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Terrestrial silicate weathering records from the tectonically active Tibetan Plateau are crucial to explore the interactions among climate change, tectonic uplift and chemical weathering during the Cenozoic. However, the complex sedimentary facies changes and frequent occurrence of coarse lithologies related to intense tectonic uplift of the Tibetan Plateau have largely limited the reliability of bulk chemical weathering indexes to reveal the silicate weathering history. Here, we present detailed records of clay minerals and geochemical compositions from clay-sized (< 2 μm) sediments collected from the well-dated Huaitoutala section (ca. 15.3–1.8 Ma) in the NE Qaidam Basin to reconstruct the chemical weathering history of the NE Tibetan Plateau during the late Cenozoic. The relatively high (illite–smectite mixed layers + smectite)/(chlorite + illite) ratio indicates a strong silicate weathering intensity from 15.3 to 12.6. Ma, while a continuous decrease in this ratio since 12.6 Ma reflects a long-term decreasing intensity of silicate weathering. By comparing the clay mineral records with the climatic reconstruction and the tectonic events in the NE Tibetan Plateau, the results reveal that middle Miocene global cooling-related drying exerted a significant influence on the decreasing weathering intensity since ca. 12.6 Ma. Furthermore, the late Cenozoic episodic and persistent uplift of the NE Tibetan Plateau may have exerted an additional influence on the long-term decrease in weathering intensity. Specifically, the dramatic fluctuation in the silicate weathering intensity during ∼11–9.6 Ma is mainly due to uplift-induced provenance changes. Moreover, the fluctuating increase in the silicate weathering intensity during ∼8–5 Ma may have been caused by intensified East Asian summer monsoon precipitation. Our study suggests that both climate change and tectonic deformation controlled the chemical weathering intensity in the NE Tibetan Plateau during the late Cenozoic. • Detailed 15.3–1.8 Ma clay minerals records from the northeastern Qaidam Basin. • Long-term continuous weakening of silicate weathering intensity since 12.6 Ma. • Global cooling-related drying mainly caused weakening of silicate weathering. • Uplift-induced provenance change influenced weathering proxy during 11–9.6 Ma. • Increase in silicate weathering intensity during ∼8–5 Ma caused by monsoon rainfall. [ABSTRACT FROM AUTHOR]

The uplift of the northern Tibetan Plateau (TP) has long been regarded as one of major factors accounting for both the enhanced process of aridification recorded in central Asia and the shifts in the Asian monsoonal circulations that are known to have occurred at approximately 8 Ma. Until now, there have been few sedimentary records reported on which can directly, and in an integrated fashion, shed light on the region's tectonic and climate regimes. This can be largely attributed to the fact that the influence exerted by the presence of source materials and subsequent sedimentary sorting in this tectonically active region would be likely to bias significantly any paleoclimatic interpretation of silicate-derived proxies. Based on detailed investigations of strontium (Sr) distributions revealed by multi-step leaching in a fluvial sequence from the Linxia Basin which includes paleosols, we reconstructed the long-term late Miocene regional climatic and environmental changes likely to have occurred on the northeastern TP from 12.1 to 5.2 Ma. We investigated Sr-related proxies in two typical paleosol profiles to constrain Sr mobility in paleosol weathering, and, thus, to further prompt the interpretation of Sr-related proxies along the whole section. We would suggest that carbonate-derived Sr concentrations and Sr/Ca ratios are suitable proxies for tracing regional climate change associated with weathering and pedogenesis; together, they exhibit weakened chemical weathering intensity and pedogenesis at ~ 8.6 Ma. The concomitant appearance of immature sediments through poor sedimentary sorting revealed by silicate-derived Rb/Sr, 87 Sr/ 86 Sr and Eu anomaly (Eu/Eu*) alongside a sharp increase in sedimentation rates noted at this time suggests that it was indeed tectonic uplift that principally controlled the dramatic climatic and environmental changes. This multi-proxy record of concomitant tectonic uplift and climate change in the Linxia Basin provides direct geological evidence for uplift driven climate change in the northeastern TP region. [ABSTRACT FROM AUTHOR]

