The Gunflint Chert - Fossil Ecosystems of North America: A Guide to the Sites and their Extraordinary Biotas - page 2

H ISTORY OF DISCOVERY OF THE
G UNFLINT C HERT
In 1953 Stanley Tyler, an economic
geologist from the University of Wisconsin,
was undertaking a major exploration of
the Precambrian iron deposits of
Minnesota and Ontario. He had traced
these rocks from the Biwabik Formation of
Minnesota, where the ironstone is mined
in enormous open pits in the Mesabi
Range, to the Gunflint Formation of
Ontario, which crosses the US-Canada
boundary at Gunflint Lake, extends to
Kakabeka Falls near Thunder Bay and,
finally, to isolated outcrops near Schreiber
on Lake Superior ( 1 ).
The Gunflint Formation comprises
alternating bands of ironstone (in the
form of hematite, an iron oxide) and
chert which may be red, yellow, or black.
The cherts themselves often include
layered stromatolites and the red variety,
jasper, is particularly characteristic of the
Gunflint ( 7 ). Stanley Tyler, however, was
more interested in the jet black variety and

similar to flint, which is made up of tiny
interlocking crystals of quartz (silica or
SiO 2 ). It is both resistant enough to
withstand deformation and impermeable
enough not to be corroded, and
sometimes contains within it exquisitely
preserved fossils of these early bacterial
microbes.
Both stromatolites and fossiliferous
cherts are scattered pretty thinly through
the Precambrian, and some doubt has
recently been cast on the affinities of
the 3,500 million-year-old examples (see
p. 23). It is, therefore, to the next oldest,
universally accepted candidate, the 2,000
million-year-old Gunflint Chert of
northwestern Ontario, that we turn for
a glimpse of these early microbial
ecosystems. It is a sobering thought,
however, as Andrew Knoll (2003) points
out in his thought-provoking topic, Life
on a Young Planet , that the Gunflint
Chert is almost as distant in time from
its Australian and South African
predecessors as we are from Gunflint.

1

Ontario

N

20 km

Schreiber

20 miles “Frustration Bay”

Black
Bay

Kakabeka Falls

Gunflint Lake

Thunder
Bay

Lake Superior

Minnesota

1 Locality map to show the extent of the outcrop of the Gunflint Chert after Barghoorn and
Tyler, 1965.