THE CARBONATE PALEOGENE SEQUENCE OF THE CHICXULUB IMPACT BASIN, YUCATAN PLATFORM – YAXCOPOIL-1 BOREHOLE

Chicxulub, Vredeford and Sudbury are the three largest known impact craters on Earth. With an age of 65.5 Ma, Chicxulub is the youngest of the three. Chicxulub is located in the northwest sector of Yucatan Peninsula, Mexico; it has a multi-ring morphology and an approximate diameter of 200 km. Crater is buried beneath a carbonate and evaporitic sequence in the Yucatan platform, southern Gulf of Mexico, and represents the best-preserved large impact structure documented on Earth.

The Yaxcopoil-1 borehole was drilled south of Merida, Yucatan, approximately 62 km from the center of the Chicxulub impact crater. Major objectives of the drilling project included investigations on cratering processes, post-impact carbonate deposition, and role of the Chicxulub impact event in the Cretaceous/Paleogene (K/P) boundary mass extinction. The well was drilled with continuous coring starting at 400 m, and reached a depth of 1510.6 m. In this paper, we present a detailed lithological, sedimentological and petrological study of the carbonate sequence post-impact characteristics in the interval from 404.01 m to 792.17 m above the K/P boundary.

Sequence in Yaxcopoil-1 borehole is composed mainly of marls, argillaceous limestones, dolomitized carbonates and calcarenites. We describe lithological changes, porosity and others structures sedimentary identifying twelve principal units and determinate microfacies analysis of the 231 samples for all the sequence. With microfacies studies by means of petrography we have observed major textural and cyclic changes from bottom.

The benthic foraminifera strongly depend on environmental parameters, such as nutrient supply or oxygenation of the sea bottom water. The benthic and planktic foraminiferal record allows inferences on paleoenvironmental conditions during the Paleocene and Eocene; some results micropaleontological were obtained especially for the Paleogene bottom sequence.

Results are of special interest because changes in the sedimentological and micro-paleontological records can be correlated with the faunal turnover in the Gulf of Mexico and provide a complementary tool for biostratigraphic investigations.