LATE OLIGOCENE-EARLY MIOCENE LACUSTRINE RECORDS FOR THE TECTONIC, CLIMATIC, AND LAKE BASIN EVOLUTION IN CENTRAL TIBET

The rise of the Tibetan Plateau (TP) has generated intense interest on the global level for its significance to continental tectonics and its role in interacting with global and regional climate systems. Sedimentary basins and strata accumulated in them record abundant information involving evolution of the TP. However, high-resolution temporal frameworks of sedimentary sequences and controls on geological and climatic events are still rarely reported. Here, we investigate the Oligocene-Miocene lacustrine sequences (the Dingqinghu Formation) of the Lunpola Basin, central TP using three measured sections and one newly drilled well. In this study, the four sections were correlated together to construct the integrated stratigraphic framework of the basin; cyclostratigraphic analyses are conducted with pollen data and gamma ray log to establish high resolution temporal frameworks (ca. 25.4 to 18.0 Ma) along two sections of central and marginal basin; sediment accumulation rates are calculated with orbital signals to monitor clastic input; published elemental, palynological, and isotopic data are also compiled to depict the paleoclimate and paleoelevation evolution of the basin. Integrating all these clues, we sort out a list of events in time order: regional uplift took place at 23.7 Ma; simultaneously, a distinct lake-basin transition characterized by accelerated sediment accumulation rate is identified; then, catchment scale drought occurred at 23.5 Ma and maintained to the end of the sections. Our results demonstrate that climate change did not impose decisive influence on the lake-basin evolution during this period; instead, regional uplift and its associated accelerated exhumation of the source area resulted in the lake-basin transition and paleoclimatic drought. After reviewing the Oligocene-Miocene sedimentary records distributed in and around the TP, we argue that the 23.7 Ma geological event of the Lunpola Basin is probably not a single case but a regional effect of a dramatic tectonic transition of the plateau.