PALEOZOIC TO MESOZOIC CHANGES OF LITHOFACIES AND PALEOGEOGRAPHY OF THE COQEN BASIN, CENTRAL TIBET
LI Xiang hui 1, WU Ge 2, WANG Cheng shan 1, YI Hai sheng 1, LIU Deng zhong 1, SHI He 1, MA Run ze 1, WANG Hong feng 1 (1.Chengdu University of Technology, China; 2.Petroleum Institute of Southwest Bureau, NSPC)
About eight sedimentary environment systems within three sedimentary environment system sets are recognized in the Coqen Basin of Lhasa Block, central Tibet from much geological investigations and materials, in which lots of lithofacies and sublithofacies can be differentiated. The sedimentary environment system sets are continental, transitional, and marine separately. And the eight sedimentary environment systems are weathering resident, fluvial alluvial, river, lacustrine, delta, shore, shelf (including ramp and platform), slope. The lithofacies and paleogeographic evolution can be subdivided into two stages, Late Ordovician Early Silurian and Middle Late Silurian, although the basin was in an epicontinental sea during Early Paleozoic. There are three stages of lithofacies and paleogeographic evolution in Late Paleozoic. In the first stage, it was in carbonate ramp to platform during Devonian to Early Carboniferous; in the second stage, it turned into rift basins in the northern part and isolated platforms in the southern part during Late Carboniferous to Early Permian; and in the third stage, it became a shrinkage platform in Late Permian. The basin can be divided into two durations although there were different frameworks of lithofacies and paleogeography of the Coqen Basin in each period of the Mesozoic. It is proposed that the paleogeography of the basin was patterned as an exposed territory in the southern part and temporally a marine sea water covered the northern part during Middle Late Triassic and Jurassic, and then changed to be a rising and exposed highland in the central part surrounded by the southern and northern parts of the Coqen Basin during Late Jurassic and Cretaceous. The authors suppose that the turnover of the Early and Late Carboniferous is an important event that could cause a great change of the paleogeography of the basin. Before the turnover, the basin was a epicontiental sea, there was only one depocenter , one center of basin in it. The middle part of the basin was deeper lithofacies and the eastern part shallower, and sea water transgressed onto the basin from west to east. After this, the sedimentary environment systems became more complicated, and the depocenter and center of the basin were separated into much more. The sea water transgressed onto the area in the way from north to south together. It took its source at the remnant sea along the Bangong Nujiang suture.
【Fund】： 国家重点基金研究计划 (G19980 40 86 1)和 H45 C0 0 10 0 1措勤幅 1∶ 2 5万区调 (2 0 0 130 0 0 0 9171)联合资助
【CateGory Index】： P531
【CateGory Index】： P531