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The Role of Capitan Research in the Evolution of Carbonate Conceptual Models and Paradigms

Abstract

Evolving studies of the Permian stratigraphy of the Guadalupe Mountains have established these mixed carbonate and siliciclastic rocks, particularly those relate to the Capitan shelf margin, as “analogs” for numerous similar rocks around the world. In so doing these exposures played a key role in the development of general conceptual models for carbonate shelf margins. Examples to highlight this importance are: Nature of the reef – The ongoing debate on whether the Capitian is a reef, and if so what type, has somewhat abated with results from more recent outcrop studies. A look back at the discussions reemphasizes the need for diagnositc criteria for recognizing reef textures and for the appreciation of the role of microbes in reef construction, a current hot topic. Shelf margin profile – The notion from facies associations, geopetal measurements, and fall-in bed geometry of a reef developing between 15 and 60 m of water depth is countered by the concept of syndepositional differential compaction to explain the seaward dip of outer shelf beds. The ongoing discussion has provided important characteristics to examine in other outcrop and stratal geometries as seen in seismic. Sequence stratigraphic models– Building upon the concept of reciprocal sedimentation, the interplay between a carbonate-dominated shelf and margin with a silicilastic-dominated basin was placed into context using sequence stratigrapy, with the outcrops remaining one of the principle natural laboratories for investigating different approaches of applying sequence stratigraphy at all scales. Dolomitization – Most ideas on dolomitization of the shelf strata are still consistent with the seepage reflux model, although there remains some divergence of opinion on the extent of evaporation needed to instigate reflux and the relationship of the reflux process to changing sea level. The spatial patterns and detailed petrographic and geochemical studies have provided well-constrained models for interpreting dolomite occurrences elsewhere. Nature of faults and fractures – As the Permian carbonate profile evolved from low-relief ramp to steep rimmed margin, the foreslope/margin interface changed from one characterized by gradual low-angle slopes lacking brittle failure and significant sediment gravity flows to one with steep margin collapse with syndepositional fractures in the margin facies as well as in the inner to middle shelf.