ANNEALING THE CHICXULUB IMPACT: TERTIARY YUCATAN CARBONATE PLATFORM DEVELOPMENT AND BASIN INFILLING

The Yucatan Peninsula and the southern Gulf of Mexico contain a record of one of the most important impact events in the Earth history, the Chicxulub impact at the Cretaceous-Tertiary (K/T) boundary. We report here a preliminary integration of sequence stratigraphic analysis of the Tertiary basin imaged in offshore 1996 and 2005 seismic data, and sedimentologic and stratigraphic analysis of the Tertiary sediments in the Yaxcopoil-1 drill core (YAX-1).

Interpretation of the 2-D seismic data sets indicate a series at least seven seismic units from the K/T boundary to the seafloor. The lowermost Unit A sits conformably atop the K/T boundary reflector, and is characterized by a set of strong sub-parallel reflectors that onlap the peak ring. We interpret this package as the first pelagic sediments in the basin that may correlate with the lower 100-115 m of YAX-1. Foram biostratigraphic data indicate that this section of the core spans Paleocene through the lower Eocene. The lower 100 m is characterized by coarse-grained redeposited carbonate facies and soft-sediment deformed units interbedded with fine-grained carbonates. Some units display normal grading while others are chaotic or crudely graded. The upper 15 m of logged core is characterized by repetitive m-scale cycles of marl grading up into wacke/packstones. The redeposited and soft sediment deformed carbonates record patterns of sedimentation typical of slopes undergoing readjustment and regrading, as one would expect along a newly created steep slope.

Unit B, overlying Unit A, consists of a package of parallel reflectors. Overlying Unit B on the edges of the inner crater is a series of sigmoidal clinoforms (Unit C); the reflector separating Units B and C can be mapped throughout the inner crater and the pre-existing basin to the northeast. Unit D overlies Unit B in the center of the crater and onlaps Unit C at the edges, and is in turn overlain by a comfortable package, Unit E. By Unit E time the center basin was largely filled and the sediment depocenter for Unit F, which included a phase of clinoform development, was confined to the northeast basin. Unit G lies above an erosional surface that may have formed near lowstand. This surface can be mapped more easily to the north, but is likely a regional event. Integration of Units B through G with the core data from YAX-1 is ongoing.