WorldWideScience
1

Stratigraphy of Late Pleistocene formations of the Mezen river valley  

Science.gov (United States)

Stratigraphy of Late Pleistocene formations of the Mezen river valley A.V. Maksimov, L.R. Semenova A.P. Karpinski All-Russian Geological Research Institute (VSEGEI), St.-Petersburg, Russia In recent years received extensive and contradictory evidence on the genesis, age and area of spreading of quaternary formations in NW Russia. The reason for this - the heterogeneity of investigated objects and methods of research. Within a valley of the river Mezen quaternary sediments are distributed everywhere. In outcrops opened sediments relating to the fifth and sixth stages of Middle Pleistocene, Upper Pleistocene and Holocene. Thickness of the quaternary sediments varies over a wide range, generally increasing from west to east. The authors have studied quaternary formations, opened in outcrops in valley of river Mezen (downstream) and its right tributary Peza, as well as in marine coastal cliffs. The aim of the study was to demonstrate specific features of the lithological composition of quaternary sediments from various (in age and origin) moraine complexes of the Russian NW and to reconstruction of paleogeographic sedimentary environments in the Late Pleistocene. Such attention to glacial sediments was dictated by the fact that they bear the most valuable information pertaining to the type and composition of provenances and to the geodynamic settings of feeding and sedimentation zones. To achieve these goals following tasks were set: 1. Lithostratigraphic subdivision of the section of Quaternary sediments. 2. Correlation of local stratigraphic units with stratigraphic scheme adjacent areas using the geochronological, paleontological and paleoclimatic data. 3. Reconstruction of the main geological events Late Pleistocene NW European part of Russia. First for glacial sediments in valley of the river Mezen applied lithological method, for determining the origin of formations. Was studied lithological composition of the sediments and were correlated geological sections. Also was conducted geochronological research. Based on these results, it was found that: - the glaciers of the Baltic Shield and the Czech lip penetrated into the valley of the river Mezen in Valdai time, forming moraines of different lithology; - sea waters penetrated to the valley of the river Mezen in Leningrad and Mikulino time. In Mikulino time the basin was deeper.

Maksimov, Anton; Semenova, Ljudmila

2014-05-01

2

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

3

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 (deposits within the incised-channels were marked by a transition from fluvial deposits at the base to marine deposits in the upper part of the channels. On the exposed shelf and the interfluvial area of the incised-channels, the TST is a sandy layer overlying the sequence boundary SB1. Thickness of the TST on the shelf varies from 0 to 15 m. The highstand systems tract (HST) consists of thick mud clinoforms of the modern Mekong subaqueous delta. The HST wedge prograded onto the shelf primarily after the mid-Holocene sea-level highstand was at approximately 6.5-5.5 kyr BP ago. The HST wedge extends along the southwestern shore, and its maximum thickness (30 m) was recorded in the Cape Ca Mau area. The HST wedge pinches out at modern water depths of 20-30 m, resulting in a thin HST layer on the middle and outer shelf. The proposed post-Pleistocene sequence-stratigraphic model for the SE 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

4

Glacial stratigraphy of the Bulkley River region: A depositional framework for the late Pleistocene in central British Columbia  

Science.gov (United States)

A depositional framework for late Pleistocene sediments in central British Columbia was developed from the composite stratigraphy of glacial sediments found in the Bulkley River region. Nonglacial deposits correlated to the Olympia Nonglacial Interval, are overlain in succession by sub-till, ice-advance sediments, Late Wisconsinan (Fraser Glaciation) till, and late-glacial sediments. Due to local erosion and depositional variability, some of the units are not continuous throughout the region and differ locally in their thickness and complexity. At the onset of the Fraser Glaciation, ice advance was marked by rising base levels in rivers, lake ponding, and ice marginal sub-aqueous deposition. Physiography and glacier dynamics influenced the position of drainage outlets, direction of water flow, and ponding. The region was completely ice covered during this glaciation and ice-flow directions were variable, being dominantly influenced by the migrating position of ice divides. Deglaciation was marked by the widespread deposition of fine-grained sediments in proglacial lakes and glaciofluvial sands and gravels at locations with unrestricted drainage.

Stumpf, A.J.; Broster, B.E.; Levson, V.M.

2004-01-01

5

Late Pleistocene sea-level history  

International Nuclear Information System (INIS)

The development of the U-series techniques for dating fossil corals is traced and case studies where dating and stratigraphy have provided a consistent picture of a region are presented. Finally a global curve of eustatic sea-level will be developed for the late Pleistocene and the implications of this curve for current theories of glaciations will be discussed. (author)

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

Science.gov (United States)

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

Hlal, Osama; Bennur, Sami

2014-05-01

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

Science.gov (United States)

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

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

2013-08-01

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

Energy Technology Data Exchange (ETDEWEB)

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

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

1994-09-01

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Late Pleistocene stratigraphy of IODP Site U1396 and compiled chronology offshore of south and south west Montserrat, Lesser Antilles  

Science.gov (United States)

sediments around volcanic islands contain an archive of volcaniclastic deposits, which can be used to reconstruct the volcanic history of an area. Such records hold many advantages over often incomplete terrestrial data sets. This includes the potential for precise and continuous dating of intervening sediment packages, which allow a correlatable and temporally constrained stratigraphic framework to be constructed across multiple marine sediment cores. Here we discuss a marine record of eruptive and mass-wasting events spanning ˜250 ka offshore of Montserrat, using new data from IODP Expedition 340, as well as previously collected cores. By using a combination of high-resolution oxygen isotope stratigraphy, AMS radiocarbon dating, biostratigraphy of foraminifera and calcareous nannofossils, and clast componentry, we identify five major events at Soufriere Hills volcano since 250 ka. Lateral correlations of these events across sediment cores collected offshore of the south and south west of Montserrat have improved our understanding of the timing, extent and associations between events in this area. Correlations reveal that powerful and potentially erosive density-currents traveled at least 33 km offshore and demonstrate that marine deposits, produced by eruption-fed and mass-wasting events on volcanic islands, are heterogeneous in their spatial distribution. Thus, multiple drilling/coring sites are needed to reconstruct the full chronostratigraphy of volcanic islands. This multidisciplinary study will be vital to interpreting the chaotic records of submarine landslides at other sites drilled during Expedition 340 and provides a framework that can be applied to the stratigraphic analysis of sediments surrounding other volcanic islands.

Wall-Palmer, Deborah; Coussens, Maya; Talling, Peter J.; Jutzeler, Martin; Cassidy, Michael; Marchant, Isabelle; Palmer, Martin R.; Watt, Sebastian F. L.; Smart, Christopher W.; Fisher, Jodie K.; Hart, Malcolm B.; Fraass, Andrew; Trofimovs, Jessica; Le Friant, Anne; Ishizuka, Osamu; Adachi, Tatsuya; Aljahdali, Mohammed; Boudon, Georges; Breitkreuz, Christoph; Endo, Daisuke; Fujinawa, Akihiko; Hatfield, Robert; Hornbach, Matthew J.; Kataoka, Kyoko; Lafuerza, Sara; Maeno, Fukashi; Manga, Michael; Martinez-Colon, Michael; McCanta, Molly; Morgan, Sally; Saito, Takeshi; Slagle, Angela L.; Stinton, Adam J.; Subramanyam, K. S. V.; Tamura, Yoshihiko; Villemant, Benoit; Wang, Fei

2014-07-01

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Principles of pleistocene stratigraphy, applied to the Gulf of Mexico  

Energy Technology Data Exchange (ETDEWEB)

This study of one of the world's major oil provinces is an examination of advances made in the past decade in high resolution stratigraphy of Pleistocene marine sediments. Topics covered include magnetostratigraphy, planktonic foraminiferal biostratigraphy, oxygen isotope stratigraphy, tephrochronology and a review and updating of terrestrial-marine correlations during the Pleistocene. The emphasis is on the Gulf of Mexico, but the techniques described can be applied to other marine sedimentary basins.

Fillon, R.H.; Healy-Williams, N.; Ledbetter, M.T.; Thunell, R.C.; Williams, D.F.

1984-01-01

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Palynological investigations of late Pleistocene deposits in South Eastern France  

International Nuclear Information System (INIS)

Palynological investigations were carried out on lignites and other Late Pleistocene deposits in the area north of Grenoble in southeastern France, in order to reconstruct the vegetational and climatic development in this area during the Late Pleistocene. The 14C and ionium content of several lignites were also measured. (Auth.)

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Influence of late Pleistocene glaciations on the hydrogeology of the continental shelf offshore Massachusetts, USA  

Science.gov (United States)

late Pleistocene glaciations that extended onto the continental shelf offshore Massachusetts, USA, may have emplaced as much as 100 km3 of freshwater (salinity <5 ppt) in continental shelf sediments. To estimate the volume and extent of offshore freshwater, we developed a three-dimensional, variable-density model that couples fluid flow and heat and solute transport for the continental shelf offshore Massachusetts. The stratigraphy for our model is based on high-resolution, multichannel seismic data. The model incorporates the last 3 Ma of climate history by prescribing boundary conditions of sea level change and ice sheet extent and thickness. We incorporate new estimates of the maximum extent of a late Pleistocene ice sheet to near the shelf-slope break. Model results indicate that this late Pleistocene ice sheet was responsible for much of the emplaced freshwater. We predict that the current freshwater distribution may reach depths up to 500 meters below sea level and up to 30 km beyond Martha's Vineyard. The freshwater distribution is strongly dependent on the three-dimensional stratigraphy and ice sheet history. Our predictions improve our understanding of the distribution of offshore freshwater, a potential nonrenewable resource for coastal communities along recently glaciated margins.

Siegel, Jacob; Person, Mark; Dugan, Brandon; Cohen, Denis; Lizarralde, Daniel; Gable, Carl

2014-12-01

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An attempt at correlation between the Velay pollen sequence and the Middle Pleistocene stratigraphy from central Europe.  

Czech Academy of Sciences Publication Activity Database

Ro?. 20, - (2001), s. 1593-1602. ISSN 0277-3791 R&D Projects: GA AV ?R KSK6005114 Institutional research plan: CEZ:AV0Z6005908 Keywords : Middle Pleistocene * stratigraphy * pollen sequence Subject RIV: EF - Botanics Impact factor: 3.055, year: 2001

de Beaulieu, J. L.; Andrieu-Ponel, V.; Reille, M.; Grüger, E.; Tzedakis, C.; Svobodová, Helena

2001-01-01

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Late Cenozoic stratigraphy and structure of the western margin of the central San Joaquin Valley, California  

Science.gov (United States)

Late Cenozoic Stratigraphy Late Cenozoic deposits in the west-central San Joaquin Valley and adjacent foothills of the Diablo Range consist mainly of unconsolidated, poorly-sorted to well-sorted gravel, sand, silt and clay derived primarily from the Diablo Range and secondarily from the Sierra Nevada. Sedimentary structures, such as channeled contacts, laminated bedding, cross-stratification and clast-imbrication indicate that most of the deposits were transported and laid down by running water. These deposits are described and their facies relationships are illustrated in the 'Late Cenozoic Stratigraphy' section of this report (see Figures 17, and 26, and Table 9). Sediment shed from the Diablo Range accumulated primarily as a complex of coalescing alluvial fans on the piedmont slope of a San Joaquin Valley that at one time extended across the foothill belt to the present margin of the central Diablo Range; and as local fills within stream valleys of the Diablo Range foothills tributary to the San Joaquin Valley. These deposits are well exposed in Interstate-5 roadcuts, California Aqueduct and Delta-Mendota canal cuts, and stream banks along the many ephemeral and intermittent streams draining the Diablo Range. Sediment derived from the Sierra Nevada is confined primarily to the floodbasin of the San Joaquin Valley. It includes arkosic riverine and floodbasin deposits from the San Joaquin River and associated sloughs, as well as local ephemeral and perennial pond, swamp, oxbow-lake and lake deposits. These deposits are well-exposed in stream banks of the San Joaquin River and a few of the larger sloughs such as Salt Slough, Mud Slough and Kings Slough. Well-sorted, fine- and medium-grained, quartzose, cross-bedded sand, presumably derived from the Sierra Nevada, locally interfinger with or underlie fine-grained Coast Range alluvial-fan deposits. The sand probably originated by eolian reworking of Sierran alluvium from the floodbasin of the lower San Joaquin River or from fans of the northeastern San Joaquin Valley. These deposits are locally well exposed in Interstate-5 roadcuts, primarily between Orestimba and Garzas Creeks. The geomorphic character of the alluvium laid down by streams draining the Diablo Range reflects late Cenozoic uplift of the foothills and subsidence of the valley. Within the foothills and near the foothill-valley margin, the deposits form a sequence of inset stream terraces and nested alluvial fans. Valleyward, however, each deposit forms a veneer over older alluvial-fan deposits. Based primarily on geomorphic and pedologic indicators of relative age (see Figure 19 and Table 10), and to a lesser extent on lithologic and absolute age criteria, the late Cenozoic deposits are divided into five stratigraphic units. In order of decreasing age, these include the formally recognized Tulare Formation (Watts, 1894; Anderson, 1905) of late Pliocene and Pleistocene age, and the informally named Los Banos alluvium of middle and late Pleistocene age, San Luis Ranch alluvium of late Pleistocene and early Holocene age, and Patterson alluvium and Dos Palos alluvium of Holocene age. The Los Banos and San Luis Ranch alluvium are further divided into three and two members, respectively. Each of these members ranges in thickness from less than I m up to 15 m and thus represents, at least in part, a distinct period of aggradation. The lithology age and distribution of these units is described in the 'Stratigraphie Divisions' section of this report and is summarized in Figure 25 and Table 11. Plates 1 through 23 show the local distribution of these units on 7.5-minute Quadrangles. Mapping criteria are diagrammatically illustrated in Figure 19 and described in the 'Mapping Criteria' section of this report. Indirect evidence suggests that deposition of these units resulted primarily from climatic change rather than intermittent uplift of the Diablo Range. The units are recognized throughout 1500 Km

Lettis, William R.

1982-01-01

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Late Pleistocene floras from Earith, Huntingdonshire.  

Science.gov (United States)

A pit in fluviatile gravel of the River Ouse at the western edge of the East Anglian fenland has exposed several richly organic beds of Last-glacial age. A radiocarbon date of 42 000 years from one bed confirms the terrace stratigraphy in placing the beds in a fairly early part of the Weichselian. The organic beds are succeeded by cryoturbation phenomena and ice wedge casts, indicating a severely cold climate with permafrost. The beds represent former pools on the flood-plain into which plant detritus was washed from the surroundings, chiefly by melt water in the spring. Pollen is sparse, but the macroscopic plant remains indicate a vegetation dominated by dwarf willows, accompanied by many herbs of base-rich, open habitats. Identification of the macrofossils is discussed and comments are made on the ecology and taxonomy of important species. The flora contains a mixture of northern and southern distributional types, the southern including species requiring a July mean temperature approaching 16 °C. Halophytes are frequent, and four species are considered to be obligate halophytes and to demonstrate the presence of salt in the substrate. The plant mixtures are explained as a result of the peculiarly open habitats of the glacial landscape and of the climate, which appears to have had warm summers and very cold winters, with a mean annual temperature slightly below 0 °C, resulting in discontinuous permafrost. PMID:22408832

Bell, F G

1970-07-23

16

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

Science.gov (United States)

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

Scheidt, Stephanie; Hambach, Ulrich; Rolf, Christian

2014-05-01

17

The horse in late Pleistocene and Holocene Britain  

OpenAIRE

Until now, the horse was one of the few members of the British Late Pleistocene and Holocene fauna which had yet to be fully investigated. In this thesis, chronological, palaeoecological and morphological data based on direct investigations of British and European fossil and sub-fossil horses are presented. The time-frame encompasses the latest certain wild horses in Britain and continental Europe through to the early diversification of domestic types, and thus spans the interv...

Kaagan, L. M.

2000-01-01

18

Late Pleistocene piñon pines in the Chihuahuan Desert  

Science.gov (United States)

Examination of late Pleistocene packrat middens from the northern and central Chihuahuan Desert disclosed macrofossils of Colorado piñon ( Pinus edulis) and Texas piñon ( P. remota). Radiocarbon dating indicates that Texas piñon was widespread in Trans-Pecos Texas and northeastern Mexico between 30,000 and 11,000 yr B.P. Today it is found in small refugia east of its former range. In the late Pleistocene Colorado piñon occurred at lower elevations on the northern edge of the Chihuahuan Desert. Both species occurred in the Hueco Mountains, near El Paso, Texas. No clear evidence was found of the presence of Mexican piñon ( P. cembroides), though today it is abundant in the Davis and Chisos Mountains. A paleoclimate is postulated that had the following characteristics: increased winter precipitation from Pacific frontal sources, reduced summer temperatures and precipitation, and milder winter temperatures due to a reduced frequency of Arctic airmass incursion. Winter precipitation appears to have decreased from north to south, while winter temperatures, and, possibly, summer precipitation, increased from north to south. During the late Pleistocene, the northern Chihuahuan Desert was dominated by woodlands of piñon pines, junipers, and oaks. The desert-scrub communities that characterize the area today are a Holocene phenomenon.

Lanner, Ronald M.; Van Devender, Thomas R.

1981-05-01

19

Final Pleistocene and Early Holocene at Sitio do Meio, Piauí, Brazil: Stratigraphy and comparison with Pedra Furada  

OpenAIRE

English: Sitio do Meio, in southern Piaui, Brazil, is the second rock shelter presenting fully Pleistocene dates and artefacts after Pedra Furada.  Despite the anthropogenic origin of Pedra Furada artefacts has been questioned, SDM has better chances to be accepted by the scientific community because of the absence of the most relevant stone breaking agents in this kind of site, i.e. waterfalls. This paper presents a critical revision of the history of excavations (1980-2000), stratigraphy,...

Giulia Aimola; Camila Andrade; Leidiana Mota; Fabio Parenti

2014-01-01

20

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

Science.gov (United States)

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

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

2013-05-01

21

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 pences 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.)

22

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

International Nuclear Information System (INIS)

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

23

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

24

Late Pleistocene Vertebrates and Other Fossils from Epiguruk, Northwestern Alaska  

Science.gov (United States)

Sediments exposed at Epiguruk, a large cutbank on the Kobuk River about 170 km inland from Kotzebue Sound, record multiple episodes of glacial-age alluviation followed by interstadial downcutting and formation of paleosols. Vertebrate remains from Epiguruk include mammoth, bison, caribou, an equid, a canid, arctic ground squirrel, lemmings, and voles. Radiocarbon ages of bone validated by concordant ages of peat and wood span the interval between about 37,000 and 14,000 yr B.P. The late Pleistocene pollen record is dominated by Cyperaceae, with Artemisia, Salix, Betula, and Gramineae also generally abundant. The fossil record from Epiguruk indicates that the Kobuk River valley supported tundra vegetation with abundant riparian willows during middle and late Wisconsin time. Large herbivores were present during the height of late Wisconsin glaciation as well as during its waning stage and the preceding interstadial interval. The Kobuk River valley would have been a favorable refugium for plants, animals, and possibly humans throughout the last glaciation.

Hamilton, T.D.; Ashley, G.M.; Reed, K.M.; Schweger, C.E.

1993-01-01

25

Late Pleistocene-Holocene cataclysmic eruptions at Nevado de Toluca and Jocotitlan volcanoes, central Mexico  

Science.gov (United States)

This field guide describes a five day trip to examine deposits of Late Pleistocene-Holocene cataclysmic eruptions at Nevado de Toluca and Jocotitlan volcanoes in central Mexico. We will discuss the stratigraphy, petrology, and sedimentological characteristics of these deposits which provide insights into the eruptive history, type of volcanic activity, and transport and emplacement mechanisms of pyroclastic materials. These parameters will allow us to discuss the kinds of hazards and the risk that they pose to populations around these volcanoes. The area to be visited is tectonically complex thus we will also discuss the location of the volcanoes with respect to the tectonic environment. The first four days of the field trip will be dedicated to Nevado de Toluca Volcano (19 degrees 09'N; 99 degrees 45'W) located at 23 km. southwest of the City of Toluca, and is the fourth highest peak in the country, reaching an elevation of 4,680 meters above sea level (m.a.s.l.). Nevado de Toluca is an andesitic-dacitic stratovolcano, composed of a central vent excavated upon the remains of older craters destroyed by former events. Bloomfield and Valastro, (1974, 1977) concluded that the last cycle of activity occurred nearly equal 11,600 yr. ago. For this reason Nevado de Toluca has been considered an extinct volcano. Our studies, however, indicate that Nevado de Toluca has had at least two episodes of cone destruction by sector collapse as well as several explosive episodes including plinian eruptions and dome-destruction events. These eruptions occurred during the Pleistocene but a very young eruption characterized by surge and ash flows occurred ca. 3,300 yr. BP. This new knowledge of the volcano's eruptive history makes the evaluation of its present state of activity and the geological hazards necessary. This is important because the area is densely populated and large cities such as Toluca and Mexico are located in its proximity.

Macias, J.L.; Garcia, P.A.; Arce, J.L.; Siebe, C.; Espindola, J.M.; Komorowski, J.C.; Scott, K.

1997-01-01

26

Paleosol architecture of a late Quaternary basin-margin sequence and its implications for high-resolution, non-marine sequence stratigraphy  

Science.gov (United States)

Paleosol stratigraphy, a technique commonly applied in basin-margin settings to depict cyclic alluvial architecture on time scales of 10-100 ky, can be consistent with regional accommodation trends at even higher temporal resolution (1-10 ky), having strong implications for the sequence stratigraphy of late Quaternary, non-marine deposits. Three closely-spaced late Pleistocene paleosols (P1-P3), dating back approximately to 42-39, 35-31, and 29-26 cal kyr BP, respectively, form prominent stratigraphic markers across a lithologically homogeneous interfluve succession in the subsurface of Bologna, close to the Apenninic foothills. These paleosols are weakly developed (Inceptisols) and can be tracked continuously for 6 km across the triangle-shaped interchannel zone between two gravel/sand-filled channel systems (Reno and Savena rivers). In particular, the thickest paleosol (P3) is a distinctive stiff horizon that can be traced into laterally extensive, erosional-based fluvial bodies. We infer the correlation between (P3) soil development (and channel downcutting) and the final stage of the stepwise Late Pleistocene sea-level fall that culminated at the marine isotope stage 3/2 transition around 29 cal kyr BP (low accommodation systems tract). A fourth laterally extensive Inceptisol, encompassing the Pleistocene-Holocene boundary (PH), represents the major phase of soil development since the Last Glacial Maximum and is inferred to be related to channel entrenchment at the onset of the Younger Dryas. With the exception of the Iron Age-Roman paleosol, which reflects a predominantly anthropogenic control, the Holocene paleosols are laterally discontinuous and invariably more immature (Entisols) than their Pleistocene counterparts. This trend of decreasing paleosol development (and correlatability) upsection is interpreted to reflect increasing (transgressive-equivalent) accommodation during sea-level rise, thus confirming the possible extension of models used to interpret the ancient rock record to short-term depositional cycles.

Amorosi, Alessandro; Bruno, Luigi; Rossi, Veronica; Severi, Paolo; Hajdas, Irka

2014-01-01

27

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 resea disagreement with the data of other researchers remains. (Ishimitsu, A.)

28

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.

2014-06-01

29

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

Science.gov (United States)

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

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

2012-02-01

30

Radiocarbon chronology of Late Pleistocene large mammal faunas from the Pannonian basin (Hungary).  

OpenAIRE

Geochronological data from the mammal fauna of the Pannonian basin during the Late Pleistocene are compiled. Thirty-four megafaunal samples (including both fossil bone and associated materials such as charcoal), previously radiocarbon dated by accelerator mass spectrometry and conventional methods, range from 43 to 10.3 14C ka BP (47-13 ka cal BP). Thus, most samples date within Marine Isotope Stage (MIS) 3 and 2 of the Late Pleistocene, and indicate that the mammoth st...

Kovács J

2012-01-01

31

Rethinking stratigraphy and site formation of the Pleistocene deposit at Cueva Negra del Estrecho del Río Quípar (Caravaca de la Cruz, Spain)  

Science.gov (United States)

Cueva Negra del Estrecho del Río Quípar (Caravaca de la Cruz, Murcia, Spain), hereinafter Cueva Negra, is a key-site for understanding the early peopling of Europe. Since 1990, systematic excavation has revealed an intriguing assemblage of lithic and faunal remains, and hominin teeth. It was deposited 0.99-0.78 Ma according to palaeomagnetic and biostratigraphical data; pollen data indicate warm moist conditions. Recently, possible evidence of thermal alteration was detected in a deep part of the deposit. We report here on our revision of the Cueva Negra stratigraphy, and offer information on site formation processes, based on new field observations and preliminary data from soil micromorphology. The Cueva Negra succession comprises three main stratigraphical complexes. Complex 1 is late Holocene. Complexes 2 and 3 are Pleistocene and are formed mainly of alluvial sediment, with subordinate inputs from the cave walls. Complexes 2 and 3 were accumulated almost without interruption, being separated by an erosive surface truncating a thin alluvial soil developed at the top of Complex 3. Our initial micromorphological findings indicate that anthropic inputs are mostly in derived positions, very likely having undergone inward displacement from the mouth of the rock-shelter.

Angelucci, Diego E.; Anesin, Daniela; López Martínez, Mariano; Haber Uriarte, María; Rodríguez Estrella, Tomás; Walker, Michael J.

2013-11-01

32

Late Pleistocene submarine mass movements: occurrence and causes  

Science.gov (United States)

An extensive study of Late Pleistocene continental slope submarine mass movements was undertaken. Twenty-six well-dated mass movements occurred during the last 45 ka BP in the North Atlantic sector. A latitudinal trend is observed: between 45 and 12 ka BP most events occur in the mid- to low-latitudes, post-12 ka BP high-latitude occurring events dominate. A cluster of events is associated with the Last Glacial sea level lowstand and Termination 1B. Further events are associated with Termination 1A and the Holocene. Prior to 23 ka BP no clear relationship with the ice core atmospheric methane record is observed, in contrast during and following the deglaciation there is a possible relationship with atmospheric methane. High-latitude mass movements are primarily controlled by cyrospheric-induced variations in sedimentation and local sea level. In high latitudes, the glaciation subdues mass movement activity through reduced seisimicity, sediment supply and ocean temperatures. Deglaciation increases the sediment supply, seisimicity and ocean temperatures, thus increasing the likelihood of continental slope failures. For example the Storegga event coincides with high isostatic uplift and postglacial seisimicity, while the Andøya and Trænadjupet events occur before and after the peak rates respectively. In contrast low latitudes experience greater risk of slope failures during glacial periods from falling sea levels, although during the deglacial and interglacial period there is a potential for failure from changes in deposition centres and rates, as well as warming ocean temperatures potentially leading to dissociation of gas hydrates. The ongoing rapid deglaciation of coastal Greenland and Antarctica and consequent rapid input of sediment, isostatic uplift, crustal stress release and warming bottom water temperature at the shelf break will increase the risk of continental slope failure in these regions.

Owen, Matthew; Day, Simon; Maslin, Mark

2007-04-01

33

Late Pleistocene raised beaches of coastal Estremadura, central Portugal  

Science.gov (United States)

We present new stratigraphic, sedimentological, and chronological data for a suite of tectonically raised beaches dating to Marine Isotope Stages 5, 4, and 3 along the Estremadura coast of west-central Portugal. The beach deposits are found in association with ancient tidal channels and coastal dunes, pollen bearing mud and peat, and Middle Paleolithic archaeological sites that confirm occupation of the coastal zone by Neanderthal populations. The significance of these deposits is discussed in terms of the archaeological record, the tectonic and geomorphic evolution of the coast, and correlation with reconstructions of global climate and eustatic sea-level change. Direct correlation between the Estremadura beach sections is complicated by the tectonic complexity of the area and the age of the beach deposits (which are near or beyond the limit of radiocarbon dating). Evidence from multiple sites dated by AMS radiocarbon and optical luminescence methods suggests broad synchroneity in relative sea-level changes along this coast during Marine Isotope Stage 3. Two beach complexes with luminescence and radiocarbon age control date to about 35 ka and 42 ka, recording a rise in relative sea level around the time of Heinrich Event 4 at 39 ka. Depending on assumptions about eustatic sea level at the time they were deposited, we estimate that these beaches have been uplifted at rates of 0.4-4.3 mm yr -1 by the combined effects of tectonic, halokinetic, and isostatic processes. Uplift rates of 1-2 mm yr -1 are likely if the beaches represent sea level stands at roughly 40 m below modern, as suggested by recent eustatic sea level reconstructions. Evidence from coastal bluffs and the interior of the study area indicates extensive colluvial, fluvial, and aeolian sedimentation beginning around 31 ka and continuing into the Holocene. These geomorphic adjustments are related to concomitant changes in climate and sea level, providing context that improves our understanding of Late Pleistocene landscape change and human occupation on the western Iberian margin.

Benedetti, Michael M.; Haws, Jonathan A.; Funk, Caroline L.; Daniels, J. Michael; Hesp, Patrick A.; Bicho, Nuno F.; Minckley, Thomas A.; Ellwood, Brooks B.; Forman, Steven L.

2009-12-01

34

Canyon Creek: A late Pleistocene vertebrate locality in interior Alaska  

Science.gov (United States)

The Canyon Creek vertebrate-fossil locality is an extensive road cut near Fairbanks that exposes sediments that range in age from early Wisconsin to late Holocene. Tanana River gravel at the base of the section evidently formed during the Delta Glaciation of the north-central Alaska Range. Younger layers and lenses of fluvial sand are interbedded with arkosic gravel from Canyon Creek that contains tephra as well as fossil bones of an interstadial fauna about 40,000 years old. Solifluction deposits containing ventifacts, wedge casts, and rodent burrows formed during a subsequent period of periglacial activity that took place during the maximum phase of Donnelly Glaciation about 25,000-17,000 years ago. Overlying sheets of eolian sand are separated by a 9500-year-old paleosol that may correlate with a phase of early Holocene spruce expansion through central Alaska. The Pleistocene fauna from Canyon Creek consists of rodents (indicated by burrows), Mammuthus primigenius (woolly mammoth), Equus lambei (Yukon wild ass), Camelops hesternus (western camel), Bison sp. cf. B. crassicornis (large-horned bison), Ovis sp. cf. O. dalli (mountain sheep), Canis sp. cf. C. lupus (wolf), Lepus sp. cf. L. othus or L. arcticus (tundra hare), and Rangifer sp. (caribou). This assemblage suggests an open landscape in which trees and tall shrubs were either absent or confined to sheltered and moist sites. Camelops evidently was present in eastern Beringia during the middle Wisconsin interstadial interval but may have disappeared during the following glacial episode. The stratigraphic section at Canyon Creek appears to demonstrate that the Delta Glaciation of the north-central Alaska Range is at least in part of early Wisconsin age and was separated from the succeeding Donnelly Glaciation by an interstadial rather than interglacial episode.

Weber, Florence R.; Hamilton, Thomas D.; Hopkins, David M.; Repenning, Charles A.; Haas, Herbert

1981-09-01

35

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

36

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

37

Hominin teeth from the early Late Pleistocene site of Xujiayao, Northern China.  

Science.gov (United States)

It is generally accepted that from the late Middle to the early Late Pleistocene (?340-90 ka BP), Neanderthals were occupying Europe and Western Asia, whereas anatomically modern humans were present in the African continent. In contrast, the paucity of hominin fossil evidence from East Asia from this period impedes a complete evolutionary picture of the genus Homo, as well as assessment of the possible contribution of or interaction with Asian hominins in the evolution of Homo sapiens and Homo neanderthalensis. Here we present a comparative study of a hominin dental sample recovered from the Xujiayao site, in Northern China, attributed to the early Late Pleistocene (MIS 5 to 4). Our dental study reveals a mosaic of primitive and derived dental features for the Xujiayao hominins that can be summarized as follows: i) they are different from archaic and recent modern humans, ii) they present some features that are common but not exclusive to the Neanderthal lineage, and iii) they retain some primitive conformations classically found in East Asian Early and Middle Pleistocene hominins despite their young geological age. Thus, our study evinces the existence in China of a population of unclear taxonomic status with regard to other contemporary populations such as H. sapiens and H. neanderthalensis. The morphological and metric studies of the Xujiayao teeth expand the variability known for early Late Pleistocene hominin fossils and suggest the possibility that a primitive hominin lineage may have survived late into the Late Pleistocene in China. PMID:25329008

Xing, Song; Martinón-Torres, María; Bermúdez de Castro, Jose María; Wu, Xiujie; Liu, Wu

2015-02-01

38

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

39

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.)

40

Iwo Eleru's place among Late Pleistocene and Early Holocene populations of North and East Africa.  

Science.gov (United States)

The Iwo Eleru site in Nigeria preserves the only terminal Pleistocene fossil from tropical West Africa. The peoples of this region contributed to significant population movements throughout the continent during the Holocene. As such, characterizing the phenotype of Late Pleistocene West African populations is critical for disentangling the evolutionary signatures of a highly complex African population history and structure. Previous research approached the calvaria's morphology from a paleoanthropological perspective, noting its mosaic of archaic and modern neurocranial features and distinctiveness from Pleistocene fossil taxa and contemporary modern human samples. In this paper, I compare Iwo Eleru with contemporary Late Pleistocene Africans and also consider the specimen's affinities with Holocene populations of the central and western Sahara, Nile Valley, and East Africa. Craniometric data were recorded for 22 neurocranial dimensions and subjected to principal components analysis and Mahalanobis distance estimation. Multidimensional scaling of distances indicated that Iwo Eleru fell outside the observed range of variation of other terminal Pleistocene supra-equatorial African populations, confirming previous results that documented its divergence from Neanderthals, Upper Paleolithic Europeans, and modern Africans. The calvaria was also distinct from Holocene Saharan, Nile Valley, and East African populations, which suggests limited West African input into the Sahara during the African Humid Period. Results presented here bolster previous research that suggested Iwo Eleru's anatomy reflected either admixture with archaic humans or the long-term survival of populations with more archaic neurocranial anatomy until the end of the Pleistocene. PMID:25065342

Stojanowski, Christopher M

2014-10-01

41

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

42

Late Devonian conodonts and event stratigraphy in northwestern Algerian Sahara  

Science.gov (United States)

Conodonts recovered from the Late Devonian South Marhouma section comprise 5 genera with 31 species (3 undetermined). The fauna establishes the presence of MN Zones 5, undifferentiated 6/7, 8/10 for the Middle Frasnian, the MN Zones 11, 12, 13 for the Upper Frasnian as well as the Early through Late triangularis Zones in the basal Famennian. The outcropping lithological succession is one of mostly nodular calcilutites alternating with numerous marly and shaly deposits, which, in the lower and upper part, comprise several dysoxic dark shale intervals. Among these the Upper Kellwasser horizon can be precisely dated and as such the presence of the terminal Frasnian Kellwasser Event is recognized for the first time in Algeria. Both the Middlesex and Rhinestreet Events cannot yet be precisely located, but supposedly occur among the dark shale horizons in the lower part of the section. However, their assignment to a precise level has so far not been established. Though poor in conodont abundance the South Marhouma section provides first evidence of the presence of several Montagne Noire conodont zones within the so far widely unstudied Frasnian of the Ougarta Chain. As such it is considered representative for the northwestern Algerian Saoura region.

Mahboubi, Abdessamed; Gatovsky, Yury

2015-01-01

43

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

Scientific Electronic Library Online (English)

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

Marcelo, Zárate; Adriana, Mehl.

2008-09-01

44

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

Directory of Open Access Journals (Sweden)

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

Marcelo Zárate

2008-09-01

45

New records of temperate mollusks in two Late Pleistocene terrestrial localities from northeastern Oaxaca, Southern Mexico  

Science.gov (United States)

The Mixteca Alta Oaxaqueña is in the state of Oaxaca, southern Mexico. This region is characterized by numerous Pleistocene fossiliferous localities. The objective of this study is to describe a diverse assemblage of Late Pleistocene freshwater and terrestrial mollusks in two localities from northeastern Oaxaca, Coixtlahuaca District. We identified 10 taxa of gastropods and one of bivalves. By the sedimentological characteristics and the mollusks assemblage, it is possible to relate the first locality with meandriform river deposits, without vegetation. The second locality was associated with a floodplain with short-lived associated vegetation. Five identified species constitute the most austral records of these taxa in Neartic Realm. In all the taxa, the Late Pleistocene occurrences constitute the last records of the identified mollusks in the study zone.

Guerrero-Arenas, Rosalía; Jiménez-Hidalgo, Eduardo; García-Barrera, Pedro

2013-11-01

46

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

47

Underground temperatures - evidence of Late Pleistocene-Holocene orbital forcing  

Science.gov (United States)

An analysis of temperature-depth profiles measured in deep boreholes (more than 1 km) allows determining ground surface temperature (GST) and surface heat flux (SHF) histories in the period of global climate change at the border of Pleistocene and Holocene. We reconstructed past 40 kyr GST and SHF histories using data obtained from two deep boreholes in Russia (Middle Urals and Karelia). GST histories reveal 12-20 degrees of warming during the Pleistocene-Holocene transition 20-10 kyr BP and much smaller changes during Holocene. SHF changes precede the surface temperature changes by 1-2 kyr. The heat flux started to raise 22 kyr BP, reached its maximum value of 0.09-0.12 watts per square meter 15-10 kyr BP and then began to decrease. A comparison of SHF histories with mean annual variations of insolation at a latitude of 60° N (I), which is determined by changes in the Earth's orbital parameters, shows that all three curves are very similar. The synchronous changes of the heat flux and insolation indicate that ground surface temperature changes were mainly governed by external radiative forcing. While the amplitude ratio SHF/I is approximately 1 per cent. A comparison of the reconstructed GST and SHF with the atmospheric carbon dioxide changes (from the Antarctic ice cores) leads to another important conclusion. Carbon dioxide changes by its shape and chronology are much closer to temperature changes than they are to heat flux changes. The heat flux increase occurred faster, and then 12 kyr ago it began to fall, while the increase in carbon dioxide continues to the present. On the assumption that the reconstructed SHF generally reproduces changes in radiative forcing, one can challenge the hypothesis of the primary role of carbon dioxide and the greenhouse effect in Pleistocene-Holocene transition.

Demezhko, Dmitry; Gornostaeva, Anastasia

2014-05-01

48

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

49

Reconstructing the Last Pleistocene (Late Devensian) Glaciation on the Continental Margin of Northwest Britain  

OpenAIRE

The continental margin in the area west of Shetland was subjected to repeated and extensive ice sheet advances during the Late Pleistocene. Seabed imagery, seismic survey and borehole core data show the Late Devensian ice sheets expanded across the continental shelf three times, two of these advances reaching the shelf edge. On the inner shelf, where present-day water depths are generally less than 100m, only thin sediments from the last retreat phase and exposed rock surfaces ...

Davison, Stephen

2005-01-01

50

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

51

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

International Nuclear Information System (INIS)

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

52

Radiocarbon chronology of Late Pleistocene large mammal faunas from the Pannonian basin (Hungary.  

Directory of Open Access Journals (Sweden)

Full Text Available Geochronological data from the mammal fauna of the Pannonian basin during the Late Pleistocene are compiled. Thirty-four megafaunal samples (including both fossil bone and associated materials such as charcoal, previously radiocarbon dated by accelerator mass spectrometry and conventional methods, range from 43 to 10.3 14C ka BP (47-13 ka cal BP. Thus, most samples date within Marine Isotope Stage (MIS 3 and 2 of the Late Pleistocene, and indicate that the mammoth steppe fauna was able to colonize this region during a period of rapid environmental change. The radiocarbon evidence fits well into the known colonization pattern of the mammoth steppe and shows a continuous distribution in the Late Weichselian grassland areas of East Central Europe.

Kovács J

2012-02-01

53

High resolution stable isotope stratigraphy of the latest Pleistocene and Holocene of three northern Bermuda Rise cores  

International Nuclear Information System (INIS)

Stable isotopic analyses of the planktonic foraminifer Globorotalia inflata from three late Pleistocene-Holocene high sedimentation rate cores from the northern Bermuda Rise are used for correlation. The detailed delta180 records show the change from maximum (glacial) to minimum (interglacial) values in each core as well as other significant changes which are stratigraphically useful. One such change may reflect either a low-salinity layer on the ocean surface due to glacial meltwater or an interval of pronounced surface water warming about 15,000 years ago. The detailed correlations of these cores suggest lateral and temporal stability of sedimentation over the past 20,000 years at the location of these cores on the northern Bermuda Rise. Alternatively, if there have been discontinuities in sedimentation they were regional in extent and cannot be recognized by studying cores from a small area

54

Late quaternary stratigraphy and sedimentology of the inner part of southwest Joseph Bonaparte Gulf  

International Nuclear Information System (INIS)

Joseph Bonaparte Gulf is a large embayment on the northwestern continental margin of Australia. It is approximately 300 km east-west and 120 km north-south with a broad continental shelf to seaward. Maximum width from the southernmost shore of Joseph Bonaparte Gulf to the edge of the continental shelf is 560 km. Several large rivers enter the gulf along its shores. The climate is monsoonal. sub-humid, and cyclone-prone during the December-March wet season. A bedrock high (Sahul Rise) rims the shelf margin. The sediments within the gulf are carbonates to seaward, grading into clastics inshore. A seaward-thinning wedge of highstand muds dominates the sediments of the inner shelf of Joseph Bonaparte Gulf. Mud banks up to 15m thick have developed inshore. Coarse-grained sand ridges up to 15m high are found off the mouth of the Ord River. These overlie an Upper Pleistocene transgressive lag of mixed carbonate and gravelly siliciclastic sand. Four drowned strandlines are present on the inner shelf at depths of 20, 25, 28 and 30 m below datum. These are interpreted as having formed during stillstands in the Late Pleistocene transgression. Older strandlines at great depths are inferred as having formed during the fall in sea-level following the last highstand. For the most part the Upper Pleistocene-Holocene marine sediments overlie an erosion surface cut into older Pleistocene sediments. Incised valleys cut into this erosion surface are up to 5 km wide and have a relief of aare up to 5 km wide and have a relief of at least 20 m. The largest valley is that cut by the Ord River. Upper Pleistocene sediments deposited in the incised valleys include interpreted lowstand fluvial gravels, early transgressive channel sands and floodplain silts, and late transgressive estuarine sands and gravels. Spot samples were collected and subjected to 14C dating, x-ray diffraction and palynological studies. Older Pleistocene sediments are inferred to have been deposited before and during the 120 ka highstand (isotope stage 5). They consist of sandy calcarenites deposited in high-energy tide-dominated shelf environments. Still older shelf and valley-fill sediments underlie these. The contrast between the Holocene muddy clastic sediments and the sandy carbonates deposited by the 120 ka highstand suggests that either the climate was more arid in the past, with less fluvial transport. or that mud was more effectively trapped in estuaries, allowing development of carbonate depositional environments inshore. Copyright (2000) Geological Society of Australia

55

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

Directory of Open Access Journals (Sweden)

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

E. Vallejo Gómez

2006-05-01

56

The late Middle Pleistocene hominin fossil record of eastern Asia: synthesis and review.  

