Paper No. 13
Presentation Time: 11:15 AM
PALEOECOLOGY OF DISASTER FAUNA SPONGES AFTER THE END-TRIASSIC MASS EXTINCTION
RITTERBUSH, Kathleen A., Department of Geophysical Sciences, University of Chicago, 5734 S Ellis Ave, Chicago, IL 60637 and BOTTJER, David, Department of Earth Sciences, University of Southern California, Los Angeles, CA 90089, ritterbush@uchicago.edu
After the end-Triassic mass extinction, silicious sponges expanded their ecological role to dominate widespread level-bottom habitats for ~2 Ma, in an interval of survival and opportunism prior to ecological recovery. This phenomenon is global in extent. Contemporaneous extensive sponge-dominated assemblages that occur over 100 km are known from the Tethys and southern Panthalassa, exemplified in the European Austroalpine and Peruvian Pucara Group, respectively. These are significant expansions of sponge habitat occupation, compared to underlying Upper Triassic rocks. A new study in Nevada details a thick stratigraphic package (20-30 m) of sponge cherts. The Ferguson Hill Member of the Sunrise Formation is interpreted to record increasingly shallow facies from the Triassic – Jurassic system boundary into the Pleinsbachian stage. The sponges apparently occupied a storm-influenced middle shelf throughout the earliest Jurassic (Hettangian and early Sinemurian stages). These strata, traceable for kilometers, outcrop throughout the New York Canyon area.
Medium to thick bedded cherts contain accumulated silicious sponge debris, and minimal terrigenous sediment. Common carbonate tempestites coincide with extensive ‘calcareous mummy’ preservation of sponge body shapes. Where these bedding planes are exposed, Weyla scallops in life-position are common at the base of, and among, fossil sponges. Co-occuring gastropods are very rare. Despite representation in allochthonous storm deposits, other molluscs and corals have not been found in life position within the sponge beds. Preserved sponges contain megasclere spicules and mineralized frameworks with potential taphonomic affinities to modern Bahaman sponges. ‘Peloidal’ replacement fabrics are also common. Lack of preserved microscleres limits taxonomic description to the ordinal level. Demosponges (Astrophorids) are identified, but Hexactinellids are not apparent. Sponges are not documented from the conformably underlying Upper Triassic Gabbs Formation.
The widespread and enduring success of sponges in Mesozoic seas after Triassic time is potentially related to global shifts in habitat and silica availability. These continued investigations relate complications in recovery from mass extinction to long-term patterns of marine ecology.
