Sequence stratigraphy and coal accumulation of fluvial delta under low accommodation conditions

Abstract：The Permian of Shanxi formation in southwestern Shandong province was studied to unveil the accumulation pattern of coal in the fluvial delta under low accommodation. Key stra- tigraphic surfaces, i.e. terrestrial unconformity caused by forced regression （BFSR） and its correlative conformity （CC＊）, fluvial erosional surface （RES）, paleosol seam （PSS）, maxi- mum regression surface （MRS）, flooding surface （FS） as well as maximum flooding surface （MFS） were recognized. The target coal measures was delineated into one 3rd sequence, two 4th order sequences, and twelve parasequences （two parasequences types）. Subsequently, a coal accumulation model of fluvial delta in sequence stratigraphic framework under low accom- modation conditions was proposed. The result shows that, in low accommodation settings, the base level coincides with the sedimentary boundaries of fluvial delta; the parasequences are dominantly formed during the semi-cycle of the rising base level~ and the formation of the se- quence boundary is predominantly driven by the absolute sea level fall which is＇faster than thefalling base level; The major coal seams were found to have been developed during transgress- ive system tracts, mainly in lower deltaic plain and interdistributary lacustrine, It is suggested that the size of residual accommodation during coal accumulation and the rate of accommodation increase are dominant controls of the peat accumulation.