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Late Pleistocene Stratigraphy and Palaeobotany of the Isles of Scilly  

Science.gov (United States)

A re-evaluation of the Pleistocene stratigraphy of the Isles of Scilly has enabled the formal definition of eight lithostratigraphic units of member status grouped into two formations. A chronology of events has been provided by radiocarbon (14C) determinations, optical and thermoluminescene (TL) dates. Intersite correlations have been strengthened by palynology, which has aided palaeoenvironmental reconstruction. The defined units have been incorporated into two lithostratigraphic models, one for the `northern' (glacial) Scillies and one for the `southern' (extra-glacial) Scillies. Raised beach sediments of the Watermill Sands and Gravel in the southern Scillies are overlain by the Porthloo Breccia, a unit of soliflucted material derived exclusively from the weathering of local granite. Organic sequences at Carn Morval, Watermill Cove, Porth Askin, Porth Seal and Bread and Cheese Cove occur within the Porthloo Breccia, and are interpreted as the infillings of ponds associated with active solifluction. Radiocarbon determinations from these organic sediments are critical because they pre-date units associated with a glacial event. The 14C determinations indicate deposition of the organic material between 34500-800+885 (Q-2410) and 21500-800+890 (Q-2358) years BP and provide a maximum age for the glacial event and the first radiometric dates for the coastal `head' sediments of southwest England. The pollen assemblages from these organic sites all record open grassland vegetation, and represent the earliest vegetational record for the Scillies. High Pinus values are interpreted as evidence of climatic deterioration. In the southern Scillies, the Porthloo Breccia is overlain by the Old Man Sandloess, a coarse aeolian silt with subdominant fine sand, TL-dated to 18600-3700+3700 years (QTL-ld and lf; Wintle 1981) and optically dated to 20000-7000+7000 and 26000-9000+10000 years (two samples; 738al and 741al; Smith et al. 1990). This material occurs in a variety of facies related to different modes of reworking. In the northern Scillies, the Porthloo Breccia is overlain by three units that are all related to a single glacial event. The Scilly Till, a massive, poorly sorted, clay-rich pale brown diamicton containing abundant striated and faceted erratics of northern derivation, occurs at Bread and Cheese Cove, and Pernagie and White Island Bars. This sediment is of uncertain depositional facies, although the available data suggest that it may be a lodgement till. At Bread and Cheese Cove the Scilly Till occurs in association with a matrix-supported sandy gravel, the Tregarthen Gravel, which has an erratic assemblage consistent with the underlying Till. The distributional relation between the glacially derived sediments, marine bars and morphological varieties of granite tors suggest that some of the bars may be remnant moraines, and that the glacier was crosive in the northern Scillies. Aeolian loessic processes in association with the glacial advance resulted in the deposition of the Old Man Sandloess in the southern Scillies. The relative coarseness of this material is interpreted as a function of its proximity to glacially derived source material. The mineralogy of the Scilly Till is sufficiently similar to the Old Man Sandloess to suggest a genetic link between the two units. Overlying the Scilly Till and Tregarthen Gravel in the northern Scillies is the Hell Bay Gravel, an extremely widespread matrix-supported gravel containing a similar assemblage of striated and faceted erratics to the underlying Till, but alongside a considerable proportion of locally derived granitic material. The matrix of the Hell Bay Gravel is identical to colluvially reworked facies of the Old Man Sandloess. This material represents an initial phase of solifluction, post-dating the glacial event in which the Scilly Till, Tregarthen Gravel and Old Man Sandloess were mixed and transported downslope. In situations where these sediments were stripped from the land surface, weathered granite once again became the dominant raw material for solifluction, t

Scourse, J. D.

1991-12-01

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

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

Miidel, Avo

2007-03-01

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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 (valleys (5-15 km wide and valleys, where its thickness reaches 15-25 m. Sediment core analysis results and seismic facies reveal that the TST 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

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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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Ground-penetrating radar (GPR) stratigraphy of late-Pleistocene relict foredunes on a coastal barrier: Matakana Island, New Zealand  

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Matakana Island, North Island, New Zealand, forms a c. 24 km long barrier island between the Bay of Plenty and Tauranga Harbour, which it encloses. The island is of two distinct parts, with the larger seaward part comprising a Holocene sand barrier, extending parallel to the shoreline, and a harbourward (Pleistocene) part, adjoining the centre of the Holocene barrier. The Pleistocene section of the barrier consists of three terraces at 10, 40 and 70 m above sea level, although the precise process-origin and significance of the features are unknown. We focus on the relatively flat lowest (1.0-1.5 km wide) terrace, as oblique aerial photography indicates the presence of subdued ridges (amplitude 1 m) trending NW-SE, parallel to the current coastline. An investigation of this lower terrace using a 100 MHz pulseEKKO ground penetrating radar (GPR) along a 1 km SW-NE profile normal to the axis of the subdued ridges was undertaken. Following topographic correction, the profile revealed a continuous undulating reflector at 8-12 m depth, which corresponds with the low ridges visible on the surface. The ridge-and-swale nature of the reflector, coupled with the surface topography indicates it represents a relict foredune plain, mainly below present-day sea level. The age of the relict foredune plain is intriguing, with a maximum age of 780,000 due to the absence of Te Puna Ignimbrite, which is present on the higher terraces. Published maps indicate the lowest terrace is covered by lacustrine beds of the Matua Subgroup (minimum age c. 220,000 yr), yet it is difficult to reconcile the survival of ridge-and-swale foredune morphology under several metres of lacustrine deposits, suggesting that a tephra origin for the coverbeds is more likely. Nevertheless, the presence of a Pleistocene foredune plain slightly below present-day sea level indicates no significant long-term uplift, and possibly minor subsidence in this sector of the North Island.

Brook, M.; Shepherd, M.; Tinkler, R.; Williams, J.

2012-04-01

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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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Radiocarbon ages on late pleistocene loess stratigraphy of Nebraska and Kansas, Central Great Plains, U.S.A.  

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In the central Great Plains of the United States, radiocarbon dating of loess and buried soils is clarifying the late Quaternary loess chronology for the period 25,000 to 10,000 BP. Along Harland Lake, Nebraska, a soil developed in the Gilman Canyon Formation and overlain by Peoria Loess has radiocarbon ages on soil humates of 30,700 to 21,500 BP. At one site, two Picea charcoal bands in the lower meter of Peoria Loess have radiocarbon ages of 21,250 and 19,730 BP. Therefore, in the vicinity of Harlan Lake, deposition of Peoria Loess apparently began around 21,000 BP. Peoria Loess deposition appears to have been interrupted by an episode of river entrenchment prior to 12,600 BP. Spring activity shortly thereafter suggests that incision was coeval to an increase in effective moisture. The termination of Peoria Loess deposition is marked by the Brady Soil, which in the Harlan Lake area has radiocarbon ages on soil humates of 11,800 to 10,200 BP. Comparison of the Harlan Lake chronology with chronologies completed elsewhere in the central Great Plains reveals general synchrony among periods of pedogenesis and Peoria Loess deposition. Little is known, however, about vegetation conditions in the region when loess was accumulating. Charcoal has been noted chiefly in the basal Peoria Loess, suggesting that some trees were present during initial Peoria Loess deposition. The extent of this tree cover is unknown, however. Charcoal is rare in the middle and upper Peoria Loess.

Martin, Charles W.

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

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

Ekman, Sten R.

1998-09-01

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K-Ar age of the late Pleistocene eruption of Toba, North Sumatra  

International Nuclear Information System (INIS)

It is stated that the late Pleistocene eruption of Toba is the largest magnitude explosive eruption documented from the Quaternary. K-Ar dating of the uppermost unit of the Toba Tuff gives an age of approximately 75,000 yr. A chemically and petrographically equivalent ash layer in deep-sea cores helps calibrate the Stage 4-5 boundary of the standard oxygen isotope stratigraphy. A similar ash in Malaya that overlies finds of Tampan Palaeolithic tools indicates that they are older than 75,000 yr. (author)

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

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

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

1999-02-01

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Extended Late Pleistocene Sea Level Record  

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Several hundred new closed system 230Th/234U and radiocarbon dates and the addition of more cores and coral samples from the islands of Barbados, Kiritimati and Araki contribute to an enhanced sea level record for the late Pleistocene ranging from the present to 240,000 yrs BP. Application of more rigorous sample screening criteria, including redundant 231Pa/235U dates have resulted in more closed system ages and better sea level resolution. In addition, a multibeam survey has mapped an extensive glacial lowstand reef on a ridge south of Barbados that is capped by a set of pinnacle reefs that grew during the early deglaciation. Among our new observations, the more detailed Barbados sea level record now resolves a Younger Dryas still- stand and a sea level drop between 16,140 and 14,690, overlapping the timing of H1 by some age estimates. The coral ages bracketing melt water pulse 1A have been further refined to 14,082 +/- 28 yrs BP and 13,632 +/- 32 yrs BP (2-sigma). The Isotope Stage 3 interstadial ended with sea level near 87.5 meters below present at 29,500 years ago before dropping to full glacial levels. The last glacial sea level lowstand began as early as 26,000 yrs BP. Extensive dating of Marine Isotope Stage 3 interstadial reefs on the islands of Araki and Barbados have added considerable resolution to this time interval and reliably bracket lowstand intervals separating the interstadials. A new diagenesis model has improved our prospecting success for closed system ages from older reefs and added some critical dates to the sparse closed-system data set for MIS-5 and MIS-7 high stand reefs..

Fairbanks, R. G.; Cao, L.; Mortlock, R. A.

2006-12-01

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Late Pleistocene Variations in Oxygen Minimum Zone: Southern California Margin  

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Oceanic carbon cycling is strongly influenced by the Oxygen Minimum Zone (OMZ). Studies of sediments from ODP Sites 893 (~595m) and 1017 (~955m) demonstrate that the strength of the OMZ off the Southern California margin (between ~500 and ~1000m) has fluctuated on orbital and millennial time scales during the late Pleistocene, affecting the preservation of organic carbon in marine sediments. Existing records do not adequately describe the history over the depth range of the OMZ. To augment the existing depth transect, we generated oxygen isotope and benthic foraminiferal assemblage records from core NBP0206 JPC1 (755m) located near the center of the OMZ. The chronology for this core was determined using radiocarbon analyses and oxygen isotope stratigraphy. The planktonic d18O record correlates well with the orbital and millennial- scale fluctuations recorded in nearby ODP Holes 893 and 1017. Benthic d18O data reflect orbital variations in upper intermediate waters, including a decrease of 1.6 ‰ across the last glacial termination, implying a temperature increase of 1-2 deg C (after ice volume correction). The millennial scale isotopic oscillations recorded in Hole 893 are absent here. Benthic foraminiferal assemblages are sensitive recorders of bottom water oxygenation. On orbital time scales, the fauna record an oxic Marine Isotope Stage 3 and Last Glacial Interval (LGI), and a dysoxic Holocene, supporting previous interpretations of orbital scale ventilation changes in intermediate water depths. The benthic assemblages record as low oxygen intervals 9 of the 13 interstadials of the last 50ka. An absence of associated changes in the benthic d18O on millennial scales implies that the low oxygen interstadials largely reflect changes in surface productivity, similar to those seen at Hole 1017. Millennial scale intermediate water ventilation changes, as interpreted in Hole 893, occurred above the depth of this core. During the LGI and the stadials of MIS 3, the OMZ appears to have entirely disappeared on the Southern California margin. This has major implications for the cycling of oceanic carbon.

Murphy, D. P.; Kennett, J. P.; Southon, J. R.

2006-12-01

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BISON ANTIQUUS OCCURRENCE AND PLEISTOCENE-HOLOCENE STRATIGRAPHY, CANADA DEL BUEY, PAJARITO PLATEAU, NEW MEXICO  

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A Bison. (probable Bison antiguus) distal humerus fragment was found within a Pleistocene colluvial deposit on a hillslope above Canada del Buey near White Rock, New Mexico. The Bison fossil is preserved within a buried soil with an inferred age of ca. 50-100 ka, based on soil properties and on stratigraphic position below a deposit of ca. 50-60 ka EI Cajete pumice. This represents the second oldest dated Bison in New Mexico, and one of the few occurrences of this genus in the northern mountains of the state. It is also only the second record of a Pleistocene vertebrate from Los Alamos County, and is a rare occurrence of a pre-25 ka Bison fossil in good stratigraphic context. Hillslopes in the study area are underlain by a sequence of truncated Pleistocene and Holocene soils that are inferred to represent colluvial deposition and soil formation followed by erosion in the mid Pleistocene (buried soil 'b3'), the late Pleistocene (buried soil 'b2'), and the mid-to-late Holocene (buried soil 'b1'). The surface soil is developed in depOSits that overlie 600-800 year-old Ancestral Puebloan sites. Colluvium is dominated by relatively fine-grained (fine to very fine sand) slopewash colluvium deposited by overland flow, but also includes rocky colluvium on hillslopes below mesas. The fine-grained colluvium is likely derived mainly from reworking of eolian deposits. Episodic colluvial deposition appears to, at least in part, accompany and follow episodic eolian events, with intervening periods dominated by erosion and the development of truncated soils.

RENEAU, STEVEN L. [Los Alamos National Laboratory; DRAKOS, PAUL G. [Los Alamos National Laboratory; MORGAN, GARY S. [Los Alamos National Laboratory

2007-02-12

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Late Pleistocene drainage systems beneath Delaware Bay  

Science.gov (United States)

Analyses of an extensive grid of seismic-reflection profiles, along with previously published sedimentary data and geologic information from surrounding coastal areas, outline the ancestral drainage systems of the Delaware River beneath lower Delaware Bay. Major paleovalleys within these systems have southeast trends, relief of 10-35 m, widths of 1-8 km, and axial depths of 31-57 m below present sea level. The oldest drainage system was carved into Miocene sands, probably during the late Illinoian lowstand of sea level. It followed a course under the northern half of the bay, continued beneath the Cape May peninsula, and extended onto the present continental shelf. This system was buried by a transgressive sequence of fluvial, estuarine, and shallow-marine sediments during Sangamonian time. At the height of the Sangamonian sea-level transgression, littoral and nearshore processes built the Cape May peninsula southward over the northern drainage system and formed a contiguous submarine sedimentary ridge that extended partway across the present entrance to the bay. When sea level fell during late Wisconsinan time, a second drainage system was eroded beneath the southern half of the bay in response to the southerly shift of the bay mouth. This system, which continued across the shelf, was cut into Coastal Plain deposits of Miocene and younger age and included not only the trunk valley of the Delaware River but a large tributary valley formed by the convergence of secondary streams that drained the Delaware coastal area. During the Holocene rise of sea level, the southern drainage system was covered by a transgressive sequence of fluvial, estuarine, and paralic deposits that accumulated due to the passage of the estuarine circulation cell and to the landward and upward migration of coastal sedimentary environments. Some Holocene deposits have been scoured subsequently by strong tidal currents. The southward migration of the ancestral drainage systems beneath Delaware Bay is analogous to that found under nearby Chesapeake Bay. In both areas, shifts in the bay mouths and river courses have preserved the morphologies and sedimentary fill of former drainage systems and provided a clear record of major sea-level fluctuations. Data from this study demonstrate that important information concerning ancient estuarine environments can be derived from the locations and characteristics of former fluvial systems. ?? 1988.

Knebel, H. J.; Circe, R.C.

1988-01-01

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Late Pleistocene and Holocene hydrological change in central Indonesia from Lake Towuti, Sulawesi  

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The tropical Pacific plays a fundamentally important role in global climate change due to the interaction between the El Niño Southern Oscillation (ENSO), the Intertropical Convergence Zone (ITCZ), and the Asian monsoons. Indonesia sits at the heart of the tropical western Pacific, yet we have very few terrestrial paleoclimate records from Indonesia to evaluate hydrological changes in the tropical western Pacific during the last 21,000 years. Here we present new sediment piston core and seismic reflection data from Lake Towuti, a large tectonic lake in central Sulawesi, that document the region’s late Pleistocene to Holocene climate evolution. Lithologic and magnetic susceptibility variations in ten piston cores from the lake can be clearly correlated to acoustic reflectors in our seismic stratigraphy and document substantial, basin-wide variations in precipitation and surface runoff through time. Our provisional age model suggests wetter conditions than present in central Indonesia during the latest Pleistocene and early to mid-Holocene. This behavior is generally in phase with the northern hemisphere tropics, despite the near-equatorial (2.7 degrees South) location of our site, suggesting that early Holocene intensification of the Asian monsoon and northward migration of the tropical rain belt did not result in drier conditions at the equator. Multiproxy analyses of our new cores, including compound-specific stable isotope data, will further elucidate centennial- to millennial-scale climate variations in the region.

Russell, J. M.; Bijaksana, S.; Wattrus, N. J.; Noren, A. J.; Konecky, B.; Wicaksono, S. A.

2010-12-01

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Late Pleistocene braided rivers of the Atlantic Coastal Plain, USA  

Science.gov (United States)

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

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

2004-01-01

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

International Nuclear Information System (INIS)

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

19

Late Pleistocene and Holocene mammal extinctions on continental Africa  

Science.gov (United States)

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

Faith, J. Tyler

2014-01-01

20

Stratigraphy and Subaerial Exposure of Late Quaternary Tidal Deposits in Haenam Bay, Korea (South-eastern Yellow Sea)  

Science.gov (United States)

Late Quaternary stratigraphy of the coastal deposits in Haenam Bay, south-western coast of Korea (south-eastern Yellow Sea) consists of two depositional units: a Holocene intertidal deposit (Unit I), and an underlying Late Pleistocene tidal deposit (Unit II), both of which are distinguished by distinct unconformity. The yellowish colour and more consolidated and oxidized nature are characteristics of the sediments in the upper part of Unit II. In spite of the lack of primary sedimentary structures, a conspicuous cryogenic structure was found in the upper part of Unit II, reflecting cold and dry conditions. The magnetic susceptibility enhancement in the upper part of Unit II added the possibility of pedogenesis during subaerial exposure. The upper part of Unit II is characterized by the deficiency of smectite and chlorite, in contrast to the clay mineral suites of Unit I and lower part of Unit II, which may be attributed to post-depositional and diagenetic alteration. The degree of weathering measured by the chemical index of alteration shows that the removal of labile minerals by leaching also occurred in the upper part of Unit II. Thus, the upper part of this unit appears to have undergone subaerial exposure and weathering during low sea-level stands. The supporting evidence of the sediment properties, including sediment colour and structure, water contents and shear strength, geochemical and clay mineralogical data, and magnetic susceptibility, provides the potential signature of the subaerial exposure and weathering of Late Pleistocene sediments in the tidal-dominated Haenam Bay sedimentary basin.

Park, Y. A.; Lim, D. I.; Khim, B. K.; Choi, J. Y.; Doh, S. J.

1998-10-01

21

Strontium isotope stratigraphy and geochemistry of the late Neogene ocean  

International Nuclear Information System (INIS)

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

22

Seismic sequence stratigraphy and depositional history of the Pliocene-Pleistocene fans in the Ganal Block, offshore Kutai Basin, Indonesia  

Science.gov (United States)

A seismic stratigraphy study was conducted to develop a stratigraphic framework for Pliocene-Pleistocene sediments in the Ganal area, Makassar Strait, Indonesia. The study area, physiographically located in the continental slope of the offshore Kutai basin, is very attractive for deep water sequence stratigraphy analysis. The sediment interval exhibits a series of geologic features of deep water sedimentation such as a submarine fan associated with canyons and channels-levees complex. Analysis of over 4000 km of multichannel seismic data serves to detail documentation of such features and the stratigraphic evolution of the area. On the basis of their termination patterns, two types of significant stratigraphic surfaces, unconformity and flooding surfaces, can be identified as seismic boundaries on the seismic sections. The unconformity surfaces can be recognized by erosional, truncation, and onlap termination patterns. The distribution of these surface can be correlated in the area from the slope to the basin floor, which is commonly associated with scour channels. The flooding surfaces can be recognized by downlap termination patterns of the younger layers into the older strata below. Both of these surfaces provide important information to reveal the depositional history of the deep water sedimentation in the study area. Regional seismic profiles indicate that the Pliocene-Pleistocene sediments were deposited in the slope to basin floor setting, from the west to the east respectively. The structural and stratigraphic analysis suggests that this basin configuration strongly influenced the distribution and thickness of the seismic sequences and stratigraphic development of the Pliocene-Pleistocene sedimentary succession. Isochron maxima correspond to the depocenters that are close to sedimentary pathways and are associated with submarine channels and canyons. The isochron patterns show that depocenters and sediment pathways during deposition of the Pliocene-Pleistocene interval coincide with regional basin setting. Six seismic sequences have been identified within the Pliocene-Pleistocene interval. Each sequence consists of lowstand deposits that can be recognized by its seismic facies units. The seismic characteristics vary from sequence to sequence as well as within lowstand system tracts. Lowstand features including submarine canyons, channels, and fan lobes have been identified and mapped. Identification of these features substantially reduces the reservoir risk associated with deep water depositional environments. The canyons, channels, and fan lobes in the study area were superimposed and presented in the composite map and served as a good model and unique example for deep water sedimentation. Finally, a depositional model of lowstand deposits for the study area has been established and may play an important role in future exploration and development in this region and elsewhere in the world.

Alam, Syamsu

23

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

24

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.

2014-04-01

25

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

26

Late Pleistocene and Holocene environments in the Nile basin  

Science.gov (United States)

Owing to the very gently sloping nature of the flood plain in the lower White Nile valley, which is underlain by a former lake-bed, the depositional record in that area is unusually well preserved. In Egypt and along the Blue Nile phases of erosion have destroyed segments of the sedimentary record, but the White Nile sequence is a good proxy for both the main Nile and the Blue Nile. During the last 15 ka, at least, times of high flow in the Blue Nile and main Nile were synchronous with those in the White Nile. Not all the White Nile flood deposits have been preserved but calibrated radiocarbon dates obtained on fossil freshwater and amphibious Pila shells and fish bones indicate that White Nile levels were high around 14.7-13.1 ka, 9.7-9.0 ka, 7.9-7.6 ka, 6.3 ka and 3.2-2.8 ka. The Blue Nile record is more fragmentary and that of the main Nile even more so except for the Holocene Nile delta. Calibrated radiocarbon ages for high Blue Nile flows indicate very high flood levels towards 13.9-13.2 ka, 8.6 ka, 7.7 ka and 6.3 ka. Incision by the Blue Nile and main Nile has caused progressive incision in the White Nile amounting to at least 4 m since the terminal Pleistocene ˜ 15 ka ago and at least 2 m over the past 9 ka. The Blue Nile seems to have cut down at least 10 m since ˜ 15 ka and at least 4 m since 9 ka. The time-transgressive and relatively late inception of plant domestication in the Nile valley may partly reflect this history of incision. Nile incision would propagate upstream into the White Nile valley, draining previously swampy areas along the valley floor, which would then become accessible to cultivation.

Williams, Martin A. J.

2009-10-01

27

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

28

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

29

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

Science.gov (United States)

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

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

2008-12-01

30

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

31

Stratigraphy of the late Cenozoic sediments beneath the 216-B and C crib facilities  

International Nuclear Information System (INIS)

The stratigraphy of the late Cenozoic sediments beneath the 216-B and C Crib Facilities is presented as lithofacies cross sections and is based on textural variations of the sedimentary sequence lying above the basalt bedrock. The primary source of data in this study is geologic information obtained from well drilling operations and geophysical logging. Stratigraphic interpretations are based primarily on textural analysis and visual examination of sediment samples and supplemented by drillers logs and geophysical logs

32

Stratigraphy of the late Cenozoic sediments beneath the 216-A Crib Facilities  

International Nuclear Information System (INIS)

The stratigraphy of the late Cenozoic sediments beneath the 216-A Crib Facilities is presented as lithofacies cross sections and is based on textural variations of the sedimentary sequence lying above the basalt bedrock. The primary source of data in this study is geologic information obtained from well drilling operations and geophysical logging. Stratigraphic interpretations are based primarily on textural analysis and visual examination of sediment samples and supplemented by drillers logs and geophysical logs

33

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

34

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.)

35

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. Am J Phys Anthropol 156:224-240, 2015. © 2014 Wiley Periodicals, Inc. PMID:25329008

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

2015-02-01

36

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

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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

38

Origin of late pleistocene formation water in Mexican oil reservoirs  

International Nuclear Information System (INIS)

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

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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

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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

41

Late Cenozoic structure and stratigraphy of south-central Washington  

Energy Technology Data Exchange (ETDEWEB)

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.

Reidel, S.P. [Westinghouse Hanford Co., Richland, WA (United States)]|[Washington State Univ., Pullman, WA (United States). Dept. of Geology; Campbell, N.P. [Yakima Valley Coll., WA (United States); Fecht, K.R.; Lindsey, K.A. [Westinghouse Hanford Co., Richland, WA (United States)

1993-09-01

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Late Cenozoic structure and stratigraphy of south-central Washington  

International Nuclear Information System (INIS)

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

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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

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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

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Surficial geology and stratigraphy of Pleistocene Lake Manix, San Bernardino County, California  

Science.gov (United States)

Pluvial Lake Manix and its surrounding drainage basin, in the central Mojave Desert of California, has been a focus of paleoclimate, surficial processes, and neotectonic studies by the U.S. Geological Survey (USGS) since about 2004. The USGS initiated studies of Lake Manix deposits to improve understanding of the paleoclimatic record and the shifts in atmospheric circulation that controlled precipitation in the Mojave Desert. Until approximately 25,000 years ago, Lake Manix was the terminus of the Mojave River, which drains northeasterly from the San Bernardino Mountains; the river currently terminates in the Soda Lake and Silver Lake playas. Pleistocene Lake Manix occupied several subbasins at its maximum extent. This map focuses on the extensive exposures created by incision of the Mojave River and its tributaries into the interbedded lacustrine and alluvial deposits within the central (Cady) and northeastern (Afton) subbasins of Lake Manix, and extends from the head of Afton Canyon to Manix Wash. The map illuminates the geomorphic development and depositional history of the lake and alluvial fans within the active tectonic setting of the eastern California shear zone, especially interactions with the left-lateral Manix fault. Lake Manix left an extraordinarily detailed but complex record of numerous transgressive-regressive sequences separated by desiccation and deposition of fan, eolian, and fluvial deposits, and punctuated by tectonic movements and a catastrophic flood that reconfigured the lake basin. Through careful observation of the intercalated lacustrine and fan sequences and by determining the precise elevations of unit contacts, this record was decoded to understand the response of the lake and river system to the interplay of climatic, geomorphic, and tectonic forces. These deposits are exposed in steep badland topography. Mapping was carried out mostly at scales of 1:12,000, although the map is presented at 1:24,000 scale, and employs custom unit nomenclature, with multiple subdivided lacustrine and alluvial fan units. In addition, many important units are very thin and cannot be mapped separately, or are covered by thin eolian sand, so these are commonly portrayed as stacks of units or combined units. These details are more accurately portrayed in the measured sections that accompany the map. Altitudes of many contacts were obtained using differentially corrected Global Positioning System (GPS) or, in some cases, lidar (light detection and ranging) data.

