Search

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]

The relationship between tectonic uplift, climate change and continental silicate weathering has long been debated because deconstructing the tectonic and climatic impacts on continental silicate weathering is challenging. To address this issue, we present long-term climatic and silicate weathering records since 7.3 Ma on tectonically active NE Tibet retrieved from the SG-1 and SG-1b lake sediment drill cores in the western Qaidam Basin. We find distinct correlations between silicate weathering and regional climate on long-term (>106 years) and short-term (105–106 years) time scales. On long-term scales, silicate weathering intensity exhibits a consistent evolution with regional climate, both of which are dominantly controlled by global climate change. This evolution resulted in a stable weathering intensity during 7.3–~3.6 Ma and a weakening of weathering intensity since ~3.6 Ma, followed by a continuous decreasing trend after 2.6 Ma. However, on short-term scales, silicate weathering intensity displays out-of-phase changes with the regional climate at 6.9–3.7 Ma and 0.2–0.1 Ma and in-phase changes at 7.3–6.9 Ma and 3.7–0.2 Ma. We attribute this long-term consistency between the weathering intensity and climate to aridification in inland Asia, but the short-term inconsistencies at 6.9–3.7 Ma and 0.2–0.1 Ma to the change in the sediment routing system impacted by the regional climate within a tectonically active setting. Such a change in the sediment routing system along with sediment recycling may bias weathering indication on orbital time scales, and our study therefore suggests a more complex response of silicate weathering to tectonic and climatic forcings. [Display omitted] [ABSTRACT FROM AUTHOR]