NEW K/PG LOCALITIES ALONG THE EASTERN GULF COASTAL PLAIN: MORE EVIDENCE OF IMPACT AND TSUNAMIS

Three localities in Mississippi and Alabama (Ellis Pit, near New Albany MS, East Bound Street, Starkville MS and “Mooseland” near Prairie Bluff AL) expose the K/Pg boundary, including a variety of sequences related to the Chicxulub impact and the events that followed. The Mooseland locality exposes the upper Maastrichtian Prairie Bluff Chalk and the overlying Danian Clayton Formation. The Prairie Bluff Chalk is composed of very fine grained muddy chalk, while the Clayton Fm is a fine to medium grained quartz sand with small amounts of mica and glauconite. The two formations are separated by a sharp undulating contact. The overlying Clayton Fm preserves two distinct fining upwards sequences each 30-35 cm thick, possibly related to two high energy events. The lower event bed is normally graded and composed of an indurated shell hash with abundant impact spherules at the base. The upper event bed is marked by a sharp contact at the base with multiple rip-ups 2-10 cm in diameter that are identical in lithology to the underlying Prairie Bluff. The two event beds are similar to the clastic unit interpreted by Smit et al. (1996) and Schulte et al. (2010) as tsunami deposits associated with the impact and subsequent shelf collapse. At Ellis Pit, the typical impact sequence is truncated. Above the upper Maastrichtian Owl Creek Fm (a facies change from the Prairie Bluff Chalk), 8-12 cm of fine to medium quartz sand with abundant impact spherules is preserved corresponding to the base of the clastic unit. The spherule bed is unconformably truncated by a gastropod limestone hash potentially representing a Danian transgressive lag deposit. At Starkville, the Prairie Bluff Chalk is overlain by the Clayton Fm. The two are separated by a heavily bioturbated (Thalassinoides) contact. The clastic unit (quartz-rich sand with spherules) is absent. This suggests the events directly related to the Chicxulub impact are not preserved, possibly erased during the Paleogene transgression. Although all three localities expose the K/Pg boundary, each reflects a different aspect of the K/Pg sequence. Whereas Mooseland represents a complete sequence including the impact and subsequent tsunamis, Ellis Pit preserves a truncated sequence, and Starkville exhibits no obvious evidence of the impact.