Science.gov (United States)

Traditionally, Middle Pleistocene hominin fossils that cannot be allocated to Homo erectus sensu lato or modern H. sapiens have been assigned to different specific taxa. For example, in eastern Asia, these hominin fossils have been classified as archaic, early, or premodern H. sapiens. An increasing number of Middle Pleistocene hominin fossils are currently being assigned to H. heidelbergensis. This is particularly the case for the African and European Middle Pleistocene hominin fossil record. There have been suggestions that perhaps the eastern Asian late Middle Pleistocene hominins can also be allocated to the H. heidelbergensis hypodigm. In this article, I review the current state of the late Middle Pleistocene hominin fossil record from eastern Asia and examine the various arguments for assigning these hominins to the different specific taxa. The two primary conclusions drawn from this review are as follows: 1) little evidence currently exists in the eastern Asian Middle Pleistocene hominin fossil record to support their assignment to H. heidelbergensis; and 2) rather than add to the growing list of hominin fossil taxa by using taxonomic names like H. daliensis for northeast Asian fossils and H. mabaensis for Southeast Asian fossils, it is better to err on the side of caution and continue to use the term archaic H. sapiens to represent all of these hominin fossils. What should be evident from this review is the need for an increase in the quality and quantity of the eastern Asian hominin fossil data set. Fortunately, with the increasing number of large-scale multidisciplinary paleoanthropological field and laboratory research projects in eastern Asia, the record is quickly becoming better understood. PMID:21086528

Bae, Christopher J

2010-01-01

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Nuclear gene sequences from a late pleistocene sloth coprolite.  

Science.gov (United States)

The determination of nuclear DNA sequences from ancient remains would open many novel opportunities such as the resolution of phylogenies, the sexing of hominid and animal remains, and the characterization of genes involved in phenotypic traits. However, to date, single-copy nuclear DNA sequences from fossils have been determined only from bones and teeth of woolly mammoths preserved in the permafrost. Since the best preserved ancient nucleic acids tend to stem from cold environments, this has led to the assumption that nuclear DNA would be retrievable only from frozen remains. We have previously shown that Pleistocene coprolites stemming from the extinct Shasta sloth (Nothrotheriops shastensis, Megatheriidae) contain mitochondrial (mt) DNA from the animal that produced them as well as chloroplast (cp) DNA from the ingested plants. Recent attempts to resolve the phylogeny of two families of extinct sloths by using strictly mitochondrial DNA has been inconclusive. We have prepared DNA extracts from a ground sloth coprolite from Gypsum Cave, Nevada, and quantitated the number of mtDNA copies for three different fragment lengths by using real-time PCR. We amplified one multicopy and three single-copy nuclear gene fragments and used the concatenated sequence to resolve the phylogeny. These results show that ancient single-copy nuclear DNA can be recovered from warm, arid climates. Thus, nuclear DNA preservation is not restricted to cold climates. PMID:12842016

Poinar, Hendrik; Kuch, Melanie; McDonald, Gregory; Martin, Paul; Pääbo, Svante

2003-07-01

58

New insights into mid-late Pleistocene fossil hominin paranasal sinus morphology.  

Science.gov (United States)

Mid-late Pleistocene fossil hominins such as Homo neanderthalensis and H. heidelbergensis are often described as having extensively pneumatized crania compared with modern humans. However, the significance of pneumatization in recognizing patterns of phyletic diversification and/or functional specialization has remained controversial. Here, we test the null hypothesis that the paranasal sinuses of fossil and extant humans and great apes can be understood as biological spandrels, i.e., their morphology reflects evolutionary, developmental, and functional constraints imposed onto the surrounding bones. Morphological description of well-preserved mid-late Pleistocene hominin specimens are contrasted with our comparative sample of modern humans and great apes. Results from a geometric morphometric analysis of the correlation between paranasal sinus and cranial dimensions show that the spandrel hypothesis cannot be refuted. However, visualizing specific features of the paranasal sinus system with methods of biomedical imaging and computer graphics reveals new aspects of patterns of growth and development of fossil hominins. PMID:18951483

Zollikofer, Christoph P E; Ponce De León, Marcia S; Schmitz, Ralf W; Stringer, Christopher B

2008-11-01

59

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

Directory of Open Access Journals (Sweden)

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

DILIAN GEORGIEV

2010-11-01

60

Climatic tolerances and zoogeography of the Late Pleistocene beetle fauna of Beringia  

OpenAIRE

The study of fossil beetles has played an important role in the reconstruction of Beringian paleoenvironments. More than 25 fossil localities have yielded Late Pleistocene beetle assemblages, comprising more than 300 species, of which about 147 are predators and scavengers, groups which are suitable for paleoclimatic reconstruction. The author has developed climate envelopes (climatic parameters characterizing the modern localities in which species are found) for these species, in order to pe...

Elias, S. A.

2000-01-01

61

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

OpenAIRE

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 associ...

Sauque?, Vi?ctor; Rabal-garce?s, Raquel; Sola-almagro, Cristina; Cuenca-besco?s, Gloria

2014-01-01

62

Large Late Pleistocene landslides from the marginal slope of the Flysch Carpathians.  

Czech Academy of Sciences Publication Activity Database

Ro?. 11, ?. 6 (2014), s. 981-992. ISSN 1612-510X R&D Projects: GA MŠk LM2010008 Institutional support: RVO:67985891 ; RVO:67985939 Keywords : fossil landslide * radiocarbon dating * electrical resistivity tomography * pollen analysis * Late Pleistocene * Flysch Carpathians * Marine Isotope Stage 3 Subject RIV: DE - Earth Magnetism, Geodesy, Geography; EF - Botanics (BU-J) Impact factor: 2.814, year: 2013

Pánek, T.; Hartvich, Filip; Jankovská, Vlasta; Klimeš, Jan; Tábo?ík, Petr; Bubík, M.; Smolková, V.; Hradecký, J.

2014-01-01

63

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

64

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

65

Distribution of late Pleistocene ice-rich syngenetic permafrost of the Yedoma Suite in east and central Siberia, Russia  

Science.gov (United States)

This digital database is the product of collaboration between the U.S. Geological Survey, the Geophysical Institute at the University of Alaska, Fairbanks; the Los Altos Hills Foothill College GeoSpatial Technology Certificate Program; the Alfred Wegener Institute for Polar and Marine Research, Potsdam, Germany; and the Institute of Physical Chemical and Biological Problems in Soil Science of the Russian Academy of Sciences. The primary goal for creating this digital database is to enhance current estimates of soil organic carbon stored in deep permafrost, in particular the late Pleistocene syngenetic ice-rich permafrost deposits of the Yedoma Suite. Previous studies estimated that Yedoma deposits cover about 1 million square kilometers of a large region in central and eastern Siberia, but these estimates generally are based on maps with scales smaller than 1:10,000,000. Taking into account this large area, it was estimated that Yedoma may store as much as 500 petagrams of soil organic carbon, a large part of which is vulnerable to thaw and mobilization from thermokarst and erosion. To refine assessments of the spatial distribution of Yedoma deposits, we digitized 11 Russian Quaternary geologic maps. Our study focused on extracting geologic units interpreted by us as late Pleistocene ice-rich syngenetic Yedoma deposits based on lithology, ground ice conditions, stratigraphy, and geomorphological and spatial association. These Yedoma units then were merged into a single data layer across map tiles. The spatial database provides a useful update of the spatial distribution of this deposit for an approximately 2.32 million square kilometers land area in Siberia that will (1) serve as a core database for future refinements of Yedoma distribution in additional regions, and (2) provide a starting point to revise the size of deep but thaw-vulnerable permafrost carbon pools in the Arctic based on surface geology and the distribution of cryolithofacies types at high spatial resolution. However, we recognize that the extent of Yedoma deposits presented in this database is not complete for a global assessment, because Yedoma deposits also occur in the Taymyr lowlands and Chukotka, and in parts of Alaska and northwestern Canada.

Grosse, Guido; Robinson, Joel E.; Bryant, Robin; Taylor, Maxwell D.; Harper, William; DeMasi, Amy; Kyker-Snowman, Emily; Veremeeva, Alexandra; Schirrmeister, Lutz; Harden, Jennifer

2013-01-01

66

A re-evaluation of the late Pliocene - Pleistocene behavior of the Scoresby Sund sector of the Greenland Ice Sheet  

Science.gov (United States)

A major conclusion of Ocean Drilling Program Leg 162, drilling the western Svalbard and eastern Greenland continental margins, was that the Svalbard - Barents Sea Ice Sheet reached the shelf edge during peak glaciations much more frequently than the Greenland Ice Sheet during the late Pliocene - Pleistocene period. Both areas have a continental margin dominated by large, across-shelf oriented troughs terminating at the shelf edge. In front of these troughs, large depocenters of glacigenic sediments, Trough-Mouth-Fans (TMFs), are located. Ice streams drained the ice sheets through these troughs during glacials, eroding and transporting large quantities of sediments to the shelf edge from where they subsequently were remobilized as glacigenic debris flows. The deposits of the latter have a characteristic lens-formed morphology in cross-section. In order to tie the stratigraphy of ODP Site 987, located on the very distal part of the Scoresby Sund TMF on the east Greenland continental margin, to the more proximal parts where most of the glacigenic sediments have been deposited, a regional seismic line was acquired. The seismic line reveals that lithological unit IIA of site 987, interpreted to be debris flow deposits, corresponds to an acoustically transparent unit. The overlying lithological unit I, found to be dominated by hemipelagic sediments comprising varying amounts of ice-rafted debris, is acoustically laminated. Tracing this unit south-westwards shows a transition from an acoustically laminated facies to stacked sub-units of transparent lenses of glacigenic debris flows, very similar to the signature of other TMFs. This shows that ODP Site 987 was located too distal to sample the glacigenic debris-flow deposits that dominate the deposits of the last ~2.58Ma on the more proximal part of the fan. From this we conclude that at least the Scoresby Sund sector of the East Greenland Ice Sheet had a much more dynamic behavior during the late Pleiocene - Pleistocene period than previously realized. These fluctuations were most likely responses to the pronounced climatic fluctuations characterizing this period. The new observations have important implications for assessing the behavior of the Greenland Ice Sheet to future climate.

Laberg, J. S.; Forwick, M.; Husum, K.

2012-04-01

67

An Arctic perspective on dating Mid-Late Pleistocene environmental history  

DEFF Research Database (Denmark)

To better understand Pleistocene climatic changes in the Arctic, integrated palaeoenvironmental and palaeoclimatic signals from a variety of marine and terrestrial geological records as well as geochronologic age control are required, not least for correlation to extra-Arctic records. In this paper we discuss, from an Arctic perspective, methods and correlation tools that are commonly used to date Arctic Pleistocene marine and terrestrial events. We review the state of the art of Arctic geochronology, with focus on factors that affect the possibility and quality of dating, and support this overview by examples of application of modern dating methods to Arctic terrestrial and marine sequences. Event stratigraphy and numerical ages are important tools used in the Arctic to correlate fragmented terrestrial records and to establish regional stratigraphic schemes. Age control is commonly provided by radiocarbon, luminescence or cosmogenic exposure ages. Arctic Ocean deep-sea sediment successions can be correlated over large distances based on geochemical and physical property proxies for sediment composition, patterns in palaeomagnetic records and, increasingly, biostratigraphic data. Many of these proxies reveal cyclical patterns that provide a basis for astronomical tuning. Recent advances in dating technology, calibration and age modelling allow for measuring smaller quantities of material and to more precisely date previously undatable material (i.e. foraminifera for 14C, and single-grain luminescence). However, for much of the Pleistocene there are still limits to the resolution of most dating methods. Consequently improving the accuracy and precision (analytical and geological uncertainty) of dating methods through technological advances and better understanding of processes are important tasks for the future. Another challenge is to better integrate marine and terrestrial records, which could be aided by targeting continental shelf and lake records, exploring proxies that occur in both settings, and by creating joint research networks that promote collaboration between marine and terrestrial geologists and modellers

Alexanderson, Helena; Backman, Jan

2014-01-01

68

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

69

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

70

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

Energy Technology Data Exchange (ETDEWEB)

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

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

1993-03-01

71

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

Science.gov (United States)

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

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

2006-08-01

72

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

73

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

Science.gov (United States)

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

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

2006-01-01

74

Ancient DNA reveals that bowhead whale lineages survived Late Pleistocene climate change and habitat shifts  

DEFF Research Database (Denmark)

The climatic changes of the glacial cycles are thought to have been a major driver of population declines and species extinctions. However, studies to date have focused on terrestrial fauna and there is little understanding of how marine species responded to past climate change. Here we show that a true Arctic species, the bowhead whale (Balaena mysticetus), shifted its range and tracked its core suitable habitat northwards during the rapid climate change of the Pleistocene-Holocene transition. Late Pleistocene lineages survived into the Holocene and effective female population size increased rapidly, concurrent with a threefold increase in core suitable habitat. This study highlights that responses to climate change are likely to be species specific and difficult to predict. We estimate that the core suitable habitat of bowhead whales will be almost halved by the end of this century, potentially influencing future population dynamics.

Foote, Andrew D; Kaschner, Kristin

2013-01-01

75

Late Pleistocene glaciolacustrine sedimentation and paleogeography of southeastern Michigan, USA  

Science.gov (United States)

The geomorphic, stratigraphic and sedimentological characteristics of glaciolacustrine sediments in the metropolitan Detroit, Michigan area were studied to determine environments of deposition and make paleogeographic reconstructions. Nine lithofacies were identified and paleoenvironments interpreted based on their morphostratigraphic relationships with relict landforms. The sediments studied are found southeast of the Defiance and Birmingham moraines lying beneath a lowland characterized by a low morainal swell (Detroit moraine) and a series of lacustrine terraces that descend progressively in elevation southeastward. The glaciolacustrine sediments were deposited approximately 14.3-12.4 kA BP during the Port Bruce and Port Huron glacial phases of late Wisconsinan time, and are related to proglacial paleolakes Maumee, Arkona, Whittlesey, Warren, Wayne, Grassmere, Lundy and Rouge. The glaciolacustrine section is typically 2-4 m thick and consists of a basal unit of wavy-bedded clayey diamicton overlain by a surficial deposit of stratified and cross-stratified sand and gravel. The basal unit is comprised of subaqueous debris flow deposits that accumulated as subaqueous moraine in paleolake Maumee along the retreating front of the Huron lobe. The surficial deposits of sand and gravel were formed by traction, resulting from lacustrine wave activity and fluvial processes, in lakebed plain, beach ridge and deltaic depositional settings. Much of the lake-margin sand and gravel was derived from clayey diamicton by lacustrine wave action and winnowing, and that associated with paleolakes of the Port Huron phase is largely reworked Port Bruce sediment. Paleogeographic reconstructions show that the Defiance, Birmingham and Detroit moraines, Defiance and Rochester channels, and the Rochester delta, were deposited penecontemporaneously as paleolake Maumee expanded northward across the map area. A unique type of wavy bedform is characteristic of clayey diamicton deposited by subaqueous mass flow in the study area that is useful for differentiating sediment: 1) deposited by mass flow in subaqueous vs. subaerial settings, and 2) deposited by subaqueous mass flow vs. basal till. These bedforms are a useful tool for identifying subglacial meltwater deposits, and facilitate the mapping and correlation of glacial sediments based on till sheets. The map area provides a continental record of ice sheet dynamics along the southern margin of the Laurentide ice sheet during Heinrich event H-1. The record reveals rapid glacial retreat (˜ 0.8 km/yr) contemporaneous with the discharge of a large volume of meltwater. Evidence in the study area for subglacial meltwater is problematic, but indications that periglacial conditions persisted in the map area until ˜ 12.7 kA BP, and extended for 200 km or more south of the ice front suggest that a frozen substrate may have contributed to instability of the LIS.

Howard, Jeffrey L.

2010-01-01

76

Comparison of Geodetic and Late Pleistocene Slip Rates for the Southern Dead Sea Fault System  

Science.gov (United States)

Comparisons of short-term (geodetic) and Late Quaternary slip rates have been used to assess time-variable fault kinematics along various active faults, globally. Differences between such types slip rates may have implications for crustal rheology and/or temporal variations in plate motion. This research aims to compare the geodetically-derived slip rates with slip rates based on Late Pleistocene landforms along the southern Dead Sea fault system (DSFS). The DSFS is an active, left-lateral transform that accommodates differential movement between the Arabian and Sinai plates. A number of slip rates have been previously reported ranging from 2 to 6mm/yr. However, comparison of various slip rates requires ensuring that associated uncertainties are assessed using a standard. New GPS velocities from Jordan are combined with other available GPS data, and are used to model slip rates using elastic block models. Resulting slip rates are 4.3 to 5.3 mm/yr with fault locking depths of 8 - 15 km. Late Pleistocene rates are assessed from published observations, as well as new data. New mapping of offset alluvial fans in the southern Wadi Araba was facilitated by multi-spectral imagery and high-resolution digital elevation model. These fans correlate with regional aggradation events, with the resulting Late Pleistocene slip rates ranging from 4.2 to 5.1 mm/yr. Statistically, the geodetic and neotectonic slip rates are identical. Additionally, a 3-dimensional slip vector for the last earthquake in the northern Wadi Araba is constructed using close-range photogrammetry of a faulted Byzantine aqueduct that indicates both horizontal and vertical displacements. Previous studies suggested characteristic earthquake slip, so slip rates and this slip vector provide a means of assessing mean EQ recurrence interval, as well as the role of earthquakes in constructing the long-term topography along this part of the transform.

Cochran, W. J.; Gomez, F.; Abu Rajab, J. S.; Al-Tarazi, E.

2012-12-01

77

A late Middle Pleistocene temperate periglacial temperate sequence (Oxygen Isotope Stages 7 5e) near Marsworth, Buckinghamshire, UK  

Science.gov (United States)

River-channel and colluvial deposits, near Marsworth, Buckinghamshire, record a temperate-periglacial-temperate sequence during the late Middle Pleistocene. The deposits of a lower channel contain tufa clasts bearing leaf impressions that include Acer sp., and Sorbus aucuparia and containing temperate arboreal pollen attributed to ash-dominated woodland. The tufa probably formed at the mouth of a limestone spring before being redeposited in a small river whose deposits contain plant remains, Mollusca, Coleoptera, Ostracoda and vertebrate bones of temperate affinities. The sediments, sedimentary structures and limited biological remains above the Lower Channel deposits indicate that fluvial deposition preceded climatic cooling into periglacial conditions. Fluvial deposition recurred during a later temperate episode, as shown by the mammalian bone assemblage in stratigraphically higher channel deposits. The Upper Channel deposits are confidently attributed to Oxygen Isotope Sub-Stage 5e (Ipswichian) on the basis of their vertebrate remains. However, the age of the Lower Channel deposits is less clear. The mammalian and coleopteran remains in the Lower Channel strongly suggest correlation with Oxygen Isotope Stage 7 on the basis of their similarities to other sites whose stratigraphy is better known and the clear difference of the Lower Channel assemblage from well-established faunas of Ipswichian or any other age. By contrast, U-Th dating of the tufa clasts suggests an age post 160 ka BP, while Aile/Ile ratios on Mollusca point to an Ipswichian age and younger. Four ways of interpreting this age discrepancy are considered, the preferred one correlating the Lower Channel deposits with Oxygen Isotope Stage 7.

Murton, J. B.; Baker, A.; Bowen, D. Q.; Caseldine, C. J.; Coope, G. R.; Currant, A. P.; Evans, J. G.; Field, M. H.; Green, C. P.; Hatton, J.; Ito, M.; Jones, R. L.; Keen, D. H.; Kerney, M. P.; McEwan, R.; McGregor, D. F. M.; Parish, D.; Robinson, J. E.; Schreve, D. C.; Smart, P. L.

2001-12-01

78

Mandibular molar root morphology in Neanderthals and Late Pleistocene and recent Homo sapiens.  

Science.gov (United States)

Neanderthals have a distinctive suite of dental features, including large anterior crown and root dimensions and molars with enlarged pulp cavities. Yet, there is little known about variation in molar root morphology in Neanderthals and other recent and fossil members of Homo. Here, we provide the first comprehensive metric analysis of permanent mandibular molar root morphology in Middle and Late Pleistocene Homo neanderthalensis, and Late Pleistocene (Aterian) and recent Homo sapiens. We specifically address the question of whether root form can be used to distinguish between these groups and assess whether any variation in root form can be related to differences in tooth function. We apply a microtomographic imaging approach to visualise and quantify the external and internal dental morphologies of both isolated molars and molars embedded in the mandible (n=127). Univariate and multivariate analyses reveal both similarities (root length and pulp volume) and differences (occurrence of pyramidal roots and dental tissue volume proportion) in molar root morphology among penecontemporaneous Neanderthals and Aterian H. sapiens. In contrast, the molars of recent H. sapiens are markedly smaller than both Pleistocene H. sapiens and Neanderthals, but share with the former the dentine volume reduction and a smaller root-to-crown volume compared with Neanderthals. Furthermore, we found the first molar to have the largest average root surface area in recent H. sapiens and Neanderthals, although in the latter the difference between M(1) and M(2) is small. In contrast, Aterian H. sapiens root surface areas peak at M(2). Since root surface area is linked to masticatory function, this suggests a distinct occlusal loading regime in Neanderthals compared with both recent and Pleistocene H. sapiens. PMID:20719359

Kupczik, Kornelius; Hublin, Jean-Jacques

2010-11-01

79

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

80

Human influence on distribution and extinctions of the late Pleistocene Eurasian megafauna.  

Science.gov (United States)

Late Pleistocene extinctions are of interest to paleontological and anthropological research. In North America and Australia, human occupation occurred during a short period of time and overexploitation may have led to the extinction of mammalian megafauna. In northern Eurasia megafaunal extinctions are believed to have occurred over a relatively longer period of time, perhaps as a result of changing environmental conditions, but the picture is much less clear. To consider megafaunal extinction in Eurasia, we compare differences in the geographical distribution and commonness of extinct and extant species between paleontological and archaeological localities from the late middle Pleistocene to Holocene. Purely paleontological localities, as well as most extinct species, were distributed north of archaeological sites and of the extant species, suggesting that apart from possible differences in adaptations between humans and other species, humans could also have a detrimental effect on large mammal distribution. However, evidence for human overexploitation applies only to the extinct steppe bison Bison priscus. Other human-preferred species survive into the Holocene, including Rangifer tarandus, Equus ferus, Capreolus capreolus, Cervus elaphus, Equus hemionus, Saiga tatarica, and Sus scrofa. Mammuthus primigenius and Megaloceros giganteus were rare in archaeological sites. Carnivores appear little influenced by human presence, although they become rarer in Holocene archaeological sites. Overall, the data are consistent with the conclusion that humans acted as efficient hunters selecting for the most abundant species. Our study supports the idea that the late Pleistocene extinctions were environmentally driven by climatic changes that triggered habitat fragmentation, species range reduction, and population decrease, after which human interference either by direct hunting or via indirect activities probably became critical. PMID:18199470

Pushkina, Diana; Raia, Pasquale

2008-06-01

81

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

OpenAIRE

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

82

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

OpenAIRE

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

83

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

International Nuclear Information System (INIS)

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

84

Direct radiocarbon dates for Vindija G1 and Velika Pe?ina Late Pleistocene hominid remains  

OpenAIRE

New accelerator mass spectrometry radiocarbon dates taken directly on human remains from the Late Pleistocene sites of Vindija and Velika Pe?ina in the Hrvatsko Zagorje of Croatia are presented. Hominid specimens from both sites have played critical roles in the development of current perspectives on modern human evolutionary emergence in Europe. Dates of ?28 thousand years (ka) before the present (B.P.) and ?29 ka B.P. for two specimens from Vindija G1 establish them as the most recent ...

Smith, Fred H.; Trinkaus, Erik; Pettitt, Paul B.; Karavanic?, Ivor; Paunovic?, Maja

1999-01-01

85

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

OpenAIRE

Stable carbon isotopic signature (?13C) of soil organic matter (SOM) is used as a high-spatial resolution tool to infer environmental changes during late Pleistocene to Present in the Teotihuacan valley, Mexico. Interpretation was based on climatic preferences of C3, CAM and C4 plant groups. ?13C values of modern plant types are clearly distinguished. C3 plants display values around –27‰, while C4 and CAM plants have values around––13‰. Data from soil profiles range from -25.7 to ...

Vallejo Go?mez, E.; Sedov, S.; Cienfuegos Alvarado, E.; Cabadas Ba?ez, H. V.; Morales Puente, P.; Lounejeva Baturina, E.; Solleiro Rebolledo, E.

2006-01-01

86

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

87

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)

88

Dynamic landscape change during the late Early to early Middle Pleistocene: evidence from East Anglia, UK  

OpenAIRE

The late Early to early Middle Pleistocene (0.9-0.48 Ma) is one of the most dynamic periods of Quaternary-time, coinciding with the transition from obliquity- to eccentricity-forced climate. East Anglia possesses Britain’s most complete (albeit highly-fragmented) onshore record of environmental change during this time-interval and was situated within the western margins of the North Sea Basin of the time. The geological record from the region offers an important insight into the complex pat...

Lee, Jonathan; Rose, James; Candy, Ian

2015-01-01

89

The first radiation dates of syngenetic Late Pleistocene ice-wedges  

International Nuclear Information System (INIS)

Direct radiocarbon dating of organic mater extracted directly from ice wedges of the Late Pleistocene wedges of Siberia using the accelerating mass spectrometry was carried out. It is shown that the ice wedges opened in the cross section base at a height from 0 to +1 m started their formation about 21 thousand years ago. The rate of the wedges vertical growth in the course of 21-14.7 thousand of years. Subhorizontal age stratification of the ice-wedges formed by consecutive penetration of thawing ice water along with accumulation of precipitate on the surface, was confirmed

90

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

91

Cryostratigraphy of late Pleistocene syngenetic permafrost (yedoma) in northern Alaska, Itkillik River exposure  

Science.gov (United States)

Extremely ice-rich syngenetic permafrost, or yedoma, developed extensively under the cold climate of the Pleistocene in unglaciated regions of Eurasia and North America. In Alaska, yedoma occurs in the Arctic Foothills, the northern part of the Seward Peninsula, and in interior Alaska. A remarkable 33-m-high exposure along the lower Itkillik River in northern Alaska opened an opportunity to study the unmodified yedoma, including stratigraphy, particle-size distribution, soil carbon contents, morphology and quantity of segregated, wedge, and thermokarst-cave ice. The exposed permafrost sequence comprised seven cryostratigraphic units, which formed over a period from > 48,000 to 5,000 14C yr BP, including: 1) active layer; 2) intermediate layer of the upper permafrost; 3-4) two yedoma silt units with different thicknesses of syngenetic ice wedges; 5) buried peat layer; 6) buried intermediate layer beneath the peat; and 7) silt layer with short ice wedges. This exposure is comparable to the well known Mus-Khaya and Duvanny Yar yedoma exposures in Russia. Based on our field observations, literature sources, and interpretation of satellite images and aerial photography, we have developed a preliminary map of yedoma distribution in Alaska.

Kanevskiy, M.; Shur, Y.; Fortier, D.; Jorgenson, M. T.; Stephani, E.

2011-05-01

92

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.

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

2012-08-01

93

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

Directory of Open Access Journals (Sweden)

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

Li Shouhsien

2009-06-01

94

A reappraisal of the stratigraphy and depositional development of the Upper Greensand (Late Albian) of the Devizes District, southern England  

OpenAIRE

A reappraisal of the stratigraphy and depositional development of the Upper Greensand (Late Albian) of the Devizes District, southern England. Proceedings of the Geologists’ Association, XXX. 000 - 000. Three members are recognised within the Upper Greensand Formation of the Devizes district on the basis of outcrop, newly acquired cored borehole and petrographical data. These are, in ascending stratigraphical order, Cann Sand Member, Potterne Sandstone Member and Easterton...

Woods, Mark; Wilkinson, Ian; Lott, Graham; Booth, Kathryn; Farrant, Andrew; Hopson, Peter; Newell, Andrew

2008-01-01

95

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

Science.gov (United States)

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

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

2007-01-01

96

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

Science.gov (United States)

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

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

2013-03-01

97

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

DEFF Research Database (Denmark)

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

Buylaert, Jan-Pieter; Jain, M.

2012-01-01

98

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

Science.gov (United States)

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

99

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

100

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

101

Stratigraphy of Late-Phase Caldera Deposits: Pululagua Volcanic Complex, Ecuador  

Science.gov (United States)

The Pululagua Volcanic Complex (PVC), located 15 km north of Quito, Ecuador, includes numerous lava domes, pre and post-caldera dome deposits, an elongate caldera, and multi-phase ignimbrite deposits. Caldera formation resulted from four eruptive episodes within a span of several hundred years. The focus of this work is a late-phase pyroclastic flow deposit dispersed in an ESE direction. In order to better understand deposit stratigraphy, we couple GPR interpretations with stratigraphic observations. Four GPR study sites were chosen based on the proximity to observable deposits and accessibility. In general, our GPR transects run both normal and parallel to the direction of flow. The use of 100 and 200 MHz antennas yields a penetration depth of 10 to 18 meters. This depth range allows us to constrain pyroclastic flow thickness as it varies with distance from the vent and with paleotopography. In outcrop, it is evident that the Pululagua deposits show transitions between those of pyroclastic flows and pyroclastic surges. Whether these transitions can be identified in the GPR record is the subject of ongoing investigation.

Petriello, J.; Kruse, S.; Connor, C.; Connor, L.

2006-12-01

102

Environmental evolutions of the Alzette valley (Grand Duchy of Luxembourg) since Late Pleistocene  

Science.gov (United States)

The Alzette River rises within France, approximately 4 km south of the French-Luxembourg border, and has a total length of 73 kilometres before joining the Sauer which is a left-bank tributary of the Moselle River. During the construction of the "Nordstrooss" motorway (going north from Luxembourg city towards Ettelbruck) a viaduct was built that crosses the wide alluvial plain (about 1 km) of the Alzette River valley near Lorentzweiler. A lot of drillings were also made for geotechnical purposes by the Geological survey of Luxembourg (SGL). The drillings were able to provide informations about the sediments preserved in the Alzette River valley floor. This information has allowed the construction of a cross-profile through the valley showing the stratigraphy of the quaternary deposits, and illustrating that it was the result of a rather complex evolution (aggradation and incision periods leading to terraces formation, input of slope deposits at the valley margins, possible eolian input, …). A multidisciplinary research project thus started, aiming to reconstruct the paleoenvironment of the Alzette region during the late Pleistocene and Holocene periods. The drilling results make it possible to reconstruct the geometry of the quaternary sedimentary units of the Alzette valley. Three stepped alluvial units are recognized along the cross profile: the lower one (Az0) corresponds with the maximal incision of the Alzette. It is preserved in the western part of the floodplain, with base being located at about 212 m a.s.l.. In the eastern part of the valley the contact between the fluvial deposits and the substratum is located at about 215 m a.s.l.: these deposits may also be allocated to a lower terrace Az1 (relative height : +3 m). A third alluvial unit Az2 was recognized in two drillings, with bedrock located at about 224 m a.s.l. (+12 m). The channel migration in the valley and the assumed meandering dynamics (suggested by the weakness of the longitudinal slope) led to meander downcuttings and to the formation of oxbow lakes. These former oxbow-lakes are subjected either to a mineral or organic filling, the predominance of this latter leading to the formation of peat bogs. Radiocarbon datings were obtained on peaty levels from two drillings, FR-200-364 (Beta-249559:3400±40 BP, Beta-249560:4660±40 BP, Beta-249561:9390±60 BP) and FR-200-365 (Beta-240994:7250±40 BP, Beta-249562:12100±70 BP, Beta-249563:11910±70 BP). Taking account of this dating, sequences of peats found in recent drillings, downstream the viaduct, could belong to the first part of the Holocene. In one of this new drillings (FR-207-353), it is also important to note presence of an organic level within the coarse sediments. It is located at approx. 211 m a.s.l., and contains numerous rests of mollusc shells. Further radiocarbon dating and palynological study are consequently be realised for this level and the new sequence of peats. Two studies in the area are also to considerate: - in the drilling FR-201-055 (located at the western part of the valley), the dating of moss remains (bryophyts) preserved in a clayey level gave an age estimate of about 25280±220 BP (Beta-182249). This result is in good agreement with palynological data, suggesting a dry and cold environment. This age has however to be confirmed due, first to a possible reservoir effect (more study of the bryophyts remains is needed), and secondly to the incoherence and heterogeneity of the drilling samples (mix of alluvial and slope deposits); - in a western tributary called "Seisselbaach stream" a molluscan analysis from a tufaceous holocene deposit has done and a radiocarbon age of 9820±120 BP (Beta-181807) was obtained on charcoal fragments too small for identification. The upstream course of this small river valley offers very convenient conditions to study the end of the glacial period and the beginning of the warmer period in a continental setting. Further results should then lead to improve the global environmental evolution in the Luxembourg area since the last c

Naton, H.-G.; Ruffaldi, P.; Meyrick, R.; Maquil, R.; Colbach, R.; Kausch, B.; Baes, R.; Stead, A.; Le Brun-Ricalens, F.; Brou, L.; Schoellen, A.

2009-04-01

103

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

Directory of Open Access Journals (Sweden)

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

Costa Marta D

2010-12-01

104

The end-Ordovician glaciation and the Hirnantian Stage: A global review and questions about Late Ordovician event stratigraphy  

Science.gov (United States)

This paper proposes a global review of Hirnantian event stratigraphy. The Hirnantian GSSP in south China is tentatively correlated with latest Ordovician strata from the peri-Gondwanan "glacial" regions. Problems of biostratigraphical correlation are highlighted. At a worldwide scale, the major biostratigraphically useful fossil groups (graptolites, chitinozoans, brachiopods, conodonts, acritarchs) are analysed and their limits for global correlation of the uppermost Ordovician are discussed. Palaeobiogeographical disparities are invoked as the primary cause of the difficulty in establishing an effective Late Ordovician global biostratigraphical scheme. As an alternative correlative tool, the HICE (Hirnantian Isotopic Curve Excursion) event is often put forward in the literature. However, carbon isotope chemostratigraphy shows, like biostratigraphy, some limits to the present state of knowledge. No good independent biostratigraphical control of the HICE exists in both shallow carbonate deposits and deeper shaly ones. Recent studies have also demonstrated inconsistencies between carbon isotopic signals obtained from organic ( ?13C org) and inorganic ( ?13C carb) carbon species, further complicating the use of the HICE as an isochronous benchmark. All of these difficulties for Hirnantian event stratigraphy are discussed in detail in order to enable them to be overcome in the future. Precise Late Ordovician and early Silurian event stratigraphies are essential for the understanding of the mechanisms linked to the first of the "Big Five" extinctions.

Delabroye, A.; Vecoli, M.

2010-02-01

105

Using obsidian transfer distances to explore social network maintenance in late Pleistocene hunter-gatherers.  

Science.gov (United States)

Social behaviour is notoriously difficult to study archaeologically and it is unclear how large the networks of prehistoric humans were, or how they remained connected. Maintaining social cohesion was crucial for early humans because social networks facilitate cooperation and are imperative for survival and reproduction. Recent hunter-gatherer social organisation typically comprises a number of nested layers, ranging from the nuclear family through to the ~1500-strong ethnolinguistic tribe. Here we compare maximum obsidian transfer distances from the late Pleistocene with ethnographic data on the size of the geographic areas associated with each of these social grouping layers in recent hunter-gatherers. The closest match between the two is taken to indicate the maximum social layer within which contact could be sustained by Pleistocene hominins. Within both the (sub)tropical African and Subarctic biomes, the maximum obsidian transfer distances for Pleistocene modern humans (~200km and ~400km respectively) correspond to the geographic ranges of the outermost tribal layer in recent hunter-gatherers. This suggests that modern humans could potentially sustain the cohesion of their entire tribe at all latitudes, even though networks are more dispersed nearer the poles. Neanderthal obsidian transfer distances (300km) indicate that although Neanderthal home ranges are larger than those of low latitude hominins, Neanderthals travelled shorter distances than modern humans living at the same high latitudes. We argue that, like modern humans, Neanderthals could have maintained tribal cohesion, but that their tribes were substantially smaller than those of contemporary modern humans living in similar environments. The greater time taken to traverse the larger modern human tribal ranges may have limited the frequency of their face-to-face interactions and thus necessitated additional mechanisms to ensure network connectivity, such as the exchange of symbolic artefacts including ornaments and figurines. Such cultural supports may not have been required to the same extent by the Neanderthals due to their smaller tribes and home ranges. PMID:25214705

Pearce, Eiluned; Moutsiou, Theodora

2014-12-01

106

Loess deposition and Paleolithic human activity in late Pleistocene in North China  

Science.gov (United States)

Loess is one of the best geological records in the world for reconstruction of paleoenvironment. Loess deposited widely in North China in Quaternary, composing the famous Chinese Loess Plateau where loess sections could be as thick as 200 m. In these thick loess profiles, various archaeological remains including human fossils are found across the Chinese Loess Plateau, which indicates the aeolian loess deposition provides a good preservation environment for archaeological remains or the environment when loess is deposited in North China is favorable for human subsistence. Therefore, well developed loess studies using conventional methods such as grain size, magnetism, carbonate contents, TOC and biological or chemical methods like pollen, phytolith, stable isotopes, could provide important information for archaeologists about site formation process, human subsistence environment and human adaptation behaviors. This study focuses on late Pleistocene environment change and human adaptation in Chinese Western Loess Plateau. Over fifty Paleolithic sites were found buried in loess sections in two small rive catchments about 400 km2 in Chinese Western Loess Plateau in this study. Based on the well loess study in this region, the ages of most of the sites could be easily assumed in the field, which were usually confirmed by later radiocarbon or OSL dating results. Paleoenvironment of human subsistence is reconstructed using pollen, grain size, magnetism studies on the loess profiles producing archaeological remains. The chronological framework built with absolute dating results and loess-paleosol sequence comparison shows that humans first appear in the study area during warm and humid MIS5, may have abandoned the area in cold MIS4, reappeared in cool but humid MIS3 and continued thereafter, even extremely cold and dry LGM. A comprehensive study of 3727 pieces of stone artifacts shows that small-flake-tool industry is dominant through most of the late Pleistocene and microblade technology appeared and prevailed after the LGM. Combined with paleoenvironmental studies, settlement patterns indicate that late Pleistocene hunter-gatherers in the region exploited multiple landforms during MIS 3, while more central-place strategies were employed beginning during the LGM, which is closely related to environment change and human behavioral adaptation strategy developments. From this study, human-environment interaction, including human technological and mobility adaptation, is better understood benefited from the well-developed loess studies. Hence, a good combination of paleoenvironment study of loess and archaeology provides important information about ancient human subsistence strategy or even provides some useful suggestions for modern people.

Zhang, D.

2013-12-01

107

Late Cenozoic deposits, landforms, stratigraphy, and tectonism in Kittitas Valley, Washington  

Science.gov (United States)

Kittitas Valley, a structurally determined wide segment of the Yakima River valley, is partly filled with the Pliocene Thorp Gravel and with Pleistocene till, outwash, and related sediment that accumulated during three glaciations. The Thorp Gravel, whose age according to fission-track dating is about 3.7 m.y., forms a conspicuous fill terrace locally as high as 130 m. Bodies of drift, all younger than the Thorp Gravel, form nested fill terraces along the Yakima River. The massive moraines, intermediate morphostratigraphic position, and well-developed soil of the Kittitas Drift suggest its correlation with the penultimate northern-hemisphere glaciation of about 0.13 m.y. ago. The Lakedale Drift, which composes a single outwash terrace in Kittitas Valley, evidently correlates with the classical late Wisconsin Glaciation. The newly named Lookout Mountain Ranch Drift, which forms moraines at higher altitudes than and is older than the Kittitas Drift, lacks an attendant valley train. Three faults disrupt the Thorp Gravel but apparently not the Kittitas Drift, and therefore probably are between 0.13 and 3.7 m.y. old. The eastward trend and up-to-the-basin throw of the faults probably reflect reverse faulting due to a regional north-south compression that uparched several east-trending anticlines in central Washington. The southeast trend of the dextrally echelon arrangement of the faults apparently is due to a right-lateral couple across a zone parallel to the Olympic-Wallowa lineament.

Waitt, Richard B.

