Woodleigh crater
Encyclopedia
Woodleigh is a large meteorite
impact crater
(astrobleme) in Western Australia
, centred on Woodleigh Station east of Shark Bay
. A team of four scientists at the Geological Survey of Western Australia
and the Australian National University
, led by Arthur J. Mory, announced the discovery in the 15 April 2000 issue of Earth and Planetary Science Letters.
The crater is not exposed at the surface and therefore its size is uncertain. The original discovery team believe it may be up to 120 km (74.6 mi) in diameter, but others argue it may be much smaller, with one study suggesting a diameter closer to 60 km (37.3 mi). The larger estimate, if correct, would make this the fourth largest confirmed impact structure in the world, and imply a bolide (asteroid or comet) about 5 – in diameter.
The central uplift, interpreted to be 20 km (12.4 mi) in diameter, was first intersected by drilling activities in the late 1970s; however its significance as an impact structure was only realised in 1997 during a gravity survey. In 1999 a new core sample was taken. The thin veins of melted glass, breccia
, and shocked quartz
found would have formed under pressures 100,000 times greater than atmospheric pressure at sea level, or between 10 and 100 times greater than those generated by volcanic or earthquake activity. Only a large impact could have generated such conditions.
The Woodleigh impact event
, originally thought to have occurred between the Late Triassic
and Late Permian
, is now thought to date from 364 ± 8 million years (Late Devonian
). This time corresponds approximately to a minor extinction event
when around 40% of species disappeared. There is evidence for other large impact events at around the same time, so if the extinction is related to impact, perhaps more than one crater was involved.
Of the two dozen or more impact craters known in Australia, the three largest are Woodleigh, Acraman
, and Tookoonooka
.
The proximity to Shark Bay
and its orientation suggest the bay is the incipient part of the track of the Woodleigh impact. Most of the track, which is cut off at the edge of the continental shelf, would be lost after the break-up of Gondwana.
Meteorite
A meteorite is a natural object originating in outer space that survives impact with the Earth's surface. Meteorites can be big or small. Most meteorites derive from small astronomical objects called meteoroids, but they are also sometimes produced by impacts of asteroids...
impact crater
Impact crater
In the broadest sense, the term impact crater can be applied to any depression, natural or manmade, resulting from the high velocity impact of a projectile with a larger body...
(astrobleme) in 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...
, centred on Woodleigh Station east of Shark Bay
Shark Bay
Shark Bay is a World Heritage listed bay in Western Australia. The term may also refer to:* the locality of Shark Bay, now known as Denham* Shark Bay Marine Park* Shark Bay , a shark exhibit at Sea World, Gold Coast, Australia* Shire of Shark Bay...
. A team of four scientists at the Geological Survey of Western Australia
Geological Survey of Western Australia
The Geological Survey of Western Australia is an authority within the Department of Mines and Petroleum of the Government of Western Australia that is responsible for surveying and exploration of Western Australia's geological resources....
and the Australian National University
Australian National University
The Australian National University is a teaching and research university located in the Australian capital, Canberra.As of 2009, the ANU employs 3,945 administrative staff who teach approximately 10,000 undergraduates, and 7,500 postgraduate students...
, led by Arthur J. Mory, announced the discovery in the 15 April 2000 issue of Earth and Planetary Science Letters.
The crater is not exposed at the surface and therefore its size is uncertain. The original discovery team believe it may be up to 120 km (74.6 mi) in diameter, but others argue it may be much smaller, with one study suggesting a diameter closer to 60 km (37.3 mi). The larger estimate, if correct, would make this the fourth largest confirmed impact structure in the world, and imply a bolide (asteroid or comet) about 5 – in diameter.
The central uplift, interpreted to be 20 km (12.4 mi) in diameter, was first intersected by drilling activities in the late 1970s; however its significance as an impact structure was only realised in 1997 during a gravity survey. In 1999 a new core sample was taken. The thin veins of melted glass, breccia
Breccia
Breccia is a rock composed of broken fragments of minerals or rock cemented together by a fine-grained matrix, that can be either similar to or different from the composition of the fragments....
, and shocked quartz
Shocked quartz
Shocked quartz is a form of quartz that has a microscopic structure that is different from normal quartz. Under intense pressure , the crystalline structure of quartz will be deformed along planes inside the crystal...
found would have formed under pressures 100,000 times greater than atmospheric pressure at sea level, or between 10 and 100 times greater than those generated by volcanic or earthquake activity. Only a large impact could have generated such conditions.
The Woodleigh impact event
Impact event
An impact event is the collision of a large meteorite, asteroid, comet, or other celestial object with the Earth or another planet. Throughout recorded history, hundreds of minor impact events have been reported, with some occurrences causing deaths, injuries, property damage or other significant...
, originally thought to have occurred between the Late Triassic
Triassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
and Late Permian
Permian
The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...
, is now thought to date from 364 ± 8 million years (Late Devonian
Devonian
The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...
). This time corresponds approximately to a minor extinction event
Extinction event
An extinction event is a sharp decrease in the diversity and abundance of macroscopic life. They occur when the rate of extinction increases with respect to the rate of speciation...
when around 40% of species disappeared. There is evidence for other large impact events at around the same time, so if the extinction is related to impact, perhaps more than one crater was involved.
Of the two dozen or more impact craters known in Australia, the three largest are Woodleigh, Acraman
Acraman crater
Acraman crater is a deeply eroded impact crater in the Gawler Ranges of South Australia. Its location is marked by Lake Acraman, a circular ephemeral playa lake about 20 km in diameter....
, and Tookoonooka
Tookoonooka crater
Tookoonooka is a large meteorite impact crater situated in southwestern Queensland, Australia. It lies deeply buried within Mesozoic sedimentary rocks of the Eromanga Basin and is not visible at the surface....
.
The proximity to Shark Bay
Shark Bay
Shark Bay is a World Heritage listed bay in Western Australia. The term may also refer to:* the locality of Shark Bay, now known as Denham* Shark Bay Marine Park* Shark Bay , a shark exhibit at Sea World, Gold Coast, Australia* Shire of Shark Bay...
and its orientation suggest the bay is the incipient part of the track of the Woodleigh impact. Most of the track, which is cut off at the edge of the continental shelf, would be lost after the break-up of Gondwana.