Australia: The Land Where Time Began |
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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.
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Author: M.H.Monroe Email: admin@austhrutime.com Sources & Further reading |