Questions that have puzzled me for the last few years include: Are the raised forms fossils? If the raised forms are fossils, are they body fossils or trace fossils? and If the raised forms aren’t fossils, how were they formed? I’ve not found a convincing answer to any of those questions. My initial impression was that the raised forms were dubious fossils (markings possibly not of biogenic origin), and that is still how I would classify them.
Interestingly, I’ve found some photographs of somewhat similar problematic forms in two papers authored or co-authored by the late Dr. Hans Hofmann in rocks reported to be of Ediacaran age. See:
Hofmann, H.J., 1988, Synopsis of Precambrian Fossil Occurrences in North America, Chapter 4 in Geology of the Precambrian Superior and Grenville Provinces and Precambrian Fossils in North America, (Co-ord.) S. B. Lucas and M. R. St-Onge, Geological Survey of Canada, Geology of Canada, No. 7, p. 271-376, Plate 2E at pages 302-303.
Hofmann, H.J., Mountjoy, E.W. and Teitz, M.W., 1991
Ediacaran fossils and dubiofossils, Miette Group of Mount Fitzwilliam area, British Columbia; Canadian Journal of Earth Sciences, v. 28(10), p. 1541-1552, Plates 8C, 8D, 8E, 8F, 8J.
www.nrcresearchpress.com/doi/abs/10.1139/e91-138
Below I’ve provided Plate 2E from Hofmann (1988) which was originally plate 8F in Hofmann, Mountjoy and Teitz (1991). The scale bar is 1 cm.
Below I’ve provided Plates 8C, 8D, 8E and 8J from Hofmann, Mountjoy and Teitz (1991).
Copyright in the photographs shown in the Plates belongs to National Research Council of Canada and Canadian Science Publishing. They are reproduced under license from NRC Research Press.
Hofmann, Mountjoy and Teitz (1991) found and reported on a number of disc and elliptical shaped fossils (including Charnodiscus and Nimbia) that are worth reading their article to look at (but don’t resemble anything that I found), a vermiform structure that they equated with Zolotytsia, and seven types of dubiofossils which they classified alphabetically under the headings from Dubiofossil A to Dubiofossil G.
Hofmann, Mountjoy and Teitz (1991) describe plate 8F as showing “Two partly overlapping vermiform markings.... The two specimens juxtaposed in such a way as to give the impression of being wound around each other ... or lying contiguous side-by-side for at least half their lengths.” They mention that “The markings appear to [be] those of some limp, soft-bodied cylindrical organism, or part of an organism, rather than a trace fossil. ... Structures of comparable physical consistency appear to be the much more regular spiraliform fossil Zolotytsia of Fedonkin (1985) and the Cylindrichnus of Glaessner (1969).
Plates 8C and 8D show two specimens which were discussed under the heading Dubiofossil C and were described as a tapering “rectilinear frond-like structure” with rounded end, which they noted “resemble an unnamed frond-like impression from the Ediacaran... [and] also are like the proximal portions of the stems of Charnodiscus oppositus ... and may represent the stalk of similar organisms.”
Plates 8E and 8J they assigned to Dubiofossil D and described as a “Cleavage reliefs of short, undulating furrow and corresponding ridges,... some portions having pinch-and-swell appearance. Cross sections indistinctly round.” They remarked that the specimens “may be burrows comparable to Phanolites or Torrowangea.”
I’m not prepared to speculate as to whether the raised markings on the slab that I photographed could be body fossils or trace fossils, and if they are such, what they resemble. All I can say is that the markings on the slab that I photographed are somewhat similar to and as problematic as the dubiofossils identified by Hofmann, Mountjoy and Teitz (1991).
Second Specimen
Below are photographs of a loose specimen of Potsdam sandstone that I collected over about two years ago in Burgess Ward of Tay Valley Township, Lanark County from a waste pile resulting from the digging of drainage ditch along Stanley Road. Both Nepean sandstone and Covey Hill sandstone of the Potsdam Group have been mapped in this area. I believe the specimen to be Nepean sandstone as numerous other specimens from the same drainage ditch display U-shaped burrows.
The circular, elliptical and spheroidal markings, which are composed of the same sandstone as the host, are problematic. Are they concretions? Trace fossils?
Christopher Brett
Perth, Ontario
Hello, Christopher--
ReplyDeleteI wouldn't venture to guess what your first specimen represents, but your second specimen could be a poorly preserved example of the trace fossil Bergaueria, which has been attributed to "nesting" burrows of coelenterate polyps/sea anemones. Good examples look as if someone dimpled the surface of the sediment with the end of a broom stick. They are locally abundant in Lower Cambrian sandstones in the Alberta Rockies, near Lake Louise. Here are a couple of references:
Arai, M.N. and McGugan, A. 1968. A problematical coelenterate(?) from the Lower Cambrian, near Moraine Lake, Banff area, Alberta. Journal of Paleontology, 42(1): 205-209.
Pemberton, S.G. and Magwood, J.P.A. 1990. A unique occurrence of Bergaueria in the Lower Cambrian Gog Group near Lake Louise, Alberta. Journal of Paleontology, 64(3): 436-440.
Cheers,
--Howard Allen, Calgary
Howard:
DeleteI had been considering the trace fossil Bergaueria, as it is one of the trace fossils that has been found in the Potsdam sandstone of Eastern Ontario. See: Rainer R. Wolf and Robert W. Dalrymple (1985), Grant 187 Sedimentology of the Cambro-Ordovician Sandstones of Eastern Ontario; Geoscience Research Grant Program Summary of Research 1984-1985, Ontario Geological Survey Miscellaneous Paper 127, pages 112 - 117 at page 116
Your description of the specimen that it looks “as if someone dimpled the surface of the sediment with the end of a broom stick” is apt, and a few of the photos is the Pemberton and Magwood paper look similar to my badly preserved specimen. However, I’m not sure, in part because I’ve not previously seen a specimen of the fossil.
Regards,
Chris Brett