1979-01-01

108

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

Science.gov (United States)

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

109

Geophysical implications of presen-day and late Pleistocene ice melting across New Zealand  

Science.gov (United States)

According to the estimation given by Chinn (2001) in total a 53 km3 of ice volume was accumulated over New Zealand during the Pleistocene covering an area of about 1160 km2 concentrated mainly along the South Island between 42 and 46 arc-deg of southern latitudes. Most recently a new mass balance monitoring program has been established with on-site support by the World Glaciers Monitoring Service (WGMS). Chinn (1996) suggests an increase retreating of glaciers with a net ice volume loss between 1977 and 2005 of about 11% (Unep, 2008). In this study we investigate the sensitivity of New Zealand's coastal regions to decadal glaciers melting (estimated by Chinn 1996) by means of sea level change and bedrock deformations. A regional present-day ice melting model, composed by disc loads with fixed positions spaced in order to minimize the overlaps, is developed and applied. We provide an estimate of the global patterns of sea level (fingerprints) associated with the melting of New Zealand's glaciers assuming an incompressible and elastic earth model. The predicted elastic deformation field is combined with the estimates of the visco-elastic deformation field associated with the melting of the late-Pleistocene ice sheets according to a set of plausible combinations of ice chronology and mantle viscosity. The total deformation field is then compared with GPS observations.

Ruggieri, G.; Tenzer, R.; Spada, G.; Fadil, A.

2012-04-01

110

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

111

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

112

Direct evidence for human reliance on rainforest resources in late Pleistocene Sri Lanka.  

Science.gov (United States)

Human occupation of tropical rainforest habitats is thought to be a mainly Holocene phenomenon. Although archaeological and paleoenvironmental data have hinted at pre-Holocene rainforest foraging, earlier human reliance on rainforest resources has not been shown directly. We applied stable carbon and oxygen isotope analysis to human and faunal tooth enamel from four late Pleistocene-to-Holocene archaeological sites in Sri Lanka. The results show that human foragers relied primarily on rainforest resources from at least ~20,000 years ago, with a distinct preference for semi-open rainforest and rain forest edges. Homo sapiens' relationship with the tropical rainforests of South Asia is therefore long-standing, a conclusion that indicates the time-depth of anthropogenic reliance and influence on these habitats. PMID:25766234

Roberts, Patrick; Perera, Nimal; Wedage, Oshan; Deraniyagala, Siran; Perera, Jude; Eregama, Saman; Gledhill, Andrew; Petraglia, Michael D; Lee-Thorp, Julia A

2015-03-13

113

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

Energy Technology Data Exchange (ETDEWEB)

We discuss the {sup 14}C 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 {sup 14}C 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 {sup 14}C dates yield for the first time a timescale (in {sup 14}C years) for paleoclimatic indicators (oxygen and hydrogen isotope ratios from the ice)

Vasil' chuk, Yurij K. E-mail: vasilch@orc.ru; Plicht, Johannes van der; Jungner, Hoegne; Vasil' chuk, Alla C

2000-10-01

114

The age of Late Pleistocene shorelines and tectonic activity of Taranto area, Southern Italy  

Science.gov (United States)

The results of isoleucine epimerization ratios in pelecypods ( Glycymeris sp., Arca sp. and Cerastoderma sp.) and U-series dating of bivalves and Cladocora caespitosa sampled from different Late Pleistocene units in the Chéradi Islands and in the coastal areas of Mar Piccolo and Mar Grande near Taranto (Apulia region, Italy) are presented. U-series measurements on pelecypods and on corals directly associated with mollusc samples provide an independent calibration of amino acid data. The D/ L ratios of isoleucine show a strong correlation with age, and thus may be considered as a predictive dating technique. This correlation also supports the reliability of U-series ages obtained for molluscs. These results, including the stratigraphic position, the lithological lateral continuity, the morphological evidence and the palaeontological characteristics of the various units, made it possible to attribute them to different marine trangressive phases referable to oxygen isotope stages (OIS) 5e-c, 5a and 3. No evidence of land emersion between OIS 5e and 5c has been found in the area. Pinkish/red sands deposits located above present sea level (˜1 m) have been referred to OIS 3. The Late Pleistocene morphological evolution and uplift of a complex area between the Apulian foreland and the Bradanic foredeep have been reconstructed. Due to the lack of incontestable indicators of past sea level stands the facies analysis has been performed on U-series dated 89.8 ka, OIS 5c shoreline north of Mar Piccolo and an uplift rate ranging from 0.21-0.27 mm/yr has been calculated.

Belluomini, G.; Caldara, M.; Casini, C.; Cerasoli, M.; Manfra, L.; Mastronuzzi, G.; Palmentola, G.; Sanso, P.; Tuccimei, P.; Vesica, P. L.

2002-02-01

115

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

116

Middle Pleistocene palaeoenvironments and the late Lower-Middle Palaeolithic of the Hrazdan valley, central Armenia  

Science.gov (United States)

The palaeogeographic importance of the southern Caucasus in the Pleistocene as a region of population expansion and contraction between Africa, the Levant and Eurasia is well established as a result of recent archaeological works in the Republics of Armenia and Georgia. Not only does the area have a unique Palaeolithic record, but the presence of volcanic layers in association with archaeological sites and off site sequences means that there is the potential for both high precision dating and correlation. The Hrazdan valley, central Armenia is a case in point. Late Lower to late Middle Palaeolithic sites found as a result of systematic survey and then explored in excavations in 2008-2011 are associated with various volcanogenic strata. 40K/40Ar and 40Ar/39Ar dating in the 1970-2000s demonstrates the onset of volcanism in the adjacent Gegham range in the period 700-500ky BP, while recent 40Ar/39Ar dates on the latest lava from the Gutanasar volcano shows the latest effusive eruption to have occurred at c. 200 ky BP. Nine Middle Pleistocene lavas from the intervening period have been mapped in the Hrazdan valley in a 15km-long study area 12km north-east of Yerevan. Several of the basalts seal terrestrial strata, and thereby bury and 'fossilize' earlier landscapes. The most significant of these is sandwiched between basalts dating to 200 and 440ky BP, where a 135m-long exposure contains a palaeosol developing in floodplain alluvium and in situ archaeological material (Nor Geghi 1). Morphological and micromorphological examination of site strata suggest that hominin activity took place during a temperate episode, which 40Ar/39Ar dating of interbedded crypotephra suggests was MIS 9e. However, strata at other locales buried beneath the same 200ky BP basalt suggest that the landscape occupied by these hominids was a mosaic of river channels, floodplains and lakes. The fossilized MIS 9 landscape is not unique as further lacustrine deposits are buried beneath earlier Middle Pleistocene basalts, although earlier archaeological sites have yet to be found.

Wilkinson, Keith; Adler, Daniel; Nahapetyan, Samvel; Smith, Victoria; Mark, Darren; Mallol, Carolina; Blockley, Simon; Gasparian, Boris

2014-05-01

117

3D seismic interpretations of the Pliocene-Pleistocene stratigraphy and tunnel valleys of the North Sea Plateau-Fladen area, northern North Sea  

Science.gov (United States)

The increasing coverage of 3D seismic data across the North Sea has allowed the detailed investigation of depositional environments extending beyond the most recent glacial advance into the basin. There are several generations of channels and incisions interpreted as tunnel valleys of varying size at varying stratigraphic depths throughout the Pliocene-Pleistocene units in the North Sea. Many of these features appear to have been reactivated on more than one occasion. The acoustic character of sediments infilling these features is also variable even within the same channel and their significance in relation to palaeo-ice sheet dynamics is still debated. We suggest that some of the observed incisions/valleys, particularly those formed around the Pliocene-Pleistocene boundary, may in fact be fluvial features rather than subglacially formed (based on size and flow path). Many of the smaller, straighter more recent generations of channels probably formed subglacially. If some of the older channels are fluvial, this has significant implications for the marine limit during this late Pliocene early Pleistocene period in the northern North Sea. Palaeo-iceberg scours are also found at certain stratigraphic horizons and these can be compared to those horizons with valleys/channels. Interpretations of the acoustic units/features will also be based on information from well and shallow core data allowing their depositional history and chronology to be investigated. Several physical properties have been measured on a number of cores from the investigated area. To be able to refine the chronology of the Pleistocene sediments for this part of the North Sea we plan to carry out new analyses and dating (strontium, radiocarbon and amino acid) on shallow cores/well material from the region. This will allow us to better constrain the times at which channels were being formed in this area and relate this to known glacial cycles in the North Sea.

Reinardy, Benedict; Hjelstuen, Berit; Petter Sejrup, Hans; Stoddart, Daniel

2014-05-01

118

The Late Middle Pleistocene biostratigraphy of the Thames Valley, England: new data from eastern Essex  

Science.gov (United States)

Coring investigations at East Hyde, near Tillingham, Essex, have revealed a sequence of fluvial and estuarine deposits infilling a channel incised into London Clay. These deposits are of Thames origin and were deposited after the river's diversion into eastern Essex late in the Anglian Stage. The detailed litho- and biostratigraphy of the deposits are described. Ostracod and molluscan data confirm that the lower parts of the sequence accumulated in a quiet, fluvial environment rich in aquatic vegetation. The upper sediments accumulated in an inner estuarine environment under conditions of rising sea level. Pollen assemblages from both units show strong biostratigraphical affinities with the Hoxnian Stage, particularly with the Hoxnian late temperate substage, Ho III. The sequence has also yielded a rare assemblage of freshwater fluvial molluscs, the 'Rhenish' fauna, which migrated into the Thames following a link with the rivers of continental Europe. The occurrence of Theodoxus serratiliniformis is exceptionally rare, representing only the second record of the species in the entire British Pleistocene. The molluscan assemblages show striking similarities with those at Clacton in northeast Essex and Swanscombe, Kent, and provide strong evidence that the three sites are contemporaneous and were connected in the same fluvial system. The timing of the migration of the 'Rhenish' fauna into Britain and the implications for sea-level reconstruction in the southern North Sea region are discussed. The episode of major climatic warmth and high eustatic sea level represented at East Hyde is correlated with Stage 11 of the deep sea record.

Roe, Helen M.

2001-10-01

119

Late Pleistocene and early Holocene rivers and wetlands in the Bonneville basin of western North America  

Science.gov (United States)

Field investigations at Dugway Proving Ground in western Utah have produced new data on the chronology and human occupation of late Pleistocene and early Holocene lakes, rivers, and wetlands in the Lake Bonneville basin. We have classified paleo-river channels of these ages as "gravel channels" and "sand channels." Gravel channels are straight to curved, digitate, and have abrupt bulbous ends. They are composed of fine gravel and coarse sand, and are topographically inverted (i.e., they stand higher than the surrounding mudflats). Sand channels are younger and sand filled, with well-developed meander-scroll morphology that is truncated by deflated mudflat surfaces. Gravel channels were formed by a river that originated as overflow from the Sevier basin along the Old River Bed during the late regressive phases of Lake Bonneville (after 12,500 and prior to 11,000 14C yr B.P.). Dated samples from sand channels and associated fluvial overbank and wetland deposits range in age from 11,000 to 8800 14C yr B.P., and are probably related to continued Sevier-basin overflow and to groundwater discharge. Paleoarchaic foragers occupied numerous sites on gravel-channel landforms and adjacent to sand channels in the extensive early Holocene wetland habitats. Reworking of tools and limited toolstone diversity is consistent with theoretical models suggesting Paleoarchaic foragers in the Old River Bed delta were less mobile than elsewhere in the Great Basin.

Oviatt, Charles G.; Madsen, David B.; Schmitt, Dave N.

2003-09-01

120

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

Directory of Open Access Journals (Sweden)

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

Huang Jen-Pan

2011-04-01

121

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

122

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

DEFF Research Database (Denmark)

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

Campos, Paula F; Willerslev, Eske

2010-01-01

123

Late Silurian and Early Devonian conodont stratigraphy in the Prague Synform and correlation of bioevents.  

Czech Academy of Sciences Publication Activity Database

Buenos Aires : Asociacio?n Paleontolo?gica Argentina, 2013 - (Albanesi, G.; Ortega , G.). s. 149-149 [Conodonts from the Andes : International Conodont Symposium /3./. 15.07.2013-19.07.2013, Mendoza] Institutional support: RVO:67985831 Keywords : conodonts * stratigraphy * Silurian * Devonian Subject RIV: DB - Geology ; Mineralogy

Slavík, Ladislav

124

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

Energy Technology Data Exchange (ETDEWEB)

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

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

1994-12-31

125

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

126

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

Science.gov (United States)

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

Kloosterman, J. B.

2007-05-01

127

Late Pliocene and Early Pleistocene vegetation history of northeastern Russian Arctic inferred from the Lake El'gygytgyn pollen record  

OpenAIRE

The 318 m thick lacustrine sediment record from Lake El'gygytgyn, northeastern Russian Arctic cored by the international El'gygytgyn Drilling Project provides unique opportunities for 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 demonstrate their value as an excellent archive of vegetation and climate changes during the Late Pliocene and Early Pleistocene. ...

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

2014-01-01

128

Glacial and Fluvial Deposits in the Aragón Valley, Central-Western Pyrenees: Chronology of the Pyrenean Late Pleistocene Glaciers  

OpenAIRE

[EN] The Aragón Valley glacier (Central Western Pyrenees) has been studied since the late nineteenth century and has become one of the best areas in the Pyrenees to study the occurrence of Pleistocene glaciations and the relationships between moraines and fluvial terraces. New morphological studies and absolute ages for moraines and fluvial terraces in the Aragón Valley allow a correlation with other Pyrenean glaciers and provide solid chronologies about the asynchroneity between global las...

Garci?a-ruiz, Jose? Mari?a; Marti? Bono, Carlos Enrique; Pen?a Monne?, Jose? Luis; Sancho, C.; Rhodes, E. J.; Valero-garce?s, Blas L.; Gonza?lez-sampe?riz, Pene?lope; Moreno Caballud, Ana

2013-01-01

129

Mamíferos del pleistoceno terminal de la localidad de El Hatillo, Panamá / Late pleistocene mammals from El Hatillo, Panama  

Scientific Electronic Library Online (English)

Full Text Available SciELO Costa Rica | Language: Spanish Abstract in spanish Documentamos aquí por primera vez los mamíferos del Pleistoceno tardío de la localidad de El Hatillo en la península de Azuero en Panamá, originalmente reportado por C. L. Gazin en 1957. Los siguientes taxa están presente: Hoplophorinae?, Glyptotherium floridanum, Eremotherium laurillardi, Paramylod [...] on harlani, Equus conversidens, Platygonus sp., Odocoileus sp., Mixotoxodon larensis y Cuvieronius hyodon. Este es un conjunto característico de mamíferos del Pleistoceno Tardío de Centroamérica destacado por fósiles de Eremotherium en asociación con fósiles de Mixotoxodon y Equus. Me refiero a este tipo de asociación como montaje EME y postulo que la mayoría de estos montajes de Centroamérica son de edad del Pleistoceno Tardío. Los montajes EME representan una fauna mixta de pasteadores y ramoneadores que eran muy común en toda Centroamérica durante uno o más de los fines interestadiales del Pleistoceno. Abstract in english Late Pleistocene mammals from the El Hatillo locality on the Azuero Peninsula in Panama, originally reported by C. L. Gazin in 1957, are documented here for the first time. The following taxa are present: Hoplophorinae?, Glyptotherium floridanum, Eremotherium laurillardi, Paramylodon harlani, Equus [...] conversidens, Platygonus sp., Odocoileus sp., Mixotoxodon larensis and Cuvieronius hyodon. This is a characteristic assemblage of late Pleistocene mammals from Central America that is dominated by fossils of Eremotherium in association with fossils of Mixotoxodon and Equus. I refer to such associations as EME assemblages and posit that most of these assemblages from Central America are of Late Pleistocene age. EME assemblages represent a mixed fauna of grazers and browsers that was common across Central America during one or more of the Late Pleistocene interstadials.

Spencer G., Lucas.

2014-06-01

130

A Late Pleistocene ice field in the Godeanu Mountains, Southern Carpathians  

Directory of Open Access Journals (Sweden)

Full Text Available The possible existence of plateau type glaciations – ice caps, ice fields or plateau glaciers - in the Godeanu Mountains, Southern Carpathians during the Late Pleistocene is the main topic of this investigation. The Godeanu Mountains is one of the westernmost mountain range of the Southern Carpathians. It is located north of the River Cerna and south of the ?arcu and Retezat Mountains. The question about the existence of former plateau type glaciers in the Godeanu Mountains emerged due to the widespread presence of the Bor?scu surface in the region. The Bor?scu surface, which was described for the first time in the early 20th century by Martonne (1907, is an uplifted peneplain, which could be found in many mountain ranges in the Southern Carpathians. It’s main features are a quite small relief and a high elevation range of 1800- 2200 m a.s.l.. The most typical appearance of it is located in the Godeanu Mountains, where shallow glacial valleys surround the central plateaus.

Ádám IGNÉCZI

2014-11-01

131

Late Pleistocene age and archaeological context for the hominin calvaria from GvJm-22 (Lukenya Hill, Kenya).  

Science.gov (United States)

Kenya National Museums Lukenya Hill Hominid 1 (KNM-LH 1) is a Homo sapiens partial calvaria from site GvJm-22 at Lukenya Hill, Kenya, associated with Later Stone Age (LSA) archaeological deposits. KNM-LH 1 is securely dated to the Late Pleistocene, and samples a time and region important for understanding the origins of modern human diversity. A revised chronology based on 26 accelerator mass spectrometry radiocarbon dates on ostrich eggshells indicates an age range of 23,576-22,887 y B.P. for KNM-LH 1, confirming prior attribution to the Last Glacial Maximum. Additional dates extend the maximum age for archaeological deposits at GvJm-22 to >46,000 y B.P. (>46 kya). These dates are consistent with new analyses identifying both Middle Stone Age and LSA lithic technologies at the site, making GvJm-22 a rare eastern African record of major human behavioral shifts during the Late Pleistocene. Comparative morphometric analyses of the KNM-LH 1 cranium document the temporal and spatial complexity of early modern human morphological variability. Features of cranial shape distinguish KNM-LH 1 and other Middle and Late Pleistocene African fossils from crania of recent Africans and samples from Holocene LSA and European Upper Paleolithic sites. PMID:25730861

Tryon, Christian A; Crevecoeur, Isabelle; Faith, J Tyler; Ekshtain, Ravid; Nivens, Joelle; Patterson, David; Mbua, Emma N; Spoor, Fred

2015-03-01

132

Provenance of Palouse Loess and Relation to Late Pleistocene Glacial Outburst Flooding, Washington State  

Science.gov (United States)

The eolian system of the Pacific Northwest is a product of long-term deflation of expansive sedimentary units by prevailing winds throughout the Quaternary. The Palouse loess is a deposit of wind-blown silt that covers approximately 10,000 sqare km up to 75 m thick. Late Quaternary units of the loess become finer texturally and thinner to the northeast, suggesting that they were derived from sedimentary basins south and west. The source of the loess has been inferred and hypothesized but never directly determined. A geochemical study of the late-Pleistocene to Holocene L1 unit of the Palouse loess and its possible sources was conducted to determine its provenance. There are two sedimentary units that lie upwind of the loess that may have contributed sediment via eolian deflation: 1) sand- and silt-rich slackwater sediment derived from late-Pleistocene outburst flooding of glacial Lake Missoula, and 2) sand- and silt-rich sediment from the Miocene-Pliocene Ringold Formation. Both are very similar in mineral composition, being derived from plutonic, metamorphic, and volcanic rocks of the western United States and southern British Columbia. Major and trace element data determined by x-ray fluorescence (XRF) of silt to very fine sand from loess and potential source sediments was used to pinpoint the exact source of the loess. A one-to-one relationship of major and trace elements exists between eolian and flood sediments, whereas Ringold Formation sediments have elevated Ti, P, Mg, and Ca oxides and lower K oxide values as well as scattered trace element values relative to Palouse loess. These trends may be due to the presence of basalt lithic grains in flood sediment that have been broken down and distributed throughout the loess. The Ringold Formation lacks appreciable amounts of basalt. The geochemical data from this study demonstrates that flood sediment is the dominant source of eolian material for the Palouse loess. The spatial distribution of the possible source sediments also suggests that flood slackwater sediment is the dominant source. Slackwater flood sediments rest in basins upwind of loess, where deflation is documented today. The Ringold Formation has limited exposure near the present day Columbia River and was eroded by outburst floods or covered by slackwater sediments. Its limited extent and exposure makes the Ringold Formation an less likely candidate for a source of the L1 loess. Study of the oldest units of Palouse loess will show whether or not the Ringold contributed a larger proportion of eolian material prior to the onset of glacial outburst flooding. This new provenance data will allow estimates to be made of the volume of dust ejected into the atmosphere from the Palouse eolian system since the last glacial maximum, which is essential to modeling of atmospheric dust fluxes that force climate fluctuations.

Sweeney, M. R.; Busacca, A. J.; Gaylord, D. R.; Zender, C. S.

2002-12-01

133

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

Science.gov (United States)

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

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

2013-04-01

134

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

Scientific Electronic Library Online (English)

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

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

2006-06-01

135

Relationship between Late Pleistocene sea-level variations, carbonate platform morphology and aragonite production (Maldives, Indian Ocean)  

DEFF Research Database (Denmark)

A piston core from the Maldives carbonate platform was investigated for carbonate mineralogy, grain-size distributions, calcium carbonate content and organic carbon. The sedimentary record was linked to Late Pleistocene sea-level variations, using an age model based on oxygen isotopes obtained from planktonic foramanifera, nannofossil biostratigraphy and C age determinations. The correlation between the sedimentary record and Late Pleistocene sea-level showed that variations in aragonite and mud during the past 150000years were clearly related to flooding and sea floor exposure of the main lagoons of the atolls of the Maldives carbonate platform. Platform flooding events were characterized by strongly increased deposition of aragonite and mud within the Inner Sea of the Maldives. Exposure events, in contrast, can be recognized by rapid decreases in the values of both proxy records. The results show that sediments on the Maldives carbonate platform contain a continuous record of Pleistocene sea-level variations. These sediments may, therefore, contribute to a better understanding of regional and even global sea-level changes, and yield new insights into the interplay between ocean currents and carbonate platform morphology. © 2011 The Authors. Journal compilation © 2011 International Association of Sedimentologists.

Paul, A.; Reijmer, J.J.G.

2012-01-01

136

Quantifying late Pleistocene lithospheric flexure and fault movements in the Mississippi Delta  

Science.gov (United States)

It is well known that a significant portion of the Mississippi Delta (MD) land surface is subsiding at rates on the order of a centimeter per year. Several recent studies have argued that lithospheric flexure due to sediment loading in the MD and fault movements in southeast Louisiana induce as much as ~6 mm/yr of subsidence, and therefore would be major driving forces of land-surface subsidence in the MD. However, geological rates of lithospheric flexure and fault movements have rarely been quantified. In this study, we quantify geological rates of these two processes in and near the MD by means of quartz optically-stimulated luminescence (OSL) dating of late Pleistocene sediments. Lithospheric flexure is quantified by studying long profiles of the Lower Mississippi River (LMR). Recent OSL dating of the Prairie Complex strata in the Lower Mississippi Valley (LMV) and MD identified segments of ~80 ka (MIS 5a) old LMR remnants. Comparing the reconstructed MIS 5a LMR long profile with the present-day long profile demonstrates that the former has been deformed due to lithospheric flexure associated with MD sediment loading, featuring uplift in the southern LMV and down-warping in the MD. Using the present-day long profile as a proxy for deformation of the MIS 5a long profile, the bulge in the southern LMV exhibits an average uplift rate of <0.15 mm/yr, whereas most of the MD north of 29.6°N has subsided <0.4 mm/yr on average during the past 80 ka. Farther south, where the Prairie Complex occurs 100 to 150 m below present-day sea level, subsidence rates due to lithospheric flexure may be up to 1 to 2 mm/yr. The half-wavelength of the flexural bulge in the LMV suggests a minimum elastic thickness of the lithosphere for this region of ~60 km. Fault movements were quantified at four locations along the Baton Rouge fault zone (BRFZ) in southeast Louisiana. Geomorphic and stratigraphic studies were used to identify fault-displaced strata that were subsequently OSL dated. Time-averaged fault slip rates are ~0.04 mm/yr, irrespective of strata age (ranging from 30 to 130 ka), suggesting that the fault slip rates exhibited little change over late Pleistocene time. Hillslope morphology along the surface expression of the BRFZ is consistent along-strike and from segment to segment; this observation, plus the consistency of slip rates temporally and spatially, suggests a creeping fault interpretation. Our new findings indicate that fault slip in the BRFZ is geologically slow (by several orders of magnitude) relative to the rapid land-surface subsidence in the MD. Furthermore, the MIS 5a long profile shows no abrupt slope change in the MD as would be expected if tectonic movements were driven by faulting. The combined effect of fault movement and lithospheric flexure, while geologically highly significant, is not a major cause of present-day land-surface subsidence on a regional scale in the MD.

Shen, Z.; Tornqvist, T. E.; Dawers, N. H.; Gasparini, N. M.; Milne, G. A.; Mauz, B.

2011-12-01

137

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

138

Atmospheric circulation patterns during late Pleistocene climate changes at Lake Malawi, Africa  

Science.gov (United States)

The climate of tropical Africa transitioned from an interval of pronounced, orbitally-paced megadroughts to more humid and stable conditions approximately 70,000 years ago (Scholz et al., 2007). The regional atmospheric circulation patterns that accompanied these climatic changes, however, are unclear due to a paucity of continental paleoclimate records from tropical Africa extending into the last interglacial. We present a new 140-kyr record of the deuterium/hydrogen isotopic ratio of terrestrial leaf waxes (?D wax) from drill cores from Lake Malawi, southeast Africa, that spans this important climatic transition. ?D wax shifts from highly variable and relatively D-depleted to more stable and D-enriched around 56 ka, contemporary with the onset of more humid conditions in the region. Moisture source and transport history dominate the ?D wax signal at Lake Malawi, with local rainfall amount playing a secondary role for much of the paleorecord. Analysis of modern moisture sources for Lake Malawi suggests that D-depletion of waxes during the megadroughts may have been caused by an enhanced contribution of the drier, D-depleted air mass currently located in central southern Africa to the Lake Malawi catchment. This D-depleted air mass is associated with the descending limb of the Hadley cell, which implies significant changes in the Hadley circulation during the megadroughts and related changes in the position of the Intertropical Convergence Zone over Africa. These findings demonstrate the ability of ?D wax to serve as an atmospheric tracer when used in conjunction with additional proxy records for moisture balance, and elucidate potential mechanisms for pronounced hydrological change in southeast Africa during the late Pleistocene.

Konecky, Bronwen L.; Russell, James M.; Johnson, Thomas C.; Brown, Erik T.; Berke, Melissa A.; Werne, Josef P.; Huang, Yongsong

2011-12-01

139

Sedimentary facies of the subaqueous Changjiang River delta since the late Pleistocene  

Science.gov (United States)

The sedimentary facies of the subaqueous Changjiang (Yangtze) River delta since the late Pleistocene was studied based on lithology and foraminifera analysis for two boreholes, CJK07 and CJK11, along with 14C dating. Four sedimentary facies were identified, namely fluvial, tidal flat, offshore, and prodelta facies. The fluvial sedimentary facies is comprised of fluvial channel lag deposits, fluvial point bar deposits, and floodplain deposits, showing a fining-upward sequence in general with no benthic foraminifera. A layer of stiff clay overlies the fluvial deposits in core CJK07, indicating a long-term exposure environment during the Last Glacial Maximum (LGM). During the postglacial sea-level rise around 13-7.5 cal ka BP, the tidal flat facies was deposited in core CJK11, characterized by abundant silt-clay couplets. Euryhaline species dominate the subtidal flat foraminiferal assemblages, while almost no foraminifera was found in the intertidal flat. The offshore environment was the major sedimentary environment when the sea level reached its highest level around 7.5 cal ka BP, with a maximum accumulation rate of 10 mm/a found in core CJK11. Prodelta sediments have been deposited in core CJK11 since ˜3 cal ka BP, after the formation of the Changjiang River delta. The difference in sedimentary facies between core CJK07 and CJK11 is due to their location: core CJK07 was in an interfluve while core CJK11 was in an incised valley during the LGM. Furthermore, AMS 14 C dating of core CJK07 shows poor chronological order, indicating that the sediments were reworked by strong tidal currents and that sediment deposited since ˜7.7 cal ka BP in core CJK07 was eroded away by modern hydrodynamic forces caused by the southward shift of the Changjiang River delta depocenter.

Xu, Taoyu; Shi, Xuefa; Wang, Guoqing; Qiao, Shuqing; Yang, Gang; Liu, Shengfa; Wang, Xuchen; Zhao, Quanhong

2013-09-01

140

Late Pleistocene-Holocene volcanism on the Kamchatka Peninsula, Northwest Pacific Region  

Science.gov (United States)

Late Pleistocene-Holocene volcanism in Kamchatka results from the subduction Pacific Plate under the peninsula and forms three volcanic belts arranged in en echelon manner from southeast to northwest. The cross-arc extent of recent volcanism exceeds 250 km is one of the widest worldwide. All the belts are dominated by mafic rocks. Eruptives SiO2>57% constitute ˜25% of the most productive Central Kamchatka Depression belt ˜30% of the Eastern volcanic front, but type signatures and are represented by basalt-rhyolite series differing in alkalis. Typical Kamchatka arc basalts display a strong increase in LILE, LREE and HFSE from the front to the back-arc. La/Yb and Nb/Zr increase from the arc front to the back arc while B/Li and As, Sb, B, Cl and S concentrations decrease. The initial mantle source below Kamchatka ranges from N-MORB-like in the volcanic and Central Kamchatka Depression to more enriched in the back arc. Rocks from the Central Kamchatka Depression range in 87Sr/86Sr ratios from 0.70334 to 0.70366, but have almost constant Nd isotopic ratios (143Nd/144Nd 0.51307-0.51312). This correlates with the highest U/Th ratios in these rocks and suggest the highest fluid-flux in the source region. Holocene large eruptions and eruptive histories of individual Holocene volcanoes have studied with the help of tephrochronology and 14C dating that permits analysis of time- patterns of volcanic activity, evolution of the erupted products, and volcanic hazards.

Ponomareva, Vera; Melekestsev, Ivan; Braitseva, Olga; Churikova, Tatiana; Pevzner, Maria; Sulerzhitsky, Leopold

141

Late Pleistocene and Recent geology of the Housatonic River region in northwestern Connecticut  

Science.gov (United States)

An investigation of Late Pleistocene and Recent surficial deposits in western Connecticut and adjacent areas was undertaken, to determine characteristics of Wisconsin glaciation and the history and chronology of deglaciation in part of the finely dissected New England Uplands. The study area lies along the midreach of the Housatonic River in western Connecticut, and has local relief exceeding 1,200 feet. Surface morphology and internal characteristics of glacial and glaciofluvial erosional and depositional features were examined and mapped in detail in the Kent and Ellsworth, Connecticut, USGS 7? minute quadrangles, and by reconnaissance in the surrounding quadrangles. This study contributes to the expanding detailed knowledge of glaciation and geomorphology in western New England and eastern New York state. Ice along the lateral east margin of the southward-waxing, Wisconsin-age, Hudson-Champlain Valley ice lobe successively overran ridges trending northeast-to-southwest. Late Wisconsin ice flow was consistently toward the southeast in the study area. Glacial erosion on the upland surfaces was weak, and several early or pre-Wisconsin meltwater channels persist, which evidence little late Wisconsin glacial or glaciofluvial modification. Deeply weathered rock has been locally preserved beneath unweathered till. Till deposits are generally thin, averaging from 10 to 15 feet in thickness, but till deposits exceeding 200 feet in thickness have been observed. Direct evidence for two or more cycles of till deposition is lacking, although multiple glaciations can be inferred from drainage derangement of the Housatonic River and from anomalies in configuration of old, upland melt-water channels which were re-occupied and eroded by melt water during subsequent deglaciations. The orientation of ridges and the local terrain relief exerted minor control on ice flow during waxing phases of glaciation. Local relief and ridges which were oriented transverse to ice flow became the dominant control factors for ice flow during late phases of deglaciation and ultimately initiated marginal stagnation zones. Late Wisconsin deglaciation evolved in three stages. First, the active ice margin receded rapidly northwestward across, and almost transverse to, the upland ridge crests in response to factors of both backwasting and downwasting. Second, local terrain relief restricted active ice flow, initiated stagnation, diverted melt-water flow and controlled deposition of small active ice-marginal deposits on the northwest slopes of ridges. Third, melting and thinning of stagnant ice tongues in valleys with ice surfaces which were low gradient and southward-sloping caused rapid northward recession of the stagnant ice margin. Sequences of related outwash deposits have been correlated with inferred ice-marginal, recessional positions. In this region, the zone of stagnant ice distal to active ice ranged from 6 to 15 miles in average width. Lacustrine sediments accumulated as stagnant ice blocks melted in isolated basins and other depressions where through-flowing melt-water drainage was restricted or absent. The paucity of ice-contact and outwash deposits in the isolated basins indicates that little entrained debris was present in the stagnant ice. Prograding outwash along the Housatonic River and other major drainage routes infilled glacially overdeepened underlying lacustrine sediments sand and gravel. rock basins and buried beneath upward-coarsening Upland bogs, which have developed postglacially, contain as much as 22 feet of organic material mixed with silt and clay. An age of 12,750 ? 230 years B.P. was determined for materials immediately above three feet of older organic-rich clay layers. This dated material correlates with the upper part of the pollen T zone reported elsewhere in Connecticut and New York.

Kelley, George C.

1977-01-01

142

Origin and stratigraphy of phreatomagmatic deposits at the Pleistocene Sinker Butte Volcano, Western Snake River Plain, Idaho  

Science.gov (United States)

Sinker Butte is the erosional remnant of a very large basaltic tuff cone of middle Pleistocene age located at the southern edge of the western Snake River Plain. Phreatomagmatic tephras are exposed in complete sections up to 100 m thick in the walls of the Snake River Canyon, creating an unusual opportunity to study the deposits produced by this volcano through its entire sequence of explosive eruptions. The main objectives of the study were to determine the overall evolution of the Sinker Butte volcano while focusing particularly on the tephras produced by its phreatomagmatic eruptions. Toward this end, twenty-three detailed stratigraphic sections ranging from 20 to 100 m thick were examined and measured in canyon walls exposing tephras deposited around 180° of the circumference of the volcano. Three main rock units are recognized in canyon walls at Sinker Butte: a lower sequence composed of numerous thin basaltic lava flows, an intermediate sequence of phreatomagmatic tephras, and a capping sequence of welded basaltic spatter and more lava flows. We subdivide the phreatomagmatic deposits into two main parts, a series of reworked, mostly subaqueously deposited tephras and a more voluminous sequence of overlying subaerial surge and fall deposits. Most of the reworked deposits are gray in color and exhibit features such as channel scour and fill, planar-stratification, high and low angle cross-stratification, trough cross-stratification, and Bouma-turbidite sequences consistent with their being deposited in shallow standing water or in braided streams. The overlying subaerial deposits are commonly brown or orange in color due to palagonitization. They display a wide variety of bedding types and sedimentary structures consistent with deposition by base surges, wet to dry pyroclastic fall events, and water saturated debris flows. Proximal sections through the subaerial tephras exhibit large regressive cross-strata, planar bedding, and bomb sags suggesting deposition by wet base surges and tephra fallout. Medial and distal deposits consist of a thick sequence of well-bedded tephras; however, the cross-stratified base-surge deposits are thinner and interbedded within the fallout deposits. The average wavelength and amplitude of the cross strata continue to decrease with distance from the vent. These bedded surge and fall deposits grade upward into dominantly fall deposits containing 75-95% juvenile vesiculated clasts and localized layers of welded spatter, indicating a greatly reduced water-melt ratio. Overlying these "dryer" deposits are massive tuff breccias that were probably deposited as water saturated debris flows (lahars). The first appearance of rounded river gravels in these massive tuff breccias indicates downward coring of the diatreme and entrainment of country rock from lower in the stratigraphic section. The "wetter" nature of these deposits suggests a renewed source of external water. The massive deposits grade upward into wet fallout tephras and the phreatomagmatic sequence ends with a dry scoria fall deposit overlain by welded spatter and lava flows. Field observations and two new 40Ar- 39Ar incremental heating dates suggest the succession of lavas and tephra deposits exposed in this part of the Snake River canyon may all have been erupted from a closely related complex of vents at Sinker Butte. We propose that initial eruptions of lava flows built a small shield edifice that dammed or disrupted the flow of the ancestral Snake River. The shift from effusive to explosive eruptions occurred when the surface water or rising ground water gained access to the vent. As the river cut a new channel around the lava dam, water levels dropped and the volcano returned to an effusive style of eruption.

Brand, Brittany D.; White, Craig M.

2007-02-01

143

Evolution of permafrost on the Qinghai-Xizang (Tibet) Plateau since the end of the late Pleistocene  

Science.gov (United States)

The present distribution of permafrost on the Qinghai-Xizang (Tibet) Plateau (QTP) is largely a relict of the permafrost formed during the late Pleistocene. It has been degrading and shrinking in areal extent under the fluctuating climates, with a general trend of warming, during the Holocene. The major criteria for the occurrence of relict permafrost include the remnants of ancient buried permafrost, relict permafrost tables, thawed sandwiches (taliks), thick-layered ground ice, and periglacial phenomena such as pingo scars, cryoturbations, primary sand and clayey silt wedges, ice wedge casts, aeolian sand dunes and loesses, thick layers of peat, and humic soils. On the basis of 14C dating of soils, comprehensive analyses, and comparisons of the spatiotemporal distribution of relict and modern permafrost and periglacial phenomena, the evolution of permafrost and periglacial environments since the late Pleistocene was divided into seven stages: (1) the cold period at the end of the late Pleistocene (35,000 to 10,800 years B.P.); (2) the period of significant climatic change during the early Holocene (10,800 to ˜8500-7000 years B.P.), (3) the Megathermal period in the middle Holocene (˜8500-7000 to ˜4000-3000 years B.P.), (4) the cold period in the late Holocene (˜4000-3000 to 1000 years B.P.), (5) the warm period in the later Holocene (1000 to 500 years B.P.), (6) the Little Ice Age (500 to 100 years B.P.), and (7) the recent warming period (100 years B.P. to present). The conditions for permafrost development, distribution, and the paleoclimates and paleoenvironments are discussed for each stage.

Jin, H. J.; Chang, X. L.; Wang, S. L.

2007-06-01

144

Late Pleistocene Slip Rates Along the Panamint Valley Fault Zone, Eastern California  

Science.gov (United States)

In an effort to assess the rate of shear across eastern California during the Late Pleistocne, we present new slip rate estimates from the central and southern Panamint Valley fault zone (PVFZ). We utilize displaced alluvial deposits at two localities along the southern portion of the fault system and reconstruct fault slip from field surveys and airborne LiDAR topography. Chronologic control is provided by radiocarbon dating of lacustrine tufa associated with shoreline deposits, soil development, and terrestrial cosmogenic nuclide (10Be) dating of alluvial fan surfaces. Together, these provide the first radiometric control for slip-rate estimates along this major fault system. The PVFZ is characterized by dextral, oblique-normal displacement along a moderately to shallowly-dipping range front fault. Along the range front, high-angle faults offset late Pleistocene alluvial and lacustrine surfaces. In southern Panamint Valley, near Manly Canyon, oblique-slip appears to be partitioned into fault strands with primarily right lateral and normal slip. The same fan surface is displaced by ~10m along the normal fault and debris-flow levees are right-laterally offset by ~26m. 10Be surface exposure ages from unweathered boulders suggest a maximum surface age of 14 ka, consistent with soil characteristics and cross-cutting relationships with shoreline features. Our results suggest a minimum slip rate ~ 1.75-2 mm/yr at Manly Canyon. Near Happy Canyon, a releasing step in the fault zone forms a 2-3 km long embayment where displacement on NE-trending faults is dip-slip, affording an opportunity to constrain fault displacement directly from the vertical offset of varying fan surfaces. Cosmogenic 10Be surface clast dating of the oldest fan suggests a surface age of 30-35 ka, whereas the youngest inset surface appears to have been deposited synchronously with a shallow MIS stage 2 lake (~15-25 ka). We are working to refine this estimate with additional dating from multiple depth profiles, radiocarbon from tufa samples, and soil characterization, but our preliminary estimates suggest a minimum oblique- slip rate of 1.5-2 mm/yr at Happy Canyon. Although our results confirm that the PVFZ accommodates a significant component of right-lateral shear in eastern California, it remains difficult to reconcile geologic slip rates along structures north of the Garlock fault with the total rate of shear observed geodetically.

Hoffman, W.; Kirby, E.; McDonald, E.; Walker, J. D.; Gosse, J.

2009-12-01

145

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

146

Late Miocene to Pleistocene potassic volcanism in the Republic of Macedonia  

Science.gov (United States)

The potassic (K) to ultrapotassic (UK) volcanic rocks cropping out in the Vardar Zone of Macedonia and southern Serbia span in age from Late Miocene (6.57 ??) to Pleistocene (1.47 ??). The main identified outcrops are in the Kumanovo, Sveti Nikole, Shtip and Demir Kapia areas; the southernmost occurrences of these volcanic rocks are located in the large Kozuf Massif (Voras Massif in Greece) at the Macedonia Greek border. Three distinct groups may be distinguished. The first group has a shoshonitic affinity and occurs in the Kozuf Massif (LMg-K group); it includes shoshonites to rare rhyolites, with latites and trachytes being the most widespread products. The second group consists of potassic rocks (HMg-K group, K2O/Na2O between 1.0 and 1.8) occurring in both southern Serbia (Cer and Slavujevci) and Macedonia (Djuristhe, near Sveti Nikole). The third group, present only in Macedonia, consists of ultrapotassic rocks (UK group, K2O/Na2O >1.8, Mg# >71) classified as UK shoshonites, UK latites and UK phonotephrites; overall, they show a “Roman Province type” affinity (Group III of Foley, Venturelli, Green, Toscani, Earth Sci Rev 24:81 134, 1987). Geochemically, the studied rocks exhibit strong enrichment in LILE, Th and Pb, as well as relative depletion in Ta Nb and Hf; such signatures are typical of magmas generated in convergent geotectonic settings. In the HMg-K and UK rocks, Sr and Nd isotopic ratios vary from 0.70768 to 0.71040, and 0.51243 to 0.512149, respectively. The rocks of the LMg-K group show relatively limited Sr and Nd isotope variations (0.7087 0.7093 and 0.51233 0.51229), which correlate with a decrease in MgO and increase in SiO2 contents. The geochemical features of the LMg-K volcanic rocks indicate that their evolution was mainly driven by fractional crystallization coupled with contamination by feldspar-rich crustal materials. In contrast, the HMg-K and UK rocks have not been significantly modified by crustal contamination, and their geochemical features are considered to reflect lithospheric mantle heterogeneity acquired during the subduction of the Western Vardar Ocean and the Apulian plate. The metasomatizing agent was apparently more enriched in Zr, Th, Ta and Ce than in fluid-mobile elements, such as Pb and Cs, suggesting that it was characterized by a high melt/fluid ratio. The potassic and ultrapotassic magmatic activity developed in response to the Pliocene Pleistocene extension in the Vardar Zone, in turn related to the opposite propagation of extension in the Aegean and Pannonian basins (respectively SW and NE).

