Initial microfacies and lithostratigraphy of permian carbonate sedimentsin the vicinity of Khao lamphean, amphoe Nong Muang, changwat Lop Buri.

Abstract

The objective of this study is to establish the lithomicrofacies and lithostratigraphy of the Permian carbonate succession in the study area. Additional attempts have been made to identify fossils of corals and fusulinids and to reconstruct the depositional environment of Permian carbonate sediments. Five measured sections, totally 553.5 meters long, were examined and 310 stratified rock samples were carefully studied by petrographic method. Nine microlithofacies were distinguished, namely, 1) algal packed biomicrite , 2) shell fragments biomicrudite, 3) encrenite, 4) argillaceous sparse biomicrite, 5) foraminiferal biomicrudite, 6) sparse biomicrite, 7) biosparite, 8) biopelsparite, and 9) biopelmicrite. The lithostratigraphy of the studied sequence can be divided into four members, notably, 1) member I (90 meter-thick) characterized by the coral biostromes, 2) member II (55 meter-thick) comprising of mixed bioclasts and peloidal micritic rocks, 3) member Ill (58 meter-thick) characterized by biosparite and biopelsparite with algae and forams, 4) member IV (42.5 meter-thick) consists dominantly of algal packed biomicrite. The coral fossils discovered are: Multimurinus sp., lpciphyllum sp., Waagenophyllum sp., Sinopora sp., and fusulinid fossils of: Colania sp., Sumatrina cf. longissima, Chusenella sp., Verbeekina sp., Codonofusiella sp. indicating Lower to Upper Capitan ian age. The depositional environment was believed to be subtidal zone in middle and inner ramps and locally restricted by patchy reefs.