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Abstract: Capitan "Reef": Evolution of a Concept

J. M. Cys, J. L. Brezina, E. Greenwood

The Capitan "reef" complex of West Texas and southeastern New Mexico is, perhaps, the best known shelf-edge deposit attributed to an organic reef origin. The Capitan "reef" is essentially a single stratigraphic unit termed the Capital Formation which shows an upper massive ("reef") facies and a lower bedded (fore-reef) facies with some intergradation. Fusulinids and other fossils date it as Late Permian. It is a part of the type section of the North American Guadalupian Series. Outcrops of the Capitan Formation border the Delaware basin in a shelfedge position, although most of its 450-mi (720 km) length is in the subsurface. Significant outcrops are in the Guadalupe, Apache, and Glass Mountains; the best studied are those in the Guadalupe Mountains.

Several modern workers have suggested a bank or marginal mound origin for the Capitan, although some modern workers adhere to an organic reef origin. Recent studies have revealed that the most abundant component of the Capitan originated as early diagenetic submarine calcium carbonate which acted as inorganic interstitial cement in the lower Capitan and an inorganic framework in the middle and upper Capitan. There is no evidence of large-scale recrystallization. New evidence suggests that pisolites previously attributed to a vadose origin more properly are attributed to an intertidal marine origin. From definitions put forth in this paper, and on the basis of much early diagenetic calcium carbonate, the Capitan appears to be primarily a stratigraphic or inorganic-framework reef with a significant organic reef component.

Shelf to basin correlations through the Capitan are a major problem, and cause divergent opinions. The shelf to basin correlations presented here are based on physical stratigraphy and paleontology. Accordingly, the Seven Rivers, Yates, and Tansill Formations of the shelf correlate to the entire Capitan Formation of the shelf edge, and to the Bell Canyon Formation of the basin. Modern paleontologic and physical stratigraphic data further suggest correlation of the Lamar Member of the Bell Canyon Formation with the Tansill Formation.

AAPG Search and Discovery Article #90970©1977 AAPG Southwest Section Meeting, Abilene, Texas