ANNEALING THE CHICXULUB IMPACT: PALEOGENE YUCATÀN CARBONATE SLOPE DEVELOPMENT IN THE CHICXULUB IMPACT BASIN, MEXICO

MICHAEL T. WHALEN
Department of Geology and Geophysics, University of Alaska–Fairbanks, Fairbanks, Alaska 99775, USA

SEAN S.P. GULICK
Institute for Geophysics, Jackson School of Geosciences, University of Texas at Austin, J.J. Pickle Research Campus, 10100 Burnet Road, Austin, Texas 78758, USA

ZULMACRISTINA F. PEARSON
Department of Geology and Geophysics, University of Alaska–Fairbanks, Fairbanks, Alaska 99775, USA

RICHARD D. NORRIS
Scripps Institution of Oceanography, 301 Vaughan Hall, MS-0244, La Jolla, California 92093, USA

LIGIA PEREZ CRUZ AND JAIME URRUTIA FUCUGAUCHI
Instituto de Geofisica, Universidad Nacional Auto´noma de Me´xico, Ciudad Universitaria, Mexico City, CP 04510, Mexico

ABSTRACT: Stratigraphic analysis of the Yaxcopoil-1 core (Yax-1) and seismic analysis of offshore two-dimensional (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 interpreted as sub-storm wave base suspension deposits. Depositional setting ranged from a steep bathyal slope inside the crater rim to neritic outer carbonate platform environments of the seaward prograding Yucatàn platform.

Through sequence stratigraphic analysis of Yax-1, we documented five sequences based on identification of transgressive and maximum flooding surfaces and facies stacking patterns. Biostratigraphic ages are equivocal, but they imply that sequences 1 and 2 are Early Paleocene, sequences 3 and 4 are Early Eocene, and sequence 5 is Middle Eocene. Coarse-grained redeposited carbonates in lower sequences 1 to 4 indicate slope gravity flow processes. Upper sequence 3 records the first evidence of fine-grained turbidites, indicating progradation of the Yucatàn platform. By the top of sequence 4, facies indicate that the platform margin had prograded over the position of Yax-1.

Seismic analysis identified six units, the lower five of which appear to correlate 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 tops of units D and E, in proximal settings, are erosionally truncated. This unconformity marks the base of unit F, which is characterized by discontinuous reflectors and is restricted to the northeastern portion of the basin.

Stratal patterns in seismic units C to E are more controlled by relative sea-level change, as suggested by the development of clinoforms and regional unconformities. If Chicxulub and others like the Chesapeake Bay structure are representative, large marine impacts in tectonically quiescent regions may dominate local depositional environments for millions to tens of millions of years postimpact before returning control to eustasy.

KEY WORDS: Chicxulub, Yucata`n, seismic stratigraphy, Paleogene

Whalen MT, Gulick SSP, Pearson ZF, Norris RD, Perez Cruz L, Urrutia Fucugauchi J. Annealing the Chicxulub Impact: Paleogene Yucatàn carbonate slope development in the Cheicxulub Impact Basin, Mexico. In Verwer K, Playton TE, Harris PM (Editors). Deposits, Architecture, and Controls of Carbonate Margin, Slope, and Basinal Settings, Special Publication 105: SEPM (Society for Sedimentary Geology), Tulsa, OK. doi: 10.2110/sepmsp.105.04.