PALEOECOLOGY OF A NEW GIGANTOSPONGIA SPECIES, GUADALUPE MOUNTAINS NATIONAL PARK, TEXAS, USA

The Permian Capitan reef complex of west Texas and New Mexico is correctly considered to be one of Earth’s best studied fossil reef systems, however, much remains to be understood about these rocks. Relatively recent conceptualizations (by others) concerning deposition and structure of the reef include: 1) crypts roofed by explanate sponges and fenestellate bryozoans of the Upper and Middle Capitan reefs, and 2) the importance of microbial influences over production and accumulation of micrite in the Middle Capitan reef. Both have helped expand our understanding of these portions of the reef complex.

Recent fieldwork has identified seven Middle and Lower Capitan reef localities (Yates and Seven Rivers formations equivalents) preserving crypt fabrics formed by the en echelon growth habit of a new species of Gigantospongia that grew in a vertical to sub-vertical orientation (45-90°). Three localities are known from float only, while four expose in situ organisms over outcrop distances between 10 and 150 meters. Skeletal orientations are parallel or sub-parallel to the reef trend with distances between adjacent specimens on the order of a few centimeters to a few tens of centimeters. Crypt habitats were generated between individual sponges and whatever was reef ward of them, either another Gigantospongia frond or perhaps the reef face itself. Attachment of epibionts, such as bryozoans and other sponges, was dominantly on the reef-facing sides of these sponges. Skeletal elements of epibionts enhanced niche partitioning within these crypts. Rims of isopachous cement are common on the reef-facing sides of Gigantospongia fronds and on their epibionts. Microbially mediated micrite is present in portions of these crypts, however, some of crypt space was preserved in an unfilled state, and was later filled with coarse, blocky calcite. Microbial micrite is the dominant material in contact with the basin-facing surface of these large sponges; isopachous cements are uncommon on this surface. Based upon measurable vertical separation from overlying shelf lithologies, these Gigantospongia communities are inferred to have grown in water depths between one and 30 meters.