5 Marine Paleontology (Posters)

VERTICAL GROWTH FORM OF GIGANTOSPONGIA: A NEW LITHOLOGICAL REEF FABRIC FROM THE MIDDLE CAPITAN LIMESTONE (PERMIAN; GUADALUPIAN), WEST TEXAS, USA

Paper number: 5-6
Program: Technical Sessions
Time: 8:00 AM – 12:00 PM

Authors

Abstract

New lithological fabrics and fossil species are periodically discovered from reef outcrops of the Capitan Limestone in West Texas and New Mexico, USA. Recent discoveries and interpretations have illustrated the important role played by sponge-roofed crypts in the construction of this fossil reef. Explanate sphinctozoan and inozoid sponges grew outward into the water column, forming meter- and sub-meter scale crypts beneath them. A community of cryptobionts that included sphinctozoan sponges, bryozoans, crinoids, brachiopods, and corals occupied resulting crypts. Recesses of older crypts were sealed by growth of a secondary community that included Archaeolithoporella, Shamovella,and microbial micrite, and by the precipitation of syndepositional cements. Crypts roofed by Gigantospongiaand Guadalupiaare known from the Middle Capitan and Upper Capitan Limestone; roof elements are typically horizontal or sub-horizontal in orientation.

A new crypt fabric was recently discovered from Middle Capitan Limestone outcrops in Bear Canyon, Guadalupe Mountains National Park, Texas, USA. In these crypts the inozoid "roofing" sponge Gigantospongiagrew in vertical, rather than horizontal, orientation. These explanate sponges appear to have stood a short distance (10-15 centimeters) from the reef face or from other Gigantospongiaspecimens, thus forming crypts behind, rather than beneath, them. These crypts were occupied by solitary sphinctozoan sponges and ramose bryozoans. Epibiont attachment was restricted to the crypt-facing side of Gigantospongiaspecimens. The secondary community responsible for sealing the crypt was restricted to microbial micrite; Archaeolithoporellaand Shamovellahave not yet been discovered. Gravity-defying caps of microbial micrite are perched on top of some sphinctozoan fossils within the crypts. Isopachous cement rinds are present on skeletal framework within these crypts.