in areas where additional hydrologic, geologic, and aquifer-test data are needed.

  8. Mesozoic-Cenozoic sequence stratigraphy of European basins

    SciTech Connect

    Vail, P.R. ); Jacquin, T. )

    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.

  9. 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.

  10. Ediacaran sedimentology and paleoecology of Newfoundland reconsidered

    NASA Astrophysics Data System (ADS)

    Retallack, Gregory J.

    2016-03-01

    Ediacaran fossils of Mistaken Point and other localities in Newfoundland have been reconstructed as denizens of a deep, dark ocean, based on a turbidite interpretation of their sedimentary context. Objections to this view include geochemical indications of fresh water and volcanological and sedimentological evidence that they lived in soils of coastal plains and tidal flats. Two distinct assemblages of these fossils are recognized: a low-diversity Aspidella-Heimalora community on sulfidic grey paleosols (Sulfaquent) and a high diversity Fractofusus-Charniodiscus community on red ferruginous paleosols (Fluvent and Udept). These two assemblages and their paleosols were comparable in habitat with Phanerozoic intertidal salt marsh and coastal woodlands, respectively. Paleosol chemical composition is also evidence that Ediacaran communities of Newfoundland lived in humid, cool temperate paleoclimates, unlike arid paleoclimates of the classical Ediacaran biota of South Australia.

  11. Updated glacial chronology of the South Fork Hoh River valley, Olympic Peninsula, Washington through detailed stratigraphy and OSL dating

    NASA Astrophysics Data System (ADS)

    Wyshnytzky, C.; Rittenour, T. M.; Thackray, G. D.

    2012-12-01

    The Olympic Peninsula lies within a maritime climatic zone under the direct influence of westerly atmospheric flow and Pacific Ocean sea surface temperature variations (i.e. ENSO and PDO). During the last glaciation, large valley glaciers extended radially from the Mt. Olympus area and carved deep valleys, which preserve glacial diamicton, outwash, and lacustrine sediment emplaced during ice advance and retreat. Previous work by Thackray (1996) mapped glacial deposits through several key drainages in the western Olympic Mountains and used exposures along the South Fork Hoh River to reconstruct MIS 2 glaciation and determine the relative extent of the LGM ice margin in the region. Findings suggest that the extent of mountain glaciers in the western Olympics were much reduced during MIS 2 in comparison to MIS 3/4, with glacier mass balance primarily controlled by moisture delivery. Here we discuss new data constraining the style and timing of deglaciation in the South Fork Hoh River valley of the western Olympic Mountains, Washington, USA. Previous research in the South Fork Hoh River used radiocarbon ages, geomorphic mapping, and general stratigraphic relationships to establish a chronostratigraphic framework (Thackray, 1996). To further that understanding and provide new insight on the style and timing of MIS 2 glaciation, we examine the sedimentology and stratigraphic architecture of glacial landforms, which contain invaluable information about glacial processes and style. Optically stimulated luminescence (OSL) dating, commonly regarded as problematic in glacial sediments, constrains the ages of proximal glacial outwash and glaciolacustrine deposits that were traditionally difficult to date due to the lack of organic matter for radiocarbon dating. OSL ages are internally coherent and stratigraphically consistent with previous radiocarbon ages. Results from this research in the South Fork Hoh River valley and associated work in the Queets River valley, the next major drainage to the south, provide an update on the style and timing of local ice advance during MIS 2 and the LGM. Glacial advances represented in the stratigraphy of these exposures, with ages constrained by radiocarbon dating, OSL dating, or both, include the Hoh Oxbow II (>23 ka), Twin Creeks I (~19 ka), and Twin Creeks II (<17 ka) advances. Weakly to moderately stratified diamicton mark ice advances and are overlain by one or more distinct packages of outwash. Glaciolacustrine sediments, probably impounded by ice in the Hoh River valley, mark the retreat from the Hoh Oxbow II advance.

  12. Surface-based aeolian stratigraphy

    NASA Astrophysics Data System (ADS)

    Swanson, T.; Mohrig, D. C.; Kocurek, G.; Wolinsky, M. A.; Hern, C.

    2014-12-01

    Aeolian dune stratification arises from the migration, interaction and deformation of bedforms driven by an allogenic forcing. Recognizing the contribution of bedform deformation and interaction on the architecture of aeolian dune deposits is helpful for reconstruction of ancient dune morphology and wind circulation. Surface-based aeolian stratigraphy is generated by translating a surface model of dynamic bedform topography through space. The surface model of bedform topography responds realistically to allogenic signals and captures the growth and motion of bedform migration, deformation and interaction. The regular and irregular dynamic motions of bed geometry are distinctly encoded into the geometry of stratigraphic surfaces within the synthetic volume. Criteria for the recognition of stratigraphic surfaces originating from the passage of bedform defects and deformation accrued by bedform interactions are presented.

  13. Eolian cover sands: a sedimentologic model and paleoenvironmental implications

    SciTech Connect

    Lea, P.D.

    1985-01-01

    In periglacial areas, accumulations of eolian sand commonly form low-relief blankets without well-developed dunes. Internally, these sandsheet deposits exhibit subhorizontal lamination rather than high-angle cross-bedding. Such cover sands of late-Pleistocene age mantle extensive areas in northern Europe, but have been reported more rarely from North America. The processes by which cover sands, as opposed to dunes, accumulate have not yet been determined conclusively. Wind ripples and sand dunes do not form a continuum; flow separation and avalanching and negligible in the former and vital in the latter. Accretion of a sand patch into a mound sufficient to cause flow separation and dune growth requires a consistently available supply of loose sand. In cover-sand areas, sand may be immobilized prior to dune development by several factors: (1) a sparse vegetation cover, (2) moist ground conditions, (3) snow cover, and (4) a shallow permafrost table and/or an ice-cemented active layer. Detailed sedimentologic studies may allow discrimination among these various controls. The importance of the individual controlling factors can vary seasonally in a given deposit, as well as between deposits in different paleogeographic settings. However, all factors imply more mesic conditions than those associated with many dune deposits. The association of cover sands with paraboloid dunes is also consistent with somewhat moist conditions. The relatively mesic nature of cover sands controls their Pleistocene distribution; they become decreasingly important relative to dunes in maritime-to-continental transects across Alaska and northern Europe.

  14. 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.

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

    SciTech Connect

    Jack C. Pashin; Robert A. Gastaldo

    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.

  16. Journey of Time in Stratigraphy

    NASA Astrophysics Data System (ADS)

    Gani, M. R.

    2014-12-01

    In stratigraphy, stratal surfaces (e.g. bedding planes) are generally considered as discrete time lines. However, expression of time in stratigraphic record can be quite complex. Unlike flat stratal surfaces, time surfaces are mostly undulating. Moreover, time was not only elapsed vertically across stratal surfaces, it was also elapsed horizontally along such surfaces. These complexities can generate contentions when it comes to dividing stratigraphic packages into chronostratigraphic or genetic units. Since many stratal surfaces are composite in nature, they represent a diachronous interval of time. This is particularly true for active depositional systems where undulating geomorphic units migrate in time and space to fill a basin. At each level of hierarchy from ripple- to basin-scale clinoformal packages, composite stratal surfaces can develop, where deposits above such a stratal surface are NOT everywhere younger than deposits below the same stratal surface. This may violate the Law of Superposition, which states that, in an undisturbed stratigraphic record, each layer is always younger than the layer beneath it. In fact, this Law holds true in one location moving strictly vertically through an undisturbed succession. While moving vertically, if an observer also moves laterally along a stratal surface for some distance, this Law may break down. These observations have critical implications in interpreting stratigraphic record, particularly in testing sequence stratigraphic concepts.

  17. 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.

  18. Structural stratigraphy of Austin Chalk

    SciTech Connect

    Corbett, K.P.; Friedman, M.

    1983-03-01

    The mechanical behavior (structural stratigraphy) of the Upper Cretaceous Austin Chalk is established from the study of fracture intensity along its outcrop trend from Dallas to San Antonio and westward to Langtry, Texas, and in the subsurface from the study of core and/or fracture identification logs from 39 wells. Three mechanical-stratigraphic units are recognized as: (1) an upper, fractured massive chalk corresponding to the Bid House Chalk Member, (2) a middle, ductile chalk-marl corresponding to the Dessau Chalk and Burditt Marl Members, and (3) a lower, fractured massive chalk corresponding to the Atco Chalk Member. Representative samples from these units were experimentally shortened dry, at 10, 17 34, and 70-MPa confining pressure, 24/sup 0/C (75/sup 0/F), and at 2.5 x 10/sup -4/ s/sup -1/ to determine if the relative mechanical behavior observed at the surface could be extrapolated into the subsurface at different simulated depths of burial. The experimentally determined ductilities do parallel those determined from outcrop and subsurface studies. Through multiple linear regression analyses of strength versus intrinsic rock properties and environmental parameters, it appears that first porosity and then smectite-content are most strongly correlated with strength. For low-porosity specimens (9 to 13.5%) smectite present in amounts as little as 1% by volume has the highest correlation with strength accounting for 83% of its variability. SEM photomicrographs show that the clays are smeared-out along the induced shear fracture surfaces where they are greatly reduced in grain-size. These observations suggest that the smectite acts mechanically as a soft-inclusion, localizing shear failure and correspondingly weakening the material.

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

    SciTech Connect

    Martin, M.W.; Walker, J.D. )

    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.

  20. Sedimentological and paleoenvironmental constraints of the Statherian and Stenian Espinhaço rift system, Brazil

    NASA Astrophysics Data System (ADS)

    Santos, M. N.; Chemale, F.; Dussin, I. A.; Martins, M.; Assis, T. A. R.; Jelinek, A. R.; Guadagnin, F.; Armstrong, R.

    2013-05-01

    The Espinhaço Basin in eastern Brazil contains depositional sequences developed in the São Francisco paleoplate and its margins. Detailed mapping was conducted and combined with U-Pb detrital zircon dating to determine the sedimentological-stratigraphic framework, provenance and minimum and maximum ages of the syn-rift-deposits. The two cycles have minimum ages of 1192 and 923 Ma and maximum ages of 1785 and 1685 Ma. The first depositional cycle, represented by the Bandeirinha and São João da Chapada formations, is marked by contributions of Neoarchean and Paleoproterozoic detrital zircons. The second cycle, the diamond-bearing Sopa-Brumadinho Formation, also contains Mesoproterozoic zircons formed between 1300 and 1190 Ma, which suggests an additional external source of Grenvillian age, that was not previously recorded in the São Francisco Craton. The investigation of such Mesoproterozoic intraplate sedimentary records, provides clues to understanding the history of the Rodinia active margins and, therefore, the kinematic reconstruction of its paleoplates.

  1. 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?

  2. Potentiality of the ground-penetrating radar for the analysis of the stratigraphy and sedimentology of Mars

    NASA Astrophysics Data System (ADS)

    Ori, G. G.; Ogliani, F.

    1996-11-01

    The ground-penetrating radar (GPR) is a good candidate for the exploration of the Martian subsurface because it is smaller and lighter than seismic instruments, and, due to the lack of water in the Martian rocks, has great penetration capability. The modelling of the GPR signal response has been performed by computing the dielectric properties of each simulated layer as a linear function of porosity, known values of the solids, and the nature of the material filling the voids (ice water, carbou dioxide ice, gas, liquid water). The synthetic response was computed by reflecting ray-tracing at various peak frequencies. The complex results show that reflections are due to variations in mineralogy, porosity and porc-filling material. The reflectors produced by the reflection of the electromagnetic waves provide a picture of the geometries of the layers of the subsurface and give elues on the nature of rocks. Permafrost and liquid water can be investigated, chiefly their seasonal changes can be analysed by means of repeated profiles. The use of the GPR would be a major breakthrough in the reconstruction of the past geological history of the planet.

  3. 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.

  4. The Sinemurian carbonate mud-mounds from central High Atlas (Morocco): stratigraphy, geometry, sedimentology and geodynamic patterns

    NASA Astrophysics Data System (ADS)

    Chafiki, Driss; Canérot, Joseph; Souhel, Abdellatif; el Hariri, Khadija; Eddine, Kamal Taj

    2004-06-01

    The Moroccan Central High Atlasic mud-mounds correspond to carbonate sponge-algal buildups developed in open marine conditions towards the Lower-Upper Sinemurian boundary. The structures gradually increase in size through time, from the small-sized lenses included in the Idikel coarse-bedded Lower Sinemurian grainstones to the high domes observed in the succeeding Aberdouz and Ouchbis Upper Sinemurian thin-bedded mudstones. The biological communities (mainly algae, sponges, thrombolites, stromatolites, annelids, bryozoans, brachiopods, pelecypods, gastropods, echinoderms, corals and scarce foraminifera) comprise common, well conserved remains in the rising core frameworks and small reworked bioclasts in the surrounding sedimentary depressions. These buildups are closely linked to tectonic processes as they grew on the normal synsedimentary faults which affected the central Atlasic area during the Lower Liassic period, leading to the breakup of the Early Sinemurian carbonate platform and the resultant initiation of the Upper Sinemurian subsiding basin. Silting conditions under hernipelagic sedimentation led to their death. Similar palaeogeographic changes and geodynamic evolution have been described recently from different structures in North Africa, Western Europe and North America.

  5. Sedimentology and stratigraphy of the Kanayut Conglomerate, central and western Brooks Range, Alaska; report of 1981 field season

    USGS Publications Warehouse

    Nilsen, T.H.; Moore, T.E.

    1982-01-01

    The Upper Devonian and Lower Mississippian(?) Kanayut Conglomerate forms a major stratigraphic unit along the crest of the Brooks Range of northern Alaska. It crops out for an east-west distance of about 900 km and a north-south distance of about 65 km. The Kanayut is wholly allochthonous and has probably been transported northward on a series of thrust plates. The Kanayut is as thick as 2,600 m in the east-central Brooks Range. It thins and fines to the south and west. The Kanayut forms the middle part of the allochthonous sequence of the Endicott Group, an Upper Devonian and Mississippian clastic sequence underlain by platform limestones of the Baird Group and overlain by platform limestone, carbonaceous shale, and black chert of the Lisburne Group. The Kanayut overlies the marine Upper Devonian Noatak Sandstone or, where it is missing, the marine Upper Devonian Hunt Fork Shale. It is overlain by the marine Mississippian Kayak Shale. The Kanayut Conglomerate forms the fluvial part of a large, coarse-grained delta that prograded to the southwest in Late Devonian time and retreated in Early Mississippian time. Four sections of the Kanayut Conglomerate in the central Brooks Range and five in the western Brooks Range were measured in 1981. The sections from the western Brooks Range document the presence of fluvial cycles in the Kanayut as far west as the shores of the Chukchi Sea. The Kanayut in this area is generally finer grained than it is in the central and eastern Brooks Range, having a maximum clast size of 3 cm. It is probably about 300 m thick. The upper and lower contacts of the Kanayut are gradational. The lower Kanayut contains calcareous, marine-influenced sandstone within channel deposits, and the upper Kanayut contains probable marine interdistributary-bay shale sequences. The members of the Kanayut Conglomerate cannot be differentiated in this region. In the central Brooks Range, sections of the Kanayut Conglomerate at Siavlat Mountain and Kakivilak Creek are typically organized into fining-upward fluvial cycles. The maximum clast size is about 3 cm in this area. The Kanayut in this region is 200-500 m thick and can be divided into the Ear Peak, Shainin Lake, and Stuver Members. The upper contact of the Kanayut with the Kayak Shale is very gradational at Kakivilak Creek and very abrupt at Siavlat Mountain. Paleocurrents from fluvial strata of the Kanayut indicate sediment transport toward the west and south in both the western and central Brooks Range. The maximum clast size distribution generally indicates westward fining from the Shainin Lake region.

  6. 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.

  7. Morphology, sedimentology and stratigraphic implication of debris-covered glacier deposits from the LGM and Lateglacial (Eastern Alps, Austria)

    NASA Astrophysics Data System (ADS)

    Reitner, Jürgen M.; Seidl, Sabrina; Wagreich, Michael

    2013-04-01

    Understanding the genesis of Quaternary sediments is crucial for establishing a climato-stratigraphy and, further on, to infer paleoclimatic conditions, if possible. Especially diamictons in the high-mountain environment may be formed by variety of processes, i.e. glacial, periglacial and gravitational. On the other hand, the interpretation of morphological features might be ambiguous as for example ridges may document latero-frontal dump moraines, flow of a rock avalanche event or constituents of a rock-glacier. In addition, equilibrium line altitudes (ELAs) of paleo-glaciers are mostly based on calculations using the reconstructed glacier size and applying a more or less fixed accumulation area ration (e.g. AAR - method). However, such ELAs are of no use for stratigraphic correlations and climatic considerations, if the former glacial system was strongly influenced by supraglacial debris deriving from steep back walls of cirques. We present two examples of reconstructed debris-covered or more specifically debris-mantled paleo-glaciers, their geological and morphological setting as well as their documented sedimentology and morphology. The first example is from the easternmost part of the European Alps (Northern Calcareous Alps / Schneeberg mountains / Puchberg) where an up to 60 m high moraine systems of LGM age shows some striking morphological similarities with relict rock glacier. However, based especially on lithofacies analyses as well as on the lithology of the matrix a glacial genesis could be proven. Lateglacial glacier deposits from the interior of the Alps (Lienz Dolomites / area of Karlsbader Hütte) display a quite similar glacial system. The geometry of the deposits in relation to proglacial sturzstrom sediments, showing typical indications of dynamic fragmentation, and the amount of angular, passively transported clasts in the till point to a rock avalanche event which had hit the glacier surface during a glacier advance. As the glacial system shows the morphostratigraphic characteristics of Younger Dryas (Egesen) stadial with multiple, sharp crested moraine ridges (e.g. Ivy-Ochs et al. 2008), the unusual large glacier extent is due to the rock avalanche debris cover and its insulating effect. In both cases the maximum elevation of lateral moraines (MELM - method) gave the most reliable estimates of ELAs with reconstructed low AARs of around 0.5 compared to the standard assumption for Lateglacial glaciers with a ratio around 0.65. Thus, stratigraphic correlations of moraines should be done not until morphological features and lithofacies have been analyzed considering the whole geological setting. Ivy-Ochs, S., Kerschner, H., Reuther, A., Preusser, F., Heine, K., Maisch, M., Kubik, P.W. and Ch. Schlüchter (2008):Chronology of the last glacial cycle in the Northern European Alps. Journal of Quaternary Science 23(6-7), 559-573.

  8. 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.

  9. Stratigraphy of the Caloris basin, Mercury

    NASA Astrophysics Data System (ADS)

    McCauley, J. F.; Guest, J. E.; Schaber, G. G.; Trask, N. J.; Greeley, R.

    1981-08-01

    A formal rock stratigraphic nomenclature in proposed for the ejecta units of the 1300-km diameter Caloris impact basin of Mercury. The ejecta units can be recognized for more than 1000 km radially outward from the basin edge, and are collectively called the Caloris Group. The formations recognized within the Caloris Group include: (1) the Caloris Montes; (2) the Nervo; (3) the Odin; and (4) two Van Eyck Formations, one with lineated facies and the other with secondary crater facies. It is shown that of the craters in the 30-100-km size range superposed on the Caloris ejecta assemblage, most are of the c(4) and c(5) type. The youngest craters are assigned the highest subscript numbers. If other basins and craters can be tied into the Caloris basin over the rest of Mercury using data from Mariner 10, the stratigraphy described may help establish a time stratigraphy consisting of formal systems and periods in the history of Mercury.

  10. Testing the limits of high-resolution whole-rock δ13Ccarb 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 δ13Ccarb signals has been a principal obstacle in interpreting whole-rock δ13Ccarb stratigraphy. We have evaluated the fidelity of the whole-rock δ13Ccarb 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 δ13Ccarb is an extraordinarily robust signal of global marine δ13C compositions. Correlative sections show strikingly similar δ13Ccarb values and patterns regardless of location, facies and rock type. Closely spaced successions of pristine limestone show highly reproducible δ13Ccarb profiles. Remarkably, δ13Ccarb trends cut across zones of alteration with no offset, and sections completely replaced by diagenetic/hydrothermal dolomite produce the same δ13Ccarb profiles as their unaltered counterparts. Our study confirms that whole-rock δ13Ccarb is an unprecedented chronostratigraphic tool. Our high-resolution approach identified abrupt offsets in δ13Ccarb 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 δ13Ccarb 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.

  11. Sedimentology of mega-scale glacial lineations on the Dubawnt Lake Palaeo-Ice Stream bed, Canada and implications for lineation genesis

    NASA Astrophysics Data System (ADS)

    O'Cofaigh, Colm; Stokes, Chris R.; Lian, Olav B.; Clark, Chris D.; Tulaczyk, Slawek

    2014-05-01

    Mega-scale glacial lineations (MSGLs) are highly elongate, subglacial landforms produced beneath zones of fast-flowing ice. While qualitative data on their morphology have existed for several decades, studies of their composition and sedimentology are comparatively rare. Sediment exposures along the course of the Finnie River in Nunavut, northern Canada, provide a window into the internal stratigraphy and sedimentology of MSGLs formed by the Dubawnt Lake Palaeo-Ice Stream during regional deglaciation of the Laurentide Ice Sheet. Stratigraphic sections record evidence for an initial advance of ice into the study area followed by ice sheet recession and deposition of glacifluvial and glacilacustrine outwash. Subsequently, the Dubawnt Lake Palaeo-Ice Stream overrode and reworked this outwash subglacially forming an 'MSGL till'. This till comprises a sandy, red diamicton facies, forming the core of the MSGL ridges and containing variably deformed lenses, stringers and rafts of outwash. The sedimentology of this diamicton is consistent with an origin as a glacitectonite and hybrid till formed by a combination of non-pervasive subglacial sediment deformation and lodgement. Facies variations from stratified to massive diamicton reflect, in turn, variations in strain and subglacial transport distance. The occurrence of stratified glacifluvial sediments within these ridges and the well-preserved nature of many of the sandy inclusions within the diamicton imply relatively short transport distances and incomplete mixing. MSGLs under the Dubawnt Lake Palaeo-Ice Stream formed through a combination of subglacial erosion and deposition. This included non-pervasive, subglacial sediment deformation and the reworking of pre-existing sediment depocentres during streaming flow. These results highlight the importance of sediment supply to MSGL formation with the presence of abundant pre-existing sediments which were subsequently overridden being critical to lineation formation.

  12. 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.

  13. Magnetic stratigraphy of Peralkaline Volcanism in Sierra Libre, Sonora, Mexico

    NASA Astrophysics Data System (ADS)

    Olguin-Villa, A. E.; Stock, J. M.; Vidal-Solano, J. R.

    2011-12-01

    Middle Miocene (~12 Ma) magmatism in NW Mexico was dominated by the appearance of anorogenic liquids associated with the Proto-Gulf of California. These correspond to a few occurrences of mafic volcanic rocks with transitional signatures (geochemically) and to a larger silicic volcanic event of peralkaline affinity. The silicic event is primarily composed of a large ignimbritic deposit widely recognized in Baja California as the Tuff of San Felipe (TSF), and in Sonora as the Hermosillo Ignimbrite. These are correlated by a number of characteristics including a unique low-inclination, reversed magnetization, probably associated with a field transition or a geomagnetic excursion within a reversed polarity subchron at 11.531-11.935 Ma (base of C5r.3r; Cande and Kent, 1995). Thick sections of deposits of this peralkaline volcanism crop out at Sierra Libre, geographically located ~45 km south of Hermosillo, Sonora. In this locality, a ~180m thick stack of middle Miocene volcanic units (both pyroclastic and lavas) were sampled for paleomagnetic studies focusing on the magnetic stratigraphy of a set of 9 units (7 to 12 cores per unit) from El Galindro Canyon, which represents the thickest volcanic pile genetically related to Tuff of San Felipe and Hermosillo ignimbrite. Previous studies indicated that the anomalous magnetization from TSF could be either an excursion or a reversal transition - its age is unconstrained except by direct radiological isotopes and relative stratigraphy. But most excursions recorded in high-deposition rate lakebeds, and less often in volcanic piles, trace simple "there-and-back" paths away from and returning to the ordinary geomagnetic secular variation locus for an age. By contrast, the Sierra Libre magnetizations wander erratically in declination and inclination, without following a simple sequential ''Path''. Polarity reversal transitions recorded in high-deposition rate lakebeds do behave that way. We therefore interpret TSF (and remarkably, most or all of the Sierra Libre peralkaline pile) as recording a reversal transition rather than an excursion.

  14. 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.

  15. Devonian stratigraphy of the Appalachians

    SciTech Connect

    Ferrill, B.A.; Thomas, W.A.

    1985-01-01

    Lower and lower Middle Devonian (below the top of the Onondaga and equivalent) strata in the Appalachian unmetamorphosed fold-thrust belt are relatively thin and are laterally variable in lithology, thickness, and age. South of Virginia, thickness is less than 100 m; in Virginia and farther north, thickness ranges from 100 to 450 m. Locally, rocks of this age are unconformably absent in Pennsylvania and in Virginia and farther south. Clastic rocks dominate the interval in places along the southeastern margin of the fold-thrust belt and near pinch-outs at unconformities. Elsewhere, the interval is dominated by carbonate rocks. In contrast, thick sequences of lower Devonian rocks are preserved in Appalachian metamorphic belts in New England and in Alabama. The stratigraphic distribution of upper Middle (above the top of the Onondaga and equivalent) and Upper Devonian rocks is dominated by the widespread semicircular Catskill clastic wedge, centered on southeastern Pennsylvania. Near the depocenter, the succession grades upward from deep-water black shale, through shallow-marine sandstones and mudstones, to deltaic and fluvial red beds. These facies prograde both northwestward toward the craton and southwestward along structural strike. Pelitic rocks dominate the distal part of the wedge. Distribution of the Catskill clastic wedge reflects sediment transport onto the earlier Devonian shelf from an Acadian orogenic uplift. Local basins in Maine were probably not interconnected and reflect fault-block uplifts and pull-apart basins associated with wrench faults.

  16. Depositional architecture and sequence stratigraphy of Pleistocene coarse-grained deltas along the Ligurian coast (Italy)

    NASA Astrophysics Data System (ADS)

    Ciampalini, A.; Firpo, M.

    2015-12-01

    This study aims to develop a better understanding of the stratigraphy of the southern side of the Maritime Alps and of the Ligurian Sea during the Plio-Pleistocene. Five stratigraphic sections were measured and studied in the Segno River valley (Liguria, Italy). These sections are composed of Lower to Middle Pleistocene marine and continental deposits. Based on detailed mapping and sedimentological analysis, 12 marine and deltaic facies were identified. These facies were grouped into facies associations. Two allostratigraphic units were recognized, namely U1 and U2 from oldest to youngest. The lower unit (U1) represents the evolution of a coarse-grained delta developed in a valley or embayment. Within the deltaic sequence, transgressive and highstand systems tracts were recognized. The coarsening/shallowing upward trend observed within the sections suggests that the delta prograded rapidly in the landward portion of the canyon adjacent to the paleo-river outlet. The upper boundary of U1 is represented by a subaerial unconformity overlain by U2, which is composed of sediments deposited by several alluvial fan systems.

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

    SciTech Connect

    Tew, B.H.; Mancini, E.A.; Mink, R.M. )

    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.

  18. Sequence stratigraphy and depositional systems of the Lower Silurian Medina Group, northern Appalachian basin

    SciTech Connect

    Castle, J.W. )

    1991-08-01

    Detailed sedimentological analysis of 3500 ft of continuous core from 44 wells in Pennsylvania, Ohio, Ontario, New York, and West Virginia, combined with regional study of geophysical logs, results in new interpretations of sequence stratigraphy and depositional systems in Lower Silurian siliciclastic rocks of the northern Appalachian basin. Above a type-1 sequence boundary at the base of the Medina Group are a lowstand systems tract and a transgressive systems tract that are represented, respectively, by the Whirlpool Sandstone and by the overlying Cabot Head Shale. The thickest sandstones in the Medina Group occur in the Grimsby Sandstone, which is interpreted as a highstand systems tract with basinward-prograding parasequences. Sea level rise after Grimsby parasequence deposition is represented by marine-shelf shale in the uppermost part of the Medina Group. Based on facies successions in the cores, four mappable depositional systems are interpreted for the Grimsby Sandstone and correlative sandstone units; (1) wave-dominated middle shelf, (2) wave- and tide-influenced inner shelf, (3) tide dominated shoreline, and (4) fluvial. The wave-dominated middle-shelf system, which includes very fine-grained shelf-ridge sandstones encased in marine shale, is the most basinward system, occurring from Ontario through parts of eastern Ohio. Shoreward, across the northern Appalachian basin, the influence of tidal processes relative to wave processes generally increased, which may have been related to distance across the shelf, water depth, and shoreline configuration. The shoreline may have been deltaic in some areas and straight in other areas.

  19. The Utility of Proximal-Accretion Stratigraphy in Lateral Moraines

    NASA Astrophysics Data System (ADS)

    Samolczyk, M. A.; Osborn, G.

    2010-12-01

    Lateral-moraine stratigraphy is a valuable tool that can be used to constrain the timing and magnitude of alpine glacier fluctuations. Numerous lateral moraines, conventionally thought to have been constructed during the Little Ice Age (LIA), have been shown to be composite landforms that contain multiple till layers deposited by successively larger glacier advances. Organic matter and/or tephra sandwiched between the till layers constrain times of advance and retreat; wood fragments within till may provide the age of the till. Observation of contemporary lateral moraines has lead to the recognition of two means of lateral moraine construction: (1) accretion of tills onto the distal flank of the pre-existing lateral moraine, and (2) accretion or plastering of tills onto the proximal flank of the pre-existing moraine. In composite lateral moraines, distal and proximal accretion result in paleosurfaces that trend parallel to the current distal and proximal slope, respectively. Published work using lateral-moraine stratigraphy, for example at Bugaboo and Stutfield glaciers in the Canadian Rockies, has used evidence only from distal-accretion moraines. However, proximal-accretion moraines that provide chronological information have been found at Nisqually Glacier on Mount Rainier in Washington State, USA, and Columbia Glacier, an outlet of the Columbia Icefield in the Canadian Rockies. A gully cut into the left-lateral moraine at Nisqually Glacier exposes a sandy seam, with associated wood fragments, that runs parallel to the proximal moraine flank for ~20 m. Wood collected from different elevations along the seam have radiocarbon ages of 1715±15, 1700±15, and 1670±50 14C yr BP, indicating that the seam is similar in age along its extent and likely marks a paleosurface separating older till below and till of the First Millennium advance above. At Columbia Glacier, some till exposures in the prominent right-lateral moraine show a fissility dipping variably 40 to 50° toward the valley axis; this orientation is semi-parallel to the proximal flank of the moraine, which however is steeper due to ongoing erosion. Five wood fragments encased in the till over a broad area of the flank, and exposed by gullying, have ages ranging from 1920±70 to 2340±70 14C yr BP. This suggests that (1) most of what appears to be a LIA moraine was deposited in earlier Neoglacial time, and (2) that the glacier was nearly as extensive ca. 2400-1900 ka as it was during the LIA.

  20. Carboniferous stratigraphy of the Appalachians

    SciTech Connect

    Hines, R.A.; Thomas, W.A.

    1985-01-01

    Carboniferous rocks in the Appalachian fold-thrust belt and foreland basins include parts of four clastic wedges. Distribution, composition, and ages of the clastic wedges record diachronous orogenic uplifts along the Appalachian margin. Lower Mississippian Pocono sandstones form the upper part of the Catskill-Pocono clastic wedge, which includes the Devonian Catskill deltaic facies. Pocono rocks reflect clastic sediments transport toward the northwest and west from an orogenic source east of the Pennsylvania salient. The upper Mississippian-Pennsylvanian Mauch Chunk-Pottsville clastic wedge prograded westward and southwestward from the Pennsylvania salient over Mississippian limestone. The southwestern limit of the Mauch Chunk-Pottsville clastic wedge is overlapped in the Virginia recess by the oppositely directed Pennington-Lee clastic wedge. The Upper Mississippian-Pennsylvanian Pennington-Lee clastic wedge prograded northeastward and northwestward from the Tennessee salient. Southwestward in the Alabama recess, the Pennington clastic facies grades into Mississippian limestone, and Lee-equivalent sandstones extend over the limestone. In the western part of the Alabama recess, Upper Mississippian-Lower Pennsylvanian delta systems prograded northeastward over the Mississippian carbonate facies. These clastic sediments are an eastern shelf-delta part of a thick clastic wedge that consists of turbidites in the Ouachita salient. The eastern fringe of the Ouachita clastic wedge merges with the southwestward-prograding Pennington-Lee clastic wedge above Mississippian carbonate rocks in the Alabama recess.

  1. Sedimentological and geophysical properties of a ca. 4000 year old tsunami deposit in southern Spain

    NASA Astrophysics Data System (ADS)

    Koster, Benjamin; Reicherter, Klaus

    2014-12-01

    The coastlines around the Gulf of Cádiz were affected by numerous tsunami events damaging infrastructure and causing countless human losses. A tsunami deposit at Barbate-Zahara de los Atunes, Spain, is located at various heights above mean sea level and shows several characteristics indicative of high-energy event deposition. This study uses sedimentology, foraminifera assemblage, magnetic susceptibility, X-ray fluorescence analysis, ground penetrating radar (GPR) to support an interpretation of high-energy deposition and determine the deposit's transport mechanisms and sediment source. Radiocarbon and optically stimulated luminescence dating of the tsunami deposit reveals ages of ~ 4000 BP and does not support the AD 1755 Lisbon event as suggested in former publications.

  2. Mesozoic stratigraphy of central Honduras

    SciTech Connect

    Finch, R.C.

    1981-07-01

    Geologic mapping near Lake Yojoa in central Honduras has shown the need to modify the published Mesozoic stratigraphic column. The Ilama Formation is not a useful unit for regional mapping inasmuch as Ilama-type strata are discontinuous and in various stratigraphic positions. The formal name Ilama Formation should be abandoned. A new formal name, the Jaitique Formation, is introduced to designate a major Cenomanian limestone unit that is stratigraphically about midway in the Valle de Angeles Group in the Santa Barbara-Lake Yojoa region. The Jaitique Formation consists of up to 140 m of shallow-marine strata that can be divided into two members: (1) a lower member of thick-bedded shelf carbonate strata, and (2) a distinctive upper member of thin-bedded, laminated, nonfossiliferous limestone which may represent a shallow, possibly hypersaline, lagoon or intertidal mud-flat environment. Because the lower member of this Cenomanian limestone was formerly misidentified as the Atima Formation of the Yojoa Group, the upper, thin-bedded member was originally defined as the Guare Formation of the Yojoa Group. The name Guare is retained, but the unit is downgraded to the Guare Member of the newly defined Jaitique Formation within the Valle de Angeles Group. Although the Jaitique Formation is similar in stratigraphic position and age to the Esquias Formation in the Minas de Oro area on the east, it is lithologically distinct, and probably slightly older. The two units are not thought to be lithostratigraphically contiguous. Recognition of major Cenomanian limestone units within the Valle de Angeles Group has led to reappraisal of the hydrocarbon potential of certain structural zones in Honduras. 6 figures.

  3. Towards the standardization of sequence stratigraphy

    NASA Astrophysics Data System (ADS)

    Catuneanu, O.; Abreu, V.; Bhattacharya, J. P.; Blum, M. D.; Dalrymple, R. W.; Eriksson, P. G.; Fielding, C. R.; Fisher, W. L.; Galloway, W. E.; Gibling, M. R.; Giles, K. A.; Holbrook, J. M.; Jordan, R.; Kendall, C. G. St. C.; Macurda, B.; Martinsen, O. J.; Miall, A. D.; Neal, J. E.; Nummedal, D.; Pomar, L.; Posamentier, H. W.; Pratt, B. R.; Sarg, J. F.; Shanley, K. W.; Steel, R. J.; Strasser, A.; Tucker, M. E.; Winker, C.

    2009-01-01

    Sequence stratigraphy emphasizes facies relationships and stratal architecture within a chronological framework. Despite its wide use, sequence stratigraphy has yet to be included in any stratigraphic code or guide. This lack of standardization reflects the existence of competing approaches (or models) and confusing or even conflicting terminology. Standardization of sequence stratigraphy requires the definition of the fundamental model-independent concepts, units, bounding surfaces and workflow that outline the foundation of the method. A standardized scheme needs to be sufficiently broad to encompass all possible choices of approach, rather than being limited to a single approach or model. A sequence stratigraphic framework includes genetic units that result from the interplay of accommodation and sedimentation (i.e., forced regressive, lowstand and highstand normal regressive, and transgressive), which are bounded by 'sequence stratigraphic' surfaces. Each genetic unit is defined by specific stratal stacking patterns and bounding surfaces, and consists of a tract of correlatable depositional systems (i.e., a 'systems tract'). The mappability of systems tracts and sequence stratigraphic surfaces depends on depositional setting and the types of data available for analysis. It is this high degree of variability in the precise expression of sequence stratigraphic units and bounding surfaces that requires the adoption of a methodology that is sufficiently flexible that it can accommodate the range of likely expressions. The integration of outcrop, core, well-log and seismic data affords the optimal approach to the application of sequence stratigraphy. Missing insights from one set of data or another may limit the 'resolution' of the sequence stratigraphic interpretation. A standardized workflow of sequence stratigraphic analysis requires the identification of all genetic units and bounding surfaces that can be delineated objectively, at the selected scale of observation, within a stratigraphic section. Construction of this model-independent framework of genetic units and bounding surfaces ensures the success of the sequence stratigraphic method. Beyond this, the interpreter may make model-dependent choices with respect to which set of sequence stratigraphic surfaces should be elevated in importance and be selected as sequence boundaries. In practice, the succession often dictates which set of surfaces are best expressed and hold the greatest utility at defining sequence boundaries and quasi-chronostratigraphic units. The nomenclature of systems tracts and sequence stratigraphic surfaces is also model-dependent to some extent, but a standard set of terms is recommended to facilitate communication between all practitioners.

  4. 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.

  5. The applicability of OSL as a sedimentological proxy: new avenues to distinguish extreme events

    NASA Astrophysics Data System (ADS)

    Lopez, G. I.

    2012-12-01

    Signature underwater tsunami deposits have been relatively recently found in the upper Mediterranean shelf offshore Israel. They have been attributed as a potential cause for the demise of the ancient Roman city of Caesarea Maritima and its artificial Herodian harbour of Sebastos. Present annual large winter storm activity (2010-2011; waves heights up to 14 m) has severely impacted the area, showing increased coastal erosion and rigorous movement of nearshore sands, complicating the stratigraphical histories of the near offshore record. Recent sedimentological and geoarchaeological studies conducted in and around the harbour have been aimed to investigate extreme event characterization by different means, using Optically Stimulated Luminescence (OSL). A comparative study of modern and palaeo-storm sediments was launched in order to obtain physical correlation between offshore sediments, enabling further comparison with historical tsunami deposits, as well as modern and ancient sands emplaced during normal marine conditions. A suite of previously collected and identified sediment samples was selected from the same area where the modern storm analogues were collected. The palaeo-samples came from long-vertical hydraulic percussion cores (14-30 m depths) and small horizontal tubes pushed into excavated underwater sediment walls (2-12 m depths). The uniqueness of OSL relays on its capacity to date the last time a mineral grain was effectively exposed to sunlight, just prior to its burial. It is intrinsically related to final depositional process, which should reflect the completeness of the OSL signal resetting (zeroing process), evidenced by the normality and modality of the Equivalent Dose (DE) distribution. In Optical Dating, DE over-dispersion values have been used as a measure of inhomogeneitiy in the natural palaeo-dose of sediments. Such heterogeneity can be due to an array of causes, including insufficient zeroing during transport and deposition, or turbation processes after burial. Environments where sediments are well exposed to daylight at deposition (e.g. aeolian and some coastal) do not show extreme over-dispersion values but rather well clustered DE's as noted by probability-distribution plots. The degrees of variance and skewness of Gaussian or relative-probability distributions are intrinsically related to the scatter factor. Hence, the latter could be used to differentiate between depositional mechanisms and/or environmental settings. In this study, the single-aliquot regenerative-dose (SAR) protocol was used to measure the OSL signals from single grains of quartz from tsunami, storm and normal marine conditions deposits. Over-dispersion analyses were conducted on all samples. Preliminary results suggest the possibility of differentiating between all three types of deposits based on pre-established over-dispersion values and representative single-dose population distributions. Further comparative OSL experiments are currently being carried out on other known tsunamigenic analogues to further evaluate OSL signal behaviours and constrain the findings (2011 Tohoku Tsunami; 1979 night Petatlán Tsunami). Rather than a dating tool, OSL was used to identify signal patterns exclusive to known depositional conditions, in hope of applying it as sedimentological proxy in event stratigraphy and palaeoseismic tsunami research.

  6. 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.

  7. 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.

  8. Stratigraphy and dissolution of the Rustler Formation

    SciTech Connect

    Bachman, G.O.

    1985-04-23

    The Rustler Formation is the uppermost evaporite-bearing unit in the Permian Ochoan series in southeastern New Mexico. It rests on the Salado Formation which includes the salt beds where the mined facility for the Waste Isolation Pilot Plant (WIPP) is being constructed. An understanding of the physical stratigraphy of the Rustler Formation is pertinent to studies of the WIPP site because some portions of the Rustler are water-bearing and may provide paths for circulating waters to come into contact with, and dissolve, evaporites within the Ochoan sequence. Knowledge of the processes, magnitude, and history of evaporite dissolution in the vicinity of the WIPP site is important to an evaluation of the integrity of the site. 2 refs., 2 figs.

  9. STRATIGRAPHY OF GLACIAL LAKE OJIBWAY AND IMPLICATIONS FOR THE 8200 YR EVENT

    NASA Astrophysics Data System (ADS)

    Lowell, T.; Stroup, J. S.; Breckenridge, A. J.; Smith, C. A.; Moser, J. V.; Sagredo, E.

