Burrows or Not Burrows?

Adolf  Seilacher (1925 – 2014) was a German palaeontologist who made major contributions to the study of trace fossils.  He is credited with advancing the concept that trace fossil assemblages are far from random, that the range of associated trace fossils is constrained by the environment of the trace-making organisms, and that the sedimentary environment  at its time of deposition can be deduced by noting the fossils that are in association with one another.  He taught at both the University of Tübingen and Yale University, wrote numerous papers, and authored a text book entitled Trace Fossil Analysis that I find helpful.   While his text book is designed to be used as a course book in conjunction with real material (including representative specimens and plaster casts), the book is so informative and well written that one cannot help but learn something every time it is opened.  There is however one comment in the book with which I disagree, namely Professor Seilacher’s introductory sentence to Plate 58 dealing with Synsedimentary Structures.   He states:

“The repetitive patterns of ordinary depositional structures, such as ripple marks in sand and sun cracks in mud, are too familiar from modern environments to be mistaken for fossils in the fossil record.”   

(Adolf  Seilacher, 2007, Trace Fossil Analysis,  Springer;  226 pages at page 166)

That statement is just not true:  I have no problem making those mistakes.  While there are many specimens that are obvious ripple marks or obvious sun cracks (what others call mud cracks or desiccation cracks), there are specimens where it is not clear whether one is looking at a trace fossil.

Below I provide a few problematic examples from the Potsdam Group sandstones and March Formation sandstone.  I periodically look at outcrops of  Potsdam Group sandstone and March formation sandstone in Lanark County and south of Perth down towards Kingston.   The outcrops are composed of any or all of (oldest to youngest):

(A) pink to brick red to burnt umber to greyish purple to almost  black (mostly) aeolian and (minor) fluvial sandstones – the Hannawa Falls Member of the Covey Hill Formation of the Potsdam Group;
(B)  white to buff to grey-green  fluvial and alluvial sandstones  and conglomerate (with minor aeolian sandstone) – the Chippewa Bay member of the Covey Hill Formation of the Potsdam Group; 
(C)  white to buff  marginal and shallow marine sandstones – the Nepean Formation of the Potsdam Group;
(D) white to buff to grey to black to green to maroon sandstones and siltstones - the March Formation

Below are photographs of specimens of those rocks.

Specimen 1.   Greyish purple sandstone, definitely the Hannawa Falls Member of the Covey Hill Formation of the Potsdam Group

When I first looked at the sample I assumed that I was looking at desiccation cracks, because the linear features on the surface intersect at almost right angles.  However if you look closely you will see (a) that the linear features are tubes that cross over one another, and (b) that the tubes pinch and swell.  This suggests that the linear features are backfill burrows. 

While the sample appears to be light grey, the rock is actually a darker grey purple colour.  I took the photograph near noon on a bright sunny day, and the sunlight washed out the photograph.

Sanford and Arnott 2010 report that the Hannawa Falls Member is divisible into two units:
- a lower unit of probable fluvial origin that is composed of brick-red shale, pink to maroon sandstone and quartz pebble to cobble conglomerate
- a dominant upper unit of eolian origin composed of red to pink quartz arenite containing a basal quartz-cobble conglomerate
Both units outcrop at this location.   It is not clear whether Specimen 1 is a sample from the lower or upper unit.

Hagadorn,  Collette  and  Belt  2011 discuss the rock and trace fossils in the Hannawa Falls Member in upstate New York, reporting that they examined mainly eolian beds but also found a minor subaqueous facies which they interpret as flooding in coastal dunes.   I assume that they were looking at the upper unit of the Hannawa Falls Member.  Based on trilobites found in underlying and overlying formations, they assign deposition of the Hannawa Falls Member in upper New York State to from early to mid-middle Cambrian time, which I assume to be the age of comparable rocks in Ontario.  They found Arenicolites U-shaped burrows in the subaqueous facies and Protichnites trackways, Diplichnites trackways, and Diplopodichnus trackways in the eolian beds. 

Specimen  2.   Greyish purple sandstone,  the Hannawa Falls Member of the Covey Hill Formation of the Potsdam Group

This is a polygonal pattern.   Many polygonal patterns are sun cracks (desiccation cracks).   Some polygonal patterns are trace fossils.  This one looks more like burrowing than a desiccation pattern.

Specimen 3.    Loose specimen of sandstone at quarry, either  Chippewa Bay member or Nepean Formation

To me this looked like either really bad burrows or poor desiccation cracks.  I passed this photograph to a geologist who has worked on these rocks and his comment was that the specimen “might include some burrows but much of the surface is reminiscent of the blocky texture produced by microfaulting of a water-stabilized sand dune surface.”  Not something that I can identify.

