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Alan L Deino - One of the best experts on this subject based on the ideXlab platform.
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Chronostratigraphy and age modeling of pleistocene drill cores from the olduvai basin tanzania olduvai gorge coring project
Palaeogeography Palaeoclimatology Palaeoecology, 2021Co-Authors: Alan L Deino, Ian G Stanistreet, Jackson K. Njau, Lindsay J. Mchenry, Harald Stollhofen, Clifford W Heil, John W King, Joshua MwankundaAbstract:Abstract The Olduvai Gorge Coring Project drilled a total of 611.72 m of core (575.48 m recovered) of mostly fluvio-lacustrine and fan-delta volcaniclastic Pleistocene strata at three sites in the Olduvai Basin, Tanzania, in 2014. We have developed a chronostratigraphic framework for three of the cores based on 40Ar/39Ar dating of core and outcrop volcanic and volcaniclastic units, core paleomagnetic stratigraphy, and tephrochemical correlation between cores and from core to outcrop. This framework is then used to constrain Bayesian stratigraphic age models which permit age estimates for desired core levels with realistic confidence intervals. The age models reveal that the deepest core level reached at 245 mbs is ~2.24 Ma, ~210 kyr older than the oldest strata exposed at Olduvai Gorge. Strata net accretion rates in this early phase of basin history were relatively rapid (57–69 cm/kyr), but decreased within ~250 kyr to ~15 cm/kyr in Lower Bed I. Rates rebounded partially in Upper Bed I, but subsequently declined to
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40ar 39ar dating of bed i olduvai gorge tanzania and the chronology of early pleistocene climate change
Journal of Human Evolution, 2012Co-Authors: Alan L DeinoAbstract:Abstract 40 Ar/ 39 Ar dating of tuffs and lavas of the late Pleistocene volcanic and sedimentary sequence of Olduvai Gorge, north-central Tanzania, provides the basis for a revision of Bed I Chronostratigraphy. Bed I extends from immediately above the Naabi Ignimbrite at 2.038 ± 0.005 Ma to Tuff IF at 1.803 ± 0.002 Ma. Tuff IB, a prominent widespread marker tuff in the basin and a key to understanding hominin evolutionary chronologies and paleoclimate histories, has an age of 1.848 ± 0.003 Ma. The largest lake expansion event in the closed Olduvai lake basin during Bed I times encompassed the episode of eruption and emplacement of this tuff. This lake event is nearly coincident with the maximum precessional insolation peak of the entire Bed I/Lower Bed II interval, calculated from an astronomical model of the boreal summer orbital insolation time-series. The succeeding precessional peak also apparently coincides with the next youngest expansion of paleo-Lake Olduvai. The extreme wet/dry climate shifts seen in the upper part of Bed I occur during an Earth-orbital eccentricity maximum, similar to episodic lake expansions documented elsewhere in the East African Rift during the Neogene.
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40ar 39ar dating paleomagnetism and tephrochemistry of pliocene strata of the hominid bearing woranso mille area west central afar rift ethiopia
Journal of Human Evolution, 2010Co-Authors: Alan L Deino, Gary R Scott, Beverly Z Saylor, Mulugeta Alene, Joshua D Angelini, Yohannes HaileselassieAbstract:Abstract 40 Ar/ 39 Ar dating of tuffs and mafic lavas, tephra geochemistry, and paleomagnetic reversal stratigraphy have been used to establish the Chronostratigraphy of the Pliocene hominid-bearing fossiliferous succession at Woranso-Mille, a paleontological study area in the western part of the central Afar region of Ethiopia. The succession in the northwestern part of the study area ranges in 40 Ar/ 39 Ar age from 3.82–3.570 Ma, encompassed by paleomagnetic subchron C2Ar (4.187–3.596 Ma). One of the major tuff units, locally named the Kilaytoli tuff, is correlative on the basis of age and geochemistry to the Lokochot Tuff of the Turkana Basin. A hominid partial skeleton (KSD-VP-1) was found in strata whose precise stratigraphic position and age is still under investigation, but is believed to correspond to the later part of this interval. Woranso-Mille fills a significant gap in the fossil record of northeastern Africa at the time of the lower to middle Pliocene transition, when many extant species lineages of African fauna were established.
Markus Fuchs - One of the best experts on this subject based on the ideXlab platform.
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luminescence based loess Chronostratigraphy of the upper palaeolithic site krems wachtberg austria
Quaternary International, 2014Co-Authors: Johanna Lomax, Markus Fuchs, Frank Preusser, Markus FiebigAbstract:Abstract The loess section Krems-Wachtberg (Lower Austria) is well known for its Upper Palaeolithic find layer, which contains a double and a single infant burial. The layer containing the grave (archaeological horizon AH 4.4) was dated to 26,580 ± 160 14 C BP ( Einwogerer et al., 2006 ), corresponding to ca. 31 ka cal BP and is embedded in an 8 m thick loess sequence. In order to provide a Chronostratigraphy of the entire section, 38 samples for luminescence dating were taken at high resolution from below and above the find layer. The samples were dated using the quartz coarse grain fraction, the quartz fine grain fraction and/or the polymineral fine grain fraction. The resulting ages are in correct chronostratigraphic order and, in case samples were measured with different protocols, agree within errors with each other and with the radiocarbon age of the find layer. The polymineral fine grain ages are systematically slightly lower than the quartz ages, although no fading could be detected in laboratory experiments. Loess deposition at the site commenced ca. 40 ka ago and reaches up to ca. 22 ka. The ages indicate nearly continuous loess sedimentation throughout this time span. Short breaks in sedimentation probably exist but cannot be resolved due to the uncertainties of luminescence ages.
