TECTONO-STRATIGRAPHIC CHARACTERISTICS OF CAOHU SAG, NORTHEAST TARIM BASIN AND ITS EVOLUTION

The Caohu Sag is located in the northeast of Tarim Basin. There are multiple cycles of tectonic movement in the region, and oil and gas have been discovered in the well Cao 2 and well Cao 4. Study of its tectono-stratigraphic characteristics and evolution history are critical for further exploration of oil and gas resources in the sag. In this study, the stratigraphic system is established based on the data from drilling wells, seismic survey and 1∶200 000 regional geological mapping. Unconformities are critical to the division of evolutionary stages and the establishment of the basin history. Since the Sinian, 10 unconformities have been recognized in the Caohu Sag,including the angular unconformities under the bottoms of the Sinian, the Upper Ordovician, the Upper Devonian, the Carboniferous, the Triassic, and disconformities on the top boundary of the Cambrian, the Jurassic, the Cretaceous and the Paleogene. Upon these unconformities, we have recognized 4 structural layers and 10 structural sub-layers in the Sag. Based on the tectonic evolution stages, using equilibrium profile software, the tectonic evolution of the Caohu Sag is restored, and the tectonic evolution is divided into four periods: the basement forming period before Sinian, the development period from Sinian to Silurian, the final formation period from Devonian to Permian, and the adjustment period from Triassic to the present.