Andrew’s Outcrops

Andrew is one of the many polite teenagers that Lanark County produces by the bushel load.   He also has a keen interest in geology.  This past weekend I took the opportunity to visit outcrops that Andrew had been telling me about.  

Most of the outcrops that Andrew showed me consist of flat lying sandstone exhibiting paired vertical burrows on the top surface.   I expect that everyone would identify this sandstone as a shallow marine facies of the Nepean (upper Keeseville) Formation of the Potsdam Group.   Below are photographs of the top surfaces of  two such sandstone outcrops, each showing paired vertical burrowing.

One outcrop stood out as being particularly impressive and is likely worth a second visit.  Below are photographs of this outcrop.This outcrop can be divided into three parts, with at least two visible unconformities (separating layers 1 and 2; and separating layers 2 from 3).  Starting from the base you notice:
1.)  at least 30 vertical feet of a silicious quartz cobble conglomerate; 
2.)  followed by a foot of sandstone with layers of quartz pebbles and a pitted layer (that may represent eroded evaporite minerals?);
3.)  with a top layer showing bedded  sandstone cut by vertical burrows, some of which extend down into the middle layer (perhaps evidencing the transgression of Cambrian/Ordovician seas and the reworking of fluvial sandstone?).

The two lower layers are of continental/fluvial origin, while the upper layer is of shallow marine origin.  

The first three photographs show the basal quartz cobble conglomerate.   The fourth photograph shows two unconformities, with the basal quartz cobble conglomerate at the bottom of the photo.   The fifth photo shows vertical burrowing and an uncomformity.  The sixth photo shows vertical burrowing in the top layer (shallow marine sandstone), overlying what appears to be two fluvial events: a pebble layer, over  sandstone, over a pebble layer, over sandstone (with the pebble layers possibly being lag deposits formed by aeolian deflation?).

           
I expect that everyone would assign the top burrowed bed to a shallow marine facies of  the Nepean (upper Keeseville) Formation.    Most people would likely  assign the quartz cobble conglomerate bed  to the Covey Hill (Ausable) Formation of the Cambrian/Ordovician Potsdam Group, with some assigning it a Precambrian age.   The middle bed is likely a fluvial facies of the Nepean (lower Keeseville) formation.

Andrew also showed me a mica mine in the Precambrian rocks and a lichen covered, deeply fractured, sandstone ridge that lies on an adjoining property

The photographed outcrops fall within Lot 7 of Concession VIII in North Burgess Township (now Burgess Ward of Tay Valley Township), about four miles (6.5 kilometers) south of Perth, and west of the intersection of Stanley Road with the road to McLaren Lake.   The lichen covered sandstone ridge can be found east of the road to McLaren Lake, on Lot 8 of Concession VIII.

If you were one of the original settlers who had been granted the land upon which Andrew’s parents have their house, or granted one of the adjoining lots, I suspect you’d have complained about the lack of soil.  If you have an interest in geology, which Andrew has, you’d be pleased to be living there.

Christopher Brett
Perth, Ontario   

Suggested Reading:
David G. Lowe, R.W.C. Arnott, Godfrey S. Nowlan, A.D. McCracken, 2017
Lithostratigraphic and allostratigraphic framework of the Cambrian–Ordovician Potsdam Group and correlations across Early Paleozoic southern Laurentia; Canadian Journal of Earth Sciences, Published on the web 6 February 2017,    doi: 10.1139/cjes-2016-0151

The Cylindrical Structures in Lanark County reported in Jean Dugas’ 1952 Doctoral Thesis

In my  August 27, 2015 blog posting I mentioned that Jean Dugas,in the notes to geological  Map 1089A, reported that cylindrical or conical structures in sandstone can be found in North Elmsley Township,  Lanark County.   He commented:

“Peculiar bands showing cylindrical or conical structures noted in the Nepean formation, and best observed on lot 24, Con. VI, North Elmsley tp., are the same composition as the surrounding sandstone , but cut sharply across the beds and are themselves bedded parallel with the walls of the structures.  They are probably formed by slumping of the sand due to water action.”

Morley E. Wilson and Jean Dugas, 1961,
Map 1089A, Geology, Perth, Lanark and Leeds Counties, Ontario, Geological Survey of Canada; Geology by Morley E. Wilson, 1930 and Jean Dugas, 1949; Descriptive notes by Jean Dugas.
                 
