Saturday, November 25, 2006

Appalachian Origins, Revisited

For today's new insight into Appalachia, I need to thank Michael J. Ryan of Paleoblog for passing along a New Origin for the Appalachian Mountains. The original article is Acatlán Complex, southern Mexico: Record spanning the assembly and breakup of Pangea by R.D. Nance, et al. Geology 34:857-860 (2006). Dr. Ryan quotes from the press release:

According to the conventional map of 420 million years ago, two main land masses were separated by the Rheic Ocean. In the south sat Gondwana, a supercontinent consisting of South America, Africa, India, Australia and Antarctica. To the north was Laurussia, made up of North America, Greenland, Europe and part of Asia. The old map showed the Acátlan Complex attached to Laurussia. The complex broke off Gondwana about 80 million years earlier, drifted toward North America along with the other land masses, closing an older ocean, known as the Iapetus Ocean, as it did so. The collision created the Appalachian Mountains.

The new map looks rather different. Based on the new evidence the Acatlán Complex collision with Laurussia actually occurred about 120 million years later. The rocks once existed on an ancient ocean floor, but this ocean has proven to be the Rheic, not Iapetus as previously thought.

Same trilobites, different ocean.

1 comment:

prairie mary said...

This geological stuff is endlessly fascinating. I'm on the edge of an ancient and dried-up sea here, one that once had many lagoons alongside it, the habitat for dinosaurs -- which is why their bones are all over the place. I can never find out enough about it!

The Appalachians are unknown entirely to me.

Prairie Mary