Forward modeling synsedimentary deformation associated with a prograding steep-sloped carbonate margin

Differential compaction associated with prograding and aggrading steep-sloped carbonate margins leads to penecontemporaneous and post-depositional modifications of stratal geometries and tensile and shear stress concentrations that might result in brittle deformation. In an effort to investigate controls on these deformation processes, we employ a step-wise gravity loaded elastic model that captures pre-failure displacement and stress field patterns for a depositional geometry based on the Permian Capitan depositional system, Guadalupe Mountains, West Texas and New Mexico, USA. We consider four model geometries with varying progradation to aggradation (P/A) ratios, from strongly prograding (P/A = 10) to strongly aggrading (P/A = 0.1). The strongly prograding case (P/A = 10) is used for sensitivity analysis that investigates the effects of varying rock mechanical properties of basin and platform facies. Model results yield relatively consistent patterns of deformation and stress that include: (1) a region of enhanced subsidence centered near the platform margin, (2) basinward displacement of the platform margin that decreases down slope, and (3) positive maximum Coulomb stress and positive (tensile) stress, both in-plane and out-of-plane, near the platform margin and in adjacent slope and platform facies. The patterns of deformation for the strongly progradational model are strikingly similar to present day stratal geometries of the Capitan depositional system that are often inferred to be primarily depositional in origin. Model results suggest that these geometries are established immediately upon deposition and may therefore affect the stratal architecture of the margin, but significant additional deformation also occurs during subsequent platform growth. We interpret the regions of positive Coulomb stress and tensile stress as areas likely to fail by faulting or jointing, respectively. This inference is corroborated by field observations of early-formed brittle deformation features in the Capitan margin. Our geomechanical models of the Capitan margin suggest that early-formed deformation is an integral part of the general steep-sloped carbonate system.