The Gunflint Chert - Fossil Ecosystems of North America: A Guide to the Sites and their Extraordinary Biotas - page 9

examples are extremely abundant from
the Kakabeka Falls locality, hence their
name. Amazingly some extant forms of
this genus have since been discovered
in modern soil samples from the latrines
of Harlech Castle, North Wales, where
they live in reducing, ammonia-rich
environments (Siegel and Giumarro,
1966). Where were they during the
intervening 2 billion years?

other Gunflint microbes are prokaryotic.
Similar spherical unicells have been found
in the coeval Duck Creek Formation of
Western Australia (Knoll and Barghoorn,
1975).

P ALEOECOLOGY OF THE G UNFLINT
C HERT
The Gunflint Iron Formation represents a
Paleoproterozoic assemblage of chemical
and siliciclastic sedimentary rocks
deposited in a shallow water, south-facing
shelf setting on the southern margin of
Superior Province, Ontario, Canada. The
occurrence of near-shore tidal flat
sequences in the Gunflint requires
unrestricted connection with a large
ocean basin. Correlative units to the
Gunflint Formation outcrop over several
hundred kilometres to the southwest (e.g.
the Biwabik Formation of Minnesota), and
represent progressively deeper-water
deposits with no evidence of basin closure.
Therefore, deposition of the Gunflint
Formation most probably occurred in a
shelf-slope setting with open connection
to the ocean, although some authorities
have suggested that it was a large lake.
The Gunflint is a classic example of a
Banded Ironstone Formation or 'BIF' - a
sedimentary deposit of iron oxides

Eosphaera
This is another very distinctive fossil,
consisting of a sphere within a sphere. On
the outer surface of the thick-walled inner
sphere are rugose spheroidal tubercles.
The radius of the inner sphere is from
10-12 microns ( 13 ).

Leptoteichos
This is a larger spherical microfossil (up to
31 microns diameter) usually occurring
singly, but sometimes in clumps of up
to 100 individuals. The most important
feature is that many specimens contain an
internal dark spot ( 14 ), which some
workers have been tempted to interpret as
a cell nucleus and hence to suggest that
this genus is a very early eukaryote.
However, much more evidence would be
required to confirm such a hypothesis; all

13

13 The double-sphered
bacteria EosphaeraPC.
Radius of the inner sphere
1012 micron.