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Australia’s Impact Craters

Henbury Meteorite Craters, NT

These craters are located in the Northern Territory of Australia. The largest crater is approximately 180 metres in diameter. At Henbury there are 13 to 14 craters ranging from 7 to 180 metres in diameter and up to 15 metres in depth that were formed when the meteor broke up before impact. Several tonnes of iron-nickel fragments have been recovered from the site. The craters are named for Henbury Station, a nearby cattle station named in 1875 for the family home of its founders at Henbury in Dorset, England. The first detailed survey of the crater area did not take place until 1937. More than 1200 kilograms of iron meteorite fragments have been collected from around the craters.
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  • Bedout High Crater (WA)

    The underwater Bedout structure 300km west of Broome, in the Canning Basin off the coast of Western Australia, has been sited as one of the possible impacts that contributed to one of the greatest extinction events known. At the end of the Permian Period, around 250 MYA, it has been estimated that more than 90% of marine species, and 70% of terrestrial species, may have become extinct. The extinction event seems to have been a sudden, global occurrance, lasting less than a million years (which in geological terms is very rapid).

    The Bedout structure has a central uplift of around 40km in diamater, with a transient crater size of around 100km diameter. The original crater probably measured around 200km in diameter in total, comparable to the Chicxulub crater in Mexico which may have contributed to the extinction of (non-avian) dinosaurs at the end of the Cretaceous Period. Several other Permian/Triassic sites from this region of the world have yielded evidence of large impacts. At Graphite Peak in Antarctica, the large size of the shocked quartz grains (>100 micrometres) seem to indicate a large impact occurred close to that site. Shocked quartz grains ranging from 150 micrometers in size have also been found at Fraser Park, adjacent to the site at Wybung Head in the Sydney Basin.

    Meteorite fragments from the P/Tr boundary at Graphite Peak range in size from 50-400mm, and the chemical composition of the fragments matches that of similar finds in Meishan, southern China, and perhaps Sasayama, Japan, these also dating to the Permian/Triassic boundary. This may indicate that several objects impacted the earth at around the same time. Indeed, the Araguainha Dome in Brazil is an impact structure 40km wide that also dates to the P/Tr boundary. Alternatively, all of these sites yeilding shocked quartz and meteorific fragments may be evidence of one large impact in Southern Gondwana, which managed to spread ejecta over a significant portion of the ancient world.
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    • Gosses Bluff Impact Crater (NT)

      Gosses Bluff is located west of Alice Springs and south of the Macdonnell Ranges, in the arid Missionary Plain in the Northern Territory. The bluff itself is a circular ring of hills 5km in diameter and 200m high, in the centre of a crater. It was formed 142 million years ago by the impact of an asteroid or comet up to 2km in diameter. The hills are part of the crater’s central uplift, which formed when the earth’s surface recoiled from the impact. A circular drainage system 24km in diameter marks the outer ring of the crater. The bluff is deeply significant to the Western Arrernte Aboriginal people, who own the Tnorala Conservation Reserve that contains the crater.

      This impact is believed to have occurred at the very end of the Jurassic Period at a time when the largest dinosaurs, the sauropods, declined in number. This impact alone would not have been large enough to cause mass extinctions on a broad scale, but would certainly have caused a lot of local damage. The Morokweng crater in South Africa dates to roughly the same time period, although at 70km in diameter was a much larger impact than that which created Gosses Bluff.
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      • Woodleigh Crater (WA)

        The Woodleigh crater, mostly hidden beneath red sand, is located on Woodleigh Station, east of Shark Bay in Western Australia. The crater is up to 120km in diameter, and is recorded as the fourth largest impact crater on Earth’s surface. Research suggests a bolide (asteroid or comet) 5km in diameter caused the crater. The impact structure is entirely underground. The central uplift structure 20km in diameter was first detected 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 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, originally thought to be Late Triassic or Late Permian, most likely dates to around 364 MYA, corresponding to a minor extinction event in the Late Devonian Period when around 40% of species disappeared. Evidence for another impact in the Moroccan desert at around the same time suggests that more than one impact was involved in the extinction event.
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        • Wolfe Creek Meteorite Crater (WA)

          130km south of Halls Creek, Western Australia, is Wolfe Creek Meteorite Crater National Park, covering an area of 1 460 ha. Formed by a giant meteorite which crashed to earth thousands of years ago, the crater is 800 metres wide and 25 metres deep. The second largest meteorite crater in the world, access can be gained by an unsealed road off Highway 1. The road is generally passable from May to November but a check with the Halls Creek Shire Office for a road condition report is recommended throughout the year.