    2009-12-01

    Determining the timing and routing of meltwater discharges from relic ice sheets into the oceans remains problematic. One example is the suggested Holocene drainage of Lake Ojibway that covered portions Ontario and Quebec. Radiocarbon ages on marine shells overlying proglacial lake sediments south of Hudson’s Bay provide minimum ages about 8200 cal yr BP leading Barber et al. (1999) to suggest drainage of this lake was a trigger for the so-called 8200 yr cold event. Anteves (1925) reported multiple varve sections that he suggested represented some 1800 years covering the evolution of Lake Ojibway and its precursor. Thus placing the varve stratigraphy into an absolute time framework could confirm the Barber hypothesis. Alternatively, if the lake drained before the 8200 yr event or drained multiple times, it would imply a more complex relationship between meltwater discharge and climate change. One complication is that evidence for a reactivation of the Laurentide Ice Sheet, locally called the Cochrane Readvance, exists in the basin. Subottom profiling of some 30 lakes reveals that in areas outside the Cochrane limit, bedrock basins contain thick (up to 30 m) glaciaolacustrine sequences. These are generally conformable sequences draping over the bedrock. In limited cases slight unconformities lie below the most recent erosion (at local wave base) and organic lacustrine sediments. Areas covered by the Cochrane advance display a thin stratigraphy; notably lacking are glaciolacustrine sequences. The stratigraphy recovered in core sequences (N=16) show a similar pattern: thin with very limited varves over the Cochrane and thicker sequences in the larger basins. However examination of sediments show that the stratigraphy is predominately glacier proximal sediment (not distal varves) with local unconformities and evidence of slumping. This implies localized sedimentation sources. Of these only two are classic varves which allow potential correlation with the sequence established by Anteves (1925). This localized complexity has thus far prevents any regional events from being identified. Given the regional sediment patterns and detailed stratigraphy we suggest the possibility that Lake Ojibway sequence is largely a local one and that the drainage history is not a simple one. Further evidence to date is unclear rather the Cochrane advance occured before or after the 8200 yr cold event.

  10. Extensional tectonics and stratigraphy of the North Atlantic margins

    SciTech Connect

    Tankard, A.J.; Balkwill, H.R.

    1989-01-01

    The tectonics and stratigraphy or the north Atlantic continental margins are discussed. Forty articles are included in the book. Each of these items have been abstracted and indexed for the U.S. Department of Energy Energy Data Base.

  11. Event Stratigraphy and Paleoceanography in the Fortuna Basin (Southeast Spain): A Scenario for the Messinian Salinity Crisis

    NASA Astrophysics Data System (ADS)

    Müller, Daniel W.; Hsü, Kenneth J.

    1987-12-01

    The timing and duration of evaporitic deposition during the Messinian in the Mediterranean is poorly known. To assist with this problem, we have correlated sedimentological events at widely separated locations in the Mediterranean and dated paleoceanographic events in the world ocean (event stratigraphy). Our working hypothesis is as follows: The Messinian Salinity Crisis caused the formation of evaporites in a deep desiccated basin which implies that (1) the evaporites were deposited during a steady marine influx, (2) multiple intervals of isolation led to drastic changes in the sediments and in the fauna of the Mediterranean, (3) the sea level of the Mediterranean Sea was mostly several hundreds of meters below that of the Atlantic Ocean, and (4) the seaways (Betic and Rif Strait) connecting the Mediterranean with the Atlantic during the late Miocene were affected by eustatic sea level changes caused by Antarctic glaciation. We found supporting evidence in the sedimentological and paleoceanographic records in the Betic Strait (Fortuna and Sorbas basins) which was one of the sites of major inflow into the late Miocene Mediterranean Sea. Drastic sea level changes and fluctuations during the late Tortonian and Messinian caused chronologically: (1) the deposition of brackish sediments overlying marine deposits, (2) the progradation of deltas, (3) reef growth at lower levels and their destruction by erosion and coverage by conglomerates, (4) evaporite deposition alternating with marine marls containing Atlantic diatom assemblages, and (5) five marine/terrestrial cycles associated with coral reefs. Based on event stratigraphy the following scenario for the Messinian "Salinity Crisis" is proposed: The Tripoli Formation (Chron 6R1/5N2: 5.93-5.7 Ma), the Lower Evaporites (Chron 5N2, 5R: 5.7-5.5 Ma), and the Upper Evaporites (lowermost Gilbert c: 5.25-5.15 Ma) were deposited during influx of Atlantic water into the Mediterranean. During this time, a unidirectional circulation dominated from the Atlantic through the Betic Strait. Only during the intra-Messinian inundation (Chron 5N1 into lowermost Gilbert c: 5.4-5.25 Ma) that occurred after a short intra-Messinian erosional event (Chron 5N1: 5.5-5.4 Ma) was a normal bidirectional circulation pattern established. This is reflected in the diatomites of the Chicamo Formation and the Mediterranean (site 124) as well as most likely in a reef on Cyprus. The marine record of the Pliocene filling of the Mediterranean is missing in these basins. Overall, marine water inflow into the Mediterranean through the Betic Strait dominated during the Messinian. The threefold marine/terrestrial cyclicity with severe paleoceanographic changes in the Fortuna and Sorbas basins favor the "deep, desiccated basin" model.

  12. High-Resolution Subsurface Imaging and Stratigraphy of Quaternary Deposits, Marapanim Estuary, Northern Brazil

    NASA Astrophysics Data System (ADS)

    Silva, C. A.; Souza Filho, P. M.; Gouvea Luiz, J.

    2007-05-01

    The Marapanim estuary is situated in the Para Coastal Plain, North Brazil. It is characterized by an embayed coastline developed on Neogene and Quaternary sediments of the Barreiras and Pos-Barreiras Group. This system is strongly influenced by macrotidal regimes with semidiurnal tides and by humid tropical climate conditions. The interpretation of GPR-reflections presented in this paper is based on correlation of the GPR signal with stratigraphic data acquired on the coastal plain through five cores that were taken along GPR survey lines from the recent deposits and outcrops observed along to the coastal area. The profiles were obtained using a Geophysical Survey Systems Inc., Model YR-2 GPR, with monostatic 700 MHz antenna that permitted to get records of subsurface deposits at 20m depth. Were collected 54 radar sections completing a total of 4.360m. The field data were analyzed using a RADAN software and applying different filters. The interpretation of radar facies following the principles of seismic stratigraphy that permitted analyze the sedimentary facies and facies architecture in order to understand the lithology, depositional environments and stratigraphic evolution of this sedimentary succession as well as to leading to a more precise stratigraphic framework for the Neogene to Quaternary deposits at Marapanim coastal plain. Facies characteristics and sedimentologic analysis (i.e., texture, composition and structure aspects) were investigated from five cores collected through a Rammkernsonde system. The locations were determined using a Global Positioning System. Remote sensing images (Landsat-7 ETM+ and RADARSAT-1 Wide) and SRTM elevation data were used to identify and define the distribution of the different morphologic units. The Coastal Plain extends west-east of the mouth of the Marapanim River, where were identified six morphologic units: paleodune, strand plain, recent coastal dune, macrotidal sandy beach, mangrove and salt marsh. The integration of GPR profiles and stratigraphy data allowed for the recognition of paleochannel geometry, with width of 150m and depth of 20m, developed on Barreiras Group, two discontinuity surfaces and three facies associations organized into sedimentary facies: (i) Tidal channel with mottled sand, Conglomerate with clay pebble and Ophiomorpha/linear Skolithos, channel-fill and tabular cross-bedding sand and sand/mud interlayer facies. (ii) Dune/interdune with wavy bedding and cross-bedding sand and planar bedding and tabular cross-bedding sand facies. (iii) infilled tidal channel with mottled sand, planar/flaser bedding sand, lenticular bedding clay and sand/mud interlayer facies. The present study demonstrates that some facies associations occur restricts to tidal paleochannels and shows features well preserved that are very important to reconstruction of the relative sea-level history in the Marapanim Estuary.

  13. Late tertiary structure and stratigraphy of north Sinai continental margin

    SciTech Connect

    Ben-Avraham, Z.; Mart, Y.

    1981-06-01

    New seismic data provide information on the structural development and late Tertiary stratigraphy of the continental slope and rise off northern Sinai. The upper continental slope is characterized by a marginal plateau composed of a series of platforms or steps. The lower continental slope is smooth, except for a low ridge paralleling the western part. Numerous diapiric structures along the continental margin north of the Sinai Peninsula emerge from an evaporitic layer of late Tertiary age. The diapirs usually are aligned along west-northwest-trending faults. A salt ridge 90 km long produces a submarine ridge in the lower continental rise. Two main fault trends have been mapped. In the western part of the continental margin they trend west-northwest and, in the eastern part, northeast. These trends parallel the continental slopes of northern Sinai and southern Israel, respectively. The structural grain of the Sinai margin appears to be controlled by two main tectonic elements: (1) rejuvenated basement faults of the continent-ocean transition zone; and (2) salt diapirism due to loading of Messinian evaporites with Nile-derived upper Tertiary clastics.

  14. Osmium isotope stratigraphy of a marine ferromanganese crust [rapid communication

    NASA Astrophysics Data System (ADS)

    Klemm, Veronika; Levasseur, Sylvain; Frank, Martin; Hein, James R.; Halliday, Alex N.

    2005-09-01

    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.

  15. 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.

  16. The crustal stratigraphy of Mercury from impact craters

    NASA Astrophysics Data System (ADS)

    Ernst, C. M.; Murchie, S. L.; Barnouin-Jha, O. S.; Robinson, M. S.; Denevi, B. W.; Blewett, D. T.; Head, J. W.; Izenberg, N. R.

    2009-12-01

    MESSENGER’s Mercury Dual Imaging System (MDIS), consisting of a monochrome, narrow-angle camera and an 11-band (430-1020 nm), wide-angle camera, imaged approximately 80% of the surface of Mercury during its first two flybys. These images confirm that the surface of Mercury exhibits subtle color variations, which are associated with changes in the steepness of the spectral slope over the MDIS wavelength range. Although the first-order color variations are due to maturity effects, some color variations can be attributed to compositional differences. In many areas, impact craters are associated with material that is spectrally distinct from the surrounding surface. These deposits can be located on the crater floor, rim, wall, or central peak, or in the ejecta blanket, and represent material that originally resided at depth and was subsequently excavated by impacts. The resulting craters make it possible to investigate the stratigraphy of Mercury’s upper crust. Studies of laboratory, terrestrial, and lunar craters provide a means to estimate, or at least bound, the depth of origin of the spectrally distinct ejecta and central peak structures. Craters of varying size in the same region can be used to constrain the vertical and horizontal extent of subsurface materials. Excavated red material (RM), with comparatively steep or “red” spectral slope, and low-reflectance material (LRM) stand out prominently from the surrounding terrain in enhanced-color images, as they are spectral end-members in Mercury’s compositional continuum. Examples of RM were found to be spectrally similar to the relatively red, high-reflectance plains (HRP), suggesting that they may represent deposits of HRP-like material that were subsequently covered by thinner (~1 km thick) intermediate plains. In one area, craters with diameters ranging from 30 km to 130 km have excavated and incorporated RM into their rims, suggesting that the underlying RM layer may be several kilometers thick. LRM deposits are often associated with ejecta from large craters and basins, but not all large craters and basins have excavated LRM, indicating a heterogeneous distribution across the planet. The presence of LRM in the central peaks of some large craters indicates that this material is at least locally present at a depth of several kilometers. Some RM and LRM were excavated by pre-Tolstojan basins, indicating a relatively old age (> 4.0 Ga). The examination of several small areas on Mercury reveals the complex nature of the local stratigraphy and supports sequential buildup of most of the upper ~5 km of crust by volcanic flows with compositions spanning the range of material now visible on the surface, distributed heterogeneously across the planet. MESSENGER’s third flyby of Mercury on 29 September 2009 collected new high-resolution color and monochrome images of specific targets. These images allow additional in-detail examinations of local areas, improving our understanding of Mercury’s crustal stratigraphy.

  17. Geomorphic and sedimentologic evidence for the separation of Lake Superior from Lake Michigan and Huron

    USGS Publications Warehouse

    Johnston, J.W.; Thompson, T.A.; Wilcox, D.A.; Baedke, S.J.

    2007-01-01

    A common break was recognized in four Lake Superior strandplain sequences using geomorphic and sedimentologic characteristics. Strandplains were divided into lakeward and landward sets of beach ridges using aerial photographs and topographic surveys to identify similar surficial features and core data to identify similar subsurface features. Cross-strandplain, elevation-trend changes from a lowering towards the lake in the landward set of beach ridges to a rise or reduction of slope towards the lake in the lakeward set of beach ridges indicates that the break is associated with an outlet change for Lake Superior. Correlation of this break between study sites and age model results for the strandplain sequences suggest that the outlet change occurred sometime after about 2,400 calendar years ago (after the Algoma phase). Age model results from one site (Grand Traverse Bay) suggest an alternate age closer to about 1,200 calendar years ago but age models need to be investigated further. The landward part of the strandplain was deposited when water levels were common in all three upper Great Lakes basins (Superior, Huron, and Michigan) and drained through the Port Huron/Sarnia outlet. The lakeward part was deposited after the Sault outlet started to help regulate water levels in the Lake Superior basin. The landward beach ridges are commonly better defined and continuous across the embayments, more numerous, larger in relief, wider, have greater vegetation density, and intervening swales contain more standing water and peat than the lakeward set. Changes in drainage patterns, foreshore sediment thickness and grain size help in identifying the break between sets in the strandplain sequences. Investigation of these breaks may help identify possible gaps in the record or missing ridges in strandplain sequences that may not be apparent when viewing age distributions and may justify the need for multiple age and glacial isostatic adjustment models. ?? 2006 Springer Science+Business Media B.V.

  18. Geomorphological and sedimentological characteristics of cyclone-generated landforms and washover deposits along the coasts of NW Australia

    NASA Astrophysics Data System (ADS)

    May, Simon Matthias; Engel, Max; Brückner, Helmut; Pint, Anna; Kelletat, Dieter; Scheffers, Anja; Squire, Peter

    2013-04-01

    Palaeotempestology, the study of prehistoric storms, uses sedimentary evidence to enlarge the temporal frame of storm occurrence patterns given by historical records. Different sedimentary archives storing traces of tropical cyclone impact (washover fans and sediments, beach ridge systems) were investigated along the coasts of the Exmouth Gulf and the NW Cape(W Australia) in order to evaluate their use for palaeotempestological research. (1) Along the W coast of the Exmouth Gulf, distinct lobate washover fans exhibit washover terraces, channel systems and delta-type sedimentation patterns. Their stratigraphy consists of shell debris layers, sand, coarse coral fragments and entire shells. Multiple reactivation of the washover fans is inferred from their complex pattern of accumulation and incision and a minimum of three palaeosols, each of them indicating one depositional event and a subsequent period of geomorphologic stability. (2) In Giralia Bay, S Exmouth Gulf, sandy chenier-like beach ridges characterize the landward boundary of extensive mud flats. Their geomorphology and stratigraphical architecture reflect the influence of intermittent phases of morphodynamic activity due to littoral-type processes and are assumed to record recurring cyclone impact. (3) Along the W coast of the NW Cape, subrecent tsunami sediments detected in back-barrier archives contain reworked foraminifers from the shelf and the littoral zone and are most likely related to the 1994 Java Tsunami. Below, several thin clastic sand layers intercalate carbonate mud sediments. In contrast to the mud units, most of the sandy layers are reflected by increased mean grain size and contain reworked foraminifers from the shelf and littoral zone. Underlying mud sediments and mangrove remains reflect coastal and palaeoenvironmental changes on Holocene time scales. Our preliminary findings suggest that the investigated sedimentary archives have a high potential for improving extreme wave histories (tsunamis, cyclone landfalls) of W Australia. Main challenges include dating (14C, OSL) and distinguishing between event and non-event processes, and between event types, based on sedimentology, microfauna, and shell taphonomy.

  19. Time-stratigraphic reconstruction and integration of paleopedologic, sedimentologic, and biotic events (Willwood Formation, lower Eocene, northwest Wyoming, USA)

    SciTech Connect

    Brown, T.M. ); Kraus, M.J. )

    1993-02-01

    Relative paleosol maturities are inversely proportional to the accumulation rates of the sediment upon which they formed, and are therefore excellent relative indicators of how much geologic time elapsed between any two horizons. 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 revised 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 aspects 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. The first faunal turnover occurs at the base of the Willwood Formation. It coincides with a major increase in pedogenic maturity, reflecting a major decrease in sediment accumulation rate, and accompanying general climatic warming at about the time of the Paleocene-Eocene boundary. Throughout the remainder of Willwood time, there was a gradual, yet continual, decrease in paleosol maturity and degree of hydromorphy, probably related to the progressive structural elevation of the Owl Creek antiform bounding the south and southeast margins of the Bighorn Basin. This gradual decrease was punctuated by two intervals of more significant decline in paleosol maturity and in the incidence of hydromorphic soils. Both intervals are also marked by faunal turnovers. These sedimentologic and biologic events may reflect tectonic, periods when the rate of basin subsidence increased more rapidly. 58 refs., 7 figs., 2 tabs.

  20. Sedimentologic and stratigraphic framework of some modern crevasse splay sands

    SciTech Connect

    Bowels, K.W.; Moslow, T.F.

    1984-04-01

    A series of cores taken along strike and dip transects through the Baptiste Collette crevasse splay, modern Mississippi River delta, have been analyzed to determine the sedimentologic nature and potential reservoir quality of modern crevasse splay sands. Internal geometry, lateral and vertical continuity, and sedimentary characteristics were determined to construct a model of crevasse splay depositional systems applicable to hydrocarbon exploration. Channel sands have the greatest reservoir potential, being more laterally continuous along dip, clean (5% silt and clay), well sorted fine-grained and more homogeneous, with few permeability barriers (i.e., mud layers and laminae). Conversely, the shallower bar and levee deposits have poorer reservoir quality, being less clean, less continuous laterally along dip, and with more permeability barriers. It is felt that this study will complement the limited knowledge of modern crevasse splay systems as well as provide insights into the exploration or enhanced recovery of hydrocarbons in ancient equivalents, such as the Admire 650' Sandstone of Kansas.

  1. Upper Jurassic of east Texas, a stratigraphic sedimentologic reevaluation

    SciTech Connect

    Moore, C.H.; McGillis, K.; Stewart, S.; Wilkinson, S.; Harwood, G.

    1985-02-01

    The Smackover-Haynesville of east Texas has long been modeled as a simple progradational carbonate-evaporite ramp. Recent data indicate that the conventional ramp model for this sequence should be abandoned in favor of an evolving rimmed shelf to platform model, forming in response to changes in rate of relative sea level rise during the Late Jurassic. Evidence for Smackover-Haynesville shelves include: (1) thick high-energy carbonates along the basin margin in the Smackover and throughout the Haynesville, (2) low-energy pellet-dominated lagoonal carbonates, evaporites, and evaporitic siliciclastics occurring landward of, and interfingering with, the Smackover and Haynesville basin-margin carbonate barriers, (3) deeper water, open-marine low-energy limestones with black shales seaward of the basin-margin barriers (Smackover-Gilmer undifferentiated), and (4) the Gilmer shale forms a siliciclastic wedge seaward of the Haynesville basin margin and its zero isopach defines the Kimmeridgian shelf margin. The Smackover and Haynesville seem to represent 2 distinct sedimentologic cycles, with each cycle reflecting an initial relative sea level rise during which a rimmed shelf and lagoon are developed, and a terminal sea level standstill during which the shelf evolved into a high-energy platform. Although these sedimentologic patterns seem compatible with accepted Jurassic sea level curves, they may also reflect differential basin-margin subsidence combined with variable carbonate production rates. Finally, the shelf-platform model more clearly defines future exploration strategies for Smackover-Haynesville targets in east Texas and perhaps across the Gulf of Mexico, if eustatic sea level changes were the dominant causative factor for shelf development in the Late Jurassic.

  2. Carbon isotope stratigraphy of an ancient (Ordovician) Bahamian-type carbonate platform: Implications for preservation of global seawater trends

    NASA Astrophysics Data System (ADS)

    Saltzman, M.; Leslie, S. A.; Edwards, C. T.; Diamond, C. W.; Trigg, C. R.; Sedlacek, A. R.

    2013-12-01

    Carbon isotope stratigraphy has a unique role in the interpretation of Earth history as one of the few geochemical proxies that have been widely applied throughout the geologic time scale, from the Precambrian to the Recent, as both a global correlation tool and proxy for the carbon cycle. However, in addition to consideration of the role of diagenesis, numerous studies have raised awareness of the fact that C-isotope trends derived from ancient carbonate platforms may not be representative of dissolved inorganic carbon from a well-mixed global ocean reservoir. Furthermore, the larger carbon isotopic fractionation in the formation of aragonite versus calcite from seawater must be taken into account. All three of these variables (diagenesis, water mass residence time, % aragonite) may change in response to sea level, producing trends in C-isotopes on ancient carbonate platforms that are unrelated to the global carbon cycle. Global carbon cycle fluxes may also have a cause-effect relationship with sea level changes, further complicating interpretations of stratigraphic trends in carbon isotopes from ancient platform environments. Studies of C-isotopes in modern carbonate platform settings such as the Great Bahama Bank (GBB) provide important analogues in addressing whether or not ancient platforms are likely to preserve a record of carbon cycling in the global ocean. Swart et al. (2009) found that waters of the GBB had generally the same or elevated values (ranging from +0.5‰ to +2.5‰) compared to the global oceans, interpreted as reflecting differential photosynthetic fractionation and precipitation of calcium carbonate (which lowers pH and converts bicarbonate into 12-C enriched carbon dioxide, leaving residual bicarbonate heavier). Carbonate sediments of the GBB have elevated C-isotopes, not only because of the high C-isotope composition of the overlying waters, but also due to the greater fractionation associated with precipitation of aragonite versus calcite. Few studies of ancient carbonates have attempted to explicitly compare C-isotope trends in both restricted platform settings and open marine settings (e.g., Immenhauser et al. 2002). We studied a restricted Bahamian-type carbonate platform of Middle-Late Ordovician (Darriwilian-early Sandbian) age included in the St. Paul Group of Maryland, notable for sedimentologic evidence of severe restriction and a general lack of open marine macrofauna. We are able to correlate the C-isotope curve from the St. Paul Group to other sections globally by using a combination of conodont microfossils and measurement of Sr isotopes on conodont apatite. Coeval C-isotope trends from open marine settings in the western United States and Estonia are comparable to the restricted platform in Maryland. In our Ordovician example, local factors appear to have modified the magnitude of the global trends, but not the timing and direction. A remaining question is whether magnitude differences are a function of sedimentation rate and completeness. We continue to test hypotheses of global correlations of C-isotope trends in the Middle-Late Ordovician by utilizing the rapidly changing Sr isotope curve at that time.

  3. 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.

  4. 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.

  5. Malacological and sedimentological evidence for ``warm'' glacial climate from the Irig loess sequence, Vojvodina, Serbia

    NASA Astrophysics Data System (ADS)

    Markovi?, Slobodan B.; Oches, Eric A.; McCoy, William D.; Frechen, Manfred; Gaudenyi, Tivadar

    2007-09-01

    Four loess units and three paleosol layers are preserved in the Irig brickyard, Vojvodina, Serbia. Amino acid geochronology provides stratigraphic correlations between loess units V-L1 and V-L2 at the Irig section with loess of glacial cycles B and C, respectively, described from other central European localities. Luminescence dating results for the upper loess layers V-L1L1 and V-L1S1L1 confirm the geological interpretations, although in samples below paleosol V-L1S1S2, the age increase with depth is less than in our proposed age model. Magnetic susceptibility and sedimentological evidence from the Irig loess-paleosol sequence show general similarities with the MIS 6-1 pattern of the SPECMAP oxygen-isotope curve. Malacogical investigations at the Irig site reveal the continuous presence of the Chondrula tridens and Helicopsis striata faunal assemblages throughout the last glacial and final part of the penultimate glacial loess. The loess snail fauna, which is characterized by the complete absence of cold-resistant species, suggests a stable, dry, and relatively warm glacial climate, compared with other central European loess localities. Furthermore, these data suggest that the southern slope of Fru\\vska Gora was a refugium for warm-loving and xerophilus mollusc taxa during the otherwise unfavorable glacial climates of the Late Pleistocene.

  6. Jurassic stratigraphy of the Wiggins Arch, Mississippi

    SciTech Connect

    Rhodes, J.A.; Maxwell, G.B. )

    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.

  7. Late quaternary sequence stratigraphy, South Florida margin

    SciTech Connect

    Locker, S.D.; Hine, A.C.

    1995-12-01

    Late Quaternary sea-level change and the Florida Current have combined to produce a progradational shelf-slope margin along the western portion of the south Florida Platform facing the Straits of Florida. Analysis of high resolution seismic reflection profiles suggest at least eight 5th order late Quaternary sequences downlap onto the Pourtales Terrace at 250 m water depth. Along most of the south Florida margin, this Late Quaternary section is very thin, and only where significant accumulations occur can the stratigraphic patterns produced by sea-level change be clearly observed. Recognition of systems tracts and their boundaries from high-resolution seismic data is important for prediction of sedimentary facies and stratigraphic development of margins. Many south Florida seismic boundaries can be fit to the Exxon sequence stratigraphy model. Others appear to reflect the added effect of bottom-current erosion that complicates the signal produced by sea-level change. Overall, the sea-level signal appears to dominate the stratigraphic record, especially from the 2-dimensional perspective of dip-oriented seismic profiles. However, the 3-dimensional geometry of deposits are strongly influenced by along slope accumulation patterns controlled by the Florida Current. This study provides new insight on the importance of both geostrophic boundary currents and sea-level change in controlling stratigraphic development of a carbonate platform margin. Similar anomalously thick slope deposits in ancient sequences may indicate similar controls on accumulation and could lend to predictions of related paleo-platform configurations.

  8. Eolian event stratigraphy - A conceptual framework

    SciTech Connect

    Kocurek, G.; Havholm, K.G. )

    1991-03-01

    A basis for eolian event stratigraphy is to distill the impact of events into fundamental processes and products. For accumulation (net deposit through time) to occur, the sediment budget must be positive. If the sediment budget becomes neutral or negative, accumulation ceases and a bypass or erosional super bounding surface, respectively, forms capping the genetic unit. Within the three types of eolian systems (dry, wet, stabilized), the mechanisms of accumulation and super-surface formation differ. In the dry system, accumulation occurs because of areal deceleration of sand-carrying winds. Because of dune-interdune flow conditions, accumulation begins when interdune flats are closed, requiring sand supply, time, and conditions for dune growth at the expense of interdune flats. In the wet system, accumulation of dune and interdune deposits occurs by trapping with a rising water table. Accumulations vary with the nature of the water table rise, proportion of dunes and interdune flats, and interdune topography. In the stabilized system, accumulation occurs with rapid stabilization of elements of active eolian systems; super surfaces form when the causes of stabilization cease. The eolian rock record consists of preserved accumulations and super surfaces. Accumulation space is distinct from preservation space. Preservation space is made by subsidence and water table rise. Without preservation space, an unconformity results. The dominance of subsidence versus water table rise is reflected in dry and wet accumulations respectively, such as the Jurassic Navajo and Entrada sandstones.

  9. Cement stratigraphy of the Lisburne Group, northeastern Brooks Range, Alaska

    SciTech Connect

    Carlson, R.C.; Goldstein, R.H. . Geology Dept.)

    1992-01-01

    Cement stratigraphy serves as a descriptive framework for the interpretation of the diagenetic history of the Carboniferous Lisburne Group, northeastern Brooks Range, Alaska. The Lisburne is a sequence of shallow-water, marine carbonate rocks that have experienced a wide spectrum of diagenetic events: early marine diagenesis, early subaerial exposure, significant erosion and karstification following final Lisburne deposition, deep burial of at least 3,000 meters, compressional tectonism, and final uplift into modern mountain ranges. Compositional zones in the calcite cements were identified by using stains for ferroan calcite and cathodoluminescence microscopy. The cements are, from oldest to youngest: A1-nonferroan, nonluminescent or multibanded calcite; B1-nonferroan to low-ferroan, dull luminescent calcite; C1-ferroan, very-dull luminescent calcite; B2-nonferroan, dull luminescent calcite; A2-nonferroan calcite with 1 or 2 sets of nonluminescent and bright zones; C2-ferroan, very-dull luminescent calcite; Be-nonferroan, dull luminescent calcite. Petrographic studies of cross-cutting relationships show that A1 cements predate or are synchronous with surfaces of subaerial exposure within the Lisburne Group. The cross-cutting relationships include truncation of cements by early fractures, non-marine fissure fills, and at clast margins of autoclastic breccias. Similarly, B1 and C1 cements predate the major unconformity at the top of the Lisburne Group, hence, these cements are pre-Permian in age and may well have precipitated from fresh groundwaters introduced during development of the sub-Permian unconformity. B2 and C2 cements are present in the Permian Echooka formation overlying the Lisburne Group and, thus, can be dated as post-Pennsylvanian. B3 cements are Cretaceous or younger in age.

  10. A new Approach at Long Distance, High Resolution Magnetic Stratigraphy Applicable to Both Marine and Terrestrial Records

    NASA Astrophysics Data System (ADS)

    Stoner, J. S.

    2012-12-01

    The paleomagnetic record of geomagnetic change has a long history as a supreme stratigraphic tool for marine and terrestrial sediments. The development of paleointensity represents one of the latest and greatest advances in magnetic stratigraphy, providing suborbital correlation at a global scale. Millennial and even centennial scale correlation can be provided through past directional changes known as paleomagnetic secular variation (PSV), though such correlations have remained limited to small regions. Recent improvements in our understanding of geomagnetic change is allowing the development of a processed based PSV stratigraphy, that in contrast to a simple wiggle matching, offers high resolution correlation over a much larger spatial scale. So far tested from Europe to Alaska, this approach results in improved age accuracy, resolution, and new stratigraphic opportunities. As with all magnetic stratigraphies, the primary limitation results from the difficulty in extracting demonstrably accurate geomagnetic information from any paleomagnetic record. Additional uncertainties, even in well-constrained high quality records, reflect our often-poor understanding of the difference between the age of the magnetization relative to the age of the sediment.

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

    SciTech Connect

    Le Nindre, Y.M.; Manivit, J.; Vaslet, D. ); Manivit, H. Univ. Pierre et Marie Curie, Paris )

    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.

  12. Interpretation of seismic stratigraphy on the Amazon continental shelf

    SciTech Connect

    Alexander, C.R. Jr.; Nittrouer, C.A.; Demaster, D.J.

    1985-01-01

    The stratigraphy of the Amazon subaqueous delta has been examined using high-resolution reflection profiles. 15 piston cores from the Amazon Shelf were used to interpret the significance of the reflectors evident in the seismic profiles. Acoustic reflectors correlate with changes in grain size within cores, and generally represent coarser layers within the muddy deposits of the delta. Measurement of compressional-wave seismic velocity and saturated bulk density demonstrate that the correlation results from changes in acoustic impedance, caused by the grain-size variations. The reflectors reveal two predominant types of seismic stratigraphy: depositional and erosional. The depositional stratigraphy contains reflectors formed by relatively subtle change in grain size. Gently dipping topset and steeply dipping foreset demonstrate upward and seaward progradation of the subaqueous delta. This stratigraphy is truncated by erosional reflectors, which are significantly coarser layers. The erosional reflectors divide the depositional stratigraphy into distinct sets. The prevalence of erosional reflectors is greatest in the topset region near the river mouth, suggesting that sediment in this region, which is rapidly accumulating on 100-year time scales, has been eroded over longer time scales within the Holocene.

  13. 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.

  14. Quaternary stratigraphy of northern Chukchi Sea, Alaska

    SciTech Connect

    Phillips, R.L.; Barnes, P.W.; Colgan, M.W., Miley, J.M.

    1986-05-01

    A widespread ash deposit within Quaternary marine sediments of the northern Chukchi Sea, Alaska, provides a unique time-stratigraphic horizon that defines both regions of sediment erosion and regions of deposition on a shallow, ice-covered epeiric sea. High-resolution seismic profiles show a thin, usually less than 5 m thick, Quaternary sediment cover overlying folded bed rock, which is incised by filled fluvial channels. Vibracores, to 6 m depth, record the stratigraphy and depositional history preserved within the thin blanket deposit. The basal units cored consist of overconsolidated silt, sand, and pebbly mudstone. They represent the underlying bed rock, channel-fill deposits, or Quaternary shallow-marine sequences containing ice-rafted cobbles. The ash deposit, ranging in thickness from 2 m to over 3 m, covers the basal stratigraphic units. It lies from 1 to 4 m beneath the sea floor and forms a distinctive reflector on 3.5 khz seismic profiles. The ash extends laterally at least 100 km east-west and 200 km north-south. The well-sorted, massive to laminated ash was deposited in a marine environment based on the occurrence of diatoms, foraminifera, and sponge spicules. Overlying the ash is a thin, less than 1 m thick, pebbly mudstone or marine sand. An abrupt textural break separates the uppermost depositional sequence from the strata overlying the ash. The uppermost sequence grades vertically from a gravel-shell lag, granules, or coarse sand to bioturbated mud and represents marine sediments deposited since the Holocene transgression. Recognition of the stratigraphic sequences bounding the ash deposit will aid in correlating and interpreting the depositional events and processes on this shallow sea.

  15. 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.

  16. Upper Kamthi: A riddle in the Gondwana stratigraphy of India

    NASA Astrophysics Data System (ADS)

    Dutta, Prodip K.

    The upper Kamthi, characterized by quartz arenite and interbedded with quartz conglomerate and highly indurated purple clays tone, forms a distinct lithological association in the Pranhita-Godavari basin, India. Stratigraphically, the unit was considered the upper section of the Kamthi Group (Upper Permian), occupying a conformable position between the underlying lower section of the Kamthi and presumably the overlying Maleri (Middle to Upper Triassic). Both the latter units have similar lithological attributes; they are characterized by feldspathic sandstone and interbedded mudstone and are distinctly different from the upper Kamthi unit. Between them, the upper Kamthi stands out "like a sore thumb." On the other hand, it shows remarkable lithological and petrographical similarities to the lower part of the Kota Group (Lower Jurassic) in the Pranhita-Godavari basin and Parsora Bed (Rhaetic Lower Jurassic) of the Rewa Gondwana basin in central India. In spite of a distinctly different lithological association, the upper Kamthi rocks have been merged with the lower section of Kamthi, solely on the basis of the rare occurrence of fragmentary fossils whose chronological significance is in doubt. Such a stratigraphic interpretation has led to many structural and stratigraphic anomalies involving only the upper Kamthi rocks. Lithofacies mapping demonstrates that the upper Kamthi overlies both the lower section of Kamthi and the Maleri. This stratigrahic relationship removes all the structural and stratigraphic anomalies and makes the upper Kamthi equivalent in time and stratigraphy to the Lower Jurassic Kota. Independent evidence based on the compositional maturity of upper Kamthi arenites and paleomagnetic poles obtained from the upper Kamthi also indicate an Early Jurassic age for the unit.

  17. Seismic stratigraphy of western Colombian basin, Caribbean Sea

    SciTech Connect

    Bowland, C.

    1984-04-01

    Multichannel seismic reflection profiles disclose the regional stratigraphy of the western Colombian basin. The basement complex is the seismic unit below the deepest, continuous reflection horizon that can be traced throughout the basin. The basement complex reflection signature on the flanks of the Mono Rise and adjacent areas is smooth, continuous, and characterized by local occurrences of internal reflectors, and is equivalent to the Late Cretaceous Horizon B in the Venezuelan basin. In the central basin, the reflection signature is rough with abundant diffractions typical of normal oceanic crust. The sediment overlying the basement complex is subdivided into five mapping units. Unit CB5, which directly overlies the basement complex, is thickest on the Mono Rise and thins down the flanks of the rise. This unit is equivalent to the Upper Cretaceous to the Middle Eocene pelagic unit bounded by seismic horizons A'' and B'' in the Venezuelan basin. Unit CB4, characterized by pervasive, small offset faulting, is restricted to the crest of the Mono Rise. Units CB3 and CB2 contain subparallel, variable amplitude, continuous reflectors that fill the regional basement complex relief. They are Middle Tertiary terrigenous distal turbidites and hemipelagic deposits. Unit CB1 thickens toward southern Central America and shows complicated reflection patterns typical of a deep-sea fan complex. A jump correlation to Deep Sea Drilling Project Site 154 is used to assign a Late Miocene to Quaternary age to unit CB1. Development of unit CB1 was concurrent with the uplift of and magmatic activity in southern Central America.

  18. Hydrated mineral stratigraphy of Ius Chasma, Valles Marineris

    USGS Publications Warehouse

    Roach, L.H.; Mustard, J.F.; Swayze, G.; Milliken, R.E.; Bishop, J.L.; Murchie, S.L.; Lichtenberg, K.

    2010-01-01

    New high-resolution spectral and morphologic imaging of deposits on walls and floor of Ius Chasma extend previous geomorphic mapping, and permit a new interpretation of aqueous processes that occurred during the development of Valles Marineris. We identify hydrated mineralogy based on visible-near infrared (VNIR) absorptions. We map the extents of these units with CRISM spectral data as well as morphologies in CTX and HiRISE imagery. Three cross-sections across Ius Chasma illustrate the interpreted mineral stratigraphy. Multiple episodes formed and transported hydrated minerals within Ius Chasma. Polyhydrated sulfate and kieserite are found within a closed basin at the lowest elevations in the chasma. They may have been precipitates in a closed basin or diagenetically altered after deposition. Fluvial or aeolian processes then deposited layered Fe/Mg smectite and hydrated silicate on the chasma floor, postdating the sulfates. The smectite apparently was weathered out of Noachian-age wallrock and transported to the depositional sites. The overlying hydrated silicate is interpreted to be an acid-leached phyllosilicate transformed from the underlying smectite unit, or a smectite/jarosite mixture. The finely layered smectite and massive hydrated silicate units have an erosional unconformity between them, that marks a change in surface water chemistry. Landslides transported large blocks of wallrock, some altered to contain Fe/Mg smectite, to the chasma floor. After the last episode of normal faulting and subsequent landslides, opal was transported short distances into the chasma from a few m-thick light-toned layer near the top of the wallrock, by sapping channels in Louros Valles. Alternatively, the material was transported into the chasma and then altered to opal. The superposition of different types of hydrated minerals and the different fluvial morphologies of the units containing them indicate sequential, distinct aqueous environments, characterized by alkaline, then circum-neutral, and finally very acidic surface or groundwater chemistry. ?? 2009 Elsevier Inc. All rights reserved.

  19. 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.

  20. 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.

  1. 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.

  2. Surface soil variability and stratigraphy at the Apollo 16 site

    NASA Technical Reports Server (NTRS)

    Mitchell, J. K.; Houston, W. N.; Carrier, W. D., III; Costes, N. C.; Scott, R. F.

    1973-01-01

    The results of penetration tests, analyses of footprint and Lunar Roving Vehicle track depths, and core tube sample data have been used to deduce details of near-surface stratigraphy (to depths of several tens of cm) and lateral variability in soil conditions. Local variations (meter scale) in penetration resistance and porosity may be large, and soil stratigraphy may be complex. Since average properties are about the same at all sites, these variations probably reflect individual cratering and depositional events. These local variations cannot be anticipated on the basis of surface appearance or behavior.

  3. 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.

  4. Mapping the Stratigraphy of Booming Sand Dunes

    NASA Astrophysics Data System (ADS)

    Vriend, N. M.; Hunt, M. L.; Clayton, R. W.

    2008-12-01

    Booming dunes emit a loud rumbling sound after a man-made or natural sand avalanche is generated on the slip face of a large desert dune. The sound consist of one dominant frequency (70 - 105 Hz) with several higher harmonics. A recent publication (Vriend et al., 2007) presented a model of an internal, natural waveguide that propagates the booming emission, amplifies the sound, and sets the booming frequency. The mapping of the subsurface layering, which is necessary for the existence of a waveguide, prompted additional work on the dune structure and stratigraphy. The current work highlights geophysical measurements at Eureka Dunes in Death Valley National Park, CA and Dumont Dunes in the Mojave Desert, CA. Seismic refraction studies indicate strong layering with large velocity jumps across the interfaces. Ground Penetrating Radar (GPR) profiles, at frequencies of 100 MHz and 200 MHz, map out the stratigraphic structure of the dunes. Variations in the near surface layering are able to predict the seasonal variability in booming frequency both quantitatively and qualitatively. The Kirchhoff migrated GPR profiles are superimposed on the local topography obtained with a laser rangefinder. The complex dune structure is resolved to a depth of over 30 meters for the 100 MHz antenna. The GPR profiles of the longitudinal Eureka dune display complex internal structures from old dune crests. Both slopes have slip faces at 30 degrees with parallel layering (< 2m) at the near surface. At the transverse Dumont dune the GPR profile exhibits strong parallel layering on the booming leeward slipface only. The shallower windward face features a remarkable tilted repetitive layering that cuts through the surface. At Dumont Dunes the layering on the leeward face explains the change in booming frequency between 70 - 95 Hertz in the period 2005 - 2008. The tilted layering structure of the shallow windward face prevents the formation of a waveguide and is never able to sustain the booming sound. The Dumont dune progresses slowly, estimated at ~ 1 m/year from correlating satellite images, by forming new slip faces on the leeward face over time. Large precipitation events may cause a new layer to form. Sand sampling provides a quantitative measure on the chemical composition and water content of the layering.

  5. 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.

  6. Cone-penetrometer exploration of sinkholes: Stratigraphy and soil properties

    SciTech Connect

    Bloomberg, D.; Upchurch, S.B.; Hayden, M.L. ); Williams, R.C. )

    1988-10-01

    Four sinkholes with varying surficial expressions were subjected to detailed stratigraphic and soil analysis by means of Standard Penetration Tests (SPT) and Electric Friction Cone Penetration Tests (CPT) in order to evaluate applications of CPT to sinkhole investigations. Although widely used, SPT data are of limited value and difficult to apply to sinkhole mapping. CPT is sensitive to minor lithologic variability and is superior to SPT as a cost-effective technique for determining geotechnical properties of sinkholes. The effectiveness of CPT data results from the force measurements made along the sleeve of the cone. The friction ratio (ratio of sleeve to tip resistance) is a good indicator of soil stratigraphy and properties. By smoothing the friction-ratio data, general stratigraphy and changes in soil properties are easily identified. Stratigraphy of the sinks has been complicated by intense weathering, karstification and marine transgressions. The resulting deposits include five stratigraphic units. 1 and 2 represent Plio-Pleistocene marine sediments with Unit 2 being the zone of soil clay accumulation. 3 and 4 are horizons residual from Miocene strata and indicate an episode of karstification prior to deposition of Units 1 and 2. CPT provides sufficient information for recognition of sinkhole stratigraphy and geotechnical properties. When coupled with laboratory soil analysis, CPT provides unique information about sinkhole geometry and dynamics. In contrast, SPT indicates general, inconclusive trends.

  7. 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)

  8. 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.

