Pre-Mississippian Tectonism on the Southern Margin of Laurentia: Stratigraphic Evidence from Southern Missouri and Northern Arkansas.
Dulce C. Cruz
Missouri State University, Department of Geography, Geology and Planning Springfield, MO 65897.
In southwestern Missouri and northern Arkansas the Bachelor Formation, the basal Mississippian (Kinderhookian) stratigraphic unit, records the initial sea-level rise above a subaerial exposure surface. Lower Ordovician through Upper Devonian strata are progressively cut out below the sub-Mississippian unconformity. The truncation of units seemingly was associated with flexure and an early phase of tectonism in the hinterland of the Ouachita Orogen.
Sequence stratigraphy, gamma-ray spectrometry, and carbonate petrography are used in this study to facilitate high-resolution correlation and document the possible tectonic and depositional setting of these rocks.
At 15 km north of Springfield, MO, the Mississippian Bachelor Formation rests with angular discordance on the Ordovician Cotter Dolomite; about 2.5 m of strata below the unconformity are cut out over a horizontal distance of 83.5 m (29 m/km). Other investigators have shown that this unit progressively is cut out 80km to the north. In northern Arkansas, Middle and Upper Ordovician strata are present but have been partly cut out by erosion at the base of the Mississippian. These units are gradually younger toward the east.
This study is important because it contributes into a better understanding of stratigraphic traps and seals, and distribution of carbonate reservoir facies. This work is particularly pertinent to exploration for hydrocarbon accumulations in the Mississippian Hugoton Embayment and in karstified Lower Ordovician reservoirs such as the Ellenberger and Knox groups in Texas and Tennessee. Furthermore, the sub-Mississippian strata of southwest Missouri are oil reservoirs in Texas and Appalachians mountains.
AAPG Search and Discovery Article #90070 © 2007 AAPG Foundation Grants in Aid