Newsletter of the Subcommission on Permian Stratigraphy Number ...

Permophiles Issue #38 2001been published. In addition, intrinsic and extrinsic control mechanismson reef formation have been investigated. The most importantresults are summarized below.I. Taxonomic affinities, diversity, and guild structureAnalysis <strong>of</strong> large acetate sheet tracings, close-up photos, andpolished quadrat surfaces at four localities near <strong>the</strong> base <strong>of</strong> <strong>the</strong>Guadalupe Mountains escarpment indicate that <strong>the</strong> Upper CapitanLimestone reef was built by 34 species <strong>of</strong> “calcareous” spongesand demosponges, 9 bryozoans, <strong>the</strong> richth<strong>of</strong>eniid brachiopodSestropoma cribriferum Cooper and Grant, 1969, <strong>the</strong> phylloid algaEugonophyllum sp., 4 Problematica, and microbes. Demosponge“sphinctozoans” and inozoid calcareous sponges are major constituents<strong>of</strong> <strong>the</strong> Middle Permian upper Capitan Limestone. Thefauna appears diverse on local scale, but compared to <strong>the</strong> diversity<strong>of</strong> assemblages <strong>of</strong> similar age in Tunisia and in Sou<strong>the</strong>rn China,<strong>the</strong> assemblage is species poor. Gigantospongia disc<strong>of</strong>orma Rigbyand Senowbari-Daryan 1996, a discoidal inozoid calcareous spongeat least 2.5 m in diameter, is <strong>the</strong> largest described Permian sponge.In addition to previously described reef-builders <strong>of</strong> o<strong>the</strong>r taxonomicaffiliation, Lercaritubus problematicus Flügel, Senowbari-Daryan, and Di Stefano, 1990, an organism <strong>of</strong> unknown affinity,was identified in <strong>the</strong> Capitan Limestone for <strong>the</strong> first time. A reevaluation<strong>of</strong> <strong>the</strong> Guild Concept highlights <strong>the</strong> validity <strong>of</strong> <strong>the</strong> functionalroles <strong>of</strong> <strong>the</strong> Constructor, Binder, and Baffler Guilds for reefconstruction. Although members <strong>of</strong> <strong>the</strong> Baffler Guild are abundant,<strong>the</strong> lack <strong>of</strong> baffled sediment suggests that <strong>the</strong> importance <strong>of</strong><strong>the</strong>ir role in building <strong>the</strong> upper Capitan reef needs to be reconsidered.Interpretations <strong>of</strong> <strong>the</strong> importance <strong>of</strong> microbes and crypticbiota remain controversial.Publications:Rigby, J.K. and Senowbari-Daryan, B., 1996, Gigantospongia, newgenus, <strong>the</strong> largest known Permian sponge, Capitan Limestone,Guadalupe Mountains, New Mexico: Journal <strong>of</strong> Paleontology,v. 70, p. 347-355.Senowbari-Daryan, B. and Rigby, J.K., 1996a, First report <strong>of</strong>Lercaritubus in North America, from <strong>the</strong> Permian Capitan Limestone,Guadalupe Mountains, New Mexico: Journal <strong>of</strong> Paleontology,v. 70, p. 22-26.Rigby, J.K., Senowbari-Daryan, B. and Liu, H., 1998, Sponges <strong>of</strong><strong>the</strong> Permian upper Capitan Limestone, Guadalupe Mountains,New Mexico and Texas: Brigham Young Univ., Geology Studies,v. 42, p. 19-118.Fagerstrom, J.A. and Weidlich, O., 1999, Strengths and weaknesses<strong>of</strong> <strong>the</strong> reef guild concept and quantitative data: application to<strong>the</strong> upper Capitan-Massive community (Permian), GuadalupeMountains, New Mexico-Texas: Facies, v. 40, p. 131-156.II. Reef typesOf <strong>the</strong> 10 reef types known from <strong>the</strong> Permian, algal/cement reefsand sponge reefs formed most <strong>of</strong> <strong>the</strong> upper Capitanian framework.Phylloid algal reefs, brachiopod reefs, and calcimicrobe reefs alsocontributed to <strong>the</strong> accretion <strong>of</strong> <strong>the</strong> platform rim in differentpaleoenvironmental