  9. Aragats stratovolcano in Armenia - volcano-stratigraphy and petrology

    NASA Astrophysics Data System (ADS)

    Meliksetian, Khachatur; Savov, Ivan; Connor, Charles; Halama, Ralf; Jrbashyan, Ruben; Navasardyan, Gevorg; Ghukasyan, Yura; Gevorgyan, Hripsime; Manucharyan, Davit; Ishizuka, Osamu; Quidelleur, Xavier; Germa, Aurélie

    2014-05-01

    In this contribution we discuss the geological structure and volcano-stratigraphy of the Quaternary Aragats stratovolcano in Armenia based on recent age determinations as well as petrological and geochemical features of magma generation processes specific for collision zones. Armenia is situated in the NE part of the Anatolian-Armenian-Iranian plateau, an intensely deformed segment of the Alpine-Himalayan belt. The complex geological structure of the region is represented by a mosaic of tectonic blocks comprising fragments of volcanic arcs, continental crust and exhumed oceanic crust. Collision of the Arabian plate with the Eurasian margin in early Miocene resulted in orogenic uplift associated with intense volcanism. Aragats (4090m) is one the largest volcanoes in the entire region and produced central vent (inc. Plinian VEI>4) and monogenetic type flank eruptions and periphery plateaus within a total area greater than 5000 km2, known as Aragats volcanic province (AVP). The Aragats volcanic province (AVP) comprises the composite cone of Aragats volcano, the peak of which is built on a summit plateau, ~45 km in diameter shield structure with dozens of flank vents, scattered monogenetic cinder cones on the adjacent volcanic plateaus as well as the neighboring stratovolcano Arailer. New K-Ar and 40Ar/39Ar age determinations of groundmass and separated plagioclase samples indicate that volcanism at AVP began ~2.5 Ma, while most recent volcanic activity is 0.49 Ma for Plinian eruption of dacites from Irind flank vent and basaltic trachyandesite lava flows from Tirinkatar (0.48-0.61 Ma), Kakavasar, (0.52-0.54 Ma) and Ashtarak (0.58 Ma) monogenetic flank centers, as well as trachyandesites of Jrbazhan volcano on the summit plateau of Aragats (0.52 Ma). Based on bulk rock geochemical data (major, minor and low abundance trace elements, Sr and Nd isotopes) and mineral chemistry, we conclude that volcanic rocks of AVP are largely recording a complex mixing between deep asthenospheric mantle and remnants of subduction-modified and metasomatically enriched mantle sources, followed by fractionation in large magma chamber(s). Mineral-melt equilibria studies reveal dry (<1%H2O) and very hot source, fluid inclusions study reveal pronounced enrichment with CO2 over H2O in fluid phase. Noteworthy are high eruption temperatures compared to global volcanic arcs, explaining the very long (up to 25 km) and thick (>200m) trachydacitic lava flows.

  10. New Isotopic and Sedimentological Measurements of the Thabaseek Deposits (South Africa) and the Dating of the Taung Hominid

    NASA Astrophysics Data System (ADS)

    Tobias, Phillip V.; Vogel, John C.; Oschadleus, H. Dieter; Partridge, Timothy C.; McKee, Jeffrey K.

    1993-11-01

    Earlier attempts to date the Taung hominid type specimen of Australopithecus africanus Dart yielded conflicting results. Recent faunal studies pointed to an age of 2.3 myr. Radioisotopic results suggested 1.0 myr. New uranium studies reveal that the Thabaseek (the oldest Taung tufa) was not a closed system and that younger uranium entered the tufa after initial deposition, producing an apparent isotopic age younger than the age of deposition. The Thabaseek isotopic dates provide only a terminus ad quem and this technique is therefore not applicable to the older Taung tufas. Delson's dating (2.3 myr) of cercopithecoids from Hrdlicka's pinnacle ca. 50 m from the hominid site provides the best available approximation to the age of the hominid. In our new Taung excavation, stratigraphic analysis indicates that the hominid may somewhat predate most identified fauna. Sedimentologically the hominid matrix proves to be of fluvial deposition, and hence closely resembles one Hrdlicka deposit, both samples differing appreciably from all other Taung samples which bespeak eolian deposition. Thus, the conditions under which the hominid-bearing stratum was deposited were virtually identical to those pertaining to one of the Hrdlicka deposits. The newest results show that Taung was not the youngest South African australopithecine site and eliminate the discrepancy between the relative ages of the Taung A. africanus africanus and the Sterkfontein A. africanus transvaalensis.

  11. 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).

  12. Sedimentation studies relevant to low level radioactive effluent dispersal in the Irish Sea. Part 2. Sea bed morphology, sediments and shallow sub-bottom stratigraphy of the eastern Irish Sea

    SciTech Connect

    Williams, S.J.; Kirby, R.; Smith, T.J.; Parker, W.R.

    1981-01-01

    A detailed survey of the Eastern Irish Sea between the Isle of Man and the Cumbrian coast was carried out during 1979-80 using sidescan sonar, pinger and echo sounder seismic equipment supplemented by box cores, gravity cores and grab samples. The objective of the study was to provide a firm sedimentological basis for any further work concerning the horizontal and vertical distributions of radionuclides discharged from the Windscale nuclear fuel reprocessing plant within the sea bed sediments. The sidescan data were used to map the distribution of surface sediments and infer net sand transport paths, whilst the continous seismic profile records were used to study the sub-bottom stratigraphy and geological structures. The sediment samples were analyzed for faunal content and evidence of animal-sediment interaction.

  13. Cone-penetrometer exploration of Sinkholes: Stratigraphy and soil properties

    NASA Astrophysics Data System (ADS)

    Bloomberg, D.; Upchurch, S. B.; Hayden, M. L.; Williams, R. C.

    1988-10-01

    Four sinkholes with varying surficial expressions were subjected to detailed stratigraphic and soil analysis by means of Standard Penetration Tests (SPT) and Electric Friction Cone Penetration Tests (CPT) in order to evaluate applications of CPT to sinkhole investigations. Although widely used, SPT data are of limited value and difficult to apply to sinkhole mapping. CPT is sensitive to minor lithologic variability and is superior to SPT as a cost-effective technique for determining geotechnical properties of sinkholes. The effectiveness of CPT data results from the force measurements made along the sleeve of the cone. The friction ratio (ratio of sleeve to tip resistance) is a good indicator of soil stratigraphy and properties. By smoothing the friction-ratio data, general stratigraphy and changes in soil properties are easily identified. Stratigraphy of the sinks has been complicated by intense weathering, karstification and marine, transgressions. The resulting deposits include five stratigraphic units. I and II represent Plio-Pleistocene marine sediments with Unit II being the zone of soil clay accumulation. III and IV are horizons residual from Miocene strata and indicate an episode of karstification prior to deposition of Units I and II. Conduit fill is a mixture of materials with low cohesion. The fill materials indicate centripetal and downward movement of insoluble sediments derived from the surrounding strata. Loss of cohesion results in near-zero friction ratios. Very low friction ratios, coupled with materials with little cohesion, indicate potentially-liquefiable soils in the immediate vicinity of zones where piping failure may be imminent. SPT does not provide sufficient data to predict these zones of potential, failure. CPT provides sufficient information for recognition of sinkhole stratigraphy and geotechnical properties. When coupled with laboratory soil analysis, CPT provides unique information about sinkhole geometry and dynamics. In contrast, SPT data fail to produce consistent indicators of sinkhole stratigraphy or properties. With laboratory soil data, SPT indicates general, inconclusive trends.

  14. 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. . 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.

  15. Autocyclic progradation and allocyclic ravinement of a shoreface: Sedimentology and sequence stratigraphy of the Panther Sandstone Tongue (Upper Cretaceous, Campanian), Wasatch plateau, Utah, U. S. A

    SciTech Connect

    Krause, F.F.; Aitken, S.A.; Braunberger, W.F.; Chung, P.; Macrae, A.; Meyer, R.O.; Nunez-Betelu, L.; Williams, C.A.; Hol, H.M. )

    1993-04-01

    The Panther Sandstone Tongue of the Star Point Formation exposed in the vicinity of Helper, Utah reflects a coarse-grained, clastic wedge that penetrated the Mancos Shale basin in Early Campanian (Late Cretaceous) time. Panther Sandstone rocks may be grouped into six lithofacies: (1) thin-bedded, bioturbated and rippled, mudstone and very fine-grained sandstone; (2) thin- to medium-bedded, bioturbated, rippled and parallel laminated, mudstone and very fine-grained sandstone; (3) thick- to very thick-bedded HCS and parallel-laminated, mudstone and fine- to medium-grained sandstone; (4) medium- to thick-bedded, Ophiomorpha bioturbated, medium- to coarse-grained sandstone; (5) medium- to very-thick bedded, current bedded and hydroplasticly deformed sandstone, and (6) medium- to thick-bedded, trough cross-stratified and bundle-laminated, fine grained sandstone. Lithofacies are arranged in definable vertical and lateral successions. L. 1, 2 and 3 are upward coarsening and shoaling and are common in the Helper area. L. 5 and 6 are common to the west. L. 4 is a transgressive and ravinement lag that rests on all other lithofacies. Interpreted environments reflect a storm modified, microtidal, strandplain system. Rocks, except L. 4, are contained in a parasequence system that built into the basin during relative sea-level fall. This system prograded episodically suggesting varying sediment supply and event-controlled sediment reworking -- responses associated with autocyclic forcing. In contrast, ravinement decapitated the parasequence intersecting progressively shallower lithofacies. These responses suggest that ravinement was driven by allocyclic forcing, perhaps in response to tectonism in the foreland.

  16. Sedimentology and sequence stratigraphy of the Shanxi Formation (Lower Permian) in the northwestern Ordos Basin, China: an alternative sequence model for fluvial strata

    NASA Astrophysics Data System (ADS)

    Zhang, Zhouliang; Sun, Keqin; Yin, Jarun

    1997-08-01

    The Lower Permian Shanxi Formation in the northwestern Ordos Basin was deposited in fluvial environments under warm and humid climatic conditions. Braided, anastomosing and meandering fluvial facies associations can be recognized in the lower, middle and upper parts of the Shanxi Formation, respectively. They form a complete type-1 fluvial sequence. Based on this sequence as well as on the analysis of base level changes and their effect on fluvial deposition, an alternative sequence model for fluvial strata is proposed. The lowstand systems tract in the model comprises braided river deposits, the transgressive systems tract consists mainly of fine-grained anastomosing river deposits, and meandering river deposits dominate in the highstand systems tract. Braided sandstones in the lowstand systems tract seem to be widely distributed and have high lateral continuity. Anastomosing channel sand-bodies in the transgressive systems tract appear to be isolated and display relative low lateral continuity.

  17. Stratigraphie et sédimentologie des « calcaires à Productus » du Carbonifère inférieur de la Montagne noire (Massif central, France)Stratigraphy and sedimentology of the Lower Carboniferous 'Calcaires à Productus' of the Montagne Noire (Massif Central, France)

    NASA Astrophysics Data System (ADS)

    Poty, Édouard; Aretz, Markus; Barchy, Laurent

    The 'Calcaires à Productus' of the Montagne Noire are microbial build-ups. Two formations are defined and dated respectively as Uppermost Visean (Upper Warnantian-Brigantian) and Serpukhovian on the basis on corals. That makes these limestones out to be younger than previously stated (Lower and base of Upper Warnantian-Asbian and base of Brigantian) and indicates that the development of the olistoliths and thrusts including them, due to the Variscan orogeny, was at least as young as the Upper Serpukhovian. The Serpukhovian limestones of the Montagne Noire are correlated with the Lanet Limestone (Mouthoumet Massif, Corbières) and Ardengost Limestone (central Pyrenees). To cite this article: É. Poty et al., C. R. Geoscience 334 (2002) 843-848.

  18. Mechanical stratigraphy of deep-water sandstones: insights from a multisciplinary field and laboratory study

    NASA Astrophysics Data System (ADS)

    Agosta, Fabrizio; di Celma, Claudio; Tondi, Emanuele; Corradetti, Amerigo; Cantalamessa, Gino

    2010-05-01

    Turbidite sandstones found in deep-water fold-and-thrust belts are increasingly exploited as hydrocarbon reservoirs. Within these rocks, the fluid flow is profoundly affected by the complex interaction between primary sedimentological and stratigraphic attributes (i.e, facies, layering, reservoir quality, stacking patterns, bed connectivity and lateral extent) and fracture characteristics (i.e., length, spacing, distribution, orientation, connectivity). Unfortunately, most of these features are at, or below, the resolution of conventional seismic datasets and, for this reason, their identification and localization represent one of the fundamental challenges facing exploration, appraisal and production of the sandstone reservoirs. In this respect, whereas considerable effort has been afforded to a characterization of the sedimentological and stratigraphic aspects of sandstones, detailed analysis of fractures in this type of successions has received significantly less attention. In this work, we combine field and laboratory analyses to assess the possible mechanical control exerted by the rock properties (grain size, intergranualr porosity, and Young modulus), as well as the influence of bed thickness, on joint density in turbidite sandstones. Joints are mode-I fractures occurring parallel to the greatest principle stress axis, which solve opening displacement and do not show evidence of shearing and enhance the values of total porosity forming preferential hydraulic conduits for fluid flow. Within layered rocks, commonly, joints form perpendicular to bedding due to overburden or exhumation. The empirical relation between joint spacing and bed thickness, documented in the field by many authors, has been mechanically related to the stress perturbation taking place around joints during their formation. Furthermore, close correlations between joint density and rock properties have been already established. In this present contribution, we focus on the bed-perpendicular joint spacing/bed thickness (S/T) relationships on sandstone bodies that experienced similar diagenetic and tectonic histories. The field area is located in the Periadriatic foreland basin, eastern central Italy, which show late Pliocene slope turbidites in excellent 3d views. The Periadriatic foreland basin is an elongated, roughly N-S oriented trough located immediately east of the Apennines fold-thrust belt. The basin fill mostly consists of deepwater Plio-Pleistocene sediments partially incorporated into the frontal part of the orogenic wedge. During the late Pliocene, gravel and sand originated from the uplifting Apennines were abundantly supplied to the deep-water basin through a series of erosional conduits that, in the rock record, appear as a series of N-S oriented slope submarine canyon systems deeply incised into the hemipelagic mudstones of the adjacent slope. The studied exposure allows direct observation of spatial and temporal relationships among the various depositional elements comprising the canyon system and related lithofacies, as well as the bed-perpendicular joint density within each lithofacies. We performed a multidisciplinary work involving the following tasks: (i) 3D stratigraphic model of the depositional architecture of the Castignano and Ascensione canyon systems (Marche region, Italy); (ii) 2D scanline survey of several outcrops displaying bed-perpendicular joints; (iii) digital image analysis of selected thin-section obtained from oriented hand samples to characterize the 3D intergranualr porosity; (iv) Stiffness analysis of representative sandstone bodies by mean of Schmidt hammer tests. The first results of this ongoing study on the mechanical stratigraphy of the two Late Pliocene canyon systems are consistent with the joint density being effected by both geometrical (i.e., bed thickness) and mechanical properties. This data set will help field and experimental geologists to better define common strategies to assess the controlling factors on joint distribution within layered media. Furthermore, this knowledge can be very import

  19. 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.

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

    SciTech Connect

    Dubiel, R.F.; Potter, C.J.; Snee, L.W. ); Good, S.C. )

    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.

  1. Combining rock physics and sedimentology for seismic reservoir characterization of North Sea turbidite systems

    NASA Astrophysics Data System (ADS)

    Avseth, Per Age

    The petroleum industry is increasing its focus on the exploration of reservoirs in turbidite systems. However, these sedimentary environments are often characterized by very complex sand distributions. Hence, reservoir description based on conventional seismic and well-log interpretation may be very uncertain. There is a need to employ more quantitative seismic techniques to reveal reservoirs units in these complex systems from seismic amplitude data. In this study we focus on North Sea turbidite systems. Our goal is to improve the ability to use 3D seismic data to map reservoirs in these systems. A cross-disciplinary methodology for seismic reservoir characterization is presented that combines rock physics, sedimentology, and statistical techniques. We apply this methodology to two turbidite systems of Paleocene age located in the South Viking Graben of the North Sea. First, we investigate the relationship between sedimentary petrography and rock physics properties. Next, we define seismic scale sedimentary units, referred to as seismic lithofacies. These facies represent populations of data that have characteristic geologic and seismic properties. We establish a statistically representative training database by identifying seismic lithofacies from thin-sections, cores, and well-log data. This procedure is guided by diagnostic rock physics modeling. Based on the training data, we perform multivariate classification of data from several wells in the area. Next, we assess uncertainties in amplitude versus offset (AVO) response related to the inherent natural variability of each seismic lithofacies. We generate bivariate probability density functions (pdfs) of two AVO parameters for different facies combinations. By combining the bivariate pdfs estimated from well-logs with the AVO parameters estimated from seismic data, we use both quadratic discriminant analysis and Bayesian classification to predict lithofacies and pore fluids from seismic amplitudes. The final results are spatial maps of the most likely facies, and their occurrence probabilities. These maps can be used as input data for well log planning and risk analysis in hydrocarbon exploration and reservoir development.

  2. 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.

  3. 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.

  4. Integrated stratigraphy of the Cenomanian-Turonian boundary interval: improving understanding of Oceanic Anoxic Events

    NASA Astrophysics Data System (ADS)

    Jarvis, Ian

    2014-05-01

    The Cenomanian-Turonian boundary (CTB) interval ~ 94 Ma represented a period of major global palaeoenvironmental change. Increasingly detailed multidisciplinary studies integrating sedimentological, palaeontological and geochemical data from multiple basins, are enabling the development of refined but complex models that aid understanding of the mechanisms driving changes in ocean productivity and climate. This paper reviews some of the exciting new developments in this field. Facies change characterizes the CTB interval in most areas. In the Chalk seas of northern Europe, a widespead hiatus was followed by the deposition of clay-rich organic-lean beds of the Plenus Marl and its equivalents, and then nodular chalks. In the North Sea basin and its onshore extension in eastern England and northern Germany, black shales of the Black Band (Blodøks Formation, Hasseltal Formation) occur. Similarly, in northern Tethys, a brief interval of black shale accumulation within a predominantly carbonate succession, is exemplified by the Niveau Thomel in the Vocontian Basin (SE France), and the Livello Bonarelli in Italy. Widespread deposition of organic-rich marine sediments during CTB times led to 12C depletion in surface carbon reservoirs (oceans, atmosphere, biosphere), and a large positive global ?13C excursion preserved in marine carbonates and both marine and terrestrial organic matter (Oceanic Anoxic Event 2). Significant biotic turnover characterises the boundary interval, and inter-regional correlation may be achieved at high resolution using integrated biostratigraphy employing macrofossils (ammonites, inoceramid bivalves), microfossils (planktonic foraminifera, dinoflagellate cysts) and calcareous nannofossils. Correlations can be tested against those based on comparison of ?13C profiles - carbon isotope chemostratigraphy, supplemented by oxygen isotope and elemental data. Interpretation of paired carbonate - organic matter ?13C data from multiple CTB sections implicates rising atmospheric pCO2 linked to volcanic outgassing as a major forcing mechanism for palaeoclimate warming and palaeoceanographic change accompanying OAE2. New marine 187Os/188Os isotope stratigraphy further reveals the interaction of volcanism and ocean circulation during OAE2, and provides a further chemostratigraphic tool. Li isotope (? 7Li) data may be interpreted as evidence that increased silicate weathering promoted by rising pCO2 acted as both a forcing and negative feedback mechanism driving OAE2 history. Neodymium and sulphur isotopes offer further insights into interactions between global biogeochemical cycles and ocean circulation changes.

  5. Orbitally Tuned Stratigraphies From 2.5 to 8 Ma at Sites 1237 and 1241

    NASA Astrophysics Data System (ADS)

    Tiedemann, R.; Sturm, A.; Steph, S.; Stoner, J. S.; Lund, S. P.; Flores, J.; Holbourn, A. E.; Abrantes, F. F.

    2004-12-01

    The astronomical tuning technique is at present the most accurate absolute dating method for sediment records spanning the time interval of the last 35 Ma for which astronomers provide a valid and precise orbital solution for variations in Earth's orbital parameters (eccentricity, obliquity, precession). The orbitally tuned geological time scale already became the standard chronology for the last 5 Ma. The late Miocene magnetic Polarity Times Scale (PTS) was tuned by two groups. Hilgen et al. (1995, 2003) used land-based sediment sections and Shackleton et al. (1995) used marine sediment records from Leg 138 to calibrate the PTS. Both time scales, however, differ by about 180 kyr. More recently, Shackleton and Crowhurst (1997) and Shackleton et al. (1999) established a Miocene astronomical time scale at sediment records from Leg 154 (Ceara Rise). The lack of magnetostratigraphic information, however, complicates comparisons with the tuned magnetic polarity timescales. Our goal is to expand and to astronomically calibrate the 'Magnetic Polarity Time Scale', the oxygen isotope stratigraphy and biostratigraphy to 12 Ma at east Pacific Sites 1237 and 1241. So far, we developed an oxygen isotope stratigraphy from 2.5 to 6 Ma at Site 1241 that was based on tuning cyclic fluctuations in benthic d13C values and sand percentages of the carbonate fraction to orbital obliquity and precession, respectively. The isotope stratigraphy is nearly identical with that from Leg 154 (Sites 925/926). Site 1237 was orbitally tuned from 2 to 6.5 Ma. The tuning was mainly based on the GRAPE-density record although other proxy records were considered (magnetic susceptibility, color, carbonate sand fraction, isotopes). The astronomically calibrated ages for geomagnetic reversal boundaries are almost identical with those from the Cande and Kent timescale for the time interval from 2 to 5.2 Ma. Although geomagnetic reversal boundaries are not well defined between 5.2 and 6.5 Ma, our tuning suggests considerable differences to earlier APTS. Orbital tuning at Site 1237 suggests ages for late Miocene magnetic reversal boundaries to be about 150 kyr older than those from the Cande and Kent time scale and to be about 80 kyr older than those from Hilgen et al. (1995).

  6. Stratigraphy and Tectonics of Southeastern Serenitatis. Ph.D. Thesis

    NASA Technical Reports Server (NTRS)

    Maxwell, T. A.

    1976-01-01

    Results of investigations of returned Apollo 17 samples, and Apollo 15 and 17 photographs have provided a broad data base on which to interpret the southeastern Serenitatis region of the moon. Although many of the pre-Apollo 17 mission interpretations remain valid, detailed mapping of this region and correlation with earth-based and orbital remote-sensing data have resulted in a revision of the local mare stratigraphy.

  7. 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.

  8. 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.

  9. Sedimentological analyses of Martian gullies: the subsurface as the key to the surface

    NASA Astrophysics Data System (ADS)

    de Haas, T.; Ventra, D.; Hauber, E.; Conway, S. J.; Kleinhans, M. G.

    2015-10-01

    Here, we aim to constrain the formative processes of Martian gullies based on outcrop sedimentology (as deposits are generally reworked at their surface but not internally). Secondly, we aim to resolve the apparent discrepancy between genetic interpretations from gully-fan surface and morphometry.

  10. OSL dating of Glacial Sediments from New Zealand and Olympic Mountains: Using Stratigraphy to our Advantage

    NASA Astrophysics Data System (ADS)

    Rittenour, T. M.; Thackray, G. D.; Shulmeister, J.

    2012-12-01

    Optically stimulated luminescence (OSL) dating provides an age estimate for the last time sediment was exposed to light. In glacial environments solar resetting of the luminescence signal prior to deposition is not assured and can lead to significant age overestimates. Sediments derived from glacial settings also commonly have other deleterious properties such as weak quartz luminescence signals, feldspar contamination and high levels of electron thermal transfer. Despite these potential problems, OSL commonly provides the only means to date glacial deposits due to limited material for radiocarbon and/or surface exposure dating, discrepancies between the age of a landform and the targeted underlying sediment, or deposit age beyond the range for radiocarbon. As part of a larger project to reconstruct MIS 3/4 glacial chronologies, OSL samples were collected from the Rangitata and Clutha River basins along the eastern Southern Alps, New Zealand and from the Hoh and Queets River basins, western Olympic Mountains, Washington USA. Samples for quartz OSL dating were collected from carefully selected shallow-water and well-sorted facies of glaciofluvial and glaciolacustrine sediments to select sediments most likely to have been exposed to light prior to deposition. OSL dating is preferred over other dating methods in the study areas because evidence for multiple pre-LGM glaciations is commonly preserved as buried and over-run packages of diamicton, outwash and lacustrine sediment, excluding application of surface-exposure techniques. Further, where the sediments are in fact associated with surficial landforms, detailed description of the underlying stratigraphy permits interpretation of the glacial processes at work and thus provides a more thorough understanding of the relevance of the ages to the advance. Results indicate that while some samples contain evidence for partial bleaching, most show symmetric equivalent dose distributions, and ages are in stratigraphic order and are consistent with other age constraints. OSL results from both field areas indicate significant glacial advances during MIS 3/4 and MIS 2. Importantly, although OSL dating has been reported to be problematic in New Zealand due to poor luminescence characteristics related to source bedrock and sediment immaturity, our results indicate that sediment from eastern drainages of the southern Alps (Rangitata and Clutha River basins) contain quartz with good luminescence characteristics. Despite potential problems, recent advances in instrumentation and methodology have made OSL a viable method for dating many glacial sequences and we recommend that OSL dating be applied to more settings with buried glacial stratigraphy, although care is needed in appropriate sample selection.

  11. 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.

  12. The Late Pleistocene Duoi U'Oi cave in northern Vietnam: palaeontology, sedimentology, taphonomy and palaeoenvironments

    NASA Astrophysics Data System (ADS)

    Bacon, Anne-Marie; Demeter, F.; Duringer, P.; Helm, C.; Bano, M.; Vu, The Long; Kim Thuy, Nguyen Thi; Antoine, P.-O.; Thi Mai, Bui; Huong, Nguyen Thi Mai; Dodo, Y.; Chabaux, F.; Rihs, S.

    2008-08-01

    This paper describes new fossil materials recovered at the Duoi U'Oi site, in December 2003, by a Vietnamese-French-Japanese team. The Duoi U'Oi cave is located in Man Duc village, 25 km of Hoà Binh city in northern Vietnam. It belongs to a karstic network developed in a dark grey micritic marine limestone dated from the Lower to the Middle Triassic. The sedimentary fill produced a rich mammalian fauna, essentially composed of isolated teeth of middle- to large-sized mammals (Artiodactyla, Perissodactyla, Proboscidea, Carnivora, Rodentia, Primates), and characteristic of Late Pleistocene. The results of the Duoi U'Oi fieldwork are of great interest for the following reasons: (1) the biochronological age of the fauna is consistent with 230Th/ 234U/ 238U dating from the calcitic floors (66±3 ka). The Duoi U'Oi fauna is thus the oldest well-dated modern fauna known for the Southeast Asian mainland; (2) in terms of sedimentology, the analysis of the formation of the fossiliferous breccia and that of the processes of deposits shows a close relation between the karstic deposits inside the cave and the deposits in the alluvial terraces. The observation of three levels of alluvial terraces associated with three caves situated at 62, 10 and 3 m above the present alluvial plain suggests that exokarstic and endokarstic sediments evolved together; (3) in terms of palaeobiogeography, Duoi U'Oi is the continental fauna showing the strongest resemblance with the Late Pleistocene faunas from Indonesian islands (Punung, Gunung Dawung, Lida Ajer, Sibrambang and Djambu caves); this implies that, at the time of Duoi U'Oi, ca 70 ka, the Sundaland was mainly characterised by faunas of modern aspect; (4) the analysis of major taphonomic factors that led to the mammal assemblage reveals a combination of selective agents (selective role of predators and porcupines, selective destruction of age classes for some species, selective preservation of fossils due to the deposition processes in the karstic network), which contribute to the poor representation of the diversity of the fauna; no arguments show that humans, present at Duoi U'Oi, might have a possible role in the taphonomic process; (5) the palaeoenvironmental reconstruction based on the composition of the faunal assemblage suggests a forested area and some open habitats, under warm and humid conditions.

  13. Archaeological sedimentology of overbank silt deposits on the floodplain of the Ohio river near Louisville, Kentucky

    USGS Publications Warehouse

    Gray, H.H.

    1984-01-01

    The surface of the floodplain of the Ohio River about 20km southwest of Louisville, Kentucky, is a series of linear ridges and swales that are subparallel to the channel of the river, which here is relatively straight and flows southward. Numerous prehistoric occupational sites are located on these ridges. The sediments that underlie the ridges, which were examined in four archaeological excavations as deep as 8 m, are predominantly sandy silt and silty fine to very fine sand and appear to be mainly the product of overbank deposition from suspended load. Abundant cultural material and occupational sites dating as early as 10,000 years BP are found in the sediments at depths as great as 6??5 m. The fine sediments of the floodplain are underlain by sand and gravel. The context of the cultural materials and the stratigraphy and morphology of the deposits indicate that the ridged deposits began as linear riverside sand and gravel bars. These were succeeded upward by fine-grained overbank deposits in which the ridged morphology was maintained because the overbank silt and fine sand were deposited as prograding elongate bars at high water. As the floodplain ridge built upward, the sedimentation rate decreased and the sand content of the sediments diminished, and as the river channel occasionally shifted, the ridged deposits were built in successive subparallel sequences. Two archaeological consequences are implicit in this depositional model of orderly growth of the floodplain. First, available archaeological data from floodplain segments along other parts of the river should confirm the model; and second, the model should make it possible to search the floodplains of the Ohio River for stratified sites of any desired age. ?? 1984.

  14. 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.

  15. 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.

  16. Identifying climate change signals in the late Quaternary gravel-bed, braided river stratigraphy of the Canterbury Plains, New Zealand

    NASA Astrophysics Data System (ADS)

    Jones, M. A.; Rowan, A. V.; Covey-Crump, S. J.; Brocklehurst, S. H.; Roberts, H. M.; Duller, G. A.

    2010-12-01

    The gravel-bed, braided river stratigraphy of the Canterbury Plains, central South Island, New Zealand, was deposited over several Quaternary glacial-interglacial cycles and so potentially offers an important insight into fluvial responses to climate change. The uppermost 20 m of the section which is exposed along the east coast has yielded a radiocarbon age at the base of the coastal cliffs of ~33 ka cal BP and is capped by a Holocene loess sheet, implying that it includes New Zealand’s Last Glacial Maximum (22-18 ka). This part of the section contains several laterally-continuous surfaces representing periods of low aggradation or non-deposition, and it is tempting to link these hiatuses to one or more periods of glacial advance, still-stand or retreat. However, this requires a reliable chronology with which to tie the stratigraphy to the excellent high-resolution climate history established for the region. Optically stimulated luminescence (OSL) dating of quartz grains from sand bodies within the gravel stratigraphy provides the potential to develop this chronology. However, there is a perception that quartz from this area is a difficult candidate for luminescence dating for reasons connected with the short sediment transport distances and limited number of erosion-transport cycles which together reduce opportunities for sensitization of the luminescence signal and give low signal intensities. Recent advances in OSL dating techniques provide the opportunity to revisit this issue. In this study, nine samples from the Canterbury coastal stratigraphy were dated using OSL. The samples were collected from large sand channel fills and bar margins, five of them in vertical succession at one locality. A Single Aliquot Regenerative (SAR) dose protocol was used to generate equivalent dose (De) values from coarse-grained quartz. Standard screening criteria were applied to the SAR data prior to statistical analysis of the De distributions. The relative intensity and behaviour of the fast and medium components in the OSL signal used for dating was evaluated using signal deconvolution. The ages generated are in chronostratigraphic order and have uncertainties of about 2-3 ka (12%). We will discuss the methods used to verify the robustness of these ages and their implications for the late Quaternary depositional history of the Canterbury Plains.

  17. Stratigraphy and palaeoenvironmental evolution of the mid- to upper Palaeozoic succession in Northwest Peninsular Malaysia

    NASA Astrophysics Data System (ADS)

    Amir Hassan, Meor H.; Aung, Aye-Ko; Becker, R. T.; Abdul Rahman, Noor Atirah; Ng, Tham Fatt; Ghani, Azman A.; Shuib, Mustaffa Kamal

    2014-04-01

    The stratigraphy of the Devonian to Permian succession in Northwest Peninsular Malaysia is revised. The Timah Tasoh Formation consists of black mudstone containing graptolites and tentaculitids indicating a Pragian or earliest Emsian age. The Sanai Limestone overlies the Timah Tasoh Formation at Sanai Hill B and contains conodonts indicating a Late Devonian (Frasnian to possibly early Famennian) age. In other places, Late Tournaisian chert of the Telaga Jatoh Formation overlies the Timah Tasoh Formation. The overlying Kubang Pasu Formation is predominantly composed of mudstone and sandstone, and can be divided into 3 subunits, from oldest to youngest: (1) Chepor Member; (2) Undifferentiated Kubang Pasu Formation; (3) Uppermost Kubang Pasu Formation. The ammonoid Praedaraelites tuntungensis sp. nov. is reported and described from the Chepor Member of Bukit Tuntung, Pauh. The genus indicates a Late Viséan age for part of the subunit. Dropstones and diamictites from the Chepor Member indicate a glacial marine depositional environment. The Carbo-Permian, undifferentiated Kubang Pasu Formation consists of similar interbedded mudstone and sandstone. The uppermost Kubang Pasu Formation of Kungurian age consists of coarsening upward cycles of clastics, representing a shallow marine, wave- and storm-influenced shoreline. The Permian Chuping Limestone also represents shallow marine, wave- and storm-influenced deposits. A Mid-Palaeozoic Unconformity separating Early-Late Devonian rocks from overlying Late Devonian-Carboniferous deposits probably marks initiation of rifting on Sibumasu, which eventually led to the separation of Sibumasu from Australian Gondwana during the late Sakmarian (Early Permian).

  18. 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.

  19. Geochronology and subsurface stratigraphy of Pukapuka and Rakahanga atolls, Cook Islands: Late Quaternary reef growth and sea level history

    USGS Publications Warehouse

    Gray, S.C.; Hein, J.R.; Hausmann, R.; Radtke, U.

    1992-01-01

    Eustatic sea-level cycles superposed on thermal subsidence of an atoll produce layers of high sea-level reefs separated by erosional unconformities. Coral samples from these reefs from cores drilled to 50 m beneath the lagoons of Pukapuka and Rakahanga atolls, northern Cook Islands give electron spin resonance (ESR) and U-series ages ranging from the Holocene to 600,000 yr B.P. Subgroups of these ages and the stratigraphic position of their bounding unconformities define at least 5 periods of reef growth and high sea-level (0-9000 yr B.P., 125,000-180,000 yr B.P., 180,000-230,000 yr B.P., 300,000-460,000 yr B.P., 460,000-650,000 yr B.P.). Only two ages fall within error of the last interglacial high sea-level stand (???125,000-135,000 yr B.P.). This paucity of ages may result from extensive erosion of the last intergracial reef. In addition, post-depositional isotope exchange may have altered the time ages of three coral samples to apparent ages that fall within glacial stage 6. For the record to be preserved, vertical accretion during rising sea-level must compensate for surface lowering from erosion during sea-level lowstands and subsidence of the atoll; erosion rates (6-63 cm/1000 yr) can therefore be calculated from reef accretion rates (100-400 cm/1000 yr), subsidence rates (2-6 cm/1000 yr), and the duration of island submergence (8-15% of the last 600,000 yr). The stratigraphy of coral ages indicates island subsidence rates of 4.5 ?? 2.8 cm/1000 yr for both islands. A model of reef growth and erosion based on the stratigraphy of the Cook Islands atolls suggests average subsidence and erosion rates of between 3-6 and 15-20 cm/1000 yr, respectively. ?? 1992.

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

    NASA Astrophysics Data System (ADS)

    Yazıcı, 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 Şermat Quartzite of presumably Permo-Triassic age (Çağlayan 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 Şermat 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 Şermat 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 Şermat Basin. Nevertheless, all available relicts indicate the transportation of sediments from a source area in the south. If the Şermat 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 Şermat 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, İstanbul Zone, Sedimentary Basin, Turkey References Çağlayan, 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 Kırklareli-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 - Kıyıköy 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., Satır, 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.

  1. Stratigraphy of Maastrichtian sediments, southeastern N. C

    SciTech Connect

    Laws, R.A.; Dockal, J.A.; Harris, W.B. . Dept. of Earth Sciences)

    1994-03-01

    The Martin-Marietta limestone quarry at Castle Hayne and a series of core-holes in northern New Hanover County expose a moderate to dark gray silty, dolomitic very fine to fine grained quartz sand that is paraconformable with the underlying Rocky Point member of the Peedee Formation and disconformable with the overlying Eocene Castle Hayne Limestone. The unit which has a maximum thickness of about 2 m is absent to the north and west, thickens to the south and east and is exposed on the east bank of the Northeast Cape Fear River at Hilton Park, Wilmington, NC. All traces of original bedding have been removed by extensive bioturbation. Thin sections indicate that the unit ranges from a very fine to fine argillaceous-dolomitic quartz sand to a sandy dolomitic clay. A moderately well-preserved, low diversity calcareous nannofossil assemblage including Arkhangelskiella cymbiformis, Ceratolithodes acculeus, Eiffellithus eximius, Microrhabdulus attenuatus, M. decoratus, Micula staurophora, Prediscosphaera cretacea, Quadrum trifdum, and Wartznauria biporta, indicates correlation to the Quadrum trifdum Zone (CC22b to CC23b) of latest Campanian to earliest Maastrichtian age. This correlation suggests that the unit is a lithofacies of the Rocky Point Member. Stable isotopic analyses of the dolomite indicates that [delta][sup 18]O varies between +2.16[per thousand] to +3.73[per thousand] and [delta][sup 13]C between [minus]0.43[per thousand] to +0.62[per thousand], and suggests two mechanisms to explain the origin of the dolomite: (1) dolomitization of calcite/aragonite bioclasts under marine aqueous conditions or (2) inorganic dolomite precipitation under anoxic marine aqueous conditions with light carbon enrichment.

  2. 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.

  3. The story of landscape evolution in Lower Austria told by sedimentological analysis and luminescence dating

    NASA Astrophysics Data System (ADS)

    Hofer, Ingo; Thiel, Christine; Terhorst, Birgit; Jaburova, Iva; Buylaert, Jan-Pieter; Murray, Andrew; Frechen, Manfred

    2010-05-01

    Loess/palaeosol sequences contain detailed information about palaeoenvironmental changes during the Quaternary. Furthermore, because of its long distance aeolian transport, which resets the luminescence signal to zero prior to deposition, loess is highly suitable for luminescence dating. This allows the determination of geodynamic processes with time. The loess deposits in the Kremser Feld (Lower Austria) are up to 30 m thick. The loess/paleosol sequence of Stratzing is situated at the eastern margin of the west-east elongated hill of the ‘Galgenberg'; this location is famous for its archaeological finds, e.g. the sculpture "Fanny", one of the oldest identifiable representations of the human figure (Neugebauer-Maresch, 1993). The loess profile examined here has a total depth of 7.5 m and is subdivided into 19 prominent horizons. For each horizon the grain size distribution, pH-value, total carbonate content, total organic content and sulphur content was derived in order to reconstruct the environmental conditions leading to sedimentation and soil formation. To set up a geochronological framework for the loess deposition and the subsequent soil formation, nine samples were dated by means of elevated temperature post-IR IRSL (Thiel et al., submitted). Besides a general discussion about the sedimentological data we will discuss horizon 18 in more detail; this is a paleosol rich in clay and poor in mineralic carbonate. The sulphur content is relatively high and indicates higher humidity and warmer climate, all making the unexpectedly low organic carbon content of particular interest. The luminescence ages reveal an important hiatus above this well-developed palaeosol (from ~ 100 to ~ at least 200 ka) clearly showing that this loess/palaeosol sequence is not a continuous record. This implies either significant erosion or lack of loess deposition in this area. Neugebauer-Maresch, C., 1993. Kunst und geistige Welt. - In: Neugebauer-Maresch, C., (ed): Altsteinzeit im Osten Österreichs. Wissenschaftliche Schriftenreihe Niederösterreich 95/96/97 (St. Pölten). Thiel, C., Buylaert, J. P., Terhorst, B., Murray, A. S., Hofer, I., Tsukamoto, S., Frechen, M., submitted. Luminescence dating of the Stratzing loess profile (Austria) - Testing the potential of an elevated temperature post-IR IRSL protocol. Quaternary International.

  4. Sedimentological processes and environmental variability at Lake Ohrid (Macedonia, Albania) between 640 ka and present day

    NASA Astrophysics Data System (ADS)

    Francke, A.; Wagner, B.; Just, J.; Leicher, N.; Gromig, R.; Baumgarten, H.; Vogel, H.; Lacey, J. H.; Sadori, L.; Wonik, T.; Leng, M. J.; Zanchetta, G.; Sulpizio, R.; Giaccio, B.

    2015-09-01

    Lake Ohrid (FYROM, Albania) is thought to be more than 1.2 million years old and hosts more than 200 endemic species. As a target of the International Continental Scientific Drilling Program (ICDP), a successful deep drilling campaign was carried out within the scope of the Scientific Collaboration on Past Speciation Conditions in Lake Ohrid (SCOPSCO) project in 2013. Here, we present lithological, sedimentological, and (bio-)geochemical data from the upper 247.8 m of the overall 569 m long DEEP site sediment succession from the central part of the lake. According to an age model, which is based on nine tephra layers (1st order tie points), and on tuning of biogeochemical proxy data to orbital parameters (2nd order tie points) and to the global benthic isotope stack LR04 (3rd order tie points), respectively, the analyzed sediment sequence covers the last 640 ka. The DEEP site sediment succession consists of hemipelagic sediments, which are interspersed by several tephra layers and infrequent, thin (< 5 cm) mass wasting deposits. The hemipelagic sediments can be classified into three different lithotypes. Lithotype 1 and 2 deposits comprise calcareous and slightly calcareous silty clay and are predominantly attributed to interglacial periods with high primary productivity in the lake during summer and reduced mixing during winter. The data suggest that high ion and nutrient concentrations in the lake water promoted calcite precipitation and diatom growth in the epilmnion in during MIS15, 13, and 5. Following a strong primary productivity, highest interglacial temperatures can be reported for MIS11 and 5, whereas MIS15, 13, 9, and 7 were comparable cooler. Lithotype 3 deposits consist of clastic, silty clayey material and predominantly represent glacial periods with low primary productivity during summer and longer and intensified mixing during winter. The data imply that most severe glacial conditions at Lake Ohrid persisted during MIS16, 12, 10, and 6 whereas somewhat warmer temperatures can be inferred for MIS14, 8, 4, and 3. Interglacial-like conditions occurred during parts of MIS14, and 8.

  5. 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

  6. 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.

