Monday , November 30 2020

Scientists have found hidden evidence of ancient ice currents in the African desert



Once about 300 million years ago, when southern Africa joined South America's hip, the now dry region was covered by a broad glacier.

You wouldn't know today and look out over the dry volcanic desert in the Twyfelfontein area of ​​northern Namibia. But all of its 4.5 billion years of history, our planet has had a habit of reinventing itself.

If we scare the teams, we can sometimes get a glimpse of who it used to be – all it takes is for someone to try.

Geologists Graham Andrews and Sarah Brown are some of the first to do so in Namibia, and their recent research has led to an unexpected discovery.

It turns out that this region was once home to a large ice stream – the arteries that flow directly from a glacier's center to the edge – and this was so impressive it would have rivaled those we now see in modern Antarctica.

During the exploration of the desert land on a field trip, these two geologists from West Virginia University noticed some peculiarities in the area's sprinkling of long, steep hills, commonly known as the Namibia drum.

"We quickly understood what we were looking at because we both grew up in worlds that had been under glaciers, me in Northern Ireland and Sarah in northern Illinois," said Andrews, whose expertise is based on volcanic provinces throughout the North American Cordillera.

But although the origin of this foreign landscape seemed clear to Andrews, he was surprised to find out that the subject had never been investigated.

"People knew, of course, that part of the world had been covered in ice at one time, but no one had ever mentioned anything about how the drums were formed or even in there," Andrews explains.

By analyzing the shape and size of the unique landscape using information from Google Earth, Andrews and his team tried to find out if the drums could have been carved from the growth and decay of a now obsolete glacier.

Through their findings, the researchers found large, long grooves in the region's rocks. The proof was clear: this must have been caused by old ice forms that moved very quickly – soon enough that the ice could dig into volcanic landscape (about 800 meters a year).

The results represent the very first evidence of a massive ice stream responsible for the drainage of ice covering southern Africa in the late Paleozoic age.

Turning and turning for an estimated two hundred kilometers, this stream would have flowed in the north-west direction, emptying the area's ice cap into a low-seas environment in today's modern Brazil.

Flat reconstruction of Gondwana during the late Paleozoic at 310 Ma(Kathryn Pauls)

The study not only confirms another bond between these two southern continents, it also confirms the location of southern Africa 300 million years ago, spanned by South America just above the South Pole.

"This work is very important because there is not much publicity on these glacial features in Namibia," says co-author Andy McGrady, another geologist from West Virginia University.

"It is interesting to think that this was pioneer work in such a way that this is one of the first papers to cover the characteristics of these functions and to give an insight into how they were formed."

This study has been published in PLOS Toe.


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