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Sample records for late quaternary marine

  1. Late Quaternary marginal marine deposits and palaeoenvironments from northeastern Buenos Aires Province, Argentina: A review

    NASA Astrophysics Data System (ADS)

    Aguirre, M. L.; Whatley, R. C.

    The late Quaternary marginal marine deposits along eastern Argentina (Southwestern Atlantic) are reviewed according to our present knowledge. In the northeastern coastal area of Buenos Aires Province they have been assigned to a series of transgressions and regressions ranging from the late Pliocene to the late Quaternary. The most widely accepted model is Frenguelli's (1957) classical chronostratigraphical scheme of: 'Belgranense', late Pleistocene marine sediments at 3-6 m above m.s.l. and ca. 26,000->35,000 14C years BP, the 'Querandinense', Pleistocene-Holocene estuarine sediments below or at present m.s.l., and the most extensive 'Platense', mid-Holocene marine deposits at 4.5-2 m above m.s.l. dated at ca. 8000-1340 14C years BP. The restricted 'Belgranense' deposits, recorded in Samborombon Bay, in Magdalena at ca. 32,000 BP, near Mar Chiquita at ca. 24,900 and 30,500 BP and southwards in Bahía Blanca at ca. 26,000-35,500 BP, may belong to an interstadial (González et al., 1986). The molluscan composition suggests a marine invasion of the area but not a typical interglacial cycle characterized by euhaline and warm water elements. However, the oxygen isotope record argues against an interstadial during the interval 34-27 ka and the chronological control for these deposits is very poor, suggesting that they most probably have been elevated neotectonically. The Pleistocene-Holocene 'Querandinense' deposits, extensively distributed along the Bonaerensian coastal plain and continental shelf (ca. 11,000 14C years BP), with very low faunal diversity, abundance of freshwater ostracods and absence of the warm water molluscs characteristic of the Holocene ridges, indicate low salinity and cool water conditions. Further dating and isotope analysis of these deposits are required for a better understanding of the chronology of climatic events by the end of the Pleistocene in this area and to establish whether or not they could correspond to the Younger Dryas event of

  2. Late Quaternary fluvial incision rates in a marine terraced landscape, southeastern Crete, Greece

    NASA Astrophysics Data System (ADS)

    Karymbalis, Efthimios; Papanastassiou, Dimitris; Valkanou, Kanella; Gaki-Papanastassiou, Kalliopi

    2014-05-01

    Along the southern coast of the island of Crete, a series of five east-west oriented Late Pleistocene marine terraces exist, demonstrating the significant coastal uplift of this area. These terraces, ranging in elevation from 10 to 160m, are deformed by the vertical movements of the NNE-SSW trending and dipping west normal fault of Ierapetra. This study focuses on defining rates of fluvial incision for the last 410 Ka along valley systems that drain the tectonically uplifting area of Ierapetra, south Crete. The studied streams have a N-S flow direction and discharge into the Libyan Sea. Some of them are developed on the uplifted block of the Ierapetra normal fault whereas others drain the subsiding area west of the fault. The lower reaches of the study streams cut down through these marine terraces, which have been recognized, mapped in detail and correlated with Late Pleistocene Oxygen-Isotope Stages of high sea-level stands following the global sea-level fluctuations. These terraces of known age were used as reference surfaces in order to determine fluvial incision rates as the lower reaches of the streams cut down through these platforms. To evaluate incision rates, thirty five topographic valley cross-sections were drawn through fieldwork measurements as well as using a digital elevation model (DEM) produced by detailed topographic diagrams at the scale of 1:5,000. Cross valley profiles were constructed at specific locations where streams cut down the inner edges of the marine terraces because these points correspond precisely to the age of the palaeo-shoreline during the interglacial stage. For each cross-section the ratio of valley floor width to valley height (Vf) and long-term mean stream incision rates were estimated for the last 410 Ka. The geomorphic evolution of the valleys has been mainly affected by the lithology of the bedrock, sea level fluctuations during the late Quaternary, the head-ward erosion and incision of the channels, as well as both the

  3. Late Quaternary marine records from High Arctic Canada: problems, solutions, and multiproxy perspectives

    NASA Astrophysics Data System (ADS)

    Pienkowski, Anna; Furze, Mark; England, John; MacLean, Brian; von Prause, Markus; Blasco, Steve

    2013-04-01

    The Canadian Arctic Archipelago (= CAA) constitutes a significant geographic region within the Arctic Ocean Basin, influencing its oceanography, biology, ecology, and climate. Yet comparatively little is known about the long-term (post-Late Wisconsinan) environmental history of the marine channels of this region (the "Northwest Passage" = NWP). New marine data emerging from the central CAA extending back to regional deglaciation highlight the potential of multiproxy approaches in high-latitude settings. Five long (piston and trigger-weight) cores in an east-west transect through the NWP, investigated for sedimentological characteristics, microfossils (dinocysts, non-pollen palynomorphs, benthic and planktonic foraminifera, ostracods), and stable isotope ratios, show a dynamic late Quaternary environmental history. Our data suggest grounded glacial ice, rapid deglaciation, and a characteristic progression from ice-proximal to ice-distal conditions. Despite chronological complexities (scarcity of dateable materials, Portlandia Effect), age model extrapolations place deglaciation at ~11.0-10.3 cal ka BP (location dependent). Noticeable biological activity is marked by the appearance of planktonic foraminifera (Neogloboquadrina pachyderma) at ~10.0 cal ka BP. This signals the penetration of (Atlantic-derived) Arctic Intermediate Water (AIW) into the central NWP following deglaciation, likely facilitated by higher sea-levels permitting increased flow across inter-channel sills. Subsequent (~9.0-7.0 cal ka BP) ameliorated conditions (open-water season greater than present) marked by substantial diversification and abundance across all microfossil groups may correspond to a previously postulated "Holocene Thermal Optimum". After ~7.0 cal ka BP increased sea-ice and modern microfossil assemblages imply conditions similar to modern, likely due to the exclusion of AIW due to glacioisostatic shallowing combined with climate cooling. Remaining micropalaeontological challenges

  4. Late Quaternary deformation and slip rates in the northern San Andreas fault zone at Olema Valley, Marin County, California

    NASA Astrophysics Data System (ADS)

    Grove, Karen; Niemi, Tina M.

    2005-06-01

    Quaternary sedimentary deposits along the structural depression of the San Andreas fault (SAF) zone north of San Francisco in Marin County provide an excellent record of rates and styles of neotectonic deformation in a location near where the greatest amount of horizontal offset was measured after the great 1906 San Francisco earthquake. A high-resolution gravity survey in the Olema Valley was used to determine the depth to bedrock and the thickness of sediment fill along and across the SAF valley. In the gravity profile across the SAF zone, Quaternary deposits are offset across the 1906 fault trace and truncated by the Western and Eastern Boundary faults, whose youthful activity was previously unknown. The gravity profile parallel to the fault valley shows a basement surface that slopes northward toward an area of present-day subsidence near the head of Tomales Bay. Surface and subsurface investigations of the late Pleistocene Olema Creek Formation (Qoc) indicate that this area of subsidence was located further south during deposition of the Qoc and that it has migrated northward since then. Localized subsidence has been replaced by localized contraction that has produced folding and uplift of the Qoc. This apparent alternation between transtension and transpression may be the result of a northward-diverging fault geometry of fault strands that includes the valley-bounding faults as well as the 1906 SAF trace. The Vedanta marsh is a smaller example of localized subsidence in the fault zone, between the 1906 SAF trace and the Western Boundary fault. Analyses of Holocene marsh sediments in cores and a paleoseismic trench indicate thickening, and probably tilting, toward the 1906 trace, consistent with coseismic deformation observed at the site following the 1906 earthquake. New age data and offset sedimentary and geomorphic features were used to calculate four late Quaternary slip rate estimates for the SAF at this latitude. Luminescence dates of 112-186 ka for the

  5. Physical data of soil profiles formed on late Quaternary marine terraces near Santa Cruz, California

    USGS Publications Warehouse

    Munster, Jennie; Harden, Jennifer W.

    2002-01-01

    The marine terraces in and around Santa Cruz, California, represent a set of well-preserved terraces formed as a product of geology, sea level, and climate. A marine terrace begins as a wave cut platform. Eustatic sea level changes, seacliff erosion, and tectonic uplift work together to generate marine terraces. "When a wave-cut platform is raised (due to tectonic activity) above sea level and cliffed by wave action it becomes a marine terrace" (Bradley, 1957, p. 424). During glacial periods, eustatic sea level is estimated to have dropped by 150 meters (Fairbanks, 1989). Cliff retreat measured from aerial photographs between 1930 and 1980 vary from 0.0 to 0.2 m yr–1 (Best and Griggs, 1991). Estimates of uplift rates along the Santa Cruz coastline vary from 0.10 to 0.48 m kyr–1 (Bradley and Griggs, 1976; Weber and others, 1999). Uplift mechanisms include coseismic uplift associated both with a reverse component of slip on the steeply SW dipping Loma Prieta fault in the restraining bend of the San Andreas Fault and a small component of reverse slip on the steeply SE dipping San Gregorio fault (Anderson and Menking 1994). Previous work studying physical properties on these terraces include Pinney and others (in press) and Aniku (1986) and Bowman and Estrada (1980). Sedimentary deposits of the marine terraces are a mixture of terrestrial and marine sediments but generally consist of a sheet of marine deposits overlying the old platform and a wedge of nonmarine deposits banked against the old sea cliff (Bradley, 1957). Bedrock underlying the terraces in the Santa Cruz area is generally either Santa Margarita Sandstone or Santa Cruz Mudstone. The Santa Margarita Sandstone represents an upper Miocene, transgressive, tidally dominated marine-shelf deposit with crossbedded sets of sand and gravel and horizontally stratified and bioturbated invertebrate-fossils beds (Phillips, 1990). The siliceous Santa Cruz Mudstone, of late Miocene age, conformably overlies the Santa

  6. Late Quaternary vegetational and climate dynamics in northeastern Brazil, inferences from marine core GeoB 3104-1

    NASA Astrophysics Data System (ADS)

    Behling, Hermann; W. Arz, Helge; Pätzold, Jürgen; Wefer, Gerold

    2000-06-01

    Late Quaternary paleoenvironments from northeastern (NE) Brazil have been studied by pollen analysis of marine sediment. The studied core GeoB 3104-1 (3°40' S, 37°43' W, 767 m b.s.l.) from the upper continental slope off NE Brazil is 517 cm long and >42,000 14C yr BP old. Chronological control was obtained by 12 radiocarbon (AMS) dates from individuals of the foraminiferal species Globigerinoides sacculifer. Modern pollen analogs were received from 15 river, lake and forest soil surface samples from NE Brazil. Marine pollen dates indicate the predominance of semi-arid caatinga vegetation in NE Brazil during the recorded period between >42,000 and 8500 14C yr BP. The increased fluvial input of terrigenous material, with high concentrations of pollen and specially fern spores, into the marine deposits, about 40,000, 33,000 and 24,000 14C yr BP and between 15,500 and 11,800 14C yr BP, indicate short-term periods of strong rainfall on the NE Brazilian continent. The expansion of mountain, floodplain and gallery forests characterize the interval between 15,500 and 11,800 14C yr BP as the wettest recorded period in NE Brazil, which allowed floristic exchanges between Atlantic rain forest and Amazonian rain forest, and vice versa. The paleodata from core GeoB 3104-1 confirm the, in general, dry pre-Last Glacial Maximum (LGM) and LGM conditions and the change to wet Lateglacial environments in tropical South America. The annual movement of the intertropical convergence zone over NE Brazil, the strong influence of the Antarctic cold fronts and changes of the high-pressure cell over the southern Atlantic, may explain the very wet Lateglacial period in NE Brazil. The documented NE Brazilian short-term signals correlate with the documented Dansgaard-Oeschger cycles and Heinrich events from the northern Hemisphere and suggest strong teleconnections.

  7. Reevaluation of the temperature/ice volume proportionality of the O-18 records of Late Quaternary marine carbonates

    SciTech Connect

    Aharon, P.

    1985-01-01

    Documentation of O-18 variations imprinted on Late Quaternary marine carbonates leads to the inference that temporal and spatial redistribution of O-18/O-16 isotopes occurred episodically between the ocean and the expanded polar ice caps. If O-18 data of deep sea benthic foraminifera are simple recorders of ocean chemistry changes, then the ice volumes they reflect must agree with the paleosea levels from raised corals reefs. Discrepancies between the O-18 and sea level events were previously ascribed to inherent deficiencies in either one (or both) of the ice volume records. Here the author presents an objective test to evaluate the glacio-eustatic assumption of sea levels on the one hand, and the temperature constancy assumption of the tropical surface waters and of the deep ocean on the other. The analysis entails paired O-18/sea levels in the context of raised coral reefs in new Guinea and paired O-18/O-18 from coral reefs and benthic foraminifera representing interstadial culmination events during isotope stages 5 and 3. The results indicate that the ice volume effect accounts fully for the observed O-18 changes in tropical surface waters during isotope stage 5 but only for 40% during isotope stage 3. The O-18 records of the deep ocean overestimate the ice volumes by 0.5 per thousand during all stages except the interglacials.

  8. The mass balance of soil evolution on late Quaternary marine terraces, northern California

    NASA Technical Reports Server (NTRS)

    Merritts, Dorothy J.; Chadwick, Oliver A.; Hendricks, David M.; Brimhall, George H.; Lewis, Christopher J.

    1992-01-01

    Mass-balance interpretation of a soil chronosequence provides a means of quantifying elemental addition, removal, and transformation that occur in soils from a flight of marine terraces in northern California. Six soil profiles that range in age from several to 240,000 yr are developed in unconsolidated, sandy-marine, and eolian parent material deposited on bedrock marine platforms. Soil evolution is dominated by (1) open-system depletion of Si, Ca, Mg, K, and Na; (2) open-system enrichment of P in surface soil horizons; (3) relative immobility of Fe and Al; and (4) transformation of Fe, Si, and Al in the parent material to secondary clay minerals and sesquioxides. Net mass losses of bases and Si are generally uniform with depth and substantial, in some cases approaching 100 percent; however, the rate of loss of each element differs markedly, causing the ranking of each by relative abundance to shift with time. Loss of Si from the sand fraction by dissolution and particle-size diminution, from about 100 percent to less than 35 percent over 240 ky, mirrors a similar gain in the silt and clay size fractions. The Fe originally present in the sand fraction decreases from greater than 80 percent to less than 10 percent, whereas the amount of Fe present in the clay and crystalline oxyhydroxide fractions increases to 25 percent and 70 percent, respectively.

  9. Late Quaternary Multiproxy Paleoclimate Record From a Marine Core Offshore SE Brazil

    NASA Astrophysics Data System (ADS)

    de Toledo, M. B.; Barreto, C. F.; Ramos, R. P.; Freitas, A. S.; Crud, M. B.; Souza, R.; Souza, T. C.

    2012-12-01

    Even though accurate comparisons between marine and continental paleoclimate records play a major role in understanding the effects and also measuring the timing of global climate changes, this task poses many challenges due mainly to differences in chronology, sampling resolution, and intrinsic aspects of each proxy record. The simplest way to work around these problems is to conduct several different analyses on the same samples. In order to integrate both the continental and marine paleoenvironment and paleoclimate records, we used a multi-proxy approach on a 20-meter-long sediment core from offshore (1400m depth) SE Brazil. Analyses of pollen and spores, to assess vegetation changes, and microcharcoal, to assess frequency of paleofires (representing a continent signal), as well as planktonic forams, dinoflagellate cysts, diatoms, and marine palynomorphs (representing a marine signal), were carried out on the same samples. The integrated age model, based on biostratigraphic boundaries (planktonic forams), AMS radiocarbon dates, and stable isotopes in forams, provided ages between 600-135,000 years BP (top and bottom of the core), suggesting that we have a complete interglacial-glacial-interglacial cycle (MIS5e-MIS1). The effects of major climate states (i.e. glacial x interglacial) seem to have been recorded by the studied microfossil groups, which is evidenced by well marked changes in the assemblages throughout the record (e.g. increase in abundance of cold-adapted taxa during glacial time, and increased abundance of warm-adapted taxa during interglacial times). The pollen record, however, does not show such dramatic changes as the other microfossil groups do. These apparently small fluctuations in the pollen data could be due to a few reasons, such as, higher resiliency of regional vegetation, influence of relative sea-level variations, and the geographical amplitude of the pollen record (i.e. the effective vegetation area that is recorded by the pollen

  10. Developing a robust tephrochronological framework for Late Quaternary marine records in the Southern Adriatic Sea: new data from core station SA03-11

    NASA Astrophysics Data System (ADS)

    Matthews, I. P.; Trincardi, F.; Lowe, J. J.; Bourne, A. J.; MacLeod, A.; Abbott, P. M.; Andersen, N.; Asioli, A.; Blockley, S. P. E.; Lane, C. S.; Oh, Y. A.; Satow, C. S.; Staff, R. A.; Wulf, S.

    2015-06-01

    Tephra layers are assuming an increasingly important role in the dating and correlation of Late Quaternary marine sequences. Here we demonstrate their potential by reporting a new study of the sediment sequence of marine core SA03-11, recovered from the Southern Adriatic Sea, which spans the last c. 39 ka. A total of 28 discrete tephra layers are reported from this sequence, 10 of which are visible in the core and a further 18 are non-visible cryptotephra layers. These have been analysed using more than 1400 WDS-EPMA measurements of glass chemistry and results have been compared with published chemical measurements obtained from relevant proximal and distal sites which preserve eruptive material dating to within the same time interval. The data show that a high proportion of the layers originate from the Campi Flegrei volcanic field but more distinctive layers are sourced from Vesuvius, the Aeolian Islands and Vulcano, and these provide key marker horizons. The results show that the sequence extends in time to the Campanian Ignimbrite at the base, that a number of the layers have robust age estimates that permit a better constrained age-depth model to be constructed for the sequence, and that the potential exists for importing terrestrially-based age estimates into marine contexts, thereby circumventing problems of incorporating reservoir uncertainties associated with marine radiocarbon dates. The WDS-EPMA dataset generated here also provides important new data that constrain key Late Quaternary tephra layers in the central Mediterranean region.

  11. Late Quaternary change in the North American (Mexican) Monsoon: variability in terrestrial and marine records and possible mechanisms

    NASA Astrophysics Data System (ADS)

    Metcalfe, S. E.; Barron, J. A.; Roy, P.; Davies, S.

    2013-05-01

    The Late Quaternary history of the North American (or Mexican) monsoon (NAM) remains poorly understood, with continuing debates about the relative importance of insolation forcing, the role of the Laurentide Ice Sheet (LIS), the expression of warm (D-O) and cold (H) events in the North Atlantic and the influence of the Pacific. To date, more information has been available from the southern and northern margins of the NAM region than from its tropical and subtropical core. This is significant because to the south of the NAM region, the direct effect of ITCZ location is likely to be stronger and any potential influence of the LIS weaker, and to the north, there is an important change in present day precipitation seasonality (from summer to winter), an opposite response to forcings such as ENSO/PDO and AMO and probably a stronger influence of the LIS. As a result, the interpretation of speleothem records from New Mexico (e.g. Asmerom et al., 2010) and Arizona (e.g. Wagner et al., 2010), in the southwestern USA and marine records such as Cariaco (Peterson and Haug, 2006) and lake records such as Peten Iztá (Hodell et al., 2008) may not be applicable to the tropical NAM core. Here we present results from two lacustrine sequences in Mexico (Sayula 20oN; Babicora 29oN) and a marine core record from the central part of the Gulf of California (27oN) all extending back at least through MIS3 (ca. 60 kyr BP). Although lacking the chronological precision of the speleothem sequences, these multiproxy records preserve evidence of centennial and millennial scale variability. MIS3 is marked by generally wetter conditions in the lake basins and warmer SSTs in the marine record, particularly during D/O events, which can be attributed to a stronger monsoon as well northward displacement of the ITCZ. This contrasts with the standard interpretation of the speleothem sequences where D/O events are dry. In contrast, H events are usually drier/cooler (weaker NAM, reduced summer

  12. Episodic intraplate deformation of stable continental margins: evidence from Late Neogene and Quaternary marine terraces, Cape Liptrap, Southeastern Australia

    NASA Astrophysics Data System (ADS)

    Gardner, Thomas; Webb, John; Pezzia, Claudia; Amborn, Terri; Tunnell, Robert; Flanagan, Sarah; Merritts, Dorothy; Marshall, Jeffrey; Fabel, Derek; Cupper, Matthew L.

    2009-01-01

    The Waratah Fault is a northeast trending, high angle, reverse fault in the Late Paleozoic Lachlan Fold Belt at Cape Liptrap on the Southeastern Australian Coast. It is susceptible to reactivation in the modern intraplate stress field in Southeast Australia and exhibits Late Pliocene to Late Pleistocene reactivation. Radiocarbon, optically stimulated luminescence (OSL), and cosmogenic radionuclide (CRN) dating of marine terraces on Cape Liptrap are used to constrain rates of displacement across the reactivated Waratah Fault. Six marine terraces, numbered Qt 6-Tt 1 (youngest to oldest), are well developed at Cape Liptrap with altitudes ranging from ˜1.5 m to ˜170 m amsl, respectively. On the lowest terrace, Qt 6, barnacles in wave-cut notches ˜1.5 m amsl, yielded a radiocarbon age of 6090-5880 Cal BP, and reflect the local mid-Holocene sea level highstand. Qt 5 yielded four OSL ages from scattered locations around the cape ranging from ˜80 ka to ˜130 ka. It formed during the Last Interglacial sea level highstand (MIS 5e) at ˜125 ka. Inner edge elevations (approximate paleo high tide line) for Qt 5 occur at distinctly different elevations on opposite sides of the Waratah Fault. Offsets of the inner edges across the fault range from 1.3 m to 5.1 m with displacement rates ranging from 0.01 mm/a to 0.04 mm/a. The most extensive terrace, Tt 4, yielded four Early Pleistocene cosmogenic radionuclide (CRN) ages: two apparent burial ages of 0.858 Ma ± 0.16 Ma and 1.25 Ma ± 0.265 Ma, and two apparent exposure ages of 1.071 Ma ± 0.071 Ma ( 10Be) and 0.798 Ma ± 0.066 Ma ( 26Al). Allowing for muonic production effects from insufficient burial depths, the depth corrected CRN burial ages are 1.8 Ma ± 0.56 Ma and 2.52 Ma ± 0.88 Ma, or Late Pliocene. A Late Pliocene age is our preferred age. Offsets of Tt 4 across the Waratah Fault range from a minimum of ˜20 m for terrace surface treads to a maximum of ˜70 m for terrace bedrock straths. Calculated displacement rates

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

    NASA Astrophysics Data System (ADS)

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

    2014-01-01

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

  14. Late Quaternary continental and marine sediments of northeastern Buenos Aires province (Argentina): Fossil content and paleoenvironmental interpretation

    NASA Astrophysics Data System (ADS)

    Fucks, Enrique; Aguirre, Marina; Deschamps, Cecilia M.

    2005-10-01

    Abundant invertebrate and vertebrate fossil remains that exhibit excellent preservation and were collected from deposits of both continental and marine origins at Pilar (Buenos Aires, Argentina) add paleoenvironmental data from the northeastern Buenos Aires province area linked to sea-level oscillations and climate variability since approximately 120 ka BP (marine oxygen isotope stage [MOIS] 5e). Two new fossiliferous localities discovered in the Luján River Valley allow for detailed geological studies and new dating of molluscan shells and bones. The studies suggest salinity changes during the Last Interglacial (8 m above m.s.l., min. 14C>40 ka) and the mid-Holocene transgression (5 m above m.s.l., 7-3 14C ka BP) compared with the modern pattern along the adjacent littoral (Río de la Plata). The marine sequences represent the innermost boundary of the sea-level transgression in that area and contain a biogenic record (bivalves, gastropods, forams, ostracods) that indicates marginal marine environments (higher salinity than at present). Vertebrates and molluscs from the continental sequence suggest a freshwater habitat in which remains of marine fish must be allochthonous, probably incorporated by postmortem fluvial transport to the final depositional environment.

  15. (Model) Peatlands in late Quaternary interglacials

    NASA Astrophysics Data System (ADS)

    Kleinen, Thomas; Brovkin, Victor

    2016-04-01

    Peatlands have accumulated a substantial amount of carbon, roughly 600 PgC, during the Holocene. Prior to the Holocene, there is relatively little direct evidence of peatlands, though coal deposits bear witness to a long history of peat-forming ecosystems going back to the Carboniferous. We therefore need to rely on models to investigate peatlands in times prior to the Holocene. We have developed a dynamical model of wetland extent and peat accumulation, integrated in the coupled climate carbon cycle model of intermediate complexity CLIMBER2-LPJ, in order to mechanistically model interglacial carbon cycle dynamics. This model consists of the climate model of intermediate complexity CLIMBER2 and the dynamic global vegetation model LPJ, which we have extended with modules to determine peatland extent and carbon accumulation. The model compares reasonably well to Holocene peat data. We have used this model to investigate the dynamics of atmospheric CO2 in the Holocene and two other late Quaternary interglacials, namely the Eemian, which is interesting due to its warmth, and Marine Isotope Stage 11 (MIS11), which is the longest interglacial during the last 500ka. We will also present model results of peatland extent and carbon accumulation for these interglacials. We will discuss model shortcomings and knowledge gaps currently preventing an application of the model to full glacial-interglacial cycles.

  16. Late quaternary sequence stratigraphy, South Florida margin

    SciTech Connect

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

    1995-12-01

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

  17. Marine record of late quaternary glacial-interglacial fluctuations in the Ross Sea and evidence for rapid, episodic sea level change due to marine ice sheet collapse

    NASA Technical Reports Server (NTRS)

    Anderson, John B.

    1991-01-01

    Some of the questions to be addressed by SeaRISE include: (1) what was the configuration of the West Antarctic ice sheet during the last glacial maximum; (2) What is its configuration during a glacial minimum; and (3) has it, or any marine ice sheet, undergone episodic rapid mass wasting. These questions are addressed in terms of what is known about the history of the marine ice sheet, specifically in Ross Sea, and what further studies are required to resolve these problems. A second question concerns the extent to which disintegration of marine ice sheets may result in rises in sea level that are episodic in nature and extremely rapid, as suggested by several glaciologists. Evidence that rapid, episodic sea level changes have occurred during the Holocene is also reviewed.

  18. Late Quaternary climate change shapes island biodiversity.

    PubMed

    Weigelt, Patrick; Steinbauer, Manuel Jonas; Cabral, Juliano Sarmento; Kreft, Holger

    2016-04-01

    Island biogeographical models consider islands either as geologically static with biodiversity resulting from ecologically neutral immigration-extinction dynamics, or as geologically dynamic with biodiversity resulting from immigration-speciation-extinction dynamics influenced by changes in island characteristics over millions of years. Present climate and spatial arrangement of islands, however, are rather exceptional compared to most of the Late Quaternary, which is characterized by recurrent cooler and drier glacial periods. These climatic oscillations over short geological timescales strongly affected sea levels and caused massive changes in island area, isolation and connectivity, orders of magnitude faster than the geological processes of island formation, subsidence and erosion considered in island theory. Consequences of these oscillations for present biodiversity remain unassessed. Here we analyse the effects of present and Last Glacial Maximum (LGM) island area, isolation, elevation and climate on key components of angiosperm diversity on islands worldwide. We find that post-LGM changes in island characteristics, especially in area, have left a strong imprint on present diversity of endemic species. Specifically, the number and proportion of endemic species today is significantly higher on islands that were larger during the LGM. Native species richness, in turn, is mostly determined by present island characteristics. We conclude that an appreciation of Late Quaternary environmental change is essential to understand patterns of island endemism and its underlying evolutionary dynamics. PMID:27027291

  19. Late Quaternary glaciation in the Kyrgyz Tien Shan

    NASA Astrophysics Data System (ADS)

    Koppes, Michéle; Gillespie, Alan R.; Burke, Raymond M.; Thompson, Stephen C.; Stone, John

    2008-04-01

    The Tien Shan of Kyrgyzstan contains multiple moraines and drift from late Quaternary glaciations. The spatial/temporal distribution of the glaciers inferred from the moraines suggests that the main factor controlling glacier advance here was the availability of moisture. The dominant modern climatic signatures in northern Central Asia include orographic thunderstorms in summer, cold and dry Siberian high-pressure cells in winter, and westerly cyclonic storms from the North Atlantic and eastern Mediterranean in spring and fall. Changes in any of these systems during the late Quaternary would have varied precipitation delivery to, and glacier growth in the Kyrgyz Tien Shan. Geomorphic mapping and reconnaissance-level 10Be cosmic-ray exposure dating of moraine sequences in six drainages indicate that there were multiple "maximum" advances of similar extents and equilibrium-line depressions across the range. Glaciers in the north and east of the Kyrgyz Tien Shan last advanced to their maximum positions during marine oxygen isotope stage (MIS) 5 and again during MIS 4, while in the south and west of the range advance occurred during MIS 3. In contrast to maritime Europe and North America, there is no evidence of a major glacial advance during MIS 2. Glacier advances during MIS 2 and since were restricted to the vicinity of modern glaciers, allowing the older glacial record to be preserved well.

  20. Formation of Late Quaternary paleoshorelines in Crete, Eastern Mediterranean

    NASA Astrophysics Data System (ADS)

    Mouslopoulou, Vasiliki; Begg, John; Nicol, Andrew; Oncken, Onno; Prior, Christine

    2015-12-01

    Paleoshorelines of Late Quaternary age in western Crete do not exclusively increase in age with rising altitude as is generally observed worldwide. At numerous sites, for example, Late-Holocene paleoshorelines decrease in age with increasing altitude while in other cases paleoshorelines at similar altitude vary in age by tens of thousands of years. We propose that the observed paleoshoreline altitude-age relationships can be accounted for by eustatic sea-level changes and tectonic rock uplift without requiring substantial errors on radiocarbon ages or tectonic subsidence, as has been previously proposed. To test this model we use a dataset consisting of altitude and age data for 71 individual paleoshorelines sampled from 21 sites distributed along the entire Cretan coastline. These data include radiocarbon ages of marine biota (40 new dates) within beachrock resting on paleoshorelines ranging up to 48 kyr BP in age and ≤20 m above present sea-level. We find that paleoshoreline formation reflects Late Holocene tectonic rock uplift in western Crete, preceded by eustatic sea-level rise and by >10 kyr BP rock uplift along the entire island. Our observations contravene existing models as they suggest that some paleoshorelines, and their associated lithified beachrock, survived passage through the wave-zone multiple times and formed throughout the sea-level cycle (i.e., preservation is not restricted to highstand deposits). These results may have application globally in regions where erosion-resistant carbonate beachrock mantles paleoshorelines.

  1. Late Quaternary land-sea correlations, northern Labrador, Canada

    SciTech Connect

    Clark, P.; Josenhans, H.

    1985-01-01

    Late Quaternary glacial and postglacial units in the Torngat Mountains, northern Labrador, are correlated with units identified on the adjacent continental shelf. The late Wisconsinan Laurentide Ice Sheet drained through major valleys of the Torngat Mountains as outlet glaciers, depositing the Saglek Moraines. These are of regional extent and have been mapped from Saglek Fiord north to Noodleook Fiord. A C-14 date of 18,210 +/- 1900 BP on total organic matter (TOM) from lake sediment dammed by a segment of the Saglek Moraines is interpreted as a maximum date for deposition of the Saglek Moraine system because of possible contamination. Glacial sediments comprising the Saglek Moraines are correlated with upper till mapped in troughs and saddles on the continental shelf. Outlet glaciers depositing a late Wisconsinan unit flowed through Labrador fiords and onto the shelf at low basal shear stresses, particularly on the shelf where, although grounded, they were hydrostatically buoyed up and moved principally by sliding. A glaciomarine unit conformably overlies late Wisconsinan till on the shelf and on the land. This unit is a gravelly clayey silt, contains abundant foraminifera, and has up to 60% limestone in the pebble fraction. C-14 dates suggest deposition of this unit began ca. 10,000 BP on the shelf and 9000 BP on the land, an ended by 8000 BP. Limestone pebbles in this unit suggest a source in part from sediment-laden icebergs and pack-ice from the north. Marine deposition from ca. 8000-0 BP is characterize by basinal sedimentation.

  2. Reply to Discussion: a critique of Possible waterways between the Marmara Sea and the Black Sea in the late Quaternary: evidence from ostracod and foraminifer assemblages in lakes İznik and Sapanca, Turkey, Geo-Marine Letters, 2011

    NASA Astrophysics Data System (ADS)

    Nazik, Atike; Meriç, Engin; Avşar, Niyazi

    2012-06-01

    In their discussion of our 2011 paper dealing with possible waterways between the Marmara Sea and the Black Sea in the "late" Quaternary, based on data from ostracod and foraminifer assemblages in lakes İznik and Sapanca, Turkey, Yaltırak et al. (Geo-Mar Lett 32:267-274, 2012) essentially reject the idea of any links whatsoever, be they between the Marmara Sea and the lakes İznik and Sapanca, or further to the Black Sea via the valley of the Sakarya River. The evidence they provide in support of their view, however, is essentially circumstantial, in part conjectural, and also inconclusive considering the findings in favour of linkage between the Marmara Sea and the lakes at the very least, while the proposed connection with the Sakarya River valley remains speculative because of the lack of unambiguous data. On the other hand, Yaltırak et al. (Geo-Mar Lett 32:267-274, 2012) do raise valid points of concern which deserve careful future investigation, the most important being the possibility of sample contamination from dumped marine sediment used for construction purposes along some parts of the shore of Lake İznik. We agree that a concerted multidisciplinary effort is required to address the many unresolved issues in connection with the potential waterways proposed by us and others before us.

  3. Spatial Response of Mammals to Late Quaternary Environmental Fluctuations

    PubMed

    Graham; Lundelius; Graham; Schroeder; Toomey; Anderson; Barnosky; Burns; Churcher; Grayson; Guthrie; Harington; Jefferson; Martin; McDonald; Morlan; Semken; Webb; Werdelin; Wilson

    1996-06-14

    Analyses of fossil mammal faunas from 2945 localities in the United States demonstrate that the geographic ranges of individual species shifted at different times, in different directions, and at different rates in response to late Quaternary environmental fluctuations. The geographic pattern of faunal provinces was similar for the late Pleistocene and late Holocene, but differing environmental gradients resulted in dissimilar species composition for these biogeographic regions. Modern community patterns emerged only in the last few thousand years, and many late Pleistocene communities do not have modern analogs. Faunal heterogeneity was greater in the late Pleistocene. PMID:8662471

  4. Ice Age Earth: Late Quaternary geology and climate

    SciTech Connect

    Dawson, A.G.

    1992-01-01

    This book is a concise and readable account of the most important geologic records of the late Quaternary. It provides a synopsis of the major environmental changes that took place from approximately 13,000 to 7,000 years ago, highlighting the complexity and rapidity of past climate changes and the environmental responses they produced. The text is well illustrated, though some figures are rough and need more explanation. Also needed is a critical appraisal of the geochronology which places the paleoenvironmental records into the temporal domain. However, as a whole the book reaches its objective of summarizing the most important scientific findings about the nature of the late Quaternary climate changes.

  5. Paleoclimatic forcing of magnetic susceptibility variations in Alaskan loess during the late Quaternary

    SciTech Connect

    Beget, J.E.; Stone, D.B.; Hawkins, D.B. )

    1990-01-01

    Visual matches and statistical tests suggest correlations between marine isotope curves, retrodictive solar insolation at lat 65{degree}N, and magnetic susceptibility profiles through late Quaternary age Alaskan loess sections. The susceptibility changes largely appear to reflect variability in magnetite content due to climatically controlled changes in wind intensity and competence. Magnetic susceptibility profiles through massive loess can provide stratigraphic context for intercalated paleosols and tephras. A prominent paleosol correlated with marine isotope stage 5 occurs several metres above the Old Crow ash in loess sections, indicating that this important tephra is older than suggested by thermoluminescence dates, and may have been deposited ca. 215 {plus minus}25 ka.

  6. Late Quaternary rates of stream incision in Northeast Peloponnese, Greece

    NASA Astrophysics Data System (ADS)

    Karymbalis, Efthimios; Papanastassiou, Dimitrios; Gaki-Papanastassiou, Kalliopi; Ferentinou, Maria; Chalkias, Christos

    2016-05-01

    This study focuses on defining rates of fluvial incision for the last 580±5 kyr along valley systems of eight streams that drain the eastern part of the northern Peloponnese. The streams are developed on the uplifted block of the offshore-running Xylokastro normal fault, one of the main faults bounding the southern edge of the Gulf of Corinth half-graben, and have incised a set of ten uplifted marine terraces having an amphitheatric shape. These terraces range in age from 60±5 kyr to 580±5 kyr and have been mapped in detail and correlated with late Pleistocene oxygen-isotope stages of high sea-level stands by previous studies. The terraces were used in this paper as reference surfaces in order to define fluvial incision rates at the lower reaches of the studied streams. To evaluate incision rates, thirty-three topographic valley cross-sections were drawn using fieldwork measurements as well as using a highly accurate (2×2 cell size) Digital Elevation Model (DEM) at specific locations where streams cut down the inner edges of the marine terraces. For each cross-section the ratio of valley floor width to valley height (Vf) and long-term mean stream incision rates were estimated for the last 580±5 kyr, while rock uplift rates were estimated for the last 330±5 kyr. The geomorphic evolution of the valleys on the uplifted block of the Xylokastro fault has been mainly driven by the lithology of the bedrock, sea level fluctuations during the late Quaternary, and incision of the channels due to the tectonic uplift. Stream incision rates range from 0.10±0.1 mm/yr for the last 123±7 kyr to 1.14±0.1 mm/yr for the last 310±5 kyr and are gradually greater from east to west depending on the distance from the trace of the fault. Downcutting rates are comparable with the rock uplift rates, which range from 0.4±0.02 mm/yr to 1.49±0.12 mm/yr, over the last 330±5 kyr.

  7. Late Quaternary rates of stream incision in Northeast Peloponnese, Greece

    NASA Astrophysics Data System (ADS)

    Karymbalis, Efthimios; Papanastassiou, Dimitrios; Gaki-Papanastassiou, Kalliopi; Ferentinou, Maria; Chalkias, Christos

    2016-09-01

    This study focuses on defining rates of fluvial incision for the last 580±5 kyr along valley systems of eight streams that drain the eastern part of the northern Peloponnese. The streams are developed on the uplifted block of the offshore-running Xylokastro normal fault, one of the main faults bounding the southern edge of the Gulf of Corinth half-graben, and have incised a set of ten uplifted marine terraces having an amphitheatric shape. These terraces range in age from 60±5 kyr to 580±5 kyr and have been mapped in detail and correlated with late Pleistocene oxygen-isotope stages of high sea-level stands by previous studies. The terraces were used in this paper as reference surfaces in order to define fluvial incision rates at the lower reaches of the studied streams. To evaluate incision rates, thirty-three topographic valley cross-sections were drawn using fieldwork measurements as well as using a highly accurate (2×2 cell size) Digital Elevation Model (DEM) at specific locations where streams cut down the inner edges of the marine terraces. For each cross-section the ratio of valley floor width to valley height (Vf) and long-term mean stream incision rates were estimated for the last 580±5 kyr, while rock uplift rates were estimated for the last 330±5 kyr. The geomorphic evolution of the valleys on the uplifted block of the Xylokastro fault has been mainly driven by the lithology of the bedrock, sea level fluctuations during the late Quaternary, and incision of the channels due to the tectonic uplift. Stream incision rates range from 0.10±0.1 mm/yr for the last 123±7 kyr to 1.14±0.1 mm/yr for the last 310±5 kyr and are gradually greater from east to west depending on the distance from the trace of the fault. Downcutting rates are comparable with the rock uplift rates, which range from 0.4±0.02 mm/yr to 1.49±0.12 mm/yr, over the last 330±5 kyr.

  8. Late Quaternary history of the Atacama Desert

    USGS Publications Warehouse

    Latorre, Claudio; Betancourt, Julio L.; Rech, Jason A.; Quade, Jay; Holmgren, Camille; Placzek, Christa; Maldonado, Antonio; Vuille, Mathias; Rylander, Kate A.

    2005-01-01

    Of the major subtropical deserts found in the Southern Hemisphere, the Atacama Desert is the driest. Throughout the Quaternary, the most pervasive climatic influence on the desert has been millennial-scale changes in the frequency and seasonality of the scant rainfall, and associated shifts in plant and animal distributions with elevation along the eastern margin of the desert. Over the past six years, we have mapped modern vegetation gradients and developed a number of palaeoenvironmental records, including vegetation histories from fossil rodent middens, groundwater levels from wetland (spring) deposits, and lake levels from shoreline evidence, along a 1200-kilometre transect (16–26°S) in the Atacama Desert. A strength of this palaeoclimate transect has been the ability to apply the same methodologies across broad elevational, latitudinal, climatic, vegetation and hydrological gradients. We are using this transect to reconstruct the histories of key components of the South American tropical (summer) and extratropical (winter) rainfall belts, precisely at those elevations where average annual rainfall wanes to zero. The focus has been on the transition from sparse, shrubby vegetation (known as the prepuna) into absolute desert, an expansive hyperarid terrain that extends from just above the coastal fog zone (approximately 800 metres) to more than 3500 metres in the most arid sectors in the southern Atacama.

  9. Ecological impacts of the late Quaternary megaherbivore extinctions.

    PubMed

    Gill, Jacquelyn L

    2014-03-01

    As a result of the late Quaternary megafaunal extinctions (50,000-10,000 before present (BP)), most continents today are depauperate of megaherbivores. These extinctions were time-transgressive, size- and taxonomically selective, and were caused by climate change, human hunting, or both. The surviving megaherbivores often act as ecological keystones, which was likely true in the past. In spite of this and extensive research on the causes of the Late Quaternary Extinctions, the long-term ecological consequences of the loss of the Pleistocene megafauna remained unknown until recently, due to difficulties in linking changes in flora and fauna in paleorecords. The quantification of Sporormiella and other dung fungi have recently allowed for explicit tests of the ecological consequences of megafaunal extirpations in the fossil pollen record. In this paper, I review the impacts of the loss of keystone megaherbivores on vegetation in several paleorecords. A growing number of studies support the hypothesis that the loss of the Pleistocene megafauna resulted in cascading effects on plant community composition, vegetation structure and ecosystem function, including increased fire activity, novel communities and shifts in biomes. Holocene biota thus exist outside the broader evolutionary context of the Cenozoic, and the Late Quaternary Extinctions represent a regime shift for surviving plant and animal species. PMID:24649488

  10. Late Quaternary environments in Ruby Valley, Nevada

    USGS Publications Warehouse

    Thompson, R.S.

    1992-01-01

    Palynological data from sediment cores from the Ruby Marshes provide a record of environmental and climatic changes over the last 40,000 yr. The modern marsh waters are fresh, but no deeper than ???3 m. A shallow saline lake occupied this basin during the middle Wisconsin, followed by fresh and perhaps deep waters by 18,000 to 15,000 yr B.P. No sediments were recovered for the period between 15,000 and 11,000 yr B.P., possibly due to lake desiccation. By 10,800 yr B.P. a fresh-water lake was again present, and deeper-than-modern conditions lasted until 6800 yr B.P. The middle Holocene was characterized by very shallow water, and perhaps complete desiccation. The marsh system deepened after 4700 yr B.P., and fresh-water conditions persisted until modern times. Vegetation changes in Ruby Valley were more gradual than those seen in the paleolimno-logical record. Sagebrush steppe was more widespread than at present through the late Pleistocene and early Holocene, giving way somewhat to expanded shadscale vegetation between 8500 and 6800 yr B.P. Shadscale steppe contracted by 4000 yr B.P., but had greater than modern coverage until 1000 to 500 yr ago. Pinyon-juniper woodland was established in the southern Ruby Mountains by 4700 yr B.P. ?? 1992.

  11. Late-quaternary vegetational dynamics and community stability reconsidered

    NASA Astrophysics Data System (ADS)

    Delcourt, Paul A.; Delcourt, Hazel R.

    1983-03-01

    Defining the spatial and temporal limits of vegetational processes such as migration and invasion of established communities is a prerequisite to evaluating the degree of stability in plant communities through the late Quaternary. The interpretation of changes in boundaries of major vegetation types over the past 20,000 yr offers a complementary view to that provided by migration maps for particular plant taxa. North of approximately 43°N in eastern North America, continual vegetational disequilibrium has resulted from climatic change, soil development, and species migrations during postglacial times. Between 33° and 39°N, stable full-glacial vegetation was replaced by a relatively unstable vegetation during late-glacial climatic amelioration; stable interglacial vegetation developed there after about 9000 yr B.P. Late-Quaternary vegetation has been in dynamic equilibrium, with a relatively constant flora, south of 33°N on upland interfluves along the northern Gulf Coastal Plain, peninsular Florida, and west-central Mexico.

  12. Precise timing and rate of massive late Quaternary soil denudation

    NASA Astrophysics Data System (ADS)

    Cooke, M. Jennifer; Stern, Libby A.; Banner, Jay L.; Mack, Lawrence E.; Stafford, Thomas W., Jr.; Toomey, Rickard S., III

    2003-10-01

    Strontium isotopes are a unique tool to study soil-erosion dynamics. Changes in Sr isotope ratios (87Sr/86Sr) provide a record of late Quaternary landscape denudation of the Edwards Plateau of central Texas, United States. The use of Sr isotopes as a tracer for soil erosion is based on the observation that, in central Texas, the 87Sr/86Sr ratio of soil correlates with soil thickness. Plants and animals express the 87Sr/86Sr ratio of exchangeable Sr in the soil. Therefore, we use changes in Sr isotope ratios through a well-dated stratigraphic sequence of fossil plants and animals in Hall's Cave, Kerr County, Texas, as a proxy for temporal changes in soil thickness. By using this record we are able to characterize late Quaternary climate-driven soil-erosion dynamics on the Edwards Plateau. We find that continuous erosion removed at least 180 cm of soil at a constant minimum rate of 11 cm/k.y.; this continuous phase of erosion ended ca. 5 ka. The Sr isotope record of soil erosion is consistent with late Quaternary environmental change in central Texas that has been independently modeled by using local and regional climate records. However, the rate of this climate-driven soil-erosion event was an order of magnitude slower than recent soil erosion caused by human land use. These results link erosion to century- to millennial-scale climate change and are cautionary evidence that even greater landscape degradation may result from coincident climatic variability and anthropogenic influences.

  13. Late Neogene marine Ostracoda from Tjornes, Iceland

    USGS Publications Warehouse

    Cronin, T. M.

    1991-01-01

    On the western side of the Tjornes Peninsula in northern Iceland exposures of fossiliferous marine sediments, basalts, and glacial tills record the climatic history of this region of the North Atlantic Ocean. Seventy-five marine ostracode species were recovered from the Pliocene Tjornes sediments and Quaternary sediments known as the Breidavik beds. New species Bensonocythere eirikssoni, Robertsonites williamsi, Hemicythere rekaensis, Thaerocythere mayburyae, Thaerocythere whatleyi, Leptocythere tjornesensis, Tetracytherura bardarsoni, and Cytheromorpha einarssoni are described. -from Author

  14. Late Quaternary terrestrial vertebrate coprolites from New Zealand

    NASA Astrophysics Data System (ADS)

    Wood, Jamie R.; Wilmshurst, Janet M.

    2014-08-01

    Over the past decade, concerted efforts to find and study Late Quaternary terrestrial vertebrate coprolites in New Zealand have revealed new insights into the diets and ecologies of New Zealand's prehistoric birds. Here, we provide a broader review of the coprolites found in natural (non-archaeological) Late Quaternary deposits from New Zealand. We summarise the morphological diversity of the coprolites, and discuss the taphonomy of the sites in which they are found. Since the 1870s more than 2000 coprolites have been discovered from 30 localities, all restricted to the South Island. The distribution of coprolite localities appears to reflect the presence of geological and climatic factors that enhance the potential for coprolite preservation; coprolites require dry conditions for preservation, and have been found on the ground surface within drafting cave entrances and at shallow (<300 mm) depths beneath rock overhangs with a northerly aspect. We classify the coprolites into eleven morphotypes, each of which may represent a range of different bird and/or reptile species. A review of genetically identified specimens shows that coprolites of different bird species overlap in size and morphology, reinforcing the need for identifications to be based on ancient DNA analysis.

  15. Late Quaternary sedimentation on the North Aegean continental margin, Greece

    SciTech Connect

    Piper, D.J.W. ); Perissoratis, C. )

    1991-01-01

    The late Quaternary seismic stratigraphy of the North Aegean continental shelf and adjacent basins has been interpreted from boomer and 3.5-kHz seismic profiles. Ages derived from shallow cores and offshore wells, and relative offsets on small synsedimentary faults, provide chronological control. Sea level history inferred from seismic stratigraphy correlates with the global eustatic sea level record based on oxygen isotopic curves. The present depth of the delta plain formed on the outer shelf during the late stage 6 lowstand provides a dated and originally horizontal marker for estimating rates of tectonic subsidence. Gross distribution of sediment facies is similar in both tectonically stable and active areas. The shell break formed by delta progradation, but is marked by faults in most places because of the accommodation provided by graben subsidence rates of 0.3-1.5 mm/yr. Standard sequence stratigraphic analysis can be applied to these sediments deposited during high-amplitude Quaternary sea level oscillations. High rates of subsidence result in the preservation an unusually complete record of sea level change. Major lowstand progradation is dependent on the duration, rather than the magnitude, of sea level lowstand. The long glaciations in isotopic stages 6, 12, 16, and 22 resulted in the most prominent seaward progradation on the margin. Sandy lowstand turbidite deposits formed only when there was rapid fall in sea level; otherwise sand was trapped on delta tops and silty muds were deposited in deep water.

  16. Global warming: Perspectives from the Late Quaternary paleomammal record

    SciTech Connect

    Graham, R.W. )

    1993-03-01

    Global warming at the end of the Pleistocene caused significant environmental changes that directly and indirectly effected biotic communities. The biotic response to this global warming event can provide insights into the processes that might be anticipated for future climatic changes. The megafauna extinction may have been the most dramatic alteration of mammalian communities at the end of the Pleistocene. Late Quaternary warming also altered regional diversity patterns for some small mammal guilds without extinction. Reductions in body size for both small and large mammal species were also consequences of these environmental fluctuations. Geographic shifts in the distributions of individual mammal species resulted in changes in species composition of mammalian communities. The individualistic response of biota to environmental fluctuations define some boundary conditions for modeling communities. Understanding these boundary conditions is mandatory in planning for the preservation of biodiversity in the future. Finally, it is essential to determine how global warming will alter seasonal patterns because it is apparent from the paleobiological record that not all Quaternary warming events have been the same.

  17. Asynchronous extinction of late Quaternary sloths on continents and islands

    PubMed Central

    Steadman, David W.; Martin, Paul S.; MacPhee, Ross D. E.; Jull, A. J. T.; McDonald, H. Gregory; Woods, Charles A.; Iturralde-Vinent, Manuel; Hodgins, Gregory W. L.

    2005-01-01

    Whatever the cause, it is extraordinary that dozens of genera of large mammals became extinct during the late Quaternary throughout the Western Hemisphere, including 90% of the genera of the xenarthran suborder Phyllophaga (sloths). Radiocarbon dates directly on dung, bones, or other tissue of extinct sloths place their “last appearance” datum at ≈11,000 radiocarbon years before present (yr BP) or slightly less in North America, ≈10,500 yr BP in South America, and ≈4,400 yr BP on West Indian islands. This asynchronous situation is not compatible with glacial–interglacial climate change forcing these extinctions, especially given the great elevational, latitudinal, and longitudinal variation of the sloth-bearing continental sites. Instead, the chronology of last appearance of extinct sloths, whether on continents or islands, more closely tracks the first arrival of people. PMID:16085711

  18. Late Quaternary folding of coral reef terraces, Barbados

    NASA Astrophysics Data System (ADS)

    Taylor, Frederick W.; Mann, Paul

    1991-02-01

    Uplifted late Ouaternary coral reefs on the island of Barbados record folding of the emergent crest of the Lesser Antilles accretionary prism (Barbados Ridge complex) since ca. 1 Ma. Three northeast striking folds are defined by systematic changes in altitudes in the crest of First High Cliff, a mostly constructional reef terrace about 125 ka, and Second High Cliff, a partially erosional reef terrace about 500 ka. The folds have wavelengths of 6 to 8 km and fold axes extend about 10 km. The largest anticline rises to the northeast, where it has been breached by erosion exposing highly deformed Eocene to lower Miocene rocks of the Scotland District. Uplift rates based on heights of the last interglacial First High Cliff range from 0.07 to 0.44 mm/yr. Quaternary folding on Barbados indicates that the crest of the accretionary prism continues to be an active fold belt undergoing northwestsoutheast shortening.

  19. Late Quaternary sea-level changes of the Persian Gulf

    NASA Astrophysics Data System (ADS)

    Lokier, Stephen W.; Bateman, Mark D.; Larkin, Nigel R.; Rye, Philip; Stewart, John R.

    2015-07-01

    Late Quaternary reflooding of the Persian Gulf climaxed with the mid-Holocene highstand previously variously dated between 6 and 3.4 ka. Examination of the stratigraphic and paleoenvironmental context of a mid-Holocene whale beaching allows us to accurately constrain the timing of the transgressive, highstand and regressive phases of the mid- to late Holocene sea-level highstand in the Persian Gulf. Mid-Holocene transgression of the Gulf surpassed today's sea level by 7100-6890 cal yr BP, attaining a highstand of > 1 m above current sea level shortly after 5290-4570 cal yr BP before falling back to current levels by 1440-1170 cal yr BP. The cetacean beached into an intertidal hardground pond during the transgressive phase (5300-4960 cal yr BP) with continued transgression interring the skeleton in shallow-subtidal sediments. Subsequent relative sea-level fall produced a forced regression with consequent progradation of the coastal system. These new ages refine previously reported timings for the mid- to late Holocene sea-level highstand published for other regions. By so doing, they allow us to constrain the timing of this correlatable global eustatic event more accurately.

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

    SciTech Connect

    Peterson, F.F.; Bell, J.W.; Ramelli, A.R.; Dorn, R.I.; Ku, T.L.

    1995-04-01

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

  1. Late Quaternary river drainage and fish evolution, Southland, New Zealand

    NASA Astrophysics Data System (ADS)

    Craw, D.; Burridge, C.; Anderson, L.; Waters, J. M.

    2007-02-01

    Late Quaternary to Holocene landscape evolution in southern New Zealand was dominated by glacial outwash processes. Evolution of the drainage network on a regional scale was punctuated by numerous river capture events associated with outwash transport and deposition. River capture events can be inferred from geological and topographic observations throughout the region. Independent evidence for river capture and drainage reorientation can be obtained from genetic studies of a freshwater-limited fish ( Galaxias 'southern', informal name). Regionally extensive interlinking of principal rivers (Mataura, Oreti, Aparima) via coalescence of alluvial plains onshore, and offshore at sea level lowstands, has resulted in a widespread genetic homogenisation of fish populations (< 0.9% mtDNA divergence). Genetically similar populations of G. 'southern' are present in an adjacent catchment (Von) that was captured episodically by the neighbouring major river system (Clutha). The low degree of genetic divergence between Oreti and Von catchments (< 0.15% mtDNA divergence) demonstrates that genetic interaction between fish populations was severed recently, probably during the early Holocene. This is in accord with radiocarbon dating (11-13 ka) of the youngest gravel level within the intervening divide. In contrast, morphologically similar fish in another adjacent major river (Waiau) have a minimum mtDNA divergence of 2.4% from the fish in the Mataura, Oreti, and Aparima Rivers. This genetic separation occurred at ca. 145-240 ka, based on the late Quaternary outwash terrace dating, in agreement with "molecular clock" estimates. Geological and genetic data in combination provide powerful tools for the elucidation of local and regional geomorphic evolution where river capture is an important process. The potential is strong for genetic data alone to provide information on the relative and absolute timing of river capture events, but must be interpreted in the context of severance of

  2. Study on the Late Quaternary Activity of Niyang River Fault

    NASA Astrophysics Data System (ADS)

    Fangtou, T.

    2015-12-01

    Niyang River fault with north-west trending is located on the west side of the Eastern Himalayan Syntaxis. It dislocated the eastern segment of Brahmaputra fault zone. We study the late Quaternary activity of the Niyang River fault by the high-resolution image data in combination with detailed field investigation, GPS observation, trenching and radiocarbon dating of charcoal samples. The GPS observation data shows that the movement characteristics of Niyang River fault is dextral strike-slip with extrusion at present, its strike-slip rate is 3~4mm/a and its extrusion rate is 2~3mm/a. The trench at Bayi town revealed that the first terraces of Niyang River was dislocated 50cm by the fault and it is dated to be 1220±40cal.a BP.. We found that third Lake terraces of the Linzhi ancient lakes was dislocated about 1.5m at Mirui town and it is dated to be 18060±60cal.a BP.. By the fault influence, there are different elevations at the same level terraces of Niyang river and the Linzhi ancient lakes both sides of Niyang river near Bayi town. The altitude of the second terraces of Niyang River is about 20 meters at eastern side higher than western side and it is dated to be between 8860±40cal.a BP. and 9870±50cal.a BP., the altitude of the third lake terraces of the Linzhi ancient lakes is about 60 meters at eastern side higher than western side. So, the average vertical slip rate of Niyang River fault was about 2mm/a since Holocene and its average vertical slip rate was about 3mm/a since late period of the late Pleistocene. This is consistent with GPS observation data. All these data suggest that Niyang River fault is active since Holocene. So further detailed research will be necessary to determine the range of the latest activity of this fault, movement characteristics and velocity and recurrence intervals of major earthquakes. These data will be a great significance for earthquake zonation and assessment of seismic risk in this region. Keywords:Niyang River fault

  3. Late Quaternary slip on the Santa Cruz Island fault, California

    USGS Publications Warehouse

    Pinter, N.; Lueddecke, S.B.; Keller, E.A.; Simmons, K.R.

    1998-01-01

    The style, timing, and pattern of slip on the Santa Cruz Island fault were investigated by trenching the fault and by analysis of offset late Quaternary landforms. A trench excavated across the fault at Christi Beach, on the western coast of the island, exposed deformation of latest Pleistocene to Holocene sediments and pre-Quaternary rocks, recording repeated large-magnitude rupture events. The most recent earthquake at this site occurred ca. 5 ka. Coastal terraces preserved on western Santa Cruz Island have been dated using the uranium-series technique and by extrapolation using terrace elevations and the eustatic record. Offset of terraces and other landforms indicates that the Santa Cruz Island fault is predominantly left lateral, having a horizontal slip rate of not more than 1.1 mm/yr and probably about 0.8 mm/yr. The fault also has a smaller reverse component, slipping at a rate of between 0.1 and 0.2 mm/yr. Combined with measurements of slip per event, this information suggests a long-term average recurrence interval of at least 2.7 k.y. and probably 4-5 k.y., and average earthquake magnitudes of Mw 7.2-7.5. Sense of slip, recurrence interval, and earthquake magnitudes calculated here for the Santa Cruz Island fault are very similar to recent results for other faults along the southern margin of the western Transverse Range, including the Malibu Coast fault, the Santa Monica fault, the Hollywood fault, and the Raymond fault, supporting the contention that these faults constitute a continuous and linked fault system, which is characterized by large but relatively infrequent earthquakes.

  4. Ecostratigraphic datums and sequence stratigraphy: Application to the marine Quaternary

    SciTech Connect

    Martin, R.E. ); Neff, E. ); Johnson, G.W. ); Krantz, D. )

    1991-03-01

    The marine Quaternary is characterized by few evolutionary appearances and extinctions of planktonic foraminifera. Because climatic fluctuations are a fundamental characteristic of Pleistocene, however, better stratigraphic resolution of the marine Quaternary can be gained by the establishment of biozones based on climatically controlled foraminiferal assemblages. Utilizing relative abundances of the warm-water Globorotalia menardii complex and temperature-water G. inflata, supplemented by left- and right-coiling varieties of G. truncatulinoides, the authors have subdivided the prezone-W Pleistocene of the tropical Atlantic (Core V16-205), Caribbean Sea (DSDP Core 502B), and northeast Gulf of Mexico (ODP Core 625B, Eureka Core E67-135) into 17 subzones, each with an average duration of {approximately}100,000 yrs. The subzones appear to reflect water mass shifts and disjunct species distributions resulting from expansion and contraction of northern hemisphere ice sheets. Hence, subzonal boundaries should also reflect change in eustatic sea level and sequence boundaries. Indeed, graphic correlation of the subzones, along with biostratigraphic markers and paleomagnetic and oxygen isotope datums, reveals changes in sediment accumulation rate (especially on the continental slope) and missing section, as well as intervals of deformation (core breaks) that affect the occurrence of subzonal boundaries and biostratigraphic markers.

  5. Late Quaternary carbonate deposition at the bottom of the world

    NASA Astrophysics Data System (ADS)

    Frank, Tracy D.; James, Noel P.; Bone, Yvonne; Malcolm, Isabelle; Bobak, Lindsey E.

    2014-05-01

    Carbonate sediments on polar shelves hold great potential for improving understanding of climate and oceanography in regions of the globe that are particularly sensitive to global change. Such deposits have, however, not received much attention from sedimentologists and thus remain poorly understood. This study investigates the distribution, composition, diagenesis, and stratigraphic context of Late Quaternary calcareous sediments recovered in 15 piston cores from the Ross Sea shelf, Antarctica. Results are used to develop a depositional model for carbonate deposition on glaciated, polar shelves. The utility of the deposits as analogs for the ancient record is explored. In the Ross Sea, carbonate-rich lithofacies, consisting of poorly sorted skeletal sand and gravel, are concentrated in the west and along the outer reaches of the continental shelf and upper slope. Analysis of fossil assemblages shows that deposits were produced by numerous low-diversity benthic communities dominated locally by stylasterine hydrocorals, barnacles, or bryozoans. Radiocarbon dating indicates that carbonate sedimentation was episodic, corresponding to times of reduced siliciclastic deposition. Most accumulation occurred during a time of glacial expansion in the lead-up to the Last Glacial Maximum. A more recent interval of carbonate accumulation postdates the early Holocene sea level rise and the establishment of the modern grounding line for the Ross Ice Shelf. When carbonate factories were inactive, fossil debris was subjected to infestation by bioeroders, dissolution, fragmentation, and physical reworking. This study reveals the episodic nature of carbonate deposition in polar settings and a reciprocal relationship with processes that deliver and redistribute siliciclastic debris. Carbonate production is most active during colder periods of the glacial-interglacial cycle, a potential new sedimentological paradigm for polar carbonate systems. Low accumulation rates and long residence

  6. Late Quaternary in a South Atlantic estuarine system: Stratigraphic and paleontologic indicators of coastal evolution

    NASA Astrophysics Data System (ADS)

    Aliotta, Salvador; Ginsberg, Silvia S.; Spagnuolo, Jorge O.; Farinati, Ester; Giagante, Darío; Vecchi, Laura G.

    2013-08-01

    The decisive influence of Late Quaternary sea level changes on the geological evolution of the coastal plain and adjacent continental shelf around the world has long been recognized. Coastal environments evolve actively during transgressive-regressive cycles whose development depends on sea level and sediment supply variations. The interaction of these variables was key to the current morphological and sedimentological configuration of coastal regions. Particularly, the estuarine system of Bahía Blanca (Argentina) presents various types of deposits and marine fossil accumulations, such as paleochannels in the subbottom, sand-shell ridges and extensive layers with fossils in life position. These features are important geological indicators, because its analysis allows us to define different paleoenvironmental conditions that prevailed during the coastal evolutionary process.

  7. North atlantic deepwater temperature change during late pliocene and late quaternary climatic cycles

    USGS Publications Warehouse

    Dwyer, G.S.; Cronin, T. M.; Baker, P.A.; Raymo, M.E.; Buzas, Jeffrey S.; Correge, T.

    1995-01-01

    Variations in the ratio of magnesium to calcium (Mg/Ca) in fossil ostracodes from Deep Sea Drilling Project Site 607 in the deep North Atlantic show that the change in bottom water temperature during late Pliocene 41,000-year obliquity cycles averaged 1.5??C between 3.2 and 2.8 million years ago (Ma) and increased to 2.3??C between 2.8 and 2.3 Ma, coincidentally with the intensification of Northern Hemisphere glaciation. During the last two 100,000-year glacial-to-interglacial climatic cycles of the Quaternary, bottom water temperatures changed by 4.5??C. These results show that glacial deepwater cooling has intensified since 3.2 Ma, most likely as the result of progressively diminished deep-water production in the North Atlantic and of the greater influence of Antarctic bottom water in the North Atlantic during glacial periods. The ostracode Mg/Ca data also allow the direct determination of the temperature component of the benthic foraminiferal oxygen isotope record from Site 607, as well as derivation of a hypothetical sea-level curve for the late Pliocene and late Quaternary. The effects of dissolution on the Mg/Ca ratios of ostracode shells appear to have been minimal.

  8. Patterns of late Quaternary shelf-margin sedimentation, southwest Louisiana

    SciTech Connect

    Suter, J.R.; Berryhill, H.L.

    1986-09-01

    Late Quaternary extension of the continental shelf in the northern Gulf of Mexico has been largely accomplished by deposition at the shelf margin during sea level lowstands. The distribution and geometry of facies suggest that delta progradation during sea level fall and lowstand is a principal process for shelf accretion. Along the shelf margin of southwest Louisiana, sets of deltaic deposits corresponding to the last two lowstands of sea level have been mapped from high-resolution seismic profiles. Individual deltas extend farther than 5000 m/sup 2/ and are more than 160 m thick. Diapirism has had a controlling effect on sedimentation patterns of the shelf-margin deltas throughout their depositional histories. Shelf-margin deltas have also been the loci for the transfer of large volumes of sediment from the shelf to the upper slope by mass transport, with buried submarine troughs formed by retrogressive shelf-edge failure in association with major streams acting as conduits for sediment movement. In southwest Louisiana, mass transport deposits follow depressions formed by salt diapirism rather than creating broad aprons on the slope.

  9. Late Quaternary environments, vegetation and agriculture in northern New Zealand

    NASA Astrophysics Data System (ADS)

    Horrocks, M.; Nichol, S. L.; Augustinus, P. C.; Barber, I. G.

    2007-03-01

    A sedimentological and plant microfossil history of the Late Quaternary is preserved in two sediment cores from early Polynesian ditch systems on southern Aupouri Peninsula. The study places human activities into a geomorphological and ecological context and allows comparison of natural and anthropogenic effects on two different geological settings: a floodplain and a relatively closed peat swamp. The data fill part of the current gap in the environmental record from northern New Zealand, namely MIS 3 (57k-26k yr BP). There is evidence for an increase in fire frequency in the region after 40k 14C yr BP, suggesting a shift to drier (and cooler) conditions. Pollen records show that conifer-hardwood forest dominated by podocarps (especially Dacrydium) prevailed prior to Polynesian arrival and deforestation within the last millennium, with Fuscopsora insignificant throughout. Both cores show sections with gaps in deposition or preservation, possible flood-stripping of peat during the pre-Holocene and mechanical disturbance by early Polynesians. The identification of prehistoric starch grains and other microremains of introduced Colocasia esculenta (taro) in both cores supports indirect evidence that the ditch systems of far northern New Zealand were used for the extensive cultivation of this crop. Copyright

  10. Possible Late Quaternary faulting in the Benton Hills, southeastern Missouri

    SciTech Connect

    Palmer, J.R.; Hoffman, D. . Dept. of Natural Resources)

    1993-03-01

    Geologic mapping in the 1930's by Dan Stewart and Lyle McManamy identified numerous faults in the Thebes Gap area of the Benton Hills, including two post-late Quaternary faults (max. of 10 m displacement) along the southeastern escarpment. Recent geologic mapping (Richard Harrison, pers. comm.) suggests dextral strike-slip displacement on most of these faults; some deformation post-dates the Pliocene-Pleistocene Mounds gravel. Small historical earthquake epicenters have been recorded in the Benton Hills area. Review of these data and analysis of the geologic and structural relationships to small- and large-scale drainage and alluvial features suggest tectonic control of the southeastern escarpment of the Benton Hills. The authors propose the coincidence of geologic structures and landforms resembles tectonically active alluvial basin margins, with the Benton Hills southeastern margin representing a fault block uplift escarpment. Future seismic reflection, drilling and trenching studies are planned to determine if the escarpment is fault controlled and of recent origin.

  11. Late Quaternary Pollen Record from Cheyenne Bottoms, Kansas

    NASA Astrophysics Data System (ADS)

    Fredlund, Glen G.

    1995-01-01

    A sediment and pollen record from Cheyenne Bottoms, a large (166 km 2) enclosed basin in central Kansas, provides evidence for local and regional vegetation and climate change during the late Quaternary (ca. 30,000 yr.). Although radiocarbon dating of the carbonate-rich lacustrine sediments remains problematic, a basic chronological framework for the section is established. Two major litho- and biostratigraphic units, a Farmdalian zone (ca. 30,000 to 24,000 yr B.P.) and a Holocene zone (ca. 11,000 yr B.P. to present), are separated by a major unconformity spanning the Woodfordian (ca. 24,000 to 11,000 yr B.P.). Pollen and sedimentary data indicate a period of basin-wide drying preceding this unconformity. The sustained absence of sediment accumulation within this playa-like basin suggests that early Woodfordian conditions were increasingly arid with strengthened surface winds. Before this, persistent shallow water marshland dominated the local basin-bottom vegetation. Regional upland vegetation was an open grassland-sage steppe throughout the Farmdalian with limited populations of spruce, juniper, aspen, birch, and boxelder in riparian settings and escarpments. Throughout the Holocene, water levels within the basin fluctuated. Changes in wetland vegetation resulting from water level fluctuation have increased during the last 3,000 yr indicating that periodic episodes of wetland loss and rebound are not unique to postsettlement conditions but are an ongoing phenomenon at Cheyenne Bottoms.

  12. Slope Deposits and (Paleo)Soils as Geoarchives to Reconstruct Late Quaternary Environments of Southern Africa

    NASA Astrophysics Data System (ADS)

    Huerkamp, K.; Voelkel, J.; Heine, K.; Bens, O.

    2009-04-01

    Although it is clear that large, rapid temperature changes have occurred during the last glacial-interglacial cycle and the Holocene in southern Africa, we have only limited, and often imprecise, knowledge of how the major moisture-bearing atmospheric circulation systems have reacted to these changes. Using slope deposits and soils as palaeoclimatic geoarchives we will overcome these constraints. The role of many geoarchives in the reconstruction of the Quaternary climate in southern Africa remains controversial, since the paleoclimate data are based on evidence from marine cores, lake sediments, speleothems and spring sinter, fluvial sediments, aeolian sands and dust, colluvium, and coastal sediments. To elucidate climate controls on Quaternary landscape evolution and to use these data for palaeoclimatic reconstructions, thus far slope deposits and soils have been investigated. Climatic controls on these cycles are incompletely known. The availability of results from earlier fieldwork, micromorphology, Optical Stimulated Luminescence (OSL), 14C dating and stable carbon isotope analysis will permit a thorough assessment of slope deposits and soils in terms of their palaeoenvironmental potential. The knowledge of suitable areas and sites in different climatic zones of southern Africa where slope deposits and soils have already been found document the late Quaternary climatic history and even climatic anomalies (e.g. Younger Dryas period at Eksteenfontein, 8.2 ka event at Tsumkwe, 4 ka event in the Auob valley, Little Ice Age in the Namib Desert). The findings will show the late Quaternary history of precipitation fluctuations, of the shifting of the ITCZ (and the ABF - Agulhas-Benguela Front), of wind intensities and directions, and of extreme precipitation events. The project will employ state-of-the-art geoscience methodology to interpret the record of precipitation changes of the late Quaternary, including the shifting of the summer and winter rain belts, the

  13. A model of late quaternary landscape development in the Delaware Valley, New Jersey and Pennsylvania

    USGS Publications Warehouse

    Ridge, J.C.; Evenson, E.B.; Sevon, W.D.

    1992-01-01

    In the Delaware Valley of New Jersey and eastern Pennsylvania the late Quaternary history of colluviation, fluvial adjustment, and soil formation is based on the ages of pre-Wisconsinan soils and glacial deposits which are indicated by feld relationships and inferred from mid-latitude climate changes indicated by marine oxygen-isotope records. The area is divided into four terranes characterized by sandstone, gneiss, slate and carbonate rocks. Since the last pre-Wisconsinan glaciation (> 130 ka, inferred to be late Illinoian), each terrane responded differently to chemical and mechanical weathering. During the Sangamon interglacial stage (??? 130-75 ka) in situ weathering is inferred to have occurred at rates greater than transportation of material which resulted in the formation of deep, highly weathered soil and saprolite, and dissolution of carbonate rocks. Cold climatic conditions during the Wisconsinan, on the other hand, induced erosion of the landscape at rates faster than soil development. Upland erosion during the Wisconsinan removed pre-Wisconsinan soil and glacial sediment and bedrock to produce muddy to blocky colluvium, gre??zes lite??es, and alluvial fans on footslopes. Fluvial gravel and overlying colluvium in the Delaware Valley, both buried by late Wisconsinan outwash, are inferred to represent episodes of early and middle Wisconsinan (??? 75-25 ka) upland erosion and river aggradiation followed by river degradation and colluvium deposition. Early-middle Wisconsinan colluvium is more voluminous than later colluvium despite colder, possibly permafrost conditions during the late Wisconsinan ??? 25-10 ka). Extensive colluviation during the early and middle Wisconsinan resulted from a longer (50 kyr), generally cold interval of erosion with a greater availability of easily eroded pre-Wisconsinan surficial materials on uplands than during the late Wisconsinan. After recession of late Wisconsinan ice from its terminal position, soil formation and

  14. Late quaternary geologic framework, north-central Gulf of Mexico

    USGS Publications Warehouse

    Kindinger, Jack G.; Penland, Shea; Williams, S. Jeffress; Brooks, Gregg R.; Suter, John R.; McBride, Randolph A.

    1991-01-01

    The geologic framework of the north-central Gulf of Mexico shelf is composed of multiple, stacked, delta systems. Shelf and nearshore sedimentary facies were deposited by deltaic progradation, followed by shoreface erosion and submergence. A variety of sedimentary facies has been identified, including prodelta, delta fringe, distributary, lagoonal, barrier island, and shelf sand sheet. This study is based on the interpretation and the synthesis of > 6,700 km of high-resolution seismic profiles, 75 grab samples, and 77 vibracores. The nearshore morphology, shallow stratigraphy, and sediment distribution of the eastern Louisiana shelf are the products of transgressive sedimentary processes reworking the abandoned St. Bernard delta complex. Relatively recent Mississippi delta lobe consists primarily of fine sand, silt, and clay. In the southern portion of the St. Bernard delta complex, asymmetrical sand ridges (>5 m relief) have formed as the result of marine reworking of distributary mouth-bar sands. Silty sediments from the modern Mississippi Birdsfoot delta onlap the St. Bernard delta complex along the southern edge. The distal margin of the St. Bernard complex is distinct and has a sharp contact on the north near the Mississippi Sound barrier island coastline and a late Wisconsinan delta to the south. The Chandeleur Islands and the barrier islands of Mississippi Sound have been formed by a combination of Holocene and Pleistocene fluvial processes, shoreface erosion, and ravinement of the exposed shelf. Sediments underlying the relatively thin Holocene sediment cover are relict fluvial sands, deposited during the late Wisconsinan lowstand. Subsequent relative sea-level rise allowed marine processes to rework and redistribute sediments that formed the nearshore fine-grained facies and the shelf sand sheet.

  15. Late Quaternary Advance and Retreat of an East Antarctic Ice Shelf System: Insights from Sedimentary Beryllium-10 Concentrations

    NASA Astrophysics Data System (ADS)

    Guitard, M. E.; Shevenell, A.; Domack, E. W.; Rosenheim, B. E.; Yokoyama, Y.

    2014-12-01

    Observed retreat of Antarctica's marine-based glaciers and the presence of warm (~2°C) modified Circumpolar Deep Water on Antarctica's continental shelves imply ocean temperatures may influence Antarctic cryosphere stability. A paucity of information regarding Late Quaternary East Antarctic cryosphere-ocean interactions makes assessing the variability, timing, and style of deglacial retreat difficult. Marine sediments from Prydz Bay, East Antarctica contain hemipelagic siliceous mud and ooze units (SMO) alternating with glacial marine sediments. The record suggests Late Quaternary variability of local outlet glacier systems, including the Lambert Glacier/Amery Ice Shelf system that drains 15% of the East Antarctic Ice Sheet. We present a refined radiocarbon chronology and beryllium-10 (10Be) record of Late Quaternary depositional history in Prydz Channel, seaward of the Amery Ice Shelf system, which provides insight into the timing and variability of this important outlet glacier system. We focus on three piston cores (NBP01-01, JPC 34, 35, 36; 750 m water depth) that contain alternating SMO and granulated units uninterrupted by glacial till; the record preserves a succession of glacial marine deposits that pre-date the Last Glacial Maximum. We utilize the ramped pyrolysis preparatory method to improve the bulk organic carbon 14C-based chronology for Prydz Channel. To determine if the SMO intervals reflect open water conditions or sub-ice shelf advection, we measured sedimentary 10Be concentrations. Because ice cover affects 10Be pathways through the water column, sedimentary concentrations should provide information on past depositional environments in Prydz Channel. In Prydz Channel sediments, 10Be concentrations are generally higher in SMO units and lower in glacial units, suggesting Late Quaternary fluctuations in the Amery Ice Shelf. Improved chronologic constraints indicate that these fluctuations occurred on millennial timescales during the Last Glacial

  16. Imprint of Late Quaternary Climate Change on the Mid-Atlantic Landscape

    NASA Astrophysics Data System (ADS)

    Pavich, M.; Markewich, H.; Newell, W. L.; Litwin, R.; Smoot, J.; Brook, G.

    2009-12-01

    Recent geomorphic, lithostratigraphic, palynologic and chronostratigraphic investigations of the mid-Atlantic region show that much of the modern landscape flanking the Chesapeake Bay and the Potomac River is developed on late Quaternary sediments. These deposits, dated by OSL and 14C, include transgressive marine and estuarine sediments deposited between 120ka and 32ka, and parabolic dunes formed between 32ka and 15ka. The stacked estuarine units were deposited in a subsiding basin as eustatic sea level fell from +7m to -60m. The estuarine units contain pollen that provides evidence for millennial scale climate fluctuations. The dunes formed during the period of rapid expansion of the Laurentide Ice Sheet as sea level fell to -120m. Permafrost features such as frost wedges and periglacial “pots” formed during cold intervals associated with marine oxygen isotope stages 4 and 2. This periglacial climate, along with glacioisostatic adjustments to growth and decay of the Laurentide Ice Sheet, affected landscape processes at least as far south as the Potomac River valley. While many of these features were recognized in earlier mapping and stratigraphic investigations, OSL dating has greatly extended the range of available dates and significantly improved our understanding of the impacts of highly variable periglacial climate on this region.

  17. A rock-magnetic record from Lake Baikal, Siberia: Evidence for Late Quaternary climate change

    USGS Publications Warehouse

    Peck, J.A.; King, J.W.; Colman, Steven M.; Kravchinsky, V.A.

    1994-01-01

    Rock-magnetic measurements of sediment cores from the Academician Ridge region of Lake Baikal, Siberia show variations related to Late Quaternary climate change. Based upon the well-dated last glacial-interglacial transition, variations in magnetic concentration and mineralogy are related to glacial-interglacial cycles using a conceptual model. Interglacial intervals are characterized by low magnetic concentrations and a composition that is dominated by low coercivity minerals. Glacial intervals are characterized by high magnetic concentrations and increased amounts of high coercivity minerals. The variation in magnetic concentration is consistent with dilution by diatom opal during the more productive interglacial periods. We also infer an increased contribution of eolian sediment during the colder, windier, and more arid glacial conditions when extensive loess deposits were formed throughout Europe and Asia. Eolian transport is inferred to deliver increased amounts of high coercivity minerals as staining on eolian grains during the glacial intervals. Variations in magnetic concentration and mineralogy of Lake Baikal sediment correlate to the SPECMAP marine oxygen-isotope record. The high degree of correlation between Baikal magnetic concentration/mineralogy and the SPECMAP oxygen-isotope record indicates that Lake Baikal sediment preserves a history of climate change in central Asia for the last 250 ka. This correlation provides a method of estimating the age of sediment beyond the range of the radiocarbon method. Future work must include providing better age control and additional climate proxy data, thereby strengthening the correlation of continental and marine climate records. ?? 1994.

  18. Late quaternary evolution of the Orinoco Delta, Venezuela

    USGS Publications Warehouse

    Warne, A.G.; Guevara, E.H.; Aslan, A.

