High Quality Content by WIKIPEDIA articles! The Nam Phong Formation is the basal unit of the Khorat Group. It consists of resistant, red-brown micaceous sandstones, conglomerates, siltstone and mudstone of mainly fluvial origin. The sandstones are medium to very fine-grained and are usually calcareous. The conglomerates contain pebbles of quartz, brown and grey chert, and redish brown siltstone. Cross bedding and plane-bed stratification are common in the sandstones and conglomerates. The sandstones and conglomerates make up approximately 30% of the formation. This sedimentary rock formation is found in Changwat Khon Kaen, Thailand. It is of Norian to Rhaetian age (Upper Triassic) to (Lower Jurrasic) age, and is notable for its fossils of early dinosaurs.