Geoscience Reference
In-Depth Information
Ministry of Northern Development and Mines. The farmer's disappoint-
ment was our good fortune, and after carefully sampling the core, we
returned to the lab for a suite of chemical analyses.
I won't dwell on the details of the analyses, but we subjected the sam-
ples to various chemical treatments.
13
Our analyses, in the end, told us
that the Fe
2+
-enriched ocean waters precipitating the Gunflint BIF gave
way to sulfidic waters from which the Rove Formation deposited. This
was very consistent with the Canfield Ocean model. Indeed, at about
the same time we presented this, Gail Arnold was working with Ariel
Anbar from Arizona State University and Tim Lyons from the Univer-
sity of California Riverside (and an old graduate student pal from Yale)
and presented further support for the Canfield Ocean model from the
isotopes of the molybdenum preserved in 1.6 billion year old black
shales. For an explanation as to how this isotope system works, follow
this endnote.
14
The story seemed to be taking shape, but one should never get too
comfortable with an idea. In a stroke of good luck, Phil Fralik identified
a series of cores that represented environments ranging from the shal-
low waters where the Gunlint-Rove Formations deposited, to far off-
shore, where the waters were well over 100 meters deep. There was a total
of over 100 kilometers between the cores. Through painstaking work,
Phil was able to draw time lines between all of these cores, and Simon
spent nearly a year working up all of the geochemical data, but it was
well worth the trouble. hat emerged was a spectacular, one of a kind
picture of ocean chemistry stretching from nearshore to well out to sea
(
ig. 9.4)
. As we saw before, the Gunflint Formation gave way to the
sulfidic Rove nearshore. Moving offshore, however, we saw that anoxia
persisted, but we also saw that the sulfidic waters disappeared. Indeed,
we saw that the sulfidic waters gave way to Fe
2+
-containing waters, some-
thing like (but not completely like, as explored below) the waters from
which the Gunflint BIF deposited. We call such Fe
2+
- enriched waters
“ferruginous.” This is an amazing two-dimensional look at ocean chem-
istry deep in time. Hats off to Simon and Phil!
Others have also contributed to this story including Andy Knoll's
group, Andrey Bekker and his colleagues, as well as Tim Lyons and his
group. Altogether, we can paint a picture of, yes, more widespread ma-
rine sulfidic conditions compared to time before the GOE, but with lots
