1:create a time column of your own. Begin by creating a relative time column with key events. Then y

  

1:create a time column of your own. Begin by creating a relative time
column with key events. Then you will assign years to these events fixing them in absolute time. 2:Using the principle of superposition, look at the sections below and compose a stratigraphic
column3: Draw lines between the columns
indicating the lateral continuation of the different strata.4:Using lithology and index fossils to correlate the
columns
assignment2_geology.pdf

assignment2_geology.pdf

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Geology 1203 Earth History
Assignment: stratigraphic correlation
Understanding the history of the Earth involves determining the sequence of
geologic events which occurred over immense spans of time. The geological
time scale that we use today was first developed in the 1800’s and did not
really extend much beyond the Cambrian Period; however it is constantly
being revised as our understanding improves.
Era
Period
Cenozoic
Quaternary
Teritary
Mesozoic
Cretaceous
Jurassic
Triassic
Permian
Geologists deal with time in two different ways:
Relative Time – the occurrence of events is determined relative to one
another (from oldest to most recent). This can be a local series of events or be
applied to global events. The eras and periods of the geological time column
were established using relative time (mostly based upon the fossil content).
Carboniferous
Paleozoic
Devonian
Silurian
Ordovician
Cambrian
Precambrian
Absolute Time – The discovery of radiometric dating allowed geologists to assign a numerical age
to the formation of certain types of rocks; fixing how old they actually were in billions (Ga), millions
(Ma) or thousands (Ka) of years before the present. Hence the term “absolute” time.
These two ways of looking at time are not unique to geologists. You use them everyday. If you agree
to meet a friend “after class” – that is a relative time. The time of day when you actually meet is
dependent upon when your class is scheduled and when it is finished. If instead you arrange to
meet at 1:00pm -that is absolute time.
Part A: Creating A Personal Time Column
In this exercise you are going to create a time column of your own. Begin by creating a relative time
column with key events. Then you will assign years to these events fixing them in absolute time.
Remember that when ordering events you must start with the oldest on the bottom (when listing
vertical) or on the left (when listing horizontally). It is also good practice to indicate the oldest and
youngest events (this will help you to avoid putting them in the wrong order).
To give you an idea how to proceed I have provided a template with the starting and ending events
you should use (on the last two pages of this handout).
You may include whatever events you wish in between but you must have at least ten more events.
Part B: Stratigraphic columns
In the previous section you created a very simplified column – the list of events on the left were
organized based upon relative time, the list of dates on the right fix the events in absolute time.
Geologists use the principles of relative time to order a sequence of strata (or beds) to produce
what is called a stratigraphic column for a particular area.
Stratigraphic sections
A stratigraphic section is a detailed record of the rocks exposed at one particularly location.
Data about the type of rock, structures, fossils, and thicknesses are compiled by a stratigrapher.
Information from several sections is added to make a stratigraphic column. This column
represents a composite record of all the strata occurring in a particular area. According to The
Principle of Superposition the oldest beds are at the base and the youngest at the top.
50 metres
youngest
a
b
cliff
a
c
b
p
to
d
c
f
e
h
g
A
d
e
C
f
g
a
d
b
B
f
e
c
f
d
1
h
g
oldest
h
stratigraphic column
g
2
3
For the example above we have 3 sections from different locations or exposures along a cliff
(Figure A ). For simplicity let us assume that they are relatively undeformed strata (or beds) and
have only been tilted and not completely overturned. The upper surface of the beds (the “way
up”) is indicated by the small arrow on bed a). The location of our stratigrpahic sectiosn is
indicated by the red columns.
Next look at Figure B In section 1 we can see that bed d is older than bed c which is in turn
older than bed b. In section 2 we can see that bed e is older than bed d and bed f is older than
e and so on. Similarly for section 3 we can deduce that bed h is older than bed g.
So to construct our composite column we try to match similar beds across the sections. Lets say
that we match bed d in section 1 with bed d in section 2. We can now say that bed g is older
than f which is older than e and so on. If we then correlate bed g in section 2 with bed g in
section 3 we can then say that bed h is older that bed g which is older than bed e.
