Palaeontological study of the Middle-Late Jurassic in Shatuwan Lake area of northern Qiangtang Basin and its significance

The study of Middle to Late Jurassic paleontology is great significance for establishing chronostratigraphic framework, restoring sedimentary environment and guiding oil and gas exploration in Shatuwan Lake area of Northern Qiangtang Basin. Based on the systematic identification of fossils and regional geological data, the age of fossils is determined and the stratigraphic attribution is discussed. The results show that:(1) The original division of the Bailong-binghe Formation belongs to Suowa Formation; (2) The Burmirhynchia, Holcothyris and Ceratomya cocentrica (J. Sowerby), Ceratomya striata (J. Sowerby) and Goniomya cf. trapezicostata (Pusch)、Pholadomya cf. ginghaiensis were found in the Suowa Formation and represents Mid-Jurassic Bathonian to Early Callovian; (3) The lower limit of the Suowa Formation should be extended to Mid-Jurassic Bathonian, and the formation has the characteristics of penetrating time; (4) The living habits of the fossil indicate that they were deposited in a warm normal shallow marine environment. These geological records provide reliable geological basis for reconstruction and inversion of the time and space distribution and lithofacies paleogeographic pattern of the Suowa Formation in the Shatuwan Lake area of Northern Qiangtang Basin.