The Australasian strewnfield is the youngest and largest of the tektite strewnfields, with recent estimates suggesting it might cover 10%–30% of the Earth's surface. Research indicates that the impact forming the tektites occurred around 790,000 years ago, probably in Southeast Asia.
The c. 790,000-year-old strewnfield (Schneider, 1992) includes most of Southeast Asia (Thailand, Laos, Vietnam, Cambodia, and Southern China). The material from the impact stretches across the ocean to include the Philippines, Indonesia, Malaysia, and Java. It also reaches far west out into the Indian Ocean, and south to Australia, including Tasmania. Since the 1960s, it has been accepted that the strewnfield included Hainan in southern China to Australia or about 10% of the Earth's surface. This was later extended by finds in Africa and Tasmania to 20%. Recent additional finds in northern Tibet and Guangxi increased the strewnfield to about 30% of the Earth's surface, or almost 150 million km2, or about the size of the entire world's landmass.
The Earth Impact Database lists about 26 known craters younger than a million years old, almost all of which are less than 2 km in diameter (except the 3 km Agoudal Crater in Morocco). Very close to this time frame is the 14-km Zhamanshin crater in Kazakhstan which at one time (Glass, 1979) was proposed as the source of the Australasian strewn field.
However, due to the enormous size of the Australasian strewn field, the impact crater has been conjectured to be significantly larger than the known ones. Schmidt and Wasson (1993) suggested it could be a 14–17 km crater beneath the Mekong Valley, Hartung and Koeberl (1994) proposed the elongated 100 km x 35 km Tonlé Sap lake in Cambodia, Glass (1994) estimated it to be between 32–114 km in diameter in Cambodia, while Schnetzler (1996) suggested a 35–40 km structure in southern Laos. Later, Glass (1999) also considered southern Laos or an adjacent area as a possible source. Lee and Wei (2000) gave its size as 90–116 km and P. Ma et al. (2001) using beryllium-10 postulated the crater as between southern Laos and Hainan, possibly within the Gulf of Tonkin. More recently in 2019, Sieh et al. proposed on the basis of 4 lines of evidence that the crater lies buried beneath the Bolaven volcanic field in southern Laos.
Alternatively, Wasson, who found layered tektites in central Thailand, conjectured it could have been a multiple impact event spread out over the region, though it seems this scenario also raises substantial problems.
The Wilkes Land crater in Antarctica has been proposed as a possible source. It has also been suggested that the impact may have triggered the Brunhes–Matuyama reversal of 781,000 years ago.
Stone tools have been found within the debris field along with a charcoal layer likely caused by fires from the impact. It has been suggested that the subsequent local deforestation after the fires allowed this population easier access to stones useful for tool-making.
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