Orbital-paced silicate weathering intensity and climate evolution across the Eocene-Oligocene transition in the southeastern margin of the Tibetan Plateau

Abstract

The Eocene-Oligocene transition (EOT, ∼33.9 Ma), a period of dramatic global cooling marking the onset of the Antarctic ice sheet. However, paleoclimatic reconstructions indicate a notable spatial heterogeneity in both the marine and terrestrial realms. While limited temporal resolution terrestrial records have hindered the precise understanding of short-term climate events and orbital-scale changes during this transition. Here, we present a chemical weathering data sequence from a fluvial-lacustrine deposition from Lühe Basin, which is located at southeastern margin of the Tibetan Plateau. Based on the radioisotope, paleomagnetic and 405 kyr orbital tuning of the elemental datasets, the deposition age of Lühe Basin is dated to ∼35.5–25.5 Ma. Two weakening stages of the weathering intensity are detected around Eocene-Oligocene boundary: 34.1 to 33.9 Ma and 33.8 to 33.6 Ma, which are temporally equivalent to the two global main climatic steps of EOT (EOT-1 and Oi-1). We find the chemical weathering intensity sequence paced the 1.2 Myr obliquity amplitude modulation and 405 kyr long-eccentricity cycles. Notably, the minima of 1.2 Myr obliquity amplitude and 405 kyr eccentricity are synchronous with the Oil-1 event. These patterns highlight the role of orbital forcing in shaping the cooling trend across the EOT and may trigger Antarctic glaciation.