Putting it all together we have our composite stratigraphic column from oldest to youngest
(Figure C ). Notice that the oldest is at the bottom.
Stratigraphic columns come in many different styles from the very simple, like above, to very
complex ones that display not only relative ages of the strata but also the thickness of the beds,
type of rock, the size of the grains, and any structures or fossils.
Part C: Correlation
The Principle of Lateral Continuity states that rock beds can be traced across a wide area and
matching strata at one locality with strata at another is the process of correlation. Several (or
more) stratigraphic columns can therefore be correlated to give a picture of what changes occur
in the rocks horizontally. All this information allows geologists to reconstruct the geologic history
of an area. There are, however, several types of correlation.
Lithological Correlation is the matching of the strata based upon their composition and other
features such as structures, colour and thickness. This primarily matches strata that were
deposited under the same conditions.
Chronological Correlation is matching rocks that were deposited at the same time.
Radiometric dating (this is absolute time) can only be used to a limited extent because it has a
fairly large margin of error (several million years). Most geological events usually occur over a
long period of time, but there are occasional events that occur almost instantaneously. Volcanic
eruptions are one type, and volcanic ash is often a good time marker. Perhaps the best know
time marker is the iridium layer that marks the Cretaceous-Tertiary boundary. This records the
asteroid impact that is now believed to be associated with the extinction of the dinosaurs.
Biological Correlation uses fossils to establish age equivalency in strata. Fossils are not more
accurate that volcanic ash, but they are more common. Fossils used to correlate strata are
called index fossils, but not just any fossil will do; an index fossil has to be distinctive, abundant,
with a wide geographic distribution, and a short time range. Trilobites are a good example.
Correlating strata
A stratigrapher will place several stratigraphic columns side by side and draw lines between the
columns indicating the lateral continuation of the different strata. The lines are drawn indicating
those points in the columns that are similar – this is usually at the boundary where there is a
change in the type of rock, or perhaps the size of the grains, or some other structure.
In the example below the solid lines mark the boundaries between rock types (as indicate by
colour and patterns). Look closely at the columns – make sure you understand what the
correlation is showing you.
The very top and bottom of the columns are not connected with lines
because usually a column will only show what was exposed, or was recorded
stratigraphic
column a
stratigraphic
column b
solid lines indicate that the
boundary between beds are
similar in both columns
unconformities are
indicated with a
wavy line
where the bed is missing
the lines automatically
point to an unconformity
a dashed line indicates that there is not enough information
to determine if there is a corresponding bed in the other column
The figure above shows two simple columns for which I have drawn lines correlating the
different beds. You can see in one column where erosion has occurred creating an unconformity
(indicated by the wavy line). You cannot tell by looking at this column alone how much has been
removed. We can tell that the limestone (grey) unit is missing, and so might be some of the
older bed below.
Remember when drawing the lines you are connecting surfaces (often bedding planes) and so
these lines should connect strata that are similar. Done correctly you should be able to colour
the area between the lines so that you can see the lateral continuation of the strata.
Biological Correlation
Strata will normally vary in thickness horizontally and may naturally thin or pinch as they reach
the edges of their depositional area, or there may be changes in the composition or texture (for
example an increase in the size of sand grains). So some beds may not appear in all columns
or sometimes there will not be enough similarities to match the beds across column – this is
where fossils come in handy. Biological Correlation uses fossils to establish age equivalency
(the sediment was deposited around the same time) in strata. Index fossils have a short time
range and a wide geographic distribution. Even though the beds may not be identical if they
have the same index fossils it means they were deposited around the same time. Biological
correlation uses index fossils and the Principle of Faunal Succession, along with lithological to
correlate beds.
Look a the example below and make sure you understand how the presence of fossils are used
to match the strata in each column with the equivalent stratum in the second column.
stratigraphic
column a
the presence of this
index fossil
indicates
that these beds
were deposited around
the time, and so are of
the same age rather than
the bed higher up in the
column with a different
index fossil
stratigraphic
column b
same
age
where the bed is missing
the lines automatically
point to an unconformity
same age
notice that there is no line at the bottom – because you
do not know if there are more strata below this point
What do I submit?