In my August 27, 2015 blog posting I also mentioned that I had not been able to find  Dugas’ occurrence on Lot 24 or his thesis.

I  recently located and read Jean Dugas’ doctoral thesis:

Dugas, Jean, 1952,
 Geology of the Perth map area, Lanark and Leeds Counties, Ontario; Ph. D., McGill, 189 pages, four  maps.          

In his thesis he includes five clear  photographs of the conical and cylindrical structures, and good written descriptions of the structures, together with a review of the leading papers discussing theories for their origin.  He concludes that his structures, because of their conical shape, were formed by slumping, and suggests that “as most of the structures are underlain by [crystalline] limestone and it is common to find solution cavities in the [crystalline] limestone” the slumping was likely into cavities in the limestone.

Interestingly, while the the captions to his photographs place the structures on lot 24, the  text of Jean Dugas’ thesis mentions that the structures are found on lot 23.   Both the text and the captions place the structures in concession VI.  In the text of his thesis he comments (at page 99):
      
"Good exposures of an unusual structure in the Nepean sandstone can be seen on lot 23, concession VI of North Elmsley township. A section of the sandstone shows a decisive break in bedding. Across the stratification, two conical structures occur with the apex down, about six feet high and five feet at the base of the cone (cf. photos nos. 29,  30,  31, p. 100). There is a distinct irregular banding, the bands being slightly twisted (cf. photos nos. 31, p. 100, and 32, p. 101). In horizontal section the structure is obviously concentric, forming a circle or a spiral (cf. photo. no. 33 , p. 101).  Though no other exposures of vertical sections have been found, concentric layers were observed at other places in the sandstone.”

Lots 23 and 24 of Concession VI in North Elmsley Township are a few kilometers west of Rideau Ferry and lie south of County Road 1.   Perhaps armed with the photographs I will have better luck locating the outcrops, particularly if I look in both lots.

Christopher Brett
Lanark County

A Possible Conical Fossil Near the Base of the Potsdam Group

In my blog posting for  March 2, 2017 I reported on a sandstone outcrop in Lanark County on the north side of Highway 7 approximately 5 km west of Wemyss.  This is an outcrop first reported by Dr. Easton (2015).   For that blog posting I attached three photos.   The second photo shows siltstone/mudstone layers draped over the Grenville marble and underlying a friable layer; overlain by massive  sandstone beds.

While at the outcrop I collected a loose specimen that had obviously fallen off the outcrop.  The specimen is comprised of the siltstone/mudstone layers and the friable layer.  Below are two photographs of that specimen.

In the first photograph I’ve placed a magenta box around the texture that might be a fossil.  I believe it to be a fossil (rather than dessication cracks)  because the two sides of the item are the same width and arguably represents the cross-section of a conical shape.     Further, the conical shape also arguably ends at an upper cap like shape.

In Eastern Ontario the base of the Potsdam Group is believed to be middle Cambrian in age. 
There are  numerous conical shaped fossils in the Cambrian (e.g., Volborthella, cephalopods, hyoliths), and the specimen may not be distinct enough to be identified.    

Below I’ve provided a reference to a fairly recent paper by Hagadorn  and Waggoner (2002) that is available over the internet and  which contains a discussion of the fossil Volborthella.

I’ve also provided two references to a very recent paper on hyoliths.

Anyone wanting the specimen for research purposes should send me an email.  Unfortunately it is one of those specimens where every time you pick it up another piece falls off.

Christopher Brett
Perth, Lanark County

References

Bettam, S.,  2017
U of T undergrad leads team of paleontologists, classifying mysterious ancient cone-shaped sea creatures, U of T News, Global Lens Breaking Research, January 11, 2017
https://www.utoronto.ca/news/u-t-undergrad-leads-team-paleontologists-classifying-mysterious-ancient-cone-shaped-sea
          
Easton, R. M., 2015
Project Unit 15-014. Precambrian and Paleozoic Geology of the Perth Area, Grenville Province, in Summary of Field Work and Other Activities, 2015. Ontario Geological Survey, OFR 6313
at pages 18-1 to 18- 13
http://www.mndm.gov.on.ca/en/news/mines-and-minerals/summary-field-work-and-other-activities-2015  

Hagadorn, J.W., and Waggoner, B.M., 2002
The Early Cambrian problematic fossil Volborthella: New insights from the Basin and Range, in F. A. Corsetti, ed.,  Proterozoic-Cambrian of the Great Basin and Beyond, Pacific Section  SEPM Book 93, p. 135-150.

