Geological Period And Environmental Change Of Daohugou Biota

Ningcheng is in the southeast of Inner Mongolia, adjoins the west areas of Liaoning province and the north areas of Hebei province, which are famous for the Jehol Biota. There are abundant fossils in the area, which were considered as a part of Jehol Biota by geologists and paleontologists until the year 1998. Since then, many new kind of fossils are discovered, such as primitive mammals, feathered pterosaurs, amblystomas, insects and gymnospermous plants. Their particularities are quite different from Jehol biota. That attracts many scholars, some of them named the fossils Daohugou biota. But for years, detailed regional geology survey had never been preceded. The stratums in the area have not been divided and named congruously. There are three different opinions on the geological age of the biota, middle Jurassic, late Jurassic and early Cretaceous, they will be discussed in this paper.The paper builds the complete stratigraphic sequence of Mesozoic and unifies the names of the stratums based on the survey of region geology and profiles. It includes Jiulongshan Formation, Tiaojishan Formation, Tuchengzi Formation and Yixian Formation from the bottom to the top. And the geology age of the Daohugou Biota is also been discussed. We considered that the biota belongs to middle Jurassic based on biostratigraphy and isotope-dating. It should be a part of Yanliao Biota instead of Jehol Biota.The paper discusses the tectonics environment, climate and sedimentation environment based on the paleobiology characteristic and lithology characteristic. The opinion is that the evolution of Daohugou Basin is earlier than surrounding regions. The sedimentation period began from middle Jurassic and stopped by late Jurassic. At that time, Daohugou was a part of the edge of a lake, the depth of water is less than 1 meter, the lakefront was a forest. The climate was warm and wet. Periodical volcanic activities led to environmental deteriorations, and caused the burying of the fossils.