    2002-01-01

    The modern Orinoco Delta is the latest of a series of stacked deltas that have infilled the Eastern Venezuelan Basin (EVB) since the Oligocene. During the late Pleistocene sea-level lowstand (20,000 to 16,000 yrs BP), bedrock control points at the position of the present delta apex prevented the river channel from incising as deeply as many other major river systems. Shallow seismic data indicate that the late Pleistocene Orinoco incised into the present continental shelf, where it formed a braided-river complex that transported sediment to a series of shelf-edge deltas. As sea level rose from 16,000 to 9,500 yrs BP, the Orinoco shoreline shifted rapidly landward, causing shallow-marine waves and currents to form a widespread transgressive sand unit. Decelerating sea-level rise and a warmer, wetter climate during the early Holocene (9,500 to 6,000 yrs BP) induced delta development within the relatively quiet-water environment of the EVB embayment. Sea level approached its present stand in the middle Holocene (6,000 to 3,000 yrs BP), and the Orinoco coast prograded, broadening the delta plain and infilling the EVB embayment. Significant quantities of Amazon sediment began to be transported to the Orinoco coast by littoral currents. Continued progradation in the late Holocene caused the constriction at Boca de Serpientes to alter nearshore and shelf hydrodynamics and subdivide the submarine delta into two distinct areas: the Atlantic shelf and the Gulf of Paria. The increased influence of littoral currents along the coast promoted mudcape development. Because most of the water and sediment were transported across the delta plain through the Rio Grande distributary in the southern delta, much of the central and northwestern delta plain became sediment starved, promoting widespread accumulation of peat deposits. Human impacts on the delta are mostly associated with the Volca??n Dam on Can??o Manamo. However, human activities have had relatively little effect on the

  19. Late Quaternary Megafaunal Extinctions in Northern Eurasia: Latest Results

    NASA Astrophysics Data System (ADS)

    Stuart, Anthony

    2010-05-01

    Anthony J. Stuart1 & Adrian M. Lister2 1 Biological and Biomedical Sciences, Durham University, South Road, Durham DH1 3LE, UK. Email: tony.s@megafauna.org.uk 2 Department of Palaeontology, The Natural History Museum, Cromwell Road, London SW7 5BD, UK. Email: a.lister@nhm.ac.uk. The global extinction of many spectacular species of megafauna (large terrestrial mammals, together with a few large reptiles and birds) within the last c. 50,000 years (Late Quaternary) has been attributed on the one hand to ‘overkill' by human hunters and on the other to environmental change. However, in spite of more than half a century of active interest and research the issue remains unresolved, largely because there are insufficient dated records of megafaunal species for most parts of the world. Northern Eurasia is an especially fruitful region in which to research megafaunal extinctions as it has a wealth of megafaunal material and crucially most extinctions occurred well within the range of radiocarbon dating. Our approach, in a series of projects over the last decade funded by the UK Natural Environment Research Council (NERC), involves amassing radiocarbon dates made directly on megafaunal material from across the entire region: a) by submitting a substantial number of samples (so far c. 500 dates) for AMS dating at Oxford (ORAU); b) obtaining AMS dates from colleagues working on aDNA projects; and c) carefully screening (‘auditing') dates from the literature. The dates (calibrated using OxCal) are plotted as time-sliced maps and as chronological/geographical charts. In our previous work we targeted a range of extinct species from Northern Eurasia: woolly mammoth, woolly rhinoceros, giant deer, cave bear (in collaboration with Martina Pacher), cave lion, and spotted hyaena (which survives today only in Sub-Saharan Africa). By this means we have established a reliable chronology for these extinctions which we are able to compare with the climatic, vegetational and

  20. Fluvial sensitivity to Late Quaternary climate changes in NW Romania

    NASA Astrophysics Data System (ADS)

    Perşoiu, Ioana; Rădoane, Maria; Robu, Delia; Tanţău, Ioan

    2013-04-01

    Fluvial archives became increasingly important for the reconstruction of past environments, as they record a sum of climate, vegetation, hydrologic and anthropic changes. This is especially important for the Late Quaternary, when climate and human activities had recorded large spatial and temporal variations. Here we present a tale of fluvial behavior during the last ca. 24.000 years in NW Romania, based on 1) absolute ages and fluvial architecture of sediments exposed in 8 openings located along the Someşu Mic River, and 2) depth-age models, grain size, LOI and gastropods assemblage analysis on 2 cores located upstream from Ştiucilor Lake, a natural lake along a small tributary of the Someşu Mic River, formed by salt disolution on top of a narrow diapiric anticline. During the Late Glacial (LG), Ştiucilor Lake was more extended then is today, with a high input of coarse materials (sands) from the slopes; and dramatically reducing its size in the Early Holocene, a transition marked by the abrupt occurrence of Holocene gyttja on top of LG sands, 1 km upstream from the present lake. Further upstream, at ca. 4 km from the present day edge of the lake, clays and sandy clays were deposited during the Bolling - Allerod (BA), followed by fine - medium sands of Younger Dryas (YD) age. On top of these sands, clays, sandy clays and gyttja occur, suggesting a returning to a less energetic sedimentary environment in the Holocene. In both cores, the sediments become lacustrine, with clays and fine sands, attesting the expansion of the lake's surface, followed by large fluctuations during the Holocene. The river fed by this stream - Someşu Mic, was a coarse gravel, shallow braided river before the Last Glacial Maximum and until the YD. The channel metamorphosis into a narrow, incised, meandering one, occurred ca. 1500 years after the beginning of the Holocene. However, sedimentological evidences suggest that this transition from braided to meandering channel was not a

  1. Minimal erosion of Arctic alpine topography during late Quaternary glaciation

    NASA Astrophysics Data System (ADS)

    Gjermundsen, Endre F.; Briner, Jason P.; Akçar, Naki; Foros, Jørn; Kubik, Peter W.; Salvigsen, Otto; Hormes, Anne

    2015-10-01

    The alpine topography observed in many mountainous regions is thought to have formed during repeated glaciations of the Quaternary period. Before this time, landscapes had much less relief. However, the spatial patterns and rates of Quaternary exhumation at high latitudes--where cold-based glaciers may protect rather than erode landscapes--are not fully quantified. Here we determine the exposure and burial histories of rock samples from eight summits of steep alpine peaks in northwestern Svalbard (79.5° N) using analyses of 10Be and 26Al concentrations. We find that the summits have been preserved for at least the past one million years. The antiquity of Svalbard’s alpine landscape is supported by the preservation of sediments older than one million years along a fjord valley, which suggests that both mountain summits and low-elevation landscapes experienced very low erosion rates over the past million years. Our findings support the establishment of northwestern Svalbard’s alpine topography during the early Quaternary. We suggest that, as the Quaternary ice age progressed, glacial erosion in the Arctic became inefficient and confined to ice streams, and high-relief alpine landscapes were preserved by minimally erosive glacier armour.

  2. Variable Quaternary chemical weathering fluxes and imbalances in marine geochemical budgets.

    PubMed

    Vance, Derek; Teagle, Damon A H; Foster, Gavin L

    2009-03-26

    Rivers are the dominant source of many elements and isotopes to the ocean. But this input from the continents is not balanced by the loss of the elements and isotopes through hydrothermal and sedimentary exchange with the oceanic crust, or by temporal changes in the marine inventory for elements that are demonstrably not in steady state. To resolve the problem of the observed imbalance in marine geochemical budgets, attention has been focused on uncertainties in the hydrothermal and sedimentary fluxes. In recent Earth history, temporally dynamic chemical weathering fluxes from the continents are an inevitable consequence of periodic glaciations. Chemical weathering rates on modern Earth are likely to remain far from equilibrium owing to the physical production of finely ground material at glacial terminations that acts as a fertile substrate for chemical weathering. Here we explore the implications of temporal changes in the riverine chemical weathering flux for oceanic geochemical budgets. We contend that the riverine flux obtained from observations of modern rivers is broadly accurate, but not representative of timescales appropriate for elements with oceanic residence longer than Quaternary glacial-interglacial cycles. We suggest that the pulse of rapid chemical weathering initiated at the last deglaciation has not yet decayed away and that weathering rates remain about two to three times the average for an entire late Quaternary glacial cycle. Taking into account the effect of the suggested non-steady-state process on the silicate weathering flux helps to reconcile the modelled marine strontium isotope budget with available data. Overall, we conclude that consideration of the temporal variability in riverine fluxes largely ameliorates long-standing problems with chemical and isotopic mass balances in the ocean. PMID:19325631

  3. Paleoclimatic Comparisons Between Three Late Quaternary Amazonian Lacustrine Records

    NASA Astrophysics Data System (ADS)

    Cordeiro, R. C.; Martins, G. S.; Fontes, D.; Turcq, B.; Sifeddine, A.; Seoane, J. S.; Conceição, M. G.; Barbosa, M.; Rodrigues, R. A.; Moreira, L.

    2012-12-01

    In recent years many records made in the cores of ice has shown significant changes in temperature associated with changes in atmospheric composition. The most notable changes occur between the glacials and interglacials cycles. Climatic changes in tropical areas during the global climatic changes is highly debatable. Even today, there are many controversies about the extent of the occurrence of dry weather in the Amazon during glacial periods. In the region of São Gabriel da Cachoeira, polynic diagram of Lagoa da Pata showed that vegetation remained with elements of forest trees, with replacement of elements of cold weather during the last glacial. In Carajás were observed substitution forest to savannah, during the last glacial. We present here a comparison of organic and inorganic geochemical sediment record of tree distinct Amazonian sectors: Morro dos Seis Lagos (AM) is located at 0°17‧9.68″ N and 66°40‧36.18″ W (Lagoa da Pata, LPT V core position) located in the forested upper Rio Negro basin in humid climate area (~3000 mm/yr), Carajás Region at 5°50‧ to 6°35‧ S and 49°30‧ to 52°00‧ situated 800 m high in lateritic crust in south eastern Amazonia (1800mm/yr) and São Benedito Region (PA) at 9°7'0.87"S and 56°16'0.00"W (Lago do Saci, Sac01/05 core position) in south Amazonia with a mean precipitation as Carajás around 1800 mm/yr. A comparison of these records reveals important changes in the environmental history of the Amazonian hydrological regime during the late Quaternary. The results of geochemical analyses reveal three hydrological and climatic regimes from 50,000 cal yr BP until the present. The first phase, between 50,000 until ~25,000 cal yr BP, was characterized by relatively high lake level as suggested by high organic carbon values in Lagoa da Pata and Carajás principally in the beginning of the period. In Saci Lake in the beginning of the record (35,500 cal yr BP) high values of TOC were observed relatively to last

  4. Tropical Rain Forest and Climate Dynamics of the Atlantic Lowland, Southern Brazil, during the Late Quaternary

    NASA Astrophysics Data System (ADS)

    Behling, Hermann; Negrelle, Raquel R. B.

    2001-11-01

    Palynological analysis of a core from the Atlantic rain forest region in Brazil provides unprecedented insight into late Quaternary vegetational and climate dynamics within this southern tropical lowland. The 576-cm-long sediment core is from a former beach-ridge "valley," located 3 km inland from the Atlantic Ocean. Radio-carbon dates suggest that sediment deposition began prior to 35,000 14C yr B.P. Between ca. 37,500 and ca. 27,500 14C yr B.P. and during the last glacial maximum (LGM; ca. 27,500 to ca. 14,500 14C yr B.P.), the coastal rain forest was replaced by grassland and patches of cold-adapted forest. Tropical trees, such as Alchornea, Moraceae/Urticaceae, and Arecaceae, were almost completely absent during the LGM. Furthermore, their distributions were shifted at least 750 km further north, suggesting a cooling between 3°C and 7°C and a strengthening of Antarctic cold fronts during full-glacial times. A depauperate tropical rain forest developed as part of a successional sequence after ca. 12,300 14C yr B.P. There is no evidence that Araucaria trees occurred in the Atlantic lowland during glacial times. The rain forest was disturbed by marine incursions during the early Holocene period until ca. 6100 14C yr B.P., as indicated by the presence of microforaminifera. A closed Atlantic rain forest then developed at the study site.

  5. Late Quaternary paleosols, stratigraphy and landscape evolution in the Northern Pampa, Argentina

    NASA Astrophysics Data System (ADS)

    Kemp, Rob A.; Zárate, Marcelo; Toms, Phillip; King, Matthew; Sanabria, Jorge; Arguello, Graciella

    2006-07-01

    The field properties, micromorphology, grain-size, geochemistry, and optically stimulated luminescence (OSL) ages of two late Quaternary sections have been used to reconstruct the sequence of pedosedimentary processes and to provide insights into landscape evolution in part of the Northern Pampa of Argentina. Paleosols developed in paludal sediments adjacent to the Paraná river at Baradero and in loess at Lozada can both be correlated and linked to other sites, thus enabling for the first time the tentative recognition and tracing of a diachronous soil stratigraphic unit that probably spans the equivalent of at least part of marine oxygen isotope stage (OIS) 5. The paleosol at Lozada was truncated and buried beneath fluvial sediments during the time span of OIS 4 and 3. Eolian gradually replaced paludal inputs at Baradero over this period, and there were also two clearly defined breaks in sedimentation and development of paleosols. The period corresponding to OIS 2 was marked by significant loess accumulation at both sites with accretion continuing into the mid-Holocene only at Lozada. The more developed nature of the surface soil at Baradero probably reflects a combination of a moister climate and a longer soil-forming interval.

  6. Sequence stratigraphy and composition of late quaternary shelf-margin deltas, Northern Gulf of Mexico

    SciTech Connect

    Morton, R.A.; Suter, J.R.

    1996-04-01

    High-resolution seismic profiles and foundation borings from the northwestern Gulf of Mexico record the physical attributes and depositional histories of several late Quaternary sequences that were deposited by wave-modified, river-dominated shelf-margin deltas during successive periods of lowered sea level. Each progressively younger deltaic sequence is thinner and exhibits a systematic decrease in the abundance and concentration of sand, which is attributed to a shift in the axes of trunk streams and greater structural influence through time. Our study shows that (1) contemporaneous structural deformation controlled the thickness of each sequence, the oblique directions of delta progradation, the axes of major fluvial channels, and the geometries of delta lobes at the shelf margin; (2) sedimentation was rapid in response to rapid eustatic fluctuations and structural influence; (3) boundaries of these high-frequency sequences are the correlative conformities of updip fluvial incision and coincide with downlap surfaces at the shelf margin; (4) the downlap surfaces are not true surfaces, but zones of parallel reflections that become progressively higher and younger in the direction of progradation; (5) the downlap zones are composed of marine muds that do not contain the high concentrations of shell debris expected in condensed sections; (6) possible paleosols capping the two oldest sequences are regressive surfaces of subaerial exposure that were preserved during transgressions; and (7) no incised valleys or submarine canyons breach the paleoshelf margin, even though incised drainages were present updip and sea level curves indicate several periods of rapid fall.

  7. Ionian marine terraces of southern Italy: Insights into the Quaternary tectonic evolution of the area

    NASA Astrophysics Data System (ADS)

    Caputo, R.; Bianca, M.; D'Onofrio, R.

    2010-08-01

    New detailed morphotectonic analyses of a well exposed flight of marine terraces along the Ionian coast of southern Italy has been carried out. The area represents a key transect for investigating the middle-late Quaternary evolution of the Southern Apennines chain-foredeep-foreland geodynamic system. A major result of the research is the reconstruction of a virtually complete 3D geometry of the marine surfaces along a coastal sector of ca. 70 km, which (1) documents the occurrence of 18 paleo-shorelines and (2) provides evidence for a strong regional uplift affecting the investigated area. Following a systematic critical review of literature relating to geochronological data, integrated with a morphogenetic model based on the interaction between tectonic uplift and eustatic sea level changes, the different terraces are correlated to as many highstand sea level peaks, dating the highest/oldest terrace to ca. 600 ka (MIS 15). The vertical and horizontal distribution of the terraces show a general convergence of the paleo-shorelines toward NNE, which indicates a decreasing trend in differential uplift in that direction ranging from almost 2 mm/a in the southwestern sector to about 0.2 mm/a in the northeastern sector. Detailed mapping and 3D reconstruction also emphasize the partitioning of the area into three distinct sectors characterized by different tilting rates. This behavior is likely caused by the combined role and activity of three major tectonic structures working at different scales and rates including (1) the reactivation of an out-of-sequence thrust, (2) sliding along the basal detachment of the external Apennines wedge and (3) a lithospheric-scale duplexing (crustal or deeper). As a major conclusion, within the external sector of the Southern Apennines chain and its foredeep, regional shortening and a contractional tectonic regime persisted throughout the whole Quaternary and it is probably still active.

  8. Late Quaternary stream incision rates due to tectonic uplift in North Peloponnese, Greece

    NASA Astrophysics Data System (ADS)

    Karymbalis, E.; Ferentinou, M.; Gaki-Papanastassiou, K.; Papanastassiou, D.; Maroukian, H.

    2012-04-01

    of erosion so bedrock incision rates can be directly calculated. For each cross-section the high (Hv) and the width (Wv) of the valley were measured while the ratio of valley width and valley high (Vf) was also estimated. Valley side slope angles were also determined and their distribution along the study streams was discussed. The mean incision rate of each stream for the last 350kyrs was estimated and both spatial and temporal variations of incision rates along the reaches of the studied streams were reconstructed. Valley morphometric parameters were also studied utilizing Artificial Neural Networks. The geomorphic evolution of the studied streams has been affected by the lithology of the bedrock, the tectonic uplift of the area, sea level fluctuations during the Late Quaternary and the head-ward erosion and incision of the channels. The high of the valleys for each marine terrace is gradually greater from east to west. This indicates that incision rates are comparable with the component of regional uplift and with the slip rate of the Xylokastro fault over the last 350 kyrs.

  9. Deep-sea ostracode species diversity: Response to late Quaternary climate change

    USGS Publications Warehouse

    Cronin, T. M.; DeMartino, D.M.; Dwyer, G.S.; Rodriguez-Lazaro, J.

    1999-01-01

    Late Quaternary ostracode assemblages from the North Atlantic Ocean were studied to establish the effect of climatic changes of the past 210,000 yr (marine oxygen isotope stages 7-1) on deep-sea benthic biodiversity and faunal composition. Two-hundred and twenty five samples from the Chain 82-24 Core 4PC (41??43'N, 32??51'W, 3427 m water depth) on the western Mid-Atlantic Ridge revealed high amplitude fluctuations in ostracode abundance and diversity coincident with orbital and suborbital scale climate oscillations measured by several paleoceanographic proxy records. During the past 210,000 yr, ostracode biodiversity as measured by species number (S) and the Shannon-Weaver index, H(S), oscillated from H(S) = 0.4 during glacial periods (marine isotope stages 6, 5d, 5b, 4, and 2) to H(S) = 1.1 during interglacial and interstadial periods (stages 7, 5e, 5c, 5a, 3 and 1). A total of 23 diversity peaks could be recognized. Eleven of these signify major periods of high diversity [H(S) > 0.8, S = 10-21] occurring every 15-20 ka. Twelve were minor peaks which may represent millennial-scale diversity oscillations. The composition of ostracode assemblages varies with Krithe-dominated assemblages characterizing glacial intervals, and Argilloecia-Cytheropteron characterizing deglacials, and trachyleberid genera (Poseidonamicus, Echinocythereis, Henryhowella, Oxycythereis) abundant during interglacials. Diversity and faunal composition changes can be matched to independent deep-sea paleoceanographic tracers such as benthic foraminiferal carbon isotopes, Krithe trace elements (Mg/Ca ratios), and to North Atlantic region climate records such as Greenland ice cores. When interpreted in light of ostracode species' ecology, these faunal and diversity patterns provide evidence that deep-sea benthic ecosystems experience significant reorganization in response to climate changes over orbital to millennial timescales.

  10. Discussion: a critique of Possible waterways between the Marmara Sea and the Black Sea in the late Quaternary: evidence from ostracod and foraminifer assemblages in lakes İznik and Sapanca, Turkey, Geo-Marine Letters, 2011

    NASA Astrophysics Data System (ADS)

    Yaltırak, Cenk; Ülgen, Umut B.; Zabcı, Cengiz; Franz, Sven Oliver; Ön, Sena Akçer; Sakınç, Mehmet; Çağatay, M. Namık; Alpar, Bedri; Öztürk, Kurultay; Tunoğlu, Cemal; Ünlü, Selma

    2012-06-01

    The identification of past connection routes between the Black Sea and the Sea of Marmara, other than the traditional one through to the Bosphorus Strait, would be of considerable interest to the international scientific community. Nazik et al. (Geo-Mar Lett 31:75-86 (2011) doi:10.1007/s00367-010-0216-9) suggest the possibility of two alternative waterway connections via lakes Sapanca and İznik. Their Black Sea to Sea of Marmara multi-connection hypothesis, which is based on undated marine fossils collected in both lakes from surficial grab samples, conflicts with many earlier studies. In this contribution, the hypothesis and the underlying data are discussed in the light of previous tectonic, sedimentological and limnological findings showing that it is impossible to have had marine connections through lakes Sapanca and İznik during the last 11.5 ka. Global sea-level trends and tectonic uplift rates would accommodate a connection between the Sea of Marmara and Lake İznik in the middle Pleistocene. Uplift rates for the northern block of the North Anatolian Fault, when compared with the global sea-level curve, clearly indicate that there cannot have been a connection through the İzmit Gulf-Lake Sapanca-Sakarya Valley for at least the past 500 ka. Moreover, borehole sediments along the western shores of Lake Sapanca, which reach down to the bedrock, do not contain any marine fossils.

  11. Recent shallow marine ostracods from high latitudes: Implications for late Pliocene and Quarternary palaeoclimatology

    USGS Publications Warehouse

    Brouwers, E.M.; Cronin, T. M.; Horne, D.J.; Lord, A.R.

    2000-01-01

    New information about modern high-latitude marine ostracod faunas and about their occurrence in late Pliocene and Quaternary sequences promotes the application of these microfossils to palaeoenvironmental, palaeobiogeographical and palaeoclimatological problems. Five poorly known species (Cluthia cluthae, Finmarchinella logani, Roundstonia globulifera, Roundstonia macchesneyi and Semicytherura complanata) from North Atlantic, North Pacific and Arctic areas are confirmed as extant and are used to demonstrate the potential of marine ostracods as tools for palaeoclimate studies. The genus Bonnyannella Athersuch, 1982 is shown to be a junior synonym of Roundstonia Neale, 1973.

  12. Late Quaternary stratigraphy of the eastern Gulf of Maine

    SciTech Connect

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

    1993-03-01

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

  13. Late Quaternary environments and biogeography in the Great Basin

    NASA Astrophysics Data System (ADS)

    Thompson, R. S.; Mead, J. I.

    1982-01-01

    Plant and animal remains found in packrat ( Neotoma spp.) middens and cave fill from the eastern and southern Great Basin region reveal the presence of subalpine conifers and boreal mammals at relatively low elevations during the Late Wisconsin. Limber pine ( Pinus flexilis) and bristlecone pine ( P. longaeva) were important in the late Pleistocene plant communities throughout this region. Spruce ( Picea cf. engelmannii) and common juniper ( Juniperus communis) were present in some of the more northerly localities, and Douglas fir ( Pseudotsuga menziesii) and white fir ( Abies concolor) were present in southern and eastern localities. Single needle pinyon pine ( Pinus monophylla), common across this region today, was apparently not present north of the Sheep Range of southern Nevada during the Late Wisconsin. Pikas ( Ochotona cf. princeps), small boreal mammals present in only a few Great Basin mountain ranges today, were common throughout the region. Heather voles ( Phenacomys cf. intermedius) have been found in two cave fill deposits in Nevada, though they are unknown in the Great Basin today. Limber and bristlecone pines are generally restricted to rocky substrates in modern subalpine habitats in the Great Basin, and this may also have been the case when these plants grew at lower elevations during the Late Wisconsin. Subalpine conifers were present on the rock outcrops sampled by the packrat middens, but shrub communities, perhaps dominated by sagebrush ( Artemisia spp.), may have been present on alluvial valley-bottom substrates. Forested habitats would thus have been isolated habitat islands, as they are today. Boreal small mammals, including pikas and heather voles, were able to colonize the Great Basin mountain ranges during the late Pleistocene. We suggest that these mammals were able to survive in the intervening valley-bottoms under a cool-summer climatic regime, and that continuous forest or woodland corridors were not necessary for migration.

  14. Measuring Late Quaternary Ursid Diminution in the Midwest

    NASA Astrophysics Data System (ADS)

    Wolverton, Steve; Lyman, R. Lee

    1998-05-01

    Paleobiologists generally agree that within the past 10,000 yr North American black bears ( Ursus americanus) have decreased in body and tooth size. Some researchers infer that diminution was gradual and continuous; thus, one might infer that a specimen is old if it is larger than an average-size modern bear. Ursid remains recovered in the 1950s from Lawson Cave, Missouri, that are larger than some modern bears have been reported to date to the late Pleistocene, but association with modern taxa, taphonomic considerations, and a radiocarbon date of 200 yr B.P. indicate that they are modern. Modern specimens from Lawson Cave and other parts of the American Midwest are relatively large compared to modern North American black bears from other areas, suggesting that many supposed late Pleistocene bears from the area might be modern also.

  15. Mapping the late Quaternary evolution of the lower Mississippi Valley

    NASA Astrophysics Data System (ADS)

    Haugerud, R. A.; Simon, K. M.; James, T. S.

    2013-12-01

    The lower Mississippi Valley (LMV) extends from Cape Girardeau to Natchez and from Little Rock to Memphis. Extensive Quaternary terraces within the LMV have been considered to reflect downstream changes in base level (global sea level) and (or) upstream changes in water and sediment input because of glaciation. We suggest that the first-order control on terrace development was glacial-isostatic adjustment (GIA). Observed variation in heights of Quaternary alluvial surfaces at Memphis is 50 m (Rittenour et al., 2007). GIA modeling by Clark et al. (1994) predicted vertical displacement of as much as 130 m at Memphis over the last 18,000 years. ICE-5G models predict smaller displacement and reinforce the viability of GIA as the primary cause of LMV aggradation and incision. Existing analyses of LMV terraces are built on geomorphic maps by Saucier and colleagues (1974, 1994; Autin et al., 1991) that were interpreted from aerial photographs and inch-to-the-mile contour maps. Geomorphic mapping from high-resolution DEMs is more accurate, more rapid, and more reproducible than mapping from aerial photography and intermediate-resolution contours. Working from lidar DEMs (1-5 m XY resolution) and the 10 m National Elevation Dataset (NED) DEM largely derived from 1:24,000 scale contours, Haugerud is mapping the geomorphology of the LMV at ~1:500,000 scale. Goals are to explore the GIA-terrace hypothesis and improve the geomorphic and stratigraphic context for studies of New Madrid seismicity. Mapping leads to several observations: 1. The Holocene floodplain of the Mississippi River onlaps older surfaces. The river appears to be filling a hole created by collapse of the Laurentide forebulge. Continued filling of this accommodation space will, barring human intervention, enable the river to abandon its course through Thebes Gap in favor of a lower-elevation route through Oran Gap. 2. Within Holocene meander belts, younger levee crests are higher than older levee crests. The

  16. Late Quaternary depositional history of the Albemarle Embayment, NC

    SciTech Connect

    Riggs, S.R.; Klingman, C.R.; Wyrick, R.A. . Dept. of Geology)

    1993-03-01

    The depositional history of Albemarle Embayment documents deep fluvial incisement by the Roanoke River system during glacial episodes and subsequent infilling by fluvial-estuarine-barrier island sediment sequences during interglacial transgressions. Unraveling the Holocene time slice will help reconstruct complex Quaternary records of multiple incisement and backfilling. A network of drill holes, vibracores, and seismic data suggest a four-phase infill history over the last 12,000 years. (1) Lower Roanoke River: (a) Bedload-charged, braided fluvial systems deposited basal sequences of sand and gravel prior to [approximately]5,000 BP. (b) Aggradational, swamp-forest floodplains developed [approximately]5,000 BP and bound the modern incised channels characterized by minimal bedload sedimentation. (2) Albemarle sound: (a) In the central basin, the basal channel sand sequence is overlain by an open estuarine, highly interlaminated sand and mud sequence that accumulated between [approximately]12,000 BP and [approximately]2,000 BP. (b) Depositional patterns within this unit suggest multiple oscillations of Holocene sea level that caused channel reincisement and subsequent backfilling. (c) Present estuarine marsh sedimentation began in protected coastal areas [approximately]5,000 BP. (3) Outer banks: (a) Barrier islands first influenced sedimentation in the area after [approximately]5,000 BP producing a semi-enclosed Albemarle Sound. (b) Deposition within the central basin shifted to uniform organic-rich muds that grade eastward into overwash and inlet sands. (4) Modern man: (a) colonial development within the drainage basins in the early 1700's AD produced a wedge of orange mud in inner Albemarle Sound. (b) Dam construction in the 1950's terminated orange mud deposition and the central basin reverted to organic-rich mud sedimentation.

  17. Synthesis of Late Cretaceous-Quaternary tectonic, sedimentary and magmatic processes and basin formation related to episodic subduction-collision in the easternmost Mediterranean region

    NASA Astrophysics Data System (ADS)

    Robertson, Alastair; Kinnaird, Timothy; McCay, Gillian; Palamakumbura, Romesh; Taslı, Kemal

    2015-04-01

    Mesozoic oceanic crust of the easternmost Mediterranean has experienced northwards subduction during Late Cretaceous-Cenozoic, either continuously or discontinuously based on kinematic evidence. Much of the existing information on sedimentation within the easternmost Mediterranean oceanic basin comes from the non-emplaced continental margins of the Levant and North Africa. In addition, sedimentary basins related to plate convergence are recorded along the northern margin of the Southern Neotethyan ocean, mainly in the Kyrenia Range of northern Cyprus and its extension into the Misis Mountains of southern Turkey, coupled with the adjacent submerged areas. In a setting of only incipient continental collision such as the easternmost Mediterranean the sedimentary basins would be expected to remain entirely submarine. In contrast, the Kyrenia Range has been strongly uplifted and subaerially exposed during Late Pliocene-Quaternary time. This allows the recognition of a number of discrete phases of sedimentary basin formation: 1. Late Cretaceous (Campanian-Maastrichtian): silicic volcanism to create a subaqueous volcaniclastic apron; 2. Maastrichtian-Paleocene: pelagic carbonate deposition interspersed with proximal gravity flows and within-plate type alkaline volcanics; 3. Early Eocene: large-scale sedimentary melange (olistostrome) emplacement; 4. Late Eocene-Late Miocene: terrigenous gravity-flow deposition in a deep-water fault dissected 'fore arc' setting. Initial, Late Eocene non-marine coarse clastic alluvial fan deposition was succeeded by Oligocene-Miocene deep-marine siliciclastic gravity flow deposits, fining and shallowing upwards during the Late Miocene; 5. Messinian: localised precipitation of evaporites in small fault-controlled basins; 6. Pliocene: shallow-marine siliciclastic-carbonate deposition in a shelf-depth, overall regressive setting; 7. Latest Pliocene to mid-Pleistocene: gravitational accumulation of coarse talus along a strongly uplifting

  18. Seismic stratigraphy of the Bering Trough, Gulf of Alaska: Late Quaternary history of Bering Glacier dynamics

    NASA Astrophysics Data System (ADS)

    Montelli, A.; Gulick, S. P. S.; Worthington, L. L.; Mix, A. C.; Zellers, S.; Jaeger, J. M.

    2014-12-01

    Sedimentary architecture of the cross-shelf Bering Trough is studied using 5 high resolution seismic profiles integrated with the drilling data acquired during Integrated Ocean Drilling Program (IODP) Expedition 341. The objectives of this work are to constrain the number of advance-retreat cycles that have occurred through the Late Quaternary, examine the impact of the Bering Glacier on the continental shelf and slope, and reconstruct Bering Glacier dynamics. By tying these sequences with δ18O stratigraphy, we can test the Bering Glacier's relation to global ice sheet evolution and better understand the degree to which the glacial advance-retreat cycles were in phase with global events. Our results show that: (1) Identification of erosional surfaces and glacigenic landforms that record positions of stillstand events and diagnose the style of retreat allow us to distinguish nine phases of glacial advances and subsequent retreats. (2) Mapping shows that glacier pathways and flow directions through time are influenced by the occurrence of thick grounding-zone deposits and shifting foci of erosion. (3) Continuous buildup of glacigenic sediment fills tectonically created accommodation space and allows the glacier to advance seaward for the last three advances. Discovery of systematic, prominent deposition of glacial diamict and ice-rafted debris (IRD) during phases of glacial retreat is supported by the drilling data and suggests reconsideration of IRD impact on slope sedimentation. (4) The trough mouth fan started its development during marine isotope stage (MIS) 6, progressively advancing to the position of present shelf edge during the subsequent MIS 4 and MIS 2 and is recognized by evidence of extensive deposition of glacigenic debris flows on the slope. (5) Sedimentation rates in the depocenter are exceptionally high and are estimated to be 1-2 m/k.y. through the middle Pleistocene on the shelf and 4-5 m/k.y. average through MIS 6 on the slope.

  19. Late quaternary plant zonation and climate in southeastern Utah

    SciTech Connect

    Betancourt, J.L.

    1984-01-31

    Plant macrofossils from packrat middens in two southeastern Utah caves outline development of modern plant zonation from the late Wisconsin. Allen Canyon Cave (2195 m) and Fishmouth Cave (1585 m) are located along a continuous gradient of outcropping Navajo Sandstone that extends from the Abajo Mountains south to the San Juan River. By holding the site constant, changes in the floral composition for a plot of less than one hectare can be observed, even if sporadically, over tens of millennia. At Allen Canyon Cave, Engelmann spruce-alpine fir forest was replaced by the present vegetation consisting of pinyon-juniper woodland on exposed ridgetops and cliffside stands of Douglas fir, ponderosa pine, and aspen. Xerophytic woodland plants such as pinyon, plains prickly pear, and narrowleaf yucca arrived sometime in the middle Holocene between 7200 and 3400 B.P. At Fishmouth Cave, Utah juniper in Holocene middens replaced blue spruce, limber pine, Douglas fir, and dwarf and Rocky Mountain junipers in late Wisconsin samples. Quantitative climatic estimates are derived for the late Wisconsin by applying vertical gradients for temperature and precipitation to the amount of vegetation depression. The Fishmouth Cave sequence indicates a minimum lowering of 850 m for blue spruce, limber pine, and dwarf juniper. A depression of at least 700 m for Engelmann spruce and alpine fir is suggested for the Allen Canyon locality. Use of conservatively low gradients for stations below 2080 m yields a 3-4 C cooling from present mean annual temperature and 35 to 60% more rainfall than today. Steeper gradients associated with more mountainous terrain suggest a 5 C lowering in temperature and up to 120% increase over modern precipitation. 81 references, 6 figures, 10 tables.

  20. Evidence against Late Quaternary activity along the Northern Karakoram Fault

    NASA Astrophysics Data System (ADS)

    Robinson, A. C.; Owen, L. A.; Hedrick, K.; Blisniuk, K.; Sharp, W. D.; Chen, J.; Schoenbohm, L. M.; Imrecke, D. B.; Yuan, Z.; Li, W.

    2012-12-01

    Although the entire 1000 km long Karakoram fault has long been interpreted to be active, recent work based primarily on interpretation of satellite imagery suggests that the northern end of the fault, where it enters the Pamir mountains, is inactive. We present field observations and geochronologic data from the southern end of the Tashkurgan valley, in the Pamir, on the Karakoram fault where it splits into two identifiable strands; an eastern strand which is the main trace of the Karakoram fault, and a western strand called the Achiehkopai fault. These results support the interpretation that the northern Karakoram fault is currently inactive, and has been for at least 200 ka: 1) Near the village of Dabudaer in the southern Tashkurgan valley the main trace of the Karakoram fault is orthogonally cut by a narrow incised valley with no observed lateral offset across the fault. Within this valley, a strath terrace ~50 m above the active drainage which overlies the main trace of the Karakoram fault which is capped by a carbonate cemented conglomerate. U-series analyses of carbonate cement from a correlative deposit located several km away yields a minimum depositional age of 76±12 ka. This age is coeval with the local Tashkurgan glacial stage we dated using Be-10 surface exposure dating (66±10 ka; Owen et al., 2012, Quaternary Science Reviews) suggesting both the conglomerate and strath terrace formed during this glacial stage. 2) ~25 km south of Dabudar, the main trace of the Karakoram projects beneath Tashkurgan glacial stage moraine and fluvial-glacial deposits which similarly show no evidence of disturbance by strike-slip deformation. Both of the above results demonstrate the main trace of the Karakoram fault has been inactive since at least ~70 ka. 3) Both the Karakoram and Achiehkopai faults are overlain by older Dabudaer glacial stage moraine deposits which are interpreted to be at least as old as the penultimate glacial, but may be >200 ka based on our Be-10

  1. The strength and characteristics of interglacials in the late Quaternary

    NASA Astrophysics Data System (ADS)

    Lang, N.; Wolff, E. W.

    2009-04-01

    Analysis of the EPICA Dome C ice core has provided high resolution records of climate variability over the last 800ka and reveal, for example, variations in the duration, 'shape' and strength of interglacial and glacial periods during this time. This variability is also seen in other palaeoclimate records such as foraminiferal ^18O records; however no synthesis of available 800ka ice, marine and terrestrial records has yet been made to compare and contrast interglacial and glacial characteristics. Records of ^D, CO2, CH4, temperature and Ca flux from EDC, globally distributed high resolution benthic & planktonic ^18O records, loess records from the Chinese Loess Plateau, Lake Baikal biosilica and the Tenaghi Philippon pollen record have been selected for their length, resolution, continuity and spatial distribution. Marine records have been aligned with the LR04 stack using the graphic alignment program Match to enable comparison with ice core records on the EDC3 timescale, as the differences between these two age models have already been evaluated. Terrestrial records are evaluated on their existing published age models. Variations in age model construction, orbital tuning of age models and graphic alignment of the records mean it is not possible to address phasing (and duration) in this study. A suite of characteristics from these records, including average and peak values of interglacial and glacial intensity & termination magnitude, are being compared to discover what the similarities and differences can suggest about the character and mechanisms of long term climate change over the last 800ka. Termination magnitude is defined as simply the difference between peak (average) interglacial and glacial values. Rampfit was used to objectively estimate average glacial and interglacial values, and the beginning and end of the glacial-interglacial transition and uncertainties for these parameters. We are thus able to derive spatial patterns of the strength and

  2. The strength and characteristics of late Quaternary interglacials

    NASA Astrophysics Data System (ADS)

    Lang, Nicola; Wolff, Eric

    2010-05-01

    Analysis of the EPICA Dome C ice core has provided high resolution records of climate variability over the last 800ka and reveal, for example, variations in the duration, ‘shape' and strength of interglacial and glacial periods during this time. This variability is also seen in other palaeoclimate records such as foraminiferal δ18O records; however no synthesis of available 800ka ice, marine and terrestrial records has yet been made to compare and contrast interglacial and glacial characteristics. Records of δD, CO2, CH4, temperature and Ca flux from EDC, globally distributed high resolution benthic & planktonic δ18O records, loess records from the Chinese Loess Plateau, Lake Baikal biosilica and the Tenaghi Philippon pollen record have been selected for their length, resolution, continuity and spatial distribution. Marine records have been aligned with the LR04 stack using the graphic alignment program Match to enable comparison with ice core records on the EDC3 timescale, as the differences between these two age models have already been evaluated. Terrestrial records are evaluated on their existing published age models. Variations in age model construction, orbital tuning of age models and graphic alignment of the records mean it is not possible to address phasing (and duration) in this study. A suite of characteristics from these records, including average and peak values of interglacial and glacial intensity & termination magnitude, are being compared to discover what the similarities and differences can suggest about the character and mechanisms of long term climate change over the last 800ka. Termination magnitude is defined as simply the difference between peak (average) interglacial and glacial values. Rampfit was used to objectively estimate average glacial and interglacial values, and the beginning and end of the glacial-interglacial transition and uncertainties for these parameters. We are thus able to derive spatial patterns of the strength and

  3. Biotic response to late Quaternary rapid climate switches in Santa Barbara Basin: Ecological and evolutionary implications

    SciTech Connect

    Cannariato, K.G.; Kennett, J.P.; Behl, R.J.

    1999-01-01

    Benthic foraminiferal assemblages from Santa Barbara Basin exhibit major faunal and ecological switches associated with late Quaternary millennial- to decadal-scale global climate oscillations. Repeated turnovers of entire faunas occurred rapidly (<40--400 yr) without extinction or speciation in conjunction with Dansgaard-Oeschger shifts in thermohaline circulation, ventilation, and climate, confirming evolutionary model predictions of Roy et al. Consistent faunal successions of dysoxic taxa during successive interstadials reflect the extreme sensitivity and adaptation of the benthic ecosystem to the rapid environmental changes that marked the late Quaternary and possibly other transitional intervals in the history of the Earth`s ocean-atmosphere-cryosphere system. These data support the hypothesis that broad segments of the biosphere are well adapted to rapid climate change.

  4. Foraminiferal biostratigraphy of the shelf edge: a key to late Quaternary paleoenvironments

    USGS Publications Warehouse

    Poag, C. Wylie; Sidner, B.R.

    1976-01-01

    Foraminiferal assemblages in eight piston cores from West Flower Garden Bank at the edge of the Texas continental shelf contain a nearly complete record of late Quaternary paleoclimatic and geologic events. The faunas are divisible into three distinct successive biofacies on the basis of both planktonic and benthic foraminifers: the basal Inflata Facies accumulated in cool shallow waters during late Pleistocene glaciation; the middle Crassaformis Facies represents a deepening sea that had warming surface waters; the upper Cultrata Facies is characteristic of the Holocene outer-shelf environment. Sea level was at -73 m and -53 m at the end of deposition of the Inflata and Crassaformis Facies, respectively. The biostratigraphic events at West Flower Garden Bank can be accurately correlated with those recorded in the middle and inner shelf and in deep-sea cores. The sequence of late Quaternary sea level and paleotemperature changes in the northern Gulf of Mexico can thereby be reconstructed. Eventually, this knowledge can be integrated with similar data from the shelf edge in other parts of the world to help bridge the gap between the known Quaternary record of the deep sea and that of the continents. ?? 1976.

  5. Stable isotopes in collagen and Late Quaternary carnivore palaeoecology

    NASA Astrophysics Data System (ADS)

    Bocherens, Hervé

    2010-05-01

    Several taxa of large carnivores co-occurred during the late Pleistocene in the steppe-tundra ecosystem, such as wolf Canis lupus, cave lion Panthera leo spelaea, cave hyaena Crocuta crocuta spelaea, brown bear Ursus arctos and cave bear Ursus spelaeus and Ursus ingressus. This abundance of taxa belonging to the same guild raises questions about niche partitioning, especially in terms of dietary specialization and prey selection. Observations of the dietary ecology of the extant relatives of these late Pleistocene carnivores does not provide unambiguous answers as these populations live under very different environmental conditions where other potential prey species are present, but it appears that most of these modern large carnivores are relatively flexible in their prey selection. Palaeontological investigations dealing with faunal associations and activity marks on fossil bones also have their limitations, such as taphonomic biases (palimpsests rather than biological associations) and do not allow the quantification of consumption of various preys. In contrast, carbon and nitrogen isotopic signatures of bone collagen depend directly on those of the average diet. Since different potential prey species occurring in the steppe-tundra exhibit consistent isotopic differences for these chemical elements, it is possible to relate the carbon and nitrogen isotopic signatures measured in fossil carnivores with the preferential consumption of some prey species. Some amount of quantification can be provided using modified versions of mixing models developed for modern ecosystems. In addition, this isotopic approach is individual-based and it is therefore possible to investigate intra- and inter-population differences in prey selection, as well as possible chronological trends and differences linked to genetic differences by combining isotopic and ancient DNA studies on the same material. The isotopic approach has already shown that among the tested large carnivores, cave

  6. Soil-landscape development and late Quaternary environmental change in coastal Estremadura, Portugal

    NASA Astrophysics Data System (ADS)

    Daniels, Michael; Haws, Jonathan; Benedetti, Michael; Bicho, Nuno

    2015-04-01

    This poster integrates soil-landscape analysis with archaeological survey and paleoenvironmental reconstruction. Soils in surface and buried contexts in Estremadura, Portugal, provide evidence of landscape stability and instability, relative age relationships between landforms, and general paleoenvironmental conditions during the late Quaternary. These factors provide insight into the distribution and condition of Paleolithic archaeological sites and help understand the record of human settlement in the region. Late Pleistocene and Holocene dunes extend inland approximately 10 km from coastal source regions. Surface soils in Holocene dunes under maritime pine (Pinus pinaster) forest exhibit A, E, C/Bh and A, C horizon sequences and classify as Quartzipsamments. Surface soils in late Pleistocene dunes exhibit A, E, Bh, Bhs, Bs horizon sequences and classify as Haplorthods. Both Pleistocene and Holocene dunes commonly bury a heavily weathered soil formed in calcareous sandstone. The boundary between underlying buried soils and overlying surface soils is characterized by a lag deposit of medium to coarse, moderately-rounded gravels, underlain immediately by subsurface Bt and Bss horizons. The lag deposit and absence of buried A horizons both indicate intense and/or prolonged surface erosion prior to burial by late Quaternary dunes. Soil-geomorphic relationships therefore suggest at least two distinct episodes of dune emplacement and subsequent landscape stability following an extensive episode late Pleistocene landscape instability and soil erosion. A conceptual model of soil-landscape evolution through the late Quaternary and Holocene results from the integration of soil profile data, proxy paleoenvironmental data, and the partial record of human settled as revealed in the archaeological record.

  7. Tectonic control on the Late Quaternary hydrography of the Upper Tiber Basin (Northern Apennines, Italy)

    NASA Astrophysics Data System (ADS)

    Benvenuti, Marco; Bonini, Marco; Moroni, Adriana

    2016-09-01

    We examine the intramontane Upper Tiber Basin in the Northern Apennines (central Italy), where sub-orthogonal fault systems forced river deviation and the abandonment of alluvial fans since the late Middle Pleistocene. Archaeological material, spanning the Middle Palaeolithic-Iron Age, was collected mostly from the surface of the Late Quaternary alluvial landforms and related deposits (MUP and HOL units). This information contributed to the partial dating of seven major stages of drainage development. Normal faults parallel and transverse to the basin trend were active at different times and conditioned the valley pattern of the Middle (MUP1-2)-Late (MUP3) Pleistocene Tiber, Singerna, Sovara and Tignana rivers, which still flow today into the basin. The MUP1 and the MUP3 fans were beheaded by the displacement of their feeder valleys along the basin-transverse Carmine and Montedoglio faults. In some cases, the former feeder rivers underwent stream piracy but their courses mostly deviated in response of the topographic gradient created by faulting, as well as through the incision of new valleys that exploited the lithological contrast along the fault lines. The MUP3 Tignana fan was abandoned mostly due to the activity of the basin-parallel, dip-slip Sansepolcro fault. Subsidence driven by the basin-parallel Anghiari and Sansepolcro fault systems also provided the accommodation space for the MUP3 and HOl1-2 Afra fans between Late Pleistocene and early-mid Holocene. This study exemplifies the interplay between longitudinal and transverse fault systems, and the Late Quaternary hydrographic evolution of an extensional basin settled in the axial zone of an active fold-and-thrust belt. Although the faulting has interacted with the forcing exerted by the Late Quaternary climate fluctuations on the basin drainage systems, the tectonic rates are sufficiently high to represent the prime controller on base-level change and drainage routing patterns.

  8. Late Quaternary vegetation and climate of southern Tierra del Fuego

    NASA Astrophysics Data System (ADS)

    Heusser, Calvin J.

    1989-05-01

    Vegetation and climate over approximately the past 13,000 yr are reconstructed from fossil pollen in a 9.4-m mire section at Caleta Róbalo on Beagle Channel, Isla Navarino (54°56'S, 67°38'W), southern Tierra del Fuego. Fifty surface samples reflecting modern pollen dispersal serve to interpret the record. Chronologically controlled by nine radiocarbon dates, fossil pollen assemblages are: Empetrum-Gramineae- Gunnera-Tubuliflorae (zone 3b, 13,000-11,850 yr B.P.), Gramineae- Empetrum-assorted minor taxa (zone 3a, 11,850-10,000 yr B.P.), Nothofagus-Gramineae-Tubuliflorae-Polypodiaceae (zone 2, 10,000-5000 yr B.P.), Nothofagus-Empetrum (zone 1b, 5000-3000 yr B.P.), and Empetrum-Nothofagus (zone 1a, 3000-0 yr B.P.). Assemblages show tundra under a cold, dry climate (zone 3), followed by open woodland (zone 2), as conditions became warmer and less dry, and later, with greater humidity and lower temperatures, by closed forest and the spread of mires (zone 1). Comparisons drawn with records from Antarctica, New Zealand, Tasmania, and the subantarctic islands demonstrate broadly uniform conditions in the circumpolar Southern Hemisphere. The influences of continental and maritime antarctic air masses were apparently considerable in Tierra del Fuego during cold late-glacial time, whereas Holocene climate was largely regulated by interplay between maritime polar and maritime tropical air.

  9. Late Quaternary environmental change in the Bonneville basin, western USA

    USGS Publications Warehouse

    Madsen, D.B.; Rhode, D.; Grayson, D.K.; Broughton, J.M.; Livingston, S.D.; Hunt, J.; Quade, Jay; Schmitt, D.N.; Shaver, M. W., III

    2001-01-01

    Excavation and analyses of small animal remains from stratified raptor deposits spanning the last 11.5 ka, together with collection and analysis of over 60 dated fossil woodrat midden samples spanning the last 50 ka, provide a detailed record of changing climate in the eastern Great Basin during the late Pleistocene and Holocene. Sagebrush steppe dominated the northern Bonneville basin during the Full Glacial, suggesting that conditions were cold and relatively dry, in contrast to the southern basin, which was also cold but moister. Limber pine woodlands dominated ???13-11.5 ka, indicating increased dryness and summer temperatures ???6-7??C cooler than present. This drying trend accelerated after ???11.5 ka causing Lake Bonneville to drop rapidly, eliminating 11 species of fish from the lake. From ???11.5-8.2 ka xerophytic sagebrush and shadscale scrub replaced more mesophilic shrubs in a step-wise fashion. A variety of small mammals and plants indicate the early Holocene was ???3??C cooler and moister than at present, not warmer as suggested by a number of climatic models. The diversity of plants and animals changed dramatically after 8.2 ka as many species disappeared from the record. Some of the upland species returned after ???4 ka and Great Salt Lake became fresh enough at ???3.4 and ???1.2 ka to support populations of Utah chub. ?? 2001 Elsevier Science B.V.

  10. Buried palaeosols of the Nevado de Toluca: an alternative record of Late Quaternary environmental change in central Mexico

    NASA Astrophysics Data System (ADS)

    Sedov, Sergey; Solleiro-Rebolledo, Elizabeth; Gama-Castro, Jorge E.; Vallejo-Gómez, Ernestina; González-Velázquez, Arelia

    2001-05-01

    Buried palaeosols of central Mexico, not previously analysed from a palaeopedological standpoint, have helped to develop a reliable regional model of Late Quaternary climatic change. This paper focuses upon morphological and micromorphological properties, particle-size distribution, and extractable Fe, Al and Si of seven palaeosols (named PT1-PT7) in the vicinity of the Nevado de Toluca volcano. The characteristics of Andic Cambisol PT1, similar to those of modern soils in semi-arid environments, indicate a drier climate in the first half of the Holocene. Humic Andosols PT2-PT4 are analogous to modern volcanic soils of humid forest environments. They show evidence that a moist palaeoclimate prevailed during marine oxygen isotope stages (OIS) 2 and 3. Luvisols PT5 and PT6, which are assumed to have formed at the end of marine OIS 5 to marine OIS 4, also indicate humid conditions. We attribute the differences between Andosols PT2-PT4 and Luvisols PT5-PT7 to variations in the duration in the pedogenesis rather than to changes in palaeoclimate. Micromorphological features of Andosol to Luvisol transition confirm that these soils form an evolutionary sequence. Being for the most part consistent with lacustrine records, the palaeosol properties do not reflect the episodes of drier climate during the Last Glacial Maximum, however, as shown by diatom and palynological data from lake sediments. Mesoclimate variations and/or incompleteness of soil memory, reflecting mostly periods of humid pedogenesis, probably provide the reason for this disagreement.

  11. Late Quaternary paleosols and climate change in southern New Mexico

    SciTech Connect

    Monger, H.C. . Agronomy Dept.); Cole, D.R. ); Gish, J.W. )

    1992-01-01

    A climate change toward more arid conditions in the southwest US has been postulated for a period around 7 ka. In southern NM, deposition of the youngest generation of alluvial fans surrounding arid mountains began around 7 ka based on radiocarbon dates of charcoal. The deposition of these fans has been interpreted as evidence for aridity because plant cover would have declined, thus making the landscape more susceptible to erosion and sedimentation. Isotopes of pedogenic calcite and pollen content in well-preserved paleosols associated with alluvial fans provide additional evidence for testing the aridity hypothesis. Buried paleosols, ranging from 23,070 [+-] 190 to 9,070 [+-] 70 yr BP, contain pedogenic calcite that is isotopically heavier in carbon than calcite in soils younger than 7 ka. The buried paleosols have a mean delta C-13 values of [minus]2.2 [+-] 0.8 [per thousand] (PDP). In contrast, soils younger than 7 ka have a man delta C-13 value of [minus]7.8 [+-] 1.3 [per thousand]. The higher delta C-13 values in buried paleosols may reflect the presence of abundant C[sub 4] grasses, similar to the present vegetation in the southern High Plains, which would have curtailed erosion. Pollen analysis reveals that buried paleosols contain more grass pollen than soils younger than 7 ka, which contain high proportions of desertscrub pollen taxa. delta O-18 values of pedogenic calcite are similar for the buried paleosols ([minus]5.2 [+-] 0.3 [per thousand] PDB) and soils younger than 7 ka ([minus]5.1 [+-] 0.6 [per thousand]). These values indicate a relatively constant mean annual temperature of approximately 14C, which prevailed throughout late Pleistocene and Holocene time.

  12. Late Quaternary activity along the Ferrara thrust inferred from stratigraphic architecture and geophysical surveys

    NASA Astrophysics Data System (ADS)

    Stefani, Marco; Bignardi, Samuel; Caputo, Riccardo; Minarelli, Luca; Abu-Zeid, Nasser; Santarato, Giovanni

    2010-05-01

    Since Late Miocene, the Emilia-Romagna portion of the Po Plain-Adriatic foredeep basin was progressively affected by compressional deformation, due to the northward propagation of the Apennines fold-and-thrust belt. The major tectonic structures within the basin have been recognised and are relatively well known, thanks to the widespread, even if outdated, seismic survey, performed after WW II, for hydrocarbon exploration. More recently, a large amount of surface and shallow-subsurface information has been provided by the CARG geological mapping project. The region therefore provides a valuable opportunity to discuss the genetic relationship between tectonic deformation, eustatic-paleoclimatic fluctuations, and depositional architecture. The activity of blind thrusts and fault-propagation folds induced repeated angular unconformities and impressive lateral variations in the Pliocene-Quaternary stratigraphy, causing thickness changes, from a few metres, close to the Apennines piedmont line, to more than 9 km, in fast subsiding depocenters (e.g. Lido di Savio). In the Ferrara region, the post-Miocene succession ranges from about 4 km, west of Sant'Agostino, to less than 200 m, on the Casaglia anticline, where Late Quaternary fluvial strata rest on Miocene marine marls, with an angular unconformity relationship. In this sector of the Po Plain, the tip-line of the northernmost thrust has been reconstructed north of the Po River (Occhiobello) and is associated with the growth of a large fold (Ferrara-Casaglia anticline), cross-cut by a complex splay of minor backthrusts and reverse faults. The thrust-anticline structure hosts an energy producing geothermal field, whose hydrogeological behaviour is largely influenced by the fracture pattern. The Apennines frontal thrust probably provided the seismic source for the earthquakes that severely damaged Ferrara, during the 1570 a.D. fall season, as documented by the structural damage still visible in many historic buildings (e

  13. Reconstructing late Quaternary deep-water masses in the eastern Arctic Ocean using benthonic Ostracoda

    USGS Publications Warehouse

    Jones, R. Ll; Whatley, R.C.; Cronin, T. M.; Dowsett, H.J.

    1999-01-01

    The distribution of Ostracoda in three long cores from the deep eastern Arctic Ocean was studied to determine the palaeoceanographical history of the Eurasian Basin during the late Quaternary. The samples for this study were obtained from the Lomonosov Ridge, Morris Jesup Rise and Yermak Plateau during the Arctic 91 expedition. Ostracoda previously studied in coretops at the same sites as the present study have shown that individual species have a strong association with different water masses and bathymetry. Throughout the late Quaternary, cores exhibit ostracod-rich layers separated by barren intervals. On the basis of biostratigraphical, isotopic and palaeomagnetic data the fossiliferous levels are interpreted as representing interglacial stages. The twenty most significant species were selected for subsequent quantitative investigation using Cluster and Factor analyses, in order to determine similarity and variance between the assemblages. An additional statistical method employing Modern Analogues and the Squared Chord Distance dissimilarity coefficient was utilized to compare the present late Quaternary fossil samples with a modern Arctic database. The results reveal a major faunal division within the Arctic Ocean Deep Water (AODW). Highly abundant and diverse assemblages within the cores were found to group and have good analogues with the Recent bathyal depth (1000-2500 m) upper AODW assemblages. Conversely, assemblages with low abundance and diversity correlate well with abyssal depth (> 3000 m) lower AODW assemblages. The palaeoceanographical history is complicated by the influence of adjacent water masses such as Canada Basin Deep Water (CBDW), Greenland Sea Deep Water (GSDW) and most importantly, Arctic Intermediate Water (AIW), which all had an influence on the ostracod assemblages during the late Quaternary. An enhanced flow of warm saline AIW into the Eurasian Basin results in species-rich upper AODW assemblages having good analogues down to 2750 m

  14. Late Quaternary palaeoenvironmental reconstruction from Lake Ohrid using stable isotopes

    NASA Astrophysics Data System (ADS)

    Lacey, Jack H.; Leng, Melanie J.; Francke, Alexander; Vogel, Hendrik; Zanchetta, Giovanni; Wagner, Bernd

    2016-04-01

    Lake Ohrid is a large, deep lake located on the Balkan Peninsula at the border between Macedonia and Albania, and is considered the oldest extant lake in Europe. An International Continental scientific Drilling Program (ICDP) deep drilling campaign was carried out in 2013 as part of the interdisciplinary Scientific Collaboration On Past Speciation Conditions in Lake Ohrid (SCOPSCO) project. Over 1500 m of sediment were recovered from six coring locations at the main target site in the central basin, where the maximum drill depth reached 569 m below the lake floor. Initial results indicate continuous lacustrine conditions over the past >1.2 Ma (Wagner et al., 2014). Here, we present oxygen and carbon isotope data (δ18O and δ13C) from carbonate from the upper 248 m of the SCOPSCO succession, which covers the last 640 ka, spanning marine isotope stages 15-1, according to an age model based on tephra and orbital tuning (Francke et al., 2015). Modern monitoring data show Lake Ohrid to be an evaporative system, where variations in δ18O of endogenic carbonate are primarily a function of changes in water balance, and δ13C largely reflects fluctuations in the amount of soil-derived CO2 and organic matter recycling. Our results indicate a trend from wetter to drier conditions through the Holocene, which is consistent with regional and hemispheric processes related to changes in insolation and progressive aridification. Over the last 640 ka, relatively stable climate conditions are inferred before ca. 450 ka, a transition to a wetter climate between ca. 400-250 ka, and a trend to drier climate after ca. 250 ka. Higher frequency, multi-millennial-scale oscillations observed during warm stages are most likely associated with regional climate change as a function of orbital forcing. This record is one of the most extensive and highly-resolved continental isotope records available, and emphasises the potential of Lake Ohrid as a valuable archive of long-term palaeoclimate and

  15. Rock varnish microlamination dating of late Quaternary geomorphic features in the drylands of western USA

    NASA Astrophysics Data System (ADS)

    Liu, Tanzhuo; Broecker, Wallace S.

    2008-01-01

    Varnish microlamination (VML) dating is a correlative age determination technique that can be used to date and correlate various geomorphic features in deserts. In this study, we establish a generalized late Quaternary (i.e., 0-300 ka) varnish layering sequence for the drylands of western USA and tentatively correlate it with the SPECMAP oxygen isotope record. We then use this climatically correlated varnish layering sequence as a correlative dating tool to determine surface exposure ages for late Quaternary geomorphic features in the study region. VML dating of alluvial fan deposits in Death Valley of eastern California indicates that, during the mid to late Pleistocene, 5-15 ky long aggradation events occurred during either wet or dry climatic periods and that major climate shifts between glacial and interglacial conditions may be the pacemaker for alteration of major episodes of fan aggradation. During the Holocene interglacial time, however, 0.5-1 ky long brief episodes of fan deposition may be linked to short periods of relatively wet climate. VML dating of alluvial desert pavements in Death Valley and the Mojave Desert reveals that pavements can be developed rapidly (< 10 ky) during the Holocene (and probably late Pleistocene) in the arid lowlands (< 800 m msl) of these regions; but once formed, they may survive for 74-85 ky or even longer without being significantly disturbed by geomorphic processes operative at the pavement surface. Data from this study also support the currently accepted, "being born at the surface" model of desert pavement formation. VML dating of colluvial boulder deposits on the west slope of Yucca Mountain, southern Nevada, yields a minimum age of 46 ka for the emplacement of these deposits on the slope, suggesting that they were probably formed during the early phase of the last glaciation or before. These results, combined with those from our previous studies, demonstrate that VML dating has great potential to yield numerical age

  16. Late Quaternary deformation rates in the Pamir-Tian Shan collision zone, NW China

    NASA Astrophysics Data System (ADS)

    Thompson, J. A.; Li, T.; Burbank, D. W.; Chen, J.; Bookhagen, B.; Bufe, A.; Yang, H.

    2014-12-01

    Deformation of the Pamir and Tian Shan orogens initiated during the Neogene as a result of the Indo-Eurasian colision. The arid landscape in the western Tarim Basin, NW China, preserves suites of fluvial terraces crossing many of the Late Neogene active structures, creating fault and fold scarps. We present new deformation rates on five faults and folds, which in combination with previous studies, highlight the spatial and temporal patterns of deformation during the Late Quaternary. Suites of terraces spanning ~130 ka to ~8 ka document the basinward propagation of deformation, with the fastest rates currently located on actively deforming structures at the interface of the Pamir-Tian Shan orogens. During the last ~6 ka, the Pamir deformation front has stepped north, creating the Mingyaole South Thrust, which produced the 1985 M7.4 Wuqia Earthquake. Trenching on several sections of this fault reveal an earthquake reoccurence interval of ~1.0 ky. The Late Quaternary deformation rates on faults and folds along the Pamir-Tian Shan collision zone indicate that the locus of deformation was not concentrated on a single structure, but rather was concurrently distributed across a zone of structures. Despite numerous structures accommodating the shortening and the locus of deformation shifting throughout the Late Quaternary, the total shortening across the Pamir-Tian Shan collision zone since ~0.35 Ma has remained steady and is approximately equal to the current geodetic rate of 6-9 mm/a, as well as broadly similar to preliminary InSAR-derived deformation rates across the region.

  17. Late Quaternary environmental changes in Marguerite Bay, Antarctic Peninsula, inferred from lake sediments and raised beaches

    NASA Astrophysics Data System (ADS)

    Hodgson, Dominic A.; Roberts, Stephen J.; Smith, James A.; Verleyen, Elie; Sterken, Mieke; Labarque, Minke; Sabbe, Koen; Vyverman, Wim; Allen, Claire S.; Leng, Melanie J.; Bryant, Charlotte

    2013-05-01

    The Antarctic Peninsula is one of the fastest-warming regions on Earth, but its palaeoenvironmental history south of 63° latitude is relatively poorly documented, relying principally on the marine geological record and short ice cores. In this paper, we present evidence of late-Quaternary environmental change from the Marguerite Bay region combining data from lake sediment records on Horseshoe Island and Pourquoi-Pas Island, and raised beaches at Horseshoe Island, Pourquoi-Pas Island and Calmette Bay. Lake sediments were radiocarbon dated and analysed using a combination of sedimentological, geochemical and microfossil methods. Raised beaches were surveyed and analysed for changes in clast composition, size and roundness. Results suggest a non-erosive glacial regime could have existed on Horseshoe Island from 35,780 (38,650-33,380) or 32,910 (34,630-31,370) cal yr BP onwards. There is radiocarbon and macrofossil evidence for possible local deglaciation events at 28,830 (29,370-28,320) cal yr BP, immediately post-dating Antarctic Isotopic Maximum 4, and 21,110 (21,510-20,730 interpolated) cal yr BP coinciding with, or immediately post-dating, Antarctic Isotopic Maximum 2. The Holocene deglaciation of Horseshoe Island commenced from 10,610 (11,000-10,300) cal yr BP at the same time as the early Holocene temperature maximum recorded in Antarctic ice cores. This was followed by the onset of marine sedimentation in The Narrows, Pourquoi-Pas Island, before 8850 (8480-9260) cal yr BP. Relative sea level high stands of 40.79 m above present at Pourquoi-Pas Island and 40.55 m above present at Calmette Bay occurred sometime after 9000 cal yr BP and suggest that a thicker ice sheet, including grounded ice streams, was present in this region of the Antarctic Peninsula than that recorded at sites further north. Isolation of the Narrows Lake basin on Pourquoi-Pas Island shows relative sea level in this region had fallen rapidly to 19.41 m by 7270 (7385-7155) cal yr BP

  18. Is late Quaternary climate change governed by self-sustained oscillations in atmospheric CO2?

    NASA Astrophysics Data System (ADS)

    Wallmann, Klaus

    2014-05-01

    A simple earth system model is developed to simulate global carbon and phosphorus cycling over the late Quaternary. It is focused on the geological cycling of C and P via continental weathering, volcanic and metamorphic degassing, hydrothermal processes and burial at the seabed. A simple ocean model is embedded in this geological model where the global ocean is represented by surface water, thermocline and deep water boxes. Concentrations of dissolved phosphorus, dissolved inorganic carbon, and total alkalinity are calculated for each box. The partial pressure of CO2 in the atmosphere (pCO2A) is determined by exchange processes with the surface ocean and the continents. It serves as key prognostic model variable and is assumed to govern surface temperatures and global sea-level. The model is formulated as autonomous system, in which the governing equations have no explicit time-dependence. For certain parameter values, the model does not converge towards a steady-state but develops stable self-sustained oscillations. These free oscillations feature pCO2A minima and maxima consistent with the ice-core record when vertical mixing in the ocean is allowed to vary in response to pCO2A-controlled temperature change. A stable 100-kyr cycle with a rapid transition from glacial to interglacial conditions is obtained when additional non-linear equations are applied to calculate deep ocean mixing, iron fertilization and the depth of organic matter degradation as function of pCO2A-controlled surface temperature. The δ13C value of carbon in the ocean/atmosphere system calculated in these model runs is consistent with the benthic δ13C record. However, the simulated 13C depletion in the glacial ocean is not driven by the decline in terrestrial carbon stocks but by sea-level change controlling the rates of organic carbon burial and weathering at continental margins. The pCO2A- and δ13C oscillations develop without any form of external Milankovitch forcing. They are induced and

  19. Late Quaternary Sea-Ice Variability at the North Icelandic Shelf (Sub-Arctic): Reconstruction from Biomarkers

    NASA Astrophysics Data System (ADS)

    Xiao, X.; Zhao, M.; Jiang, H.; Eiriksson, J.; Guo, Z.

    2015-12-01

    Sea ice, prevailing in the polar region and characterized by distinct seasonal and interannual variability, plays a pivotal role in Earth's climate system (Thomas and Dieckmann, 2010). In order to understand processes controlling the recent dramatic reduction in Arctic sea-ice cover, it is essential to determine temporal changes in sea-ice occurrence and its natural variability in the past. The North Icelandic shelf, bordering a marginal area of the Arctic Ocean, is located at the present-day boundary between the cold polar currents and warm Atlantic water masses, very sensitive to the changes in sea-ice cover, ice sheet and oceanic circulation patterns (Knudsen and Eiriksson, 2002). All these processes have been recorded in the marine shelf-sediment cores. We determined the concentrations of sea-ice diatom-derived biomarker "IP25" (monoene highly-branched isoprenoid with 25 carbon atom; Belt et al., 2007), phytoplankton-derived biomarkers (brassicasterol and dinosterol) and terrigenous biomarkers (campesterol and ß-sitosterol) in a sediment core from the North Icelandic shelf to reconstruct the Late Quaternary sea-ice conditions and related surface-water processes. The sea-ice cover reached its maximum during the cold period (i.e., Last Glacial Maximum and Younger dryas), while an open ocean environment existed during less severe periods (e.g. Bølling-Allerød and 8.2 ka event) in the study area. The biomarker records from this sediment core give insights into the variability in sea ice and circulation patterns as well as primary productivity in the Arctic marginal area during the Late Quaternary. References Belt, S.T., Massé, G., Rowland, S.J., Poulin, M., Michel, C., LeBlanc, B., 2007. A novel chemical fossil of palaeo sea ice: IP25. Org. Geochem. 38, 16-27. Knudsen, K.L. and Eiriksson, J., 2002. Application of tephrochronology to the timing and correlation of palaeoceanographic events recorded in Holocene and Late Glacial shelf sediments off North Iceland

  20. Styles of glaciation on Kilimanjaro, Tanzania, in response to late Quaternary climate change

    NASA Astrophysics Data System (ADS)

    Boston, Clare; Lovell, Harold; Mills, Stephanie; Cullen, Nicolas; Sirguey, Pascal

    2016-04-01

    The recognition of geomorphological evidence for more extensive ice masses in a number of areas near the equator provides a direct link to climate change in the tropics. Kilimanjaro in Tanzania consists of the highest elevations in Africa, and sets of moraines document that ice was significantly more extensive in the past. The most extensive moraines around Kibo, the highest peak, suggest that glaciers may have extended down to around 3800 m at the Last Glacial Maximum (LGM). A more recent set of moraines, at 4600-4800 m on the western side of the peak, document the maximum position that ice reached during the Little Ice Age (LIA). Both of these sets of moraines indicate significant recession has occurred throughout the late Quaternary, and particularly during the 20th century. Present-day ice is restricted to rapidly-receding glaciers and icefields on the uppermost flanks and summit of Kibo, between ~5000-5800 m. The area is therefore important for understanding the timing, magnitude and style of glacier response to changes in climate in the tropics in the late Quaternary. This research presents the results of new field and remotely-sensed mapping of moraines relating to the Late Pleistocene and LIA, providing greater detail on the glacial geomorphology of the area than in previous mapping. This allows an assessment of the styles of glaciation, and particularly the role of topography and aspect on influencing response to climate and patterns of glacier recession.

  1. Seismic expression of Late Quaternary Banda submarine canyon and fan offshore northern Baja California

    SciTech Connect

    Legg, M.R.

    1987-05-01

    High-resolution seismic reflection profiles obtained throughout the inner California continental borderland offshore northwestern Baja California, Mexico, show the presence of numerous modern submarine canyons and associated fans. One set of these, the Banda submarine canyon/fan, is of relatively recent origin, as demonstrated by onlap of the basal fan sediments against an acoustically transparent, presumably hemipelagic deposit. Late Quaternary sedimentation rates inferred from isotopically dated piston core samples place the age of the postulated hemipelagic unit at approximately 650,000 years ago. The Banda submarine canyon heads within the Bahia Todos Santo and passes through a narrow gorge between Punta Banda and Islas Todos Santos. It is proposed that this submarine canyon and fan system formed entirely during late Quaternary time, following the breach of the Punta Banda ridge during a late Pleistocene high sea level stand. The presence of an ancient, buried channel exiting to the north out of Bahia Todos Santos probably marks the head of an earlier submarine canyon which acted as the conduit of clastic sediments from Valle Maneadero to the deep borderland basins. The now active Banda submarine canyon pirated the supply of terrigenous clastics from this older canyon. The active Agua Blanca fault zone cuts across the head of Banda submarine canyon, suggesting that tectonic movements may have played a role in the development of the Banda submarine canyon and fan system.

  2. Fluvial responses to late Quaternary climate change in the Shiyang River drainage system, western China

    NASA Astrophysics Data System (ADS)

    Gao, Hongshan; Li, Zongmeng; Pan, Baotian; Liu, Fenliang; Liu, Xiaopeng

    2016-04-01

    As a drainage system located in arid western China, the Shiyang River, combined with considerable fluvial strata and landform information, provides an environmental context within which to investigate fluvial responses to late Quaternary climate change. Sedimentological analysis and optically stimulated luminescence (OSL) dating enabled us to reconstruct the processes and fluvial styles of three sedimentary sequences of the Shagou and Hongshui rivers in the Shiyang drainage system. Our results present a variety of river behaviors during the late Quaternary in these areas. In the upstream Shiyang River, Zhangjiadazhuang (ZJDZ) profile of the Shagou was dominated by aggradation and a meandering channel pattern at 10.6-4.2 ka, while a noticeable channel incision occurred at ~ 4.2 ka followed by lateral channel migration. In the downstream Shiyang River, Datugou (DTG) profile of the Hongshui was an aggrading meandering river from 39.7 to 7.2 ka while channel incision occurred at 7.2 ka. Another downstream profile, Wudunwan (WDW) of the Hongshui was also characterized by aggradation from 22.4 to 4.8 ka; however, its channel pattern shifted from braided to meandering at ~ 13 ka. A discernable downcutting event occurred at ~ 4.8 ka, followed by three channel aggradation and incision episodes prior to 1.8 ka. The last 1.8 ka has been characterized by modern channel and floodplain development. The fluvial processes and styles investigated have a close correlation with late Quaternary climate change in the Shiyang River drainage. During cold phases, the WDW reach was dominated by aggradation with a braided channel pattern. During warm phases, the rivers that we investigated were also characterized by aggradation but with meandering channel patterns. Channel incision events and changes of fluvial style occurred mainly during climate transitions.

  3. Seismic stratigraphy and depositional history of late Quaternary deposits in the Yellow Sea.

    NASA Astrophysics Data System (ADS)

    Lee, Gwang-Soo; Yoo, Dong Geun; Bae, Sungho; Choul Kim, Dae; Yi, Hi-Il

    2016-04-01

    To identify the seismic stratigraphy and depositional history of late Quaternary deposits in the Yellow Sea, approximately 52,600 line-km of Chirp seismic profiles and 5,060 line-km of Sparker seismic profiles were analyzed. The Yellow Sea are correspond to 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). Based on the seismic stratigraphic analysis of seismic profiles, the late Quaternary deposits in the Yellow Sea are divided into five distinctive seismic units (units CY1~5), consisting of two depositional sequences that can be defined as erosional and disconformable strata. Each unit show different seismic facies and geometry, and is clearly separated by each bounding surface. The major depositional processes and sediment dispersal systems during the late Quaternary in the 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.

  4. Thermoluminescence and new 14C age estimates for late quaternary loesses in southwestern Nebraska

    USGS Publications Warehouse

    Maat, P.B.; Johnson, W.C.

    1996-01-01

    Loess of late Quaternary age mantles most of Nebraska south of the Platte River Valley. At least five late Quaternary loesses are recognized: from oldest to youngest, one or more undifferentiated pre-lllinoian loesses, the Loveland Loess, the Gilman Canyon Loess, which exhibits a well developed soil and rests unconformably on the Sangamon soil, the Peoria Loess capped by the Brady soil, and the Bignell Loess, which is distributed discontinuously. Previous research shows that the Loveland Loess is Illinoian. the Gilman Canyon Loess and Peoria Loess are Wisconsin, and the Bignell Loess is Holocene. We present here the first thermoluminescence (TL) age estimates and new C ages for these late Quaternary loesses at two key sections in southwestern Nebraska, the Eustis ash pit and the Bignell Hill road cut. TL age estimates from all samples collected from Eustis ash pit and Bignell Hill were internally consistent. TL and C age estimates from these two sections generally agree and support previous age determinations. The TL age estimate on Loveland Loess indicates deposition at 163 ka. TL and radiocarbon age estimates indicate that Oilman Canyon Loess, believed to be deposited during the Farmdale interstade, first began to accumulate at about 40 ka: the lower part of the Gilman Canyon Loess is 36 ka at Eustis and the middle of the unit is 30 ka at Bignell Hill. The lower and upper parts of the Peoria Loess give age estimates of 24 ka and 17 ka, respectively. TL age estimates for deposition of the Bignell Loess are 9 ka near the base, in agreement with radiocarbon age estimates, and 6 ka immediately below the modern soil, substantiating its Holocene age. Comparisons of TL age estimates with ??18O and insolation curves which show loess deposition during interglacial and interstadial as well as glacial periods, indicate that loess deposition on the Great Plains can occur under a variety of climatic conditions.

  5. Late quaternary insects of Rancho La Brea and McKittrick, California

    NASA Astrophysics Data System (ADS)

    Miller, Scott E.

    1983-07-01

    Asphalt-impregnated sediments at Rancho La Brea (Los Angeles County) and McKittrick (Kern County) in California provide a rich Quaternary insect record. Ages of various sites at Rancho La Brea range from more than 40,000 14C yr B.P. to modern. McKittrick insects studied by W. D. Pierce are not contemporaneous with the late Pleistocene vertebrate fauna, but are only about 7000 14C yr old. The major paleoecological groupings are: (1) ground dwellers, (2) aquatics. (3) scavengers, and (4) miscellaneous. Contrary to conclusions of earlier authors, most specimens represent modern species. Only two apparent terminal Pleistocene extinctions are recognized. both dung beetles (Scarabaeidae).

  6. Palaeoenvironmental dynamics inferred from late Quaternary permafrost deposits on Kurungnakh Island, Lena Delta, Northeast Siberia, Russia

    NASA Astrophysics Data System (ADS)

    Wetterich, Sebastian; Kuzmina, Svetlana; Andreev, Andrei A.; Kienast, Frank; Meyer, Hanno; Schirrmeister, Lutz; Kuznetsova, Tatyana; Sierralta, Melanie

    2008-08-01

    Late Quaternary palaeoenvironments of the Siberian Arctic were reconstructed by combining data from several fossil bioindicators (pollen, plant macro-fossils, ostracods, insects, and mammal bones) with sedimentological and cryolithological data from permafrost deposits. The record mirrors the environmental history of Beringia and covers glacial/interglacial and stadial/interstadial climate variations with a focus on the Middle Weichselian interstadial (50-32 kyr BP). The late Pleistocene to Holocene sequence on Kurungnakh Island reflects the development of periglacial landscapes under changing sedimentation regimes which were meandering fluvial during the Early Weichselian, colluvial or proluvial on gently inclined plaines during the Middle and Late Weichselian, and thermokarst-affected during the Holocene. Palaeoecological records indicate the existence of tundra-steppe vegetation under cold continental climate conditions during the Middle Weichselian interstadial. Due to sedimentation gaps in the sequence between 32 and 17 kyr BP and 17 and 8 kyr BP, the Late Weichselian stadial is incompletely represented in the studied outcrops. Nevertheless, by several palaeoecological indications arctic tundra-steppe vegetation under extremely cold-arid conditions prevailed during the late Pleistocene. The tundra-steppe disappeared completely due to lasting paludification during the Holocene. Initially subarctic shrub tundra formed, which later retreated in course of the late Holocene cooling.

  7. Human Dispersals Along the African Rift Valley in the Late Quaternary

    NASA Astrophysics Data System (ADS)

    Tryon, C. A.; Faith, J. T.; Peppe, D. J.

    2014-12-01

    Climate- and tectonic-driven environmental dynamics of the East African Rift System (EARS) during the Quaternary played an important role in the demographic history of early Homo sapiens, including expansions of modern humans across and out of Africa. Human forager population size, geographic range, and behaviors such as hunting strategies and residential mobility likely varied in response to changes in the local and regional environment. Throughout the Quaternary, floral and faunal change was linked at least in part to variations in moisture availability, temperature, and atmospheric CO2, which in addition to uplift and faulting, contributed to the expansion and contraction of a number of large lakes that served as biogeographic barriers to many taxa. This is particularly clear for the Lake Victoria basin, where biogeographic, geological, and paleontological evidence documents repeated expansion and contraction of the ranges of species in response to lake level and vegetation change. Across much of eastern Africa, the topography of the rift facilitated north-south dispersals, the timing of which may have depended in part on the expansion and contraction of the equatorial forest belt. Dispersal potential likely increased during the more arid periods of the late Quaternary, when the roles of lakes and forests as dispersal barriers was reduced and the extent of low net primary productivity dry grasslands increased, the latter requiring large home ranges for human foragers, conditions suitable for range expansions within H. sapiens.

  8. A late Wisconsinan marine incursion into Cape Cod Bay, Massachusetts

    USGS Publications Warehouse

    Oldale, R.N.

    1988-01-01

    Reinterpretation of seismic-reflection data from Cape Cod Bay has produced a revised late Wisconsinan history. Acoustically laminated deposits, originally inferred to be glaciolacustrine, are shown to be glaciomarine by tracing them to glaciomarine mud in Stellwagen Basin, north of Cape Cod Bay. A late Wisconsinan marine deposit of nonglacial origin overlies the glaciomarine deposits in Cape Cod Bay. Both deposits indicate that the crust was isostatically depressed below the late Wisconsinan eustatic sea level and that deglaciation and marine submergence occurred simultaneously. Valleys cut into the marine deposits, both glacial and nonglacial, indicate that a low sea-level stand, the result of isostatic rebound, occurred shortly after the marine incursion. A transgressive uncomformity and marine deposits, both mostly of Holocene age, overlie the late Wisconsinan deposits. The marine incursion, regression, and Holocene transgression represent the northward passage of an isostatically induced peripheral bulge following deglaciation. In turn, the bulge, a response to crustal loading and unloading, indicates thick glacier ice in the terminal zone and lends support to arguments for a maximum Laurentide ice model. Evidence for a late Wisconsinan marine incursion, regression, and the passage of a peripheral bulge should be sought in the other bays and sounds of the New England terminal zone. ?? 1988.

  9. Reconstruction of the Late Quaternary Glaciation of the Macha Khola valley (Gorkha Himal, Nepal) using relative and absolute ( 14C, 10Be, dendrochronology) dating techniques

    NASA Astrophysics Data System (ADS)

    Zech, W.; Glaser, B.; Abramowski, U.; Dittmar, C.; Kubik, P. W.

    2003-11-01

    Late Quaternary glacier fluctuations in the Macha Khola valley (Gorkha Himal, Nepal) were reconstructed using relative and absolute dating techniques. Our results indicate that younger moraine complexes were left by Late Holocene (<1.7 cal. ka BP), mid-Holocene (ca 3 cal. ka BP), and Lateglacial (ca 13 cal. ka BP) ice advances. Older Late Quaternary glacier advances occurred during Marine Oxygen Isotope Stages (MIS) 2 and 3-4. No relics of Middle or Early Pleistocene glaciations could be found. During MIS 3-4, glaciers advanced down to an altitude of at least 2150 m a.s.l., corresponding to an ELA depression of approximately 1300 m. At about 3500 m a.s.l., the MIS 2 Macha Khola glacier reached almost the thickness of the former MIS 3-4 glacier and retreated some time before 17.9 cal. ka BP. The Lateglacial glacier advanced again several times to altitudes between 2450 and 3400 m a.s.l. The mid-Holocene glaciers extended much farther down-valley than the Late Holocene ones. Dendrochronological data of Abies spectabilis suggested several periods of unfavourable growth conditions especially at the beginning of the 19th (1820) and 20th (1905) centuries.

  10. Late Neogene to Quaternary environmental changes in the Antarctic Peninsula region: evidence from drift sediments

    NASA Astrophysics Data System (ADS)

    Hillenbrand, Claus-Dieter; Ehrmann, Werner

    2005-02-01

    Clay-mineral composition and biogenic opal content in upper Miocene to Quaternary drift sediments recovered at two Ocean Drilling Program (ODP) sites from the continental rise in the Bellingshausen Sea had been analyzed in order to reconstruct the climatic and glacial history of the Antarctic Peninsula. The clay mineral composition at both sites is dominated by smectite, illite, and chlorite, and alternates between a smectite-enriched and a chlorite-enriched assemblage throughout the last 9.3 my. The spatial distribution of clay minerals in Holocene sediments west of the Antarctic Peninsula facilitates the identification of particular source areas, and thus the reconstruction of transport pathways. The similarity to clay mineral variations reported from upper Quaternary sequences suggests that the short-term clay-mineralogical fluctuations in the ODP cores reflect glacial-interglacial cyclicity. Thus, repeated ice advances and retreats in response to a varying size of the Antarctic Peninsula ice cap are likely to have occurred throughout the late Neogene and Quaternary. The clay minerals in the drift sediments exhibit only slight long-term variations, which are caused by local changes in glacial erosion and in supply of source rocks, rather than by major climatic changes. The opal records at the ODP sites are dominated by long-term variations since the late Miocene. We infer that the opal content in the drift sediments, although it is influenced by dissolution in the water column and the sediment column and by the burial with lithogenic detritus, provides a signal of paleoproductivity. Because the annual sea-ice coverage is regarded as the main factor controlling biological productivity, the opal signal helps to reconstruct paleoceanographic changes in the Bellingshausen Sea. Slightly enhanced opal deposition during the late Miocene indicates slightly warmer climatic conditions in the Antarctic Peninsula area than at present. During the early Pliocene, enhanced

  11. Arctic-alpine blockfields in the northern Swedish Scandes: late Quaternary - not Neogene

    NASA Astrophysics Data System (ADS)

    Goodfellow, B. W.; Stroeven, A. P.; Fabel, D.; Fredin, O.; Derron, M.-H.; Bintanja, R.; Caffee, M. W.

