EARTH 235_ STRATIGRAPHY AND EARTH HISTORY LAB 8 (2)
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University of Waterloo *
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MISC
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Geology
Date
Apr 3, 2024
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EARTH 235: STRATIGRAPHY AND EARTH HISTORY
LAB #7: GEOLOGY OF ONTARIO – 3D Digital Model (Total = 26 Marks)
Please navigate to Learn and read these sections carefully:
·
Introduction
·
Tips for navigating through the 3D Geological Model of southern Ontario in the
Viewer
·
Resources
·
Preparation
·
Steps to complete Lab 7
Becoming Familiar with Leapfrog Viewer (8 marks)
1.
In three to four sentences, explain the level of detail and organization of the rock units
shown in the left column (or the side bar under “Shapes”) of the new 3D digital
model. (2 marks)
The left column is very well organized in a way that lets you easily
understand each layer of rock as well as each lake around it. You have the
ability to turn off and not see different things on the 3d model. It is organized
with topography and geological time in mind as you go from youngest at the
top to the oldest at the bottom of the left column. The Overburden is at the
top and the Precambrian bedrock at the bottom. Below the Precambrian
bedrock there is also listed fault planes, water bodies and different features
such as highways, counties and much more. These geological features are
very important to have as things such as shorelines and highways are
interesting to have on or off when doing questions. There is much more detail
in this 3d model then compared to the 3d printed piece we had in person last
week. For example being able to see the specific layers of rock inside each
category in very good detail that you can’t see on the 3d print model.
2.
Spend a couple minutes experimenting with turning on and off the available layers
under section labelled shapes, as well as panning, zooming, and rotating around in the
3D digital model. Once you’ve got the hang of navigating, you can start to answer the
questions below.
a.
There are 4 major groups of shape layers shown in the left sidebar. One of
these are the rock units, as described in question one. What are the other 3
types of layers, and why are they useful to understanding the model? (3
marks)
1.
Topography
2.
Salt mines
3.
The Water bodies
The topography adds depth and shows you the valleys, mountains and ridges
of the surface. It gives you the full visuals, so it helps you see and understand
what you’re looking at better.
The salt mines at layers to the strata that show shapes and size of each
different salt mines in there own area on the 3d map.
The water bodies show where the shorelines are and allow you to see where
the water and the topography meet. It also shows you where everything is in
comprehension of the 3d map.
b.
Underneath the Paleozoic bedrock lies a fascinating Precambrian bedrock
surface. This surface can be described in the 3D digital model by elevation
above mean sea level (vertical description relative to a consistent datum) and
location of coloured faces (lateral or spatial description shown by various
coloured regions near towns). Describe the major patterns in elevation of the
top surface of the Precambrian specifically referring to numerical ranges in
elevation relative to mean sea level related to spatial locations in southern
Ontario. (2 marks)
{Hint: Turn off all the layers on top of the Precambrian. You can turn off many
layers at once by selecting the first layer and then scrolling to the last layer while
pressing the shift key on your keyboard. Once multiple layers are selected then
click the ‘eye’ button to hide all the selected layers. Then you can start by finding
the lowest and highest elevations of the Precambrian bedrock surface.}
Starting from the Orillia area (197 above sea level) there is a start of decrease
in elevation towards the south west direction heading towards Port Lambton
(-1010 below sea level), this is following along the Algonquin arch. At
Goderich (-266 below sea level), you can see from either side of the line that
there is a major drop of elevation as well.
c.
In the previous lab, you were asked to consider whether the Paleozoic bedrock
appears at the Earth’s surface in Ontario. Unless you are somewhere where the
bedrock outcrops (such as a cuesta), there are actually sediments from the
Quaternary period that sit on top of the Paleozoic bedrock in the form of sand,
gravel, silt, and clay. In the Leapfrog viewer, what shape layer represents these
Quaternary sediments? (1 mark)
The overburden (Formation 001). It represents these overlying sediments.
Cuestas, Arches, and Basins (Top 10 # 1,2,3) (14 marks)
3.
Using the “Draw slicer line” tool, draw a line striking perpendicular to the strike of
the rock units. The line should cut the contact between the beige units (Medina and
Clinton Groups or layers labelled Whirlpool, Manitoulin, Cabot Head, etc.) and the
blue units (Queenston, Georgian Bay-Blue Mountain, Cobourg, etc). (Go to the
coordinates) The slicing plane should be near 600000E and 4820000N {Hint: Look at
the green latitude and red longitude lines, and the coordinates in the bottom right of
the screen}. In the “Slicing plane” side panel, set the Dip to 90°, Dip azimuth to 340°,
and select the purple box ‘remove back’.
a.
The most prominent Cuesta in Southern Ontario is the Niagara Escarpment.
