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The sedimentary sequence recovered from the Voka outcrops, northeastern Estonia: implications for late Pleistocene stratigraphy  

Directory of Open Access Journals (Sweden)

Full Text Available New palaeoenvironmental and geological data, which may be integrated with the results from the neighbouring regions, were collected from two well-exposed continuous outcrops in the vicinity of Voka village, northeastern Estonia. These outcrops, situated in a klint depression – klint bay –, show an about 22 m thick stacked sequence of sandy to clayey subaqueous deposits. This succession of water-lain sediments documents the response to climate change during the late Pleistocene. On the basis of grain size characteristics, sedimentological structures, and luminescence chronostratigraphical data, the sequence is subdivided into two main units – A and B. Optical dating of 18 samples from the upper unit A shows that the unit is of middle Järva (= middle Weichselian) age (marine isotope stage (MIS) 3). Representative pollen spectra derived from 45 samples from the pollen-bearing part of unit A provide convincing evidence of noticeable changes in vegetation and climate in NE Estonia during the time period from 39 to 33 kyr BP, within which two intervals of severe climate and two relatively milder ones have been recognized. Preliminary data from the underlying unit B indicate that deposits of the last interglacial sensu lato and those of early pleniglacial age correlating with MIS 5 and MIS 4, respectively, occur here as well. Thus, the data obtained during the present study show unambiguously that in contrast with the expectations, the greater part of the late Pleistocene sequence is represented in the Voka section. No evidence was found for glacial activity during the late Pleistocene period predating the last glacial maximum. The use of the Voka event stratigraphy as a template facilitates search for correlative horizons in the neighbouring regions.

Molodkov, Anatoly; Bolikhovskaya, Nataliya; Miidel, Avo; Ploom, Kuldev

2007-01-01

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Late Pleistocene Holocene stratigraphy and radiocarbon dating of La Malinche volcano, Central Mexico  

Science.gov (United States)

Previous studies of La Malinche identified and radiocarbon dated several volcanic layers, the youngest of which yielded an age of ca. 7.5 ka. An additional ash fallout layer that crops out at high altitudes was considered the most recent deposit, with an estimated age of 6 ka. In the present work 38 new radiocarbon ages are presented. From these, several date the young ash fallout layer and lie around 3.1 ka. With the aid of these dates a new and comprehensive stratigraphy documenting the Late Pleistocene Holocene eruptive history of La Malinche is presented. The stratigraphy indicates two main stages of volcanic activity: Pre-Malinche and Malinche. The first undoubtedly comprises the major part of the eruptive history, but its deposits are largely covered by the products of the latter stage, on which this study is focused. The Malinche stage was subdivided into three eruptive periods. Period 1 started with the emplacement of the Huamantla Pumice more than 45 ka ago. This deposit consists of a thick pumice fallout overlain by pyroclastic flow deposits. Subsequently, several episodes of construction and collapse of summit domes occurred. The oldest dome was dated at ca. 45 ka. Period 2 started 21.5 ka ago with the Malinche Pumice I, a widespread pumice fallout covering the entire slopes of the volcano. Pyroclastic flows and lahars related to this eruption were channeled along deep barrancas and reached considerable distances. Deposits produced by partial sector collapse and dated at ca. 20.9 ka, and a pumice-and-ash flow deposit dated at 15.9 ka were also generated during this period. The last period started with the eruption of the Malinche Pumice II, a distinctive fallout deposit overlain by ash flow deposits on the NE slope of the volcano. The age of this pumice layer is estimated between 12 and 9 ka. Formation of block-and-ash flows, lahars and pumice-and-ash flows followed during this period, and peaked in a most intensive episode that was dated at 7.5 ka. After this, a long interval of quiescence was interrupted 3.1 ka ago, with the eruption of an ash fallout accompanied by small pyroclastic flows, whose deposits are the youngest volcanic products recognized at La Malinche. The new stratigraphic findings identify La Malinche as a potentially active and dangerous volcano that could severely affect densely populated areas at its lower slopes. In addition, the results of this work can shed some light on archaeological research that is being carried out in the Puebla Tlaxcala region.

Castro-Govea, Renato; Siebe, Claus

2007-04-01

3

Late Pleistocene to recent sedimentation and stratigraphy of the Gulf of Mexico outer continental shelf, offshore Louisiana  

Energy Technology Data Exchange (ETDEWEB)

The Late Pleistocene to Recent sedimentation and stratigraphy of the Louisiana outer continental shelf was studied using sediment from a 480-ft engineering boring and hazard survey data from the Eugene Island Block 366 area. The major findings of this research include the following. (1) A sequence of condensed sections (rising to high sea level) and expanded sections (falling to low sea level) along with strong evidence for four major drops in sea level over the last 300,000 yr. (2) Condensed sections characterized by fine-grained sediment containing significant amounts of diagenetic pyrite, benthonic and planktonic foraminifera, and echinoid fragments; CaCO{sub 3} content decreasing downward; the percentage of quartz and feldspar grains increasing downward; the presence of a basal shell concentration with a glauconitic sand found in unit 7; and seismic facies dominated by sheet drape (hemipelagic deposits). (3) The existence of a meltwater facies (associated with high glacial meltwater influx from the Mississippi River) and a highstand facies (associated with no significant glacial meltwater influx) with the condensed sections. (4) Expanded sections characterized by a higher percentage of coarse material in the sediment than in the condensed sections; exposure surfaces at the top of the section; erosional truncation of seismic reflections; coarsening-upward sequences; rare microfossils, diagenetic pyrite, and echinoid fragments; CaCO{sub 3} increasing downward; wood fragments, muscovite mica, and biotite mica that are not found in the condensed sections; and seismic facies that include oblique progradational (delta), sigmoid progradational (low-energy outbuilding), and mounded chaotic (mass transport facies). (5) The existence of sedimentary magnetite in the expanded sections and associated magnetic anomalies that were mapped.

Crane, J.H. (Chevron U.S.A., Inc., Lafayette, LA (USA)); Sheriff, R.E.; Dupre, W.R. (Univ. of Houston, TX (USA))

1990-05-01

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Significance of Late Pliocene-Early Pleistocene stratigraphy to development of Buena Vista field, San Joaquin Valley, California  

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Late Pliocene to early Pleistocene depositional patterns of upper Etchegoin and lower San Joaquin Formation sand and shale units in the Buena vista field area were controlled by changes in clastic input, eustatic sea level, structural growth, and circulation patterns in the south end of the San Joaquin Valley. Wireline and drill-strip logs, core depositions, paleontology, and petrographic data from these units suggest the interpretation of a series of shallow to marginal marine deposits with distinctive morphologic features and production characteristics. Late Pliocene marginal marine drainage systems transported clastics from southerly sources as structural and/or eustatic changes shoaled the southern area. An erosional hiatus and shallow marine transgression marked the extent of Plio-Pleistocene shoaling and rapid early Pleistocene foundering. Later Pleistocene changes in sediment supply and structural growth isolated the area from marine conditions as the basin filled with nonmarine sediments. Early field development was influenced by the areal distribution and reservoir characteristics of these sands as well as by the timing of such development activity. Depositional models derived from these data are useful in constructing paleogeographic models with regional hydrocarbon significance.

Kuespert, J.G.

1987-05-01

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Late Pleistocene glacial stratigraphy of the Kumara-Moana region, West Coast of South Island, New Zealand  

Science.gov (United States)

On the South Island of New Zealand, large piedmont glaciers descended from an ice cap on the Southern Alps onto the coastal plain of the West Coast during the late Pleistocene. The series of moraine belts and outwash plains left by the Taramakau glacier are used as a type section for interpreting the glacial geology and timing of major climatic events of New Zealand and also as a benchmark for comparison with the wider Southern Hemisphere. In this paper we review the chronology of advances by the Taramakau glacier during the last or Otira Glaciation using a combination of exposure dating using the cosmogenic nuclides 10Be and 36Cl, and tephrochronology. We document three distinct glacial maxima, represented by the Loopline, Larrikins and Moana Formations, separated by brief interstadials. We find that the Loopline Formation, originally attributed to Oxygen Isotope Chronozone 4, is much younger than previously thought, with an advance culminating around 24,900 ± 800 yr. The widespread late Pleistocene Kawakawa/Oruanui tephra stratigraphically lies immediately above it. This Formation has the same age previously attributed to the older part of the Larrikins Formation. Dating of the Larrikins Formation demonstrates there is no longer a basis for subdividing it into older and younger phases with an advance lasting about 1000 years between 20,800 ± 500 to 20,000 ± 400 yr. The Moana Formation represents the deposits of the last major advance of ice at 17,300 ± 500 yr and is younger than expected based on limited previous dating. The timing of major piedmont glaciation is restricted to between ˜25,000 and 17,000 yr and this interval corresponds to a time of regionally cold sea surface temperatures, expansion of grasslands at the expense of forest on South Island, and hemisphere wide glaciation.

Barrows, Timothy T.; Almond, Peter; Rose, Robert; Keith Fifield, L.; Mills, Stephanie C.; Tims, Stephen G.

2013-08-01

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Sequence stratigraphy of Late Pliocene and Pleistocene sediments of northwestern Green Canyon Area/western Ewing Bank, northern Gulf of Mexico  

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Northwestern Green Canyon and Western Ewing Bank lease areas are characterized by complex faulting and salt deformation affecting the late Pliocene-Pleistocene sediments. The sequence stratigraphy has been studied using 1300 km of multifold seismic data, and 40 wells with biostratigraphy data (12 with high-resolution analysis). Fossil abundance and diversity curves were used to recognize condensed sections. Eight depositional sequences have been recognized (2.4, 1.9, 1.4, 0.8, 0.7, 0.5, and 0.4 Ma). Maximum thickness of these sediments is 6 km. Paleobathymetry indicates that sequences were deposited primarily in bathyal water depths. Most of the sediments are in the lowstand systems tracts and consist of basin-floor fans, slope fans, and prograding complexes. Thick blocky sand packages (basin-floor fan) are present in two major sequences (1.4 and 1.1 Ma) and represent potential reservoirs in the area. Transgressive and highstand systems tracts are fairly thin across the area and are thicker only in the younger sequences (< 0.5 Ma). The syndepositional structures play an important role in controlling the geometry and distribution of the depositional units, as well as creating structural highs for petroleum entrapment. Existing discoveries in the area include Green Canyon Blocks 6, 52, 184, and 228, and are associated primarily with amplitude anomalies on the flanks of salt structures and/or faults.

Martinez, R.E.; Weimer, P. [Univ. of Colorado, Boulder, CO (United States)

1994-09-01

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Late quaternary sequence stratigraphy, South Florida margin  

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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.

Locker, S.D.; Hine, A.C. [Univ. of South Florida, St. Petersburg, FL (United States). Dept. of Marine Science

1995-12-01

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Late pleistocene faunal extinctions in southern patagonia.  

UK PubMed Central (United Kingdom)

Major environmental changes recorded in pollen records from various sites in southern Patagonia and Tierra del Fuego are also reflected in pollen and cuticle data from dung of the late Pleistocene groundsloth. The most prominent change was the large-scale reduction of steppe environment about 10,000 years ago, which coincides with the latest dates for extinctions of many large grazers such as the giant groundsloth. Stress on food resources for all the large grazers may well have hastened their extinction. Hunting pressure by paleoindians may have been the final blow.

Markgraf V

1985-05-01

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Current research on the late Pliocene and Pleistocene deposits north of Homa Mountain, southwestern Kenya.  

Science.gov (United States)

The late Pliocene and Pleistocene sediments of the Homa Peninsula in southwestern Kenya are richly fossiliferous, preserve Early Stone Age archaeological traces and provide one of the few paleoanthropological data sets for the region between the branches of the East African Rift Valley. This paper presents preliminary results of our ongoing investigation of late Pliocene and Pleistocene deposits at the localities of Rawi, Kanam East, Kanam Central and Kanjera. While fossils have been collected from the peninsula since 1911, little systematic effort has been made to place them into a broader litho-and chronostratigraphic framework. This project has conclusively demonstrated that fossils occur in good stratigraphic context at all of the study localities and that claims of sediment slumping (Boswell, 1935) have been greatly overstated (Behrensmeyer et al., 1995; Plummer & Potts, 1989). A provisional chronostratigraphic framework based on magneto- and biostratigraphy is presented here. We have revised the Plio-Pleistocene stratigraphy of the Rawi and Kanam gullies to include three formations: the Rawi, Abundu and Kasibos Formations. Based on magneto- and biostratigraphy, these formations are dated between approximately three and one m.y.a. (Gauss Chron-Jaramillo Subchron) (Cande & Kent, 1995). The Apoko Formation unconformably overlies the others and may be middle to late Pleistocene in age. All formations contain rich patches of fossils, and Acheulean artifacts have been surface collected from the Abundu and Kasibos Formations. Deposition of the fossil- and artefact-bearing sediments at Kanjera North began in the early Pleistocene and continued into the middle Pleistocene. Deposition at Kanjera South began over one million years earlier than previously thought, at approximately 2.2 m.y.a., and continued into the Olduvai Subchron (1.770-1.950 m.y.a.; Cande & Kent, 1995). Excavations have recovered Oldowan artefacts in association with well-preserved fossil fauna near the base of the sequence, the oldest archaeological traces yet known from southwestern Kenya. PMID:10068063

Ditchfield, P; Hicks, J; Plummer, T; Bishop, L C; Potts, R

1999-02-01

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Current research on the late Pliocene and Pleistocene deposits north of Homa Mountain, southwestern Kenya.  

UK PubMed Central (United Kingdom)

The late Pliocene and Pleistocene sediments of the Homa Peninsula in southwestern Kenya are richly fossiliferous, preserve Early Stone Age archaeological traces and provide one of the few paleoanthropological data sets for the region between the branches of the East African Rift Valley. This paper presents preliminary results of our ongoing investigation of late Pliocene and Pleistocene deposits at the localities of Rawi, Kanam East, Kanam Central and Kanjera. While fossils have been collected from the peninsula since 1911, little systematic effort has been made to place them into a broader litho-and chronostratigraphic framework. This project has conclusively demonstrated that fossils occur in good stratigraphic context at all of the study localities and that claims of sediment slumping (Boswell, 1935) have been greatly overstated (Behrensmeyer et al., 1995; Plummer & Potts, 1989). A provisional chronostratigraphic framework based on magneto- and biostratigraphy is presented here. We have revised the Plio-Pleistocene stratigraphy of the Rawi and Kanam gullies to include three formations: the Rawi, Abundu and Kasibos Formations. Based on magneto- and biostratigraphy, these formations are dated between approximately three and one m.y.a. (Gauss Chron-Jaramillo Subchron) (Cande & Kent, 1995). The Apoko Formation unconformably overlies the others and may be middle to late Pleistocene in age. All formations contain rich patches of fossils, and Acheulean artifacts have been surface collected from the Abundu and Kasibos Formations. Deposition of the fossil- and artefact-bearing sediments at Kanjera North began in the early Pleistocene and continued into the middle Pleistocene. Deposition at Kanjera South began over one million years earlier than previously thought, at approximately 2.2 m.y.a., and continued into the Olduvai Subchron (1.770-1.950 m.y.a.; Cande & Kent, 1995). Excavations have recovered Oldowan artefacts in association with well-preserved fossil fauna near the base of the sequence, the oldest archaeological traces yet known from southwestern Kenya.

Ditchfield P; Hicks J; Plummer T; Bishop LC; Potts R

1999-02-01

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Soil Stratigraphy from Three Pleistocene Archaeological Sites of the Middle Ter River Valley, Catalonia, Spain  

Directory of Open Access Journals (Sweden)

Full Text Available This dissertation summarizes the stratigraphic description of three Pleistocene archaeological sites inthe middle Ter river valley. A long history of archaeological research in this region suggests thepossibility of developing contextual studies. This work is basically an investigation of two soilformation processes from the deep soil horizons of the Mediterranean region: clay illuviation andcarbonatation. This approach has been developed by soil micromorphology, a technique well suitedfor this type of record, supplemented by fundamental field descriptions and basic cartography of the geomorphological terraces of the middle Ter river valley. The soil stratigraphy of archaeological sites and Pleistocene landscapes opens the opportunity to investigate a complex subject of study. The soils and paleosols are a source of information for palaeoecology and human occupations. It has been attempted here only to lay the groundwork for the interpretation of genetic factors pointing to the classification of soils.

Sayantani NEOGI

2010-01-01

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Late Pleistocene floras from Earith, Huntingdonshire.  

UK PubMed Central (United Kingdom)

A pit in fluviatile gravel of the River Ouse at the western edge of the East Anglian fenland has exposed several richly organic beds of Last-glacial age. A radiocarbon date of 42 000 years from one bed confirms the terrace stratigraphy in placing the beds in a fairly early part of the Weichselian. The organic beds are succeeded by cryoturbation phenomena and ice wedge casts, indicating a severely cold climate with permafrost. The beds represent former pools on the flood-plain into which plant detritus was washed from the surroundings, chiefly by melt water in the spring. Pollen is sparse, but the macroscopic plant remains indicate a vegetation dominated by dwarf willows, accompanied by many herbs of base-rich, open habitats. Identification of the macrofossils is discussed and comments are made on the ecology and taxonomy of important species. The flora contains a mixture of northern and southern distributional types, the southern including species requiring a July mean temperature approaching 16 °C. Halophytes are frequent, and four species are considered to be obligate halophytes and to demonstrate the presence of salt in the substrate. The plant mixtures are explained as a result of the peculiarly open habitats of the glacial landscape and of the climate, which appears to have had warm summers and very cold winters, with a mean annual temperature slightly below 0 °C, resulting in discontinuous permafrost.

Bell FG

1970-07-01

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Late Middle Pleistocene hominin teeth from Panxian Dadong, South China.  

UK PubMed Central (United Kingdom)

The hominin teeth and evidence of hominin activities recovered from 1991 to 2005 at the Panxian Dadong site in South China are dated to the late Middle Pleistocene (MIS 8-6 or ca. 130-300 ka), a period for which very little is known about the morphology of Asian populations. The present study provides the first detailed morphometric description and comparisons of four hominin teeth (I(1), C1, P(3) and P3) from this site. Our study shows that the Panxian Dadong teeth combine archaic and derived features that align them with Middle and Upper Pleistocene fossils from East and West Asia and Europe. These teeth do not display any typical Neanderthal features and they are generally more derived than other contemporaneous populations from Asia and Africa. However, the derived traits are not diagnostic enough to specifically link the Panxian Dadong teeth to Homo sapiens, a common problem when analyzing the Middle Pleistocene dental record from Africa and Asia. These findings are contextualized in the discussion of the evolutionary course of Asian Middle Pleistocene hominins, and they highlight the necessity of incorporating the Asian fossil record in the still open debate about the origin of H. sapiens.

Liu W; Schepartz LA; Xing S; Miller-Antonio S; Wu X; Trinkaus E; Martinón-Torres M

2013-05-01

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Late Middle Pleistocene hominin teeth from Panxian Dadong, South China.  

Science.gov (United States)

The hominin teeth and evidence of hominin activities recovered from 1991 to 2005 at the Panxian Dadong site in South China are dated to the late Middle Pleistocene (MIS 8-6 or ca. 130-300 ka), a period for which very little is known about the morphology of Asian populations. The present study provides the first detailed morphometric description and comparisons of four hominin teeth (I(1), C1, P(3) and P3) from this site. Our study shows that the Panxian Dadong teeth combine archaic and derived features that align them with Middle and Upper Pleistocene fossils from East and West Asia and Europe. These teeth do not display any typical Neanderthal features and they are generally more derived than other contemporaneous populations from Asia and Africa. However, the derived traits are not diagnostic enough to specifically link the Panxian Dadong teeth to Homo sapiens, a common problem when analyzing the Middle Pleistocene dental record from Africa and Asia. These findings are contextualized in the discussion of the evolutionary course of Asian Middle Pleistocene hominins, and they highlight the necessity of incorporating the Asian fossil record in the still open debate about the origin of H. sapiens. PMID:23465337

Liu, Wu; Schepartz, Lynne A; Xing, Song; Miller-Antonio, Sari; Wu, Xiujie; Trinkaus, Erik; Martinón-Torres, María

2013-03-05

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The Pliocene and Pleistocene of Pampean region (Argentina): systematic aspects on taphonomy and bio stratigraphy  

International Nuclear Information System (INIS)

Canids in South America were first recorded in the Vorohuean (Middle Pliocene) at southeast marine cliff of Pampean region. These records were assigned to Dusicyon cultridens. D. gymnocercus has it oldest record in the Ensenadan (Early to Middle Pleistocene) of the Pampean Region (Argentina) and Tarija (Bolivia). Remains of this species are frequents in the Bonaerian and Lujanian (Middle to Late Pleistocene) of the Buenos Aires and Entre Rios provinces. Outside Argentina D. gymnocercus was recorded in the Lujanian of Brazil and Uruguay. Two new records of Dusicyon from Punta San Andres (Buenos Aires province) are presented here. The first one (MLP 07-V-2-1) comes from Arroyo Seco Formation(Bonaerian, Middle Pleistocene) and is assigned here to D. gymnocercus. MLP 07-V-2-1 constitutes the first record of this species at Arroyo Seco Formation. The other one (MLP 07-V-2-2) was exhumed from a paleocave excavated in San Andres Formationsediments (Sanandresian, Late Pliocene) and filled with sanandresian sediments. Also, rodent remains (Ctenomys chapadmalalensis and cavids) were collected inside of the paleocave. Although, the study carried out prevents the assignation of MLP 07-V-2-2 to any of the Dusicyon species, this remain shows some affinity with D. gymnocercus. If this is confirmed in the future MLP 07-V-2-2 could be the oldest record of D. gymnocercus. In addition we discuss some litoestratigraphic and bioestratigraphic aspects of Punta San Andres and taphonomic implications related with the paleocave were MLP 07-V-2-2 was founded.(author)

2007-01-01

16

Sequence stratigraphy of late Mesozoic rocks of the Colorado plateau  

Energy Technology Data Exchange (ETDEWEB)

The Zuni sequence, as defined by Sloss, encompasses rocks ranging in age from the latest Early Jurassic to about the Cretaceous-Tertiary boundary. In current Exxon sequence stratigraphic charts this Sloss sequence is divided into three global supersequence sets, all of which can be readily recognized in the rocks of the Colorado Plateau: (1) the lower Zuni A (global) corresponds to the San Rafael Group, (2) the lower Zuni B is represented by the Morrison Formation, and (3) the upper Zuni is the Late Cretaceous deltaic and marine package (Mancos Shale and equivalents). The global Zuni sequence is divisible into twelve supersequences, the boundaries of which generally correspond to major regional unconformities in the Rocky Mountains. Not all unconformities correspond to Exxon's global sequence boundaries, however, because processes such as regional marine transgression (base Curtis SS; J3 unconformity), foredeep rebound (intraformational unconformity in the Sanpete Formation) and forebulge migration (Dakota SS truncation) produce local unconformities totally independent of regional sea-level change. The stratigraphy of the Zuni sequence of the Colorado Plateau clearly supports the concept that global sea-level change is the principal determinant of large-scale lithofacies architecture, including those of mostly nonmarine origin. At the scale of the supersequences (10 m.y.), the globally recognized episodes of sea-level fall have all produced major unconformities within Zuni rocks of the Colorado Plateau. This suggests that the large-scale packaging of rocks in the Phanerozoic reflects eustatic cycles, not tectonic ones as maintained by Sloss.

Nummedal, D. (Louisiana State Univ., Baton Rouge (United States))

1991-03-01

17

Strontium isotope stratigraphy and geochemistry of the late Neogene ocean  

International Nuclear Information System (INIS)

A curve describing the variation of the strontium isotopic composition of seawater for the late Neogene (9 to 2 Ma) was constructed from 87Sr/86Sr analyses of marine carbonate in five Deep Sea Drilling Project (DSDP) sites: 502, 519, 588, 590, and 593. The strontium isotopic composition of the oceans increased between 9 and 2 Ma with several changes in slope. From 9 to 5.5 Ma 87Sr/86Sr values were nearly constant at ? 0.708925. Between 5.5 and 4.5 Ma, 87Sr/86Sr ratios increased monotonically at a rate of ? 1 x 10-4 per million years. The steep slope during this interval provides the potential for high resolution strontium isotope stratigraphy across the Miocene/Pliocene boundary. The rate of change of 87Sr/86Sr decreases to near zero again during the interval 4.5-2.5 Ma, and ratios average 0.709025. The relatively rapid increase of 87Sr/86Sr between 5.5 and 4.5 Ma must be related to changes in the flux or average 87Sr/86Sr ratios of the major inputs of Sr to the oceans. Quantitative modelling of these inputs suggests that the increase was most probably caused by an increase in the dissolved riverine flux of strontium to the oceans, an increase in the average 87Sr/86Sr composition of river water, or some combination of these parameters. Modelling of this period as a transient-state requires a pulse-like increase in the input of 87Sr to the oceans between 5.5 and 4.5 Ma. Alternatively, the 5.5-4.5 Ma period can be modelled as a simple transition from one steady-state to another if the oceanic residence time of strontium was eight times less than the currently accepted value of 4 Ma. (orig./Shoe).

1989-01-01

18

Late Pleistocene voles (Arvicolinae, Rodentia) from the Baranica Cave (Serbia)  

Science.gov (United States)

Baranica is a cave system situated in the south-eastern part of Serbia, four kilometers south to Knjaževac, on the right bank of the Trgovi\\vski Timok. The investigations in Baranica were conducted from 1994 to 1997 by the Faculty of Philosophy from Belgrade and the National Museum of Knjaževac. Four geological layers of Quaternary age were recovered. The abundance of remains of both large and small mammals was noticed in the early phase of the research. In this paper, the remains of eight vole species are described: Arvicola terrestris (Linnaeus, 1758), Chionomys nivalis (Martins, 1842), Microtus (Microtus) arvalis (Pallas, 1778) and Microtus (Microtus) agrestis (Linnaeus, 1761), Microtus (Stenocranius) gregalis (Pallas, 1779), Microtus (Terricola) subterraneus (de Sélys-Longchamps, 1836), Clethrionomys glareolus (Schreber, 1780) and Lagurus lagurus (Pallas, 1773). Among them, steppe and open area inhabitants prevail. Based on the evolutionary level and dimensions of the Arvicola terrestris molars, as well as the overall characteristics of the fauna, it was concluded that the deposits were formed in the last glacial period of the Late Pleistocene. These conclusions are rather consistent with the absolute dating of large mammal bones (23.520 ± 110 B.P. for Layer 2 and 35.780 ± 320 B.P. for Layer 4).

Bogi?evi?, Katarina; Nenadi?, Draženko; Mihailovi?, Dušan

2012-02-01

19

Ecological consequences of early Late Pleistocene megadroughts in tropical Africa.  

UK PubMed Central (United Kingdom)

Extremely arid conditions in tropical Africa occurred in several discrete episodes between 135 and 90 ka, as demonstrated by lake core and seismic records from multiple basins [Scholz CA, Johnson TC, Cohen AS, King JW, Peck J, Overpeck JT, Talbot MR, Brown ET, Kalindekafe L, Amoako PYO, et al. (2007) Proc Natl Acad Sci USA 104:16416-16421]. This resulted in extraordinarily low lake levels, even in Africa's deepest lakes. On the basis of well dated paleoecological records from Lake Malawi, which reflect both local and regional conditions, we show that this aridity had severe consequences for terrestrial and aquatic ecosystems. During the most arid phase, there was extremely low pollen production and limited charred-particle deposition, indicating insufficient vegetation to maintain substantial fires, and the Lake Malawi watershed experienced cool, semidesert conditions (<400 mm/yr precipitation). Fossil and sedimentological data show that Lake Malawi itself, currently 706 m deep, was reduced to an approximately 125 m deep saline, alkaline, well mixed lake. This episode of aridity was far more extreme than any experienced in the Afrotropics during the Last Glacial Maximum (approximately 35-15 ka). Aridity diminished after 95 ka, lake levels rose erratically, and salinity/alkalinity declined, reaching near-modern conditions after 60 ka. This record of lake levels and changing limnological conditions provides a framework for interpreting the evolution of the Lake Malawi fish and invertebrate species flocks. Moreover, this record, coupled with other regional records of early Late Pleistocene aridity, places new constraints on models of Afrotropical biogeographic refugia and early modern human population expansion into and out of tropical Africa.

Cohen AS; Stone JR; Beuning KR; Park LE; Reinthal PN; Dettman D; Scholz CA; Johnson TC; King JW; Talbot MR; Brown ET; Ivory SJ

2007-10-01

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Late Pleistocene Megafaunal Extinction Consistent With YDB Impact Hypothesis at Younger Dryas Onset  

Science.gov (United States)

At least 35 mammal and 19 bird genera became extinct across North America near the end of the Pleistocene. Modern increases in stratigraphic and dating resolution suggest that this extinction occurred relatively rapidly near 12.9 ka (11 radiocarbon kyrs). Within the context of a long-standing debate about its cause, Firestone et al., (2007) proposed that this extinction resulted from an extraterrestrial (ET) impact over North America at 12.9 ka. This hypothesis predicts that the extinction of most of these animals should have occurred abruptly at 12.9 ka. To test this hypothesis, we have critically examined radiocarbon ages and the extinction stratigraphy of these taxa. From a large data pool, we selected only radiocarbon dates with low error margins with a preference for directly dated biological materials (e.g., bone, dung, etc.) and modern chemical purification techniques. A relatively small number of acceptable dates indicate that at least 16 animal genera and several other species became extinct close to 12.9 ka. These taxa include the most common animals of the late Pleistocene such as horses, camels, and mammoths. Also, the remains of extinct taxa are reportedly found up to, but not above, the base of a widely distributed carbon-rich layer called the black mat. This stratum forms an abrupt, major biostratigraphic boundary at the Younger Dryas onset (12.9 ka), which also contains multiple ET markers comprising the impact layer (the YDB). Surviving animal populations were abruptly reduced at the YDB (e.g., Bison), with major range restrictions and apparent evolutionary bottlenecks. The abruptness of this major extinction is inconsistent with the hypotheses of human overkill and climatic change. We argue that extinction ages older than 12.9 ka for many less common species result from the Signor-Lipps effect, but the impact hypothesis predicts that as new dates are acquired, they will approach ever closer to 12.9 ka. The megafaunal extinction is strongly associated with abrupt and major vegetation changes, abrupt cooling, and widespread biomass burning at the onset of the Younger Dryas over North America. The stratigraphic and chronologic data are consistent with megafaunal extinction being caused by continental-scale ecosystem disruption due to an ET impact.

Kennett, J. P.; Kennett, D. J.

2008-12-01

 
 
 
 
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Macroecological analyses support an overkill scenario for late Pleistocene extinctions.  

UK PubMed Central (United Kingdom)

The extinction of megafauna at the end of Pleistocene has been traditionally explained by environmental changes or overexploitation by human hunting (overkill). Despite difficulties in choosing between these alternative (and not mutually exclusive) scenarios, the plausibility of the overkill hypothesis can be established by ecological models of predator-prey interactions. In this paper, I have developed a macroecological model for the overkill hypothesis, in which prey population dynamic parameters, including abundance, geographic extent, and food supply for hunters, were derived from empirical allometric relationships with body mass. The last output correctly predicts the final destiny (survival or extinction) for 73% of the species considered, a value only slightly smaller than those obtained by more complex models based on detailed archaeological and ecological data for each species. This illustrates the high selectivity of Pleistocene extinction in relation to body mass and confers more plausibility on the overkill scenario.

Diniz-Filho JA

2004-08-01

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Macroecological analyses support an overkill scenario for late Pleistocene extinctions.  

Science.gov (United States)

The extinction of megafauna at the end of Pleistocene has been traditionally explained by environmental changes or overexploitation by human hunting (overkill). Despite difficulties in choosing between these alternative (and not mutually exclusive) scenarios, the plausibility of the overkill hypothesis can be established by ecological models of predator-prey interactions. In this paper, I have developed a macroecological model for the overkill hypothesis, in which prey population dynamic parameters, including abundance, geographic extent, and food supply for hunters, were derived from empirical allometric relationships with body mass. The last output correctly predicts the final destiny (survival or extinction) for 73% of the species considered, a value only slightly smaller than those obtained by more complex models based on detailed archaeological and ecological data for each species. This illustrates the high selectivity of Pleistocene extinction in relation to body mass and confers more plausibility on the overkill scenario. PMID:15622839

Diniz-Filho, J A F

2004-08-01

23

Middle to Late Pleistocene ice extents, tephrochronology and paleoenvironments of the White River area, southwest Yukon  

Science.gov (United States)

Sedimentary deposits from two Middle to Late Pleistocene glaciations and intervening non-glacial intervals exposed along the White River in southwest Yukon, Canada, provide a record of environmental change for much of the past 200 000 years. The study sites are beyond the Marine Isotope stage (MIS) 2 glacial limit, near the maximum regional extent of Pleistocene glaciation. Non-glacial deposits include up to 25 m of loess, peat and gravel with paleosols, pollen, plant and insect macrofossils, large mammal fossils and tephra beds. Finite and non-finite radiocarbon dates, and twelve different tephra beds constrain the chronology of these deposits. Tills correlated to MIS 4 and 6 represent the penultimate and maximum Pleistocene glacial limits, respectively. The proximity of these glacial limits to each other, compared to limits in central Yukon, suggests precipitation conditions were more consistent in southwest Yukon than in central Yukon during the Pleistocene. Conditions in MIS 5e and 5a are recorded by two boreal forest beds, separated by a shrub birch tundra, that indicate environments as warm or warmer than present. A dry, treeless steppe-tundra, dominated by Artemisia frigida, upland grasses and forbs existed during the transition from late MIS 3 to early MIS 2. These glacial and non-glacial deposits constrain the glacial limits and paleoenvironments during the Middle to Late Pleistocene in southwest Yukon.

Turner, Derek G.; Ward, Brent C.; Bond, Jeffrey D.; Jensen, Britta J. L.; Froese, Duane G.; Telka, Alice M.; Zazula, Grant D.; Bigelow, Nancy H.

2013-09-01

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Deep water drilling shallow water flows: Practical applications of Pleistocene seismic stratigraphy  

Energy Technology Data Exchange (ETDEWEB)

Water flowage from shallow sands during deep water drilling operations is a relatively common phenomenon; because drilling operations are vulnerable at shallow depths below the sea floor before casing is set and blowout preventers are installed. The shallow water flow phenomenon is caused by the presence of fluids under greater than hydrostatic pressure within highly permeable loose sands at shallow beneath the sea floor. Massive sand formations are regularly deposited during sea level lowstands and can be identified by the seismic stratigraphic method. When applied to the interpretation of high resolution geophysical survey records sequence stratigraphy permits identification and mapping of potential problem-causing sands. Once the depth and thickness of sand formations are established an appropriate casing and drilling program can be set up to reduce the risk of encountering shallow water flow problems during drilling operations.

Trabant, P.K.

1995-12-01

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Estratigrafía y geocronología de los dépositos del Pleistoceno tardío/Holoceno de la cuenca del arroyo La Estacada, departamentos de Tunuyán y Tupungato (Valle de Uco), Mendoza Stratigraphy and geochronology of the Late Pleistocene-Holocene of the Arroyo La Estacada Basin, Departmets of Tunuyán and Tupungato (Uco Valley), Mendoza  

Directory of Open Access Journals (Sweden)

Full Text Available La cuenca del arroyo La Estacada, tributario del río Tunuyán, está situada en el piedemonte andino distal (Departamentos de Tupungato y Tunuyán, Mendoza). En este ámbito se realizaron estudios que abarcaron aspectos estratigráficos, sedimentológicos, geomorfológicos y geocronológicos (dataciones radiocarbónicas y luminiscencia óptica estimulada) de los depósitos del Pleistoceno tardío-Holoceno. Los resultados señalan que los depósitos componen tres unidades geomorfológicas (planicie de agradación regional, terraza de relleno y planicie de inundación actual) que representan sendos ciclos de agradación. La planicie agradacional está integrada por una sucesión sedimentaria dominantemente areno-limosa, con niveles de tefras y de gravas, cuya edad es mayor a 48.000 años AP y se extiende hasta alrededor de los 3.000 años 14C AP. La terraza de relleno está compuesta por una sucesión granodecreciente, que abarca un intervalo iniciado antes de los 5.500 14C AP hasta los 400-500 años 14C AP. Con posterioridad a estas últimas fechas, comenzaría la formación de la planicie de inundación actual, caracterizada por el apilamiento de bancos horizontales de arena. El levantamiento de perfiles estratigráficos, la litología de los depósitos y su expresión geomorfológica, así como las edades numéricas obtenidas, señalan que los límites estratigráficos, atribuidos originalmente a las Formaciones La Estacada y el Zampal, transgreden lateralmente los paquetes sedimentarios asignados a cada unidad. Considerando la litología y las relaciones estratigráficas observadas se propone agrupar los depósitos de ambas unidades, así como los de la planicie de inundación actual, en una sola unidad litoestratigráfica con rango de formación y de nombre Formación El Zampal.Arroyo La Estacada is a tributary of Rio Tunuyán situated in the distal Andean piedmont of Mendoza, Argentina. Stratigraphic, sedimentological and geomorphological analysis along with numerical dating by 14C and optical stimulated luminescence were performed on the late Pleistocene-Holocene deposits. Three geomorphological units (regional aggradational plain, fill terrace and the present floodplain) have been identified. The regional aggradational plain is made up of a sedimentary succession dominantly composed of sandy-silty deposits; the sediment accumulation started prior to 48,000 years BP and continued until circa 3,000 14C years AP. The fill terrace is composed of a fining upward sequence encompassing a time interval older than 5,500 14C BP and extending until 400-500 14C years BP. The present floodplain, made up of sand beds, was formed after 400-500 14C years BP. Based on the results obtained, the stratigraphic boundaries originally attributed to La Estacada Formation and El Zampal Formation are laterally transgressive in relation to the sedimentary beds included in each of these lithostratigraphic units. Considering both their lithology and stratigraphic relationships we propose to group these deposits into a single lithostratigaphic unit named El Zampal Formation.

Marcelo Zárate; Adriana Mehl

2008-01-01

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Estratigrafía y geocronología de los dépositos del Pleistoceno tardío/Holoceno de la cuenca del arroyo La Estacada, departamentos de Tunuyán y Tupungato (Valle de Uco), Mendoza/ Stratigraphy and geochronology of the Late Pleistocene-Holocene of the Arroyo La Estacada Basin, Departmets of Tunuyán and Tupungato (Uco Valley), Mendoza  

Scientific Electronic Library Online (English)

Full Text Available Abstract in spanish La cuenca del arroyo La Estacada, tributario del río Tunuyán, está situada en el piedemonte andino distal (Departamentos de Tupungato y Tunuyán, Mendoza). En este ámbito se realizaron estudios que abarcaron aspectos estratigráficos, sedimentológicos, geomorfológicos y geocronológicos (dataciones radiocarbónicas y luminiscencia óptica estimulada) de los depósitos del Pleistoceno tardío-Holoceno. Los resultados señalan que los depósitos componen tres unidades (more) geomorfológicas (planicie de agradación regional, terraza de relleno y planicie de inundación actual) que representan sendos ciclos de agradación. La planicie agradacional está integrada por una sucesión sedimentaria dominantemente areno-limosa, con niveles de tefras y de gravas, cuya edad es mayor a 48.000 años AP y se extiende hasta alrededor de los 3.000 años 14C AP. La terraza de relleno está compuesta por una sucesión granodecreciente, que abarca un intervalo iniciado antes de los 5.500 14C AP hasta los 400-500 años 14C AP. Con posterioridad a estas últimas fechas, comenzaría la formación de la planicie de inundación actual, caracterizada por el apilamiento de bancos horizontales de arena. El levantamiento de perfiles estratigráficos, la litología de los depósitos y su expresión geomorfológica, así como las edades numéricas obtenidas, señalan que los límites estratigráficos, atribuidos originalmente a las Formaciones La Estacada y el Zampal, transgreden lateralmente los paquetes sedimentarios asignados a cada unidad. Considerando la litología y las relaciones estratigráficas observadas se propone agrupar los depósitos de ambas unidades, así como los de la planicie de inundación actual, en una sola unidad litoestratigráfica con rango de formación y de nombre Formación El Zampal. Abstract in english Arroyo La Estacada is a tributary of Rio Tunuyán situated in the distal Andean piedmont of Mendoza, Argentina. Stratigraphic, sedimentological and geomorphological analysis along with numerical dating by 14C and optical stimulated luminescence were performed on the late Pleistocene-Holocene deposits. Three geomorphological units (regional aggradational plain, fill terrace and the present floodplain) have been identified. The regional aggradational plain is made up of a s (more) edimentary succession dominantly composed of sandy-silty deposits; the sediment accumulation started prior to 48,000 years BP and continued until circa 3,000 14C years AP. The fill terrace is composed of a fining upward sequence encompassing a time interval older than 5,500 14C BP and extending until 400-500 14C years BP. The present floodplain, made up of sand beds, was formed after 400-500 14C years BP. Based on the results obtained, the stratigraphic boundaries originally attributed to La Estacada Formation and El Zampal Formation are laterally transgressive in relation to the sedimentary beds included in each of these lithostratigraphic units. Considering both their lithology and stratigraphic relationships we propose to group these deposits into a single lithostratigaphic unit named El Zampal Formation.

Zárate, Marcelo; Mehl, Adriana

2008-09-01

27

Elevated reefs and related Pleistocene stratigraphy of the southern Exuma Islands, Bahamas  

Energy Technology Data Exchange (ETDEWEB)

At least seven elevated coral reefs are exposed on the lee side of an inner chain of low islands on the eastern margin of Great Bahama Bank in the Southern Exumas. Starting at Fowl Cay in the north, they extend at least to Pigeon Cay in the south, a distance of about 44 nautical mi (81 km). These reefs formed around preexisting Pleistocene core-islands and hardgrounds during a transgressive higher than present stand of sea level, prior to the Holocene. As sea level dropped, the reefs were karstedand capped by caliche crusts, a unique paleosol breccia containing land snails (Cerithidea. sp.) and a now lithified dune system with well-developed rhizomorphs. Shallow sea caves eroded into steep, clifflike notches are often located on ridges shoreward of the reef, with roof heights of up to 5 m above the top of the elevated reefs. The reefs form a 5- to 10-m wide terrace, approximately 1 m above present sea level. Shoreline exposures often exceed 300 m (1,000 ft). Most exposures have a base thicket of interwoven branches of Acropora cervicornus approximately 70-cm thick. The badly corroded branches are surrounded by a cemented matrix of ooid sands, marine cement, and coralline debris. The upper 30 cm is formed by a much more diverse reef community of broken shells and corals (Montastrea, Diploria Agaricia, Porites, and Acropora). Crustose coralline algae and colonial foraminifera (Homotrema) form a cementing crust around many corals. These reefs and their relationship to paleosols within subaerial dune deposits provide stratigraphic markers that play an important role in interpreting the development of Pleistocene deposits of the Great Bahama Bank.

Dill, R.F. (Univ. of South Carolina, Columbia (United States) Caribbean Marine Research Center, San Diego, CA (United States)); Halley, R.B.; Shinn, E.A.; Kindinger, J.L. (Geological Survey, St. Petersburg, FL (United States)); Muhs, D.R. (Geological Survey, Denver, CO (United States))

1991-03-01

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Sequence stratigraphy of the Nukumaruan stratotype (Pliocene-Pleistocene, c. 2.08-1.63 Ma), Wanganui Basin, New Zealand  

International Nuclear Information System (INIS)

Late Pliocene to Early Pleistocene (c. 2.08-1.63 Ma) strata exposed in coastal cliffs along Nukumaru and Ototoka beaches near Wanganui, between the top of the Nukumaru Limestone and the base of the Butlers Shell Conglomerate, comprise 11 depositional sequences of a total thickness of c. 86 m. The sequences consist predominantly of siliciclastic shoreline facies. Non-marine facies (including palaeosols), and a variety of shallow-marine shellbed facies, are also represented. Patterns in facies composition and sequence architecture reveal three sequence motifs (Maxwell, Nukumaru, and Birdgrove) that represent progressively increasing maximum palaeowater depths within a broadly basin-margin palaeogeographic setting. The sequence motif changes systematically up section and records a lower order tectonic influence on accommodation that has modulated the stacking patterns of individual sequences. Correlation of the sequences with oxygen isotope stages 77-57 is achieved using the basin-wide Ototoka tephra, and indicates that the sequences accumulated in response to obliquity driven (41 k.y. duration) glacio-eustatic sea-level oscillations. Correlation of the Nukumaru coast sequences with other sections along basin strike, and the global oxygen isotope record indicates that (i) 500 k.y. (?18O stages MIS 56-34) is missing at the unconformity between the Nukumaruan and overlying Castlecliffian stratotypes on the Wanganui coast, and (ii) the Pliocene-Pleistocene boundary lies within sequence NC7 at the base of the Lower Maxwell Formation. (author). 52 refs., 15 figs., 2 tabs.

2005-01-01

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Pleistocene carbonate stratigraphy of South Florida: Evidence for high-frequency sea-level cyclicity  

Science.gov (United States)

Pleistocene carbonates of south Florida and islands of the Florida Keys are currently divided into five marine sequences designated, from oldest to youngest, the Q1–Q5 units. The units include a mosaic of freshwater and shallow marine deposits that accumulated on the Florida platform during high sea-level stands. The units are separated by regional-scale subaerial-exposure surfaces that formed during glacioeustatic lowstands. Analyses of cores recovered at Grossman Ridge Rock Reef and Joe Ree Rock Reef in the Florida Everglades reveal additional subaerial-exposure surfaces that are used to delineate subdivisions within units Q1 (Q1a–Q1b), Q2 (Q2a–Q2d), and Q4 (Q4a–Q4b). Units Q1–Q5 preserve evidence of at least 10 separate sea-level highstands, rather than 5 as indicated by previous studies. Compilation of available uranium-series dates on corals recovered from the Florida Keys indicates that the Q4 unit accreted during sea-level maxima associated with marine oxygen-isotope Stage 9 (Q4a) and isotope Stage 7 (Q4b). The Q5 unit formed during isotope Stage 5. No reliable dates are available for units Q1–Q3. We infer that unit Q3 was formed during the extended sea-level highstand of isotope Stage 11 and that units Q2 and Q1 predate isotope Stage 11.

Hickey, Todd D.; Hine, Albert C.; Shinn, Eugene A.; Kruse, Sarah E.; Poore, Richard Z.

2010-01-01

30

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

Energy Technology Data Exchange (ETDEWEB)

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.

Humphrey, J.D.; Kimbell, T.N. (Univ. of Texas, Richardson (USA))

1990-11-01

31

Late Pleistocene to Holocene environmental changes from ?13C determinations in soils at Teotihuacan, Mexico  

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Full Text Available Stable carbon isotopic signature (?13C) of soil organic matter (SOM) is used as a high-spatial resolution tool to infer environmental changes during late Pleistocene to Present in the Teotihuacan valley, Mexico. Interpretation was based on climatic preferences of C3, CAM and C4 plant groups. ?13C values of modern plant types are clearly distinguished. C3 plants display values around –27‰, while C4 and CAM plants have values around––13‰. Data from soil profiles range from -25.7 to -15.5 ‰. Cerro Gordo site ?13C varyies around -20‰, indicating long-term, time-stable co-existence between C3 and C4 or CAM plants. The more depleted signatures (-23 ± 2 ‰) are, dominated by carbon from C3 vegetation of late Pleistocene swamp paleosols in the Tepexpan profile of the Lake Texcoco. Younger paleosols from lower valley sites, have less depleted values (-17 ± 1) ‰, dominated by C4 and CAM carbon. Late Holocene and modern soils present slightly more negative values (1-2 ‰) with respect to ?13C of underlying soils. Our results show 1) an increase of 10-70 % depending on the site, during the transition from the late Pleistocene to early Holocene, and 2) a dominance of C4 vegetation, up to 84%, in valley environment during the middle Holocene. These data support a climatic change from cold and wet conditions in the Last Glacial Maximum and late Pleistocene, to warm and dry conditions in middle Holocene. A slight rise in moisture availability during late Holocene is inferred based on the 4-10% increase in C3 plant carbon in soils from the valley. Conditions remained generally warm and dry, much as they are at present, favouring the development of agriculture in the valley. Our interpretation agrees with results of paleoenvironmental studies at Texcoco Lake based on diatom and pollen analyses in lake.

E. Lounejeva Baturina; P. Morales Puente; H. V. Cabadas Báez; E. Cienfuegos Alvarado; S. Sedov; E. Vallejo Gómez; E. Solleiro Rebolledo

2006-01-01

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Late Cenozoic structure and stratigraphy of south-central Washington  

International Nuclear Information System (INIS)

The structural framework of the Columbia Basin began developing before Columbia River Basalt Group (CRBG) volcanism. Prior to 17.5 Ma, the eastern part of the basin was a relatively stable area, with a basement of Paleozoic and older crystalline rock. The western part was an area of subsidence in which large volumes of sediment and volcanic rocks accumulated. Concurrent with eruption of the CRBG, anticlinal ridges of the Yakima Fold Belt (YFB) were growing under north-south compression. Topographic expression of these features was later masked by the large volume of CRBG basalt flowing west from fissures in the eastern Columbia Basin. The folds continued to develop after cessation of volcanism, leading to as much as 1,000 m of structural relief in the past 10 million years. Post-CRBG evolution of the Columbia Basin is recorded principally in folding and faulting in the YFB and sediments deposited in the basins. The accompanying tectonism resulted in lateral migration of major depositional systems into subsiding structural lows. Although known late Cenozoic faults are on anticlinal ridges, earthquake focal mechanisms and contemporary strain measurements indicate most stress release is occurring in the synclinal areas under north-south compression. There is no obvious correlation between focal mechanisms for earthquakes whose foci are in the CRBG and the location of known faults. High in situ stress values help to explain the occurrence of microseismicity in the Columbia Basin but not the pattern. Microseismicity appears to occur in unaltered fresh basalt. Faulted basalt associated with the YFB is highly brecciated and commonly altered to clay. The high stress, abundance of ground water in confined aquifers of the CRBG, and altered basalt in fault zones suggest that the frontal faults on the anticlinal ridges probably have some aseismic deformation. 85 refs.

1993-01-01

33

Sequence stratigraphy of Pleistocene sediments, Northwestern Green Canyon, Gulf of Mexico  

Energy Technology Data Exchange (ETDEWEB)

A sequence stratigraphic study of Pleistocene sediments in northwestern portion of the Green Canyon Area has identified five depositional sequences: 1.1-0.8, 0.8-0.7, 0.7-0.5, 0.5-0.4, and 0.4-0.3 Ma. Detailed seismic and geologic facies maps were constructed for reach of these sequences. The data base for this study comprises 882 miles (1419 km) of multifold seismic, petrophysical information from 20 wells and 23 biostratigraphic reports. The area is characterized by several large mini-basins, separated by complex salt bodies and minor faults. The depositional settings are structurally controlled by these salt bodies and normal faults. Paleoecology indicates that the sequences were deposited in water depths ranging from lower slope to middle shelf. Bathyal turbidite systems represent most of sediments in the study area. Prominent basin-floor fan deposits are interpreted to be present only in sequences 1.1-0.8 Ma and 0.8-0.7 Ma in the southeastern portion of the study area. All of the sequences consist primarily of channel-levee systems and overbank deposits (slope fan facies). Abrupt facies changes within these deposits are common. Well logs indicate that most of the area is mud-dominated, with sands primarily occurring in channel-fill facies. Extensive slides are also present in these slope fan facies, and are the product of ragid rates of sedimentation and possibly high gradient or inclination of the slope. In the northern part of the study area, the younger sequences (0.7 Ma and younger) also contain sediments deposited in prodelta/delta environments (prograding complex/HST). Upward-coarsening log trends are present in well logs. Relatively thick TST are also present and stacked along the downthrown sides of faults. Fields/discoveries in the study area are in Green Canyon 18, and in the Mahogany sub-salt discovery (SS 349). The petroleum potential for additional prospects the area is good for both supra-salt and sub-salt targets.

Naravvro, A.F.; Weimer, P. [Univ. of Colorado, Boulder, CO (United States)

1995-10-01

34

Late Pleistocene Desiccation of Lake Victoria and Rapid Evolution of Cichlid Fishes  

Science.gov (United States)

Lake Victoria is the largest lake in Africa and harbors more than 300 endemic species of haplochromine cichlid fish. Seismic reflection profiles and piston cores show that the lake not only was at a low stand but dried up completely during the Late Pleistocene, before 12,400 carbon-14 years before the present. These results imply that the rate of speciation of cichlid fish in this tropical lake has been extremely rapid.

Johnson, Thomas C.; Scholz, Christopher A.; Talbot, Michael R.; Kelts, Kerry; Ricketts, R. D.; Ngobi, Gideon; Beuning, Kristina; Ssemmanda, Immacculate; McGill, J. W.

1996-08-01

35

New Late Pleistocene locality of the Alpine Ibex (Capra ibex L.) (Mammalia: Bovidae) in Bulgaria  

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Full Text Available There were a total of 12 localities of fossil Alpine Ibex (Capra ibex) in Bulgaria till now, all of Late Pleistocene. Most of them were from the West part of Stara Planina Mountain. The paper reports the easternmost cave locality of this species from the Pchena Cave (Tvardishki Balkan area, Stara Planina Mnt.), near the town of Tvarditsa. The find represents a cranial fragment, bearing the horn shafts.

DILIAN GEORGIEV; SLAVEYA STOYCHEVA

2010-01-01

36

Late Pleistocene to Holocene eruptive activity of Pico de Orizaba, Eastern Mexico  

Science.gov (United States)

The Late Pleistocene to Holocene eruptive history of Pico de Orizaba can be divided into 11 eurptive episodes. Each eruptive episode lasted several hundred years, the longest recorded being about 1000 years (the Xilomich episode). Intervals of dormancy range from millenia during the late Pleistocene to about 500 years, the shortest interval recorded in the Holocene. This difference could reflect either changes in the volcano's activity or that the older stratigraphic record is less complete than the younger. Eruptive mechanisms during the late Pleistocene were characterized by dome extrusions, lava flows and ash-and-scoria-flow generating eruptive columns. However, in Holocene time plinian activity became increasingly important. The increase in dacitic plinian eruptions over time is related to increased volumes of dacitic magma beneath Pico de Orizaba. We suggest that the magma reservoir under Pico de Orizaba is stratified. The last eruptive episode, which lasted from about 690 years bp until ad 1687, was initiated by a dacitic plinian eruption and was followed by effusive lava-forming eruptions. For the last 5,000 years the activity of the volcano has been gradually evolving towards such a trend, underlining the increasing importance of dacitic magma and stratification of the magma reservoir. Independent observations of Pico de Orizaba's glacier early this century indicate that some increase in volcanic activity occurred between 1906 and 1947, and that it was probably fumarolic.

Hoskuldsson, Armann; Robin, Claude

1993-12-01

37

Did the West Antarctic Ice Sheet collapse during late Pleistocene interglacials: A reassessment  

Science.gov (United States)

Ever since John Mercer's provocative paper, "West Antarctic ice sheet and CO2 Greenhouse effect: a threat of disaster" (Nature 271:321-325; 1978), researchers have grappled with questions regarding whether, when, how frequently, and, especially, how quickly the West Antarctic Ice Sheet has disintegrated and reformed during the Pliocene and Pleistocene (and whether and when it may again in the future). Oxygen isotope records, being global averages, are insufficient to answer these questions, because (1) the WAIS signal is relatively small, and (2) antiphased behavior between the poles of the precession cycle will tend to cancel part of the signal, as outlined by Raymo et. al. (Science 313, 492-495, 2006). Previously, Antarctica lacked proximal, well-dated Pleistocene and Pliocene marine geologic records, so eustatic, mostly tropical sea-level records were used to infer past WAIS collapses. The first direct evidence of past Pleistocene WAIS collapse came from diatoms recovered from beneath the WAIS on the Whillans Ice Stream (UpB). Scherer (GPC, 4, 395-412, 1991) and Scherer et al. (Science, 281, 82-85, 1998) interpreted these results as most likely reflecting WAIS retreat during MIS-11, but could not rule out other interglacials, including MIS-5e, the penultimate interglacial discussed by Mercer. More recently, proximal evidence of WAIS retreat (or collapse) during early Pleistocene MIS-31 came from drilling at Cape Roberts (CRP-1) and the ANDRILL McMurdo Ice Shelf project (AND-1B) (Scherer et al., GRL, 35, doi:10.1029/2007GL032254, 2008). These diatom results provide evidence of ice sheet retreat events, but no constraint on the rate of ice sheet "collapse," which is critical to assessing the threat of future collapse. These results provided impetus and constraints for new coupled climate/ice sheet models, which are yielding significant insights (Pollard and DeConto, Nature, in press). The ANDRILL-MIS site contains no clear evidence of WAIS collapse events subsequent to MIS-31, but there is poor age control in the recovered diamictons. Furthermore, evidence of significant interglacials may have been lost in glacial erosion. A reassessment of diatom data from UpB indicates that the Pleistocene diatoms identified from beneath the WAIS are compatible with MIS-31 deposition as well as late Pleistocene marine deposition. This, once again, leaves the question of the configuration of the WAIS during MIS-11, MIS-5e and other late Pleistocene interglacials open for discussion.

Scherer, R. P.

2009-04-01

38

Distributional patterns of herbivore megamammals during the Late Pleistocene of South America.  

UK PubMed Central (United Kingdom)

The geographic distribution of 27 species of the South American megafauna of herbivore mammals during the Late Pleistocene was analyzed in order to identify their distributional patterns. The distribution of the species was studied using the panbiogeographical method of track analysis. Six generalized tracks (GTs) and two biogeographic nodes were obtained. The GTs did not completely superpose with the areas of open savanna present in Pleistocene, nor with the biotic tracks of some arthropods typical of arid climate, indicating that these animals avoided arid environment. Overall, the GTs coincided with some biogeographic provinces defined on the basis of living taxa, indicating that certain current distributional patterns already existed in Pleistocene. The biogeographic nodes coincided with the borders between the main vegetal formations of the Pleistocene, showing that the type of vegetation had great influence in the distribution of the mammalian megafauna. The node 1 confirmed the existence of contact zones between paleobiogeographic regions near Argentina-Uruguay border. The node 2 connects the Brazilian Intertropical regions.

Gallo V; Avilla LS; Pereira RC; Absolon BA

2013-04-01

39

Evolution of middle-late Pleistocene human cranio-facial form: a 3-D approach.  

Science.gov (United States)

The classification and phylogenetic relationships of the middle Pleistocene human fossil record remains one of the most intractable problems in paleoanthropology. Several authors have noted broad resemblances between European and African fossils from this period, suggesting a single taxon ancestral to both modern humans and Neanderthals. Others point out 'incipient' Neanderthal features in the morphology of the European sample and have argued for their inclusion in the Neanderthal lineage exclusively, following a model of accretionary evolution of Neanderthals. We approach these questions using geometric morphometric methods which allow the intuitive visualization and quantification of features previously described qualitatively. We apply these techniques to evaluate proposed cranio-facial 'incipient' facial, vault, and basicranial traits in a middle-late Pleistocene European hominin sample when compared to a sample of the same time depth from Africa. Some of the features examined followed the predictions of the accretion model and relate the middle Pleistocene European material to the later Neanderthals. However, although our analysis showed a clear separation between Neanderthals and early/recent modern humans and morphological proximity between European specimens from OIS 7 to 3, it also shows that the European hominins from the first half of the middle Pleistocene still shared most of their cranio-facial architecture with their African contemporaries. PMID:20708775

Harvati, Katerina; Hublin, Jean-Jacques; Gunz, Philipp

2010-08-13

40

Evolution of middle-late Pleistocene human cranio-facial form: a 3-D approach.  

UK PubMed Central (United Kingdom)

The classification and phylogenetic relationships of the middle Pleistocene human fossil record remains one of the most intractable problems in paleoanthropology. Several authors have noted broad resemblances between European and African fossils from this period, suggesting a single taxon ancestral to both modern humans and Neanderthals. Others point out 'incipient' Neanderthal features in the morphology of the European sample and have argued for their inclusion in the Neanderthal lineage exclusively, following a model of accretionary evolution of Neanderthals. We approach these questions using geometric morphometric methods which allow the intuitive visualization and quantification of features previously described qualitatively. We apply these techniques to evaluate proposed cranio-facial 'incipient' facial, vault, and basicranial traits in a middle-late Pleistocene European hominin sample when compared to a sample of the same time depth from Africa. Some of the features examined followed the predictions of the accretion model and relate the middle Pleistocene European material to the later Neanderthals. However, although our analysis showed a clear separation between Neanderthals and early/recent modern humans and morphological proximity between European specimens from OIS 7 to 3, it also shows that the European hominins from the first half of the middle Pleistocene still shared most of their cranio-facial architecture with their African contemporaries.

Harvati K; Hublin JJ; Gunz P

2010-11-01

 
 
 
 
41

First ancient DNA sequences from the Late Pleistocene red deer (Cervus elaphus) in the Crimea, Ukraine  

Science.gov (United States)

The Late Pleistocene has been a period of significant population and species turnover and extinctions among the large mammal fauna. Massive climatic and environmental changes during Pleistocene significantly influenced the distribution and also genetic diversity of plants and animals. The model of glacial refugia and habitat contraction to southern peninsulas in Europe as areas for the survival of temperate animal species during unfavourable Pleistocene glaciations is at present widely accepted. However, both molecular data and the fossil record indicate the presence of northern and perhaps north-eastern refugia in Europe. In recent years, much new palaeontological data have been obtained in the Crimean Peninsula, Ukraine, following extensive investigations. The red deer (Cervus elaphus) samples for aDNA studies were collected in Emine-Bair-Khosar Cave, situated on the north edge of Lower Plateau of the Chatyrdag Massif (Crimean Mountains). The cave is a vertical shaft, which functioned as a huge mega-trap over a long period of time (probably most of the Pleistocene). The bone assemblages provided about 5000 bones belonging to more than 40 species. The C. elaphus bones were collected from three different stratigraphical levels, radiocarbon dated by accelerator mass spectrometry (AMS) method. The bone fragments of four specimens of red deer were used for the DNA isolation and analysis. The mtDNA (Cytochome b) was successfully isolated from three bone fragments and the cytochrome b sequences were amplified by multiplex PCR. The sequences obtained so far allowed for the reconstruction of only preliminary phylogenetic trees. A fragment of metatarsus from level dated to ca. 48,500±2,000 years BP, yielded a sequence of 513 bp, allowing to locate the specimen on the phylogenetic tree within modern C. elaphus specimens from southern and middle Europe. The second bone fragment, a fragment of mandible, collected from level dated approximately to ca. 33,500±400 years BP, yielded a sequence (696 bp) locating this specimen much closer to the modern C. elaphus specimens from China and Far East. From the third bone fragment (metatarsus), dated between ca. 12,000 years BP and 30,000 years BP, the sequence of only 346 bp has been obtained. It locates this specimen between European and Asiatic haplogroups. The preliminary results of analysis of the DNA from Crimean C. elaphus fossils reveal the great genetic heterogeneity and a complex phylogeographical pattern of the material studied. The obtained results support the opinion that Crimean Peninsula was the most north-eastern refugium in Europe during Late Pleistocene playing a major role in recolonization and dispersal processes of temperate species during and after the Late Pleistocene in this part of the Euro-Asian continent.