  7. Sedimentological imprint on subseafloor microbial communities in Western Mediterranean Sea Quaternary sediments

    NASA Astrophysics Data System (ADS)

    Ciobanu, M.-C.; Rabineau, M.; Droz, L.; Révillon, S.; Ghiglione, J.-F.; Dennielou, B.; Jorry, S.-J.; Kallmeyer, J.; Etoubleau, J.; Pignet, P.; Crassous, P.; Vandenabeele-Trambouze, O.; Laugier, J.; Guégan, M.; Godfroy, A.; Alain, K.

    2012-09-01

    An interdisciplinary study was conducted to evaluate the relationship between geological and paleoenvironmental parameters and the bacterial and archaeal community structure of two contrasting subseafloor sites in the Western Mediterranean Sea (Ligurian Sea and Gulf of Lion). Both depositional environments in this area are well-documented from paleoclimatic and paleooceanographic point of views. Available data sets allowed us to calibrate the investigated cores with reference and dated cores previously collected in the same area, and notably correlated to Quaternary climate variations. DNA-based fingerprints showed that the archaeal diversity was composed by one group, Miscellaneous Crenarchaeotic Group (MCG), within the Gulf of Lion sediments and of nine different lineages (dominated by MCG, South African Gold Mine Euryarchaeotal Group (SAGMEG) and Halobacteria) within the Ligurian Sea sediments. Bacterial molecular diversity at both sites revealed mostly the presence of the classes Alphaproteobacteria, Betaproteobacteria and Gammaproteobacteria within Proteobacteria phylum, and also members of Bacteroidetes phylum. The second most abundant lineages were Actinobacteria and Firmicutes at the Gulf of Lion site and Chloroflexi at the Ligurian Sea site. Various substrates and cultivation conditions allowed us to isolate 75 strains belonging to four lineages: Alpha-, Gammaproteobacteria, Firmicutes and Actinobacteria. In molecular surveys, the Betaproteobacteria group was consistently detected in the Ligurian Sea sediments, characterized by a heterolithic facies with numerous turbidites from a deep-sea levee. Analysis of relative betaproteobacterial abundances and turbidite frequency suggested that the microbial diversity was a result of main climatic changes occurring during the last 20 ka. Statistical direct multivariate canonical correspondence analyses (CCA) showed that the availability of electron acceptors and the quality of electron donors (indicated by age) strongly influenced the community structure. In contrast, within the Gulf of Lion core, characterized by a homogeneous lithological structure of upper-slope environment, most detected groups were Bacteroidetes and, to a lesser extent, Betaproteobacteria. At both site, the detection of Betaproteobacteria coincided with increased terrestrial inputs, as confirmed by the geochemical measurements (Si, Sr, Ti and Ca). In the Gulf of Lion, geochemical parameters were also found to drive microbial community composition. Taken together, our data suggest that the palaeoenvironmental history of erosion and deposition recorded in the Western Mediterranean Sea sediments has left its imprint on the sedimentological context for microbial habitability, and then indirectly on structure and composition of the microbial communities during the late Quaternary.

  8. Sedimentological processes and environmental variability at Lake Ohrid (Macedonia, Albania) between 637 ka and the present

    NASA Astrophysics Data System (ADS)

    Francke, Alexander; Wagner, Bernd; Just, Janna; Leicher, Niklas; Gromig, Raphael; Baumgarten, Henrike; Vogel, Hendrik; Lacey, Jack H.; Sadori, Laura; Wonik, Thomas; Leng, Melanie J.; Zanchetta, Giovanni; Sulpizio, Roberto; Giaccio, Biagio

    2016-02-01

    Lake Ohrid (Macedonia, Albania) is thought to be more than 1.2 million years old and host more than 300 endemic species. As a target of the International Continental scientific Drilling Program (ICDP), a successful deep drilling campaign was carried out within the scope of the Scientific Collaboration on Past Speciation Conditions in Lake Ohrid (SCOPSCO) project in 2013. Here, we present lithological, sedimentological, and (bio-)geochemical data from the upper 247.8 m composite depth of the overall 569 m long DEEP site sediment succession from the central part of the lake. According to an age model, which is based on 11 tephra layers (first-order tie points) and on tuning of bio-geochemical proxy data to orbital parameters (second-order tie points), the analyzed sediment sequence covers the last 637 kyr. The DEEP site sediment succession consists of hemipelagic sediments, which are interspersed by several tephra layers and infrequent, thin (< 5 cm) mass wasting deposits. The hemipelagic sediments can be classified into three different lithotypes. Lithotype 1 and 2 deposits comprise calcareous and slightly calcareous silty clay and are predominantly attributed to interglacial periods with high primary productivity in the lake during summer and reduced mixing during winter. The data suggest that high ion and nutrient concentrations in the lake water promoted calcite precipitation and diatom growth in the epilimnion during MIS15, 13, and 5. Following a strong primary productivity, highest interglacial temperatures can be reported for marine isotope stages (MIS) 11 and 5, whereas MIS15, 13, 9, and 7 were comparably cooler. Lithotype 3 deposits consist of clastic, silty clayey material and predominantly represent glacial periods with low primary productivity during summer and longer and intensified mixing during winter. The data imply that the most severe glacial conditions at Lake Ohrid persisted during MIS16, 12, 10, and 6, whereas somewhat warmer temperatures can be inferred for MIS14, 8, 4, and 2. Interglacial-like conditions occurred during parts of MIS14 and 8.

  9. Elastic-Wavefield Seismic Stratigraphy: A New Seismic Imaging Technology

    SciTech Connect

    Bob A. Hardage; Milo M. Backus; Michael V. DeAngelo; Sergey Fomel; Khaled Fouad; Robert J. Graebner; Paul E. Murray; Randy Remington; Diana Sava

    2006-07-31

    The purpose of our research has been to develop and demonstrate a seismic technology that will provide the oil and gas industry a better methodology for understanding reservoir and seal architectures and for improving interpretations of hydrocarbon systems. Our research goal was to expand the valuable science of seismic stratigraphy beyond the constraints of compressional (P-P) seismic data by using all modes (P-P, P-SV, SH-SH, SV-SV, SV-P) of a seismic elastic wavefield to define depositional sequences and facies. Our objective was to demonstrate that one or more modes of an elastic wavefield may image stratal surfaces across some stratigraphic intervals that are not seen by companion wave modes and thus provide different, but equally valid, information regarding depositional sequences and sedimentary facies within that interval. We use the term elastic wavefield stratigraphy to describe the methodology we use to integrate seismic sequences and seismic facies from all modes of an elastic wavefield into a seismic interpretation. We interpreted both onshore and marine multicomponent seismic surveys to select the data examples that we use to document the principles of elastic wavefield stratigraphy. We have also used examples from published papers that illustrate some concepts better than did the multicomponent seismic data that were available for our analysis. In each interpretation study, we used rock physics modeling to explain how and why certain geological conditions caused differences in P and S reflectivities that resulted in P-wave seismic sequences and facies being different from depth-equivalent S-wave sequences and facies across the targets we studied.

  10. Base line sequence stratigraphy, Arkoma Basin to Chautauqua Arch

    SciTech Connect

    Bennison, A.P.

    1993-02-01

    Use of sequence stratigraphy concepts requires some caution, especially if these are based almost solely on theoretical models enhanced by a computer data base or by seismic records where lithologic interpretations are assumed rather than observed. Optimum input for sequence models is obtained from actual stratigraphic data from outcrops, cuttings and cores across sedimentary strike, such as those from the Arkoma Basin northward to the Chautauqua Arch along the Oklahoma-Kansas border area. Sequence stratigraphy involving Pennsylvanian data indicates a major northward shift of the Arkoma Basin paleobathymetric axis from the southern Ouachita Mountains to southern Kansas with some occasional backward and forward motion. This long base line is also needed to ascertain the total number of parasequences (transgressive-regressive cycles), their geometric succession, and interrelationship of low-stand, shelf-margin, transgressive high-stand, and condensed system tracks. The first two system tracts are important for productive reservoirs, whereas the latter three usually serve as prime source beds. Usually not all parasequences are present at any one place along an established base line or transect. The low-stand or shelf-margin parasequences are usually absent on the craton or on interbasinal or intrabasinal arches such as the Chautauqua Arch, whereas the transgressive and high-stand parasequences commonly thin basinward into condensed sequences or disappear through downlapping. Actual Pennsylvania outcrop data commonly differ from the standard sequence stratigraphy model of Exxon and Peter Vai. Sequence boundaries based on unconformities may occur at any place within a parasequence and may change places along the baseline.

  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 Stratigraphy and Evolution of the Lunar Crust

    NASA Technical Reports Server (NTRS)

    McCallum, I. Stewart

    1998-01-01

    Reconstruction of stratigraphic relationships in the ancient lunar crust has proved to be a formidable task. The intense bombardment during the first 700 m.y. of lunar history has severely perturbed the original stratigraphy and destroyed the primary textures of all but a few nonmare rocks. However, a knowledge of the crustal stratigraphy as it existed prior to the cataclysmic bombardment about 3.9 Ga is essential to test the major models proposed for crustal origin, i.e., crystal fractionation in a global magmasphere or serial magmatism in a large number of smaller bodies. Despite the large difference in scale implicit in these two models, both require an efficient separation of plagioclase and mafic minerals to form the anorthositic crust and the mafic mantle. Despite the havoc wreaked by the large body impactors, these same impact processes have brought to the lunar surface crystalline samples derived from at least the upper half of the lunar crust, thereby providing an opportunity to reconstruct the stratigraphy in areas sampled by the Apollo missions. As noted, ejecta from the large multiring basins are dominantly, or even exclusively, of crustal origin. Given the most recent determinations of crustal thicknesses, this implies an upper limit to the depth of excavation of about 60 km. Of all the lunar samples studied, a small set has been recognized as "pristine", and within this pristine group, a small fraction have retained some vestiges of primary features formed during the earliest stages of crystallization or recrystallization prior to 4.0 Ga. We have examined a number of these samples that have retained some record of primary crystallization to deduce thermal histories from an analysis of structural, textural, and compositional features in minerals from these samples. Specifically, by quantitative modeling of (1) the growth rate and development of compositional profiles of exsolution lamellae in pyroxenes and (2) the rate of Fe-Mg ordering in orthopyroxenes, we can constrain the cooling rates of appropriate lunar samples. These cooling rates are used to compute depths of burial at the time of crystallization, which enable us to reconstruct parts of the crustal stratigraphy as it existed during the earliest stages of lunar history.

  13. Elastic-Wavefield Seismic Stratigraphy: A New Seismic Imaging Technology

    SciTech Connect

    Bob A. Hardage

    2005-07-31

    We have developed a numerical technique that will adjust 3-D S-wave seismic images so that they are depth equivalent to 3-D P-wave seismic images. The ability to make this type of P-SV to P-P depth registration is critical to our elastic wavefield seismic stratigraphy research because we now have higher confidence that depth-equivalent data windows are being used in the P-SV to P-P comparisons that we are making.

  14. 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.

  15. 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

  16. Cenozoic stratigraphy of the Sahara, Northern Africa

    USGS Publications Warehouse

    Swezey, Christopher S.

    2009-01-01

    This paper presents an overview of the Cenozoic stratigraphic record in the Sahara, and shows that the strata display some remarkably similar characteristics across much of the region. In fact, some lithologies of certain ages are exceptionally widespread and persistent, and many of the changes from one lithology to another appear to have been relatively synchronous across the Sahara. The general stratigraphic succession is that of a transition from early Cenozoic carbonate strata to late Cenozoic siliciclastic strata. This transition in lithology coincides with a long-term eustatic fall in sea level since the middle Cretaceous and with a global climate transition from a Late Cretaceous–Early Eocene “warm mode” to a Late Eocene–Quaternary “cool mode”. Much of the shorter-term stratigraphic variability in the Sahara (and even the regional unconformities) also can be correlated with specific changes in sea level, climate, and tectonic activity during the Cenozoic. Specifically, Paleocene and Eocene carbonate strata and phosphate are suggestive of a warm and humid climate, whereas latest Eocene evaporitic strata (and an end-Eocene regional unconformity) are correlated with a eustatic fall in sea level, the build-up of ice in Antarctica, and the appearance of relatively arid climates in the Sahara. The absence of Oligocene strata throughout much of the Sahara is attributed to the effects of generally low eustatic sea level during the Oligocene and tectonic uplift in certain areas during the Late Eocene and Oligocene. Miocene sandstone and conglomerate are attributed to the effects of continued tectonic uplift around the Sahara, generally low eustatic sea level, and enough rainfall to support the development of extensive fluvial systems. Middle–Upper Miocene carbonate strata accumulated in northern Libya in response to a eustatic rise in sea level, whereas Upper Miocene mudstone accumulated along the south side of the Atlas Mountains because uplift of the mountains blocked fluvial access to the Mediterranean Sea. Uppermost Miocene evaporites (and an end-Miocene regional unconformity) in the northern Sahara are correlated with the Messinian desiccation of the Mediterranean Sea. Abundant and widespread Pliocene paleosols are attributed to the onset of relatively arid climate conditions and (or) greater variability of climate conditions, and the appearance of persistent and widespread eolian sediments in the Sahara is coincident with the major glaciation in the northern hemisphere during the Pliocene.

  17. Application of carbon isotope stratigraphy to late miocene shallow marine sediments, new zealand.

    PubMed

    Loutit, T S; Kennett, J P

    1979-06-15

    A distinct (0.5 per mil) carbon-13/carbon-12 isotopic shift in the light direction has been identified in a shallow marine sedimentary sequence of Late Miocene age at Blind River, New Zealand, and correlated with a similar shift in Late Miocene Deep Sea Drilling Project sequences throughout the Indo-Pacific. A dated piston core provides an age for the shift of 6.2 +/- 0.1 million years. Correlations based on the carbon isotopic change require a revision of the previously established magnetostratigraphy at Blind River. The carbon shift at Blind River occurs between 6.2 and 6.3 +/- 0.1 million years before present. A new chronology provides an age for the evolutionary first appearance datum of Globorotalia conomiozea at 6.1 +/- 0.1 million years, the beginning of a distinct latest Miocene cooling event associated with the Kapitean stage at 6.2 +/- 0.1 million years, and the beginning of a distinct shallowing of water depths at 6.1 +/- 0.1 million years. The Miocene-Pliocene boundary as recognized in New Zealand is now dated at 5.3 +/- 0.1 million years. Extension of carbon isotope stratigraphy to other shallow Late Miocene sequences should provide an important datum for international correlation of Late Miocene shallow and deep marine sequences. PMID:17772422

  18. 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.

  19. A consistent magnetic polarity stratigraphy of Plio-Pleistocene fluvial sediments from the Heidelberg Basin (Germany)

    NASA Astrophysics Data System (ADS)

    Scheidt, Stephanie; Hambach, Ulrich; Rolf, Christian

    2014-05-01

    Deep drillings in the Heidelberg Basins provide access to one of the thickest and most complete successions of Quaternary and Upper Pliocene continental sediments in Central-Europe [1]. In absence of any comprehensive chronostratigraphic model, these sediments are so far classified by lithological and hydrogeological criteria. Therefore the age of this sequence is still controversially discussed ([1], [2]). In spite of the fact that fluvial sediments are a fundamental challenge for the application of magnetic polarity stratigraphy we performed a thorough study on four drilling cores (from Heidelberg, Ludwigshafen and nearby Viernheim). Here, we present the results from the analyses of these cores, which yield to a consistent chronostratigraphic framework. The components of natural remanent magnetisation (NRM) were separated by alternating field and thermal demagnetisation techniques and the characteristic remanent magnetisations (ChRM) were isolated by principle component analysis [3]. Due to the coring technique solely inclination data of the ChRM is used for the determination of the magnetic polarity stratigraphy. Rock magnetic proxies were applied to identify the carriers of the remanent magnetisation. The investigations prove the NRM as a stable, largely primary magnetisation acquired shortly after deposition (PDRM). The Matuyama-Gauss boundary is clearly defined by a polarity change in each core, as suggested in previous work [4]. These findings are in good agreement with the biostratigraphic definition of the base of the Quaternary ([5], [6], [7]). The Brunhes-Matuyama boundary could be identified in core Heidelberg UniNord 1 and 2 only. Consequently, the position of the Jaramillo and Olduvai subchron can be inferred from the lithostratigraphy and the development of fluvial facies architecture in the Rhine system. The continuation of the magnetic polarity stratigraphy into the Gilbert chron (Upper Pliocene) allows alternative correlation schemes for the cores Viernheim and Heidelberg. All things considered, the application of magnetic polarity stratigraphy on Pliocene and Pleistocene fluvial sediments from the Heidelberg Basin provides a consistent and independent chronology and opens the perspective for global correlations where other approaches hardly come to results. [1] GABRIEL, G., ELLWANGER, D., HOSELMANN, C. & WEIDENFELLER, M. 2008. Preface: The HeidelbergBasin Drilling Project. E & G (Quaternary Science Journal), 57, 253-260. [2] ELLWANGER, D. & WIELAND-SCHUSTER, U. 2012. Fotodokumentation und Schichtenverzeichnis der Forschungsbohrungen Heidelberg UniNord I und II. LGRB-Informationen, 26, 25-86. [3] KIRSCHVINK, J. L. 1980. The least-squares line and plane and the analysis of palaeomagnetic data. Geophysical Journal, Royal Astronomical Society, 62, 699-718. [4] ROLF, C., HAMBACH, U. & WEIDENFELLER, M. 2008. Rock and palaeomagnetic evidence for the Plio-/Pleistocene palaeoclimatic change recorded in Upper Rhine Graben sediments (Core Ludwigshafen-Parkinsel), Neth. J. Geosci., 87 (1), 41-50. [5] KNIPPING, M. 2008. Early and Middle Pleistocene pollen assemblages of deep core drillings in the northern Upper Rhine Graben, Germany, Neth. J. Geosci., 87(1), 51-65. [6] HEUMANN, G., pers. Comm. [7] HAHNE, J., pers. Comm.

  20. Reverse engineering mother nature — Shale sedimentology from an experimental perspective

    NASA Astrophysics Data System (ADS)

    Schieber, Juergen

    2011-06-01

    Experimental study of the sedimentology of shales can take a variety of forms. At its simplest one can experiment with suspensions in a glass jar and try to understand their settling behavior, or one can manipulate mud in a tank or bucket to gain insights into its rheology. This approach was championed over a century ago by Sorby, and the insights gained can be quite profound. More recently, tank and settling tube experiments of animal-sediment interactions, compaction behavior, and sediment unmixing via re-suspension have proven to be highly informative in spite of their simplicity. Flumes can be used to obtain quantitative information about depositional and erosional parameters and to generate fundamental bedforms. In flume experiments, however, it is of critical importance that the flume be designed in a way that flocculated materials move under shear stress conditions that would be reasonable in natural environments. Although much flume work on muds has been conducted by hydraulic engineers, the transfer of that knowledge to sedimentology is hampered by the fact that engineers and sedimentologists are interested in different (though not mutually exclusive) products from such experiments. Engineers and hydrologists are commonly concerned with quantifying fluid flow properties, whereas sedimentogists are particularly interested in the sedimentary products that result from a variety of flow conditions. Recent sedimentologically oriented flume studies have shown that muds can form deposits at flow velocities and shear stresses that would suffice to transport and deposit medium grained sand. Mud suspensions are prone to flocculation and the resulting floccules travel in bedload and form ripples that accrete into beds. The latter finding suggests that many laminated shales were deposited from currents rather than by settling from slow moving or still water. There are many other sedimentary features in shales that can potentially be reproduced in flume studies and in the future serve to provide a quantitative basis for shale sedimentology.

  1. Application of Sedimentologic-Geophysical Analysis for Coastal Zone Management in Albania.

    NASA Astrophysics Data System (ADS)

    Kavaja, V. S.; Durmishi, C.; Alikaj, P.; Jata, I.

    2004-12-01

    The areas under investigation encompassing a large expense of land of south- western part of Albanian coast zone. The paper examines the Quaternary history of dual (sedimentologic models and the evaluation impact of the geological environment in expansion of ancient civilization in this region). The work presented here is result of continued study about four last years and goes on in our days. The neotectonic structure of Butrint region is consisted off horst- graben structure, E-W trending. The Quaternary formations fill the lowest part of the region and have different origins and consisted of alluvial and lagoon deposits, about 80-m thickness. The lagoonal deposits are common around Butrint lake wile ancient town (Hellenistic- Roman- Byzantine) was extended mainly on the soft Holocene sediments. The soundings data, particularly resistivity variation are the base of sedimentologic and lithological studies due to the lack of boreholes. Two cycles of sedimentation can be observed within the thickness of 40- 50m: the first, gravel and sands and second mainly of clays in upper part of the cross section. In addition to, V.E.S. data and resistivity maps point out the features of sedimentologic environment distinguishing Pleistocene and Holocene deposits, delineated of water-bearing coarse-grained sands and gravels and land-sea interaction separating salty waters areas. Based on the sedimentologic and structural factors studied and geophysical maps and cross-sections, plenty of geomorphic problems are obvious now. This studies show the evidence to the advancement of the coastline is still occurring and the shoreline is still on the move.

  2. Eustatic curve for the middle Jurassic-Cretaceous based on Russian platform and Siberian stratigraphy: Zonal resolution

    SciTech Connect

    Sahagian, D.; Pinous, O.; Olferiev, A.; Zakharov, V.

    1996-09-01

    We have used the stratigraphy of the central part of the Russian platform and surrounding regions to construct a calibrated eustatic curve for the Bajocian through the Santonian. The study area is centrally located in the large Eurasian continental craton, and was covered by shallow seas during much of the Jurassic and Cretaceous. The geographic setting was a very low-gradient ramp that was repeatedly flooded and exposed. Analysis of stratal geometry of the region suggests tectonic stability throughout most of Mesozoic marine deposition. The paleogeography of the region led to extremely low rates of sediment influx. As a result, accommodation potential was limited and is interpreted to have been determined primarily by eustatic variations. The central part of the Russian platform thus provides a useful frame of reference for the quantification of eustatic variations throughout the Jurassic and Cretaceous. The biostratigraphy of the Russian platform provides the basis for reliably determining age and eustatic events. The Mesozoic section of the central part of the Russian platform is characterized by numerous hiatuses. In this study, we filled the sediment gaps left by unconformities in the central part of the Russian platform with data from stratigraphic information from the more continuous stratigraphy of the neighboring subsiding regions, such as northern Siberia. Although these sections reflect subsidence, the time scale of variations in subsidence rate is probably long relative to the duration of the stratigraphic gaps to be filled, so the subsidence rate can be calculated and filtered from the stratigraphic data. We thus have compiled a more complete eustatic curve than would be possible on the basis of Russian platform stratigraphy alone.

  3. 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

  4. Constraining 3D Process Sedimentological Models to Geophysical Data Using Image Quilting

    NASA Astrophysics Data System (ADS)

    Tahmasebi, P.; Da Pra, A.; Pontiggia, M.; Caers, J.

    2014-12-01

    3D process geological models, whether for carbonate or sedimentological systems, have been proposed for modeling realistic subsurface heterogeneity. The problem with such forward process models is that they are not constrained to any subsurface data whether to wells or geophysical surveys. We propose a new method for realistic geological modeling of complex heterogeneity by hybridizing 3D process modeling of geological deposition with conditioning by means of a novel multiple-point geostatistics (MPS) technique termed image quilting (IQ). Image quilting is a pattern-based techniques that stiches together patterns extracted from training images to generate stochastic realizations that look like the training image. In this paper, we illustrate how 3D process model realizations can be used as training images in image quilting. To constrain the realization to seismic data we first interpret each facies in the geophysical data. These interpretation, while overly smooth and not reflecting finer scale variation are used as auxiliary variables in the generation of the image quilting realizations. To condition to well data, we first perform a kriging of the well data to generate a kriging map and kriging variance. The kriging map is used as additional auxiliary variable while the kriging variance is used as a weight given to the kriging derived auxiliary variable. We present an application to a giant offshore reservoir. Starting from seismic advanced attribute analysis and sedimentological interpretation, we build the 3D sedimentological process based model and use it as non-stationary training image for conditional image quilting.

  5. Sedimentological and Geostatistical Characterization of the Paleozoic Wajid Sandstone Aquifer, Saudi Arabia

    NASA Astrophysics Data System (ADS)

    Abdullatif, Osman; Makkawi, Mohamed

    2010-05-01

    Paleozoic siliciclastic successions form important primary groundwater aquifers in different parts of Saudi Arabia. Determination of aquifer sedimentological heterogeneity is important for realistic aquifer evaluation, development and management. This study aims to establish, from outcrop aquifer analog description, a geological and petrophysical model for the Paleozoic Wajid Sandstone aquifer in southwest Saudi Arabia. This study examined and studied several outcrop analogs for Wajid Sandstone. The methods of study included field and laboratory sedimentological investigations including facies, petrographic, porosity, permeability and statistical and geostatistical analysis techniques. The sedimentological field study revealed that the Wajid Sandstone vary facies, grain size, texture, composition and deposition environments. All these aspects appear to have impacted the porosity and permeability patterns at outcrop scale. The sedimentary facies vary in type, abundances and their vertical and lateral stacking patterns. Depositional environments also vary from fluvial braided stream to shallow marine environments. Grain size of sandstone varies from very fine to very coarse and from moderately sorted to well sorted. Sandstone composition varies from quartz arenite to subarkose. Both depositional and post depositional controls appear to have affected aquifer heterogeneity and porosity and permeability distribution. In general 2D geostatistical porosity and permeability models show agreement at outcrop scale, especially at high values; however, some variability is encountered among Wajid members. The 2D permeability models also reflect depositional factors including depositional environment and sub environment change layering, stratigraphic hierarchy, vertical and lateral facies changes and the superimposition of post depositional changes expresses in matrix and cement content, and cement type and styles.

  6. Sedimentologic and diagenetic controls on reservoir development at Rosevear gas field, Swan Hills Formation (upper Devonian), central Alberta

    SciTech Connect

    Kaufman, J.; Hanson, G.N.; Meyers, W.J.

    1988-02-01

    Carbonate strata at the Rosevear gas field consist of three major sedimentological packages: (1) basal platform, (2) platform reef, and (3) capping platform. Gas production is localized within two narrow trends of porous, massive, replacive dolostone occurring in the platform-reef sequence; tight limestones updip form the reservoir seal. Porosity trends are primarily restricted to the margins of a marine channel developed through the platform reef, but not the basal platform. Channel-margin strata consist mostly of dolomitized branching-stromatoporoid floatstones and rudstones. Massive replacive dolostone is composed of inclusion-rich coarsely crystalline nonferroan euhedral to anhedral rhombs that show a red cathodoluminescence. This dolomite has selectively replaced the limemud matrix; fossils were replaced to a much lesser extent. Fossils not dolomitized were selectively leached, resulting in well-developed biomoldic and vuggy porosity that forms the reservoir. Dolomitization occurred after cementation by clear, equant calcite and after early pressure solution. Secondary porosity in the dolostone trends was only partially reduced during later diagenesis, which consisted of, in order of decreasing age, precipitation of saddle dolomite, anhydrite, and coarsely crystalline calcite. Hydrocarbon migration occurred after the saddle dolomites, but before some late-stage calcite cement.

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

    SciTech Connect

    Haq, B.U. )

    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. Delineation of shallow stratigraphy using ground penetrating radar

    NASA Astrophysics Data System (ADS)

    Dominic, David F.; Egan, Kathleen; Carney, Cindy; Wolfe, Paul J.; Boardman, Mark R.

    1995-01-01

    Ground penetrating radar surveys were conducted at four sites to investigate the shallow stratigraphy and to determine the applicability and performance of the radar technique. A basic analog-recording radar system with a single 80 MHz antenna was used for all of the surveys. Good stratigraphic control existed at all of the sites so that the effectiveness of the radar could be evaluated. The four sites were distinctly different in composition and extent. At an upland farm site in the glaciated region of southwestern Ohio a clay-rich soil covers shallow bedrock. Some soil horizons were identifiable on the radar profiles, but only to a depth of 1.4 m. At a sand and gravel quarry in southwestern Ohio the depositional patterns of the unsaturated deposits were clearly imaged to a depth greater than 4 m. At a hydraulic fill dam in western Ohio the changes in the internal composition of the earthen fill were observed on the radar records to depths of 4 m. On San Salvador in the Bahamas radar profiles over partially consolidated carbonate sand revealed an extensive series of buried beach ridges to depths of 4 m. These data were useful in understanding the depositional history of the area, which could not be determined from surface and pit sampling alone. These studies show that ground penetrating radar is an important tool for studying shallow stratigraphy where the ground conductivity is low enough to permit radar reflections from depths of interest.

  10. Perspective on the sequence stratigraphy of continental strata

    SciTech Connect

    Shanley, K.W. ); McCabe, P.J. )

    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.

  11. 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.

  12. Ordovician ocean plate stratigraphy and thrust duplexes of the Ballantrae Complex, SW Scotland: Implications for the pelagic deposition rate and forearc accretion in the closing Iapetus Ocean

    NASA Astrophysics Data System (ADS)

    Fujisaki, Wataru; Asanuma, Hisashi; Suzuki, Kazue; Sawaki, Yusuke; Sakata, Shuhei; Hirata, Takafumi; Maruyama, Shigenori; Windley, Brian F.

    2015-11-01

    The Ballantrae Complex (at Bennane Lea in SW Scotland) contains important ocean plate stratigraphy (basalt, chert, mudstone, sandstone) in an accretionary prism that is associated with a classic Ordovician ophiolite. We used the ocean plate stratigraphy to sub-divide the prism into 11 tectonic units. To determine the depositional age of bedded cherts, zircons were separated from 9 tuff beds from 6 different units. All the tuffs have early to middle Ordovician ages, even though their present positions are mutually distant. These ages are consistent with microfossil records of radiolaria and graptolites. The stratigraphic-structural relationships demonstrate that the ocean plate stratigraphy has been repeated by bedding-parallel thrusts; this is typical of a modern accretionary duplex. We calculated the sedimentation rate of Early to Middle Ordovician bedded cherts at Bennane Lea on the basis of U-Pb zircon ages obtained from several tuff beds; the data indicate that the depositional rate (0.6-3 m/myr) was as slow as that of Mesozoic-Cenozoic equivalents defined by radiolaria. The age spectra of detrital zircons from Ballantrae sandstones show prominent single peaks at ca. 467 and 478 Ma, and a lack of Precambrian zircons. Integration of our new zircon ages with published isotopic data and palaeo-geographic maps indicates that the sandstones were deposited near an intra-oceanic arc and far from any continent containing Precambrian rocks. The pelagic-to-clastic sediments at Bennane Lea were deposited in the closing Iapetus Ocean from ca. 477 Ma to ca. 464 Ma, when they were accreted with the intra-oceanic arc of Ballantrae.

  13. Linking distal volcaniclastic sedimentation and stratigraphy with the development of Ruapehu volcano, New Zealand

    NASA Astrophysics Data System (ADS)

    Tost, M.; Cronin, S. J.

    2015-11-01

    Long-lived stratovolcanoes are often characterized by cycles that include pulses of explosive and effusive eruptive activity, periodic flank collapses, and long periods of eruptive quiescence. Reconstructing these solely from exposures on volcanic edifices is difficult because deposits are dominantly from comparatively recent reconstruction episodes, while older sequences are buried or have long been eroded. Long-runout mass-flow deposits, on the other hand, offer insights into the older eruptive history and long-term eruptive behavior of composite volcanoes. At Mt. Ruapehu, New Zealand, 40Ar/39Ar dating of lava clasts within distal mass-flow sequences, combined with new mapping and sedimentological descriptions, reveal three hitherto unknown eruptive episodes of the volcano and extend its minimum age to at least 340 ka. Plinian to subplinian eruptions were followed by periods of subdued volcanic activity. Voluminous (>1 km3) inter-eruptive flank failures were precursors to major reconstruction episodes, associated with numerous syn-eruptive mass flows emplaced up to 90 km from the volcano. Syn-eruptive collapse triggered large plinian eruptions associated with pyroclastic density currents. Rapid ring-plain aggradation dominated during periods of subdued volcanic activity when intensive edifice erosion induced frequent inter-eruptive lahars.

  14. 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.

    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.

  15. 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. )

    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.

  16. 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

  17. Pleistocene pollen stratigraphy from borehole 81/34, devil's hole area, central north sea

    NASA Astrophysics Data System (ADS)

    Ekman, Sten R.

    1998-09-01

    Twelve pollen assemblage zones are identified in a 229 m deep borehole (BH 81/34) from the Devil's Hole area in the central North Sea (British sector). The sediment from this borehole is Early to Late Pleistocene in age and the observation of massulae from Azolla filiculoides in sediment with reversed polarity indicates an age younger than the Olduvai geomagnetic event for the entire sequence. The Early Pleistocene sediments were at least partly deposited in the vicinity of a river outlet and can be correlated either with the Eburonian or the Menapian cold stage and with the Bavel interglacial and the Linge glacial within the Bavelian stage in the Dutch stratigraphy. The Middle Pleistocene sequence contains an interval rich in Abies, Picea and Pinus, probably deposited during the end of either Cromerian Complex interglacial IV (Noordbergum) or possibly the Holsteinian. The uppermost 80 m of the core contains high frequencies of pre-Quaternary and deteriorated palynomorphs indicating extensive glacial or glaciofluvially reworked sediment.

  18. Wasatch fossils in so-called Fort Union beds of the Powder River Basin, Wyoming, and their bearing on the stratigraphy of the region

    USGS Publications Warehouse

    Wegemann, Carroll H.

    1917-01-01

    Northeastern Wyoming is occupied by a broad structural basin opening to the north and bounded on the east, south, and west by three mountain uplifts - the Black Hills, the Laramie Mountains, and the Big Horn Mountains. (See fig. 16.) Throughout much of this basin the surface rocks are of Tertiary age. They contain the principal coal beds of the region and have been classified in all the most recent Survey reports as Fort Union. The true age of these rocks and the general stratigraphy of the fresh-water beds that underlie them are the theme of this paper.

  19. North polar region of Mars: Advances in stratigraphy, structure, and erosional modification

    NASA Astrophysics Data System (ADS)

    Tanaka, Kenneth L.; Rodriguez, J. Alexis P.; Skinner, James A.; Bourke, Mary C.; Fortezzo, Corey M.; Herkenhoff, Kenneth E.; Kolb, Eric J.; Okubo, Chris H.

    2008-08-01

    We have remapped the geology of the north polar plateau on Mars, Planum Boreum, and the surrounding plains of Vastitas Borealis using altimetry and image data along with thematic maps resulting from observations made by the Mars Global Surveyor, Mars Odyssey, Mars Express, and Mars Reconnaissance Orbiter spacecraft. New and revised geographic and geologic terminologies assist with effectively discussing the various features of this region. We identify 7 geologic units making up Planum Boreum and at least 3 for the circumpolar plains, which collectively span the entire Amazonian Period. The Planum Boreum units resolve at least 6 distinct depositional and 5 erosional episodes. The first major stage of activity includes the Early Amazonian (˜3 to 1 Ga) deposition (and subsequent erosion) of the thick (locally exceeding 1000 m) and evenly-layered Rupes Tenuis unit (A Brt), which ultimately formed approximately half of the base of Planum Boreum. As previously suggested, this unit may be sourced by materials derived from the nearby Scandia region, and we interpret that it may correlate with the deposits that regionally underlie pedestal craters in the surrounding lowland plains. The second major episode of activity during the Middle to Late Amazonian ( ˜<1 Ga) began with a section of dark, sand-rich and light-toned ice-rich irregularly-bedded sequences (Planum Boreum cavi unit, A Bb c) along with deposition of evenly-bedded light-toned ice- and moderate-toned dust-rich layers (Planum Boreum 1 unit, A Bb 1). These units have transgressive and gradational stratigraphic relationships. Materials in Olympia Planum underlying the dunes of Olympia Undae are interpreted to consist mostly of the Planum Boreum cavi unit (A Bb c). Planum Boreum materials were then deeply eroded to form spiral troughs, Chasma Boreale, and marginal scarps that define the major aspects of the polar plateau's current regional topography. Locally- to regionally-extensive (though vertically minor) episodes of deposition of evenly-bedded, light- and dark-toned layered materials and subsequent erosion of these materials persisted throughout the Late Amazonian. Sand saltation, including dune migration, is likely to account for much of the erosion of Planum Boreum, particularly at its margin, alluding to the lengthy sedimentological history of the circum-polar dune fields. Such erosion has been controlled largely by topographic effects on wind patterns and the variable resistance to erosion of materials (fresh and altered) and physiographic features. Some present-day dune fields may be hundreds of kilometers removed from possible sources along the margins of Planum Boreum, and dark materials, comprised of sand sheets, extend even farther downwind. These deposits also attest to the lengthy period of erosion following emplacement of the Planum Boreum 1 unit. We find no evidence for extensive glacial flow, topographic relaxation, or basal melting of Planum Boreum materials. However, minor development of normal faults and wrinkle ridges may suggest differential compaction of materials across buried scarps. Timing relations are poorly-defined mostly because resurfacing and other uncertainties prohibit precise determinations of surface impact crater densities. The majority of the stratigraphic record may predate the recent (<20 Ma) part of the orbitally-driven climate record that can be reliably calculated. Given the strong stratigraphic but loose temporal constraints of the north polar geologic record, a comparison of north and south polar stratigraphy permits a speculative scenario in which major Amazonian depositional and erosional episodes driven by global climate activity is plausible.

  20. North polar region of Mars: Advances in stratigraphy, structure, and erosional modification

    USGS Publications Warehouse

    Tanaka, K.L.; Rodriguez, J.A.P.; Skinner, J.A., Jr.; Bourke, M.C.; Fortezzo, C.M.; Herkenhoff, K. E.; Kolb, E.J.; Okubo, C.H.

    2008-01-01

    We have remapped the geology of the north polar plateau on Mars, Planum Boreum, and the surrounding plains of Vastitas Borealis using altimetry and image data along with thematic maps resulting from observations made by the Mars Global Surveyor, Mars Odyssey, Mars Express, and Mars Reconnaissance Orbiter spacecraft. New and revised geographic and geologic terminologies assist with effectively discussing the various features of this region. We identify 7 geologic units making up Planum Boreum and at least 3 for the circumpolar plains, which collectively span the entire Amazonian Period. The Planum Boreum units resolve at least 6 distinct depositional and 5 erosional episodes. The first major stage of activity includes the Early Amazonian (???3 to 1 Ga) deposition (and subsequent erosion) of the thick (locally exceeding 1000 m) and evenly-layered Rupes Tenuis unit (Abrt), which ultimately formed approximately half of the base of Planum Boreum. As previously suggested, this unit may be sourced by materials derived from the nearby Scandia region, and we interpret that it may correlate with the deposits that regionally underlie pedestal craters in the surrounding lowland plains. The second major episode of activity during the Middle to Late Amazonian (??? <1 Ga) began with a section of dark, sand-rich and light-toned ice-rich irregularly-bedded sequences (Planum Boreum cavi unit, Abbc) along with deposition of evenly-bedded light-toned ice- and moderate-toned dust-rich layers (Planum Boreum 1 unit, Abb1). These units have transgressive and gradational stratigraphic relationships. Materials in Olympia Planum underlying the dunes of Olympia Undae are interpreted to consist mostly of the Planum Boreum cavi unit (Abbc). Planum Boreum materials were then deeply eroded to form spiral troughs, Chasma Boreale, and marginal scarps that define the major aspects of the polar plateau's current regional topography. Locally- to regionally-extensive (though vertically minor) episodes of deposition of evenly-bedded, light- and dark-toned layered materials and subsequent erosion of these materials persisted throughout the Late Amazonian. Sand saltation, including dune migration, is likely to account for much of the erosion of Planum Boreum, particularly at its margin, alluding to the lengthy sedimentological history of the circum-polar dune fields. Such erosion has been controlled largely by topographic effects on wind patterns and the variable resistance to erosion of materials (fresh and altered) and physiographic features. Some present-day dune fields may be hundreds of kilometers removed from possible sources along the margins of Planum Boreum, and dark materials, comprised of sand sheets, extend even farther downwind. These deposits also attest to the lengthy period of erosion following emplacement of the Planum Boreum 1 unit. We find no evidence for extensive glacial flow, topographic relaxation, or basal melting of Planum Boreum materials. However, minor development of normal faults and wrinkle ridges may suggest differential compaction of materials across buried scarps. Timing relations are poorly-defined mostly because resurfacing and other uncertainties prohibit precise determinations of surface impact crater densities. The majority of the stratigraphic record may predate the recent (<20 Ma) part of the orbitally-driven climate record that can be reliably calculated. Given the strong stratigraphic but loose temporal constraints of the north polar geologic record, a comparison of north and south polar stratigraphy permits a speculative scenario in which major Amazonian depositional and erosional episodes driven by global climate activity is plausible. ?? 2008 Elsevier Inc. All rights reserved.

  1. Correlating the Pleistocene Sediment Stratigraphy Across the Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Sellen, E.; Jakobsson, M.

    2008-12-01

    An extensive sediment coring program was carried out during the Healy-Oden Trans-Arctic Expedition in 2005 (HOTRAX) from USCGC Healy. In total, 29 piston cores, on average 12 m long, were retrieved along a transect from the Alaskan margin, across the Arctic Ocean, to the Yermak Plateau off Svalbard. One of the purposes for the expedition was to establish the Pleistocene sediment stratigraphy for the Arctic Ocean and to resolve the issue of determining sedimentation rates in the central Arctic. Here, we present an attempt to correlate the cores along the HOTRAX transect in order to set a base for the chronostratigraphy. The cores taken from the Mendeleev Ridge and the Alpha Ridge can readily be correlated using gamma density and magnetic susceptibility measurements from the onboard Multi Sensor Core Logger as well as grain size measurements. The stratigraphic ties between the Alpha Ridge cores and the Mendeleev Ridge cores north of 80°N are detailed with many similar features. The most useful feature is an interval of five peaks in the magnetic susceptibility record. However, a correlation between the Mendeleev Ridge cores located further to the south and closer to the shelf edge was less straightforward, possibly indicating that depositional processes here are affected by other factors than in the central Arctic Ocean. Bridging the Amerasian and Eurasian Basin stratigraphies through the cores retrieved from the Lomonosov Ridge proved to be far less straightforward. None of the prominent physical property features that occur in the Mendeleev Ridge and Alpha Ridge cores are recognized in the Lomonosov Ridge stratigraphy. This may imply that the Lomonosov Ridge sediments predominantly originated from a different source area during the Pleistocene than the Alpha and Mendeleev Ridge sediments. Applying this as a working hypothesis, we focus on linking the cores within the Eurasian Basin for further correlation. However, the presence of alternating dark and light brown layers in all cores seem to indicate that the climatic signal should be recorded in all of them. Although no correlation across the entire Arctic Ocean has been achieved, the present results suggest that accurate core-to-core correlations are possible over large areas in the Amerasian Basin and that the depositional environment in the central Amerasian Basin has not varied significantly.