    2014-07-01

    Autochthonous blockfield mantles may indicate alpine surfaces that have not been glacially eroded. These surfaces may therefore serve as markers against which to determine Quaternary erosion volumes in adjacent glacially eroded sectors. To explore these potential utilities, chemical weathering features, erosion rates, and regolith residence durations of mountain blockfields are investigated in the northern Swedish Scandes. This is done, firstly, by assessing the intensity of regolith chemical weathering along altitudinal transects descending from three blockfield-mantled summits. Clay / silt ratios, secondary mineral assemblages, and imaging of chemical etching of primary mineral grains in fine matrix are each used for this purpose. Secondly, erosion rates and regolith residence durations of two of the summits are inferred from concentrations of in situ-produced cosmogenic 10Be and 26Al in quartz at the blockfield surfaces. An interpretative model is adopted that includes temporal variations in nuclide production rates through surface burial by glacial ice and glacial isostasy-induced elevation changes of the blockfield surfaces. Together, our data indicate that these blockfields are not derived from remnants of intensely weathered Neogene weathering profiles, as is commonly considered. Evidence for this interpretation includes minor chemical weathering in each of the three examined blockfields, despite consistent variability according to slope position. In addition, average erosion rates of ~16.2 and ~6.7 mm ka-1, calculated for the two blockfield-mantled summits, are low but of sufficient magnitude to remove present blockfield mantles, of up to a few metres in thickness, within a late Quaternary time frame. Hence, blockfield mantles appear to be replenished by regolith formation through, primarily physical, weathering processes that have operated during the Quaternary. The persistence of autochthonous blockfields over multiple glacial-interglacial cycles confirms

  12. Genetic footprints of demographic expansion in North America, but not Amazonia, during the Late Quaternary.

    PubMed

    Lessa, Enrique P; Cook, Joseph A; Patton, James L

    2003-09-01

    The biotic consequences of climate change have attracted considerable attention. In particular, the "refugial debate" centers on the possible retraction of habitats to limited areas that may have served as refuges for many associated species, especially during glaciations of the Quaternary. One prediction of such scenarios is that populations must have experienced substantial growth accompanying climatic amelioration and the occupation of newly expanded habitats. We used coalescence theory to examine the genetic evidence, or lack thereof, for late Pleistocene refugia of boreal North American and tropical Amazonian mammals. We found substantial and concordant evidence of demographic expansion in North American mammals, particularly at higher latitudes. In contrast, small mammals from western Amazonia appear to have experienced limited or no demographic expansion after the Late Pleistocene. Thus, demographic responses to climate change can be tracked genetically and appear to vary substantially across the latitudinal gradient of biotic diversity. PMID:12913123

  13. Morphology and stratigraphy of the late Quaternary lower Brazos valley: Implications for paleo-climate, discharge and sediment delivery

    NASA Astrophysics Data System (ADS)

    Sylvia, Dennis A.; Galloway, William E.

    2006-08-01

    A shallow coring and geophysical logging program has recorded the sedimentary fill of the Brazos River valley in the Texas Gulf Coastal Plain. Thermoluminescence dates together with new and recalibrated published radiocarbon dates show the valley fill to include extensive, sandy, buried falling stage and lowstand Oxygen Isotope Stage (OIS) 3 and 2 deposits. These alluvial deposits are punctuated by numerous paleosoil horizons that record alternating periods of cutting, bypass and accumulation. Maximum valley incision and two periods of terrace formation preceded marine lowstand conditions, suggesting significant discordance between preserved fluvial and classical marine system tracts. The latest Pleistocene incision and fill history appears related to cycles of increased discharge and incision, followed by system equilibration and terrace formation. Analysis of the Brazos River incised valley and its contained paleochannels indicates that latest Pleistocene mean annual discharge was as much as four times greater than that of today. This magnitude of discharge in the Brazos would require a two-fold increase in precipitation across the drainage basin. Such an increase is comparable to the present day measured positive El Niño winter precipitation anomaly across the region. Paleochannel geometries and the stratigraphic and sedimentologic data from this investigation support the hypothesis that periods of high-amplitude, El Niño-like climatic perturbations characterized the late Quaternary climate of the south-central and southwestern U.S. This period of high discharge coincides, at least in part, with late OIS 3 progradation of the Brazos delta to the shelf margin, OIS 3 and 2 valley incision across the Texas shelf, and concomitant sand bypass to intraslope basins beyond the shelf edge.

  14. Late Tertiary and Quaternary geology of the Tecopa basin, southeastern California

    SciTech Connect

    Hillhouse, J.W.

    1987-12-31

    Stratigraphic units in the Tecopa basin, located in southeastern California, provide a framework for interpreting Quaternary climatic change and tectonism along the present Amargosa River. During the late Pliocene and early Pleistocene, a climate that was appreciably wetter than today`s sustained a moderately deep lake in the Tecopa basin. Deposits associated with Lake Tecopa consists of lacustrine mudstone, conglomerate, volcanic ash, and shoreline accumulations of tufa. Age control within the lake deposits is provided by air-fall tephra that are correlated with two ash falls from the Yellowstone caldera and one from the Long Valley caldera. Lake Tecopa occupied a closed basin during the latter part, if not all, of its 2.5-million-year history. Sometime after 0.5 m.y. ago, the lake developed an outlet across Tertiary fanglomerates of the China Ranch Beds leading to the development of a deep canyon at the south end of the basin and establishing a hydrologic link between the northern Amargosa basins and Death Valley. After a period of rapid erosion, the remaining lake beds were covered by alluvial fans that coalesced to form a pediment in the central part of the basin. Holocene deposits consist of unconsolidated sand and gravel in the Amargosa River bed and its deeply incised tributaries, a small playa near Tecopa, alluvial fans without pavements, and small sand dunes. The pavement-capped fan remnants and the Holocene deposits are not faulted or tilted significantly, although basins to the west, such as Death Valley, were tectonically active during the Quaternary. Subsidence of the western basins strongly influenced late Quaternary rates of deposition and erosion in the Tecopa basin.

  15. Eolian sediment responses to late Quaternary climate changes: Temporal and spatial patterns in the Sahara

    USGS Publications Warehouse

    Swezey, C.

    2001-01-01

    This paper presents a compilation of eolian-based records of late Quaternary climate changes in the Sahara. Although the data are relatively sparse, when viewed as a whole, they reveal a general pattern of widespread eolian sediment mobilization prior to 11,000 cal. years BP, eolian sediment stabilization from 11,000 to 5000 cal. years BP, and a return to widespread eolian sediment mobilization after 5000 cal. years BP. Furthermore, an eolian-based record from southern Tunisia reveals the existence of millennial-scale changes in eolian sediment behavior. These millennial-scale variations provide examples of eolian sediment responses to climate changes at a scale intermediate between seasonal and orbital ('Milankovitch') changes, and they are also coincident with abrupt atmospheric and oceanic changes. The general synchroneity of the eolian stratigraphic records and their coincidence with various oceanic and atmospheric changes suggest that global forcing mechanisms have influenced late Quaternary eolian sediment behavior in the Sahara. ?? 2001 Elsevier Science B.V.

  16. Estimates of late Quaternary mode and intermediate water silicic acid concentration in the Pacific Southern Ocean

    NASA Astrophysics Data System (ADS)

    Rousseau, Jonathon; Ellwood, Michael J.; Bostock, Helen; Neil, Helen

    2016-04-01

    The Southern Ocean plays a critical role in the exchange of carbon between the ocean and atmosphere over glacial-interglacial timescales. Hypotheses used to explain late Quaternary variations in atmospheric carbon dioxide (CO2) implicate changes in the nutrient dynamics and circulation of the Southern Ocean. Here we present silicon isotope (δ30Si) records of late Quaternary sponges and diatoms from the NZ-sector of the Southern Ocean. Analysis of our sponge δ30Si records strongly suggests that the silicic acid concentration at mode and intermediate depths was higher during the LGM and the deglacial period compared to the present day. Our diatom δ30Si record suggests biological productivity near of the Polar Front was greater during the deglacial period, but not significantly different during the LGM compared to the present day. Taking our dataset in context with other regional paleoceanographic records, we interpret the predicted elevation in LGM and deglacial silicic acid concentration to reflect a shoaling of water masses during the LGM and 'leakage' of excess Southern Ocean dissolved silicon during the deglacial period.

  17. Stratigraphic evidence for late Quaternary dune activity near Hudson on the Piedmont of northern Colorado

    SciTech Connect

    Forman, S.L.; Maat, P. )

    1990-08-01

    Stabilized dune fields are common features near Hudson, on the Piedmont of northern Colorado. Exposures in dune and interdune sites expose a sequence of eolian sediments and paleosols that record a complex history of eolian activity during the late Quaternary. Radiocarbon and thermoluminescence age estimates on A horizons buried by eolian sand indicate that dunes were reactivated sometime between 7 and 9 ka. On the basis of morphology of surface soils, the dunes were most recently stabilized <3 ka. At present that are no data to indicate if there were multiple periods of dune movement and stabilization during the Holocene. The penultimate pre-Holocene dune-forming episode probably terminated ca. 13 ka and may be coincident with the Pinedale glaciation. The stratigraphy at interdune sites shows at least two eolian depositional events prior to the penultimate event; they were separated by periods of pedogenesis, one of which may have exceeded 40 ka. This analysis indicates that dunes in northern Colorado were active during both cold-arid and warn-arid periods in the late Quaternary.

  18. Distinguishing allogenic from autogenic causes of bed elevation change in late Quaternary alluvial stratigraphic records

    NASA Astrophysics Data System (ADS)

    Daniels, J. Michael

    2008-10-01

    Allogenic and autogenic mechanisms both cause changes in the bed elevation of rivers and thereby influence the characteristics of alluvial stratigraphic records (ASRs). Allogenic forcing mechanisms can be grouped into five categories whose relative influence varies with timescale: climate, tectonism, base level, land use/land cover and direct human modification of channels. Late Quaternary ASRs are influenced by the greatest range of allogenic forcing variables with climate among the most important. Autogenic mechanisms of bed elevation change are ubiquitous throughout fluvial systems and are always time-transgressive. Autogenic bed elevation change propagates through drainage networks at predictable rates and results in a time-space envelope within which its effects are capable of operating. ASRs that can be correlated over geographical areas large enough and time intervals small enough to exist outside this envelope most likely result from allogenic forcing. This formulation represents a quantitative and geographic set of threshold criteria for distinguishing between autogenic and allogenic mechanisms. Over late Quaternary timescales (10 2 to 10 5 years) in tectonically stable regions climate change is the dominant allogenic mechanism and, therefore, the first-order control on the morphology, sedimentology, pedologic characteristics and chronology of alluvial stratigraphic records that meet or exceed the threshold criteria for demonstrating allogenic causality.

  19. Geochemical evidence for the origin of late Quaternary loess in central Alaska

    USGS Publications Warehouse

    Muhs, D.R.; Budahn, J.R.

    2006-01-01

    Loess is extensive in central Alaska, but there are uncertainties about its source and the direction of paleo-winds that deposited it. Both northerly and southerly winds have been inferred. The most likely sources of loess are the Tanana River (south), the Nenana River (southeast), and the Yukon River (north). Late Quaternary loess in central Alaska has immobile trace-element compositions (Cr/Sc, Th/Ta, Th/ Sc, Th/U, Eu/Eu*, GdN/YbN) that indicate derivation mostly from the Tanana River. However, other ratios (As/Sb, Zr/Hf, LaN/YbN) and quantitative modeling indicate that the Yukon River was also a source. During the last glacial period, there may have been a longer residence time of the Siberian and Canadian high-pressure cells, along with a strengthened Aleutian low-pressure cell. This would have generated regional-scale northeasterly winds and explains derivation of loess from the Yukon River. However, superim-posed upon this synoptic-scale circulation, there may have been strong, southerly katabatic winds from expanded glaciers on the northern flank of the Alaska Range. These winds could have provided eolian silt from the Tanana River. Yukon River and Tanana River sediments are highly calcareous, whereas Fairbanks-area loess is not. This suggests that carbonate leaching in loess kept ahead of sedimentation and that late Quaternary loess in central Alaska was deposited relatively slowly. ?? 2006 NRC Canada.

  20. Astronomically calibrated 40Ar/39Ar age for the Toba supereruption and global synchronization of late Quaternary records

    PubMed Central

    Storey, Michael; Roberts, Richard G.; Saidin, Mokhtar

    2012-01-01

    The Toba supereruption in Sumatra, ∼74 thousand years (ka) ago, was the largest terrestrial volcanic event of the Quaternary. Ash and sulfate aerosols were deposited in both hemispheres, forming a time-marker horizon that can be used to synchronize late Quaternary records globally. A precise numerical age for this event has proved elusive, with dating uncertainties larger than the millennial-scale climate cycles that characterized this period. We report an astronomically calibrated 40Ar/39Ar age of 73.88 ± 0.32 ka (1σ, full external errors) for sanidine crystals extracted from Toba deposits in the Lenggong Valley, Malaysia, 350 km from the eruption source and 6 km from an archaeological site with stone artifacts buried by ash. If these artifacts were made by Homo sapiens, as has been suggested, then our age indicates that modern humans had reached Southeast Asia by ∼74 ka ago. Our 40Ar/39Ar age is an order-of-magnitude more precise than previous estimates, resolving the timing of the eruption to the middle of the cold interval between Dansgaard–Oeschger events 20 and 19, when a peak in sulfate concentration occurred as registered by Greenland ice cores. This peak is followed by a ∼10 °C drop in the Greenland surface temperature over ∼150 y, revealing the possible climatic impact of the eruption. Our 40Ar/39Ar age also provides a high-precision calibration point for other ice, marine, and terrestrial archives containing Toba sulfates and ash, facilitating their global synchronization at unprecedented resolution for a critical period in Earth and human history beyond the range of 14C dating. PMID:23112159

  1. Astronomically calibrated 40Ar/39Ar age for the Toba supereruption and global synchronization of late Quaternary records

    NASA Astrophysics Data System (ADS)

    Storey, Michael; Roberts, Richard G.; Saidin, Mokhtar

    2012-11-01

    The Toba supereruption in Sumatra, ∼74 thousand years (ka) ago, was the largest terrestrial volcanic event of the Quaternary. Ash and sulfate aerosols were deposited in both hemispheres, forming a time-marker horizon that can be used to synchronize late Quaternary records globally. A precise numerical age for this event has proved elusive, with dating uncertainties larger than the millennial-scale climate cycles that characterized this period. We report an astronomically calibrated 40Ar/39Ar age of 73.88 ± 0.32 ka (1σ, full external errors) for sanidine crystals extracted from Toba deposits in the Lenggong Valley, Malaysia, 350 km from the eruption source and 6 km from an archaeological site with stone artifacts buried by ash. If these artifacts were made by Homo sapiens, as has been suggested, then our age indicates that modern humans had reached Southeast Asia by ∼74 ka ago. Our 40Ar/39Ar age is an order-of-magnitude more precise than previous estimates, resolving the timing of the eruption to the middle of the cold interval between Dansgaard-Oeschger events 20 and 19, when a peak in sulfate concentration occurred as registered by Greenland ice cores. This peak is followed by a ∼10 °C drop in the Greenland surface temperature over ∼150 y, revealing the possible climatic impact of the eruption. Our 40Ar/39Ar age also provides a high-precision calibration point for other ice, marine, and terrestrial archives containing Toba sulfates and ash, facilitating their global synchronization at unprecedented resolution for a critical period in Earth and human history beyond the range of 14C dating.

  2. Late-Quaternary exhumation rates constrained by OSL thermochronometry at the Franz Josef Glacier, New Zealand

    NASA Astrophysics Data System (ADS)

    Duverger, Arnaud; King, Georgina; Valla, Pierre; Cox, Simon; Herman, Frederic

    2016-04-01

    The Southern Alps of New Zealand are often cited as the primary example of a mountain range that has reached exhumation and topographic steady state, especially on the West Coast where exhumation rates reach up to about 10 mm/yr. However, cyclic climatic changes, throughout the Quaternary period have meant that the Alps cycled between being completely glaciated and ice free. The impact that such glacial cycles may have had on the spatial variability of erosion rates remains poorly constrained. Here we use Optically Stimulated Luminescence (OSL) as a very low temperature thermochronometer to constrain rock cooling histories at 10-100 kyr timescales on samples collected near the Franz Josef glacier. OSL-thermochronometry is based on the amount of electrons accumulated in the lattice defects of natural minerals such as quartz or feldspar, due to the competing effects of charge trapping due to the natural radioactivity within the rock and charge detrapping due to thermal loss during rock exhumation towards the surface. We collected 9 samples along the Waiho valley (crossing the Alpine Fault) and the Franz Josef glacier to quantify late-Quaternary exhumation rates and their potential spatial variations. Bedrock samples have been crushed to extract the light-safe rock interiors which have then been processed to isolate potassium-rich feldspars (K-feldspars). We used the Infra-Red Stimulated Luminescence at 50°C (IRSL50) protocol, including the measurement of the natural IRSL50 trapped charge population and the laboratory characterization of sample-specific thermal and athermal kinetic parameters. Once measured, the luminescence signal can be inverted into cooling histories. We also explored the potential of the recently developed multi-OSL-thermochronometer (King et al., accepted) to better constrain the cooling path. Our first OSL measurements show that samples are not in saturation and thus contain useful thermochronometric information over the last ~100 kyr. Inverse

  3. The Late Quaternary tephrostratigraphy of annually laminated sediments from Meerfelder Maar, Germany

    NASA Astrophysics Data System (ADS)

    Lane, Christine S.; Brauer, Achim; Martín-Puertas, Celia; Blockley, Simon P. E.; Smith, Victoria C.; Tomlinson, Emma L.

    2015-08-01

    The record of Late Quaternary environmental change within the sediments of Meerfelder Maar in the Eifel region of Germany is renowned for its high precision chronology, which is annually laminated throughout the Last Glacial to Interglacial transition (LGIT) and most of the Holocene. Two visible tephra layers are prominent within the floating varve chronology of Meerfelder Maar. An Early Holocene tephra layer, the Ulmener Maar Tephra (∼11,000 varve years BP), provides a tie-line of the Meerfelder Maar record to the varved Holocene record of nearby Lake Holzmaar. The Laacher See Tephra provides another prominent time marker for the late Allerød, ∼200 varve years before the transition into the Younger Dryas at 12,680 varve years BP. Further investigation has now shown that there are also 15 cryptotephra layers within the Meerfelder Maar LGIT-Holocene stratigraphy and these layers hold the potential to make direct comparisons between the Meerfelder Maar record and other palaeoenvironmental archives from across Europe and the North Atlantic. Most notable is the presence of the Vedde Ash, the most widespread Icelandic eruption known from the Late Quaternary, which occurred midway through the Younger Dryas. The Vedde Ash has also been found in the Greenland ice cores and can be used as an isochron around which the GICC05 and Meerfelder Maar annual chronologies can be compared. Near the base of the annual laminations in Meerfelder Maar a cryptotephra is found that correlates to the Neapolitan Yellow Tuff, erupted from Campi Flegrei in southern Italy, 1200 km away. This is the furthest north that the Neapolitan Yellow Tuff has been found, highlighting its importance in the construction of a European-wide tephrostratigraphic framework. The co-location of cryptotephra layers from Italian, Icelandic and Eifel volcanic sources, within such a precise chronological record, makes Meerfelder Maar one of the most important tephrostratotype records for continental Europe

  4. Late Quaternary distribution dynamics and phylogeography of the red deer ( Cervus elaphus) in Europe

    NASA Astrophysics Data System (ADS)

    Sommer, R. S.; Zachos, F. E.; Street, M.; Jöris, O.; Skog, A.; Benecke, N.

    2008-04-01

    Here we present spatial-temporal patterns for European late Quaternary red deer (Cervus elaphus), based on radiocarbon-supported evidence derived mainly from archaeological sites. This is followed by an overview of the recent phylogeography of this species using haplogroup studies of recent molecular data. The implications of the synthesis of palaeontological and genetic data are discussed and we propose that present day European red deer haplogroup distributions are best explained against the history of late Quaternary population contractions into and expansions from glacial refugia. Around 800 records of Cervus elaphus were assigned to the period covering the later part of the Last Glacial and the Early to Middle Holocene. Red deer becomes increasingly visible in faunal assemblages dated to late OIS-3 (<40.0 ka 14C BP). The species persisted throughout the LGM on the Iberian Peninsula, in adjacent regions of South-Western France (Gascony, Dordogne, Languedoc), on the Italian Peninsula, in the Balkans and Greece, and east of the Carpathians in Moldavia. We suggest that genetic exchange between the populations of the Balkans and the East of the Carpathians remained uninterrupted during the LGM. The expansion of red deer from its southern refugia into Central and Northern Europe begins rapidly at 12,500 14C BP. The expansion of red deer coincides with the sudden rise in temperature at the onset of Greenland Interstadial 1e and the dispersion of open birch woodland into the northern half of Europe. Radiocarbon supported records show a more or less universal distribution of Cervus elaphus across Europe following the Pleistocene/Holocene climatic change at 10.0 ka 14C BP for the first time. Molecular data and fossil record combined provide a clearer temporal and spatial pattern for the Lateglacial recolonisation process of the northern part of Europe.

  5. Late Pliocene and Quaternary Eurasian locust infestations in the Canary Archipelago

    USGS Publications Warehouse

    Meco, J.; Muhs, D.R.; Fontugne, M.; Ramos, A.J.; Lomoschitz, A.; Patterson, D.

    2011-01-01

    The Canary Archipelago has long been a sensitive location to record climate changes of the past. Interbedded with its basalt lavas are marine deposits from the principal Pleistocene interglacials, as well as aeolian sands with intercalated palaeosols. The palaeosols contain African dust and innumerable relict egg pods of a temperate-region locust (cf. Dociostaurus maroccanusThunberg 1815). New ecological and stratigraphical information reveals the geological history of locust plagues (or infestations) and their palaeoclimatic significance. Here, we show that the first arrival of the plagues to the Canary Islands from Africa took place near the end of the Pliocene, ca. 3Ma, and reappeared with immense strength during the middle Late Pleistocene preceding MIS (marine isotope stage) 11 (ca. 420ka), MIS 5.5 (ca. 125ka) and probably during other warm interglacials of the late Middle Pleistocene and the Late Pleistocene. During the Early Holocene, locust plagues may have coincided with a brief cool period in the current interglacial. Climatically, locust plagues on the Canaries are a link in the chain of full-glacial arid-cold climate (calcareous dunes), early interglacial arid-sub-humid climate (African dust inputs and locust plagues), peak interglacial warm-humid climate (marine deposits with Senegalese fauna), transitional arid-temperate climate (pedogenic calcretes), and again full-glacial arid-cold climate (calcareous dunes) oscillations. During the principal interglacials of the Pleistocene, the Canary Islands recorded the migrations of warm Senegalese marine faunas to the north, crossing latitudes in the Euro-African Atlantic. However, this northward marine faunal migration was preceded in the terrestrial realm by interglacial infestations of locusts. ??? Locust plagues, Canary Islands, Late Pliocene, Pleistocene, Holocene, palaeoclimatology. ?? 2010 The Authors, Lethaia ?? 2010 The Lethaia Foundation.

  6. Late Quaternary sea-ice history of northern Fram Strait/Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Kremer, Anne; Stein, Rüdiger; Fahl, Kirsten; Matthießen, Jens; Forwick, Matthias; O'Regan, Matt

    2016-04-01

    One of the main characteristics of the Arctic Ocean is its seasonal to perennial sea-ice cover. Variations of sea-ice conditions affect the Earth's albedo, primary production, rate of deep-water etc.. During the last decades, a drastic decrease in sea ice has been recorded, and the causes of which, i.e., natural vs. anthropogenic forcings, and their relevance within the global climate system, are subject of intense scientific and societal debate. In this context, records of past sea-ice conditions going beyond instrumental records are of major significance. These records may help to better understand the processes controlling natural sea-ice variability and to improve models for forecasts of future climatic conditions. During RV Polarstern Cruise PS92 in summer 2015, a 860 cm long sediment core (PS92/039-2) was recovered from the eastern flank of Yermak Plateau north of the Svalbard archipelago (Peeken, 2015). Based on a preliminary age model, this sediment core probably represents the time interval from MIS 6 to MIS 1. This core, located close to the modern summer ice edge, has been selected for reconstruction of past Arctic sea-ice variability based on specific biomarkers. In this context, we have determined the ice-algae-derived sea-ice proxy IP25 (Belt et al., 2007), in combination with other biomarkers indicative for open-water conditions (cf., Müller et al., 2009, 2011). Furthermore, organic carbon fluxes were differentiated using specific biomarkers indicative for marine primary production (brassicasterol, dinosterol) and terrigenous input (campesterol, β-sitosterol). In this poster, preliminary results of our organic-geochemical and sedimentological investigations are presented. Distinct fluctuations of these biomarkers indicate several major, partly abrupt changes in sea-ice cover in the Yermak Plateau area during the late Quaternary. These changes are probably linked to changes in the inflow of Atlantic Water along the western coastline of Svalbard into

  7. Dynamics of Late Quaternary North African humid periods documented in the clay mineral record of central Aegean Sea sediments

    NASA Astrophysics Data System (ADS)

    Ehrmann, Werner; Seidel, Martin; Schmiedl, Gerhard

    2013-08-01

    The ratio between the clay minerals kaolinite and chlorite has been investigated in high resolution in a late Quaternary sediment core from the central Aegean Sea. The record spans the last ca. 105 ka. The kaolinite/chlorite ratio was used to reconstruct the fine-grained aeolian dust influx from the North African deserts, mainly derived from desiccated lake depressions. It therewith can be used as a proxy for wind activity, aridity and vegetation cover in the source area. The data document three major humid phases in North Africa bracketing the formation of sapropel layers S4, S3 and S1. They occur at > 105-95 ka, 83.5-72 ka and 14-2 ka. The first two phases are characterised by relatively abrupt lower and upper boundaries suggesting a non-linear response of vegetation to precipitation, with critical hydrological thresholds. In contrast, the onset and termination of the last humid period were more gradual. Highest kaolinite/chlorite ratios indicating strongest aeolian transport and aridity occur during Marine Isotope Stage (MIS) 5b, at ca. 95-84 ka. The long-term decrease in kaolinite/chlorite ratios during the last glacial period indicates a gradual decline of deflatable lake sediments in the source areas.

  8. Recurrent neomorphic and cement microtextures from different diagenetic environments, Quaternary to Late Neogene carbonates, Great Bahama Bank

    NASA Astrophysics Data System (ADS)

    Maliva, Robert G.

    1995-06-01

    The cores Clino and Unda, taken near the western margin of Great Bahama Bank, contain a diverse suite of Quaternary to Late Neogene carbonates that have a variety of neomorphic and cement microtextures. The microtextures of each of the different neomorphosed aragonitic grain types, such as corals, mollusks, and plates of the calcareous green algae Halimeda, are very similar wherever the neomorphosed grains are present in the cores. Limestone samples that contain neomorphosed aragonitic fossils are cemented predominantly with blocky calcite. Despite the similar neomorphic and cement microtextures, light-stable isotope data reveal that these calcites precipitated in different diagenetic environments in different parts of the cores. The neomorphic calcites and associated calcite cements in the upper parts of Clino and Unda precipitated in meteoric-influenced pore waters, as indicated by δ18O values ranging from -1.9%. to -3.7%., whereas in the lower part of Clino the calcites precipitated in marine pore waters, as indicated by δ18O values ranging from -0.1%. to +2.4‰. Essentially identical diagenetic microtextures were thus produced in different diagenetic environments, revealing a significant limitation in the use of microtextural data to determine the diagenetic histories of carbonate rocks.

  9. Late quaternary dynamics in the Madeira River basin, southern Amazonia (Brazil), as revealed by paleomorphological analysis.

    PubMed

    Hayakawa, Ericson H; Rossetti, Dilce F

    2015-03-01

    Ancient drainage systems are being increasingly documented in the Amazon basin and their characterization is crucial for reconstructing fluvial evolution in this area. Fluvial morphologies, including elongate belts, are well preserved along the Madeira River. Digital Elevation Model from the Shuttle Radar Topography Mission favored the detection of these features even where they are covered by dense rainforest. These paleomorphologies are attributed to the shifting position of past tributaries of the Madeira River through avulsions. These radial paleodrainage networks produced fan-shaped morphologies that resemble distributary megafans. Distinguishing avulsive tributary systems from distributary megafans in the sedimentary record is challenging. Madeira´s paleodrainage reveals the superposition of tributary channels formed by multiple avulsions within a given time period, rather than downstream bifurcation of coexisting channels. Channel avulsion in this Amazonian area during the late Quaternary is related to tectonics due to features as: (i) straight lineaments coincident with fault directions; (ii) northeastward tilting of the terrain with Quaternary strata; and (iii) several drainage anomalies, including frequent orthogonal drainage inflections. These characteristics altogether lead to propose that the radial paleodrainage present at the Madeira River margin results from successive avulsions of tributary channels over time due to tectonics. PMID:25806978

  10. Landscape evolution of the Ulan Buh Desert in northern China during the late Quaternary

    NASA Astrophysics Data System (ADS)

    Chen, Fahu; Li, Guoqiang; Zhao, Hui; Jin, Ming; Chen, Xuemei; Fan, Yuxin; Liu, Xiaokang; Wu, Duo; Madsen, David

    2014-05-01

    The evolution of arid environments in northern China was a major environmental change during the Quaternary. Here we present the dating and environmental proxy results from a 35 m long core (A-WL10ZK-1) collected from the Ulan Buh Desert (UBD), along with supplemental data from four other cores. The UBD is one of the main desert dune fields in China and our results indicate the UBD has undergone complex evolution during the late Quaternary. Most of the present UBD was covered by a Jilantai-Hetao Mega-paleolake lasting until ~ 90 ka ago. A sandy desert environment prevailed throughout the UBD during the last glacial period and early Holocene. A wetland environment characterized by the formation of numerous interdunal ponds in the northern UBD occurred at ~ 8-7 ka, although a dune field persisted in the southern UBD. The modern UBD landscape formed after these wetlands dried up. During the last 2000 years, eolian sand from the Badain Jaran Desert has invaded the northern UBD, while farming and overgrazing resulted in the formation of the eastern UBD. We suggest that the formation of UBD landforms is related to the disintegration of the megalake Jilantai-Hetao and to summer monsoon changes during the last glaciation and Holocene.

  11. Tropical forest changes during the late quaternary in African and South American lowlands

    NASA Astrophysics Data System (ADS)

    Servant, Michel; Maley, Jean; Turcq, Bruno; Absy, Maria-Lucia; Brenac, Patrice; Fournier, Marc; Ledru, Marie-Pierre

    1993-05-01

    Arboreal pollen and montane elements of Late Quaternary pollen assemblages from three lacustrine cores (West Cameroon, southeastern Amazonia and central Brazil) are correlated, by the radiocarbon chronology, with other palaeoenvironmental records in Africa and South America. We observe in both continents a well-developed dense forest at 30,000 and 9000 yr B.P. The succession of vegetation types during the Late Quaternary appeared strongly related to the regional conditions: (1) the dense forest was more or less degraded depending on the regions during the last full glacial period (20,000-15,000 yr B.P.); (2) a slow increase of tree elements is evidenced in some areas during the Late Glacial (15,000-10,000 yr B.P.), whereas short-term fluctuations occurred in central Brazil during the same time; (3) a strong regression of the forest during the middle Holocene (6000-5000 yr B.P.), in the southern tropical zone of South America, was in opposition to a full forest development in Africa. In both continents two main features characterize the tropical forest evolution: (1) Montane elements developed in the lowlands during the last glacial period and in some southern or northern regions during the early Holocene; and (2) the climate seasonality was enhanced in several regions since 8500-7500 yr B.P. For a tentative explanation, we relate the cold or cool climate, inferred by palaeoecological evidences in the glacial period and glacial-interglacial transition, to polar air-masses reaching more frequently the tropical zone. This interpretation explains the apparent contradiction between the markedly low temperature of the continental lowlands opposed: (1) at 18,000 yr B.P., to the 1-2°C lower Sea Surface Temperature of tropical oceans and (2) to the global warming during the late glacial. During the middle and Late Holocene, climate evolution was mainly influenced by the latitudinal shift of the ITCZ positions in July and January and, in South America, by short-term changes

  12. Mapped plant macrofossil and pollen records of late Quaternary vegetation change in eastern North America

    SciTech Connect

    Jackson, S.T.; Overpeck, J.T.; Webb, T. III ||

    1995-06-01

    We compiled a plant macrofossil database for 12 eastern North American tree and shrub taxa (Picea sp., P. glauca, P. mariana, Larix laricina, Abies balsamea, Tsuga canadensis, Pinus strobus, P. banksiana, P. resinosa, Betula papyrifera, B. alleghaniensis, B. Series Humiles) at 264 late Quaternary sites. Presence/absence maps for these taxa at 18,000, 15,000, 12,000, 9000, 6000, 3000, and 0 {sup 14}C yr B.P. show changes in geographic ranges of these species in response to climatic change. Comparison of the macrofossil maps with isopoll maps for corresponding taxa corroborates inferences from the pollen data, and reveals species-level patterns not apparent in the pollen maps.

  13. Late Quaternary environments and prehistoric occupation in the lower White Nile valley, central Sudan

    NASA Astrophysics Data System (ADS)

    Williams, Martin A. J.; Usai, Donatella; Salvatori, Sandro; Williams, Frances M.; Zerboni, Andrea; Maritan, Lara; Linseele, Veerle

    2015-12-01

    Despite the major contributions provided over fifty years ago by A.J. Arkell and J.D. Tothill to our understanding of late Quaternary environments and prehistoric occupation near the confluence of the Blue and White Nile in central Sudan, three key questions have remained unresolved since then. (a) Was the decline in Nile flood levels from early Holocene times onwards caused by a reduction in Nile discharge, or by channel incision, or both? (b) Was the regional climate wetter during times of high Nile floods and drier during times of low Nile floods? (c) Given the high degree of disturbance of Mesolithic and later prehistoric sites, is it possible to identify primary-context, stratified and undisturbed occupation? Drawing upon dated evidence from three sites to the east of and three to the west of the lower White Nile, we provide a qualified answer to the first question and documented affirmative answers to the second and third questions.

  14. A protocol for subsampling Late Quaternary coprolites for multi-proxy analysis

    NASA Astrophysics Data System (ADS)

    Wood, Jamie R.; Wilmshurst, Janet M.

    2016-04-01

    The study of Late Quaternary coprolites can provide unique insights into various aspects of the biology and ecology of extinct species and prehistoric humans. Coprolite studies are becoming increasingly multi-disciplinary, allowing a greater amount of information to be obtained from individual specimens. Subsampling is a critical part of multi-proxy coprolite analysis, yet no standardised subsampling protocols exist, and details of subsampling methods have rarely been reported in published studies. Here, we outline a procedure for the subsampling of coprolites for multi-proxy analysis. The method is designed to minimise the risk of sample contamination for sensitive analyses (e.g. ancient DNA, palynology), thereby maximising the robustness of interpretations made from the results. We also stress the need for voucher samples to be retained to ensure the repeatability of results and allow for further analytical methods to be applied to specimens in the future.

  15. Response to comment on "No late Quaternary strike-slip motion along the northern Karakoram fault"

    NASA Astrophysics Data System (ADS)

    Robinson, Alexander C.; Owen, Lewis A.; Chen, Jie; Schoenbohm, Lindsay M.; Hedrick, Kathryn A.; Blisniuk, Kimberly; Sharp, Warren D.; Imrecke, Daniel B.; Li, Wenqiao; Yuan, Zhaode; Caffee, Marc W.; Mertz-Kraus, Regina

    2016-06-01

    In their comment on "No late Quaternary strike-slip motion along the northern Karakoram fault", while Chevalier et al. (2016) do not dispute any of the results or interpretations regarding our observations along the main strand of the northern Karakoram fault, they make several arguments as to why they interpret the Kongur Shan Extensional System (KES) to be kinematically linked to the Karakoram fault. These arguments center around how an "active" fault is defined, how slip on segments of the KES may be compatible with dextral shear related to continuation of the Karakoram fault, and suggestions as to how the two fault systems might still be connected. While we appreciate that there are still uncertainties in the regional geology, we address these comments and show that their arguments are inconsistent with all available data, known geologic relationships, and basic kinematics.

  16. Long-Term Changes In The Behaviour Of Jakobshavns Isbrae, West Greenland During The Late Quaternary-Holocene

    NASA Astrophysics Data System (ADS)

    O'Cofaigh, C.; Jennings, A.; Moros, M.; Andrews, J. T.; Kilfeather, A.; Dowdeswell, J. A.; Richter, T.

    2008-12-01

    This poster shows the initial results of a joint scientific project to reconstruct the Late Quaternary-Holocene behavior of Jakobshavns Isbrae in central west Greenland, one of the largest ice streams draining the modern Greenland Ice Sheet. The underlying rationale for this research is to determine if recent observed changes to the mass balance of the Greenland Ice Sheet are part of the natural variability in ice-sheet dynamics, or if they relate to anthropogenically-induced climate warming. Key to resolving this question is an understanding of long-term changes in ice sheet behavior during the Late Quaternary and the Holocene. This research will allow assessment of the links between deglaciation and internal and external environmental controls, such as the influence of inflowing Atlantic Water, and will facilitate modelling of the likely future behavior of the GIS. Currently, four marine sediment cores arrayed along a transect from the Disko Bugt Fan to Disko Bay are providing information on changes in sediment flux and sedimentation style, such as abrupt intervals of iceberg-rafting vs. "normal" hemipelagic sedimentation, as well as the paleoceanographic setting and ice sheet-ocean interactions. The cores are being analysed using a variety of proxies including IRD, mineralogy, oxygen isotopes, foraminiferal assemblages, lithofacies analysis and AMS radiocarbon dating. Data are presented from two piston cores from the continental slope at the trough-mouth fan collected during the HE0006 'shakedown' cruise to Baffin Bay and from two gravity cores recovered in 2007 during MS Merian cruise MSM 05/03 to West Greenland. Slope cores contain sequences of laminated facies interpreted as fine-grained turbidites and intervals of massive, bioturbated, hemipelagic mud. The two Merian cores, contributed to this project by the Baltic Sea Research Institute, were collected from the southern entrance to Disko Bugt and the Vaigat channel north of Disko. Radiocarbon dates from the

  17. Micromorphological investigations of the Late Quaternary loess-paleosol sequences of the Kashmir Valley, India

    NASA Astrophysics Data System (ADS)

    Dar, Reyaz Ahmad; Chandra, Rakesh; Romshoo, Shakil Ahmad; Kowser, Nazia

    2015-11-01

    The loess-paleosol sequences of the Karewa Group preserve a valuable repository of the Late Quaternary climatic changes and the landscape evolution history of the Karewa Basin of Kashmir Valley in their lithological and pedogenic records. Three representative loess-paleosol sections at Shankerpora (SP), Khan Sahib (KS) and Pattan (PT) localities were chosen for detailed lithostratigraphic fieldwork and micromorphological observations of thin sections. Lithostratigraphic analysis revealed lateral and vertical variation in thickness and number of paleosol profiles from south-west to north-west of the Karewa Basin suggesting the availability of land-surface for periodic loess deposition. The SP section is marked by 6 (SP-S6, S7, S8, S9, S10, S12), KS section by 3 (KS-S2, S4, S5) and PT section by 2 (PT-S1, S3) thick mature paleosol profiles. Theses paleosols have well developed 'Ah' and 'Btk' horizons representing prolonged land-surface stability when pedogenic processes outpace loess deposition. On the other hand comparatively thin to thick paleosol profiles represent weak to moderate pedogenic maturity indicating short stratigraphic breaks with rapid loess deposition. Micromorphological observations of thin sections suggested that clay illuviation and CaCO3 accumulation have operated within the paleosol profiles. CaCO3 features are often associated with clay coatings suggesting decalcification of carbonates followed by clay illuviation. Pedogenic CaCO3 probably resulted from the precipitation of the soil solution near the average depth of wetting front. The pedogenic CaCO3, illuvial clay, mottles, iron manganese features, pedal microstructure and blocky aggregates reveal variation in the pedogenic maturity among and within the loess-paleosol sections. The morphological (both micro- and macro-morphological) attributes of loess-paleosols suggest variation of climatic conditions during the Late Quaternary period in the Karewa Basin of Kashmir Valley, India.

  18. Spatiotemporal patterns of tundra fires: late-Quaternary charcoal records from Alaska

    NASA Astrophysics Data System (ADS)

    Chipman, M. L.; Hudspith, V.; Higuera, P. E.; Duffy, P. A.; Kelly, R.; Oswald, W. W.; Hu, F. S.

    2015-07-01

    Anthropogenic climate change has altered many ecosystem processes in the Arctic tundra and may have resulted in unprecedented fire activity. Evaluating the significance of recent fires requires knowledge from the paleofire record because observational data in the Arctic span only several decades, much shorter than the natural fire rotation in Arctic tundra regions. Here we report results of charcoal analysis on lake sediments from four Alaskan lakes to infer the broad spatial and temporal patterns of tundra-fire occurrence over the past 35 000 years. Background charcoal accumulation rates are low in all records (range is 0-0.05 pieces cm-2 yr-1), suggesting minimal biomass burning across our study areas. Charcoal peak analysis reveals that the mean fire-return interval (FRI; years between consecutive fire events) ranged from ca. 1650 to 6050 years at our sites, and that the most recent fire events occurred from ca. 880 to 7030 years ago, except for the CE 2007 Anaktuvuk River Fire. These mean FRI estimates are longer than the fire rotation periods estimated for the past 63 years in the areas surrounding three of the four study lakes. This result suggests that the frequency of tundra burning was higher over the recent past compared to the late Quaternary in some tundra regions. However, the ranges of FRI estimates from our paleofire records overlap with the expected values based on fire-rotation-period estimates from the observational fire data, and the differences are statistically insignificant. Together with previous tundra-fire reconstructions, these data suggest that the rate of tundra burning was spatially variable and that fires were extremely rare in our study areas throughout the late Quaternary. Given the rarity of tundra burning over multiple millennia in our study areas and the pronounced effects of fire on tundra ecosystem processes such as carbon cycling, dramatic tundra ecosystem changes are expected if anthropogenic climate change leads to more

  19. Assessing Timescales and Controls of Floodplain Evolution in Monsoonal Australia during the Late Quaternary

    NASA Astrophysics Data System (ADS)

    May, J. H.; Preusser, F.

    2014-12-01

    Subtropical and tropical river systems are considered unique and sensitive archives for the detection of past changes in global circulation patterns due to their strategic position between significant atmospheric phenomena. In semi-arid to arid Central Australia, many of the hydrological variations have generally been attributed to variations in monsoon strength and position. While an increasing number of studies has recently addressed the reconstruction of monsoonal variations from high-resolution proxy records in tropical Australasia, very little data is available on the landscape-scale impacts such as weathering, erosion, flooding and sediment transport. Therefore, unraveling the impacts of past changes in monsoonal intensity on fluvial systems in Australia's tropical north - the 'Top End' - will substantially contribute to our understanding of cause and effect of climate change. Our study presents first results from the Adelaide River, one of the major river systems draining the 'Top End'. Here, extensive but currently inactive floodplains have accreted along the middle reaches of the catchment upstream of bedrock constrictions. Virtually no data is so far available from these floodplains although their stratigraphic and sedimentary record should contain valuable information on the late Quaternary evolution of the fluvial system in northern Australia. We have cored a transect of nine sediment profiles across the floodplains and levees associated with the Adelaide River. Based on these profiles, we (i) document their geomorphologic setting based on the analysis of high-resolution (LIDAR) elevation models and remote sensing data, (ii) establish a first stratigraphy for these floodplains based on field description, grain sizes and detailed total element data, (iii) present a chronological framework for the sediments based on luminescence dating, and (iv) discuss the significance of these results in terms of the larger-scale evolution of paleoenvironments and sea

  20. Delineation of Late Quaternary depositional sequences by high-resolution seismic stratigraphy, Louisiana continental shelf

    SciTech Connect

    Suter, J.R.; Berryhill, H.L. Jr.; Penland, S.

    1987-05-01

    Interpretations of over 20,000 line km of single-channel, high-resolution seismic reflection profiles, coupled with nearshore vibracores and logs of industrial platform borings, provide the data base for determining the history and stratigraphy of late Quaternary sea level fluctuations on the Louisiana continental shelf. Regional unconformities, formed by subaerial exposure of the shelf during glacio-eustatic sea level withdrawals and modified by shoreface erosion during ensuing transgression, serve as markers to identify the boundaries of depositional sequences. Unconformities are recognizable on seismic profiles by high-amplitude reflectors as well as discordant relationships between reflectors. Within the upper Quaternary section, six depositional sequences have been recognized. Five of these are related to glacio-eustatic sea level fluctuations, involving sea level fall close to, or beyond, the margin of the continental shelf. Three of these fluctuations culminated in the deposition of shelf margin delta sequences. Extensive fluvial channeling characterizes the regressive phase of these sequences. Transgressive phases are marked by infilling of fluvial channels, flood-plain aggradation, truncation, or deposition of sand sheets, depending upon sediment supply and rate of sea level rise. Sequences 4 and 5 are correlated with the late Wisconsinan glacial stage and Holocene transgression. The upper portion of sequence 5 consists of an early Holocene Mississippi delta complex. Abandonment and transgression of this delta are responsible for the formation of sequence 6. Although these deposits cover a smaller area, this demonstrates that deltaic processes can produce sequences similar to those driven by glacially controlled sea level changes.

  1. Stable isotopes reflect the ecological stability of two high-elevation mammals from the late Quaternary of Colorado

    NASA Astrophysics Data System (ADS)

    McLean, Bryan S.; Emslie, Steven D.

    2012-05-01

    The vertebrate fossil record of Cement Creek Cave, Colorado, spans from > 45,000 yr ago to the present and represents the richest stratified series of high-elevation (> 2900 m) mammal remains known from the late Quaternary of North America. Stable carbon and oxygen isotope analyses of tooth enamel were used to assess potential ecological responses of two species found commonly throughout the cave, Yellow-bellied marmots (Marmota flaviventris) and Bushy-tailed woodrats (Neotoma cinerea), to late Quaternary climate and environmental changes of the Southern Rocky Mountains. Results indicate that despite such perturbations, the dietary ecologies of both species were maintained across this period. Neither taxon shifted to consuming C4 taxa or different C3 functional groups; similarly, no significant shifts in surface water use were detected. Variations in enamel δ13C were observed, however, that represent the physiological responses of high-elevation plants to changing levels of late Quaternary atmospheric CO2. While our findings extend both the geographic and elevational record of this plant CO2 response, they simultaneously highlight the ecological stability of high-elevation M. flaviventris and N. cinerea during climate changes of late Quaternary magnitude.

  2. Dinoflagellate cysts as indicators of millennial scale climatic and oceanographic variability in Guaymas Basin, Gulf of California (Mexico) during the Late Quaternary

    NASA Astrophysics Data System (ADS)

    Price, Andrea M.; Mertens, Kenneth N.; Pospelova, *Vera; Pedersen, Thomas F.; Ganeshram, Raja S.

    2015-04-01

    A high-resolution record of organic-walled dinoflagellate cyst production in Guaymas Basin, Gulf of California (Mexico) reveals a complex paleoceanographic history over the last ~40 ka. Guaymas Basin is an excellent location to perform high resolution studies of changes in Late Quaternary climate and paleo-productivity because it is characterized by high primary productivity, high sedimentation rates, and low oxygen bottom waters. These factors contribute to the deposition and preservation of laminated sediments throughout large portions of core MD02-2515. This is one of the first studies in the Northeast Pacific to document dinoflagellate cyst production at a centennial to millennial scale throughout the Late Quaternary. Based on the cyst assemblages three major dinoflagellate cyst zones were established, and roughly correspond to Marine Isotope Stages 1 to 3. The most dominant dinoflagellate cyst taxa found throughout the core were Brigantedinium spp. and Operculodinium centrocarpum. Dansgaard-Oeschger event 8 is observed in the dinoflagellate cyst record, and is characterized by an increase in warm water taxa such as Spiniferites pachydermus. Other intervals of interest are the Younger Dryas where cooler sea-surface conditions are not recorded, and the Holocene which is characterized by the consistent presence of warm water species Stelladinium reidii, Tuberculodinidum vancampoae, Bitectatodinium spongium and an increase in Quinquecuspis concreta. Changes in cyst assemblages, concentrations and species diversity, along with geochemical data reflect major orbital to millennial-scale climatic and oceanographic changes. Keywords: Dansgaard-Oeschger events; dinoflagellate cyst; Gulf of California; late Quaternary climate change; upwelling; Younger Dryas.

  3. Radiocarbon dating late Quaternary loess deposits using small terrestrial gastropod shells

    NASA Astrophysics Data System (ADS)

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

    2013-09-01

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

  4. Radiocarbon dating late Quaternary loess deposits using small terrestrial gastropod shells

    USGS Publications Warehouse

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

    2013-01-01

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

  5. Late Quaternary Paleohydrology of the Madre de Dios River, southwestern Amazon Basin, Peru

    NASA Astrophysics Data System (ADS)

    Rigsby, Catherine A.; Hemric, Erin M.; Baker, Paul A.

    2009-12-01

    Late Quaternary climatic and hydrologic variability triggered changes in fluvial deposition and erosion along the course of the Madre de Dios River, Peru, the largest tributary basin of the Madeira basin, itself the largest tributary basin of the Amazon. Three laterally extensive, Quaternary-age, terrace tracts are present within the Madre de Dios basin. Analysis of sedimentary facies, present in the modern cut banks and terraced sequences, along with radiocarbon dates on fossil wood and leaf material preserved in the terraced strata, allow reconstruction of the Late Quaternary depositional history of the sedimentary sequences, including determination of the approximate timing of aggradation and downcutting episodes and its relationship to the timing of past climate change in this portion of the Amazon basin and beyond. The Quaternary sediments underlying the terraces most often recorded deposition in a coarse-grained meandering fluvial system. The T3 terrace, the highest terrace, is underlain by the Miocene (?) Ipururi Formation, which is unconformably overlain by the late Miocene-Pleistocene (?) (> 48,000 cal yrs BP) Madre de Dios Formation, a multistory coarse-sandy to gravelly channel and point bar complex. The latter was downcut before 29,850 ± 100 cal yrs BP. This downcut landscape was infilled by meandering fluvial strata characterized by gravelly channel deposits in a sequence dominated by floodplain and lateral accretion deposits. These strata were in turn downcut to form the T2 terrace before 11,970 ± 100 cal yrs BP. A third episode of aggradation resulted in the deposition of a sand-dominated meandering channel complex that infilled the T2 valley and was subsequently downcut after 3780 ± 50 cal yrs BP. This most recent terrace is infilled by the modern fluvial sediment, which has been actively aggrading since at least 870 ± 50 cal yrs BP. Importantly, the Madre de Dios fluvial system actively aggraded between 30,000 and 25,000 cal yrs BP, (and likely

  6. Late Neogene marine incursions and the ancestral Gulf of California

    USGS Publications Warehouse

    McDougall, K.

    2008-01-01

    The late Neogene section in the Salton Trough, California, and along the lower Colorado River in Arizona is composed of marine units bracketed by nonmarine units. Microfossils from the marine deposits indicate that a marine incursion inundated the Salton Trough during the late Miocene. Water depths increased rapidly in the Miocene and eventually flooded the region now occupied by the Colorado River as far north as Parker, Arizona. Marine conditions were restricted in the Pliocene as the Colorado River filled the Salton Trough with sediments and the Gulf of California assumed its present configuration. Microfossils from the early part of this incursion include a diverse assemblage of benthic foraminifers (Amphistegina gibbosa, Uvigerina peregrina, Cassidulina delicata, and Bolivina interjuncta), planktic foraminifers (Globigerinoides obliquus, G. extremus, and Globigerina nepenthes), and calcareous nannoplankton (Discoaster brouweri, Discoaster aff. Discoaster surculus, Sphenolithus abies, and S. neoabies), whereas microfossils in the final phase contain a less diverse assemblage of benthic foraminifers that are diagnostic of marginal shallow-marine conditions (Ammonia, Elphidium, Bolivina, Cibicides, and Quinqueloculina). Evidence of an earlier middle Miocene marine incursion comes from reworked microfossils found near Split Mountain Gorge in the Fish Creek Gypsum (Sphenolithus moriformis) and near San Gorgonio Pass (Cyclicargolithus floridanus and Sphenolithus heteromorphus and planktic foraminifers). The middle Miocene incursion may also be represented by the older marine sedimentary rocks encountered in the subsurface near Yuma, Arizona, where rare middle Miocene planktic foraminifers are found. ?? 2008 The Geological Society of America.

  7. Late Quaternary landscape evolution in the Great Karoo, South Africa: Processes and drivers.

    NASA Astrophysics Data System (ADS)

    Oldknow, Chris; Hooke, Janet; Lang, Andreas

    2016-04-01

    The Great Karoo spans the north-central part of South Africa at a major climatic boundary. The characteristics, sequences, spatial patterns and drivers of river response to Late Quaternary climate changes in this region remain unclear due to the fragmentary alluvial/colluvial stratigraphic record and the lack of dated palaeoclimatic archives. Dendritic gully networks incised into deep deposits (up to 6 m) of colluvium and alluvium in the upper Sundays River catchment expose a legacy of "cut and fill" features. In 1st order tributaries, these are predominantly discontinuous palaeochannels and flood-outs with localised palaeosols, whereas in 2nd & 3rd order tributaries there are: 1) incised palaeo-geomorphic surfaces, 2) semi-continuous inset terrace sequences, 3) buried palaeo-gully topography. Using a combination of field mapping, logging of sediment outcrops, soil micromorphological and grain size analysis, mineral magnetic measurements and radiometric dating (OSL & 14C), we derive a stratigraphic evolution model which demonstrates a) the number of phases of incision, aggradation and pedogenesis, b) the spatial and temporal extent of each phase and c) the drivers of alluviation and associated feedbacks. Our reconstruction of regional valley alluviation indicates four distinct terrace units of contrasting depositional age. The base of the succession reflects slow aggradation under periglacial conditions associated with the Last Glacial Maximum. Subsequent channel entrenchment, causing terrace abandonment (T1) occurred in the deglacial period when vegetation and rainfall were in anti-phase. Re-instatement of connectivity with deep upland colluvial stores resulted in the injection of a pulse of sediment to valley floors, triggering compartmentalised backfilling (aggradation of T2) which propagated upstream as far as the second order drainage lines. This backfilling restructured the local hydrology, which, in concert with enhanced summer-rainfall, contributed to a

  8. Late Quaternary river channel migrations of the Kura River in Transcaucasia - tectonic versus climatic causes

    NASA Astrophysics Data System (ADS)

    von Suchodoletz, Hans; Gärtner, Andreas; Hoth, Silvan; Umlauft, Josefine; Godoladze, Tea; Faust, Dominik

    2015-04-01

    Large-scale river channel migrations either in the form of avulsions or combing, i.e. progressive lateral migrations, are global phenomena during the Late Quaternary. Such channel migrations were triggered by tectonics, climate change, human activity or a combination of those factors. River channel migrations have the potential to cause significant human and economic losses. Thus, a more thorough knowledge about underlying causes and process rates is essential. Furthermore, such studies will elucidate the sensitivity or robustness of rivers to different external and internal forcing-agents, i.e. they help to identify the dominant drivers of regional landscape evolution. The Caucasus region is part of the active collision zone between the Africa-Arabian and the Eurasian plates, and is characterized by high current tectonic activity. Furthermore, significant environmental changes took place during the Late Quaternary, i.e. the shrinking or even disappearance of glaciers in the Greater and Lesser Caucasus or fundamental changes of the vegetation cover varying between woodland and grassland-dominated vegetation. The Kura River is the main gaining stream of the Transcaucasian Depression located between the Greater Caucasus Mountains in the north and the Lesser Caucasus Mountains in the south, and receives several tributaries from both mountain ranges. This study focusses on the middle course of the Kura River in eastern Georgia, SE of the city of Tbilisi. Integration of fluvial geomorphology, geochronology, heavy mineral analyses and seismo-tectonic analyses demonstrates that this part of the Kura River underwent large-scale channel migrations up to >10 km during Late Pleistocene and Holocene. It is interpreted that these movements followed both tectonic and climatic triggers: Whereas SW-ward migrations were caused by tectonic uplift in and SW-directed advance of the Kura fold and thrust belt as part of the Greater Caucasus, NE-ward migrations occurred during cold

  9. Synthesis of Late Cretaceous-Quaternary tectonic, sedimentary and magmatic processes and basin formation related to episodic subduction-collision in the easternmost Mediterranean region

    NASA Astrophysics Data System (ADS)

    Robertson, Alastair; Kinnaird, Timothy; McCay, Gillian; Palamakumbura, Romesh; Taslı, Kemal

    2015-04-01

    Mesozoic oceanic crust of the easternmost Mediterranean has experienced northwards subduction during Late Cretaceous-Cenozoic, either continuously or discontinuously based on kinematic evidence. Much of the existing information on sedimentation within the easternmost Mediterranean oceanic basin comes from the non-emplaced continental margins of the Levant and North Africa. In addition, sedimentary basins related to plate convergence are recorded along the northern margin of the Southern Neotethyan ocean, mainly in the Kyrenia Range of northern Cyprus and its extension into the Misis Mountains of southern Turkey, coupled with the adjacent submerged areas. In a setting of only incipient continental collision such as the easternmost Mediterranean the sedimentary basins would be expected to remain entirely submarine. In contrast, the Kyrenia Range has been strongly uplifted and subaerially exposed during Late Pliocene-Quaternary time. This allows the recognition of a number of discrete phases of sedimentary basin formation: 1. Late Cretaceous (Campanian-Maastrichtian): silicic volcanism to create a subaqueous volcaniclastic apron; 2. Maastrichtian-Paleocene: pelagic carbonate deposition interspersed with proximal gravity flows and within-plate type alkaline volcanics; 3. Early Eocene: large-scale sedimentary melange (olistostrome) emplacement; 4. Late Eocene-Late Miocene: terrigenous gravity-flow deposition in a deep-water fault dissected 'fore arc' setting. Initial, Late Eocene non-marine coarse clastic alluvial fan deposition was succeeded by Oligocene-Miocene deep-marine siliciclastic gravity flow deposits, fining and shallowing upwards during the Late Miocene; 5. Messinian: localised precipitation of evaporites in small fault-controlled basins; 6. Pliocene: shallow-marine siliciclastic-carbonate deposition in a shelf-depth, overall regressive setting; 7. Latest Pliocene to mid-Pleistocene: gravitational accumulation of coarse talus along a strongly uplifting

  10. Environmental and Archaeological Implications of a Late Quaternary Palynological Sequence, Poyang Lake, Southern China

    NASA Astrophysics Data System (ADS)

    Jiang, Qinhua; Piperno, Dolores R.

    1999-09-01

    Paleoecological data from Poyang Lake, southern China, indicate that significant natural and human-induced vegetational changes have occurred during the Late Quaternary in the Middle Yangtze River valley, the likely location of rice (Oryza sativa L.) domestication. During the late Pleistocene (from ca. 12,830 to ca. 10,500 yr B.P.), the climate was cooler and drier than today's. The subtropical, mixed deciduous-evergreen broad-leaved forest which constitutes the modern, potential vegetation was reduced and herbaceous vegetative cover expanded. A hiatus in sedimentation occurred in Poyang Lake, beginning sometime after ca. 10,500 yr B.P. and lasting until the middle Holocene (ca. 4000 yr B.P.). At ca. 4000 yr B.P., the regional vegetation was a diverse, broad-leaved forest dominated by many of the same arboreal elements (e.g., Quercus, Castanopsis, Liquidambar) that grow in the area today. A significant reduction of arboreal pollen and an increase of herbaceous pollen at ca. 2000 yr B.P. probably reflect human influence on the vegetation and the expansion of intensive rice agriculture into the dryland forests near the river valleys.

  11. The calculation of climatic indices for Late Quaternary faunal assemblages from South African sites

    NASA Astrophysics Data System (ADS)

    Thackeray, Francis

    2013-04-01

    The relative abundance of rodents and insectivores from several Late Quaternary sites in South Africa have been studied using multivariate analysis (notably factor analysis). The highest loadings on the first factor (F1) are obtained for taxa that are today found in warm subtropical environments, contrasting with taxa which have low F1 loadings and which are today distributed in more southerly latitudes and at high altitudes. The latter taxa with low loadings on F1 are able to tolerate cold conditions (and are relatively common in Terminal Pleistocene assemblages associated with Oxygen Isotope Stage 2). A summary statistic based on F1 (SSF1) is calculated and interpreted as a temperature index. The dated temperature indices for Boomplaas cave correlate well (r=0.95) with dated deuterium isotope ratios for a Vostok core in Antarctica. Similarly, a moisture index (SSF3) is calculated from factor analysis of the relative abundances of the same faunal assemblages. The results are assessed in terms of a non-linear pattern of variability in temperature and moisture indices calculated from pollen as well as mammalian microfauna. The changes in climate are likely to have influenced the distribution and abundance of human populations in the Late Pleistocene in southern Africa.

  12. Dynamics of Mediterranean late Quaternary fluvial activity: An example from the River Ebro (north Iberian Peninsula)

    NASA Astrophysics Data System (ADS)

    Soria-Jáuregui, Ángel; González-Amuchástegui, María José; Mauz, Barbara; Lang, Andreas

    2016-09-01

    Late Pleistocene and Holocene fluvial evolution of the upper River Ebro (Miranda basin, north Spain) is analysed using geomorphological, sedimentological, and optical dating techniques. Maximum regional crustal uplift of 0.98 m/ka approximately helped preserve a suite of terraces in the Miranda basin: 5 river terraces (T1-5) were identified and their formation attributed to MIS 6 (T1), MIS 5d (T2), MIS 4 (T3), MIS 2 (T4), MIS 1 (T5). Alluvium deposited in terraces T1, T2, T3, and T4 is well-sorted, clast-supported gravels; whereas the T5 deposit is exclusively composed of silt. Gravels were deposited during cold and dry periods when reduced vegetation cover on hillslopes increased sediment supply to the trunk river. Silt was deposited in overbank settings under warmer and wetter climate conditions when vegetation cover stabilised hillslopes and restricted sediment supply. It also resulted in lower peak discharge and reduced flow velocities over vegetated floodplains. The chronological sequence of terraces indicates that incision occurred during climatic transitions. We conclude that the upper River Ebro responded to fluctuations in sediment supply and discharge controlled by late Quaternary climate cycles.

  13. Late Quaternary dietary shifts of the Cape grysbok ( Raphicerus melanotis) in southern Africa

    NASA Astrophysics Data System (ADS)

    Faith, J. Tyler

    2011-01-01

    The Cape grysbok is endemic to southern Africa's Cape Floral Region where it selectively browses various species of dicotyledonous vegetation. Fossil evidence indicates that the grysbok persisted under glacial and interglacial conditions throughout the late Quaternary and inhabited a range of environments. This study employs mesowear analysis to reconstruct grysbok diets over time and in response to changing environments at Nelson Bay Cave, Die Kelders Cave 1, Klasies River Mouth, and Swartklip 1. Results indicate that the amount of grasses (monocots) versus leafy vegetation (dicots) included in the diet fluctuated over time and largely in agreement with changes in faunal community structure. The case for dietary flexibility is particularly clear at Nelson Bay Cave, where there is a significant trend from mixed feeding towards increased browsing from the late Pleistocene (~ 18,500 14C yr BP) through the Holocene. Dietary shifts at Nelson Bay Cave are consistent with the hypothesis that declining grassland productivity is responsible for the terminal Pleistocene extinction of several large ungulates in southern Africa. Furthermore, the short-term dietary shifts demonstrated here (100s to 1000s of years) provide an important caution against relying on taxonomic uniformitarianism when reconstructing the dietary preferences of fossil ungulates, both extant and extinct.

  14. Late-Quaternary Dynamics of Temperate Forests: Applications of Paleoecology to Issues of Global Environmental Change

    NASA Astrophysics Data System (ADS)

    Delcourt, Paul A.; Delcourt, Hazel R.

    Paleoecological evidence recently summarized from 162 fossil-pollen sites in eastern North America provides new insights concerning the nature and rate of response of temperate forest ecosystems to late Pleistocene and Holocene environmental changes. Across this subcontinental region (25°N to 60°N; 50°W to 100°W), temperate forests have changed in composition, location and area occupied in adjustment to major episodes of climatic cooling and warming during glacial-interglacial cycles of the Quaternary. Forest taxa have migrated differentially, reflecting their individualistic life-history characteristics, dispersal and competitive abilities, and tolerance thresholds to environmental changes, as well as the geographic distribution of corridors and barriers to plant migration. Gradient analysis and ecological ordination of paleovegetational data illustrate that: (1) both positions and breadth of major vegetational ecotones have shifted latitudinally over the past 20 ka; (2) good modern analogues exist for certain full-glacial warm-temperate and boreal forests; (3) during the transition from Pleistocene to Holocene conditions, mixed conifer-northern hardwoods forests, spreading across newly deglaciated terrain, lacked good analogues within the modern vegetation; and (4) most cool-temperate deciduous forest communities north of 35°N developed in the Holocene. Forest clearance and cultivation by Native Americans along principal riverways resulted in a transformation from natural to cultural landscapes during the mid- and late Holocene intervals. Fragmentation of temperate forests accelerated with the onset of EuroAmerican settlement and technologic developments after the Industrial Revolution.

  15. Sedimentary development and correlation of Late Quaternary terraces in the Kyrenia Range, northern Cyprus, using a combination of sedimentology and optical luminescence data

    NASA Astrophysics Data System (ADS)

    Palamakumbura, Romesh N.; Robertson, Alastair H. F.; Kinnaird, Tim C.; Sanderson, David C. W.

    2016-01-01

    This study focuses on the younger of a series of Quaternary terraces along the flanks of the Kyrenia Range in northern Cyprus, specifically the Kyrenia (Girne) and the Koupia terraces. The Kyrenia (Girne) terrace is tentatively correlated with oxygen isotope stage 5 (125 Ka), and the Koupia terrace with oxygen isotope stage 3 (<50 Ka). Along the northern flank of the range, the Kyrenia (Girne) terrace deposits (5-20 m above modern sea level) typically begin with a basal lag conglomerate and then pass upwards into shallow-marine calcarenites and then into variable aeolianites, paleosols and fluvial deposits (up to 20 m thick). In contrast, the Koupia terrace (<2 m above modern sea level) consists of aeolianites and shallow-marine calcarenites (up to 8 m thick). The equivalent deposits along the southern flank of the range are entirely non-marine fluvial mud, sands and conglomerates. The marine to continental terrace systems can be tentatively correlated based on mapping, height above modern sea level and sedimentary facies. However, variable preservation and patchy exposure require such correlations to be independently tested. To achieve this, a portable optically stimulated luminescence (OSL) reader was used to determine the luminescence characteristics of the two terrace systems. Luminescence profiles show major differences in luminescence characteristics between the two terrace depositional systems, which can be related to sedimentary processes, provenance and age. These features allow sections in different areas to be effectively correlated. Individual sections show luminescence properties that are generally consistent with an expected up-sequence decrease in age. However, the younger Koupia terrace deposits show higher luminescence intensities compared with the older Kyrenia (Girne) terrace deposits. This can be explained by multiple phases of reworking of the Kyrenia (Girne) terrace deposits, which changed the luminescence characteristics of the sediment. The

  16. Shoreline and Lacustrine Records of Late Quaternary Climate Change in the Chihuahuan Desert, Mexico

    NASA Astrophysics Data System (ADS)

    Castiglia, P. J.; Fawcett, P. J.

    2001-12-01

    Spatial and temporal patterns of Quaternary moisture and temperature variability in northern Mexico are difficult to reconstruct given the paucity of continuous, long-term Quaternary climate records from the region. Preliminary shoreline age dates and a pair of lacustrine sediment cores from Laguna Fresnal in northern Chihuahua, Mexico, record climate-driven variations in both lake level and sedimentologic input. Reeves (1969) first described Laguna Fresnal as part of Pluvial Lake Palomas, a Pleistocene lake composed of 3 interconnected sub-basins: Laguna Guzman, Santa Maria, and Fresnal. Six AMS 14C age dates from previously unrecognized lake fauna on a beach ridge complex indicate a number of Holocene lakes as well. These preserved shorelines increase in age with distance and elevation from the playa surface and include early Holocene (8456\\pm97 14C yrs BP; 1225 m asl), middle Holocene (6180\\pm53, 6401\\pm58, and 6721\\pm68 14C yrs BP; 1200 m asl), and Little Ice Age (435\\pm39 14C yrs BP; 1175 m asl) lake stands. These ages correlate with beach ridge chronologies throughout the western US and northern Mexico. However, during the middle Holocene Laguna Fresnal exhibits a pronounced high stand while other records show a prolonged dry episode. Two 17 m-long cores from the basin center provide a continuous record of sedimentation during the late Quaternary. Several abrupt changes in lake level are indicated by mud cracks preserved as sharp, light gray lineations (487-548 cm and 975-1130 cm), sharply overlain by finely laminated silt and clay. Drying episodes are preserved in the basal section of the cores as several 0.5-2 cm-thick gypsum horizons, overlain by 3-5 cm-thick, carbon-poor (0.02-0.05% TOC), light gray silt. Five distinct zones of coupled, alternating relatively high and low average magnetic susceptibility (MS) and bulk density further reveals changes in lacustrine sedimentation. Peaks in MS generally correlate with peaks in bulk density, with the

  17. Raised marine sequences of Lanzarote and Fuerteventura revisited—a reappraisal of relative sea-level changes and vertical movements in the eastern Canary Islands during the Quaternary

    NASA Astrophysics Data System (ADS)

    Zazo, Cari; Goy, José Luis; Hillaire-Marcel, Claude; Gillot, Pierre-Yves; Soler, Vicente; González, José Ángel; Dabrio, Cristino J.; Ghaleb, Bassam

    2002-10-01

    Systematic mapping and morphosedimentary analysis of Fuerteventura and Lanzarote Islands supported by laboratory techniques (U-series mostly by TIMS, 14C analysis and allo-isoleucine measurements on biogenic carbonates from raised marine deposits, paleomagnetic and a few K/Ar measurements on volcanic formations related to marine deposits) provide a basis for constraining the age of Late Cainozoic marine units. The most complete sequences of raised marine terraces are found at similar elevations in both islands. They include up to 12 marine terraces (Episodes) at elevations between 0 m and 70 m above mean sea level (asl). At least six terraces should be of Quaternary age, and more recent than 1.2 Myr. Throughout the whole marine sequence with the exception of the Holocene terrace, the warm fauna assemblage is characterized by the presence of Ostrea virleti, Nerita emiliana, and Strombus ( S. cf. coronatus-S. cf. bubonius). However, there is a major change, highlighted by the disappearance of the first two species, below the 8-10 m terrace, that could possibly correspond to MIS 11. K-Ar measurements allow an estimate for mean uplift rate of 1.7 cm/ka during the last million years. The present elevation of the Last Interglacial deposits (about 1 and 2 m asl) shows discontinuous vertical movements with possibly a reverse trend since MIS 9 in eastern Canary Islands.

  18. Late Quaternary stratigraphy and geochronology of the western Killpecker Dunes, Wyoming, USA

    USGS Publications Warehouse

    Mayer, J.H.; Mahan, S.A.

    2004-01-01

    New stratigraphic and geochronologic data from the Killpecker Dunes in southwestern Wyoming facilitate a more precise understanding of the dune field's history. Prior investigations suggested that evidence for late Pleistocene eolian activity in the dune field was lacking. However, luminescence ages from eolian sand of ???15,000 yr, as well as Folsom (12,950-11,950 cal yr B.P.) and Agate Basin (12,600-10,700 cal yr) artifacts overlying eolian sand, indicate the dune field existed at least during the latest Pleistocene, with initial eolian sedimentation probably occurring under a dry periglacial climate. The period between ???13,000 and 8900 cal yr B.P. was characterized by relatively slow eolian sedimentation concomitant with soil formation. Erosion occurred between ???8182 and 6600 cal yr B.P. on the upwind region of the dune field, followed by relative stability and soil formation between ???5900 and 2700 cal yr B.P. The first of at least two latest Holocene episodes of eolian sedimentation occurred between ???2000 and 1500 yr, followed by a brief (???500 yr) episode of soil formation; a second episode of sedimentation, occurring by at least ???700 yr, may coincide with a hypothesized Medieval warm period. Recent stabilization of the western Killpecker Dunes likely occurred during the Little Ice Age (???350-100 yr B.P.). The eolian chronology of the western Killpecker Dunes correlates reasonably well with those of other major dune fields in the Wyoming Basin, suggesting that dune field reactivation resulted primarily due to departures toward aridity during the late Quaternary. Similar to dune fields on the central Great Plains, dune fields in the Wyoming Basin have been active under a periglacial climate during the late Pleistocene, as well as under near-modern conditions during the latest Holocene. ?? 2003 University of Washington. All rights reserved.

  19. Lake sediments documented late Quaternary humid pulses in the Gobi Desert of southern Mongolia: Vegetation, hydrologic and paleoglaciation inferences

    NASA Astrophysics Data System (ADS)

    Yu, Kaifeng; Lehmkuhl, Frank; Schlütz, Frank; Diekmann, Bernhard; Mischke, Steffen; Grunert, Jörg; Murad, Waheed; Nottebaum, Veit; Stauch, Georg

    2016-04-01

    Considerable efforts have been devoted to decipher the late Quaternary moisture and thermal history of the arid central Asia. However, an array of paramount aspects has inhibited our complete understanding of the broad pattern and underlying mechanisms: (i) Biased or even contradictory conclusions may be achieved due to the interpretations of different proxies. (ii) Most of the works poured attention into Holocene period, only few records can extend back to earlier marine isotope stages. (iii) Substantial spatial heterogeneity is noteworthy in the area. Exceeding amounts of studies were carried out in Lake Baikal catchments, northern and western Mongolia, while only two works were hitherto conducted in southern Mongolia. (iv) It remains elusive with respect to how and to what extent have East Asian Summer Monsoon and Westerlies affected the thermal and moisture signals in this spectacular arid region. To address this set of issues, two parallel cores (ONW I, 6.00 m; ONW II, 13.36 m) were retrieved from Orog Nuur, Gobi Desert of southern Mongolia. An array of multidisciplinary investigations involving geomorphologic mapping, radiocarbon dating, geochemical and biotic studies (i.e., palynological and ostracod valve analyses) provide a comprehensive data set for inferences of hydrological perturbations, vegetation development and phases of glacier expansions over the last ~50 ka. Orog Nuur catchment depicted a broadly vulnerable ecosystem that was dominated by Artemisia steppe community in the late Pleistocene, and Chenopodiaceae desert steppe in the Holocene. In addition, the Termination I is ideally documented in a complete suite of geochemical, palynological, and ostracod signatures. In general, the thermal and moisture history in the Gobi Desert were as follows: (i) MIS3 had a relatively warm temperature and sufficient moisture supply in particular between ~40 ka and ~26 ka; (ii) The MIS2 was subject to cold temperature and moisture deficit, which was interrupted

  20. Late Quaternary environmental change in the African sector of Southern Hemisphere mid-latitudes: trends and teleconnections. (Invited)

    NASA Astrophysics Data System (ADS)

    Chase, B. M.

    2013-12-01

    At the northern boundary of the Southern Hemisphere westerly wind belt, and the northern limit of the related frontal systems, SW African environments are particularly sensitive to variations in mid-latitude oceanic and atmospheric circulation systems. It has long been postulated that during relatively cold periods of the late Quaternary, SW Africa - if not much of southern Africa - has experienced an increase in the precipitation linked to phenomena related to an equatorward shift/expansion of the westerly storm track (for review see Chase and Meadows, 2007, Earth-Science Reviews). However, a reliable chain of evidence to support this hypothesis has been elusive, and studies from both the data and modelling communities have yet to resolve the debate. This paper will present the state-of the-art in our understanding of how environments in SW Africa have changed during the course of the last glacial-interglacial cycle. New evidence from both the marine and terrestrial realms, particularly in the form of high resolution stable isotope and pollen records obtained from fossilised rock hyrax middens (Chase et al., 2012, Quaternary Science Reviews; www.hyrax.univ-montp2.fr), is providing a detailed, and coherent, but complex picture of climate dynamics and forcing mechanisms along the northern boundary of westerly influence. While records from the continental interior remain rare, and thus the degree to which an expansion of the westerlies may have influenced southern Africa as a whole remains to be adequately resolved, sites from the SW continental margin do appear to indicate that shifts of the oceanic Subtropical Front and westerly storm track strongly affect the amount of precipitation the region receives. The dynamics of this system, however, do not operate in isolation, and conditions north of the Subtropical Front are very sensitive to variations in the position and intensity of the South Atlantic Anticyclone, which appears to be most responsive to changes in

  1. Late Quaternary river incision rate from L'Aquila-Scoppito Basin (central Apennines, Italy)

    NASA Astrophysics Data System (ADS)

    Nocentini, Marco; Tallini, Marco; Asti, Riccardo; Cosentino, Domenico

    2014-05-01

    L'Aquila-Scoppito Basin (ASB) is part of the wider L'Aquila Basin, one of the most tectonically active intermontane basins of central Apennines (Italy). ASB is a semi-enclosed intermontane sedimentary basin of morphotectonic origin, W-E trending and approximately 20 km2 wide, with mean elevations ranging between 850 and 650 m a.s.l. and it is crossed by two main water courses: the Aterno River and the Raio Creek. Structurally, the ASB may be considered as an half-graben, bordered northerly by the south-dipping Scoppito-Preturo normal Fault and easterly by the southwest dipping Pettino Fault. In the L'Aquila-Scoppito Basin a series of erosional and depositional post Middle Pleistocene events generated three order of fluvial terraces, generally not completely preserved. The first order of fluvial terrace, the Vetoio Synthem (T1), is a fill terrace carved into both the L'Aquila Breccia Synthem (Middle Pleistocene) and the Madonna della Strada Synthem (Lower Pleistocene), whose top is preserved near the L'Aquila airport and the S. Salvatore hospital, approximately at 20-25 m above the present thalweg of the Aterno River. The second order of terrace, the Pile Synthem (T2), is a strath terrace embedded into T1 and carved into both the Lower Pleistocene deposits and the pre-Quaternary bedrock. The top of T2 is located at 10-13 m above the present thalweg of the Raio Creek. Charcoaled plant remains founded within the sandy layers of T2 give a 14C 2σ age of 41854-40464 BP (MIS 3). This age is in agreement with traces of lithic industry of Mousterian age (late Middle Paleolithic) inside the gravels. The youngest order of terrace, Ponte Peschio Synthem (T3), lies 5-7 m above both the Raio and the Aterno thalwegs. T3 is embedded into T1 and carved in the L'Aquila Breccia Synthem, near the S. Salvatore hospital, while at Ponte Peschio it is embedded into T2 and is carved directly into the pre-Quaternary bedrock. Then, also T3 may be interpreted as a strath terrace. River

  2. Los Angeles Seismotectonics: Evidence from Shotgun Seismicity Patterns and the Gridlock of Late Quaternary Faults and Folds

    NASA Astrophysics Data System (ADS)

    Hauksson, E.; Michael, A.

    2001-12-01

    The high tectonic strain rates in the Los Angeles region are caused by the San Andreas fault to the north that strikes more westerly than the relative plate motion velocity, and secondary effects such as basin formation, and possibly the upper mantle drip beneath the Transverse Ranges. The last 25 years of background seismicity in this region is spatially scattered and cannot easily be associated with the complex network of existing late Quaternary faults or folds. To explain the regionally distributed seismicity and faulting patterns we propose the following model of seismotectonic deformation for the Los Angeles region. First, the regional tectonic strain loading is spread almost uniformly from east to west across the region, causing only minor variations in the loading rate of late Quaternary faults. Second, these late Quaternary faults that have cumulative offsets of at least few kilometers are aseismic during the interseismic period and only accommodate large earthquakes. Third, most of the late Quaternary faults have similar slip rate and are of similar importance for accommodating crustal deformation, and thus have similar repeat times for large earthquakes. Fourth, the background seismicity mostly accommodates secondary deformation associated with geometrical complexities of existing geological structures. In a few cases the background seismicity however, forms halos around the faults suggesting narrow central locked fault zones and an adjacent seismic zone of ongoing buildup of tectonic strain. To refine these patterns of seismicity we have relocated the last 25 years of Los Angeles seismicity using double-difference earthquake location methods to refine hypocenters based on three-dimensional velocity models to obtain high-resolution hypocenters. These DD hypocenters provide improved resolution of seismicity patterns and facilitate improved association between seismicity and late Quaternary faults and active geological structures. The background seismicity

  3. Chronology of late Quaternary glaciation and landform evolution in the upper Dhauliganga valley, (Trans Himalaya), Uttarakhand, India

    NASA Astrophysics Data System (ADS)

    Bisht, Pinkey; Ali, S. Nawaz; Shukla, Anil D.; Negi, Sunil; Sundriyal, Y. P.; Yadava, M. G.; Juyal, Navin

    2015-12-01

    Detailed field mapping of glacial and paraglacial landforms supported by optical and radiocarbon dating is used to reconstruct the history of late Quaternary glaciation and landform evolution in the Trans Himalayan region of the upper Dhauliganga valley. The study identifies four events of glaciations with decreasing magnitude which are termed as Purvi Kamet Stage -Ia (PKS-Ia), PKS-Ib, PKS-II, PKS-III and PKS-IV respectively. The oldest PKS-Ia and Ib are assigned the Marine Isotopic Stgae-3 (MIS-3), the PKS-II to the Last Glacial Maximum (MIS-2), PKS-III dated to 7.9 ± 0.7 ka, and the PKS-IV is dated to 3.4 ± 0.3 ka and 1.9 ± 0.2 ka respectively. The largest valley glaciations viz. the (PKS-Ia) occurred during the strengthened summer monsoon corresponding to the MIS-3, following this, the recessional moraines (PKS-Ib) represent the gradual decline in summer monsoon towards the later part of MIS-3. The valley responded to the global Last Glacial Maximum (LGM), which is represented by the PKS-II moraine implying the influence of strengthened mid-latitude westerlies during the LGM. The post-LGM deglaciation was associated with the onset of summer monsoon and is represented by the deposition of four distinct outwash gravel terraces. The early Holocene PKS-III glaciation occurred around 7.9 ± 0.7 ka and broadly coincides with the early Holocene cooling event (8.2 ka). This was followed by the deposition of stratified scree deposits and the alluvial fan (between 5.5 ka and 3 ka) during the mid to late Holocene aridity. This was followed by marginal re-advancement of the valley glacier (viz. PKS-IV) during the late Holocene cool and moist climate. Although glaciers respond to a combination of temperature and precipitation changes, however during the Holocene it seems that temperature played a major role in driving the glaciation.

  4. Late Quaternary development of the Croatan Beach Ridge Complex, Bogue Sound, Bogue Banks, NC, USA and implications for coastal evolution

    NASA Astrophysics Data System (ADS)

    Lazar, Kelly B.; Mallinson, David J.; Culver, Stephen J.

    2016-06-01

    Foraminiferal, sedimentological, geophysical, and geochronologic data were utilized to elucidate the late Quaternary geologic development of the Croatan Beach Ridge Complex (CBRC), Bogue Sound, and Bogue Banks, North Carolina, USA. The CBRC is a relict beach ridge feature located on the mainland. It is separated from the modern barrier island, Bogue Banks, by Bogue Sound. Seventeen cores along shore-normal and shore-parallel transects provided material for sedimentologic and foraminiferal analysis and resulted in the recognition of seven depositional facies representing a variety of coastal depositional environments. Chronologic and depositional facies data suggest the CBRC was initiated during MIS 5a and rapid southward progradation produced a cape structure. Eolian reactivation of the upper sand of the CBRC occurred during the last glacial maximum (∼18 ka). The age of flood tide delta deposits in Bogue Sound suggests that the Holocene barrier island, Bogue Banks, had formed by ∼6 ka. Shoreface ravinement resulted in a shoreface landward of the present shoreline by ∼3.5 ka. Seaward and westward spit progradation of Bogue Banks began ∼1.7 ka and continued to ∼1.3 ka. Normal marine salinity conditions were present in Bogue Sound ∼1.1 ka, suggesting removal of at least the narrowest parts of the barrier island, coeval with a previously documented segmentation of the southern Outer Banks barrier islands. Previous work has linked this segmentation to climate warming and increased tropical storm activity during the Medieval Climate Anomaly. This study illustrates the complex response of this coastal system to Pleistocene and Holocene sea-level and climate change over two major sea-level cycles. In particular, the regional geomorphology during MIS5a and the Holocene sea-level highstand differ significantly and this, in large part, was controlled by the antecedent geologic framework, resulted in the contrasting more localized coastal geomorphic response.

