1. Geologic Sequencing: The order of geologic events
The Grand Canyon Gorge

2. Superposition youngest to oldest
Click anywhere in picture to skip back to LAWS.

3. Correlating Outcrops Shale with trilobites is oldest in “A”
9th Oldest
8th Oldest
7th Oldest
6th Oldest
5th Oldest
YOUNGEST
4th Oldest
10th Oldest
9th Oldest
8th Oldest
7th Oldest
6th Oldest
3rd Oldest
5th Oldest
2nd Oldest
4th Oldest
3rd Oldest
2nd Oldest
5th Oldest
OLDEST
Shale with trilobites is oldest in “A”
Conglomerate on bottom in “B” but WAY higher in other outcrops
Shale with trilobites is ABOVE gray sandstone so sandstone is older

4. Shale with trilobites is oldest in “A”
Youngest
5th
4th
3rd
2nd
10th
9th
8th
7th
6th
5th
4th
3rd
2nd
5th
OLDEST
Shale with trilobites is oldest in “A”
Sandstone on bottom in “B” but WAY higher in other outcrops
Shale with trilobites is ABOVE gray limestone so limestone is older

5. FOLDS and TILTS: ALWAYS older than the rocks they are found in!

6. Folded/Tilted Layers

7. Marker Beds

8. VOLCANIC ASH LAYER AT THE SAME TIME AS THE DINOSAURS BECAME EXTINCT LEAD SCIENTISTS TO LOOK FOR METEORITE CRATER Chicxulub Crater 65 mya km. Wide

9. Igneous Intrusion - Cross Cutting: Always younger than the layers they are found in

10. Cross Cutting
Intrusions and Faults: Always younger than the layers they are found in
Click to skip back to LAWS.

14. Taconic Unconformity Late Silurian Limestone
Early Ordovician Shale and Sandstone
We stopped along the side of the road where engineers had cut into the rock formations to make the road. The unconformity was clearly visible showing banded carbonate rock overlying tilted shales and sandstones.
unconformity
Taconic Unconformity

15. Practice: what happened here?
Click to see arrows shoot in one at a time. #1= included fragments #2=intrusion, cross-cutting #3= angular unconformity #4=erosion. This is the outcome of the previous slide.
1: Tilting 2: Igneous Intrusion
3: Erosion (unconformity) 4: Deposition of New Layers

16. The sandstone layer is common to all the columns. Glacial deposits
Youngest 
The sandstone layer is common
to all the columns. Glacial deposits
are on top. They are youngest
and gray limestone is on the
bottom. It is oldest.
Why do you think the layer
of black shale is thicker in
column C than in column A?
Not sure?
Ask your teacher
Oldest 

17. Youngest 
According to the ‘law of
supersposition’ the youngest
rock layer will be on top and
the oldest layer will be on the bottom
Oldest

18. Here’s another example from a different regents exam. There are four
columns from neighboring regions. The numbers represent different
fossils found in the rock layers. Unconformities (buried erosional
surfaces) indicate that material is missing. Try to find a fossil (number)
that is common to all four columns and use it to line them up as in the
previous example.

19. Youngest  Oldest  The fossil common The rock with fossil #6 is the
to all columns is #7.
The rock with fossil #6 is the
youngest because it’s on top.
Youngest 
Oldest 
The rock with fossil #8 is the oldest. It’s on the
bottom. The layer with fossil #3 is missing from
the rightmost column due to erosion.

20. Now try to reconstruct the geohistory of this region by listing the
layers in order from the oldest to the youngest:
Youngest  6 4 1
7,9 2 10 3
Each column by itself is incomplete but by using
information from all of them we can develop a
complete history of a geologic region. 5
Oldest  8

21. What is the geologic age of layer B?
(1) Cambrian (3) Devonian
(2) Ordovician (4) Permian

22. What is the correct order of development from oldest to youngest?

23. (1) A fault exists between outcrops A and B.
Bedrock outcrops A and B are located at two different locations along the Genesee River in western New York State. Rock layers 1, 2, and 4 are the same in both outcrops.
Which statement best explains why rock layer 3 is missing from outcrop B?
(1) A fault exists between outcrops A and B.
(2) Erosion created an unconformity between rock layers 2 and 4 in outcrop B.
(3) A volcanic eruption destroyed rock layer 3 in outcrop B.
(4) Metamorphism of outcrop A created rock layer 3.

25. f02_11_pg20
f02_11_pg20.jpg

26. Sediments deposited, sea-level lowered, layers intruded, layers tilted, erosion and deposition under sea, sea-level lowered again. Click arrow to continue.

27. The trip route stays very close to the edge of the Catskill Mountains.

28. Mr. Orgonik pointing out the Taconic Unconformity

29. Applying Principles of Relative Dating to Determine Geologic History of an Area
The process of matching rocks or geologic events occurring at different locations of the same age is called
CORRELATION

32. Correlation of rock layers often relies upon fossils
William Smith (late l700’s) noted that rock layers in widely separated areas could be identified and correlated by their distinctive fossil content
This led to the "principle of fossil succession“
Fossils succeed one another in a definite and determinable order, and therefore any time period can be recognized by its fossil content

33. f03_09_pg37
f03_09_pg37.jpg

35. 1. Which layers are the same?
2. Which layer is older E or F?
3. What is correct sequence of rock layers from oldest to youngest?
4. An unconformity is represented by the interface between which 2 layers?

36. Which fossil might be found in Devonian rock layers?

39. Eurypterus
NY State Fossil
Silurian index
fossil

40. Index fossils – Page 8-9 ESRT
Index fossils - any animal or plant that is characteristic of a particular span of geologic time or environment.
2 criteria must be met
Life form lived over a wide geographic area – horizontal distribution
Life form existed for a short period of time – short vertical distribution

41. Which letter would make a good index fossil?
Location A
Location B
Location C
Rock layer 1 W
W Z
Rock layer 2
W Z Y Z
Rock layer 3
W X X
X Z
Which letter would make a good index fossil?

42. OTHER METHODS OF CORRELATION
Layers of bedrock exposed (outcrops) on either sides of river valleys/excavations
“walking the outcrop”
Volcanic ash – large eruption – widely distributed – represents a small time interval
LIKE AN INDEX FOSSIL