Western continental shelves of Australia

Geologically, the Sahul Shelf () is a part of the

continental shelf A continental shelf is a portion of a continent that is submerged under an area of relatively shallow water, known as a shelf sea. Much of these shelves were exposed by drops in sea level during glacial periods. The shelf surrounding an island ...

of the Australian continent, lying off the northwest coast of

mainland Australia Mainland Australia is the main landmass of the Australian continent, excluding the Aru Islands, New Guinea, Tasmania, and other Australian offshore islands. The landmass also constitutes the mainland of the territory governed by the Commonw ...

Etymology

The name "Sahull" or "Sahoel" appeared on 17th century Dutch maps applied to a submerged sandbank between Australia and

Timor Timor is an island at the southern end of Maritime Southeast Asia, in the north of the Timor Sea. The island is divided between the sovereign states of East Timor on the eastern part and Indonesia on the western part. The Indonesian part, ...

. On his 1803 map,

Matthew Flinders Captain Matthew Flinders (16 March 1774 – 19 July 1814) was a British navigator and cartographer who led the first inshore circumnavigation of mainland Australia, then called New Holland. He is also credited as being the first person to ut ...

noted the "Great Sahul Shoal" where Malays came from

Makassar Makassar (, mak, ᨆᨀᨔᨑ, Mangkasara’, ) is the capital of the Indonesian province of South Sulawesi. It is the largest city in the region of Eastern Indonesia and the country's fifth-largest urban center after Jakarta, Surabaya, Meda ...

to fish for ''trepang'' (

sea cucumber Sea cucumbers are echinoderms from the class Holothuroidea (). They are marine animals with a leathery skin and an elongated body containing a single, branched gonad. Sea cucumbers are found on the sea floor worldwide. The number of holothuri ...

). The name Sahul Shelf ( nl, Sahoel-plat) was coined in 1919 by G.A.F. Molengraaff, an authority on the geology of the then

Dutch East Indies The Dutch East Indies, also known as the Netherlands East Indies ( nl, Nederlands(ch)-Indië; ), was a Dutch colony consisting of what is now Indonesia. It was formed from the nationalised trading posts of the Dutch East India Company, whic ...

Geography

The Sahul Shelf proper stretches northwest from Australia much of the way under the Timor Sea towards Timor, ending where the seabed begins descending into the

Timor Trough The Timor Trough is an oceanic trough that is a continuation of the Sunda Trench (Java Trench) that marks the boundary between the Indo-Australian Plate and the Timor Plate. It is separated from the Sunda Trench by a sag near Sumba Island at the ...

. To the northeast, the Sahul Shelf merges into the Arafura Shelf, which runs from the northern coast of Australia under the Arafura Sea north to

New Guinea New Guinea (; Hiri Motu: ''Niu Gini''; id, Papua, or , historically ) is the world's second-largest island with an area of . Located in Oceania in the southwestern Pacific Ocean, the island is separated from Australia by the wide Torres ...

. The Aru Islands rise from the Arafura Shelf. The Sahul Shelf is sometimes taken to also include the Rowley Shelf to the southwest of

Cape Leveque Cape Leveque is at the northernmost tip of the Dampier Peninsula in the Kimberley region of Western Australia. Cape Leveque is (via the Cape Leveque Road) north of Broome, and is remote with few facilities. Nevertheless, the Cape's sandy beach ...

, girding the north coast of

Western Australia Western Australia (commonly abbreviated as WA) is a state of Australia occupying the western percent of the land area of Australia excluding external territories. It is bounded by the Indian Ocean to the north and west, the Southern Ocean to t ...

as far as

North West Cape North West Cape is a peninsula in the north-west of Western Australia. Cape Range runs down the spine of the peninsula and Ningaloo Reef runs along the western edge. It is in the Gascoyne region and includes the town of Exmouth. History In 161 ...

. The existence of an extensive Sahul Shelf was suggested in 1845 by George Windsor Earl who called it the "Great Australian Bank" and noted that macropods (kangaroos) were found on Australia, New Guinea, and the Aru Islands. Earl also suggested the existence of the Sunda Shelf (which he called the "Great Asiatic Bank") covering the western

Malay Archipelago The Malay Archipelago ( Indonesian/ Malay: , tgl, Kapuluang Malay) is the archipelago between mainland Indochina and Australia. It has also been called the " Malay world," " Nusantara", "East Indies", Indo-Australian Archipelago, Spices Arc ...

and the

Malay Peninsula The Malay Peninsula ( Malay: ''Semenanjung Tanah Melayu'') is a peninsula in Mainland Southeast Asia. The landmass runs approximately north–south, and at its terminus, it is the southernmost point of the Asian continental mainland. The ar ...

. In the 1970s, biogeographers coined "

Sundaland Sundaland (also called Sundaica or the Sundaic region) is a biogeographical region of South-eastern Asia corresponding to a larger landmass that was exposed throughout the last 2.6 million years during periods when sea levels were lower. It ...

" and " Sahul" as contrastive names for the continental regions extending from the adjacent shelves.

Geology

When sea levels fell during the

Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fina ...

ice age An ice age is a long period of reduction in the temperature of Earth's surface and atmosphere, resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers. Earth's climate alternates between ice ages and gre ...

, including the

Last Glacial Maximum The Last Glacial Maximum (LGM), also referred to as the Late Glacial Maximum, was the most recent time during the Last Glacial Period that ice sheets were at their greatest extent. Ice sheets covered much of Northern North America, Northern Eu ...

about 18,000 years ago, the Sahul Shelf was exposed as dry land. Evidence of the shoreline of this time has been identified in locations which now lie 100 to 140 metres below sea level. A Flash-based interactive timeline of sea level changes was developed by Monash University in the 2000s.

Ecology

The Arafura Shelf formed a land bridge between Australia, New Guinea, and the Aru Islands, and these lands share many

Marsupial Marsupials are any members of the mammalian infraclass Marsupialia. All extant marsupials are endemic to Australasia, Wallacea and the Americas. A distinctive characteristic common to most of these species is that the young are carried in ...

mammals, land birds, and freshwater fish as a result.

Lydekker's Line Richard Lydekker (; 25 July 1849 – 16 April 1915) was an English naturalist, geologist and writer of numerous books on natural history. Biography Richard Lydekker was born at Tavistock Square in London. His father was Gerard Wolfe Lydekker, ...

, a

biogeographical Biogeography is the study of the distribution of species and ecosystems in geographic space and through geological time. Organisms and biological communities often vary in a regular fashion along geographic gradients of latitude, elevation, ...

line, runs along the edge of Sahul Shelf where it drops off into the deep waters of the

Wallacea Wallacea is a biogeographical designation for a group of mainly Indonesian islands separated by deep-water straits from the Asian and Australian continental shelves. Wallacea includes Sulawesi, the largest island in the group, as well as ...

biogeographical area. Wallacea sits in a gap between the Sahul Shelf and the Sunda Shelf, part of the continental shelf of Southeast Asia. The land bridge enabled early human migrations to Australia.

References

{{Submerged landmasses Continental shelves Geology of the Pacific Ocean Landforms of Oceania Landforms of Southeast Asia Landforms of the Pacific Ocean Landforms of Indonesia Landforms of Papua New Guinea Landforms of Western New Guinea Coastline of the Northern Territory Coastline of Western Australia

Etymology

Geography

Geology

Ecology

See also

References