Moysiuk, J.,  Smith, M. R.  and  Caron, J.-B., 2017
Hyoliths are Palaeozoic lophophorates,  Nature 541,   394–397  (19 January 2017)   doi:10.1038/nature20804
http://www.nature.com/nature/journal/v541/n7637/abs/nature20804.html

Ebenezer Emmons’, Sir William E. Logan’s, Professor Amadeus W. Grabau’s and Professor Greggs’ Comments on Potsdam Sandstone

I find it interesting,  when considering how the theory of the origin of  the Potsdam Group sandstones (of Ontario, Quebec and New York State)  has evolved over time, to note that numerous early writers made insightful comments, but were ignored or had their contributions overlooked.  In this posting I will mention a few of the geologists who deserve more credit.    While the title to this posting singles out Emmons, Logan, Grabau and Greggs, numerous others made insightful comments.

Ebenezer Emmons named the Potsdam sandstone.   His earliest downloadable report dates from 1842.  In this report he mentions that the Potsdam sandstone is found with conglomerate and that there a number of varieties of sandstone.  He identifies two principal varieties: 1st a sandstone variety that he subdivides into two further varieties found at quarries  (a)  at Potsdam (St. Lawrence County), and (b) at Bangor (Franklin County) and “Moore” (later spelt Mooers) ; 2nd a sandstone found at Keeseville, Whitehall and Kent, which he later says he has sometimes given “a compound name– the Potsdam and Keeseville sandstone”.  He also mentions other varieties of sandstone.    Interestingly, his sandstone from the Potsdam quarry we would now call the Hannawa  Falls Formation; his sandstone from Mooers area is likely the one we would call the Ausable Formation sandstone (for rocks in New York State; or the Covey Hill Formation, for rocks in Ontario and Quebec), and his sandstone from Keeseville we could call the Keeseville Formation (or Nepean formation, for rocks in Ontario; Cairnside Formation, in Quebec).

 In addition, Emmons comments that “Though the rock is generally even-bedded, I have noticed several places where it has been subject to violent forces, so as to greatly derange the strata”, and included drawings of folded and faulted outcrops.   He also comments on the differences in beds, singling out  materials “that appear to have been borne along by a moderate current, which has been given a diversity of stratification resembling inclined beds”, and includes a drawing of such strata, a drawing that looks like fluvial facies.

Emmons (1846) summarizes the Potsdam sandstone, summarizes  the varieties of sandstone, and notes that “In many places it is a coarse conglomerate”.

Logan makes at least the following important points:

- the Potsdam sandstone that is found in New York state extends into the Provinces of Ontario and Quebec (Logan 1844; Logan 1863)

- the Potsdam sandstones at Beauharnois which produced Protichnites trackways contain both wave ripple marks and wind ripples– they are littoral sandstones (Logan, 1860; Logan, 1861, Logan, 1863 )

- The Potsdam sandstone is better referred to as part of the Potsdam Group as the “sandstone is a member of a series of strata” and includes conglomerate  (Logan 1863)

Intriguingly, both Logan’s identification of wind ripples and his comment that the Potsdam sandstones at Beauharnois are littoral sandstones were referred to in papers published for over forty years,  but then disappeared from the literature.

Professor Amadeus W. Grabau makes the following points:

- where the Potsdam is “a transgressive overlapping series of strata deposited by a transgressing sea, the basal sand member would naturally rise in the series in the direction of transgression and overlap, and that hence a basal sand is not everywhere of the same age” (Grabau, 1909; also Grabau, 1913)

- the earlier parts of the Potsdam are of continental origin, commenting: “in many, if not in most, regions the Paleozoic series begins with a formation of continental origin, the upper portion of which was reworked by the transgressing sea”; “the Potsdam sandstone, ... in many sections, still shows characters pointing to torrential or eolian origin of a considerable portion of the rock”; and “In many cases this northern “Potsdam” sandstone shows evidence of continental origin in pre-marine time by the occurrence of well-marked torrential cross-bedding in parts which apparently have not been reworked.”

