Characterization of Folds in the Roubidoux Fm. Near Licking, MO

The Roubidoux Formation, near Licking, Missouri is folded into anticline-syncline pairs, which contrasts with horizontal sedimentary strata typical for the state. This folding reflects either 1) sagging of the strata (i.e., folding) due to karsting (cave collapse) in the underlying layers, or 2) a period of compressional plate tectonic activity leading to shortening of the strata by folding. To test these hypotheses I used detailed geologic mapping of an 80 meter road cut using a digital photomosaic, collection of orientation data of the bedding planes with a Brunton compass, and stereographic analysis to determine fold type and fold orientation. Ten separate folds form three coherent groups with each group having distinct orientations for the fold axial surfaces. Similarity of the fold axis orientations within each group suggests a common tectonic origin for these folds. However, the deflection of fold orientations from one group to the next suggests subsequent deformation event(s) leading to the rotation of fold axes. The younger event(s) may also have been tectonic, followed by late karsting