1.State Key Laboratory of Oil and Gas Reservior Geology and Exploitation, Southwest Petroleum University;2.Chengdu Center, China Geological Survey;3.PetroChina Southwest Oil &4.Gas Field Company
The development characteristics and spatial distribution of source rocks in the Qiangtang Basin are of great significance for oil and gas exploration in the basin. Two sets of important source rocks were well developed in the Qiangtang Basin during the Late Triassic-Early Jurassic, and their development characteristics and spatial distribution may be related to various tectonic history. In the present study, we discuss the sedimentary records of the Late Triassic tectonic inversion. The Middle Triassic sequence has typically shallowing-upward changes and a marine regression related regional uplift. However, the Early Jurassic sequence displays typically deeping-upward changes due to the tectonic subsidence and transgression. We also identify paleogeographic inversion during the Late Triassic in the Qiangtang Basin. In the northern Qiangtang depression, the pre-existing (Middle-early Late Triassic) marine depositional areas turned into terrestrial units during the Norian. In contrast, the previously (Middle Triassic) terrestrial part of the sourthern Qiangtang depression became marine units. Our study suggests that the distribution of source rocks in the Qiangtang Basin was mainly controlled by the sedimentary change and paleogeographic inversion during the Late Triassic. The Late Triassic source rocks were probably related to the foreland basin and developed in the deep water area of the northern Qiangtang depression, while the coal-bearing source rocks were developed around the basin. The Early Jurassic source rocks are probably related to the passive continental margin basin and developed in the deep-water area of southern Qiangtang depression. Oil shale-bearing source rocks are well developed in the lagoon in the northern part of Southern Qiangtang depression.