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1

Late Pleistocene upland stratigraphy of the western Delmarva Peninsula, USA  

Science.gov (United States)

New pedological, geological, archaeological, and geochronological data from the Miles Point site in eastern Maryland are compared with similar data from other nearby sites to develop a framework for interpreting the upland stratigraphy in the western Delmarva Peninsula. Our results indicate the presence of two different intervals of loess deposition. The earlier loess (Miles Point Loess) was deposited between 41 and 25 ka. A paleosol (Tilghman Soil) formed in this loess was initially developed in grasslands and boreal environments during a subsequent period of landscape stability between 25 and 18 ka. Between 18 and 12.8 ka, the Miles Point Loess and the Tilghman Soil were eroded in many areas as evidenced by diagnostic ca. 12.8 ka Clovis-age artifacts lying unconformably on the Tilghman Soil. Cores adjacent to the deep channel area of the Chesapeake Bay confirm this erosional unconformity prior to 12.7 ka. A relatively uniform terminal-Pleistocene loess (Paw Paw), deposited prior to the Early Archaic period, buried Clovis-age lag artifacts and other archaeological remains older than 13.2 ka. Stratigraphic evidence from the Late Pleistocene lower Susquehanna River Valley suggests that the Paw Paw Loess is the result of eolian redeposition and reworking of non-glacial eroded upland sediments that filled the valley between 12.7 and 11.5 ka.

Lowery, Darrin L.; O'Neal, Michael A.; Wah, John S.; Wagner, Daniel P.; Stanford, Dennis J.

2010-06-01

2

Improved method for correlating late Pleistocene/Holocene records from the Bering Sea: application of a biosiliceous/geochemical stratigraphy  

Science.gov (United States)

The combination of high-resolution siliceous biostratigraphy and radiocarbon dating provides a mechanism for detailed assessment of the depositional history in late Pleistocene sediments from the Bering Sea where average accumulation rates are uncharacteristically high compared to rates calculated for most other ocean basins. Vital to the development of this stratigraphy was the recognition that the abundance pattern of the radiolarian species Cycladophora davisiana in Bering Sea cores is quite similar to this species' previously correlated abundance curve in a late Pleistocene/Holocene record from the northwest Pacific. Comparison of this high-resolution stratigraphy with other recently developed floral and lithologic stratigraphies for late Pleistocene Bering Sea sediments shows that the various stratigraphies do not always yield identical results when applied to a particular sediment sequence. With this new stratigraphy based upon a combination of siliceous microfaunal abundance patterns and radiocarbon dating, one can identify reworking, discontinuities and other interruptions in the depositional sequence more precisely than with previously devised stratigraphies, thereby improving the correlation techniques for comparison of late Pleistocene/Holocene records from this marginal sea.

Morley, Joseph J.; Robinson, Stephen W.

1986-09-01

3

Stratigraphy and chronology of late pleistocene reefs in the Southern Cook Islands, south Pacific  

Science.gov (United States)

The Makatea Islands in the southern Cook Islands consist of a degraded volcanic core surrounded by emergent "makatea" limestones. While much of this reefal limestone is of Tertiary age, the seawardmost reefs are late Pleistocene. Last-interglacial reefs (oxygen isotope substage 5e) identified by U-series dating reach 12.2 m on Atiu (mean age of three samples 126,000 ± 5000 yr B.P.), 9.8 m on Mitiaro (mean age of five samples 119,000 ± 3000 yr B.P.), 10.0-12.7 m on Mauke (mean age of four samples 128,000 + 5000, -4,000 yr B.P.), and 14.5-20.0 m on Mangaia (mean age of four samples 115,000 ± 7000 yr B.P.). On Atiu, Mauke, and Mitiaro a lower reef unit has been identified, and is separated from the overlying substage 5e reef by a sharp discontinuity, often with a crust of coralline algae. U-series dating from Atiu and Mauke indicates that this is a stage 7 reef formed in the penultimate interglaciation. The Makatea Islands have emerged as a result of flexure of the lithosphere in response to loading by the Pleistocene volcanic island of Rarotonga. Isolated outcrops of makatea limestone on Rarotonga reach 3.5 m and are probably of substage 5e age. Elastic and viscoelastic models of lithospheric flexure predict that much of the compensatory movement should occur shortly after the emplacement of the load. However, the age and elevation of late Quaternary reefs on the southern Cook Islands, where a Pleistocene volcanic island has loaded relatively old ocean floor (>80 myr), indicate that differential uplift has been continuing over the last 250,000 yr.

Woodroffe, Colin D.; Short, Stephen A.; Stoddart, David R.; Spencer, Tom; Harmon, Russell S.

1991-03-01

4

Late Pleistocene-Holocene seismic stratigraphy of the Southeast Vietnam Shelf  

Science.gov (United States)

The Late Pleistocene-Holocene sedimentary architecture of the Southeast (SE) Vietnam Shelf was investigated using high-resolution seismic profiles and core samples. Three systems tracts and a prominent seismic reflection surface at the base of the sequence were revealed. This surface (SB1) is interpreted as a sequence boundary formed by subaerial processes during the Late Pleistocene sea-level fall and subsequent marine reworking during transgression. A surface map of the lowstand surface, compiled from seismic profiles and sediment cores, revealed the W-E to N-S oriented incised-valley system of the paleo-Mekong River. The incised valleys show a clear change in morphology from the north to the south in the study area. The northern incised-valley system off Vung Tau appears as a narrow and deep V-shape in cross-section (Vietnam Shelf is a variation on the theoretical model of Vail (1987). The thick highstand wedge on the SE Vietnam Shelf is confined to the inner shelf due to the broad and low-gradient shelf morphology and the strong local hydrodynamic conditions driven by the monsoon system. Except for the one deposited within the incised-valley system, the TST deposits on the SE Vietnam Shelf tend to disperse over the shelf instead of forming a thick backstepping unit. The accommodation space was probably created faster than the sediment supply during the rapid transgression.

Dung, Bui Viet; Stattegger, Karl; Unverricht, Daniel; Phach, Phung Van; Thanh, Nguyen Trung

2013-11-01

5

High-resolution seismic stratigraphy of a late Pleistocene submarine fan ponded by salt-withdrawal mini-basins on the Gulf of Mexico continental slope  

Energy Technology Data Exchange (ETDEWEB)

The late Pleistocene Brazos-Trinity Fan, a structurally ponded fan completely exposed and undisturbed on the seafloor, was mapped with a combination of conventional and high-resolution seismic data. This fan occupies three salt-withdrawal mini-basins (1, 2, 4) and a graben (3), each filled with an onlapping package consisting of alternating bedded and non-bedded units evident on high-resolution data. Basins 1--3 are filled to their topographic spill points; the onlap-fill succession of each is incised by a channel system which bypassed sediment to the next basin(s) downdip. Seismic continuity generally increases distally in the system and within individual basins, believed to reflect the increasing prevalence of turbidity currents over high-density sediment gravity flows.

Winker, C.D.

1996-12-31

6

Late Pleistocene Environments of the Central Ukraine  

Science.gov (United States)

The Vyazivok loess sequence from the Dnieper Plain, Ukraine, documents regional environmental changes during the late Pleistocene and Holocene. Pedological and palynological analyses and low-field magnetic susceptibility document changes from dense temperate forest during the last interglacial maximum to open, harsh, loess-steppe during the latest Pleistocene. The Vyazivok section overlies hillwash derived from a lower Pleistocene terrace and consists of two stratified soil complexes (Kaydaky and Pryluky; marine isotope stage [MIS] 5 equivalent) separated by a layer of eolian dust (Tyasmyn silt). The lower soils in both complexes formed within forest. These soils are overlain by the Uday (MIS4) and Bug (MIS2) loess units, which are separated by boreal soils of the Vytachiv (MIS3) complex. The coldest conditions within the record occurred in the youngest loess. Holocene soils cap the Bug loess. The Vyazivok section shows remarkable similarities with other classical loess sequences in western Europe, the Czech Republic, and Austria. The Kaydaky, Pryluky, and Vytachiv deposits, correlate with the PKIII, PKII, and PKI soil complexes, respectively, of the Czech Republic. The Tyasmyn and Prylyky silt layers correspond to marker horizons from central Europe.

Rousseau, Denis-Didier; Gerasimenko, Natalia; Matviischina, Zhanna; Kukla, George

2001-11-01

7

Late Pleistocene dune activity in the central Great Plains, USA  

Science.gov (United States)

Stabilized dunes of the central Great Plains, especially the megabarchans and large barchanoid ridges of the Nebraska Sand Hills, provide dramatic evidence of late Quaternary environmental change. Episodic Holocene dune activity in this region is now well-documented, but Late Pleistocene dune mobility has remained poorly documented, despite early interpretations of the Sand Hills dunes as Pleistocene relicts. New optically stimulated luminescence (OSL) ages from drill cores and outcrops provide evidence of Late Pleistocene dune activity at sites distributed across the central Great Plains. In addition, Late Pleistocene eolian sands deposited at 20-25 ka are interbedded with loess south of the Sand Hills. Several of the large dunes sampled in the Sand Hills clearly contain a substantial core of Late Pleistocene sand; thus, they had developed by the Late Pleistocene and were fully mobile at that time, although substantial sand deposition and extensive longitudinal dune construction occurred during the Holocene. Many of the Late Pleistocene OSL ages fall between 17 and 14 ka, but it is likely that these ages represent only the later part of a longer period of dune construction and migration. At several sites, significant Late Pleistocene or Holocene large-dune migration also probably occurred after the time represented by the Pleistocene OSL ages. Sedimentary structures in Late Pleistocene eolian sand and the forms of large dunes potentially constructed in the Late Pleistocene both indicate sand transport dominated by northerly to westerly winds, consistent with Late Pleistocene loess transport directions. Numerical modeling of the climate of the Last Glacial Maximum has often yielded mean monthly surface winds southwest of the Laurentide Ice Sheet that are consistent with this geologic evidence, despite strengthened anticyclonic circulation over the ice sheet. Mobility of large dunes during the Late Pleistocene on the central Great Plains may have been the result of cold, short growing seasons with relatively low precipitation and low atmospheric CO2 that increased plant moisture stress, limiting the ability of vegetation to stabilize active dune sand. The apparent coexistence of large mobile dunes with boreal forest taxa suggests a Late Pleistocene environment with few modern analogs. ?? 2011 Elsevier Ltd.

Mason, J. A.; Swinehart, J. B.; Hanson, P. R.; Loope, D. B.; Goble, R. J.; Miao, X.; Schmeisser, R. L.

2011-01-01

8

Late Pleistocene vegetation of Kings Canyon, Sierra Nevada, California  

Science.gov (United States)

Seven packrat midden samples make possible a comparison between the modern and late Pleistocene vegetation in Kings Canyon on the western side of the southern Sierra Nevada. One modern sample contains macrofossils and pollen derived from the present-day oak-chaparral vegetation. Macrofossils from the six late Pleistocene samples record a mixed coniferous forest dominated by the xerophytic conifers Juniperus occidentalis, Pinus cf. ponderosa, and P. monophylla. The pollen spectra of these Pleistocene middens are dominated by Pinus sp., Taxodiaceae-Cupressaceae-Taxaceae (TCT), and Artemisia sp. Mesophytic conifers are represented by low macrofossil concentrations. Sequoiadendron giganteum is represented by a few pollen grains in the full glacial. Edaphic control and snow dispersal are the most likely causes of these mixed assemblages. The dominant macrofossils record a more xeric plant community than those that now occur on similar substrates at higher elevations or latitudes in the Sierra Nevada. These assemblages suggest that late Wisconsin climates were cold with mean annual precipitation not necessarily greater than modern values. This conclusion supports a model of low summer ablation allowing for the persistence of the glaciers at higher elevations during the late Wisconsin. The records in these middens also suggest that S. giganteum grew at lower elevations along the western side of the range and that P. monophylla was more widely distributed in cismontane California during the Pleistocene.

Cole, Kenneth

1983-01-01

9

Late Pleistocene geomagnetic excursion in Icelandic lavas  

International Nuclear Information System (INIS)

In 1980 Kristjansson and Gudmundsson reported a late glacial geomagnetic excursion in three hills in the Reykjanes peninsula, Iceland, with shallow negative inclinations and westerly declinations. They named it the Skalamaelifell excursion. More extensive field work has identified the same excursional paleomagnetic direction (declination = 258deg, inclination = -15deg) at four additional outcrops in a 10x10 km area in the Reykjanes peninsula. The excursion lavas are olivine tholeiites with similar petrography and chemical compositions. Paleointensity determinations by the Thellier method average 4.2±0.2 ?T for 8 samples, more than an order of magnitude weaker than the present geomagnetic field in Iceland. Together, these results suggest extrusion of the excursion lavas in a very brief span of time, probably less than a few hundred years. K-Ar dating of the excursion lavas gives a mean age for 19 determinations of 42.9±7.8 ka (2?). Compilation of thirty K-Ar ages of the Laschamp and Olby flows by three laboratories yield a new age for the Laschamp excursion in France of 46.6±2.4 ka (2?). The age of the excursion in southwestern Iceland is statistically indistinguishable from the Laschamp excursion at the 95% confidence level, and both have very low paleointensities. Therefore, we suggest that the Laschamp and Olby flows in France and the Skalamaelifell units of Iceland recorded essentially the same geomagnetic excursion. Differences in the virtual paleomagnetic poles (VGPs) of these excursions may be due to (1) the probable non-dipole character of the geomagnetic field during the excursion, (2) rapid geomagnetic secular variation and possible small age differences of the extrusive rocks in France and Iceland, and/or (3) crustal magnetic anomalies which might dominate the local geomagnetic field during the excursion at either or both locations. (orig.)

1990-01-01

10

Late Pleistocene braided rivers of the Atlantic Coastal Plain, USA  

Science.gov (United States)

Infrared Landsat imagery (band 4) clearly reveals braided river patterns on late Pleistocene terraces of unglaciated rivers in the Atlantic Coastal Plain of the southeastern United States, a region that presently exhibits meandering patterns that have existed throughout the Holocene. These Pleistocene braided patterns provide a unique global example of river responses to late Quaternary climate changes in an unglaciated humid subtropical region at 30-35° north latitude. Detailed morphological and chronological results are given for the Oconee-Altamaha River valley in Georgia and for the Pee Dee River valley in South Carolina, including 15 optically stimulated luminescence (OSL) dates and four radiocarbon dates. Correlative examples are drawn from additional small to large rivers in South- and North Carolina. OSL and radiocarbon ( 14C) dates indicate distinct braiding at 17-30 ka, within oxygen isotope stage 2 (OIS 2), and braiding probably existed at least during parts of OIS 3 and possibly OIS 4 back to ca 70 ka. The chronology suggests that braiding is the more common pattern for the late Quaternary in the southeastern United States. Braided terraces appear to have been graded to lower sea-levels and are onlapped by Holocene floodplain deposits up to 10-60 km from the coast. The braiding probably reflects the response of discharge and sediment yield to generally cooler and drier paleoclimates, which may have had a pronounced runoff season. Sedimentation of eolian dunes on the braid plains is coeval with braiding and supports the conclusion of dry soils and thin vegetation cover during the late Pleistocene. Our chronological data contribute to a body of literature indicating that reliable OSL age estimates can be obtained from quartz-rich bed load sand from braided rivers, based on good correlations with both radiocarbon dates from braided fluvial sediment and OSL dates from stratigraphically correlative eolian sand.

Leigh, David S.; Srivastava, Pradeep; Brook, George A.

2004-01-01

11

Late Pleistocene/Holocene radiolarian and pollen records from sediments in the Sea of Okhotsk  

Science.gov (United States)

In two cores with oxygen isotope stratigraphy from the southern Okhotsk Sea, marine pollen and siliceous microfauna record concurrent late glacial through Holocene variations in regional terrestrial and marine environments. Glacial vegetation around the southern Okhotsk basin, which resembles the present tundra/steppe of the northwest coast of this marginal sea, yields to spruce-dominated boreal forests during the glacial/interglacial transition. Temperate forest components, such as oak, peak during the mid-Holocene. Decreasing oak accompanied by increasing spruce reflects the effect of global cooling on local vegetation during the last 4 kyr. Although the radiolarian fauna in the Okhotsk Sea samples is similar to that present in the northwest Pacific, the dominant species in both regions differ. Concentrations of radiolarians are low in latest glacial samples, with higher concentrations occurring above and below this interval. Cycladophora davisiana, the dominant radiolarian species in the majority of Holocene Okhotsk Sea sediments, is present at lower percentages in late glacial samples from our two sites. Thus, this species' Holocene/latest Pleistocene abundance pattern in Sea of Okhotsk sediments is the reverse of that recorded in high-latitude open ocean sites. The combined marine pollen and radiolarian records indicate changes in the Sea of Okhotsk's physical oceanographic conditions and surrounding vegetation during the late glacial which were associated with this region's response to global climate change.

Morley, Joseph J.; Heusser, Linda E.; Shackleton, Nicholas J.

1991-02-01

12

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

Science.gov (United States)

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

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

2010-10-01

13

On the Interpretation of Late Pleistocene 100-kyr Phases  

Science.gov (United States)

Phase calculations are often used to measure leads and lags in paleoclimate records and then make inferences about the causal mechanisms associated with orbitally forced glacial cycles. Fourier and wavelet spectral analyses work well for near-sinusoidal cycles, but Late Pleistocene 100-kyr glacial cycles are typically sawtooth shaped (e.g., 10 kyr of warming followed by 90 kyr of cooling) and are thus extremely non-sinusoidal. Here I present phase calculations for a variety of 100-kyr sawtooth shapes similar to those observed in paleoclimate records. These calculations demonstrate that variations in cycle shape can produce apparent differences in 100-kyr phase even when records experience synchronous warming and cooling. For example, changing the amplitude of MIS 5e in otherwise identical records can shift the 100-kyr wavelet phase by 13° (3.6 kyr). Therefore, spectral phase calculations are not well-suited for characterizing leads, lags, or response times of 100-kyr cyclicity in paleoclimate records. Direct comparison of the timing of distinctive features (e.g., termination onset or the onset of cooling at the end of an interglacial) is more appropriate for evaluating possible causal sequences in Late Pleistocene 100-kyr cycles.

Lisiecki, L. E.

2013-12-01

14

Late Pleistocene and Holocene mammal extinctions on continental Africa  

Science.gov (United States)

Understanding the cause of late Quaternary mammal extinctions is the subject of intense debate spanning the fields of archeology and paleontology. In the global context, the losses on continental Africa have received little attention and are poorly understood. This study aims to inspire new discussion of African extinctions through a review of the extinct species and the chronology and possible causes of those extinctions. There are at least 24 large mammal (> 5 kg) species known to have disappeared from continental Africa during the late Pleistocene or Holocene, indicating a much greater taxonomic breadth than previously recognized. Among the better sampled taxa, these losses are restricted to the terminal Pleistocene and early Holocene, between 13,000 and 6000 yrs ago. The African extinctions preferentially affected species that are grazers or prefer grasslands. Where good terrestrial paleoenvironmental records are present, extinctions are associated with changes in the availability, productivity, or structure of grassland habitats, suggesting that environmental changes played a decisive role in the losses. In the broader evolutionary context, these extinctions represent recent examples of selective taxonomic winnowing characterized by the loss of grassland specialists and the establishment of large mammal communities composed of more ecologically flexible taxa over the last million years. There is little reason to believe that humans played an important role in African extinctions.

Faith, J. Tyler

2014-01-01

15

Strontium isotope stratigraphy and geochemistry of the late Neogene ocean  

Energy Technology Data Exchange (ETDEWEB)

A curve describing the variation of the strontium isotopic composition of seawater for the late Neogene (9 to 2 Ma) was constructed from /sup 87/Sr//sup 86/Sr 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 /sup 87/Sr//sup 86/Sr values were nearly constant at approx. = 0.708925. Between 5.5 and 4.5 Ma, /sup 87/Sr//sup 86/Sr ratios increased monotonically at a rate of approx. = 1 x 10/sup -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 /sup 87/Sr//sup 86/Sr decreases to near zero again during the interval 4.5-2.5 Ma, and ratios average 0.709025. The relatively rapid increase of /sup 87/Sr//sup 86/Sr between 5.5 and 4.5 Ma must be related to changes in the flux or average /sup 87/Sr//sup 86/Sr 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 /sup 87/Sr//sup 86/Sr 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 /sup 87/Sr 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).

Hodell, D.A.; Mueller, P.A.; McKenzie, J.A.; Mead, G.A.

1989-03-01

16

Ages of late pleistocene terrace deposits in the Kuromatsunai lowland  

International Nuclear Information System (INIS)

Kuromatsunai lowland which lies at the neck of Oshima Peninsula extends from Oshamambe to Suttsu, and is considered as a remarkable neo-tectonic zone. In this region, the data for determining the age of terraces and pyroclastic material which is related to the terraces are short. The determination of the age of lower fluvial terraces was attempted using the wood piece specimens collected from three localities in Kuromatsunai town. The determination of the 14C age of three specimens was conducted, and the obtained values were about 26 x 103 yBP, about 30 x 103 yBP and 37 x 103 yBP, respectively. The consideration on the conditions of the existence of specimens and the results of geologival observation of the localities where the specimens were collected, led to the conclusion as follows. 1. The age of the aeolian deposit of volcanic ash is earlier than about 30 x 103 yBP. 2. In Kuromatsunai lowland, the lower fluvial terrace, which is not overlain by the volcanic ash of Pleistocene can be roughly divided into two levels. The age of one level is about 30 x 103 yBP, and another is later than 26 x 103 yBP, which are corresponding to late Pleistocene. The age of the Neppu pyroclastic flow deposit, which is related to the formation of those terraces, was determined as 0.13+-0.03 MaBP by fission track method. Further studies seem to be necessary because some disagreement with the data of other researchers remains. (Ishimitsu, A.)

1984-01-01

17

Seismic Stratigraphy of Pleistocene Deltaic Deposits in Bahía Blanca Estuary, Argentina  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in portuguese O estuário da Bahía Blanca (Argentina) tem uma configuração morfológica resultante de processos hidrológicos e sedimentares relacionados a mudanças do nível do mar durante o Quaternário Tardio. Este sistema estuarino ocupa uma ampla planície costeira com uma densa rede de canais de marés, ilhas de b [...] aixa altitude e extensas áreas de intermarés com baixa declividade. Nesta área, pouco se conhece sobre as unidades sedimentares do fundo marinho. Portanto, análise estratigráfica da costa norte do estuário da Bahía Blanca foi realizada usando sísmica de alta resolução (3,5 kHz) com a finalidade de: i) definir sequências quaternárias, ii) descrever estruturas sedimentares, e iii) determinar as condições paleoambientais de sedimentação. Os dados estratigráficos sísmicos obtidos e suas correlações litológicas com dados de perfuração apresentaram cinco sequências sísmicas (S1, S2, S3, S4 e S5), das quais S1-S2 foram correlacionadas com um paleoambiente continental referente ao Mioceno-Pleistoceno. Sequências S3 e S4, de fácies litológicas e sísmicas (estruturas de paleocanais e configurações de reflexão progradantes) foram definidas nestas sequências, evidenciando o desenvolvimento de um ambiente ancestral deltaico que foi parte de um amplo sistema de drenagem do Pleistoceno. A sequência S5 foi formada durante os processos transgressivo-regressivos do Holoceno e preenche a coluna sismo-estratigráfica definida neste estudo. Abstract in english The Bahía Blanca estuary (Argentina) has a morphological configuration resulting from hydrological and sedimentary processes related to Late Quaternary sea level changes. This estuarine system occupies a large coastal plain with a dense net of tidal channels, low-altitude islands and large intertida [...] l flats. Little is known about the sedimentary units of the marine subbottom. Therefore, a stratigraphical analysis of the northern coast of Bahía Blanca estuary was carried out using high resolution seismic (3.5 kHz) in order to: i) define Quaternary sequences, ii) describe sedimentary structures, and iii) determine the paleoenvironmental conditions of sedimentation. The seismic stratigraphic data collected and their correlation with drilling lithological data show five seismic sequences (S1, S2, S3, S4 and S5), of which S1-S2 were found to be associated with a continental paleoenvironment of Miocene-Pleistocene age. Sequences S3 and S4, whose lithology and seismic facies (paleochannel structures and prograding reflection configurations), were defined on these materials, to evidence the development of an ancient deltaic environment which was part of a large Pleistocene drainage system. The S5 sequence was formed during the Holocene transgressive-regressive process and complete the seismostratigraphic column defined in the present study.

SALVADOR, ALIOTTA; SILVIA S., GINSBERG; DARÍO, GIAGANTE; LAURA G., VECCHI; MARTA M., SALVATIERRA.

18

Late Pleistocene and Holocene depositional history of sediments in Flathead Lake, Montana: Evidence from high-resolution seismic reflection interpretation  

Science.gov (United States)

This paper presents an interpretation of 3.5 kHz reflection seismic data together with information from lower frequency seismic data and sediment cores from Flathead Lake in northwestern Montana. Flathead Lake is located at the margin of the Cordilleran Ice Sheet during the last glacial maximum and is the repository for about 160 m of syn- and post-glacial sediment. Six seismic stratigraphic units (A-F) are identified in Flathead Lake above the acoustic basement reflector. The deepest unit is interpreted to be late Pleistocene glacial till (unit A) overlain by well-layered glaciolacustrine sediments (unit B). Overlying seismic reflectors (unit C) include slump deposits, turbidites fed by meltwater surges associated with retreat of the Flathead glacial lobe, and homogeneous silty mud. Preliminary age models suggest that the transition from glacial rhythmites (unit B) to more homogenous lake sediments (unit C) occurred approximately between 14,500 and 13,180 cal.y.b.p. Parallel high amplitude reflectors of the oldest Holocene unit (unit D) drape Pleistocene stratigraphy. Sediment core analyses suggest that these fine sediments were deposited below wave base by suspension settle out in a lake similar to today's. The Mt. Mazama tephra (7630 ± 80 cal.y.b.p.) is interpreted as the top reflector of unit D. Onlap geometries between units D and E imply a significant drop in lake level before deposition of unit E. Sedimentation of unit E was confined to several sub-basins that were separated by bedrock highs. Lake level rose gradually during deposition of unit E to form the well-developed basal onlap geometry. Parallel high amplitude reflectors of the youngest Holocene sediments (unit F) drape all of the older stratigraphy and bedrock highs across the lake basin, suggesting a late Holocene lake highstand.

Hofmann, M. H.; Hendrix, M. S.; Moore, J. N.; Sperazza, M.

2006-02-01

19

Late Pleistocene carbonate dissolution in the Venezuela Basin, Caribbean Sea  

Energy Technology Data Exchange (ETDEWEB)

Piston cores from water depths greater than 4000 m in the Venezuela Basin (Caribbean Sea) provide continuous late Pleistocene records of carbonate dissolution and accumulation. The authors examination of multiple dissolution indices indicate that, at least for the last 150,000 years, dissolution of carbonate in the Venezuela Basin has been more intense during interglacial than glacial periods, a pattern opposite to more general observations from the deep Atlantic and Gulf of Mexico. By virtue of its shallow sill depth (1815 m), the Venezuela Basin is relatively isolated from the mainstream of Atlantic thermohaline circulation, and presently is filled with homogeneous, relatively warm (3.8/sup 0/C) waters primarily derived from Upper North Atlantic Deep Water. During the last glacial, the enhanced preservation of carbonate in the Venezuela Basin suggests the presence of a less corrosive, more oxygenated water mass in the Atlantic near sill depth. However, this simple interpretations is potentially complicated by past changes in the rain of biogenic materials from surface waters to the deep basin in what must be an essentially closed system below sill depth. Their observations of increased interglacial dissolution may help to explain previously noted discrepancies in the local glacial to interglacial amplitude of delta/sup 18/O variations recorded by coccoliths and planktonic foraminifera.

Cofer-Shabica, N.B.; Peterson, L.C.

1985-01-01

20

Late Pleistocene glaciers and climate in the Mediterranean  

Science.gov (United States)

Evidence for Late Pleistocene glaciers and rock glaciers in the Pindus Mountains, Greece, is used to reconstruct palaeoclimate for this part of the Mediterranean during the last cold stage (Tymphian/ Würmian). Mean annual precipitation was c. 2300 ± 200 mm and the mean summer temperature (June/July/August) was c. 4.9 °C at 2174 m a.s.l., the equilibrium line altitude of the former glaciers, at the last local glacier maximum. The glacier-climate relationship in the northern Pindus Mountains during the local glacier maximum of the Tymphian Stage closely resembled that found today at the equilibrium line altitude of Norwegian glaciers. The local glacier maximum on Mount Tymphi is likely to have preceded both the most severe phase of climate indicated in the pollen record at nearby Ioannina and also the global last glacial maximum. Major stadials, including the most severe phase of the last cold stage, were characterised by cold sea surfaces temperatures, which inhibited atmospheric moisture supply creating unfavourable conditions for glacier formation. Such stadial conditions are likely to have favoured periglacial conditions and the formation of features such as rock glaciers. Conversely, warm summer temperatures during major interstadials would have promoted glacier ablation, offsetting increased precipitation enabled by warmer sea surface temperatures. Thus, the most favourable conditions for glacier formation would have occurred during intermediate conditions between major stadials and interstadials. It is clear that former glacier behaviour in the mountains of this region is best understood with reference to temporally dynamic glacier-climate models, which take into account millennial-scale changes in both precipitation and temperature.

Hughes, P. D.; Woodward, J. C.; Gibbard, P. L.

2006-02-01

 
 
 
 
21

Late Pleistocene marine transgression of North Slope coastal plain  

Energy Technology Data Exchange (ETDEWEB)

Two late Pleistocene marine transgressions of contrasting character are recorded by deposits of the Arctic coastal plain. Deposits of the oldest trangression extend from Harrison Bay west to near Barrow and contain a fauna that documents interglacial conditions. Five thermoluminescence (TL) dates on the marine deposits average 127 Ka and indicate a correlation with oxygen isotope stage 5e. Sedimentary structures characteristic of the swash zone occur at altitudes within the commonly accepted range (6 not equal 4m) for eustatic high sea level at that time, showing that this part of the coastal plain has been tectonically stable for the past 125,000 years. Deposits of the youngest transgression are glaciomarine sediments that contain ice-rafted erratics of Canadian provenance. They compose the flaxman member of the Gubik Formation and occur locally along the Beaufort Sea coast and inland to altitudes of about 7 m. TL dates on these sediments suggest that the Flaxman transgression occurred between 70 and 80 ka and is correlative with deposits dated to this interval that are exposed near sea level on the North Carolina coastal plain. However, the deep-sea oxygen-isotope record is commonly interpreted to indicate that sea level was below its modern position at that time. The present altitude of the Flaxman deposits cannot be attributed to tectonism because their distribution includes the part of the coastal plain determined to be tectonically stable for the past 125 ka. Isostatic depression and subsequent elevation are unlikely considering the correlative deposits of North Carolina. This paradox could be explained if enormous volumes of floating glacial ice were produced by the rapid breakup of a large part of the Laurentide ice sheet, and recent work indeed suggests that the Hudson Bay lowlands were ice free at this time.

Carter, L.D.

1985-04-01

22

Stratigraphy and paleontology of Pliocene-Pleistocene sediments on Five Fingers Peninsula, Dusky Sound, Fiordland  

Energy Technology Data Exchange (ETDEWEB)

An isolated outlier of Pliocene-Pleistocene sediment on Five Fingers Peninsula, Fiordland, has been re-examined. Further outcrops of fossiliferous marine and nonmarine sediment, including lignite, were located and contain unusual macrofauna and palynofloras respectively. All faunal (including microfaunal) and floral collections support a middle Pliocene-early Pleistocene (Waipipian-Hautawan) age. The sediments record rapid subsidence and a transgression from alluvial plain to shallow marine environments, and are fault bounded on both sides. Faulting that allowed the deposition and preservation of sediments was related to movement of the Fiordland microplate. A new pollen taxon Biplanipollis whidbeyensis n. gen., n. sp. is described.

Turnbull, J.M.; Lindqvist, J.K.; Mildenhall, D.C.; Hornibrook, N.B.; Beu, A.G.

1985-01-01

23

Late Miocene to Pleistocene Biostratigraphy of Equatorial Pacific Sediments.  

Science.gov (United States)

Combined foraminiferal, diatom, radiolarian, and paleomagnetic studies of tropical deep-sea-sediment cores permit establishment of multiple criteria for recognizing the Miocene/Pliocene and Pliocene/Pleistocene boundaries which can be used for correlation...

T. Saito L. H. Burckle J. D. Hays

1975-01-01

24

Late Pleistocene and Holocene Fire History of the California Islands  

Science.gov (United States)

Charcoal has been recovered from a range of late Pleistocene and Holocene sites on Santa Cruz Island and Santa Rosa Island, both islands part of California's Northern Channel Islands, U.S.A. Sediments have been dated using radiocarbon measurements based on wood charcoal, fungal sclerotia, glassy carbon and fecal pellets and are given as calendar years BP. This charcoal has been used to interpret the fire history of the Islands. Charcoal assemblages from samples dating from 24,690 to 12,900 years are dominated by coniferous wood charcoal. Little angiosperm charcoal was recovered in any of the samples. Fungal sclerotia are frequent in a number of samples from a range of ages both on Santa Cruz and Santa Rosa. Fecal pellets are common in most samples and abundant in others. Some of the fecal pellets have hexagonal sides and are likely to represent termite frass. The sediments are fluvial in origin and the distribution of charcoal is irregular making interpretation of fire return intervals and fire frequency difficult. The charcoal indicates a significant record of fire before the earliest documented human arrival on the islands. Charcoal reflectance data shows the occurrence of predominantly low temperature charcoals suggesting common surface fires in the coniferous forest. Soledad Pond sediments from Santa Rosa Island (Anderson et al., 2010) dating from 11,800 cal years BP show a distinctively different vegetation dominated by angiosperms and showing a very different fire history. Pinus stands, coastal sage scrub dominated by Baccharis sp. and grassland replaced the conifer forest as the climate warmed. The early Holocene became increasingly drier, particularly after ca. 9150 cal yr BP. By ca. 6900 cal yr BP grasslands recovered. Introduction of non-native species by ranchers occurred subsequent to AD 1850. Charcoal influx is high early in the Soledad Pond record, but declines during the early Holocene when minimal biomass suggests extended drought. A general increase occurs after ca. 7000 cal yr BP, and especially after ca. 4500 cal yr BP. The Holocene pattern closely resembles population levels constructed from the archaeological record, and suggests a potential influence by humans on the fire regime of the islands, particularly during the late Holocene. Reference: ANDERSON, R.S., STARRATT, S., JASS, R.M.B.,PINTER, N., 2010. Fire and vegetation history on Santa Rosa Island, Channel Islands, and long-term environmental change in southern California. Journal of Quaternary Science 25, 782-797.

Scott, A. C.; Hardiman, M.; Pinter, N.; Anderson, R.

2013-12-01

25

Testing the correlation of fragmented pollen records of the middle and late Pleistocene temperate stages  

DEFF Research Database (Denmark)

Quaternary temperate stages have long been described based on changing pollen abundances of various tree taxa in lacustrine sediments. Later, attempts have been made to assign such biostratigraphic units to distinct marine isotope stages (MIS). Existing continuous chronosequences from Southern Europe provide good chronologies and thus enable a biostratigraphic definition of at least younger MIS. In Northern Europe, however, the fragmentary character of the records and the weaknesses of absolute dating prevent good age estimates. Therefore, age-determination of the majority of fragmentary records depends on site-to-site correlations. This comparison has often been performed on a visual basis, lacking clearly defined protocols and statements of underlying assumptions. Here I test the correlation of well and poorly known pollen records of the middle- and late-Pleistocene temperate stages from Northern-Central Europe and evaluate the usefulness of several numerical techniques. TWINSPAN analysis identifies groupsof temperate stages based on presence/absence of their indicative taxa and may be useful for distinguishing between older and younger interglacials. Site-to-site sequence slotting allows the determination of the most similar pairs of records, based on sample dissimilarity following their stratigraphic constraints. Sequence slotting performs well when correlating the Holsteinian interglacial and Cromerian stage II, and also provides tentative correlation of some problematic records. Ordination compares main trends in pollen stratigraphies of all pollen sequences. It finds very similar patterns between Eemian records and Cromerian stage II. Although different methods show sometimes inconsistent results, they can certainly contribute to the discussion of the age of poorly known interglacials. The implications for future directions suggest focusing on better sampling resolution, multi-proxy approaches to climatic reconstruction and obtaining better independent dating.

Kuneš, Petr; Odgaard, Bent Vad

26

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

27

Atlantic-type carbonate stratigraphy in the late Miocene Pacific  

International Nuclear Information System (INIS)

Results are reported showing a negative correlation between carbonate content and benthic isotopes in a late Miocene (6.14 - 6.53 Myr) deep-sea sediment core from the eastern equatorial Pacific (DSDP Site 158), which is similar to that found in Quaternary records of the Atlantic rather than the Pacific. An explanation is suggested. (U.K.)

1981-05-21

28

Age determination of late Pleistocene marine transgression in western Alaska  

Science.gov (United States)

Dating molluscs from sediments representing the Kotzebuan marine transgression in Alaska yields an average uranium-series age of 104,000 ?? 22,000 yrs B.P. This and other selected Pleistocene marine deposits of western Alaska are tentatively correlated with radiometrically dated units of eastern Baffin Island, Arctic Canada. ?? 1982.

Szabo, B. J.

1982-01-01

29

Probabilistic sequence alignment of Late Pleistocene benthic ?18O data  

Science.gov (United States)

The stratigraphic alignment of ocean sediment cores plays a vital role in paleoceanographic research because it is used to develop mutually consistent age models for climate proxies measured in these cores. The most common proxy used for alignment is the The stratigraphic alignment of ocean sediment cores plays a vital role in paleoceanographic research because it is used to develop mutually consistent age models for climate proxies measured in these cores. The most common proxy used for alignment is the ?18O of calcite from benthic or planktonic foraminifera because a large fraction of ?18O variance derives from the global signal of ice volume. To date, alignment has been performed either by manual, qualitative comparison or by deterministic algorithms (Martinson, Pisias et al. Quat. Res. 27 1987; Lisiecki and Lisiecki Paleoceanography 17, 2002; Huybers and Wunsch, Paleoceanography 19, 2004). Here we present a probabilistic sequence alignment algorithm which provides 95% confidence bands for the alignment of pairs of benthic ?18O records. The probabilistic algorithm presented here is based on a hidden Markov model (HMM) (Levinson, Rabiner et al. Bell Systems Technical Journal, 62,1983) similar to those that have been used extensively to align DNA and protein sequences (Durbin, Eddy et al. Biological Sequence Analysis, Ch. 4, 1998). However, here the need to the alignment of sequences stems from expansion and/or contraction in the records due to changes in sedimentation rates rather than the insertion or deletion of residues. Transition probabilities that are used in this HMM to model changes in sedimentation rates are based on radiocarbon estimates of sedimentation rates. The probabilistic algorithm considers all possible alignments with these predefined sedimentation rates. Exact calculations are completed using dynamic programming recursions. The algorithm yields the probability distributions of the age at each point in the record, which are probabilistically inferred from the LR04 stack. The complication of the central (1-?)% intervals of these distributions yields the confidence bands. In an extension of this work we are rebuilding the stack using a profile HMM model (Durbin, Eddy et al, Ch. 5). We analyze the confidence bands produced for the alignments of 35 Late Pleistocene benthic ?18O records to the LR04 benthic ?18O stack. We find that the mean width of 95% confidence bands for core alignments varies between 3-23 kyr depending on the resolution and noisiness of the core's ?18O signal. Confidence bands within individual cores also vary greatly, ranging from ~0 to >40 kyr. These alignment confidence bands will allow researchers to examine the robustness of their conclusions with respect to alignment uncertainty at all points in the record. Additionally, they should aid in the identification of possible errors in inferred ages in the input record (e.g., due to core disturbances) because such errors are likely to be associated with large, local uncertainty.

Lawrence, C.; Lin, L.; Lisiecki, L. E.; Stern, J.

2013-12-01

30

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

31

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

32

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

33

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

34

A morphometric analysis of the Late Pleistocene Human Skeleton from the Moh Khiew Cave in Thailand.  

Science.gov (United States)

Few Late Pleistocene human remains have been found in Southeast Asia and the morphological features of the people of that age are still largely unknown due to the virtual lack of human remains in the area. Recent excavations at the Moh Khiew Cave in Thailand resulted in the discovery of a Late Pleistocene human skeleton in a relatively good state of preservation. An AMS radiocarbon date on the charcoal sample gathered from the burial gave a result of 25,800 +/- 600 BP, implying that the inhabitants of Moh Khiew Cave resided in a part of Sundaland during the last glacial age. In debates on the population history of Southeast Asia, it has been repeatedly advocated that Southeast Asia was occupied by indigenous people akin to present-day Australo-Melanesians prior to an expansion of migrants from Northeast Asia into this area. Morphometric analyses were undertaken to test the validity of this hypothesis. In the present study, cranial and dental measurements recorded from the Moh Khiew remains are compared with those of early and modern samples from Southeast Asia and Australia. These comparisons demonstrate that the Moh Khiew specimen resembles the Late Pleistocene series from Coobool Creek, Australia in both cranial and dental measurements. These results suggest that the Moh Khiew skeleton, as well as other fossil remains from the Tabon, Niah and Gua Gunung sites, represents a member of the Sundaland population during the Late Pleistocene, who may share common ancestry with the present-day Australian Aborigines and Melanesians. PMID:16130834

Matsumura, Hirofumi; Pookajorn, Surin

2005-01-01

35

Origin of late pleistocene formation water in Mexican oil reservoirs  

Energy Technology Data Exchange (ETDEWEB)

Brine water invasion into petroleum reservoirs, especially in sedimentary basins, are known from a variety of global oil field, such as the Western Canada sedimentary basin and, the central Mississippi Salt Dome basin (Kharaka et al., 1987). The majority of oil wells, especially in the more mature North American fields, produce more water than they do oil (Peachey et al., 1998). In the case of Mexican oil fields, increasing volumes of invading water into the petroleum wells were detected during the past few years. Major oil reserves in the SE-part of the Gulf of Mexico are economically affected due to decreases in production rate, pipeline corrosion and well closure. The origin of deep formation water in many sedimentary basins is still controversial: Former hypothesis mainly in the 60's, explained the formation of formation water by entrapment of seawater during sediment deposition. Subsequent water-rock interaction processes explain the chemical evolution of hydrostatic connate water. More recent hydrodynamic models, mainly based on isotopic data, suggest the partial migration of connate fluids, whereas the subsequent invasion of surface water causes mixing processes (Carpenter 1978). As part of the presented study, a total of 90 oil production wells were sampled from 1998 to 2004 to obtain chemical (Major and trace elements) and isotopic composition ({sup 2}H, {sup 13}C, {sup 14}C, {sup 18}O {sup 36}Cl, {sup 37}Cl, {sup 87}Sr, {sup 129}I, tritium) of deep formation water at the Mexican Gulf coast. Samples were extracted from carbonate-type reservoirs of the oil fields Luna, Samaria-Sitio Grande, Jujo-Tecominoac (on-shore), and Pol-Chuc (off-shore, including Abkatun, Batab, Caan, and Taratunich) at a depth between 2,900 m b.s.l. and 6,100 m b.s.l. During the field work, the influence of atmospheric contamination e.g. by CO{sub 2}-atmospheric input was avoided by using an interval sampler to get in-situ samples from the extraction zone of selected bore holes. For wellhead samples, a 20 liter-sampling-reagent was previously filled with N{sub 2}-gas for the collection and phase separation of the pressurized gas-water-crude oil mixture. No differences in {sup 14}C-concentrations were detected applying, both, conventional and AMS-techniques. In contradiction to the expected 'fossil age' of reservoir water as part of a stagnant hydraulic system, measured {sup 14}C-concentrations between 0.89 pmC and 31.86 pmC indicate a late Pleistocene-early Holocene, regional event for the infiltration of surface water into the reservoir. The variety in water mineralization from meteoric (TDS{sub max} = 0.5 g/l) to hyper-saline composition (TDS{sub max} = 338 g/l) is not caused by halite dissolution from adjacent salt domes, as shown by elevated Br/Cl ratios. In contrary, the linear correlation between {sup 18}O and Cl values reflect varying mixing proportions of two components - meteoric water and evaporated seawater. Instead of water/rock-interaction, evaporation of seawater at the surface prior to infiltration represents the principal process for fluid enrichment in {sup 18}O and chlorine, with maximum values of 17.2 %o and 228 g/l, respectively. The young residence time of formation water in Mexican oil reservoirs implies following: - The common assumption of 'hydraulically-frozen' reservoirs is not correct, as main descending fluid migration occurred during glacial period. Probably, major infiltration processes are related to periods with climatic changes and increased humidity - as observed for the adjacent Yucatan region in SE-Mexico during early-mid Holocene (6,000 yr BP) (Metcalfe et al. 2000) - with the probable transgression of Mexican Gulf seawater into the recent Mexican coastal plain. - The common hypothesis of hydrocarbon maturation within Jurassic organic-rich layers, and its subsequent expulsion and migration into Cretaceous/Tertiary sedimentary units must be expanded by a last-step-process: As glacial ground water level is actually located below the hydrocarbon column (due to differences in densit

Birkle, P. [Instituto de Investigaciones Electricas, Cuernavaca (Mexico)

2004-07-01

36

Origin of late pleistocene formation water in Mexican oil reservoirs  

International Nuclear Information System (INIS)

Brine water invasion into petroleum reservoirs, especially in sedimentary basins, are known from a variety of global oil field, such as the Western Canada sedimentary basin and, the central Mississippi Salt Dome basin (Kharaka et al., 1987). The majority of oil wells, especially in the more mature North American fields, produce more water than they do oil (Peachey et al., 1998). In the case of Mexican oil fields, increasing volumes of invading water into the petroleum wells were detected during the past few years. Major oil reserves in the SE-part of the Gulf of Mexico are economically affected due to decreases in production rate, pipeline corrosion and well closure. The origin of deep formation water in many sedimentary basins is still controversial: Former hypothesis mainly in the 60's, explained the formation of formation water by entrapment of seawater during sediment deposition. Subsequent water-rock interaction processes explain the chemical evolution of hydrostatic connate water. More recent hydrodynamic models, mainly based on isotopic data, suggest the partial migration of connate fluids, whereas the subsequent invasion of surface water causes mixing processes (Carpenter 1978). As part of the presented study, a total of 90 oil production wells were sampled from 1998 to 2004 to obtain chemical (Major and trace elements) and isotopic composition (2H, 13C, 14C, 18O 36Cl, 37Cl, 87Sr, 129I, tritium) of deep formation water at the Mexican Gulf coast. Samples were extracted from carbonate-type reservoirs of the oil fields Luna, Samaria-Sitio Grande, Jujo-Tecominoac (on-shore), and Pol-Chuc (off-shore, including Abkatun, Batab, Caan, and Taratunich) at a depth between 2,900 m b.s.l. and 6,100 m b.s.l. During the field work, the influence of atmospheric contamination e.g. by CO2-atmospheric input was avoided by using an interval sampler to get in-situ samples from the extraction zone of selected bore holes. For wellhead samples, a 20 liter-sampling-reagent was previously filled with N2-gas for the collection and phase separation of the pressurized gas-water-crude oil mixture. No differences in 14C-concentrations were detected applying, both, conventional and AMS-techniques. In contradiction to the expected 'fossil age' of reservoir water as part of a stagnant hydraulic system, measured 14C-concentrations between 0.89 pmC and 31.86 pmC indicate a late Pleistocene-early Holocene, regional event for the infiltration of surface water into the reservoir. The variety in water mineralization from meteoric (TDSmax = 0.5 g/l) to hyper-saline composition (TDSmax = 338 g/l) is not caused by halite dissolution from adjacent salt domes, as shown by elevated Br/Cl ratios. In contrary, the linear correlation between 18O and Cl values reflect varying mixing proportions of two components - meteoric water and evaporated seawater. Instead of water/rock-interaction, evaporation of seawater at the surface prior to infiltration represents the principal process for fluid enrichment in 18O and chlorine, with maximum values of 17.2 %o and 228 g/l, respectively. The young residence time of formation water in Mexican oil reservoirs implies following: - The common assumption of 'hydraulically-frozen' reservoirs is not correct, as main descending fluid migration occurred during glacial period. Probably, major infiltration processes are related to periods with climatic changes and increased humidity - as observed for the adjacent Yucatan region in SE-Mexico during early-mid Holocene (6,000 yr BP) (Metcalfe et al. 2000) - with the probable transgression of Mexican Gulf seawater into the recent Mexican coastal plain. - The common hypothesis of hydrocarbon maturation within Jurassic organic-rich layers, and its subsequent expulsion and migration into Cretaceous/Tertiary sedimentary units must be expanded by a last-step-process: As glacial ground water level is actually located below the hydrocarbon column (due to differences in density), a general mobilization of the entire column of reservoir fluids and the displacement of the organic phase must be pos

2004-09-06

37

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

38

Cougars' key to survival through the Late Pleistocene extinction: insights from dental microwear texture analysis.  

