NEW INTERPRETATIONS FOR THE DEPOSITION OF MISSISSIPPIAN LIMESTONES IN THE MID-CONTINENT: A REFLECTION OF SEQUENCE STRATIGRAPHY AND ASSOCIATED MIGRATION OF FACIES MOSAICS

The Mid-Continent Mississippian Limestone represents a geologically complex system containing different depositional environments and dynamic diagenetic and tectonic histories. This thick (up to 500 ft) carbonate unit was deposited in an east-west oriented belt with a northern and southern boundary within 5°-30° of the paleo-equator. Its subsurface equivalent is an unconventional oil and gas play in Oklahoma and Kansas with well-exposed outcrops in Missouri and Arkansas. The Mississippian-age strata in this area has been interpreted by some to be deposited in a shelf margin environment based on over-simplified paleo-depositional maps. In this study, detailed outcrop analysis has revealed the depositional environment is more consistent with a distally steepened ramp and that complex and dynamic facies mosaics exist across the distally steepened ramp due to lateral migration of facies, complicating the lithology-based nomenclature used throughout the Mid-Continent.

Integrating a sequence stratigraphic approach with an understanding of the probable complexity of facies mosaics from modern analogs has led to a modified time-series of paleo-depositional maps that better illustrate the complex facies mosaics associated with Milankovitch-scale sea level change. The high resolution sequence stratigraphic architecture developed at the Jane outcrop provides a datum for a more accurate interpretation of how Mississippian lithofacies fit into the sequence stratigraphic framework. This study includes analyses of facies vertically and horizontally to identify geometries and vertical stacking patterns on the third-, fourth-, and fifth-order scales. This outcrop-based data was applied to the regional depositional model of Mississippian-age strata in the Mid-Continent to produce more accurate paleo-depositional maps, leading to a better understanding of overall shifts in depositional facies throughout the Mississippian.