MICROTEKTITE MORPHOLOGY AND AFFINITIES AT THE CRETACEOUS-PALEOGENE BOUNDARY INTERVAL IN SOUTHEAST MISSOURI

Cretaceous-Paleogene boundary interval is present within the lower Paleocene Clayton Formation overlying Cretaceous Owl Creek Formation in the Missouri portion of the Mississippi Embayment. We collected and measured this interval at a strip mine and nearby outcrops in Stoddard County, Missouri. Lowest 30 cm of the Clayton Formation is tsunamite containing a dense assemblage of reworked Cretaceous marine fossils and rip-up clasts.

Most rip-up clasts contain abundant spherical and splashform microtektites that we isolated by hand. Microtektites are between 0.5 mm and 3 mm in diameter or length. Clasts containing microtektites contain no fossils. Some clasts contain distinct microtektite layers.Cephalopods are abundant in the Owl Creek Formation in Missouri and include Eutrephoceras dekayi (Morton), Sphenodiscus lobatus (Tuomey), S. pleurisepta (Conrad), Eubaculites carinatus (Morton), E. latecarinatus (Brunnschweiler), Discoscaphites iris (Conrad), and D. sphaeroidalis (Kennedy and Cobban). Almost none of these specimens are preserved with the outer shell, although gaps between the specimens and the matrix indicate that the specimens were buried with the original shell intact. Scaphite jaws are also present, both as isolated specimens and in situ in the body chamber. The same cephalopods occur in the overlying Clayton Formation, and are presumably reworked. Most of these specimens retain their original shell.

This site may contain some of the northernmost marine proximal ejecta from the Chicxulub impact. These findings indicate the ejecta within the Mississippi Embayment were deposited first and were subsequently reworked by a tsunami.