# Griman Creek Formation

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 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.

## 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

Dipnoi of the Griman Creek Formation :
| Taxa | Species | Material |
| Ceratodus | C. diutinus | Isolated tooth plates |
| Metaceratodus | M. wollastoni | Isolated tooth plates |
| Neoceratodus | N. potkooroki | Isolated tooth plates |

### Actinopterygii

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

### Mammals
#### Monotremes

Mammals :
| Genus | Species | Materials | Notes |
| 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

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

### 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.
Dinosaurs :
| Genus | Species | Presence | Notes |
| 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

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

### Testudines

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