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ABSTRACT: The Cretaceous-Tertiary Boundary at Moscow Landing, West-Central Alabama


Cretaceous-Tertiary boundary exposures at Moscow Landing along the western bank of the Tombigbee River in southeastern Sumter County, Alabama, represent the most geologically intriguing contact between the Mesozoic and Cenozoic within the southeastern portion of the United States.

Stratigraphically, this site consists of about 7 m of bioturbated chalky limestone assignable to the Upper Cretaceous Prairie Bluff Chalk. 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 channel fills up to 2.6 m deep gouged into the upper Prairie Bluff surface. About 2 m of interbedded marl and sandy limestone of the upper Clayton disconformably overlie the truncated lower 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 Markalius inversus Zone (NP1) 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.

AAPG Search and Discovery Article #90941©1997 GCAGS 47th Annual Meeting, New Orleans, Louisiana