Reconstruction of the early Eocene paleoclimate and paleoenvironment of the southeastern Neo-Tethys Ocean

Abstract

The early Eocene is thought to be the warmest period of the Cenozoic Era, with global temperatures ~10 °C higher than today. Few studies have focused on the paleoclimatic history of the early Eocene southeastern Neo-Tethys Ocean despite its tectonic significance. Here, we report new geochemical data that reveal the paleoclimate conditions of the early Eocene (~ 53.7 to 52.6 Ma) from the Qumiba section in the Tingri region of the southern Tibetan Plateau, China, which likely represents the youngest marine strata in the southeastern Neo-Tethys Ocean. The studied Qumiba section consists of the Enba and Zhaguo Formations characterized by silty marls, mudstones and thin layers of lithic sandstones. The paleoclimate and paleoenvironment history of the Qumiba section is reconstructed using stable carbon and oxygen isotopes of marine carbonates (δ13Ccarb and δ18Ocarb), major, trace and rare earth elements. At least one early Eocene hyperthermal event (I1 or I2; ~53.6 Ma) has been recorded in the Qumiba section supported by abrupt negative excursions in δ13Ccarb in Unit 2. This is further supported by enhanced chemical weathering (e.g., chemical index of alteration), which can be attributed to increased temperature and precipitation. The continued negative δ13Ccarb excursions in Unit 3 may have been caused by the release of 13C-depleted carbon from volcanic activities. The volcanic inputs may have increased nutrient availability and promoted marine primary productivity (e.g., higher enrichment factors of P, Ba, Ni and Cu). Furthermore, the basin may have experienced bottom water anoxia as suggested by the redox-sensitive proxies (e.g., higher enrichment factors of U and V and Ce/Ce*) during this period (Unit 3). Our findings support warming-induced changes in paleoenvironmental conditions in the southeastern Neo-Tethys Ocean during the early Eocene.