Facies Characteristics of a Permian Carbonate Platform of Pha Nok Khao Formation from Khroat Basin, Thailand

Key words: 
• Khroat Basin /
• Permian /
• carbonate platform /
• Pha Nok Khao Formation /
• Thailand

Abstract: Based on core data description, logging data analyses, thin section analyses, SEM observations, X-ray diffraction (XRD) analysis, C/O isotopic analyses and trace element analyses, sedimentary facies and depositional environments of Permian carbonate rocks taken from Pha Nok Khao Formation of Khroat basin were systemacially examined. This study shows that the Permian depositional sequence belongs to carbonate ramp deposits with no barrier. The study area locates in the fore-slope area of carbonate platform, which can be divided into shallow water fore-slope sub-facies and relatively deeper water fore-slope sub-facies. The former indicates a weak hydrodynamic condition, weak oxidation-weak reduction environment, with depositional water depth below or around sea wave base within a slope environment. The latter indicates a relatively deeper water depth than the former. Its environment is characterized by weak oxidation-moderate oxidation environment, with its depositional water depth below sea wave base. The Permian carbonate stata in the study area is a typically low-energy depositonal sequence with a relatively deeper water depth and weak hydrodynamic condition, and the vertical evolution of sedimentary environment is stable. High-energy sedimentary facies does not develop in the study area, indicating that the basic conditions for favorable reservoir development possibly do not exist and the development of potential carbonate reservoirs in Pha Nok Khao Formation will be controlled by alteration of tectonic movements or diagenesis.