Clint Barineau, Columbus State University, barineau_cllinton@columbusstate.edu; Diana
Ortega-Ariza, Kansas Geological Survey, University of Kansas, dianalo@ku.edu.
Description: This field trip will take place in a live Zoom session with
field-trip leaders discussing key outcrops along the Coastal Plain unconformity (i.e.,
Fall Line) of southwestern Georgia (GA) and southeastern Alabama (AL) as they relate to
the presence of Late Cretaceous (ca. 100 Ma) paleodrainage systems. The field trip will
begin near the AL-GA state line at a rare exposure of the unconformity itself, where
fluvial sedimentary rocks of the Tuscaloosa Formation overlie highly weathered
crystalline rocks of the Gondwanan-affinity Uchee belt. The trip will then move westward
to similar exposures east of Tallassee, AL, in order to demonstrate similarity in
character, including localized relief on the unconformity and the presence of a
regionally-extensive, Upper Cretaceous residual paleosol built on the underlying
crystalline basement rocks. Afterward, we will explore a more typical, discontinuous
group of exposures near the campus of Columbus State University in Columbus, GA,
beginning in metamorphic rocks of the Phenix City gneiss and progressively working up
section through the residual paleosol and overlying detrital sedimentary units of the
Tuscaloosa Formation. The field trip will conclude at an exposure of the paleosol,
overlying detrital Tuscaloosa Formation, and intervening unconformity west of Columbus,
GA, to demonstrate lateral continuity of this stratigraphic relationship over a distance
>125 km. Afterward, field-trip leaders will discuss geospatial analysis of the
unconformity, including how distribution of the stratigraphy in three-dimensions reveals
broad, incised paleovalleys below detrital units of the Tuscaloosa Formation and within
the igneous-metamorphic Appalachian basement rocks and their residual paleosol. Regional
analysis suggests the identified paleodrainage system may be a forerunner to the modern
Chattahoochee River.