Triassic carbonate rocks in the Phatthalung area, Peninsular Thailand

Abstract

Carbonate rocks in the Phatthalung area and others in Peninsular Thailand have been known as the Permian Rat Buri Limestone. The study area is characterized by several isolated limestone mountains and is located in Phatthalung province. Micropaleontological study of these carbonate rocks indicates that they should be assigned a late Early to Late Triassic age. The Chaiburi Formation is newly proposed and divided into three members: the Phukhaothong Dolomite, Chiak Limestone and Phanomwang Limestone in ascending order. The Phukhaothong Dolomite consists of thickly bedded to massive dolomite and yields Neospathodus kummeli Sweet, N. waageni Sweet, N. cfr. waageni Sweet and other conodonts that indicate Dienerian to Smithian (Early Triassic). The Chiak Limestone Member consists of bedded and laminated limestone with intercalated thin chert layers and nodules. This limestone commonly yields Early Triassic to Middle Triassic conodonts such as Neospathodus timorensis (Nogami) and Neospathodus kockeli (Tatge), both reliable indicators of latest Spathian to early Anisian, and rare occurrences of Neogondolella bulgarica (Budurov and Stefanov), an indicator of the middle Anisian. The Phanomwang Limestone Member is mostly massive limestone with intercalated reef limestone (coral buildups) and yields abundant fossils that indicate Carnian (Late Triassic). Microfacies analysis and stratigraphic sequences of carbonate rocks in this area show the gradual change of depositional environment from low to high energy conditions.