- the Potsdam sandstone includes both quartz sandstone and arkosic sandstone (Grabau, 1920).

Professor Greggs, in combination with co-authors from the Geology Department at Queen’s University at Kingston, differentiated between typical Nepean and typical Potsdam (Hannawa Falls) sandstones, finding that both occurred in Ontario and both occurred in New York State, noting that “These sandstone units  appear to bear consistent stratigraphic relationships to one another” [Greggs and Bond, 1972].  Further, “Periods of erosion punctuated the development of the Potsdam sandstones (Cushing, 1910; Chadwick, 1919; Clarke, 1966), and at some stratigraphic horizon not yet determined by detailed field studies, the environment of deposition of the Potsdam appears to have changed from continental, wind-blown sandstones, possibly reworked by coastal waters, to a shallow marine depositional environment.” [Greggs and Gorman, 1976]

Interestingly, Professor Greggs’ distinction between the shallow marine Nepean sandstone and typical continental, wind- blown Potsdam (Hannawa Falls) sandstone in part reflects the distinction drawn by Ebenezer Emmons (1842) who distinguished between the variety at Keeseville and the other at Potsdam, St. Lawrence County.  

(Numerous others who studied and reported on the rocks of New York State, including Professor Cushing, distinguished between the varieties of Potsdam sandstone.   There are just too many to summarize.)

Christopher Brett
Perth, Ontario

References

Emmons, Ebenezer, 1842
Survey of the Second Geological District, In Geology of New York, Part II; W. & A. White & J. Visscher, Albany, New York

Emmons, Ebenezer, 1846
Agriculture of New York;   C. Van Benthuysen & Co., Albany, New York

Grabau,  Amadeus W., 1909
Physical and Faunal Evolution of North America during Ordovicic, Siluric, and Early Devonic Time, The Journal of Geology, Volume 17, 209-252

Grabau, Amadeus W., 1913
Principles of Stratigraphy; A.G. Seiler and Company, New York

Grabau, Amadeus W., 1920
A Comprehensive Geology; Part 1, D. C. Heath & Co., New York           

Greggs, R. G.  and Bond, 1972
A principal reference section proposed for the Nepean  Formation of probable  Tremadocian age near Ottawa, Ontario. Canadian Journal of Earth Sciences, 9, pp. 933-941.

Greggs, R.G.  and Gorman, W.A.  1976
Geology of the Thousand Islands,  by Parks Canada
http://www.oliverkilian.com/ecology/thousand-islands/island-insights/geology/rocks.html

 Logan, W. E.,  1844
Geological Survey of Canada, Report of Progress For the Year 1843

Logan, W. E., 1860
On the Tracks of an Animal lately found in the Potsdam Formation ,  read before the Natural History Society of Montreal in June, 1860, volume V of The Canadian Naturalist and Geologist, article XXXIX, pages 279-285

Logan, W. E., 1861
Considerations relating to the Quebec Group, and the Upper Copper-bearing Rocks of Lake Superior;  read before the Natural History Society of Montreal in May, 1861, volume VI of The Canadian Naturalist and Geologist, page 199-207

Logan, W. E., 1863
Geology of Canada, Geological Survey of Canada, Report of Progress from its commencement to 1863,

Sandstone Filled Cracks Extending into Marble at an Outcrop Near The Cat’s Meow

In my last blog posting I mentioned that Dr. Easton (2015) had reported “A previously unknown exposure of Potsdam group sandstone and conglomerate that he “identified on the north side of Highway 7 approximately 5 km west of Wemyss (385510E 4967646N)” and that the outcrop is worth a visit.    The outcrop is just east of signs on Highway 7 for The Cat's Meow, an upscale inn for cats, at  20619 Highway 7.

