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Formation of fine crystalline dolomites in lacustrine carbonates of the Eocene Sikou Depression, Bohai Bay Basin, East China

查看全文 作　　者：Yong-Qiang [1]Yang;Long-Wei [1]Qiu;Jay [2]Gregg;Zheng [1]Shi;Kuan-Hong [1]Yu 高影响力作者 机构地区：[1]School of Geosciences, China University of Petroleum;[2]Department of Geology, Oklahoma State University高影响力机构 出　　处：《Petroleum Science》索引2016年第13卷第4期,共15页高影响力期刊 基　　金：supported by the National Basic Research Program of China (Grant No. 2014CB239002);Natural Science Foundation of Shandong Province, China (Grant No. ZR2014DQ016) 摘　　要：The genesis of the fine crystalline dolomites that exhibit good to excellent reservoir properties in the upper fourth member of the Eocene Shahejie Formation(Es_4~s)around the Sikou Sag, Bohai Bay Basin, is uncertain. This paper investigates the formation mechanisms of this fine crystalline dolomite using XRD, SEM, thin section analysis and geochemical data. The stratigraphy of the Sikou lacustrine carbonate is dominated by the repetition of metre-scale, high-frequency deposition cycles, and the amount of dolomite within a cycle increases upward from the cycle bottom. These dolomite crystals are 2–30 μm in length, subhedral to anhedral in shape and typically replace both grains and matrix. They also occur as rim cement and have thin lamellae within ooid cortices. Textural relations indicate that the dolomite predates equant sparry calcite cement and coarse calcite cement. The Sr concentrations of dolomites range from 900 to 1200 ppm. Dolomite δ^(18)O values(-11.3 to-8.2 ‰ PDB) are depleted relative to calcite mudstone(-8.3 to-5.4 ‰ PDB) that precipitated from lake water, while δ^(13)C values(0.06–1.74 ‰ PDB) are within the normal range of calcite mudstone values(-2.13 to 1.99 ‰ PDB). High^(87)Sr/^(86)Sr values(0.710210–0.710844) indicate that amounts of Ca^(2+) and Mg^(2+)have been derived from the chemical weathering of Palaeozoic carbonate bedrocks. The high strontium concentration indicates that hypersaline conditions were maintainedduring the formation of the dolomites and that the dolomites were formed by the replacement of precursor calcite or by direct precipitation. 关 键 词：湖相碳酸盐岩 渤海湾盆地 白云岩 细晶 华东地区 凹陷 始新世 地球化学数据
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