Contrasting the Stratigraphic Architecture of Carbonate Shelves and Slopes across a Foreland Basin: Permian of the Delaware Basin
Authors: Janson Xavier , Hairabian Alex , Hurd Greg 
Published: November 2019

The Permian strata on the shelves around the Delaware Basin represent more than 1000 meters of carbonates and mixed carbonate/siliciclastic deposits. These strata host vast amount of hydrocarbon, and their stratigraphic architecture is very well understood based on numerous studies form the outcrop in the northern and western part of the basin and a wealth of subsurface data in and around the basin. The stratigraphic evolution of the early to middle Permian mixed carbonate-siliciclastic system is the combined result of a waning tectonic activity and a transition from an ice-house to greenhouse climatic-eustatic signal. Comparing two classic outcrop localities between the south (Glass Mountains) and the north (Guadalupe Mountains) of the basin shows some striking difference in the overall stratigraphic architecture of the Woflcampian, Leonardian, and Guadalupian strata.

The Woflcampian and Leonardian in the Glass Mountains is about 75% the thickness of the similar interval in the north and has an overall retrograding architecture compared to an overall prograding motif in the north. In the Glass Mountains, the Leonardian slope (Bone Spring Fm. equivalent) is dominated by silt and coarse-grained gravity flow deposits (turbidites and megabreccia) compared to the huge volume of muddy dilute carbonate turbidites in the Bone Spring Formation of the Guadalupe Mountains. The thinner and mostly retrograding architecture of the Leonardian in the south compared to the northern margins indicates a larger accommodation space versus sediment supply ratio. This difference may be due to either an increased subsidence due to waning tectonic activity or a reduced sediment production and accumulation compared to the north, or a combination of the two. A potential explanation for a reduced sediment production rate might be the large amount of siliciclastics mixed into the carbonate system in the south due to the proximity of the orogenic front compared to a larger mostly purely carbonate Leonardian shelf in the north that produced huge amount of carbonate mud that is exported to the slope and allows for the shelf margin to prograde by more effectively infilling the basin topography.

The Guadalupian interval and especially the section from the Vidrio Formation to the end of the Capitan Formation is much more prograding (17 km of basinward step for 500m of thickness) compared to the similar interval in the Guadalupe Mountains (6 km of basinward step from Goat Seep Formation to end Tansill Formation for 300m of thickness). That equates to a P/A ratio of 34 in the Glass Mountains compared to 20 in the Guadalupe Mountains. We hypothesize that the strong influx of sand on the slope and in the basin allowed the Guadalupian reef in the south to build outward in a similar fashion that the mud exported in the basin during the Bone Spring time promoted the progradation of the northern Leonardian shelf in the Guadalupe Mountains.

These two overall architecture differences between the south and northern part of the basin point toward a strong control of the overall sediment production rate and accumulation of sediment on the slope combined with antecedent topography and subsidence rate on the stratigraphic architecture of those carbonate shelves experiencing the same eustatic and climatic signal.