Friday, 13 September 2013

A Selection of Fossils from the March Formation in Lanark County, Ontario

A year ago I collected a number of specimens of fossils, and photographs of fossils, from a quarry in Lanark County about a five minute drive north of Perth.  The quarry is in lot 10, concession  IV of Drummond Township.  The quarry falls in an area that has been mapped as the March Formation.   It is a section of flat lying beds of sedimentary rock (primarily sandstone)  that in an earlier posting I described as the Drummond Sequence as it falls in an area that was surveyed as Drummond Township.   The Drummond Sequence is bounded by faults that separate it on the west from Nepean Formation (Potsdam Group) sandstones, on the southeast from March Formation, on the northeast from Nepean Formation sandstones, on the north from Precambrian Shield and on the northwest from Precambrian Shield.  It has an irregular shape and covers over 100 square kilometers.  It can be viewed on Ontario Geological Survey Maps P2724 and P 2725 that can be downloaded from:

P2724 - Paleozoic geology, Perth area, southern Ontario
http://www.geologyontario.mndmf.gov.on.ca/mndmfiles/pub/data/imaging/P2724/P2724.pdf

P2725 - Paleozoic geology, Carleton Place area, southern Ontario
http://www.geologyontario.mndmf.gov.on.ca/mndmfiles/pub/data/imaging/P2725/P2725.pdf

 (The March Formation is unit “3" on the maps, while the Nepean Formation is unit  “2".)

The March Formation is generally considered to be Lower Ordovician in age and is equivalent to the Theresa Formation in Quebec and New York State.  As originally envisaged by Sir William Logan of the Geological Survey of Canada it was the passage or transition beds between the underlying Potsdam Sandstone and the overlying Calciferous formation.   In 1937, 1938 & 1946  Alice E. Wilson of the Geological Survey of Canada renamed the Potsdam Sandstone as the Nepean Sandstone (overlooking the older portions of the Potsdam), renamed Logan’s passage beds as the March Formation, and renamed the Calciferous as the Oxford Formation.

Wilson (1937 & 1938),  described the March Formation unit as being composed of "thick beds of interstratified grey sandstones with a calcareous cement and sandy blue-grey dolomites, both weathering a rusty brown".   Her 1946 description was “The March formation consists of alternating grey sandstone and sandy dolomite or blue-grey dolomite, all weathering dark rusty brown. ... The formation represents a transition from the Nepean sandstone to the Oxford Dolomite, the sand content being most evident at the base..”  She stated that “The lower contact [with the Nepean sandstone] is placed arbitrarily at the lowest dolomitic layer.”



In the quarry where I was collecting things are more complicated.  Anything goes.   While the predominant rock is sandstone, I’ve found dolostone, mudstone, siltstone, minor shale, and a bit of limestone.  The sandstones, mudstones and siltstones can be just about any colour (reddish, brown, ochre, black, grey, tan, etc.).   There are many examples of mud cracks and ripple marks, and possible microbial mat structures.   

[2019:  I have retracted a number of paragraphs from the original post.  I did this because I failed to recognize that I had found Ediacaran fossils.    The discs shown under number 7 below are Aspidella.  Under number 4, the sixth and seventh photos show Ediacaran fronds.   Most of the photos show  Ediacaran fossils or microbial mat textures.  See my March, 2019 postings for a better explanation.
At most only the top layers of the quarry are March Formation.  ]

The Fossils

Below I’ve provided the photographs.  I had hoped to go through and look up the scientific names for the fossils.  As that hasn’t happened over the past year,  I’ve decided to put a selection of photographs on my blog to stimulate interest in the Drummond Sequence..   I’ve grouped the fossils in a way that makes sense to me.

