Sedimentary facies and stratigraphy of the marine jurassic Hua Fai group in Mae Sot-Phop Phra basin Changwat Tak, Thailand

Abstract

This study aims to establish detailed studies in terms of general geology and to define facies, rock units, and stratigraphy of marine Jurassic sedimentary strata of the Hua Fai Group in the Mae Sot-Phop Phra Basin, Tak Province, Thailand. Additional purposes are to evaluate the lithostratigraphy, sedimentary structure and to reconstruct the depositional environment and tectonic setting. Based mainly on 7 measured sections in the Mae Sot-Phop Phra basin, the Hua Fai Group can be divided into 3 formations, 17 units and the total thickness varies from 200-832 m approximately. The Khun Huai Formation consists of conglomerate, sandstone interbedded with mudstone and siltstone, limestone and dolomitic limestone, and sandstone and oolitic limestone with abundant bivalves, gastropods, trace fossils, plant remains and vertebrate fossils. The formation varies approximately 93-345 m thick. The Doi Yot Formation, approximately 103-139 m thick, consists of well bedded, medium- to thick-bedded marl interbedded with mudstone and argillaceous limestone with abundant ammonites and bivalves. The formation is composed of intercalation of sandstone, mudstone, siltstone, oolitic limestome and limestone with abundant bivalves, ammonites, gastropods, corals, trace fossils and plant remains. This formation is approximately 67-221 m thick. As a whole, the sedimentary sequences of the Hua Fai Group are analyzed in terms of lithofacies association representing the shoreface, fan-deltas, protected lagoon, intertidal, subtidal and inner to outer ramp environments with occasional carbonate platform and reef flat. The Toarcian rocks were represented by transgressive-regressive (T-R) cycles and gradually changed to the highest sea level and water depth in the Aalenian. In late Aalenian to early Bajocian, sea level was still changing to transgressive phase. After early Bajocian, the sea level was retreated from this area. The eustatic curves in this study during Toarcian-early Bajocian correspond to the global curves, but differ significantly in the Late Jurassic-Cretaceous. In Late Jurassic-Cretaceous, T-R phases were conversely and probably caused by local tectonic movements. The study area is located in central part of the Shan-Thai terrrane. The multiple collisions during Late Triassic terminated completely in the Paleotethys. The eastern part of the Shan-Thai terrane may have been uplifted and emerged, becoming a central part of Southeast Asian landmass, whilst the central and western parts of the terrane was rifted in the Early Jurassic. Subsequently, the lagoon and shallow marine sedimentation began in late Early Jurassic and continued to early Middle Jurassic in the NW-SE trend. During Late Jurassic-Cretaceous, the western and central parts of Shan-Thai terrane were uplifted and became western Southeast Asian landmass, which represented by conglomerate and red sandstone units overlying marine Jurassic sequence.