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holocene moist period recorded by the Chronostratigraphy of a lake sedimentary sequence from lake tangra yumco on the south tibetan plateau
Quaternary Geochronology, 2012Co-Authors: Hao Long, Markus Fuchs, Zhongping Lai, Peter Frenzel, Torsten HaberzettlAbstract:Abstract Palaeolimnological studies together with geomorphological investigations of exposed lacustrine sections on the Tibetan Plateau provided valuable palaeoclimate records. Radiocarbon dating is the most commonly used method for establishing chronologies of lake sediments. However, 14 C dating of such sediments could be problematic due to the lack of organic matter or a reservoir effect, which commonly appears in radiocarbon ages of lacustrine sediments from the Tibetan Plateau. OSL dating is an alternative for dating the lake sediments and also provides the opportunity to independently test radiocarbon chronologies. The current study tries to compare OSL and 14 C dating results in order to evaluate the reservoir effect of 14 C dating, and then based on quartz OSL dating and stratigraphic analysis, to construct the Chronostratigraphy of a lacustrine sedimentary sequence (TYC section), an offshore profile from Tangra Yumco lake on the southern Tibetan Plateau. Results suggest that: (1) it is possible to obtain robust OSL age estimates for these lake sediments and the OSL ages of the three samples range from ca. 7.6 ka to ca. 2.3 ka; (2) The discrepancy between the OSL and 14 C ages is ca. 4–5 ka, which possibly results from the age overestimate of 14 C dating due to a reservoir effect in the studied lake; (3) the Chronostratigraphy of TYC section and sedimentological environmental analysis show a large lake with a lake level distinctively above the present during ca. 7.6–2.7 ka indicating a wet mid-Holocene in the study area.
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chronology of the last climatic cycle upper pleistocene of the surduk loess sequence vojvodina serbia
Boreas, 2008Co-Authors: Markus Fuchs, Pierre Antoine, Denisdidier Rousseau, Caroline Gauthier, Slobodan B. Marković, Christine Hatté, L ZoellerAbstract:The Surduk loess section in Serbia provides a 20 m thick pedosedimentary record of the last interglacial–glacial climatic cycle (Upper Pleistocene). Based on optical dating, a Chronostratigraphy could be established for the last climatic cycle, yielding the first numerical ages of a loess record from the middle Danube basin. Infrared-stimulated luminescence (IR-OSL) dating has been applied to the polymineral silt fraction using a multiple aliquot additive-dose protocol to determine the equivalent dose (DE). Within error limits, all age estimates are in stratigraphic order. Owing to the application of shine-plateau tests, the samples showed no evidence of insufficient bleaching. The Surduk loess section comprises three major periods of soil formation. Based on the IR-OSL Chronostratigraphy, the lowermost pedocomplex is attributed to the Last Interglacial and to the Early Glacial (Marine Isotope Stage – MIS 5e to 5a). The middle part of the section exhibits a succession of weakly developed brown soils and a humic horizon, named 'Surduk soil', formed during MIS 3. On top of the section, recent soil formation is related to the Holocene. Thick loess deposits are preserved between these palaeosols and are attributed to the Lower and Upper Pleniglacials (MIS 4 and 2), respectively. Estimated mean sedimentation rates are 0.1–0.2 mm/yr for the last glacial cycle, with a strong increase to 0.6 mm/yr with onset of the Pleniglacial.
Joshua Mwankunda - One of the best experts on this subject based on the ideXlab platform.
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Chronostratigraphy and age modeling of pleistocene drill cores from the olduvai basin tanzania olduvai gorge coring project
Palaeogeography Palaeoclimatology Palaeoecology, 2021Co-Authors: Alan L Deino, Ian G Stanistreet, Jackson K. Njau, Lindsay J. Mchenry, Harald Stollhofen, Clifford W Heil, John W King, Joshua MwankundaAbstract:Abstract The Olduvai Gorge Coring Project drilled a total of 611.72 m of core (575.48 m recovered) of mostly fluvio-lacustrine and fan-delta volcaniclastic Pleistocene strata at three sites in the Olduvai Basin, Tanzania, in 2014. We have developed a chronostratigraphic framework for three of the cores based on 40Ar/39Ar dating of core and outcrop volcanic and volcaniclastic units, core paleomagnetic stratigraphy, and tephrochemical correlation between cores and from core to outcrop. This framework is then used to constrain Bayesian stratigraphic age models which permit age estimates for desired core levels with realistic confidence intervals. The age models reveal that the deepest core level reached at 245 mbs is ~2.24 Ma, ~210 kyr older than the oldest strata exposed at Olduvai Gorge. Strata net accretion rates in this early phase of basin history were relatively rapid (57–69 cm/kyr), but decreased within ~250 kyr to ~15 cm/kyr in Lower Bed I. Rates rebounded partially in Upper Bed I, but subsequently declined to
Thomas Westerhold - One of the best experts on this subject based on the ideXlab platform.
