THE SEARCH FOR KOBE: LOCATING THE KINDERHOOK-OSAGE BOUNDARY EXCURSION IN THE IOWA, ILLINOIS, AND MISSOURI TRI-STATE AREA

The Early Mississippian was an intriguing time in Earth’s history as it was marked by significant changes in the ocean-atmosphere-biosphere system. This interval followed the end-Devonian mass extinction, and records two of the largest positive δ¹³C excursions of the Phanerozoic; the Hangenberg excursion (which occurs at the Devonian-Mississippian boundary) and the Kinderhook-Osage Boundary Excursion (KOBE) which marks the K-O boundary. Some of the best exposed Lower Mississippian strata in the world are located in the US mid-continent, notably the Iowa, Illinois, and Missouri tri-state region, which includes the type area for the Kinderhookian Stage. Despite the significance of these strata, this stratigraphic interval is poorly refined in the tri-state region due to the sub-Burlington unconformity, a southeastward expanding hiatal surface present at the K-O boundary.

Through integration of sequence stratigraphy, δ¹³C chemostratigraphy, and conodont biostratigraphy, this study aims to create a new high-resolution chronostratigraphic framework for the Lower Mississippian of the tri-state area in order to more precisely refine the K-O boundary and the KOBE. This is achieved through integration of subsurface data from cores across central and southeast Iowa with outcrop data from the type sections near the Mississippi River. Preliminary results indicate the sub-Burlington unconformity is more expanded than previously thought in northeast Missouri, where the entire KOBE is absent. However, data from the central Iowa subsurface reveal a more continuous succession across the K-O boundary interval. Unexpectedly there appears to be less missing time in the up-ramp strata of central Iowa than in the classical type areas along the Mississippi River.