PALEOECOLOGICAL COMPOSITION AND SUCCESSION IN NORIAN (LATE TRIASSIC) PANTHALASSIC BENTHIC FAUNAS

The duration of the Norian stage (late Triassic) may be expanded to nearly half of the Triassic period in light of new absolute dates for Carnian-Norian age ash beds from Pizzo Mondello, Italy. This expansion highlights the temporal uncertainties of established biostratigraphic zone durations, and baseline research is needed to correlate well-known biostratigraphic groups with geologic events and regional paleoecology. This research attempts to (1) characterize the paleoecological succession of two Norian sedimentary sequences in west-central Nevada, and (2) place these sequences into an evolutionary and biostratigraphic context. This approach integrates the extensive biostratigraphic research of this period with an evolutionary and ecological perspective, and enables correlation of biotic and abiotic events.

Abundance data collected from two Panthalassic sites representing shallow marine depositional environments indicate that brachiopod taxa were important paleoecological components within the Norian, long after the Permo-Triassic mass extinction event. Ecologically, Norian community structure is remarkably stable, with many ecological niche proportions remaining nearly constant even as the species abundances change. Biostratigraphic marker groups were identified at many intervals sampled (index groups of bivalves, ammonoids, conodonts, and/or brachiopods), allowing for correlation with other regional and global Triassic marine sedimentary sequences. Biostratigraphic and paleoecological data, along with absolute dates for the boundary, facilitated the investigation of Norian biotic response to environmental catastrophes, such as the Manicouagan impact event in the mid-Norian.