Chicxulub crater stratigraphy
The Chicxulub crater is a 145 km wide depression in subsurface of the northwestern Yucatan Peninsula of Mexico. It is thought to be the result of an asteroid impact approximately 65.5 Ma., dating at around the same time as the Cretaceous-Paleogene (K/T) extinction event. This mass extinction resulted in the loss of roughly 75% or plant and animal life on Earth, including non-avian dinosaurs. The impact crater formed a sedimentary basin that allowed for deposition and diagenesis to occur throughout the Cenozoic Era.
Evidence of impact
Seismic images have described the structure as a circular depression, complete with annular troughs and peak ring, similar in structure to craters seen on the Moon and Mars. Though the impact occurred mostly in deep water, the peak rings are granitic, suggesting the asteroid penetrated deeper into the Earth's crust than previously thought.
Evidence for the impact include tektites, shocked quartz, tsunami deposits and high traces of iridium along the K/T boundary in areas surrounding the Yucatan.
Seismic imaging has revealed the underlying structure of the basin, with which depositional sequences can be deduced. The crater floor has a composition of both impact breccias and melt rocks. During the Paleocene immediately following the impact, shallow-water deposition of pelagic sediment began to infill the basin. Sparse reef growth developed within a shallow platform until the early Miocene. From the middle Miocene through Pleistocene, restricted water deposits filled the basin to its current flat surface. Subaerial exposure and freshwater diagenesis led to replacive dolomite and karsting. On the northern Yucatan peninsula, the perimeter of the crater can be identified by cenotes at the surface.
Western Annular Trough
Reflectors show toplap that extends from west, suggesting overall progradation to the east. The tops of these clinoforms indicate a sea-level of roughly 100m. Early to middle Eocene sedimentation continued to deposit in shallow-water. Clinoform geometry suggest a marine regression occurred with sedimentation decreasing in the western trough. Carbonate and evaporite deposits resulted from subaerial exposure of the carbonate platform. The upper part of this unit displays a truncation surface that marks a major boundary as well as a change in depositional environment. Chaotic reflectors in the seismic images can be interpreted as mass flow deposits during a regression. Using dates obtained from well data, the western and northwestern basins were filled entirely by 40 Ma.
Eastern Annular Trough
The eastern trough shows a different depositional history than the western trough. The facies characterization suggests a delta system. A prograding shelf sequence downlaps onto the unconformity in the eastern annular trough. Above this unit, a regression can be seen by offlapping clinoforms. During the late Eocene to early Oligocene, the exposed surface underwent freshwater diagenesis, which led to extensive dolomitization. Chaotic geometries suggest a mass flow resulting from the drop in sea-level.
- Barton, P.J., Christeson, G.L., Grieve, R.A.F., Gulick, S.P.S., Morgan, J.V., Urrutia-Fucugauchi, J. (2013) Geophysical characterization of the Chicxulub impact crater. Retrieved from https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/rog.20007
- Bell, C., Hampson, G.J., Morgan, J.V., Trudgill, B. (2004) Stratigraphic and sedimentological observations from seismic data across the Chicxulub impact basin. Retrieved from https://onlinelibrary-wiley-com.ezproxy.lib.uh.edu/doi/epdf/10.1111/j.1945-5100.2004.tb01130.x
- Lefticariu, L., Lefticariu, M., Perry, E.C., Ward, W.C. (2006) Post-Chicxulub depositional and diagenetic history of the northwestern Yucatan Peninsula, Mexico. Retrieved from https://www-sciencedirect-com.ezproxy.lib.uh.edu/science/article/pii/S0037073805003118