1.  Bedding Parallel Burrows in a bed close to the top of this section of the quarry.
Sam_0180 and 182
 





2.  Simple cylindrical, curving burrows roughly parallel to bedding plane
Sam_0037




3.  Larger, rougher, cylindrical, curving burrows  roughly parallel to bedding plane
Sam_0525


4   Branching, overlapping, possibly interpenetrating, roughly parallel to bedding plane
P820760, Sam_0016,  Sam_0023,  Sam_00 31, Sam_00 34, Sam_0102, Sam_0140






5    Faint Circles: Medusae or discoid holdfast?
P820758






6   Discs and concentric cylindrical features parallel to bedding plane: discoid holdfasts.
Sam_00 40,    Sam_0138, Sam_0149














7   A Congestion/Colony of Multiple discoid holdfasts
Sam_0121 & 123 - same slab


 8    Lindt Truffles (circular, about the size of the candy, with a thin 2-4 mm rim and a different coloured centre)  - 
Sam_0046 & 47    




9    Thin Film, barely there
Sam_0053



10   Sam_0070, 71, 73, 75




11   Stromatolite  (Dr. Al Donaldson's identification)
Sam_0129





I hope these photographs stimulate interest in these rocks.

Christopher Brett
Perth, Ontario

Thursday, 29 August 2013

Abraham, Logan and Owen: The Discovery of the First Protichnites trackways – Part 1


“Protichnites is from the Greek Protos, the first, – Ichnos, foot-print, or track, – and Lithos, stone; literally – The first stone foot-prints.”  (Elkanah Billings, 1857) 

“PROTICHNITES (Gr. protos, first; ichnos, footprint)” (H. Alleyne Nicholson, 1876)

I suspect that everyone who has looked at the trackway that is the trace fossil Protichnites is aware that the first specimens were found in a quarry on the west side of the St. Louis River at Beauharnois, Quebec, that the first reports in the scientific papers were papers read before the Geological Society of London on April 30, 1851 by W. E. Logan and Professor Owen, that in the field season of 1851 W. E. Logan returned to Canada and with the aid of Mr. Richardson found numerous examples of similar trackways, principally at Henault’s field (a half mile west of the quarry on the River St. Louis),  that in 1852 W. E. Logan and Professor Owen again presented papers before the Geological Society of London, that numerous drawings of the trackways accompanied the two papers,  and that in Professor Owen’s paper the trackways were given the name Protichnites.  

In his papers and reports Logan named the others besides himself  who deserved credit for finding the initial trackways, and while Logan named the most significant contributors, their contributions are often overlooked.  These named individuals are:

 - Mr. Abraham, Editor of the Montreal Gazette,
 - Mr. James Richardson, an employee of the Geological Survey of Canada, and
 - Mr. Alexander Murray, Assistant Provincial Geologist at the Geological Survey of Canada.

Various unnamed quarrymen were also singled out by Logan.

Below I’ve also mentioned two other individuals:  Sir Charles Lyell (a British lawyer and the foremost geologist of his day, who in his era  published the most widely read books on geology) and Sir Roderick Impey Murchison (the author of comprehensive work on the Silurian System in Great Britain and elsewhere).   Lyell promoted Logan’s discovery  while Murchison initially questioned its importance.  In part this is because Logan’s discovery called into question part of the latter’s book, Siluria, which described the geology and fossil content of much of the  Paleozoic.

Today we accept that the trackmakers that left the Protichnites  trackways were likely the first creatures to leave the oceans and walk on land.   It is interesting to step back in time and take a brief look at the disbelief, the furor and amazement that the discovery of Protichnites trackways created, and at the speed with which the discovery circulated among geologists in England, Canada and the United States.

Below I’ve provided the important dates.  When looking at the dates it is important to keep in mind that before Logan and Owen presented their papers in 1851 and 1852  the accepted belief was that before the Devonian  no creature walked on land.   It is also worth noting that what we now call the Cambrian and Ordovician were encompassed at that time within the Lower Silurian.  It was an important time in the development of geology, and ideas were changing rapidly.   In 1852  Lyell and Dawson made the celebrated discovery of tetrapod fossils entombed within an upright fossil tree at Joggins, Nova Scotia.     It was not until 1859 that Darwin published On the Origin of Species and it was not until 1879 that the Ordovician was defined.   It had not  been two decades since Charles Lyell's multi-volume Principles of Geology was published from 1830 to 1833 .   Wikipedia comments that Lyell “developed Hutton's idea that the earth was shaped entirely by slow-moving forces still in operation today, acting over a very long period of time. The terms uniformitarianism for this idea, and catastrophism for the opposing viewpoint, were coined by William Whewell in a review of Lyell's book.  Principles of Geology was the most influential geological work in the middle of the 19th century.”