Dr. Easton describes the outcrop as follows:
“A previously unknown exposure of Covey Hill Formation strata, or possibly the Abbey Dawn Formation of Sanford and Arnott (2010), was identified on the north side of Highway 7 approximately 5 km west of Wemyss (385510E 4967646N). Here, a channel, at least 3 m deep and up to 20 m wide, was cut down into weathered calcite marble. The deeper (>3 m) west side of the channel is filled with red-weathering pebbly conglomerate containing subangular to subrounded rock fragments and quartz pebbles, which grade upward into thin-bedded reddish coarse sandstone. The shallower (~2 m) east side of the channel consists of red mudstone and siltstone beds (up to 1 cm thick) that immediately overlie the marble basement, and which are overlain, in turn, by thin-bedded reddish coarse sandstone.”

I visited the outcrop last year.   Fifty percent  of the outcrop is marble.  I noted that Dr. Easton had described  the sandstone and conglomerate at the center and east end of the outcrop.   A small amount of sandstone/mudstone also occurs at the west end of the outcrop in cracks in the marble.  There are vugs in the marble filled with calcite crystals.   There is a small hematite gossan at the west end of the outcrop and a larger example in the center of the outcrop.   At least two faults cut the outcrop.  I would not have identified the sandstone/conglomerate as the Covey Hill Formation strata  or the Abbey Dawn Formation.  The sandstone is more likely the Hannawa Falls Member of Sanford and Arnott (2010) /the Hannawa Falls Formation of Lowe (2016).    

The most interesting feature of the outcrop is the beds of siltstone/mudstone at the base of the sandstone, which drape over the marble and underlie a thin friable layer comprised of pea sized pebbles of marble.   

Attached are three of the photos that I took.  The first shows sandstone fissures in the marble at the west end of the outcrop.   The second photo shows siltstone/mudstone layers draped over the marble and underlying a friable layer; overlain by massive  sandstone beds.  The base of blue ruler is along the contact with the Grenville marble.  The third photo shows the hematite gossan and possibly a fault.

There have been numerous reports in the literature of tongues of sandstone extending into the underlying marble.  Where the sandstone is described it is invariably a dark red sandstone, possibly what we would now identify as the eolian Hannawa Falls Formation of the Potsdam Group.  Below are a few of the less often cited reports:

Helmstaedt,  Gorman & McBride (1987) in a field trip guide for the Kingston, Ontario area mention a “paleokarst cave” near the entrance to the Portland Conservation Area, on the east side of Highway 38, about 2 km south of Verona, noting that a “Cut on east side of road shows a paleokarst cave in Precambrian marble filled with sandstone breccia of Nepean Formation (Fig. 11). Sandstones with local cross-bedding extend as horizontal ‘tongues' into the marble.” [Note: this guide appears to have been written when all of the sandstones of the Potsdam Group were referred to in Ontario as Nepean Formation.]
   
Smyth (1893, at page 104) reports that “North of Gouverneur [New York]  the [crystalline] limestone and sandstone are in direct contact... From the irregular line of contact it is clear that the material of the sandstone was deposited upon a  [crystalline]  limestone surface that had been subject to erosion.  An interesting confirmation of this conclusion is seen in the presence of narrow, irregular cracks extending several feet into the  [crystalline] limestone and filled with sandstone.”
   
Winchell (1893, pages 107-108) reports on a trip to look at the  Potsdam sandstone in Upper New York State.  He also reports on hematite ore bodies in marble noting that for many occurrences the ore lies “at the base of the Potsdam.”    For outcrops near Richland, New York, he noted that “The sandstone grades into soft hematite, which appears like a good ore.  The upper surface of the marble is fissured in places, and the hematitic material of the sandstone extends down into these fissures (fig. 7).”

Cushing et al (1910) reported on the Geology of the Thousand Islands Region, New York State.  They reported a “dark red, very thoroughly indurated and vitreous sandstone that differs from the general run of sandstone in the district” and that “all the sand-filled cracks seen in the Grenville [crystalline] limestone were filled with this type of sandstone...”.

Cushing and Newland (1923) report on sand filled cracks in marble mentioning that outcrops “may be seen in several places in the Gouverneur quadrangle” and that “on the bared [crystalline] limestone surfaces the red sandstone stands out in relief”.

