Sequence Stratigraphy of Classic Carbonate Outcrops in West Texas and Southeast New Mexico with Subsurface Analogs
Stratigrapher and Exploration Geologist, Cobalt International Energy, Houston, Texas
West Texas and southeast New Mexico contain many classic carbonate exposures with large vertical and lateral extents that allow delineation of major sequence stratigraphic relationships. Sequence stratigraphic relationships help to predict geometries, facies, and early diagenesis in analogous systems in the subsurface. Isolated carbonate buildups are present in Mississippian and Pennsylvanian outcrops in the Sacramento Mountains, and they grew during transgressions when accommodation (relative sea level rise) was greater than or approximately equal to carbonate sediment production. Drowned isolated buildups are commonly excellent carbonate reservoirs throughout the world, including the nearby Horseshoe Atoll.
Ramp carbonates of the Permian San Andres Formation are exposed along the western side of the Guadalupe Mountains. The San Andres has a thick lower transgressive systems tract (TST) overlain by a prograding highstand systems tract (HST). Major hydrocarbon reservoirs occur in similar sequences in the subsurface. Reservoirs are commonly shelf-crest grainstones and adjacent packstones in the upper San Andres HST with structures created by differential compaction over packstone-grainstone buildups in the TST of the lower San Andres.
The Capitan Formation is part of a classic carbonate shelf system dominated by HST progradation. The same system occurs in the subsurface. The structural configuration of the prograding margin is dominated by basinward dip caused by differential compaction associated with the progradation. As a result, the fractured Capitan reef is generally structurally low and wet. Hydrocarbons occur in backreef carbonates and shelfal sands with updip, landward seals formed by impermeable lagoonal evaporites.
AAPG Search and Discovery Article #90159©2012 AAPG Foundation Distinguished Lecturer Series 2012-2013.