Yanev, Yotzo; Boev, Blazo; Doglioni, Carlo; Innocenti, Fabrizio; Manetti, Piero; Pecskay, Zoltan; Tonarini, Sonia; D'Orazio, Massimo

2008-09-01

147

Subsidence of the Texas coast: inferences from historical and late Pleistocene sea levels  

Science.gov (United States)

Changes in sea level observed at tide gauges are caused by actual changes in water level and by changes in elevation at the observing station. Recent research has focused on the relationship between climatic change and sea level, but vertical land movement can be just as important, particularly in subsiding sedimentary basins. The purpose of this study is to compare long-term rates of subsidence estimated from upper Pleistocene strata along the central Texas coast with historical subsidence rates from the same area obtained from geodetic surveys and tide gauge data. This comparison shows that historical subsidence rates are much greater than long-term averages and are equal or greater than actual sea-level change along the Texas coast south of Galveston Bay. Long-term (~ 10 5 yr) subsidence rates were estimated by establishing the extent of marine, marine-influenced, and nonmarine strata within the upper Pleistocene Beaumont Formation in the Copano Bay area of the central Texas coast, and comparing the maximum elevation of in-place, marine-influenced deposits with published maximum sea level estimates of 5-8 m above mean sea level (MSL) from correlative, well-dated coral terraces from stable and uplifted areas. In-place, shell-bearing horizons deposited at or below sea level occur no higher than 2 m MSL in the Copano Bay area, suggesting that there has been no more than 6 m of subsidence since the probable time of deposition during the Sangamon interglacial at ~ 120 ka. The long-term, average subsidence rate for this part of the Texas coast is thus 0.05 mm/yr or less. Historical subsidence rates were obtained by: (1) calculating relative elevation changes between National Geodetic Survey first-order leveling surveys conducted in the early 1950s with those conducted in the late 1970s to early 1980s; (2) normalizing the relative elevation differences between surveys to annual rates of change relative to an arbitrarily chosen benchmark; (3) referencing these lines to sea level at three tide gauges; and (4) comparing calculated rates of relative sea-level (RSL) rise along the lines with estimates of eustatic sea-level (ESL) rise. Rates of RSL rise for the Texas coast south of Galveston Bay were generally 4-8 mm/yr; locally, rates were as high as 23 mm/yr. These rates are significantly higher than global averages of ~ 1 mm/yr. Much of the difference is probably caused by subsidence of the Texas coastal zone at rates of 1-22 mm/yr, or 20-440 times the long-term average of 0.05 mm/yr. The highest subsidence rates were found locally where there has been historical water-level decline in shallow aquifers. Lower subsidence rates of 3-7 mm/yr occur regionally where groundwater decline is minimal or nonexistent. Increased subsidence over the long-term average in these areas may be caused by pressure decline in underlying oil and gas reseivoirs.

Paine, Jeffrey G.

1993-07-01

148

Carbon and oxygen stable isotope compositions of late Pleistocene mammal teeth from dolines of Ajoie (Northwestern Switzerland)  

Science.gov (United States)

Fossils of megaherbivores from eight late Pleistocene 14C- and OSL-dated doline infillings of Ajoie (NW Switzerland) were discovered along the Transjurane highway in the Swiss Jura. Carbon and oxygen analyses of enamel were performed on forty-six teeth of large mammals (Equus germanicus, Mammuthus primigenius, Coelodonta antiquitatis, and Bison priscus), coming from one doline in Boncourt (~ 80 ka, marine oxygen isotope stage MIS5a) and seven in Courtedoux (51-27 ka, late MIS3), in order to reconstruct the paleoclimatic and paleoenvironmental conditions of the region. Similar enamel ?13C values for both periods, ranging from - 14.5 to - 9.2‰, indicate that the megaherbivores lived in a C3 plant-dominated environment. Enamel ?18OPO4 values range from 10.9 to 16.3‰ with a mean of 13.5 ± 1.0‰ (n = 46). Mean air temperatures (MATs) were inferred using species-specific ?18OPO4-?18OH2O-calibrations for modern mammals and a present-day precipitation ?18OH2O-MAT relation for Switzerland. Similar average MATs of 6.6 ± 3.6°C for the deposits dated to ~ 80 ka and 6.5 ± 3.3°C for those dated to the interval 51-27 ka were estimated. This suggests that these mammals in the Ajoie area lived in mild periods of the late Pleistocene with MATs only about 2.5°C lower than modern-day temperatures.

Scherler, Laureline; Tütken, Thomas; Becker, Damien

2014-09-01

149

Paleoseismic investigation along Nalagarh Thrust: Evidence of Late Pleistocene earthquake in Pinjaur Dun, Northwestern sub-Himalaya  

Science.gov (United States)

The present article is the first time reporting of a paleoearthquake that occurred during Late Pleistocene time along the Nalagarh Thrust (NT) in the Pinjaur Dun in northwestern sub-Himalaya. Using CORONA satellite photographs, multi-spectral IRS satellite data, and aerial photographs, a prominent active fault has been identified at Nalagarh in Pinjaur Dun. This fault in the alluvial fan is located very close to the NT which borders the topographic front of the Tertiary rocks against Quaternary deposits. A trench excavation survey was carried out at Nalagarh for detailed paleoseismic studies across this thrust fault. Displacing all the lithologic units of the fan sequence, the fault plane has an average dip of 30° due ENE and a vertical displacement of 1.6 m and slip of ˜2.5 m along the fault. The lithological units, consisting of alternating sand and gravel, show back tilting and asymmetrical tight folding. Based on Optically Stimulated Luminescence (OSL) ages, the oldest litho-unit in the trench is 85.83 ± 7.2 ka and the youngest is 67.05 ± 8.4 ka. The OSL age of the sample collected from the easterly exposure of the fault shows an age of 20 ka. The faulting and associated induced deformation features suggest occurrence of a Late Pleistocene large magnitude earthquake along NT in the Nalagarh region of the Pinjaur Dun following the deposition of the Quaternary sedimentary units. The Late Pleistocene fault substantiates the seismic potential of Pinjaur Dun and calls for more exhaustive study of paleoearthquakes in this fast developing industrial belt and highly populous mountainous region.

Philip, G.; Suresh, N.; Bhakuni, S. S.; Gupta, V.

2011-03-01

150

Late Pleistocene and Holocene slip rate of the Northern Wadi Araba fault, Dead Sea Transform, Jordan  

Science.gov (United States)

The Wadi Araba Valley is a morphotectonic depression along part of theDead Sea Transform (DST) plate boundary that separates the Arabian plateon the east from the Sinai subplate on the west. The Wadi Araba fault(WAF) is the main strike-slip faults one of between the Gulf of Aqaba and the E-Wtrending Khunayzira (Amatzayahu) fault that bounds the southern end ofthe Dead Sea. Just south of the Dead Sea, the WAF cuts across severalgenerations of alluvial fans that formed on tributaries to the Wadi Dahalafter the regression of Late Pleistocene Lake Lisan ca. 15 ka. Geomorphicand stratigraphic evidence of active faulting, including left-laterally offsetstream channels and alluvial-fan surfaces, yielded fault slip-rate data for thenorthern segment of WAF. Typical cumulative displacements of 54 m,39 m, and 22.5 m of stream channels and alluvial-fan surfaces acrossthe fault were measured from detailed geologic and topographic mapping.The 54 m offset of the oldest alluvial-fan surface (Q f1 ) occurredafter the final lowering of Lake Lisan (16-15 ka) and before 11 ka yieldinga slip-rate range of 3.4 mm/yr to 4.9 mm/yr. Based on radiocarbonages of charcoal and landsnail shell samples from the buried Q f2 alluvial-fan deposits exposed in trenches excavated across the fault, the39 m and 22.5 m offsets occurred after 9 ka and 5.8 ka, respectively. These data yield a slip-rate range between 3.9 mm/yr and 6.0 mm/yr.The small variability in these slip-rate estimates for different time periodssuggests that the northern Wadi Araba fault has maintained a relativelyconstant slip rate in the past 15 ka. We calculate an average slip rate of 4.7± 1.3 mm/yr since 15 ka based on the three separate displacementsand age estimates. Five separate offsets of 3 m were measured from gullybends and the offset of small fault-scarp alluvial fans. These displacementdata suggest a coseismic slip of 3 m in the last earthquake, or acumulative slip of 3 m in the past few earthquakes. A maximum slip of3 m correspond to a Mw 7 earthquake that ruptures about 49 km offault length. Using an average slip rate of 4.7 ± 1.3 mm/yr togetherwith a 3-m slip-per-event suggests a maximum earthquake recurrence intervalof this fault segment of 500 to 885 years.

Niemi, Tina M.; Zhang, Hongwei; Atallah, Mohammad; et al.

151

New data on the late Pleistocene history of lake fluctuations in the Sevier Desert, Utah  

Science.gov (United States)

The chronology of lake-level changes during the late Pleistocene in the Lake Bonneville basin, Utah, is currently understood in a general way. Because the regressive phase of the lake occurred during a critical time in the history of the basin (climate was changing rapidly, humans were moving into suitable habitats that were being made available by the decline of the large lake), it is important to improve the dating of paleohydrologic and paleoclimatic events. We have initiated field and laboratory studies in a part of the Sevier Desert that was studied at a reconnaissance scale 25 to 30 years ago. Our work consists of describing critical stratigraphic sections in natural exposures along the Sevier River and in a core of lake and fluvial sediments, and in dating suitable materials from these sections using radiocarbon and optically stimulated luminescence (OSL). The Sevier basin was integrated with the rest of Lake Bonneville during the time when its highest shorelines were being formed, including during the long period of development of the Provo shoreline (~17.6-14.6 cal ka). The lake regressed rapidly from the Provo shoreline (~1465 m) to the altitude of the divide between the Sevier basin and the Great Salt Lake (GSL) basin (~1390 m), then split into two lakes. In the GSL basin the lake continued to decline as a closed-basin lake, and the lake in the shallow Sevier basin overflowed into it along a large river (the ancestral Sevier River). An extensive wetland, fed by runoff from the Sevier and Beaver Rivers, and by groundwater discharge, developed over much of the Sevier Desert floor during the early Holocene. We have measured new OSL ages that compare favorably with previously obtained radiocarbon ages for the same stratigraphic units. Part of our work is aimed at evaluating the hypothesis that rapid draw-downs in lake level would cause increased groundwater discharge to the lake, and therefore a potential radiocarbon reservoir effect that would have been spatially and temporally heterogeneous.

Oviatt, C. G.; Spencer, J. Q.; Fan, Y.; Leggett, A.

2010-12-01

152

Late Pleistocene outburst flooding from pluvial Lake Alvord into the Owyhee River, Oregon  

Science.gov (United States)

At least one large, late Pleistocene flood traveled into the Owyhee River as a result of a rise and subsequent outburst from pluvial Lake Alvord in southeastern Oregon. Lake Alvord breached Big Sand Gap in its eastern rim after reaching an elevation of 1292 m, releasing 11.3 km3 of water into the adjacent Coyote Basin as it eroded the Big Sand Gap outlet channel to an elevation of about 1280 m. The outflow filled and then spilled out of Coyote Basin through two outlets at 1278 m and into Crooked Creek drainage, ultimately flowing into the Owyhee and Snake Rivers. Along Crooked Creek, the resulting flood eroded canyons, stripped bedrock surfaces, and deposited numerous boulder bars containing imbricated clasts up to 4.1 m in diameter, some of which are located over 30 m above the present-day channel. Critical depth calculations at Big Sand Gap show that maximum outflow from a 1292- to 1280-m drop in Lake Alvord was ??? 10,000 m3 s- 1. Flooding became confined to a single channel approximately 40 km downstream of Big Sand Gap, where step-backwater calculations show that a much larger peak discharge of 40,000 m3 s- 1 is required to match the highest geologic evidence of the flood in this channel. This inconsistency can be explained by (1) a single 10,000 m3 s- 1 flood that caused at least 13 m of vertical incision in the channel (hence enlarging the channel cross-section); (2) multiple floods of 10,000 m3 s- 1 or less, each producing some incision of the channel; or (3) an earlier flood of 40,000 m3 s- 1 creating the highest flood deposits and crossed drainage divides observed along Crooked Creek drainage, followed by a later 10,000 m3 s- 1 flood associated with the most recent shorelines in Alvord and Coyote Basins. Well-developed shorelines of Lake Alvord at 1280 m and in Coyote Basin at 1278 m suggest that after the initial flood, postflood overflow persisted for an extended period, connecting Alvord and Coyote Basins with the Owyhee River of the Columbia River drainage. Surficial weathering characteristics and planktonic freshwater diatoms in Lake Alvord sediment stratigraphically below Mt. St. Helens set Sg tephra, suggest deep open-basin conditions at ??? 13-14 ka (14C yr) and that the flood and prominent shorelines date to about this time. But geomorphic and sedimentological evidence also show that Alvord and Coyote Basins held older, higher-elevation lakes that may have released earlier floods down Crooked Creek. ?? 2006 Elsevier B.V. All rights reserved.

Carter, D.T.; Ely, L.L.; O'Connor, J. E.; Fenton, C.R.

2006-01-01

153

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

International Nuclear Information System (INIS)

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

154

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2009-07-01

155

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

1992-01-01

156

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 (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, J. C., III; David, B.T.; Ebbs, V.M.

2008-01-01

157

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

Science.gov (United States)

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

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

2005-10-01

158

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

Science.gov (United States)

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

Capra, L.; Bernal-Uruchurtu, J. P.; Carrasco, G.

2013-05-01

159

Late Pleistocene and Holocene uplift history of Cyprus: implications for active tectonics along the southern margin of the Anatolian microplate  

Science.gov (United States)

The nature of the southern margin of the Anatolian microplate during the Neogene is complex, controversial and fundamental in understanding active plate-margin tectonics and natural hazards in the Eastern Mediterranean region. Our investigation provides new insights into the Late Pleistocene uplift history of Cyprus and the Troodos Ophiolite. We provide isotopic (14C) and radiogenic (luminescence) dates of outcropping marine sediments in eastern Cyprus that identify periods of deposition during marine isotope stages (MIS) 3, 4, 5 and 6. Past sea-levels indicated by these deposits are c. 95±25 m higher in elevation than estimates of worldwide eustatic sea-level. An uplift rate of c. 1.8 mm/year and possibly as much as c. 4.1 mm/year in the past c. 26–40 ka is indicated. Holocene marine deposits also occur at elevations higher than those expected for past SL and suggest uplift rates of c. 1.2–2.1 mm/year. MIS-3 marine deposits that crop out in southern and western Cyprus indicate uniform island-wide uplift. We propose a model of tectonic wedging at a plate-bounding restraining bend as a mechanism for Late Pleistocene to Holocene uplift of Cyprus; uplift is accommodated by deformation and seismicity along the margins of the Troodos Ophiolite and re-activation of its low-angle, basal shear zone.

Harrison, R.W.; Tsiolakis, E.; Stone, B.D.; Lord, A.; McGeehin, J.P.; Mahan, S.A.; Chirico, P.

2013-01-01

160

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

161

Preliminary Results from a Late Pleistocene to Holocene Paleoclimate Study of the Lake Sediment Cores, Northern New Mexico  

Science.gov (United States)

We present the preliminary results from an integrated, paleoclimatic study of sediment cores collected from the Las Vegas National Wildlife Refuge (LVNWR) and surrounding region that bear on the late Pleistocene to Holocene paleoclimatic variations in northeastern NM. We collected sedimentologic, midge fossil, and rock magnetic data from sediment cores to characterize the materials, identify stratigraphic changes, document shifting lake levels, assess temperature changes, and infer paleoclimate conditions. Data from McAllister and Wallace Lake are encouraging and reveal depth dependent changes in fossil assemblages, grain size, and rock magnetic properties that we interpret to reflect climatic driven variations impacting the depositional system. We recognize three different types of chironomid subfamilies (Chironomini, Tanypodinae, and Orthocladiinae). Based on the fossil results, the water has been warm in the most recent years. Grain size distribution from the lower to upper core levels reveal that the amount of fine sand-sized sediment (0.125 mm diameter) increases while the amount of medium (0.25) to coarse (0.50) sand-sized sediment decreases implying that there may have been a reduction in stream energy and hence precipitation over the time period represented by the core. Bulk low-field magnetic susceptibility decreases by an order of magnitude from the surface to the base of the measured core suggesting a change in detrital magnetic influx into the lacustrian system. Curie point estimates indicate that the dominant magnetic mineral in all samples is cubic, low-Ti titanomagnetite phase. We postulate that concurrent with alpine glacial activity during the Pleistocene, the LVNWR and the transitional Great Plains region to the northeast was an expansive single lake or interconnected lake system, analogous to the Pleistocene lakes of the Estancia Basin (Lake Estancia) and the Tularosa Basin (Lake Otero) of central and southern NM. Following the end of glacial activity, these lacustrian systems shrank to their current condition of minor low-volume isolated lakes and numerous playas and pluvial bodies. We hypothesize that sediments from the LVNWR and surrounding playas contain an invaluable and untapped record of late Pleistocene to Holocene climatic change.

Cedillo, D. N.; Brister, A. R.; LoPresti, C. A.; Maldonado, M.; Pitrucha, R. M.; West, C.; Martinez, E.; Lineline, J.; Petronis, M. S.

2011-12-01

162

Late Pliocene and Early Pleistocene vegetation history of northeastern Russian Arctic inferred from the Lake El'gygytgyn pollen record  

Science.gov (United States)

The 318 m thick lacustrine sediment record from Lake El'gygytgyn, northeastern Russian Arctic cored by the international El'gygytgyn Drilling Project provides unique opportunities for 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 demonstrate their value as an excellent archive of vegetation and climate changes during the Late Pliocene and Early Pleistocene. About 3.5-3.35 Myr BP, the vegetation at Lake El'gygytgyn, now an area of tundra was dominated by spruce-larch-fir-hemlock forests. After ca. 3.35 Myr BP dark coniferous taxa gradually disappeared. A very pronounced environmental change took place ca. 3.31-3.28 Myr BP, corresponding to the Marine Isotope Stage (MIS) M2, when treeless tundra- and steppe-like habitats became dominant in the regional vegetation. Climate conditions were similar to those of Late Pleistocene cold intervals. Numerous coprophilous fungi spores identified in the pollen samples suggest the presence of grazing animals around the lake. Following the MIS M2 event, larch-pine forests with some spruce mostly dominated the area until ca. 2.6 Myr BP, interrupted by colder and drier intervals ca. 3.043-3.025, 2.935-2.912, and 2.719-2.698 Myr BP. At the beginning of the Pleistocene, ca. 2.6 Myr BP, noticeable climatic deterioration occurred. Forested habitats changed to predominantly treeless and shrubby environments, which reflect a relatively cold and dry climate. Peaks in observed green algae colonies (Botryococcus) around 2.53, 2.45, 2.32-2.305, 2.20 and 2.16-2.15 Myr BP suggest a spread of shallow water environments. A few intervals (i.e., 2.55-2.53, ca. 2.37, and 2.35-2.32 Myr BP) with a higher presence of coniferous taxa (mostly pine and larch) document some relatively short-term climate ameliorations during Early Pleistocene glacial periods.

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

2014-05-01

163

Stratigraphy and fission track ages of late Cretaceous to Paleogene tertiary volcanic rocks  

International Nuclear Information System (INIS)

Downstream of riber Hime correspond to the northern-most of Itoigawa-Shizuoka tectonic line (ISTL). On the west side of ISTL, late Cretaceous to Neogene formations are distributed and they are divided into five formations, namely Akahageyama sandstone, Ipponmatsuyama sandstone, Ishizaka rhyolite, Yamato and Imai. The distribution of igneous rocks of those formations are scattered by elevation of base rock followed by erosion, and Neogene deposition. Additionally, fossils are very rare. Consequently, the time correlation of formation which has important meaning for the formation process of Fossa Magna, was impossible. Fission track age determination of late Cretaceous to Paleogene igneous rocks were carried out using ''external detection method''. The results were 94.2 ± 5.9 Ma for Akahageyama formation; 66.4 ± 2.4 Ma for Ipponmatsuyama formation; 54.7 ± 1.9 Ma for Ishizaka formation; 74.8 ± 2.9 Ma for Azakiri; 55.7 ± 2.3 Ma for Sasagawa tuff formation; 92.7 ± 5.9 Ma for Omi granite and 62.2 ± 3.5 Ma for garnet porphylite. From obtained ages along with stratigraphical studies of the region, the late Cretaceous to Neogene igneous activities in the northern area along ISTL were found to be devided into 4 periods: 1) plutonic activity in early Cretaceous, Omi granite, 2) local andestic volcanism from the end of late Cretaceous to early Paleocene characterized by Ipponmatsuyama formation, 3) wide acidic volcanism from late Paleocene to early Eocene, characterized by Ishizaka rhyolite and 4) middle Miocene volcanism, so-called ''Green tuff'' movement. (Ishimitsu, A.)

164

Aeolian to shallow-marine shelf architecture off a major desert since the Late Pleistocene (northern Mauritania)  

Science.gov (United States)

Continental shelves off major desert regions are not expected to host substantial amounts of sediments due to long-lasting and unfocused material supply and a high re-mobilization potential of aeolian material. This study, in contrast, demonstrates that significant volumes of sediments have accumulated on the northern Mauritanian shelf under the arid climate conditions and prevail over consecutive climatic cycles. Eight late Pleistocene to Holocene depositional units, each formed under contrasting depositional conditions, are identified in high-resolution seismo-acoustic data and dated sediment cores. These are: (1) a highly differentiated Pleistocene paleo-landscape older than the past climatic cycle, (2) a continental dune complex (MIS-4), (3) a thick regressive shallow-water clinoform (late MIS-3), (4) a regressive to lowstand shore deposit (latest MIS-3), and (5) a local transgressive cover (LGM to deglacial). Additionally, (6) an open-shelf highstand cover, (7) an outer-shelf highstand wedge and (8) mid-shelf mud depocenters have formed during the Holocene sea-level highstand. The common local offshore formation and preservation of confined stratigraphic units, in particular from during MIS-3, mark the interplay of: a) episodes of pronounced arid climatic conditions resulting in enhanced aeolian and coastal sediment input, b) shelf current patterns focusing sediment deposition locally, and c) early post-depositional sediment stabilization providing protection against erosion. Prominent internal surfaces at 63 and 115 m modern water depths indicate widespread and intense erosional activity during late MIS-3 regression and MIS-2 lowstand to post-LGM transgression, hosting coarse shell sands and gravels from beach and shoreface paleo-environments. The reasons for the high preservation potential of confined stratigraphic units are: a) carbonaceous cementation, b) sediment composition (massive widespread shore-related gravel and shell beds with subtle minor admixtures of cohesive material), and c) morphological protection (inside seafloor depressions and behind sheltering relief).

Hanebuth, T. J. J.; Mersmeyer, H.; Kudrass, H. R.; Westphal, H.

2013-12-01

165

Stratigraphy, landsnail faunas, and paleoenvironmental history of Late Holocene coastal dunes, Tauroa Peninsula, northern New Zealand  

International Nuclear Information System (INIS)

The post -700 years BP depositional history of the Holocene coastal dunebelt on northwestern Tauroa Peninsula involved an initial progradational phase, then a subsequent predominantly stable phase that began some time after 650 years BP, followed by a highly unstable phase from late prehistoric time to the present-day. Fossil landsnail faunas indicate that sandfield and prostrate shrubland have been the main vegetation types on the dunefield since at least 700 years BP, but that taller shrubland established locally during the later part of the prehistoric period of dunefield stability. Five species of landsnails became extinct on the dunefield in late prehistoric-historic time, probably as a result of vegetation disturbance caused by widespread dune mobilisation and erosion. (author). 19 refs., 3 figs., 1 tab

166

The stratigraphy and sedimentology of the Dunscombe Mudstone Formation (late Triassic) of south-west England  

OpenAIRE

The mid to late Triassic Mercia Mudstone Group exposed on the east Devon coast between Sidmouth and Seaton consists of c. 450 m of predominantly red mudstones that were deposited in low-relief sabkha environments in hot deserts. In marked contrast to this, the Dunscombe Mudstone Formation in the middle part of the group consists of 35-40 m of interbedded and interlaminated green, purple and grey mudstones, breccias, muddy limestones and lenticular siltstones/sandstones that were d...

Gallois, Ramues W.; Porter, R. J.

2006-01-01

167

Aeolian stratigraphy and thermoluminescence dating of sediments of late Holocene age from Sola, southwest Norway  

International Nuclear Information System (INIS)

Thermoluminescence age determinations were performed on four aeolian sand samples of late Holocene sediments from Stavanger airport, Sola, in southwest Norway. The locality is well suited for testing thermoluminescence dating because of a good agreement between radiocarbon ages and age information based on archaeological typology and sea level changes. The conclusion from a comparison of thermoluminescence and radiocarbon dates is that it is possible to date well bleached sediments as young as 1600 years with thermoluminescence. 57 refs., 7 figs., 6 tabs

168

Field Geological Evidence Supporting a Stick-Slip Mechanism of Basal ice Flow From a Late Pleistocene ice Sheet  

Science.gov (United States)

Microseismicity data from beneath Antarctic ice streams show the occurrence of episodic stick-slip events upon the failure of 'sticky spots', which support a disproportionate amount of glacial shear stress, leading to a temporary period of enhanced ice flow (slip). Flow velocity peaks rapidly then decreases as basal ice 'sticks' again at the end of the stick-slip cycle. Despite this evidence from modern glaciers, stick-slip behaviour has not been invoked for the flow of the late Pleistocene ice sheets. For the first time, field geological evidence from beneath the former late Pleistocene ice sheet in Ireland supports the stick-slip ice flow model. In the southern Sperrin Mountains subglacial sediment sequences comprise tabular bedrock rafts which are interbedded with diamicton (till) and brecciated bedrock and separated by glaciotectonic shears. Bedrock rafts and diamicton beds alternate laterally and vertically in the sediment profile, suggesting that the ice-bed interface was chequered spatially with both high-strength (rock rafts) and low-strength (diamicton) patches during accumulation of the sediment pile. Overall, the facies architecture is interpreted qualitatively to reflect stick-slip basal ice flow which is closely related to the redistribution of free subglacial meltwater at the ice-bed interface. Stick phases occur over bedrock rafts, forcing meltwater migration to lower-pressure regions and infilling shallow cavities on the surrounding diamicton surface. Slip occurs when porewater pressure over the diamicton increases and the meltwater layer backfills across bedrock raft surfaces, causing ice-bed uncoupling and fast ice flow. Pervasive deformation of subglacial sediments (also invoked for supporting Antarctic ice streams) may occur only at the end of the stick-slip cycle during ice-bed recoupling. On a macroscale the formation of drumlins, as a substrate obstruction, may be related to similar cycles of instability and feedback at the ice-bed interface. Proto-drumlin apices may act as sticky spots with drumlinisation occurring during short, high-magnitude slip phases. Stick-slip and similar processes on a range of scales may help explain some of the flow dynamics, landforms and sediment sequences of both drumlinised and non-drumlinised areas of the late Pleistocene mid-latitude ice sheets, and may be more common beneath both past and present glaciers than has been recognised hitherto.

Knight, J.

2001-12-01

169

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

170

Genetic consequences of population expansions and contractions in the common hippopotamus (Hippopotamus amphibius) since the Late Pleistocene  

DEFF Research Database (Denmark)

Over the past two decades, an increasing amount of phylogeographic work has substantially improved our understanding of African biogeography, in particular the role played by Pleistocene pluvial-drought cycles on terrestrial vertebrates. However, still little is known on the evolutionary history of semi-aquatic animals, which faced tremendous challenges imposed by unpredictable availability of water resources. In this study, we investigate the Late Pleistocene history of the common hippopotamus (Hippopotamus amphibius), using mitochondrial and nuclear DNA sequence variation and range-wide sampling. We documented a global demographic and spatial expansion approximately 0.1-0.3 My ago, most likely associated with an episode of massive drainage overflow. These events presumably enabled a historical continent-wide gene flow among hippopotamus populations, and hence no clear continental-scale genetic structuring remains. Nevertheless, present-day hippopotamus populations are genetically disconnected, probably as aresult of the mid-Holocene aridification and contemporary anthropogenic pressures. This unique pattern contrasts with the biogeographic paradigms established for savannah-adapted ungulate mammals and should be further investigated in other water-associated taxa. Our study has important consequences for the conservation of the hippo, an emblematic but threatened species that requires specific protection to curtail its long-term decline. This article is protected by copyright. All rights reserved.

Stoffel, Céline; Dufresnes, Christophe

2015-01-01

171

Fossils in Late Cretaceous to early Palaeocene flint nodules embedded in pleistocene glaciofluvial sediments near Fukov (D??ín District, Northern Bohemia).  

Czech Academy of Sciences Publication Activity Database

Ro?. 68, 3/4 (2012), s. 119-131. ISSN 0036-5343 Institutional support: RVO:67985831 Keywords : Erratic boulders * Flint * Glaciofluvial sediments * Late Cretaceous * Northern Bohemia * Palaeocene * Pleistocene glaciation * Taphocoenosis Subject RIV: DB - Geology ; Mineralogy http://www.nm.cz/publikace/archiv.php?id=4&rok=68&kcislu=3-4&f_=Zobrazit

Pokorný, R.; Kaše, J.; Kva?ek, J.; Zágoršek, K.; Ko?í, T.; Žítt, Ji?í

2012-01-01

172

Tocuila Mammoths, Basin of Mexico: Late Pleistocene-Early Holocene stratigraphy and the geological context of the bone accumulation  

Science.gov (United States)

We report new stratigraphic, tephrochronology and dating results from the Tocuila Mammoth site in the Basin of Mexico. At the site there is evidence for a thin meteorite airburst layer dated between 10,878 and 10,707 cal BC at the onset of the Younger Dryas (YD) cool period. The Upper Toluca Pumice (UTP) tephra marker, caused by a Plinian eruption of the Nevado de Toluca volcano, dated from 10,666 to 10,612 cal BC, is above that layer. The eruption must have caused widespread environmental disruption in the region with evidence of extensive reworking and channelling by the Lake Texcoco shoreline and contributed to the widespread death and/or extinction of megafaunal populations, as suggested by earlier authors, but the new work reinforces the view that both catastrophic events must have caused large environmental disruption in a short time period of around two hundred years. There is no evidence for megafauna (mammoths, sabre toothed cats, camels, bison, glyptodonts) after the UTP volcanic event and subsequent lahars in the Basin of Mexico. At Tocuila, although there are some in situ tephra markers in nearshore lake sediments, such as the Great Basaltic Ash (GBA) and the UTP Ash, there is evidence of much reworking of several tephra populations in various combinations. The mammoth bone accumulation is reworked in a lahar sequence (volcanic mudflow) derived from several source sediments but associated with the major UTP Plinian eruption. Paleoindian populations were also present in the Basin of Mexico during the YD period, where several Paleoindian skeletons were found associated with the UTP ash deposits, e.g. Metro Man, Chimalhuacan Man and Tlapacoya Man.

Gonzalez, Silvia; Huddart, David; Israde-Alcántara, Isabel; Dominguez-Vazquez, Gabriela; Bischoff, James

2014-07-01

173

Stratigraphy and complex fluvial geomorphology in a Middle and Late Pleistocene endmoraine setting of the European Alpine Foreland  

Science.gov (United States)

The Alpine Foreland was repeatedly covered by massive Piedmont glaciers during Quaternary peak glacial periods. Glacial and associated glaciofluvial landforms are especially well preserved in the area of the former Salzach Piedmont glacier (Austria/Germany), where remnants of at least 4 glacial maxima, minor anthropogenic overprint and comprehensive geological and topographic data provide a unique opportunity to study glacial and glaciofluvial sediment/landform associations. In this presentation we focus on a local setting containing deposits from the last ("Würm"; MIS 2) and penultimate ("Riß"; MIS 6) glacial maximum. Foreland glacier area, typically representing sediment/landform associations at the glacial lobe terminus. Specifically, we investigate the transition from the endmoraine system to the glaciofluvial outwash in order to make statements on the internal built up, the timing and the subsequent degradation associated with glaciofluvial reorganization during deglaciation. Investigations were carried out using outcrop information, drillcore logs, near-surface geophysics (ground penetrating radar and seismic refraction), as well as luminescence dating of selected sand-sized samples. The geometry and lateral extension of remnants of a thick interglacial paleosol were investigated using core log information and terrestrial lascerscan data. Detailed topographical information benefitted from high resolution airborne laserscan imagery. We identify two main glaciofluvial depositional systems for the LGM: (i) sheet flow dominated landforms (i.e. alluvial fans) broadly attached to the end moraine system and (ii) braided river deposits from meltwater streams initiating at distinct meltwater outlets. Our first results point to a very short period of active deposition. With the onset of deglaciation and ice meltdown back into the tongue basin, partial degradation of deposits started, leading to multiple terrace level formation along the meltwater pathways. Where sheet flow of the LGM dominates, it overlies MIS6-deposits almost without any unconformity well preserving thick and laterally extensive paleosol deposits.

Salcher, Bernhard; Joachim, Götz; Reinhard, Starnberger

2014-05-01

174

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

Directory of Open Access Journals (Sweden)

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

Tiiu Koff

2011-06-01

175

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

176

Stratigraphy and facies development of the marine Late Devonian near the Boulongour Reservoir, northwest Xinjiang, China  

Science.gov (United States)

Late Devonian to Early Carboniferous stratigraphic units within the 'Zhulumute' Formation, Hongguleleng Formation (stratotype), 'Hebukehe' Formation and the Heishantou Formation near the Boulongour Reservoir in northwestern Xinjiang are fossil-rich. The Hongguleleng and 'Hebukehe' formations are biostratigraphically well constrained by microfossils from the latest Frasnian linguiformis to mid-Famennian trachytera conodont biozones. The Hongguleleng Formation (96.8 m) is characterized by bioclastic argillaceous limestones and marls (the dominant facies) intercalated with green spiculitic calcareous shales. It yields abundant and highly diverse faunas of bryozoans, brachiopods and crinoids with subordinate solitary rugose corals, ostracods, trilobites, conodonts and other fish teeth. The succeeding 'Hebukehe' Formation (95.7 m) consists of siltstones, mudstones, arenites and intervals of bioclastic limestone (e.g. 'Blastoid Hill') and cherts with radiolarians. A diverse ichnofauna, phacopid trilobites, echinoderms (crinoids and blastoids) together with brachiopods, ostracods, bryozoans and rare cephalopods have been collected from this interval. Analysis of geochemical data, microfacies and especially the distribution of marine organisms, which are not described in detail here, but used for facies analysis, indicate a deepening of the depositional environment at the Boulongour Reservoir section. Results presented here concern mainly the sedimentological and stratigraphical context of the investigated section. Additionally, one Late Devonian palaeo-oceanic and biotic event, the Upper Kellwasser Event is recognized near the section base.

Suttner, Thomas J.; Kido, Erika; Chen, Xiuqin; Mawson, Ruth; Waters, Johnny A.; Frýda, Ji?í; Mathieson, David; Molloy, Peter D.; Pickett, John; Webster, Gary D.; Frýdová, Barbora

2014-02-01

177

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

Science.gov (United States)

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

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

2013-01-01

178

Late Pleistocene and Early Holocene Rock Art from the Mongolian Altai: The Material and its Cultural Implications  

Directory of Open Access Journals (Sweden)

Full Text Available Rock-pecked images from the northern Mongolian Altai attest to the presence of human communities within the high valleys of that region during the Late Pleistocene and Early Holocene. The material provides evidence that is hitherto largely missing from the archaeological record of that region. This paper reviews the rock art, its find sites and larger physical contexts and uses evidence from paleoenvironmental studies to propose dating and cultural significance. The material is compared with other sites said to have Paleolithic imagery from Mongolia and the adjoining Russian Altai. The body of presented material offers a major resource for the study of early hunter-gatherer communities at the interface of Central and North Asia.

Esther Jacobson-Tepfer

2013-09-01

179

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) < Pedon 2 < Pedon 1, reflected e. g. in increasing Fed/Fet ratios, decreasing molar ratios of (Ca+K+Na)/Al, and decreasing pH. However, it needs to be considered that lapilli are more readily weatherable than gneiss fragments. The profile morphology of the paleosol, characterized by reddish-brown color (7.5YR), strong angular blocky structure and well-expressed illuvial clay coatings, rather indicates that it developed over a longer time-span and/or warmer climate than the two yellowish-brown surface soils. Since the morphology of the paleosol clearly reflects interglacial climatic conditions and forest cover, it most likely started developing during the Eemian. Steblich et al. (2009) reconstructed for the period 16.7-14.45 ka BP steppe with 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

180

Push moraines in the upper valley of Santa Cruz river, southwest Argentina. Structural analysis and relationship with Late Pleistocene paleoclimate  

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The upper cliff of the Santa Cruz River was used to assess the proglacial environments of the Argentino Glacier outlet of Late Pleistocene age. These cliffs show glaciolacustrine, fluvioglacial and till deposits, where only the first one are deformed. Glacial landforms in the area and these structures suggest that the ice mass advanced, topographically controlled, towards the east from the Patagonian Ice Sheet pushing up the proglacial sediments. The spatial arrangement of thrusts and overturned folds, the drumlins-flutes moraine directions and the end moraines shape, allow inferring the dynamic and the Argentino glacier profile. Detailed analyses of the glaciotectonic structures indicate that these have two origins: load in the north with stress transfer to the southeast, and push from the west. Through the analysis of deformed sediments, their thickness and their sedimentary and structural features, three zones of deformations were recognized. Each of these zones was associated to glacial advances because of changes of the regional climate conditions.

Goyanes, Gabriel; Massabie, Armando

2015-01-01

181

Late Pleistocene sedimentary history of multiple glacially dammed lake episodes along the Yarlung-Tsangpo river, southeast Tibet  

Science.gov (United States)

We present a reconstructed lithologic column compiled from a series of lacustrine outcrops along a tributary of the Nyang River, a major tributary of the Yarlung-Tsangpo in southeast Tibet. The deposits were preserved between terraces at altitudes of 2950-3100 m asl. The stratigraphic record features at least two sets of coarsening-upward sequences depicting episodic aggradation and progradation of a glacially dammed lake related delta. Recognized facies changes illustrate the evolution cycles of depositional environments from pro-delta, delta front, to delta plain. Radiocarbon and optically stimulated luminescence dates reveal an aging-downward trend in stratigraphic order and provide an approximate timeline for the formation of glacially dammed lakes in late Pleistocene. This result reflects that the Zelunglung Glacier had progressively advanced to block the Yarlung-Tsangpo river and the dam materials had stepwise stacked up to an altitude of 3095 m asl during Marine Oxygen Isotope Stages 4 to 2.

Huang, Shao-Yi; Chen, Yue-Gau; Burr, George S.; Jaiswal, Manoj K.; Lin, Yunung Nina; Yin, Gongming; Liu, Jingwei; Zhao, Shujun; Cao, Zhongquan

2014-09-01

182

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

183

Rock-magnetic study of Late Pleistocene-Holocene sediments from the Babícora lacustrine basin, Chihuahua, northern Mexico  

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Full Text Available Rock-magnetic and sedimentological studies of the Quaternary sequence of lake Babícora (29.4°N, 107.7°W; 2,100 m a.s.l. from Late Wisconsin to Holocene are reported. Two vertical profiles have been studied. Magnetic susceptibilities and natural remanence (NRM and isothermal remanence (IRM intensities correlate with sand, silt and clay contents in the sediments, suggesting that magnetic minerals are allogenic. IRM acquisition curves and alternating field coercivity spectra document the occurrence of Ti-poor titanomagnetites, hematites and iron-hydroxides. The fluctuations in the input of sedi¬ment correlate with changes in erosional processes, climate and tectonics in the catchment basin. Five radiocarbon dates ranging from 4,346 to 16,343 yr B.P. were obtained. The southern profile covers a longer time span than the western pro¬file, which spans from 11,000 to 6,000 yr B.P., when the lake extended over a larger area. Two major periods of increased rainfall and high lake levels in Late Pleistocene and Early Holocene are recognized. The Late Wisconsin wet period was fol¬lowed by gradual drying up to around 6,000 yr B.P. Between 11,000 and 8,000 yr B.P. there was another wet period, related to increased summer rainfall. The dry period between 3,000 and 2,000 yr B.P. was followed by widespread erosion.