Science.gov (United States)

Cougars (Puma concolor) are one of only two large cats in North America to have survived the Late Pleistocene extinction (LPE), yet the specific key(s) to their relative success remains unknown. Here, we compare the dental microwear textures of Pleistocene cougars with sympatric felids from the La Brea Tar Pits in southern California that went extinct at the LPE (Panthera atrox and Smilodon fatalis), to clarify potential dietary factors that led to the cougar's persistence through the LPE. We further assess whether the physical properties of food consumed have changed over time when compared with modern cougars in southern California. Using dental microwear texture analysis (DMTA), which quantifies surface features in three dimensions, we find that modern and Pleistocene cougars are not significantly different from modern African lions in any DMTA attributes, suggesting moderate durophagy (i.e. bone processing). Pleistocene cougars from La Brea have significantly greater complexity and textural fill volume than Panthera atrox (inferred to have primarily consumed flesh from fresh kills) and significantly greater variance in complexity values than S. fatalis. Ultimately, these results suggest that cougars already used or adopted a more generalized dietary strategy during the Pleistocene that may have been key to their subsequent success. PMID:24759373

Desantis, Larisa R G; Haupt, Ryan J

2014-01-01

39

El Nino-like climate teleconnections in new england during the late pleistocene  

Science.gov (United States)

A glacial varve chronology from New England spanning the 4000-year period from 17,500 to 13,500 calendar years before the present was analyzed for evidence of climate variability during the late Pleistocene. The chronology shows a distinct interannual (3 to 5 years) band of enhanced variability suggestive of El Nino-Southern Oscillation (ENSO) teleconnections into North America during the late Pleistocene, when the Laurentide ice sheet was near its maximum extent and climatic boundary conditions were different than those of today. This interannual variability largely disappears by the young end of the 4000-year chronology, with only the highest frequency components (roughly 3-year period) persisting. This record provides evidence of ENSO-like climate variability during near-peak glacial conditions. PMID:10807572

Rittenour; Brigham-Grette; Mann

2000-05-12

40

Stratigraphic framework for the late Pleistocene in the northwest Pacific Ocean  

Science.gov (United States)

Analyses of the relative abundance of Cycladophora davisiana in 10 northwest Pacific deep-sea cores show that the species exhibits abundance variations during the late Pleistocene (?450,000 years) comparable to those in the subantarctic and North Atlantic. Comparison of the C. davisiana curves in the cores with tephra-stratigraphic and biostratigraphic datum levels indicates that the major features of the C. davisiana records are synchronous within the northwest Pacific. Calculated ages for the most recent abundance peak and a distinctively low abundance interval of the C. davisiana curve are similar to the estimated ages for the last glacial and interglacial maxima, respectively. With the development of a detailed stratigraphic framework for late Pleistocene northwest Pacific sediments we have been able to revise the estimated ages of the upper limits of Lychnocanium grande, the Rhizosolenia complex, and Druppatractus acquilonius to 49,000, 276,000, and 329,000 y B.P., respectively.

Morley, Joseph J.; Hays, James D.; Robertson, James H.

1982-12-01

 
 
 
 
41

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

42

Dimensions and architecture of late Pleistocene submarine lobes off the northern margin of East Corsica  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Sandy lobe deposits on submarine fans are sensitive recorders of the types of sediment gravity flows supplied to a basin and are economically important as hydrocarbon reservoirs. This study investigates the causes of variability in 20 lobes in small late Pleistocene submarine fans off East Corsica. These lobes were imaged using ultra-high resolution boomer seismic profiles (< 1 m vertical resolution) and sediment type was ground truthed using piston cores published in previous studies. Repeat...

Deptuck, M.; Piper, D.; Savoye, Bruno; Gervais, A.

2008-01-01

43

Radiocarbon age of late pleistocene-holocene paleogeographic events of the Northern Precaspian  

International Nuclear Information System (INIS)

Results of radiocarbon dating of material of mollusks shells and phyto remnants from holocene sedimentations of the Northern Caspian Sea region are provided. The established age of the carbonate-organogenic material permits quantitative estimation of paleographic events in the Northern Caspian Sea region in the end of late pleistocene-holocene period. It is pointed out that employment in the study of the radiocarbon dating method permits improving essentially the reliability of the results obtained

2000-04-01

44

Sedimentary environment and sequence stratigraphy of the late Quaternary deposits in the central Yellow Sea  

Science.gov (United States)

In the central Yellow Sea, approximately 52,600 line-km of Chirp seismic profiles and 5,060 line-km of Sparker seismic profiles were used to define the sedimentary environments and to investigate the sequence stratigraphy of the late Quaternary deposits. On the basis of topography, depth, formation of deposition, and seismic facies, the central Yellow Sea are classified into three sedimentary environments: (1) a various scale sand ridges/waves and mud belt (the western inner-shelf of the Korean Peninsula), (2) recent- and paleo-channels, erosional and broad surface (the center of the Yellow Sea), and (3) prodelta mud patch (the eastern offshore of China). According to correlation of high-resolution seismic data and sediment cores in the central Yellow Sea, the late Quaternary deposits in the central Yellow Sea are divided into five distinctive sedimentary units (units CY1~5), consisting of two depositional sequences that can be defined as erosional and disconformable strata. The major depositional processes and sediment dispersal systems during the late Quaternary in the central Yellow Sea are: (1) regressive estuarine/deltaic deposits (unit CY1), (2) transgressive incised channel fill (unit CY2), (3) transgressive sand sheet (unit CY3), (4) transgressive sand ridges (unit CY4), and (5) prodelta/recent mud (unit CY5). The depositional sequences follow the general concepts of sequence stratigraphy very well. Lower sequence (DI) correspond to the falling stage systems tract regarded as regressive estuarine or deltaic deposits (unit CY1), whereas upper sequence (DII) consists of a set of the transgressive (units CY2, CY3, and CY4) and highstand systems tract (unit CY5) formed since the last-glacial period.

Lee, G.; Yoo, D.; Kim, D. C.; Kim, S.; Choi, H.; Yi, H.

2013-12-01

45

Late Pleistocene differential uplift inferred from the analysis of fluvial terraces (southern Apennines, Italy)  

Science.gov (United States)

The stratigraphic architecture and morphological assemblage of the Pleistocene fluvial terraces contained in two contiguous fluvial valleys are used to understand the spatial distribution and the timing of the differential uplift that affected two different geological and geomorphological settings of an active orogen. The study areas, both placed in the eastern sector of the southern Apennines of Italy, are the Sant'Arcangelo sedimentary basin and the Valsinni Ridge anticline. Pleistocene uplift rate of 0.7-0.9 mm y- 1 and historical earthquakes affecting those areas suggest active tectonics. Based on the synthem units used to classify the fluvial deposits in the field, several strath, fill, and fill-cut terraces have been mapped in the middle valleys of the Agri and Sinni rivers. Four Middle Pleistocene high terraces (Qes) are found in the Sant'Arcangelo Basin and cut its infill, and three Late Pleistocene low terraces (Qt) are found at both the Agri and Sinni valley flanks. The Agri and Sinni rivers cross-cut the NW-SE-oriented fold-and-thrust belt of the southern Apennines from W to E, producing a transverse drainage. As a result, ten- to hundred-metre deep gorges and wide floodplains were created in the middle reach of the river valleys. Computation of the bedrock incision rates from the Qes1, Qes4, and SQt1 terraces, corresponding to 1.2 ± 0.2 mm y- 1 at 400-240 ka and 0.8 ± 0.2 mm y- 1 in the last 240 ka, together with the terrace profile arrangements in the Agri and Sinni valleys, allow for the documentation of i) the differential uplift of the study area and ii) the age of terrace abandonment corresponding to the beginning age of the vertical incision in the valley floor sediments to form the Qt terraces. The differential uplift is subsequently discussed in a space and time-sequence evolution of the Late Pleistocene to assess the complex morphotectonic development that occurred in the eastern threshold of the basin. The differential uplift of both the Sant'Arcangelo Basin and Valsinni Ridge would appear to indicate that buried fold-and-thrust structures that affect the Mesozoic-Cenozoic sedimentary nappes are still active, and they also controlled the slab retreat processes in the Mediterranean region during the Late Pleistocene.

Giano, Salvatore Ivo; Giannandrea, Paolo

2014-07-01

46

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

47

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

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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

Environmental changes at the Holocene-Late Pleistocene transition: Sedimentation on Akademicheskii Ridge (Lake Baikal, Russia)  

Science.gov (United States)

Akademicheskii Ridge of Lake Baikal represents a 300 m deep underwater rise, which separates the Central Basin (1647 m water depth) and the North Basin (970 m water depth) of 640 km long lake. The large distance to the turbid load of particle-carrying tributaries and coastal areas as well as the absence of slide induced turbidites are responsible for low sedimentation rates. A large number of short cores (approx. 120 cm) was used to study in detail the Holocene-Late Pleistocene transition, using lithological composition, magnetic susceptibility, microfossils, pollen and spores, chemistry, grain size and mineral composition. Holocene sediments show sedimentation rates from 0.015 to 0.25 mm y-1 and are mainly composed of biogenic material with rare admixtures of aeolian and ice-rafted terrigenous particles [1]. The sediments are characterized by abundant microfossils, such as diatoms, spicules of sponges, chrysophyte cysts, pollen and spores. Holocene diatom assemblages are representated by Aulacoseira baicalensis, A. skvortzowii, Cyclotella minuta, C. baicalensis, Synedra acus var.radians, Stephanodiscus meyerii, Crateriportula inconspicuus and Cyclostephanos dubius [2]. Concentrations of Corg.,Ntot.,and Sibiog.indicate clearly higher productivity of the lake during the Holocene [1]. Late Pleistocene sediments are composed of clastic, fine-grained, clayey material, mainly of terrigenous origin. This includes also aeolian particles and rare ice-transported sandy material and rock debris. A peak of the diatom species Stephanodiscus flabellatus, observed within the upper part of clayey sediments, defines the Late Pleistocene-Holocene transition [2]. Very low contents of microfossils (diatoms, spicules of sponges, chrysophyte cysts etc.) within Late Pleistocene deposits indicate lower productivity of Lake Baikal. Glacial melt-water dominated the sediment transport processes within the lake during this time. The main minerals of the sand fraction are quartz, feldspars and mica. The heavy mineral assemblage contains amphiboles, pyroxenes, epidote, sphene, magnetite, garnet and chloritoide. Within the Holocene, contents of chloritoide are low (0.6-1.2 %), but they are distinctly higher within the Late Pleistocene sediments (3.2-14.6 %) [1]. An increase of chloritoide in sediments points towards an intensification of aeolian transport by stronger winds and longer-lasting periods of ice cover during the Late Pleistocene [3]. Results of pollen analyses support these findings. They indicate that mountain slopes of the catchment of Lake Baikal were mostly uncovered by vegetation. A polymineral composition is characteristic for the clay fraction of Late Pleistocene deposits: hydro-mica, kaolinite, smectite and chlorite. This is caused by extensive glaciation of the catchment of the lake during this time [4], generating increased transport of terrigenous material to the lake by glacial melt water [5]. References [1] Vologina, E.G. and Sturm, M. 2009. Types of Holocene deposits and regional pattern of sedimentation in Lake Baikal. Russian Geology and Geophysics 50, 1-6. [2] Bradbury, J.P., Bezrukova, Ye.V., Chernyaeva, G.P. et al. 1994. A synthesis of post-glacial diatom records from Lake Baikal. J. Paleolimnol. 10, 213-252.

Vologina, Elena G.; Sturm, Michael

2010-05-01

49

Re-evaluating the origins of late Pleistocene fire areas on Santa Rosa Island, California, USA  

Science.gov (United States)

At the close of the Pleistocene, fire regimes in North America changed significantly in response to climate change, megafaunal extinctions, anthropogenic burning and, possibly, even an extraterrestrial impact. On California's Channel Islands, researchers have long debated the nature of late Pleistocene "fire areas," discrete red zones in sedimentary deposits, interpreted by some as prehistoric mammoth-roasting pits created by humans. Further research found no evidence that these red zones were cultural in origin, and two hypotheses were advanced to explain their origin: natural fires and groundwater processes. Radiocarbon dating, X-ray diffraction analysis, and identification of charcoal from six red zones on Santa Rosa Island suggest that the studied features date between ~ 27,500 and 11,400 cal yr BP and resulted from burning or heating, not from groundwater processes. Our results show that fire was a component of late Pleistocene Channel Island ecology prior to and after human colonization of the islands, with no clear evidence for increased fire frequency coincident with Paleoindian settlement, extinction of pygmy mammoths, or a proposed Younger Dryas impact event.

Rick, Torben C.; Wah, John S.; Erlandson, Jon M.

2012-09-01

50

The Ob?azowa 1 early modern human pollical phalanx and Late Pleistocene distal thumb proportions.  

Science.gov (United States)

The human distal thumb phalanx from the earlier Upper Paleolithic of Ob?azowa Cave, southern Poland, exhibits features of its palmar surface that align it morphologically principally with early modern humans. These aspects include the configurations of the proximal palmar fossa, the flexor pollicis longus tendon insertion, the proximal margin of the palmar apical tuft, and especially its low ulnar deviation angle. If it is assumed that it possessed the pollical phalangeal length proportions of an early modern human, it would exhibit modest base and tuft breadths. However, given Late Pleistocene archaic-modern contrasts in relative pollical phalanx lengths, the isolated nature of the phalanx prevents secure assessment of its radioulnar interphalangeal articular and apicaltuft hypertrophy. Similar constraints apply to the assessment of other Pleistocene Homo pollical phalanges. PMID:24616929

Trinkaus, E; Haduch, E; Valde-Nowak, P W; Wojtal, P

2014-02-01

51

Coalescence and fragmentation in the late Pleistocene archaeology of southernmost Africa.  

Science.gov (United States)

The later Pleistocene archaeological record of southernmost Africa encompasses several Middle Stone Age industries and the transition to the Later Stone Age. Through this period various signs of complex human behaviour appear episodically, including elaborate lithic technologies, osseous technologies, ornaments, motifs and abstract designs. Here we explore the regional archaeological record using different components of lithic technological systems to track the transmission of cultural information and the extent of population interaction within and between different climatic regions. The data suggest a complex set of coalescent and fragmented relationships between populations in different climate regions through the late Pleistocene, with maximum interaction (coalescence) during MIS 4 and MIS 2, and fragmentation during MIS 5 and MIS 3. Coalescent phases correlate with increases in the frequency of ornaments and other forms of symbolic expression, leading us to suggest that population interaction was a significant driver in their appearance. PMID:24746546

Mackay, Alex; Stewart, Brian A; Chase, Brian M

2014-07-01

52

Drainage reversals in Mono Basin during the late pliocene and Pleistocene  

Science.gov (United States)

Mono Basin, on the eastern flank of the central Sierra Nevada, is the highest of the large hydrographically closed basins in the Basin and Range province. We use geomorphic features, shoreline deposits, and basalt-filled paleochannels to reconstruct an early to middle Pleistocene record of shorelines and changing spillways of Lake Russell in Mono Basin. During this period of time, Lake Russell repeatedly attained altitudes between 2205 and 2280 m-levels far above the present surface of Mono Lake (~1950 m) and above its last overflow level (2188 m). The spill point of Lake Russell shifted through time owing to late Tertiary and Quaternary faulting and volcanism. During the early Pleistocene, the lake periodically discharged through the Mount Hicks spillway on the northeastern rim of Mono Basin and flowed northward into the Walker Lake drainage basin via the East Walker River. Paleochannels recording such discharge were incised prior to 1.6 Ma, possibly between 1.6 and 1.3 Ma, and again after 1.3 Ma (ages of basaltic flows that plugged the paleochannels). Faulting in the Adobe Hills on the southeastern margin of the basin eventually lowered the rim in this area to below the altitude of the Mount Hicks spillway. Twice after 0.76 Ma, and possibly as late as after 0.1 Ma, Lake Russell discharged southward through the Adobe Hills spillway into the Owens-Death Valley system of lakes. This study supports a pre-Pleistocene aquatic connection through Mono Basin between the hydrologically distinct Lahontan and Owens-Death Valley systems, as long postulated by biologists, and also confirms a probable link during the Pleistocene for species adapted to travel upstream in fast-flowing water.

Reheis, M. C.; Stine, S.; Sarna-Wojcicki, A. M.

2002-01-01

53

Deciphering Late-Pleistocence landscape evolution: linking proxies by combining pedo-stratigraphy and luminescence dating  

Science.gov (United States)

Interpreting former landscape evolution asks for understanding the processes that sculpt such landforms by means of deciphering complex systems. For reconstructing terrestrial Quaternary environments based on loess archives this might be considered, at least, as a three step process: (1) Identifying valuable records in appropriate morphological positions in a previously defined research area, (2) analysing the profiles by field work and laboratory methods and finally (3) linking the previously considered pseudo-isolated systems to set up a comprehensive picture. Especially the first and the last step might bring some pitfalls, as it is tempting to specify single records as pseudo-isolated, closed systems. They might be, with regard to their preservation in their specific morphological position, but in fact they are part of a complex, open system. Between 2008 and 2013, Late-Pleistocene loess archives in Saxony have been intensively investigated by field and laboratory methods. Linking pedo- and luminescence dating based chronostratigraphies, a composite profile for the entire Saxonian Loess Region has been established. With this, at least, two-fold approach we tried to avoid misinterpretations that might appear when focussing on one standard profile in an open morphological system. Our contribution focuses on this multi-proxy approach to decipher the Late-Pleistocene landscape evolution in the Saxonian Loess Region. Highlighting the challenges and advantages of combining different methods, we believe that (1) this multi-proxy approach is without alternative, (2) the combination of different profiles may simplify the more complex reality, but it may be a useful generalisation to understand and reveal the stratigraphical significance of the landscape evolution in this region.

Kreutzer, Sebastian; Meszner, Sascha; Faust, Dominik; Fuchs, Markus

2014-05-01

54

Sequence stratigraphy of the late Quaternary deposits in the central Yellow Sea  

Science.gov (United States)

High-resolution (Chirp and Sparker system) seismic profiles and piston core samples were analyzed to investigate the sequence stratigraphy of late Quaternary in the central Yellow Sea. Approximately 52,610 line-km data of chirp and sparker profiles was acquired. Along with seismic profiling, 16 piston core samples collected in 1998 and 1999. We also used a deep drill core to interpret the sedimentary sequences. In this study High-resolution seismic profiles and deep drill core show the complex sedimentary structure. The late Quaternary deposits in the study area can be divided into five sedimentary units (units CY1, CY2, CY3, CY4, and CY5 from the oldest to youngest) bounded by an erosional surface and internal seismic reflectors: (1) regressive estuarine/deltaic deposits (unis CY1), (2) transgressive incised channel fill (unit CY2), (3) transgressive sand sheet (unit CY3), (4) transgressive sand ridges (unit CY4), and (5) prodelta/recent mud (unit CY5). Based on the interpretation of high-resolution seismic records and correlation with the YSDP-105 and piston cores, lower sequence (DI) correspond to the falling stage systems tract regarded as regressive estuarine or deltaic deposits (unit CY1), whereas upper sequence (DII) consists of a set of the transgressive (units CY2, CY3, and CY4) and highstand systems tract (unit CY5) formed since the last-glacial period.

Bae, S.-H.; Kim, D.-C.; Lee, G.-S.; Yi, H.-I.; Cho, H.-G.

2012-04-01

55

Response of methanogenic archaea to Late Pleistocene and Holocene climate changes in the Siberian Arctic  

Science.gov (United States)

order to investigate the link between the methane dynamics in permafrost deposits and climate changes in the past, we studied the abundance, composition, and methane production of methanogenic communities in Late Pleistocene and Holocene sediments of the Siberian Arctic. We detected intervals of increased methane concentrations in Late Pleistocene and Holocene deposits along a 42 ka old permafrost sequence from Kurungnakh Island in the Lena Delta (northeast Siberia). Increased amounts of archaeal life markers (intact phospholipid ethers) and a high variety in genetic fingerprints detected by 16S ribosomal ribonucleic acid gene analyses of methanogenic archaea suggest presently living and presumably active methanogenic archaea in distinct layers predominantly in Holocene deposits, but also in deep frozen ground at 17 m depth. Potential methanogenic activity was confirmed by incubation experiments. By comparing methane concentrations, microbial incubation experiments, gene analysis of methanogens, and microbial life markers (intact phospholipid esters and ethers) to already partly degraded membrane lipids, such as archaeol and isoprenoid glycerol dialkyl glycerol tetraethers, we demonstrated that archaeol likely represents a signal of past methanogenic archaea. The archaeol signal was used to reconstruct the response of methanogenic communities to past temperature changes in the Siberian Arctic, and the data suggest higher methane emissions occurred during warm periods, particularly during an interval in the Late Pleistocene and during the Holocene. This new data on present and past methanogenic communities in the Siberian terrestrial permafrost imply that these microorganisms will respond to the predicted future temperature rise in the Arctic with increasing methane production, as demonstrated in previous warmer periods.

Bischoff, Juliane; Mangelsdorf, Kai; Gattinger, Andreas; Schloter, Michael; Kurchatova, Anna N.; Herzschuh, Ulrike; Wagner, Dirk

2013-04-01

56

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

2013-10-01

57

Size Analysis of the Late Pliocene-Early Pleistocene Upper Siwalik Sediments, Northwestern Himalaya, India  

Directory of Open Access Journals (Sweden)

Full Text Available Size analysis of the Late Pliocene-Early Pleistocene Upper Siwalik sediments comprising the Pinjor Formation in the type area and adjoining regions reveals that the sediments are bimodal to polymodal in nature, medium to fine grained and are moderately sorted. The inclusive graphic standard deviation and moment standard deviation values suggest the deposition of sediments in shallow to moderately deep fluvial agitated water. The log probability plots reveal that saltation mode is the dominant mode of transportation of detritus. The sediments are continental in character and are derived from crystalline, metamorphic and sedimentary rocks of the Himalaya exposed to the North of the type area Pinjor.

Mahavir Singh

2013-10-01

58

AMS-dating of Late Pleistocene and Holocene syngenetic ice-wedges  

International Nuclear Information System (INIS)

We discuss the 14C dating (both conventional and AMS) of Siberian permafrost sediments and ice-wedge ice. Direct dating of Late Pleistocene and Holocene syngenetic ice-wedges was done on organic material included in the ice. The time of ice formation (in 14C years) is 21,000-14,000 BP for Seyaha, and 7100 BP for Shchuch'ya. The AMS dates show that the ice-wedges stratification is normal, i.e., the older ice is located below the younger. The 14C dates yield for the first time a timescale (in 14C years) for paleoclimatic indicators (oxygen and hydrogen isotope ratios from the ice)

2000-10-01

59

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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, tempo...

Campos, Paula F.; Willerslev, Eske; Sher, Andrei; Orlando, Ludovic; Axelsson, Erik; Tikhonov, Alexei; Aaris-sørensen, Kim; Greenwood, Alex D.; Kahlke, Ralf-dietrich; Kosintsev, Pavel; Krakhmalnaya, Tatiana; Kuznetsova, Tatyana; Lemey, Philippe; Macphee, Ross; Norris, Christopher A.

2010-01-01

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An Enlarged Parietal Foramen in the Late Archaic Xujiayao 11 Neurocranium from Northern China, and Rare Anomalies among Pleistocene Homo  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We report here a neurocranial abnormality previously undescribed in Pleistocene human fossils, an enlarged parietal foramen (EPF) in the early Late Pleistocene Xujiayao 11 parietal bones from the Xujiayao (Houjiayao) site, northern China. Xujiayao 11 is a pair of partial posteromedial parietal bones from an adult. It exhibits thick cranial vault bones, arachnoid granulations, a deviated posterior sagittal suture, and a unilateral (right) parietal lacuna with a posteriorly-directed and enlarge...

Wu, Xiu-jie; Xing, Song; Trinkaus, Erik

2013-01-01

 
 
 
 
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First record of Procyon cancrivorus (G. Cuvier, 1798) (Carnivora, Procyonidae) in stratigraphic context in the Late Pleistocene of Brazil  

Science.gov (United States)

Although five genera of procyonids are currently present in South America, only two of the extant genera, Procyon and Nasua are represented in the South American fossil record. A recent discovery of a procyonid lower second molar in Late Pleistocene deposits of Aurora do Tocantins, northern Brazil, offers potential to further our understanding of the stratigraphic and temporal range of South American fossil procyonids. We use geometric morphometric analysis of two-dimensional landmarks and semilandmarks to explore morphological variation in the lower second molars of extant Procyon lotor and Procyon cancrivorus and multivariate methods to support the identification of the Pleistocene specimen as P. cancrivorus. This material represents the second fossil record of P. cancrivorus in South America Procyonids entered South America in two phases: the first comprising by Cyonasua and Chapadmalania during the Late Miocene, and the other recent genera, beginning in the Late Pleistocene. These Late Miocene procyonids were more carnivorous than Late Pleistocene-Recent omnivorous taxa and possible went extinct due to competition with other placental carnivorans that entered South America and diversified during the latest Pliocene-Early Pleistocene.

Rodriguez, Sergio G.; Soibelzon, Leopoldo H.; Rodrigues, Shirlley; Morgan, Cecilia C.; Bernardes, Camila; Avilla, Leonardo; Lynch, Eric

2013-08-01

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

Scientific Electronic Library Online (English)

Full Text Available SciELO Mexico | Language: English 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 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 e [...] specially 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 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.

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

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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.

Li Shouhsien

2009-06-01

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Identification of density-stratified waters in the late-Pleistocene North Atlantic: A faunal derivation  

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An expanded study of the radiolarian Cycladophora davisiana in late-Pleistocene North Atlantic marine sediments shows that over the last several hundred thousand years this species exhibits large variations in relative abundance. The C. davisiana curves in the North Atlantic cores are quite similar, with easily recognizable features common to all records. Minor deviations from the general pattern of this species' abundance apparently reflect the response of C. davisiana to specific oceanographic conditions characteristic of a particular area within the North Atlantic. C. davisiana occurs today in high abundance (>20%) only in the Sea of Okhotsk. Extensive winter and early spring sea-ice cover coupled with low surface-water salinities during summer and fall is responsible for maintaining near-freezing subsurface temperatures in this northwest Pacific marginal sea as well as relatively stable temperatures and salinities at depths below a shallow subsurface temperature minimum. During periods in the late Pleistocene, high C. davisiana abundances (>20%) in the North Atlantic were probably associated with oceanographic properties similar to those that exist in the Sea of Okhotsk today. Because of the relationship between relatively stable subsurface temperatures and salinities and high abundance levels of C. davisiana, analysis of this species' abundance pattern at several locations throughout the high-latitude North Atlantic should assist in identifying source areas of deep-water formation and determining the duration of deep convective processes at these sites.

Morley, Joseph J.

1983-11-01

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Mastodon herbivory in mid-latitude late-Pleistocene boreal forests of eastern North America  

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Skeletal remains of the extinct American mastodon have often been found with deposits of short, decorticated twigs intermixed with plant fragments presumed to be gastrointestinal or fecal material. If such deposits are digesta, paleobotanical evidence may be used to analyze mastodon foraging strategy, with implications for assessing habitat selection, ecological roles, and response to environmental change. To identify components of mastodon diet in mid-latitude late-Pleistocene boreall forests of eastern North America, plant macrofossils and pollen from a molar socket (Hyde Park site, New York) were compared with dispersed deposits associated with skeletal remains (Hiscock and Chemung sites, New York). Similar macrofossil condition and twig morphology among samples, but difference from a modern boreal fen analog, confirmed the deposits were digesta. Comparison of twigs with material from other paleontological sites and modern elephants suggested dimensions generally indicative of digesta. Picea formed the bulk of each sample but Pinus may have been locally important. Wintertime browsing of Salix and Populus, and springtime consumption of Alnus, were indicated. Evidence for Cyperaceae, Gramineae, and Compositae was ambiguous. If conifers, broadleaf trees, shrubs, and herbs were necessary to fulfill dietary requirements, mastodons would have been nutritionally stressed by rapid late-Pleistocene decrease in vegetational diversity.

Teale, Chelsea L.; Miller, Norton G.

2012-07-01

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Rodent burrows in late Pleistocene paleosols at Korean Palaeolithic sites and their implications for paleoclimate changes  

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Rodent burrows are commonly found at many Paleolithic archaeological sites in Korea. They are nearly straight in horizontal view and gently inclined in lateral view. Burrow diameters are mostly 7 - 10cm, and burrow length may reach a few meters. Vertical penetration depths are generally about 1 m from the surface, and the thickness of the burrow-bearing layer is about 1-2 m. Although no remains (bones, teeth, claws, and coprolites) were found within burrows, they are interpreted to have been produced by rodent-like mammals (probably ground squirrels) based on the size and architecture. According to the previous study, the age of these burrows was constrained to be between ca. 40,000 and 25,000 yr BP by tephrochronology, radiocarbon and optically stimulated luminescence dating results (Lim et al., 2007). However, little is known about the reason why these burrows have disappeared after late Pleistocene time. For this question, two explanations can be considered: extinction or migration. Since same kinds of burrows are still found in the high-latitude regions, such as Mongolia and North America, the possibility of extinction can be ruled out. Therefore, migration seems to be the most likely explanation. Our results show that the destruction of habitat caused by climate change during this period is the main reason for the northward migration of burrowing animals. This study suggests that rodent burrows found in the late Pleistocene paleosols can provide useful information on paleoclimate and paleoenvironmental changes.

Lim, H.; Park, S.; Lee, J.; Lee, Y.

2013-12-01

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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

2012-06-01

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Late pleistocene aggradation and degradation of the lower colorado river: Perspectives from the Cottonwood area and other reconnaissance below Boulder Canyon  

Science.gov (United States)

Where the lower Colorado River traverses the Basin and Range Province below the Grand Canyon, significant late Pleistocene aggradation and subsequent degrada tion of the river are indicated by luminescence, paleomagnetic, and U-series data and stratigraphy. Aggradational, finely bedded reddish mud, clay, and silt are underlain and overlain by cross-bedded to plane-bedded fine sand and silt. That sequence is commonly disconformably overlain by up to 15 m of coarse sand, rounded exotic gravel, and angular, locally derived gravel. Luminescence dates on the fine sediments range from ca. 40 ka to 70 ka, considering collective uncertainties. A section of fine grained sediments over a vertical range of 15 m shows normal polarity magnetization and little apparent secular variation beyond dispersion that can be explained by com paction. Aggradation on large local tributaries such as Las Vegas Wash appears to have been coeval with that of the Colorado River. The upper limits of erosional rem nants of the sequence define a steeper grade above the historical river, and these late Pleistocene deposits are greater than 100 m above the modern river north of 35??N. Ter race gravels inset below the upper limit of the aggradational sequence yield 230Th dates that range from ca. 32 ka to 60 ka and indicate that degradation of the river system in this area closely followed aggradation. The thick sequence of rhythmically bedded mud and silt possibly indicates set tings that were ponded laterally between valley slopes and levees of the aggrading river. Potential driving mechanisms for such aggradation and degradation include sediment-yield response to climate change, drought, fire, vegetation-ecosystem dynam ics, glaciation, paleofloods, groundwater discharge, and building and destruction of natural dams produced by volcanism and landslides. ?? 2008 The Geological Society of America.

Lundstrom, S. C.; Mahan, S. A.; Paces, J. B.; Hudson, M. R.; House, P. K.; Malmon, D. V.; Blair, J. L.; Howard, K. A.

2008-01-01

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Late Pleistocene and Holocene Beringia vegetation dynamic reconstructions based on a yedoma exposure, Itkillik (Alaska)  

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The Itkillik river area in Alaska (69°34? N, 150°52?W), is part of the loosely defined region of Beringia, which was largely unglaciated during the last ice age. Beringia is known to have acted as a refugium for boreal trees and shrubs during the Pleistocene, but questions remain about the environmental history of North-Eastern Beringia, especially the extent and dynamics of the now extinct tundra-steppe biome. The 33-m-high Itkillik river exposure formed over the late Pleistocene / early Holocene (48,000 to 5,000 14C yr BP) and the exposed eolian sediments are largely undisturbed, offering a unique opportunity to examine a long term vegetation sequence in high latitude environment and link the vegetation reconstructions with the sedimentology and cryostratigraphy of the region. Because of the very low concentration of pollen in the sediments, we utilized an extraction method based on heavy-liquid (Sodium Polytungstate (SPT)) separation. Our results show a tundra-steppe vegetation type, characterized by the abundance of cyperacea and graminea taxa. Overall the pollen record of the Itkillik exposure will provide an important point of comparison to other sites localised in the circumpolar circle, especially in Siberia, as yedoma remains one of the most noticeable structures of the cold and dry periglacial environment of the Arctic and subarctic east Siberia. Implications of our findings for local climate reconstructions using pollen-climate transfer functions are discussed.

Lapointe Elmrabti, L.; Fortier, D.; Shur, Y.; Kanevskiy, M. Z.; Talbot, J.

2013-12-01

70

Late Quaternary stratigraphy and sedimentation patterns in the western Arctic Ocean  

Science.gov (United States)

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

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

2009-01-01

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Bone Accumulation by Leopards in the Late Pleistocene in the Moncayo Massif (Zaragoza, NE Spain)  

Science.gov (United States)

Eating habits of Panthera pardus are well known. When there are caves in its territory, prey accumulates inside them. This helps to prevent its kill from being stolen by other predators like hyenas. Although the leopard is an accumulator of bones in caves, few studies have been conducted on existing lairs. There are, however, examples of fossil vertebrate sites whose main collecting agent is the leopard. During the Late Pleistocene, the leopard was a common carnivore in European faunal associations. Here we present a new locality of Quaternary mammals with a scarce human presence, the cave of Los Rincones (province of Zaragoza, Spain); we show the leopard to be the main accumulator of the bones in the cave, while there are no interactions between humans and leopards. For this purpose, a taphonomic analysis is performed on different bone-layers of the cave.

Sauque, Victor; Rabal-Garces, Raquel; Sola-Almagro, Cristina; Cuenca-Bescos, Gloria

2014-01-01

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

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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

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Bone accumulation by leopards in the Late Pleistocene in the Moncayo massif (Zaragoza, NE Spain).  

Science.gov (United States)

Eating habits of Panthera pardus are well known. When there are caves in its territory, prey accumulates inside them. This helps to prevent its kill from being stolen by other predators like hyenas. Although the leopard is an accumulator of bones in caves, few studies have been conducted on existing lairs. There are, however, examples of fossil vertebrate sites whose main collecting agent is the leopard. During the Late Pleistocene, the leopard was a common carnivore in European faunal associations. Here we present a new locality of Quaternary mammals with a scarce human presence, the cave of Los Rincones (province of Zaragoza, Spain); we show the leopard to be the main accumulator of the bones in the cave, while there are no interactions between humans and leopards. For this purpose, a taphonomic analysis is performed on different bone-layers of the cave. PMID:24642667

Sauqué, Víctor; Rabal-Garcés, Raquel; Sola-Almagro, Cristina; Cuenca-Bescós, Gloria

2014-01-01

74

Relic Late Pleistocene fluvial forms as geomorphic archives indicating periods of high climatic runoff over the East European Plain  

Science.gov (United States)

In water balance estimations within palaeoenvironmental studies river runoff is estimated as the difference between precipitation and evapotranspiration. The other technique is numerical modeling using general circulation models. Both approaches fail to recognize epochs of extremely high surface runoff characteristic for the Pleistocene cold epochs and recorded in geomorphic outcomes of this runoff. We have studied two kinds of such archives that have wide spatial coverage over the East European Plain (EEP). 1. Post-LGM large palaeochannels (macromeanders) in river valleys with channel width and meander wavelength 5-15 times as great as that of modern rivers. Massive measurements of their parameters and application of specially constructed transfer function provided estimations of palaeo-runoff from large river basins: in the Black Sea and Caspian Sea catchments it carried from 2.2 (Kama River) to 3.1 (Don, Dnieper Rivers) times as great as modern runoff. High runoff lasted long enough to provide formation of 2-3 generations of macromeanders characteristic for many valleys. Macromeanders were radiocarbon dated at 6 sites over EEP in the range 13-19 cal ka BP, but it is not clear whether high runoff was characteristic for the entire period or it performed during short isolated epochs within this interval. Therefore, it is not clear to what exact time palaeohydrological estimations should be attributed. 2. Dendritic and parallel systems of gentle hollows clearly designated in vegetation-free areas south from 55-57ºN. Distinctive spatial patterns and full integration into water transportation through modern fluvial landscapes provides interpretation of these hollow systems as partially or totally buried networks of small dry valleys (balkas). It is supported by revelation of buried incisions up to 10 m deep by coring and trenching across hollows. Ancient erosion network demonstrates erosion density much higher and Horton's "belt of no erosion" much narrower and therefore exhibits much abundant surface runoff than those at present. Dating of buried balkas has until recent times been based either on pollen spectra from peat deposits (in central EEP), or on stratigraphy of paleosoils found in the bottom of paleoforms (in southern EEP). Both markers point at Eemian (MIS 5e) age of their stabilization and therefore pre-Eemian (late MIS 6?) age of incision. However first attempt of OSL dating gave the contradictory result of filling of a 6-m deep balka by slopewash sediments during 80-70 ka BP. Questionable is the >30-ka delay between the soil formation in the balka bottom and start of its filling. It may mean either post-Eemian age of the soil, which would be unfortunate for the regional soil stratigraphy, or insufficient sensitivity of local quartz at ages close to Eemian. The conclusion is that geomorphic evidences make unique palaeohydrological archives that document changes not recorded in other types of palaeoenvironmental data, but they suffer from uncertainties and low resolution of dating. This presentation contributes to RFBR Projects 14-05-00119 and 14-05-00146.

Panin, Andrei; Belyaev, Yury; Eremenko, Ekaterina; Sidorchuk, Alexei

2014-05-01

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Late Pleistocene and Holocene vegetation and climate changes in the Lake Baikal region  

Science.gov (United States)

Palynological high-resolution records from Lake Baikal sediments document strong vegetational changes during the transitions from an open landscape to Late Glacial shrublands and Holocene forests. For three core sites, investigated within EU-Project CONTINENT, sporomorph concentrates were used for AMS 14C dating of environmental changes. The pollen record from the northern lake site, located in vicinity to the Barguzin Mountains, shows pronounced maxima of Salix and Picea corresponding to late Pleistocene warming. A peak maximum in Alnus fruticosa during the Younger Dryas cooling coincided with low abundance of green algae in the lake and a decline in Picea trees. Fern-rich forests with Picea, Larix and Betula developed during early Holocene. With an abrupt expansion of Pteridium ferns Abies appeared in the northeastern Baikal region, reflecting optimum conditions for dark taiga. Among pines Pinus sibirica prevailed prior to the spread of P. sylvestris. Expansion of pines points to a distinct decrease in precipitation. A palynological sequence from the same site reflects the vegetation development during the last interglacial, with differences indicated by higher abundance of Abies. The upper part of the interglacial record comprises the transition to stadial conditions. Further pollen spectra are probably equivalent to first interstadials of the early glacial period (Zyryansk). Comparison with southern sites, in vicinity to the Selenga Delta and the Khamar-Daban Mountains, reveals that regional and temporal differentiation of Holocene vegetation development and climate conditions was closely related to the distribution of mountain ranges.

Demske, D.; Heumann, G.; Granoszewski, W.; Mamakowa, K.; Piotrowska, N.; Bluszcz, A.; Goslar, T.

2003-04-01

76

The Late Pleistocene distribution of vicuñas (Vicugna vicugna) and the “extinction” of the gracile llama (“Lama gracilis”): New molecular data  

Science.gov (United States)

We present the results of a palaeogenetic analysis of two Late Pleistocene camelids originating in southern Chile. Our analysis of two mitochondrial DNA fragments (control region and cytochrome b gene) reveals that these specimens do not belong to an extinct taxon, but rather to extant vicuña ( Vicugna vicugna), whose modern distribution is restricted to the extreme elevations of the Andes, more than 3500 km to the north of where these specimens originated. Our results also suggest fossil specimens from Patagonia that are currently assigned to the extinct taxon Lama gracilis, may actually belong to V. vicugna, implying a continuous distribution of the latter from the southern tip of South America to the Andes during the Final Pleistocene. The haplotypes of both specimens are not present in modern populations, suggesting a loss of genetic diversity concomitant with the contraction of the vicuña geographical distribution during the Final Pleistocene or early Holocene.

Weinstock, Jaco; Shapiro, Beth; Prieto, Alfredo; Marín, Juan Carlos; González, Benito A.; Gilbert, M. Thomas P.; Willerslev, Eske

2009-07-01

77

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

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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

2011-04-01

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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

79

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

Science.gov (United States)

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 ?45,000 radiocarbon years before present (14C YBP). Subsequently, musk ox genetic diversity reincreased at ca. 30,000 14C YBP, recontracted at ca. 18,000 14C 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; Sher, Andrei; Orlando, Ludovic; Axelsson, Erik; Tikhonov, Alexei; Aaris-S?rensen, Kim; Greenwood, Alex D.; Kahlke, Ralf-Dietrich; Kosintsev, Pavel; Krakhmalnaya, Tatiana; Kuznetsova, Tatyana; Lemey, Philippe; MacPhee, Ross; Norris, Christopher A.; Shepherd, Kieran; Suchard, Marc A.; Zazula, Grant D.; Shapiro, Beth; Gilbert, M. Thomas P.

2010-01-01

80

Is Jiali Fault still an active fault in the late Pleistocene?  

Science.gov (United States)

The Karakoram-Jiali Fault Zone (KJFZ) is the most important active structure system in the Tibetan Plateau. This zone consists of two major faults (i.e., Karakoram fault and Jiali fault) and other minor faults in between. The Karakoram fault strikes NW to SE in the western Tibet, while the Jiali fault roughly EW in the eastern Tibet, According to previous study, the Jiali fault possesses rapid dextral slip rate (15-20mm/yr) and the maximum observed offset is ca. 1.5km. Above mentioned minor faults in the middle of KJFZ can be divided into two groups. One strikes N120°-130°E, such as the Beng Co fault, the Gyaring Co fault, the Lamu Co fault, and the Awong Co fault. They are all previously reported as right-lateral strike-slip faults. The other group striking N70°-80°E seems to be conjugated with the first group. In the east of Beng Co fault and Jiali Fault, there are still several lineations striking similar to Beng Co fault. They are located in 31°-32°N, en echelon in configuration, similar length, and subparallel to each other. In this study they are tentatively regarded as part of the KJFZ. In the spring of 2007, after the feature identification by satellite imagery we conducted a field investigation to western Jiali fault and other minor faults located in its immediate west. Both of our image analysis and field survey found no evidence to indicate the late Pleistocene activity of the main trace of the Jiali fault. One of the minor faults mentioned above, on the contrary, shows lots of active fault evidence, such as ~360m offset of the last glacial moraine, many abandon channels, offset streams, and shutter ridges, etc. Based on a previously published TL date, the slip rate of this minor fault is ca. 15±2 mm/yr. The recently published GPS velocities show a relatively large WNW-ESE extension in the plateau interior (~22±3 mm/yr) and the speeds increasingly toward the east. There is also no symptom across the main trace of the Jiali fault. We therefore would like to conclude that the main Jiali fault is no longer active at least since late Pleistocene, which may be attributed to that the orientation of the Jiali fault is parallel to the extension axis and no differential stress occurs across the fault. On the other hand, the minor conjugated faults, instead, play essential roles to accommodate the stress under certain tectonic system. Based on this findings, the crustal flow model may be preferred, but fault locked model still cannot be entirely ignored.

Chung, L.; Chen, Y.; Lai, K.; Yin, G.; Cao, Z.

2007-12-01

 
 
 
 
81

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

Science.gov (United States)

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

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

2008-08-01

82

Reconstructing the climate states of the Late Pleistocene with the MIROC climate model  

Science.gov (United States)

The Late Pleistocene was a period which lasted from the Eemian interglacial period to the start of the warm Holocene and was characterized mostly by widespread glacial ice. It was also a period which saw modern humans spread throughout the world and other species of the same genus, like the Neanderthals, become extinct. Various hypotheses have been put forward to explain the extinction of Neanderthals, about 30,000 years ago. Among these is one which involves changes in past climate and the inability of Neanderthals to adapt to such changes. The last traces of Neanderthals coincide with the end of Marine Isotope Stage 3 (MIS3) which was marked by large fluctuations in temperature and so-called Heinrich events, as suggested by geochemical records from ice cores. It is thought that melting sea ice or icebergs originating from the Laurentide ice sheet led to a large discharge of freshwater into the North Atlantic Ocean during the Heinrich events and severely weakened the Atlantic meridional overturning circulation, with important environmental ramifications across parts of Europe such as sharp decreases in temperature and reduction in forest cover. In order to assess the effects of past climate change on past hominin migration and on the extinction of certain species, it is first important to have a good understanding of the past climate itself. In this study, we have used three variants of MIROC (The Model for Interdisciplinary Research on Climate), a global climate model, for a time slice experiment within the Late Pleistocene: two mid-resolution models (an atmosphere model and a coupled atmosphere-ocean model) and a high-resolution atmosphere model. To obtain a fuller picture, we also look at a cool stadial state as obtained from a 'freshwater hosing' coupled-model experiment, designed to mimic the effects of freshwater discharge in the North Atlantic. We next use the sea surface temperature response from this experiment to drive the atmosphere models. We discuss the general features of the model-simulated climates and how model resolution can affect these results. We also compare our results with some available proxy data to elucidate where model simulations show good agreement.

Chan, Wing-Le; Abe-Ouchi, Ayako; O'ishi, Ryouta; Takahashi, Kunio

2014-05-01

83

Seismic stratigraphy of the Antarctic Peninsula pacific margin: A record of Pliocene-Pleistocene ice volume and paleoclimate  

Energy Technology Data Exchange (ETDEWEB)

Multichannel seismic profiles across the Pacific margin of the Antarctic Peninsula show a series of oblique progradational sequences. These sequences exhibit a variety of unusual characteristics that suggest they were produced by the action of ice sheets grounded out to the shelf edge at times of glacial maximum. Reflection events from deeper stratigraphic levels, followed down the continental slope and onto the rise, overlie ocean crust of known age, showing that at least eight such glacial sequences have been deposited within the past 6 m.y. Similar groundings have probably occurred on most Antarctic margins, but the depositional record is particularly well preserved at this margin because of Pliocene-Pleistocene thermal subsidence. Neogene global sea-level fluctuations have been attributed to changes in volume of continental ice sheets. The depositional sequences on the Pacific margin of the Antarctic Peninsula are thought to record West Antarctic ice-sheet fluctuations directly. Further investigation of these sequences would assess the relation between fluctuations in ice volume and the low-latitude record of global sea-level change.

Larter, R.D.; Barker, P.F. (Natural Environment Research Council, Cambridge (England))

1989-08-01

84

Late Pleistocene deglaciation chronology in the NW of the Iberian Peninsula using cosmic-ray produced 21Ne in quartz  

International Nuclear Information System (INIS)

Late Pleistocene glaciations in the NW Iberian Peninsula over Serra de Queixa and Serra de Xures, all with granite substrata, were studied by mass spectrometry using cosmogenic 21Ne. Rock cores were drilled in glacial polished surfaces and push-moraine boulders, and were analyzed to determine their integral exposure time to cosmic rays. First results, which are consistent with the relative geomorphologic model estimates, allow the identification of at least three different glacial stages, with the latest terminating about 15 ka BP

2000-10-01

85

Time spans of soil formation and late Pleistocene-Holocene climate changes in the Somma-Vesuvius volcano area, southern Italy  

Science.gov (United States)

Time spans of soil formation and climate changes occurred during the late Pleistocene to the middle Holocene are investigated in a pedostratigraphic succession located in the piedmont of the Somma-Vesuvius volcano (Campania region, southern Italy) using a multidisciplinary approach. We focused on five well-known and well-dated primary tephra and four interlayered volcanic soils developed on and/or buried by them. The pyroclastic layers give detailed chronological constraints to the stratigraphy. From bottom to top the following tephra were identified in the field: Pomici di Base (22 ka BP), Pomici Verdoline (19 ka BP), Agnano Pomici Principali (12.26 ka BP), Mercato (8.9 ka BP) and Avellino (3.9 ka BP), all of them representing volcanic products of explosive eruptions of the Somma-Vesuvius, except the third one, sourced from the westerly Phlegrean Fields. The four pedons were characterized in terms of morphological, physical, chemical, mineralogical and micromorphological features. Special attention was given to reconstruct the main soil-forming processes, paleoenvironmental and paleoclimatic conditions, degree of soil development and associated time ranges. Moreover, further tephra were identified in the field within some of above pedons. One of them was easily recognized and referred to the Agnano Monte Spina eruption (4.2-4.3 ka BP, Phlegrean Fields provenance), whereas the others were not previously known in the Somma-Vesuvius stratigraphy. On the basis of SEM-EDS analyses (chemical composition and morphoscopic observations), coupled with their stratigraphic position and literature compositional databases, they were related to the Soccavo 4-5 and the Tufi Biancastri eruptions from the Phlegrean Fields. This interpretation permitted to fix further age constrains for more detailed assessment of rates of soil formation and climatic interpretation. Major late Quaternary climatic phases are suggested by changes in the extent of development of andic properties, iron-oxide staining, silt-clay translocation, carbonate accumulation and soil microstructure, which are consistent with climate shifts since the upper Last Glacial Maximum to the Lateglacial and the early-middle Holocene climatic optimum.

