Abstract

Shelf sediments of the Delaware Basin crop out in the Guadalupe Mountains near the Texas-New Mexico border and form a wedge of sediments pro-grading southeastward or basinward. They include shallow-water carbonates, aeolian quartz silts and supratidal evaporites. The following depositional environments are reflected by the sediments: shelf-edge (massive calcareous algal and sponge biolithite and silt-sized bioclastic intrasparite); apron (irregularly bedded, silt-sized, bioclastic intrasparite and boulder breccia); an island barrier and tidal flat complex (cross-bedded, well-sorted carbonate sands and fenestral, partly dolomitized intrasparite with and without pisolites of primary marine and secondary concretionary origin); lagoons (aphanitic to stromatolitic dolomitized carbonate muds); supratidal flats (aeolian quartz silt and sand inter-bedded westward with gypsum). The type of carbonate grains formed (for example, oölite or grapestone) depended on the rate of CaCO3 precipitation and the hydrodynamics.

During low sea level stands, seaward erosion of the island barrier complex beds produced low cliffs and rubble, partial infill of some voids and cracks with aeolian quartz, and development of desiccation polygons (over 30 m in diameter) with fractured and upturned “tepee”-like edges. High sea level stands and storm-induced marine floods resulted in an influx of marine sediments into fissures and voids, a solution of evaporites at the seaward edge of the supratidal flat (with dedolomitization of their matrix and the brecciation of up to 20 m of overlying beds), and reworking of shelf sediments. Penecontemporaneous cementation, neomorphism and dolomitization at shelf edge and barrier islands and flats occurred in highly saline, marine-derived waters. Penecontemporaneous dolomitization also occurred in the lagoonal and supratidal sediments.

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