Thursday, August 27, 2009

Chicxulub Impact Crater: Not All About A Catastrophe

Let's take a breather from the K-T mass extinction debates.

From the August issue of Geology:

The surface geology of the site of the Chicxulub impact crater in northwestern Yucatán, Mexico, has not been studied extensively since the discovery of the crater almost two decades ago. Strontium isotope (87Sr/86Sr) measurements in carbonate rock outcrops reveal near-uniform strontium signatures of 0.70905 inside the ring of cenotes (water-filled sinkholes), which represents the rim of the crater basin. Measured strontium isotope ratios were used to infer rock ages, employing the marine Sr isotope curve. We estimate the age of the exposed limestone within the Chicxulub crater basin to be late Miocene to early Pliocene, representing the age of the youngest sediment fill. Discovery of a large terrain of near-uniform strontium isotope ratios in northwestern Yucatán offers new geoarchaeological opportunities to track ancient Maya migration and determine sources of manufactured goods. Our results have implications for applying the Sr isotope method to Maya archaeological sites, such as Mayapán, the last Maya capital, and Chichén Itzá.

Late Mesozoic impact resulting in ecosystem upheavals, faunal turnovers, chaotic sediment deposits followed later in the Cenozoic by serene limestone deposition.

The extended story of Chicxulub has an ironic ring to it. Uniformitarianism in a place which is one of the best known examples of catastrophism.

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