Shifts in the silicate weathering regime in South China during the Meso-Cenozoic linked to Asian summer monsoon evolution

Abstract

The scarcity of reliable and relatively continuous Meso-Cenozoic weathering records hinders the accurate temporal tracing of silicate weathering regimes and their possible shifts, which has resulted in a knowledge gap in our understanding of the interactions of the weathering-CO2-climate system on geological timescales. Here, we present a detailed compilation of Meso-Cenozoic silicate weathering records from South China. The results show that a trend of increasing weathering occurred in South China during the Meso-Cenozoic, coupled with increases in the average silicate weathering intensity (expressed by the chemical index of alteration (CIA) and the Kaolinite/(Illite+Chlorite) ratio), characterized by three stages. Comparison of silicate weathering regimes with the CIA reveals that expansions of a supply-limited weathering regime in the study region occurred at ~47 Ma and ~2.6 Ma, potentially caused by increases in Asian summer monsoon (ASM) precipitation. Also, we speculate that an increase in the land-sea thermal contrast induced by the global sea-level fall and the India-Asia suture and the initial retreat of the Neotethys Sea may have caused the initial strengthening of the ASM at ~47 Ma; and that the substantially increased cross-equatorial airflow may have contributed substantially to the increase in interglacial ASM precipitation since ~2.6 Ma. A significant implication of the two expansions is that the ASM may have prevailed over South China since at least 47 Ma.