In this posting I will mention microbial mat structures and possible microbial mat structures in rocks photographed at Tackaberry’s quarry on Highway 7 about three miles north of Perth. I’ve provided photos that look like structures that have been identified by others as evidence of microbial mats. All probably aren’t. I’ve included all of them in the hope that this posting and the others for this month are enough incentive to encourage someone with knowledge of microbial mats to study the textures exhibited by the rocks at the quarry.
The origin of polygonal crack patterns is particularly problematic, as these cracks have attracted a wide variety of suggestions for their origin: sub-aerial exposure (dessication; sun cracks), a sub-aqueous origin at the water sediment interface (synaeresis), a microbial mat origin, organic burrowing, frost wedging, gravitational loading, gravitationally unstable density inversion, sand injectites, seismic shock, interstratal cracking, water- release (interstratal dewatering), and layer parallel contraction resulting from compaction due to burial. Interestingly, one paper reviewed a particular suite of rocks where five of those suggestions had been raised in successive peer reviewed publications to explain the origin of the polygonal cracks, and the writer of the paper suggested a sixth.
Manchuriophycus and Rhysonetron
In my November 5, 2012 posting I discussed circular, branching lines that are found in the troughs between wave ripples, which I identified as a special kind of microbial mat shrinkage structure. These have been given the names Manchuriophycus (sinuous curved lines) and Rhysonetron (corrugated circular and sinuous lines). The specimens featured on that blog posting were loose specimens at Tackaberry’s quarry about 3 miles north of Perth. For ease of reference, I am providing additional photo Sam_64 below.
Microbial Earth
Below are photographs that I took at Tackaberry’s quarry on Highway 7 a few miles north of Perth of what I believe to be pustular microbial earth textures. These photographs (Sam_24, Sam_44) compare favourably with photos of pustular microbial earth textures in Retallack (2011).
Petees/Petee Ridges/Renticulate Pattern of Flattened Petee Ridges
Eriksson et al.’s ( 2007) paper on Mat-Destruction Features is worth reading, as I believe that I photographed a number specimens with features similar to those shown in their photographs that they have named petees, petee ridges and reticulate patterns of flattened petee ridges, and which they identify as resulting from tears or cracks in a microbial mat that were filled from above or below. In particular, look at their photos:
- Figure 4(c)-8: Petees/petee ridges – which shows spindle shaped forms and longer, more sinuous shapes. Their photo (B), a dense packing for two orders of petee ridges, is comparable to slabs that I photographed.
- Figure 4(c) 10: Petees/petee ridges, with (B) and (C) being a reticulate pattern of flattened petee ridges
Petees/petee ridges might be the explanation for a few of the photos on my September 13, 2013 blog posting entitled ‘A Selection of Fossils from the March Formation in Lanark County, Ontario’ which appear under the heading 4: Branching, overlapping, possibly interpenetrating, roughly parallel to bedding plan. In particular the first, second, and fifth photograph could each show a reticulate pattern of petee ridges. In addition the last two photos on my November 5, 2012 posting show single spindles that could be petees (or have a synaeresis origin). Below, I’ve provided photo Sam_033 as an example of the reticulate texture, Sam_17 as an intermediate texture, and Sam_0198 as an example showing single spindles (which are more likely to have a synaeresis than microbial mat origin) .
Cracks
Numerous specimens at the quarry exhibit cracks, for example the slabs shown in Sam_0137 and Sam_0144:
Polygonal Mud Cracks
In June 30, 2015 blog posting I included a photograph of what I had identified as ‘mud cracks’ in a specimen at Tackaberry’s quary and mentioned that 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.” Below is an additional photo of these ‘mud cracks’, Sam_ 26.
The rock in which the ‘mud cracks’ occur outcrops near the base of the quarry. In addition to the outcrops, the same cracks appeared on bed tops of very large blocks used to keep people from driving into a large hole. There is little chance of finding, examining or lifting the overlying slabs.
Microbial Mat Crusts on Ripples
The third and fourth photos [Sam_133 (a bed sole) and 135 (a bed top)] on March 17, 2019 blog posting show a crust on the ripples, that I believe might result from a microbial mat. I say might, because although very similar to photographs of ‘loaded ripples’ in other publications that have been identified as microbial mat structures such as Bottjer and Hagadorn (2007), I did not check for clay.
One Odd Photo
Sam_0160. I’m open to suggestions on what this is.
Christopher Brett
Ottawa
References and Suggested Reading
Bottjer, D. and Hagadorn, J.W., 2007
Mat growth features, chapter 4(a) in Atlas of Microbial Mat Features Preserved within the Siliciclastic Rock Record, J. Scheiber et al. (Editors), Elsevier, pages 53-71
Eriksson, P.G., H. Porada, S. Banerjee, E. Bouougri, S. Sarkar and A.J. Bumby, 2007
Mat-Destruction Features, chapter 4(c) in Atlas of Microbial Mat Features Preserved within the Siliciclastic Rock Record, J. Scheiber et al. (Editors), Elsevier, pages 76-105
Retallack, Gregory J., 2011
Criteria for distinguishing microbial mats and earths. in Microbial Mats in Siliciclastic Depositional Systems Through Time, SEPM Special Publication No. 101, p. 139–152.
Schieber,Juergen, Pradip Bose, P.G. Eriksson, Santanu Banerjee, Subir Sarkar, Wladyslaw Altermann, and Octavian Catuneanu, [Editors] 2007
Atlas of Microbial Mat Features Preserved within the Siliciclastic Rock Record, Elsevier, volumes, 324 pages
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