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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 hominoid distribution is consistent with advance-retreat of South Asian Monsoon. • Humidity is a controlling factor on the Miocene hominoid migration in East-South Asia. • Clay mineral and δ18O records suggest a hot-wet climate for hominoid-bearing deposits. The discovery of hominoids dated to the Middle–Late Miocene in the southeastern Tibetan Plateau (SE TP) has attracted widespread attention and highlighted the significance of the SE TP as an important refuge for hominoids. However, research on the living environment of hominoids in the region has primarily focused on the Late Miocene, and there are solely few earlier records on earlier migrations. A recently investigated sedimentary sequence within the Xiaolongtan Basin in the SE TP, which contains two hominoid-bearing levels dated respectively to 12.5 Ma and 11.7 Ma, provides a unique window to characterize and understand the living environment that attracted hominoids to the region. The clay mineral, geochemical and sedimentary analyses of the sequence, characterized by the highest kaolinite content and chemical weathering intensity and the coeval occurrence of thick lignite layers during ∼ 12.6–11.6 Ma, suggest that the climate when hominoids occupied the area was hot with higher humidity compared to the preceding and succeeding intervals. A spatiotemporal analysis of the hominoid distribution in the SE TP and the adjacent Indo-China Peninsula indicates a north–south–north pattern of movement, with their ages of ∼ 13–12.5 Ma, ∼11 to 8–7 Ma, and after ∼ 8–7 Ma. These movements accord roughly with the timing of the advance and retreat of the South Asian monsoon (SAM). We therefore infer that, against the overall cooling climatic trend of the Middle–Late Miocene, the increased precipitation and flourishing vegetation promoted by the SAM expansion, was the principal factor that attracted the hominoids to the region. Overall, our results provide new insights into the relationship between the paleoenvironment and hominoid migration/settlement. [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]