          In southwest Tasmania, the Darwin meteorite impact crater contains small seams of glass produced by the collision of the meteor with local rocks. Small pieces of Darwin glass in the form of flakes and tools has been identified in dated archaeological deposits up to 28,000 BP. The distance of the sites from the Darwin crater, in terms of the actual routes humans would need to take in this terrain, varies from 25 to over 100km.
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          • Veevers Crater (WA)

            The Veevers Crater in Western Australia (Long. 22°58’S Lat:125°22’E) is named after an Australian Geologist, Professor John Veevers. It was first discovered in 1975 and it is estimated to be around One million years old. The crater is one of only two impact craters where group IIAB meteorites have been discovered. The other is the Sikhote-Alin crater group in Russia. It is approximately 70 metres in diameter and approximately 1 kilogram of fragments have been recovered.
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            • Dalgaranga Crater (WA)

              The red earth of Dalgaranga Station 75 kilometres west of Mount Magnet in Western Australia is scarred by the impact of a huge meteorite which, not that long ago, slammed a crater into the ground. The crater, the smallest in australia with a diameter of just 21 metres, was discovered by an Aboriginal stockman, Billy Seward in 1921 when he almost rode full-tilt into it during mustering. He showed it to station manager Gerard Wellard, who recognized it for what it was.

              Realizing the crater’s scientific importance, he gathered up enough fragments of the meteorite to fill a gallon tin (about 4.5 litres) and sent them to the WA Museum. Unfortunately, the Museum and the Mines Department shared the same building at that stage, and the samples were misplaced. By the time Wellard showed up in Perth almost a year later, the Mines Department was no longer in the same building as the Museum and nobody knew where the fragments were. One of the fragments was found years later among the dust and red tape and a report analysing this piece was released in 1938. Unfortunately, the report contained a few mistakes, the chief error being that the crater was first reported by a Mr Willard, not Wellard. This caused a major problem in years to come. It was only resolved by the most extraordinary coincidence. Scientific interest in the Dalgaranga Crater grew after the publication of a scientific paper in 1960.
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              • Tookoonooka Crater (Qld)

                The Tookoonooka crater in south central Queensland is about 55km in diameter. It was discovered in the early 1980s when petroleum exploration revealed an anomalous circular structure. Tookoonooka has a central uplift dome that is 22km in diameter.

                Impact melt breccias have been found about 25km southeast of the central uplift structure, and have also been found filling the annular structure around the central uplift. The clasts consist of impact breccia fragments, as well as devitrified impact melt glass. Breccia samples have also been found during drilling into the central uplift dome; these breccias have a devitrified glassy matrix, with angular clasts.

                Tookoonooka has been dated to around 128 MYA, based on studies of local pollen sequences. At this time a large inland sea covered much of Queensland, suggesting this impact landed somewhere off-shore. No dinosaur remains are known from Queensland from around this time, so the effect of the impact on local species is uncertain. Most Queensland species date to 110 MYA or later, with the sauropod Rhoetosaurus living 40-50 million years before the impact. It may have had more of an effect on marine species, however most Queensland marine reptiles are also only known from 110 MYA or later. Without a good sample of species from immediately before the impact, it is impossible to say whether the Tookoonooka impact caused an extinction event. Extinction event or not, an impact of this size would still have done a lot of damage to the local area.

About Impact Craters

It is estimated that each year the Earth receives about 100,000 tonnes of material from space. If this mass all arrived at once it would be a catastrophe! Most of it comes in meteor showers and is burned up by friction with air molecules in the upper atmosphere: a “shooting star” is a meteoroid either burning up or just grazing our atmosphere. These objects may approach Earth at speeds up to 70 km per second! The hundreds of impact craters on the earth’s surface were caused by asteroids or comets colliding with our plant.

Around twenty four impact craters are known in Australia, ranging in size from less than 20m in diameter to perhaps more than 100km (see the World Crater Inventory). Some date back hundreds of millions (even billions) of years. Others are as recent as just a few thousand years old. Most probably did little more than localised damage. At least two Australian impacts may have contributed to mass extinctions.

There are several features geologists look for when identifying a geological structure as that of an ancient impact. Most craters are circular in shape, with an inner ring of raised rock known as an uplift. The central uplift structure forms when the underlying rocks rebound after the impact, throwing up a central mound or ring of rock. Surrounding the uplift will be a depression that is usually several times larger than the raised area. In time the outer ring may weather away, leaving only the central uplifted structure.

Other evidence for a large impact comes in the form of shocked quartz or breccia, or even veins of melted glass. These altered minerals form when sediments are heated and compressed by the impact, often to a greater degree than volcanism or earthquake activity could have produced. Occasionally elements that are rare on earth may occur in abundance in an asteroid or comet. The Chicxulub impact in Mexico, thought to be one of the causes of the extinction event that killed off non-avian dinosaurs, left an elemental calling card that can be found in many places around the world. The element known as iridium is rare here on earth (although does exist in the earths molten core), but can occur in higher concentrations in asteroids or comets. An iridium ‘spike’ occurs as a thin layer just above Late Cretaceous sediments all over the world, suggesting that a large impact threw up enough dust (containing iridium from the vaporised asteroid or comet) into the atmosphere for it to eventually settle almost everywhere. Of the two dozen or so impact structures known in Australia, these are the four largest.

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