Diagenetic and Isotopic Evolution Recorded in Calcite Cements in a Large Indosinian Fault Zone in Permian Platform-interior Carbonates, North Central Thailand

Abstract

Diagenetic evolution and fracture style is recorded in calcite cements in fault-damage zones in outcrops of a strike-slip fault and a nearby thrust fault in the Permian Saraburi (Ratburi) Limestone, western Khorat Plateau, Northeast Thailand. Two fractures patterns were identified with respect to the strike slip and thrust fault zones. Releasing bends of the strike-slip fault facilitated higher fluid mobility than the damage zone in the nearby thrust fault. Such releasing bends show a higher degree of calcite infilling and preserve multiples stage of cementation.  Petrography and isotopic data indicate a sequential diagenetic evolution, which started with marine diagenesis (eogenesis), followed by early mesogenetic (early burial) dolomitization and chert nodule development in the matrix, then mesogenetic calcite cementation (nonferroan and ferroan calcite) and later mesogenetic calcite cementation as high temperature hydrothermal non ferroan cement focused in the fault related fractures. Radiogenic concentrations in the later stages of the cementation history give an elevated peak to the gamma ray signature which in similar uncored intervals in the subsurface could be misinterpreted as a shale zone or a flooding surface in the carbonate platform.