To understand what is written below one also  has to have at least  a passing understanding of the references to the “Old red sandstone.”   This is a  British a sequence of rock strata  which is of considerable importance to early paleontology.  In Logan’s time they were known as a sequence of Devonian rocks  that are continental rather than marine in origin.  The fossil fauna is characterized by primitive fishes.  Near the top of the  succession were found the first terrestrial tetrapod vertebrates.  Today these rocks are mapped as extending from the late Silurian into the Devonian and on into the earliest part of the Carboniferous.  Many early papers reference the Old Red Sandstone.

The Important Dates Concerning  the Discovery of Protichnites

These are the important dates:

1847 - Mr.  Robert Abraham, Editor of the Montreal Gazette, reports in his newspaper the discovery of the track in a sandstone quarry at Beauharnois, Quebec

1847 - Mr. Abraham brings the  tracks  to the attention of W. E. Logan.  They are delayed by circumstances one year, and a premature and early snow the next, from visiting the occurrence.

1849 or 50 - W. E. Logan and Robert Abraham visit the site .  (Later Mr. Sterry Hunt, Chemist to the Geological Survey of Canada, visits the site and finds many more tracks.)

December, 1850 - W. E. Logan has two specimens quarried from the quarry on the west side of the St. Louis River at Beauharnois, Quebec and has casts made of the larger specimen

Winter of 1851 – After the boats have left the St. Lawrence, Logan sails for London from Boston, taking with him a small slab bearing the trackway and six plaster casts of the large specimen, which weighs over a ton and is 12 and half feet in length. The original slab, because of its size, is left  in the museum at Montreal connected with the Geological Survey of Canada.

March 18, 1851- Professor Owen sends a letter to Sir Charles Lyell, President to the Geological Society of London, commenting on the tracks (which is published as an addendum to Lyell’s February 18th Anniversary Address of the President to the Geological Society of London).  The letter is a condensed version of the paper he presents in April.

April 30, 1851 -  W. E. Logan and Professor Owen read papers before the Geological Society of London, exhibiting the small specimen and the casts.    Important geologists, including Sir Roderick I. Murchison, contest the conclusions in the paper, doubting that the rock is as old as proposed by Logan.

July, 1851 - W. E. Logan exhibits the small specimen and the casts at a Meeting of the British Association for the Advancement of Science held at Ipswich, England.  Logan’s talk is well received.

July, 1851 - The addendum to Lyell’s February 18th Anniversary Address of the President, including  Professor Owen’s letter to Sir Charles Lyell, is published in The American Journal of Science and Arts

Field Season 1851 - Forty-three  trackways are found in four areas in  Henault’s field (a half mile west of the quarry on the River St. Louis).  Additional  trackways are found two and a half miles further westward close to the mouth of the Beauharnois Canal, on one of the Islands of St. Géneviève, in the vicinity of Point Cavagnol (on the south side of Lake of Two Mountains in Vaudreuil), in the vicinity of Pointe du Grand Détroit in Vaudreuil, at the summit of the escarpment along the Rivière du Nord at Lachute,  and in Lansdowne and Bastard counties in Ontario.

September, 1851 - Robert Abraham publishes an article describing finding the occurrence, bringing it to Mr. Logan’s attention, his visit to the site with Logan

January 6, 1852 -  Logan again sails for London, taking with him the original 12 ½ foot slab, a second slab from Henault’s field measuring 8 feet,  a third slab with two tracks and ripple marks upon it from one of the Islands of St. Géneviève, and one hundred casts of trackways  from Henault’s field.

