The Vichada river in Colombia is a tributary of the Orinoco. In 2004 part-time geologist Max Rocca discovered that it skirts South America's largest impact crater. It measures 50 km in diameter, nearly a third of the Chicxulub crater caused by the space rock that killed off the non-avian dinos.
This image visualises two important things.
1. Our planet is just another crater-pocked space rock, though here surface erosion acts much faster than on nearby worlds, and we have plate tectonics, all obscuring the impact scars. The Vichada example is a recent one, being less than 30 million years old.
2. Geological time is looong. Look at that meandering river doing a little detour around the crater's edge!
There's a good feature piece on the Vichada crater at the Planetary Society's web site.
[More blog entries about craters, geology, Colombia, spaceimpacts; kratrar, geologi, Colombia, asteroidnedslag.]
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I opened up google earth to see what it looked like without odd false coloring stuff. Didn't expect it'd be as easy to find as it is. A huge pock mark.
Jungle covered inside yes, looks marshy too, the rim is mostly uncovered. There's a lot of slash and burn going on in the area, if I'm reading the picture right.
There was nothing in the linked article about dating this feature.
Any chance that the Vichada crater could be the result of a mass which separated from the Chicxulub impactor?
Apparently not. I got the date from here.
And the date of the impact has some relation with extinctions on southamerica?
That would be interesting to learn. I don't know, except that there hasn't been a major extinction event since the dino-killing K/T one. Unless you count the one going on right now because of humans.
What about the Swedish impact crater?
Lake Siljan. That rock struck 365 mya according to Wikipedia.
Martin: About South American extinctions and regarding Edgar's question consider this text,
"The South American mammalian fauna of the late Pleistocene-early Holocene (Lujanian Land-mammal Age) is considered impressive relative to any modern or extinct mammalian fauna (Patterson & Pascual 1972; Simpson 1980). Among the more than one hundred and twenty genera compiled in Marshall et al. (1984), the estimated adult masses of 38 extinct herbivore genera exceeded 100 kg; about 20 of them were megaherbivores, that is, their masses were measured in megagrams, or metric tonnes (Owen-Smith 1988). No other fossil mammalian fauna is known to contain that number of megaherbivores. In contrast, the whole African continent, indisputably the most diverse mammal fauna known today, has only four species of megaherbivores: the African elephant (Loxodonta africana), the white rhinoceros (Ceratotherium simum), the black rhinoceros (Diceros bicornis), and the hippopotamus (Hippopotamus amphibius). A fifth species, the giraffe (Giraffa camelopardalis), might also be considered as belonging to this category. The Lujanian mammalian megafauna appears to be more comparable to dinosaur faunas, which of course had species of even larger body size. But even these dinosaur faunas not very often contained so many large-bodied species in a relatively short span of time and a limited area."
The Farina paper concerns the Lujanian, which was the last age before the recent. See SLAMA in the Wikipedia.
These extinctions are much more recent than 30my, and the inferred causes include us.
So ... I think I am seeing this around +4° 30' 20.34", -69° 9' 42.88" Is this correct?
Looks right to me!
Perhaps this formation is related to the impact crater at the mouth of the Chesapeake Bay.
I suppose that only further investigations will result in better dating and analysis of the impactor.
E.P. Grondine
Man and Impact in the Americas
Right now the extent of the YD impacts is not known. The South American excavations linked through here may have some bearing on the problem:
http://www.palanth.com/legacy/index.php/topic,1202.0.html
If the Vichada River impact is related to the Chesapeake Bay one, we should also be seeing South American extinctions around 35 million years ago.
E.P. Grondine
Man and Impact in the Americas