THE APPALACHIAN-OUACHITA CONNECTION: Paleozoic Orogenic Belt at the Southern Margin of North America

Abstract

Late Paleozoic orogenic belt structures exposed in the Appalachian Mountains of Alabama and in the Ouachita Mountains of Arkansas plunge from opposite directions beneath postorogenic Mesozoic-Cenozoic strata in the Mississippi Embayment of the Gulf Coastal Plain (Figure 1). The Paleozoic stratigraphic sequence and details of structural style in the Ouachita outcrops contrast strongly with those in the Appalachian outcrops. Furthermore, straight-line projection of structural strike from the outcrops does not lead to a simple connection of structures beneath the Coastal Plain. Concealed by the Coastal Plain cover are answers to questions such as the following: Are the orogenic belts continuous, discontinuous, offset, or intersecting? How are along-strike changes in stratigraphy and structural style expressed? What is the sequence of tectonic evolution? Early attempts to interpret the subsurface relationships between the Appalachian and Ouachita structures were of necessity based on the first few scattered wells that were drilled through Coastal Plain strata into Paleozoic rocks. Subsequent studies have enjoyed the availability of progressively more numerous deep wells and a growing accumulation of geophysical data. Various stages in the evolution of thought were outlined by King (1950, 1961, 1975) and by Thomas (1973, 1976). This review summarizes available subsurface data in a pre-Mesozoic paleogeologic