Professor Bruce Selleck (2005) of Colgate University in a field trip guide mentions “Sand from the Potsdam is also found within open fractures and filling hydrothermal karst tunnels and pipes [in marble].  These fillings are often deeply colored red or maroon by abundant hematite cement, and the sand is usually tightly cemented by quartz and carbonate minerals, but rounded sand grains can usually be seen with a hand lens.  Some of the conglomerates within the Potsdam contain chert clasts that are the result of silicification of marble clasts.  Pebbles of jasper and clasts of laminated sandstone that had been silica-cemented, reworked and re-deposited are also present in the conglomerate and pebbly sandstone beds. 

 Professor Selleck commented on the association of hematite and the Potsdam as follows:“The hematite deposits also share the common presence of nearby or directly overlying inliers of Potsdam Sandstone (Chamberlain 1984). The paragenesis of the hematite deposits is generally interpreted as multi-stage with pre-Potsdam surface weathering of Proterozoic iron sulfide leading to accumulation of locally thick gossans of limonite/hematite prior to Potsdam Sandstone deposition (Chamberlain 1984).  Post-Potsdam reconstitution of the iron oxides involved hydrothermal fluids that dissolved and re-deposited hematite within Potsdam Sandstone as thick botryoidal masses, specular crystalline aggregates, veins and disseminated cements in sandstone and highly altered Proterozoic basement gneiss.”    There are too many other reports of hematite at the Potsdam/Grenville marble interface to mention.
                   
Christopher Brett
Perth, Ontario



---------------------------------------------------------------
References
           
Cushing, H.P., Fairchild, H.L., Ruedemann, R. And Smyth, C.H. Jr., 1910
Geology of the Thousand Islands Region, New York State Museum Bulletin  No. 485 at pages 62-63

Cushing, H.P., and Newland, D. H., 1925
Geology of the Gouverneur Quadrangle, New York State Museum Bulletin  No. 259 at page 49 and Plate 11

R. M. Easton, 2015
Project Unit 15-014. Precambrian and Paleozoic Geology of the Perth Area, Grenville Province, in Summary of Field Work and Other Activities, 2015. Ontario Geological Survey, OFR 6313
at pages 18-1 to 18- 13
http://www.mndm.gov.on.ca/en/news/mines-and-minerals/summary-field-work-and-other-activities-2015  

Helmstaedt,  H.H.,  Gorman W.A. & McBride, S.L. 1987
Field Tripping: Geology of the Kingston Area,
By the  Department of Geological Sciences, Queen's University, Kingston,  
www.whaton.uwaterloo.ca/waton/s906.html
   
Lowe, D.G.,  2016  
Sedimentology, Stratigraphic Evolution and Provenance of the Cambrian – Lower Ordovician Potsdam Group in the Ottawa Embayment and Quebec Basin;
Doctoral Thesis, University of Ottawa,
http://www.ruor.uottawa.ca/handle/10393/35303

Sanford, B.V.  and Arnott, R.W.C.,  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

Selleck, B., 2005
Exploring the root zone of an ancient fault-driven hydrothermal system in the Adirondack Lowlands, New York; NYSGA Field Trip Guidebook, 77th Annual Meeting, 12-31

Smyth, C. H., Jr., 1893
Geological Reconnoissance in the Vicinity of Gouverneur, N. Y.; Transactions of the New York Academy of Sciences, Vol. XII, pages 97-108  at 104

Winchell, N. H., 1893
The Potsdam sandstone at Potsdam, New York; in Field Observations of N. H. Winchell in 1892;
The Geological and Natural History Survey of Minnesota, Twenty-first Annual Report for the year 1892, pages 99- 111       

Ontario Geological Survey Remapping the Perth Map Sheet

I was driving into Perth in August when I noticed an individual taking a sledge hammer to an outcrop of granite along Scotch Line (County Road 10) within the town limits of Perth.    My initial thought was that it must be a geologist taking a sample to age date the granite, so I stopped, introduced myself, and asked the individual if that was what he was doing.   I was glad that I’d stopped.   It was Dr.  Michael  Easton of the Ontario Geological Survey and he was collecting a sample in order to later determine its age.   I suspect that this was the first time he has been asked the question of whether he was collecting a sample in order to age date the rock.    (I often get asked in an accusing tone to explain what I’m doing when I just stop to look at an outcrop.)  

Dr. Easton  was good enough to tell me that he was working on the Perth map sheet and that his initial report had been published in the Summary of Field Work and Other Activities, 2015.   The following is a link to that report.