Stankovi?, Ana; Nadachowski, Adam; Doan, Karolina; Stefaniak, Krzysztof; Baca, Mateusz; Socha, Pawe?; Wegle?ski, Piotr; Ridush, Bogdan

2010-05-01

42

Denali fault slip rates and Holocene-late Pleistocene kinematics of central Alaska  

Science.gov (United States)

The Denali fault is the principal intracontinental strike-slip fault accommodating deformation of interior Alaska associated with the Yakutat plate convergence. We obtained the first quantitative late Pleistocene-Holocene slip rates on the Denali fault system from dating offset geomorphic features. Analysis of cosmogenic 10Be concentrations in boulders (n = 27) and sediment (n = 13) collected at seven sites, offset 25-170 m by the Denali and Totschunda faults, gives average ages that range from 2.4 ?? 0.3 ka to 17.0 ?? 1.8 ka. These offsets and ages yield late Pleistocene-Holocene average slip rates of 9.4 ?? 1.6, 12.1 ?? 1.7, and 8.4 ?? 2.2 mm/yr-1 along the western, central, and eastern Denali fault, respectively, and 6.0 ?? 1.2 mm/yr-1 along the Totschunda fault. Our results suggest a westward decrease in the mean Pleistocene-Holocene slip rate. This westward decrease likely results from partitioning of slip from the Denali fault system to thrust faults to the north and west. ?? 2006 Geological Society of America.

Matmon, A.; Schwartz, D. P.; Haeussler, P. J.; Finkel, R.; Lienkaemper, J. J.; Stenner, H. D.; Dawson, T. E.

2006-01-01

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Dietary controls on extinction versus survival among avian megafauna in the late Pleistocene  

Science.gov (United States)

The late Pleistocene extinction decimated terrestrial megafaunal communities in North America, but did not affect marine mammal populations. In coastal regions, marine megafauna may have provided a buffer that allowed some large predators or scavengers, such as California condors (Gymnogyps californianus), to survive into the Holocene. To track the influence of marine resources on avifaunas we analyzed the carbon, nitrogen, and hydrogen isotope composition of collagen from late Pleistocene vultures and raptors, including species that survived the extinction (condor, bald eagle, golden eagle) and extinct species (teratorn, black vulture). At the Rancho La Brea and McKittrick tar pits of southern California, isotope values for extinct teratorns (Teratornis merriami, n = 10) and black vultures (Coragyps occidentalis, n = 8) show that they fed entirely in a terrestrial C3 ecosystem. In contrast, La Brea condors cluster into two groups, one with a terrestrial diet (n = 4), and the other with a strong marine influence (n = 5). At localities in the American southwest, Texas, and Florida, where condors became extinct, they have isotope values indicating entirely terrestrial diets (n = 10). Our results suggest that dependence upon terrestrial megafaunal carrion as a food source led to the extinction of inland California condor populations and coastal populations of teratorns and black vultures at the Pleistocene-Holocene boundary, whereas use of marine foods allowed coastal condor populations to survive.

Fox-Dobbs, Kena; Stidham, Thomas A.; Bowen, Gabriel J.; Emslie, Steven D.; Koch, Paul L.

2006-08-01

44

Strontium and carbon isotope stratigraphy of the Late Jurassic shallow marine limestone in western Palaeo-Pacific, northwest Borneo  

Science.gov (United States)

Application of Sr isotopic stratigraphy to Late Jurassic limestone in NW Borneo.First ?13C profile reported from the upper Jurassic in Southeast Asia.Inter-regional correlation of ?13C between Tethys, Boreal, and Palaeo-Pacific.Regional variety of ?13C reflected from the global palaeoceanography.

Kakizaki, Yoshihiro; Weissert, Helmut; Hasegawa, Takashi; Ishikawa, Tsuyoshi; Matsuoka, Jun; Kano, Akihiro

2013-09-01

45

People of the ancient rainforest: late Pleistocene foragers at the Batadomba-lena rockshelter, Sri Lanka.  

Science.gov (United States)

Batadomba-lena, a rockshelter in the rainforest of southwestern Sri Lanka, has yielded some of the earliest evidence of Homo sapiens in South Asia. H. sapiens foragers were present at Batadomba-lena from ca. 36,000 cal BP to the terminal Pleistocene and Holocene. Human occupation was sporadic before the global Last Glacial Maximum (LGM). Batadomba-lena's Late Pleistocene inhabitants foraged for a broad spectrum of plant and mainly arboreal animal resources (monkeys, squirrels and abundant rainforest snails), derived from a landscape that retained equatorial rainforest cover through periods of pronounced regional aridity during the LGM. Juxtaposed hearths, palaeofloors with habitation debris, postholes, excavated pits, and animal and plant remains, including abundant Canarium nutshells, reflect intensive habitation of the rockshelter in times of monsoon intensification and biome reorganisation after ca. 16,000 cal BP. This period corresponds with further broadening of the economic spectrum, evidenced though increased contribution of squirrels, freshwater snails and Canarium nuts in the diet of the rockshelter occupants. Microliths are more abundant and morphologically diverse in the earliest, pre-LGM layer and decline markedly during intensified rockshelter use on the wane of the LGM. We propose that changing toolkits and subsistence base reflect changing foraging practices, from shorter-lived visits of highly mobile foraging bands in the period before the LGM, to intensified use of Batadomba-lena and intense foraging for diverse resources around the site during and, especially, following the LGM. Traces of ochre, marine shell beads and other objects from an 80 km-distant shore, and, possibly burials reflect symbolic practices from the outset of human presence at the rockshelter. Evidence for differentiated use of space (individual hearths, possible habitation structures) is present in LGM and terminal Pleistocene layers. The record of Batadomba-lena demonstrates that Late Pleistocene pathways to (aspects of) behavioural 'modernity' (composite tools, practice of symbolism and ritual, broad spectrum economy) were diverse and ecologically contingent. PMID:21777951

Perera, Nimal; Kourampas, Nikos; Simpson, Ian A; Deraniyagala, Siran U; Bulbeck, David; Kamminga, Johan; Perera, Jude; Fuller, Dorian Q; Szabó, Katherine; Oliveira, Nuno V

2011-07-20

46

People of the ancient rainforest: late Pleistocene foragers at the Batadomba-lena rockshelter, Sri Lanka.  

UK PubMed Central (United Kingdom)

Batadomba-lena, a rockshelter in the rainforest of southwestern Sri Lanka, has yielded some of the earliest evidence of Homo sapiens in South Asia. H. sapiens foragers were present at Batadomba-lena from ca. 36,000 cal BP to the terminal Pleistocene and Holocene. Human occupation was sporadic before the global Last Glacial Maximum (LGM). Batadomba-lena's Late Pleistocene inhabitants foraged for a broad spectrum of plant and mainly arboreal animal resources (monkeys, squirrels and abundant rainforest snails), derived from a landscape that retained equatorial rainforest cover through periods of pronounced regional aridity during the LGM. Juxtaposed hearths, palaeofloors with habitation debris, postholes, excavated pits, and animal and plant remains, including abundant Canarium nutshells, reflect intensive habitation of the rockshelter in times of monsoon intensification and biome reorganisation after ca. 16,000 cal BP. This period corresponds with further broadening of the economic spectrum, evidenced though increased contribution of squirrels, freshwater snails and Canarium nuts in the diet of the rockshelter occupants. Microliths are more abundant and morphologically diverse in the earliest, pre-LGM layer and decline markedly during intensified rockshelter use on the wane of the LGM. We propose that changing toolkits and subsistence base reflect changing foraging practices, from shorter-lived visits of highly mobile foraging bands in the period before the LGM, to intensified use of Batadomba-lena and intense foraging for diverse resources around the site during and, especially, following the LGM. Traces of ochre, marine shell beads and other objects from an 80 km-distant shore, and, possibly burials reflect symbolic practices from the outset of human presence at the rockshelter. Evidence for differentiated use of space (individual hearths, possible habitation structures) is present in LGM and terminal Pleistocene layers. The record of Batadomba-lena demonstrates that Late Pleistocene pathways to (aspects of) behavioural 'modernity' (composite tools, practice of symbolism and ritual, broad spectrum economy) were diverse and ecologically contingent.

Perera N; Kourampas N; Simpson IA; Deraniyagala SU; Bulbeck D; Kamminga J; Perera J; Fuller DQ; Szabó K; Oliveira NV

2011-09-01

47

Late Wisconsinan glacial, lacustrine and marine stratigraphy in the Champlain Valley, New York and Vermont  

Energy Technology Data Exchange (ETDEWEB)

The stratigraphy of late-glacial, and postglacial deposits and landforms in the Champlain Lowland is interpreted from high-resolution (3.5 khz transducer) acoustical profiling and piston core analysis of sediments beneath Lake Champlain in conjunction with detailed morphologic sequence mapping of surficial deposits. The sediments of Lake Champlain have been grouped by acoustic, lithologic, and biostratigraphic criteria into three stratigraphic units that were deposited successively into Lake Vermont, the Champlain Sea, and Lake Champlain. The maximum thickness of unconsolidated sediment is known to exceed 200 meters locally. Biostratigraphic subdivision of these units using pollen, diatoms, ostracodes, and foraminifera provides further definition of late-glacial and postglacial events in the region and indicates that transitional environments occurred as conditions changed from proglacial lake to marine estuary to freshwater lake. The stratigraphy of surficial deposits records proglacial lake sequences in the Champlain Valley and its tributaries. Interbasinal correlation of the tributary proglacial lake sequences and reconstructed ice marginal positions, is consistent with a model of generally synchronous, northward recession controlled primarily by backwasting of active continental ice lobes. Minor asynchroneity of retreat rates may be attributed to local differences in subglacial topography and changes in proglacial lake level, both of which may affect calving rates. Northward ice recession of the Champlain Lobe allowed successive inundation of tributary valleys by Lake Vermont. Elevations of deltaic sandplains reveal at least three distinct lake levels in the northwestern Champlain Valley. The highest level corresponds to the Coveville Stage while the lower two represent levels of the Fort Ann Stage.

Franzi, D.A. (Stat Univ. of New York, Plattsburgh, NY (United States). Center for Earth and Environmental Science); Hunt, A.S. (Univ. of Vermont, Burlington, VT (United States). Dept. of Geology)

1993-03-01

48

A life-history approach to the late pleistocene megafaunal extinction.  

UK PubMed Central (United Kingdom)

A major criticism of the "overkill" theory for the late Pleistocene extinction in the Americas has been the seeming implausibility of a relatively small number of humans selectively killing off millions of large-bodied mammals. Critics argue that early Paleoindian hunters had to be extremely selective to have produced the highly size-biased extinction pattern characteristic of this event. Here, we derive a probabilistic extinction model that predicts the extinction risk of mammals at any body mass without invoking selective human harvest. The new model systematically analyzes the variability in life-history characteristics, such as the instantaneous mortality rate, age of first reproduction, and the maximum net reproductive rate. It captures the body size-biased extinction pattern in the late Pleistocene and precisely predicts the percentage of unexpectedly persisting large mammals and extinct small ones. A test with a global late Quaternary mammal database well supports the model. The model also emphasizes that quantitatively analyzing patterns of variability in ecological factors can shed light on diverse behaviors and patterns in nature. From a macro-scale conservation perspective, our model can be modified to predict the fate of biota under the pressures from both climate change and human impacts.

Zuo W; Smith FA; Charnov EL

2013-10-01

49

A life-history approach to the late pleistocene megafaunal extinction.  

Science.gov (United States)

A major criticism of the "overkill" theory for the late Pleistocene extinction in the Americas has been the seeming implausibility of a relatively small number of humans selectively killing off millions of large-bodied mammals. Critics argue that early Paleoindian hunters had to be extremely selective to have produced the highly size-biased extinction pattern characteristic of this event. Here, we derive a probabilistic extinction model that predicts the extinction risk of mammals at any body mass without invoking selective human harvest. The new model systematically analyzes the variability in life-history characteristics, such as the instantaneous mortality rate, age of first reproduction, and the maximum net reproductive rate. It captures the body size-biased extinction pattern in the late Pleistocene and precisely predicts the percentage of unexpectedly persisting large mammals and extinct small ones. A test with a global late Quaternary mammal database well supports the model. The model also emphasizes that quantitatively analyzing patterns of variability in ecological factors can shed light on diverse behaviors and patterns in nature. From a macro-scale conservation perspective, our model can be modified to predict the fate of biota under the pressures from both climate change and human impacts. PMID:24021404

Zuo, Wenyun; Smith, Felisa A; Charnov, Eric L

2013-08-20

50

U-series component dating for late pleistocene basalt Longgang, Jilin province  

International Nuclear Information System (INIS)

Longgang volcanic swarm belongs to one of volcanic areas which have been active since modern times. In view of multiple eruptions during histories, it is very important to determine age of every eruption for evaluating volcanic hazards. The alkaline basalt samples taken from Dayizishan and diaoshuihu are analyzed by U-series component method, after magnetic separation. The ages of the two samples are (71 ± 9) ka, (106 ± 13) ka before presence, respectively. These data indicate that there exist intensively eruptive activities during late Pleistocene

2003-01-01

51

Late Pleistocene mammals from Chivacabé, Huehuetenango, Guatemala/ Mamíferos del Pleistoceno tardío de Chivacabé, Huehuetenango, Guatemala  

Scientific Electronic Library Online (English)

Full Text Available Abstract in spanish Se ha publicado poca información paleontológica detallada de la fauna del Pleistoceno para gran parte de Centroamérica. Probablemente la localidad más rica de vertebrados en Centroamérica es Tomayate, en El Salvador, que data del Pleistoceno temprano a medio. La literatura de especies de vertebrados delPleistoceno tardío de Guatemala es especialmente escasa. El propósito de este trabajo es presentar los restos de mamíferos del Pleistoceno tardío de Chivacabé, en (more) las tierras altas occidentales de Guatemala. La edad de radiocarbono de la fauna de Chivacabé data de entre 15,700 y 12,920 años calendario. Los especímenes recobrados de excavaciones entre 1977 y 1992 son probablemente una pequeña porción de toda la fauna que existe bajo 4 a 5 m de tefra redepositada y aluvión. Los especímenes recobrados incluyen un individuo de Glyptotherium sp., tres de Cuvieronius cf. C. hyodon, uno de Equus sp. y dos de Odocoileus cf. O. virginianus. Un individuo que originalmente se pensaba que representaba una cornamenta de venado es de hecho un hueso flotante de Cuvieronius. Reportes previos de "pecaríes" y de Eremotherium de Chivacabé no son sustentados por fósiles archivados. Ningún espécimen de fauna exhibe las supuestas marcas humanas de modificación dadas a entender por investigadores previos; todas las aberraciones observadas en los huesos y en los dientes pueden ser explicadas por otros procesos tafonómicos. La fauna de Chivacabé representa una de las muy pocas faunas del Pleistoceno tardío de Guatemala descritas hasta ahora. Una lista preliminar de localidades del Pleistoceno tardío de Guatemala sugiere que son necesarios estudios detallados de estas faunas. Abstract in english Few Pleistocene paleontological faunas are published in detail for most of Central America. Probably the richest locality of vertebrates in Central America is at Tomayate, El Salvador, and dates to the early-middle Pleistocene. Literature about late Pleistocene vertebrate species from Guatemala is especially scarce. The purpose of the present paper is to introduce the late Pleistocene mammalian remains from Chivacabé, in the western highlands of Guatemala. The Chivacabé (more) fauna radiocarbon dates to between 15,700 and 12,920 calendar years ago. The specimens recovered from excavations between 1977 and1992 are probably only a small portion of the entire fauna likely to exist under 4 to 5 m of redeposited tephra and valley alluvium. Recovered specimens include at least one individual of Glyptotherium sp., three individuals of Cuvieronius cf. C. hyodon, one individual of Equus sp., and two individuals of Odocoileus cf. O. virginianus. One specimen that originally was thought to represent a deer antler is in fact a hyoid bone of Cuvieronius. Previous reports of 'peccary ' and Eremotherium from Chivacabé are not supported by archived fossils. No faunal specimens exhibit supposed human modification marks purported by previous investigators; all aberrations observed on the bones and teeth can be explained by other taphonomicprocesses. The Chivacabé fauna represents one of the very few late Pleistocene faunas from Guatemala described thus far. A preliminary list of late Pleistocene localities known in Guatemala suggests that detailed studies of these faunas are warranted.

Mead, Jim I.; Baez, Arturo; Swift, Sandra L.; Lohse, Jon; Paiz, Lorena

2012-08-01

52

Lineage-specific late pleistocene expansion of an endemic subtropical gossamer-wing damselfly, Euphaea formosa, in Taiwan.  

UK PubMed Central (United Kingdom)

BACKGROUND: Pleistocene glacial oscillations have significantly affected the historical population dynamics of temperate taxa. However, the general effects of recent climatic changes on the evolutionary history and genetic structure of extant subtropical species remain poorly understood. In the present study, phylogeographic and historical demographic analyses based on mitochondrial and nuclear DNA sequences were used. The aim was to investigate whether Pleistocene climatic cycles, paleo-drainages or mountain vicariance of Taiwan shaped the evolutionary diversification of a subtropical gossamer-wing damselfly, Euphaea formosa. RESULTS: E. formosa populations originated in the middle Pleistocene period (0.3 Mya) and consisted of two evolutionarily independent lineages. It is likely that they derived from the Pleistocene paleo-drainages of northern and southern Minjiang, or alternatively by divergence within Taiwan. The ancestral North-central lineage colonized northwestern Taiwan first and maintained a slowly growing population throughout much of the early to middle Pleistocene period. The ancestral widespread lineage reached central-southern Taiwan and experienced a spatial and demographic expansion into eastern Taiwan. This expansion began approximately 30,000 years ago in the Holocene interglacial period. The ancestral southern expansion into eastern Taiwan indicates that the central mountain range (CMR) formed a barrier to east-west expansion. However, E. formosa populations in the three major biogeographic regions (East, South, and North-Central) exhibit no significant genetic partitions, suggesting that river drainages and mountains did not form strong geographical barriers against gene flow among extant populations. CONCLUSIONS: The present study implies that the antiquity of E. formosa's colonization is associated with its high dispersal ability and larval tolerance to the late Pleistocene dry grasslands. The effect of late Pleistocene climatic changes on the subtropical damselfly's historical demography is lineage-specific, depending predominantly on its colonization history and geography. It is proposed that the Riss and Würm glaciations in the late Pleistocene period had a greater impact on the evolutionary diversification of subtropical insular species than the last glacial maximum (LGM).

Huang JP; Lin CP

2011-01-01

53

Phylogeography of the Alcippe morrisonia (Aves: Timaliidae): long population history beyond late Pleistocene glaciations  

Directory of Open Access Journals (Sweden)

Full Text Available Abstract Background The role of Pleistocene glacial oscillations in current biodiversity and distribution patterns varies with latitude, physical topology and population life history and has long been a topic of discussion. However, there had been little phylogeographical research in south China, where the geophysical complexity is associated with great biodiversity. A bird endemic in Southeast Asia, the Grey-cheeked Fulvetta, Alcippe morrisonia, has been reported to show deep genetic divergences among its seven subspecies. In the present study, we investigated the phylogeography of A. morrisonia to explore its population structure and evolutionary history, in order to gain insight into the effect of geological events on the speciation and diversity of birds endemic in south China. Results Mitochondrial genes cytochrome b (Cytb) and cytochrome c oxidase I (COI) were represented by 1236 nucleotide sites from 151 individuals from 29 localities. Phylogenetic analysis showed seven monophyletic clades congruent with the geographically separated groups, which were identified as major sources of molecular variance (90.92%) by AMOVA. TCS analysis revealed four disconnected networks, and that no haplotype was shared among the geographical groups. The common ancestor of these populations was dated to 11.6 Mya and several divergence events were estimated along the population evolutionary history. Isolation by distance was inferred by NCPA to be responsible for the current intra-population genetic pattern and gene flow among geographical groups was interrupted. A late Pleistocene demographic expansion was detected in the eastern geographical groups, while the expansion time (0.2–0.4 Mya) was earlier than the Last Glacial Maximum. Conclusion It is proposed that the complicated topology preserves high genetic diversity and ancient lineages for geographical groups of A. morrisonia in China mainland and its two major islands, and restricts gene exchange during climate oscillations. Isolation by distance seems to be an important factor of genetic structure formation within geographical populations. Although glacial influence to population fluctuation was observed in late Pleistocene, it seems that populations in eastern China were more susceptible to climate change, and all geographical groups were growing stably through the Last Glacial Maximum. Coalescence analysis suggested that the ancestor of A. morrisonia might be traced back to the late Miocene, and the current phylogeographical structure of A. morrisonia is more likely to be attributable to a series geological events than to Pleistocene glacial cycles.

Song Gang; Qu Yanhua; Yin Zuohua; Li Shouhsien; Liu Naifa; Lei Fumin

2009-01-01

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A robust feldspar luminescence dating method for Middle and Late Pleistocene sediments  

DEFF Research Database (Denmark)

Luminescence dating is used extensively to provide absolute chronologies for Late Pleistocene sediments. Nowadays, most optical dates are based on quartz optically stimulated luminescence (OSL). However, the application of this signal is usually limited to the last ~100 ka because of saturation of the quartz luminescence signal with dose. In contrast, the feldspar infrared stimulated luminescence (IRSL) dose–response curve grows to much higher doses; this has the potential to extend the datable age range by a factor of 4–5 compared with quartz OSL. However, it has been known for several decades that this IRSL signal is unstable, and this instability often gives rise to significant age underestimation. Here we test against independent age control the recently developed feldspar post-IR IRSL approach to the dating of sediments, which appears to avoid signal instability. A physical model explaining our observations is discussed, and the method is shown to be accurate back to 600 ka. The post-IR IRSL signal is reduced by exposure to daylight more slowly than that from quartz and low-temperature IRSL, preventing its general application to young (e.g. Holocene) sediments. Nevertheless, this new approach is widely applicable (feldspar of appropriate luminescence behaviour is even more ubiquitous than quartz). These characteristics make this a method of great importance for the dating of Middle and Late Pleistocene deposits.

Buylaert, Jan-Pieter; Jain, Mayank

2012-01-01

55

A Pathological Late Pleistocene canid from San Sidero (Italy): implications for social- and feeding-behaviour  

Science.gov (United States)

Evidence of diseases on vertebrate fossil bones can provide detailed information on many aspects of extinct animals. This study focused on pathological craniodental remains (left maxilla and dentary) referred to the canid Cuon alpinus unearthed from a Late Pleistocene karst filling deposit at San Sidero (Apulia, southern Italy). These fossils show clear evidence of a chronic periodontitis that caused the animal's death. Clinical diagnosis of the disease and the timing of its development have been defined on the basis of a veterinary odontostomatology approach, in addition to radiographic and tomographic techniques. From the initiation of the infection until death, a time span of at least 6 months occurred, and three main steps have been defined: (1) the bacterial infections of the buccal cavity turning into severe periodontitis, (2) the fracture of the lower carnassial and (3) the loss of teeth due to the worsening infection that deformed and/or eroded maxillary and mandibular bones and enlarged alveoli. The analysis of the palaeopathology also provides information about the biomechanics of the bite, on the feeding behaviour and on the relationships of injured members in a pack of Late Pleistocene canids.

Iurino, Dawid Adam; Fico, Rosario; Petrucci, Mauro; Sardella, Raffaele

2013-03-01

56

A pathological Late Pleistocene canid from San Sidero (Italy): implications for social- and feeding-behaviour.  

UK PubMed Central (United Kingdom)

Evidence of diseases on vertebrate fossil bones can provide detailed information on many aspects of extinct animals. This study focused on pathological craniodental remains (left maxilla and dentary) referred to the canid Cuon alpinus unearthed from a Late Pleistocene karst filling deposit at San Sidero (Apulia, southern Italy). These fossils show clear evidence of a chronic periodontitis that caused the animal's death. Clinical diagnosis of the disease and the timing of its development have been defined on the basis of a veterinary odontostomatology approach, in addition to radiographic and tomographic techniques. From the initiation of the infection until death, a time span of at least 6 months occurred, and three main steps have been defined: (1) the bacterial infections of the buccal cavity turning into severe periodontitis, (2) the fracture of the lower carnassial and (3) the loss of teeth due to the worsening infection that deformed and/or eroded maxillary and mandibular bones and enlarged alveoli. The analysis of the palaeopathology also provides information about the biomechanics of the bite, on the feeding behaviour and on the relationships of injured members in a pack of Late Pleistocene canids.

Iurino DA; Fico R; Petrucci M; Sardella R

2013-03-01

57

A pathological Late Pleistocene canid from San Sidero (Italy): implications for social- and feeding-behaviour.  

Science.gov (United States)

Evidence of diseases on vertebrate fossil bones can provide detailed information on many aspects of extinct animals. This study focused on pathological craniodental remains (left maxilla and dentary) referred to the canid Cuon alpinus unearthed from a Late Pleistocene karst filling deposit at San Sidero (Apulia, southern Italy). These fossils show clear evidence of a chronic periodontitis that caused the animal's death. Clinical diagnosis of the disease and the timing of its development have been defined on the basis of a veterinary odontostomatology approach, in addition to radiographic and tomographic techniques. From the initiation of the infection until death, a time span of at least 6 months occurred, and three main steps have been defined: (1) the bacterial infections of the buccal cavity turning into severe periodontitis, (2) the fracture of the lower carnassial and (3) the loss of teeth due to the worsening infection that deformed and/or eroded maxillary and mandibular bones and enlarged alveoli. The analysis of the palaeopathology also provides information about the biomechanics of the bite, on the feeding behaviour and on the relationships of injured members in a pack of Late Pleistocene canids. PMID:23371350

Iurino, Dawid Adam; Fico, Rosario; Petrucci, Mauro; Sardella, Raffaele

2013-02-01

58

A chronology of Late-Pleistocene permafrost events in southern New Jersey, eastern USA  

Science.gov (United States)

Frost fissures, filled with wind-abraded sand and mineral soil, and numerous small-scale non-diastrophic deformations, occur in the near-surface sediments of the Pine Barrens of southern New Jersey. The fissures are the result of thermal-contraction cracking and indicate the previous existence of either permafrost or seasonally-frozen ground. The deformations reflect thermokarst activity that occurred when permafrost degraded, icy layers melted and density-controlled mass displacements occurred in water-saturated sediments. Slopes and surficial materials of the area reflect these cold-climate conditions. Optically-stimulated luminescence permits construction of a tentative Late-Pleistocene permafrost chronology. This indicates Illinoian, Early-Wisconsinan and Late-Wisconsinan episodes of permafrost and/or deep seasonal frost and a Middle-Wisconsinan thermokarst event. Copyright ?? 2007 John Wiley & Sons, Ltd.

French, H. M.; Demitroff, M.; Forman, S. L.; Newell, W. L.

2007-01-01

59

Paleosoils and pedogenic calcretes formations in Fray Bentos (Oligocene - early miocene) Raigon (late pliocene and middle pleistocene) and Libertad (early - middle pleistocene)  

International Nuclear Information System (INIS)

The Fray Bentos formation is composed by loessic deposits based on paleosoils and pedogenic calcretes (Oligocene - early miocene). In this deposits are tubular and lamellar formations which would have been formed in arid climates.The fluvial origen of Raigon Formation, (late pliocene and middle pleistocene) presents a paleosoil roof which is generated under a subhumid climate.The Libertad Formation during the glacial intervals consisted of loess deposits

2012-01-01

60

Population expansion in the North African Late Pleistocene signalled by mitochondrial DNA haplogroup U6  

Directory of Open Access Journals (Sweden)

Full Text Available Abstract Background The archaeology of North Africa remains enigmatic, with questions of population continuity versus discontinuity taking centre-stage. Debates have focused on population transitions between the bearers of the Middle Palaeolithic Aterian industry and the later Upper Palaeolithic populations of the Maghreb, as well as between the late Pleistocene and Holocene. Results Improved resolution of the mitochondrial DNA (mtDNA) haplogroup U6 phylogeny, by the screening of 39 new complete sequences, has enabled us to infer a signal of moderate population expansion using Bayesian coalescent methods. To ascertain the time for this expansion, we applied both a mutation rate accounting for purifying selection and one with an internal calibration based on four approximate archaeological dates: the settlement of the Canary Islands, the settlement of Sardinia and its internal population re-expansion, and the split between haplogroups U5 and U6 around the time of the first modern human settlement of the Near East. Conclusions A Bayesian skyline plot placed the main expansion in the time frame of the Late Pleistocene, around 20 ka, and spatial smoothing techniques suggested that the most probable geographic region for this demographic event was to the west of North Africa. A comparison with U6's European sister clade, U5, revealed a stronger population expansion at around this time in Europe. Also in contrast with U5, a weak signal of a recent population expansion in the last 5,000 years was observed in North Africa, pointing to a moderate impact of the late Neolithic on the local population size of the southern Mediterranean coast.

Pereira Luísa; Silva Nuno M; Franco-Duarte Ricardo; Fernandes Verónica; Pereira Joana B; Costa Marta D; Martins Haidé; Soares Pedro; Behar Doron M; Richards Martin B; Macaulay Vincent

2010-01-01

 
 
 
 
61

The Jinniushan hominin pedal skeleton from the late Middle Pleistocene of China.  

UK PubMed Central (United Kingdom)

Bipedalism has long been recognized as the seminal adaptation of the hominin radiation and thus used to distinguish hominins from great ape fossils. Notwithstanding preconceptions and varied interpretations, the distinctive features of the modern human foot and accompanying striding gait, appear to be recent innovations that are largely absent in the earliest facultative bipeds. These distinctive features are mainly components of fixed longitudinal and transverse pedal arches, and of a uniquely derived hallucal metatarsophalangeal joint. They enhance ankle joint plantar flexor function and accommodate localized peak plantar pressures at the medial ball during terminal stance. To date, the paleontological record has yielded very little of the hominin foot, especially of the Middle Pleistocene hominins. New specimens from this time interval should help provide insights into the timing and pattern of what appears to be a mosaic pattern of evolution of the modern human foot features. Here we describe the fossil hominin foot skeleton recovered from the Jinniushan site, Liaoning Province, People's Republic of China. It affords a singular glimpse of the pedal morphology of a late Middle Pleistocene hominin (c.f. Homo heidlebergensis). Dated to 200ka or older, this foot offers the earliest evidence for increased stability of the medial longitudinal arch, while retaining a number of primitive features apparently characteristic of robust premodern hominins, including lower arches and a less stable hallucal metatarsophalangeal joint (medial ball) than in modern humans. These features reflect different foot capabilities and suggest the bipedal stride of the Jinniushan hominin differed subtlety from that of modern humans.

Lu Z; Meldrum DJ; Huang Y; He J; Sarmiento EE

2011-12-01

62

Exposure of late Pleistocene Mississippi River meander-belt facies at Mt. Pleasant, Louisiana  

Energy Technology Data Exchange (ETDEWEB)

Exposure of a sedimentary sequence along a Mississippi River bluff at Mt. Pleasant, Louisiana, provides insight into the construction of the Prairie Terraces. This site serves as a type section for a late Pleistocene meander belt of the Mississippi River, and stratigraphic features have been traced beneath the Prairie Terraces in southeastern Louisiana. A 23.35-m measured section reveals upper units of Peoria loess and mixed loess. The described meander-belt facies are of a probable Wisconsin age and are here named the Mt. Pleasant Bluff alloformation. This age designation is based on position in the stratigraphic section, degree of preservation of sedimentary facies, character and degree of development of the upper paleosol, preservation of constructional topography beneath the loess, and correlation of this sequence to nearby sites with Wisconsin-age radiocarbon dates.

Autin, W.J.; Davison, A.T.; Miller, B.J.; Day, W.J.; Schumacher, B.A.

1988-09-01

63

Environmentally controlled succession in a late Pleistocene coral reef (Sinai, Egypt)  

Science.gov (United States)

The concept of ecological succession has been frequently applied in the study of ancient reefs. Whereas Paleozoic and Mesozoic reefs are commonly thought to reveal an autogenic primary—climax zonation, patterns in Neogene and Quaternary reefs are much more diverse. Here, we describe a well-preserved late Pleistocene coral reef from Dahab on Sinai Peninsula (Egypt), which shows a distinct zonation that resembles an ecological succession. In contrast to classical examples of ecological successions, species composition, paleoenvironmental conditions, and coral biodiversity of the Dahab reef indicate an allogenic, sea-level controlled community change, from marginal marine to reef slope and back reef. A review of the literature confirms that autogenic, short-term successions are virtually absent in Quaternary reefs. We predict that long generation times of corals make it unlikely that classical autogenic successions develop in reefs at all, unless environmental conditions are unusually stable.

Mewis, H.; Kiessling, W.

2013-03-01

64

Stratigraphy around Kansai International Airport - reconstruction of the Plio-Pleistocene Osaka Group in the southern Osaka Basin  

Science.gov (United States)

Tectonic sedimentary basin in Osaka is formed by the activation of fault system with E-W trending fault (MTL and AL) and N-S trending fault (Ikoma fault and Osaka wan fault). This sedimentary basin during Quaternary time is aligned in the central part of Japan (Takemura, 1985). In this basin, thick sedimentary sequences deposited and these are including marine clay deposit. These marine clay deposit are formed at least 15 layers. The stratigraphy of the Osaka Group in the hill areas was summarized on the basis of intercalation of marine clay bed and volcanic ash layers. The stratigraphy of submarine strata at Kansai International Airport is summarized based on correlation of four 400m deep cores obtained during 1994 and 1995, and previous results published by Nakaseko et. al., (1984). In 2007, deep borehole core drilling was carried out at Kansai Airport again. It over 1200m depth and this drilling point is most near central axis in Osaka sedimentary basin. In this study, we are analysis by micropaleontological, tephrochronological and magnetostratigraphical method, and correlated around borehole data. The sequences are called upper group (Kukojima) and lower group (Sennanoki) (Nakaseko et al., 1984). These Kukojima and Sennanoki formations are include marine deposit. In this study, we can analysis deeper part formation and it appeared that deeper deposits are formed in the lake. It means these are non-marine deposit not include marine clay and seems to big lake because of main grain size are silt and sand. In this poster, we would like to show the stratigraphy at center of Osaka basin and its characteristics.

Kitada, N.; Inoue, N.; Takemura, K.; Masuda, F.; Hayashida, A.; Tabata, T.

2007-12-01

65

Lineage-specific late pleistocene expansion of an endemic subtropical gossamer-wing damselfly, Euphaea formosa, in Taiwan  

Directory of Open Access Journals (Sweden)

Full Text Available Abstract Background Pleistocene glacial oscillations have significantly affected the historical population dynamics of temperate taxa. However, the general effects of recent climatic changes on the evolutionary history and genetic structure of extant subtropical species remain poorly understood. In the present study, phylogeographic and historical demographic analyses based on mitochondrial and nuclear DNA sequences were used. The aim was to investigate whether Pleistocene climatic cycles, paleo-drainages or mountain vicariance of Taiwan shaped the evolutionary diversification of a subtropical gossamer-wing damselfly, Euphaea formosa. Results E. formosa populations originated in the middle Pleistocene period (0.3 Mya) and consisted of two evolutionarily independent lineages. It is likely that they derived from the Pleistocene paleo-drainages of northern and southern Minjiang, or alternatively by divergence within Taiwan. The ancestral North-central lineage colonized northwestern Taiwan first and maintained a slowly growing population throughout much of the early to middle Pleistocene period. The ancestral widespread lineage reached central-southern Taiwan and experienced a spatial and demographic expansion into eastern Taiwan. This expansion began approximately 30,000 years ago in the Holocene interglacial period. The ancestral southern expansion into eastern Taiwan indicates that the central mountain range (CMR) formed a barrier to east-west expansion. However, E. formosa populations in the three major biogeographic regions (East, South, and North-Central) exhibit no significant genetic partitions, suggesting that river drainages and mountains did not form strong geographical barriers against gene flow among extant populations. Conclusions The present study implies that the antiquity of E. formosa's colonization is associated with its high dispersal ability and larval tolerance to the late Pleistocene dry grasslands. The effect of late Pleistocene climatic changes on the subtropical damselfly's historical demography is lineage-specific, depending predominantly on its colonization history and geography. It is proposed that the Riss and Würm glaciations in the late Pleistocene period had a greater impact on the evolutionary diversification of subtropical insular species than the last glacial maximum (LGM).

Huang Jen-Pan; Lin Chung-Ping

2011-01-01

66

The Jinniushan hominin pedal skeleton from the late Middle Pleistocene of China.  

Science.gov (United States)

Bipedalism has long been recognized as the seminal adaptation of the hominin radiation and thus used to distinguish hominins from great ape fossils. Notwithstanding preconceptions and varied interpretations, the distinctive features of the modern human foot and accompanying striding gait, appear to be recent innovations that are largely absent in the earliest facultative bipeds. These distinctive features are mainly components of fixed longitudinal and transverse pedal arches, and of a uniquely derived hallucal metatarsophalangeal joint. They enhance ankle joint plantar flexor function and accommodate localized peak plantar pressures at the medial ball during terminal stance. To date, the paleontological record has yielded very little of the hominin foot, especially of the Middle Pleistocene hominins. New specimens from this time interval should help provide insights into the timing and pattern of what appears to be a mosaic pattern of evolution of the modern human foot features. Here we describe the fossil hominin foot skeleton recovered from the Jinniushan site, Liaoning Province, People's Republic of China. It affords a singular glimpse of the pedal morphology of a late Middle Pleistocene hominin (c.f. Homo heidlebergensis). Dated to 200ka or older, this foot offers the earliest evidence for increased stability of the medial longitudinal arch, while retaining a number of primitive features apparently characteristic of robust premodern hominins, including lower arches and a less stable hallucal metatarsophalangeal joint (medial ball) than in modern humans. These features reflect different foot capabilities and suggest the bipedal stride of the Jinniushan hominin differed subtlety from that of modern humans. PMID:22040649

Lu, Z; Meldrum, D J; Huang, Y; He, J; Sarmiento, E E

2011-10-29

67

Ancient DNA analyses exclude humans as the driving force behind late Pleistocene musk ox (Ovibos moschatus) population dynamics  

DEFF Research Database (Denmark)

The causes of the late Pleistocene megafaunal extinctions are poorly understood. Different lines of evidence point to climate change, the arrival of humans, or a combination of these events as the trigger. Although many species went extinct, others, such as caribou and bison, survived to the present. The musk ox has an intermediate story: relatively abundant during the Pleistocene, it is now restricted to Greenland and the Arctic Archipelago. In this study, we use ancient DNA sequences, temporally unbiased summary statistics, and Bayesian analytical techniques to infer musk ox population dynamics throughout the late Pleistocene and Holocene. Our results reveal that musk ox genetic diversity was much higher during the Pleistocene than at present, and has undergone several expansions and contractions over the past 60,000 years. Northeast Siberia was of key importance, as it was the geographic origin of all samples studied and held a large diverse population until local extinction at approximately 45,000 radiocarbon years before present ((14)C YBP). Subsequently, musk ox genetic diversity reincreased at ca. 30,000 (14)C YBP, recontracted at ca. 18,000 (14)C YBP, and finally recovered in the middle Holocene. The arrival of humans into relevant areas of the musk ox range did not affect their mitochondrial diversity, and both musk ox and humans expanded into Greenland concomitantly. Thus, their population dynamics are better explained by a nonanthropogenic cause (for example, environmental change), a hypothesis supported by historic observations on the sensitivity of the species to both climatic warming and fluctuations.

Campos, Paula F; Willerslev, Eske

2010-01-01

68

Late Pliocene to Pleistocene sensitivity of the Greenland Ice Sheet in response to external forcing and internal feedbacks  

Energy Technology Data Exchange (ETDEWEB)

The timing and nature of ice sheet variations on Greenland over the last {proportional_to}5 million years remain largely uncertain. Here, we use a coupled climate-vegetation-ice sheet model to determine the climatic sensitivity of Greenland to combined sets of external forcings and internal feedbacks operating on glacial-interglacial timescales. In particular, we assess the role of atmospheric pCO{sub 2}, orbital forcing, and vegetation dynamics in modifying thresholds for the onset of glaciation in late Pliocene and Pleistocene. The response of circum-Arctic vegetation to declining levels of pCO{sub 2} (from 400 to 200 ppmv) and decreasing summer insolation includes a shift from boreal forest to tundra biomes, with implications for the surface energy balance. The expansion of tundra amplifies summer surface cooling and heat loss from the ground, leading to an expanded summer snow cover over Greenland. Atmospheric and land surface fields respond to forcing most prominently in late spring-summer and are more sensitive at lower Pleistocene-like levels of pCO{sub 2}. We find cold boreal summer orbits produce favorable conditions for ice sheet growth, however simulated ice sheet extents are highly dependent on both background pCO{sub 2} levels and land-surface characteristics. As a result, late Pliocene ice sheet configurations on Greenland differ considerably from late Pleistocene, with smaller ice caps on high elevations of southern and eastern Greenland, even when orbital forcing is favorable for ice sheet growth. (orig.)

Koenig, Sebastian J.; DeConto, Robert M. [University of Massachusetts, Department of Geosciences, Amherst, MA (United States); Pollard, David [Pennsylvania State University, Earth and Environmental Systems Institute, College of Earth and Mineral Sciences, University Park, PA (United States)

2011-09-15

69

Mass wasting deposits in the upper Sehonghong valley, eastern Lesotho: Late Pleistocene climate implications  

Science.gov (United States)

Despite considerable research attention on apparent periglacial, glacial and sedimentary phenomena in the Maluti-Drakensberg alpine environment, knowledge on the Quaternary environmental history of this important watershed and climate-divide is still rather rudimentary. The dearth of Quaternary environmental indicators (proxy data) in the high Drakensberg is partly owing to the harsh climate (e.g. high wind speeds and high seasonal precipitation), which offers a poor preservation of past biological remains (e.g. bones, dung, middens, pollen). Possibly the best opportunity to reconstruct high Drakensberg palaeoenvironments is from sedimentary sequences exposed along fluvially-incised valley fills. The upper Sehonghong River (3000 to 3200 m a.s.l.) flows in a westerly direction and is flanked by north- and south-facing slopes reaching 3465 m a.s.l. Sediment is exposed on both the north- and south-facing slopes along the river. Despite uniform regional environmental conditions (geology, topography, climate, vegetation), there is a notable absence of similar north-facing deposits in adjacent upper valley catchments to the north and south of Sehonghong Valley. The upper Sehonghong Valley thus presents somewhat ‘unique' evidence for palaeo-slope mass movement in this alpine region. Thick colluvial deposits are most prominent on the south-facing slopes along the Sehonghong River and occur at altitudes between 3100 m a.s.l. and 3150 m a.s.l. The colluvial mantles are approximately 7 m in thickness, however reach up to 13 m in some areas. Although the north-facing lower valley side-slopes are generally absent of deposits, the notable exception is the thick stratified deposit located a few kilometres upstream. Whilst the south-facing deposits are relatively uniform in nature, the north-facing deposits consist of alternating units of gravel and organic sediment, dated to 36 600 ± 1400 14C yrs BP, and reflecting environmental changes during the Late Pleistocene. Mass wasting deposits support enhanced periglacial activity during the Late Pleistocene, particularly on south-facing slopes, and also where conditions were conducive to enhanced sediment transport on the adjacent north-facing slope of the Sehonghong River. Recent published work has suggested evidence for marginal glaciation in the high Drakensberg within 10 km of the Sehonghong Valley, suggesting that whilst particular environmental settings host deposits classified as glacial moraine, adjacent valleys are occupied by deep (~8 m) valley deposits flanking south-facing slopes. We demonstrate that the variable nature of adjacent valley slope deposits at similar altitudes is a product of a past climate that was within the glacial/periglacial equilibrium zone, and influenced by specific topographic and associated micro-climatic thresholds.

Mills, S. C.; Grab, S. W.

2009-04-01

70

Sequence stratigraphy of upper pliocene and pleistocene sedimentary rocks of northwestern Green Canyon area, northern Gulf of Mexico  

Energy Technology Data Exchange (ETDEWEB)

The sequence stratigraphy of northwestern Green Canyon has been studied using 900 mi of multifold seismic data and 39 wells with biostratigraphic data (14 with high-resolution analysis). Variations in fossil abundance and diversity were used in the recognition of condensed sections. Eight depositional sequences (2.4, 1.9, 1.4, 0.8, 0.7, 0.5, 0.6, and 0.4 Ma) have been recognized. Paleobathymetry indicates that sequences were deposited primarily in bathyal water depths. Most of the sediments compose lowstand systems tracts and consist of basin-floor fan, slope fan, and prograding complex. Thick bathyal sandstones are present in three major sequences (1.9, 1.4, and 1.1 Ma) and represent potential reservoirs in the area. These are interpreted as basin-floor fan deposits. Slope-fan complexes compose most of the sediment in the area; levee channel complexes, overbank deposits, slope fills, slump-debris flows, and canyon fills were recognized in these turbidite complexes. Transgressive and highstand systems tracts are thin across the area and are well developed in the younger sequences (<0.6 Ma). Syndepositional structures characterize the study area. Growth faults and salt diapirism play a role important in the geometry and distribution of the depositional units, as well as creating structural features for petroleum entrapment.

Martinez, R.E.; Weimer, P. [Univ. of Colorado, Boulder, CO (United States)

1994-12-31

71

Correlation of the Late Pleistocene Usselo Horizon (Europe) and the Clovis Layer (North America)  

Science.gov (United States)

In 1940, a dark charcoal-rich layer, 10 to 15cm thick, was found within the Late Pleistocene Coversands of the Netherlands, and named the Usselo Layer (de Laag van Usselo) by its discoverer, archaeologist CCJW Hijszeler (1902-1982). Usselo is a village near Enschedé, a few kilometres from the Dutch-German border. Research started after the war, and publications, both scientific and popular, came forth in the 1950s. By pollen content, the layer was dated to the Alleröd, the last interstadial of the Würm (Wisconsin) glaciation; radiocarbon dating indicated (pre-AMS) dates of about 11,200 14C BP. Identification of the layer at other localities was visual, and it was found in Belgium, France, Germany, Poland, and Belarus; it was also found in the UK and in Denmark, in which countries, however, no correlation was made with the other occurrences. Hijszeler had found the layer all over the Netherlands and abroad from Ostende to Hamburg, and he hypothesized the cause as a general wildfire provoked by the eruption of an Eiffel volcano. The European geologists and archaeologists, however, did not adopt his views and interpreted the layer as a paleosol, vitiating the chronology by representing the layer as the result of a long development, instead of as an eolian sediment laid down perhaps in a day or even less that provides us with a sharp marker horizon. The prehistoric Clovis culture of North America was found in the 1930s and dated to the Twocreekan, the last interstadial of the Wisconsin glaciation. The Clovis layer was especially investigated by archaeologist C.Vance Haynes Jr. Visually, the layer is easily identifiable with the Usselo Horizon of Europe. Its stratigraphic position is coincident with the end of the Clovis culture and with the disappearance of the Pleistocene megafauna. In Europe, there is a clear correlation with the sudden demise of the Magdalenian culture, best known for the Franco-Cantabrian cave paintings, and with megafaunal extinctions such as those of the Irish elk, the cave bear, and cave lion. Recently, Richard Firestone and Allen West in North America have carried out an intensive field and laboratory investigation, suspecting an extraterrestrial cause for the extinctions and the cultural discontinuity, with the Clovis layer as the extinction layer, an all-important witness to the catastrophe. They achieved positive results, the most spectacular one perhaps being the iridium content, because that element became well-known in the 1980s as an impact indicator in the K-T boundary layer. Other results include the presence of glass-like carbon, magnetic microspherules, and high levels of potassium-40. Being aware of the similarities in the Late Pleistocene stratigraphical records of Europe and North America, I contacted Firestone and West in 2005, and early in 2006 I sent them samples of the Usselo Horizon from Lommel, Belgium. The analyses they carried out yielded high levels of impact indicators, including magnetic grains, metallic spherules, carbon glass, charcoal, and in the magnetic fraction, high iridium content. These findings largely confirm the identity of the two ET impact layers on either side of the Atlantic Ocean. Hijszeler(1957) Geol.Mijnb.NS 19: 288-302. Haynes and Hemmings (1968) Science 159: 186-7. Wolbach, et al. (1985) Science 230: 167-170. Kloosterman (1999) Symp. New Scenarios of Solar System Evolution, Univ.Bergamo. (Abstract 2002). Kloosterman (2000) De Laag van Usselo, de Wereldbrand en de Verdwijntruc. Bres 201: 63-74. Kloosterman (2006) "De Komeetinslag van 13.000 jaar geleden." Frontier Mag. 12/1: 44- 45. Firestone, et al. (2006) The Cycle of Cosmic Catastrophes. Bear and Co., Rochester, Vermont.

Kloosterman, J. B.

2007-05-01

72

Characteristics of the active Luoshan Fault since Late Pleistocene, North Central China  

Directory of Open Access Journals (Sweden)

Full Text Available The Luoshan Fault located at the northeastern margin of Tibet plateau strikes roughly N-S, and is composed of six left-stepping sections with a total length of 60 km. Much evidence suggests that the Luoshan Fault is a reverse right-lateral strike-slip fault. The largest right-lateral strike-slip displacement and the most abundant dextral offset phenomena are located along the central section. Based on the right-lateral strike-slip offsets of the oldest alluvial fan, and of a gully and on the average displacement of the same order of gullies, the minimum slip-rate has been 2.15 ± 0.2 mm/yr since Late Pleistocene. Many surface rupture phenomena, such as fault scarps with fresh free-face, ground fissures, displacements of very young gullies, imply that a recent earthquake occurred along this fault. Combining the historical catalogue and our results, we believe that the 1561 A.D. earthquake was produced by the Luoshan Fault. Three paleoearthquakes were determined by means of paleoseismic studies along the Luoshan Fault: they occurred after 8200 ± 600 years BP, between 3130 ± 240 years BP and 4150 ± ± 120 years C.BP, and before 2230 ± 170 years BP, respectively.

M. Wei; J. Decheng; C. Chizhang; Z. Peizhen; M. Fengying

2003-01-01

73

Rapid thinning of the late Pleistocene Patagonian Ice Sheet followed migration of the Southern Westerlies  

Science.gov (United States)

Here we present the first reconstruction of vertical ice-sheet profile changes from any of the Southern Hemisphere's mid-latitude Pleistocene ice sheets. We use cosmogenic radio-nuclide (CRN) exposure analysis to record the decay of the former Patagonian Ice Sheet (PIS) from the Last Glacial Maximum (LGM) and into the late glacial. Our samples, from mountains along an east-west transect to the east of the present North Patagonian Icefield (NPI), serve as ‘dipsticks' that allow us to reconstruct past changes in ice-sheet thickness, and demonstrates that the former PIS remained extensive and close to its LGM extent in this region until ~19.0?ka. After this time rapid ice-sheet thinning, initiated at ~18.1?ka, saw ice at or near its present dimension by 15.5?ka. We argue this rapid thinning was triggered by a combination of the rapid southward migration of the precipitation bearing Southern Hemisphere (SH) westerlies and regional warming.

Boex, J.; Fogwill, C.; Harrison, S.; Glasser, N. F.; Hein, A.; Schnabel, C.; Xu, S.

2013-01-01

74

Aeolian activity in northern Amazonia: optical dating of Late Pleistocene and Holocene palaeodunes  

Science.gov (United States)

Palaeodunes were examined on the eastern margin of the Rio Branco-Rupununi savanna, northeast Amazonia. Optical dating suggests that the onset of aeolian activity was between 17 000 and 15 000 yr ago, just after the Last Glacial Maximum. Both the palaeodune axes and modern dominant wind directions have northeast to east-northeast directions, implying no significant shift in atmospheric circulation patterns over northeast Amazonia during the Late Pleistocene to Holocene. Major regional climate change events, such as the Younger Dryas, do not appear to have had any effect on the rates of aeolian deposition at the study site. Aeolian activity appears to have continued to the present day, showing a remarkably constant deposition rate of around 0.13 m kyr-1 initially, increasing smoothly to the present. Until more palaeodunes in northern Amazonia are dated, it is impossible to determine if this record of gradual aeolian deposition is a reliable regional palaeoclimate indicator, rather than being the result of local bioclimatic and geomorphological effects. Copyright

Teeuw, Richard M.; Rhodes, Edward J.

2004-01-01

75

A Late Pleistocene-Holocene wetland megafan in the Brazilian Amazonia  

Science.gov (United States)

Despite the growing interest in megafans, definitions provided for this type of environmental setting have not yet been widely agreed upon. A record of sedimentary facies distribution in both space and time including a larger number of analogs is particularly needed for improving megafan facies models. This work focuses on a large fan-like feature from an Amazonian wetland in northern Brazil. Morphological data based on remote sensing, as well as sedimentary facies and radiocarbon analyses, were integrated to propose that this feature is related to a megafan system active during the Late Pleistocene to Holocene. The megafan displays a divergent drainage network, gently-dipping slope, and concave-up and convex-up longitudinal and transverse profiles, respectively. Near surface deposits correspond to fining and coarsening upward sands related to active channels and overbank sand sheets/terminal fan lobes. Sediments are interbedded with abandoned channel/floodplain and lake/pond muds. Morphostructural analyses and drainage anomalies revealed a geological setting affected by reactivation of pre-existing faults contemporaneous with sediment accumulation. Establishment of a megafan system in this wetland most likely occurred within a slightly tectonically subsiding basin under favorable climatic conditions. During wet seasons, high water discharge would have favored sediment transport from highlands into this depositional site. High summer temperatures and drought under a monsoonal regime kept the water levels low. The described megafan could serve as an analog for contemporary tropical wetland megafans formed under a monsoonal climate regime.

Rossetti, D. F.; Zani, H.; Cohen, M. C. L.; Cremon, É. H.

2012-12-01

76

The view from the Lincoln Cave: mid- to late Pleistocene fossil deposits from Sterkfontein hominid site, South Africa.  

Science.gov (United States)

The Lincoln-Fault cave system lies adjacent to the Sterkfontein Cave system in the Cradle of Humankind World Heritage Site, Gauteng Province, South Africa. Lincoln Cave contains a mid- to late Pleistocene fossiliferous deposit which has been dated using uranium series methods to between 252,600+/-35,600 and 115,300+/-7,700 years old. Although speleologists presumed that there was no connection between the Lincoln Cave and Sterkfontein Cave systems, results of excavations conducted in 1997 suggest a link between the deposits. Detailed comparisons of artifacts, fauna, hominid material, and a statistical correspondence analysis (CA) of the macromammalian fauna in the deposits strongly support this hypothesis. The recovery of Early Acheulean-type artifacts from the Lincoln Cave suggests that older artifacts eroded out of Sterkfontein Member 5 West and were redeposited into the younger Lincoln Cave deposits. The close physical proximity of these deposits, and the nature of the material recovered from them, indicates that the material was probably redeposited via a link between the two cave systems. Although faunal mixing is present, it is possible to say that large carnivorans become more scarce at Sterkfontein during the mid- to late Pleistocene, while small canids and felids appear to become more abundant, indicating that large and small carnivorans probably varied their use of the site through time. This may also reflect an increasing presence of humans in the Sterkfontein area during the mid- to late Pleistocene. PMID:17624409

Reynolds, S C; Clarke, R J; Kuman, K A

2007-07-10

77

Radiolarian Indices of Paleoproductivity Variation in the late Pleistocene Benguela Upwelling System, ODP Site 1084  

Science.gov (United States)

Changes in export productivity play a significant role in ocean carbon budgets and global climate change. Proxies for export productivity can be difficult to interpret: benthic foraminifera accumulation rates (BFAR) can be affected by carbonate dissolution in organic-carbon rich sediments; bulk opal can be affected by silica limitation of source waters. Recent work (Lazarus et al. 2006; Mar. Micropal.) has shown that a new index based on radiolarian faunal changes (WADE ratio) correlates well to total organic carbon (TOC) values from the same samples over the long term (latest Miocene-Recent) history of productivity in the Benguela Upwelling System (BUS). We present new data on variation in export productivity proxies (WADE, TOC, carbonate, radiolarian opal, BFAR) for the last glacial-interglacial cycle from ODP Site 1084, located just offshore from the main coastal upwelling cells of the BUS. Our age model, from mean Quaternary sedimentation rates (Leg 175 Scientific Results), is in accordance with cyclic variation in other climate sensitive parameters (carbonate and color reflectance). Although opal content and radiolarian preservation is only moderate in our samples, WADE values vary significantly and suggest higher productivity during the last glacial, in accordance with current interpretations of BUS history. Radiolarian opal accumulation is also higher during the last glacial, suggesting that silica limitation (opal paradox) conditions did not dominate over this time period. Similar results for bulk opal have been reported from late Quaternary piston cores from the more northerly Congo upwelling region (Schneider et al, 1997; Paleoc.). We conclude that WADE ratios are a useful proxy for late Pleistocene productivity in the BUS at glacial- interglacial time scales.

Bittniok, B. B.; Lazarus, D. B.; Diester-Haass, L.; Billups, K.; Meyers, P.

2006-12-01

78

Sequence stratigraphy of Pliocene-Pleistocene sediments in north central Green Canyon and western Ewing Bank, northern Gulf of Mexico  

Energy Technology Data Exchange (ETDEWEB)

The Pliocene-Pleistocene sediments of north central Green Canyon and western Ewing Bank are deformed by complex salt features and normal and high-angle reverse faults. A sequence-stratigraphic interpretation of the area was done using 2140 km of 2-D multifold migrated seismic data, biostratigraphic data from 31 wells, and well logs. The study area covers 2447 km{sup 2} and was informally subdivided into five mini-basins within which sediments were deposited in bathyal and abyssal environments. Nine depositional sequences were recognized (4.2, 3.8, 3.4, 3.0, 1.4, 1.1, 0.8, 0.7, and 0.5 Ma). Most of sediments were deposited in lowstand systems tracts consisting of basin-floor fan, slope-fan complex, and prograding complex. Transgressive system tracts and highstand system tracts arc thin where present. A major condensed interval (3.0 to 1.4 Ma) is relatively thin (80-100 ft) and is widespread across the entire study area. In general, the sequences are dominantly shale as indicated by well penetrations. Sandy intervals are present within the sequences 4.2-3.8 Ma and 1.4-1.1 Ma. A prominent basin-floor fan is present in the 1.4-1.1 Ma sequence as indicated by the subparallel, high-amplitude reflections and the blocky well log patterns (140 ft). The slope-fan complex has wide variability in its seismic expression and sand percentage both within and between sequences; it consists of hummocky, chaotic, and subparallel reflections interpreted to reflect a number of depositional processes (channel fill, overbank, slides). The complex salt and faulting generated structures that control the geometry of the depositional units and the entrapment of petroleum. Discoveries in the area include Green Canyon Blocks 22 and 65 (Bullwinkle) and are associated with amplitude anomalies on the flank of salt features.

Acosta, Z.; Weimer, P. [Univ. of Colorado, Boulder, CO (United States)

1994-09-01

79

South Caspian Sea: a Unique Setting to Evaluate Proposed Mechanisms for Late-Pleistocene Large-Scale Submarine Slope Failure  

Science.gov (United States)

A large (640 km*2), industry-quality, 3-D multichannel seismic reflection dataset (3 s) and well-logs from the South Caspian basin, offshore Azerbaijan, were interpreted and analyzed in order to clarify the origin, age, and areal extent of a large-scale (2,500 km*2) late-Pleistocene zone of seafloor deformation and submarine slumping, the Absheron Allochthon. These data are uniquely set to evaluate proposed mechanisms for late-Pleistocene large-scale submarine slope failure, and favor a genetic relationship with dissociation of underlying gas hydrates when the sea level was at a minimum. Previous analysis of two regional seismic reflection profiles from the study area documented the occurrence of gas hydrates concealed beneath the seafloor (300 m) in water depths ranging between 400 and 650 m. Historic sea level changes in the Caspian basin have exceeded 3 m over the last century, and were significantly amplified in comparison to global sea level changes during the Pleistocene time. In the Quaternary, the Caspian Sea level oscillations reportedly exceeded the eustatic sea level oscillations both in amplitude and frequency, with a range between +50 m in the Last Glacial period and -113 m during the Early Holocene. Since the inland Caspian Sea is affected by sea level fluctuations at much shorter time scales and much larger amplitudes than the world's oceans, the premise is that climate-induced changes in sea level were responsible for large scale slope failure and seabed deformation through massive dissociation of buried gas hydrates during the sea level lowstands in the late-Pleistocene. Due to the historic large-scale variations of sea level of the landlocked Caspian Sea, this region represents a natural laboratory to study the relationships among the gas hydrate dissociation and seafloor deformation, and can be used as a proxy for similar processes in the world oceans.

Knapp, C. C.; Knapp, J. H.; Duff, P.

2005-12-01

80

Morpho-Sedimentary Impacts By The Late-Pleistocene - Holocene Jökulhlaups In The Þjórsá-Tungnaá Fluvio-Glacial System  

Science.gov (United States)

In Iceland, jökulhlaups correspond to glacial outburst floods that are generally related to sublagial volcanic and hydrothermal activities. They affect the main fluvial outwash plains around the ice caps. They result of the sudden outflow of a large volume of melt water with variable sediment charges drained from a (sub)glacial or an ice-dammed marginal lake that feeds short (hours to days) cataclysmic floods with peak discharges (103 to 107 m3.s-1), up to 10-100 times the magnitude of classical hydrometeorological fluvial floods. Despite their short duration, and because of large peak discharges, they have important erosive and sediment transport capacities. Consequently, repeated events have a strong morpho-sedimentary impact on the inundated areas. The connected watersheds of the Þjórsá and Tungnaá rivers (200 km long; ˜5000 km2, South Island), west of Vatnajökull, correspond to the largest periglacial fluvial system in Iceland. It has drained numerous jökulhlaup floods during the Late Pleistocene deglaciation and the Holocene during periods of increase of the volcanic activity and heat flow. Jökulhlaups were emitted from at least two outlets along the western edge of Vatnajökull that fed the Kaldakvísl and Tungnaá rivers. The subglacial depressions (calderas) of the Bárðarbunga-Hamarinn volcanic system are favorable to the storage of large volumes of water that can feed major jökulhlaups. The Þjórsá-Tungnaá jökulhlaup system can be subdivided into three parts: (1) the source located at the outlets of the subglacial hydraulic network, (2) a proximal transit zone along which erosional processes are dominant (erosively incised rocky substratum - scablands, abraded scoria cones, scour structures, residual buttes of the sedimentary cover) with minor lateral slackwater deposits, flood overflow ponded lakes, and hydraulic dunes along constrictions of the fluvial network, and (3) a distal depositional zone that corresponds to the coastal sandur, the area of main sedimentation before possible floods entrance into the sea as hyperpycnal plumes. Erosion and sedimentation along the system are controlled by the geometry of the fluvial network. Main erosional processes occur along steep slopes and constrictions, and in areas of fluvial channels confluences. These erosional and depositional structures were mapped along the system and summarized on a DEM. Preliminary 2D and 3D hydraulic simple modeling of the floods has been conducted for the Kaldakvísl-Þjórsá jökulhlaup sub-system with an outlet located in the present-day lake Hágöngulón area. The modeling is based on the solutions of Saint-Venant equations obtained by both eulerian (VF2D; IRSTEA) and lagrangian (TELLUS, CSIRO) approaches. Results provide theoretical velocity fields and flood heights along the flooded area. The preliminary results of this modeling were compared to the location of the field structures along the system, and significant correlations between the structures into the field and the velocity fields have been identified. In conclusion, a large jökulhlaup system is mainly erosive, with limited sedimentation located on its edges and on the coastal plain. Works in progress on the Þjórsá-Tungnaá jökulhlaup system deal with the stratigraphy of past large-scale outburst events, their modeling and the estimate of their recurrence. These are some of the main objectives of the JOKER project submitted to the French Research Agency.

