Congo Impact Crater Confirmed

A previously recognized crater inthe Congohas been confirmed as an impact crater. It struck during the past few hundred millions of years or so and willbe amenable to proper age measurement. It is about ten miles across which puts it up there in size.  It surely caused a local extinction event andplenty of temperature problems until the ash came out of the atmosphere.

A clay marker horizon shouldexist as with the K-T marker.

Recall that clay starts out as anash that then weathers into clay.

It is too soon to remark on theimportance of this event until we determine its precise age and the extent ofits ash halo.  It certainly caused plentyof damage but in the order perhaps of a super volcano, but far less than the Yucatan disaster.

Huge Impact CraterFound in Remote Congo

A computer model of the Luizi crater based on satellite data.
Diagram courtesy Ludovic Ferriere and SRTM/NASA

NatGeo -A circular depression deep in the Democratic Republic of the Congo (DRC) hasbeen confirmed as the first known impact crater in central Africa, a new studysays. The find brings the number of known meteor craters on Earth to 182.

The so-called Luizi structure was first described in a German geological reportfrom 1919. But without further fieldwork, it was impossible to say for surethat the 10.5-mile-wide (17-kilometer-wide) feature had been made by a meteorimpact.

On other planets, such as Mercury and Mars, it's easier to identify impactcraters based only on their shapes, since these worlds no longer have geologicforces making major changes to their surfaces.

But on Earth, many older craters have likely been erased by tectonic activityor erosion, while others are so covered with dense vegetation or sediments,like Luizi, that they're almost impossible to spot without satellites.

What's more, the crater-like structures we do see may have been made byvolcanoes, collapsed underground chambers, and other forces that have nothingto do with impacts, said study leader Ludovic Ferrière, curator of the rockcollection at the Natural History Museumof Vienna in Austria.

"On Earth, to confirm it's an impact, you have to go in the field becauseyou need evidence of high pressures and temperatures," Ferrière said.

Crater Expedition Had Brushes With Snakes, Poachers

The researcher first became interested in the Luizi structure afterseeing satellite pictures published in the 1990s.

By studying the available satellite data, Ferrière and colleaguesestimated that the structure has an elevated rim about 1,148 feet (350 meters)high, as well as an interior ring and a central depression.

But to truly confirm Luizi as an impact crater, the researchers had to mount anexpedition to the politically tumultuous DRC. (Related: "Rare Gorillas atRisk as Rebels Seize Congo Park.")

"I was working for a year just to find a contact there, because you need alocal person to help you find your way around," Ferrière said.

With funding from the National Geographic Society/Waitt Foundationprogram, Ferrière—then a postdoc at the Universityof Western Ontario in Canada—visitedthe crater site in June 2010 with colleagues from the University of Lubumbashi.(TheNational Geographic Society owns National Geographic News.)

"I flew direct to Lubumbashi,the second largest city in the DRC. From there we had to drive from the city tothe crater," he said.

"I had looked at maps and planned a route before I left. But when I gotthere, my contact told me there is no bridge across part of my intended path.We had to take some crazy gravel roads with big potholes inside. These are notgood roads to drive on, even with a four-wheel-drive car."

The team set up camp in a small village about 8 miles (13 kilometers) from thecrater rim, recruiting two local guides/porters and a soldier to help themsafely navigate the wild terrain.

"The crater is in a national park, and I thought it would be like thejungles of South America," Ferrière said."Instead it was a tree savanna—a big plataeu with dry grass. The grass wassometimes more than a meter [3.2 feet] high."

Standing on the rim of the Luizi structure, Ferrière could see skinny treesthat seemed to fill the depression, with the crater's distant edge rising likesmall hills.

Despite the remote, wooded terrain, "we saw no large animals, only snakes.But we did see a lot of remnants of poachers. Sometimes we'd come to a site andthe doused fires were still hot."

Ferrière's team spent about a week at the crater collectingsamples, whichwere sent back to the lab in Canada for analysis.

"I found so-called shatter cones, which are features in the rock onlyfound in impact structures," he said. The nested, conical shapes in suchfeatures are evidence that the bedrock has been exposed to extreme pressurefrom a shock wave.

The crater rocks also contained an abundance of shocked quartz, a version ofthe mineral known to form only from impacts or nuclear blasts, Ferrière said.

"Everybody will believe me now, I think, that this is an impactsite."

The scientists think the Luizi crater was made by a meteor more than 0.6 mile(a kilometer) wide that slammed into what is now the DRC at about 45,000 miles(72,000 kilometers) an hour.

For now it's unclear how old the crater is—the scientists can say only that theaffected rocks are about 575 million years old, "but we know it's youngerthan that, because the rocks have been excavated," Ferrière said.

"It would be nice to do more fieldwork, because the shape of the structurewith this inner ring can tell us about the exactformation process involved," he added. In the meantime, theresearcher will continue to study the rock samples, now housed at the Vienna museum.

"There is still a lot to discover" about Luizi, he said.

No comments:

Post a Comment