Earth:Winton crustal anomaly

The Winton crustal anomaly is a geological structure theoretically caused by an impact event that is believed by scientists from Geoscience Australia to have happened about 300,000,000 years ago in what is now the Channel Country in Central West Queensland, Australia in the region west of the small town of Winton. The consequent cataclysm would have released an enormous amount of energy and had far-reaching consequences. If further research can prove that there was indeed such an impact, it is likely that it would be considered a major event in Earth’s geological history.

Site

A map showing the rough extent of the crustal anomaly west of Winton that may be a Palaeozoic impact structure.

The zone in which the Winton asteroid impact theoretically happened lies in a sparsely populated area in the Australian Outback centred roughly at [ ⚑ ] 22.15°S 141.9°E / -22.15; 141.9. It is roughly circular and its diameter measures some 130 km (and it thus has an area of about 408 km²). The depopulated town of Middleton and Dagworth Station – famous for the part it played in the creation of “Waltzing Matilda” – lie within the anomaly discovered here. Skirting the anomaly zone for more than half its circumference, mostly on the north and east sides, round from its headwaters to well below its confluence with the Western River, is the Diamantina River, an intermittent stream with, in most places, several braided channels of the kind that give the Channel Country its name. It was this particular hooked shape in the upper Diamantina that first raised questions.

Name

Although this article calls it the “Winton crustal anomaly”, it is clear from what has been written about the round zone in Queensland and its theoretical cosmic creation that the matter of a proper name has not yet been settled. Geoscience Australia refers to the “Woodstock-Winton circular drainage ring” in a map caption (Woodstock is another station in the zone where research was done) in reference to the Diamantina’s course there, whereas Winton’s local news outlet, the Winton Herald, refers to the “Winton Asteroid Theory”.

Discovery

The countryside within the anomalous area, here looking roughly north from Cornpore Lookout near Middleton. The road is the Kennedy Developmental Road.

The Diamantina River’s hook-shaped upper reaches had long been a puzzle to science. To Dr. Andrew Glikson, whose research interests include “early crustal evolution with focus on the role of asteroid impacts”, the near-circular course was the first indication that there might be an anomaly in the crust in this region. Glikson’s research into the matter revealed several noteworthy things about this round zone.

For instance, the circular zone inside the upper Diamantina is a “magnetically quiet zone”, according to data yielded by studies of the local magnetic fields, whereas the neighbouring rock shows a more linear pattern in its magnetic signatures. Reflection seismology, used on a line transecting the zone’s outer rim, also revealed “dramatic” differences between the rock within the anomaly and outside it. It can thus be inferred that the possible cause is a disturbance of the deep crust by something like a great impact. Gravimetry revealed some interesting information about the anomaly’s centre, which itself contains a gravimetric anomaly. This told the researchers about differences in rock densities as compared to neighbouring areas of crust, likewise suggesting that there could long ago have been a major impact event.

On the whole, the information gathered at Woodstock Station is comparable to that found at buried asteroid impact structures, but currently, final proof is lacking. The Winton crustal anomaly was, after all, discovered in 2015.

Proof

Proof is the one thing currently wanting in any quest to label the anomalous round zone on the upper Diamantina an asteroid impact structure. However, the scientists involved see that as rather a straightforward matter of drilling core samples in the zone and then analyzing them. Richard Blewett from Geoscience Australia quoted the needed depth for these samples as “about three kilometres”, whereas Geoscience Australia says in its own report, somewhat more conservatively, that the depth will have to be “many hundreds of metres”. Analysis of the core samples would involve, among other things, the detection of “shock textures” in the rock, caused by the great energy of an asteroid impact.

Impact event

The impact event is, as of this writing, only theoretical. Its reality is far from certain. Richard Blewett, mentioned above, admits that there are other possible explanations for the geological anomaly on the upper Diamantina, but adds “but they become difficult to explain”.

Whether the round zone in question was truly created by an asteroid falling out of the sky or not, the scientists at Geoscience Australia have some very definite ideas about this theoretical natural missile. It is believed, for instance, that the event happened some 300,000,000 years ago, in the Palaeozoic. At that time, Australia lay quite a long way south of where it now lies. It had not yet rifted apart from Antarctica; both continents, and others, were joined together as parts of Gondwana.

The theoretical asteroid itself is reckoned to have measured ten kilometres across, and when it struck, the energy that it released was equivalent to 650 million Hiroshima A-bombs (and thus roughly 41 zettajoules). Richard Blewett believes that the course of Earth’s history would have been changed by the enormous blast unleashed by such a strike, and pointed out that there has been an association between these events and great changes in the course of evolution. Geoscience Australia, on the other hand, only pointed out the importance that such an event has to understanding the evolution of Earth’s crust and the economic significance, as such formations may contain petroleum or other mineral wealth.