EVOLUTIONARY AND ECOLOGICAL DYNAMICS OF MACROBENTHIC COMMUNITIES ACROSS THE TOARCIAN OCEANIC ANOXIC EVENT IN NORTHEAST PANTHALASSA (YA HA TINDA, ALBERTA, CANADA)
At Ya Ha Tinda, the initiation of the T-OAE carbon isotope excursion has a major effect on the biota. The pre-T-OAE community is composed of large epifaunal suspension-feeders (bivalves and brachiopods), lobsters, crinoids, and burrowing organisms represented as trace fossils. At the onset of the isotope excursion, the benthic community experiences wholesale turnover of bivalve and brachiopod genera as well as a significant diminution in body size of the community. The intra-T-OAE community largely consists of opportunistic, low-oxygen tolerant benthic taxa that colonized the seafloor sporadically for short periods with some facultatively pseudoplanktonic taxa. Unlike the contemporary deposits in Europe and the pelagic record in Panthalassa, there is no sign of recovery at Ya Ha Tinda in the middle Toarcian Planulata ammonite zone; abundance, richness, and functional diversity of benthic taxa remain extremely low and the size of the community remains small. The primary stress on this system is interpreted to be oxygen limitation, which persisted longer than in northwest Europe. The benthic record is in stark contrast to the pelagic record suggesting a decoupling of the benthic and pelagic communities in this region during the Early Jurassic.