I expect that many people reading the title of this posting, if they have a working knowledge of the sedimentary rocks of Eastern Ontario, will read the title at least twice, and will ask themselves the following three questions:
- How can there be Paleozoic shale under the Potsdam given that the Potsdam Group is considered to be the oldest sedimentary series in Eastern Ontario?
- If Liberty reported shale under the Potsdam, why hasn’t anyone followed up on it?
- How does this shale formation tie in with Dalrymple, Narbonne and Smith’s 1985 paper “Eolian action and the distribution of Cambrian shales in North America” (Geology, 13, 607–610)?
I have to admit that I can’t presently answer those questions and may not have an answer until 2018. Below I’ve provided the source for the title, a summary of my investigations, what I hope to find, and why it will take to 2018.
The title to this posting is derived from statements in the following paper and in the legend to the following map.
Liberty, B. A, 1971.
Paleozoic geology of Wolfe Island, Bath, Sydenham and Gananoque map areas, Ontario. Geological Survey of Canada Paper 70-35, 1971, ; 12 pages (4 sheets), doi:10.4095/102360
Liberty, B. A, 1970 ,
Geology Sydenham Ontario, Map 17-1970, Geological Survey of Canada , Preliminary Series, to accompany Paper 70-35. Geology by B. A. Liberty, 1961, 1964, 1966
Liberty devotes the first paragraph at page 2 of his paper to the Potsdam Formation, and concludes with the following three sentences:
“At least 70 feet of the formation occur in outcrop in the area and a boring at Knowlton Lake indicates a total thickness there of 149 feet. An additional 81 feet of dark grey Paleozoic shale was logged, by the writer, at the base of the formation in the first Dominion Observatory boring
at Knowlton Lake. This unit is separated as a lower member at this one location only.”
I thought at first that Liberty’s reference to “81 feet of dark grey Paleozoic shale” at the base of the Potsdam must have been a mistake, but on his accompanying Map 17-1970 Liberty has the legend:
“2 POTSDAM SANDSTONE: red, white, grey and yellow, evenly textured, fine-grained sandstone, and siltstone: in Knowlton Lake area this formation includes
81 feet of underlying dark grey shale as lower member (not included above).” [my emphasis]
One of my initial thoughts was that someone else must have noted Liberty’s statements and commented on the underlying shale. While I found that a number of authors reference Liberty’s paper, I’ve been unable to find a reference to the shale. For example, when Carson (1981a, 1981b) re-mapped this area for the Ontario Geological Survey he referenced Liberty’s earlier work, but doesn’t mention the shale. Carson (1981a) mentions that “Geological mapping of the Kingston area involved the reexamination of three map-areas previously mapped by B.A. Liberty for the Geological Survey of Canada (Liberty1971)” and that “Although no fossils have been recovered from the Potsdam formation, it is considered to be of Cambrian age (Liberty 1971)” , but doesn’t mention the shale. Carson (1981b) mentions that “Liberty (1971) estimated a total thickness in excess of 21 m” for the Potsdam Formation, but doesn’t mention the shale.
Carson, D.M., 1981a:
No. S13 Paleozoic Geology of the Kingston Area, Southern Ontario; in Ontario Geological Survey Miscellaneous Paper 100, Summary of Field Work, 1981, pages 134-136
Carson, D.M., 1981b:
Paleozoic Geology of the Tichborne-Sydenham Area, Southern Ontario; Ontario Geological Survey Preliminary Map P. 2413, Geological Series. Scale 1:50000. Geology 1980.
Sanford and Arnott (2010, GSC Bulletin 597, page 14) mention that Liberty (1971) “established the presence of a large number of sandstone outliers, which were identified as a single unit, the Potsdam Formation” but again fail to mention Liberty’s description of the shale.
I knew from prior research that Liberty had been an authority on the Paleozoic rocks of Ontario. (Liberty authored or co-authored over fifty papers and maps for the Geological Survey of Canada on the Paleozoic sedimentary rocks of Ontario that were published over a period from about 1950 to 1973.) As he had a wealth of knowledge on the Paleozoic rocks of Ontario, I thought it unlikely that he could have mistaken, for example, Precambrian shale for Paleozoic shale. I could have looked briefly at the core and assumed black shale to be Paleozoic, but Liberty logged the core and made that decision. Accordingly, why did he think the shale was Paleozoic in age? The answer to that question has to be found in the core and in his notes from when he logged the core.
I expect everyone reading this posting is asking themselves the question “Where would one look for the core from the Dominion Observatory boring at Knowlton Lake and for Liberty’s notes when he logged the core?” I expect that there are many others like me who grew up in Ottawa knowing that the Dominion Observatory was on Carling Avenue in Ottawa, that geophysicists had been associated with the observatory, and that those geophyicists later worked for various sections of Energy Mines and Resources, now Natural Resources Canada, and worked with the geologists at the Geological Survey of Canada, also now Natural Resources Canada, and would check first with the Natural Resources Canada.
As a first stab at finding the core I looked on GEOSCAN, Natural Resources Canada’s online database of Geological Survey of Canada publications. I did locate "A user's guide to core-storage facilities in Canada ', Geological Survey of Canada Paper 84-23, 1985 doi:10.4095/120217 " but it wasn't much help, other than for telling me that the Ontario Geological Survey had core from Eastern Ontario stored at Tweed.
I then sent an email to a contact at the Geological Survey of Canada/Natural Resources Canada and was told that they didn’t have the core or Liberty’s notes.