Reheis, Marith C.; Redwine, Joanna R.; Wan, Elmira; McGeehin, John P.; VanSistine, D. Paco

2014-01-01

46

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

OpenAIRE

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

DILIAN GEORGIEV; SLAVEYA STOYCHEVA

2010-01-01

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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

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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

49

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

50

Late Pleistocene and Holocene History at Mubwindi Swamp, Southwest Uganda  

Science.gov (United States)

Deposits beneath Mubwindi Swamp provide a partial record of vegetation history since at least 43,000 yr ago. We studied pollen from two cores and obtained nine radiocarbon ages from one of these cores and three radiocarbon ages from the other. Pollen deposited before and soon after the last glacial maximum represents vegetation very different from the modern vegetation of the Mubwindi Swamp catchment. Although species now associated with higher altitudes were dominant some elements of moist lower montane forest persisted, possibly because of favorable soils or topography. The pollen data provides evidence for a late glacial montane forest refuge near Mubwindi Swamp. Moist lower montane forest became much more widespread soon after the glacial maximum. The only irrefutably Holocene sediments from Mubwindi Swamp date to the past 2500 yr. During this time a combination of climatic and human-induced changes in vegetation can be seen in the pollen records.

Marchant, Robert; Taylor, David; Hamilton, Alan

1997-05-01

51

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

52

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

53

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

54

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

Science.gov (United States)

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

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

2013-12-01

55

Late Pleistocene Estuarine Channel-Fill Sediments on the New Jersey Shelf: Response to Glacio-eustatic Sea Level Rise  

Science.gov (United States)

The shallow New Jersey continental shelf has been an area of study for many decades. Evidence for the shelf's response to the Late Pleistocene glacio-eustatic sea level rise, confined principally to interpreted estuarine fill strata within fluvial channel systems, has been imaged extensively with high resolution chirp seismic data. However, little work has been done on sediment samples of these units. This study aids in the ground truthing of previous seismic stratigraphic work done on the New Jersey shelf channel-fill sediments by analyzing cores collected during the summer of 2007. The infilled channels from the study area are characterized as fossil riverine systems that developed on the exposed shelf during the Last Glacial Maximum lowstand ~18 ka. Subsequent sea level rise ~15-10 ka flooded and modified the valleys, forming estuaries. Allen and Posamentier's (1993) stratigraphic model of transgressive estuarine deposition posits the following ordered sequence: (1) a fluvial lag deposit, (2) estuarine mixed sands and muds (3) basin fill mud, and finally (4) estuarine mouth complex sediments. Seismic data over the buried channels on the outer New Jersey shelf (~80 m water depth) exhibit clearly identifiable seismic facies bounded by mostly horizontal boundaries that can be correlated to this interpretation (Nordfjord et al. 2006) We collected one core into these sediments, which likely sampled the estuarine mouth complex and basin fill muds. Previously collected cores supplement our analysis of these sediments. Seismic data over mid-shelf (~30 m water depth) valley channel fill stratigraphy is strikingly different, with finely-laminated U-shaped layering throughout the section, and often with cut-and-fill sequences. We collected 7 cores into these sediments. The cores ranged from 25cm to 5.8m in length. Thus far we have conducted grain size analysis via gross division of the percent of sand, silt, and clay. Initial results indicate that the laminated mid-shelf channel fill units are dominated by fine sands, suggesting a much higher-energy estuarine environment than when the outer-shelf channels were filled. Further grain size analysis will be conducted by sedigraph and settling tube. Radiocarbon analysis of the stratigraphy is being provided by the shell fragments and organic mud within the samples. We obtained one reliable shell fragment 14C date of 9389 ±79 years and eight bulk carbon 14C dates ranging from 10975 to 11445 years, with a strong terrestrial signature. The foraminiferal assemblages found within the sediment samples should eventually aid in determining the depositional environment.

Stackhouse, S.; Goff, J. A.; Christensen, B. A.; Austin, J. A.

2008-12-01

56

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

57

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

58

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

International Nuclear Information System (INIS)

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

59

Intestinal contents of a late Pleistocene mastodont from midcontinental north America  

Science.gov (United States)

Salvage excavations of a nearly complete and remarkably well-preserved skeleton of an American mastodont ( Mammut americanum) in Licking County, Ohio, yielded a discrete, cylindrical mass of plant material found in association with articulated vertebrae and associated ribs. This material is interpreted as intestinal contents of the mastodont and paleobotanical analyses indicate that the mastodont diet included significant amounts of low, herbaceous vegetation. Enteric bacteria ( Enterobacter cloacae), isolated from a sample of this material, are believed to represent survivors or descendants of the intestinal microflora of the mastodont. This is the first report of the isolation of bacteria associated with late Pleistocene megafauna.

Lepper, Bradley T.; Frolking, Tod A.; Fisher, Daniel C.; Goldstein, Gerald; Sanger, Jon E.; Wymer, Dee Anne; Ogden, J. Gordon; Hooge, Paul E.

1991-07-01

60

The late Pleistocene glacial sequence in the middle Maruia valley, southeast Nelson, New Zealand  

International Nuclear Information System (INIS)

Glacial and fluvioglacial landforms and deposits preserved in the middle reaches of the Maruia valley, southeast Nelson, New Zealand, record the activity of the Maruia glacier during the late Pleistocene Otira Glaciation. Five advances are recognised, from oldest to youngest: Creighton 1, 2, 3, and the Reid Stream 1, 2 advances. There was an interstadial interval between the Creighton 3 and Reid Stream 1 advances. The Reid Stream 1 advance occurred shortly after 14 800 years B.P. (NZ536, old T/sub 0.5/). (auths)

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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

62

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

63

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

64

Late Pleistocene and Holocene landscape formation in a gully catchment area in Northern Hesse, Germany  

DEFF Research Database (Denmark)

Permanent gully channels under forest are common geomorphological features in Central European low mountain areas. In the Rehgraben/Fuchslöchergraben gully catchment in Northern Hesse, Germany the Late Pleistocene landscape formation is reconstructed based on periglacial cover beds. In addition, the Holocene landscape development and soil erosion history are investigated using anthropogenic soil sediments and alluvial fan sediments. Until now, a combination of these approaches has not been applied to a gully catchment to this extent. The distribution of the different Quaternary sediments enables the differentiation between Pleistocene and Holocene landforms. Radiocarbon and optically stimulated luminescence dating are applied to add numerical data to the relative ages of the sediments and landforms. The gully channels are oriented along Pleistocene depressions that are built up of periglacial cover beds and intercalated reworked loess. As the gully channels cut through the periglacial cover beds, especially the upper layer, the gully system is of Holocene age. At least two phases of gully erosion are identified in the alluvial fan sediments. The initial gully erosion is dated to the time span between the Late Bronze Age and Roman Times. A second gully erosion phase is dated to the 14th century and may be correlated to the severe precipitation events during this time. Gully erosion started during the Younger Holocene and is connected to human settlement and land use activity. The intense human impact hampers the application of the concept of periglacial cover beds to reconstruct landscape formation and limits it to areas where the periglacial upper layer is still preserved. © 2014 Elsevier Ltd and INQUA. All rights reserved.

Döhler, Susanne; Damm, Bodo

2014-01-01

65

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

66

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

Science.gov (United States)

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

Teale, Chelsea L.; Miller, Norton G.

2012-07-01

67

Extraordinary incidence of cervical ribs indicates vulnerable condition in Late Pleistocene mammoths  

Directory of Open Access Journals (Sweden)

Full Text Available The number of cervical vertebrae in mammals is highly conserved at seven. We have shown that changes of this number are selected against due to a coupling with major congenital abnormalities (pleiotropic effects. Here we show that the incidence of abnormal cervical vertebral numbers in Late Pleistocene mammoths from the North Sea is high (33.3% and approximately 10 times higher than that of extant elephants (3.6%. Abnormal numbers were due to the presence of large cervical ribs on the seventh vertebra, which we deduced from the presence of rib articulation facets on sixth (posterior side and seventh (anterior side cervical vertebrae. The incidence of abnormal cervical vertebral numbers in mammoths appears to be much higher than in other mammalian species, apart from exceptional sloths, manatees and dugongs and indicates a vulnerable condition. We argue that the increased incidence of cervical ribs in mammoths is probably caused by inbreeding and adverse conditions that impact early pregnancies in declining populations close to extinction in the Late Pleistocene.

Jelle W.F. Reumer

2014-03-01

68

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

69

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

70

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

71

Late Pleistocene alluvial plain sedimentation in Lower Narmada Valley, Western India: Palaeoenvironmental implications  

Science.gov (United States)

Late Pleistocene fluvial sediments that were deposited in a slowly sinking basin are now exposed as 30-50 m high incised vertical cliffs all along the Lower Narmada Valley in western India. The exposed fluvial deposits have been classified into two sediment packages, alluvial fan sediments overlain by alluvial plain sediments. The alluvial plain sequence has not been studied previously. It consists mainly of sands and silts and is dominated by overbank deposits. Occurrence of large scale bedforms in the alluvial plain sequence points to the existence of a large sand bed river in an alluvial plain setting. The major sedimentary facies in stratigraphic order include large channel fills, giant epsilon cross bedded strata, overbank fines occurring in horizontal, massive and undulatory stratified forms associated with crevasse splay and backswamp deposits, and a reddish brown palaeosol overlain by thinly stratified sands and silts at the top of the exposed sediment succession. Large sized channel fills occur at two stratigraphic levels, which are morphologically similar and are indicative of high rates of deposition and avulsion. The large channel fill structures and the giant epsilon cross bedded strata indicate a large single channel river that was consistently 10-15 m deep and about 70-80 m wide even during the dry seasons. These dimensions are larger than those of the present day Narmada River at low discharge levels. The overbank sediments indicate rapid deposition through frequent overbank floods and floodplain aggradation by a laterally shifting river. Available chronologic data suggests that the reddish brown palaeosol correlates with a regional phase of pedogenesis in the alluvial plain of Gujarat prior to the Last Glacial Maximum (LGM). The thinly stratified sands and silts overlying the palaeosol were deposited by a considerably depleted but perennial river during the arid phase of the Last Glacial Maximum. Overall, the alluvial plain sediments of the Lower Narmada valley, particularly those below the palaeosol, have been attributed to a hyper-avulsive large river with low sinuosity whose high discharge levels were determined primarily by a large catchment area further to the east and not by the semiarid climate prevailing in the Gujarat alluvial plain during the upper part of the Late Pleistocene. The study concludes that the Narmada River has maintained a large catchment at least since the last 100 ka, however, the river was characterised by a much bigger channel during much of the Late Pleistocene with discharge levels higher than the present day.

Bhandari, S.; Maurya, D. M.; Chamyal, L. S.

2005-01-01

72

Timing and dynamics of Late Pleistocene mammal extinctions in southwestern Australia.  

Science.gov (United States)

Explaining the Late Pleistocene demise of many of the world's larger terrestrial vertebrates is arguably the most enduring and debated topic in Quaternary science. Australia lost >90% of its larger species by around 40 thousand years (ka) ago, but the relative importance of human impacts and increased aridity remains unclear. Resolving the debate has been hampered by a lack of sites spanning the last glacial cycle. Here we report on an exceptional faunal succession from Tight Entrance Cave, southwestern Australia, which shows persistence of a diverse mammal community for at least 100 ka leading up to the earliest regional evidence of humans at 49 ka. Within 10 millennia, all larger mammals except the gray kangaroo and thylacine are lost from the regional record. Stable-isotope, charcoal, and small-mammal records reveal evidence of environmental change from 70 ka, but the extinctions occurred well in advance of the most extreme climatic phase. We conclude that the arrival of humans was probably decisive in the southwestern Australian extinctions, but that changes in climate and fire activity may have played facilitating roles. One-factor explanations for the Pleistocene extinctions in Australia are likely oversimplistic. PMID:21127262

Prideaux, Gavin J; Gully, Grant A; Couzens, Aidan M C; Ayliffe, Linda K; Jankowski, Nathan R; Jacobs, Zenobia; Roberts, Richard G; Hellstrom, John C; Gagan, Michael K; Hatcher, Lindsay M

2010-12-21

73

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

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in portuguese A distribuição geográfica de 27 espécies da megafauna de mamíferos herbívoros sul-americanos durante o Pleistoceno Superior foi analisada, visando à identificação de seus padrões de distribuição. A distribuição das espécies foi estudada com o uso do método pan-biogeográfico de análise de traços. Sei [...] s traços generalizados (TGs) e dois nós biogeográficos foram obtidos. Os TGs não superpõem completamente com as áreas de savana aberta presentes no Pleistoceno, nem com os traços bióticos de alguns artrópodes típicos de clima árido, indicando que estes animais evitavam ambiente árido. De um modo geral, os TGs coincidiram com algumas das províncias biogeográficas definidas com base em táxons viventes, indicando que certos padrões de distribuição atuais já existiam no Pleistoceno. Os nós biogeográficos coincidiram com as bordas entre as principais formações vegetais do Pleistoceno, mostrando que o tipo de vegetação teve grande influência na distribuição da megafauna mamaliana. O nó 1 confirmou a existência de zonas de contato entre regiões paleobiogeográficas próximo à borda Argentina-Uruguai. O nó 2 conecta as regiões intertropicais brasileiras. Abstract in english The geographic distribution of 27 species of the South American megafauna of herbivore mammals during the Late Pleistocene was analyzed in order to identify their distributional patterns. The distribution of the species was studied using the panbiogeographical method of track analysis. Six generaliz [...] ed tracks (GTs) and two biogeographic nodes were obtained. The GTs did not completely superpose with the areas of open savanna present in Pleistocene, nor with the biotic tracks of some arthropods typical of arid climate, indicating that these animals avoided arid environment. Overall, the GTs coincided with some biogeographic provinces defined on the basis of living taxa, indicating that certain current distributional patterns already existed in Pleistocene. The biogeographic nodes coincided with the borders between the main vegetal formations of the Pleistocene, showing that the type of vegetation had great influence in the distribution of the mammalian megafauna. The node 1 confirmed the existence of contact zones between paleobiogeographic regions near Argentina-Uruguay border. The node 2 connects the Brazilian Intertropical regions.

VALERIA, GALLO; LEONARDO S., AVILLA; RODRIGO C.L., PEREIRA; BRUNO A., ABSOLON.

2013-06-01

74

ENSO-like forcing on oceanic primary production during the Late Pleistocene.  

Science.gov (United States)

Late Pleistocene changes in oceanic primary productivity along the equator in the Indian and Pacific oceans are revealed by quantitative changes in nanoplankton communities preserved in nine deep-sea cores. We show that variations in equatorial productivity are primarily caused by glacial-interglacial variability and by precession-controlled changes in the east-west thermocline slope of the Indo-Pacific. The precession-controlled variations in productivity are linked to processes similar to the Southern Oscillation phenomenon, and they precede changes in the oxygen isotopic ratio, which indicates that they are not the result of ice sheet fluctuations. The 30,000-year spectral peak in the tropical Indo-Pacific Ocean productivity records is also present in the Antarctica atmospheric CO2 record, suggesting an important role for equatorial biological productivity in modifying atmospheric CO2. PMID:11577233

Beaufort, L; de Garidel-Thoron, T; Mix, A C; Pisias, N G

2001-09-28

75

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

76

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

77

Carbon cycle instability as a cause of the late Pleistocene ice age oscillations - Modeling the asymmetric response  

Science.gov (United States)

A dynamical model of the Pleistocene ice ages is presented, which incorporates many of the qualitative ideas advanced recently regarding the possible role of ocean circulation, chemistry, temperature, and productivity in regulating long-term atmospheric carbon dioxide variations. This model involves one additional term (and free parameter) beyond that included in a previous model (Saltzman and Sutera, 1987), providing the capacity for an asymmetric response. It is shown that many of the main features exhibited by the delta(O-18)-derived ice record and the Vostok core/delta(C-13)-derived carbon dioxide record in the late Pleistocene can be deduced as a free oscillatory solution of the model.

Saltzman, Barry; Maasch, Kirk A.

1988-01-01

78

Incised palaeo-channels of the late Middle Pleistocene Thames: age, origins and implications for fluvial palaeogeography and sea-level reconstruction in the southern North Sea basin  

Science.gov (United States)

Multidisciplinary investigations of the infills of steeply-incised buried channels on the coast of Essex, England, provide important insights into late Middle Pleistocene climate and sea-level change and have a direct bearing on the differentiation of MIS 11 and MIS 9 in terrestrial records. New data are presented from Rochford and Burnham-on-Crouch where remnants of two substantial palaeo-channels filled with interglacial sediment can be directly related to the terrace stratigraphy of the Thames. The sediments in both channels accumulated in an estuarine environment early in an interglacial when mixed oak forest was becoming established. Lithological evidence suggests that the interglacial beds post-date the brackish-water infill of an older palaeo-channel ascribed to the Hoxnian and correlated with part of MIS 11, and pre-date terrace gravels (Barling Gravel) ascribed to MIS 8. An MIS 9 attribution is supported by molluscan biostratigraphy, palaeo-salinity and amino-acid racemization data. The relative sea-level record in this area thus includes evidence for two major marine transgressions during MIS 11 and MIS 9, with local maxima of >10 m O.D. Both are associated with sediments that show 'Hoxnian' palynological affinities. The wider significance of these findings, and of an intermediate phase of pronounced fluvial incision during MIS 10, is discussed.

Roe, Helen M.; Preece, Richard C.

2011-09-01

79

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

80

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

81

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

82

Late Pleistocene flank collapse of Zempoala volcano (Central Mexico) and the role of fault reactivation  

Science.gov (United States)

Zempoala is an extinct Pleistocene (˜ 0.7-0.8 Ma) stratovolcano that together with La Corona volcano (˜ 0.9 Ma) forms the southern end of the Sierra de las Cruces volcanic range, Central Mexico. The volcano consists of andesitic and dacitic lava flows and domes, as well as pyroclastic and epiclastic sequences, and has had a complex history with several flank collapses. One of these collapses occurred during the late Pleistocene on the S-SE flank of the volcano and produced the Zempoala debris avalanche deposit. This collapse could have been triggered by the reactivation of two normal fault systems (E-W and NE-SW), although magmatic activity cannot be absolutely excluded. The debris avalanche traveled 60 km to the south, covers an area of 600 km 2 and has a total volume of 6 km 3, with a calculated Heim coefficient (H/L) of 0.03. Based on the textural characteristics of the deposit we recognized three zones: proximal, axial, and lateral distal zone. The proximal zone consists of debris avalanche blocks that develop a hummocky topography; the axial zone corresponds with the main debris avalanche deposit made of large clasts set in a sandy matrix, which transformed to a debris flow in the lateral distal portion. The deposit is heterolithologic in composition, with dacitic and andesitic fragments from the old edifice that decrease in volume as bulking of exotic clasts from the substratum increase. Several cities (Cuernavaca, Jojutla de Juárez, Alpuyeca) with associated industrial, agricultural, and tourism activities have been built on the deposit, which pose in evidence the possible impact in case of a new event with such characteristics, since the area is still tectonically active.

Arce, José Luis; Macías, Rodolfo; García Palomo, Armando; Capra, Lucia; Macías, José Luis; Layer, Paul; Rueda, Hernando

2008-11-01

83

Middle-Late Pleistocene polycyclic evolution of a stable coastal area (southern Apulia, Italy)  

Science.gov (United States)

The Otranto-Leuca coastal tract is marked by the presence of numerous sea caves placed close to present sea level. They are located generally at the back of a shore platform covered by a sequence of breccia deposits, marine sediments and speleothems. At Grotta di Masseria dell'Orte, marine cemented sands rest on a narrow shore platform at about 6.2 m above mean sea level and are covered by speleothems older than 185 ka. At Grotta del Diavolo, which is mostly filled by breccia deposits, three beach levels have been detected at about 3.0, 3.5 and 5.9 m above msl. They are either covered by or overlie speleothems that yield an U/Th age of 340, 78 ka and between 170.3 and 146.5, respectively. Geomorphological evidence and radiometric ages indicate that the area after a period of uplift has been tectonically stable since the last part of the Middle Pleistocene so that marine landforms close to the present shoreline underwent a polycyclic evolution. The sedimentary fills of sea caves formed during Middle-Late Pleistocene glacial stages, when arid or semiarid conditions promoted the removal of regolith and the development of thick breccia deposits. During Marine Isotope Stages (MIS) 9.3, 5.5 and 5.1, cave sediments were partially eroded whereas beach layers and related speleothems developed. These are, in fact, the only marine isotope stages marked by a sea level position which in this Mediterranean region was either close to, or slightly higher than, the present one.

Mastronuzzi, Giuseppe; Quinif, Yves; Sansò, Paolo; Selleri, Gianluca

2007-05-01

84

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

85

Late Pleistocene and Holocene Glacial Evolution and Isotasy in the Antarctic Peninsula  

Science.gov (United States)

Employing a numerical model of Payne et al. that simulates the late-Pleistocene evolution of the former Antarctic Peninsula Ice Sheet (APIS) as a basis, we compute the present-day postglacial vertical isostasy of this region. The region may also experience significant mid-to late-Holocene glacial mass changes. Climate and oceanographic studies indicate that the ice mass imbalance of this region may be of larger magnitude that elsewhere in Antarctica. We compute the crustal response to these more recent ice mass changes and Holocene fluctuations with a simple gravitating Earth model consisting of an elastic lithosphere and a viscoelastic mantle (half-space). The calculations demonstrate that the present-day response could be significant, possibly at the level of about 4 - 11 mm/yr. Such significant crustal motion could be driven by glacial mass changes integrated over the last 1000 years if the regional mantle viscosity is below about 2 x 10(exp 20) Pa sec. In this lower viscosity range, present-day crustal motion has a significant phase-lagged character and the composite lithosphere/mantle viscoelastic response to late-Holocene events dominates over purely elastic (instantaneous) responses to present-day ice mass changes. For a higher mantle viscosity, greater than about 5 x 10(exp 20) Pa sec, the predicted present-day vertical isostasy is dominated by gravitational response to glacial unloading during the 18 - 6 kyr BP collapse of the APIS, and is analogous to that known to be occurring in the Gulf of Bothnia and Hudson Bay.

Ivins, E. R.; Raymond, Carol A.; Heflin, M. B.; James, T. S.

1989-01-01

86

Augustine Volcano's late Pleistocene rhyolite eruption and its modern-day residuum  

Science.gov (United States)

The pre-Holocene eruptive history of Augustine Volcano, the most active volcano in the populated Cook Inlet region of Alaska, is poorly known due to the effects of glaciation and voluminous products of Holocene eruptions that cover the majority of this island volcano. Among its oldest known deposits, thought to be latest Pleistocene in age, are a basalt-rhyolite hyaloclastite, which is interbedded with an overlying pumiceous rhyolite tephra fall, that crop out on the south side of the island (Waitt and Beget, 2009). Dense and pumiceous rhyolite clasts from the deposits are compositionally similar (71-74 wt. % SiO2; Larsen et al., 2010) and contain phenocrysts of plagioclase, quartz, amphibole, and Fe-Ti oxides. These basalt-rhyolite deposits are the most compositionally extreme products of the volcano; Holocene eruptions, including historical eruptions in 1976, 1986, and 2006, produced andesites and dacites. In 2006, one such eruption produced gabbro inclusions (54.4-60.2 wt% SiO2) that consist of plagioclase, amphibole, pyroxenes, Fe-Ti oxides, and small amounts of interstitial glass, suggesting a cumulate origin. Both the Pleistocene-age rhyolite and the 2006 gabbro inclusions fall along a whole-rock compositional trend depleted in incompatible elements relative to mid-Holocene-present andesites and dacites. To investigate differentiation and the timing of rhyolite magma generation at Augustine, we have determined high-spatial resolution 238U-230Th ages of zircon crystallization for the rhyolite as well as for the gabbros and high-silica andesites erupted in 2006. Sensitive high-resolution ion microprobe (SHRIMP-RG) analyses of indium-mounted, unpolished zircon rims from the rhyolite yield a single 238U-230Th isochron age of ca. 27 ka, which we interpret to reflect the final interval of crystallization immediately prior to eruption. Sectioned core ages for rhyolite zircon, however, fall into two populations: one at ca. 27 ka, and a second, smaller population that appears as old as ca. 50 ka. Thus zircon crystallization in the rhyolite dominantly occurred just prior to eruption, with subordinate entrainment of older antecrysts. Gabbro inclusions erupted in 2006 contain zircons with core 238U-230Th ages that are indistinguishable from the dominant rhyolite age of ca. 27 ka. A few small zircons from gabbros are in 238U-230Th secular equilibrium, yield U-Pb ages of ca. 80-1800 Ma, and are true xenocrysts inherited from basement rocks. Based on the similarity in zircon ages and whole-rock geochemical affinity between late Pleistocene rhyolite and 2006 gabbroic inclusions, we suggest that the rhyolite formed via melt extraction from an andesitic crystal mush, of which the 2006 gabbro xenoliths are the residuum. A scarcity of zircons older than ca. 50 ka suggests that Augustine may not be underlain by a long-lived magmatic system, or conversely, that small but frequent andesitic eruptions of the sort that occurred prior to and after the generation of the Pleistocene rhyolite do not allow for significant zircon crystallization. Larsen, J.F., et al., 2010, USGS Prof. Paper 1769, Chap. 15, p. 335-382 Waitt, R.B., and Beget, J.E., 2009, USGS Prof. Paper 1762

Coombs, M. L.; Vazquez, J. A.