Scarciglia, Fabio; Zumpano, Veronica; Sulpizio, Roberto; Terribile, Fabio; Pulice, Iolanda; La Russa, Mauro F.

2013-04-01

86

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

87

Optically stimulated luminescence age controls on late Pleistocene and Holocene coastal lithosomes, North Carolina, USA  

Science.gov (United States)

Luminescence ages from a variety of coastal features on the North Carolina Coastal Plain provide age control for shoreline formation and relative sea-level position during the late Pleistocene. A series of paleoshoreline ridges, dating to Marine Isotope Stage (MIS) 5a and MIS 3 have been defined. The Kitty Hawk beach ridges, on the modern Outer Banks, yield ages of 3 to 2??ka. Oxygen-isotope data are used to place these deposits in the context of global climate and sea-level change. The occurrence of MIS 5a and MIS 3 shorelines suggests that glacio-isostatic adjustment (GIA) of the study area is large (ca. 22 to 26??m), as suggested and modeled by other workers, and/or MIS 3 sea level was briefly higher than suggested by some coral reef studies. Correcting the shoreline elevations for GIA brings their elevation in line with other sea-level indicators. The age of the Kitty Hawk beach ridges places the Holocene shoreline well west of its present location at ca. 3 to 2??ka. The age of shoreline progradation is consistent with the ages of other beach ridge complexes in the southeast USA, suggesting some regionally contemporaneous forcing mechanism. ?? 2007 University of Washington.

Mallinson, D.; Burdette, K.; Mahan, S.; Brook, G.

2008-01-01

88

Middle and Late Pleistocene paleoscape modeling along the southern coast of South Africa  

Science.gov (United States)

Changing climates, environment, and sea levels during the Middle and Late Pleistocene must have had significant impacts on early modern humans and their behavior. However, many important archaeological sites occur along the current coastline of South Africa where the gradual slope of the offshore Agulhas Bank meant that small changes to sea level height potentially caused significant shifts in coastline position. The geographic context of these currently coastal sites would have been transformed by sea level shifts from coastal to near-coastal to fully terrestrial. To understand human adaptations as reflected in the archaeological deposits of these now-coastal sites we need to accurately model coastline position through time. Here, we introduce a Paleoscape model as a conceptual tool to ground the records for human behavioral evolution within a dynamic model of paleoenvironmental changes. Using integrated bathymetric datasets, GIS, and a relative sea level curve we estimate the position of the coastline at 1.5 ka increments over the last ˜420,000 years. We compare these model predictions to strontium isotope ratios from speleothems as an independent test and then compare the coastline predictions to evidence for shellfish exploitation through time. Both tests suggest our model is relatively robust. We then widen our paleoscape model to most of the Cape region and compare the predictions of this broadened model to evidence from Blombos cave.

Fisher, Erich C.; Bar-Matthews, Miryam; Jerardino, Antonieta; Marean, Curtis W.

2010-06-01

89

Late Pleistocene record of elevated UV radiation in an Antarctic lake  

Science.gov (United States)

Elevated ultraviolet irradiance (UVR, 280-400 nm) damages DNA and induces reorganisation within biological communities at the Earth's surface. Southern high latitude aquatic ecosystems may be particularly susceptible because of low stratospheric ozone levels and extremely low contents of photoprotective dissolved organic matter (DOM). Surveys of shallow lakes and ponds in eastern Antarctica show that cyanobacteria survive elevated UVR exposure by increasing extra-cellular concentrations of photoprotective compounds, which are preserved in sediments together with photosynthetic pigments. Thus, reconstruction of long-term changes in biological UVR receipt, to provide a context for evaluating the long-term significance of recent changes in ozone column depth, is feasible in Antarctic settings. The sediment in Lake Reid (69° 23' S, 76° 53' E), Antarctica, spans the late-Pleistocene and contains UVR-absorbing pigments from benthic cyanobacteria. Here we show that mean exposure of these benthic cyanobacteria to UVR during the last glacial was more than three times higher than during the Holocene, likely due to short periods of photosynthetic activity coinciding with relatively high UVR fluxes, or due to increased UVR transmission to the Earth's surface resulting from changes in external factors such as stratospheric ozone levels, cloud cover and surface albedo.

Hodgson, Dominic A.; Vyverman, Wim; Verleyen, Elie; Leavitt, Peter R.; Sabbe, Koen; Squier, Angela H.; Keely, Brendan J.

2005-08-01

90

An enlarged parietal foramen in the late archaic Xujiayao 11 neurocranium from Northern China, and rare anomalies among Pleistocene Homo.  

Science.gov (United States)

We report here a neurocranial abnormality previously undescribed in Pleistocene human fossils, an enlarged parietal foramen (EPF) in the early Late Pleistocene Xujiayao 11 parietal bones from the Xujiayao (Houjiayao) site, northern China. Xujiayao 11 is a pair of partial posteromedial parietal bones from an adult. It exhibits thick cranial vault bones, arachnoid granulations, a deviated posterior sagittal suture, and a unilateral (right) parietal lacuna with a posteriorly-directed and enlarged endocranial vascular sulcus. Differential diagnosis indicates that the perforation is a congenital defect, an enlarged parietal foramen, commonly associated with cerebral venous and cranial vault anomalies. It was not lethal given the individual's age-at-death, but it may have been associated with secondary neurological deficiencies. The fossil constitutes the oldest evidence in human evolution of this very rare condition (a single enlarged parietal foramen). In combination with developmental and degenerative abnormalities in other Pleistocene human remains, it suggests demographic and survival patterns among Pleistocene Homo that led to an elevated frequency of conditions unknown or rare among recent humans. PMID:23527224

Wu, Xiu-Jie; Xing, Song; Trinkaus, Erik

2013-01-01

91

Discovery of a second human molar and cranium fragment in the late Middle to Late Pleistocene cave of Ma U'Oi (Northern Vietnam).  

Science.gov (United States)

In November 2002, during the second season of work by a Vietnamese-French-Japanese team, we discovered a human molar and a fragment of an occipital bone in the late Middle to Late Pleistocene cave of Ma U'Oi (Bacon et al., Geobios. 37 (2004) 305). The layer from which this material comes is the same as that in which a human lower molar was found in 2001. Both molars can be attributed to archaic Homo, and both exhibit archaic and modern traits. PMID:15788185

Demeter, Fabrice; Bacon, Anne-Marie; Nguyen, Kim Thuy; Vu, The Long; Duringer, Philippe; Roussé, Stéphane; Coppens, Yves; Matsumura, Hirofumi; Dodo, Yukio; Nguyen, Mai Huong; Tomoko, Anezaki

2005-04-01

92

Unravelling Late Pleistocene and Holocene landscape dynamics: The Upper Guadalentín Basin, SE Spain  

Science.gov (United States)

Landscapes in SE Spain have developed in response to tectonics, climate fluctuations and, more recently, human activity. Fluvial and colluvial sediments such as river terraces and slope deposits found in the valleys reflect a complex interplay between landscape forming processes. Investigating these sediment archives, we reconstructed landscape evolution for the Upper Guadalentín Basin, SE Spain, placing recent erosion processes in a landscape evolution context. Palaeo-lake sediments dated between ~ 17 and ~ 13.8 ka evidence that a Late Glacial lake existed in the area, probably formed by a sudden blockage of the Guadalentín river. Differences in relative height above the floodplain and age between the river terraces of parts of the Guadalentín river indicate that they have not been in equilibrium in the Late Quaternary. Deposition of river terraces along the upstream part of the river is recorded at ~ 13 and ~ 9.5 ka, whereas no evidence of deposition is found for that period along the lower part of the river. There, episodes of sedimentation occur at ~ 7.5-5 ka, ~ 3.4, ~ 1.6, ~ 0.7 and ~ 0.4 ka. This discrepancy is explained by the palaeo-lake and its influence on erosion and sedimentation processes through base level changes. Combining these processes, we propose a schematic model of Late Pleistocene and Holocene landscape evolution. From the model we can conclude that i) the influence of the palaeo-lake on deposition and erosion processes both upstream and downstream is evident; and for the younger river terraces that ii) episodes of deposition seem to coincide in time, but iii) episodes of erosion in between terrace level aggradation do not coincide and neither do terrace level heights and iv) no evidence of deposition is found for the upstream part of the river. Correlation of erosion and sedimentation episodes with climate change and human impact is discussed. Although some correlations can be made, there is strong evidence that climate was not the main driver of landscape processes. We suggest that internal dynamics and local processes are more important drivers for landscape dynamics in the Upper Guadalentín Basin than external and regional factors.

Baartman, J. E. M.; Veldkamp, A.; Schoorl, J. M.; Wallinga, J.; Cammeraat, L. H.

2011-01-01

93

Large Quantities of Melt-Quenched Impact Spherules in Late Pleistocene Alaskan and Yukon "Muck" Deposits  

Science.gov (United States)

The so-called "muck" deposits of Alaska and the upper Yukon are wind-transported, silt-dominated, organic-rich sediments, including paleosols, erosional unconformities, and buried forests with in situ stumps, that have accumulated in creek valleys over at least the last 2 million years. Underlying the frozen muck are gold-bearing gravels, and removal of Late Pleistocene muck layers in mining operations has uncovered a remarkable collection of usually broken and disarticulated megafaunal bones and carcasses. Previously, Fe-rich particles have been found embedded in a number of mammoth tusks and a bison skull, and those particles have high-Ni and low-Ti compositions indicative of an extraterrestrial origin. These fossils range in age from ~21 to 37 ka B.P. Additional fossil skulls (bison, rangifer, mammoth) and a mammoth tusk from Alaska and the Yukon Territory have been found in museum and government collections with embedded Fe-rich particles as well, and nine skulls also contain significant quantities of original host sediment within them. This associated sediment was removed and examined for the presence of spherules and other cosmic impact proxies. The additional megafaunal bones are estimated to date from between 13 to 40 ka, and radiocarbon dating of samples from these specimens is currently underway. Magnetic grains were extracted from aliquots of bulk sediment from each of the fossil skulls. The magnetic fractions ranged from ~5 to 44 g/kg, averaging 23.6 g/kg. We then examined each sample fraction for magnetic spherules. Two samples contained rounded detrital magnetite and no spherules, while the other seven samples contained numerous melt-quenched magnetic spherules ranging in abundance from ~1000 to 18,000/kg, averaging ~8000/kg. We performed SEM-EDS analyses on 49 selected spherules and identified two distinct compositional populations. One group from a mammoth skull is predominately aluminosilicate (Al2O3 = 30.7 wt.%, SiO2 = 34.4 wt.%, FeO = 23.4 wt.%, CaO = 2.9 wt.%, all other oxides <2.3 wt.%). The second group from all other skulls is typically iron-rich (FeO = 87.4 wt.%, Al2O3 = 2.0 wt.%, SiO2 = 2.3 wt.%, CaO = 4.0 wt.%, all other oxides <1.1 wt.%). Using ternary diagrams, we plotted various oxides of the 49 spherules against those for known populations of other spherule types. The results indicate that the 49 spherule compositions are consistent with those of known impact spherules; apparently they are not cosmic, anthropogenic, or volcanic in origin. These preliminary results suggest that large quantities of melt-quenched impact spherules were deposited across Alaska and western Canada (Beringia) within the last 40 kyr. We propose that they were most likely produced by hypervelocity impact/airburst events in the region during the Late Pleistocene. The presence of geochemically distinct populations indicates that there were at least two such impacts/airbursts into different source rocks.

Hagstrum, J. T.; Firestone, R. B.; West, A.; Weaver, J. C.; Bunch, T. E.; Kimbel, D. R.

2012-12-01

94

Characterizing the Late Pleistocene MSA Lithic Technology of Sibudu, KwaZulu-Natal, South Africa  

Science.gov (United States)

Studies of the African Middle Stone Age (MSA) have become central for defining the cultural adaptations that accompanied the evolution of modern humans. While much of recent research in South Africa has focused on the Still Bay and Howiesons Poort (HP), periods following these technocomplexes were often neglected. Here we examine lithic assemblages from Sibudu that post-date the HP to further the understanding of MSA cultural variability during the Late Pleistocene. Sibudu preserves an exceptionally thick, rich, and high-resolution archaeological sequence that dates to ?58 ka, which has recently been proposed as type assemblage for the “Sibudan”. This study presents a detailed analysis of the six uppermost lithic assemblages from these deposits (BM-BSP) that we excavated from 2011–2013. We define the key elements of the lithic technology and compare our findings to other assemblages post-dating the HP. The six lithic assemblages provide a distinct and robust cultural signal, closely resembling each other in various technological, techno-functional, techno-economic, and typological characteristics. These results refute assertions that modern humans living after the HP possessed an unstructured and unsophisticated MSA lithic technology. While we observed several parallels with other contemporaneous MSA sites, particularly in the eastern part of southern Africa, the lithic assemblages at Sibudu demonstrate a distinct and so far unique combination of techno-typological traits. Our findings support the use of the Sibudan to help structuring this part of the southern African MSA and emphasize the need for further research to identify the spatial and temporal extent of this proposed cultural unit.

Will, Manuel; Bader, Gregor D.; Conard, Nicholas J.

2014-01-01

95

The Balitx landslide (Mallorca, Spain) and its possible seismic origin: active spreading since the Late Pleistocene  

International Nuclear Information System (INIS)

The Balitx landslide, located on the steep coastal side of the Tramuntana range on the island of Mallorca, is a large translational rock landslide in which the failure surface coincides with the reactivation of an earlier normal fault. The dating of calcite striae on the fault plane with U/Th techniques reveals that the last movement was over 400 kyr ago, which falls outside of the range of this method. The volume of the landslide is estimated to be over 700 million cubic metres, with a north-westward displacement of 300 m. Active extensional cracks as well as block spreads have been identified along the main scarp, together with displacement and toppling of blocks, the beginning of which coincides with oxygen isotope stage OIS 5a (Late Pleistocene = 83 kyr), a wetter and warmer period than the present. Currently active decametre-long cracks up to 50 m wide can be seen to affect the displaced materials. They reveal the rupture of the displaced block into several units at different speeds. A retrospective analysis of slope stability has been carried out, taking into account different scenarios according to three critical sea stands. All the scenarios are stable, with a safety factor of over 1.35. These results support the thesis that the Balitx landslide could have been triggered by seismicity. A study of the Balitx landslide under dynamic conditions reveals that the landslide could have been triggered by a moderate-to-high-magnitude earthquake (Mw=6.0) located close to the landslide (10-30 km) and probably related to some of the active faults identified in Majorca, such as the Palma Fault. (Author) 58 refs.

2013-01-01

96

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

2003-03-01

97

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

98

Late Pleistocene to recent incision dynamics near the western Tibetan Plateau margin, Zanskar, India  

Science.gov (United States)

Bedrock gorges are typically portrayed as natural conveyor belts for incoming lateral and upstream sediment. Their potential to store sediment has so far received lesser attention. Here we report on cyclic aggradation and re-incision of fluvial terraces in deeply incised bedrock gorges in the Ladakh and Zanskar Ranges of India. We infer that fluvial bedrock incision is highly episodic and buffered by intermittent sediment storage along the western Tibetan Plateau margin. Recently reported fluvial bedrock incision rates of up to 3 mm/yr derived from cosmogenic nuclide (10Be) exposure dating suggest highly localized transients in this (semi-)arid high-altitude mountain desert otherwise characterized by low (~0.02 mm/yr) denudation rates and some of the oldest glacial sediments in the Himalaya-Tibet orogen. We test for this transience and present a first dataset of OSL-derived fluvial fill terrace ages together with new 10Be exposure ages from abandoned fluvially polished surfaces in the lower Zanskar gorge, a major tributary of the upper Indus River. Our data cover ~30 km upstream of the confluence with the Indus and suggest that rates of aggradation and re-incision into fill terraces over comparable timescales range from 0.5 mm/yr to 2.6 mm/yr. Remnants of fluvial terraces are ubiquitous in the lower Zanskar gorge with elevations of up to >180 m above river level, and host sediments mainly originating from the High Himalaya, which constitutes only ~30% of the upstream drainage area. The dates from the fill terraces point to a phase of continuous aggradation from ~60 ka to ~12 ka, which we attribute either to a Late Glacial or postglacial sediment pulse from the Zanskar headwaters in the High Himalaya, or to natural damming downstream. Accounting for potential sediment cover effects, our incision rate estimates into these former valley fill are >1.8 mm/yr, and document at least two cut-and-fill cycles involving >40 m of vertical channel-bed migration since the late Pleistocene. Because of this sedimentary cover effect, we infer that the average 10Be-derived bedrock incision rate in the Zanskar has not exceeded 1 mm/yr over the last 60 ka, which is only but a fraction of the rates recently proposed for the Zanskar-Indus confluence.

Blöthe, J. H.; Munack, H.; Fülling, A.; Kubik, P. W.; Korup, O.

2012-04-01

99

The circumboreal tundra-taiga interface: late Pleistocene and Holocene changes.  

Science.gov (United States)

Creating a global perspective on past treeline changes is problematic due to the varying methods and definitions used. A general lack of a detailed description of the modern treeline position and vegetation complicates any comparative analysis of the magnitude of the most important changes. However, one seemingly common factor in most regions was an extremely rapid dispersal of trees when climate warmed drastically from full glacial conditions. Most Arctic treelines reached their northernmost positions in the early Holocene and receded to present positions starting at about 5.8 ka. The early occupation of the northernmost sites in ice-free and early deglaciated areas was possible because of the close proximity of invading trees in nearby glacial refugia, particularly in Fennoscandia and northern Russia. In Canada, the Northwest Territories and Quebec-Labrador were out of phase with this general trend due to their late deglaciation. However, even here colonization was rapid, indicating that the tree species were present adjacent to the glaciers. Following this trend and based on the present evidence, we propose a scenario of a continuous but modest occupation of eastern Beringia by spruce during the late-Pleistocene instead of an exceptionally rapid spread of conifers from the glacial refugium south of the Laurentide ice sheet (2000 to 3000 km in about 200 years), which typically has been assumed. Macrofossil evidence of scattered occurrences of "exotic species" (for instance Siberian larch in central Sweden) far from their natural range limits in the early Holocene highlight the disparity between pollen and macrofossil analyses. It questions the validity of assigned pollen percentages to indicate the presence of a species within a region as these species were not observed in the pollen record. Thus, it is likely that trees were present at any given site well before the rise in pollen abundance. There is still a large potential to improve our knowledge about the environmental history of the circumboreal treeline areas. In particular, future research should concentrate not only on patterns of species displacement, but on finding the factors, apart from climate, which cause treeline shifts. PMID:12374054

Payette, S; Eronen, M; Jasinski, J J P

2002-08-01

100

Vegetation Dynamics in the Kenai Lowlands, Alaska during the Late Pleistocene and Holocene  

Science.gov (United States)

The use of paleoinformation through ecosystem reconstruction can help us understand the behavior and sensitivity of the boreal forest as climate continues to change. A 2.5-meter sediment core extracted from Swanson Fen, a muskeg in the northern Kenai Lowlands on the Kenai Peninsula, Alaska, provides a sensitive Holocene paleoenvironmental record that lies in an ecotone between interior boreal forest and maritime coastal forest today. The core was sampled at 2-cm intervals and processed for pollen and spores. Five intervals were dated using AMS radiocarbon dating, and the basal macrofossils produced an age of 12,245 ±45 radiocarbon years. The central Kenai Peninsula Lowlands underwent a number of marked vegetational and climatic changes since deglaciation. Four distinct vegetation zones reveal changes starting in the late Pleistocene. The pioneer vegetation includes a dominance of herbaceous ( Artemisia, Apiaceae, Asteroideae)and shrubby ( Betula) species. The second zone (beginning at 9890±45 radiocarbon years) and marking the Holocene boundary, shows a striking increase in Polypodiaceae (ferns) and Picea (spruce) and a decrease in shrubby species such as Betula, indicative of warming. The third zone indicates a decline in Polypodiaceae and a reemergence of Betula species, while the final most recent zone reveals a rapid resurgence in Picea and Tsuga mertensiana (Mountain hemlock) species. While a general warming trend occurred following deglaciation, vegetation patterns suggest extended periods of increased precipitation, for example in the early Holocene, as is evidenced by the plethora of Polypodiaceae. A movement and an intensification of the Aleutian Low could explain these periods of increased precipitation over the Kenai Peninsula. Alternatively, this spike in Polypodiaceae can be explained by increased disturbance. The presence of 10 % Picea pollen at the base of the core suggests that one of the Picea species may have survived the last glaciation in the region. A decrease in Picea pollen and an increase in herbaceous ( Artemisia, Apiaceae, Asteroideae) pollen in the late Quaternary suggest a reversal to cooler conditions before warming resumed at the Holocene boundary, and Picea once again increased. This coincides with the timing of the Younger Dryas in the North Atlantic, and suggests that this phenomenon was felt on the Kenai Peninsula.

Jones, M. C.; Peteet, D. M.

2005-12-01

 
 
 
 
101

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

Science.gov (United States)

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. PMID:20212118

Campos, Paula F; Willerslev, Eske; Sher, Andrei; Orlando, Ludovic; Axelsson, Erik; Tikhonov, Alexei; Aaris-Sørensen, Kim; Greenwood, Alex D; Kahlke, Ralf-Dietrich; Kosintsev, Pavel; Krakhmalnaya, Tatiana; Kuznetsova, Tatyana; Lemey, Philippe; MacPhee, Ross; Norris, Christopher A; Shepherd, Kieran; Suchard, Marc A; Zazula, Grant D; Shapiro, Beth; Gilbert, M Thomas P

2010-03-23

102

Stratigraphy and chronology of offshore to nearshore deposits associated with the Provo shoreline, Pleistocene Lake Bonneville, Utah  

Science.gov (United States)

Stratigraphic descriptions and radiocarbon data from eleven field locations are presented in this paper to establish a chronostratigraphic framework for offshore to nearshore deposits of Lake Bonneville. Based on key marker beds and geomorphic position, the deposits are interpreted to have accumulated during the period from the late transgressive phase, through the overflowing phase, into the regressive phase of the lake. Radiocarbon ages of sediments associated with the Provo shoreline indicate that Lake Bonneville dropped rapidly from the Provo shoreline at about 12,600 14C yr BP (15,000 cal yr B.P.). The presence of one or more sand beds in the upper part of the Provo-aged marl indicates rapid lowering of lake level or storm events at the end of the Provo episode. An accurate understanding of the timing and nature of Lake Bonneville's climate-driven regression from the Provo shoreline is critical to correlations with records of regional and hemispheric climate change. The rapid descent of the lake from the Provo shoreline correlates with the decline of Lakes Lahontan and Estancia, and with the onset of the B??lling-Aller??d warming event. ?? 2011 Elsevier B.V.

Godsey, H. S.; Oviatt, C. G.; Miller, D. M.; Chan, M. A.

2011-01-01

103

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

Science.gov (United States)

Strontium and carbon isotope stratigraphy was applied to a 202 m-thick shallow marine carbonate section within the Late Jurassic Bau Limestone at the SSF quarry in northwest Borneo, Malaysia, which was deposited in the western Palaeo-Pacific. Strontium isotopic ratios of rudist specimens suggest that the SSF section was formed between the latest Oxfordian (155.95 Ma) and the Late Kimmeridgian (152.70 Ma), which is consistent with previous biostratigraphy. The ?13Ccarb values of bulk carbonate range from ?0.10 to +2.28‰ and generally show an increasing upward trend in the lower part of the section and a decreasing upward trend in the upper part of the section. A comparable pattern is preserved in the ?13Corg isotope record. Limestone samples of the SSF section mainly preserve the initial ?13Ccarb values, except for the interval 84–92 m, where an apparent negative anomaly likely developed as a result of meteoric diagenesis. Comparing with the Tethyan ?13Ccarb profile, a negative anomaly in the lower SSF section can be correlated with the lowered ?13C values around the Oxfordian/Kimmeridgian boundary. In addition, ?13Ccarb values of the Bau Limestone are generally ˜1‰ lower than the Tethyan values, but comparable with the values reported from Scotland and Russia, located in Boreal realm during the Late Jurassic. This suggests that either the Tethyan record or the other records have been affected by the ?13C values of regionally variable dissolved inorganic carbon (DIC). The Late Jurassic ?13CDIC values are thought to have been regionally variable as a result of their palaeoceanographic settings. This study shows that ?13C chemostratigraphy of the Palaeo-Pacific region contributes to an improved understanding of global carbon cycling and oceanography during this time period.

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

2013-09-01

104

Late Pleistocene to Holocene soil development and environments in the Long Gang Volcanic Field area, Jilin Province, NE China  

Science.gov (United States)

Late Pleistocene to Holocene shifts of climate and vegetation in the Long Gang Volcanic Field in NE China have been reconstructed, e. g. by Steblich et al. (2009), based on Maar lake sediment cores. In this study, we investigated soil development during the Late Pleistocene and Holocene and linked it to the climate and vegetation reported in the literature. Three pedons were described and analyzed on a crater wall surrounding a maar. The lower part of the slope is covered by basic pyroclastics that are obviously younger than the maar itself. Pedon 1 is located on the upper slope, where the younger pyroclastics are not present; thus it developed over the entire Holocene and part of the Late Pleistocene. Pedon 2 is on the toe slope and developed from the young basic pyroclastics. Vegetation remains, charred by fire that was caused by the volcanic ash fall, were found in the lowermost part of the pyroclastics layer, on top of a paleosol. Charcoal fragments were dated to 18950-18830 cal BP (using INTCAL 09). Thus, pedon 2 developed since around 18.9 ka BP, whereas the development of the paleosol that was buried under the pyroclastics (pedon 3), was stopped at this time. Pedons 1 and 2 are Vitric Andosols, developed mainly from basic pyroclastics, as evidenced by the composition of rock fragments in the soils, comprising 78 / 81 mass % lapilli and 22 / 19 mass % gneiss fragments, respectively. Pedon 3 is a Cutanic Luvisol (Chromic) that developed entirely from gneiss fragments produced by the maar explosion. Lab data suggest increasing intensity of pedogenesis in the direction: Pedon 3 (paleosol) Betula (and minor proportions of Larix, Alnus, Picea and Salix). We assume a similar environment for the time of the deposition of the pyroclastics (18.9 ka BP) in the toe slope profile. The character of the steppe was probably more open at this time, but the presence of at least few scattered trees over the steppe is evidenced by a charred tree trunk that was found in the profile. During Holocene, vegetation consisted mainly of deciduous forest, until anthropogenic influence increased from around 1850 AD on. Reference: Steblich, M., Mingram, J., Han, J., Liu, Y. (2009): Late Pleistocene spread of (cool-)temperate forests in Northeast China and climate changes synchronous with the North Atlantic region. Global and Planetary Change, 65, 56-70.

Sauer, Daniela; Zhang, Xinrong; Knöbel, Jette; Maerker, Lutz

2014-05-01

105

Late Pleistocene desiccation of Lake Tana, source of the Blue Nile  

Science.gov (United States)

High-resolution seismic data from Lake Tana, the source of the Blue Nile in northern Ethiopia, reveal a deep sedimentary sequence divided by four strong reflectors. Data from nearshore cores show that the uppermost strong reflector represents a stiff silt unit, interpreted as a desiccation surface. Channel cuts in this surface, bordered by levee-like structures, are apparent in the seismic data from near the lake margin, suggesting fluvial downcutting and over-bank deposition during seasonal flood events. Periphytic diatoms and peat at the base of a core from the deepest part of the lake overlie compacted sediments, indicating that desiccation was followed by development of shallow-water environments and papyrus swamp in the central basin between 16,700 and 15,100 cal BP. As the lake level rose, open-water evaporation from the closed lake caused it to become slightly saline, as indicated by halophytic diatoms. An abrupt return to freshwater conditions occurred at 14,750 cal BP, when the lake overflowed into the Blue Nile. Further reflection surfaces with downcut structures are identifiable in seismic images of the overlying sediments, suggesting at least two lesser lake-level falls, tentatively dated to about 12,000 and 8000 cal BP. Since Lake Victoria, the source of the White Nile, was also dry until 15,000 cal BP, and did not reach overflow until 14,500 cal BP, the entire Nile system must have been reduced to intermittent seasonal flow until about 14,500 cal BP, when baseflow was re-established with almost simultaneous overflow of the headwater lakes of both the White and Blue Nile rivers. Desiccation of the Nile sources coincides with Heinrich event 1, when cessation of northward heat transport from the tropical Atlantic disrupted the Atlantic monsoon, causing drought in north tropical Africa. The strong reflectors at deeper levels in the seismic sequence of Lake Tana may represent earlier desiccation events, possibly contemporaneous with previous Late Pleistocene Heinrich events.

Lamb, Henry F.; Bates, C. Richard; Coombes, Paul V.; Marshall, Michael H.; Umer, Mohammed; Davies, Sarah J.; Dejen, Eshete

2007-02-01

106

Evolution of Middle to Late Pleistocene Sandy Calcareous Palaeosols Underlying the Northwestern Negev Desert Dunefield (Israel)  

Science.gov (United States)

Calcareous palaeosols in the northwestern (NW) Negev Desert dunefield, Israel, at the eastern end of the Sinai-Negev erg were studied in relation to their overlying stabilized dunes and downwind loess deposits, using sedimentological analyses, spectroscopy, and optically stimulated luminescence (OSL) dating. During the Middle to Late Pleistocene, between around MIS 7 and through MIS 3, several cycles of sand veneer (sheet) deposition, stabilization, pedogenesis, and erosion formed a spatially variable sequence of sandy calcareous palaeosols in the NW Negev. Periods of stability on the order of several thousand years to over ten thousand years, characterized by post-depositional illuviation of aeolian silts, clays, and salts, enabled the formation of diagnostic, often-indurated, calcareous, Bk horizons (stages I-III), with orthic carbonate nodules. The primary particle-size mode of the palaeosol (127 µm) is intermediate between the modes of the overlying (MIS 2) dune sand and the mode of primary northern Negev (~MIS 6 through MIS 2) loess deposits in the dunefield periphery. The sand fraction of the palaeosols is slightly finer than the dune sand, and its spatial sedimentation pattern correlates with the pattern of the subsequent dune incursions. These observations suggest that (1) Bk palaeosol horizons were resistant to (MIS 6 - MIS 3) sand veneer aeolian erosion and formed chronologically differentiated and durable surfaces; (2) these surfaces remained in equilibrium for extensive periods, being intermittently covered and preserved by shifting sand veneers; (3) the MIS 2 dune incursion episodes followed the same transport routes of the underlying palaeosol sand substrate while producing a limited amount of aeolian erosion on the Bk horizons, and; (4) the similar sedimentological and chronological framework of the palaeosols and loess deposits suggests a partial genetic connection. As for the overlying dunes, aeolian sand supply to the parent material of the palaeosols was initially controlled by sediment availability originating in the Nile Delta and probably linked to glacial-interglacial eustatic cycles and glacial and cold-event windiness. The NW Negev sand deposition episodes that markedly differ from the ages of a nearby sandy palaeosol sequence of coastal origin exemplify the role of sand supply on the development of palaeosol sequences in a similar palaeoclimate.

Roskin, Joel; Katra, Itzhak; Porat, Naomi; Zilberman, Ezra

2014-05-01

107

Chronologic evidence for multiple periods of loess deposition during the Late Pleistocene in the Missouri and Mississippi River Valley, United States: Implications for the activity of the Laurentide ice sheet  

Science.gov (United States)

The loess stratigraphy of the mid-continental U.S. is an important proxy record for the activity of the Laurentide Ice Sheet in North America. One of the most outstanding problems is deciphering the age of loess deposits in this area during the late Pleistocene. Radiocarbon dating of snails and thermoluminescence dating of the fine-silt fraction (4-11 ??m) from loess at the Loveland Loess type section, Loveland, Iowa and a recent excavation at the Pleasant Grove School section. Madison County, Illinois provide new chronologic control on loess deposition in the Mississippi/Missouri River Valley chronology indicates that the Loveland Loess is Illinoian in age (135??20 ka) but is not correlative with the Teneriffe Silt which is dated to 77 ?? 8 ka. Concordant radiocarbon and thermoluminescence age estimates demonstrate that the Roxana Silt and a correlative loess in Iowa, the Pisgah Formation, is probably 40-30 ka old. These age estimates in conjunction with previous results indicate that there were four periods of loess deposition during the last 150 ka at 25-12 ka, 45-30 ka, 85-70 ka and at ca. 135 ?? 20 ka. This chronology of loess deposition supports the presence of both a late Illinoian and early Wisconsinan loess and associated soils. Thus, there may be more than one soil in the loess stratigraphy of the mid-continental U.S. with morphologies similar to the Sangamon Soil. The last three periods of loess deposition may be correlative with periods of elevated dust concentrations recorded in the Dye 3 ice core from southern Greenland. This is particularly significant because both areas possibly had the same source for eolian particles. Reconstructions of atmospheric circulation for glacial periods show a southerly deflected jet stream that could have transported dust from the mid-continental USA to southern Greenland. Lastly, the inferred record of loess deposition is parallel to a chronology for deglaciation of the Laurentide Ice Sheet deciphered from chronologic and stratigraphic studies of raised glacial and marine sediments in the Hudson Bay Lowlands, Canada. These chronologies indicate that the Laurentide Ice Sheet was quite dynamic during the late Pleistocene, advancing and retreating across North America at least four times during the last 150 ka. ?? 1992.

Forman, S. L.; Arthur, Bettis, III, E.; Kemmis, T. J.; Miller, B. B.

1992-01-01

108

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 (projected 14C dates onto a single composite core. Forty-two AMS 14C dates from bivalve mollusk shells were used to construct a wiggle-matching-based age-depth model for the late Holocene sequence and to 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

109

First record of fossil wood and phytolith assemblages of the Late Pleistocene in El Palmar National Park (Argentina)  

Science.gov (United States)

Two paleoxylologic assemblages and two phytolith assemblages were recovered from Late Pleistocene sediments of El Palmar Formation. These deposits are found in outcrops along the western margin of the Uruguay River. The spectra of taxa obtained in both sets by different methods is complementary. The fossil remains are characterized in terms of floristic composition and paleoclimate. Seven families are recognized: Podostemaceae, Myrtaceae, Anacardiaceae, Mimosoideae, Arecaceae, Poaceace, and Cyperaceae. Sponge siliceous spicules also have been found in these assemblages. The state of preservation of the phytoliths and their weathering degree is analyzed. These studies can be used as a potential paleoecological tool for alluvial sediments. The comparison of fossil assemblages with modern analogs clarifies the paleoecological requirements and composition of two paleocommunities, one dominated by woody forests and the other by palms. The climatic conditions inferred from the reconstructed vegetation and sedimentary deposits indicate a temperate-warm, humid climate. The results constitute the first evidence of the floral diversity of the vegetation in El Palmar National Park during the Late Pleistocene.

Zucol, A. F.; Brea, M.; Scopel, A.

2005-10-01

110

Quaternary Stratigraphy, Drainage-Basin Development, and Geomorphology of the Lake Manix Basin, Mojave Desert: Guidebook for Fall Field Trip, Friends of the Pleistocene, Pacific Cell, October 4-7, 2007  

Science.gov (United States)

The 2007 field trip of the Pacific Cell, Friends of the Pleistocene, visited features of the Quaternary geology and geomorphology of the Lake Manix basin in the Mojave Desert. This report is the guidebook for this trip and includes some discussion of relations observable along the road and at various field trip stops. The Mojave River originates in the San Bernardino Mountains and in high-water years flows north and east to its terminus in Silver Lake playa north of Baker, Calif. Along this course, the river passes through or near several basins that were internally drained prior to integration by the Mojave River, including the Victorville, Harper, Manix, and Soda Lake basins. Sediments in the Lake Manix basin record Mojave River discharge and lake fluctuations that began during the middle Pleistocene and continued through most of the late Pleistocene.

Reheis, Marith C.; Miller, David M.; Redwine, Joanna L.

2007-01-01

111

Stratigraphy of the Late Cretaceous-Paleogene deposits of the Western Cordillera Ecuador: Geodynamic implications.  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Two accreted oceanic terranes are classically recognized in the Cordillera Occidental of Central Ecuador, the Macuchi island arc to the West, and the Pallatanga oceanic terrane to the East. Detailed stratigraphic studies of the sedimentary cover of the "Pallatanga terrane" show that it actually comprises two terranes. During the late Campanian-early Maastrichtian, the eastern terrane received partially continent-derived turbidites, demonstrating that it was accreted to the Andean margin befor...

Jaillard, Etienne; Ordonez, Martha; Suarez, Johnny; Toro Alava, Jorge; Iza, Danilo; Lugo, William

2004-01-01

112

Late Frasnian mass extinction: Conodont event stratigraphy, global changes, and possible causes  

Science.gov (United States)

Several abrupt changes in conodont biofacies are documented to occur synchronously at six primary control sections across the Frasnian-Famennian boundary in Euramerica. These changes occurred within a time-span of only about 100,000 years near the end of the latest Frasnian linguiformis Zone, which is formally named to replace the Uppermost gigas Zone. The conodont-biofacies changes are interpreted to reflect a eustatic rise followed by an abrupt eustatic fall immediately preceding the late Frasnian mass extinction. Two new conodont species are named and described. Ancyrognathus ubiquitus n.sp. is recorded only just below and above the level of late Frasnian extinction and hence is a global marker for that event. Palmatolepispraetriangularis n.sp. is the long-sought Frasnian ancestor of the formerly cryptogenic species, Pa. triangularis, indicator of the earliest Famennian Lower triangularis Zone. The actual extinction event occurred entirely within the Frasnian and is interpreted to have been of brief duration-from as long as 20,000 years to as short as several days. The eustatic rise-and-fall couplet associated with the late Frasnian mass extinction is similar to eustatic couplets associated with the demise of most Frasnian (F2h) reefs worldwide about 1 m.y. earlier and with a latest Famennian mass extinction about 9.5 m.y. later. All these events may be directly or indirectly attributable to extraterrestrial triggering mechanisms. An impact of a small bolide or a near miss of a larger bolide may have caused the earlier demise of Frasnian reefs. An impact of possibly the same larger bolide in the Southern Hemisphere would explain the late Frasnian mass extinction. Global regression during the Famennian probably resulted from Southern-Hemisphere glaciation triggered by the latest Frasnian impact. Glaciation probably was the indirect cause of the latest Famennian mass extinction.

Sandberg, Charles A.; Ziegler, Willi; Dreesen, Roland; Butler, Jamie L.

1988-01-01

113

Sedimentology and sequence stratigraphy of the Lopingian (Late Permian) coal measures in southwestern China  

Energy Technology Data Exchange (ETDEWEB)

The Lopingian coal measures of southwestern China were deposited within a range of facies associations spanning a spectrum of settings from fluvial to marine carbonate platform. The transitional to terrestrial coal measures are dominated by siliciclastics, but they also contain fifteen laterally extensive marine bands (limestone beds and mudstone). These bands act as marker horizons that enable correlation between fully marine and terrestrial facies. Examination of this range of facies and their sedimentology has enabled the development of a high-resolution sequence stratigraphic framework. Set against the established backdrop of second-order Lopingian transgression, sixteen fourth-order sequences and three composite sequences (third-order) are recognized. Results show that, in the composite sequences, peat accumulation in the seaward parts of the study area predominantly correlates with early transgressive sequence sets (TSS), while in more landward areas it correlates with the middle TSS to late highstand sequence sets (HSS). Differences in peat-accumulation regimes within the sequence stratigraphic framework are attributed to variations in subsidence and background siliciclastic input rates in different depositional settings, with these combining to produce differences in the rate of accommodation change. The preservation of coal resources in the middle to late HSS in this area was most likely related to the rise of the regional base level throughout the Lopingian. (author)

Wang, Hao [School of Geosciences and Surveying Engineering, China University of Mining and Technology, Beijing (China); School of Earth and Environment, University of Leeds (United Kingdom); Shao, Longyi; Hao, Liming; Zhang, Pengfei [School of Geosciences and Surveying Engineering, China University of Mining and Technology, Beijing (China); Glasspool, Ian J. [Department of Geology, Field Museum of Natural History, Chicago, Illinois (United States); Wheeley, James R.; Hilton, Jason [School of Geography, Earth and Environmental Sciences, University of Birmingham (United Kingdom); Wignall, Paul B. [School of Earth and Environment, University of Leeds (United Kingdom); Yi, Tongsheng [Guizhou Bureau of Coal Geological Exploration, Guiyang, Guizhou (China); Zhang, Mingquan [Coal Geology and Prospecting Institute of Yunnan Province, Kunming, Yunnan (China)

2011-01-01

114

The late Pleistocene environment of the Eastern West Beringia based on the principal section at the Main River, Chukotka  

DEFF Research Database (Denmark)

Chukotka is a key region for understanding both Quaternary environmental history and transcontinental migrations of flora and fauna during the Pleistocene as it lies at the far eastern edge of Asia bordering the Bering Sea. The now submerged land bridge is the least understood region of Beringia yet the most critical to understanding migrations between the Old and New Worlds. The insect fauna of the Main River Ledovy Obryv (Ice Bluff) section, which is late Pleistocene in age (MIS 3-2), is markedly different from coeval faunas of areas further to the west, as it is characterized by very few thermophilous steppe elements. From the fauna we reconstruct a steppe-tundra environment and relatively cold conditions; the reconstructed environment was moister than that of typical steppe-tundra described from further west. The data from this locality, if typical of the Chukotka Peninsula as a whole, may indicate that a barrier associated with the environments of the land bridge restricted trans-Beringian migrations, particularly the more thermophilous and xeric-adapted elements of the Beringian biota, supporting the hypothesis of a cool but moist land-bridge filter inferred from evidence from several other studies.

Kuzmina, Svetlana A.; Sher, Andrei V.

2011-01-01

115

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

2013-08-01

116

Sedimentation and paleoenvironmental evolution in the China seas since the late Pleistocene  

Science.gov (United States)

Chinese seas include the Bohai Sea, Yellow Sea, East China Sea and South China Sea. Systematic investigations on the sedimentary geology of the above-mentioned seas have been carried out during 2004-2011 through the project of "Synthetic Investigation and Research on the Chinese Marginal Seas". Around 21700 surface sediment samples and 1250 sediment cores have been collected for the detailed study. Around 75300 km of seismic profiles and 15220 sites of suspended matter investigation have been completed. Major advances of our study are as follows. 1. Sedimentary distribution map of 1:25 0000 of Chinese shallow seas has been complied, with the special emphasis on the harbor, bay and delta regions at 1:50000 scale. Meanwhile, an atlas of the marine sediments has been published. Several issues related to the sediments partition and variations in suspended matters and their controlling factors have been discussed. The sedimentary classification, provenance, characteristics of mineralogy, geochemistry, microfossils, physical and mechanical characteristics, content and turbidity of suspended matter have also been addressed. 2. We also compiled images of seismic profiles and its interpreted pictures, depth of representative strata boundary for Chinese seas. We have attempted to clarify the characteristics of sequence stratigraphy in these four seas since the Last Deglacial Period. Disaster geological bodies, such as sea-bottom sand waves, shallow gas and buried channel/exposed rock have been delineated. 3. High-resolution Holocene stratigraphy and time series of estuary, subaqueous delta and mud deposits in the inner shelf regions of Chinese seas have been established by using sedimentology, mineralogy, geochemistry and sequence stratigraphy. The possible responses of sea-level variations to environmental changes have also been clarified tentatively. 4. Based on the investigation of sedimentary cores, we have constructed the lithostratigraphy and magnetostratigraphy of the Bohai Sea for the last 1 Ma, and recognized nine transgression-regression cycles in this region. Likewise, based on the core from south Yellow Sea, we reconstructed the lithostratigraphy and magnetostratigraphy of the south Yellow Sea since 1.9 Ma and discussed the sedimentary environmental change and its relation with past climatic conditions and sea-level changes.

Shi, Xuefa; Liu, Yanguang; Liu, Shengfa; Qiao, Shuqing

2014-05-01

117

Reconstructing late Pliocene to middle Pleistocene Death Valley lakes and river systems as a test of pupfish (Cyprinodontidae) dispersal hypotheses  

Science.gov (United States)

During glacial (pluvial) climatic periods, Death Valley is hypothesized to have episodically been the terminus for the Amargosa, Owens, and Mojave Rivers. Geological and biological studies have tended to support this hypothesis and a hydrological link that included the Colorado River, allowing dispersal of pupfish throughout southeastern California and western Nevada. Recent mitochondrial deoxyribonucleic acid (mtDNA) studies show a common pupfish (Cyprinodontidae) ancestry in this region with divergence beginning 3-2 Ma. We present tephrochronologic and paleomagnetic data in the context of testing the paleohydrologic connections with respect to the common collection point of the Amargosa, Owens, and Mojave Rivers in Death during successive time periods: (1) the late Pliocene to early Pleistocene (3-2 Ma), (2) early to middle Pleistocene (1.2-0.5 Ma), and (3) middle to late Pleistocene (<0.70.03 Ma; paleolakes Manly and Mojave). Using the 3.35 Ma Zabriskie Wash tuff and 3.28 Ma Nomlaki Tuff Member of the Tuscan and Tehama Formations, which are prominent marker beds in the region, we conclude that at 3-2 Ma, a narrow lake occupied the ancient Furnace Creek Basin and that Death Valley was not hydrologically connected with the Amargosa or Mojave Rivers. A paucity of data for Panamint Valley does not allow us to evaluate an Owens River connection to Death Valley ca. 3-2 Ma. Studies by others have shown that Death Valley was not hydrologically linked to the Amargosa, Owens, or Mojave Rivers from 1.2 to 0.5 Ma. We found no evidence that Lake Manly flooded back up the Mojave River to pluvial Lake Mojave between 0.18 and 0.12 Ma, although surface water flowed from the Amargosa and Owens Rivers to Death Valley at this time. There is also no evidence for a connection of the Owens, Amargosa, or Mojave Rivers to the Colorado River in the last 3-2 m.y. Therefore, the hypothesis that pupfish dispersed or were isolated in basins throughout southeastern California and western Nevada by such a connection is not supported. Beyond the biologically predicted time frame, however, sparse and disputed data suggest that a fluvial system connected Panamint (Owens River), Death, and Amargosa Valleys, which could account for the dispersal and isolation before 3 Ma. ?? 2008 The Geological Society of America.

Knott, J. R.; Machette, M. N.; Klinger, R. E.; Sarna-Wojcicki, A. M.; Liddicoat, J. C.; Tinsley, III, J. C.; David, B. T.; Ebbs, V. M.

2008-01-01

118

Sites without stratigraphy: Devesa do Rei, a cultual site in Galician late Prehistory and the Iron Age?  

Directory of Open Access Journals (Sweden)

Full Text Available In this text we explore a singular site that offers a series of important novelties, both in terms of its discontinuous pattern of use in different periods (covering a lengthy period from the Neolithic to the Iron Age, and its apparent use for ritual purposes in all of them, as well as the possible identification of a funerary structure from the Galician Iron Age. At the same time, this work is proposed as a case for study that makes it possible to define a procedure to reconstruct the sequence and function of open sites from Late Prehistory in Galicia characterized by a lack of vertical stratigraphy. This problem is solved by combining different analytical techniques, all based on a record of high quality excavation that makes use of analyses of material culture, radiocarbon dating, distribution patterns, as well as soil and sediment analysis.

Se estudia en este texto un yacimiento singular que ofrece importantes novedades, tanto por su reocupación discontinua en épocas distintas (con una secuencia amplia que cubre desde el Neolítico a la Edad del Hierro, como por su aparente funcionalidad ritual en todas ellas, y la posible identificación de una estructura funeraria de la Edad del Hierro de Galicia. Al mismo tiempo, este trabajo se plantea como caso de estudio que permite definir un procedimiento para reconstituir la secuencia y función de yacimientos abiertos de la Prehistoria Reciente de Galicia caracterizados por no presentar estratigrafía vertical. Este problema se solventa con el entrecruzamiento de diferentes técnicas de análisis basadas todas ellas en un registro de excavación de calidad que se sirve de análisis de cultura material, radiocarbónicos, distributivos, sedimentológicos y edafológicos.