R. Cruz-Gatica

1997-01-01

184

Late Permian cycle-stratigraphy in the continental deposits of the Karoo basin (South Africa) (Invited)  

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Magnetostratigraphic and geochronological studies of late Permian Waterford and Abrahamskraal Formations (uppermost Ecca Group and lowermost Beaufort Group, respectively) in the Karoo Basin of South Africa yielded age-constrained magnetostratigraphy that can be correlated with the most recent reference geomagnetic polarity time scale. This precise chronological framework provides the basis for a chemostratigraphic analysis of cyclicity based on the measured major and trace element composition of these fluvial mudstones and sandstones. Our multi-taper spectral power analysis was computed using the concentration of major oxides, showing clear peaks at frequencies that are compatible with the expected orbital periodicities according to the magnetostratigraphic chronology. Given the length of the studied section (~500 m) and the relatively high sedimentation rate (~100m/Myr), we consider that the short hiatuses that are to be expected in river deposits are not likely to obliterate long-period cyclicity such as orbital eccentricity. We interpret long period cyclicity as reflecting orbital eccentricity (ca. 400 kyr), with even shorter period orbital frequencies observed in the record. Statistical analysis suggests that the chemical composition does not correlate with the sediments grain size but is related to the lithology through their relative abundance of clays and SiO2-rich clastic material. Although chemical changes might partly reflect stochastic fluctuation due to fluvial hydrodynamics, their orbital periodicity suggests that they are mainly paced by environmental changes that in turn may control the sediment weathering and/or fluvial dynamics. Recognition of the orbitally controlled sedimentation allows very precise dating of the time involved in the deposition of these sedimentary rocks. Astronomical tuning provides an improved calibration of this portion of the polarity time scale and give hints on the variability of the environmental conditions during the Late Permian.

Lanci, L.; Tohver, E.; Wilson, A.; Ratcliffe, K. T.; Flint, S.

2013-12-01

185

The Late Holocene to Pleistocene tephrostratigraphic record of Lake Ohrid (Albania)  

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We present in this work a tephrostratigraphic record from a sediment piston core (JO 2004) from Lake Ohrid. Five tephra layers were recognised, all from explosive eruptions of southern Italy volcanoes. A multidisciplinary study was carried out, including stratigraphy, AMS 14C chronology and geochemistry. The five tephra layers were correlated with terrestrial proximal counterparts and with both marine and lacustrine tephra layers already known in the central Mediterranean area. The oldest is from Pantelleria Island (P11, 131 ka BP). Other three tephra layers are from Campanian volcanoes: X6, Campanian Ignimbrite-Y5 and SMP1-Y3 (107, 39 and 31 ka BP respectively). The youngest tephra layer corresponds to the FL eruption from Etna Volcano (3.4 ka BP). In three cases these recognitions confirm previous findings in the Balkans, while two of them were for the first time recognised in the area, with a significant enlargement of the previous assessed dispersal areas.

Caron, Benoît; Sulpizio, Roberto; Zanchetta, Giovanni; Siani, Giuseppe; Santacroce, Roberto

2010-06-01

186

The Late Holocene Stratigraphy of an Inlet-Dominated Barrier Island, Pea Island, North Carolina.  

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Sedimentological, foraminiferal, geochemical, and geophysical data sets as well as aerial photographs have been used to investigate the natural processes (inlet dynamics, ocean/estuarine washover, and sea-level change) responsible for the late Holocene units preserved in the barrier island subsurface at Pea Island National Wildlife Refuge. Historic nautical charts indicate that three inlets characterized Pea Island between early European exploration (1590) and the late 19th century; aerial photographs show New Inlet open in 1932 and 1940. Vibracores (up to 5.5 m) collected along three transects across Pea Island extend our knowledge of the geological evolution of this region to pre-historic times. The section in the longest core (PI01S6) consists of four fining-upwards depositional sequences. The basal unit of each sequence is a bedded, medium to fine, clean quartz sand with increasing concentrations of organic matter (3-4 % detrital and 5-7 % in situ Spartina alterniflora roots) or irregular mud clasts (2-5 cm) to spherical mud balls (1-2 cm) up core. The clean sand units have so far proven to be barren of foraminifera except for a shelly unit at ca. 220 cm below MSL. The foraminiferal assemblage in this unit is of open shelf character (Elphidium excavatum, Hanzawaia strattoni, and Buccella inusitata). A 14C age on a disarticulated Chione cancellata valve from this unit is cal. 930+/-60 BP. The sand grades into a gray, tight mud in the first two sequences and into an inter-laminated mud and in situ peat in the third sequence. The peat contains leaf fragments and rhizomes of the marsh plants Juncus roemarianus, Spartina cynosuroides, and/or Phragmites spp. The peat and muddy sand units contain marsh foraminifera (Trochammina spp., Miliammina fusca, Arenoparrella mexicana), which are also found in modern marsh deposits. A peat sample from the third fining upward sequence (the only one to grade into a true peat) has a 14C age of cal. 395+/-35 BP, cal. 295+/-35 BP, or cal 180+/-40 BP. The four fining-upwards sequences have sharp erosional basal contacts. These deposits appear to reflect back-barrier processes including sequential deposition of flood-tide delta sands and/or sound sands adjacent to marshes. The shelly sands, containing open shelf foraminiferal assemblages, represent oceanic overwash, inlet deposits, or open embayment sands deposited behind a laterally extensive breach in the barrier island. The sequences are capped by the deposits of modern environments that include algal flats, tidal creeks, high and low marshes, back-barrier berms, overwash fans, and aeolian dunes. Several of the modern environments became covered with marsh vegetation after the construction of barrier dune ridges in the late 1930?s.

Smith, C. G.; Ames, D.; Corbett, D. R.; Culver, S.; Mallinson, D.; Riggs, S. R.; Vance, D.

2002-12-01

187

Late Quaternary stratigraphy and sedimentology of the central North Atlantic: A progress report  

International Nuclear Information System (INIS)

The marine geological research program of the Department of Sedimentary Geology at the Free University of Amsterdam focuses on three areas: Banda Sea, central North Atlantic and the Mediterranean. Late Quaternary deep-sea cores taken in these areas are analysed in order to reconstruct changes in paleoceanography as reflected in the sedimentary record. Radiocarbon datings through the cores provide the necessary stratigraphic framework. The Utrecht tandem Accelerator Mass Spectrometer (AMS) allows radiocarbon dating on minutes samples (10-25 mg carbonate) and is therefore an excellent tool for core studies. This paper concentrates on results obtained from the central North Atlantic material. The Atlantic CaCO3 profile shows a maximum at the last climate optimum at 6 ka and a minimum at the last glacial maximum at 18 ka. This is also observed in our material, and confirmed by radiocarbon dating. It is shown that sedimentation rates are distinctly higher during the period of deglaciation. The dating also provides a framework for the timing of the retreat of the polar front. A surface layer of pteropod shells covers parts of the Atlantic Ocean floor at about 3000 m depth. Many shells show Fe/Mn staining. The AMS technique allows dating of single shells, and proves that the stained specimens are considerably oder than the unstained shells. Implications for this phenomenon and for the contribution of aragonite to the sediment are given. (orig.)ent are given. (orig.)

188

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

189

Late Pleistocene and Holocene palaeoenvironments in and around the middle Caspian basin as reconstructed from a deep-sea core  

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Late Pleistocene and/or Holocene high-resolution palynological studies are available for the south basin of the Caspian Sea (CS), the world's largest lake. However, the north and middle basins have not been the object of high-resolution palynological reconstructions. This new study presents the pollen, spores and dinoflagellate cysts records obtained from a 10 m-long sediment core recovered in the middle basin, which currently has brackish waters and is surrounded by arid and semi-arid vegetation. An age-depth model built based on six radiocarbon dates on ostracod shells indicates that the sequence spans the period from 14.47 to 2.43 cal. ka BP. The present palaeoenvironmental study focuses on the top 666 cm, or from 12.44 to 2.43 cal. ka BP. At the vegetation level, the Younger Dryas is characterised by an open landscape dominated by desert vegetation composed by Amaranthaceae with shrubs and salt-tolerant plants. However, although the Early Holocene is also characterised by desert vegetation, it is enriched in various shrubs such as Ephedra and Calligonum, but tree expansion is not important at the Holocene onset. After a major shift at 8.19 cal. ka BP, the Middle Holocene displays now both the character of desert and of steppe, although some trees such as Quercus and Corylus slightly spread. The Late Holocene records steppe vegetation as dominant, with more tree diversity. Regarding the lacustrine signal, the dinocyst assemblage record fluctuates between slightly brackish conditions highlighted by Pyxidinopsis psilata and Spiniferites cruciformis, and more brackish ones - similar to the present day - with the dominance of Impagidinium caspienense. The Late Pleistocene is characterised by low salinities, related to the Khvalynian highstand. From 11.56 cal. ka BP, slightly more saline waters are reconstructed with an increase of I. caspienense for a period of 1000 years, which could be attributed to the Mangyshlak lowstand. From 10.55 cal. ka BP, low salinity conditions return with remains such as Anabaena and Botryococcus abundant until 8.83 cal. ka BP, followed by a slow, progressive decrease of P. psilata and S. cruciformis until 4.11 cal. ka BP, which is the main assemblage change at lacustrine scale. Since then, higher salinities, similar to the present one, are reconstructed. Finally, Lingulodinium machaerophorum starts its development only at 2.75 cal. ka BP, in the Late Holocene. The present research revealed fundamental differences from previously published sea-level curves, in that a 6000 yr-long highstand suggested by low salinities is shown between 10.55 and 4.11 cal. ka BP. Amongst other arguments, using a comparison to a similar palynological regard but in the south basin, a N-S salinity gradient that is the reverse of the present one across the CS, suggests that the Amu Darya was flowing in the CS. Hence the CS levels during the Late Pleistocene and Holocene were influenced by a combination of precipitation over the high European latitudes and the indirect influence of the Indian summer monsoon over the Pamirs.

Leroy, Suzanne A. G.; López-Merino, Lourdes; Tudryn, Alina; Chalié, Françoise; Gasse, Françoise

2014-10-01

190

Late Neogene Volcanic Stratigraphy in the Southern Puertecitos Volcanic Province of Baja California: Time Constraints and Vent Source Location  

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Late Neogene syn-rift explosive volcanism occurred in the Puertecitos Volcanic Province along the western margin of the Gulf of California. This volcanic episode is possibly related to extension during opening of the lower Delfin basin in mid-late Pliocene time. The volcanic stratigraphy in the southern Puertecitos Volcanic Province comprises three main groups: group 1 is a mid-Miocene, arc-related volcanic and sedimentary apron. Groups 2 and 3 are syn-rift volcanic units interstratified within alluvial conglomerate. Group 2 includes a non-welded, crystal-rich pyroclastic flow deposit, and a dark glassy dacite lava flow. Distinctive mineralogy of the crystal tuff is augite, sanidine-microcline and quartz. Two 39Ar/40Ar laser step-heating experiments on sanidine grains yielded an 6.18 ± 0.03 Ma isochron age, consistent with a 6.1 ± 0.4 Ma plateau age obtained in the dacite lava. Thickness of the crystal tuff varies from 35 m in the northeast to 10 m in the southwest along 5 km of distance. Group 3 is characterized by the lack of quartz and potassic feldspar phenocrysts. Three laser step heating experiments on groundmass samples constrain this pulse of explosive volcanism between 2.9 ± 0.1 and 2.3 ± 0.03 Ma. Thicknesses of individual units increase to the northeast and collectively reach up to 150 m. Isopath maps for distinctive flow-units indicate consistent dispersion direction to the SW (average azimuth 210° ± 15°). This inferred flow direction is similar to the orientation of magnetic susceptibility axes measured in 20 oriented samples that yield a mean azimuth of 214°± 24°. In group 3 flow-units eutaxitic foliation is concordant and dips 8-20° to the ENE. Tilting of the volcanic sequence is produced by a series of NNW-trending, west-dipping, high-angle normal faults with less than 40 m of throw. Balanced cross- sections in the southern Puertecitos Volcanic Province indicates that post-2.8 Ma extension is less than 15% suggesting that major deformation during the opening of the Lower Delfin basin has been accommodated to the east. Our data support multiple source vents located offshore the central Puertecitos Volcanic Province. These pyroclastic flows may constitute useful marker horizons in marine seismic lines for reconstructing the timing and amount of extension across conjugate margins in the Lower Delfin basin.

Garcia-Carrillo, P.; Martin, A.; Lopez-Martinez, M.; Cañon, E.

2007-05-01

191

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

192

Geothermal evidence of the Late Pleistocene-Holocene orbital forcing (example from the Urals, Russia)  

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We use early obtained in the Middle Urals geothermal reconstruction of the ground surface temperature (GST) history to determine the surface heat flux (SHF) history over the past 35 kyr. A new algorithm of GST-SHF transformation was applied to solve this problem. The time scale of geothermal reconstructions has been corrected by comparing the estimated heat flux and annual insolation at the latitude of 60° N. The consistency of SHF and insolation changes on the interval 35-6 kyr BP (the linear correlation coefficient R = 0.99) points to orbital factors as the main cause of climatic changes during the Pleistocene-Holocene transition. The amplitude of SHF variations is about 1.3% of the insolation changes amplitude. The increase of carbon dioxide concentrations lagged by 2-3 kyr from the SHF increase and occurred synchronously with GST changes.

Demezhko, D. Y.; Gornostaeva, A. A.

2014-08-01

193

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 sreflects 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

194

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

195

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

196

The late Early Pleistocene human dental remains from Uadi Aalad and Mulhuli-Amo (Buia), Eritrean Danakil: macromorphology and microstructure.  

Science.gov (United States)

Fieldwork performed during the last 15 years in various Early Pleistocene East African sites has significantly enlarged the fossil record of Homo erectus sensu lato (s.l.). Additional evidence comes from the Danakil Depression of Eritrea, where over 200 late Early to early Middle Pleistocene sites have been identified within a ?1000 m-thick sedimentary succession outcropping in the Dandiero Rift Basin, near Buia. Along with an adult cranium (UA 31), which displays a blend of H. erectus-like and derived morpho-architectural features and three pelvic remains, two isolated permanent incisors (UA 222 and UA 369) have also been recovered from the 1 Ma (millions of years ago) Homo-bearing outcrop of Uadi Aalad. Since 2010, our surveys have expanded to the nearby (4.7 km) site of Mulhuli-Amo (MA). This is a fossiliferous area that has been preliminarily surveyed because of its exceptional concentration of Acheulean stone tools. So far, the site has yielded 10 human remains, including the unworn crown of a lower permanent molar (MA 93). Using diverse analytical tools (including high resolution ?CT and ?MRI), we analysed the external and internal macromorphology and microstructure of the three specimens, and whenever possible compared the results with similar evidence from early Homo, H. erectus s.l., H. antecessor, H. heidelbergensis (from North Africa), Neanderthals and modern humans. We also assessed the UA 369 lower incisor from Uadi Aalad for root completion timing and showed that it compares well with data for root apex closure in modern human populations. PMID:24852385

Zanolli, Clément; Bondioli, Luca; Coppa, Alfredo; Dean, Christopher M; Bayle, Priscilla; Candilio, Francesca; Capuani, Silvia; Dreossi, Diego; Fiore, Ivana; Frayer, David W; Libsekal, Yosief; Mancini, Lucia; Rook, Lorenzo; Medin Tekle, Tsegai; Tuniz, Claudio; Macchiarelli, Roberto

2014-09-01

197

LATE PLIOCENE TO PLEISTOCENE TECTONIC ACTIVITY IN SW PORTUGAL: NEW DATA FROM FIELD OBSERVATIONS AND TRENCHING  

Science.gov (United States)

P.M. Figueiredo 1, J. Cabral 1,2, T. Rockwell 3, 1 IDL, Instituto Dom Luis, Lisbon University 2 GEOFCUL, Geology Department, Science Faculty of Lisbon University 3 SDSU, San Diego State University, San Diego, CA 92182 Corresponding author : pmfigueiredo@fc.ul.pt Southwestern Portugal is located close to the Eurasia-Nubia plate boundary, near the Azores-Gibraltar fracture zone. East of the Gloria transform fault, this boundary becomes complex and diffuse, where deformation related to the NW-SE convergence of Iberia and Nubia, at a rate of ca. 4-5 mm/ year, becomes distributed across a few hundred kilometres wide zone. This area corresponds to the inferred seismogenic source zone for the 1755 earthquake and tsunami (estimated ? Mw 8), and also for the Mw 7.9 1969 event. Inland, the São Teotónio-Aljezur-Sinceira fault system (STASFS) extends NNE-SSW for 50 km, parallel and close to the southwest Portuguese coast, and controls the development of small Cenozoic tectonic basins. It comprises onshore faults that may accommodate some of the ongoing plate boundary deformation. This fault system expresses primarily sinistral strike-slip with a minor reverse component, and is compatible with NW-SE maximum horizontal compressive stress. Four cenozoic strike-slip basins occur along the STASFS: from north to south, they are the S. Miguel (Odeceixe), Aljezur, Ribeira de Alfambras and Pedralva-Sinceira troughs. These basins generally have lengths of less than 5 km and a maximum width of 1.5 km, and are filled with Miocene to Pleistocene sediments. In some areas, fault-related post-Pliocene vertical displacements of up to 100 m may have occurred, but generally they only reach a few tens of meters. A trench exposure shows that at least on strand of this fault zone has sustained significant motion during the Quaternary. Recent studies in Alfambras basin based on geomorpholy analysis and detail field survey, conducted to the recognition of surface deformation parallel to the main fault trace althought further into the basin. Several trenches were openned showing fluvial sediments underlaying pleistocene(?) coarse colluvium from a nearsource likely to be related with a small axiall drainage. The fluvial package is faulted and folded, deformed by a major sub-vertical structure and the colluvium seems to be tilteld and do not crosses the fault trace. A paleosoil sequence (alfisoil) developed mainly on the colluvium unit was identified and it might be 700 ky in age. This paleosoil is faulted allowing to infer a vertical offset circa 1,5m. The structure identified is N10E on strike and was identified as a left strike-slip fault with a minor reverse component. In order to constrain the sediments ages, OSL samples were collected and samples for micro paleontological studies. Althought we have not identified references to quatify lateral displacements or individualize deformational events, these trenches evidencied pleistocene deformation on Alfambras segment on a site were was not previsiouly recognized.

Marques Figueiredo, P.; Cabral, J.; Rockwell, T. K.

2009-12-01

198

Late Pleistocene to Holocene Volcanism in the Lassen Domefield and Surrounding Region, California  

Science.gov (United States)

The Lassen Volcanic Center (LVC) marks the southernmost limit of active volcanism in the Cascade Range. Prior to the 1980 eruption of Mount St. Helens, Lassen Peak was the last volcano in the conterminous U.S. to erupt. Three eruptions in the last 1,100 years, (Chaos Crags, 1,103 × 13 years B.P.; Cinder Cone, 1666; and Lassen Peak 1914-1917) plus the most vigorous hydrothermal system in the Cascades, attest to an active magmatic system beneath LVC. We recently completed a modern volcano-hazards assessment of the Lassen segment of the Cascade arc that is based primarily on the recently published geologic map of Lassen Volcanic National Park (Clynne and Muffler, 2010; available at http://pubs.er.usgs.gov/publication/sim2899). The Lassen segment covers 75 linear km of arc from near the southern boundary of Lassen Volcanic National Park north to the Pit River. We define hazard zones for mafic and silicic tephra fall, mafic and silicic lava flows, pyroclastic flows and surges, and lahars and associated floods (Clynne et. al., 2012; available at http://pubs.usgs.gov/sir/2012/5176/a/). In the Lassen segment, volcanism occurs on two scales. Distributed mafic to intermediate calc-alkaline volcanism builds cinder cones and small shield volcanoes with intervening tholeiitic lava flows. Over time, these deposits coalesce to form a broad platform of volcanic material. In the last 100,000 years, at least 58 eruptions of regional volcanoes took place, and at least 40 more eruptions are only slightly older. Most are located in a few zones associated with regional faulting. The annual probability of eruption of a regional volcano is 0.00065 (0.065%), which corresponds to an average recurrence interval of 1,550 years. Although several eruptions occurred around the Pleistocene-Holocene boundary, none are demonstrably Holocene (system at present consists of crystal-rich mush formed during an extended lull in volcanic activity between ~190-100 ka. The latest Pleistocene to Holocene eruptions resulted from local rejuvenation of crystal mush by intrusion of mafic magma that is preserved as mafic inclusions. The most significant implication of this configuration is that no large body of eruptible silicic magma is present and that a large caldera-forming eruption at Lassen is unlikely in the foreseeable future.

Clynne, M. A.; Robinson, J. E.; Nathenson, M.; Muffler, L. J.

2013-12-01

199

Climate change, adaptive cycles, and the persistence of foraging economies during the late Pleistocene/Holocene transition in the Levant.  

Science.gov (United States)

Climatic forcing during the Younger Dryas (?12.9-11.5 ky B.P.) event has become the theoretical basis to explain the origins of agricultural lifestyles in the Levant by suggesting a failure of foraging societies to adjust. This explanation however, does not fit the scarcity of data for predomestication cultivation in the Natufian Period. The resilience of Younger Dryas foragers is better illustrated by a concept of adaptive cycles within a theory of adaptive change (resilience theory). Such cycles consist of four phases: release/collapse (?); reorganization (?), when the system restructures itself after a catastrophic stimulus through innovation and social memory--a period of greater resilience and less vulnerability; exploitation (r); and conservation (K), representing an increasingly rigid system that loses flexibility to change. The Kebarans and Late Natufians had similar responses to cold and dry conditions vs. Early Natufians and the Pre-Pottery Neolithic A responses to warm and wet climates. Kebarans and Late Natufians (?-phase) shifted to a broader-based diet and increased their mobility. Early Natufian and Pre-Pottery Neolithic A populations (r- and K-phases) had a growing investment in more narrowly focused, high-yield plant resources, but they maintained the broad range of hunted animals because of increased sedentism. These human adaptive cycles interlocked with plant and animal cycles. Forest and grassland vegetation responded to late Pleistocene and early Holocene climatic fluctuations, but prey animal cycles reflected the impact of human hunting pressure. The combination of these three adaptive cycles results in a model of human adaptation, showing potential for great sustainability of Levantine foraging systems even under adverse climatic conditions. PMID:22371591

Rosen, Arlene M; Rivera-Collazo, Isabel

2012-03-01

200

Seasonality of the late Pleistocene Dawson tephra and exceptional preservation of a buried riparian surface in central Yukon Territory, Canada  

Science.gov (United States)

The late Pleistocene Dawson tephra was deposited by one of the largest Quaternary eruptions in northwestern North America. Its distribution is known sparsely from sites near the source area in southwestern Alaska and central Yukon Territory, where more than 20 occurrences are documented in the Klondike region. Dawson tephra erupted about 25,300C yr BP, near the onset of the last glaciation, and provides a stratigraphic marker across Eastern Beringia. We report radiocarbon ages, paleobotanical data, and cryostratigraphic observations from a new Dawson tephra locale at Goldbottom Creek, in the Klondike region of Yukon Territory, which collectively indicate that the eruption occurred in the late winter or early spring. Multiple, fining-upward tephra-rich ice beds are interpreted as remnants of surface icings, which presently are common in the region during spring. A buried in situ riparian meadow, preserved below the icing and tephra, consists of abundant tufted hair grass ( Deschampsia caespitosa), with interspersed horsetails ( Equisetum cf. palustre) and mosses. Detrital plant remains and preserved in situ grass inflorescences entombed in the icing had expelled their fruits, consistent with a late season surface when the icing was active. The extraordinary thickness of Dawson tephra in central Yukon likely reflects reworking of a winter-deposited tephra by snow melt in the spring following the eruption, indicating that the primary thickness may be overestimated at valley-bottom sites. Winter deposition of the tephra may have, in part, minimized the terrestrial ecological impacts of the eruption on zonal "steppe-tundra" vegetation through the retransportation of tephra from hillslopes to the riparian areas, where the tephra became incorporated into local fluvial systems.

Froese, Duane G.; Zazula, Grant D.; Reyes, Alberto V.

2006-07-01

201

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

Science.gov (United States)

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

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

2013-03-01

202

Late Pleistocene and Holocene activity of the Atacazo Ninahuilca Volcanic Complex (Ecuador)  

Science.gov (United States)

The Atacazo-Ninahuilca Volcanic Complex (ANVC) is located in the Western Cordillera of Ecuador, 10 km southwest of Quito. At least six periods of Pleistocene to Holocene activity (N1 to N6) have been preserved in the geologic record as tephra fallouts and pyroclastic flow deposits. New field data, including petrographic and whole-rock geochemical analyses of over forty soil and tephra sections, 100 pumice and lithic samples, and 10 new 14C ages allow us to constrain: (1) the tephra fall isopachs and detailed characteristics of the last two events (N5-N6) including volume estimates of the tephra and pyroclastic flow deposits and the corresponding volcanic explosivity index (VEI); (2) the petrographical and geochemical correlations between domes, tephras, and pyroclastic flow deposits; and, (3) the timing of the last 4 eruptive events and a period of quiescence that endured a few thousand years (1000-4000). The last two eruptive events (N5 and N6) took place at around 4400 ± 35 yr BP and 2270 ± 15 yr BP, producing huge plinian and pyroclastic flow deposits. Taking into account the widely spread deposits of these VEI 5 eruptions, the present population of about 70 000 people, and the current infrastructure; the development of mitigation plans and deployment of monitoring systems at ANVC is highly recommended.

Hidalgo, Silvana; Monzier, Michel; Almeida, Eduardo; Chazot, Gilles; Eissen, Jean-Philippe; van der Plicht, Johannes; Hall, Minard L.

2008-09-01

203

A late Pleistocene long pollen record from Lake Urmia, NW Iran  

Science.gov (United States)

A palynological study based on two 100-m long cores from Lake Urmia in northwestern Iran provides a vegetation record spanning 200 ka, the longest pollen record for the continental interior of the Near East. During both penultimate and last glaciations, a steppe of Artemisia and Poaceae dominated the upland vegetation with a high proportion of Chenopodiaceae in both upland and lowland saline ecosystems. While Juniperus and deciduous Quercus trees were extremely rare and restricted to some refugia, Hippophaë rhamnoides constituted an important phanerophyte, particularly during the late last glacial period. A pronounced expansion in Ephedra shrub-steppe occurred at the end of the penultimate late-glacial period but was followed by extreme aridity that favoured an Artemisia steppe. Very high lake levels, registered by both pollen and sedimentary markers, occurred during the middle of the last glaciation and late part of the penultimate glaciation. The late-glacial to early Holocene transition is represented by a succession of Hippophaë, Ephedra, Betula, Pistacia and finally Juniperus and Quercus. The last interglacial period (Eemian), slightly warmer and moister than the Holocene, was followed by two interstadial phases similar in pattern to those recorded in the marine isotope record and southern European pollen sequences.

Djamali, Morteza; de Beaulieu, Jacques-Louis; Shah-hosseini, Madjid; Andrieu-Ponel, Valérie; Ponel, Philippe; Amini, Abdolhossein; Akhani, Hossein; Leroy, Suzanne A. G.; Stevens, Lora; Lahijani, Hamid; Brewer, Simon

2008-05-01

204

Late Pleistocene zircon ages for intracaldera domes at Gölcük (Isparta, Turkey)  

Science.gov (United States)

Pleistocene to Quaternary volcanism in the Isparta region (SW Anatolia, Turkey) comprises potassic lavas and pyroclastic deposits, which are largely centered around Gölcük caldera. Trachytic intracaldera lava domes represent the latest eruptive event at Gölcük, and their eruption age is crucial for defining a minimum age for the preceding caldera-forming explosive eruption. Here, we present combined U-Th and (U-Th)/He zircon geochronological data for two intracaldera lava domes constraining their crystallization and eruption ages, respectively. U-Th zircon crystallization ages peak between ca. 15 and 25 ka. In rare instances U-Th zircon crystallization ages date back to ca. 59 and 136 ka. U-Th zircon crystallization ages also permit (U-Th)/He eruption ages from the same crystals to be individually corrected for uranium series decay chain disequilibrium, which is mainly due to the deficit of the intermediate daughter 230Th in zircon. Average disequilibrium-corrected (U-Th)/He zircon ages are 14.1 ± 0.5 and 12.9 ± 0.4 ka (1?). These ages are indistinguishable within analytical uncertainties suggesting that both lavas erupted quasi simultaneously. This contradicts published K-Ar ages that suggest an extended hiatus from ca. 52 to 24 ka between intracaldera dome eruptions. Evidence for protracted zircon crystallization over several thousands of years prior to eruption indicates the presence of a long-lived magma reservoir underneath Gölcük caldera. Implications of the revised eruptive geochronology presented here include younger ages for the latest effusive eruptions at Gölcük, and potentially also a more recent explosive eruption than previously assumed.

Schmitt, Axel K.; Danišík, Martin; Siebel, Wolfgang; Elitok, Ömer; Chang, Yu-Wei; Shen, Chuan-Chou

2014-10-01

205

Reconstructing the migration patterns of late Pleistocene mammals from northern Florida, USA  

Science.gov (United States)

We used analyses of the strontium isotope ( 87Sr/ 86Sr) ratios of tooth enamel to reconstruct the migration patterns of fossil mammals collected along the Aucilla River in northern Florida. Specimens date to the late-glacial period and before the last glacial maximum (pre-LGM). Deer and tapir displayed low 87Sr/ 86Sr ratios that were similar to the ratios of Florida environments, which suggest that these taxa did not migrate long distance outside of the Florida region. Mastodons, mammoths, and equids all displayed a wide range of 87Sr/ 86Sr ratios. Some individuals in each taxon displayed low 87Sr/ 86Sr ratios that suggest they ranged locally, while other animals had high 87Sr/ 86Sr ratios that suggest they migrated long distances (> 150 km) outside of the Florida region. Mastodons were the only taxa from this region that provided enough well-dated specimens to compare changes in migration patterns over time. Pre-LGM mastodons displayed significantly lower 87Sr/ 86Sr ratios than late-glacial mastodons, which suggests that late-glacial mastodons from Florida migrated longer distances than their earlier counterparts. This change in movement patterns reflects temporal changes in regional vegetation patterns.

Hoppe, Kathryn A.; Koch, Paul L.

2007-11-01

206

Fossil record of holococcoliths and selected hetero-holococcolith associations from the Mediterranean (Holocene–late Pleistocene): Evaluation of carbonate diagenesis and palaeoecological–palaeocenographic implications  

OpenAIRE

The Holocene–late Pleistocene distribution of holococcoliths, is quantified by light microscopy from cores from the Western Mediterranean, the Aegean Sea and eight eastern Mediterranean cores recovering sapropel S1. The diversity of fossil holococcoliths is much lower than is seen in the plankton, indicating selective preservation. However the holococcolith phases of Syracosphaera pulchra and Helicosphaera carteri are abundantly preserved allowing a comparison of fossil records of heterococ...

Crudeli, D.; Young, J. R.; Erba, E.; Geisen, M.; Ziveri, P.; Lange, G. J.; Slomp, C. P.

2006-01-01

207

Contemporaneous Trace and Body Fossils from a Late Pleistocene Lakebed in Victoria, Australia, Allow Assessment of Bias in the Fossil Record  

OpenAIRE

The co-occurrence of vertebrate trace and body fossils within a single geological formation is rare and the probability of these parallel records being contemporaneous (i.e. on or near the same bedding plane) is extremely low. We report here a late Pleistocene locality from the Victorian Volcanic Plains in south-eastern Australia in which demonstrably contemporaneous, but independently accumulated vertebrate trace and body fossils occur. Bite marks from a variety of taxa are also present on t...

Camens, Aaron Bruce; Carey, Stephen Paul

2013-01-01

208

Late Pleistocene-Holocene earthquake-induced slumps and soft-sediment deformation structures in the Acequion River valley, Central Precordillera, Argentina  

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Full Text Available Evidence of earthquake-induced liquefaction features in the Acequión river valley, central western Argentina, is analysed. Well-preserved soft-sediment deformation structures are present in Late Pleistocene deposits; they include two large slumps and several sand dikes, convolutions, pseudonodules, faults, dish structures and diapirs in the basal part of a shallow-lacustrine succession in the El Acequión River area. The water-saturated state of these sediments favoured deformation.

Perucca Laura P

2014-07-01

209

Discovery of sediment indicating rapid lake-level fall in the late Pleistocene Gokarna Formation, Kathmandu Valley, Nepal: implication for terrace formation  

OpenAIRE

Sediment indicating a rapid fall in lake level has been discovered in the late Pleistocene Gokarna Formation, Kathmandu Valley, Nepal. The indicator is observed along a widely traceable erosional surface in this formation, and is characterized by (1) gently inclined (ca. 10°) tabular cross-stratified sand beds of delta front origin consisting of coarser material and showing gradual decrease in elevation of its top to the progradation direction, (2) an antidune cross-laminated sand bed that i...

Sakai, Tetsuya; Takagawa, Tomohiro; Gajurel, Ananta Prasad; Tabata, Hideo; Ooi, Nobuo; Upreti, Bishal Nath

2006-01-01

210

Leafcutter Bee Nests and Pupae from the Rancho La Brea Tar Pits of Southern California: Implications for Understanding the Paleoenvironment of the Late Pleistocene  

OpenAIRE

The Rancho La Brea Tar Pits is the world’s richest and most important Late Pleistocene fossil locality and best renowned for numerous fossil mammals and birds excavated over the past century. Less researched are insects, even though these specimens frequently serve as the most valuable paleoenvironemental indicators due to their narrow climate restrictions and life cycles. Our goal was to examine fossil material that included insect-plant associations, and thus an even higher potential for ...

Holden, Anna R.; Koch, Jonathan B.; Griswold, Terry; Erwin, Diane M.; Hall, Justin

2014-01-01

211

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

212

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

213

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

214

Controls on Sr/Ca in benthic foraminifera and implications for seawater Sr/Ca during the late Pleistocene  

Science.gov (United States)

Changes in the Sr to Ca ratio of sea water have important implications for the interpretation of past climate. It has proven difficult to interpret Sr/Ca of foraminiferal calcite as a measure of seawater Sr/Ca or as reflecting the influence of deep water carbonate ion saturation (?[CO32-]) on the incorporation of Sr into benthic foraminiferal carbonate. Here, we address this issue by measurements of paired benthic foraminiferal Sr/Ca and B/Ca (a proxy for deep water ?[CO32-]) for core-tops from the global ocean and three down cores at different settings during the Last Glacial-interglacial cycle. These new data suggest a significant control of deep water ?[CO32-] on benthic foraminiferal Sr/Ca, and that down-core shell Sr/Ca variations can be largely accounted for by past deep water ?[CO32-] changes. We conclude that seawater Sr/Ca has likely remained near-constant on glacial-interglacial timescales during the late Pleistocene, in agreement with model results. With due caution, benthic Sr/Ca may be used as an auxiliary proxy for deep water ?[CO32-] if seawater Sr/Ca is constant.

Yu, Jimin; Elderfield, Henry; Jin, Zhangdong; Tomascak, Paul; Rohling, Eelco J.

2014-08-01

215

Charophytes as bio-indicators for lake level high stand at “Trou au Natron”, Tibesti, Chad, during the Late Pleistocene  

Science.gov (United States)

The present paper deals with the charophytes collected by H. Faure and P. M. Vincent from outcrops of lacustrine deposits inside the caldera "Trou au Natron" at an altitude of 1875 m above sea level. Characeae represent up to 93% of these carbonates and characterise a new type of sediment, defined as "Characeite". The remains consist in vegetative (thallus) fragments and in gyrogonites (the calcified fructifications of the Characeae). The presence of both these types of materials and their high frequency indicate in situ fossilisation of the former fresh water vegetation, termed a "charophyte meadow". The topographical position of the deposits corresponds to a rocky plateau or bench on the slopes of the caldera, located c. 300 m above the present-day floor of the caldera. The development and preservation of the charophytes lead to conclude that the lake was at least 300 m deep at the time when the plants grew. Radiocarbon dating of the thallus fragments provided an age of 14,260 ± 300 yr B.P. This age is consistent with analyses obtained previously on gastropod shells from Trou au Natron and indicates high lake level in the Tibesti Mountains during the Late Pleistocene.

Soulié-Märsche, I.; Bieda, S.; Lafond, R.; Maley, J.; M'Baitoudji; Vincent, P. M.; Faure, Hugues

2010-07-01

216

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

217

Assessing the strength of the monsoon during the late Pleistocene in southwestern United States  

Science.gov (United States)

Improved predictions of drought require an understanding of natural and human-induced climate variability. Long-term records across glacial-interglacial cycles provide the natural component of variability, however few such records exist for the southwestern United States (US) and quantitative or semi-quantitative records of precipitation are absent. Here we use the hydrogen isotope (?D) value of C28n-alkanoic acid in lacustrine sediments of Pleistocene age to reconstruct ?D values of precipitation in northern New Mexico over two glacial-interglacial cycles (?550,000-360,000 years before present) and obtain a record of monsoon strength. Overall, reconstructed ?D values range from -53.8‰ to -94.4‰, with a mean value of -77.5 ± 8‰. Remarkably, this variation falls within the measured present-day summer monsoonal and winter weighted means (-50.3 ± 3‰ and -106.4 ± 20‰ respectively), suggesting that processes similar to those of present time also controlled precipitation during Marine Isotope Stage (MIS) 13 to 10. Using the ?D summer monsoonal and winter mean values as end-members, we interpret our reconstructed ?D record of precipitation as a direct, and semi-quantitative, indicator of monsoon strength during MIS 13 to 10. Interglacial periods were characterized by greater monsoon strength but also greater variability compared to glacial periods. Pronounced cycles in the strength of the monsoon occurred during interglacial periods and in general were positively correlated with maximum mean annual temperatures. Our estimates of monsoon strength are supported by independent proxies of ecosystem productivity, namely, TOC, ?13C of TOC and Si/Ti ratio and warm pollen taxa Juniperus and Quercus. Interglacial variability in the strength of the monsoon resembles a response to the land-sea surface temperature contrast (LSTC) except for the early part of MIS 11. During this period, LSTC would have remained relatively strong while monsoonal strength decreased to a minimum. This minimum occurred following the warmest interval of MIS 11, suggesting a more complex driving of monsoon strength during warm periods. In addition, this period of monsoon minimum coincided with a core section of mud-cracked sediments that suggest low monsoonal precipitation was an important factor in the onset of drought. Our estimates of monsoon strength represent a record of natural variability in the region that is relevant to present time, in particular the variability during interglacial MIS 11, which is considered an analog for the current interglacial. Our results suggest that natural variability can cause significant reductions in monsoonal precipitation with the implication of a potentially adverse effect from sustained warming.

Cisneros-Dozal, Luz M.; Huang, Yongsong; Heikoop, Jeffrey M.; Fawcett, Peter J.; Fessenden, Julianna; Anderson, R. Scott; Meyers, Philip A.; Larson, Toti; Perkins, George; Toney, Jaime; Werne, Josef P.; Goff, Fraser; WoldeGabriel, Giday; Allen, Craig D.; Berke, Melissa A.

2014-11-01

218

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

219

Didelphidae marsupials (Mammalia, Didelphimorphia) from the Late Pleistocene deposit of the Gruta dos Moura Cave, northern Brazil  

Scientific Electronic Library Online (English)

Full Text Available Neste estudo pretende-se reconhecer a diversidade de marsupiais fósseis da Gruta dos Moura além dos seus aspectos ambientais e climáticos durante o Quaternário. Constatou-se que esta é a maior diversidade de marsupiais Pleistocênicos coletados em uma única caverna: Didelphis albiventris, D. aurita, [...] Gracilinaus agilis, G. microtarsus, Marmosa murina, Monodelphis brevicaudata, M. domestica e Sairadelphys tocantinensis. Além disso, esses marsupiais também reúnem a única assembleia fossilífera que seguramente está associada ao Neopleistoceno. Estudos paleontológicos realizados sugerem uma íntima associação com ambientes secos, abertos e de alta profusão de recursos hídricos. Assim, como a maioria dos táxons identificados são característicos de florestas abertas e matas de galerias, essa poderia ser de fato a paisagem do entorno da Gruta dos Moura. Estudos recentes identificaram simpatria entre espécies de ambientes secos/abertos e de florestas úmidas dos táxons aqui identificados e característicos de regiões úmidas. Assim, essas espécies poderiam habitar matas de galeria e capões, ou até ecótonos, em um ambiente mais seco e aberto. Além disso, a extinção de Sairadelphys pode ser outro indício de que as condições climático-ambientais mudaram ou que o ambiente pretérito era mais heterogêneo que o encontrado atualmente na região. Abstract in english The present study acknowledges the diversity of fossil marsupials from the Gruta dos Moura cave, as well as environmental and climatic aspects during the Quaternary. The results show that this is the largest diversity of Pleistocene marsupials recorded in a single cave: Didelphis albiventris, D. aur [...] ita, Gracilinanus agilis, G. microtarsus, Marmosa murina, Monodelphis brevicaudata, M. domestica and Sairadelphys tocantinensis. Furthermore, the described specimens are also part of the only fossil assemblage unequivocally referable to the late Pleistocene. Paleontological studies suggest an intimate association with dry and open environments with high abundance of water sources. Since most of the identified taxa are characteristic of open forests and gallery forests, this could represent the actual environment around the Gruta dos Moura cave. Recent studies identified sympatric occurrences between species from open and dry environments and species from humid forests that were identified among our material and are characteristic of humid regions. Therefore, these species could inhabit gallery forests and capons, or even ecotones, inside a dry and open environment. Moreover, the extinction of Sairadelphys could also indicate that the climatic and environmental conditions changed or that the past environment was more heterogeneous than the current environment of the region.

Patricia Villa, Nova; Leonardo S., Avilla; Édison V., Oliveira.