Schneider, Jean Luc; van Vliet-Lanoe, Brigitte; Naaim, Mohamed; Salles, Tristan; Bjornsson, Helgi; Palsson, Finnur

2013-04-01

 
 
 
 
81

Late Pleistocene to Holocene sea surface temperature development in the NW-Pacific and its marginal seas  

Science.gov (United States)

The subarctic N-Pacific acts as terminus of the modern ocean circulation with water masses highly enriched in dissolved nutrients and carbon dioxide. Today a permanent halocline results in strong upper-ocean stratification, which hampers the atmospheric-oceanic gas exchange and the supply of nutrients into the photic zone. Past changes in sea surface conditions in the subarctic Pacific are proposed to impact climate but are less well known than in the N-Atlantic. The onset and timing of past oceanographic changes are suggested to be driven by changes in oceanic circulation and/or atmospheric teleconnections. Here, we present a suite of sediment records from the continental slope off Kamchatka (NW-Pacific), the western Bering Sea and the Sea of Okhotsk. All cores were obtained well above the shallow carbonate compensation depth (CCD) and provide sufficient material for detailed late Pleistocene to Holocene reconstructions of past changes in oceanographic conditions. The stratigraphy is based on high-resolution X-ray fluorescence scans (XRF) together with spectrophotographic measurements (color b*), which were aligned to the NGRIP oxygen isotope record and further confirmed by AMS 14C ages. Alkenone measurements were applied to reconstruct sea surface temperatures (SST) by use of the Uk'37 index (Müller et al., 1998). Our SST reconstructions span the last ˜15 ka BP. Prior alkenone concentrations were below the detection limit and thus indicate the absence of coccolithophoride blooms during the last glacial. After ˜14.7 ka BP the SST records in the NW-Pacific and western Bering Sea indicate an early increase in SST (Bolling/Allerod), followed by a cold spell at ˜12.8 ka BP (Younger Dryas) and the onset of warm Holocene climate conditions around ˜10.7 ka BP. During the early Holocene the SST increased by up to 4°C. This pronounced warming is interpreted as amplified stratification of the upper water column, which is paralleled by laminae formation at the sea floor. The SST record, derived from the Sea of Okhotsk, shows a slightly different pattern and indicates a more gradual warming towards the Holocene. Finally, a drop in SST by ca. 2°C is observed towards the middle Holocene, which also challenges the proposed idea of a SST seesaw pattern between the N-Atlantic and N-Pacific (Kim et al., 2004). References Kim, J.-H., Rimbu, N., Lorenz, S.J., Lohmann, G., Nam, S.-I., Schouten, S., Rühlemann, C. & Schneider, R.R. (2004): North Pacific and North Atlantic sea-surface temperature variability during the Holocene. - Quaternary Science Reviews 23, 2141-2154. Müller, P.J., G. Kirst, G. Ruhland, I. von Storch & A. Rosell-Melé, (1998): Calibration of the alkenone paleotemperature index (UK'37) based on core-tops from the eastern South Atlantic and the global ocean (60 degrees N - 60 degrees S) - Geochimica Et Cosmochimica Acta 62, 1757-1772.

Max, L.; Riethdorf, J.; Tiedemann, R.; Nuernberg, D.; Abelmann, A.

2011-12-01

82

Late Pleistocene to Holocene environmental changes from ?13C determinations in soils at Teotihuacan, Mexico  

Scientific Electronic Library Online (English)

Full Text Available Abstract in spanish Utilizamos la firma de isótopos estables de carbono, medida como ?13C, en la materia orgánica de suelo (SOM) como un método de alta resolución espacial para inferir algunos cambios ambientales durante el Pleistoceno tardío y el Holoceno en el valle de Teotihuacan. La interpretación se basa en la diferencia de ?13Cy preferencias climáticas correspondientes de las plantas referidas como C3, C4 y CAM. Los valores de ?13Cobtenidos de plantas que crecen e (more) n el valle hoy en día difieren claramente entre dos grupos: los de las plantas C3 con un promedio de -27%o, y los de C4 y CAM con un promedio cerca de -13%o. Los datos obtenidos para los suelos se encuentran en el intervalo de -25.72 a -15.54 %o. Las secuencias de suelos Pleistoceno tardío- Reciente del valle alto (posición geomorfológica alta), localizadas en el perfil de Cerro Gordo, se caracterizan por una ?13Ccon poca variabilidad alrededor de -20%o, indicando una coexistencia duradera entre las plantas C3 y C4 (y CAM). Las firmas más empobrecidas (-23 ± 2) %o, dominadas por carbono derivado de la vegetación tipo C3, corresponden a los suelos de pantano del Pleistoceno tardío en el perfil retrógrado de transición Tepexpan del antiguo lago de Texcoco-Xaltocan. Los paleosuelos en el valle bajo (Pleistoceno tardío - Holoceno medio), incluyendo los de la Pirámide de la Luna, están menos empobrecidos (-17 ± 1) %o, o bien, dominados por carbono de plantas C4 y CAM. Los suelos del Holoceno tardío y modernos presentan una disminución (1-2 %o) respecto a las ?13Cde los suelos subyacentes. A partir de las ?13Cde suelos se estimó la porción relativa de la contribución de las plantas C4 a la materia orgánica del mismo. Nuestros resultados implican un incremento, dependiendo del lugar, de entre 10 y 70%, durante el período de transición entre el Pleistoceno tardío y Holoceno temprano, y un dominio de la vegetación tipo C4 en el ambiente del valle, hasta en un 84%, durante Holoceno medio. Nuestros datos apoyan la idea de un cambio natural de un clima más frío y húmedo durante el último Máximo Glacial y el Pleistoceno tardío a uno más seco y caluroso en el Holoceno medio. Un ligero incremento de humedad y establecimiento de un clima semejante al actual, aún cálido y seco, se infiere del incremento en todo el valle, dependiendo del lugar, de 4 a 10%, de la población de plantas C3. Sugerimos que este último cambio climático pudo favorecer el desarrollo de la antigua agricultura. Nuestra interpretación general de los primeros datos de isótopos estables del carbono concuerda con interpretaciones paleoambientales para el área basadas en registros palinológicos y paleolimnológicos en sedimentos lacustres. Abstract in english Stable carbon isotopic signature (?13C) of soil organic matter (SOM) is used as a high-spatial resolution tool to infer environmental changes during late Pleistocene to Present in the Teotihuacan valley, Mexico. Interpretation was based on climatic preferences of C3, CAM and C4 plant groups. ?13Cvalues of modern plant types are clearly distinguished. C3 plants display values around -27%o, while C4 and CAM plants have values around-13%o. Data from soil profiles r (more) ange from -25.7 to -15.5 %o. Cerro Gordo site ?13Cvaryies around -20%o, indicating long-term, time-stable co-existence between C3 and C4 or CAM plants. The more depleted signatures (-23 ± 2 %o) are, dominated by carbon from C3 vegetation of late Pleistocene swamp paleosols in the Tepexpan profile of the Lake Texcoco. Younger paleosols from lower valley sites, have less depleted values (-17 ± 1) %o, dominated by C4 and CAM carbon. Late Holocene and modern soils present slightly more negative values (1-2 %o) with respect to ?13Cof underlying soils. Our results show 1) an increase of 10-70 % depending on the site, during the transition from the late Pleistocene to early Holocene, and 2) a dominance of C4 vegetation, up to 84%, in valley environment during the middl

Lounejeva Baturina, E; Morales Puente, P; Cabadas Báez, H. V; Cienfuegos Alvarado, E; Sedov, S; Vallejo Gómez, E; Solleiro Rebolledo, E

2006-06-01

83

Late Pleistocene landslide-dammed lakes along the Rio Grande, White Rock Canyon, New Mexico  

Energy Technology Data Exchange (ETDEWEB)

Massive slump complexes composed of Pliocene basaltic rocks and underlying Miocene and Pliocene sediments flank the Rio Grande along 16 km of northern White Rock Canyon, New Mexico. The toe area of at least one slump complex was active in the late Pleistocene, damming the Rio Grande at least four times during the period from 18 to 12 {sup 14}C ka and impounding lakes that extended 10-20 km upriver. Stratigraphic relationships and radiocarbon age constraints indicate that three separate lakes formed between 13.7 and 12.4 {sup 14}C ka. The age and dimensions of the ca. 12.4 ka lake are best constrained; it had an estimated maximum depth of {approx}30 m, a length of {approx}13 km, a surface area of {approx}2.7 km{sup 2}, and an initial volume of {approx}2.5 x 10{sup 7} m{sup 3}. The youngest landslide-dammed lakes formed during a period of significantly wetter regional climate, strongly suggesting that climate changes were responsible for reactivation of the slump complexes. We are not certain about the exact triggering mechanisms for these landslides, but they probably involved removal of lateral support due to erosion of the slope base by the Rio Grande during periods of exceptionally high flood discharge or rapid incision; increased pore pressures associated with higher water tables; higher seepage forces at sites of ground-water discharge; or some combination of these processes. Seismic shaking could also have contributed to triggering of some of the landslides, particularly if aided by wet antecedent conditions. 54 refs., 19 figs., 3 tabs.

Reneau, S.L. [Los Alamos National Lab., NM (United States); Dethier, D.P. [Williams College, Williamstown, MA (United States)

1996-11-01

84

Late-Pleistocene avifaunas from Cape Wanbrow, Otago, South Island, New Zealand  

International Nuclear Information System (INIS)

Fossil avifaunas from the Hillgrove Formation at Boatmans Harbour, Ruby Gully, and Old Rifle Butts, all on Cape Wanbrow, Oamaru, north-east Otago, are listed. The marine beach sands and gravels at Old Rifle Butts that form the lowest part of the Hillgrove Formation and overlie the palaeo-wave platform were deposited during the last interglacial ? 130-110 kyr BP (Oxygen Isotope Stage 5). There are a few small avifaunas (totalling 11 spp.) from these beach sediments (J41/f8710, f8214, f8227). The colluvial, valley-fill deposits in Ruby Gully and at its mouth are the youngest in the sequence. Radiocarbon dating indicates their emplacement between 27 and 34 kyr BP, or the later part of Oxygen Isotope Stage 3. If these ages are representative of the true age of the samples and not the limitations of radiocarbon technology, they indicate that these deposits in Ruby Gully are much younger than the beach deposits. Radiocarbon ages on a pitfall fauna from a small cave 3-4 m above the base of the Hillgrove Formation indicate that the cave fauna has a similar age as that in Ruby Gully. The dune and interdune waterlaid deposits at Old Rifle Butts (>2 m above the wave platform) may date from an unknown time between 100 and 35 kyr BP or be coeval with those in Ruby Gully. Fifty-three species of bird (32 land and freshwater taxa) are represented in the combined avifaunas making this the richest Pleistocene avifauna known from New Zealand. All bird taxa are known from Late Holocene avifaunas in the eastern South Island. Key taxa (Pachyornis elephantopus, Emeus crassus, Euryapteryx geranoides, Coturnix, Chenonetta, Cnemiornis, Harpagornis, Fulica, Porphyrio, Gallinula) indicate that the habitat was mainly grassland and shrubland. Tuatara, indeterminate skinks, and seals are also present. (author). 57 refs., 10 figs., 2 tabs.

2003-01-01

85

Isotopic evidence for omnivory among European cave bears: Late Pleistocene Ursus spelaeus from the Pestera cu Oase, Romania.  

UK PubMed Central (United Kingdom)

Previous bone collagen carbon and nitrogen isotopic studies of Late Pleistocene European cave bears (Ursus spelaeus) have shown that these bears frequently had low nitrogen isotope values, similar to those of herbivores and indicating either unusual physiology related to hibernation or a herbivorous diet. Isotopic analysis of animal bone from the Pe?tera cu Oase (Cave with Bones), Romania, shows that most of its cave bears had higher nitrogen isotope values than the associated herbivores and were, therefore, omnivorous. The Oase bears are securely identified as cave bears by both their morphology and DNA sequences. Although many cave bear populations may have behaved like herbivores, the Oase isotopic data demonstrate that cave bears were capable of altering their diets to become omnivores or even carnivores. These data therefore broaden the dietary profile of U. spelaeus and raise questions about the nature of the carnivore guild in Pleistocene Europe.

Richards MP; Pacher M; Stiller M; Quilès J; Hofreiter M; Constantin S; Zilhão J; Trinkaus E

2008-01-01

86

New Proxies from Loess-Paleosols on Mount Kilimanjaro document Late Pleistocene Megadroughts in East Africa  

Science.gov (United States)

Innovative, new proxies from loess and paleosol sediments hold great potential to obtain more quantitative information about paleoclimate changes in terrestrial environments. Here we present results from lipid biomarkers (GDGTs) and hydrogen isotopic measurements on long-chain fatty acids and alkanes that we extracted from 69 paleosol samples from Mt Kilimanjaro, Tanzania (~3°S). The respective soil pit and sediment core at ~2700 m above sea level is radiocarbon-dated to 38.4 ka BP, and probably covers most of the Late Pleistocene, making it one of the longest, continuous, terrestrial archives in the East African tropics. Our compound-specific deuterium measurements show lowest ?D values from ~9 to 5 ka in the Early/Middle Holocene, consistent with regional evidence for an “African Humid Period,” followed by a shift towards more arid conditions during the Late Holocene (~5‰ shift). The Younger Dryas is characterized by a ?D enrichment (=aridity) of ~15‰ compared to the Early/Middle Holocene, almost reaching LGM values (~20‰ shift). The enrichment during the LGM is, however, significantly smaller than the 50‰ change as observed in Lake Tanganyika further southwest. At present it is not possible to determine whether these differences result from geographic variations in precipitation and humidity, or isotopic distillation processes along the vapor transport trajectories across East Africa. Much more arid conditions (~40‰ enrichment) can be inferred for the paleosols older than ~60 ka. Although further dating efforts are required to determine the exact timing, this corroborates earlier findings from African lakes that suggested ‘megadroughts’ occurred during Marine Isotope Stages 5 and 4. Acknowledging the general perception that precipitation in East Africa is strongly controlled by ITCZ positioning, we highlight the role of (strong) eccentricity in modulating the precessional forcing, which - in combination with high-latitude glacial boundary conditions - may have caused extreme amplitudes of seasonal ITCZ migration and corresponding variability of climate conditions in the tropics on orbital timescales. Counter-intuitively, our GDGT temperature reconstruction based on MBT and CBT indices shows temperatures ~5°C warmer throughout the LGM and MIS3 than during the Holocene. Although local soil temperature may be affected by vegetation and/or cloud cover, such results advice caution and highlight the necessity to further validate and develop these new biomarker proxies.

Zech, R.; Huang, Y.; Russell, J. M.; Tarozo, R.; Gao, L.; Hemp, A.; Zech, W.

2009-12-01

87

Late Cenozoic tephrochronology, stratigraphy, geomorphology, and neotectonics of the Western Black Mountains Piedmont, Death Valley, California: Implications for the spatial and temporal evolution of the Death Valley fault zone  

Science.gov (United States)

This study presents the first detailed tephrochronologic study of the central Death Valley area by correlation of a Nomlaki-like tuff (>3.35 Ma), tuffs of the Mesquite Spring family (3.1 -- 3.35 Ma), a tuff of the lower Glass Mountain family (1.86 -- 2.06 Ma), and tephra layers from the upper Glass Mountain family (0.8 -- 1.2 Ma), the Bishop ash bed (0.76 Ma), the Lava Creek B ash bed (~0.66 Ma), and the Dibekulewe ash bed (~0.51 Ma). Correlation of these tuffs and tephra layers provides the first reliable numeric-age stratigraphy for late Cenozoic alluvial fan and lacustrine deposits for Death Valley and resulted in the naming of the informal early to middle Pleistocene Mormon Ploint formation. Using the numeric-age stratigraphy, the Death Valley fault zone (DVFZ) is interpreted to have progressively stepped basinward since the late Pliocene at Mormon Point and Copper Canyon. The Mormon Point turtleback or low-angle normal fault is shown to have unequivocal late Quaternary slip at its present low angle dip. Tectonic geomorphic analysis indicates that the (DVFZ) is composed of five geomorphic segments with the most persistent segment boundaries being the en-echelon step at Mormon Point and the bedrock salient at Artists Drive. Subsequent geomorphic studies resulting from the numeric-age stratigraphy and structural relations include application of Gilberts field criteria to the benches at Mormon Point indicating that the upper bench is a lacustrine strandline and the remaining topographically-lower benches are fault scarps across the 160--185 ka lake abrasion platform. In addition, the first known application of cosmogenic 10Be and 26Al exposure dating to a rock avalanche complex south of Badwater yielded an age of 29.5 +/- 1.9 ka for the younger avalanche. The 28 meter offset of the older avalanche may be interpreted as post-160--185 ka yielding a 0.1 mm/year slip rate, or post-29.5 +/- 1.9 ka yielding a maximum slip rate of 0.9 nun/year for the DVFZ. A consequence of these studies is the hypothesis that the turtleback or low-angle normal faults represent a thermally-warped detachment fault related to the Black Mountains igneous complex and do not conform with the present domino or a rolling-hinge models of low-angle normal fault development.

Knott, Jeffrey Rayburn

88

Palynology and provenance of the coal fragments contained in the late-Pleistocene Lleiniog gravels of Anglesey, North Wales  

Energy Technology Data Exchange (ETDEWEB)

The numerous coal clasts in the late-Pleistocene fluvoglacial Lleniog Gravels of eastern Anglesey contain a varied assemblage of Westphalian (and possibly also early Westphalian B) spores. Directional sedimentary structures indicate that the meltwater currents which deposited the gravels come mainly from the north and east, while glacial striae and erratic trains indicate that the parent glacier flowed from the northeast. Consideration is given to the possibility that the coal clasts were derived from the breaking-up, fairly locally, of far-travelled rafts of Coal Measures. It is concluded however, that the most probable explanation is that the source is a yet-to-be identified submarine outcrop of Lleiniog.

Welsh, P.T.

1982-01-01

89

Drainage system inversion in the Guadalentin Depression during the Late Pleistocene-Holocene (Murcia, Spain)  

International Nuclear Information System (INIS)

[en] This article presents the results of studies conducted in the central sector of Guadalentin depression (Murcia) for the abnormal accumulation (more than 17 m) of Pleistocene and Holocene deposits upstream of Romeral tectonic threshold (Librilla). 14C dating. ruins and archaeological sites, together with its stratigraphic analysis show that the three sequences that constitute the Holocene detrital filling of the Depression, prograded are superimposed on the upper Pleistocene travertine upstream from the confluence of the River Guadalentin the Rambla de Librilla. Between Librilla and threshold Romeral Holocene deposits only appear along the left bank (15-17m). By contrast the right side shows significant lifting of the Pleistocene travertine up area Romeral threshold, where the substrate allora Neogene. (Author) 11 refs.

2009-01-01

90

Drainage system inversion in the Guadalentin Depression during the Late Pleistocene-Holocene (Murcia, Spain)  

Energy Technology Data Exchange (ETDEWEB)

This article presents the results of studies conducted in the central sector of Guadalentin depression (Murcia) for the abnormal accumulation (more than 17 m) of Pleistocene and Holocene deposits upstream of Romeral tectonic threshold (Librilla). {sup 1}4C dating. ruins and archaeological sites, together with its stratigraphic analysis show that the three sequences that constitute the Holocene detrital filling of the Depression, prograded are superimposed on the upper Pleistocene travertine upstream from the confluence of the River Guadalentin the Rambla de Librilla. Between Librilla and threshold Romeral Holocene deposits only appear along the left bank (15-17m). By contrast the right side shows significant lifting of the Pleistocene travertine up area Romeral threshold, where the substrate allora Neogene. (Author) 11 refs.

Calmel-Avila, M.; Silva, P. G.; Bardaji, T.; Goy, J. L.; Zazo, C.

2009-07-01

91

Paleomagnetic record of the late Pleistocene reef sequence of Tahiti (French Polynesia): A contribution to the chronology of the deposits  

Science.gov (United States)

Rock- and paleomagnetic investigations were performed on the late Pleistocene reef sequence of Tahiti, and take part of a multidisciplinary study of the Holocene and Pleistocene reef sequences, carried out by the IODP (Integrated Ocean Drilling Program) Expedition 310. The objectives were to characterize the natural remanent magnetization and its mineral carriers, in order to identify high-resolution magnetostratigraphic markers of the late Brunhes chron. A series of 85 specimens subsampled within a 79 m-thick silty-carbonate sequence cored at the Maraa site (SW of Tahiti) display a strong and stable natural remanent magnetization (NRM) carried by titanomagnetite inherited from the basalts which form the bulk of the island. The average negative inclination is assignable to the field generated by the normal polarity axial dipole field at the site latitude. A few specimens (103-119 m below modern sea level) carry a reversed primary magnetization acquired in a weak excursional field. Based on subsidence rate estimates ranging from 0.25 to 0.4 m/kyr, this suggests the identification either the Laschamp excursion (˜ 40 ka) or the Blake event (115-120 ka). Radiometric dates of ˜ 131 to ˜ 134 ka at 117 m below modern sea level confirm that these layers were deposited during the marine isotope stage 5.5 and recorded the direction and intensity anomaly associated with the Blake event. Another sea-level highstand reef unit, occurring deeper in the Pleistocene sequence has seemingly recorded another paleomagnetic intensity anomaly which is not yet definitely identified. Reef systems, which developed around volcanic islands, contain geological records of excursions. But, it is necessary to improve the understanding of NRM acquisition and the role of carbonate diagenesis in order to establish radiometrically dated records of geomagnetic excursions.

Ménabréaz, Lucie; Thouveny, Nicolas; Camoin, Gilbert; Lund, Steven P.

2010-05-01

92

Climatic fluctuations as a significant contributing factor for volcanic collapses. Evidence from Mexico during the Late Pleistocene  

Science.gov (United States)

Climate oscillations have significantly contributed to the planet's evolution, including volcanic activity. Major glaciations have been considered not only as a triggering mechanism for large magmatic eruptions but also inducing volcano instability. Generally, volcano instability can be inferred from detailed volcanological and structural studies of a volcano and its associated depositional sequence, but the triggering mechanism has been always difficult to infer. In this paper, we present evidence of how climatic variations during the Late Pleistocene could have forced sector collapses of the main Mexican stratovolcanoes and enhanced the mobility of associated massive flows inducing the transformation of debris avalanche into debris flows. In particular, the climatic record based on atmospheric moisture content from robustly dated lake record from Guatemala and a U/Th dated speleothem from New Mexico are used here as indicators of summer and winter precipitation. Depositional sequences associated with Late Pleistocene sector collapses of Volcán de Colima, Nevado de Toluca, Citlaltépetl (Pico de Orizaba) and Cofre de Perote volcanoes are here analyzed. Comparing the timing of the event with the climatic record, a combination of summer and/or winter pluvial conditions could have forced and triggered the failure of already unstable volcanoes, even during glacier advances (as for the Citlaltépetl event). Independent of the main cause of the volcano instability (magmatic or tectonic) it is important to highlight that the climatic factor played an important role in enhancing the volcano instability and promoted the lateral transformation of debris avalanches, which under dry conditions would have affected more limited areas.

Capra, L.; Bernal, J. P.; Carrasco-Núñez, G.; Roverato, M.

2013-01-01

93

A novel radiocarbon dating technique applied to an ice core from the Alps indicating late Pleistocene ages  

Science.gov (United States)

Ice cores retrieved from high-altitude glaciers are important archives of past climatic and atmospheric conditions in midlatitude and tropical regions. Because of the specific flow behavior of ice, their age-depth relationship is nonlinear, preventing the application of common dating methods such as annual layer counting in the deepest and oldest part. Here we present a new approach and technique, allowing dating of any such ice core at arbitrary depth for the age range between ˜500 years B.P. and the late Pleistocene. This new, complementary dating tool has great potential for numerous ice core related paleoclimate studies since it allows improvement and extension of existing and future chronologies. Using small to ultrasmall sample size (100 ?g > carbon content > 5 ?g) accelerator mass spectrometry, we take advantage of the ice-included, water-insoluble organic carbon fraction of carbonaceous aerosols for radiocarbon (14C) dating. Analysis and dating of the bottom ice of the Colle Gnifetti glacier (Swiss-Italian Alps, 45°55'50?N, 7°52'33?E, 4455 m asl) has been successful in a first application, and the results revealed the core to cover most of the Holocene at the least with indication for late Pleistocene ice present at the very bottom.

Jenk, Theo M.; Szidat, SöNke; Bolius, David; Sigl, Michael; GäGgeler, Heinz W.; Wacker, Lukas; Ruff, Matthias; Barbante, Carlo; Boutron, Claude F.; Schwikowski, Margit

2009-07-01

94

Sedimentologic and paleontologic study of the southeast coast of Buenos Aires province, Argentina: A late Pleistocene Holocene paleoenvironmental reconstruction  

Science.gov (United States)

A paleoenvironmental reconstruction of the southeast coast of Buenos Aires province, Argentina, is made mainly on the basis of paleontological and paleoichnological studies, supported by sedimentological analyses and radiocarbon dating. Continental late Pleistocene and continental, transitional, and marine Holocene stratigraphic units are identified. The former comprises fossil mammals and ichnites of 16000 12,000 BP. The continental early Holocene time, ca. 8100 BP, is represented by an interdune paleoenvironment in which shallow brackish ponds were colonized by diatoms, fish, rodents, and birds. A transitional paleoenvironment in the middle Holocene—6930 6570 BP—is recorded by deposits formed by estuarine crabs. During the late Holocene, between 5000 and 4800 BP, a marine transgression was recorded by a rich mollusc fauna.

Aramayo, S. A.; Téllez, B. Gutiérrez; Schillizzi, R. A.

2005-10-01

95

Stratigraphy and wiggle-matching-based age-depth model of late Holocene marine sediments in Beppu Bay, southwest Japan  

Science.gov (United States)

We analyzed the lithology, magnetic susceptibility, bulk density, and X-ray radiographs of 14 sediment cores (1-9 m long) from Beppu Bay in the western Seto Inland Sea, Japan, to establish the late Holocene stratigraphy in the deepest part of the bay and to develop an age-depth model for the sediments there. The cores contained 18 thick (major event) high-density layers (16 turbidites and two volcanic ash; >1 cm thick), and both lithological observations and density variations in the hemipelagic mud that is dominant in the cores revealed a further 55 thin (minor event) high-density layers (determine the local reservoir effect (?R). The age-depth model showed a sedimentation rate of 0.23-0.30 cm/yr for a 7.8 m-long composite core and an age of ˜2800 cal yr BP at the base. Wiggle-matching provided ?R values of 115-155 yr for late Holocene bivalve samples from Beppu Bay, which is consistent with previous estimates reported from coastal areas near the Kuroshio Front. Comparison of wiggle-matching-derived ages of thick turbidites with the ages of historical earthquakes showed differences within ±25 yr. Our study demonstrated that wiggle matching with optimal fitting based on either the weighted least-squares or maximum likelihood method can minimize the effect of scatter of age data due to reworking and burrowing of bivalves and thus improve the accuracy of age-depth models.

Kuwae, Michinobu; Yamamoto, Masanobu; Ikehara, Ken; Irino, Tomohisa; Takemura, Keiji; Sagawa, Takuya; Sakamoto, Tatsuhiko; Ikehara, Minoru; Takeoka, Hidetaka

2013-06-01

96

Early Late Cretaceous to Holocene seismic stratigraphy and geologic history of southeastern Gulf of Mexico  

Energy Technology Data Exchange (ETDEWEB)

Multifold seismic reflection profiles were used in conjunction with results from Deep Sea Drilling Project (DSDP) Leg 77 to interpret the early Late Cretaceous to Holocene geologic history of the southeastern Gulf of Mexico. During the mid-Cenomanian(.) to early Paleocene(.), this region began to record the effects of a collision between a northward-migrating island arc (now part of Cuba) and a salient of the North American plate. More than 2 km (6,560 ft) of gravity-flow deposits accumulated in an elongate structural corridor or foredeep along the base of the modern Cuban slope, while the slope itself was the site of both folding and overthrusting. Clastics continued to dominate the depositional regime until the late Eocene, at which time the Cuban arc had been firmly welded to North America. A late middle to early late Eocene hiatus in Site 540, which coincides with a prominent regional seismic unconformity, marks the transition from predominantly terrigenous input to pelagic/hemipelagic deposition. Since the late Eocene, the southeastern gulf has recorded multiple cycles of deposition and erosion. Unconformities displayed on seismic profiles are numerous. Erosional agents have included the Gulf Stream system, and turbidity currents and debris flows concentrated in the vicinity of submarine canyons. Continuing slope instability is indicated by slide/slump planes along canyon walls.

Angstadt, D.M.; Austin, J.A.; Buffler, R.T.

1985-06-01

97

Assessing the impact of late Pleistocene megafaunal extinctions on global vegetation and climate  

Directory of Open Access Journals (Sweden)

Full Text Available The end of the Pleistocene was a turning point for the Earth system as climate gradually emerged from millennia of severe glaciation in the Northern Hemisphere. The deglacial climate change coincided with an unprecedented decline in many species of Pleistocene megafauna, including the near-total eradication of the woolly mammoth. Due to an herbivorous diet that presumably involved large-scale tree grazing, the mammoth extinction has been associated with the rapid expansion of dwarf deciduous trees in Siberia and Beringia, thus potentially contributing to the changing climate of the period. In this study, we use the University of Victoria Earth System Climate Model (UVic ESCM) to simulate the possible effects of these extinctions on climate during the latest deglacial period. We have explored various hypothetical scenarios of forest expansion in the northern high latitudes, quantifying the biogeophysical effects in terms of changes in surface albedo and air temperature. These scenarios include a Maximum Impact Scenario (MIS) which simulates the greatest possible post-extinction reforestation in the model, and sensitivity tests which investigate the timing of extinction, the fraction of trees grazed by mammoths, and the southern extent of mammoth habitats. We also show the results of a simulation with free atmospheric CO2-carbon cycle interactions. For the MIS, we obtained a surface albedo increase and global warming of 0.006 and 0.175 °C, respectively. Less extreme scenarios produced smaller global mean temperature changes, though local warming in some locations exceeded 0.3 °C even in the more realistic extinction scenarios. In the free CO2 simulation, the biogeophysical-induced warming was amplified by a biogeochemical effect, whereby the replacement of high-latitude tundra with shrub forest led to a release of soil carbon to the atmosphere and a small atmospheric CO2 increase. Overall, our results suggest the potential for a small, though non-trivial, effect of megafaunal extinctions on Pleistocene climate.

M.-O. Brault; L. A. Mysak; H. D. Matthews; C. T. Simmons

2013-01-01

98

Contribution of changes in opal productivity and nutrient distribution in the coastal upwelling systems to late Pliocene/early Pleistocene climate cooling  

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The global late Pliocene/early Pleistocene cooling (~3.0–2.0 million years ago, Ma) concurred with extremely high diatom and biogenic opal production in most of the major coastal upwelling regions. This phenomenon was particularly pronounced in the Benguela Upwelling System (BUS), off Namibia, where...

J. Etourneau; C. Ehlert; M. Frank; P. Martinez; R. Schneider

99

Contribution of changes in opal productivity and nutrient distribution in the coastal upwelling systems to Late Pliocene/Early Pleistocene climate cooling  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The global Late Pliocene/Early Pleistocene cooling (~3.0–2.0 million years ago – Ma) concurred with extremely high diatom and biogenic opal production in most of the major coastal upwelling regions. This phenomenon was particularly pronounced in the Benguela upwelling system (BUS), off Namibia, wher...

J. Etourneau; C. Ehlert; M. Frank; P. Martinez; R. Schneider

100

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

Energy Technology Data Exchange (ETDEWEB)

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.

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

1989-03-01

 
 
 
 
101

Assessing the impact of late Pleistocene megafaunal extinctions on global vegetation and climate  

Directory of Open Access Journals (Sweden)

Full Text Available The end of the Pleistocene marked a turning point for the Earth system as climate gradually emerged from millennia of severe glaciation in the Northern Hemisphere. It is widely acknowledged that the deglacial climate change coincided with an unprecedented decline in many species of large terrestrial mammals, including the near-total eradication of the woolly mammoth. Due to an herbivorous diet that presumably involved large-scale tree grazing, the mammoth expansion would have accelerated the expansion of dwarf deciduous trees in Siberia and Beringia, thus contributing to the changing climate of the period. In this study, we use the University of Victoria Earth System Climate Model (UVic ESCM) to simulate the possible effects of megafaunal extinctions on Pleistocene climate change. We have explored various hypothetical scenarios of forest expansion in the Northern Continents, quantifying the regional and global biogeophysical effects in terms of changes in surface albedo and air temperature. In particular, we focus our attention on a Maximum Impact Scenario (MIS) which simulates the greatest possible post-extinction reforestation in the model. More realistic experiments include sensitivity tests based on the timing of extinction, the fraction of trees grazed by mammoths, and the size of mammoth habitats. We also show the results of a simulation with free (non-prescribed) atmospheric CO2. For the MIS, we obtained a surface albedo increase of 0.006, which resulted in a global warming of 0.175 °C. Less extreme scenarios produced smaller global mean temperature changes, though local warming in some locations exceeded 0.3 °C even in the more realistic extinction scenarios. In the free CO2 simulation, the biogeophysical-induced warming was amplified by a biogeochemical effect whereby the replacement of high-latitude tundra with shrub forest led to a release of soil carbon to the atmosphere and a small atmospheric CO2 increase. Overall, our results suggest the potential for a small, though non-trivial, effect of megafaunal extinctions on Pleistocene climate change.

M.-O. Brault; L. A. Mysak; H. D. Matthews; C. T. Simmons

2013-01-01

102

Late Pleistocene and Holocene environmental and climatic conditions in the eastern Andean piedmont of Mendoza (33°-34°S, Argentina)  

Science.gov (United States)

The main goal of this paper is to analyze the late Quaternary alluvial record of the Andean piedmont between 33° and 34°S (Mendoza, Argentina) reconstructing the prevailing paleoenvironmental conditions and discussing their regional significance. The analysis was carried out along the outcrops of Arroyo La Estacada and its tributary Arroyo Anchayuyo, complementary sections were described at Arroyo Grande and Arroyo Yaucha. The sedimentological, stratigraphical and geochronological (radiocarbon and OSL dating) results as well as the paleoenvironmental interpretation are presented and discussed on the basis of the geomorphological units identified at the piedmont fluvial systems.Late Quaternary deposits of Arroyo La Estacada compose three main geomorphological units consisting of an extensive aggradational plain, a fill terrace and the present floodplain -which is not analyzed in this contribution-. At the aggradational plain a distal alluvial fan lithofacial association was determined, mainly related to overbank sheet fluid overflows and probably temporary inactive channels of sandy-like braided streams between ˜50 ka BP and the early Holocene. The mid-late Holocene fining upward alluvial sequence of the fill terrace corresponds to a sinuous fluvial system lithofacial association. The mid-to late Holocene alluvial sequence exposed at Arroyo Grande banks shows a fining upward sequence probably related to a sinuous fluvial system lithofacial association. Finally, in the Arroyo Yaucha the upper and lower terraces analyzed in this study record a Late Glacial and Holocene fining upward alluvial sequence of a sinuous fluvial system lithofacial association.The late Pleistocene - early Holocene dynamic of the Andean piedmont documents an interval of alluvial aggradation characterized by the occurrence of sandy systems similar to braided rivers in the distal fan environments. The mid-late Holocene is marked by aggradation in sinuous fluvial systems and by two major episodes of degradation registered across the fluvial systems of the study area. This paleoenvironmental reconstruction allowed us to propose an evolutionary scheme and chronology of the major fluvial landscape landforms contributing to the general understanding of the sedimentological and geomorphological dynamic during the late Quaternary.

Mehl, A. E.; Zárate, M. A.

2012-08-01

103

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

Science.gov (United States)

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.

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

2013-01-01

104

The sedimentary sequence from the Lake ??ži outcrop, central Latvia: implications for late glacial stratigraphy  

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Full Text Available Sediment samples from an outcrop in the near-shore area of Lake ??ži (Vidzeme Heights, Central Latvia) were investigated using palaeobotanical (pollen and macrofossil analysis) and lithological (grain-size analysis) methods and accelerator mass spectrometry 14C dating. A dark, organic-rich sediment layer was found below 1.7 m of sandy layers approximately 30 cm above the present lake level. Radiocarbon dating of a wood sample from the lowermost layer (11 050 ± 60 14C BP, 13 107–12 721 cal BP) shows that the layer is of late glacial age. The composition of the pollen spectra is characterized by Betula nana, Cyperaceae pollen and spores of Equisetum, confirming that the lowermost sediments were formed during the late glacial. Fossils of obligate aquatic organisms in the upper layer, which include oospores of Characeae and seeds of Potamogeton, indicate an open water environment. Pollen of Myriophyllum and Potamogeton and non-pollen palynomorphs, such as algal Botryococcus and Pediastrum cf. boryanum, confirm this conclusion. The pollen assemblage from the greyish loam layer following this lacustrine phase shows a pattern characteristic of the Younger Dryas vegetation before the start of the real expansion of birch forests at the beginning of the Holocene.

Tiiu Koff; Jaanus Terasmaa

2011-01-01

105

Late Paleocene- Early Eocene paleoenvironments in the Southwest Pacific (ODP Leg 189): Revised Stratigraphy of an Antarctic PETM Record.  

Science.gov (United States)

The Late Paleocene and Early Eocene (~60 ¡V 50 Ma) were characterized by globally warm climates. Superimposed on this general warmth, several episodes of further warming occurred (so-called hyperthermals), including the Paleocene-Eocene thermal maximum (PETM, ~55 Ma) and Eocene thermal maximum 2 (ETM2, ~53 Ma). While the PETM is by now well documented from Northern Hemisphere, and some equatorial locations, southern high-latitude records are still rare. Here we present high-resolution palynological, XRF, bulk organic stable carbon isotope (Ô13CTOC), and TEX86 palaeothermometry data across Upper Paleocene through Lower Eocene pro-deltaic deposits from the Southwest Pacific Ocean, at ~65¢XS palaeolatitude (ODP Site 1172). Based on a revised integrated biomagnetostratigraphic age model and Ô13CTOC stratigraphy, we identify the southernmost marginal marine PETM ever encountered. Moreover, there is every indication that ETM2 was recovered as well at Site 1172. Despite a high latitude source of the surface waters at this site, the PETM is marked by the characteristic acme of representatives of the (sub) tropical dinoflagellate cyst (dinocyst) Apectodinium, confirming the truly global nature of this PETM event. TEX86 values indicate that surface ocean temperatures rose from ~23¢XC to ~30¢XC during the PETM at Site 1172, hence by a similar magnitude as recorded in other PETM successions globally. Before and after the CIE, mass abundances of low salinity tolerant dinocysts are recorded, taken as indicative of increased runoff. These trends are analogous to those recorded at northern high latitudes, indicating a similar climate response at both polar regions during the PETM. Yet, some distinct differences are apparent, and are discussed.

Bijl, P. K.; Brinkhuis, H.; Sluijs, A.; Reichart, G.; Schouten, S.; Röhl, U.

2007-12-01

106

First record of Bison antiquus from the Late Pleistocene of southern Mexico  

Science.gov (United States)

In Mexico, just 54% of the reported Pleistocene Bison material has been identified to species. Current paleontological research in northwestern Oaxaca, southern Mexico, has allowed collection of several specimens of Bison antiquus that are part of the Viko Vijin Local Fauna. B. antiquus had a very wide geographic distribution, from lowlands to mountainous landscapes of North and Central America. The B. antiquus record from southern Mexico links their former records from central Mexico and middle Central America and confirms this wide geographic distribution. The univariate mesowear score of the B. antiquus specimens from Oaxaca is in the lower extreme of grazers and the upper end of mixed-feeders, suggesting that they had a less abrasive diet than the modern plains Bison, as has been observed in other samples of this species from diverse parts of North America. The presence of B. antiquus in the Viko Vijin L. F. constrains the age of this fossil assemblage within a range from 60 Ka to 11.7 Ka.

Jiménez-Hidalgo, Eduardo; Cabrera-Pérez, Lucía; MacFadden, Bruce J.; Guerrero-Arenas, Rosalía

2013-03-01

107

Amplicon pyrosequencing late Pleistocene permafrost: the removal of putative contaminant sequences and small-scale reproducibility.  

UK PubMed Central (United Kingdom)

DNA sequencing of ancient permafrost samples can be used to reconstruct past plant, animal and bacterial communities. In this study, we assess the small-scale reproducibility of taxonomic composition obtained from sequencing four molecular markers (mitochondrial 12S ribosomal DNA (rDNA), prokaryote 16S rDNA, mitochondrial cox1 and chloroplast trnL intron) from two soil cores sampled 10 cm apart. In addition, sequenced control reactions were used to produce a contaminant library that was used to filter similar sequences from sample libraries. Contaminant filtering resulted in the removal of 1% of reads or 0.3% of operational taxonomic units. We found similar richness, overlap, abundance and taxonomic diversity from the 12S, 16S and trnL markers from each soil core. Jaccard dissimilarity across the two soil cores was highest for metazoan taxa detected by the 12S and cox1 markers. Taxonomic community distances were similar for each marker across the two soil cores when the chi-squared metric was used; however, the 12S and cox1 markers did not cluster well when the Goodall similarity metric was used. A comparison of plant macrofossil vs. read abundance corroborates previous work that suggests eastern Beringia was dominated by grasses and forbs during cold stages of the Pleistocene, a habitat that is restricted to isolated sites in the present-day Yukon.

Porter TM; Golding GB; King C; Froese D; Zazula G; Poinar HN

2013-09-01

108

A warm thermal enclave in the late Pleistocene of the south-eastern United States.  

UK PubMed Central (United Kingdom)

Physical and biological evidence supports the probable existence of an enclave of relatively warm climate located between the Southern Appalachian Mountains and the Atlantic Ocean in the United States during the Last Glacial Maximum. The region supported a mosaic of forest and prairie habitats inhabited by a "Floridian" ice-age biota. Plant and vertebrate remains suggest an ecological gradient towards Cape Hatteras (35 degreesN) wherein forests tended to replace prairies, and browsing proboscideans tended to replace grazing proboscideans. Beyond 35 degreesN, warm waters of the Gulf Stream were deflected towards the central Atlantic, and a cold-facies biota replaced "Floridian" biota on the Atlantic coastal plain. Because of niche diversity and relatively benign climate, biodiversity may have been greater in the south-eastern thermal enclave than in other unglaciated areas of North America. However, the impact of terminal Pleistocene megafaunal extinctions may also have been shorter and more severe in the enclave than further north. A comparison with biotic changes that occurred in North America approximately 55 million years (ma) ago at the Paleocene-Eocene Thermal Maximum suggests that similar processes of change took place under both ice-house and greenhouse climates.

Russell DA; Rich FJ; Schneider V; Lynch-Stieglitz J

2009-05-01

109

Late Pleistocene glaciation of the Mt Giluwe volcano, Papua New Guinea  

Science.gov (United States)

The Mt Giluwe shield volcano was the largest area glaciated in Papua New Guinea during the Pleistocene. Despite minimal cooling of the sea surface during the last glacial maximum, glaciers reached elevations as low as 3200 m. To investigate changes in the extent of ice through time we have re-mapped evidence for glaciation on the southwest flank of Mt Giluwe. We find that an ice cap has formed on the flanks of the mountain on at least three, and probably four, separate occasions. To constrain the ages of these glaciations we present 39 new cosmogenic 36 Cl exposure ages complemented by new radiocarbon dates. Direct dating of the moraines identifies that the maximum extent of glaciation on the mountain was not during the last glacial maximum as previously thought. In conjunction with existing potassium/argon and radiocarbon dating, we recognise four distinct glacial periods between 293-306 ka (Gogon Glaciation), 136-158 ka (Mengane Glaciation), centred at 62 ka (Komia Glaciation) and from >20.3-11.5 ka (Tongo Glaciation). The temperature difference relative to the present during the Tongo Glaciation is likely to be of the order of at least 5 °C which is a minimum difference for the previous glaciations. During the Tongo Glaciation, ice was briefly at its maximum for less than 1000 years, but stayed near maximum levels for nearly 4000 years, until about 15.4 ka. Over the next 4000 years there was more rapid retreat with ice free conditions by the early Holocene.

Barrows, Timothy T.; Hope, Geoffrey S.; Prentice, Michael L.; Fifield, L. Keith; Tims, Stephen G.

2011-09-01

110

Late Pleistocene human occupation of the hyperarid core in the Atacama Desert, northern Chile  

Science.gov (United States)

Few archeological sites in South America contain uncontroversial evidence for when the first peopling of the continent occurred. Largely ignored in this debate, extreme environments are assumed either as barriers to this early wave of migration or without potential for past habitability. Here, we report on a rare 12-13 ka human occupation from Quebrada Maní (site QM12), a plantless, near rainless landscape (1240 m asl and 85 km from the Pacific Ocean) located in the hyperarid core of the Atacama Desert. This location harbored wetlands and riparian woodlands that were fed by increased rainfall further east in the central Andes during the latest Pleistocene. Excavations at QM12 yielded a diverse cultural assemblage of lithics, burned and cut bones, marine gastropods, pigments, plant fibers, and wooden artifacts alongside a prepared fireplace. Sixteen radiocarbon dates from site QM12 on charcoal, marine shells, animal dung, plant remains and wood reveal that the occupation took place between 12.8 and 11.7 ka. These results demonstrate that the Atacama Desert was not a barrier to early American settlement and dispersal, and provide new clues for understanding the cultural complexity and diversity of the peopling of South America during the Last Glacial-interglacial transition.

Latorre, Claudio; Santoro, Calogero M.; Ugalde, Paula C.; Gayo, Eugenia M.; Osorio, Daniela; Salas-Egaña, Carolina; De Pol-Holz, Ricardo; Joly, Delphine; Rech, Jason A.

2013-10-01

111

Late Pliocene to early Pleistocene millennial-scale fluctuations in SST and stratification within the North Atlantic  

Science.gov (United States)

The late Pliocene to early Pleistocene (5.6-1.8 Ma) represents in many ways a key interval of Cenozoic palaeoceanography, including two major changes of the Earth system: the significant glaciation of the northern hemisphere, cluminating in a major expansion of Arctic ice sheets (Northern Hemisphere Glaciation, NHG) and the closure of the Panama Gateway. The impact of changes associated with the NHG on surface-water hydrology (SST and stratification) of the subpolar North Atlantic is, however, not fully understood yet. Given its proximity to the large dynamic ice-sheets of the northern hemisphere and the role in deep-water formation, however, the North Atlantic represents one of the climatically sensitive regions on Earth. This study focuses on the combination of Mg/Ca and ?18O analyses on planktic foraminifera in order to understand and reconstruct millennial-scale climate variability during the final stage of the NHG, especially marine oxygen isotope stages (MIS) 103-95 (late Pliocene to early Pleistocene, 2.6 to 2.4 Ma). In particular, this is relevant to better understand fluctuations in the magnitude of SST and stratification changes and their link to the intensification of NHG. Stable isotope and Mg/Ca analyses have been carried out on the deep-dwelling planktic foraminiferal species Globorotalia crassaformis from IODP Site U1313 (North Atlantic, 41°N). This site is located at the base of the upper western flank of the Mid-Atlantic Ridge. It therefore is under direct influence of North Atlantic Deep Water and lies on the southerly limit of the so-called 'IRD belt'. Samples are taken in millenial-scale resolution from 2.6 to 2.4 Ma, comprising isotope stages 103 to 95. Samples from this site were already used before to test the existence of a relationship between the emergence of large-amplitude millennial-scale climate oscillations and an intensification of glacial conditions during the intensification of NHG by measuring mixed-layer stable isotope data on the surface-dwelling planktic foraminifera Globigerinoides ruber. Comparison of our results with these surface-water data reveal relatively stable conditions in surface waters while intermediate waters show strong fluctuations on a glacial-interglacial time scale, most probably reflecting changing intermediate-water masses.

Koch, M.; Friedrich, O.; Wilson, P. A.

2012-04-01

112

Stratigraphy and depositional environments of Fox Hills Formation (Late Cretaceous), Williston basin  

Energy Technology Data Exchange (ETDEWEB)

The Fox Hills Formation (Late Cretaceous, Maestrichtian) was investigated where it crops out along the southern flank of the Williston basin and in the subsurface over the central portion of the basin, using 300 well logs. The formation is conformable and gradational with the underlying Pierre formation and can be either conformable or unconformable with the overlying Hell Creek Formation. The Fox Hills Formation is younger, thicker, and stratigraphically more complex to the east and is comprised of marginal marine sediments deposited during the final Cretaceous regression. To the west, the Fox Hills Formation is an upward-coarsening unit generally 30 to 45 m thick and usually contains three members: from the base, Trail City, Timber Lake, and Colgate. The lower Fox Hills (Trail City, Timber Lake) is generally dominated by hummocky bedding and contains a variety of trace fossils, most notably Ophiomorpha. The upper Fox Hills (Colgate), where present, is characterized by cross-bedding. To the east, including the type area, the section is generally 80 to 100 m thick and contains four members: from the base, Trail City, Timber Lake, Iron Lightning (Colgate and Bullhead lithofacies), and Linton. In contrast to the section in the west, this section is as much as three times thicker, contains abundant body fossils, generally lacks hummocky bedding, and contains the Bullhead and Linton strata. In the west, the strata represent lower shoreface deposits, predominantly of storm origin (lower Fox Hills), overlain by upper shoreface and fluvial deposits (upper Fox Hills). In the east, the lower Fox Hills contains deposits of the lower shoreface (Trail City) and a barrier bar complex (Timber Lake), overlain by the deltaic deposits of the upper Fox Hills (Iron Lightning, Linton).

Daly, D.J.

1986-08-01

113

Late Middle Pleistocene deposits at Norton Farm on the West Sussex coastal plain, southern England  

Science.gov (United States)

The coastal plain of West Sussex, southern England, is internationally important because of the sequence of discrete high-sea-level events preserved at various elevations across it. New evidence is presented from a site at Norton Farm, near Chichester, on the Lower Coastal Plain, where Pleistocene marine sands, fining upwards into silts, occur between 5.3 m and 9.1 m OD. The sequence reflects a regressive tendency at the transition from an interglacial to a cold stage. The marine sands have yielded foraminifera, ostracods and molluscs that indicate a declining marine influence through the sequence, culminating in a tidal mudflat, strongly weathered in places. Cool-climate foraminifera (including Elphidium clavatum, Cassidulina reniformis and Elphidium albiumbilicatum) and ostracods have been recovered from the marine sands. Some species with an apparent preference for warmer water conditions, however, are also present. Freshwater taxa washed into the terminal marine sediments include some cold climate indicators, such as Pisidium stewarti and P. obtusale lapponicum. Additional evidence for cool climatic conditions during the deposition of the upper part of the marine sequence is provided by the lack of tree taxa in the pollen record and by features of the micromorphology. The marine sediments probably began accumulating during OIS 7, a conclusion based on their elevation, on amino acid ratios from shells, but especially on vertebrate evidence, particularly the presence of a small form of horse, together with a large, distinctive, form of northern vole (Microtus oeconomus). The occurrence of cool climate indicators in these marine sediments may demonstrate a lag between the climatic deterioration and the expected glacio-eustatic fall in relative sea-level. This evidence appears to support the conclusions drawn from the study of coral terraces in Barbados. Such a scenario would provide the conditions necessary for the emplacement of the large erratic boulders reported from the Lower Coastal Plain of West Sussex.

Bates, Martin R.; Bates, C. Richard; Gibbard, Philip L.; MacPhail, Richard I.; Owen, Frederick J.; Parfitt, Simon A.; Preece, Richard C.; Roberts, Mark B.; Robinson, J. Eric; Whittaker, John E.; Wilkinson, Keith N.

2000-01-01

114

Late ordovician stratigraphy, zircon provenance and tectonics, Lachlan Fold Belt, southeastern Australia  

International Nuclear Information System (INIS)

Ordovician quartz turbidites of the Lachlan Fold Belt in southeastern Australia accumulated in a marginal sea and overlapped an adjoining island arc (Molong volcanic province) developed adjacent to eastern Gondwana. The turbidite succession in the Shoalhaven River Gorge, in the southern highlands of New South Wales, has abundant outcrop and graptolite sites. The succession consists of, from the base up, a unit of mainly thick-bedded turbidites (undifferentiated Adaminaby Group), a unit with conspicuous bedded chert (Numeralla Chert), a unit with common thin-bedded turbidites [Bumballa Formation (new name)] and a unit of black shale (Warbisco Shale). Coarse to very coarse sandstone in the Bumballa Formation is rich in quartz and similar to sandstone in the undifferentiated Adaminaby Group. Detrital zircons from sandstone in the Bumballa Formation, and from sandstone at a similar stratigraphic level from the upper Adaminaby Group of the Genoa River area in eastern Victoria, include grains as young as 453-473 Ma, slightly older than the stratigraphic ages. The dominant detrital ages are in the interval 500-700 Ma (Pacific Gondwana component) with a lessor concentration of Grenville ages (1000-1300 Ma). This pattern resembles other Ordovician sandstones from the Lachlan Fold Belt and also occurs in Triassic sandstones and Quaternary sands from eastern Australia. The Upper Ordovician succession is predominantly fine grained, which reflects reduced clastic inputs from the source in the Middle Cambrian to earliest Ordovician Ross-Delamerian Fold Belts that developed along the eastern active margin of Gondwana. Development of subduction zones in the Late Ordovician marginal sea are considered to be mainly responsible for the diversion of sediment and the resulting reduction in the supply of terrigenous sand to the island arc and eastern part of the marginal sea. Sixty zircons from each sample were analysed and results are presented. Methods following standard procedures were undertaken on SHRIMP I, the analyses comprised four scans through the mass spectrum (Williams 1998 and references therein). The U/Pb ratios have been calibrated relative to the AS3 Duluth Gabbro reference zircon (Paces and Miller 1993) and relative probability plots with stacked histograms were compiled using ISOPLOT/EX (Ludwig 1999). Copyright (2002) Geological Society of Australia

1993-01-00

115

Conceptual hydrochemical model of late Pleistocene aquifers at the Samario-Sitio Grande petroleum reservoir, Gulf of Mexico  

Energy Technology Data Exchange (ETDEWEB)

Carbon-14 concentrations between 0.83 and 11.79 pmC of formation water from the Activo Samaria-Sitio Grande petroleum reservoir in SE-Mexico, extracted from 3500 to 4500 m.b.s.l., indicate a common infiltration event of surface water during the late Pleistocene period. Mixing of two components - meteoric water and seawater, previously evaporated at the surface - explain the widespread mineralization (TDI = 15-257 g/L) of Na-Cl and Na-Ca-Cl type reservoir water. Statistical discrimination by clustering and a heterogeneous chemical-isotopic fluid composition indicate the existence of 4 different water types as part of local aquifer systems, which are separated by normal and thrust faults. Tectonic horst and graben structures show an ambiguous, individual hydraulic behaviour - as permeable conduits and/or as impermeable barriers, causing the local limitation of aquifer extent. The recent increase of water production in petroleum wells is not related to the injection of surface water, but the long-term extraction of oil reserves is modifying the original position and flow direction of the reservoir aquifers. The rise of the initial groundwater level reflects the final stage of an exhausted petroleum reservoir with coning effects of underlying aquifer systems. The flexible change towards superior production intervals could represent a feasible technique to avoid the abrupt closure of invaded production wells. (Author)

Birkle, P. [Instituto de Investigaciones Electricas, Gerencia de Geotermia, Cuernavaca, Mor. (Mexico); Angulo, M. [PEMEX-Exploracion y Produccion, Chiapas (Mexico)

2005-06-01

116

Conceptual hydrochemical model of late Pleistocene aquifers at the Samario-Sitio Grande petroleum reservoir, Gulf of Mexico, Mexico  

International Nuclear Information System (INIS)

Carbon-14 concentrations between 0.83 and 11.79 pmC of formation water from the Activo Samaria-Sitio Grande petroleum reservoir in SE-Mexico, extracted from 3500 to 4500 m.b.s.l., indicate a common infiltration event of surface water during the late Pleistocene period. Mixing of two components - meteoric water and seawater, previously evaporated at the surface - explain the widespread mineralization (TDI = 15-257 g/L) of Na-Cl and Na-Ca-Cl type reservoir water. Statistical discrimination by clustering and a heterogeneous chemical-isotopic fluid composition indicate the existence of 4 different water types as part of local aquifer systems, which are separated by normal and thrust faults. Tectonic horst and graben structures show an ambiguous, individual hydraulic behaviour - as permeable conduits and/or as impermeable barriers, causing the local limitation of aquifer extent. The recent increase of water production in petroleum wells is not related to the injection of surface water, but the long-term extraction of oil reserves is modifying the original position and flow direction of the reservoir aquifers. The rise of the initial groundwater level reflects the final stage of an exhausted petroleum reservoir with coning effects of underlying aquifer systems. The flexible change towards superior production intervals could represent a feasible technique to avoid the abrupt closure of invaded production wells

2005-01-01

117

Late Pleistocene human evolution in Sicily: comparative morphometric analysis of Grotta di San Teodoro craniofacial remains.  

UK PubMed Central (United Kingdom)

The paleoanthropological remains from Grotta di San Teodoro near Acquedolci (province of Messina, Italy) represent the oldest and largest skeletal collection yet found documenting human settlement of Sicily. The sample, attributed to the Late Epigravettian (between 14,000 and 10,000 years B.P.), consists of seven variously complete adult individuals (San Teodoro 1-7). We compare the cranial sample to an array of both prehistoric and recent samples using multivariate techniques including D(2) distance analysis, canonical variate analysis, cluster analysis, and multidimensional scaling. Overall, the San Teodoro cranial sample displays a morphometric pattern close to Western European groups of similar antiquity, in particular those from Central and Southern Italy. The morphometric affinities indicate that these people probably came from peninsular Italy by sea during the Late Epigravettian epoch. An alternative hypothesis is that they descended from immigrants that arrived by land during a low sea level episode corresponding to the maximum Würmian regression, about 18,000 years B.P, with gene flow accounting for the morphological homogeneity with the populations of peninsular Italy. The San Teodoro skeletal sample provides the first reliable evidence for human settlement of Sicily.

D'Amore G; Di Marco S; Tartarelli G; Bigazzi R; Sineo L

2009-06-01

118

Holocene-Late pleistocene climatic ice core records for Qinghai-Tibetan plateau  

Energy Technology Data Exchange (ETDEWEB)

Three ice cores to bedrock from the Dunde ice cap on the north-central Qinghai-Tibetan Plateau of China provide a detailed record of Holocene and Wisconsin-Wuerm late glacial stage (LGS) climate changes in the subtropics. The records reveal that LGS conditions were apparently colder, wetter, and dustier than Holocene conditions. The LGS part of the cores is characterized by more negative {delta}{sup 18}O ratios, increased dust content, decreased soluble aerosol concentrations, and reduced ice crystal sizes than the Holocene part. These changes occurred rapidly {approximately} 10,000 years ago. In addition, the last 60 years were apparently one of the warmest periods in the entire record, equalling levels of the Holocene maximum between 6000 and 8000 years ago.

Thompson, L.G.; Mosley-Thompson, E.; Davis, M.E.; Bolzan, J.F.; Dai, J.; Klien, L. (Ohio State Univ., Columbus (USA)); Yao, T.; Wu, X.; Xie, Z. (Lanzhou Institute of Glaciology and Geocryology (China)); Gundestrup, N. (Univ. of Copenhagen (Denmark))

1989-10-27

119

Pollen evidence for late pleistocene bering land bridge environments from Norton Sound, Northeastern Bering Sea, Alaska  

Science.gov (United States)

After more than half a century of paleoenvironmental investigations, disagreements persist as to the nature of vegetation type and climate of the Bering land bridge (BLB) during the late Wisconsin (Sartan) glacial interval. Few data exist from sites on the former land bridge, now submerged under the Bering and Chukchi Seas. Two hypotheses have emerged during the past decade. The first, based on pollen data from Bering Sea islands and adjacent mainlands of western Alaska and Northeast Siberia, represents the likely predominant vegetation on the Bering land bridge during full-glacial conditions: graminoid-herb-willow tundra vegetation associated with cold, dry winters and cool, dry summer climate. The second hypothesis suggests that dwarf birch-shrub-herb tundra formed a broad belt across the BLB, and that mesic vegetation was associated with cold, snowier winters and moist, cool summers. As a step towards resolving this controversy, a sediment core from Norton Sound, northeastern Bering Sea was radiocarbon dated and analyzed for pollen content. Two pollen zones were identified. The older, bracketed by radiocarbon ages of 29,500 and 11,515 14C yr BP, contains pollen assemblages composed of grass, sedge, wormwood, willow, and a variety of herb (forb) taxa. These assemblages are interpreted to represent graminoid-herb-willow tundra vegetation that developed under an arid, cool climate regime. The younger pollen zone sediments were deposited about 11,515 14C yr BP, when rising sea level had begun to flood the BLB. This younger pollen zone contains pollen of birch, willow, heaths, aquatic plants, and spores of sphagnum moss. This is interpreted to represent a Lateglacial dwarf birch-heath-willow-herb tundra vegetation, likely associated with a wetter climate with deeper winter snows, and moist, cool summers. This record supports the first hypothesis, that graminoid-herb-willow tundra vegetation extended into the lowlands of the BLB during full glacial conditions of the late Wisconsin. ?? 2008 Regents of the University of Colorado.

Ager, T. A.; Phillips, R. L.

2008-01-01

120

Spring deposits and late pleistocene ground-water levels in southern Nevada  

Energy Technology Data Exchange (ETDEWEB)

Ground-water discharge deposits dating to the last glacial cycle and to several earlier cycles crop out in at least ten valleys in the southern Great Basin. The elevation and distribution of these deposits allow us to reconstruct the elevation of the water table during periods of wetter climate over much of the region, including the area around Yucca Mountain, site of the proposed high-level nuclear waste repository. Results from areas undisturbed by recent ground-water pumpage reveal that water levels have varied by < 115 m, and in most cases much less, in the latter half of the Quaternary. The extent of ground-water discharge during older wet cycles is similar in scale to discharge during the last full-glacial period. This places most of the proposed repository horizon at least 85 to 285 m above the maximum levels attained by the water table under full-glacial climates. During the late-glacial period ({approximately}11,500 to 8000 B.P.), a pulse of renewed discharge, perhaps corresponding to the Younger Dryas event well-documented elsewhere, produced organic-rich mats and flowing streams in many localities.

Quade, J. [Univ. of Arizona, Tucson, AZ (United States)

1994-12-31

 
 
 
 
121

Millennial-scale varnish microlamination dating of late Pleistocene geomorphic features in the drylands of western USA  

Science.gov (United States)

Varnish microlamination (VML) dating is a climate-based correlative age determination technique used to correlate and date various geomorphic features in deserts. In this study, we establish a generalized late Pleistocene (18-74 ka) millennial-scale microlamination sequence in fine-grained, fast-accumulating rock varnish for the drylands of western USA, radiometrically calibrate the sequence and correlate it with the ?18O record in the GISP2 Greenland ice core. We then use this climate-correlated varnish microstratigraphy to estimate surface exposure ages for radiometrically dated late Pleistocene geomorphic features in the study region. The VML dating of debris flow deposits on the Sehoo recessional shorelines of Lake Lahontan at the Jessup embayment of central Nevada yields a minimum-limiting age of 14.95-15.95 ka, in good agreement with a calibrated 14C age of 15.22 ± 0.12 ka for the timing of the lake recession. The VML dating of a giant ejecta block on the rim of Meteor Crater in northern Arizona yields a minimum-limiting age of 49.15 ka, closely matching a thermoluminescence (TL) age of 49 ± 3 ka and slightly younger than a recently updated cosmogenic 36Cl age of 56.0 ± 2.4 ka for the meteor impact event. The VML dating of distal Q2c fan surfaces on Hanaupah Canyon alluvial fan in Death Valley, California, yields a minimum-limiting age of 73.55 ka, in accord with cosmogenic 36Cl depth-profile ages of 66 + 22/-14 ka and 72 + 24/- 20 ka for the same fan deposits. The close agreement between the VML age estimates and the independently derived radiometric ages for these geomorphic features attests to the validity and reliability of millennial-scale VML dating.To further assess its potential in desert geomorphological research, we use the VML method to study alluvial-fan responses to millennial-scale climatic changes. The VML dating of a small tributary fan in Death Valley reveals two episodes of fan aggradation, one ceasing at 73.55-86.75 ka during the dry period of the last interglacial (MIS 5a) and the other finishing at 66.15 ka during the wet period of the last glacial (MIS 4). The VML and 36Cl dating of the distal Q2c fan surfaces on Hanaupah Canyon fan reveal two episodes of large-scale fan aggradation ended at 72 + 24/- 20 ka and 73.55 ka during the wet period of MIS 4. Fanhead incision and associated within-channel or fantoe aggradation are found to take place during the relatively dry period of the glacial-to-interglacial climatic transition (12-24 ka) and the Holocene interglacial dry period (0-12 ka). These data indicate that, on the millennial to sub-Milankovitch timescale (~ 103-104 years), fan aggradation is a discrete sedimentational process under various climatic conditions. Because fan aggradation is ultimately controlled by the intensity and frequency of precipitation events — which in turn are modulated by major climatic oscillations such as Heinrich events, Dansgaard/Oeschger (DO) events, and glacial/interglacial shifts — these major climatic changes could be the pacemaker of regionally contemporaneous large-area fan segmentation.

