The upper crustal structure of the Qiangtang Basin revealed by seismic reflection data

The Qiangtang Basin, located in central Tibet, is a thick and widely developed Jurassic marine sedimentary stratum, and it is the largest marine basin on the Chinese mainland without a breakthrough in oil or gas exploration. Various forms of crustal movement related to the convergence between the Eurasian and Indian plates in the Cenozoic have played significant roles in the formation and preservation of the oil and gas resources of the Qiangtang Basin. To determine the shallow crustal structure of the Qiangtang Basin and forecast its prospects for oil and gas extraction, we reprocessed the seismic reflection data (0–6s TWT) from 11 reflection sections acquired at different times by different groups and connected them to form a 350-km shallow seismic reflection profile across the Qiangtang Basin. This profile provides reliable data on the north to south changes of the basement and the upper crustal structures of the Qiangtang Basin. We speculated that the reflective events at 3–4s TWT in the Qiangtang Basin represent the Paleozoic basement, which runs shallow beneath the central anticline. The location of the Proterozoic basement was determined from the discontinuous reflection events at approximately 4.5s TWT. The data indicate that the basements of the Qiangtang Basin are deeper in the south and shallower in the north. The shallow crustal deformations (approximately 0–3s TWT) are quite different between the north and south Qiangtang Basin. In the north Qiangtang Basin, there are strong fold deformations alternating between uplifts and depressions, while the deformations are relatively flat in the south Qiangtang Basin. Continuous arc reflections, interpreted as Paleozoic strata, were found beneath the central anticline of the Qiangtang block. A half graben on the north side of the central anticline represents a possible location for oil and gas resources.