Reflux dolomitization of the Upper Permian Changxing Formation and the Lower Triassic Feixianguan Formation,NE Sichuan Basin,China
作者单位：Key Laboratory of Petroleum Resources ResearchInstitute of Geology and GeophysicsChinese Academy of Sciences Graduate University of Chinese Academy of Sciences Department of Geology and GeophysicsSchool of Environmental SciencesLiverpool UniversityLiverpoolUK Department of Geology and GeophysicsSchool of Environmental SciencesLiverpool universityLiverpoolUK
会议名称：《中国科学院地质与地球物理研究所2013年度（第13届）学术年会》
会议日期：2014年
学科分类：081803[工学-地质工程] 08[工学] 0818[工学-地质资源与地质工程]
基 金：supported by united foundation of NSFC and China’s Petroleum Chemical Industry(grant no.40839906) State Key Lab of Petroleum Resources & Prospecting,China University of Petroleum and China National Funds for Distinguished Young Scientists (41125009) the Chinese Scholarship Council
关 键 词：anhydrite calcite carbonate reservoir cement diagenesis dolomite lagoon sabkha
摘 要：Natural gas is found in Upper Permian and Lower Triassic dolomite reservoirs of the NE Sichuan Basin,China. Studying the mechanisms for porosity-modifying dolomitization and predicting its spatial distribution is of great importance for exploration and field *** core samples from the oolitic Lower Triassic Feixianguan Formation and outcrop samples reef carbonate Upper Permian Changxing Formation were studied using cathodoluminescence (CL),electron microprobe,fluid inclusion and isotope studies(δO,δC and～(87)Sr/～(86)Sr),in an attempt to determine the origin of the dolomitizing *** element and isotope data show that Lower Triassic seawater was most likely responsible for dolomitization of both the Permian and Triassic ***/Ca molar ratios, calculated for the diagenetic fluid,suggest seawater was involved in *** isotope data suggest that seawater～(87)Sr/～(86)Sr during the Jialingjiang(Lower Triassic) reached 0.7078;this ratio is recorded ubiquitously in both Lower Triassic oolitic dolomite and the underlying Lower Permian reef *** the Permian Changxing Formation,elevated Triassic～(87)Sr/～(86)Sr values have overprinted the significantly lower～(87)Sr/～(86)Sr ratio characteristic of Upper Permian *** inclusion analysis led to the conclusion that dolomitization must have commenced at a temperature lower than about 50℃.Integrating the sedimentology,petrology and geochemistry data,we conclude that coeval Lower Triassic(Feixianguan or slightly younger) seawater caused dolomitization by a reflux-seepage process for both the Lower Triassic and Upper Permian *** is no evidence for deep burial or meteoric-marine mixing-zone *** is likely that evaporating seawater initially flowed into the highly porous oolitic Feixianguan Formation in a sabkha/lagoonal setting and precipitated anhydrite nodules and beds. Concomitant dolomitization,in the underlying Permian reef carbonates,continued during