Oligocene lacustrine stromatolites in the Tuotuohe basin, Qinghai-Tibet Plateau : paleoclimate conditions recorded by the rhythmic laminations

A group of lacustrine stromatelites growing in the process of the flooding lake is discovered in the Oligocene Yaxicuo Group of Tongtianhe section, Tuotuohe Basin. The shape patterns and microstructure of stromatolite laminations show the rhythm demonstrated by microbial micrite layers(dark layers) and grain-rich layers(light layers), three-level growth rhythm, gradational contact relation in the middle of the couplet while abrupt in the lamina growth bands. 16 pairs of carbon and oxygen isotopic data are collected systematically from 8 couplets of 4 samples. The value in microbial micrite layers are on the whole higher than in grain-rich layers, showing positive correlation. It's showed that the climate was hot and wet in the growth period of dark layers, while colder and drier in the growth period of light layers. The lacustrine stromatelites are controlled by periodic climate change, which preserve plentiful paleoclimate informations.