| Mittagong Formation | |
| Period: | Triassic |
| Type: | Geological formation |
| Underlies: | Ashfield Shale |
| Overlies: | Hawkesbury sandstone |
| Thickness: | up to 10m (30feet) |
| Location: | Sydney Basin |
| Country: | Australia |
| Region Ts: | Mittagong |
| Country Ts: | Australia |
| Thickness Ts: | 15 metres |
The Mittagong Formation is a sedimentary rock unit in the Sydney Basin in eastern Australia.[1]
Laid down in the Triassic Period, it may be seen as an interval of interbedded fine-grained sandstone and shale between the Ashfield Shale (above) and the Hawkesbury sandstone (below). The maximum thickness around Sydney may be ten metres.[2] Near Town Hall railway station, the formation is 8 metres thick. In the type area at Mittagong it is 15 metres thick.
In northern Sydney it can be seen in several areas, such as West Pymble[3] and Mount Ku-ring-gai.[4] This rock formation is associated with the critically endangered Sydney Turpentine-Ironbark Forest.[5]