  2. Magnetic polarity stratigraphy of the Permian and Carboniferous: The extension of the magnetic reversal record into the Paleozoic

    SciTech Connect

    Opdyke, N.D. )

    1991-03-01

    Magnetic polarity stratigraphy has revolutionized stratigraphic studies in Jurassic to Pleistocene sediments. These studies have been greatly facilitated by the reversal record that is recorded in rocks of the ocean floor. For times prior to the Jurassic, the reversal history of the magnetic field must be determined and eventually related through the type section concept. The magnetic reversal history of the late Paleozoic is dominated by the Permo-Carboniferous reversed superchron (PCRS), which extends from the late Permian to the Carboniferous (Westphalian). Recent studies by the author and his students in Middle Carboniferous sediments of eastern Canada, Pennsylvania, Arizona, and Nevada reveal that the magnetic field has reversed frequently in late Mississippian and early Pennsylvanian times (Meramecian through late Morrowan). The polarity of the magnetic field over this interval is approximately 50% normal and 50% reversed. The frequency of reversal appears to be about one reversal per m.y. The possibility, therefore, exists that this pattern may be used for continental and intercontinental correlation. Attempts are currently underway to correlate this magnetic stratigraphy to fossiliferous marine sections. The base of the PCRS is probably of Atokan age.

  3. 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.

  4. Stratigraphy of the Odessa shelf, Ukrainian Black Sea: existing problems and their solution

    NASA Astrophysics Data System (ADS)

    Khriachtchevskaia, O.; Stovba, S.

    2009-04-01

    The stratification of sedimentary cover within the Odessa Shelf of the Black Sea is traditionally based on biostratigraphy. Data of microfauna began to collect 37 years ago since drilling first wells within the shelf. More than 80 wells have been drilled up to nowadays. The detailed stratigraphy with the determination of biozones developed for adjoining Crimea Peninsula that had been studied in well exposed outcrops was extrapolated on sedimentary sections penetrated by offshore wells. However, there are substantial errors, which are usually caused by limited core data describing only 4-5 percents of well depths and consequently by limited microfaunal variety in core samples. Moreover, the core distribution along boreholes is not regular, and core samples were not taken at all in upper parts of boreholes (< 500-700 m). More complete and continuous information on well sections is given by well-logging records. However, there is a wide well spacing only and thus, correlation of the records does not allow substantially improve a determination of even-aged sedimentary layers. Objective ambiguity of geological and geophysical data obtained from wells has resulted in multichoice stratification over the same subcrops. It has accordingly generated difficulties to interpret seismic data in a crosswell extent as well as it makes problems for oil and gas exploration. Integrated interpretation of a new dense set of regional seismic reflection profiles, microfauna data and well-logging records has allowed us to eliminate some existing uncertainties in stratigraphy of Odessa Shelf as well as to trace the main even-aged sedimentary units from the shelf to the deep water part of the Ukrainian Black Sea, where no well has been drilled up to nowadays. The main sedimentary units are determined through the tracking of regional lithological marker beds, angular unconformities, sedimentation gaps, changes of lithology. Our results demonstrate that the following stratigraphical units are fixed confidently: 1) Middle Miocene - Quaternary; 2) Lower Miocene - Oligocene; 3) Upper Eocene; 4) Middle Eocene; 5) Lower Eocene; 6) Paleocene; 7) Upper Cretaceous; 8) Cenomanian - Albian; 9) Lower Cretaceous; 10) pre-Cretaceous. The units are well distinguished by microfaunal data, well-logging records and seismic data. They serve as a reliable basis for reconstructions of tectonics and evolution of the Black Sea region.

  5. Geoacoustic character, sedimentology and chronology of a cross-shelf Holocene sediment deposit off Cabo Frio, Brazil (southwest Atlantic Ocean)

    NASA Astrophysics Data System (ADS)

    Mendoza, Ursula; Ayres Neto, Arthur; C. Abuchacra, Rodrigo; Fernandes Barbosa, Cátia; G. Figueiredo, Alberto; C. Gomes, Manoela; Belem, Andre L.; Capilla, Ramsés; S. Albuquerque, Ana Luiza

    2014-08-01

    The Cabo Frio region in the state of Rio de Janeiro, southeast coast of Brazil, is characterized by a local coastal upwelling system and converging littoral sediment transport systems that are deflected offshore at Cabo Frio, as a consequence of which a thick cross-shelf sediment deposit has developed over time. To investigate the evolution of this muddy deposit, geophysical, sedimentological and geochemical data from four sediment cores (3.8-4.1 m in length) recovered in water depths between 88 and 141 m were analyzed. The high-resolution seismic data show variable sediment thicknesses ranging from 1 to 20 m, comprising two sedimentary units separated by a high-impedance layer at a depth of about 10 m below the seafloor at the coring sites. According to the available age datings, the upper sedimentary unit is late Pleistocene to Holocene in age, whereas the lower unit (not dated) must, by implication, be entirely Pleistocene in age. The boomer-seismic reflection signal can be divided into three echo-types, namely transparent (inner shelf), stratified (middle shelf) and reflective (outer shelf), each type seemingly related to the local sediment composition. The upper 4 m of the upper sedimentary unit is dominated by silty sediment on the middle shelf, and by upward-fining sediments (silty sand to sandy silt) on the inner and outer shelf. The downcore trends of P-wave velocity, gamma-ray density and acoustic impedance are largely similar, but generally reversed to those of water and organic carbon contents. Total organic carbon contents increase with decreasing mean grain size, periodic fluctuations suggesting temporal changes in the regional hydrodynamics and primary productivity fuelled by the local upwelling system. The reconstruction of sedimentation rates in the course of the Holocene is based on 35 AMS age datings of organic material recovered from variable downcore depths. These range from a maximum of 13.3 cm/decade near the base of the inner shelf core (7.73-7.70 ka BP) to generally very low values (<0.11 cm/century) over the last thousand years in all cores. Over the last 6 ka there appear to have been three distinct sedimentation peaks, one between 6 and 5 ka BP, another between 4 and 3 ka PB, and one around 1 ka BP. Due to different time intervals between dates, not every peak is equally well resolved in all four cores. Based on the similar sedimentology of the inner and outer shelf cores, an essentially identical sedimentation model is proposed to have been active in both cases, albeit at different times. Thus, already during the last glacial maximum, alongshore sediment transport was deflected offshore by a change in shoreline orientation caused by the Cabo Frio structural high. The source of terrigenous material was probably a barrier-island complex that was subsequently displaced landward in the course of sea-level rise until it stabilized some 6.5 ka BP along the modern coast.

  6. Seismic reflection applied to sedimentology and gas discovery in the Gulf of Cadiz

    SciTech Connect

    Delaplanche, J.; Lafet, Y.; Sineriz, B.G.; Remon Gil, M.A.

    1982-02-01

    In the Gulf of Cadiz, a Tertiary basin became filled by clastic series during Miocene and Pliocene times. This terrigenous influx, derived from the Iberic Meseta in the north, is characterized by a sandy episode during the Tortonian and Messinian. The sand deposits were probably connected with uplift and major erosion of the Meseta during the sliding of the olistostrome, which occupied the south of the basin from late Helvetian to middle Tortonian. High-resolution seismic techniques produced a good picture of the stratigraphy and of the depositional environment of the sands. A further study, using the amplitude of the reflections, inversion of seismic traces into acoustic impedance traces, and modeling, provides a remarkable example of the possibilities of seismic stratigraphy for depicting the lateral evolution of facies and localizing hydrocarbon occurrences. Out of seven exploratory wells based upon seismic information, six encountered gas-bearing sands with economic potential.

  7. Sedimentologic and tectonic aspects of the Archean Limpopo belt

    SciTech Connect

    Erikkson, K.A.; Kidd, W.S.F.

    1985-01-01

    There are marked lithic differences between the central Limpopo belt and other well-studied Archean high-grade and greenstone-granitoid terranes, in particular the presence, in thick sections of supracrustals including approx. 15% of each of 1) carbonate and calc-silicate rocks and 2) pure metaquartzite, often fuchsite-bearing, with the lithic character of quartz arenite, not metachert. Isotopic ages suggest these sediments are 3.3-3.5 Ga old. The sequence and distribution of lithic, plutonic, metamorphic, and structural events in the Limpopo belt resembles that in younger orogens where there has been rifting of continental lithosphere, deposition of sediments at an Atlantic-type margin, then convergence and collision with another continental block. The southern margin of the central Limpopo belt is a wide (20 km) zone of vertically-dipping, horizontally-lineated mylonites, clearly representing the deeper ductile levels of a major strike-slip fault. This fault resembles large strike-slip systems that allow tectonic escape during collision in young orogenic belts. The authors conclude that continental fragments large enough to provide a substrate for significant platform arenite and carbonate sedimentation existed by 3.3-3.5 Ga, and that Tibetan-Himalayan style collisional tectonics greater than or equal to 2.6 Ga ago accounts for the large-scale relationships between the Limpopo belt and the adjacent Archean greenstone-granitoid terrane cratons. By inference, other more fragmentary Archean gneissic terranes may have once been part of such collisional zones.

  8. La stratigraphie oligo-miocène et la surface d'érosion messinienne en mer Noire, stratigraphie sismique haute résolutionThe Oligo-Miocene stratigraphy and the Messinian erosional surface in Black Sea, high-resolution seismic stratigraphy

    NASA Astrophysics Data System (ADS)

    Gillet, Hervé; Lericolais, Gilles; Rehault, Jean-Pierre; Dinu, Corneliu

    2003-10-01

    The stratigraphy of the Black Sea western margin is revisited through seismic data acquired during two French-Romanian surveys. These data are calibrated by industrial and DSDP drillings; they display several major discontinuities regarded as Tertiary erosional surfaces. The major seismic discontinuity underlines the base of Miocene formations and corresponds to a composite surface including at least three erosional phases ranging from Oligocene to Pontian times. Moreover, a Messinian erosional surface is clearly identified. This is in agreement with the Hsü's proposition [Palaeogeogr. Palaeoclimatol. Palaeoecol. 29 (1979) 75-93] suggesting a Messinian sea-level drop of Black Sea related to the Messinian Salinity Crisis described in the Mediterranean Sea. To cite this article: H. Gillet et al., C. R. Geoscience 335 (2003).

  9. Relation of sequence stratigraphy to modern sedimentary environments

    SciTech Connect

    Boyd, R. ); Suter, J.; Penland, S. )

    1989-10-01

    One method of testing the concept of sequence stratigraphy is to compare it to Quaternary sediments in which chronology, stratigraphic relations, and facies geometry are more clearly understood than in older rocks. Rapid deposition rates during Quaternary glacial-eustatic cycles in large deltaic depocenters generate sequences comparable to those in the ancient stratigraphic record. In the northern Gulf of Mexico, the late Wisconsinan-Holocene Mississippi River has deposited a Type 1 sequence that includes lowstand, transgressive, and high-stand systems tracts. Characteristics of modern Mississippi River sedimentary environments support the methodology used in sequence analysis, but the short time taken for sequence generation here raises important questions about sequence time scales, correlation, and driving mechanisms.

  10. Phaneorozoic sequence stratigraphy of Bolivia and adjacent regions

    SciTech Connect

    Sempere, T. )

    1993-02-01

    Phaneorozoic sequence stratigraphy of the Pacific margin of western South America, particularly the Bolivian section, has been completed and new interpretations and hypotheses have been proposed as a result of data analyses of this information. The Paleozoic margin was initially passive (late Cambrian-Llanvirn, [open quotes]Puna aulacogen[close quotes]), but became active during a middle Ordovician compressional episode. Most of late Cambrian to early Triassic Bolivian rocks are of marine origin, with dark shale units recording sea level rises, whereas middle Triassic to Recent rocks were mainly deposited in continental environments (except six restricted-marine ingressions in the late Cretaceous-Danian, and one in the late Miocene, all with hydrocarbon potential). A noteworthy similarity exists between the Devonian to Jurassic stratigraphies of Bolivia and the Parana basin, suggesting that Bolivia behaved as part of the Brazilian craton from late Cambrian to late Jurassic, when it was captured into the Pacific margin geotectonic system. Organic-rich units correlate with Paleozoic highstand deposits and younger ingressions. The Bolivian Phanerozoic strata is characterized by thick layers, partly due to middle Ordovician-Carboniferous and late Cretaceous-Cenozoic foreland basins. Paleozoic foreland geometries include northeastern onlaps and, potentially, stratigraphic traps. Hydrocarbon generation, migration and trapping mainly depended on Cenozoic structural loading and burial and on propagation of Andean deformation which are comprised of Paleozoic shale decollements. Precise knowledge of the evolution of the Phanerozoic geodynamic contexts and basin geometries through sedimentation and subsequent deformations is crucial for hydrocarbon exploration strategies in these regions.

  11. Magnetic polarity stratigraphy of the Miocene Rio Azul section, Precordillera thrust belt, San Juan Province, Argentina

    SciTech Connect

    Jordan, T.E.; Beer, J.A. ); Rutty, P.M. Stanford Univ., CA ); McRae, L.E.; Tabbutt, K. ); Damanti, J.F. )

    1990-07-01

    The chronostratigraphy of synorogenic strata of Rio Azul in the Bermejo foreland basin, Argentine Andes, reveals details of Miocene tectonic activity and deposition. Chronostratigraphic interpretations are based on magnetic polarity stratigraphy and zircon fission-track dates of interbedded volcanic ashes. The Rio Azul section is located within the Precordillera thrust belt, uplifted and rotated by motion on subjacent faults. The 3,200 m thick section coarsens upward, from sandstone and mudstone (Cuculi Formation) to conglomerate (El Corral Formation). The radiometric ages indicate the entire section is of middle to late Miocene age, and the authors correlate the magnetic polarity pattern of each fault block to the magnetic polarity time scale. The lower 500 m of the section apparently ranges from approximately 16 to 12 Ma, although the age of the lowest 100 m is quite uncertain. The fault-bounded block from 500 to 1,000 m probably correlates to approximately 13.5-12.5 Ma. The block from 1,000 to 2,000 m correlates to approximately 12.5-10 Ma. Given the lack of unconformities in the coarse uppermost 1,200 m of section and a zircon fission track age within the conglomerates, the authors speculate that the upper part of the section was deposited very rapidly; the top of the section is probably no younger than about 8 to 9 Ma. These correlations and similarities of facies, paleocurrents, and provenance imply that the Cuculi Formation represents the proximal facies correlative to the Jarillal Formation of Sierra de Huaco, and that the El Corral conglomerates are the up-dip equivalent of the Huachipampa Formation of Huaco. These results are consistent with a paleogeographic model of a major drainage reorganization in the Bermejo foreland basin at about 10 Ma. It is clear, however, that thrusting in the Precordillera began more than 2 m.y. prior to the drainage reorganization.

  12. Volcanic stratigraphy of the Barrel Springs--Wild Cherry Formations, Davis Mountains, Trans-Pecos Texas

    SciTech Connect

    Parker, D.F. . Dept. Geology); Henry, C.D. . Bureau of Economic Geology); Kunk, M.J. )

    1993-02-01

    Detailed mapping, stratigraphy, [sup 40]Ar/[sup 39]Ar ages, and geochemistry allow, for the first time, a coherent volcanic history of the Barrel Springs--Wild Cherry (BS-WC) units, the most widespread of the Davis Mountains volcanic field (DMVF). These units erupted dominantly from the [approximately] 20 km-diameter Paradise Mountain caldera (PMC), in the west-central DMVF, where thick, locally silicified and kaolinized intracaldera tuffs and interbedded lavas were resurgently domed by an 8 x 5-km-diameter syenitic intrusion. BS-WC units, all rhyolites, consist dominantly of a lower, moderately porphyritic ash-flow tuff; a petrographically similar, middle ash-flow tuff; and an upper group of voluminous, abundantly porphyritic lavas. The lower ash-flow tuff is strongly rheomorphic throughout its occurrence. The middle ash-flow is also rheomorphic in thick outcrops near the PMC but not in thin ([<=]10m), distal outcrops. These three units are interbedded with lavas lithologically similar to the tuffs near the PMC and with volcaniclastic sedimentary rocks in more distal area. The two ash-flow tuffs are separated by strongly porphyritic trachyte lavas of the Mount Locke Formation in the vicinity of the PMC. Sources and extents of individual flows of the upper lavas have not been positively identified. [sup 40]Ar/[sup 39]Ar ages of alkali feldspar phenocrysts from thirteen samples constrain most BS-WC to a 300 ka span. The lower tuff erupted about 35.6 Ma. The middle tuff and part of the voluminous lava package erupted at 35.3 Ma. Ages of two lavas are 35.1 Ma, which suggests prolonged eruption. Correlations based on lithology and age relations are supplemented by trace element and mineral studies that confirm close geochemical affinities.

  13. Sedimentological analyses of martian gullies: The subsurface as the key to the surface

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

    Gullies are among the youngest landforms formed by liquid water on Mars, and therefore of critical importance in resolving the planets most recent hydrologic and climatic history. Water-free sediment flows, debris flows and fluvial flows have all been identified in gullies. These processes require very different amounts of liquid water, and therefore their relative contribution to gully-formation is of key importance for climatic inferences. We show that many gullies dominantly formed by debris flows, based on sedimentological analysis of outcrops in gully-fans in 51 HiRISE images widely distributed over the southern midlatitudes. The great majority (96%) of outcrop exposures in gully-fans fed by catchments which mainly comprise bedrock and thus host boulders, contain sedimentological evidence for debris-flow formation. These exposures contain many randomly distributed large boulders (>1 m) suspended in a finer matrix and in some cases lens-shaped and truncated layering. Such diagnostic features are rare in gully-fan exposures mainly fed by catchments comprising abundant latitude dependent mantle deposits (LDM; a smooth, often meters-thick deposit consisting mainly of ice and dust), wherein boulders are largely absent. These LDM-fed gullies may have formed by fine-grained debris flows, but this cannot be determined from outcrop sedimentology alone because of the lack of boulders in these systems. The fan surface morphology, in contrast to the subsurface, is dominated by secondary, post-depositional, processes, mainly weathering, wind erosion, and ice-dust mantling. These processes have removed or severely reworked the original, primary, debris-flow morphology over time. This explains the controversy between previously published morphometric analyses implying debris-flow formation and observations of gully-fan surfaces, which are often interpreted as the product of fluvial flows because of the absence of surficial debris-flow morphology. The inferred debris-flow origin for many gullies implies limited and ephemeral liquid water during gully-formation.

  14. 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.

  15. Geomorphological and sedimentological record of accelerated deglaciation of small mountain glacier, Ragnarbreen, Svalbard

    NASA Astrophysics Data System (ADS)

    Ewertowski, Marek

    2010-05-01

    Most of the Svalbrad glaciers have been in retreat since the end of the Little Ice Age (LIA). Hence, they give a good opportunity to study the geomorphological and sedimentological record of deglaciation. The aim of the study is to describe main landsystem elements of Ragnar glacier and relate them to different stages of the glacier recession. The Ragnar glacier is located in the Svalbard archipelago, in the central part of the West Spitsbergen Isle, in the north branch of Billefjorden. Ragnar is a small (~ 6 km2), outlet glacier, which current clean ice edge has retreated ca. 1500 m from the position related to the maximum LIA extent. Fieldworks of the study comprised detailed geomorphological mapping and sedimentary works. Four main elements of the landsystem of the Ragnar glacier can be distinguished: 1) Clean glacier surface. Currently, the ice surface of Ragnar glacier is almost completely debris-free and with only several supraglacial streams. 2) Ice-marginal lake. The lake started to form after 1980 year. Since that time, its length has reached 1000 m. Distant (from the ice-edge) part of the lake is shallow (< 2 m) with several small islands. Part proximal to the current ice edge is deeper (up to 16 m) and devoid of islands. At the bottom of the lake some ice (probable of glacier origin) was detected. 3) Lateral moraines - were developed along the both valley sides, from frontal moraine complex - to ca. 2 km upward the glacier valley. 4) Frontal moraine complex. This complex comprises of several chains of ridges and depressions and is relatively distinct - elevated about 35 m above the valley bottom. The elements of the landsystem of the Ragnar glacier have undergone several transformations since the LIA maximum: 1) Formation of the frontal moraine complex can be related to the state of dynamic equilibrium of the glacier during the LIA maximum. During formation of the complex and shortly after it the main depositional agents were intense debris flows, which are recorded by thick covers of the old debris flow deposits. Nowadays, despite of ice-cores, frontal moraine complex is much more stable than the lateral moraines or ice-marginal lake. 2) As a consequence of lowering of the clean glacier surface and formation of the distinct lateral moraines, the debris delivering from the valley sides is limited only to very narrow zone of the glacier (i.e. only to the lateral moraine). 3) Accelerated recession of the ice mouth and limitation in delivery of debris from sides of the valley caused that amount of deposits released in the ice front is small. 4) Increasing amount of water flowing from the glacier was blocked by frontal moraine complex and the ice marginal lake was created. 5) The debris cover on the lateral moraines is relatively thin. In addition, as a consequence of the clean ice surface lowering, slopes of the lateral moraines are very steep. It causes that mass movement processes (especially debris flows) are ubiquitous. Contemporary, lateral moraines are the elements undergoing the most intense transformations. Observations made in the Ragnar marginal zone revealed spatial-temporal changes in distribution of the sediments and landforms. They also add some premises that in the first stage of deglaciation debris flow and other mass wasting processes are most common. In the later phase glaciolacustrine and glaciofluvial deposition also plays important role in transformation of landforms and sediments.

  16. Insights into the Stratigraphy of Mars' Northern Plains from Impact Crater Mineralogy

    NASA Astrophysics Data System (ADS)

    Pan, L.; Ehlmann, B. L.; Carter, J.; Ernst, C. M.

    2015-09-01

    We study the newest CRISM images over large craters to probe the buried stratigraphy of the northern plains and place the identified hydrated minerals and unaltered mafic minerals into geologic context using impact scaling models.

  17. 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.

  18. Thrust faults and extensional detachment faults in Cretan tectono-stratigraphy: Implications for Middle Miocene extension

    NASA Astrophysics Data System (ADS)

    Papanikolaou, Dimitrios; Vassilakis, Emmanuel

    2010-06-01

    The revised tectono-stratigraphy of Crete and especially of the "Phyllites-Quartzites" complex demonstrated the distinction of the probable Paleozoic low-medium grade metamorphic rocks of the Arna unit from the underlying Permo-Triassic phyllites and associated carbonate sediments (Trypali facies) of Western Crete unit as well as the overlying Permo-Triassic phyllites and associated sediments of the Tyros/Ravdoucha Beds at the base of the Tripolis unit. The pre-existing mixture of the above tectono-stratigaphic units in a single complex created a number of misinterpretations as far as stratigraphy, metamorphism and interpretation of low angle faults as thrusts or detachments. Especially in cases where the inferred tectonic contact concerns the transition between the Tyros Beds and the base of the Tripolis carbonate platform there is no structural omission and therefore the contact represents a minor disharmonic sliding surface and not a detachment. Based on the revised tectono-stratigraphic analysis the determination of the structural omission for each tectonic contact was possible and several detachments were described for the first time. Footwall rocks of the detachments comprised several tectonic units usually from the lower nappes and hanging wall rocks comprised several tectonic units usually from the upper nappes. The detachment may separate not only metamorphosed units in the footwall (Mani, Western Crete, Arna) from non metamorphosed units in the hanging wall (Tripolis, Pindos and higher nappes) but also all other possible combinations from the Cretan nappe pile. Extension in Crete started in the Middle-Late Miocene with the formation of extensional detachment faults. The reported extensional structures of Oligocene to Early Miocene age do not correspond to crustal extension of Crete but to localized shear zones related to nappe stacking and the exhumation of metamorphic rocks. Extensional detachments in Crete form a tectonic horst through two oppositely dipping E-W-trending zones; one dipping north, related to the opening of the Cretan basin, and the other dipping south, related to the formation of the Messara supra-detachment basin. The deformation history of units within Crete can be summarized as: (i) compressional deformation producing arc-parallel east-west-trending south-directed thrust faults in Oligocene to Early Miocene time; (ii) extensional deformation along arc-parallel, east-west-trending detachment faults in Middle Miocene time, with hanging wall motion to the north and south; and (iii) Late Miocene-Quaternary transtensional deformation along high-angle normal and oblique normal faults that disrupt the older arc-parallel structures.

  19. Magnetic polarity stratigraphy of the Siwalik sequence in Nurpur area, NW Himalaya, India

    NASA Astrophysics Data System (ADS)

    Venkateshwarlu, M.

    2015-08-01

    Magnetic polarity stratigraphy studies were carried out on Jabbar Khad section of Nurpur area, Kangra District, Himachal Pradesh, India. Oriented block samples were collected at 202 sites with 3-5 samples per site from a 2350-m thick continuous sedimentary sequence consisting of sandstone-mudstone alternating beds. Specimens were subjected to thermal demagnetization (100-700?C) after measuring their natural remanent magnetization (NRM). Palaeolatitudes of virtual geomagnetic pole (VGP) from each site were calculated from the acquired characteristic remanent magnetization (ChRM) directions. The observed remanence carrier could be haematite. Magnetic polarity scale (MPS) was erected. This MPS is correlated with the standard geomagnetic polarity time scale (GPTS) of Lourens et al. (2004). The MPS readily matched from chron C2An.1n to chron C4n.2n, therefore assigning an age 8.20-2.60 Ma to the middle and upper Siwalik sections at Nurpur. The rate of sedimentation in middle Siwalik is 29 mm/yr and upper Siwalik is 59 mm/yr.

  20. Cambrian/Early Ordovician sequence stratigraphy and Mt. Simon sandstone petrology - Michigan basin

    SciTech Connect

    Cottingham, J.T.

    1990-05-01

    Rocks of Cambrian and Early Ordovician age are well known in Wisconsin and otber areas surrounding the Michigan basin but because of burial depth ranging from 3,000 to 16,000 ft relatively little is known about these rocks in Michigan. Core and cuttings examination demonstrate that similar stratigraphic sequences exist between the central Michigan basin and surrounding regions. Basinal lithofacies are similar to their outcrop counterparts in Wisconsin and are correlated on the basis of sediment types, sedimentary structures, and the concept of sequence stratigraphy. The Mount Simon Sandstone in Michigan correlates with that observed in Indiana, Illinois, Wisconsin, and Iowa. Isopach data throughout the Midwest indicates a single depocenter in northeastern Illinois, with an arm extending into the central Michigan basin. Sedimentary structures and lithology indicate a subtidal marine environment that may be a transition to a shoreward nonmarine fluvial to eolian environment. Observed diagenetic facies are influenced primarily by depth of burial. The deep facies (below 14,250 ft) exhibits extreme physical and chemical compaction of quartz grains. Quartz cement is predominant with less than 1% porosity present. The shallow facies (above 8,900 ft) exhibits pervasive dolomite and quartz cements and authigenic clays, Secondary porosity developed from dissolution of carbonate, quartz, and K-feldspar.

  1. 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.

  2. Caloris impact basin: Exterior geomorphology, stratigraphy, morphometry, radial sculpture, and smooth plains deposits

    NASA Astrophysics Data System (ADS)

    Fassett, Caleb I.; Head, James W.; Blewett, David T.; Chapman, Clark R.; Dickson, James L.; Murchie, Scott L.; Solomon, Sean C.; Watters, Thomas R.

    2009-08-01

    The Mariner 10 flybys revealed the eastern third of the Caloris basin and demonstrated its importance as a chronostratigraphic marker for the geological history of Mercury. Uncertain after that mission were the size of the basin, the full distribution of materials deposited or modified during the impact process, and the stratigraphic and age relationships between Caloris and surrounding terrain. Images obtained during MESSENGER's January 2008 flyby of Mercury revealed that the Caloris basin is ˜ 15% larger than previously estimated and moderately elliptical (˜ 1525 by ˜ 1315 km). Basin-related sculpture and secondary craters are dispersed widely in areas surrounding the basin, confirming the widespread significance of this event as a stratigraphic marker. Units mapped around Caloris on the basis of Mariner 10 data are generally recognized in regions observed for the first time by MESSENGER, including most facies of the Caloris Group (the Caloris Montes, Odin Formation, and Van Eyck Formation). The only unit without obvious exposures in MESSENGER images is the Nervo Formation, which was originally interpreted as impact melt or fallback ejecta. New measurements of the size-frequency distribution of impact craters both within the Caloris basin and on surrounding units, particularly the Odin Formation, support the hypothesis that the vast majority of circum-Caloris plains postdate the basin and are likely volcanic. The MESSENGER observations re-emphasize the importance of understanding the exterior stratigraphy of the basin in order to utilize the Caloris event as a discrete time horizon in the geological history of Mercury.

  3. Stratigraphy and geochronology of pitfall accumulations in caves and fissures, Bermuda

    NASA Astrophysics Data System (ADS)

    Hearty, Paul J.; Olson, Storrs L.; Kaufman, Darrell S.; Edwards, R. Lawrence; Cheng, Hai

    2004-05-01

    Deep fractures ("fissures") and avens ("skylights") in limestone cave roofs create natural traps for sediments and biota. Fissures fill quickly with surface sediment and organisms soon after opening. Debris cones are formed as materials fall, wash, or drift on air through openings in cave skylights. Such deposits in Admiral's and Grand Canyon Cave, Bermuda contain distinct beds and are composed of mixtures of sediment and charcoal, together with fossils of land snails, crabs, birds, reptiles, and bats. The "pitfall" accumulations were periodically sealed over by calcite flowstone. A stratigraphic record of surface activity and fauna through both glacial and interglacial periods has been preserved. The succession also provides an ideal setting in which to compare several geochronological methods. Calibrated 14C ages on charcoal and shells provide dated horizons at 1600, 12,800, and about 35,000 14C yr BP. Thermal ionization mass spectrometric (TIMS) ages on several flowstone layers constrain the entire sequence in the Admiral's Cave sequence between 126,300±900 yr (Termination II) and historical times. A continuous relative-age record generated by amino acid epimerization (AAE) geochronology ( D-alloisoleucine/ L-isoleucine or aIle/Ile) on the pulmonate land gastropod Poecilozonites verifies the biostratigraphy, reveals a minimal degree of mixing between stratigraphic units, and establishes an independent temporal link between the subterranean and subaerial deposits of Bermuda. This convergence between stratigraphy and geochronology yields a precisely dated succession from the oceanic island of Bermuda, and thus presents a unique opportunity to assess the rates and processes of evolutionary and climate change during that interval.

  4. Sequence stratigraphy of the Maturin sub-basin (Eastern Venezuela)

    SciTech Connect

    Gonzales, G.; Mata, S.; Santiago, N.

    1996-08-01

    The prolific Eastern Venezuela Basin has an area of about 160,000 km{sup 2} and is bounded by the Pilar Fault to the North, the Guayana Shield to the South, the Baul Arch to the West and beyond the Orinoco Delta to the East. Sequence analysis of three N-S and one W-E regional transects covered by over one thousand km of seismic lines and sedimentological, biostratigraphic and electrofacies studies of 80 wells allowed the definition of the sequence stratigraphic column of the basin. Seven major unconformity bounded depositional sequences were defined from Barremian to Recent, three in the Cretaceous and four in the Tertiary. Twenty-one third-order cycles were recognized in the Tejas B supercycle (Upper Oligocene-Recent). This cycle correlates very well with the Gulf of Mexico and Global chronostratigraphic charts. In the proximal, southern area, each sequence shows transgressive sandstones in its lower section and regressive ones in the upper part, separated by claystones that include a maximum flooding surface. In the distal area, fine marine sediments predominate with local turbidities. Some electrical markers and planktonic fossils are traceable over long distances. Regional transacts show two distinct structural zones: tensional to the South and compressional to the North. The best petroleum reservoirs occur in Tertiary and to a lesser extent in Cretaceous sequences. In this basin occurs the largest oil accumulation of the world (Orinoco), as well as several giant oil fields.

  5. 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).

  6. The Influence of Sampling Density on Bayesian Age-Depth Models and Paleoclimatic Reconstructions - Lessons Learned from Lake Titicaca - Bolivia/Peru

    NASA Astrophysics Data System (ADS)

    Salenbien, W.; Baker, P. A.; Fritz, S. C.; Guedron, S.

    2014-12-01

    Lake Titicaca is one of the most important archives of paleoclimate in tropical South America, and prior studies have elucidated patterns of climate variation at varied temporal scales over the past 0.5 Ma. Yet, slow sediment accumulation rates in the main deeper basin of the lake have precluded analysis of the lake's most recent history at high resolution. To obtain a paleoclimate record of the last few millennia at multi-decadal resolution, we obtained five short cores, ranging from 139 to 181 cm in length, from the shallower Wiñaymarka sub-basin of of Lake Titicaca, where sedimentation rates are higher than in the lake's main basin. Selected cores have been analyzed for their geochemical signature by scanning XRF, diatom stratigraphy, sedimentology, and for 14C age dating. A total of 72 samples were 14C-dated using a Gas Ion Source automated high-throughput method for carbonate samples (mainly Littoridina sp. and Taphius montanus gastropod shells) at NOSAMS (Woods Hole Oceanographic Institute) with an analytical precision higher than 2%. The method has lower analytical precision compared with traditional AMS radiocarbon dating, but the lower cost enables analysis of a larger number of samples, and the error associated with the lower precision is relatively small for younger samples (< ~8,000 years). A 172-cm-long core was divided into centimeter long sections, and 47 14C dates were obtained from 1-cm intervals, averaging one date every 3-4 cm. The other cores were radiocarbon dated with a sparser sampling density that focused on visual unconformities and shell beds. The high-resolution radiocarbon analysis reveals complex sedimentation patterns in visually continuous sections, with abundant indicators of bioturbated or reworked sediments and periods of very rapid sediment accumulation. These features are not evident in the sparser sampling strategy but have significant implications for reconstructing past lake level and paleoclimatic history.

  7. Sedimentology and diagenesis of windward-facing fore-reef calcarenites, Late Pleistocene of Barbados, West Indies

    SciTech Connect

    Humphrey, J.D.; Kimbell, T.N.

    1989-03-01

    Late Pleistocene reef terraces in southeastern Barbardos developed extensive fore-reef sand facies during deposition in response to high-energy windward-facing conditions. Sedimentology and diagenesis of these deposits illustrate significant contrasts with previous studies from the leeward west coast. These calcarenites are dominantly skeletal packstones with less common grainstones and wackestones present. The fore-reef sand facies occurs within progradational reef sequences, being conformably overlain by deep-water head coral facies. Medium-bedded, laterally continuous sand sheets retain original depositional slopes, dipping seaward at 10/degrees/-15/degrees/. These fore-reef deposits, in places, are over 30 m thick (average 20 m) and developed rapidly during late Pleistocene glacio-eustatic sea level highstands. Sedimentation rate ranges from 2 to 5 m/1000 years. Areal extent of fore-reef calcarenites in southeastern Barbados is estimated to be 8-10 km/sup 2/. Lithologically, the packstones are composed of an abundance of coralline red algae and the benthic foraminifer Amphistegina sp. Other volumetrically significant allochems include echinoids, mollusks, rhodoliths, peloids, and micritized grains. Micrite in the wackestone and packstone lithologies is likely derived from intense physical/mechanical abrasion of shoal-water reef facies. Diagenesis of these lithologies reflects a complex interplay of meteoric, mixing zone, and marine environments as a result of glacio-eustasy. Differences in diagenetic character are derived from differences in terrace ages, terrace geometry, a paleotopographic control on meteoric ground-water distribution, and high-energy coastal conditions. Diagenetic fabrics include equant, blocky meteoric phreatic calcite; limpid dolomite of mixing zone origin: and peloidal and isopachous fibrous cements from marine precipitation.

  8. 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.

  9. Sedimentology of resedimented carbonates: Facies and geometrical characterisation of an upper Cretaceous calciturbidite system in Albania

    NASA Astrophysics Data System (ADS)

    Rubert, Yolaine; Jati, Mohamed; Loisy, Corinne; Cerepi, Adrian; Foto, Gjergji; Muska, Kristaq

    2012-06-01

    Carbonate turbidite systems are not as well studied as their siliciclastic counterparts, resulting in a lack of knowledge on their vertical and lateral organisation. Thus, a preliminary detailed sedimentological study was undertaken in the upper Cretaceous limestones of Albania, which have been described as brecciated limestones and, more recently, as calciturbidites. The sedimentological study of three outcrops (Piluri, Vanister and Muzina) allows the definition of different lithologies grading from fine- to coarse-grained sequences representing the calciturbidites, intercalated with debris flow deposits and thick slumped levels. The thin-section examination of several facies defined in the field shows a dominance of mud-rich microfacies with variable granulometry, texture (mainly wackestone to packstone and floatstone), and the mixing of bioclastic and lithoclastic grains from both shallow-water (intertidal/infratidal) and deep-water settings (slope/basin). The microfacies description and fauna determination support the gravity origin of these calciclastic limestones. According to previous studies of the Ionian Basin and the surrounding platforms, the upper Cretaceous calciturbidite system could be reasonably linked to regional tectonic instabilities in relation to the beginning of the convergence between the Africa and Eurasian plates. The lateral and vertical organisation of these carbonate gravity deposits favours a depositional model over the apron model and that these deposits were fed by material derived from either the Apulian or the Kruja platform, through faulted shelf breaks.

  10. The INTIMATE event stratigraphy and recommendations for its use

    NASA Astrophysics Data System (ADS)

    Rasmussen, Sune O.

    2014-05-01

    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 manuscript under review for publication in Quaternary Science Reviews. Author team: S.O. Rasmussen, M. Bigler, S.P.E. Blockley, T. Blunier, S.L. Buchardt, H.B. Clausen, I. Cvijanovic, D. Dahl-Jensen, S.J. Johnsen, H. Fischer, V. Gkinis, M. Guillevic, W.Z. Hoek, J.J. Lowe, J. Pedro, T. Popp, I.K. Seierstad, J.P. Steffensen, A.M. Svensson, P. Vallelonga, B.M. Vinther, M.J.C. Walker, J.J. Wheatley, and M. Winstrup (deceased).

  11. 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.

  12. 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.

  13. Modeling the stratigraphy and preservation potential of meandering stream deposits

    NASA Astrophysics Data System (ADS)

    Tucker, G. E.; Clevis, Q.; Lock, G.; Lancaster, S.; Desitter, A.

    2003-12-01

    Both natural and human-induced modes of river and floodplain behavior have the potential to obscure, expose, or even destroy portions of the archaeological record. In valley systems with actively meandering channels much material can be lost to lateral bank erosion. Conversely, floodplain aggradation can bury and therefore obscure sites. In this study we aim to quantify the preservation potential of fluvial units containing archaeological sites as a function of the natural process of meandering, climate change and increased land-use during the Holocene. We used the CHILD simulation model of landscape evolution to explore alternative scenarios in which these three factors are both varied independently and combined. Boundary and initial conditions for the model scenarios are based on the Holocene evolution of the archaeologically-rich Upper Thames Valley, which is known to have witnessed variations in flood frequency, land-clearance, episodic alluviation and river entrenchment. The CHILD model is set up to combine four components that simulate the development of valley and floodplain system: hillslope and channel erosion, lateral stream meandering, overbank deposition, and the accumulation of a 3D stratigraphy. The landscape is represented by an adaptable triangular mesh of nodes, especially suited for simulating the gradual shifting of meander bends. The new stratigraphic layering routine recently added to the model in improves the resolution of the stratigraphic record accumulated by the model. Simulation results reveal systematic controls on preservation potential, and suggest potential sources of bias in the archaeological record.

  14. Fracture development and mechanical stratigraphy of Austin Chalk, Texas

    SciTech Connect

    Corbett, K.; Friedman, M.; Spang, J.

    1987-01-01

    The mechanical stratigraphy of the Upper Cretaceous Austin Chalk is established from study of fracture intensity along its outcrop trend from Dallas to San Antonio and westward to Langtry, Texas, and in the subsurface from study of cores and/or fracture identification logs from 30 wells. Three mechanical-stratigraphic units are recognized. Representative samples from the three mechanical-stratigraphic units were experimentally shortened, dry, at 10, 17, 34, and 70 MPa confining pressure, at 24/sup 0/C, and at a strain rate of 2.5 x 10/sup -4/ sec/sup -1/ to determine if the relative mechanical behavior observed at the surface could be extrapolated into the subsurface at different simulated burial depths. SEM photomicrographs of undeformed specimens show that smectite and other clays are distributed as large (30 ..mu..m), discrete, amorphous, concentrated masses throughout the chalk. They are comminuted along the induced fracture surfaces where their grain size is 0.5 ..mu..m or less. These observations suggest that smectite acts as a soft-inclusion, localizing shear failure and corresponding weakening the material. 9 figures, 5 tables.

  15. 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.

  16. Ferron sandstone - stratigraphy and reservoir analogs, East-Central Utah

    SciTech Connect

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

    1996-06-01

    The Ferron Sandstone (Upper Cretaceous) crops out along the west flank of the San Rafael Swell of east-central Utah. Exposures were described on photomosaics to better define the stratigraphy, to enhance facies prediction, and establish rules for reservoir modeling within fluvial-deltaic rocks. Major regressive cycles are recognized as parasequence sets composed of several to many parasequences. Each of the seaward-stepping parasequence sets recognized in the Ferron begins with a rapidly thickening and stratigraphically climbing, wave-modified shoreface. In later stages of progradation, deposition is dominated by river influences. Continued regression of the seaway is recorded in outcrop and shows a complex history of delta lobe progradation, switching, and abandonment. Onlapping and stacking of parasequences creates a collage of potential reservoir sweet spots, baffles, and barriers within a parasequence set. Shoreface and delta-front deposits of the older parasequences are commonly eroded by younger distributary and meanderbelt systems that fed younger parasequences of the parasequence sets. The result is numerous and locally thick channel sandstone bodies incised into shoreface and delta-front deposits. Published studies and recently completed work show that upper shoreface, stream mouth-bar, and channel sandstones constitute the best potential reservoir rocks within the Ferron Sandstone.

  17. Cenozoic seismic stratigraphy of the SW Bermuda Rise

    SciTech Connect

    Mountain, G.S.; Driscoll, N.W.; Miller, K.G.