Aboal Fernández, Roberto

2005-12-01

119

Carbon and oxygen isotopes in sequence stratigraphy of late Paleozoic strata in Hedong coal field  

Energy Technology Data Exchange (ETDEWEB)

Through testing 45 samples collected from Permo-Carboniferrous coal measures of the Hedong coal field, the distributions characteristics of carbon and oxygen isotopes in sequences are analyzed. The feasibility for sequence subdivision and correlation, as well as for the study of relative sea level variations and late Paleozoic facies are also discussed. It is shown that the distribution of carbon and oxygen isotopes in sequences (third order) are different between C{sub 2} and P{sup 1}{sub 1}. In the sequences of C{sub 2} the values of {delta}{sup 13}C and {delta}{sup 18}O gets heavier from TST to HST. In the sequences of P{sup 1}{sub 1} the values of {delta}{sup 13}C become lighter from TST to HST, whereas the values of {delta}{sup 18}O become heavier, both of which presenting rhythmicity vertically. Laterally the values of {delta}{sup 13}C and Z generally present an increasing trend southwards. The distribution of carbon and oxygen isotopes in sequences are controlled by various factors such as coal accumulation, terrigenous supply, paleoclimate, depositional environment and geologic time. 5 refs., 2 figs., 1 tab.

Li, G.; Wen, X. [China University of Geosciences, Beijing (China)

1999-06-01

120

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

Science.gov (United States)

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

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

2007-01-01

 
 
 
 
121

Late Holocene stratigraphy of coastal deposits between Auckland and Dunedin, New Zealand  

International Nuclear Information System (INIS)

Three chronostratigraphic units based on accumulative deposits and their respective soils are proposed for late Holocene coastal deposits between Auckland and Dunedin, New Zealand: Tamatean Chronozone (c. 1,800 to 450 years BP), Ohuan Chronozone (c. 450 to 150 years BP), and Hoatan Chronozone (c. 150 years to present day). The chronozones represent depositional episodes each consisting of two phases: a high rate of deposition (unstable phase), followed by a low rate of deposition and soil formation (stable phase). Vegetation on soils formed during the stable phases is inferred principally from landsnails recovered from archaeological sites. Forest on Tamatean soil (600 to 450 years BP) advanced almost to the coast in the Manawatu, the southeast Wairarapa, and on the East Coast. Sediment thickness measured at sections along the eastern North Island coast show that rates of deposition during unstable phases have decreased during the last 650 years. The depositional episodes appear to be unrelated to sea level changes, tectonic activity, volcanic eruptions or cultural influence. Unstable phases appear to correlate with times of high temperatures, and stable phases with time of low temperatures; it is suggested that the episodes may be related to changes in the frequency of tropical and extratropical cyclones. Inferred climate during unstable phases is windy and dry, and during stable phases, less windy and moist

1985-03-01

122

A critical evaluation of carbon isotope stratigraphy and biostratigraphic implications for Late Cretaceous global correlation  

Science.gov (United States)

Climate variability is driven by a complex interplay of global-scale processes and our understanding of them depends on sufficient temporal resolution of the geologic records and their precise inter-regional correlation, which in most cases cannot be obtained with biostratigraphic methods alone. Chemostratigraphic correlation based on bulk sediment carbon isotopes is increasingly used to facilitate high-resolution correlation over large distances, but complications arise from a multitude of possible influences from local differences in biological, diagenetic and physico-chemical factors on individual ?13C records that can mask the global signal. To better assess the global versus local contribution in a ?13C record it is necessary to compare numerous isotopic records on a global scale. As a contribution to this objective, this paper reviews bulk sediment ?13Ccarb records from the Late Cretaceous in order to identify differences and similarities in secular ?13C trends that help establish a global reference ?13C record for this period. The study presents a global-scale comparison of twenty ?13C records from sections representing various palaeo-latitudes in both hemispheres and different oceanic settings from the Boreal, Tethys, Western Interior, Indian Ocean and Pacific Ocean, and with various diagenetic overprinting. The isotopic patterns are correlated based on independent dating with biostratigraphic and paleomagnetic data and reveal good agreement of the major isotope events despite offsets in absolute ?13C values and variation in amplitude between the sites. These differences reflect the varying local influences e.g. from depositional settings, bottom water age and diagenetic history, whereas the concordant patterns in ?13C shifts might represent ?13C fluctuations in the global seawater dissolved inorganic carbon. The latter is modulated by variations in organic matter burial relative to re-mineralization, in the global-scale formation of authigenic carbonate, and in partitioning of carbon between organic carbon and carbonate sinks. These variations are mainly controlled by changes in climate and eustasy. Additionally, some globally synchronous shifts in the bulk ?13Ccarb records could result from parallel variation in the contribution of authigenic carbonate to the sediment. Formation of these cements through biologically mediated early diagenetic processes is related to availability of oxygen and organic material and, thus, can be globally synchronized by fluctuations in eustasy, atmospheric and oceanic oxygen levels or in large-scale oceanic circulation. Because the influence of early diagenetic cements on the bulk ?13Ccarb signal can, but need not be synchronized, chemostratigraphy should not be used as a stand-alone method for trans-continental correlation, and especially minor isotopic shifts have to be interpreted with utmost care. Nevertheless, the observed consistency of the ?13C correlations confirms global scale applicability of bulk sediment ?13C chemostratigraphy for the Late Cretaceous, including sediments that underwent lithification and burial diagenesis such as the sediments from the Himalayan and Alpine sections. Limitations arise from increased uncertainties (1) in sediments with very low carbonate content, (2) from larger ?13C variability in sediments from very shallow marine environments, (3) from unrecognized hiatuses or strong changes in sedimentation rates, and (4) in sections with short stratigraphic coverage or with few biostratigraphic marker horizons.

Wendler, Ines

2013-11-01

123

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

2013-01-01

124

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

2002-06-01

125

Mammoth tracks indicate a declining Late Pleistocene population in southwestern Alberta, Canada  

Science.gov (United States)

Much debate has raged over the role that early humans played in this most recent large extinction. Fossil mammoth ( Mammuthus primigenius) footprints were discovered at the St. Mary Reservoir in southwestern Canada (Wally's Beach DhPg-8). They are located in aeolian sediment dated at 11,300-11,000 years BP. By comparing the size distribution of these tracks with those of modern African elephants ( Loxodonta africana), the age distribution of this mammoth population was determined. Containing far fewer juveniles than would be expected for an expanding or stable population, these tracks provide the first evidence that a living mammoth population, coexisting with human inhabitants, was in decline. Additionally, the same site provides corroborating evidence of humans hunting megafauna (horse and bovids). This suggests that humans, in addition to climate change, played a role in the end Pleistocene extinctions in North America.

McNeil, Paul; Hills, L. V.; Kooyman, B.; Tolman, Shayne M.

2005-05-01

126

[The possible contribution of late pleistocene biota to biodiversity in present permafrost zone].  

Science.gov (United States)

During the last decade a wide range of biological objects, which have preserved their viability for tens and hundreds of thousands of years, was found in the samples of permafrost sediments from North-East Eurasia. Among them are bacteria, fungi, algae, moss spores, seeds of higher plants, protists. Along with physiological mechanisms of cryoconservation and constant low temperature of great importance for long-term preservation of biological objects in permafrost layers are ways of burying the organisms and conditions that prevail before the transition of sediments to the permafrost state. The analysis of viability showed by preserved biological objects gives reasons to suppose that some representatives of Pleistocene biota buried in permafrost thickness may contribute to the biodiversity of present cryolite zone. PMID:12723372

Gubin, S V; Maksimovich, S V; Davydov, S P; Gilichinski?, D A; Shatilovich, A V; Spirina, E V; Iashina, S G

2003-01-01

127

High-resolution sequence stratigraphy from piezocone tests: an example from the Late Quaternary deposits of the southeastern Po Plain  

Science.gov (United States)

Cone penetration tests are traditionally regarded as a major tool for geotechnical investigations. This study, based upon interpretation of 234 cone penetration tests with pore-pressure measurements (piezocone tests or CPTU), carried out in the Late Quaternary deposits of the southeastern Po Plain, shows how CPTU tests can also be used for sedimentological purposes, including detailed facies characterization, subsurface stratigraphic correlations, and identification of the key surfaces for sequence-stratigraphic interpretation. The Late Quaternary depositional history of the southeastern Po Plain, reconstructed on the basis of data from seventeen continuously cored boreholes, includes (1) alluvial plain development during the Late Quaternary lowstand and the early stages of transgression, (2) formation of a rapidly migrating barrier-lagoon system during the late transgressive phases (8800-6000 y BP), (3) construction and progradation of a wave-dominated delta (ancient Po delta) during the following sea-level highstand (6000-800 y BP), and (4) development of the present-day alluvial plain, following the delta lobe abandonment in the 13th century A.D. Local execution of CPTU tests in coincidence with drilling sites enables the calibration of borehole data with piezocone penetration profiles. Lithofacies characterization is based upon estimation of three major parameters: corrected cone resistance ( qt), sleeve friction ( fs), and pore water pressure ( u). Plotting of qt versus the ratio of cone friction to cone bearing (FR) is adopted as the major tool for sediment texture classification. Eight major facies associations for the southeastern Po Plain are identified. These are, for decreasing qt values: (1) fluvial channel sands, (2) beach-ridge sands, (3) transgressive barrier sands, (4) crevasse sands and silts, (5) levee silts and sands, (6) floodplain silts and clays, (7) prodelta clays, and (8) marsh clays and peats. CPTU profile interpretation also provides the basis for the identification of the three major key surfaces within the Late Quaternary 4th-order depositional sequence. (1) The transgressive surface (TS), marking the boundary between the locally pedogenized, stiff Pleistocene alluvial clays and the overlying Holocene transgressive paralic deposits, has a distinctive pore-pressure response, with very low u values, and is characterized by a sharp downward increase in fs, which is paralleled by a moderate increase in qt. (2) The ravinement surface (RS), corresponding to the boundary between fine-grained back-barrier deposits and the overlying transgressive barrier sands, is invariably marked by a sharp upward increase in qt (and decrease in FR). (3) The maximum flooding surface (MFS), which is not clearly recognizable on the sole basis of core data, is identified within shallow-marine (prodelta) clays in combination with minor peaks of qt, which have been interpreted to reflect a laterally extensive fossil lag, with transition in proximal areas to sand (shell-rich?) layers. Simplicity, speed, and comparatively low costs of CPTU tests imply that an extensive use of this method, when used in conjunction with core programs, can be a very attractive alternative to economically less convenient methods for the geological mapping of alluvial/coastal plain areas consisting of non-gravel deposits.

Amorosi, Alessandro; Marchi, Nazaria

1999-10-01

128

Compilation of information on the climate and evaluation of the hydrochemical and isotopic composition during Late Pleistocene and Holocene  

Energy Technology Data Exchange (ETDEWEB)

This report summarises and evaluates some of the existing information on the Late Pleistocene and Holocene climates, i.e. the last 130 000 years. An estimation of the conditions at the Aespoe island (southeast Sweden) has also been made during this time span. The knowledge about Late Pleistocene (Eemian Interglacial and Weichselian glacial) is not yet fully understood. There are still a lot of assumptions concerning this period and more information is needed to be able to establish the climatic conditions. This is not the case for the Weichselian deglaciation and the present interglacial, Holocene, for which the environmental conditions are quite certain. It has been concluded, however, that the Eemian climatic development probably was similar to the Holocene but perhaps somewhat warmer and more humid. The Eemian Baltic Sea level was probably also higher than the present Baltic Sea level and there was a connection between it and the White Sea in the northeast. Aespoe was probably situated below sea level during the greater part of Eemian. Not much is known about the last glacial period, the Weichselian glaciation, until the final deglaciation. The ice sheet during Early Weichselian was probably mostly concentrated to the Scandinavian mountain area and in northern Scandinavia. At least two intervals with higher temperatures have been recorded, the Broerup and Odderade interstadials. The Middle Weichselian substage is characterised by fluctuations, melting and re-advances. Aespoe was probably not glaciated until the middle or latter part of Middle Weichselian. The maximum extension of the Weichselian ice sheet occurred in Late Weichselian, around 20 to 18 ka BP, which was succeeded by the final deglaciation. The retreat of the Weichselian ice sheet is described by for example end moraines and glacial varved clay. The Aespoe area was glaciated until 12 500 BP. Huge quantities of glacial meltwater was released into the Baltic basin as the ice receded. Due to different causes the basin was sometimes in contact with the sea and, sometimes large freshwater lakes were formed in it. Aespoe island was situated below sea or lake level to around 3000 years BP. 72 refs, 17 figs, 1 tab.

Andersson, Cecilia [Intera KB (Sweden)

1998-01-01

129

Compilation of information on the climate and evaluation of the hydrochemical and isotopic composition during Late Pleistocene and Holocene  

International Nuclear Information System (INIS)

This report summarises and evaluates some of the existing information on the Late Pleistocene and Holocene climates, i.e. the last 130 000 years. An estimation of the conditions at the Aespoe island (southeast Sweden) has also been made during this time span. The knowledge about Late Pleistocene (Eemian Interglacial and Weichselian glacial) is not yet fully understood. There are still a lot of assumptions concerning this period and more information is needed to be able to establish the climatic conditions. This is not the case for the Weichselian deglaciation and the present interglacial, Holocene, for which the environmental conditions are quite certain. It has been concluded, however, that the Eemian climatic development probably was similar to the Holocene but perhaps somewhat warmer and more humid. The Eemian Baltic Sea level was probably also higher than the present Baltic Sea level and there was a connection between it and the White Sea in the northeast. Aespoe was probably situated below sea level during the greater part of Eemian. Not much is known about the last glacial period, the Weichselian glaciation, until the final deglaciation. The ice sheet during Early Weichselian was probably mostly concentrated to the Scandinavian mountain area and in northern Scandinavia. At least two intervals with higher temperatures have been recorded, the Broerup and Odderade interstadials. The Middle Weichselian substage is characterised by fluctuations, melting and re-advances. Aespoe was probably not glaciated until the middle or latter part of Middle Weichselian. The maximum extension of the Weichselian ice sheet occurred in Late Weichselian, around 20 to 18 ka BP, which was succeeded by the final deglaciation. The retreat of the Weichselian ice sheet is described by for example end moraines and glacial varved clay. The Aespoe area was glaciated until 12 500 BP. Huge quantities of glacial meltwater was released into the Baltic basin as the ice receded. Due to different causes the basin was sometimes in contact with the sea and, sometimes large freshwater lakes were formed in it. Aespoe island was situated below sea or lake level to around 3000 years BP

1998-01-01

130

Late Pleistocene and Holocene drought events at Lake Tana, the source of the Blue Nile  

Science.gov (United States)

Magnetic and geochemical core data spanning the last 17,000 years are correlated with new seismic stratigraphy from Lake Tana, Ethiopia, to infer past lake-level change and hence effective precipitation. The data confirm that low lake-level coincides with Heinrich Event 1 (H1) in the North Atlantic, as previously shown from diatom and pollen evidence (Lamb et al., 2007). The lake deepened at 15.3 cal kyr BP and abruptly returned to freshwater conditions, when the lake overflowed into the Blue Nile. Low runoff and lake levels and therefore rainfall are inferred between 13.0 and 12.5 cal kyr BP and may represent southerly suppression of the ITCZ and the associated monsoon front at the time of the Younger Dryas. Two drought episodes occurred at 8.4 and 7.5 cal kyr BP, and are also interpreted as a southward shift in the monsoon front. The first of these events appears to have preceded and been more significant than the 8.2 cal kyr BP. Precipitation declined after 6.8 cal kyr BP, although we do not see an abrupt end to the African Humid Period. This period culminated in a dry episode at ~ 4.2 cal kyr BP, supporting the view that reduced Nile flow was a contributing factor to the demise of the Egyptian Old Kingdom.

Marshall, Michael H.; Lamb, Henry F.; Huws, Dei; Davies, Sarah J.; Bates, Richard; Bloemendal, Jan; Boyle, John; Leng, Melanie J.; Umer, Mohammed; Bryant, Charlotte

2011-08-01

131

Insights into the western tropical Pacific's role in late Pleistocene hydroclimate variability: 160ky Borneo stalagmite ?18O record (Invited)  

Science.gov (United States)

The presence of multiple physical mechanisms at play throughout the Late Pleistocene makes it difficult to confidently attribute climate variability to particular forcings. The tropical Pacific's role in past climate change is especially ambiguous because most tropical records lack the resolution, length, and chronological control to completely resolve rapid variability - including abrupt climate change events, ice age terminations, and sea level shifts - against a background of orbital-scale variations. Stalagmites from Gunung Mulu, located in northern Borneo, allow for the construction of reproducible centennial-scale records of hydrologic variability that are precisely-dated and continuous throughout most of the late Pleistocene. Comparison of such records to other regional and global paleorecords as well as relevant simulations from numerical climate models provide valuable insights into the mechanisms responsible for western tropical Pacific hydroclimate variability on centennial to multi-millennial scales. Here we present a large compilation of overlapping U/Th-dated Gunung Mulu stalagmite ?18O records spanning the last 160ky. The composite records demonstrate the complex response of northern Borneo convection to both high-latitude and low-latitude forcings and external insolation. The ice-volume-corrected Borneo ?18O records show little correspondence between regional convective activity and either global sea level shifts (e.g. 1) or Sunda Shelf areal exposure. This result stands in marked contrast to a recently published Last Glacial Maximum (LGM) data-model synthesis that implicates sea level as a dominant driver of tropical Indo-Pacific hydroclimate variability (2). Alternatively, when precessional signals are not muted, the composite Borneo ?18O record varies in phase with equatorial fall insolation, suggesting that precessional forcing is the dominant cause of tropical western Pacific hydroclimate variability on orbital timescales. This is best illustrated across Termination II, when the oscillation of equatorial fall insolation is large and out of phase with ice sheet decay (e.g. 3). During this transition, Borneo stalagmite ?18O begins a shift to more negative ?18O values at 128.8 × 0.9 kybp, almost directly overlapping the equatorial fall insolation cycle. The muted response of tropical western Pacific hydrology to global temperature change and sea level rise relative to precessional insolation represents an important observational constraint on the sequence of climate feedbacks responsible for glacial terminations. 1. M. Medina-Elizalde. Earth Planet. Sci. Lett. 362, 310 (Jan, 2013). 2. P. N. DiNezio, J. E. Tierney. Nature Geoscience 6, 485 (Jun, 2013). 3. A. L. Thomas et al. Science 324, 1186 (May, 2009).

Carolin, S. A.; Cobb, K.; Adkins, J. F.; Clark, B.; Lejau, S.; Lynch-Stieglitz, J.; Malang, J.; Tuen, A. A.

2013-12-01

132

Response of the paleomagnetic record to environmental changes in the late Pleistocene  

Science.gov (United States)

During revisiting the Upper Pleistocene Pekla loess-soil section located on the Sea of Azov coast of the Taman Peninsula, its lower 6 m were continuously sampled, which led to an increase in the age range from ˜50 to 400 ka. The detailed rock magnetic study of the structure, grain-size, and concentrations of magnetic mineral (natural remanent magnetization (NRM) carrier) in the collected rock samples revealed regular changes in rock magnetic characteristics along the section and their correlation with climatic fluctuations. Magnetite and hematite both deposited during the transport of sedimentary material and formed during pedogenesis, which involved the entire section to a varying extent, represent the main magnetic minerals in the examined rocks. Automorphic paleosoils that were formed during warm and humid periods corresponding to odd stages of the MIS scale are characterized by elevated concentrations of magnetic mineral (NRM, magnetic susceptibility ( K lf), saturation isothermal remanent magnetization (SIRM), and anhysteresis (ideal) remanent magnetization (ARM)) parameters and share of superparamagnetic particles (up to 80%, according to elevated values of the frequency-dependent magnetic susceptibility K td) as well as by lowered rigidity parameter ( B cr) and grain size (ARM/ K parameter). Such changes in the paleosoils may be explained by the occurrence of newly formed fine-grained magnetite particles close in size to its superparamagnetic and single-domain varieties due to the activation of bio/geochemical processes during warm stages. The growth of the above-mentioned rock magnetic parameters in automorphic soils may be considered as serving a quantitative criterion for defining the boundary between warm and cold periods even in poorly developed soils.

Pilipenko, O. V.; Trubikhin, V. M.; Abrahamsen, H.; Buylaert, J.-P.

2010-12-01

133

Temperature and hydrologic variability of Lake Victoria, East Africa since the Late Pleistocene  

Science.gov (United States)

Recent organic geochemical advances have facilitated the comparison between continental temperature change and hydrologic variability. TEX86, a proxy based on the lipids of aquatic Crenarchaeota that show a positive correlation with growth temperature, was used to reconstruct surface water temperatures from Lake Victoria, East Africa during the latest Pleistocene-Holocene. Hydrologic conditions were interpreted using paleoecological implications of shifting pollen and diatom assemblages found in the lake (Kendall, 1969; Stager et al., 2003) and will be compared with future compound specific ?13C data from terrestrial biomarkers in order to determine the patterns of rainfall and aridity in this region. Initial comparisons of climatic changes seen in temperature and hydrologic records appear to show consistency between warm/wet intervals and cool/dry intervals that is often assumed, but more rarely shown, in tropical Africa. Lake Victoria temperatures show a steady warming beginning 16 cal ka, with a pause around the Younger Dryas, dominated by arid conditions and strong savannah grassland development during this interval. There is continued warming to a sustained thermal maximum for this portion of the record at ~10.5-8.5 ka, which generally coincides with the beginning of the Holocene Hypsithermal, an interval of elevated temperatures and precipitation throughout much of tropical Africa. This thermal maximum occurs during the most humid interval of this record (~9.5-8.3 ka), shown by an increase of humid forest pollen and high diatom abundance (due to increased water column mixing and nutrient runoff). Temperatures abruptly cool ~1.5°C in Lake Victoria, this portion of the record shows a temperature inflection and variable hydrologic signals, potentially marking a response to the end of the Holocene Hypsithermal, where temperatures begin to rise ~3°C over the remainder of the record.

Berke, M. A.; Johnson, T. C.; Werne, J. P.; Schouten, S.; Sinninghe Damste, J. S.

2010-12-01

134

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 36Cl 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. ?? 2011 Elsevier Ltd.

Barrows, T. T.; Hope, G. S.; Prentice, M. L.; Fifield, L. K.; Tims, S. G.

2011-01-01

135

Late Miocene-early Pleistocene paleoclimate history of the Chinese Loess Plateau revealed by remanence unmixing  

Science.gov (United States)

studies show that the Quaternary loess sequence and the late Miocene-Pliocene red clay sequence on the Chinese Loess Plateau (CLP) share similar magnetic properties despite their being deposited under different climate conditions. To solve this paradox, we apply a novel remanence unmixing technique and demonstrate that loess and red clay on the central CLP contain a similar low-coercivity pedogenic component, but their high-coercivity components differ dramatically, reflecting different oxidation and temperature conditions. We infer that temperatures on the Chinese Loess Plateau cooled from the late Miocene to the Quaternary, in a manner similar to sea surface temperature records for the same time interval. This coherency between marine and terrestrial records argues for a CO2 forcing on long-term paleoclimatic variations.

Nie, Junsheng; Zhang, Rui; Necula, Cristian; Heslop, David; Liu, Qingsong; Gong, Lisha; Banerjee, Subir

2014-03-01

136

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, 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 var...

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

2012-01-01

137

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, 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 ...

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

2012-01-01

138

Late Pliocene and early Pleistocene environments of the north-eastern Russian Arctic inferred from the Lake El'gygytgyn pollen record  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The 318 m thick lacustrine sediment record in Lake El'gygytgyn, northeastern Russian Arctic cored by the international El'gygytgyn Drilling Project provides unique opportunities allowing the time-continuous reconstruction of the regional paleoenvironmental history for the past 3.6 Myr. Pollen studies of the lower 216 m of the lacustrine sediments show their value as an excellent archive of vegetation and climate changes during the Late Pliocene and Early Pleistocene. About 3.50–3.35 ...

Andreev, A. A.; Tarasov, P. E.; Wennrich, V.; Raschke, E.; Herzschuh, U.; Nowaczyk, N. R.; Brigham-grette, J.; Melles, M.

2013-01-01

139

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

2005-06-01

140

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

Birkle, Peter [Instituto de Investigaciones Electricas, Gerencia de Geotermia, Av. Reforma 113, Col. Palmira, Cuernavaca, Mor., 62490 (Mexico)]. E-mail: birkle@iie.org.mx; Angulo, Maricela [PEMEX - Exploracion y Produccion, Diseno de Explotacion Cactus-Nispero Sitio Grande, Zona Industrial S/N, Reforma, Chiapas (Mexico)

2005-06-15

 
 
 
 
141

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

142

Age calibration of carbonate rind thickness in late Pleistocene soils for surficial deposit age estimation, Southwest USA  

Science.gov (United States)

Carbonate rinds have been used for cross-correlation of landforms as well as a quantitative indicator of soil age. Using the measured rind thickness of clasts found within a deposit, whose age has been independently determined, allows the construction of a calibrated surface-age proxy. Measurements were taken at sites within the Mojave Desert, the northwestern Sonoran Desert, the southern Great Basin, and the western Colorado Plateau. These sites are all within about 300 km of the intersection of the borders of the states of California, Arizona, and Nevada. In the study area, elevation varied from 200 to 1200 m, MAP was from 95 to 195 mm, and MAT was from 18.4?? to 23.3??. The calibrated proxy, while not accounting for the effects of parent material or climate on rind development, does show a strong correlation (R2 = 0.74, P thickness and surface age for deposits of late to middle Pleistocene age. The calibrated chronosequence, rind thickness = 0.0889 + 0.0079 [surface age]), is in general valid over a large region of southwestern United States. This statistical relation suggests that parent material, climate, and elevation may not be as strong a control on carbonate accumulation as is age for younger soils.

Amoroso, L.

2006-01-01

143

A simple mixing explanation for late Pleistocene changes in the Pacific-South Atlantic benthic ?13C gradient  

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Full Text Available The fact that the deep-ocean benthic ?13C minimum shifted from the North Pacific to the South Atlantic during the Last Glacial Maximum is often interpretted as evidence of a change in deep water circulation, such as the development of deep water ventilation in the North Pacific. This study re-evaluates the implications of changes in benthic ?13C gradients by comparing Pacific Deep Water (PDW ?13C measurements with the values expected for the null hypothesis that PDW ventilation sources remained unchanged throughout the Late Pleistocene. The ?13C compositions of PDW, Northern Component Water (NCW and Southern Component Water (SCW are estimated from regional benthic ?13C stacks of 3–6 sites. Changes in PDW ?13C and PDW-SCW ?13C gradients over the past 800 kyr are found to be well described by a constant mixture of 60% NCW and 40% SCW plus a constant Pacific "age" offset of ?0.5‰. Thus, an additional ventilation source for glacial PDW (e.g., in the North Pacific cannot be inferred solely on the basis of changes in the Pacific-South Atlantic benthic ?13C gradient.

L. E. Lisiecki

2009-12-01

144

First dated human occupation of Italy at ~ 0.85 Ma during the late Early Pleistocene climate transition  

Science.gov (United States)

A candidate for the oldest human occupation site in Italy is Monte Poggiolo where the lithic tool-bearing levels are currently dated to ~ 1 Ma based on electron spin resonance (ESR). The low analytical precision of ± 30% at 2? makes it unclear whether the date actually conflicts with a recent reassessment of age constraints on key hominin sites from Italy, France, and Spain pointing to a uniformly young timing for the earliest habitation of southern Europe during the late Early Pleistocene climate transition within reverse magnetic polarity subchron C1r.1r (0.988-0.781 Ma). Our new magnetostratigraphic and biostratigraphic results show a sequence of stable normal and reverse polarities in a regional lithostratigraphic context that indicate the Monte Poggiolo tool-bearing site post-dates the Jaramillo normal polarity subchron, most probably occurring at ~ 0.85 Ma immediately after the pronounced cooling that culminated with marine isotope stage 22 when the associated regression may have opened new migration routes through the Po Valley for large mammals and hominins.

Muttoni, Giovanni; Scardia, Giancarlo; Kent, Dennis V.; Morsiani, Enrico; Tremolada, Fabrizio; Cremaschi, Mauro; Peretto, Carlo

2011-07-01

145

Nonassociation of Paleoindians with AMS-Dated Late Pleistocene Mammals from the Dutchess Quarry Caves, New York  

Science.gov (United States)

AMS 14C ages of 10 bones of the caribou ( Rangifer tarandus), flat-headed peccary ( Platygonus compressus), and giant beaver ( Castoroides ohioensis) from the Dutchess Quarry Caves, New York, range from 13,840 ± 80 to 11,670 ± 70 yr B.P. No bones from any of these species are demonstrably associated with Paleoindian artifacts (fluted points) or other cultural materials from the sites because the bones lack unequivocal stratigraphic association with artifacts, as well as physical (taphonomic) evidence for human association (e.g., burning, cut marks, distinctive breakage). Together with the Holocene conventional 14C dates of charcoal and the varied stratigraphic proveniences of the fluted points and the dated bones, the new AMS 14C dates argue that most strata at the Dutchess Quarry Caves contain a mixture of late Pleistocene and Holocene materials. This mixing probably resulted from post-depositional bioturbation (by humans, rodents, carnivores, and scavengers) and cryoturbation (annual freeze-thaw cycles). Rather than being of cultural origin, the bones of caribou, flat-headed peccary, and giant beaver likely were deposited in the Dutchess Quarry Caves by nonhuman predators or scavengers, such as ursids, canids, felids, condors, or eagles.

Steadman, David W.; Stafford, Thomas W.; Funk, Robert E.

1997-01-01

146

Late Pleistocene/Holocene craniofacial morphology in Mesoamerican Paleoindians: implications for the peopling of the New World.  

Science.gov (United States)

Several studies on craniofacial morphology showed that most Paleoindians, who were the first settlers of the New World, clearly differ from modern Amerindians and East Asians, their supposed descendants and sister group, respectively. Here we present new evidence supporting this view from the Late Pleistocene/Early Holocene horizon from Mexico, as well as from the most complete set of dated Paleoindian remains. We analyzed the phenotypic resemblance of early Mexicans with other South Paleoamerican and modern human series. Two independent approaches to the data were used. In the first case, individual specimens were tested for morphological similarity with a set of modern reference samples. In the second analysis, Mexican specimens were treated as a sample in order to compute minimum genetic distances. Results from both approaches tend to associate early Mexican skulls with Paleoindians from Brazil, an Archaic sample from Colombia, and several circum-Pacific populations. These results give support to a model in which morphologically generalized groups of non-Northeast Asian descent (the so-called Paleoamericans) entered the continent first, and then dispersed from North to South America through Central America. The large geographic dispersal of Paleoamericans, and their presence in Mexico in the Early Holocene, raise new issues about the continent's settlement scenario. PMID:16028226

González-José, Rolando; Neves, Walter; Lahr, Marta Mirazón; González, Silvia; Pucciarelli, Héctor; Hernández Martínez, Miquel; Correal, Gonzalo

2005-12-01

147

New stratigraphic and taphonomic data from the late Pleistocene deposits of the San Teodoro Cave (North-Eastern Sicily, Italy  

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Full Text Available In previous excavations at the San Teodoro Cave (North-Eastern Sicily the Authors distinguished an upper Late Glacial sedimentary unit (Unit A and a lower sedimentary unit (Unit B containing Upper Pleistocene endemic mammal remains. New data collected during 2002 and 2003 excavations come from a trench located on the eastern side of the cave at a distance of 30-34 m from the entrance. In the new trench the composition and taphonomic characters of the faunal assemblage of the Unit B deposits are similar to those recognized in 1998 in a trench located on the eastern side of the cave at a distance of 9-13 m from the entrance. The Unit B contains a highly diversified assemblage of vertebrates, invertebrates and vegetal remains. Damages on bones and abundant coprolites testify to intense hyena activity. Complete and undamaged remains of elephant and deer are actually a novelty from a taphonomic point of view. A new sterile sedimentary unit (Unit C has been brought to light. The characters of the new sedimentary Unit C suggest a correlation with the older lacustrine deposits located at the base of the vertical cliffs where the San Teodoro cave is located.

Gabriella Mangano

2005-10-01

148

Evidence for prolonged El Nino-like conditions in the Pacific during the Late Pleistocene: a 43 ka noble gas record from California groundwaters  

Science.gov (United States)

Information on the ocean/atmosphere state over the period spanning the Last Glacial Maximum - from the Late Pleistocene to the Holocene - provides crucial constraints on the relationship between orbital forcing and global climate change. The Pacific Ocean is particularly important in this respect because of its dominant role in exporting heat and moisture from the tropics to higher latitudes. Through targeting groundwaters in the Mojave Desert, California, we show that noble gas derived temperatures in California averaged 4.2 ?? 1.1 ??C cooler in the Late Pleistocene (from ???43 to ???12 ka) compared to the Holocene (from ???10 to ???5 ka). Furthermore, the older groundwaters contain higher concentrations of excess air (entrained air bubbles) and have elevated oxygen-18/oxygen-16 ratios (??18O) - indicators of vigorous aquifer recharge, and greater rainfall amounts and/or more intense precipitation events, respectively. Together, these paleoclimate indicators reveal that cooler and wetter conditions prevailed in the Mojave Desert from ???43 to ???12 ka. We suggest that during the Late Pleistocene, the Pacific ocean/atmosphere state was similar to present-day El Nino-like patterns, and was characterized by prolonged periods of weak trade winds, weak upwelling along the eastern Pacific margin, and increased precipitation in the southwestern U.S.

Kulongoski, J. T.; Hilton, D. R.; Izbicki, J. A.; Belitz, K.

2009-01-01

149

Late Pliocene - Early Pleistocene paleoenvironmental reconstruction based on stable isotope compositions of Stephanorhinus sp. and Mammut sp. teeth  

Science.gov (United States)

Stable isotope measurements of skeletal apatite from herbivorous mammals are often used to provide information on the terrestrial paleoenvironment and paleoclimate. In this study fossil teeth of Stephanorhinus Kretzoi 1942 (rhinoceros) and Mammut Blumenbach 1799 (mastodon), amongst others, were investigated from the Carpathian Basin. According to the biostratigraphy, the age of the samples has a range from Late Pliocene to Early Pleistocene. Reconstructing paleoclimate and paleoenvironment of this era is important as it can be an analogue for the future climate. Oxygen and carbon isotopic compositions were measured from the tooth enamel, because it is believed to be the most resistant to diagenetic alteration (e.g., Kohn & Cerling, 2002). The carbon isotopic composition in the carbonate fraction of apatite can be related to the diet of the animal (Kohn & Cerling, 2002). Hence, it can reflect the photosynthetic pathway (C3 or C4) of the plants consumed by these herbivores. The ?18O values were determined in the phosphate fraction of apatite. In the case of large mammals that are obligate drinkers, the ?18O values closely track those of the environmental water (Bryant & Froelich, 1995). Knowing the ?18O values of environmental water and relating it to local precipitation, the mean annual temperature (MAT) of the site can be calculated (Dansgaard, 1964). The ?13C values range from -10 to -15 o (VPDB). The result clearly shows that these animals consumed C3 plants. Most of the ?13C values indicate mixed grassland-open woodland rather than a closed canopy forest. Although there is variation in the ?18O values (mean 14.2 ± 1.0 o VSMOW, n=17), most of the samples would support a MAT range of 8-12 ° C. This is in good agreement with other proxies for the localities and time period (Kovács et al., 2013). Bryant, D.J. & Froelich, P.N. (1995) A model of oxygen-isotope fractionation in bodywater of large-mammals. Geochimica et Cosmochimica Acta 59, 4523-4537. Dansgaard, W. (1964) Stable isotopes in precipitation. Tellus 16, 436-468. Kohn, M.J. & Cerling, T.E. (2002) Stable isotope compositions of biological apatite. Reviews in Mineralogy and Geochemistry 48, 455-488. Kovács, J. et al. (2013) Clay Mineralogy of Red Clay Deposits from the Central Carpathian Basin (Hungary): Implications for Plio/Pleistocene Chemical Weathering and Paleoclimate. Turkish J. Earth. Sci. 22, 414-426.

Szabó, Péter; Kovács, János; Kocsis, László; Gasparik, Mihály; Vennemann, Torsten; Demény, Attila; Virág, Attila

2014-05-01

150

Integrated stratigraphy and paleoenvironmental reconstruction for the Late Cretaceous Danish chalk based on the Stevns-2 core  

DEFF Research Database (Denmark)

An integrated stratigraphy of the Stevns-2 core located in eastern Denmark is hereby presented based on calcareous nannofossil biostratigraphy and carbon isotope stratigraphy. Carbon and oxygen isotope have been performed on 419 bulk samples. Calcareous nannofossil biostratigraphy has been applied, based on the analysis of 57 samples. Original gamma-ray data from the well-log analysis are also presented. The calcareous nannofossil data span the upper Campanian (UC16a) to the lower Danian (NNT1). These new stratigraphic data are compared and correlated to other Boreal, Tethyan and Tropical sites in order to provide an age-model for Stevns-2. While using this age-model, differences in the sedimentation rates of Stevns-1 and Stevns-2 borehole are nicely expressed, although the two sites are only 8 km apart from each other. The mechanisms responsible for these changes are under investigation, but are probably related to a combination of variations in paleoproductivity, paleocurrents, geodynamics and paleotopography.

Boussaha, Myriam; Thibault, Nicolas Rudolph

151

Late pleistocene-holocene ostracod assemblages of the Northern Caspian Sea shelf  

Science.gov (United States)

Analysis of the ostracod assemblages and the distribution of benthic foraminifera Ammonia beccarii in the core section GS 194-08-1 recovered at a depth of 7.5 m near the Volga delta front showed changes in environmental conditions in response to sea-level fluctuations. The pre-Novocaspian ostracod assemblage reflects the conditions that were dominant during the Late Khvalynian transgression, with a depth of about 20-30 m, and a salinity range of 12-13‰. The Early Novocaspian sediments contain an ostracod assemblage that represents a deeper water environment compared to the present, with an inferred depth of 12-16 m. The faunas from the younger Novocaspian sediments with abundant monospecific populations of Cyprideis torosa and co-occurring benthic foraminifera Ammonia beccarii represent modern-like environmental conditions.

Chekhovskaya, M. P.; Stepanova, A. Yu.; Khusid, T. A.; Matul, A. S.; Rakowski, A. Z.

2014-03-01

152

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

153

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

International Nuclear Information System (INIS)

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 (?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

1994-05-22

154

Stable carbon isotope reconstructions of diet and paleoenvironment from the late Middle Pleistocene Snake Cave in Northeastern Thailand  

Science.gov (United States)

Thailand’s geographical location in the tropics and almost complete, relatively uninterrupted forest cover makes it valuable for paleodiet and paleoclimate research. We present the first dietary and environmental reconstructions in Northeastern Thailand, using stable isotope abundances in mammalian tooth enamel from the late Middle Pleistocene locality, Tham Wiman Nakin (Snake Cave), which reflect a much higher (over 70%) than modern (13%) occurrence of C4 plants. Bovids and cervids appear to have had almost entirely a C4 plant diet. Carnivores consumed a mixture of C3 (suids) and C4 (bovids, cervids) consumers. Rhinoceroses and orangutan appear to have maintained their preference through time for forested or open C3 environment, respectively. 13C/12C from bone bioapatite, horn and hair of modern Southeast Asian mammals almost exclusively demonstrate C3 vegetation dominance. C4 consumption is rare in analysed modern species and it could be related to anthropogenic influences such as ingestion of domestic crops or livestock. Interesting implications emerge in the C4 vegetation distribution in southern Eurasian ecosystems, indicating that Southeast Asia, south of the Tibet, could be part of the global C4 vegetation spread, which occurred around 7 Ma. However, the C4 percentage in ecosystems varied geographically. Despite modern reversal towards C3 habitats due to factors such as increasing CO2, we think that anthropological influences may be responsible for habitat and dietary changes in extant species. Bovids demonstrate the most significant shift in diet and habitat through time, from C4-dominated open habitats to C3-dominated habitats indicative of dense forest understory.

Pushkina, Diana; Bocherens, Herve; Chaimanee, Yaowalak; Jaeger, Jean-Jacques

2010-03-01

155

Late Pleistocene Climatic Changes in the Western Mediterranean Inferred from Temperature, Productivity and Eolian Input Records: Implications for Human Dispersal  

Science.gov (United States)

The relation between climate and hominid dispersal has yet a number of unsettled issues, largely due to the lack of regional climate records in areas with significant hominid remains. Scientific evidence from the Mediterranean region indicates that humans evolved into their present form during key climatic intervals as indicated by the records of the earliest Europeans from Atapuerca (Spain) and Dmanisi (Georgia). However, it remains unclear which route was used by the early hominids to populate Europe (via the strait of Gibraltar or the Levantine Corridor). In this sense, it is still not clear if the climatic conditions during this period were favorable for hominid crossing via the strait of Gibraltar or not. To gain a better insight into the Iberian peninsular climate during the late Pleistocene, a marine sediment core from the Alboran Sea, Western Mediterranean, is used to reconstruct climate relevant variables related to surface ocean and atmospheric circulation by applying a set of organic geochemical proxies (biomarkers). In a first approach we present high resolution data (2 ky) for the interval from 0 to 500 ky. The results of this multi-biomarker analysis give new insights into past ocean climate conditions as well as into the processes that occurred onshore during this period. The reconstruction of sea surface temperatures is done by the analysis of alkenones (UK37-index). Total chlorins concentration is used as proxy for paleoproductivity. Terrestrial eolian inputs and vegetation changes are determined by the analysis of n-alkyl compounds (long chain n-alkanes, n-alkenols and n-alkanoic acids) which are major components of leaf waxes from terrestrial higher plants. Like mineral aerosols, these compounds are wind-transported from local vegetation sources to adjacent oceans where the particles settle and are preserved in ocean sediments with very little diagenetic alteration. These biomarkers offer a promising tool for reconstructing terrestrial vegetation from marine sequences and help to understand the link between climate change in the Mediterranean and human evolution in this area.

Hambach, B.; Rosell Mele, A.; Martinez-Garcia, A.

2009-12-01

156

Dating upper plate normal fault slip events in Late Pleistocene and Holocene sediments of northern Chile  

Science.gov (United States)

In order to understand how subduction earthquakes along the Nazca-South America plate boundary affect upper plate faults in the coastal forearc of northern Chile, we are developing the first detailed paleoseismological study to characterize the Late Quaternary activity of the Mejillones and Salar del Carmen faults, located around 40 km north and 15 km east of Antofagasta, respectively. There is currently a lack of basic palaeo-seismological data on these and other upper plate faults, such as long term slip rates, amount of slip per event, palaeo-earthquake magnitude and recurrence intervals. This lack of knowledge impedes understanding of how large subduction earthquakes, occurring at depths of around 50 km in this region, relate to upper plate seismicity and deformation. We have used OSL dating of fault-related sediments, and cosmogenic-ray nuclide dating of terrace surfaces, to constrain slips rates over the last 45 ka. Several trenches were excavated across both faults in order to expose and log the most recent fault-related sediments. In the hanging wall of these normal faults, vertically stacked colluvial wedges and hillslope deposits are the product of discrete slip events and post-slip fault scarp degradation. Multiple trenches along each fault permit the spatial variability in slip amount and fault-related sedimentation to be investigated. Long-term slip rates have been measured using cosmogenic-ray nuclide exposure dating of the alluvial terraces offset by the Mejillones Fault. OSL dating of the fault-related sediments in the trenches has been used to compare the ages of individual slip events on both faults, and the age of events recorded along the trace of each fault. The application of both cosmogenic-ray nuclide and OSL methods in this type of setting (hyper-arid with low erosion rates, yet tectonically active) is non-trivial, due to cosmogenic inheritance accumulated in cobbles on the terrace surfaces, low sensitivity of the quartz for OSL dating, and the potential for partial bleaching in both quartz and feldspar. However, we have established that slip events occur about the same time (within uncertainty) on both faults, but that fault slip rate and the estimated earthquake magnitudes are greater on the Mejillones Fault than the Salar del Carmen Fault. Since 13 ka, there have been 3 - 4 slip events on both faults and the recurrence interval of the largest predicted palaeo-earthquake (Mw ~7) on the Mejillones Fault is about 4.8 ka.

Robinson, R. A.; Binnie, S.; Gonzalez, G.; Cortés, J.

2011-12-01

157

The Late Pleistocene and Holocene palaeoenvironmental context of Wonderwerk Cave in the southern Kalahari, South Africa  

Science.gov (United States)

Wonderwerk Cave, located in the arid southern Kalahari in South Africa, is an exceptional site, since it preserves a two million year long record of human occupation. While research on older levels in various excavation sections of the cave deposits is ongoing, we focus here on the younger levels that span the last 35,000 years. We present the results of past and recent work on zooarchaeology, macrobotany, palynology, phytoliths, stable isotopes, micromorphology and speleothem growth, which track marked diachronic environmental fluctuations. Except for a hiatus of ~33-23 ka, growth and isotope data for a speleothem near the cave entrance suggests moist conditions from ~35-33, and ~22-14 ka with brief, dry episodes at ~34, ~22 and ~15 ka. Temperatures were cool except for an increase ~16-14 ka after which cold conditions equivalent to the Younger Dryas event occurred. In Stratum 5 (>12.5 ka in Excavation 1), relatively low carbon isotope (?13C) values, pollen in the speleothem, and pollen in dung deposits indicate that the vegetation included a large C3 component during this phase. While the climate experienced sharp fluctuations in moisture when stalagmite growth was interrupted, more severe drying occurred by ~12 ka as indicated by dung pollen. Pollen in Stratum 4d (undifferentiated by stratum sub-phases) suggest that warmer grassy conditions developed before 11 ka, which is supported by ?13C values in OES that suggest a greater C4plant component in Stratum 4dII associated with the Oakhurst-like archaeological industry. Undifferentiated Stratum 4d indicates moderate moisture availability (pollen) but sub-phase 4dII suggest drying (OES ?18O). C3-presence (OES ?13C) in the vegetation became stronger again in Stratum 4dI (Oakhurst) and Stratum 4cII (Wilton). This is supported by Asteraceae pollen especially ~8.5 ka. Except for a fluctuation in OES ?18O values in Stratum 4cII, ?18O and pollen and micromammal composition suggest progressive aridity until ~6 ka (Stratum 4bII). ?18O values on OES indicate a marked shift to a moister episode in the mid-Holocene between 5.9 and 4.9 ka while pollen, phytoliths and microfauna indicate that more grassy vegetation with woodland developed ~5.5-4.4 ka (Strata 4bI-4aLH, Wilton). A trend towards more arid conditions culminated ~2.8-1.2 ka (Strata 3a-2b, the Ceramic Later Stone Age) as suggested by oxygen and carbon isotopes in OES, and is consistent with pollen and phytolith data indicating vegetation with C4 grasses. The macrofaunal data corroborate this picture, with grassland environments increasing through the Holocene as reflected in an increase in grazers; frequencies of springbok (Antidorcas marsupialis), a species that suggests aridity, rises from 0% in the early Holocene, to 10% in the mid-Holocene, and further to 16% in the Late Holocene. The general arid trend has continued until a slight increase in moisture availability ~0.8 ka leading up to modern semi-arid conditions in the uppermost disturbed strata.

Scott, Louis; Avery, Margaret; Bamford, Marion; Berna, Francesco; Brink, James; Brook, George; Chazan, Michael; Ecker, Michaela; Fernandez-Jalvo, Yolanda; Goldberg, Paul; Lee-Thorp, Julia; Rossouw, Lloyd; Thackeray, Francis; Horwitz, Liora

2014-05-01

158

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

159

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)

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

160

Molecular records of climate variability and vegetation response since the Late Pleistocene in the Lake Victoria basin, East Africa  

Science.gov (United States)

New molecular proxies of temperature and hydrology are helping to constrain tropical climate change and elucidate possible forcing mechanisms during the Holocene. Here, we examine a ˜14,000 year record of climate variability from Lake Victoria, East Africa, the world's second largest freshwater lake by surface area. We determined variations in local hydroclimate using compound specific ?D of terrestrial leaf waxes, and compared these results to a new record of temperature utilizing the TEX86 paleotemperature proxy, based on aquatic Thaumarchaeotal membrane lipids. In order to assess the impact of changing climate on the terrestrial environment, we generated a record of compound specific ?13C from terrestrial leaf waxes, a proxy for ecosystem-level C3/C4 plant abundances, and compared the results to previously published pollen-inferred regional vegetation shifts. We observe a general coherence between temperature and rainfall, with a warm, wet interval peaking ˜10-9 ka and subsequent gradual cooling and drying over the remainder of the Holocene. These results, particularly those of rainfall, are in general agreement with other tropical African climate records, indicating a somewhat consistent view of climate over a wide region of tropical East Africa. The ?13C record from Lake Victoria leaf waxes does not appear to reflect changes in regional climate or vegetation. However, palynological analyses document an abrupt shift from a Poaceae (grasses)-dominated ecosystem during the cooler, arid late Pleistocene to a Moraceae-dominated (trees/shrubs) landscape during the warm, wet early Holocene. We theorize that these proxies are reflecting vegetation in different locations around Lake Victoria. Our results suggest a predominantly insolation-forced climate, with warm, wet conditions peaking at the maximum interhemispheric seasonal insolation contrast, likely intensifying monsoonal precipitation, while maximum aridity coincides with the rainy season insolation and the interhemispheric contrast gradient minima. We interpret a shift in conditions at the Younger Dryas to indicate a limited switch in insolation-dominated control on climate of the Lake Victoria region, to remote teleconnections with the coupled Atlantic and Pacific climate system.

