Geology
Doug Finlayson
The landscapes of the Yass-Canberra region are the deeply eroded remnants of rocks that were formed 488 - 359 million years ago. During those times Australia was part of a super-continent called Gondwanaland that also included Antarctica, South America and India.
The area of the Murrumbidgee - Ginninderra Gorges National Park is located in a topographic low region defined by three major fault systems: -
- Pig Hill Fault - one of many north-south trending faults to the west of the park.
- Winslade Fault - a northeast-southwest trending cross-fault to the south of the park evident at the Cotter water pumping station on the Murrumbidgee River.
- Deakin Fault - a northwest-southeast trending cross-fault that extends through central Canberra.
The area as a whole is dominated by elements of two volcanic suites of igneous rocks recognised throughout the whole Canberra region - the Hawkins Volcanic Suite aged about 428-424 million years (Ma), and the slightly younger Laidlaw Volcanic Suite aged about 424-422 Ma. These suites are both within the Silurian geological period (444-416 Ma).
Some granite pluton outcrops are also evident along the bed of the Murrumbidgee River.
Outcrop of the Walker Volcanics, Hawkins Volcanic Suite, along the Murrumbidgee River in the Woodstock Nature Reserve.
Ginninderra Porphyry outcrop of the Laidlaw Volcanic Suite downriver from Cusaks Crossing.