Specimen 4  - March Formation sandstone

When I saw this specimen I thought ‘mud cracks’ – the term that I had been using since high school.  I showed the specimen to two geologists and they told me that it couldn’t be a mud cracks because sand doesn’t shrink that much and it must be a  microbial mat shrinkage feature.  I sent the photo to a geologist who has written extensively on microbial mats and he told unless I could find the top slab and underlying slab (in order to ensure that no mud was present) I couldn’t identify this as microbial mat shrinkage feature.

Specimen 5.   Same sandstone as produced the Protichnites trackways mentioned in my blog posting from July 9, 2013 - Likely the Nepean Formation of the Potsdam Group

I have been assuming that this photograph shows ripple marks.   However, there is a chance that it could be the burrowing trace fossil Climactichnites youngi as the bars in the photograph, particularly the J-hooks at the end of the bars, compare favourably with the bar bifurcations  in Figure 5.3 in Getty and Hagadorn, 2008, and with Figure 43 in Yochelson and Fedonkin, 1993,
My suggestion notwithstanding, the ripple marks in the Potsdam can be quite variable, and the photograph is more likely to record ripples than to be a trace fossil.       

Christopher Brett
Perth, Ontario           


References and Suggestions for Further Reading:

Bruce V. Sanford and Robert W.C. Arnott, 2010
Stratigraphic and structural framework of the Potsdam Group in eastern Ontario, western Quebec, and northern New York State.  Geological Survey of Canada, Bulletin 597, 85 pages
publications.gc.ca/collections/collection_2010/nrcan/M42-597-eng.pdf

David G. Lowe,  Robert W. C. Arnott, and Bruce V. Sanford, 2013, 
Before the Great North American Carbonate Bank: A Complex Cambrian-Lower Ordovician Transgressive History Recorded in Siliciclastic Strata of the Potsdam Group, Southeast Laurentia
 Adapted from extended abstract prepared in conjunction with oral presentation at AAPG Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19 -22, 2013
http://www.searchanddiscovery.com/pdfz/documents/2013/50859lowe/ndx_lowe.pdf.html   

Ellis L. Yochelson and Mikhail A. Fedonkin, 1993,    
Paleobiology of Climactichnites, an Enigmatic Late Cambrian Fossil
Smithsonian Contributions to Paleobiology • Number 74 
 Smithsonian Institution Press ,Washington, D.C. 1993
http://www.sil.si.edu/smithsoniancontributions/Paleobiology/pdf_lo/SCtP-0074.pdf

Patrick Ryan Getty  and J. Whitey Hagadorn, 2008,
Reinterpretation of Climactichnites Logan 1860 to Include Subsurface Burrows, and Erection of Musculopodus for Resting Traces of the Trailmaker
Journal of Paleontology 82(6):1161-1172. 
http://dx.doi.org/10.1666/08-004.1

J. Whitey Hagadorn, Joseph H. Collette  and Edward S. Belt,  2011,
Eolian-aquatic deposits and faunas of the middle Cambrian Potsdam Group: Palaios, v. 26, p. 314-334.       

Hunting for Whales in Eastern Ontario - Part 2

In my last posting I mentioned that Professor J. W. Dawson of McGill University had described the finding in 1882 of two vertebrae, a part of another, and a fragment of a rib of a Humpback whale in a ballast pit at Welshe's, on a line of the C. P. Railway, 3 miles north of Smith's Falls.  The bones were found in gravel at a depth of 30 feet and about 50 feet from the original face of the pit.

Last month I decided to visit the location.   I have to admit that I was not expecting much, based on my background research.   That is what I found: no historical plaque celebrating the finding of the Humpback whale, no train station, no train tracks, and little evidence that a gravel pit was close to the abandoned rail line.   I suspect that over time most of the gravel and sand was dug up and taken away.

I should note that Dawson misspelt the location: it is Welsh’s Station, rather than Welshe’s  (and certainly not Walsh Station as shown on the current official plan for Montague Township). 

Welsh’s Station is shown on the following extract that I’ve taken from a map of  Montague Township that appeared in the  Illustrated Atlas of Lanark County (maps from surveys under the direction of H.F. Walling,  Published by D. P. Putnam, Prescott, Canada West, 1868).

Illustrated Atlas of Lanark County, 1880; H. Belden & Co., Toronto.
http://digital.library.mcgill.ca/countyatlas/searchmapframes.php

Numogate, which appears on the map, still exists.  The road that runs from Smith’s Falls through Numogate is now Highway 15.  The road just south of Welsh’s Station, between Concession VII and Concession VIII is now called Ferguson Tetlock Road.    The railroad line identified on this extract as the Main Line of the Canada Central Railway, had become a line of C. P. Railway when Professor Dawson penned his article on the finding of the humpback whale.   Regrettably, the tracks have been torn up.   However, the track ballast identifies where the rail line used to run.  

The following is an extract from the map that is Schedule A to the Official Plan of the Township of Montague. 

