The Deniliquin geological structure in southeastern Australia may have resulted from the impact of a huge meteorite that left a crater more than 500 kilometers in diameter. This catastrophe may have been the trigger for the ancient Ordovician-Silurian mass extinction.
From time to time, celestial bodies fall on our planet, sometimes quite large. However, high geologic activity over time smooths out the depressions and furrows left by such impacts. The largest credibly impact crater is considered to be South African Vredefort, whose diameter reaches 250-300 kilometers. This is one and a half to two times larger than even the famous Chicxulub, which participated in the extinction of the flightless dinosaurs.
Wilkes Land crater in Antarctica gains up to 500 kilometers, but fully investigate it and confirm the shock origin has not yet been able to. However, the new work of Australian scientists allowed to name a possible new record holder, ready to beat both contenders: the structure Denilikuin, located in southeastern Australia and exceeds 500 kilometers in diameter. An article about it is published in the journal Tectonophysics.
For many years, in the search for large and ancient craters, scientists focused only on their "external" signs: the presence of a rounded depression, a central elevation, and ring rises. However, these structures are subject to erosion, can go under a layer of sedimentary rocks and so on. Only in recent decades have new methods based on the analysis of specific minerals that are produced by a tremendous impact and scattered in the vicinity begun to appear. This makes it possible to estimate the size and age of the original, often almost completely destroyed structure.
As early as the end of the last century, Professor Andrew Glikson of the University of New South Wales (Andrew Glikson) showed that minerals in the Murray Basin could indicate the presence of a powerful and ancient structure with a central elevation characteristic of an impact structure. The new analysis uses more detailed geophysical data already collected between 2015 and 2020. They confirmed the first conclusions and made it possible to estimate the diameter of the structure at a record 520 kilometers.
The distribution of minerals showed that the central deformation reaches a depth of 30 kilometers and rises 10 kilometers above the neighboring layers of the mantle. A series of rings diverge from it, cut by cracks in which the substance of the magma poured out has accumulated. Such details are very typical of large impact craters, although so far the results are based on the analysis of minerals remaining at the surface, and to confirm them, it will be necessary to drill and examine deeper layers.
If the Deniliquin structure is indeed the remnant of an ancient crater, it appeared long before the continent itself. Scientists attribute this to the time of the Ordovician-Silurian extinction event that occurred about 450 million years ago, when Australia was part of the Gondwana supercontinent.
It may have been this blow that caused the global climate catastrophe that led to the mass extinction and death of most of the species that had lived before. However, geologists have made a caveat that Deniliquin is probably even older. Only future, more detailed studies will help to find out.