There has some geology about “Planet Earth”, please finish those questions. You have to do the right answer. If you need any materials just let me know.
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Geol 1202 Planet Earth
Assignment: Geologic History of the Valley
The rocks that form the crust of the Earth are often exposed as complicated sequences of layered,
folded and faulted strata. A geologist has to be able to look at these rocks and unravel the sequence
of events to reconstruct the geological history for that area. In Lecture Three we covered the concepts
of Relative and Absolute Time.
The Principles of Relative Time can be a very powerful tool for determining age relationships between
different rock units. Combined with absolute dating it allows us to reconstruct the structural history of
a valley, a coast or even an entire continent. In this assignment you are going to apply the concepts
we covered in this lecture to a well known region of Nova Scotia; the Annapolis Valley.
To get you started applying these concepts I have given a simple example below. Take a few minutes
to see if you can work out the sequence of events. List the letters representing the rock units and
structures from oldest to youngest. Then compare your answers to the sequence on the next page.
Make sure you understand how the sequence of events were determined before moving on to the
actual exercise.
There is also a primer on the Principles of Relative Time in the Media Library that you should read
before attempting the assignment.
PRACTICE EXAMPLE
F
G
A
20 Ma
B
D
C
10 Ma
H
In this simple example we can quickly determine the sequence of events and the relative ages
of the rocks given the isotopic ages of the 2 intrusions.
Youngest
F – this means that the last layers of rocks have to be younger than 10 million years because they
include fragments of the 10 Ma intrusion.
H – there was another period of erosion less than 10 million years ago (can you see the unconformity
that truncates the middle layer of sedimentary rocks (B) and the 10 Ma intrusion (C) ?)
C – the rocks were intruded again 10 million years ago (isotopic date of 10 Ma)
B – the middle layer of sedimentary rocks were deposited and has to be younger than 20 Ma because
it includes fragments of the 20 Ma old intrusion,
G – there was a period of erosion between 20 and 10 million years ago. (can you see the
unconformity, marked in red, that truncates the 20 Ma intrusion?)
A – the rocks were intruded 20 million years ago. (isotopic date of 20 Ma)
D – the lowest sequence of sedimentary rocks were deposited and then deformed more than 20
million years ago. (the 20 Ma intrusion cuts across the deformed layers)
Oldest
Notice that this list of events starts with the oldest at the bottom and the youngest or most recent at
the top- there is also text indicating this so as to avoid any confusion. This is the convention for listing
time ordered events and you should follow this when completing the assignment.
[you will not see “oldest” and “youngest” listed on maps or on geological columns because it is given
that they are ordered this way, but for this exercise you will do so as a check that you are listing them
correctly]
Part One: Identify formations
Legend
FUNDY COAST
South
J
rth
Ba
yo
T
un
Dg
ED
Mo
lis V
alle
Dg
tai
dy
n
CO
ED
J
TJ
OSW
T
25
OSW
CO
tain
y
un
fF
Moun
apo
No
N
TJ
Ann
layered rocks
Isotopic age
of 370 Ma
km
folded layers
Triassic Period dinosaur
fossils found here
Study the block diagram of the Annapolis Valley above. Notice that the different rock units (strata) are
represented by different colours and patterns These are illustrated in the rectangles to the left of the
figure – the “Legend”. There are also some labels on each – these give the age of the rocks. On
geology maps it is convention to have sort of stylised text that explains the age and name (or type of
rock) of each unit on the map. In our figure the middle unit is represented by Dg – The D stands for
Devonian and the g indicates it is granite (a type of igneous rock).
The other thing that a legend (or list of units) illustrates is the relative age of the units. Convention is to
have the oldest at the bottom and the youngest at the top – so in our legend the unit indicated by Dg is
the oldest and J is the youngest.
This figure is a replication from the Nova Scotia Geology Map that you have access to through the link
in this week’s folder. You should open the map and find the figure. The map also has a legend – or
Table of Formations (as they call it) that provides more information about the unit. Notice that it
divides the province into four distinct regions based upon their geologic history (we will learn why later
in the course). We are going to be looking at the Southern Mainland region. Along the left side it has
the geologic time scale. You are going to use these to fill in legend on our figure.
What to do!
The last page of this assignment there is a plain version of the legend (no colour so you will not need
a colour printer). Use the Table of Formations from the digital map to fill in the following information
next to each of the rectangles:
Age of the unit
just give the period
some units will span two periods
Name of the unit
for some there will be more than one unit or formation
I have done one for you.
Part Two: Reconstructing the geologic history of the Annapolis Valley.
Look at the block figure and read each of the event statements below carefully. Remember when
looking at a specific event to ask yourself, “what has to happen first before this can occur?”.
The rocks in this area record a number of episodes in the geologic history. You are going to use
the block figure to deduce the order of events based on the principles introduced in this module
(superposition, cross-cutting relationships, etc.).
In the list below, the order of events has been scrambled. Read each of the event statements
below carefully. Remember when looking at a specific event to ask yourself, “what has to
happen first before this can occur?”
Determine the order in which events took place and list them in the correct order, starting with
the oldest. For example, if you thought the order of events given below is already correct (it’s
not), you would write “A B C D E F G H I J K L”.
To make it easier on the next page I have created a list – you just need to fill it in with the letters
(in the correct order hopefully)
EVENTS
A – The crust was tilted, giving the Triassic sedimentary and volcanic rocks a ‘dip’ to the North.
B – Sediment layers were deposited and lithified, to produce sedimentary rocks of the Meguma
Group
C – The magma cooled and solidified to form the South Mountain granite
D – Erosion removed rock from all six of the units producing the Annapolis valley, and exposing
the North and South Mountains
E – Sedimentary rocks of the Torbrook Formation were deposited on top of the White Rock
Formation
F – Erosion took place, exposing Meguma rocks and Granite at the surface
G – Sedimentary rocks of the Scots Bay Formation were deposited on the North Mountain Basalt
H – The rocks of the Torbrook Formation, White Rock Formation, and Meguma Group were
folded by tectonic movements
I – Granite Magma was intruded into the folded rocks of the Meguma Group
J – Lava that formed the North Mountain Basalt was erupted and solidified
K – Sedimentary rocks of the Fundy Group were deposited on the folded Meguma Group rocks
creating an unconformity.
L – Volcanic rocks of the White Rock (and other) Formation were deposited on top of the
Meguma Group rocks.
Student Number:
Name:
Part One: Identify formations
Legend
age
name
J
TJ
T
Dg
Devonian
granite
ED
OSW
CO
Part Two: Reconstructing the geologic history of the Annapolis Valley.
youngest
oldest
B
What to submit?
Fill out this page then scan or photograph it and submit it to the Assignment Two dropbox.