TRENCHING OPERATIONS FOR STRATIGRAPHIC STUDY AT K/T BOUNDARY IN SOUTHEAST MISSOURI

Cretaceous-Tertiary boundary deposit was identified approximately three years ago at the Ralston Purina (now Nestle-Purina) open pit clay mine in Stoddard County, Missouri. Paleocene Porters Creek clay is mined for kitty litter. As part of the mining operations, a large sump was excavated to collect runoff from the mine face. The sump was deep enough to penetrate through Paleocene Clayton formation and into Cretaceous Owl Creek formation. The sump was full of water and in situ measurements were impossible. However, diverse and abundant samples were available in the spoil pile. These samples contained a rich assortment of Cretaceous invertebrate and some vertebrate fossils mixed together in a carbonate coquina. Additional fossils as casts and molds were found in a glauconitic clay. Closer examination of the coquina revealed clasts containing many microtektites of the type reported from the Chicxulub impact event.

In July, 2003 mining operations at this location ceased and we were allowed unrestricted access to the pit floor. We were very eager to measure the K/T boundary section in place. Four large and deep trenches were excavated over six weeks allowing in-situ, detailed measurements and sampling. Our time was limited as the mine was to be reclaimed and allowed to fill with water. Each trench filled with water within twenty-four hours necessitating pumping. However, we were able to sample and collect most weekends until October, 2003.

Preliminary results are exciting. Cretaceous invertebrate fossils collected are the most diverse and finest quality ever found in Missouri. The section consists of approximately 185 cm of graded mega-tsunami deposit. Depending on funding, we hope to determine the extent of this deposit by trenching other sites in the northwest portion of the Mississippi Embayment in Missouri.