ABSTRACT

Cretaceous-Tertiary boundary exposures at Moscow Landing in west-central Alabama represent the most geologically intriguing contact between Mesozoic and Cenozoic strata within the southeastern United States. At this site, about 7 m of bioturbated chalky limestone assignable to the Upper Cretaceous Prairie Bluff Chalk are exposed. The upper surface of the Prairie Bluff is marked by abundant burrows filled with marl from the overlying Paleocene Clayton Formation. Discontinuous, crescentic-shaped wedges of basal Clayton coarse quartzose sand mark channels up to 2.6 m deep scoured into the upper Prairie Bluff surface. About 2 m of interbedded marl and sandy limestone of the upper Clayton disconformably overlie the truncated basal Clayton channel fills and adjacent burrowed Prairie Bluff surface.

Paleontological investigations indicate that the uppermost Prairie Bluff Chalk is assignable to the planktonic foraminiferal Racemiguembelina fructicosa Zonule and to the nannofossil Nephrolithus frequens Zone (CC26) of late middle Maastrichtian age. The overlying Clayton Formation is assignable to the planktonic foraminiferal Morozovella pseudobulloides Zone (Zone P1b) and to the Cruciplacolithus tenuis Zone (NP2) of middle early Paleocene age. Microfossil biostratigraphy, the truncation of high-angle normal faults at the Prairie Bluff-Clayton contact, and the burrowed and channeled upper Prairie Bluff surface all document nondeposition or erosional removal of late Maastrichtian and early Danian sediments along the disconformable Prairie Bluff-Clayton contact at Moscow Landing.