Evolution of Cambrian to Ordovician trace fossils in pelagic deep-sea chert, Australia

Abstract

Cambrian to Ordovician pelagic radiolarian cherts in the Lachlan Fold Belt in southeastern Australia contain trace fossils demonstrating the faunal diversification that occurred during the Ordovician on the deep-sea floor. The Cambro-Ordovician Howqua Chert has a very low degree of bioturbation, and the trace fossils are small and shallow. In contrast, the late Middle to Late Ordovician cherts are strongly bioturbated with larger, deeper burrows, and contain more morphologically diverse trace fossils. This records a substantial increase in the size, abundance and activity of deep-ocean benthic animals living on the floor of the ocean bordering Australia.

Key Words:

• biodiversity
• bioturbation
• Cambrian
• evolution
• Lachlan Fold Belt
• Ordovician
• pelagic chert
• trace fossil

Acknowledgements

Fons VandenBerg and Ian Stewart kindly provided detailed locality information for the Cambrian cherts in Victoria. Comments by C. L. Fergusson and an anonymous reviewer improved the manuscript.