Next I sent an email to the District Geologist at the Ontario Geological Survey in Tweed and was told they didn’t have the core.
Partly in desperation, I sent emails to two geologists (both retired, but still active) that I knew had worked for Energy Mines and Resources or the Geological Survey of Canada at the same time as Liberty. The first, a geophysicist, replied that he had no idea where the core would be, that after the GSC, Bruce Liberty was at Brock University and Guelph, that I might look there for his records, but that many records had been tossed out on various reorganizations. The second, a geologist, also had no knowledge of the core, but noted “Instead of older Paleozoic, perhaps it is an unrecognized unit of post-Grenville Proterozoic strata, or maybe a thick patch of regolith developed on Grenville? I've seen shale-like regolith of unknown thickness below Potsdam SS elsewhere.”
I also sent an email to Mark Badham, the curator of the Miller Museum at Queen's, asking if he had any knowledge of the core. He assumed that I was talking about three drill holes drilled by the Dominion Observatory at the Holleford Crater and sent me the following paper by Brian St. John.
Brian E. St. John, 1968
Paleolacustrine arenites in the Holleford meteorite Crater, Ontario. Canadian Journal of Earth Sciences, 5, 935-943 www.nrcresearchpress.com/doi/pdf/10.1139/e68-090
Mark also told me that Queen’s has select pieces of the core from the three drill holes, mostly from the sediment layers in the crater.
I'd forgotten how close the Holleford crater was to Knowlton Lake, but suspect that Brian St. John's work does not explain Liberty finding shale below the Potsdam. Brian St. John comments on three holes drilled within the boundary of the crater. None of these intersected Potsdam sandstone. The drill hole I'm looking for would be outside the crater, but only a half mile due south of Diamond Drill Hole 3 on Brian St. John's Figure 1, and on the southwest shore of Knowlton Lake.
Brian St. John reported that the Holleford Crater is filled by sedimentary rocks which he divided into seven lithic units. The top two units, his Units 6 and 7, he correlated with the Rideau formation and the Pamela formation that outcrop in Eastern Ontario. He included a basal “explosion breccia” which he designated unit 1, overlain by unit 2, a thin breccia layer, both related to the meteor impact. His units 3, 4 and 5 are:
Unit 3: calcareous shales and argillaceous limestones and sandstones, which contain a small quantity of carbonaceous matter, “which imparts a black colour to most of the unit”,
Unit 4: gray calcareous quartz arenite, and
Unit 5: white calcareous quartz arenite.
It is only St. John’s unit 3 that sounds remotely like Liberty’s “ 81 feet of dark grey Paleozoic shale.” While I suspect that St. John’s unit 3 is not Liberty’s shale, if Liberty’s shale is the same shale that St. John reported then it answers a question St. John posed in his paper as to whether the crater is pre-Potsdam or post-Potsdam.
I was subsequently contacted by my source at the GSC/NRC. She had done some more sleuthing and told me that “The core might be stored at our Tunney’s Pasture collections facility but I’m afraid that the collections are closed for the next many months as we are moving out of the building. If [another person at the GSC/NRC] is not able to help out with information, I’m afraid you will have to wait until the collection is reopened in 2018. There is no one from collections who can look this up at this time.” Accordingly, it appears that my search will be placed on hold until 2018.
In 2018 it will be interesting to see if the core stored at Tunney’s Pasture is the core from the three holes drilled within the Holleford Crater, or from the hole I’m looking for that was drilled at the edge of Knowlton Lake. If the core can be located, is Liberty’s “dark grey Paleozoic shale” actually Paleozoic shale, or is it Precambrian shale or Precambrian regolith? If it is shale, does it correlate with the shale within the Holleford Crater? If it is a new formation that is older than the Potsdam what secrets will it yield?
What is interesting about Liberty’s report from 1971 is how much has changed. In 1971 when Liberty logged 81 feet of dark grey Paleozoic shale he did so before geologists recognized the Ediacaran/Vendian period, before geologists were interested in Ediacaran/Vendian fossils, and before geologists were interested in small shelly fossils. What prompted Liberty to identify the core as being Paleozoic shale? Did he see find small shelled fossils?
The core in the possession of Queen’s, particularly the carbonaceous material, might also be worth a fresh look with modern techniques. In 1968 when Brian St. John looked at the sedimentary rocks in the Holleford crater he did so before the Queen’s Geology Department had a scanning electron microscope. I can remember using the electron microscope in the Geology Department at Queen’s. I had to modify the software every time I went on the machine, and then had to take my results over to campus mainframe computer to get the results of my analysis. Today when results are available instantaneously, it would be a shame not to re-analyze St. John’s core.
Christopher Brett
Perth, Ontario
Below is an extract from Liberty's map 17-1970. On the map I’ve used red squares to show the locations of the three Dominion Observatory drill holes within the Holleford meteorite crater that were described by Brian St. John. I’ve shown in acquamarine where Potsdam sandstone outcrops at the southwest corner of Knowlton Lake, and where I believe Dr. Bruce A. Liberty reported the Dominion Observatory drill hole where he logged “ 81 feet of dark grey Paleozoic shale” at the base of the Potsdam. Liberty's Unit 1 is Precambrian; Unit 2, Potsdam Formation; Unit 3, Shadow Lake Formation; Unit 4, Gull River Formation, Member A; Unit 5, Gull River Formation, Member B.