2012-12-01

87

Late Pliocene/Early Pleistocene environments inferred from the Lake El'gygytgyn pollen record  

Science.gov (United States)

The Arctic is known to play a crucial role within the global climate system. The mid-Pliocene (3-3.5 Ma) is considered to be the most probable scenario of the future climate changes. However, reliable climate projections are hampered by the complexity of the underlying natural variability and feedback mechanisms. An important prerequisite for the validation and improvement of the future projections is a better understanding of the long-term environmental history of the Arctic. Unfortunately, formation of continuous paleoenvironmental records in the Arctic was widely restricted due to repeated glaciations. Continuous sequences that penetrate the entire Quaternary and further into the Pliocene are highly desired and would enable to validate the temperature rise during the mid-Pliocene that was proposed by former studies. Such a record has now become available from Lake El'gygytgyn (67º30'N, 172º05E') located in a meteorite impact crater in north-eastern Siberia. The impact nearly 3.6 Ma ago formed an 18 km wide hole in the ground that then filled with water. The retrieved lake sediments have trapped pollen from a several thousand square-kilometer source area providing reliable insights into regional and over-regional millennial-scale vegetation and climate changes of the Arctic since the Pliocene. The ''El'gygytgyn Drilling Project" of ICDP has completed three holes in the center of the lake, penetrating about 318 m thick lake sediments and about 200 m of the impact rocks below. Because of its unusual origin and high-latitude setting in western Beringia, scientific drilling at Lake El'gygytgyn offered unique opportunities for paleoclimate research, allowing time-continuous climatic and environmental reconstructions back into the Pliocene. Late Pliocene and Early Pleistocene pollen assemblages can be subdivided into 55 pollen zones, which reflect the main environmental fluctuations in the region 3.55-2.15 Ma BP. Pollen-based climate reconstructions show that conditions in the study area were the warmest about 3.55-3.4 Ma BP when spruce-pine-fir-hemlock-larch-Pseudotsuga forests dominated in nowadays tundra area. After ca 3.4 Ma BP dark coniferous taxa gradually disappeared from the vegetation. Very pronounced environmental changes are revealed about ca 3.35-3.275 Ma BP when treeless tundra and steppe habitats dominated. Treeless and shrubby environments are also indicative after ca 2.6 Ma. Dry and cold climate conditions were similar to those during the Late Pleistocene. The Early Pleistocene sediments contain pollen assemblages reflecting alternation of treeless intervals with cold and dry climate and warmer intervals when larch forests with stone pines, shrub alders and birches were also common in the region. Very dry environments are revealed after ca 2.175 Ma BP. High amounts of green algae colonies (Botryococcus) in the studied sediments point to shallow-water conditions ca 2.55, 2.45, and ca 2.175 Ma BP. Thus, pollen studies show that sediments accumulated in Lake El'gygytgyn are an excellent archive of environmental changes since 3.55 Myr BP. The record well reflects main regional paleoenvironmental fluctuations. The further high-resolution palynological study of the core will reveal climate fluctuations inside the main glacial/interglacial intervals and will give the first continuous and detailed scheme of environmental changes for a whole Arctic.

Andreev, Andrei; Wennrich, Volker; Tarasov, Pavel; Raschke (Morozova), Elena; Brigham-Grette, Julie; Nowaczyk, Norbert; Melles, Martin

2014-05-01

88

Late Pleistocene ice export events into the Arctic Ocean from the M'Clure Strait Ice Stream, Canadian Arctic Archipelago.  

OpenAIRE

Rapidly-flowing sectors of an ice sheet (ice streams) can play an important role in abrupt climate change through the delivery of icebergs and meltwater and the subsequent disruption of ocean thermohaline circulation (e.g., the North Atlantic's Heinrich events). Recently, several cores have been raised from the Arctic Ocean which document the existence of massive ice export events during the Late Pleistocene and whose provenance has been linked to source regions in the Canadian Arctic Archipe...

Stokes, C. R.; Clark, C. D.; Darby, D. A.; Hodgson, D. A.

2005-01-01

89

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

90

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

91

California condor associated with spruce-jack pine woodland in the late Pleistocene of New York  

Science.gov (United States)

A humerus, coracoid, and pedal phalanx of the California Condor, Gymnogyps californianus, were recovered from the Hiscock Site in western New York, in an inorganic stratum containing wood that is 11,000 radiocarbon years old. Associated vertebrates include mastodont, wapiti, and caribou. Pollen and plant macrofossils from the sediments indicate a spruce-jack pine woodland and a local, herb-dominated wetland community. Historic records (all from western North America) and previous late Pleistocene fossils of the California Condor are associated mainly with warm-temperate climates and floras. The New York fossils show that this bird was able to live in a colder climate and in a boreal, coniferous setting at a time when appropriate food (large mammal carrion) was available. The California Condor, which survives only in captivity, has suffered a greater reduction in geographical range than previously suspected. Much of this reduction in range probably occurred ca. 11,000 yr B.P. when the extinction many North American large mammals resulted in severely reduced availability of food for the California Condor and other large scavenging birds.

Steadman, David W.; Miller, Norton G.

1987-11-01

92

Evidence for Late Pleistocene-Holocene Activity along a Potential Seismic Source in southern Apennines (Italy)  

Science.gov (United States)

The Lucanian Apennines in southern Italy has experienced major and destructive earthquakes (Intensity * VIII) in 1561, 1694, 1826, 1857, 1980. Except for the 1980 Irpinia event for which coseismic faulting has been observed, no fault-event relationship has been definitely established for the rest of the mentioned earthquakes.Immediately south to the 1980 event zone and north to the 1857 one, a noteworthy area, where no clear relationship between seismogenic structures and historical seismic activity, has been identified. Structural and geomorphological analysis based on spot images, DEM, aerial photos interpretation and field observations, helped to point out 20 km length normal fault running on the western edge of two basins named Melandro and Pergola. The fault is composed by two main NNW-trending, ENE- dipping segments, showing an en-echelon pattern. The fault affects recent soft sediments, producing scarps up to 10 m high. Evidence for Late Pleistocene-Holocene tectonic activity along the trace were also observed at several outcrops and quarries, such as tilted and deformed colluvial and alluvial deposits. Radiocarbon dating from deformed sediments revealed a faulting age of at least 12 ka old. The far- and near- field data analysis and interpretations lead to consider this fault as a potential large earthquake source in this area.

Moro, M.; Amicucci, L.; Cinti, F. R.; Fawzi, D.; Montone, P.; Pierdominici, S.; Saroli, M.

2003-12-01

93

Implications for Late Pleistocene Mastodon Diet from Opal Phytoliths in Tooth Calculus  

Science.gov (United States)

Calculus removed from the molar teeth of four American mastodons (Mammut americanum) contained opal phytoliths which reflect major dietary components. Three samples contained abundant grass phytoliths (ca. 86% of total), with long cells and trapezoidal pooid short cells dominant (ca. 25 and 31%, respectively). Dicot phytoliths from hackberry (Celtis sp.) seeds and indeterminate deciduous trees were rare (1-3%), though well preserved, whereas phytoliths from conifer trees were not recognizable in any of the samples. Comparative analysis of calculus from modern and fossil browsers and mixed feeders implies that dicots and conifers are nearly invisible in the phytolith record. This scarcity may result from poor preservation, low silica production in woody taxa, and/or animals' selection of young, silica-poor leaves and shoots. However, abundant grass phytoliths in the mixed feeders suggest that presence versus absence of grass phytoliths may distinguish mixed feeders and grazers from browsers. Mastodons are traditionally considered browsers, but grass phytolith assemblages in three individual mastodons contained similarly high concentrations of pooids, suggesting that these grasses were a significant part of the diet. Abundant pooid phytoliths, in addition to diatoms, indicate that these mastodons grazed in a cool, moist late Pleistocene environment, possibly near water.

Gobetz, Katrina E.; Bozarth, Steven R.

2001-03-01

94

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

International Nuclear Information System (INIS)

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

95

Upper Cretaceous to Pleistocene sequence stratigraphy of the Beaufort-Mackenzie and Banks Island areas, Northwest Canada  

Energy Technology Data Exchange (ETDEWEB)

An understanding of the stratigraphy of the Beaufort-Mackenzie Basin is essential for evaluating the economic potential of this significant source of oil and gas, and for evaluating the environmental safeguards needed to produce those hydrocarbons. The Upper Cretaceous to Holocene sediments in the Beaufort-Mackenzie and Banks Island areas consist of clastic rocks deposited in deltaic, shelf, slope, and deep water environments. At the basin margin, alternating sandstone- and shale-dominant successions that can be classified into discrete lithostratigraphic units are present. Basinward, the succession is predominantly shale, and conventional lithostratigraphic units can be less readily identified. Sequence analysis has been used to identify stratigraphic units within the basin fill. Stratigraphic and facies interpretation of reflection seismic, well, and outcrop data form the main basis for identifying sequences, unconformities, maximum flooding surfaces, and internal depositional facies. Eleven regionally extensive sequences have been identified, many of which are associated with tectonic events. Paleogeographic reconstructions are attempted for various time periods and basic lithological descriptions and sedimentological interpretations are presented. 149 refs., 69 figs., 2 tabs.

Dixon, J.; Dietrich, J.R.; McNeil, D.H.

1992-01-01

96

Late Pleistocene and Holocene sedimentary facies on the Ebro continental shelf  

Science.gov (United States)

Late Pleistocene-Holocene history of the Ebro continental shelf of northeastern Spain is recorded in two main sedimentary units: (1) a lower, transgressive unit that covers the shelf and is exposed on the outer shelf south of 40??40???N, and (2) an upper, progradational, prodeltaic unit that borders the Ebro Delta and extends southward along the inner shelf. The lower transgressive unit includes a large linear shoal found at a water depth of 90 m and hardground mounds at water depths of 70-80 m. Some patches of earlier Pleistocene prodelta mud remain also, exposed or covered by a thin veneer of transgressive sand on the northern outer shelf. This relict sand sheet is 2-3 m thick and contains 9000-12,500 yr old oyster and other shells at water depths of 78-88 m. The upper prodelta unit covers most of the inner shelf from water depths of 20-80 m and extends from the present Ebro River Delta to an area to the southwest where the unit progressively thins and narrows. Interpretation of high-resolution seismic reflection data shows the following facies occurring progressively offshore: (1) a thick stratified facies with thin progradational "foresets beds", (2) a faintly laminated facies with sparse reflectors of low continuity, and (3) a thin transparent bottomset facies underlain by a prominent flat-lying reflector. Deposition in the northern half of the prodelta began as soon as the shoreline transgressed over the mid-shelf, but progradation of the southern half did not begin until about 1000-3000 yrs after the transgression. A classic deltaic progradational sequence is shown in the Ebro prodelta mud by (1) gradation of seismic facies away from the delta, (2) coarsening-upward sequences near the delta and fining-upward sequences in the distal mud belt deposits, and (3) thin storm-sand layers and shell lags in the nearshore stratified facies. The boundaries of the prodeltaic unit are controlled by increased current speeds on the outer shelf (where the shelf narrows) and by development of the shoreface sand body resulting from shoaling waves on the inner shelf. ?? 1990.

Diaz, J.; Nelson, C.H.; Barber, J.H., Jr.; Giro, S.

1990-01-01

97

Stratigraphy and U-series geochronology of Late Quaternary megatsunami deposits in Hawaii  

Science.gov (United States)

Our previous work on Kohala, Hawaii, established that the elevated marine basalt boulder conglomerates found there represent at least one, and probably two megatsunami events in the late Pleistocene. Together with the evidence for giant submarine landslides off western Hawaii island from contemporaneous flank failures of Mauna Loa volcano and identical sequences of submarine terraces off the NW coasts of the islands of Hawaii and Lanai, our hydrodynamic modeling indicates that all islands in the Hawaiian chain must have been affected by these giant waves. We present new dating of these deposits on Hawaii, Lanai and Maui islands together with stratigraphic interpretations of their impacts and origins. We used uranium-series dating of in situ coral clasts to constrain the age of the marine conglomerates, using multiple ion counting- inductively coupled plasma-mass spectrometry techniques, and used 87Sr/86Sr ratios of carbonates to help delineate their origins where marine fossils were absent. Southern Lanai records at least four megatsunami events: at 110 ka, 135 ka, 200 ka, and 240 ka, that likely correspond to the Alika phase 2, Alika phase 1, and two stages of the older South Kona giant submarine landslides. These event dates also correspond to O- isotopic stages 5d, 5e, 7a and 7b, and are in agreement with a changing-climate trigger mechanism for volcanic flank collapse proposed in previous work by ourselves and others. On southern Lanai, there is evidence for two megatsunami deposits in stratigraphic succession in the vicinity of Manele Bay, as well as higher-elevation deposits there containing reworked coral-bearing debris from two older megatsunami events. Coral clasts have been dated from all four events within the high-elevation gullies within Kaluakapo Crater on southern Lanai in this study and Moore and Moore (1988), indicating enormous runups to more than 626 m and wave heights of more than 240 m there that are in agreement with the latest hydrodynamic modeling. There is presently evidence for the 110 ka event on Hawaii, Lanai and West Maui, and for the 200 ka and 240 ka events on the islands of Lanai, Molokai and probably Hawaii. The 135 ka event has so far only been recorded on southern Lanai, but will likely turn up in future work elsewhere.

McMurtry, G. M.; Fryer, G. J.; Tappin, D. R.; Fietzke, J.

2008-12-01

98

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

99

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

100

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

101

A composite record of Late Pleistocene relative geomagnetic paleointensity from the Wilkes Land Basin (Antarctica)  

Science.gov (United States)

We report high-resolution paleomagnetic records obtained from six piston cores recovered on the continental rise of the Wilkes Land Basin (WLB), East Antarctica, in the frame of the Italian/Australian Wilkes Land Glacial History (WEGA) project. The studied cores, with a length of ca. 4 m each, were collected from the gentle and steep sides of sedimentary ridges present in the lower part of the continental rise, and consist of very fine-grained sediments. Paleomagnetic measurements were carried out on u-channel samples. Apart from a low-coercivity magnetic overprint, removed after the first steps of alternating field demagnetization, each core is characterized by a well defined characteristic remanent magnetization. Paleomagnetic inclinations fluctuate around the expected value (of ca. -77°) for such high latitude sites and always indicate normal magnetic polarity. Short period oscillations to anomalously shallow paleomagnetic inclinations (up to -20°) were identified at different levels of the sampled sequences; positive (reverse) inclination values were however not observed. Specific rock magnetic measurements indicate a substantial homogeneity of the magnetic mineralogy in the sampled sequences. For each core we reconstructed curves of relative paleointensity (RPI, as computed by NRM 20 mT / ? and NRM 20 mT /ARM 20 mT ) variation of the geomagnetic field. An original age model was established by tuning the individual RPI curves with the available global and regional reference RPI stacks. Paleomagnetic results, supported by other limited bio- and chronostratigraphic constraints, establish that all the cores are Late Pleistocene in age: two provide an expanded record of the last ca. 30 ka (PC18 and PC19), three span the last ca. 100, 200 and 300 ka (respectively, PC25, PC27 and PC26), and one reaches back to ca. 780 ka (PC20), approaching the Brunhes-Matuyama transition. Thus, the WEGA paleomagnetic record provides the first experimental data documenting the dynamics and amplitude of the geomagnetic field variations at high southern latitudes during the Brunhes Chron. The individual normalized RPI records were merged in a WEGA RPI stacking curve spanning the last 300 kyr. The comparison of the WEGA RPI individual and stacked curves with the global references RPI stacks shows that geomagnetic paleointensity variations, with periods longer than a few to tens kyr depending on the sedimentation rate, can be safely recognized in this sector of the peri-Antarctic margins. Furthermore, the stacking of the individual ChRM inclination records indicates that the recurrent swings to shallow paleomagnetic inclinations may be correlated to the main known geomagnetic excursions of the Brunhes Chron, supporting the validity of the age models. The reconstructed average sediment accumulation rates for the individual cores range from 0.6 to 19 cm/ka and are compatible with their position within the WLB, with the lowest rates found close to the ridge of the sedimentary drifts. Moreover, the high-resolution age models obtained in this study provide original constraints to assess chronology, rates and amplitudes of the climatic and environmental processes affecting this key area of the peri-Antarctic margins during the Late Pleistocene.

Macrì, Patrizia; Sagnotti, Leonardo; Dinarès-Turell, Jaume; Caburlotto, Andrea

2005-08-01

102

Morphological Chronoclines among Late Pleistocene Muskrats ( Ondatra zibethicus: Muridae, Rodentia) from Northern Florida  

Science.gov (United States)

The muskrat ( Ondatra zibethicus) is presumed to have undergone a rapid phyletic size decrease near the end of the Pleistocene. Evolutionary changes in the size of middle to late Wisconsinan (ca. 32,000-12,300 14C yr B.P.) muskrats from the Aucilla River, Jefferson County, Florida, were reconstructed by examining length and width of the lower first molar (m1). Body mass, estimated from m1 length, was relatively stable from 32,000 to 16,000 14C yr B.P. and decreased only slightly by 12,300 14C yr B.P. If the size trend found in the Aucilla River material is characteristic of the southeastern United States, a body size decrease after 12,300 14C yr B.P. is needed to explain the smaller size of modern populations. It was previously thought that the length/width (l/w) ratio of the muskrat m1 was a paleoenvironmental indicator based on its presumed correlation with latitude in modern populations. We examined the length and width of modern muskrats from several geographic regions and found only a very weak trend in the size of the m1 between northern and southern populations; however, highly significant differences were found between regions of similar latitude. Our data indicate that chronoclines in the m1 of the Aucilla muskrat material and other such documented trends among fossil muskrats have paleoenvironmental significance, but it is not yet clear which environmental variables can best be predicted from them.

Mihlbachler, Matthew C.; Hemmings, C. Andrew; Webb, S. David

2002-11-01

103

Sector collapses and large landslides on Late Pleistocene Holocene volcanoes in Kamchatka, Russia  

Science.gov (United States)

On Kamchatka, detailed geologic and geomorphologic mapping of young volcanic terrains and observations on historical eruptions reveal that landslides of various scales, from small (0.001 km 3) to catastrophic (up to 20-30 km 3), are widespread. Moreover, these processes are among the most effective and most rapid geomorphic agents. Of 30 recently active Kamchatka volcanoes, at least 18 have experienced sector collapses, some of them repetitively. The largest sector collapses identified so far on Kamchatka volcanoes, with volumes of 20-30 km 3 of resulting debris-avalanche deposits, occurred at Shiveluch and Avachinsky volcanoes in the Late Pleistocene. During the last 10,000 yr the most voluminous sector collapses have occurred on extinct Kamen' (4-6 km 3) and active Kambalny (5-10 km 3) volcanoes. The largest number of repetitive debris avalanches (> 10 during just the Holocene) has occurred at Shiveluch volcano. Landslides from the volcanoes cut by ring-faults of the large collapse calderas were ubiquitous. Large failures have happened on both mafic and silicic volcanoes, mostly related to volcanic activity. Orientation of collapse craters is controlled by local tectonic stress fields rather than regional fault systems. Specific features of some debris avalanche deposits are toreva blocks — huge almost intact fragments of volcanic edifices involved in the failure; some have been erroneously mapped as individual volcanoes. One of the largest toreva blocks is Mt. Monastyr' — a ˜ 2 km 3 piece of Avachinsky Somma involved in a major sector collapse 30-40 ka BP. Long-term forecast of sector collapses on Kliuchevskoi, Koriaksky, Young Cone of Avachinsky and some other volcanoes highlights the importance of closer studies of their structure and stability.

Ponomareva, Vera V.; Melekestsev, Ivan V.; Dirksen, Oleg V.

2006-11-01

104

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

International Nuclear Information System (INIS)

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

105

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

Science.gov (United States)

Previous bone collagen carbon and nitrogen isotopic studies of Late Pleistocene European cave bears (Ursus spelaeus) have shown that these bears frequently had low nitrogen isotope values, similar to those of herbivores and indicating either unusual physiology related to hibernation or a herbivorous diet. Isotopic analysis of animal bone from the Pe?tera cu Oase (Cave with Bones), Romania, shows that most of its cave bears had higher nitrogen isotope values than the associated herbivores and were, therefore, omnivorous. The Oase bears are securely identified as cave bears by both their morphology and DNA sequences. Although many cave bear populations may have behaved like herbivores, the Oase isotopic data demonstrate that cave bears were capable of altering their diets to become omnivores or even carnivores. These data therefore broaden the dietary profile of U. spelaeus and raise questions about the nature of the carnivore guild in Pleistocene Europe. PMID:18187577

Richards, Michael P; Pacher, Martina; Stiller, Mathias; Quilès, Jérôme; Hofreiter, Michael; Constantin, Silviu; Zilhão, João; Trinkaus, Erik

2008-01-15

106

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

107

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

108

The application of regional-scale geochemical data in defining the extent of aeolian sediments : the Late Pleistocene loess and coversand deposits of East Anglia, UK  

OpenAIRE

The ‘European Coversand Sheet’ is a discontinuous ‘sheet’ of aeolian (windblown) loess and coversand that extends through eastern and southern England, across the English Channel into northern France, Belgium and the Netherlands (Kasse, 1997; Antoine et al., 2003). Whilst some of the earlier aeolian sediments date from the Middle Pleistocene, most correspond to the Late Pleistocene Weichselian / Devensian and earliest Holocene stages. East Anglia contains consider...

Scheib, Andreas; Lee, Jonathan R.

2010-01-01

109

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.

110

Magnetostratigraphy and sedimentary evolution of the late Miocene to early Pleistocene sediments, Quseir region, Egyptian Red Sea  

Science.gov (United States)

An integrated sedimentological and magnetostratigraphic study has allowed a detailed understanding of the late Miocene to early Pleistocene evolution of the sediments in the Quseir region of the Egyptian Red Sea coast. Palaeomagnetic samples were collected from sections in six wadis, covering the Shagara Formation, the Gabir and Samh members of the Wardan Formation, and the Abu Dabbab Formation evaporites. Remanence properties are carried by magnetite, haematite and goethite. The characteristic remanence is typically carried by detrital magnetite and haematite, with more recent overprints predominantly associated with haematite and goethite, produced by the weathering of diagenetic pyrite. The magnetostratigraphy has allowed the following detailed age assignments for the lithostratigraphic units. The Shagara Formation ranges in age from late Pliocene (late Piacenzian) to middle Pleistocene (0.6-2.5Ma). The Gabir Member is latest Messinian to earliest Piacenzian in age (~3.5-5.5Ma) and the Samh Member, late Tortonian to mid-Messinian (~6.0-7.5Ma). The age of the top of the Abu Dabbab Formation is probably mid-Tortonian (~8Ma). Disconformities occur between all the lithostratigraphic units, with a local angular unconformity between the Shagara and Wardan Formations. Lowstands in global sea level appear to have a strong influence on the timing of these disconformities. Characteristic mixed alluvial and reef facies of the Shagara formation are a response to the ephemeral wetter climate following the initiation of northern hemisphere glaciation at ~2.4Ma, enhanced by rift-margin uplift of basement complexes to the west. This tectonic activity was concentrated in the early Piacenzian. The marine Gabir Member was deposited during the early Pliocene and latest Messinian high-sea-level stands. The late Tortonian/early Messinian age and sedimentological character of the Samh Member indicates this unit was affected by marine flooding events, which ultimately produced, during drawdown phases, the off-shore Zeit Formation evaporites in half-graben depocentres.

Lean, Candida B.; Hounslow, Mark W.; Vine, Fred J.; Harwood, Gill M.; Elvidge, Liz; Fisk, Kevin; Kendall, Alan C.; Montgomery, Paul

1998-05-01

111

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

112

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

113

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

Science.gov (United States)

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

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

2009-07-01

114

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

Science.gov (United States)

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

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

2013-09-01

115

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

116

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

OpenAIRE

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 transit...

Foote, Andrew D.; Kaschner, Kristin; Schultze, Sebastian E.; Garilao, Cristina; Ho, Simon Y. W.; Post, Klaas; Higham, Thomas F. G.; Stokowska, Catherine; Es, Henry; Embling, Clare B.; Gregersen, Kristian; Johansson, Friederike; Willerslev, Eske; Gilbert, M. Thomas P.

2013-01-01

117

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

OpenAIRE

The end of the Pleistocene marked a turning point for the Earth system as climate gradually emerged from millennia of severe glaciation in the Northern Hemisphere. It is widely acknowledged that the deglacial climate change coincided with an unprecedented decline in many species of large terrestrial mammals, including the near-total eradication of the woolly mammoth. Due to an herbivorous diet that presumably involved large-scale tree grazing, the mammoth expansion would have accelerated the ...

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

2013-01-01

118

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

119

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.)

120

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

121

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

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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

122

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

123

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

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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) 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

124

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

Science.gov (United States)

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

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

2013-08-01

125

Late Pleistocene climatic variations as recorded in two Italian maar lakes (Lago di Mezzano, Lago Grande di Monticchio)  

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Sediment profiles from two maar lakes, Lago di Mezzano (central Italy) and Lago Grande di Monticchio (southern Italy), were investigated with respect to their minerogenic and biogenic sediment accumulation rates for a time window spanning the final 20,000 yr of the last glaciation. The chronological framework is provided by calibrated radiocarbon ages, varve counting, calculation of sedimentation rates and tephrochronology. In the time slice between 34,000 and 14,000 cal BP periods of increased minerogenic input are observed in both lacustrine records, interrupted by periods of low minerogenic input. These cyclic variations have an average recurrence time of 1785 yr for Lago di Mezzano and 2875 yr for Lago Grande di Monticchio, comparing well with marine and ice core data. Explanations for these pulses of increased minerogenic sedimentation include enhanced erosion and runoff. The higher precipitation/evaporation ratio required for this interpretation was possibly restricted to winter months as earlier published pollen analyses on sediments from Lago Grande di Monticchio show a contemporary development of steppe vegetation, an indicator for cool/dry climatic conditions. This may be connected with a southward shift of the westerlies and a reinforced jet stream. Agreement of lacustrine data from Italy with late Pleistocene glacial events in central Italy, with events recorded in marine archives from the North Atlantic (Heinrich events) and with oxygen isotope data from Greenland ice cores is interpreted as evidence for the Late Pleistocene climate in Europe being influenced by North Atlantic climatic forcing which may be related to Dansgaard-Oeschger cycles.

