Sedimentology, sediment dispersal patterns, and stratigraphic architecture of progradational carbonate sand bodies, lower Lake Valley Formation (Mississippian), Sacramento Mountains, south-central New Mexico

Abstract

The Alamogordo, Nunn, and Tierra Blanca Members of the Lake Valley Formation comprise one of at least four transgressive-regressive sequences found within Mississippian strata of the Sacramento Mountains, south-central New Mexico. Excellent exposures along the dip-trending western escarpment of the Sacramento Mountains, as well as within several strike-trending canyons that dissect the mountain front, provide a three-dimensional view of the stratal relationships and facies components within the Alamogordo-Tierra Blanca Sequence. The Alamogordo Member consists of thick, evenly bedded, skeletal-spiculitic mudstone/wackestone and represents deposition during transgression. Waulsortian-type mud mounds were mostly initiated during Alamogordo deposition. The Nunn-Tierra Blanca interval consists of thin to medium, wavy-bedded skeletal grainstone/packstone with lesser amounts of massive, lithoclastic-skeletal grainstone that prograded over the Alamogordo deposits. Grainy facies grade laterally and downdip into thin to medium bedded skeletal mudstone/wackestone. Deposition by sediment gravity flow processes, particularly by debris flows and sandy debris flows, was dominant during Nunn Tierra Blanca time. The Nunn-Tierra Blanca interval prograded into outer ramp-to-basin areas as lobate carbonate sand bodies that thin and become muddier both along strike and downdip. Internal stratal relationships indicate that these sand lobes prograded across the outer ramp through a complex interaction of sedimentation, erosion and sediment bypass. Progradation of carbonate platform margin and slope facies is commonly thought to occur because the platform margin acts as a "line source" of sediment, whereby platform-derived sediment forms a base-of-slope apron with consistent thickness and facies distribution along depositional strike. In contrast, the low-relief (<50m synoptic relief), km-scale (laterally), lobate morphologies and lateral facies distributions within the Nunn-Tierra Blanca interval suggest deposition within systems that were more akin to low-relief submarine fans. Lobate morphologies further suggest that shallow-water carbonate sand was transported to outer portions of the ramp from a series of discrete point sources located (but no longer exposed) updip of the study area.