  5. Late Quaternary development of the Croatan Beach Ridge Complex, Bogue Sound, Bogue Banks, NC, USA and implications for coastal evolution

    NASA Astrophysics Data System (ADS)

    Lazar, Kelly B.; Mallinson, David J.; Culver, Stephen J.

    2016-06-01

    Foraminiferal, sedimentological, geophysical, and geochronologic data were utilized to elucidate the late Quaternary geologic development of the Croatan Beach Ridge Complex (CBRC), Bogue Sound, and Bogue Banks, North Carolina, USA. The CBRC is a relict beach ridge feature located on the mainland. It is separated from the modern barrier island, Bogue Banks, by Bogue Sound. Seventeen cores along shore-normal and shore-parallel transects provided material for sedimentologic and foraminiferal analysis and resulted in the recognition of seven depositional facies representing a variety of coastal depositional environments. Chronologic and depositional facies data suggest the CBRC was initiated during MIS 5a and rapid southward progradation produced a cape structure. Eolian reactivation of the upper sand of the CBRC occurred during the last glacial maximum (∼18 ka). The age of flood tide delta deposits in Bogue Sound suggests that the Holocene barrier island, Bogue Banks, had formed by ∼6 ka. Shoreface ravinement resulted in a shoreface landward of the present shoreline by ∼3.5 ka. Seaward and westward spit progradation of Bogue Banks began ∼1.7 ka and continued to ∼1.3 ka. Normal marine salinity conditions were present in Bogue Sound ∼1.1 ka, suggesting removal of at least the narrowest parts of the barrier island, coeval with a previously documented segmentation of the southern Outer Banks barrier islands. Previous work has linked this segmentation to climate warming and increased tropical storm activity during the Medieval Climate Anomaly. This study illustrates the complex response of this coastal system to Pleistocene and Holocene sea-level and climate change over two major sea-level cycles. In particular, the regional geomorphology during MIS5a and the Holocene sea-level highstand differ significantly and this, in large part, was controlled by the antecedent geologic framework, resulted in the contrasting more localized coastal geomorphic response.

  6. Late quaternary sea level changes of Gabes coastal plain and shelf: Identification of the MIS 5c and MIS 5a onshore highstands, southern Mediterranean

    NASA Astrophysics Data System (ADS)

    Gzam, Maher; Mejdoub, Noureddine El; Jedoui, Younes

    2016-02-01

    The continental shelf of the Gulf of Gabes is outlined, during the MIS 5c and MIS 5a onshore highstands, by the genesis of forced regressive beach ridges situated respectively at -19 m b.s.l/100 ka and -8 m b.s.l/80 ka. This area, considered as a stable domain since at least the last 130 ka (Bouaziz et al. 2003), is a particular zone for the reconstruction of the late quaternary sea-level changes in the region. Shuttle Radar Topography Mission (SRTM) data and field observations are highlighted to deduce interaction between hydrodynamic factors and antecedent topography. Variations in geomorphology were attributed to geological inheritance. Petrography and sedimentary facies of the submerged coastal ridges reveal that the palaeocoastal morphology was more agitated than today and the fluvial discharges are consistent. Actual morphologic trend deduced from different environment coasts (sandy coasts, sea cliffs and tidal flat) is marked by accumulation of marine sands and progradation.

  7. Salt lake Laguna de Fuente de Piedra (S-Spain) as Late Quaternary palaeoenvironmental archive

    NASA Astrophysics Data System (ADS)

    Höbig, Nicole; Melles, Martin; Reicherter, Klaus

    2014-05-01

    This study deals with Late Quaternary palaeoenvironmental variability in Iberia reconstructed from terrestrial archives. In southern Iberia, endorheic basins of the Betic Cordilleras are relatively common and contain salt or fresh-water lakes due to subsurface dissolution of Triassic evaporites. Such precipitation or ground-water fed lakes (called Lagunas in Spanish) are vulnerable to changes in hydrology, climate or anthropogenic modifications. The largest Spanish salt lake, Laguna de Fuente de Piedra (Antequera region, S-Spain), has been investigated and serves as a palaeoenvironmental archive for the Late Pleistocene to Holocene time interval. Several sediment cores taken during drilling campaigns in 2012 and 2013 have revealed sedimentary sequences (up to 14 m length) along the shoreline. A multi-proxy study, including sedimentology, geochemistry and physical properties (magnetic susceptibility) has been performed on the cores. The sedimentary history is highly variable: several decimetre thick silty variegated clay deposits, laminated evaporites, and even few-centimetre thick massive gypsum crystals (i.e., selenites). XRF analysis was focussed on valuable palaeoclimatic proxies (e.g., S, Zr, Ti, and element ratios) to identify the composition and provenance of the sediments and to delineate palaeoenvironmental conditions. First age control has been realized by AMS-radiocarbon dating. The records start with approximately 2-3 m Holocene deposits and reach back to the middle of MIS 3 (GS-3). The sequences contain changes in sedimentation rates as well as colour changes, which can be summarized as brownish-beige deposits at the top and more greenish-grey deposits below as well as highly variegated lamination and selenites below ca. 6 m depth. The Younger Dryas, Bølling/Allerød, and the so-called Mystery Interval/Last Glacial Maximum have presumably been identified in the sediment cores and aligned to other climate records. In general, the cores of the Laguna de

  8. Late Quaternary Tephrostratigraphy of South-Central Chile (~ 38 - 40 °S)

    NASA Astrophysics Data System (ADS)

    Fontijn, K.; Rawson, H. L.; Van Daele, M. E.; Moernaut, J.; Abarzúa, A. M.; Pyle, D. M.; Mather, T. A.; De Batist, M. A. O.; Moreno-Roa, H.; Naranjo, J. A.

    2014-12-01

    The volcanoes of the Siete Lagos region ("Lake District") in South-Central Chile form part of the Southern Volcanic Zone of the Andes and include some of the most active volcanoes in South America, i.e. Villarrica and Llaima. The Late Quaternary (~ last 15 ka) regional tephrostratigraphic record for this region is however still poorly developed. We combine detailed stratigraphic logging of terrestrial sections in the vicinity of Llaima, Sollipulli, Villarrica, Quetrupillan, Mocho-Choshuenco and Puyehue-Cordón Caulle volcanoes with petrological, whole-rock and glass geochemical data, and 14C dating on charcoal entrained in volcanic deposits, and correlate the on-land sequences with tephra layers in existing 14C-dated lacustrine records of Laguna Las Ranas and Lagos Villarrica, Calafquén and Riñihue. The combined record includes previously described major eruptions, e.g. Llaima Pumice (Llaima) and Alpehue Pumice (Sollipulli), which help to constrain the relative timing of events. These correlations suggest that several widespread volcanic units are several hundreds to thousands of years older than previously thought. The record also includes newly described pumice-producing events, e.g. for the poorly studied Quetrupillan volcano, and provides new insights into the post-glacial eruptive frequency in the Southern Volcanic Zone. The newly updated stratigraphy with high-quality geochemical data also contributes to the regional tephrochronological framework which helps to significantly improve age models for lacustrine palaeoseismological and palaeoenvironmental archives.

  9. A Mid-Late Quaternary loess-paleosol record in Simmons Farm in southern Illinois, USA

    USGS Publications Warehouse

    Wang, Hongfang; Lundstrom, C.C.; Zhang, Z.; Grimley, D.A.; Balsam, W.L.

    2009-01-01

    In unglaciated areas of the Mississippi Valley region, the typical full loess-paleosol succession contains the Modern Soil developed in Peoria Silt, weakly developed Farmdale Geosol developed in Roxana Silt, Sangamon Geosol developed in Loveland Silt, and Yarmouth Geosol developed in Crowley's Ridge Silt. Although a fifth loess called the Marianna Silt is reported at one area, the paleosol that separates the Crowley Ridge and Marianna Silts is not well defined. Previous thermoluminescence (TL) and optical stimulated luminescence (OSL) age chronology has suggested multiple phases of Sangamon Geosol developed in Loveland Silt, but clear morphological evidence of polygenetic Sangamon Geosol profiles have not been found. Recently, a thick loess-paleosol sequence has been studied in the middle Mississippi Valley in unglaciated southern Illinois, USA. Soil morphology and analytical results revealed five loesses and associated paleosol units. Two Sangamon Bt horizons were found separated by a thick ACtk horizon, interpreted to indicate two phases of Sangamon Geosol development. This well-preserved loess-paleosol succession provides one of the most complete mid-late Quaternary loess records in the middle Mississippi Valley to date, and is important for studying the stratigraphic framework and paleoclimate and environment changes. ?? 2008 Elsevier Ltd. All rights reserved.

  10. Late quaternary history and uranium isotopic compositions of ground water discharge deposits, Crater Flat, Nevada

    SciTech Connect

    Paces, J.B.; Taylor, E.M.; Bush, C.

    1993-12-31

    Three carbonate-rich spring deposits are present near the southern end of Crater Flat, NV, approximately 18 km southwest of the potential high-level waste repository at Yucca Mountain. We have analyzed five samples of carbonate-rich material from two of the deposits for U and Th isotopic compositions. Resulting U-series disequilibrium ages indicate that springs were active at 18 {+-} 1, 30 {+-} 3, 45 {+-} 4 and >70 ka. These ages are consistent with a crude internal stratigraphy at one site. Identical ages for two samples at two separate sites suggest that springs were contemporaneous, at least in part, and were most likely part of the same hydrodynamic system. In addition, initial U isotopic compositions range from 2.8 to 3.8 and strongly suggest that ground water from the regional Tertiary-volcanic aquifer provided the source for these hydrogenic deposits. This interpretation, along with water level data from near-by wells suggest that the water table rose approximately 80 to 115 m above present levels during the late Quaternary and may have fluctuated repeatedly. Current data are insufficient to allow reconstruction of a detailed depositional history, however geochronological data are in a good agreement with other paleoclimatic proxy records preserved throughout the region. Since these deposits are down gradient from the potential repository site, the possibility of higher ground water levels in the future dramatically shortens both vertical and lateral ground water pathways and reduces travel times of transported radionuclides to potential discharge sites.

  11. Vertical tectonics in northern Escanaba Trough as recorded by thick late Quaternary turbidites

    USGS Publications Warehouse

    Normark, W.R.; Serra, F.

    2001-01-01

    Escanaba Trough, the southernmost segment of the Gorda Ridge, is filled by as much as 500 m of late Quaternary turbidite and hemipelagic sediment. Coring at Deep Sea Drilling Project Site 35 and Ocean Drilling Program (ODP) Sites 1037 and 1038 together with 4.5-kHz deep-tow and 3.5-kHz surface-ship seismic reflection profiles enable a distinct pattern of reflections to be mapped throughout Escanaba Trough in the upper part of this sediment fill. The uppermost 80 m of turbidite sediment, which includes at least 11 turbidity current events, were deposited in 3200 m. The turbidity currents were trapped upon entering Escanaba Trough, resulting in all of the sediment in suspension in the flows being deposited. The thickness of the turbidite layers reflects both the flow thickness and the vertical grain concentration within the flow that deposited the layer. Variations in the turbidite thickness with respect to water depth can be used to estimate the degree of relative vertical movement within the floor of Escanaba Trough. In the area of hydrothermal activity near ODP Site 1038, uplift of as much as 140 m has occurred over the past 8 kyr. Copyright 2001 by the American Geophysical Union.

  12. Species-specific responses of Late Quaternary megafauna to climate and humans.

    PubMed

    Lorenzen, Eline D; Nogués-Bravo, David; Orlando, Ludovic; Weinstock, Jaco; Binladen, Jonas; Marske, Katharine A; Ugan, Andrew; Borregaard, Michael K; Gilbert, M Thomas P; Nielsen, Rasmus; Ho, Simon Y W; Goebel, Ted; Graf, Kelly E; Byers, David; Stenderup, Jesper T; Rasmussen, Morten; Campos, Paula F; Leonard, Jennifer A; Koepfli, Klaus-Peter; Froese, Duane; Zazula, Grant; Stafford, Thomas W; Aaris-Sørensen, Kim; Batra, Persaram; Haywood, Alan M; Singarayer, Joy S; Valdes, Paul J; Boeskorov, Gennady; Burns, James A; Davydov, Sergey P; Haile, James; Jenkins, Dennis L; Kosintsev, Pavel; Kuznetsova, Tatyana; Lai, Xulong; Martin, Larry D; McDonald, H Gregory; Mol, Dick; Meldgaard, Morten; Munch, Kasper; Stephan, Elisabeth; Sablin, Mikhail; Sommer, Robert S; Sipko, Taras; Scott, Eric; Suchard, Marc A; Tikhonov, Alexei; Willerslev, Rane; Wayne, Robert K; Cooper, Alan; Hofreiter, Michael; Sher, Andrei; Shapiro, Beth; Rahbek, Carsten; Willerslev, Eske

    2011-11-17

    Despite decades of research, the roles of climate and humans in driving the dramatic extinctions of large-bodied mammals during the Late Quaternary period remain contentious. Here we use ancient DNA, species distribution models and the human fossil record to elucidate how climate and humans shaped the demographic history of woolly rhinoceros, woolly mammoth, wild horse, reindeer, bison and musk ox. We show that climate has been a major driver of population change over the past 50,000 years. However, each species responds differently to the effects of climatic shifts, habitat redistribution and human encroachment. Although climate change alone can explain the extinction of some species, such as Eurasian musk ox and woolly rhinoceros, a combination of climatic and anthropogenic effects appears to be responsible for the extinction of others, including Eurasian steppe bison and wild horse. We find no genetic signature or any distinctive range dynamics distinguishing extinct from surviving species, emphasizing the challenges associated with predicting future responses of extant mammals to climate and human-mediated habitat change. PMID:22048313

  13. A high-resolution geochemical record of Late Quaternary paleohydrological conditions from Chihuahuan Desert, Mexico

    NASA Astrophysics Data System (ADS)

    Quiroz-Jiménez, J.; Roy, P.

    2013-05-01

    Paleolake Babicora is located at 29°N in the northern Mexico and sediments deposited in the basin provide useful information about the late Quaternary paleohydrological conditions of Chihuahuan Desert. The proxy-records of productivity, pluvial discharge into the basin, lake water salinity and aeolian activity in surroundings of the basin over the last 80 cal ka BP were reconstructed by analyzing the concentrations of total organic carbon, carbonates, C/N, Ti, Sr and Zr/Al in a 976 cm long sediment core. During 80-58 cal ka BP, the pluvial discharge was higher and the water column was characterized by lower salinity (wet conditions). Terrestrial vegetation had higher influence on the organic carbon deposited between 71 and 53 cal ka BP. We record paleohydrological instability with millennial-scale fluctuations in the last 40 cal ka BP. Arid conditions possibly reached its maximum at ca. 40 cal ka BP, characterized with a hiatus in sedimentation related to aeolian activity. Comparison between the paleohydrological record from Babicora and variability of winter precipitation from southwest USA suggest that the runoff into Babicora was controlled by summer season precipitation. The periods of more pluvial discharge were contemporary to the north Atlantic interstadials and vice versa.

  14. Enhanced insights into late Quaternary African hydroclimate dynamics using a water-isotope enabled climate model

    NASA Astrophysics Data System (ADS)

    Singarayer, Joy; Holloway, Max

    2016-04-01

    The climate of intertropical Africa is strongly governed by the dynamics of the tropical rainbelt, which is often associated with the Intertropical Convergence Zone (ITCZ). On millennial time-scales the primary drivers of variation in the rainbelt include orbital configuration changes to insolation seasonality and high-latitude forcing (e.g. Heinrich events). The spatial pattern of precipitation variability in tropical and subtropical Africa over the late Quaternary is complex and has long been debated. Stable water isotopes from inland lakes and off-shore ocean core records have provided longitudinal records, variously interpreted as changes to precipitation intensity or changes to moisture source location due to atmospheric circulation changes (or a combination of several factors). In this preliminary study we have used a global climate model, HadCM3, in which water isotopes are interactively coupled to produce snapshots at 1000-year intervals covering the last deglaciation (21kyr to pre-industrial). In conjunction with a comparison to available palaeodata, this enables us to better elucidate the connections between precipitation and other climate factors with changes to the water isotope signature, as well as how this varies regionally and through time.

  15. Identification of a late Quaternary alluvial-aeolian sedimentary sequence in the Sichuan Basin, China

    NASA Astrophysics Data System (ADS)

    Feng, Jin-Liang; Ju, Jian-Ting; Chen, Feng; Hu, Zhao-Guo; Zhao, Xiang; Gao, Shao-Peng

    2016-03-01

    The late Quaternary sedimentary sequence in the northwestern part of the Sichuan Basin consists of five lithological units and with increasing depth include the: Chengdu Clay; Brown Clay; Red Clay; Sandy Silt; and basal Muddy Gravel. The genesis, provenance and age of the sediments, as well as the possible presence of hiatuses within this sequence are debated. Measurements of grain-size, magnetic susceptibility, quartz content, quartz δ18O values, element composition, and Sr-Nd isotopic concentrations of samples from a typical sedimentary sequence in the area provides new insights into the genesis and history of the sequence. The new data confirm that the sediments in study site are alluvial-aeolian in origin, with basal alluvial deposits overlain by aeolian deposits. Like the uppermost Chengdu Clay, the underlying Brown Clay and Red Clay are aeolian in origin. In contrast, the Silty Sand, like the basal Muddy Gravel, is an alluvial deposit and not an aeolian deposit as previously thought. Moreover, the succession of the aeolian deposits very likely contains two significant sedimentary hiatuses. Sedimentological analysis demonstrates that the source materials for the aeolian deposits in the northwestern part of the Sichuan Basin and those on the eastern Tibetan Plateau are different. Furthermore, the loess deposits on the eastern Tibetan Plateau are derived from heterogeneous local sources.

  16. Two late quaternary pollen records from the upper Kolyma region, Soviet Northeast: A preliminary report

    SciTech Connect

    Anderson, P.M.; Brubaker, L.; Andreev, A.A.; Chernenky, B.I.; Federova, I.N.

    1992-03-01

    Pollen records from Sosednee and Elikchan Lakes provide the first continuous late Quaternary vegetation history for the upper Kolyma drainage of the Soviet Northeast. Full-glacial spectra at these sites are similar to those from Eastern Beringia, with high percentages of grass, sedge, and wormwood pollen indicative of herb tundra. In the Elikchan area at approximately 12,500 B.P., herb tundra was replaced by a stone pine-larch forest, perhaps similar to forests in the modern region. In contrast, the herb tundra near Sosednee Lake was succeeded by a birch-alder shrub tundra followed by a larch woodland. Stone pine increased in the region after larch and prior to 8600 B.P. A Holocene decline in stone pine, which is evident at Elikchan Lake, is less marked or absent at Sosednee Lake. The differences in these pollen records is somewhat surprising given the proximity of the two sites. Such differences indicate that numerous well-dated sites will be needed to describe the vegetation and climate histories of Western Beringia.

  17. Eolian additions to late Quaternary alpine soils, Indian Peaks Wilderness Area, Colorado Front Range

    USGS Publications Warehouse

    Muhs, D.R.; Benedict, J.B.

    2006-01-01

    Surface horizons of many alpine soils on Quaternary deposits in high-mountain settings are enriched in silt. The origin of these particles has been debated, particularly in the Rocky Mountain region of North America. The most common explanations are frost shattering of coarser particles and eolian additions from distant sources. We studied soil A horizons on alpine moraines of late-glacial (Satanta Peak) age in the Colorado Front Range. Surface horizons of soils on these moraines are enriched in silt and have a particle size distribution that resembles loess and dust deposits found elsewhere. The compositions of sand and silt fractions of the soils were compared to possible local source rocks, using immobile trace elements Ti, Nb, Zr, Ce, and Y. The sand fractions of soils have a wide range of trace element ratios, similar to the range of values in the local biotite gneiss bedrock. In contrast, silt fractions have narrower ranges of trace element ratios that do not overlap the range of these ratios in biotite gneiss. The particle size and geochemical results support an interpretation that silts in these soils are derived from airborne dust. Eolian silts were most likely derived from distant sources, such as the semiarid North Park and Middle Park basins to the west. We hypothesize that much of the eolian influx to soils of the Front Range occurred during an early to mid-Holocene warm period, when sediment availability in semiarid source basins was at a maximum.

  18. Characteristics and formation of rain forest soils derived from late Quaternary basaltic rocks in Leyte, Philippines

    NASA Astrophysics Data System (ADS)

    Navarrete, Ian A.; Tsutsuki, Kiyoshi; Asio, Victor B.; Kondo, Renzo

    2009-09-01

    This study was conducted to evaluate the physical, chemical, and mineralogical characteristics of rain forest soils derived from late Quaternary basaltic rocks in Leyte, Philippines. Four sites along a catena were selected at an elevation of 75-112 m above sea level with an average annual rainfall of 3,000 mm and an average temperature of 28°C. Results indicate that the soils are deep, clayey, and reddish in color, which is indicative of the advanced stage of soil development. They also posses excellent physical condition (friable and highly porous) although they are plastic and sticky when wet as is usual for clayey soils. In terms of chemical characteristics, the soils are acidic with low CEC values and generally low in organic matter and nutrient contents. The clay mineralogy of the soils is dominated by halloysite and kaolinite with minor amounts of goethite and hematite, and they also have generally high dithionite-extractable Fe contents confirming the advanced stage of their development. The soils in the more stable slope positions (PL-1, PL-2, and PL-4) have generally similar characteristics and appeared more developed than the one in the less stable position (PL-3). The most important pedogenic processes that formed the soils appear to be weathering, loss of bases and acidification, desilification, ferrugination, clay formation and translocation, and structure formation. The nature of the parent rock and climatic conditions prevailing in the area as well as slope position appear to have dominant effects on the development of the soils.

  19. Climate change not to blame for late Quaternary megafauna extinctions in Australia.

    PubMed

    Saltré, Frédérik; Rodríguez-Rey, Marta; Brook, Barry W; Johnson, Christopher N; Turney, Chris S M; Alroy, John; Cooper, Alan; Beeton, Nicholas; Bird, Michael I; Fordham, Damien A; Gillespie, Richard; Herrando-Pérez, Salvador; Jacobs, Zenobia; Miller, Gifford H; Nogués-Bravo, David; Prideaux, Gavin J; Roberts, Richard G; Bradshaw, Corey J A

    2016-01-01

    Late Quaternary megafauna extinctions impoverished mammalian diversity worldwide. The causes of these extinctions in Australia are most controversial but essential to resolve, because this continent-wide event presaged similar losses that occurred thousands of years later on other continents. Here we apply a rigorous metadata analysis and new ensemble-hindcasting approach to 659 Australian megafauna fossil ages. When coupled with analysis of several high-resolution climate records, we show that megafaunal extinctions were broadly synchronous among genera and independent of climate aridity and variability in Australia over the last 120,000 years. Our results reject climate change as the primary driver of megafauna extinctions in the world's most controversial context, and instead estimate that the megafauna disappeared Australia-wide ∼13,500 years after human arrival, with shorter periods of coexistence in some regions. This is the first comprehensive approach to incorporate uncertainty in fossil ages, extinction timing and climatology, to quantify mechanisms of prehistorical extinctions. PMID:26821754

  20. Late Quaternary vegetation history of North Stradbroke Island, Queensland, eastern Australia

    NASA Astrophysics Data System (ADS)

    Moss, Patrick T.; Tibby, John; Petherick, Lynda; McGowan, Hamish; Barr, Cameron

    2013-08-01

    Currently there is a paucity of records of late Quaternary palaeoenvironmental variability available from the subtropics of Australia. The three continuous palaeoecological records presented here, from North Stradbroke Island, subtropical Queensland, assist in bridging this large spatial gap in the current state of knowledge. The dominance of arboreal taxa in the pollen records throughout the past >40,000 years is in contrast with the majority of records from temperate Australia, and indicates a positive moisture balance for North Stradbroke Island. The charcoal records show considerable inter-site variability indicating the importance of local-scale events on individual records, and highlighting the caution that needs to be applied when interpreting a single site as a regional record. The variability in the burning regimes is interpreted as being influenced by both climatic and human factors. Despite this inter-site variability, broad environmental trends are identifiable, with changes in the three records comparable with the OZ-INTIMATE climate synthesis for the last 35,000 years.

  1. Late Quaternary strata and carbon burial records in the Yellow River delta, China

    NASA Astrophysics Data System (ADS)

    Zhao, Guangming; Ye, Siyuan; Li, Guangxue; Ding, Xigui; Yuan, Hongming

    2015-06-01

    Sediment carbon sequestration plays an essential role in mitigating atmospheric CO2 increases and the subsequently global greenhouse effect. To clarify the late Quaternary strata and carbon burial records in Yellow River delta (YRD), detailed analysis of benthic foraminifera, total carbon (TC), organic carbon (Corg), sedimentary characteristics and moisture contents of sediments, was performed on core ZK3, 30.3 m in length and obtained from YRD in 2007. Eight depositional units (designated U1-U8 in ascending order) were identified. A comprehensive analysis method of historical geography and sedimentary geology was used to determine the precise depositional ages of the modern Yellow River delta (MYRD), from which pre-MYRD ages were deduced. The results indicates that the maximum burial rates of TC, inorganic carbon (IC) and Corg occurred in the delta front (U5), and the minimum in the shallow sea (U3). Remarkable high sedimentation rates in the MYRD are responsible for burial efficiency of carbon, with an average rate of Corg burial reaching 2087±251 g (m2 yr)-1, and that of IC reaching 13741±808 g (m2 yr)-1, which are much higher than those of other regions with high contents of Corg. Therefore, YRD has a significant burial efficiency for carbon sequestration.

  2. Climate change not to blame for late Quaternary megafauna extinctions in Australia

    PubMed Central

    Saltré, Frédérik; Rodríguez-Rey, Marta; Brook, Barry W.; Johnson, Christopher N; Turney, Chris S. M.; Alroy, John; Cooper, Alan; Beeton, Nicholas; Bird, Michael I.; Fordham, Damien A.; Gillespie, Richard; Herrando-Pérez, Salvador; Jacobs, Zenobia; Miller, Gifford H.; Nogués-Bravo, David; Prideaux, Gavin J.; Roberts, Richard G.; Bradshaw, Corey J. A.

    2016-01-01

    Late Quaternary megafauna extinctions impoverished mammalian diversity worldwide. The causes of these extinctions in Australia are most controversial but essential to resolve, because this continent-wide event presaged similar losses that occurred thousands of years later on other continents. Here we apply a rigorous metadata analysis and new ensemble-hindcasting approach to 659 Australian megafauna fossil ages. When coupled with analysis of several high-resolution climate records, we show that megafaunal extinctions were broadly synchronous among genera and independent of climate aridity and variability in Australia over the last 120,000 years. Our results reject climate change as the primary driver of megafauna extinctions in the world's most controversial context, and instead estimate that the megafauna disappeared Australia-wide ∼13,500 years after human arrival, with shorter periods of coexistence in some regions. This is the first comprehensive approach to incorporate uncertainty in fossil ages, extinction timing and climatology, to quantify mechanisms of prehistorical extinctions. PMID:26821754

  3. Shifting sources and transport paths for the late Quaternary Escanaba Trough sediment fill (northeast Pacific)

    USGS Publications Warehouse

    Zuffa, G.G.; De Rosa, R.; Normark, W.R.

    1997-01-01

    Escanaba Trough, which forms the southernmost part of the axial valley of the actively spreading Gorda Ridge, is filled with several hundred meters of sediment of presumed late Quaternary age. Surficial sediment samples from gravity cores, deeper samples (as much as 390 m) from Site 35 of the Deep Sea Drilling Program (Leg 5), and the acoustic character of the sediment fill observed on seismic-reflection profiles indicate that much of the sediment fill is of turbidite origin. Gross composition and heavy- mineral analyses of sand samples show that two distinct petrofacies comprise the sediment fill. The lower part of the fill was derived primarily from the Klamath River source of northern California while the younger fill, including the surficial sand beds, are from the Columbia River drainage much farther north. The Escanaba Trough sediment provides an opportunity to evaluate concepts for paleogeographic and paleotectonic reconstructions that are based on facies analysis and compositional and textural data for the volcanic components because both intrabasinal and extrabasinal sources are present as well as coeval (neovolcanic) and non coeval (paleovolcanic) sourcre This study of a modern basin shows, that although the sediment sources could be identified, it was useful to have some knowledge of the sediment pathway(s), the effects of diagenesis, and the possible effects of sediment sorting as a result of long transport distances from the source area for some components. Application of these same techniques to ancient deposits without benefit of the additional parameters will face limitations.

  4. A fractal analysis of quaternary, Cenozoic-Mesozoic, and Late Pennsylvanian sea level changes

    NASA Technical Reports Server (NTRS)

    Hsui, Albert T.; Rust, Kelly A.; Klein, George D.

    1993-01-01

    Sea level changes are related to both climatic variations and tectonic movements. The fractal dimensions of several sea level curves were compared to a modern climatic fractal dimension of 1.26 established for annual precipitation records. A similar fractal dimension (1.22) based on delta(O-18/O-16) in deep-sea sediments has been suggested to characterize climatic change during the past 2 m.y. Our analysis indicates that sea level changes over the past 150,000 to 250,000 years also exhibit comparable fractal dimensions. Sea level changes for periods longer than about 30 m.y. are found to produce fractal dimensions closer to unity and Missourian (Late Pennsylvanian) sea level changes yield a fractal dimension of 1.41. The fact that these sea level curves all possess fractal dimensions less than 1.5 indicates that sea level changes exhibit nonperiodic, long-run persistence. The different fractal dimensions calculated for the various time periods could be the result of a characteristic overprinting of the sediment recored by prevailing processes during deposition. For example, during the Quaternary, glacio-eustatic sea level changes correlate well with the present climatic signature. During the Missourian, however, mechanisms such as plate reorganization may have dominated, resulting in a significantly different fractal dimension.

  5. Late Quaternary tectonic landforms and fluvial aggradation in the Saryu River valley: Central Kumaun Himalaya

    NASA Astrophysics Data System (ADS)

    Kothyari, Girish Ch.; Luirei, Khayingshing

    2016-09-01

    The present study has been carried out with special emphasis on the aggradational landforms to explain the spatial and temporal variability in phases of aggradation/incision in response to tectonic activity during the late Quaternary in the Saryu River valley in central Kumaun Himalaya. The valley has preserved cut-and-fill terraces with thick alluvial cover, debris flow terraces, and bedrock strath terraces that provide signatures of tectonic activity and climate. Morphostratigraphy of the terraces reveals that the oldest landforms preserved south of the Main Central Thrust, the fluvial modified debris flow terraces, were developed between 30 and 45 ka. The major phase of valley fill is dated between 14 and 22 ka. The youngest phase of aggradation is dated at early and mid-Holocene (9-3 ka). Following this, several phases of accelerated incision/erosion owing to an increase in uplift rate occurred, as evident from the strath terraces. Seven major phases of bedrock incision/uplift have been estimated during 44 ka (3.34 mm/year), 35 ka (1.84 mm/year), 15 ka (0.91 mm/year), 14 ka (0.83 mm/year), 9 ka (1.75 mm/year), 7 ka (5.38 mm/year), and around 3 ka (4.4 mm/year) from the strath terraces near major thrusts. We postulate that between 9 and 3 ka the terrain witnessed relatively enhanced surface uplift (2-5 mm/year).

  6. An improved age framework for late Quaternary silicic eruptions in northern Central America

    NASA Astrophysics Data System (ADS)

    Rose, William I.; Conway, F. Michael; Pullinger, Carlos R.; Deino, Alan; McIntosh, William C.

    Five new stepwise-heating 40Ar/39Ar ages and one new high-sensitivity 14C date of ash-fall and ash-flow deposits from late Quaternary silicic volcanoes in northern Central America document the eruption rates and frequencies of five major rhyodacite and rhyolite calderas (Atitlán, Amatitlán, Ayarza, Coatepeque, and Ilopango) located north of the basalt, andesite, and dacite stratovolcanoes of the Central American volcanic front. These deposits form extensive time-stratigraphic horizons that intercalate regionally, and knowledge of dates and stratigraphy provides a valuable framework for age determinations of more localized volcanic and nonvolcanic events. The new data, especially when integrated with previous stratigraphic and dating work, show that all five calderas erupted several times in the past 200ka and, despite a lack of historic activity, should be considered as active centers that could produce highly explosive eruptions again. Because of their locations near the highly vulnerable economic hearts of Guatemala and El Salvador, the risks of eruptions from these calderas should be carefully considered along with risks of major earthquakes and volcanic front volcanoes, which are much more frequent but inflict less severe and extensive damage. This investigation also includes some examples of dating efforts that failed to produce reasonable results.

  7. Late Quaternary loess in northeastern Colorado: Part I - Age and paleoclimatic significance

    USGS Publications Warehouse

    Muhs, D.R.; Aleinikoff, J.N.; Stafford, Thomas W., Jr.; Kihl, R.; Been, J.; Mahan, S.A.; Cowherd, S.

    1999-01-01

    Loess in eastern Colorado covers an estimated 14000 km2, and is the westernmost part of the North American midcontinent loess province. Stratigraphic studies indicate there were two periods of loess deposition in eastern Colorado during late Quaternary time. The first period spanned ca. 20 000 to 12 000 14C yr B.P. (ca. 20-14 ka) and correlates reasonably well with the culmination and retreat of Pinedale glaciers in the Colorado Front Range during the last glacial maximum. The second period of loess deposition occurred between ca. 11 000 and 9000 14C yr B.P. This interval may be Holocene or may correlate with a hypothesized Younger Dryas glacial advance in the Colorado Front Range. Sedimentologic, mineralogic, and geochemical data indicate that as many as three sources could have supplied loess in eastern Colorado. These sources include glaciogenic silt (derived from the Colorado Front Range) and two bedrock sources, volcaniclastic silt from the White River Group, and clays from the Pierre Shale. The sediment sources imply a generally westerly paleowind during the last glacial maximum. New carbon isotope data, combined with published faunal data, indicate that the loess was probably deposited on a cool steppe, implying a last glacial maximum July temperature depression, relative to the present, of at least 5-6??C. Overall, loess deposition in eastern Colorado occurred mostly toward the end of the last glacial maximum, under cooler and drier conditions, with generally westerly winds from more than one source.

  8. Century scale climatic rhythms in the equatorial Indian Ocean during the late Quaternary: Faunal and geochemical proxies from the Maldivian Archipelago

    NASA Astrophysics Data System (ADS)

    Sarkar, S.; Gupta, A. K.

    2012-04-01

    The equatorial Indian Ocean is swept by the Indian Ocean equatorial westerlies (IEW) which are strong during monsoon transitions in April-May and October-November, driving Eastward Equatorial Current (EEC) in the upper ocean. This study is based on the biogenic sediments from Ocean Drilling Program (ODP) Hole 716A, recovered beneath the narrow equatorial track (7 Degree North to 7 Degree South) along which the IEW prevail. We analyzed 300 Kyr record of benthic and planktic foraminifera, pteropods combined with stable isotope values measured on planktic foraminifer Globigerinoides ruber from 451 core samples to understand paleoceanographic and paleoclimatic changes in the equatorial Indian Ocean during the late Quaternary (~450 - 150 Kyrs). Factor and cluster analyses of the 53 highest-ranked benthic foraminiferal species enabled to identify five biofacies, indicating varied nature of deep-sea environments during the late Quaternary, with a major shift across the middle Brunhes epoch (across Marine Isotope Stage 9 and 8). Biofacies Robulus nicobarensis - Trifarina reussi (Rn-Tr), Uvigerina porrecta - Reussella simplex (Upo-Rs) and Cymbaloporetta squammosa - Bolivinita sp. (Cs-Bsp) document high organic flux with low oxygen paleoenvironment dominating before the mid-Brunhes event, similar to Globigerina bulloides population, while benthic foraminiferal biofacies Hoeglundina elegans - Miliolinella subrotunda (He-Ms) and Uvigerina peregrina - Quinqueloculina seminulum (Upe-Qs) record high seasonality in food supply with well-oxygenated deep water after ~300 Kyr. These changes are also visible in planktic foraminifera and pteropod record. In the present day, the strength of the IEW is inversely related to the Indian Ocean Dipole (IOD). The IEW weakened across MIS 9/8 during which time the IOD strengthened, causing heavy rains and floods over the equatorial East Africa and deficient rainfall over Australasia. The proxy response changed from low to high frequency cycles

  9. Late Quaternary Alluvial Fans and Beach Ridge Systems in Jakes Valley, Central Great Basin, USA

    NASA Astrophysics Data System (ADS)

    Garcia, A. F.; Stokes, M.; Benitez, L.

    2002-12-01

    Alluvial fan and lake beach ridge landforms provide archives of the geomorphic response to Late Quaternary climate change within the Great Basin region. This study presents the first detailed results of landform mapping and soil characterization from Jakes Valley, a high altitude (1920m) and internally drained basin, located within a previously unstudied part of White Pine County, East-Central Nevada. Mountain front alluvial fans sourced from the White Pine and Egan Ranges (west-east basin margins) are characterized by four morphostratigraphic units: Qf0 (oldest) through to Qf3 (youngest). Analysis of the soil properties of these stratigraphic units reveals two landform-soil assemblages: 1) Qf0-1, characterized by well-developed calcic soils (stages III+ to IV) and 2) Qf2-3, characterized by less well-developed calcic soils (stages I to II). Beach ridge systems formed during pluvial lake highstands are extensively developed into the mid and distal parts of alluvial fans. Integrated field and aerial photograph mapping has revealed a sequence of between 4-6 ridges with linear and / or highly curved / arcuate morphologies. Beach ridge soil properties are characterized by less well-developed calcic soils (stages I+ to II) that are similar to soils formed in Qf2 alluvial fan units. The interaction between the alluvial fan and beach ridge landforms can be utilized to explore the geomorphic response in relation to climatic amelioration during the Late Pleistocene-Holocene transition. Of particular interest is the common occurrence of the curved / arcuate beach ridges which may correspond to a period of fan progradation coincident with base-level lowering.

  10. Human impact on late Quaternary landscapes in the Central Spanish Pyrenees

    NASA Astrophysics Data System (ADS)

    Hirsch, F.; Raab, T. A.

    2011-12-01

    Like the Alps in Central Europe the Pyrenees in Southeast Europe are well known for their glacial history. Within the scope of the ongoing research project Post-LGM pedogenesis and geomorphodynamics in the Aragonese Pyrenees, Spain, funded by the Deutsche Forschungsgemeinschaft (DFG), we are studying the landscapes in the Gallego valley and the Aragon valley formed during the late Quaternary period. The aim of this research is to describe and characterize the soil development since the retreat of the valley glaciers from the LGM-moraines which are supposed to have an age of up to 60 ka yrs. To these purposes soil profiles are excavated in sediments and landforms of different ages (LGM to Holocene) and different genesis (glacigenic, glacifluvial, fluvial, gravitational). The soil profiles are arranged as catenas and provide insight into the pedo-stratigraphy of moraines, fluvial terraces, glacis and alluvial fans. Our preliminary results show that besides geogenic process past human land use must be considered as a main trigger of landscape development during the late Holocene. Truncated soil profiles in the backslopes and the correlate sediments of soil erosion burying soil horizons in the footslopes clearly indicate one or even more periods of re-shaping the landforms after deglaciation. Considerable amounts of small charcoal and tile fragments in the translocated sediments hint to an anthropogenic agent. The disturbance in the soil profiles and sediments is visible in the field and by micromorphology. Although 14C and OSL datings on the base of the correlate sediments of soil erosion indicate at least one phase of erosion and redeposition at the end of the 17th century, the onset of afresh pedogenic processes in the correlate sediments of soil erosion indicate young soil formation.

  11. Late tertiary and quaternary fluvial deposits in the Mesilla and Hueco bolsons, El Paso area, Texas

    NASA Astrophysics Data System (ADS)

    Stuart, Charles J.; Willingham, Daniel L.

    1984-03-01

    The late Tertiary to Quaternary Fort Hancock and Camp Rice Formations fill several extensional basins of the southern Rio Grande Rift. Interior drainage and central playa lakes characterize most of these rift basins. However, sedimentation in two basins located in the central part of the southern rift, the Mesilla and Hueco bolsons, was also greatly influenced by a northern segment of the ancestral Rio Grande river system. During the late Pliocene, a large-scale stream system entered the north end of the Mesilla bolson and deposited a south-sloping fluvial plain that overwhelmed playa lake and bolson-margin areas. The fluvial plain subsequently advanced across the eastern or southeastern margins of the Mesilla bolson then inundated a playa lake in the adjacent Hueco bolson. The Fort Hancock Formation was deposited during fluvial inundation of the bolsons. Four lithofacies of the Fort Hancock Formation are recognized: claystone, mudstone and sandstone, channelized sandstone, and conglomerate. The conglomerate and claystone facies were deposited in bolson-margin and playa depositional environments, respectively. The channelized sandstone facies formed the proximal fluvial plain of the ancestral Rio Grande system. The mudstone and sandstone facies formed in both playa-margin and distal fluvial-plain environments. By the middle Pleistocene, a major drainage basin south of the Hueco bolson, which formed the southern segment of the ancestral Rio Grande system, extended northward into the Hueco and Mesilla bolsons. At this time, the Rio Grande system was entirely integrated from southern Colorado to the Gulf of Mexico. Pebbly, coarse sand transported through this channel system formed the middle Pleistocene Camp Rice Formation.

  12. Morphology and Late Quaternary sedimentation in the Gulf of Oman Basin

    NASA Astrophysics Data System (ADS)

    Uchupi, Elazar; Swift, S. A.; Ross, D. A.

    The morphology of the Gulf of Oman Basin, a 3,400 m deep oceanic basin between Oman and southern Pakistan and southern Iran, ranges from a convergent margin (Makran margin) along the north side, a passive type (Oman margin) along the south side, translation types along the basin's west (Zendan Fault-Oman Line) and east (Murray Ridge) sides and a narrow continental rise and a wide abyssal plain in the centre of the basin. Sediment input into the basin during the Late Quaternary has been mainly from the north as a result of the uplift of the Coast Makran Mountains in the Late Miocene-Pliocene. Today most of this detritrus is deposited on the shelf and upper continental slope and perched basins behind the fold/fault ridges on the lower slope. The presence of fans and channels on the continental rise on the north side of the basin indicate, however, that continental derived debris was, and possibly is, being transported to the deep-sea by turbidity currents via gaps in the ridges on the lower slope. In addition to land derived terrigenous sediments, the basin deposits also contain biogenic (organic matter and calcium carbonate), eolian detritus and hydrates and authigenic carbonates from the tectonic dewatering of the Makran accretionary wedge. The eolian sediment is carried into the Gulf of Oman Basin from Arabia and the Mesopotamia Valley by the northwesterly Shamal winds. This type of detritus was particularly abundant during the glacial arid periods 21,000-20,000 and 11,000 (Younger Dryas) years ago when exposure of the Persian (Arabian) Gulf increased the area of dust entrainment and shifted the position of the source of the eolian sediments closer to the basin.

  13. Patterns and processes of Late Quaternary environmental change in a montane region of southwestern Europe

    NASA Astrophysics Data System (ADS)

    Carrión, José S.

    2002-10-01

    This paper examines the Late Quaternary (c. 20,300-<505 cal yr BP) environmental history of Siles, a lake situated at 1320 m in the Segura mountains of southern Spain, with the goal of establishing the mechanisms exerting control on vegetation change. Palaeoecological indicators include pollen, microcharcoal, spores of terrestrial plants, fungi, and non-siliceous algae, and other microfossils. The Siles sequence is shown to be sensitive to climatic change, although the control exerted by climate on vegetation is ultimately shaped by disturbances and species interactions, determining the occurrence of century-scale lags and threshold responses. Biotically induced changes of vegetation are also shown at the intrazonal level of variation. The new sequence is placed in the context of two previous records to postulate a picture of Holocene environmental change for the Segura region. The existence of mid-elevation glacial refugia for a number of temperate and Mediterranean trees is shown. A mid-Holocene phase (c. 7500-5200 cal yr BP) emerges regionally as the time of maximum forest development and highest lake levels. The early Holocene occurs as a generally dry, pyrophytic period of pine forests, with grassland scrub in high altitudes, and the late Holocene as a period of protracted vegetation sensitivity, with return to development of pine forests, spread of xerophytic communities, and increased fire activity, under the context of dry spells, localized anthropogenic disturbance, and shallowing and desiccation of lakes. Several events described here correlate with established times of abrupt transitions in the climates of northern Europe, the Mediterranean basin, north Africa, and the Sahel.

  14. Calibrating Late Quaternary terrestrial climate signals: radiometrically dated pollen evidence from the southern Sierra Nevada, USA

    USGS Publications Warehouse

    Litwin, Ronald J.; Smoot, Joseph P.; Durika, Nancy J.; Smith, George I.

    1999-01-01

    We constructed a radiometrically calibrated proxy record of Late Pleistocene and Holocene climate change exceeding 230,000 yr duration, using pollen profiles from two cores taken through age-equivalent dry lakes - one core having greater age control (via 230Th alpha mass-spectrometry) and the other having greater stratigraphic completeness. The better dated of these two serial pollen records (Searles Lake) served as a reference section for improving the effective radiometric age control in a nearby and more complete pollen record (Owens Lake) because they: (1) are situated ~90 km apart in the same drainage system (on, and immediately leeward of, the eastern flank of the Sierra Nevada), and (2) preserved strikingly similar pollen profiles and concordant sequences of sedimentological changes. Pollen assemblages from both lakes are well preserved and diverse, and document serial changes in Late Pleistocene and Holocene plant zone distribution and composition in the westernmost Great Basin; they consist of taxa now inhabiting montane forest, woodland, steppe, and desert-scrub environments. The studied core intervals are interpreted here to be the terrestrial equivalent of marine δ18O stages 1 through 9; these pollen profiles now appear to be among the best radiometrically dated Late Pleistocene records of terrestrial climate change known.

  15. Profiling of late Trias-early Quaternary surface in the Eskisehir basin using microtremors

    NASA Astrophysics Data System (ADS)

    Tün, Muammer; Pekkan, Emrah; Özel, Oğuz

    2015-04-01

    Earthquakes in our country and in the world cause damage and collapse of engineering structures due to several reasons. Settlement areas are under the effect of strong and long-duration seismic vibrations due to resonance and focusing effects. In this study, we propose the first approximation for thickness of Quaternary sediment and late Trias topography for the Eskisehir basin in microtremor methods. The 3-D basin structures and site resonance frequencies in the Eskişehir Basin were investigated by geophysical measurements based on the 318 single station and 9 array sites microtremor methods situated on soft soil sediments and rock units within the study area. The microtremor data collection, processing, and interpretation of the H/V curves were carried out following the recommendations and guidelines of the SESAME consortium (Site EffectS assesment using AMbient Excitation) The signals recorded were analysed for horizontal to the vertical (H/V) spectral ratio using GEOPSY software. The H/V ratios were calculated for the frequency range 0.2 to 20 Hz, using 60 s as a time window length and removing time windows contaminated by transients. Almost of the HVSR curves on the alluvium deposits have a low-frequency peak at 0.6-0.8 Hz and a second peak at 4-10 Hz. We used the Spatial Autocorrelation (SPAC) method in Eskisehir Basin using broadband seismometers distributed in triangular arrays. We derive a power-law relationship that correlates the fundamental site resonance frequencies with the sedimentary cover thickness obtained from the seismic reflection data, borehole data and shear wave velocity data in the study area. We use this relationship to estimate bedrock depth and thickness of alluvial deposits in the Eskisehir basin. Our estimation of maximum basin depths is 650 m for the Muttalip. The thickness of quaternary sediment is 25 m for Eskisehir alluvium. The estimated thickness is used to plot digital elevation model and cross profiles correlating with

  16. Late Quaternary changes in intermediate water oxygenation and oxygen minimum zone, northern Japan: A benthic foraminiferal perspective

    NASA Astrophysics Data System (ADS)

    Shibahara, Akihiko; Ohkushi, Ken'ichi; Kennett, James P.; Ikehara, Ken

    2007-09-01

    A strong oxygen minimum zone (OMZ) currently exists at upper intermediate water depths on the northern Japanese margin, NW Pacific. The OMZ results largely from a combination of high surface water productivity and poor ventilation of upper intermediate waters. We investigated late Quaternary history (last 34 kyr) of ocean floor oxygenation and the OMZ using quantitative changes in benthic foraminiferal assemblages in three sediment cores taken from the continental slope off Shimokita Peninsula and Tokachi, northern Japan, at water depths between 975 and 1363 m. These cores are well located within the present-day OMZ, a region of high surface water productivity, and in close proximity to the source region of North Pacific Intermediate Water. Late Quaternary benthic foraminiferal assemblages experienced major changes in response to changes in dissolved oxygen concentration in ocean floor sediments. Foraminiferal assemblages are interpreted to represent three main groups representing oxic, suboxic, and dysoxic conditions. Assemblage changes in all three cores and hence in bottom water oxygenation coincided with late Quaternary climatic episodes, similar to that known for the southern California margin. These episodes, in turn, are correlated with orbital and millennial climate episodes in the Greenland ice core including the last glacial episode, Bølling-Ållerød (B/A), Younger Dryas, Preboreal (earliest Holocene), early Holocene, and late Holocene. The lowest oxygen conditions, marked by dysoxic taxa and laminated sediments in one core, occurred during the B/A and the Preboreal intervals. Suboxic taxa dominated mainly during the last glacial, the Younger Dryas, and most of the Holocene. Dysoxic conditions during the B/A and Preboreal intervals in this region were possibly caused by high surface water productivity at times of reduced intermediate ventilation in the northwestern Pacific. Remarkable similarities are evident in the late Quaternary sequence of benthic

  17. Late Quaternary accretion and decline of syngenetic ice-rich permafrost

    NASA Astrophysics Data System (ADS)

    Wetterich, Sebastian; Strauss, Jens; Fuchs, Margret C.; Schirrmeister, Lutz

    2016-04-01

    The region of perennially frozen ground constitutes one quarter of the northern hemisphere landmass. Negative annual mean air temperatures and ground freezing periods exceeding ground thaw periods are the prerequisites for downward freezing of loose deposits and bedrock in non-glaciated regions. Hence, permafrost distribution and thickness on Earth are closely related to late Quaternary climate variations and ecosystem modifications. Generally, glacial stages are expected to promote permafrost accretion and ground ice formation in accumulating sediments, whereas interglacial stages lead to intense permafrost thaw and ground-ice melt. Deep freezing synchronous with ongoing sedimentation is termed as syngenetic while epigenetic freezing occurs in pre-existing deposits. Typical landforms of syngenetic permafrost are ice-wedge polygons of past tundra environments. Ice-rich silty and/or peaty deposits intersected by large ice wedges (up to several decameters in height and meters in with) build-up unique Ice Complex (IC) strata, which are aligned to mid- and late Pleistocene stadial and interstadial stages. The most prominent example for such formations is the Yedoma IC of MIS 3 interstadial age. Increasing air and ground temperatures during warm stages disturbed the thermal equilibrium at the upper permafrost boundary and subsequently led to permafrost thaw, ground-ice melt and surface subsidence. Typical permafrost degradation processes are thermokarst and thermo-erosion that result in large lake-filled basins (up to kilometers in diameter) and valley structures, respectively. The modern periglacial surface in Alaskan and East Siberian lowlands preserves Yedoma IC remnants in uplands and hills next to widely-distributed thermokarst basins since lateglacial and Holocene warming affected up to 70% of the original IC distribution on an area of more than 1,000,000 km2. The overarching climate-driven pattern of cold-stage IC permafrost accretion and warm-stage IC permafrost

  18. Geochemical and Sedimentological Records of Late Quaternary Climate Change, Lake Tanganyika, Tropical East Africa

    NASA Astrophysics Data System (ADS)

    Felton, A. A.; Russell, J. M.; Cohen, A. S.; Baker, M. E.; McGlue, M. M.; Lezzar, K. E.

    2005-12-01

    We have analyzed piston core records from Lake Tanganyika (western Tanzania, East African Rift Valley) to investigate possible signals of tropical paleoclimate change during the Late Quaternary. Long paleoclimate records from East Africa are of importance for understanding climatic processes such as the role of solar variability in regulating tropical climates at Milankovitch time scales, and the relationship between abrupt climate changes, migration of Intertropical Convergence Zone, and regional climate variability (Nicholson, 2000). However, records of pre-Holocene climate variability from tropical African lakes (>25ka) are still quite rare. Long records from Lake Tanganyika are of particular interest given the lake's antiquity and its demonstrated potential for producing high resolution (frequently annually laminated) sedimentary records (Cohen et al., 1993). We analyzed physical properties, grain size, total organic carbon, major, minor and trace element variability, and biogenic silica data for a 7.75 m core from the Kalya slope and horst region of central Lake Tanganyika at 640m water depth. Nine 14C dates provide an age model for the core, which spans ~62 cal kyr. Elemental concentrations preserved in Lake Tanganyika sediments record variability in deposition and runoff into the lake basin. Under conditions of rapid erosion, exposure and rapid weathering of bedrock has been shown to generate high concentrations of original silicate minerals enriched in soluble cations such as sodium and potassium, elements that are also biologically conservative. Prior to 40ka cal yr. core sediments are characterized by high magnetic susceptibility, intermediate levels of organic carbon, low to intermediate levels of biogenic silica, and fine grain size, indicative of relatively high precipitation. There is a profound decrease in magnetic susceptibility, a decrease in organic carbon and an increase in grain size at 40ka cal yr, which persists until ~16ka cal yr. Seismic

  19. Fluvio-deltaic progradation in forced regressive deglacial succession: lessons from the Lake Saint-Jean (Québec, Canada, late Quaternary)

    NASA Astrophysics Data System (ADS)

    Nutz, Alexis; Ghienne, Jean-François; Schuster, Mathieu; Roquin, Claude; Dietrich, Pierre; Bouchette, Frédéric; Cousineau, Pierre A.

    2015-04-01

    Deltas simultaneously respond to modifications in water discharge, sediment supply and base-level change. As a consequence, they provide accurate archive for deciphering environmental change through times. In this contribution, a Late Quaternary deglacial sequence is documented from Lake Saint-Jean basin (Québec, Canada) where sediments have recorded the Laurentide ice sheet (LIS) retreat accompanied by the invasion of marine waters (Laflamme Gulf) from ca. 12.9 cal. ky BP. Subsequently, fluvio-deltaic and then coastal prograding wedges emplaced following the base level fall induced by the glacio-isostatic rebound. The related succession, representing a transition from glacial to post-glacial periods within a previously glaciated area, was investigated through recent geological mapping, preserved landforms, facies analysis, and new optical stimulated luminescence (OSL) and radiocarbon (14C) dates. Three basin-scale geological sections are presented focusing on the architectures and facies of fluvio-deltaic progradations emplaced from 12.9 cal. ka BP to present-day in Lake Saint-Jean. Overlying the bedrock, isolated ice-contact fan deposits are capped by glacimarine muds. Above, fluvio-deltaic and coastal prograding systems were deposited following four major evolutions through time: (i) deltaic systems progressively increased in width, (ii) coastal influence on sedimentation increased, (iii) hydrographic drainage systems became more organised, and (iv) delta graded from steep (Gilbert delta) to low-angle foresets (mouth-bar delta). These evolutions in fluvio-deltaic systems are attributed to the modifications in water discharge, sediment supply and rate of base level fall driven by the deglaciation. The presented succession is considered as representative of the sedimentological signature of fluvial progradations in forced regressive deglacial sequences. Derived from the Lake Saint-Jean basin, this study provides new elements for the recognition and interpretation

  20. Coral reef complexes at an atypical windward platform margin: Late Quaternary, southeast Florida

    USGS Publications Warehouse

    Lidz, B.H.

    2004-01-01

    Major coral reef complexes rim many modern and ancient carbonate platforms. Their role in margin evolution is not fully understood, particularly when they border a margin atypical of the classic model. Classic windward margins are steeply inclined. The windward margin of southeast Florida is distinct with a very low-gradient slope and a shelf edge ringed with 30-m-high Quaternary outlier reefs on a shallow upper-slope terrace. A newly developed synthesis of temporally well-constrained geologic events is used with surface and subsurface seismic-reflection contours to construct morphogenetic models of four discontinuous reef-complex sequences. The models show uneven subsurface topography, upward and landward buildups, and a previously unreported, rapid, Holocene progradation. The terms backstepped reef-complex margin, backfilled prograded margin, and coalesced reef-complex margin are proposed for sections exhibiting suitable signatures in the stratigraphic record. The models have significant implications for interpretation of ancient analogues. The Florida record chronicles four kinds of geologic events. (1) Thirteen transgressions high enough for marine deposition occurred between ca. 325 ka and the present. Six gave rise to stratigraphically successive coral reef complexes between ca. 185 and ca. 77.8 ka. The seventh reef ecosystem is Holocene. (2) Two primary coral reef architectures built the outer shelf and margin, producing respective ridge-and-swale and reef-and-trough geometries of very different scales. (3) Massive outlier reefs developed on an upper-slope terrace between ca. 106.5 and ca. 80 ka and are inferred to contain corals that would date to highstands at ca. 140 and 125 ka. (4) Sea level remained below elevation of the shelf between ca. 77.8 and ca. 9.6 ka. ?? 2004 Geological Society of America.

  1. Late Quaternary glacial relief evolution revealed by luminescence thermochronometry (Granite Range, Alaska)

    NASA Astrophysics Data System (ADS)

    Valla, P.; Guralnik, B.; Lowick, S.; Champagnac, J.; Herman, F.; Jain, M.; Murray, A.

    2012-12-01

    Long-term exhumation and topographic evolution of mountain belts arise from complex coupling between tectonics, climate and surface processes. Glacial and periglacial processes are especially potent agents to reshape the alpine landscapes by valley carving and/or limiting topography. The recent development of luminescence thermochronometry (e.g., Herman et al., 2010) and its very low closure temperature (0-60°C) opens a new spatial and temporal "window" for the study of latest stages of rock exhumation and thus to address potential topographic relief changes during the late Quaternary. We apply this new method in the Wrangell-St Elias National Park (Alaska), an alpine landscape that exhibits typical glacial features (U-shaped valleys, cirques, moraines). This setting provides an exceptional opportunity to infer potential differences in relief evolution under a gradient of glacial forcing. The Granite Range presents a consistent and progressive eastward increase in the mean elevation, glacier activity, and topographic relief, while low-temperature thermochonometry data display rather homogeneous, yet largely scattered (apatite (U-Th)/He ages of ~15±7 Ma) throughout the massif (e.g., Spotila and Berger, 2010 and references therein). We sampled four elevation profiles over an 80-km East-West transect across the Granite Range (bounded by Tana River to the West and Chitina River to the North). Feldspar separates from 15 bedrock surface samples were dated using an IR-50 SAR protocol (e.g., Murray et al., 2000), and exhibit good internal reproducibility. Apparent ages vary from ~250 ka in the western part of the range, towards younger ages of ~30 ka in the east, thus supporting the notion of high rates of erosion correlated with intense glacial/periglacial activity. We then use a kinetic model to convert apparent ages in mean cooling histories, and couple it with Pecube model (Braun et al., 2012) to extract tectono-geomorphic scenarios. Our results reveal spatially

  2. Evolution and floodplain history of the Middle Sacramento River from the late Quaternary to modern times

    NASA Astrophysics Data System (ADS)

    Will, M.; Aalto, R. E.; Fuchs, M.

    2011-12-01

    California has an extensive and storied research history in fluvial geomorphology dating back to G.K.Gilbert's studies of sediment transport in the Feather and Sacramento Rivers a century ago. Given the importance of Californian river systems in the field of geomorphology it is therefore surprising that there are still major gaps in understanding the late Quaternary evolution of the Sacramento River and the continuing responses of the modern system. Studies of river response to environmental change have been popular in Europe, but the Western US lacks so many similar investigations of the late Quaternary evolution of major rivers. We help to address this shortcoming by presenting detailed geochronology and other results from a research campaign along the largest natural reach of the largest river in California. The unique ownership history of the Rancho Llano Seco has preserved a near-pristine floodplain structure with an extensive network of natural floodplain channels. This therefore provides an excellent research environment to investigate natural occurring infilling processes and to study the fluvial history of the Sacramento River and modern floodplain development. Our research documents both the long-term evolution of the Sacramento River system and provides extensive, quantitative insight into modern day sedimentation rates in regards to topographic location. At Llano Seco there are 3 types of channels interpreted as Holocene meander belt, and anastomosing or braiding floodplain channel systems, and other floodplain units - these have been previously mapped from air photos and geologic surveys. However, the temporal control on these geologic units has been poor, with no absolute dating. To provide dates we sampled and analyzed 22 deep pits (3-5m) and more than 70 shallow cores (~1m), establishing a thorough chronology with OSL and 14-C (for long-term system dynamics) and high resolution 210-Pb and 137-Cs dating (to document modern evolution of an extensive

  3. Waxing and Waning of Forests: Late Quaternary Biogeography of Lake Malawi, Southeast Africa

    NASA Astrophysics Data System (ADS)

    Ivory, S.; Lézine, A. M.; Vincens, A.; Cohen, A. S.

    2014-12-01

    African ecosystems are at great risk due to climate and land-use change. Despite the status of several of these regions as biodiversity hotspots, long-standing ideas about African ecology and biogeography have been unable to be tested until now due to lack of sufficiently long records. Here, we present the first long, continuous terrestrial record of vegetation from Lake Malawi, East Africa which goes back to the early Late Quaternary, permitting us to investigate changes in physiognomy and forest composition over many transitions. In this record, we observe eight phases of forest expansion and collapse. Although diversity is much greater during forest phases, composition varies little from phase to phase. Very high abundances of afromontane taxa suggest frequent widespread colonization of the lowlands by modern high elevation trees. Although there are clear successional stages within each forest such that turnover is great within a single phase, among forest samples between phases, there is little dissimilarity. Each forest phase is interrupted by rapid decline of arboreal taxa and expansion of semi-arid grasslands or woodlands whose composition varies greatly from phase to phase. The variable composition of the more open phases, all occurring during arid periods, is likely dynamically linked to thresholds in regional hydrology associated with lake level and moisture recycling within the watershed. This vegetation is unlike any found at Malawi today, with assemblages suggesting strong Somali-Masai affinities. Furthermore, nearly all semi-arid assemblages contain small abundances of forest taxa typically growing in areas with wetter edaphic conditions, suggesting that moist lowland gallery forests were present but restricted to waterways during exceptionally arid times. The waxing and waning of forests throughout this interval has important implications for early human biogeography across Africa as well as disturbance regimes that are crucial for the maintenance of

  4. Late quaternary temperature record from buried soils of the North American Great Plains

    USGS Publications Warehouse

    Nordt, L.; Von Fischer, J.; Tieszen, L.

    2007-01-01

    We present the first comprehensive late Quaternary record of North American Great Plains temperature by assessing the behavior of the stable isotopic composition (??13C) of buried soils. After examining the relationship between the ??13C of topsoil organic matter and July temperature from 61 native prairies within a latitudinal range of 46??-38??N, we applied the resulting regression equation to 64 published ??13C values from buried soils of the same region to construct a temperature curve for the past 12 k.y. Estimated temperatures from 12 to 10 ka (1 k.y. = 1000 14C yr B.P.) fluctuated with a periodicity of ???1 k.y. with two cool excursions between -4.5 and -3.5 ??C and two warmer excursions between -1 and 0 ??C, relative to modern. Early Holocene temperatures from ca. 10-7.5 ka were -1.0 to -2.0 ??C before rising to +1.0 ??C in the middle Holocene between 6.0 and 4.5 ka. After a cool interlude from 4.2 to 2.6 ka, when temperatures dropped to slightly below modern, another warm interval ensued from 2.6 to 1 ka as temperatures increased to ???+0.5 ??C. A final decline in temperature to below modern occurred beginning ca. 0.5 ka. Cooler than present temperatures in the Great Plains indicate telecommunications with cool-water episodes in the Gulf of Mexico and North Atlantic potentially governed by a combination of glacial meltwater pulses and low solar irradiance. ?? 2007 Geological Society of America.

  5. Late Quaternary paleodune deposits in Abu Dhabi Emirate, UAF: Paleoclimatic implications

    SciTech Connect

    Brouwers, E.M.; Bown, T.M. ); Hadley, D.G. )

    1993-04-01

    Remnants of late Quaternary paleodunes are exposed near the coast of the Arabian Gulf and in large inland playas and interdunal areas in central and western Abu Dhabi Emirate over a distance of >45 km normal to the coast. Paleodunes occur south of Madinat Zayed (lat. 23[degree]35 N), which marks the northern limit of a modern dune field that grades into the mega-dune sand sea of the ar Rub al Khali, Saudi Arabia. Coastal paleodunes are composed of weakly cemented millolid foraminifers, ooids, and rounded biogenic grains, whereas inland and southward the paleodunes show a progressive increase in the proportion of eolian quartz sand. The paleodunes exhibit large-scale trough foresets in remnant exposures 0.5 to 10 m thick, indicating paleowind directions from 65[degree] to 184[degree] (dominantly southeast transport). Scattered paleoplaya remnants provide paleodune scale. Paleoplaya deposits form buttes 30--50 m high. If coeval with the Paleodunes, large-scale paleodune fields are implied (100+ m high), comparable to star dunes and sand mountains at the northwestern edge of the ar Rub al Khali. Based on U-Th isotopic analyses, the carbonate paleodune sands are >160ka and probably >250ka. The carbonate source was a shallow, nearly dry Arabian Gulf at a time when large areas were exposed during a low sea-level stand. Paleowind direction indicates that Pleistocene prevailing winds were northwesterly, the direction of the dominant (winter shamal) wind today. The geographic extend and implied magnitude of the paleodunes suggest large-scale eolian transport of carbonate sand during the Pleistocene disiccation, and admixed quartz sand identifies a youthful stage of contemporaneous evolution of the ar Rub al Khali. Wave-eroded paleodunes probably floor much of the present-day Gulf and extend beneath the modern dunes and sand mountains.

  6. Setting the Time Frame - Investigating Culture-Environment Interactions in the Late Quaternary

    NASA Astrophysics Data System (ADS)

    Klasen, N.; Just, J.; Rethemeyer, J.

    2015-12-01

    We present a status update of luminescence age estimates of sediments from Ethiopia and the Iberian Peninsula that are related to human occupation and are currently being investigated in the interdisciplinary Collaborative Research Center "Our way to Europe - Culture-Environment Interaction and Human Mobility in the Late Quaternary" (CRC806). The aim of the project is to investigate the dispersal of anatomically modern humans from Africa to Europe, and a robust chronology is essential. In the CRC806, dating is provided by luminescence, palaeomagnetic and radiocarbon techniques. A key site of the CRC806 is Chew Bahir in Ethiopia. This lake basin is located in the source area of the emergence of anatomically modern humans. Radiocarbon, luminescence and palaeomagnetic dating have been used to develop an age-depth model for drill core sediments that date back to 115 ka over 42 m depth. The model is independent of palaeoclimatic proxy interpretation. On the Iberian Peninsula cave deposits have been dated with luminescence techniques and compared to radiocarbon ages wherever applicable. Recently, existing radiocarbon chronologies on the Iberian Peninsula have been revised in light of methodological developments. Robust luminescence dating is therefore especially important in this region, where the stratigraphy is difficult to constrain. We aim to improve the precision of luminescence age estimates by comparing different measurement techniques for equivalent dose and dose-rate determinations, and by using Bayesian statistics to develop age-depth models. Combining different chronological techniques has enabled the development of accurate and precise chronologies, which will allow a better understanding of the emergence of modern humans.

  7. Late Quaternary stratigraphy and sedimentation patterns in the western Arctic Ocean

    USGS Publications Warehouse

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

    2009-01-01

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

  8. Holarctic phylogeography of the root vole (Microtus oeconomus): implications for late Quaternary biogeography of high latitudes.

    PubMed

    Brunhoff, C; Galbreath, K E; Fedorov, V B; Cook, J A; Jaarola, M

    2003-04-01

    A species-wide phylogeographical study of the root vole (Microtus oeconomus) was performed using the whole 1140 base pair mitochondrial (mt) cytochrome b gene. We examined 83 specimens from 52 localities resulting in 65 unique haplotypes. Our results demonstrate that the root vole is divided into four main mtDNA phylogenetic lineages that seem to have largely allopatric distributions. Net divergence estimates (2.0-3.5%) between phylogroups, as well as relatively high nucleotide diversity estimates within phylogroups, indicate that the distinct phylogeographical structure was initiated by historical events that predated the latest glaciation. European root voles are divided into a Northern and a Central mtDNA phylogroup. The mtDNA data in concert with fossil records imply that root voles remained north of the classical refugial areas in southern Europe during the last glacial period. The currently fragmented populations in central Europe belong to a single mtDNA phylogroup. The Central Asian and the North European lineages are separated by the Ural Mountains, a phylogeographical split also found in collared lemmings (Dicrostonyx) and the common vole (M. arvalis). The Beringian lineage occurs from eastern Russia through Alaska to northwestern Canada. This distribution is congruent with the traditional boundaries of the Beringian refugium and with phylogeographical work on other organisms. In conclusion, similarities between the phylogeographical patterns in the root vole and other rodents, such as Arctic and subarctic lemmings, as well as more temperate vole species, indicate that late Quaternary geological and climatic events played a strong role in structuring northern biotic communities. PMID:12753215

  9. Erosion and deposition on the eastern margin of the Bermuda Rise in the late Quaternary

    NASA Astrophysics Data System (ADS)

    McCave, I. N.; Hollister, C. D.; Laine, E. P.; Lonsdale, P. F.; Richardson, M. J.

    1982-05-01

    A near-bottom survey has been made on the Eastward Scarp (32°50'N, 57°30'W) of the Bermuda Rise, which rises 1150 m above the 5500-m deep Sohm Abyssal Plain in the western North Atlantic. The survey reveals evidence of erosion and deposition at present and in the late Quaternary by the deeper levels of the westward flowing Gulf Stream Return Flow. Four distinct regions of increasing bed gradient show increasing sediment smoothing and scour in the transition from plateau to abyssal plain. Bedforms observed are current crescents, crag and tail, triangular ripples, elongate mounds, transverse mud ripples, lineations, and furrows ranging from 10 to 1 m or less in depth, decreasing generally with bed gradient. Measured near-bottom current speeds are up to 20 cm s -1. Temperature structure on the lower, steep, slopes suggests that detachment of bottom mixed layers may occur there. Extensive net erosion appears to be confined to the lower steep slopes of the scarp. Reflection profiles (4 kHz) show that there has been erosion in areas thinly draped with recent sediments and in areas that show development of small scarps. The distribution of subsurface acoustic characteristics of the region corresponds broadly to the areas characterized by bed gradient and distinct sedimentation conditions. Subsurface hyperbolae, possibly caused by buried furrows, show furrow persistence through several tens of metres of deposition. Erosion occurs up to the top of the scarp during episodes of presumed stronger currents, which may correspond with intensified circulation during glacials.

  10. Late Quaternary Arc-parallel Extension of the Kongur Extensional System (KES), Chinese Pamir

    NASA Astrophysics Data System (ADS)

    Chen, Jie; Schoenbohm, Lindsay M.; Yuan, Zhaode; Li, Wenqiao; Li, Tao; Owen, Lewis A.; Sobel, Edward R.; Hedrick, Kate

    2015-04-01

    Active deformation in the Chinese Pamir plateau is dominated by east-west extension along the active Kongur extensional system (KES). The KES lies along the northeastern margin of the Pamir at the western end of the Himalayan-Tibetan orogenic belt, and is part of a regional fault system which accommodates east-west extension in the hanging wall of the active Main Pamir Thrust (MPT). Previous work has shown that the MPT has been active since at least the Late Oligocene and accommodates northward motion of the Pamir salient over the Tarim and Tajik basins. It has been proposed that North-directed thrusting along the Main Pamir thrust has been interpreted to be related to east-west extension in the northern Pamir by either extensional collapse of over-thickened crust, or radial thrusting, or oroclinal bending along the Main Pamir Thrust. Alternatively, the east-west extension is related to northward propagation of the right-slip Karakoram fault. A newer model relates the extension to gravitational collapse of the Pamir into the Tadjik depression. Clearly the precise driver remains poorly understood. To better understand the nature of extension in the Pamir and to test the existing models, late Quaternary slip rate along the KES need to be defined using geomorphic mapping, geodetic surveying, Be-10 surface exposure and depth profile dating to quantify rates of fault slip using multiple landforms as strain markers such as offset outwash terraces, lateral moraines, and landslides at five sites, to identify spatial patterns in deformation rates. The preliminary results show that the overall extension direction is subhorizontal, is oriented E-W, and occurs at a high rate of about 7 mm/yr along the Muji and Qimugan faults to the north and deceased to about 1 mm/yr at Kuzigan to the south near Tashkurgan town, which matches the pattern of GPS data. A regional compilation from this study and existing data shows that recent extension along the KES is arc-parallel extension

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

    NASA Astrophysics Data System (ADS)

    Huckleberry, Gary; Onken, Jill; Graves, William M.; Wegener, Robert

    2013-03-01

    Recent archaeological excavations along the lower Salt River, Arizona resulted in the unexpected discovery of buried late Pleistocene soils and cultural features dating 5800-7100 cal YBP (Early Archaic), the latter representing the earliest evidence of human activity in the lower Salt River floodplain thus far identified. Because the lower Salt River floodplain has been heavily impacted by recent agriculture and urbanization and contains few stratigraphic exposures, our understanding of the river's geological history is limited. Here we present a late Quaternary alluvial chronology for a segment of the lower Salt River based on 19 accelerator mass spectrometry 14C and four optically stimulated luminescence ages obtained during two previous geoarchaeological investigations. Deposits are organized into allostratigraphic units and reveal a buried late Pleistocene terrace inset into middle-to-late Pleistocene terrace deposits. Holocene terrace fill deposits unconformably cap the late Pleistocene terrace tread in the site area, and the lower portion of this fill contains the Early Archaic archaeological features. Channel entrenchment and widening ~ 900 cal YBP eroded much of the older terrace deposits, leaving only a remnant of fill containing the buried latest Pleistocene and middle-to-late Holocene deposits preserved in the site area. Subsequent overbank deposition and channel filling associated with a braided channel system resulted in the burial of the site by a thin layer of flood sediments. Our study confirms that the lower Salt River is a complex mosaic of late Quaternary alluvium formed through vertical and lateral accretion, with isolated patches of buried soils preserved through channel avulsion. Although channel avulsion is linked to changes in sediment load and discharge and may have climatic linkages, intrinsic geomorphic and local base level controls limit direct correlations of lower Salt River stratigraphy to other large rivers in the North American

  12. Sedimentary architecture and chronostratigraphy of a late Quaternary incised-valley fill: A case study of the late Middle and Late Pleistocene Rhine system in the Netherlands

    NASA Astrophysics Data System (ADS)

    Peeters, J.; Busschers, F. S.; Stouthamer, E.; Bosch, J. H. A.; Van den Berg, M. W.; Wallinga, J.; Versendaal, A. J.; Bunnik, F. P. M.; Middelkoop, H.

    2016-01-01

    This paper describes the sedimentary architecture, chronostratigraphy and palaeogeography of the late Middle and Late Pleistocene (Marine Isotope Stage/MIS 6-2) incised Rhine-valley fill in the central Netherlands based on six geological transects, luminescence dating, biostratigraphical data and a 3D geological model. The incised-valley fill consists of a ca. 50 m thick and 10-20 km wide sand-dominated succession and includes a well-developed sequence dating from the Last Interglacial: known as the Eemian in northwest Europe. The lower part of the valley fill contains coarse-grained fluvio-glacial and fluvial Rhine sediments that were deposited under Late Saalian (MIS 6) cold-climatic periglacial conditions and during the transition into the warm Eemian interglacial (MIS 5e-d). This unit is overlain by fine-grained fresh-water flood-basin deposits, which are transgressed by a fine-grained estuarine unit that formed during marine high-stand. This ca. 10 m thick sequence reflects gradual drowning of the Eemian interglacial fluvial Rhine system and transformation into an estuary due to relative sea-level rise. The chronological data suggests a delay in timing of regional Eemian interglacial transgression and sea-level high-stand of several thousand years, when compared to eustatic sea-level. As a result of this glacio-isostatic controlled delay, formation of the interglacial lower deltaic system took only place for a relative short period of time: progradation was therefore limited. During the cooler Weichselian Early Glacial period (MIS 5d-a) deposition of deltaic sediments continued and extensive westward progradation of the Rhine system occurred. Major parts of the Eemian and Weichselian Early Glacial deposits were eroded and buried as a result of sea-level lowering and climate cooling during the early Middle Weichselian (MIS 4-3). Near complete sedimentary preservation occurred along the margins of the incised valley allowing the detailed reconstruction presented

  13. First High-Resolution Record of Late Quaternary Environmental Changes in the Amundsen Sea, West Antarctica, Revealed by Multi-proxy Analysis of Drift Sediments

    NASA Astrophysics Data System (ADS)

    Horrocks, J.; Ó Cofaigh, C.; Lloyd, J. M.; Hillenbrand, C. D.; Kuhn, G.; Smith, J.; Ehrmann, W. U.; Esper, O.

    2015-12-01

    The Amundsen Sea sector of the West Antarctic Ice Sheet (WAIS) is experiencing rapid mass loss and there is a pressing need to place the contemporary ice-sheet changes into a longer term context. The continental rise in this region is characterised by large sediment mounds that are shaped by westward flowing bottom currents and that resemble contouritic drifts existing offshore from the Antarctic Peninsula. Similar to the Antarctic Peninsula drifts, marine sediment cores from the poorly studied sediment mounds in the Amundsen Sea have the potential to provide reliable records of dynamical ice-sheet behaviour in West Antarctica and palaeoceanographic changes in the Southern Ocean during the Late Quaternary that can be reconstructed from their terrestrial, biogenic and authigenic components. Here we use multi-proxy data from three sediment cores recovered from two of the Amundsen Sea mounds to present the first high-resolution study of environmental changes on this part of the West Antarctic continental margin over the glacial-interglacial cycles of the Late Quaternary. Age constraints for the records are derived from biostratigraphy, AMS 14C dates and lithostratigraphy. We focus on the investigation of processes for drift formation, thereby using grain size and sortable silt data to reconstruct changes in bottom current speed and to identify episodes of current winnowing. Data on geochemical and mineralogical sediment composition and physical properties are used to infer both changes in terrigenous sediment supply in response to the advance and retreat of the WAIS across the Amundsen Sea shelf and changes in biological productivity that are mainly controlled by the duration of annual sea-ice coverage. We compare our data sets from the Amundsen Sea mounds to those from the well-studied Antarctic Peninsula drifts, thereby highlighting similarities and discrepancies in depositional processes and climatically-driven environmental changes.

  14. Late Quaternary climatic and oceanographic changes in the Northeast Pacific as recorded by dinoflagellate cysts from Guaymas Basin, Gulf of California (Mexico)

    NASA Astrophysics Data System (ADS)

    Price, Andrea M.; Mertens, Kenneth N.; Pospelova, Vera; Pedersen, Thomas F.; Ganeshram, Raja S.

    2013-01-01

    A high-resolution record of organic-walled dinoflagellate cyst production in Guaymas Basin, Gulf of California (Mexico) reveals a complex paleoceanographic history over the last ~40 ka. Guaymas Basin is an excellent location to perform high resolution studies of changes in late Quaternary climate and paleo-productivity because it is characterized by high primary productivity, high sedimentation rates, and low oxygen bottom waters. These factors contribute to the deposition and preservation of laminated sediments throughout large portions of the core MD02-2515. In this study, we document dinoflagellate cyst production at a centennial to millennial scale throughout the late Quaternary. Based on the cyst assemblages, three dinoflagellate cyst zones were established and roughly correspond to Marine Isotope Stages (MISs) 1 to 3. MISs 1 and 3 are dominated by cysts of heterotrophic dinoflagellates, whereas MIS 2 is characterized by enhanced variability and a greater proportion of cysts produced by autotrophic taxa. The most dominant dinoflagellate cyst taxa found throughout the core were Brigantedinium spp. and Operculodinium centrocarpum. Dansgaard-Oeschger event 8 is observed in the dinoflagellate cyst record where it is characterized by an increase in warm taxa, such as Spiniferites pachydermus. Other intervals of interest are the Younger Dryas where warmer conditions are recorded and the Holocene which is characterized by the consistent presence of tropical species Stelladinium reidii, Tuberculodinidum vancampoae, Bitectatodinium spongium, and an increase in Quinquecuspis concreta. Changes in cyst assemblages, concentrations, and species diversity, along with geochemical data reflect major orbital to millennial-scale climatic and oceanographic changes.