Easton, R. M.,  2015
Project Unit 15-014. Precambrian and Paleozoic Geology of the Perth Area, Grenville Province; in Summary of Field Work and Other Activities, 2015. Ontario Geological Survey, OFR 6313
at pages 18-1 to 18- 13
http://www.mndm.gov.on.ca/en/news/mines-and-minerals/summary-field-work-and-other-activities-2015   

Dr. Easton has recently sent to me electronic copies of two recently published  reports from this year’s field season that deal with rocks in the Perth area:
               
Easton, R.M.,  2016a.
Precambrian and Paleozoic geology of the Perth area, Grenville Province; in Summary of Field Work and Other Activities, 2016, Ontario Geological Survey, Open File Report 6323, p.17-1 to 17-13.

Easton, R.M.,  2016b.
Metasomatism, syenite magmatism and rare earth element and related metallic mineralization in Bancroft and Frontenac terranes: A preliminary deposit model; in Summary of Field Work and Other Activities, 2016, Ontario Geological Survey, Open File Report 6323, p.18-1 to 18-9.

Both reports can be downloaded from:
http://www.mndm.gov.on.ca/en/news/mines-and-minerals/summary-field-work-and-other-activities-2016
       
In his reports from 2015 and 2016a, Dr. Easton discusses A) the medium-pressure granulite- and upper amphibolite-facies rocks of the Frontenac terrane, B) the upper greenschist- to lower amphibolite-facies rocks of the Sharbot Lake domain, C) separated  by the Maberly shear zone, and includes maps showing the locations of the terranes and shear zone.   Easton 2015 discusses the Maberly Shear Zone and directs one to a “spectacular, 150 m long roadcut on the south side of Highway 7   (385925E, 4967751N) [which is] a microcosm of the Maberly shear zone, and consists of alternating panels, 10 to 15 m wide, of marble breccia interlayered with thin-layered, highly flattened, compositional silicate tectonites.”   For anyone that has not previously driven out to look at the shear zone, the outcrop is worth a look.  Below is a photograph of the outcrop.

The ruler in the photo is one meter long.

Easton (2015 and 2016a) divided the Frontenac terrane in the Perth map area into 3 subdomains, and reports on differences in the marbles present in the 3 subdomains of the Frontenac terrane.    His petrographic study of rocks in the Frontenac terrane suggests metamorphic pressures and temperatures higher than previously reported for the Perth Map sheet.  He found assemblages suggesting “pressures and temperatures greater than 8 kilobars and higher than 670◦C” and other assemblages “indicating metamorphic pressures as high as 11 to 14 kilobars and temperatures approaching 1000◦C.”    He notes that “a significant metamorphic pressure change occurs along a north-northeast-trending fault located southeast of Smiths Falls”, a “fault that trends north-northeast from Chaffey’s Lock to Portland to Glen Elm just south-southeast of Smiths Falls”, which he names the Chaffey’s Lock fault.  He puts the Perth map area in bathozone 6 of  Carmichael, noting that bathozone 4 conditions exist 20 km south of the Perth map area near Lyndhurst, adding that a "difference of 2 kilobars between the Perth and Lyndhurst areas would involve at least a vertical displacement of 7 km” across the fault but because the fault “places rocks of the Nepean Formation against rocks of the upper March and Oxford formations”  there was “no more than 100 m of post-Ordovician displacement across the fault.”

In his reports from 2015 and 2016, Dr. Easton also discusses the metallic mineral potential of the Perth map sheet, principally the potential for Kiruna-Type magnetite-apatite mineralization and the  rare earth potential of numerous mica-apatite deposits.   Dr. Easton mentions finding “a strontium equivalent of the mineral haunghoite (BaCe(CO3)2F). A strontium equivalent of haunghoite has not been previously identified, and this may represent a new mineral species.” 

He also discusses the industrial mineral potential (sandstone as potential source for silica; marble as a carbonate source; vermiculite), and includes analyses of sandstones and marbles.

