Transcript Sequence Stratigraphy PowerPoint

Relative Time:
 Ages of events are placed in
order of occurrence.
 No exact date is identified.
Ex. WWI and WWII
 Ex. I am the second child in my
family.

Absolute Time:
 Identifies the exact date of an
event.
Ex. 65 Million Years Ago
 Ex. 1990

Let’s practice with a
sequencing example…
A
C
I
D
E
H
B
Finding age with relative time:
Principles used to determine relative
order of geological events:
1. The Law of Superposition
In a sequence of
undisturbed sedimentary
rocks, the oldest rocks will
be at the bottom.
Picture the pile of clothes in
your room. Where is the
first thing that you put on
the floor now?
2. The law of cross-cutting
relationships – anything that
cuts across layers of rock is
younger than the rocks that it
has intruded into. This applies to
faults and igneous intrusions.
Rock
formed first
Igneous
rock cuts
earlier
layering
Which statement is true?
1. D crosscuts B
A
2. D crosscuts C
B
3. C crosscuts D
4. B was
deposited
before E
E
D
3. The law of included fragments
- the fragments that make up a
rock are older than the entire
sample.
4. Original HorizontalityRocks are usually deposited
flat and level.
5. The Law of Folds or Tilts: Folds
and tilts in rocks are younger
than the rocks themselves.
Other Guidelines for figuring out a
sequence:
 Sedimentary rocks are usually
formed under water.
 Weathering and erosion usually
happen above water (on dry
land).
 Contact metamorphism
(“igneous intrusion”) shows that
the rock that was changed was
there first when the intrusion
happened.
Now sequence that stratigraphy!
Sequence 1: Uplift & Erosion
1.
2.
3.
4.
5.
First limestone is
deposited
Then sandstone is
deposited
Then shale is
deposited
Then the layers are
uplifted
Lastly, erosion takes
place
Sequence 2
Sequence 2: Faulting
1. First, limestone
is deposited
2. Then sandstone
is deposited
3. Next shale is
deposited
4. Then faulting
occurs
Sequence 3
Sequence 3: Folding
1. First limestone is
deposited
2. Then sandstone is
deposited
3. Next shale is
deposited
4. Lastly folding
occurs
Sequence 4
Sequence 4: Igneous Intrusion
1. Limestone
deposited
2. Sandstone
deposited
3. Shale deposited
4. Igneous Intrusion
Note: contact
metamorphism is
the same event as
the intrusion.
What is an Unconformity?
 A buried erosional
surface.
 Look for a “wavy” line
that is buried beneath
the surface (indicates
that at one time this
layer was at the surface
and weathering and
erosion took place).
Formation of an unconformity
Layers are formed according to superposition.
Something happens to uplift the area
(folding, faulting, etc.)
Erosion wears away the uppermost layers
Area submerges and deposition begins again.
Here’s the
unconformity