February 21, 1852 - Logan writes to his brother James that “I am engaged night after night with Owen in the examination of the tracks, which make a wonderful display on the floor of the Geological Society. They cover the whole centre of the room. .. The anniversary of the Society took place yesterday, and the tracks excited great interest.”

After February 20, 1852- Owen sends a communication  to William Hopkins, the new President of the Geological Society of London, advising that the tracks belong to Crustaceans.  This is published as an addendum to the Anniversary Address of the President that was delivered on February 20th

1852 - Before March 24 - The fourth edition of Sir Charles Lyell’s  text A Manual of Elementary Geology is published.  Lyell devotes over two pages to the tracks, noting that “numerous other trails have since been observed ...and Mr. Logan, who has visited those places, will shortly publish a description of the phenomena.”

March 24, 1852 - W. E. Logan and Professor Owen read papers before the Geological Society of London.  Following the papers, Logan reports “there was a glorious discussion.”  Logan temporarily deposits the 8 foot slab from Henault’s field (bearing Protichnites latus) with the Society’s Museum, and deposits casts from Henault’s field (including the tracks Protichnites 7-notatus, Protichnites lineatus and Protichnites alternans) in the British Museum

Robert Abraham’s Discovery

The discovery of the first trackway that was later identified as Protichnites is reported concisely in a paper by Elkanah Billings published in 1857, who mentions:

    “In 1847, the late Mr. Abraham, then Editor of the Montreal Gazette, announced in his paper that the tracks of a tortoise had been discovered in the sandstone of Beauharnois.  He supposed this rock to be the equivalent of the old red sandstone, and, as previous to the publication of his notice no remains of reptiles had been found in formations of so ancient a date, these were regarded by him as particularly interesting.  Mr. Logan’s attention was afterwards drawn to the discovery...”

Logan acknowledged Mr. Abraham’s contribution stating  (a) in his 1851 paper that “My attention was first drawn to the track by Mr. Abraham, then editor of the Montreal Gazette, who duly appreciated its possible geological importance, and inserted a notice of it in his daily journal.”, (b) in the Report of Progress for the Year 1851-52 “The occurrence of the track near the mill by the St. Louis River at Beauharnois, had been pointed out to me by Mr. Arbraham, then editor of the Montreal Gazette, who had introduced a notice of it in his Journal, in which he compared it to the track of a tortoise.” and (c) in his 1863 book the Geology of Canada “The first track discovered was met with near the mill on the St. Louis River at Beauharnois; and the late Mr. Abraham, editor of the Montreal Gazette, was the first to draw attention to it, by notice in his journal, in which he compared it to a tortoise.”

Mr. Abraham’s contribution was acknowledged by Sir Charles Lyell, who commented in the addendum to his Anniversary Address  mentioned above, that  “The markings were first pointed out to Mr. Logan by Mr. Abraham, editor of the Montreal Gazette, who appreciated their geological significance.”

Sir Charles Lyell gave Robert Abraham even more credit in 1852 when he published the fourth edition of  his text A Manual of Elementary Geology, where  two full pages,  and a part of a third,  are devoted to the tracks.  Lyell starts off his report with the sentences “In the year 1847, Mr. Robert Abraham announced in the Montreal Gazette, of which he was the editor, that the track of a freshwater tortoise had been observed on the surface of stratum of sandstone in a quarry opened on the banks of the St. Lawrence at Beauharnois in Upper Canada.... Imagining the rock to be the lowest member of the old red sandstone, he was aware that no traces had as yet been found of a reptile in strata of such antiquity.   He was soon informed by Mr. Logan ... that the white sandstone above Montreal was really much older than the “Old Red, ” or Devonian.  It had in fact been ascertained ... to lie at the base of the whole Silurian series.”   Later  Lyell  notes that Mr. Abraham “was aware that no traces had as yet been found of a reptile in strata of such high antiquity” and that “Mr. Abraham has inferred that breadth of the quadruped was from five to seven inches.”