While Dr. Easton’s reports concentrate on Precambrian rocks, he also mapped the Paleozoic rocks (the Cambrian  to Lower Ordovician Covey Hill and Nepean formations, the Lower Ordovician March and Oxford formations, and the Middle Ordovician Rockcliffe Formation). In his reports Dr. Easton mentions that he has found a number of  previously unknown exposures of Potsdam Group sandstone  and conglomerate (both Covey Hill and Nepean formations).   A previously unknown exposure of Potsdam group sandstone and conglomerate that he “identified on the north side of Highway 7 approximately 5 km west of Wemyss (385510E 4967646N)” is worth looking at.


The 2017 Annual meeting of the Geological Association of Canada/Mineralogical Association of Canada will be held in Kingston, Ontario from May 14-18, 2017 and  will coincide with the 175th anniversary of the founding of the Geological Survey of Canada by the legislature of the Province of Canada in 1842, in Kingston, Canada West.  As part of the conference Dr. Michael Easton of the Ontario Geological survey will be leading a one day field trip on May 14th  entitled New Insights into the Tectonic and Metamorphic Architecture of the Composite Arc Belt and the Frontenac-Adirondack Belt near Perth, Ontario, Grenville Orogen which highlights the results of his recent mapping, geochemistry, petrology and new geophysical data collected in the Perth area.   See:  http://www.kingstongacmac.ca/en/field-trips/


Christopher Brett
Perth, Ontario

Gypsum Pseudomorphs that formed in the Sabkha Environment of the Potsdam Group

“Sabkhas are supratidal, forming along arid coastlines and are characterized by evaporite-carbonate deposits with some siliciclastics” Wikipedia . 

In my  October 7,  2016 blog posting I mentioned that I had attended the official re-opening and rededication of the Metcalfe Geoheritage Park in Almonte, Lanark County.   While I was there and admiring structures preserved in Potsdam sandstone slabs that had been rescued during the enlargement of Highway 417 in Kanata, Dr. Donaldson suggested that I should look at other rescued slabs of sandstone that had been placed in the Last Duel Park in Perth, Ontario.  Below are three photographs of slabs that now reside in the Last Duel Park.

I believe the structures shown in the first two photographs  to be relic pseudomorphs of gypsum rosettes.  The third photo shows convolute, tightly folded sandstone beds, that were held together likely as the result of microbial binding.

My  October 31st  blog posting mentioned that I had attended the second day of the Niagara Peninsula Geological Society Field Trip to Eastern Ontario and visited the Potsdam sandstone quarry at Ellisville.  While there Paul Musiol of Kingston pointed out an interesting structure that he had found in the sandstone.  Below is a photograph of Paul’s find.

I told Paul that my best guess is that his structure is a  pseudomorph of gypsum or another evaporite mineral (barite).

The addendum to my blog posting from December 29, 2015 summarizes various reports on
on evaporites in Potsdam sandstone.    Recently, in his doctoral thesis, Dave Lowe described gypsum and evaporite pseudomorphs found in Potsdam sandstone:       

David G. Lowe, 2016   
Sedimentology, Stratigraphic Evolution and Provenance of the Cambrian – Lower Ordovician Potsdam Group in the Ottawa Embayment and Quebec Basin;
Doctoral Thesis, University of Ottawa,
http://www.ruor.uottawa.ca/handle/10393/35303

Dave has recognized six siliciclastic paleoenvironments in the Potsdam:  a) braided fluvial,  b) ephemeral fluvial, c) aeolian erg, d) coastal sabkha, e) tide-dominated marine and  f) open-coast tidal flat.   He discusses the coastal sabkha environment and the formation of gypsum pseudomorphs at pages 87-92 of his thesis.  His figure 3.8 at page 90 is worth a look, as it provides photographs of  evaporite minerals, pseudomorphs and textures in coastal sabkha strata. Figure 3.8A shows impressions of sparry, nodular radiating mineral aggregates in sandstone from Kanata, which Dave compared to evaporitic desert rose nodules.  He recognized possible swallowtail twin textures suggesting that the nodules were originally formed as gypsum.  His Figure 3.8B shows cubic impressions possibly of halite in sandstone.  His Figure 3.9 shows kinked and tightly-folded sandstone intraclasts in coastal sabkha strata.

Those with an interest in microbial binding in the sabkha environment might also want to read pages 201-203 of Dave’s thesis.

Christopher Brett
Perth