西藏自治区革吉县米多南地区欧利组厘定的古生物证据及其意义

Biological evidence and its significance of Ouli Formation in Miduonan hamlets of Geji County,Tibet

研究区位于羌塘地块与班公湖-怒江结合带交汇处,保存有一套晚侏罗世-早白垩世海相沉积记录,是研究晚侏罗世-早白垩世班公湖-怒江特提斯洋沉积环境演化及其沉积盆地类型的理想地区。通过对岩性组合、沉积环境、古生物化石等方面进行研究,厘定出欧利组,并探讨了欧利组时代归属及沉积盆地类型。根据欧利组中发现的小光星珊瑚、轮形异通珊瑚、米契林柱剑珊瑚、安多准柱剑珊瑚等化石,确定欧利组时代为晚侏罗世。初步分析沉积环境为局限台地-潮坪沉积,局部具潮汐水道沉积,沉积相分析表明研究区晚侏罗世-早白垩世沉积盆地类型为弧后前陆盆地。

The study area is located at the interseltion of Qiangtang plots and Bangong-Nujiang junction. Since there is well-preserved Late Jurassic-Early Cretaceous marine sedimentary record,this area is believed to be an ideal site for the research of Late Jurassic-Early Cretaceous environmental evolution and basin sediment types. In order to discuss the stratigraphic age of Ouli Formation and types of sedimentary basins in this area,careful study was taken on lithology combination,sedimentary environment,paleontological characteristics and so on. A lot of Late Jurassic fossils,such as Actinastraea minor Wu,Allocoenia trochiformis Etallon,Stylina andoensis Liao et Li,Stylosmilia michelini Milne-Edwards et Haime,were found in the Ouli Formation. The presentence of these fossils provides strong evidence to verify that the stratigraphic age of Ouli Formation is the Late Jurassic. The Ouli Formation is mainly made up of the restricted platform-tidal flat siliciclastic deposits intercalated with the carbonate deposits and sandwiched tidal channel gravel limestone. The results show that the sedimentary basin is a backarc foreland basin in the study area in the Late Jurassic-Early Cretaceous.