Sequence stratigraphy and coal accumulation of continental basin with gentle slope margin

The Middle Jurassic of Dameigou Formation and Shimengou Fomation in Tuanyushan area of Qaidam Basin was studied to unveil the sequence stratigraphy and coal accumulation pattern of the continental basin with gentle slope margin. By using borehole data and well logs,authors studied its sedimentary facies,sequence stratigraphy and coal accumulation characteristics. Fluvial,delta and lacustrine depositional systems and related facies were recognized. Five kinds of key stratigraphic surfaces,i. e. terrestrial unconformity caused by forced regression ( FR) and its correlative conformity (CC* *),fluvial erosional surface (RES),first flooding surface (FFS) as well as maximum flooding surface (MFS) were recognized. A sequence stratigraphy pattern and coal accumulation model in sequence stratigraphic framework of the continental basin with gentle slope margin was proposed. The results show that the sequence boundary of the continental basin with gentle slope margin is similar to the type-I sequence boundary of passive continental margin basin. In the delta plain,the thick coal seam (M5) was developed around the maximum flooding surface,while in the shore shallow lake area,the thick coal seam (M7) was developed near the transgressive surface.