The Griman Creek Formation is a geological

formation Formation may refer to: Linguistics * Back-formation, the process of creating a new lexeme by removing or affixes * Word formation, the creation of a new word by adding affixes Mathematics and science * Cave formation or speleothem, a secondar ...

in northern New South Wales and southern Queensland, Australia whose strata date back to the

Albian The Albian is both an age of the geologic timescale and a stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early/Lower Cretaceous Epoch/ Series. Its approximate time range is 113.0 ± 1.0 Ma to 100.5 ± 0 ...

Cenomanian The Cenomanian is, in the ICS' geological timescale, the oldest or earliest age of the Late Cretaceous Epoch or the lowest stage of the Upper Cretaceous Series. An age is a unit of geochronology; it is a unit of time; the stage is a unit in ...

of the

Early Early may refer to: History * The beginning or oldest part of a defined historical period, as opposed to middle or late periods, e.g.: ** Early Christianity ** Early modern Europe Places in the United States * Early, Iowa * Early, Texas * Early ...

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', ...

.Bell et al., 2019 It is most notable being a major source of

opal Opal is a hydrated amorphous form of silica (SiO2·''n''H2O); its water content may range from 3 to 21% by weight, but is usually between 6 and 10%. Due to its amorphous property, it is classified as a mineraloid, unlike crystalline form ...

, found near the town of Lightning Ridge, New South Wales. Alongside the opal opalised fossils are also found, including those of dinosaurs and primitive monotremes.Weishampel ''et al.'', 2004, pp.573-574

Description

As a whole, the formation primarily consists of thinly bedded medium to fine sandstone, siltstone and mudstone, with sporadic coal seams. In the vicinity of Lightning Ridge, it is divided up into two informal members the underlying Wallangulla Sandstone Member which primarily consists of red fine grained sandstone, light siltstone and grey claystone and is up to thick while the overlying Coocoran Claystone consists of about 10 metres of claystone. The contact between the two units is sudden and unconformable. Discontinuous clay lens beds within the Wallangulla Sandstone Member near Lightning Ridge, referred to as the Finch Clay Facies, are one of Australia's primary sources of commercial precious opal, with many mines dug in the area. These deposits are also the primary source of fossils within the formation, a large proportion of which are preserved as semi-precious opalized

pseudomorphs In mineralogy, a pseudomorph is a mineral or mineral compound that appears in an atypical form ( crystal system), resulting from a substitution process in which the appearance and dimensions remain constant, but the original mineral is replaced b ...

. The fauna found in lightning ridge indicates that the depositonal environment of the Finch Clay Facies was in near-coastal freshwater lagoons.

Background

Fossil content

Indeterminate avialan, euornithopod, and sauropod remains that were once misidentified as brachiosaurid are present in New South Wales, Australia. Euornithopod tracks are also present in New South Wales.

Dipnoi

Mammals

Crocodyliformes

Dinosaurs

Indeterminate ornithopods and iguanodontians are known from the formation. Indeterminate avetheropods and megaraptorans are known from the formation. Two species of titanosauriforms and one species of titanosaur are known from teeth.Frauenfelder ''et al.'' 2020

Pterosaurs

Testudines

References

Bibliography

* * * * * * * * * {{ISBN, 0-520-24209-2 Geologic formations of Australia Cretaceous System of Australia Early Cretaceous Australia Cenomanian Stage Sandstone formations Siltstone formations Mudstone formations Fluvial deposits Ichnofossiliferous formations Fossiliferous stratigraphic units of Oceania Paleontology in New South Wales Paleontology in Queensland Geology of New South Wales Geology of Queensland