PALEOENVIRONMENTAL AND EVOLUTIONARY PATTERNS IN CAMBRIAN–ORDOVICIAN BIOTURBATION (Invited Presentation)

Bioturbation—sediment mixing and ventilation by burrowing animals—shapes seafloor ecology, sediment properties and biogeochemical cycling throughout the modern oceans. The early Paleozoic emergence of bioturbating animals has therefore long been assumed to have led to substantial changes in marine biogeochemistry, ecosystem structure and the preservation potential of both sedimentary and fossil archives. However, the timing of the rise of bioturbation and environmental patterns in its expansion have been subjects of sustained debate—resolution of which has been hampered, in part, by a paucity of high-resolution bioturbation data or of systematic investigations of facies trends in lower Paleozoic bioturbation. Integrated sedimentological and ichnological characterization of the Cambrian–Ordovician Port au Port succession and Cow Head Group of western Newfoundland, encompassing over 350 meters of stratigraphy logged at the sub-decimeter scale, provides an ideal opportunity to address these questions. Across a wide range of marine facies, bioturbation does not, on average, exceed moderate intensities—corroborating observations from other lower Paleozoic successions indicating that the early Paleozoic development of bioturbation was a protracted process. Moreover, bioturbation intensities in the Port au Port succession and Cow Head Group are characterized by considerable variability at even fine scales of stratigraphic resolution and correlate strongly with variability in sedimentary facies. Facies recording nearshore depositional environments and carbonate-rich lithologies are each characterized by the highest intensities of both burrowing and sediment-mixing. These data highlight the need for a high-resolution and facies-specific approach to reconstructing the evolutionary history of bioturbation and suggest that, in contrast to previous models, bioturbation levels increased earlier in onshore relative to offshore marine settings.