Paleogeolography of early Coal-Forming of late Permian in Chongqing

Abstract

A total of two third-order sequences are subdivided in Late Permian. Sequence 1 is from the bottom of the Longtan Formation to the bottom of C16 coal in Longtan Formation,representing a transgressive to regressive cycle,and the Sequence 2 is from the bottom of C16 coal in Longtan formation to the top of the Changxing Formation. From Maokou formation to the first flooding surface (the bottom of the C25) is the low systems tract in sequence 1(the earlier stage of coal accumulation). The palaeogeographic map has been reconstructed based on the contour maps of a variety of palaeogeographic parameters including total thickness of strata,thickness of sandstone,thickness of mudstone,and sandstone-mudstone ratio. The paleogeographic units include lowlandhighland eluvial plain and bay-lagoon-tidal. The transgression comes from south and the sediment provenances are mainly from the Kangdian old land in the west.