I have not been able to find the original article from the 1847 Montreal Gazette.  I did find an article by Robert  Abraham that was submitted on August 25, 1851 and published in September, 1851  where he describes finding the track, publishing his announcement in the Montreal Gazette, bringing it to the attention of W.E. Logan, and visiting the site with Logan.   Here is a condensed  version, in Robert  Abraham's own words:

    “About four years ago, when on the road to Beauharnois, I met Mr. Macmaster, of the Seigniory Mill of that village, who... told me that in the quarries above him, there were the tracks visible of a common mud-turtle or terrapin...  I told him it was impossible, that no animal existed or could exist, at the time those rocks were deposited.    He persisted... We accordingly went up to the quarry, when I wondered,  and was convinced.   Doubt there could be none that this was the path of a quadruped of some sort or other...

    Mr. Logan was at that time from home, I think surveying the basins on the New Brunswick frontier.  I published an account of the discovery in the Montreal Gazette... At that time I as under the impression ... that the rock was the oldest member of the old red sandstone series... Bold and brash that I was, I did not hesitate to express my opinion that the track really was that of a tortoise.

    When Mr. Logan returned, towards the close of the autumn, he saw my paper, and though he had no doubt that the traces were those of an undescribed animal, he could not believe that they were those of a Chelonian reptile...  And, moreover, he told me that the rock was even older than I had supposed;... belonging...to the lower Silurian series.   The track might, he thought, be a of a gigantic centipede or millipede... I made a rude drawing... To this he objected, that an idle boy might have made a series of marks with a pickaxe, to produce the effect delineated.    I answered ... that no human skill could produce the median trail with raised edges, whether due to a tail or to the convexity of a breastplate dragging through mud; that there were twelve or fifteen feet of a stratum of rock, about fifteen inches thick, under which the trail entered, and the other came out...

    [Mr. Logan] arranged with me to go and look at the rock.  Circumstances prevented him from doing so that year.  The next year we were interrupted by a premature and heavy snow.  On the third year he went with me, and wondered, as I had wondered before.  The portions exposed had suffered from much from the action of frost and sun, but there was quite enough unexposed, to be quarried out, fresh and perfect.  Mr. Logan took the opportunity of the great Exhibition, to lay casts and specimens before the Geological Society of London.    ... [He] placed my original article in the hands of the Society, and Sir Charles Lyell has distinctly stated the material point, that I was aware of the importance of the discovery.

    ...  I saw three impressions, including the one preserved;  but Mr. Hunt, Chemist to the Geological establishment, has since been to the spot, and has found many more, including one striking phenomenon,  where the foot of the creature has struck against a wave-marked ripple on what was then the sand.  Mr. Logan has just informed me that many more have been detected.”

An interesting description by a person that Logan and others describe merely as the editor of the Montreal Gazette.   It begs the question:  Who was Robert Abraham?  Various sources provide the answer:  he was a man for all seasons.  He was an Englishman from Cumberland.    He trained as a medical doctor, graduating from the University of Edinburgh, but soon was drawn  to journalism.   He was medical editor of the Liverpool Journal before he emigrated to Canada and bought the Montreal Gazette in 1843 or 1844.  He was the editor of the Gazette until 1848, and is supposed to have been an able writer but a militant journalist.  After he sold the Montreal Gazette he became a lawyer, and was admitted to practice as an advocate in Lower Canada.  He then returned as an editor of a newspaper and of an agricultural journal.   He died at Montreal on November 10,  1854.

Above all, Robert Abraham was a writer.   An example of his legal writing is the booklet published in 1849 entitled Some remarks upon the French tenure of "franc aleu roturier", and on its relation to the feudal and other tenures (that is available from archive.org).   An example of Robert Abraham's writing on natural history is his 1851 article entitled Tracks of a Chelonian Reptile in the Lower Silurian formation, at Beauharnois , The British American Medical & Physical Journal, Volume 7, pages 195-200 (an article that I suspect had probably not seen the light of day for well over a century until I happened upon it).  An example of his medical writing is Case of Sanguineous Apolexy, 1825, The Edinburgh Medical and Surgical Journal, volume 24, pages 301-304

Medical doctor, editor, militant journalist, lawyer,  writer and the first to realize the significance of the tracks at Beauharnois.  Quite a career.