Berke, Melissa A.; Johnson, Thomas C.; Werne, Josef P.; Grice, Kliti; Schouten, Stefan; Sinninghe Damsté, Jaap S.

2012-11-01

 
 
 
 
161

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

162

Late Miocene-Pleistocene evolution of a Rio Grande rift subbasin, Sunshine Valley-Costilla Plain, San Luis Basin, New Mexico and Colorado  

Science.gov (United States)

The Sunshine Valley–Costilla Plain, a structural subbasin of the greater San Luis Basin of the northern Rio Grande rift, is bounded to the north and south by the San Luis Hills and the Red River fault zone, respectively. Surficial mapping, neotectonic investigations, geochronology, and geophysics demonstrate that the structural, volcanic, and geomorphic evolution of the basin involves the intermingling of climatic cycles and spatially and temporally varying tectonic activity of the Rio Grande rift system. Tectonic activity has transferred between range-bounding and intrabasin faults creating relict landforms of higher tectonic-activity rates along the mountain-piedmont junction. Pliocene–Pleistocene average long-term slip rates along the southern Sangre de Cristo fault zone range between 0.1 and 0.2 mm/year with late Pleistocene slip rates approximately half (0.06 mm/year) of the longer Quaternary slip rate. During the late Pleistocene, climatic influences have been dominant over tectonic influences on mountain-front geomorphic processes. Geomorphic evidence suggests that this once-closed subbasin was integrated into the Rio Grande prior to the integration of the once-closed northern San Luis Basin, north of the San Luis Hills, Colorado; however, deep canyon incision, north of the Red River and south of the San Luis Hills, initiated relatively coeval to the integration of the northern San Luis Basin. Long-term projections of slip rates applied to a 1.6 km basin depth defined from geophysical modeling suggests that rifting initiated within this subbasin between 20 and 10 Ma. Geologic mapping and geophysical interpretations reveal a complex network of northwest-, northeast-, and north-south–trending faults. Northwest- and northeast-trending faults show dual polarity and are crosscut by north-south– trending faults. This structural model possibly provides an analog for how some intracontinental rift structures evolve through time.

Ruleman, C. A.; Thompson, R. A.; Shroba, R. R.; Anderson, M.; Drenth, B. J.; Rotzien, J.; Lyon, J.

2013-01-01

163

Late Pleistocene to Holocene Uplift Rates in the frontal part of the Fold-and-Thrust Belts in Northern Hokkaido, Japan  

Science.gov (United States)

In Hokkaido to Sakhalin, Late Cenozoic compressional processes have produced N-S trending fold-and-thrust belts. Active tectonics started in late Pliocene time (Ito, 1999) was poorly constrained from the previous studies on seismicity, geodesy and structural geology because of the complicated tectonic framework. In northern Hokkaido, coarsening upward Pliocene-Pleistocene basin-fill successions, which named the Koetoi, Yuchi and Sarabetsu Formations in ascending order, have been deformed by west verging stepped folds structures. The Teshio fault zone constitutes the frontal part of the fold-and-thrust belts and contributes to the history of uplifting along the western coast of northern Hokkaido. Terraces distributed in the study area are classified into Higher terraces group (Terrace I-III), Middle terraces group (Terrace IV) and Lower terraces group (Terrace V-VI). On the basis of tephrochronology and 14C dating methods, Terrace IV and VI are correlated with MIS 5e and 1, respectively (Koike and Machida eds, 2001). The author clarifies the tectonic processes of the Teshio fault zone by using the dislocation model and balanced cross-sections to determine the Plio-Quaternary shortening deformation. The N-S trending Kitakawaguchi anticline is a typical fault-propagation-fold defined by a steeply west dipping forelimb and a more gently east dipping and broader back limb. Western part of the anticline, the Yuchi Formation has up to 30° dip to the west, and Terrace II and IV tilt westward. The elevation of the shoreline angle of Terrace IV and II are about 55-60 m and 110 m a.s.l., respectively. The Kitakawaguchi anticline has started to grow in the Early Pleistocene when the Yuchi Formation deposited, and has continued to move during Late Pleistocene time, shown in the seismic reflection profile (Ogura and Kamon, 1992). The Teshio fault zone extends 5-10 km west off shore farther south of the Kitakawaguchi anticline. According to Hydrographic Department, Maritime Safety Agency (1992, 1994), Early-Middle Pleistocene successions containing stratigraphic growth architecture have thickly deposited in front of the forelimb of the flexure. In consideration of the Late Pleistocene to Holocene uplift of the coastal area, the Teshio fault zone has continued to develop during Quaternary. In order to evaluate the activity of the Teshio fault zone, Echigo et al. (2006) simulated the surface deformation for the blind thrust beneath the Teuri and Yagishiri islands using the dislocation model. Assuming a east- dipping (20°) fault for a total length of 40 km at depth of -500 to -800 m a.s.l., the amount of net slip since the Last interglacial is calculated at 50 m, and the average slip rate attains to 0.40 mm/yr. Further studies are needed to constrain the amount and rate of shortening since late Pliocene time.

Morishita, N.

2006-12-01

164

Secuencias pleistocenas «lujanenses» en su sección tipo: Primeras dataciones 14C e implicancias estratigráficas, arqueológicas e históricas, Luján - Jáuregui, provincia de Buenos Aires / Pleistocene Lujanense sequences in the type section: First 14C datings and their implications on stratigraphy, archaeology and history, Luján Jauregui, provincia de Buenos Aires  

Scientific Electronic Library Online (English)

Full Text Available SciELO Argentina | Language: Spanish Abstract in spanish Se dan a conocer las primeras dataciones 14C del Pleistoceno terminal o "Lujanense" en su sección tipo. Se propone un modelo secuencial preliminar en vista a ordenar las unidades litoestratigráficas y proveer un marco temporal a los descubrimientos arqueológicos del siglo XIX. Las secuencias lujanen [...] ses se datan entre >40.000 AP y >11.000 AP y se discuten las evidencias de poblamiento arcaico en este período. Se identifica la discordancia intralujanenense atribuida al comienzo del último máximo glaciario (LGM) en 30.000 AP. Son resultados preliminares de un proyecto de caracterización estratigráfica y arqueológica del Pleistoceno del nordeste pampeano. Abstract in english The main purpose of this note is to communicate the first 14C dating of the Pleistocene sequences in the Lujan type section. A preliminary sequence stratigraphy model is presented in order to organize the lithostratigrafic units and provide a coherent stratigraphic framework to XIX century archeolog [...] ical discoveries. "Lujanense" sequences are dated between > 40,000 and >11,000 BP and is discussed the peopling evidence within this time interval. The base sequence boundary of the last glacial maximum (LGM) is identified and called "intralujanense" at 30.000 BP. This is a preliminary result of an integral project on sequence stratigraphy and archeological characterization of the Pleistocene of the northeastern pampas.

M.J., Toledo.

165

Preliminary Findings of the Balkan Paleo Project: Evidence of Human Activity at the “Gateway” of Europe During the Late Pleistocene  

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Full Text Available This paper describes the initial findings of the Balkan Paleo Project (BPP. The project seeks: 1 – to augment the evidence that can be used to test hypotheses about hominin and faunal dispersals into and out of Europe during the Pleistocene; 2 – to gather data for testing the hypotheses regarding the adaptation of early human populations to Eurasian ecosystems, the adjustment of their tool technologies, anatomical characteristics and behaviors in response to local climates and faunal evidence.These research objectives can only be achieved by identifying and excavating a broad spectrum of archaeological and paleontological sties that span the Pleistocene within the Balkan Peninsula. Results of BPP activities conducted in southern Bulgaria are reported here. These include excavations at the Arkata rockshelter and associated caves overlooking the Arda River near (Eastern Rhodopes, Krumovgrad district, the Leyarna caves and the previously known paleontological locality of Mechata Dupka (Strandzha Mountains, Malko Tarnovo district. These activities have expanded our understanding of ecological conditions along a potentially important pathway along which early humans may have dispersed into and out of Europe, and have for the first time documented the presence of Pleistocene humans within southeastern Bulgaria.

Tsanko Tzankov

2012-12-01

166

Paleoamerican morphology in the context of European and East Asian late Pleistocene variation: implications for human dispersion into the New World.  

Science.gov (United States)

Early American crania show a different morphological pattern from the one shared by late Native Americans. Although the origin of the diachronic morphological diversity seen on the continents is still debated, the distinct morphology of early Americans is well documented and widely dispersed. This morphology has been described extensively for South America, where larger samples are available. Here we test the hypotheses that the morphology of Early Americans results from retention of the morphological pattern of Late Pleistocene modern humans and that the occupation of the New World precedes the morphological differentiation that gave rise to recent Eurasian and American morphology. We compare Early American samples with European Upper Paleolithic skulls, the East Asian Zhoukoudian Upper Cave specimens and a series of 20 modern human reference crania. Canonical Analysis and Minimum Spanning Tree were used to assess the morphological affinities among the series, while Mantel and Dow-Cheverud tests based on Mahalanobis Squared Distances were used to test different evolutionary scenarios. Our results show strong morphological affinities among the early series irrespective of geographical origin, which together with the matrix analyses results favor the scenario of a late morphological differentiation of modern humans. We conclude that the geographic differentiation of modern human morphology is a late phenomenon that occurred after the initial settlement of the Americas. PMID:21302270

Hubbe, Mark; Harvati, Katerina; Neves, Walter

2011-03-01

167

Stratigraphy of Late Cenozoic sediments of the western Chukchi Sea: New results from shallow drilling and seismic-reflection profiling  

Science.gov (United States)

The Quaternary history of Beringia and of the Arctic-Pacific marine connection via the Bering Strait is poorly understood because of the fragmentary stratigraphic record from this region. We report new borehole and seismic-reflection data collected in 2006 in the southwestern Chukchi Sea. Sediment samples were analyzed for magnetic properties, grain size, heavy minerals, and biostratigraphic proxies (spores and pollen, foraminifers, ostracodes, diatoms, and aquatic palynomorphs). Two shallow boreholes drilled between the Chukotka Peninsula and the Wrangel Island recovered sediments of two principal stratigraphic units with a distinct unconformity between them. Based on predominantly reverse paleomagnetic polarity of the lower unit and pollen spectra indicative of forested coasts and climate warmer than present, the age of this unit is estimated as Pliocene to early Pleistocene (broadly between ca. 5 and 2 Ma). Attendant sedimentary environments were likely alluvial to nearshore marine. These deposits can be correlated to the seismic unit infilling valleys incised into sedimentary bedrock across much of the study area, and possibly deposited during a transgression following the opening of the Bering Strait. The upper unit from both boreholes contains Holocene 14C ages and is clearly related to the last, postglacial transgression. Holocene sediments in Borehole 2 indicate fast deposition at the early stages of flooding (between ca. 11 and 9 ka) to very low deposition, possibly related to expansive sea ice. Closer to shore, deposition at Borehole 1 resumed much later (ca. 2 ka), likely due to a change in the pattern of coastal erosional processes and/or the demise of a landbridge between the Chukotka Peninsula and the Wrangel Island inferred from studies on mammoth distribution.

Gusev, E. A.; Andreeva, I. A.; Anikina, N. Y.; Bondarenko, S. A.; Derevyanko, L. G.; Iosifidi, A. G.; Klyuvitkina, T. S.; Litvinenko, I. V.; Petrova, V. I.; Polyakova, E. I.; Popov, V. V.; Stepanova, A. Y.

2009-07-01

168

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  

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Full Text Available 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 Cerrillos 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.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 reverse 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.

Gustavo González Bonorino

2012-03-01

169

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 SciELO Argentina | Language: Spanish 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 Cerrillos 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 L [...] erma 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 reverse 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.

Gustavo, González Bonorino; Liliana, Del Valle Abascal.

170

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

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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

171

Late Cenozoic stable isotope stratigraphy and paleoceanography of DSDP sites from the East equatorial and central north Pacific Ocean  

International Nuclear Information System (INIS)

Stable isotopic analyses of Middle Miocene to Quaternary foraminiferal calcite from east equatorial and central north Pacific DSDP cores have provided much new information on the paleoceanography of the Pacific Neogene. The history of delta18O change in planktonic foraminifera reflects the changing isotopic composition and temperature of seawater at the time of test formation. Changes in the isotopic composition of benthonic foraminfera largely reflect changes in the volume of continental ice. Isotopic data from these cores indicates the following sequence of events related to continental galaciation: (1) A permanent Antarctic ice sheet developed late in the Middle Miocene (about 13 to 11.5 m.y. ago). (2) The Late Miocene (about 11.5 to 5 m.y. ago) is marked by significant variation in delta18O of about 0.5% throughout, indicating instability of Antarctic ice cap size or bottom-water temperature. (3) The early Pliocene (5 to about 3 m.y. ago) was a time of relative stability in ice volume and bottom-water temperature. (4) Growth of permanent Northern Hemisphere ice sheets is inferred to have begun about 3 m.y. ago. (5) The late Pliocene (3 to about 1.8 m.y. ago) is marked by one major glaciation or bottom-water cooling dated between about 2.1 to 2.3 m.y. (6) There is some evidence that the frequency of glacial-interglacial cycles increased at about 0.9 m.y. (Auth.)

1979-01-01

172

Invertebrate Paleontology of the Wilson Grove Formation (Late Miocene to Late Pliocene), Sonoma and Marin Counties, California, with some Observations on Its Stratigraphy, Thickness, and Structure  

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The Wilson Grove Formation is exposed from Petaluma north to northern Santa Rosa, and from Bennett Valley west to Bodega Bay. A fauna of at least 107 invertebrate taxa consisting of two brachiopods, 95 mollusks (48 bivalves and 46 gastropods), at least eight arthropods, and at least two echinoids have been collected, ranging in age from late Miocene to late Pliocene. Rocks and fossils from the southwest part of the outcrop area, along the Estero de San Antonio, were deposited in a deep-water marine environment. At Meacham Hill, near the Stony Point Rock Quarry, and along the northern margin of the outcrop area at River Road and Wilson Grove, the Wilson Grove Formation was deposited in shallow marine to continental environments. At Meacham Hill, these shallow water deposits represent a brackish bay to continental environment, whereas at River Road and Wilson Grove, fossils suggest normal, euhaline (normal marine salinity) conditions. A few taxa from the River Road area suggest water temperatures slightly warmer than along the adjacent coast today because their modern ranges do not extend as far north in latitude as River Road. In addition, fossil collections from along River Road contain the bivalve mollusks Macoma addicotti (Nikas) and Nuttallia jamesii Roth and Naidu, both of which are restricted to the late Pliocene. The late Miocene Roblar tuff of Sarna-Wojcicki (1992) also crops out northeast of the River Road area and underlies the late Pliocene section at Wilson Grove by almost 300 m. Outcrops in the central part of the region are older than those to the northeast, and presumably younger than deposits to the southwest. The Roblar tuff of Sarna-Wojcicki (1992) occurs at Steinbeck Ranch in the central portion of the outcrop area. At Spring Hill, also in the central part of the outcrop area, the sanddollar Scutellaster sp., cf. S. oregonensis (Clark) has been recently collected. This species, questionably identified here, is restricted to the late Miocene from central California through Oregon. Outcrops at Salmon Creek, northeast of Steinbeck Ranch and also in the central part of the outcrop area, contain Aulacofusus? recurva (Gabb) and Turcica brevis Stewart, which are both restricted to the Pliocene, as well as Lirabuccinum portolaensis (Arnold) known from the early Pliocene of central and northern California and into the late Pliocene in southern California. These data suggest an overall pattern of older rocks and deeper water to the south and west, and younger rocks and shallower water to the east and north. Outcrops to the southwest, south of the Bloomfield fault, are not well dated but presumably are older than the late Miocene Roblar tuff of Sarna-Wojcicki (1992). Fossils in this part of the section are rare and are not useful in determining a precise age or environment of deposition for the lower part of the Wilson Grove Formation. However, sedimentary sequences and structures in the rocks here are useful and suggest probable outer shelf and slope water depths. Lituyapecten turneri (Arnold) which occurs in this part of the section has previously been restricted to the Pliocene, but its occurrence below the Roblar tuff of Sarna-Wojcicki (1992) indicates a revised late Miocene age for this taxon. Three possibly new gastropods (Mollusca) are reported here: Calyptraea (Trochita) n. sp. and Nucella sp., aff. N. lamellosa (Gmelin), both from the Bloomfield Quarry area, and Acanthinucella? n. sp. from the River Road area. These species are not described here because this venue is deemed insufficient for the description of new taxa.

Powell, Charles L., II; Allen, James R.; Holland, Peter J.

2004-01-01

173

Palynological evidence for late miocene, pliocene and early pleistocene climate changes in the middle U.S. Atlantic Coastal Plain  

Science.gov (United States)

Palynomorph assemblages from eight geologic formations in the Middle Atlantic Coastal Plain, ranging in age from latest Miocene to Early Pleistocene, have been interpreted in terms of terrestrial paleoclimates. The data suggest that a warm-temperate to subtropical climate, warmer than at present, prevailed at the close of the Miocene and the beginning of the Pliocene. At that time, there was little or no temperature gradient within the study area (36??30??? to 39??N). This warm period was followed by a warm-temperate interval in Virginia and North Carolina, with temperatures probably not very different from those of today, although a slight warming trend probably occurred during the deposition of the Colerain Beach Member of the Chowan River Formation. A definite cool interval is indicated by the presence of spruce pollen in the Bacons Castle Formation of Virginia. This interval is interpreted to have begun about 2.3-2.4 Ma, or possibly slightly later, simultaneous with the cooling that has been recorded in deep-sea cores of the North Atlantic Ocean, and in the pre-Tiglian of western Europe. This was followed by a warmer-than-present period that may be correlated with the Tiglian of the latest Pliocene. Finally, palynological data from the Cape May Formation of New Jersey suggest that a warm-temperate (warmer than at present) climate prevailed during the Early Pleistocene. ?? 1991.

Groot, J. J.

1991-01-01

174

High-resolution seismic stratigraphy of the late Neogene of the central sector of the Colombian Pacific continental shelf: A seismic expression of an active continental margin  

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The sedimentary prism of the central Pacific continental shelf of Colombia was affected by regional folding and faulting, and probably later mud diapirism, from the Late Miocene to the Holocene. Interpretation of high-resolution seismic lines (2 s/dt) revealed that the prism consists of 13 high-resolution seismic units, that can be separated into 5 seismic groups. Deposition of the prism and the associated stacking pattern, are probably the response to variable uplift and subsidence in a fore-arc basin that underwent important tectonic events by the end of the Miocene. Throughout the Pliocene, the continental shelf sedimentation was affected by the growing of a dome structure probable due to mud diapirism. This fact caused peripheral faults both normal and reverse that controlled the distribution of some of the seismic units. During the Late Pleistocene (Wisconsin stage?) a eustatic sea level fall caused the shoreline to advance about 50 km westward of its present position. Because of this eustatic sea level change, a strong fluvial dissection took place and is interpreted as the probable extension of the San Juan River to the south of the present day river mouth. Within this framework it is believed that the Malaga and Buenaventura Bays were the passageways of branches of the old drainage system of the San Juan River. The inner branch circulated through the present Buenaventura Bay and runs southward leaving the mark of an apparent valley identified in the seismic information in the eastern sector of the study area. This old fluvial valley and its filling material located in the present day inner continental shelf front of Buenaventura are postulated as important targets to find placer minerals such as gold and platinum.

Martínez, Jaime Orlando; López Ramos, Eduardo

2011-02-01

175

Millennial-scale ice rafting events and Hudson Strait Heinrich(-like) Events during the late Pliocene and Pleistocene: a review  

Science.gov (United States)

Various types of abrupt/millennial-scale climate variability such as Dansgaard/Oeschger and Heinrich Events characterized the last glacial period. Over the last decade, a number of studies demonstrated that such millennial-scale climate variability was not limited to the last glacial but inherent to Quaternary climate. Here we review the occurrence and origin of millennial ice-rafting events in the North Atlantic during the late Pliocene and Pleistocene (last 3.4 Ma) with a special focus on North Atlantic Hudson Strait (HS) Heinrich(-like) Events. We show that Heinrich Layers 5, 4, 2, and 1 in marine sediment cores from across the North Atlantic all bear the organic geochemical fingerprint of the Hudson area. Using this framework and combining previously published results, detailed investigations into the organic and inorganic chemistry of ice-rafted debris (IRD) found across the North Atlantic demonstrate that prior to MIS 16 (˜650 ka) IRD in the North Atlantic did not originate from the Hudson area of northern Canada. The signature of this early IRD is distinctly different compared to that of HS Heinrich Layers. Rather ice-rafting events during the late Pliocene and early Pleistocene predominantly emanated from the calving of the Greenland and Fennoscandian ice sheets and possibly minor contributions from local ice streams from the North American and British ice sheets. Compared to North Atlantic HS Heinrich Events, these early Pleistocene IRD-events had a limited impact on surface water characteristics in the North Atlantic. North Atlantic HS Heinrich(-like) Events first occurred during MIS 16. At the same time, the dominant frequency in silicate-rich IRD accumulation shifted from the obliquity (41-ka) to a 100-ka frequency across the North Atlantic. Iceberg survivability or a change in iceberg trajectory likely did not control this change in IRD-regime. These results lend further support for the existing hypothesis that an increase in size (thickness) of the Laurentide ice sheet controls the occurrence of North Atlantic HS Heinrich Events, favoring an internal dynamic mechanism for their occurrence.

Naafs, B. D. A.; Hefter, J.; Stein, R.

2013-11-01

176

Regional seismic stratigraphy and controls on the Quaternary evolution of the Cape Hatteras region of the Atlantic passive margin, USA  

Science.gov (United States)

Seismic and core data, combined with amino acid racemization and strontium-isotope age data, enable the definition of the Quaternary stratigraphic framework and recognition of geologic controls on the development of the modern coastal system of North Carolina, U.S.A. Seven regionally continuous high amplitude reflections are defined which bound six seismic stratigraphic units consisting of multiple regionally discontinuous depositional sequences and parasequence sets, and enable an understanding of the evolution of this margin. Data reveal the progressive eastward progradation and aggradation of the Quaternary shelf. The early Pleistocene inner shelf occurs at a depth of ca. 20-40 m beneath the western part of the modern estuarine system (Pamlico Sound). A mid- to outer shelf lowstand terrace (also early Pleistocene) with shelf sand ridge deposits comprising parasequence sets within a transgressive systems tract, occurs at a deeper level (ca. 45-70 m) beneath the modern barrier island system (the Outer Banks) and northern Pamlico Sound. Seismic and foraminiferal paleoenvironmental data from cores indicate the occurrence of lowstand strandplain shoreline deposits on the early to middle Pleistocene shelf. Middle to late Pleistocene deposits occur above a prominent unconformity and marine flooding surface that truncates underlying units, and contain numerous filled fluvial valleys that are incised into the early and middle Pleistocene deposits. The stratigraphic framework suggests margin progradation and aggradation modified by an increase in the magnitude of sea-level fluctuations during the middle to late Pleistocene, expressed as falling stage, lowstand, transgressive and highstand systems tracts. Thick stratigraphic sequences occur within the middle Pleistocene section, suggesting the occurrence of high capacity fluvial point sources debouching into the area from the west and north. Furthermore, the antecedent topography plays a significant role in the evolution of the geomorphology and stratigraphy of this marginal system. ?? 2009 Elsevier B.V.

Mallinson, D. J.; Culver, S. J.; Riggs, S. R.; Thieler, E. R.; Foster, D.; Wehmiller, J.; Farrell, K. M.; Pierson, J.

2010-01-01

177

Stratigraphy and tectonosedimentary evolution of a late Aptian-Albian carbonate margin: the northeastern Jebel Akhdar (Sultanate of Oman)  

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Upper Aptian-Albian shallow-water carbonates with rudists, large foraminifera and calcareous algae are described from northern Oman, in the northeastern part of the parautochton of Jebel Akhdar. The corresponding lithostratigraphic unit, the Al Hassanat Formation, is partly a time equivalent of the Nahr Umr Shales of Albian p.p. age which have a wide extent on the Arabian craton. The Al Hassanat platform developed in two main phases. First, during the late Aptian-early Albian, the platform was fringing an emerged area (central Jebel Akhdar) with a limited extent basinward. Then, during the middle Albian the flooding of the central Jebel Akhdar resulted in an extensive development of the platform and a connection with the Nahr Umr shelf. This sedimentary evolution and its palaeogeographic expressions were mainly controlled by structural patterns: extensive uplift and block faulting to the edge of the antecedent (early Aptian) platform, with a significant differential subsidence then a sag of the Arabian promontory. This tectonosedimentary dynamics was related to the migration of the oceanic adjacent Tethyan plate, and took place during the global geodynamic Albian revolution.

Masse, Jean-Pierre; Borgomano, Jean; Maskiry, Salim Al

1997-11-01

178

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. The four kinds of syndepositional fault slope-break zones controlled the stratal architecture of sequences and the distribution of lowstand systems tracts. Sand bodies within lowstand systems tracts provide suitable conditions for the formation of hydrocarbon reservoirs when they are overlain by sediments from transgressive systems tracts, and are therefore favorable sites for lithostratigraphic trap exploration.

Feng, Youliang; Li, Sitian; Lu, Yongchao

2013-09-01

179

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

180

Evidence for geographic variation in the diets of late Pleistocene and early Holocene Bison in North America, and differences from the diets of recent Bison  

Science.gov (United States)

During the late Pleistocene and early Holocene , Bison was widely dispersed across North America and occupied most regions not covered by ice sheets. A dietary study on Bison paleopopulations from Alaska, New Mexico, Florida, and Texas was performed using two methods that relate dental wear patterns to diet, mesowear analysis and microwear analysis. These data were compared to a mixed sample of extant Bison from the North American central plains, extant wood Bison from Alberta (Canada) and a variety of other modern ungulates. Mesowear relates macroscopic molar facet shape to levels of dietary abrasion. The mesowear signature observed on fossil Bison differs significantly from the hyper-abrasive grazing diet of extant Bison. Tooth microwear examines wear on the surface of enamel at a microscopic scale. The microwear signal of fossil samples resembles to modern Bison, but the fossil samples show a greater diversity of features, suggesting that fossil Bison populations regularly consumed food items that are texturally inconsistent with the short-grass diet typical of modern plains Bison. Mesowear and microwear signals of fossil Bison samples most closely resemble a variety of typical mixed feeding ungulates, all with diets that are substantially less abrasive than what is typical for modern plains Bison. Furthermore, statistical tests suggest significant differences between the microwear signatures of the fossil samples, thus revealing geographic variability in Pleistocene Bison diets. This study reveals that fossils are of value in developing an understanding of the dietary breadth and ecological versatility of species that, in recent times, are rare, endangered, and occupy only a small remnant of their former ranges.

Rivals, Florent; Solounias, Nikos; Mihlbachler, Matthew C.

2007-11-01

 
 
 
 
181

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

Directory of Open Access Journals (Sweden)

Full Text Available 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.

J. Etourneau

2013-08-01

182

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

183

Late Middle Pleistocene climate in southwestern China: inferences from the stratigraphic record of Panxian Dadong Cave, Guizhou  

Science.gov (United States)

Panxian Dadong Cave, situated in the subtropical zone of southwestern China, preserves a fan-like sedimentary sequence close to its entrance that spans the period between MIS 8 and 5 (300-130 ka). The frequent alternation of flowstone formation, cementation, clastic deposition, and frost activity in the depositional sequence makes it ideal for reconstructing the environmental conditions prevailing during the later Middle Pleistocene on the Guizhou Plateau. Macroscopic and microscopic sedimentary analyses determine that clastic deposits were entering the cave in the form of intermittent cohesive debris flows and sheetflows during cold and relatively dry climatic conditions when vegetation cover was reduced. Interlayered impure flowstones were forming during wetter phases but still under glacial conditions. Seasonally freezing temperatures are deduced from the frequent occurrence of cycles of well-developed freeze-thaw features affecting both the clastic parts of the sequence and the flowstones as they were deposited. The described depositional processes were responsible for lateral redistribution on the fan surface of bone remains and lithic artifacts that were accumulating on the surface as a result of hominid activities. During the intervening interglacial stages (MIS 7 and possibly MIS 5) clastic deposition was considerably reduced and only thin flowstone caps and weathering manganese-iron crusts were forming. It is suggested that precipitation was much higher during glacial intervals than interglacials under a predominantly cold climate. Dadong Cave provides a good example of very cold and wet climatic conditions during glacials in the subtropics of East Asia.

Karkanas, Panagiotis; Schepartz, Lynne A.; Miller-Antonio, Sari; Wang, Wei; Huang, Weiwen

2008-08-01

184

A late-Middle Pleistocene (Marine Isotope Stage 6) vegetated surface buried by Old Crow tephra at the Palisades, interior Alaska  

Science.gov (United States)

A 40??cm thick primary bed of Old Crow tephra (131??????11??ka), an important stratigraphic marker in eastern Beringia, directly overlies a vegetated surface at Palisades West, on the Yukon River in central Alaska. Analyses of insect, bryophyte, and vascular plant macrofossils from the buried surface and underlying organic-rich silt suggest the local presence of an aquatic environment and mesic shrub-tundra at the time of tephra deposition. Autochthonous plant and insect macrofossils from peat directly overlying Old Crow tephra suggest similar aquatic habitats and hydric to mesic tundra environments, though pollen counts indicate a substantial herbaceous component to the regional tundra vegetation. Trace amounts of arboreal pollen in sediments associated with the tephra probably reflect reworking from older deposits, rather than the local presence of trees. The revised glass fission-track age for Old Crow tephra places its deposition closer to the time of the last interglaciation than earlier age determinations, but stratigraphy and paleoecology of sites with Old Crow tephra indicate a late Marine Isotope Stage 6 age. Regional permafrost degradation and associated thaw slumping are responsible for the close stratigraphic and paleoecological relations between Old Crow tephra and last interglacial deposits at some sites in eastern Beringia. ?? 2009 Elsevier Ltd.

Reyes, A. V.; Jensen, B. J. L.; Zazula, G. D.; Ager, T. A.; Kuzmina, S.; La, Farge, C.; Froese, D. G.

2010-01-01

185

A late-Middle Pleistocene (Marine Isotope Stage 6) vegetated surface buried by Old Crow tephra at the Palisades, interior Alaska  

Science.gov (United States)

A 40 cm thick primary bed of Old Crow tephra (131 ± 11 ka), an important stratigraphic marker in eastern Beringia, directly overlies a vegetated surface at Palisades West, on the Yukon River in central Alaska. Analyses of insect, bryophyte, and vascular plant macrofossils from the buried surface and underlying organic-rich silt suggest the local presence of an aquatic environment and mesic shrub-tundra at the time of tephra deposition. Autochthonous plant and insect macrofossils from peat directly overlying Old Crow tephra suggest similar aquatic habitats and hydric to mesic tundra environments, though pollen counts indicate a substantial herbaceous component to the regional tundra vegetation. Trace amounts of arboreal pollen in sediments associated with the tephra probably reflect reworking from older deposits, rather than the local presence of trees. The revised glass fission-track age for Old Crow tephra places its deposition closer to the time of the last interglaciation than earlier age determinations, but stratigraphy and paleoecology of sites with Old Crow tephra indicate a late Marine Isotope Stage 6 age. Regional permafrost degradation and associated thaw slumping are responsible for the close stratigraphic and paleoecological relations between Old Crow tephra and last interglacial deposits at some sites in eastern Beringia.

Reyes, Alberto V.; Jensen, Britta J. L.; Zazula, Grant D.; Ager, Thomas A.; Kuzmina, Svetlana; La Farge, Catherine; Froese, Duane G.

2010-03-01

186

Geological history and potential hazards of the late-Pleistocene to Recent Plat Pays volcanic complex, Dominica, Lesser Antilles  

Science.gov (United States)

During 1998-2000, the island of Dominica in the Lesser Antilles experienced a major volcanic earthquake swarm spatially associated with volcanic centres in the south of the island. This swarm provided the motivation for a major re-assessment of geologic history and volcanic hazards in this region. This has led to a re-interpretation of the south-western-most corner of the island as a large volcanic complex, termed the Plat Pays volcanic complex, which has exhibited a wide range of past eruptive activity and which, in the Quaternary, experienced a major caldera collapse triggered by a voluminous pyroclastic eruption. Stratigraphy and new 14C age determinations reveal a complicated history of development. The earliest activity is represented by the formation of the Plat Pays stratovolcano and associated parasitic domes. A major explosive eruption 39,000 years B.P. produced the Grand Bay ignimbrite and triggered a major caldera collapse of the summit and south-western flank of the Plat Pays stratovolcano. Following the major eruption, re-injection of Plat Pays magma resulted in the extrusion of approximately 12 lava domes both within and outside the resulting depression. Caldera collapse was followed by at least one catastrophic flank collapse, but it is unclear whether or not this was triggered by caldera formation. The only on-shore evidence of flank collapse is the breach of the caldera rim and truncation of post-caldera deposits emplaced on or near the caldera rim; we find no evidence of on-shore large-magnitude rock avalanche deposits within the stratigraphic framework of the Plat Pays volcanic complex. Frequent seismic swarms of volcanic earthquakes and vigorous geothermal activity indicate that south Dominica is still underlain by an active magma reservoir system. Our new geological observations, combined with an interpretation of recent seismic swarm activity, suggest that an eruption (probably dome-forming) from the Plat Pays volcanic complex is probable within the next 100 years.

Lindsay, Jan; Stasiuk, Mark; Shepherd, John

2002-12-01

187

Combined Stable Oxygen and Silicon Isotope Analysis of Biogenic Silica - Method and Application to the Late Pleistocene NW Pacific  

Science.gov (United States)

Paleoceanographic studies of (sub-)polar North Pacific sediments are generally hampered by the poor carbonate preservation of that region, but sediments show a rather high content of siliceous ooze. Here we present a combined oxygen (?18O) and silicon (?30Si) stable isotope record of diatom silica from the NW Pacific, Detroit Seamount (MD01-2416), to gain new insights in its last deglacial to Holocene hydrography and nutrient utilization, also considering data obtained from the diatom species composition record. Samples were analysed using a new instrumentation setup for combined ?18O and ?30Si analyses, modified after [1]. This setup allows routine measurements of both proxies from the same sample aliquot. The measured sample fraction consisted almost entirely of Coscinodiscus spp. diatoms and the gained record spans the time from the Boelling/Alleroed (B/A) to the mid-Holocene. Diatom ?18O shows a high similarity to the ?18O record obtained from the planktic foraminifers N. pachyderma (sin.); both records decrease in ?18O between the Younger Dryas (YD) and the mid-Holocene. This similarity suggests no changes in the water mass structure of surface waters from the B/A to the mid-Holocene. The diatom ?18O record does not support local changes in sea surface salinity and can be used as an oxygen stratigraphy signal. Such records are particularly useful in sediments rich in biogenic opal but lacking continuous carbonate preservation. Diatom ?30Si is almost constant throughout the studied interval but shows a deviation to higher ?30Si during the YD. This suggests higher nutrient utilization during that time and coincides with increased YD dust supply as documented in the NGRIP ice core record. [1] Leng and Sloane, 2008, JQS 23, 313-319.

Maier, E.; Abelmann, A.; Chapligin, B.; Gersonde, R.; Ren, J.; Tiedemann, R.

2011-12-01

188

Late Pleistocene paleoclimatic history documented by an oxygen isotope record from carbonate sediments in Qarhan Salt Lake, NE Qinghai-Tibetan Plateau  

Science.gov (United States)

Late Pleistocene paleoclimatic variability on the northeastern Qinghai-Tibetan Plateau (NE QTP) was reconstructed using a chronology based on AMS 14C and 230Th dating results and a stable oxygen isotopic record. These are derived from lake carbonates in a 102-m-long Qarhan sediment core (ISL1A) collected from the eastern Qaidam Basin. Previous research indicates that the ?18O values of lacustrine carbonates are mainly controlled by the isotopic composition of lake water, which in turn is a function of regional P/E balance and the proportion of precipitation that is monsoon-derived on the NE QTP. Modern isotopic observations indicate that the ?18O values of lake carbonates in hyper-arid Qaidam Basin are more positive during the warm and wet period. Due to strong evaporation and continental effect in this basin, the positive ?18O values in the arid region indicate drier climatic conditions. Based on this interpretation and the ?18O record of fine-grained lake carbonates and dating results in ISL1A, the results imply that drier climatic conditions in the Qarhan region occurred in three intervals, around 90-80 ka, 52-38 ka and 10-9 ka, which could correspond to late MIS 5, middle MIS 3 and early Holocene, respectively. These three phases were almost coincided with low lake level periods of Gahai, Toson and Qinghai Lakes (to the east of Qarhan Lake) influenced by ASM on the orbital timescales. Meanwhile, there was an episode of relatively high ?18O value during late MIS 3, suggesting that relatively dry climatic condition in this period, rather than “a uniform Qarhan mega-paleolake” spanning the ˜44 to 22 ka period. These results insight into the understanding of “the Greatest Lake Period” on the QTP.

Fan, QiShun; Ma, HaiZhou; Wei, HaiCheng; Shan, FaShou; An, FuYuan; Xu, LiMing; Madsen, David B.

2014-05-01

189

ODP Sites 967 and 968 (eastern Mediterranean) revisited and implications for the global oxygen stable isotope chronology of the late Pleistocene  

Science.gov (United States)

ODP Sites 967 and 968 (eastern Mediterranean) revisited and implications for the global oxygen stable isotope chronology of the late Pleistocene ODP Sites 967 and 968, located in the Eastern Mediterranean at the Eratosthenes Seamount, are ideally situated to study both regional and global climate signals. Evidently, changes in the titanium to aluminum ratio of the bulk sediment reflect variations in North African aridity, and hence North African monsoon strength: increased levels of titanium are associated with enhanced windblown dust input from the Sahara and increased levels of aluminum with enhanced runoff from the river Nile. In addition, changes in the benthic foraminiferal stable isotope composition reflect primarily changes in global ice volume and deep sea temperature (Lourens et al., 2010; Ziegler et al., 2010). Here we completed and spliced the Ti/Al and benthic d18O data sets of ODP Site 968 and 967 for the past one million years at approximately 200-400 year resolution. The Ti/Al ratio reflect dominantly precession-controlled African monsoon intensity changes and was used to build an astronomically tuned age model for the composite record. This approach enabled us in first instance to establish an alternative and highly accurate chronology for sapropels in the Eastern Mediterranean, and lead to revisions of existing age models, especially around MIS 11 and 19, when the 405-kyr eccentricity cycle is at a minimum. Color reflectance, typically indicative of sapropels, appears incongruent with insolation forcing during these episodes. Secondly our Ti/Al-based chronology provides an independent age model for the benthic d18O record, which may shed new light upon the relationship between insolation and global climate (e.g. ice volume) changes. Our research indicates negligible differences between our record and the global benthic stack of Lisiecki and Raymo (LR04) between the present and MIS 11. However, there are significant discrepancies in the timing of terminations and onset of glaciation for several isotope stages prior to MIS 11 of up to 10,000 years. The direct comparison of our stable isotope record to insolation appears to suggest a dominant role of obliquity forcing in ice volume behavior for much further into the Pleistocene than generally assumed. References Lourens, L.J., J. Becker, R. Bintanja et al. (2010), Linear and non-linear response of late Neogene glacial cycles to obliquity forcing and implications for the Milankovitch theory. Quaternary Science Reviews 29(1-2), pp.352-365. Ziegler, M., E. Tuenter & L.J. Lourens. (2010), The precession phase of the boreal summer monsoon as viewed from the eastern Mediterranean (ODP Site 968). Quaternary Science Reviews 29(11-12), pp.1481-1490.

Konijnendijk, Tiuri; Lourens, Lucas; Ziegler, Martin

2013-04-01

190

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

191

Late Pliocene and early Pleistocene sea-level timing and amplitudes derived from fossil ostracod assemblages: Canterbury Basin, New Zealand  

Science.gov (United States)

IODP Expedition 317 cruise drilled cores at three shelf sites (U1353, U1354 and U1351) and one slope site (U1352), in water depths between 85 and 344 m, to understand relationships between sea-level change and sequence stratigraphy. The shelf sites are well suited to reconstruction of high-resolution sea-level fluctuations because of high sedimentation rates from the uplifting Southern Alps. We examined fossil ostracod assemblages from the shelf sites to reconstruct paleo-water depth fluctuations and their amplitudes. We identified 178 ostracod species and 70 genera from more than 160 samples. Q-mode factor analysis was performed on ostracod taxa with abundances of >3.5 % in each sample containing >50 specimens. Six varimax factors were explained 70.8% of the total variance. Paleo-water depths in each factor were calibrated with reference to recent ostracodes occurring around the sites as follows: first factor, middle shelf (50-80 m); second factor, middle to outer shelf (60-130 m); third factor, middle to outer shelf (55-115 m); fourth factor, lagoon, estuary and inner shelf (0-50 m); fifth factor, middle to outer shelf (80-200 m); sixth factor, outer shelf (130-200 m). Factor analysis of ostracod assemblages reveal at least, eight transgressive- and regressive-cycles at Site U1353, seventeen at Site U1354 and two at Site U1351. These cycles probably correspond to a subset of MIS stages between MIS M2 and MIS 40. Furthermore, amplitudes of these paleo-water-depth cycles are expected to equate to eustatic amplitudes because shelf sedimentation has been continuous and minimal subsidence can have occurred during the short time period involved. We therefore estimate that eustatic amplitudes were: 10 - 30 m from 3.1 to 2.8 Ma, ca. 100 m from 2.8 to 2.6 Ma, and 30 - 115 m from 1.8 to1.2 Ma. These amplitudes, together with the timing of the increase in amplitudes (~2.7 Ma), agree with estimates derived from oxygen isotopic records (Raymo et al., 2005), suggesting that the Canterbury Basin sequences responded to global climate change. However, comparison with sea-level amplitude estimates from the North Island of New Zealand (Naish, 1997) suggests that sea-level amplitudes increased in the Canterbury Basin 200 thousand years earlier than in the North Island.

Nakamura, M.; Kusunoki, S.; Yamada, K.; Hoyanagi, K.

2013-12-01

192

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  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 i...

Diedrich C G

2011-01-01

193

Vegetation dynamics during the late Pleistocene in the Barreirinhas region, Maranhão State, northeastern Brazil, based on carbon isotopes in soil organic matter  

Science.gov (United States)

The study place is in the Barreirinhas region, Maranhão State, northeastern Brazil. A vegetation transect of 78 km was studied among four vegetation types: Restinga (coastal vegetation), Cerrado (woody savanna), Cerradão (dense woody savanna), and Forest, as well as three forested sites around Lagoa do Caçó, located approximately 10 km of the transect. Soil profiles in this transect were sampled for ?13C analysis, as well as buried charcoal fragments were used for 14C dating. The data interpretation indicated that approximately between 15,000 and ˜9000 14C yr B.P., arboreal vegetation prevailed in the whole transect, probably due to the presence of a humid climate. Approximately between ˜9000 and 4000-3000 14C yr B.P., there was the expansion of the savanna, probably related to the presence of drier climate. From ˜4000-3000 14C yr B.P. to the present, the results indicated an increase in the arboreal density in the area, due to the return to a more humid and probably similar climate to the present. The presence of buried charcoal fragments in several soil depths suggested the occurrence of palaeofires during the Holocene. The vegetation dynamic inferred in this study for northeastern Brazil is in agreement with the results obtained in areas of Amazon region, based on pollen analysis of lake sediments and carbon isotope analysis of soil organic matter (SOM), implying than similar climatic conditions have affected these areas during the late Pleistocene until the present.

Pessenda, Luiz Carlos Ruiz; Ribeiro, Adauto de Souza; Gouveia, Susy Eli Marques; Aravena, Ramon; Boulet, Rene; Bendassolli, José Albertino

2004-09-01

194

A draft de novo genome assembly for the northern bobwhite (Colinus virginianus) reveals evidence for a rapid decline in effective population size beginning in the Late Pleistocene.  

Science.gov (United States)

Wild populations of northern bobwhites (Colinus virginianus; hereafter bobwhite) have declined across nearly all of their U.S. range, and despite their importance as an experimental wildlife model for ecotoxicology studies, no bobwhite draft genome assembly currently exists. Herein, we present a bobwhite draft de novo genome assembly with annotation, comparative analyses including genome-wide analyses of divergence with the chicken (Gallus gallus) and zebra finch (Taeniopygia guttata) genomes, and coalescent modeling to reconstruct the demographic history of the bobwhite for comparison to other birds currently in decline (i.e., scarlet macaw; Ara macao). More than 90% of the assembled bobwhite genome was captured within 14,000 unique genes and proteins. Bobwhite analyses of divergence with the chicken and zebra finch genomes revealed many extremely conserved gene sequences, and evidence for lineage-specific divergence of noncoding regions. Coalescent models for reconstructing the demographic history of the bobwhite and the scarlet macaw provided evidence for population bottlenecks which were temporally coincident with human colonization of the New World, the late Pleistocene collapse of the megafauna, and the last glacial maximum. Demographic trends predicted for the bobwhite and the scarlet macaw also were concordant with how opposing natural selection strategies (i.e., skewness in the r-/K-selection continuum) would be expected to shape genome diversity and the effective population sizes in these species, which is directly relevant to future conservation efforts. PMID:24621616

Halley, Yvette A; Dowd, Scot E; Decker, Jared E; Seabury, Paul M; Bhattarai, Eric; Johnson, Charles D; Rollins, Dale; Tizard, Ian R; Brightsmith, Donald J; Peterson, Markus J; Taylor, Jeremy F; Seabury, Christopher M

2014-01-01

195

Late Pleistocene fault slip rate, earthquake recurrence, and recency of slip along the Pyramid Lake fault zone, northern Walker Lane, United States  

Science.gov (United States)

Up to 25% of Pacific-North America plate relative transform motion is accommodated east of the Sierra Nevada. Most of that 25% is taken up by deformation in the Walker Lane, a discontinuous zone of strike-slip and normal faults approximately parallel to the San Andreas. The Pyramid Lake fault zone is a northwest trending right-lateral fault in the northern Walker Lane, Nevada. Recent geodetic surveys report 6 ± 2 mm/year of right-lateral shear strain accumulation across the northern Walker Lane. Interpretation of displaced geomorphic features preserved in post-Lake Lahontan (˜15,500 cal. yr B.P.) surfaces indicate the Pyramid Lake fault zone has accommodated at least 2.6 ± 0.3 mm/year of right-lateral shear during the late Pleistocene. Additionally, a minimum of two earthquakes have occurred since deposition of the Mazama tephra (˜7630 cal. yr B.P.), and at least four earthquakes have occurred on the fault after desiccation of Lake Lahontan (˜15.5 ka), with the most recent earthquake occurring after 1705 ± 175 cal. yr B.P. The observations indicate that the Pyramid Lake fault zone accommodates the major portion (?25%-70%) of right-lateral slip east of the Sierra Nevada at the latitude of ˜39°45'N.

Briggs, Richard W.; Wesnousky, Steven G.

2004-08-01

196

Sequence stratigraphy and architecture of a late Early-Middle Aptian carbonate platform succession from the western Maestrat Basin (Iberian Chain, Spain)  

Science.gov (United States)

The attributes of a 'four-systems-tract' sequence are at times difficult to identify in outcrop-scale carbonate successions. Poor exposure conditions, variable rates of sediment production, erosion and/or superposition of surfaces that are intrinsic to the nature of carbonate systems frequently conceal or remove its physical features. The late Early-Middle Aptian platform carbonates of the western Maestrat Basin (Iberian Chain, Spain) display facies heterogeneity enabling platform, platform-margin and slope geometries to be identified, and provide a case study that shows all the characteristics of a quintessential four systems tract-based sequence. Five differentiated systems tracts belonging to two distinct depositional sequences can be recognized: the Highstand Systems Tract (HST) and Forced Regressive Wedge Systems Tract (FRWST) of Depositional Sequence A; and the Lowstand Prograding Wedge Systems Tract (LPWST), Transgressive Systems Tract (TST) and subsequent return to a highstand stage of sea-level (HST) of Depositional Sequence B. An extensive carbonate platform of rudists and corals stacked in a prograding pattern marks the first HST. The FRWST is constituted by a detached, slightly cross-bedded calcarenite situated at the toe of the slope in a basinal position. The LPWST is characterized by a small carbonate platform of rudists and corals downlapping over the FRWST and onlapping landwards. The TST exhibits platform backstepping and marly sedimentation. Resumed carbonate production in shelf and slope settings characterizes the second HST. A basal surface of forced regression, a subaerial unconformity, a correlative conformity, a transgressive surface and a maximum flooding surface bound these systems tracts, and are well documented and widely mappable across the platform-to-basin transition area analyzed. Moreover, the sedimentary succession studied is made up of four types of parasequence that constitute stratigraphic units deposited within a higher-frequency sea-level cyclicity. Ten lithofacies associations form these basic accretional units. Each facies assemblage can be ascribed to an inferred depositional environment in terms of bathymetry, hydrodynamic conditions and trophic level. The architecture of the carbonate platform systems reflects a flat-topped non-rimmed depositional profile. Furthermore, these carbonate shelves are interpreted as having been formed in low hydrodynamic conditions. The long-term relative fall in sea-level occurred during the uppermost Early Aptian, which subaerially exposed the carbonate platform established during the first HST and resulted in the deposition of the FRWST, is interpreted as one of global significance. Moreover, a possible relationship between this widespread sea-level drop and glacio-eustasy seems plausible, and could be linked to the cooling event proposed in the literature for the late Early Aptian. Because of the important implications in sequence stratigraphy of this study, the sedimentary succession analyzed herein could serve as an analogue for the application of the four-systems-tract sequence stratigraphic methodology to carbonate systems.