Liu, Tanzhuo; Broecker, Wallace S.

2013-04-01

122

Mitochondrial DNA indicates late pleistocene divergence of populations of Heteronympha merope, an emerging model in environmental change biology.  

UK PubMed Central (United Kingdom)

Knowledge of historical changes in species range distribution provides context for investigating adaptive potential and dispersal ability. This is valuable for predicting the potential impact of environmental change on species of interest. Butterflies are one of the most important taxa for studying such impacts, and Heteronympha merope has the potential to provide a particularly valuable model, in part due to the existence of historical data on morphological traits and glycolytic enzyme variation. This study investigates the population genetic structure and phylogeography of H. merope, comparing the relative resolution achieved through partial DNA sequences of two mitochondrial loci, COI and ND5. These data are used to define the relationship between subspecies, showing that the subspecies are reciprocally monophyletic. On this basis, the Western Australian subspecies H. m. duboulayi is genetically distinct from the two eastern subspecies. Throughout the eastern part of the range, levels of migration and the timing of key population splits of potential relevance to climatic adaptation are estimated and indicate Late Pleistocene divergence both of the Tasmanian subspecies and of an isolated northern population from the eastern mainland subspecies H. m. merope. This information is then used to revisit historical data and provides support for the importance of clinal variation in wing characters, as well as evidence for selective pressure acting on allozyme loci phosphoglucose isomerase and phosphoglucomutase in H. merope. The study has thus confirmed the value of H. merope as a model organism for measuring responses to environmental change, offering the opportunity to focus on isolated populations, as well as a latitudinal gradient, and to use historical changes to test the accuracy of predictions for the future.

Norgate M; Chamings J; Pavlova A; Bull JK; Murray ND; Sunnucks P

2009-01-01

123

Paleohydrology of the southern Great Basin, with special reference to water table fluctuations beneath the Nevada Test Site during the Late Pleistocene  

International Nuclear Information System (INIS)

[en] The magnitude of water table rise during Pleistocene pluvial climates, and of the resultant shortening of ground-water flow path and reduction in unsaturated zone thickness, is investigated. The distribution of calcitic veins in alluvium and lakebeds, and of tufa deposits, between the Ash Meadows spring discharge area and the Nevada Test Site suggests that discharge from the regional Paleozoic carbonate aquifer during the Late Pleistocene occurred at distances as much as 14 kilometers northeast of Ash Meadows and at altitudes up to 50 meters higher than at present. Use of the underflow equation (relating discharge to transmissivity, aquifer width, and hydraulic gradient), and various assumptions regarding pluvial recharge, transmissivity, and altitude of ground-water base level, suggest possible rises in potentiometric level in the carbonate aquifer of 6 to 90 meters beneath central Frenchman Flat, 58 kilometers northeast of Ash Meadows. During Wisconsin time the rise probably did not exceed 30 meters. Water-level rises beneath Frenchman Flat during future pluvials are unlikely to exceed 30 meters, and future levels might even be 10 meters lower than the modern one, 210 meters beneath the center of the valley. Neither the cited rise in potentiometric level in the regional carbonate aquifer, nor the shortened flow path during the Late Pleistocene precludes utilization of the NTS as a repository for high-level or transuranic-element radioactive wastes provided other requisite conditions are met at this site. Deep water tables, attendant thick (up to several hundred meter) unsaturated zones, and ground-water flow paths tens of kilometers in length characterized the region during Wisconsin time and possibly throughout the Pleistocene, and are likely to so characterize it during future pluvial climates

1980-01-01

124

Paleohydrology of the southern Great Basin, with special reference to water table fluctuations beneath the Nevada Test Site during the Late Pleistocene  

Energy Technology Data Exchange (ETDEWEB)

The magnitude of water table rise during Pleistocene pluvial climates, and of the resultant shortening of ground-water flow path and reduction in unsaturated zone thickness, is investigated. The distribution of calcitic veins in alluvium and lakebeds, and of tufa deposits, between the Ash Meadows spring discharge area and the Nevada Test Site suggests that discharge from the regional Paleozoic carbonate aquifer during the Late Pleistocene occurred at distances as much as 14 kilometers northeast of Ash Meadows and at altitudes up to 50 meters higher than at present. Use of the underflow equation (relating discharge to transmissivity, aquifer width, and hydraulic gradient), and various assumptions regarding pluvial recharge, transmissivity, and altitude of ground-water base level, suggest possible rises in potentiometric level in the carbonate aquifer of 6 to 90 meters beneath central Frenchman Flat, 58 kilometers northeast of Ash Meadows. During Wisconsin time the rise probably did not exceed 30 meters. Water-level rises beneath Frenchman Flat during future pluvials are unlikely to exceed 30 meters, and future levels might even be 10 meters lower than the modern one, 210 meters beneath the center of the valley. Neither the cited rise in potentiometric level in the regional carbonate aquifer, nor the shortened flow path during the Late Pleistocene precludes utilization of the NTS as a repository for high-level or transuranic-element radioactive wastes provided other requisite conditions are met at this site. Deep water tables, attendant thick (up to several hundred meter) unsaturated zones, and ground-water flow paths tens of kilometers in length characterized the region during Wisconsin time and possibly throughout the Pleistocene, and are likely to so characterize it during future pluvial climates.

Winograd, I.J.; Doty, G.C.

1980-12-31

125

Late Pleistocene sediments and fossils near the mouth of Mad River, Humboldt County, California: Facies analysis, sequence development, and possible age correlation  

Energy Technology Data Exchange (ETDEWEB)

Study of late Pleistocene-age sediments near the mouth of the Mad River revealed a sequence of nearshore marine and shallow bay deposits. This sequence, bounded by unconformities, is informally named the Mouth of Mad unit. The Mouth of mad unit can be divided into four distinct depositional facies at the study site. The lowest facies are the Nearshore Sand and Estuarine Mud, which lie unconformably on a paleosol. The sand facies grades upward into a high-energy, interbedded Nearshore Sand and Gravel facies containing storm and rip-channel deposits. Above the sand and gravel is a Strand-Plain Sand facies. This sand is overlain by a laterally variable sequence of shell-rich Bay facies. The bay deposits can be further divided into five subfacies: (1) a Bioturbated Sand; (2) a Lower Tidal Flat Mud; (3) a Mixed Sand and Mud; (4) an oyster-rich Bay Mud; and (5) an Upper Tidal Flat Mud. The bay sequence is overlain unconformably by younger late Pleistocene-age marine terrace deposits. The depositional environments represented by these facies progress from a shoreline estuary to nearshore deposits, above storm wave base, and slowly back to shoreline and finally shallow bay conditions. The Mouth of Mad unit represents a transgressive-regressive sequence, involving the development of a protective spit. The uppermost mud within the Mouth of Mad unit has been dated, using thermoluminescence age estimation, at 176 [+-] 33 ka, placing it in the late Pleistocene. The Mouth of Mad unit appears to be younger than the fossiliferous deposits at Elk Head, Crannell Junction, Trinidad Head, Moonstone Beach, and the Falor Formation near Maple Creek, and possibly time equivalent with gravel deposits exposed at the western end of School Road in McKinleyville.

Harvey, E.W. (Ohio State Univ., Columbus, OH (United States). Dept. of Geological Sciences)

1994-04-01

126

Contribution of changes in opal productivity and nutrient distribution in the coastal upwelling systems to Late Pliocene/Early Pleistocene climate cooling  

Directory of Open Access Journals (Sweden)

Full Text Available The global Late Pliocene/Early Pleistocene cooling (~3.0–2.0 million years ago – Ma) concurred with extremely high diatom and biogenic opal production in most of the major coastal upwelling regions. This phenomenon was particularly pronounced in the Benguela upwelling system (BUS), off Namibia, where it is known as the Matuyama Diatom Maximum (MDM). Our study focuses on a new diatom silicon isotope (?30Si) record covering the MDM in the BUS. Unexpectedly, the variations in ?30Si signal follow biogenic opal content, whereby the highest ?30Si values correspond to the highest biogenic opal content. We interpret the higher ?30Si values during the MDM as a result of a stronger degree of silicate utilisation in the surface waters caused by high productivity of mat-forming diatom species. This was most likely promoted by weak upwelling intensity dominating the BUS during the Late Pliocene/Early Pleistocene cooling combined with a large silicate supply derived from a strong Southern Ocean nutrient leakage responding to the expansion of Antarctic ice cover and the resulting stratification of the polar ocean 3.0–2.7 Ma ago. A similar scenario is hypothesized for other major coastal upwelling systems (e.g. off California) during this time interval, suggesting that the efficiency of the biological carbon pump was probably sufficiently enhanced in these regions during the MDM to have significantly increased the transport of atmospheric CO2 to the deep ocean. In addition, the coeval extension of the area of surface water stratification in both the Southern Ocean and the North Pacific, which decreased CO2 release to the atmosphere, led to further enhanced atmospheric CO2 drawn-down and thus contributed significantly to Late Pliocene/Early Pleistocene cooling.

J. Etourneau; C. Ehlert; M. Frank; P. Martinez; R. Schneider

2012-01-01

127

Palynological records of climate and oceanic conditions in late Pleistocene and Holocene sediments of the Nile cone, southeastern Mediterranean  

Science.gov (United States)

ariations in palynomorph concentrations and relative abundances, including pollen and spores, organic-walled dinoflagellate cysts, and Amorphous Organic Matter (AOM), were studied in a sediment core, NC Core 2, from the upper slope (1030 m water depth) of the Nile Cone, southeastern Mediterranean, Egypt. Each sample represents palynomorph deposition for intervals of ca. 500-1,000 years and provides the first detailed palynological record for the Nile Cone. The dinocyst assemblages and AOM production reflect changes in surface water temperature and river discharge in response to climate forcing as marked by variations in pollen and spore indicators of semi-desert vegetation and tropical Monsoon intensity. The basal sediments (ca.14600 - 9500 yr BP) contain high concentrations and relative abundances of Spiniferites elongatus, Polysphaeridium zoharyi and other Polysphaeridium and Spiniferites species during the transition from postglacial to interglacial conditions. Variations in these taxa and total Impagidinium species suggest a gradual temperature increase, interrupted by a pre-Holocene cool interval around 11000 yr BP. The high African monsoon index for this pre-Holocene time corresponds with pollen evidence of relatively high Nile discharge. The organic-rich S1 sapropel sediments, dated ca. 9500 - 6270 yr BP, were deposited several thousand years later, during a time of lower Monsoon index, warmer surface water and increased dinocyst production. This was accompanied by moderate Nile flooding and oxygen-deficient or anoxic bottom water on the upper Nile Cone, mainly supporting the increased production and carbon import hypothesis for Eastern Mediterranean S1 formation. Dinocyst assemblages in the Nile Cone S1 differ from those of the deeper, more northern Levantine and Cretan basins in the near absence of heterotrophic protoperidinioid cysts, despite the uniformly high organic S1 carbon content. The prevailing climate during the formation of sapropelic sediments in the Southeastern Mediterranean was tropical to subtropical, but was interrupted by an early cooler interval with reduced humidity, as marked by re-appearance of Spiniferites elongatus and increased Ephedra pollen. The carbonate-rich surface layers were probably deposited under warm dry climatic conditions with minimum Nile input, but evidence of oxidation prevents detailed interpretation. Key words: dinocysts; pollen; spores; Nile Cone; Amorphous Organic Matter; sapropel S1; Late Pleistocene; Holocene.

Kholeif, S.; Mudie, P.

2009-04-01

128

Radiocarbon dates on cave bear (Ursus spelaeus) and brown bear (Ursus arctos) from Late Pleistocene of Poland  

Science.gov (United States)

Although cave bear (Ursus spelaeus) is far more abundant in last glacial in Europe than brown bear (Ursus arctos), the co-occurrence of both species during Oxygen Isotope Stage 3 (OIS 3) is not questioned. The cave bear (Ursus spelaeus) has been an important part of the European large mammal fauna of last glaciation. Most of the remains come from karst areas where larger caves were used as hibernation sites. In Poland caves occur in the Sudetes Mts, Kraków-Cz?stochowa Upland, ?wi?tokrzyskie Mts and in the Carpathians (especially in Tatra and Pieniny Mts). The AMS 14C dates were obtained for 14 sites (23 dates) distributed in all karst areas of Poland. All samples dated in Pozna? Radiocarbon Laboratory (Poz) were subject of pre-treatment procedures (ultrafiltration and removal of consolidants). Dates are given as an uncalibrated radiocarbon dates (BP) and as calendar dates (cal. BP). The Eastern Sudetes sites are represented by two cave bear remains from Nied?wiedzia Cave, Kletno. Most of samples come from several localities located in different parts of Kraków-Cz?stochowa Upland (Nietoperzowa, Mamutowa, Ciemna, Wylotne and Zawalona caves - all near Kraków; Komarowa, Deszczowa, Stajnia and Nied?wiedzia near Olsztyn caves - all from the middle part of the Upland). Raj Cave is located in ?wi?tokrzyskie Mts. The Carpathians samples come from two caves in Tatra Mts: Magurska and Poszukiwaczy Skarbów. Results obtained suggest that in the early part of OIS 3, ca. 50-33 ka (ca. 54-37,5 cal. ka), when the climate was relatively stable and warm, cave bears occurred probably more or less continuously from Sudetes Mts to Kraków-Cz?stochowa Upland and in the Carpathians. The available 18 dates range from >52,000 BP (Poz-24205) to 33,000±400 BP (Poz-23655) (cal. 38,571±1,449 BP). Around 33 ka BP (cal. 38,5 ka BP) cave bears probably disappeared, or at least reduced their number, in the area north from Sudetes and the Carpathians for next ca. 4-5 millennia. However, this evidence requires further investigation. The dates younger than 29 ka BP (cal. 33 ka BP) include 4 dates ranging from 28,500±500 BP (GdA-94) (this conventional 14C date is doubtful due to pre-treatment methods used) to 26,010±150 BP (OxA-14406) (cal. 30,971±344 BP). The youngest available so far AMS date from Poland is a fragment presumably of cave bear skull (we cannot exclude the brown bear) from Komarowa Cave (layer C), 24,550±220 BP (Poz-339) (cal. 29,361±508 BP). However, this date must be regarded with considerable caution because the improved pre-treatment methods were not used. Although the data are still limited at present, there are strong indications that the cave bear (Ursus spelaeus) did not survived to the Last Glacial Maximum (LGM), and become extinct ca. 26 ka BP (ca. cal. 31 ka BP) at areas north from the Sudetes and the Carpathians ranges, thus earlier than in the Alps (ca. 24 ka BP, ca. cal. 28 ka BP). The direct dating of brown bear remains are still scarce. The AMS 14C dates were obtained for 10 remains of Ursus arctos previously dated for late Pleistocene on the basis of stratigraphic position of remains and archaeological chronology. The Eastern Sudetes sites are represented by a single date of brown bear skull described previously by Zotz (1939) from a cave (most probably Kammerberghöhle) near Wschodnia Cave (Po?om Mt.). Most of samples come from few archaeological sites located in different parts of Kraków-Cz?stochowa Upland (Mamutowa, Komarowa, Deszczowa and Dziadowa Ska?a caves). A single date obtained for Kraków Spadzista Street (from a trench near site B) is surprising, because of extreme rarity of brown bears in archaeological open-air sites in Poland. In six cases the late Pleistocene age of Ursus arctos remains was confirmed, however only one obtained date agree with the opinion of possible co-occurrence of the brown bear and cave bear during OIS 3 in Poland (Kadzielnia in Kielce, ca. 37,7 ka BP). The oldest available date (ca. 24,4 ka BP) of brown bear found in Kraków Spadzista Street, is younger from al

Nadachowski, Adam; Lipecki, Grzegorz; Stefaniak, Krzysztof; Wojtal, Piotr

2010-05-01

129

Sequence stratigraphy of plio-pleistocene sedimentary rocks in north-central Green Canyon and Western Ewing Bank, northern Gulf of Mexico  

Energy Technology Data Exchange (ETDEWEB)

A sequence-stratigraphic analysis of the Plio-Pleistocene sedimentary rocks of the north-central Green Canyon and western Ewing Bank areas was conducted using 1,330 mi of two-dimensional multifold migrated seismic profiles, biostratigraphic data from 31 wells, and logs. The study area covers 945 mi{sup 2} and was informally subdivided into five minibasins within which sediments were deposited in abyssal to middle neritic environments. Nine depositional sequences were recognized and correlated (4.2, 3.8, 3.4, 3.0, 1.4, 1.1, 0.8, 0.7, and 0.5 Ma). Most of the sediments were deposited in lowstand systems tracts consisting of basin-floor fan, slope-fan, and prograding wedge facies. Transgressive systems tracts and highstand systems tracts are thin in sequences older than 0.7 Ma and thicker in sequences 0.7 and 0.5 Ma. A major condensed interval (3.0 to 1.4 Ma) is relatively thin (70 to 1,600 ft) and is widespread across the entire study area. In general, sequences range from 70 to 3,400 ft thick, and they consist dominantly of shale. Sandstone content ranges from 7 to 36% and is present mainly within the sequences 3.8 to 3.0 Ma, 1.4 to 1.1 Ma, and 1.1 to 0.8 Ma. Prominent basin-floor fans are present in the 1.4 to 1.1. and 1.1. to 0.8 Ma sequences and are indicated by subparallel, high-amplitude reflections and blocky well log patterns. Slope-fan complexes have wide variability in seismic expression and sandstone percentage both within and between sequences. They consist of hummocky, chaotic, and subparallel reflections interpreted to reflect a number of depositional processes recorded in channel-levee, overbank, slump-slide, and hemipelagic facies. Complex salt structures and related faults control the geometry of the depositional units and the entrapment of petroleum. Discoveries in the area, which include Green Canyon blocks 65 (Bullwinkle), 110, and 19, are associated with amplitude anomalies on the flanks of salt features.

Acosta, Z.; Weimer, P. [Univ. of Colorado, Boulder, CO (United States)

1994-12-31

130

Contribution of changes in opal productivity and nutrient distribution in the coastal upwelling systems to late Pliocene/early Pleistocene climate cooling  

Directory of Open Access Journals (Sweden)

Full Text Available The global late Pliocene/early Pleistocene cooling (~3.0–2.0 million years ago, Ma) concurred with extremely high diatom and biogenic opal production in most of the major coastal upwelling regions. This phenomenon was particularly pronounced in the Benguela Upwelling System (BUS), off Namibia, where it is known as the Matuyama Diatom Maximum (MDM). Our study focuses on a new diatom silicon isotope (?30Si) record covering the MDM in the BUS. Unexpectedly, the variations in ?30Si signal follow biogenic opal content, whereby the highest ?30Si values correspond to the highest biogenic opal content. We interpret the higher ?30Si values during the MDM as a result of a stronger degree of silicate utilization in the surface waters caused by high productivity of mat-forming diatom species. This was most likely promoted by weak upwelling intensity dominating the BUS during the Plio/Pleistocene cooling combined with a large silicate supply derived from a strong Southern Ocean nutrient leakage responding to the expansion of Antarctic ice cover and the resulting stratification of the polar ocean 3.0–2.7 Ma ago. A similar scenario is hypothesized for other major coastal upwelling systems (e.g. off California) during this time interval, suggesting that the efficiency of the biological carbon pump was probably sufficiently enhanced in these regions during the MDM to have significantly increased the transport of atmospheric CO2 to the deep ocean. In addition, the coeval extension of the area of surface water stratification in both the Southern Ocean and the North Pacific, which decreased CO2 release to the atmosphere, led to further enhanced atmospheric CO2 drawn-down and thus contributed significantly to late Pliocene/early Pleistocene cooling.

J. Etourneau; C. Ehlert; M. Frank; P. Martinez; R. Schneider

2012-01-01

131

Volcaniclastic debris-flow occurrences in the Campania region (Southern Italy) and their relation to Holocene Late Pleistocene pyroclastic fall deposits: implications for large-scale hazard mapping  

Science.gov (United States)

The Campania Region (southern Italy) is characterized by the frequent occurrence of volcaniclastic debris flows that damage property and loss of life (more than 170 deaths between 1996 and 1999). Historical investigation allowed the identification of more than 500 events during the last four centuries; in particular, more than half of these occurred in the last 100 years, causing hundreds of deaths. The aim of this paper is to quantify debris-flow hazard potential in the Campania Region. To this end, we compared several elements such as the thickness distribution of pyroclastic fall deposits from the last 18 ka of the Vesuvius and Phlegrean Fields volcanoes, the slopes of relieves, and the historical record of volcaniclastic debris flows from A.D. 1500 to the present. Results show that flow occurrence is not only a function of the cumulative thickness of past pyroclastic fall deposits but also depends on the age of emplacement. Deposits younger than 10 ka (Holocene eruptions) apparently increase the risk of debris flows, while those older than 10 ka (Late Pleistocene eruptions) seem to play a less prominent role, which is probably due to different climatic conditions, and therefore different rates of erosion of pyroclastic falls between the Holocene and the Late Pleistocene. Based on the above considerations, we compiled a large-scale debris-flow hazard map of the study area in which five main hazard zones are identified: very low, low, moderate, high, and very high.

Bisson, M.; Pareschi, M. T.; Zanchetta, G.; Sulpizio, R.; Santacroce, R.

2007-11-01

132

Contemporaneous trace and body fossils from a late Pleistocene Lakebed in Victoria, Australia, allow assessment of bias in the fossil record.  

UK PubMed Central (United Kingdom)

The co-occurrence of vertebrate trace and body fossils within a single geological formation is rare and the probability of these parallel records being contemporaneous (i.e. on or near the same bedding plane) is extremely low. We report here a late Pleistocene locality from the Victorian Volcanic Plains in south-eastern Australia in which demonstrably contemporaneous, but independently accumulated vertebrate trace and body fossils occur. Bite marks from a variety of taxa are also present on the bones. This site provides a unique opportunity to examine the biases of these divergent fossil records (skeletal, footprints and bite marks) that sampled a single fauna. The skeletal record produced the most complete fauna, with the footprint record indicating a markedly different faunal composition with less diversity and the feeding traces suggesting the presence, amongst others, of a predator not represented by either the skeletal or footprint records. We found that the large extinct marsupial predator Thylacoleo was the only taxon apparently represented by all three records, suggesting that the behavioral characteristics of large carnivores may increase the likelihood of their presence being detected within a fossil fauna. In contrast, Diprotodon (the largest-ever marsupial) was represented only by trace fossils at this site and was absent from the site's skeletal record, despite its being a common and easily detected presence in late Pleistocene skeletal fossil faunas elsewhere in Australia. Small mammals absent from the footprint record for the site were represented by skeletal fossils and bite marks on bones.

Camens AB; Carey SP

2013-01-01

133

Orogénesis y drenaje en la región del Valle de Lerma (cordillera oriental, Salta, Argentina) durante el Pleistoceno Tardío/ Orogeny and drainage in the Lerma Valley region (Eastern Cordillera, Salta, Argentina) during the late Pleistocene  

Scientific Electronic Library Online (English)

Full Text Available Abstract in spanish En el Pleistoceno tardío, luego de la incipiente elevación de las serranías subandinas, la contracción retornó al interior del orógeno. En aquel tiempo un piedemonte conectaba los contrafuertes occidentales de la Cordillera Oriental (sierras de Lesser y Obispo) con la llanura subandina, a través de la región que hoy7 ocupan el valle de Lerma y la serranía Mojotoro-Castillejo. La contracción dio origen a las elevaciones interiores en la sierra de Vaqueros y los C (more) errillos de San Miguel, y luego se propagó al este una falla que derivó en el desarrollo de la serranía Mojotoro-Castillejo y el cierre del valle de Lerma. Algunos ríos incidieron a través de las nacientes barreras topográficas mientras que otros fueron a una cuenca endorreica inundada por un antiguo lago Lerma. La capacidad de incisión fue mayor en el valle de Lerma septentrional, donde los ríos llegaban con gradientes de cauce elevados a los sitios de ascenso topográfico, y donde el río Mojotoro persistió como cauce antecedente. En el sur, el lago Lerma colmató la cuenca hasta un punto de derrame por bajos estructurales en capas del Grupo Salta, y el agua labró el cauce subsecuente del actual río Juramento a través de la sierra de Castillejo. Más de 800 m de sedimento (aquí denominado Grupo Valle de Lerma) se acumularon en el valle de Lerma durante el Pleistoceno tardío. Información de subsuelo permite hacer una revisión crítica de la estratigrafía de este relleno y proponer una subdivisión más detallada. En particular se acota la extensión geográfica de la Formación Tajamar y se revisan las extrapolaciones que de ella se han hecho. Abstract in english In the late Pleistocene, following uplift of the first subandean ranges, contraction returned to the orogen interior. At the time, a wide piedmont connected the western ramparts of the Eastern Cordillera (Lesser and Obispo ranges) to the subandean plain, spanning the zone presently occupied by the Lerma Valley and the Mojotoro and Castillejo ranges. Contraction gave rise to the interior Vaqueros Range and the San Mguel Hills, and then propagated eastward with a regional r (more) everse fault that derived in the development of the Mojotoro and Castillejo ranges and closure of the Lerma Valley. Some river courses incised across the rising barriers, whereas others were diverted to an internally drained basin flooded by ancient Lake Lerma. Incision power was greater in the northern Lerma Valley, where the rivers reached the sites of topographic uplift with high bed gradients, and where the Mojotoro River persisted as an antecedent course. In the south, Lake Lerma filled the basin to a pour point through structural lows in Salta Group strata, and the issuing water carved the subsequent channel of the present Juramento River across the Castillejo Range. More than 800 m of sediment (herein designated Lerma Valley Group) accumulated in the Lerma Valley during the late Pleistocene. Subsurface information allowed a critical revision of the stratigraphy of this fill and a more detailed subdivision. In particular, the geographical extension of the Tajamar Formation is restricted and previously proposed extrapolations for it are revised.

González Bonorino, Gustavo; Del Valle Abascal, Liliana

2012-03-01

134

Studying travertines for neotectonics investigations: Middle-Late Pleistocene syn-tectonic travertine deposition at Serre di Rapolano (Northern Apennines, Italy)  

Science.gov (United States)

Middle-Late Pleistocene tectonic activity has been inferred through studies on travertine deposits exposed in a tract of the hinterland Northern Apennines. A detailed study on the relationships between tectonics and travertine deposition coupled with 230Th/234U age determination of travertines at Cava Oliviera quarry, located close to Serre di Rapolano village (southern Tuscany, Northern Apennines), allowed us to recognise Pleistocene faults, whose activity has been referred to 157-24 ka, at least. Travertine deposition was tectonically controlled by WSW-ENE striking, oblique and normal faults, associated to a main fault (named as the Violante Fault). This structure dissected a regional normal fault (known as the Rapolano Fault) Early-Middle Pliocene in age, which bounded the eastern side of the Pliocene Siena Basin, and gave rise to space accommodation for clayey and sandy marine sediments. Hydrothermal circulation (and related travertine deposition) was favoured by the damaging enhancement due to the fault-fault intersection. Tectonic activity has been also documented by deformation recorded by travertines, which suggest a main tectonic event between 64 ± 5 and 40 ± 5 ka. The tectonic activity described for the study area agrees with the Quaternary tectonic evolution documented in the surrounding areas (e.g. Mt. Amiata and Mt. Vulsini), as well as the Tyrrhenian margin of the Central Apennines, indicating that a widespread tectonic activity affected the inner part of the Apennines until the latest Quaternary.

Brogi, Andrea; Capezzuoli, Enrico; Aqué, Riccardo; Branca, Marilì; Voltaggio, Mario

2010-09-01

135

Evolution of the Northern Caspian Sea Region and the Volga delta in the late Pleistocene-Holocene  

Science.gov (United States)

On the basis of geologic-geomorphologic studies, an alternative concept regarding the evolution of the Northern Caspian Sea Region and the adjacent areas in the boundary of the Pleistocene-Holocene is presented. A supposition is made about the existence of a large lagoon in the North Caspian Region that the Volga River emptied into forming a delta. Later, water from the lagoon flowed as a "stratum" stream into the Black Sea through the Manych Strait. A conclusion is reached that the Baer mounds were formed on the bottom of this stream.

Badyukova, E. N.

2010-12-01

136

Sedimentation and erosion processes in Middle to Late Pleistocene sequences exposed in the brickyard of Langenlois/Lower Austria  

DEFF Research Database (Denmark)

The correlation of sedimentary and pedogenetic processes in Lower Austria is difficult due to significant discontinuities and local variability in soil formation. This hampers landscape reconstruction at a regional scale. However, at a local scale distinct landscape formation processes represented by a shift from fluvial to aeolian deposition can be observed in the brickyard of Langenlois, Lower Austria. Sedimentological and mineralogical analyses in combination with palaeontological finds suggest that the fluvial deposition took place during the Middle Pleistocene. This attribution is confirmed by infra-red stimulated luminescence (IRSL) dating, which gives a minimum age of 300 ka for the palaeosurface on which the fluvial sediments were deposited. This is consistent with a small faunal assemblage including Stephanorhinus sp., Dama sp. and an alcine cervid. Such a fauna is previously unknown in Austria; it indicates a Middle Pleistocene interglacial period. The low degree of weathering as well as Cryosols found in the loess sequence point to loess accumulation during the Last Glacial; the dating results (35–55 ka) indicate prolonged loess deposition. No signs of pedogenesis could be found; this is surprising because in other areas this period is known for weak soil development. The lack of soil formation seems to be specific to the western part of Lower Austria, as is the complete erosion of the last glacial maximum (LGM) loess, which can not be found at Langenlois.

Thiel, Christine; Terhorst, Birgit

2011-01-01

137

Sedimentation and erosion processes in Middle to Late Pleistocene sequences exposed in the brickyard of Langenlois/Lower Austria  

Science.gov (United States)

The correlation of sedimentary and pedogenetic processes in Lower Austria is difficult due to significant discontinuities and local variability in soil formation. This hampers landscape reconstruction at a regional scale. However, at a local scale distinct landscape formation processes represented by a shift from fluvial to aeolian deposition can be observed in the brickyard of Langenlois, Lower Austria. Sedimentological and mineralogical analyses in combination with palaeontological finds suggest that the fluvial deposition took place during the Middle Pleistocene. This attribution is confirmed by infra-red stimulated luminescence (IRSL) dating, which gives a minimum age of 300 ka for the palaeosurface on which the fluvial sediments were deposited. This is consistent with a small faunal assemblage including Stephanorhinus sp., Dama sp. and an alcine cervid. Such a fauna is previously unknown in Austria; it indicates a Middle Pleistocene interglacial period. The low degree of weathering as well as Cryosols found in the loess sequence point to loess accumulation during the Last Glacial; the dating results (35-55 ka) indicate prolonged loess deposition. No signs of pedogenesis could be found; this is surprising because in other areas this period is known for weak soil development. The lack of soil formation seems to be specific to the western part of Lower Austria, as is the complete erosion of the last glacial maximum (LGM) loess, which can not be found at Langenlois.

Thiel, Christine; Terhorst, Birgit; Jaburová, Iva; Buylaert, Jan-Pieter; Murray, Andrew S.; Fladerer, Florian A.; Damm, Bodo; Frechen, Manfred; Ottner, Franz

2011-12-01

138

Sequence stratigraphy and depositional controls in late Proterozoic-early Cambrian sediments of Amadeus basin, central Australia  

Energy Technology Data Exchange (ETDEWEB)

The Amadeus basin is an isolated intracratonic basin at the center of the Australian continent which, because of its location and geometry, provides an ideal opportunity to investigate depositional controls. To this end, more than 6000 km of seismic data, in conjunction with a field and well-log program, have been used in a study of the late Proterozoic-Early Cambrian Arumbera Sandstone. 17 figures.

Lindsay, J.F.

1987-11-01

139

Timing and depositional environments of a Middle Pleistocene glaciation of northeast England: New evidence from Warren House Gill, County Durham  

Science.gov (United States)

At various times during the Quaternary, north-eastern England was a zone of confluence between dynamic ice lobes sourced from the Pennines, northern Scotland, the Cheviots, and Scandinavia. The region thus has some of the most complex exposures of Middle to Late Pleistocene sediments in Britain, with both interglacial and glacial sediments deposited in terrestrial and marine settings. We investigated sedimentary sequences exposed on the coastline of County Durham at Warren House Gill, and present a new model of British and Fennoscandian Ice Sheet interaction in the North Sea Basin during the Middle Pleistocene.The stratigraphy at Warren House Gill consists of a lower diamicton and upper estuarine sediments, both part of the Warren House Formation. They are separated from the overlying Weichselian Blackhall and Horden tills by a substantial unconformity. The lower diamicton of the Warren House Formation is re-interpreted here as an MIS 8 to 12 glaciomarine deposit containing ice-rafted lithics from north-eastern Scotland and the northeast North Sea, and is renamed the 'Ash Gill Member'. It is dated by lithological comparison to the Easington Raised Beach, Middle Pleistocene Amino Acid Racemisation values, and indirectly by optically stimulated luminescence. The overlying shallow subaqueous sediments were deposited in an estuarine environment by suspension settling and bottom current activity. They are named the 'Whitesides Member', and form the uppermost member of the Warren House Formation. During glaciation, ice-rafted material was deposited in a marine embayment. There is no evidence of a grounded, onshore Scandinavian ice sheet in County Durham during MIS 6, which has long been held as the accepted stratigraphy. This has major implications for the currently accepted British Quaternary Stratigraphy. Combined with recent work on the Middle Pleistocene North Sea Drift from Norfolk, which is now suggested to have been deposited by a Scottish ice sheet, the presence of a Scandinavian ice sheet in eastern England at any time during the Quaternary is becoming increasingly doubtful.

Davies, B. J.; Roberts, D. H.; Bridgland, D. R.; Ó Cofaigh, C.; Riding, J. B.; Demarchi, B.; Penkman, K. E. H.; Pawley, S. M.

2012-06-01

140

Possible Late Pleistocene volcanic activity on Nightingale Island, South Atlantic Ocean, based on geoelectrical resistivity measurements, sediment corings and (14)C dating  

DEFF Research Database (Denmark)

Tristan da Cunha is a volcanic island group situated in the central South Atlantic. The oldest of these islands, Nightingale Island, has an age of about 18Ma. In the interior of the island, there are several wetlands situated in topographic depressions. The ages of these basins have been unknown, and their genesis has been debated. Aiming towards the reconstruction of the geomorphological history of these basins, we conducted geoelectrical resistivity measurements to map the subsurface topography, extracted peat and sediment cores and dated the onset of sedimentation applying the radiocarbon method. The irregular shapes of the basins and the lack of clear erosional features indicate that they are not eruption craters and were not formed by erosion. Instead, we regard them as morphological depressions formed between ridges of trachytic lava flows and domes at a late stage of the formation of the volcanic edifice. The onset of sedimentation within these basins appears to have occurred between 24 and 37 ka with the highest situated wetland yielding the highest ages. These ages are very young compared to the timing of the main phase of the formation of the island, implying volcanic activity on the island during the Late Pleistocene.

BjØrk, Anders Anker; Björck, Svante

2011-01-01

 
 
 
 
141

Equatorial Pacific peak in biological production regulated by nutrient and upwelling during the late Pliocene/early Pleistocene cooling  

Science.gov (United States)

The largest increase in export production in the eastern Pacific of the last 5.3 Myr (million years) occurred between 2.2 and 1.6 Myr, a time of major climatic and oceanographic reorganization in the region. Here, we investigate the causes of this event using reconstructions of export production, nutrient supply and oceanic conditions across the Pliocene-Pleistocene in the eastern equatorial Pacific (EEP) for the last 3.2 Myr. Our results indicate that the export production peak corresponds to a cold interval marked by high nutrient supply relative to consumption, as revealed by the low bulk sedimentary 15N/14N (?15N) and alkenone-derived sea surface temperature (SST) values. This ?0.6 million year long episode of enhanced delivery of nutrients to the surface of the EEP was predominantly initiated through the upwelling of nutrient-enriched water sourced in high latitudes. In addition, this phenomenon was likely promoted by the regional intensification of upwelling in response to the development of intense Walker and Hadley atmospheric circulations. Increased nutrient consumption in the polar oceans and enhanced denitrification in the equatorial regions restrained nutrient supply and availability and terminated the high export production event.

Etourneau, J.; Robinson, R. S.; Martinez, P.; Schneider, R.

2013-08-01

142

East-west genetic differentiation in Musk Ducks (Biziura lobata) of Australia suggests late Pleistocene divergence at the Nullarbor Plain  

Science.gov (United States)

Musk Ducks (Biziura lobata) are endemic to Australia and occur as two geographically isolated populations separated by the Nullarbor Plain, a vast arid region in southern Australia. We studied genetic variation in Musk Duck populations at coarse (eastern versus western Australia) and fine scales (four sites within eastern Australia). We found significant genetic structure between eastern and western Australia in the mtDNA control region (??ST = 0. 747), one nuclear intron (??ST = 0.193) and eight microsatellite loci (FST = 0.035). In contrast, there was little genetic structure between Kangaroo Island and adjacent mainland regions within eastern Australia. One small population of Musk Ducks in Victoria (Lake Wendouree) differed from both Kangaroo Island and the remainder of mainland eastern Australia, possibly due to genetic drift exacerbated by inbreeding and small population size. The observed low pairwise distance between the eastern and western mtDNA lineages (0.36%) suggests that they diverged near the end of the Pleistocene, a period characterised by frequent shifts between wet and arid conditions in central Australia. Our genetic results corroborate the display call divergence and Mathews' (Austral Avian Record 2:83-107, 1914) subspecies classification, and confirm that eastern and western populations of Musk Duck are currently isolated from each other. ?? 2010 Springer Science+Business Media B.V.

Guay, P. -J.; Chesser, R. T.; Mulder, R. A.; Afton, A. D.; Paton, D. C.; McCracken, K. G.

2010-01-01

143

Late Pleistocene-Holocene Volcanism of the Mexico Basin and Assessment of Volcanic Hazards in One of the World’s Largest Cities  

Science.gov (United States)

The Mexico City metropolitan area is home to more than 22 million people living in sight of, or living on, several volcanoes that either are currently active or show evidence of Late Pleistocene-Holocene activity (e.g., pyroclastic flows, debris avalanches and lahars). The volcanic rocks are located in five main belts or ranges: Sierra Nevada, Sierra de las Cruces, Sierra Guadalupe, Sierra de Santa Catarina, and the Chichinautzin Volcanic Field which surround the Mexico Basin and belong to the Trans-Mexican Volcanic Belt, preserving approx. 14 Ma of geologic history. Much attention has been devoted to the youngest of the volcanoes such as Popocatépetl in the Sierra Nevada which resumed activity in 1994-present and Chichinautzin which includes the 1600 year bp Xitle volcano. Surprisingly, the pre-Holocene history is not well constrained in the Mexico City area, due of the lack of detailed mapping coupled with high precision geochronology. Our new 40Ar/39Ar and petrologic data and detailed mapping focus on the earliest history of these volcanic systems and their temporal, spatial and geochemical evolution. For example, data from Tlaloc and Telapón volcanoes in the Sierra Nevada show at least two significant periods of edifice building (1.0 to 1.5 Ma and 0 to 400 ka) with an apparent long period of quiescence that clearly suggests that volcanism in the region did not migrate from north to south but that it has a more complex evolution that continues to pose a serious threat to the population of Mexico City. In addition, a 450 ka age, based on dome and pumice dating, constrains the timing of a major sector collapse of Iztaccíhuatl volcano that produced a Mt. St. Helens - sized debris avalanche deposit towards the present metropolitan area of the City of Puebla. In the Sierra de las Cruces Range, volcanic centers do show a north-south age progression from ~5 Ma, cumulating with the Zempoala edifice collapse approximately 900 ka, producing lahars and block and ash deposits that now underlie the city of Cuernavaca. Zempoala is located at the southern end of Sierra de las Cruces and is in the intersection of the late Pleistocene-Holocene Chichinautzin Volcanic Field. We have obtained Santa Catarina, which are now surrounded by densely populated areas. Our preliminary data show that there are many of these poorly understood, but potentially hazardous, volcanic centers throughout the Mexico Basin that have evidence of Late Pleistocene-Holocene activity. Further geological mapping and geochronologic data will allow us to better understand the complex migration patterns and eruption occurrence rate of the volcanic centers around Mexico City, evaluate their potential hazards, and understand the evolution of these ranges in relation to the tectonic framework in central Mexico.

Layer, P. W.; Macías, J.; Arce, J.; García, F.

2009-12-01

144

Turbidite Megabeds in an Oceanic Rift Valley Recording Jokulhlaups of Late Pleistocene Glacial Lakes of the Western United States.  

UK PubMed Central (United Kingdom)

Escanaba Trough is the southernmost segment of the Gorda Ridge and is filled by sandy turbidites locally exceeding 500 m in thickness. New results from Ocean Drilling Program (ODP) Sites 1037 and 1038 that include accelerator mass spectrometry (AMS) 14C dates and revised petrographic evaluation of the sediment provenance, combined with high-resolution seismic-reflection profiles, provide a lithostratigraphic framework for the turbidite deposits. Three fining-upward units of sandy turbidites from the upper 365 m at ODP Site 1037 can be correlated with sediment recovered at ODP Site 1038 and Deep Sea Drilling Program (DSDP) Site 35. Six AMS 14C ages in the upper 317 m of the sequence at Site 1037 indicate that average deposition rates exceeded 10 m/k.yr. between 32 and 11 ka, with nearly instantaneous deposition of one approximately 60-m interval of sand. Petrography of the sand beds is consistent with a Columbia River source for the entire sedimentary sequence in Escanaba Trough. High-resolution acoustic stratigraphy shows that the turbidites in the upper 60 m at Site 1037 provide a characteristic sequence of key reflectors that occurs across the floor of the entire Escanaba Trough. Recent mapping of turbidite systems in the northeast Pacific Ocean suggests that the turbidity currents reached the Escanaba Trough along an 1100-km-long pathway from the Columbia River to the west flank of the Gorda Ridge. The age of the upper fining-upward unit of sandy turbidites appears to correspond to the latest Wisconsinan outburst of glacial Lake Missoula. Many of the outbursts, or jökulhlaups, from the glacial lakes probably continued flowing as hyperpycnally generated turbidity currents on entering the sea at the mouth of the Columbia River.

Zuffa GG; Normark WR; Serra F; Brunner CA

2000-05-01

145

Multidecadal to Millenial-Scale Variability of Productivity and Oxygenation in the Main Peruvian Upwelling Zone Since the Late Pleistocene  

Science.gov (United States)

Mud-belts containing laminated or near-laminated sedimentary sequences exist in the central Peruvian continental margin beneath the oxygen minimum zone (12 - 14°S, 150 - 400 m), an area where upwelling-favorable alongshore winds are active year-round. The sediments here are dominated by siliceous and phosphatic biogenic remains, organic matter aggregates and lithogenic particles. Sediment cores collected in these belts record past climatic and biogeochemical conditions associated to the Peruvian upwelling system, providing decadal or even sub-decadal time-resolution for the reconstruction of past variabilities. We have examined paleorecords of past productivity and oxygenation in these continental margin sediments since the Last Glacial Maximum (0 - 22Ky BP), as inferred from stratigraphy (absence of bioturbation), geochemical and isotopic proxies, the latter for the past millenium. Laminated sequences are best preserved for the LGM, the Bolling/Allerod period, the early Holocene and the last millennium. In these sequences, the Mo:Al ratio, a proxy for anoxic conditions in the sediments is higher, suggesting an intensification of the oxygen minimum zone. Here also siliceous sedimentation is dominant and carbonate preservation is enhanced. For the past millennium, multiproxy records indicate a less intense OMZ and lower productivity during the Little Ice Age. There is a correspondence between the periods of high (low) lithogenic input and low (high) siliceous productivity with global/Northern Hemisphere cool (warm) climatic conditions since the deglaciation. The main mechanism driving this behavior for the Peruvian upwelling system appears to be the southward/northward migration of the ITCZ, modulating the inland precipitation and the alongshore wind field off Peru. Nevertheless, recent studies in other eastern boundary upwelling systems suggest that local land-sea pressure gradients under hemispheric warming or cooling modulate upwelling and biological productivity, which may contribute to oxygen depletion over the continental margins at these time-scales.

Gutierrez, D. A.; Sifeddine, A.; Skilbeck, C. G.; Salvatteci, R.

2011-12-01

146

Quantitative chemical stratigraphy of offshore exploration wells, northern Gulf of Mexico  

Energy Technology Data Exchange (ETDEWEB)

Isotope chronostratigraphy is now a proven form of chemical stratigraphy for high-resolution stratigraphic correlations in late Miocene through Pleistocene sections of exploration wells from the northern Gulf of Mexico (GOM). Detailed oxygen and carbon isotope records from wells spanning the GOM margin from Mississippi Canyon to East Breaks permit the development of a GOM type chemical stratigraphic section. The use of modern techniques of signal-to-noise identification enable us to compare our regional GOM type section to the global isotope record derived from deep-sea sections using coherence, auto-correlation, cross-correlation, and spectral analysis. These quantitative techniques enables us to recognize nearly 200 oxygen and carbon isotope zones or stages in the Piocene-Pleistocene. This chemical stratigraphy zonation offers unparalleled, fine-scaled correlation and depositional modeling of exploration wells. Removal of the global isotope signal from the regional GOM record permit us to determine the effects of meltwater-fluvial discharge episodes and regional sea level fluctuations on sedimentation along the GOM margin.

Trainor, D.M.; Williams, D.S.; Lerche, I.

1988-01-01

147

Quantitative chemical stratigraphy of offshore exploration wells, northern Gulf of Mexico  

Energy Technology Data Exchange (ETDEWEB)

Isotope chronostratigraphy is now a proven form of chemical stratigraphy for high-resolution stratigraphic correlations in late Miocene through Pleistocene sections of exploration wells from the northern Gulf of Mexico (GOM). Detailed oxygen and carbon isotope records from wells spanning the GOM margin from Mississippi Canyon to East Breaks permit the development of a GOM type chemical stratigraphic section. The use of modern techniques of signal-to-noise identification enable them to compare our regional GOM type section to the global isotope record derived from deep-sea sections using coherence, auto-correlation, cross-correlation, and spectral analysis. These quantitative techniques enable them to recognize nearly 200 oxygen and carbon isotope zones or stages in the Pliocene-Pleistocene. This chemical stratigraphy zonation offers unparalleled, fine-scaled correlation and depositional modeling of exploration wells. Removal of the global isotope signal from the regional GOM record permits them to determine the effects of meltwater-fluvial discharge episodes and regional sea level fluctuations on sedimentation along the GOM margin.

Trainor, D.M.; Williams, D.F.; Lerche, I.

1988-02-01

148

Late Pleistocene leopards across Europe - northernmost European German population, highest elevated records in the Swiss Alps, complete skeletons in the Bosnia Herzegowina Dinarids and comparison to the Ice Age cave art  

Science.gov (United States)

European leopard sites in Europe demonstrate Early/Middle Pleistocene out of Africa lowland, and Late Pleistocene Asian alpine migrations being driven by climatic changes. Four different European Pleistocene subspecies are known. The final European Late Pleistocene "Ice Age leopard" Panthera pardus spelaea (Bächler, 1936) is validated taxonomically. The skull shows heavy signs of sexual dimorphism with closest cranial characters to the Caucasian Panthera pardus ciscaucasica (Persian leopard). Late Pleistocene leopards were distributed northernmost, up to S-England with the youngest stratigraphic records by skeletons and cave art in the MIS 2/3 (about 32,000-26,000 BP). The oldest leopard painting left by Late Palaeolithics (Aurignacians/Gravettians) in the Chauvet Cave (S-France) allows the reconstruction of the Ice Age leopard fur spot pattern being close to the snow or Caucasian leopards. The last Ice Age glacial leopard habitat was the mountain/alpine boreal forest (not mammoth steppe lowland), where those hunted even larger prey such as alpine game (Ibex, Chamois). Into some lairs, those imported their prey by short-term cave dwelling (e.g. Baumann's Cave, Harz Mountains, Germany). Only Eurasian Ice Age leopards specialized, similar as other Late Pleistocene large felids (steppe lions), on cave bear predation/scavenging partly very deep in caves. In Vjetrenica Cave (Dinarid Mountains, Bosnia Herzegovina), four adult leopards (two males/two females) of the MIS 3 were found about two km deep from the entrance in a cave bear den, near to one cave bear skeleton, that remained articulated in its nest. Leopards died there, partly being trapped by raising water levels of an active ponor stream, but seem to have been killed possibly either, similar as for lions known, in battles with cave bears in several cave bear den sites of Europe (e.g. Baumann's Cave, Wildkirchli Cave, Vjetrenica Cave). At other large cave sites, with overlap of hyena, wolf and dhole dens at the cave entrances, leopard bones with bite damages indicate their remains to have been imported and consumed by predators in alpine regions due to reduced prey availability. The best models for the competition/taphonomy of large predators - felids, hyenids, canids - within large cave bear dens of Europe is represented in combination of the Zoolithen Cave and Vjetrenica Cave taphonomy.

Diedrich, Cajus G.

2013-09-01

149

Late Pleistocene climate change and landscape dynamics in the Eastern Alps: the inner-alpine Unterangerberg record (Austria)  

Science.gov (United States)

Drill cores from the inner-alpine valley terrace of Unterangerberg, located in the Eastern Alps of Austria, offer first insights into a Pleistocene sedimentary record that was not accessible so far. The succession comprises diamict, gravel, sand, lignite and thick, fine grained sediments. Additionally, cataclastic deposits originating from two paleo-landslide events are present. Multi-proxy analyses including sedimentological and palynological investigations as well as radiocarbon and luminescence data record the onset of the last glacial period (Würmian) at Unterangerberg at ?120–110 ka. This first time period, correlated to the MIS 5d, was characterised by strong fluvial aggradation under cold climatic conditions, with only sparse vegetation cover. Furthermore, two large and quasi-synchronous landslide events occurred during this time interval. No record of the first Early Würmian interstadial (MIS 5c) is preserved. During the second Early Würmian interstadial (MIS 5a), the local vegetation was characterised by a boreal forest dominated by Picea, with few thermophilous elements. The subsequent collapse of the vegetation is recorded by sediments dated to ?70–60 ka (i.e. MIS 4), with very low pollen concentrations and the potential presence of permafrost. Climatic conditions improved again between ?55 and 45 ka (MIS 3) and cold-adapted trees re-appeared during interstadials, forming an open forest vegetation. MIS 3 stadials were shorter and less severe than the MIS 4 at Unterangerberg, and vegetation during these cold phases was mainly composed of shrubs, herbs and grasses, similar to what is known from today's alpine timberline. The Unterangerberg record ended at ?45 ka and/or was truncated by ice during the Last Glacial Maximum.

Starnberger, Reinhard; Drescher-Schneider, Ruth; Reitner, Jurgen M.; Rodnight, Helena; Reimer, Paula J.; Spotl, Christoph

2013-01-01

150

Late Pleistocene climate change and landscape dynamics in the Eastern Alps: the inner-alpine Unterangerberg record (Austria).  

UK PubMed Central (United Kingdom)

Drill cores from the inner-alpine valley terrace of Unterangerberg, located in the Eastern Alps of Austria, offer first insights into a Pleistocene sedimentary record that was not accessible so far. The succession comprises diamict, gravel, sand, lignite and thick, fine grained sediments. Additionally, cataclastic deposits originating from two paleo-landslide events are present. Multi-proxy analyses including sedimentological and palynological investigations as well as radiocarbon and luminescence data record the onset of the last glacial period (Würmian) at Unterangerberg at ?120-110 ka. This first time period, correlated to the MIS 5d, was characterised by strong fluvial aggradation under cold climatic conditions, with only sparse vegetation cover. Furthermore, two large and quasi-synchronous landslide events occurred during this time interval. No record of the first Early Würmian interstadial (MIS 5c) is preserved. During the second Early Würmian interstadial (MIS 5a), the local vegetation was characterised by a boreal forest dominated by Picea, with few thermophilous elements. The subsequent collapse of the vegetation is recorded by sediments dated to ?70-60 ka (i.e. MIS 4), with very low pollen concentrations and the potential presence of permafrost. Climatic conditions improved again between ?55 and 45 ka (MIS 3) and cold-adapted trees re-appeared during interstadials, forming an open forest vegetation. MIS 3 stadials were shorter and less severe than the MIS 4 at Unterangerberg, and vegetation during these cold phases was mainly composed of shrubs, herbs and grasses, similar to what is known from today's alpine timberline. The Unterangerberg record ended at ?45 ka and/or was truncated by ice during the Last Glacial Maximum.

Starnberger R; Drescher-Schneider R; Reitner JM; Rodnight H; Reimer PJ; Spötl C

2013-05-01

151

Late Pleistocene sediment provenance on the Mendeleev Ridge, Arctic Ocean, from XRF Elemental Analysis and Diffuse Spectral Reflectance measurements  

Science.gov (United States)

During the 2005 Healy-Oden Trans-Arctic Expedition (HOTRAX), core HLY0503-JPC08 was raised from the Mendeleev Ridge at the modern junction of the Beaufort Gyre and the Transpolar Drift. This core with sedimentation rates estimated on the order of 2 cm/ka is well situated to sample variations in sedimentation, and thus circulation patterns during the Quaternary. Some characteristic features such as a distinctive change in lithology and prominent IRD layers provide the basis for correlation with previously developed stratigraphies. This overall correlation is confirmed by 1 cm post-cruise diffuse spectral reflectance measurements generated using a Minolta CM-2600d spectrophotometer. Downcore analysis of principle components extracted from the DSR data indicate an inverse correlation between smectite-chlorite which reaches maxima during interglacial/interstadial intervals when sediment Mn is also high, and illite and goethite which reach maxima during glacial intervals when sediment Mn is low. These glacial-interglacial cycles are also evident in elemental composition measured using a handheld, Innov-X Alpha series XRF analyzer which we employ on Arctic sediment for the first time. Estimates of sediment Mn content inferred by diffuse spectral reflectance agree well with XRF based measurements. We observe three distinct end-members based on physical properties and elemental composition. Low density, fine- grained, glacial sediment exhibit low Mn, low Sr, and high Rb values, and thus a high Rb/Sr ratio. Moderately sandy interglacial sediment exhibits high Mn, high Sr, and low Rb values, while sediment from the transitions in to and out of glacial periods are marked by prominent spikes in density, coarse grains, and Zr concentration. Elevated Rb/Sr ratios during glacial periods may result from the re-suspension of fine-grained sediment previously deposited on the outer shelf during higher sea level, and/or by discharge from proglacial lakes. The increase in grain-size accompanied by lows in the Rb/Sr ratio during interglacial/interstadial conditions provides a proxy for fluvial sediment transport and sea-ice rafting from inner shelf environments. Zr spikes mark IRD events corresponding to ice-sheet instabilities. Because the Zr spikes are generally not associated with elevated Ca, a proxy for detrital carbonate, we infer that these spikes represent predominantly iceberg-rafted sediment of Eurasian origin, whereas three distinct Ca maxima indicate prominent iceberg events originating from the Laurentide ice sheet.

Ortiz, J. D.; Polyak, L.; Adler, R.; Jakobsson, M.; Darby, D.

2007-12-01

152

Sequence stratigraphy and architectural variability in Late Eocene lacustrine strata of the Dongying Depression, Bohai Bay Basin, Eastern China  

Science.gov (United States)

Stratigraphic sequences and architectural variability in the Late Eocene lacustrine strata of the Dongying Depression, eastern China, were investigated using the interpretation of 2-D and 3-D high-resolution seismic profiles, analysis of spontaneous potential and resistivity curves, and observation of drill cores. Four third-order sequences controlled by syndepositional faults or fault slope break zones were identified, based on the characteristics of sequence boundaries and sedimentary successions. The architecture of the sequences in the different structural belts of the depression is complicated by the relationship between the rate at which fault-controlled accommodation was created and the rate of sediment supply. At fault margins, the rate of sediment supply exceeded accommodation space. Here, lowstand systems tracts consist of lowstand fan deltas with small progradational to retrogradation stacking patterns controlled by steeply dipping, parallel and cross-shaped syndepositional faults or fault slope-break zones; transgressive systems tracts consist of fan deltas with retrogradational to aggradational stacking patterns; and highstand systems tracts consist of fan deltas with normal regressive or progradational stacking pattern. At hinged margins, the rate of sediment supply was equal to or exceeded accommodation controlled by faults. Lowstand systems tracts at hinged margins consist of incised channel fills deposited on the landward side of gently dipping parallel and broom-shaped syndepositional faults or fault slope break zones and lowstand fans or sublacustrine fans deposited on the shores of lakes. Transgressive systems tracts consist of delta systems and shore to shallow-lake subfacies with retrogradational stacking patterns. Highstand systems tracts consist of braided deltas and fluvial delta systems with progradational or normal regressive and aggradational stacking patterns. Along the axis, the rate of sediment supply far exceeded accommodation. Only the lowstand systems tracts developed, consisting of lowstand deltas deposited on the landward side of the syndepositional faults or fault slope break zones, and lowstand fans or sublacustrine fans deposited on the lakeward side of the zones. Here, transgressive systems tracts consist of thin, deep lacustrine deposits and fluvial delta systems with retrogradational or transgressive stacking patterns; and highstand systems tracts consist of thick fluvial delta systems with a progradational configuration or normal regressive stacking patterns.

Feng, Youliang; Li, Sitian; Lu, Yongchao

2013-09-01

153

Stratigraphic context and paleoenvironmental significance of minor taxa (Pisces, Reptilia, Aves, Rodentia) from the late Early Pleistocene paleoanthropological site of Buia (Eritrea).  

UK PubMed Central (United Kingdom)

The Buia Homo site, also known as Wadi Aalad, is an East African paleoanthropological site near the village of Buia that, due to its very rich yield from the late Early Pleistocene, has been intensively investigated since 1994. In this paper, which reports on the finds of the 2010-2011 excavations, we include new fossil evidence on previously identified taxa (i.e., reptiles), as well as the very first description of the small mammal, fish and bird remains discovered. In particular, this study documents the discovery of the first African fossil of the genus Burhinus (Aves, Charadriiformes) and of the first rodent from the site. This latter is identified as a thryonomyid rodent (cane rat), a relatively common taxon in African paleoanthropological faunal assemblages. On the whole, the new occurrences documented within the Buia vertebrate assemblage confirm the occurrence of taxa characterized by strong water dependence. The paleoenvironmental characteristics of the fauna are confirmed as fully compatible with the evidence obtained through sedimentology and facies analysis, documenting the sedimentary evolution of fluvio-deltaic and lacustrine systems.

Rook L; Ghinassi M; Carnevale G; Delfino M; Pavia M; Bondioli L; Candilio F; Coppa A; Martínez-Navarro B; Medin T; Papini M; Zanolli C; Libsekal Y

2013-01-01

154

Late Pleistocene to Holocene climate and seasonality in North Africa from the stable isotope analysis of marine and terrestrial mollusc shells (Haua Fteah, Libya)  

Science.gov (United States)

The Haua Fteah cave in Libya contains one of the longest and most complete sequences of human occupation in North Africa. This rich archaeological assemblage occurs in tandem with abundant material for paleoenvironmental reconstruction. In this study, stable isotope analyses of the archaeological mollusc assemblage from the Haua Fteah have allowed the reconstruction of paired marine and terrestrial climate records that extend from c.22,000 to 5,500 cal BP. In the marine topshell Osilinus turbinatus, ?18O records fluctuations in sea surface temperature. In the terrestrial mollusc Helix melanostoma, ?18O varies according to the water ingested by the animal as the shell grows, which in turn is linked to water and air temperature at the moment of precipitation whilst ?13C provides a proxy for palaeovegetation patterns and water stress. Intrashell stable isotope series from these shells record snapshots of sub-seasonal climatic variations covering rapid and profound climatic fluctuations from MIS 2 to MIS 1. This high-resolution climatic framework coupled with the well-dated record of cultural change, allows an examination of human-environment interactions during critical periods of late Pleistocene to Holocene climate change.

Prendergast, A.; Stevens, R.; O'Connell, T.; Hunt, C.; Barker, G.

2011-12-01

155

Palaeohydrological and palaeoecological studies on South Cameroonian alluvial sedimentary basins - New evidence on the palaeoenvironmental evolution of western Central Africa since the Late Pleistocene  

Science.gov (United States)

A new valuable and innovative contribution will be presented to ascertain the timing and extension of climatic and ecological changes in western equatorial Africa. Main focus is laid on the dynamics of climate, fluvial systems and the high sensitive tropical ecosystems (dense evergreen and semi-deciduous rain forest and savanna-rain forest margin) since the Late Pleistocene (~50 kyrs. BP). For this purpose extended fieldworks were carried out in South Cameroon (2004-2008) by the ReSaKo-Project (sub-project of DFG-Project 510) with abundant investigations on alluvial sedimentary basins of equatorial tropical fluvial systems. Suitable alluvial sediment-archives for palaeoenvironmental research were uncovered along selected braiding, meandering and anabranching/anastomosing reaches of major southwestern, into the Gulf of Guinea (Ntem, Nyong and Sanaga) and southeastern, into the Congo basin (Boumba, Dja and Ngoko) draining rivers (RUNGE et al. 2006, SANGEN 2008). Among geomorphological investigations and cross section discussions, 150 corings (Edelman, 20 cm layers) reaching maximum depths of 550 cm were carried out on river benches, levees, cut-off and periodical branches, islands and terraces as well as in seasonal inundated floodplains and backswamps. Corresponding sedimentary profiles and catenae recovered multilayered, sandy to clayey alluvia containing sedimentary form-units and palaeosurfaces which contribute to the reconstruction of palaeoenvironmental conditions in western equatorial Africa. Several (59) radiocarbon (AMS) dated samples (Erlangen and Lecce) from fossil organic layers and macro-rests embedded in these units yielded Late Pleistocene to recent ages (14C-ages around 48 to 0.2 kyrs. BP), spanning also the Last Glacial Maximum (LGM) and Holocene record. Abrupt grain-size modifications and alternating form-units (sandy and clayey layers, palaeosurfaces) in the stratigraphic records display fluctuations in the fluvial-morphological response of the fluvial systems to climatic variability and other extrinsic and intrinsic impacts. Although the sedimentary record varies among the studied river reaches, fossil organic sediment layers (palaeosurfaces) containing valuable proxy data were found in almost all alluvia basins of examined southern Cameroonian rivers. Around 56 ^13C-values corresponding to the dated samples (-31.4 to -18.0 ) evidence that despite major disturbances of the African rain forest over geological times (MALEY 2001) mainly rain forest ecosystems have prevailed during the corresponding time periods, presumably as gallery forests, which were able to persist in this fluvial habitat ("fluvial refuge"), even during arid periods (e.g. LGM). The results are consistent with earlier findings from lacustrine (SERVANT & SERVANT-VILDARY 2000), marine (WELDEAB et al. 2007) and additional sediment archives (GASSE et al. 2008) and will add additional insights and information to the unravelling of the complex respond of the African monsoon, the Central African ecosystems and fluvial systems to Late Quaternary climatic and environmental fluctuations within a globally teleconnected system. References: GASSE, F., CHALIé, F., VINCENS, A., WILLIAMS, M.A.J. & WILLIAMSON, D. (2008): Climatic patterns in equatorial and southern Africa from 30,000 to 10,000 years ago reconstructed from terrestrial and near-shore proxy data. Quaternary Science Reviews, 27 (25-26), 2316-2340. MALEY, J. (2001): The impact of arid phases on the African rain forest through geological history. In: WEBER, W., WHITE, L., VEDDER, A., NAUGHTON-TREVES, L. (Eds.): African rain forest ecology and conservation - An interdisciplinary perspective. Yale University Press, New Haven, 68-87. RUNGE, J., EISENBERG, J., SANGEN, M. (2006): Geomorphic evolution of the Ntem alluvial basin and physiogeographic evidence for Holocene environmental changes in the rain forest of SW Cameroon (Central Africa) - preliminary results. Z. Geomorph. N.F., Suppl. Bd. 145, 63-79. SERVANT, M. & SERVANT-VILDARY, S. (2000): Dynamique à long terme des

Sangen, M.

