MICROTECTITE CLASTS IN TSUNAMI DEPOSIT AT K/T BOUNDARY OF SOUTHEAST MISSOURI

Cretaceous and Tertiary sediments are preserved within Crowleys Ridge along the northwestern edge of the Mississippi Embayment in southeast Missouri. Mining operations in Paleocene Porters Creek formation have exposed the contact between the upper Cretaceous Owl Creek formation and lower Paleocene Clayton formation.

Paleocene Porters Creek is a thick uniform montmorillonite clay mined for "kitty litter". Cretaceous Owl Creek is an extensively bioturbated gray to black, glauconitic, slightly micaceous, sandy, transgressive marine clay containing a rich assortment of invertebrate micro and macrofossils with phosphatized burrows and nodules.

Sandwiched between is one meter of Paleocene Clayton formation composed of two distinct units. Upper unit is light gray, well-indurated, burrowed, virtually unfossiliferous, calcarous marine clay. Lower Clayton unit is greenish gray to light brown, unsorted marine coquina containing numerous Cretaceous invertebrate macro and microfossils and vertebrate marine fossils. Mixed in with the fossils are clasts containing splashform and bubbly spherule microtectites.

Clasts contain microtectites between 0.5mm and 3.0mm in size. A typical 2.0 gram clast contains 0.5 grams of microtectites, approximately 75% spherical and 25% splashform.

The Mississippi Embayment would have been a natural focus for high energy deposition resulting from Chicxulub impact generated tsunamis. I propose that lower Clayton coquina clay in southeast Missouri is such a unit and is composed of allochthonous Cretaceous sediments containing microtectites from the Chicxulub impact ejecta blanket that were redeposited at the head of the Mississippi Embayment. The unfossiliferous upper Clayton clay represents a return to marine transgression but under almost lifeless conditions.