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late miocene to holocene high resolution eastern equatorial pacific carbonate records stratigraphy linked by dissolution and paleoproductivity
Climate of The Past, 2019Co-Authors: Mitchell W Lyle, Anna Joy Drury, Jun Tian, Roy H Wilkens, Thomas WesterholdAbstract:Abstract. Coherent variation in CaCO3 burial is a feature of the Cenozoic eastern equatorial Pacific. Nevertheless, there has been a long-standing ambiguity in whether changes in CaCO3 dissolution or changes in equatorial primary production might cause the variability. Since productivity and dissolution leave distinctive regional signals, a regional synthesis of data using updated age models and high-resolution stratigraphic correlation is an important constraint to distinguish between dissolution and production as factors that cause low CaCO3 . Furthermore, the new Chronostratigraphy is an important foundation for future paleoceanographic studies. The ability to distinguish between primary production and dissolution is also important to establish a regional carbonate compensation depth (CCD). We report late Miocene to Holocene time series of XRF-derived (X-ray fluorescence) bulk sediment composition and mass accumulation rates (MARs) from eastern equatorial Pacific Integrated Ocean Drilling Program (IODP) sites U1335, U1337, and U1338 and Ocean Drilling Program (ODP) site 849, and we also report bulk-density-derived CaCO3 MARs at ODP sites 848, 850, and 851. We use physical properties, XRF bulk chemical scans, and images along with available Chronostratigraphy to intercorrelate records in depth space. We then apply a new equatorial Pacific age model to create correlated age records for the last 8 Myr with resolutions of 1–2 kyr. Large magnitude changes in CaCO3 and bio- SiO2 (biogenic opal) MARs occurred within that time period but clay deposition has remained relatively constant, indicating that changes in Fe deposition from dust is only a secondary feedback to equatorial productivity. Because clay deposition is relatively constant, ratios of CaCO3 % or biogenic SiO2 % to clay emulate changes in biogenic MAR. We define five major Pliocene–Pleistocene low CaCO3 % (PPLC) intervals since 5.3 Ma. Two were caused primarily by high bio- SiO2 burial that diluted CaCO3 (PPLC-2, 1685–2135 ka, and PPLC-5, 4465–4737 ka), while three were caused by enhanced dissolution of CaCO3 (PPLC-1, 51–402 ka, PPLC-3, 2248–2684 ka, and PPLC-4, 2915–4093 ka). Regional patterns of CaCO3 % minima can distinguish between low CaCO3 caused by high diatom bio- SiO2 dilution versus lows caused by high CaCO3 dissolution. CaCO3 dissolution can be confirmed through scanning XRF measurements of Ba. High diatom production causes lowest CaCO3 % within the equatorial high productivity zone, while higher dissolution causes lowest CaCO3 percent at higher latitudes where CaCO3 production is lower. The two diatom production intervals, PPLC-2 and PPLC-5, have different geographic footprints from each other because of regional changes in eastern Pacific nutrient storage after the closure of the Central American Seaway. Because of the regional variability in carbonate production and sedimentation, the carbonate compensation depth (CCD) approach is only useful to examine large changes in CaCO3 dissolution.
Jackson K. Njau - One of the best experts on this subject based on the ideXlab platform.
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Chronostratigraphy and age modeling of pleistocene drill cores from the olduvai basin tanzania olduvai gorge coring project
Palaeogeography Palaeoclimatology Palaeoecology, 2021Co-Authors: Alan L Deino, Ian G Stanistreet, Jackson K. Njau, Lindsay J. Mchenry, Harald Stollhofen, Clifford W Heil, John W King, Joshua MwankundaAbstract:Abstract The Olduvai Gorge Coring Project drilled a total of 611.72 m of core (575.48 m recovered) of mostly fluvio-lacustrine and fan-delta volcaniclastic Pleistocene strata at three sites in the Olduvai Basin, Tanzania, in 2014. We have developed a chronostratigraphic framework for three of the cores based on 40Ar/39Ar dating of core and outcrop volcanic and volcaniclastic units, core paleomagnetic stratigraphy, and tephrochemical correlation between cores and from core to outcrop. This framework is then used to constrain Bayesian stratigraphic age models which permit age estimates for desired core levels with realistic confidence intervals. The age models reveal that the deepest core level reached at 245 mbs is ~2.24 Ma, ~210 kyr older than the oldest strata exposed at Olduvai Gorge. Strata net accretion rates in this early phase of basin history were relatively rapid (57–69 cm/kyr), but decreased within ~250 kyr to ~15 cm/kyr in Lower Bed I. Rates rebounded partially in Upper Bed I, but subsequently declined to