New evidence suggests that the world’s largest known asteroid impact structure is buried deep in southeastern Australia

Acknowledgments: I would like to thank my colleague Tony Yates, who pioneered the view of Deniliquin’s polycyclic structure as an effect structure – and who was instrumental in this work.

in Recent research Published by my colleague Tony Yates and I in the journal Tectonophysics, we are investigating what we believe – based on many years of experience in asteroid impact research – is the largest known impact structure in the world, buried deep underground in southern New South Wales.

Deniliquin’s structure, which has not yet been tested by drilling, extends up to 520 kilometers in diameter. This exceeds the size of nearly 300 kilometers wide Fredfort The structure of influence in South Africa, which is still considered the largest in the world.

Hidden Traces of Earth’s Early History

The history of the bombing of the Earth by asteroids is largely hidden. There are several reasons for this. The first is erosion: the process by which gravity, wind, and water slowly erode Earth’s materials through time.

When an asteroid strikes, it creates a crater with a raised core. This is similar to how a drop of water splashes upwards from a passing crater when a pebble falls into a pond.

This raised central dome is a major feature of the large impact structures. However, it can erode over thousands to millions of years, making it difficult to determine the structure.

Structures can also be buried by sediment through time. Or it may disappear as a result of subduction, where tectonic plates can collide and slide under each other in the Earth’s mantle layer.

However, new geophysical discoveries are revealing the signatures of collision structures formed by asteroids that may have reached tens of kilometers across – heralding a paradigm shift in our understanding of how Earth has evolved across eons. These include groundbreaking discoveries of impact “projectiles,” which are materials that are thrown out of a crater during an impact.

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researchers believe The oldest layers of these projectiles, found in sediments in early terrains around the world, may indicate the tail end of the Earth’s Late Heavy Bombardment. the Latest evidence It indicates that Earth and other planets in the solar system were heavily bombarded by asteroids until about 3.2 billion years ago, and intermittently since then.

Some significant impacts are associated with mass extinction events. For example, file Alvarez hypothesisNamed after father and son scientists Luis and Walter Alvarez, it explains how non-avian dinosaurs were wiped out as a result of a large asteroid impact some 66 million years ago.

Read more: We found the world’s oldest asteroid impact in Western Australia. It may have caused the global melting of ice

Deniliquin structure revealed

the Australian continent and its predecessor, Gondwana, has been the target of several asteroid impacts. This has resulted in at least 38 confirmed structures and 43 possible impacts, ranging from relatively small craters to large, completely buried structures.

This map shows the distribution of circular structures of uncertain, probable or probable impact origin on the Australian continent and overseas. Green dots represent confirmed craters. The red dots represent confirmed impact structures greater than 100 km wide, while the red dots within the white circles are more than 50 km wide. Yellow dots represent potential trauma structures.
Andrew Glickson and Franco Bergano

As you’ll recall with the puddle and pebbles analogy, when a large asteroid hits Earth, the core crust responds with a transient elastic bounce that results in Central dome.

These domes, which can slowly erode and/or become buried over time, may be all that is preserved of the original impact structure. It represents the deep rooted “root zone” of influence. Famous examples are found in the 170 km wide Vredefort impact structure Chicxulub crater in Mexico. The latter represents the impact that caused the extinction of the dinosaurs.

Between 1995 and 2000, Tony Yates proposed magnetic patterns below the Moray Basin in New South Wales. Most likely represented Huge impact structure buried. Analysis of geophysical data updated in the area between 2015 and 2020 confirmed the presence of a structure 520 kilometers in diameter with a seismically defined dome at its center.

Deniliquin’s structure has all the features expected of a large-scale impact structure. For example, magnetic readouts of the region reveal a symmetric ripple pattern in the crust around the core of the structure. This likely occurred during the impact as the extremely high temperatures created intense magnetic forces.

The central low magnetic region corresponds to a 30 km-deep deformation above the seismically defined mantle dome. The height of the top of this dome is about 10 kilometers shallow from the top from the regional mantle.

Magnetic measurements also show evidence of ‘radial defects’: fractures radiating from the center of a large impact structure. It is also accompanied by small magnetic anomalies that may be igneous “dams”, which are sheets of magma injected into fractures in a pre-existing rocky body.

The ‘total magnetic intensity’ image of the Deniliquin impact structure shows a multi-ring pattern with a diameter of 520 km, the central core, radial faults and the location of the shallow drill holes.
Data from Geoscience Australia, published in Glikson and Yeates, 2022

Radial faults, the igneous sheets of rock that form within them, are typical of large impact structures and can be found in the Vredefort Structure and Sudbury Effect Structure in Canada.

Currently, the bulk of the evidence for Deniliquin’s influence is based on geophysical data obtained from the surface. To prove the impact, we would need to collect physical evidence of the impact, which could only come from drilling deep into the structure.

Read more: These 5 amazing impact craters on Earth shed light on our planet’s wild history

When did Deniliquin effect occur?

The Deniliquin structure likely existed in the eastern part of the Gondwana continent, before it split into several continents (including the Australian continent) some time later.

The Deniliquin structure was most likely created in eastern Gondwana during the Late Ordovician.
Zhen Qiu et al, 2022And CC BY

The impact it caused may have occurred during what is known as the Late Ordovician mass extinction. Specifically, I think it may have triggered the so-called Hirnantian glaciation stagethat lasted between 445.2 and 443.8 million years ago, also known as The Ordovician-Silurian extinction event.

This glacial event and massive mass extinction Excluded About 85% of the planet’s species. It was more than double the scale Chicxulub effect that killed the dinosaurs.

It is also possible that the Deniliquin structure is older than the Hirnantian event, and may be of ancient Cambrian origin (about 514 million years ago). The next step will be to collect samples to determine the exact age of the structure. This would require drilling a deep hole in its magnetic core and dating the extracted material.

It is hoped that further studies on the effect structure of Deniliquin will shed light on the nature of the early age Paleozoic Land.

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