Podocarpium from the Oligocene of NW Qaidam Basin, China and its implications

Here, we report fossil Podocarpium podocarpum (A. Braun) Herendeen in Ganchaigou area, on the edge of the western Qaidam Basin, which is located in the north of the Tibetan Plateau, China. The current fossil is the first Oligocene record of Podocarpium in Tibetan Plateau. Fossils' thermophilous and moisture-loving habits allowed us to reconstruct the paleoclimate there. Two parameters of valves: the length:width ratio and the area were used in analysis of fossil valves to discover the potential paleoclimate information. Generally, Podocarpium valves is slenderer (larger L/W ratio) and smaller (in area) under the gradually cooling climatic conditions from the Eocene to Oligocene and then in the Miocene, the valves becoming more rounded and larger. The fossil report is also a complementary clue to Podocarpium's migratory pattern from South China to Eurasian. Given the spatiotemporal distribution of this genus, we proposed that two distribution ranges where Podocarpium fossils have been found in China as 'Changchang-Qaidam' belt and 'Tiantai-Chifeng' belt. Similarly, the direction ranges of two belts are subparallel to the direction of the East Asian Summer monsoon. The appearance of Podocarpium in Qaidam Basin in Oligocene indicate that there might be a durative period of warmer environment, and the East Asian monsoon might made an effect on the climate of Qaidam Basin in Oligocene.