Element Geochemical Implications for Carbonate Karstification Interpretation──Taking Well S60 in Taihe as an example

Key words: 
• calcite /
• element geochemistry /
• micrographology /
• karstification

Abstract: Paleocave systems form an important type of carbonate reservoirs. The studies illustrates that there are widely developed passage caves in the Middle-Upper Ordovician carbonate of Taihe, including branchwork passage, network maze, anastomotic maze, spongework maze and ramiform maze as desoribed by Robert.G.L(1999), and near-surface solution enlarged fractures, sedimentation, rebrecciated chaotic breakdown and collapse as well as mechanical compaction in burial process are probably associated with the formation of collapsed-paleocave system. The approach in terms of chemical composition of carbonate and calcite cement samples and micrographology of calcite crystals associated with karstification has been carried out in Ordovician carbonate of well S60 in Taihe. The results indicates that the carbonate breccias,fractures and sediment fill well developed at the depth of 5 433.20 m～5 435 m belonging to a large-scale paleocave system sedimentation with more than 2 m in height; while the calcites grown in caves at the depth of 5 435m are the products of mixed zone of hypergen fresh water and seawater at the early-middle stage of near-surface karst terrain. Moreover, The author believe that the mineralogic and geochemical studies on carbonate karst process have an important implication for the uncovering the effective depth,periods and intensity of epigenic karst process as well as diagentic sequence and sedimentary environment.