Tectonic and climatic controls on long-term silicate weathering in Asia since 5 Ma

Abstract

Determining the interplay between tectonic deformation, climate, atmospheric CO 2 concentrations and continental weathering and erosion is key to understanding the mechanisms that forced Cenozoic global cooling. In contrast with studies of paleo-climate and pCO 2, the history of long-term silicate weathering in the Himalaya and Tibetan Plateau (HTP) during the late Cenozoic remains unclear. We reconstruct 5m.y. of silicate sedimentary records at Ocean Drilling Program (ODP) Site 1143 in the South China Sea to explore the weathering history of the Mekong River basin that supplied the sediment. Coherent variation of weathering proxies from the South China Sea, Bay of Bengal, Loess Plateau, as well as the Yangtze and Yellow Rivers, indicates weakening chemical weathering intensity since the late Pliocene, as the climate cooled. This cooling, coupled with tectonic activity, shifted the dominant weathering regime from more transport-limited to more weathering-limited, causing less chemical depletion of silicate minerals. While silicate weathering rates became strongly correlated to erosion rates, they were decoupled from chemical weathering intensity. Physical denudation and associated silicate weathering rates in the HTP area increased in the Pliocene, driven by both rock uplift and stronger monsoon precipitation, decreasing atmospheric CO 2 concentrations, and so contributing to Northern Hemisphere Glaciation (NHG). © 2012. American Geophysical Union. All Rights Reserved.