  15. Geochemical proxies for weathering and provenance of Late Quaternary alluvial core-sediments from NW India

    NASA Astrophysics Data System (ADS)

    Singh, Ajit; Amir, Mohd; Paul, Debajyoti; Sinha, Rajiv

    2014-05-01

    The Indo-Gangetic alluvial plains are formed by sediment deposition in the foreland basin as a result of upliftment and subsequent erosion of the Himalaya. Earlier study (Sinha et al., 2013) has shown the subsurface existence of buried channel bodies beneath the Ghaggar plains in NW Indo-Gangetic plains. The mapped sand bodies follow trace of a paleochannel that begins at the mountain front near the exit of river Sutlej and extends to the northern margin of the Thar desert, suggesting existence of a large Himalayan-sourced river (Singh et al., 2011) in the past. The buried sand bodies hold potential records of erosion history over the Himalaya that could be used to assess climate-controlled erosion over the Himalaya. Geochemical variations in the sediments from two (~45m long) cores drilled below the trace of the paleochannel (upstream) near Sirhind, Punjab and two cores (GS-10 & 11) from downstream near Kalibangan, Rajasthan, are used in this study to understand the erosional pattern over the Himalaya during Late Quaternary. Down-core variations in chemical index of alteration (CIA=51-79) along with K2O/Na2O and Al2O3/(CaO+Na2O) ratios are consistent with the trends of SW summer monsoonal fluctuations during the Glacial-Interglacial periods indicating climate controlled weathering at the source; higher values during Interglacial and lower during Glacial periods with maximum value during the Holocene. Sr-Nd isotopic compositions of drill-cores sediments, 87Sr/86Sr (0.7314-0.7946), ɛNd (-23.2 to -14) are within the range of silicate rocks from the Higher and Lesser Himalaya. Significant down-core variations in 87Sr/86Sr and ɛNd are observed that reflect the mixing of varying proportions of the Higher and Lesser Himalayan sediments, the two dominant sources to the core sites. Sediments deposited during MIS-2 and MIS-4, cold and dry Glacial periods, show high 87Sr/86Sr and low ɛNd suggesting an enhanced contribution from the Lesser Himalayan rocks that are

  16. Coastal tectonics on the eastern margin of the Pacific Rim: Late Quaternary sea-level history and uplift rates, Channel Islands National Park, California, USA

    USGS Publications Warehouse

    Muhs, Daniel R.; Simmons, Kathleen R.; Schumann, R. Randall; Groves, Lindsey T.; DeVogel, Stephen B.; Minor, Scott A.; Laurel, Deanna

    2014-01-01

    The Pacific Rim is a region where tectonic processes play a significant role in coastal landscape evolution. Coastal California, on the eastern margin of the Pacific Rm, is very active tectonically and geomorphic expressions of this include uplifted marine terraces. There have been, however, conflicting estimates of the rate of late Quaternary uplift of marine terraces in coastal California, particularly for the orthern Channel Islands. In the present study, the terraces on San Miguel Island and Santa Rosa Island were mapped and new age estimates were generated using uranium-series dating of fossil corals and amino acid geochronology of fossil mollusks. Results indicate that the 2nd terrace on both islands is ~120 ka and the 1st terrace on Santa Rosa Island is ~80 ka. These ages correspond to two global high-sea stands of the Last Interglacial complex, marine isotope stages (MIS) 5.5 and 51, respectively. The age estimates indicate that San Miguel Island and Santa Rosa Island have been tectonically uplifted at rates of 0.12e0.20 m/ka in the late Quaternary, similar to uplift rates inferred from previous studies on neighboring San Cruz Island. The newly estimated uplift rates for the northern Channel Islands are, however, an order of magnitude lower than a recent study that generated uplift rates from an offshore terrace dating to the Last Glacial period. The differences between the estimated uplift rates in the present study and the offshore study are explained by the magnitude of glacial isostatic adjustment (GIA) effects that were not known at the time of the earlier study. Set in the larger context of northeastern Pacific Rim tectonics, Channel Islands uplift rates are higher than those coastal localities on the margin of the East Pacific Rise spreading center, but slightly lower than those of most localities adjacent to the Cascadia subduction zone. The uplift rates reported here for the northern Channel Islands are similar to those reported for most other

  17. Coastal tectonics on the eastern margin of the Pacific Rim: late Quaternary sea-level history and uplift rates, Channel Islands National Park, California, USA

    NASA Astrophysics Data System (ADS)

    Muhs, Daniel R.; Simmons, Kathleen R.; Schumann, R. Randall; Groves, Lindsey T.; DeVogel, Stephen B.; Minor, Scott A.; Laurel, DeAnna

    2014-12-01

    The Pacific Rim is a region where tectonic processes play a significant role in coastal landscape evolution. Coastal California, on the eastern margin of the Pacific Rim, is very active tectonically and geomorphic expressions of this include uplifted marine terraces. There have been, however, conflicting estimates of the rate of late Quaternary uplift of marine terraces in coastal California, particularly for the northern Channel Islands. In the present study, the terraces on San Miguel Island and Santa Rosa Island were mapped and new age estimates were generated using uranium-series dating of fossil corals and amino acid geochronology of fossil mollusks. Results indicate that the 2nd terrace on both islands is ˜120 ka and the 1st terrace on Santa Rosa Island is ˜80 ka. These ages correspond to two global high-sea stands of the Last Interglacial complex, marine isotope stages (MIS) 5.5 and 5.1, respectively. The age estimates indicate that San Miguel Island and Santa Rosa Island have been tectonically uplifted at rates of 0.12-0.20 m/ka in the late Quaternary, similar to uplift rates inferred from previous studies on neighboring Santa Cruz Island. The newly estimated uplift rates for the northern Channel Islands are, however, an order of magnitude lower than a recent study that generated uplift rates from an offshore terrace dating to the Last Glacial period. The differences between the estimated uplift rates in the present study and the offshore study are explained by the magnitude of glacial isostatic adjustment (GIA) effects that were not known at the time of the earlier study. Set in the larger context of northeastern Pacific Rim tectonics, Channel Islands uplift rates are higher than those coastal localities on the margin of the East Pacific Rise spreading center, but slightly lower than those of most localities adjacent to the Cascadia subduction zone. The uplift rates reported here for the northern Channel Islands are similar to those reported for most

  18. Late Quaternary sea-level history and the antiquity of mammoths (Mammuthus exilis and Mammuthus columbi), Channel Islands National Park, California, USA

    NASA Astrophysics Data System (ADS)

    Muhs, Daniel R.; Simmons, Kathleen R.; Groves, Lindsey T.; McGeehin, John P.; Randall Schumann, R.; Agenbroad, Larry D.

    2015-05-01

    Fossils of Columbian mammoths (Mammuthus columbi) and pygmy mammoths (Mammuthus exilis) have been reported from Channel Islands National Park, California. Most date to the last glacial period (Marine Isotope Stage [MIS] 2), but a tusk of M. exilis (or immature M. columbi) was found in the lowest marine terrace of Santa Rosa Island. Uranium-series dating of corals yielded ages from 83.8 ± 0.6 ka to 78.6 ± 0.5 ka, correlating the terrace with MIS 5.1, a time of relatively high sea level. Mammoths likely immigrated to the islands by swimming during the glacial periods MIS 6 (~ 150 ka) or MIS 8 (~ 250 ka), when sea level was low and the island-mainland distance was minimal, as during MIS 2. Earliest mammoth immigration to the islands likely occurred late enough in the Quaternary that uplift of the islands and the mainland decreased the swimming distance to a range that could be accomplished by mammoths. Results challenge the hypothesis that climate change, vegetation change, and decreased land area from sea-level rise were the causes of mammoth extinction at the Pleistocene/Holocene boundary on the Channel Islands. Pre-MIS 2 mammoth populations would have experienced similar or even more dramatic changes at the MIS 6/5.5 transition.

  19. Late Quaternary sea-level history and the antiquity of mammoths (Mammuthus exilis and Mammuthus columbi), Channel Islands NationalPark, California, USA

    USGS Publications Warehouse

    Muhs, Daniel R.; Simmons, Kathleen R.; Groves, Lindsey T.; McGeehin, John P.; Schumann, R. Randall; Agenbroad, Larry D.

    2015-01-01

    Fossils of Columbian mammoths (Mammuthus columbi) and pygmy mammoths (Mammuthus exilis) have been reported from Channel Islands National Park, California. Most date to the last glacial period (Marine Isotope Stage [MIS] 2), but a tusk of M. exilis (or immature M. columbi) was found in the lowest marine terrace of Santa Rosa Island. Uranium-series dating of corals yielded ages from 83.8 ± 0.6 ka to 78.6 ± 0.5 ka, correlating the terrace with MIS 5.1, a time of relatively high sea level. Mammoths likely immigrated to the islands by swimming during the glacial periods MIS 6 (~ 150 ka) or MIS 8 (~ 250 ka), when sea level was low and the island–mainland distance was minimal, as during MIS 2. Earliest mammoth immigration to the islands likely occurred late enough in the Quaternary that uplift of the islands and the mainland decreased the swimming distance to a range that could be accomplished by mammoths. Results challenge the hypothesis that climate change, vegetation change, and decreased land area from sea-level rise were the causes of mammoth extinction at the Pleistocene/Holocene boundary on the Channel Islands. Pre-MIS 2 mammoth populations would have experienced similar or even more dramatic changes at the MIS 6/5.5 transition.

  20. Late-Quaternary Speleothem Records from the Balkan Peninsula - Potential, Objectives and First Results

    NASA Astrophysics Data System (ADS)

    John, I.; McCoy, W. D.; Markovic, S.; Endlicher, W.

    2010-12-01

    Mid-latitude speleothems often contain detailed, high-resolution records of local and regional interglacial climate changes. Many speleothem records of Holocene (MIS 1) and Eemian (MIS 5e) climate evolution have been investigated, but there is very little work being done in the Balkan region, despite the fact that the area is very rich in limestone caves with speleothems. Situated at the interface between temperate-continental and Mediterranean climates, present-day climate on the Balkan Peninsula is determined by two major upper-level jet streams, the polarfront jet (PFJ) and the subtropical jet (STJ). On a seasonal scale, both features exert varying influence and determine frontogenesis processes, cyclonic activity and precipitation. On decadal to millennial time-scales, changes and fluctuations in the position and permanency of these atmospheric circulation features influence the isotope signature in rainfall and ultimately in cave drip waters and related speleothems. We are investigating speleothems from Serbia, Montenegro and Bosnia-Herzegovina to study Late Quaternary climatic changes and to learn how both synoptic-scale systems were linked during the Holocene and previous interglacial periods. By example of a stalagmite collected in Vernjikica Cave, Serbia (Carpatho-Balkans), the project's potential to address important aspects of paleoclimatic research in the Mediterranean realm is discussed. The first studied, fine-laminated calcite stalagmite is about 50 cm tall and extends conically from the base to the top, presenting at least two visible growth discontinuities. Four preliminary uranium-series ages (234U/230Th) constrain the general period of growth to MIS 5d to MIS 5b. Preliminary results suggest that the stable oxygen isotope profile obtained from the axial zone largely reflects the unaltered isotopic composition of the cave drip water. The observed shifts in the isotope records display long-term changing climate conditions from temperate warm and

  1. Sedimentology and paleohydrology of Late Quaternary lake deposits in the northern Namib Sand Sea, Namibia

    NASA Astrophysics Data System (ADS)

    Teller, James T.; Rutter, Nat; Lancaster, N.

    The Namib Sand Sea is the largest active desert dunefield in southern Africa, and is comprised mainly of large north-south linear dunes. In the interdune areas of the northern Sand Sea eleven small areas of calcareous lacustrine sediment have been studied. These beds are typically less than a metre thick and are dominantly comprised of calcareous sandstones to mudstones and sandy limestones. The carbonates are mainly magnesian calcites (1-14% MgCO 3) with some protodolomite and aragonite. Calcified reed casts and fresh to brackish water gastropods, diatoms, and ostracods are present in some beds. δ18O values indicate a hot and dry climate. A number of enriched δ13C values may reflect high salinity, low organic populations, or carbonate recrystallization. These carbonate-rich lacustrine deposits are indicative of increased periods of moisture availability in this normally hyperarid region during the Late Quaternary. The origin of the water responsible for depositing these sediments may be: (1) ponding at the end point of the Tsondab River, which at one time extended farther west into the Sand Sea; (2) flooding into interdune corridors when water levels rose in rivers such as the Kuiseb; (3) groundwater seepage into depressions either through dunes that border rivers or from the underlying Tsondab Sandstone; and (4) increased rainfall. We do not believe that there is evidence to support a major increase in precipitation over the region. However, even a small increase in precipitation in the headwaters of valleys that drain toward the Sand Sea might: (1) generate enough additional runoff to extend the terminal point of rivers such as the Tsondab farther into the dunes; (2) cause lateral flooding from major valleys into interdune corridors; and (3) recharge aquifers. The sedimentary records at Narabeb, Ancient Tracks, and West Pan, which lie along the old course of the Tsondab River, favor a ponded river origin for them, whereas groundwater seepage is favored at

  2. Modern Climate Analogues of Late-Quaternary Paleoclimates for the Western United States.

    NASA Astrophysics Data System (ADS)

    Mock, Cary Jeffrey

    This study examined spatial variations of modern and late-Quaternary climates for the western United States. Synoptic climatological analyses of the modern record identified the predominate climatic controls that normally produce the principal modes of spatial climatic variability. They also provided a modern standard to assess past climates. Maps of the month-to-month changes in 500 mb heights, sea-level pressure, temperature, and precipitation illustrated how different climatic controls govern the annual cycle of climatic response. The patterns of precipitation ratios, precipitation bar graphs, and the seasonal precipitation maximum provided additional insight into how different climatic controls influence spatial climatic variations. Synoptic-scale patterns from general circulation model (GCM) simulations or from analyses of climatic indices were used as the basis for finding modern climate analogues for 18 ka and 9 ka. Composite anomaly maps of atmospheric circulation, precipitation, and temperature were compared with effective moisture maps compiled from proxy data to infer how the patterns, which were evident from the proxy data, were generated. The analyses of the modern synoptic climatology indicate that smaller-scale climatic controls must be considered along with larger-scale ones in order to explain patterns of spatial climate heterogeneity. Climatic extremes indicate that changes in the spatial patterns of precipitation seasonality are the exception rather than the rule, reflecting the strong influence of smaller-scale controls. Modern climate analogues for both 18 ka and 9 ka clearly depict the dry Northwest/wet Southwest contrast that is suggested by GCM simulations and paleoclimatic evidence. 18 ka analogues also show the importance of smaller-scale climatic controls in explaining spatial climatic variation in the Northwest and northern Great Plains. 9 ka analogues provide climatological explanations for patterns of spatial heterogeneity over several

  3. A Late Quaternary shortening rate for the frontal thrust of the Andean Precordillera north of Mendoza

    NASA Astrophysics Data System (ADS)

    Schmidt, S.; Kuhlmann, J.; Hetzel, R.; Mingorance, F.; Ramos, V. A.

    2009-12-01

    Although large historical earthquakes occurred in the Andean back-arc region between 28° and 34°S - for instance Mendoza was destroyed by an earthquake of magnitude MS = 7.0 in 1861 - the slip rates of active faults remain unknown. We report a slip rate for the 50-km-long Las Penas thrust, which constitutes the frontal thrust of the Precordillera. In its southern part, a well preserved fluvial terrace along La Escondida Creek (Costa et al., 2000) is displaced vertically by 10.6 ± 0.7 m as documented by several fault scarp profiles. Apart from radiocarbon dating of plant remnants, three different approaches for 10Be exposure dating have been applied to constrain the age of the terrace. Amalgamated sandstone pebbles (corrected for an inherited 10Be component using similar pebbles from the active creek) and a depth profile obtained from four sand samples yield 10Be exposure ages of 12.2 ± 1.5 and 11.3 ± 2.0 kyr, respectively. Both ages are in excellent agreement with the 14C age of 12.61 ± 0.20 cal kyr BP. In contrast, 10Be ages of five sandstone boulders vary significantly and exceed the age of the terrace by 10 to 70 kyr, which demonstrates that the widely used assumption of a negligible inherited component is not valid here. The age of the river terrace combined with the vertical fault offset yields an uplift rate of ~0.8 mm/yr for the Las Penas thrust. Combined with the fault dip of 25°, we determine a Late Quaternary horizontal shortening rate of ~1.8 mm/yr, which is about 40% of the GPS derived shortening rate of 4.5 ± 1.7 mm/yr in the back-arc region of the Andes (Brooks et al., 2003). References Brooks, B.A., Bevis, M., Smalley, R., Kendrick, E., Manceda, R., Lauria, E., Maturana, R. & Araujo, M. (2003): Crustal motion in the Southern Andes (26° - 36°S): Do the Andes behave like a microplate? Geochem. Geophys. Geosyst., 4 (10), pp. 14, 1085, doi 10.1029/2003GC000505. Costa, C.H., Gardini, C.E., Diederix, H., Cortés, J.M. (2000): The Andean orogenic

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

    NASA Astrophysics Data System (ADS)

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

    2008-12-01

    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

  5. Origin, age, and paleoclimatic setting of the Late Quaternary deposits in Wadi Feiran, Sinai Peninsula: Geomorphologic, geochronologic, and isotopic constraints

    NASA Astrophysics Data System (ADS)

    Farag, A. Z. A.; Sultan, M.; Forman, S. L.; Krishnamurthy, R. V.

    2015-12-01

    There is considerable debate on the origin, age, and paleoclimatic setting of Late Quaternary deposits within the basement complex of the Sinai Peninsula. Our research in Wadi Feiran focused on documenting the sedimentology, stratigraphy, geochemistry and chronology of Late Quaternary deposits in the Feiran (lat. 28.706 N; long. 33.665; elevation: 715 to 772 m a.m.s.l) and Tarfa (lat. 28.692 N; long. 33.933 E; elevation: 1160 to 1244 m a.m.s.l) oases. Sequence stratigraphy, analysis of remote sensed images, and groundwater levels in these two areas indicate that the investigated deposits are structurally-controlled as they are found in areas with anomalously elevated groundwater levels and upstream from shear zone/wadi intersections. Sediments are largely arenaceous upstream and transition downstream to marly successions. We infer that these sediments were not deposited in lake settings because of the absence of shorelines and associated littoral, sublittoral and deeper water facies, and the presence of rhizoliths, secondary calcite veins and gastropods, all of which suggest deposition in a spring or wetland environment. A short hydrologic residence time and/or deposition in an open water system is supported by the lack of correlation (R = 0.08) between δ18O and δ13C values in carbonate deposits. Our findings are consistent with deposition of sediments by alluvial, fluvial and paludal processes under variable hydrologic conditions and higher water table conditions. Quartz extracts from these sediments yielded optically stimulated luminescence ages between ca. 27 and 11 ka and place these wetter conditions during the last glacial period and extend the "greening" of North Africa further eastward. Our findings are consistent with models which identify the wet periods in the Late Quaternary in the Sinai Peninsula and in North Africa as being glacial periods.

  6. Radiocarbon dates and late-Quaternary stratigraphy from Mamontova Gora, unglaciated central Yakutia, Siberia, U.S.S.R.

    USGS Publications Warehouse

    Pewe, T.L.; Journaux, A.; Stuckenrath, R.

    1977-01-01

    A fine exposure of perennially frozen ice-rich silt and associated flora and vertebrate fauna of late-Quaternary age exists at Mamontova Gora along the Aldan River in central Yakutia, Siberia, U.S.S.R. The silt deposit caps a 50-m-high terrace and consists of three units. An upper layer 1-2 m thick overlies a 10-15-m-thick brownish to black silt layer. The lower silt layer is greenish to gray and about 15 m thick. All the silt is well sorted with 60% of the particles falling between 0.005 and 0.5 mm in diameter and is generally chemically and mineralogically homogeneous. The middle unit contains may extinct vertebrate mammal remains and ice wedges. The lower unit contains little vegetation and no ice wedges. The silt is widespread and exists as a loamy blanket on terraces at various elevations on both sides of the lower Aldan River. The origin of the silt blanket of late-Quaternary age in central Yakutia has long been controversial. Various hypotheses have been suggested, including lacustrine and alluvial, as well as frost-action origins. It is sometimes referred to as loess-like loam. Pe??we?? believes the silt at Mamontova Gora is loess, some of which has been retransported very short distances by water. The silt probably was blown from wide, braided, unvegetated flood plains of rivers draining nearby glaciers. The silt deposits are late Quaternary in age and probably associated with the Maximum glaciation (Samarov) and Sartan and Syryan glaciations of Wisconsinan age. On the basis of biostratigraphy, 10 radiocarbon dates, and their relation to the nearby glacial record, it is felt that the upper unit at Mamontova Gora is Holocene and the middle unit is Wisconsinan. The youngest date available from the middle unit at this particular location is 26,000 years. Dates greater than 56,000 years were obtained in the lower part of the middle unit. The lower unit is definitely beyond the range of radiocarbon dating and probably is older than the last interglacial. The

  7. River terrace sequences: templates for Quaternary geochronology and marine-terrestrial correlation

    NASA Astrophysics Data System (ADS)

    Bridgland, David; Maddy, Darrel; Bates, Martin

    2004-02-01

    Fluvial sequences, particularly terrace staircases, represent archives of Quaternary palaeoclimatic fluctuation and can serve as stratigraphical frameworks for geochronology and for correlation with other depositional environments, in particular, the global marine oxygen isotope record. Fluvial lithostratigraphical frameworks also provide contexts for records, from fossils and artefacts, of faunal evolution and human occupation; conversely, both records can be means of relative dating of riverine sequences.Three fluvial sequences are examined as case studies. First is the Severn-Avon system in the English Midlands, which has biostratgraphical evidence and an amino acid geochronology, together with marker inputs from three different glaciations. The Somme sequence of northern France, famous for its Palaeolithic artefact assemblages, again has biostratigraphy and an amino acid geochronology and has also been dated with reference to overlying loess/palaeosols sequences. The fluvial terraces of the River Arun, the final case study, lack dating evidence but are interspersed within the Sussex raised beach staircase. Although various lines of evidence suggest that the rivers discussed have formed terraces in response to climatic fluctuation, an intriguing difference is that interglacial sediments occur at the bases of terrace formations in the Severn-Avon, whereas in the Somme they occur at the tops of sequences, beneath loessic overburden. Copyright

  8. Synchronous Late Quaternary slip rate variability on two strands of the San Jacinto fault, California

    NASA Astrophysics Data System (ADS)

    Le, K. N.; Oskin, M.

    2007-12-01

    We present new results that show slip rates varied synchronously by a factor of two over the past 35 kyr along two parallel strands of the San Jacinto fault. Our results combine high-resolution LiDAR digital topography, field mapping and 10Be exposure-age dating from two of the most active strands of the southern San Jacinto fault: the Clark fault (CLF) and Coyote Creek fault (CCF). These faults form numerous NW-striking scarps that offset three generations of Quaternary alluvial fan surfaces, Q2b, Q3a, and Q3b. We dated alluvial fans along both the CCF and CLF using 10Be sampling methods adapted for available material and degradation of the surface. For younger surfaces with well-preserved bar and swale morphology, we used a new sampling method where 12 to 20 chips from quartz-bearing boulders lodged within a bar were amalgamated into a single sample. For older surfaces we either sampled individual meter-sized boulders or collected samples from a 2 m-deep depth profile. Surface ages are consistent between CCF and CLF sites: 40 ± 12 ka and 31 ± 6 ka for Q2b, 7.1 ± 1.6 ka and 4.6 ± 1.6 ka for Q3a, respectively. Samples from Q3b near the CLF yielded ages of 1.0 ± 0.2 ka and 2.1 ± 0.3 ka. CCF samples have not yet been corrected 10Be inheritance, thus we use the CLF ages to calculate preliminary slip rates. Late Pleistocene to present rates are CLF: 2.2 ± 0.5 mm/yr, CCF: 3.4 ± 0.9 mm/yr, and 5.6 ± 1.4 mm/yr combined. Mid-Holocene to present rates are CLF: 4.1 ± 1.5 mm/yr, CCF: 6.7 ± 2.8 mm/yr, and 10.9 ± 4.3 mm/yr combined. Latest Holocene CLF slip rate exceeds 3 mm/yr. The combined Late Pleistocene to present slip rate for the southern San Jacinto fault is less than one third the rate deduced from the onset of faulting ca. 1 Ma. Mid-Holocene to present slip rates for both the CLF and CCF are about double their ca. 35 kyr rates, but are less than the 16 - 20 mm/yr geodetic loading rates and the >16 mm/yr slip rate since 1 ka at Hog Lake. We conclude that (1

  9. The Rise of Late Tertiary and Quaternary Erosion and Weathering Rates revisited (Ralph Alger Bagnold Medal Lecture)

    NASA Astrophysics Data System (ADS)

    von Blanckenburg, Friedhelm

    2010-05-01

    increased, the isotope ratio of Be-10 to Be-9 would have decreased by roughly the same factor. Over the past 10 My, records of chemical marine deposits (Fe-Mn crusts and authigenic deep sea sediments) show no change in this ratio after correction for radioactive decay of Be-10. Therefore, these records support the hypothesis of constant global erosion and weathering fluxes. If this hypothesis is true, neither Late Tertiary mountain building nor Quaternary cooling affected or was affected by a change in silicate weathering rates. Instead, a more continuous mechanism is suggested in that subtle ongoing hillslope rejuvenation in any soil-mantled hillslopes in kinetically-limited settings enable the feedback that stabilizes atmospheric CO2 and climate levels through silicate weathering. In fact, in steep, active mountain belts an increase of relief and erosion rates to those that are in excess of conditions were soils are stable lead to a decrease, not an increase of weathering rate. But the aim here is not to discount active mountains as premier agents of CO2 withdrawal. Silicate weathering may still take place within the adjacent sedimentary basins, and large carbon deposits could also be buried there in the organic form. (1) P. Z. Zhang, P. Molnar, W. R. Downs, Nature 410, 891 (2001). (2) J. Kuhlemann, W. Frisch, B. Székely, I. Dunkl, M. Kázmér, Int J Earth Sci) 91, 818 (2002). (3) F. Métivier, Y. Gaudemer, P. Tapponier, M. Klein, Geophys. J. Int 137, 280 (1999). (4) P. M. Sadler, GeoResearch Forum 5, 15 (1999). (5) F. von Blanckenburg, R. K. O'Nions, Earth and Planet. Sci. Letters 167, 175 (1999).

  10. Late quaternary depositional systems and sea level change-Santa Monica and San Pedro Basins, California continental borderland

    SciTech Connect

    Nardin, T.R.

    1983-07-01

    A suite of seismic reflection data that provides different degrees of resolution and penetration was used to map the depositional systems that have developed in Santa Monica and San Pedro basins during the late Quaternary. Submarine fan growth, particularly at the mouths of Hueneme and Redondo Canyons, has been the dominant mode of basin filling. Mass movement processes, ranging from creep to large-scale catastrophic slumping, have been important locally. In general, large-scale fan growth fits Normark's model in which the suprafan is the primary locus of coarse sediment deposition. Smaller scale morphologic and depositional patterns on the Hueneme and Redondo fans (e.g., distributary channels and coarse sediment concentrations basinward of the inner suprafan) suggest that a significant amount of coarse sediment presently bypasses the suprafans, however. Long-distance coarse sediment transport was particularly pronounced during late Wisconsinan lowstand of sea level and resulted in progradation of lower mid-fan and lower fan deposits.

  11. Morphometric analysis of drainage network in the northern sector of the southern Italian foredeep: implications for fluvial denudation processes and Late Quaternary geomorphological evolution

    NASA Astrophysics Data System (ADS)

    Gioia, D.; Moretti, M.; Gallicchio, S.; Schiattarella, M.

    2012-04-01

    We present new data about the morphological and stratigraphic evolution and the rates of fluvial denudation of an area located in the northernmost sector of the foredeep of the southern Apennines. The study area is the medium- to low-relief sector located between the easternmost part of the Daunia Apennine and the Apulian foreland of the Gargano promontory. This area is characterized by several orders of terraced fluvial deposits disconformably overlying lower Pleistocene marine clay and organized in a staircase geometry, which recorded the emersion and the long-term incision history of this sector since mid-Pleistocene times. Geomorphological analyses have been carried out in order to retrace the landscape evolution of the area and its relationships with tectonic- and eustatic-induced variations of base-levels of erosion. Drainage network morphometry and the estimation of several topographic attributes have been added to the data collected through photo-aerial geomorphological interpretation and field survey. Drainage pattern, morphometric indexes and geological data seem to indicate that the thrust front is not active in the Late Quaternary. Paleotopographic reconstruction of ancient base-levels of erosion has permitted to calculated missing volumes. The estimation of eroded volumes in river valleys was performed through a GIS-aided calculation supported by a DEM with spatial resolution of 8 m, using the several orders of terraced deposits recognized in the area. The mapped remnants of relict geomorphological land surfaces have been interpolated by geospatial analysis and subtracted pixel by pixel to the present-day topography. Then, denudation rates were calculated on the basis of the relative age assigned to the deposits. Middle to upper Pleistocene denudation rates estimated by means of such an approach are about 0.1 mm/y, in good agreement with data coming from direct and indirect evaluation of transport sediment yield. The analysis of longitudinal river

  12. Coupling Genetic and Species Distribution Models to Examine the Response of the Hainan Partridge (Arborophila ardens) to Late Quaternary Climate

    PubMed Central

    Chang, Jiang; Chen, De; Ye, Xinping; Li, Shouhsien; Liang, Wei; Zhang, Zhengwang; Li, Ming

    2012-01-01

    Understanding the historical dynamics of animal species is critical for accurate prediction of their response to climate changes. During the late Quaternary period, Southeast Asia had a larger land area than today due to lower sea levels, and its terrestrial landscape was covered by extensive forests and savanna. To date, however, the distribution fluctuation of vegetation and its impacts on genetic structure and demographic history of local animals during the Last Glacial Maximum (LGM) are still disputed. In addition, the responses of animal species on Hainan Island, located in northern Southeast Asia, to climate changes during the LGM are poorly understood. Here, we combined phylogeographic analysis, paleoclimatic evidence, and species distribution models to examine the response of the flightless Hainan Partridge (Arborophila ardens) to climate change. We concluded that A. ardens survived through LGM climate changes, and its current distribution on Hainan Island was its in situ refuge. Range model results indicated that A. ardens once covered a much larger area than its current distribution. Demographic history described a relatively stable pattern during and following the LGM. In addition, weak population genetic structure suggests a role in promoting gene flow between populations with climate-induced elevation shifts. Human activities must be considered in conservation planning due to their impact on fragmented habitats. These first combined data for Hainan Partridge demonstrate the value of paired genetic and SDMs study. More related works that might deepen our understanding of the responses of the species in Southeast Asia to late Quaternary Climate are needed. PMID:23185599

  13. Chronology and stratigraphy of Late Quaternary sediments in the Konya Basin, Turkey: Results from the KOPAL Project

    NASA Astrophysics Data System (ADS)

    Roberts, N.; Black, S.; Boyer, P.; Eastwood, W. J.; Griffiths, H. I.; Lamb, H. F.; Leng, M. J.; Parish, R.; Reed, J. M.; Twigg, D.; Yiǧitbaşioǧlu, H.

    1999-04-01

    The Late Quaternary environmental history of the Konya plain, in south central Turkey, is used to examine sediment facies changes in a shallow non-outlet basin which has experienced major climatically driven changes in lake extent. Two principal types of sedimentary archive are used to reconstruct a palaeoenvironmental record, namely alluvial sequences on the Çarşamba alluvial fan and sediments from residual lakes. The latter have been used to investigate broader climatic and vegetational histories via palaeolimnological techniques including pollen, diatom and stable isotope analysis. These changes are dated here by radiometric techniques including radiocarbon (AMS and conventional), OSL, and U-Th. Chronological agreement is generally good between the different dating techniques, although typically there is greatly reduced precision beyond ca. 25 ka. Lake sediment cores investigated have basal ages beyond the range of 14C dating, but contain hiatuses as a result of subsequent alternation between phases of lacustrine sedimentation and aeolian deflation. In contrast to most deepwater non-outlet lake systems, the Konya basin may have been occupied by a single extensive lake for as little as 10% of Late Quaternary time, mainly around the time of the LGM. This lake highstand was followed by an important arid interval. In the absence of unbroken chronostratigraphic sequences, palaeohydrological investigation of shallow non-outlet lakes may require analysis of basin-wide changes in sedimentation rather than reliance on single core records. Stratigraphic continuity in such sedimentary environments cannot be assumed, and requires independent chronological control through radiometric dating.

  14. Idiosyncratic responses of evergreen broad-leaved forest constituents in China to the late Quaternary climate changes

    PubMed Central

    Fan, Dengmei; Hu, Wan; Li, Bo; Morris, Ashley B.; Zheng, Min; Soltis, Douglas E.; Soltis, Pamela S.; Zhang, Zhiyong

    2016-01-01

    Subtropical evergreen broad-leaved forest (EBLF) is one of the most important vegetation types in China. Inferences from palaeo-biome reconstruction (PBR) and phylogeography regarding range shift history of EBLF during the late Quaternary are controversial and should be reconciled. We compared phylogeographic patterns of three EBLF constituents in China, Castanopsis tibetana, Machilus thunbergii and Schima superba. Contrary to a chorus of previous phylogeographic studies and the results of species distribution modelling (SDM) of this study (in situ survival during the LGM), the three species displayed three different phylogeographic patterns that conform to either an in situ survival model or an expansion-contraction model. These results are partially congruent with the inference of PBR that EBLF was absent to the north of 24° N at the LGM. This study suggests that the constituents of EBLF could have responded idiosyncratically to climate changes during the Late Quaternary. The community assemblages of EBLF could have been changing over time, resulting in no palaeo-analogs to modern-day EBLF, which may be the main reason responsible for the failure of PBR to detect the occurrence of EBLF north of 24° N at the LGM. PMID:27534981

  15. Idiosyncratic responses of evergreen broad-leaved forest constituents in China to the late Quaternary climate changes.

    PubMed

    Fan, Dengmei; Hu, Wan; Li, Bo; Morris, Ashley B; Zheng, Min; Soltis, Douglas E; Soltis, Pamela S; Zhang, Zhiyong

    2016-01-01

    Subtropical evergreen broad-leaved forest (EBLF) is one of the most important vegetation types in China. Inferences from palaeo-biome reconstruction (PBR) and phylogeography regarding range shift history of EBLF during the late Quaternary are controversial and should be reconciled. We compared phylogeographic patterns of three EBLF constituents in China, Castanopsis tibetana, Machilus thunbergii and Schima superba. Contrary to a chorus of previous phylogeographic studies and the results of species distribution modelling (SDM) of this study (in situ survival during the LGM), the three species displayed three different phylogeographic patterns that conform to either an in situ survival model or an expansion-contraction model. These results are partially congruent with the inference of PBR that EBLF was absent to the north of 24° N at the LGM. This study suggests that the constituents of EBLF could have responded idiosyncratically to climate changes during the Late Quaternary. The community assemblages of EBLF could have been changing over time, resulting in no palaeo-analogs to modern-day EBLF, which may be the main reason responsible for the failure of PBR to detect the occurrence of EBLF north of 24° N at the LGM. PMID:27534981

  16. Late Quaternary tectonic activity and crustal shortening rate of the Bogda mountain area, eastern Tian Shan, China

    NASA Astrophysics Data System (ADS)

    Wu, Chuanyong; Wu, Guodong; Shen, Jun; Dai, Xunye; Chen, Jianbo; Song, Heping

    2016-04-01

    The Bogda mountain range is the highest range among the northern Tian Shan mountains. Based on geologic and geomorphologic field surveys, trench excavation and optically stimulated luminescence (OSL) dating, we targeted the active Fukang fault along the Bogda mountain range and identified the late Quaternary deformation characteristics of this area. We found that the Fukang fault dislocated different geomorphic surfaces of the northern Bogda piedmont. The vertical fault displacement corresponds to the topographic relief of the Bogda over long time scales. Since the late Quaternary, the crustal shortening rate was estimated to be 0.90 ± 0.20 mm/yr, which is less than that of the western segment of the northern Tian Shan. We interpret the Bogda fold and thrust belt to be a thick-skinned structure, since a high angle thrust fault bounds the Bogda mountain range and the foreland basin. The deformation characteristics of this region have been dominated by vertical uplift, and the component of propagation toward the basin has been very limited. This tectonic deformation is evidenced as vertical growth. Although the deformation rate is small, the uplift amplitude is very significant in this region.

  17. Late Quaternary hydrological and ecological changes in the hyperarid core of the northern Atacama Desert (~ 21°S)

    NASA Astrophysics Data System (ADS)

    Gayo, Eugenia M.; Latorre, Claudio; Jordan, Teresa E.; Nester, Peter L.; Estay, Sergio A.; Ojeda, Karla F.; Santoro, Calogero M.

    2012-07-01

    The hyperarid core of the Atacama Desert possesses important reserves of "fossil" or ancient groundwater, yet the extent and timing of past hydrologic change during the late Quaternary is largely unknown. In situ and/or short-distance transported leaf-litter deposits abound along relict fluvial terraces inserted within four dry and unvegetated valleys that drain into the endorheic basin of Pampa del Tamarugal (PDT, 21°S, 900-1000 m), one of the largest and economically important aquifers in northern Chile. Our exceptional archive offers the opportunity to evaluate the response of low-elevation desert ecological and hydrological systems to late Quaternary climate variability. Three repeated expansions of riparian/wetland ecosystems, and perennial rivers occurred along the southernmost PDT basin between 17.6-14.2 ka, 12.1-11.4 ka and from 1.01-0.71 ka. Both early and late archaic archaeological artefact are present in clear association with our fossil riparian/wetland assemblages, which suggests that these palaeoenvironmental changes facilitated past human occupations in the hyperarid core of the Atacama Desert. Using modern analogues, we estimate that these ecological and hydrological changes were triggered by a threefold increase in rainfall along the headwaters of what are presently inactive canyons. Comparisons with other regional palaeoclimatic records from the central Andes indicate that these changes were synchronous with the widespread pluvial stages now termed the Central Andean Pluvial Event (CAPE— 17.5-14.2 ka and 13.8-9.7 ka). In addition, we summarize new evidence for perennial runoff, riparian ecosystems and a major human settlement during the latest Holocene. Our findings clearly show that local hydrological changes in the PDT were coupled with precipitation variability in the adjacent eastern highlands during the late Quaternary. The long-term dynamics of low-elevation desert ecological and hydrological systems are likely driven by changes in

  18. Modern Gas Vents in the St. Lawrence Estuary (Eastern Canada); Linking Palaeozoic Rocks, Quaternary Sediments and the Marine Environment.

    NASA Astrophysics Data System (ADS)

    Duchesne, M. J.; Pinet, N.; Bolduc, A.; Lavoie, D.; Campbell, D. C.

    2007-12-01

    Since 2003, the seafloor and the subsurface of the St. Lawrence Estuary (eastern Canada) were surveyed with various geophysical tools such as high and very-high resolution seismic reflection systems, sidescan sonar and multibeam echo sounder; moreover several cores were collected. The most striking features on the multibeam bathymetric imagery are numerous pockmarks (n>750) ranging in diameter from tens to hundreds of meters. The use of multi-resolution geophysical systems allowed the documenting of their fractal nature as micro and macro seeps are observed. Pockmarks are isolated, associated with submarine landslides, linearly distributed or included in cluster features. Sidescan sonar coverage confirms that some vents are active whereas backscatter images show several highly- reflective pockmarks. Carbonate crusts were sampled in some of these highly-reflective features whereas in other pockmarks similar crusts, located at various depths in the sedimentary column, indicate possible intermittent chemosynthetic microbial activity through recent times. Seismic sections permitted to image gas chimneys beneath the pockmarks that are rooted into the bedrock and gas-related amplitude anomalies within the Quaternary succession. In addition several seismic anomalies are found over either bedrock highs or slightly- dipping features imaged near the top of the bedrock. The pockmarks distribution correlates with both the bedrock geology and the thickness of the Quaternary deposits. Pockmarks are preferentially found above the Paleozoic autochtonous domain (St. Lawrence platform) and located where the Quaternary sediment cover is the thinnest (<200 m) although seismic anomalies attributed to the presence of gas, are observed over the entire basin including where the Quaternary succession is the thickest (>420 m). The results of the study suggest that gas release in the marine environment is likely of thermogenic origin and controlled by one or several of the following

  19. Late Quaternary hydrology in North Africa and the Near East (Hans Oeschger Medal Lecture)

    NASA Astrophysics Data System (ADS)

    Gasse, Françoise

    2010-05-01

    from Arabia(9) and inferred from lake archives and nearshore marine cores for the Sahara coincide with Marine Isotopic Stages 9, 7, 5.5 and 5.3. Stable isotope and vegetation data indicate that there, precipitation is of tropical origin as a result of an intensified monsoon and a northward migration of the Intertropical Convergence zone. These regional patterns are discussed in the light of general climatic models: roles of orbital forcing, extent/decrease of the northern ice sheet and marine ice, atmospheric content in greenhouse gases, large-scale atmospheric and oceanic circulation and related latitudinal shifts of major climatic belts. At a shorter time-scale, several abrupt changes can also be related to climatic events in high northern latitudes. Pronounced dry spells in the Lisan basin are correlated with Heinrich events(5). The Younger Dryas (YD) and the 8.2 ka events often coincide with arid intervals. During the Holocene, the best-resolved records suggest close relationships between solar activity, northern high-latitude temperature and rainfall intensity. The rapid Mid-Late Holocene aridification leading to modern climates affected both the temperate and subtropical domains. Its mechanisms have been intensively debated. To-date, the best explanations derive from a transient simulation of the North Africa aridification using a general circulation ocean-atmosphere-terrestrial ecosystem model(10); it suggests that the vegetation collapse in southern Sahara is driven by a gradual monsoonal climate response to orbital forcing, increased climate variability and precipitation threshold, rather than a positive vegetation feedback as previously suggested. Long and short-term hydrological changes have obviously induced adjustments or migrations of human societies. For exemple, in the Levant, the YD drought placed the sedentary hunter-gatherers Natufians under severe stress that they circumvented by two strategies : (i) people were forced to switch from a passive

  20. The modern diatom spectra of Madagascar and diatom-inferred Late Quaternary climatic changes in northeastern and central Madagascar

    SciTech Connect

    Reyes, N.E.

    1993-01-01

    A study was conducted to classify diatoms in modern sediment surface samples in freshwater sites into assemblages and to assess the historical changes in lake level changes and climatic conditions in Madagascar during the Late Quaternary. Analysis of taxonomic percentages of diatoms in recently deposited sediments from various sites shows that diatom communities in these sites can be grouped by means of cluster analysis into distinct assemblages, some of which show similarities to groupings found in East Africa. pH and conductivity appear to be important factors correlating with differences in diatom communities in these study sites. Trends in diatom assemblages in a sediment core taken from Lake Alaotra, supplemented by those in sediments of the paleolake Ampasambazimba, suggest that the late Pleistocene in northeastern Madagascar was arid, though aridity was probably not as constant or as severe as in many areas of eastern and northern Africa; the Holocene was a period of moderate but variable conditions, marked by a distinct dry episode ca 5000 yr B.P. and a drying trend toward the late Holocene. Changes in diatom assemblages in a sediment core from Lake Kavitaha in central Madagascar suggest changes in the surrounding environment during at least two periods in the late Holocene. These coincide with increases in charcoal influx and, around 700 yr B.P., with the intensification of agricultural activity in the area.

  1. Exceptionally well preserved late Quaternary plant and vertebrate fossils from a blue hole on Abaco, The Bahamas.

    PubMed

    Steadman, David W; Franz, Richard; Morgan, Gary S; Albury, Nancy A; Kakuk, Brian; Broad, Kenneth; Franz, Shelley E; Tinker, Keith; Pateman, Michael P; Lott, Terry A; Jarzen, David M; Dilcher, David L

    2007-12-11

    We report Quaternary vertebrate and plant fossils from Sawmill Sink, a "blue hole" (a water-filled sinkhole) on Great Abaco Island, The Bahamas. The fossils are well preserved because of deposition in anoxic salt water. Vertebrate fossils from peat on the talus cone are radiocarbon-dated from approximately 4,200 to 1,000 cal BP (Late Holocene). The peat produced skeletons of two extinct species (tortoise Chelonoidis undescribed sp. and Caracara Caracara creightoni) and two extant species no longer in The Bahamas (Cuban crocodile, Crocodylus rhombifer; and Cooper's or Gundlach's Hawk, Accipiter cooperii or Accipiter gundlachii). A different, inorganic bone deposit on a limestone ledge in Sawmill Sink is a Late Pleistocene owl roost that features lizards (one species), snakes (three species), birds (25 species), and bats (four species). The owl roost fauna includes Rallus undescribed sp. (extinct; the first Bahamian flightless rail) and four other locally extinct species of birds (Cooper's/Gundlach's Hawk, A. cooperii/gundlachii; flicker Colaptes sp.; Cave Swallow, Petrochelidon fulva; and Eastern Meadowlark, Sturnella magna) and mammals (Bahamian hutia, Geocapromys ingrahami; and a bat, Myotis sp.). The exquisitely preserved fossils from Sawmill Sink suggest a grassy pineland as the dominant plant community on Abaco in the Late Pleistocene, with a heavier component of coppice (tropical dry evergreen forest) in the Late Holocene. Important in its own right, this information also will help biologists and government planners to develop conservation programs in The Bahamas that consider long-term ecological and cultural processes. PMID:18077421

  2. Exceptionally well preserved late Quaternary plant and vertebrate fossils from a blue hole on Abaco, The Bahamas

    PubMed Central

    Steadman, David W.; Franz, Richard; Morgan, Gary S.; Albury, Nancy A.; Kakuk, Brian; Broad, Kenneth; Franz, Shelley E.; Tinker, Keith; Pateman, Michael P.; Lott, Terry A.; Jarzen, David M.; Dilcher, David L.

    2007-01-01

    We report Quaternary vertebrate and plant fossils from Sawmill Sink, a “blue hole” (a water-filled sinkhole) on Great Abaco Island, The Bahamas. The fossils are well preserved because of deposition in anoxic salt water. Vertebrate fossils from peat on the talus cone are radiocarbon-dated from ≈4,200 to 1,000 cal BP (Late Holocene). The peat produced skeletons of two extinct species (tortoise Chelonoidis undescribed sp. and Caracara Caracara creightoni) and two extant species no longer in The Bahamas (Cuban crocodile, Crocodylus rhombifer; and Cooper's or Gundlach's Hawk, Accipiter cooperii or Accipiter gundlachii). A different, inorganic bone deposit on a limestone ledge in Sawmill Sink is a Late Pleistocene owl roost that features lizards (one species), snakes (three species), birds (25 species), and bats (four species). The owl roost fauna includes Rallus undescribed sp. (extinct; the first Bahamian flightless rail) and four other locally extinct species of birds (Cooper's/Gundlach's Hawk, A. cooperii/gundlachii; flicker Colaptes sp.; Cave Swallow, Petrochelidon fulva; and Eastern Meadowlark, Sturnella magna) and mammals (Bahamian hutia, Geocapromys ingrahami; and a bat, Myotis sp.). The exquisitely preserved fossils from Sawmill Sink suggest a grassy pineland as the dominant plant community on Abaco in the Late Pleistocene, with a heavier component of coppice (tropical dry evergreen forest) in the Late Holocene. Important in its own right, this information also will help biologists and government planners to develop conservation programs in The Bahamas that consider long-term ecological and cultural processes. PMID:18077421

  3. A tale of two species: Extirpation and range expansion during the late Quaternary in an extreme environment

    NASA Astrophysics Data System (ADS)

    Smith, Felisa A.; Crawford, Dolly L.; Harding, Larisa E.; Lease, Hilary M.; Murray, Ian W.; Raniszewski, Adrienne; Youberg, Kristin M.

    2009-02-01

    Death Valley, California is today the hottest hyperarid area in the western Hemisphere with temperatures of 57 °C (134 °F) recorded. During the late Quaternary, pluvial Lake Manly covered much of the Valley and contributed to a much more moderate climate. The abrupt draining of Lake Manly in the mid-Holocene and coincident dramatic shifts in temperature and aridity exerted substantial selection pressure on organisms living in this area. Our research investigates the adaptive response of Neotoma (woodrats) to temperature change over the late Quaternary along a steep elevational and environmental gradient. By combining fieldwork, examination of museum specimens, and collection of paleomiddens, our project reconstructs the divergent evolutionary histories of animals from the valley floor and nearby mountain gradients (- 84 to > 3400 m). We report on recent paleomidden work investigating a transition zone in the Grapevine Mountains (Amargosa Range) for two species of woodrats differing significantly in size and habitat preferences: N. lepida, the desert woodrat, and N. cinerea, the bushy-tailed woodrat. Here, at the limits of these species' thermal and ecological thresholds, we demonstrate dramatic fluctuations in the range boundaries over the Holocene as climate shifted. Moreover, we find fundamental differences in the adaptive response of these two species related to the elevation of the site and local microclimate. Results indicate that although N. cinerea are currently extirpated in this area, they were ubiquitous throughout the late Pleistocene and into the middle Holocene. They adapted to climate shifts over this period by phenotypic changes in body mass, as has been demonstrated for other areas within their range; during colder episodes they were larger, and during warmer intervals, animals were smaller. Their presence may have been tied into a much more widespread historical distribution of juniper ( Juniperus sp.); we document a downward displacement of

  4. Late Quaternary stream sedimentation in the humid tropics: a review with new data from NE Queensland, Australia

    NASA Astrophysics Data System (ADS)

    Thomas, Michael F.; Nott, Jonathan; Price, David M.

    2001-07-01

    There is now a wide agreement that temperature depression in the humid tropics during the Last Glacial Maximum (LGM) was at least 5°C. Most estimates of precipitation reduction at the LGM range from 25-30% to 50-65%, based on proxy data, but the recent CCM1 model envisages only around 12%. Dates obtained from river sediments indicate major changes to fluvial activity in the late Quaternary. Isotope Zone 3 sediments (58-28 ka BP) are widespread and possibly indicate cooler conditions. Post-28 ka BP, and certainly post-21 ka BP, river regimes altered radically towards fan building, braiding or major reduction in all activity. This paper reports on fan formation in NE Queensland between 26 and 14 ka BP and reviews evidence for comparable changes in humid tropical areas of S America, W Africa and SE Asia, including records of Holocene sedimentation. Within a global rhythm of major changes to river regimes in the humid tropics during the late Quaternary, it is now possible to detect regional variations in stream response to climatic change. At the LGM, reductions in stream power may have led to fan formation in NE Queensland, while vegetation changes may have contributed to increased sediment loads and braiding in some forest marginal areas. But, in W Africa, greater aridity may have been responsible for enfeebled streams leaving few records. Channel cutting, then deposition of coarse sediment in braided rivers marked the transition to the early Holocene in W Africa, and fans became entrenched in NE Queensland. This regime persisted until forest recovery was complete by 9.5-8.5 ka BP, when widespread overbank deposition occurred and a change towards meandering channels took place widely across the humid tropical zone, followed by several cut-and-fill episodes in the middle and late Holocene.

  5. Evolution and flooding history of the Sacramento River over the late Quaternary illustrated on pristine floodplains near Chico, California

    NASA Astrophysics Data System (ADS)

    Will, M.; Aalto, R. E.; Singer, M. B.; Fuchs, M.

    2009-12-01

    Different river systems are often seen to respond individually to climate and environmental forcing during the late Quaternary, with a large number of prior studies investigating the unique history of various European rivers. In order to broaden our understanding of climate-induced late Quaternary morpho-dynamic change within a wider range of fluvial environments, more studies are needed from regions that differ substantially from Europe. The Sacramento River downstream of the city of Chico, California, features three different types of surface (palaeo) channel systems - meandering, braiding and anastomosing. This provides an excellent study region to investigate controls on channel and floodplain development by external (and internal) forcing over the Quaternary. This and the fact that two of these palaeochannel systems play a major role in flood and sediment conveyance make this area attractive for research on flooding and river/floodplain development. Furthermore, the climate and sea level forcing over the Quaternary are substantially different here from most European study areas, providing valuable new perspective. We present results from our investigation of a near-pristine fluvial environment along the largest river in California - the Llano Seco reach of the Sacramento River, between Chico and the downstream wetlands of Butte Sink. The Llano Seco Ranch has a unique ownership history that makes it the only remaining significant undisturbed floodplain along the Sacramento River, featuring more than 20,000 acres of superb habitat nourished by a natural geomorphic system. Despite its importance to science and society and the prior recognition of beautifully preserved Quaternary and Holocene channel systems, fluvial features in this area have not been rigorously dated. Furthermore, there have been no detailed studies of deep stratigraphic profiles afforded by the extensive, well preserved deposits of fluvial sediments and floodplain soils. Our research

  6. Variations in Late Quaternary behavior along and among range-front faults of the Sierra Nevada, California

    SciTech Connect

    Clark, M.M. ); Gillespie, A.R. . Geological Sciences)

    1993-04-01

    Late Quaternary slip rates of the 11 or so recognized active range-front faults of the Sierra Nevada from Owens Lake northwestward to Carson Valley show enough variation with time and location that a proper understanding of slip behavior of these faults may require slip histories at many places for each. Late Quaternary traces of these normal faults vary in length from 13 to 45 km. Most faults trend more northerly than the [approximately]MW trend of the range front. The faults are separated by < 5 to > 20 km of apparently unfaulted terrain; many have echelon overlap. None of the faults has a significant component of strike slip, including those of Owens Valley. The largest late Quaternary slip rates (> 2 mm/yr) occur on the Hilton Creek fault at Long Valley and 20 km to the north on the Mono Lake fault. Slip rates > 1 mm/yr occur on at least one fault north of Mono Lake and in Round Valley, south of Long Valley. Farther south (Owens Valley) range-front faults have slip rates < 1 mm/yr and have notably discontinuous traces. Displacements of moraines across the Hilton Creek fault at 4 sites are compatible with slip rates that increase northward from the south end of the fault, but stay constant through time at a site. The slip rates are 0.1 to 0.4 mm/yr near the south end; 0.1 to 0.8 mm/yr at Hilton Lakes, 3 km to the northwest; 1.4 to 3 mm/yr at McGee Creek, 9 km farther northwest; and 1.1 to 2 mm/yr at Tobacco Flat, 5 km farther northwest in Long Valley and > 15 km from the north end of the fault. At McGee Creek, slip rate since 10--15 ka is 1.3--2.5 mm/yr; since 13--20 ka, 1.4--2.6 mm/yr; since 25--40 ka, 1.4--4.2 mm/yr, and since 65--140 ka, 1.1--3.5 mm/yr. The apparently uniform rate through time at McGee Creek (and also at Hilton Lakes and Tobacco Flat, but for fewer periods; the south end site is for only one period) is interesting, but not yet convincing, mainly because of uncertain dates.

  7. Late Quaternary sediment deposition of core MA01 in the Mendeleev Ridge, the western Arctic Ocean: Preliminary results

    NASA Astrophysics Data System (ADS)

    Park, Kwang-Kyu; Kim, Sunghan; Khim, Boo-Keun; Xiao, Wenshen; Wang, Rujian

    2014-05-01

    Late Quaternary deep marine sediments in the Arctic Ocean are characterized by brown layers intercalated with yellowish to olive gray layers (Poore et al., 1999; Polyak et al., 2004). Previous studies reported that the brown and gray layers were deposited during interglacial (or interstadial) and glacial (or stadial) periods, respectively. A 5.5-m long gravity core MA01 was obtained from the Mendeleev Ridge in the western Arctic Ocean by R/V Xue Long during scientific cruise CHINARE-V. Age (~450 ka) of core MA01 was tentatively estimated by correlation of brown layers with an adjacent core HLY0503-8JPC (Adler et al., 2009). A total of 22 brown layers characterized by low L* and b*, high Mn concentration, and abundant foraminifera were identified. Corresponding gray layers are characterized by high L* and b*, low Mn concentration, and few foraminiferal tests. Foraminifera abundance peaks are not well correlated to CaCO3 peaks which occurred with the coarse-grained (>0.063 mm) fractions (i.e., IRD) both in brown and gray layers. IRDs are transported presumably by sea ice for the deposition of brown layers and by iceberg for the deposition of gray layers (Polyak et al., 2004). A strong correlation coefficient (r2=0.89) between TOC content and C/N ratio indicates that the major source of organic matter is terrestrial. The good correlations of CaCO3 content to TOC (r2=0.56) and C/N ratio (r2=0.69) imply that IRDs contain detrital CaCO3 which mainly originated from the Canadian Arctic Archipelago. In addition, high kaolinite/chlorite (K/C) ratios mostly correspond to CaCO3 peaks, which suggests that the fine-grained particles in the Mendeleev Ridge are transported from the north coast Alaska and Canada where Mesozoic and Cenozoic strata are widely distributed. Thus, the Beaufort Gyre, the predominant surface current in the western Arctic Ocean, played an important role in the sediment delivery to the Mendeleev Ridge. It is worthy of note that the TOC and CaCO3 peaks are

  8. Late Quaternary Spring-Fed Deposits of the Grand Canyon and Their Implication for Deep Lava-Dammed Lakes

    NASA Astrophysics Data System (ADS)

    Kaufman, Darrell S.; O'Brien, Gary; Mead, Jim I.; Bright, Jordon; Umhoefer, Paul

    2002-11-01

    One of the most intriguing episodes in the Quaternary evolution of the Grand Canyon of the Colorado River, Arizona, was the development of vast lakes that are thought to have backed up behind lava erupted into the gorge. Stratigraphic evidence for these deep lava-dammed lakes is expectedly sparse. Possible lacustrine deposits at six areas in the eastern canyon yielded no compelling evidence for sediment deposited in a deep lake. At two of the sites the sediment was associated with late Quaternary spring-fed pools and marshes. Water-lain silt and sand at lower Havasu Creek was deposited ˜3000 cal yr ago. The deposit contains an ostracode assemblage similar to that living in the modern travertine-dammed pools adjacent to the outcrop. The second deposit, at Lees Ferry, formed in a spring-fed marsh ˜43,000 cal yr ago, as determined by 14C and amino acid geochronology. It contains abundant ostracode and mollusk fossils, the richest assemblages reported from the Grand Canyon to date. Our interpretation of these sediments as spring-fed deposits, and their relative youth, provides an alternative to the conventional view that deposits like these were formed in deep lava-dammed lakes that filled the Grand Canyon.

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

    USGS Publications Warehouse

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

    2013-01-01

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

  10. Permafrost sequences on Kurungnakh Island, Lena Delta (NE Siberia, Russia) as key site of the late Quaternary environmental history of West Beringia

    NASA Astrophysics Data System (ADS)

    Wetterich, S.; Kuzmina, S.; Andreev, A. A.; Kienast, F.; Meyer, H.; Schirrmeister, L.; Kuznetsova, T.; Sierralta, M.

    2009-04-01

    Late Quaternary permafrost sequences are widely distributed in the arctic lowlands of Siberia. Because the existence of permafrost has been sensitive to climate changes during the Quaternary past, such frozen deposits are regarded as an archive of palaeoenvironmental dynamics. Late Quaternary palaeoenvironments of the Siberian Arctic were reconstructed by combining data from several fossil bioindicators (pollen, plant macro-fossils, ostracods, insects, and mammal bones) with sedimentological and cryolithological data from permafrost deposits. The late Pleistocene to Holocene sequence on Kurungnakh Island (Lena Delta, NE Siberia) reflects the environmental history of West Beringia and covers glacial/interglacial and stadial/interstadial climate variations with a focus on the Middle Weichselian interstadial (50-32 kyr BP). The record mirrors the development of periglacial landscapes under changing sedimentation regimes which were meandering fluvial during the Early Weichselian, colluvial or proluvial on gently inclined plaines during the Middle and Late Weichselian, and thermokarst-affected during the Holocene. Palaeoecological records indicate the existence of tundra-steppe vegetation under cold continental climate conditions during the Middle Weichselian interstadial. Due to sedimentation gaps in the sequence between 32 and 17 kyr BP and 17 and 8 kyr BP, the Late Weichselian stadial is incompletely represented in the studied outcrops. Nevertheless, by several palaeoecological indications arctic tundra-steppe vegetation under extremely cold-arid conditions prevailed during the late Pleistocene. The tundra-steppe disappeared completely due to lasting paludification during the Holocene. Initially subarctic shrub tundra formed, which later retreated in course of the late Holocene cooling.

  11. From mud and grains to curves and concepts: Late Quaternary climatic history from Chew Bahir, southern Ethiopia

    NASA Astrophysics Data System (ADS)

    Foerster, V. E.; Junginger, A.; Asrat, A.; Lamb, H. F.; Gebru, T.; Wennrich, V.; Weber, M. E.; Rethemeyer, J.; Nowaczyk, N.; Frank, U.; Brown, M. C.; Trauth, M. H.; Schaebitz, F.

    2012-12-01

    Chew Bahir, a tectonically bound basin between the Main Ethiopian Rift and the Omo -Turkana basin, responded sensitively to past climatic fluctuations. Now a saline mudflat, its sediments contain an extensive archive of climatic and environmental history within the source region of anatomically modern humans. Here we present new Late Quaternary paleoclimatic data from six cores (9-18 m long) retrieved in a NW-SE transect across the basin. Multiproxy analysis, including geochemical, geophysical, biological, paleomagnetic and sedimentological analyses, combined with six AMS radiocarbon dates, has been applied to the cores. This reveals that Chew Bahir recorded climatic events at centennial to millennial resolution, including Dansgaard-Oeschger cycles and Heinrich events. The data correlate with both high-latitude and tropical climatic records. Chew Bahir therefore represents a key site from which to understand the timing and mechanisms of local, regional and global climatic events.

  12. The occurrence and fission-track ages of late neogene and quaternary volcanic sediments, Siwalik group, Northern Pakistan

    USGS Publications Warehouse

    Johnson, G.D.; Zeitler, P.; Naeser, C.W.; Johnson, N.M.; Summers, D.M.; Frost, C.D.; Opdyke, N.D.; Tahirkheli, R.A.K.

    1982-01-01

    Volcanic sediments, now mostly bentonites and bentonitic mudstones, occur throughout the Late Neogene and Quaternary Siwalik Group of northern Pakistan. A number of these deposits have been dated by the fission-track method, utilizing zircon phenocrysts from these deposits, and provide the chronometric constraints upon which a paleomagnetic stratigraphy is developed for the Siwalik Group. Notable in the occurrence of these altered tuff horizons is an apparent mode in their stratigraphic development from approximately 3.0 to 1.5 m.y. B.P. which coincides with the period of activity of the Dacht-e-Nawar volcanic complex of east-central Afghanistan. Fission-track ages of certain tuffs for critical areas of northern Pakistan are reported herein. ?? 1982.

  13. Accumulation rates or percentages? How to quantify Sporormiella and other coprophilous fungal spores to detect late Quaternary megafaunal extinction events

    NASA Astrophysics Data System (ADS)

    Wood, Jamie R.; Wilmshurst, Janet M.

    2013-10-01

    Spores of coprophilous fungi, and in particular those of Sporormiella, are a routinely used proxy for detecting late Quaternary herbivore extinction events in sedimentary records. Spore abundance is typically quantified as a percentage of the total, or dryland, pollen sum. Although this is a quick method that does not require the development of site-specific age-depth models, it relies on stable pollen accumulation rates and is therefore highly sensitive to changes in vegetation. This may lead to incorrect placement of extinction events in sedimentary records, particularly when they occur contemporaneously with major climatic/vegetation transitions. We suggest that the preferred method of quantification should be accumulation rate, and that pollen abundance data should also be presented, particularly for periods of major vegetation change. This approach provides a more reliable record of past herbivore abundance independent of vegetation change, allowing extinction events to be more accurately placed in stratigraphic sequences.

  14. The ``Problem of the quaternary'' and the taxonomic rank of the late cenozoic in the international stratigraphic scale

    NASA Astrophysics Data System (ADS)

    Zubakov, V. A.

    2011-02-01

    An international scientific conflict has arisen around the International Stratigraphic Scale, the main document that regulates the rules of reading of geological records and, hence, concerns all Earth sciences. The matter of debate is the geological time scale of 2004, developed by the International Commission on Stratigraphy, where the Quaternary system was abandoned. This ICS decision triggered a protest among Quaternary geologists, members of INQUA, and became the subject of much controversy. This article provides a comprehensive analysis of the Quaternary problem and proposes a reasonable scientific solution that may be appropriate for both parties. The subject of Late Cenozoic geology is discussed: glaciations, human evolution, and recent deposits. In contrast to Charles Lyell's definition of the Plio-Pleistocene according to the percentage of modern mollusk species, it is defined here as a blanket formation, which is correlative to the topography and consists of mapped stratogens hosting fossils of modern biogeocenoses. Features of the description of the Plio-Pleistocene in terms of gravitational orbital tuning are considered. Four paleogeographic phases of modern environment evolution are recognized and ranked as stages: (1) The Messinian evolutionary explosion involved the appearance of many biogeocenoses and the bipedal walking of our extinct ancestors armed with sticks. It was a consequence of the Early Greenland (7.6 Ma BP) and Patagonian (6.7 Ma BP) hyperglaciations. (2) The Zanclean age is marked by climatic and hydrological but not evolutionary boundaries. (3) The appearance of the Villafranchian animal assemblage and Australopithecus, who used stones as weapon: 4.0-3.6 Ma BP. Orogeny and isolation of the Arctic Ocean changed the global climate dramatically. (4) The sexual revolution became the third evolutionary jump: the appearance of the first woman, "Eve", and the genus Homo with her: 1.9 Ma BP. According to the current view, the Plio

  15. Late Quaternary slip rate of the Batang Fault and its strain partitioning role in Yushu area, central Tibet

    NASA Astrophysics Data System (ADS)

    Huang, Xuemeng; Du, Yi; He, Zhongtai; Ma, Baoqi; Xie, Furen

    2015-06-01

    The late Quaternary activity of Yushu segment is poorly understood compared with other segments within Ganzi-Yushu Fault system. We focused on the Batang Fault, a major branch fault of the Yushu segment. Interpretation of remote sensing images and field investigations reveals that this fault has a clear geomorphic expression which is characterized by prominent fault escarpment and systematically offset gullies, fluvial terraces and alluvial fans along strike. Morphotectonic mapping, combined with optically stimulated luminescence (OSL) and radiocarbon (14C) data, suggest that the Batang Fault is a late Holocene active left-lateral strike-slip fault, along with some reverse component. The average left-lateral slip rate of this fault is 2-4 mm/yr and vertical slip rate is 0.2-0.6 mm/yr since Late Pleistocene. Comparison with the slip rates of other faults within the Ganzi-Yushu Fault system demonstrates that the Batang Fault partitioned nearly a third of the strike slip deformation within Yushu segment. This study provides insights into the reasons why the Yushu Fault is relatively less active when compared with other segments within Ganzi-Yushu Fault system and is crucial to the seismic hazard assessment in Yushu area especially after the occurrence of 2010 Ms 7.1 Yushu earthquake.

  16. Late Quaternary high resolution sequence stratigraphy of an active rift, the Sperchios Basin, Greece: An analogue for subtle stratigraphic plays

    SciTech Connect

    Eliet, P.P.; Gawthorpe, R.L.

    1996-12-31

    The Sperchios Basin is an active asymmetric graben, bounded to the south by a major border fault system with major fault segments typically 20-30 km long. The basin is dominated by a major axial fluvio-deltaic system which enters the partially enclosed Maliakos Gulf to the east. Lateral sourced depositional systems within the basin comprise hanging-wall and footwall-derived alluvial fans and a narrow coastal plain along the footwall scarp bordering the Maliakos Gulf. High resolution seismic data from the Maliakos Gulf reveals three late Quaternary progradational parasequences sourced from axial and lateral depositional systems, with a regional late-Pleistocene transgressive surface dated at circa. 10 ka BP within the Maliakos Gulf. Differential subsidence of the late Pleistocene transgressive surface indicates marked variation in subsidence from 2.4 m ka{sup -1} at fault segment centers to 0.8 m ka{sup -1} at segment boundaries. The geometry and internal variability of each parasequence is controlled by the interplay of the local accommodation development and fluctuations in sediment supply and climatic conditions. The Sperchios Rift provides a modem analogue for subtle stratigraphic plays within ancient extensional basins. The study of controls on sediment source and transport patterns within active rifts has refined our appreciation of the controls on potential reservoir distribution and geometries.

  17. Late Quaternary high resolution sequence stratigraphy of an active rift, the Sperchios Basin, Greece: An analogue for subtle stratigraphic plays

    SciTech Connect

    Eliet, P.P. ); Gawthorpe, R.L. )

    1996-01-01

    The Sperchios Basin is an active asymmetric graben, bounded to the south by a major border fault system with major fault segments typically 20-30 km long. The basin is dominated by a major axial fluvio-deltaic system which enters the partially enclosed Maliakos Gulf to the east. Lateral sourced depositional systems within the basin comprise hanging-wall and footwall-derived alluvial fans and a narrow coastal plain along the footwall scarp bordering the Maliakos Gulf. High resolution seismic data from the Maliakos Gulf reveals three late Quaternary progradational parasequences sourced from axial and lateral depositional systems, with a regional late-Pleistocene transgressive surface dated at circa. 10 ka BP within the Maliakos Gulf. Differential subsidence of the late Pleistocene transgressive surface indicates marked variation in subsidence from 2.4 m ka[sup -1] at fault segment centers to 0.8 m ka[sup -1] at segment boundaries. The geometry and internal variability of each parasequence is controlled by the interplay of the local accommodation development and fluctuations in sediment supply and climatic conditions. The Sperchios Rift provides a modem analogue for subtle stratigraphic plays within ancient extensional basins. The study of controls on sediment source and transport patterns within active rifts has refined our appreciation of the controls on potential reservoir distribution and geometries.

  18. Pre-Wisconsinan mammals from Jamaica and models of late Quaternary extinction in the greater Antilles

    NASA Astrophysics Data System (ADS)

    MacPhee, R. D. E.; Ford, Derek C.; McFarlane, Donald A.

    1989-01-01

    The vertebrate fauna recovered from indurated conglomerates at Wallingford Roadside Cave (central Jamaica) is shown to be in excess of 100,000 yr old according to uranium series and electron spin resonance dating. The Wallingford local fauna is therefore pre-Wisconsinan in age, and Roadside Cave is now the oldest radiometrically dated locality in the West Indies containing identifiable species of land mammals. In the absence of a good radiometric record for Quaternary paleontological sites in the Caribbean, there is no satisfactory basis for determining whether most extinct Antillean mammals died out in a "blitzkrieg"-like event immediately following initial human colonization in the mid-Holocene. Fossils of Clidomys (Heptaxodontidae, Caviomorpha), the giant Wallingford rodent, have never been found in situ in sediments of demonstrably Holocene age, and its extinction may antedate the middle Holocene. This is also a possibility for the primate Xenothrix mcgregori, although its remains have been found in loose cave earth. A major, climate-driven bout of terrestrial vertebrate extinction at about 14,000-12,000 yr B.P. has been hypothesized for the West Indies by G. Pregill and S. L. Olson ( Annual Review of Ecology and Systematics12, 75-98, 1981), but at present there is nothing to connect the disappearance of Clidomys with this event either. Quaternary extinctions in the Caribbean may prove to be of critical significance for evaluating the reality of New World blitzkrieg, but not until an effort is mounted to constrain them rigorously using modern radiometric approaches.

  19. Multiple submarine-cemented grainstone sequences along leeward carbonate margins: examples from late Quaternary of Little and Great Bahama Banks

    SciTech Connect

    Jude, W.R.; Hine, A.C.; Neumann, C.

    1985-02-01

    Coarse-grained, leeward-margin sand shoals, developed during the late Quaternary along the western edges of Little and Great Bahama Bank, have been deposited and preserved in response to regional sediment-transport process and local physicochemical conditions. These sand bodies are fundamental depositional sequences, chronostratigraphically bounded by subaerial exposure crusts, and thus are of major importance in determining rates of bank-margin growth and in understanding the dynamics of carbonate margin buildup. Surficial sediment is composed of coarse sand and granules dominated by composite-ooid grains. Submarine cementation is active and has led to the development of coarser grains are cemented with fibrous aragonite and surficially coated at the tidally active margin. The resultant composite-ooid sediment is more hydrodynamically stable and is rapidly cemented into hardgrounds characterized by a smooth upper surface. Lithification is gradational through a thickness of 50-100 m to an irregular lower boundary transitional with uncemented material. These hardgrounds are submarine discontinuity surfaces developed during inter-storm conditions of winnowing and bypass sedimentation along a depositional profile of equilibrium. Rock cores into the Pleistocene section have recovered sediments and submarine discontinuity surfaces identical to those in the Holocene. These are present in the two latest Pleistocene sequences representing the last major interglacial intervals. Both the Holocene and Pleistocene sequences have one or two cemented zones per meter in the upper section. The presence of these deposits throughout the preserved stratigraphic package indicates the persistence of characteristic leeward depositional processes during the late Quaternary and their importance in bank-margin growth.

  20. Influence of late Quaternary climatic changes on geomorphic and pedogenic processes on a desert piedmont, Eastern Mojave Desert, California

    USGS Publications Warehouse

    Wells, S.G.; McFadden, L.D.; Dohrenwend, J.C.

    1987-01-01

    Radiocarbon dating of late Quaternary deposits and shorelines of Lake Mojave and cation-ratio numerical age dating of stone pavements (Dorn, 1984) on the adjacent Soda Mountains piedmont provide age constraints for alluvial and eolian deposits. These deposits are associated with climatically controlled stands of Lake Mojave during the past 15,000 yr. Six alluvial fan units and three eolian stratigraphic units were assigned ages based on field relations with dated shorelines and piedmont surfaces, as well as on soil-geomorphic data. All but one of these stratigraphic units were deposited in response to time-transgressive climatic changes beginning approximately 10,000 yr ago. Increased eolian flux rates occurred in response to the lowering of Lake Mojave and a consequent increase in fine-sediment availability. Increased rates of deposition of eolian fines and associated salts influenced pedogenesis, stone-pavement development, and runoff-infiltration relations by (1) enhancing mechanical weathering of fan surfaces and hillslopes and (2) forming clay- and silt-rich surface horizons which decrease infiltration. Changes in alluvial-fan source areas from hillslopes to piedmonts during the Holocene reflect runoff reduction on hillslopes caused by colluvial mantle development and runoff enhancement on piedmonts caused by the development of less-permeable soils. Inferred increased in early to middle Holocene monsoonal activity resulted in high-magnitude paleo-sheetflood events on older fan pavements; this runoff triggered piedmont dissection which, in turn, caused increased sediment availability along channel walls. Thus, runoff-infiltration changes during the late Quaternary have occurred in response to eolian deposition of fines, pedogenesis, increased sheetflood activity in the Holocene, and vegetational changes which are related to many complicated linkages among climatic change, lake fluctuations, and eolian, hillslope, and alluvial-fan processes. ?? 1987.

  1. Erosion and deposition on the Pajarito Plateau, New Mexico, and implications for geomorphic responses to late Quaternary climatic changes

    SciTech Connect

    Reneau, S.L.; McDonald, E.V.; Gardner, J.N.; Longmire, P.A.; Kolbe, T.R.; Carney, J.S.; Watt, P.M.

    1996-04-01

    The Pajarito Plateau of northern New Mexico contains a rich and diverse record of late Quaternary landscape changes in a variety of geomorphic settings that include gently-sloping mesa tops, steep canyon walls, and canyon bottoms. A broad range of investigations during the past decade, motivated by environmental and seismic hazard concerns, have resulted in examination of the characteristics, stratigraphy, and age of sediments and soils at numerous locations throughout the Plateau. Geochronologic control is provided by >140 radiocarbon dates supplemented by soil characterization and tephrochronology. In this paper we first summarize some of the results of recent and ongoing work on late Quaternary deposits on the Pajarito Plateau, illustrating both the complexity of the geomorphic record and some common elements that have been observed in multiple locations. We then use these observations, in combination with other work in the Southwest, to make some inferences about the local geomorphic response to regional climatic changes. Because the geomorphic and paleoclimatic records are fragmentary, and because the relations between large scale climate changes and local variations in precipitation, vegetation, and geomorphic processes are not fully understood, many uncertainties exist concerning the response of the local landscape to past climatic fluctuations. In addition, variations in local landscape sensitivity related to prior erosional history and spatial variations in vegetation, and the localized nature of many storms, probably contribute to the complexity of the geomorphic record. Nevertheless, the work discussed in this paper suggests a strong relation between regional climatic changes and local geomorphic history, and provides a framework for considering relations between modem processes, the record of past landscape changes, and future erosion and deposition on the Plateau and in surrounding areas.

  2. Late Quaternary dynamics of a South African floodplain wetland and the implications for assessing recent human impacts

    NASA Astrophysics Data System (ADS)

    Tooth, S.; Rodnight, H.; McCarthy, T. S.; Duller, G. A. T.; Grundling, A. T.

    2009-05-01

    Knowledge of the long-term geomorphological dynamics of wetlands is limited, so currently there is an inadequate scientific basis for assessing anthropogenically induced changes and for developing conservation, remediation, and/or sustainable management guidelines for these fragile ecosystems. Along the upper Klip River, eastern South Africa, geomorphological and sedimentological investigations, geochronology, and remote sensing have been used to establish the late Quaternary dynamics of some internationally important floodplain wetlands, thus providing a reference condition against which to assess the extent of recent human impacts. Optically stimulated luminescence dating reveals that the wetlands have developed over at least the last 30 ky as a result of slow meander migration (< 0.2 m y - 1 ), irregular cutoff events, and infrequent avulsions (approximately one every 3-6 ky) that have occurred autogenically as a natural part of meander-belt development. Following European settlement in the Klip valley (late nineteenth century), however, modifications to local flora and fauna, as well as the initiation of local wetland drainage schemes, have had major impacts. In particular, proliferation of exotic willows and associated debris jams, and the artificial excavation of a 1.2-km-long channel section across the wetlands have initiated an ongoing avulsion that is characterised by failure (gradual abandonment) of the main channel and rapid incision of a headcutting channel. Compared to the pre-settlement condition, little change in lateral migration activity has occurred, but this avulsion provides a clear example of anthropogenically accelerated change, occurring only ~ 1 ky after the last natural avulsion and in a part of the wetlands where avulsions have not occurred previously. Subsequent human interventions have included installing weirs in an attempt to control the resulting erosion and promote reflooding, but ongoing maintenance has been required. In areas that

  3. Infilling of the Younger Kathmandu-Banepa intermontane lake basin during the Late Quaternary (Lesser Himalaya, Nepal): a sedimentological study

    NASA Astrophysics Data System (ADS)

    Dill, H. G.; Khadka, D. R.; Khanal, R.; Dohrmann, R.; Melcher, F.; Busch, K.

    2003-01-01

    The Kathmandu and Banepa Basins, Central Nepal, are located in a large syncline of the Lesser Himalayas. The Older Kathmandu Lake evolved during the Pliocene and early Pleistocene; the Younger Kathmandu Lake, which is the focus of this study, is infilled with late Quaternary sediments. Three formations, arranged in stratigraphical order, the Kalimati, Gokarna and Thoka Formations formed during the infilling stage of this lacustrine basin. Structural and textural sedimentological analyses, a chemical survey across the basin and mineralogical investigations of fine-grained sediments form the basis of this palaeogeographical study. The basin under investigation was covered by a perennial freshwater lake before 30 000 yr BP. The lake was infilled with alluvial and fluvial sediments delivered mainly from the mountains north of the basin. A fairly low gradient was favourable for the formation of diatomaceous earths, carbonaceous mudstones and siltstones, which were laid down in the centre of the lake and in small ponds. Towards the basin edge, lacustrine sediments gave way to deltaic deposits spread across the delta plain. Crevasse splays and anastomosing rivers mainly delivered suspended load for the widespread siltstones and mudstones. The proximal parts of the alluvial-fluvial sedimentary wedge contain debris flows that interfinger with fine-grained floodplain deposits. Three highstands of the water-level (>30 000 yr BP, 28 000-19 000 yr BP, 11 000-4000 yr BP (?)) have been recognised in the sedimentary record of the younger Kathmandu Lake in the Late Quaternary. Second-order water-level fluctuations are assumed to be triggered by local processes (damming by tectonically induced landslides). First-order water-level fluctuations are the result of climatic changes.

  4. Lidar-Based Mapping of Late Quaternary Faulting Along the Grizzly Valley Fault, Walker Lane Seismic Belt, California

    NASA Astrophysics Data System (ADS)

    Hitchcock, C. S.; Hoirup, D. F.; Barry, G.; Pearce, J.; Glick, F.

    2012-12-01

    The Grizzly Valley fault (GVF) is located within the northern Walker Lane, a zone of right-lateral shear between the Sierra Nevada and the Basin and Range in Plumas County. The GVF extends southeasterly from near Mt. Ingalls along the eastern side of Lake Davis. It may partially connect with the Hot Creek fault within Sierra Valley and extend south to Loyalton with an overall approximate length of 50 km. Comparison of high-resolution topography developed from LiDAR data with published bedrock geologic mapping documents the presence of geomorphic features that provide information on fault activity of the GVF. Field mapping verified tectonically deformed and offset late Quaternary surfaces identified on bare-earth LiDAR imagery across the GVF within glacial deposits on the eastern margin of Lake Davis, and alluvial deposits in Sierra Valley. Along the GVF, conspicuous geomorphic and hydrologic features include scarps in alluvial surfaces, elongated depressions aligned with adjacent linear escarpments, truncated bedrock spurs, closed depressions, linear swales, right-lateral deflections of creeks and river courses, and shutter ridges, as well as springs and linear seeps consistent with right-lateral strike-slip faulting. The discontinuous nature of observed fault traces combined with the apparent down-to-the-west offset of alluvial surfaces at the southern and northern ends of the eastern margin of Lake Davis are consistent with a broad bend or step over in the fault. Scarp profiles of apparently faulted surfaces extracted from LiDAR data document vertical offsets of up to 14 m. Our study suggest that the GVF is an oblique, right-lateral fault that has been active in the late Quaternary. This study complements on-going investigations by DWR to assess the impact of seismic hazards on State Water Project infrastructure.

  5. Late Quaternary Deformation Along the Wairarapa Fault, North Island, New Zealand

    NASA Astrophysics Data System (ADS)

    Schermer, E. R.; Little, T. A.

    2006-12-01

    The Wairarapa fault, one of the largest active faults in the hanging wall of the Hikurangi subduction margin, New Zealand, averaged 16m dextral slip during the M >8.1 1855 earthquake. Previous workers inferred that uplift of 2.7m at the coast, observed by a surveyor in 1855, occurred on the southern continuation of the Wairarapa fault, the Wharekauhau (WH) thrust. New mapping, stratigraphic, and paloseismologic results from the WH thrust suggest the pattern of surface rupture in 1855 and earlier earthquakes was significantly different than previously inferred, requiring a more complex model for seismic hazard and tectonic evolution of the region. Detailed mapping indicates that the coastal segment of the WH thrust did not rupture the surface in 1855. The thrust, a major range-bounding fault, emplaces Mesozoic graywacke over ~80-100 ka last- interglacial marine, and lacustrine rocks, and in part coeval to younger alluvial gravels. Fault activity is indicated by facies and thickness changes. This older sequence is tilted and overlapped unconformably by a silt layer and much less deformed alluvial fan gravels that range in age from >22ka to <9 ka. These younger gravels were deposited in a valley incised across the fault scarp, in-filled this topography, and show no evidence of syn-depositional deformation. New 14C ages record a period of fault inactivity from 14 - 9 ka (calib yrs BP). The abandoned, overlapping fan surface is slightly deformed across the fault (15 m of folding- related throw). We infer that the thrust has propagated eastward in the subsurface, uplifting the abandoned WH fault, an inference that is supported by the pattern of Holocene incision. The only recent faulting consists of subvertical en echelon segments that have undergone minor dip-slip and dextral slip. A trench excavated across the fault scarp in late Holocene gravels suggests that the only fault along the trace of the WH thrust that broke within 3 m of the surface in 1855 was a minor

  6. Glaciomarine sedimentation and bottom current activity on the north-western and northern continental margins of Svalbard during the late Quaternary

    NASA Astrophysics Data System (ADS)

    Chauhan, Teena; Noormets, Riko; Rasmussen, Tine L.

    2016-04-01

    Palaeo-bottom current strength of the West Spitsbergen Current (WSC) and the influence of the Svalbard-Barents Sea Ice Sheet (SBIS) on the depositional environment along the northern Svalbard margins are poorly known. Two gravity cores from the southern Yermak Plateau and the upper slope north of Nordaustlandet, covering marine isotope stage (MIS) 1 to MIS 5, are investigated. Five lithofacies, based on grain size distribution, silt/clay ratio, content and mean of sortable silt (SS), are distinguished to characterise the contourite-dominated sedimentary environments. In addition, depositional environments are described using total organic carbon (TOC), total sulphur (TS) and calcium carbonate (CaCO3) contents of sediments. Facies A, containing coarse SS, suggests strong bottom current activity and good bottom water ventilation conditions as inferred from low TOC content. This facies was deposited during the glacial periods MIS 4, MIS 2 and during the late Holocene. Facies B is dominated by fine SS indicating weak bottom current and poor ventilation (cf. high TOC content of 1.2-1.6%), and correlates with the MIS 4/3 and MIS 2/1 transition periods. With an equal amount of clay and sand, fine SS and high content of TOC, facies C indicates reduced bottom current strength for intervals with sediment supply from proximal sources such as icebergs, sea ice or meltwater discharge. This facies was deposited during the last glacial maximum. Facies D represents mass-flow deposits on the northern Svalbard margin attributed to the SBIS advance at or near the shelf edge. Facies E sediments indicating moderate bottom current strength were deposited during MIS 5 and MIS 3, and during parts of MIS 2. This first late Quaternary proxy record of the WSC flow and sedimentation history from the northern Svalbard margin suggests that the oceanographic conditions and ice sheet processes have exerted first-order control on sediment properties.

  7. Magnitude of late Quaternary left-lateral displacements along the north edge of Tibet

    NASA Technical Reports Server (NTRS)

    Peltzer, Gilles; Tapponnier, Paul; Armijo, Rolando

    1989-01-01

    Images taken by the earth observation satellite SPOT of the Quaternary morphology at 18 sites on the 2000-kilometer-long Altyn Tagh fault at the north edge of Tibet demonstrate that it is outstandingly active. Long-term, left-lateral strike-slip offsets of stream channels, alluvial terrace edges, and glacial moraines along the fault cluster between 100 and 400 meters. The high elevation of the sites, mostly above 4000 meters in the periglacial zone, suggests that most offsets resulted from slip on the fault since the beginning of the Holocene. These data imply that slip rates are 2 to 3 centimeters per year along much of the fault length and support the hypothesis that the continuing penetration of India into Asia forces Tibet rapidly toward the east.

