3D animation showing Gosses Bluff crater remnants in Australia.
Gosses Bluff (Gosse’s Bluff) is thought to be the eroded remnant of central uplift of larger impact crater. It is located in the southern Northern Territory, near the centre of Australia, about 175 km west of Alice Springs and about 212 km to the northeast of Uluru. The original crater is thought to have been formed by the impact of an asteroid or comet approximately 142.5 ± 0.8 million years ago, very close to the Jurassic – Cretaceous boundary. The original crater rim has been estimated at about 22 km in diameter, but this has been eroded away. The 5 km diameter, 180 m high crater-like feature, still visible, is interpreted as the eroded relic of the crater’s central uplift. The impact origin of this topographic feature was first proposed in the 1960s, the strongest evidence coming from the abundance of shatter cones. In the past the crater has been the target of petroleum exploration, and two abandoned exploration wells lie near its centre.
The bolide struck a flat land surface that was higher than the present surface. The explosion on impact could only be described as cataclysmic, completely vaporising the bolide, sending up a mushroom cloud, similar to that produced by the detonation of a nuclear bomb, thousands of metres into the atmosphere. It has been estimated that the energy of the impact would have been at least 200,000 times that of the Hiroshima atomic bomb. As well as devastating thousands of square kilometres around the impact it is believed it would have been felt globally.
The size of the impacting bolide is unknown but it is thought that it must have been travelling at about 70 km/second. It is thought the bolide penetrated less than 600 m below the surface before vaporising but the impact was so great that breakage of rock strata deeper than 4 km occurred. The impact caused very severe compression followed by rebound which produced a very large crater (20-25 km across) and brought the central core rocks to the surface from thousands of metres below. The rocks of the central section came from 3000+ m below the surface and those of the outer section from about 200 m. It has been estimated that the present surface is about 2 km lower than the original impact surface.
The rim, 180 m above the surrounding plain, is bounded by steep cliffs. The depression in the centre of the structure is only slightly above the level of the surrounding plain, on the northern edge of the Amadeus Basin, a syncline with a flat floor comprised of strata dated to the Proterozoic and Palaeozoic, about 8 km thick. On the northeast side of the crater the rim has been breached by stream erosion. On the crest of the rim, about 900 m above sea level, there is an ancient erosion surface that is believed to be of Late Cretaceous or Tertiary age.
Evidence implicating a meteorite impact, according to Twidale & Campbell, includes sediments that are steeply dipping and locally overturned, many shatter cones, deformation lamellae, as well as planar features in quartz, strongly brecciated sediments, that include fragments up to tens of metres in diameter, and devitrified glass. There are also gravity and magnetic anomalies over Gosses Bluff similar to those from other structures that are presumed to be impact structures. The most recent rocks deformed by the impact have been dated to the Late Devonian, absolute age determinations giving an age of about 144 Ma, in the Late Jurassic.
The remnant crater was named Gosses Range by the explorer Ernest Giles in 1872 after H. Gosse, a fellow of the Royal Society.
To the Western Arrernte Aboriginal people this site is known as Tnorala, and is a sacred place w. It is now located in the Tnorala Conservation Reserve. A Western Arrernte story attributes its origins to a cosmic impact: in the Dreaming, a group of celestial women were dancing as stars in the Milky Way. One of the women grew tired and placed her baby in a wooden basket. As the women continued dancing, the basket fell and plunged into the earth. The baby fell to the earth and forced the rocks upward, forming the circular mountain range. The baby’s parents, the evening and morning star, continue to search for their baby to this day.
Sources:
Leave a Reply