2009-04-01

156

Age estimates and uplift rates for late Pleistocene marine terraces: Southern Oregon portion of the Cascadia forearc  

Energy Technology Data Exchange (ETDEWEB)

Interest in the Cascadia subduction zone has increased because recent investigations have suggested that slip along plates at certain types of convergent margins is characteristically accompanied by large earthquakes. In addition, other investigations have suggested that convergent margins can be broadly classified by the magnitude of their uplift rates. The authors generated new uranium series, amino acid, and stable isotope data for southern Oregon marine terrace fossils. These data, along with terrace elevations and two alternative estimates of sea level at the time of terrace formation, allow one to determine terrace ages and uplift rates. Uranium series analysis of fossil coral yields an age of 83 {plus minus} 5 ka for the Whisky Run terrace at Coquille Point in Bandon, Oregon. A combination of amino acid and oxygen isotope data suggest ages of about 80 and 105 ka for the lowest two terraces at Cape Blanco. These ages indicate uplift rates of 0.45-1.05 and 0.81-1.49 m/kyr for Coquille Point and Cape Blanco, respectively. In order to assess the utility of the southern Oregon uplift rates for predicting the behavior of the Cascadia subduction zone, the authors compared late Quaternary uplift rates derived from terrace data from subduction zones around the world. On the basis of this comparison the southern Oregon rates of vertical deformation are not usually high or low. Furthermore, late Quaternary uplift rates show little relationship to the type of convergent margin. In the case of the southern Oregon coast, variability in uplift rate probably reflects local structures in the overriding plate, and the rate of uplift cannot be used as a simple index of the potential for great earthquakes along the southern Cascadia subduction zone.

Muhs, D.R.; Whelan, J.F. (Geological Survey, Denver, CO (United States)); Kelsey, H.M.; McInelly, G.W. (Western Washington Univ., Bellingham (United States)); Miller, G.H. (Univ. of Colorado, Boulder (United States)); Kennedy, G.L. (Los Angeles County Museum of Natural History, CA (United States))

1990-05-10

157

Chronostratigraphy and changes of environment of Late Pleistocene and Holocene at Starunia palaeontological site and vicinity (Carpathian region, Ukraine)  

Directory of Open Access Journals (Sweden)

Full Text Available This paper presents the results of absolute dating and biostratigraphical analysis carried out for alluvial sediments of an abandoned Starunia ozokerite mine located in the Velyky Lukavets River valley, in which large mammal remains were discovered in the first half of the 20th century. The sediments build up three terrace levels. The highest one, up to 8 m high (terrace II), is likely to be associated with a stage of aggradation, as well as with a short episode of valley broadening, which occurred in the Weichselian Late Pleniglacial. The lower one, 4 m high (terrace I), is most likely to be linked with the Holocene, despite a considerable transformation of its top due to mining activity. The lower part of this terrace cover bears coarse-grained channel sediments dated to 120.6-58.9 ka BP (Eemian Interglacial?-Early Pleniglacial - OIS 5e, 4 and 3), and overbank (distal floodplain) mud with intercalations of biogenic deposits (peat, peat mud and biogenic mud). The overbank deposits are dated to 48.2-11.11 ka BP (Glinde Interstadial?-Younger Dryas, OIS 3-2) and are overlain by Holocene (OIS 1) mud and biogenic deposits. In boreholes drilled in the vicinity of the present-day river channel, younger sediments occur more frequently. These include sediments originating from the Late Weichselian overlain by Holocene sediments. However, sediments originating exclusively from the Holocene are infrequent. The deposition of sediments took place in specific conditions of a permanent saturation of the environment with brine, petroleum and thickened bitumen. In the longest period of deposition (48.2-1.27 ka BP), ephemeral swamps, ponds and lakes were developed in different parts of the floodplain. They were marked by the presence of: Juncus glaucus/effusus, J. articulatus, Typha sp., Batrachium sp., Potamogeton filliformis, Bidens tripartita, Ranunculus sceleratus and Phragmites communis, as well as by halophytic species, like: Zannichellia palustris, Triglochin maritimum, Schoenoplectus tabernemontani, Puccinelia distans and Eleocharis palustris. Rhythmic oscillations between cold and warm climatic conditions, typical of the Weichselian age and well identified in Western Europe, are here marked by the changes of plant communities (woody assemblages passing into steppe and tundra), but are not noticeably recorded in the sediments of the Velyky Lukavets River. This shows that the greatest part of the discussed period involved the formation of poorly differentiated silty overbank sediments with intercalations of biogenic sediments. However, the variability of sediments provides evidence for extreme events which occurred in the Holocene.

Tadeusz SOKO?OWSKI; Renata STACHOWICZ-RYBKA

2009-01-01

158

Foraminíferos y ostrácodos del Pleistoceno tardío (Mar Chiquita, provincia de Buenos Aires, Argentina)/ Late Pleistocene Foraminifera and Ostracoda (Mar Chiquita, Buenos Aires Province, Argentina)  

Scientific Electronic Library Online (English)

Full Text Available Abstract in spanish Sobre la base del estudio de foraminíferos y ostrácodos, se describe la evolución de ambientes marino- costeros al sudeste de la provincia de Buenos Aires afectados por las variaciones del nivel del mar durante el Pleistoceno tardío. Fueron estudiadas dos perforaciones realizadas al sur de la laguna Mar Chiquita. En las secciones inferiores de las perforaciones (A y B) se registran ambientes marinos marginales que pueden ser asignados a la Formación Canal 5 correlaci (more) onable con el último máximo interglacial (subestadio isotópico 5e). En los niveles fértiles inferiores de la perforadión A y en toda la sección B las asociaciones de foraminíferos, dominadas por Ammonia beccarii (Linné), permiten inferir ambientes marinos litorales a lagunas costeras. Las asociaciones de ostrácodos indican ambientes de depositación costeros, litorales a de plataforma interna cercanos a estuarios o lagunas costeras, con niveles relativamente altos de energía que han provocado mezcla de material por transporte y retrabajo. Estos ambientes pueden ser asociados al ascenso del nivel del mar durante la última transgresión pleistocena y asignados a la Facies Los Médanos de la Formación Canal 5. Hacia arriba (en la Perforación A), estos ambientes gradan a otros con mayor influencia continental, lagunares, oligo-mesohalinos, de baja energía, evidenciados por el aumento de las proporciones de taxones mixohalinos (Cyprideis) y dulceacuícolas-oligohalinos, por el buen estado de preservación de los ejemplares y la coexistencia de adultos y juveniles de los taxones de ostrácodos, así como por asociaciones de foraminíferos con baja diversidad dominadas por Ammonia beccarii. Estos ambientes pueden ser asignados a la Facies Santa Ana de la misma Formación. Sobreyacen sedimentos continentales no microfosilíferos. Abstract in english The evolution of Late Pleistocene marginal marine environments in the southeast of Buenos Aires province are described based upon the associations of foraminifera and ostracoda. Two drilling performed in the southern coastal plain of Mar Chiquita coastal lagoon were studied. The lowest sections of the drillings (A and B) indicate marginal marine environments that could be assigned to Canal 5 Formation and correlated to Last Interglacial Maximum, (marine oxygen isotope sub (more) stage 5e). Along the whole studied section of drilling B and the lowest levels of drilling A, foraminiferal associations are dominated by Ammonia beccarii (Linné) and could be interpreted as characterizing littoral marine environments or coastal lagoons. Ostracoda associations suggest littoral marine environments close to an estuary or a coastal lagoon, with relatively high energetic conditions shown by reworked and mixed material. These environments represent the transgressive/ highstand phase of the Late Pleistocene transgression and could be assigned to Los Médanos Facies of Canal 5 Formation. Upward (Drilling A) increasing percentages of mixohaline (Cyprideis) and non-marine taxa, along with a good preservation of valves, tests and the presence of juvenile and adults of ostracoda and lower diversity associations of foraminifera dominated by Ammonia becarii, suggest the evolution towards lagoonal, low energy environments. These levels represent the regressive phase corresponding to Santa Ana Facies of Canal 5 Formation and are covered by non-microfossiliferous continental muds.

Ferrero, Laura

2009-12-01

159

Hippidion saldiasi Roth, 1899 (Mammalia, Perissodactyla) en el Pleistoceno tardío de Calama, norte de Chile/ Late Pleistocene Hippidion saldiasi Roth, 1899 (Mammalia, Perissodactyla) from Calama, northern Chile  

Scientific Electronic Library Online (English)

Full Text Available Abstract in spanish Se describen restos del género Hippidion procedentes de la zona del desierto de Atacama (Calama, Segunda Región de Chile). El conjunto analizado corresponde a un esqueleto bastante completo proveniente del yacimiento Betecsa 1, así como escasas unidades del yacimiento Kamac Mayu. En ambos sitios se identifica H. saldiasi. A partir de dos dataciones radiométricas por AMS del ejemplar estudiado, los restos se sitúan estratigráficamente en el Pleistoceno Superior (21.0 (more) 70 ± 100 AP y 21.380 ± 100 14C AP). Se infieren datos ambientales y de dieta a partir de análisis de isótopos estables en los restos de Hippidion saldiasi del sitio Betecsa 1 cuyo valor de ?13C en hueso fue de -15,45 y el valor en esmalte de dientes fue de -16,68, sugiriendo una alimentación con pastos C3. El cráneo recuperado es el primero conocido de esta especie Abstract in english This paper describes the Hippidion bones recovered from the Atacama Desert (Calama, Second Region of Chile). The analyzed assemblage corresponds to a nearly complete skeleton from Betecsa 1 site and more poorly preserved remains from Kamac Mayu site. In both H. saldiasi is identified. Two 14C radiometric determinations indicate late Pleistocene age for these remains (21,070 ± 100 BP and 21,380 ± 100 BP). Environmental and diet inferences from stable isotope analysis are (more) also presented. The ?13C value from Betecsa 1 horses (-15.45 from bone sample and -16.68 from enamel sample) suggest a dietary adaptation exclusively C3 feeders. This is the first skull and associated skeleton recovered of this species

ALBERDI, MARÍA TERESA; PRADO, JOSÉ LUIS; LÓPEZ, PATRICIO; LABARCA, RAFAEL; MARTÍNEZ, ISMAEL

2007-06-01

160

Late Pleistocene (Rancholabrean) Glyptodont and Pampathere (Xenarthra, Cingulata) from Sonora, Mexico/ Gliptodonte y Pampaterio (Xenarthra, Cingulata) del Pleistoceno tardío (Rancholabreano) de Sonora, México  

Scientific Electronic Library Online (English)

Full Text Available Abstract in spanish Los yacimientos ricos en fósiles de Térapa (área centro-oriental de Sonora) contienen más de 60 taxon zoológicas, muchos con afinidades tropicales como Crocodylus (crocodrilo), Hydrochaeris (capibara), y muchas aves. Los depósitos contienen además la dermis ósea de oído (osteodermis) de dos xenartros extintos, un gliptodonte (Glyptotherium cylindricum) y un armadillo gigante (Pampatherium cf. mexicanum) (Mammalia, Xenarthra). También se han hallado restos de gli (more) ptodonte en otras localidades de Sonora menos estudiadas. Las faunas de estas localidades contienen además el género Bison, lo cual indica que los depósitos son del Rancholabreano (Rancholabrean Land Mammal Age), Pleistoceno tardío. La presencia de Pampatherium en Térapa y de Glyptotherium en Térapa y los sitios del Río Mayo/Río Yaqui representa el primer recuento publicado de estas especies en Sonora y extiende grandemente su distribución conocida durante el Rancholabreano, o pleistoceno tardío, en unos 1,100 kms hacia el noroeste de México. Abstract in english The fossil-rich deposits of Térapa (east-central Sonora) contain more than 60 zoological taxa, many with tropical affinities such as Crocodylus (crocodylian), Hydrochaeris (capybara), and many birds. The deposits also contain the dermal ossicles (osteoderms) of two extinct xenarthrans, a glyptodont (Glyptotherium cylindricum) and a pampathere (giant armadillo; Pampatherium cf. mexicanum). Glyptodont remains are also known from other less-well studied localities in Sonora (more) . The faunas from these localities also contain the genus Bison, which indicates that the deposits are of the Rancholabrean Land Mammal Age, late Pleistocene. The presence of Pampatherium at Térapa and the presence of Glyptotherium at Térapa and the Río Mayo/Río Yaqui sites represent the first published accounts of these species from Sonora, and greatly extends their known geographical distribution during the Rancholabrean by about 1,100 km into northwestern Mexico.

Mead, Jim I.; Swift, Sandra L.; White, Richard S.; McDonald, H. Greg; Baez, Arturo

2007-12-01

 
 
 
 
161

Marine paleoproductivity at warmer climate conditions during the Late Pliocene and Early Pleistocene in the Ross Sea  

Science.gov (United States)

The ice-uncovered Ross Sea, Antarctica, is a place with almost the highest bioproductivity rates in the Southern Ocean. In the past melting and collapse of large ice shelves caused highly variable conditions according to paleoproductivity in the McMurdo Sound (Ross Sea). The ANDRILL (Antarctic Geological Drilling) MIS deep drilling project (McMurdo Sound, NE Ross Ice Shelf, core AND-1B) drilled during austral summer 2006/2007 a well-preserved, outstanding record of approximately 14 million years of paleoclimate history. High-resolution geochemical data (XRF core scanning) and colour data (line scanning and reflectance measurements) in addition to quantitative chemistry data (e.g. opal, TOC and minor and major elements) and XRD on discrete samples were achieved. Colour data and XRF-CS counts are correlated to sample data to receive more and higher resolved information about the sediment composition. The interpretation of rapid paleoclimatic changes in the Antarctic realm, especially to understand the behaviour of the Ross Ice Shelf during the past million years, is one target of our study. From the Late Pliocene transitions from diamictite to diatomites are described which imply shifting from a retreating ice sheet to open marine conditions. The diatomites represent time spans with high bioproductivity and reflect warmer conditions at the Antarctic margin than today. The opal content increased to ~60-80% during 6 interglacials (151.70 - 224.45 mbsf). Within these interglacials, the paleoproductivity show variations that seem to be forced by small-scale climate variations.

Helling, D.; Kuhn, G.; von Eynatten, H.

2009-04-01

162

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

Energy Technology Data Exchange (ETDEWEB)

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.

Opdyke, N.D. (Univ. of Florida, Gainesville (United States))

1991-03-01

163

Palaeovegetation dynamics of an ecotone forest-savanna in southern Brazilian Amazon during the late Pleistocene and Holocene based on carbon isotopes of soil organic matter  

International Nuclear Information System (INIS)

This study was carried out in the Brazilian southern Amazon region (Rondonia state and Humaita, southern Amazon state). Carbon isotope data on soil organic matter have been collected along an ecosystem transect of about 750 km that includes a savanna, a wooded savanna (cerrado), a tropical semideciduous forest (cerradao), a forest transition type and a tropical forest. The main objective is to evaluate the expansion-regression dynamics of these vegetation units in relation to climate changes during the Late Pleistocene (Late Glacial) and Holocene. Large ranges in ?13 values were observed in soil organic matter collected from profiles in the savanna (-27 to -14 per mille and forest regions (-26 to -19 per mille) reflecting changing distribution of 13C-depleted C3 forest and 13C enriched C4 savanna vegetation in response to climate change. 14C data of humin fraction and buried charcoal indicate that the organic matter in these soils is at least 17,000 years BP at 300-cm depth. In this period, the entire ecosystem transect are characterized by ?13C soil depth profiles, generated typically by C3 plants (forest), inferring a humid climate in the southern Amazon region after the end of last glaciation. 13C data also indicate that C4 plants (grasses) have influenced significantly the vegetation at the transitional fthe cerrado sites of southern Rondonia state and two distinct points in the forest ecosystem in the southern Amazon state. These typical C4 type isotopic signatures probably reflect a drier climate during about 9000-8000 yr BP to 3000 yr BP and the savanna and wooded savanna expansion in distinct points of the transect. The 13C records representing the 3000 yr show an expansion of the forest, due to a climatic improvement, in areas previously occupied by savanna vegetation. This study adds to the mounting evidence that extensive forested areas existed in the Amazon during the last glacial and that savanna vegetation expanded in response to warm and dry conditions during the early to middle Holocene. (author)

2002-01-01

164

Cambrian Stratigraphy  

Science.gov (United States)

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

165

Potential Interference Among The Campanian Ignimbrite Eruption, Heinrich Event 4 and The Middle/upper Palaeolithic Shift In Late Pleistocene Europe  

Science.gov (United States)

The Campanian Ignimbrite (CI) eruption (Phlegraean Fields Caldera) was the largest volcanic eruption in the Greater Mediterranean area over the past 200 Ka (at least 150 km3 DRE). Ash layers correlated with CI have been found in sediments of the eastern Mediterranean Sea (Y5) and East Europe, from Italy to the former USSR. The recent dating of the CI eruption at 39.3 Ka BP draws attention to the coincidence be- tween this volcanic catastrophe and the suite of coeval biocultural modifications in Old World prehistory, here termed the European Late Pleistocene shift (ELPS). These included the Middle to Upper Palaeolithic cultural transition and the supposed change from Neanderthal to "modern" Homo sapiens anatomy, still a subject of sustained de- bate. The first results of our investigations show that: (1) at several archaeological sites of peninsular Italy a distinct tephra layer corresponding to the CI is regularly interbedded between the last documented Middle Palaeolithic and the earliest appear- ance of unquestionable Upper Palaeolithic assemblages; (2) at the same sites the CI tephra coincides with a interruption of occupation, several millennia long; (3) in the GISP2 Greenland ice-core, Lago Grande di Monticchio (southern Italy) lacustrine se- quences, and KET 8003 Tyrrhenian sea-core, a large volcanogenic sulfate signal (375 ppb, at 40,062 yr BP) to be correlated with the CI eruption and/or CI tephra layer occurs just before a sharp climatic shift which coincides with the onset of Heinrich event 4 (HE4). The concurrence of the CI eruption, Palaeolithic site abandonment and beginning of HE4 suggests that the overlapping of CI eruption and HE4 climatic im- pacts induced ecosystem crisis on a fairly large scale - human systems included - and well beyond the direct-impact zone. Moreover, the occurrence of the CI eruption just before HE4 probably corroborates the positive climate-volcanism feedback supposed for other high magnitude eruptions (e.g. Toba, 74 Ka). Without obviously claiming for the CI an overall evolutionary relevance within the ELPS, on the available data we nevertheless suggest that it deserves careful consideration as a contributing factor to the regional expression - or re-orientation - of cultural and population change.

Fedele, F. G.; Giaccio, B.; Isaia, R.; Orsi, G.

166

Geophysical Characterization of Late Pleistocene Coquina and Eolianite on Western Black Sea Coast of Turkey By Using Electrical Resistivity Tomography Survey  

Science.gov (United States)

Electrical resistivity tomography (ERT) survey was carried out in order to investigate the nature and subsurface geometry of cemented coquina and eolianite on western Black Sea coast of NW Turkey. The study area is located about 13 km west of the ?ile district of Istanbul in the Marmara Region. The coquinite beds lie ahead of a 150-m-long and 10-30 m-wide sandy beach and are backed by a coastal dune field that rests on carbonate cemented eolianite. Three coastline-parallel ERT transects were measured for imaging the subsurface structure of the studied coastal area. The first tomogram was taken along the wave swash zone where coquina beds are widely exposed. The second tomogram was obtained from the transition zone between the sandy beach and incipient foredunes in order to monitor the landward extension of coquina beds under the beach sands. Space limitation due to the width of the beach (maximum 15 m) did not allow the measuring of transects perpendicular to the coastline. Therefore, and because the beach is backed by Late Pleistocene eolianites encased in foredune sands, we obtained a third transect from the foredune area at the back to identify the resistivity difference between the eolianites and coquinite. First tomogram showed a large resistivity range varying between 1-900 ohm-m. Relatively high resistivity values observed at the beginning and end of the transect indicated that the exposed blocks are protrusions of a body of coquinite buried under the beach sands. On the other hand, lower values (500 ohm-m) rugged bedrock at the bottom. Second tomogram, obtained 13 m back from the first one, showed very similar subsurface patterns and revealed a landward extension of the coquinite beds under the beach sands. The thicknesses of the coquinite beds here are not more than 5 m, based on tomographic images. The last transect helped ensure the existence of coquinite beds under the beach sands. Unlike to the coquinite, the 3-8 m thick eolianite body showed very high resistivity values of between 400-900 ohm-m. The overlying coastal dune characterized by moderate resistivity values have a maximum thickness of 3 m and sand and clay levels were displayed in the lowermost part of the resistivity tomogram. Keywords: Coquina, Eolianite, Electrical Resistivity Tomography, Black Sea

Ekinci, Yunus Levent; Demirci, Alper; Ekinci, Rezzan; Evren Erginal, Ahmet

2013-04-01

167

Radiocarbon date on megafauna from the late Pleistocene-early Holocene of Córdoba province, Argentina: Stratigraphic and paleoclimatic significance/ Fechamiento por radiocarbono de megafauna del Peistoceno tardío-Holoceno temprano de la provincia de Córdoba, Argentina: significado estratigráfico y paleoclimático  

Scientific Electronic Library Online (English)

Full Text Available Abstract in spanish Se presenta el primer fechamiento por radiocarbono (7550 ± 60 yr 14C AP) para la provincia de Córdoba, obtenido a partir de colagéno presente en huesos de Scelidotherium leptocephalum, un perezoso terrestre extinto. Los materiales fósiles fueron exhumados de sedimentos asignados a la Formación La Invernada, en el Departamento de Río Cuarto, provincia de Córdoba, Argentina. Lafecha aquí presentada soporta la asignación temporal de la Formación La Invernada al Ple (more) istoceno tardío-Holoceno temprano y permite la correlación de estos sedimentos con los eventos climáticos que tuvieron lugar durante ese periodo. Asimismo, es uno de los fechamientos por radiocarbono más jóvenes de megamamíferos de Argentina. Abstract in english A radiocarbon date (7550 ± 60 yr 14C BP) was obtained from bone collagen of an extinct ground sloth (Scelidotherium leptocephalum) from the locality of Río Cuarto (Córdoba province, Argentina). The fossil remains were recovered from the La Invernada Formation (late Pleistocene- Holocene). The date presented in this paper is the first radiocarbon date obtainedfrom megafauna in Córdoba province, Argentina. It supports the temporal assignation of the La Invernada Formati (more) on to the late Pleistocene-early Holocene, and it will allow correlation of these sediments with climatic events that took place during this time. Moreover, it is the youngest radiocarbon date from megamammals recorded in central Argentina.

Cruz, Laura Edith; Bargo, María Susana; Tonni, Eduardo Pedro; Figini, Aníbal Juan

2010-12-01

168

Tendencias climáticas para los pastizales pampeanos durante el Pleistoceno tardío-Holoceno: estimaciones cuantitativas basadas en secuencias polínicas fósiles/ Climatic trends for the pampa grasslands during the late Pleistocene-Holocene: quantitative estimations based on fossil pollen sequences  

Scientific Electronic Library Online (English)

Full Text Available Abstract in spanish Se presentan los modelos de calibración polen-clima de temperatura media anual (Tan), precipitación anual (Pan) y eficiencia de la precipitación (EP) para la región de los pastizales pampeanos (33º-41ºS y 56º-67ºO). Los modelos de Pan y EP fueron óptimos (r² boot s=0,669 y 0,717 respectivamente; RMSEPboots= 16%) para obtener estimaciones cuantitativas aplicando la Técnica del Análogo Moderno a datos polínicos fósiles de dos sucesiones aluviales del Pleistoce (more) no tardío-Holoceno. En el centro de los pastizales los valores de Pan y EP fueron entre 100 y 200 mm menores a los actuales durante el Pleistoceno tardío (16.000-12.000 años cal AP) y similares a los actuales durante la transición Pleistoceno-Holoceno, el Holoceno temprano y el Holoceno tardío. En el sudoeste los valores de Pan y EP fueron c. 200 mm mayores a los actuales durante el Holoceno medio (5500-3000 años cal AP) y disminuyeron durante el Holoceno tardío alcanzando valores similares a los actuales durante los últimos 500 años cal. Las inferencias climáticas son coincidentes con las interpretaciones paleoclimáticas previas al señalar condiciones secas a semiáridas durante el Pleistoceno tardío y subhúmedas húmedas durante la transición Pleistoceno-Holoceno y el Holoceno temprano. Sin embargo, existen discrepancias a partir de 5000 años cal AP, probablemente por la diferente sensibilidad de los registros proxies de clima. El gradiente NE-SO de precipitación durante los últimos c. 5500 años cal habría sido más pronunciado que en la actualidad. Estas estimaciones son las primeras reconstrucciones climáticas cuantitativas para la región de los pastizales pampeanos, y deberían considerarse como tendencias hasta que nuevas reconstrucciones permitan su convalidación. Abstract in english Pollen-climate calibration models for mean annual temperature (Tan), annual precipitation (Pan) and precipitation efficiency (EP) are presented for the Pampa grasslands region (33º-41ºS and 56º-67ºW). The Pan and EP models were optimal (r²boots =0,669 and 0,717; RMSEPboots= 16%) to apply Modern Analog Technique and to obtain late Pleistocene-Holocene quantitative climatic estimations based on fossil pollen from two alluvial sequences. In the central Pampa grasslands, (more) Pan and EP values were 100 to 200 mm lower than present ones during the late Pleistocene (16000-12000 yr cal BP). During the Pleistocene- Holocene transition, early Holocene and late Holocene the values were similar to modern ones. In the southwest, Pan and EP values were c. 200 mm higher than present ones during the mid-Holocene (5500-3000 yr cal BP), and decreased during the late Holocene reaching similar modern values during the last 500 years cal. The climatic inferences agree with previous paleoclimatic interpretations that state dry to semiarid conditions during the late Pleistocene, and subhumid humid conditions during the Pleistocene-Holocene transition and early Holocene. However, there are discrepancies as from 5000 yr cal BP, probably related to the different sensitivity of the climate proxy data. The NE-SW precipitation gradient during the last c. 5500 yr cal may have been steeper than at present. These estimations are the first quantitative climatic reconstructions for the Pampa grasslands region, and should be taken as trends until new reconstructions confirm them.

Tonello, Marcela Sandra; Prieto, Aldo Raúl

2010-12-01

169

Contribution to the stratigraphy of the onshore Paraiba Basin, Brazil  

Energy Technology Data Exchange (ETDEWEB)

Several publications have contributed to improve the stratigraphy of the Paraiba Basin in northeastern Brazil. However, the characterization and distribution of sedimentary units in onshore areas of this basin are still incomplete, despite their significance for reconstructing the tectono- sedimentary evolution of the South American passive margin. This work provides new information to differentiate among lithologically similar strata, otherwise entirely unrelated in time. This approach included morphological, sedimentological and stratigraphic descriptions based on surface and sub-surface data integrated with remote sensing, optically stimulated luminescence dating, U+Th/He dating of weathered goethite, and heavy mineral analysis. Based on this study, it was possible to show that Cretaceous units are constrained to the eastern part of the onshore Paraiba Basin. Except for a few outcrops of carbonatic-rocks nearby the modern coastline, deposits of this age are not exposed to the surface in the study area. Instead, the sedimentary cover throughout the basin is constituted by mineralogically and chronologically distinctive deposits, inserted in the Barreiras Formation and mostly in the Post-Barreiras Sediments, of early/middle Miocene and Late Pleistocene-Holocene ages, respectively. The data presented in this work support tectonic deformation as a factor of great relevance to the distribution of the sedimentary units of the Paraiba Basin. (author)

Rossetti, Dilce F.; Valeriano, Marcio M., E-mail: rossetti@dsr.inpe.br [Instituto Nacional de Pesquisas Espaciais (INPE), Sao Jose dos Campos, SP (Brazil). Divisao de Sensoriamento Remoto; Goes, Ana M.; Brito-Neves, Benjamim B. [Universidade de Sao Paulo (USP), Sao Paulo, SP (Brazil). Inst. de Geociencias; Bezerra, Francisco H.R.; Ochoa, Felipe L. [Universidade Federal do Rio Grande do Norte (UFRN), Natal, RN (Brazil). Centro de Ciencias Exatas e da Terra. Departamento de Geologia

2012-06-15

170

Digital landscapes and Late Pleistocene environments of deglaciation: The use of LiDAR data to test outburst flood hypotheses of lowland river gorge formation  

Science.gov (United States)

We report on the quantitative interrogation of DEMs developed from airborne LiDAR data for the identification and reconstruction of Late Pleistocene glacial lake outburst floods (GLOFs). There is much importance attached to the quantification of geomorphic processes associated with deglaciation given global warming and current observations of rapidly melting glaciers and ice caps (e.g. Greenland). Given the period of direct observation is short, recourse can be made to the study of past ice sheets and associated landforms in order to reconstruct the rates and magnitudes of change during deglaciation. Meltwater channels, lakes and outflow channels are examples of landforms that can be used to identify the position, timing and retreat of former ice margins. With regards lake drainage there is a need to distinguish 'instantaneous' outburst floods from long term downcutting in order to improve our interpretations on the rates and magnitudes of geomorphic processes. There has been success in this regards at the megaflood scale but less attention has been paid to low magnitude outburst floods that can nevertheless have important regional implications for geomorphic processes. Here we use 5m DEMs and 2m resolution LiDAR data using ArcMap10, in combination with fieldwork, to investigate outflow channels in lowland environments of northern England, and develop methodological guidelines to aid the identification of GLOF events in previously glaciated landscapes. We identified a suite of distinguishing landforms from the 2m LiDAR data, not always identifiable in the 5m DEM, that indicate rapid erosion as opposed to long-term incision: 1) abandoned head cuts; 2) spillways representing sudden incision events once a downstream blockage has failed; 3) headcut extension of incised gorges upstream of the breach site; and 4) sedimentary deposits of 'chaotic' poorly sorted, water-lain sediments mapped at low elevations in the gorge; and run-up bars at higher elevations. All of these features are present in the River Till gorge, previously thought to be the outflow of Glacial Lake Milfield in northern England but here interpreted as a new drainage pathway resulting from an outburst event. Our reconstruction of the Till flood shows complex initial flow hydraulics with water flooding over undulating drumlin terrain. However once the gorge has incised we quantify palaeodischarges of between 2000-4000 m3/s, based on hydraulic modelling using the DEM-derived topography, with floodwater elevations delimited by terrace levels associated with incision phases (caused by the sudden failure of downstream blockages). This suggests that the 1.27 km3 lake took less than one week to drain, during this time eroding approximately 0.04 km3 of material from the gorge. We also briefly report on results from another UK site, the River Derwent outflow gorge of Glacial Lake Pickering.

Thorndycraft, Varyl; Cripps, Jonathan; Passmore, Dave; Oldknow, Christopher; Eades, Gwilym

2013-04-01

171

Size and shape stasis in late Pleistocene mammals and birds from Rancho La Brea during the Last Glacial-Interglacial cycle  

Science.gov (United States)

Conventional neo-Darwinian theory views organisms as infinitely sensitive and responsive to their environments, and considers them able to readily change size or shape when they adapt to selective pressures. Yet since 1863 it has been well known that Pleistocene animals and plants do not show much morphological change or speciation in response to the glacial-interglacial climate cycles. We tested this hypothesis with all of the common birds (condors, golden and bald eagles, turkeys, caracaras) and mammals (dire wolves, saber-toothed cats, giant lions, horses, camels, bison, and ground sloths) from Rancho La Brea tar pits in Los Angeles, California, which preserves large samples of many bones from many well-dated pits spanning the 35,000 years of the Last Glacial-Interglacial cycle. Pollen evidence showed the climate changed from chaparral/oaks 35,000 years ago to snowy piñon-juniper forests at the peak glacial 20,000 years ago, then back to the modern chaparral since the glacial-interglacial transition. Based on Bergmann's rule, we would expect peak glacial specimens to have larger body sizes, and based on Allen's rule, peak glacial samples should have shorter and more robust limbs. Yet statistical analysis (ANOVA for parametric samples; Kruskal-Wallis test for non-parametric samples) showed that none of the Pleistocene pit samples is statistically distinct from the rest, indicating complete stasis from 35 ka to 9 ka. The sole exception was the Pit 13 sample of dire wolves (16 ka), which was significantly smaller than the rest, but this did not occur in response to climate change. We also performed a time series analysis of the pit samples. None showed directional change; all were either static or showed a random walk. Thus, the data show that birds and mammals at Rancho La Brea show complete stasis and were unresponsive to the major climate change that occurred at 20 ka, consistent with other studies of Pleistocene animals and plants. Most explanations for such stasis (stabilizing selection, canalization) fail in this setting where climate is changing. One possible explanation is that most large birds and mammals are very broadly adapted and relatively insensitive to changes in their environments, although even the small mammals of the Pleistocene show stasis during climate change, too.

Prothero, Donald R.; Syverson, Valerie J.; Raymond, Kristina R.; Madan, Meena; Molina, Sarah; Fragomeni, Ashley; DeSantis, Sylvana; Sutyagina, Anastasiya; Gage, Gina L.

2012-11-01

172

Stable isotope systematics in Pleistocene deep-sea sediment records  

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The distribution of stable isotopes of oxygen and carbon in deep-sea sediments is a prime information carrier in paleoceanography. Isotope stratigraphies from deep-sea cores provide a tool for correlation, as well as an index for monitoring paleoclimate. Stable isotope systematics have been examined at several levels: 1) Data precision. Stable isotope data quality for a number of foraminifera species and size fractions is assessed by performing multiple analyses on subgroups of a given sample. Error measures have been determined which can be used to plan sampling. 2) Benthic mixing. Stratigraphic signals recovered from the deep-sea have been subjected to distortion from the activity of benthic organisms. A quantitative look at the effects of the mixing on the recovery of stratigraphic signals is presented. The unmixing problem, that is the problem of recovering high-frequency information lost in the mixing process, is also examined. A technique is developed, which allows determination of the benthic mixing parameters from certain stratigraphic relationships in multiple delta/sup 18/O signals. 3) Sedimentation rate nonlinearity. Spectral analyses are almost routinely performed on deep-sea delta/sup 18/O records, usually with the intent of finding climatic driving signals. This type of analysis assumes a linear sedimentation rate. Nonlinearity of sedimentation rate is examined at two levels. A long period (500 ka) dissolution cycle in the late Pleistocene is examined. It is demonstrated that this dissolution has affected stable isotopes and that considerable carbonate material has been dissolved.

Schiffelbein, P.A.

1984-01-01

173

Sobre la presencia de un supuesto Haplodontheriinae (Mammalia, Toxodontidae) en el Pleistoceno tardío de la provincia de Corrientes (Argentina) On the presence of an alleged Haplodontheriinae (Mammalia, Toxodontidae) from the late Pleistocene of the Corrientes province (Argentina)  

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Full Text Available En el extremo sur de Sudamérica se han postulado varias áreas que podrían haber actuado como reservorio de taxones supérstites, especialmente en el lapso Mioceno-Pleistoceno tardío ("Araucanense"-Lujanense). Así, en el Pleistoceno tardío (ca. 58-28 ka) de la provincia de Corrientes, Argentina, se ha reconocido la persistencia de ciertos taxones ya desaparecidos en la región pampeana de Argentina, particularmente entre los Xenarthra Glyptodontidae, Artiodactyla Cervidae y Notoungulata "Haplodontheriinae". Aquí se efectua una revisión con criterios taxonómicos modernos de los materiales (3 restos dentarios) asignados a Toxodontidae Haplodontheriinae, cuyos registros últimos en la región pampeana provienen del Montehermosense (Plioceno). El estudio comparado indica que los 2 "caniniformes" superiores derechos (CTES-PZ 1608, 1609) corresponden en realidad a un Xenarthra Phyllophaga (Lestodon), en tanto que el tercero (CTES-PZ 1610) debe ser asignado a un Notoungulata (Toxodon), ambos géneros típicos del Pleistoceno de América del Sur. Por último, las revisiones sistemáticas que se llevan a cabo son claves para refinar el registro paleontológico regional, y brindar un aporte fundamental al esquema bioestratigráfico en áreas extra-pampeanas.In southern South America, some regions have been postulated as containing supersite taxa, especially during the Miocene-late Pleistocene lapse. Thus, from the Late Pleistocene (ca. 58-28 ka) of the current territory of the Corrientes Province, Argentina, it has been recognized the presence of some taxa, which were extinct from the Pampean region of Argentina: Xenarthra Glyptodontidae, Artiodactyla Cervidae and Notoungulata "Haplodontheriinae". In this contribution, we carried out a review with modern taxonomic criteria of the materials belonging to Toxodontidae "Haplodontheriinae" (represented by 3 teeth), whose last record in the Pampean region corresponds to Montehermosan Age/Stage (Pliocene). The comparative study clearly shows that 2 of the 3 teeth (CTES-PZ 1608, 1609) belong to the Xenrthra Phyllophaga (Lestodon), whereas the other (CTES-PZ 1610) corresponds to the Notoungulata (Toxodon). Both genera are typical of the Pleistocene of South America. Finally, this kind of taxonomic revisions are essentials to depurate the regional paleontological record, and thus to provide a key contribution to the biostratigraphic scheme in extra-pampean areas.

Ángel R. Miño-Boilini; Alfredo E. Zurita; Mariano Bond; Analía Francia; Esteban Soibelzon

2012-01-01

174

Macroecological analyses support an overkill scenario for late Pleistocene extinctions Análises macroecológicas apoiam o cenário de sobreexploração para as extinções do final do Pleistoceno  

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Full Text Available The extinction of megafauna at the end of Pleistocene has been traditionally explained by environmental changes or overexploitation by human hunting (overkill). Despite difficulties in choosing between these alternative (and not mutually exclusive) scenarios, the plausibility of the overkill hypothesis can be established by ecological models of predator-prey interactions. In this paper, I have developed a macroecological model for the overkill hypothesis, in which prey population dynamic parameters, including abundance, geographic extent, and food supply for hunters, were derived from empirical allometric relationships with body mass. The last output correctly predicts the final destiny (survival or extinction) for 73% of the species considered, a value only slightly smaller than those obtained by more complex models based on detailed archaeological and ecological data for each species. This illustrates the high selectivity of Pleistocene extinction in relation to body mass and confers more plausibility on the overkill scenario.A extinção da megafauna no final do Pleistoceno tem sido tradicionalmente explicada por grandes mudanças climáticas ou pelo efeito de "sobreexploração" por parte dos primeiros caçadores (overkill). Apesar das dificuldades e controvérsias na distinção desses dois cenários não mutuamente exclusivos, a plausibilidade do cenário de sobreexploração pode ser avaliada por modelos de interação predador-presa. Neste estudo, demonstrou-se como um modelo macroecológico determinístico (isto é, utilizando parâmetros derivados de relações alométricas para diferentes espécies pode ser utilizado para avaliar a dinâmica das presas potenciais dos primeiros caçadores na América. Esse modelo previu corretamente o destino de 73% das espécies, valor apenas pouco inferior ao obtido por outros modelos mais complexos para o cenário. Isso ilustra a elevada seletividade do cenário de sobreexploração em relação ao tamanho do corpo e sua plausibilidade como explicação para as extinções da megafauna no final do Pleistoceno.

J. A. F. Diniz-Filho

2004-01-01

175

Macroecological analyses support an overkill scenario for late Pleistocene extinctions/ Análises macroecológicas apoiam o cenário de sobreexploração para as extinções do final do Pleistoceno  

Scientific Electronic Library Online (English)

Full Text Available Abstract in portuguese A extinção da megafauna no final do Pleistoceno tem sido tradicionalmente explicada por grandes mudanças climáticas ou pelo efeito de "sobreexploração" por parte dos primeiros caçadores (overkill). Apesar das dificuldades e controvérsias na distinção desses dois cenários não mutuamente exclusivos, a plausibilidade do cenário de sobreexploração pode ser avaliada por modelos de interação predador-presa. Neste estudo, demonstrou-se como um modelo macroecoló (more) gico determinístico (isto é, utilizando parâmetros derivados de relações alométricas para diferentes espécies pode ser utilizado para avaliar a dinâmica das presas potenciais dos primeiros caçadores na América. Esse modelo previu corretamente o destino de 73% das espécies, valor apenas pouco inferior ao obtido por outros modelos mais complexos para o cenário. Isso ilustra a elevada seletividade do cenário de sobreexploração em relação ao tamanho do corpo e sua plausibilidade como explicação para as extinções da megafauna no final do Pleistoceno. Abstract in english The extinction of megafauna at the end of Pleistocene has been traditionally explained by environmental changes or overexploitation by human hunting (overkill). Despite difficulties in choosing between these alternative (and not mutually exclusive) scenarios, the plausibility of the overkill hypothesis can be established by ecological models of predator-prey interactions. In this paper, I have developed a macroecological model for the overkill hypothesis, in which prey po (more) pulation dynamic parameters, including abundance, geographic extent, and food supply for hunters, were derived from empirical allometric relationships with body mass. The last output correctly predicts the final destiny (survival or extinction) for 73% of the species considered, a value only slightly smaller than those obtained by more complex models based on detailed archaeological and ecological data for each species. This illustrates the high selectivity of Pleistocene extinction in relation to body mass and confers more plausibility on the overkill scenario.

Diniz-Filho, J. A. F.

2004-08-01

176

Last straw versus Blitzkrieg overkill: Climate-driven changes in the Arctic Siberian mammoth population and the Late Pleistocene extinction problem  

Science.gov (United States)

A set of radiocarbon dates on woolly mammoth were obtained from several regions of Arctic Siberia: the New Siberian Islands ( n = 68), north of the Yana-Indigirka Lowland ( n = 43), and the Taimyr Peninsula ( n = 18). Based on these and earlier published dates ( n = 201) from the East Arctic, a comparative analysis of the time-related density distribution of 14 C dates was conducted. It was shown that the frequencies of 14 C dates under certain conditions reflect temporal fluctuations in mammoth numbers. At the end of the Pleistocene the number of mammoths in the East Arctic changed in a cyclic manner in keeping with a general "Milankovitch-like" trend. The fluctuations in numbers at the end of the Pleistocene occurred synchronously with paleoenvironmental changes controlled by global climatic change. There were three minima of relative mammoth numbers during the last 50?000 years: 22?000, 14?500-19?000, and 9500 radiocarbon years ago, or around 26?000, 16-20?000, and 10?500 calendar years respectively. The last mammoths lived on the New Siberian Islands, which were connected to the continent at that time, 9470 ± 40 radiocarbon years ago (10?700 ± 70 calendar years BP). This new youngest date approximates the extinction time of mammoths in the last continental refugium of the Holarctic. The adverse combination of environmental parameters was apparently a major factor in the critical reduction in mammoth numbers. The dispersal of humans into the Arctic areas of Siberia no later than 28?000 radiocarbon years ago did not overtly influence animal numbers. Humans were not responsible for the destruction of a sustainable mammoth population. The expanding human population could have become fatal to mammoths during strong the minima of their numbers, one of which occurred at the very beginning of the Holocene.

Nikolskiy, P. A.; Sulerzhitsky, L. D.; Pitulko, V. V.

2011-08-01

177

Using high-resolution stratigraphy and structural analysis to constrain polyphase tectonics in wedge-top basins: Inferences from the late Tortonian Scillato Basin (central-northern Sicily)  

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The present paper aims to show, both from a stratigraphic and structural points of view, the main features of a wedge-top syntectonic basin which evolved recording polyphase and non-coaxial tectonics. The study area is the Scillato Basin (SB), a roughly N-S-oriented structural depression located in the central-northern sector of the Sicililian Maghrebides. There, an approximately 1300 m-thick upper Serravallian to upper Tortonian succession of clastic units outcrops as a portion of the Neogene syntectonic covers of the Sicilian fold and thrust belt. Within the outcropping succession the upper Tortonian Terravecchia Fm represents the main topic of this paper. A multidisciplinary approach was carried out through an integration of sedimentology, facies, stratal pattern and structural analyses; this was applied to the formation enabling one to recognize in the Scillato Basin a fining to coarsening upward succession, deposited recording an early transgressive and a late regressive depositional stage. In our model these two main depositional stages developed and are directly relatable to a two-step structural evolution of the basin. During the first step, a NW-SE-oriented structural depression existed, enclosed between structural highs and accommodating the lower and middle portion of the upper Tortonian succession. Subsequently, during the second step, the NW-SE depression was non-coaxially deformed by superimposition of high-angle transpressive faults (many of which were SE-dipping), developed in response to the upward propagation of structures enucleated at deeper structural levels. This step was recorded in the basin by development of both depositional and structural interferences recognizable along the upper portion of the Scillato Basin succession. A comparison between field data and deep geophysical data interpreted at the preliminary stage, raises questions about the late Miocene geological evolution of this sector of the Sicilian chain, including: (i) the syn-tectonic deposition of the Terravecchia Fm. in the Scillato Basin clearly recorded the interference of two main and non-coaxial tectonic events; (ii) the younger of these two events has a clear tranpressional character and was active during the very late Tortonian; (iii) as also indicated by many authors in neighboring orogenic wedges, the main control on the location, geometry and depositional evolution of the Scillato wedge-top Basin was carried out by compressional and transpressional structures developed at a deeper structural level. Their deformation propagated upward both into the shallow structural level and sedimentary covers; therefore (iv) the late Miocene structural scenario here depicted is not consistent either with the back-arc-related extension or with the late orogenic gravitational collapse models previously invoked by other authors with regard to this sector of the Sicilian thrust belt.

Gugliotta, C.; Gasparo Morticelli, M.

2012-10-01

178

The Cassignol technique for potassium-argon dating, precision and accuracy: examples from the Late Pleistocene to Recent volcanics from southern Italy  

International Nuclear Information System (INIS)

A particular K-Ar technique, the Cassignol technique, has been developed in order to date Upper Pleistocene and Holocene volcanic rocks. We describe here its principles and its technology. The limit of detectability of the radiogenic Ar portion corresponds to an error of less than 103 a for K-rich minerals and a few 103 a for basalts. The reliability of the results and the validity of the correction for atmospheric contamination have been checked by analysing historical lavas and by comparison with data obtained from radiocarbon and thermoluminescence dating methods. The results demonstrate that the technique is capable of achieving K-Ar dates as young as 2000 a with a few centuries accuracy. A precision of ± 1.5% is obtained for samples older than 105 a. Moreover, in rocks older than 107a, the technique permits the accurate dating of minute amounts of pure separated mineral phases. A reconstruction of the recent volcano-tectonic evolution of the Naples area has been carried out. It allows us to establish a model for estimating volcanic hazards in the Phlegrean Fields. The dated terrestrial pyroclastic deposits have been recovered from cores collected in the central Tyrrhenian Sea. The land-sea correlations allow us to refine the chronology of the marine oxygen isotope records for the past 60,000 a. 59 refs.; 7 figs.; 5 tabs.

1986-01-01

179

Late Triassic - Early Jurassic successions of the Atuel depocenter: sequence stratigraphy and tectonic controls Sucesiones del Triásico Tardío - Jurásico Temprano del depocentro Atuel: estratigrafía secuencial y controles tectónicos  

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Full Text Available Biostratigraphic correlations of the Late Triassic - Early Jurassic successions of the Atuel depocenter allowed determining the accommodation changes and the possible tectonic controls on sedimentation. The Rhaetian - late Early Sinemurian deposits contain facies of slope-type fan deltas, braided fluvial systems and low sinuosity rivers with alternate bars deposited during a synrift phase. The late Early Sinemurian - Toarcian series host facies of intermediate (Gilbert to shelf) type fan deltas, braided and low sinuosity fluvial systems, wave-dominated estuaries, transgressive storm-dominated and turbidite-influenced marine shelves which record the sag phase. According to different criteria two stratigraphic schemes are proposed, the first one considering tectosedimentary units (TSU) and the second one using "Exxon-like" sequences. In the first scheme the synrift TSU matches the actual Precuyo Mesosequence and the sag TSU is partly equivalent to the Cuyo Mesosequence, mainly keeping the current mesosequence scheme for the Neuquén basin but assigning the fandeltaic deposits to the Precuyo Mesosequence. The second sequence scheme considers the whole Late Triassic - Early Jurassic succession as a part of the Cuyo Mesosequence, where the synrift deposits composes the detached lowstand system tract (LST) and most of the sag deposits makes the transgressive system tract (TST). The basal sequence boundary does not crop out, the flooding surface at the TST base and the maximum flooding surface at the TST top are respectively marked by the lowest estuarine levels and by black shales with suboxic-compatible bivalves (Bositra sp.).La correlación bioestratigráfica de las sucesiones del Triásico Tardío - Jurásico Temprano del depocentro Atuel permitió determinar los cambios del espacio de acomodación y los posibles controles tectónicos de la sedimentación. La sección del Retiano - Sinemuriano Temprano tardío contiene facies de abanicos deltaicos de talud, ríos entrelazados y ríos de baja sinuosidad con desarrollo de barras alternas, depositados durante una fase de sinrift. La sucesión del Sinemuriano Temprano tardío - Toarciano alberga facies de abanicos deltaicos intermedios (entre los de tipo Gilbert y los de plataforma), ríos entrelazados, ríos de baja sinuosidad, estuarios dominados por oleaje y plataformas marinas transgresivas (desde plataformas dominadas por tormentas hasta otras influídas por corrientes de turbidez), todos los cuales registran la fase de sag. Se proponen dos esquemas estratigráficos según diferentes criterios: el primero considerando unidades tectosedimentarias (TSU) y el segundo usando secuencias depositacionales (o de tipo "Exxon"). En el primer esquema la TSU de sinrift se corresponde con la Mesosecuencia Precuyo y la TSU de sag equivale parcialmente a la Mesosecuencia Cuyo, manteniendo en gran parte el esquema de mesosecuencias vigente para la cuenca Neuquina aunque asignando los depósitos de abanicos deltaicos a la Mesosecuencia Precuyo. En el segundo esquema se considera a toda la sucesión del Triásico Tardío - Jurásico Temprano como parte de la Mesosecuencia Cuyo, donde los depósitos de sinrift componen el cortejo de mar bajo (LST) y la mayoría de los depósitos de sag forman parte del cortejo transgresivo (TST). El límite de secuencia basal no aflora, la superficie de inundación en la base del TST y la superficie de máxima inundación en el tope del TST están marcados, respectivamente, por los niveles estuáricos más bajos y por las lutitas negras con bivalvos subóxicos (Bositra sp.).

Silvia Lanés; Laura Giambiagi; Florencia Bechis; Maisa Tunik

2008-01-01

180

Late Triassic - Early Jurassic successions of the Atuel depocenter: sequence stratigraphy and tectonic controls/ Sucesiones del Triásico Tardío - Jurásico Temprano del depocentro Atuel: estratigrafía secuencial y controles tectónicos  

Scientific Electronic Library Online (English)

Full Text Available Abstract in spanish La correlación bioestratigráfica de las sucesiones del Triásico Tardío - Jurásico Temprano del depocentro Atuel permitió determinar los cambios del espacio de acomodación y los posibles controles tectónicos de la sedimentación. La sección del Retiano - Sinemuriano Temprano tardío contiene facies de abanicos deltaicos de talud, ríos entrelazados y ríos de baja sinuosidad con desarrollo de barras alternas, depositados durante una fase de sinrift. La sucesión d (more) el Sinemuriano Temprano tardío - Toarciano alberga facies de abanicos deltaicos intermedios (entre los de tipo Gilbert y los de plataforma), ríos entrelazados, ríos de baja sinuosidad, estuarios dominados por oleaje y plataformas marinas transgresivas (desde plataformas dominadas por tormentas hasta otras influídas por corrientes de turbidez), todos los cuales registran la fase de sag. Se proponen dos esquemas estratigráficos según diferentes criterios: el primero considerando unidades tectosedimentarias (TSU) y el segundo usando secuencias depositacionales (o de tipo "Exxon"). En el primer esquema la TSU de sinrift se corresponde con la Mesosecuencia Precuyo y la TSU de sag equivale parcialmente a la Mesosecuencia Cuyo, manteniendo en gran parte el esquema de mesosecuencias vigente para la cuenca Neuquina aunque asignando los depósitos de abanicos deltaicos a la Mesosecuencia Precuyo. En el segundo esquema se considera a toda la sucesión del Triásico Tardío - Jurásico Temprano como parte de la Mesosecuencia Cuyo, donde los depósitos de sinrift componen el cortejo de mar bajo (LST) y la mayoría de los depósitos de sag forman parte del cortejo transgresivo (TST). El límite de secuencia basal no aflora, la superficie de inundación en la base del TST y la superficie de máxima inundación en el tope del TST están marcados, respectivamente, por los niveles estuáricos más bajos y por las lutitas negras con bivalvos subóxicos (Bositra sp.). Abstract in english Biostratigraphic correlations of the Late Triassic - Early Jurassic successions of the Atuel depocenter allowed determining the accommodation changes and the possible tectonic controls on sedimentation. The Rhaetian - late Early Sinemurian deposits contain facies of slope-type fan deltas, braided fluvial systems and low sinuosity rivers with alternate bars deposited during a synrift phase. The late Early Sinemurian - Toarcian series host facies of intermediate (Gilbert to (more) shelf) type fan deltas, braided and low sinuosity fluvial systems, wave-dominated estuaries, transgressive storm-dominated and turbidite-influenced marine shelves which record the sag phase. According to different criteria two stratigraphic schemes are proposed, the first one considering tectosedimentary units (TSU) and the second one using "Exxon-like" sequences. In the first scheme the synrift TSU matches the actual Precuyo Mesosequence and the sag TSU is partly equivalent to the Cuyo Mesosequence, mainly keeping the current mesosequence scheme for the Neuquén basin but assigning the fandeltaic deposits to the Precuyo Mesosequence. The second sequence scheme considers the whole Late Triassic - Early Jurassic succession as a part of the Cuyo Mesosequence, where the synrift deposits composes the detached lowstand system tract (LST) and most of the sag deposits makes the transgressive system tract (TST). The basal sequence boundary does not crop out, the flooding surface at the TST base and the maximum flooding surface at the TST top are respectively marked by the lowest estuarine levels and by black shales with suboxic-compatible bivalves (Bositra sp.).

Lanés, Silvia; Giambiagi, Laura; Bechis, Florencia; Tunik, Maisa

2008-12-01

 
 
 
 
181

A Late Pleistocene macrobenthic assemblage in Caleta Patillos, northern Chile: paleoecological and paleobiogeographical interpretations Un ensamble macrobéntico del Pleistoceno Tardío en Caleta Patillos, norte de Chile: interpretaciones paleoecológicas y paleobiogeográflcas  

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Full Text Available In the present study, we describe and analyze the structure of a Late Pleistocene (likely last interglacial) marine macrobenthic assemblage in Caleta Patillos (20°45'S, 70°12'W), northern Chile. A taphonomic analysis suggests the existence of a shallow subtidal paleonvironment, mainly soft-bottom, of high energy and intense mixing from several benthic habitats. The total number of 38 taxa recorded, mainly gastropods and bivalves, was not different than the ones reported in other Late Pleistocene assemblages in northern Chile. At a biogeographic scale, the composition of mo Husk species showed remarkable similarities with present-day fauna, and no extralimital species were recorded. At local scale, however, a comparison with the living assemblage in the same area of study showed a dramatic shift in the species' composition, a result that cannot be explained by sampling bias. A deep and perhaps very recent (i.e., at historical times) alteration of the structure of local macrobenthic assemblages is hypothesizedEn este trabajo se describe y analiza la estructura de un ensamble fósil marino macrobentónico del Pleistoceno Tardío (posiblemente último interglacial) en Caleta Patillos, norte de Chile (20°45'S, 70°12'O). Un análisis tafonómico sugiere la existencia de un ambiente de depositación submareal somero, primariamente de fondo blando, de alta energía, e intensa mezcla de especies desde varios tipos de habitats bentónicos. El total de 38 taxa identificados, correspondientes en su mayoría a especies de moluscos, gastrópodos y bivalvos, no fue distinto de lo registrado en otros ensambles pleistocénicos tardíos en el norte de Chile. A una escala biogeográfica, la composición del ensamble de moluscos mostró notables similitudes con la fauna actual, y no se registraron especies extralimitales. A una escala local, sin embargo, una comparación con el ensamble viviente en el mismo sitio de estudio mostró una dramática alteración en la composición de especies, un resultado que no puede ser explicado por sesgos de muestreo. Se plantea una profunda y quizás muy reciente (i.e., en tiempos históricos) alteración en la estructura de los ensambles macrobentónicos locales

Marcelo M Rivadeneira; Erico R Carmona

2008-01-01

182

A Late Pleistocene macrobenthic assemblage in Caleta Patillos, northern Chile: paleoecological and paleobiogeographical interpretations/ Un ensamble macrobéntico del Pleistoceno Tardío en Caleta Patillos, norte de Chile: interpretaciones paleoecológicas y paleobiogeográflcas  

Scientific Electronic Library Online (English)

Full Text Available Abstract in spanish En este trabajo se describe y analiza la estructura de un ensamble fósil marino macrobentónico del Pleistoceno Tardío (posiblemente último interglacial) en Caleta Patillos, norte de Chile (20°45'S, 70°12'O). Un análisis tafonómico sugiere la existencia de un ambiente de depositación submareal somero, primariamente de fondo blando, de alta energía, e intensa mezcla de especies desde varios tipos de habitats bentónicos. El total de 38 taxa identificados, correspo (more) ndientes en su mayoría a especies de moluscos, gastrópodos y bivalvos, no fue distinto de lo registrado en otros ensambles pleistocénicos tardíos en el norte de Chile. A una escala biogeográfica, la composición del ensamble de moluscos mostró notables similitudes con la fauna actual, y no se registraron especies extralimitales. A una escala local, sin embargo, una comparación con el ensamble viviente en el mismo sitio de estudio mostró una dramática alteración en la composición de especies, un resultado que no puede ser explicado por sesgos de muestreo. Se plantea una profunda y quizás muy reciente (i.e., en tiempos históricos) alteración en la estructura de los ensambles macrobentónicos locales Abstract in english In the present study, we describe and analyze the structure of a Late Pleistocene (likely last interglacial) marine macrobenthic assemblage in Caleta Patillos (20°45'S, 70°12'W), northern Chile. A taphonomic analysis suggests the existence of a shallow subtidal paleonvironment, mainly soft-bottom, of high energy and intense mixing from several benthic habitats. The total number of 38 taxa recorded, mainly gastropods and bivalves, was not different than the ones reported (more) in other Late Pleistocene assemblages in northern Chile. At a biogeographic scale, the composition of mo Husk species showed remarkable similarities with present-day fauna, and no extralimital species were recorded. At local scale, however, a comparison with the living assemblage in the same area of study showed a dramatic shift in the species' composition, a result that cannot be explained by sampling bias. A deep and perhaps very recent (i.e., at historical times) alteration of the structure of local macrobenthic assemblages is hypothesized

Rivadeneira, Marcelo M; Carmona, Erico R

2008-01-01

183

Paudorf locus typicus (Lower Austria) revisited – The potential of the classic loess outcrop for Middle to Late Pleistocene landscape reconstructions  

DEFF Research Database (Denmark)

The more than 12 m thick loess-paleosol sequence in Paudorf, Lower Austria, has been known for decades as locus typicus of the “Paudorfer Bodenbildung” (Paudorf paleosol). The upper section of the outcrop contains an up to 1 m thick pedocomplex that developed during MIS 5. The differentiated sequence of loess-like sediment below, including a more than 2 m thick pedocomplex in its basal part, is an exceptional archive of landscape evolution from the Middle Pleistocene. Herein we present detailed paleopedological and sedimentological surveys, as well as first micromorphological observations to address the sequence in its entirety and the processes leading to its genesis. Furthermore, high resolution color and carbonate analyses, as well as detailed texture analyses, have resulted in a substantial database. The studies show that the loess sediments were subject to a polygenetic development under periglacial conditions reflected in eolian silt and fine sand accumulation, admixture of local material during (mostly solifluidal) redeposition and in situ processes. Horizons with signs of pedogenesis, particularly the two pedocomplexes, document longer phases of stability; the stages of development can be correlated to equivalent sequences and seen as paleoclimatic signals where chronological data are available. The upper pedocomplex is a Chernozem of the early last glacial (MIS 5c–[a?]), which developed in a solifluidal redeposited (MIS 5d) interglacial Cambisol (MIS 5e). Cryosols, typical for MIS 6 sequences, are present in the loess sediment below. The lower pedocomplex formed during several warm stages of varying intensities, with interruptions caused by colluvial processes and admixture of eolian sediment during colder stages.

Sprafke, Tobias; Terhorst, Birgit

2013-01-01

184

Stratigraphy of the Harwell boreholes  

International Nuclear Information System (INIS)

[en] Seven boreholes, five of them partially cored, were drilled at the Atomic Energy Research Establishment at Harwell as part of a general investigation to assess the feasibility of storing low- and intermediate-level radioactive waste in underground cavities. Two of the deeper boreholes were almost wholly cored to provide samples for hydrogeological, hydrochemical, mineralogical, geochemical, geotechnical, sedimentological and stratigraphical studies to enable variations in lithology and rock properties to be assessed, both vertically and laterally, and related to their regional geological setting. This report describes the lithologies, main faunal elements and stratigraphy of the Cretaceous, Jurassic, Triassic and Carboniferous sequences proved in the boreholes. More detailed stratigraphical accounts of the late Jurassic and Cretaceous sequences will be prepared when current studies of the faunal assemblages are complete. (author)

1983-01-01

185

Computer sedimentary simulation models sequence stratigraphy  

Energy Technology Data Exchange (ETDEWEB)

Sedpak is a collection of integrated computer programs written in the C programming language, under the MIT X Window System and Motif, for a UNIX workstation environment. It is a graphical simulation program designed to aid in the analysis and classification of stratigraphic sequences derived from seismic and well data. It permits the extrapolation of facies and structure away from control, embodying the concepts and processes of sequence stratigraphy, for a wide variety of basins. Sedpak has been used for a variety of different depositional settings. This article describes the findings for the following: the Cretaceous/Tertiary of the South Carolina Coastal Plain, the Plio-Pleistocene of the Gulf of Mexico, the Neogene of the Canterbury basin of New Zealand, the Cretaceous of the Baltimore Canyon, and the Triassic Dolomite Alps of northern Italy.

Kendall, C.G.S.C.; Whittle, G.L.; Ehrlich, R.; Moore, P.D.; Cannon, R.L.; Hellmann, D.R. (Univ. of South Carolina, Columbia (United States))

1993-04-26

186

New evidence of the sabertooth cat Smilodon (Carnivora: Machairodontinae) in the late Pleistocene of southern Chilean Patagonia Nueva evidencia del gato dientes de sable Smilodon (Carnivora: Machairodontinae) en el Pleistoceno tardío de Patagonia meridional chilena  

Directory of Open Access Journals (Sweden)

Full Text Available Southern Patagonia is rich in late Pleistocene mammals, especially herbivores such as Camelids, Equids and Xenarthrans. Carnivores, on the other hand, are not commonly found in the paleontological record. One genus, Smilodon, is of particular interest because its presence in the region has not been demonstrated. In this paper, we present new fossil dental evidence that supports the presence of Smilodon populator (Lund) in the region. This evidence corresponds to the most southern record of the genus in the world, and the final step in the colonization of South America after the Great American Biotic Interchange. An AMS radiocarbon date on teeth indicates that the remains from Southern Chilean Patagonia are the most recent record for the genus in South America.Surpatagonia es particularmente rica en mamíferos finiplesitocenos, particularmente camélidos, équidos y xenartros. Los carnívoros, por su parte, se encuentran representados en menor número en el registro paleontológico. Dentro de estos, el género Smilodon, es de particular interés debido a que su presencia en la región no ha sido convincentemente demostrada. En este trabajo presentamos evidencia dental que permite confirmar la presencia de Smilodon populator (Lund) en la región. Esta evidencia corresponde al registro más sureño de este taxón y al paso final en la colonización de América del Sur después del Gran Intercambio Biótico Americano. Un fechado radiocarbónico directo AMS indica que los restos de Patagonia del Sur corresponden a los registros más tardíos para este género en el subcontinente.

