Trilobite biofacies of the Cambrian-Ordovician boundary interval in northern North America

Abstract

Regional biofacies analysis has been neglected in biostratigraphic studies of the Cambrian-Ordovician boundary interval. Cluster analysis of relative abundance data of trilobites in thirty-seven large collections from ten localities in North America outlines eleven biofacies in the mid-Trempealeauan to early Tremadocian interval. The biofacies are largely lithofacies-specific and are differentiated at generic and familial levels. The composition of trilobite zonal associations in the boundary interval is controlled principally by the sequence of biofacies. Available trilobite zonal schemes can be used only within single lithofacies. The biofacies patterns and faunal dynamics across the upper boundary of the Ptychaspid Biomere do not support hypotheses requiring catastrophic events. In coherence and geographic distribution, Late Cambrian trilobite biofacies are similar to post-Cambrian benthic biofacies.