Sequence Stratigraphy of Quaternary Seven Spring Group of Sanhu Depression and Prediction of Favorable Targets

By combining drilling, logging and seismic data with the Milankovitch cycle, we have carried out a high-resolution sequence stratigraphy research on the Sanhu depression Seven Spring Group in the Qaidam Basin. We identified six sequence surfaces in the Seven Spring Group, and further divided the Group into five triple pole sequences. Based on the comparative analysis of the contents of the Artemisiaepollenites pollen and carbonates, δ18O composition, the GR (Gamma Ray) curves, and the contents of chlorine ions, we could draw the following conclusions. Overall, the climate in this area has changed from warm to cold. There are five secondary cycles of this climate change, from warm and humid to cold and dry. These five cycles correspond to the five stratigraphic sequences of the sq1, sq2, sq3, sq4 and sq5. In each cycle, the inner fluctuations are coincident with the rise of the base level in upper half cycles and the fall of the base level in lower half cycles. The delta front sandstone out pinch and the sandstone lens traps developed during the upper half cycles of the rise of the base level of Sequence (sq2) are prospective targets for the further exploration for hydrocarbons.