ALFREDO PRIETO; RAFAEL LABARCA; VÍCTOR SIERPE

2010-01-01

187

Rapid Anthropogenic Response to Short-Term Local Aeolian and Fluvial Palaeoenvironmental Changes during the Late Pleistocene-Holocene Transition (at the Edge of the Northwestern Negev Dunefield, Israel)  

Science.gov (United States)

Several prehistoric camp sites, mainly attributed to the Natufian culture, were excavated over the past decades along Nahal Sekher on the eastern edge of Israel's northwestern Negev Desert dunefield. In this research we reconstruct the aeolian and fluvial environs of these sites by integrating field mapping, stratigraphic sections, particle-size analysis, sand spectroscopy, optically stimulated luminescence ages, and radiocarbon dates. Intermittent surface stabilization and aeolian deflation are hypothesized to explain the appearance of the Natufians who probably inhabited the region during the last main Negev dune encroachment in a windy palaeoenvironment. It is argued that the residual sequences of diagnostic low-energy fluvial fine-grained deposits (LFFDs) documented around the Natufian sites resemble the ephemeral event-layers of hyper-concentrated flow into the ever-emptying dryland-type reservoirs formed by dunes that dammed wadis. The location of the Natufian sites along the shorelines of these water bodies point to rapid but temporary anthropogenic responses to short-term and improved local palaeoenvironmental conditions during the Late Pleistocene-Holocene transition.

Roskin, Joel; Barzilai, Omry; Goring-Morris, Nigel; Katra, Itzhak; Porat, Naomi; Agha, Nuha; Boaretto, Elisabetta

2013-04-01

188

Diagenetic rejuvenation of raised coral reefs and precision of dating. The contribution of the Red Sea reefs to the question of reliability of the Uranium-series datings of middle to late Pleistocene key reef-terraces of the world  

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Full Text Available This paper is a general review of the dating of reefs on the coasts of the Red Sea, including those of Egypt, Jordan, Sudan, Eritrea, Saudi Arabia and Djibouti. New methods of sampling and dating (U/Th) already tested on the reefs and associate deposits of the African coast of Egypt have demonstrated that processes of rejuvenation shown to exist in the best-preserved corals are probably attributable to the diagenesis of the organic material in their bio-minerals, thus justifying a revision of a great many datings of corals supposedly younger or older than the age assigned to the high-level isotopic substage (?18O) MIS 5.5 (= 5e). During this late Pleistocene substage, a rapid lowering of sea level, short and limited to about ten meters, was detected and associated with a glacio-eustatic episode of global influence. A comparison of these Middle East reef chronologies with those of New Guinea, Australia and the western Atlantic that are referred only with difficulty to the ?18O global sea-level curves, casts doubt on the reliability of many regional reconstructions. Moreover the most "classic" reef chronologies, more or less out-of-phase with global isotopic records calls for a reexamination of the chronologic basis of the reference curves derived from marine isotopic data.

Plaziat Jean-Claude; Reyss Jean-Louis; Choukri Abdelmajid; Cazala Charlotte

2008-01-01

189

New evidence of the sabertooth cat Smilodon (Carnivora: Machairodontinae) in the late Pleistocene of southern Chilean Patagonia/ Nueva evidencia del gato dientes de sable Smilodon (Carnivora: Machairodontinae) en el Pleistoceno tardío de Patagonia meridional chilena  

Scientific Electronic Library Online (English)

Full Text Available Abstract in spanish Surpatagonia es particularmente rica en mamíferos finiplesitocenos, particularmente camélidos, équidos y xenartros. Los carnívoros, por su parte, se encuentran representados en menor número en el registro paleontológico. Dentro de estos, el género Smilodon, es de particular interés debido a que su presencia en la región no ha sido convincentemente demostrada. En este trabajo presentamos evidencia dental que permite confirmar la presencia de Smilodon populator (Lu (more) nd) en la región. Esta evidencia corresponde al registro más sureño de este taxón y al paso final en la colonización de América del Sur después del Gran Intercambio Biótico Americano. Un fechado radiocarbónico directo AMS indica que los restos de Patagonia del Sur corresponden a los registros más tardíos para este género en el subcontinente. Abstract in english Southern Patagonia is rich in late Pleistocene mammals, especially herbivores such as Camelids, Equids and Xenarthrans. Carnivores, on the other hand, are not commonly found in the paleontological record. One genus, Smilodon, is of particular interest because its presence in the region has not been demonstrated. In this paper, we present new fossil dental evidence that supports the presence of Smilodon populator (Lund) in the region. This evidence corresponds to the most (more) southern record of the genus in the world, and the final step in the colonization of South America after the Great American Biotic Interchange. An AMS radiocarbon date on teeth indicates that the remains from Southern Chilean Patagonia are the most recent record for the genus in South America.

PRIETO, ALFREDO; LABARCA, RAFAEL; SIERPE, VÍCTOR

2010-06-01

190

Pleistocene horses (genus Equus) in the central Balkans  

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Full Text Available A review of the fossil horses of the genus Equus from the central Balkans, a mountainous area comprising Serbia and Montenegro, is presented in this paper. The time period covered by the finds is from the late Early to and including the Late Pleistocene, but the record is not complete: the dated finds are Late Pleistocene in age, while Early and Middle Pleistocene are poorly represented. The horses found resemble those from neighbouring countries from the same time period, probably showing the importance of river valleys as migration routes. The Morava River valley runs in a roughly south-to-north direction, connecting, via the Danube and Tisa River valleys the Hungarian Pannonian Plain in the north with northern Greece in the south, via the Vardar River valley in Macedonia. In Pleistocene, large mammals, including horses, probably used this route for dispersal.

Forsten Ann; Dimitrijevi? Vesna M.

2003-01-01

191

Biochronology and biostratigraphy of the Uquía Formation (Pliocene early Pleistocene, NW Argentina) and its significance in the Great American Biotic Interchange  

Science.gov (United States)

The Uquía Formation crops out in the Quebrada de Humahuaca in Jujuy province, Eastern Cordillera, NW Argentina. This unit is composed of a sequence of fluviatile sediments and water-laid air-fall tuff beds; it is approximately 260 m thick and unconformably overlain by Pleistocene conglomerates and Quaternary alluvium. The sediments have been folded into a syncline and broken by several faults that generally trend northwest southeast. Following Castellanos stratigraphy, we characterize three units (Lower, Middle, and Upper) of the Uquía Formation. Biochronologically, the Lower Unit is assigned to the late Chapadmalalan, the Middle Unit (“Uquian fauna”) to the late Vorohuean and Sanandresian, and the Upper Unit to the Ensenadan. Biostratigraphic evidence provides a calibration of important biochronologic events in the Great American Biotic Interchange (GABI), namely, the first appearances of Erethizon, Hippidion, and proboscideans at 2.5 Ma (late Pliocene) in South America. Geological and paleobiological evidence suggest that during the late Pliocene, the area could have been a wide intermountain valley at 1400 1700 m elevation, with a more humid environment than that of the present day and some wet dry seasonality that permitted the coexistence of forest and open areas. Uquian mammals also indicate that northwestern Argentina and the Pampean region have represented distinct biogeographical areas since at least the late Pliocene.

Reguero, M. A.; Candela, A. M.; Alonso, R. N.

2007-01-01

192

Subsurface geology at the Lake Mikata and Nakayama lowlands, Fukui Prefecture, central Japan. Implications on the late pleistocene activity for the Mikata fault zone  

International Nuclear Information System (INIS)

The Lake Mikata and Nakayama lowlands are situated along the central coast of Wakasa Bay, at the center of the Japan Sea side of Honshu Island, and fringed by the Mikata fault zone at the east side. The 1662 Kanbun Great Earthquake (estimated magnitude of 7.2 to 7.6) occurred there with vertical crustal movements up to 3 to 4 meters. Submerged topography with thick alluvial deposits in the lowlands might have been caused by Late Quaternary crustal movements of the Mikata fault zone. We analyzed the subsurface geology of the lowlands using many drilling cores recently obtained for scientific purpose such as the 60-m long MK09 core and highway construction (represented by NEXCO core). The main results are summarized below. (1) Subsurface geology beneath the eastern basin and eastern coast of Lake Mikata is clarified by detailed investigations of many drilling cores up to 100 m deep including the NEXCO core. Many radiocarbon (14C) dating and tephrochronological correlations have elucidated the standard chronostratigraphy during the Late Quaternary in this area. At least 100-m thick sediments have deposited continuously for about 130 kyr, recording climatic and seismic events etc. during the last glacial period. (2) The MK09 core is composed of a repeated coarsening-upward sequence with rapid facies changes at unit boundaries. We infer that these units reflect the rapid rise of a relative level of a paleo-lake and subsequent progradation of alluvial fans. The mean interval of individual units is estimated to be about 7.7 kyr from the sedimentary age of each unit, and is considered to be an upper limit of the recurrence interval of the Mikata fault zone. (3) The Mikata fault is recognized for observations of new outcrops and core inspections at the northeastern part of the Nakayama lowland. The vertical displacement across the Mikata fault is inferred to be 30-35 m, and probably reached further after formation of a higher terrace. (4) The concealed Mikata fault extending N-S parallel to the Mikata fault on the east, is estimated from our drilling data. On the basis of the displacements of tephra horizons such as the Aira-Tn volcanic ash beds (AT) in deposits of the Nakayama lowland, it is possible that activity of this fault is equivalent to or larger than that of the Mikata fault. Further detailed studies by deeper drilling cores and seismic refraction surveys are required to clarify the E-W direction underground structure across the Mikata fault zone. They will unravel major development histories of this lowland with many datable materials. (author)

2010-01-01

193

Strontium isotope evidence for migration in late Pleistocene Rangifer: implications for Neanderthal hunting strategies at the Middle Palaeolithic site of Jonzac, France.  

Science.gov (United States)

In order to understand the behaviours and subsistence choices of Palaeolithic hunter-gatherers, it is essential to understand the behavioural ecology of their prey. Here, we present strontium isotope data from sequentially-sampled enamel from three reindeer (Rangifer tarandus ssp.) and a single bison (Bison cf. priscus) from the late Middle Palaeolithic site of Jonzac (Chez-Pinaud), France. The results are used to investigate the ranging and migratory behaviours of these important prey species. We found that the bison had isotope values most consistent with a local range, while the three reindeer had values indicating a seasonal migration pattern. Due to the similarity of the patterning of two of the three reindeer and in conjunction with zooarchaeological results, we suggest that they may have been from the same herd, were likely killed around the same point during their seasonal round and may therefore be the product of a single hunting event or a small number of successive hunting events. The isotope analyses complement the zooarchaeological data and have allowed greater insight into the palaeoecology of these species, the palaeoenvironment, and Neanderthal site use and hunting strategies. PMID:21497882

Britton, Kate; Grimes, Vaughan; Niven, Laura; Steele, Teresa E; McPherron, Shannon; Soressi, Marie; Kelly, Tegan E; Jaubert, Jacques; Hublin, Jean-Jacques; Richards, Michael P

2011-04-16

194

Strontium isotope evidence for migration in late Pleistocene Rangifer: implications for Neanderthal hunting strategies at the Middle Palaeolithic site of Jonzac, France.  

UK PubMed Central (United Kingdom)

In order to understand the behaviours and subsistence choices of Palaeolithic hunter-gatherers, it is essential to understand the behavioural ecology of their prey. Here, we present strontium isotope data from sequentially-sampled enamel from three reindeer (Rangifer tarandus ssp.) and a single bison (Bison cf. priscus) from the late Middle Palaeolithic site of Jonzac (Chez-Pinaud), France. The results are used to investigate the ranging and migratory behaviours of these important prey species. We found that the bison had isotope values most consistent with a local range, while the three reindeer had values indicating a seasonal migration pattern. Due to the similarity of the patterning of two of the three reindeer and in conjunction with zooarchaeological results, we suggest that they may have been from the same herd, were likely killed around the same point during their seasonal round and may therefore be the product of a single hunting event or a small number of successive hunting events. The isotope analyses complement the zooarchaeological data and have allowed greater insight into the palaeoecology of these species, the palaeoenvironment, and Neanderthal site use and hunting strategies.

Britton K; Grimes V; Niven L; Steele TE; McPherron S; Soressi M; Kelly TE; Jaubert J; Hublin JJ; Richards MP

2011-08-01

195

Late Pleistocene Panthera leo spelaea (Goldfuss, 1810) skeletons from the Czech Republic (central Europe); their pathological cranial features and injuries resulting from intraspecific fights, conflicts with hyenas, and attacks on cave bears  

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Full Text Available The world’s first mounted "skeletons" of the Late Pleistocene Panthera leo spelaea (Goldfuss, 1810) from the Sloup Cave hyena and cave bear den in the Moravian Karst (Czech Republic, central Europe) are compilations that have used bones from several different individuals. These skeletons are described and compared with the most complete known skeleton in Europe from a single individual, a lioness skeleton from the hyena den site at the Srbsko Chlum-Komín Cave in the Bohemian Karst (Czech Republic). Pathological features such as rib fractures and brain-case damage in these specimens, and also in other skulls from the Zoolithen Cave (Germany) that were used for comparison, are indicative of intraspecific fights, fights with Ice Age spotted hyenas, and possibly also of fights with cave bears. In contrast, other skulls from the Perick and Zoolithen caves in Germany and the Ur?ilor Cave in Romania exhibit post mortem damage in the form of bites and fractures probably caused either by hyena scavenging or by lion cannibalism. In the Srbsko Chlum-Komín Cave a young and brain-damaged lioness appears to have died (or possibly been killed by hyenas) within the hyena prey-storage den. In the cave bear dominated bone-rich Sloup and Zoolithen caves of central Europe it appears that lions may have actively hunted cave bears, mainly during their hibernation. Bears may have occasionally injured or even killed predating lions, but in contrast to hyenas, the bears were herbivorous and so did not feed on the lion carcasses. The articulated lion skeletons found in cave bear dens deep within caves scattered across Europe (such as those from the Sloup, Zoolithen and Ur?ilor caves) can therefore now be explained as being the result of lions being killed during predation on cave bears, either by the cave bears defending themselves or as a result of interspecific fights.

Diedrich C G

2011-01-01

196

Pleistocene To Holocene Human, Climatic and Environmental Changes In Central and Eastern Java (indonesia)  

Science.gov (United States)

The period between 21,000 and 6000 BP, which includes the Pleistocene-Holocene boundary, is likely to have known drastic environmental changes in the Indones ian archipelago, as seen from various sedimentary, pollen analytic, and archaeological records. In a low altitude swampy basin of central Java which yielded a thick clay and peat stratigraphy, several steps can be pointed between the driest period noticed prior 15,000 BP up to a climatic optimum c. 8,000 BP: a significant increase in humidity from c. 15,000 BP onwards, an extension of the forest after 10,500 BP, completion of almost everwet conditions c. 8,500 BP before a forest regression at c.6000 BP. Correlative excavations of the cave fillings near the coast of the Indian ocean, in the Southern Mountains of Java island, reflect conspicuous changes in the archaeological record: a more or less occasional human occupation of the caves during the late Plaistocene is followed by an intensive one in the early Holocene. Human groups, who brought new technologies (like sophisticated bone tools) had to adapt to and get their subsistence in an extending rain forest like environment, with a faunal turnover (Macaca and Presbytis dominance) or in the numerous flooded basins which formed during that period (fresh water molluscs gathering and smaller tortoise hunting). They carried out close contacts with the coastal area and used also the caves as burial places.

Sémah, A.-M.; Sémah, F.; Simanjuntak, H. T.

197

I depositi a vertebrati continentali del pleistocene della Calabria  

Directory of Open Access Journals (Sweden)

Full Text Available The inventory of Pleistocene mammal-bearing deposits of Calabria is reported, on the basis of the data available in the literature. Most of the deposits are represented by open-air sites, while cave deposits, always containing human artifacts too, are very scarce; this is to be referred to the lithology of the region, having few outcrops of carbonatic rocks. In many cases, precise informations on the stratigraphy and the composition of the faunal assemblages are lacking. A revision of the faunal assemblages is needed, also to better define times and modalities of the dispersal of the taxa to Sicily.

Mangano, G

2007-01-01

198

Carboniferous stratigraphy in Jingyuan, Gansu  

Energy Technology Data Exchange (ETDEWEB)

A guide book prepared for Excursion 3 of the 11th International Congress of Carboniferous Stratigraphy and Geology. Its purpose is to provide detailed explanation for the Carboniferous stratigraphy near the Ciyao Coal mine, Jingyuan district and Gansu province. Included in this book are 9 plates. 12 refs., 16 figs., 6 tabs.

Shen Guang-long; Wu An-bin; Tong Zhai-shan; Li Lan; Li Xing-xue; Wa Xiu-yuan; Pan Shui-Xian

1987-01-01

199

Interhemispheric correlation of late pleistocene glacial events  

Energy Technology Data Exchange (ETDEWEB)

A radiocarbon chronology shows that piedmont glacier lobes in the Chilean Andes achieved maxima during the last glaciation at 13,900 to 14,890, 21,000, 23,060, 26,940, 29,600, and {ge}33,500 carbon-14 years before present ({sup 14}C yr B.P.) in a cold and wet Subantarctic Parkland environment. The last glaciation ended with massive collapse of ice lobes close to 14,000 {sup 14}C yr B.P., accompanied by an influx of North Patagonian Rain Forest species. In the Southern Alps of New Zealand, additional glacial maxima are registered at 17,720 {sup 14}C yr B.P., and at the beginning of the Younger Dryas at 11,050 {sup 14}C yr B.P. These glacial maxima in mid-latitude mountains rimming the South Pacific were coeval with ice-rafting pulses in the North Atlantic Ocean. Furthermore, the last termination began suddenly and simultaneously in both polar hemispheres before the resumption of the modern mode of deep-water production in the Nordic Seas. Such interhemispheric coupling implies a global atmospheric signal rather than regional climatic changes caused by North Atlantic thermohaline switches or Laurentide ice surges. 51 refs., 3 figs., 1 tab.

Lowell, T.V. [Univ. of Cincinnati, OH (United States); Heusser, C.J. [Clinton Woods, Tuxedo, NY (United States); Andersen, B.G. [Univ. of Oslo (Norway)] [and others

1995-09-15

200

Análisis de las nomenclaturas y de los esquemas estratigráficos del Pleistoceno tardío-Holoceno en la cuenca del río Luján, Buenos Aires, Argentina/ Late Pleistocene- Holocene stratigraphic nomenclature and scheme analyses at the Luján River Basin, Buenos Aires, Argentina  

Scientific Electronic Library Online (English)

Full Text Available Abstract in spanish Los depósitos sedimentarios expuestos en las barrancas del río Luján en la ciudad homónima constituyen, para los estudios geológicos y paleontológicos del noreste de la región pampeana de Argentina, la localidad tipo del Cuaternario tardío. Las nomenclaturas y esquemas de ordenamiento estratigráfico propuestos a lo largo de más de un siglo, se han utilizado para correlacionar con otras sucesiones sedimentarias de Argentina, norte de Uruguay y sur de Brasil. Las (more) progresivas modificaciones y la creación de nuevos esquemas, han causado el caos estratigráfico actual. Con el objetivo de comprender el significado estratigráfico y la ubicación geocronológica de las unidades referidas al lapso Pleistoceno tardío - Holoceno, se realizó una revisión histórica de los antecedentes evaluando el significado de los términos asignados a las diferentes unidades. La información se ordenó en tres períodos, que comprenden los intervalos 1847-1920, 1920-1960 y 1995-2005. Se construyó una escala geocronométrica para establecer un marco temporal para los depósitos sedimentarios continentales y marinos, frecuentemente denominados Lujanense, Platense y Querandinense en la localidad tipo. Se analizó la validez actual de los términos y se propuso (1) abandonar las denominaciones estratigráficas formales e informales en uso para el sector (2) definir esquemas estratigráficos mediante la descripción de unidades depositacionales limitadas por discontinuidades, sus litofacies y diferencias faciales, (3) realizar dataciones numéricas y (4) evitar la creación de nomenclaturas estratigráficas que no cumplan con las normativas vigentes. Abstract in english The sedimentary deposits exposed in cutbanks along the Luján River are considered to be the late Quaternary type locality for geological and paleontological studies of the northeastern Pampas of Argentina. The stratigraphic nomenclatures and sequences proposed for over a century have been used to correlate with sedimentary successions from other regions of Argentina, north of Uruguay and south of Brazil. This long history abounds in mistakes and misinterpretations, and t (more) he result is evident in the current stratigraphic nomenclature 'chaos'. In order to understand the stratigraphic meaning and the geochronological placement of the units referring to the late Pleistocene-Holocene period, a critical historical study of the antecedents was carried out, evaluating the meaning of the terms assigned to the different units. The information is organized into three periods: 1847-1920, 1920-1960, and 1995-2005. A geochronometric scale that sets the temporal frame for the continental and marine deposits known as Lujanense, Platense and Querandinense in its type-locality was made. The validity of some of the terms currently in use was analyzed, and the following was proposed: (1) to leave behind the both formal and informal stratigraphic terms in use for the area, (2) to define stratigraphic schemes through the description of depositional units limited by unconformities, their lithofacies and facies differences (3) to carry out numerical dating and, (4) to avoid the creation of stratigraphical nomenclatures that are not in accordance with the current normatives.

Blasi, Adriana; Prieto, Aldo R.; Fucks, Enrique; Figini, Aníbal

2009-06-01

 
 
 
 
201

Contribution to the stratigraphy of the onshore Paraíba Basin, Brazil  

Directory of Open Access Journals (Sweden)

Full Text Available Several publications have contributed to improve the stratigraphy of the Paraíba Basin in northeastern Brazil. However, the characterization and distribution of sedimentary units in onshore areas of this basin are still incomplete, despite their significance for reconstructing the tectono-sedimentary evolution of the South American passive margin. This work provides new information to differentiate among lithologically similar strata, otherwise entirely unrelated in time. This approach included morphological, sedimentological and stratigraphic descriptions based on surface and sub-surface data integrated with remote sensing, optically stimulated luminescence dating, U+Th/He dating of weathered goethite, and heavy mineral analysis. Based on this study, it was possible to show that Cretaceous units are constrained to the eastern part of the onshore Paraíba Basin. Except for a few outcrops of carbonatic rocks nearby the modern coastline, deposits of this age are not exposed to the surface in the study area. Instead, the sedimentary cover throughout the basin is constituted by mineralogically and chronologically distinctive deposits, inserted in the Barreiras Formation and mostly in the Post-Barreiras Sediments, of early/middle Miocene and Late Pleistocene-Holocene ages, respectively. The data presented in this work support tectonic deformation as a factor of great relevance to the distribution of the sedimentary units of the Paraíba Basin.Várias publicações têm contribuído para melhorar a estratigrafia da Bacia Paraíba no nordeste do Brasil. Entretanto, a caracterização e distribuição das unidades sedimentares em áreas continentais desta bacia são ainda incompletas, apesar de sua importância para reconstruir a evolução tectono-sedimentar da margem passiva sulamericana. Este trabalho fornece novas informações para diferenciar entre estratos litologicamente similares que, por outro lado, não são relacionados no tempo. Esta abordagem incluiu descrições morfológica, sedimentológica e estratigráfica baseadas em dados de superfície e sub-superfície, integrada com sensoriamento remoto, datação por luminescência opticamente estimulada, datação de goetita intempérica por U+Th/He e análise de minerais pesados. Baseado neste estudo, foi possível mostrar que unidades cretáceas são restritas à parte leste da porção continental da Bacia Paraíba. Exceto por poucos afloramentos de rochas carbonáticas próximo da linha de costa atual, depósitos desta idade não são expostos à superfície na área de estudo. Ao invés disto, a cobertura sedimentar ao longo da bacia é constituída por depósitos mineralogicamente e cronologicamente distintos, inseridos na Formação Barreiras e, principalmente, nos Sedimentos Pós-Barreiras, de idade eo/mesomiocena e pleistocena tardia-holocena, respectivamente. Os dados apresentados neste trabalho suportam deformação tectônica como um fator de grande relevância na distribuição das unidades sedimentares da Bacia Paraíba.

Dilce F. Rossetti; Ana M. Góes; Francisco H.R. Bezerra; Márcio M. Valeriano; Benjamim B. Brito-Neves; Felipe L. Ochoa

2012-01-01

202

Contribution to the stratigraphy of the onshore Paraíba Basin, Brazil  

Scientific Electronic Library Online (English)

Full Text Available Abstract in portuguese Várias publicações têm contribuído para melhorar a estratigrafia da Bacia Paraíba no nordeste do Brasil. Entretanto, a caracterização e distribuição das unidades sedimentares em áreas continentais desta bacia são ainda incompletas, apesar de sua importância para reconstruir a evolução tectono-sedimentar da margem passiva sulamericana. Este trabalho fornece novas informações para diferenciar entre estratos litologicamente similares que, por outro lado, nã (more) o são relacionados no tempo. Esta abordagem incluiu descrições morfológica, sedimentológica e estratigráfica baseadas em dados de superfície e sub-superfície, integrada com sensoriamento remoto, datação por luminescência opticamente estimulada, datação de goetita intempérica por U+Th/He e análise de minerais pesados. Baseado neste estudo, foi possível mostrar que unidades cretáceas são restritas à parte leste da porção continental da Bacia Paraíba. Exceto por poucos afloramentos de rochas carbonáticas próximo da linha de costa atual, depósitos desta idade não são expostos à superfície na área de estudo. Ao invés disto, a cobertura sedimentar ao longo da bacia é constituída por depósitos mineralogicamente e cronologicamente distintos, inseridos na Formação Barreiras e, principalmente, nos Sedimentos Pós-Barreiras, de idade eo/mesomiocena e pleistocena tardia-holocena, respectivamente. Os dados apresentados neste trabalho suportam deformação tectônica como um fator de grande relevância na distribuição das unidades sedimentares da Bacia Paraíba. Abstract in english Several publications have contributed to improve the stratigraphy of the Paraíba Basin in northeastern Brazil. However, the characterization and distribution of sedimentary units in onshore areas of this basin are still incomplete, despite their significance for reconstructing the tectono-sedimentary evolution of the South American passive margin. This work provides new information to differentiate among lithologically similar strata, otherwise entirely unrelated in time (more) . This approach included morphological, sedimentological and stratigraphic descriptions based on surface and sub-surface data integrated with remote sensing, optically stimulated luminescence dating, U+Th/He dating of weathered goethite, and heavy mineral analysis. Based on this study, it was possible to show that Cretaceous units are constrained to the eastern part of the onshore Paraíba Basin. Except for a few outcrops of carbonatic rocks nearby the modern coastline, deposits of this age are not exposed to the surface in the study area. Instead, the sedimentary cover throughout the basin is constituted by mineralogically and chronologically distinctive deposits, inserted in the Barreiras Formation and mostly in the Post-Barreiras Sediments, of early/middle Miocene and Late Pleistocene-Holocene ages, respectively. The data presented in this work support tectonic deformation as a factor of great relevance to the distribution of the sedimentary units of the Paraíba Basin.

Rossetti, Dilce F.; Góes, Ana M.; Bezerra, Francisco H.R.; Valeriano, Márcio M.; Brito-Neves, Benjamim B.; Ochoa, Felipe L.

2012-06-01

203

Paleomagnetic Results From the Pleistocene Sediments of Lomonosov Ridge, Central Artic Ocean, IODP Leg 302  

Science.gov (United States)

Two major conclusions can be drawn from magnetic studies of Pleistocene sediments drilled on Lomonosov Ridge, central Arctic Ocean during IODP Leg 302. The first conclusion is that central Arctic Ocean sedimentation rates approach 2 cm/ka during the Pleistocene, thereby resolving the Arctic sedimentation rate controversy in favor of "fast" rates. The second conclusion is that abundant broad intervals of reversed polarity during the Pleistocene are a consistent characteristic of Arctic sedimentary records. These broad reversed intervals have helped perpetuate the Arctic sedimentation rate controversy. The weight of evidence strongly indicates that these reversal intervals are excursions. They do not occur during the late Brunhes Epoch (approximately 0-250,000 BP), but occur during the mid to lower Brunhes Epoch and persist into the upper Matuyama Epoch. We observe a strong correlation between rock magnetic variations, color changes, and physical property stratigraphy and these excursions. The model for Arctic sedimentation indicates that the excursions primarily occur during "interglacial" intervals. Previous high quality paleomagnetic studies of Bermuda Rise sediments have shown that approximately 85 % of Brunhes age excursions occur during interglacial periods (Lund, et al., 2001). In addition, similar excursions do not appear to occur at high southern latitudes (e.g. Acton, et al., 2002). For these reasons, we feel that hypotheses that attribute the interesting observed Arctic paleomagnetic behavior to environmental controls (e.g. sedimentation processes) are favored over those involving geomagnetic field behavior within the tangent cylinder. Acton, G. D., Guyodo, Y., and S. A. Brachfeld, 2002. Magnetostratigraphy of sediment drifts on the continental rise of West Antarctica (ODP Leg 178, Sites 1095, 1096, and 1101). In Barker, P. F., Camerlenghi, A., Acton, G. D., and Ramsay, A.T.S (Eds.), Proc. ODP Sci. Results, v. 178; 1-61 (CD ROM). Lund, S. P., G. D. Acton, B. Clement, M. Okada, and T. Williams. 2001. Brunhes chron magnetics excursions recovered from Leg 172 sediments. In Keigwin, L. D., Rio, D., Acton, G. D., and Arnold, E., (eds.) Proc. ODP Sci. Results, v. 172; p. 1-18 (Online)

King, J. W.; Heil, C.; O'Regan, M.; Moran, K.; Gattacecca, J.; Backman, J.; Jakobsson, M.; Moore, T.

2005-12-01

204

Una sucesión de paleosuelos superpuestos del pleistoceno medio - tardio, holoceno: Zona sur de La Plata, Provincia de Buenos Aires A succession of superposed paleosols (Middle-Late Pleistocene and Holocene) in the south area of La Plata. Argentina  

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Full Text Available Se estudia una sucesión (Pleistoceno medio-tardío y Holoceno) de 11 m de exposición, ubicada en un interfluvio plano de la zona sur de la ciudad de la Plata (34º55´ 00´´S y 57º57´30´´O). El objetivo del trabajo es analizar los procesos sedimentario-pedológicos acaecidos a fin de obtener: a) nuevas evidencias que permitan hacer consideraciones sobre el modelo sedimentario-pedológico propuesto por Teruggi e Imbellone (1987); b) correlacionar los eventos indicados en la descripción del perfil tipo en los diferentes frentes de exposición de la cantera, y c) correlacionar el contenido de vitroclastos con otros perfiles de la zona. En el perfil tipo se identifican 6 unidades constituidas por loess retrabajado y paleosuelos asociados con rasgos semejantes al de suelos actuales. La porción superior muestra cambios morfológicos más sutiles que la inferior hasta la base y correspondería a la Fm La Postrera y Fm Buenos Aires hasta 2,10 y 4,45 m de profundidad, respectivamente. Se identifican dos paleosuelos además del suelo actual separados por una superficie de erosión suave y discontinua, y una discontinuidad temporal insinuada p or cambios de color y características de las calcretas. A partir de 4,45 m de profundidad (Fm Ensenada) la sucesión refleja acontecimientos sedimentario-pedológicos identificables claramente en el campo y laboratorio. Se identifican tres paleosuelos superpuestos separados por superficies de erosión. Dos de ellas onduladas y acompañadas por concreciones de carbonato de calcio subparalelas a la superficie de erosión a 4,45 y 9,60 m, respectivamente, y otra totalmente planar a 7,30 m sólo interrumpida en su continuidad lateral por megacrotovinas. La variación lateral de las paleosuperficies muestra unidades de contactos concordantes, paralelos y subparalelos con escasa variación de espesores entre ellas. Los rasgos pedológicos con mayor variación entre uno y otro frente son los de carbonatación e hidromorfismo. La ciclicidad sedimentariopedológica está mejor definida en la base de la cantera. Toda la sección posee clases texturales arcillo limosas y franco limosas, y con característica de loess retrabajado. El intervalo modal es 62-31mm (limo grueso) y 62-125 mm (arena muy fina) con escasa representatividad de las subfracciones de mayor tamaño. La arena se incrementa en la mitad inferior de la sucesión por aumento de pseudopartículas. La micromorfología fue instrumental en la verificación de a) procesos pedogenéticos superpuestos de iluviación, hidromorfismo y carbonatación indicados por rasgos texturales, amorfos y cristalinos; b) presencia de biorasgos como pedotúblulos y fábrica excremental de fundamental importancia en procesos de bioturbación, y c) presencia de microestructura laminar, sedirelictos y pedorelictos que aseguran el carácter retrabajado del loess. En los paleosuelos inferiores la evidencia micromorfológica se corresponde con la observación de campo. En cambio, en los superiores los aparentes rasgos macroscópicos de iluviación pertenecerían a superficies de fricción muy finas en correspondencia con abundante fábrica plásmica poro, grano estriada y reticulada. El modelo clásico de sedimentación y pedogénesis episódica se aplicaría a los tres paleosuelos inferiores. Ellos están separados espacialmente en la columna sedimentaria, con el material originario identificable, y decapitados por una superficie de erosión. Se habrían desarrollado con aporte discontinuo de sedimentos y un período de pedogénesis suficiente para desarrollar un suelo maduro. En los paleosuelos superiores habría existido un aporte continuo o levemente discontinuo pero lento, que permitió la formación de rasgos pedológicos mientras el paisaje se elevaba acrecionalmente y se producía la superposición de pedogénesis.A 11-m deep pedological sedimentary succession (Middle-Late Pleistocene and Holocene) has been studied in a quarry exposure located on a flat interfluve, in the vicinity of La Plata airport, Argentina (34º55´00´´S y 5

Perla A Imbellone; Andrea Cumba

2003-01-01

205

Una sucesión de paleosuelos superpuestos del pleistoceno medio - tardio, holoceno: Zona sur de La Plata, Provincia de Buenos Aires/ A succession of superposed paleosols (Middle-Late Pleistocene and Holocene) in the south area of La Plata. Argentina  

Scientific Electronic Library Online (English)

Full Text Available Abstract in spanish Se estudia una sucesión (Pleistoceno medio-tardío y Holoceno) de 11 m de exposición, ubicada en un interfluvio plano de la zona sur de la ciudad de la Plata (34º55´ 00´´S y 57º57´30´´O). El objetivo del trabajo es analizar los procesos sedimentario-pedológicos acaecidos a fin de obtener: a) nuevas evidencias que permitan hacer consideraciones sobre el modelo sedimentario-pedológico propuesto por Teruggi e Imbellone (1987); b) correlacionar los eventos indicad (more) os en la descripción del perfil tipo en los diferentes frentes de exposición de la cantera, y c) correlacionar el contenido de vitroclastos con otros perfiles de la zona. En el perfil tipo se identifican 6 unidades constituidas por loess retrabajado y paleosuelos asociados con rasgos semejantes al de suelos actuales. La porción superior muestra cambios morfológicos más sutiles que la inferior hasta la base y correspondería a la Fm La Postrera y Fm Buenos Aires hasta 2,10 y 4,45 m de profundidad, respectivamente. Se identifican dos paleosuelos además del suelo actual separados por una superficie de erosión suave y discontinua, y una discontinuidad temporal insinuada p or cambios de color y características de las calcretas. A partir de 4,45 m de profundidad (Fm Ensenada) la sucesión refleja acontecimientos sedimentario-pedológicos identificables claramente en el campo y laboratorio. Se identifican tres paleosuelos superpuestos separados por superficies de erosión. Dos de ellas onduladas y acompañadas por concreciones de carbonato de calcio subparalelas a la superficie de erosión a 4,45 y 9,60 m, respectivamente, y otra totalmente planar a 7,30 m sólo interrumpida en su continuidad lateral por megacrotovinas. La variación lateral de las paleosuperficies muestra unidades de contactos concordantes, paralelos y subparalelos con escasa variación de espesores entre ellas. Los rasgos pedológicos con mayor variación entre uno y otro frente son los de carbonatación e hidromorfismo. La ciclicidad sedimentariopedológica está mejor definida en la base de la cantera. Toda la sección posee clases texturales arcillo limosas y franco limosas, y con característica de loess retrabajado. El intervalo modal es 62-31mm (limo grueso) y 62-125 mm (arena muy fina) con escasa representatividad de las subfracciones de mayor tamaño. La arena se incrementa en la mitad inferior de la sucesión por aumento de pseudopartículas. La micromorfología fue instrumental en la verificación de a) procesos pedogenéticos superpuestos de iluviación, hidromorfismo y carbonatación indicados por rasgos texturales, amorfos y cristalinos; b) presencia de biorasgos como pedotúblulos y fábrica excremental de fundamental importancia en procesos de bioturbación, y c) presencia de microestructura laminar, sedirelictos y pedorelictos que aseguran el carácter retrabajado del loess. En los paleosuelos inferiores la evidencia micromorfológica se corresponde con la observación de campo. En cambio, en los superiores los aparentes rasgos macroscópicos de iluviación pertenecerían a superficies de fricción muy finas en correspondencia con abundante fábrica plásmica poro, grano estriada y reticulada. El modelo clásico de sedimentación y pedogénesis episódica se aplicaría a los tres paleosuelos inferiores. Ellos están separados espacialmente en la columna sedimentaria, con el material originario identificable, y decapitados por una superficie de erosión. Se habrían desarrollado con aporte discontinuo de sedimentos y un período de pedogénesis suficiente para desarrollar un suelo maduro. En los paleosuelos superiores habría existido un aporte continuo o levemente discontinuo pero lento, que permitió la formación de rasgos pedológicos mientras el paisaje se elevaba acrecionalmente y se producía la superposición de pedogénesis. Abstract in english A 11-m deep pedological sedimentary succession (Middle-Late Pleistocene and Holocene) has been studied in a quarry exposure located on a flat interfluve, in the vicinity of

Imbellone, Perla A; Cumba, Andrea

2003-07-01

206

Aspectos sedimentológicos de arenas eólicas del Pleistoceno tardío-Holoceno de la provincia de La Pampa Sedimentologic aspects of eolian sands from the Late Pleistocene-Holocene of the La Pampa Province  

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Full Text Available El objetivo general de este trabajo es analizar la procedencia, génesis y dinámica de transporte de los depósitos eólicos arenosos del centro-este de la provincia de la Pampa. Para ello, se analizaron el marco geológico-geomorfológico y los aspectos estratigráficos de tres sectores considerados como sendos estudios de casos: cordón medanoso La Pastoril-Santa Isabel, cordón medanoso Toay y cordón medanoso General Acha. Estos cordones se caracterizaron sedimentológicamente (granulometría, mineralogía) a través del análisis de 20 muestras. Se identificaron dos unidades eólicas asociadas a dos ciclos de sedimentación, informalmente denominadas inferior (Pleistoceno tardío-Holoceno medio) y superior (originado por acción antrópica durante el siglo XX) relacionados con vientos del cuadrante O-NO en Santa Isabel y del S y SO en General Acha. Los resultados obtenidos sugieren que la topografía sería un factor de control importante en la distribución de los sedimentos, además de la distancia al sistema fluvial, que determinaría su tamaño de grano. Los análisis mineralógicos indicarían un aporte mixto de materiales, tanto distal (sistema fluvial del Bermejo-Desaguadero-Salado-Curacó), como local (afloramientos rocosos de la provincia).The main goal of this paper is to analyze the provenience of sandy eolian deposits of the central eastern part of La Pampa Province. Considering present eolian models proposed by different authors, the hypothesis tested in this paper is that eolian sediments are the result of deflation of alluvial deposits from the Bermejo-Desaguadero-Salado-Curacó fluvial system. With this purpose in mind, three case studies were selected (La Pastoril-Santa Isabel, Toay and General Acha) (Fig. 1). The analysis was made following the concept of spatial scale hierarchy which considered the geological and general environmental setting of the studied areas along with fundamental geomorphological features of the analyzed dune systems. This was complemented by the stratigraphic survey of selected sections from which 20 samples were collected for sedimentological analysis (grain-size and mineralogy). Also, due to the lack of information, three samples were collected from the present Desaguadero fluvial system for general characterization. At the regional scale two main geoforms were identified: an extensive plain and the paleovalley of the Desaguadero fluvial system. The plain grades eastward and includes several longitudinal depressions (longitudinal valleys). A sandy silt mantle is covering the plain, whereas the main dune system is located along the longitudinal depressions and the Desaguadero paleovalley (Fig. 1). In the three studied areas two eolian units, informally named lower and upper, were identified. These units, separated by a buried soil, were generated by winds from the W-NW in Santa Isabel and from the S and SW in General Acha. Wind directions coincide with present wind systems. The upper part of the lower unit is modified by the development of a buried soil showing an A-C horizon sequence. This soil is only buried in areas deeply affected by anthropic activities. Away from these impacted settings, the soil is on the present groundsurface. In Toay, fossil remains of Megatherium americanum were exhumed from the lowermost part of the sampled section which together with regional evidences indicate a late Pleistocene-Holocene age to the lower eolian unit. The upper eolian unit is also restricted to areas deeply modified by human activities, where the vegetation cover was removed and the sediments exposed to eolian reactivation. The occurrence of cultural artifacts (pieces of wire fences, plastic bags) as well as written documents suggest that this eolian reactivation occurred during the XXth century. Based on the stratigraphic results, the sedimentolo-gical analysis was focused on the lower eolian unit. In all three areas the eolian sediments are medium to fine sands with unimodal distribution, transported in saltation and modified saltation or short term suspe

Manuel Szelagowski; Marcelo A Zárate; Adriana M Blasi

2004-01-01

207

Reading Pleistocene eustasy in a tectonically active siliciclastic shelf setting (Crotone peninsula, southern Italy)  

Science.gov (United States)

Transgressive-regressive cycles are recognized in early to middle Pleistocene siliciclastic shelf sediments that crop out in the tectonically active Crotone basin (southern Italy). Chronological constraints from calcareous nannofossil biostratigraphy and magnetostratigraphy indicate that these cycles are synchronous with oxygen isotope stages 19 to 33 and hence with global sea-level fluctuations. A major facies break in the succession correlates with oxygen isotope stages 22 24, corresponding to the major mid-Pleistocene climatic shift. These findings indicate that Pleistocene eustatic oscillations can be recognized in the lithostratigraphy of a tectonically active siliciclastic shelf setting. By integrating biomagnetostratigraphy with physical stratigraphy, a highly resolved chronology can be developed for these settings similar to that available for deep-sea sediments.

Rio, D.; Channell, J. E. T.; Massari, F.; Poli, M. S.; Sgavetti, M.; D'Alessandro, A.; Prosser, G.

1996-08-01

208

Periglacial process and Pleistocene environment in northern China  

Energy Technology Data Exchange (ETDEWEB)

In the present time, five kinds of periglacial phenomena have been defined: ice wedges, periglacial involutions, congelifolds, congeliturbations, and loess dunes. From the stratigraphical and geochronological data, the periglacial process is divided into six stages. (1) Guanting periglacial stage, characterized by the congeliturbative deposits that have developed in early Pleistocene Guanting loess-like formation. Paleomagnetic dating gives 2.43 Ma B.P. (2) Yanchi periglacial stage, characterized by the congelifold that has developed in middle Pleistocene Yanchi Lishi loess formation. Paleomagnetic dating gives 0.50 Ma B.P. (3) Zhaitang periglacial stage (II), characterized by the periglacial involutions that have developed in lower middle Pleistocene Lishi loess formation. Paleomagnetic dating gives 0.30 Ma B.P. (4) Zhaitang periglacial state (I), characterized by the ice (soil) wedge that has developed in upper-middle Pleistocene Lishi loess formation. Paleomagnetic dating gives 0.20 Ma B.P. (5) Qiansangyu periglacial stage (II), characterized by the ice (sand) wedges that has developed in late Pleistocene Malan loess formation. Paleomagnetic dating gives 0.13 Ma B.P. (6) Qiansangyu periglacial stage (I), characterized by the ice (soil) wedge that has developed in late Pleistocene Malan loess-like formation. Thermoluminescent dating gives 0.018 Ma B.P. Spore-pollen composition analysis shows that the savannah steppe environment prevailed in northern China during Pleistocene periglacial periods. These fossilized periglacial phenomena indicate a rather arid and windy periglacial environment with a mean annual temperature estimated some 12-15C colder than that in the present.

Guo Xudong; Liu Dongsheng (Academia Sinica, Beijing (China)); Yan Fuhua (State Seismological Bureau, Beijing (China))

1991-03-01

209

Evaluation of the structure and stratigraphy over Richton Dome, Mississippi  

International Nuclear Information System (INIS)

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

1986-01-01

210

Rapid body size decline in Alaskan Pleistocene horses before extinction.  

Science.gov (United States)

About 70% of North American large mammal species were lost at the end of the Pleistocene epoch. The causes of this extinction--the role of humans versus that of climate--have been the focus of much controversy. Horses have figured centrally in that debate, because equid species dominated North American late Pleistocene faunas in terms of abundance, geographical distribution, and species variety, yet none survived into the Holocene epoch. The timing of these equid regional extinctions and accompanying evolutionary changes are poorly known. In an attempt to document better the decline and demise of two Alaskan Pleistocene equids, I selected a large number of fossils from the latest Pleistocene for radiocarbon dating. Here I show that horses underwent a rapid decline in body size before extinction, and I propose that the size decline and subsequent regional extinction at 12,500 radiocarbon years before present are best attributed to a coincident climatic/vegetational shift. The present data do not support human overkill and several other proposed extinction causes, and also show that large mammal species responded somewhat individualistically to climate changes at the end of the Pleistocene. PMID:14614503

Guthrie, R Dale

2003-11-13

211

Rapid body size decline in Alaskan Pleistocene horses before extinction.  

UK PubMed Central (United Kingdom)

About 70% of North American large mammal species were lost at the end of the Pleistocene epoch. The causes of this extinction--the role of humans versus that of climate--have been the focus of much controversy. Horses have figured centrally in that debate, because equid species dominated North American late Pleistocene faunas in terms of abundance, geographical distribution, and species variety, yet none survived into the Holocene epoch. The timing of these equid regional extinctions and accompanying evolutionary changes are poorly known. In an attempt to document better the decline and demise of two Alaskan Pleistocene equids, I selected a large number of fossils from the latest Pleistocene for radiocarbon dating. Here I show that horses underwent a rapid decline in body size before extinction, and I propose that the size decline and subsequent regional extinction at 12,500 radiocarbon years before present are best attributed to a coincident climatic/vegetational shift. The present data do not support human overkill and several other proposed extinction causes, and also show that large mammal species responded somewhat individualistically to climate changes at the end of the Pleistocene.

Guthrie RD

2003-11-01

212

Workshop on quantitative dynamic stratigraphy  

Energy Technology Data Exchange (ETDEWEB)

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)

Cross, T.A.

1988-04-01

213

A Re-appraisal of the Stratigraphy, Palaeontology and Dating of Cow Cave, Chudleigh, Devon, England  

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Full Text Available Cow Cave is an important Quaternary paleontological site in Chudleigh Gorge, Devon, UK., now known to have a sequence of cave-earths and stalagmite floors that range in age from Upper Middle Pleistocene (~MIS 7 interglacial) through to the Holocene (Flandrian) and the present day. Excavations in 1927-1934, and again in 1962-3, have provided a rich fauna, with some artefacts. Here, the stratigraphy of the deposits is now more fully described and the faunal remains are considered in their stratigraphical contexts. Data supporting the existence of former cave entrances are presented along with an analysis of the processes of sedimentation and taphonomy with their climatic interpretations. Based on recent U-Th dating of a critical Stalagmite horizon, a chronology of the mid-Pleistocene to Holocene sequence is discussed. Finally, further excavation in Cow Cave and nearby sites is recommended.

Simons Jim W.

2010-01-01

214

First record of coralline demosponges in the Pleistocene: implications for reef ecology  

Science.gov (United States)

We report the first discovery of coralline sponges from Pleistocene reef limestones of Vanuatu. Sponges of the genus Acanthochaetetes were identified from two reef terraces of Middle and Late Pleistocene age. As these sponges document cryptic habitats in modern coral reefs, they may be index fossils of cryptic habitats in the Pleistocene as well, thereby providing clues on growth conditions in fossil reefs. The small size of the discovered specimens may be attributed to the transient nature of their cryptic habitats, either due to reef growth or the occurrence of an unusual event.

Millet, J.; Kiessling, W.

2009-12-01

215

Volcanic stratigraphy and geological evolution of the Apan region, east-central sector of the Trans-Mexican Volcanic Belt  

Directory of Open Access Journals (Sweden)

Full Text Available The Apan region, which straddles the central and eastern sectors of the Trans-Mexican Volcanic Belt (TMVB), was geologically shaped by interrelated, intermittent tectonism and volcanism. The oldest volcanic rocks in the area were erupted about 13.5 Ma ago, followed by a nearly 10-million year volcanic hiatus. Volcanism in the area then resumed ~3.0-1.5 Ma; the most recent volcanic activity occurred in the late Pleistocene (~42-31 ka). The volcanic rocks in the Apan region range in composition from basalt to rhyolite (50-75 wt.% SiO2) and exhibit calc-alkaline affinity; their geochemical characteristics suggest that they are subduction-zone eruptive products. Detailed geologic and stratigraphic studies using a new digital 1:100 000 scale base map for compilation of new and previous data, coupled with new K-Ar age determinations, demonstrate that the loci of volcanic centers in the region were controlled largely by a system of NE-SW-trending normal faults and associated horst-and-graben structures, resulting from a stress field with a least principal stress (?3) oriented to the NW. Moreover, the results of this study, combined with a reexamination of geologic and age data from other investigations of the TMVB, make possible a refined correlation of the volcanic stratigraphy of the Apan region with the stratigraphic sequences of volcanic rocks in other areas of the TMVB. An important conclusion of our study is that volcanic activity in the TMVB was initiated during the Middle Miocene.

A. García-Palomo; J. L. Macías; G. Tolson; G. Valdez; J. C. Mora

2002-01-01

216

Registros de fluctuaciones paleobatimétricas del sistema lacustre Pueyrredon-Posadas-Salitroso durante el Pleistoceno Tardío? - Holoceno Temprano, noroeste de Santa Cruz, Argentina/ Register of paleobametric fluctuations of the Pueyrredon-Posadas-salitroso Lacustrine System during the Late Pleistocene? -Early holocene (Northwestern of Santa Cruz, Argentina  

Scientific Electronic Library Online (English)

Full Text Available Abstract in spanish El estudio de depósitos lacustres datados entre el Pleistoceno Tardío? - Holoceno Temprano vinculado con un modelo de elevación digital han permitido reconstruir la posición de las paleocostas del Sistema lacustre Pueyrredón - Posadas - Salitroso, demostrando la conexión entre ellos, que se verifica en algunos niveles específicos de paleocotas. En este trabajo, se utilizaron como indicadores paleobatimétricos: la ubicación altitudinal relativa de depósitos glaci (more) lacustres, depósitos de arenas costeras, depósitos de abanico deltaico en la margen sur del lago Pueyrredón, dataciones absolutas (AMS y 14C), trazas fósiles y comparaciones de malacofauna fósil con la actual para las interpretaciones paleoambientales. Abstract in english The palaeocoast line positions of the lacustrine system of Pueyrredón - Posadas - Salitroso lakes were determined through the study of the lacustrine deposits, which were dated between the Late Pleistocene? - Early Holocene, together with a digital elevation model (DEM). This has demonstrated the link among them verified on some specific palaeoheight levels. In this research, paleo-bathymetric geoindicators, as relative height of glaci-lacustrine, coastal sand and fandel (more) ta deposits onto the southern margin of Pueyrredon Lake, and absolute dating techniques (AMS & 14C), fossil trace and fossil and current malacofauna comparison were used in order to develop palaeoenvironment interpretations.

Horta, Luis R; Georgieff, Sergio M; Console Gonella, Carlos A; Busnelli, José; Aschero, Carlos A

2011-12-01

217

Cambios en lagos y circulación fluvial vinculados al calentamiento climático del Pleistoceno tardío-Holoceno temprano en Patagonia e isla 25 de mayo, islas Shetland del Sur, Antártida Changes in lakes and fluvial circulationlinked to climate warming in Late Pleistocene - Early Holocene in Patagonia and 25 de Mayo Island, Shetland del Sur Islands, Antarctica  

Directory of Open Access Journals (Sweden)

Full Text Available El calentamiento clim ático que afectó a la Patagonia en el Pleistoceno tardío-Holoceno temprano produjo cambios en la morfología del paisaje, incluyendo la génesis, desarrollo y desintegración de grandes lagos al este de los Andes. Hasta entonces, los glaciares y sus morenas formaban diques naturales que embalsaron las aguas de deshielo y mantenían alto el nivel de las aguas en los grandes paleolagos. Posteriormente, la migración hacia el sur de la mejoría climática ocasionó la progresiva fusión del campo de hielo regional, y las morenas fueron cortadas por la erosión fluvial, cuando el calentamiento climático impactó plenamente en la región. El proceso afectó a la región de norte a sur en tiempos diferentes: 1) hace c. 13.200 años en el norte, 2) durante la transición Pleistoceno/Holoceno en la parte central, y 3) finalmente, en Tierra del Fuego hace unos 7.800 años. El rápido retroceso de los glaciares produjo el desalojo de los valles andinos a ambos lados de la cordillera, lo cual abrió cauces fluviales que atraviesan la cordillera desde entonces, inaugurando el drenaje hacia el océano Pacífico de grandes lagos glaciales que existían al oriente de los Andes. Esto resultó en el rápido descenso del nivel de los paleolagos. Un proceso similar ocurrió en las islas Shetland del Sur (Antártida) hace unos 6.000 años.The climate warming that affected Patagonia region during late Pleistocene-early Holocene times produced changes in landscape morphology, including the formation, development, breakdown and disintegration of big lakes at the eastern side of Andes. Before these times, glaciers and their moraines formed natural dams that maintained a high water level in large paleolakes. The subsequent southward migration of climate amelioration produced the melting of the regional ice field, and moraines were cut by fluvial erosion, when climate warming strongly impacted in the region. The process occurred in the region from north to south at different times: 1) in the northern part c. 13,200 years ago, 2) in the central part during the Pleistocene/Holocene transition and 3) finally, in Tierra del Fuego c. 7,800 years ago. With the rapid retreat of glaciers from the Andean valleys during prominent regional deglaciation, outflow from the eastern side of Andes to the Pacific Ocean was formed. As a result, the water level in glacial paleolakes fell down rapidly in stages. A similar process occurred in South Shetland Islands (Antarctica) c. 6,000 years ago.

R.A. del Valle; A. Tatur; C.A. Rinaldi

2007-01-01

218

Sedimentología de unidades loéssicas (Pleistoceno tardío - Holoceno) del centro-sur de Santa Fe/ Sedimentology of loessic units (Late Pleistocene - Holocene) of the center-south of Santa Fe  

Scientific Electronic Library Online (English)

Full Text Available Abstract in spanish Se presenta una caracterización integral de las secuencias loess-paleosuelos aflorantes en un área típica de la Pampa Norte, basada en el análisis estratigráfico y en la variabilidad granulométrica y mineralógica. El estudio sedimentológico de detalle del loess fue practicado en dos perfiles del centro-sur de Santa Fe (Tortugas y Carcarañá). El loess está representado por la Fm Tezanos Pinto, integrada por dos miembros separados por una discordancia intraformac (more) ional (generados durante el Ultimo Máximo Glacial y el Pleistoceno tardío-Holoceno temprano, respectivamente). Esta unidad está coronada por un suelo parcialmente erodado, desarrollado durante el Período Hypsithermal. Una formación loéssica delgada (Fm San Guillermo; Holoceno tardío) yace sobre el suelo decapitado. La fracción granulométrica dominante de la Fm Tezanos Pinto en ambos perfiles es el limo (?70%), con participación subordinada de arena muy fina y arcilla. En general, el tamaño medio corresponde a la fracción limo entre 4 y 6 ?; con una tendencia granodecreciente y un mejoramiento del coeficiente de selección desde el miembro inferior hacia el superior. Las curvas de frecuencias acumuladas evidencian una subpoblación transportada por saltación y dos subpoblaciones de partículas asociadas a transporte por suspensión. Cada una de estas dos subpoblaciones representa entre el 30 y el 50% de la distribución. La población mayoritaria de minerales livianos de la fracción modal de arenas (125- 63µm) del loess aflorante en ambos perfiles está formada por materiales volcaniclásticos andinos aportados por vía eólica (cuarzo policristalino, microaglomerados, vidrio volcánico, fragmentos líticos y plagioclasas). La fuente minoritaria integra minerales provenientes del basamento cristalino de las Sierras Pampeanas, transportados y depositados por acción fluvial (cuarzo y feldespatos potásicos). El limo (63-4µm) está compuesto por cuarzo, con menor cantidad de feldespatos; la illita es el mineral arcilloso más abundante. En la arcilla ( Abstract in english An integral characterization of the outcropping loess-paleosols sequence in a type area of North Pampa is presented, based on the stratigraphic analyses and the grain size and mineralogic variability. Two loess profiles representative of interfluve areas of southern Santa Fe province were selected for detailed sedimentological analyses (Tortugas and Carcarañá Profiles). The loessic cover is part of the quaternary aeolian sedimentary body of the Argentine plain, defined (more) as "Pampean Aeolian System" by Iriondo (1990a) and Iriondo and Kröhling (1995). Both geomorphological and sedimentological systems compose the Pampean Aeolian System: a Sand Sea and a Peripheral Loess Belt. The Loess Belt, about 2,000 Km long and 250-300 Km wide in North Pampa, is located at the northeast of the Sand Sea. The sediments of the Pampean Aeolian System accumulated during the first stages of the last Pleistocene glaciation; later on they were partially reworked during successive dry phases and underwent pedogenesis in humid periods (Iriondo and Kröhling, 1995). The outcropping sedimentary sequence of the area is represented by fine aeolian units interbedded with buried soils. The Tezanos Pinto Fm (Iriondo, 1987) is the typical loessic unit of the North Pampa. In most places (Carcarañá Profile) it lays in erosive contact on a dissipation deposit of aeolian sand (Carcarañá Fm; Kröhling, 1999a). The loess is a loose deposit, silt with subordinated clay and very fine sand, light brown in colour. The loess thickness generally ranges from 4 to 10 m in the interfluves. The loess is a homogeneous, massive and permeable deposit. The sedimentary mass is calcareous; it contains powdery concentrations and hard concretions of CaCO3. The loess body is crossed by fine rhizoid ramified canalicula and very fine micropores of tubular forms. It is stable in steep walls, in parts altered by subcutaneous subfussion and shaped by columnar disjunc

Kröhling, Daniela; Orfeo, Oscar

2002-12-01

219

Sedimentología de unidades loéssicas (Pleistoceno tardío - Holoceno) del centro-sur de Santa Fe Sedimentology of loessic units (Late Pleistocene - Holocene) of the center-south of Santa Fe  

Directory of Open Access Journals (Sweden)

Full Text Available Se presenta una caracterización integral de las secuencias loess-paleosuelos aflorantes en un área típica de la Pampa Norte, basada en el análisis estratigráfico y en la variabilidad granulométrica y mineralógica. El estudio sedimentológico de detalle del loess fue practicado en dos perfiles del centro-sur de Santa Fe (Tortugas y Carcarañá). El loess está representado por la Fm Tezanos Pinto, integrada por dos miembros separados por una discordancia intraformacional (generados durante el Ultimo Máximo Glacial y el Pleistoceno tardío-Holoceno temprano, respectivamente). Esta unidad está coronada por un suelo parcialmente erodado, desarrollado durante el Período Hypsithermal. Una formación loéssica delgada (Fm San Guillermo; Holoceno tardío) yace sobre el suelo decapitado. La fracción granulométrica dominante de la Fm Tezanos Pinto en ambos perfiles es el limo (?70%), con participación subordinada de arena muy fina y arcilla. En general, el tamaño medio corresponde a la fracción limo entre 4 y 6 ?; con una tendencia granodecreciente y un mejoramiento del coeficiente de selección desde el miembro inferior hacia el superior. Las curvas de frecuencias acumuladas evidencian una subpoblación transportada por saltación y dos subpoblaciones de partículas asociadas a transporte por suspensión. Cada una de estas dos subpoblaciones representa entre el 30 y el 50% de la distribución. La población mayoritaria de minerales livianos de la fracción modal de arenas (125- 63µm) del loess aflorante en ambos perfiles está formada por materiales volcaniclásticos andinos aportados por vía eólica (cuarzo policristalino, microaglomerados, vidrio volcánico, fragmentos líticos y plagioclasas). La fuente minoritaria integra minerales provenientes del basamento cristalino de las Sierras Pampeanas, transportados y depositados por acción fluvial (cuarzo y feldespatos potásicos). El limo (63-4µm) está compuesto por cuarzo, con menor cantidad de feldespatos; la illita es el mineral arcilloso más abundante. En la arcilla (An integral characterization of the outcropping loess-paleosols sequence in a type area of North Pampa is presented, based on the stratigraphic analyses and the grain size and mineralogic variability. Two loess profiles representative of interfluve areas of southern Santa Fe province were selected for detailed sedimentological analyses (Tortugas and Carcarañá Profiles). The loessic cover is part of the quaternary aeolian sedimentary body of the Argentine plain, defined as "Pampean Aeolian System" by Iriondo (1990a) and Iriondo and Kröhling (1995). Both geomorphological and sedimentological systems compose the Pampean Aeolian System: a Sand Sea and a Peripheral Loess Belt. The Loess Belt, about 2,000 Km long and 250-300 Km wide in North Pampa, is located at the northeast of the Sand Sea. The sediments of the Pampean Aeolian System accumulated during the first stages of the last Pleistocene glaciation; later on they were partially reworked during successive dry phases and underwent pedogenesis in humid periods (Iriondo and Kröhling, 1995). The outcropping sedimentary sequence of the area is represented by fine aeolian units interbedded with buried soils. The Tezanos Pinto Fm (Iriondo, 1987) is the typical loessic unit of the North Pampa. In most places (Carcarañá Profile) it lays in erosive contact on a dissipation deposit of aeolian sand (Carcarañá Fm; Kröhling, 1999a). The loess is a loose deposit, silt with subordinated clay and very fine sand, light brown in colour. The loess thickness generally ranges from 4 to 10 m in the interfluves. The loess is a homogeneous, massive and permeable deposit. The sedimentary mass is calcareous; it contains powdery concentrations and hard concretions of CaCO3. The loess body is crossed by fine rhizoid ramified canalicula and very fine micropores of tubular forms. It is stable in steep walls, in parts altered by subcutaneous subfussion and shaped by columnar disjunction. Two members of the loess unit are differentiated i

Daniela Kröhling; Oscar Orfeo

2002-01-01

220

Reconstruction of pliocene-pleistocene ecological conditions of Western Transbaicalia  

Science.gov (United States)

The aim of this study is to examine paleoenvironmental conditions and soil evolution during the Late Pliocene and the Early -Middle Pleistocene in the Western Transbaikalia (Eastern Siberia, Russia). The basic objects of study are the palaeontologycal sites Udunga and Tologoy. Our researches based on pedohumic method (Dergacheva, 1997), when the pedogenic humus properties of site sediments analysed and used as the basis for reconstructing soil-forming processes. On the basis study of pliocene sediments of the Udunga site has revealed three different pedogenetic cycles, depending on water regime and duration of pedogenesis in subtropical environment. The stratigraphic section of the early -middle pleistocene part of the Tologoy site has 4 zones of pedogenesis that are distinguishable by pedogenic humus and other features, and consequently by the character of ancient soil forming processes. Climatic change trends both to humidity and to aridity, the landscape was similar to today, an environmental ?ombination of dry steppes, wetlands and alkaline areas.

