Elora Gorge 1.0
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Geology
Date
Apr 3, 2024
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Uploaded by DoctorBear1290
Elora Gorge
1.
Elora Gorge location:
The Elora Gorge is in Elora, Ontario. It is located roughly 23 km north of the University of Waterloo and roughly 25 km
North West of Guelph, Ontario. The exact location of the Elora Gorge coordinates is
43.6719° N, -80.4444° W.
(Fig. 1-1), The location of the Elora Gorge relative to The University Of Waterloo
Latitude: 43.6719, Longitude: -80.4444, Scale: 1:315,068
2.
Basic information on the gorge:
The closest, naturally exposed outcrop to the University of Waterloo is the Elora Gorge. This outcrop is an amazing free
opportunity to study and learn the stratigraphy that is all around us. The main three rock types the gorge is composed of
are dolostone, travertine, and limestone, and it is part of the Guelph Formation. The limestone and dolostone rock that the
gorge is mostly composed of were formed during the Silurian period (around 450 million years ago), while travertine rock
is much younger, having been formed in the Quaternary period (around 14,000 years ago). The Elora Gorge was formed
by river and glacier melt eroding the rock to form a gorge. Therefore, while the rock layers are extremely old (450 million
years old), the Elora Gorge formed not that long ago when put into geologic time.
3.
Rocks that form in the Elora Gorge:
In the Elora Gorge, you will see primarily three different types of rock, travertine (Fig. 3-1), limestone (Fig. 3-2), and
dolostone (Fig. 3-3). Since the Elora Gorge cuts through dolostone bedrock, the vast majority of the exposed rock you will
see is dolostone. The Dolostone was formed roughly 420 million years ago by marine sediment depositing in the sea.
During the Paleozoic era, shallow water covered some of North America, which is how the marine sediment deposited. On
top of dolostone, limestone is also visible in the Elora Gorge. While much less common, limestone is a very similar rock to
dolostone. The difference between limestone and dolostone rock is that limestone is a calcium carbonate rock composed
mostly of
calcite and aragonite
, and dolostone is mostly composed of mineral dolomite.
The third and youngest rock that the Elora Gorge is made of is travertine, which forms in the caves of the gorge. Travertine
is a calcium carbonate like limestone, which causes both rocks to have the same chemical composition. In little holes in
the caves, it forms from minerals like calcite that seep through and evaporate, which triggers precipitation, and eventually,
once the calcium carbonate precipitates, it produces travertine. So even though travertine and limestone have the same
chemical composition, they are formed in much different settings, which causes them to have different structures in the
Elora Gorge.
While these three rocks are similar to the eye, the best way to differentiate limestone is to use the HCL acid test, as
limestone is the only one out of the three to react with HCL. So to separate limestone from dolostone, do a HCL test, and
since dolostone is slightly higher on the hardness scale, you can also use that to distinguish between the two.
All images used are from geology.com, which is a family run website started by Geology. Limestone, dolomite, calcite
(King, 2005-2023). They are individually sourced in the reference list.
Image
Rock Name
Colour
Texture
Hardness
HCL
Effervescence
Test
(Fig. 3-1)
Travertine
Cream, white and
tan
Fine Grained
4
No
(Fig. 3-2)
Limestone
Dark grey, white,
and brown (Can
be white to light
grey; however,
more common
white at gorge.)
Fine Grained
3.5
Yes
(Fig. 3-3)
Dolostone
Grey to white
Fine Grained
4
No
4.
Important Features of Elora Gorge:
In the Elora Gorge, there are reef and lagoonal rocks, and while they are fairly similar to the naked eye, there are multiple
factors that can help differentiate them from each other. Reef rocks tend to be massive units of gray to pale white dolostone
that are often in shallow waters (in this case, they are overhanging across the river), whereas lagoonal rocks are rock layer
strata that tend to be in deep waters (in this case, the bottom of the gorge). Reef rocks are mainly composed of calcium
carbonate, while lagoonal rocks are composed of a mix of clay minerals, organic matter, and some calcium carbonate.
Another important feature of the Elora Gorge are mass movements like rockfalls and rockslides. In steep, rocky areas like
the Elora Gorge, rockfalls are frequent. They happen when boulders and rocks separate from the cliff faces and fall to the
ground as a result of gravity. On the other hand, rockslides happen from the rapid downward movement of large rocks and
debris. They are commonly the larger mass movements, as they are more forceful and destructive than rock falls. These
two mass movements happen during the spring thaw and floods. These movements cause large amounts of bedrock to get
removed from the sides of the gorge, which moves the fallen debris and rock to fall into the bed of the Elora Gorge.
Fractures and joints are a huge part of geology, especially at the Elora Gorge. These fractures and joints are formed by
rock movement over long periods of geologic time, which creates holes/fractures in the rock that get bigger and bigger.
