Reef Pattern of the Permian Keziliqiman Formation in Pishan of Xinjiang
[Objective]The Permian strata in the southwestern Tarim Basin include an organic reef with good explo-ration prospects.[Methods]Based on outcrop observations and thin section examination of the Permian Keziliqiman Formation reef in the Sangzhu profile of Pishan county,Xinjiang,this study explores the basic reef characteristics.[Results]The Keziliqiman reef is a point reef that grew along the platform margin and consists of a base,core,front,back,and cap sub-facies.The lithology of the reef core close to the high-energy front is primarily coral skeleton rock,and that of the reef core close to the low-energy back is primarily sponge barrier rock.The development of the reef was subject to the rise and fall of sea level;it emerged when the sea level rose in the southwestern Tarim Basin and disappeared when the sea level fell rapidly.Rhe fall of the sea level reduced the Sangzhu area to a hot and dry su-pratidal zone where algae began to flourish,dolomitization intensified,and then reef building organisms died en masse.Paleontological and geochemical characteristics of the reef indicate that the sea-level fall in the southwesterb Tarim Basin was likely related to the Early Permian glaciation.When there were no more building organisms,the Keziliqiman reef was transformed by diagenesis.[Conclusions]Overall,the impact of diagenetic transformation was rather small,and its diagenetic process had reliant more on marine fluids in its sedimentary period than on non-marine fluids,for non-marine fluids were powerful enough to affect biodetritus but powerless against the argillaceous matrix.
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