Exmouth Plateau

Exmouth Plateau
Image of the Northern Carnarvon Basin and other outlying structure on the coast of the Northwest Australian Margin
Type	Extensional Passive Margin
Location
Coordinates	19° 00'00" S, 114° 00'00" E
Region	Northwestern Australia
Country	Australia

The Exmouth Plateau is an elongate northeast striking extensional passive margin located in the Indian Ocean roughly 3,000 meters offshore from western and northwestern Western Australia.

The plateau makes up the westernmost structural unit of the Northern Carnarvon Basin, which comprises the Exmouth, Barrow, Dampier, and Beagle Sub-basins, and the Rankin Platform. The Exmouth Plateau was once a part of the northern shore of eastern of Gondwanaland until it broke away during Late Jurassic to Early Cretaceous, leaving behind the oceanic crust of the Argo, Cuvier, and Gascoyne abyssal plains that now surround the distal margins of Exmouth Plateau.

In the Late Jurassic, Gondwanaland begins to break apart creating Western Gondwana, which was composed of the South American and African continental land masses, and Eastern Gondwana. The Eastern Gondwanian continent was made Madagascar, Greater India, Antarctica, and Australia. During this period of time Australia shared its southern margin with Antarctica and the western margin (now the Exmouth Plateau) with Greater India. The formation of the Exmouth's northern margin, the Argo Abyssal Plain, was not initiated until 155 million years ago when Australia broke apart from a continental fragment of the Burma plate that's present location is argued to be subsumed under Asia. It wasn't until 20 million years later that the Greater Indian land mass broke from western Australia, forming the central and southern margins of the Exmouth Plateau now known as the Gascoyne and Cuvier Abyssal Plains. As Australia continued to diverge away from the Antarctic land mass, it migrated in a northeastern direction and rotated counterclockwise to it present location, leaving the Exmouth Plateau along the continent's western margin.

In the begin of the late Triassic, high volumes of sediments accumulate off of the shoreline of western Australia to the northern extend of the Exmouth Plateau by the Mungaroo Deltas. The Carnian (237-228 Ma) to Norian (228-209 Ma) aged fluviodeltaic sediments deposited were siliciclastic claystones and sandstones, and detritus which would late make up the coals found in Mungaroo Formation. As extensional rifting between Greater Indian and the Australian continued, magmatic intrusion along the westernmost section of the Exmouth Plateau caused further rifting to the outer margins. By the end of the Late Triassic (209-201 Ma) tectonic activity had relatively slowed down and less deltaic sediments were deposited compared to the Carnian and Norian. More marine sedimentary deposit such as carbonates are found during this time period.