Wallabi Limestone is the name given to the dense calcretised, limestone

Limestone

Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....

 platform that underlies the Wallabi Group

Wallabi Group

The Wallabi Group is the northern-most group of islands in the Houtman Abrolhos. Nominally located at , it is 58 kilometres from the Australian mainland, and about 9 kilometres from the Easter Group....

 of the Houtman Abrolhos

Houtman Abrolhos

The Houtman Abrolhos is a chain of 122 islands, and associated coral reefs, in the Indian Ocean off the west coast of Australia. Nominally located at , it lies about eighty kilometres west of Geraldton, Western Australia...

, an archipelago

Archipelago

An archipelago , sometimes called an island group, is a chain or cluster of islands. The word archipelago is derived from the Greek ἄρχι- – arkhi- and πέλαγος – pélagos through the Italian arcipelago...

 off the coast of Western Australia

Western Australia

Western Australia is a state of Australia, occupying the entire western third of the Australian continent. It is bounded by the Indian Ocean to the north and west, the Great Australian Bight and Indian Ocean to the south, the Northern Territory to the north-east and South Australia to the south-east...

. This platform, which arises abruptly from a flat shelf, is about 40 metres thick, and is of marine

Marine (ocean)

Marine is an umbrella term. As an adjective it is usually applicable to things relating to the sea or ocean, such as marine biology, marine ecology and marine geology...

 biogenic origin, having originated as a coral reef

Coral reef

Coral reefs are underwater structures made from calcium carbonate secreted by corals. Coral reefs are colonies of tiny living animals found in marine waters that contain few nutrients. Most coral reefs are built from stony corals, which in turn consist of polyps that cluster in groups. The polyps...

. It reached its maximum size during the Eemian Stage (about 125,000 years ago), when sea levels were higher than at present. The subsequent fall in sea level resulted in the reef becoming emergent in places, thus forming the basement of the group's "central platform" islands, namely West Wallabi Island

West Wallabi Island

West Wallabi Island is an island in the Wallabi Group of the Houtman Abrolhos, located in the Indian Ocean off the west coast of mainland Australia.-History:...

, East Wallabi Island

East Wallabi Island

East Wallabi Island is an island in the Wallabi Group of the Houtman Abrolhos, located in the Indian Ocean off the west coast of mainland Australia.-History:East Wallabi Island played an important role in the story of the Batavia shipwreck and massacre...

 and North Island

North Island (Houtman Abrolhos)

North Island is the northernmost island in the Houtman Abrolhos, a coral reef archipelago in the Indian Ocean off the coast of Mid West Western Australia. Located about 14 km from the nearest island group, it is one of the largest islands in the Houtman Abrolhos, and one of the few to support...

.