    1985-01-01

    The seismic Horizon A-Complex (Tucholke, 1979) readily explains reflector patterns observed along the western third of the Bermuda Rise; farther east, basement is much more rugged and gravity flows shed from local topographic highs complicate the stratigraphy. Distal turbidites on the southwestern Bermuda Rise onlap reflector A* from the west, suggesting early Paleocene mass wasting of the North American margin. Locally erosive bottom currents cut into the middle Eocene section of the SW Bermuda Rise; these northward flowing currents preceded those that formed reflector Au along the North American margin near the Eocene-Oligocene boundary. Southward flowing currents swift enough to erode the sea floor and to form reflector Au did not reach as far east as the SW Bermuda Rise. Instead, the main effect of these Au currents was to pirate sediment into contour-following geostrophic flows along the North American margin and to deprive the deep basin and the Bermuda Rise of sediment transported down-slope. Consequently, post-Eocene sediments away from the margin are fine-grained muds. Deposition of these muds on the SW Bermuda Rise was controlled by northward flowing bottom currents. The modern Hatteras Abyssal Plain developed in the late Neogene as turbidites once again onlapped the SW Bermuda Rise. Today, these deposits extend farthest east in fracture zone valleys and in the swales between sediment waves. Northward flowing currents continue at present to affect sediment distribution patterns along the western edge of the Bermuda Rise.

  18. Subsurface sequence stratigraphy of Devonian carbonates, Canning basin, Western Australia

    SciTech Connect

    Southgate, P.N.; Jackson, J.; Kennard, J.M.; O'Brien, P.E.; Passmore, V.L.; Lindsay, J.F. ); Holmes, A.E.; Christie-Blick, N. )

    1991-03-01

    The Canning basin of Western Australia is best known for its Devonian reef complexes. in 1990 the Australian Bureau of Mineral Resources (BMR) began a sequence stratigraphic study of key parts of the basin. This work integrates industry seismic and well data with two deep-crustal, regional seismic lines acquired by BMR in 1988. Initial work on the Lennard Shelf and adjacent Fitzroy trough has established a new sequence stratigraphy. At the margin of the Fitzroy trough, the most prominent features on seismic sections are alternating wedge-shaped and tabular bodies up to 150 m and 50 m thick, respectively. Internal reflections in the wedge-shaped bodies show downlap toward the basin and onlap toward the platform margin. On strike lines these wedges exhibit complex lensoidal geometries. Drillcore indicates that the wedges comprise basement-derived conglomerates with a sandy calcareous matrix. Seismic and well data suggest five Late Devonian sequences. The wedges and oblique prograding units are thickest and most easily recognized in the upper three sequences (Late Frasnian-Famennian ). The underlying thinner sequences probably correlate with the classic back-stepping Frasnian reefs identified in outcrop by Playford. Recognition of lowstand deposits in the Devonian reef complexes represent a new hydrocarbon exploration play.

  19. Seismic stratigraphy a solution to deepwater drilling problems

    SciTech Connect

    Trabant, P.K.

    1993-09-27

    Serious drilling problems have been encountered by a number of deepwater operators in the Gulf of Mexico. The problem stems from the presence of geologically young unconsolidated sands that provide an excellent conduit for high-pressured interstitial fluids when pierced by the drillbit. Furthermore, the shallow nature of these formations is problematic in that casing is not always installed when the sands are perforated, and mud weights necessary to overcome formation pressures cannot be used as these may in turn fracture the sands and cause a rapid loss in circulation. A partial solution to the problem may be obtained by mapping the shallow seismic sequence stratigraphy, with emphasis on the depth, thickness, and types of sand-bearing facies or systems tracts, according to the model of Vail et al. This article reviews the application of the seismic stratigraphic concept as a basis for the interpretation of Pleistocene sedimentary sequences to depths of 3,000 ft on the continental slope, northern Gulf of Mexico.

  20. 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.

  1. Mediterranean tephra stratigraphy revisited: Results from a long terrestrial sequence on Lesvos Island, Greece

    NASA Astrophysics Data System (ADS)

    Margari, V.; Pyle, D. M.; Bryant, C.; Gibbard, P. L.

    2007-06-01

    A composite 40.2 m sediment sequence from Megali Limni, Lesvos Island, Greece, spanning the interval from 22 to 62 ka BP, contains six Pleistocene tephra layers, which can be identified on the basis of their major and trace elemental compositions. The youngest tephra deposit correlates with the 22 ka Y-2 marker, erupted during the Cape Riva eruption of Santorini. The second tephra originates from the Campanian area in Italy and corresponds to the Campanian Ignimbrite eruption (the 39 ka Y-5 marker). The next two layers are compositionally identical, and originate from Eastern islands of the Hellenic Arc; they could potentially correspond to the Upper and Lower Pumice eruptions of Nisyros or some other previously unidentified eruption from Yali. The fifth stratum corresponds to the Y-6 marker, which erupted during the Green Tuff eruption of the Pantelleria Island. The source of the last tephra layer is either the Yali-Nisyros complex or Central Anatolia; no specific corresponding eruption has yet been found. Long distal tephra sequences within terrestrial settings are rare in the eastern Mediterranean and the Megali Limni record contains the most complete sequence to date. Moreover, its age model, based on independent chronologies such as AMS and conventional radiocarbon dates and high-resolution pollen stratigraphy, provides new ages for these eruptions and places them within the context of the millennial-scale palaeoenvironmental variability of the last glacial period. Finally, the recognition of the Pantelleria tephra in this locality considerably extends the confirmed Northerly and Easterly distribution of this widespread and distinctive unit, while the existence of the Nisyros-Yali tephras on Lesvos refutes the current belief of limited tephra dispersal and small magnitude of these eruptions.

  2. Molecular and isotopic stratigraphy in an ombrotrophic mire for paleoclimate reconstruction

    NASA Astrophysics Data System (ADS)

    Xie, Shucheng; Nott, Chris J.; Avsejs, Luke A.; Maddy, Darrel; Chambers, Frank M.; Evershed, Richard P.

    2004-07-01

    A 40 cm deep Sphagnum-dominated peat monolith from Bolton Fell Moss in Northern England was systematically investigated by lipid molecular stratigraphy and compound-specific ? 13C and ?D analysis using gas chromatography (GC), GC-mass spectrometry (GC-MS), GC-combustion-isotope ratio-MS (GC-C-IRMS) and GC-thermal conversion-IRMS (GC-TC-IRMS) techniques. 210Pb dating showed the monolith accumulated during the last ca. 220 yr, a period encompassing the second part of Little Ice Age. While the distributions of lipids, including n-alkan-1-ols, n-alkan-2-ones, wax esters, sterols, n-alkanoic acids, ?,?-alkandioic acids and ?-hydroxy acids, display relatively minor changes with depth, the cooler climate event was recorded in the concentrations of n-alkanes and organic carbon, CPI values of n-alkanes and n-alkanoic acids, and the ratio of 5- n-alkylresorcinols/sterols. Superimposed on the fossil fuel effect, the relatively cooler climate event was also recorded by ? 13C values of individual hydrocarbons, especially the C 23n-alkane, a major compound in certain Sphagnum spp. The ?D values of the C 29 and C 33n-alkanes correlated mainly with plant composition and were relatively insensitive to climatic change. In contrast the C 23n-alkane displayed variation that correlated strongly with recorded temperature for the period represented by the monolith, agreeing with previously reported deuterium records in tree ring cellulose spanning the same period in Scotland, Germany and the USA, with more negative values occurring during the second part of Little Ice Age. These biomarker characteristics, including the compound-specific ? 13C and ?D records, provide a new set of proxies of climatic change, potentially independent of preserved macrofossils which will be of value in deeper sections of the bog where the documentary records of climate are unavailable and humification is well advanced.

  3. Stratigraphy, geochronology and evolution of the Mt. Melbourne volcanic field (North Victoria Land, Antarctica)

    NASA Astrophysics Data System (ADS)

    Giordano, Guido; Lucci, Federico; Phillips, David; Cozzupoli, Domenico; Runci, Valentina

    2012-11-01

    Mt. Melbourne (2,732 m a.s.l.) is a large quiescent stratovolcano located in Northern Victoria Land (Antarctica) and is one of a handful of volcanoes on the Antarctic plate with the potential for large-scale explosive eruptions. During the XVIII Italian Expedition in 2002-2003, the Mt. Melbourne volcanic succession was studied in terms of stratigraphy and sampled for 40Ar/39Ar age determinations and geochemistry. The early, Lower Pleistocene, volcanism was largely alkali basaltic to hawaiitic in composition and monogenetic in style, producing tens of small scoria cones and lava flows scattered over a wide area across the Transantarctic Mountains (Random Hills Period). During the Middle Pleistocene, volcanic activity focused to the area of the Mt. Melbourne stratovolcano, where several monogenetic centres show the transition from early sub-glacial/subaqueous conditions to emergent subaerial conditions (Shield Nunatak Period). The oldest exposed deposit associated with the early activity of the Mt. Melbourne stratovolcano (Mt. Melbourne Period) is a trachytic subaerial ignimbrite dated at 123.6 ± 6.0 ka, which reflects the establishment of a crustal magma chamber. Above the ignimbrite a succession of alkali basaltic, hawaiitic, and subordinate benmoreitic lavas and scoria cones is exposed, dated at 90.7 ± 19.0 ka. The Holocene deposits are exposed at the top of Mt. Melbourne, where the crater rim is composed of trachytic to rhyolitic pumice fall deposits, which are also extensively dispersed around the volcano, likely originated from Plinian-scale eruptions. The most recent explosive deposit proved difficult to date accurately because very low quantities of radiogenic 40Ar were released, resulting in imprecise plateau ages of 50 ± 70 and 35 ± 22 ka.

  4. Correlation of sea level falls interpreted from atoll stratigraphy with turbidites in adjacent basins

    SciTech Connect

    Lincoln, J.M. )

    1990-05-01

    Past sea levels can be derived from any atoll subsurface sediments deposited at or near sea level by determining the ages of deposition and correcting the present depths to the sediments for subsidence of the underlying edifice since the times of deposition. A sea level curve constructed by this method consists of discontinuous segments, each corresponding to a period of rising relative sea level and deposition of a discrete sedimentary package. Discontinuities in the sea level curve derived by this method correspond to relative sea level falls and stratigraphic hiatuses in the atoll subsurface. During intervals of relative sea level fall an atoll emerges to become a high limestone island. Sea level may fluctuate several times during a period of atoll emergence to become a high limestone island. Sea level may fluctuate several times during a period of atoll emergence without depositing sediments on top of the atoll. Furthermore, subaerial erosion may remove a substantial part of the depositional record of previous sea level fluctuations. For these reasons the authors must look to the adjacent basins to complement the incomplete record of sea level change recorded beneath atolls. During lowstands of sea level, faunas originally deposited near sea level on an atoll may be eroded and redeposited as turbidites in deep adjacent basins. Three such turbidites penetrated during deep-sea drilling at Sites 462 and 315 in the central Pacific correlate well with a late Tertiary sea level curve based on biostratigraphic ages and {sup 87}Sr/{sup 86}Sr chronostratigraphy for core from Enewetak Atoll in the northern Marshall Islands. Further drilling of the archipelagic aprons adjacent to atolls will improve the sea level history that may be inferred from atoll stratigraphy.

  5. The origin of 17O-depleted barite in Neoproterozoic cap carbonates in South China: A sedimentological perspective

    NASA Astrophysics Data System (ADS)

    Zhou, C.; Bao, H.; Yuan, X.

    2009-12-01

    Barite deposits are known from the Marinoan cap carbonate sequence in NW Africa, NW Canada, and many other localities worldwide, including South China, where the barite has been found to have distinct, non-mass-dependent depletion in 17O. It has been proposed that the negative anomalies most likely reflect an extremely high pCO2 atmosphere at the initiation of a global glacial meltdown. While widespread in occurrence and distinct in isotopic composition, the barite’s origin remains elusive. Field observation shows that the 17O-anomalous barite occurs only at one specific horizon/surface of the cap dolostone. A satisfying formation model based on geochemical data for the barite must corroborate evidence from geological, tectonic, sedimentological, and petrographic contexts. The Nantuo glacial deposit (Marinoan in age) and its cap carbonate occur widely on the Yangtze Block of South China. The thickness of the Nantuo tillites increases evidently from the shallow platform to basinal settings. The overlying cap carbonates, consisting mainly of dolostone, however, are generally around 3~4 meters thick and remain relatively stable on the Yangtze Block. There is a widespread occurrence of voids and cavities in the lower part of cap dolostones, in both shallow platform facies and transitional zones of the Yangtze Block. Barite deposits occur as fans or coatings on pre-existing surfaces or on walls of voids and fractures, probably marking a synchronous event affecting the entire Yangtze Block. Void and cavity fills generally start with aragonite crystal fans and barite fans, followed by opal (silica) or quartz, or calcite. The remaining space was finally filled with large blocky calcite crystals in shallower settings or pyrite crystals in deeper settings. We propose that the voids and cavities are the result of carbonate dissolution after the initial deposition of cap dolostones. The dissolution may imply a regional or even a global sedimentation hiatus during the deposition of Marinoan cap carbonates. One possibility is that the initially deposited cap carbonate may have been uplifted into a zone influenced by meteoric water due to glacioeustasy and lithospheric rebound as a result of a quick unloading of a massive continental ice cap on the Yangtze Block. Karstic dissolution has also been recognized in cap dolostones in NW Africa and NW Canada. While the voids and cavities in South China may be of a similar karst origin as those in NM Africa, sedimentological evidence, together with multiple sulfur and oxygen isotope data, suggests that the precipitation of the barite in South China may be related to an episode of free Ba2+ supply from deep, anoxic water, in association with a transgression (instead of an sea-level fall) after a karst dissolution. Thus, we suggest that SO42- was present in seawater prior to the beginning of Marinoan meltdown. It was the Ba2+ supply that limited the occurrence of barite to specific stratigraphic horizons in the cap carbonates. If the above inference is true, the 17O-depleted barite has recorded an atmospheric/hydrological condition well after the initial meltdown of the Marinoan "snowball" Earth.

  6. 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.

  7. Implications of sedimentological and hydrological processes on the distribution of radionuclides in a salt marsh near Sellafield, Cumbria

    SciTech Connect

    Carr, A.P.; Blackley, M.W.L.

    1985-01-01

    The report examines sedimentological and hydrological processes affecting a salt marsh in the Ravenglass estuary, which is situated south of the Sellafield nuclear-fuel-reprocessing plant. The results are discussed in the context of the distribution of low-level radioactive effluent at the site.

  8. The Absolute Dating Potential of Proximal-Distal Tephra Correlations in an Aegean Marine Stratigraphy (Core LC21).

    NASA Astrophysics Data System (ADS)

    Satow, Christopher; Lowe, John; Rohling, Eelco; Blockley, Simon; Menzies, Martin; Grant, Katharine; Smith, Vicki; Tomlinson, Emma

    2010-05-01

    Quaternary marine stratigraphies frequently suffer from poor absolute age control. Radiocarbon dating is intuitively the most appropriate technique for most marine stratigraphies, but its application is limited to the last 50ka or so by the decay rate of carbon. There are also uncertainties related to reservoir effects and the calibration of radiocarbon time to real time. However, precise dating and correlation of marine cores is essential to understand the timing and spatial relationships of the valuable environmental records they preserve. Here we demonstrate the potential of both visible and "invisible" micro-tephra layers to precisely date an important marine environmental record (Core LC21 from the Southern Aegean Sea). This is done by geochemically correlating the distal marine tephra layers to proximal volcanic deposits from Italy, Greece and Turkey. We use both Major Element (EPMA- Oxford Archaeology) and Trace Element (LA-ICP-MS, Royal Holloway Earth Sciences) analyses on individual tephra shards to determine the source of the tephra, and to make the correlations to explosive eruptive events. The most precise date (14C, 39Ar:40Ar or U-Th) from the event's proximal deposit is then imported into the equivalent distal tephra found in the marine core. Many of these distal "micro-tephras" were previously undetected by standard core logging techniques such as visual stratigraphy or scanning XRF. The extent and potential application of these tephras is now being realised. This study will provide the first direct (same core) and independent, absolute chronological markers for sapropels S3, S4 and S5, three major anoxic events found in the Eastern Mediterranean. In addition, the major and trace element geochemistry will be used to robustly correlate three marine cores spanning the Mediterranean. This work forms the Marine Tephrostratigraphy component (Work Package 5) of the UK Natural Environment Research Council (NERC) consortium project "RESET" (Response of Humans to Abrupt Environmental Transitions). In collaboration with a number of European research teams, the programme aims to construct a secure chronological framework for assessing the timing and effects of rapid environmental changes during the late Quaternary. See http://c14.arch.ox.ac.uk/reset/embed.php?File=index.html

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

    NASA Astrophysics Data System (ADS)

    Price, Katie; Leigh, David S.

    2006-08-01

    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 impact on stream channels. Basins were chosen for this study to represent the end members of the range of human impact in the area, with the forest cover of the basin used as a proxy for level of impact (ranging from about 70-100% regionally). Two pairs of lightly impacted (> 90% forest) and moderately impacted (70-80% forest) sub-basins of the upper Little Tennessee River were identified for comparison. Reach characteristics (e.g., slope, drainage area, and riparian cover) were aligned in each pair to isolate contrasting forest cover as the primary driver of any detected differences in morphology and sedimentology. A suite of standard cross-sectional and longitudinal data was collected for each reach for characterization of the sedimentology and morphology of the streams. Difference of means tests were conducted to identify parameters significantly differing between the lightly and moderately impacted streams in both pairs. Consistent and significant differences within both pairs were demonstrated in bankfull width/depth ratios, baseflow wetted width, and particle size on the stream bed both in the thalweg and throughout the channel bed. The moderately impacted streams are narrower than the lightly impacted streams, and the bed texture of the moderately impacted streams is finer than that of the lightly impacted streams. The moderately impacted streams contain a higher percentage of < 2 mm particles in riffles, a metric which has been shown to be highly correlated with biotic integrity in the southern Appalachian Highlands. Although this study has shown that human impact in these basins has resulted in an overall fining of bed texture, few conclusions can be drawn regarding the morphological response of the streams to the levels of impact affecting the upper Little Tennessee River basin. Levels of disturbance in the southern Blue Ridge Mountains may be below the thresholds of morphological sensitivity or have not persisted for sufficient duration for morphological response to be evident. Additionally, morphological adjustment to disturbance may be more effectively addressed system-wide, as opposed to at the reach scale.

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

    SciTech Connect

    Bolton, J.C. )

    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.

  11. A martian case study of segmenting images automatically for granulometry and sedimentology, Part 1: Algorithm

    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 planetary exploration, delineating individual grains in images via segmentation is a key path to sedimentological comparisons with the extensive terrestrial literature. Samples that contain a substantial fine grain component, common at Meridiani and Gusev at Mars, would involve prohibitive effort if attempted manually. Unavailability of physical samples also precludes standard terrestrial methods such as sieving. Furthermore, planetary scientists have been thwarted by the dearth of segmentation algorithms customized for planetary applications, including Mars, and often rely on sub-optimal solutions adapted from medical software. We address this with an original algorithm optimized to segment whole images from the Microscopic Imager of the Mars Exploration Rovers. While our code operates with minimal human guidance, its default parameters can be modified easily for different geologic settings and imagers on Earth and other planets, such as the Curiosity Rover’s Mars Hand Lens Instrument. We assess the algorithm’s robustness in a companion work.

  12. Sedimentology models from activity concentration measurements: application to the "Bay of Cadiz" Natural Park (SW Spain).

    PubMed

    Ligero, R A; Vidal, J; Meléndez, M J; Hamani, M; Casas-Ruiz, M

    2009-03-01

    A previous study on seabed sediments of the Bay of Cadiz (SW of Spain) enabled us to identify several relations between sedimentological variables and activity concentrations of environmental radionuclides such as (137)Cs, (226)Ra, (232)Th and (40)K. In this paper the study has been extended to a large neighbouring inter-tidal area in order to establish if the above mentioned models can be generalized. As a result we have determined that the measured activity concentrations are closely to the values predicted by the theoretical models (correlation coefficient range=0.85-0.93). Furthermore, the proposal model for granulometric facies as a function of activity concentrations of the abovementioned radionuclides provides for the sediments distribution a representation which agrees with the values of the tidal energy distribution obtained using numeric models calibrated with experimental data from current meters and water level recorders. PMID:19136180

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

    SciTech Connect

    Mehadi, Z. )

    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.

  14. The February 27, 2010 Chile Tsunami - Sedimentology of runup and backflow deposits at Isla Mocha

    NASA Astrophysics Data System (ADS)

    Bahlburg, H.; Spiske, M.

    2010-12-01

    On February 27, 2010, at 3:34 am local time, an earthquake with Mw 8.8 occurred off the town of Constitución in Central Chile and caused a major tsunami beween Valaparaiso (c. 33°S) and Tirua (c. 38°S). Maximum runup heights of up to 10 m were measured on coastal plains. The cliff coast at Tirua recorded a runup height between 30 m and 40 m. Considering past tsunami events, respective deposits may be the only observable evidence, even though their preservation potential is limited. To understand how tsunami deposits form and how they can be identified in the geological record, it is of paramount importance to undertake detailed studies in the wake of such events. Here we report initial field data of a sedimentological post-tsunami field survey undertaken in Central Chile between March 31 and April 18, 2010. At selected localities we measured detailed topographic profiles including runup heights and inundation distances, and recorded the thickness, distribution and sedimentological features of the respective tsunami deposits, as well as erosional features caused by the tsunami. We found the most instructive and complete sedimentological record of the February 27, 2010 tsunami at the northern tip of Isla Mocha, a small island off the Chilean coast at c. 28.15°S. Runup distances vary between 400 m and 600 m, the flow depth exceeded 3 m at ca. 100 m from the coast. Runup heights reached up to 21 m above sea level. In a rare sedimentological case, deposits of tsunami runup and backwash could be distinguished. The runup phase was mainly documented by fields of boulders extending c. 360 m inland. Boulders had maximum weights of 12 t. They were oriented with their long axis parallel to the coast and the wave front. Algal veneers and barnacles on the boulder faces give evidence of entrainment in intertidal water depths. The boulders are now embedded in mostly structureless coarse shelly sand. These sands were originally entrained during near shore supratidal erosion of coastal plain terraces by the tsunami and transported inland during runup. Flow structures indicate that the sands were then re-deposited during backwash. Downcurrent of terrace steps the tsunami backwash produced large erosional gullies. The backwash deposits occur either as widespread covers blanketing microtopography consisting of dark pre-tsunami soils, or as depositional fans which prograde seaward over soils free of a sediment cover. The coarse to very coarse shell debris is comprised of fragmented or entire mollusk and crab cascs. Some coarser deposits also contain significant amounts of Tertiary sandstone bedrock gravels in parts freshly eroded by the tsunami. The deposits are either massive or imbricated, the imbrication identifying them as a product of backflow currents. The deposit thickness is commonly c. 10 to 15 cm. Around large boulders backflow partitioning and associated erosion and deposition permitted the generation of 0.8 m deep scours and accumulation of up to 80 cm thick backflow sands. The depositional angles at the fan fronts vary between 27° and 36°. Backflow fan surfaces are characterized by channel and overbank regions and flow structures like current ripples. Clusters of bedrock pebbles and mollusk cascs are distributed irregularly over the fan surfaces.

  15. 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.

  16. 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.

  17. Lithofacies, depositional environments, and regional stratigraphy of the lower Eocene Ghazij Formation, Balochistan, Pakistan

    USGS Publications Warehouse

    Johnson, Edward A.; Warwick, P.D.; Roberts, S.B.; Khan, I.H.

    1999-01-01

    A regional stratigraphic investigation of one of the most important coal-bearing lithostratigraphic units in Pakistan, the report includes sedimentologic observations taken from outcrops and measured sections, information derived from petrographic and paleontologic analyses, depositional interpretations, and descriptions of regional trends.

  18. Biotic and Sedimentologic Signals Associated with Tempestite Deposition from Baffin Bay, Texas

    NASA Astrophysics Data System (ADS)

    Van Nieuwenhuise, D. S.

    2014-12-01

    In efforts to determine hurricane frequency prior to historical records, the often used model of counting presumed washover fans as coarse-grained hurricane deposits that interfinger with fine-grained, quiet, lagoon sediments may be oversimplified. The complexities of hurricane depositional events versus the usual dynamic sedimentological processes of barrier island complexes often makes it difficult to distinguish between expected and typical migrating coarse-grained facies from true hurricane deposits. To avoid some of this potential confusion and to better recognize the frequency of strong hurricane events, it is suggested that studies be focused further inland than the washover fans and that in addition to sedimentological indicators, they include biotic and chemical discriminators as well. These results are part of a broader study examining hurricane deposition along the Texas coast. The focus of this study is on slowly accumulating algal mats near Baffin Bay, Texas, that are punctuated by known hurricane deposits. This marginal lagoonal setting is more than 16 miles away from the Padre Island shorefront. Two cores were taken in 1974 that captured sediments from Hurricane Carla (1970) and Hurricane Beulah (1967). Algal mat depositional rates are on the order of 1.25 cm per year whereas the hurricane sediments are on the order of 45 cm per event. Sediments display flood and ebb surge stages for each event. Additional cores in other parts of the coast have similar sediment accumulation rates. In general, periods of relatively quiet deposition are dominated by Cyprideis ovata and Ammonia becarrii which can tolerate the conditions of these euryhaline and algal-floored ponds. In contrast, hurricane deposits show clear evidence of additional bay and shallow marine assemblages along with coarse-grained sediments, shell and shell fragments, and significant amounts of mud settling after the retreat of the storm surge.

  19. Sedimentological and geochemical characterization of the Cretaceous strata of Calabar Flank, southeastern Nigeria

    NASA Astrophysics Data System (ADS)

    Boboye, O. A.; Okon, E. E.

    2014-11-01

    An integrated sedimentological and geochemical evaluation has been carried out on the Cretaceous sediments of the Calabar Flank. This study is to characterize the provenance, depositional environments and hydrocarbon potentials. The techniques involved field descriptions, textural parameters, petrographic analysis and biostratigraphic studies using standard sedimentological methods. The geochemical studies involved the determination of major oxides and trace elements using Inductively Coupled Plasma-Mass Spectrometry (ICP-MS); Total Organic Carbon (TOC) and Rock Eval Pyrolysis. Results show that sandstone from Awi Formation have elongation ratio ranging from 0.4b to 0.9, oblate-prolate index and maximum sphericity index range from 9.6 to 9.7 and 0.5 to 0.9 respectively. The sandstone units are arkosic and mineralogically immature (MI = 3); ZTR indexes range from 54.6% to 82.5%, with tourmaline, zircon, staurolite, garnet, apatite, augite and rutile grains being angular-sub-angular. This suggests nearness to source, and that Awi Formation was deposited in a fluvial environment. The limestone deposit of Mfamosing Formation is predominantly bioclastic consisting of algal stromatolites, oolitic and pelloidal grainstones/packstones with high carbonate content. The dark grey fissile shales of Nkporo and Ekenkpon Formations indicate deposition in quiet oxic and/or anoxic conditions. Average TOC suggests good source rocks. Predominance of Type III kerogen, Tmax and hydrocarbon source potential of Mfamosing, Ekenkpon, New Netim Marl and Nkporo Formations suggest marginal mature to mature source rocks deposited in shallow continental to open marine setting that some gas may have been generated. The sediments are derived from passive continental margin in plutonic humid palaeoclimatic setting of continental block province.

  20. Evidence for a dynamic 'Snowball Earth' in Neoproterozoic Svalbard through magnetic, structural and sedimentological analysis

    NASA Astrophysics Data System (ADS)

    Fleming, Edward; Benn, Doug; Hambrey, Mike; Stevenson, Carl; Petronis, Mike; Fairchild, Ian

    2013-04-01

    In recent years, our understanding of glacial sedimentation has improved through observations of current glacial environments,aided by the development of new techniques. Anisotropy of magnetic susceptibility (AMS) has been shown to provide insights into till formation and deformation. This technique, along with field, structural and sedimentological analysis has been applied to the Neoproterozoic Wilsonbreen Formation in Svalbard. Fabrics within sediments normally result from processes acting on the sediment either during or shortly after deposition. Fabrics can therefore be used to provide information on genetic environment, palaeo-ice flow directions in subglacially generated or deformed sediments and palaeo-slope in mass flow units. Primary fabrics (not subsequent tectonic fabrics) are confirmed through comparison of AMS with pebble. Both sets of data reveal almost identical fabric orientations suggesting that AMS does indeed record primary fabrics and that these fabrics indicate flow initially north-south but switching to northwest - southeast upwards in the succession. Through analysis of AMS, sedimentology and structures at both macro and microscopic scales, a range of glacial-depositional environments (subglacial, glaciomarine and proglacial) as well as non-glacial (terrestrial, lacustrine and fluvial) are recognised, which are highly variable both spatially and temporally. Glacial cycles are observed, some which appear analogous to processes occurring in modern glacial environments. The range of facies seen and the possible cyclicity in some of the deposition reveal that in contrast to a single advance meltback cycle, the Wilsonbreen is composed of a series of oscillations where glaciers advanced and retreated. This variability could possible provide challenges to the classic 'Snowball Earth' model.

  1. Sedimentological, Geochemical and Magnetic Properties of Colima Beach Sands, Mexico - Influence of Climate and Coastal Processes

    NASA Astrophysics Data System (ADS)

    Sanchez-Guillen, L.; Carranza-Edwards, A.; Perez-Cruz, L. L.; Fucugauchi, J. U.

    2011-12-01

    Studies of sediments on beaches contribute to understanding of sedimentological processes and source, transport and dynamics of sandy coastlines. Results of a geological and geophysical study of sandy beaches on the coast of Colima, Mexico employing sedimentological, geochemical and magnetic methods are presented and used to investigate on climate and coastal processes. Colima is part of the active subduction margin in southern Mexico. We studied thirteen different beaches distributed along the coast. The coastal transect investigated crosses three river drainage basins of the Cihuatlan, Armeria and Coahuayana rivers. Along the coastline there are abundant medium to fine sands moderately sorted to well-sorted. Towards the southeast, sediments are fine-grained, darker colors and better classified compared with sediments at the northwest sector. Towards the southeast there is greater abundance of heavy minerals of volcanic origin with high-rank, higher values of natural remnant magnetization and high magnetic susceptibilities associated with the abundance of iron and titanium oxides. The magnetic hysteresis loops are characterized by saturation in low fields, suggesting titanomagnetites and magnetite as major minerals. In the plot of hysteresis ratio parameters, samples plot in the pseudo-single domain field, suggesting mixtures of single and multiple domain states. Silica is the main constituent and shows a trend to decrease towards the southeast. Results show that sediments are primarly derived from the volcanic and plutonic rocks in the margin. There is an attenuation of one order of magnitude in magnetic susceptibility in magnetic concentrates. It is inferred that there is more wave action on sands of beaches at the southeastern sector generated primarily by waves, wind and tides in volcanic rocks that outcrop in the region. Backshore area in Santiago Bay is identified as an area of protected beach off the coast where the processes of weathering of the sands seem to be limited by this natural barrier. Effects along the Pacific Ocean coast of ENSO events and ITCZ migration on precipitation and erosion are discussed.

  2. 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.

  3. Observations of fine scale stratigraphy using a digital imaging system

    NASA Astrophysics Data System (ADS)

    Gallagher, E. L.; Wadman, H. M.; Reniers, A.; Köktąs, M.; McNinch, J.

    2014-12-01

    Although beaches appear to consist of uniform sands, upon closer inspection, a broad range of sizes can exist on a beach. Recent studies have shown that not only does grain size vary on the surface of beaches, it is also correlated with the morphology and the grain size surface patterns change as the morphology changes. XBeach is now being used, with a multi grain size module, to predict transport of different grain sizes, their sorting and separation and to determine the importance of grain size variation on the beach. However, only surface grain sizes have been measured and compared with model results. In March and April of 2014, a pilot experiment was performed at the Army Corps of Engineers Field Research Facility. During the experiment, 36 stratigraphic cores were collected along a cross-shore profile from the dune to the lowest extent of the swash. These cores are being sampled with a digital imaging system (DIS) to estimate grain size. The DIS can streamline the process of collecting grain size information. Errors associated with the technique and with coring (and compaction) will be discussed. Grain size stratigraphy in the beach and its variations with location and in time are being examined at this time. These data will be used, together with observations from a large trench (see related abstract by Wadman et al.), to interpret layering in the beach owing to storms, rising and falling tides and wave-by-wave transport mechanism. In addition, the data will be used to drive model predictions to assess the importance of grain size variation, differential grain transport and layering on the morphodynamics of beaches (see related abstract by Reniers et al.).

  4. Bacterial community structure in aquifers corresponds to stratigraphy

    NASA Astrophysics Data System (ADS)

    Beyer, Andrea; Möller, Silke; Neumann, Stefan; Burow, Katja; Gutmann, Falko; Lindner, Julia; Müsse, Steffen; Kothe, Erika; Büchel, Georg

    2014-05-01

    So far, groundwater microbiology with respect to different host rocks has not been well described in the literature. However, factors influencing the communities would be of interest to provide a tool for mapping groundwater paths. The Thuringian Basin (Germany) studied here, contains formations of the Permian (Zechstein) and also Triassic period of Buntsandstein, Muschelkalk and Keuper, all of which can be found to crop out at the surface in different regions. We analyzed the bacterial community of nine natural springs and sixteen groundwater wells of the respective rock formations as well as core material from the Zechstein salts. For that we sampled in a mine 3 differnet salt rock samples (carnallitite, halite and sylvinitite). To validate the different approaches, similar rock formations were compared and a consistent microbial community for Buntsandstein could be verified. Similary, for Zechstein, the presence of halophiles was seen with cultivation, isolation directly from the rock material and also in groundwater with DNA-dependent approaches. A higher overlap between sandstone- and limestone-derived communities was visible as if compared to the salt formations. Principal component analysis confirmed formation specific patterns for Muschelkalk, Buntsandstein and Zechstein for the bacterial taxa present, with some overlaps. Bacilli and Gammaproteobacteria were the major groups, with the genera Pseudomonas, Marinomonas, Bacillus, Marinobacter and Pseudoalteromonas representing the communities. The bacteria are well adapted to their respective environment with survival strategies including a wide range of salinity which makes them suitable as tracers for fluid movement below the ground. The results indicate the usefulness and robustness of the approach taken here to investigate aquifer community structures in dependence of the stratigraphy of the groundwater reservoir.

  5. Late Quaternary stratigraphy of the eastern Gulf of Maine

    SciTech Connect

    Bacchus, T.S. . Oceanography Dept.); Belknap, D.F. . Geology Dept.)

    1993-03-01

    Five distinct seismic facies describe the glacial, glacial-marine and postglacial sediments in the eastern Gulf of Maine. Regional cross-sections clearly document differences in the glacial-marine and postglacial stratigraphy between basins south of Truxton Swell, and Jordan basin to its north. Till occurs throughout the region as a thin veneer within basins, but thickens significantly over the ridges and swells separating basins. The ubiquitous presence of till suggests grounded ice occupied this area some time in the recent past. Ice-proximal glacial-marine (PGM) facies sediments of varying thickness mantle the entire area, occurring as a draped unit over pre-existing topography. Transitional glacial-marine (TGM) facies also occur as a draped unit, but they show onlap onto basin margins. Sediments of the TGM facies are restricted to areas south of Truxton Swell. Ice-distal glacial-marine (DGM) facies sediments also mantle the entire area, but they occur primarily as a ponded, infilling unit. The nature and distribution of these glacial-marine facies within the eastern Gulf of Maine documents changes in the environment of deposition during deglaciation. In the authors model PGM facies sediments are considered to represent settling through the water column of coarse material from the base of an ice shelf. TGM facies sediments indicate retreat of this ice margin coupled with calving of large icebergs with significant amounts of coarse debris, DGM facies sediments indicate further retreat of the ice margin and a lessening of the influence of icebergs. Stepwise ice-margin retreat from south to north through a series of grounding lines and associated pinning points is evident by these time transgressive sedimentary facies that can be correlated across the region.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. Stratigraphy and chronology of the Galeras volcanic complex, Colombia

    NASA Astrophysics Data System (ADS)

    Calvache V, Marta Lucia; Cortés J, Gloria Patricia; Williams, Stanley N.

    1997-05-01

    An understanding of the evolution of the Galeras volcanic complex (GVC) is critical for assessing and refining hazards and eruption forecasting for the current reactivation of Galeras volcano. Detailed field geology and dating by 14C and 40Ar- 39Ar methods help establish a comprehensive stratigraphie framework, defining six different stages in the evolution of the Galeras volcanic complex. The two oldest stages, Cariaco and Pamba, represent the westernmost activity of the complex. The next stage, Coba Negra, had a caldera-forming eruption that occurred about 560 ka ago. The Coba Negra edifice, which was partially destroyed by this eruption, had a total volume of about 70 km 3. The volume of pyroclastic flow deposits related to caldera formation is about 16 km 3. The caldera, which has been partially destroyed, was about 5 km in diameter. The next constructional stage, Jenoy, had an edifice volume of about 64 km 3. The caldera-forming event that ended this stage took place sometime between 150 and 40 ka ago. Deposits from these eruptions are found in the northeastern and southeastern slopes of the complex and have a volume of approximately 2 km 3. The center of the Jenoy caldera was located east-southeast from the center of the previous Coba Negra caldera, probably along the rim of the former caldera. The diameter of the Jenoy caldera was about 4 km. A summit collapse, probably not eruption-related, occurred between 12 and 5 ka ago, during the Urcunina stage. Hydrothermally altered rocks which are found in the scar of the collapse suggest that it may have been related to instabilities created by the circulation of hydrothermal fluids in addition to a very steep slope in the western part of the edifice. The approximately 4 km 3 missing from the top of the volcano agrees very well with approximately 3 km 3 of avalanche deposits found near the town of Consaca 12 km west of the present-day summit. The system at the GVC has produced large, hazardous eruptions, although in the most recent years (less than 5 ka) the eruptions have been of small scale.

  11. Sedimentology and magnetostratigraphy of the Tierekesazi Cenozoic section in the foreland region of south West Tian Shan in Western China

    NASA Astrophysics Data System (ADS)

    Chen, Xinwei; Chen, Hanlin; Cheng, Xiaogan; Shen, Zhongyue; Lin, Xiubin

    2015-07-01

    The geology of Tian Shan provides an excellent example for understanding the intracontinental orogeny in the context of Indian-Eurasian convergence. Previous studies leave much space in basinfill deposition process to be assessed in the regions west to the Talas-Fergana fault (TFF). We improve the understanding by conducting new investigations on sedimentology and magnetostratigraphy in the Tierekesazi section of the foreland region of south West Tian Shan. Four lithofacies have been identified, (i) marine lithofacies from the Aertashi to Bashibulake Formations, (ii) lacustrine to fluvial (plain) lithofacies from the Keziluoyi to the middle Pakabulake Formations, (iii) alluvial sand-gravel sheet lithofacies in the upper Pakabulake Formation, and (iv) conglomerate lithofacies from the Atushi to Xiyu Formations. Magnetostratigraphic analysis, accompanied with biostratigraphic correlation, indicates that four lithofacies cover age intervals of ca. 65 Ma to 34 Ma, ca. 22.1 Ma to 12 Ma, 12 Ma to 5.2 Ma, and 5.2 Ma to approximately present (?), with the sediment accumulation rates increasing from ca. 2.4/3.3-3.5 (compacted/decompacted) cm/ka in the lithofacies (i), to 12.3/16-17 cm/ka in the lithofacies (ii), to 16.3/19.5-20.6 cm/ka in the lithofacies (iii), and finally to > 22.8/> 22.8 cm/ka in the lithofacies (iv). These results suggest three episodes of sedimentary events. Combined with previous results, these episodes of sedimentary events are attributed to tectonic activities that are widespread along south Tian Shan. We speculate that the Oligo-Miocene boundary event more directly and likely marks the initial underthrusting of the Tarim block beneath the south Tian Shan. The mid-Miocene and Mio-Pliocene boundary events, although approximately synchronous between the regions east and west to the TFF, have different structural expressions in the two regions. Such difference is proposed to cause the dextral slipping of the TFF, and more fundamentally, likely be driven by the northward indentation of the Pamir at this time.

  12. Holocene erosion, sedimentation, and stratigraphy at Raven Fork, Southern Blue Ridge Mountains, USA

    NASA Astrophysics Data System (ADS)

    Leigh, David S.; Webb, Paul A.

    2006-08-01

    Holocene colluvial and alluvial stratigraphy and a radiocarbon chronology are presented for the valley of the lower three kilometers of Raven Fork, a mountain stream draining 194 km 2 of high relief (1.3 km) terrain of the Southern Blue Ridge Mountains in western North Carolina, USA, which is in a region that lacks good chronological data. Lower hillslopes, alluvial/colluvial fans, alluvial bottomlands (first terrace and floodplain), and the modern stream channel are landforms described with respect to soils, stratigraphy, and sedimentary structures. Standard methods for subsurface investigations (core holes, excavation units, exposures) are used in conjunction with extensive archeological excavations and cultural chronologies. Radiocarbon ages from each landform are used to calculate long-term-average rates of sedimentation. Results indicate that the first half of the Holocene experienced somewhat more rapid rates of hillslope sedimentation (0.3 to 1.1 mm/yr) than the last half of the Holocene (0.1-0.2 mm/yr) on footslopes, toeslopes, and alluvial/colluvial fans prior to historic time. We suggest that these subtle differences in the rates of sedimentation were driven by changes in global paleoclimate that favored a high frequency of heavy rainfall, including tropical storms and/or severe thunderstorms and more (and possibly larger) floods during the first half of the Holocene. Prehistoric rates of vertical accretion on the first terrace (T1) ranged from 0.1 to 0.8 mm/yr between about 10,000 and 3000 calendar years ago, and incision below T1 formed the late Holocene floodplain beginning at about 6000 years ago. We suggest that this incision is linked to a reduction in the supply of sediment and a reduction in the magnitude of floods. Historical rates of sedimentation on all parts of the depositional landscape (2.0-2.7 mm/yr on hillslopes and fans and 5.8-6.5 mm/yr on floodplains) were about an order of magnitude greater than prehistoric rates. We attribute these rates to human impacts, such as timber harvest and land clearing, which caused accelerated erosion. We attribute the abundance of fine-grained sediment in streams of the Southern Blue Ridge province, which is atypical in many mountain streams around the world, to the regionally widespread mantle of saprolite as a source of sediment to the fluvial system. Holocene sedimentation on all depositional landforms in the valley led to sedimentary burial of archeological materials, which highlights the need to consider site burial on lower hillslopes and terraces for evaluation of the cultural resources in the Southern Blue Ridge Mountains. These findings show that the entrenched condition of the Raven Fork channel was inherited from the middle Holocene and can be considered a "natural" state for this mountain stream, casting doubt on the negative connotation that is often assigned to entrenched channels.

