| Terrigal Formation | |
| Period: | Triassic |
| Age: | Early-Mid Triassic ~ |
| Type: | Geological formation |
| Prilithology: | Sandstone and siltstone |
| Otherlithology: | Claystone |
| Unitof: | Narrabeen Group |
| Underlies: | Hawkesbury Sandstone |
| Thickness: | up to 330m (1,080feet) |
| Region: | New South Wales |
| Extent: | Sydney Basin |
The Terrigal Formation is a geologic formation in the Sydney Basin in eastern Australia. Commonly seen in the Central Coast region, this stratum is up to 330 metres thick. Formed in the early to mid Triassic, it is part of the Narrabeen Group of sedimentary rocks. This formation includes interbedded fine to medium-grained sandstone and siltstone, with minor deposits of claystone. Hawkesbury Sandstone occasionally overlies the Terrigal Formation.[1] [2] Numerous fossils are known from this area, including the temnospondyl amphibians Arenaerpeton supinatus[3] and Platycepsion wilksoni.