SEQUENCE BOUNDARIES IN THE MISSISSIPPIAN SUBSYSTEM IN SOUTHWEST MISSOURI

Sequence stratigraphy models of lower and middle Mississippian rocks in southwest Missouri are incomplete in relation to depositional environment. Recent road-cuts along Highway 71 in McDonald County near Jane, Missouri and just south of Branson, Missouri east of Highway 65 reveal stratigraphic sequence boundaries on a mid-ramp environment that assist in completing the sequence stratigraphy model in southwestern Missouri.

The lower sequence boundary occurs at the base of the lower Mississippian Bachelor Formation lying with angular unconformity on the upper Devonian Chattanooga shale. The upper sequence boundary occurs where the upper Mississippian Hindsville Formation uncomformably overlies the middle Mississippian Keokuk formation. Between these sequence boundaries lies a potential parasequence set. Cross-bedding and low-angle inter- and intraformational truncations with no evidence of sub-aerial exposure infer a transgressive systems tract bounded by the Pierson Limestone’s lower contact with the Northview Formation and upper contact with the Reeds Spring Formation.

The Northview Formation is overlain with disconformity by the Pierson Limestone and contains evidence of a potential hardground surface. The underlying Compton Limestone marks maximum flooding of a highstand systems tract. This unit is uniform and evenly bedded throughout much of its extent with exception south of Branson with downlap in the middle to upper beds and also near Jane where it contains mounds derived from slumping, flexure, and over-steepening of the underlying Chattanooga Shale. The approach of Gondwana to Laurasia is interpreted as the cause of tectonism and some relative sea-level changes.

Inclusion of the parasequence set in middle Mississippian strata in southwestern Missouri assists in creation of a more complete stratigraphic record in the state and a better understanding of the paleo-environment.