2015-03-01

220

Late Pleistocene sedimentation increase in the Gulf of Mexico and modeling of time-dependent long-wavelength flexural subsidence  

Science.gov (United States)

Global climate change occurring near the transition from Pliocene to Pleistocene epochs is the most likely source for increased rates of sedimentary deposition into the world's catchment basins. During the Pleistocene the periodicity in sedimentation rate has periods of roughly 20,000, 41,000 and 100,000 years: having a distinct fingerprint of the Milankovich orbital forcing periods (Molnar 2004). We model the forcing of the time-dependent flexure of the Gulf of Mexico by continent-wide sediment transport rate variability over the past 4 Ma. Reconstructions of changes in sediment dispersal occurring during the Late Cenozoic indicate that glacioeustasy also plays a significant role along the shore of the Northern Gulf of Mexico Basin (Galloway 2001). We employ both spherically layered and gravitating viscoelastic half-space models employing an elastic lithosphere and using Maxwell time constants that are tuned to both regional and global seismic tomography. The latter data are consistent with a rheologically stiffer than average sub-crustal environment. Hydroisostatic loading is also included in the modeling. Paleosealevel indicators, tide gauges and recent GPS results provide rich data sources for inverse modeling of the load history and solid earth rheology. The sediment rate changes are modeled, in part, as pulsed great megaflood erosional events known to be active during Glacial to Interglacial transitions (Brown and Kennett 1998). Although the model is relatively crude in both space and time, preliminary results indicate that the subsidence rate caused by long-term sedimentary changes could sustain subsidence rates of 1 - 10 mm/yr during the past 5,000 years over many hundreds of kilometers of coastline. We also discuss the gravity change and self-gravitationally induced sea level variability predicted by the models. Refinement of such modeling in space and time is a major challenge for the future. However, long-wavelength analysis of ongoing Gulf vertical motions complement the study of more local phenomenon, wherein anthropogenic-related subsidence, growth fault-related land motion and sediment compaction may drive a very concentrated large-amplitude subsidence at present-day.

Ivins, E. R.; Blom, R. G.; Wu, X.; Dokka, R.

2005-12-01

221

Contrasting Holocene vs. Late Pleistocene dynamics of sediment deposition in Laguna Potrok Aike, Argentina  

Science.gov (United States)

In the maar lake Laguna Potrok Aike (52°S, 70°W; 116 m asl.; diameter: 3.5 km, water depth: 100 m) in southern Patagonia, Argentina, in total 510 m of lacustrine sediments were recovered in the framework of the ICDP project PASADO (Potrok Aike Maar Lake Sediment Archive Drilling Project). Quadruplicate and triplicate cores down to a maximum depth of 101.5 m below lake floor were taken with a total core recovery of 94.4 % from two drillsites located 700 m apart in the central profundal plain of the lake. Seismic refraction data reveal a funnel-shaped structure originating from phreatomagmatic maar explosions embedded in the sandstone rocks of the surrounding Santa Cruz Formation. The funnel is filled by lacustrine sediments of up to 370 m in thickness with seismic velocities (sv) of 1500-2350 m s-1 which are underlain by a unit of probably volcanoclastic origin (sv >2400 m s-1). Seismic reflection data of the uppermost 100 m of the sediments reveal stratified lacustrine sediments and a rather dynamic development of the lake: on top of pelagic sediments, a desiccation horizon is found, with sand dunes in the eastern part of the lake basin. These are overlain by a series of paleo shorelines documenting the history of lake level rise in this early new lake. While this new lake formed in the central and eastern part of the maar depression, the western part was filled by stacked coarse-grained, delta-type sediments probably deriving from the only inlet that at present is sporadically active. After this early filling of the new lake, a stage of rapid lake level rise is observed in the seismic reflection data. Seismic findings are currently verified by the analyses of a 106.08 m long composite profile created by splicing of the three drilled cores of Site 2. According to a first age model, the sedimentary record from Laguna Potrok Aike reaches back to approx. 56,000 cal. BP and exhibits contrasting lithologies downcore especially in the Pleistocene part of the record. First estimates indicate that approx. 54 % of the record consist of redeposited sediments, which in the lower part seem to represent the delta-type sediments detected in the seismic profiles. The most dramatic shift of the entire record, however, occurs around 15,600 cal. BP. At this date, a more than 1 m thick layer with a fundamentally different geochemical composition follows immediately above a ca. 1 cm thick tephra layer that originated from an eruption of the Reclus volcano. This layer separates carbonate-free sediments in the lowermost 80 m of the record that are dominated by clastic input of fluvial and eolian origin and a high proportion of redeposition from a lake system characterised by authigenic carbonate precipitation in the uppermost 18 m of the record with calcite contents of up to 35 %, much lower percentages of redeposition, and lake level variations between +21 m and -35 m with respect to present day lake level.

Ohlendorf, C.; Gebhardt, C.; Hahn, A.; Kliem, P.; Zolitschka, B.; Science Team

2010-12-01

222

Late pleistocene to recent sediment deposition in the central and western Mediterranean  

Science.gov (United States)

Examination of the planktonic foraminiferal fauna in cores from the Mediterranean indicates that the present and probably the past populations do not reflect the water temperatures as in the Atlantic Ocean. Variation in the planktonic foraminiferal assemblage and the oxygen isotope values of some species of foraminifera during Late Würm to Recent times indicate changes in the water circulation pattern of the Mediterranean. The proportions of quartz and clay group minerals have an inverse relationship, quartz being more abundant during Würm times and clays during Post-Glacial and interglacial times. Calcite is essentially of biogenic origin, pyrite is found in sapropels and near stratigraphic breaks. Sapropel formation is attributed to high terrigenous and marine organic input sluggish circulation and high freshwater input from the Black Sea and the Nile. Initiation of sapropel conditions may have been triggered by the re-introduction of Atlantic water into the Mediterranean.

Buckley, H. A.; Johnson, L. R.

1988-05-01

223

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

224

Paleowaters in Silurian-Devonian carbonate aquifers: Geochemical evolution of groundwater in the Great Lakes region since the Late Pleistocene  

Science.gov (United States)

Changes in the climatic conditions during the Late Quaternary and Holocene greatly impacted the hydrology and geochemical evolution of groundwaters in the Great Lakes region. Increased hydraulic gradients from melting of kilometer-thick Pleistocene ice sheets reorganized regional-scale groundwater flow in Paleozoic aquifers in underlying intracratonic basins. Here, we present new elemental and isotopic analyses of 134 groundwaters from Silurian-Devonian carbonate and overlying glacial drift aquifers, along the margins of the Illinois and Michigan basins, to evaluate the paleohydrology, age distribution, and geochemical evolution of confined aquifer systems. This study significantly extends the spatial coverage of previously published groundwaters in carbonate and drift aquifers across the Midcontinent region, and extends into deeper portions of the Illinois and Michigan basins, focused on the freshwater-saline water mixing zones. In addition, the hydrogeochemical data from Silurian-Devonian aquifers were integrated with deeper basinal fluids, and brines in Upper Devonian black shales and underlying Cambrian-Ordovician aquifers to reveal a regionally extensive recharge system of Pleistocene-age waters in glaciated sedimentary basins. Elemental and isotope geochemistry of confined groundwaters in Silurian-Devonian carbonate and glacial drift aquifers show that they have been extensively altered by incongruent dissolution of carbonate minerals, dissolution of halite and anhydrite, cation exchange, microbial processes, and mixing with basinal brines. Carbon isotope values of dissolved inorganic carbon (DIC) range from -10 to -2‰, 87Sr/ 86Sr ratios range from 0.7080 to 0.7090, and ?34S-SO4 values range from +10 to 30‰. A few waters have elevated ?13C DIC values (>15‰) from microbial methanogenesis in adjacent organic-rich Upper Devonian shales. Radiocarbon ages and ?18O and ?D values of confined groundwaters indicate they originated as subglacial recharge beneath the Laurentide Ice Sheet (14-50 ka BP, -15 to -13‰ ?18O). These paleowaters are isolated from shallow flow systems in overlying glacial drift aquifers by lake-bed clays and/or shales. The presence of isotopically depleted waters in Paleozoic aquifers at relatively shallow depths illustrates the importance of continental glaciation on regional-scale groundwater flow. Modern groundwater flow in the Great Lakes region is primarily restricted to shallow unconfined glacial drift aquifers. Recharge waters in Silurian-Devonian and unconfined drift aquifers have ?18O values within the range of Holocene precipitation: -11 to -8‰ and -7 to -4.5‰ for northern Michigan and northern Indiana/Ohio, respectively. Carbon and Sr isotope systematics indicate shallow groundwaters evolved through congruent dissolution of carbonate minerals under open and closed system conditions ( ?13C DIC = -14.7 to-11.1‰ and 87Sr/ 86Sr = 0.7080-0.7103). The distinct elemental and isotope geochemistry of Pleistocene- versus Holocene-age waters further confirms that surficial flow systems are out of contact with the deeper basinal-scale flow systems. These results provide improved understanding of the effects of past climate change on groundwater flow and geochemical processes, which are important for determining the sustainability of present-day water resources and stability of saline fluids in sedimentary basins.

McIntosh, J. C.; Walter, L. M.

2006-05-01

225

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

226

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

Science.gov (United States)

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

Liu, Tanzhuo; Broecker, Wallace S.

2013-04-01

227

Late Pleistocene (MIS5-3) environmental reconstruction from north-eastern Iberia through microvertebrate and palaeobotanical records  

Science.gov (United States)

The aim of this work is to analyze the environmental changes during the Late Pleistocene on the basis of a multi-approach study based on natural and archaeological deposits from NE Iberian Peninsula. The focussed area, although having a small extension (some 32.000 square kilometres), covers a large range of ecosystems and bioclimatic conditions from the Mediterranean seashore to the summit of the Pyrenean mountain ranges (up to 2000 masl). This synthetical approach includes materials from various contexts including 10 archaeological deposits and a single natural deposit. In this work, plant (pollen and charcoals) and animal (small mammals, amphibians and reptiles) records are being analysed and compared in order to present an overview of the environmental changes occurred from the MIS5 to MIS3. On the first hand, we are using the small-vertebrate records recovered from archaeological deposits. These proxies are mainly the product of pellets from birds of prey and are key ecological markers. On the second hand, palaeobotanical evidences, pollen and charcoal, have different formation processes. Charcoal remains are mostly from archaeological deposits and are due to human activities related to fire showing evidences of the local vegetation. Pollen evidences from archaeological and natural contexts are deposited through natural processes (wind, insects, etc.) and show regional scale vegetation record. Results indicate the presence of temperate elements during all these periods (especially at the seashore area), with a more important representation and extension southwards or changes in altitude from taxa with eurosiberian affinities during coldest periods. Forest coverage, plant and vertebrate distribution along the territory point out a mosaic landscape formed by open areas and forests. These landscapes have probably a more or less Mediterranean or Eurosiberian character depending on the climatic moment and their location with variations along the sequence.

Allue, Ethel; Bennàssar, Maria; Biltekin, Demet; Blain, Hugues-Alexandre; Burjachs, Francesc; Euba, Itxaso; Expósito, Isabel; Fernández-García, Mónica; López-García, Juan Manuel

2014-05-01

228

Composition and provenance of Late Pleistocene-Holocene alluvial sediments of the eastern Andean piedmont between 33 and 34° S (Mendoza Province, Argentina)  

Science.gov (United States)

The Andean cordillera, and its piedmont in the central western Argentina, has been long considered as one of the main source areas of detritus for the Chaco-Pampean plain sand dune fields and loess/loess-like deposits of central Argentina. The main goal of this study is to evaluate the composition of the late Pleistocene-Holocene alluvial deposits of the Andes cordillera piedmont, from 33° to 34° S. The results are interpreted in the context of the regional geology, tectonic setting of the study area and its implications in the continent-wide perspective of modern alluvial sands proposed by Potter (1994). Sampling was conducted at the alluvial stratigraphic sequences of four study sites along three Andean piedmont arroyos; modal mineralogy in the very fine sand fraction (3 phi to 4 phi) was determined using standard petrographic microscope methods. Q:F:LF average compositions indicate that the Late Pleistocene-Holocene very fine-grained alluvial sands of the Cordillera Frontal piedmont reflects the modern lithic arenites of the Argentine Association reported by Potter (1994). The results show two geologically distinct sources in the catchment areas, volcaniclastic and metamorphic rocks. High concentrations of mica and volcanic glass are likely related to particle morphologies and to the deposition sedimentary environment recorded in the alluvial sequences—floodplains. The overabundance of micas over the volcanic glass in the mid-late Holocene alluvial sequence indicates the drainage of a metamorphic area at the expense of other lithological sources. Source areas are located mainly in the Frontal cordillera, and to a lesser extent, in the piedmont Tertiary deposits, another likely source for the analyzed Quaternary alluvial sediments. The mineralogical signature of the late Pleistocene and Holocene alluvial sequences is in agreement with the composition of the southern Pampean sand mantles, loess and loess-like deposits mainly formed by a volcanic mineral assemblage with source areas placed at the headwaters of the main Andean rivers.

Mehl, A.; Blasi, A.; Zárate, M.

2012-12-01

229

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 reqment 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

230

Late Pleistocene Climate Events and The Origin of Agriculture In SW Asia  

Science.gov (United States)

In the Eastern Mediterranean sea, the climate succession of the last deglaciation is documented and dated in marine cores by the d18-O variation of foraminiferal cal- cite and pollen records. The Last Glacial Maximum is identified by a large abundance of grass pollen from a prairie-type vegetal cover with low annual precipitation in the mountainous north and east borderlands of the sea, where the pollen mainly origi- nates. During the first phase of the last deglaciation, the Bolling/Allerod chronozone, the moisture availability increases and makes possible the spread of a deciduous for- est, as shown by the increasing pollen abundance of the deciduous oak. The cold and arid Younger Dryas is identified by a reversal to semi-desert conditions, with the in- crease of sage-brush (Artemisia) and the saline-tolerant Chenopodiaceae. The climate of the earliest Holocene is Optimum for at least 3000 years (9000-6000yr BP), with the largest spread of the deciduous forest at low-middle elevations signalling wet sum- mers and of the Pistacia woodland at low elevations signalling mild, no-frost winters. This is the time when the most recent sapropel deposited in the eastern Mediterranean under anoxic bottom conditions generated by a surface lid of lower salinity due to the concomitant largest floods of the Nile River fed by the strongest African monsoon rains in the Ethiopian Highlands. In SW Asia, the pollen records of lakes and marshes have been correlated with those of the marine cores, thereby obtaining a robust time-frame. In that area, the archaeo- logical data of human settlements are independently dated by 14C. Thus the archaeo- logical succession can be securely set against the well-dated climatic succession. The Late Palaeolithic populations of SW Asia were wandering hunter-gatherers in the prairies of the Last Glacial Maximum, where they already collected wild wheat, barley and fruit. With the Bolling/Allerod wetter and warmer climate, they began to settle in favourable locations, on a year-long or semi-permanent basis. They exploited, proba- bly more widely, the vegetal food resources of wild cereals and pulses. In Palestine, this culture is called Natufian. In Syria on the Middle Euphrates, the settlement at Tel Abu Hureira displays a first phase of occupation that yielded wild emmer wheat and two-row barley. These wild varieties of cereals are characterized by a brittle rachis of the ear that insures the wide dispersion of the spikelets at maturity. This Phase I came to an end with the abandonment of the site for several hundred years. The following occupation Phase II immediately yields the domesticated form of cereals, which are 1 mainly identified by the non-brittle, solid rachis at maturity. This mutant form makes possible for man to more efficiently collect the seeds with a sickle or a stick. Based on the local 14C dates, the settlement interruption is coeval with the cold, arid Younger Dryas, and the incipience of Phase II is coeval with the Climate Optimum of the early Holocene. It is striking that the domestication of emmer wheat appears to have taken place during the Younger Dryas. This strong climatic shift must somehow have constrained this most fundamental step in the globally earliest emergence of agriculture, that of SW Asia. The accumulation of grain surplus supported the human population increase that eventually led to the earliest emergence of urban civilization in SW Asia. 2

Rossignol-Strick, M.

231

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

232

Large mid-Holocene and late Pleistocene earthquakes on the Oquirrh fault zone, Utah  

Science.gov (United States)

The Oquirrh fault zone is a range-front normal fault that bounds the east side of Tooele Valley and it has long been recognized as a potential source for large earthquakes that pose a significant hazard to population centers along the Wasatch Front in central Utah. Scarps of the Oquirrh fault zone offset the Provo shoreline of Lake Bonneville and previous studies of scarp morphology suggested that the most recent surface-faulting earthquake occurred between 9000 and 13,500 years ago. Based on a potential rupture length of 12 to 21 km from previous mapping, moment magnitude ( Mw) estimates for this event range from 6.3 to 6.6 In contrast, our results from detailed mapping and trench excavations at two sites indicate that the most-recent event actually occurred between 4300 and 6900 yr B.P. (4800 and 7900 cal B.P.) and net vertical displacements were 2.2 to 2.7 m, much larger than expected considering estimated rupture lengths for this event. Empirical relations between magnitude and displacement yield Mw 7.0 to 7.2. A few, short discontinuous fault scarps as far south as Stockton, Utah have been identified in a recent mapping investigation and our results suggest that they may be part of the Oquirrh fault zone, increasing the total fault length to 32 km. These results emphasize the importance of integrating stratigraphic and geomorphic information in fault investigations for earthquake hazard evaluations. At both the Big Canyon and Pole Canyon sites, trenches exposed faulted Lake Bonneville sediments and thick wedges of fault-scarp derived colluvium associated with the most-recent event. Bulk sediment samples from a faulted debris-flow deposit at the Big Canyon site yield radiocarbon ages of 7650 ± 90 yr B.P. and 6840 ± 100 yr B.P. (all lab errors are ±1 ?). A bulk sediment sample from unfaulted fluvial deposits that bury the fault scarp yield a radiocarbon age estimate of 4340 ± 60 yr B.P. Stratigraphic evidence for a pre-Bonneville lake cycle penultimate earthquake was exposed at the Pole Canyon site, and although displacement is not well constrained, the penultimate event colluvial wedge is comparable in size to the most-recent event wedges. Charcoal from a marsh deposit, which overlies the penultimate event colluvium and was deposited during the Bonneville lake cycle transgression, yields an AMS radiocarbon age of 20,370 ± 120 yr B.P. Multiple charcoal fragments from fluvial deposits faulted during the penultimate event yield an AMS radiocarbon age of 26,200 ± 200 yr B.P. Indirect stratigraphic evidence for an antepenultimate event was also exposed at Pole Canyon. Charcoal from fluvial sediments overlying the eroded free-face for this event yields an AMS age of 33,950 ± 1160 yr B.P., providing a minimum limiting age on the antepenultimate event. Ages for the past two events on the Oquirrh fault zone yield a recurrence interval of 13,300 to 22,100 radiocarbon years and estimated slip rates of 0.1 to 0.2 mm/yr. Temporal clustering of earthquakes on the nearby Wasatch fault zone in the late Holocene does not appear to have influenced activity on the Oquirrh fault zone. However, consistent with findings on the Wasatch fault zone and with some other Quaternary faults within the Bonneville basin, we found evidence for higher rates of activity during interpluvial periods than during the Bonneville lake cycle. If a causal relation between rates of strain release along faults and changes in loads imposed by the lake does exist, it may have implications for fault dips and mechanics. However, our data are only complete for one deep-lake cycle (the past 32,000 radiocarbon years), and whether this pattern persisted during the previous Cutler Dam and Little Valley deep-lake cycles is unknown.

Olig, Susan S.; Lund, William R.; Black, Bill D.

1994-08-01

233

Pleistocene and Holocene geomorphological development in the Algarve, southern Portugal  

Science.gov (United States)

A detailed chronological framework for Pleistocene and Holocene geomorphology and landscape evolution in the Algarve is proposed. With regards to the Pleistocene, attention has focused on the origin, dating and stratigraphy of the Ludo Formation. Subsuming the classifications of earlier writers, it is now proposed that during the Pliocene a marine transgression occurred across a tectonically controlled basin that was constrained by the mountains of the Algarve interior to the north. Fluvial sands were then deposited in a regressive phase during the late Pliocene/early Pleistocene, while braided streams operating under semi-arid conditions subsequently laid down sands and gravels in the middle and upper Pleistocene. Lying unconformably over the Ludo Formation is an alluvial deposit (Odiáxere gravels and Loulé sands) of late Pleistocene/early Holocene date that is found within the river valleys of the Algarve. In the early-Holocene (ca.10, 000-ca.7000 BP) and early late-Holocene (ca.5000-ca.3000 BP), the situation in the Algarve was one of climatic amelioration (i.e., warmer and wetter conditions), rising sea levels, vegetation colonization, soil development and towards the end of this period trenching of the Odiáxere gravels and Loulé sands. From ca.3000 BP evidence is abundant that humans became important geomorphological agents either acting on their own or in combination with climatic factors. From around 5000 BP, conditions became dryer and, between ca.3000 BP and ca.700 BP, clearance of land by pre-Roman, Roman, and especially Islamic agricultural settlers caused widespread erosion and the deposition of extensive spreads of topsoil dominated sediment within river valleys (i.e., the Holocene terrace) and in coastal estuaries. A period followed up to 1900 CE when agricultural practices were less damaging to the soil, erosion was reduced and the Holocene terrace - together with coastal and estuarine deposits - was incised. In the past century and under increased human pressure, renewed erosion is in evidence in the interior valleys and at the coast.

Chester, David K.

2012-06-01

234

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

Energy Technology Data Exchange (ETDEWEB)

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

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

1994-04-01

235

Deep-sea ash layers reveal evidence for large, late Pleistocene and Holocene explosive activity from Sumatra, Indonesia  

Science.gov (United States)

Deep-sea tephra layers sampled from sediment cores collected within, and adjacent to the Sunda trench of offshore Sumatra reveal evidence for five previously undocumented, and apparently large (minimum volume > 0.6-> 6.3 km3; volcanic explosivity index values of 4-5) explosive eruptions over the last ~ 31,000 years, with a presumptive source of mainland Sumatra. Chemical analysis of glass shards and 14C age constraints are used to distinguish the five tephra layers, as well as a sixth that likely correlates with the Youngest Toba tuff (YTT). The tephra layers are labeled V-1 through V-6 relative to their north-to-south positioning along the Sunda trench. The three tephra layers taken from cores west of central Sumatra (V-3, V-4, V-5) are well-constrained by 14C age determinations, whereas less reliable sedimentation-rate estimates are available for the northern (V-1, V-2) and southern (V-6) tephra layers. Deposition of the northernmost tephra, layer V-1, was likely accompanied by seismicity as two chemically indistinguishable tephras are separated by 12 cm of course-grained turbidite. Layer V-2 shows a strong chemical resemblance to the YTT and age estimates do not rule out the correlation. With the exception of a likely correlation with the YTT, no other correlations were made between the tephras analyzed in this study with the marine or terrestrial record from the published literature. The most frequent, widespread, and youngest marine tephra layers were found in the central region of the study area. Layers V-3, V-4, and V-5 were all deposited within the last 17 thousand years with minimum eruptive volumes of > 0.6 to > 5.2 km3. A complex depositional sequence of layer V-6 is estimated at ~ 27.5 ka, and may be associated with Late Pleistocene ignimbrite volcanism of southern Sumatra. The ages and suggested minimum volumes represented by the deep-sea tephra layers are consistent with an active volcanic arc, and demonstrate the need for further terrestrial studies.

Salisbury, Morgan J.; Patton, Jason R.; Kent, Adam J. R.; Goldfinger, Chris; Djadjadihardja, Yusuf; Hanifa, Udrekh

2012-06-01

236

Surface-rupturing history of the Bree fault scarp, Roer Valley graben: Evidence for six events since the late Pleistocene  

Science.gov (United States)

Since 1996 paleoseismological investigations have been used to develop the surface- rupturing history of the Bree fault scarp, the morphologically best-defined segment of the southwestern border fault of the Roer Valley graben in northeastern Belgium. The first studies determined that the escarpment is associated with a surface fault, and they exposed evidence for three surface displacements since about 40 ka BP. The most recent eventprobably occurred between 1000 and 1350 yr cal BP. Geophysical and trenching studies at a new site near the southeastern end of the fault scarp reconfirmed the coincidence of the frontal escarpment with a shallow normal fault, which displaces the Middle Pleistocene `Main Terrace' of the Maas River, as well as overlying coversands of Saalian to late Weichselian age. Different amounts of displacement shown by the two youngest coversand units indicate two discrete faulting events, but primary evidence for the coseismic nature of these events is sparse. Radiocarbon and optically stimulated luminescence dating constrainthe age of these events to the Holocene and between 14.0 ± 2.3 ka BP and 15.8 ± 2.9 ka BP, respectively. In addition, four older surface-rupturing events are inferred from the presence of four wedge-shaped units of reworked Main Terrace deposits that are interbedded with coversand units in the hanging wall of the trench and in shallow boreholes. These wedges are interpreted as colluvial wedges, produced by accelerated slope processes in response torejuvenation of the fault scarp, most probably in a periglacial environment. Luminescence dating indicates that five out of a total of six identified faulting events are younger than 136.6 ± 17.6 ka. The antepenultimate event was the largest faulting event, associated with a total fault displacement in excess of 1 m. Thus, the newly investigated trench site represents the longest and most complete record of surface rupturing recovered so far along the Bree fault scarp. This study also demonstrates the viability of the paleoseismological approach to identify past large earthquakes in areas of present-day moderate to low seismic activity.

Vanneste, Kris; Verbeeck, Koen; Camelbeeck, Thierry; et al.

237

Late Pleistocene Terraces in River Valleys of the Central Russian Plain: Morphology, Structure and History of Development  

Science.gov (United States)

Morphology and sedimentary composition of low terraces of the Seim (the middle Dnieper catchment) and Khoper (the middle Don catchment) rivers were studied in the field (DGPS topographic profiling, hand and mechanical coring, examination of natural exposures) and in laboratory (grain size analysis, spore-pollen composition, 14C and OSL dating, microscopic study of quartz grains). Archaeological data have also been taken into account. It was found that Late Pleistocene river terraces were subject to complex reworking after the alluvial sedimentation had finished. Terraces may therefore contain sediments of different origin and terrace levels may vary according to the post-alluvial reworking. To establish terrace sedimentation mechanisms we supplemented lithological data collected in the field with quartz grains morphoscopy technique - microscopic study of quartz grains surfaces. The results exhibit wide participation of aeolian and slope wash sediments in terrace deposits, deep aeolian reworking of terrace alluvium during LGM that could be possible due to ground water lowering because of deep pre-LGM incision of rivers. The main difficulty in interpretation of morphoscopic results is that aeolian signals are sometimes not clear due to short duration of wind action over alluvial sands. River incision was detected within the interval since 50-60 to 25-30 ka BP (cal). High runoff increase is proposed as the reason of this incision, which is illustrated by formation of "big meanders" (macromeanders) in river valleys. There were probably several time spans of high runoff divided by low runoff intervals. By the time of LGM rivers had already been incised down to the modern river levels or deeper. The cryoaridic LGM time (20-23 ka BP cal) makes the most pronounced low runoff interval. After LGM, the last high runoff epoch started, which is dated to 13-18(19) ka BP (cal). Numerous now relict macromeanders were formed in river valleys at that time and considerable portions of modern floodplains were established. So the morphology of river valleys indicates contrasting runoff variations being the characteristic feature of the Valdai (Weichselian) cold stage.

Matlakhova, Ekaterina; Panin, Andrey

2014-05-01

238

Multi-component Magnetization Of The Late Pliocene Pyroclastic Flow Deposit In Central Japan, Indicating Early Early Pleistocene Fault Activity  

Science.gov (United States)

The Late Pliocene Ichiuda Welded Tuff Bed in central Japan acquired three magnetization components. All of primary reverse intermediate temperature component, and secondary normal low and high temperature components show positive fold tests, indicating that fault-related folding structure postdated the Olduvai normal subchron. The northern segment of Itoigawa-Shizuoka Tectonic Line that bounds the North American and Eurasian Plates in central Japan, comprises the geological Otari-Nakayama and active Kamishiro faults. The Ichiuda Welded Tuff Bed intruded by the 2.1 Ma Taro-yama Andesite is subjected to the NE-SW trending folding structure adjacent to the Otari-Nakayama fault. PAFD and PThD were performed to the drilled samples of Taro-yama Andesite and the Ichiuda Welded Tuff Bed at three and five sites on both limbs of the syncline, respectively. Positive fold test for the tilt-corrected site-mean directions of the andesite indicates prefolding magnetization. The fresh welded tuff bed at one site yields similar reverse direction. Whereas the greenly altered beds at four sites shows normal tilt-corrected site-mean directions by PAFD, and following three temperature-dependent directional components by PThD: normal below 350 degree, reverse from 350 to 530 degree, and normal above 530 degree, all which show positive fold test. IRM acquisition, thermal demagnetization of three orthogonal IRM, thermomagnetic analysis with VSM, and low temperature magnetization measurements with MPMS indicate that the Ichiuda Welded Tuff Bed with single and three magnetization components contains titanomagnetites, and both titanomagnetites and magnetite, respectively. Magnetization of the Taro-yama Andesite is dominated by titanomagnetites under high temperature oxidation state and minor proportion of titanomaghemites. The Taro-yama Andesite and the Ichiuda Welded Tuff Bed exhibit primary reverse magnetism corresponding to the Matsuyama Chron. The Ichiuda Welded Tuff Bed additionally acquired normal magnetization components by hydrothermal alternation in the Olduvai Subchron; low and high temperature components are secondary TRM by re-heating for titanomagnetites and CRM by formation of magnetite, respectively. Positive fold test for secondary magnetization of the welded tuff bed would introduce the early Early Pleistocene activity of the Otari-Nakayama fault.

Ueki, T.; Yamazaki, T.; Funaki, M.; Hoshi, H.

2003-12-01

239

Enso-like cyclicity In Late Pleistocene varve thickness measurements from two alpine lakes, Wind River Range, Wyoming, USA  

Science.gov (United States)

Spectral analyses of varve thickness measurements in sediment cores from two moraine-dammed lakes in the Wind River Range of Wyoming, USA, reveal a 2.8-to-8-yr cyclicity consistent with that expressed by ENSO. The lakes [Louis Lake (42.596°N,108.846°W, 2610 m and nearby Fiddlers Lake 42.6312°N, 108.8786°W, 2868 m] and hold the possibility of longer records of mid-continental climate change even into the last interglacial. Nine macrofossil-based 14C ages (AMS) combined with varve thicknesses indicate the lakes were deep enough during the LGM to form and preserve varves and that the minimum age for the lacustrine sediments here is ~20 kyrs. The ENSO signal is most robust in the Louis Lake varves, displaying high spectral power across the entire band of frequencies associated with ENSO. Analysis of the Fiddlers Lake varves yield predictably less significant results, a consequence of the different geomorphic settings of these two lakes. Specifically, (1) Louis Lake has a large catchment and receives surface water input from a stream, which has delivered a large quantity of sediment to the lake margin and deposited a substantial delta. In this setting, variations in precipitation appear closely linked to sediment delivery to the lake, and are reflected in sediment distributions, while (2) Fiddlers Lake is located in a small re-entrant basin with a relatively insignificant catchment area and fed almost entirely by groundwater and direct rain/snow events, with little surface runoff; (3) the deeper water of Louis Lake aids in the formation and preservation of varves, while (4) lake level fluctuations in the shallower Fiddlers Lake directly affect varve creation and preservation (the onset of glaciation in the Fiddlers Lake core is represented by thick sediment packages that eventually thin to varves by ~1m up-core). The significant ENSO-like periodicities in the the varved sediments in these lakes suggests that the effects of ENSO forcing were felt far into the western interior of North America during the late Pleistocene, a result that accords with earlier work on lacustrine sediments of similar age in New England (Rittenour et al., 2000).

Dahms, D. E.; Noren, A. J.; Geiss, C. E.; Dorale, J. A.; Myrbo, A.

2011-12-01

240

Late Pleistocene/Holocene paleoclimate reconstruction and eruptive history of Central American volcanoes from lake bottom sediments of Lake Nicaragua  

Science.gov (United States)

A shallow coring program in Lake Nicaragua was completed in May/June 2006 by the University of Texas (UT Department of Geography and UT Institute for Geophysics). A total of 35 sediment cores with lengths ranging between 12 cm and 100 cm along with five longer cores were extracted from the lake using a gravity corer and a modified manual square rod piston corer, respectively. Analyses of lake sediments have the following objectives: 1) to correlate the geophysical results with the core data to provide a stratigraphic framework for the shallow lake sediments; 2) to constrain past climate variability in this rather poorly investigated area; and 3) to establish a time series of explosive volcanic activity based on the identification and dating of tephra layers in the cores. Initial measurements of magnetic susceptibility, dry density, loss on ignition and XRF scanning indicated a dominance of fine-grained homogeneous diatomaceous sediments cover most of the lake floor. Increasing values in magnetic susceptibility in the upper part of several short cores most likely reflect increased erosion caused by land-use changes during the Spanish colonial period (1522-1822). Results on the two longest cores from the northeastern (355 cm) and southwestern (478 cm) parts of the lake reveal complete Holocene paleoclimate records in both areas that are comparable to other terrestrial and marine records in the Central and South- American tropics (i.e. Cariaco Basin). A lithologic change from homogeneous gyttia (diatomaceous mud) to blue- grayish waxy clay at the bottom of these records marks the Late Pleistocene-Holocene transition as indicated by a radiocarbon dating on plant remains. The latter dense clay forms a distinctive stratigraphic marker in the lake basin. Tephra layers to date were detected in most gravity cores recovered west of Ometepe Island (Volcan Concepcion), and in long records in the northeastern basin (San Antonio Tephra, Masaya volcano, ca. 7,400 interpolated cal yr BP) and nearby the Solentiname Archipelago (unknown eruption, Arenal volcano, Costa Rica; 8,810 +/- 25 cal yr BP). These layers allow independent dating and correlation of sediments.

Wulf, S.; Dull, R. A.; Mann, P.; McIntosh, K. D.; Gardner, J. E.

2007-12-01

241

Integrated well-log, seismic, and biostratigraphic approach to sequence stratigraphy in Late Cenozoic expanded sections, Gulf of Mexico  

Energy Technology Data Exchange (ETDEWEB)

Increased emphasis on well-log signatures and recognition criteria for stratigraphic sequence boundaries, systems tracts, and condensed sections in a sequence-stratigraphic context has enhanced facies interpretation and reservoir prediction capabilities. Integration of well logs with high-resolution biostratigraphy and paleobathymetry, high-quality seismic configuration data, and the latest eustatic cycle chart provides the best data base for sequence-stratigraphic analysis. This approach is particularly effective for thick, rapidly deposited slope and basin sediments, such as in the Plio-Pleistocene of the Gulf of Mexico basin. The general sequence-stratigraphic model consists of a depositional sequence with lowstand basin floor fan, slope fan, and prograding complex, transgressive systems tract, and highstand systems tract. Each systems tract is deposited at a predictable position in an interpreted eustatic cycle and has recognizable signatures in well logs and seismic data. Any given basin to which this model is applied is strongly controlled by its own tectonic subsidence and accommodation history, and by the type and rate of sediment supply, but the higher frequency eustatic cyclicity is superposed on the other basinal controls. A typical depositional model for the Plio-Pleistocene of the Gulf of Mexico basin is a diapir-controlled subbasin associated with a large contemporaneous expansion fault. The environment of deposition is closely related to the history of fault development. Reservoir sand distribution is characteristic and predictable for each systems tract. Carefully planned evaluation and completion techniques are based on these characteristics.

Mitchum, R.M. Jr. (R M Mitchum Exploration Inc., Houston, TX (United States)); Sangree, J.B. (Sangree Exploration Inc., Houston, TX (United States)); Vail, P.R. (Rice Univ. Houston, TX (United States)); Wornar, W.W. (Microstrat Inc., Houston, TX (United States))

1991-03-01

242

New Constraints on Late Pleistocene - Holocene Slip Rates and Seismic Behavior Along the Panamint Valley Fault Zone, Eastern California  

Science.gov (United States)

Space-time patterns of seismic strain release along active fault systems can provide insight into the geodynamics of deforming lithosphere. Along the eastern California shear zone, fault systems south of the Garlock fault appear to have experienced an ongoing pulse of seismic activity over the past ca. 1 kyr (Rockwell et al., 2000). Recently, this cluster of seismicity has been implicated as both cause and consequence of the oft-cited discrepancy between geodetic velocities and geologic slip rates in this region (Dolan et al., 2007; Oskin et al., 2008). Whether other faults within the shear zone exhibit similar behavior remains uncertain. Here we report the preliminary results of new investigations of slip rates and seismic history along the Panamint Valley fault zone (PVFZ). The PVFZ is characterized by dextral, oblique-normal displacement along a moderately to shallowly-dipping range front fault. Previous workers (Zhang et al., 1990) identified a relatively recent surface rupture confined to a ~25 km segment of the southern fault zone and associated with dextral displacements of ~3 m. Our mapping reveals that youthful scarps ranging from 2-4 m in height are distributed along the central portion of the fault zone for at least 50 km. North of Ballarat, a releasing jog in the fault zone forms a 2-3 km long embayment. Displacement of debris-flow levees and channels along NE-striking faults that confirm that displacement is nearly dip-slip, consistent with an overall transport direction toward ~340°, and affording an opportunity to constrain fault displacement directly from the vertical offset of alluvial surfaces of varying age. At the mouth of Happy Canyon, the frontal fault strand displaces a fresh debris-flow by ~3-4 m; soil development atop the debris-flow surface is incipient to negligible. Radiocarbon ages from logs embedded in the flow matrix constrain the timing of the most recent event to younger than ~ 600 cal yr BP. Older alluvial surfaces, such as that buried by the debris-flow lobe, exhibit progressively larger displacement (up to 10-12 m). Well-preserved bar and swale morphology, incipient varnishing of surface boulders, and weak soil development all suggest that this surface is Late Holocene in age. We are working to confirm this inference, but if correct, it suggests that this fault system may have experienced ~3-4 events in the relatively recent past. Finally, preliminary surface ages from even older surfaces along this portion of the fault zone place limits on the slip rate over Late Pleistocene time. Cosmogenic 10Be surface clast dating of an alluvial surface with well-developed pavement and moderate soil development near Happy Canyon suggests a surface age of 30-35 kyr. We are working to refine this estimate with new dating and soil characterization, but our preliminary reconstructions of displacement of this surface across the two primary fault strands are consistent with slip rates that exceed ~3 mm/yr. Overall, these results are consistent with the inference that the Panamint Valley fault zone is the primary structure that accomplishes transfer of right-lateral shear across the Garlock Fault.

Hoffman, W.; Kirby, E.; McDonald, E.; Walker, J.; Gosse, J.

2008-12-01

243

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

Science.gov (United States)

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

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

2010-05-01

244

Late Pleistocene and Holocene-Age Columbia River Sediments and Bedforms: Hanford Reach Area, Washington - Part 2  

Energy Technology Data Exchange (ETDEWEB)

This report presents the results of a geologic study conducted on the lower slopes of the Columbia River Valley in south-central Washington. The study was designed to investigate glaciofluvial and fluvial sediments and bedforms that are present in the river valley and formed subsequent to Pleistocene large-scale cataclysmic flooding of the region.

K.R. Fecht, T.E. Marceau

2006-03-28

245

Size variation in early human mandibles and molars from Klasies River, South Africa: comparison with other middle and late Pleistocene assemblages and with modern humans.  

Science.gov (United States)

Previous studies of the Middle Stone Age human remains from Klasies River have concluded that they exhibited more sexual dimorphism than extant populations, but these claims have not been assessed statistically. We evaluate these claims by comparing size variation in the best-represented elements at the site, namely the mandibular corpora and M(2)s, to that in samples from three recent human populations using resampling methods. We also examine size variation in these same elements from seven additional middle and late Pleistocene sites: Skh?l, Dolní Vestonice, Sima de los Huesos, Arago, Krapina, Shanidar, and Vindija. Our results demonstrate that size variation in the Klasies assemblage was greater than in recent humans, consistent with arguments that the Klasies people were more dimorphic than living humans. Variation in the Skh?l, Dolní Vestonice, and Sima de los Huesos mandibular samples is also higher than in the recent human samples, indicating that the Klasies sample was not unusual among middle and late Pleistocene hominins. In contrast, the Neandertal samples (Krapina, Shanidar, and Vindija) do not evince relatively high mandibular and molar variation, which may indicate that the level of dimorphism in Neandertals was similar to that observed in extant humans. These results suggest that the reduced levels of dimorphism in Neandertals and living humans may have developed independently, though larger fossil samples are needed to test this hypothesis. PMID:19382177

Royer, Danielle F; Lockwood, Charles A; Scott, Jeremiah E; Grine, Frederick E

2009-10-01

246

Phylogeographic heterogeneity of the brown macroalga Sargassum horneri (Fucaceae) in the northwestern Pacific in relation to late Pleistocene glaciation and tectonic configurations.  

Science.gov (United States)

Pleistocene glacial oscillations and associated tectonic processes are believed to have influenced the historical abundances and distribution of organisms in the Asia Northwest Pacific (ANP). Accumulating evidence indicates that factors shaping tempospatial population dynamics and distribution patterns of marine taxa vary with biogeographical latitude, pelagic behaviour and oceanographic regimes. To detect what kinds of historical and contemporary factors affected genetic connectivity, phylogeographic profiles of littoral macroalga Sargassum horneri in the ANP were analysed based on mitochondrial (Cox3) and chloroplast (rbcL) data sets. Five distinct clades were recovered. A strong signature of biogeographical structure was revealed (?(CT) = 0.487, P Pacific coastline. This significant differentiation between the two basins may reflect historical glacial isolation in the northwestern Pacific, which is congruent with the estimates of clade divergence and demographic expansion during the late Quaternary low sea levels. Analysis of molecular variance and the population-pair statistic F(ST) also revealed significant genetic structural differences between Chinese marginal seas and the Japanese basin. This exceptional phylogeographic architecture in S. horneri, initially shaped by historical geographic isolation during the late Pleistocene ice age and physical biogeographical barriers, can be complicated by oceanographic regimes (ocean surface currents) and relocating behaviour such as oceanic drifting. PMID:21851438

Hu, Zi-Min; Uwai, Shinya; Yu, Shen-Hui; Komatsu, Teruhisa; Ajisaka, Tetsuro; Duan, De-Lin

2011-09-01

247

Acoustic stratigraphy of Bear Lake, Utah Idaho—Late Quaternary sedimentation patterns in a simple half-graben  

Science.gov (United States)

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

Colman, Steven M.

