Unit Name: Shadow Lake Formation
Unit Type: Lithostratigraphic
Rank: Formation
Status: Formal
Usage: Currently in use
Age Interval: Blackriveran
Age Justification: Age from Thurston et al. (1992), page 927.
Province/Territory: Ontario
Originator: Okulitch, 1938
Lithology:
In central and southwestern Ontario the Shadow Lake Formation is comprised of interbedded red to green, silty, dolomitic or calcareous sandstone and terrigenous mudstone, locally with silty and sandy dolostone, whereas in eastern Ontario it is a silty to sandy, light grey to geen-grey, fine to microcrystalline dolostone, in places calcitic, with interbeds of fine-grained calcareous sandstone (Thurston et al., 1992).
Relationship:
The Shadow Lake Formation is the basal unit of the Black River Group in southwestern Ontario, the Basal group in south-central Ontario, and the Ottawa Group in Eastern Ontario. It is conformably overlain by the Gull River Formation, and overlies disconformably the Rockcliffe Formation in eastern Onatrio, and Cambrian and Precambrian rocks in central and southwestern Ontario (Thurston et al., 1992).
Remark:
includes "Glenwood shale" (Sanford, 1961).
References:
Okulitch, V.J., 1938. The Ordovician section at Coboconk, Ontario. Transactions of the Royal Canadian Institute, volume 22, part 2, pages 319-339.
Thurston, P.C., Williams, H.R., Sutcliffe, R.H. and Stott, G.M. 1992. Geology of Ontario; Ontario Ministry of Northern Development and Mines, Ontario Geological Survey Special Volume 4, 1525 p.
Source: GSC file of geological names; T.E. Bolton and J. Dougherty (compiler)
Entry Reviewed: No
Name Set: Lithostratigraphic Lexicon
LastChange: 09 Feb 2012