Mechanical stratigraphic control on deformation in a fault-propagation fold, Gobbler Anticline, Sacramento Mountains, New Mexico, USA

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Syzdek, Joseph C.

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Folded carbonates are host to a significant portion of the world’s hydrocarbon reservoirs. To date, analog data to aid prediction of the style, intensity, and distribution of critical strain elements such as opening-mode fractures is limited. Prediction of strain distribution and connectivity of fracture systems is especially problematic within interstratified carbonate and siliciclastic/argillaceous lithologies that create strong mechanical anisotropies. Documentation of the structural processes and stratigraphic architecture on a full spectrum of scales and across a well-constrained structure was conducted to provide a better understanding of deformation styles. The geometry and structural mechanisms associated with the growth of the Gobbler Anticline, a north-trending, doubly plunging, 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; specifically, thick-bedded (1.0-10.0 m) limestones intercalated with thin-bedded (laminated - 1.0 m) clay-rich intervals, characteristic of the Bug Scuffle Member of the Gobbler Formation. Measured sections (totaling 470 m) assess the distribution of facies while mechanical rock property analyses document the unconfined compressive strength of the rocks. Thin sections and X-Ray fluorescence provide improved understandings of lithological controls on deformational mechanisms. Pre-Permian unconformities and thinning of the overlying mid-upper Pennsylvanian strata indicate shallow overburden (< 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 stratigraphic model for the prediction of fracture distribution and fold geometry


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