The impact of bioturbation on infaunal ecology and evolution during the Proterozoic-Cambrian transition

Terminal Proterozoic to lower Cambrian siliciclastic sequences in North Wal es, Newfoundland, and Finnmark, Norway have been examined for evidence of c hanges in. metazoan activity, based on ichnological data. Information was c ollected on infaunal tiering, age, evolutionary complexity, ichnofabric, an d taphonomy. Averaged over lower Cambrian time, facies had Little effect on size and faunal density of trace-making organisms. A landward shift in. bi oturbation. intensity apparently occurred as larger organisms colonized fir m muddy substrates on the inner shelf through time. In the earliest stage o f the lower Cambrian, the majority of ichnodiversity relates to surface-fee ding trace fossils. Not until the Tommotian is evidence for pervasive detri tus feeding common. These changes were driven by evolutionary adaptation an d external environmental forces. In addition, the activity of infaunal meta zoans altered the intra-sediment environment in a manner that increased hab itability and primary productivity in a way that encouraged further exploit ation of sedimentary nutrients.