--> --> Abstract: High-Resolution Stratigraphy of the Sub-Mississippian Unconformity in Southwest Missouri, by Dulce C. Cruz and Kevin R. Evans; #90067 (2007)

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High-Resolution Stratigraphy of the Sub-Mississippian Unconformity in Southwest Missouri

 

Dulce C. Cruz and Kevin R. Evans. Department of Geography, Geology, and Planning, Missouri State University, 901 S. National Ave., Springfield, MO 65897  [email protected]

 

Although uplift on the Ozark Dome generally is considered to be Pennsylvanian in age, the sub-Mississippian unconformity and succeeding sedimentation record a major phase of tectonism in the southwest Missouri Ozarks. Initial phases of this study provide some tantalizing insight into this unconformity.

 

The sub-Mississippian unconformity progressively cuts out Lower Ordovician through Upper Devonian strata in southwestern Missouri. The Bachelor Formation is the basal Mississippian (Kinderhookian) stratigraphic unit in this area. It consists of quartz sandstone and shale, and it records the initial relative sea-level rise during the Mississippian. The Bachelor Formation rests with angular unconformity above the Lower Ordovician Cotter Dolomite approximately 15 km north of Springfield; the Cotter Dolomite is cut out entirely 80 km to the north. In contrast, the Lower to Middle Ordovician Powell Formation and St. Peter Sandstone are preserved in north-central Arkansas, and thin outcrops of the Upper Devonian Chattanooga Shale are preserved near the ArkansasÐMissouri state line.

 

Locally, sandstone from the Bachelor Formation fills paleokarst fissures and cavities developed at the base of the unconformity in the Cotter Dolomite. In a few road cuts near Branson, a thin limestone unit crops out below the Bachelor Formation. The origin of these strata is problematic; some sand-filled burrows seem to indicate that this unit was not lithified during the Kinderhookian, but conodonts indicate an Early Ordovician (Ibexian) age. It remains uncertain whether the elements were reworked from lower strata.

 

The distribution of Lower Mississippian strata above the unconformity also seemingly was affected by uplift. Other investigators have shown that the Northview Formation and underlying carbonate units (Kinderhookian) are appreciably thicker in an east-west-trending trough-like basin north of Springfield.

 

AAPG Search and Discover Article #90067©2007 AAPG Mid-Continent Section Meeting, Wichita, Kansas