Please examine various aspects (orientations) of this feature (including
pressing the “d” key to see a plan view) and stratigraphy that helps to explain
this feature. In the last lab, you were asked to look at this contact and explain
why it is so irregular. Look at this contact again, but in all three dimensions
and describe why the boundary is so irregular. (2 marks)
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The boundary is very irregular due to the Queenstown formation being very
old. The formation dates all the way back to the upper Ordovician period and
has had many things happen to it. Two examples I can say are that it has been
raised from the subsurface, which has caused it to stick out of the ground
around the Niagara escarpment. This has been happening for well over
hundreds of millions of years. Due to how long it has been raised from the
subsurface the formations cuesta has been eroding for so long it has caused
other contacts to happen, like with the beiger units such as Manitoulin. These
contacts have become irregular/jaded over all the geological time that has
passed.
b.
Looking at the base of the Niagara Escarpment or the Ordovician Queenston
Formation, please compare the apparent and true thickness using the ruler
function in the 3D digital model. First measure the apparent thickness of the
Queenston Formation along your cross section and write this down. {
Hint: in
the top down view, use the “Measure Distance” tool, which measures metres.
And use the coordinate given}
Then measure the actual or true thickness of the
Queenston Formation beneath the Niagara escarpment. Which one is larger
and why? (2 marks)
True thickness: 112m
Apparent thickness: 20120m
Due to the formation sticking out of the subsurface at a shallow angle there is
a huge difference between the true and apparent thickness. This angle causes
the apparent thickness to appear much bigger then the actual true thickness.
This shallow angle makes a lot of the formation exposed at the surface which
makes the apparent thickness much bigger looking then the true thickness. In
total the apparent thickness is much bigger due to the shallow incline.
4.
Draw another cross section using the slicer tool that is parallel to the approximate
path of the Algonquin arch (NE to SW) and set dip to 90 degrees.
a.
Sketch and describe the general structural trend of the rocks in cross section
from the SW of the model to the NE of the model (3 marks)
As seen on my drawing, as you go from South-West to North-East there is a
decline in the amount of rock units, as the Precambrian rises. This is due to
the Precambrian rock getting thicker as you go more North-East as it
becomes the thickest at the far North-East. When you are at the South-West
part of the cross section you see many different Palaeozoic rock formations
and they start to end as you go to the North-East. You see the most of the
different rock formations at the far South-West point above the Precambrian
older rock and below the Kettle point formation that is above them. You start
to see the Precambrian rock start to become exposed at the Niagara
escarpment because this is where we see a loss of most of the Palaeozoic
rocks.
b.
What is the general trend between spatial distribution and age of the rocks? (1
mark)
The relative thickness gets smaller as rocks get younger in age. This means
that the Precambrian older rock must be the most predominant and thickest
rock in the cross section. Then as you get younger and younger the rocks will
get thinner.
c.
What is the youngest unit consistently exposed on the top of the Niagara
Escarpment? {Hint: Include Unit number and name} (1 marks)
The youngest unit consistently exposed at the surface is The Goat Island
Formation (Unit 421).
d.
If you were to drill a borehole in London, ON, would you expect to encounter
this unit? If so, how deep below the ground surface would it be? {Hint: try
turning the layer you identified on and off to locate it in cross section near
London, and make sure that you account for the depth of overburden. You
could also try only turning on two layers and use the ruler function.} (2
marks)
If you were to drill a borehole in London, On, you would find this unit
underneath by many younger rock units. However, you would find it, and it
would be found around 460 m deep into the borehole.
5.
Slice a cross-sectional line in the model roughly NW to SE in the Unit 306; Dundee
(dark green). The cross section should be approximately perpendicular to the axis of
the Algnonquin arch. What do you notice about the trends in thickness of the units
from NW to SE? What can this tell us about the age of the arch formation? {Hint:
Look specifically at units 600; Cambrian and Units 402-407} (3 marks)
The thickest point of the bedrock unit that is under the arch is at the middle
of the arch. It gradually gets less and less thick as you go out on either side.
On the other hand the Palaeozoic rock formations work the other way as the
middle point is where the formations are the thinnest and the end points as
you go out get gradually thicker. When you look at the SE side the side of the
arch has thicker parts then the NW, and overall, you see an increase in
thickness as you go from NW to SE. The first rock unit to overly the
Precambrian rock is the Cambrian rock. This is also the first unit that is
thicker on both sides then in the middle. This is why the arch is formed when
this rock unit deposited on the Precambrian rock. With this information it is
to think the arch is from the Cambrian age.
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Summary Question (4 marks)
6.
Describe how the 3D model can be used to gain a different perspective on the
Paleozoic geology of Ontario compared to the (i) 2D paper maps and (ii) 3D print
models. Consider the different things you can see, do, and interpret with the 3D
digital model and why these could be valuable. Please take time to explain. (4 marks)
This model is special because it can explain how and why the bedrock layers
are visible at the 2D map's surface. The model also gives you access to see
structural features like inclines, and others, which give you explanations to
why some units of rock are thinner or thicker than other units of rock. This 3d
model is also very valuable since you can move around and see certain areas
at certain angles, whereas on print models you can’t manipulate it in these
ways. Although somewhat useful, the print models only split in certain
places, which limits what you can observe when looking at cross sections.
With this 3d model, you have considerably more flexibility in terms of the
data you can analyze because you can take cross sections anywhere you
choose. Overall, with the other features like faults, lakes and infrastructure
shown, the 3d model gives you much more freedom and capability to see and
learn the cross sections compared to the print models.