Bover-Arnal, Telm; Salas, Ramon; Moreno-Bedmar, Josep A.; Bitzer, Klaus

2009-07-01

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Are osseous artefacts a window to perishable material culture? Implications of an unusually complex bone tool from the Late Pleistocene of East Timor.  

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We report the discovery of an unusually complex and regionally unique bone artefact in a Late Pleistocene archaeological assemblage (c. 35 ka [thousands of years ago]) from the site of Matja Kuru 2 on the island of Timor, in Wallacea. The artefact is interpreted as the broken butt of a formerly hafted projectile point, and it preserves evidence of a complex hafting mechanism including insertion into a shaped or split shaft, a complex pattern of binding including lateral stabilization of the cordage within a bilateral series of notches, and the application of mastic at several stages in the hafting process. The artefact provides the earliest direct evidence for the use of this combination of hafting technologies in the wider region of Southeast Asia, Wallacea, Melanesia and Australasia, and is morphologically unparallelled in deposits of any age. By contrast, it bears a close morphological resemblance to certain bone artefacts from the Middle Stone Age of Africa and South Asia. Examination of ethnographic projectile technology from the region of Melanesia and Australasia shows that all of the technological elements observed in the Matja Kuru 2 artefact were in use historically in the region, including the unusual feature of bilateral notching to stabilize a hafted point. This artefact challenges the notion that complex bone-working and hafting technologies were a relatively late innovation in this part of the world. Moreover, its regional uniqueness encourages us to abandon the perception of bone artefacts as a discrete class of material culture, and to adopt a new interpretative framework in which they are treated as manifestations of a more general class of artefacts that more typically were produced on perishable raw materials including wood. PMID:24440005

O'Connor, S; Robertson, G; Aplin, K P

2014-02-01

198

Late Pleistocene-Early Holocene climatic shift recorded by the paleomorphology of the Lower Tisza fluvial system, Hungary  

Science.gov (United States)

Palaeohydrological record coupled with geochronology can serve as key tools for reconstructing past environmental and climatic change. The alluvial plains of the Carpathian Basin are hosting numerous generations of paleochannels which developed in response to highly varying water and sediment discharges. Our investigations focused on the Lower Tisza Basin where palaeomenaders remained recognisable only in a relatively narrow N-S belt along the Tisza river. The width and wavelength of these channels significantly exceed contemporary values even if compared to that of the Danube. Two major channel generations were investigated: one located on a higher level of the floodplain, having larger but more blurred pointbars and main channel, and another in the level of the present floodplain, having smaller but much fresher forms. The primary aim of the research is create the chronological framework of fluvial activity in the region and to determine palaeodischarges, thus to evaluate the trend and magnitude of climatic change. On the other hand the rate of morphological evolution is also assessed, which provides a more detailed insight to the environment in which the meanders were developing. The age and development rate of meanders were determined by the means of luminescence dating (OSL). 16 drillings were made to sample pointbar and channel sediments of two megameanders. Fluvial stratigraphy and sedimentological correlations were set up by laser grainsize analyis. Discharges were calculated on the basis of plaeohydrological equations, however by estimating palaeo cross-sectional area and slope more reasonable results were received. In all more than 30 sediment samples were measured by OSL. In numerous cases both their polymineral fine grain and quartz coarse grain fractions were also dated in order to assess the adequacy of bleaching during deposition, and the applicability of the more abundant fine grain sediments for dating purposes. Luminescence measurements show that coarse grain minimum ages are in a relatively good coincidence with fine grain ages, thus both types of sediments can be applied for OSL in this meandering system. The formation of the more elevated, larger meander was dated to the Bölling-Alleröd Interstadial (12-14 ka). The smaller meander started to evolve approx. 10 ka ago, suggesting that incision and the development of the present floodplain level took place during the shift from the Younger Dryas to the more moderate Holocene climate. Based on calculations, channel forming discharges were around 10 000 and 5 000 m3/s, respectively. The rate of lateral accretion was also very different. The older meander developed at a rate of 1 m/y, while this value could be three four times higher in case of the younger one. This refers either to much higher energies or less stabilised boundaries acting within the fluvial system in the Early Holocene.

Sipos, György; Kiss, Tímea; Koroknai, Levente; Horváth, Zsolt; Dezs?, József

2010-05-01

199

Geothermal properties and groundwater flow estimated with a three-dimensional geological model in a late Pleistocene terrace area, central Japan  

Science.gov (United States)

1. Introduction The ground source heat pump (GSHP) is a highly efficient and renewable energy technology for space heating and cooling, with benefits that include energy conservation and reductions in greenhouse gas emissions. One result of the huge Tohoku-oki earthquake and tsunami and the subsequent nuclear disasters is that GSHPs are receiving more attention from the media and they are being introduced by some local governments. Heat generated by underground GSHP installation, however, can pollute the geothermal environment or change groundwater flow patterns . In this study, we estimated possible effects from the use of GSHPs in the Tokyo area with a three-dimensional (3D) geological model. 2. Geological model The Tokyo Metropolitan Area is surrounded by the Late Pleistocene terraces called the Musashino uplands. The terrace surfaces are densely populated residential areas. One of these surfaces, the Shimosueyohi surface, formed along the Tama River during the last deglacial period. The CRE-NUCHS-1 core (Funabiki et al., 2011) was obtained from this surface, and the lithology, heat transfer coefficients, and chemical characteristics of the sediments were analyzed. In this study, we used borehole log data from a 5 km2 area surrounding the CRE-NUCHS-1 core site to create a 3D geological model. In this area, the Pleistocene Kazusa Group is overlain by terrace gravels and a volcanic ash layer called the Kanto Loam. The terrace gravels occur mainly beneath the Kanda, Kitazawa, and Karasuyama rivers , which flow parallel to the Tama River, whereas away from the rivers , the Kanto Loam directly overlies the Kazusa Group sediments. 3. Geothermal disturbance and groundwater flow Using the geological model, we calculated the heat transfer coefficients and groundwater flow velocities in the sediments. Within the thick terrace gravels, which are at relatively shallow depth (8-20 m), heat transfer coefficients were high and groundwater flow was relatively fast. The amount of disturbance of the geothermal environment and groundwater flow caused by the use of GSHPs, therefore, would depend on the thickness of these gravels. Reference Funabiki, A., Nagoya, K., Kaneki, A., Uemura, K., Kurihara, M., Obara, H., Goto, A., Chiba, T., Naya, T., Ueki, T., and Takemura, T. (2011) Sedimentary facies and physical properties of the sediment core CRE-NUCHS-1 in Setagaya district, Tokyo, central Japan. Abstracts, The 118th Annual Meeting of theGeological Society of Japan. Acknowledgement This work was supported by the Core Research for Evolutional Science and Technology (CREST) program of the Japan Science and Technology Agency (JST).

Funabiki, A.; Takemura, T.; Hamamoto, S.; Komatsu, T.

2012-12-01

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Stratigraphy and geologic age of the Neogene Shimajiri Group in Kumejima Island, Ryukyu Islands, southwestern Japan  

Energy Technology Data Exchange (ETDEWEB)

The Neogene Shimajiri Group is distributed sporadically in the Ryukyu islands. This study focuses on the Shimajiri Group in Kumejima Island, central Ryukyu, and clarifies its stratigraphy and geologic age on the basis of (1) lithostratigraphy, (2) calcareous nannofossil biostratigraphy, and (3) strontium isotope stratigraphy. The Shimajiri Group in Kumejima Island unconformably overlies the middle Miocene Aradake Formation, and is overlain by the Pleistocene Ryukyu Group. The group is divided into three formations, namely the Maja, the Aka and the Uegusukudake Formations in ascending order, and the first two are redefined in this paper based on the new geologic evidence. The Maja Formation consists mainly of fine-grained sandstone, sandy siltstone and alternating beds of them. The Aka Formation is mainly composed of cross-stratified sandstone, pumiceous sandstone and tuffaceous siltstone, and unconformably overlies the Maja Formation. The Uegusukudake Formation, conformably overlying the Aka Formation, consists of basaltic lava, tuff breccia and andesite. On the basis of calcareous nannofossil biostratigraphy, the Maja and Aka Formations can be assigned to Zone CN9 and Zone CN12b of Okada and Bukry (1980) respectively. Strontium isotope ages of the molluscan fossil specimens obtained from the Maja and Aka Formations revealed that the Maja Formation is assigned to the late Miocene (ca. 7.8-7.2 Ma) and the Aka Formation is assigned to the late Pliocene (ca. 3.2-3.1 Ma). These ages are concordant with the nannofossil biostratigraphy. The upper Miocene Maja Formation yields many molluscan fossils in which the characteristic species of the Kakegawa Fauna, such as Amussiopecten praesignis and Mimachlamys satoi are contained. The molluscan fauna of the Maja Formation is significant in understanding the origin of the Kakegawa Fauna, as the characteristic species of the Plio-Pleistocene Kakegawa Fauna already appeared in the Ryukyu Islands in the late Miocene. (author)

Nakamura, Yodai; Asahara, Yoshihiro; Ozawa, Tomowo [Nagoya Univ. (Japan); Kameo, Koji

1999-11-01

 
 
 
 
201

Spain as an emergency air traffic hub during volcanic air fall events? Evidence of past volcanic ash air fall over Europe during the late Pleistocene  

Science.gov (United States)

Past volcanic eruptions often leave visible ash layers in the geological record, for example in marine or lake sedimentary sequences. Recent developments, however, have shown that non-visible volcanic ash layers are also commonly preserved in sedimentary deposits. These augment the record of past volcanic events by demonstrating that past ash dispersals have been more numerous and widely disseminated in Europe than previously appreciated. The dispersal ‘footprints' of some large late Pleistocene European eruptions are examined here in the light of the recent Eyjafjallajökull eruption. For example, the Vedde Ash which was erupted from Iceland around 12 thousand years ago, delivered distal (and non-visible) glass deposits as far south as Switzerland and as far east as the Ural Mountains in Russia, with an overall European distribution remarkably similar to the dominant tracks of the recent Eyjafjallajökull plumes. The Eyjafjallajökull eruption has demonstrated that relatively small amounts of distal volcanic ash in the atmosphere can seriously disrupt aviation activity, with attendant economic and other consequences. It has raised fundamental questions about the likelihood of larger or more prolonged volcanic activity in the near future, and the possibility of even more serious consequences than those experienced recently. Given that there are several other volcanic centres that could cause such disruption in Europe (e.g. Campania and other volcanic centres in Italy; Aegean volcanoes), a key question is whether there are parts of Europe less prone to ash plumes and which could therefore operate as emergency air traffic hubs during times of ash dispersal. Although not generated to answer this question, the recent geological record might provide a basis for seeking the answer. For example, four palaeo-records covering the time frame of 8 - 40 Ka BP that are geographically distributed across Spain have been examined for non-visible distal ash content. All four have proved to be almost devoid of volcanic ash, which contrasts with results obtained from sites throughout central and northern Europe. This suggests that Spain has remained free of ashfall events throughout the late Pleistocene, or that any ash dispersal over Spain has been short-lived and/or infrequent. This appears to accord with the pattern of dispersal of Eyjafjallajökull ash clouds over April to May 2010. Most of the active period was characterised by low eruptive columns and the tropospheric dispersal of ash. Under these conditions, ash dispersal was multi-directional from eastern Europe to Greenland and beyond, but did not encroach on to the Iberian peninsula. In contrast, when the eruptive columns became more elevated and entrained in the jet stream, the dispersal directions were more uni-directional and passed over Iberia and North Africa. Thus the apparent lack of volcanic ash in Iberia (10 - 40ka) may have as much to do with eruptive column height and volcano location as with circulation patterns (tropospheric v. stratospheric). A more comprehensive assessment of geological records of non-visible ash layers in selected sites may hold the key to examining this matter more robustly.

Hardiman, Mark; Lane, Christine; Blockley, Simon P. E.; Moreno, Ana; Valero-Garcés, Blas; Ortiz, José E.; Torres, Trino; Lowe, John J.; Menzies, Martin A.

2010-05-01

202

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 SciELO Mexico | Language: English 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 xenartro [...] s extintos, un gliptodonte (Glyptotherium cylindricum) y un armadillo gigante (Pampatherium cf. mexicanum) (Mammalia, Xenarthra). También se han hallado restos de gliptodonte 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. 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.

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

203

Late Pleistocene Variations in the Water Current and Ice Rafting Transportations of Organic Matter in the Central Arctic Ocean (ACEX Hole M0004C)  

Science.gov (United States)

Little is known about the source of organic matter and the response of sedimentary organic matter composition to glacial-interglacial changes in the central Arctic Ocean. Here we have generated late Pleistocene records of biomarkers and ice rafted debris (IRD) from IODP-Arctic Coring Expedition (ACEX) Hole M0004C to understand the glacial-interglacial changes of mass transportation in the Arctic Ocean. Major biomarkers detected in Hole M0004C were long-chain n-alkanes, n-fatty acids and n-alkan-1-ols, derived from fresh higher plants, and gem-alkanes (branched aliphatic alkanes with a quaternary substituted carbon atom), derived from unknown source. Minor biomarkers were oleanenes of angiosperm origin, unsaturated fatty acids, bacteria-derived anteiso- and iso-fatty acids, various hydroxy acids, formed by hydroxylation of n-fatty acids by aerobic bacteria, cholesterol and sitosterol, and hopanes, formed by diagenetic alteration of bacterial biohopanoids. There was no concrete evidence for in situ production of phytoplanktons. The concentrations of these biomarkers varied with IRD number variation. During periods of abundant IRD, diagenetic hopanes were abundant, suggesting that clastic materials were supplied by ice rafting. During periods of scarce IRD, the other biomarkers such as long-chain compounds were abundant, suggesting that the riverine discharge was enhanced. The IRD and biomarker variations were synchronized with the eastward expansion of the Fennoscandinavian Ice Sheet to northen Siberia, suggesting that the ice cover of northen Siberia is critical in switching mass transportation mechanisms in the Arctic Ocean.

Yamamoto, M.; Sugisaki, S.; Sakamoto, T.

2006-12-01

204

Paleoclimatic implications of late Pleistocene and Holocene aeolian sediments in lake catchments on the northeastern part of the Tibetan Plateau  

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On the northeastern part of the Tibetan Plateau aeolian sediments, such as loess, loess-like sediments, dunes and sand sheets, have been investigated. Such archives provide additional information for paleoclimate and environmental change in the catchments of lakes. We present a detailed analysis of aeolian sediments from the Donggi Cona catchment and a loess section from the Aynemachin Mts. on the north-eastern part of the Tibetan Plateau. In the Donggi Cona catchment long and short distance transport leads to a complex pattern in the aeolian sediments. Based on the largest dataset of luminescence dating (n = 51) from a single catchment so far different periods of enhanced sediment transport have been discriminated. Enhanced aeolian deposition in this environment in elevations of more than 4000m a.s.l. started in the early Holocene with the accumulation of sands from around 12 to 7.5ka. Loess have been preserved from a period from 10.5 to 7.5ka. However, further to the east on the southern slopes of the Aynemachin Mts. the sedimentation period of loess lasted longer and was interrupted by two paleosols around 10-9 and 5 ka. Both archives, sand and loess, are related to the strengthening of the East-Asian summer monsoon with wetter and warmer climate conditions. This climate leads to the trapping of aeolian sediments, in the moisture region of the Aynemachin including the development of initial paleosols. In addition, in some parts of the Donggi Cona catchment the enhanced summer monsoon from around 10 ka onwards lead to fluvial erosion of the aeolian archives and the formation of colluvial sediments until 6 ka. A reactivation of dune sands from 3 ka to the present can be associated to dryer and cooler climate conditions in combination with an enhanced human impact on the landscape. Aeolian sediments on the Tibetan Plateau therefore indicate two different climatic modes. During the early Holocene wetter conditions were favourable to retain aeolian sediments while the reactivation of sediments in the late Holocene point to a cool and dry climate due to small scale disturbances in the vegetation cover.

Lehmkuhl, F.; Stauch, G.; IJmker, J.; Poetsch, S.; Hilgers, A.; Hui, Z.; Diekmann, B.; Hartmann, K.; Wuennemann, B.

2011-12-01

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Moluscos marinos bentónicos del Cuaternario de Bahía Anegada (sur de Buenos Aires, Argentina): variaciones faunísticas en el Pleistoceno tardío y Holoceno / Quaternary marine benthic molluscs from Anegada Bay (southern Buenos Aires, Argentina): faunistic variations in the late Pleistocene and Holocene  

Scientific Electronic Library Online (English)

Full Text Available SciELO Mexico | Language: Spanish Abstract in spanish A lo largo del área costera del Atlántico sudoccidental se observan depósitos marinos que representan los dos últimos eventos transgresivos del Cuaternario (Pleistoceno tardío y Holoceno). La región de Bahía Anegada, sur de la provincia de Buenos Aires, se caracteriza por la buena preservación y abu [...] ndancia de fauna marina fósil, en especial de gasterópodos y bivalvos en los cordones litorales. Estos registros no han sido investigados con anterioridad desde el punto de vista paleontológico, y son de utilidad como indicadores de cambios ambientales del Cuaternario. El objetivo de este trabajo ha sido describir y comparar la fauna de moluscos del Pleistoceno tardío y Holoceno en Bahía Anegada. Para ello se analizaron dos áreas de la región: Canal Villalonga y Los Pocitos. Los depósitos marinos pleistocenos (asociados al estadio isotópico marino MIS5e) analizados para Bahía Anegada mostraron mayor número de especies, tanto de gasterópodos (17 versus 9) como bivalvos (14 versus 12) respecto al Holoceno. En los depósitos pleistocenos de Canal Villalonga se destaca la presencia de Crassostrea rhizophorae (Guilding) y Abra aequalis (Say) que actualmente tienen un área de distribución en latitudes bajas. En cuanto a los micromoluscos, se menciona por primera vez Turbonilla argentina Doello -Jurado para el Pleistoceno. Con base en estos análisis se concluye para la región estudiada que el Pleistoceno tardío registró mayor número de especies, tanto de bivalvos como gasterópodos, respecto al Holoceno, y que la abundancia de las especies del Pleistoceno se ha mantenido durante el Holoceno. Dichas variaciones se interpretan en asociación con cambios de la temperatura e indicarían condiciones más cálidas para el Pleistoceno tardío (último interglacial). Abstract in english Marine deposits representing the last two transgressive Quaternary events (late Pleistocene and Holocene) are observed along the coastal area of the southwestern Atlantic. Littoral deposits in the Anegada Bay region, southern province of Buenos Aires, are characterized by good preservation and abund [...] ance of fossil marine shells, especially gastropods and bivalves. These records, which have not been previously investigated from a paleontological viewpoint, are here useful as indicators of Quaternary environmental changes. The aim of this study was to describe and to compare the molluscan fauna of late Pleistocene with the equivalent of the Holocene. For that, we analyzed two areas within this region: Canal Villalonga and Los Pocitos. Compared to the Holocene, Pleistocene marine deposits (associated to Marine Isotope Stage MIS5e) from Anegada Bay showed a greater number of species, in both gastropods (17 versus 9) and bivalves (14 versus 12). In the Pleistocene deposits of Canal Villalonga is remarkable the presence of Crassostrea rhizophorae (Guilding) and Abra aequalis (Say), which are today displaced toward low latitudes. In relation to micromolluscs, Turbonilla argentina Doello-Jurado is for the first time mentioned for the Pleistocene. Our data indicate that the number of species of bivalves and gastropods was higher during the late Pleistocene than in the Holocene, and that the abundance of species during the Pleistocene has also remained during the Holocene. These variations are interpreted in association with changes in temperature, indicating warmer conditions for the late Pleistocene (last interglacial).

Charó, Melisa P.; Fucks, Enrique E.; Gordillo, Sandra.

206

Arctic ocean sediment texture and the Pleistocene climate cycle  

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Arctic Ocean sediment texture accurately reflects the Plio-Pleistocene climate cycle. The precision of paleoclimate interpretation is improved when deglaciation is recognized as a distinct climate stage, overlapping both glacial and interglacial stages, and for the later Pleistocene, perhaps never completed. Oxygen isotope stratigraphy and foraminifera productivity are out of phase but can be understood in the context of the transitional nature of the glacial, deglacial and interglacial climate stages of the Arctic Ocean.

Clark, D.L.; Morris, T.H.

1985-01-01

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40Ar/39Ar and U-series ages of a Late Pleistocene geomagnetic excursion in Western North America: The Halina Pali event in Western North America?  

Science.gov (United States)

Here we report 40Ar/39Ar results on two mafic flows, Swift Creek (SC) andesite (17.3 ×1.6ka), located near Mount St. Helens, WA and Tabernacle Hill (TH) basalt (16.9 ×1ka) near Fillmore UT that record paleomagnetic co-latitudes of 28° for SC and 23° for TH, respectively. The remnant directions of these two flows are on the fringe of secular variation and we consider them 'excursionoid'. Because these magnetic directions are somewhat unusual, there are limited matches in the magnetic record preserved in the Mono Lake and Lake Bonneville sediments in this time interval. The best matches to the radiocarbon (calibrated to calendar year age) dated lacustrine magnetic record are at 22 and 18 for the SC flow and 22, 19, or 17 ka for the TH flows. The closest matches for the SC and TH paleomagnetic directions are between 18 and 17 ka, which stratigraphically bracket an excursion recorded in the sediments. Pending additional analyses, our best estimate for the age of the excursion is 17.1 ×1.9ka, which is concordant with the radiocarbon-calibrated age of 17.6 ka for the excursion as determined from the age calibrated paleomagnetic record of the lacustrine sections. In addition to the 40Ar/39Ar ages on the TH flow, we also report an isochron U-Th age of 15 × 4 ka on the outer surface tufa coating, which provides a minimum constraint on the age of the TH lava flows. Discussion: Evidence of a Late Pleistocene geomagnetic excursion event is quite extensive and has been reported from several localities. The earliest report of the excursion, from the Halina Pali scarp, Hawaii, suggested an age of about 17-18 ka [1]. Subsequently, there have been additional reports and age estimates of a similar age excursional event from several other localities; Lake Imurak, Alaska, USA (17-18 ka), Hokkaido, Japan (~23 ka), Lake Baikal, Russia (~20 ka), and from Tule Lake, California, USA (~23 ka), summarized in Oda, [2] and referenced therein, and in China (17-18 ka) [3]. In conclusion, the combined results suggest that the geomagnetic excursion event first reported in the Halina Pali scarp is a 'world-wide' event. The best age estimate of this event is about 17 ka. The age calibrated paleomagnetic records from the lacustrine sections indicate that the duration of this event is on the order of 0.8 to 1.2 ka. 1. Coe et al., 1978, J. Geophys. Res., 83, 1740-175. 2. Oda, 2005, J. Geog 114(2), 174-193. 3. Singer, 2011, AGU Fall meeting, GP13A-04.

Turrin, B. D.; Champion, D. E.; Mortlock, R. A.; Fairbanks, R. G.; Swisher, C. C.

2013-12-01

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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 SciELO Argentina | Language: Spanish 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; RMS [...] EPboots= 16%) para obtener estimaciones cuantitativas aplicando la Técnica del Análogo Moderno a datos polínicos fósiles de dos sucesiones aluviales del Pleistoceno 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 Anal [...] og Technique and to obtain late Pleistocene-Holocene quantitative climatic estimations based on fossil pollen from two alluvial sequences. In the central Pampa grasslands, 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.

209

Contribution to the stratigraphy of the onshore Paraiba Basin, Brazil  

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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

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The origin, nature and stratigraphy of Pleistocene-Holocene palaeosols in Wadi Es-Salqa (Gaza Strip, Palestine) / Sobre El Origen, Naturaleza Y Estratigrafía De Los Paleosuelos Pleistoceno-Holocenos En Wadi Es-Salqa (firanja De Gaza, Palestina)  

Scientific Electronic Library Online (English)

Full Text Available SciELO Argentina | Language: English Abstract in spanish La firanja de Gaza se encuentra en la parte suroeste de Palestina. Su topografía es definida por tres cordones (localmente llamado “cordones o crestas kurkar “) que son paralelas a la costa mediterránea. Las mismas se componen de areniscas calcáreas (kurkar) y depósitos de grano fino de color rojizo [...] (Hamra) del Pleistoceno - Holoceno (kurkar). Las crestas son interceptadas por tres cauces principales, de norte a sur: Beit Hanoun, Gaza y Es- Salqa (Silka). Durante el invierno Es- Salqa recoge las aguas de una cuenca de 40 km². La sección geológica de Es-Salqa muestra que la sucesión consiste en kurkar y Hamra de la Formación Gaza (Pleistoceno-Holoceno), que se incluye en el Grupo Kurkar del Plioceno-Holoceno y se superpone en contacto neto al Grupo Saqia. Las sucesiones aforantes en Es-Salqa consisten en paleosuelos de color marrón rojizo asignados a la Formación Gaza. Estos paleosuelos están constituidos por material loésico desarrollados en suelos firancos a firanco-arenosos, y suelos arenosos. El modelo de distribución del suelo loésico lo vincula genéticamente al desierto del Sinaí y el sur del Sahara, mientras que los suelos arenosos son derivados de materiales parentales de arena que generalmente cubre la parte occidental de la llanura costera del sur de Palestina. Abstract in english The Gaza Strip is located in the southwestern part of Palestine. Its topography is defined by three ridges (locally termed “kurkar ridges”) that are parallel to the Mediterranean coastline. The ridges consist of Pleistocene-Holocene calcareous sandstones (kurkar) and reddish fine-grained deposits (h [...] amra). The ridges are intersected by three main wadis, firom north to south: Wadi Beit Hanoun, Wadi Gaza, and Wadi Es-Salqa (Wadi Silka). During winter Wadi Es-Salqa collects water firom a 40 km² catchment area. The subcrop geological cross-section at Wadi Es-Salqa shows that the succession consists of kurkar and hamra of the Pleistocene-Holocene Gaza Formation, which belongs to the Pliocene-Holocene Kurkar Group and sharply overlies the Saqia Group. The outcrop successions in Wadi Es-Salqa consist of reddish-brown palaeosols of Gaza Formation. These palaeosols are loessial soils that developed in loam to sandy loam soils, as well as sandy soils. The model distribution of the loessial soil grains refects atmospheric dust that accumulated firom the Sinai and Saharan Deserts. The sandy soils are derived firom sandy parent materials that generally cover the western part of the southern coastal plain of Palestine.

Khalid F, Ubeid.

211

Causes of Late Pleistocene water level change in Lake Victoria, Equatorial East Africa, derived from clumped isotopes of land snails and fresh water mollusks. (Invited)  

Science.gov (United States)

Carbonate clumped isotope thermometry is based on the dependence of 13C-18O bond abundance in the carbonate lattice (measured as ?47) on the carbonate formation temperature. Most marine and freshwater biogenic carbonates are found to be in agreement with the clumped isotopes - temperature calibration. Clumped isotope thermometry is particularly useful in terrestrial environments where the interpretation of carbonate ?18O is limited due to difficulty in estimating the paleo-water isotopic composition. Clumped isotope-derived temperatures from land snails are generally higher than the ambient environmental temperatures, but show no evidence for disequilibrium. We attribute these higher body temperatures to snail eco-physiological adaptations through shell color, morphology, and behavior. We use the clumped isotope-derived temperatures in combination with shell ?18O to calculate snail body water ?18O composition. This parameter is interpreted as a paleo-hydrological indicator that reflects the isotopic composition of local precipitation modified by local evaporation. Rusinga and Mfangano Islands in Lake Victoria provide a unique opportunity to compare extant species of modern and fossil freshwater mollusks and land snails from the same location to examine lake paleo-hydrology. This location is particularly interesting as Lake Victoria itself is the main source of rain-water in the region such that the isotopic composition of land snail body water can be related back to the source waters. We combine clumped isotope and oxygen isotope measurements of both freshwater mollusks and land snails to examine the water balance of the lake, testing hypotheses about the mechanism of a significant rise in lake level in Lake Victoria ~35 - 40 ka BP. Outcrops of paleo-beach deposits ~18 m above the modern day lake level indicate high water stands at ~35-40 ka BP. Based on water balance models for Lake Victoria, an increase in lake level of this magnitude could be driven by local mean annual precipitation that is significantly greater than modern. However, this is inconsistent with regional climate reconstructions. This suggests that either lake level was controlled by non-climatic factors, or that local climate in the Lake Victoria basin was different than regional patterns of climate across eastern Africa. We use oxygen and clumped isotopes of modern and fossil shells (Corbicula sp., Melanoides sp. and Bellamya unicolor) from this 18 m beach outcrop on Mfangano Island to (1) compare with modern lake water ?18O values and (2) calculate paleo-water compositions. We combine these results with calculated snail body water ?18O composition (using oxygen and clumped isotopes) of land snails (Limicoloria cf. martensiana) from Rusinga and Mfangano Islands, to study hydrological changes of Lake Victoria. We use these data to evaluate the relative importance of climate change and tectonics as mechanisms for the Late Pleistocene expansion of Lake Victoria.

Zaarur, S.; Affek, H. P.; Tryon, C.; Peppe, D. J.; Faith, J.

2013-12-01

212

Late Pleistocene variations in Antarctica sea ice. I - Effect of orbital isolation changes. II - Effect of interhemispheric deep-ocean heat exchange  

Science.gov (United States)

A dynamic-thermodynamic sea-ice model is presently used to ascertain the effects of orbitally-induced insolation changes on Antarctic sea-ice cover; the results thus obtained are compared with modified CLIMAP reconstructions of sea-ice 18,000 years ago. The minor influence exerted by insolation on Pleistocene sea-ice distributions is attributable to a number of factors. In the second part of this investigation, variations in the production of warm North Atlantic Deep Water are proposed as a mechanism constituting the linkage between climate fluctuations in the Northern and Southern hemispheres during the Pleistocene; this hypothesis is tested by examining the sensitivity of the dynamic-thermodynamic model for Antarctic sea-ice changes in vertical ocean heat flux, and comparing the simulations with modified CLIMAP sea-ice maps for 18,000 years ago.

Crowley, Thomas J.; Parkinson, Claire L.

1988-01-01

213

Climatic characteristics of the late Pleistocene and Holocene continental deposits from southwestern Syria based on palynological data / Características climaticas de los depósitos continentales del Pleistoceno tardío y Holoceno del suroeste de Siria sobre la base de datos palinológicos  

Scientific Electronic Library Online (English)

Full Text Available SciELO Argentina | Language: English Abstract in spanish El objetivo de esta investigación fue reconstruir la vegetación, el clima y los cambios que han tenido lugar durante el Pleistoceno tardío y el Holoceno, en el suroeste de Siria. Esta reconstrucción se basó en datos palinológicos obtenidos del análisis de 27 sedimentos y muestras de superficie (con [...] un espesor total de 4,55 m) coleccionadas durante el verano de 1998 en el lago Al-Hijaneh (Pleistoceno tardío) y en el valle del rio Al-Aouaj (Holoceno), y analizadas en 1999. Se establecieron tres zonas de alemacenamiento de polen. La más antigua (zona A) corresponde al Pleistoceno tardío en los depósitos lacustres del lago Al-Hijaneh. Las zonas B y C quedaron definidas en los depósitos lacustres del Holoceno del valle del rio Al-Aouaj. Las tres zonas polínicas son correlativas con zonas de polen similar en territorios del Mediterráneo del este. Los climas presentes y pasados de la región, y su vegetación son tema de discusión. Abstract in english The goal of this research was to reconstruct the vegetational and climatic changes that took place during the late Pleisocene and Holocene in southwestern Syria. This reconstruction was based on palynological data obtained from the analysis of 27 sediments and surface samples (with a total thickness [...] of 4.55 m) collected from Al-Hijaneh Lake basin (late Pleistocene) and from Al-Aouaj River valley (Holocene). Three pollen zones were established. The oldest one (zone A) corresponds to the late Pleistocene lacustrine deposits of Lake Al-Hijaneh. Zones B and C were defined in the Holocene fluvial- lacustrine deposits of the Al-Aouaj River valley. These three pollen assemblage zones are correlated to synchronic and similar C14 dated pollen zones from Syria, Turkey, Iran and Greece. This allows a more definite age determination for the deposits of this study. The region's past climates and vegetation are discussed.

Kamal M., Hussein.

214

High-resolution seismic sequence stratigraphy and history of relative sea level changes since the Late Miocene, northern continental margin, South China Sea  

Science.gov (United States)

The northern South China Sea (SCS) margin is suggested as one of the ideal sites for documenting the late Cenozoic sea level changes for its characteristics of rapid sedimentation and relatively stable structural subsidence since the Late Miocene. In this study, high-resolution seismic profiles acquired by the Guangzhou Marine Geological Survey, calibrated by well control from the ODP sites 1146 and 1148, were utilized to construct a time-significant sequence stratigraphic framework, from which the history of relative sea level changes since the Late Miocene on the northern SCS margin was derived. Our study area is situated in the middle segment of the margin, between the Hainan Island to the west and the Dongsha Islands to the east. This region is to a certain degree far away from the active structural zones and is suggested as the most stable region in the margin. Totally 4000 km seismic profiles were used, which controls an area of about 6×104 km2. The seismic data have a vertical resolution of 5 to 15 m for the Upper Miocene to Quaternary interval. Three regional seismic sequence boundaries were identified. They subdivide the Late Miocene to Quaternary into three mega-sequences, which correspond to the Quaternary, Pliocene and Late Miocene, respectively by tying to well control. The Late Miocene mega-sequence, including 13 component sequences, is characterized with a basal incised canyon-developed interval overlain by three sets of progradational sequences formed in deep-water slope environments. The Pliocene mega-sequence consists of four sets of progradational sequences. Each sequence set contains one to three component sequences. At least 7 component sequences can be identified. The Quaternary mega-sequence consists of five sets of progradational sequences, in which the lower two constitute a retrogressive sequence set and the upper three a progradational sequence set. At least 9 component sequences can be recognized. Most of the component sequences within the Pliocene and Quaternary mega-sequences occur adjacent to modern shelf margin, and therefore were interpreted as shelf-marginal progradational deltaic sequences. A relative sea level curve since the Late Miocene was compiled by integrating the shift trajectory of onlap points, the stacking pattern of component sequences, and the chronostratigraphic diagrams. The curve contains about 29 cycles of relative sea level changes, showing a much higher resolution than the previous results in the region. These cycles constitute three large relative sea level rise and fall cycles. General trend of sea level variations is rising since the Late Miocene, which is opposite to the global sea level changes and is in accordance with the previous regional researches. This deviation is ascribed to the combined effects of very rapid regional subsidence and relative deficiency of sediment supply. This research was funded by the National Natural Science Foundation of China (Grant Nos. 91028003 and 41076020).

Zhong, G.; Wang, L.

2013-12-01

215

Development tendency of seismic stratigraphy  

Energy Technology Data Exchange (ETDEWEB)

Seismic stratigraphy has been developed and improved continuously in practical application in oil and gas exploration since it came out. Maybe the most outstanding progresses are sequence stratigraphy and comprehensive geologic interpretation. This article describes the two kinds of research methodology and their application effects in oil and gas explorations. It is pointed out that sequence stratigraphy is actually an improvement on seismic stratigraphy while comprehensive seismic interpretation is the true development tendency of seismic stratigraphy.

Fujin, J.

1991-01-01

216

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)  

Scientific Electronic Library Online (English)

Full Text Available SciELO Mexico | Language: Spanish Abstract in spanish 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. Abstract in english 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.

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

217

Late Mesozoic to Paleogene stratigraphy of the Salar de Atacama Basin, Antofagasta, Northern Chile: Implications for the tectonic evolution of the Central Andes  

Science.gov (United States)

The Salar de Atacama basin, the largest "pre-Andean" basin in Northern Chile, was formed in the early Late Cretaceous as a consequence of the tectonic closure and inversion of the Jurassic-Early Cretaceous Tarapacá back arc basin. Inversion led to uplift of the Cordillera de Domeyko (CD), a thick-skinned basement range bounded by a system of reverse faults and blind thrusts with alternating vergence along strike. The almost 6000-m-thick, upper Cretaceous to lower Paleocene sequences (Purilactis Group) infilling the Salar de Atacama basin reflects rapid local subsidence to the east of the CD. Its oldest outcropping unit (Tonel Formation) comprises more than 1000 m of continental red sandstones and evaporites, which began to accumulate as syntectonic growth strata during the initial stages of CD uplift. Tonel strata are capped by almost 3000 m of sandstones and conglomerates of western provenance, representing the sedimentary response to renewed pulses of tectonic shortening, which were deposited in alluvial fan, fluvial and eolian settings together with minor lacustrine mudstone (Purilactis Formation). These are covered by 500 m of coarse, proximal alluvial fan conglomerates (Barros Arana Formation). The top of the Purilactis Group consists of Maastrichtian-Danian alkaline lava and minor welded tuffs and red beds (Cerro Totola Formation: 70-64 Ma K/Ar) deposited during an interval of tectonic quiescence when the El Molino-Yacoraite Late Cretaceous sea covered large tracts of the nearby Altiplano-Puna domain. Limestones interbedded with the Totola volcanics indicate that this marine incursion advanced westwards to reach the eastern CD slope. CD shortening in the Late Cretaceous was accompanied by volcanism and continental sedimentation in fault bounded basins associated to strike slip along the north Chilean magmatic arc to the west of the CD domain, indicating that oblique plate convergence prevailed during the Late Cretaceous. Oblique convergence seems to have been resolved into a highly partitioned strain system where margin-parallel displacements along the thermally weakened arc coexisted with margin-orthogonal shortening associated with syntectonic sedimentation in the Salar de Atacama basin. A regionally important Early Paleocene compressional event is echoed, in the Salar de Atacama basin by a, distinctive, angular unconformity which separates Paleocene continental sediments from Purilactis Group strata. The basin also records the Eocene-Early Oligocene Incaic transpressional episode, which produced, renewed uplift in the Cordillera de Domeyko and triggered the accumulation of a thick blanket of syntectonic gravels (Loma Amarilla Formation).

Mpodozis, Constantino; Arriagada, César; Basso, Matilde; Roperch, Pierrick; Cobbold, Peter; Reich, Martin

2005-04-01

218

Mars Stratigraphy Mission  

Science.gov (United States)

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

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

2000-01-01

219

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

2008-12-01

220

Isotopic Constraints (U, Th, Pb, Sr, Ar) on the Timing of Magma Generation, Storage and Eruption of a Late-Pleistocene Subvolcanic Granite, Alid Volcanic Center, Eritrea  

Science.gov (United States)

Isotopic analyses demonstrate that a shallow granophyric intrusion from the Alid volcanic center (AVC) was generated, intruded and crystallized over a 20,000-year period in the latest Pleistocene. The granophyre is not exposed, but was ejected as unmelted blocks within a ~1 km3 pyroclastic flow deposit around 15 ka and is a subvolcanic equivalent of the erupted rhyolitic pumice (Lowenstern et al., 1997: J Petrol 12, p. 1707-1721). The rock contains 2.59) is 15.2+/- 5.8 ka (all errors are 2 ? ). Two other splits with lower density (thus higher in Na) yielded ages older than 24 ka, and may retain some excess Ar. Thus, the time between intrusion and complete crystallization for the granophyre was http://wrgis.wr.usgs.gov/docs/geologic/jlwnstrn/alid/ Alidpage.html

Lowenstern, J. B.; Charlier, B. L.; Wooden, J. L.; Lanphere, M. A.; Clynne, M. A.; Bullen, T. D.

2001-12-01

 
 
 
 
221

Oxygen isotope and sapropel stratigraphy in the Eastern Mediterranean during the last 3.2 million years  

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Stable oxygen isotope data from four holes drilled at the Ocean Drilling Program Site 967, which is located on the lower northern slope of the Eratosthenes Seamount, provide a continuous record of Eastern Mediterranean surface-water conditions during the last 3.2 Ma. A high-resolution stratigraphy for the Pliocene–Pleistocene sequence was established by using a combination of astronomical calibration of sedimentary cycles, nannofossil stratigraphy, and stable oxygen isotope fluctua...

Kroon, Dick; Alexander, I.; Little, M.; Lourens, L. J.; Matthewson, A.; Robertson, Alastair H. F.; Sakamoto, T.

1998-01-01

222

Taxonomía y hábito alimentario de Equus conversidens (Perissodactyla, Equidae) del Pleistoceno Tardío (Rancholabreano) de Hidalgo, centro de México / Taxonomy and dietary behavior of Equus conversidens (Perissodactyla, Equidae) from the late Pleistocene (Rancholabream) of Hidalgo, central Mexico  

Scientific Electronic Library Online (English)

Full Text Available SciELO Mexico | Language: Spanish Abstract in spanish El estudio comparado de material craneal y dental perteneciente a équidos, recuperado de sedimentos pleistocénicos innominados de origen fluvio-lacustre ubicados en la parte suroriental de Hidalgo, permitió caracterizar y asignar la muestra disponible a Equus conversidens. Este registro aporta evide [...] ncia adicional acerca de la amplia distribución que tuvo esta especie a lo largo del territorio nacional y del subcontinente Norteamericano en conjunto durante los últimos dos millones de años. Por otra parte, la interpretación del hábito alimentario mediante la implementación del método de mesodesgaste, reveló que el patrón de desgaste observado en los elementos dentales considerados en el análisis, caracterizado por una combinación de relieve oclusal bajo y cúspides romas, es estrechamente cercano al que distingue a la especie pacedora reciente Bison bison. Los resultados obtenidos indican que la población de équidos hidalguense tuvo una dieta conformada predominantemente por recursos abrasivos con un alto contenido de sílice y/o fitolitos (pastos, polvo y/o arena). El comportamiento alimentario propuesto evidencia la presencia de zonas de vegetación abierta en lo que ahora es parte del centro de México durante la segunda mitad del Pleistoceno; aunado a esto, las formas herbívoras asociadas al registro de équidos sugieren que, además de áreas donde posiblemente predominaron los pastos y otras herbáceas, también existieron zonas más arboladas, lo cual es indicativo de un hábitat heterogéneo. Abstract in english A comparative study of equid cranial and dental material, recovered from unnamed fluvio-lacustrine deposits of late Pleistocene age that crop out in southeastern Hidalgo, allowed to assign the fossil sample to Equus conversidens. The record gives additional evidence on the widespread distribution of [...] this species throughout the North American subcontinent during the last two million years. On the other hand, we evaluated the dietary behavior of this Equus population from Hidalgo by the extended mesowear analysis method. The observed mesowear pattern is comparable to that of the recent grazer species Bison bison. These species display a particular combination of low occlusal relief and blunt cusps. This suggests that the horse population from Hidalgo was a grass feeder that incoporated abrasive food items into its diet (grass and/or extrinsic grit). The results provide evidence for the existence of local grazing habitats in central Mexico during the late Pleistocene; furthermore, the associated herbivore fauna indicates wooded areas as well, thus suggesting a heterogeneous habitat.

Víctor M., Bravo-Cuevas; Eduardo, Jiménez-Hidalgo; Jaime, Priego-Vargas.

223

Arctic ground squirrels of the mammoth-steppe: paleoecology of Late Pleistocene middens (˜24 000 29 450 14C yr BP), Yukon Territory, Canada  

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This paper presents paleoecological analyses of 48 fossil arctic ground squirrel ( Spermophilus parryii) middens (nests and caches) recovered from ice-rich loess sediments in the Klondike region of west-central Yukon Territory. AMS radiocarbon dates and stratigraphic association of middens with Dawson tephra (˜25 300 14C yr BP), indicate these paleoecological data reflect the onset of glacial conditions of early Marine Isotope Stage (MIS) 2 and terminal MIS 3 (˜24 000-29 450 14C yr BP). Plant macrofossils include at least 60 plant taxa, including diverse graminoids ( Poa, Elymus trachycaulus, Kobresia myosuroides), steppe forbs ( Penstemon gormanii, Anemone patens var. multifida, Plantago cf. canescens), tundra forbs ( Draba spp., Bistorta vivipara), dwarf shrubs ( Salix cf. arctica, S. cf. polaris), sage ( Artemisia frigida) and rare trees ( Picea mariana). Many of these taxa identified in the middens represent the first recorded fossils for these plants in Eastern Beringia and add to our knowledge of the floristic composition of Pleistocene vegetation and biogeography in this region. Fossil beetles include typical members of the Eastern Beringian steppe-tundra fauna ( Lepidophorus lineaticollis and Connatichela artemisiae) and others suggesting predominantly dry, open habitats. Cache forage selection is suggested by some plant taxa which were particularly frequent and abundant in the middens ( Bistorta vivipara, Kobresia myosuroides, Ranunculus spp., Potentilla, Erysimum cf. cheiranthoides, Poa, Carex and Draba). Factors such as proximity of vegetation to burrows and abundance of fruits and seeds per plant were probably important in cache selection. Glacial conditions enabled arctic ground squirrels to form widespread and dense populations in regions such as the Klondike in which they are rare or absent at present. This fossil midden record supports previous hypotheses that suggest arctic ground squirrels evolved in and are well-adapted to the open, steppe-tundra vegetation, loessal soils and glacial climates of the mammoth-steppe biome.

Zazula, Grant D.; Froese, Duane G.; Elias, Scott A.; Kuzmina, Svetlana; Mathewes, Rolf W.

2007-04-01

224

Paudorf locus typicus (Lower Austria) revisited â?? 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 â??Paudorfer Bodenbildungâ? (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 5câ??[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

225

The hipparion from the late Pliocene of Ahl al Oughlam, Morocco, and a revision of the relationships of Pliocene and Pleistocene African hipparions  

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This paper addresses three points: 1. the description of a new species (H. pomeli n.sp.) of Late Pliocene hipparion from Morocco; 2. preliminary notes on hipparion skulls from Langebaanweg E Quarry (H. hendeyi n.sp.) and Chad Kossoum Bougoudi; 3. a new interpretation of African hipparion relations. The Appendix presents practical techniques allowing the estimation of adult dimensions in juvenile skulls and correlations between two mandibular and skull dimensions. H. pomeli was a medium-...

Eisenmann, Vera; Geraads, Denis

2007-01-01

226

Tephrochronology of the Mont-Dore volcanic Massif (Massif Central, France): new 40Ar/39Ar constraints on the Late Pliocene and Early Pleistocene activity  

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The Mont-Dore Massif (500 km2), the youngest stratovolcano of the French Massif Central, consists of two volcanic edifices: the Guéry and the Sancy. To improve our knowledge of the oldest explosive stages of the Mont-Dore Massif, we studied 40Ar/39Ar-dated (through single-grain laser and step-heating experiments) 11 pyroclastic units from the Guéry stratovolcano. We demonstrate that the explosive history of the Guéry can be divided into four cycles of explosive eruption activity between 3.09 and 1.46 Ma (G.I to G.IV). We have also ascertained that deposits associated with the 3.1-3.0-Ma rhyolitic activity, which includes the 5-km3 "Grande Nappe" ignimbrite, are not recorded in the central part of the Mont-Dore Massif. All the pyroclastites found in the left bank of the Dordogne River belong to a later explosive phase (2.86-2.58 Ma, G.II) and were channelled down into valleys or topographic lows where they are currently nested. This later activity also gave rise to most of the volcanic products in the Perrier Plateau (30 km east of the Mont-Dore Massif); three quarters of the volcano-sedimentary sequence (up to 100 m thick) was emplaced within less than 20 ky, associated with several flank collapses in the northeastern part of the Guéry. The age of the "Fournet flora" (2.69 ± 0.01 Ma) found within an ash bed belonging to G.II suggests that temperate forests already existed in the French Massif Central before the Pliocene/Pleistocene boundary. The Guéry's third explosive eruption activity cycle (G.III) lasted between 2.36 and 1.91 Ma. It encompassed the Guéry Lake and Morangie pumice and ash deposits, as well as seven other important events recorded as centimetric ash beds some 60 to 100 km southeast of the Massif in the Velay region. We propose a general tephrochronology for the Mont-Dore stratovolcano covering the last 3.1 My. This chronology is based on 44 40Ar/39Ar-dated events belonging to eight explosive eruption cycles each lasting between 100 and 200 ky. The occurrence of only one pumice deposit in the 800-ky period between 1.9 and 1.1 Ma suggests that volcanic explosive activity was strongly reduced or quiescent.

Nomade, Sébastien; Pastre, Jean-François; Nehlig, Pierre; Guillou, Hervé; Scao, Vincent; Scaillet, Stéphane

2014-03-01

227

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.

