Geophysical constraints on the size and structure of the Chicxulub impact crater

Clear images of impact craters on other planetary bodies reveal a progressive change in crater morphology with increasing crater size. Attempts to make direct comparisons between extraterrestrial and terrestrial craters have been hindered by the lack of pristine craters on Earth, particularly in the larger size range. This deficiency in ground truth data has also slowed our progress in understanding the cratering process for large impacts. However, the buried Chicxulub crater in Mexico now provides a pristine example of a large impact crater on Earth. Early structural models across Chicxulub were extremely divergent. They illustrate that we do not know how peak rings are formed, how stratigraphic uplifts are related to topographic peak rings, or how these morphological elements are related spatially to allogenic impact breccias and melt rocks. New reflection and refraction seismic data helped improve constraints on structural models of Chicxulub, and led to a better understanding of the cratering process for large impacts. There is now general agreement that the transient cavity at Chicxulub was 80-110 km in diameter. Impact-related structures within the target rocks are clearly observed in the reflection data, but there remains disagreement on the interpretation of some of these structural elements. If the outermost significant inward-facing asymmetric scarp locates the crater rim, Chicxulub has a diameter of 180-195 km. However, if the outermost topographic high locates the crater rim, Chicxulub probably has a crater diameter of between 250 and 270 km. Chicxulub has been interpreted as having the morphology of a peak ring crater and a multiring basin. There is no consensual model for the formation of rings in multiring basins. Once such a model is agreed upon, we will be in a better position to categorize the morphology of Chicxulub.