  8. Magnitude of late quaternary left-lateral displacements along the north edge of tibet.

    PubMed

    Peltzer, G; Tapponnier, P; Armijo, R

    1989-12-01

    Images taken by the earth observation satellite SPOT of the Quaternary morphology at 18 sites on the 2000-kilometer-long Altyn Tagh fault at the north edge of Tibet demonstrate that it is outstandingly active. Long-term, left-lateral strike-slip offsets of stream channels, alluvial terrace edges, and glacial moraines along the fault cluster between 100 and 400 meters. The high elevation of the sites, mostly above 4000 meters in the periglacial zone, suggests that most offsets resulted from slip on the fault since the beginning of the Holocene. These data imply that slip rates are 2 to 3 centimeters per year along much of the fault length and support the hypothesis that the continuing penetration of India into Asia forces Tibet rapidly toward the east. PMID:17832223

  9. The changing role of mammal life histories in Late Quaternary extinction vulnerability on continents and islands.

    PubMed

    Lyons, S Kathleen; Miller, Joshua H; Fraser, Danielle; Smith, Felisa A; Boyer, Alison; Lindsey, Emily; Mychajliw, Alexis M

    2016-06-01

    Understanding extinction drivers in a human-dominated world is necessary to preserve biodiversity. We provide an overview of Quaternary extinctions and compare mammalian extinction events on continents and islands after human arrival in system-specific prehistoric and historic contexts. We highlight the role of body size and life-history traits in these extinctions. We find a significant size-bias except for extinctions on small islands in historic times. Using phylogenetic regression and classification trees, we find that while life-history traits are poor predictors of historic extinctions, those associated with difficulty in responding quickly to perturbations, such as small litter size, are good predictors of prehistoric extinctions. Our results are consistent with the idea that prehistoric and historic extinctions form a single continuing event with the same likely primary driver, humans, but the diversity of impacts and affected faunas is much greater in historic extinctions. PMID:27330176

  10. Late-Quaternary recharge determined from chloride in shallow groundwater in the central Great Plains

    USGS Publications Warehouse

    Macfarlane, P.A.; Clark, J.F.; Davisson, M.L.; Hudson, G.B.; Whittemore, D.O.

    2000-01-01

    An extensive suite of isotopic and geochemical tracers in groundwater has been used to provide hydrologic assessments of the hierarchy of flow systems in aquifers underlying the central Great Plains (southeastern Colorado and western Kansas) of the United States and to determine the late Pleistocene and Holocene paleotemperature and paleorecharge record. Hydrogeologic and geochemical tracer data permit classification of the samples into late Holocene, late Pleistocene-early Holocene, and much older Pleistocene groups. Paleorecharge rates calculated from the Cl concentration in the samples show that recharge rates were at least twice the late Holocene rate during late Pleistocene-early Holocene time, which is consistent with their relative depletion in 16O and D. Noble gas (Ne, Ar, Kr, Xe) temperature calculations confirm that these older samples represent a recharge environment approximately 5??C cooler than late Holocene values. These results are consistent with the global climate models that show a trend toward a warmer, more arid climate during the Holocene. (C) 2000 University of Washington.

  11. Late Quaternary Relative Sea-level Change and Glacial Melting History Around Lutzow-Holm Bay and Mt. Riiser-Larsen Regions, East Antarctica

    NASA Astrophysics Data System (ADS)

    Maemoku, H.; Takada, M.; Okuno, J.; Nakada, M.

    2001-12-01

    The Late Quaternary Antarctic glacial history can be estimated on the basis of the raised beach stratigraphy, AMS 14C ages and oxygen isotopic ratios of the fossil shells. The AMS 14C dating revealed that the 14C ages of in situ fossil shells are clearly classified into two groups: the younger group is 3-8 ka, in the Holocene, and the older is 30-46 ka, in the late Pleistocene, probably the last interstadial. The locality containing the late Pleistocene in situ fossils is confined to the northernmost part of the Soya Coast region. The melting history can be detectable using the oxygen isotopic composition of epipelagic organisms. The Soya Coast in the Lutzow-Holm Bay region, east Dronning Maud Land, is located in the margin of East Antarctic ice sheet, where glacial advances and \\Delta18O-depleted water from melting ice at deglacial events may affect the organisms lived in shallow-water. The beach deposits in the northernmost part of Soya Coast are clearly divided stratigraphically into two marine sediment layers including in situ fossil shells of Laternula elliptica, and that the TAMS 14C ages of fossil shells of the upper layer ranged from 4 to 5 ka without a reservoir correction, and those from the lower layer ranged from 32 to 46 ka. Any marine layers and in situ fossil shells were not disturbed by ice sheet loading or scouring. And some fluvial sediments associated with the meltwater can be often observed under the Holocene marine beds or over the older marine beds. The \\Delta 18O (PDB) values of 24 fossils in the Pleistocene marine beds ranged from about 2.9 to 4.2 per mill and 27 fossils in the Holocene beds from about 3.9 to 4.6 per mill. In the Mt. Riiser-Larsen region, Enderby Land, the presence of a glacial trimline, indicating the level of the former ice sheet surface, at an elevation of about 500 m a.s.l. . Above this level, glacial erratic boulders were not seen, and the bedrock has no glacial polish or striations and is commonly deeply weathered

  12. Processes of late Quaternary turbidity current flow and deposition on the Var deep sea fan, northwest Mediterranean sea

    SciTech Connect

    Piper, D. ); Savoye, B. )

    1993-09-01

    Late Quaternary sedimentation patterns on the Var deep-sea fan are known from high-resolution seismic boomer profiles (vertical resolution < 1 m), piston cores, SAR side-scan sonargraphs, and submersible dives. Foram biostratigraphy and radiocarbon dating provide chronologic control that is seismically correlated across the fan. Regional erosional events correspond to the isotopic state 2 and 6 glacial maxima. A widespread surface sand layer was deposited from the 1979 turbidity current, which broke two submarine cables. Numerical modeling constrains its character. A small slide on the upper prodelta developed into an accelerating turbidity current, which eroded sand from the Var canyon. The current was 30 m thick in the upper valley, expanding downflow to >120 m, where it spilled over the eastern Var sedimentary ridge at a velocity of 2.5 ms[sup [minus]1]. Other Holocene turbidity currents (with a 103-yr recurrence interval) were muddier and thicker, but also deposited sand on middle fan-valley levees and are inferred to have had a similar slide-related origin. Late Pleistocene turbidity currents deposited on the high Var sedimentary ridge. The presence of sediment waves and the cross-flow slope inferred from levee asymmetry indicate that some flow were hundreds of meters thick, with velocities of 0.35 ms[sup [minus]1]. Estimated times for deposition of thick levee mud beds are many days or weeks. Late Pleistocene flows therefore are interpreted to result from hyperpycnal flow of glacial outwash in the Var River. Variation in late Pleistocene-Holocene turbidite sedimentation thus is controlled more by changes in sediment supply than by sea level.

  13. Changes in Late Cretaceous-Quaternary Caribbean plate motion directions inferred from paleostress measurements from striated fault planes

    NASA Astrophysics Data System (ADS)

    Batbayar, K.; Mann, P.; Hippolyte, J.

    2013-12-01

    We compiled paleostress analyses from previous research works collected at 591 localities of striated fault planes in rocks ranging in age from Late Cretaceous to Quaternary in the circum-Caribbean and Mexico. The purpose of the study is to quantify a progressive clockwise rotation of the Caribbean plate during its Late Cretaceous to recent subduction of the Proto-Caribbean seaway. Paleostress analysis is based on the assumption that slickenside lineations indicate both the direction and sense of maximum resolved shear stress on that fault plane. We have plotted directions of maximum horizontal stress onto plate tectonic reconstructions of the circum-Caribbean plate boundaries and infer that these directions are proxies for paleo-plate motion directions of the Caribbean plate. Plotting these stress directions onto reconstructions provided a better visualization of the relation of stress directions to blocks at their time of Late Cretaceous to recent deformation. Older, more deformed rocks of Late Cretaceous to Eocene ages yield a greater scatter in derived paleostress directions as these rocks have steeper dips, more pervasive faulting, and were likely affected by large rotations as known from previous paleomagnetic studies of Caribbean plate margins. Despite more scatter in measurements from older rock units, four major events that affected the Caribbean plate and the Great Arc of the Caribbean (GAC) are recognizable from changing orientations of stress directions: 1) Late Cretaceous collision of the GAC with southern Mexico and Colombia is consistent with NE directions of maximum compression in rocks of this age range in southern Mexico and EW directions in Colombia as the GAC approached the Proto-Caribbean seaway; 2) Paleocene-Eocene collision of the GAC with the Bahamas platform in Cuba and Hispaniola and with the South American plate in Venezuela is consistent with CW rotations of stress directions in rocks of these ages in the northern Caribbean and CCW

  14. Within-taxon morphological diversity in late-Quaternary Neotoma as a paleoenvironmental indicator, Bonneville Basin, Northwestern Utah, USA

    NASA Astrophysics Data System (ADS)

    Lyman, R. Lee; O'Brien, Michael J.

    2005-05-01

    Ecological data indicate that as the amount of precipitation in an arid areas increases, so too does mammalian taxonomic richness. This correspondence has been found in two late-Quaternary mammalian faunas from Utah, one from Homestead Cave in the Bonneville Basin. We use the remains of two species of woodrat ( Neotoma cinerea and Neotoma lepida) from Homestead Cave to test the hypothesis that as the amount of precipitation in an arid area increases, so too does morphological diversity within individual mammalian taxa. Morphological diversity is measured as corrected coefficients of variation and as richness of size classes of mandibular alveolar lengths. Coefficients of variation for N. cinerea are few and coincide with moisture history if temporally successive small samples are lumped together. More abundant coefficients of variation for N. lepida coincide only loosely with moisture history, likely because such coefficients measure dispersion but not necessarily other aspects of variation. Richness of size classes of N. lepida is high during the early and late Holocene when moisture was high, and lowest during the middle Holocene when climate was most arid.

  15. Applying DEM-SRTM for reconstructing a late Quaternary paleodrainage in Amazonia

    NASA Astrophysics Data System (ADS)

    Hayakawa, Ericson H.; Rossetti, Dilce F.; Valeriano, Márcio M.

    2010-08-01

    Remote sensing is a particularly invaluable tool that has helped the detection of paleomorphologies produced by river dislocation in a variety of landscapes, which has contributed in reconstructing the geological evolution of many fluvial systems. This technique might provide useful information to discuss the evolution of large fluvial systems, in special those located in areas of difficult access where the acquisition of field data is difficult. Application of remote sensing for paleodrainage characterization in densely vegetated tropical areas is scarce in the literature. This work records processing of the Digital Elevation Model (DEM) derived from the Shuttle Radar Topography Mission (SRTM), which succeeded in revealing an ancient drainage complex of the Madeira River, one of the main Amazonas tributaries, where other remote sensing products failed the detection. Analysis of this paleodrainage and of its modern counterpart within the geological framework available for this region leads to propose that activity along pre-existent faults during the latest Quaternary would have promoted the southeastward dislocation of a nearly 200 km long segment of the Madeira River. During this process, an impressive paleodrainage network was left behind, which was only able to be detected using the DEM-SRTM. Application of this technique might be of great help to the detection of paleodrainage morphologies in densely vegetated areas similar to the Amazonas lowland. The dynamics of channel migration in this and many other large scale tropical river systems might benefit from the investigation based on data derived from DEM-SRTM.

  16. A new contribution to the Late Quaternary tephrostratigraphy of the Mediterranean: Aegean Sea core LC21

    NASA Astrophysics Data System (ADS)

    Satow, C.; Tomlinson, E. L.; Grant, K. M.; Albert, P. G.; Smith, V. C.; Manning, C. J.; Ottolini, L.; Wulf, S.; Rohling, E. J.; Lowe, J. J.; Blockley, S. P. E.; Menzies, M. A.

    2015-06-01

    Tephra layers preserved in marine sediments can contribute to the reconstruction of volcanic histories and potentially act as stratigraphic isochrons to link together environmental records. Recent developments in the detection of volcanic ash (tephra) at levels where none is macroscopically visible (so-called 'crypto-tephra') have greatly enhanced the potential of tephrostratigraphy for synchronising environmental and archaeological records by expanding the areas over which tephras are found. In this paper, crypto-tephra extraction techniques allow the recovery of 8 non-visible tephra layers to add to the 9 visible layers in a marine sediment core (LC21) from the SE Aegean Sea to form the longest, single core record of volcanic activity in the Aegean Sea. Using a novel, shard-specific methodology, sources of the tephra shards are identified on the basis of their major and trace element single-shard geochemistry, by comparison with geochemical data from proximal Mediterranean volcanic stratigraphies. The results indicate that the tephra layers are derived from 14 or 15 separate eruptions in the last ca 161 ka BP: 9 from Santorini; 2 or 3 from Kos, Yali, or Nisyros; 2 from the Campanian province; and one from Pantelleria. The attributions of these tephra layers indicate that 1) inter-Plinian eruptions from Santorini may have produced regionally significant tephra deposits, 2) marine tephrostratigraphies can provide unique and invaluable data to eruptive histories for island volcanoes, and 3) tephra from both Pantelleria and Campania may be used to correlate marine records from the Aegean Sea to those from the Tyrrhenian, Adriatic and Ionian Seas.

  17. Non-linear response of the Golo River system, Corsica, France, to Late Quaternary climatic and sea level variations

    NASA Astrophysics Data System (ADS)

    Forzoni, Andrea; Storms, J. E. A.; Reimann, Tony; Moreau, Julien; Jouet, Gwenael

    2015-08-01

    Disentangling the impact of climatic and sea level variations on fluvio-deltaic stratigraphy is still an outstanding question in sedimentary geology and geomorphology. We used the Golo River system, Corsica, France, as a natural laboratory to investigate the impact of Late Quaternary climate and sea level oscillations on sediment flux from a catchment and on fluvio-deltaic stratigraphy. We applied a numerical model, PaCMod, which calculates catchment sediment production and transport and compared modeling output to the sedimentary record of the Golo alluvial-coastal plain, whose chronology was reinterpreted using new optical stimulated luminescence (OSL) ages on feldspars. Our modeling, OSL ages, and geomorphological results indicate that the two main phases of braidplain development in the Golo alluvial-coastal plain occurred during the cold-dry phases of MIS5 and during the late MIS4-early MIS3, as a consequence of high catchment erosion rates and low water discharge. Incision and sediment reworking occurred during sea level low stand periods (MIS4 and late MIS3-MIS2). High sediment flux pulses from the catchment outlet were generated during the Lateglacial and early Holocene, as a result of the release of sediments previously stored within the catchment and enhanced snowmelt. Our results suggest a non-linear response of the Golo River system to climatic and eustatic changes, caused by sediment storage within the catchment and geomorphological thresholds. This indicates that a direct comparison between palaeo-climate and stratigraphy is not possible without considering catchment sediment storage and sediment transport delays out of the catchment.

  18. The Late Miocene Carbon Isotope Shift and Marine Biological Productivity.

    NASA Astrophysics Data System (ADS)

    Diester-Haass, L.; Billups, K.; Emeis, K. C.

    2004-12-01

    The late Miocene global carbon isotope shift of approximately 1 per mil is not well understood. Is it linked to ocean-related processes such as the AƒAøAøâ_sA¬A.â_oBiologic BloomAƒAøAøâ_sA¬ \\(Farrell et al., 1995\\), or to changes in type \\(C3/C4 plants\\) or cover of terrestrial vegetation? Here we examine the evolution of marine biological productivity during the isotope shift at ODP Site 846 \\(Pacific equatorial upwelling, where the AƒAøAøâ_sA¬A.â_oBiologic BloomAƒAøAøâ_sA¬ has been first described, Farrell al, 1995\\) and at Indian Ocean Site 721 \\(monsoon-driven upwelling\\), and compare their productivity history with non upwelling locations in the Atlantic Ocean. The onset of the carbon isotope shift is accompanied at all locations by an increase in paleoproductivity derived from benthic foraminiferal accumulation rates \\(expressed as gC/cm2 * ky; Huerguera, 2000\\) and increased abundance of Uvigerina spp.. At the equatorial upwelling sites the increase is comparable to half present-day values to present-day values; in the Atlantic Ocean paleoproductivity increases from present-day up to 3 times present-day values. But the productivity maxima are not concurrent. The carbon isotope shift is accompanied by severe carbonate dissolution and reduced ventilation of bottom waters, as reflected in the occurrence of pyrite and good preservation of cartilageous fish debris. Carbonate preservation is good since about 6 Ma despite high productivity. We discuss changing deep water circulation patterns, increased weathering and continental nutrient delivery, as well as erosion of terrestrial vegetation as possible factors to explain our findings.

  19. Recurrent late Quaternary surface faulting along the southern Mohawk Valley fault zone, NE California

    SciTech Connect

    Sawyer, T.L.; Hemphill-Haley, M.A. ); Page, W.D. )

    1993-04-01

    The Mohawk Valley fault zone comprises NW- to NNW-striking, normal and strike-slip( ) faults that form the western edge of the Plumas province, a diffuse transitional zone between the Basin and Range and the northern Sierra Nevada. The authors detailed evaluation of the southern part of the fault zone reveals evidence for recurrent late Pleistocene to possibly Holocene, moderate to large surface-faulting events. The southern Mohawk fault zone is a complex, 6-km-wide zone of faults and related features that extends from near the crest of the Sierra Nevada to the middle of southern Sierra Valley. The fault zone has two distinct and generally parallel subzones, 3 km apart, that are delineated by markedly different geomorphic characteristics and apparently different styles of faulting. Paleoseismic activity of the western subzone was evaluated in two trenches: one across a fault antithetic to the main range-bounding fault, and the other across a splay fault delineated by a 3.7-m-high scarp in alluvium. Stratigraphic relations, soil development, and radiocarbon dates indicate that at least four mid- to late-Pleistocene surface-faulting events, having single-event displacements in excess of 1.6 to 2.6 m, occurred along the splay fault prior to 12 ka. The antithetic fault has evidence of three late Pleistocene events that may correspond to event documented on the splay fault, and a Holocene event that is inferred from youthful scarplets and small closed depressions.

  20. The Landscape Evolution of Ulan Buh Desert in North China during Late Quaternary

    NASA Astrophysics Data System (ADS)

    Chen, Fahu; Li, Guoqiang; Zhao, Hui; Jin, Ming; Fan, Yuxin; Madsen, David; Chun, Xi

    2013-04-01

    Desert evolution was one of the major environmental changes in northern China during Quaternary. Ulan Buh Desert (UBD), at margin of present summer monsoon, is one of main desert fields and dust source areas in the north and northwest China. In this paper we present the results of lithology, Optical Stimulated Luminescence (OSL) dates, grain-size, carbonate content, organic content and pollen analysis from the drilling cores in the different parts of UBD. Our results show that most area of the present Ulan Buh desert was covered by the Jilantai-Hetao mage-paleolake before ~90 ka ago, a uniform paleolake of about 34,000 km2 covering the whole Hetai palin, and sevrious eolian and desert environment was prevailing during the last glacial and early Holoccene. Then an Ulan Buh paleolake (UB paleolake), likely a desert-wetland enviroment, formed in the northern part of UBD and Jilantai salt lake at around 8-7 ka, leaving dry lake bed landform in northern UBD, while high dune landscape probably prevailed in south UBD. After that, the mordern UBD landscape formed. The Jilantai Salt Lake in western UBD continued to exist until present with high lake level during UB paleolake preiod. During the recent 2000 years aeolian sand from Badan Jaran desert invaded the north UBD through Langshan mountain to form dune landform covered on dry UB paleolake bed and seperated main Ulan Buh desert and Jilantai Salt Lake. Human activities such as changing low wetland to farmland and following abandonment resulted the formation of easten Ulan Buh desert in Han dynasty since 200 BC. The formation of UBD landfporms was suggedted to be relate to disintegration of Jilantai-Hetao mage-paleolake, and was also likely to corresponding to summer monsoon changes during during last glacial and Holocene.

  1. Late quaternary paleoseismology of the southern Steens fault zone, northern Nevada

    USGS Publications Warehouse

    Personius, S.F.; Crone, A.J.; Machette, M.N.; Mahan, S.A.; Kyung, J.B.; Cisneros, H.; Lidke, D.J.

    2007-01-01

    The 192-km-long Steens fault zone is the most prominent normal fault system in the northern Basin and Range province of western North America. We use trench mapping and radiometric dating to estimate displacements and timing of the last three surface-rupturing earthquakes (E1-E3) on the southern part of the fault south of Denio, Nevada. Coseismic displacements range from 1.1 to 2.2 ?? 0.5 m, and radiometric ages indicate earthquake times of 11.5 ?? 2.0 ka (E3), 6.1 ?? 0.5 ka (E2), and 4.6 ?? 1.0 ka (E1). These data yield recurrence intervals of 5.4 ?? 2.1 k.y. between E3 and E2, 1.5 ?? 1.1 k.y. between E2 and E1, and an elapsed time of 4.6 ?? 1.0 k.y. since E1. The recurrence data yield variable interval slip rates (between 0.2 ?? 0.22 and 1.5 ?? 2.3 mm/yr), but slip rates averaged over the past ???18 k.y. (0.24 ?? 0.06 mm/year) are similar to long-term (8.5-12.5 Ma) slip rates (0.2 ?? 0.1 mm /yr) measured a few kilometers to the north. We infer from the lack of significant topographic relief across the fault in Bog Hot Valley that the fault zone is propagating southward and may now be connected with a fault at the northwestern end of the Pine Forest Range. Displacements documented in the trench and a rupture length of 37 km indicate a history of three latest Quaternary earthquakes with magnitudes of M 6.6-7.1 on the southern part of the Steens fault zone.

  2. Late Quaternary landscape development at the margin of the Pomeranian phase (MIS 2) near Lake Wygonin (Northern Poland)

    NASA Astrophysics Data System (ADS)

    Hirsch, Florian; Schneider, Anna; Nicolay, Alexander; Błaszkiewicz, Mirosław; Kordowski, Jarosław; Noryskiewicz, Agnieszka M.; Tyszkowski, Sebastian; Raab, Alexandra; Raab, Thomas

    2015-04-01

    In Central Europe, Late Quaternary landscapes experienced multiple phases of geomorphologic activity. In this study,we used a combined geomorphological, pedological, sedimentological and palynological approach to characterize landscape development after the Last Glacial Maximum (LGM) near Lake Wygonin in Northern Poland. The pedostratigraphical findings from soil pits and drillings were extrapolated using ground-penetrating radar (GPR) and electric resistivity tomography (ERT). During the Pomeranian phase, glacial and fluvioglacial processes dominated the landscape near Lake Wygonin. At the end of the glacial period, periglacial processes became relevant and caused the formation of ventifacts and coversands containing coated sand grains. At approximately 15,290-14,800 cal yr BP, a small pond formed in a kettle hole (profile BWI2). The lacustrine sediments lack eolian sand components and therefore indicate the decline of eolian processes during that time. The increase of Juniperus and rock-rose (Helianthemum) in the pollen diagram is a prominent marker of the Younger Dryas. At the end of the Younger Dryas, a partial reshaping of the landscape is indicated by abundant charcoal fragments in disturbed lake sediments. No geomorphologic activity since the beginning of the Holocene is documented in the terrestrial and wetland archives. The anthropogenic impact is reflected in the pollen diagram by the occurrence of rye pollen grains (Cerealia type, Secale cereale) and translocated soil sediments dated to 1560-1410 cal yr BP, proving agricultural use of the immediate vicinity. With the onset of land use, gully incision and the accumulation of colluvial fans reshaped the landscape locally. Since 540-460 cal yr BP, further gully incision in the steep forest tracks has been associated with the intensification of forestry. Outside of the gully catchments, the weakly podzolized Rubic Brunic Arenosols show no features of Holocene soil erosion. Reprinted from CATENA, Volume 124

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

    SciTech Connect

    Muhs, D.R.; Whelan, J.F. ); Kelsey, H.M.; McInelly, G.W. ); Miller, G.H. ); Kennedy, G.L. )

    1990-05-10

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

  4. Improved age estimates for key Late Quaternary European tephra horizons in the RESET lattice

    NASA Astrophysics Data System (ADS)

    Bronk Ramsey, Christopher; Albert, Paul G.; Blockley, Simon P. E.; Hardiman, Mark; Housley, Rupert A.; Lane, Christine S.; Lee, Sharen; Matthews, Ian P.; Smith, Victoria C.; Lowe, John J.

    2015-06-01

    The research project 'Response of Humans to Abrupt Environmental Transitions' (RESET) used tephra layers to tie together and synchronise the chronologies of stratigraphic records at archaeological and environmental sites. With the increasing importance of tephra as chronological markers in sedimentary sequences, both in this project and more generally, comes a requirement to have good estimates for the absolute age of these volcanic horizons. This paper summarises the chronology of the key tephra in the RESET tephra lattice in the time range 10-60 ka BP, from the existing literature, from papers produced as part of the RESET project, and reanalysis conducted for this paper. The paper outlines the chronological approach taken to the dating of tephra within the RESET project, and the basis for further work, as part of the INTIMATE (INTegrating Ice core MArine and TErrestrial records) initiative. For each of the tephra layers in the lattice, the existing literature is discussed and, where relevant date estimates updated using the latest radiocarbon calibration curves (IntCal13 and Marine13) and methods. Maps show the approximate extent of tephra finds, giving a visual indication of the coverage of the lattice in different time-periods.

  5. Morphology, acoustic characteristics, and Late Quaternary growth of conception Fan, Santa Barbara basin, California

    SciTech Connect

    Kraemer, S.M.C.

    1986-04-01

    A radial borderland-basin fan in the western half of the Santa Barbara basin, the Conception Fan, shows characteristics of a debris slope. More than 3000 mi of closely spaced (3.5 kHz) high-resolution profiles, 270 gravity cores, and 8 borings were used to map channel and fan morphology, and channel, levee, and lobe acoustic facies. Two major unconformities are recognized on the seismic profiles. The upper unconformity represents the 10-k.y.B.P. horizon. The lower unconformity is the erosional surface of the late Wisconsinan lowstand of sea level, 18-26 k.y.B.P. Eustasy and tectonism produced two pulses of deposition, each from a different point source, during the Flandrian transgression. Prior to the late Pleistocene, the Conception Fan was fed by one major canyon/channel system, above the western part of the fan. During the late Pleistocene, two small submarine canyons were cut into the slope 7 mi east. Four major channels, smaller than the western channel system, were incised into the fan surface, indicating the eustatic decrease in sediment input. The fault-controlled western canyon (Sacate) fed all but the eastern channel. Faulting and slumping on the slope cut the eastern canyon (Gaviota) and formed the eastern channel. Numerous slope gullies influenced eastern canyon and channel development. Holocene currents rounding Point Conception have winnowed fine sediments in the western channel region, resulting in hummocky topography and the scoured appearance of the channel. Hemipelagic deposition dominates the lower-middle and lower fan of the eastern part of the fan. The western part of the fan seems to be receiving slope-like deposits over the relict fan surface.

  6. Late Quaternary climate and vegetation changes at Braamhoek wetland, South Africa

    NASA Astrophysics Data System (ADS)

    Norström, E.; Scott, L.; Finné, M.; Risberg, J.; Partridge, T. C.; Holmgren, K.

    2009-04-01

    This study contributes a continuous paleo-environmental record from Braamhoek wetland, eastern Free State, South Africa, covering the last 16 ka (16 000 cal yrs BP). The multi-proxy study includes analysis of microfossils (pollen, diatoms, phytoliths, charcoal fragments), stable isotopes (carbon and nitrogen) and lithological properties (carbon content, grain size). Braamhoek wetland is situated at an altitude of c. 1700 meters, a few kilometres north-west of the eastern escarpment, where the large difference in altitude results in orographic uplift of easterly air masses and annual rainfall is c. 1400 mm. The wetland is fed by ground-water springs, promoting continuous local wetness and organic preservation, which explains the accumulative conditions throughout Holocene and late Pleistocene. Analysis of fossil pollen suggests variations in vegetation patterns throughout the 16 ka period. The most important proxies for past vegetation are pollen of fynbos, forest trees, Poaceae and Asteraceae. Principal component analysis (PCA) was performed on 26 of the regional pollen taxa, yielding high positive loadings on forest trees and fynbos, which may reflect relatively moist conditions, particularly in combination with high representation of Poaceae pollen. The carbon isotope composition is a potential proxy for the relative abundance of C3 versus C4 grasses. The late Pleistocene carbon isotope values are probably an artefact of low carbon dioxide levels favouring C4 plants during late glacial conditions, while during the Holocene-Pleistocene transition and onwards, the isotopes probably reflect the local and regional C3/C4 grass ratio. The phytolith index gives additional information about environmental factors coupled to the grass distribution, while occurrences of planktonic diatoms indicate shifts in the moisture status within the wetland. We interpret depleted carbon isotope values, high PCA-score, high Poaceae/Asteraceae ratio, low phytolith index, as well as

  7. Vegetation and climate variability in tropical and subtropical South America during the late Quaternary

    NASA Astrophysics Data System (ADS)

    Behling, H.

    2013-05-01

    Detailed palynological studies from different ecosystems in tropical and subtropical South America reflect interesting vegetation and climate dynamics, in particular during glacial and late glacial times. Records from ecosystems such as the Amazon rainforest, savanna, Caatinga, Atlantic rainforest, Araucaria forest and grasslands provide interesting insight of past climate variability. The influence of events such as Dansgaard-Oeschger, Heinnrich stadials, changes in the thermohaline circulation (THC) will be discussed. In particular the Younger Dryas (YD) period shows at different places distinct vegetational changes, revealing unexpected past climatic conditions.

  8. Late Quaternary Offset of Alluvial Fan Surfaces along the Central Sierra Madre Fault, Southern California

    NASA Astrophysics Data System (ADS)

    Hanson, A.; Burgette, R. J.; Scharer, K. M.; Midttun, N. C.

    2015-12-01

    The Sierra Madre fault (SMF) is an east-west trending reverse fault system along the southern flank of the San Gabriel Mountains near Los Angeles, California. The ~140 km long SMF is separated into four segments, we focus on the multi-stranded, ~60 km long Central Sierra Madre fault (CSMF; W118.3-W117.7) as it lacks a well-characterized long-term geologic slip rate. We combine 1-m lidar DEM with geologic and geomorphic mapping to correlate alluvial fan surfaces along strike and across the fault strands in order to derive fault slip rates that cross the CSMF. We have refined mapping on two sets of terraces described by Crook et al. (1987) and references therein: a flight of Q3 surfaces (after nomenclature of Crook et al., 1987; McFadden, 1982) in Arroyo Seco with distinct terraces ~30 m, ~40 m, ~50 m, and ~55 m above the modern stream and in Pickens Canyon divided a Q3 and Q2 surface, with heights that are ~35 m and ~25 m above the modern stream respectively. Relative degree of clast weathering and soil development is consistent with geomorphic relationships; for example, hues of 7.5 YR to 10 YR are typical of Q3, while hues of 10 YR to 2.5 Y are typical of Q2. A scarp in the Q3 surface at Arroyo Seco has a vertical offset of ~16 m and a scarp in the Q3 at Pickens Canyon has a vertical offset of ~14 m, while the Q2 surface is not faulted. Our Quaternary dating strategy is focused on dating suites of terraces offset along CSMF scarps in order to provide broader stratigraphic context for the cosmogenic radionuclide and luminescence dating. We will present (pending) cosmogenic radionuclide depth profiles from the Q3 surfaces. A better-constrained slip rate for the CSMF will improve earthquake hazard assessment for the Los Angeles area and help clarify the tectonic role of the SMF in the broader plate boundary system. Additionally, the fan chronology will provide information about the timing of alluvial fan aggradation and incision in the western Transverse Ranges.

  9. Detrital cave sediments record Late Quaternary hydrologic and climatic variability in northwestern Florida, USA

    NASA Astrophysics Data System (ADS)

    Winkler, Tyler S.; van Hengstum, Peter J.; Horgan, Meghan C.; Donnelly, Jeffrey P.; Reibenspies, Joseph H.

    2016-04-01

    of enhanced limestone dissolution and cave formation (speleogenesis) during lower paleo water levels. Further work is still required to (a) determine whether precipitation of the ferromanganese deposits is inorganically or biologically mediated, (b) temporally constrain the emplacement history of the primary sedimentary styles, and (c) determine the full geographic extent of these sedimentary signals. However, these preliminary observations suggest that sedimentation in the inland underwater caves of northwestern Florida is related to Quaternary-scale hydrographic variability in the Apalachicola River drainage basin in response to broader ocean and atmospheric forcing.

  10. Late Quaternary Climate and Precipitation δ18o Variations over the Tibetan Plateau from Paleoclimate Modeling

    NASA Astrophysics Data System (ADS)

    Ehlers, T. A.; Li, J.; Werner, M.; Mutz, S.; Steger, C.; Paeth, H.; Poulsen, C. J.; Feng, R.

    2014-12-01

    The Himalaya-Tibet orogen hosts some of the largest modern climate gradients on Earth. Quaternary climate change between glacial and interglacial cycles is an important driver for landscape and ecological change in the region. A common observational approach for documenting climate change is the measurement of modern precipitation, and terrestrial archives of, δ18O. In this study, we investigate variations in Mid Holocene (MH) and Last Glacial Maximum (LGM) climate and precipitation δ18O (δ18Op). Paleoclimate model results for 3 time slices are considered including: Pre-industrial, MH and LGM conditions. These experiments bridge spatial and temporal timescales of environmental change over the plateau and provide a means for interpreting observational data sets. Climate and precipitation δ18O (δ18Op) variations over the Plateau are investigated using an atmospheric general circulation model equipped with isotope tracking capabilities (ECHAM5-wiso). Simulations are conducted at a resolution of 1.1°´1.1°, with 31 vertical levels (T106 L31). Pre-industrial boundary conditions come from AMIP2. MH and LGM boundary conditions come from a coupled atmosphere-ocean model ECHO-G, with vegetation cover from PMIP (http://pmip2.lsce.ipsl.fr). Results are presented in comparison to pre-industrial conditions. More specifically, during the MH surface temperatures were ~0.5 C higher on the central and western plateau and ~0.5 C cooler across the Himalaya. Mean annual MH precipitation was <100 mm/yr higher on the plateau and 300-500 mm/yr higher across the Himalaya. MH δ18Op is 1 per mil depleted on the plateau and 1 per mil enriched across the Himalaya. In contrast, during the LGM surface temperatures were ~2-4 C lower across the Himalaya and Tibet. Mean annual LGM precipitation was 200-600 mm/yr lower over the same region, and δ18Op was 2-4 per mil enriched relative to pre-industrial predictions. The causes for the previous δ18Op changes are discussed in the context of

  11. A late Quaternary multiple paleovalley system from the Adriatic coastal plain (Biferno River, Southern Italy)

    NASA Astrophysics Data System (ADS)

    Amorosi, Alessandro; Bracone, Vito; Campo, Bruno; D'Amico, Carmine; Rossi, Veronica; Rosskopf, Carmen M.

    2016-02-01

    A buried paleovalley system, up to 2 km wide and exceeding 50 m in relief, made up of multiple cross-cutting depressions incised into the Lower Pleistocene bedrock, is reported from the central Adriatic coastal plain at the mouth of Biferno River. Through a multi-proxy approach that included geomorphological, stratigraphic, sedimentological and paleontological (benthic foraminifers, ostracods and molluscs) investigations, the facies architecture of distinct, superposed valley fills is reconstructed and their relative chronology established along a transverse profile with extremely high data density (average borehole spacing 75 m). Regional tectonic uplift appears as the major controlling factor of initial (Middle Pleistocene) river down-cutting and paleovalley formation. In contrast, glacio-eustatic fluctuations drove fluvial-system response over the last 120 ky, when valley incision was primarily induced by the last glacial base-level lowering and climatic forcing. A fragmented record of coastal and shallow-marine deposits is available for the lower paleovalley fill, which is penetrated by a limited borehole dataset. Multiple erosion phases probably related to the post-MIS 5e sea-level fall are reconstructed from the upper paleovalley fill, where a buried fluvial terrace succession is identified a few tens of meters below the ground surface. The flat surfaces of two buried fluvial terraces suggest longer-term, stepped relative sea-level fall, and are correlated with fluvial incisions that took place possibly at the MIS 5/4 transition and at the MIS 3/2 transition, respectively. A laterally extensive gravel body developed on the valley floor during the Last Glacial Maximum. During the ensuing latest Pleistocene-early Holocene sea-level rise the Biferno paleovalley was transformed into an estuary. Upstream from the maximum shoreline ingression, the vertical succession of well-drained floodplain, poorly-drained floodplain, and swamp deposits evidences increasing

  12. The Late Quaternary biogeographic histories of some Great Basin mammals (western USA)

    NASA Astrophysics Data System (ADS)

    Grayson, Donald K.

    2006-11-01

    The Great Basin of arid western North America provides one of the most detailed late Pleistocene and Holocene mammal records available for any part of the world, though the record is by far strongest for small mammals. Of the 35 genera of now-extinct North American Pleistocene mammals, 19 are known to have occurred in the Great Basin, a list that is likely to be complete or nearly so. Of these 19, seven can be shown to have survived beyond 12,000 radiocarbon years ago, a proportion similar to that for North America as a whole. Horses, camels, mammoth, and helmeted musk-oxen appear to have been the most abundant of these genera. Pygmy rabbits ( Brachylagus idahoensis), yellow-bellied marmots ( Marmota flaviventris), and bushy-tailed woodrats ( Neotoma cinerea) declined in abundance at the end of the Pleistocene, at about the same time as populations south of their current arid western distributional boundary were extirpated. Subsequent declines occurred during the hot/dry middle Holocene. Pygmy rabbits also declined as modern pinyon-juniper woodlands developed across the Great Basin. The Snake Range of eastern Nevada has seen the late Pleistocene or Holocene extinction of both northern pocket gophers ( Thomomys talpoides) and pikas ( Ochotona princeps). Coupled with the rarity of yellow-bellied marmots here, these histories make the Snake Range a biogeographic oddity. These and other Great Basin mammal histories provide significant insights into the possible responses of Great Basin small mammals to global warming.

  13. Late Quaternary Climate and Vegetation of the Sudanian Zone of Northeast Nigeria

    NASA Astrophysics Data System (ADS)

    Salzmann, Ulrich; Hoelzmann, Philipp; Morczinek, Irena

    2002-07-01

    The Lake Tilla crater lake in northeastern Nigeria (10°23'N, 12°08'E) provides a ca. 17,000 14C yr multiproxy record of the environmental history of a Sudanian savanna in West Africa. Evaluation of pollen, diatoms, and sedimentary geochemistry from cores suggests that dry climatic conditions prevailed throughout the late Pleistocene. Before the onset of the Holocene, the slow rise in lake levels was interrupted by a distinct dry event between ca. 10,900 and 10,500 14C yr B.P., which may coincide with the Younger Dryas episode. The onset of the Holocene is marked by an abrupt increase in lake levels and a subsequent spread of Guinean and Sudanian tree taxa into the open grass savanna that predominated throughout the Late Pleistocene. The dominance of the mountain olive Olea hochstetteri suggests cool climatic conditions prior to ca. 8600 14C yr B.P. The early to mid-Holocene humid period culminated between ca. 8500 and 7000 14C yr B.P. with the establishment of a dense Guinean savanna during high lake levels. Frequent fires were important in promoting the open character of the vegetation. The palynological and palaeolimnological data demonstrate that the humid period terminated after ca. 7000 14C yr B.P. in a gradual decline of the precipitation/evaporation ratio and was not interrupted by abrupt climatic events. The aridification trend intensified after ca. 3800 14C yr B.P. and continued until the present.

  14. Late Tertiary and Quaternary landscape development in the western Grand Canyon and western Arizona strip

    SciTech Connect

    Billingsley, G.H. ); Wenrich, K.J. . Federal Center); Blackerby, B. )

    1993-04-01

    New geologic mapping of the western Grand Canyon and the Arizona Strip region, northwest Arizona, reveals young fault scarps on all faults, horsts, and graben structures. Tectonic activity here was previously thought to be at least Miocene age and older. New K-Ar age data for basalt flows in this region provide a basis for determining the age of surficial deposits in relation to elevated structural landforms. The basalts range in age from middle Miocene to late Pleistocene (17 Ma to 0.14 Ma). The Miocene basalts are found in the western Grand Canyon area and are progressively younger in a northeast direction onto the Shivwits and Uinkaret Plateaus, a distance of about 100 km. The older basalts are generally petrographically and chemically distinct from younger basalts. Those younger than one million years have less olivine and are chemically more iron- and titanium-rich suggesting they are from less primitive magmas. Basalt flows in this region older than 1 million years, are cut by faults showing equal displacement of the underlying strata and the flows. Basalt flows younger than 1 million years show offsets as much as 12 to 100 m, less than two-thirds the offset of underlying strata, implying that most tectonic activity occurred within the last 1 to 2 million years. Late Pliocene and Pleistocene faulting has extensively modified the landscape by elevated parts of the terrain resulting in young surficial deposits in lowland areas and rejuvenation of drainages in upthrown fault blocks.

  15. Lake Michigan's late Quaternary limnological and climate history from ostracode, oxygen isotope, and magnetic susptibility

    USGS Publications Warehouse

    Forester, Richard M.; Colman, Steven M.; Reynolds, Richard L.; Keigwin, Loyd D.

    1994-01-01

    The limnology of Lake Michigan has changed dramatically since the late Pleistocene in response to the expansion and contraction of continental glaciers, to differential isostatic rebound, and to climate change. The lake sediment's stratigraphic trends, magnetic susceptibility, δ18O, and ostracode species abundance ratios provide criteria to identify the lake's response to glacial ice and to differential isostatic rebound. The latter phenomena dominate the lake's late Pleistocene and early Holocene history. The lake's hydrological budget provides the primary linkage between the lake and climate, particularly effective moisture. Dissolved salts were stored in the lake's water column when the lake's output shifted toward evaporation, but were flushed when output shifted toward outflow. The lake's salt storage history may be interpreted from some ostracode, δ18O, and magnetic susceptibility records found in sediment cores. Climate change influenced the entire lake's limnological history, but became the primary limnological driver from about the middle-Holocene to the present. The complex limnological history of Lake Michigan resulted in substantial changes in the ostracode species assemblages; from about 12,000 ka to about 5,500 ka, five ostracode intervals can be identified. These ostracode intervals provide a within-lake biostratigraphy and a stratigraphic reference for reconstruction of the paleoenvironmental dynamics of the lake.

  16. Late Quaternary paleoclimate of western Alaska inferred from fossil chironomids and its relation to vegetation histories

    NASA Astrophysics Data System (ADS)

    Kurek, Joshua; Cwynar, Les C.; Ager, Thomas A.; Abbott, Mark B.; Edwards, Mary E.

    2009-05-01

    Fossil Chironomidae assemblages (with a few Chaoboridae and Ceratopogonidae) from Zagoskin and Burial Lakes in western Alaska provide quantitative reconstructions of mean July air temperatures for periods of the late-middle Wisconsin (˜39,000-34,000 cal yr B.P.) to the present. Inferred temperatures are compared with previously analyzed pollen data from each site summarized here by indirect ordination. Paleotemperature trends reveal substantial differences in the timing of climatic warming following the late Wisconsin at each site, although chronological uncertainty exists. Zagoskin Lake shows early warming beginning at about 21,000 cal yr B.P., whereas warming at Burial Lake begins ˜4000 years later. Summer climates during the last glacial maximum (LGM) were on average ˜3.5 °C below the modern temperatures at each site. Major shifts in vegetation occurred from ˜19,000 to 10,000 cal yr B.P. at Zagoskin Lake and from ˜17,000 to 10,000 cal yr B.P. at Burial Lake. Vegetation shifts followed climatic warming, when temperatures neared modern values. Both sites provide evidence of an early postglacial thermal maximum at ˜12,300 cal yr B.P. These chironomid records, combined with other insect-based climatic reconstructions from Beringia, indicate that during the LGM: (1) greater continentality likely influenced regions adjacent to the Bering Land Bridge and (2) summer climates were, at times, not dominated by severe cold.

  17. Chronology of sand ridges and the Late Quaternary evolution of the Etosha Pan, Namibia

    NASA Astrophysics Data System (ADS)

    Hipondoka, M. H. T.; Mauz, B.; Kempf, J.; Packman, S.; Chiverrell, R. C.; Bloemendal, J.

    2014-01-01

    Etosha Pan, situated at the southern border of tropical Africa, is a vast endorheic plain in Namibia's semi-arid north. The most recent studies agree that the pan was the floor of a former lake with varying water levels. Here we explored this idea further by investigating the link between lake-level change and records of late Pleistocene and Holocene climate change. The varying lake levels were inferred through sediment analysis and optical dating of sand deposits that form ridges parallel to the current shore along the northern and western margins of the pan. Our results support the view that the sand ridges are shoreline deposits of an evaporitic lake. The ridges result from the interplay between intermittent river discharge and riverine sediment supply from the north, prevailing north-easterly wind and shore-parallel waves. Therefore they are a proxy for former levels of a perennial lake. We infer higher levels during the late Pleistocene and a drastic drop shortly after 10 ka. Since around 8 ka Etosha Pan was covered by a shallow water body. This lake water-level reconstruction is not in line with the histories of ITCZ migration and strength of Benguela current upwelling. We confirm that the linkages between the evolution of the Etosha Pan and the climate mechanisms driving hydrological changes in subtropical southwest Africa are poorly resolved and need further investigation.

  18. A preliminary investigation of siliceous microfossil succession in late quaternary sediments from Lake Baikal, Siberia

    USGS Publications Warehouse

    Julius, M. L.; Stoermer, E. F.; Colman, S. M.; Moore, T. C.

    1997-01-01

    Siliceous microfossil assemblage succession was analyzed in a 100 m sediment core from Lake Baikal, Siberia. The core was recovered from the lake's central basin at a water depth of 365 m. Microfossil abundance varied greatly within the intervals sampled, ranging from samples devoid of siliceous microfossils to samples with up to 3.49 x 1011 microfossils g-1 sediment. Fluctuations in abundance appear to reflect trends in the marine δ18O record, with peak microfossil levels generally representing climate optima. Microfossil taxa present in sampled intervals changed considerably with core depth. Within each sample a small number of endemic diatom species dominated the assemblage. Changes in dominant endemic taxa between sampled intervals ranged from extirpation of some taxa, to shifts in quantitative abundance. Differences in microfossil composition and the association of variations in abundance with climate fluctuations suggest rapid speciation in response to major climatic excursions.

  19. Age determination of late Pleistocene marine transgression in western Alaska

    USGS Publications Warehouse

    Szabo, B. J.

    1982-01-01

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

  20. Morphology, mineralogy and magnetic susceptibility of epikarst-Terra Rossa developed in late Quaternary aeolianite deposits of southeastern Saurashtra, India

    NASA Astrophysics Data System (ADS)

    Khadkikar, Aniruddha S.; Basavaiah, Nathani

    2004-03-01

    The nature and development of epikarst and soil development in aeolianites under a monsoonal climatic regime has not yet been described. Late Quaternary aeolianites of the southeastern coast of Saurashtra in western India show a wide array of epikarst and red-soil formation, and serve to typify the character of aeolianite weathering under a monsoonal climate. Three varieties of epikarst are identified that represent down-profile increase in groundwater flow. Five types of Terra Rossae represent a transition from the karstified limestone to soil development. Terra Rossae differ in the content of residual aeolianite and show both simple and complex profiles. The latter at places shows ped development. The results show that an ontogenetic (growth) sequence exists from incipient epikarst to complex palaeosols. This ontogenetic sequence represents an incremental increase in the groundwater budget of the region in response to changing intensification of the Indian monsoon rainfall. Magnetic properties of the Terra Rossae formed under a monsoonal climate are described for the first time. The magnetic susceptibility together with its frequency-dependent and anhysteretic remanent magnetization (ARM) represents both the concentration of single domain and ultrafine superparamagnetic (SP) magnetite. The formation of single domain and superparamagnetic magnetite and hematite are linked genetically to weathering of the aeolianite that leads to the formation of Terra Rossa.

  1. Variable impact of late-Quaternary megafaunal extinction in causing ecological state shifts in North and South America

    PubMed Central

    Barnosky, Anthony D.; Lindsey, Emily L.; Villavicencio, Natalia A.; Bostelmann, Enrique; Hadly, Elizabeth A.; Wanket, James; Marshall, Charles R.

    2016-01-01

    Loss of megafauna, an aspect of defaunation, can precipitate many ecological changes over short time scales. We examine whether megafauna loss can also explain features of lasting ecological state shifts that occurred as the Pleistocene gave way to the Holocene. We compare ecological impacts of late-Quaternary megafauna extinction in five American regions: southwestern Patagonia, the Pampas, northeastern United States, northwestern United States, and Beringia. We find that major ecological state shifts were consistent with expectations of defaunation in North American sites but not in South American ones. The differential responses highlight two factors necessary for defaunation to trigger lasting ecological state shifts discernable in the fossil record: (i) lost megafauna need to have been effective ecosystem engineers, like proboscideans; and (ii) historical contingencies must have provided the ecosystem with plant species likely to respond to megafaunal loss. These findings help in identifying modern ecosystems that are most at risk for disappearing should current pressures on the ecosystems’ large animals continue and highlight the critical role of both individual species ecologies and ecosystem context in predicting the lasting impacts of defaunation currently underway. PMID:26504219

  2. Variable impact of late-Quaternary megafaunal extinction in causing ecological state shifts in North and South America

    NASA Astrophysics Data System (ADS)

    Barnosky, Anthony D.; Lindsey, Emily L.; Villavicencio, Natalia A.; Bostelmann, Enrique; Hadly, Elizabeth A.; Wanket, James; Marshall, Charles R.

    2016-01-01

    Loss of megafauna, an aspect of defaunation, can precipitate many ecological changes over short time scales. We examine whether megafauna loss can also explain features of lasting ecological state shifts that occurred as the Pleistocene gave way to the Holocene. We compare ecological impacts of late-Quaternary megafauna extinction in five American regions: southwestern Patagonia, the Pampas, northeastern United States, northwestern United States, and Beringia. We find that major ecological state shifts were consistent with expectations of defaunation in North American sites but not in South American ones. The differential responses highlight two factors necessary for defaunation to trigger lasting ecological state shifts discernable in the fossil record: (i) lost megafauna need to have been effective ecosystem engineers, like proboscideans; and (ii) historical contingencies must have provided the ecosystem with plant species likely to respond to megafaunal loss. These findings help in identifying modern ecosystems that are most at risk for disappearing should current pressures on the ecosystems' large animals continue and highlight the critical role of both individual species ecologies and ecosystem context in predicting the lasting impacts of defaunation currently underway.

  3. Late Quaternary History of River Discharge and Glaciation in the Southern Kara Sea, Arctic Ocean: Preliminary Results

    NASA Astrophysics Data System (ADS)

    Stein, R.; Niessen, F.; Dittmers, K.; Levitan, M.; Levitan, M.; Schoster, F.; Simstich, J.; Steinke, T.; Stepanets, O.

    2001-12-01

    Within the framework of the joint German-Russian project on "The Nature of Continental Run-Off from the Siberian Rivers and its Behavior in the Adjacent Arctic Basin (Siberian River Run-Off-SIRRO)", a multidisciplinary expedition with RV "Akademik Boris Petrov" was carried out in the Ob and Yenisei estuaries and the southern Kara Sea in August-September 2001. From the geological point of view, the variability of river discharge in relationship to climate change and the reconstruction of extent and history of glaciation in the southern Kara Sea during Late Quaternary times are major foci of interest. To reach these goals, an intensive sediment ecosounding (2-12 kHz) survey and sediment coring program has been performed. Based on profiling and sediment core data, the following preliminary statements can be given: (1) The extent of the eastern margin of the Barents Sea LGM Ice Sheet between 74 and 78oN can be mapped in detail. Different types of glacial to nonglacial facies can be distinguished. This ice barrier should have strongly influenced river discharge, diverted towards the NE probably into the Voronin Trough. (2) The local LGM (?) ice sheet on Taymyr Peninsula seems to be not connected with the Barents Sea Ice Sheet. (3) Siberian river discharge reached maximum values during the last deglaciation and displays distinct (cyclic) variability during Holocene times. Further detailed evaluation of the sediment echograph profiles as well as detailed sedimentological studies and AMS 14C datings will follow to support these ideas.

  4. Reconstructing transport pathways for late Quaternary dust from eastern Australia using the composition of trace elements of long traveled dusts

    NASA Astrophysics Data System (ADS)

    Petherick, Lynda M.; McGowan, Hamish A.; Kamber, Balz S.

    2009-04-01

    The southeast Australian dust transport corridor is the principal pathway through which continental emissions of dust from central and eastern Australia are carried to the oceans by the prevailing mid-latitude westerly circulation. The analysis of trace elements of aeolian dust, preserved in lake sediment on North Stradbroke Island, southeast Queensland, is used to reconstruct variation in the intensity and position of dust transport to the island over the past 25,000 yrs. Separation of local and long traveled dust content of lake sediments is achieved using a unique, four-element (Ga, Ni, Tl and Sc) separation method. The local and continental chronologies of aeolian deposition developed by this study show markedly different records, and indicate varied responses to climate variability on North Stradbroke Island (local aeolian sediment component) and in eastern and central Australia (long traveled dust component). The provenance of the continental component of the record to sub-geologic catchment scales was accomplished using a ternary mixing model in which the chemical identification of dusts extracted, from the lake sediments, was compared to potential chemical characteristics of surface dust from the source areas using 16 trace elements. The results indicate that the position and intensity of dust transport pathways during the late Quaternary varied considerably in response to changing atmospheric circulation patterns as well as to variations in sediment supply to dust source areas, which include the large anabranching river systems of the Lake Eyre and Murray-Darling Basins.

  5. Late Quaternary environmental and landscape dynamics revealed by a pingo sequence on the northern Seward Peninsula, Alaska

    NASA Astrophysics Data System (ADS)

    Wetterich, Sebastian; Grosse, Guido; Schirrmeister, Lutz; Andreev, Andrei A.; Bobrov, Anatoly A.; Kienast, Frank; Bigelow, Nancy H.; Edwards, Mary E.

    2012-04-01

    A terrestrial sediment sequence exposed in an eroding pingo provides insights into the late-Quaternary environmental history of the northern Seward Peninsula, Alaska. We have obtained the first radiocarbon-dated evidence for a mid-Wisconsin thermokarst lake, demonstrating that complex landscape dynamics involving cyclic permafrost aggradation and thermokarst lake formation occurred over stadial-interstadial as well as glacial-interglacial time periods. High values of Picea pollen and the presence of Larix pollen in sediments dated to 50-40 ka BP strongly suggest the presence of forest or woodland early in MIS 3; the trees grew within a vegetation matrix dominated by grass and sedge, and there is indirect evidence of grazing animals. Thus the interstadial ecosystem was different in structure and composition from the Holocene or from the preceding Last Interglacial period. An early Holocene warm period is indicated by renewed thermokarst lake formation and a range of fossil taxa. Multiple extralimital plant taxa suggest mean July temperatures above modern values. The local presence of spruce during the early Holocene warm interval is evident from a radiocarbon-dated spruce macrofossil remain and indicates significant range extension far beyond the modern tree line. The first direct evidence of spruce in Northwest Alaska during the early Holocene has implications for the presence of forest refugia in Central Beringia and previously assumed routes and timing of post-glacial forest expansion in Alaska.

  6. Quantification of Both Normal and Right-Lateral Late Quaternary Activity Along the Kongur Shan Extensional System, Chinese Pamir

    NASA Astrophysics Data System (ADS)

    Chevalier, M. L.; Pan, J.; Liu, D.; Wang, M.; Lu, H.; Li, H.

    2014-12-01

    The Pamir Mountains, located at the western end of the Indo-Asian collision zone, are one of the most tectonically active regions in central Asia. The Kongur Shan extensional system (KES), located in the Chinese Pamir, accommodates EW extension due to the India/Asia collision and has been the focus on numerous Cenozoic studies, whereas there are very few late Quaternary studies. The KES is mostly normal, except towards its NW end, where it becomes right-lateral strike-slip, along the Muji segment. From Muji to Tashkorgan, we investigated 6 sites, where active normal and/or strike-slip faults cut and offset abandoned river channels or alluvial fans and terraces, which allows us to quantify both the normal and strike-slip motions at different locations along the KES. Our preliminary results yield vertical and right-lateral rates of ~1.8 and >3.2 mm/yr along the northern KES (Muji to Bulunkou) during the Holocene, and of ~1.9-2.7 and ~1 mm/yr along the southern KES (near Taheman) since ~30 ka. These preliminary rates, consistent with GPS data and Cenozoic rates, imply that the EW extension rate due to the northward indentation of the Pamir salient as well as due to the clockwise rotation of the rigid Tarim basin, is partly accommodated by the Muji-Tashkorgan pull-apart basin, and is faster in the north than in the south (from ~5 to ~2 mm/yr).

  7. Variable impact of late-Quaternary megafaunal extinction in causing ecological state shifts in North and South America.

    PubMed

    Barnosky, Anthony D; Lindsey, Emily L; Villavicencio, Natalia A; Bostelmann, Enrique; Hadly, Elizabeth A; Wanket, James; Marshall, Charles R

    2016-01-26

    Loss of megafauna, an aspect of defaunation, can precipitate many ecological changes over short time scales. We examine whether megafauna loss can also explain features of lasting ecological state shifts that occurred as the Pleistocene gave way to the Holocene. We compare ecological impacts of late-Quaternary megafauna extinction in five American regions: southwestern Patagonia, the Pampas, northeastern United States, northwestern United States, and Beringia. We find that major ecological state shifts were consistent with expectations of defaunation in North American sites but not in South American ones. The differential responses highlight two factors necessary for defaunation to trigger lasting ecological state shifts discernable in the fossil record: (i) lost megafauna need to have been effective ecosystem engineers, like proboscideans; and (ii) historical contingencies must have provided the ecosystem with plant species likely to respond to megafaunal loss. These findings help in identifying modern ecosystems that are most at risk for disappearing should current pressures on the ecosystems' large animals continue and highlight the critical role of both individual species ecologies and ecosystem context in predicting the lasting impacts of defaunation currently underway. PMID:26504219

  8. Response of surface processes to climatic change in the dunefields and Loess Plateau of North China during the late Quaternary

    USGS Publications Warehouse

    Lu, H.; Mason, J.A.; Stevens, T.; Zhou, Y.; Yi, S.; Miao, X.

    2011-01-01

    This paper draws on recent optically stimulated luminescence (OSL) dating to evaluate the long-held assumption that dust accumulation rates in the Loess Plateau and the extent of active aeolian sand in the dunefields to the north have varied together over time, because both are controlled by the strength of the Asian monsoons and also possibly because the dunefields are proximal loess sources. The results show there is little evidence that high rates of loess accumulation coincided with well-dated episodes of extensive dune activity in the Mu Us, Otindag, and Horqin dunefields, at 11-8ka and 1-0ka. Explanations for the apparent lack of coupling include local variation in the trapping of dust and post-depositional preservation of the loess and dune sediments, in response to varying local environmental conditions. In addition, a substantial portion of the loess may be transported directly from source areas where dust emission has somewhat different climatic and geomorphic controls than aeolian sand activity within the dunefields. The results of this study cast doubt on the use of loess accumulation rate as a palaeoclimatic proxy at millennial timescale. The dunefield and loess stratigraphic records are interpreted as primarily recording changes in effective moisture at a local scale, but the timing of late Quaternary dune activity, along with a variety of other evidence, indicates that moisture changes in many of the drylands of northern China may not be in phase with precipitation in core regions of the Asian monsoons. ?? 2011 John Wiley & Sons, Ltd.

  9. Late Quaternary history of the Vakinankaratra volcanic field (central Madagascar): insights from luminescence dating of phreatomagmatic eruption deposits

    NASA Astrophysics Data System (ADS)

    Rufer, Daniel; Preusser, Frank; Schreurs, Guido; Gnos, Edwin; Berger, Alfons

    2014-05-01

    The Quaternary Vakinankaratra volcanic field in the central Madagascar highlands consists of scoria cones, lava flows, tuff rings, and maars. These volcanic landforms are the result of processes triggered by intracontinental rifting and overlie Precambrian basement or Neogene volcanic rocks. Infrared-stimulated luminescence (IRSL) dating was applied to 13 samples taken from phreatomagmatic eruption deposits in the Antsirabe-Betafo region with the aim of constraining the chronology of the volcanic activity. Establishing such a chronology is important for evaluating volcanic hazards in this densely populated area. Stratigraphic correlations of eruption deposits and IRSL ages suggest at least five phreatomagmatic eruption events in Late Pleistocene times. In the Lake Andraikiba region, two such eruption layers can be clearly distinguished. The older one yields ages between 109 ± 15 and 90 ± 11 ka and is possibly related to an eruption at the Amboniloha volcanic complex to the north. The younger one gives ages between 58 ± 4 and 47 ± 7 ka and is clearly related to the phreatomagmatic eruption that formed Lake Andraikiba. IRSL ages of a similar eruption deposit directly overlying basement laterite in the vicinity of the Fizinana and Ampasamihaiky volcanic complexes yield coherent ages of 68 ± 7 and 65 ± 8 ka. These ages provide the upper age limit for the subsequently developed Iavoko, Antsifotra, and Fizinana scoria cones and their associated lava flows. Two phreatomagmatic deposits, identified near Lake Tritrivakely, yield the youngest IRSL ages in the region, with respective ages of 32 ± 3 and 19 ± 2 ka. The reported K-feldspar IRSL ages are the first recorded numerical ages of phreatomagmatic eruption deposits in Madagascar, and our results confirm the huge potential of this dating approach for reconstructing the volcanic activity of Late Pleistocene to Holocene volcanic provinces.

  10. Assessment of Late Quaternary strain partitioning in the Afar Triple Junction: Dobe and Hanle grabens, Ethiopia and Djibouti

    NASA Astrophysics Data System (ADS)

    Polun, S. G.; Stockman, M. B.; Hickcox, K.; Horrell, D.; Tesfaye, S.; Gomez, F. G.

    2015-12-01

    As the only subaerial exposure of a ridge - ridge - ridge triple junction, the Afar region of Ethiopia and Djibouti offers a rare opportunity to assess strain partitioning within this type of triple junction. Here, the plate boundaries do not link discretely, but rather the East African rift meets the Red Sea and Gulf of Aden rifts in a zone of diffuse normal faulting characterized by a lack of magmatic activity, referred to as the central Afar. An initial assessment of Late Quaternary strain partitioning is based on faulted landforms in the Dobe - Hanle graben system in Ethiopia and Djibouti. These two extensional basins are connected by an imbricated accommodation zone. Several fault scarps occur within terraces formed during the last highstand of Lake Dobe, around 5 ka - they provide a means of calibrating a numerical model of fault scarp degradation. Additional timing constraints will be provided by pending exposure ages. The spreading rates of both grabens are equivalent, however in Dobe graben, extension is partitioned 2:1 between northern, south dipping faults and the southern, north dipping fault. Extension in Hanle graben is primarily focused on the north dipping Hanle fault. On the north margin of Dobe graben, the boundary fault bifurcates, where the basin-bordering fault displays a significantly higher modeled uplift rate than the more distal fault, suggesting a basinward propagation of faulting. On the southern Dobe fault, surveyed fault scarps have ages ranging from 30 - 5 ka with uplift rates of 0.71, 0.47, and 0.68 mm/yr, suggesting no secular variation in slip rates from the late Plestocene through the Holocene. These rates are converted into horizontal stretching estimates, which are compared with regional strain estimated from velocities of relatively sparse GPS data.

  11. Late Quaternary faulting on the Manas and Hutubi reverse faults in the northern foreland basin of Tian Shan, China

    NASA Astrophysics Data System (ADS)

    Gong, Zhijun; Li, Sheng-Hua; Li, Bo

    2015-08-01

    The Tian Shan Range lies in the actively deforming part of the India-Asia collision zone. In the northern foreland basin of Tian Shan, the strata were intensively deformed by Cenozoic folding and faulting. Slip rate studies along these faults are important for understanding the dynamics of crustal deformation and evaluating the seismic hazards in the region. Two reverse faults (the Manas and Hutubi faults) in the northern foreland basin were investigated. Due to past faulting events along these faults, the terrace treads along the Manas River were ruptured, forming fault scarps several meters in height. Loess deposits were trapped and preserved at the surface ruptures along these scarps. The thickness of the trapped loess is dependent on the size of the ruptures. The minimum and maximum ages of these scarps are constrained by dating the loess preserved at the surface ruptures and the terrace treads, respectively, using the quartz optically stimulated luminescence (OSL) dating technique. Our dating results suggest that the loess trapped at the ruptures was deposited from the early to mid-Holocene at the Hutubi Fault, and from the mid- to late-Holocene at the Manas Fault. The vertical displacements of the faults were evaluated by measuring the topographic profiles across the investigated fault scarps using the differential global position system (DGPS). Our results suggest that, during the late Quaternary in the studied region, the vertical slip rates of the Manas Fault were between ˜ 0.74 mm /yr and ˜ 1.6 mm /yr, while the Hutubi Fault had a much lower vertical slip rate between ˜ 0.34 mm /yr and ˜ 0.40 mm /yr. The tectonic implications of our results are discussed.

  12. Great Basin semi-arid woodland dynamics during the late quaternary

    SciTech Connect

    Wigand, P.E.; Hemphill, M.L.; Sharpe, S.E.

    1995-09-01

    Semi-arid woodlands have dominated the middle elevations of Great Basin mountain ranges during the Holocene where subalpine woodlands prevailed during the Pleistocene. Ancient woodrat middens, and in a few cases pollen records indicate in the late Pleistocene and early Holocene woodland history lowered elevation of subalpine woodland species. After a middle Holocene retrenchment at elevations in excess of 500 meters above today, Juniper-dominated semi-arid woodland reached its late Holocene maximum areal extent during the Neoglacial (2 to 4 ka). These records, along with others indicate contracting semi-arid woodland after the Neoglacial about 1.9 ka. Desert shrub community expansion coupled with increased precariousness of wetland areas in the southern Great Basin between 1.9 and 1.5 ka coincide with shrinking wet-lands in the west-central and northern Great Basin. Coincident greater grass abundance in northern Great Basin sagebrush steppe, reaching its maximum between 1.5 and 1.2 ka, corresponds to dramatic increases in bison remains in the archaeological sites of the northern Intermontane West. Pollen and woodrat midden records indicate that this drought ended about 1.5 ka. Succeeding ameliorating conditions resulted in the sudden northward and downward expansion of pinon into areas that had been dominated by juniper during the Neoglacial. Maximum areal extent of pinon dominated semi-arid woodland in west-central Nevada was centered at 1.2 ka. This followed by 100 years the shift in dominance from juniper to pinon in southern Nevada semi-arid woodlands. Great Basin woodlands suffered from renewed severe droughts between .5 to .6 ka. Effectively wetter conditions during the {open_quotes}Little Ice Age{close_quotes} resulted in re-expansion of semi-arid woodland. Activities related to European settlement in the Great Basin have modified prehistoric factors or imposed new ones that are affecting woodland response to climate.

  13. Late Quaternary vegetation development and disturbance dynamics from a peatland on Mount Gorongosa, central Mozambique

    NASA Astrophysics Data System (ADS)

    McWethy, David B.; Neumann, Frank H.; Steinbruch, Franziska; Ryan, Casey M.; Valsecchi, Verushka

    2016-04-01

    Few long-term climate and environmental records are available for southeast Africa where millennial scale shifts in the north-south position of the Intertropical Convergence Zone (ITCZ) and changes in Indian Ocean sea surface temperatures interact with local controls (e.g., fire, hydrology) to influence vegetation and ecosystem dynamics. Reconstruction of late-Pleistocene - Holocene environmental change from peat sediments obtained from Mount Gorongosa, central Mozambique, provides insight into vegetation, climate and disturbance interactions over the past c. 27 kyr. During the late Pleistocene, cool and wet climatic conditions supported Podocarpus forest and Ericaceae-heathland until drier conditions led to grassland expansion and a hiatus in peat deposition between c. 22.5 and 7.2 cal kBP. Increased temperatures and fire activity since c. 7.2 cal kBP led to further expansion of grasslands. Continued warming helped maintain grasslands and fostered a diverse mix of Podocarpus forest with a large number of subtropical trees and miombo woodland taxa (especially Brachystegia spp.) until regional land-use associated with the rise of Iron Age activity promoted an increase of disturbance related taxa over the last 1-2 millennia. Recent migration of people onto the Mount Gorongosa massif in the last fifty years are linked to an increase in fire activity that is unprecedented in the 27 kyr record, resulting in shifts in vegetation composition and structure. This long-term record of environmental change from central Mozambique highlights complex interaction between overlapping climatic influences and documents important vegetation transitions linked to millennial scale climatic controls, disturbance processes and more recent land-use change from a region where few records exist.

  14. Isotopic evidence for the diversity of late Quaternary loess in Nebraska: Glaciogenic and nonglaciogenic sources

    USGS Publications Warehouse

    Aleinikoff, John N.; Muhs, Daniel R.; Bettis, E. Arthur, III; Johnson, William C.; Fanning, C. Mark; Benton, Rachel

    2008-01-01

    Pb isotope compositions of detrital K-feldspars and U-Pb ages of detrital zircons are used as indicators for determining the sources of Peoria Loess deposited during the last glacial period (late Wisconsin, ca. 25–14 ka) in Nebraska and western Iowa. Our new data indicate that only loess adjacent to the Platte River has Pb isotopic characteristics suggesting derivation from this river. Most Peoria Loess in central Nebraska (up to 20 m thick) is non-glaciogenic, on the basis of Pb isotope ratios in K-feldspars and the presence of 34-Ma detrital zircons. These isotopic characteristics suggest derivation primarily from the Oligocene White River Group in southern South Dakota, western Nebraska, southeastern Wyoming, and northeastern Colorado. The occurrence of 10–25 Ma detrital zircons suggests additional minor contributions of silt from the Oligocene-Miocene Arikaree Group and Miocene Ogallala Group. Isotopic data from detrital K-feldspar and zircon grains from Peoria Loess deposits in eastern Nebraska and western Iowa suggest that the immediate source of this loess was alluvium of the Missouri River. We conclude that this silt probably is of glaciogenic origin, primarily derived from outwash from the western margin of the Laurentide Ice Sheet. Identification of the White River Group as the main provenance of Peoria Loess of central Nebraska and the Missouri River valley as the immediate source of western Iowa Peoria Loess indicates that paleowind directions during the late Wisconsin were primarily from the northwest and west, in agreement with earlier studies of particle size and loess thickness variation. In addition, the results are in agreement with recent simulations of non-glaciogenic dust sources from linked climate-vegetation modeling, suggesting dry, windy, and minimally vegetated areas in parts of the Great Plains during the last glacial period.

  15. Isotope evidence for the intensive use of marine foods by Late Upper Palaeolithic humans.

    PubMed

    Richards, M P; Jacobi, R; Cook, J; Pettitt, P B; Stringer, C B

    2005-09-01

    We report here on direct evidence for the intensive consumption of marine foods by anatomically modern humans at approximately 12,000 years ago. We undertook isotopic analysis of bone collagen from three humans, dating to the late Palaeolithic, from the site of Kendrick's Cave in North Wales, UK. The isotopic measurements of their bone collagen indicated that ca. 30% of their dietary protein was from marine sources, which we interpret as likely being high trophic level marine organisms such as marine mammals. This indicates that towards the end of the Pleistocene modern humans were pursuing a hunting strategy that incorporated both marine and terrestrial mammals. This is the first occurrence of the intensive use of marine resources, specifically marine mammals, that becomes even more pronounced in the subsequent Mesolithic period. PMID:15975629

  16. Identifying the pollen of an extinct spruce species in the Late Quaternary sediments of the Tunica Hills region, south-eastern United States

    USGS Publications Warehouse

    Luke Mander; Jacklyn Rodriguez; Pietra G. Mueller; Jackson, Stephen T.; Surangi W. Punyasena

    2014-01-01

    Late Quaternary fluvial deposits in the Tunica Hills region of Louisiana and Mississippi are rich in spruce macrofossils of the extinct species Picea critchfieldii, the one recognized plant extinction of the Late Quaternary. However, the morphology of P. critchfieldii pollen is unknown, presenting a barrier to the interpretation of pollen spectra from the last glacial of North America. To address this issue, we undertook a morphometric study of Picea pollen from Tunica Hills. Morphometric data, together with qualitative observations of pollen morphology using Apotome fluorescence microscopy, indicate that Picea pollen from Tunica Hills is morphologically distinct from the pollen of P. glauca, P. mariana and P. rubens. Measurements of grain length, corpus width and corpus height indicate that Picea pollen from Tunica Hills is larger than the pollen of P. mariana and P. rubens, and is slightly larger than P. glauca pollen. We argue that the morphologically distinctive Tunica Hills Picea pollen was probably produced by the extinct spruce species P. critchfieldii. These morphological differences could be used to identify P. critchfieldii in existing and newly collected pollen records, which would refine its paleoecologic and biogeographic history and clarify the nature and timing of its extinction in the Late Quaternary.

  17. Late Quaternary Activity and Seismogenic Potential of the Gonave microplate: South Coast Fault Zone of Southern Jamaica

    NASA Astrophysics Data System (ADS)

    Benford, B.; Mann, P.; Prentice, C.; King, W.; Wiggins-Grandison, M.; Demets, C.; Tikoff, B.

    2008-12-01

    of the fault. Further work, including geodetic surveys and fault trenching, will better constrain the amount of late Quaternary motion on the SCFZ.

  18. Late Quaternary vegetation dynamics and hydro-climate in the Drakensberg, South Africa

    NASA Astrophysics Data System (ADS)

    Norström, E.; Neumann, F. H.; Scott, L.; Smittenberg, R. H.; Holmstrand, H.; Lundqvist, S.; Snowball, I.; Sundqvist, H. S.; Risberg, J.; Bamford, M.

    2014-12-01

    A multi-proxy study of a sediment sequence from Braamhoek wetland, covering the last c. 16,000 years, reveals a record of regional climate and vegetation dynamics in the Drakensberg region, South Africa, including signals from both the organic sediment fraction (fossil pollen, charcoal, n-alkane abundance, n-alkane δ13C, TOC) and the inorganic fraction (mineral magnetic properties). The reconstruction, supported by a robust chronology, indicates two major periods of increased regional wetness during the late Pleistocene to early Holocene phase (c. 13,800-12,600 cal yr BP; c. 10,200-8500 cal yr BP) and one during the late Holocene (c. 2000 cal yr BP to present). Drier conditions are recorded during the Younger Dryas (c. 12,600-11,300 cal yr BP) and mid-Holocene (c. 7000-2000 cal yr BP). A major decline in fynbos vegetation during the early Holocene suggests a shift towards warmer temperatures and possibly towards less pronounced winter rains in eastern South Africa from c. 8500 cal yr BP. Comparison with records from interior of South Africa show relatively high inter-site variability, however, the Braamhoek moisture proxies do co-vary with the speleothem isotope records from Makapansgat, suggesting a similar hydro-climate evolution in eastern and interior parts of the summer rainfall region during the studied period. On multi-millennial time scales, an inverse hydro-climatological pattern is evident between these two South African records and reconstructions from tropical locations in southeast Africa. Such a rainfall dipole between eastern tropical and southern Africa, has previously been identified on shorter time scales, i.e. on inter-annual to millennial scales. The Braamhoek study suggests that a similar dipole pattern is acting also on a multi-millennial perspective. These long-term precipitation anomalies are tentatively coupled to teleconnections from multi-millennial changes in the dynamics of the Indian Ocean Dipole (IOD) and El Ni

  19. Late Quaternary history of the southwestern St. Lawrence Lowlands and adjacent Adirondack Highlands

    SciTech Connect

    Pair, D.L. . Dept. of Geology)

    1993-03-01

    The reconstruction of Late Wisconsinan ice retreat, proglacial lakes, and Champlain Sea history from the northwest Adirondack slope and adjacent St. Lawrence Lowlands is critical to the synthesis of a regional picture of deglacial events in the eastern Great Lakes region. Unfortunately, these same areas are well known for their limited exposures, landforms covered by thick forest, large tracts of land inaccessible to detailed field mapping, and the overall paucity of glacial materials preserved on upland surfaces. Despite these limitations, a model which utilizes multiple and field-truthed evidence has been used to designate areas where ice border deposits indicate a substantial recessional position. It employs the following criteria in this analysis: sedimentology and morphostratigraphy of morainal landform segments and related sediments; orientation and continuity of ice border drainage channels; and the relationship of ice borders and drainage systems to well documented local and regional water bodies which accompanied ice retreat. The results of this approach have provided a unique regional picture of deglaciation. Despite the inherent limitations of working in upland areas to reconstruct glacial events, detailed morphostratigraphic correlations based on multiple lines of evidence can yield important information. The positions of five former ice borders have been reconstructed from the available data. These ice margins correspond closely with those documented previously by others adjoining areas. This type of study, utilizing multiple and field-truthed lines of evidence, constitutes a tangible step towards understanding the nature and history of ice retreat along this portion of the Laurentide Ice Sheet.

  20. Thermoluminescence and excess 226Ra decay dating of late Quaternary fluvial sands, East Alligator River, Australia

    NASA Astrophysics Data System (ADS)

    Murray, Andrew; Wohl, Ellen; East, Jon

    1992-01-01

    Thermoluminescence (TL) dating was applied to seven samples of siliceous fluvial sands from the East Alligator River of Northern Australia, giving ages ranging from modern to 6000 yr B.P. Two methods of estimating the equivalent dose (ED), total bleach and regenerative, were applied to the 90- to 125-μm quartz fraction of the samples in order to determine the reliability and internal consistency of the technique. High-resolution γ and α spectroscopy were used to measure radionuclide contents; these measurements revealed an excess 226Ra activity compared with 230Th. This excess decreased with depth, and was used directly to derive mean sedimentation rates, and thus sediment ages. Both this method and one 14C date confirmed the validity of the TL values, which increased systematically with depth and were consistent with site stratigraphy. TL was of limited use in the dating of these late Holocene deposits because of age uncertainties of 500 to 1600 yr, resulting from a significant residual ED. This residual probably resulted from incomplete bleaching during reworking upstream of the sampling site. For Pleistocene deposits, the residual ED will be less significant because of higher total EDs, and TL dates will be correspondingly more accurate.

  1. Plant Functional Variability in Response to Late-Quaternary Climate Change Recorded in Ancient Packrat Middens

    NASA Astrophysics Data System (ADS)

    Holmgren, C. A.; Potts, D. L.

    2006-12-01

    Responses of plant functional traits to environmental variability are of enduring interest because they constrain organism performance and ecosystem function. However, most inferences regarding plant functional trait response to climatic variability have been limited to the modern period. To better understand plant functional response to long-term climate variability and how adjustments in leaf morphology may contribute to patterns of species establishment, persistence, or extirpation, we measured specific leaf area (SLA) from macrofossils preserved in ancient packrat middens collected along the Arizona/New Mexico border, USA. Our record spanned more than 32,000 years and included six woodland and Chihuahuan Desert species: Berberis cf. haematocarpa, Juniperus cf. coahuilensis, Juniperus osteosperma, Larrea tridentata, Prosopis glandulosa and Parthenium incanum. We predicted that regional climatic warming and drying since the late Pleistocene would result in intraspecific decreases in SLA. As predicted, SLA was positively correlated with midden age for three of the six species (L. tridentata, J. osteosperma, B. cf. haematocarpa). SLA was also negatively correlated with December (L. tridentata, J. cf. coahuilensis) or June (B. cf. haematocarpa, J. osteosperma) insolation. A unique record of vegetation community dynamics, plant macrofossils preserved in packrat middens also represent a rich and largely untapped source of information on long-term trends in species functional response to environmental change.

  2. Late Quaternary stratigraphy and luminescence geochronology of the northeastern Mojave Desert

    USGS Publications Warehouse

    Mahan, S.A.; Miller, D.M.; Menges, C.M.; Yount, J.C.

    2007-01-01

    The chronology of the Holocene and late Pleistocene deposits of the northeastern Mojave Desert have been largely obtained using radiocarbon ages. Our study refines and extends this framework using optically stimulated luminescence (OSL) to date deposits from Valjean Valley, Silurian Lake Playa, Red Pass, and California Valley. Of particular interest are eolian fine silts incorporated in ground-water discharge (GWD) deposits bracketed at 185-140 and 20-50 ka. Alluvial fan deposits proved amenable for OSL by dating both eolian sand lenses and reworked eolian sand in a matrix of gravel that occurs within the fan stratigraphy. Lacustrine sand in spits and bars also yielded acceptable OSL ages. These OSL ages fill gaps in the geochronology of desert deposits, which can provide data relevant to understanding the responses of several depositional systems to regional changes in climate. This study identifies the most promising deposits for future luminescence dating and suggests that for several regions of the Mojave Desert, sediments from previously undated landforms can be more accurately placed within correct geologic map units.

  3. Late quaternary dislocations and seismotectonics of the Racha earthquake source, the Greater Caucasus

    NASA Astrophysics Data System (ADS)

    Ovsyuchenko, A. N.; Marakhanov, A. V.; Lar'kov, A. S.; Novikov, S. S.

    2014-11-01

    The results of studying traces of ancient seismic catastrophes in epicentral zone of the 1991 Racha earthquake are set forth. The source of this earthquake is noteworthy, because it reflects the main tendency in the geological evolution of the region, i.e., thrusting of the southern slope of the Greater Caucasus over the basement of the Transcaucasus Median Mass. It has been ascertained that two large-scale seismic events were related to this source in the Holocene. The approximate duration of the middle Holocene event was 2300 yr (7300-5000 yr ago). The late Holocene event, including the Racha earthquake in 1991, lasted ˜1600 yr. The role of the Racha earthquake in the large-scale seismic cycle is discussed. A surprising circumstance was the absence of datings in the time interval of 2400-9500 yr ago. The lack of these datings could have been caused by the change in climate and absence of paleosoils or by deceleration of seismic activity. The results also allowed us to substantiate seismotectonic segmentation of the southern slope of the Greater Caucasus in the area under consideration.

  4. Late Quaternary lake records from the Anadyr Lowland, Central Chukotka (Russia)

    NASA Astrophysics Data System (ADS)

    Lozhkin, Anatoly; Anderson, Patricia

    2013-05-01

    Three lake cores provide insight into the vegetation and climate history of the past ∼45,000 14C yr in the Anadyr Lowland, a key paleogeographic link between the Bering Land Bridge (BLB) and interior Western Beringia (WB). Although not without chronological issues, these records suggest that the Late Pleistocene interstade (approximating Oxygen Isotope Stage (OIS) 3) was a time of unstable environments consistent with previous interpretations for southern areas of WB and in contrast to more stable conditions inferred for northern WB. A hiatus in the records during OIS2 implies dry, frigid environments in the Anadyr Lowland. Previous research suggested that Chuktoka was a westward extension of relatively mesic environments of the BLB, which acted as a “filter” to intercontinental migrations. The Lowland data indicate that Chukotka may have been more of a transitional zone between mesic BLB and more xeric regions of western WB. A structurally novel biome dominated by deciduous forest and high-shrub tundra was proposed as occupying much of Beringia between ∼11,000 and 9000 14C yr BP. The unusual pollen assemblage that characterizes the Lowland suggests that perhaps a second biome was also present in Beringia, one that was dominated by meadows with Betula shrub thickets.

