《Table 2.Electron microprobe analysis results of interstitial dolomite in Deng-2 dissolved cavities.

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《Reservoir characteristics and genetic differences between the second and fourth members of Sinian Dengying Formation in northern Sichuan Basin and its surrounding areas》

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Due to the impacts of Episodes I and II of the Tongwan tectonic movement，the Dengying Formation in the ROI experienced 2 phases of supergene karstification，which gave birth to two weathering surfaces at the top of the Deng-2 and Deng-4 Members，respectively.Corroded gullies and dissolved fractures filled with clastics，and dolomitic karst breccia can be seen in Deng-2 and middle and upper Deng-4 on field sections and in drilling cores（Fig.6），but no large dissolved caverns and grape lace-shaped cement，the typical product of supergene karstification，were found in the Deng-4Member.This means supergene karstification had little impact on the Deng-4 Member.In contrast，intra-stratal and inter-stratal grape lace-shaped structures and residual cavities several centimeters to tens centimeter in diameter in grape lace-shaped cements are common in middle and upper Deng-2.Fibrous dolomite in grape lace-shaped cement has lower contents of Sr2+，Na+，K+，and Fe2+than granular dolosparite forming in later two phases（Table 2）；besides，grape lace-shaped cements show weak cathode-ray luminescence，indicating grape lace-shaped cement was formed in an opened，oxidized meteoric freshwater environments，whereas granular dolosparite was produced in an enclosed burial environment with high salinity.Based on field sections and geochemical features，we conclude that the occurrence of grape laceshaped cement，similar to stalactites in modern carbonate dissolved caverns，may be related to Deng-2 supergene karstification caused by Episode-I of the Tongwan tectonic movement.