  13. Neogene stratigraphy and Andean geodynamics of southern Ecuador

    NASA Astrophysics Data System (ADS)

    Hungerbühler, Dominik; Steinmann, Michael; Winkler, Wilfried; Seward, Diane; Egüez, Arturo; Peterson, Dawn E.; Helg, Urs; Hammer, Cliff

    2002-01-01

    The present paper reviews Tertiary volcanic and sedimentary formations in the Inter-Andean region of southern Ecuador (between 2°S and 4°20'S) in order to develop a geodynamic model of the region. The formations occur in the southern shallow prolongation of the Inter-Andean Valley between the Cordillera Real to the east, and the Cordillera Occidental and Amotape-Tahu?´n Provinces to the west. One hundred fifty zircon fission-track analyses has established a detailed chronostratigraphy for the sedimentary and volcanic formations and several small intrusions. The Paleogene to early Miocene formations are dominated by intermediate and acidic volcanic and pyroclastic rocks. In addition, relics of Eocene continental sedimentary series have been identified. The Neogene sedimentary series lie unconformably on deformed and eroded metamorphic, sedimentary and volcanic formations. They were deposited in two stages, which are separated by a major unconformity dated at ?10-9 Ma. (1) During the middle and early late Miocene (?15-10 Ma) marginal marine deltaic, lagoonal, lacustrine and fluvial environments prevailed, which we group under the heading "Pacific Coastal sequences". They presumably covered a greater surface area in southern Ecuador than their present occurrence in small topographic depressions. We suggest that they were deposited in the shallow marine Cuenca and Loja Embayments. Deposition in a marginal marine environment is also supported by the occurrence of brackish water ostracods and other fauna. (2) Above the regional (angular) unconformity, the coastal facies are overlain by late Miocene (?9-5 Ma) continental alluvial fan and fluvial facies which are in turn covered by mainly airborne volcanic material. They represent the "Intermontane sequences" of the basins of Cuenca, Girón-Santa Isabel, Nabón, Loja and Malacatos-Vilcabamba. Sedimentologic and stratigraphic results are used to discuss the tectonic setting of Neogene sedimentation in the forearc and arc domain of the Ecuadorian subduction system. During the Pacific Coastal stage, northward displacement of the coastal forearc block along the Calacali-Pallatanga fault zone has driven crustal collapse in the Inter-Andean region. As a result, extensional subsidence drove the eastward ingression of shallow seas into the Cuenca and Loja Embayments from the Manab?´ and Progreso Basins to the west. Tectonic inversion in the forearc area during the early late Miocene (at ?9.5 Ma) reflects the initiation of W-E oriented compression and uplift in the Inter-Andean region and the establishment of smaller Intermontane stage basins, which host the continental sequences. Coeval topographic rise of the Cordillera Occidental is indicated by the onset of clastic input from the west. The small Intermontane Basin of Nabón (?8.5-7.9 Ma) formed during the period of maximum compression. The present data prove that the Neogene Andean forearc and arc area in southern Ecuador was a site of important but variable tectonic activity, which was presumably driven by the collision and coupling of the Carnegie Ridge with the Ecuadorian margin since ?15-9 Ma.

  14. Sedimentology and Rock Magnetism of Bailey River Peat Cores, Sudbury Area: Preliminary Results

    NASA Astrophysics Data System (ADS)

    Yurtseven, A.; Cioppa, M. T.; Dean, K.

    2009-05-01

    Magnetic measurements on peat can reveal atmospheric anthropogenic contamination. Two cores were collected from a marsh surrounding the Bailey River, 10 km north of Sudbury, Ontario, using a Russian peat borer. The BR1 core (1.4 m) was collected right at the river's edge, whereas the BR2 core (2.5 m) was collected about 50 m away from the river's edge, close to the edge of the marsh and near the forest. Significant sedimentological variation between the two cores was observed: core BR1 had several centimeter to decimeter scale fine to coarse grey sand layers at 0.14 m, 0.46 m and 0.87 m between thicker organic-rich (peat) zones, whereas core BR2 had only one 5 cm sand-rich layer at 0.94 m within the organic-rich material. The cores were subsampled at 2.5 cm intervals for laboratory magnetic analysis. Volume susceptibility was measured using a Bartington MS2B meter, and mass-specific susceptibility was then calculated. In core BR1, the sand layers had relatively higher susceptibility (13 x 10-8 m3/kg) , while the organic rich layers had very low susceptibility (0 - 2 x 10-8 m3/kg). In core BR2, which had little sand, the susceptibility variation was dominated by higher values near-surface (10 x 10-8 m3/kg), and very low susceptibility (0.3 x 10-8 m3/kg) below 0.3 m depth. Since the lithology in this core did not vary substantially, susceptibility variations may be controlled by anthropogenic deposition in the near-surface during the peak mining and smelting decades. These preliminary results suggest that any anthropogenic signal in core BR1 appears to be masked by the sedimentological variation. On pilot results from eight samples in core BR1, saturation isothermal remanence acquisition showed 95% saturation by 200 mT, and the S-ratios (0.3T/0.9T) were above 0.93, suggesting that magnetite is the major magnetization carrier. In core BR2, six out of eight samples showed similar results; however, two samples had slightly more higher coercivity minerals (90% saturation by 200 mT, and S-ratios between 0.9 and 0.93). More detailed rock magnetic property measurements could reveal variations grain size and magnetic mineralogy that could reflect climatic or watershed changes.

  15. 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.

  16. Sedimentological and radiochemical characteristics of marsh deposits from Assateague Island and the adjacent vicinity, Maryland and Virginia, following Hurricane Sandy

    USGS Publications Warehouse

    Smith, Christopher G.; Marot, Marci E.; Ellis, Alisha M.; Wheaton, Cathryn J.; Bernier, Julie C.; Adams, C. Scott

    2015-01-01

    This report serves as an archive for sedimentological and radiochemical data derived from the surface sediments and marsh cores collected March 26–April 4, 2014. Select surficial data are available for the additional sampling periods October 21–30, 2014. Downloadable data are available as Excel spreadsheets and as JPEG files. Additional files include: Field documentation, x-radiographs, photographs, detailed results of sediment grain size analyses, and formal Federal Geographic Data Committee metadata (data downloads).

  17. 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.

    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.

  18. 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.

  19. Stratigraphy and paleontology of Mid-Cretaceous rocks in Minnesota and contiguous areas

    USGS Publications Warehouse

    Cobban, William Aubrey; Merewether, E.A.

    1983-01-01

    PART A: Molluscan fossils are locally abundant at outcrops of Upper Cretaceous rocks in eastern North and South Dakota, northeastern Nebraska, northwestern Iowa, and western and northern Minnesota. Other Cretaceous mollusks have been found in the glacial deposits in Minnesota, Iowa, and Illinois. The oldest well dated marine mollusks are of earliest late Cenomanian age and occur in northwestern Iowa. Mollusks of marginal marine and nonmarine environments in northwestern Iowa and south-central Minnesota are probably of slightly younger late Cenomanian age. The youngest mollusks treated in this report are bivalves of Santonian age found in the Niobrara Formation in eastern North and South Dakota. The collections indicate the presence or former presence of the following ammonite zones in the northeastern part of the Western Interior seaway: Santonian: Scaphites depressus-Clioscaphites choteauensis Coniacian: Scaphites uentrocosus; Scaphites preuentricosus Turonian: Scaphites coruensis; Scaphites whitfieldi; Prionocyclus hyatti; Subprionocyclus percarinatus; Collignoniceras woollgari; Watinoceras coloradoense Cenomanian: Dunueganoceras albertense; Dunueganoceras pondi PART B: Sedimentary rocks of early Late Cretaceous age occur in the eastern parts of North Dakota, South Dakota, and Nebraska, and in Minnesota and western Iowa. They are generally included in, from oldest to youngest, the Dakota Formation, Graneros Shale, Greenhorn Formation, Carlile Shale, and Niobrara Formation. However, in eastern North Dakota, they are also assigned to, in ascending order, the Belle Fourche Shale, Greenhorn Formation, Carlile Shale, and Niobrara Formation. The Graneros Shale and laterally equivalent strata in the Belle Fourche Shale grade eastward into the Coleraine Formation of northeastern Minnesota and probably into the Windrow Formation of southeastern Minnesota. Cretaceous beds locally overlie rocks of Precambrian, Paleozoic, and Jurassic ages, and they are generally overlain by glacial drift and alluvium of Quaternary age. In Minnesota and adjoining areas, formations of mid-Cretaceous age commonly overlap the dissected surface of Precambrian rocks. The thickness of the lower Upper Cretaceous sequence ranges from about 223 m in eastern North Dakota and about 200 m in northeastern Nebraska to a featheredge in Minnesota and Iowa. These lower Upper Cretaceous formations are composed mainly of shale, siltstone, sandstone, and limestone units of marine and nonmarine origin and were deposited near the eastern shore of a transgressing and regressing epicontinental sea in Cenomanian Turonian Coniacian. and Santonian time. During the late Cenoanian, the strandline was in Minnesota and was oriented generally northnortheast. Interpretations of the depositional environments of the strata and of fossils from outcrops and from clasts in glacial drift indicate that the Cretaceous seaway extended from this region northeastward across Canada to Greenland in the Turonian Coniacian, and Santonian. The Cretaceous formations are deformed into broad, shallow synclines in eastern North and South Dakota and in northeastern Nebraska. A west-trending anticline, the Sioux uplift, separates the synclines in southeastern South Dakota. Sparse evidence of minor faulting in the formations exists in northeastern South Dakota, along the strike of a major southwest-trending zone of tectonism in the Precambrian basement rocks. The structural relief in the region, on the top of the Greenhorn Formation, is at least 250 m between eastern North Dakota and northeastern Minnesota, and at least 200 m between northeastern Nebraska and northwestern Iowa. A comparison of the Cretaceous stratigraphy of the Minnesota region and of areas in Wyoming indicates that some marine transgressions and regressions were synchronous in the two regions. The transgression during Greenhorn time, the regression during early Carlile time, and the transgression dur

  20. 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.

  1. 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.

  2. An overview of the Cretaceous stratigraphy and facies development of the Yazd Block, western Central Iran

    NASA Astrophysics Data System (ADS)

    Wilmsen, Markus; Fürsich, Franz Theodor; Majidifard, Mahmoud Reza

    2015-04-01

    The Cretaceous successions of the Yazd Block, the western of three structural blocks of the Central-East Iranian Microcontinent (CEIM), have been studied using an integrated approach of litho-, bio- and sequence stratigraphy associated with litho-, bio- and microfacies analyses. The Cretaceous System of that area is in excess of 5 km thick and a generalized relative sea-level curve can be inferred from the facies and thickness development. This curve can be subdivided into two transgressive-regressive megacycles (TRMs), separated by a major tectonic unconformity in the Upper Turonian. TRM 1 comprises the Early Cretaceous to Middle Turonian, TRM 2 the Coniacian to Maastrichtian. TRM 1 starts with up to 1500-m-thick conglomerates and sandstones covering Palaeozoic-Triassic basement rocks, metasediments, or Upper Jurassic-lowermost Cretaceous granites. The basal tectonic unconformity, related to the Late Cimmerian event (Jurassic-Cretaceous boundary interval), shows a pronounced palaeo-relief that is levelled by the basal siliciclastic formations. Sparse biostratigraphic data from calcareous intercalations in the upper part of these strata indicate a Hauterivian to Barremian age. The Aptian facies development is marked by the onlap of thick-bedded, micritic carbonates with abundant orbitolinid foraminifera and rudists representing a large-scale shallow-marine carbonate platform system that fringed the Yazd Block in the north and west. These platforms are up to 1000 m thick and drowned during the middle to Late Aptian, followed by up to 1500-m-thick basinal marly sediments of Late Aptian to mid-Late Albian ages, representing the maximum relative sea-level during TRM 1. During the latest Albian-Middle Turonian, a gradual shallowing is indicated by progradation of shallow-water skeletal limestones separated by marl tongues, representing a carbonate ramp system. Strata of TRM 2 overlie older units along a regional angular unconformity and indicate tectonic stability and lowered subsidence rates as shown by widespread uniform Coniacian-Maastrichtian facies and thickness development. Above a thick basal conglomerate, the Coniacian-Campanian facies is characterized by shallow-water limestones of a large-scale epeiric platform. Relative sea-level peaked in the Late Campanian, followed by Maastrichtian infilling. The Cretaceous succession is truncated along a tectonic unconformity at the base of the Palaeocene. The major tectonic unconformities recognized at the base of the succession (Late Cimmerian Event), in the Late Turonian, and in the Cretaceous-Palaeogene boundary interval are evidence of significant tectonic activity of the Yazd Block. Their formation is probably related to plate tectonic processes in response to the opening and closure of ocean basins surrounding the CEIM.

  3. 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.

  4. 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.

  5. After a century-Revised Paleogene coal stratigraphy, correlation, and deposition, Powder River Basin, Wyoming and Montana

    USGS Publications Warehouse

    Flores, Romeo M.; Spear, Brianne D.; Kinney, Scott A.; Purchase, Peter A.; Gallagher, Craig M.

    2010-01-01

    The stratigraphy, correlation, mapping, and depositional history of coal-bearing strata in the Paleogene Fort Union and Wasatch Formations in the Powder River Basin were mainly based on measurement and description of outcrops during the early 20th century. Subsequently, the quality and quantity of data improved with (1) exploration and development of oil, gas, and coal during the middle 20th century and (2) the onset of coalbed methane (CBM) development during the late 20th and early 21st centuries that resulted in the drilling of more than 26,000 closely spaced wells with accompanying geophysical logs. The closeness of the data control points, which average 0.5 mi (805 m) apart, made for better accuracy in the subsurface delineation and correlation of coal beds that greatly facilitated the construction of regional stratigraphic cross sections and the assessment of resources. The drillhole data show that coal beds previously mapped as merged coal zones, such as the Wyodak coal zone in the Wyoming part of the Powder River Basin, gradually thinned into several discontinuous beds and sequentially split into as many as 7 hierarchical orders westward and northward. The thinning and splitting of coal beds in these directions were accompanied by as much as a ten-fold increase in the thicknesses of sandstone-dominated intervals within the Wyodak coal zone. This probably resulted from thrust loading by the eastern front of the Bighorn uplift accompanied by vertical displacement along lineaments that caused subsidence of the western axial part of the Powder River Basin during Laramide deformation in Late Cretaceous and early Tertiary time. Accommodation space was thereby created for synsedimentary alluvial infilling that controlled thickening, thinning, splitting, pinching out, and areal distribution of coal beds. Equally important was differential subsidence between this main accommodation space and adjoining areas, which influenced the overlapping, for example, of the Dietz coal zone in Montana, over the Wyodak coal zone in Wyoming. Correlation in a circular track of the Wyodak coal zone in the southern part of the basin also demonstrates overlapping with lower coal zones. Recognition of this stratigraphic relationship has led to revision of the correlations and nomenclature of coal beds because of inconsistency within these zones as well as those below and above them, which have long been subjects of controversy. Also, it significantly changes the traditional coal bed-to-bed correlations, and estimates of coal and coalbed methane resources of these coal zones due to thinning and pinching out of beds. More notably, thickness isopach, orientation, and distribution of the merged Wyodak coal bodies in the south-southeast part of the basin suggest that differential movement of lineament zones active during the Cretaceous was not a major influence on coal accumulation during the Paleocene. Improved knowledge of alluvial depositional environments as influenced by external and internal paleotectonic conditions within the Powder River Basin permits more accurate correlation, mapping, and resource estimation of the Fort Union and Wasatch coal beds. The result is a better understanding of the sedimentology of the basin infill deposits in relation to peat bog accumulation.

  6. 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.

  7. Bathymetry and seismic stratigraphy of East Greenland fjords and sounds

    NASA Astrophysics Data System (ADS)

    Forwick, Matthias; Sverre Laberg, Jan; Husum, Katrine; Olsen, Ingrid L.

    2014-05-01

    Swath bathymetry and high-resolution penetration echo sounder (chirp) data from fjords and sounds between Kong Oscars Fjord (~72°30') and Bredefjord (~75°30'), East Greenland, reveal a variety of sedimentary processes related to glacial activity and mass wasting, as well as evidence of tectonic activity. The large-scale bathymetry of most fjords and sounds is characterized by sills that occasionally are shallower than 30 m, and basins reaching maximum water depths of more than 760 m. Multiple "steps", some more than 250 meters high and with gradients exceeding 60° (e.g. in Bredefjord) are most probably related to vertical movements along tectonic lineaments. The basin floors are typically smooth suggesting sedimentation predominantly from suspension settling. However, an approx. 100 m wide and 5 m deep channel in Kempefjord provides evidence of gravity-flow erosion sub-parallel to the fjord axis. Multiple sediment lobes along the fjord sides reflect repeated mass wasting. Relatively straight linear features oriented parallel to the fjord axes are interpreted to be glacial lineations that were formed beneath fast-flowing ice draining the Greenland Ice Sheet. They occur rarely on shallower plateaus and are often overlain by transverse ridges. In Youngsund, such ridges are typically 1-2 m high, 50 m wide and the distances between crests are most often approx. 100 m. The ridges are most probably 'retreat moraines' that were deposited during minor halts and/or re-advances during the last deglaciation. More curvilinear and randomly oriented furrows with raised rims are most probably iceberg ploughmarks that were formed from grounded icebergs calving off the Greenland Ice Sheet during the last deglaciation (e.g. in Rudis Bugt). Elongated to round, randomly distributed depressions of up to >10 m depth and >200 m width occur, e.g. in the inner parts of Tyrolerfjord. They are often filled with acoustically stratified sediments and we assume that they might have resulted from post-glacial tectonic activity. Up to 180 ms two-way travel time thick acoustically stratified sequences dominate the fjord-fill and sound-fill stratigraphies. These deposits are suggested to reflect repeatedly changing physical conditions in a glacimarine environment where deposition occurred from suspension fall-out, ice rafting from icebergs and sea ice, as well as smaller-scale mass wasting. An acoustically transparent drape overlies these deposits rarely (e.g. in Rudis Bugt). Multiple acoustically transparent bodies with irregular geometries intercalated within the stratified deposits are suggested to reflect repeated larger-scale mass wasting, either from slope failures along fjord sides or related to glacier advances (e.g. in Nordfjord). Occasional distortions and blanking of reflections (e.g. in Nordfjord and Kong Oscar Fjord) might be related to relatively recent tectonic activity and fluid flow/gas expansion.

  8. Regional geology and stratigraphy of Saturn's icy moon Tethys

    NASA Astrophysics Data System (ADS)

    Wagner, Roland; Stephan, Katrin; Schmedemann, Nico; Roatsch, Thomas; Kersten, Elke; Neukum, Gerhard; Porco, Carolyn C.

    2013-04-01

    Tethys, with a diameter of 1060 km one of the 6 mid-sized icy moons of Saturn, was imaged for the first time in the early 1980ies by the cameras aboard the two Voyager spacecraft at resolutions of 1 km/pxl and lower [1][2][3]. These images show that most of Tethys is densely cratered and displays two major landmarks: the ~ 400 km large impact structure Odysseus and the huge graben system of Ithaca Chasma [1][2]. Since July 2004, Cassini has been in orbit about Saturn and has made several close passes at Tethys, providing an almost complete global image coverage at regional scale (200 - 500 m/pxl). However, varying viewing geometries between images taken during different orbits still impede the identification and mapping of geologic units. In this work we present an update of Tethys' regional geology and stratigraphy, based on Cassini ISS images. Crater distribution measurements, by us and in comparison with measurements of other groups [4], are used to support stratigraphic findings. Most of Tethys' surface consists of a hilly, rugged, heavily cratered plains unit, as identified in Voyager images [1][2][3]. A smooth, less densely cratered plains unit in the trailing hemisphere was previously observed by [2] which is also identifiable in Cassini ISS, but its exact boundaries are difficult to map due to varying viewing geometries of ISS observations. Another sparsely cratered plains unit not seen in Voyager images can be located to the south of Odysseus. It features remnants of highly degraded large craters superimposed by younger fresher craters with a lower crater density compared to the heavily cratered plains. Its distinct linear northern contact with the heavily cratered plains suggests an origin related to tectonism. Again, varying viewing conditions hamper to map the exact boundaries of this unit. The prominent graben system of Ithaca Chasma represents fractured cratered plains. The high resolution of Cassini ISS images reveals that tectonism on Tethys is more widespread. Numerous fractures can be identified locally in the heavily cratered plains. Impact crater materials can be subdivided into three degradational classes. Oldest crater forms are heavily degraded impact structures, such as Telemus. Odysseus is a fresh to partly degraded large impact structure with a central peak complex, wall terraces, secondary crater chains, and slivers of smooth deposits within the heavily cratered plains, possibly impact ejecta. According to previous ISS-based crater measurements, Odysseus is younger than Ithaca Chasma and possibly did not cause the formation of this graben system [5]. The youngest and freshest craters are represented by Telemachus, characterized by a sharp crater rim, well-discernible ejecta blankets, and a low superimposed crater frequency. Locally, features of mass wasting, e.g. landslides, can be observed in craters. References: [1] Smith B. A. et al. (1981), Science 212, 163-191. [2] Smith B. A. et al. (1982), Science 215, 504-537. [3] Moore J. M. and Ahern J. L. (1983), JGR 88 (suppl.), A577-A584. [4] Kirchoff M. R. and Schenk P. M. (2010), Icarus 206, 485-497. [5] Giese B. et al. (2007), GRL 34, doi:10.1029/2007GL031467.

  9. Sedimentological research as a basis for environmental management: the Oresund fixed link.

    PubMed

    Valeur, J R; Jensen, A

    2001-02-01

    A fixed 16 km link (immersed tunnel, artificial island and peninsula, bridges) to connect the Scandinavian countries of Denmark and Sweden is being constructed during the period 1995-2000. The link crosses Oresund, one of the three sounds connecting the brackish Baltic Sea to the oceanic North Sea. Dredging of approximately 8 x 10(6) m3 of limestone bedrock and clay till is being carried out during the construction phase. Environmental planning and management when constructing the fixed link were heavily dependent on extensive sedimentological and biological research prior to construction. Base-line turbidity and seabed sediments were investigated, and sediment spill parameters were measured during test dredging and test reclamation, in addition to the environmental impact. Now, when dredging and reclamation have been finalised in Oresund, it is clear that the environmental management approach used during construction of the fixed link has safeguarded the marine environment in Oresund. At the same time it has allowed the dredging and reclamation works to be carried out within the planned time period and expenses. A detailed base-line monitoring of the regional turbidity regime and the regional sedimentation regime in Oresund made post-dredging evaluation of the regional effects possible. The measurements in Oresund showed that the construction caused no permanent regional change in turbidity and sedimentation, as the base-line conditions did not change. PMID:11258828

  10. Biostratigraphy, sedimentology and paleoenvironments of the northern Danube Basin: Ratkovce 1 well case study

    NASA Astrophysics Data System (ADS)

    Rybár, Samuel; Halásová, Eva; Hudá?ková, Natália; Ková?, Michal; Ková?ová, Marianna; Šarinová, Katarína; Šujan, Michal

    2015-02-01

    The Ratkovce 1 well, drilled in the Blatné depocenter of the northern Danube Basin penetrated the Miocene sedimentary record with a total thickness of 2000 m. Biostratigraphically, the NN4, NN5 and NN6 Zones of calcareous nannoplankton were documented; CPN7 and CPN8 foraminifer Zones (N9, 10, 11 of the global foraminiferal zonation; and MMi4a; MMi5 and MMi6 of the Mediterranean foraminiferal zonation were recognized. Sedimentology was based on description of well core material, and together with SP and RT logs, used to characterize paleoenvironmental conditions of the deposition. Five sedimentary facies were reconstructed: (1) fan-delta to onshore environment which developed during the Lower Badenian; (2) followed by the Lower Badenian proximal slope gravity currents sediments; (3) distal slope turbidites were deposited in the Lower and Upper Badenian; (4) at the very end of the Upper Badenian and during the Sarmatian a coastal plain of normal marine to brackish environment developed; (5) sedimentation finished with the Pannonian-Pliocene shallow lacustrine to alluvial plain deposits. The provenance analysis records that the sediment of the well-cores was derived from crystalline basement granitoides and gneisses and from the Permian to Lower Cretaceous sedimentary cover and nappe units of the Western Carpathians and the Eastern Alps. Moreover, the Lower Badenian volcanism was an important source of sediments in the lower part of the sequence.

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

    SciTech Connect

    Patterson, P.E.; Larson, E.E. )

    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.

  12. Sedimentology and reservoir characteristics of tight gas sandstones, Frontier formation, southwestern Wyoming

    SciTech Connect

    Moslow, T.F.; Tillman, R.W.

    1984-04-01

    The lower Frontier Formation, Moxa arch area, southwestern Wyoming, is one of the most prolific gas-producing formations in the Rocky Mountain region. Lower Frontier sediments were deposited as strandplains and coalescing wave-dominated deltas that prograding into the western margin of the Cretaceous interior seaway during the Cenomanian. In this study, sedimentologic, petrologic, and stratigraphic analyses were conducted on cores and logs of Frontier wells from the Whiskey Buttes and Moxa fields. Twelve sedimentary facies have been identified. The most common sequence consists of burrowed to cross-bedded near shore marine (delta-front and inner-shelf) sandstones disconformably overlain by cross-bedded (active) to deformed (abandoned) distributary-channel sandstones and conglomerates. The sequence is capped by delta-plain mudstones and silty sandstones. Tight-gas sandstone reservoir facies are non-homogenous and include crevasse splay, abandoned and active distributary channel, shoreface, foreshore, and inner shelf sandstones. Distributary-channel facies represent 80% of perforated intervals in wells in the southern part of the Moxa area, but only 50% to the north. Channel sandstone bodies are occasionally stacked, occur on the same stratigraphic horizon, and are laterally discontinuous with numerous permeability barriers. Percentage of perforated intervals in upper shoreface and foreshore facies increases from 20% in the south to 50% in the north.

  13. Sedimentology and reservoir characteristics of tight gas sandstones, Frontier formation, southwestern Wyoming

    SciTech Connect

    Moslow, T.F.; Tillman, R.W.

    1984-04-01

    The lower Frontier Formation, Moxa arch area, southwestern Wyoming, is one of the most prolific gas-producing formations in the Rocky Mountain region. Lowr Frontier sediments were deposited as strandplains and coalescing wave-dominated deltas that prograding into the western margin of the Cretaceous interior seaway during the Cenomanian. In this study, sedimentologic, petrologic, and stratigraphic analyses were conducted on cores and logs of Frontier wells from the Whiskey Buttes and Moxa fields. Twelve sedimentary facies have been identified. The most common sequence consists of burrowed to cross-bedded near shore marine (delta-front and inner-shelf) sandstones disconformably overlain by crossbedded (active) to deformed (abandoned) distributary-channel sandstones and conglomerates. The sequence is capped by delta-plain mudstones and silty sandstones. Tight-gas sandstone reservoir facies are nonhomogenous and include crevasse splay, abandoned and active distributary channel, shoreface, foreshore, and inner shelf sandstones. Distributary-channel facies represent 80% of perforated intervals in wells in the southern part of the Moxa area, but only 50% to the north. Channel sandstone bodies are occasionally stacked, occur on the same stratigraphic horizon, and are laterally discontinuous with numerous permeability barriers. Percentage of perforated intervals in upper shoreface and foreshore facies increases from 20% in the south to 50% in the north.

  14. Two member subdivision of the Bima Sandstone, Upper Benue Trough, Nigeria: Based on sedimentological data

    NASA Astrophysics Data System (ADS)

    Tukur, A.; Samaila, N. K.; Grimes, S. T.; Kariya, I. I.; Chaanda, M. S.

    2015-04-01

    The Early Cretaceous Bima Sandstone is a continental succession in the Upper Benue Trough, Nigeria formally divided into the Lower, Middle and Upper Bima Members. Sedimentological data presented here indicates a two member model (Lower and Upper Members) is more appropriate for the formation. The boundary separating the two proposed members is exposed at the Bollere River, Bima Hill, Wuyo II, and Kaltungo Fault sections. The lithological differences between the two members are perhaps to a large extent a reflection of the sediments sources. The Lower Bima Sandstone Member was deposited in aggradational braided alluvial systems and contains well preserved overbank fines, avulsive and crevasse splay sandstones, and channel deposits. Pedogenic carbonates are also common features of these alluvial deposits in the Bima Hill. The Kaltungo Fault section exposes sediments of brief lacustrine setting within the Lower Bima Sandstone Member. The Upper Bima Sandstone Member was deposited in fully matured braided river with well-developed accommodation space in both shallow and deep fluvial channels. Sedimentation in this braided river was mostly on braid bars and with scarce channels. Preliminary ?13CTOC data along the Bollere River lithosection shows lack of any significant carbon isotope excursion suggesting climate, especially changes in aridity was not a major contributor in differences between the two members of the Bima Sandstone.

  15. Sedimentological constraints on hydrometeor-enhanced particle deposition: 1992 Eruptions of Crater Peak, Alaska

    NASA Astrophysics Data System (ADS)

    Durant, Adam J.; Rose, William I.

    2009-09-01

    Water is a dominant component of volcanic clouds and has fundamental control on very fine particle deposition. Particle size characteristics of distal tephra-fall (100s km from source volcano) have a higher proportion of very fine particles compared to predictions based on single particle settling rates. In this study, sedimentological analyses of fallout from for the 18 August and 16-17 September 1992 eruptions of Crater Peak, Alaska, are combined with satellite observations, and cloud trajectory and microphysics modeling to investigate meteorological influences on particle sedimentation. Total grain size distributions of tephra fallout were reconstructed for both Crater Peak eruptions and indicate a predominance of fine particles < 125 μm. Polymodal analysis of the deposits has identified a particle subpopulation with mode ~ 15-18 μm involved in particle aggregation. Accounting for the magmatic water source only, calculated ice water content of the 3.7 hour old September 1992 Spurr cloud was ~ 4.5 × 10 - 2 g m - 3 (based on an estimated cloud thickness of ~ 1000 m from trajectory modeling). Hydrometeor formation on particles in the volcanic cloud and subsequent sublimation may induce a cloud base instability that leads to rapid bulk ( en masse) sedimentation of very fine particles through a mammatus-like mechanism.

  16. Sedimentologic controls on movement of contaminants through aquifers: Lessons learned from petroleum geology

    SciTech Connect

    Kystinik, L.F. ); Wyatt, D.J. )

    1990-05-01

    Most predictive hydrologic models for contaminant transport in unfractured sandstone aquifers assume sheet-like, uniform flow down a potentiometric gradient and ignore sedimentary heterogeneities. In contrast, petroleum exploitation effort document depositionally induced heterogeneities that control fluid movement through sandstone deposits. Sandstone deposits from many depositional environments contain heterogeneities capable of diverting contaminants outside the path predicted by potentiometric theory. Fluvial deposits can be linear sandstone bodies encased within impermeable mudstone, often oriented at high angles to the potentiometric gradient. Internally, fluvial sandstone bodies can be highly compartmentalized, resulting in complex but predictable flow paths. Similarly, predictable permeability relationships occur in other depositional environments. The internal stratification of eolianites causes directionally preferred flow of fluids and layered behavior. Eolianites have maximum preferred permeabilities, perpendicular to paleowind, that can exceed intermediate (parallel to paleowind) and vertical permeabilities by 2 to 3 orders of magnitude. Even sheet-like strandline deposits contain internal flow barriers that can isolate or divert contaminants. These predictable permeability relationships can have a dramatic impact upon fluid flow through aquifers, as well as hydrocarbon reservoirs. Prediction of heterogeneity requires a detailed understanding of the deposit in question. Core, well logs, and outcrop studies, rarely used in hydrogeology, are necessary to accurately predict flow characteristics. Although core and well logs are expensive, predictive sedimentology can offset these expenses by eliminating unnecessary monitor wells drilled large distances from the compartmentalized path of contaminant transport.

  17. Workshop on the Martian Northern Plains: Sedimentological, periglacial, and paleoclimatic evolution

    NASA Technical Reports Server (NTRS)

    Kargel, J. S. (Editor); Parker, T. J. (Editor); Moore, J. M. (Editor)

    1993-01-01

    The penultimate meeting in the Mars Surface and Atmosphere Through Time (MSATT) series of workshops was held on the campus of the University of Alaska in Fairbanks, Alaska, 12-13 Aug. 1993. This meeting, entitled 'The Martian Northern Plains: Sedimentological, Periglacial, and Paleoclimatic Evolution,' hosted by the Geophysical Institute at the University of Alaska, was designed to help foster an exchange of ideas among researchers of the Mars science community and the terrestrial glacial and periglacial science community. The technical sessions of the workshop were complemented by field trips to the Alaska Range and to the Fairbanks area and a low-altitude chartered overflight to the Arctic Costal Plain, so that, including these trips, the meeting lasted from 9-14 Aug. 1993. The meeting, field trips, and overflight were organized and partially funded by the Lunar and Planetary Institute and the MSATT Study Group. The major share of logistical support was provided by the Publications and Program Services Department of the Lunar and Planetary Institute. The workshop site was selected to allow easy access to field exposures of active glaciers and glacial and periglacial landforms. In all, 25 scientists attended the workshop, 24 scientists (plus 4 guests and the meeting coordinator) participated in the field trips, and 18 took part in the overflight. This meeting reaffirmed the value of expertly led geologic field trips conducted in association with topical workshops.

  18. Human impact variability on soil erosion during the Holocene based on valley floor sediments study in a Parisian basin fluvial catchment (France): crossing sedimentological, archaeological and palynological proxies

    NASA Astrophysics Data System (ADS)

    Morin, E.; Cyprien, A. L.; Gay-Ovejero, I.; Hinschberger, F.; Joly, C.; Macaire, J. J.; Poirier, N.; Visset, L.; Zadora-Rio, E.

    2009-04-01

    This work is part of the French CNRS ECLIPSE program « Impact anthropique sur l'érosion des sols et la sédimentation dans les zones humides associées durant l'Holocène ». It aims to reconstitute the evolution of human impact on soil erosion at various periods via the study of Holocene sedimentary archives. In this framework the Choisille catchment (288 km²; elevation: 50 - 200 m), tributary of the River Loire near Tours (France), has been the subject of an interdisciplinary study (sedimentology, geophysics, archaeology, palynology). 3 areas are investigated: a downstream stretch, a silicated sub-catchment area and a carbonated sub-catchment area. In the downstream stretch, located near ancient populated areas, drillings were performed along cross sections through valley floor alluviums. They show that a more or less organic clayey silty sedimentation started at the beginning of the Holocene. The sedimentation rates strongly increased at the beginning of the Subbatlantic (Bronze Age), simultaneously with the anthropogenic pressure advent (on set of agriculture), as shown by archaeological and palynological evidences (agricultural settlements, massive loggings on slopes, stockbreeding on valley-floor grasslands). In the silicated sub-catchment area, located upstream, drillings have shown that clayey silty sedimentation began at the end of the Roman Period, continued during the Early Middle Ages and increased during the High Middle Ages. Spatial archaeological prospecting has revealed a faint anthropogenic presence at the Roman Period, then a decline of population until the High Middle Ages, characterised by an agricultural revival. Palynological analyses have shown that, in this area, grasslands were dominant since the Early Middle Ages, with an increase in cereal cultures at the beginning of the High Middle Ages. In the carbonated sub-catchment area, drillings have shown that the more or less organic clayey silty sedimentation has begun during the Bronze Age. Sedimentation rates have increased during the Modern era and the Contemporary history. The high fine sediment storage appeared and evolved differently, depending on the considered period and catchment valley area, due to variation of soil erosion. The difference between a fine, early and regularly increasing sedimentation in the downstream site and the later, intense and non-univocal sedimentation in the sub-catchments doesn't seem to be strictly resulting from natural factors. This idea and the palaeoenvironnemental dataset show that the fine sedimentation basically results from an anthropogenic impact, notably in the sub-catchments. Therefore soil exploitation by humans seems to be the main sedimentary production factor. This work mainly shows that anthropogenic impact (age of appearance, intensity) highly varies spatially, even into a little catchment. This variability would be led by the agricultural potential of the considered catchment valley area.

  19. GEOELECTRICAL STRATIGRAPHY AND ANALYSIS OF A HYDROCARBON IMPACTED AQUIFER

    EPA Science Inventory

    A recently proposed geoelectrical model for hydrocarbon impacted sites predicts anomalously high conductivities coincident with aged contaminated zones. These high conductivities are attributed to an enhancement of mineral weathering resulting from byproducts of microbial redox p...

  20. 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.

  1. 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.

  2. Volcaniclastic stratigraphy of Gede Volcano, West Java, Indonesia: How it erupted and when

    NASA Astrophysics Data System (ADS)

    Belousov, A.; Belousova, M.; Krimer, D.; Costa, F.; Prambada, O.; Zaennudin, A.

    2015-08-01

    Gede Volcano, West Java (Indonesia), is located 60 km south of Jakarta within one of the regions with highest population density in the world. Therefore, knowledge of its eruption history is necessary for hazard evaluation, because even a small eruption would have major societal and economic consequences. Here we report the results of the investigation of the stratigraphy of Gede (with the focus on its volcaniclastic deposits of Holocene age) and include 23 new radiocarbon dates. We have found that a major part of the volcanic edifice was formed in the Pleistocene when effusions of lavas of high-silica basalt dominated. During this period the volcano experienced large-scale lateral gravitational failure followed by complete reconstruction of the edifice, formation of the summit subsidence caldera and its partial refilling. After a repose period of > 30,000 years the volcanic activity resumed at the Pleistocene/Holocene boundary. In the Holocene the eruptions were dominantly explosive with magma compositions ranging from basaltic andesite to rhyodacite; many deposits show heterogeneity at the macroscopic hand specimen scale and also in the minerals, which indicates interactions between mafic (basaltic andesite) and silicic (rhyodacite) magmas. Significant eruptions of the volcano were relatively rare and of moderate violence (the highest VEI was 3-4; the largest volume of erupted pyroclasts 0.15 km3). There were 4 major Holocene eruptive episodes ca. 10,000, 4000, 1200, and 1000 yr BP. The volcanic plumes of these eruptions were not buoyant and most of the erupted products were transported in the form of highly concentrated valley-channelized pyroclastic flows. Voluminous lahars were common in the periods between the eruptions. The recent eruptive period of the volcano started approximately 800 years ago. It is characterized by frequent and weak VEI 1-2 explosive eruptions of Vulcanian type and rare small-volume extrusions of viscous lava. We estimate that during last 10,000 years, Gede erupted less than 0.3 km3 DRE (Dense Rock Equivalent) of magma. Such small productivity suggests that the likelihood of future large-volume (VEI ≥ 5) eruptions of the volcano is low, although moderately strong (VEI 3-4) explosive eruptions capable of depositing pyroclastic flows and lahars onto the NE foot of the volcano are more likely.

  3. Stratigraphy of the Pleistocene, phonolitic Cão Grande Formation on Santo Antão, Cape Verde

    NASA Astrophysics Data System (ADS)

    Eisele, S.; Freundt, A.; Kutterolf, S.; Ramalho, R. S.; Kwasnitschka, T.; Wang, K.-L.; Hemming, S. R.

    2015-08-01

    The Cão Grande Formation (CGF) on the western plateau of Santo Antão Island is part of the younger volcanic sequence that originated from both, basanitic and nephelinitic magmatic suites, respectively called COVA and COROA suites. Based on our detailed revised stratigraphy of the CGF, including two yet unknown tephra units, we can show that both suites produced multiple, highly differentiated eruptions over a contemporaneous period. Correlations of CGF tephras with marine ash layers provide distal dispersal data for Cão Grande I (CG I) and also identify two highly explosive, phonolitic eruptions that pre-date the CGF tephra deposits known on land. Within the CGF, the lowermost, 220 ± 7 ka old unit Canudo Tephra (CT; COVA suite) comprises phonolitic fall deposits and ignimbrites; it is partly eroded and overlain by debris flow deposits marking a hiatus in highly differentiated eruptions. The phonolitic CG I Tephra (COROA suite) consists of an initial major Plinian fall deposit and associated ignimbrite and terminal surge deposits. This is immediately overlain by the phonolitic to phono-tephritic Cão Grande II (CG II; COVA suite), a complex succession of numerous fallout layers and density-current deposits. CG I and CG II have radiometric ages of 106 ± 3 ka and 107 ± 15 ka, respectively, that are identical within their error limits. The youngest CGF unit, the Furninha Tephra (FT; COROA suite), consists of three foidic-phonolitic fall deposits interbedded with proximal scoria deposits from a different vent. The phonolitic eruptions switched to and fro between both magmatic suites, in each case with a stronger first followed by a weaker second eruption. Each eruption evolved from stable to unstable eruption columns. During their terminal phases, both magma systems also leaked evolved dome-forming lavas next to the tephras. Distal ashes increase the CG I tephra volume to ~ 10 km3, about twice the previously published estimate. The tephra volume of CG II is ~ 3 km3; CT and FT are too poorly exposed for volume estimation. The characteristics of the CGF tephra units outline hazard conditions that may be expected from future evolved explosive eruptions on the western plateau of Santo Antão.

  4. Bayesian Uncertainty of Thwaites Glacier Catchment Radar Stratigraphy

    NASA Astrophysics Data System (ADS)

    Gutowski, G.; Jackson, C. S.; Blankenship, D. D.; Young, D. A.; Cavitte, M. G.

    2013-12-01

    Information about the history and dynamics of ice sheets is contained in basin-scale radar sounding surveys. Englacial, isochronous radar horizons traced throughout the sampled domain of these basins can give a three-dimensional picture of past ice flow by revealing significant details of deformation within the ice column. We focus our efforts in the Thwaites Glacier catchment, West Antarctica, which previous studies have shown to be a bellwether in future WAIS deglaciation scenarios. Here we present a Bayesian determination of the age-depth profile at the Byrd ice core, Antarctica, based on robust uncertainty estimates in ice core ages and radar sounding depths. A simple ice flow model is used to determine the age-depth relationship in ice near the core and a Markov Chain Monte Carlo technique is used to sample a posterior distribution of age as a function of depth to within uncertainty. We propagate the age-depth information, including uncertainty, for several prominent radar reflectors from the Byrd ice-coring site in the Interior Ross Embayment across the ice divide and throughout the Thwaites Glacier catchment using airborne ice-penetrating radar data collected and processed by the University of Texas Institute for Geophysics.

  5. Stratigraphy of the Arriaga Palaeolithic sites. Implications for the geomorphological evolution recorded by thickened fluvial sequences within the Manzanares River valley (Madrid Neogene Basin, Central Spain)

    NASA Astrophysics Data System (ADS)

    Silva, P. G.; López-Recio, M.; Tapias, F.; Roquero, E.; Morín, J.; Rus, I.; Carrasco-García, P.; Giner-Robles, J. L.; Rodríguez-Pascua, M. A.; Pérez-López, R.