Vashukevich, N. V.

2009-04-01

 
 
 
 
221

Pleistocene extinctions: haunting the survivors.  

UK PubMed Central (United Kingdom)

For many years, the megafaunal extinctions at the end of the Pleistocene have been assumed to have affected only those species that became extinct. However, recent analyses show that the surviving species may also have experienced losses in terms of genetic and ecological diversity.

Hofreiter M

2007-08-01

222

The Bishop ash bed (middle Pleistocene) and some older (Pliocene and Pleistocene) chemically and mineralogically similar ash beds in California, Nevada, and Utah  

Energy Technology Data Exchange (ETDEWEB)

Stratigraphic and mineralogical information and trace-element chemical data for a group of over 40 middle Pleistocene Bishop ash beds that occur at widely scattered localities in the Western US are presented. Seventeen newly determined K-Ar ages of the Bishop Tuff also are given. Trace-element chemical data and other information are tabulated for a group of ash beds that are chemically and mineralogically allied with the Bishop ash. These older ash beds occur in California, Nevada, and Utah, and probably formed in late Pliocene to early Pleistocene time during early volcanic stages of the evolutionary magmatic process that culminated in the eruption of the Bishop Tuff.

Izett, G.A.; Obradovich, J.D.; Mehnert, H.H.

1988-12-31

223

Contribution of stable isotopes (C,N,S) in collagen of late Pleistocene large mammal trophic ecology and landscape use: a case study in Goyet and Scladina cave (30-40,000 years BP)  

Science.gov (United States)

Two Belgian caves yielded very rich large mammal associations dating around 30 to 40,000 years ago: Goyet and Scladina cave (layer 1A). These sites are only 5 km apart but the cave entrances open on different valleys, in a quite diverse landscape ranging between open, unprotected uplands, steep cliffs and sheltered sun-exposed gorges, with the larger Meuse valley nearby. This mosaic scenery permitted during the Last Glacial a rich diversity of fossil flora and fauna. The faunal association includes a large diversity of taxa including Aurochs Bos primigenius, steppe bison Bison priscus, reindeer Rangifer tarandus, giant deer Megaloceros giganteus, horse Equus ferus, woolly rhinoceros Coelodonta antiquitatis, woolly mammoth Mammuthus primigenius, cave bear Ursus spelaeus, brown bear Ursus arctos, wolf Canis lupus, cave lion Panthera leo spelaea, and cave hyaena Crocuta crocuta spelaea. All the 90 studied bones and teeth yielded collagen with excellent collagen preservation, allowing reliable investigations of carbon, nitrogen and sulfur isotopic biogeochemistry. The combination of three different isotopic tracers allows to deciphering the effects of food selection and landscape use by different herbivorous and carnivorous taxa. This is the first study to include sulfur isotopic signatures in the study of late Quaternary large mammal palaeobiology. This new tracer yields evidence on mobility and differences in pasture areas, as different geological bedrock may exhibit various sulfur isotopic signatures that will pass on the herbivores and further on their predators. Using this feature in addition to the trophic information provided by carbon and nitrogen isotopic signatures, it appears that for some species present in both sites, such as horse and woolly rhinoceros, the individuals found in each site probably did not use the same pasture areas. This seems to also the case for the overwhelmingly vegetarian cave bears. In addition, individuals from the same species found in one site sometimes exhibit clear isotopic differences in the three isotopic tracers that suggest different pasture grounds as well, and therefore the possibility of different herds in the vicinity of the cave site. In the case of cave hyeanas, the isotopic signatures of individuals from both caves are not significantly different and suggest that these predators obtained their prey from a large territory including the pasture grounds of herbivores from both caves. In addition, direct radiocarbon dating of some of the studied collagen allows to investigating possible chronological trends. This study shows how new isotopic tracers can provide invaluable information on late Quaternary large mammal palaeobiology.

Bocherens, Hervé; Germonpré, Mietje

2010-05-01

224

Macro fossils vegetable in Palmar formation (later pleistocene) in Entre Rios - Argentina  

International Nuclear Information System (INIS)

This work is about the macro fossil knowledge preserved like wood fossils in the El Palmar Formation (Late Pleistocene) from a systematic - anatomical as well as paleoecological and paleoclimate point of view.The paleo Flora comes from various fossil located in the province of Entre Rios - Argentina

2012-01-01

225

The Murray Springs Clovis site, Pleistocene extinction, and the question of extraterrestrial impact  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Some of the evidence for the recent hypothesis of an extraterrestrial impact that caused late Pleistocene megafaunal extinctions [Firestone et al. (2007) Proc Natl Acad Sci USA 104:16016–16021] was based upon samples collected at Murray Springs, a Clovis archaeological site in southeastern Arizona. ...

Haynes, C. Vance; Boerner, J.; Domanik, K.; Lauretta, D.; Ballenger, J.; Goreva, J.

226

Análisis fitolítico de la Formación Tezanos Pinto (Pleistoceno tardío- Holoceno temprano) en el sector noroeste de su área de distribución en la provincia de Entre Ríos (Argentina)/ Phytolitic analysis of the Tezanos Pinto Formation (Late Pleistocene-early Holocene) in the northwestern sector of its distribution area, Provincia de Entre Ríos (Argentina)  

Scientific Electronic Library Online (English)

Full Text Available Abstract in spanish Los depósitos de loess son los componentes principales de las secuencias del Cuaternario Superior de la llanura pampeana (Sudamérica). La unidad loéssica generada durante el Ultimo Máximo Glacial a sotavento del Sistema Eólico Pampeano (Pampa Norte) representa un loess primario, indicando la expansión de condiciones semiáridas al noreste de dicho sistema. La Formación Tezanos Pinto es la unidad loéssica típica del Pleistoceno tardío - Holoceno temprano de la Pa (more) mpa Norte, caracterizada por su considerable continuidad espacial. En esta contribución se presentan los primeros resultados del análisis fitolítico del loess en el área noroeste de esta formación en la provincia de Entre Ríos. Las asociaciones fitolíticas analizadas presentaron una elevada homogeneidad con variaciones que permitieron su diferenciación cuantitativa a través de los perfiles analizados, mediante la presencia de fitolitos graminoides (de afinidad dantonioide, pooide-festucoide, chloridoide y panicoide), de palmeras, podostemáceas y ciperáceas. Estas variaciones posibilitaron reconocer la presencia de una estepa templada fría a templada con condiciones xéricas en los niveles basales, con episodios templados húmedos principalmente hacia las secciones medias y superiores. Abstract in english Loess deposits are the main component of the Late Quaternary sequences of Pampa plains (South America). The loess unit of the Last Glacial Maximum at the leeward side of the Pampean aeolian system represents primary loess, indicating the expansion of semiarid conditions to the NE of that system. The Tezanos Pinto Formation is the typical loessic unit of the late Pleistocene-early Holocene of North Pampa, characterized by its considerable spatial continuity. The first resu (more) lt of the phytolith analysis of the Tezanos Pinto Formation at the northwestern area of this formation in the Entre Ríos province is presented in this contribution. The analyzed phytolith assemblages show a high homogeneity with several variations that allowed their quantitative differentiation across the sedimentary sections. The presences of grass phytoliths jointly with palm, podostemoid and ciperoid elements allowed to realize this characterization. The association of danthoniod, pooid-festucoid, chloridoid and panicoid grass phytolith types described the presence of a cold temperate to temperate steppe with xeric conditions in the basal levels, with temperate episodes with major moistureprincipally in their middle and top sections.

Erra, Georgina; Zucol, Alejandro Fabián; Kröhling, Daniela Mariela

2011-12-01

227

On late Miocene abyssal hydrography  

International Nuclear Information System (INIS)

This contribution is a summary of the School's studies on late Miocene isotope stratigraphy. The authors interpret the results using simple models and present additional evidence that the delta13C shift at 6.2 Ma was a time-stratigraphic event. The average deep-water metabolic CO2 and nutrient content remained unchanged across the delta13C shift, but the net flow of deep waters towards the North Pacific was intensified. The late Miocene deep-ocean density structure was similar to that of today's oceans, and bottom water temperature were 10C warmer if constant ice volume is assumed. (Auth.)

1981-01-01

228

Pleistocene collapse of the west antarctic ice sheet  

UK PubMed Central (United Kingdom)

Some glacial sediment samples recovered from beneath the West Antarctic ice sheet at ice stream B contain Quaternary diatoms and up to 10(8) atoms of beryllium-10 per gram. Other samples contain no Quaternary diatoms and only background levels of beryllium-10 (less than 10(6) atoms per gram). The occurrence of young diatoms and high concentrations of beryllium-10 beneath grounded ice indicates that the Ross Embayment was an open marine environment after a late Pleistocene collapse of the marine ice sheet.

Scherer RP; Aldahan A; Tulaczyk S; Possnert G; Engelhardt H; Kamb B

1998-07-01

229

Late Miocene abyssal hydrography  

Energy Technology Data Exchange (ETDEWEB)

This contribution is a summary of the School's studies on late Miocene isotope stratigraphy. The authors interpret the results using simple models and present additional evidence that the delta/sup 13/C shift at 6.2 Ma was a time-stratigraphic event. The average deep-water metabolic CO/sub 2/ and nutrient content remained unchanged across the delta/sup 13/C shift, but the net flow of deep waters towards the North Pacific was intensified. The late Miocene deep-ocean density structure was similar to that of today's oceans, and bottom water temperature were 1/sup 0/C warmer if constant ice volume is assumed.

Bender, M.L.; Graham, D.W. (Rhode Island Univ., Kingston (USA). Graduate School of Oceanography)

1981-12-01

230

Cyclic stratigraphy and the significance of resolution  

Energy Technology Data Exchange (ETDEWEB)

The use of seismic data to interpret the stratal architecture of sediments has given new momentum to interpreting stratigraphy as cycles and/or sequences. Swept along with the new sequence stratigraphy is a genetic model indicates that these sequences are driven by sea level fluctuations. However, consideration of resolution of cycles (potential sequences) as observed in depth and over geologic time by different tools, points out several important constraints and limitations to sequence interpretations. (1) Geologic processes that create the sedimentary record occur over a wide frequency range, e.g., the geologic spectrum is broad. (2) All of the common tools used to interpret stratigraphy have limits of resolution of the geologic spectrum, e.g., tools are bandwidth limited. (3) The bandwidth limitations of these tools are not just a junction of the tools but of the geology, e.g., accumulation rates. (4) To properly associate particular cyclic events to a geologic process (and therefore create depositional models), the cyclicity of the geologic process should correspond to the cyclicity in the stratigraphy, e.g., absolute scale is important. (5) To match cyclicity in stratigraphy to geologic processes, it is best to observe much of the geologic spectrum by using a combination of interpretational tools.

Lopez, J.A. (Amoco Production Co., New Orleans, LA (USA))

1990-05-01

231

Sequence stratigraphy - a historical perspective  

Energy Technology Data Exchange (ETDEWEB)

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

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

1993-09-01

232

Eocene to Pleistocene lithostratigraphy, chronostratigraphy and tectono-sedimentary evolution of the Calama Basin, northern Chile Litoestratigrafía, cronoestratigrafía durante el Eoceno al Pleistoceno y evolución tectono-sedimentaria de la Cuenca de Calama, norte de Chile  

Directory of Open Access Journals (Sweden)

Full Text Available New 40Ar/39Ar radiometric, sedimentological and structural data from post-Paleocene sedimentary strata in the Calama Basin, northern Chile suggest that the established lithostratigraphy of the basin-fill requires revision. A new lithostratigraphic scheme for the Eocene-Pleistocene stratigraphy of the Calama Basin is proposed here. The key features of this scheme are that the existing Calama Formation is retained although the age of the formation is redefined as (?Lower) Eocene to (?)Lower Miocene. The El Loa Formation is elevated to group status and redefined as Lower Miocene to Upper Pliocene in age. The El Loa Group includes four newly defined formations: the Jalquinche, Opache, Lasana and Chiquinaputo formations. The existing definition of the uppermost unit within the Calama Basin, the Upper Pliocene to Pleistocene Chiu-Chiu Formation, is retained. The tectono-sedimentary evolution of the Calama Basin-fill reveals three distinct unconformity-bounded phases of sedimentation: Eocene-Oligocene, early Miocene to late mid-Miocene and late Miocene to late Pliocene. Sedimentation commenced in the Eocene with deposition of alluvial braidplain deposits (Calama Formation). This style of sedimentation occurred across northern Chile throughout the Oligocene following the Incaic Orogeny. From 22 Ma to 10 Ma ephemeral fluvial sediments were developed along the Calama Basin flanks (Lasana Formation), playa sandflat and mudflat deposits (Jalquinche Formation) in the basin centre. Equivalently-aged sediments in both the Salar de Atacama and Pampa del Tamarugal basins also indicate deposition in endorheic basins. Late Miocene sedimentation occurred diachronously across the north Chilean forearc. The Pampa del Tamarugal and Calama Basin areas were linked around 6 Ma following tectonic activity. Regional palustrine carbonate sedimentation occurred in the Calama Basin centre (Opache Formation) with fluvial sedimentation along the eastern basin margin (Chiquinaputo Formation). The change in depositional style is attributed to increased rainfall in drainage basins. At about 3 Ma the Calama Basin was subject to gentle folding, followed by entrenchment of the Río Loa and Río San Salvador through Miocene to Pliocene strata to reach a new base-level caused by breaching of the Coastal Cordillera by the Río Loa to reach the Pacific. Localised diatomite and evaporite (anhydrite) deposition took place in depressions created by either folding of older strata or geomorphic features (Chiu-Chiu Formation). Up to 5 unconformities are present in the Calama Basin-fill and occur across either the whole of the basin or localised areas of the basin. They are not present in adjacent basins which suggests they were generated by movement on the Precordilleran/West Fissure Fault Systems. Facies analysis of the Eocene to Pleistocene succession suggests that sedimentation took place under an arid/semi-arid climate throughout this time period. Occasional fluctuations in climate suggesting increased runoff are indicated by the development of diatomites together with lacustrine and palustrine limestones. However, it is unlikely that the climate was never more humid than semi-arid. Similar facies developments in the Pampa del Tamarugal and Salar de Atacama basins during the Oligocene to Pleistocene suggest that climate changes affected the whole of the forearc and were not restricted to individual basinsLos resultados obtenidos de estudios estructurales, sedimentológicos y dataciones radiométricas de las secuencias sedimentarias post Eoceno de la Cuenca de Calama, sugieren que la litoestratigrafía establecida para su relleno sedimentario, requiere una revisión. En este trabajo, se propone un nuevo esquema litoestratigráfico pos-Paleoceno para esta cuenca. Las características claves de este esquema son que la Formación Calama se mantiene aunque su edad es considerada como Eoceno Inferior (?) a Mioceno Inferior (?). La Formación El Loa es redefinida como Grupo y asignada al Mioceno Inferior-Plioceno Superior. Este Grupo incluiría la defi

Geoffrey May; Adrian J Hartley; Guillermo Chong; Fin Stuart; Peter Turner; Stephanie J Kape

2005-01-01

233

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

Science.gov (United States)

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.

Sheldon, Dane P. H.

234

La dieta y el hábitat del mamut y los caballos del Pleistoceno tardío de El Cedral con base en isótopos estables (?13C, ?18O)/ Diet and habitat of the late Pleistocene mamut and horses from El Cedral based on stable isotopes (?13C, ?18O)  

Scientific Electronic Library Online (English)

Full Text Available Abstract in spanish La dieta y el hábitat de Mammuthus columbi y de tres especies de Equus procedentes de El Cedral (San Luis Potosí, México) son inferidos a partir del análisis de isótopos estables de ?13C y ?18O en el apatito del esmalte dental. En el mamut, los valores de ?13C reflejan una dieta mixta C3/C4, mientras que los équidos tienen un intervalo que va desde individuos con una dieta mixta C3/C4 a aquéllos que sólo se alimentan de plantas C4. Las comparacio (more) nes realizadas entre los valores obtenidos de las muestras mexicanas con las publicadas para los mismos grupos de Florida, Nuevo México y Texas, señala que las preferencias alimentarias en ambos grupos eran parecidas. Asimismo, la comparación efectuada de los valores de ?13C junto con los de ?18O, para las especies de El Cedral con los valores de jabalíes, mastodontes, tapires y venados cola blanca del Pleistoceno tardío de Florida, revela que los caballos y el mamut de El Cedral habitaban en una zona abierta, como pastizales o sabanas, lo que concuerda con el estudio palinológico de la localidad. Abstract in english The diet and habitat for Mammuthus columbi and three species of Equus from El Cedral (San Luis Potosí, Mexico) were inferred from the analysis of stable isotopes, ?13C and ?18O, present in dental enamel apatite. For the mammoth, ?13C values indicate a mix C3/C4 diet, while the equids have a range of values from individuals feeding only a mix C3/C4 diet to those that ate exclusively C4 plants. Comparisons between values obtained for Mexican samples with (more) those published for the same groups from Florida, New Mexico, and Texas, point out to similar food habits in both groups. Also, comparisons of ?13C and ?18O values of the El Cedral species with those for javelinas, mastodonts, tapirs, and white-tailed deer from the Floridan late Pleistocene, showed that horses and mammoth from El Cedral lived in open spaces, with grasslands savanna, in accordance with the pollen studies for the locality.

Pérez-Crespo, Víctor Adrián; Sánchez-Chillón, Begoña; Arroyo-Cabrales, Joaquín; Alberdi, María Teresa; Polaco, Óscar J.; Santos-Moreno, Antonio; Benammi, Mouloud; Morales-Puente, Pedro; Cienfuegos-Alvarado, Edith

2009-08-01

235

Climate variability of the tropical Andes since the late Pleistocene  

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Full Text Available Available proxy records witnessing palaeoclimate of the tropical Andes are comparably scarce. Major implications of palaeoclimate development in the humid and arid parts of the Andes are briefly summarized. The long-term behaviour of ENSO has general significance for the climatic history of the Andes due to its impact on regional circulation patterns and precipitation regimes, therefore ENSO history derived from non-Andean palaeo-records is highlighted. Methodological constraints of the chronological precision and the palaeoclimatic interpretation of records derived from different natural archives, such as glacier sediments and ice cores, lake sediments and palaeo-wetlands, pollen profiles and tree rings are addressed and complementary results concerning former climatic conditions are discussed in terms of possible implications of former atmospheric circulation patterns and main climatic forcing factors. During the last years, increasing tree-ring information is getting available from the tropical Andes, providing high-resolution climate-sensitive records covering the past centuries for the study of climate variability.

A. Bräuning

2009-01-01

236

Assessing Holocene and late Pleistocene geomagnetic dipole field variability  

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Palaeomagnetic studies of continuous geological archives and archaeological artefacts are required to reconstruct geomagnetic field changes beyond the range of historical observations. In this thesis I assess the reliability of sedimentary palaeomagnetic data and Holocene dipole field reconstruction...

Nilsson, Andreas

237

Stable carbon cycle-climate relationship during the Late Pleistocene.  

UK PubMed Central (United Kingdom)

A record of atmospheric carbon dioxide (CO2) concentrations measured on the EPICA (European Project for Ice Coring in Antarctica) Dome Concordia ice core extends the Vostok CO2 record back to 650,000 years before the present (yr B.P.). Before 430,000 yr B.P., partial pressure of atmospheric CO2 lies within the range of 260 and 180 parts per million by volume. This range is almost 30% smaller than that of the last four glacial cycles; however, the apparent sensitivity between deuterium and CO2 remains stable throughout the six glacial cycles, suggesting that the relationship between CO2 and Antarctic climate remained rather constant over this interval.

Siegenthaler U; Stocker TF; Monnin E; Lüthi D; Schwander J; Stauffer B; Raynaud D; Barnola JM; Fischer H; Masson-Delmotte V; Jouzel J

2005-11-01

238

Ecological consequences of early Late Pleistocene megadroughts in tropical Africa  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Extremely arid conditions in tropical Africa occurred in several discrete episodes between 135 and 90 ka, as demonstrated by lake core and seismic records from multiple basins [Scholz CA, Johnson TC, Cohen AS, King JW, Peck J, Overpeck JT, Talbot MR, Brown ET, Kalindekafe L, Amoako PYO, et al. (2007...

Cohen, Andrew S.; Stone, Jeffery R.; Beuning, Kristina R. M.; Park, Lisa E.; Reinthal, Peter N.; Dettman, David

239

Neanderthals as part of the broader Late Pleistocene megafaunal extinctions  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Book description: What role did Ice Age climate play in the demise of the Neanderthals, and why was it that modern humans alone survived? For the past seven years a team of international experts from a wide range of disciplines have worked together to provide a detailed study of the world occupied b...

Stewart, J.R.; van Kolfschoten, T.; Markova, A.; Musil, R.

240

Coalescent-based hypothesis testing supports multiple Pleistocene refugia in the Pacific Northwest for the Pacific giant salamander (Dicamptodon tenebrosus).  

Science.gov (United States)

Phylogeographic patterns of many taxa are explained by Pleistocene glaciation. The temperate rainforests within the Pacific Northwest of North America provide an excellent example of this phenomenon, and competing phylogenetic hypotheses exist regarding the number of Pleistocene refugia influencing genetic variation of endemic organisms. One such endemic is the Pacific giant salamander, Dicamptodon tenebrosus. In this study, we estimate this species' phylogeny and use a coalescent modeling approach to test five hypotheses concerning the number, location and divergence times of purported Pleistocene refugia. Single refugium hypotheses include: a northern refugium in the Columbia River Valley and a southern refugium in the Klamath-Siskiyou Mountains. Dual refugia hypotheses include these same refugia but separated at varying times: last glacial maximum (20,000 years ago), mid-Pleistocene (800,000 years ago) and early Pleistocene (1.7 million years ago). Phylogenetic analyses and inferences from nested clade analysis reveal distinct northern and southern lineages expanding from the Columbia River Valley and the Klamath-Siskiyou Mountains, respectively. Results of coalescent simulations reject both single refugium hypotheses and the hypothesis of dual refugia with a separation date in the late Pleistocene but not hypotheses predicting dual refugia with separation in early or mid-Pleistocene. Estimates of time since divergence between northern and southern lineages also indicate separation since early to mid-Pleistocene. Tests for expanding populations using mismatch distributions and 'g' distributions reveal demographic growth in the northern and southern lineages. The combination of these results provides strong evidence that this species was restricted into, and subsequently expanded from, at least two Pleistocene refugia in the Pacific Northwest. PMID:16842421

Steele, Craig A; Storfer, Andrew

2006-08-01

 
 
 
 
241

Coalescent-based hypothesis testing supports multiple Pleistocene refugia in the Pacific Northwest for the Pacific giant salamander (Dicamptodon tenebrosus).  

UK PubMed Central (United Kingdom)

Phylogeographic patterns of many taxa are explained by Pleistocene glaciation. The temperate rainforests within the Pacific Northwest of North America provide an excellent example of this phenomenon, and competing phylogenetic hypotheses exist regarding the number of Pleistocene refugia influencing genetic variation of endemic organisms. One such endemic is the Pacific giant salamander, Dicamptodon tenebrosus. In this study, we estimate this species' phylogeny and use a coalescent modeling approach to test five hypotheses concerning the number, location and divergence times of purported Pleistocene refugia. Single refugium hypotheses include: a northern refugium in the Columbia River Valley and a southern refugium in the Klamath-Siskiyou Mountains. Dual refugia hypotheses include these same refugia but separated at varying times: last glacial maximum (20,000 years ago), mid-Pleistocene (800,000 years ago) and early Pleistocene (1.7 million years ago). Phylogenetic analyses and inferences from nested clade analysis reveal distinct northern and southern lineages expanding from the Columbia River Valley and the Klamath-Siskiyou Mountains, respectively. Results of coalescent simulations reject both single refugium hypotheses and the hypothesis of dual refugia with a separation date in the late Pleistocene but not hypotheses predicting dual refugia with separation in early or mid-Pleistocene. Estimates of time since divergence between northern and southern lineages also indicate separation since early to mid-Pleistocene. Tests for expanding populations using mismatch distributions and 'g' distributions reveal demographic growth in the northern and southern lineages. The combination of these results provides strong evidence that this species was restricted into, and subsequently expanded from, at least two Pleistocene refugia in the Pacific Northwest.

Steele CA; Storfer A

2006-08-01

242

Taphonomic aspects of the Pleistocene vertebrate assemblage of Itaboraí, state of Rio de Janeiro, southeastern Brazil  

Science.gov (United States)

Pleistocene vertebrates from Itaboraí Basin have not been taphonomically studied prior to this work, limiting the understanding of the deposition and preservation of the only Pleistocene vertebrate accumulation known for the state of Rio de Janeiro. In this work, the taphonomic signatures of the Pleistocene vertebrate assemblage of Itaboraí are identified and interpreted in order to increase the knowledge about the formation of this fossil association and the paleoecology of the region of Rio de Janeiro during the late Pleistocene. Our analysis shows that the thanatocoenosis was exposed to the biostratinomic processes during a small time span; that it is parautochthonous; and experienced short transport distances by normal fluvial streams and floods. Subsequently, the fossiliferous horizon was quickly covered by the superjacent soil. Yet, the skeletal elements were fractured and deformed during the sedimentary compaction. The differential preservation of megamammal bones is associated to the bone resistance against those destructive processes and to the specific anatomical features. Comparison between Itaboraí and other Brazilian Pleistocene vertebrate accumulations shows that the Itaboraí fossil accumulation was less affected by taphonomic processes, although it is also a time-averaged fossil concentration. Finally, some of the taphonomic features indicate an arid paleoclimate.

Araújo Júnior, Hermínio Ismael de; Dominato, Victor Hugo; Bertoni-Machado, Cristina; Avilla, Leonardo dos Santos

2013-10-01

243

Carboniferous and Permian stratigraphy in Guizhou  

Energy Technology Data Exchange (ETDEWEB)

A guide book prepared for Excursion 5 to southern Guizhou during the 11 International Congress of Carboniferous Stratigraphy and Geology. The excursion was aimed at examining some type sections of Carboniferous and Lower Permian, including the Devonian-Carboniferous boundary and the Carboniferous-Permian boundary. Mineral deposits of great economic significance are bauxite, manganese and coal.

Wei Jiayong; Xiao Weimin; Wang Hongdi; Dong Wenlan; Feng Rulin; Wu Xianghe; Zheng Shufang

1987-01-01

244

Stratigraphy and dissolution of the Rustler Formation  

International Nuclear Information System (INIS)

This report describes the physical stratigraphy of the Rustler Formation, because the Waste Isolation Pilot Plant will be constructed in salt beds that underlie this formation. Described are subdivisions of the formations, the major karst features, and a proposed method for the formation of Nash Draw. 2 refs., 2 figs.

1987-01-01

245

Stratigraphy of the Younger Dryas Chronozone and paleoenvironmental implications: Central and Southern Great Plains  

Science.gov (United States)

The Great Plains of the United States was the setting for some of the earliest research in North America into patterns and changes in the character of late Pleistocene environments and their effects on contemporary human populations. Many localities in the region have well-stratified records of terminal Pleistocene and early Holocene human (Paleoindian) activity and past environments. These have proven important in debates over the character of the Younger Dryas Chronozone (YDC; 11,000-10,000 14C BP; 12,900-11,700 cal BP) in the continental interior. This paper reviews the lithostratigraphic record of the YDC on the Central and Southern Great Plains and summarizes paleobiological records (largely isotopic). The goal is to determine if there is any uniformity in the timing, character, direction and/or magnitude of changes in depositional environments or broader geomorphic systems before, during or after the YDC in order to address the question of the character of environments through this time. The stratigraphic records of the late Pleistocene to early Holocene transition, and in particular, the stratigraphic records of the YDC vary through time and space. The data clearly show that a host of geomorphic processes produced the terminal Pleistocene and early Holocene stratigraphic records of the Great Plains. Moreover, the YDC is not necessarily manifest as a distinct lithostratigraphic or biostratigraphic entity in these different types of deposits and soils. The various geomorphic systems of the Great Plains did not behave synchronously in response to any common climate driver. These stratigraphic records reflect local environmental conditions and probably a complex response to the reorganization of mid-latitude climates in the terminal Pleistocene and early Holocene. ?? 2011 Elsevier Ltd and INQUA.

Holliday, V. T.; Meltzer, D. J.; Mandel, R.

2011-01-01

246

New carbon dates link climatic change with human colonization and Pleistocene extinctions.  

Science.gov (United States)

Drastic ecological restructuring, species redistribution and extinctions mark the Pleistocene-Holocene transition, but an insufficiency of numbers of well-dated large mammal fossils from this transition have impeded progress in understanding the various causative links. Here I add many new radiocarbon dates to those already published on late Pleistocene fossils from Alaska and the Yukon Territory (AK-YT) and show previously unrecognized patterns. Species that survived the Pleistocene, for example, bison (Bison priscus, which evolved into Bison bison), wapiti (Cervus canadensis) and, to a smaller degree, moose (Alces alces), began to increase in numbers and continued to do so before and during human colonization and before the regional extinction of horse (Equus ferus) and mammoth (Mammuthus primigenius). These patterns allow us to reject, at least in AK-YT, some hypotheses of late Pleistocene extinction: 'Blitzkrieg' version of simultaneous human overkill, 'keystone' removal, and 'palaeo-disease'. Hypotheses of a subtler human impact and/or ecological replacement or displacement are more consistent with the data. The new patterns of dates indicate a radical ecological sorting during a uniquely forage-rich transitional period, affecting all large mammals, including humans. PMID:16688174

Guthrie, R Dale

2006-05-11

247

New carbon dates link climatic change with human colonization and Pleistocene extinctions.  

UK PubMed Central (United Kingdom)

Drastic ecological restructuring, species redistribution and extinctions mark the Pleistocene-Holocene transition, but an insufficiency of numbers of well-dated large mammal fossils from this transition have impeded progress in understanding the various causative links. Here I add many new radiocarbon dates to those already published on late Pleistocene fossils from Alaska and the Yukon Territory (AK-YT) and show previously unrecognized patterns. Species that survived the Pleistocene, for example, bison (Bison priscus, which evolved into Bison bison), wapiti (Cervus canadensis) and, to a smaller degree, moose (Alces alces), began to increase in numbers and continued to do so before and during human colonization and before the regional extinction of horse (Equus ferus) and mammoth (Mammuthus primigenius). These patterns allow us to reject, at least in AK-YT, some hypotheses of late Pleistocene extinction: 'Blitzkrieg' version of simultaneous human overkill, 'keystone' removal, and 'palaeo-disease'. Hypotheses of a subtler human impact and/or ecological replacement or displacement are more consistent with the data. The new patterns of dates indicate a radical ecological sorting during a uniquely forage-rich transitional period, affecting all large mammals, including humans.

Guthrie RD

2006-05-01

248

Upper Pleistocene facies sequences and relative sea-level trends along the south coast of Ireland  

Energy Technology Data Exchange (ETDEWEB)

Upper Pleistocene sequences, deposited around 20 ka provide a record of sedimentation during the last glacial/deglacial cycle along the south coast of Ireland. A stratigraphy based on eight lithofacies associations is recognized. Typically, the facies sequences overlie a glaciated shore platform furrowed by subglacial meltwaters. Elements within the stratigraphy comprise: (1) ice advance southwards onto the continental shelf; (2) stagnation-zone retreat triggered by rising sea level related to isostatic depression coupled with subglacial meltwater events that furrowed the platform; (3) progressive rise in relative sea level recorded by a submergent facies sequence on an isostatically depressed slope (beach gravels {yields} subaqueous jet efflux sediments {yields} wave-influenced sands {yields} glaciomarine mud drape); ice-marginal oscillation is recorded by glaciotectonically deformed gravels, sands, and foliated diamict; (4) terrestrial emergence is marked by angular breccias derived from local slopes by periglacial weathering. There is a clear facies transition between the breccias and underlying wave-influenced sands. Facies sequences suggest that the local deglacial cycle was out of phase with the global eustatic cycle along the south coast of Ireland. Stagnation-zone retreat was largely dependent on magnitudes of isostatic depression, high relative sea level, and meltwater events, and not on climatic forcing.

McCabe, A.M. [Univ. of Ulster, Londonderry (Ireland). Dept. of Environmental Studies; O`Cofaigh, C. [Univ. of Alberta, Edmonton, Alberta (Canada). Dept. of Geography

1996-03-01

249

Lower Pleistocene hominids and artifacts from Atapuerca-TD6 (Spain)  

Science.gov (United States)

Human remains dating to more than 780,000 years ago are associated with a rich faunal and lithic assemblage in the Pleistocene cave site of Gran Dolina (TD), Sierra de Atapuerca, Burgos, Spain. The micromammal species represent the late Biharian (Mimomys savini zone), and the lithic objects represent pre-Acheulean technology (Mode 1) and comes from the TD6 level below the Matuyama-Brunhes boundary. The Gran Dolina hominid fossils cannot be comfortably accommodated in any of the defined Homo species. They could be considered a primitive form of Homo heidelbergensis, but a new species might be named in the future if the sample is enlarged. The new human fossil evidence demonstrates that Western Europe was settled at least since the late early Pleistocene. PMID:7638598

Carbonell, E; Bermúdez de Castro, J M; Arsuaga, J L; Díez, J C; Rosas, A; Cuenca-Bescós, G; Sala, R; Mosquera, M; Rodríguez, X P

1995-08-11

250

Lower Pleistocene hominids and artifacts from Atapuerca-TD6 (Spain)  

UK PubMed Central (United Kingdom)

Human remains dating to more than 780,000 years ago are associated with a rich faunal and lithic assemblage in the Pleistocene cave site of Gran Dolina (TD), Sierra de Atapuerca, Burgos, Spain. The micromammal species represent the late Biharian (Mimomys savini zone), and the lithic objects represent pre-Acheulean technology (Mode 1) and comes from the TD6 level below the Matuyama-Brunhes boundary. The Gran Dolina hominid fossils cannot be comfortably accommodated in any of the defined Homo species. They could be considered a primitive form of Homo heidelbergensis, but a new species might be named in the future if the sample is enlarged. The new human fossil evidence demonstrates that Western Europe was settled at least since the late early Pleistocene.

Carbonell E; Bermúdez de Castro JM; Arsuaga JL; Díez JC; Rosas A; Cuenca-Bescós G; Sala R; Mosquera M; Rodríguez XP

1995-08-01

251

Middle pleistocene dental remains from Qesem Cave (Israel).  

UK PubMed Central (United Kingdom)

This study presents a description and comparative analysis of Middle Pleistocene permanent and deciduous teeth from the site of Qesem Cave (Israel). All of the human fossils are assigned to the Acheulo-Yabrudian Cultural Complex (AYCC) of the late Lower Paleolithic. The Middle Pleistocene age of the Qesem teeth (400-200 ka) places them chronologically earlier than the bulk of fossil hominin specimens previously known from southwest Asia. Three permanent mandibular teeth (C(1)-P(4)) were found in close proximity in the lower part of the stratigraphic sequence. The small metric dimensions of the crowns indicate a considerable degree of dental reduction although the roots are long and robust. In contrast, three isolated permanent maxillary teeth (I(2), C(1), and M(3)) and two isolated deciduous teeth that were found within the upper part of the sequence are much larger and show some plesiomorphous traits similar to those of the Skhul/Qafzeh specimens. Although none of the Qesem teeth shows a suite of Neanderthal characters, a few traits may suggest some affinities with members of the Neanderthal evolutionary lineage. However, the balance of the evidence suggests a closer similarity with the Skhul/Qafzeh dental material, although many of these resemblances likely represent plesiomorphous features. Am J Phys Anthropol, 2011. © 2010 Wiley-Liss, Inc.

Hershkovitz I; Smith P; Sarig R; Quam R; Rodríguez L; García R; Arsuaga JL; Barkai R; Gopher A

2010-12-01

252

Middle Pleistocene dental remains from Qesem Cave (Israel).  

UK PubMed Central (United Kingdom)

This study presents a description and comparative analysis of Middle Pleistocene permanent and deciduous teeth from the site of Qesem Cave (Israel). All of the human fossils are assigned to the Acheulo-Yabrudian Cultural Complex (AYCC) of the late Lower Paleolithic. The Middle Pleistocene age of the Qesem teeth (400-200 ka) places them chronologically earlier than the bulk of fossil hominin specimens previously known from southwest Asia. Three permanent mandibular teeth (C(1) -P(4) ) were found in close proximity in the lower part of the stratigraphic sequence. The small metric dimensions of the crowns indicate a considerable degree of dental reduction although the roots are long and robust. In contrast, three isolated permanent maxillary teeth (I(2) , C(1) , and M(3) ) and two isolated deciduous teeth that were found within the upper part of the sequence are much larger and show some plesiomorphous traits similar to those of the Skhul/Qafzeh specimens. Although none of the Qesem teeth shows a suite of Neanderthal characters, a few traits may suggest some affinities with members of the Neanderthal evolutionary lineage. However, the balance of the evidence suggests a closer similarity with the Skhul/Qafzeh dental material, although many of these resemblances likely represent plesiomorphous features.

Hershkovitz I; Smith P; Sarig R; Quam R; Rodríguez L; García R; Arsuaga JL; Barkai R; Gopher A

2011-04-01

253

Middle Pleistocene dental remains from Qesem Cave (Israel).  

Science.gov (United States)

This study presents a description and comparative analysis of Middle Pleistocene permanent and deciduous teeth from the site of Qesem Cave (Israel). All of the human fossils are assigned to the Acheulo-Yabrudian Cultural Complex (AYCC) of the late Lower Paleolithic. The Middle Pleistocene age of the Qesem teeth (400-200 ka) places them chronologically earlier than the bulk of fossil hominin specimens previously known from southwest Asia. Three permanent mandibular teeth (C(1) -P(4) ) were found in close proximity in the lower part of the stratigraphic sequence. The small metric dimensions of the crowns indicate a considerable degree of dental reduction although the roots are long and robust. In contrast, three isolated permanent maxillary teeth (I(2) , C(1) , and M(3) ) and two isolated deciduous teeth that were found within the upper part of the sequence are much larger and show some plesiomorphous traits similar to those of the Skhul/Qafzeh specimens. Although none of the Qesem teeth shows a suite of Neanderthal characters, a few traits may suggest some affinities with members of the Neanderthal evolutionary lineage. However, the balance of the evidence suggests a closer similarity with the Skhul/Qafzeh dental material, although many of these resemblances likely represent plesiomorphous features. PMID:21404234

Hershkovitz, Israel; Smith, Patricia; Sarig, Rachel; Quam, Rolf; Rodríguez, Laura; García, Rebeca; Arsuaga, Juan Luis; Barkai, Ran; Gopher, Avi

2010-12-23

254

Oxygen and carbon stable isotope studies on Globorotalia menardii from Pleistocene DSDP cores in northern Indian ocean and their paleoclimatic and paleoceanographic implications  

International Nuclear Information System (INIS)

Stable isotope ratios of oxygen (?18O) and carbon (?13C) in tests of Globorotalia menardii from samples at 25 cm intervals of top 900 cm cores, representing different thicknesses of the Pleistocene, from DSDP(deep sea drilling project) Sites 219, 220 and 241 in the northern Indian Ocean have been measured. Isotopic ages could be assigned to the different levels of these core sections based on the correlation of ? 18O record from these sites with the SPECMAP record. Changes in sediment accumulation rates at different levels of the Pleistocene have been worked out on the basis of changes in oxygen isotopic ratio. Oscillations in ?13C stratigraphy at site 241 indicated southwest monsoon induced increase in upwelling and productivity during warmer periods. At sites 219 and 220, variations in the ?13C record were due to the mixing of bottom water. (author). 34 refs., 2 tabs., 4 figs.

1996-01-01

255

The sedimentology and stratigraphy of the Early Tertiary, Cusiana field, Colombia  

International Nuclear Information System (INIS)

The cusiana field (BP, Ecopetrol, Total and Triton is located in the llanos foothills of Eastern Colombia. There are three key reservoirs in the Cusiana field; the late Eocene to Early Oligocene Mirador Formation, the late Paleocene Barco Formation and the Santonian to Late Campanian Guadalupe Formation. The Mirador Formation contains over 50% of the original oil in place. Production for 1995 is planned at 130.000 barrels of oil per day (bopd; daily average), principally for the Mirador Formation with some production from the Guadalupe Formation. The mirador formation has therefore been the focus of a detailed reservoir description study aimed at understanding reservoir performance and putting a foundation in place for long-term reservoir management. The Mirador Formation comprises sandy (>60%), high frequency sequences dominated by the deposits of incised valleys. This paper describes the sedimentology and stratigraphy of the Mirador and the methodology chosen to construct a reservoir model fit for reservoir simulation

1995-01-01

256

Pleistocene cycles and marine records of West Antarctic Ice Sheet expansion and retreat  

Science.gov (United States)

The Pleistocene is very poorly represented in Antarctic continental shelf settings. Most piston cores do not penetrate last-glacial age diamictons. Moreover, nearly all sedimentary records have been subjected to the erosional effects of multiple expansions of the WAIS. No existing sediment core recovered from the continental shelf preserves a complete record of the last 1.2 Ma. The ANDRILL-MIS drillcore (AND-1B) from the southwestern Ross Sea may contain the best continental shelf record of the Late Pleistocene, but it is not well dated and probably incomplete. The upper 55 m of AND-1B contains sediments devoid of diatoms, including Pleistocene fragments or robust reworked Tertiary forms, suggestive of strong glacial shearing (Scherer et al., 2004, Geology). It is characterized by thick diamictites with very rare, thin mudstone units. The absence of diatoms, even in the mudstones, may result from (1) continuously expanded mid-Pleistocene ice (grounded or grounding-line proximal), (2) glacial erosion and removal of interglacial diatomaceous sediments, or (3) interglacial non-deposition of diatomaceous sediments, despite episodic open water with marine productivity. The southeastern Ross Sea, which has a non-winnowed relict glacial surface, despite high primary productivity, provides an analog for scenario 3 (Dunbar et al., 1985). McKay et al. (GSA Bull., 2009) interpret this interval as reflecting a nearly continuous Pleistocene record reflecting a predominance of grounded ice throughout much of the late Pleistocene, with the thin mudstones reflecting exclusively sub-ice shelf interglacial deposits. However, there is evidence of warmer than present interglacial conditions in Southern Ocean sediment cores (numerous references), and in East Antarctic ice cores (Sime et al., 2009, Nature). Furthermore, recent modeling of the WAIS suggests late Pleistocene instability, including episodic collapse of the Ross Ice Shelf and interior grounded ice (Pollard & Deconto, 2009, Nature). The enigmatic AND-1B record limits interpretation of Late Pleistocene interglacials and WAIS history in the Ross Sea. Although the Southern Ocean has a rich record of Pleistocene interglacial events, interpretation of WAIS collapse from these records is equivocal, in part due to lower latitude influences and their distance from the WAIS. The best sediment core available to date that is proximal to the WAIS is the Polarstern core PS58/254 from the Amundsen Sea (69°190S, 108°270W, water depth 4014 m), offshore from Pine Island Bay (Hillenbrand et al., 2009, QSR). The core is well-dated and contains a nearly continuous record of the last ca. 1.2 Ma. It's proximity to Pine Island Bay, the "weak underbelly" of the WAIS (Hughes, 1981), suggests that stratigraphic changes recognized in the core will have been strongly influenced by past WAIS collapse. We will present new diatom results from this core that bear on past WAIS fluctuations via the Pine Island Bay corridor.

Scherer, Reed; Konfirst, Matthew; Hillenbrand, Claus-Dieter; Kuhn, Gerhard

2010-05-01

257

Stratigraphy of the Jurassic system in northern Egypt  

Energy Technology Data Exchange (ETDEWEB)

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.

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

1988-08-01

258

Cenozoic seismic stratigraphy of the SW Bermuda Rise  

Energy Technology Data Exchange (ETDEWEB)

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.

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

1985-01-01

259

Osmium isotope stratigraphy of a marine ferromanganese crust  

Science.gov (United States)

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.

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

2005-01-01

260

Pátek, Levousy a Chlum?any – významné fosiliferní st?edopleistocénní lokality na pravém b?ehu Oh?e mezi Louny a Libochovicemi Pátek, Levousy and Chlum?any – important mid-pleistocene localities on the right bank of the Oh?e River between Louny and Libochovice  

Directory of Open Access Journals (Sweden)

Full Text Available Due to a complete predominance of non-calcareous fluvial sediments in the Czech Republic, any find of fossil malacofauna is always considered as rare. The present work describes three localities in the Oh?e river area, which contain, especially in the case of the Pátek locality, very abundant mid-Pleistocene malacofaunas. They were mainly collected in the floodplain fine-grained loam and back swamp deposits but also in sandy gravels. The molluscan thanatocenoses from localities near the Pátek village indicate the interglacial maximum (with up to 25 forest species s.l.), which developed directly on a 30 m thick river terrace dating back to the period, during which the Oh?e river established its present-day easterly course. The fossil molluscs from the Levousy locality come from floodplain loam deposits as well as from the underlying sandy terrace gravels. The species distribution, nevertheless, indicates only a transitional glacial-interglacial period. The somewhat higher morphologic position of the locality, as well as that of another section at Chlum?any, and complete predominance of local late Cretaceous material indicates that the Oh?e river did not flow to the east yet during the accumulation of the floodplain deposits with molluscs, but still to the north, towards Bílina. The terrestrial malacofauna from the Chlum?any section came from floodplain marls, particularly from sandy tufa deposits in the alluvium, which contains no forest-biotope elements, but the presence of the species Columella columella – distinct representative of our „coldest“ loess deposits – is an absolute surprise, since the peak of production of the sandy tufa deposits has always been associated with climate optima of the interglacials and of the Holocene. Therefore, the described malacofaunas come from a boundary period, during which the Oh?e river did not use its present-day valley (Levousy and Clum?any) yet. Then, from the oldest time span, it took up for the first time its eastward course. Stratigraphy of the localities cannot be determined with a reasonable certainty in regard to the current controversial situation in Pleistocene chronology both in the northern foothills of the Alps and in the area of the „classic“ localities belonging to the continental icesheet region in northern Germany (Kovanda 2005a). Altogether 12 mid-Pleistocene species of small mammals were found in thanaotocoenoses at localities Pátek and Levousy. Ostracod assemblages analysis was also undertaken (11 species in 8 samples were determined).

Ji?í Kovanda; Ivan Horá?ek; Radka Symonová

2005-01-01

 
 
 
 
261

Cenozoic sequence stratigraphy in the eastern North Sea  

Energy Technology Data Exchange (ETDEWEB)

The Cenozoic evolution of the epicontinental North Sea Basin is described on the basis of sequence stratigraphy, comprising analyses of seismic sections, petrophysical logs, and biostratigraphic studies of foraminifera, dinoflagellates, and calcareous nannofossils. Stratigraphic, palaeogeographic, and palaeoecological information from the Danish onshore area is integrated in the study. The deposits are subdivided into 21 sequences, which groups into seven informal major units. The sequence boundaries are identified by differences in seismic facies and by seismic onlap, toplap, and truncation features. The maximum flooding surface is placed at an internal downlap surface which correlates with high values on the gamma ray log. The source of sediments and the direction of sediment transport changed several times during the Cenozoic. Transport was mainly from the north during the Late Paleocene and Early Eocene, from the west during the Middle and Late Eocene, and from the north and northwest during the Oligocene to quaternary. The depocenters of the seven major units are generally located marginally, probably adjoining the source areas. There is only minor evidence for changes in subsidence rates in the basin. A constant rate is assumed from the Paleocene to the mid Middle Miocene. For the remaining part of the Cenozoic and increased rate is indicated. A tentative relative sea-level curve for the North Sea Basin is proposed. The overall trends of the curve are broadly comparable with the global sea-level curve of Haq et al. Discrepancies may be caused by differences in the biostratigraphic calibrations. The most pronounced Oligocene sea-level fall is dated ot the latest Oligocene. (au) (83 refs.)

Michelsen, O.; Thomsen, E.; Danielsen, M.; Heilmann-Clausen, C.; Jordt, H.; Laursen, G.V.

1995-05-01

262

Sedimentary environments processes, facies and stratigraphy  

CERN Multimedia

Sedimentary Environments is one of the most distinguished and influential textbooks in the earth sciences published in the last 20 years. The first and second editions both won universal praise and became classic works in sedimentology. Since the publication of the last edition, the study of sedimentary environments and facies has made great strides, with major advances in facies modelling, sequence stratigraphy and basin modelling. The 3rd edition of this classic text will likely set the benchmark even higher, and needless to say, will continue being the textbook of choice for sediment

Reading, Harold G

2009-01-01

263

A new Lower Pleistocene archeological site in Europe (Vallparad?s, Barcelona, Spain)  

Science.gov (United States)

Here we report the discovery of a new late Lower Pleistocene site named Vallparadís (Barcelona, Spain) that produced a rich archeological and paleontological sequence dated from the upper boundary of the Jaramillo subchron to the early Middle Pleistocene. This deposit contained a main archeological layer with numerous artifacts and a rich macromammalian assemblage, some of which bore cut marks, that could indicate that hominins had access to carcasses. Paleomagnetic analysis, electron spin resonance-uranium series (ESR-US), and the biostratigraphic chronological position of the macro- and micromammal and lithic assemblages of this layer reinforce the proposal that hominins inhabited Europe during the Lower Pleistocene. The archeological sequence provides key information on the successful adaptation of European hominins that preceded the well-known fossil population from Atapuerca and succeeded the finds from Orce basin. Hence, this discovery enables us to close a major chronological gap in the early prehistory of Iberia. According to the information in this paper and the available data from these other sites, we propose that Mediterranean Western Europe was repeatedly and perhaps continuously occupied during the late Matuyama chron.

Martinez, Kenneth; Garcia, Joan; Carbonell, Eudald; Agusti, Jordi; Bahain, Jean-Jaques; Blain, Hugues-Alexandre; Burjachs, Francesc; Caceres, Isabel; Duval, Mathieu; Falgueres, Christophe; Gomez, Manuel; Huguet, Rosa

2010-01-01

264

The Murray Springs Clovis site, Pleistocene extinction, and the question of extraterrestrial impact.  

Science.gov (United States)

Some of the evidence for the recent hypothesis of an extraterrestrial impact that caused late Pleistocene megafaunal extinctions [Firestone et al. (2007) Proc Natl Acad Sci USA 104:16016-16021] was based upon samples collected at Murray Springs, a Clovis archaeological site in southeastern Arizona. Here we describe sampling and analyses of magnetic separates from within, above, and below the lower Younger Dryas boundary (LYDB) black mat at Murray Springs, as well as radiation measurements from the LYDB at Murray Springs and two other well-stratified Clovis sites. The main magnetic fraction at Murray Springs is maghemite. Magnetic microspherules have terrestrial origins but also occur as cosmic dust particles. We failed to find iridium or radiation anomalies. The evidence for massive biomass burning at Murray Springs is addressed and found to be lacking. We could not substantiate some of the claims by Firestone and others, but our findings do not preclude a terminal Pleistocene cosmic event. PMID:20160115

Haynes, C Vance; Boerner, J; Domanik, K; Lauretta, D; Ballenger, J; Goreva, J

2010-02-16

265

The Murray Springs Clovis site, Pleistocene extinction, and the question of extraterrestrial impact.  

UK PubMed Central (United Kingdom)

Some of the evidence for the recent hypothesis of an extraterrestrial impact that caused late Pleistocene megafaunal extinctions [Firestone et al. (2007) Proc Natl Acad Sci USA 104:16016-16021] was based upon samples collected at Murray Springs, a Clovis archaeological site in southeastern Arizona. Here we describe sampling and analyses of magnetic separates from within, above, and below the lower Younger Dryas boundary (LYDB) black mat at Murray Springs, as well as radiation measurements from the LYDB at Murray Springs and two other well-stratified Clovis sites. The main magnetic fraction at Murray Springs is maghemite. Magnetic microspherules have terrestrial origins but also occur as cosmic dust particles. We failed to find iridium or radiation anomalies. The evidence for massive biomass burning at Murray Springs is addressed and found to be lacking. We could not substantiate some of the claims by Firestone and others, but our findings do not preclude a terminal Pleistocene cosmic event.

Haynes CV Jr; Boerner J; Domanik K; Lauretta D; Ballenger J; Goreva J

2010-03-01

266

Mammal diversity during the Pleistocene-Holocene transition in Eastern Europe.  

UK PubMed Central (United Kingdom)

Fossil data on the mammal diversity and species richness during the Late Pleistocene - Holocene transition are of extreme importance for the reconstruction of the evolution of terrestrial ecosystems as well as for the understanding of the present-day species phylogeography. These data can provide useful information that is relevant for the debate on how to conserve mammal genetic resources under the present-day circumstances that are the result of modern climate change. In earlier papers the dramatic transformations of North Eurasian mammal assemblages during the Pleistocene - Holocene transition have already been documented; however, the focus of these papers was mainly on changes in the zonal distribution of local faunal assemblages of the "Mammoth Fauna" complex and the extinction of key species (Vereshchagin & Baryshnikov 1992; Markova et al. 1995, 2002 a, b; 2003, 2006; Markova & Puzachenko 2007; Puzachenko & Markova 2007; Markova & Kolfschoten 2008; Baryshnikov & Markova 2009; Puzachenko 2010;).

Puzachenko AY; Markova AK

2013-10-01

267

Pleistocene avifaunas and the overkill hypothesis.  

UK PubMed Central (United Kingdom)

At the end of the North American Pleistocene, birds and mammals suffered comparable degrees of generic extinction. Both the magnitude and pattern of avian extinction are incompatible with the hypothesis that humans played a major role in causing the demise of numerous North American mammalian genera at this time.

Grayson DK

1977-02-01

268

A description of the geological context, discrete traits, and linear morphometrics of the Middle Pleistocene hominin from Dali, Shaanxi Province, China.  

Science.gov (United States)

In 1978, a nearly complete hominin fossil cranium was recovered from loess deposits at the site of Dali in Shaanxi Province, northwestern China. It was subsequently briefly described in both English and Chinese publications. Here we present a comprehensive univariate and nonmetric description of the specimen and provide comparisons with key Middle Pleistocene Homo erectus and non-erectus hominins from Eurasia and Africa. In both respects we find affinities with Chinese H. erectus as well as African and European Middle Pleistocene hominins typically referred to as Homo heidelbergensis. Specifically, the Dali specimen possesses a low cranial height, relatively short and arched parietal bones, an angled occipital bone, and a nonprominent articular tubercle relative to the preglenoid surface all of which distinguish it from Afro/European Middle Pleistocene Homo and align it with Asian H. erectus. At the same time, it displays a more derived morphology of the supraorbital torus and supratoral sulcus and a thinner tympanic plate than H. erectus, a relatively long upper (lambda-inion) occipital plane with a clear separation of inion and opisthocranion, and an absolute and relative increase in brain size, all of which align it with African and European Middle Pleistocene Homo. Finally, traits such as the form of the frontal keel and the relatively short, broad midface align Dali specifically with other Chinese specimens from the Middle Pleistocene and Late Pleistocene, including H. erectus, and differentiate these from the Afro/European specimens of this time period. PMID:23283667

Wu, Xinzhi; Athreya, Sheela

2013-01-01

269

A description of the geological context, discrete traits, and linear morphometrics of the Middle Pleistocene hominin from Dali, Shaanxi Province, China.  

UK PubMed Central (United Kingdom)

In 1978, a nearly complete hominin fossil cranium was recovered from loess deposits at the site of Dali in Shaanxi Province, northwestern China. It was subsequently briefly described in both English and Chinese publications. Here we present a comprehensive univariate and nonmetric description of the specimen and provide comparisons with key Middle Pleistocene Homo erectus and non-erectus hominins from Eurasia and Africa. In both respects we find affinities with Chinese H. erectus as well as African and European Middle Pleistocene hominins typically referred to as Homo heidelbergensis. Specifically, the Dali specimen possesses a low cranial height, relatively short and arched parietal bones, an angled occipital bone, and a nonprominent articular tubercle relative to the preglenoid surface all of which distinguish it from Afro/European Middle Pleistocene Homo and align it with Asian H. erectus. At the same time, it displays a more derived morphology of the supraorbital torus and supratoral sulcus and a thinner tympanic plate than H. erectus, a relatively long upper (lambda-inion) occipital plane with a clear separation of inion and opisthocranion, and an absolute and relative increase in brain size, all of which align it with African and European Middle Pleistocene Homo. Finally, traits such as the form of the frontal keel and the relatively short, broad midface align Dali specifically with other Chinese specimens from the Middle Pleistocene and Late Pleistocene, including H. erectus, and differentiate these from the Afro/European specimens of this time period.

Wu X; Athreya S

2013-01-01

270

Late Quaternary geomorphology and soils in Crater Flat, Yucca mountain area, southern Nevada  

Energy Technology Data Exchange (ETDEWEB)

Crater Flat is an alluvium-filled structural basin on the west side of Yucca Mountain, Nevada, which is under consideration for a high-level nuclear waste repository. North-trending, late Quaternary faults offset alluvium in Crater Flat both along the canyons of the western flanks of Yucca Mountain and out on the piedmont slope. We believe the initial lack of young offsets at Yucca Mountain was in part due to unrecognized late Quaternary stratigraphy. We hypothesize that alluviation in the Yucca Mountain region was more active during the late Quaternary than previously thought. Several techniques were tried to test this hypothesis. Results are compared with previous soils and surface-exposure dating studies, and correlated to stratigraphy of other late Quaternary units in the southern Nevada, Death Valley, and Mojave Desert areas, and provide new stratigraphic data relevant to understanding climatic-alluvial processes in the Basin and Range Province during the late Quaternary. 76 refs., 7 figs., 6 tabs.

Peterson, F.F.; Bell, J.W.; Ramelli, A.R. [Univ. of Nevada, Reno, NV (United States); Dorn, R.I. [Arizona State Univ., Tempe, AZ (United States); Ku, T.L. [Univ. of Southern California, Los Angeles, CA (United States)

1995-04-01

271

XII international congress on Carboniferous and Permian geology and stratigraphy  

Energy Technology Data Exchange (ETDEWEB)

Contains abstracts of papers and posters presented at the 12th international congress. Various aspects of Carboniferous and Permian geology and stratigraphy throughout the world are covered, including coal seams and oil shales.

1991-01-01

272

Integrated chronostratigraphy of the Pliocene-Pleistocene interval and its relationto the regional stratigraphical stages in the southern North Sea region  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Time-stratigraphic interpretations of Late Pliocene to Early Pleistocene sediments from onshore locations and from marginal marine settings of the North Sea Basin often refer to the subdivision of the Dutch and British ‘Quaternary’ regional stratigraphic stages. Since age control for these stages an...

Kuhlmann, G.; Langereis, C.G.; Munsterman, D.; Leeuwen, R.-J. van; Verreussel, R.; Meulenkamp, J.E.; Wong, Th.E.

273

Late paraphrenia.  

UK PubMed Central (United Kingdom)

This article reviews the historical development of the concept of late paraphrenia. Studies that attempt to define symptoms, demographics, and risk factors for late-onset paranoid disorders are reviewed. Differences between late-onset schizophrenia and early-onset schizophrenia are highlighted. Current research on potential brain abnormalities in these disorders is examined critically.

Addonizio GC

1995-06-01

274

Stratigraphy and dissolution of the Rustler Formation  

International Nuclear Information System (INIS)

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.

1985-03-07

275

Comment on "Deep-sea temperature and ice volume changes across the Pliocene-Pleistocene climate transitions".  

UK PubMed Central (United Kingdom)

Sosdian and Rosenthal (Reports, 17 July 2009, p. 306) used magnesium/calcium ratios in benthic foraminifera from the North Atlantic to reconstruct past bottom-water temperatures. They suggested that both ice volume change and ice-sheet dynamics played important roles during the late Pliocene and mid-Pleistocene climate transitions. We present evidence that their record of deep ocean temperature is not reliable, thus raising doubts about their conclusions.

Yu J; Broecker WS

2010-06-01

276

Comment on "Deep-sea temperature and ice volume changes across the Pliocene-Pleistocene climate transitions".  

Science.gov (United States)

Sosdian and Rosenthal (Reports, 17 July 2009, p. 306) used magnesium/calcium ratios in benthic foraminifera from the North Atlantic to reconstruct past bottom-water temperatures. They suggested that both ice volume change and ice-sheet dynamics played important roles during the late Pliocene and mid-Pleistocene climate transitions. We present evidence that their record of deep ocean temperature is not reliable, thus raising doubts about their conclusions. PMID:20558688

Yu, Jimin; Broecker, Wally S

2010-06-18

277

A mid to late Holocene history of floodplain and terrace reworking along the middle Delaware River valley, USA  

Science.gov (United States)

This study tests and refines the traditional floodplain development model for the partly confined middle Delaware River valley, which has shown that the main channel was relatively stable and flanked by a 6000-8000 year old, vertically accreting alluvial terrace. The Holocene alluvial processes and history presented here in 6 fluvial phases were reconstructed using morphostratigraphy, 36 profile descriptions, 332 grain size analyses, and 82 14C ages from soil trenches, auger borings, and archaeological excavations. Fluvial phases I-III largely validate previous reconstructions showing a late Pleistocene (I: > 10.7 ka) braided stream transition into an early Holocene wandering stream with prolonged floodplain stability (II: 10.7-8 ka), followed by early-middle Holocene erosion and then deposition (III: 8-5 ka). The early and middle Holocene changes in alluvial stratigraphy and sedimentology broadly correlate with climatically derived Holocene subdivisions, suggesting climate change partly controls alluvial response along the middle Delaware River valley. This study documents for the first time a middle Holocene episode of channel incision occurring sometime between 6.0 and 5.0 ka. Although the results reconfirm that the majority of alluvial landforms are composed of vertical accretion deposits, we present here new evidence of oblique, abandoned channel, and lateral accretion deposits inset to similar landforms with different formation histories (i.e., polycyclic terrace development), depicting a river valley that has experienced floodplain and terrace reworking. The majority of floodplain and terrace reworking occurs during the late-middle and late Holocene phases IV-VI (5.5-0 ka), following the middle Holocene incision event. These phases demonstrate floodplain reworking processes in the form of channel abandonment, stripping, flood channeling, and convex bank erosion. The subsequent space filled rapidly with evidence of multistory soil formation, and eventually resulted in alluvial fill terraces with heights comparable to older surfaces. The most recent fluvial phase, VI (1.0-0 ka), shows markedly faster sedimentation rates and coarser flood deposits associated with peak prehistoric population and the onset of Euroamerican settlement. The results presented here contribute newly documented evidence of erosion and depict a river valley that has undergone middle Holocene incision and floodplain and terrace reworking since the late-middle Holocene. Stream modelers, fluvial geomorphologists and geoarchaeologists working in the NE USA should consider floodplain reworking processes when examining alluvial history and predicting changes in stream dynamics.

Stinchcomb, Gary E.; Driese, Steven G.; Nordt, Lee C.; Allen, Peter M.

2012-10-01

278

Pleistocene to Holocene extinction dynamics in giant deer and woolly mammoth.  

Science.gov (United States)

The extinction of the many well-known large mammals (megafauna) of the Late Pleistocene epoch has usually been attributed to 'overkill' by human hunters, climatic/vegetational changes or to a combination of both. An accurate knowledge of the geography and chronology of these extinctions is crucial for testing these hypotheses. Previous assumptions that the megafauna of northern Eurasia had disappeared by the Pleistocene/Holocene transition were first challenged a decade ago by the discovery that the latest woolly mammoths on Wrangel Island, northeastern Siberia, were contemporaneous with ancient Egyptian civilization. Here we show that another spectacular megafaunal species, the giant deer or 'Irish elk', survived to around 6,900 radiocarbon yr bp (about 7,700 yr ago) in western Siberia-more than three millennia later than its previously accepted terminal date-and therefore, that the reasons for its ultimate demise are to be sought in Holocene not Pleistocene events. Before their extinction, both giant deer and woolly mammoth underwent dramatic shifts in distribution, driven largely by climatic/vegetational changes. Their differing responses reflect major differences in ecology. PMID:15470427

Stuart, A J; Kosintsev, P A; Higham, T F G; Lister, A M

2004-10-01

279

Pleistocene to Holocene extinction dynamics in giant deer and woolly mammoth.  