2006-03-01

248

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

Science.gov (United States)

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

Colman, Steven M.

2006-01-01

249

Stratigraphy, age and correlation of middle Pleistocene silicic tephras in the Auckland region, New Zealand : a prolific distal record of Taupo Volcanic Zone volcanism  

International Nuclear Information System (INIS)

Coastal sections in the Auckland region reveal highly carbonaceous and/or highly weathered clay-dominated cover-bed successions with numerous discrete distal volcanic ash (tephra) layers, fluvially reworked siliciclastic (tephric) deposits, and two widely distributed pyroclastic density current (PDC) deposits generated from explosive silicic volcanism within the Taupo Volcanic Zone (TVZ). The younger of the two PDC deposits (informally named Waiuku tephra) is glass-isothermal plateau fission-track (ITPFT) dated at 1.00 ± 0.03 Ma and occurs in a normal polarity interval interpreted as the Jaramillo Subchron. Waiuku tephra is correlated with Unit E sourced from the Mangakino Volcanic Centre of the TVZ. Waiuku tephra can be subdivided into two distinctive units enabling unequivocal field correlation: a lower stratified unit (dominantly pyroclastic surge with fall component) and an upper massive to weakly stratified unit (pyroclastic flow). At many sites in south Auckland, Waiuku tephra retains basal 'surge-like' beds (<1.4 m thickness). This provides clear evidence for primary emplacement and is an exceptional feature considering the c. 200 km this PDC has travelled from its TVZ source area. However, at many other Auckland sites, Waiuku tephra displays transitional sedimentary characteristics indicating lateral transformation from hot, gas-supported flow/surge into water-supported mass flow and hyperconcentrated flow (HCF) deposits. The older PDC deposit is dated at 1.2ts. The older PDC deposit is dated at 1.21 ± 0.09 Ma, is enveloped by tephras that are ITPFT-dated at 1.14 ± 0.06 Ma (above) and 1.21 ± 0.06 Ma (below), respectively, and occurs below a short normal polarity interval (Cobb Mountain Subchron) at c. 1.19 Ma. This PDC deposit, correlated with Ongatiti Ignimbrite sourced from the Mangakino Volcanic Centre of TVZ, has laterally transformed from a gas-supported, fine-grained pyroclastic flow deposit at Oruarangi, Port Waikato, into a water-supported volcaniclastic mass flow deposit farther north at Glenbrook Beach. The occurrence of Ongatiti Ignimbrite in Auckland significantly extends its northward distribution. Large numbers of post- and pre-Ongatiti rhyolitic tephra layers, ranging in age from c. 1.31 to 0.53 Ma, are also recognised in the region, with some up to 0.5 m in compacted fallout thickness. Although some tephras can be attributed to known TVZ eruptions (e.g., Ahuroa/Unit D), many have yet to be identified in proximal source areas and remain uncorrelated. However, some can be reliably correlated to tephra layers occurring in marine to nearshore sequences of Wanganui Basin and deep-sea cores retrieved east of North Island. The identification of previously unrecognised mid-Pleistocene TVZ-sourced tephra deposits in the Auckland region, and their correlation to the offshore marine record, represent an advance in the construction of a higher resolution history for the TVZ where, close to eruptive source, the record is fragmentary and obscured by deep burial, or erosion, or both. (author). 65 refs., 22 figs., 3 tabs

250

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

OpenAIRE

Drill cores from the inner-alpine valley terrace of Unterangerberg, located in the Eastern Alps of Austria, offer first insights into a Pleistocene sedimentary record that was not accessible so far. The succession comprises diamict, gravel, sand, lignite and thick, fine grained sediments. Additionally, cataclastic deposits originating from two paleo-landslide events are present. Multi-proxy analyses including sedimentological and palynological investigations as well as radiocarbon and lumines...

Starnberger, Reinhard; Drescher-schneider, Ruth; Reitner, Ju?rgen M.; Rodnight, Helena; Reimer, Paula J.; Spo?tl, Christoph

2013-01-01

251

Coniacian-maastrichtian calcareous nannofossil biostratigraphy and carbon-isotope stratigraphy in the Zagros Basin (Iran) : consequences for the correlation of late cretaceous stage boundaries between the Tethyan and Boreal realms  

DEFF Research Database (Denmark)

Calcareous nannofossil biostratigraphy and stable isotope stratigraphy have been investigated in the Shahneshin section of the Gurpi Formation from the Zagros Basin (Iran). The results show that the Gurpi Formation spans the late early Coniacian to late Thanetian. The age-model shows that the Shahneshin section spans the Coniacian to mid-Campanian with a good continuity whereas condensation is highlighted in the late Campanian, across the Campanian/Maastrichtian boundary and in the late Maastrichtian. Extreme condensation is recorded after the Cretaceous-Paleogene boundary with the complete absence of the Danian, and the Selandian and lower Thanetian being comprised in only 6 m at the top of the Gurpi Formation. Correlation of the carbon-isotope profile with other reference curves allows the recognition of several Late Cretaceous excursions at the Shahneshin section such as the Beeding, White Fall, Kingsdown, Michel Dean, Haven Brow, Horseshoe Bay, Buckle, Hawks Brow, Santonian/Campanian boundary (SCBE) and Campanian/Maastrichtian boundary (CMBE) events. Correlation to a recently proposed global ?13C stack for the Late Cretaceous points to a major mismatch of this compilation with magnetostratigraphy in the Santonian-early Campanian interval. The ?13C correlation, supported by calcareous nannofossil biostratigraphy, brings insights into: (1) the position of the Coniacian/Santonian, Santonian/Campanian and Campanian/Maastrichtian boundaries with respect to carbon-isotope stratigraphy and calcareous nannofossil bio-horizons, and (2) their correlation between the Tethyan and Boreal realms. © 2014 Gebrüder Borntraeger, Stuttgart, Germany.

Razmjooei, Mohammad Javad; Thibault, Nicolas

2014-01-01

252

Extreme mobility in the Late Pleistocene? Comparing limb biomechanics among fossil Homo, varsity athletes and Holocene foragers.  

Science.gov (United States)

Descriptions of Pleistocene activity patterns often derive from comparisons of long bone diaphyseal robusticity across contemporaneous fossilized hominins. The purpose of this study is to augment existing understanding of Pleistocene hominin mobility patterns by interpreting fossil variation through comparisons with a) living human athletes with known activity patterns, and b) Holocene foragers where descriptions of group-level activity patterns are available. Relative tibial rigidity (midshaft tibial rigidity (J)/midshaft humeral rigidity (J)) was compared amongst Levantine and European Neandertals, Levantine and Upper Palaeolithic Homo sapiens, Holocene foragers and living human athletes and controls. Cross-country runners exhibit significantly (pfossil hominins displayed relative tibial rigidity that exceeded, or was similar to, the highly terrestrially mobile Later Stone Age southern Africans and modern human cross-country runners. The more extreme skeletal structure of most Neandertals and Levantine H. sapiens, as well as the odd Upper Palaeolithic individual, appears to reflect adaptation to intense and/or highly repetitive lower limb (relative to upper limb) loading. This loading may have been associated with bipedal travel, and appears to have been more strenuous than that encountered by even university varsity runners, and Holocene foragers with hunting grounds 2000-3000 square miles in size. Skeletal variation among the athletes and foraging groups is consistent with known or inferred activity profiles, which support the position that the Pleistocene remains reflect adaptation to extremely active and mobile lives. PMID:23453436

Shaw, Colin N; Stock, Jay T

2013-04-01

253

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

Directory of Open Access Journals (Sweden)

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

254

The Corte Blanco garnetiferous tuff: A distinctive late Miocene marker bed in northwestern Argentina applied to magnetic polarity stratigraphy in the Rio Yacones, Salta Province  

Science.gov (United States)

We introduce the Corte Blanco Tuff, a white garnetiferous air fall unit, as a distinctive Neogene marker bed. Three whole-rock K/Ar ages from rocks at the source of this unit indicate that it was erupted 8.73 +/- 0.25 Ma from the La Pava-Ramadas Caldera on the Argentine Puna. Ash spread eastward across the foreland provinces of the Eastern Cordillera and Sierras Subandinas. Recognition of this dated marker unit in these provinces provides the first, easily identified, late Miocene time line in the vast, densely vegetated region to the east of the Puna. We encountered the unit in seven localities from all three morphostructural provinces in NW Argentina. A depositional gap in the air fall material is present between 20 and 150 km to the east of the caldera. Recognition of the Corte Blanco Tuff in the Rio Yacones, near Salta, allowed an interpretation to be made of a magnetic polarity stratigraphy section erected in marginally suitable Neogene detrital strata of the Rio Guanaco Formation. We interpret the strata we examined to have been deposited between 10.5 and 6.4 Ma and report a 10 deg clockwise rotation since the strata were deposited. This is the first numerically dated section in the Rio Guanaco Formation of NW Argentina. These results reveal that uplift of the Eastern Cordillera was in progress at this time.

Viramonte, Jose G.; Reynolds, James H.; del Papa, Cecilia; Disalvo, Alfredo

1994-02-01

255

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.

2012-03-01

256

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  

Directory of Open Access Journals (Sweden)

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

257

The Bonneville Estates Rockshelter rodent fauna and changes in Late Pleistocene-Middle Holocene climates and biogeography in the Northern Bonneville Basin, USA  

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Excavations at Bonneville Estates Rockshelter, Nevada recovered rodent remains from stratified deposits spanning the past ca. 12,500 14C yr BP (14,800 cal yr BP). Specimens from horizons dating to the late Pleistocene and early Holocene include species adapted to montane and moist and cool habitats, including yellow-bellied marmot (Marmota flaviventris) and bushy-tailed woodrat (Neotoma cinerea). Shortly after 9000 14C BP (10,200 cal yr BP) these mammals became locally extinct, or nearly so, taxonomic diversity declined, and the region became dominated by desert woodrats (Neotoma lepida) and other species well-adapted to xeric, low-elevation settings. The timing and nature of changes in the Bonneville Estates rodent fauna are similar to records reported from nearby Homestead and Camels Back caves and provide corroborative data on terminal Pleistocene-early Holocene environments and mammalian responses to middle Holocene desertification. Moreover, the presence of northern pocket gopher (Thomomys talpoides) at Bonneville Estates adds to a sparse regional record for that species and, similar to Homestead Cave, it appears that the ca. 9500 14C yr BP (10,800 cal yr BP) replacement of the northern pocket gopher by Botta's pocket gopher in the Great Salt Lake Desert vicinity was also in response to climate change.

Schmitt, Dave N.; Lupo, Karen D.

2012-07-01

258

Mineralogical composition of the clay fraction and micromorphology of the Middle and Late Pleistocene loesses and paleosols in the center of the East European Plain  

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The mineralogical composition of the clay fraction and microfabrics of the cryogenic soil-loess sequences of the Middle and Late Pleistocene ages have been studied near the northern boundary of loess sediments on the East European Plain. Poorly ordered mixed-layered mica-smectitic minerals with different portions of smectitic layers predominate in the clay fraction; di-and trioctahedral hydromicas occupy the second place. The clay fraction also contains chlorite, clay-size quartz grains, and feldspars. Individual smectite is present in some of the samples. Interstadial chernozem-like paleosols are specified by the higher content of clay, the maximum concentration of smectitic layers in the mixed-layered minerals, and the presence of individual smectite. The clay fraction in the profiles of interglacial paleosols is sharply differentiated: in the eluvial part, it is depleted of smectite and enriched in kaolinite, hydromica, and clay-size quartz. These features allow us to suppose that interglacial paleosols were subjected to podzolization processes. According to the mineralogical indices, Middle Pleistocene paleosols can be differentiated into those subjected to lessivage (the Kamenskii interglacial paleosol) and podzolization (the Inzhavin interglacial paleosol).

Chizhikova, N. P.; Morozova, T. D.; Panin, P. G.

2007-12-01

259

Thorough assessment of DNA preservation from fossil bone and sediments excavated from a late Pleistocene-Holocene cave deposit on Kangaroo Island, South Australia  

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Fossils and sediments preserved in caves are an excellent source of information for investigating impacts of past environmental changes on biodiversity. Until recently studies have relied on morphology-based palaeontological approaches, but recent advances in molecular analytical methods offer excellent potential for extracting a greater array of biological information from these sites. This study presents a thorough assessment of DNA preservation from late Pleistocene-Holocene vertebrate fossils and sediments from Kelly Hill Cave Kangaroo Island, South Australia. Using a combination of extraction techniques and sequencing technologies, ancient DNA was characterised from over 70 bones and 20 sediment samples from 15 stratigraphic layers ranging in age from >20 ka to ˜6.8 ka. A combination of primers targeting marsupial and placental mammals, reptiles and two universal plant primers were used to reveal genetic biodiversity for comparison with the mainland and with the morphological fossil record for Kelly Hill Cave. We demonstrate that Kelly Hill Cave has excellent long-term DNA preservation, back to at least 20 ka. This contrasts with the majority of Australian cave sites thus far explored for ancient DNA preservation, and highlights the great promise Kangaroo Island caves hold for yielding the hitherto-elusive DNA of extinct Australian Pleistocene species.

Haouchar, Dalal; Haile, James; McDowell, Matthew C.; Murray, Dáithí C.; White, Nicole E.; Allcock, Richard J. N.; Phillips, Matthew J.; Prideaux, Gavin J.; Bunce, Michael

2014-01-01

260

Late Pleistocene and Early Holocene lake-level fluctuations in the Lahontan Basin, Nevada: Implications for the distribution of archaeological sites  

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The Great Basin of the western U.S. contains a rich record of late Pleistocene and Holocene lake-level fluctuations as well as an extensive record of human occupation during the same time frame. We compare spatial-temporal relationships between these records in the Lahontan basin to consider whether lake-level fluctuations across the Pleistocene-Holocene transition controlled distribution of archaeological sites. We use the reasonably well-dated archaeological record from caves and rockshelters as well as results from new pedestrian surveys to investigate this problem. Although lake levels probably reached maximum elevations of about 1230-1235 m in the different subbasins of Lahontan during the Younger Dryas (YD) period, the duration that the lakes occupied the highest levels was brief Paleoindian and early Archaic archaeological sites are concentrated on somewhat lower and slightly younger shorelines (???1220-1225 in) that also date from the Younger Dryas period. This study suggests that Paleoindians often concentrated their activities adjacent to large lakes and wetland resources soon after they first entered the Great Basin. ?? 2008 Wiley Periodicals, Inc.

Adams, K.D.; Goebel, T.; Graf, K.; Smith, G.M.; Camp, A.J.; Briggs, R.W.; Rhode, D.

2008-01-01

261

Late Pleistocene terrestrial deposits on the continental shelf of western Canada: Evidence for rapid sea-level change at the end of the last glaciation  

Science.gov (United States)

A paleosol with in situ rooted plant remains has been found in a core at a water depth of 95 m on the central continental shelf of British Columbia. Fluvial sediments associated with the paleosol are sharply overlain by lagoonal or shallow pond sediments; these, in turn, are overlain by shallow-marine ediments. Radiocarbon dates on wood fragments and root recovered from the cored sediments indicate that relative sea level was at least 95 m lower 10,500 yr B.P. and that the core site was rapidly transgressed by the sea shortly thereafter. This rapid transgression was contemporaneous with an equally rapid regression at the heads of fiords on the British Columbia mainland to the east. The two are probably genetically linked and a result of late Pleistocene deglaciation and the migration and collapse of a glacial forebulge. Our evidence indicates that large areas of the British Columbia continental shelf were subaerially exposed 11-10 ka. This may have facilitated the southward migration of early humans from Beringia into mid-continental North America at the end of the Pleistocene.

Luternauer, J. L.; J., John; Conway, K. W.; Barrie, J. V.; Blaise, B.; Mathewes, R. W.

1989-04-01

262

Late Quaternary stratigraphy of an alluvial valley along an active convergence front: Interactions of fluvial processes, tectonic channel steering, and sea level in the eastern Ganges-Brahmaputra-Meghna River delta  

Science.gov (United States)

Insights into how tectonics, alluvial channels, and sediment interact to build the stratigraphy in a tectonically active depositional basin can be discovered by studying the sediment record and the current geomorphology of a system. Tectonics is an influence on basins that often gets overlooked due to overriding controls such as sea level, climate, and sediment load. The area for this study is in the Ganges Brahmaputra Meghna Delta (GBMD) in close proximity to an active convergent thrust front. To investigate the stratigraphy, we drilled 48 cores along two approximately longitudinal transects, 25-60 km apart, each spanning ~100 km. The boreholes were drilled every 3-4 km to a maximum depth of 100 m. The transects are situated across an alluvial valley and are bounded to the west by a Pleistocene terrace (Madhupur Terrace) and to the east by a fold belt (Indo-Burman Fold Belt) that continues to deform due to active tectonics at the thrust front. A seismic cruise using a mini-GI gun was conducted in conjunction with this study along the current river channel and has shown evidence of folded sediment at depth, and field studies in the area have found outcropping anticlines thus aiding in the determination of transect location. Through analysis of aerial imagery and digital elevation models (DEMs) of the transects, abandoned channels once occupied by the alluvial channel are evidence of migration and avulsion occurring recently enough to be recorded on the land surface. Initial analysis of the sediment cores shows a dramatic contrast in the stratigraphy between the two transects despite lying along the same morphological reach of the GBMD. The northern transect is dominated by fine to medium sands throughout indicating a strong fluvial influence, while the southern transect is dominated by muds and finer sands at depth indicating a tidal estuarine influence. The stratigraphy and land surface are a consequence of the controls on the system and reflect channel behavior over time. The establishment of channel behavior, including avulsions, migration, and overbank processes, is the key to investigating how rivers and tectonics interact to shape the landscape and build stratigraphy, which will be discussed in detail based on these transect and seismic datasets.

Williams, L.; Goodbred, S. L.; Steckler, M. S.; Seeber, L.; Spiess, V.; Schwenk, T.; Palamenghi, L.; Akhter, S. H.; Mondal, D.; Hossain, S.

2012-12-01

263

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.)

264

Interaction between aggrading geomorphic surfaces and the formation of a late pleistocene paleosol in the palouse loess of eastern Washington state  

Science.gov (United States)

Variable rates of loess deposition contributed to dramatic regional variation in a soil-stratigraphic unit, the Washtucna Soil, in the Palouse loess deposits in the Channeled Scabland of eastern Washington state. Throughout most of the Channeled Scabland, the morphology of the Washtucna Soil is that of a single buried soil, but it bifurcates into two well-developed and pedologically distinct buried soils in areas immediately downwind of the major source of loessial sediment. Regional loess stratigraphy confirms that the two well-developed soils formed during the same interval of time during which only one soil formed in areas that are distal to loess source areas. The variable and perhaps rapid rates of soil formation suggested by the stratigraphy resulted from an interaction between variable rates of loess deposition and the formation of superimposed calcic soils. Petrocalcic horizons with weak Stage IV morphology formed as the zone of carbonate accumulation moved up into former A and cambic horizons that had been profusely burrowed by cicadas. The development of cicada burrows in one phase of soil development that were subsequently engulfed by pedogenic carbonate under a rising land surface seems to have greatly accelerated the development of the petrocalcic horizons. Accelerated rates of formation of the petrocalcic horizons occurred when extrinsic (pulses of loess deposition) and intrinsic (engulfment of burrowed horizons) thresholds were exceeded. Stratigraphic evidence suggests that the soil formation that accompanied the rise in the land surface due to additional loess deposition may have occurred during the late Wisconsin glaciation when giant glacial outburst floods in the channeled Scabland triggered a new cycle of loess deposition.

McDonald, Eric V.; Busacca, Alan J.

1990-09-01

265

Leafcutter bee nests and pupae from the Rancho La Brea Tar Pits of Southern California: implications for understanding the paleoenvironment of the Late Pleistocene.  

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The Rancho La Brea Tar Pits is the world's richest and most important Late Pleistocene fossil locality and best renowned for numerous fossil mammals and birds excavated over the past century. Less researched are insects, even though these specimens frequently serve as the most valuable paleoenvironemental indicators due to their narrow climate restrictions and life cycles. Our goal was to examine fossil material that included insect-plant associations, and thus an even higher potential for significant paleoenviromental data. Micro-CT scans of two exceptionally preserved leafcutter bee nest cells from the Rancho La Brea Tar Pits in Los Angeles, California reveal intact pupae dated between ?23,000-40,000 radiocarbon years BP. Here identified as best matched to Megachile (Litomegachile) gentilis Cresson (Hymenoptera: Megachilidae) based on environmental niche models as well as morphometrics, the nest cells (LACMRLP 388E) document rare preservation and life-stage. The result of complex plant-insect interactions, they offer new insights into the environment of the Late Pleistocene in southern California. The remarkable preservation of the nest cells suggests they were assembled and nested in the ground where they were excavated. The four different types of dicotyledonous leaves used to construct the cells were likely collected in close proximity to the nest and infer a wooded or riparian habitat with sufficient pollen sources for larval provisions. LACMRLP 388E is the first record of fossil Megachile Latreille cells with pupae. Consequently, it provides a pre-modern age location for a Nearctic group, whose phylogenetic relationships and biogeographic history remain poorly understood. Megachile gentilis appears to respond to climate change as it has expanded its distribution across elevation gradients over time as estimated by habitat suitability comparisons between low and high elevations; it currently inhabits mesic habitats which occurred at a lower elevation during the Last Glacial Maximum ?21,000 years ago. Nevertheless, the broad ecological niche of M. gentilis appears to have remained stable. PMID:24718701

Holden, Anna R; Koch, Jonathan B; Griswold, Terry; Erwin, Diane M; Hall, Justin

2014-01-01

266

Late Cretaceous and Paleogene evolution of the Greater Antilles fold- and thrustbelt: structure and stratigraphy in the Camagüey region, Cuba  

Science.gov (United States)

The northern Caribbean margin underwent arc-continent collision in the late Cretaceous and Paleogene. On Cuba this les to the stacking of tectonic slices that comprise from top to bottom a volcanic arc unit, an ophiolite complex, a deformed belt of sedimentary rocks (the Camajuaní and Placetas belts) and finally rocks correlative to the Bahamas platform on the southern North American continental margin. On south-central and western Cuba, HP-LT metasedimentary rocks, on the Isle of Pines including a HT-LP overprint, were exhumed in the course of the late Cretaceous, probably at least partly added by extensional unroofing. These metamorphic rocks are exhumed in tectonic windows in the ophiolite and volcanic arc tectonic slices. Their exhumation quite surprisingly coincided with the arrest in arc volcanism in the Cuban periphery. Here, we present an integrated structural geological and stratigraphic study of the sedimentary units incorporated in the basal parts and underlying the ophiolite unit in the Camagüey province in northern central Cuba. Aim of this study was to constrain the direction and timing of compressional deformation contemporaneous with and following the exhumation and possibly extension in the southern internal parts of the Cuban fold-and thrust belt, and with the arrest in arc volcanism. Our results indicate that the Placetas belt in the Camagüey region consist of tightly, polyphase folded deep marine upper Jurassic to upper Cretaceous limestones, forming isolated blocks incorporated in a tectonic mélange at the base of the ophiolite unit. Timing of their deformation is likely late Cretaceous and younger. The Bahamas platform-related carbonates in the Sierra de Cubitas at the base of the Cuban nappe stack are characterized by a single, open folding phase trending sub-parallel to the main NW-SE trending structural grain of the fold- and thrust belt. This deformation marks the arrest in emplacement of the Cuban nappe stack onto the southern North American continental margin in the Mid-Eocene. (Under-)thrusting hence continued after the late Cretaceous into the Mid-Eocene, i.e. well after the arrest of arc volcanism and exhumation of metamorphic rocks in the internal parts of the Cuban collage. We will discuss the implications of this study for the northern Caribbean subduction history

van Hinsbergen, D. J.; Iturralde-Vinent, M. A.; van Geffen, P. W.; Garcia-Casco, A.

2007-12-01

267

Tectono-stratigraphy of the Çankiri Basin: Late Cretaceous to early Miocene evolution of the Neotethyan Suture Zone in Turkey  

OpenAIRE

The Çank?r? Basin straddles the ?zmir–Ankara–Erzincan Suture Zone which demarcates the former position of the northern branch of the Neotethys. It includes more than 3 km of pre-Middle Miocene in-fill related to late Cretaceous to pre-Middle Miocene evolution of the region. The basin has developed on the upper Cretaceous subduction complex and arc related basins of the Neotethys Ocean. The basin fill includes an upper Cretaceous forearc sequence overlain by Paleocene with a local unco...

Kaymakc?i, N.; O?zc?elik, Y.; White, S. H.; Dijk, P. M.

2009-01-01

268

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

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Full Text Available 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 Myr BP the vegetation at Lake El'gygytgyn, in nowadays tundra area, was dominated by spruce-larch-fir-hemlock forests. After ca. 3.4 Myr BP dark coniferous taxa gradually disappeared. A very pronounced environmental changes took place at ca. 3.305–3.275 Myr BP, corresponding with the Marine Isotope Stage (MIS M2, when treeless tundra- and steppe-like habitats became dominant in the regional vegetation. Climate conditions were similar to those of Late Pleistocene cold intervals. Numerous coprophilous fungi spores identified in the pollen samples suggest the presence of grazing animals around the lake. Following the MIS M2 event, larch-pine forests with some spruce mostly dominated in the area until ca. 2.6 Myr BP, interrupted by colder and drier intervals ca. 3.04–3.02, 2.93–2.91, and 2.725–2.695 Myr BP. At the beginning of the Pleistocene, ca. 2.6 Myr BP, noticeable climatic deterioration occurred. Forested habitats changed to predominantly treeless and shrubby environments, which reflect a relatively cold and dry climate. Revealed peaks in green algae colonies (Botryococcus around 2.53, 2.45, 2.320–2.305 and 2.175–2.150 Myr BP suggest a spread of shallow water environments. Few intervals (i.e. 2.55–2.53, ca. 2.37, and 2.35–2.32 Myr BP with a higher presence of coniferous taxa (mostly pine and larch document some relatively short-term climate ameliorations.

A. A. Andreev

2013-08-01

269

K-Ar ages and paleomagnetism of Pliocene-Pleistocene pyroclastic rocks from northern Tokachi, Hokkaido  

International Nuclear Information System (INIS)

K-Ar ages were determined on five samples of pyroclastic rocks from northern Tokachi, Hokkaido, and the results were discussed in reference to paleomagnetic, stratigraphic, and paleontological evidence for these rocks. All K-Ar ages obtained are consistent rather well with the stratigraphy and also with the magnetostratigraphy of the rocks. A sample of Meto welded tuff and a rhyolitic welded tuff collected from the downstream of the Osoushi River give nearly the same age of about 2.8 m.y., indicating successive extrusion in the late Pliocene. The Upper Osarushinai Formation is supposed to have been deposited in the early Pleistocene, based on the age obtained from an obsidian clast included in it. The Pliocene-Pleistocene boundary is not defined strictly, but it is supposed to exist in some horizon between the Ikeda and the Upper Osarushinai Formations. (author)

270

Tortugas fósiles del Pleistoceno tardío de Santiago Chazumba, Oaxaca / Late Pleistocene fossil tortoises of Santiago Chazumba, Oaxaca  

Scientific Electronic Library Online (English)

Full Text Available SciELO Mexico | Language: Spanish Abstract in spanish La fauna paleoherpetológica del Pleistoceno de México se compone de 37 géneros y 58 especies registradas para 27 localidades diferentes; en el caso de los reptiles las tortugas son el grupo más abundante en cuanto a registros se refiere. En este trabajo se reportan y describen los restos óseos de Go [...] pherus y Kinosternon aff. K. hirtipes/K. integrum procedentes del municipio de Santiago Chazumba, Oaxaca. El hallazgo de estas especies para el Pleistoceno de Oaxaca permite proponer un ambiente de matorral xerófilo como el existente actualmente en el Valle de Tehuacán-Cuicatlán, pero con una precipitación menor y una temperatura mayor, condiciones similares a las predominantes en el norte del país. Abstract in english The Paleoherpetological Pleistocene fauna record for Mexico is composed by 37 genera and 58 species recorded for 27 different localities; in the case of the reptiles, turtles are the most abundant group. In this paper, we report and describe the bones of Gopherus and Kinosternon aff. K. hirtipes/K. [...] integrum from the municipality of Santiago Chazumba, Oaxaca. The finding of those taxa for the Oaxacan Pleistocene suggest xerophilous scrub environment such the one found today in the Tehuacán-Cuicatlán Valley, but with lower rainfall and higher temperatures, conditions similar to those prevailing in northern México.

J. Alberto, Cruz; Joaquín, Arroyo-Cabrales; Ramón, Viñas-Vallverdú.

271

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

272

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

DEFF Research Database (Denmark)

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

Thiel, Christine; Terhorst, Birgit

2011-01-01

273

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  

Science.gov (United States)

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

274

First mtDNA sequencing of Volga and Ob basin taimen Hucho taimen: European populations stem from a late Pleistocene expansion of H. taimen out of western Siberia and are not intermediate to Hucho hucho.  

Science.gov (United States)

New concatenated mtDNA sequences (three genes; n = 22) of Siberian taimen Hucho taimen primarily from west Siberian and European regions of the species' range were added to 12 previously published sequences to provide a phylogeographic overview of the species. European samples show only very minor divergence from west Siberian populations, supporting a late Pleistocene expansion from Siberia into the Urals, with no particular relation to the Danube River basin huchen Hucho hucho as once hypothesized. The disjunct distribution of the genus is most likely based on an early Pleistocene vicariant event. PMID:24906052

Mari?, S; Alekseyev, S; Snoj, A; Askeyev, O; Askeyev, I; Weiss, S

2014-08-01

275

Characterization of relict Late Pleistocene and Early Holocene paleosols buried in wedge-shaped structures on the southern coast of the Finnish Gulf  

Science.gov (United States)

The physical and physicochemical properties and morphogenetic characteristics of the buried soddy gleyic and gleyed paleosols developed from the glaciolacustrine loamy sediments on the southern coast of the Finnish Gulf in the Late Pleistocene and Early Holocene (12-9 ka, calibrated) are considered. It is shown that the morphology and properties of these paleosols sharply differ from those of the enclosing gravelly sands deposited in the ancient basins. The latter substrates serve as the major type of soil-forming materials for the modern surface soils. The studied paleosols fill wedge-shaped structures dissecting the gravelly sediments. Their profiles are well preserved, though their normal horizontal orientation is disturbed; large soil blocks were displaced into the open wedges. The presence of these soils attests to the fact that the initial soil cover in the studied region was formed in the Late Glacial epoch soon after the retreat of the glacial sheet. The good degree of preservation of the paleopedogenic information recorded in the profiles of these paleosols is of great value for the paleoenvironmental reconstructions.

Rusakov, A. V.; Nikonov, A. A.

2010-07-01

276

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

277

Late Pleistocene depositional cycles of the Lapis Tiburtinus travertine (Tivoli, Central Italy): Possible influence of climate and fault activity  

Science.gov (United States)

The depositional and erosional history of the Lapis Tiburtinus endogenic travertine located circa 25 km to the east of Rome, Central Italy, near the Colli Albani quiescent volcano, is interpreted through three-dimensional stratigraphy and uranium-series geochronology. Analyses of large exposures located in active quarries and of cores obtained from 114 industrial wells reveal that the travertine deposit is about 20 km 2 wide and 60 m thick on average. The travertine thickness is over 85 m toward its western N-S-elongated side, where thermal springs and large sinkholes occur aligned over a seismically-active N-striking fault. The travertine age was calculated using the U/Th isochron method. Results constrain the onset and conclusion of travertine deposition at about 115 and 30 ka, respectively. The three-dimensional study of the travertine shows that this deposit is characterized by a succession of depositional benches grown in an aggradational fashion. The benches are separated by five main erosional surfaces, which are associated with paleosols, conglomerates, and karstic features. This evidence shows that the travertine evolution was mostly controlled by water table fluctuations. Chronological correlations between travertine evolution and paleoclimate indicators suggest that the travertine deposition was partly modulated by climate conditions. Other influencing factors may have been fault-related deformation and volcanic events.

Faccenna, Claudio; Soligo, Michele; Billi, Andrea; De Filippis, Luigi; Funiciello, Renato; Rossetti, Claudio; Tuccimei, Paola

2008-10-01

278

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

279

Spectral stratigraphy  

Science.gov (United States)

A new approach to stratigraphic analysis is described which uses photogeologic and spectral interpretation of multispectral remote sensing data combined with topographic information to determine the attitude, thickness, and lithology of strata exposed at the surface. The new stratigraphic procedure is illustrated by examples in the literature. The published results demonstrate the potential of spectral stratigraphy for mapping strata, determining dip and strike, measuring and correlating stratigraphic sequences, defining lithofacies, mapping biofacies, and interpreting geological structures.

Lang, Harold R.

1991-01-01

280

Study on the estimation method of uplift during the late quaternary by using river terraces. 1. Strategy of terrace correlation and a case study on stratigraphy of river terraces  

International Nuclear Information System (INIS)

There are a few uplift data during the late Quaternary obtained by using river terraces than those by using marine terraces, because it is difficult to date a river terrace whose age is older than the marine oxygen isotope stage 6. In this paper, at first, we reviewed the terrace correlation method, and we proposed our viewpoint of terrace correlation which is based on relationship between geomorphologic features of terraces and geology that consist of terraces. Next, we did the case study on terrace stratigraphy in the Kawasaki Basin, Miyagi pref., and showed that our method is practical. (author)

281

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

282

230Th/234U dates of late Pleistocene corals from Kita- and Minami-Diato Island, Okinawa, Japan  

International Nuclear Information System (INIS)

Alpha spectrometric Th-230/U-234 dating was applied to 50 Pleistocene corals from Kita- and Minami-Daito Islands, both have been well known as the noteworthy representatives of raised atolls. The Th-230/U-234 dates ranged from 113±6 to 133±6 ka (123±1 ka on average) in the autochthonous corals from Kita-, and from 111±5 to 159±10 ka (123±1 ka on average) in those from Minami-Daito Island, intimating that the fringing reefs have been developed during the high sea level stand of the last interglacial maximum. These dates are correlative to the oxygen isotope stage 5e. The upper limit of occurrence of the dated autochthonous corals was 8.1 m in Kita- and 11 m in Minami-Daito Island. Besides, the somewhat younger dates corresponding to OIS-5a or 5c were obtained from some allochthonous corals in a detrital limestone unit in Kita-Daito Island. However, hermatypic corals were alive, forming small scale reefs in shallow sea around Kita-Daito Island. The former shoreline was proved by the presence of raised surf bench at some localities, where the dated autochthonous corals were collected. (K.I.)

283

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

284

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

285

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

286

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

International Nuclear Information System (INIS)

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). Th 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)

287

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

288

Humidity changes in southern Tunisia during the Late Pleistocene inferred from U-Th dating of mollusc shells  

International Nuclear Information System (INIS)

Calcareous deposits, mainly consisting of mollusc shell accumulations, which have been dated by the U/Th disequilibrium method, mark the shorelines of paleolake highstands in the Great Chotts Area of Southern Tunisia. The 5 sites studied consist of discontinuous accumulations of fossils of marine-like organisms e.g.: Cerastoderma glaucum, Melania tuberculata, Melanopsis praemorsa, Cerithium rupestre. U/Th isochron plots and age frequency histograms for 39 shell samples are reported here. Limited variations for U content and 234U/238U activity ratios (AR) of shells support the hypothesis of closure of the geochemical system with respect to this element. It is remarkable that 234U/238U AR of shells collected in Chott Fejej or Chott Jerid are clustered around different values, reflecting probably different groundwater recharge from the Continental Intercalaire (CI) or Complexe Terminal (CT) aquifers. Furthermore waters collected near Wadi el Akarit show 234U/238U AR values comparable to those observed for shells. 14C determinations made on aliquots of some of these samples suggested an age distribution between 18 and 34 ka BP. The U/Th data of these 39 shell samples imply that 4 distinct flood episodes of these lakes occurred at about 30, 95-100, 130-150 and 180-200 ka. For the episode centred around 30 ka, the frequency histogram of ages shows a multimodal age group that could represent the exidal age group that could represent the existence of several humid pulses rather than a unique event. Moreover, the comparison of ?13C and ?18O with those of older humid Pleistocene phases, when very large palaeolakes have been recorded, suggests that these young carbonate shells are not related to a true highstand lake. It is suggested that they represent a period of less humid climatic conditions with carbonate accumulation in minor water ponds in which intensive biological activity could have taken place. It should be noted that this period was less arid than the present

289

Late Pleistocene barrier-island development reconstructed from genetic classification and timing of erosional surfaces, paleo-Tokyo Bay, Japan  

Science.gov (United States)

Formative processes of a retrogradational barrier-island system and associated transgressive erosional surfaces are reconstructed from the Upper Pleistocene Kioroshi Formation developed in paleo-Tokyo Bay, Japan. The Kioroshi Formation provides high-quality sedimentary records of a preserved barrier-island system. Three volcanic-ash beds intercalated in the formation provide a high-resolution chronostratigraphic framework. The barrier-island system of the Kioroshi Formation developed in a glacio-eustatically forced sea-level cycle during oxygen-isotope stages 6 to 5e. In the early stage of the transgression, paleo-Tokyo Bay was non-barred, and was exposed to the Pacific Ocean, affected by open-ocean wave processes. Shoreface erosion in such a non-barred environment developed a wave-ravinement surface (RS1). RS1 overlies incised-valley-fill deposits formed in the earliest stage of the transgression and is overlain by shoreface deposits that are further overlain by embayment deposits, such as lagoonal and flood-tidal-delta deposits, formed during succeeding barrier development. During the later stage of the same transgression, associated with the formation and landward migration of the barrier chain, tidal currents in tidal-inlet and flood-tidal deltas became active, and a tidal-ravinement surface (TRS) was formed. TRS is developed on the base of tidal-inlet and flood-tidal delta deposits. Furthermore, shoreface erosion on the open-ocean side of the barrier chain eroded underlying embayment deposits and formed a secondary wave-ravinement surface (RS2). A chronostratigraphic surface in embayment deposits defined by a volcanic-ash bed intersects TRS and is eroded by RS2. This relationship, together with associated facies architecture, indicates diachroneity of the formation of these marine erosional surfaces associated with the retrogradational barrier-island system.

Nishikawa, T.; Ito, M.

2000-12-01

290

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

Science.gov (United States)

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

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

2013-05-01

291

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

292

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

Science.gov (United States)

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

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

2007-12-01

293

The uncertainty of Late Pleistocene range expansions in the western Mediterranean: A case study of the colonization of south-eastern Spain by the spur-thighed tortoise, Testudo graeca  

OpenAIRE

Aim: Recent biogeographical studies have postulated a North African, Late Pleistocene, origin for some species of the Iberian Peninsula. However, a robust assessment of such range expansions requires high-resolution molecular tools to resolve overlapping biogeographical and cultural processes. Here we aim to determine whether the spur-thighed tortoise, Testudo graeca, arrived in south-eastern Spain during historical or prehistoric times, and whether its dispersal to the Iberian Peninsula was ...

Gra?cia, E.; Gime?nez, A.; Anado?n, J. D.; Harris, D. J.; Fritz, U.; Botella, Francisco

2013-01-01

294

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

OpenAIRE

Southern Patagonia is rich in late Pleistocene mammals, especially herbivores such as Camelids, Equids and Xenarthrans. Carnivores, on the other hand, are not commonly found in the paleontological record. One genus, Smilodon, is of particular interest because its presence in the region has not been demonstrated. In this paper, we present new fossil dental evidence that supports the presence of Smilodon populator (Lund) in the region. This evidence corresponds to the most southern record of th...

ALFREDO PRIETO; RAFAEL LABARCA; VÍCTOR SIERPE

2010-01-01

295

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

Science.gov (United States)

The Buia Homo site, also known as Wadi Aalad, is an East African paleoanthropological site near the village of Buia that, due to its very rich yield from the late Early Pleistocene, has been intensively investigated since 1994. In this paper, which reports on the finds of the 2010-2011 excavations, we include new fossil evidence on previously identified taxa (i.e., reptiles), as well as the very first description of the small mammal, fish and bird remains discovered. In particular, this study documents the discovery of the first African fossil of the genus Burhinus (Aves, Charadriiformes) and of the first rodent from the site. This latter is identified as a thryonomyid rodent (cane rat), a relatively common taxon in African paleoanthropological faunal assemblages. On the whole, the new occurrences documented within the Buia vertebrate assemblage confirm the occurrence of taxa characterized by strong water dependence. The paleoenvironmental characteristics of the fauna are confirmed as fully compatible with the evidence obtained through sedimentology and facies analysis, documenting the sedimentary evolution of fluvio-deltaic and lacustrine systems. PMID:23159190

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

2013-01-01

296

Abnormal carbonate diagenesis in Holocene-late Pleistocene sapropel-associated sediments from the Eastern Mediterranean; Evidence from Emiliania huxleyi coccolith morphology  

DEFF Research Database (Denmark)

In studying the Holocene-late Pleistocene record of the Eastern Mediterranean, considerable Emiliania huxleyi size/shape variation not clearly assignable to primary or secondary calcification was observed. Accordingly, different morphotypes were distinguished by light microscope (LM). A subsequent scanning electron microscope (SEM) analysis of selected samples has indicated that Emiliania huxleyi coccoliths are variably affected by carbonate diagenesis in these sediments. A series of diagenetic stages were qualitatively defined, comprising well-preserved specimens, three overgrowth (OG1 to OG3) and one etching (E1) stage. Comparing SEM and LM observations, a tentative correlation between the E. huxleyi calcified LM-morphotypes and E. huxleyi SEM-overgrowth stages is proposed here. Our study not only indicates that Emiliania huxleyi coccoliths are strongly influenced by carbonate diagenesis, but also that they show effects of carbonate precipitation and dissolution much more clearly than other coccoliths. The relative abundances of the different LM-morphotypes were used to define an E. huxleyi overgrowth index (EXO) that qualitatively estimates carbonate precipitation/dissolution on coccoliths in this sediment. This resulted in definition of five "Diagenetic" intervals (D1 to D5). Deposition of sapropel S1 was a time of good preservation with variable dissolution and no overgrowth of E. huxleyi coccoliths, whereas calcite overgrowth was high during the Last Glacial Maximum (LGM) and interglacial period and, to a lesser extent, during the Younger Dryas and through the last 5 ka. © 2004 Elsevier B.V. All rights reserved.

