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of the middle and upper Lorrain Fottuation were being laid down.
The clatic hematite beds in the Lorrain Formation, the hematite
ooliths in the Gordon Lake Formation and the hematite cement in the Bar
River orthoquartaites, together with the presence of suiphates in the
Gordon Lakc Formation, are indicative of an oxidising atmosphere in upper
Ruronian times. This conclusion is important in relation to uranium
exploration.
The chert, aniaydrite, gypsum, and hematite as well as demonstrating
conditions of chemical sedimentation provide nvre evidence for proposed
correlations of upper Ruronian rocks with those of the Animikie Series
Marquette Range Supergroup of Michigan. Postulation of a tropical climatic
regime during deposition of part of the upper Huronian sequence removes
one of the previous barriers to this correlation, for previously only
frigid climatic regimes have been documented in the Ruronian, while the
ferruginous sediments of Michigan were considered to have been deposited
pnder tropical or sub-tropical conditions (James et al.).
REFERENCES
Frarey, M. J. 1966. Discussion: Huronian stratigraphy of the McGregor
Bay area, Ontario: Relevance to the paleogeography of the Lake Superior
region, by Grant N. Young. Can. J. Earth Sci. 3, 997.
James, H. L., Clark, L. D., Lamey, C. A, and Pttijohn, F. J. 1961. Geology
of central Dickinson County,+Michigan, U.Sk Geol. Surv. profess. Papers,
310;