Ramrath, Antje; Zolitschka, Bernd; Wulf, Sabine; Negendank, Jörg F. W.

1999-06-01

126

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

127

The late Quaternary seismic, sedimentary and palynological stratigraphy beneath Evans Bay, Wellington Harbour  

International Nuclear Information System (INIS)

Boreholes and offshore seismic profile surveys in southern Evans Bay, Wellington Harbour, indicate that a drowned river valley has been partly infilled with sediments during two glacial/interglacial cycles. The original valley was probably eroded along the shatter zone of a late Pliocene fault situated on the eastern side of the bay. The infilling sediments include two assemblages: (1) interglacial age (including Holocene) shelly marine sands and muds, which have a palynoflora from flourishing rimu-podocarp forest, and (2) glacial age gravelly and carbonaceous terrestrial deposits, which have a palynoflora dominated by grasses or, in slightly milder times, by beech and manuka. Postdepositional deformation of early Holocene sediments may indicate either further faulting along the shatter zone of the Pliocene fault or an effect of sediment compaction during earthquake stress. Deformation of late Holocene sediments is interpreted as differential compaction and slumping being a secondary effect of earthquake shaking

128

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

129

The stratigraphy of the Penarth Group (Late Triassic) of the East Devon coast  

OpenAIRE

The cliff and foreshore exposures in the Devon part of the Dorset and East Devon Coast World Heritage Site expose an unbroken late Triassic to early Jurassic succession. The change from the terrestrial, red-bed facies of the Triassic Mercia Mudstone Group to the fully marine conditions of the Jurassic Lias Group takes place via the Penarth Group, a succession of mudstones, siltstones and limestones deposited in lagoonal and sheltered shallow-marine environments of varying salinities....

Gallois, Ramues W.

2008-01-01

130

Late Pleistocene and Holocene paleolimnology of two mountain lakes in western Tasmania.  

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The analysis of diatoms from two lake-sediment cores from southwestern Tasmania that span the Pleistocene-Holocene boundary provides insight about paleolimnological and paleoclimatic change in this region. Both Lake Vera and Eagle Tarn have lacustrine records that begin about 12 000 yr ago. Both lakes have had similar limnological histories. Each appears to have been larger and more alkaline 12 000 yr ago and both became shallower through time. Fossil diatom assemblages about 11 000 yr old indicate shallow- water environments that fluctuated in pH, and between dilute and possibly slightly saline hydrochemical conditions. Beginning 11 500 yr ago, limnological conditions of shallow, dilute water of neutral pH prevailed, indicating reduction of moisture stress. A subsequent transition to diatom assemblages indicative of acidic conditions about 10 000 yr ago parallels the establishment of rain-forest vegetation and essentially modern climatic conditions with excess precipitation over evaporation. Changes at these separate and distinctive sites suggests a regional paleoclimatic cause rather than local environmental effects. Latest Pleistocene climates were apparently more continental and drier than Holocene climates in southwestern Tasmania.-from Author

Platt, Bradbury J.

1986-01-01

131

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

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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

132

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

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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

133

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

Science.gov (United States)

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

Mehl, A. E.; Zárate, M. A.

2012-08-01

134

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

135

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

136

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

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

Tiiu Koff

2011-06-01

137

Late Pleistocene carbonate aeolianites on Mallorca, Western Mediterranean: a luminescence chronology  

Science.gov (United States)

Coastal outcrops of Upper Pleistocene deposits in north-eastern Mallorca (Balearic Islands, Spain) have been examined and a chronological framework established using Optically Stimulated Luminescence (OSL) dating. The outcrops record a complex interaction between aeolian, colluvial and alluvial fan deposition that result in a variable stratigraphical architecture. Dating and facies analysis make it possible to identify four aeolian activity episodes during MIS 5c/b, 4 and 3, and also add to the understanding of the environmental history of north-eastern Mallorca over the last 100 ka. The new data suggest enhanced aeolian transport and dune formation during cold climatic intervals when sea level was low, sediment supply (exposed marine carbonate sediment) was high, winter windiness was high, and vegetation on coastal plains at a minimum.

Fornós, Joan J.; Clemmensen, Lars B.; Gómez-Pujol, Lluís; Murray, Andrew S.

2009-12-01

138

Sedimentology, palaeontology and archaeology of late Middle Pleistocene River Thames terrace deposits at Purfleet, Essex, UK  

Science.gov (United States)

Middle Pleistocene fluvial deposits of the Corbets Tey Formation at Purfleet, Essex, provide evidence of an un-named and previously poorly recognized interglacial, thought to corrrelate with Oxygen Isotope Stage (OIS) 9. Previous attributions of the sediments to the Ipswichian (Last Interglacial) Stage are refuted. New investigations have yielded rich molluscan, mammalian and ostracod assemblages that indicate fully temperate conditions and the distal influence of marine transgression. Pollen analyses suggest a previously unrecorded phase of interglacial vegetational development. Clast composition, geomorphological evidence and the occurrence of molluscs that favour large rivers all point to deposition by the Thames, rather than in a minor tributary, as suggested previously. Three separate Palaeolithic industries in stratigraphical superposition are recognized at Purfleet, these being Clactonian, Acheulean and Levallois. Purfleet is therefore a key locality in the understanding of the early human occupation and exploitation of southern Britain, as well as for the interpretation and correlation of the terrace sequence in the Thames Valley.

Schreve, Danielle C.; Bridgland, David R.; Allen, Peter; Blackford, Jeff J.; Gleed-Owen, Christopher P.; Griffiths, Huw I.; Keen, David H.; White, Mark J.

2002-07-01

139

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

Science.gov (United States)

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

140

Facies and sequence stratigraphy of a Late Barremian wave-dominated deltaic deposit, Agadir Basin, Morocco  

Science.gov (United States)

The late Barremian succession in the Agadir Basin of the Moroccan Western High Atlas represents wave-dominated deltaic deposits. The succession is represented by stacked thickening and coarsening upwards parasequences 5-15 m thick formed during fifth- or fourth-order regression and building a third-order highstand systems tract. Vertical facies transitions in parasequences reflect flooding followed by shoaling of diverse shelf environments ranging from offshore transition interbedded mudstones, siltstones and thin sandstones, lower shoreface/lower delta front hummocky bedforms to upper shoreface/upper delta front cross-bedded sandstones. The regional configuration reflects the progradation of wave-dominated deltas over an offshore setting. The maximum sea-level fall led to the development of a sequence boundary that is an unconformity. The subsequent early Aptian relative sea-level rise contributes to the development of an extensive conglomerate lagged transgressive surface of erosion. The latter and the sequence boundary are amalgamated forming a composite surface.

Nouidar, Mohammed; Chella??, El Hassan

2002-07-01

141

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

142

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

143

High-precision constraints on timing of Alpine warm periods during the middle to late Pleistocene using speleothem growth periods  

Science.gov (United States)

A long-standing problem in the reconstruction of warm climate periods during the late Quaternary is the difficulty of determining absolute ages for undisturbed terrestrial climate archives. Speleothems offer an important source of information about the timing and duration of middle and late Pleistocene warm phases. A flowstone from the high-elevation Spannagel Cave (Zillertal Alps, Austria) provides a new absolutely dated climate record, which includes the most prominent warm phases between ˜260 and 50 ka before present. New data from the Penultimate Interglacial improve our knowledge about the timing and progression of warm periods in the Alps corresponding to marine isotope stages 7 and 8. Speleothem growth phases were identified from ˜261 to 249, from ˜236 to 229, and from ˜200 to 192 ka. An early onset of the Last Interglacial is corroborated by a growth phase commencing at 136.7 ± 2.8 ka and the youngest section of the flowstone provides further evidence for an Alpine climate during time intervals corresponding to marine isotope stages 5a and 3 sufficiently warm to allow speleothems to grow. The high-resolution stable isotope profile taken along the growth axis of the flowstone provides information about the hydrological conditions during the growth phases.

Holzkämper, Steffen; Spötl, Christoph; Mangini, Augusto

2005-08-01

144

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

Directory of Open Access Journals (Sweden)

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

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

Aboal Fernández, Roberto

2005-12-01

145

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

146

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

Science.gov (United States)

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

147

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

Science.gov (United States)

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

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

2007-01-01

148

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

149

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

Science.gov (United States)

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

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

2002-01-01

150

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

151

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

Science.gov (United States)

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

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

2013-12-01

152

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

153

Contrasted morphosedimentary activity of the lower Kert River (northeastern Morocco) during the Late Pleistocene and the Holocene. Possible impact of bioclimatic variations and human action  

Science.gov (United States)

From field observations in the lower Kert valley and 16 radiocarbon dating measurements, six alluvial units (UF1 to UF6) deposited since about 30,000 years BP have been identified, comprising 18 lithofacies and separated by six incision stages resulting in three alluvial terraces (T1 to T3). While the Late Pleistocene is mainly marked by sedimentary accretion (UF1 forming part of T1), the Holocene is marked by the alternation of major incision (I2, I3 and I4) and accretion (UF2 and UF3) stages, with roughly similar height ranges, between the current river level and polyphased T1 surface. During the Lower and Middle Holocene, this complex morphosedimentary evolution could have been the result of contrasted bioclimatic trends that did not appear during the Late Pleistocene. Human activities modified the earth surface conditions, intermittently during the Middle Holocene, and during the Upper Holocene, inducing new responses from the fluvial geosystem to the environment.

El Amrani, Mohamed; Macaire, Jean-Jacques; Zarki, Hamid; Bréhéret, Jean-Gabriel; Fontugne, Michel

2008-08-01

154

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 (currently active part of the LVC. There have been 14 eruptions or eruptive sequences in the Lassen domefield over the last 100,000 years: 7 rhyodacite or dacite pyroclastic flows and/or domes, and 7 hybrid andesite lava flows and tephra. Their volumes range from very small (0.0006 km3) to significant (4.7 km3). The annual probability of an eruption at the Lassen domefield is 0.00014 (0.014%), which corresponds to an average recurrence interval of 7,150 years. Petrographic and geologic evidence indicates that the Lassen magmatic 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

155

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

156

Late Pleistocene coastal evolution of San Giovanni di Sinis, west Sardinia (Western Mediterranean)  

Science.gov (United States)

The Upper Pleistocene succession of coastal deposits outcropping at San Giovanni di Sinis (west Sardinia) has been studied since the 1960s. However, the absence of consistent radiometric ages has allowed the production of competing stratigraphic subdivisions of these deposits with different Isotopic Stage (OIS/MIS) attributions. The succession is composed of sandy to gravelly shallow-marine, coastal aeolian and alluvial fan/plain deposits. Facies analysis and log correlations show the presence of three unconformities (T1, T2, T3) always overlain by shallow-marine deposits, cutting through the substrate, alluvial fan or aeolian sediments. We have collected three samples for Optically Stimulated Luminescence (OSL) dating at the top of each shallow-marine deposit. The succession is composed of four unconformity-bounded units (U1, U2, U3, U4), and the new OSL dates indicate the presence of three different sea-level highstands. The first Unit (U1), which is composed of shallow-marine to aeolian deposits and overlies transgressive surface T1, is related to a marine transgression during OIS 7 (186 ± 13 ky). Unit 2 is composed of continental deposits and formed during OIS 6. Unit 3 represents OIS 5 and overlies a transgressive surface (T2). More precisely, Subunit U3a is related to OIS 5e (120 ± 10 ky; Eu-Tyrrhenian or Eemian sensu strictu) and is characterized by shallow-marine to aeolian deposits developed during both transgressive and highstand phases. The following bay deposits of Subunit 3b are associated with OIS 5c (100 ± 5 ky) and record a second transgressive event (T3) and highstand phase occurred during the Neo-Tyrrhenian. The succession of San Giovanni di Sinis ends with continental deposits of Unit 4 associated to a sea-level fall that took place at the beginning of the last glacial phase (OIS 4).

Andreucci, Stefano; Pascucci, Vincenzo; Murray, Andrew S.; Clemmensen, Lars B.

2009-04-01

157

The sequence and timing of large late Pleistocene floods from glacial Lake Missoula  

Science.gov (United States)

Glacial Lake Missoula formed when the Purcell Trench lobe of the Cordilleran ice sheet dammed Clark Fork River in Montana during the Fraser Glaciation (marine oxygen isotope stage 2). Over a period of several thousand years, the lake repeatedly filled and drained through its ice dam, and floodwaters coursed across the landscape in eastern Washington. In this paper, we describe the stratigraphy and sedimentology of a significant new section of fine-grained glacial Lake Missoula sediment and compare this section to a similar, previously described sequence of sediments at Ninemile Creek, 26 km to the northwest. The new exposure, which we informally term the rail line section, is located near Missoula, Montana, and exposes 29 units, each of which consists of many silt and clay couplets that we interpret to be varves. The deposits are similar to other fine-grained sediments attributed to glacial Lake Missoula. Similar varved sediments overlie gravelly flood deposits elsewhere in the glacial Lake Missoula basin. Each of the 29 units represents a period when the lake was deepening, and all units show evidence for substantial draining of glacial Lake Missoula that repeatedly exposed the lake floor. The evidence includes erosion and deformation of glaciolacustrine sediment that we interpret happened during draining of the lake, desiccation cracks that formed during exposure of the lake bottom, and fluvial sand deposited as the lake began to refill. The floods date to between approximately 21.4 and 13.4 cal ka ago based on regional chronological data. The total number of varves at the rail line and Ninemile sites are, respectively, 732 and 583. Depending on lake refilling times, each exposure probably records 1350-1500 years of time. We present three new optical ages from the rail line and Ninemile sites that further limit the age of the floods. These ages, in calendar years, are 15.1 ± 0.6 ka at the base of the Ninemile exposure, and 14.8 ± 0.7 and 12.6 ± 0.6 ka midway through the rail line exposure. The sediment at the two sections was deposited during later stages of glacial Lake Missoula, after the largest outburst events.

Hanson, Michelle A.; Lian, Olav B.; Clague, John J.

2012-01-01

158

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

159

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

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

L. E. Lisiecki

2009-12-01

160

Late Pleistocene records of littoral processes at the Tyrrhenian Coast (Central Italy): depositional environments and luminescence chronology  

Science.gov (United States)

Two cliff-sites on the Tyrrhenian coast of central Italy have been investigated in order to investigate late Pleistocene depositional environments by microfacies analysis and chronostratigraphy by luminescence age estimations. Both sections cover the period from the Last Interglacial to the end of the Last Glaciation. In the Buca dei Corvi site an increasing rate of uplift is recognised, which is responsible for significant environmental change and formation of the modern coastal fault scarp at around 9 ka. In the Golfo di Baratti site the vertical succession of three marine horizons, previously recognised by Cortemiglia et al., (1983), is attributed to the OIS stages ?5c, 5a and 3 respectively. This cliff-section is affected by NNE-SSW orientated normal faults, confirming that extentional structural processes are still active. The coastal deposit of Stage 3, today located at 7 m a.s.l., suggests abnormal high uplift rate if the position of the palaeo-shoreline was assumed at -40 to -50 m. Both central Mediterranean coastal records strongly suggest that the eustatic sea-level has dropped to a smaller amount than that of the open oceans.

Mauz, Barbara

1999-08-01

161

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

Science.gov (United States)

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

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

2011-07-01

162

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

163

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

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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

164

Aminostratigraphy of Middle and Late Pleistocene deposits in The Netherlands and the southern part of the North Sea Basin  

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A review of all available amino acid racemization D (alloisoleucine)/L (isoleucine) data from the whole shell of four molluscan species from Late and late Middle Pleistocene deposits of the Netherlands is presented. The data allow the distinction of 5 aminostratigraphical units, NAZ (Netherlands Amino Zone) A-E, each representing a temperate stage. The zones are correlated with marine isotope stages 1, 5e, 7, 9, and 11 respectively. Apart from NAZ-D (MIS 9), in all aminozones the marine transgression reached the present-day onshore area of the Netherlands. The transgression during NAZ-C (Oostermeer Interglacial: MIS 7) seems to be at least as widespread as its counterpart during NAZ-B (Eemian: MIS 5e) in the southern bight of the North Sea Basin. The stratigraphic position of the Oostermeer Interglacial is just below deposits of the Drente phase of the Saalian and because of this position the interglacial marine deposits have formerly erroneously considered to be of Holsteinian age. Neede, the 'classic' Dutch Holsteinian site, is dated in NAZ-E (MIS 11), like Noordbergum. Although the validity of these zones has been checked with independent data, some overlap between succeeding zones may occur. The relation between amino acid data from elsewhere in the North Sea Basin and the Netherlands amino zonation is discussed. The deposits at the Holsteinian stratotype Hummelsbüttel in North West Germany are dated in NAZ-D. This interglacial correlates with MIS 9. The Belvédère Interglacial, which is of importance for its archaeology, is in NAZ-D (MIS 9) and therefore of Holsteinian age as well. The lacustroglacial 'pottery clays' in the Noordbergum area are deposits from two glacial stages, which can be correlated with MIS 8 and 10 (the Elsterian). The pottery clay that is considered equivalent to the German 'Lauenburger Ton' correlates with MIS 10.

Meijer, T.; Cleveringa, P.

2009-09-01

165

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

166

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

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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

167

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

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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

168

Constraining the physical-chemical conditions of Pleistocene cavernous weathering in Late Paleozoic granites  

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Cavernous weathering such as tafoni, alveoles and honeycomb structures have been recorded from a great variety of bedrocks and landforms. In the present study cavernous weathering from late Variscan granites was discussed as to its physical-chemical regime of formation. U/Pb dating yielded a maximum age of 1.52 ± 0.03 Ma. Supergene U mineralization is accompanied by kaolinite, nontronite and Fe(III) phosphates. Based upon Eh-pH diagrams calculated for U-Fe-P mineralization the physical-chemical conditions may be described as oxidizing with pH values fluctuating around neutral at near-ambient temperatures of 25 °C. Alteration occurs in two stages: dissolution of rock-forming minerals and neoformation of hydrosilicates under mildly acidic conditions, followed by phosphate precipitation under near-neutral conditions.

Dill, Harald G.; Weber, Berthold; Gerdes, Axel

2010-09-01

169

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

170

Hominid skull fragments from Late Pleistocene layers in Leine Valley (Sarstedt, District of Hildesheim, Germany).  

Science.gov (United States)

Three cranial fragments were recovered from coarse-grained deposits dug up by a suction dredge from gravel pits on the Leine river flats in the vicinity of Sarstedt (northwestern Germany). Also recovered were a number of artefacts which, upon careful inspection, could be assigned to the Middle Paleolithic. The geological pattern of the Leine Valley in this region suggests that these fragments were deposited in the lower terrace during a yet undetermined warm period-possibly Brörup or Odderade-during the Weichsel glaciation. However, attribution to the Eemian period or a Saale interstadial cannot be ruled out. The features of the Sarstedt (Sst) I infant temporal are known from Neanderthals (e.g., Weimar-Ehringsdorf, Engis, Krapina 1) and can be seen in specimens from the European late- Homo erectus group as well. Subadult individuals do not always exhibit full development of features characteristic for adults and-to some extent-anticipate the succeeding developmental stage (i.e., neoteny). The Neanderthal autapomorphies characterizing the fragments of the occipital and the parietal are certainly consistent with assigning both unequivocally to the species H. neanderthalensis. The presence of Middle Paleolithic artefacts recovered from the same deposits are commensurate with the presence of Neanderthals. However, there is no clear contextual association of any archaeological and fossil human material. Future DNA research will hopefully add up to the established morphological picture. PMID:11437523

Czarnetzki, A; Gaudzinski, S; Pusch, C M

2001-08-01

171

Evidence of Late Pliocene-Early Pleistocene marine environments in the deep subsurface of the Lihue Basin, Kauai, Hawaii  

Science.gov (United States)

Cuttings recovered from two deep exploratory wells in the Lihue Basin, Kauai, Hawaii, include fossiliferous marine deposits that offer an uncommon opportunity to study paleoenvironments from the deep subsurface in Hawaii and interpret the paleogeography and geologic history of Kauai. These deposits indicate that two marine incursions gave rise to protected shallow-water, low-energy embayments in the southern part of the Lihue Basin in the late Pliocene-early Pleistocene. During the first marine incursion, the embayment was initially zoned, with a variable-salinity environment nearshore and a normal-marine reef environment offshore. The offshore reef environment eventually evolved to a nearshore, variable-salinity environment as the outer part of the embayment shallowed. During the second marine incursion, the embayment had normal-marine to hypersaline conditions, which constitute a significant departure from the variable-salinity environment present during the first marine incursion. Large streams draining the southern Lihue Basin are a likely source of the freshwater that caused the salinity fluctuations evident in the fossils from the first marine incursion. Subsequent volcanic eruptions produced lava flows that buried the embayment and probably diverted much of the stream flow in the southern Lihue Basin northward, to its present point of discharge north of Kalepa Ridge. As a result, the embayment that formed during the second marine incursion received less freshwater, and a normal-marine to hypersaline environment developed. The shallow-water marine deposits, currently buried between 86 m and 185 m below present sea level, have implications for regional tectonics and global eustasy. Copyright ?? 2008, SEPM (Society for Sedimentary Geology).

Izuka, S.K.; Resig, J.M.

2008-01-01

172

10-Be Chronology of Late Pleistocene Outburst Floods in the Upper Arkansas River Basin, Colorado  

Science.gov (United States)

During the Last Glacial Maximum (LGM), several eastward-flowing glaciers originating in the Sawatch Range, CO expanded into the upper Arkansas River valley. One of these glaciers, located in the Clear Creek valley, dammed the Arkansas River impounding a large lake. At least four coarse-grained (boulders >4 meters) flood terraces in the Arkansas River basin attributed to ice-dam breaches have been identified down-valley of the Clear Creek tributary. Here, we use 10-Be dating to constrain the age of the youngest two terraces (herein referred to as upper and lower). 10-Be ages of 19.3 ± 0.8 and 20.9 ± 1.0 ka on two boulders from the upper terrace provide an age for the upper terrace and a maximum age for the lower terrace. Two additional boulders from the upper terrace and two boulders from the lower terrace are currently being processed and will provide additional chronological constraint. Preliminary results indicate that flood boulders on the upper terrace are in broad agreement with the older mode (22.0 ± 1.4 ka, n = 5) of a bimodal 10-Be age distribution of clasts from a single-crested Pinedale moraine in neighboring Pine Creek valley. The younger mode in this distribution (15.2 ± 0.9 ka, n = 7) suggests that ice was near its LGM maximum extent as late as 15.2 ka and may correlate with the younger flood terrace. Additionally, we sampled four boulders and one cobble from a single-crested, left-lateral Pinedale moraine in the Clear Creek valley to further assess the connection between moraine abandonment age and flood terrace age. 10-Be ages of large flood boulders on flat terraces may serve as better sample types than moraine clasts for determining the glacial history of the upper Arkansas River basin.

Young, N. E.; Briner, J. P.; Leonard, E. M.

2008-12-01

173

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

174

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

175

10Be surface exposure ages on the late-Pleistocene and Holocene history of Linnébreen on Svalbard  

Science.gov (United States)

Arctic glaciers were sensitive to past changes in high-latitude winter precipitation and summer temperature. Here we develop a late-Pleistocene to Holocene history for Linnébreen (Linné Glacier) in western Svalbard using 10Be surface exposure ages on isolated erratic and moraine boulders. We show that Linnébreen had separated from the larger ice sheet over Svalbard and was retreating up valley around the start of the Younger Dryas cold period. We attribute this retreat during a cold period on Svalbard to moisture starvation of Linnébreen from advanced sea ice and/or elevated shortwave boreal summer insolation that overwhelmed any reduction in sensible heat. After an ice-free period during the early to middle Holocene, Linnébreen reformed sometime after 4.6 ± 0.2 ka, and was at a position roughly equivalent to its Little Ice Age (LIA) maximum extent before it began to retreat at 1.6 ± 0.2 ka. Comparison with calibrated 14C dates from three other glaciers could suggest that this period of ice retreat at ˜1.6 ka could be regional in extent. Linnébreen occupied the pre-LIA moraine when there was an increased ratio of cold Arctic-sourced relative to warm Atlantic-sourced waters around Svalbard and advanced sea ice. The retreat of Linnébreen at ˜1.6 ka was concurrent with the increased presence of warm Atlantic waters around Svalbard and attendant sea-ice retreat. These coincident changes in ocean temperatures, sea-ice extent, and Linnébreen moraine age could imply a climatic forcing of the pre-LIA advance and retreat of Linnébreen. Summer temperatures, rather than changes in precipitation, would then be dominant in driving ice retreat, although the possibility of stochastic glacier-margin variability cannot be excluded. Our data therefore suggest that Linnébreen may have responded differently to past changes in sea-ice extent that could depend on the background climate state (deglacial climate vs. late-Holocene climate), which highlights the complexity in climatic controls on Arctic glaciers.

Reusche, Melissa; Winsor, Kelsey; Carlson, Anders E.; Marcott, Shaun A.; Rood, Dylan H.; Novak, Anthony; Roof, Steven; Retelle, Michael; Werner, Alan; Caffee, Marc; Clark, Peter U.

2014-04-01

176

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

177

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

Science.gov (United States)

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

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

2012-09-01

178

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

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

J. Etourneau

2012-09-01

179

Contrasted morphosedimentary activity of the lower Kert River (northeastern Morocco) during the Late Pleistocene and the Holocene. Possible impact of bioclimatic variations and human action  

OpenAIRE

From field observations in the lower Kert valley and 16 radiocarbon dating measurements, six alluvial units (UF1 to UF6) deposited since about 30,000 years BP have been identified, comprising 18 lithofacies and separated by six incision stages resulting in three alluvial terraces (T1 to T3). While the Late Pleistocene is mainly marked by sedimentary accretion (UF1 forming part of T1), the Holocene is marked by the alternation of major incision (I2, I3 and I4) and accretion (UF2 and UF3) stage...

