Astronomical influence on Miocene continental environments in Tibet, east-central Asia

Abstract

Abstract Studies of Cenozoic lacustrine cyclostratigraphy in northeastern Tibet have been successful in reconstructing the history of precipitation and aridification at astronomical (Milankovitch) time scales. However, the phase relationships between Milankovitch forcing mechanisms and hydrologic changes are ambiguous because of challenges in interpreting climate proxies and dating continental successions. We present an analysis of Miocene red and green mudstone rhythmites in two basins (Jiuxi and Guide, NE Tibet) using a climate proxy based on lithologic color. Time-series analysis of the color proxy indicated a dominance of 405 k.y. cycles, from which we constructed an orbital eccentricity metronome astrochronology from 18 Ma to 10 Ma. Periods of lake expansion and contraction are characterized by the green and red mudstones, respectively, and correspond to orbital eccentricity minima and maxima, respectively. We interpreted the antiphase relationship between orbital eccentricity and hydrologic evolution using a net precipitation model, with low precipitation/evaporation ratio being due to excessively high evaporation during times of high orbital eccentricity, and vice versa. High orbital eccentricity scenarios with strong seasonality and insolation extremes are analogous to anthropogenic global warming, and our results provide insights into a future of Central Asian intensified aridification, following the “dry-gets-drier” global warming projections and regionally high aridity sensitivity.