Late Cenozoic changes in chemical weathering and the dust cycle in response to the regional aridification and global cooling in the tectonically active northern Tibetan Plateau is an intriguing issue, although it remains poorly understood. The change in the 87Sr/86Sr ratio of basin water is linked to variations in the overall input of various Sr sources with different 87Sr/86Sr ratios, and analyses of such changes can be a useful tool for revealing changes in regional lithology, weathering regimes and the dust cycle linked to tectonics and climate. In this study, we collected fossil shells of ostracods and gastropods from the Miocene Dahonggou section to reconstruct the paleolake water 87Sr/86Sr ratio from 14.8 Ma to 11.1 Ma in the northern Qaidam Basin on the northeastern Tibetan Plateau. The reconstructed paleolake water 87Sr/86Sr ratios based on fossil shells and bulk carbonates from sediments display a coincident and stable 87Sr/86Sr ratio of approximately 0.7115, which did not show any detectable change in response to the enhanced aridification since ~13 Ma as inferred by the ostracod assemblage and its stable carbon and oxygen isotopes. The results indicate that the Sr influx regime from various sources did not change significantly during the aridification processes ~13 Ma, which may have been caused by a less detectable change in proportion of silicate versus carbonate weathering, and/or an overwhelming Sr source (e.g., extrabasinal eolian dust) that occurred from 14.8 Ma to 11.1 Ma. Further, the 87Sr/86Sr ratios of modern lake water and river sand carbonates in the study region are significantly higher, approximately ≥0.001, than those of the Miocene lake water. This observation can be explained by two possible mechanisms that need to be tested in the future: 1) given a Miocene Sr input regime that is similar to today, a large contribution from some extrabasinal Sr source (e.g., eolian dust) with a much lower 87Sr/86Sr ratio is expected to have prevailed from 14.8 Ma to 11.1 Ma but is absent in the modern setting or 2) given a Miocene Sr input regime that could yield an overall lower lake water 87Sr/86Sr ratio of approximately 0.7115, a significant increase in the 87Sr/86Sr ratio of catchment-scale Sr source may have occurred after 11 Ma in response to the uplift of the Qilian Mountains, which would have enhanced hydrothermal activity, metamorphism, glaciation and landslide processes, thereby resulting in more-radiogenic Sr source. Our study suggests that reconstructions of river/lake water 87Sr/86Sr ratios can place powerful constraints on the complex interactions among tectonics, climate and landscape evolution in the northeastern Tibetan Plateau based on a new perspective. • 87Sr/86Sr ratios of paleolake water at 14.8–11.1 Ma in the northern Qaidam Basin. • Ostracod shell and bulk carbonates show stable 87Sr/86Sr ratios at ~0.7115. • Paleolake water 87Sr/86Sr ratio is lower than modern lake water value of ~0.7128. • The paleo and modern lake 87Sr/86Sr contrast links to eolian input or Qilian uplift. [ABSTRACT FROM AUTHOR]

Continental weathering is a crucial factor to maintain the balance of the carbon cycle and thus the livability of the Earth. The Tibetan Plateau (TP), known as the Third Pole of the Earth, has undergone strong uplift since the Cenozoic, thus making it an ideal area to study continental weathering processes and associated driving factors. However, early Cenozoic weathering records are rare in this region. Here, we report high quality mineralogical and geochemical records of clay fraction (< 2 μm) of a middle to late Eocene sequence retrieved from the Qujing Basin, southeastern TP, to track the early Cenozoic chemical weathering history in this area. The results show that the main clay mineral assemblages contain illite-smectite mixed layers, illite and palygorskite. The chemical weathering intensity indicators (e.g., clay mineral assemblages and the chemical index of alteration (CIA)) collectively indicate a clear long-term modulation of global cooling on regional chemical weathering processes during middle to late Eocene, as indicated by high correlation between global temperatures and chemical weathering indicators and the similarity in their periodicity characteristics. Moreover, a sudden decrease of the chemical weathering intensity with large fluctuations was identified at 42–39.9 Ma, which may be linked to rapid transport of clay minerals caused by tectonic activity and/or an increased precipitation in the southeastern TP. This study indicates a control of global cooling on chemical weathering of the southeastern TP area during middle to late Eocene, while tectonic activity or other factors might exert catalytic influences at some certain periods. • Middle-late Eocene chemical weathering records in southeastern Tibetan Plateau (TP) • Control of global cooling on early Cenozoic chemical weathering in southeastern TP • Transition of chemical weathering intensity at 42–39.9 Ma [ABSTRACT FROM AUTHOR]