settings (Fig. 1).Guadalupe Mountains, New Mexico: Journal <strong>of</strong> Paleontology,v. 70, p. 697-701.Weidlich, O. and Fagerstrom, J.A., 1998, Evolution <strong>of</strong> <strong>the</strong> upperCapitan-Massive (Permian), Guadalupe Mountains, NewMexico: Brigham Young Univ., Geology Studies, v. 43, p. 167-187.III. Reef composition and developmentThe long-running controversy over <strong>the</strong> origin <strong>of</strong> <strong>the</strong> UpperCapitan Limestone concerns different interpretations <strong>of</strong> <strong>the</strong> relativeimportance <strong>of</strong> its organic versus inorganic components andwhe<strong>the</strong>r <strong>the</strong> organic components were capable <strong>of</strong> building a reefframework. Our quantitative data from <strong>the</strong> reef maps indicate aneed to reinterpret existing models. The most important constructionalelement is <strong>the</strong> micro-framework (76.7% average coverage), aconsortium <strong>of</strong> small, low-growing reefbuilders (especiallyArchaeolithoporella hidensis and Shamovella obscura) andbotryoidal marine-phreatic cements. In contrast to previous interpretations,nei<strong>the</strong>r macro-sponges nor syndepositional cementpredominated, making <strong>the</strong> Upper Capitan Limestone a poor analogfor both modern well-skeletonized metazoan and Precambrian cementreefs. Quantitative areal cover data were assessed at variousscales. Large acetate sheets generally have low coverage <strong>of</strong> macrobiota(5.4%). By contrast, analysis <strong>of</strong> small areas in selected acetatesheet quadrats, sub-vertical photographs, and quadratsamples provide detailed insights into <strong>the</strong> roles <strong>of</strong> clustered patches<strong>of</strong> high areal cover (15-21%) in building <strong>the</strong> reef framework.Facies relations determined from outcrop studies andphotomosaics have been used in conjunction with reef maps, polishedslabs, and micr<strong>of</strong>acies data to better understand <strong>the</strong> depositionalfacies, quantitative composition, and control mechanisms <strong>of</strong><strong>the</strong> Upper Capitan Limestone which differs from <strong>the</strong> outer shelf inits biotic composition and unbedded nature. A three-stage model<strong>of</strong> <strong>the</strong> seaward shelf is established comprising (1) a sponge reef/algal cement/phylloid algal stage, (2) a Shamovella (Tubiphytes)stage, and (3) prograding cyclic outer shelf beds with isolatedreefbuilders (Fig. 1). Stage 1 is characterized by progressiveshallowing as evidenced by a shift from aggradation toprogradation, by changes in boundstone composition, and finallyby disintegration <strong>of</strong> <strong>the</strong> biogenic framework. Stage 2, dominatedby Shamovella, bryozoans, microbes and small reefbuilders, exhibitsa lateral zonation triggered by <strong>the</strong> seaward dipping outershelf. Stage 3 is composed <strong>of</strong> cyclic outer shelf grainstones; scatteredsponges and Shamovella microbial level-bottom communitiesare restricted to few horizons.Publications:Fagerstrom, J.A. and Weidlich, O., 1999, Origin <strong>of</strong> <strong>the</strong> upper Capitan-Massive Limestone (Permian), Guadalupe Mountains, NewMexico-Texas: Is it a reef? Geological Society <strong>of</strong> America Bulletin,v. 111, p. 159-176.Weidlich, O. and Fagerstrom, J.A., 1998, Evolution <strong>of</strong> <strong>the</strong> upperCapitan-Massive (Permian), Guadalupe Mountains, NewMexico: Brigham Young Univ., Geology Studies, v. 43, p. 167-187.Publications:Senowbari-Daryan, B. and Rigby, J.K., 1996, Brachiopod moundsnot sponge reefs, Permian Capitan-Tansill Formations,13IV. Extrinsic control mechanismsThe entire depositional sequence <strong>of</strong> <strong>the</strong> Upper Capitan Limestoneis controlled by a third-order sea-level fall as evidenced by