Annealing the Chicxulub Impact: Paleogene Yucatàn Carbonate Slope Development in the Chicxulub Impact Basin, Mexico

Stratigraphic analysis of the Yaxcopoil-1 core (Yax-1) and seismic analysis of offshore 2D seismic data provide insight into the Paleogene history of the Chicxulub impact basin and Yucatàn platform development. Ten facies were identified based on core and petrographic analysis. Slope sediments include redeposited and background facies. The former are carbonate supportstones and finer-grained facies with evidence of soft sediment deformation deposited as gravity flows. Background facies are shales and mud-wackestone sub-storm wave base suspension deposits. Depositional setting ranged from a steep bathyal slope inside the crater rim to neritic outer carbonate ramp environments of the seaward prograding Yucatàn platform.

Preliminary sequence stratigraphic analysis of Yax-1 identified 5 sequences based on transgressive and maximum flooding surfaces and facies stacking patterns. Biostratigraphic data are equivocal but imply that the first 3 sequences span the Early Paleocene to Early Eocene. Coarse-grained redeposited carbonates in lower sequences 1- 4 indicate slope gravity flow processes. Upper sequence 3 records the first evidence of fine-grained turbidites indicating progradation of the distally steepened Yucatàn ramp. By the top of sequence 4 facies indicate that the distal ramp had prograded over the position of Yax-1.

Seismic analysis identified 6 units, the lower 5 of which appear to correlate with with cored Yax-1 sequences. The geometry and distribution of seismic units A and B indicate deposition confined to the western and central parts of the basin. Unit C, with two sets of clinoforms, records a major progradational event in the eastern part of the basin likely related to Yax-1, sequence 3 turbidites. Mainly parallel reflectors in seismic units D and E indicate relatively level bottom conditions similar to the environments of facies in upper sequence 4 and 5. The top of units D and E, in proximal settings, is erosionally truncated, marking the base of unit F that is characterized by discontinuous reflectors, restricted to the northeastern portion of the basin.

Stratal patterns in seismic units C-E appear to be controlled by sea-level change as suggested by the development of clinoforms and regional unconformities. If Chicxulub is representative, large marine impacts in tectonically quiescent regions may dominate local depositional environments for millions to tens of millions of years post-impact before returning control to eustasy.  

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California