This extract  provides the current names of the roads, shows the abandoned line of the Canadian Pacific Railway, misspells Welsh’s Station as Walsh Station, and shows a sand and gravel pit (marked with a “P”) off highway 15 just south of Numogate.  I visited that sand and gravel pit.  It appears to have been abandoned many years ago, and little if any sand or gravel is left to be taken from the pit.    Below is a photograph of the pit.

Dr.  A. P. Coleman  of the Ontario Bureau of Mines, and a professor of geology at the University of Toronto, visited the location in 1901.  He found more than I did.   Here is his description:

“The finding of bones of a whale near Smith's Falls in 1882 attracted much attention at the time. The bones, which were sent to Sir William Dawson and are now in the Peter Redpath museum at Montreal, consist of two vertebrae and a rib, the largest vertebra 11 inches in diameter and 7 inches in length ; the other 10 by 4.  It has been determined as Megaptera longimana, a species still common in the gulf of St. Lawrence and sometimes ranging some distance up the river. The bones are in good   preservation, but white and brittle from the loss of organic matter. Associated with them were shells of Macoma fragilis, a species common in the Saxicava sand. The find was made in a C. P. R. gravel pit at Welch's, three miles north of Smith's Falls, and, according to the railway levels, at a height of 440 feet above the sea. ...

    At present the gravel pit at Welch's shows a face of 52 feet consisting of coarse sand and gravel with many larger stones, the latter generally subangular or only partially rounded. Since the gravel pit has not been in use for some years the stratification is not well seen, sand having run down from above. No shells were found, but this was to be expected, since they tend to crumble when long exposed to the weather. The sand and gravel have not the look of the Saxicava sand near Ottawa, but are much coarser and less perfectly stratified; nor do they seem to have been formed on a beach. They run as a ridge having a general direction about 15 degrees east of north, not far from the same as the striae shown on well polished Potsdam sandstone a few hundred yards to the west, where 12 degrees east of north was observed. The gravel ridge has somewhat the look of a moraine and includes a shallow kettle hole with no outlet, just to the east of the highest part. The deposit seems to be a kame rather than a beach, the many large subangular boulders suggesting ice action. The ridge is not long enough or distinct enough to be an esker.

    The bones are said to have occurred 30 feet below the surface of the gravel, but apparently the carcass of the whale was enclosed in a beach deposit formed against the flank of the ridge in post-glacial times. As the level of the track at Welch's is 431 feet above sea, and the gravel rises at its highest part 52 feet higher as determined by hand levels the summit of the ridge is 483 feet above the sea. but the old beach probably 40 feet lower.”

A. P. Coleman, 1901, Sea Beaches of Eastern Ontario, Report of the Bureau of Mines, 1901, Province of Ontario, pages 215-227  at pages 216 and 2017.

The sand and gravel pit may  also have been described by A. Ledoux of the Ontario Bureau of Mines in 1918, as follows:

“There is some gravel near Smiths Falls which was extensively used by the railway companies as ballast....   The gravel pit owned by George Kerfoot, Smiths Falls, is in the township of Montague, lot 26, concession 8.  It is about 3.5 miles north of Smiths Falls, near the tracks of the Canadian Pacific railway.  The average dept of the pit is 10 feet, below which clay is found.  The material is about two parts of gravel to one of sand... There is an estimated reserve of three acres.”

A. Ledoux, 1918, Sand and Gravel in Ontario, Report of the Bureau of Mines, 1918, Province of Ontario, at page 61.

Two years ago Victoria Lee of the Ontario Geological Survey issued a report on the aggregate resources of Lanark County that included the gravel pits in the Township of Montague.  She discounts the Township of Montague as a significant source for sand and gravel, but does list eight licensed pits in the Township of Montague, including the pit south of Numogate, which is identified as pit 133 in her report and on her maps.   She describes the pit as covering 16.6 hectares, with a face height of 2-6 meters, with 20 -30 percent gravel and mentions that the “Pit has been developed in an ice-contact deposit.”    Below is part of her map showing the location of the licensed pit.  Interestingly, she shows two sand and gravel deposits close to what was Welsh’s Station: the first south of Numogate and the second northwest of Numogate.   

 (Victoria L. Lee,  2013, Aggregate resources inventory of the County of Lanark, southern Ontario: Ontario Geological Survey, Aggregate Resources Inventory Paper 189, 85 p.   
Her report can be downloaded from:
http://www.geologyontario.mndmf.gov.on.ca/mndmfiles/pub/data/imaging/ARIP189/ARIP189.pdf   )      
       
Map P2622 published three decades earlier by the Ontario Geological Survey shows four pits south of Numogate, including one to the north of Victoria Lee’s Licensed Pit 133 and just south of Ferguson Tetlock Road.  I did not find that pit.

G.A. Gorrell ;S. Margeson ;J. Lindablom ;R. Trotter, 1985,  Sand and gravel assessment, Lanark County, south half, Map P2622
URL: http://www.geologyontario.mndmf.gov.on.ca/mndmfiles/pub/data/imaging/P2622/P2622.pdf   

Christopher Brett
Perth, Ontario