2005 Salt Lake City Annual Meeting (October 16–19, 2005)

Paper No. 24
Presentation Time: 1:30 PM-5:30 PM


LAZÃR, Iuliana, Department of Geology and Paleontology, University of Bucharest, Bãlcescu 1, Bucharest, 010041, Romania, FELDMANN, Rodney M., Department of Geology, Kent State University, Kent, OH 44242, SCHWEITZER, Carrie E., Department of Geology, Kent State University Stark Campus, 6000 Frank Avenue NW, Canton, OH 44720 and SHIRK, Aubrey M., Department of Geology, Kent State Univ, Kent, OH 44242, cschweit@kent.edu

Exposures of Oxfordian (lower Upper Jurassic) carbonate rocks in central Dobrogea, Romania, record a remarkable sponge-algal bioherm complex and its associated fauna. The area of exposure, situated near the village of Cheia, is dissected by the Cheia River. The region lies on the fault-bounded Moesian Platform which is a microplate originating southeast of modern Romania. The deposits are included within the Visterna Member of the Casimcea Formation. The biostratigraphy of the formation was outlined by Bărbulescu (1961-1989). Detailed biofacies analysis was defined by Hermann (1996), and biozonation of the formation was largely defined by Bărbulescu (in Dragastan et al., 1998). Individual cylindrical sponge-algal bioherms, with diameters of approximately 30 m, stand approximately 25 m above the valley floor. Each bioherm has a hollow core filled by a limonitic carbonate breccia, and each is separated from adjacent bioherms by flanking, well-bedded talus. The bioherms formed near the distal margin of a carbonate ramp in water depths below normal wave base. Sponge biostromes were formed seaward and coral patch reefs and lagoonal deposits were formed landward of the sponge-algal bioherms. The fauna associated with the sponge-algal bioherms includes prosopid and dynomenid crabs; ammonites; belemnites; pectinid pelecypods; terebratulid, rhynchonellid, craniid, and thecideiid brachiopods; bryozoans; serpulids; and cidarid echinoids. Neither the crabs nor the belemnites has been reported previously. The associated benthic faunal elements tend to be small, probably occupying niches within the bioherms, and represent a biocoenosis. Diversity is low. Abundance of specimens is uniform and moderate in all facies. The architectural framework of the sponge-algal bioherm complex is uniquely preserved so that the composition and distribution of benthic organisms within the complex can be clearly delineated. This site is the only known cylindrical sponge-algal bioherm complex. The work was supported by collaborative grants from the National University Research Council of Romania to Lazăr and the National Science Foundation to Feldmann and Schweitzer.