El Amrani, Mohammed; Macaire, Jean-jacques; Zarki, Hamid; Bre?heret, Jean-gabriel; Fontugne, Michel

2008-01-01

180

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

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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

181

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

182

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

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

Kholeif, S.; Mudie, P.

2009-04-01

183

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

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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

184

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

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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

185

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

Science.gov (United States)

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

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

2013-01-01

186

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

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

J. Etourneau

2012-03-01

187

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

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

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

2007-11-01

188

Diet and habitat landscape of Equus sp. and Mammuthus columbi for the Late Pleistocene deposit at El Cedral, San Luis Potosi, Mexico  

Science.gov (United States)

The diet and habitat landscape for fossil specimens pertaining to Late Pleistocene horse Equus sp., and mammoth Mammuthus columbi from the deposit at Rancho La Amapola, El Cedral, San Luís Potosí, México were assayed with basis on stable isotopes analysis the carbon and oxygen found in dental enamel apatite. For horses the ? 13C values showed from C3/C4 a basic C4-plants diet ranging into a C3/C4 mixer feeder, while mammoth showed values as a C3/C4 mixer feeder, but preferring C4 plants; there was not significant differences among the average values for both groups, with -3.5 ‰ for horses and -3.8 ‰ for mammoth. Mexican data was compared with those for the same genera from US localities, including the states of Florida, New Mexico, and Texas, allowing confirmation of the inference that El Cedral species were mainly grazers, but with some C3 plants being consumed; furthermore, comparisons of El Cedral specimens, using both carbon and oxygen isotopes, with Floridan C3-plant sites showed El Cedral specimens could be defined as mixer feeders in open habitats, preferring such opn areas like grassland or savanna. Our results are in agreement with the species dental morphology, as well as with the pollen record for the same site, which showed the existence of grassland that could have extended during the Late Pleistocene from southern Canada to central Mé xico

Perez-Crespo, V. A.; Bennami, M.; Sanchez-Chillon, B.; Alberdi, M. T.; Santos-Moreno, A.

2007-05-01

189

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

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

Tsanko Tzankov

2012-12-01

190

A modern approach to the Neopleistocene stratigraphy and paleogeography of Central European Russia  

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The study compiles the current knowledge on the Neopleistocene stratigraphy and paleogeography of Central European Russia (including the limits of ice sheets in the first half of the Middle Neopleistocene and Late Neopleistocene) on the basis of new data and provides a draft of the revised regional stratigraphic scale adopted by the regional Interdepartmental Stratigraphic Committee on the Central and Southern Russian platform. The proposed scale incorporates a number of new horizons: the Setun', Moiseevo, Navlya, and Ikorets horizons of the Lower Neopleistocene; Vologda and Gorki horizons of the Middle Neopleistocene; Chermenino Horizon of the Upper Neopleistocene; and Shuvalovo Horizon of the Holocene. The adopted scale is correlated with the oxygen-isotopic stages and substages identified in the Neopleistocene by the decision of the ISC of Russia, as well as with glacials and interglacials of Lithuania, Poland, Germany, and England. The study discusses the problem of a division of the Pleistocene with respect to duration of Pleistocene stages.

Shik, S. M.

2014-03-01

191

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

192

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

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

Gustavo González Bonorino

2012-03-01

193

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

194

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

195

Evidence of late Gelasian dispersal of African fauna at Coste San Giacomo (Anagni Basin, central Italy): Early Pleistocene environments and the background of early human occupation in Europe  

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Since the late 70s, the Early Pleistocene (Gelasian) site of Coste San Giacomo (Anagni Basin, central Italy) has been known amongst palaeontologists for its diverse vertebrate fauna. During the last 5 years, new excavations and the drilling of a 46-m-deep core have provided novel pieces of information. Palaeomagnetic data, pollen and small vertebrates analyses are presented here for the first time and combined with the updated list of the large vertebrates and ostracod analysis in a multidisciplinary perspective. Large and small mammals, pollen and ostracod analyses have allowed an integrated palaeoenvironmental reconstruction of the sedimentary sequence, depicting the evolution of the alluvial plain in the surrounding landscape. Moreover, magnetostratigraphy, pollen and small mammal biochronological data have confirmed the position of the Coste San Giacomo Faunal Unit, focusing the possible age of the mammal assemblage around 2.1 Ma, in a reversed phase before the base of the Olduvai chron. In particular, the occurrence of the large vole Mimomys pliocaenicus has important biochronological significance. The Coste San Giacomo site offers a unique opportunity to investigate the faunal and environmental changes that occurred in Mediterranean Europe during the Early Pleistocene, coinciding with major climatic changes at a global scale. The occurrence of taxa such as Hippopotamus sp. in the assemblage provides evidence of early dispersal events of African taxa prior to the early Homo diffusion into Europe.

Bellucci, L.; Bona, F.; Corrado, P.; Magri, D.; Mazzini, I.; Parenti, F.; Scardia, G.; Sardella, R.

2014-07-01

196

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

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

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

2010-09-01

197

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

OpenAIRE

In the present study, we describe and analyze the structure of a Late Pleistocene (likely last interglacial) marine macrobenthic assemblage in Caleta Patillos (20°45'S, 70°12'W), northern Chile. A taphonomic analysis suggests the existence of a shallow subtidal paleonvironment, mainly soft-bottom, of high energy and intense mixing from several benthic habitats. The total number of 38 taxa recorded, mainly gastropods and bivalves, was not different than the ones reported in other Late Pleist...

Rivadeneira, Marcelo M.; Carmona, Erico R.

2008-01-01

198

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  

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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

199

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

200

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.

201

A late Pleistocene and Holocene record of vegetation and climate from an alpine lake from west-central Colorado (USA)  

Science.gov (United States)

Here we present a detailed pollen and magnetic susceptibility (MS) data from a sediment core from an alpine lake in west-central Colorado, which records changes in vegetation and sedimentation for the latest Pleistocene and Holocene. This record shows that a subalpine Picea and Abies parkland grew around the lake during the latest Pleistocene (YD) and early Holocene. Subsequently, a pine forest, probably including bristlecone and lodgepole pines (Pinus aristata and P. contorta) developed around the lake, indicating warming, which occurred throughout the early and middle Holocene, lasting until ca. 4.5 - 3.5 ka, when the warmest and summer-wettest conditions were apparent. A decrease in Pinus and, on the other hand, increases in Artemisia and piñon pine (P. edulis) indicate a progressive climate cooling and enhanced winter precipitation that occurred until today. These long-term climatic trends correlate to changes in summer insolation. Millennial-scale variability observed in the pollen record co-varies with changes in MS indicating that the sedimentation is also influenced by climate variability.

Jimenez-Moreno, G.; Anderson, R. S.

2010-12-01

202

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

Science.gov (United States)

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

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

2010-01-01

203

Quartz silt in mudrocks as a key to sequence stratigraphy (Kimmeridge Clay Formation, Late Jurassic, Wessex Basin, UK)  

OpenAIRE

Sequence-stratigraphic interpretation of mudrocks is often carried out using proxy indicators for grain size or by consideration of other aspects of lithology thought to relate to sea-level change, such as organic-matter content. An alternative stratigraphic analysis, based on direct estimation of quartz-silt content, was carried out on a major Late Jurassic mudrock (and oil source rock), the Kimmeridge Clay Formation of the Wessex Basin, Dorset, UK. The new data, generated by backscatter SEM...

Williams, Cj; Hesselbo, Sp; Jenkyns, Hc; Morgans-bell, Hs

2001-01-01

204

The granite tors of Dartmoor, Southwest England: rapid and recent emergence revealed by Late Pleistocene cosmogenic apparent exposure ages  

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Dartmoor, in SW England, is a classic periglaciated granite upland adorned with a population of over 150 tors. The origin of the tors has been controversial, but their emergence by differentiation after stripping of regolith during Pleistocene cold phases is accepted. However, their actual age has been unknown, with possible scenarios ranging from preservation since the early Middle Pleistocene to relatively short-lived landforms in a maritime climate with high denudation rates. The latter is now supported by 32 cosmogenic surface exposure dates from 28 tors across the whole upland. The distribution of apparent 10Be ages peaks strongly in the Middle Devensian (36-50 ka), which with corrections for weathering and limited ice shielding could be interpreted as Early Devensian. These ages are much younger than those found for three glacially unmodified Cairngorms tors, and somewhat younger even than glacially modified Cairngorms tors. The dates show little spatial variation. Although an ice cap has now been modelled in the heart of northern Dartmoor, tors here are of median age, suggesting that ice cover sufficient to shield tors from incoming radiation was of short duration. The few younger tor ages support the idea of continuing landform instability across the landscape, with weathering flakes redeveloping soon after inferred loss of top pillows by gelifraction or gravitational toppling. The few older tor ages have no systematic explanation, and may indicate inheritance from an earlier cycle of bedrock near-exposure. Since most tors are modest in height (typically 2-5 m), volumetrically insignificant, and often in advanced stages of disintegration, the general impression is that they are evanescent features, which emerge and quickly disappear during every Pleistocene climatic downturn. Tor populations may thus flicker across the landscape rather randomly over the Quaternary. The remarkably consistent age of the present tor population could be associated with a stripping event at the start of the Devensian, but fuller analysis must await closer controls on tor denudation rates in different climatic phases, and on ice cover extent and duration. These results only date extant tor surfaces, not the landscape, but as the best available erosion pins they have evident value in exploring theories of the evolution of Dartmoor during the Quaternary.

Gunnell, Yanni; Jarman, David; Braucher, Régis; Calvet, Marc; Delmas, Magali; Leanni, Laetitia; Bourlès, Didier; Arnold, Maurice; Aumaître, Georges; Keddaouche, Karim

2013-02-01

205

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

Science.gov (United States)

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

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

2004-01-01

206

A 50,000-year record of late Pleistocene tropical vegetation and human impact in lowland Borneo  

Science.gov (United States)

There has been considerable uncertainty about the nature of Pleistocene environments colonised by the first modern humans in Island SE Asia, and about the vegetation of the Last Glacial Maximum (LGM) in the region. Here, the palynology from a series of exposures in the Great Cave of Niah, Sarawak, Malaysian Borneo, spanning a period from ca. 52,000 to 5000 BP is described. Vegetation during this period was climate-driven and often highly unstable. Interstadials are marked by lowland forest, sometimes rather dry and at times by mangroves. Stadials are indicated by taxa characteristic of open environments or, as at the LGM, by highly disturbed rather open forest. Stadials are also characterised by taxa now restricted to 1000-1600 m above sea level, suggesting temperature declines of ca 7-9 °C relative to present, by comparison with modern lapse rates. The practice of biomass burning appears associated with the earliest human activity in the cave.

Hunt, Chris O.; Gilbertson, David D.; Rushworth, Garry

2012-03-01

207

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

208

The stratigraphy of Oxfordian-Kimmeridgian (Late Jurassic) reservoir sandstones in the Witch Ground Graben, United Kingdom North Sea  

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Oil-bearing Upper Jurassic Oxfordian-Kimmeridgian sandstones of the Sgiath and Piper formations are of major economic importance in the Witch Ground Gaben, United Kingdom North Sea. They form the reservoirs in 14 fields that originally contained 2 billion bbl of oil reserves, including Scott Field, which in 1993 will be the largest producing United Kingdom North Sea oil field to come on stream in more than a decade. The Sgiath and Piper formations represent Late Jurassic transgressive and regressive phases that began with paralic deposition and culminated in a wave-dominated delta system. These phases preceded the major grabel rifting episode (late Kimmeridgian to early Ryazanian) and deposition of the Kimmeridge Clay Formation, the principal source rock of the Witch Ground Graben oil fields. A threefold subdivision of the middle to upper Oxfordian Sgiath Formation is formally proposed, with Scott field well 15/21a-15 as the designated reference well. The basal Skene Member consists of thinly interbedded paralic carbonaceous shales, coals, and sandstones. This is overlain by transgressive marine shales of the Saltire Member. The upper-most Oxfordian Scott Member consists of shallow marine sandstones that prograded to the southwest. The contact of the Sgiath and Piper formations is a basinwide transgressive marine shale (I shale), which can act as an effective barrier to fluid communication between the Sgiath and Piper reservoir sandstones.

Harker, S.D. (Elf Enterprise Caledonia Ltd., Aberdeen (United Kingdom)); Mantel, K.A. (Narwhal, London (United Kingdom)); Morton, D.J. (Deminex UK Oil Gas Ltd., London (United Kingdom)); Riley, L.A. (Paleo Services, Hertfordshire (United Kingdom))

1993-10-01

209

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

210

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

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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

211

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

Science.gov (United States)

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

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

2012-06-01

212

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

Science.gov (United States)

The Mexico City metropolitan area is home to more than 22 million people living in sight of, or living on, several volcanoes that either are currently active or show evidence of Late Pleistocene-Holocene activity (e.g., pyroclastic flows, debris avalanches and lahars). The volcanic rocks are located in five main belts or ranges: Sierra Nevada, Sierra de las Cruces, Sierra Guadalupe, Sierra de Santa Catarina, and the Chichinautzin Volcanic Field which surround the Mexico Basin and belong to the Trans-Mexican Volcanic Belt, preserving approx. 14 Ma of geologic history. Much attention has been devoted to the youngest of the volcanoes such as Popocatépetl in the Sierra Nevada which resumed activity in 1994-present and Chichinautzin which includes the 1600 year bp Xitle volcano. Surprisingly, the pre-Holocene history is not well constrained in the Mexico City area, due of the lack of detailed mapping coupled with high precision geochronology. Our new 40Ar/39Ar and petrologic data and detailed mapping focus on the earliest history of these volcanic systems and their temporal, spatial and geochemical evolution. For example, data from Tlaloc and Telapón volcanoes in the Sierra Nevada show at least two significant periods of edifice building (1.0 to 1.5 Ma and 0 to 400 ka) with an apparent long period of quiescence that clearly suggests that volcanism in the region did not migrate from north to south but that it has a more complex evolution that continues to pose a serious threat to the population of Mexico City. In addition, a 450 ka age, based on dome and pumice dating, constrains the timing of a major sector collapse of Iztaccíhuatl volcano that produced a Mt. St. Helens - sized debris avalanche deposit towards the present metropolitan area of the City of Puebla. In the Sierra de las Cruces Range, volcanic centers do show a north-south age progression from ~5 Ma, cumulating with the Zempoala edifice collapse approximately 900 ka, producing lahars and block and ash deposits that now underlie the city of Cuernavaca. Zempoala is located at the southern end of Sierra de las Cruces and is in the intersection of the late Pleistocene-Holocene Chichinautzin Volcanic Field. We have obtained < 10 ka ages from Chichinautzin lavas near Zempoala and from volcanic edifices in the Sierra de Santa Catarina, which are now surrounded by densely populated areas. Our preliminary data show that there are many of these poorly understood, but potentially hazardous, volcanic centers throughout the Mexico Basin that have evidence of Late Pleistocene-Holocene activity. Further geological mapping and geochronologic data will allow us to better understand the complex migration patterns and eruption occurrence rate of the volcanic centers around Mexico City, evaluate their potential hazards, and understand the evolution of these ranges in relation to the tectonic framework in central Mexico.

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

2009-12-01

213

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

214

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

Science.gov (United States)

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

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

2010-01-01

215

Steppe lion remains imported by Ice Age spotted hyenas into the Late Pleistocene Perick Caves hyena den in northern Germany  

Science.gov (United States)

Upper Pleistocene remains of the Ice Age steppe lion Panthera leo spelaea (Goldfuss, 1810) have been found in the Perick Caves, Sauerland Karst, NW Germany. Bones from many hyenas and their imported prey dating from the Lower to Middle Weichselian have also been recovered from the Perick Cave hyena den. These are commonly cracked or exhibit deep chew marks. The absence of lion cub bones, in contrast to hyena and cave bear cub remains in the Perick Caves, and other caves of northern Germany, excludes the possibility that P. leo spelaea used the cave for raising cubs. Only in the Wilhelms Cave was a single skeleton of a cub found in a hyena den. Evidence of the chewing, nibbling and cracking of lion bones and crania must have resulted from the importation and destruction of lion carcasses (4% of the prey fauna). Similar evidence was preserved at other hyena den caves and open air sites in Germany. The bone material from the Perick and other Central European caves points to antagonistic hyena and lion conflicts, similar to clashes of their modern African relatives.

Diedrich, Cajus G.

2009-05-01

216

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

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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

217

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

218

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

Science.gov (United States)

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

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

2011-12-01

219

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

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The Berkine Basin is an intra- or pericratonic basin that developed during the Middle to Late Triassic on the margin of the Saharan platform. The basin lies to the east of the north-south trending Hassi Messaoud Ridge which separates it from the Oued Mya Basin to the west. These Algerian basins lie to the south and east of the network of rift basins that developed in the Iberian peninsular and along the margins of the North Atlantic seaboard. The principal hydrocarbon reservoir is the Upper Triassic Argilo-Greseux Inferieur (TAG-1) which, in Blocks 401a and 402a, is Carnian to Norian in age. Elsewhere in North Africa, especially to the south and east, there are older Triassic formations. For example, in Zarzaitine in the extreme south east of the Triassic Algedan outcrop, Anisian vertebrates are documented. The TAG-1 sits unconformably on Palaeozoic basement rocks and with the basal Lower Carbonate comprises a laterally and vertically variable sequence which has been sub-divided into four depositional sequences: Sequence 1, an unconformity-bounded, ephemeral fluvial interval that fills palaeorelief on the Hercynian unconformity; Sequence 2, an initially upward-fining, and subsequently upward-coarsening package of perennial fluvial sandstones and floodbasin shales with thin crevasse splay elements and interfluve palacosols; Sequence 3, an erosively based, fluvio-lacustrine section characterised by fluvial sandstones with associated crevasse sandstones and floodbasin/lacustrine shales. This sequence is the main hydrocarbon reservoir section and is divided into two main packages 3A and 3B; the base of 3B is distinguished by basin-wide fluvial incision and the widespread channel sand deposition; Sequence 4 (Lower Carbonate) is a coastal plain and shallow marine system comprising shales, sabkha-type evaporites and bay-fill sandstones. The four depositional sequences reflect differences in depositional style resulting from base level shifts, tectonics and climate throughout TAG-1 times. The overall increase in relative sea level was interrupted by periods of incision, which may relate to periods of rifting and erosion of the rift shoulders of the Berkine Basin. The initial valley fill (Sequence 1) was deposited under relatively and or semi-arid conditions. During Sequences 2 and 3A, perennial fluvial systems with anastomosed channels and floodplain lakes became dominant and the climate increasingly humid. At this time a major longitudinal drainage, divide developed due to intrabasinal lifting. The basin was ultimately flooded by the transgressive systems tract of Sequence 4. (author)

Turner, P.; Sabaou, N. [University of Birmingham (United Kingdom). School of Earth Sciences; Pilling, D.; Walker, D. [PM Geos, Aberdeen (United Kingdom); Exton, J.; Binnie, J. [BHP Petroleum, London (United Kingdom)

2001-07-01

220

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. PMID:23805019

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

2013-05-15

221

Late Pleistocene-Holocene Faulting History Along the Northern El Carrizal Fault, Baja California Sur, Mexico: Earthquake Recurrence at a Persistently Active Rifted Margin  

Science.gov (United States)

The El Carrizal fault is a NW striking, east dipping normal fault located 25 km west of the city of La Paz, Baja California Sur, Mexico and is the westernmost bounding fault of the gulf-margin system at this latitude. The fault is ~70 km long onshore and ~50 km long offshore to the north in La Paz Bay. As many as three Quaternary geomorphic surfaces formed on the footwall and were identified on the basis of mapping and topographic profiling. In the north, the El Carrizal fault splays into multiple strands and exhibits a pattern of alternating N-S and NW-trending segments. Results from geologic mapping, paleoseismic investigations, and preliminary optically stimulated luminescence (OSL) geochronology provide some of the first numerical constraints on late Pleistocene-Holocene faulting along the El Carrizal fault. A 20 m long, 2-3 m deep trench (Trench 28) was excavated across the fault 23 km south of La Paz Bay. The trench was photographed, hand logged, and sampled for OSL dating. The trench revealed a succession of fluvial and channel deposits of sands, gravels, and cobbles. The main fault zone is manifested by a 0.5 m thick wedge-shaped deposit that consists of silty-sand and also contains rotated blocks of caliche- cemented gravels. Preliminary OSL ages from a silty-sand unit offset 2 m by the fault average latest Pleistocene. A trench 4 km south of Trench 28 (Cuadradito Trench) was also documented and sampled for OSL analysis. Preliminary OSL ages from a fluvial sand unit deposited against faulted bedrock range from mid to late Holocene. Sedimentary comparisons and surficial mapping suggest that the Holocene unit at Cuadradito Trench may be correlative to sediment that overlies faulted units from Trench 28. Such a correlation would constrain the timing of the 2 m offset at Trench 28 to be between latest Pleistocene and mid Holocene. A quarry 10 km north of Trench 28 exposes Quaternary sand and gravels buttressed against a 5-10 m wide bedrock shear zone. Here, the sediments appear to be faulted by 3 to 4 earthquakes. The two most recent events may have experienced 1-2 m of offset each. Map relationships suggest that this faulted unit is correlative to a fluvial unit near Bonfil that yields an optical age of early Holocene. This would imply that the two most recent events at the quarry are Holocene in age. Based on preliminary OSL data and total measured offset at trench sites, the slip rates are estimated to be from 0.1 to 0.5 mm/yr. In summary, earthquake recurrence and slip rate may increase towards the north along the El Carrizal fault, consistent with footwall geologic mapping. If the El Carrizal fault abides by the rules of normal fault geometry and fault offset, it is likely that the fault is at a maximum total offset offshore of San Juan de la Costa, a prediction to be tested in the summer of 2008 by offshore imaging using Compressed High Intensity Radar Pulse (CHIRP). Improving the earthquake record along the El Carrizal fault will prove beneficial for understanding the seismic hazards to the city of La Paz. Furthermore, quantifying faulting rates throughout the southwestern margin of the Gulf of California will improve our understanding of the rift-to-drift process and how that process has operated along an oblique-divergent plate margin.

Maloney, S. J.; Umhoefer, P. J.; Arrowsmith, J. R.; Gutiérrez, G. M.; Santillanez, A. U.; Rittenour, T. R.

2007-12-01

222

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)

223

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

224

A reconstruction of late Pleistocene relative sea level in the south Bohai Sea, China, based on sediment grain-size analysis  

Science.gov (United States)

Future anthropogenic sea-level rise and its impact on coastal regions is an important issue facing human civilizations. Due to the short nature of the instrumental record of sea-level change, development of proxies for sea-level change prior to the advent of instrumental records is essential to reconstruct long-term background sea-level changes on local, regional and global scales. Here, we employ numerical methods to partition sediment grain size using a combined database of marine surface and core samples, and to quantitatively reconstruct sea-level variation since the late Pleistocene in the south Bohai Sea, China. Our sea-level reconstruction indicates that relative sea-level changes in the southern Bohai Sea track global sea-level variation for the duration of the record. The results also indicate substantial regression from 70 to 30 cal kyr BP, and potentially subarial exposure from 38 to 20 cal kyr BP. Our results document the feasibility of reconstructing relative sea-level change by numerical partitioning of sediment grain size data, demonstrating the potential for future applications.

Yi, Liang; Yu, Hongjun; Ortiz, Joseph D.; Xu, Xingyong; Qiang, Xiaoke; Huang, Haijun; Shi, Xuefa; Deng, Chenglong

2012-12-01

225

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

Science.gov (United States)

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

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

2014-01-01

226

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

227

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

228

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

Science.gov (United States)

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

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

2014-02-01

229

Distribution and three-dimensional relationship of Holocene and Late Pleistocene seismic facies beneath the Yellow Sea  

Science.gov (United States)

High-resolution reflection seismic data reveal a complex stacking pattern of seismic reflections associated with buried submarine sediment beneath the Yellow Sea. This volume offers several interpretations that seek to explain this complex stratigraphic stacking pattern using data published in the literature as well as the extensive 6,000-kilometer grid of reflection seismic profiles that was the primary dataset for this study. The first chapter describes the aggradational nature of Yellow River sedimentation and discusses several possible reasons for the absence of a pronounced incised valley that should have formed by a river of the magnitude of the Yellow River during the sea level lowstand associated with the last glacial maximum. Several hypotheses that attempt to explain this are suggested and evaluated. The second chapter focuses on the transgressive surface of erosion associated with the Early Holocene rise in sea level. This ravinement surface is similar in flatness to other ravinement surfaces found around the world, but has a larger lateral extent that may have been the site of the fastest rate of transgression in the past 20,000 years. Older transgressive surfaces are identified, and assumptions about their initial and final geometry lead to insight about sediment compaction, vertical motion, and tectonism during the Pleistocene. The third chapter in this volume incorporates the separate elements of all of the discrete sequence stratigraphic packages, relates seismic reflection geometry, stratigraphic architecture and sequence stratigraphic prediction of sediment distribution to actual distribution of sediment lithofacies revealed by borehole cores and inferred by a novel acoustic technique. This sediment distribution is different than might be predicted by general models developed on passive continental margins, specifically because lowstand sediment associated with the Yellow River appears to be primarily deposited in the Eastern Yellow Sea, away from the shore where the Yellow River currently enters and has traditionally entered the Yellow Sea, which is on the western side. The protrusion of erosion-resistant crystalline rock bodies controls the location of the Yellow River during sea level lowstands, and is responsible for this unusual situation.

