Australia: The Land Where Time Began

A biography of the Australian continent 

Cambrian Marine Shelfal Settings – Widespread mixing in the Early to Middle Cambrian

The properties of marine sediment were altered dramatically by the radiation of burrowing marine metazoans in the early Phanerozoic, the event being commonly referred to as the “Cambrian substrate Revolution” or “agronomic revolution”. The development of biogeochemical cycling in the Phanerozoic, which included nutrient fluxes, burial of organic carbon, oxygenation of the seafloor and ecology of the sediment, was impacted by the advent of infaunalisation, and especially mixing of the sediment that was biogenically-mediated. Historically, however, the timing of the development of seafloor sediments that had been mixed, has not been well constrained. In the absence of data, mixing has been assumed to have occurred at the boundary between the Precambrian and the Cambrian with the appearance of the index-fossil and 3-D burrow Treptichnus pedum. In this paper Tarhan et al. present new stratigraphic and taphonomic data that suggests that although significant developments occurred in the Early and Middle Cambrian in infaunalisation - palaeobiologically complex animal-substrate interactions, in particular the construction of burrows - mixing continued to be suppressed throughout this interval. It has been demonstrated by Tarhan et al., by the use of a novel multi-proxy approach, which in the earliest Cambrian shelfal sediment was essentially unmixed. Also, it is indicated by their findings that even as late as the Middle Cambrian, 30 Myr after the transition from the Precambrian to the Cambrian, long after the appearance of trilobites that were believed to be deposit-feeders, seafloor shelfal heterolithic sediments had remained largely unmixed on a global scale. It is currently assumed that mixing occurred with the first appearance of 3-D burrows, and this assumption is challenged by these findings, and they also have implications for the advent and development of modern-style biogeochemical cycling.

Sources & Further reading

  1. Tarhan, L. G. and M. L. Droser (2014). "Widespread delayed mixing in early to middle Cambrian marine shelfal settings." Palaeogeography, Palaeoclimatology, Palaeoecology 399(0): 310-322.


Author: M. H. Monroe
Last updated  03/11/2015
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