Strengths abd weaknesses of the reef guild concepts and quantitative data: Application to the upper Capitan-massive community (Permian), Guadalupe Mountains, New Mexico-Texas

Summary Analyses of large acatate sheet tracings, close-up photos and 105 sub-horizontal quadrat surfaces at four localities near the base of the Guadalupe Mountains Escarpment indicate that the biotic framework of the upper Capitan reef was built by about 35 species: one codiacean (Eugonophyllum sp.), 17 calcisponges, 9 bryozoans, one richthofenid brachipod, some crinoid (known only from columns), 4 Problematica and microbes. This widespread fossil community included members of the Constructor, Baffler and Binder Guilds. A re-evaluation of the Guild Concept (Fagerstrom, 1987, 1991) highlights the validity of the functional roles of the Constructor and Binder Guilds for reef construction. Members of the Baffler Guild, however, need to be revised and an interpretation of microbial micrite and cryptic biota remains controversial. Open surface phylloid algal and cryptic sponge-bryozoan dominated sub-communities were of only local importance. The upper Capitanmassive differs from its Permian conterparts in the low diversity and areal cover of the frame-building biota, low micrite content and abundant micro-frameworks, i.e, intergrown small sponges, Problematica and syndepositional cements (botryoidal and isopachous, fibrous calcite). Quantitative areal cover data were assessed at various scales. Large acetate sheets generally have low coverage of macro-biota (5.4%). By contrast, analysis of small areas of local high areal cover (selected acetate sheet quadrats, subvertical photographs, and quadrat samples: 15–21%) provide detailed insights into clustered patches forming the inital reef framework. Both data sets provide useful clues for an integrated approach to framework assessment. Mean acetate sheet data are limited by their somewhat generalized pattern, while small investigation areas may overemphasize local variation. Erect and pendant sponges with solitary, sub-cylindrical and multi-branche/clonal forms, were the predominant initial frame-builders in both open surface and cryptic habitats. Selective larval recruitment of erects sponges to firm substrates produced continous upward accretion of the initial framework. On open surfaces and in pores formed by tabular sponges and fenestrate bryozoans, erect and pendant sponges were supported in their hydrodynamically unstable growth position by encrusters, chieflyArchaeolithoporelle hidensis, Shamovella obscura, an unnamed tubular organism, and microbes. Subsequent growth ofArchaeolithoporella hidensis, microbial crusts and syndepositional cements on the outer walls of live sponges would have impeded ambient water circulation and may have led to ‘creeping sponge death by suffocation’ or complete encrustation after death. Filling of pores in the initial and encrusted reef framework by internal sediment (packstone-grainstone; derived from the framework and the back-reef shelf/platform) and voluminous syndepositional marine-phreatic cements completed the framebuilding process.