SURFICIAL GEOLOGY OF THE CHICXULUB IMPACT CRATER, YUCATAN, MEXICO

The Chicxulub impact crater in northwestern Yucatan, Mexico is the pri mary candidate for the proposed impact that caused mass extinctions at the end of the Cretaceous Period. The crater is buried by up to a kil ometer of Tertiary sediment and the most prominent surface expression is a ring of sink holes, known locally as cenotes, mapped with Landsat imagery. This 165 +/- 5 km diameter Cenote Ring demarcates a boundary between unfractured limestones inside the ring, and fractured limesto nes outside. The boundary forms a barrier to lateral ground water migr ation, resulting in increased flows, dissolution, and collapse thus fo rming the cenotes. The subsurface geology indicates that the fracturin g that created the Cenote Ring is related to slumping in the rim of th e buried crater, differential thicknesses in the rocks overlying the c rater, or solution collapse within porous impact deposits. The Cenote Ring provides the most accurate position of the Chicxulub crater's cen ter, and the associated faults, fractures, and stratigraphy indicate t hat the crater may be approximately 240 km in diameter.