Moss, Corey Charles

2002-04-01

230

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

Science.gov (United States)

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

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

2010-05-01

231

Late-Pleistocene to precolumbian behind-the-arc mafic volcanism in the eastern Mexican Volcanic Belt; implications for future hazards  

Science.gov (United States)

An area of widespread alkaline-to-subalkaline volcanism lies at the northern end of the Cofre de Perote-Citlaltépetl (Pico de Orizaba) volcanic chain in the eastern Mexican Volcanic Belt (MVB). Two principal areas were active. About a dozen latest-Pleistocene to precolumbian vents form the 11-km-wide, E-W-trending Cofre de Perote vent cluster (CPVC) at 2300-2800 m elevation on the flank of the largely Pleistocene Cofre de Perote shield volcano and produced an extensive lava field that covers >100 km 2. More widely dispersed vents form the Naolinco volcanic field (NVF) in the Sierra de Chiconquiaco north of the city of Jalapa (Xalapa). Three generations of flows are delineated by cone and lava-flow morphology, degree of vegetation and cultivation, and radiocarbon dating. The flows lie in the behind-the-arc portion of the northeastern part of the MVB and show major- and trace-element chemical patterns transitional between intraplate and subduction zone environments. Flows of the oldest group originated from La Joya cinder cone (radiocarbon ages ˜42?000 yr BP) at the eastern end of the CPVC. This cone fed an olivine-basaltic flow field of ˜20 km 2 that extends about 14 km southeast to underlie the heavily populated northern outskirts of Jalapa, the capital city of the state of Veracruz. The Central Cone Group (CCG), of intermediate age, consists of four morphologically youthful cinder cones and associated vents that were the source of a lava field>27 km 2 of late-Pleistocene or Holocene age. The youngest group includes the westernmost flow, from Cerro Colorado, and a lava flow ˜2980 BP from the Rincón de Chapultepec scoria cone of the NVF. The latest eruption, from the compound El Volcancillo scoria cone, occurred about 870 radiocarbon years ago and produced two chemically and rheologically diverse lava flows that are among the youngest precolumbian flows in México and resemble paired aa-pahoehoe flows from Mauna Loa volcano. The El Volcancillo eruption initially produced the high effusion rate, short-duration Toxtlacuaya alkaline aa lava flow from the southeastern crater. This 12-km-long hawaiite (average 50.5% SiO 2) flow was followed by extrusion of the calc-alkaline R?´o Naolinco lava flow from the northwestern crater. This large-volume (˜1.3 km 3) tube-fed basaltic pahoehoe flow (average SiO 2 49%) traveled 50 km. Inferred effusion rates suggest emplacement over a decade-long period. Flows of all three age groups are transected by Highway 140 and the railway that form major transportation arteries between Jalapa and Puebla. This area has not previously been considered to be at volcanic risk, but volcanism here has continued into precolumbian time. Future eruptions of similar magnitude and location to those documented here could pose significant hazards to transportation corridors and to densely populated areas in and to the north of Jalapa. Slight variations in vent locations could produce future flows down one or more of more than a half dozen drainages with widely varying population densities.

Siebert, Lee; Carrasco-Núñez, Gerardo

2002-06-01

232

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

233

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

234

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

Directory of Open Access Journals (Sweden)

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

Tadeusz SOKO?OWSKI

2009-01-01

235

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

Science.gov (United States)

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

236

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

Scientific Electronic Library Online (English)

Full Text Available SciELO Argentina | Language: Spanish Abstract in spanish Sobre la base del estudio de foraminíferos y ostrácodos, se describe la evolución de ambientes marino- costeros al sudeste de la provincia de Buenos Aires afectados por las variaciones del nivel del mar durante el Pleistoceno tardío. Fueron estudiadas dos perforaciones realizadas al sur de la laguna [...] Mar Chiquita. En las secciones inferiores de las perforaciones (A y B) se registran ambientes marinos marginales que pueden ser asignados a la Formación Canal 5 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

237

Maps Showing Inundation Depths, Ice-Rafted Erratics, and Sedimentary Facies of Late Pleistocene Missoula Floods in the Willamette Valley, Oregon  

Science.gov (United States)

Glacial Lake Missoula, impounded by the Purcell Trench lobe of the late Pleistocene Cordilleran Icesheet, repeatedly breached its ice dam, sending floods as large as 2,500 cubic kilometers racing across the Channeled Scabland and down the Columbia River valley to the Pacific Ocean. Peak discharges for some floods exceeded 20 million cubic meters per second. At valley constrictions along the flood route, floodwaters temporarily ponded behind each narrow zone. One such constriction at Kalama Gap-northwest of Portland-backed water 120-150 meters high in the Portland basin, and backflooded 200 km south into Willamette Valley. Dozens of floods backed up into the Willamette Valley, eroding 'scabland' channels, and depositing giant boulder gravel bars in areas of vigorous currents as well as bedded flood sand and silt in backwater areas. Also, large chunks of ice entrained from the breached glacier dam rafted hundreds of 'erratic' rocks, leaving them scattered among the flanking foothills and valley bottom. From several sources and our own mapping, we have compiled information on many of these features and depict them on physiographic maps derived from digital elevation models of the Portland Basin and Willamette Valley. These maps show maximum flood inundation levels, inundation levels associated with stratigraphic evidence of repeated floodings, distribution of flood deposits, and sites of ice-rafted erratics. Accompanying these maps, a database lists locations, elevations, and descriptions of approximately 400 ice-rafted erratics-most compiled from early 20th-century maps and notes of A.M. Piper and I.S. Allison.

Minervini, J.M.; O'Connor, J. E.; Wells, R.E.

2003-01-01

238

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

Scientific Electronic Library Online (English)

Full Text Available SciELO Chile | Language: Spanish Abstract in spanish Se describen restos del género Hippidion procedentes de la zona del desierto de Atacama (Calama, Segunda Región de Chile). El conjunto analizado corresponde a un esqueleto bastante completo proveniente del yacimiento Betecsa 1, así como escasas unidades del yacimiento Kamac Mayu. En ambos sitios se [...] identifica H. saldiasi. A partir de dos dataciones radiométricas por AMS del ejemplar estudiado, los restos se sitúan estratigráficamente en el Pleistoceno Superior (21.070 ± 100 AP y 21.380 ± 100 14C AP). Se infieren datos ambientales y de dieta a partir de análisis de isótopos estables en los restos de Hippidion saldiasi del sitio Betecsa 1 cuyo valor de ?13C en hueso fue de -15,45 y el valor en esmalte de dientes fue de -16,68, sugiriendo una alimentación con pastos C3. El cráneo recuperado es el primero conocido de esta especie Abstract in english This paper describes the Hippidion bones recovered from the Atacama Desert (Calama, Second Region of Chile). The analyzed assemblage corresponds to a nearly complete skeleton from Betecsa 1 site and more poorly preserved remains from Kamac Mayu site. In both H. saldiasi is identified. Two 14C radiom [...] etric determinations indicate late Pleistocene age for these remains (21,070 ± 100 BP and 21,380 ± 100 BP). Environmental and diet inferences from stable isotope analysis are also presented. The ?13C value from Betecsa 1 horses (-15.45 from bone sample and -16.68 from enamel sample) suggest a dietary adaptation exclusively C3 feeders. This is the first skull and associated skeleton recovered of this species

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

2007-06-01

239

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

Directory of Open Access Journals (Sweden)

Full Text Available Se describen restos del género Hippidion procedentes de la zona del desierto de Atacama (Calama, Segunda Región de Chile. El conjunto analizado corresponde a un esqueleto bastante completo proveniente del yacimiento Betecsa 1, así como escasas unidades del yacimiento Kamac Mayu. En ambos sitios se identifica H. saldiasi. A partir de dos dataciones radiométricas por AMS del ejemplar estudiado, los restos se sitúan estratigráficamente en el Pleistoceno Superior (21.070 ± 100 AP y 21.380 ± 100 14C AP. Se infieren datos ambientales y de dieta a partir de análisis de isótopos estables en los restos de Hippidion saldiasi del sitio Betecsa 1 cuyo valor de ?13C en hueso fue de -15,45 y el valor en esmalte de dientes fue de -16,68, sugiriendo una alimentación con pastos C3. El cráneo recuperado es el primero conocido de esta especieThis paper describes the Hippidion bones recovered from the Atacama Desert (Calama, Second Region of Chile. The analyzed assemblage corresponds to a nearly complete skeleton from Betecsa 1 site and more poorly preserved remains from Kamac Mayu site. In both H. saldiasi is identified. Two 14C radiometric determinations indicate late Pleistocene age for these remains (21,070 ± 100 BP and 21,380 ± 100 BP. Environmental and diet inferences from stable isotope analysis are also presented. The ?13C value from Betecsa 1 horses (-15.45 from bone sample and -16.68 from enamel sample suggest a dietary adaptation exclusively C3 feeders. This is the first skull and associated skeleton recovered of this species

MARÍA TERESA ALBERDI

2007-06-01

240

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

241

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

Science.gov (United States)

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

242

Particulate versus integrated evolution of the upper body in late pleistocene humans: a test of two models.  

Science.gov (United States)

Evolutionary biologists are largely polarized in their approaches to integrating microevolutionary and macroevolutionary processes. Neo-Darwinians typically seek to identify population-level selective and genetic processes that culminate in macroevolutionary events. Epigeneticists and structuralists, on the other hand, emphasize developmental constraints on the action of natural selection, and highlight the role of epigenetic shifts in producing evolutionary change in morphology. Accordingly, the ways in which these paradigms view and address morphological contrasts between classes of related organisms differ. These paradigms, although seldomly explicitly stated, emerge in paleoanthropology as well. Considerations of postcranial morphological contrasts between archaic and modern humans typically fall into one of two broad interpretive models. The first derives from the neo-Darwinian perspective and holds that evolution in the postcranial skeleton was largely mosaic (operating in a particulate manner), and that temporal change in specific traits informs us about behavioral shifts or genetic evolution affecting isolated anatomical regions (i.e., adaptive behavioral inferences can be made from comparative studies of individual trait complexes). The alternative model follows from the epigeneticist paradigm and sees change in specific postcranial traits as correlated responses to change in overall body form (involving shifts in regulation of skeletal growth, or selective and developmental responses to broad adaptive shifts). By this view, integration of functional systems both constrains and directs evolution of various traits, and morphological contrasts inform us about overall change in body form related to change in such things as overall growth patterns, climatic adaptation, and technological dependency. These models were tested by confirmatory factor analysis using measures of upper body form and upper limb morphological traits in Eurasian Neandertal and early modern fossils and recent human samples. Results indicate (1) a model of morphological integration fits the data better than a model of no integration, but (2) this integration accounts for less than half of the variance in upper limb traits, suggesting a high degree of tolerance for particulate evolution in the context of an integrated upper body plan. Significant relationships were detected between joint shapes and body size, between humeral shaft shape and body size and chest shape, and between measures of biomechanical efficiency and robusticity. The observed morphological differences between late archaic and early modern humans reflect particulate evolution in the context of constraints imposed by genetic and morphological integration. While particulate approaches to interpreting the fossil record appear to be justified, attention must also be paid to delineating the nature and extent of morphological integration and its role in both constraining and producing observed patterns of variation between groups. Confirmatory factor analysis provides a means of examining trait covariance matrices, and serves as a useful method of identifying patterns of integration in morphology. PMID:8842328

Churchill, S E

1996-08-01

243

Fault Slip Partitioning in the Eastern California Shear Zone-Walker Lane Belt: Pliocene to Late Pleistocene Contraction Across the Mina Deflection  

Science.gov (United States)

Two different mechanisms have been proposed for fault slip transfer between the subparallel NW-striking dextral- slip faults that dominant the Eastern California Shear Zone (ECSZ)-Walker Lane Belt (WLB). In the northern WLB, domains of sinistral-slip along NE-striking faults and clockwise block rotation within a zone of distributed deformation accommodated NW-dextral shear. A somewhat modified version of this mechanism was also proposed for the Mina deflection, southern WLB, whereby NE-striking sinistral faults formed as conjugate faults to the primary zone of NW-dextral shear; clockwise rotation of the blocks bounding the sinistral faults accommodated dextral slip. In contrast, in the northern ECSZ and Mina deflection, domains of NE-striking pure dip-slip normal faults, bounded by NW-striking dextral-slip faults, exhibited no rotation; the proposed mechanism of slip transfer was one of right-stepping, high angle normal faults in which the magnitude of extension was proportional to the amount of strike-slip motion transferred. New geologic mapping, tectonic geomorphologic, and geochronologic data from the Queen Valley area, southern Mina deflection constrain Pliocene to late Quaternary fault geometries, slip orientations, slip magnitudes, and slip rates that bear on the mechanism of fault slip transfer from the relatively narrow northern ECSZ to the broad deformation zone that defines the Mina deflection. Four different fault types and orientations cut across the Queen Valley area: (1) The NE-striking normal-slip Queen Valley fault; (2) NE-striking sinistral faults; (3) the NW-striking dextral Coyote Springs fault, which merges into (4) a set of EW-striking thrust faults. (U-Th)/He apatite and cosmogenic radionuclide data, combined with magnitude of fault offset measurements, indicate a Pliocene to late Pleistocene horizontal extension rate of 0.2-0.3 mm/yr across the Queen Valley fault. Our results, combined with published slip rates for the dextral White Mountain fault zone (0.3-0.8 mm/yr) and the eastern sinistral Coaldale fault (0.4 mm/yr) suggest that transfer of dextral slip from the narrow White Mountains fault zone is explained best by a simple shear couple whereby slip is partitioned into three different components: horizontal extension along the Queen Valley fault, dominantly dextral slip along the Coyote Springs fault, and dominantly sinistral slip along the Coaldale fault. A velocity vector diagram illustrating fault slip partitioning predicts contraction rates of Mina deflection is consistent with present-day GPS data.

Lee, J.; Stockli, D.; Gosse, J.

2007-12-01

244

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

International Nuclear Information System (INIS)

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

245

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.

246

Dark humic alluvial paleosols in Central and Southern Mexico: Micromorphological indicators of Late Pleistocene megafauna habitats Paleosuelos aluviales con humus oscuro en el Centro y Sur de México: indicadores micromorfológicos de los hábitats de la megafauna del Pleistoceno tardío Paleosolos aluviais com húmus escuro no Centro e Sul do México: indicadores micromorfológicos dos habitats da megafauna do Pleistocénico tardio  

OpenAIRE

During the Late Pleistocene, Mexico had a richer fauna than today with many different forms of megafauna that are now extinct. However, the ecosystems they inhabited and the particular ecological niches that they occupied are still poorly understood. Most of the findings of Pleistocene megafauna have been in alluvial deposits that present rich opportunities for paleoecological studies using paleopedological records. Floodplain paleosols commonly are poorly developed. However, micromorphologic...

Tovar, Rosa E.; Sergey Sedov; Berenice Solís; Elizabeth Solleiro

2013-01-01

247

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

Science.gov (United States)

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

248

Combined use of relative and absolute dating techniques for detecting signals of Alpine landscape evolution during the late Pleistocene and early Holocene  

Science.gov (United States)

A combination of three relative and two absolute (numerical) dating techniques, applied on nine soil profiles in an Alpine environment located in Val di Rabbi (Trentino, Northern Italy), was used to improve the investigation methodology of Alpine sites in response to climate change and to reconstruct the chronology of late Pleistocene and early Holocene landscape evolution. The degree of podzolisation, clay mineral evolution and the element mass balances of each site were investigated. Furthermore, the stable fraction of the soil organic matter (SOM) was extracted with 10% H 2O 2 and 14C-dated. The age of the organic residues was compared with the age of charcoal fragments found in one of the studied soils and with the age of rock boulders obtained by surface exposure dating (SED) with cosmogenic 10Be. Numerical dating and weathering characteristics of the soils showed a fairly good agreement and enabled a relative and absolute differentiation of landscape elements. The combination of 14C-dating of SOM and SED indicated that deglaciation processes in Val di Rabbi were already far advanced by around 14 000 cal BP and that glacier oscillations affected the highest part of the region until about 9000 cal BP. The development of clay minerals is time-dependent and reflects weathering intensity. We found a close link between secondary clay minerals like smectite or vermiculite and soil age as obtained by the dating of the organic residues after the H 2O 2 treatment. Calculated element mass balances strongly correlated with the ages derived from 14C measurements. Old soils have lost a major part of base cations (up to 75% compared to the parent material), Fe and Al, which indicates a continuous high weathering intensity. Results of the chemical and mineralogical analyses were in good agreement with numerical dating techniques, showing the dynamics of an Alpine landscape within a relatively small area. The combination of relative and absolute dating techniques is a promising tool for the reconstruction of landscape history in high-elevation Alpine areas on siliceous substrates.

Favilli, Filippo; Egli, Markus; Brandova, Dagmar; Ivy-Ochs, Susan; Kubik, Peter; Cherubini, Paolo; Mirabella, Aldo; Sartori, Giacomo; Giaccai, Daniele; Haeberli, Wilfried

2009-11-01

249

Polymorphism in pleistocene land snails.  

Science.gov (United States)

Under suitable conditions the colors and patterns of the shells of land snails may be preserved for thousands of years. In a late Pleistocene population of Limicolaria martensiana all the major color forms that occur in modern living snails may be distinguished, and the basic polymorphism is at least 8,000 to 10,000 year old. PMID:17830234

Owen, D F

1966-04-01

250

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

Scientific Electronic Library Online (English)

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

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

2010-12-01

251

Contribution to the stratigraphy of the onshore Paraiba Basin, Brazil  

Energy Technology Data Exchange (ETDEWEB)

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

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

2012-06-15

252

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

Scientific Electronic Library Online (English)

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

Kamal M., Hussein.

2006-12-01

253

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

Scientific Electronic Library Online (English)

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

Khalid F, Ubeid.

2013-12-01

254

Late Pleistocene steppe lion Panthera leo spelaea (Goldfuss, 1810) footprints and bone records from open air sites in northern Germany - Evidence of hyena-lion antagonism and scavenging in Europe  

Science.gov (United States)

Bone remains and a trackway of Pantheraichnus bottropensis nov. ichg. ichnsp. of the Late Pleistocene lion Panthera leo spelaea ( Goldfuss, 1810) have been recovered from Bottrop and other open air sites in northern Germany. Some of these bones are from open air hyena den sites. A relative high proportion of lion bones (20%) exhibit bite, chew or nibble marks, or bone crushing and nibbling caused by a large carnivore. Repeated patterns of similar bone damage have been compared to bone remains found at hyena dens in gypsum karst areas and cave sites in northern Germany. Ice Age spotted hyenas have been the main antagonists and the main scavengers on lion carcasses. The remains appear to have been imported often by hyenas into their communal dens, supporting the theory of strong hyena-lion antagonism, similar to the well documented antagonism between modern African lions and spotted hyenas. Most of the lion bones from the open air hyena den at Bottrop are probably a result of such antagonism, as are the rare remains of these carnivores found within large hyena prey bone accumulations along the Pleistocene rivers. The Emscher River terrace also has the largest quantity of hyena remains from open air river terrace sites in northern Germany. Their cub remains, and incomplete chewed prey bones from mammoths and woolly rhinoceroses, typical of hyena activity, underline the character of these sites as cub-raising and communal dens, where their prey was accumulated along the riverbanks in a similar manner to modern African hyenas.

Diedrich, Cajus G.

2011-07-01

255

Los mamíferos finipleistocénicos de la Formación Quebrada Quereo (IV Región-Chile): biogeografía, bioestratigrafía e inferencias paleoambientales / The Late Pleistocene mammal record of Quebrada Quereo Formation: biogeography, biostratigraphy and paleoclimatic inferences  

Scientific Electronic Library Online (English)

Full Text Available SciELO Argentina | Language: Spanish Abstract in spanish [...] Abstract in english This paper describes the fossil fauna recovered from the Quebrada Quereo Formation (Late Pleistocene - Holocene) located at Choapa Province, IV Region, Chile. In this formation, two cultural levels (Quereo I y II) with Pleistocenic fauna were detected. The remains identified include living species ( [...] Dusycion cf. D. culpaeus), as well as extinguished fauna (Palaeolama sp., Antifer sp., Equus [Amerhippus] sp., cf. Panthera onca, Milodontidae, and Gomphoteriidae). For each of these, we present taxonomic, paleogeographic and paleoclimatic remarks. The possible presence of P. onca in Quebrada Quereo Formation constitutes the first evidence of a locally extinct felid outside the Patagonic area of Chile. The identified faunal assemblage presents differences with those recorded in Argentinean territory; which is explained by the presence of the Cordillera de los Andes. The Chilean paleofaunistic assemblages, therefore, are related to those found in Bolivia and the Andean occidental sector in general, although some enrichment with taxa from the oriental side of the range is not discarded.

Rafael O., Labarca; Patricio G., López.

2006-06-01

256

Use of spectral gamma-ray data to refine subsurface fluvial stratigraphy: late Cretaceous strata in the Book Cliffs, Utah, USA  

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High-resolution (sub-seismic) stratigraphic correlation in fluvial strata is extremely difficult using conventional subsurface core and wireline-log data (e.g. gamma-ray, neutron, density, sonic logs). Spectral gamma-ray logs provide additional data on lithological composition that can aid identification of chronostratigraphic surfaces in a high-resolution sequence stratigraphic correlation framework. The application of spectral gamma-ray data in constructing such a framework is demonstrated using data from exposures and the subsurface from the Cretaceous non-marine Blackhawk Formation and Castlegate Sandstone of the Book Cliffs area, Utah, USA. The stratigraphic abundance of coals and relatively uniform Th/K ratio, which indicates uniform clay mineralogy, in mudstone sections of the non-marine Blackhawk Formation implies a humid, subtropical climate throughout its deposition. Variations in facies architecture and stratigraphy are therefore interpreted to have been driven principally by fluctuations in relative sea level and hinterland tectonics. It is concluded that within the context of a sound understanding of detrital mineralogy, diagenetic history, facies and appropriate sequence stratigraphic models, spectral gamma-ray data allow sequence boundaries to be identified and correlated in non-marine fluvial strata at least 80 km from the interpreted coeval shoreline.

Hampson, G.J.; Davies, W.; Davies, S.J.; Howell, J.A.; Adamson, K.R. [University of London Imperial College of Science Technology & Medicine, London (United Kingdom). Dept. of Earth Science & Engineering

2005-07-01

257

A new record of Equus (Mammalia: Equidae from the Late Pleistocene of central-south Chile Un nuevo registro de Equus (Mammalia: Equidae para el Pleistoceno Superior de Osorno, Chile  

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Full Text Available Fourteen dental and bone parts of a horse excavated from the Pilauco paleontological site, Osorno (40°39' S-73°07' W are analysed and interpreted. This site was formed in association with a peat bog located on the banks of the old Damas River and has conserved abundant late Pleistocene mammalian fauna and flora materials. A date of 11457 ± 140 14C yrs B.P. was obtained from a molar and agrees with our stratigraphic age model. We have identified the fossils as pertaining to the species Equus (Amerhippus andium, which confirms its presence in central-south Chile. Furthermore, the recorded geographic location indicate that the metapodial adaptations of the specimens previously described agree with the reconstructed late Pleistocene landscape of Pilauco, dominated by soft volcanic soils and isolated forest patches over large extensions of grasslands.Se analizan e interpretan 14 fósiles correspondientes a dientes y huesos de caballo registrados en el sitio Pilauco, Osorno (40°39' S-73°07' W. El sitio se formó asociado a un pantano en un borde del antiguo río Damas; en él se ha conservado abundante material de mastofauna y flora pleistocénica. Una fecha radiocarbónica de 11457 ± 140 A.P obtenida de un molar, es concordante con el modelo de edad del sitio. La identificación taxonómica permite asociar a los fósiles a la especie Equus (Amerhippus andium, lo que confirma la presencia de la especie en el centro-sur de Chile. Por otra parte, la posición geográfica de los hallazgos y la reconstrucción del paisaje indicarían que se trata de ejemplares cuyas adaptaciones en los metapodios son concordantes para el paisaje pleistocénico de Pilauco dominado por suelos volcánicos blandos, con presencia de bosquetes dispersos en grandes extensiones de praderas de gramíneas.

OMAR P RECABARREN

2011-12-01

258

A new record of Equus (Mammalia: Equidae) from the Late Pleistocene of central-south Chile / Un nuevo registro de Equus (Mammalia: Equidae) para el Pleistoceno Superior de Osorno, Chile  

Scientific Electronic Library Online (English)

Full Text Available SciELO Chile | Language: English Abstract in spanish Se analizan e interpretan 14 fósiles correspondientes a dientes y huesos de caballo registrados en el sitio Pilauco, Osorno (40°39' S-73°07' W). El sitio se formó asociado a un pantano en un borde del antiguo río Damas; en él se ha conservado abundante material de mastofauna y flora pleistocénica. U [...] na fecha radiocarbónica de 11457 ± 140 A.P obtenida de un molar, es concordante con el modelo de edad del sitio. La identificación taxonómica permite asociar a los fósiles a la especie Equus (Amerhippus) andium, lo que confirma la presencia de la especie en el centro-sur de Chile. Por otra parte, la posición geográfica de los hallazgos y la reconstrucción del paisaje indicarían que se trata de ejemplares cuyas adaptaciones en los metapodios son concordantes para el paisaje pleistocénico de Pilauco dominado por suelos volcánicos blandos, con presencia de bosquetes dispersos en grandes extensiones de praderas de gramíneas. Abstract in english Fourteen dental and bone parts of a horse excavated from the Pilauco paleontological site, Osorno (40°39' S-73°07' W) are analysed and interpreted. This site was formed in association with a peat bog located on the banks of the old Damas River and has conserved abundant late Pleistocene mammalian fa [...] una and flora materials. A date of 11457 ± 140 14C yrs B.P. was obtained from a molar and agrees with our stratigraphic age model. We have identified the fossils as pertaining to the species Equus (Amerhippus) andium, which confirms its presence in central-south Chile. Furthermore, the recorded geographic location indicate that the metapodial adaptations of the specimens previously described agree with the reconstructed late Pleistocene landscape of Pilauco, dominated by soft volcanic soils and isolated forest patches over large extensions of grasslands.

OMAR P, RECABARREN; MARIO, PINO; INÉS, CID.

