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.

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 metres (98 ft) 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.

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 of the Griman Creek Formation
Taxa	Species	Presence	Material	Notes	Images
Ceratodus	C. diutinus		Isolated tooth plates
Metaceratodus	M. wollastoni		Isolated tooth plates
Neoceratodus	N. potkooroki		Isolated tooth plates

Actinopterygians of the Griman Creek Formation
Taxa	Species	Presence	Material	Notes	Images
Calamopleurus?	sp.		Isolated jaw bones

Mammals
Genus	Species	Presence	Materials	Notes	Images
Dharragarra	D. aurora		A partial left mandibular ramus.	A monotreme.
Kollikodon	K. ritchiei		An opalised dentary fragment, with one premolar and two molars in situ, as well as a referred maxillary fragment containing the last premolar and all four molars	A monotreme.
Opalios	O. splendens		A fragmentary left dentary.	A monotreme.
Parvopalus	P. clytiei		A partial left dentary.	A monotreme.
Steropodon	S. galmani			A monotreme
Stirtodon	S. elizabethae		A large isolated premolars.	A monotreme

Crocodyliformes
Genus	Species	Presence	Materials	Notes	Images
Isisfordia	I. molnari	Lightning Ridge	Braincase and referred maxillary fragment	A crocodyliform.

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.

Dinosaurs
Genus	Species	Presence	Notes	Images
Fostoria	F. dhimbangunmal	New South Wales	A member of Rhabdodontomorpha.
Fulgurotherium	F. australe	New South Wales
Rapator	R. ornitholestoides	New South Wales	A megaraptoran; "Manual element"
Walgettosuchus	W. woodwardi	New South Wales	"Vertebra" Later determined to be an indeterminate theropod
Weewarrasaurus	W. pobeni	New South Wales	An ornithopod known from an isolated dentary
Ankylosauria	Indeterminate		Osteoderm
Enantiornithes	Indeterminate		Partial femora
Megaraptora ("Lightning Claw")	Indeterminate	New South Wales	Partial skeleton including parts of the lower arm, claws, lower leg, part of the hip, and pieces of ribs.
Noasauridae	Indeterminate		Cervical vertebra
Sauropoda	Indeterminate		A tooth

Pterosaurs
Genus	Species	Presence	Notes	Images
Anhangueria	Indeterminate		"two isolated tooth crowns", possible limb elements

Turtles
Genus	Species	Presence	Notes	Images
Spoochelys	S. ormondea		Perichelydian stem-turtle
Chelidae	Indeterminate

• List of dinosaur-bearing rock formations
• South Polar region of the Cretaceous
• Western Interior Seaway
• Cenomanian-Turonian extinction event

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