Trends and Transitions in Silicate Weathering in the Asian Interior (NE Tibet) Since 53 Ma

Abstract

The relationship between silicate weathering, Tibetan Plateau uplift, and global cooling during the Cenozoic provides a valuable case study for understanding the interaction of tectonics and climate. The Tibetan Plateau uplift is considered to have caused Cenozoic cooling via the atmospheric CO2 drawdown by increased silicate weathering. However, this hypothesis has been intensively debated over the past few decades due to the lack of complete silicate weathering records from the continental interior, which can directly track the effects of uplift on weathering. We provide the first complete long (past 53 Myr) continental silicate weathering record from the NE Tibetan Plateau, combined with a comprehensive analysis on its evolution pattern, critical transitions, and associated driving forces. The silicate weathering intensity in NE Tibet is characterized by a long-term Paleogene decrease, modulated by global cooling, and a Neogene increase that may be related to the East Asian summer monsoon (EASM) intensification. Three major system transitions in regional silicate weathering are identified at ∼26–23 Ma, ∼16 Ma and ∼8 Ma, which are linked to enhanced EASM forced primarily by tectonic uplift at these intervals, with some surbordinate influences from global climate at ∼16 Ma. We also capture an intensification of the 100-kyr cycle at ∼16 Ma and ∼8 Ma in the obtained silicate weathering record, which is in coincidence in time with the enhancement of the EASM. This might suggest some contribution of the Antarctic ice sheets on modulating the regional silicate weathering in the NE Tibetan Plateau on a timescale of 105–106 years, through its influences on the EASM as proposed by previous studies.

Neogene drainage reorganization of Longzhong Basin driven by growth of the northeastern Tibetan Plateau: A Sr isotope hydrological perspective

“…The climate factor should play a minor role in this hydrological reorganization. Although the late Oligocene‐early Miocene period is a transition period of enhanced regional weathering and monsoons in the northeastern Tibetan Plateau (e.g., Yang, Fang, et al., 2022; Yang, Han, et al., 2022), intense silicate weathering is expected to elevate all 87 Sr/ 86 Sr ratios in each basin, which is not the case as observed in the records. Therefore, based on a systematic perspective of solute Sr isotopes and detrital zircon U–Pb ages, it can be proposed that the Longzhong Basin experienced drainage reorganization at ca.…”

“…The Sr isotopic differentiation may be related to the distinct responses to tectonic uplift (Dai et al., 2006; Dupont‐Nivet et al., 2004) or climate change (Abels et al., 2011), which needs to be verified by future studies. At substage II, considering no significant change in regional climate and silicate weathering (Yang, Fang, et al., 2022; Yang, Han, et al., 2022) or global climate (Zachos et al., 2008) (Figure 10c,d), the onset of the rise in 87 Sr/ 86 Sr ratios may not reflect enhanced silicate weathering but rather an elevated proportion of solute supply from a high 87 Sr/ 86 Sr source area, that is, Qilian material input, as evidenced by a decrease in the ɛ Nd value of the GJS section close to the East Qilian Shan (Figure 8b) (Yang et al., 2023). At this time, the northeastern Tibetan Plateau experienced significant tectonic activity.…”

“…(c) Marine benthic δ 18 O record (Zachos et al., 2008). (d) (Smectite + illite/smectite mixed layers)/(illite + chlorite) ratios in the northeastern Tibetan Plateau (Yang, Han, et al., 2022). (e) Sedimentary rates of these sections in the Longzhong Basin (Fang et al., 2016; Fang, Fang, et al., 2019; Feng et al., 2022).…”