Controls on Lower Permian (Wolfcampian) carbonate sedimentation and sequence stratigraphic framework of the Hueco formation (Upper-Middle and Gastropod members), Robledo Shelf, western Orogrande Basin, New Mexico

On the western margin of the Pennsylvanian/Permian Orogrande Basin, two composite measured sections in the Lower Permian upper interval of the Middle Member of the Hueco Limestone were analyzed in regards to depositional environment, facies and sequence stratigraphy. This can elucidate where potential unconventional reservoirs can be found in the Wolfcamp Shale of the Permian Basin. Based on these analyses, 12 lithofacies were identified, including 9 carbonate lithofacies: 1) fenestral dolomudstone, 2) peloidal dolomudstone, 3) ostracode foraminifera packstone, 4) foraminifera peloidal grainstone, 5) skeletal intraclast grainstone, 6) phylloid algal peloidal grainstone, 7) echinoderm phylloid algal packstone, 8) echinoderm bivalve brachiopod packstone, and 9) Tubiphytes red algal packstone, and 3 siliciclastic lithofacies: 1) dull gray shale, 2) quartz siltstone, and 3) vertic calcisol. The carbonate lithofacies were organized into 4 depositional facies associations: 1) supratidal, 2) intertidal, 3) tidal channel, and 4) subtidal. Waltherian facies changes between these depositional facies associations indicates that the western margin of the Orogrande Basin was a shallow carbonate ramp with an incised valley located in the Doña Ana Mountains, creating a concentration of tidal channel, subtidal, and fluvial depositional facies in the area, this shows that fluvial systems in this area were funneled into the basin through topographic lows creating point sources for siliciclastics coming into the basin. In the Robledo Mountains, the Hueco Limestone experienced more restriction from the open ocean, creating a concentration of intertidal lagoons and supratidal flats with water chemistries that can vary greatly from normal marine seawater. Changes in the facies were controlled by changes in relative sealevel, driven by glacio-eustacy, as well as basin subsidence. The Gastropod interval experienced four fourth order sequences from base to top as part of one third order sequence. The upper interval of the Middle Member of the Hueco Limestone experienced just one fourth order sequence, due to its having greater bathymetric relief. The sequence stratigraphic analysis shows that the upper interval of the Middle Member and the Gastropod interval of the Hueco Limestone correlate to each other, though the upper interval of the Middle Hueco experienced less depositional time