Turning the Capitan Reef upside down; a new appraisal of the ecology of the Permian Capitan Reef, Guadalupe Mountains, Texas and New Mexico
Turning the Capitan Reef upside down; a new appraisal of the ecology of the Permian Capitan Reef, Guadalupe Mountains, Texas and New Mexico
Palaios (August 1994) 9 (4): 422-427
- algae
- Bryozoa
- calcareous composition
- Capitan Formation
- cementation
- classification
- communities
- Delaware Basin
- diagenesis
- growth
- Guadalupe Mountains
- Guadalupian
- habitat
- interpretation
- Invertebrata
- marine sedimentation
- microfossils
- New Mexico
- paleoecology
- Paleozoic
- Permian
- Plantae
- Porifera
- porosity
- progradation
- reefs
- revision
- sedimentation
- shallow-water environment
- solution cavities
- solution features
- Texas
- United States
- Capitan Reef
Study of the primary reefal cavities preserved ubiquitously within the Permian Capitan Limestone leads to a profound reappraisal of the ecology, diagenesis and construction of the Capitan reef. Contrary to established opinion, most calcareous sponges (such as the sphinctozoans Guadalupia spp., Amblysiphonella spp., Cystauletes spp. and Lemonia spp.) did not grow upright in thickets to form a reef framework or bafflestone. Rather they were pendant cryptobionts inhabiting cavities, often in considerable abundance. In addition to this distinctive cryptic community, the framework of the reef was constructed in part by microbially-bound sediment, with the walls and ceilings of the cavities frequently supported by fenestellid and ramose bryozoans. Crypts were strengthened and filled by extensive precipitation of syn-sedimentary cements (botryoids and isopachous fibrous cements) combined with algal encrustation, predominantly Archaeolithoporella. Like modern reefs, the Capitan reef biota was thus strongly differentiated into two communities: open surface and cryptic. Our reinterpretation of the ecology of the reef has far-reaching implications for reef construction, and also for sediment supply and facies geometries of adjacent lithosomes. The presence of abundant fragile and delicate skeletons in the reef does not imply tranquil conditions given their cryptic location. We suggest here that the Capitan reef was a wave resistant and highly porous structure. A shallow-water origin for the reef is also supported by the rapid overall rate of carbonate accumulation calculated for the platform as a whole. As in modern coralgal reefs, much of the overall diversity of the Capitan reef was housed within cryptic niches. Indeed, some fossil reef-dwelling organisms previously interpreted as open surface frame-builders, including Paleozoic sphinctozoans sponges, were in fact more common as cryptobionts. Yet even though crypts are an almost ubiquitous component of both modern and fossil reefs, description of fossil cryptic biotas receives relatively little attention. The presence of a well-developed cryptos in the Permian Capitan reef complex, as well as isolated reports from other Phanerozoic reefs, suggests that an appraisal of the ecology of crypts is vital to an understanding of ancient reef ecology.