Crudeli, D.; Young, J.R.

2004-01-01

297

Tectonic constraints on the late Pleistocene-Holocene relative sea-level change along the north-eastern Adriatic coast (Croatia)  

Science.gov (United States)

In spite of very favourable coastal features, late Pleistocene-Holocene relative sea-level changes along the eastern Adriatic coast are still not completely resolved mostly due to the intensive and complicated regional and local neotectonics. We gathered current knowledge that generally presents the north Adriatic area as subsiding one, and proposed a reconstruction in new light of possible very slow (local) uplift (average rate of 0.1-0.25 mm/a for last 80 ka) which is supported by well-dated submerged speleothems and tectonic reconstruction. In addition, such a scenario supports also the formation of tidal notches that are common in the north Adriatic region, but not yet entirely understood. However, according to the latest Mediterranean data on sea level during the marine isotope stage (MIS) 5.1 being at + 1 m 80 ka ago, we do not dismiss the possibility of subsidence which would have been 0.18-0.23 mm/a on average for the last 80 ka, but notch formation under such condition would not have been realistic. Apparently, the position of the north-eastern Adriatic coast on a convergence area requires extensive palaeoenvironmental studies, including structural, lithostratigraphical, palaeontological, archaeological and radiometric data and application of isostatic modelling.

Suri?, Maša; Korbar, Tvrtko; Jura?i?, Mladen

2014-09-01

298

Late Pleistocene divergence between eastern and western populations of wood ducks (Aix sponsa) inferred by the 'isolation with migration' coalescent method.  

Science.gov (United States)

During the Late Pleistocene, glaciers sundered many species into multiple glacial refugia where populations diverged in allopatry. Although deeply divergent mitochondrial DNA (mtDNA) lineages often reflect the number of refugia occupied, it is unlikely that populations that split during the recent Wisconsin glaciations will have reached reciprocal monophyly. We examined mtDNA control region sequences from eastern and western populations of wood ducks (Aix sponsa) to determine whether their current, disjunct distribution is consistent with the occupancy of two glacial refugia. We used the 'isolation with migration' coalescent method (im) to simultaneously estimate effective population sizes, maternal gene flow, and time since divergence. We found 24 unique haplotypes, none of which were shared between the eastern and western populations, but we did not find diagnostic monophyletic lineages suggestive of long-term isolation in multiple glacial refugia. However, a high Phi ST (0.31) indicates that eastern and western populations are well differentiated in mtDNA, and results from im suggest that these populations have been diverging, without extensive gene flow, for 10,000 to 124,000 years. Results from im further suggest that these populations most likely split about 34,000 years ago, and this time of divergence is consistent with the occupancy of multiple glacial refugia during the Late Wisconsin glaciation. Eastern wood ducks are characterized by high genetic diversity, a large effective population size, and a recent population expansion, while western wood ducks have much less genetic diversity, a smaller population size, and have not undergone a recent population expansion. PMID:16156812

Peters, Jeffrey L; Gretes, William; Omland, Kevin E

2005-10-01

299

Late Pliocene - Early Pleistocene geologic history of Eastern Ledi-Geraru, Ethiopia: implications for the evolution of the southern Afar Depression and hominin paleoenvironments  

Science.gov (United States)

During the late Pliocene and early Pleistocene (~ 3-2.5 Ma), the Afar region of Ethiopia was undergoing major structural reorganization (e.g., change in extension direction, increased spreading rate) leading to significant landscape modification. Concurrent with these changes in paleogeography, regional trends towards a cooler and drier climate coincide with a clustering of first appearance and extinction events in the faunal record, including the diversification of the early hominin genus Australopithecus and the emergence of our own genus, Homo. However, sediments that span the 3 to 2.5 Ma interval are sparse in eastern Africa, and are especially rare at paleoanthropological sites in the Afar. Here we present new geologic mapping results that indicate extensive deposits of late Pliocene sediments in a previously unmapped region of the lower Awash Valley referred to as the Eastern Ledi-Geraru (ELG). Numerous interbedded airfall tephras enable geochemical comparisons to the existing regional tephrostratigraphic framework as well as high precision 40Ar/39Ar dating of tephras with suitable feldspars. Feldspars from 8 such tephra deposits span the time period of 3.0 to 2.8 Ma, providing the first glimpse of depositional environments and associated landscapes that existed at that time. Geologic mapping and stratigraphic analysis shows that over a 100 meter thick section of lacustrine to fluvial sediments are exposed along faulted basalt flows following both the Red Sea Rift and Main Ethiopian Rift structural trends. We interpret the geology at ELG to reflect a northeastern migration of paleo Lake Hadar, possibly into a series of smaller basins responding to the migration of the triple junction, a thinning lithosphere, and an increased period of volcanism. Combined with recently collected paleontological assemblages this work provides an opportunity to test proposed links between biotic events, global/regional climate change, and local tectonic events during a critical interval of evolutionary and structural change in southern Afar.

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

2012-12-01

300

Pollen analyses of Pleistocene hyaena coprolites from Montenegro and Serbia  

OpenAIRE

The results of pollen analyses of hyaena coprolites from the Early Pleistocene cave of Trlica in northern Montenegro and the Late Pleistocene cave of Baranica in southeast Serbia are described. The Early Pleistocene Pachycrocuta brevirostris, and the Late Pleistocene Crocuta spelaea are coprolite-producing species. Although the pollen concentration was rather low, the presented analyses add considerably to the much-needed knowledge of the vegetation of the central Balkans during the Pleistoce...

Argant Jacqueline; Dimitrijevi? Vesna

2007-01-01

301

Time-dependent flexural subsidence caused by Holocene and Late Pleistocene sedimentation in the Gulf of Mexico: New inversion modeling of vertical motion data  

Science.gov (United States)

The rate of sedimentary deposition into the world's catchment basins abruptly increased during the transition from Pliocene to Pleistocene climate. Pleistocene periodicity in sedimentation rate has the distinct fingerprints of Milankovich orbital forcing periods 20,000, 41,000 and 100,000 years. We model time-dependent flexure of the Gulf of Mexico by continent-wide sediment transport rate variability over the past 4 Ma. Reconstructions of changes in sediment dispersal occurring during the Late Cenozoic indicate that glacioeustasy may also be a significant role along the shore of the Northern Gulf of Mexico Basin. We employ both spherically layered and self-gravitating viscoelastic models along with a half-space model of very high resolution. We also incorporate the long-wavelength background crustal motion associated with the main Laurentide deglaciation which produces a non-negligible bulge migration. The elastic lithospheric thickness and Maxwell time constants are tuned to both regional and global seismic tomography. The latter data are consistent with a rheologically stiffer than average sub-crustal environment. Hydro-isostatic loading is included in the modeling. Paleosealevel indicators, tide gauges and recent GPS results provide rich data sources for inverse modeling of the load history and solid earth rheology. The sediment rate changes are modeled, in part, as pulsed great megaflood erosional events known to be active during Glacial to Interglacial transitions. Although the model is relatively crude in both space and time, preliminary results indicate that the subsidence rate caused by long-term sedimentary changes could sustain subsidence rates dw/dt of roughly 1 - 12 mm/yr during the past 5,000 years over many hundreds of kilometers of coastline. Geodetic data in the Mississippi Delta region of southern Louisiana show subsidence at rates greater than 5 mm/yr, having many of the spatial characteristics predicted by the sedimentary load model. These data are interpreted in terms of a formal inverse approach and we report optimum solutions for sedimentary loading in for regions where it may be freed as a model parameter.

Ivins, E. R.; Dokka, R.; Blom, R. G.; Wu, X.

2006-12-01

302

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

303

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

Science.gov (United States)

Marine terraces are prominent landforms along the southern Oregon coast, which forms part of the forearc region of the Cascadia subduction zone. Interest in the Cascadia subduction zone has increased because recent investigations have suggested that slip along plates at certain types of convergent margins is characteristically accompanied by large earthquakes. In addition, other investigations have suggested that convergent margins can be broadly classified by the magnitude of their uplift rates. With these hypotheses in mind, we generated new uranium series, amino acid, and stable isotope data for southern Oregon marine terrace fossils. These data, along with terrace elevations and two alternative estimates of sea level at the time of terrace formation, allow us to determine terrace ages and uplift rates. Uranium series analysis of fossil coral yields an age of 83±5 ka for the Whisky Run terrace at Coquille Point in Bandon, Oregon. A combination of amino acid and oxygen isotope data suggest ages of about 80 and 105 ka for the lowest two terraces at Cape Blanco. These ages indicate uplift rates of 0.45-1.05 and 0.81-1.49 m/kyr for Coquille Point and Cape Blanco, respectively. Late Quaternary uplift rates of marine terraces yield information about deformation in the overriding plate, but it is unclear if such data vary systematically with convergent margin type. In order to assess the utility of the southern Oregon uplift rates for predicting the behavior of the Cascadia subduction zone, we compared late Quaternary uplift rates derived from terrace data from subduction zones around the world. On the basis of this comparison the southern Oregon rates of vertical deformation are not unusually high or low. Furthermore, late Quaternary uplift rates show little relationship to the type of convergent margin. These observations suggest that local structures may play a large role in uplift rate variability. In addition, while the type of convergent margin may place an upper limit on possible uplift rate, greater upper limits serve to increase the range of possible uplift rates. In the case of the southern Oregon coast, variability in uplift rate probably reflects local structures in the overriding plate, and the rate of uplift cannot be used as a simple index of the potential for great earthquakes along the southern Cascadia subduction zone.

Muhs, Daniel R.; Kelsey, Harvey M.; Miller, Gifford H.; Kennedy, George L.; Whelan, Joseph F.; McInelly, Galan W.

1990-05-01

304

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

Science.gov (United States)

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

Sangen, M.

2009-04-01

305

Soft-sediment deformation of Late Pleistocene sediments along the southwestern coast of the Baltic Sea (NE Germany)  

Science.gov (United States)

A 1,460-m-long profile of a Late Glacial subglacial, glacio-fluvial, glacio-limnic and glacio-deltaic sequence exposed at a cliff section on Usedom Island (SW Baltic Sea coast) is described. The sequence is up to 31 m thick and shows sedimentary structures typical of a glacial setting. Soft-sediment deformation is encountered and is associated with changes in lithology. These deformations include liquefaction, slumping, and faulting. As the most plausible cause, earthquake-induced shaking is discussed. The associated neotectonic activity is seen as a consequence of the postglacial isostatic crustal rebound. As the deglaciation earthquake ratio diminishes with time and as the rebound is phasing out, no large earthquakes are anticipated for northern Germany, although in conclusion the lithosphere of the North German Basin has to be regarded as weakened by repeated ice loading and deloading.

Hoffmann, Gösta; Reicherter, Klaus

2012-01-01

306

Geochemical evidence of pollutants from coalfired generating stations in late Pleistocene palaeosols in the Dalijia Shan, northwestern China.  

Science.gov (United States)

Surface palaeosols in two tills and a diamicton from an area in northwestern China were analysed for geochemical pollutants. Elevated levels of Br, As and Sb indicate that pollution from coal-burning and/or coal-fired electricity generating stations is delivered by aeolian transport into palaeosols dating from the last glaciation. Because the climate in the field area is sub-humid (precipitation movement of soluble elements in palaeosols dating from early and late stades of the last glaciation is not expected to be high. The glacial and aeolian parent materials of the palaeosols indicate differences that are probably related to their source areas and to the incorporation of geochemical pollutants. PMID:24194367

Mahaney, W C; Hancock, R G

1996-03-01

307

Late Miocene to Plio-Pleistocene fluvio-lacustrine system in the Karacasu Basin (SW Anatolia, Turkey): Depositional, paleogeographic and paleoclimatic implications  

Science.gov (United States)

The sedimentary record of the late Cenozoic Karacasu Basin, a long-lived continental half-graben from southwestern Turkey, is characterized by siliciclastic and carbonate deposits. Sedimentation was controlled by an active NW-SE trending major normal fault along the basin's southern margin and by climatically-induced lake-level changes. Detailed facies analysis subdivides the entire Neogene-Quaternary basin-fill into three distinct litostratigraphic units representing paleogeographic changes and sedimentation patterns throughout the basin evolution. Sedimentation commenced in the late Miocene with the deposition of proximal-medial alluvial fan and fluvial facies (Damdere Formation; FA1). At this stage, alluvial fans developed in elevated areas to the south, prograding towards the basin center. At the beginning of the Pliocene, fresh to slightly alkaline, shallow lake deposits (FA2a) of the Karacaören Formation formed. The lake became open and meromictic conditions developed (FA2b). Pollen data from the FA2b facies show that climate was arid to humid. Climate probably changed cyclically through time producing alternation of Artemisia steppe (cold and dry periods) and more forested vegetation (warm and wet). The open lake facies passes upwards into lake margin facies (FA2c), but it was still dominated by alkaline to slightly saline lake conditions. Sedimentation was almost continuous from the late Miocene to Pleistocene. In the early Quaternary, the basin was dissected by the re-activation of basin bounding faults. The unconformable base of the overlying Quaternary deposits (Karacasu Formation; FA3) reflected the basin's transformation from a half-graben into a full-graben system. Oxygen isotope data from carbonates show an alternation of humid climatic periods, when freshwater settings predominated, and semiarid/arid periods in which the basin hosted alkaline and saline water lakes. Neotectonic activity has rejuvenated many of the basin-bounding faults, causing development of talus aprons and local alluvial fans. The basin was progressively incised by modern rivers that have largely smoothed out the topographic relief of the graben margins. id="ab0010" The study highlights to the paleo-geography/-climatology in the east Mediterranean.

Alçiçek, Hülya; Jiménez-Moreno, Gonzalo

2013-06-01

308

Cambrian Stratigraphy  

Science.gov (United States)

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

309

Tectonic control on the stratigraphic framework of Late Pleistocene and Holocene deposits in Marajó Island, State of Pará, eastern Amazonia  

Directory of Open Access Journals (Sweden)

Full Text Available The traditional view that the Brazilian Amazonia is located in a tectonically stable area since the Cretaceous is changing in front of the increasing documentation of fault reactivations even during the Holocene. How the sedimentary record has responded to these events is an issue that remains to be approached with basis on field data. This work focuses on the stratigraphic correlation of late Quaternary deposits from eastern Marajó Island, with the goal of demonstrating the role of fault reactivation on the origin and preservation of these deposits. Despite the location in a stable platform of a continental passive margin, three studied stratigraphic units display significant vertical offsets that define two depocenters that are better explained through tectonic displacements. This interpretation is reinforced by several morphostructural features related to faults that occur between the studied drills. Without the influence of tectonics, sediment preservation in this characteristically low-lying terrain would have been negligible. The results of the present work motivate to look for other tectonically-influenced areas in Amazonia, which similarly might have acted as sites for sediment accommodation during the late Quaternary. These sedimentary records have great potential to be the source of valuable information for reconstructing Quaternary geological events in Northern Brazil.A visão tradicional de que a Amazônia brasileira localiza-se em ma área tectonicamente estável desde o Cretáceo está mudando perante a crescente documentação de reativações de falha, até mesmo durante o Holoceno. Como o registro sedimentar respondeu a esses eventos é um tema que permanece por ser abordado com base em dados de campo. Este trabalho enfatiza a correlação estratigráfica de depósitos quaternários tardios no leste da Ilha do Marajó, com o objetivo de demonstrar a importância de reativações de falha na origem e preservação desses depósitos. Apesar da localização em área de plataforma de uma margem continental passiva, três unidades estratigráficas estudadas mostram significantes rejeitos verticais, que definem dois depocentros, explicados por deslocamentos tectônicos. Esta interpretação é reforçada por várias feições morfoestruturais relacionadas com falhas localizadas entre os poços estudados. Sem influência tectônica, a preservação de sedimentos nesse terreno, caracteristicamente plano, seria imperceptível. Os resultados do presente trabalho motivam a procurar outras áreas tectonicamente influenciadas da Amazônia, que possam ter atuado como sítios de acomodação de sedimentos durante o Quaternário tardio. Esses registros sedimentares têm grande potencial de serem fontes de informações valiosas para auxiliar na reconstrução de eventos geológicos quaternários no norte do Brasil.

Dilce F. Rossetti

2010-06-01

310

Tectonic control on the stratigraphic framework of Late Pleistocene and Holocene deposits in Marajó Island, State of Pará, eastern Amazonia  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in portuguese A visão tradicional de que a Amazônia brasileira localiza-se em ma área tectonicamente estável desde o Cretáceo está mudando perante a crescente documentação de reativações de falha, até mesmo durante o Holoceno. Como o registro sedimentar respondeu a esses eventos é um tema que permanece por ser ab [...] ordado com base em dados de campo. Este trabalho enfatiza a correlação estratigráfica de depósitos quaternários tardios no leste da Ilha do Marajó, com o objetivo de demonstrar a importância de reativações de falha na origem e preservação desses depósitos. Apesar da localização em área de plataforma de uma margem continental passiva, três unidades estratigráficas estudadas mostram significantes rejeitos verticais, que definem dois depocentros, explicados por deslocamentos tectônicos. Esta interpretação é reforçada por várias feições morfoestruturais relacionadas com falhas localizadas entre os poços estudados. Sem influência tectônica, a preservação de sedimentos nesse terreno, caracteristicamente plano, seria imperceptível. Os resultados do presente trabalho motivam a procurar outras áreas tectonicamente influenciadas da Amazônia, que possam ter atuado como sítios de acomodação de sedimentos durante o Quaternário tardio. Esses registros sedimentares têm grande potencial de serem fontes de informações valiosas para auxiliar na reconstrução de eventos geológicos quaternários no norte do Brasil. Abstract in english The traditional view that the Brazilian Amazonia is located in a tectonically stable area since the Cretaceous is changing in front of the increasing documentation of fault reactivations even during the Holocene. How the sedimentary record has responded to these events is an issue that remains to be [...] approached with basis on field data. This work focuses on the stratigraphic correlation of late Quaternary deposits from eastern Marajó Island, with the goal of demonstrating the role of fault reactivation on the origin and preservation of these deposits. Despite the location in a stable platform of a continental passive margin, three studied stratigraphic units display significant vertical offsets that define two depocenters that are better explained through tectonic displacements. This interpretation is reinforced by several morphostructural features related to faults that occur between the studied drills. Without the influence of tectonics, sediment preservation in this characteristically low-lying terrain would have been negligible. The results of the present work motivate to look for other tectonically-influenced areas in Amazonia, which similarly might have acted as sites for sediment accommodation during the late Quaternary. These sedimentary records have great potential to be the source of valuable information for reconstructing Quaternary geological events in Northern Brazil.

Dilce F., Rossetti.

2010-06-01

311

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

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

Tadeusz SOKO?OWSKI

2009-01-01

312

Late Pleistocene glaciation of the Kodar Mountains, south-central Siberia, constrained by Be-10 exposure dating  

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The glacial history of the mountainous Transbaikalia region NE of Lake Baikal, Siberia, has so far received little attention. The Kodar Mountains exceed 3000 m in elevation and small cirque glaciers currently occur in the central parts of the range. Yet, greatly expanded glaciation in the past is evidenced by massive moraine complexes at the mouth of glacial valleys in the Chara Depression (part of the Baikal rift system), and along the Vitim River valley to the NW. The moraines document the existence of large valley glaciers that reached to over 120 kilometres in length. We applied Be-10 exposure dating to determine the timing of glacier advances that formed the major moraines: 19 samples from boulders on 8 moraine ridges in 5 moraine complexes. Our results indicate extensive glaciation in the Kodar Mountains at the time of the Last Glacial Maximum, with our ages spanning from about 20 ka to the Late Glacial. We attribute the age spread on some of the moraines to boulder exhumation linked to permafrost dynamics.

Margold, Martin; Jansen, John D.; Gurinov, Artem L.; Reznichenko, Natalya V.; Codilean, Alexandru T.; Fink, David

2014-05-01

313

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

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

Laura, Ferrero.

2009-12-01

314

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

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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.

2007-12-01

315

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

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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

316

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).

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

2013-08-01

317

Sea-level and tectonic control of middle to late Pleistocene turbidite systems in Santa Monica Basin, offshore California  

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Small turbidite systems offshore from southern California provide an opportunity to track sediment from river source through the turbidity-current initiation process to ultimate deposition, and to evaluate the impact of changing sea level and tectonics. The Santa Monica Basin is almost a closed system for terrigenous sediment input, and is supplied principally from the Santa Clara River. The Hueneme fan is supplied directly by the river, whereas the smaller Mugu and Dume fans are nourished by southward longshore drift. This study of the Late Quaternary turbidite fill of the Santa Monica Basin uses a dense grid of high-resolution seismic-reflection profiles tied to new radiocarbon ages for Ocean Drilling Program (ODP) Site 1015 back to 32 ka. Over the last glacial cycle, sedimentation rates in the distal part of Santa Monica Basin averaged 2-3 mm yr-1, with increases at times of extreme relative sea-level lowstand. Coarser-grained mid-fan lobes prograded into the basin from the Hueneme, Mugu and Dume fans at times of rapid sea-level fall. These pulses of coarse-grained sediment resulted from river channel incision and delta cannibalization. During the extreme lowstand of the last glacial maximum, sediment delivery was concentrated on the Hueneme Fan, with mean depositional rates of up to 13 mm yr-1 on the mid- and upper fan. During the marine isotope stage (MIS) 2 transgression, enhanced rates of sedimentation of > 4 mm yr-1 occurred on the Mugu and Dume fans, as a result of distributary switching and southward littoral drift providing nourishment to these fan systems. Longer-term sediment delivery to Santa Monica Basin was controlled by tectonics. Prior to MIS 10, the Anacapa ridge blocked the southward discharge of the Santa Clara River into the Santa Monica Basin. The pattern and distribution of turbidite sedimentation was strongly controlled by sea level through the rate of supply of coarse sediment and the style of initiation of turbidity currents. These two factors appear to have been more important than the absolute position of sea level. ?? 2006 The Authors. Journal compilation 2006 International Association of Sedimentologists.

Normark, W.R.; Piper, D.J.W.; Sliter, R.

2006-01-01

318

Pleistocene horses (genus Equus) in the central Balkans  

OpenAIRE

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 th...

Forsten Ann; Dimitrijevi? Vesna M.

2003-01-01

319

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

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

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

2015-03-01

320

Traces of Late Miocene and Pleistocene tectonics on recent surface morphology in the Western Pannonian Alpine Foothills - a case study of geomorphometry  

Science.gov (United States)

The study area is located at the eastern foothills of the Eastern Alps, which is a transition zone between the still uplifting mountainous region and the subsiding Danube Basin, part of the Pannonian Basin. As the Pannonian Lake filled up during Late Miocene, totally plain surface left behind covering the rugged pre-Tertiary basement. Nowadays, totally flat alluvial plain only recognizable on the easternmost and northeastern part of the investigated area. Slightly undulating hilly surface dissected by N-S and E-W oriented steep scarps prevail the middle part of the area. West from the Austrian-Hungarian border, landscape is quite different. Steep scarps are either observable, however the hills are much more eroded by mostly N-S directed creeks. As Pleistocene rivers drained the Eastern Alps, wide area covered by fluvial, mostly gravel sediments. The whole process span the Pleistocene era with different intensity, forcing drainage reorganization occurred in several steps. Modification of the drainage network were triggered by the general tilting of the study area, normal faults and effects of the basement morphology. In our earlier study, correspondence between surface and basement morphology was detected. Results revealed the differences of the general morphology depend on the pre-Tertiary basement height under the coverage of basement fill. Above South Burgenland Swell (basement ridge of ca. -500 m asl.), recent surface is elevated with ~50 m compared to the close environment. Due to the elevated position of the surface and approximately the same base level, incision of streams are clearly deeper. In this paper we reveal the importance of geomorphometry as a prior investigation method in tectonic geomorphology studies, we show the applicability of tools such as mode of slope, standard deviation of slope in impoundment of surface blocks under different tectonic forces. Sinuosity evaluation of alluvial rivers compared with surface aspect was proven to be very effective method on apparently totally flat area in showing location of tectonic forces. We compared the revealed features with the basement morphology using previously composed basement maps and industrial seismic sections. Latter proved that morphological similarities are not only observable between the basement and the surface, but the geometry of basin-fill lacustrine sediment horizons strengthen the correspondence and in some cases explain the root causes. Our results provide additional information to the geodynamic sketch of the Alpine-Pannonian transition zone and emphasize the applicability of geomorphometry in tectonic studies. The study was supported by Hungarian Scientific Research Fund (OTKA NK83400) and was realized in the frames of TÁMOP 4.2.4.A/2-11-1-2012-0001 high priority "National Excellence Program - Elaborating and Operating an Inland Student and Researcher Personal Support System convergence program" project's scholarship support.

Kovács, Gábor; Telbisz, Tamás; Székely, Balázs

2014-05-01

321

Study on the estimation method of uplift during the late Quaternary by using river terraces (2). Stratigraphy of fluvial terraces along the Naka Rivers  

International Nuclear Information System (INIS)

To develop the reliable method of terrace correlation and chronology, which is a key technique for uplift characterization in an inland area, verification of terrace correlation and chronology is examined along the Naka and Hoki rivers, Ibaraki and Tochigi Prefectures. The results obtained indicate that the basic concept of terrace correlation and chronology proposed by Hataya (2005). Also, weathering grade of terrace gravels is classified into 4 levels and shows a good agreement with the terrace chronology. It shows that weathering grade of terrace gravels is a good stratigraphic index. Therefore, it is stressed that it is very important to combine the information of geomorphologic stratigraphy, geomorphologic analysis, geologic stratigraphy, tephra chronology and numerical dating data comprehensively, in particular, is of great importance to obtain the detailed geomorphologic information. Furthermore, it is pointed out that it is probable to redefine the general idea of 'higher, middle, lower terraces' by tephra chronology and numerical dating data. For instance, MIS6 fluvial terrace that is important for uplift estimation is probably considered as 'a middle terrace in an inland area'. (author)

322

Pollen and lithological data from the Bukovynka Cave deposits as recorders of the Late Pleistocene and Holocene climatic change in the eastern foothills of the Carpathian Mountains (Ukraine  

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Full Text Available The study of clastic sediments of the BukovynkaCaveshows biotic and climatic changes during the Middle Pleniglacial (the Trapeznyi Chamber, Late Glacial and Holocene (the Sukhyi Chamber in the south-eastern part of the Ukrainian Carpathians. The artesian BukovynkaCaveis located near the villageof Stal’nivtsi(the Chernivtsi region, in the PrutRiver basin. It is developed in the Miocene gypsum strata. The Quaternary clastic infilling of the cave, as well as mammal taphonomy has been previously studied in the Trapeznyi Chamber (Vremir et al., 2000; Ridush, 2004; Ridush et al., 2012, whereas palaeomagnetic research and its palaeoenvironmental implication has been provided for the Sukhyi Chamber (Bondar and Ridush, 2014. The results of pollen and grain-size studies of clastic deposits in both chambers, supported by mammal finds, are presented in this paper. In the Chernivtsi region, the pollen study has been previously performed (without 14C-dating on the Upper Pleistocene loess-paleosol section of Snyatyn and on the Onut site of the Holocene flood-plain deposits of the River Prut (Artyushenko et al., 1982. 39 samples from the cave sediments have been processed for grain-size analyses using the ‘pipette’ technique by Kachinsky (1965. In order to get pollen from clastic sediments, the following technique has been applied: heating with 10% HCl and 10% KOH, cold treatment with HF, disintegration in a solution of Na4P2O7 and separation in heavy liquid (CdI2 and KI with a specific gravity 2.2. The abundance and good preservation of pollen show that the cave chambers turned periodically into sedimentation traps. Mammal bones are also mostly well preserved. Re-deposited pollen are abundant in the Trapeznyi Chamber but occur very rarely in the Suchyi Chamber. The present-day vegetation near the cave is a meadow-steppe surrounded by Carpinus-Quercus forest. The high proportion of Pinus sylvestris pollen in the surface soil samples (30-40% does not correspond to the limited role that pine has in the modern vegetation. On the basis of this fact, pine pollen in the cave deposits are also regarded as over-represented because of its ability to travel farther on the wind than other pollen and its better preservation in rocks.

Nataliia GERASIMENKO

2015-11-01

323

The generation of a diverse suite of Late Pleistocene and Holocene basalt through dacite lavas from the northern Cascade arc at Mount Baker, Washington  

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Mt. Baker is a dominantly andesitic stratovolcano in the northern Cascade arc. In this study, we show that the andesites are not all derived from similar sources, and that open-system processes were dominant during their petrogenesis. To this end, we discuss petrographic observations, mineral chemistry, and whole rock major and trace element chemistry for three of Mt. Baker's late Pleistocene to Holocene lava flow units. These include the basalt and basaltic andesite of Sulphur Creek (SC) (51.4-55.8 wt% SiO2, Mg# 57-58), the Mg-rich andesite of Glacier Creek (GC) (58.3-58.7 wt% SiO2, Mg# 63-64), and the andesite and dacite of Boulder Glacier (BG) (60.2-64.2 wt% SiO2, Mg# 50-57). Phenocryst populations in all units display varying degrees of reaction and disequilibrium textures along with complicated zoning patterns indicative of open-system processes. All lavas are medium-K and calc-alkaline, but each unit displays distinctive trace element and REE characteristics that do not correlate with the average SiO2 content of the unit. The mafic lavas of SC have relatively elevated REE abundances with the lowest (La/Yb)N (~4.5). The intermediate GC andesites (Mg- and Ni-rich) have the lowest REE abundances and the highest (La/Yb)N (~6.7) with strongly depleted HREE. The more felsic BG lavas have intermediate REE abundances and (La/Yb)N (~6.4). The high-Mg character of the GC andesites can be explained by addition of 4% of a xenocrystic olivine component. However, their depleted REE patterns are similar to other high-Mg andesites reported from Mt. Baker and require a distinct mantle source. The two dominantly andesitic units (GC and BG) are different enough from each other that they could not have been derived from the same parent basalt. Nor could either of them have been derived from the SC basalt by crystal fractionation processes. Crystal fractionation also cannot explain the compositional diversity within each unit. Compositional diversity within the SC unit (basalt to basaltic andesite) can, however, be successfully modeled by mixing of basalt with compositions similar to the dacites in the BG unit. Given that the BG dacites erupted at ~80-90 ka, and a similar composition was mixed with the SC lavas at 9.8 ka, the process that produced this felsic end-member must have been repeatedly active for at least 70 ka.

Baggerman, Troy David; Debari, S. M.

2011-01-01

324

Thermoluminescence dating of late Pleistocene loess and tephra from eastern Washington and southern Oregon and implications for the eruptive history of Mount St. Helens  

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The first numeric dating of late Pleistocene loess from the Palouse region of eastern Washington is reported. This loess is interbedded with thin, distal tephra layers, some identified as Mount St. Helens products. Both the interbedded tephra layers and thick paleosols that have developed in the loess have previously been correlated across the region. A thicker correlative of one of these tephra layers (Mount St. Helens set C) was collected from Summer Lake, Oregon, for direct dating by thermoluminescence (TL). Polymineral, fine grain TL ages for loess from three chosen sections in Washington range from 17 to 83 ka. These imply ages for some tephra beds that are significantly older than implied by earlier radiocarbon (14C) dating. For example, TL ages of 17-21 ka for loess bracketing a tephra layer correlated to Mount St. Helens set S suggests a somewhat older age for this ash than the previously accepted 14C age of ˜15.5±0.5 ka cal yr (corrected to calendar years). TL ages of 46±6 (1?) ka and 57±7 ka for loess above, and of 53 ± 7 ka and <75±6 ka below a tephra bed correlated to a Mount St. Helens set Cw layer, along with a TL age of 46±5 ka for fine-silt-sized glass from a Mount St. Helens set Cy bed in Oregon, revise upward from ˜38 ka cal yr (14C age is ˜36 ka B.P.) to ˜50 ka the age of this regionally important marker ash set. Several TL ages, taken together, imply a much longer eruptive history for Mount St. Helens than previously thought. A TL age of 83±8 ka just below a previously undated tephra layer from Mount St. Helens (EMSH ash) suggests that the eruptive history of the mountain extends back to at least 80 ka. Furthermore, age depth extrapolation through our sections to an ash (WA-5C) probably correlated to Mount St. Helens suggests an eruptive history of at least 120 ka.

Berger, Glenn W.; Busacca, Alan J.

1995-11-01

325

Isotopic (Sr-Nd) and major element fingerprinting of distal tephras: an application to the Middle-Late Pleistocene markers from the Colli Albani volcano, central Italy  

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We describe the diagnostic lithological and chemical features of distal tephras from major Middle-Late Pleistocene (560-36 ka) explosive eruptions of the Colli Albani volcanic district, central Italy. In particular, we explore the time-dependent variability of the Sr and Nd isotope compositions as a tool for recognising and pinpointing individual Colli Albani tephra in distal settings. The distal tephras investigated are in lacustrine and fluvial sediments of central Apennine intermountain basins located 70 km-100 km east of Colli Albani. The recognition of the Colli Albani tephras is essentially based on the K-foiditic composition of their glass, which, within the Italian volcanological framework, is a distinctive character of the Colli Albani pyroclasts. In detail, these tephras are attributed to the following eruptive units: Tufo Pisolitico di Trigoria (561 ± 2 ka); Tufo del Palatino-Tufo di Bagni Albule (530 ± 2/527 ± 2 ka), Tufo di Bagni Albule-Pozzolane Rosse air-fall sequence (517 ± 1 to 500 ± 3 ka), Pozzolane Rosse (457 ± 4 ka), Villa Senni (365 ± 4 ka), and Albano 5-7 (41 ± 7 to 36 ± 1 ka). These correlations are supported by 40Ar/39Ar dating of the distal tephras correlated to the Pozzolane Rosse (457.4 ± 1.7 ka), Villa Senni (365 ± 2 ka) and Albano 5-7 (41 ± 9 ka) and by 87Sr/86Sr measured on clinopyroxene crystals and fresh glassy scoria from distal Colli Albani tephras that range from ˜0.711 to ˜0.709. These ratios are similar to those that characterise the individual proximal correlative units, and show the same decreasing trend over time. In contrast, the 143Nd/144Nd ratios for proximal and distal bulk samples and clinopyroxene increase from ˜0.51212 to ˜0.51215 from the oldest to the youngest tephra deposit. In summary, the study of Sr and Nd isotope compositions that is here applied on products from the Colli Albani volcanic district is a powerful, complementary tool to the more traditional tephrostratigraphic methods (e.g., componentry and electron microprobe analysis) for fingerprinting of distal tephras over a large region of the central Mediterranean, and over a large time interval, such as from 560 ka to 36 ka.

Giaccio, Biagio; Arienzo, Ilenia; Sottili, Gianluca; Castorina, Francesca; Gaeta, Mario; Nomade, Sebastien; Galli, Paolo; Messina, Paolo

2013-05-01

326

Rapid anthropogenic response to short-term aeolian-fluvial palaeoenvironmental changes during the Late Pleistocene-Holocene transition in the northern Negev Desert, Israel  

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Archaeological investigations along Nahal Sekher on the eastern edge of Israel's northwestern Negev Desert dunefield revealed concentrations of Epipalaeolithic campsites associated respectively with ancient water bodies. This study, aimed at better understanding the connections between these camps and the water bodies, is concerned with a cluster of Natufian sites. A comprehensive geomorphological study integrating field mapping, stratigraphic sections, sedimentological analysis and optically stimulated luminescence (OSL) ages was conducted in the vicinity of a recently excavated Natufian campsite of Nahal Sekher VI whose artifacts directly overlay aeolian sand dated by OSL to 12.4 ± 0.7 and 11.7 ± 0.5 ka. Residual sequences of diagnostic silty sediments, defined here as low-energy fluvial fine-grained deposits (LFFDs), were identified within the drainage system of central Nahal Sekher around the Nahal Sekher VI site. LFFD sections were found to represent both shoreline and mid-water deposits. The thicker mid-water LFFD deposits (15.7 ± 0.7-10.7 ± 0.5 ka) date within the range of the Epipalaeolithic campsites, while the upper and shoreline LFFD units that thin out into the sands adjacent to the Nahal Sekher VI site display slightly younger ages (10.8 ± 0.4 ka-7.6 ± 0.4 ka). LFFD sedimentation by low-energy concentrated flow and standing-water developed as a result of proximal downstream dune-damming. These water bodies developed as a result of encroaching sand that initially crossed central Nahal Sekher by 15.7 ± 0.7 ka and probably intermittently blocked the course of the wadi. LFFD deposition was therefore a response to a unique combination of regional sand supply due to frequent powerful winds and does not represent climate change in the form of increased precipitation or temperature change. The chronostratigraphies affiliate the Natufian sites to the adjacent ancient water bodies. These relations reflect a rapid, but temporary anthropogenic response to a transient ‘window' of improved local aeolian-fluvial palaeoenvironmental conditions during the Late Pleistocene-Holocene transition, but don't necessarily point to a wetter or drier palaeoclimate.

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

2014-09-01

327

Geochronology of the Baye Mn oxide deposit, southern Yunnan Plateau: Implications for the late Miocene to Pleistocene paleoclimatic conditions and topographic evolution  

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40Ar/39Ar laser incremental heating analyses of supergene K-Mn oxides from weathering profiles at the Baye Mn deposit, southern Yunnan Plateau, SW China, were carried out to place constraints on the timing of weathering and derive insights into local paleoclimatic and landscape evolution. Weathering profiles in the Baye Mn mine are dominated by 20-30 m thick saprolites, which are locally covered by unconsolidated alluvial deposits. We analyzed 70 grains from 35 hand samples collected from four sites located at distinct elevations. In most cases, different grains from the same hand sample and different samples from the same site have reproducible 40Ar/39Ar plateau ages. The plateau ages of individual grains are also consistent with the respective isochron, integrated, and ideogram ages. This age consistency attests to the reliability of the geochronological results as numerical constraints on the formation and evolution of these weathering profiles. Sixty-four grains from 32 hand samples collected from weathering profiles at four sites (A to D) yield well-defined plateau or pseudoplateau ages ranging from 2.98 ± 0.07 to late Pliocene, and permits estimating the weathering rates at 3.3 ± 3.8, 6.6 ± 1.2, and 11.1 ± 1.9 m Myr-1 during the time periods of 2.98-2.83, 2.91-2.08, and 1.25 to river incision rates estimated from the surface exposed ages range from 235 ± 10 to 416 ± 19 m Myr-1 during the past 3 million years. The incision rate calculated from minimum exposed ages at sites B-D is 33 ± 2 m Myr-1 for the time period of 2.91-1.25 Ma, which is consistent with the slow incision of streams on the ridges over the Yunnan Plateau since the early Pleistocene. Three Mn oxide pebbles contained in the alluvial deposits overlying the saprolite-dominated weathering profiles at the two highest sites provided additional information on the timing of weathering. Four grains from two pebbles yield plateau ages of 6.32 ± 0.19 to 5.27 ± 0.10 Ma, whereas the other two grains from the third pebble indicate the minimum formation ages of 8.2 ± 0.4 and 9.3 ± 0.3 Ma. These ages confirm the existence of older weathering profiles, now dismantled, in the region. Manganese oxide 40Ar/39Ar ages of the Baye deposit, when combined with results from other localities, indicate that lateritic weathering and supergene Mn enrichment and, by inference, warm and humid climates conducive to intense weathering have prevailed over the Plateau since the middle to late Miocene. The climatic conditions inferred from the weathering geochronology are consistent with multiple independent marine and terrestrial sedimentary and paleontological records, confirming that supergene Mn oxides can be used as a useful proxy for past climate. Age clusters of Mn oxides at 2.9-2.4, 1.2-0.8, and 0.6-0.4 Ma are broadly coincident with and thus likely reflect intensification events of the Indian Summer Monsoon that brings moisture and abundant precipitation to the Yunnan Plateau. These clusters also coincide with the periods of significant surface uplift in the Yunnan Plateau, demonstrating a causal link between topographic evolution, plateau uplift, and intensification of the monsoonal climate.

Deng, Xiao-Dong; Li, Jian-Wei; Vasconcelos, Paulo M.; Cohen, Benjamin E.; Kusky, Timothy M.

2014-08-01

328

Climatic, geomorphic, and archaeological implications of a late Quaternary alluvial chronology for the lower Salt River, Arizona, USA  

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Recent archaeological excavations along the lower Salt River, Arizona resulted in the unexpected discovery of buried late Pleistocene soils and cultural features dating 5800-7100 cal YBP (Early Archaic), the latter representing the earliest evidence of human activity in the lower Salt River floodplain thus far identified. Because the lower Salt River floodplain has been heavily impacted by recent agriculture and urbanization and contains few stratigraphic exposures, our understanding of the river's geological history is limited. Here we present a late Quaternary alluvial chronology for a segment of the lower Salt River based on 19 accelerator mass spectrometry 14C and four optically stimulated luminescence ages obtained during two previous geoarchaeological investigations. Deposits are organized into allostratigraphic units and reveal a buried late Pleistocene terrace inset into middle-to-late Pleistocene terrace deposits. Holocene terrace fill deposits unconformably cap the late Pleistocene terrace tread in the site area, and the lower portion of this fill contains the Early Archaic archaeological features. Channel entrenchment and widening ~ 900 cal YBP eroded much of the older terrace deposits, leaving only a remnant of fill contain