Stratigraphic Features of Upper Jurassic Suowa Formation in Tuonamu Region, Tibet

The Qiangtang Basin in an area of 180 000 km² is situa ted in the Northern Tibet Plateau.Its northern and southern boundaries are the Lazhulong-Jinshajiang suture zone and Bangongcuo-Nujiang suture zone,respectively.The basin can be divided in to the northern Qiangtang depression,the central uplift zone and the southern Qiangtang depression.The Tuonam uregion where the upper Jurassic Suowa Formation is extensively developed is in between the central uplift zone and northern Qiangtang depression.This study proposes a new division of four lithological members for the Suowa Formation based on its stratigraphic sequence and assemblage.The member 1 to member 4 of the Suowa are carbonate platform,mixing accumulated gentle slope,mixing accumulated carbonate platform and mixing accumulated shallow water out site shift environments,respectively and reflect an complete transgressive to regressive sequences,The finding of biogenicreef and oil shale from the member 3 of the Suow a Formation is significant for recon structing ancient environmental and petroleum geology studies; Also,the study establishes coral combination and bivalve combination according to the distribution and integrated characteristics of paleobiotologic strata,which means that the Suowa Formation is of upper Jurassic,to be exact,the Oxfordian to Kimmeridgian.