2011-12-01

259

Palaeoecology of well-preserved coral communities in a siliciclastic environment from the Late Pleistocene (MIS 7), Kish Island, Persian Gulf (Iran): the development of low-relief reef frameworks (biostromes) in increasingly restricted environments  

Science.gov (United States)

Major changes in community structure and depositional relief of high-latitude coral communities in the southern Persian Gulf between marine isotope stage (MIS) 7 and the present day suggest that the area has become increasingly restricted. Corals and bivalves from outcrops on Kish Island, Iran, were identified in order to interpret the Late Pleistocene palaeoenvironmental setting. U/Th disequilibrium dating was used to constrain the ages of the stratigraphic units. During MIS 7, two coral-bearing sequences were deposited on what is now Kish Island. The lower sequence is dated as MIS 7.5 and changes laterally from an assemblage dominated by Cyphastrea sp. and Platygyra daedalea in the west to one characterized by branching Montipora in the east. By contrast, the upper sequence, dated as MIS 7.1, transitions from an assemblage dominated by platy Montipora in the west to a diverse assemblage of Platygyra and other faviids in the east. The assemblages of both sequences are within a marl matrix and bounded by thin lithified mollusc-rich layers. Corals and bivalves indicate that the sequences were deposited on gentle slopes in sheltered environments less than 20 m deep. The MIS 7 deposits may be classified as coral carpets or biostromes that developed a low-relief framework. During MIS 5, coral communities were no longer framework building and are now limited to an Acropora-rich layer of coral rubble that covers large parts of the island, and two small incipient reefs with sparse faviids. Similarities between the MIS 5 and modern nearshore coral communities suggest that the environmental conditions during MIS 5 were comparable to those of today. The late Pleistocene coral carpets and non-framework coral communities of the southern Persian Gulf may serve as models for coral biostromes in the fossil record, which formed under restricted environmental conditions such as elevated terrigenous input, high turbidity, and strong seasonal changes in temperature and/or salinity.

Mossadegh, Zahra Karimi; Parker, Justin; Gischler, Eberhard; Oschmann, Wolfgang; Blakeway, David; Eisenhauer, Anton

2013-03-01

260

Synthetic seismograms from vibracores: A case study in correlating the late quaternary seismic stratigraphy of the New Jersey inner continental shelf  

Science.gov (United States)

A new technique, using empirical relationships between median grain size and density and velocity to calculate proxy values for density and velocity, avoids many of the problems associated with the use of well logs and shipboard measurements to construct synthetic seismograms. This method was used to groundtruth and correlate across both analog and digital shallow high-resolution seismic data on the New Jersey shelf. Sampling dry vibracores to determine median grain size eliminates the detrimental effects that coring disturbances and preservation variables have on the sediment and water content of the core. The link between seismic response to lithology and bed spacing is more exact. The exact frequency of the field seismic data can be realistically simulated by a 10-20 cm sampling interval of the vibracores. The estimate of the percentage error inherent in this technique, 12% for acoustic impedance and 24% for reflection amplitude, is calculated to one standard deviation and is within a reasonable limit for such a procedure. The synthetic seismograms of two cores, 4-6 m long, were used to correlate specific sedimentary deposits to specific seismic reflection responses. Because this technique is applicable to unconsolidated sediments, it is ideal for upper Pleistocene and Holocene strata. Copyright ?? 1996, SEPM (Society for Sedimentary Geology).

Esker, D.; Sheridan, R.E.; Ashley, G.M.; Waldner, J.S.; Hall, D.W.

1996-01-01

261

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

Scientific Electronic Library Online (English)

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

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

2012-06-01

262

Pollen analyses of Pleistocene hyaena coprolites from Montenegro and Serbia  

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Full Text Available 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 Pleistocene. Pollen extracted from a coprolite from the Baranica cave indicates an open landscape with the presence of steppe taxa, which is in accordance with the recorded conditions and faunal remains. Pollen analysis of the Early Pleistocene samples from Trlica indicate fresh and temperate humid climatic conditions, as well as the co-existence of several biotopes which formed a mosaic landscape in the vicinity of the cave.

Argant Jacqueline

2007-01-01

263

Geochemical evidence for enhanced preservation of organic matter in the oxygen minimum zone of the continental margin of northern California during the Late Pleistocene  

Science.gov (United States)

The present upper water mass of the northeastern Pacific Ocean off California has a well-developed oxygen minimum zone between 600 and 1200 m wherein concentrations of dissolved oxygen are less than 0.5 mL/L. Even at such low concentrations of dissolved oxygen, benthic burrowing organisms are abundant enough to thoroughly bioturbate the surface and near-surface sediments. These macro organisms, together with micro organisms, also consume large quantities of organic carbon produced by large seasonal stocks of plankton in the overlying surface waters, which are supported by high concentrations of nutrients within the California Current upwelling system. In contrast to modern conditions of bioturbation, laminated sediments are preserved in upper Pleistocene sections of cores collected on the continental slope at water depths within the present oxygen minimum zone from at least as far north as the California-Oregon border and as far south as Point Conception. Comparison of sediment components in the laminae with those delivered to sediment traps as pelagic marine "snow" demonstrates that the dark-light lamination couplets are indeed annual (varves). These upper Pleistocene varved sediments contain more abundant lipid-rich "sapropelic" (type II) organic matter than the overlying bioturbated, oxidized Holocene sediments. The baseline of stable carbon isotopic composition of the organic matter in these slope cores does not change with time, indicating that the higher concentrations of type II organic matter in the varved sediments represent better preservation of organic matter rather than any change in the source of organic matter.

Dean, Walter E.; Gardner, James V.; Anderson, Roger Y.

1994-02-01

264

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

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

Zhong, G.; Wang, L.

2013-12-01

265

Pleistocene subglacial tunnel valleys in the central North Sea basin: 3-D morphology and evolution  

Science.gov (United States)

Four phases of cross-cutting tunnel valleys imaged on 3-D seismic datasets are mapped within the Middle-Late Pleistocene succession of the central North Sea basin (Witch Ground area). In plan the tunnel valleys form complex anastomosing networks, with tributary valleys joining main valleys at high angles. The valleys have widths ranging from 250 to 2300 m, and base to shoulder relief varying between 30 and 155 m, with irregular long-axis profiles characteristic of erosion by water driven by glaciostatic pressures. The youngest phase of tunnel valleys are smaller and have a thinner infill than the older generations. The fill of the larger valleys comprises three seismic facies, the lowermost of which has high amplitudes and is discontinuous. The middle facies consists of wedge-shaped packages of low-angle dipping reflectors and is overlain by a facies characterised by sub-horizontal reflectors, which onlap the valley margins. The seismic character, and comparison with lithologies identified in other northwest European Pleistocene tunnel valleys both onshore and offshore, suggests that the lower two seismic facies are most likely sand and gravel-dominated, while the uppermost facies consists of glaciolacustrine and marine muds. The 3-D morphology of the valley margins combined with the geometry of the infill packages suggest that episodic discharge of subglacial meltwater was responsible for incising the valleys and depositing at least some of the infill. Proglacial glaciofluvial deposits are inferred to account for some of the fill overlying the subglacial deposits. Glaciolacustrine and marine muds filled remaining valley topography as the ice sheet retreated. The preserved valley margins are shown to be time-transgressive erosion surfaces that record changes in geometry of the tunnel valley system as it evolved through time, implying that valleys associated with each ice-sheet advance/retreat cycle were dynamic and probably long-lived. Within the constraints of the existing stratigraphy the oldest tunnel valleys in the Witch Ground area of the central North Sea are most likely to be Marine Isotope Stage (MIS) 12 (Elsterian, ca. 470 ka) in age and the youngest pre-MIS 5e (last interglacial, ca. 120 ka). If each tunnel valley phase was formed during the retreat of a major ice sheet then four glaciations with ice coverage of the central North Sea are recorded in the pre-Weichselian, Middle-Late Pleistocene stratigraphy. Copyright

Lonergan, Lidia; Maidment, Susannah C. R.; Collier, Jenny S.

2006-12-01

266

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

Science.gov (United States)

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

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

2001-12-01

267

Late Oligocene larger foraminifera from Nosara (Nicoya Peninsula, Costa Rica) and Indward (Carriacou, Lesser Antilles), calibrated by 87SR/86SR isotope stratigraphy  

International Nuclear Information System (INIS)

The late Oligocene first occurrence of Miogypsina gunteri Cole and Miogypsina tani Drooger is verified in the light of larger foraminiferal assemblages from Nosara (Nicoya Peninsula, Costa Rica) and Windward (Carriacou, Grenada, Lesser Antilles). At Windward, they co-occur with planktonic foraminifera and nannofossils studied by earlier workers. 87SR/86SR isotope ratios were measured in calcite of larger foraminifera at both sites to determine independent absolute ages of the two outcrops. Late Oligocene shallow water formations unconformably overlie Paleocene-Eocene distal turbidites and siliceous shales in the outcrops in Costa Rica. The shallow-water lithostratigraphy includes near shore volcanic sandstones that alternate with sandy bioclastic limestones. The latter have yielded rich assemblages of larger foraminifera that have been studied in oriented sections, SEM for split material and polished rock thin sections for transmitted light and cathodoluminescence (CL) observation. The association of larger foraminifera includes Heterostegina antillea Cushman, Miogypsina tani Drooger, Miogypsina gunteri Cole, Miogypsina c.f (Miolepidocyclina) panamensis (Cushman), Miogypsina sp., Lepidocyclina (nephrolepidina) vaughani Cushman, Lepidocyclina yurnagurensis Cushman, Lepidocyclina undosa Cushman. At Windward, scattered outcrops of the Belvedere Formation expose mass flow deposits rich in larger foraminifera associated with an early late Oligocene (Nassociated with an early late Oligocene (NP24) planktonic foraminifa assemblage. Planktonic foraminifera and nannofossils recovered in rocks slightly downsection indicate an upper Middle Oligocene age. Larger foraminifera species collected just north of Windward include Lepidocyclina undosa Cushman and Miogypsina gunteri Cole. The 87SR/86SR ratio was measured in 11 specimens of megalosphaeric Lepidocyclina spp., mechanically extracted from 2 rock samples collected at Punta Peladas (Costa Rica) Ratios range from 0.709088 to 0.708196, which correspond to a model age of 27.4 to 24.94 Ma. Very similar ratios, ranging from 0.708150 to 0.708167 were obtained from Windward Village (Carriacou). All measured 87SR/86SR ratios fall within a Chattian (Late Oligocene) age. Nannofossils, planktonic foraminifera and identical 87SR/86SR ratios from Punta Peladas and Windward clearly indicate a Chattian (Upper Oligocene) first occurrence of Miogypsina gunteri and Miogypsina tani and confirm this age range for the other larger foraminifera cited above. The first occurrence of Miogypsina gunteri in the lower Aquitanian and Miogypsina tani in the upper Aquitanian as proposed by European workers cannot be confirmed. (author)

268

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

Science.gov (United States)

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

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

2005-04-01

269

Cogenetic late Pleistocene rhyolite and cumulate diorites from Augustine Volcano revealed by SIMS 238U-230Th dating of zircon, and implications for silicic magma generation by extraction from mush  

Science.gov (United States)

Volcano, a frequently active andesitic island stratocone, erupted a late Pleistocene rhyolite pumice fall that is temporally linked through zircon geochronology to cumulate dioritic blocks brought to the surface in Augustine's 2006 eruption. Zircon from the rhyolite yield a 238U-230Th age of ˜25 ka for their unpolished rims, and their interiors yield a bimodal age populations at ˜26 ka and a minority at ˜41 ka. Zircon from dioritic blocks, ripped from Augustine's shallow magmatic plumbing system and ejected during the 2006 eruption, have interiors defining a ˜26 ka age population that is indistinguishable from that for the rhyolite; unpolished rims on the dioritic zircon are dominantly younger (?12 ka) indicating subsequent crystallization. Zircon from rhyolite and diorite overlap in U, Hf, Ti, and REE concentrations although diorites also contain a second population of high-U, high temperature grains. Andesites that brought dioritic blocks to the surface in 2006 contain zircon with young (?9 ka) rims and a scattering of older ages, but few zircon that crystallized during the 26 ka interval. Both the Pleistocene-age rhyolite and the 2006 dioritic inclusions plot along a whole-rock compositional trend distinct from mid-Holocene-present andesites and dacites, and the diorites, rhyolite, and two early Holocene dacites define linear unmixing trends often oblique to the main andesite array and consistent with melt (rhyolite) extraction from a mush (dacites), leaving behind a cumulate amphibole-bearing residue (diorites). Rare zircon antecrysts up to ˜300 ka from all rock types indicate that a Quaternary center has been present longer than preserved surficial deposits.

Coombs, Michelle L.; Vazquez, Jorge A.

2014-12-01

270

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

Directory of Open Access Journals (Sweden)

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

Silvia Lanés

2008-12-01

271

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

Scientific Electronic Library Online (English)

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

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

2008-12-01

272

Calibration of amino acid racemization (AAR) kinetics in United States mid-Atlantic Coastal Plain Quaternary mollusks using 87Sr/ 86Sr analyses: Evaluation of kinetic models and estimation of regional Late Pleistocene temperature history  

Science.gov (United States)

The use of amino acid racemization (AAR) for estimating ages of Quaternary fossils usually requires a combination of kinetic and effective temperature modeling or independent age calibration of analyzed samples. Because of limited availability of calibration samples, age estimates are often based on model extrapolations from single calibration points over wide ranges of D/L values. Here we present paired AAR and 87Sr/ 86Sr results for Pleistocene mollusks from the North Carolina Coastal Plain, USA. 87Sr/ 86Sr age estimates, derived from the lookup table of McArthur et al. [McArthur, J.M., Howarth, R.J., Bailey, T.R., 2001. Strontium isotopic stratigraphy: LOWESS version 3: best fit to the marine Sr-isotopic curve for 0-509 Ma and accompanying Look-up table for deriving numerical age. Journal of Geology 109, 155-169], provide independent age calibration over the full range of amino acid D/L values, thereby allowing comparisons of alternative kinetic models for seven amino acids. The often-used parabolic kinetic model is found to be insufficient to explain the pattern of racemization, although the kinetic pathways for valine racemization and isoleucine epimerization can be closely approximated with this function. Logarithmic and power law regressions more accurately represent the racemization pathways for all amino acids. The reliability of a non-linear model for leucine racemization, developed and refined over the past 20 years, is confirmed by the 87Sr/ 86Sr age results. This age model indicates that the subsurface record (up to 80m thick) of the North Carolina Coastal Plain spans the entire Quaternary, back to ???2.5Ma. The calibrated kinetics derived from this age model yield an estimate of the effective temperature for the study region of 11??2??C., from which we estimate full glacial (Last Glacial Maximum - LGM) temperatures for the region on the order of 7-10??C cooler than present. These temperatures compare favorably with independent paleoclimate information for the region. ?? 2011 Elsevier B.V.

Wehmiller, J. F.; Harris, W.B.; Boutin, B.S.; Farrell, K.M.

2012-01-01

273

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

International Nuclear Information System (INIS)

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

274

Stratigraphy and structural geology  

Science.gov (United States)

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

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

1976-01-01

275

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

Scientific Electronic Library Online (English)

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

Marcelo M, Rivadeneira; Erico R, Carmona.

2008-01-01

276

The significance of large sediment supply, active tectonism, and eustasy on margin sequence development: Late Quaternary stratigraphy and evolution of the Ganges Brahmaputra delta  

Science.gov (United States)

Borehole data from the Ganges-Brahmaputra delta system unveil an intriguing Late Quaternary history controlled by immense sediment discharge, tectonics, and eustasy. Sea level first intersected a major portion of the lowstand surface ˜10,000-11,000 cal yr BP, marking the onset of sediment trapping and delta growth. Despite rapid sea-level rise (>1 cm/yr), sediment load was sufficient to maintain relative shoreline stability during this time. By ˜7000 cal yr BP, accommodation was quickly infilled with slowed sea-level rise, leading to upstream channel migration and widespread dispersal of sands. This forced coastal progradation along the western delta front where the Ganges was situated, and much of the river's fine-grained discharge bypassed the subaerial delta and formed a prograding deltaic clinoform on the shelf. Concurrently, Brahmaputra sediments were sequestered to an inland tectonic basin, thus starving the adjacent shoreline and leading to transgression along the eastern delta. By ˜5000 cal yr BP, the two rivers had migrated or changed course to discharge along the eastern delta shoreline which began to prograde into what is now the modern river-mouth estuary. Present delta configuration appears to have developed by ˜3000 cal yr BP. Evolution of the tectonically active Ganges-Brahmaputra (G-B) system reveals important similarities and differences with other deltas. Overall facies succession follows that of basic models, progressing from an alluvial valley to coastal marine delta front to a prograding subaerial delta plain. However, the timing, thickness, and controls of these deposits differ. Immense sediment discharge from the Ganges and Brahmaputra rivers allowed initial delta growth 2000-3000 yr earlier than the global average, despite debouching onto a canyon-incised, high-energy margin. Subsequently, a thick (˜50 m) transgressive systems tract was formed during the early Holocene phase of delta aggradation, contrasting with extensive shoreline retreat documented along most margins. Highstand progradation of coastal and shelf sequences ensued by the middle Holocene, but subsiding inland basins also favored accumulation of a thick (to 40 m) highstand sequence in the lower floodplains. Unlike many other delta systems, subsidence in the subaerial G-B delta is not dominated by compaction, but rather by plate-driven tectonic processes that generate rates up to 4 mm/year. Overall, the huge sediment load, tectonic subsidence, major seismic events, and a nearshore canyon system have led to widespread sediment dispersal and sequence formation across the subaerial delta, shelf, and deep-sea Bengal Fan throughout the Late Quaternary.

Goodbred, S. L.; Kuehl, S. A.

2000-06-01

277

Pleistocene seismic sequences may result from eustatic change but can they be used for global correlations? New Insights from the Canterbury Basin, New Zealand  

Science.gov (United States)

To understand the influence of eustasy on continental margin sedimentation and test the concepts of sequence stratigraphy, Integrated Ocean Drilling Program Expedition 317 drilled four sites on the continental shelf and upper slope of the Canterbury Basin, eastern South Island, New Zealand. We present results from upper slope Site U1352 (320 m water depth). A high-resolution multiproxy approach involving geochemical elemental analyses, lithostratigraphy and biostratigraphy, calibrated to an oxygen isotope scale, was applied to understand sedimentation over the past ~1.8 million years. Multichannel seismic data (EW00-01 survey) provided a seismic sequence stratigraphic framework against which to interpret the data. Seismic sequence boundaries are represented by a unique geochemical signature and arrangement of overlying sedimentary facies. However, several such geochemical-lithologic units are commonly contained within each seismic sequence. These higher frequency, intrasequence geochemical units generally correlate with100 ky glacial-interglacial Milankovic variability in the late Pleistocene, revealing that it took several glacio-eustatic cycles to build each seismic sequence. These findings support prior results obtained from Pleistocene sediments recovered by Ocean Drilling Program Leg 174A that drilled on the New Jersey margin with similar objectives to those of Expedition 317. In both northern and southern hemisphere siliciclastic settings there is a strong correlation between seismic sequences and glacio-eustasy, but the correlation between isotopic cycles and sequence boundaries is not one-to-one: only a subset of the glacioeustatic cycles result in a preserved seismic sequence boundary. Furthermore, late Pleistocene sequence boundaries on the two margins are not synchronous. Local conditions cause different isotopic peaks to be preferentially preserved as sequence boundaries in each location and preserved seismic sequences contain different groupings of marine isotope stages. Therefore, high-frequency Pleistocene seismic sequences may not correlate globally even though they are driven by glacio-eustasy.

McHugh, C. M.; Fulthorpe, C.; Hoyanagi, K.; Blum, P.

2013-12-01

278

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

DEFF Research Database (Denmark)

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

Sprafke, Tobias; Terhorst, Birgit

2013-01-01

279

Orbitally tuned age model for the late Pliocene-Pleistocene lacustrine succession of drill core SG-1 from the western Qaidam Basin (NE Tibetan Plateau)  

Science.gov (United States)

The availability of accurate and reliable age control is a crucial prerequisite for palaeoclimate studies, particularly when different archives are to be compared. Here we present a detailed depth-to-time transformation for the lacustrine sediments of a ˜940-m-long drill core (SG-1) from the western Qaidam Basin (NE Tibetan Plateau). To establish a more precise age model than the one previously available, which was based solely on magnetostratigraphic dating using polarity boundaries as tie points, we applied time-series analysis on magnetic susceptibility (?) variation. The ? data are available in high resolution and are considered to be closely linked to orbital forcing. Since the sediment accumulation rate (SAR) varies strongly throughout the succession of core SG-1, conventional cyclostratigraphy by bandpass filtering cannot be applied. We present two alternative age models based on spectral characteristics and orbital tuning. The first age model (TPspec) is based on the assumption that changes in SAR occurred when the frequency spectra revealed obviously different characteristics in the spectral pattern. For the second age model (SARA), SAR was adjusted every 2 m by comparing observed with expected orbital cycles in accordance with the age of magnetic reversals. This age model appears more robust and shows the most convincing spectral results in the frequency and wavelet power spectrum of ?. According to the SARA age model, SAR varies between 14 and 73 cm kyr-1, and the bottom of SG-1 has an age of 2.69 Ma. Our results show that orbital tuning can be successfully applied for sequences with strongly variable SAR. The age model SARA can be used for a more detailed analysis of the existing multiproxy data set in terms of palaeoclimate evolution. The most prominent feature of ? spectra using the SARA age model is the identification of the middle Pleistocene transition.

Herb, Christian; Appel, Erwin; Voigt, Silke; Koutsodendris, Andreas; Pross, Jörg; Zhang, Weilin; Fang, Xiaomin

2015-01-01

280

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

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

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

2007-04-01

281

Post-last glacial alluvial fan and talus slope associations (Northern Calcareous Alps, Austria): A proxy for Late Pleistocene to Holocene climate change  

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Near Innsbruck city (Austria, Eastern Alps), following the Last Glacial Maximum (LGM), an alluvial fan-to-talus slope succession was supplied from a carbonate-rock cliff more than 1000 m in height. 234U/ 230Th ages of 9.5 to 9.37 isotope kyrs of diagenetic cements in the alluvial-fan succession suggest that the fan/talus deposit accumulated mainly during late-glacial to, perhaps, early Holocene times. The deepest-exposed interval of the fan succession contains cracked lithoclasts probably fractured by overburden from late-glacial ice; this interval is topped by an intra-sequence unconformity. Following final glacial retreat, and rapid aggradation of the alluvial fan and talus slope, the geomorphic regime changed to erosion, as recorded by fanhead trenching and cutting of fluvial terraces, abandonment and vegetating of scree slopes, and excavation of 'talus flatirons'. The changeover from the accumulation of fan and talus to abandonment and dissection probably took place during the terminal late-glacial interval to perhaps the early Holocene. This erosional regime persists until present. A record of rapid late-glacial to early Holocene accumulation of an alluvial fan/talus deposit followed by: (i) abandonment and vegetation growth, combined with (ii) cutting of intra-sequence unconformities of limited lateral extent, is typical of Alpine mountain-flank deposystems situated at comparatively low altitudes. This record consists of (a) an autocyclic component, that is, progressive lowering of sediment input due to onlap and burial of freshly-deglaciated mountain flanks supplying alluvial fans and talus slopes, and (b) an allocyclic component, that is, deglacial climatic warming and upward rise of an altitudinal range with a maximum number of freeze-thaw cycles ('talus window'), also leading to progressive vegetation-induced hillslope stabilization and lowering of scree production.

Sanders, Diethard; Ostermann, Marc

2011-08-01

282

Tectonic and sedimentary evolution of the late Miocene-Pleistocene Dali Basin in the southeast margin of the Tibetan Plateau: Evidences from anisotropy of magnetic susceptibility and rock magnetic data  

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The Cenozoic Dali Basin, located at the northeast of Diancang Shan and south of the first bend of Yangtze River, is tectonically controlled by the Dali fault system in the southeast margin of the Tibetan Plateau. The basin is filled with late Miocene to Pleistocene fluviolacustrine sediments, which provide invaluable information about the tectonic deformation and drainage network reorganization in this area. In this study, we discuss the anisotropy of magnetic susceptibility (AMS) of the Dasongping section in the Dali Basin, which spans an interval from 7.6 to 1.8 Ma. Although rock magnetic experiments indicate that magnetite and hematite are the main remanence carriers, hysteresis loops, low values of bulk susceptibility and low temperature susceptibility suggest that paramagnetic minerals are major contributors to low-field AMS. The rock magnetic parameters indicate that the Dali Basin experienced four stages of infilling and the sediment sources may have changed at 4.2 Ma. The clustering of the minimum principle axes (Kmin) nearly perpendicular to the bedding plane and the pronounced N-S magnetic lineation parallel to the bedding plane indicate that the AMS of the Dali Basin is a superimposed fabric consisting of a sedimentary-compaction and a mild initial deformation overprint. The well-defined N-S magnetic lineation is likely due to the NNW and NNE oblique shear caused by the Heqing and Red River faults.

Li, Shihu; Deng, Chenglong; Paterson, Greig A.; Yao, Haitao; Huang, Sheng; Liu, Chengying; He, Huaiyu; Pan, Yongxin; Zhu, Rixiang

2014-08-01

283

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

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

Choukri Abdelmajid

2008-03-01

284

Stratigraphy of the Harwell boreholes  

International Nuclear Information System (INIS)

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

285

Combined use of relative and numerical dating techniques for detecting signals of Alpine landscape evolution during the late Pleistocene and early Holocene in Val di Rabbi (Trentino, northern Italy)  

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A combined use of relative and absolute dating techniques was applied on nine soil profiles in order to reconstruct late Pleistocene and early Holocene landscape evolution in an Alpine environment located in Val di Rabbi (Trentino, northern Italy). The degree of podzolisation, clay mineral evolution and element mass balances of each site were investigated. Furthermore, the stable fraction of the soil organic matter (SOM) was extracted from selected horizons with 10% H2O2 and 14C-dated. The ages of the organic residues were compared with the ages of charcoal fragments found in one of the studied soils and with the ages of rock boulders obtained by the surface exposure dating (SED) method with cosmogenic 10Be. The combination of 14C dating of SOM and SED indicated that deglaciation processes in Val di Rabbi were very much advanced around 14000 cal BP and that glacier oscillations have affected the highest part of the region until about 9000 cal BP. The development of clay mineral reflects weathering intensity. We found a close link between secondary clay minerals like smectite and vermiculite and soil age as obtained by H2O2. The degree of podzolisation is time dependent and was used as an evidence of surface stability. The amount of Fe and Al forms that migrated and accumulated in the illuvial horizon correlated well with the time of soil development. Element mass balance calculations strongly correlated with the ages derived from 14C measurements. Old soils have lost a major part of base cations (up to 75%), Fe and Al. Chemical and mineralogical analyses were in good agreement with numerical dating techniques, showing the dynamics of an Alpine landscape within a relatively small area and enabling a relative and absolute differentiation of landscape elements. The combination of relative and numerical dating techniques is a promising tool to understand landscape evolution and to provide absolute chronologies of the Late glacial in high-elevation Alpine areas with siliceous parent material.

