The Griman Creek Formation is a geological formation in northern New South Wales and southern Queensland, Australia whose strata date back to the Albian-Cenomanian stages of the mid-Cretaceous. It is most notable being a major source of opal, 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.

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 30 m 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. The fauna found in lightning ridge indicates that the depositional 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

Actinopterygii

Mammals

Monotremes

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.

Pterosaurs

Testudines