2002 Denver Annual Meeting (October 27-30, 2002)

Paper No. 17
Presentation Time: 1:30 PM-5:30 PM


BELL Jr, Gorden L., National Park Service, Guadalupe Mountains National Park, HC 60 Box 400, Salt flat, TX 79847, CROW, Christopher J., Department of Geosciences, Indiana Univ Purdue Univ-Fort Wayne, 2101 É. Coliseum Blvd, Fort Wayne, IN 46805-1499 and RIGBY, J. Keith, Department of Geology, Brigham Young Univ, PO Box 24606, Provo, UT 84602-4606, gorden_bell@nps.gov

A heretofore unrecognized reef fabric was recently found in two localities in the Middle Capitan reef (Yates Formation equivalent). The framework for this fabric consists of sub-parallel colonies of Gigantospongia growing in a semi-erect or procumbent orientation. Individual plates are 0.5 to 2 meters wide and are often spaced 5-10 centimeters from immediate neighbors. Vertical orientation ranges from 40 to 70 degrees. Upwardly oriented sides are generally covered by micritic limestone or wackestone with few, if any, epibionts. Downwardly oriented sides exhibit many attached epibionts surrounded by botryoidal marine cements with voids coated or filled by isopachous marine cements, indicating the framework provided cryptic habitat for many smaller organisms. The largest area covered by this fabric is at least 30 meters across, probably larger, and the horizontal axes of platy sponges in this colony are generally oblique to the regional reef trend. The center of this distribution as currently known is about 15 meters below the top of characteristic reefal lithologies. The second area is currently only identifiable over a distance of 3 meters, but weathering and vegetation obscure the outcrops laterally. The horizontal axes of these sponges are generally sub-parallel to regional reef trend, and the occurrence is within one or two meters of the top of the highest local reef lithologies.

This is also the first report of Gigantospongia in Middle Capitan reef lithologies and the first from the southern end of the Guadalupe Mountains. This Gigantospongia is probably a new species, as it is smaller than G. discoforma in overall proportions and thickness and has a significantly different growth habit. It has been found at six different locations in Guadalupe Mountains National Park, all within Middle Capitan reefs. It is not known if the other four localities represent the same reef fabric due to restricted outcrop size and weathering which obscures surficial details. However, one occurrence is on a float boulder that contains two parallel individuals spaced 5 centimeters apart.