Abstract

The geometry and deformational mechanisms associated with the growth of the Gobbler Anticline, a north-trending, doubly plunging, tight fold that is interpreted to be a fault-propagation fold above a blind, basement-rooted reverse fault with en echelon tear faults was constrained via a balanced cross-section, virtual outcrop models, and orthomosaic photographs. The Gobbler Anticline consists of tightly folded and faulted mixed lithofacies. Here, thick-bedded (1.0-10.0 m) limestones intercalated with thin-bedded (laminated - 1.0 m) shale, characteristic of the Bug Scuffle Member of the Pennsylvanian Gobbler Formation. Measured sections (totaling 470 m) document the distribution of facies while mechanical rock property analyses document the unconfined compressive strength of the rocks. Thin sections and X-Ray fluorescence indicate lithological controls on deformational mechanisms. Pre-Permian unconformities and thinning of the overlying mid-upper Pennsylvanian strata indicate shallow burial (<500 m) at the time of initial fold deformation (Missourian, ∼307 Ma). We find that argillaceous wackestones are disproportionately weakened when involved in folding soon after deposition and mechanical layering is the dominant control on fracture development in more deformed areas. This study illustrates the value of a tightly constrained mechanical strati-graphic model for the prediction of fracture distribution and fold geometry in deformed carbonate rocks.