Late Oligocene monsoonal climate in the Lunpola Basin, central Tibetan Plateau: evidence from paleosol records

Abstract

The Asian monsoon affects the natural environmental climate pattern in China, and its origin and evolution have been a debated issue in paleoclimatology. Results from recent studies indicate the Asian monsoon reached the subtropical zone at least ∼ 41 Ma and expanded to the central Tibetan Plateau during the Late Oligocene, but more geological evidence is still required to confirm its spatial and temporal evolution. The well-developed Late Oligocene paleosol in the Lunpola Basin, central TP, is ideal material for addressing the issue. In this paper, observations of various climatic indicators suggest these paleosols were forest cinnamon soils, shown by the compound Bt and Bk horizons, abundant clay coating and carbonate nodules, and diagnostic clay chemical composition in Bt horizons. High CIA values, Rb/Sr ratios, and high contents of illite/smectite mixed layer minerals show paleosols experienced intense weathering and leaching pedogenesis. Furthermore, the mean annual temperature and mean annual precipitation during the paleosol developmental period were 10.4∼14.8 ℃ and 615∼1128 mm, respectively, as estimated by the empirical formulas, which are comparable to the parameters of cinnamon soils in monsoon climate. This study provides important independent evidence of paleosol for the study of the evolution of the Asian monsoon. Thematic collection: This article is part of the Mesozoic and Cenozoic tectonics, landscape and climate change collection available at: https://www.lyellcollection.org/topic/collections/mesozoic-and-cenozoic-tectonics-landscape-and-climate-change Supplementary material: https://doi.org/10.6084/m9.figshare.c.6850703