The Early Cretaceous Phu Kradung Formation is the lowest member of the Mesozoic Khorat Group which outcrops on the Khorat Plateau in Isan, Thailand. This geological formation consists of micaceous, brown to reddish-brown siltstone beds with minor brown and grey shale and sandstone beds. Occasional lime-noduled conglomerate occurs. The Phu Kradung Formation sediments were deposited in a lake-dominated floodplain cut by meandering and occasionally braided river channels. The Phu Kradung Formation is considered, on the basis of recent vertebrae fossil discoveries, to be Late Jurassic in age. However, new palynology and biostratigraphic data suggests an age of Early Cretaceous for the upper section. More recent datations trought detrital zircon U–Pb ages of samples from the conglomerates have stablished a lowermost age of late Early Jurassic (Toarcian), with a maximum depositional age of 180 Ma, which is older than the previously estimated Late Jurassic–Berriasian age based on fossil evidence. This discrepancy suggests the absence of syn-depositional zircons. The zircon data also help clarify the timing of the Indosinian III Event, placing the Indosinian III Unconformity between 201-182 Ma, marking a hiatus of about 20 million years. The Phu Kradung Formation deposition likely occurred after the Nam Phong Formation and may correlate with the Upper part of the last in the Khorat Basin subsurface. Dinosaur remains have been recovered from this formation, although few have been referred to a specific genus. Chalawan, an extinct genus of pholidosaurid mesoeucrocodylian, is currently known solely from its holotype, a nearly complete mandible collected in the early 1980s from a road-cut near the town of Nong Bua Lamphu in the upper part of the Phu Kradung Formation. This single specimen is the most well preserved vertebrate fossil that has been found from the formation. It contains a single species, Chalawan thailandicus.

Fossil content

Amphibians

Archosaurs

Dinosaurs

Pseudosuchians

Pterosaurs

Turtles

Fish

Bony fish

Cartilaginous fish

Multiple fin spines have been found in the Phu Kradung Formation which cannot be precisely identified.

Plants