The Heterogeneous Shear Model to Explain Polyphase Folding in the Baraboo Syncline Located around Baraboo, Wisconsin

The Baraboo Syncline is a macroscale fold that deforms both Baraboo Quartzite and associated layers of phyllite. Syndeformational shearing of the limbs of the Baraboo Syncline created parasitic mesoscale folds that show a normal sense of vergence. These folds are also associated with a set of anti-parasitic mesoscale folds showing a reverse sense of vergence. Two models were proposed to explain the formation and kinematic significance of these anti-parasitic folds. The gravitational slump model falls apart when no deformed parasitic folds were present. The kink band model does a good job explaining the structures but falls apart when the scale of deformation is considered. The heterogeneous shear model introduced in this paper better explains the anti-parasitic structures.