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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]

Graphical abstract Highlights • Detailed 15.3–1.8 Ma clay elemental geochemistry records for the northeastern Qaidam Basin are presented. • Long-term and persistent weakening of the chemical weathering intensity has occurred since the Middle Miocene. • Global cooling-related drying played a key role in the chemical weathering intensity. • Miocene uplift of the northern Tibetan Plateau might exert some influence on the weakened chemical weathering intensity at 12–8 Ma. Abstract Cenozoic basin sediments around the Tibetan Plateau are valuable archives that can be used to reveal long-term interactions among tectonics, climate and weathering. However, the reconstruction of silicate weathering histories in this tectonically active region is consistently hindered by the presence of frequently embedded conglomerate and sandstone in the long sedimentary sequences. Here, we present detailed geochemical compositions of the clay components of the sediments in the Huaitoutala section (ca. 15.3–1.8 Ma) of the northeastern Qaidam Basin to reconstruct the chemical weathering history of the catchment since the Middle Miocene. Major element ratio proxies reveal evidence of four stages of change: from ca. 15.3 to 12.6 Ma, in which the clay components are characterized by relatively high Chemical Index of Alteration (CIA) values (75–88, average = 81) but low mobile/immobile oxide ratios (e.g., K 2 O/Al 2 O 3 , Na 2 O/Al 2 O 3 and CaO/Al 2 O 3), thus indicating the occurrence of intense chemical weathering conditions; from ca. 12.6 to 6.6 Ma, in which decreasing CIA values, together with increasing mobile/immobile oxide ratios, suggesting that a long-term decrease in silicate weathering intensity occurred in the source area; from 6.6 to 2.6 Ma, in which the clay components in the sediments exhibit persistently low CIA values (66–81, average = 76.8) and high oxide ratios, which are indicative of mild to moderate chemical weathering; and since 2.6 Ma, in which the CIA values (64–80, average = 75.5) have continued to decrease with increasing oxide ratios, thus reflecting mild chemical weathering conditions. The geochemical proxy records demonstrate that the intensity of chemical weathering has continually decreased and that the Qaidam Basin has experienced continuous aridification since ca. 12.6 Ma. We suggest that Middle-Miocene global cooling-related drying has exerted a significant influence on the trend of decreasing chemical weathering intensity since ca. 12.6 Ma. In addition, the Late Cenozoic rapid uplift and exhumation of the NE Tibetan Plateau could have limited the time that the silicate rocks were exposed in the weathering profile prior to the deposition, which may have led to their weakened intensity of chemical weathering. [ABSTRACT FROM AUTHOR]