Choukri Abdelmajid

2008-03-01

228

Dating Lake Tahoe (CA/NV) and Mono Lake (CA) sediment using palaeomagnetic secular variation as a chronology for late Pleistocene palaeoclimate in the U.S. Great Basin  

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In 1976, six meters of graded and varved sediment were recovered in three piston cores from Lake Tahoe, CA/NV, and used for palaeomagnetic and sedimentologic investigations (Palmer et al., 1979; Denham, 1981). The long-term changes (secular variation) in the Lake Tahoe palaeomagnetic record were compared to secular variation in exposed lacustrine sediment of the Wilson Creek Formation (Lajoie, 1993) in the Mono Basin, CA, (Denham and Cox, 1971), 100 km away. During the more than 30 years since the coring was done in Lake Tahoe, the record of palaeomagnetic secular variation in the Mono Basin and elsewhere in the Great Basin has been refined (Liddicoat and Coe, 1979; Lund et al., 1988, Liddicoat and Coe, 1997; Liddicoat and Coe, 1998; Benson et al., 1998; Negrini and Davis, 1992; Kent et al., 2002; Zimmerman et al., 2006) to allow a reexamination of the palaeomagnetic directions and environmental magnetic record in the Lake Tahoe cores and the age of those sediments. Inferences are also possible about the sedimentological importance during the recording of the palaeomagnetic field at Lake Tahoe and possibly in the Mono Basin, and the age of the Lake Tahoe sediment recovered, which postdates the Mono Lake Excursion. The age of the Mono Lake Excursion and Wilson Creek Formation is relevant to investigations of Late Pleistocene palaeoclimate reconstructions for the U.S. Great Basin (Zimmerman et al., 2006).

Liddicoat, Joseph

2010-05-01

229

Paleoceanographic interpretations of late Pleistocene to Holocene sedimentological and geochemical proxy-data from SE-Atlantic abyssal plains (Cape, Angola and Guinea Basin)  

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Sediments of the deep abyssal regions of the Southeast Atlantic (Cape Basin, Angola Basin and Guinea Basin) were studied to reconstruct changes in surface and deep water circulation, bioproductivity, and terrigenous sediment flux. To gain these results various sedimentological and geochemical proxies were imposed, including grain size data, foraminiferal fragmentation, carbonate and organic carbon content, as well as stable oxygen and carbon isotope contents of foraminiferal tests. Samples were gained with a multicorer device during Meteor cruise 63/2 (2005) in water depths between ~5,100 and ~5,600 m. The superficial 30 cm of sediment, sampled in 1/2, 1 and 5 cm steps, were processed for this study. The record covers parts of the Pleistocene and Holocene. Even if the sedimentation conditions seem to be similar in the deep-sea regions of the SE-Atlantic there are clear differences between the three sampled locations. This is caused by major changes in deep water corrosiveness leading to fluctuations in the sedimentation rate and carbonate preservation. Cape Basin localities show a pattern of enhanced carbonate preservation around 12 ka BP possibly indicating a delayed Last Glacial Maximum signal. This pattern, which is typical for Indo-Pacific records, clearly points to an influence of Antarctic Bottom Water (AABW) at water depths below 5000 m in the Northern Cape Basin. The non-correlation between carbonate content and grain size distribution is owing to a coccoliths' dominated carbonate production possibly caused by low nutrient availability in surface waters and the higher dissolution susceptibility of foraminiferal tests. Angola Basin samples delivered highest sand contents, a carbonate peak and low organic carbon values around 8.2 ka BP which indicate a reduced bioproduction and nutrient supply in superficial waters. A connection of the 8.2 ka cold event in the northern hemisphere and central African precipitation, equatorial East Atlantic (EEA) upwelling intensity and bioproduction is likely. Thus we expect the observed peak to be a response to the mentioned cold event at about 8.2 ka. The overall sedimentological record indicates that the Northern Angola Basin sedimentation may not be triggered by changes in the influence of North Atlantic Deep Water (NADW) and AABW as observed in the Northern Cape Basin. Therefore, the Walvis Ridge is expected to be an effective barrier for AABW. Studied Guinea Basin sediments (>5000 m) show quite uniform spatial bioproduction caused by the EEA divergence zone overlying the sample sites. Concerning the Holocene, temporal variations are mirrored in the grain size distribution which can possibly be correlated to changes in the thermocline depth. The trend to higher sand contents, especially in the uppermost sediment layers hints to increasing bioproductivity (foraminifers) and thus upwelling intensity during the Holocene. Dissolution, even in the deepest parts of the Guinea Basin, is minimal during the sampled timespan (low foraminferal fragmentation) owing to a predominant influence of NADW north of the Guinea Rise. Differences in the carbonate content are therefore expected to be caused by dilution by terrigenous material delivered by fluvial (Niger River) and eolian (Trade Winds) transport in combination with a change in bioproductivity.

Piller, W. E.; Müllegger, S.

2009-04-01

230

Late Pleistocene monsoon variability in northwest Thailand: an oxygen isotope sequence from the bivalve Margaritanopsis laosensis excavated in Mae Hong Son province  

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Long, continuous records of Late Quaternary environmental change are rare in Southeast Asia, yet they are crucial for understanding the nature of early human dispersal and occupation in the Australasian region. We present a new record of palaeomonsoon activity extending back to 35,000 BP (years before the present), based on the analysis of oxygen isotope ratios (? 18O) in the freshwater bivalve Margaritanopsis laosensis excavated from the Tham Lod and Ban Rai rockshelters in Mae Hong Son Province, northwest Thailand. Long-term changes in the M. laosensis ? 18O record reflect changes in the ? 18O of the river water in which these organisms grew, and correlate well with changes in speleothem ? 18O records of east Asian monsoon rainfall from Hulu Cave and Dongge Cave in China. The new northwest Thailand ? 18O sequence indicates wetter and relatively unstable climatic conditions from 35,000 to 20,000 BP, followed by drier conditions from 20,000 to 11,500 BP. A period of peak aridity occurred around 15,600 BP during Heinrich Event 1, suggesting that the intertropical convergence zone shifted southward when the North Atlantic region cooled. However, there is little evidence for the Younger Dryas event at ˜12,800-11,500 BP. After 9,800 BP, precipitation increased substantially and climatic variability declined. Our findings provide an improved baseline against which to gauge interactions between early humans and climate change in Southeast Asia. For example, there was no significant change in the prehistoric flake stone technology used at Tham Lod and Ban Rai despite the bivalve ? 18O evidence for substantial climate change in the region. Also, the climatic impact of the Younger Dryas event appears to have been less intense in northwest Thailand compared to the cooling and drying observed in China, and may explain why agriculture made a relatively late appearance in Thailand, possibly involving migrants from China.

Marwick, Ben; Gagan, Michael K.

2011-10-01

231

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

2003-01-01

232

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)

2010-10-01

233

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

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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

2011-08-01

234

Late Pleistocene eolian features in southeastern Maryland and Chesapeake Bay region indicate strong WNW-NW winds accompanied growth of the Laurentide Ice Sheet  

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Inactive parabolic dunes are present in southeastern Maryland, USA, along the east bank of the Potomac River. More elongate and finer-grained eolian deposits and paha-like ridges characterize the Potomac River-Patuxent River upland and the west side of Chesapeake Bay. These ridges are streamlined erosional features, veneered with eolian sediment and interspersed with dunes in the low-relief headwaters of Potomac- and Patuxent-river tributaries. Axis data for the dunes and ridges indicate formation by WNW-NW winds. Optically stimulated luminescence and radiocarbon age data suggest dune formation from ??? 33-15??ka, agreeing with the 30-13??ka ages Denny, C.S., Owens, J.P., Sirkin, L., Rubin, M., 1979. The Parsonburg Sand in the central Delmarva Peninsula, Maryland and Delaware. U.S. Geol. Surv. Prof. Pap. 1067-B, 16??pp. suggested for eolian deposits east of Chesapeake Bay. Age range and paleowind direction(s) for eolian features in the Bay region approximate those for late Wisconsin loess in the North American midcontinent. Formation of midcontinent loess and Bay-region eolian features was coeval with rapid growth of the Laurentide Ice Sheet and strong cooling episodes (??18O minima) evident in Greenland ice cores. Age and paleowind-direction coincidence, for eolian features in the midcontinent and Bay region, indicates strong mid-latitude WNW-NW winds for several hundred kilometers south of the Laurentide glacial terminus that were oblique to previously simulated anticyclonic winds for the last glacial maximum.

Markewich, H. W.; Litwin, R. J.; Pavich, M. J.; Brook, G. A.

2009-01-01

235

Late Pliocene/Pleistocene changes in Arctic sea-ice cover: Biomarker and dinoflagellate records from Fram Strait/Yermak Plateau (ODP Sites 911 and 912)  

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Sea ice is a critical component in the (global) climate system that contributes to changes in the Earth's albedo (heat reduction) and biological processes (primary productivity), as well as deep-water formation, a driving mechanism for global thermohaline circulation. Thus, understanding the processes controlling Arctic sea ice variability is of overall interest and significance. Recently, a novel and promising biomarker proxy for reconstruction of Arctic sea-ice conditions was developed and is based on the determination of a highly-branched isoprenoid with 25 carbons (IP25; Belt et al., 2007; PIP25 when combined with open-water phytoplankton biomarkers; Müller et al., 2011). Here, we present biomarker data from Ocean Drilling Program (ODP) Sites 911 and 912, recovered from the southern Yermak Plateau and representing information of sea-ice variability, changes in primary productivity and terrigenous input during the last about 3.5 Ma. As Sites 911 and 912 are close to the modern sea-ice edge, their sedimentary records seem to be optimal for studying past variability in sea-ice coverage and testing the applicability of IP25 and PIP25 in older sedimentary sequences. In general, our biomarker records correlate quite well with other climate and sea-ice proxies (e.g., dinoflagellates, IRD, etc.). The main results can be summarized as follows: (1) The novel IP25/PIP25 biomarker approach has potential for semi-quantitative paleo-sea ice studies covering at least the last 3.5 Ma, i.e., the time interval including the onset (intensification) of major Northern Hemisphere Glaciation (NHG). (2) These data indicate that sea ice of variable extent was present in the Fram Strait/southern Yermak Plateau area during most of the time period under investigation. (3) Elevated IP25/PIP25 values indicative for an extended spring sea-ice cover, already occurred between 3.6 and 2.9 Ma, i.e., prior to the onset of major NHG. This may suggest that sea-ice and related albedo effects might have been important for general cooling and ice-sheet build-up. (4) Maxima in sea ice occurred near 3.3, 2.7, 2.1, 1.7 and during the last 1.2 Ma whereas between about 2.6 and 2.2 Ma the sea-ice cover was surprisingly reduced. The IP25 maxima are similar to those determined for the late Holocene. (5) Both, dinoflagellate and IP25/PIP25 data indicate that also during the Late Pliocene Warming Event at least occasionally sea ice must have occurred. (6) This low-resolution pilot study motivates to carry out further detailed high-resolution sea-ice biomarker research on ODP/IODP material in order to prove or disprove these preliminary interpretations. References Belt, S.T., Massé, G., Rowland, S.J., Poulin, M., Michel, C., LeBlanc, B., 2007. A novel chemical fossil of palaeo sea ice: IP25. Organic Geochemistry 38, 16-27. Müller, J., Wagner, A., Fahl, K., Stein, R., Prange, M., Lohmann, G., 2011. Towards quantitative sea ice reconstructions in the northern North Atlantic: A combined biomarker and numerical modelling approach. Earth Planetary Science Letters 306, 137-148.

Stein, Ruediger; Fahl, Kirsten; Matthiessen, Jens

2014-05-01

236

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

2011-11-01

237

The Balitx landslide (Mallorca, Spain) and its possible seismic origin: active spreading since the Late Pleistocene; El deslizamiento de Balitx (Mallorca) y su posible origen sismico. Procesos activos desde el Pleistoceno superior  

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The Balitx landslide, located on the steep coastal side of the Tramuntana range on the island of Mallorca, is a large translational rock landslide in which the failure surface coincides with the reactivation of an earlier normal fault. The dating of calcite striae on the fault plane with U/Th techniques reveals that the last movement was over 400 kyr ago, which falls outside of the range of this method. The volume of the landslide is estimated to be over 700 million cubic metres, with a north-westward displacement of 300 m. Active extensional cracks as well as block spreads have been identified along the main scarp, together with displacement and toppling of blocks, the beginning of which coincides with oxygen isotope stage OIS 5a (Late Pleistocene = 83 kyr), a wetter and warmer period than the present. Currently active decametre-long cracks up to 50 m wide can be seen to affect the displaced materials. They reveal the rupture of the displaced block into several units at different speeds. A retrospective analysis of slope stability has been carried out, taking into account different scenarios according to three critical sea stands. All the scenarios are stable, with a safety factor of over 1.35. These results support the thesis that the Balitx landslide could have been triggered by seismicity. A study of the Balitx landslide under dynamic conditions reveals that the landslide could have been triggered by a moderate-to-high-magnitude earthquake (Mw=6.0) located close to the landslide (10-30 km) and probably related to some of the active faults identified in Majorca, such as the Palma Fault. (Author) 58 refs.

Mateos, R. M.; Rodriguez-Peces, M. J.; Azanon, J. M.; Rodriguez-Fernandez, J.; Roldan, F. J.; Garcia-Moreno, I.; Galabert, B.; Garcia-Mayordomo, J.

2013-02-01

238

Mesozoic-Cenozoic stratigraphy of the Fuegian Andes, Argentina  

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The stratigraphy of the Argentinean Fuegian Andes reveals contrasting Mesozoic-Cenozoic tectonic regimes. The Lemaire Formation, submarine complex of bimodal volcanites, breccias, and sedimentary rocks; the Yahgán Formation, volcaniclastic apron of deep-marine andesite-rich turbidites and mudstones; and the Beauvoir Formation, slope mudstones, all evidence late Jurassic early Cretaceous extension and consequent origination of the Rocas Verdes Marginal Basin. The basal late Cretaceous ductile...

Olivero, Eduardo Bernardo

2008-01-01

239

Morphology and palaeoenvironmental interpretation of deformed soft-sediment clasts: examples from within Late Pleistocene glacial outwash, Tempo Valley, Northern Ireland  

Science.gov (United States)

Glacial outwash, deposited during deglaciation of the late Devensian ice sheet, is present as a flat-topped valley fill in the Tempo Valley on the southern flanks of the Fintona Hills, Northern Ireland. Sedimentologically, the outwash comprises well-sorted and interbedded rippled to massive sands which record distal deposition within a proglacial water body. Beds of ripple-drift cross-laminated sands contain deformed (folded and contorted) soft-sediment clasts which are composed mainly of silt and clay. The soft-sediment clasts were deformed prior to final deposition because clast a- b planes lie conformable to sand laminae which are undeformed. Morphological characteristics of the soft-sediment clasts, and their facies context, provide evidence for transport mechanisms, depositional environment, and processes of clast deformation. The soft-sediment clasts were transported into a proglacial water body by unidirectional water currents (˜1.5-2.5 m s -1). Sediment transport processes include sediment bypassing within the water column, a low bedload component, and grain flow activity during waning flow stages. The overall morphology of soft-sediment clasts records between 1 and 3 distinct phases of hydroplastic deformation prior to emplacement. The deformation phases are recognised on the basis of morphologically `unrolling' the superimposed folds of the soft-sediment clasts. Deformation structures (i.e. fold style) and direction of the principal stress axis relative to clast axes suggest that clasts were reoriented with respect to water flow direction following each deformation phase. Processes of deformation include folding-over of the clast along its b axis into two or more components, crumpling and abrasion of the outer margins of the b plane, and squashing of the clast c axis (some of which may be post-depositional deformation). The presence of silt- and clay-rich soft-sediment clasts within the outwash succession suggests that they were ripped-up from shallow and irregular pools on the glacier forefield, into which fine sediments accumulated after flood or meltwater events, and transported distally into a proglacial water body. These inferences based on facies evidence and styles of hydroplastic deformation impact on reconstructions of local palaeogeography, and the wider interpretation of similar soft-sediment clasts in the geological record.

Knight, Jasper

1999-10-01

240

Coral associations of the Pleistocene Ironshore Formation, Grand Cayman  

Science.gov (United States)

The 125-ka sea level, which was approximately 6 m above present-day sea level, led to the partial flooding of many Caribbean islands. On Grand. Cayman, this event led to the formation of the large Ironshore Lagoon that covered most of the western half of the island and numerous, small embayments along the south, east, and north coasts. At that time, at least 33 coral species grew in waters around Grand Cayman. This fauna, like the modern coral fauna of Grand Cayman, was dominated by Montastrea annularis, Porites porites, Acropora polmata, and A. cervicornis. Scolymia cubensis and Mycetophyllia ferox, not previously identified from the Late Pleistocene, are found in the Pleistocene patch reefs. Madracis mirabilis, Colpophyllia breviserialis, Agaricia tenuifolia, A. lamarcki, A. undata, Millepora spp., Mycetophyllia reesi, M. aliciae, and M. danaana, found on modern reefs, have not been identified from the Late Pleistocene reefs. Conversely, Pocillopora sp. cf. P. palmata, which is found in Late Pleistocene reefs, is absent on the modern reefs around Grand Cayman. The corals in the Ironshore Formation of Grand Cayman have been divided into 10 associations according to their dominant species, overall composition, and faunal diversity. Many of these associations are similar to the modern associations around Grand Cayman. Each of the Pleistocene coral associations, which can be accurately located on the known Late Pleistocene paleogeography of Grand Cayman, developed in distinct environmental settings. Overall trends identified in the modern settings are also apparent in the Late Pleistocene faunas. Thus, the diversity of the coral faunas increased from the interior of the Ironshore Lagoon to the reef crest. Similarly, the coral diversity in the Pleistocene patch reefs was related to the size of the reefs and their position relative to breaks in the barrier reef. The barrier reef included corals that are incapable of sediment rejection; whereas the patch reefs lacked such corals.

Hunter, I. G.; Jones, B.

1996-11-01

 
 
 
 
241

Palaeoseismic evidence for a medieval earthquake, and preliminary estimate of late Pleistocene slip-rate, on the Firouzkuh strike-slip fault in the Central Alborz region of Iran  

Science.gov (United States)

The ˜55 km-long Firouzkuh fault is located in the Central Alborz Mountains of Iran. It is a left-lateral fault, which dips to the south, and possesses a small dip-slip component of motion that we interpret to result from extension. The ratio of horizontal to vertical displacement across the fault, calculated from the cumulative displacement of landscape features, is 7.6. We provide constraints on the timing of the last earthquake on the Firouzkuh fault from two trenches (T1 and T2) across the fault zone, excavated in 2004, and located east of Firouzkuh city. The trenches expose faulted sedimentary deposits. Two optically-stimulated luminescence (OSL) ages from sediments in the lower part of trench T1 date from the late Pleistocene (15.9 ± 0.9 ka and 27.1 ± 1.7 ka). The younger of the two dated units in T1 is displaced vertically across the fault by 2.2-4.4 m, from which we estimate a strike-slip displacement of 18.2-33.4 m, and hence a average horizontal slip-rate of 1.1-2.2 mm/yr. The sediments exposed in T1 do not yield constraints on the most recent earthquake history. In trench T2, however, human skeletal remains of a middle aged male, which yield a radiocarbon age of 1159 ± 28 BP (corresponding to a mean calendar age of 791 AD), were found within a faulted alluvial layer at a depth of 60-70 cm from the surface. The existence of these medieval human places shows that a surface-rupturing earthquake occurred at some time after 1159 ± 28 BP. The amount of slip in each earthquake on the Firouzkuh fault is difficult to estimate, but assuming the entire ˜55 km fault length ruptures in each event, they will have had a maximum magnitude of 7.1. At our estimated late Quaternary slip-rate of ˜1.1-2.2 mm/yr magnitude 7.1 earthquakes, involving ˜1.2 m average displacement, would be expected to occur every ˜1100-540 years. As the last earthquake on the Firouzkuh fault may be up to ˜700 years in age we suggest that the Firouzkuh fault is a major hazard for earthquakes in the near future.

Nazari, H.; Ritz, J.-F.; Walker, R. T.; Salamati, R.; Rizza, M.; Patnaik, R.; Hollingsworth, J.; Alimohammadian, H.; Jalali, A.; Kaveh Firouz, A.; Shahidi, A.

2014-03-01

242

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

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Full Text Available SciELO Argentina | Language: English 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 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 co [...] rrelate with sedimentary successions from other regions of Argentina, north of Uruguay and south of Brazil. This long history abounds in mistakes and misinterpretations, and the 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.

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

243

Pleistocene Paleoart of Australia  

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Full Text Available Pleistocene rock art is abundant in Australia, but has so far received only limited attention. Instead there has been a trend, begun over a century ago, to search for presumed depictions of extinct megafauna and the tracks of such species. All these notions have been discredited, however, and the current evidence suggests that figurative depiction was introduced only during the Holocene, never reaching Tasmania. Nevertheless, some Australian rock art has been attributed to the Pleistocene by direct dating methods, and its nature implies that a significant portion of the surviving corpus of rock art may also be of such age. In particular much of Australian cave art is of the Ice Age, or appears to be so, and any heavily weathered or patinated petroglyphs on particularly hard rocks are good candidates for Pleistocene antiquity. On the other hand, there is very limited evidence of mobiliary paleoart of such age in Australia.

Robert G. Bednarik

2014-02-01

244

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

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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

245

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  

Scientific Electronic Library Online (English)

Full Text Available SciELO Argentina | Language: Spanish Abstract in spanish 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). Abstract in english 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 d [...] eposits 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

Manuel, Szelagowski; Marcelo A, Zárate; Adriana M, Blasi.

246

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 suspensions unde

Manuel Szelagowski

2004-12-01

247

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 SciELO Argentina | Language: Spanish 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 e [...] videncias 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. 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

Perla A, Imbellone; Andrea, Cumba.

248

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 57º57´30´´

Perla A Imbellone

2003-07-01

249

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

250

Plio-Pleistocene magnetostratigraphy of the Turkana basin, Kenya  

Science.gov (United States)

Archaeological and fossil sites from the Turkana basin provide a unique record of important human evolutionary junctures, which have been linked to terrestrial environmental change as a consequence of late Cenozoic climate phenomenon. However, because of low geochronological resolution, spatial discontinuities, and the episodic nature of sedimentation in the half-graben basins of the East African Rift System, it has been difficult to directly connect the terrestrial sites with marine archives of Pliocene and Pleistocene climate. For the purpose of addressing these issues, a magnetic polarity stratigraphy and a corresponding geochronology are presented for 12 sampling sites spanning about 400 m of continental sediments that crop out in eastern (Areas 118 and 130 of the Karari ridge, Areas 102 and 104 of the Koobi Fora ridge, Areas 107 and 123 of Bara Hasuma) and western (Kokiselei, Naiyena Engol, Kalochoro, Lomekwi, South Turkwel, and Kanapoi) parts of the Turkana basin. Characteristic magnetizations isolated through thermal demagnetization experiments on mudstone specimens pass reversal tests and are indistinguishable in mean direction regardless if samples were collected from ancient fluvial floodplain or lacustrine strata of correlative stratigraphic intervals. The sequence of the composite paleomagnetic reversal stratigraphy consists of 15 magnetozones that vary from less than a meter to tens of meters thick and can be unambiguously correlated within limits of the previously established tephrochronology to the Gilbert through Matuyama portion of the Geomagnetic Polarity Time Scale dated to about 4.0-1.5 Ma. Sedimentation rates through lacustrine intervals (e.g., 22-29 cm/kyr) are comparable with high-fidelity marine cores. This factor coupled with copious amounts of magnetic mineral detritus from basin-bounding rift volcanics probably contributes to a high natural remanent magnetization of the sediments and the recording of temporally brief magnetozones (e.g., Vrica Subchron, upper and lower Reunion Subchrons, Kaena and Mammoth Subchrons) typically often not observed in continental records. Across-basin (50-100 km) comparisons of the stratigraphic positions for the same reversal boundaries demonstrate not only heterogeneity in paleoenvironmental records based on the stable-isotopic composition of paleosol carbonates and sedimentary facies, but also diachroneity for the onset of lacustrine systems that mark transitions from fluvial-dominated intervals of the basin's history. Although some lake-level oscillations might be linked with global climate changes operating at timescales on the order of 20-40 thousand years, differences between the nature and timing of the spatially disparate paleoenvironmental records are interpreted to reflect a strong influence on sedimentary patterns by local reorganizations of basin-boundary faults, underlying half-graben structure, and volcano-tectonic events. Conflicting aridity and humidity hypotheses of human evolution for the period of 3.5-1.5 Ma are compared using the newly constructed magnetostratigraphy to directly integrate the basin's paleoenvironmental and evolutionary records with dust-flux chronologies, Mediterranean sapropel sequences, and oxygen isotope proxies of global ice volume.

Lepre, C. J.; Quinn, R.; Feibel, C. S.; Brown, F. H.; Kent, D. V.

2012-12-01

251

Sequence stratigraphy: Fact, fantasy, or work in progress  

Energy Technology Data Exchange (ETDEWEB)

Sequence stratigraphy has been hailed as a magic elixir to cure exploration problems in mature and frontier basins. Yet, like most cure-alls, analyses of modern depositional systems show that critical assumptions regarding sequence stratigraphy merit further review. An example from the modern Canterbury Plains, New Zealand, demonstrates some of the potential pit- falls of sequence stratigraphy and its application to hydrocarbon exploration. The Canterbury Plains, New Zealand, bounded by the Southern Alps and Pacific Ocean, are 60 km wide and 185 km long, and traversed by four large gravel rivers. The Canterbury basin is up to 750 m deep, filled primarily with gravel. The coastline is wave dominated and microtidal, with high rates of north-directed longshore drift. The southern coast is transgressive with 22 in wave-cut cliffs in Pleistocene gravel. Beaches are gravel and sand. Coastal erosion at approximately 1 m/yr steepens the fluvial gradient, causing the rivers to incise 1.5-4.2 mm/yr during the present highstand. River headwaters in the Southern Alps are uplifting, tectonically causing incision, which decreases seaward. Thus, fluvial incision takes place in the west due to mountain uplift and in the east due to the transgressing shoreline. A zone of null valley incision occurs 8-15 km from the coast. Existing sequence stratigraphic models suggest that downcutting should occur during falling sea level, not during transgression. The southern coastline is separated from the northern coast-line by Banks Peninsula, a resistant volcanic complex that acts as a large groyne to southerly waves. The northern coastline progrades approximately I m/yr and is largely sandy. Thus, the coastline within the same basin during the present sea level highstand is at one locale progradational and elsewhere transgressive. Gravel reaches the transgressive coast, where a steep gradient is maintained by downcutting.

Leckie, D.A. [Geological survey of Canada, Calgary, Alberta (Canada)

1995-11-01

252

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

253

Pleistocene oceanographie changes indicated by deep sea benthic foraminifera in the northern Indian Ocean  

Science.gov (United States)

An attempt has been made to understand the Pleistocene bottom water history in response to the paleoclimatic changes in the northern Indian Ocean employing quantitative analyses of deep sea benthic foraminifera at the DSDP sites 219 and 238. Among the 150 benthic foraminifera recorded a few species show dominance with changing percent frequencies during most of the sequence. The dominant benthic foraminiferal assemblages suggest that most of the Pleistocene bottom waters at site 219 and Early Pleistocene bottom waters at site 238 are of North Indian Deep Water (NIDW) origin. However, Late Pleistocene assemblage at site 238 appears to be closely associated with a water mass intermediate between North Indian Deep Water (NIDW) and Antarctic Bottom Water (AABW). Uvigerina proboscidea is the most dominant benthic foraminiferal species present during the Pleistocene at both the sites. A marked increase in the relative abundance of U. proboscidea along with less diverse and equitable fauna during Early Pleistocene suggests a relative cooling, an intensified oceanic circulation and upwelling of nutrient rich bottom waters resulting in high surface productivity. At the same time, low sediment accumulation rate during Early Pleistocene reveals increased winnowing of the sediments possibly due to more corrosive and cold bottom waters. The Late Pleistocene in general, is marked by relatively warm and stable bottom waters as reflected by low abundance of U. proboscidea and more diverse and equitable benthic fauna. The lower depth range for the occurrence of Bulimina aculeate in the Indian Ocean is around 2300 m, similar to that of many other areas. B. aculeata also shows marked increase in its abundance near the Pliocene/Pleistocene boundary while a sudden decrease in the relative abundance of Stilostomella lepidula occurs close to the Early/Late Pleistocene boundary.

Rai, Ajai K.; Srinivasan, M. S.

1994-12-01

254

Linking Top-down Forces to the Pleistocene Megafaunal Extinctions  

Science.gov (United States)

Humans, in conjunction with natural top-down processes and through a sequence of cascading trophic interactions, may have contributed to the Pleistocene megafaunal extinctions. The arrival of the first humans, as hunters and scavengers, through top-down forcing, could have triggered a population collapse of large herbivores and their predators. We present evidence that the large mammalian herbivores of the North American Pleistocene were primarily predator limited and at low densities, and therefore highly susceptible to extinction when humans were added to the predator guild. Our empirical evidence comes from data on carnivore dental attrition, proboscidean age structure, life history, tusk growth rates, and stable isotopes from the fossil record. We suggest a research agenda for further testing of this hypothesis that will provide a more detailed comprehension of late Pleistocene megafaunal ecology, and thereby allow us to better understand and manage remaining megafauna.

William Ripple (Oregon State University;Forest Ecosystems and Society); Blaire Van Valkenburgh (UCLA;Ecology and Evolutionary Biology)

2010-07-14

255

Towards the standardization of sequence stratigraphy  

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Sequence stratigraphy emphasizes facies relationships and stratal architecture within a chronological framework. Despite its wide use, sequence stratigraphy has yet to be included in any stratigraphic code or guide. This lack of standardization reflects the existence of competing approaches (or models) and confusing or even conflicting terminology. Standardization of sequence stratigraphy requires the definition of the fundamental model-independent concepts, units, bounding surfaces and workf...

Catuneanu, O.; Abreu, V.; Bhattacharya, J. P.; Blum, M. D.; Dalrymple, R. W.; Eriksson, P. G.; Fielding, C. R.; Fisher, W. L.; Galloway, W. E.; Gibling, M. R.; Giles, K. A.; Holbrook, J. M.; Jordan, R.; Kendall, C. G. St C.; Macurda, B.

2009-01-01

256

The Tephra Stratigraphy of two Lakes in South-Central British Columbia, Canada and its Implications for the Middle-Late Holocene Volcanic Activity at Glacier Peak, Washington, USA  

Science.gov (United States)

Several mid-late Holocene Glacier Peak tephras along with Mazama and Mount St. Helens Wn and P tephras were found in cores from Cooley and Rockslide Lakes in southeastern British Columbia, Canada approximately 300 km northeast of Glacier Peak. The sediments in Cooley Lake host the early Holocene Glacier Peak A tephra (2010 cal years BP), four separate, closely timed airfalls of Glacier Peak Dusty Creek tephra (5780-5830 cal years BP) and a Glacier Peak set D tephra (6060 cal years BP). This is the first report of Glacier Peak A and D tephras from British Columbia. The A tephra has been correlated on the basis of glass composition and age to a late Holocene Glacier Peak tephra in the sediments of Big Twin Lake, 75 km northeast of Glacier Peak. The glasses in the four Glacier Peak Dusty Creek tephra layers from Cooley Lake are compositionally indistinguishable from those in Mount Barr Cirque and Frozen Lakes in southwestern British Columbia. The layers represent four eruptions taking place over approximately 50 years (5780-5830 cal years BP). Although set D tephra has not been correlated to a known proximal/distal deposit, its glass bears the Glacier Peak glass compositional signature and its interpolated age (6060 cal. years BP) corresponds to the initiation of the set D eruptive period. The presence of Dusty Creek tephra in lake sediments across southern British Columbia and northern Washington State suggests a broad plume trajectory to the north and northeast. In contrast the apparent presence of the Glacier Peak A in only Cooley Lake in British Columbia and in lakes in Washington on the same linear trajectory suggests a narrow plume with a northeasterly direction.

Gavin, D. G.; Foit, F. F.; Hu, F.

2004-12-01

257

Paleozoic cratonal/miogeoclinal stratigraphy in the western Mojave Desert  

Energy Technology Data Exchange (ETDEWEB)

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

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

1991-02-01

258

Stratigraphy and tectonics of a time-transgressive ophiolite obduction onto the eastern margin of the Pelagonian platform from Late Bathonian until Valanginian time, exemplified in northern Evvoia, Greece  

Science.gov (United States)

The obduction of an ophiolite sheet onto the eastern Pelagonian carbonate platform complex of the Hellenides began during the Late Bathonian and ended with the final emplacement of the ophiolite during Valanginian time. The early stages of obduction caused subaerial exposure of the platform, recorded by an unconformity of Callovian age, which is marked by laterites overlying folded and faulted, karstic substrates. The laterites have distinct ophiolitic geochemical signatures, indicating that emergent ophiolite had been undergoing lateritic weathering. This unconformity coincides with widespread western Tethyan, Callovian gaps, indicating that the obduction in the Hellenides was probably related to far-reaching plate tectonic processes. Resumed gravitational pull and rollback of the subducted, oceanic leading edge of the temporarily exposed ophiolite. Platform drowning continued into Tithonian-Valanginian time, documented initially by reefal carbonates and then by below-CCD, carbonate-free radiolarian cherts and shales. Subsequently, siliciclastic turbidites, which apparently originated from uplifted Variscan basement, were deposited together with and over the radiolarite as the ophiolite nappe sheet advanced. The nappe substrate underwent tectonic deformations of varying intensity, while polymictic mélange and syntectonic sedimentary debris accreted beneath the ophiolite and at the nappe front. The provenience of the ophiolite nappe complexes of northern Evvoia most probably has to be looked for in the Vardar ocean.

Scherreiks, Rudolph; Meléndez, Guillermo; BouDagher-Fadel, Marcelle; Fermeli, Georgia; Bosence, Dan

2014-06-01

259

Biostratigraphic correlation of Pleistocene marine deposits and sea levels, Atlantic coastal plain of the southeastern United States  

Science.gov (United States)

Marine ostracodes from 50 localities were studied to determine the age and elevation of Pleistocene sea levels in the Atlantic coastal plain from Maryland to northern Florida. Using ostracode taxon and concurrent ranges, published planktic biostratigraphic, paleomagnetic, and radiometric data, ostracode assemblage zones representing early (1.8-1.0 my), middle (0.7-0.4 my), and late (0.3-0.01 my) Pleistocene deposition were recognized and used as a basis for correlation. Ostracode biofacies signifying lagoonal, oyster bank, estuarine, open sound, and inner sublittoral environments provided estimated ranges of paleodepths for each locality. From these data the following minimum and maximum Pleistocene sea-level estimates were determined for the southeastern coastal plain: late Pleistocene, 2-10 m from Maryland to northern Florida; middle Pleistocene, 6-15 m in northern South Carolina; early Pleistocene, 4-22 m in central North Carolina, 13-35 m in southern North Carolina, and 6-27 m in South Carolina. Climatically induced glacio-eustatic sea-level fluctuations adequately account for the late Pleistocene sea-level data, but other factors, possibly differential crustal uplift, may have complicated the early Pleistocene record. ?? 1980.

Cronin, T. M.

1980-01-01

260

A new Lower Pleistocene archeological site in Europe (Vallparadís, Barcelona, Spain)  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 r...

Marti?nez, Kenneth; Garcia, Joan; Carbonell, Eudald; Agusti?, Jordi; Bahain, Jean-jaques; Blain, Hugues-alexandre; Burjachs, Francesc; Ca?ceres, Isabel; Duval, Mathieu; Falgue?res, Christophe; Go?mez, Manuel; Huguet, Rosa

2010-01-01

 
 
 
 
261

The Pleistocene Gomphotheres (Proboscidea) from South America: Diversity, Habitats and Feeding Ecology  

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Gomphotheres were recorded in South America from the early-middle Pleistocene (Ensenadan Land-mammal Age) to the late Pleistocene (Lujanian Land-mammal Age). They arrived in South America during the “Great American Biotic Interchange”. Only two genera are recognised: Cuvieronius, which has only one species, Cuvieronius hyodon; and Stegomastodon, which has two species, Stegomastodon waringi and Stegomastodon platensis. The small Cuvieronius utilised the Andean corridor and it w...

Prado, J. L.; Alberdi Alonso, Mari?a Teresa; Azanza, B.; Sa?nchez Chillo?n, Begon?a; Frassinetti, D.

2001-01-01

262

Stratigraphical subdivision of the Middle Pleistocene glacigenic sequence of the Ivrea amphitheatre (Piedmont, NW Italy)  

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In the NW Italy southalpine plain the large (505 km2) Ivrea morainic amphitheatre (IA) develops at the outlet of the Dora Baltea River Valley. The IA forms a wide complex of lateral and terminal moraines and kame terraces, dated from the end of the Early Pleistocene (on paleomagnetic basis) to the end of the Late Pleistocene (14C radiometric and 10Be exposure ages). Some embedded paleosols and palustrine deposits within the glacial deposits, interpretable as interglacial layers, outcrop along...

Gianotti, Franco

2011-01-01

263

An Online Guide to Sequence Stratigraphy  

Science.gov (United States)

This online guide focuses primarily on the application of sequence stratigraphy to outcrops. Topics covered include sediment accumulation and the accommodation space equation, parasequences, stacking patterns, depositional sequences, surfaces, type I and type II sequences, application of this information to outcrops, chronostratigraphic applications and carbonate sequence stratigraphy. There are references for this material and a glossary of terms to use with this guide.

Holland, Steven

264

Late Triassic and Early Cretaceous sedimentary sequences of the northern Isfahan Province (Central Iran): stratigraphy and paleoenvironments / Paleoecología y paleogeografía de secuencias del Triásico Superior al Cretácico Inferior en el área de Isfahan (Irán central)  

Scientific Electronic Library Online (English)

Full Text Available SciELO Mexico | Language: English Abstract in spanish Este estudio provee de un esquema general de las secuencias del Triásico Superior y Cretáceo Inferior localizadas al norte de Isfahan, en el Centro de Irán. La formación Nayband del Triásico Superior está subdividida en los miembros Gelkan, Bidestan, Howz-e-Sheikh, Howz-e-Khan y Qadir. Dos niveles d [...] e biostroma están documentados en los miembros Bidestan y Howz-e-Khan. Debido a las condiciones favorables en el Triásico tardío que incluyeron luz, oxígeno y nutrientes, fauna como: corales, esponjas, hidrozoarios, bivalvos, gasterópodos, braquiópodos, equinodermos y Dicroidium prosperaron en el agua y la flora en tierra. La presencia de Heterastridium spp. en el nivel del Miembro Bidestan es aparentemente el primer registro de este taxón el Centro de Irán. El miembro Qadir tiene varios estratos índice, uno de ellos con flora terrestre Clathropteris spp., y tres estratos índice con el bivalvo Indopecten glabra, fechados como etapa Rhaetian. Una disconformidad angular se puede trazar entre los sedimentos Rhaetian, conglomerados rojos, y areniscas provenientes de Secuencias del Cretáceo inferior en el área de Isfahan que incluye a todas las rocas del Jurásico. Esta discontinuidad puede estar relacionada con la fase tectónica Cimmeriana. Abstract in english This research gives a general outline of the Upper Triassic and Lower Cretaceous sequences cropping out north of Isfahan, Central Iran. Upper Triassic Nayband Formation subdivided into the Gelkan, Bidestan, Howz-e-Sheikh, Howz-e Khan and Qadir members. Two biostromal levels are documented in the Bid [...] estan and Howz-e-Khan members. Due to a suitable condition in Late Triassic time including light, oxygen and nutrient, fauna such as: corals, sponges, hydrozoas, bivalves, gastropods, brachiopods, echinoderms and Dicroidium were fourished in water and flora on land. The first appearance of Heterastridium spp. in level of the Bidestan Member is apparently the first occurrence of this taxon in Central Iran. Qadir Member has several key beds, one key bed with land flora Clathropteris spp., and three key beds with bivalve Indopecten glabra, dating as Rhaetian Stage. An angular unconformity can be traced between Rhaetian sediments and red conglomerates and sandstones of Lower Cretaceous Sequences in Isfahan area which encompasses all Jurassic rocks. This gap can be related to Cimmerian tectonic phase.

Maryam, Mannani; Mehdi, Yazdi.

265

Presencia de Antifer ultra Ameghino (=Antifer niemeyeri Casamiquela (Artiodactyla, Cervidae en el Pleistoceno tardío-Holoceno temprano de Chile central (30-35°S Presence of Antifer ultra Ameghino (=Antifer niemeyeri Casamiquela in the late Pleistocene-early Holocene of Central Chile (30-35°S  

Directory of Open Access Journals (Sweden)

Full Text Available El presente trabajo discute el estatus taxonómico de la especie Antifer niemeyeri Casamiquela, 1984, definida a partir de astas completas procedentes de la laguna Taguatagua y la quebrada de Quereo (Pleistoceno tardío-Holoceno temprano, en Chile central (30-35°S. Se concluye, a partir de un estudio morfológico y morfométrico detallado, que Antifer niemeyeri debe ser considerado sinónimo de Antifer ultra Ameghino, 1889 dados los caracteres anatómicos compartidos con esta especie. Los resultados amplían la distribución geográfica del taxón, que previamente se registraba en Argentina, Uruguay y sur de Brasil, y confirman su biocrón para el Pleistoceno tardío-Holoceno temprano (edad Lu-janense, aun cuando las fechas radiocarbónicas de Chile central (ca. 9.900 años 14C AP corresponden a las más tardías para la especie. A la luz de la evidencia paleoclimática disponible, se vincula A ultra durante el Pleistoceno de Chile central a ambientes cálidos y abiertos. Considerando estos requerimientos, se discute su posible vía de ingreso al actual territorio chileno a través de corredores ubicados hacia el sur del macizo andino, y su coexistencia con Hippocamelus bisulcus Molina, 1782. De acuerdo a la información estratigráfica y paleoambiental, se postula que ambas especies habrían sido alopátridas, por lo menos en el área de estudio.This paper discusses the taxonomic status of Antifer niemeyeri Casamiquela, 1984, defined from complete antlers from Taguatagua lake and Quereo canyon, both located in central Chile (30-35°S. From a detailed morphological and moiphometrical study, it is concluded that Antifer niemeyeri should be considered synonymous with Antifer ultra Ameghino, 1889, due to the anatomical characters shared between both forms. These results expand the geographical distribution of this taxa previously recorded in Argentina, Uruguay and southern Brazil, confirming their late Pleistocene-early Holocene biochron, in spite the fact that radiocarbon dates obtained in central Chile (ca. 9.900 14C yr BP imply the youngest age for the species. According to the available paleoclimate evidence, A. ultra is linked to warm climate and an open landscape during the late Pleistocene of central Chile. Its possible routes of entry to central Chile through corridors located at the south of the Andean range and its coexistence with Hippocamelus bisulcus Molina, 1782, are also discussed. According to the stratigraphic and paleoenvironmental data we suggest that both species have been allopatric, at least in the study area.

Rafael Labarca E

2011-01-01

266

Presencia de Antifer ultra Ameghino (=Antifer niemeyeri Casamiquela) (Artiodactyla, Cervidae) en el Pleistoceno tardío-Holoceno temprano de Chile central (30-35°S) / Presence of Antifer ultra Ameghino (=Antifer niemeyeri Casamiquela) in the late Pleistocene-early Holocene of Central Chile (30-35°S)  

Scientific Electronic Library Online (English)

Full Text Available SciELO Chile | Language: Spanish Abstract in spanish El presente trabajo discute el estatus taxonómico de la especie Antifer niemeyeri Casamiquela, 1984, definida a partir de astas completas procedentes de la laguna Taguatagua y la quebrada de Quereo (Pleistoceno tardío-Holoceno temprano), en Chile central (30-35°S). Se concluye, a partir de un estudi [...] o morfológico y morfométrico detallado, que Antifer niemeyeri debe ser considerado sinónimo de Antifer ultra Ameghino, 1889 dados los caracteres anatómicos compartidos con esta especie. Los resultados amplían la distribución geográfica del taxón, que previamente se registraba en Argentina, Uruguay y sur de Brasil, y confirman su biocrón para el Pleistoceno tardío-Holoceno temprano (edad Lu-janense), aun cuando las fechas radiocarbónicas de Chile central (ca. 9.900 años 14C AP) corresponden a las más tardías para la especie. A la luz de la evidencia paleoclimática disponible, se vincula A ultra durante el Pleistoceno de Chile central a ambientes cálidos y abiertos. Considerando estos requerimientos, se discute su posible vía de ingreso al actual territorio chileno a través de corredores ubicados hacia el sur del macizo andino, y su coexistencia con Hippocamelus bisulcus Molina, 1782. De acuerdo a la información estratigráfica y paleoambiental, se postula que ambas especies habrían sido alopátridas, por lo menos en el área de estudio. Abstract in english This paper discusses the taxonomic status of Antifer niemeyeri Casamiquela, 1984, defined from complete antlers from Taguatagua lake and Quereo canyon, both located in central Chile (30-35°S). From a detailed morphological and moiphometrical study, it is concluded that Antifer niemeyeri should be co [...] nsidered synonymous with Antifer ultra Ameghino, 1889, due to the anatomical characters shared between both forms. These results expand the geographical distribution of this taxa previously recorded in Argentina, Uruguay and southern Brazil, confirming their late Pleistocene-early Holocene biochron, in spite the fact that radiocarbon dates obtained in central Chile (ca. 9.900 14C yr BP) imply the youngest age for the species. According to the available paleoclimate evidence, A. ultra is linked to warm climate and an open landscape during the late Pleistocene of central Chile. Its possible routes of entry to central Chile through corridors located at the south of the Andean range and its coexistence with Hippocamelus bisulcus Molina, 1782, are also discussed. According to the stratigraphic and paleoenvironmental data we suggest that both species have been allopatric, at least in the study area.

Labarca E, Rafael; Alcaraz, M. Alejandra.

267

On the Pleistocene extinctions of Alaskan mammoths and horses  

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The fossil record has been used to shed light on the late Pleistocene megafaunal extinctions in North America and elsewhere. It is therefore important to account for variability due to the incompleteness of the fossil record and error in dating fossil remains. Here, a joint confidence region for the extinction times of horses and mammoths in Alaska is constructed. The results suggest that a prior claim that the extinction of horses preceded the arrival of humans cannot be made with confidence.

Solow, Andrew R.; Roberts, David L.; Robbirt, Karen M.

2006-01-01

268

Late Quaternary faulting in Clayton Valley, Nevada: Implications for distributed deformation in the eastern California shear zone-Walker Lane  

Science.gov (United States)

The Walker Lane is a key component of the Pacific-North America plate boundary. This transtensional region of right lateral strike-slip and normal faulting accommodates ~25% of the total relative motion between the Pacific and North American plates. Recent studies indicate a discrepancy between short- and long-term rates of right-lateral shear in the Walker Lane with geodetic measurements of ~9.3 mm/yr being more than double the late Pleistocene geologic rate of Clayton Valley fault system of the Silver Peak-Lone Mountain extensional complex (SPLM) is a prime candidate to account for part of the “missing” strain in the Walker Lane due to its dominantly down-to-the-NW orientation, which ultimately accommodates right lateral shear in the region. The distribution of late Quaternary faults and alluvial fan deposits in Clayton Valley was determined through detailed geologic mapping (1:10,000 scale), which resulted in eight individual units that are consistent with the well-established western U.S. alluvial stratigraphy. Differential GPS was used to survey the prominent normal fault scarps displacing the fan deposits and cosmogenic nuclide (TCN) geochronology depth profile samples were collected from four units (Q2b, Q2c, Q2d, and Q3a). Displacement measured from the scarp profiles combined with TCN ages of the deformed fans will allow us to determine extension rates over multiple late Pleistocene time scales. Analysis of the Clayton Valley extension rates coupled with those from nearby structures, such as the Lone Mountain and Lida faults, will help determine if slip along these extensional faults can account for the observed discrepancy between short- and long-term rates of deformation along this important component of the Pacific-North America plate boundary.

Foy, T. A.; Lifton, Z. M.; Frankel, K. L.; Johnson, C.

2010-12-01

269

Fragilariopsis diatom evolution in Pliocene and Pleistocene Antarctic shelf sediments  

Science.gov (United States)

The late Pliocene – early Pleistocene sediment record in the AND-1B core from the McMurdo Sound, Ross Sea, Antarctica, displays a rich diversity and high abundance of diatoms, including several new morphologies within the genus Fragilariopsis. These new morphologies exhibit similarities to the extinct late Miocene/early Pliocene species Fragilariopsis aurica Gersonde and Fragilariopsis praecurta Gersonde, as well as to the modern sea ice-associated species Fragilariopsis ritscheri Hustedt and Fragilariopsis obliquecostata van Heurck. From the diverse morphologies present, we use light microscopy and scanning electron microscopy to identify and describe the characteristics of three new taxa, Fragilariopsis laqueata Riesselman, Fragilariopsis bohatyi Sjunneskog et Riesselman, and Fragilariopsis robusta Sjunneskog, which are common in the diatom-bearing intervals from ~3.2 to 1.95 Ma. Comparisons with extant and extinct species are made to assess possible environmental affinities, evolutionary relationships, and potential for future biostratigraphic utility. This complex of newmorphologies diversified as conditions cooled during the Pliocene, then went into decline as heavy sea ice conditions of the Pleistocene were established. Only the lineage of F. robusta appears to continue into the late Pleistocene, where it is interpreted to have evolved into F. obliquecostata.

