Sequence-paleogeography and coal accumulation of Lopingian in Guizhou Province

Based on outcrop sections and borehole data, the sequence stratigraphy, paleogeography, and coal accumulation of Lopingian(Upper Permian) in Guizhou Province have been studied. According to distribution of marine limestone beds which reflects variation of the transgressions, we have subdivided the Lopingian into 3 third-order composite sequences(CSⅠ, CSⅡ, CSⅢ) and related lowstand, transgressive, highstand sequence sets. CSⅠcorresponds to the lower and middle parts of the Lower Member of Longtan Formation. CSⅡcorresponds to the upper part of the Lower Member of Longtan Formation. CSⅢcorresponds to upper part of the Upper Member of Longtan Formation and Changxing Formation. The paleogeography map of these three sequences are reconstructed based on the contour maps of stratal thickness, percentage of limestones, sandstone to mudstone thickness ratios, and total coal thickness. Transgression direction for the three sequences was from east and the provenance was from western Khangdian Oldland. From west to east, there was a variation in facies units from terrestrial fluvial plain, transitional delta plain and tidal flat-lagoon, marine carbonate platform, to deep water basin. In general, Guizhou Province experienced the transgression of CSⅠ, the regression of CSⅡand the continuous transgression of CSⅡduring the Lopingian. In western Guizhou, each paleogeographic unit migrated landwards in CSⅠ, seawards in CSⅡ, and landwards again in CSⅡ. The coals were mainly formed in the delta plain and tidal flat environments of transitional facies, and the coal-accumulating centers migrated with regional transgression and regression. The coal-accumulating centers of CSⅠwere mainly distributed in the Fa'er and Nayong areas, the coal-accumulating centers of CSⅡwere mainly distributed around the Pu'an-Liupanshui and Zhijin areas, and the coal-accumulating centers of CSⅢwere mainly distributed around Liupanshui, Panxian and Zhijin areas. These results of coal accumulation analysis can provide theoretical support for the exploration and development of coal and coalbed methane resources.