  5. Late Quaternary Water-Level Variations and Vegetation History at Crooked Pond, Southeastern Massachusetts

    NASA Astrophysics Data System (ADS)

    Shuman, Bryan; Bravo, Jennifer; Kaye, Jonathan; Lynch, Jason A.; Newby, Paige; Webb, Thompson, III

    2001-11-01

    Sediment cores collected along a transect in Crooked Pond, southeastern Massachusetts, provide evidence of water-level changes between 15,000 cal yr B.P. and present. The extent of fine-grained, detrital, organic accumulation in the basin, inferred from sediment and pollen stratigraphies, varied over time and indicates low water levels between 11,200 and 8000 cal yr B.P. and from ca. 5300 to 3200 cal yr B.P. This history is consistent with the paleohydrology records from nearby Makepeace Cedar Swamp and other sites from New England and eastern Canada and with temporal patterns of regional changes in effective soil moisture inferred from pollen data. The similarities among these records indicate that (1) regional conditions were drier than today when white pine ( Pinus strobus) grew abundantly in southern New England (11,200 to 9500 cal yr B.P.); (2) higher moisture levels existed between 8000 and 5500 cal yr B.P., possibly caused by increased meridonal circulation as the influence of the Laurentide ice sheet waned; and (3) drier conditions possibly contributed to the regional decline in hemlock ( Tsuga) abundances at 5300 cal yr B.P. Although sea-level rise may have been an influence, moist climatic conditions during the late Holocene were the primary reason for a dramatic rise in water-table elevations.

  6. The lost Adventure Archipelago (Sicilian Channel, Mediterranean Sea): Morpho-bathymetry and Late Quaternary palaeogeographic evolution

    NASA Astrophysics Data System (ADS)

    Civile, Dario; Lodolo, Emanuele; Zecchin, Massimo; Ben-Avraham, Zvi; Baradello, Luca; Accettella, Daniela; Cova, Andrea; Caffau, Mauro

    2015-02-01

    The rise in sea level following the Last Glacial Maximum (LGM) radically altered pre-existing geography, pushing back the former shorelines. The effect of this eustatic change was particularly intense and dramatic in flat lands and shelves, such as the Sicilian Channel. High-resolution bathymetric maps and Chirp seismic profiles analyzed in this study show that the Sicilian Channel, now lying at depths rarely exceeding 150 m, has emerged several times during its geological history. The last emergence was during the Early Holocene, when kilometre-sized islands punctuated the north-western sector of the Sicilian Channel, the Adventure Plateau, forming a broad archipelago. Many of these islands, now located in water ranging in depth from - 10 to - 40 m, are composed of highly deformed Neogene sedimentary rocks (Talbot, Ante-Talbot, Nereo, and Pantelleria Vecchia banks), while others represent submarine Pleistocene volcanic edifices (Galatea, Anfitrite and Tetide banks). Sedimentary cover in all of these banks is virtually absent. High-resolution seismic profiles allowed the identification of post-LGM morphological markers associated with the marine transgression, some of which are characterized by melt water-pulses, as demonstrated by the presence of specific and distinct erosional features. Combining swath bathymetric data with the seismic profiles, we have generated two palaeogeographic maps of the former Adventure Archipelago at two specific time frames: (1) at the end of the Younger Dryas stadial (11,500 yr B.P., corresponding to a former sea level of - 60 m), and (2) at the end of the melt-water pulse 1B (11,200 yr B.P., corresponding to a former sea level of - 42 m). Maps clearly show that in just 300 years the geography of the archipelago has changed dramatically, so much so that some islands have disappeared and some have decreased by more than 80% of their pre-Younger Dryas size.

  7. Multiple ash layers in late Quaternary sediments from the Central Indian Basin

    NASA Astrophysics Data System (ADS)

    Mascarenhas-Pereira, M. B. L.; Nagender Nath, B.; Iyer, S. D.; Borole, D. V.; Parthiban, G.; Jijin, R.; Khedekar, V.

    2016-04-01

    We have investigated three sediment cores collected from water depths > 5000 m along the transect 76°30‧E in close proximity to a fracture zone in the Central Indian Basin (CIB). The cores yielded five volcanic horizons of which four have visual and dispersed shards. Rhyolitic glass shards of bubble wall, platy, angular and blocky types were retrieved from various stratigraphic horizons in the cores. The abundance of glass shards, composition of bulk sediments, and 230Thexcess ages of the host sediments were used to distinguish the volcanic horizons. Of the four volcanic horizons, three are now newly reported and correspond to ages of ~ 85, 107-109 and 142-146 ka while the fourth horizon is of 70-75 ka. By using trace element ratios and Cr and Nb-based normative calculations, cryptotephra has been identified for the first time from the CIB sediment. The cryptotephra forms the fifth ash horizon and is of ~ 34 ka. A comparison with the published data on volcanic tephra in and around the Indian Ocean indicate the shard rich horizon (SRH) of 70-75 ka to resemble the Younger Toba Tuffs (YTT), while the other volcanic horizons that were deposited during different time periods do not correlate with any known marine or terrestrial records. These tephra layers have produced a tephrostratigraphic framework across the tectonically and volcanically complex regions of the CIB. Due to the lack of terrestrial equivalents of these tephra, it is hypothesized that the newly found volcanic horizons may have been derived from submarine volcanic eruptions. Multiple layers of submarine volcaniclastic deposits found at water depths as great as 5300 m reaffirm the growing belief that submarine phreatomagmatic eruptions are much more common in the intraplate region of the Indian Ocean than previously reported.

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

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

    The Walker Lane is a key component of the Pacific-North America plate boundary. This transtensional region of right lateral strike-slip and normal faulting accommodates ~25% of the total relative motion between the Pacific and North American plates. Recent studies indicate a discrepancy between short- and long-term rates of right-lateral shear in the Walker Lane with geodetic measurements of ~9.3 mm/yr being more than double the late Pleistocene geologic rate of <3.5 mm/yr. The Walker Lane, therefore, provides an excellent natural laboratory in which to address one of the major unresolved questions in active tectonics: are rates of strain accumulation and release along active plate boundaries constant through space and time or are significant temporal and spatial variations common? The Clayton Valley fault system of the Silver Peak-Lone Mountain extensional complex (SPLM) is a prime candidate to account for part of the “missing” strain in the Walker Lane due to its dominantly down-to-the-NW orientation, which ultimately accommodates right lateral shear in the region. The distribution of late Quaternary faults and alluvial fan deposits in Clayton Valley was determined through detailed geologic mapping (1:10,000 scale), which resulted in eight individual units that are consistent with the well-established western U.S. alluvial stratigraphy. Differential GPS was used to survey the prominent normal fault scarps displacing the fan deposits and cosmogenic nuclide (TCN) geochronology depth profile samples were collected from four units (Q2b, Q2c, Q2d, and Q3a). Displacement measured from the scarp profiles combined with TCN ages of the deformed fans will allow us to determine extension rates over multiple late Pleistocene time scales. Analysis of the Clayton Valley extension rates coupled with those from nearby structures, such as the Lone Mountain and Lida faults, will help determine if slip along these extensional faults can account for the observed discrepancy

  9. Late Quaternary slip rate of the frontal thrust of the Qilian Shan , NE Tibetan plateau

    NASA Astrophysics Data System (ADS)

    Champagnac, J.-D.; Molnar, P.; Yuan, D.-Y.; Ge, W.-P.; Zheng, W.-J.

    2009-04-01

    The Qilian Shan, with peak elevations >5500 m, seems to have been built largely during late Miocene time (e.g. Tapponnier et al., 2001) and continues to be seismically active (Hetzel et al., 2004), having produced the very large the Gulang earthquake in 1927 (M=8.0) (e.g., Zheng et al., 2005). Associated deformation is partitioned into thrust faulting on planes dipping south-southwest and north-northeast and large sinistral strike-slip faults oriented WSW-ENE to WNW-ESE, as well as second order dextral faults oriented NNW-SSW. The thickened crust of the Qilian Shan seems to be due to reverse faulting in a region that seems to have grown east-northeastward as the Altyn Tagh fault extended eastward (e.g. Burchfiel et al., 1989). We constrain the slip rate of a frontal thrust of the Qilian Shan over millennial time scale by cosmogenic (10Be) exposure age dating of terraces offset by the reverse fault, combined with structural investigations, satellite imagery, topographic profiling, and exposure dating. We surveyed two terrace levels, and from each we took 6-7 samples in profiles dug to depths of two meters. These allowed us to constrain inheritance (equivalent to ~0-2 ka, for each) and to determine precise ages of abandonment of the terraces: 29.9 ± 7.8 kyrs for the upper terrace and 16.3 ± 4.4 kyrs for the lower one. Topographic profiles 4 km in length, with a determination of probable burial of the footwall by sediments, yield offsets of the surfaces of 96.4 ± 4.4 m and 40.1 ± 2.8 m.The average vertical rate is 2.8 ± 1.3 mm/yr, with a horizontal slip rate of ~2.5 ± 2.0 mm/yr. The vertical and horizontal rates determined by this study contrast with slower rates determined farther north by Hetzel et al. (2004) on a similar thrust fault. Our results are consistent with GPS constraints, which show a NNE shortening direction across the Qilian Shan at a rate of 5.5 ± 1.8 mm/yr (Zhang et al., 2004). Slip on the studied thrust fault over millennial timescale account

  10. Late Quaternary deglacial history of the Mérida Andes, Venezuela

    NASA Astrophysics Data System (ADS)

    Stansell, Nathan D.; Abbott, Mark B.; Polissar, Pratigya J.; Wolfe, Alexander P.; Bezada, Maximiliano; Rull, Valentí

    2005-10-01

    Radiocarbon-dated sediment cores from seven lakes and two bogs spanning the Cordillera de Mérida in the Venezuelan Andes were used to identify and date the regional history of late Pleistocene and Holocene glacial activity. Coring sites were selected at different elevations across a pronounced rain shadow from southeast (wet) to northwest (dry). Sediment lithostratigraphy and magnetic susceptibility, in conjunction with AMS radiocarbon dates on macrofossils and charcoal, were used to constrain deglaciation. The local expression of the Last Glacial Maximum occurred between 22 750 and 19 960 cal. yr BP. On the wetter southeastern side of the Cordillera de Mérida, glaciers had significantly retreated by 15 700 cal. yr BP, followed by several minor glacial advances and retreats between 14 850 and 13 830 cal. yr BP. At least one major glacial readvance occurred between 13 830 and 10 000 cal. yrBP in the wetter southeastern sector of the region. The drier northwest side of the Cordillera de Mérida records initial glacial retreat by 14240cal.yrBP. Multiple sites on both sides of the Mérida Andes record a further phase of extensive deglaciation approximately 10000cal.yrBP. However, the north-northwest facing Mucubají catchment remained partially glaciated until ca. 6000cal.yrBP. Deglacial ages from the Venezuelan Andes are consistently younger than those reported from the Southern Hemisphere Andes, suggesting an inter-hemispheric deglacial lag in the northern tropics of the order of two thousand years.

  11. Late Quaternary sediments on the outer shelf of the Korea Strait and their paleoceanographic implications

    NASA Astrophysics Data System (ADS)

    Lim, D. I.; Kang, S.; Yoo, H. S.; Jung, H. S.; Choi, J. Y.; Kim, H. N.; Shin, I. H.

    2006-11-01

    Sedimentological and micropaleontological characteristics of core sediments from the outer shelf of the Korea Strait, which connects the northern East China Sea and the East Sea (Sea of Japan), were investigated to elucidate the paleoceanographic environment, especially the timing of the Kuroshio inflow, since the last glacial maximum. The core sediments, containing continuous records of the last 15,000 years, are characterized by a relatively high mud content (more than 50%, on average) and well-developed tide-influenced sedimentary structures. Their mineralogy suggests that the material originated from the paleo-Nakdong River system, which extended across the shelf of the Korea Strait during low sea-level periods. Planktonic foraminifers reveal a series of well-defined changes in paleoceanographic conditions during the late Pleistocene Holocene. Down-core variations in the abundance of four foraminiferal assemblages, i.e., cold, coastal, tropical subtropical, and Kuroshio water groups comprising characteristic planktonic species, suggest the occurrence of a distinct paleoenvironmental change in the surface water at 7,000 years b.p., i.e., from 15,000 to 7,000 years b.p., the area was influenced by coastal waters whereas since ca. 7,000 years b.p., it has been under the influence of open-sea water related to the Kuroshio Current flow, associated with both higher temperature and higher salinity. In particular, Pulleniatina obliquiloculata increased markedly in abundance at this time, documenting the inflow of the Kuroshio into the study area. These data indicate that the coastal water stage terminated at ca. 7,000 years b.p. when the warm Kuroshio and its major branch, the Tsushima Current, began to flow into the East Sea, as is the case today. The intrusion of the Tsushima Current through the Korea Strait after ca. 7,000 years b.p. resulted in abrupt changes in sedimentation rates and a dramatic increase in abundance of the Kuroshio indicator species, P

  12. The late Quaternary extinction and future resurrection of birds on Pacific islands

    NASA Astrophysics Data System (ADS)

    Steadman, David W.; Martin, Paul S.

    2003-04-01

    People have lived on tropical Pacific islands over the past 30,000 years (Bismarcks, Solomons) or 3000 to 1000 years (the rest of Oceania). Their activities have led to the loss of many thousands of populations and as many as 2000 species of birds that probably otherwise would exist today. This extinction event is documented by avian fossils from archaeological (cultural) and paleontological (noncultural) sites from nearly 70 islands in 19 island groups. Extinction of birds in Oceania rivals the late Pleistocene loss of large mammals in North America as the best substantiated rapid extinction episode in the vertebrate fossil record. Some avian extinctions in Oceania occurred within a century or less after human arrival, while others required millennia or even tens of millennia. Any of these time frames is rapid in an evolutionary or geochronological sense. Inter-island differences in the speed and extent of extinction can be explained by variation in abiotic (A), biotic (B), and cultural (C) factors. Levels of extinction on large, near islands can be comparable to those on small, remote islands when C factors (such as high human population density and introduction of invasive plants and animals) override A factors (such as large land area or little isolation) or B factors (such as rich indigenous floras and faunas). An innovative, proactive conservation strategy is needed not only to prevent further extinctions of birds in Oceania, but also to restart evolution of some of the lineages that have suffered the most loss, such as flightless rails. This strategy should focus on islands with ABC traits that retard rather than enhance extinction.

  13. Late Quaternary Depositional History and Anthropogenic Impacts of Western Long Island Sound, New York

    NASA Astrophysics Data System (ADS)

    McHugh, C. M.; Cormier, M.; Marchese, P.; Zheng, Y.; Stewart, G.; Acosta, V.; Bowman, A.; Cortes, A.; Leon, L.; Rosa, M.; Semple, D.; Thaker, N.; Vargas, W.; Williams, L.

    2006-12-01

    In June 2006, we surveyed the seafloor of western Long Island Sound with the R/V HUGH SHARP and collected multibeam bathymetry, chirp subbottom profiling, side-scan sonar imagery, and sediment samples (25 gravity cores, 11 multicores, and 10 grabs). In addition, 36 CTD hydrocast stations measured O, pH, alkalinity, trace metals, nutrients, Polonium-210, Lead-210, Thorium-234, organic carbon, and pigments. Continuous weather measurements, and water column properties using both CTD casts and a towed Scanfish were also carried out. Biological sampling included benthic grabs and plankton nets. The National Science Foundation under the "Opportunities to Enhance Diversity in the Geosciences" Program funded this one-week survey. Nine students from underrepresented groups in the geosciences and five P.I.'s participated in the field program. The major scientific objectives were to study the deglaciation of the Laurentide Ice Sheet and Holocene transgression of sea level to document age, sedimentation processes, and climate, and the impact of anthropogenic activities in the sediments, biota, and waters of the estuary. A deep (35 m) and narrow (< 1km) channel incised into bedrock characterizes the East River section of western Long Island Sound. In contrast, thick sedimentary deposits characterize the eastern part of the study area, 20 to 45 km east of New York City. Subbottom penetration reached in some instances 40 m, but is limited to less than 5 m where sediments are gas-charged. Four seismic sequences are imaged in the chirp records that we interpret to span the Last Glacial Maximum to Present: strong irregular erosional surfaces beneath parallel seismic reflectors are interpreted as glacial erosional surface and/or moraines, and as Glacial lake Connecticut sediments ~25 m thick, respectively. A thin veneer (<1 m) of acoustically transparent sediment is interpreted as recent deposits. It overlays a roughly 15 m thick unit interpreted as Holocene transgressive marine

  14. Late Quaternary Variability in the Deep Water Exchange Between South Atlantic, Southern and Indian Oceans

    NASA Astrophysics Data System (ADS)

    Leuschner, D. C.; Krueger, S.; Ehrmann, W.; Schmiedl, G.; Kuhn, G.; Mackensen, A.; Diekmann, B.

    2005-12-01

    The Southern Ocean, south of Africa, is an important mixing region for northern and southern derived deep-water masses. In this region, the North Atlantic Deep Water (NADW) extends southward into the Circumpolar Deep Water (CDW) dividing it into an upper (UCDW) and a lower (LCDW) layer. Thus, marine sediments from this area are a sensitive recorder for changes of the paleocirculation and relative variations in the deep-water formation in both, the northern Atlantic and Antarctic regions. Here we present results from the EXCHANGE Project which is located in this transition zone of the South Atlantic, the Southern Ocean and the Indian Ocean. In this project we investigate six sediment cores taken along a transect from continental slope at the southern tip of Africa towards the Conrad Rise. Pronounced glacial/interglacial variations in the dominance of NADW and LCDW across the transect are reflected in the clay mineral assemblage and carbon isotope composition of benthic foraminifera. High kaolinite/chlorite-ratios associated with high stable carbon isotope ratios indicate stronger influence of NADW during interglacials. In contrast, glacials are dominated by southern-derived LCDW. Our results suggest a fast southward advance of NADW-dominance during the last two terminations while the northward retreat of NADW, with the onset of glacial conditions, is more gradual. In general, interglacial sediments are also characterized by higher mean grain size diameters in the terrigenous silt fraction (10 to 63 microns), thus indicating stronger bottom currents. However, maximum grain size and sortable silt values are reached at the early stages of the last two glacial periods. Due to the generally weakened bottom current strength, as a result of reduced deep water formation, we would expect smaller values when compared with interglacial conditions. We therefore assume that eolian dust input from the Patagonian region plays a significant role especially in the early glacial

  15. Rainy Periods and Bottom Water Stagnation Initiating Brine Accumulation and Metal Concentrations: 1. The Late Quaternary

    NASA Astrophysics Data System (ADS)

    Rossignol-Strick, Martine

    1987-06-01

    A working hypothesis is proposed to account for the present accumulation of brines in isolated pockets of the ocean floor and for the formation of the underlying organic and metal-rich sediments. These are the Tyro and Bannock basins in the East Mediterranean, the Red Sea Deeps, and the Orca Basin in the northern Gulf of Mexico. Initiation of brine-derived deposition in the Red Sea Deeps and Orca Basin occurred between 12,000 and 8000 years B.P. This time bracket also encompasses the formation of the latest East Mediterranean sapropel and the wettest global climate since the last glacial maximum. This wet period first appeared in the tropics around 12,000 years B.P, then in the subtropical and middle latitudes. During the same period, the 23,000 year precession cycle brought the summer insolation of the northern hemisphere to its peak at 11,000 years B.P. with retreating northern hemisphere ice sheets. The Red Sea Deeps and the Orca Basin became anoxic during this humid period, and metal-rich sapropel deposition then began. In contrast, the Tyro and Bannock basins began accumulating a brine long before and persisted beyond this climatic stage. The hypothesis involves two propositions: (1) As in the Eastern Mediterranean Sea, marine anoxia was mainly the consequence of the large influx of continental runoff and local precipitation. Longer residence time of bottom waters, so-called "stagnation," in silled rimmed basins would have resulted from lower salinity at the sea surface in areas of deep water formation in the Eastern Mediterranean, the Red Sea, and the Gulf of Mexico and (2) Miocene or older evaporites underlie these basins or outcrop on their flanks. Leaching from these evaporites was an ongoing process before the quasi-stagnation phase, but the initial leachate, much less saline than the present brines, was continuously flushed by bottom circulation. The climate-induced quiescence of bottom waters in these basins enabled the leachate to accumulate. The

  16. Compound-Specific Hydrogen Isotope Ratios Record Late-Quaternary Temperature Changes at Crooked Pond, Massachusetts.

    NASA Astrophysics Data System (ADS)

    Shuman, B. N.; Huang, Y.; Wang, Y.; Webb, T.

    2001-12-01

    We show that compound-specific hydrogen isotope ratios from sedimentary biomarkers (organic compounds produced by aquatic algae) provide a useful record of past climate. The biomarkers preserve the hydrogen isotopic composition of lake water, which is controlled by annual and seasonal changes in the temperature of precipitation, evaporation, and the path of moisture transport. A transect of lake water and modern sediment samples from Ontario to Florida reveals parallel 100 per mille shifts in the δ D values of the lake water and sedimentary biomarkers. The water and biomarker hydrogen isotope ratios follow a linear relationship with a slope of ~1 (correlation coefficient of 0.93). The correlation between δ D values of the biomarkers and annual mean temperature is, therefore, also linear (correlation coefficient of 0.85). Consistent trends were revealed by an analysis of sedimentary biomarkers in a core spanning ca. 15,000 years, from Crooked Pond, a small closed kettle lake in Massachusetts. The pond is an outcrop of groundwater in a glacial alluvium aquifer, with a large aquifer-to-surface-exposure ratio ( ~100). The aquifer is recharged mainly by local precipitation and its water has a residence time of a decade or less. Therefore, the analysis of the biomarkers showed hydrogen isotope ratios that were 1) minimally influenced by evaporation and 2) reflected century- and longer scale changes in the temperature of precipitation. The δ D record is consistent with quantitative estimates of temperature, based on fossil pollen data. The δ D values increase ~65 per mille from 15,000 to 5000 cal yr B.P., with a negative 25-50 per mille excursion during the cold Younger Dryas interval (12,900-11,600 cal yr B.P.). A positive δ D shift of 15 per mille records warming after the collapse of the Laurentide ice sheet (ca. 8000 cal yr B.P); and, a gradual cooling during the late Holocene is captured by a steady decline in δ D values.

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

    USGS Publications Warehouse

    Smith, George I.; Stuiver, Minze

    1979-01-01

    Searles Lake is a dry salt pan, about 100 km 2 in area, that lies on the floor of Searles Valley, in the desert of southeast California. Several salt bodies of late Quaternary age lie beneath the surface, mostly composed of sodium and potassium carbonate, sulfate, chloride, and borate minerals. Mud layers separate the salt bodies, which contain interstitial brine that is the source of large quantities of industrial chemicals. The value of annual production from the deposit exceeds $30 million; total production to date exceeds $1 billion. The salts and muds were deposited during Pleistocene and Holocene times by a series of large lakes (200 m maximum depth, 1,000 km 2 maximum area) that fluctuated in size in response to climatic change. Salts were deposited during major dry (interpluvial) episodes, muds during wet (pluvial) episodes that correlate with glacial advances in other parts of North America and the world. Data based on cores from the deposit are used in this paper to establish the stratigraphy of the deposit, the chemical and mineral compositions of successive units, and the total quantities of components contained by them. These parameters are then used to determine the geochemical evolution of the sedimentary layers. The results provide a refined basis for reconstructing the limnology of Searles Lake and the regional climate during late Quaternary time. Six main stratigraphic units were distinguished and informally named earlier on the basis of their dominant composition: Unit Typical thickness 14C age, uncorrected (in meters) (years B.P.) Overburden Mud 7 0 to >3,500 Upper Salt 15 >3,500 to 10,500 Parting Mud 4 10,500 to 24,000 Lower Salt 12 24,000 to 32,500 Bottom Mud 30 32,500 to 130,000 Mixed Layer 200+ > 130,000 (The age of 130,000 years for the Mixed Layer is based on extrapolated sedimentation rates.) The Lower Salt is subdivided into seven salt units (S-l to S-7) and six mud units (M-2 to M-7), the Mixed Layer into six units (A to F). For each

  18. Black Carbon as a marker for paleofires during the Late Quaternary in sedimentary record of Saci lake (PA) -Brazil

    NASA Astrophysics Data System (ADS)

    Martins, G. S.; Cordeiro, R. C.; Turcq, B.; Sifeddine, A.; Rodrigues, R.; Santos, A. B.; Moreira, L.; Guilles, M. C.; Seoane, J. S.

    2012-12-01

    Controversies still exist about the climate in the South American tropical forest over the Late Quaternary. In the present work, we show a sedimentary profile (SACI-1) of 243 cm in Saci Lake, located in the south of Para state. The paleoclimatic reconstruction was made by several geochemical markers, working as indicators of environmental changes in this lake during the Late Quaternary. Seventeen samples along the SACI-1 core were dated, and an age model was construct used a non-Bayesian, 'classical' age-depth models, showing a basal age of 35,500 cal years BP. The lithological description allows identifying six sedimentary units. Unit VI (35,500-29,900 cal yrs BP) and unit V (29,900-16,400 cal yr BP) are characterized by lowest concentrations of TOC, high values of C/N ratio and δ15N, and low values of chlorophyll derivates. These characteristics suggest a predominance of allochthonous organic matter. Unit V, covers the LGM (Last Maximum Glacial), when was observed the lowest values of TOC and moderate values of both BC concentration and flux (at approximately 162 cm), suggesting a dry period with low water level and wildfires in the region. Unit IV (9,100-8,300 cal years BP), presented a transition from a wetter to a drier climate with decreasing values of TOC and biogeochemical changes associated with a sandy sedimentation, indicating a higher intensity of run-off events. The higher values of C/N ratio and incresing δ13C values in this phase, suggest an increase in C4 vascular plants. The unit III (8,300-5,800 cal years BP) is characterized by a dry climate, with the lowest average values of total organic carbon, suggesting low lake levels. Low values of chlorophyll derivatives indicate a low productivity environment and high levels of clay suggest a low hydrodynamic depositional energy environment. The highest concentration of Black Carbon data indicated an increased occurrence of fires related to this dry climate. This phase was characterized by lower C

  19. The linkage between hillslope vegetation changes and late-Quaternary fluvial-system aggradation in the Mojave Desert revisited

    NASA Astrophysics Data System (ADS)

    Pelletier, J. D.

    2014-03-01

    Valley-floor-channel and alluvial-fan deposits and terraces in the southwestern US record multiple episodes of late Quaternary fluvial aggradation and incision. Perhaps the most well constrained of these episodes took place from the latest Pleistocene to the present in the Mojave Desert. One hypothesis for this episode, i.e. the paleo-vegetation change hypothesis (PVCH), posits that a reduction in hillslope vegetation cover associated with the transition from Pleistocene woodlands to Holocene desert scrub generated a pulse of sediment that triggered a primary phase of aggradation downstream, followed by channel incision, terrace abandonment, and initiation of a secondary phase of aggradation further downstream. A second hypothesis, i.e. the extreme-storm hypothesis, attributes episodes of aggradation and incision to changes in the frequency and/or intensity of extreme storms. In the past decade a growing number of studies has advocated the extreme-storm hypothesis and challenged the PVCH on the basis of inconsistencies in both timing and process. Here I show that in eight out of nine sites where the timing of fluvial-system aggradation in the Mojave Desert is reasonably well constrained, measured ages of primary aggradation and/or incision are consistent with the predictions of the PVCH if the time-transgressive nature of paleo-vegetation changes with elevation is fully taken into account. I also present an alternative process model for PVCH that is more consistent with available data and produces sediment pulses primarily via an increase in drainage density (i.e. a transformation of hillslopes into low-order channels) rather than solely via an increase in sediment yield from hillslopes. This paper further documents the likely important role of changes in upland vegetation cover and drainage density in driving fluvial-system response during semiarid-to-arid climatic changes.

  20. Late quaternary vegetation and climatic history of the Long Valley area, west-central Idaho, U.S.A.

    USGS Publications Warehouse

    Doerner, J.P.; Carrara, P.E.

    2001-01-01

    Paleoenvironmental data, including pollen and sediment analyses, radiocarbon ages, and tephra identifications of a core recovered from a fen, provide a ca. 16,500 14C yr B.P. record of late Quaternary vegetation and climate change in the Long Valley area of west-central Idaho. The fen was deglaciated prior to ca. 16,500 14C yr B.P., after which the pollen rain was dominated by Artemisia, suggesting that a cold, dry climate prevailed until ca. 12,200 14C yr B.P. From ca. 12,200 to 9750 14C yr B.P. temperatures gradually increased and a cool, moist climate similar to the present prevailed. During this period a closed spruce-pine forest surrounded the fen. This cool, moist climate was briefly interrupted by a dry and/or cold interval between ca. 10,800 and 10,400 14C yr B.P. that may be related to the Younger Dryas climatic oscillation. From ca. 9750 to 3200 14C yr B.P. the regional climate was significantly warmer and drier than at present and an open pine forest dominated the area around the fen. Maximum aridity occurred after the deposition of the Mazama tephra (ca. 6730 14C yr B.P). After 3200 14C yr B.P. regional cooling brought cool, moist conditions to the area; the establishment of the modern montane forest around the fen and present-day cool and moist climate began at ca. 2000 14C yr B.P. ?? 2001 University of Washington.

  1. Provenance of the Late Quaternary sediments in the Andaman Sea: Implications for monsoon variability and ocean circulation

    NASA Astrophysics Data System (ADS)

    Awasthi, Neeraj; Ray, Jyotiranjan S.; Singh, Ashutosh K.; Band, Shraddha T.; Rai, Vinai K.

    2014-10-01

    present a geochemical and Sr-Nd isotopic study on a sediment core collected from the Andaman Sea in an attempt to reconstruct the Late Quaternary weathering and erosion patterns in the watersheds of the river systems of Myanmar and understand their controlling factors. Age control is based on nine radiocarbon dates and δ18O stratigraphy. The rate of sedimentation was strongly controlled by fluctuations of the monsoon. We identify three major sediment provenances: (1) the Irrawaddy catchment, (2) the western slopes of the Indo-Burman-Arakan (IBA) mountain ranges and the Andaman Islands, and (3) the catchments of Salween and Sittang and the Bengal shelf, with the first two contributing 30-60% of the material. Enhanced contributions from juvenile sources and corresponding positive shifts of δ18O are observed at seven time periods (11-14, 20-23, 36, 45, 53, 57, and 62 ka) of which five are synchronous with cooling of the northern hemisphere, suggesting a link between the changes in sediment provenances and the shifting of the locus of the summer monsoon, southward from the Himalayas, without substantial reduction in intensity. Our data, and that from other cores in the region suggest that an eastward moving surface current disperses sediments, derived from the Bengal shelf and western margin of Myanmar, from the eastern Bay of Bengal into the western Andaman Sea and that its strength has increased since the LGM. The existence of this current during the LGM implies that the Andaman Sea and the Bay of Bengal were well connected during the last glacial period.

  2. High precision thorium-230 ages of corals and the timing of sea level fluctuations in the late Quaternary

    SciTech Connect

    Edwards, R.L.

    1988-01-01

    Mass spectrometric techniques for the measurement of {sup 230}Th and {sup 234}U have been developed. These techniques have made it possible to reduce the analytical errors in {sup 230}Th dating of corals using very small samples (10{sup 7} to 10{sup 10} atoms). The time range over which useful data on corals can now be obtained ranges from 15 to 500,000 years. For young corals, this approach may be preferable to {sup 14}C dating. The precision with which the age of a coral can not be determined makes it possible to determine the timing of sea level fluctuations in the late Quaternary. Analyses of a number of corals that grew during the last interglacial period yield ages of 122 to 130 ky. The ages coincide with or slightly postdate the summer solar insolation high at 65{degree}N latitude, which occurred 128 ky ago. This supports the idea that changes in Pleistocene climate can be the result of orbital forcing. Coral ages may allow us to resolve the ages of individual coseismic uplift events and thereby date prehistoric earthquakes. This possibility has been examined at two localities, northwest Santo Island and north Malekula Island, Vanuatu. The {sup 230}Th growth dates of the surfaces of adjacent emerged coral heads, collected from the same elevation on northwest Santo Island, were, within analytical error, identical (A.D. 1866 {plus minus} 4 and A.D. 1864 {plus minus} 4). This indicates that the corals died at the same time and is consistent with the idea that they were killed by coseismic uplift. Similar adjacent coral heads on north Malekula Island yielded {sup 230}Th growth dates of A.D. 1729 {plus minus} 3 and A.D. 1718 {plus minus} 5. The ages are similar but analytically distinguishable. The difference may be due to erosion of the outer, younger, portion of the latter coral head.

  3. Geochemical record of Late Quaternary paleoclimate from lacustrine sediments of paleo-lake San Felipe, western Sonora Desert, Mexico

    NASA Astrophysics Data System (ADS)

    Roy, P. D.; Caballero, M.; Lozano, R.; Ortega, B.; Lozano, S.; Pi, T.; Israde, I.; Morton, O.

    2010-04-01

    Stratigraphy, mineralogy, major and trace elements, organic carbon, carbonate, sulfate and AMS 14C dates are used to infer Late Quaternary depositional environments and paleo-hydrological conditions in the paleo-lake San Felipe located in the western part of Sonora Desert. Sediment stratigraphy divides the depth profile into aeolian and pluvio-lacustrine regimes. Aeolian regime is constrained to >44.5 14C kyr BP. The pluvio-lacustrine regime consists of two stratigraphic units with characteristic geochemical proxies indicating changing chemical weathering, clastic input, salinity and provenance and provides a measure of varying climatic conditions between ca. 37 and 3 14C kyr BP. Lower catchment erosion and inflow into the basin, higher lake productivity, precipitation of Na-sulfate mineral and higher clastic input from the proximal aeolian deposits during ca. 37-14 14C kyr BP are comparable to the regional registers of dominant winter rainfall related to westerly storm tracks and colder conditions. In the last 12 14C kyr BP, higher sedimentation and inflow and lower productivity are comparable to dominant summer rainfall. Higher humidity and lake productivity during ca. 37-29 14C kyr BP is possibly due to the position of westerly storm tracks at 31°N and the gradually reducing humidity till ca. 14 14C kyr BP is related to northerly migration of westerly storm tracks. Regional arid conditions during ca. 11 14C kyr BP and ca. 6 14C kyr BP are characterized by influx of coarser quartz and feldspars into the basin.

  4. Marine Sedimentary Record of the Gulf of Tehuantepec in the Late Quaternary: paleoceanographic and paleoclimatic implications

    NASA Astrophysics Data System (ADS)

    Pavón-Moreno, J. A.; Pérez-Cruz, L.; Urrutia-Fucugauchi, J.; Monreal-Gómez, M. A.

    2012-04-01

    The aim of this study is reconstruct the paleoceanographic and paleoclimatic conditions in the northern Gulf of Tehuantepec, through the use of geochemical and magnetic proxies. The sediment core MD02-2523 was collected using a giant piston corer during the oceanographic campaign MD126 (IMAGES VIII - MONA) in the Gulf of Tehuantepec, on June 2002 aboard the R/V "Marion Dufresne". The core was collected at 202 m depth and it has an 18.19 m length. Age control is established from AMS radiocarbon dating on four samples from the first 700 cm, which were converted to calendar years by applying a reservoir correction of 456 yr (ΔR 162±50) with the CALIB 6.1.0 radiocarbon program. This provides an initial age control for the core from 900 to 47,000 cal yr BP. A linear age model extends the record to ~120,000 cal yr BP, with a mean sedimentation rate of about 0.15 mm/ yr. Sediments in the core are composed mostly of silty clays, with some horizons containing fossil fragments presented as disarticulated bivalve shells with average sizes of 1 cm, as well as foraminifera and nannofossils. At different depths we observed cream to white ash layers, with thicknesses ranging from 2 to 10 cm. For this study, mineral magnetic and XRF analyses were carried out along the core. For mineral magnetic analyses, standard 2.2 × 2.2 × 2.2 cm samples were taken throughout the core split. The low-field magnetic susceptibility was measured in all samples at low and high frequencies (0.465 kHz and 4.65 kHz) with the MS2 Bartington susceptibility instrument equipped with the MS2B dual-frequency sensor. For the geochemical study, samples were taken every ~2 cm and elemental chemical concentration was measured using an X-ray fluorescence analyzer (Niton XL3t GOLDD). Magnetic susceptibility shows a cyclic pattern with peaks along the core indicating apparent increases in the amount of magnetic minerals. The peaks could be associated to (about 20 ka) precession cycles. Magnetic susceptibility correlates with terrigenous input and is related to material transported by the strong northerly winds in the gulf and isthmus region. Frequency dependence susceptibility factors indicate presence of fine-grained superparamagnetic minerals throughout the core, which could indicate that the sediment source may have relatively stable during the last 120,000 years, with variations in the amount of terrigenous input. There is a strong correlation between Mo and V, and between Ti and Fe, which are used as proxies of oxygenation and terrigenous input, respectively. An increase in these elements is observed between ~16,000 and 15,000 cal yr BP. Also most elements showed changes in concentrations from ~30,000 to 31,000 cal yr BP. Correlations and interpretations among other elements and magnetic susceptibility are in progress as well as additional dating with different methods to improving the age control.

  5. Aminostratigraphy and faunal correlations of late Quaternary marine terraces, Pacific Coast, USA

    USGS Publications Warehouse

    Kennedy, G.L.; Lajoie, K.R.; Wehmiller, J. F.

    1982-01-01

    Recent studies using the extent of racemization of amino acids to date fossil mollusc shells in the Arctic1, the British Isles2 and on the Atlantic3,4 and Pacific5-13 coasts of North America have relied mainly on theoretical kinetic models of racemization. Ages generated in this fashion are highly model dependent and require estimates of integrated long-term diagenetic temperatures. We present here an alternative, empirical approach to aminostratigraphy in which we plot amino acid enantiomeric ratios versus latitude (for localities along the Pacific coast of the United States), and generate isochronal correlations by connecting data points of geographically proximal localities that have similar D:L ratios and zoogeographic aspect. Isochrons are calibrated at a few localities by independent radiometric dates. The diagenetic temperature effect on racemization is reflected in the slope of the isochrons, but the need to quantify temperature is eliminated. ?? 1982 Nature Publishing Group.

  6. Geological and geophysical evidences of late Quaternary activity of the range-front fault along the mid-segment of the Longmen Shan thrust belt

    NASA Astrophysics Data System (ADS)

    Ren, J.; Xu, X.; Sun, X.; Tan, X.; Li, K.; Kang, W.; Liu, B.

    2011-12-01

    The Longmen Shan fault zone consists of three main Longmen Shan faults and the blind fault in the Chengdu Basin. Along the range front of the middle segment of the Longmen Shan, there is the lithological border in published geological maps. The existence and the latest active time of the range-front fault along the mid-segment of the Longmen Shan thrust belts are controversial for a long period. Petroleum seismic reflection and high-resolution shallow seismic reflection profile discovered the existence of the range-front fault and the fault offset the Quaternary strata. Based on detailed field observation, we found that there is an obvious linear feature along the mid-segment of the Longmen Shan front and the range-front fault displaced the late Quaternary fluvial terrace. Trench log indicates that a surface-rupture event occurred before ~1500a along the range-front fault. Differential GPS surveying and dating of fluvial terrace show that the range-front fault during late Quaternary underwent a vertical slip rate of bigger than 0.36mm/a, approximately equivalent to that along the main faults of the longmen Shan thrust belts, which demonstrates that the range-front fault also took an important role in accommodating the deformation of the Longmen Shan thrust zone. This study not only provides the fundamental data for seismic hazard assessment of the Chengdu Plain, but is helpful for the overall understanding of uplift mechanism of east Tibet.

  7. Late Quaternary chronostratigraphic framework of terraces and alluvium along the lower Ohio River, southwestern Indiana and western Kentucky, USA

    USGS Publications Warehouse

    Counts, Ronald C.; Murari, Madhav K.; Owen, Lewis A.; Mahan, Shannon; Greenan, Michele

    2015-01-01

    The lower Ohio River valley is a terraced fluvial landscape that has been profoundly influenced by Quaternary climate change and glaciation. A modern Quaternary chronostratigraphic framework was developed for the lower Ohio River valley using optically stimulated luminescence (OSL) dating and allostratigraphic mapping to gain insights into the nature of fluvial responses to glacial–interglacial/stadial–interstadial transitions and Holocene climate change. River deposits, T0 (youngest) to T7 (oldest), were mapped along a 75 km reach of the lower Ohio River and were dated using 46 OSL and 5 radiocarbon samples. The examination of cores combined with OSL and radiocarbon dating shows that fluvial sediments older than marine oxygen isotope stage (MIS) 2 are present only in the subsurface. Aggradation during MIS 6 (Illinoian glaciation) filled the valley to within ∼7 m of the modern floodplain, and by ∼114 ka (MIS 5e/Sangamon interglacial) the Ohio River had scoured the MIS 6 sediments to ∼22 m below the modern floodplain surface. There were no fluvial sediments in the valley with ages between MIS 5e and the middle of MIS 3. The MIS 3 ages (∼39 ka) and stratigraphic position of T5 deposits suggest the Ohio River aggraded 8–14 m during MIS 4 or MIS 3. Near the end of MIS 3, the Ohio River incised the mid Last Glacial (mid-Wisconsinan) deposits ∼10 m and began aggrading again by ∼30 ka. Aggradation continued into MIS 2, with maximum MIS 2 aggradation occurring before ∼21 ka, which is coincident with the global Last Glacial Maximum (LGM). As the Ohio River adjusted to changing fluxes in sediment load and discharge following the LGM, it formed a sequence of fill-cut terraces in the MIS 2 outwash that get progressively younger with decreasing elevation, ranging in age from ∼21 ka to ∼13 ka. From ∼14 ka to ∼13 ka the Ohio River rapidly incised ∼3 m to form a new terrace, and by ∼12 ka at the onset of the Holocene, the Ohio River

  8. Paleomagnetism and rock magnetism of Quaternary volcanic rocks and Late Paleozoic strata, VC-1 core hole, Valles Caldera, New Mexico, with emphasis on remagnetization of Late Paleozoic strata

    NASA Astrophysics Data System (ADS)

    Geissman, John W.

    1988-06-01

    Paleomagnetic and rock magnetic data obtained from azimuthally unoriented core samples, collected at approximately 1- to 3-m intervals, of Continental Scientific Drilling Program core hole VC-1 have prompted reinterpretations of the Quaternary volcanic stratigraphy intersected by the bore and have aided in evaluating the thermal regime within late Paleozoic strata attending fluid circulation and mineral deposition during and after development of the Toledo and Valles calderas. The results from Quaternary units (Banco Bonito Obsidian: I = +35.4°, a95 = 2.8° (inclination only determinations), n = 33; Battleship Rock Tuff: D = 359.6°, I = +42.4°, a95 = 2.8°, n = 5 site means (surface sites); VC-1 Rhyolite: I = +39.2°, a95 = 12.8°, n = 7; Upper VC-1 Tuff: I = +37.2°, a95 = 10.7°, n = 13; Middle VC-1 Tuff: I = +42.1°, a95 = 2.1°, n = 39; South Mountain Rhyolite: D = 350.9°, I = +49.9°, a95 = 3.4°, n = 10 (one surface site)) are consistent with isotopic age data, indicating that the entire moat volcanic sequence intersected is less than 650 kyr. Monitoring of natural remanent magnetization (NRM) intensity, NRM directions, directions of magnetizations isolated during progressive demagnetization, median destructive forces, and rock magnetization parameters has identified systematic variations within the thick Banco Bonito Obsidian and VC-1 Tuff units. The Permian Abo Formation, Pennsylvanian to earliest Permian Madera Limestone, and Pennsylvanian Sandia Formation typically contain a moderate positive inclination magnetization component (Abo Formation: I = +52.2°, a95 = 7.4°, n = 16; Madera Limestone: I = +58.4°, a95 = 2.8°, n = 105; Sandia Formation: I = +53.9°, a95 = 4.8°, n = 21); when residing in magnetite, it is usually unblocked in the laboratory by 350°C; when carried by hematite it is unblocked by 550°C. A moderate negative inclination (e.g., Madera and Abo strata: D = 173.1°, I = -46.6°, a95 = 5.5°; n = 47 samples; assuming a north seeking

  9. Episodic speleothem deposition in Ireland during the late Quaternary; implications for Greenland ice core chronology and British-Irish Ice Sheet dynamics

    NASA Astrophysics Data System (ADS)

    McDermott, Frank; Fankhauser, Adelheid

    2016-04-01

    In shallow caves, episodes of speleothem deposition during the late Quaternary, constrained by U-series dates, provide unequivocal evidence for periods of climate amelioration (presence of liquid water, elevated soil pCO2). U-series data for speleothems from several cave systems in Ireland (Crag, Ballynamintra and Marble Arch) provide clear evidence for episodic speleothem deposition, ranging in age from Marine Isotope Stage (MIS) 7 to the Last Glacial Termination. Speleothem deposition and non-depositional phases within these caves are particularly sensitive to regional-scale climatic conditions, reflecting Ireland's mid-latitudinal, Atlantic margin location. Currently, the earliest dated speleothems from the region are sparsely preserved and thin MIS 7 and MIS 5 flowstones from Ballynamintra and Crag caves respectively. Relatively short-lived depositional phases also occurred at Crag cave during MIS4 and MIS3 and are coeval with the Greenland Interstadials (GI), supporting the recently modified GICC05 Greenland ice core chronology (Buizert et al., 2015), and new providing evidence for synchronous or nearly-synchronous climate amelioration in the N. hemisphere mid- and high-latitudes during the GI events. On the other hand, there is strong evidence that conditions at Crag cave site during stadials and the Heinrich stadials were not conducive to speleothem deposition. Episodes of non-deposition occur synchronously in several speleothems from Crag cave, providing independent constraints on the timing of Heinrich stadials HS-6 to HS-2. The new data also provide independent new insights into the behaviour of the British Irish Ice Sheet (BIIS) during MIS2. In this regard, the presence of a short depositional pulse at 23.35 ± 0.1 ka at Crag cave coincides precisely with the weak and short-lived GI2.2 event within MIS 2, suggesting a dynamic BIIS margin. Simple conductive thermal models for the propagation of surface air temperatures through the limestone karst

  10. A 200,000-year record of late Quaternary Aeolian sedimentation on the Southern High Plains and nearby Pecos River Valley, USA

    NASA Astrophysics Data System (ADS)

    Rich, J.; Stokes, S.

    2011-03-01

    Presently stabilized Southern High Plains (SHP) dune systems have been repeatedly re-activated during the past 200,000 years, providing an archive of environmental and related climatic change for the late Quaternary. Our data set of 38 optically dated samples from four different localities identifies eolian activity from late-middle Pleistocene to the historic period. Oldest eolian sediments are from the Blackwater Draw Formation and indicate accretion during late-middle to late Pleistocene. Younger sediments dating from the later Pleistocene through the Holocene are found in the Muleshoe, Lea-Yoakum, Mescalero, and Monahans dunes that overlie the Blackwater Draw Formation. Muleshoe dunes accreted during the Late Pleistocene between 31 ± 3 and 27 ± 2 ka, while Holocene deposition transpired 7.5 ± 0.4, 4.0 ± 0.7 ka through 3.6 ± 0.4 ka, and between 1.3 ± 0.2 and 1.1 ± 0.1 ka. A period of dune building for Lea-Yoakum dune sediments occurred during the late Pleistocene (48 ± 5 ka), and the later Holocene (3.6 ± 0.4 ka). Mescalero and Monahans dunes were accreting during the later Pleistocene between 29 ± 3 and 22 ± 2 ka followed by a sequence of eolian sand deposited ca. 15 ka. Holocene eolian sedimentation for the Mescalero and Monahans dunes occurred 7.5 ± 0.8, 5.1 ± 0.5, 4.3 ± 0.4, and 2.0 ± 0.3 ka. Historic eolian deposition is identifiable in the dune chronology with multiple optical age estimates overlapping established drought events recorded ca. 1890, 1910, 1920, and during the 1930's when the North American "Dust Bowl" transpired. These Quaternary eolian deposits mantling the Southern High Plains are an important component of the surficial material of the region and provide a rich archive of past climatic change.

  11. Late Quaternary paleoenvironmental changes revealed by multi-proxy records from the Chukchi Abyssal Plain, western Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Wang, Rujian; Xiao, Wenshen; März, Christian; Li, Qianyu

    2013-09-01

    Late Quaternary paleoenvironmental changes in the western Arctic Ocean are revealed by multi-proxy records of core 03M03 from the Chukchi Abyssal Plain (CAP). Proxy parameters include lithology, grain size fractions, and mineralogy and petrology of ice-rafted detritus (IRD), element contents, biogenic components, δ18O, δ13C and Mg/Ca of planktonic foraminifera Neogloboquadrina pachyderma (sin.) (Nps). Seven IRD (> 250 μm) peaks are interpreted as marking detrital input by rafting sea ice or icebergs during MIS 3 interstadials and early MIS 1. High MnO, CaO and MgO contents and high Ca/Al and Mg/Al ratios during MIS 3 and MIS 1 correspond to increases in ice-rafted detrital carbonates and the synchronous declines in siliciclastic elements (e.g., Al2O3, Fe2O3). Therefore, these warmer periods were characterized by a high detrital carbonate input entrained in icebergs from the Canadian Arctic Archipelago coeval with an increased input of Mn through rivers and/or coastal erosion. Relatively stable contents of siliciclastic elements and their ratios in the grayish sediment units are interpreted from turbid surface water plumes or nepheloid flows delivered by meltwater and/or brine rejection from ice-sheet margins at the Arctic Ocean periphery. Relatively stable clay- and silt-sized fractions were attributed mainly to sea ice entrainment over glacial-interglacial cycles. High foraminiferal abundances in the brown units during MIS 3 and 1 are related to enhanced calcareous plankton productivity under more open water conditions and/or the incremental input of Atlantic water masses. Relatively high TOC and opal contents in the grayish units of MIS 3 appear to have accumulated by lateral transport of organic matter from the Chukchi shelf to the deep abyssal plain. Lower contents of biogenic material in the brown units probably result from increased dilution by rapid IRD deposition, and from early diagenetic degradation. Depletions in Nps-δ18O and -δ13C concurrent with

  12. Late Quaternary pollen data collection and application in land-cover reconstruction for East Asia and Siberia

    NASA Astrophysics Data System (ADS)

    Cao, Xianyong; Tian, Fang; Ni, Jian; Herzschuh, Ulrike

    2016-04-01

    The various climatic systems and vegetation zones in the East Asia cause the numerous open questions concerning the evolution of the Asian Monsoon and vegetation change on various time-scales. Fossil pollen is one of the most spatially extensive terrestrial palaeoenvironmental proxies during the late Quaternary, and the multi-record fossil pollen synthesis is a potential solution for the open questions in palaeoecology and palaeoclimatology. We collected and selected 274 pollen records from eastern continental Asia (70°135°E and 18°55°N). After pollen percentage recalculations, taxonomic homogenization, age-depth model revision, and pollen abundance linear interpolation, a taxonomically harmonized and temporally standardized fossil pollen dataset established at a 500-year resolution covering the last 22 ka. In addition, we also established a modern pollen dataset including 2626 modern pollen data from China and Mongolia. We used the calibration-set based on modern pollen and satellite-based Advanced Very High Resolution Radiometer (AVHRR) observations of woody cover, to reconstruct woody cover for the 274 fossil pollen records. The spatial range of forest has not noticeably changed in eastern continental Asia during the last 22 ka, although woody cover has, especially at the margin of the eastern Tibetan Plateau and in the forest-steppe transition area of north-central China. Vegetation was sparse during the LGM in the present forested regions, but woody cover increased markedly at the beginning of the Bølling/Allerød period (B/A; ca. 14.5 ka BP) and again at the beginning of the Holocene (ca. 11.5 ka BP), and is related to the enhanced strength of the East Asian Summer Monsoon. Forest flourished in the mid-Holocene (ca. 8 ka BP) possibly due to favourable climatic conditions. In contrast, cover was stable in southern China (high cover) and arid central Asia (very low cover) throughout the investigated period. Forest cover increased in the north

  13. Late Quaternary Sedimentary Records of Core MA01 in the Mendeleev Ridge, the Western Arctic Ocean: Preliminary Results

    NASA Astrophysics Data System (ADS)

    Park, K.; Kim, S.; Khim, B. K.; Wang, R.; Mei, J.; Xiao, W.; Polyak, L. V.

    2014-12-01

    Late Quaternary deep sea sediments in the Arctic Ocean are characterized by brown layers intercalated with yellowish to olive gray layers. It has been known that the brown and gray layers were deposited during interglacial (or interstadial) and glacial (or stadial) periods, respectively. A 5.5-m long gravity core MA01 was obtained from the Mendeleev Ridge in the western Arctic Ocean by R/V Xue Long during scientific cruise CHINARE-V. Age (~1.0 Ma) of core MA01 was tentatively decided by correlation of sediment color cycles, XRF Mn and Ca cycles, and geomagnetic inclinations with core HLY0503-8JPC (Adler et al., 2009) and core HLY0503-06JPC(Cronin et al., 2013) that were also collected from the Mendeleev Ridge area. A total of 23 brown layers are characterized by low L* and b*, high Mn concentration, and abundant foraminifera. In contrast, gray layers are characterized by high L* and b*, low Mn concentration, and few foraminiferal tests. Foraminifera abundance peaks are not well correlated to CaCO3 peaks which are accompanied with the coarse-grained (>63 μm) fractions (i.e., IRD) both in brown and gray layers. A strong positive correlation coefficient (r2=0.89) between TOC content and C/N ratio indicates that the major source of organic matter is terrestrial. The good correlations of CaCO3 content to TOC (r2=0.56) and C/N ratio (r2=0.69) imply that IRDs contain detrital CaCO3 fraction which mainly originated from the Canadian Arctic Archipelago. In addition, high kaolinite/chlorite (K/C) ratios mostly correspond to CaCO3 peaks, also suggesting that the fine-grained particles in the Mendeleev Ridge were transported from the northern coasts of the Alaska and Canada. Thus, the Beaufort Gyre, the predominant surface current in the western Arctic Ocean, has played an important role in the sediment delivery to the Mendeleev Ridge. It is worthy of note that TOC and CaCO3 peaks are obviously distinct in the upper part of core MA01, whereas these peaks are reduced in the

  14. Late Quaternary geomorphic history of a glacial landscape - new sedimentary and chronological data from the Cordillera de Cochabamba (Bolivia)

    NASA Astrophysics Data System (ADS)

    May, J.-H.; Preusser, F.; Zech, R.; Ilgner, J.; Veit, H.

    2009-04-01

    Throughout the Central Andes, glacial landscapes have long been used for the reconstruction of Late Quaternary glaciations and landscape evolution. Much work has focused on the Andes in Peru, Chile and the Bolivian Altiplano, whereas relatively little data has been published on glaciation history in the eastern Andean ranges and slopes. Even less is known with regard to the postglacial evolution of these glacial landscapes. In the Cordillera de Cochabamba (Bolivia), local maximum advances probably peaked around 20-25 ka BP and were followed by significant readvances between ~12-16 ka BP. This generally points to temperature controlled maximum glacial advances along the humid eastern slopes of the Central Andes, which is supported by glacier-climate-modelling studies. However, most studies include only marginal information with regard to the complex geomorphic and sedimentary situation in the Cordillera de Cochabamba. Furthermore, the chronological results are afflicted with several methodological uncertainties inherent to surface exposure dating and call for application of alternative, independent age dating methods. Therefore this study aims at i) documenting and interpreting the complex glacial geomorphology of the Huara Loma valley in the Cordillera de Cochabamba (Bolivia), ii) analyzing the involved units of glacial sediments, and iii) improving the chronological framework by applying optically stimulated luminescence (OSL) and radiocarbon dating (14C). For this purpose, geomorphic mapping was combined with field documentation of sedimentary profiles. The involved sediments were subject to geochemical and mineralogical analysis in order to deduce information on their erosional and weathering histories. In addition, the interpretation of OSL ages from glacial and proglacial sediments integrated several methodological procedures with regard to sample preparation and statistical analysis of the measurements in order to increase the degree of confidence. These

  15. Evaluating the timing of late Quaternary geomorphodynamics and soil formation: a review of geochronological data from northeastern Germany

    NASA Astrophysics Data System (ADS)

    Kappler, Christoph; Kaiser, Knut; Küster, Mathias; Fülling, Alexander; Bens, Oliver; Raab, Thomas

    2016-04-01

    A comprehensive review of late Quaternary terrestrial stratigraphical records from northeastern Germany requires the collection, evaluation and statistical processing of preferably all geochronological data from paleosols and corresponding sediments available so far. Therefore, a database has been established, comprising a multitude of published and unpublished age data. The database regionally covers the entire Weichselian glacial belt ('young morainic' area) and the immediately adjacent Saalian glacial belt ('old morainic' area) of northeastern Germany. The collected ages comprise a time interval of the last c. 50,000 years. More specifically we pursue the following aspects: (1) identification of the spatiotemporal pattern of dated records and their stratigraphical context; (2) dating of certain types of buried paleosols, corresponding sediments and reconstruction of the environmental conditions during soil formation; (3) timing and identification of specific geomorphic processes (triggered by e.g. climate change or land use) which led to burial of former surfaces. We have collected a total of c. 450 radiocarbon datings (AMS, conventional) and c. 400 luminescence datings (OSL, IRSL, TL) from a total of c. 200 sites. Each date is characterised by specific dating attributes (age with standard error, reliability, lab number, dated material) and by further information (e.g. coordinates, stratigraphy, references). Most of the radiocarbon and luminescence data were collected in the 1990s to 2010s. Among the radiocarbon dates charcoal (53 %) and peat (19 %) dominate the dated materials. Holocene ages prevail with a majority within the last 5000 years. Most dated paleosols are developed from peat (Histosols) as well as from glacial and aeolian sands (Arenosols, Podzols). Most luminescence dates come from aeolian (84 %) and colluvial sands (11 %), which are scattered over the whole Lateglacial-Holocene and the Holocene period, respectively. Furthermore, the collected ages

  16. Large-scale avulsion of the late Quaternary Sutlej river in the NW Indo-Gangetic foreland basin

    NASA Astrophysics Data System (ADS)

    Singh, Ajit; Gupta, Sanjeev; Sinha, Rajiv; Carter, Andrew; Thomsen, Kristina J.; Mark, Darren F.; Buylaert, Jan-Pieter; Mason, Philippa J.; Murray, Andrew S.; Jain, Mayank; Paul, Debajyoti

    2015-04-01

    River avulsions are important processes in the spatial evolution of river systems in tectonically active sedimentary basins as they govern large-scale patterns of sediment routing. However, the pattern and timing of avulsions in large river systems are poorly documented and not well understood. Here we document late Quaternary paleo-river channel changes in the Indo-Gangetic basin of northwest India. Using a combination of satellite remote sensing and detailed sediment coring, we analyse the large-scale planform geometry, and detailed sedimentary and stratigraphic nature of a major fluvial sedimentary deposit in the shallow subsurface. This sediment body records aggradation of multiple fluvial channel fills. Satellite remote sensing analysis indicates the trace of the buried channel complex and demonstrates that it exists in region of the Himalayan foreland where no major rivers are currently present. Thus it records the former drainage pathway of a major river, which has since been diverted. We use optically stimulated luminescence dating techniques to develop an age model for the stratigraphic succession and hence constrain the timing of river channel existence and diversion. Provenance analysis based on U-Pb dating of detrital zircons and detrital mica Ar-Ar ages indicate sediment sources in the Higher Himalayan Crystalline and Lesser Himalayan Crystalline Series indicating that this paleo-river channel system formed a major perennial river derived from the main body of the Himalaya. Specifically we are able to fingerprint bedrock sources in the catchment of the present-day Sutlej river indicating that the paleo-fluvial system represents the former course of the Sutlej river prior to a major nodal avulsion to its present day course. Our results indicate that on geologically relatively short time-scales, we observe dramatic along strike shifts in the location of major Himalayan rivers. Our sediment records when combined with high-resolution dating and

  17. Late Quaternary paleomagnetic secular variation, relative paleointensity, and environmental magnetism from Cascade Lake, Brooks Range, Arctic Alaska

    NASA Astrophysics Data System (ADS)

    Steen, D. P.; Kaufman, D. S.; Stoner, J. S.; Reilly, B. T.

    2015-12-01

    Two sediment cores from Cascade Lake (68.38°N, 154.60°W), Arctic Alaska were selected for paleomagnetic analysis to compare 14C age control with paleomagnetic secular variation (PSV) and relative paleointensity (RPI) age control derived from field models and other local sedimentary records. Rock magnetic experiments were performed to quantify variability in magnetic properties and to infer sediment sourcing during the late Quaternary. U-channels were studied through AF demagnetization of the natural remanent magnetization, and laboratory-induced magnetizations including anhysteretic remanent magnetization (ARM) acquisition, ARM demagnetization, and isothermal remanent magnetization (IRM). Maximum angular deviation values average <2°, indicating a strong, well-defined characteristic remanent magnetization dominated by a low-coercivity component that increases up core. Average inclinations are within 4° of the expected geocentric axial dipole, and major inclination features can be correlated across the two cores. Correlation of inclination changes with the Burial Lake record, 200 km to the west (Dorfman, 2013, unpub. thesis), indicates that the Cascade Lake sedimentary sequence overlying the basal diamicton likely spans at least 16 ka. Cascade Lake sediments may be suitable for RPI estimation using the ARM or IRM as a normalizer, following a more detailed examination of magnetic properties. A systematic offset between the Cascade Lake 14C chronology and PSV and RPI chronologies wiggle-matched to field models suggests a hard-water effect of ~1000 yr, although we cannot rule out the possibility that at least some of the age offset represents a post-depositional remanent magnetization lock-in effect at Cascade Lake. S-ratios (IRM0.3T/SIRM) and ARM-ratios (ARM/SIRM) show a sharp decrease in low-coercivity material across the transition from clastic sediments to organic-rich sediments, followed by an increase in the concentration of fine-grained magnetic material and

  18. CO2 outburst events in relation to seismicity: Constraints from microscale geochronology, geochemistry of late Quaternary vein carbonates, SW Turkey

    NASA Astrophysics Data System (ADS)

    Ünal-İmer, Ezgi; Uysal, I. Tonguç; Zhao, Jian-Xin; Işık, Veysel; Shulmeister, James; İmer, Ali; Feng, Yue-Xing

    2016-08-01

    calcite veins. Vein calcite formed in fault-induced fractures offers insights into structural features, genetic characterisation of the parental fluids, and late Quaternary degassing of subsurface CO2 accumulations.

  19. Late Quaternary tectonic deformation in the Cape Arago-Bandon region of coastal Oregon as deduced from wave-cut platforms

    SciTech Connect

    McInelly, G.W.; Kelsey, H.M. )

    1990-05-10

    The Cape Arago region of south central Oregon sits on the upper plate of the Cascadia subduction zone about 80 km east of the base of the continental slope. The style of late Pleistocene deformation along the Cascadia forearc near Cape Arago is well expressed by the altitudinal variation of a set of five uplifted wave-cut platforms. These platforms record open folding, with a half wavelength of about 6-7 km, as well as late Quaternary offset on flexural-slip reverse faults that parallel bedding in the underlying bedrock. The folds have produced both landward and seaward tilts to the uplifted wave-cut platforms. Because the folds cut obliquely across the coastline, the magnitude of coastal uplift is variable. In the case of the lowest, 80 ka wave-cut platform, this variable uplift has resulted in coastal deformation ranging from subsidence to a maximum uplift of 0.8 m/kyr. Quantitative analysis of the mechanism of flexural slip folding for the South Slough syncline near Cape Arago indicates that the late Quaternary strain rate has decreased in the last 200 kyr. Evidence of past great subduction-style earthquakes, such as regional uplift and regional landward tilting of wave-cut platforms, or regional submergence of coastlands, is lacking in the Cape Arago region. Instead, the deformational style is controlled by folding. Though localized folding is dominant, the occurrence of great subduction-style earthquakes is not precluded because localized folding could occur concurrently with regional coseismic deformation.

  20. Reconciling late Quaternary transgressions in the Bohai Sea, China to the global sea level changes, and new linkage of sedimentary records to three astronomical rhythms

    NASA Astrophysics Data System (ADS)

    Yi, Liang

    2013-04-01

    noticeable feature of these coastal sediment variations is the little internal similarity between records compared with high similarity with external forcing indicating that the coastal sediments in the south Bohai Sea integrate different influences from various environmental factors: (1) the grain-size variation represents Asian monsoon intensity which was dominated by both solar insolation (major) and global ice volume (minor) forcing; (2) the magnetic susceptibility indicates river incision processes which were sensitive to orbital tilt with influence from solar insolation; (3) the vegetation coverage responded to global ice volume coupled obliquity changes; and that (4) neither external nor internal factors could dominate the paleoenvironmental evolution on orbital timescales in an independent way, and they are both integrated in a complex pattern. Therefore, combining all of these results, we report those great similarities between regional and global sea-level patterns and the nonlinear interaction and the complex response to driving processes in a coastal evolution. However, all of these studies only used the upper part of cores within marine strata, and the rest containing lacustrine sediment is still in process. Sediment grain size, magnetic susceptibility, color reflectance were finished, and the magnetostratigraphic, environmental magnetism and element analysis are ongoing. More results about high-/low-latitude interaction and relative sea level will be released in three years, and anyone who has interests in cooperation will be welcome (Email: yi.liang82@gmail.com). References Chappell, J., Omura, A., Esat, T., McCulloch, M., Pandolfi, J., Ota, Y., Pillans, B., 1996. Reconciliation of late Quaternary sea levels derived from coral terraces at Huon Peninsula with deep sea oxygen isotope records. Earth and Planetary Science Letters 141, 227-236. Cheng, H., Edwards, R.L., Broecker, W.S., Denton, G.H., Kong, X., Wang, Y., Zhang, R., Wang, X., 2009. Ice Age

  1. Late-Quaternary morphodynamics of Ejina Basin, Inner Mongolia, China: Quantification of neotectonic subsidence and palaeohydrological implications

    NASA Astrophysics Data System (ADS)

    Hartmann, Kai; Wünnemann, Bernd; Reicherter, Klaus; Rudersdorf, Andreas; Blaauw, Maarten; Diekmann, Bernhard; Bölscher, Judith; Lu, Huayu

    2014-05-01

    From space, the Ejina Basin (Gaxun Nur Basin) - enclosed by the Tibetan Plateau in the south and the Gobi -Tien Shan in the north - appears as the world's second largest inland delta of approx. 28,000 km2. Today, the crescent-shaped series of terminal lakes (Gaxun Nur, Sogo Nur and Juyanze) represent the endorheic erosion base for the Black River (Hei River) drainage system originating in the Qilian Mountains (>5,000 m asl.). The up to 300 m thick Quaternary basin fill of lacustrine and alluvial origin was deposited during the last approx. 250,000 yrs. Gobi gravel plains protecting Late Pleistocene fine sediments against deflation cover most parts of the basin. They are considered to be a unique sequence within the sediment stratigraphy of the entire basin. The slightly convex-shaped surface of the western basin resembles the prograding formation of an alluvial fan with clear evidence of local subsidence to the north and west, as indicated by the concave shaped surface there. However, the recent terminal lake basins at the northern margin of Ejina Basin are structurally related to tectonic pull-apart basins that were active since Late Pleistocene. The rhomb-shaped Gaxun Nur basin is the most distinct pull-apart feature indicating a left-lateral strike-slip movement parallel to the continental Gobi-Tien-Shan Fault in the north. New radiocarbon dates of lacustrine sediments within a fossil cliff at the southern shore support the estimated subsidence rate of >0.8m per kyr (Hartmann et al. 2011) after the Last Glacial Maximum (LGM). The more trapezoid fault system of the Juyanze pull-apart basin exhibits a more manifold set of tectonically induced geomorphological features. Whereas Hartmannn et al. (2011) assumed a W-E-striking fault by comparing dating inversions along yardangs of lacustrince chalks that host seismites. A nearby new railway construction pit revealed a normal fault that affected the lake sediments that are 35±1 kyr BP in age. The most impressive set

  2. Late Quaternary slip rates and paleoearthquakes along the Yabrai range-front fault in the southern Gobi-Alashan block

    NASA Astrophysics Data System (ADS)

    Yu, Jingxing; Zheng, Wenjun; Lei, Qiyun; Shao, Yanxiu; Ge, Weipeng

    2014-05-01

    Study on the active faults of the southern Gobi-Alashan block is significant to understand the tectonic deformation processes associated with the Tibetan Plateau and Ordos block. With this knowledge in mind, the present study aims to answer what the major process is governing the tectonic deformation and the structural relationships between Gobi-Alashan and adjacent regions. Since this area was featured by late Quaternary active tectonics, the activities and paleoearthquakes around the block need be studied and reconciled. So, we will focus on one of those active structures, the ranger-front fault along Yabrai Shan, to address some basic problems. Three aspects are analyzed, i.e., geomorphology, kinematic characteristics and paleoearthquakes of the range-front fault along the Yabrai Shan. By combining previous studies and Differential GPS measurements, implications of the fault for the regional tectonics has been discussed. The main conclusions are summarized as follows: This fault consists of three segments. The most active segment is in the southwest. The southwest segment is about 35 km long. Its scarp, about 1-2 m high, might be the result of the most recent event (MRE) and stretches NE60° almost the full segment. Existence of free surface indicates that the elapsed time of the last event must be not long. The middle segment is about 31 km in length. Just a single fault plane was identified along the main bounds of the Yabrai Shan, but the fault consists of several splays in the north. In contrast to the simple geometric structure of the middle segment, the northeast segment comprises several faults. Scarps of the most recent earthquake event are clear but tend not to be continued. Field investigation reveals about 0.5-1.5 m up to 2 m height. This work determined slip rates by combining fault-scarp measurements and cosmogenic exposure age dating. Study on slip rates shows that the Holocene dip-slip rate of the Yabrai fault is 0.11±0.03 mm/a. Scarp vertical

  3. Disappearance of the last lions and hyenas of Europe in the Late Quaternary - a chain reaction of large mammal prey migration, extinction and human antagonism

    NASA Astrophysics Data System (ADS)

    Diedrich, Cajus G.

    2010-05-01

    In the Eemian to Early/Middle Weichselian (Late Pleistocene), when the Scandinavian and Alpine Glaciers were still small, and northern Germany under mammoth steppe to taiga palaoenvironment conditions, Late Quaternary steppe lions were well distributed in northern to central Germany, whereas generally all over Central Europe bones and rarely articulated skeletons were found less at open air but mainly at cave sites (Diedrich 2007a, 2008a-b, 2009a-b, 2010a-c, k, in review a-b; Diedrich and Rathgeber in review). A similar distribution, but more dense, is reported for the Late Quaternary Ice Age spotted hyenas (Diedrich 2005, 2006, 2007b-c, 2008a, c, 2010f-j, in review c-d, Diedrich and Žák 2006). The last lions of northern Europe were thought to have reached into the final Magdalénan (cf. Musil 1980). This can be not concluded with a restudy of the bone material from the Late Magdalenian (V-VI) Teufelsbrücke stone arch site near Saalfeld (Thuringia, Central Germany) and many other Magdalenian stations (open air and caves) in northern to central Germany (Münsterland Bay, Sauerland Karst, Harz Mountain Karst, Thuringian Karst). None of those sites yield remains of final Upper Pleistocene spotted hyenas or steppe lion bones anymore, nor in the few preserved Late Magdalenian mobile art can those be recognized in those regions. The last lion remains seem to reach into the Aurignacian or possibly into the Early Gravettian (early Late Weichselian) documented especially at the cave bear den, hyena den and overlapping Neandertalian to Modern human camp site Balve Cave (Sauerland Karst, cf. archaeology in Günther 1964) where still a mammoth fauna is documented for that time (Diedrich 2010a). The last and by archaeological layers dated hyena remains were also found in the Balve Cave and are from the Late Middle Palaeolithic cave site reaching a maximum Aurignacian age documenting an overlapping of hyena den and human camp site use (Diedrich 2010a, b). In northern Germany

  4. Late Quaternary geology of small basaltic volcanic centers, SW USA: Disparity among dating methods and implications for volcanic and geomorphic studies

    SciTech Connect

    Wells, S.; McFadden, L.; Perry, F.; Forman, S.; Crowe, B.; Pothis, J.; Olinger, C.

    1992-12-31

    Evaluation of volcanic hazards near the proposed high-level radioactive waste repository at Yucca Mountain provides the impetus for a series of detailed field and geochronologic studies of selected small late Quaternary basaltic scoria cones and lava flows in Nevada and California. Two of the most significant results of these studies are: the presence of chronostratigraphic units which indicate multiple eruptions with significant intervals of no activity between events (polycyclic volcanism); and a marked difference between conventional, numerical ages derived from K-Ar and Ar-40/Ar-39 methods and numerical, calibrated, and relative ages derived from thermoluminescence, cosmogenic He-3, the degree of soil development, and geomorphology of these volcanic landforms. Soil-bounded unconformities and buried stone pavements define the boundaries of chronostratigraphic units within these small volume basaltic centers. Volcanic centers displaying this type of stratigraphy may appear morphological simple but cannot be considered mongenetic. Recent studies by Perry and Crowe demonstrate that geochemical variations within a single basaltic volcanic center in NV are consistent with several magma batches forming a complex polycyclic volcano. The K-Ar and Ar-40/Ar-39 ages are 1--2 orders of magnitude older than either TL or cosmogenic He-3 and appear to have insufficient precision to constrain the ages of chronostratigraphic units within polycyclic volcanoes. In contrast, preliminary data indicate the TL and cosmogenic He-3 dating methods have the ability to resolve the late Quaternary volcanic stratigraphy, and results from these dating methods are consistent with the degree of soil development and geomorphic modification of the volcanic units. K-Ar and Ar-40/Ar-39 dates from these small basaltic volcanic centers have been used to calibrate new Quaternary dating methods, e.g. rock varnish, which in turn have been used to interpret landscape evolution in the SW US.

  5. The geomorphology of Patagonian ice dammed lake basins: Insights from remote sensing of a modern lake and reconstruction of a Late Quaternary lake drainage event

    NASA Astrophysics Data System (ADS)

    Thorndycraft, Varyl

    2016-04-01

    The geomorphology of ice dammed lake basins can be complex due to geomorphic responses to multiple base level changes from repeated filling and emptying, as well as the potential for catastrophic drainage events. Refining landscape models of Quaternary ice dammed palaeolake systems has the potential to improve our understanding of glacier and meltwater dynamics during deglaciation phases. In this poster two case studies are presented to shed light on the range of geomorphic processes exhibited within ice dammed lake basins. Using Google Earth Pro and repeat LANDSAT imagery the geomorphology resulting from multiple base level changes of an ice dammed lake of the Viedma Glacier (Southern Patagonia Icefield) is presented. The LANDSAT imagery shows transgressive lake phases inundating already formed delta and terrace surfaces, whilst the high resolution Google Earth Pro images reveal a complex suite of incised terrace levels developed on the valley floor following lake drainage events. Secondly, the impact of catastrophic drainage of the Late Pleistocene Palaeolake Cochrane (Northern Patagonia Icefield) is investigated through geomorphological mapping. Here an outburst flood and rapid lowering of the lake has led to large scale eddy scouring of glacio-lacustrine sediments, with scarp slopes of ca. 30-40 m in height, and the formation of boulder bars during the final stages of lake fall. The implications of the mapping for interpretations of Late Quaternary palaeolake sediment-landform assemblages and rates of landscape change are discussed.

  6. Interpreting Quaternary uplift rates at the Mendocino triple junction, northern California, from uplifted marine terraces

    SciTech Connect

    Merritts, D. ); Bull, W.B. )

    1989-11-01

    Analysis of the altitudinal spacing of 14 flights of marine terraces indicates a spatial pattern of varying uplift rates that agrees with that determined from previously dated terraces for the past 3-81 ka, and temporal changes in uplift rates from <1 m/ka to 3-5 m/ka that may reflect response to changes in tectonic regime during passage of the Mendocino triple junction (MTJ). A possible mechanism for regional uplift is growth of a slab window south of the MTJ. The region of most rapid uplift is 25-43 km south of the MTJ, immediately south of the northern boundary of the slab window. The coastline is tilted upward to the south in the region directly above the southern edge of the subducted Gorda plate. At Point Delgada, 55 km south of the present MTJ, where the northern edge of the slab window passes {approximately}300 ka, uplift rates have been 1.2 m/ka for at least 330 ka. More than 1.4 m.y. after passage of the southern edge of the subducted slab, at the Mendocino coast, uplift rates have been less than 0.4 m/ka for at least 330 ka.

  7. Linking glacial melting to Late Quaternary sedimentation in climatically sensitive mountainous catchments of the Mount Chlemos compex, Kalavryta, southern Greece

    NASA Astrophysics Data System (ADS)

    Pope, Richard; Hughes, Philip

    2014-05-01

    Compared to the mountainous areas of northern Greece (e.g. Woodward et al., 2008), the influence of deglaciation cycles on sedimentation in mountainous catchments in southern Greece remains poorly understood due to the poor preservation of small moraines and limited opportunities to date glacial and fluvial sediment dynamics fluvial sediments (Pope, unpublished data). Nevertheless, intriguing new insight into links between glacial cycles and sediment transfer/deposition phases in upland catchments have emerged by applying multiple dating techniques to well-preserved multiple generations of moraines and extensive glacio-fluvial fan systems on Mount Chelmos (2355 m a.s.l.). U-series dating of calcites within proximal fan sediments constrain the earliest phase of glacio-fluvial sedimentation to 490 (±21.0)(ka (MIS 12), while OSL dating of fine sands constrains the deposition of extensive medial glacio-fluvial gravels in (valley we walked down through trees) to between 250.99 (±20.67) and 160.82 (±11.08) ka. By comparison, cosmogenic dating of moraine boulders indicates that three generations of well-preserved moraines in the highest cirque areas date to 31-23 ka, 17-16 ka and 12-11.5 ka. OSL dating also provides ages of 18 and 17 (±11.08) for an extensive glacio-fluvial terrace in a major valley draining the southern flanksof Mount Chelmos. The initial Mount Chelmos geochronology suggests that the earliest and middle phases of glacio-fluvial sedimentation are coincident with the Middle Pleistocene glacial stages stages recorded in the Pindus range (Hughes et al, 2006). These include the Skamnellian (MIS 12) and the Vlasian (MIS 6) Stages as well as other cold stage between these (e.g. MIS 8).Evidence of glacio-fluvial outwash in MIS 8 is interesting since evidence for this in the moraine records has remained elusive although is suggested further north in the Balkans (Hughes et al., 2011). The valley moraines and glacio-fluvial terraces (late MIS 2) post-date the

  8. Quaternary marine terraces and maximum tectonic uplift rate of the Peruvian coast at 15. 5/sup 0/S latitude

    SciTech Connect

    Hsu, J.T.; Bloom, A.L.

    1985-01-01

    Numerous and well preserved marine terraces near San Juan de Marcona, Peru are a result of tectonic uplift related to subduction of the Nazca Plate, combined with Quaternary sea level fluctuations. A flight of 10 terraces from modern sea level up to 310 m has been sampled and surveyed along two transects. The lowest terrace surface is covered with cobble beach ridges and is truncated by a modern sea cliff 29 m above sea level. It may be the continuation of an abrasion platform with a well developed shoreline angle at 41 m. The extreme aridity of the Peruvian coastal desert is responsible for the preservation and lack of alteration of the terrace deposits. All landforms and sedimentary facies of the modern surf zone are still recognizable on the terraces. Abundant and well preserved mollusk shells, all of which are nearshore or surf zone species, can be found on most of the terraces. Uncorrected radiocarbon ages of pelecypods in growth position on the lowest terrace were >40,000 year B.P. If this lowest terrace is older than 40,000 yr. B.P. then its next most likely time of formation was during the 62,000 year B.P. interstadial event. By this hypothesis, a wide and well developed terrace at 148 m would have been formed during the 125,000 year B.P. interglacial high sea level, and the average uplift rate would have been 1.2 m/1000 year. This uplift rate is the maximum that can be assumed for this section of the Peruvian coast, because if the terraces are even older, the uplift rate must have been less.

  9. Late Paleocene Arctic Ocean shallow-marine temperatures from mollusc stable isotopes

    USGS Publications Warehouse

    Bice, Karen L.; Arthur, Michael A.; Marincovich, Louie, Jr.

    1996-01-01

    Late Paleocene high-latitude (80°N) Arctic Ocean shallow-marine temperatures are estimated from molluscan δ18O time series. Sampling of individual growth increments of two specimens of the bivalve Camptochlamys alaskensis provides a high-resolution record of shell stable isotope composition. The heavy carbon isotopic values of the specimens support a late Paleocene age for the youngest marine beds of the Prince Creek Formation exposed near Ocean Point, Alaska. The oxygen isotopic composition of regional freshwater runoff is estimated from the mean δ18O value of two freshwater bivalves collected from approximately coeval fluviatile beds. Over a 30 – 34‰ range of salinity, values assumed to represent the tolerance of C. alaskensis, the mean annual shallow-marine temperature recorded by these individuals is between 11° and 22°C. These values could represent maximum estimates of the mean annual temperature because of a possible warm-month bias imposed on the average δ18O value by slowing or cessation of growth in winter months. The amplitude of the molluscan δ18O time series probably records most of the seasonality in shallow-marine temperature. The annual temperature range indicated is approximately 6°C, suggesting very moderate high-latitude marine temperature seasonality during the late Paleocene. On the basis of analogy with modern Chlamys species, C. alaskensis probably inhabited water depths of 30–50 m. The seasonal temperature range derived from δ18O is therefore likely to be damped relative to the full range of annual sea surface temperatures. High-resolution sampling of molluscan shell material across inferred growth bands represents an important proxy record of seasonality of marine and freshwater conditions applicable at any latitude. If applied to other regions and time periods, the approach used here would contribute substantially to the paleoclimate record of seasonality.

  10. Disappearance of the last lions and hyenas of Europe in the Late Quaternary - a chain reaction of large mammal prey migration, extinction and human antagonism

    NASA Astrophysics Data System (ADS)

    Diedrich, Cajus G.

    2010-05-01

    In the Eemian to Early/Middle Weichselian (Late Pleistocene), when the Scandinavian and Alpine Glaciers were still small, and northern Germany under mammoth steppe to taiga palaoenvironment conditions, Late Quaternary steppe lions were well distributed in northern to central Germany, whereas generally all over Central Europe bones and rarely articulated skeletons were found less at open air but mainly at cave sites (Diedrich 2007a, 2008a-b, 2009a-b, 2010a-c, k, in review a-b; Diedrich and Rathgeber in review). A similar distribution, but more dense, is reported for the Late Quaternary Ice Age spotted hyenas (Diedrich 2005, 2006, 2007b-c, 2008a, c, 2010f-j, in review c-d, Diedrich and Žák 2006). The last lions of northern Europe were thought to have reached into the final Magdalénan (cf. Musil 1980). This can be not concluded with a restudy of the bone material from the Late Magdalenian (V-VI) Teufelsbrücke stone arch site near Saalfeld (Thuringia, Central Germany) and many other Magdalenian stations (open air and caves) in northern to central Germany (Münsterland Bay, Sauerland Karst, Harz Mountain Karst, Thuringian Karst). None of those sites yield remains of final Upper Pleistocene spotted hyenas or steppe lion bones anymore, nor in the few preserved Late Magdalenian mobile art can those be recognized in those regions. The last lion remains seem to reach into the Aurignacian or possibly into the Early Gravettian (early Late Weichselian) documented especially at the cave bear den, hyena den and overlapping Neandertalian to Modern human camp site Balve Cave (Sauerland Karst, cf. archaeology in Günther 1964) where still a mammoth fauna is documented for that time (Diedrich 2010a). The last and by archaeological layers dated hyena remains were also found in the Balve Cave and are from the Late Middle Palaeolithic cave site reaching a maximum Aurignacian age documenting an overlapping of hyena den and human camp site use (Diedrich 2010a, b). In northern Germany

  11. Late Quaternary changes in bat palaeobiodiversity and palaeobiogeography under climatic and anthropogenic pressure: new insights from Marie-Galante, Lesser Antilles

    NASA Astrophysics Data System (ADS)

    Stoetzel, Emmanuelle; Royer, Aurélien; Cochard, David; Lenoble, Arnaud

    2016-07-01

    Data on Lesser Antillean Late Quaternary fossil bat assemblages remains limited, leading to their general exclusion from studies focusing on Caribbean bat palaeobiodiversity and palaeobiogeography. Additionally, the role of climatic versus human pressure driving changes in faunal communities remains poorly understood. Here we describe a fossil bat assemblage from Blanchard Cave on Marie-Galante in the Lesser Antilles, which produced numerous bat remains from a well-dated, stratified context. Our study reveals the occurrence of at least 12 bat species during the Late Pleistocene and Early Holocene on Marie-Galante, whereas only eight species are currently known on the island. Among these 12 species, six are extirpated and one is extinct. Faunal changes within the Blanchard sequence indicate variations in Pleistocene bat species representation in the Lesser Antilles to have been influenced by climatic conditions, with "northern species" (Greater Antilles) favored during glacial conditions and "southern species" (southern Lesser Antilles) during interglacial events. However, few species disappeared at the end of the Late Pleistocene, with most of the extinction/extirpation events occurring during the Holocene. This pattern suggests human activities in the Lesser Antilles to have played a major role in bat turnover during the late Holocene.

