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The huge Chicxulub impact crater discovered in northern Yucatán helps explain both the end of the dinosaur era on Earth and the creation of water sources called cenotes in the peninsula's limestone bedrock. The warm dinosaur era may have ended catastrophically about 65 million years ago with major atmospheric disturbances, causing sudden cooling of the atmosphere and increased sulfur content. This seems to correlate in the stratigraphic record with unusual amounts of intrusive elements such as iridium at the Cretaceous-Tertiary (K-T) boundary.
[Fig.1: Gravity map of Chicxulub crater, showing outline of Yucatán coast. White dots are cenotes concentrated along the crater rim (after Hildebrand et al 1995).]
The giant meteor causing the Chicxulub Crater is presently the best candidate for the source of this intrusive iridium at the K-T Boundary. This crater is one of the largest impact structures known on Earth, or elsewhere in the solar system. The transient crater, or hole from the initial impact, was about 85 km in diameter, caused by a 10-14 km meteor. Initial identification in the 1980's was aided by correlation with hundreds of limestone sinkholes or cenotes in northern Yucatán which clustered around the ancient crater. Much cenote formation resulted from gradual dissolution of limestone over broken-up rocks, or breccia, around the crater's original impact rim .
The Chicxulub structure is classified as a multi-ring crater, the largest of several major types now known from planetary study. Gravity research by Hildebrand (1991) and Sharpton (1993) located several concentric rings of Bouguer anomalies, indicating a 180-200 km-wide basin, and a 300 km periphery. More recent research using seismic reflection data from the offshore portion of the crater (Morgan et al. 1997) shows the overall crater had three rings: a peak ring 80 km in diameter, a 130 km inner ring, and a 195 km outer ring. When newly formed, this structure would have resembled other multi-ringed craters, as on Venus, Mercury, Europa, or the Moon.
[Fig.2: Three-dimensional gravity map of Chicxulub Crater in Yucatán (Sharpton, Lunar and Planetary Institute).]
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