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Contrasting the Stratigraphic Architecture of Carbonate Platform Across a Foreland Basin: Permian Carbonate Shelves of the Delaware Basin

Abstract

The Permian strata on the shelves around the Delaware Basin represent more than 1000 meters of carbonates and mixed carbonate/siliciclastic deposits. 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. First, the Wolfcampian and Leonardian in the Glass Mountains is about 75% the thickness of the similar interval in the north and has an overall retrograding architecture compare to an overall prograding motif in the north. In addition, in the Glass Mountains, the Leonardian slope (Bone Spring Fm. equivalent) is dominated by silt and coarse gravity flow deposits (turbidites and megabreccia) compared to the huge volume of muddy dilute carbonate turbidites in the Bone Spring Fm. of the Guadalupe Mountains. The thinner and mostly retrograding architecture of the Leonardian in the south results from either a smaller available accommodation space due to reduced subsidence rate, or a smaller sediment production and accumulation compared to the north, or a combination of the two. A potential explanations for a reduce sediment production rate might be the large amount of siliciclastic 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 produce 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. Second, the Guadalupian interval, and especially the section from the Vidrio Fm. to the end of the Capitan 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 Fm. to end Tansill Fm. for 300m of thickness). That equate to a PA ratio of 34 in the Glass Mountains compared to 20 in the Guadalupe Mountains. We hypothesized that the strong influx of sand on the slope and in the basin allows the Guadalupian reef in the South to build outward in a similar fashion that the mud exported in the basin (during the Bone Spring Fm. time) allows the Leonardian shelf in the Guadalupe Mountains to prograde more than in the south. 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 its effect on the slope combined with antecedent topography, subsidence rate on the stratigraphic architecture of those carbonate shelf experiencing the same eustatic and climatic signal.