Geology of Cambodia

There are no dated Precambrian rocks in Cambodia, but the gneiss and schist of the Proterozoic Kontum Massif Vietnam extend into the northeast of the country from Vietnam. High-grade metamorphic rocks that may be from the Precambrian are also found at Pailin in the west. This area has gneiss and amphibolite, diorite, granodiorite and relatively uniform mineralogy including quartz, plagioclase and hornblende.^[1]

Extensive Permian limestone rocks are found at Sisophon in the west and to the south at Kampot, containing coral and brachiopod fossils. These fossils helped to establish the age of the limestone which is sometimes interbedded with clastic rocks. There is extensive karst landscape with many caves underlying much of Cambodia.^{[citation needed]}

Triassic rocks are very common in Cambodia, although they do not contain many fossils. Marine Triassic rocks are well documented near Rovieng in the north. Triassic rocks include shale, sandstone, conglomerates and some fragments of volcanic rocks including andesite. The Indosinian Orogeny in the Triassic affected the region with some moderate folding. Hydrocarbon research on the Khorat Plateau suggests that the Indochina Terrane was a series of continental fault blocks separated by Permian rifting.^[2] Marine conditions were common, although the later periods were marked by lagoon and continent conditions and red beds formed.

During the Jurassic marine conditions returned. A fossil ammonite was found at one location in eastern Cambodia. The Sre Pok Valley has numerous beds of rock with ammonite fossils, recording deep water sediments near the Vietnamese border by the Middle Jurassic. Continental conditions were the norm and thick sequences of sandstone and conglomerate formed during the Cretaceous. These comprise much of the Cardamome Mountains in the southwest and can be up to one to two kilometers thick. Sometimes these rocks also contain plant and pollen remains.^[1]

As far as dinosaurs go there have been no findings in Cambodia however it is not unlikely that they lived there.

There are very few Cenozoic rocks in Cambodia. However, there is quite a bit of evidence from the Quaternary, the last 2.5 million years, particularly in floodplains and valleys where terraces in the sediment are common. However, sometimes these deposits are very thin over underlying bedrock.^{[citation needed]}