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Syndepositional Deformation of High-Relief Prograding Carbonate Platforms: Insights From the Yates/Tansill Capitan Platform, Guadalupe Mountains, NM, USA

Abstract

High-relief prograding and aggrading carbonate platform margins are subject to syndepostional deformation. In the subsurface it is important to understand and predict how the resultant fault and fracture systems are distributed as they impart significant heterogeneity in permeability that focuses diagenetic processes and fluid flow. In order to better predict failure and understand its relationship to platform margin geometry, we have integrated field mapping with detailed LiDAR-derived 3D photorealistic mapping of platform strata and syndepositional faults across 100km2 area of the Guadalupe Mts. The study area extends 20 km along margin strike from Rattlesnake to Double Canyon and 5 km shelfward of the present-day escarpment. A photorealistic model of the area was constructed by draping color orthoimagery over a 1-m DEM created from airborne LiDAR collected in 2008 by the Bureau of Economic Geology at the University of Texas. Stratigraphy and faults were mapped onto the model using a 3D digitizer. Data from field mapping and photorealistic modeling were integrated in a GIS to create a geologic map, and to facilitate construction of orthorectified cross sections. Data were also imported into GoCAD and interpolated to create a surface-based stratigraphic and structural model of the platform. Mapping demonstrates that the Capitan platform had a scalloped margin that likely persisted throughout deposition of the Yates and Tansill Fms. Syndepositional faults initiated and propagated in clusters 300-600 m shelfward of the active margin, typically forming asymmetric graben with dominant basinward-dipping and lesser shelfward-dipping faults. The overall abundance of faults is greatest where the reef margin is basinward-convex in plan view. Individual fault systems comprise a series of linked or en-echelon segments up to 3 km in length with up to 30 m throw. Displacement-to-length ratios are thus quite low, consistent with faults that are confined within a brittle layer. We interpret these observations as evidence of a mode of margin-driven failure that differs from catastrophic collapse, namely quasi-stable failure of the entire thickness of the platform. This mode of failure is likely a response to integrated effects of differential compaction and slope perpendicular extension that responds to, rather than creates, scalloped margin geometry. These results hold important implications for fracture prediction in subsurface high relief carbonate platforms.