A few additional details of his life can be found in a paper presented in 1869 by Sir Robert Gibb entitled Discoveries in Science by the Medical Philosopher, An Oration delivered to the Medical Society of London, which discusses the contributions of numerous medical doctors.   Sir Robert Gibb mentions that Robert Abraham, an Englishman,  “whom I had the pleasure of knowing well”, “was a surgeon, a Member of the London College, who at one time was in practice in Carlisle, and emigrated to Canada, where he became the Editor of the Montreal Gazette, a daily newspaper.”  Those are the only facts about Mr. Abraham that Gibb can provide, though he speculates  “Although we have no information concerning the student life of and early history of Robert Abraham, ... it is but fair to infer that the study of the animal world was not neglected by him before he became a member of the profession of which we all feel proud.” 

In the notice of Robert Abraham's passing the Gazette highlighted his editorial writing, but also mentioned:

“ As a geologist and naturalist (particularly in his favourite branch of Natural History, Entomology) he had few equals in Canada– perhaps no superior on this continent.”

[I have not been able to find any of Robert Abraham’s writings on Entomology, but note that Canadians would have been more likely to have chosen W. E. Logan as the preeminent geologist on the continent, while Americans might have chosen Ebenezeer Emmons, James Hall or James Dwight Dana.]

Interestingly, Sir William Gibb, M.D.,  visited Abraham’s discovery in August, 1851.   He states:

    “Possessing myself some knowledge of the Science of Geology, ... I was forcibly struck with Abraham’s discovery, and when I first visited the locality where these impressions existed in August 1851 – eighteen years ago, before many of them had been disturbed,....”

Wouldn’t we all have liked to have visited the Beauharnois area in 1851.

Sadly,  after about 1910  Mr. Abraham’s name is rarely mentioned in conjunction with the discovery of the trackways at Beauharnois.  The discovery is often credited to Logan and Owen.

++++++++++++++++++++++++++++++++++++++++++

Part 2 on Protichnites will cover Logan’s two visits to England in 1851 and 1852

Christopher P. Brett
Perth, Ontario

Tuesday, 27 August 2013

Odd. Even for the Potsdam


Below are a number of photographs of slabs of sandstone from Burgess Ward, Tay Valley Township, Lanark County, Ontario.   The area has been consistently mapped as Potsdam Group sandstone, which is from Middle to Upper Cambrian in age. 

The sandstone at this location exhibits two facies: a wind blown facies evidenced by very fine cross bedding, and an aquatic facies evidenced by burrows (including  U-shaped burrows that are Diplocraterion, and single burrows perpendicular to the bedding plane).  The outcrop at this location is a drainage ditch, close to which are a number of piles of sandstone.   Every time I visit I find something interesting. 

First Slab: Photographs Sam_0499, 0500, 0501

These photos are likely of the sole of the slab, as it appears from photo 501 that the sand filled in a depression.  Whether the depression was caused by burrowing or a vortex (caused by wind or water) is not clear.  It is unfortunate that half of the depression is missing as one needs the missing half to tell whether the depression is a spiral.


Second Slab
Both the top and bottom of this slab are interesting.  The top can be determined because of the V-shaped burrowing on one side.

Thin Brown Lines on Top of Second Slab: Photographs Sam_0471 and 0472

While these could easily be recent staining along roots, or staining cause by water seeping along fine cracks, I’ll have to pass this by an ichnologist and paleontologist  before I rule it out as being a fossil.  It would be particularly interesting if it were an algae from the Middle to Upper Cambrian.



