Eccentricity and obliquity forcing of East Asian hydroclimate during the latest Cretaceous to early Paleocene

Abstract

The latest Cretaceous to early Paleocene was characterized by a global ‘greenhouse’ climate, and may provide a useful analogue for understanding hydroclimate responses to elevated atmospheric CO₂ and temperature. However, a paucity of high-resolution and temporally well-constrained continental sedimentary records spanning this time interval hinders our understanding. We address this issue via a high-resolution paleoenvironmental analysis of a ∼1305 m thick terrestrial succession from the Asian interior (Gonjo Basin, Southeast Tibet). Cyclostratigraphic analysis of element abundance data, combined with a published magnetostratigraphy, allows us to establish an astronomical timescale spanning the latest Cretaceous to early Paleocene (∼69.4 Ma to ∼58.5 Ma) and investigate climatic variations at an orbital time-scale. We show that the paleoenvironment of the Gonjo Basin underwent two key transitions, with a shift from braided river conditions to floodplain-dominated conditions at ∼68.8 Ma, followed by a return to braided river conditions with likely high seasonality at ∼63.5 Ma. Eccentricity and obliquity forcing exerted a strong control on the regional hydrological cycle. We show that the relative strength of obliquity was likely amplified compared to coeval marine records. Obliquity may have modulated meridional heat and moisture transport into the Asian interior, which, combined with feedbacks from quasi-stable carbon reservoirs, mediated hydroclimate. This study improves our understanding of continental paleoclimate evolution in the latest Cretaceous to early Paleocene, and establishes the role and mechanisms of orbital forcing as a driver of hydrological cycle change in East Asia at this time.