The

Early Cretaceous The Early Cretaceous (geochronology, geochronological name) or the Lower Cretaceous (chronostratigraphy, chronostratigraphic name) is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 143.1 ...

Phu Kradung Formation is the lowest member of the

Mesozoic The Mesozoic Era is the Era (geology), era of Earth's Geologic time scale, geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceous Period (geology), Periods. It is characterized by the dominance of archosaurian r ...

Khorat Group which outcrops on the

Khorat Plateau The Khorat Plateau (; ) is a plateau in the northeastern Thai region of Isan. The plateau forms a natural region, named after the short form of Nakhon Ratchasima, a historical barrier controlling access to and from the area. Geography The avera ...

Isan Northeast Thailand or Isan (Isan language, Isan/, ; ; also written as Isaan, Isarn, Issarn, Issan, Esan, or Esarn; from Pāli ''isāna'' or Sanskrit ईशान्य ''īśānya'' "northeast") consists of 20 provinces in northeastern Thai ...

, Thailand. This

geological formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics (lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock expo ...

consists of micaceous, brown to reddish-brown

siltstone Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility. Although its permeabil ...

beds with minor brown and grey

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of Clay mineral, clay minerals (hydrous aluminium phyllosilicates, e.g., Kaolinite, kaolin, aluminium, Al2Silicon, Si2Oxygen, O5(hydroxide, OH)4) and tiny f ...

and

sandstone Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sand ...

beds. Occasional lime-noduled conglomerate occurs.Suteetorn and Jarnyahran (1986). "Geological Map of Thailand 1:250,000, Sheet NE 48-14 (Roi Et). The Phu Kradung Formation sediments were deposited in a lake-dominated floodplain cut by meandering and occasionally braided river channels.Racey and Goodall (2009). "Late Palaeozoic and Mesozoic Ecosystems in SE Asia". Geological Society. London. Special Publication 315 Pp 69-84. The Phu Kradung Formation is considered, on the basis of recent vertebrae fossil discoveries, to be

Late Jurassic The Late Jurassic is the third Epoch (geology), epoch of the Jurassic Period, and it spans the geologic time scale, geologic time from 161.5 ± 1.0 to 143.1 ± 0.8 million years ago (Ma), which is preserved in Upper Jurassic stratum, strata.Owen ...

in age. However, new

palynology Palynology is the study of microorganisms and microscopic fragments of mega-organisms that are composed of acid-resistant organic material and occur in sediments, sedimentary rocks, and even some metasedimentary rocks. Palynomorphs are the mic ...

and biostratigraphic data suggests an age of

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 The Toarcian is, in the International Commission on Stratigraphy, ICS' geologic timescale, an age (geology), age and stage (stratigraphy), stage in the Early Jurassic, Early or Lower Jurassic. It spans the time between 184.2 Megaannum, Ma (million ...

), with a maximum depositional age of 180 Ma, which is older than the previously estimated Late Jurassic–

Berriasian In the geological timescale, the Berriasian is an age/ stage of the Early/Lower Cretaceous. It is the oldest subdivision in the entire Cretaceous. It has been taken to span the time between 143.1 ±0.6 Ma and 137.05 ± 0.2 (million years ago) ...

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 and 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 Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...

remains have been recovered from this formation, although few have been referred to a specific

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

.Weishampel, et al. (2004). "Dinosaur distribution." Pp. 517-607.Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press. 861 pp. . '' Chalawan'', an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

pholidosaurid Pholidosauridae is an extinct Family (biology), family of aquatic neosuchian mesoeucrocodylian crocodylomorphs. Fossils have been found in Europe (Denmark, England, France, Germany, Spain and Sweden), Africa (Algeria, Niger, Mali, Morocco and Tu ...

mesoeucrocodylia Mesoeucrocodylia is the clade that includes Eusuchia and crocodyliforms formerly placed in the paraphyletic group Mesosuchia. The group appeared during the Early Jurassic, and continues to the present day. Diagnosis It was long known that Me ...

n, is currently known solely from its

holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

, a nearly complete

mandible In jawed vertebrates, the mandible (from the Latin ''mandibula'', 'for chewing'), lower jaw, or jawbone is a bone that makes up the lowerand typically more mobilecomponent of the mouth (the upper jaw being known as the maxilla). The jawbone i ...

collected in the early 1980s from a road-cut near the town of

Nong Bua Lamphu Nong Bua Lam Phu () is a town in Thailand Thailand, officially the Kingdom of Thailand and historically known as Siam (the official name until 1939), is a country in Southeast Asia on the Mainland Southeast Asia, Indochinese Peninsula. Wi ...

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

References

{{Reflist Geologic formations of Thailand Lower Cretaceous Series of Asia Cretaceous Thailand Berriasian Stage Sandstone formations Mudstone formations Paleontology in Thailand Jurassic System of Asia Tithonian Stage