[Added September 15, 2022:]   Another possibility is that this is a fossil graptolite.  See the graptolites in Figure 3 in the following paper:
Geyer, G., Landing, E., Meier, S. et al. , 2022, Oldest known West Gondwanan graptolite: Ovetograptus? sp. (lower Agdzian/lowest Wuliuan; basal Middle Cambrian) of the Franconian Forest, Germany, and review of pre-Furongian graptolithoids. PalZ (2022). 
https://doi.org/10.1007/s12542-022-00627-5



Sole of Second Slab
White polygonal  pattern within troughs in ripple marks: Photographs Sam_0507 and 0487



 




A number of the polygons are hexagons, but many are not.   The sides of the polygons are about 5 mm in length and about 2 mm thick.    Normally one would think that a polygonal pattern found on the bedding plane of a sedimentary rock is made by the infilling of desiccation cracks.   However, there are two reasons why the polygonal shapes in the photos  may not be desiccation cracks.  First,  this rock is sandstone and sand on drying doesn’t contract by the amount required to form the polygons shown in the photos.   Second, the sides of the polygons are  ellipsoidal to  cylindrical in cross-section and resemble burrows.

Is this  a trace fossil somewhat like Paleodictyon?  Possibly.  Paleodictyon consists of a network of hexagonal meshes and has been found in rocks ranging in age from the Cambrian to recent times.   Photographs of Paleodictyon can be found on Wikipedia  and by simply searching the word in Google images   (See, for example:  http://en.wikipedia.org/wiki/Paleodictyon
 http://hexnet.org/content/paleodictyon  )   The polygonal pattern on the slab that I have found resembles a number of the examples of trace fossils that others have identified as Paleodictyon.
   
Another possibility for the polygonal  patterns is that they are evidence of microbial mat shrinkage cracks.

Crystals on Sole of Second Slab: Photo Sam_0506 (and above two photos)

These crystals are interesting.   They are not calcite, as they don’t effervesce in dilute acid.  From the colour and luster they appear to be gypsum, but the crystal system appears to be wrong for gypsum.   I might have to beg a favour and pass a sample to a friend with access to a scanning electron microprobe.







Third Slab: Microbial Mat Shrinkage Cracks

The next photo, Sam_0510, shows three crescent shapes in the troughs of ripple marks in sandstone.   I believe these curved shapes  to be evidence of microbial mat shrinkage cracks (see my blog posting from November 5, 2012).




Fourth Slab: Burrowing in Ripple Marks: Sam_0475

I believe this to be burrowing as the hand specimen shows one sandstone tube going under the other.  (I admit that the photo could be clearer.)









Fifth Slab: Diplocraterion: Sam_0464

I’m including this photo, not because the trace fossil is odd (it’s fairly common), but because I found a sample that shows a good cross-section of three Diplocraterion traces.  (The top of the slab is on the right hand side of the photo.)







Christopher Brett
Perth, Ontario

Monday, 12 August 2013

The Trace Fossil Diplichnites – A New Occurrence in Eastern Ontario

 The trace fossil Diplichnites was named by Professor Dawson of McGill University in a paper presented about 140 years ago.   It is a trackway that consists of two parallel rows of blunt to elongate to ellipsoidal, closely spaced tracks.   It can be contrasted with the trace fossil Protichnites which is a trackway that consists of two parallel rows of imprints surrounding a medial impression.

Interestingly, the trace fossil Protichnites and the trace fossil Diplichnites are often found at the same occurrence.    For example, Alexander Murray of the Geological Survey of Canada reported on such an occurrence in 1852, the same year  William E. Logan and Professor Owen were presenting the initial papers on Protichnites.  

