Sequence Stratigraphy of the Lower and Middle Mississippian Subsystem in Southwestern Missouri
Jeremiah S. Jackson and Kevin R. Evans
Missouri State University, Department of Geography, Geology, and Planning, Springfield, MO 65897, [email protected]
The detailed sequence stratigraphy of lower and middle Mississippian rocks in southwestern Missouri is incompletely understood; previous studies primarily have focused on biostratigraphy, lithostratigraphy, and depositional environments. Provisional field studies of new road cuts along Highway 71 provide for an interpretive sequence stratigraphy model that can be correlated from mid-ramp to platform and inner shelf settings in a southwest-northeast transect.
A sequence boundary is interpreted at the base of the Bachelor Formation (Kinderhookian), which rests with angular unconformity on Upper Devonian shale. An upper sequence boundary is recognized where the upper Mississippian Hindsville Formation (Chesterian) uncomformably overlies the middle Mississippian Keokuk Limestone (Osagean). Meramecian strata are missing or greatly thinned. Between these sequence boundaries are one or more potential sequence or parasequence set boundaries.
The Compton Limestone (Kinderhookian) records relative deepening. It is truncated locally with low-angle discordance below the Northview Formation (Kinderhookian), a mixed shale and siltstone succession. The Northview accumulated in a small inner-shelf basin and prograded across the platform and middle ramp. The overlying Pierson Formation (Osagean) records relative deepening. The top of the Pierson, however, is truncated at the base of the Reeds Spring (Osagean), where the “Wolfpen Gap Shale” and interbedded lime mudstone and chert record marked deepening. In contrast, the overlying Elsie and Keokuk formations (Osagean) record shoaling.
The mechanism for sea-level change remains uncertain, but the approach of Gondwana to Laurasia provides a possible explanation for tectonism and truncation of stratigraphic units at the base and top of this interval.
AAPG Search and Discovery Article #90095©2009 AAPG Eastern Section Meeting, Evansville, Indiana, September 20-22, 2009