Conodont paleoecology and biofacies analysis of the Lower Triassic Thaynes Formation in the Cordilleran Miogeocline

The Lower Triassic (Smithian) Thaynes Formation represents a broad spectrum of paleoenvironments. Samples collected along a depth-related gradient from tidal flats to a relatively deep, commonly dysaerobic, basin yielded an abundant conodont fauna. Simple chi-square tests and multivariate analyses using six conodont entities indicate the presence of three distinctive biofacies related to the general environmental gradient. The restricted inner shelf is characterized by PARACHIROGNATHUS: The outer shelf is distinguished by a diverse conodont fauna including FURNISHIUS: Basinward, the low diversity conodont fauna is dominated by species of NEOGONDOLELLA: Some Early Triassic conodonts such as Neospathodus are ubiquitous and provide the best foundation for inter-basinal conodont zonation. Correlation of assemblages with corresponding position along an environmental gradient defined on lithologic criteria indicates that quantitative measures of conodont faunas are potentially useful in the analysis of paleogeography and changes in relative position of sea level.