Favilli, F.; Egli, M.; Brandova, D.; Ivy-Ochs, S.; Kubik, P.; Cherubini, P.; Mirabella, A.; Sartori, G.; Giaccai, D.; Haeberli, W.

2009-04-01

286

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

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

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

2014-03-01

287

Palaeoclimatic implications of the growth history and stable isotope (? 18O and ? 13C) geochemistry of a Middle to Late Pleistocene stalagmite from central-western Italy  

Science.gov (United States)

The age structure and stable isotope composition of a stalagmite (CC1) from an upland cave in central-western Italy were studied to investigate regional response to global climatic changes. Four growth phases are constrained by 28 thermal ionization and multi-collector inductively coupled plasma mass spectrometry Th-U ages and reveal intermittent deposition through the period between Marine Isotope Stage (MIS) 11 and 3 (˜380 and ˜43 kyr). Most of the growth took place between ˜380 and ˜280 kyr, a period punctuated briefly by a hiatus in deposition through the glacial maximum of MIS 10. Growth was terminated abruptly at 280 kyr just prior to the MIS 8 glacial maximum. With a present-day chamber temperature of 7.5 °C, the timing of hiatuses close to these glacial maxima point to freezing conditions at the time. No deposition was recorded through the entirety of MIS 7 and most of MIS 6, whilst two minor growth phases occurred at ˜141-125 and ˜43 kyr. Growth at 141 kyr indicates temperatures >0 °C at a time when MIS 6 ice volumes were close to their maximum. High stable carbon isotope (? 13C) values (-2.8‰ to +3.1‰) throughout the stalagmite's growth reflect a persistently low input of biogenic CO 2, indicating that the steep, barren and alpine-like recharge area of today has been in existence for at least the last ˜380 kyr. During MIS 9, the lowest ? 13C values occur well after maximum interglacial conditions, suggesting a lag in the development of post-glacial soils in this high-altitude karst. The stable oxygen isotope (? 18O) trends match the main structural features of the major climate proxy records (SPECMAP, Vostok and Devils Hole), suggesting that the ? 18O of CC1 has responded to global-scale climate changes, whilst remarkable similarity exists between CC1 ? 18O and regional sea-surface temperature reconstructions from North Atlantic core ODP980 and southwest Pacific marine core MD97-2120 through the most detailed part of the CC1 record, MIS 9-8. The results suggest that CC1 and other stalagmites from the cave have the potential to capture a long record of regional temperature trends, particularly in regards to the relative severity of Pleistocene glacial stages.

Drysdale, Russell N.; Zanchetta, Giovanni; Hellstrom, John C.; Fallick, Anthony E.; Zhao, Jian-xin; Isola, Ilaria; Bruschi, Giuseppe

2004-11-01

288

Seismic stratigraphy and Late Quaternary evolution of Mobile Bay and Mississippi Sound, Alabama -- A record of large- and small-scale fluvial systems through multiple sea-level cycles  

Science.gov (United States)

Examination of the Mississippi and Alabama shelf, mapping of offshore incised valleys and shelf-edge deltas, and determination of their feeder systems has been the subject of numerous investigations focusing on the Mobile River with considerable variation. To address this controversy approximately 750 km of high-resolution seismic data, 11 rotary drill cores, 16 vibracores, and 1 GeoProbe core were collected from Mobile Bay, the Mobile Bay-head Delta, Mississippi Sound, and along Cedar Point Peninsula to map the headward components of previously published offshore valleys and to compare the incised-valley fill to the idealized model of Zaitlin et al. (1994). Seismic data show that the Late Quaternary stratigraphy is composed of four unconformity-bound stacked seismic units. This study focuses on the upper two Seismic Units. The older unconformable surface is an exposure surface sampled in cores and interpreted as the Oxygen Isotope Stage 6 Sequence Boundary. Mapping of the Stage 6 Sequence Boundary shows a complex network of sinuous channels that flowed across Mobile Bay and eastern Mississippi Sound separated by a well-developed terraced morphology. The youngest unconformity is an exposure surface sampled in cores and based on 14C data is interpreted as the Oxygen Isotope Stage 2 Sequence Boundary of the last lowstand in sea-level. Mapping of the Stage 2 Sequence Boundary indicates that all systems re-incised their older lowstand valleys in approximately the same locations and are again bound by a well-developed terrace morphology. Lithologic data show that the valley-fill sequences differ from the idealized model. The Stage 6 to 5e valley fill is composed of alluvial sediment capped by bay-head delta facies whereas Stage 2 to 1 valley fill is solely composed of central basin sediments. The absence of Stage 2 to 1 bay-head delta facies implies backstepping of bay-head deltas from the Alabama shelf to the northern shorelines of Mobile Bay and Mississippi Sound. Based on sea-level curves and 14C data, these backstepping events must have occurred before 9.5 ka in Mobile Bay and 7.0 ka in Mississippi Sound. The two estuaries, while different in their orientations and timing of initial inundation, have similar evolutionary histories.

Greene, David Lawrence, Jr.

289

Deep-sea pleistocene biostratigraphy.  

Science.gov (United States)

The first detailed paleontological analysis of a deep-sea pistoncore from the Caribbean Sea has been completed. The core, P6304-8, was raised from 3927 meters, east of Beata Ridge at 14 degrees 59'N, 69 degrees 20'W. Formerly, stratigraphic works in this area were based on studies of paleotemperature, measured by the oxygen isotope mass spectrometry method, or on micropaleontological analysis by means of rapid or cursory examinations. For core P6304-8, samples for foraminiferal analysis were taken at 10-centimeter intervals and split into smaller samples containing an average of 710 individuals (smallest sample, 517 individuals); all individuals were then identified and counted. By use of data derived from populations of this size, a statistical reliability was insured within a 5 percent limnit. Temperature oscillations, the best method of portraying Pleistocene stratigraphy, were shown by using ratios of the relative abundances of tropical and subtropical planktonic foraminifera to those found in temperate and cooler waters. These ratios correlate well with existing paleotemperature measurements for the same core, obtained by the oxygen isotope mass spectrometry method. PMID:17821563

Lidz, L

1966-12-16

290

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

International Nuclear Information System (INIS)

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

291

AMS radiocarbon dating of the marine late Pleistocene-Holocene sediment cores from the western Ulleung Basin, East/Japan Sea  

International Nuclear Information System (INIS)

We present the results on radiocarbon dating of planktonic foraminifera samples from two piston cores collected from the western part of the Ulleung Basin, East/Japan Sea. Until recently, there were no radiocarbon dates from late Quaternary sediments of this location. Eight samples from the Ulleung Basin cores were accelerator mass spectrometry (AMS) 14C-dated, and reservoir-corrected using R-values as 400 yr. The results indicate that the cores cover the time interval from the middle stage of marine isotope stage (MIS) 3 through last glacial maximum (LGM) to Holocene, and the average sedimentation rate of the cores vary from 17.61 cm/kyr to 19.96 cm/kyr. Particularly, it is shown using the calibrated 14C data that in the cores hemipelagic muds (bioturbated and slightly laminated mud facies) were mainly formed during interglacial periods (MIS 1/3), whereas non-hemipelagic muds (laminated and homogenous mud facies) were deposited during glacial period (MIS 2)

292

Coral associations of the Pleistocene Ironshore Formation, Grand Cayman  

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

Hunter, I. G.; Jones, B.

1996-11-01

293

Late Pleistocene vertebrates from Touro Passo Creek (Touro Passo Formation), southern Brazil: a review / Vertebrados del Pleistoceno Tardío del arroyo Touro Passo (Formación Touro Passo), sur de Brasil: Una revisión  

Scientific Electronic Library Online (English)

Full Text Available SciELO Mexico | Language: English Abstract in spanish El Arroyo Touro Passo es una de las más importantes localidades con fósiles pleistocénicos del sur de Brasil. Aunque los vertebrados colectados en esta localidad han sido estudiados desde la década de 1970, varias preguntas siguen abiertas. En este trabajo se presenta una revisión del conocimiento a [...] cumulado desde la proposición original de la Formación Touro Passo en 1976. Las asociaciones fosilíferas contienen una predominancia de fósiles de mamíferos, y entre estos, los artiodáctilos y cingulados son los más diversos. Las edades absolutas muestran que los niveles litológicos de grano fino (por lo menos) se depositaron durante condiciones más húmedas, en los estadios isotópicos 3 y 2. Los vertebrados muestran una mezcla de afinidades entre taxones de afinidad pampeana e intertropical. El largo intervalo de tiempo en que se depositaron los estratos del Arroyo Touro Passo pudo haber contribuido a esta mezcla de fauna. Abstract in english Touro Passo Creek is one of the most important fossiliferous late Pleistocene localities from southern Brazil. Although fossil vertebrates collected from this locality have been studied since the 1970s, several questions remain open. This paper provides a review of the knowledge on this subject accu [...] mulated since the original proposition of the Touro Passo Formation in 1976. The fossil assemblages of Touro Passo Creek show a predominance of mammals, and among them, artiodactyls and cingulates are the most diverse. The available absolute ages indicate that the fine-grained lithological levels (at least) were deposited during humid conditions of the Last Glacial Maximum, within oxygen isotope stages 3 and 2. The mammal assemblages contain a mixture of intertropical and pampean taxa. The large span of time that encompasses the deposition of the Touro Passo Creek beds could have contributed to this faunal mixture.

Leonardo, Kerber; Vanessa Gregis, Pitana; Ana Maria, Ribeiro; Annie Schmaltz, Hsiou; Edison V., Oliveira.

294

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

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

Diedrich C G

2011-11-01

295

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

Scientific Electronic Library Online (English)

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

ALFREDO, PRIETO; RAFAEL, LABARCA; VÍCTOR, SIERPE.

2010-06-01

296

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

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

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

2013-02-01

297

New camelid (Artiodactyla: Camelidae) record from the late Pleistocene of Calama (Second Region, Chile): a morphological and morphometric discussion / Nuevo registro de camélido (Artiodactyla: Camelidae) del Pleistoceno final de Calama (Segunda Región, Chile): una discusión morfológica y morfométrica  

Scientific Electronic Library Online (English)

Full Text Available SciELO Mexico | Language: English Abstract in spanish En el presente trabajo se describe el material correspondiente a restos fósiles de camélidos del sitio Kamac Mayu (II Región, Chile). Este registro, fue recobrado a partir de excavaciones sistemáticas en depósitos de grava arenosa y arena dispuestos sobre una formación kárstica, erosionadas por curs [...] os fluviales durante el Pleistoceno tardío. Además de los restos de camélidos se recobró material fósil diverso compuesto por Hippidion saldiasi (Mammalia, Equidae), Macrauchenia patachonica (Mammalia, Litopterna), xenarthros indeterminados (Mammalia, Xenarhra) y aves (Aves, Rheidae), junto a especímenes de Planorbidae, Hydrobiidaee and Sphaeriidae (Mollusca) dentro de depósitos formados por el desagüe de la antigua cuenca Chiu Chiu-Calama. El estudio anatómico comparado de los restos fósiles permitió la asignación taxonómica a Lama gracilis (Gervais y Ameghino 1880), constituyéndose en un hallazgo inédito para esta región del país. Abstract in english A description of fossil remains belonging to camelids from the Kamac Mayu site (Second Region, Chile) is presented. This record was recovered from deposits of gravel and sand on karstic formations eroded by rivers during the late Pleistocene. In addition to the remains of camelids, diverse fossil ma [...] terial composed ofHippidion saldiasi (Mammalia, Equidae), Macraucheniapatachonica (Mammalia, Litopterna), undeterminedxenarthrans (Mammalia, Xenarhra) and birds (Aves, Rheidae), were recovered, along with specimens of Planorbidae, Hydrobiidaee and Sphaeriidae (Mollusca) from deposits formed by the drainage of the Chiu Chiu-Calama basin. The comparative anatomical study of the fossil material enabled the taxonomic assignment of the camelid remains to Lama gracilis (Gervais and Ameghino 1880), constituting an unprecedented finding for this region of the country.

Isabel, Cartajena; Patricio, López; Ismael, Martínez.

2010-08-01

298

Mesozoic-Cenozoic stratigraphy of the Fuegian Andes, Argentina  

OpenAIRE

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

Olivero, Eduardo Bernardo

2008-01-01

299

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

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

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

2013-08-01

300

The intensification of northern component deepwater formation during the mid-Pleistocene climate transition  

Science.gov (United States)

reconstruct mid-Pleistocene (marine isotope stages (MISs) 13-18) deepwater hydrography at Ocean Drilling Program Site 1063 (4583 m water depth, subtropical North Atlantic) using benthic foraminiferal stable isotope records. These new records complete an ~900 kyr long stratigraphy spanning MISs 8-29 (~250-1030 Ka) when combined with previously published records from Site 1063. The results indicate a change in the circulation regime of the abyssal subtropical North Atlantic during MIS 17. Prior to MIS 17, no significant glacial or interglacial ?13C gradients are evident between Site 1063 and the deep South Atlantic. After MIS 17, interglacial intervals at Site 1063 are characterized by ?13C values that consistently approach those recorded in the deep North Atlantic. Comparing Site 1063 ?13C values to 26 additional published records throughout the entire Atlantic basin supports the idea that this ?13C increase is unique to the deep North Atlantic. After MIS 17, the basin-wide influence of higher ?13C values suggests an increased relative flux of northern sourced bottom waters during interglacial periods. The timing of northern sourced water influence at Site 1063 is consistent with the timing of a shift in the orientation of the Arctic Front. Thus, this shift may signify a link between the northward penetration of relatively warm, saline surface waters into the Norwegian-Greenland Seas stimulating deep convection. Our findings fit well with the model of Imbrie et al. (1993) for the importance of the Nordic heat pump in establishing strong 100 kyr cyclicity in late Pleistocene glacial cycles.

Poirier, Robert K.; Billups, Katharina

2014-11-01

301

Carbon cycling, aquatic productivity and environmental changes during the Holocene and Late Pleistocene in NW North America: a high-resolution multiproxy study of carbon isotopes in lacustrine marl and organic matter from Spirit Lake, Yukon Territory, Canada  

Science.gov (United States)

Long-term climate records with decadal to sub-decadal resolution are rare despite the fact that they are exceptionally important, in that they provide for a better understanding of the mechanisms that force climate variability, as well as the timing of onset, duration, and variability of large climatic perturbations. An 11 m sediment core from Spirit Lake, a subarctic marl lake located in the southern Yukon Territory, Canada, recorded variation in local aquatic productivity, along with regional landscape and climate variability during the Holocene and Late Pleistocene. These environmental inferences were quantified by analysis of authigenic sediment, including carbon isotopes of carbonates ( ?13CCaCO3), carbon and nitrogen isotopes of organic matter (?13Corg and ?15Norg), as well as other sedimentological and chemical proxies (e.g. grain size, carbonate, carbon, and nitrogen content, carbon to nitrogen ratios, total organic carbon, and total organic matter). Relatively high sedimentation rates and sampling frequency of 1 mm to 10 cm for ?13CCaCO3 yielded a total of ~3000 carbonate isotope samples with an annual to decadal temporal resolution. We observe substantial variability, extremely positive values, and one of the largest shifts in ?13CCaCO3 values observed in lake sediment. A positive shift of ~25‰ in ?13CCaCO3 values occurred during the last glacial/interglacial transition, marking the onset of significantly higher rates of carbonate production. Notable decadal variability and significant shifts in the other measured proxy values mimic the large ?13CCaCO3 excursion, including a negative 6-10‰ shift in ?13Corg values. The record of ?13CCaCO3 and ?13Corg values indicates variability in the sources of carbon input into the lake sediment from isotopically discrete sources, thus directly and/or indirectly depicting lake's productivity, regional climate variability, terrestrial changes and the plant types/abundances around the lake. Moreover, this sediment record extends beyond the last glacial/interglacial transition, providing the longest regional lacustrine carbon record to date, with major implications for regional paleoclimatic interpretations.

Timsic, S.; Patterson, W. P.; Besic, D.; Eglington, B. M.

2013-12-01

302

The orbital record in stratigraphy  

Science.gov (United States)

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

Fischer, Alfred G.

1992-01-01

303

Quaternary stratigraphy: Recent changes  

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Full Text Available Corrections to the Quaternary stratigraphic division of Serbia was updated/renewed by lowering limit of the Pleistocene / Quaternary to the beginning of the Gelasian that is at approximately 2.588 million years. Rather than the officially rejected Penck & Brückner Alpine stratigraphic model, the use of oxygen isotope stages (OIS / MIS is recommended. Climatostratigraphic terms glacial and interglacial have a regional applicability and their use is recommended only in areas where there are traces of glaciation, while the terms cold and warm stage (or moderate stages should be used within the global context. Eopleistocene is a regional term for the former Soviet Union and due to its uniqueness it can hardly be applied in the stratigraphical scheme of the Quaternary depostis in Serbia. With the latest extension of the Lower Pleistocene, further use of Eopleistocene would lead to further confusion in stratigraphic correlation as such the use of the Lower / Early Pleistocene or other appropriate stratigraphic units is recommended. [Projekat Ministarstva nauke Republike Srbije, br. 47007

Gaudenji Tivadar

2012-01-01

304

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

Scientific Electronic Library Online (English)

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

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

2009-06-01

305

Contribution to the stratigraphy of the onshore Paraíba Basin, Brazil  

Scientific Electronic Library Online (English)

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

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

2012-06-01

306

Contribution to the stratigraphy of the onshore Paraíba Basin, Brazil  

Directory of Open Access Journals (Sweden)

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

Dilce F. Rossetti

2012-06-01

307

A phase-space model for Pleistocene ice volume  

CERN Document Server

We present a phase-space model that simulates Pleistocene ice volume changes based on Earth's orbital parameters. Terminations in the model are triggered by a combination of ice volume and orbital forcing and agree well with age estimates for Late Pleistocene terminations. The average phase at which model terminations begin is approximately 90 +/- 90 degrees before the maxima in all three orbital cycles. The large variability in phase is likely caused by interactions between the three cycles and ice volume. Unlike previous ice volume models, this model produces an orbitally driven increase in 100-kyr power during the mid-Pleistocene transition without any change in model parameters. This supports the hypothesis that Pleistocene variations in the 100-kyr power of glacial cycles could be caused, at least in part, by changes in Earth's orbital parameters, such as amplitude modulation of the 100-kyr eccentricity cycle, rather than changes within the climate system.

Imbrie, John Z; Lisiecki, Lorraine E

2011-01-01

308

Is the modern koala ( Phascolarctos cinereus) a derived dwarf of a Pleistocene giant? Implications for testing megafauna extinction hypotheses  

Science.gov (United States)

The modern Australian koala ( Phascolarctos cinereus) is commonly regarded as a dwarf descendent of a Late Pleistocene giant koala ( Ph. stirtoni). The implication of that hypothesis is that the giant koala survived the Late Pleistocene megafaunal extinction "event", albeit as a smaller body-sized form. It is important to be able to constrain rates of Late Pleistocene faunal turnover, an aspect reliant on having accurate taxonomic information of extinct species. The koala dwarfing hypothesis is tested here by using a temporally-constrained biogeographical record of fossil koalas, and a morphological character analysis. The contemporary occurrence of both taxa in pre-Late Pleistocene deposits and significant differences in dental morphologies between those forms suggests that the modern koala is not a derived dwarf of the Pleistocene giant koala. Thus, the giant-form was among a number of other giant mammals, lizards and birds that suffered extinction sometime during the Late Pleistocene. The potential phenomenon of dwarfing of other Late Pleistocene and Recent faunas, such as grey kangaroos, is commonly used as a test for or against various megafaunal extinction hypotheses. However, the results of this study also demonstrate that the dwarfing hypothesis has not been adequately tested for a suite of other taxa. Thus, until the dwarfing hypothesis can be more fully tested, a clear understanding of the fate of Late Pleistocene faunas that apparently survived the extinction "event", and the origins of many extant forms will remain elusive.

Price, Gilbert J.

2008-12-01

309

Pleistocene Paleoart of Australia  

Directory of Open Access Journals (Sweden)

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

Robert G. Bednarik

2014-02-01

310

Early and Middle Pleistocene Faunal and Hominins Dispersals through Southwestern Asia  

OpenAIRE

This review summarizes the paleoecology of the Early and Middle Pleistocene of southwestern Asia, based on both flora and fauna, retrieved from a series of ‘windows’ provided by the excavated sites. The incomplete chrono-stratigraphy of this vast region does not allow to accept the direct chronological correlation between the available sites and events of faunal and hominin dispersals from Africa. It also demonstrates that hominins survived in a mixed landscape of open parkland with fores...

Bar-yosef, Ofer; Belmaker, Miriam

2010-01-01

311

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

Scientific Electronic Library Online (English)

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

Perla A, Imbellone; Andrea, Cumba.

2003-07-01

312

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

Directory of Open Access Journals (Sweden)

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

Manuel Szelagowski

2004-12-01

313

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

Directory of Open Access Journals (Sweden)

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

Perla A Imbellone

2003-07-01

314

The magnetic polarity stratigraphy of the Mauch Chunk Formation, Pennsylvania  

OpenAIRE

Three sections of Chesterian Mauch Chunk Formation in Pennsylvania have been studied paleomagnetically to determine a Late Mississippian magnetic polarity stratigraphy. The upper section at Lavelle includes a conglomerate with abundant red siltstone rip-up clasts that yielded a positive conglomerate test. All samples were subjected to progressive thermal demagnetization to temperatures as high as 700°C. Two components of magnetization were isolated: a synfolding “B” component and the pre...

Opdyke, Neil D.; Divenere, Victor J.

2004-01-01

315

Evaluation of the structure and stratigraphy over Richton Dome, Mississippi  

International Nuclear Information System (INIS)

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

316

A long-lasting steady period of isotopically heavy carbon in the late Silurian ocean: evolution of the ?13 record and its significance for an integrated ?13, graptolite and conodont stratigraphy  

Directory of Open Access Journals (Sweden)

Full Text Available The mid-Ludfordian carbon isotope excursion (CIE is probably the most intensively studied of all Palaeozoic geochemical events. This is mainly due to the fact that it represents the largest perturbation of the global carbon cycle during the entire Phanerozoic and the second largest in Earth’s history. Herein an uninterrupted and complete ?13C record is presented for the first time across the mid-Ludfordian carbon isotope excursion from the middle palaeolatitudes (Barrandian, Perunica, northern peri-Gondwana. Similar evolution of the ?13C geochemical anomaly identified in middle palaeolatitudinal and palaeotropical regions enables three distinct chemostratigraphic zones (R-Zone, S-Zone and F-Zone to be established, differentiated on the basis of their ?13C dynamics. Application of the ?13C chemostratigraphy has considerably improved correlation of earlier described Barrandian sections and allows re-evaluation of the duration of several gaps in sedimentary records. Detailed comparison of the ?13C chemostratigraphic zonation with graptolite and conodont biostratigraphic zonations has resulted in a proposal for an integrated ?13C, graptolite and conodont stratigraphy for the mid-Ludfordian interval. Analysis of the available ?13C data on the global mid-Ludfordian CIE revealed that high ?13C values attain a similar level during a long-lasting steady period. There is no statistically significant difference in the level of these high values among the ?13C records obtained from different palaeocontinents. This fact suggests that the mid-Ludfordian ?13C anomaly from different palaeocontinents originated from the same global oceanic isotopic reservoir rather than being independently evolved within small restricted epeiric basins.

Frýda J

2013-06-01

317

Upper Neogene stratigraphy and tectonics of Death Valley - A review  

Science.gov (United States)

New tephrochronologic, soil-stratigraphic and radiometric-dating studies over the last 10 years have generated a robust numerical stratigraphy for Upper Neogene sedimentary deposits throughout Death Valley. Critical to this improved stratigraphy are correlated or radiometrically-dated tephra beds and tuffs that range in age from > 3.58 Ma to < 1.1 ka. These tephra beds and tuffs establish relations among the Upper Pliocene to Middle Pleistocene sedimentary deposits at Furnace Creek basin, Nova basin, Ubehebe-Lake Rogers basin, Copper Canyon, Artists Drive, Kit Fox Hills, and Confidence Hills. New geologic formations have been described in the Confidence Hills and at Mormon Point. This new geochronology also establishes maximum and minimum ages for Quaternary alluvial fans and Lake Manly deposits. Facies associated with the tephra beds show that ???3.3 Ma the Furnace Creek basin was a northwest-southeast-trending lake flanked by alluvial fans. This paleolake extended from the Furnace Creek to Ubehebe. Based on the new stratigraphy, the Death Valley fault system can be divided into four main fault zones: the dextral, Quaternary-age Northern Death Valley fault zone; the dextral, pre-Quaternary Furnace Creek fault zone; the oblique-normal Black Mountains fault zone; and the dextral Southern Death Valley fault zone. Post -3.3 Ma geometric, structural, and kinematic changes in the Black Mountains and Towne Pass fault zones led to the break up of Furnace Creek basin and uplift of the Copper Canyon and Nova basins. Internal kinematics of northern Death Valley are interpreted as either rotation of blocks or normal slip along the northeast-southwest-trending Towne Pass and Tin Mountain fault zones within the Eastern California shear zone. ?? 2005 Elsevier B.V. All rights reserved.

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

2005-01-01

318

Stratigraphy of the crater Copernicus  

Science.gov (United States)

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

Paquette, R.

1984-01-01

319

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

OpenAIRE

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

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

2001-01-01

320

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

OpenAIRE

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

Gianotti, Franco

2011-01-01