A team of geologists has accumulated extensive evidence that contradicts a previous view of how the continents which formed Gondwana collided and came apart to form what is now North and South America.
University of Cincinnati geologist Warren Huff will explain the evidence during a talk Tuesday, Nov. 14 during the annual meeting of the Geological Society of American in Reno, Nevada. Huff has been working with Dennis Kolata of the University of Illinois and Stig Bergstrom of Ohio State for several years to collect and analyze deposits from ancient volcanoes.
The deposits, known as K-bentonites, were formed after massive volcanism in the Ordovician Period roughly 450 million years ago. By tracking these deposits across continents, Huff and his collaborators can reconstruct how the ancient land masses moved.
A previous model (Dalziel et al., 1994) concluded that the continents which became North and South America went through a massive collision, before moving apart into their present-day locations. "We don't agree with that model," said Huff. "Technically, it's possible, but in the time frame we're considering, it doesn't make much sense. "
For example, Huff explained that fossil evidence indicates South America went through an Ice Age at the end of Ordovician. However, the previous model requires the South American land mass to be nearly at the equator during that time.
Huff and his colleagues don't dispute that a collision occurred. The massive volcanism which produced the deep K-bentonite beds is clear evidence that land masses were crunching together. "The question is...what was colliding with what? We believe it was a group of very small terrains much like the western Pacific today where island chains are moving toward mainland Asia. Bits and pieces attached over time."
The strongest evidence for the "bits and pieces" approach comes from the Argentine Precordillera where bentonites have been recovered from dozens of s
Contact: Chris Curran
University of Cincinnati