Outcrop-derived facies model and cycle architecture of the Tansill G27-G28 high-frequency sequences, Rattlesnake Canyon, New Mexico
High-relief, steep-rimmed carbonate margins are significant geologic features documented in a variety of locations throughout the geologic record. The Tansill Formation, the shallow-water platform equivalent of the steep-rimmed Capitan Reef, is the end member of a depositional system that progressively narrowed through time and has the most compressed outer-shelf-facies tract of Permian strata on the Northwest Shelf. Extensive precipitation of in-situ marine cements allowed for early lithification and oversteepening of the narrow outer-shelf and resulted in the most extensive network of syndepositional fractures and the best margin collapse features documented in the Late Guadalupian. Tansill shelfal strata is well constrained and served as part of the the archetype high-frequency cycle (HFC)/sequence (HFS) stratigraphic framework developed and modified over decades of extensive outcrop studies (Tyrrell, 1969), making it one of the type locations to study depositinal processes of a structurally dynamic platform. This study provides the opportunity to examine the terminal phase of carbonate deposition of a dynamically restrictive basin and better understand the associated platform geometries and facies architecture of a steep-rimmed platform leading up to the extreme reorganization of basin fill as evaporite precipitation took over during the Wuchiapingian Stage, Ochoan Series. The stratigraphic framework at Rattlesnake Canyon for the lower and middle Tansill was built from eight detailed measured sections within the Guadalupian HFS G27-G28 interval, totaling 467 m. Sections were described on the northern wall of Rattlesnake Canyon where detailed characterization of the G25 and G26 (Hairpin and Triplet) HFSs had been resolved. Distinct bedding planes within each measured sections were correlated using photomosaic panels of the canyon walls and airborne LIDAR-based digital outcrop models, creating a high degree of certainty when correlating and interpreting cycle architecture along a palinspastically reconstructed dip-oriented cross section. The spacing between sections ranges between 58 m – 232 m, and when projected onto a true dip profile they span a distance of 1.1 km, beginning 300 m inland of the G28 platform margin. The close spacing of measured sections was mandated by the abrupt lateral facies tract changes within the narrow Tansill shelf. A more extensive record of the G27 and G28 HFSs were documented in Rattlesnake Canyon than in adjacent canyons where exposure is incomplete because of covered intervals (Dark Canyon) or the collapse of the time-equivalent platform margin and removal of outer-shelf strata (Walnut Canyon). The framework of the G27-G28 HFSs further constrains the maximum flooding surface (MFS) of the CS13 and indicates a rocky shoreline juxtaposed against the windward side of shelf-crest tepee-pisolite barrier-island complexes. Previous studies have emphasized the stacking patterns comprising the outer few kilometers of the platform but have given little to no recognition to the breccia prone high-energy shorelines deposits and have not incorporated this distinct facies into depositional models. Comparison of data from this study with the proximal Walnut and Dark Canyon profiles help to further delineate the G27 – G28 platform geometries and facies tract widths and can be incorporated into the larger scale stratigraphic framework of Permian strata exposed in the Guadalupe Mountains.