Australasian strewnfield
The Australasian strewnfield is the youngest and largest of the tektite strewnfields, with recent estimates suggesting it may cover 10%-30% of the Earth's surface.
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 and Tasmania. Since the 1960s, it has been accepted that the strewn field 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.
The Earth Impact Database lists about 25 known craters less than a million years old, almost all of which are less than 2 km in diameter. The notable exception 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, Schnetzler (1996) considered a 35–40 km structure in southern Laos, Hartung and Koeberl (1994) proposed the elongated 100 km x 35 km Tonlé Sap lake in Cambodia (visible in the map at the side), while Glass (1994) estimated it to be between 32 and 114 km in diameter in Cambodia. Glass (1999) also suggested southern Laos or an adjacent area as a possible source. More recently, Lee and Wei (2000) gave its size as 90 to 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.
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