Article: New observations on the ecology of the Permian Capitan Reef, Texas and New Mexico
Rachel Wood, J. A. D. Dickson and Brenda L. Kirkland
The Permian Capitan reef was a predominantly heterotrophic ecosystem strongly differentiated into open surface and cryptic communities. Unlike modern phototrophic coralgal reefs, most of the preservabh epibenthos was housed within the cryptos and zonation developed only in the shallow parts of the reef Contrary to established opinion, most sphinctozoan sponges did not grow upright to form a baffling framework but rather were pendent cryptobionts, as were nodular bryozoans and rare solitary rugose coral: and crinoids. Indeed, many members of the cryptos were obligate cryptobionts. Much of the Middle Capital reef framework was constructed by a scaffolding of large frondose bryozoans, with the subsidiary platy sphinctozoan Guadalupia zitteliana. Bathymetrically shallow areas of both the Middle and Upper Capitan reef however, were characterized by platy sponges. In parts of the Upper Capitan, some platy sponge; (Gigantospongia discoforma) reached up to 2 m in diameter and formed the ceilings of huge cavities which supported an extensive cryptos.In the absence of destructive forces (both biotic and physical) prevalent on modern reefs, the relatively fragili Capitan reef remained intact after the death of the constructing organisms. Rigidity was imparted to this community by a post-mortem encrustation of Tubiphytes and Archaeolithoporella, together with microbia micrite. The resultant cavernous framework was partially infilled with sediment and preserved by syn sedimentary intergrowth of aragonitic botryoids and Archaeolithoporella. Extensive cement precipitation was favoured by a number of factors including deep anoxia, which generated upwelling waters with elevated alkalinity. Although the accumulation rate of the Capitan may have been comparable to that of moden coralgal reefs, both the trophic structure and relative contributions of inorganic and organic carbonate wen profoundly different.