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Syndepositional Fault Control on Dolomitization of a Steep-Walled Carbonate Platform Margin, Yates Formation (Permian), Guadalupe Mountains, New Mexico


Syndepositional deformation features are fundamental components of carbonate platforms both in the subsurface and in seismic-scale field analogs. These deformation features are commonly opening-mode, solution-widened fractures that can evolve into extensional faults, and reactivate frequently through the evolution of the platform. They also have potential to act as fluid flow conduits from the earliest phases of platform growth through burial and uplift, and are present during hydrocarbon generation. As such, diagenetic alteration in the margins of these carbonate platforms is often intense, may demonstrate a preferential spatial relationship to the deformation features rather than the depositional fabrics of the strata, and may impact the permeability development of reservoir strata near deformation features. This study investigates the distribution of 2 generations of dolomite in the Permian Yates Fm. in Rattlesnake Canyon, Guadalupe Mountains, NM. The dolomites were sampled along a 1 km dip-oriented outcrop, covering two high-frequency sequences (HFSs; approx. 300ky each) and cut by a margin parallel syndepositional fault graben. 100 samples from 6 transects (3 lateral through the reef, outer-shelf, and shelf crest updip of the graben; 3 vertical from reef to shelf crest updip of the graben, downdip of the proximal fault, and across the basinal fault) were classified by petrographic, CL, and trace element data. The data show an early mimetic, dully-luminescent, aphanocrystalline dolomite attributed to brine reflux from a mid-platform lagoon; and a late fabric destructive, brightly-luminescent dolomite that is strongly associated with deformation features. The former is pervasive in the older HFS within/updip of the graben as well as in the shallowest strata downdip, while the latter utilized the permeability conduits created by faults and fractures, particularly those filled with inner platform siliciclastics, to form patchy haloes around the features. These haloes overlap to result in a dolomitized reef updip/in the graben, and fabric-destructive lenses extending from deformation features into beds of more permeable shelf strata. The geometries are consistent with a similar fault-related dolomite study in the Tansill Fm., Dark Canyon (Frost et al., 2012), though alteration is more extensive in the Rattlesnake Canyon window. In combination, these works prove that fault and fracture related diagenesis is not trivial to the evolution of platform margins.