Abstract: Origin of Early Vuggy Porosity in Carbonate-Mudbank Buildups, Pennsylvanian and Permian, Sacramento Mountains, New Mexico
J. M. Parks
The presence of botryoidal "radiaxial aragonite fibrous aggregates" (rafa) in modern coral reefs now is known to indicate submarine cementation in void spaces. Extensive identical rafa masses, now altered to calcite but preserving identical microstructure and relations to surrounding host sediment, in Pennsylvanian and Permian carbonate buildups of the Sacramento Mountains imply early, large void spaces in carbonate-mud phylloid-algae mudbanks.
Six hypotheses for the origin of the large vugs are: (1) subaerial solution, (2) submarine solution, (3) decay of preexisting soft-bodied organisms, (4) "umbrella-effect" of curved phylloid-algal plates, (5) dewatering contraction, (6) gas bubbles.
Void space approaching 50% composed of large tabular vugs seems an unlikely result of subaerial solution. Submarine solution of carbonates in an actively precipitating carbonate depositional environment is not plausible. There is not and probably cannot be evidence to support hypothesis 3. Although some voids have upper bounding algal plates, most do not. Dewatering contraction may not produce tabular voids, but this process could enhance voids initiated and localized by processes 3 and 6. Large flattened gas bubbles are present in organic-rich sediments (e.g., Mississippi delta muds)--the ancient carbonate muds were rich in organic matter, and water and mud depths are comparable.
Gas-bubble voids could be at least partly preserved as pore spaces if the mudbanks were removed rapidly from the environment conducive to rafa growth, and if later sparite precipitation were inhibited by the early presence of (photo-) hydrocarbon solutions.
AAPG Search and Discovery Article #90968©1977 AAPG-SEPM Annual Convention and Exhibition, Washington, DC