  12. Functional diversity of marine ecosystems after the Late Permian mass extinction event

    NASA Astrophysics Data System (ADS)

    Foster, William J.; Twitchett, Richard J.

    2014-03-01

    The Late Permian mass extinction event about 252 million years ago was the most severe biotic crisis of the past 500 million years and occurred during an episode of global warming. The loss of around two-thirds of marine genera is thought to have had substantial ecological effects, but the overall impacts on the functioning of marine ecosystems and the pattern of marine recovery are uncertain. Here we analyse the fossil occurrences of all known benthic marine invertebrate genera from the Permian and Triassic periods, and assign each to a functional group based on their inferred lifestyle. We show that despite the selective extinction of 62-74% of these genera, all but one functional group persisted through the crisis, indicating that there was no significant loss of functional diversity at the global scale. In addition, only one new mode of life originated in the extinction aftermath. We suggest that Early Triassic marine ecosystems were not as ecologically depauperate as widely assumed. Functional diversity was, however, reduced in particular regions and habitats, such as tropical reefs; at these smaller scales, recovery varied spatially and temporally, probably driven by migration of surviving groups. We find that marine ecosystems did not return to their pre-extinction state, and by the Middle Triassic greater functional evenness is recorded, resulting from the radiation of previously subordinate groups such as motile, epifaunal grazers.

  13. Spotted hyena and steppe lion predation behaviours on cave bears of Europe - ?Late Quaternary cave bear extinction as result of predator stress

    NASA Astrophysics Data System (ADS)

    Diedrich, Cajus G.

    2010-05-01

    Cave bears hibernated in caves all over Eurasia (e.g. Rabeder et al., 2000) including alpine regions using mainly larger caves for this purpose. Late Quaternary spotted hyenas Crocuta crocuta spelaea instead occupied mainly areas close to the cave entrances as their dens (Diedrich and Žák 2006, Diedrich 2010). The largest predator, the steppe lion Panthera leo spelaea was only a sporadic cave dweller (Diedrich 2007b, 2009b). His presence and its remains from caves all over Europe can be recently explained best as result of imported carcasses after killing by their largest antagonists, the Late Quaternary spotted hyenas. In some cases the kill might have happened in the hyena den cave itself during the theft of prey remains by lions (Diedrich 2009a). Another reason of their remains in caves of Europe is the hunting onto the herbivorous cave bears, especially during hibernation times, when megafauna prey was less available in the open environments (Diedrich 2009c). These lion remains from caves of Europe, nearly all of which were from adult animals, provide evidence of active predation by lions onto cave bears even in medium high alpine regions (Diedrich 2009b, in review). Lion skeletons in European cave bear dens were therefore often found amongst originally articulated cave bear skeletons or scattered cave bear remains and even close to their hibernation nests (Diedrich et al. 2009c, in review). Not only lions fed on cave bears documented mainly by the large quantities of chewed, punctured and crushed cave bear long-bones; even damaged skulls reveal that hyenas scavenged primarily on cave bear carcasses which were mainly responsible for the destruction of their carcasses and bones (Diedrich 2005, 2009d). Predation and scavenging on cave bears by the two largest Late Quaternary predators C. c. spelaea and P. l. spelaea explains well the large quantity of fragmented cave bear bones over all European caves in low to medium high mountainous elevations, whereas in

  14. A multi-proxy geochemical investigation of late-Quaternary paleoenvironmental change from Burial Lake, Noatak National Preserve, Alaska

    NASA Astrophysics Data System (ADS)

    Finkenbinder, M. S.; Abbott, M.; Stoner, J. S.; Dorfman, J. M.

    2012-12-01

    Here we present a new multi-proxy geochemical analysis of paleoenvironmental change inferred from sediment cores recovered from Burial Lake (68.434° N, 159.174° W; 430 m ASL) in northwest Alaska. Previous work on cores from 7.9 m water depth sampled at comparatively low resolution revealed basal sediments date to ~ 40,000 cal yr BP and an unconformity during a period of aridity around the Last Glacial Maximum (LGM). We therefore collected multiple overlapping Livingston cores from the lake depocenter (21.5 m water depth) in the summer of 2010 in an effort to develop a temporally continuous, high resolution record spanning prior to the LGM to the present. We focus our interpretations on a 6.51 m core developed through wiggle matching proxy data from core sites A10 and C10. We use traditional laboratory methods and investigate new approaches to assess changes in sedimentation and productivity. We are measuring dry bulk density, organic matter via Loss-on-ignition at 550° C, biogenic silica, magnetic susceptibility, grain size via laser diffractometry, and elemental abundances via scanning x-ray fluorescence (XRF). Future research seeks to test the reliability of two commonly used XRF proxies, for organic matter (incoherence/coherence ratios) and aquatic productivity (Si/Ti ratios). Age control is provided by 12 Accelerator Mass Spectrometry radiocarbon dates of discrete terrestrial macrofossils. Results from these analyses indicate that the depocenter core is continuous and the sediment record spans the last ~ 38,000 cal yr BP and most importantly contains sediments spanning the LGM. Preliminary geochemical results demonstrate substantial cyclicity in organic matter and aquatic productivity beginning in the late-glacial. We seek to analyze the periodicity of these proxies through spectral analysis, although initial observations suggest multi-century to millennial scale variability. In addition, we note the presence of two abrupt, non-linear transitions in organic

  15. Spotted hyena and steppe lion predation behaviours on cave bears of Europe - ?Late Quaternary cave bear extinction as result of predator stress

    NASA Astrophysics Data System (ADS)

    Diedrich, Cajus G.

    2010-05-01

    Cave bears hibernated in caves all over Eurasia (e.g. Rabeder et al., 2000) including alpine regions using mainly larger caves for this purpose. Late Quaternary spotted hyenas Crocuta crocuta spelaea instead occupied mainly areas close to the cave entrances as their dens (Diedrich and Žák 2006, Diedrich 2010). The largest predator, the steppe lion Panthera leo spelaea was only a sporadic cave dweller (Diedrich 2007b, 2009b). His presence and its remains from caves all over Europe can be recently explained best as result of imported carcasses after killing by their largest antagonists, the Late Quaternary spotted hyenas. In some cases the kill might have happened in the hyena den cave itself during the theft of prey remains by lions (Diedrich 2009a). Another reason of their remains in caves of Europe is the hunting onto the herbivorous cave bears, especially during hibernation times, when megafauna prey was less available in the open environments (Diedrich 2009c). These lion remains from caves of Europe, nearly all of which were from adult animals, provide evidence of active predation by lions onto cave bears even in medium high alpine regions (Diedrich 2009b, in review). Lion skeletons in European cave bear dens were therefore often found amongst originally articulated cave bear skeletons or scattered cave bear remains and even close to their hibernation nests (Diedrich et al. 2009c, in review). Not only lions fed on cave bears documented mainly by the large quantities of chewed, punctured and crushed cave bear long-bones; even damaged skulls reveal that hyenas scavenged primarily on cave bear carcasses which were mainly responsible for the destruction of their carcasses and bones (Diedrich 2005, 2009d). Predation and scavenging on cave bears by the two largest Late Quaternary predators C. c. spelaea and P. l. spelaea explains well the large quantity of fragmented cave bear bones over all European caves in low to medium high mountainous elevations, whereas in

  16. Dating of the late Quaternary volcanic events using Uranium-series technique on travertine deposit: A case study in Ihlara, Central Anatolia Volcanic Province

    NASA Astrophysics Data System (ADS)

    Karabacak, Volkan; Tonguç Uysal, İ.; Ünal-İmer, Ezgi

    2016-04-01

    Dating of late Quaternary volcanism is crucial to understanding of the recent mechanism of crustal deformation and future volcanic explosivity risk of the region. However, radiometric dating of volcanic products has been a major challenge because of high methodological error rate. In most cases, there are difficulties on discrimination of the volcanic lava flow relations in the field. Furthermore, there would be unrecorded and unpreserved volcanoclastic layers by depositional and erosional processes. We present a new method that allows precise dating of late Quaternary volcanic events (in the time range of 0-500,000 years before present) using the Uranium-series technique on travertine mass, which is thought to be controlled by the young volcanism. Since the high pressure CO2 in the spring waters are mobilized during crustal strain cycles and the carbonates are precipitated in the fissures act as conduit for hot springs, thus, travertine deposits provide important information about crustal deformation. In this study we studied Ihlara fissure ridge travertines in the Central Anatolia Volcanic Province. This region is surrounded by many eruption centers (i.e. Hasandaǧı, Acıgöl and Göllüdaǧı) known as the late Quaternary and their widespread volcanoclastic products. Recent studies have suggested at least 11 events at around Acıgöl Caldera for the last 180 ka and 2 events at Hasandaǧı Stratovolcano for the last 30 ka. Active travertine masses around Ihlara deposited from hotwaters, which rise up through deep-penetrated fissures in volcanoclastic products of surrounding volcanoes. Analyses of the joint systems indicate that these vein structures are controlled by the crustal deformation due to young volcanism in the vicinity. Thus, the geological history of Ihlara travertine mass is regarded as a record of surrounding young volcanism. We dated 9 samples from 5 ridge-type travertine masses around Ihlara region. The age distribution indicates that the crustal

  17. Late Quaternary slip rate of the Owl Lake fault and maximum age of the latest event on the easternmost Garlock fault, S. California

    SciTech Connect

    McGill, S.F. . Dept. of Geological Sciences)

    1993-04-01

    The Owl Lake fault is an active, left-lateral oblique-slip fault in the southwestern Basin and Range province. It intersects the left-lateral Garlock fault in the Quail Mountains and extends about 19 km northeastern toward southern Death Valley. The eastern wall of a channel incised into Late Tertiary or Quaternary fanglomerate north of the fault and into Late Quaternary alluvial fan deposits south of the fault has been offset at least 43 meters left-laterally. This slip estimate is a minimum because of possible erosion of the channel wall upstream from (north of) the fault. If the upstream channel prior to offset was of comparable width to the modern channel, the offset is no more than about 80 m. Organic matter entombed beneath rock varnish on two boulders on the alluvial fan surface into which the channel incised has conventional radiocarbon ages of 29,470 [+-] 270 and 30,820 [+-] 280 years B.P. Abandonment of the fan surface was probably caused by incision of the offset channel, so the channel wall probably has a similar age. This suggests a preliminary left-lateral slip rate of about 1--3 mm/yr for the Owl Lake fault. Fault scarp heights suggest relative uplift of the northwestern side of the fault by at least 1--2 meters and possibly more since deposition of the Late Quaternary fan. At a site in the Avawatz Mountains, within 2 km of the eastern end of the Garlock fault (Leach Lake strand), a terrace riser has been offset 2.7 [+-] 0.6 m left-laterally and 0.2 m south-side-up. This offset probably occurred during the most recent large earthquake on this part of the fault. Organic matter beneath varnish on two cobbles on the upper terrace has conventional radiocarbon ages of 1,583 [+-] 90 and 1,656 [+-] 88 years B.P. This suggests the most recent slip event occurred after a date of A.D. 150--590. This is significantly older than the maximum age (AD 1490) of the most recent slip event on the central Garlock fault in Searles Valley.

  18. Paleomagnetic and paleoenvironmental implications of magnetofossil occurrences in late Miocene marine sediments from the Guadalquivir Basin, SW Spain.

    PubMed

    Larrasoaña, Juan C; Liu, Qingsong; Hu, Pengxiang; Roberts, Andrew P; Mata, Pilar; Civis, Jorge; Sierro, Francisco J; Pérez-Asensio, José N

    2014-01-01

    Although recent studies have revealed more widespread occurrences of magnetofossils in pre-Quaternary sediments than have been previously reported, their significance for paleomagnetic and paleoenvironmental studies is not fully understood. We present a paleo- and rock-magnetic study of late Miocene marine sediments recovered from the Guadalquivir Basin (SW Spain). Well-defined paleomagnetic directions provide a robust magnetostratigraphic chronology for the two studied sediment cores. Rock magnetic results indicate the dominance of intact magnetosome chains throughout the studied sediments. These results provide a link between the highest-quality paleomagnetic directions and higher magnetofossil abundances. We interpret that bacterial magnetite formed in the surface sediment mixed layer and that these magnetic particles gave rise to a paleomagnetic signal in the same way as detrital grains. They, therefore, carry a magnetization that is essentially identical to a post-depositional remanent magnetization, which we term a bio-depositional remanent magnetization. Some studied polarity reversals record paleomagnetic directions with an apparent 60-70 kyr recording delay. Magnetofossils in these cases are interpreted to carry a biogeochemical remanent magnetization that is locked in at greater depth in the sediment column. A sharp decrease in magnetofossil abundance toward the middle of the studied boreholes coincides broadly with a major rise in sediment accumulation rates near the onset of the Messinian salinity crisis (MSC), an event caused by interruption of the connection between the Mediterranean Sea and the Atlantic Ocean. This correlation appears to have resulted from dilution of magnetofossils by enhanced terrigenous inputs that were driven, in turn, by sedimentary changes triggered in the basin at the onset of the MSC. Our results highlight the importance of magnetofossils as carriers of high-quality paleomagnetic and paleoenvironmental signals even in

  19. Paleomagnetic and paleoenvironmental implications of magnetofossil occurrences in late Miocene marine sediments from the Guadalquivir Basin, SW Spain

    PubMed Central

    Larrasoaña, Juan C.; Liu, Qingsong; Hu, Pengxiang; Roberts, Andrew P.; Mata, Pilar; Civis, Jorge; Sierro, Francisco J.; Pérez-Asensio, José N.

    2014-01-01

    Although recent studies have revealed more widespread occurrences of magnetofossils in pre-Quaternary sediments than have been previously reported, their significance for paleomagnetic and paleoenvironmental studies is not fully understood. We present a paleo- and rock-magnetic study of late Miocene marine sediments recovered from the Guadalquivir Basin (SW Spain). Well-defined paleomagnetic directions provide a robust magnetostratigraphic chronology for the two studied sediment cores. Rock magnetic results indicate the dominance of intact magnetosome chains throughout the studied sediments. These results provide a link between the highest-quality paleomagnetic directions and higher magnetofossil abundances. We interpret that bacterial magnetite formed in the surface sediment mixed layer and that these magnetic particles gave rise to a paleomagnetic signal in the same way as detrital grains. They, therefore, carry a magnetization that is essentially identical to a post-depositional remanent magnetization, which we term a bio-depositional remanent magnetization. Some studied polarity reversals record paleomagnetic directions with an apparent 60–70 kyr recording delay. Magnetofossils in these cases are interpreted to carry a biogeochemical remanent magnetization that is locked in at greater depth in the sediment column. A sharp decrease in magnetofossil abundance toward the middle of the studied boreholes coincides broadly with a major rise in sediment accumulation rates near the onset of the Messinian salinity crisis (MSC), an event caused by interruption of the connection between the Mediterranean Sea and the Atlantic Ocean. This correlation appears to have resulted from dilution of magnetofossils by enhanced terrigenous inputs that were driven, in turn, by sedimentary changes triggered in the basin at the onset of the MSC. Our results highlight the importance of magnetofossils as carriers of high-quality paleomagnetic and paleoenvironmental signals even in

  20. Combining the least cost path method with population genetic data and species distribution models to identify landscape connectivity during the late Quaternary in Himalayan hemlock.

    PubMed

    Yu, Haibin; Zhang, Yili; Liu, Linshan; Qi, Wei; Li, Shicheng; Hu, Zhongjun

    2015-12-01

    Himalayan hemlock (Tsuga dumosa) experienced a recolonization event during the Quaternary period; however, the specific dispersal routes are remain unknown. Recently, the least cost path (LCP) calculation coupled with population genetic data and species distribution models has been applied to reveal the landscape connectivity. In this study, we utilized the categorical LCP method, combining species distribution of three periods (the last interglacial, the last glacial maximum, and the current period) and locality with shared chloroplast, mitochondrial, and nuclear haplotypes, to identify the possible dispersal routes of T. dumosa in the late Quaternary. Then, both a coalescent estimate of migration rates among regional groups and establishment of genetic divergence pattern were conducted. After those analyses, we found that the species generally migrated along the southern slope of Himalaya across time periods and genomic makers, and higher degree of dispersal was in the present and mtDNA haplotype. Furthermore, the direction of range shifts and strong level of gene flow also imply the existence of Himalayan dispersal path, and low area of genetic divergence pattern suggests that there are not any obvious barriers against the dispersal pathway. Above all, we inferred that a dispersal route along the Himalaya Mountains could exist, which is an important supplement for the evolutionary history of T. dumosa. Finally, we believed that this integrative genetic and geospatial method would bring new implications for the evolutionary process and conservation priority of species in the Tibetan Plateau. PMID:26811753

  1. Size variation in Tachyoryctes splendens (East African mole-rat) and its implications for late Quaternary temperature change in equatorial East Africa

    NASA Astrophysics Data System (ADS)

    Faith, J. Tyler; Patterson, David B.; Blegen, Nick; O'Neill, Chris J.; Marean, Curtis W.; Peppe, Daniel J.; Tryon, Christian A.

    2016-05-01

    This study develops a new proxy for Quaternary temperature change in tropical Africa through analysis of size variation in East African mole-rat (Tachyoryctes splendens). In modern mole-rats, mandibular alveolar length is unrelated to annual precipitation, precipitation seasonality, temperature seasonality, or primary productivity. However, it is inversely correlated with mean annual temperature, in agreement with Bergmann's rule. This relationship is observed at temperatures below ∼17.3 °C, but not at higher temperatures. We apply these observations to late Quaternary mole-rats from Wakondo (∼100 ka) and Kisaaka (∼50 ka) in the Lake Victoria region and Enkapune ya Muto (EYM; ∼7.2-3.2 ka) in Kenya's central rift. The Lake Victoria mole-rats are larger than expected for populations from warm climates typical of the area today, implying cooler temperatures in the past. The magnitude of temperature decline needed to drive the size shift is substantial (∼4-6 °C), similar in magnitude to the degree of change between the Last Glacial Maximum and Holocene, but is consistent with regional temperature records and with scenarios linking equatorial African temperature to northern hemisphere summer insolation. Size changes through time at EYM indicate that rising temperatures during the middle Holocene accompanied and potentially contributed to a decline in Lake Naivasha and expansion of grassland vegetation.

  2. Late quaternary distribution of the Cycladophora davisiana radiolarian species: Reflection of possible ventilation of the North Pacific intermediate water during the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Matul, A. G.; Abelmann, A.; Gersonde, R.; Nürnberg, D.; Tiedemann, R.; Kruglikova, S. B.

    2015-02-01

    A comparison of micropaleontological data on the distribution of the Cycladophora davisiana radiolarian species in the surface sediment layer and the Late Quaternary sediments from the Subarctic Pacific and Far East marginal seas allowed conclusions concerning the possible conditions and occurrence of intermediate waters during the last glacial maximum. We used the modern data on the C. davisiana species, which is a micro-paleontological indicator of the cold oxygen-rich upper intermediate water mass, which is now forming only in the Sea of Okhotsk. The high amount of C. davisiana in sediments of the last glacial maximum may point to the possible formation and expansion of the ventilated intermediate water in the most part of the Subarctic paleo-Pacific: the Bering Sea, the Sea of Okhotsk, within the NW Gyre, and in the Gulf of Alaska.

  3. An evaluation of the diatom response to Late Quaternary environmental change in two lakes in the Konya Basin, Turkey, by comparison with stable isotope data

    NASA Astrophysics Data System (ADS)

    Reed, J. M.; Roberts, N.; Leng, M. J.

    1999-04-01

    In palaeolimnological studies of closed-basin lakes, diatoms provide an excellent source of palaeoclimate data owing to their sensitivity to salinity and lake-level change. One of the best ways of assessing the relationships between diatom species response, salinity and lake-level change is comparison with other proxy indicators, such as stable isotopes. The sensitivity of different lake systems to climate change (changes in the ratio of precipitation to evapotranspiration) depends to a large extent on the character of the basin hydrology. Here, we compare evidence for Late Quaternary palaeohydrological change in two lakes which have contrasting groundwater hydrology, located in close proximity to each other in the Konya Basin, southern central Turkey, and whose sediment core chronologies show considerable overlap. Süleymanhacı gölü has alternated between being hydrologically closed and open during its history, and the diatom record shows clear evidence for changes in palaeoconductivity and lake level which correspond well to inferred changes in evaporative concentration during the Late Pleistocene and part of the Holocene. In contrast, the diatom record of the karstic spring-fed pool, Pinarbaşi, indicates that it remained fresh throughout the Late Pleistocene; it is subject to major aquifer flow and behaves effectively as an open system. In this case the complacency of the diatom record is important in allowing inferences on temperature effects to be drawn from relatively subtle shifts in stable isotope values.

  4. Lake level and watershed vegetation changes from C and N isotopic analysis of lacustrine organic matter: Implications for late Quaternary hydroclimate variability in Interior Alaska

    NASA Astrophysics Data System (ADS)

    Brady, S.; Finney, B. P.

    2012-12-01

    Understanding climate controls over lake level and watershed vegetation changes throughout the Holocene is important to determine how future hydroclimates will affect freshwater and terrestrial systems. This study seeks to provide a detailed record of late Quaternary climate variability for interior Alaska by quantifying lake level and vegetation changes via C and N isotopic compositions of lacustrine organic matter. C and N stable isotopes are important paleoclimate proxies from lake sediments that identify general plant types growing in and around lakes at the time of deposition. At Little Harding Lake (N 64.409207, W 146.902278), low lake levels are inferred around 12,285 cal yr BP, a time when sediment organic matter is characterized by enriched δ13C and low C/N ratios, carbonate deposition occurred, and herb vegetation dominated the landscape. Concentration dependent mixing models suggest that terrestrial organic matter contributed 51% to lake sediments during this time. An intensified Aleutian Low during the latter half of the Younger Dryas may have created cold, dry conditions in the Alaskan interior. Lake level fluctuated and began to rise after 11,400 cal yr BP as moisture delivery increased to the Alaskan interior and birch expanded in the region. Rising lake level and C3 plant expansion are documented by depleted δ13C, higher C/N ratios, and a 30% increase in terrestrial organic matter contribution to Little Harding Lake. Further increases in lake level until 8,400 cal yr BP correlate with expansion of poplar, spruce and alder and higher organic matter accumulation rates. C3 tree expansion and increasing lake levels into the middle Holocene may be attributed to greater summer precipitation in the interior as the result of an increased East Asian trough to the west accompanied by ridging over Alaska. Comparisons with other regional records will be assessed to determine likely patterns of past atmospheric circulation that may explain late Quaternary lake

  5. Molecular signals for late Tertiary/early Quaternary range splits of an Eurasian steppe plant: Clausia aprica (Brassicaceae).

    PubMed

    Franzke, A; Hurka, H; Janssen, D; Neuffer, B; Friesen, N; Markov, M; Mummenhoff, K

    2004-09-01

    Several vegetation belts stretch continuously from Europe to Asia, taiga and steppe being most prominent. Numerous plant species within these belts share a conspicuous distribution area, which is longitudinally contracted or disrupted approximately along longitude 70 degrees E. To date no hypothesis for this intriguing distribution pattern has been put forward. We detected molecular footprints in the contemporary genetic composition in nuclear DNA (ITS1, ITS2) and chloroplast DNA (trnL-trnF spacer region) of the steppe element Clausia aprica (Brassicaceae) providing evidence for a severe longitudinal range split and genetic differentiation east of the Ural Mountains about 1 million years ago caused by Quaternary climatic oscillations. Clausia aprica provides the first phylogeographical analysis on the intraspecific evolution of an Eurasian steppe plant. PMID:15315689

  6. Late Miocene carbon isotope records and marine biological productivity: Was there a (dusty) link?

    NASA Astrophysics Data System (ADS)

    Diester-Haass, Liselotte; Billups, Katharina; Emeis, Kay C.

    2006-12-01

    We examine whether or not a relationship exists between the late Miocene carbon isotope shift (˜7.6-6.6 Ma) and marine productivity at four sites from the Indian and Pacific Oceans (Ocean Drilling Program Sites 721, 1146, 1172, and 846). We use a multiproxy approach based on benthic foraminiferal accumulation rates, elemental ratios, and dissolution indices, and we compare these data to benthic foraminiferal δ13C values measured on the same samples. Although some of these sites have been targeted previously in studies of either the late Miocene/early Pliocene "biogenic bloom" (Sites 721 and 846) or the late Miocene carbon isotope shift (Site 1172), our records are the first to establish paired proxy records of carbon isotopes and paleoproductivity allowing a direct assessment of a potential link. Our results indicate that at all sites, productivity increased sometime during the δ13C shift; at three sites (721, 1146, and 846), productivity increased at the beginning of the shift. The correlation coefficients derived from linear regression between micropaleontologically derived productivity and foraminiferal δ13C values are relatively high during the time interval containing the late Miocene δ13C shift (and statistically significant at three of the sites). Carbon flux and isotope mass balance considerations illustrate that transfer of organic matter between the terrestrial and marine reservoirs together with enhanced oceanic upwelling best approximates observed changes in carbon isotope records and paleoproductivity. We note that long-term trend in the Site 846 paleoproductivity record can be correlated to the long-term trend in the Site 848 eolian flux reconstructions of Hovan (1995) hinting at a link between strengthened wind regime and productivity during the late Miocene.

  7. Late Quaternary sedimentary dynamics in Western Amazonia: Implications for the origin of open vegetation/forest contrasts

    NASA Astrophysics Data System (ADS)

    Rossetti, D. F.; Bertani, T. C.; Zani, H.; Cremon, E. H.; Hayakawa, E. H.

    2012-12-01

    This work investigated the evolution of sedimentary environments during the latest Quaternary and their influence on the paradoxical occurrence of open vegetation patches in sharp contact with the Amazonian forest. The approach integrated pre-existing geological and floristic data from lowlands in the Brazilian Amazonia, with remote sensing imagery including multispectral optical images (TM, ETM+, and ASTER), Phased Array L-band Synthetic Aperture Radar (PALSAR), InSAR C-band SRTM-DEMs, and high resolution images obtained from Google Earth™. The detection of an abundance of paleomorphologies provided evidence of a scenario in which constant environmental shifts were linked to the evolution of fluvial and megafan depositional systems. In all studied areas, the open vegetation patches are not random, but associated with sedimentary deposits representative of environments either deactivated during the Holocene or presently in the process of deactivation. Sedimentary evolution would have determined the distribution of wetlands and terra firme in many areas of the Amazonian lowlands, and would have a major impact on the development of open vegetated patches within the modern rainforest. Subsiding areas were filled up with megafan deposits, and many fluvial tributaries were rearranged on the landscape. The close relationship between vegetation and the physical environment suggests that sedimentary history related to the evolution of depositional settings during the latest Quaternary played a major role in the distribution of flooded and non-flooded areas of the Amazonian lowlands, with a direct impact on the distribution of modern floristic patterns. As the depositional sites were abandoned and their sedimentary deposits were exposed to the surface, they became sites suitable for vegetation growth, first of herbaceous species and then of forest. Although climate fluctuations might have been involved, fault reactivation appears to have been the main cause of changes in

  8. Differential insect and mammalian response to Late Quaternary climate change in the Rocky Mountain region of North America

    NASA Astrophysics Data System (ADS)

    Elias, Scott A.

    2015-07-01

    Of the 200 beetle species identified from Rocky Mountain Late Pleistocene insect faunal assemblages, 23% are no longer resident in this region. None of the 200 species is extinct. In contrast to this, only 8% of 73 identified mammal species from Rocky Mountain Late Pleistocene assemblages are no longer resident in the Rockies, and 12 species are now extinct. Since both groups of organisms are highly mobile, it would appear that their responses to the large-scale fluctuations of climate associated with the last 125,000 years have been considerably different. Most strikingly contrasting with the insects, there are no mammals in the Rocky Mountain Late Pleistocene fossil record that are found exclusively today in the Pacific Northwest (PNW) region. The PNW does have a distinctive modern mammalian fauna, but only one of these, Keen's Myotis, has a fossil record outside the PNW region, in the eastern and central United States. No modern PNW vertebrate species have been found in any Rocky Mountain fossil assemblages. Based on these data, it appears that there has been little or no mammalian faunal exchange between the PNW region and the Rocky Mountains during the Late Pleistocene or Holocene. This is in stark contrast to the fossil beetle record, where PNW species are a substantial component in many faunas, right through to the Late Holocene.

  9. Late Quaternary cave bears and brown bears in Europe: implications for distribution, chronology, and extinction based on a multidisciplinary approach

    NASA Astrophysics Data System (ADS)

    Pacher, Martina

    2010-05-01

    Cave bear remains are one of the most numerous fossils found in European caves. Despite their frequency of occurrence, many aspects of cave bear palaeontology still remain poorly understood. New methodological approaches and ongoing studies led to controversial results and discussion about its taxonomy, palaeoecology, and final extinction. Are we dealing with one single or several species of cave bears? Was cave bear exclusively vegetarian or after all more omnivorous? Did he go extinct before or after the Late Glacial Maximum? Was cave bear restricted to Europe or did he also occur in Asia? Late Pleistocene brown bears, on the other hand, are often rare and little is known about the possible co-occurrence of cave and brown bears during the Late Pleistocene. Based on direct radiocarbon dates the distribution pattern of both, cave and brown bears is reconstructed during the Late Pleistocene in Europe. In addition, the reasons for the achieved pattern will be tested leading to the main question - why did cave bear become extinct while brown bears survived until today? To answer this question palaeobiological data of Late Pleistocene cave and brown bears will be tested against results from isotope analyses, while aDNA data may contribute to the question of distinct local population or even species of bears. The current state of evidence will be presented and on the basis of resulting pattern implications for further multi-disciplinary studies will be discussed.

  10. Late Quaternary sediment-accumulation rates within the inner basins of the California Continental Borderland in support of geologic hazard evaluation

    USGS Publications Warehouse

    Normark, W.R.; McGann, M.; Sliter, R.W.

    2009-01-01

    An evaluation of the geologic hazards of the inner California Borderland requires determination of the timing for faulting and mass-movement episodes during the Holocene. Our effort focused on basin slopes and turbidite systems on the basin floors for the area between Santa Barbara and San Diego, California. Dating condensed sections on slopes adjacent to fault zones provides better control on fault history where high-resolution, seismic-reflection data can be used to correlate sediment between the core site and the fault zones. This study reports and interprets 147 radiocarbon dates from 43 U.S. Geological Survey piston cores as well as 11 dates from Ocean Drilling Program Site 1015 on the floor of Santa Monica Basin. One hundred nineteen dates from 39 of the piston cores have not previously been published. Core locations were selected for hazard evaluation, but despite the nonuniform distribution of sample locations, the dates obtained for the late Quaternary deposits are useful for documenting changes in sediment-accumulation rates during the past 30 ka. Cores from basins receiving substantial sediment from rivers, i.e., Santa Monica Basin and the Gulf of Santa Catalina, show a decrease in sediment supply during the middle Holocene, but during the late Holocene after sea level had reached the current highstand condition, rates then increased partly in response to an increase in El Ni??o-Southern Oscillation events during the past 3.5 ka. ?? 2009 The Geological Society of America.

  11. Inferences about winter temperatures and summer rains from the late Quaternary record of C4 perennial grasses and C3 desert shrubs in the northern Chihuahuan Desert

    USGS Publications Warehouse

    Holmgren, Camille A.; Norris, Jodi; Betancourt, Julio L.

    2007-01-01

    Late Quaternary histories of two North American desert biomes—C4 grasslands and C3 shrublands—are poorly known despite their sensitivity and potential value in reconstructing summer rains and winter temperatures. Plant macrofossil assemblages from packrat midden series in the northern Chihuahuan Desert show that C4 grasses and annuals typical of desert grassland persisted near their present northern limits throughout the last glacial-interglacial cycle. By contrast, key C3 desert shrubs appeared somewhat abruptly after 5000cal.yrBP. Bioclimatic envelopes for select C4 and C3 species are mapped to interpret the glacial-interglacial persistence of desert grassland and the mid-to-late Holocene expansion of desert shrublands. The envelopes suggest relatively warm Pleistocene temperatures with moist summers allowed for persistence of C4 grasses, whereas winters were probably too cold (or too wet) for C3 desert shrubs. Contrary to climate model results, core processes associated with the North American Monsoon and moisture transport to the northern Chihuahuan Desert remained intact throughout the last glacial-interglacial cycle. Mid-latitude effects, however, truncated midsummer (July-August) moisture transport north of 35° N. The sudden expansion of desert shrublands after 5000cal.yrBP may be a threshold response to warmer winters associated with increasing boreal winter insolation, and enhanced El Niño-Southern Oscillation variability.

  12. A late Quaternary lake record from the Qilian Mountains (NW China): evolution of the primary production and the water depth reconstructed from macrofossil, pollen, biomarker, and isotope data

    NASA Astrophysics Data System (ADS)

    Herzschuh, Ulrike; Zhang, Chengjun; Mischke, Steffen; Herzschuh, Rainer; Mohammadi, Farhid; Mingram, Birgit; Kürschner, Harald; Riedel, Frank

    2005-04-01

    The history (45-0 ka BP) of the aquatic vegetation composition of the shallow alpine Lake Luanhaizi from the NE Tibetan Plateau is inferred from aquatic plant macrofossil frequencies and aquatic pollen and algae concentrations in the sediments. C/N (range: 0.3-100), δ 13C (range: -28 to -15‰), and n-alkane measurements yielded further information on the quantitative composition of sedimentary organic matter. The inferred primary production of the former lake ecosystem has been examined in respect of the alternative stable state theory of shallow lakes [Scheffer, M., 1989. Alternative stable states in eutrophic, shallow freshwater systems: a minimal model. Hydrobiological Bulletin 23, 73-83]. Switches between clear and turbid water conditions are explained by a colder climate and forest decline in the catchment area of Lake Luanhaizi. The macrofossil-based reconstruction of past water depth and salinity ranges, as well as other organic matter (OM) proxies allowed climatic inferences of the summer monsoon intensity during the late Quaternary. Around 45 ka BP, conditions similar to or even moister than present-day climate occurred. The Lake Luanhaizi record is further evidence against an extensive glaciation of the Tibetan Plateau and its bordering mountain ranges during the Last Glacial Maximum. Highest lake levels and consequently a strong summer monsoon are recorded for the early Holocene period, while gradually decreasing lake levels are reconstructed for the middle and late Holocene.

  13. Width of late Quaternary deformation of the Enriquillo-Plantain Garden strike-slip fault zone in Haiti and the Jamaica Passage and implications for accumulated stress

    NASA Astrophysics Data System (ADS)

    Mann, P.; Bachhuber, J. L.

    2010-12-01

    The devastating Haiti earthquake of January 12, 2010, is now known to have occurred on multiple rupture planes with most of the seismic energy release along a north-dipping thrust fault located from 0.5 to 15 km north of the main late Quaternary trace of the EPGFZ. Two alternative views of this rupture are that this north-dipping thrust is unrelated to the main trace of the fault - which showed no rupture during the event - or this north-dipping thrust is part of its larger, subsurface “flower zone” of deformation poorly understood because we have no seismic reflection images crossing the EGPFZ in epicentral area of the 2010 earthquake. The significance of distinguishing these two views of fault behavior relates to whether centuries of accumulated stress were not released on the main trace of the EPGFZ (first model) or whether some accumulated stress was released on the low-angle thrust as part of a broad and linked “flower zone” of deformation parallel to the EPGFZ (second model). In this talk we review observations on the width of the EPGFZ deformation to support the latter view that the EPGFZ is in fact a broad zone of deformation commensurate with its tectonic role as a major, active plate boundary fault. Three areas of broad late Quaternary tectonic deformation varying from transpressional to transtensional in structural style are examined using DEM, imagery, surface geologic maps, and aftershock locations. The Cul-de-Sac basin of Haiti is the xx-km-wide, fault bounded alluvial plain upon which the city of Port-au-Prince was constructed in the early 18th century. Merged DEM and geologic map data from the Cul-de-Sac plain show that an en echelon array of large, open folds deforming uplifted and deeply dissected Plio-Pleistocene fans can be traced 3 to 7 km north of the main trace of the EPGFZ. Map studies show that west-northwest-striking, sub-parallel reverse-oblique/strike-slip faults can be mapped transecting the folds at distances of 3 to 5 km north

  14. A magnetostratigraphic record of landscape development in the eastern Ordos Plateau, China: Transition from Late Miocene and Early Pliocene stacked sedimentation to Late Pliocene and Quaternary uplift and incision by the Yellow River

    NASA Astrophysics Data System (ADS)

    Pan, Baotian; Hu, Zhenbo; Wang, Junping; Vandenberghe, Jef; Hu, Xiaofei

    2011-01-01

    A continuous fluviolacustrine record provides the geochronological framework to reconstruct the fluvial landscape evolution of the middle reach of the Huanghe (Yellow River). Magnetostratigraphic records from six sections at the north of the Jinshaan Gorge indicate that an isolated fluviolacustrine system occupied this gorge from 8.3 to 3.7 Ma. Local fluvial incision initiated at the lake margin around 5.3-4.9 Ma, and concomitant fluvial deposits intruded laterally into fine lacustrine strata increasing the sedimentation rate (ca. 3.1 cm/ky) within the isolated lake. The temporal coincidence of the onset of uplift-driven valley incision at 3.7 Ma along the Yellow River and the onset of basin excavation suggest that uplift possibly played an important role in the late Pliocene-Quaternary drainage evolution. Consequently, incision of the Yellow River upstream in the Jinshaan Gorge initiated at 3.7 Ma.

  15. A stacked Late Quaternary fluvio-periglacial sequence from the Axe valley, southern England with implications for landscape evolution and Palaeolithic archaeology

    NASA Astrophysics Data System (ADS)

    Brown, A. G.; Basell, L. S.; Toms, P. S.

    2015-05-01

    The current model of mid-latitude late Quaternary terrace sequences, is that they are uplift-driven but climatically controlled terrace staircases, relating to both regional-scale crustal and tectonic factors, and palaeohydrological variations forced by quasi-cyclic climatic conditions in the 100 K world (post Mid Pleistocene Transition). This model appears to hold for the majority of the river valleys draining into the English Channel which exhibit 8-15 terrace levels over approximately 60-100 m of altitudinal elevation. However, one valley, the Axe, has only one major morphological terrace and has long-been regarded as anomalous. This paper uses both conventional and novel stratigraphical methods (digital granulometry and terrestrial laser scanning) to show that this terrace is a stacked sedimentary sequence of 20-30 m thickness with a quasi-continuous (i.e. with hiatuses) pulsed, record of fluvial and periglacial sedimentation over at least the last 300-400 K yrs as determined principally by OSL dating of the upper two thirds of the sequence. Since uplift has been regional, there is no evidence of anomalous neotectonics, and climatic history must be comparable to the adjacent catchments (both of which have staircase sequences) a catchment-specific mechanism is required. The Axe is the only valley in North West Europe incised entirely into the near-horizontally bedded chert (crypto-crystalline quartz) and sand-rich Lower Cretaceous rocks creating a buried valley. Mapping of the valley slopes has identified many large landslide scars associated with past and present springs. It is proposed that these are thaw-slump scars and represent large hill-slope failures caused by Vauclausian water pressures and hydraulic fracturing of the chert during rapid permafrost melting. A simple 1D model of this thermokarstic process is used to explore this mechanism, and it is proposed that the resultant anomalously high input of chert and sand into the valley during terminations

  16. Late Pliocene-Quaternary evolution of outermost hinterland basins of the Northern Apennines (Italy), and their relevance to active tectonics

    NASA Astrophysics Data System (ADS)

    Sani, Federico; Bonini, Marco; Piccardi, Luigi; Vannucci, Gianfranco; Delle Donne, Dario; Benvenuti, Marco; Moratti, Giovanna; Corti, Giacomo; Montanari, Domenico; Sedda, Lorenzo; Tanini, Chiara

    2009-10-01

    We examine the tectonic evolution and structural characteristics of the Quaternary intermontane Mugello, Casentino, and Sansepolcro basins, in the Northern Apennines fold-and-thrust belt. These basins have been classically interpreted to have developed under an extensional regime, and to mark the extension-compression transition. The results of our study have instead allowed framing the formation of these basins into a compressive setting tied to the activity of backthrust faults at their northeastern margin. Syndepositional activity of these structures is manifested by consistent architecture of sediments and outcrop-scale deformation. After this phase, the Mugello and Sansepolcro basins experienced a phase of normal faulting extending from the middle Pleistocene until Present. Basin evolution can be thus basically framed into a two-phase history, with extensional tectonics superposed onto compressional structures. Analysis of morphologic features has revealed the occurrence of fresh fault scarps and interaction of faulting with drainage systems, which have been interpreted as evidence for potential ongoing activity of normal faults. Extensional tectonics is also manifested by recent seismicity, and likely caused the strong historical earthquakes affecting the Mugello and Sansepolcro basins. Qualitative comparison of surface information with depth-converted seismic data suggests the basins to represent discrete subsiding areas within the seismic belt extending along the axial zone of the Apennines. The inferred chronology of deformation and the timing of activity of normal faults have an obvious impact on the elaboration of seismic hazard models.

  17. Late Quaternary Ostracodes and Paleoceanography from HOTRAX core HLY0503-18, Lomonosov Ridge, Central Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Gemery, L.; Cronin, T. M.; Darby, D. A.; Jakobsson, M.; Polyak, L. V.

    2009-12-01

    Most Quaternary sediment records from the central Arctic Ocean have low temporal resolution (1-2 cm/kyr), limiting our understanding of millennial-scale climate events such as the Younger Dryas, Preboreal Oscillation and early Holocene thermal maximum. Cores recovered on the 2005 HOTRAX cruise to the central Lomonosov Ridge include intervals with sedimentation rates as high as 10 cm/kyr for the last deglacial interval. Using modern species’ ecology from a modern ostracode database, we analyzed ostracode assemblages from core HLY0503-18TC to reconstruct deglacial and early Holocene bottom water conditions and surface ocean circulation, productivity, and sea-ice conditions. Results show millennial-scale changes in the dominance of indicator ostracode taxa (Polycope, Krithe, Cytheropteron) during the BØlling/AllerØd, Younger Dryas, and early Holocene that we interpret as signifying rapid changes in surface productivity, surface-to-benthic flux of organic material and reduced sea-ice or even ice-free summer conditions. In addition to paleoceanographic implications, ostracode assemblages provide faunal tiepoints that can be used to correlate central Arctic cores, augmenting nannofossil and foraminiferal biostratigraphy and radiocarbon dates complicated by reservoir effects.

  18. 10Be and U-series dating of late Quaternary landforms along the southern San Jacinto fault: Implications for temporal slip rate variability

    NASA Astrophysics Data System (ADS)

    Blisniuk, K.; Oskin, M. E.; Fletcher, K.; Sharp, W. D.; Rockwell, T. K.

    2009-12-01

    Robust age control on faulted landforms with well-constrained offsets is essential to documenting the heterogeneous behavior of a fault zone over time. However, showing late Quaternary temporal slip rate variation is often challenging due to the difficultly of obtaining reliable ages for Quaternary deposits. Exposure ages from cosmogenic isotopes can be significantly affected by surface processes, and U-series dating of pedogenic carbonate provides only minimum ages because carbonate accumulation occurs after deposition. Fortunately, the controlling factors for the resulting age uncertainties of each method are relatively independent from each other, so a combination of cosmogenic isotope and U-series dating may significantly improve the reliability of landform dating and yield more robust slip rate estimates. We present preliminary results of this dual-dating approach at 4 sites along the southern San Jacinto fault zone in California: 2 sites along the Coyote Creek fault, and 2 sites along the Clark fault. These results show age agreement between the two dating methods. Along the southern Clark fault, a 10Be depth profile model age of 34.5 ±6.6 ka and a U-series age of 33.2 ±1.1 ka were obtained for an offset Q2b fan surface, and a Q3b surface yielded a weighted mean 10Be surface exposure age of 5.9 ±1.5 ka, similar to an U-series age of 6.3 ±0.4 ka. Along the northern Coyote Creek fault, preliminary data indicate a 10Be surface exposure age of 11.3 ±3.4 ka and a U-series age of 11.7 ±1.8 ka for an offset Q3a surface, and a 10Be surface exposure age of 6.9 ±1.0 ka and a U-series age of 7.8 ± 0.9 ka for an offset Q3b surface. The remarkable consistency among ages from the two dating methods suggest that: (1) U-series ages of pedogenic carbonate clast rinds closely approach depositional ages of the host alluvium; (2) erosion may be negligible at the sampled sites; and (3) inherited 10Be has been accurately quantified (via depth profile) for the late

  19. Late Quaternary evolution of the La Cantera Fault System (Central Precordillera, Argentina): A morphotectonic and paleoseismic analysis

    NASA Astrophysics Data System (ADS)

    Perucca, Laura; Rothis, Martín; Bezerra, Francisco Hilario; Vargas, Nicolás; Lima, Jean

    2015-10-01

    The La Cantera Fault System (LCFS) is the most active Quaternary structure in the Central Precordillera of San Juan, in central-western Argentina; the system extends for 47 km along the intermountain valley that separates the Sierra de La Cantera and La Invernada, north of the San Juan River. The average fault trend is 20°; it dips at angles varying between 15° and 30° W in the northern section, to approximately 40° W in the central section, and up to 60° W in the southern section. The fault affects Holocene to recent alluvium deposits in the western piedmont of the Sierra de La Cantera and is defined by a series of landforms found in compressive tectonic environments, including simple and compound counterslope fault scarps, staircased alluvial terraces, sag ponds, flexural scarps, aligned springs, broom-shaped drainage patterns, river diversions, beheaded channels, changes in incision depths, sinuosity and a river gradient along channels. Trench investigations indicated that at least three events occurred in the past 1.1-10.1 ky. The topographic profiles of the selected channels and interfluves cutting across the northern and central trace of the fault were analyzed using a Stonex Vector GPS differential system to establish the relationship between the topography and slope of the rivers. This morphometric analysis of scarps indicates that active tectonics have played an essential role in controlling the drainage pattern in the piedmont, leading the rivers to adjust to these slope variations. Based on the analyzed geomorphologic, stratigraphic and structural characteristics, the LCFS is considered to be a relevant seismogenic source in the intraplate portion of southern South America, with a recurrence interval of at least 2000 ± 500 years for moderate magnitude earthquakes during the last 11,000 years.

  20. Late Quaternary paleoseismic evidence on the Munébrega half-graben fault (Iberian Range, Spain)

    NASA Astrophysics Data System (ADS)

    Gutiérrez, Francisco; Masana, Eulàlia; González, Álvaro; Lucha, Pedro; Guerrero, Jesús; McCalpin, James P.

    2009-10-01

    The Munébrega Plio-Quaternary half-graben is a NW-SE trending neotectonic depression located in the central sector of the intraplate Iberian Range (NE Spain). The master fault of the half-graben offsets an Upper Pleistocene pediment deposit, forming an upslope-facing scarp. A trench dug across the fault scarp exposed a 25-m wide deformation zone consisting of graben and horst fault blocks with fissures in the upper part of the scarp, and a monoclinal flexure affected by normal and reverse faults in the lower part of the scarp. We infer a minimum of three faulting events over the past 72 ka, yielding an average (maximum) recurrence interval of 24 ka. The oldest event (72-41 ka) produced an antislope scarp on the relict pediment surface, confining deposition to the downthrown block. Cross-cutting faults affecting sedimentary units deposited in the sediment trap produced by the first event provide evidence for at least two younger events (33-19? ka). The measured cumulative vertical displacement (7.4 m) yield a minimum vertical slip rate of 0.10 ± 0.01 mm/year (2σ error) for the past 72 ka. If the paleoearthquakes ruptured the whole mappable length of the fault (ca. 20 km), they probably had moment magnitudes ca. 6.9 (Stirling et al. Bull Seismol Soc Am, 2002). Such earthquakes would have been more than a magnitude unit larger than the largest ones recorded historically in the Iberian Range. These results suggest that the official seismic hazard assessments, based solely on the historic and instrumental record, may underestimate the seismic hazard in the area.

  1. The evolution of a thermokarst-lake landscape: Late Quaternary permafrost degradation and stabilization in interior Alaska

    NASA Astrophysics Data System (ADS)

    Edwards, Mary; Grosse, Guido; Jones, Benjamin M.; McDowell, Patricia

    2016-07-01

    Thermokarst processes characterize a variety of ice-rich permafrost terrains and often lead to lake formation. The long-term evolution of thermokarst landscapes and the stability and longevity of lakes depend upon climate, vegetation and ground conditions, including the volume of excess ground ice and its distribution. The current lake status of thermokarst-lake landscapes and their future trajectories under climate warming are better understood in the light of their long-term development. We studied the lake-rich southern marginal upland of the Yukon Flats (northern interior Alaska) using dated lake-sediment cores, observations of river-cut exposures, and remotely-sensed data. The region features thick (up to 40 m) Quaternary deposits (mainly loess) that contain massive ground ice. Two of three studied lakes formed ~ 11,000-12,000 cal yr BP through inferred thermokarst processes, and fire may have played a role in initiating thermokarst development. From ~ 9000 cal yr BP, all lakes exhibited steady sedimentation, and pollen stratigraphies are consistent with regional patterns. The current lake expansion rates are low (0 to < 7 cm yr- 1 shoreline retreat) compared with other regions (~ 30 cm yr- 1 or more). This thermokarst lake-rich region does not show evidence of extensive landscape lowering by lake drainage, nor of multiple lake generations within a basin. However, LiDAR images reveal linear "corrugations" (> 5 m amplitude), deep thermo-erosional gullies, and features resembling lake drainage channels, suggesting that highly dynamic surface processes have previously shaped the landscape. Evidently, widespread early Holocene permafrost degradation and thermokarst lake initiation were followed by lake longevity and landscape stabilization, the latter possibly related to establishment of dense forest cover. Partial or complete drainage of three lakes in 2013 reveals that there is some contemporary landscape dynamism. Holocene landscape evolution in the study area

  2. Interplay between down-slope and along-slope sedimentary processes during the late Quaternary along the Capo Vaticano margin (southern Tyrrhenian Sea, Italy)

    NASA Astrophysics Data System (ADS)

    Martorelli, Eleonora; Bosman, Alessandro; Casalbore, Daniele; Falcini, Federico

    2016-04-01

    Late Quaternary along-slope and down-slope sedimentary processes and structures in the upper slope-shelf sector of the Calabro-Tyrrhenian continental margin off Capo Vaticano have been investigated using very high-resolution single-channel seismic profiles and multibeam bathymetric data. The results show that a competition among along-slope bottom currents-vs down-slope mass-wasting mostly contributed in shaping the seafloor and controlling deposition of sedimentary units during the Late Quaternary. Along-slope processes mostly formed elongated drifts located on the upper continental slope and outer shelf, between -90 and -300 m. The contourite deposits and associated erosive elements indicate the presence of a northwestward geostrophic flow that can be related to the modified-LIW issued by the Messina Strait. According to the proposed stratigraphic reconstruction it is likely that the activity of bottom-currents off Capo Vaticano was intensified around the LGM period and during the post-glacial sea-level rise, whereas they were less intense during the Holocene. Gravity-driven down-slope processes formed mass-transport deposits and turbidite systems with erosive channels, locally indenting the present-day shelf. Several slide events affected the upper 10-20 m of the stratigraphic record, dismantling considerable volume of contourite sediment. High-resolution seismic profiles indicate that failure processes appear to be dominated by translational sliding with glide plains mainly developed within contourite deposits. The most striking feature is the Capo Vaticano slide complex, which displays a large spatial coverage (area of about 18 km2) and is composed by several intersecting slide scars and overlapping deposits; these characteristics are peculiar for the Tyrrhenian continental margins, where slide events developed in open-slope areas are usually less complex and smaller in size. The presence of high-amplitude reflectors within contourite deposits (representing

  3. Late Quaternary alluvial processes in the north piedmont of Wutai Mountain in the graben system of north China and the influencing factors

    NASA Astrophysics Data System (ADS)

    Zhang, S.; Gong, Z.; Ding, R.; Li, T.

    2012-12-01

    The alluvial processes in the piedmont may be controlled by tectonics, climate fluctuations and base level of erosion, etc. To distinguish the contributions of each factors is a hot field in fluvial geomorphology. The north piedmont of Wutai Mountain in Shanxi graben is an ideal area for this kind of study. The piedmont fault is very active with a slip rate of no less than 1 millimeter per year in late Quaternary. This semiarid region experienced significant climatic fluctuations in Quaternary time which is indicated by striking contrast in colors between loess and paleosoils in loess strata. The stratigraphic sequence of alluvial fans in late Pleistocene and Holocene is established through field surveying and trenching. Ages of the strata have been well constrained by the method of radiocarbon dating. It is discovered that the alluvial processes in front of the mountain were strong and weak alternately. The strong periods were from 32 ka to 29 ka B.P., from 7.5 ka to 4.7 ka B.P., and since 1 ka B.P., when coarse-grained sediments deposited and the sediment rate is relatively high. The other times are weak periods when fine-grained sediments deposited and the sediment rate is much lower. The three strong periods correspond either with the transform stages from warm to cool climates, or with the intense fluctuation stage after the maximum of warm climate. These three periods share a common feature of intense fluctuations of weather whose amplitudes are larger than other periods. According to former studies on Holocene paleoearthquakes about Wutai Mountain piedmont fault, two events happened in strong periods of alluvial processes, one event in weak period. Strong earthquakes may lead to landslides and rock-falls in mountain area, which increment the clastic provenance and contribute to alluvial processes, but the limited information of paleoearthquakes cannot support a salient effect of big earthquakes on alluvial processes in front of mountain. As our preliminary

  4. The Sand Seas of northern China: Important sinks and sources of global sediment fluxes and their changing roles during different climate conditions of Late Quaternary

    NASA Astrophysics Data System (ADS)

    Yang, X.

    2014-12-01

    Although the occurrence of aeolian sands in sedimentary sequences has been widely used as indicators of desert formation or proxies of desert climate, one should be aware that accumulation of aeolian sands does occur along river channels, in lake shores not necessarily associated with arid environment. Our ongoing geomorphological and paleoenvironmental studies in the deserts of northern China reconfirm that formation of sand seas is dependent on not only erodibility (arising from bare surface due to aridity) and wind power but more importantly sand availability related to sediment cycles under interactions between fluvial, lacustrine and aeolian processes. Here we present our ongoing geomorphological and paleoclimatic research on the Late Quaternary landscape and climatic changes in the Taklamkan Desert of northwestern China, the largest sand sea of China in arid zone, and in the Hunshandake Sandy Land at the east part of the Asian mid-latitude desert belt under semiarid climate. We find out that the occurrence of tall sand dunes in the over 300,000 km2 large Taklamakan Sand Sea is closely related to the sites of intensive fluvial sedimentation and convergence zone of surface winds. In the case of Hunshandake, the dunes (although much smaller) mainly occur along the shorelines of the former lake basins, and sediment sources are generally limited because of open hydrological systems in the south and east portions of this desert. The sedimentological and geomorphological records suggest that the climate has changed between arid and less-arid conditions in both of these deserts during Late Quaternary. Under wetter conditions the Taklamakan acts as an important sink of sediments brought by rivers with headwaters in the Tibetan Plateau and Tianshan, while under more arid conditions it acts as an important global sediment source whose dust is transported not only to East Asia and Pacific but also to Greenland ice via westerlies. The Hunshandake has the same pattern of

  5. Palaeoecological and morphofunctional interpretation of bone mass increase: an example in Late Cretaceous shallow marine squamates.

    PubMed

    Houssaye, Alexandra

    2013-02-01

    Bone mass increase (BMI; i.e. osteosclerosis with possible additional pachyostosis) is characteristically displayed by many Late Cretaceous squamates that adapted to shallow marine environments-plesiopelvic mosasauroids, stem-ophidians and pachyophiids. A combined morphological and microanatomical analysis of vertebrae and, to a lesser extent, ribs of these fossil squamates provides new data about the distribution and variability of this osseous specialization in these taxa. Classical thin sections and third generation synchrotron microtomography and laminography were used for the microanatomical analysis. Following the explanation of the likely involvement of this specialization in the control of buoyancy, body trim and Carrier's constraint, new palaeoecological inferences and new hypotheses about the locomotor abilities and life environment of these organisms are produced. The taxa displaying BMI are considered to have undertaken long dives, hovering slowly and maintaining a horizontal trim, in shallow and protected water environments. Conversely, marine stem-ophidians deprived of this specialization are regarded as slow surface swimmers able to live in more open marine environments. This study highlights the importance of microanatomical data for palaeoecological studies. It also discusses the significance of the use of this specialization as a character in phylogenetic studies. PMID:22943660

  6. The last interglacial period at Guantanamo Bay, Cuba and an estimate of late Quaternary tectonic uplift rate in a strike-slip regime

    NASA Astrophysics Data System (ADS)

    Schweig, E. S.; Muhs, D. R.; Simmons, K. R.; Halley, R. B.

    2015-12-01

    Guantanamo Bay, Cuba is an area dominated by a strike-slip tectonic regime and is therefore expected to have very low Quaternary uplift rates. We tested this hypothesis by study of an unusually well preserved emergent reef terrace around the bay. Up to 12 m of unaltered, growth-position reef corals are exposed at about 40 sections examined around ˜40 km of coastline. Maximum reef elevations in the protected, inner part of the bay are ˜11-12 m, whereas outer-coast shoreline angles of wave-cut benches are as high as ˜14 m. Fifty uranium-series analyses of unrecrystallized corals from six localities yield ages ranging from ˜134 ka to ˜115 ka, when adjusted for small biases due to slightly elevated initial 234U/238U values. Thus, ages of corals correlate this reef to the peak of the last interglacial period, marine isotope stage (MIS) 5.5. Previously, we dated the Key Largo Limestone to the same high-sea stand in the tectonically stable Florida Keys. Estimates of paleo-sea level during MIS 5.5 in the Florida Keys are ~6.6 to 8.3 m above present. Assuming a similar paleo-sea level in Cuba, this yields a long-term tectonic uplift rate of 0.04-0.06 m/ka over the past ~120 ka. This estimate supports the hypothesis that the tectonic uplift rate should be low in this strike-slip regime. Nevertheless, on the southeast coast of Cuba, east of our study area, we have observed flights of multiple marine terraces, suggesting either (1) a higher uplift rate or (2) an unusually well-preserved record of pre-MIS 5.5 terraces not observed at Guantanamo Bay.

  7. Tectonic paleostress fields and structural evolution of the NW-Caucasus fold-and-thrust belt from Late Cretaceous to Quaternary

    NASA Astrophysics Data System (ADS)

    Saintot, Aline; Angelier, Jacques

    2002-11-01

    Eastern Black Sea Basin. Strong NNE-SSW to NE-SW compression characterises Late Eocene tectonism. The fold-and-thrust belt developed at this time as a result of the direct collision of the Shatsky Ridge with the Scythian Plate. A NE-SW extension followed the Late Eocene event, related to basin development around the newly formed fold belt. A WNW-ESE oblique contraction affected the belt during the early Miocene as the result of Arabian Plate convergence with the Caucasian system. The latest inferred event is a compressional regime, with NNW-SSE trending σ1 that is affecting the NW-Caucasus belt from Sarmatian times until the present. Under this oblique compression, the belt has deformed as in a dextral shear zone and the thrust surfaces have acquired lenticular shapes. This study highlights the occurrence of oblique movements in the NW-Caucasus area prior to and after the dominant Late Eocene compression. From the Late Cretaceous until the Eocene, the structural development of the NW-Caucasus was closely related to the evolution of the Eastern Black Sea Basin. From the Late Eocene until Quaternary times, it was rather related to the Arabia-Eurasia plate convergence.

  8. Late Quaternary reef growth history of Les Saintes submarine plateau: a key to constrain active faulting kinematics in Guadeloupe (FWI)

    NASA Astrophysics Data System (ADS)

    Leclerc, F.; Feuillet, N.; Deplus, C.; Cabioch, G.; Tapponnier, P.; LeBrun, J.; Bazin, S.; Beauducel, F.; Boudon, G.; Le Friant, A.; De Min, L.; Melezan, D.

    2012-12-01

    The damaging November 21 2004 earthquake (Mw 6.3) occurred on a large normal fault system offshore Les Saintes archipelago in Guadeloupe. To better constrain the seismic hazard related to this fault system, new data were acquired in 2009 and 2010 during the GWADASEIS and BATHYSAINTES cruises. Digital Elevation Models (DEM), with a horizontal resolution of 2.5 m, were calculated with the bathymetric data acquired at shallow depth on Les Saintes insular shelf. Together with seismic reflection profiles, this data makes it possible to identify and map the fault system and to understand its kinematics with respect to the plateau formation. The 15km wide, -45m deep drowned plateau of Les Saintes is composed of four coral terraces, down to 110 m bsl, piled-up on the Upper Pliocene to Quaternary Les Saintes volcanic centres. The shallowest terrace corresponds to a drowned Holocene reef system. Reef typical features, as double barriers, pinnacles, spurs and grooves, are well identified in the bathymetry. Seismic reflection profiles indicate that the Holocene terrace overlays Pleistocene ones. Geophysical data and reef growth modeling tend to show that the reef plateau has formed under subsidence conditions (~0.35 mm/yr) since Ionian ages, recording the main sea level highstands, before being drowned during the last sea level rise, around 11ka BP. The four terraces are crosscut by several NW-SE striking normal faults, which have scarps up to 8m. They offset them, the older, the more, inducing syntectonic sedimentation. The fault system extends from the northern plateau's edge to Les Saintes channel, toward Dominica, constituting the eastern side of Les Saintes graben. In the channel, the Roseau Fault, responsible for the 2004 earthquake, bounds the graben western side. The new data confirms its extent to the north, as the fault offsets the plateau's western cliff by several tens of meter, counter-slope like, dipping under Les Saintes islands and inducing a high seismic

  9. The evolution of a thermokarst-lake landscape: Late Quaternary permafrost degradation and stabilization in interior Alaska

    USGS Publications Warehouse

    Edwards, Mary E.; Grosse, Guido; Jones, Benjamin M.; McDowell, Patricia F.

    2016-01-01

    Thermokarst processes characterize a variety of ice-rich permafrost terrains and often lead to lake formation. The long-term evolution of thermokarst landscapes and the stability and longevity of lakes depend upon climate, vegetation and ground conditions, including the volume of excess ground ice and its distribution. The current lake status of thermokarst-lake landscapes and their future trajectories under climate warming are better understood in the light of their long-term development. We studied the lake-rich southern marginal upland of the Yukon Flats (northern interior Alaska) using dated lake-sediment cores, observations of river-cut exposures, and remotely-sensed data. The region features thick (up to 40 m) Quaternary deposits (mainly loess) that contain massive ground ice. Two of three studied lakes formed ~ 11,000–12,000 cal yr BP through inferred thermokarst processes, and fire may have played a role in initiating thermokarst development. From ~ 9000 cal yr BP, all lakes exhibited steady sedimentation, and pollen stratigraphies are consistent with regional patterns. The current lake expansion rates are low (0 to < 7 cm yr− 1 shoreline retreat) compared with other regions (~ 30 cm yr− 1 or more). This thermokarst lake-rich region does not show evidence of extensive landscape lowering by lake drainage, nor of multiple lake generations within a basin. However, LiDAR images reveal linear “corrugations” (> 5 m amplitude), deep thermo-erosional gullies, and features resembling lake drainage channels, suggesting that highly dynamic surface processes have previously shaped the landscape. Evidently, widespread early Holocene permafrost degradation and thermokarst lake initiation were followed by lake longevity and landscape stabilization, the latter possibly related to establishment of dense forest cover. Partial or complete drainage of three lakes in 2013 reveals that there is some contemporary landscape dynamism. Holocene landscape

  10. The Late Miocene Quaternary Antofalla volcanic complex, southern Puna, NW Argentina: Protracted history, diverse petrology, and economic potential

    NASA Astrophysics Data System (ADS)

    Richards, Jeremy P.; Ullrich, Thomas; Kerrich, Robert

    2006-04-01

    The Antofalla volcanic complex (AVC) is located on the southern Puna plateau of NW Argentina, ˜100 km east of the main axis of the Cordillera Occidental volcanic arc. It lies on the NW-SE Archibarca lineament, one of several transverse structures that cut across the Andes from Chile, and divert arc magmatism in SE-trending fingers across the Puna. 40Ar/ 39Ar dating of volcanic products from the AVC reveals a protracted magmatic history from 10.9 to ≤ 1.6 Ma. Initial volcanism was characterized by eruption of voluminous rhyolitic ignimbrites, deposited directly onto exposed crystalline basement and supracrustal sedimentary rocks. These rhyolites record significant geochemical evidence for crustal contamination, or derivation by crustal melting, which decreases upwards through the pyroclastic sequence. They were followed by extrusion of potassic lavas of the shoshonite-latite-trachydacite suite from 10.1 to 9.5 Ma. Subsequent magmatism (9.1-1.6 Ma) was of basaltic andesite-andesite-dacite composition, with localized, smaller volume, dacitic and rhyolitic ignimbrites. Monogenetic basaltic andesite cinder cones and lava flows were erupted in the Quaternary in response to a change to transtensional tectonics in the Puna. The volcanic sequence is interpreted to record the early development of a lower crustal MASH zone at ˜11 Ma, where mantle-derived arc magmas interacted extensively with felsic lower crustal rocks to produce evolved shoshonitic compositions, and crustal melts that erupted to form rhyolitic ignimbrites (common at this time throughout the Puna). After establishment of a steady-state MASH zone by ˜9 Ma, subsequent basaltic andesite-andesite magmas show less evidence of felsic crustal contamination, and may have developed largely by interaction with previous ultramafic-mafic fractionates of early magmas in the lower crust. More felsic dacitic magmas appear to have evolved largely by fractional crystallization from basaltic andesites and andesites, with

  11. Late Quaternary loess in northeastern Colorado: Part II - Pb isotopic evidence for the variability of loess sources

    USGS Publications Warehouse

    Aleinikoff, J.N.; Muhs, D.R.; Sauer, R.R.; Fanning, C.M.

    1999-01-01

    A new application of the Pb isotopic tracer technique has been used to determine the relative importance of different silt sources for late Wisconsin loess in the central Great Plains of eastern Colorado. Samples of the Peoria Loess collected throughout the study area contain K-feldspar derived from two isotopically and genetically distinct sources: (1) glaciogenic material from Early and Middle Proterozoic crystalline rocks of the Colorado province, and (2) volcaniclastic material from the Tertiary White River Group exposed on the northern Great Plains. Pb isotopic compositions of K-feldspar in loess from two dated vertical sections (at Beecher Island and Last Chance, Colorado) vary systematically, implying climatic control of source availability. We propose a model whereby relatively cold conditions promoted the advance of Front Range valley glaciers discharging relatively little glaciogenic silt, but strong winds caused eolian erosion of White River Group silt due to a decrease in vegetation cover. During warmer periods, valley glaciers receded and discharged abundant glaciogenic silt, while surfaces underlain by the White River Group were stabilized by vegetation. Isotopic data from eastern Colorado loess sections record two warm-cold-warm cycles during late Wisconsin time between about 21 000 and 11 000 radiocarbon yr B.P., similar to results from other studies in the United States and Greenland.

  12. Provenance and accommodation pathways of late Quaternary sediments in the deep-water northern Ionian Basin, southern Italy

    NASA Astrophysics Data System (ADS)

    Perri, Francesco; Critelli, Salvatore; Dominici, Rocco; Muto, Francesco; Tripodi, Vincenzo; Ceramicola, Silvia

    2012-12-01

    The northern Calabria along the southeastern coast of Italy provides a favorable setting in which to study complete transects from continental to deep-marine environments. The present northern Ionian Calabrian Basin is a wedge-top basin within the modern foreland-basin system of southern Italy. The Ionian margin of northern Calabria consists of a moderately developed fluvial systems, the Crati and Neto rivers, and diverse smaller coastal drainages draining both the Calabria continental block (i.e., Sila Massif) and the southern Apennines thrust belt (i.e., Pollino Massif). The main-channel sand of the Crati and Neto rivers is quartzofeldspathic with abundant metamorphic and plutonic lithic fragments (granodiorite, granite, gneiss, phyllite and sedimentary lithic fragments). Sedimentary lithic fragments were derived from Jurassic sedimentary successions of the Longobucco Group. The mud samples contain mostly phyllosilicates, quartz, calcite, feldspars and dolomite. Traces of gypsum are present in some samples. The I-S mixed layers, 10 Å-minerals (illite and micas), chlorite and kaolinite are the most abundant phyllosilicates, whereas smectite and chlorite/smectite mixed layers are in small amounts. The geochemical signatures of the muds reflect a provenance characterized by both felsic and mafic rocks with a significant input from carbonate rocks. Furthermore, the degree of source-area weathering was most probably of low intensity rather than moderately intense because CIA values for the studied mud samples are low. Extrapolation of the mean erosion budget from 1 to 25 Ma suggests that at least 5 to 8 km of crust have been removed from the Calabrian orogenic belt and deposited in the marine basins. The Calabrian microplate played an important role in the dynamic evolution of southern Italian fossil and modern basins, representing the key tectonic element of the entire orogenic belt.

  13. Influence of the Atlantic inflow and Mediterranean outflow currents on late Quaternary sedimentary facies of the Gulf of Cadiz continental margin

    USGS Publications Warehouse

    Nelson, C.H.; Baraza, J.; Maldonado, A.; Rodero, J.; Escutia, C.; Barber, J.H., Jr.

    1999-01-01

    The late Quaternary pattern of sedimentary facies on the Spanish Gulf of Cadiz continental shelf results from an interaction between a number of controlling factors that are dominated by the Atlantic inflow currents flowing southeastward across the Cadiz shelf toward the Strait of Gibraltar. An inner shelf shoreface sand facies formed by shoaling waves is modified by the inflow currents to form a belt of sand dunes at 10-20 m that extends deeper and obliquely down paleo-valleys as a result of southward down-valley flow. A mid-shelf Holocene mud facies progrades offshore from river mouth sources, but Atlantic inflow currents cause extensive progradation along shelf toward the southeast. Increased inflow current speeds near the Strait of Gibraltar and the strong Mediterranean outflow currents there result in lack of mud deposition and development of a reworked transgressive sand dune facies across the entire southernmost shelf. At the outer shelf edge and underlying the mid-shelf mud and inner shelf sand facies is a late Pleistocene to Holocene transgressive sand sheet formed by the eustatic shoreline advance. The late Quaternary pattern of contourite deposits on the Spanish Gulf of Cadiz continental slope results from an interaction between linear diapiric ridges that are oblique to slope contours and the Mediterranean outflow current flowing northwestward parallel to the slope contours and down valleys between the ridges. Coincident with the northwestward decrease in outflow current speeds from the Strait there is the following northwestward gradation of contourite sediment facies: (1) upper slope sand to silt bed facies, (2) sand dune facies on the upstream mid-slope terrace, (3) large mud wave facies on the lower slope, (4) sediment drift facies banked against the diapiric ridges, and (5) valley facies between the ridges. The southeastern sediment drift facies closest to Gibraltar contains medium-fine sand beds interbedded with mud. The adjacent valley floor

  14. Stable isotopes in yellow-bellied marmot (Marmota flaviventris) fossils reveal environmental stability in the late Quaternary of the Colorado Rocky Mountains

    NASA Astrophysics Data System (ADS)

    Reynard, Linda M.; Meltzer, David J.; Emslie, Steven D.; Tuross, Noreen

    2015-03-01

    High elevation plant and animal communities are considered extremely sensitive to environmental change. We investigated an exceptional fossil record of yellow-bellied marmot (Marmota flaviventris) specimens that was recovered from Cement Creek Cave (elev. 2860 m) and ranged in age from radiocarbon background circa 49.8 cal ka BP to ~ 1 cal ka BP. We coupled isotopic and radiocarbon measurements (δ18O, δD, δ15N, δ13C, and 14C) of bone collagen from individually-AMS dated specimens of marmots to assess ecological responses by this species to environmental change over time in a high elevation basin in the Rocky Mountains of southwestern Colorado, USA. We find little change in all four isotope ratios over time, demonstrating considerable environmental stability during periods when the marmots were present. The stable ecology and the apparent persistence of the small mammal community in the cave fauna throughout the late Quaternary are in marked contrast to the changes that occurred in the large mammal community, including local extirpation and extinction, at the end of the Pleistocene.

  15. Reconstruction of a complex late Quaternary glacial landscape in the Cordillera de Cochabamba (Bolivia) based on a morphostratigraphic and multiple dating approach

    NASA Astrophysics Data System (ADS)

    May, Jan-Hendrik; Zech, Jana; Zech, Roland; Preusser, Frank; Argollo, Jaime; Kubik, Peter W.; Veit, Heinz

    Although glacial landscapes have previously been used for the reconstruction of late Quaternary glaciations in the Central Andes, only few data exist for the Eastern Cordillera in Bolivia. Here, we present results from detailed morphostratigraphic mapping and new data of surface exposure dating (SED), optically stimulated luminescence (OSL), and radiocarbon dating ( 14C) from the Huara Loma Valley, Cordillera de Cochabamba (Bolivia). Discrepancies between individual dating methods could be addressed within the context of a solid geomorphic framework. We identified two major glaciations. The older is not well constrained by the available data, whereas the younger glaciation is subdivided into at least four major glacial stages. Regarding the latter, a first advance dated to ~ 29-25 ka occurred roughly contemporaneous with the onset of the global last glacial maximum (LGM) and was followed by a less extensive (re-)advance around 20-18 ka. The local last glacial maximum (LLGM) in the Huara Loma Valley took place during the humid lateglacial ~ 17-16 ka, followed by several smaller readvances until ~ 10-11 ka, and complete deglaciation at the end of the Early Holocene.

  16. Late quaternary geomorphology of the Great Salt Lake region, Utah, and other hydrographically closed basins in the western United States: A summary of observations

    NASA Technical Reports Server (NTRS)

    Currey, Donald R.

    1989-01-01

    Attributes of Quaternary lakes and lake basins which are often important in the environmental prehistory of semideserts are discussed. Basin-floor and basin-closure morphometry have set limits on paleolake sizes; lake morphometry and basin drainage patterns have influenced lacustrine processes; and water and sediment loads have influenced basin neotectonics. Information regarding inundated, runoff-producing, and extra-basin spatial domains is acquired directly from the paleolake record, including the littoral morphostratigraphic record, and indirectly by reconstruction. Increasingly detailed hypotheses regarding Lake Bonneville, the largest late Pleistocene paleolake in the Great Basin, are subjects for further testing and refinement. Oscillating transgression of Lake Bonneville began about 28,000 yr B.P.; the highest stage occurred about 15,000 yr B.P., and termination occurred abruptly about 13,000 yr B.P. A final resurgence of perennial lakes probably occurred in many subbasins of the Great Basin between 11,000 and 10,000 yr B.P., when the highest stage of Great Salt Lake (successor to Lake Bonneville) developed the Gilbert shoreline. The highest post-Gilbert stage of Great Salt Lake, which has been one of the few permanent lakes in the Great Basin during Holocene time, probably occurred between 3,000 and 2,000 yr B.P.

  17. Late Quaternary vegetation and climate history of the central Bering land bridge from St. Michael Island, western Alaska

    NASA Astrophysics Data System (ADS)

    Ager, Thomas A.

    2003-07-01

    Pollen analysis of a sediment core from Zagoskin Lake on St. Michael Island, northeast Bering Sea, provides a history of vegetation and climate for the central Bering land bridge and adjacent western Alaska for the past ≥30,000 14C yr B.P. During the late middle Wisconsin interstadial (≥30,000-26,000 14C yr B.P.) vegetation was dominated by graminoid-herb tundra with willows ( Salix) and minor dwarf birch ( Betula nana) and Ericales. During the late Wisconsin glacial interval (26,000-15,000 14C yr B.P.) vegetation was graminoid-herb tundra with willows, but with fewer dwarf birch and Ericales, and more herb types associated with dry habitats and disturbed soils. Grasses (Poaceae) dominated during the peak of this glacial interval. Graminoid-herb tundra suggests that central Beringia had a cold, arid climate from ≥30,000 to 15,000 14C yr B.P. Between 15,000 and 13,000 14C yr B.P., birch shrub-Ericales-sedge-moss tundra began to spread rapidly across the land bridge and Alaska. This major vegetation change suggests moister, warmer summer climates and deeper winter snows. A brief invasion of Populus (poplar, aspen) occurred ca.11,000-9500 14C yr B.P., overlapping with the Younger Dryas interval of dry, cooler(?) climate. During the latest Wisconsin to middle Holocene the Bering land bridge was flooded by rising seas. Alder shrubs ( Alnus crispa) colonized the St. Michael Island area ca. 8000 14C yr B.P. Boreal forests dominated by spruce ( Picea) spread from interior Alaska into the eastern Norton Sound area in middle Holocene time, but have not spread as far west as St. Michael Island.

  18. Late Quaternary depositional history, Holocene sea-level changes, and vertical crustal movement, southern San Francisco Bay, California

    USGS Publications Warehouse

    Atwater, Brian F.; Hedel, Charles W.; Helley, Edward J.

    1977-01-01

    Sediments collected for bridge foundation studies at southern San Francisco Bay, Calif., record estuaries that formed during Sangamon (100,000 years ago) and post-Wisconsin (less than 10,000 years ago) high stands of sea level. The estuarine deposits of Sangamon and post-Wisconsin ages are separated by alluvial and eolian deposits and by erosional unconformities and surfaces of nondeposition, features that indicate lowered base levels and oceanward migrations of the shoreline accompanying low stands of the sea. Estuarine deposits of mid-Wisconsin age appear to be absent, suggesting that sea level was not near its present height 30,000–40,000 years ago in central California. Holocene sea-level changes are measured from the elevations and apparent 14C ages of plant remains from 13 core samples. Uncertainties of ±2 to ±4 m in the elevations of the dated sea levels represent the sum of errors in determination of (1) sample elevation relative to present sea level, (2) sample elevation relative to sea level at the time of accumulation of the dated material, and (3) postdepositional subsidence of the sample due to compaction of underlying sediments. Sea level in the vicinity of southern San Francisco Bay rose about 2 cm/yr from 9,500 to 8,000 years ago. The rate of relative sea-level rise then declined about tenfold from 8,000 to 6,000 years ago, and it has averaged 0.1–0.2 cm/yr from 6,000 years ago to the present. This submergence history indicates that the rising sea entered the Golden Gate 10,000–11,000 years ago and spread across land areas as rapidly as 30 m/yr until 8,000 years ago. Subsequent shoreline changes were more gradual because of the decrease in rate of sea-level rise. Some of the sediments under southern San Francisco Bay appear to be below the level at which they initially accumulated. The vertical crustal movement suggested by these sediments may be summarized as follows: (1) Some Quaternary(?) sediments have sustained at least 100 m of

  19. Tracing late Quaternary tropical wetland dynamics in the Congo catchment using microbial biomarker records from deep sea fan sediments

    NASA Astrophysics Data System (ADS)

    Spencer-Jones, Charlotte Louise; Schefuβ, Enno; Wagner, Thomas; Handley, Luke; Talbot, Helen Marie

    2014-05-01

    Methane is a climatically active gas with a global warming potential 72 time that of CO2 over 20 years. Release of methane into the atmosphere has been suggested as a potential source of warming in palaeoclimate studies. This has implications for future climate as increased global temperatures could destabilise sources of sedimentary methane releasing it to the atmosphere. It is therefore important to establish the possible sinks of methane that could attenuate methane emissions. We present a high resolution record from the Congo deep sea fan (ODP 1075) of amino-bacteriohopanepolyols (amino-BHPs). The methanotrophic source of aminopentol, a biomarker for aerobic methane oxidation (AMO), in ODP 1075 is supported by compound specific δ13C isotope values of -41‰ for aminopentol precursors. High resolution intervals of isotope stages 10 to 13 (~500 to ~400 kyrs BP) confirm aminopentol to vary on glacial-interglacial timescales. High concentrations of amino-BHPs are recorded during warm, interglacial stages 11 and 13 with low concentrations of amino-BHPs during cold, glacial stages 10 and 12. This increase in AMO intensity (as suggested by aminopentol concentrations) during stages 11 and 13 is likely an imported signature from the Congo hinterland. Sediments analysed for amino-BHPs from floodplain wetlands show similar biomarker signatures as the marine sediments, suggesting a common source. Wetlands are important and widespread sub-environments in all large tropical river catchments. Their extent responds to fluctuations in humidity, which changes at glacial-interglacial and shorter time scales in response to the level of humidity. Humidity in the interior of tropical Africa has been shown to be driven by fluctuations in the difference in sea surface temperature (SST) between the subtropical and tropical South Atlantic (Schefuss et al., 2004). D-SST profiles based on UK 37 from the Angola (ODP 1082) and Congo basins (ODP 1077, Geob 1082) show an inverse relationship

  20. Logs of exploratory trenches through liquefaction features on late Quaternary terraces in the Obion River Valley, northwestern Tennessee

    USGS Publications Warehouse

    Rodbell, Donald T.; Bradley, Lee-Ann

    1993-01-01

    -12 earthquake series (Obermeier, 1989, Obermeier and others, 1990) and the probably development of similar features during previous large-magnitude seismic events (mb≥6.2, Nuttli, 1982) have been the basis for several attempts to document the history of paleoliquefaction. Haller and Crone (1986) found evidence of only one episode of sand-blow development in exploratory trenches in late Pleistocene alluvium in eastern Arkansas and concluded that this liquefaction event was probably associated with the 1811-12 earthquake series. Saucier (1989) reported evidence of three liquefaction events in the past approximately 1,000 yrs in an exploratory trench in eastern Arkansas. On the basis of the apparent absence of post-depositional erosion separating the three sand-blow deposits, Saucier (1989) concluded that they formed in a relatively short period of time, probably during the 1811-12 earthquake series. Similarly, Schweig and Marple (1991) found evidence of only recent (probably 1811-12) liquefaction in exploratory trenched on late Wisconsin braided-stream deposits in southeastern Missouri. Leffler and Wesnousky (1991) and Wesnousky and Leffler (written commun., 1991) examined tens of kilometers of recently excavated drainage ditches in late Wisconsin braided-stream deposits in eastern Arkansas and found no evidence for prehistorical liquefaction events during the last 10,000 yrs. In contrast, Saucier (1991) estimated an average recurrence interval about 470 yrs on the basis of historical ages of liquefaction in the NMSZ. The lack of similar evidence from other sites implies a prehistorical liquefaction-producing seismic event in southeastern Missouri that was considerably smaller than the 1811-12 earthquake series. The apparent absence of paleoliquefaction features in late Wisconsin fluvial deposits in the zone of most intense 1811-12 liquefaction indicates that the repeat time of large (mb≥7.0) seismic events in the NMSZ is at least 10,000 yrs (Saucier, 1991; Wesnousky and