In my March, 2019 blog postings I reported finding the concentric, circular, Ediacaran fossil Aspidella together with Ediacaran fronds and various microbial mat structures, in sedimentary rocks northeast of Perth, Ontario that I designated as the Drummond Sequence. The Drummond Sequence is found in Drummond/North Elmsley Township in Lanark County. The rocks at the top of the Drummond Sequence have been mapped as the Ordovician March Formation by the Ontario Geological Survey, but it is not clear that they belong to the March Formation.
In various blog postings dated from 2014 to 2016 I mentioned and included photographs of cylindrical dewatering structures in the Cambrian Potsdam sandstone of Eastern Ontario.
Below are photographs of a circular structure observed in a slab of rock at a quarry in the United County of Leeds and Grenville, Ontario that has been mapped as the Ordovician Gull River Formation by the Ontario Geological Survey.
The outermost of the light coloured inner concentric rings is about five inches in diameter. The darker spiral ring is about a foot in diameter.
My initial guess for this structure was that it is more likely to be a cross-section of a dewatering structure or a cross-section of a concretion, than an Ordovician fossil. However, the specimen bears more that a passing similarity to some photographs of Eldonids including Eldonia ludwigi from the Cambrian Burgess Shale (Walcott, 1914, Figure 5 at page 47, and Plates 9-12; Caron et al., 2010, Figure 1; MacGabhann, 2012, volume 2, Figure 4.02 - 4.18), Eldonia berbera (Alessandrello and Bracchi, 2003) and Eldonia eumorpha (Chen et al., 1995; Anonymous, 20??), all Cambrian or Ordovician in age . If it is a fossil Eldonid then the dark gray spiral structure is probably a digestive organ, while the light patches and light grey ribbons outside of the dark spiral are part of the outer ring.
An alternate interpretation is that this represents a concentric microbial discoid structure similar to microbial-related biogenic structures from the Middle Ordovician slates of northern Portugal reported by Neto de Carvalho, Couto, Figueiredo and Baucon (2016)
The part and counterpart of the slab were available for collecting, but both were too heavy for me to lift. The slabs are at the edge of a blast pile at the quarry. I did not ask when the pile is slated to be crushed, but it will likely be before next spring.
Despite an hour searching, no other fossils were found in these beds.
These rocks have been mapped as the Gull River Formation by the Ontario Geological Survey. Williams (1991) notes that “Brachiopods, bryozoa, corals, crinoids, ostracods, gastropods, pelecypods, cephalopods, trilobites, and stromatolites are abundant” in the Gull River formation. I
found no indication of any of those fossils at this location. An individual who has looked at these beds told me prior to my search that there are no fossils at this location. However, the OGS reports an ostracod in shale from this location that had earlier been reported from this formation in Aylmer, Quebec (just across the river from Ottawa) by Raymond (1911, p.190) and described and figured by Jones (1891, page 65, plate 11, figures 7 and 8). One figured specimen from Aylmer is 4.1 mm in length with a height of 2.5 mm. It could easily have been overlooked by me.
I did find a small trace fossil in an outcrop of an overlying chalky bed that may or may not to be part of the sequence mapped by the Ontario Geological Survey as the Gull River Formation. Below is a photograph of this trace fossil. The numbers on the ruler record centimeters.
This specimen was found in a bed on an upper bench at the quarry that is scheduled for blasting next spring.
Christopher Brett
Ottawa
Addendum, July 14, 2022: My interpretation of the photographs of this circular structure has been bothering me since my initial posting. Accordingly, I've changed the emphasis of the paragraph under the first three photographs. I have not been back to the quarry to look for the specimens.
Referenced, And Suggested Reading
Alessandrello, Anna and Bracchi, Giacomo , 2003
Eldonia berbera n. sp., a new species of the enigmatic genus Eldonia Walcott, 1911 from the Rawtheyan (Upper Ordovician) of Anti-Atlas (Erfoud, Tafilalt, Morocco). Atti della Società Italiana di Scienze Naturali e del Museo Civico di Storia Naturale in Milano, Vol. 144, pages 337-358
https://www.biodiversitylibrary.org/part/324891
https://www.biodiversitylibrary.org/page/58420660#page/341/mode/1up
Anonymous, 20??
