THE ORIGIN OF COAL IN HESHAN FORMATION STUDIED BY OUTCROP SEQUENCE METHOD IN HESHAN COALFIELD

The origin of coal beds in the Upper Permian Heshan Formation in the Heshan coalfield has been disputed for long time.The authors divide the coals in the Heshan coalfield into two types based on the outcrop sequences study in the study area.One type is developed in low-water wedges formed in a carbonate platform.This type of coal has a larger thickness,simpler structure and higher quality,and was formed in the swamps resulted from the filling-up of paralic lakes,Another type of coal is developed in transgressive depositional system tracts.This type of coal is small in thickness,complex in structure and poor in quality,and was accumulated in littoral supertidal environment.The unique carbonate rock type coal measures in the Heshan coalfield was caused by the specific paleo-geological setting in which the terrigenous supply is lack.