TY - JOUR A1 - Mischke, Steffen A1 - Lai, Zhongping A1 - Zhang, Chengjun T1 - Re-assessment of the paleoclimate implications of the Shell Bar in the Qaidam Basin, China JF - Journal of paleolimnolog N2 - The Shell Bar in the Qaidam Basin, China, is a prominent geological feature composed of millions of densely packed Corbicula shells. Since the mid 1980s, it has been regarded as evidence for existence of a large lake during Marine Isotope Stage (MIS) 3 in the presently hyper-arid Qaidam Basin. Early studies suggested the bivalve shells accumulated at the shore of a large lake, whereas more recent work led to the conclusion that the Shell Bar was formed within a deeper water body. Based on our re-assessment of sediments and fossils from the Shell Bar, investigation of exposed fluvio-lacustrine sections upstream of the Shell Bar and study of nearby modern streams, we infer that the Shell Bar represents a stream deposit. Corbicula is a typical stream-dweller around the world. Preservation of Corbicula shells of different sizes, as well as occurrence of many articulated shells, provide evidence against post-mortem transport and accumulation along a lake shore. Additionally, the SE-NW alignment of the Shell Bar is similar to modern intermittent stream beds in its vicinity and corresponds to the present-day slope towards the basin centre further NW, and furthermore, the predominantly sandy sediments also indicate that the Shell Bar was formed in a stream. Abundant ostracod shells in the Shell Bar sediments originated from stream-dwelling species that are abundant in modern streams in the vicinity of the Shell Bar, or in part from fluvio-lacustrine sediments exposed upstream of the Shell Bar, as a result of erosion and re-deposition. Deflation of alluvial fine-grained sediments in the Shell Bar region and protection of the stream deposits by the large and thick-walled Corbicula shells reversed the former channel relief and yielded the modern exposure, which is a prominent morphological feature. Occurrence of Corbicula shells in the Qaidam Basin indicates climate was apparently warmer than present during the formation of the Shell Bar because Corbicula does not live at similar or higher altitudes in the region today. Because the Shell Bar is no longer considered a deposit formed within a lake, its presence does not indicate paleoclimate conditions wetter than today. KW - Qaidam Basin KW - Tibetan Plateau KW - Late Pleistocene KW - Corbicula KW - Ostracoda KW - Taphonomy Y1 - 2014 U6 - https://doi.org/10.1007/s10933-012-9674-6 SN - 0921-2728 SN - 1573-0417 VL - 51 IS - 2 SP - 179 EP - 195 PB - Springer CY - Dordrecht ER - TY - JOUR A1 - Mischke, Steffen A1 - Almogi-Labin, Ahuva A1 - Al-Saqarat, Bety A1 - Rosenfeld, Arik A1 - Elyashiv, Hadar A1 - Boomer, Ian A1 - Stein, Mordechai A1 - Lev, Lilach A1 - Ito, Emi T1 - An expanded ostracod-based conductivity transfer function for climate reconstruction in the Levant JF - Quaternary science reviews : the international multidisciplinary research and review journal N2 - We present the first modern calibration dataset linking ostracod assemblage composition to water chemistry, and other site-specific variables, in the hydrologically and geopolitically sensitive southern Levant region. A total of 42 ostracod taxa were recorded from the 178 sampled sites in Israel and Jordan. Ilyocypris spp., Heterocypris salina and Cypridopsis vidua are the most abundant taxa. Species strictly confined to freshwater conditions are Prionocypris zenkeri, Gomphocythere ortali and Prionocypris olivaceus. In contrast, H. sauna, Bradleytriebella lineata and Cyprideis torosa show high frequencies in brackish waters (waters with higher conductivity). Humphcypris subterranea, G. ortali, P. olivaceus and Cypridopsis elongata apparently prefer flowing waters. Specific conductivity optima and tolerance ranges were calculated for the recorded ostracod species and may be used for the palaeoenvironmental assessment of fossil ostracod assemblages. In addition, a transfer-function for quantitative specific conductivity estimation based on 141 samples was established with weighted averaging partial least squares regression (WA-PLS). The resulting coefficient of determination r(2) between observed and predicted conductivity values (0.72) and the root-mean-square error of prediction (RMSEP) in % gradient length (13.1) indicate that conductivity may be reliably estimated from ostracod assemblage data. The transfer function was first applied to last glacial ostracod assemblage data from an archaeological trench in the Sea of Galilee (northern Israel). Relatively large conductivity fluctuations between ca 1 and 7 mS cm(-1) were inferred for the period 24-20 cal ka BP. In addition, four episodes of freshwater influx near the site of the trench were identified from the presence of shells of freshwater and stream-dwelling species intermingled with very abundant shells of Cyprideis torosa. The results of our study allow a better use of Quaternary ostracods from the Levant as palaeoenvironmental indicators of water-body types and past conductivity levels and will contribute to a better understanding of Quaternary environmental and climate change in the Levant. (C) 2014 Elsevier Ltd. All rights reserved. KW - Ostracoda KW - Transfer function KW - Conductivity KW - Salinity KW - Near East KW - Sea of Galilee KW - Ohalo Site Y1 - 2014 U6 - https://doi.org/10.1016/j.quascirev.2014.04.004 SN - 0277-3791 VL - 93 SP - 91 EP - 105 PB - Elsevier CY - Oxford ER -