Group Ⅲ long-chain alkenones preserved in Miocene lacustrine deposits of the Qaidam Basin

Abstract:

The paleoaltitudinal history of the northern Tibetan Plateau (NTP) remains critically controversial, yet it provides important insight into understanding the uplift mechanism of the entire plateau and the relationship between plateau growth and regional climate reorganization. The Qaidam Basin (QB), the largest intermontane basin inside the NTP, records important information regarding the tectonic evolution of the NTP. Here, we report the newly discovered Group Ⅲ long-chain alkenone (LCA) from the Honggou section in the QB. The Group Ⅲ LCA, commonly produced by marine-type haptophytes, has been recovered since the Mid-Miocene. This finding is consistent with previous discovery of its diagenetic remnant, the Group Ⅲ long-chain saturated ketone (LCSK), from contemporary strata in the western basin. Based on collective evidence and previously reported results, we infer that the biological source of the LCAs might be associated with the remnant of stepwise Eocene proto-Paratethys transgressions or a possible seawater intrusion during the Miocene. If the latter inference is correct, the QB would be expected at almost sea-level height during the Mid-Miocene epoch. Thereby the uplift history of the NTP and the uplift mechanism of the entire plateau may need to be reconsidered on such basis.