Various researchers have commented on the association of Protichnites with Diplichnites.  A few have suggested that “the Diplichnites may have been undertracks that penetrated to the underlying layer of sediment, and the fossil trackways thus produced on the top surface (preserving the impression of the dragging tail) were Protichnites” (Wikipedia).     In contrast, others suggest that the Diplichnites tracks occur on the surface.  For example, a recent paper discussing a few Diplichnites trackways in the Potsdam Group sandstones in Quebec mentions that  “Examples with pushback mounds and examples that occur on bed surfaces with adhesion structures are not likely undertracks; their lack of central drag marks suggest that some tracemakers held their tails aloft...” (Hagadorn, Lacelle and Groulx, 2012).   A third possibility is that the tracksways grade into one another.    This was noted by a researcher who reported that  “Several tracks of  Diplichnites are also present, with a medial drag mark appearing in places, grading into  Protichnites.” (Charles. T. Hoxie, 2005).

Below I’ve provided photographs of specimens of Diplichnites trackways from the same outlier of Potsdam Group sandstone between Kingston and Perth where I found the specimens of Protichnites mentioned in my last blog posting.

Photos SAM_0491  and SAM_0492 were taken of the same slab.  They show a Diplichnites trackway (two parallel rows of  tracks) crossing ripple marks.   This is likely the sole of an overturned slab, as the footprints are in positive relief.



Photo SAM_0435.JPG is a different slab.    It clearly shows two parallel rows of tracks.






Photo SAM_0438.JPG  is a  specimen  that  was collected close to the specimen shown in Photo SAM_0435.JPG.  There is one good  line of circles (arguably paired  with another line of circles),  plus     crossing lines of  circles,  plus numerous  other circles.




  

Below are photos   SAM_0495 and SAM_0497 of two slabs that might bear the trackway Diplichnites.






       

Christopher P. Brett
Perth, Ontario

Tuesday, 9 July 2013

A New Occurrence of Protichnites in Potsdam Group Sandstone near Kingston, Ontario

Below I’ve provided photographs of slabs of sandstone bearing the trace fossil Protichnites that I collected on July 4th with Wayne Jackson. The specimens were collected from a quarry in an outlier that has been mapped as Potsdam Group, and is considered to be Cambrian in age.  The specimens belong to the Nepean (Keeseville) formation of the Potsdam Group.

The first two photos show three specimens that were offered to the Miller Museum of Geology at Queen’s University and were picked up by the Museum Curator on July 5th. The other photographs are closeup shots of the specimens, some as they were awaiting pickup and others as they were found.  

Each of the Protichnites trackways is roughly 16 to 17 cm ( 6 ½ inches) wide and cuts across ripple marks in the sandstone. In the first two photos the slabs at the top and bottom are the natural cast in the sediment laid down on top of the original trackway, while the middle slab records the original trackway.   The Protichnites trace fossil is a trackway that is believed to have been made by a creature with multiple legs and a tail, with the central furrow in the trackway being a tail drag mark. (The furrow appears as a ridge in the cast.)  In the  specimens in the photographs the central furrow is 3 to 4 cm wide and some of the footprints are up to 1 cm in diameter.













This is a new occurrence of Protichnites in the Potsdam Group Sandstones and was found near Kingston, Ontario.

I should thank my wife for meeting me for coffee on July 4th and encouraging me to take the rest of the afternoon off to go look for fossils. Without her encouragement I might have stayed in the office and worked.


Christopher Brett
Perth, Ontario

(July 12th, 2013 Addendum :   Since posting the above I have been contacted by a friend, Dave Lowe, who is studying the Potsdam Group, who has told me that in addition to the Chippewa Bay member this outlier also exhibits a younger facies similar to the Nepean Formation near Ottawa, with an angular erosional unconformity between the two.   I was wrong in assigning the specimens that I collected to the Covey Hill Formation.  [ April 26, 2023, Addendum:] When I originally wrote  this posting I relied on Sanford and Arnott (2010) and identified the sandstone as the Chippewa Bay Member, Covey Hill Formation, of the Potsdam Group.  In July, 2013 Dave Lowe told me that the outlier also exhibits a younger facies similar to the Nepean Formation near Ottawa.   Now I would clearly identify the sandstone where the specimens were found as Nepean (Keeseville) formation as I found Protichnites, Diplichnites, Climactichnites and the basal, U shaped, part of Arenicolites or Diplocraterion  fossils in this sandstone.    ]