Abstract

Cretaceous-Tertiary boundary (i.e., Chicxulub impact-related) bed couplets consisting of a microtektite-bearing bed or beds with overlying tsunami sand deposits as well as other types of Cretaceous-Tertiary boundary microtektite-bearing beds are known from ~ 20 localities spanning parts of the marine Western Interior, Gulf Coastal Plain, Atlantic Coastal Plain, and Mexican Coastal Plain, as well as some Atlantic and Gulf of Mexico DSDP and ODP sites. At Shell Creek stratigraphic section, Wilcox County, Alabama, outcrop characteristics that are intermediate in character between Atlantic and Mexican Coastal Plain sites crop out. Specifically, Shell Creek is thin (< 1 m) like Atlantic sections, but has a textural dichotomy like Mexican sections. The density of microtektites at Shell Creek is also remarkable; in fact it is much like the density seen in Haitian sections. The preservation state of the Shell Creek microtektites is also notable. Even though the microtektites are altered to smectitic clays, the alteration has not obliterated fine details of the glass such as vesicles and other internal structures.