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Sedimentary Responses to Syndepositional Faulting in a Prograding Platform: Permian, Guadalupe Mountains, USA


Syndepositional faulting is an integral feature of the prograding Permian Capitan Platform, Guadalupe Mountains, New Mexico and Texas, USA. To understand the distribution and impact of faulting on platform architecture, stratigraphy and facies, we have undertaken studies at two different scales: 1) mapping of the platform stratigraphy and fault systems in the outer 5 km of the platform over 20 km along strike, and 2) construction of a 0.4 x 0.4 km 3D model detailing the sedimentary responses to two syndepositional faults that bound a narrow graben. Detailed field mapping, measured sections and petrographic work is augmented by the digitization of faults, palaeokarst and key stratigraphic horizons within digital outcrop models derived from ground and air-based LIDAR. At the largest scale of observation it is shown that the Capitan platform comprises several discrete structural zones delimited by normal fault systems that bound graben systems. In the youngest parts of the platform the grabens have surprising continuity in position/width relative to the Capitan margin. In contrast older graben systems show an en-echelon arrangement, varying along strike with respect to platform margin trends. The overall platform profile is characterized by abrupt changes in dip, thickness and facies association, marked by clusters of normal faults that normally tip upwards within the platform succession. Detailed work at the scale of an individual graben system is captured within a 3D digital outcrop model. It reveals surprising complexity of fault movement, stratigraphic response and correlation. Subsidence patterns are irregular, with individual faults accommodating episodes of normal and reverse movement. This unusual behavior is considered a response to tilting of the platform during deposition, acting in conjunction with steep fault dips and possibly dissolution-driven processes that were focused along the fault zones. Because the faults tip-out upwards, little of this structural complexity is apparent in the youngest platform strata. The Capitan platform has a strong structural imprint on its architecture and stratigraphy, and shows unexpected stratigraphic complexity. Comparable behavior and deformation may be a common feature of platforms that prograde over wedges of soft sediment and/or develop significant margin relief. Although fault offsets are generally of sub seismic scale their heterogeneous fill may help subsurface recognition.