Bob pointed out that the layers alternate sandy layers with clay layers, with a massive grey clay at the bottom of the pit, and a thin layer of soil forming the top layer of the sequence. In the photographs the clay layers are dark grey while the sandy layers are a buff to beige colour.
An interesting question is whether these sediments were deposited in the Champlain Sea or in Lake Iroquois. Lake Iroquois, a precursor of Lake Ontario, was a freshwater lake that formed adjacent to the retreating glacier, encompassed all of present day Lake Ontario and covered Prince Edward County, Kingston and what is now the town of Perth. In contrast, the Champlain Sea was a marine body of water that formed after the glacier had retreated far enough north for the ocean to flood the St. Lawrence River valley, the lower Ottawa River valley and much of Eastern Ontario. The maximum westward extent of the Champlain Sea is generally considered to fall just east of the town of Perth. The sediments deposited in both the Champlain Sea and Lake Iroquois can consist of stratified clay, silt and sand, with one of the differences between the deposits being that marine fossils are found in the Champlain Sea deposits while freshwater fossils are found in Lake Iroquois deposits. A further complication is that the western part of the Champlain Sea basin displays a “sequence of depositional environments from freshwater [glacial lake] to marine (Champlain Sea) to freshwater" (Rodriques, 1987). While the Leda clay deposits of the Champlain Sea are well exposed throughout Eastern Ontario, and have been extensively described in the literature (e.g., see Gadd, 1986), comparatively little has been written about the deposits of Lake Iroquois other than the deposits which are exposed in the Toronto-Hamilton region.
I included a map of the maximum extent of the Champlain Sea as part of my April 24, 2015 blog posting entitled ‘Hunting for Whales in Eastern Ontario.’ I included a map of Lake Iroquois as part of my September 17, 2014 blog posting entitled ‘Lake Iroquois and the Glaciofluvial Deltaic Deposit at Joes Lake, Lanark Highlands, Ontario.’ That map of Lake Iroquois was prepared in 1936 by A.P. Coleman of the Ontario Department of Mines. Since Coleman prepared his map, new investigations have found Lake Iroquois deposits further north. Below is a map that I adapted from a map that appeared in Anderson (1987), which is part of Fulton (1987), showing both (A) the boundaries of Lake Iroquois and other proglacial freshwater lakes (including Glacial Lake Vermont that formed in the Lake Champlain valley) and (B) the extent of the Champlain Sea.
I referenced I. M. Kettles’ map showing the Surficial Geology of the Perth Area with my April 18, 2013 blog posting entitled ‘Glacial Erratics and Eskers in the Township of Lanark Highlands, Lanark County, Ontario’ and included extracts from her map as part of that posting. Below is an additional extract from her map on which I have marked with a florescent pink square the location of St. Paul's United Church in Perth, Ontario .
Map units 5a and 5b, which are blue, represent Champlain Sea deposits. Map units 4a and 4b, which are purple, represent glacial lake deposits. Map unit 5a is just to the east of Perth and within about 300 meters of St. Paul's United Church. Map unit 4a can be found east, west, north and south of Perth.
On her map I. M. Kettles used the symbol of a lower case letter ‘f’ within a circle to identify a fossil locality for a freshwater species and an upper case letter ‘F’ in a circle to identify a fossil locality for a marine species. I do not see any such localities on the extract that I have provided.
Those wanting to look at the layered deposit in the basement of St. Paul's United Church should act promptly, as the construction of the elevator will destroy the view.
Christopher Brett
Perth and Ottawa
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Suggested Reading and References:
Anderson, T. W., 1987
Terrestrial Environments and age of the Champlain Sea based on Pollen Stratigraphy of the Ottawa Valley - Lake Ontario region, pages 31-42, in Fulton, R. J., editor, 1987, Quaternary Geology of the Ottawa Region, Ontario and Quebec. Geological Survey of Canada Paper 86-23, 47 pages https://doi.org/10.4095/122374
Barnett, P. J., 1992
Quaternary Geology of Ontario, Chapter 21 in Geology of Ontario, Special Volume 4, Part 2, Ontario Geological Survey, Special Publication, SV04-02
http://www.geologyontario.mndmf.gov.on.ca/mndmfiles/pub/data/imaging/SV04-02/SV04-02.pdf
Donnelly, Jeffrey P., Neal W. Driscoll, Elazar Uchupi, Lloyd D. Keigwin, William C. Schwab, E. Robert Thieler, Stephen A. Swift, 2005
Catastrophic meltwater discharge down the Hudson Valley: A potential trigger for the Intra-Allerød cold period. Geology (2005) 33 (2): 89-92.
https://doi.org/10.1130/G21043.1
Fulton, R. J., 1987
Quaternary Geology of the Ottawa Region, Ontario and Quebec. Geological Survey of Canada Paper 86-23, 47 pages https://doi.org/10.4095/122374
Gadd, N. R., 1986
Lithofacies of Leda Clay in the Ottawa Basin of the Champlain Sea. Geological Survey of Canada Paper 85-21, 44 pages https://doi.org/10.4095/120619
Karrow, P. F., 1989
Quaternary geology Great Lakes subregion; in Chapter 4 Quaternary Geology of Canada an Greenland, ed., R. J. Fulton, J. A. Heginbottom, and S. Funder; Geological Survey of Canada. Geology of Canada, No. 1., 1989 p. 326-350, 839 pages (5 sheets) https://doi.org/10.4095/131535
Karrow, P. F. , Clarke, A. H. and Herrington, H. B., 1972
Pleistocene Molluscs from Lake Iroquois Deposits in Ontario. Canadian Journal of Earth Sciences, 1972, 9(5): 589-595, https://doi.org/10.1139/e72-047
Kettles, I. M., 1992
Surficial Geology, Perth, Ontario. Geological Survey of Canada, "A" Series Map 1800A, 1992, 1 sheet,
https://doi.org/10.4095/183815
Kettles, I. M., 1992
Glacial geology and glacial sediment geochemistry in the Clyde Forks - Westport area of Ontario, Geological Survey of Canada, Paper no. 91-17, 39 pages,
https://doi.org/10.4095/133492
Kettles, I. M. And Rodrigues, C. G., 1993
Evaluation of glacial Lake Iroquois shoreline data from south-central and eastern Ontario; in, Current Research, Part E; Geological Survey of Canada; Paper no. 93-1E, 1993 p. 271-274, https://doi.org/10.4095/184120
Lewis, C. F. M.; Todd, B. J.; 1995
Sediments and Late Quaternary history of Lake Ontario, in, Regional geology and tectonic setting of Lake Ontario region; Sharpe, D R; Geological Survey of Canada, Open File 3114, 1995 p. 1-14, https://doi.org/10.4095/205054
Lougheed, Stephen C. and Morrill, Natalie
Quaternary History of Eastern Ontario: Impacts on Physical Landscape and Biota
http://opinicon.wordpress.com/physical-environment/quaternary/
Rodriquez, Cyril G., 1987
Late Pleistocene Invertebrate Macrofossils, Microfossils and Depositional Environments of the Western Basin of the Champlain Sea, pages 16-23, in Fulton, R. J., editor, 1987, Quaternary Geology of the Ottawa Region, Ontario and Quebec. Geological Survey of Canada Paper 86-23, 47 pages https://doi.org/10.4095/122374