Print out the last two pages of the assignment and complete the exercises on them.
Make sure you put your name and student number on the sheets.
Photograph or scan the completed exercises.
Submit the images to the dropbox folder on the course site.
You should check that the images are clear and readable.
Name:
Student #
Exercise 1
Create a time column of your own. Begin by creating a relative time column with key events. Then
you will assign years to these events fixing them in absolute time. Remember that when ordering
events you must start with the oldest on the bottom (when listing vertical) or on the left (when listing
horizontally).
Year
you enrolled in GEOL 1203
2018
Youngest
relative time
absolute time
Event
Ý
Oldest
you were born
?
Exercise 2
Using the principle of superposition, look at the sections below and compose a stratigraphic
column. List the units by their letter, from oldest to youngest (be sure to indicate in this in your
answer). Assume that the Priciple of Superpostion applies. Remember you are working with the
units with the letters ( which represent different types of rocks) and not the sections.
YOUNGEST
C
K
K
J
T
M
P
S
J
C
T
J
D
P
M
T
S
M
D
D
OLDEST
Name:
Student #
Exercise 3
The figure below is a set of three fairly simple columns. Draw lines between the columns
indicating the lateral continuation of the different strata. Remember to use solid line where the
strata are similar and dashed lines where there is not enough information to determine if there is
a similar stratum. Mark any location where a bed is missing (an unconformity) with a wavy line.
In this correlation we are applying the Principles of Superposition and Lateral Continuity.
a
b
c
lithology
limestone
shale
sandstone
mudstone
unconformity
Exercise 4
In the figure below you are give three columns. Using lithology and index fossils to correlate the
columns. Remember to use solid lines where the strata are similar and dashed lines where
there is not enough information to determine if there is a similar stratum. Mark any location
where a strata is missing (an unconformity) with a wavy line.
column b
column a
column c
lithology
index fossils
limestone
shale
sandstone
conglomerate
unconformity
Geology 1203 Earth History
Assignment: stratigraphic correlation
Understanding the history of the Earth involves determining the sequence of
geologic events which occurred over immense spans of time. The geological
time scale that we use today was first developed in the 1800’s and did not
really extend much beyond the Cambrian Period; however it is constantly
being revised as our understanding improves.
Era
Period
Cenozoic
Quaternary
Teritary
Mesozoic
Cretaceous
Jurassic
Triassic
Permian
Geologists deal with time in two different ways:
Relative Time – the occurrence of events is determined relative to one
another (from oldest to most recent). This can be a local series of events or be
applied to global events. The eras and periods of the geological time column
were established using relative time (mostly based upon the fossil content).
Carboniferous
Paleozoic
Devonian
Silurian
Ordovician
Cambrian
Precambrian
Absolute Time – The discovery of radiometric dating allowed geologists to assign a numerical age
to the formation of certain types of rocks; fixing how old they actually were in billions (Ga), millions
(Ma) or thousands (Ka) of years before the present. Hence the term “absolute” time.
These two ways of looking at time are not unique to geologists. You use them everyday. If you agree
to meet a friend “after class” – that is a relative time. The time of day when you actually meet is
dependent upon when your class is scheduled and when it is finished. If instead you arrange to
meet at 1:00pm -that is absolute time.
Part A: Creating A Personal Time Column
In this exercise you are going to create a time column of your own. Begin by creating a relative time
column with key events. Then you will assign years to these events fixing them in absolute time.
Remember that when ordering events you must start with the oldest on the bottom (when listing
vertical) or on the left (when listing horizontally). It is also good practice to indicate the oldest and
youngest events (this will help you to avoid putting them in the wrong order).
To give you an idea how to proceed I have provided a template with the starting and ending events
you should use (on the last two pages of this handout).
You may include whatever events you wish in between but you must have at least ten more events.
Part B: Stratigraphic columns
In the previous section you created a very simplified column – the list of events on the left were
organized based upon relative time, the list of dates on the right fix the events in absolute time.
Geologists use the principles of relative time to order a sequence of strata (or beds) to produce
what is called a stratigraphic column for a particular area.
