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 788,000 years ago, most likely in Southeast Asia.
Introduction
The c. 788,000-year-old strewnfield 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%. Additional finds in northern Tibet, Guangxi and Antarctica increased the strewnfield to about 30% of the Earth's surface, or almost , or about the size of the entire world's landmass.
Source crater
The current consensus is that the source impact crater for the Australasian strewnfield lies somewhere in Southeast Asia. It is argued that due to the enormous size of the Australasian strewnfield, the source impact crater must be significantly larger in size than the source impact craters of the other known strewnfields. Many locations have been proposed for this missing source crater. Schmidt and Wasson (1993) suggested there could be a , in diameter source crater beneath the Mekong Valley, Hartung and Koeberl (1994) proposed the elongated Tonlé Sap lake in Cambodia, Glass (1994) estimated the source crater to be between in diameter and located in Cambodia, and 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) concluded that the source of the Australasian strewnfield is a large impact crater in Indochina and estimated it to be in diameter. Other proposed locations are between southern Laos and Hainan by Ma et al. (2001) and possibly within the Gulf of Tonkin as argued by Whymark. More recently in 2020, Sieh et al. proposed on the basis of various lines of evidence that the crater lies buried beneath the Bolaven volcanic field in southern Laos. In 1991, Wasson et al. studied layered tektites in central Thailand and explained the lack of a large recognizable source crater by occurrence of small, diffuse, multiple impact event spread out over the region. This explanation raises some problems, in particular the strewnfield's tektites having a different chemical composition than Cambodian sandstone from the time of impact.
The lack of a recognizable source crater in Southeast Asia has also been explained by proposing it being located outside of Southeast Asia. Some of these proposed locations for the source of the Australasian strewnfield lying outside of Southeast Asia include the Wilkes Land crater in Antarctica, the Zhamanshin crater in Kazakhstan, and the Elgygytgyn crater in Siberia.