    2013-08-01

    The Arriaga Palaeolithic sites, located within the Middle-Late Pleistocene thickened terrace (TCMZ: + 18-22 m) of the Manzanares River valley (Madrid, Central Spain), were subject to intensive archaeological and palaeontological prospecting during the 1980s. Compilation of documents from these old excavations, together with new geoarchaeological, sedimentological, pedological and geophysical data, allow us to locate the morpho-stratigraphic position of the analysed sites within the overall stratigraphy of the TCMZ. This thickened terrace comprises two main fluvial sequences (Lower and Upper) topped by a thick (2.5-5 m) alluvial-colluvial formation. The fluvial sequences are stacked in the study site located in the lowermost reach of the valley, but display complex inset relationships upstream, where they are individualized in two different terrace levels at + 18-22 and + 12-15 m. Terrace thickening was primarily controlled by synsedimentary subsidence caused by dissolution of the evaporitic substratum and locally influenced and backfed by tectonic activity. The regional analysis of the dated (TL and OSL) fluvial sequences containing Palaeolithic sites within the TCMZ, together with new TL dates provided in this study, indicate that the three sedimentary sequences in the TCMZ are time-transgressive valley-fill bodies. Terrace thickening started before the Last Interglacial Period (MIS 6 or older) and continued during whole MIS 5 (lower fluvial sequence) and MIS 4 (upper fluvial sequence) reaching the MIS 3 (top alluvial formation), the latter characterized by the accumulation of alluvial-colluvial sequences derived from the main tributaries and valley slopes. The TCMZ records the Middle-Late Pleistocene boundary, but also the transition between the Lower and Middle Palaeolithic periods during the Late MIS 5 (ca. 96 to 74 ka). The studied Arriaga sites contain evolved Lower Palaeolithic industry (evolved Acheulean techno-complexes) and warm faunal assemblages located within the Lower fluvial sequence, but apparently well constrained Middle Palaeolithic sites are placed within the Upper fluvial sequence at other upstream locations. Deposition of the thickened alluvium was mainly controlled by the upstream advance of dissolution-induced subsidence phenomena, blurring the impact of Late Pleistocene climatic cycles and producing time-transgressive longitudinal valley-fill bodies (i.e. sedimentary sequences). Late Quaternary climatic changes only seem to control the incision/aggradation cycles after the termination of the TCMZ from the Late MIS 3. Dates related to the development of younger inset terraces indicate that they are apparently linked with cold Heinrich events H4 to H1. These younger inset terraces yield cold faunal assemblages and abundant Middle Palaeolithic "Mousterian" assemblages.

  6. Using NIR Photography to Document Snow Stratigraphy Quickly: Lessons from Three Field Campaigns

    NASA Astrophysics Data System (ADS)

    Sturm, M.; Tape, K.; Liston, G. E.; Rutter, N.

    2008-12-01

    We began using near-infrared (NIR) photography as a quick way to document snow stratigraphy in 2006 as part a snow validation campaign in Barrow, Alaska. Seventeen snow pits (30 to 80 cm deep) were photographed using a Sony DSC-P200 Cybershot 7.2-megapixel digital camera supported on a mini-tripod and equipped with a NIR filter (850 nm). Standard layer measurements of thickness, density, grain size, hardness, and grain type were also made in each pit. During the 2007 SnowSTAR traverse across Alaska and Canada, 43 snow pits were photographed and measured in the same fashion. During the CLPX-Alaska campaign of 2008, three trenches each about 10 m long were photographed in their entirety as well as documented in a traditional manner, this time using a Fuji S9100 9 mega-pixel digital camera with an 850 nm filter. For the trenches, the camera was supported on a sliding rail system. NIR photographs were processed using Image-J software and a simple algorithm that enhanced contrast based on grain size. Our goal is to develop a method of documenting stratigraphy that is faster than recording the results in a field book. For a 50 cm deep pit prior methods of recording stratigraphy would have required about 30 minutes. We succeeded in reducing the average time to acquire a pit photograph to less than 15 minutes. However, pit face preparation time increased by about 15 minutes because of the need to produce a smooth, divot-free snow surface. Required protocols to compute grain size from the photos added a further 20 minutes or more if used, so frequently these were omitted. While at present there is no real net reduction in the time to record stratigraphy using NIR photography vs. older methods, the result is superior in all ways to our best previous efforts to "map" the stratigraphy though hand-recorded data. A combination of older traditional methods and NIR photography is strongly recommended as the best method to document the snow stratigraphy.

  7. Role of mechanical stratigraphy on fracture development in carbonate reservoirs: Insights from outcropping shallow water carbonates in the Umbria Marche Apennines, Italy

    NASA Astrophysics Data System (ADS)

    Di Naccio, D.; Boncio, P.; Cirilli, S.; Casaglia, F.; Morettini, E.; Lavecchia, G.; Brozzetti, F.

    2005-10-01

    Studies on mechanical stratigraphy show that a link exists among facies, sedimentary cycles, diagenesis and fracturing. Understanding this link is fundamental for characterising fluid flow in natural reservoirs, especially carbonate ones. This work investigates the field of evidence through a case study in the Umbria-Marche Apennines: the Lower Jurassic shallow water carbonates of the Calcare Massiccio unit, a potential carbonate reservoir. A multidisciplinary approach is used, involving stratigraphy, sedimentology and structural geology. The studied succession crops out at the core of an ENE-verging anticline, located at Campolarzo, within the Umbria-Marche Apennines. The Calcare Massiccio here consists of high-frequency, metre-scale, shallowing upward, peritidal cycles. Three different cycles (thickness ranging from 0.3 to 3 m) have been recognised: type A (incomplete asymmetric cycle), type B (complete asymmetric cycle with sheet cracks) and type C (complete asymmetric cycle with tepees). Sedimentary textures vary according to the depositional environment. The subtidal facies is almost entirely mud-supported, with the exception of type A cycle, which locally can be grain-supported. The intertidal facies is from mud- to grain-supported and commonly laminated. The supratidal facies may be either absent (type A) or represented by vadose pisoid caliches, sheet cracks (type B) and tepees (type C). The overprinting of diagenetic facies (early diagenesis) is particularly evident in the supratidal intervals of type C cycle (tepee structures) and in the inter-supratidal intervals of type B cycle (sheet cracks). The fracture pattern within the Calcare Massiccio mainly consists of systematic joints organized in two prominent mutually perpendicular sets (orthogonal joints) and two subordinate non-perpendicular sets (diagonal joints). The orthogonal sets are interpreted as tensile joints developed sub-parallel (longitudinal joints) and sub-perpendicular (cross joints) to the NNW-SSE axial trend of the host anticline. The diagonal joints are interpreted as shear joints. In the study area, the fracture density is strongly controlled by heterogeneities of rock properties between and within facies, which in turn are determined by sedimentary textures and, dominantly, by the combination of sedimentary and diagenetic facies, e.g., by the petrofacies. The control played by the petrofacies distribution across the stratigraphic succession may justify strong variations in the fracture density (up to ca. 80% or more) within the same sedimentary cycle, as well as fracture terminations, independently from tectonic causes. A systematic decrease in fracture density going from subtidal to intertidal to inter-supratidal and tepee facies is evident. Minimum values are observed on tepee structures; fractures often terminate against supratidal intervals with tepee. The lowest fracture density characterises petrofacies where early diagenetic processes are more pronounced (i.e., the intertidal facies and the inter-supratidal facies with tepee, strongly affected by early dissolution cavities filled by early cements). No obvious correlation is observed between the fracture density and the thickness of the petrofacies layer.

  8. Sedimentological features of the surge emitted during the August, 2006 pyroclastic eruption at Tungurahua volcano (Ecuador)

    NASA Astrophysics Data System (ADS)

    Douillet, G.; Goldstein, F.; Lavallee, Y.; Hanson, J. B.; Kueppers, U.; Robin, C.; Ramon, P.

    2009-12-01

    Tungurahua volcano, Ecuador, is a stratovolcano, which began a new eruptive phase in 1999. Notable pyroclastic Density Currents (PDC) were generated in July (VEI 2) and August (VEI 3) 2006 and covered its N and W flanks. PDCs and associated lahars represent a major hazard for 20,000 inhabitants and an hydrological dam. The volcano has been monitored by the Instituto Geofisico of the Escuela Politécnica Nacional of Quito, since 1988. Field work carried out in 2009 provide information on the behavior of the fine-grained fraction of the PDC (i.e., surge) during transport and deposition. We mapped out the sedimentological characteristics of the deposits and distinguished three depositional environments: 1- The core of the deposit, up to several m in thickness, is confined to valleys and consists of poorly-sorted lapilli scoria and blocks (cm to m scale) and a small fraction of ash matrix. Ongoing analysis of the ash matrix will help to understand the link between the main PDC and the associated surge. 2- On ridges and outer margins of valleys, the deposits total a thickness of 10s to 100s cm and consist of fine- to coarse-grain ashes organized in cm-scale beds. Horizontal to cross bed laminations with 10-cm long wavelength prevail. They are typical of deposition under sustained high-energy current, which we associate with the flow of a surge. 3- In the distal part of surge deposits, we observe fine grained surge deposits with a thickness up to ca. 5 m. The characteristic structures are curved crested dunes, 10s of cm high and up to 10s of m long, with dip angles ranging from 15 to 35° and a strongly asymmetric shape. The steepest side tends to be the upslope face. Dunes show mainly a climbing structure, with beds cm in thickness, but some are more complicated, containing cut and fill structures, interpreted as late-stage pulses of energetic turbulence. No displacement dunes were observed in this area. Using the flow direction given by 100s of dunes, we provide precise information on the surge behavior in this part, and map the currents. This depositional environment marks the end of the surge flow, where insufficient energy was left to transport the material. Sedimentological structures show that in contrast to usual depositional environments where the particles are entrained by a fluid and are only sediments, ashes play the role of both the vector of transport and the sediment in the third zone. This surge is interpreted as an end member of the PDC. The surge remains with the PDC in steady conditions but the two can separate from one another because of different flow behavior; this distinction is especially visible at the main flow front or where the valleys kink. However, the three zones are very close to each other (100s m ) and we believe that the surge has a dissipative behavior; that is, he requires a sustained income of energy from the main flow. We thus make a distinction between the present surge, base surges (that are independent blast fine grained PDCs) and ash falls. This study provides a better understanding of the relationships between fine and coarse material in PDCs, and the energy transfers in the flow.

  9. 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.

  10. 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.

  11. Sedimentological effects of tsunamis, with particular reference to impact-generated and volcanogenic waves

    NASA Technical Reports Server (NTRS)

    Bourgeois, Joanne; Wiberg, Patricia L.

    1988-01-01

    Impulse-generated waves (tsunamis) may be produced, at varying scales and global recurrence intervals (RI), by several processes. Meteorite-water impacts will produce tsunamis, and asteroid-scale impacts with associated mega-tsunamis may occur. A bolide-water impact would undoubtedly produce a major tsunami, whose sedimentological effects should be recognizable. Even a bolide-land impact might trigger major submarine landslides and thus tsunamis. In all posulated scenarios for the K/T boundary event, then, tsunamis are expected, and where to look for them must be determined, and how to distinguish deposits from different tsunamis. Also, because tsunamis decrease in height as they move away from their source, the proximal effects will differ by perhaps orders of magnitude from distal effects. Data on the characteristics of tsunamis at their origin are scarce. Some observations exist for tsunamis generated by thermonuclear explosions and for seismogenic tsunamis, and experimental work was conducted on impact-generated tsunamis. All tsunamis of interest have wave-lengths of 0(100) km and thus behave as shallow-water waves in all ocean depths. Typical wave periods are 0(10 to 100) minutes. The effect of these tsunamis can be estimated in the marine and coastal realm by calculating boundary shear stresses (expressed as U*, the shear velocity). An event layer at the K/T boundary in Texas occurs in mid-shelf muds. Only a large, long-period wave with a wave height of 0(50) m, is deemed sufficient to have produced this layer. Such wave heights imply a nearby volcanic explosion on the scale of Krakatau or larger, or a nearby submarine landslide also of great size, or a bolide-water impact in the ocean.

  12. Sedimentology of a Late Cenozoic collisional sequence: the Misis Complex, Adana, southern Turkey

    NASA Astrophysics Data System (ADS)

    Gökçen, Sungu L.; Kelling, Gilbert; Gökçen, Nuran; Floyd, Peter A.

    1988-10-01

    This study is concerned with Miocene sequences formed within part of the Cukurova Basin of southern Turkey, a major downwarp created during the early stages of collision between the Afro-Arabian plate and the Tauride-Anatolian microplate assemblage. We report here the results of a combined stratigraphical, sedimentological, structure and geochemical study of the Misis Complex, a structurally elevated segment of Cukurova basin-fill. This analysis has demonstrated the structurally imbricated nature of the Misis sequences and the tectonic juxtaposition of originally well-separated coeval facies. The initial discernible phase of basin-filling (pre-Burdigalian) was marked by deep marine conditions and marginal tectonic instability (probably related to a late phase of Tauride nappe advance). The subsequent phase of crustal extension (Burdigalian/Early Tortonian) produced expansion of the Cukurova basin limits and an upwards-shoaling succession, in which sediment transport towards the southwest gradually became dominant, as a result of earlier suturing and uplift in northeasterly sectors of the collision zone. The Miocene arenites of the Misis Complex are petrographically diverse (with common siliciclastic and carbonate detrital admixtures) and mineralogically immature and their position in petrotectonic fields indicates a compound provenance from both recycled orogen and magmatic arc sources. A noteworthy petrographic feature is the compositional similarity of arenites from both shallow and deep marine facies. The general succession of Neogene facies observed in the Cukurova Basin and Misis Complex is consistent with their evolution within a perisutural foreland basin, but this interpretation is complicated by petrographic and geochemical features attributed to remnants of an older magmatic arc. Later stages of basin-filling are also marked by the local occurrence of "anomalous" palaeoenvironmental associations (including olistostromic units) attributed to contemporaneous intra-basinal tectonism.

  13. 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

  14. Sedimentology, diagenesis, and oil habitat of Lower Cretaceous Qamchuqa Group, Northern Iraq

    SciTech Connect

    Al Shdidi, S.; Thomas, G.; Delfaud, J.

    1995-05-01

    The Zagros basin (Iraq) constitutes a rich petroleum province. The Lower Cretaceous Qamchuqa Group comprises on of its major reservoirs. Data from about 30 wells, drilled in a limited sector corresponding to a northwest-southeast anticlinal structure situated in the Kirkuk region, permit analysis of serveral sedimentological and diagenetic events that led to the formation of this reservoir. Facies changes took place and divided the structure into three parts: the northwestern part in which neritic facies dominate, the central part in which basinal influence is considerable, and the southeastern part that shows basinal mudstone type facies. The Lower Cretaceous carbonate platform in the northwestern part of the study area displays good primary porosity. During the course of burial, high secondary porosity related to dolomitization appeared. However, a major part of the porosity was produced when the reservoir was fractured during the Priabonian after the collision between the Arabian and Eurasian plates. Lopatin`s method suggests that organic matter maturation started during the Turonian (around 90 MA), whereas most of the maturation developed during the Miocene due to the rapid accumulation of foreland basin sediments containing evaporite facies (lower Fars Formation) followed by the accumulation of thick upper molasse-type sediments from the erosion of the Zagros Mountains. The accumulation of sediments enhanced the total tectonic subsidence. During this period, the relatively brief time spent by the source rock in a given temperature interval was compensated for by a rapid rise in temperature. This late thermal maturation period controlled most of the transformation of the organic matter into hydrocarbons.

  15. Hydrological and sedimentological variability of the peri-fluvial wetlands of the middle Loire river (France)

    NASA Astrophysics Data System (ADS)

    Gautier, E.; Kunesch, S.; Negrel, P.; Petelet-Giraud, E.

    2003-04-01

    With a catchment basin of 112,120 km^2 and a length of 1012 km, the Loire River is one of the most important fluvial hydrosystems in France. Notwithstanding numerous modifications (dikes, dams, nuclear power plants, gravel extractions), the Loire River hydrology has been saved from a total regularisation. Therefore, the spatial diversity of fluvial landforms creates a patchwork of wetlands: ox-bow lakes, dewatered channels... As one aim of this work was to determine the hydrological and sedimentological processes in the various wetlands, in a context of spatial variability of the fluvial landforms, we used a pluridisciplinarity approach: geomorphology, hydrology, geochemistry. The present study has targeted the functioning between the various hydro-geomorphologic units of the floodplain (main and secondary active channels, abandoned branches and the riverbank [alluvial] and perched aquifers), with regard to the spatial heterogeneity of the different fluxes and the temporal variations of bottom water level, full-bank stage and overflow discharge. In the upper part of the study area, mobile meanders prevail. The meanders migration results in oxbow lakes and the connection between the lakes and the other water reservoirs (e.g. river- and groundwaters) induce a strong lateral variability and a time delayed water input by the river as evidenced by the different geochemical and isotopic signatures. Downstream, the Loire River develops a multiple-channels pattern, of which numerous are abandoned. They are often dewatered along the year, only reconnected to the main channel during the periods of overflow discharges and the influence of the Loire riverwater is progressively substituted by the input of groundwaters (alluvial and perched aquifers). It appears that the submersion duration and the type of connection between the wetlands and the various reservoirs (inlet or outlet connection with the river, connection with the aquifers.) strongly influence the sedimentation rate and granulometric features.

  16. The Ardross reservoir gridblock analogue: Sedimentology, statistical representivity, and flow upscaling

    SciTech Connect

    Ringrose, P.; Pickup, G.; Jensen, J.

    1997-08-01

    We have used a reservoir gridblock-sized outcrop (10m by 100m) of fluvio-deltaic sandstones to evaluate the importance of internal heterogeneity for a hypothetical waterflood displacement process. Using a dataset based on probe permeameter measurements taken from two vertical transacts representing {open_quotes}wells{close_quotes} (5cm sampling) and one {open_quotes}core{close_quotes} sample (exhaustive 1mm-spaced sampling), we evaluate the permeability variability at different lengthscales, the correlation characteristics (structure of the variogram, function), and larger-scale trends. We then relate these statistical measures to the sedimentology. We show how the sediment architecture influences the effective tensor permeability at the lamina and bed scale, and then calculate the effective relative permeability functions for a waterflood. We compare the degree of oil recovery from the formation: (a) using averaged borehole data and no geological structure, and (b) modelling the sediment architecture of the interwell volume using mixed stochastic/deterministic methods. We find that the sediment architecture has an important effect on flow performance, mainly due to bedscale capillary trapping and a consequent reduction in the effective oil mobility. The predicted oil recovery differs by 18% when these small-scale effects are included in the model. Traditional reservoir engineering methods, using averages permeability values, only prove acceptable in high-permeability and low-heterogeneity zones. The main outstanding challenge, represented by this illustration of sub-gridblock scale heterogeneity, is how to capture the relevant geological structure along with the inherent geo-statistical variability. An approach to this problem is proposed.

  17. Sedimentologic succession of uplifted coral community, Urvina Bay, Isabela Island, Galapagos Archipelago, Ecuador

    SciTech Connect

    Colgan, M.W.; Hollander, D.

    1987-05-01

    In March 1954, along the west-central coast of Isabela Island, an upward movement of magma suddenly raised Urvina Bay over 6 m and exposed several square kilometers of carbonate deposits covering a young aa lava flow (around 1000 years old). Results from 6 transect lines across the uplift, 30 cores, and 10 trenches describe the sedimentologic and ecologic transition from barren basalt to diverse carbonate sediments with small coral reefs. Along horizontal transects spanning from 0 to 7 m paleowater depth, there is a seaward progression from beaches, mangroves, and basalt to thick deposits (> 1.6 m) of carbonate sands and small coral reefs. Variation in water depth, degree of wave exposure, and irregularity of the aa lava topography provided many microhabitats where coral, calcareous algae, and mollusks settled and grew. Eight hermatypic coral species are found throughout the shelf, and three species (i.e., Pavona clavus, Pocillopora damicornis, and Porites lobata) produced five small, isolated, monospecific, coral-reef frameworks. The vertical section seen in cores and trenches shows that calcium carbonate increased upward, whereas volcanic sediments decreased; however, episodic layers occur with high concentrations of basaltic sands. In vertical samples from the central portion of the shelf, the coral population changed from small, isolated colonies of Psammocora (Plesioseris) superficalis near the basalt basement to large reef-forming colonies of Pocillopora damicornis farther upsection. Reefs of the Galapagos Islands are small and less diverse than most Pacific reefs. Nonetheless, understanding their temporal successional development should throw light on the origin and history of larger oceanic reefs in the Pacific.

  18. Distribution and Stratigraphy of Basaltic Lavas in the Southwest Portion of the Quaternary Big Pine Volcanic Field, California

    NASA Astrophysics Data System (ADS)

    Woolford, J.; Vazquez, J.

    2007-12-01

    The Pleistocene Big Pine Volcanic Field (BPVF), located in the Owens Valley of eastern California, is dominated by basaltic cinder cones and lavas, and poses a potential volcanic hazard to local infrastructure, in particular Highway 395 and the Los Angeles Aqueduct. However, despite numerous petrologic studies, the volcanic history and distribution of products from individual BPVF eruptions are poorly known. Using detailed field mapping and petrology, we have determined the distribution and stratigraphy of basaltic lavas in the southwest portion of the BPVF, which contains the largest number exposed vents and lava. In the Aberdeen area, individual cinder cones and fissure vents are aligned along N-S trending lineaments, with local clustering of vents and lavas. Approximately 19 cones, and at least 14 lava flows occur in the area. Two cinder cones located near the valley floor are partly buried by younger lavas and alluvium. In most cases, lavas are aa in character and traveled ca. 7 km down alluvial fans (8% gradient) towards the Owens River. On average, individual lavas cover ca. 10-12 km2, with average individual volumes of ca. 0.065 km3. Two general groups of basaltic lavas characterize the Aberdeen area: 1) xenocryst-rich and 2) xenolith-poor basalts. Xenolith-rich basalts contain variable amounts of ultramafic, mafic, granitic, and metamorphic lithologies, whereas xenolith-poor lavas are dominated by olivine phenocrysts. Overlapping flow margins define relative ages between adjacent basalts. In both north and south portions of the Aberdeen area, flows composing the base of the volcanic stratigraphy are the xenolith-rich variety, and are typically overlain by xenolith-poor flows. In general, these younger xenolith-poor lavas are approximately 25% larger in volume than the older xenolith-rich lavas. Several vents record changes in lava type during individual eruptions, suggesting transitions in magma discharge rate. At one vent cluster, pahoehoe is restricted to within ca. 1.5 km of its fissure vent and overlies more extensive aa from the same vent, suggesting a decrease in discharge rate of basalt over the course of the eruption. In contrast, lavas from a cinder cone on the eastern portion of BPVF comprise thin (<0.5 m) pahoehoe capped by thicker (1-2 m) aa flows, suggesting increasing discharge rate over the course of this eruption.

  19. The stratigraphy, timing and climatic implications of glaciolacustrine deposits in the middle Rakaia Valley, South Island, New Zealand

    NASA Astrophysics Data System (ADS)

    Shulmeister, J.; Thackray, G. D.; Rieser, U.; Hyatt, O. M.; Rother, H.; Smart, C. C.; Evans, D. J. A.

    2010-08-01

    Stratigraphic interpretations and infrared stimulated luminescence (IRSL) ages document the glacial history of the Middle Rakaia Gorge section of the Rakaia Valley, Canterbury, New Zealand, during the last two glacial cycles. Sheets of glaciolacustrine sediments several tens of metres in thickness can be traced at least 10 km upstream of the Rakaia Gorge. The stratigraphic package is capped by outwash gravels associated with the last glacial maximum (LGM) advances. The dominant inferred sedimentary environments in the sequence are 1) pro-glacial and paraglacial lake beds, 2) sub-aqueous ice-contact fans, 3) sub-aqueous mass flow deposits 4) supraglacial dump material and 5) outwash gravels. Syndepositional deformation, associated with glacitectonic deformation, is common. The stratigraphy records glacier margin oscillations, including six significant advances. These occurred in early MIS 6, mid-MIS 6, MIS 5b (c100-90 ka), MIS 5a/4 (c 80 ka), mid-MIS 3 (c 48 ka), and late MIS 3 (c 40ka). All the post-MIS 6 advances can be corroborated from other sites in New Zealand and the timings appear to coincide with both Southern Hemisphere insolation minima and maxima, suggesting variable combinations of climatic forcing in New Zealand glaciation.

  20. 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.

  1. 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.; Lancaster, D.E.; Elphick, R.Y.; Pendleton, V.M.

    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.

  2. 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.

  3. Effect of explicit representation of detailed stratigraphy on brine and gas flow at the Waste Isolation Pilot Plant

    SciTech Connect

    Christian-Frear, T.L.; Webb, S.W.

    1996-04-01

    Stratigraphic units of the Salado Formation at the Waste Isolation Pilot Plant (WIPP) disposal room horizon includes various layers of halite, polyhalitic halite, argillaceous halite, clay, and anhydrite. Current models, including those used in the WIPP Performance Assessment calculations, employ a ``composite stratigraphy`` approach in modeling. This study was initiated to evaluate the impact that an explicit representation of detailed stratigraphy around the repository may have on fluid flow compared to the simplified ``composite stratigraphy`` models currently employed. Sensitivity of model results to intrinsic permeability anisotropy, interbed fracturing, two-phase characteristic curves, and gas-generation rates were studied. The results of this study indicate that explicit representation of the stratigraphy maintains higher pressures and does not allow as much fluid to leave the disposal room as compared to the ``composite stratigraphy`` approach. However, the differences are relatively small. Gas migration distances are also different between the two approaches. However, for the two cases in which explicit layering results were considerably different than the composite model (anisotropic and vapor-limited), the gas-migration distances for both models were negligible. For the cases in which gas migration distances were considerable, van Genuchten/Parker and interbed fracture, the differences between the two models were fairly insignificant. Overall, this study suggests that explicit representation of the stratigraphy in the WIPP PA models is not required for the parameter variations modeled if ``global quantities`` (e.g., disposal room pressures, net brine and gas flux into and out of disposal rooms) are the only concern.

  4. 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.

  5. The Cretaceous stratigraphy of the Western Cordillera Oriental, Columbia

    SciTech Connect

    Allen, R.B.; Alfonso, C.A.; Ressetar, R.; Salazar, A. ); Ballesteros, I.; Cardozo, E.; Laverde, F.; Ramirez, C. ); Moreno, J.M. ); Rubiano, J.; Sarmiento, L. )

    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.

  6. 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.

  7. Modeling of the Sedimentary Interbedded Basalt Stratigraphy for the Idaho National Laboratory Probabilistic Seismic Hazard Analysis

    SciTech Connect

    Suzette Payne

    2007-08-01

    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. Core segment 15008 - Regolith stratigraphy at Apennine Front Station 2 using multispectral imaging

    NASA Technical Reports Server (NTRS)

    Pieters, C. M.; Meloy, A.; Hawke, B. R.; Nagle, J. S.

    1982-01-01

    High precision multispectral images for Apennine Front core segment 15008 are presented. These data have a spatial resolution less than approximately 0.5 mm and are analyzed for their compositional information using image analysis techniques. The stratigraphy of the regolith sampled by 15008 is documented here as three distinct zones, the most prominent of which is a feldspathic fragment-rich zone with a chaotic fabric that occurs between 10 and 18 cm depth. It is suggested that this material is the primary rim crest deposit of the local 10 m crater. Above this zone the stratigraphy is more horizontal in nature. Below this zone the soil is observed to be relatively homogeneous with no distinctive structure to 23 cm depth.

  9. Stratigraphy and erosional landforms of layered deposits in Valles Marineris, Mars

    NASA Astrophysics Data System (ADS)

    Komatsu, G.; Geissler, P. E.; Strom, R. G.; Singer, R. B.

    1993-06-01

    Satellite imagery is used to identify stratigraphy and erosional landforms of 13 layered deposits in the Valles Marineris region of Mars (occurring, specifically, in Gangis, Juventae, Hebes, Ophir-Candor, Melas, and Capri-Eos Chasmata), based on albedo and erosional styles. Results of stratigraphic correlations show that the stratigraphy of layered deposits in the Hebes, Juventae, and Gangis Chasmata are not well correlated, indicating that at least these chasmata had isolated depositional environments resulting in different stratigraphic sequences. On the other hand, the layered deposits in Ophir-Candor and Melas Chasmata appear to have been connected in each chasma. Some of the layered deposits display complexities which indicate changes in space and time in the dominant source materials.

  10. Stratigraphy and erosional landforms of layered deposits in Valles Marineris, Mars

    NASA Technical Reports Server (NTRS)

    Komatsu, G.; Geissler, P. E.; Strom, R. G.; Singer, R. B.

    1993-01-01

    Satellite imagery is used to identify stratigraphy and erosional landforms of 13 layered deposits in the Valles Marineris region of Mars (occurring, specifically, in Gangis, Juventae, Hebes, Ophir-Candor, Melas, and Capri-Eos Chasmata), based on albedo and erosional styles. Results of stratigraphic correlations show that the stratigraphy of layered deposits in the Hebes, Juventae, and Gangis Chasmata are not well correlated, indicating that at least these chasmata had isolated depositional environments resulting in different stratigraphic sequences. On the other hand, the layered deposits in Ophir-Candor and Melas Chasmata appear to have been connected in each chasma. Some of the layered deposits display complexities which indicate changes in space and time in the dominant source materials.

  11. Effects of sequence stratigraphy on distribution of Cambro-Ordovician siliciclastic hydrocarbon reservoirs in Michigan basin

    SciTech Connect

    Horne, J.C.; Reel, C.L.; Cummins, G.D. )

    1989-08-01

    The lateral and vertical distribution of Cambrian-Ordovician siliciclastic reservoir-potential rock types in the Michigan basin is governed by the sequence stratigraphy. The sequence stratigraphy is controlled primarily by the interaction of four variables: subsidence, eustasy, volume of sediments, and climate. Seven sequential stratigraphic intervals can be defined in the pre-Utica, Cambrian-Ordovician deposits of the Michigan basin. Each of these unconformity-bounded sequences begins with a siliciclastic unit deposited over a lowstand surface of erosion. These lowstand surfaces developed during periods when eustatic sea level decline exceeded the rate of subsidence in the basin, and much or all of the basin became exposed. Where the sedimentation rate was less than the sum of the rate of subsidence and sea level change, a transgressive sequence developed with more open-marine carbonates overlying shallower water and/or non-marine facies. Reservoir-potential siliciclastics accumulated in incised valley-fill and transgressive reworked deposits.

  12. 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.

  13. Image analysis for measuring stratigraphy in sand-gravel laboratory experiments

    NASA Astrophysics Data System (ADS)

    Orrú, C.; Chavarrías, V.; Uijttewaal, W. S. J.; Blom, A.

    2013-11-01

    Measurements of spatial and temporal changes in the grain size distribution are crucial to improving the modelling of sediment transport and associated grain size-selective processes. We present three complementary techniques to determine such variations in the grain size distribution in sand-gravel laboratory experiments, as well as the resulting stratigraphy: (1) particle colouring, (2) removal of sediment layers, and (3) image analysis. The resulting stratigraphy measurement method has been evaluated in two sets of experiments. In both sets three grain size fractions within the range of coarse sand to fine gravel were painted in different colours. Sediment layers are removed using a wet vacuum cleaner. Subsequently areal images are taken of the surface of each layer. The areal fraction content, i.e. the relative presence of each size fraction over the bed surface, is determined using a colour segmentation algorithm which provides the areal fraction content of a specific colour (i.e., grain size) covering the bed surface. Particle colouring is not only beneficial to this type of image analysis but also observing and understanding grain size-selective processes. The stratigraphy based on areal fractions is measured with sufficient accuracy. Other advantages of the proposed stratigraphy measurement technique are: (a) rapid collection and processing of a large amount of data, (b) very high spatial density of information on the grain size distribution (so far unequalled in other methods), (c) the lack of disturbances to the bed surface, (d) only minor disturbances to the substrate due to the removal of sediment layers, and (e) the possibility to return a sediment layer at its original elevation and continue the flume experiment. The areal fractions can be converted into volumetric fractions using a conversion model. The proposed empirical conversion model is based on a comparison between the photogrammetry results and dry sieve analysis.

  14. Micropaleontology and sedimentology across the Cretaceous/Tertiary boundary at La Ceiba (Mexico): impact-generated sediment gravity flows

    NASA Astrophysics Data System (ADS)

    Arz, J. A.; Arenillas, I.; Soria, A. R.; Alegret, L.; Grajales-Nishimura, J. M.; Liesa, C. L.; Meléndez, A.; Molina, E.; Rosales, M. C.

    2001-10-01

    A micropaleontological and sedimentological study across the Cretaceous/Tertiary boundary-officially Cretaceous/Paleogene (K/P) boundary from the La Ceiba section (Mexico) was performed to examine the K/P planktic foraminiferal biostratigraphy, the sedimentology of a controversial K/P clastic unit, and the benthic and planktic foraminiferal assemblages turnover across this boundary. The clastic unit is stratigraphically placed between two pelagic marly units (Méndez and Velasco Formations) and displays a fining-upward gradation similar to a turbidite sequence. This K/P clastic unit contains a basal subunit consisting of calcareous marls rich in millimeter-sized spherules (microtektites) altered to clay minerals, abundant detrital quartz, mica minerals, and shocked quartz. According to the K/P stratotype definition from El Kef (Tunisia), the K/P boundary at La Ceiba must be placed at the base of the clastic (microspherules) unit since it is equivalent to the base of the boundary clay at El Kef. A short hiatus affects the lower part of the Danian, including the Guembelitria cretacea and Parvularugoglobigerina eugubina biozones and the lower part of the Parasubbotina pseudobulloides biozone. Nearly all commonly recorded Maastrichtian planktic foraminiferal species were found in the uppermost Maastrichtian interval, and there was no support for a gradual mass extinction pattern in the terminal Cretaceous. Benthic foraminiferal assemblages suggest that the La Ceiba section was deposited at lower bathyal depths. Oscillating megatsunami waves and/or a sea-level lowstand cannot explain the nature of the clastic deposits because of the observed deposition paleodepth (more than 1000 m). There is also evidence that the clastic unit was deposited under a high-sedimentation rate in upper flow regimes and that was emplaced as a single-pulse event as turbidites. This datum and other sedimentological features support a sediment gravity flow genesis for the clastic unit. All these results are consistent with the K/P impact theory and the asteroid impact on the Yucatan Peninsula.

  15. Postglacial eruptive history of Laguna del Maule volcanic field in Chile, from fallout stratigraphy in Argentina

    NASA Astrophysics Data System (ADS)

    Fierstein, J.; Sruoga, P.; Amigo, A.; Elissondo, M.; Rosas, M.

    2012-12-01

    The Laguna del Maule (LdM) volcanic field, which surrounds the 54-km2 lake of that name, covers ~500 km2 of rugged glaciated terrain with Quaternary lavas and tuffs that extend for 40 km westward from the Argentine frontier and 30 km N-S from the Rio Campanario to Laguna Fea in the Southern Volcanic Zone of Chile. Geologic mapping (Hildreth et al., 2010) shows that at least 130 separate vents are part of the LdM field, from which >350 km3 of products have erupted since 1.5 Ma. These include a ring of 36 postglacial rhyolite and rhyodacite coulees and domes that erupted from 24 separate vents and encircle the lake, suggesting a continued large magma reservoir. Because the units are young, glassy, and do not overlap, only a few ages had been determined and the sequence of most of the postglacial eruptions had not previously been established. However, most of these postglacial silicic eruptions were accompanied by explosive eruptions of pumice and ash. Recent investigations downwind in Argentina are combining stratigraphy, grain-size analysis, chemistry, and radiocarbon dating to correlate the tephra with eruptive units mapped in Chile, assess fallout distribution, and establish a time-stratigraphic framework for the postglacial eruptions at Laguna del Maule. Two austral summer field seasons with a tri-country collaboration among the geological surveys of the U.S., Chile, and Argentina, have now established that a wide area east of the volcanic field was blanketed by at least 3 large explosive eruptions from LdM sources, and by at least 3 more modest, but still significant, eruptions. In addition, an ignimbrite from the LdM Barrancas vent complex on the border in the SE corner of the lake traveled at least 15 km from source and now makes up a pyroclastic mesa that is at least 40 m thick. This ignimbrite (72-75% SiO2) preceded a series of fall deposits that are correlated with eruption of several lava flows that built the Barrancas complex. Recent 14C dates suggest that most of the preserved LdM fallout eruptions were between 7 ka and 2 ka. However, the oldest and perhaps largest fall unit yet recognized is correlated with the Los Espejos rhyolite lava flow that dammed the lake and yields a 40Ar/39Ar age of 23 ka. Pumice clasts as large as 8.5 cm and lithics to 4 cm were measured 32 km ENE of source. It is the only high-silica rhyolite (75.5-76% SiO2) fall layer yet found, correlates chemically with the Los Espejos rhyolite lava flow, and includes distinctive olivine-bearing lithics that are correlated with mafic lavas which underlie the Espejos vent. Extremely frothy pumice found near the vent is also consistent with the bubble-wall shards and reticulite pumice distinctive of the correlative fall deposit. Another large rhyolite fall deposit (74.5% SiO2), 4 m thick 22 km E of source, has pumice clasts to 9.5 cm and includes ubiquitous coherent clasts of fine, dense soil that suggests it erupted through wet ground; 14C dates (uncalibrated) yield ages ~7 ka. Stratigraphic details suggest that pulses of fallout were accompanied by small pyroclastic flows. Ongoing field and lab work continues to build the LdM postglacial eruptive story. The numerous postglacial explosive eruptions from the LdM field are of significant concern because of ongoing 33 cm/year uplift along the western lakeshore, as measured by InSAR and verified by GPS.

  16. Bio-, Magneto- and event-stratigraphy across the K-T boundary

    NASA Technical Reports Server (NTRS)

    Preisinger, A.; Stradner, H.; Mauritsch, H. J.

    1988-01-01

    Determining the time and the time structure of rare events in geology can be accomplished by applying three different and independent stratigraphic methods: Biostratigraphy, magneto-stratigraphy and event-stratigraphy. The optimal time resolution of the two former methods is about 1000 years, while by means of event-stratigraphy a resolution of approximately one year can be achieved. For biostratigraphy across the Cretaceous-Tertiary (K-T) boundary micro- and nannofossils have been found best suited. The qualitative and quantitative analyses of minerals and trace elements across the K-T boundary show anomalies on a millimeter scale and permit conclusions regarding the time structure of the K-T event itself. The results of the analyses find a most consistent explanation by the assumption of an extraterrestrial impact. The main portion of the material rain from the atmosphere evidently was deposited within a short time. The long-time components consist of the finest portion of the material rain from the atmosphere and the transported and redeposited fall-out.

  17. Neogene carbonate exploration play concepts for Northern New Guinea: New iteration from field work and seismic stratigraphy along the Northern New Guinea Fault Zone

    SciTech Connect

    Pigott, J.D.; Geiger, C. )

    1994-07-01

    Recent field reconnaissance, petrography, nanno and foraminifera age determinations, and seismic stratigraphy of the Sepik and Piore subbasins of northern New Guinea reveal the existence of an extensive, tectonically unstable, Miocene-Pliocene carbonate shelf system. These findings represent the first recorded evidence of northern Papuan limestones coeval in age to those of the hydrocarbon productive Salawati Basin of Irian Jaya. Moreover, these observations also demonstrate the significance of episodic activities of the northern New Guinea fault zone upon the changes in carbonate sedimentation and diagenesis. During the Neogene, algal biosparites to foraminiferal biomicrites defined the clean portion of a mixed clastic-carbonate shelf system of the northern New Guinea basin, which began at the central New Guinea cordillera and deepened northward. This shelf was interrupted by coral-coralline algal boundstone fringing- to patch-reef buildups with associated skeletal grainstones. Clean carbonates were spatially and temporally restricted to basement blocks, which episodically underwent uplift while terrigenous dilutes carbonates were more common in adjacently subsiding basement block bathymetric lows. These tectonic expressions were caused by the spatially transient nature of constraining bends of the evolving north New Guinea faults. As shown by seismic stratigraphy, by the late Miocene to the early Pliocene the uplift of the Bewani-Torricelli Mountains sagittally divided the shelf of the northern New Guinea basin into the Ramu-Sepik and the Piore basins. Continued regional sinistral transpression between the Pacific and the New Guinea leading edge of the Indo-Australian plates led to the reverse tilting of the Piore basin, the shallowing of the former distal shelf with concomitant extensive biolithite development (e.g., on subsiding volcanic islands) eventual uplifting of the Oenake Range, and en echelon faulting of the Bewani-Torricelli Mountains.

  18. Depositional sequence analysis and sedimentologic modeling for improved prediction of Pennsylvanian reservoirs

    SciTech Connect

    Watney, W.L.

    1994-12-01

    Reservoirs in the Lansing-Kansas City limestone result from complex interactions among paleotopography (deposition, concurrent structural deformation), sea level, and diagenesis. Analysis of reservoirs and surface and near-surface analogs has led to developing a {open_quotes}strandline grainstone model{close_quotes} in which relative sea-level stabilized during regressions, resulting in accumulation of multiple grainstone buildups along depositional strike. Resulting stratigraphy in these carbonate units are generally predictable correlating to inferred topographic elevation along the shelf. This model is a valuable predictive tool for (1) locating favorable reservoirs for exploration, and (2) anticipating internal properties of the reservoir for field development. Reservoirs in the Lansing-Kansas City limestones are developed in both oolitic and bioclastic grainstones, however, re-analysis of oomoldic reservoirs provides the greatest opportunity for developing bypassed oil. A new technique, the {open_quotes}Super{close_quotes} Pickett crossplot (formation resistivity vs. porosity) and its use in an integrated petrophysical characterization, has been developed to evaluate extractable oil remaining in these reservoirs. The manual method in combination with 3-D visualization and modeling can help to target production limiting heterogeneities in these complex reservoirs and moreover compute critical parameters for the field such as bulk volume water. Application of this technique indicates that from 6-9 million barrels of Lansing-Kansas City oil remain behind pipe in the Victory-Northeast Lemon Fields. Petroleum geologists are challenged to quantify inferred processes to aid in developing rationale geologically consistent models of sedimentation so that acceptable levels of prediction can be obtained.

  19. Geology and stratigraphy of the San Lorenzo Tezonco deep well and its correlation to surrounding ranges, Mexico Basin

    NASA Astrophysics Data System (ADS)