Impact Geology of the U.S. Gulf Coastal States

Impact geology is the study of hypervelocity impact craters and structures, their ejecta, and distal effects within the stratigraphic record. The U.S. Gulf Coastal states have a remarkable variety of confirmed and suspected impact craters and structures and impact-related stratigraphy given the area involved. Texas has the most confirmed craters and structures (Marquez, Odessa, and Sierra Madera) and suspected impacts features (Bee Bluff, Hico, and an unnamed structure). There is a similar record in other Gulf Coast states: Louisiana (Brushy Creek - suspected), Mississippi (Kilmichael - suspected), Alabama (Wetumpka - confirmed), and Georgia (Woodbury - suspected). Impact stratigraphy with distal ejecta occurs at the Cretaceous-Paleogene boundary, at lower and upper Eocene horizons, and within Pleistocene formations. Gulf Coastal distal ejecta include tektites, microtektites, impact spherules, and shocked grains. Confirmed Chicxulub impact ejecta (mainly impact spherules) occur at sites in three states (Alabama, Mississippi, and Texas) and confirmed Chesapeake Bay impact ejecta (tektites) occur within upper Eocene strata in multi-county areas within both Georgia and Texas. In addition, impact ejecta, specifically microtektites and shocked mineral grains, which likely came from Chesapeake Bay, are found in Alabama and Georgia, respectively. Beyond these occurrences, there are other possible, probable, and confirmed impact ejecta in the Gulf Coastal states, including lower and upper Eocene deposits in Texas and Pleistocene occurrences in Louisiana and Texas. In this paper, we review these confirmed and suspected craters and structures, and impact-related stratigraphy in the Gulf Coast and present some new findings about some of these features.