ICHNOLOGY OF THE CLAYTON CHALK (DANIAN CLAYTON FORMATION), MOSCOW LANDING, SUMTER COUNTY, WESTERN ALABAMA: IMPLICATIONS FOR EARLY PALEOCENE SEA-LEVEL DYNAMICS

At Moscow Landing, Sumter County, Alabama, a single, thin pelagic carbonate bed, herein referred to as the Clayton chalk, occurs near the top of the lower Paleocene (Danian) Clayton Formation, just a few meters below the clay-dominated Porters Creek Formation. The chalk bed, which lacks a clastic sand component, has an average carbonate content of ~80% and is bounded immediately below and above by darker marls (CaCO₃ = ~60%). While the chalk and associated marls are thoroughly bioturbated, ichnofabrics are best expressed in the chalk’s piped zone, i.e., the ~50-cm-thick marl-to-chalk transition wherein lighter chalk-filled ichnofossils contrast markedly with darker host marls. Chalk-related ichnofabrics are characterized by Chondrites, Phycosiphon, Planolites, Taenidium(?), Teichichnus, Thalassinoides, Zoophycos, and other identified traces. The chalk also contains rare Teredolites-bored relict and ghost log-grounds. Based on cross-cutting relationships and vertical distribution of ichnofossils in the piped zone, producers of Chondrites appear to have occupied the deepest tiers, whereas other trace producers occupied shallow to intermediate levels of the substrate. In comparison to those expressed in chalk units of the Cretaceous Selma Group, Clayton chalk ichnofabrics most resemble those of the relatively pure Demopolis Chalk and suggest deposition in a relatively quiet outer to middle shelf setting. The Clayton chalk represents the final, albeit brief, phase of shelf chalk deposition in the Gulf coastal plain, marks the condensed section of depositional sequence TAGC-1.2, and likely records a significant transgressive pulse. Deposition of the Clayton chalk in the east central Gulf coastal plain may have been contemporaneous with deposition of marine and marginal marine clastic facies manifest within otherwise terrestrial Paleocene depositional sequences in the U.S. Western Interior. The abrupt switch from pelagic carbonate deposition to clastic deposition manifest in the Clayton-Porters Creek transition likely records the final draining of interior seas and the full-fledged development of the proto-Mississippi River drainage system.