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This study focuses on the concentration of major and trace elements in the diluted acetic acid-soluble fraction of SG-1 core lacustrine sediments from the western Qaidam Basin (Tibetan Plateau) in order to explore the potential of applying bulk carbonate analysis to tracing paleolake evolution and climate change. The SG-1 core sediments are considered highly suited to the exploration of the paleoenvironmental significance of bulk carbonate geochemistry, because most carbonates in the core are authigenic in origin. Based on a principal component analysis of the elemental composition of diluted acetic acid leachate, four major components with distinct characteristics have been extracted, accounting for ~ 80% of the total variance. The first and most important component is associated with a high positive loading of Mn, P, Y, Sc and rare earth elements (REE); the second component is characterized by a high positive loading of Ca, Sr, and U; the third component displays a high negative loading of Mg, Li, and B; and the fourth component is associated with a relatively high positive loading of Fe, V and Cr. After considering the geochemical behavior of these element assemblies during acid leaching, we have concluded that these four components contain information indicative of watershed climate conditions, carbonate precipitation, lake water salinity and iron oxide content, respectively. Reconstructions of watershed climate change and paleolake evolution using the component scores are comparable to those reconstructed from other independent proxy records, indicating a long-term trend of lake shrinkage and climatic drying since ~ 2.7 Ma with abrupt drying events at ~ 2.5 Ma, ~ 1.8 Ma, ~ 1.2 Ma and ~ 0.6 Ma. Our results suggest that lake carbonates bear more information about watershed climate and lake evolution than expected, and that occurrences of some elements, in particular trace elements, in the diluted acetic acid leachate are not solely and necessarily linked to carbonate minerals. [ABSTRACT FROM AUTHOR]

Abstract: Phosphorus (P) provides an important biologically limiting nutrient in lake ecosystems, and its concentrations furnish significant information on lake nutrient status, climatic change, and landscape development within a drainage area. This study explores the potential of calcium-bound P and iron-bound P in calcareous lacustrine sediments to reveal variations of the paleolake nutrient status and its related climatic changes. Data come from the nearly 1000-m long core (SG-1) from the western Qaidam Basin (NE Tibetan Plateau), which has been well-dated by paleomagnetism to between 2.77 and 0.1 Ma. Calcium-bound P and iron-bound P make up the two most frequent phases of inorganic phosphorus pools in the calcareous sediment. This study compares the variations of calcium-bound P and iron-bound P with the independent proxy for biologic production proxy Total Organic Carbon (TOC) as well as a climatic proxy for lake level fluctuation from the borehole. Those results indicate that calcium-bound P responds sensitively to paleolake nutrients and climatic changes, while the iron-bound P responds to more complex factors, more specific, to the content of iron oxides. Variations of the calcium-bound P in the core SG-1 show a long-term, stepwise decrease, with shifts at ∼2.5 Ma, 1.8 Ma, 1.2 Ma, and 0.6 Ma, indicating a long-term stepwise decrease of the paleolake nutrient supply in the drainage. This suggests that the ecologic systems experienced a long-term deterioration, and the climate in central Asia became increasingly arid since after the late Pliocene. [Copyright &y& Elsevier]

• The late Cretaceous–early Eocene paleoclimate of the Jianghan Basin was studied. • The salinity of the paleolake was mainly controlled by climate change. • The temporal differentiation of the evaporite deposits resulted from tectonics. • The widespread evaporites indicate an extremely arid climate during the Paleocene. • The climate became semi-humid during the early Eocene. The Jianghan Basin, Central China, contains a thick, continuous sequence of early Cenozoic evaporite-bearing deposits that provide a wealth of information about early Cenozoic climate change and evaporites accumulation in East Asia. However, the paleoclimatic history of the basin and its effect on the evaporites are largely unknown. We obtained a deep drill core (SKD1, 2346.5 m long) from the late Cretaceous to early Eocene evaporite-bearing deposits in the Jianghan Basin. Detailed analyses of the lithofacies, mineralogy and geochemistry of the core indicate that salinization and deepening of the lake occurred (corresponding to the Yuyang Formation to the lower Xingouzui Formation), followed by desalting and shallowing (corresponding to the upper Xingouzui Formation). Reconstruction of the spatiotemporal evolution of the evaporites in the Jiangling depression suggests a transition from semi-arid conditions in the late Cretaceous to extremely arid conditions in the initial stage of the Eocene. The climate then became semi-humid during the deposition of the upper Xingouzui Formation, indicating a monsoon or monsoon-like climate in East Asia during the early Eocene. The southward migration of the depocenter of the Jiangling depression, coupled with a warm and extremely arid climate, resulted in the precipitation of evaporites during the accumulation of the upper Shashi Formation and the lower Xingouzui Formation. These results indicate great potential for identifying potash resources within the subsag in the southern Jiangling depression. [ABSTRACT FROM AUTHOR]