Anatomy, dimensions, and significance of the penultimate Yates tepee-shelf crest complex, G25 Hairpin HFS, Guadalupe Mountains, New Mexico and Texas

Voorhees, Kristopher James
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The steep-rimmed Permian Capitan platform in the Guadalupe Mountains has been studied in extensive detail to understand the effect of eustacy on platform architecture as seen in continuously exposed 700 m relief shelf-to-basin depositional profile. The Guadalupian Hairpin member (G25 High-Frequency Sequence) of the Yates Formation represents a major regional shelf marker and displays continuous 2.5 km dip-width exposures of the Capitan platform in McKittrick, Big, Double, Gunsight, Slaughter, Rattlesnake, and Walnut Canyons. Compared to the sequences above and below it, the G25 HFS is unique in that it reveals pronounced expansion of the shelf crest tepee-pisolite complex from an average of 1 km width to greater than 2 km. Tepee structures are 2-20 m diameter expansion megapolygons with compressional ridges formed by syndepositional expansive crystallization of micritic cement in arid to evaporitic supratidal settings. Increased dip-width of the shelf crest tepee-belt reflects a prolonged period where repeated cycles of wetting, evaporation, precipitation, and buckling of storm-ridge washover facies (grainy tidal flats/beaches) dominated the shelf. This study seeks to examine the role that eustacy/accommodation play in expansion of the shelf crest tepee complex by quantifying the dimensions of Capitan-equivalent shelf facies in McKittrick and Rattlesnake Canyons. Dip-oriented regional cross sections in Rattlesnake and McKittrick Canyons were created from 21 measured sections from 50-500 m spacing covering 30 to 70 m in thickness calibrated to 3 high-resolution gigapan photomosaics that are in turn constrained spatially using airborne lidar data. Cross sections in both canyons constrain facies tract dimensions as well as depositional topography and spatial distribution of the tepee complexes, allowing construction of a new tightly controlled depositional profile. 29 thin sections aid in grain identification, cement composition, and facies classification. Two main results of this study are (1) a new tightly constrained model for the Capitan shelf unequivocally showing that the tepee-belt is the topographic high-point of the profile, and (2) the Hairpin G25 highstand marks a period of prolonged supratidal exposure of the shelf and rapid volumetrically significant marine cementation from a supersaturated fluid, marking the first phase of silling of the Delaware Basin and onset of basinal restriction prior to end-Capitan Castile evaporite deposition.