These fractures are a huge component of the Elora Gorge, as they allow water to flow through the bedrock, which forms
karsts and caves.
In the Elora Gorge, there are a vast number of interesting cave systems that go through it. This happens because the
limestone, when weak carbonic acid dissolves the limestone, seeps into cracks in the rock. As long periods of time pass,
those little holes expand into big cave systems. The carbonic acid usually forms from the water of the gorge mixed with
dissolved CO2.
5.
Fossils in the Elora Gorge:
In the Elora Gorge, there is a fascinating amount of different fossil types you can see within the rocks. These fossils are so
interesting because they can give important information about ancient marine ecosystems that existed during the time
period, and they also help scientists relatively date samples of rock they take as these fossil species reflect a unique period
of time in earth's history. As the dolostone and limestone rocks were formed way before the younger travertine, they are
covered in many different types of fossil species that show marine life since the limestone specifically was made from
marine life that was around when the gorge was a shallow sea. There have been around 150 different fossil species
discovered in the gorge that date back all the way to the Silurian period (around 450 million years ago). There are over 150
different fossil species in the Elora Gorge; however, there are six main ones that are the most abundant. In the Elora Gorge,
shellfish fossils are the most abundant; these are gastropods (Fig. 5-1), bivalves (Fig. 5-2) and cephalopods (Fig. 5-3), all
of which are the ancestors of modern day shellfish. The gorge also has many different fossils of coral (Fig. 5-4), which
show where possible coral reefs were at sea. On top of that, there are also multiple brachiopods (Fig. 5-5), which are
modern day clams. The last of the main 6 fossil types are stromatoporoids (Fig. 5-6), These are very interesting ancient
creatures that are very rare. It is said that these species were sponge-like and are extremely rare to find fossils of.
Chart of The main 6 fossil types
All images of these fossils were used from Elora Gorge, A visitor’s guide (Hewitt, 1995)
Image
Fossil Type
Description of what fossil looks like
(Fig. 5-1)
Gastropods
have a coiled or conical shell that
looks like a cone.
(Fig. 5-2)
Bivalves
Bivalves are characterized by having
two symmetrical valves and a
two-part hinged shell that can be
elongated.
(Fig. 5-3)
Cephalopods
Cephalopods have a cone and tube
like structure and are connected by an
internal tube.
(Fig. 5-4)
Corals
Corals look like a bunch of tubes that
are connected together.
(Fig. 5-5)
Brachiopods
Brachiopods are similar to bivalves as
they have two valves; however,
brachiopod valves are not equal.
(Fig. 5-6)
Stromatoporoids
Stromatoporoids are huge and have a
bumpy surface feel.
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6.
The Guelph Formation:
The Guelph Formation is a geologic formation mainly covering southern Ontario and is known for predominantly being
composed of reefal limestones and dolostones. However, travertine is also apparent in the upper, younger layers of the
formation, as seen in the Elora Gorge. The Guelph Formation formed during the Silurian period (roughly 450 million years
ago). The full geographical distance of the Guelph Formation goes from southern Ontario all the way far into New York
State. The Guelph formation lays on top of the carbonate dolostones of the Amabel Formation and underneath the
dolostone/shale combination of the Salina Formation. Down below is a map that shows the Guelph Formation’s relative
size within the Southern Ontario portion. The red part of the map is the Guelph Formation (Fig. 6-1).
(Fig. 6-1), The Guelph Formation, showing mineral potential and the Paleozoic Bedrock geology (Rowell, 2015)
References:
Hewit, K., (1995) Elora Gorge – A visitors guide, Boston Mills Press, Toronto, ON, 70p.
Burt, A.K. and Dodge, J.E.P. 2016. Three-dimensional modelling of surficial deposits in the Orangeville–Fergus area of
southern Ontario; Ontario Geological Survey, Groundwater Resources Study 15, 155p.
Derek Armstrong and Terry Carter (2010) The Subsurface Paleozoic Stratography of Southern Ontario, Ontario Geological
Survey Special Volume 7.
Limestone: Mineral information, data, and localities - mindat.org. Available at: https://www.mindat.org/min-49160.html
Rowell, D.J. 2015. Aggregate and industrial mineral potential of the Guelph Formation, southern Ontario; Ontario
Geological Survey, Open File Report 6307, 66p.
King, H. (2005-2023).
Calcite
. geology. Available at: https://geology.com/minerals/calcite.shtml
King, H. (2005-2023).
Dolomite
. geology.Available at: https://geology.com/rocks/dolomite.shtml
King, H. (2005-2023).
Limestone
. Geology. Available at: https://geology.com/rocks/limestone.shtml