Stratigraphic sections
A stratigraphic section is a detailed record of the rocks exposed at one particularly location.
Data about the type of rock, structures, fossils, and thicknesses are compiled by a stratigrapher.
Information from several sections is added to make a stratigraphic column. This column
represents a composite record of all the strata occurring in a particular area. According to The
Principle of Superposition the oldest beds are at the base and the youngest at the top.
50 metres
youngest
a
b
cliff
a
c
b
p
to
d
c
f
e
h
g
A
d
e
C
f
g
a
d
b
B
f
e
c
f
d
1
h
g
oldest
h
stratigraphic column
g
2
3
For the example above we have 3 sections from different locations or exposures along a cliff
(Figure A ). For simplicity let us assume that they are relatively undeformed strata (or beds) and
have only been tilted and not completely overturned. The upper surface of the beds (the “way
up”) is indicated by the small arrow on bed a). The location of our stratigrpahic sectiosn is
indicated by the red columns.
Next look at Figure B In section 1 we can see that bed d is older than bed c which is in turn
older than bed b. In section 2 we can see that bed e is older than bed d and bed f is older than
e and so on. Similarly for section 3 we can deduce that bed h is older than bed g.
So to construct our composite column we try to match similar beds across the sections. Lets say
that we match bed d in section 1 with bed d in section 2. We can now say that bed g is older
than f which is older than e and so on. If we then correlate bed g in section 2 with bed g in
section 3 we can then say that bed h is older that bed g which is older than bed e.
Putting it all together we have our composite stratigraphic column from oldest to youngest
(Figure C ). Notice that the oldest is at the bottom.
Stratigraphic columns come in many different styles from the very simple, like above, to very
complex ones that display not only relative ages of the strata but also the thickness of the beds,
type of rock, the size of the grains, and any structures or fossils.
Part C: Correlation
The Principle of Lateral Continuity states that rock beds can be traced across a wide area and
matching strata at one locality with strata at another is the process of correlation. Several (or
more) stratigraphic columns can therefore be correlated to give a picture of what changes occur
in the rocks horizontally. All this information allows geologists to reconstruct the geologic history
of an area. There are, however, several types of correlation.
Lithological Correlation is the matching of the strata based upon their composition and other
features such as structures, colour and thickness. This primarily matches strata that were
deposited under the same conditions.
Chronological Correlation is matching rocks that were deposited at the same time.
Radiometric dating (this is absolute time) can only be used to a limited extent because it has a
fairly large margin of error (several million years). Most geological events usually occur over a
long period of time, but there are occasional events that occur almost instantaneously. Volcanic
eruptions are one type, and volcanic ash is often a good time marker. Perhaps the best know
time marker is the iridium layer that marks the Cretaceous-Tertiary boundary. This records the
asteroid impact that is now believed to be associated with the extinction of the dinosaurs.
Biological Correlation uses fossils to establish age equivalency in strata. Fossils are not more
accurate that volcanic ash, but they are more common. Fossils used to correlate strata are
called index fossils, but not just any fossil will do; an index fossil has to be distinctive, abundant,
with a wide geographic distribution, and a short time range. Trilobites are a good example.
Correlating strata
A stratigrapher will place several stratigraphic columns side by side and draw lines between the
columns indicating the lateral continuation of the different strata. The lines are drawn indicating
those points in the columns that are similar – this is usually at the boundary where there is a
change in the type of rock, or perhaps the size of the grains, or some other structure.
In the example below the solid lines mark the boundaries between rock types (as indicate by
colour and patterns). Look closely at the columns – make sure you understand what the
correlation is showing you.
The very top and bottom of the columns are not connected with lines
because usually a column will only show what was exposed, or was recorded
stratigraphic
column a
stratigraphic
column b
solid lines indicate that the
boundary between beds are
similar in both columns
unconformities are
indicated with a
wavy line
where the bed is missing
the lines automatically
point to an unconformity
a dashed line indicates that there is not enough information
to determine if there is a corresponding bed in the other column
The figure above shows two simple columns for which I have drawn lines correlating the
different beds. You can see in one column where erosion has occurred creating …
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