Eldonia eumorpha Enigmatic Taxon from Chengjiang.
http://www.fossilmuseum.net/Fossil_Sites/Chengjiang/Eldonia-eumorpha/Eldonia.htm
Brett, Christopher, 2014-2016
January 29, 2014 - Cylindrical Structures in Potsdam Group Sandstone in Eastern Ontario
August 27, 2015 - Cylindrical Structures in Potsdam Group Sandstone in Eastern Ontario - Part 2
September 28, 2015 - A Map Showing the Location of Cylindrical and Conical Structures in Potsdam (Group) Sandstone of Ontario and New York
October 22, 2015 - Cylindrical structures in Sandstone: A Type of Soft-Sediment Deformation Sometimes Linked to Seismic Activity
December 23, 2015 - Dewatering Structures, Biofilm Structures, Glacial Striae and Chatter Marks in Potsdam Sandstone near Newboro, Eastern Ontario
September 22, 2016 - Frothed Sandstone and Cylindrical Structures Found in Potsdam Sandstone
Fossilslanark.blogspot.ca
Brett, Christopher, 2019a
Concentric Structures in the Sedimentary Rocks of Lanark County, Ontario that are identical to the Ediacaran Holdfast Aspidella. http://fossilslanark.blogspot.com/2019/03/holdfasts-in-lower-ordovician-march.html
Brett, Christopher, 2019b
If the Ediacaran discoid holdfast Aspidella, why not Ediacaran Stalks, Spindles and Fronds in Lanark County?
http://fossilslanark.blogspot.com/2019/03/if-ediacaran-discoid-holdfast-aspidella.html
Chen Jun-yuan, Zhu Mao-yan, & Zhou Gui-qing. 1995.
The Early Cambrian medusiform metazoan Eldonia from the Chengjiang Lagerstatte. Acta Paleontologica Polonica 40, 3, 213-244.
https://www.app.pan.pl/archive/published/app40/app40-213.pdf
Caron, J.; Conway Morris, S.; Shu, D.; Soares, D., 2010.
In Soares, Daphne (ed.). "Tentaculate fossils from the Cambrian of Canada (British Columbia) and China (Yunnan) interpreted as primitive deuterostomes". PLOS ONE. 5 (3): e9586. Bibcode:2010PLoSO...5.9586C. doi:10.1371/journal.pone.0009586. PMC 2833208. PMID 20221405.
Jones, T. Rupert, 1891
6. BEYRICHIA CLAVIGERA (sp. nov.), 7. BEYRICHIA CLAVIGERA (sp. nov.) Var. CLAVIFRACTA (nov.)., in Contributions to Canadian Micro-Palaeontology. Part III. Geological Survey of Canada, (pages numbered 59-99 ; plus plates), at page 65, and plate 11, figures 7 and 8
https://doi.org/10.4095/106564
MacGabhann, Breandán Anraoi, 2012
A Solution to Darwin's Dilemma: Differential Taphonomy of Ediacaran and Palaeozoic Non-Mineralised Discoidal Fossils. Ph.D. Thesis. National University of Ireland, Galway . Volume 1 - Text and References (1.104Mb) Volume 2 - Figures and Tables (27.43Mb). http://hdl.handle.net/10379/3406 Collections: NUI Galway Theses (PhD Theses)
Neto de Carvalho, C. , Couto, H., Figueiredo, M. V., and A. Baucon, 2016
Microbial-related biogenic structures from the Middle Ordovician slates of Canelas (northern Portugal). Comunicações Geológicas (2016) 103, Especial I, 23-38
https://www.academia.edu/30274936/Microbial-related_biogenic_structures_from_the_Middle_Ordovician_slates_of_Canelas_northern_Portugal_?auto=download
Raymond, P. E, 1911
Preliminary Notes on the "Chazy" Formation in the Vicinity of Ottawa. The Ottawa Naturalist, Volume 24, Number 11, p.189-197,
https://www.biodiversitylibrary.org/item/94742#page/201/mode/1up
Williams, D.A., 1991.
Paleozoic Geology of the Ottawa-St. Lawrence Lowland, Southern Ontario; Ontario Geological Survey, Open File Report 5770, 292p.
Walcott, Charles D., 1914.
No. 3 Middle Cambrian Holothurians and Medusae, pp. 41 -68, pls 8-13, in Cambrian geology and paleontology, II. Smithsonian Miscellaneous Collections, Volume 57
https://archive.org/details/smithsonianmisce571914smit/page/n166/mode/1up?view=theater