UK PubMed Central (United Kingdom)

The extinction of the many well-known large mammals (megafauna) of the Late Pleistocene epoch has usually been attributed to 'overkill' by human hunters, climatic/vegetational changes or to a combination of both. An accurate knowledge of the geography and chronology of these extinctions is crucial for testing these hypotheses. Previous assumptions that the megafauna of northern Eurasia had disappeared by the Pleistocene/Holocene transition were first challenged a decade ago by the discovery that the latest woolly mammoths on Wrangel Island, northeastern Siberia, were contemporaneous with ancient Egyptian civilization. Here we show that another spectacular megafaunal species, the giant deer or 'Irish elk', survived to around 6,900 radiocarbon yr bp (about 7,700 yr ago) in western Siberia-more than three millennia later than its previously accepted terminal date-and therefore, that the reasons for its ultimate demise are to be sought in Holocene not Pleistocene events. Before their extinction, both giant deer and woolly mammoth underwent dramatic shifts in distribution, driven largely by climatic/vegetational changes. Their differing responses reflect major differences in ecology.

Stuart AJ; Kosintsev PA; Higham TF; Lister AM

2004-10-01

280

The hydrologic cycle of the western coast of North America since the late Miocene  

Science.gov (United States)

To investigate the development of the modern climate of coastal California from the relatively wet and warm conditions of the late Miocene, we measured the hydrogen isotopic composition of terrestrial leaf-wax n-alkanes preserved in marine sediments from ODP Site 1010. To provide additional context for the 1010 results, we also generated a N-S transect of leaf-wax ?D from early Pleistocene samples along the California Margin. The early Pleistocene transect shows depletion in the ?D of the C29 and C31 n-alkanes associated with increasing latitude: we observed a 12.1 ‰ gradient in C29 ?D and a 14.9 ‰ gradient in C31 ?D over 10° of latitude. These gradients are similar to the ~15 to 20 ‰ ?D gradients estimated for modern coastal California precipitation and indicate that the early Pleistocene ?D values from Site 1010 reflect an arid southern California alkane source while northern California conditions were relatively wet. Our preliminary down-core results from ODP Site 1010 show an overall depletion of 6.4 ‰ in southern California leaf-wax ?D between the late Miocene and the late Pleistocene: mean late Miocene C29 values were -151.7 ‰ and mean late Pleistocene C29 values were -158.1‰. Because the modern winter precipitation in southern California generally originates from central and North Pacific air masses and is isotopically light compared to the summer precipitation that originates from Gulf of Mexico and Gulf of California air masses, we believe that the down-core trend in isotopic values at Site 1010 reflects a transition from year-round precipitation during the late Miocene to an increasingly mediterranean climate (with wet winters and relatively dry summers) in the late Pleistocene. Our interpretation is consistent with a recent modeling effort that found an increase in summer precipitation over southwestern North America during the early Pliocene as a result of the reduced meridional North Pacific SST gradient.

Lariviere, J.; Ravelo, A. C.; Polissar, P.

2010-12-01

 
 
 
 
281

Evidence from molecular systematics for decreased avian diversification in the pleistocene Epoch.  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Pleistocene glaciations have been suggested as major events influencing speciation rates in vertebrates. Avian paleontological studies suggest that most extant species evolved in the Pleistocene Epoch and that species' durations decreased through the Pleistocene because of heightened speciation rate...

Zink, R M; Slowinski, J B

282

North Atlantic climate evolution through the Plio-Pleistocene climate transitions  

Science.gov (United States)

During the Plio-Pleistocene, the Earth witnessed the growth of large northern hemisphere ice sheets and profound changes in both North Atlantic and global climate. Here, we present a ~ 3.2 Myr long, orbitally-resolved alkenone sea surface temperature (SST) record from Deep Sea Drilling Project (DSDP) Site 607 (41°N, 33°W, water depth 3427 m) in the North Atlantic Ocean. We employ a multi-proxy approach comparing these new observations with existing bottom water temperature (BWT) and stable isotope time series from the same site and SST time series from other sites, shedding new light on Plio-Pleistocene climate change. North Atlantic temperature records show a long-term cooling with two major steps occurring during the late Pliocene (3.1 to 2.4 Ma) and the mid-Pleistocene (1.5 to 0.8 Ma), closely timed with intervals of major change in northern hemisphere ice sheets. Existing evidence suggests that the late Pliocene cooling may have been caused by a thresholded response to secular changes in atmospheric carbon dioxide (CO 2). While an explanation for the mid-Pleistocene cooling may involve glacial-interglacial changes in atmospheric CO 2, it seems to also require a change in the behavior of the ice sheets themselves. North Atlantic climate responses were closely phased with benthic oxygen isotope (? 18O) changes during the "41 kyr world," indicating a strong common northern hemisphere high latitude imprint on North Atlantic climate signals. After the mid-Pleistocene transition (MPT), North Atlantic SST records and the Site 607 benthic carbon isotope (? 13C) record are more closely phased with ? 18O, whereas BWT significantly leads ? 18O in the 100 kyr band, suggesting a shift from a northern to a southern hemisphere influence on North Atlantic BWT. We propose that the expansion of the West Antarctic ice sheet (WAIS) across the MPT increased the production and export of Antarctic Bottom Water from the Southern Ocean and subsequently controlled its incursion into the North Atlantic, especially during glacial intervals. It follows that the early 100 kyr response of BWT implies an early response of the WAIS relative to the northern hemisphere deglaciation. Thus, in the "100 kyr world," both northern hemisphere and southern hemisphere processes affect climate conditions in the North Atlantic Ocean.

Lawrence, K. T.; Sosdian, S.; White, H. E.; Rosenthal, Y.

2010-12-01

283

Stratigraphy and hydrologic conditions at the Brookhaven National Laboratory and vicinity, Suffolk County, New York, 1994-97  

Science.gov (United States)

Brookhaven National Laboratory (BNL) has installed many test borings as part of an effort to delineate the extent of ground-water contamination at the site. In 1994, the U.S. Geological Survey began a study in cooperation with BNL to define the stratigraphy in the 28-square-mile area encompassing BNL, and to monitor ground-water levels in the 300 squaremile area of central Suffolk County that surrounds BNL. The uppermost geologic units at BNL are of Pleistocene age. These sediments are underlain unconformably by the Matawan Group-Magothy Formation, undifferentiated (referred to as the Magothy Formation), of Cretaceous age, which typically consists of light- to dark-gray, variably sorted sand interbedded with light- to dark-gray clay layers; it also contains beds of grayish-brown to brownish-gray sand. Bed thicknesses differ substantially within each boring and tend to be laterally discontinuous as a result of their terrestrial deltaic depositional environment, although a prominent clay unit, referred to as the ?grayish-brown clay? in this report, was encountered at many borings. Pollen-sample analyses confirm that this unit is of Cretaceous age and is the uppermost unit of Cretaceous sediments in several parts of the study area. The upper surface of the Cretaceous deposits is irregular within the 28-square-mile study area and has relief of about 120 feet. Several prominent channels and ridges in the surface are aligned generally northwest-southeast. The Cretaceous surface beneath BNL is characterized more by local erosional features than by the regional cuesta shape that was suggested by previous authors. The overlying Pleistocene-aged units include (1) a sand layer overlain by the Gardiners Clay, (2) the Gardiners Clay, and (3) upper Pleistocene deposits, which include the Upton unit, glacial outwash, glaciolacustrine deposits, and terminal moraine deposits. The sand unit below the Gardiners Clay was the first Pleistocene unit to be deposited atop the irregular surface of the Cretaceous deposits in this area. The Gardiners Clay was deposited during a major rise in sea level as the sea encroached into parts of the present-day BNL study area. The shallow part of the upper Pleistocene deposits generally consists of light-brown sand and gravel but overlies green to grayish-green, variably sorted sand, silt, and clay at altitudes of 50 to 70 feet below sea level in some parts of the study area. This lower part of the upper Pleistocene deposits in the study area was referred to by previous investigators as the unidentified unit and has been designated as the Upton unit in this report. The discharge of ground water to the Peconic and Carmans Rivers locally affects the water-table configuration. The main ground-water divide on Long Island is about 0.5 miles north of the site; a secondary divide originates near the start of flow of the Peconic River and extends east-southeastward toward the South Fork. The water-table configuration on the BNL site is affected by pumping from supply wells and remediation wells, by infiltration of the water through recharge basins, by discharge from the sewage-treatment plant, and by local near-surface clay units. The horizontal hydraulic gradient at BNL typically is 0.001 foot per foot but can steepen near recharge basins and pumping wells. Vertical flow gradients within the upper Pleistocene deposits (upper glacial aquifer) were as large as 0.007 foot per foot (downward) in the northern part of BNL and were negligible in the southern part. Downward vertical gradients between the lower part of the upper glacial aquifer and the upper part of the Magothy Formation (Magothy aquifer) were about 0.018 foot per foot throughout the site.

Scorca, Michael P.; Dorsch, William R.; Paquette, Douglas E.

1999-01-01

284

Dispersal of Pleistocene Equus (Family Equidae) into South America and calibration of GABI 3 based on evidence from Tarija, Bolivia.  

UK PubMed Central (United Kingdom)

The dispersal of Equus into South America during the Great American Biotic Interchange (GABI) represented a major event for Pleistocene land-mammal age chronology on that continent. It has been argued that this dispersal occurred during the late Pleistocene, ?0.125 Ma, and it defines the base of the Lujanian South American Land Mammal Age (SALMA). In this scenario, Equus dispersed during the fourth and latest recognized phase of the interchange, i.e., GABI 4. Although Equus was widely distributed in South America during the Pleistocene, only a few localities are calibrated by independent chronostratigraphic data. In this paper, new biostratigraphic evidence documents that Equus occurs from 15 superposed faunal horizons or zones throughout the Tolomosa Formation at Tarija, Bolivia. This biostratigraphic sequence is independently calibrated to occur between ?0.99 to <0.76 Ma during the middle Pleistocene Ensenadan SALMA and coincident with GABI 3, not GABI 4. Tarija remains the only well calibrated Ensenadan locality at which Equus is found. The new biostratigraphic data presented here are unambiguous and document the earlier (pre-Lujanian) occurrence of this genus in South America. The hypothesized dispersal of the genus Equus into South America at ?0.125 Ma is no longer supportable in light of the new biostratigraphic evidence presented here. The new data from Tarija thus have continent-wide implications for the origins and biogeography of Equus in South America as well as the calibration of GABI 3.

MacFadden BJ

2013-01-01

285

Quantitative palaeodrainage analysis in the Pleistocene of the Po Plain (Italy)  

Science.gov (United States)

During the Pleistocene, Po Plain deposits recorded repeated waxing and waning of Alpine ice caps, and thus provide an excellent opportunity to investigate the interactions between pronounced climatic fluctuations and background tectonic activity (Scardia et al., 2006), resulting in frequent changes of drainage patterns. A high-resolution Pleistocene stratigraphy, with a complete sedimentological, paleontological, petrographic-mineralogical, magneto-stratigraphic, and seismic data base, was recently obtained from eleven continuous cores drilled in the Lombardy Po Plain north of the Po River (ENI and Regione Lombardia, 2002). In the present study we focus on two cores in the proximal (Cilavegna) and distal plain (Pianengo), which best exemplify the drastic change in sedimentary systems and drainage patterns associated with the onset of major Pleistocene glaciations in the Alps (˜870ky; Muttoni et al., 2003). This climatic event is recorded by a regional unconformity (named R-unconformity by Muttoni et al., 2003), traced all across the Po Basin and encountered at -81 m depth in the Pianengo Core and at -98 m depth in the Cilavegna Core. The Cilavegna Core consists of metamorphiclastic floodplain sediments, capped by the R-unconformity and overlain by quartzofeldspathic braidplain deposits. The Pianengo Core consists of metamorphiclastic deltaic to floodpain sediments, capped by the R-unconformity and overlain by alluvial-fan gravels rich in carbonate pebbles; another unconformity at -39 m depth is overlain by metamorphiclastic braidplain deposits. Our quantitative approach to paleodrainage analysis is based on comprehensive information obtained from modern settings (Garzanti et al., 2004; 2006). End-member modelling and similarity analysis allows us to objectively compare detrital modes from modern and ancient deposits, and to reconstruct the evolution of sediment pathways through geologic time (Vezzoli and Garzanti 2009). The Cilavegna Core documents stepwise south-westward shifts of major tributaries draining the axial belt. The Pianengo Core records the rapid southward progradation of transverse alluvial fans fed locally from the Southern Alps, followed by progressive establishment of the modern Adda river system. Evolving drainage patterns and river avulsions represent a major cause of compositional change in foreland-basin deposits. Lateral shifts of river courses, commonly associated with unconformities and favoured by an increase in the ratio between sediment fluxes and subsidence, provide crucial information on tectonic or climatic events, and should be given full consideration in provenance studies. ENI and Regione Lombardia. 2002. Geologia degli acquiferi padani della Regione Lombardia. Firenze, Società Elaborazioni Cartografiche s.r.l., 130 p. Muttoni G., Carcano C., Garzanti E., Ghielmi M., Piccin A., Pini R., Rogledi S., and Sciunnach D. 2003. Onset of major Pleistocene glaciations in the Alps. Geology, 31, 989-992. Scardia G., Muttoni G., and Sciunnach D. 2006. Subsurface magnetostratigraphy of Pleistocene sediments from the Po Plain (Italy): constraints on rates of sedimentation and rock uplift. Geological Society of America Bulletin, 118, 1299-1312. Vezzoli G. and Garzanti E. 2009. Tracking paleodrainage in foreland-basin sequences. Journal of Geology, In press.

Vezzoli, G.; Garzanti, E.; Sciunnach, D.

2009-04-01

286

Upside-down sequence stratigraphy, sandy highstands, and muddy prograding complexes in the Surma Basin, Bangladesh  

Energy Technology Data Exchange (ETDEWEB)

Several large, TCF-size gas fields have been discovered in the Surma Basin, Bangladesh. Detailed sequence stratigraphy was performed on log and seismic data to study these fields and future potential of the area. The prospective section is Upper Miocene sands caught up in a series of younger compressional fault-related folds caused by the Indian Plate colliding with S.E. Asia in the late Tertiary. World-class gas/water contacts are observed on the seismic data over the fields. Sequence stratigraphic techniques reveal an ordered, predictable stratigraphic architecture of sandy highstands and transgressions, and muddy aggraded prograding complexes with deep incisions at each sequence boundary. This serves as a framework to understand the hydrocarbon accumulations in the area. Cyclostratigraphy is used to understand the unusual lithology distributions in the basin.

Radovich, B.J.; Hoffman, M.W.; Perlmutter, M.A. [and others

1995-12-31

287

Stratigraphy of Upper Permian and Lower Triassic Strata of the Žiri Area (Slovenia)  

Directory of Open Access Journals (Sweden)

Full Text Available The paper deals with the stratigraphy of Late Permian and Early Triassic strata of the Luka? section in the Žiri area of western Slovenia. This is the only section presently known in the External Dinarides where the Permian-Triassic boundary is defined following international criteria based on the first appearance of the conodont Hindeodus parvus. The following lithostratigraphic units have been formalized: the Bellerophon Limestone and Evaporite-dolomite Members of the Bellerophon Formation and the Luka~ Formation with the three members,the Transitional Beds, Streaky Limestone and Carbonate-clastic Member. The paper presents the results of micropaleontologicalstudy based on foraminifers and conodonts as well as petrographic and sedimentologic research results. The investigation of conodont assemblages enabled the conodont biozonation of the Permian-Triassic interval of the studied Luka? section.

Tea Kolar-Jurkovšek; Bogdan Jurkovšek; Dunja Aljinovi?; Galina P. Nestell

2011-01-01

288

Foraminiferal stratigraphy of Ranikot (Paleocene) of Pakistan  

Energy Technology Data Exchange (ETDEWEB)

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

Kureshy, A.A.

1983-03-01

289

Indications of Pleistocene man on Sardinia  

Energy Technology Data Exchange (ETDEWEB)

Human fossils found in a Pre-Neolithic cave deposit (Corbeddu cave, Sardinia) represent the first human remains associated with an endemic impoverished island fauna. Radiocarbon dating by AMS in Utrecht provided the chronological framework of the cave sediments for better understanding of the time-related human activities. The aberrant morphology of the human fossils and the unique character of worked deer bones discovered, suggest the development of an endemic Pleistocene human culture, adapted to the restricted island conditions and the hunting of ochotonids and deer.

Klein Hofmeijer, G.; Sondaar, P.Y.; Alderliesten, C.; Borg, K. van der; Jong, A.F.M. de

1987-11-01

290

Regional depositional history of the miocene-pleistocene Louisiana slope, Green Canyon-Mississippi Canyon  

Energy Technology Data Exchange (ETDEWEB)

A regional sequence stratigraphic analysis was recently completed for the Tertiary slope sediments in Green Canyon, Ewing Bank, and Mississippi Canyon to provide a chronostratigraphic framework for basin reconstructions and to predict lithofacies distributions of reservoir and seal rocks. Sixteen third-order sequences of lowstand deepwater deposits were interpreted for the Middle Miocene-Pleistocene section. Thirty regional lithofacies maps were made of predominantly lowstand deposits showing the distribution of shale and sand-prone sediments, slumps, channel/levee systems, and fan lobes based on distinctive seismic reflection and well log patterns. These maps were combined with isochrons of selected sequences to identify depositional fairways, depocenters, and paleosalt positions that constantly changed through time. Depositional trends were principally north-south but were also observed to be east-west as salt modified the gradient on the gently dipping slope. In some cases, the structural and stratigraphic trends could be projected under allochthonous tabular salt. Miocene channel and fan lobe sands were concentrated on the middle-lower paleoslope across the study area. The sedimentation rate doubled to 2.3 m/1000 yr in the early Middle Pliocene, which caused large-scale salt movements and trapped sand-prone turbidities along the upper to middle slope. A four-fold decrease in sediment influx during the Late Pliocene-Early Pleistocene produced a stacked condensed section of four sequences over the eastern Louisiana slope. A return to rapid sedimentation (up to 6.9 m/1,000 yr) during the Late Pleistocene reactivated salt movements and depocenters in the Green Canyon, Ewing Bank, and Mississippi Trough areas.

Risch, D.L.; Choudhury, A.N.; Hannan, A.E. [Geco-Prakla, Houston, TX (United States)

1994-12-31

291

Cenozoic stratigraphy of the southern Salar de Antofalla region, northwestern Argentina  

Directory of Open Access Journals (Sweden)

Full Text Available In the region of the southern Salar de Antofalla (Catamarca Province, northwestern Argentina), Late Eocene to Pliocene/(?)Pleistocene successions are exposed with thicknesses of up to 1,600 m. They consist of fluvial, lacustrine and eolian sediments with intercalations of pyroclastic rocks and lava flows. The sedimentary deposits represent 'alluvial fan-playa-complexes' accumulated under a semi-arid to arid climate. From the Late Eocene to the Early Miocene, the sedimentation took place in broken-foreland basins, while from the Early Miocene to the Late Pliocene/(?)Early Pleistocene, the sediments mainly accumulated within compressional retroarc basins in which volcanoes partly formed additional basin boundaries. Seven stratigraphic units can be differentiated on the basis of different lithofacies, angular unconformities and different regional distributions: the Late Eocene to Early Miocene Quiñoas Formation, which can be subdivided into the Campo Negro Member, the Cadillo Member and the Aguada Member, the Early/(?)Middle Miocene Potrero Grande Formation, the Late Miocene Antofalla Formation, which can be subdivided into the Cajeros Member and Bordo Blanco Member, the Late Miocene Salina beds, the Late Miocene Pozuelos Formation (Orilla Member), the (?)Late Miocene/Early Pliocene Sijes Formation (Uncal Grande Member) and the Late Pliocene/(?)Early Pleistocene Singuel Formation (Agua Escondida Member). While the Quiñoas Formation, the Potrero Grande Formation, the Antofalla Formation and the Salina beds have been newly introduced, the strata which represent the other formations can be assigned to the existing stratigraphic division of the southern Puna. Owing to the fact that these strata had no lateral connection to the strata of their type localities, which crop out near the Salar Pastos Grandes, they were defined as lateral membersEstratigrafía del Cenozoico en la región sur del Salar de Antofalla, noroeste de Argentina. En la parte sur del Salar de Antofalla (Provincia de Catamarca; noroeste de Argentina) afloran sedimentitas continentales de edad eocena tardío a plio-pleistocena con espesores de hasta 1.600 m. Están compuestas por materiales aluviales, lacustres, eólicos e intercalaciones de lavas y rocas piroclásticas. Las sedimentitas continentales representan complejos de abanicos aluviales y depósitos de playa acumulados bajo condiciones climáticas áridas y semiáridas. Desde el Eoceno Tardío al Mioceno Temprano la sedimentación se desarrolló en cuencas de antepaís desmembradas, mientras que a partir del Mioceno Temprano al Plioceno Tardío-Pleistoceno temprano(?) la sedimentación se desarrolló, en su mayoría, dentro de cuencas de retroarco compresionales. Volcanes formaron límites locales de estas cuencas. Sobre la base de diferencias de litofacies y discordancias angulares se distinguieron siete unidades estratigráficas: Formación Quiñoas del Eoceno Tardío a Mioceno Temprano, la cual a su vez, puede ser subdividida en los miembros Campo Negro, Miembro Cadillo y Aguada; la Formación Potrero Grande del Mioceno Temprano/Medio; Formación Antofalla la cual puede ser subdividida en los miembros Cajeros y Bordo Blanco; las capas Salina del Mioceno Tardío; Formación Pozuelos del Mioceno Tardío (Miembro Orilla); Formación Sijes del Mioceno/Plioceno Temprano (Miembro Uncal Grande) y Formación Singuel del Plioceno/Pleistoceno temprano (Miembro Agua Escondida). Las formaciones Quiñoas, Potrero Grande y Antofalla y las capas Salina constituyen unidades nuevas, en tanto que las otras formaciones son conocidas en la división estratigráfica de la Puna meridional. Los estratos que no tienen conexión lateral con aquellos de sus localidades tipos, y que afloran cerca del Salar Pastos Grandes, se definieron como miembros laterales

Reno Voss

2002-01-01

292

Late-Glacial radiocarbon- and palynostratigraphy in the Swiss Plateau  

International Nuclear Information System (INIS)

A detailed Late-Glacial radiocarbon stratigraphy for the Swiss Plateau has been established on the basis of over 90 accelerator 14C dates on terrestrial plant macrofossils. A comparison of the radiocarbon ages derived from terrestrial, telmatic and limnic material at different sites on the Swiss Plateau yields a proposal for modifying the zonation system of Welten for the Late-Glacial. By retaining the limits of chronozones and by refining the palynostratigraphic criteria for the limits of biozones, a separation between chrono- and biozonation at the beginning of the Boelling and the Younger Dryas becomes obvious. 54 refs.

1989-01-01

293

Deep-sea temperature and ice volume changes across the Pliocene-Pleistocene climate transitions.  

UK PubMed Central (United Kingdom)

Earth has undergone profound changes since the late Pliocene, which led to the development [approximately 2.7 million years ago (Ma)] and intensification (approximately 0.9 Ma) of large-scale Northern Hemisphere ice sheets, recorded as transitions in the benthic foraminiferal oxygen isotope (delta18Ob) record. Here we present an orbitally resolved record of deep ocean temperature derived from benthic foraminiferal magnesium/calcium ratios from the North Atlantic, which shows that temperature variations are a substantial portion of the global delta18Ob signal. The record shows two distinct cooling events associated with the late Pliocene (LPT, 2.5 to 3 Ma) and mid-Pleistocene (MPT, 1.2 to 0.85 Ma) climate transitions. Whereas the LPT increase in ice volume is attributed directly to global cooling, the shift to 100,000-year cycles at the MPT is more likely to be a response to an additional change in ice-sheet dynamics.

Sosdian S; Rosenthal Y

2009-07-01

294

Solute Transport Modeling In An Experimental Stratigraphy  

Science.gov (United States)

A high-resolution, multiscale hydraulic conductivity map is created based on an experimental stratigraphy. A heterogeneous model is created, incorporating the complete conductivity variation. A 14-unit hydrostratigraphic model (HSM) is also created for which an equivalent conductivity is estimated for each unit via a novel upscaling method. Under a lateral hydraulic gradient, steady-state, incompressible flow experiment is conducted in both models. Compared to the heterogeneous model prediction, HSM-predicted, global mean relative error of hydraulic head is 1.5%, that of groundwater flux is 0.77%. A conservative pulse-input line- source tracer is then simulated. In the heterogeneous model, the tracer exhibits both scale-dependency in the observed longitudinal macrodispersivity and persistent long tailing associated with anomalous, non-Fickian dispersion. Using (small) hydrodynamic dispersivities, the HSM closely predicts the tracer displacement, moments and their derivatives. In solute breakthrough, a certain degree of tailing is also predicted by the HSM which captures the large-scale, between-unit velocity variation. However, detailed plume shape is not captured, nor are the arrival and tailing of the breakthrough curves. Using macrodispersivity (both unit-specific and time- dependent), the breakthrough prediction of the HSM has improved from that using hydrodynamic dispersivities, especially in early times before encountering significant non-stationarity. However, the HSM model fails to capture the development of a steep breakthrough front and multiple peak concentrations. The plume shape is also too diffused. For all HSM simulations, the largest error occurs in a fluvial-floodplain unit where irregular trend exists and in a turbidite unit which contains preferential flow. Finally, macrodispersive displacement mapping reveals that heterogeneity-induced dispersion is correlated both in time and space, a likely result of the correlated velocity field.

Zhang, Y.

2006-12-01

295

Paleobotanical analysis of materials from fossil gopher burrows and upper pleistocene host deposits, the Kolyma River lower reaches  

Science.gov (United States)

The comparative analysis of palynomorphs and plant megafossils (fruits, seeds, twigs, leaves) in the Upper Pleistocene host sediments and materials filling in fossil burrows of gophers, their coprolites included, at the Duvannyi Yar, Stanchikovskii Yar and Zelenyi Mys sites of the Kolyma Lowland is carried out. Genera Salix, Lychnis, Silene, Draba, Potentilla, Larix, and families Poaceae, Polygonaceae, Cyperaceae, Compositae, and Leguminosae are determined among palynological remains and megafossils. Factors responsible for qualitative and quantitative differences in taxonomic compositions of palynological and megafossil assemblages are biological peculiarities of plants, different character of fossilization of palynomorphs and large plant remains, geographic conditions, different genesis of assemblages (allochthonous for microfossils and autochthonous for megafossils), and inadequately known morphology of certain spore and pollen taxa. The comprehensive paleobotanical analysis leads to the conclusion that the study region was occupied in the Late Pleistocene by plant communities of humid to somewhat dryer tundra with separate areas of pioneering and steppe vegetation.

Lopatina, D. A.; Zanina, O. G.

2006-10-01

296

The transition from wave-dominated estuary to wave-dominated delta: The Late Quaternary stratigraphic architecture of Tiber River deltaic succession (Italy)  

Science.gov (United States)

This paper presents a detailed description of the stratigraphic architecture of the Late Pleistocene/Holocene Tiber delta succession in order to document the passage from wave-dominated estuary to wave-dominated delta in the broader context of Late Quaternary sea level fluctuations.This succession constitutes a sequence-stratigraphic unit known as Tiber Depositional Sequence (TDS), which was deposited during the last glacial-interglacial cycle (last 120 ka). Our study is based on the examination of an enormous amount of data derived from the stratigraphy of about 300 wells, petrographical and paleontological data (foraminifera, ostracoda, pollen, and plant macrofossils), 14C dating, and from the integration of geomorphological and geoarcheological data. Recently a 100 m deep core (Pesce Luna well) was studied through a multidisciplinary approach and a detailed description of sedimentary facies, foraminifer and ostracod assemblages, pollen and 14C dating is presented in this paper. The new data allowed to produce three new correlation panels and to describe in more detail, with respect to previous interpretations, the stratigraphic-depositional architecture of the TDS, which internally shows the preservation of sediment deposited during the early and late lowstand, the transgressive and the highstand systems tracts. Alluvial and coastal depositional systems characterize the early lowstand phase of the TDS, which developed during the eustatic sea-level fall between about 120 and 30-26 yr BP. During the late lowstand phase, which is characterized by stillstand and slow eustatic sea-level rise a prograding delta and an aggrading incised-valley fluvial fill developed. The Tiber incised valley was transformed into a wave-dominated estuary during the transgressive phase (TST), whereas a coastal-shelf sedimentation took place during the subsequent highstand phase (HST). This study confirms the lithofacies distribution resulting from transgression and infilling of the wave-dominated estuaries, but also shows how the transition to a wave-dominated delta, prograding at the time of sea-level highstand occurred. Changes in sediment input, climatic variations and, more recently, human activities played a major role in the development of the Tiber delta during the last 20,000 yr BP. In the last 3000 years a relationship between progradational phases of the delta and flood events of the Tiber river has been highlighted, suggesting also the formation and merging of barrier-spits to the mainland.

Milli, Salvatore; D'Ambrogi, Chiara; Bellotti, Piero; Calderoni, Gilberto; Carboni, Maria Gabriella; Celant, Alessandra; Di Bella, Letizia; Di Rita, Federico; Frezza, Virgilio; Magri, Donatella; Pichezzi, Rita Maria; Ricci, Valeria

2013-02-01

297

The Mid-Pleistocene Transition: Deep Sea Temperature And Global Ice Volume From Mg/Ca and ?18O In Benthic Foraminifera  

Science.gov (United States)

The mid-Pleistocene transition (MPT), which occurred between ~1 to 0.7 Ma, is recorded in benthic foraminiferal oxygen isotope (?18Ob) records as a shift in the periodicity of northern hemisphere glaciations from low amplitude 41-kyr to large amplitude 100-kyr glacial-interglacial cycles. The MPT has variably been attributed to either global cooling associated with a long-term decreasing trend in greenhouse gases, or changes in internal ice sheets dynamics, independent of changes in atmospheric pCO2. Evidence in support of global cooling during the MPT is inconclusive. Whereas, sea surface temperature (SST) records from upwelling regions show a cooling trend throughout the Pleistocene, no discernible SST trend is observed in the Western Pacific Warm Pool (WPWP). The ostracode Mg/Ca record of Dwyer et al., (1995) suggests a cooling from the late Pliocene to Pleistocene, but the record is of low resolution and does not document the transition. Here we present a new high-resolution record of benthic foraminifera Mg/Ca from North Atlantic DSDP site 607. The Mg/Ca-based bottom water temperature (BWT) allows us to quantify the extent of global cooling and, paired with ?18Ob, to estimate the concomitant increase in ice volume. The new BWT record shows a shift in both the periodicity (from ~41 to 100 kyr) and amplitude (from ~2 to 4° C) of glacial-interglacial cycles from the late Pliocene-early Pleistocene to the late Pleistocene, and is generally coherent with the ?18Ob record. Across the MPT, glacial periods become progressively cooler and suggest a long term cooling of ~2° C associated with the increase in ice volume. The long term cooling of the high latitude, as recorded in BWT, in contrast with the stability of WPWP SST suggests that changes in meridional transport of heat and moisture might have played a key role in the MPT.

Sosdian, S. M.; Rosenthal, Y.; Raymo, M.

2006-12-01

298

Estratigrafía y sedimentología de las unidades del Cretácico superior-Paleógeno aflorantes en la margen sureste del lago Viedma, provincia de Santa Cruz, Argentina/ Stratigraphy and sedimentology of the Late Cretaceous-Paleogene units cropping out at the south-eastern margin of Lake Viedma, Santa Cruz Province, Argentina  

Scientific Electronic Library Online (English)

Full Text Available Abstract in spanish En el sureste del lago Viedma afloran sedimentitas del Cretácico superior y Paleógeno de la cuenca Austral. En el perfil de Barrancas Blancas se describen 28 m de areniscas y fangolitas amarillentas correspondientes al Miembro La Asunción de la Formación Anita que son cubiertas en forma concordante y transicional por 390 m de areniscas y pelitas grisáceas de la Formación Cerro Fortaleza. Las primeras representan la progradación de ambientes de plataforma marina dom (more) inada por el oleaje mientras que las segundas atestiguan la sedimentación en ambientes transicionales, fluviales y fluviales con acción mareal. La evolución general de los paleoambientes sedimentarios y secuencias depositacionales, la procedencia de las areniscas y direcciones de paleocorrientes indican que estas rocas fueron depositadas durante la etapa de cuenca de retroarco (sag). En el cerro Pirámides se hallan presentes sedimentitas terciarias que se disponen en contacto tectónico sobre las rocas de la Formación Cerro Fortaleza. El escaso espesor preservado de las areniscas verdes de la Formación Man Aike ( Abstract in english Late Cretaceous and Paleogene sedimentary rocks of the Austral Basin crop out on the south-eastern margin of Lake Viedma. In the Barrancas Blancas section, 28 m of yellowish sandstone and mudstone of the La Asunción Member of the Anita Formation are transitionally covered by 390 m of greyish sandstone and mudstone of the Cerro Fortaleza Formation. The former represent a prograding barred nearshore system, whereas the latter correspond to paralic, fluvial and fluvial-tida (more) l sedimentation. The evolution of the depositional sequences, sedimentary palaeoenvironments, sandstone provenance and palaeocurrents indicate that the sediments were deposited during the back-arc (sag) stage of the basin. At Cerro Piramides, Tertiary sedimentary rocks rest with fault contact on top of the Cerro Fortaleza Formation. The limited thickness (

Marenssi, SA; Casadío, S; Santillana, SN

2003-09-01

299

Workshop on quantitative dynamic stratigraphy. Final conference report  

Energy Technology Data Exchange (ETDEWEB)

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)

Cross, T.A.

1988-04-01

300

Estratigrafía y sedimentología de las unidades del Cretácico superior-Paleógeno aflorantes en la margen sureste del lago Viedma, provincia de Santa Cruz, Argentina Stratigraphy and sedimentology of the Late Cretaceous-Paleogene units cropping out at the south-eastern margin of Lake Viedma, Santa Cruz Province, Argentina  

Directory of Open Access Journals (Sweden)

Full Text Available En el sureste del lago Viedma afloran sedimentitas del Cretácico superior y Paleógeno de la cuenca Austral. En el perfil de Barrancas Blancas se describen 28 m de areniscas y fangolitas amarillentas correspondientes al Miembro La Asunción de la Formación Anita que son cubiertas en forma concordante y transicional por 390 m de areniscas y pelitas grisáceas de la Formación Cerro Fortaleza. Las primeras representan la progradación de ambientes de plataforma marina dominada por el oleaje mientras que las segundas atestiguan la sedimentación en ambientes transicionales, fluviales y fluviales con acción mareal. La evolución general de los paleoambientes sedimentarios y secuencias depositacionales, la procedencia de las areniscas y direcciones de paleocorrientes indican que estas rocas fueron depositadas durante la etapa de cuenca de retroarco (sag). En el cerro Pirámides se hallan presentes sedimentitas terciarias que se disponen en contacto tectónico sobre las rocas de la Formación Cerro Fortaleza. El escaso espesor preservado de las areniscas verdes de la Formación Man Aike (Late Cretaceous and Paleogene sedimentary rocks of the Austral Basin crop out on the south-eastern margin of Lake Viedma. In the Barrancas Blancas section, 28 m of yellowish sandstone and mudstone of the La Asunción Member of the Anita Formation are transitionally covered by 390 m of greyish sandstone and mudstone of the Cerro Fortaleza Formation. The former represent a prograding barred nearshore system, whereas the latter correspond to paralic, fluvial and fluvial-tidal sedimentation. The evolution of the depositional sequences, sedimentary palaeoenvironments, sandstone provenance and palaeocurrents indicate that the sediments were deposited during the back-arc (sag) stage of the basin. At Cerro Piramides, Tertiary sedimentary rocks rest with fault contact on top of the Cerro Fortaleza Formation. The limited thickness (<1m) preserved of greenish sandstone of the Man Aike Formation precludes any attempt to interpret its depositional environment. Conglomerate, sandstone and mudstone (locally carbonaceous) of the Río Leona Formation (75 m) rest with erosional contact on the former. These rocks represent a rapid transition from a high energy to low energy fluvial systems that eventually graded into marginal marine environments represented by the fossiliferous sandstones of the Centinela Formation (<3m). The facies arrangement, evolution of the palaeoenvironments, and palaeocurrents suggest that these sediments were deposited during the foreland basin stage.

SA Marenssi; S Casadío; SN Santillana

2003-01-01

 
 
 
 
301

Influence of barrier island stratigraphy and bathymetry on shoreline change  

Energy Technology Data Exchange (ETDEWEB)

The barrier island chain off the Atlantic coast of Virginia exhibits anomalous rates of shoreline change, from [minus]40 m/year to +20 m/year. To determine the causes of these anomalous rates the relationships between stratigraphy, bathymetry, orientation of the islands, and rate of shoreline change were investigated. The stratigraphy of the islands if variable along their length and from island to island. Areas of the islands that contain more cohesive materials, such as mud and buried marsh, may be more resistant to erosion than areas of less cohesive material such as fine sand. Vibracoring was conducted at sites exhibiting extremely high rates of shoreline change to see if there is a relation between stratigraphy and rates of shoreline change. Variations in offshore slope and along the islands may affect wave approach so that their energy is unevenly dispersed along island strike. When the offshore slope is steep the waves may dissipate more of their energy on the shore and cause significant erosion. Where a more gradual slope induces wave dissipation farther offshore and diminishes the energy which may cause less erosions. Ebb tidal deltas appear to play a major role in distributing wave energy along the barrier shoreline. Island segments to the south of ebb tidal delta platforms are sheltered from large northeasterly storm waves by the ebb tidal deltas. Results show that neither stratigraphy nor bathymetry alone appear to exhibit a dominating influence on shoreline change of the Virginia Barrier Islands. However, in combination with other factors, such as beach cusp periodicity and inlet migration, stratigraphy and bathymetry may cause a strong influence on shoreline changes.

Kowalski, K.A. (Bucknell Univ., Lewisburg, PA (United States). Dept. of Geology)

1993-03-01

302

The Role of the Western Fennoscandia Uplift For Neogene Depositional Environments and Stratigraphy in the North Viking Graben  

Energy Technology Data Exchange (ETDEWEB)

Uplift of Western Fennoscandia caused erosion of the offshore Norway Mesozoic-Cenozoic successions. In particular, the Neogene section has been deeply truncated with only the toes of large-scale cliniforms preserved. The stratigraphic and environmental interpretation of these remnant features have been possible using seismic stratigraphy criteria. Five second-order Transgressive/Regressive facies cycles have been recognized within the Mio-Pleistocene succession. These second-order cycles are bounded by major erosional surfaces. The Lower and Middle Miocene T/R Cycles are reduced to valley-fill deposits over most of the Northern North Sea area. Therefore they have been mapped together, individual cycles being under seismic resolution. The Upper Miocene-Pliocene T/R cycles form most of the Neogene succession, with thick well expressed depositional units. They have been split into ten mappable depositional seismic sequences (or sequence sets). Wireline log/seismic correlations confirm the seismic stratigraphic interpretation, and also indicate that higher frequency depositional sequences occur within the seismic sequence stratigraphic framework.

Tongban, H.; Courme, B.; Jacquin, T.; Dunay, R.

1999-07-01

303

Cryptic lineages and Pleistocene population expansion in a Brazilian Cerrado frog.  

UK PubMed Central (United Kingdom)

Diversification of South American species endemic to open habitats has been attributed to both Tertiary events and Pleistocene climatic fluctuations. Nonetheless, phylogeographical studies of taxa in these regions are few, precluding generalizations about the timing and processes leading to differentiation and speciation. We inferred population structure of Hypsiboas albopunctatus, a frog widely distributed in the Brazilian Cerrado. Three geographically distinct lineages were recovered in our phylogeny. The Chapada dos Guimarães (CG) clade was the first to diverge from other populations and contains multiple haplotypes from a single population in western Cerrado, probably representing a cryptic species. The southeast clade (SE) includes populations along the southeastern limit of the range within the historical distribution of the Brazilian Atlantic forest. Finally, the Central Cerrado (CC) group includes haplotypes from the interior of Brazil that are paraphyletic relative to the SE clade. Analyses of historical demography indicate significant population expansion in the CC and SE populations, likely associated with colonization of newly formed open habitats. The divergence of populations in the CG clade occurred in the late Miocene, concordant with the uplift of the central Brazilian plateau. Divergence of the SE clade from the CC occurred during the mid-Pleistocene. Thus, both Tertiary geological events and Pleistocene climatic fluctuations promoted divergences among lineages. Our study reveals a complex history of diversification in the Cerrado, a morphoclimatic domain highly threatened because of anthropogenic habitat alteration. We identified surprisingly deep divergences in a widely distributed frog, indicating that the Cerrado is not a barrier-free habitat and that its diversity is likely underestimated.

Prado CP; Haddad CF; Zamudio KR

2012-02-01

304

Regional depositional history of the Miocene-Pleistocene Louisiana Slope, Green Canyon and Mississippi Canyon  

Energy Technology Data Exchange (ETDEWEB)

A regional sequence-stratigraphic analysis was recently completed for the Tertiary slope sediments in Green Canyon, Ewing Bank, and Mississippi Canyon to provide a chronostratigraphic framework for basin reconstructions and predict lithofacies distributions of reservoir and seal rocks. Sixteen third-order sequences of lowstand deep-water deposits were interpreted for the middle Miocene-Pleistocene section. Thirty regional lithofacies maps were made of predominantly lowstand deposits showing the distribution of shale and sand-prone sediments, slumping, channel levee systems, and fan lobes based on distinctive seismic reflection and well log patterns. These maps were combined with isochrons of selected sequences to identify depositional fairways, depocenters, and paleosalt positions that constantly changed through time. Depositional trends were principally north to south but were also observed to be east-west as salt modified the gradient on the gently dipping slope. In some cases, the structural and stratigraphic trends could be projected under allochthonous tabular salt. Miocene channel and fan lobe sands were found concentrated on the middle-lower paleoslope across the study area. The sedimentation rate doubled (0.7 m/1000 yr) in the early-middle Pliocene, which caused large-scale salt movements and trapped sand-prone turbidites along the upper-middle slope. A four-fold decrease in sediment influx during the late Pliocene-early Pleistocene produced a stacked condensed section of four sequences over the eastern Louisiana slope. A return to rapid sedimentation (up to 2.1 m/1000 yr.) during the Pleistocene reactivated salt movements and depocenters in the Green Canyon, Ewing Bank, and Mississippi Trough areas.

Risch, D.L.; Chowdhury, A.N.; Hannan, A.E. [Geco-Prakla, Houston, TX (United States)

1994-09-01

305

Tenth international congress on Carboniferous stratigraphy and geology - proceedings. Volume 4. Dixieme congres international de stratigraphie at de geologie du Carbonifere - compte rendu. Volume 4  

Energy Technology Data Exchange (ETDEWEB)

This volume contains the papers presented at symposia 1-10 and to Working Group 2 (IUGS Subcommission on Carboniferous Stratigraphy) Working Group 3 (Carboniferous Permian boundary - subcommission Permian stratigraphy) and Working Groups 5 and 6 (on the genus sphenopteris and on Carboniferous and Permian compression floras). 10 papers have been abstracted separately.

1985-01-01

306

Mechanical stratigraphy of sedimentary section - implications for petroleum exploration, Gulf of Suez, Egypt  

Energy Technology Data Exchange (ETDEWEB)

Mechanical response of sedimentary units to extension varies, depending on their rheology. In the Gulf of Suez, knowledge of the mechanical stratigraphy assures better control for seismic interpretation, structural analysis, and delineation of possible hydrocarbon traps. Recent field studies and seismic analysis allow delineation of the structural response of a range of prerift and synrift lithologies. The prerift section is divided into three major mechanical/stratigraphic units: Precambrian basement, Nubian sandstone, and Cenomanian through Eocene shallow marine platform rocks. Single fault planes in the basement are expressed in the overlying Nubian sandstone as closely spaced parallel faults and fractures. In contrast, the inhomogeneous Late Cretaceous-Paleogene section of alternating brittle and ductile beds drapes over the underlying normal faults. The synrift section may comprise three mechanical/stratigraphic units: (1) early Miocene carbonates and clastics; (2) middle-late Miocene evaporites; and (3) Pliocene-Recent clastics. The lower synrift rocks respond to faulting much like the Cenomanian-Eocene units. The evaporite section acts as a major detachment zone, with underlying faults dying out upward. Onshore, faults in the more brittle passive cover rocks sole into the underlying evaporites. Thus, faults at the surface may be entirely decoupled from master faults in the early synrift and prerift strata. Mechanical response in the synrift section is complicated by syntectonic processes such as growth faulting, compaction, and lateral facies changes.

Gawarecki, S.L.; Coffield, D.Q.; Schamel, S.

1987-05-01

307

Pliocene and pleistocene volcanism in Southern Kyushu  

International Nuclear Information System (INIS)

Southern Kyushu has been the site of intense volcanism at least since Pliocene time. One of the characteristics is the prevalence of large scale pyroclastic flow eruption, most of which originated from the volcano-tectonic depression now occupied by Kagoshima Bay. The deposits of these pyroclastic flows cover wide areas, serving as excellent stratigraphic marker horizons, but the radiometric age of the volcanic rocks in the area has been hardly available so far. A sample of Isaku pyroclastic flow was taken from an abandoned quarry. Ushine andesite, Fumoto pyroclastic flow, Ushine basalt and Ushine rhyolite were collected from a 300 m high cliff toward the top from the bottom. Kiyoura horn-blende andesite was collected from the southeastern foot of Yaeyama. K-Ar age was determined for these rocks. It was indicated that from 2 to 3 Ma (i.e., million years) ago, large scale pyroclastic eruption had taken place in the northern part of Kagoshima Bay, and extensive andesitic to basaltic volcanism occurred in both Ushine and Yaeyama areas. The establishment of the volcanic stratigraphy in the areas must await until more radiometric age determination becomes available. (Kako, I.)

1984-01-01

308

Complete mitochondrial genome sequence of a Middle Pleistocene cave bear reconstructed from ultrashort DNA fragments.  

Science.gov (United States)

Although an inverse relationship is expected in ancient DNA samples between the number of surviving DNA fragments and their length, ancient DNA sequencing libraries are strikingly deficient in molecules shorter than 40 bp. We find that a loss of short molecules can occur during DNA extraction and present an improved silica-based extraction protocol that enables their efficient retrieval. In combination with single-stranded DNA library preparation, this method enabled us to reconstruct the mitochondrial genome sequence from a Middle Pleistocene cave bear (Ursus deningeri) bone excavated at Sima de los Huesos in the Sierra de Atapuerca, Spain. Phylogenetic reconstructions indicate that the U. deningeri sequence forms an early diverging sister lineage to all Western European Late Pleistocene cave bears. Our results prove that authentic ancient DNA can be preserved for hundreds of thousand years outside of permafrost. Moreover, the techniques presented enable the retrieval of phylogenetically informative sequences from samples in which virtually all DNA is diminished to fragments shorter than 50 bp. PMID:24019490

Dabney, Jesse; Knapp, Michael; Glocke, Isabelle; Gansauge, Marie-Theres; Weihmann, Antje; Nickel, Birgit; Valdiosera, Cristina; García, Nuria; Pääbo, Svante; Arsuaga, Juan-Luis; Meyer, Matthias

2013-09-09

309

Co-operation between Gda?sk and Vilnius Universities in Pleistocene geochronology investigations  

Science.gov (United States)

The thermoluminescence (TL) dating of aquatic sand'y sediments, carried out as a co-operation between Gda?sk and Vilnius Universities, provided a more accurate chronology of the Middle-Upper Pleistocene in Lithuania. Based on TL dating, Middle and Upper Pleistocene fine-grained sands of aquatic origin have been attributed to the But?nai (Holsteinian) Interglacial (Tartokai outcrop), Snaigup?l? (Drenthe-Wartha) Interglacial (Tartokai and Valakampiai (Valakupiai) outcrops), Merkin? (Eemian) Interglacial (Tartokai and Netiesos outcrops) and Nemunas (Vistulian) Glacial (Tartokai, Netiesos and Rokai outcrops). The dating of samples from the outcrops studied show the age of the But?nai Interglacial to be 430.2 to 280.3 ka years BP, of the Snaigup?l? Interglacial 239.4 to 179.3 ka years BP and the Merkin? Interglacial 135.9 to 103.2 ka years BP. The Early Nemunas and the Middle Nemunas non-glacial sediments accumulated between 67.2-30.6 ka years BP. Tills in the upper part of the Tartokai and Rokai outcrops are younger than 30,000 BP and belong to the Late Nemunas glacial maximum in Lithuania. Different dosimetric (TL, OSL) ages of granular fractions of the same sample indicate different parametres predetermined by the distribution of grain size fractions during aquatic sedimentation of quartz sand. The granulometry of sand or the grain size distribution of quartz particles in samples reflect the state of the hydrodynamic sedimentation space.

Gaigalas, Algirdas; Fedorowicz, Stanis?aw

2009-10-01

310

Cenozoic stratigraphy of the Sahara, Northern Africa  

Science.gov (United States)

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.

Swezey, Christopher S.

2009-01-01

311

Pliocene-Pleistocene diatom biostratigraphy of nearshore Antarctica from the AND-1B drillcore, McMurdo Sound  

Science.gov (United States)

The near-shore open-marine diatom record recovered in the ANtarctic geological DRILLing (ANDRILL) McMurdo Ice Shelf Project (MIS) AND-1B drillcore, McMurdo Sound, Antarctica, advances our understanding of the marine conditions present in the southern Ross Sea during the Pliocene and early Pleistocene. This diatom history is recorded within alternating diamictite and diatomite that reflect alternating glacial activity and high marine primary productivity. The diatomite units were deposited in a continental shelf open-marine setting during periods of reduced ice cover in West Antarctica. A new diatom biostratigraphic scheme spanning the last ca. 5 Ma is proposed for the Antarctic near-shore area, based on prior work from high latitude drillcores. Four new zones are proposed for the Pliocene/Pleistocene, with eight in total for the new zonal scheme, utilizing Actinocylus fasciculatus, Actinocyclus maccollumii, Fragilariopsis bohatyii, Rouxia antarctica, and Thalassiosira fasciculata as new zonal markers. The early Pliocene shares the most assemblage commonality with that of the Southern Ocean with greater numbers of endemic species observed in the late Pliocene and early Pleistocene; a group of related Fragilaripsis species characterizes much of this later part of the time column. Two new species are proposed, Fragilariopsis tigris sp. nov. Riesselman and Thalassiosira teres sp. nov. Winter; a formal name is also proposed for another species, Rhizosolenia harwoodii sp. nov. Winter. The new zonation is tied to a robust chronology utilizing diatom biostratigraphy, volcanic 40Ar/39Ar ages and magnetostratigraphy.

Winter, D.; Sjunneskog, C.; Scherer, R.; Maffioli, P.; Riesselman, C.; Harwood, D.

2012-10-01

312

LATE SYPHILIS  

Directory of Open Access Journals (Sweden)

Full Text Available A case of late syphilis involving cardiovascular system andeye is presented here. The patient presented with 2 months history of headache, visual disturbance and shortnessof breath. He had aortic regurgitation with violaceous sclerae, only perception of light in left eye, 6/18 visionin right eye and disc swelling and exudative retinal detachment in left eye. Work up confirmed the diagnosis ofsyphilis for which specific and supportive treatment has been started and advised follow up.

SQUADRON LEADER FAYYAZ HASSAN

2004-01-01

313

An enhanced role for the Tropical Pacific on the humid Pleistocene–Holocene transition in southwestern North America  

Science.gov (United States)

Climate effects on landscape evolution during the Late Pleistocene–Holocene transition (˜14.6–8 ka) in southwestern North America traditionally are linked to the activity of the North American Monsoon and to vegetation change related to a decrease in winter precipitation acting in response to orbital cyclicity. We performed an integrated analysis of regional alluvial fan, lacustrine and paleobotanical records for the area comparing them with hemispheric and regional paleoclimate proxies. Our focus was on the potential role the Tropical Pacific has as a synoptic pattern modulator and moisture source for hydrogeomorphic activity in the region.

Antinao, Jose Luis; McDonald, Eric

2013-10-01

314

Lower Palaeogene stratigraphy of the northern North Sea  

Energy Technology Data Exchange (ETDEWEB)

The Lower Palaeogene stratigraphy of the northern North Sea is described using wireline log and biostratigraphic data. At group and formation level a close similarity can be shown with the stratigraphy defined in the Outer Moray Firth area of the central North Sea. A two-fold subdivision into the Montrose and Moray Groups is recognized. The Montrose Group consists of the Maureen and Lista Formations while the succeeding Moray Group contains the Sele, Balder, Dornoch and Beauly Formations. The Maureen and Lista Formations are dominantly argillaceous units that contain poorly defined sandstones; the most laterally extensive of these is the Heimdal Member developed within the Lista Formation. The Dornoch and Beauly Formations are shelfal sandstone units that pass eastwards and northwards into the age equivalent, dominantly argillaceous Sele and Balder Formations. The Sele Formation contains the Hermod Member while the Balder Formation contains the Odin Member. (author)

Mudge, D.C. (Nevis Associates Ltd., Helensburgh (United Kingdom)); Copestake, Philip (IEDS Ltd., Nailsworth (United Kingdom))

1992-06-01

315

Sequence stratigraphy, fluvial reservoirs, and subtle oil bearing traps  

Energy Technology Data Exchange (ETDEWEB)

The types of hydrocarbon reservoirs and oil-bearing traps associated with fluvial depositional deposits interbedded with volcanic rocks were documented along with their distribution patterns for the Sand River Street 3 (SRS3), located in the Liaohe basin in northeast China. The area has been of interest for petroleum exploration since the 1970s. Well drilling at structural traps located along the anticline structures have often failed because the sand reservoirs were poorly developed. The objective of this study was to identify the paleoenvironmental factors that affect the distribution of reservoirs and to predict the spatial and temporal distribution of reservoir facies in areas away from well control. The work will also help to identify subtle oil bearing traps. Collected data on the stratigraphy, sedimentology and paleobiology of the region was used to reconstruct a general stratigraphic sequence and the channel reservoirs were predicted through stratigraphy correlations and JASON reversion software. 4 refs., 1 fig.

Hongwei, L.; Zhu, Y.J.; Xiao, Q.H. [Liaohe Exploration and Development Research Inst., (China)

2000-06-01

316

Upper pleistocene fossil hominids from Sri Lanka.  

UK PubMed Central (United Kingdom)

Between 1978 and 1983 hominid skeletal remains were collected from the cave sites of Batadomba lena and Beli lena Kitulgala in Sri Lanka (formerly Ceylon). These are the most ancient specimens of anatomically modern Homo sapiens found thus far in South Asia, radiocarbon dates placing them in the Upper Pleistocene. Morphometric analysis of the remains of some 38 individuals from the two sites indicates that these populations were characterized by medium stature, moderate to pronounced cranial and postcranial robusticity, medium-size permanent tooth crown measurements, prognathic alveolar facial proportions, and low incidence of osseous and dental pathological conditions. Comparisons of these ancient Sri Lankans with other prehistoric skeletal series from South Asia and elsewhere support the hypothesis that muscular-skeletal robusticity was a significant physical adaptation of earlier hunting-foraging populations. A trend towards reduction of sexual dimorphism and development of more gracile body form and smaller teeth appears to have accelerated with the socioeconomic transition to food-production strategies involving agriculture and pastoralism and refinement of technologies for food procurement and preparation, as documented by morphometric studies of later prehistoric inhabitants of South Asia.

Kennedy KA; Deraniyagala SU; Roertgen WJ; Chiment J; Disotell T

1987-04-01

317

Western closure of the Corinth Rift: Stratigraphy and structure of the Lakka fault block  

Science.gov (United States)

In the Corinth Gulf, seismicity is highest in the west, where the active Psathopyrgos-Neos Erineos-Aegion fault zone (PNEAFZ;30 km long, N dip) defines the south coast. To the south and SE the inactive early rift records N and NW migration of deformation since the Pliocene. When was the PNEAFZ initiated? How did it grow? What is the relevance of this fault zone within the full rift history? This paper presents new data for the onshore westernmost rift, indicating that it had a distinct early rifting history (Early to Middle Pleistocene) before being overprinted around 400 ka by the NW migrating Corinth rift. Two syn rift stratigraphic groups are recognised in the uplifted Lakka fault block in the footwall of the PNEAFZ. The youngest Galada group, comprises marine deposits and terraces that mainly document footwall uplift since initiation of the PNEAFZ at around 400-350 ka (Palyvos et al. 2010). The oldest sediments derived from the footwall of the Lakka fault are the 400-350 ka old Aravonitsa Gilbert delta (Palyvos et al. 2010), suggesting this fault is not significantly older than the PNEAFZ. The Galada group records a gradual eastward block tilting due to differential footwall uplift as the PNEAFZ propagated east. The underlying Profitis Ilias group, (pre 400 ka, < 600 m) is characterised by south and southeastward fining continental facies from coarse alluvial conglomerates in the immediate footwall of the Psathopyrgos fault (Rodini formation) passing east and south to fluvial sandstones and conglomerates (Salmoniko formation), to deltaic and shallow water sandstones interfingering with lacustrine marls, silts and fine sandstones with rare conglomerates and lignites (Synania formation). Faunal assemblages in the Synania formation indicate freshwater to brackish conditions with occasional marine levels and support an Early to Middle Pleistocene age. To the ESE, the Synania formation passes laterally and up into a 200 m succession of fine sandstones with rare conglomerates, lignites and mudstones (Koumaris formation). In the area of the Meganitis and Selinous rivers, the Profitis Ilias group underlies and may be partly laterally equivalent to the Early to Middle Pleistocene Middle group comprising Gilbert deltas sourced from the south. New data indicate that the Profitis Ilias group was a fluvio-lacustrine system sourced from the north. Accommodation was probably created by an, as yet, unidentified south dipping fault on the north side of or below the present Gulf. The same fluvio-lacustrine system may be traced into the Patras area, further west. The Profitis Ilias group depocentre may have been part of the NE limit of the Patras rift. The westernmost Corinth rift was therefore dominated by continental facies until late Middle Pleistocene. The Rion Straits did not open west to the Mediterranean until well after 400 Ka. Any marine influence in the earlier rift came from the east. Palyvos N., Mancini M., Sorel D., Lemeille F., Pantosti D., Julia R., Triantaphyllou M., De Martini P.M. (2010) - Geomorphological, stratigraphic and geochronologic evidence of fast Pleistocene coastal uplift in the westernmost part of the Corinth Gulf (Greece). Geological Journal, 45, 78-104.

Palyvos, Nikos; Ford, Mary; Mancini, Marco; Esu, Daniela; Girotti, Odoardo; Urban, Brigitte

2013-04-01

318

Age of Middle Pleistocene fauna and Lower Palaeolithic industries from Kent's Cavern, Devon  

Science.gov (United States)

Kent's Cavern has long been known as potentially among the oldest Palaeolithic sites in the country, with the basal Breccia deposit containing a sparse Lower Palaeolithic industry. The sediment consists of a chaotic clayey conglomerate emplaced as a series of debris flows, which entered the cave via blocked entrances at its southwest end. The Breccia contains a fauna dominated by the bear Ursus deningeri, with lion Felis leo and the voles Arvicola cantiana and Microtus oeconomus, establishing a late Cromerian age for the deposit. The artefacts comprise an industry of crudely manufactured handaxes and flakes, and show damage suggesting that they were brought into the cave by the debris flows, and may thus predate the sediment and fauna. We demonstrate an age of >340 ka for the Breccia using two independant dating methods, consistent with existing models of the age of the British Middle Pleistocene sequence.

Proctor, C. J.; Berridge, P. J.; Bishop, M. J.; Richards, D. A.; Smart, P. L.

2005-05-01

319

Upper Neogene stratigraphy and tectonics of Death Valley — a review  

Science.gov (United States)

New tephrochronologic, soil-stratigraphic and radiometric-dating studies over the last 10 years have generated a robust numerical stratigraphy for Upper Neogene sedimentary deposits throughout Death Valley. Critical to this improved stratigraphy are correlated or radiometrically-dated tephra beds and tuffs that range in age from > 3.58 Ma to Mormon Point. This new geochronology also establishes maximum and minimum ages for Quaternary alluvial fans and Lake Manly deposits. Facies associated with the tephra beds show that ˜3.3 Ma the Furnace Creek basin was a northwest-southeast-trending lake flanked by alluvial fans. This paleolake extended from the Furnace Creek to Ubehebe. Based on the new stratigraphy, the Death Valley fault system can be divided into four main fault zones: the dextral, Quaternary-age Northern Death Valley fault zone; the dextral, pre-Quaternary Furnace Creek fault zone; the oblique-normal Black Mountains fault zone; and the dextral Southern Death Valley fault zone. Post - 3.3 Ma geometric, structural, and kinematic changes in the Black Mountains and Towne Pass fault zones led to the break up of Furnace Creek basin and uplift of the Copper Canyon and Nova basins. Internal kinematics of northern Death Valley are interpreted as either rotation of blocks or normal slip along the northeast-southwest-trending Towne Pass and Tin Mountain fault zones within the Eastern California shear zone.

Knott, J. R.; Sarna-Wojcicki, A. M.; Machette, M. N.; Klinger, R. E.

2005-12-01

320

Archaeological recording and chemical stratigraphy applied to contaminated land studies.  

Science.gov (United States)

The method used by archaeologists for excavation and recording of the stratigraphic evidence, within trenches with or without archaeological remains, can potentially be useful to contaminated land consultants (CLCs). The implementation of archaeological practice in contaminated land assessments (CLAs) is not meant to be an exercise in data overkill; neither should it increase costs. Rather, we suggest, that if the excavation and recording, by a trained archaeologist, of the stratigraphy is followed by in-situ chemical characterisation then it is possible that much uncertainty associated with current field sampling practices, may be removed. This is because built into the chemical stratigraphy is the temporal and spatial relationship between different parts of the site reflecting the logic behind the distribution of contamination. An archaeological recording with chemical stratigraphy approach to sampling may possibly provide 'one method fits all' for potentially contaminated land sites (CLSs), just as archaeological characterisation of the stratigraphic record provides 'one method fits all' for all archaeological sites irrespective of period (prehistoric to modern) or type (rural, urban or industrial). We also suggest that there may be practical and financial benefits to be gained by pulling together expertise and resources stemming from different disciplines, not simply at the assessment phase, but also subsequent phases, in contaminated land improvement. PMID:21962595

Photos-Jones, Effie; Hall, Allan J

2011-10-02

 
 
 
 
321

Archaeological recording and chemical stratigraphy applied to contaminated land studies.  

UK PubMed Central (United Kingdom)

The method used by archaeologists for excavation and recording of the stratigraphic evidence, within trenches with or without archaeological remains, can potentially be useful to contaminated land consultants (CLCs). The implementation of archaeological practice in contaminated land assessments (CLAs) is not meant to be an exercise in data overkill; neither should it increase costs. Rather, we suggest, that if the excavation and recording, by a trained archaeologist, of the stratigraphy is followed by in-situ chemical characterisation then it is possible that much uncertainty associated with current field sampling practices, may be removed. This is because built into the chemical stratigraphy is the temporal and spatial relationship between different parts of the site reflecting the logic behind the distribution of contamination. An archaeological recording with chemical stratigraphy approach to sampling may possibly provide 'one method fits all' for potentially contaminated land sites (CLSs), just as archaeological characterisation of the stratigraphic record provides 'one method fits all' for all archaeological sites irrespective of period (prehistoric to modern) or type (rural, urban or industrial). We also suggest that there may be practical and financial benefits to be gained by pulling together expertise and resources stemming from different disciplines, not simply at the assessment phase, but also subsequent phases, in contaminated land improvement.

Photos-Jones E; Hall AJ

2011-11-01