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Coming from the Lower Ordovician Oneota Formation, these stromatolites
are some 500 million years old, from a time that Prokaryotic life
forms no longer had exclusive use of earth's shorelines. The earth’s
coastal habitats had markedly reduced stromatolite reefs, compared
with the Proterozoic. The form genera is conophyton, denoting
successive laminae with an overall conical shape.
Interestingly, this specimen actually contains some interstitial
sand, as a result of its proximity to Cambrian sandstone immediately
below the Oneota Formation. Most stromatolites are carbonates
with only post-depositional silica replacement. In this case,
the carbonate stromatolites grew in a semi-silicastic environment,
thus incorporating sand into their growth structure.
By
this time in geological history that these stromatolites were
formed, microbial communities consisted of complex consortia of
both prokaryotic and eukaryotic forms with diverse metabolic needs,
and competition for resources and differing motility among them
made for an intriguing microcosm of interacting life, some autotrophic,
some chemotrophic and some heterotrophic. However, stromatolite
reefs are believed to have regained a temporary foothold following
the extinctions even that concluded the Cambrian Period. Sine
these stromatolites are at the very base of the Ordovician, they
may well have been part of the resurgence when predation by other
organisms was temporarily, at least, suppressed.
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