Sjunneskog, Charlotte; Riesselman, Christina; Winter, Diane; Scherer, Reed

2012-01-01

270

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 SciELO Argentina | Language: Spanish 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 glacilacustres, 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 li [...] nk among them verified on some specific palaeoheight levels. In this research, paleo-bathymetric geoindicators, as relative height of glaci-lacustrine, coastal sand and fandelta 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.

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

271

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  

Scientific Electronic Library Online (English)

Full Text Available SciELO Argentina | Language: Spanish Abstract in spanish 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 natural [...] es 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. Abstract in english 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 form [...] ed 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.

272

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 SciELO Argentina | Language: Spanish 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 cen [...] tro-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 ( 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 f [...] or 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 subfu

Kröhling, Daniela; Orfeo, Oscar.

273

Mechanics of wind ripple stratigraphy.  

Science.gov (United States)

Stratigraphic patterns preserved under translating surface undulations or ripples in a depositional eolian environment are computed on a grain by grain basis using physically based cellular automata models. The spontaneous appearance, growth, and motion of the simulated ripples correspond in many respects to the behavior of natural ripples. The simulations show that climbing strata can be produced by impact alone; direct action of fluid shear is unnecessary. The model provides a means for evaluating the connection between mechanical processes occurring in the paleoenvironment during deposition and the resulting stratigraphy preserved in the geologic column: vertical compression of small laminae above a planar surface indicates nascent ripple growth; supercritical laminae are associated with unusually intense deposition episodes; and a plane erosion surface separating sets of well-developed laminae is consistent with continued migration of mature ripples during a hiatus in deposition. PMID:17816833

Forrest, S B; Haff, P K

1992-03-01

274

El registro más completo de un Hoplophorini (Xenarthra: Glyptodontidae) para los Pisos/Edades Chapadmalalense-Marplatense (Plioceno tardío-Pleistoceno temprano) / The most complete record of a Hoplophorini (Xenarthra: Glyptodontidae) for the Chapadmalalan-Marplatan Stages (Late Pliocene-Early Pleistocene)  

Scientific Electronic Library Online (English)

Full Text Available SciELO Argentina | Language: Spanish Abstract in spanish Los Glyptodontidae del Neógeno tardío (Pisos/Edades Chapadmalalense-Marplatense; ca. 3.9-1.8 Ma) constituyen un grupo escasamente conocido, en tanto la mayoría de los registros están limitados a restos aislados de la coraza dorsal y/o caudal. Las únicas excepciones están representadas por Paraglypto [...] don chapalmalensis (Ameghino in Rovereto), un fósil guía para el Chapadmalalense superior, y el Plohophorini Plohophorus figuratus Ameghino. Por otro lado, los "Hoplophorinae" Hoplophorini son gliptodontes que tienen sus primeros registros durante los Pisos Huayqueriense (Mioceno tardío) y "Araucanense" (Mioceno tardío-Plioceno), pero están prácticamente ausentes durante los Pisos Chapadmalalense-Marplatense (Plioceno-Pleistoceno temprano). Posteriormente, los Hoplophorini (Neosclerocalyptus Paula Couto) son, junto con Glyptodon Owen, los Glyptodontidae de registro más frecuente en el Pleistoceno de América del Sur. En esta contribución damos a conocer el primer registro de un Hoplophorini de antigüedad Chapadmalalense, asignado al género Eosclerocalyptus C. Ameghino (Eosclerocalyptus cf. E. lineatus). Este nuevo material, representado por una coraza dorsal, fue exhumado de la sección superior de la Fm. Chapadmalal, Mar del Plata, provincia de Buenos Aires. Desde una perspectiva morfológica, esta coraza presenta un tamaño intermedio entre E. tapinocephalus Cabrera, E. proximus (Moreno & Mercerat) y Neosclerocalyptus Paula Couto. Junto con cf. Paraglyptodon chapalmalensis y Plohophorus figuratus Ameghino, estos registros representan los Glyptodontidae Pliocenos más completos que se conocen; a su vez, completa parcialmente la distribución estratigráfica de los Glyptodontidae Hoplophorini. Abstract in english The late Neogene (Chapadmalalan-Marplatan Stages; ca. 3.9-1.8 Ma) Glyptodontidae from southern South America are poorly known since most of the record are limited to remains of the dorsal and/or caudal armour. In this sense, the exceptions are represented by Paraglyptodon chapadmalensis (Ameghino in [...] Rovereto), a fossil guide of the Upper Chapadmalalan Stage, and the Plohophorini Plohophorus figuratus Ameghino. On the other hand, the "Hoplophorinae" Hoplophorini are glyptodonts that have its first records during the Huayquerian (late Miocene) and "Araucanian" Stages (late Miocene-early Pliocene), but they are almost absents during the Chapadmalalan-Marplatan Stages (Pliocene-early Pleistocene). Later, the Hoplophorini (Neosclerocalyptus Paula Couto) are, together with Glyptodon Owen, the most common South American Pleistocene Glyptodontidae. In this contribution we report the first record of a Chapadmalalan Hoplophorini, assigned to the genus Eosclerocalyptus C. Ameghino (Eosclerocalyptus cf. E. lineatus), coming from the Mar del Plata locality, Buenos Aires province (Argentina). This new material, represented by a complete dorsal carapace, was exhumed from the upper section of the Chapadmalalan Formation. From a morphological perspective, this dorsal carapace shows an intermediate size between E. tapinocephalus Cabrera, E. proximus (Moreno & Mercerat) and Neosclerocalyptus Paula Couto. Together with cf. Paraglyptodon chapadmalensis and Plohophorus figuratus Ameghino those records represents the most entire Pliocene Glyptodontidae known and, in addition, it partially complete the stratigraphical distribution of the Glyptodontidae Hoplophorini.

Alfredo E, Zurita; Cristian, Oliva; Alejandro, Dondas; Esteban, Soibelzon; Federico I, Isla.

275

El registro más completo de un Hoplophorini (Xenarthra: Glyptodontidae para los Pisos/Edades Chapadmalalense-Marplatense (Plioceno tardío-Pleistoceno temprano The most complete record of a Hoplophorini (Xenarthra: Glyptodontidae for the Chapadmalalan-Marplatan Stages (Late Pliocene-Early Pleistocene  

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Full Text Available Los Glyptodontidae del Neógeno tardío (Pisos/Edades Chapadmalalense-Marplatense; ca. 3.9-1.8 Ma constituyen un grupo escasamente conocido, en tanto la mayoría de los registros están limitados a restos aislados de la coraza dorsal y/o caudal. Las únicas excepciones están representadas por Paraglyptodon chapalmalensis (Ameghino in Rovereto, un fósil guía para el Chapadmalalense superior, y el Plohophorini Plohophorus figuratus Ameghino. Por otro lado, los "Hoplophorinae" Hoplophorini son gliptodontes que tienen sus primeros registros durante los Pisos Huayqueriense (Mioceno tardío y "Araucanense" (Mioceno tardío-Plioceno, pero están prácticamente ausentes durante los Pisos Chapadmalalense-Marplatense (Plioceno-Pleistoceno temprano. Posteriormente, los Hoplophorini (Neosclerocalyptus Paula Couto son, junto con Glyptodon Owen, los Glyptodontidae de registro más frecuente en el Pleistoceno de América del Sur. En esta contribución damos a conocer el primer registro de un Hoplophorini de antigüedad Chapadmalalense, asignado al género Eosclerocalyptus C. Ameghino (Eosclerocalyptus cf. E. lineatus. Este nuevo material, representado por una coraza dorsal, fue exhumado de la sección superior de la Fm. Chapadmalal, Mar del Plata, provincia de Buenos Aires. Desde una perspectiva morfológica, esta coraza presenta un tamaño intermedio entre E. tapinocephalus Cabrera, E. proximus (Moreno & Mercerat y Neosclerocalyptus Paula Couto. Junto con cf. Paraglyptodon chapalmalensis y Plohophorus figuratus Ameghino, estos registros representan los Glyptodontidae Pliocenos más completos que se conocen; a su vez, completa parcialmente la distribución estratigráfica de los Glyptodontidae Hoplophorini.The late Neogene (Chapadmalalan-Marplatan Stages; ca. 3.9-1.8 Ma Glyptodontidae from southern South America are poorly known since most of the record are limited to remains of the dorsal and/or caudal armour. In this sense, the exceptions are represented by Paraglyptodon chapadmalensis (Ameghino in Rovereto, a fossil guide of the Upper Chapadmalalan Stage, and the Plohophorini Plohophorus figuratus Ameghino. On the other hand, the "Hoplophorinae" Hoplophorini are glyptodonts that have its first records during the Huayquerian (late Miocene and "Araucanian" Stages (late Miocene-early Pliocene, but they are almost absents during the Chapadmalalan-Marplatan Stages (Pliocene-early Pleistocene. Later, the Hoplophorini (Neosclerocalyptus Paula Couto are, together with Glyptodon Owen, the most common South American Pleistocene Glyptodontidae. In this contribution we report the first record of a Chapadmalalan Hoplophorini, assigned to the genus Eosclerocalyptus C. Ameghino (Eosclerocalyptus cf. E. lineatus, coming from the Mar del Plata locality, Buenos Aires province (Argentina. This new material, represented by a complete dorsal carapace, was exhumed from the upper section of the Chapadmalalan Formation. From a morphological perspective, this dorsal carapace shows an intermediate size between E. tapinocephalus Cabrera, E. proximus (Moreno & Mercerat and Neosclerocalyptus Paula Couto. Together with cf. Paraglyptodon chapadmalensis and Plohophorus figuratus Ameghino those records represents the most entire Pliocene Glyptodontidae known and, in addition, it partially complete the stratigraphical distribution of the Glyptodontidae Hoplophorini.

Alfredo E Zurita

2011-06-01

276

Paleosuelos y niveles límnicos desarrollados en sucesiones aluviales del Pleistoceno tardío y Holoceno del Piedemonte Andino de Mendoza (33°-34° ls), Argentina / Paleosoils and limnic levels in the late Pleistocene and Holocene alluvial successions of the Andean Piedmont of Mendoza (33°-34° LS), Argentina  

Scientific Electronic Library Online (English)

Full Text Available SciELO Argentina | Language: Spanish Abstract in spanish Los depósitos aluviales del Pleistoceno tardío y Holoceno de la cuenca del Arroyo La Estacada, en el piedemonte andino mendocino, entre los 33° y 34° LS, componen tres unidades geomorfológicas conspicuas: una planicie de agradación regional (PAR, Pleistoceno tardío - Holoceno temprano), una terraza [...] de relleno aluvial (TRA, Holoceno medio y tardío) y la planicie de inundación actual (posterior a los 400 a AP). La PAR y la TRA registran procesos alternantes de agradación y pedogénesis, siendo estos últimos más frecuentes en los depósitos holocenos, caracterizados también por una mayor abundancia de niveles con contenido orgánico elevado (niveles límnicos). Este trabajo evalúa el registro de paleosuelos y niveles límnicos de la cuenca, con el objetivo de inferir sus implicancias en la dinámica paleoambiental y paleoclimática de la región centrooeste de Argentina durante el Pleistoceno tardío y Holoceno, y aportar información al marco paleoclimático del extremo sur de Sudamérica. Se muestrearon depósitos aluviales que exhiben paleosuelos y niveles límnicos en cuatro perfiles litoestratigráficos en las márgenes del Arroyo La Estacada y su tributario el Arroyo Anchayuyo; se utilizó el color como indicador de campo. Se describieron atributos en forma cualitativa (granulometría, color; consistencia, tipo y grado de estructuración de los sedimentos; forma y tipo de límites, sustancias cementantes y/o aglutinantes, rasgos redoximórficos, etc) y cuantitativa (contenido de materia orgánica y carbonato de calcio); se realizaron análisis micromorfológicos en muestras de sedimentos no disturbadas. Los resultados se presentan con un criterio cronológico decreciente basado en la calibración cronológica de los depósitos aluviales. Los paleosuelos de la PAR revelan un pobre desarrollo pedológico, con presencia de carbonato de calcio en la masa, y en forma de nódulos y concreciones. Por su parte, los paleosuelos de la TRA presentan mayor desarrollo relativo, y ausencia de carbonatos en general. Los niveles límnicos reflejan un incremento en la productividad vegetal en ambientes de la planicie de inundación saturados en agua; y quizás también un mayor transporte de MO por parte de las corrientes de agua en el valle fluvial. La mayor concentración de rasgos de carbonatación de la PAR reflejaría condiciones de mayor evaporación en los ambientes depositacionales del Pleistoceno tardío - Holoceno temprano; mientras que la abundancia de rasgos redoximórficos en los niveles de la TRA, registraría la saturación en agua de los depósitos del Holoceno medio y tardío, quizás en respuesta a frecuentes fluctuaciones del nivel freático. Las sucesiones aluviales analizadas registran los cambios paleoambientales / paleoclimáticos acaecidos en el piedemonte andino oriental entre los 33° y 34° LS, en vinculación con la transición climática del Pleistoceno tardío - Holoceno. Los paleosuelos y niveles límnicos observados resultaron herramientas útiles para la calibración geocronológica de las sucesiones aluviales estudiadas. Abstract in english The late Pleistocene and Holocene alluvial deposits of the Arroyo La Estacada basin, located in the Andean piedmont of Mendoza province between 33° and 34° SL (Fig. 1a-b), are arranged in three conspicuous geomorphological units, a regional aggradational plain (RAP, late Pleistocene - early Holocene [...] ), a fill terrace (FT, middle and late Holocene) and a present floodplain (developed ca. 400 yr BP) (A-A', B-B', Fig. 1c). The RAP (Figs. 2a, 3a) and the FT (Figs. 2b, 3b) record aggradational and pedological proccesses; the latter are more frequents in the Holocene deposits together with abundant sedimentary levels showing high organic matter content (limnic levels). High organic matter content deposits have been studied by the international scientific community, particularly in North America, where some authors discussed the paleoenvironmental and paleoclimatic imp

Adriana, Mehl; Marcelo, Zárate.

277

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 delta"1"3C shift at 6.2 Ma was a time-stratigraphic event. The average deep-water metabolic CO_2 and nutrient content remained unchanged across the delta"1"3C 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"0C warmer if constant ice volume is assumed. (Auth.)

1981-01-01

278

Uranium series ages of corals from the upper Pleistocene Mulege terrace, Baja California Sur, Mexico  

Energy Technology Data Exchange (ETDEWEB)

Specimens of Porites californica contained in the sediments of upper Pleistocene, +12-m marine terrace deposits developed on the east coast of the Baja California (Mexico) peninsula at Mulege have yielded /sup 239/Th//sup 234/U dates of 124 +/- 5 and 144 +/- 7 ka (+/- 1 sigma). These dates can be assigned to the well-documented late Pleistocene oxygen-isotope stage 5e high sea stand. Differences between the eustatic and present elevations of this terrace indicate average uplift rates since terrace formation of approximately 4 to 5 cm/1000 yr, indicating a relative stability and lack of major vertical deformation since the late Pleistocene. This terrace in the Mulege area can now be correlated with other marine terraces throughout the Baja California peninsula and southern California.

Ashby, J.R.; Ku, T.L.; Minch, J.A.

1987-02-01

279

A ~276 years cyclicity of western pacific coastal upwelling during Late Pleistocene (Termination I) and Holocene as revealed by the microscale facies and elemental analysis of the varved record of Saanich Inlet, BC  

Science.gov (United States)

Using core MD02-2490, recovered by the French research ship, RV Marion Dufresne, from the central basin of Saanich Inlet, BC, the last glacial-to-interglacial transition (Termination I) and Holocene laminated marine sediments of Saanich Inlet, BC, were characterized to infer the sedimentary processes responsible for their deposition, their sedimentary environments, and their provenance (i.e. source). This is achieved by examining sedimentary facies from thin-sections using backscattered scanning electron imagery (BSEI) and Energy Dispersive Spectrometry (EDS) coupled with a Scanning Electron Microscope (SEM), and an Itrax™ micro-XRF core scanner. The elemental intensities obtained by the Itrax™ micro-XRF core scanner showed - 27 abrupt changes in elemental ratios throughout the selected periods throughout the Termination I and Holocene along core MD02-2490, of which eleven peaks demonstrate abrupt increases in both Mn/Ti and Fe/Ti (10469, 100385, 10070, 9923, 8474, 8005, 7672, 5171, 4996, 4585, and 2420 C14 cal yr BP). All eleven peaks correspond with anomalous increases in Ca/Ti and Sr/Ca ratios and most of them are consistent with low gray values and Compton and Rayleigh scattering ratios (inc/coh). These chemical and physical property changes of the sediment (mineralogy and grain size-related density) suggest occurrences of deepwater flushing events associated with a basin slope failure. Indeed, in Saanich Inlet, coastal upwellings eventually cause an overturning of the bottom water, providing abundant oxygen and nutrients to the stagnant bottom water. Peaks of Mn/Ti and Fe/Ti (indicators of manganese and Iron oxides) are expected in abruptly oxygenated bottom waters, and peaks of Ca/Ti (indicators of manganese carbonate) seems to point to a abrupt enrichment of CaCO3 (only available in shallowest parts of the basin) mixed with the sediment pore water. The possible mechanisms to cause these abrupt transitions may be related to coastal upwelling. The occurrences of these events are roughly every 276 years, except between 4585 and 2420 C14 cal yr BP where no elemental data is obtained, and between 9923 and 8474 C14 cal yr BP when sediments are significantly disturbed. Furthermore, coupling of EDS and image analyses illustrates that there is evidence of a shift in precipitation season during the Holocene. Illite appearance, which suggests a Fraser Lowland provenance, shifts from late winter in the early Holocene to early spring in the mid-Holocene, indicating a change in the timing of major snowmelt events. Micro-scale sediment analyses, including sediment facies, processes, and chemical compositions, are proved to be efficient tools for analyzing and assessing sediment provenance.

Kanamaru-Shinn, K.; Francus, P.; Jercinovic, M. J.

2009-12-01

280

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

 
 
 
 
281

Middle Pleistocene to Holocene fluvial terrace development and uplift-driven valley incision in the SE Carpathians, Romania  

Science.gov (United States)

This study reveals that in the SE Carpathians terrace development and fluvial incision during the Middle Pleistocene-Holocene are predominantly controlled by tectonic uplift as shown by terrace distributions and uplift amounts and rates. The work focuses on a transect from the internal nappes and Bra?ov intramontane basin (western domain) to the external nappes and Foc?ani foredeep basin (eastern domain). New infrared stimulated luminescence ages were obtained and minimum terrace formation ages were determined to derive fluvial incision rates, and thereby, to constrain tectonic uplift. In the eastern domain, non-uniform terrace distributions in adjacent sub-parallel more active Punta and less active ?u?i?a rivers and an eastward migrated fluvial incision from the orogen to the foredeep basin indicate tectonic uplift as dominant control on terrace development. Strath-terraces in the western and eastern domains indicate repeated events of vertical fluvial incision and lateral erosion during the early Middle Pleistocene and late Middle Pleistocene-Holocene, respectively. These events imply successive recurrent disturbances of equilibrium conditions due to pulses of increased tectonic uplift. Fill-terraces in the western domain show that initial aggradation periods were followed by uplift-driven vertical incision during the late Middle-Late Pleistocene. As fill-terraces show a wide-spread development, climatic change and complex response cannot be excluded as contributing factors. Synchronous to terrace development, loess deposition periods during the late Middle-Late Pleistocene and Latest Pleistocene and intercalated episodes of palaeosol formation during the Late Pleistocene imply comparable climatic conditions across the SE Carpathians. Dominant strath-terraces of the eastern domain indicate stronger fluvial incision (~ 240 m) since the late Middle Pleistocene, whereas older strath- and younger dominant fill-terraces of the western domain designate a lower amount (~ 90 m) since the early Middle Pleistocene. Middle Pleistocene-Holocene fluvial incision rates document higher tectonic uplift in the external nappes and lower towards the western intramontane and eastern foredeep basins.

Necea, D.; Fielitz, W.; Kadereit, A.; Andriessen, P. A. M.; Dinu, C.

2013-08-01

282

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 SciELO Mexico | Language: Spanish 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 expansi [...] ón de condiciones semiáridas al noreste de dicho sistema. La Formación Tezanos Pinto es la unidad loéssica típica del Pleistoceno tardío - Holoceno temprano de la Pampa 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 result 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.

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

283

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

2012-06-01

284

Late Quaternary activity along the Scorciabuoi Fault (Southern Italy as inferred from electrical resistivity tomographies  

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Full Text Available The Scorciabuoi Fault is one of the major tectonic structures affecting the Southern Apennines, Italy. Across its central sector, we performed several electrical resistivity tomographies with different electrode spacing (5 and 10 m and using a multielectrode system with 32 electrodes. All tomographies were acquired with two different arrays, the dipole-dipole and the Wenner-Schlumberger. We also tested the different sensitivity of the two arrays with respect to the specific geological conditions and research goals. Detailed geological mapping and two boreholes were used to calibrate the electrical stratigraphy. In all but one tomography (purposely performed off the fault trace, we could recognise an abrupt subvertical lateral variation of the main sedimentary bodies showing the displacement and sharp thickening of the two youngest alluvial bodies in the hanging-wall block. These features are interpreted as evidence of synsedimentary activity of the Scorciabuoi Fault during Late Pleistocene and possibly as recently as Holocene and allow accurate location of the fault trace within the Sauro alluvial plain.

A. Loperte

2007-06-01

285

Tephrochronology of rare Plio-Pleistocene fossiferous strata in south-central Afar, Ethiopia  

Science.gov (United States)

Sedimentary basins in the south and central Afar Depression archive the complex structural, climatic, volcanic, and biologic development of the region during the Pliocene and Pleistocene. The lower Awash Valley in central Afar has long served as a focus for these investigations, including the extensive work conducted to place fossil assemblages (including hominins) into stratigraphic and temporal context. Here we present a detailed analysis of tephra chemistry, correlations, and ages of the newly mapped and fossiliferous area of eastern Ledi-Geraru (ELG) in the lower Awash Valley (~3-2.5 Ma). Our results allow us to construct a tephrostratigraphic framework that provides important constraints for regional studies previously lacking a calibrated sedimentary record spanning 3 to 2.7 Ma. Based on glass chemistry and morphology, 40Ar/39Ar dating of feldspars, and stratigraphic mapping, we identified 23 distinct tephras (8 of which were dated) in >100 m of newly mapped fluvial and lacustrine sediments at ELG. The oldest tuff at ELG (Kuhulta Tuff; 2.994 Ma) is exposed in lake sediments (diatomite) that lie 3-5 m above basalt flows dated to ca. 3 Ma. The youngest ELG tephra (ca. 2.44 Ma) outcrops as a lenticular channel tuff in sediments faulted against older strata (~2.7 Ma). Between these two tephras lies the Gurumaha Tuff (ca. 2.82 Ma) and the Daáma and Bulinan Tuffs (both ca. 2.85 Ma), which provide excellent stratigraphic ties across a distance of 7.5 km, allowing us to document a lateral facies change from lacustrine in northern ELG to more nearshore in the south. These tuffs also confirm the presence of a fossiferous sedimentary record spanning the late Pliocene sedimentary gap in lower Awash Valley stratigraphy (ca. 2.94 - 2.7 Ma). While the youngest and oldest tephras at ELG temporally overlap with dated tephras from the well-described Hadar (3.8 - 2.94 Ma) and Busidima (2.7 - 0.016 Ma) Formations, we have yet to confirm geochemical correlates to any tephra layer external to ELG. Our work provides an exciting opportunity to examine local basin structure and its influences on paleogeography, test proposed links between biotic events and global/regional climate change, and to study sediments that may help resolve long-standing evolutionary questions about the origin of our genus, Homo.

DiMaggio, E.; Arrowsmith, R.; Campisano, C. J.; Deino, A. L.

2013-12-01

286

Role of regional extension and uplift in the Plio-Pleistocene evolution of the Aksu Basin, SW Turkey  

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The Aksu Basin, within the Isparta Angle area of SW Turkey, documents Plio-Pleistocene crustal processes at the interface between the Tauride Mountains and the Eastern Mediterranean Sea. Basin sedimentation began in the Late Miocene, following an earlier history of emplacement of Mesozoic allochthonous units (Antalya Complex), Miocene basin development and localized Late Miocene compression (Aksu Phase). Late Miocene–Early Pliocene transtension deformed the Aksu Basin, exploiting pre-existi...

Glover, Clare P.; Robertson, Alastair H. F.

1998-01-01

287

Entrampamientos en la Formación Luján (Pleistoceno tardío): Análisis tafonómico de un espécimen de Hippidion Owen de la cuenca del río Salado (provincia de Buenos Aires, Argentina) / Miring In The Lujan Formation (Late Pleistocene): Taphonomic Analysis Of A Specimen Of Hippdion Owen From The Salado River Basin (Buenos Aires Province, Argentina)  

Scientific Electronic Library Online (English)

Full Text Available SciELO Argentina | Language: Spanish Abstract in spanish Se da a conocer un interesante hallazgo de un espécimen de Hippidion en sedimentos referidos al Miembro Guerrero de la Formación Luján (Pleistoceno tardío) del noreste de la provincia de Buenos Aires. Se considera preliminarmente, que el nivel portador representa un ambiente de depositación similar [...] a las actuales planicies de inundación mal drenadas. El análisis de diversos atributos tafonómicos (e.g. posición, grado de articulación, moldes de tejidos blandos) permiten considerar que la incorporación del espécimen mediante un proceso de entrampamiento, lo que además produjo la muerte del animal. La información paleoautoecológica disponible del taxón, permite considerar la posibilidad de que el ambiente de acumulación del espécimen, haya sido un hábitat utilizado regularmente por el taxón. La reconstrucción de la trayectoria tafonómica de este espécimen, supone que al menos algunos sitios de la planicie de inundación funcionaron como trampas. La presencia de este modo tafonómico en la cuenca del río Salado, es de relevancia ya que por un lado da cuenta de cierta abundancia de esqueletos relativamente completos y articulados, y por otro evidencia un posible sesgo tafonómico relacionado con la regularidad en que fue utilizado dicho ambiente por cada taxón. Abstract in english The interesting finding of a Hippidion specimen in sediments referred to the Guerrero Member of the Luján Formation (late Pleistocene) in northeast Buenos Aires Province is reported. Preliminary considerations indicate that the bearing level represents a deposition environment similar to existing po [...] orly-drained flood plains. Analysis of several taphonomic characteristics (e.g. position, degree of articulation, soft tissue molds) allows considering that the specimen was incorporated through swamp-miring that also led to its death. Available palaeoautoecological information for this taxon allows the possibility that the accumulation environment of this specimen was a habitat used regularly by the taxon. Reconstruction of the taphonomic path of this specimen admits the assumption that at least some parts of the floodplain could have worked as swamp-miring sites. The occurrence of this taphonomic mode in the Salado River Basin is particularly relevant because it accounts for the relative abundance of relatively complete and well-articulated skeletons, and it also evidences possible taphonomic bias related to the frequency of use of this environment by each taxon.

Lucas H, Pomi.

288

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 SciELO Mexico | Language: Spanish 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 mi [...] xta 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 comparaciones 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 equi [...] ds 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 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.

289

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

2009-10-01

290

Importance of active tectonics during karst formation. A Middle Eocene to Pleistocene example of the Lina Moutains (Irian Jaya, Indonesia)  

Science.gov (United States)

The Lina Moutains show a typical example of karst formation associated to recent and active tectonics. The limestone samples were collected from giant potholes present beneath the heavy rainforest, during speleological expeditions to the Bird's Head of Irian-Jaya. Micropalaeontological data allow us to give a Middle Pleistocene age for the most recent karst formation. A detailed stratigraphy between the Upper Lutetian and the Middle Pleistocene was recorded, with tectonic events during the Oligocene and Pleistocene. The edge of the resurgence layer was also dated. We also conclude the probable existence of a subterraneous network downhill of the karst within the most recent levels of the Kais Limestone formation. We replace this formation within the tectonic evolution of this area between the Eocene and the Middle Pleistocene, in conjunction with the oblique convergence of the Pacific plate carrying volcanic arc fragments and the Australian margin, which resulted in folding, normal faulting associated with local extension, and wrench motion, which are settings capable of creating uplift of the carbonated platform.

Thery, J.-M.; Pubellier, M.; Thery, B.; Butterlin, J.; Blondeau, A.; Adams, C. G.

1999-05-01

291

Glaciers and rivers: Pleistocene uncoupling in a Mediterranean mountain karst  

Science.gov (United States)

Large-scale coupling between headwater catchments and downstream depocentres is a critical influence on long-term fluvial system behaviour and on the creation of the fluvial sedimentary record. However, it is often difficult to examine this control over multiple Quaternary glacial cycles and it has not been fully explored in karst basins. By investigating the Pleistocene glacial and fluvial records on and around Mount Orjen (1894 m) in Montenegro, we show how the changing connectivity between glaciated mountain headwater source zones and downstream alluvial basins is a key feature of long-term karst system behaviour - especially in relation to the creation and preservation of the surface sedimentary record. Middle and Late Pleistocene glacial deposits are well preserved on Mount Orjen. Uranium-series dating of 27 carbonate cements in fluvial sediments shows that many alluvial depocentres were completely filled with coarse glacial outwash before 350 ka during the largest recorded glaciation. This major glaciation is correlated with the Skamnellian Stage in Greece and Marine Isotope Stage 12 (MIS 12, c 480-420 ka). This was a period of profound landscape change in many glaciated catchments on the Balkan Peninsula. Later glaciations were much less extensive and sediment supply to fluvial systems was much diminished. The extreme base level falls of the Late Miocene produced the world's deepest karst networks around the Mediterranean. After MIS 12, the subterranean karst of Mount Orjen formed the dominant pathway for meltwater and sediment transfer so that the depositional basins below 1000 m became disconnected (uncoupled) from the glaciated headwaters. There is little evidence of post-MIS 12 aggradation or incision in these basins. This absence of later Pleistocene and Holocene fluvial activity means these basins contain some of the thickest and best-preserved outwash deposits in the Mediterranean.

Adamson, K. R.; Woodward, J. C.; Hughes, P. D.

2014-06-01

292

Thermoluminescence dating of pleistocene sediments  

International Nuclear Information System (INIS)

After a short introduction on recent trends in quaternary geochronology, this article focuses on the thermoluminescence (TL) dating of sediments, whose principles, present limits and prospects are discussed. Results are presented for TL behavior of sands from various geological contexts in Brazil. They show that the coarse (approx. 100-200 ?m) quartz fraction of coastal and intracontinental, eolian and fluvial - type deposits, might be datable by TL from the upper Holocene to at least the base of the upper Pleistocene, with a precision of +- 10-15%. (Author)

1984-11-04

293

A low-order dynamical model of global climatic variability over the full Pleistocene  

Energy Technology Data Exchange (ETDEWEB)

A previously formulated dynamical model of the late Pleistocene ice ages (based on the hypothesis that the global CO{sub 2} system can provide the instability to drive a natural oscillation involving feedbacks between the cryosphere, atmosphere, and ocean) is extended to include (1) additive earth orbital forcing (summer insolation changes at 65{degree}N) and (2) tectonic forcing in the form of a postulated variation in the multiplicative parameters (rate constants) of the model system. The structural (e.g., bifurcation) properties of the model are examined in detail to reveal the regions of parameter space wherein the geologically inferred features of the full Pleistocene can be simulated, including the observed chronology, the phase relationships between ice, CO{sub 2}, and North Atlantic Deep Water formation, and the mid-Pleistocene transition.

Maasch, K.A.; Saltzman, B. (Yale Univ., New Haven, CT (United States))

1990-02-20

294

Terminal Pleistocene/Early Holocene Environmental Change at the Sunshine Locality, North-Central Nevada, U.S.A.  

Science.gov (United States)

Sedimentological, faunal, and archaeological investigations at the Sunshine Locality, Long Valley, Nevada reveal a history of human adaptation and environmental change at the last glacial-interglacial transition in North America's north-central Great Basin. The locality contains a suite of lacustrine, alluvial, and eolian deposits associated with fluvially reworked faunal remains and Paleoindian artifacts. Radiocarbon-dated stratigraphy indicates a history of receding pluvial lake levels followed by alluvial downcutting and subsequent valley filling with marsh-like conditions at the end of the Pleistocene. A period of alluvial deposition and shallow water tables (9,800 to 11,000 14C yr B.P.) correlates to the Younger Dryas. Subsequent drier conditions and reduced surface runoff mark the early Holocene; sand dunes replace wetlands by 8,000 14C yr B.P. The stratigraphy at Sunshine is similar to sites located 400 km south and supports regional climatic synchroneity in the central and southern Great Basin during the terminal Pleistocene/early Holocene. Given regional climate change and recurrent geomorphic settings comparable to Sunshine, we believe that there is a high potential for buried Paleoindian features in primary association with extinct fauna elsewhere in the region yet to be discovered due to limited stratigraphic exposure and consequent low visibility.

Huckleberry, Gary; Beck, Charlotte; Jones, George T.; Holmes, Amy; Cannon, Michael; Livingston, Stephanie; Broughton, Jack M.

2001-05-01

295

Plio-Pleistocene cliff-bound, wedge-shaped, warm-temperate carbonate deposits from Rhodes (Greece): Sedimentology and facies  

Science.gov (United States)

The Pliocene to Pleistocene temperate carbonates of Rhodes were deposited in a tectonically active region, strongly influenced by a complicated and rapidly changing topography, provided by the highly tectonised late Cretaceous Lindos Limestone as basement rock. Deposition on this basement took place in accommodation loci restricted to micrograbens and their downslope extension, to the foot of steep submarine cliffs, to basement neptunian dykes and depressions in the basement rock. Consequently the sediments comprise a high degree of facies variability, and are typically thin and laterally discontinuous. The integration of several outcrops is necessary for the reconstruction of the stratigraphy and the relative sea-level changes. The sediments were deposited during a large-scale, tectonically driven transgressive-regressive cycle in water depths changing from zero to several hundreds of metres. At the studied Lindos-Pefkos Road cutting the Kolymbia Limestone, bound to the foot of Lindos Limestone cliffs, marks the onset of the marine deposition in the late Pliocene. Its fabric is a rudstone consisting of unsorted angular Lindos Limestone clasts (up to boulder-size) with a matrix dominated by molluscs and coralline algae. The overlying Plio-Pleistocene St. Paul's Bay Limestone consists of deep-water float- and rudstones containing the 'white coral community' dominated by the coral Lophelia pertusa. Its matrix shows a complex fabric of up to five sediment zones separated by differing states of lithification. In this maximum flooding phase, mineralised hardgrounds indicate depositional hiati. The subsequent shallowing phase is represented by the Cape Arkhangelos Calcarenite, a series of distinctive facies of very patchy distribution. They are characterised by the Bryozoan-Brachiopod Facies, overlain by a facies heavily dominated by the bivalve Mytilaster sp. ( Mytilaster Facies). Conspicuous for the Mytilaster Facies is the inverse, concave-up, stacking pattern of shelly material. This facies is followed by a serpulid framestone and associated serpulid rudstone. Neptunian dykes cut through the first two facies and are filled with an intraformational breccia grading into a breccia with abundant Mytilaster Facies clasts (Neptunian Dyke Facies). The sedimentology and interpretation of each facies include a description of the ichnology, in particular the bioerosion peculiar to each facies. The separation of different gravity transport processes in steep submarine environments is rarely described and most of the literature concentrates on siliciclastic-dominated coarse-grained, sandy or gravely sand delta environments. For a classification of the transport processes of the examined deposits, the following criteria were evaluated: sediment body symmetry, inclination of the palaeorelief, sediment constituents, fabric complexity, sedimentary structures and availability of fine matrix. Sedimentary structures and grading can be camouflaged in carbonates due to density differences of bioclasts; however bioclast-orientations such as bivalve stacking patterns can give information about the sedimentary process. We suggest the inverse, concave-up, stacking pattern of bivalve shells to be a texture potentially indicative for debris falls. Because of the above-mentioned criteria we classified the Kolymbia Limestone as rock-fall deposits and the St. Paul's Bay Limestone as well as the Mytilaster Facies of the Cape Arkhangelos Calcarenite as debris-fall deposits. The Bryozoan-Brachiopod Facies could not be classified with certainty because of the lack of sedimentary structures and bioclast-orientation. However, a grain-flow or most likely a debris-fall transport process seems probable.

Titschack, Jürgen; Bromley, Richard G.; Freiwald, André

2005-10-01

296

The Digital Integrated Stratigraphy Project (DISP)  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The Digital Integrated Stratigraphy Project (DISP) aims to eliminate the stratigraphical ambiguity associated with sample position within a stratigraphical section. For example, it is often impractical or impossible to compare one author’s measured section and data precisely against another author’s geographically identical measured section and data due to discrepancies in the measured thicknesses of units, variations in the assignments of litho- and chronostratigraphical terms, and/or th...

Munnecke A; Cramer B D; Boon D P; Kharwat R; Aiken C L; Schofield D I

2012-01-01

297

Spatial distribution of Pleistocene/Holocene warming amplitudes in Northern Eurasia inferred from geothermal data  

Directory of Open Access Journals (Sweden)

Full Text Available We analyze 48 geothermal estimates of Pleistocene/Holocene warming amplitudes from various locations in Greenland, Europe, Arctic regions of Western Siberia, and Yakutia. The spatial distribution of these estimates exhibits two remarkable features. (i In Europe and part of Asia the amplitude of warming increases toward the northwest and displays clear asymmetry with respect to the North Pole. The region of maximal warming is close to the North Atlantic. A simple parametric dependence of the warming amplitudes on the distance to the warming center explains 91% of the amplitude variation. The Pleistocene/Holocene warming center is located northeast of Iceland. We claim that the Holocene warming is primarily related to the formation (or resumption of the modern system of currents in the North Atlantic. (ii In Arctic Asia, north of the 68-th parallel, the amplitude of temperature change sharply decreases from South to North, reaching zero and even negative values. These small or negative amplitudes could be attributed partially to a joint influence of Late Pleistocene ice sheets. Using a simple model of the temperature regime underneath the ice sheet we show that, depending on the relationship between the heat flow and the vertical ice advection velocity, the base of the glacier can either warm up or cool down. Nevertheless, we speculate that the more likely explanation of these observations are warm-water lakes thought of have formed in the Late Pleistocene by the damming of the Ob, Yenisei and Lena Rivers.

D. Y. Demezhko

2007-09-01

298

Snapshots of the Greenland ice sheet configuration in the Pliocene to early Pleistocene  

DEFF Research Database (Denmark)

The geometry of the ice sheets during the Pliocene to early Pleistocene is not well constrained. Here we apply an ice-flow model in the study of the Greenland ice sheet (GIS) during three extreme intervals of this period constrained by geological observations and climate reconstructions. We study the extent of the GIS during the Mid-Pliocene Warmth (3.3-3.0 Ma), its advance across the continental shelf during the late Pliocene to early Pleistocene glaciations (3.0-2.4 Ma) as implied by offshore geological studies, and the transition from glacial to interglacial conditions around 2.4 Ma as deduced from the deposits of the Kap Kobenhavn Formation, North Greenland. Our experiments show that no coherent ice sheet is likely to have existed in Greenland during the Mid-Pliocene Warmth and that only local ice caps may have been present in the coastal mountains of East Greenland. Our results illustrate the variability of the GIS during the Pliocene to early Pleistocene and underline the importance of including independent estimates of the GIS in studies of climate during this period. We conclude that the GIS did not exist throughout the Pliocene to early Pleistocene, and that it melted during interglacials even during the late Pliocene climate deterioration.

Reeh, Niels

2011-01-01

299

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

1995-12-01

300

Patterns in fish radiation are compatible with Pleistocene desiccation of Lake Victoria and 14,600 year history for its cichlid species flock.  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Geophysical data are currently being interpreted as evidence for a late Pleistocene desiccation of Lake Victoria and its refilling 14,600 years ago. This implies that between 500 and 1000 endemic cichlid fish species must have evolved in 14,600 years, the fastest large-scale species radiation known. A recent review concludes that biological evidence clearly rejects the postulated Pleistocene desiccation of the lake: a 14,600 year history would imply exceptionally high speciation rates across ...

Seehausen, Ole

2002-01-01

 
 
 
 
301

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

302

A Pleistocene lacustrine episode in southeastern Libya  

International Nuclear Information System (INIS)

Results of an investigation of the Th/U dating and isotopic (stable carbon and oxygen) palaeohydrology of the fossiliferous lacustrine deposits of middle Pleistocene age found in Central Fezzan (Libya) are reported. (U.K.)

1981-03-12

303

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. 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 f...

2010-01-01

304

Late Pliocene Quaternary tectonics in the frontal part of the SE Carpathians: Insights from tectonic geomorphology  

Science.gov (United States)

The Romanian East Carpathians display large-scale heterogeneities along the mountain belt, unusual foredeep geometries, significant post-collisional and neotectonic activity, and major variations in topography, mostly developed in the aftermath of late Miocene (Sarmatian; ˜11 Ma) subduction/underthrusting and continental collision between the East European/Scythian/Moesian foreland and the inner Carpathians Tisza-Dacia unit. In particular, the SE corner of the arcuate orogenic belt represents the place of still active large-scale differential vertical movements between the uplifting mountain chain and the subsiding Foc?ani foredeep basin. In this key area, we have analysed the configuration of the present day landforms and the drainage patterns in order to quantify the amplitude, timing and kinematics of these post-collisional late Pliocene-Quaternary vertical movements. A river network is incising in the upstream a high topography consisting of the external Carpathians nappes and the Pliocene-Lower Pleistocene sediments of the foreland. Further eastwards in the downstream, this network is cross-cutting a low topography consisting of the Middle Pleistocene-Holocene sediments of the foreland. Geological observations and well-preserved geomorphic features demonstrate a complex succession of geological structures. The late Pliocene-Holocene tectonic evolution is generally characterised by coeval uplift in the mountain chain and subsidence in the foreland. At a more detailed scale, these vertical movements took place in pulses of accelerated motion, with laterally variable amplitude both in space and in time. After a first late Pliocene uplifting period, subsidence took place during the Earliest Pleistocene resulting in a basal Quaternary unconformity. This was followed by two, quantifiable periods of increased uplift, which affected the studied area at the transition between the Carpathians orogen and the Foc?ani foreland basin in the late Early Pleistocene and the late Middle to late Pleistocene. Both large-scale deformation events affected the western Foc?ani basin flank, tilting the entire structure with ˜9° during the late Early Pleistocene and uplifted it as a block during the early Late Pleistocene. The late Early Pleistocene tilting resulted in ˜750 m uplift near the frontal monocline and by extrapolation in a presumed 3000 m uplift near the central parts of the Carpathians. The late Middle to late Pleistocene cumulative uplift reaches ˜250 m and correlates with a contemporaneous progradation of the uplifted areas towards the Foc?ani Basin. The uplifting events are separated by a second Quaternary unconformity. On the whole, the late Pliocene-Quaternary evolution of the Carpathians orogen/Foc?ani basin structure indicate large-scale differential uplift during the latest stages of a continuous post-collisional orogenic evolution.

Necea, Diana; Fielitz, W.; Matenco, L.

2005-12-01

305

Th/U disequilibria, allo/isoleucine ratios and 18O content of mollusc shells from pleistocene littoral deposits of southern Peru: a basis for geochronological assessments  

International Nuclear Information System (INIS)

None of the dating methods of marine faunal remains allows unequivocal age assessments. However, by combining several approaches, such as amino-acid racemization rates measured on a statistically significant number of samples, Th/U disequilibria, and by taking into account environmental isotope data (18O), it has been possible to set a stratigraphy of raised marine deposits of Pleistocene age in southern Peru and to identify unambiguously the terrace formed during the highest sea level of the last interglacial (isotopic substage 5 e)

1992-01-01

306

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

1996-06-01

307

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

Science.gov (United States)

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

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

2014-04-01

308

Bathymetry and seismic stratigraphy in St. Jonsfjorden, Spitsbergen  

Science.gov (United States)

St. Jonsfjorden is an approx. 21 km long and maximum ~5 km wide fjord on west Spitsbergen where modern sediment supply is glacifluvial and from tidewater glaciers. Its large-scale bathymetry is characterised by shoals and ridges as shallow as 20 m thick, were deposited beyond the outermost terminal moraine. Fjord parallel linear features overlain by multiple small transverse ridges characterise the seafloor between the innermost terminal moraine and the present glacier fronts. Whereas the linear features are interpreted to be glacial lineations providing evidence of one or several relatively rapid glacier advances, the small ridges are suggested to be 'annual retreat moraines' that were formed during halts and/or small re-advances during the retreat of the ice front(s) after its/their maximum extent(s). The heights of these ridges exceed rarely 2 meters and the distances between their crests indicate that the annual retreat rate of the ice front(s) was mainly in the order of 30-40 m. Apart from local variations, the general seismo-stratigraphy of the sub-seafloor in St. Jonsfjorden is similar to stratigraphies observed in other Spitsbergen fjords. It includes 1) a lowermost acoustically transparent to semi-transparent unit of glacigenic landforms and deposits above bedrock/acoustic basement, 2) acoustically stratified deposits reflecting frequently changing physical conditions in a glacier-proximal glacimarine environment during the last deglaciation, 3) an acoustically more transparent sequence with rare and discontinuous reflections that was deposited in a glacimarine environment with more stable physical conditions due to reduced glacial activity, and 4) an uppermost interval with strong and continuous reflections deposited during a time of increased glacial activity during the late Holocene. Crater-like features (pockmarks) of maximum 5 m depth and 110 m diameter occur. Whereas these features are almost absent in the inner fjord, they are relatively abundant close to the fjord mouth. This may reflect localised fluid flow along tectonic lineaments as observed in other Spitsbergen fjords.

Forwick, Matthias; Sverre Laberg, Jan; Husum, Katrine

2014-05-01

309

Radiocarbon dating late Quaternary loess deposits using small terrestrial gastropod shells  

Science.gov (United States)

Constraining the ages and mass accumulation rates of late Quaternary loess deposits is often difficult because of the paucity of organic material typically available for 14C dating and the inherent limitations of luminescence techniques. Radiocarbon dating of small terrestrial gastropod shells may provide an alternative to these methods as fossil shells are common in loess and contain ˜12% carbon by weight. Terrestrial gastropod assemblages in loess have been used extensively to reconstruct past environmental conditions but have been largely ignored for dating purposes. Here, we present the results of a multi-faceted approach to understanding the potential for using small terrestrial gastropod shells to date loess deposits in North America. First, we compare highly resolved 14C ages of well-preserved wood and gastropod shells (Succineidae) recovered from a Holocene loess section in Alaska. Radiocarbon ages derived from the shells are nearly identical to wood and plant macrofossil ages throughout the section, which suggests that the shells behaved as closed systems with respect to carbon for at least the last 10 ka (thousands of calibrated 14C years before present). Second, we apply 14C dating of gastropod shells to late Pleistocene loess deposits in the Great Plains using stratigraphy and independent chronologies for comparison. The new shell ages require less interpretation than humic acid radiocarbon ages that are commonly used in loess studies, provide additional stratigraphic coverage to previous dating efforts, and are in correct stratigraphic order more often than their luminescence counterparts. Third, we show that Succineidae shells recovered from historic loess in the Matanuska River Valley, Alaska captured the 20th century 14C bomb spike, which suggests that the shells can be used to date late Holocene and historic-aged loess. Finally, results from Nebraska and western Iowa suggest that, similar to other materials, shell ages approaching ˜40 ka should be viewed with caution as they may reflect trace amounts of contamination. In sum, our results show that small terrestrial gastropod shells, especially from the Succineidae family, provide reliable ages for late Quaternary loess deposits in North America.

Pigati, Jeffrey S.; McGeehin, John P.; Muhs, Daniel R.; Bettis, E. Arthur

2013-09-01

310

Late Neogene and Quaternary evolution of the northern Albemarle Embayment (mid-Atlantic continental margin, USA)  

Science.gov (United States)

Seismic surveys in the eastern Albemarle Sound, adjacent tributaries and the inner continental shelf define the regional geologic framework and provide insight into the sedimentary evolution of the northern North Carolina coastal system. Litho- and chronostratigraphic data are derived from eight drill sites on the Outer Banks barrier islands, and the Mobil #1 well in eastern Albemarle Sound. Within the study area, parallel-bedded, gently dipping Miocene beds occur at 95 to > 160 m below sea level (m bsl), and are overlain by a southward-thickening Pliocene unit characterized by steeply inclined, southward-prograding beds. The lower Pliocene