1. Stratigraphy

2. Geologic History Earth is 4.5 billion years old
Much of Earth’s history is recorded in the rocks.
Geologic history is the study and interpretation of Earth’s past.
Evidence of faulting, uplift, rock types, fossils, igneous activity, and many other clues are contained in the rock record.
Interpreting what has happened to Earth over time is like solving a puzzle.
The clues are examined, and Earth’s geologic history is inferred.

3. Geologic Events
Geologic processes that are going on today – weathering, erosion, volcanism, earthquakes – also went on in the past.
This is known as the principle of uniformitarianism – the present is the key to the past.
There are places today where the layers of sediments are forming a particular pattern. The same can be found in rocks formed long ago.
Since the pattern are the same, it can be inferred that the processes that are layering sediments are the same that layered sediments long ago.

4. Sequence of Geologic Events
Much can be learned from the rock record, but it is difficult to determine exactly when a particular event took place.
It is much easier to determine the sequence of a series of geologic events, without putting an absolute date any one of them.
When the age of a rock or event is compared to the ages of other rocks or events in a geologic sequence, the relative age of the rock/event is determined.
The actual age of a rock/event is called its absolute age.

5. Relative age, then absolute age
The first goal of a historical geologist is to determine the relative ages of events and rocks.
If possible, the absolute age of the event/rock can be determined.

6. Chronology of Layers
In determining the chronology of rock layers, geologists use two major principles as starting points in making interpretations of geologic history.
The first is the principle of original horizontality – sediments are deposited in horizontal layers that are parallel to the surface on which they were deposited.
Tilted or folded layers indicate that the crust has been deformed.

8. Principle of Superposition
In a series of undisturbed layers, the oldest layer is on the bottom and each successive overlying layer is progressively younger.
The principle of superposition does not apply in cases where layers have been overturned or where older rocks have been forced over younger layers along a fault.

10. Evidence of Events
When molten magma forces its way into cracks or crevices in crustal rock and solidifies, it forms a mass of igneous rock called an intrusion.
Since the rocks through which the magma moved existed prior to the intrusion, they must be older than the intrusion.

12. Faults, Joints, and Folds
Features such as faults, joints, and folds must be younger than the rocks in which they are found.
A joint is a crack in a rock formation.
A joint is similar to a fault except that the rock only separates along a joint – there is no displacement.
The presence of faults, joints, and folds indicates that some force was exerted on the rocks in the past.

13. Synclines and Anticlines
A syncline is a trough or fold of stratified rock in which the strata slope upward from the axis.
On a geologic map, synclines are recognized as a sequence of rock layers that grow younger, followed by the youngest layer at the fold's center, and by a reverse sequence of the same rock layers on the opposite side of the hinge.
An anticline is a ridge-shaped fold of stratified rock in which the strata slope downward from the crest.
Anticlines can be recognized by a sequence of rock layers that become progressively older toward the center of the fold.

16. The Catskills began with a syncline…

17. Internal Characteristics
Some internal characteristics of rocks include rock fragments, cracks, veins, and mineral cement.
Rock fragments found in larger rock masses are older than the rock in which they appear.
At some earlier time, the fragments were broken away from existing rock.
The sediments in a sedimentary rock are older than the rock itself.
In non-sedimentary rocks, the mineral grains are older than the rocks in which they appear.

19. Buried Erosional Surfaces
An unconformity is a gap in the geological time record.
The geological time record has been destroyed by a series of four processes:
Uplift
Erosion
Subsidence
Deposition

20. Types of Unconformities
Angular unconformity – tilted, folded or faulted rocks which have been eroded and covered again.
Parallel unconformity (disconformity) – parallel rock layers of different ages are separated by an erosional surface.
Non-conformity – sedimentary rocks are deposited on an eroded surface of igneous rocks.

21. Historical Development of a Geologic Profile
  
   
 

24. Outcrop Block Diagram Sequencing
5. _________________________________ (youngest) 4. ________________________________ 3 .________________________________ 2. ________________________________ 1. _______________________________ (oldest)

25. 4._________________________(youngest)
3.________________________________
2. _______________________________
1. __________________________(oldest)

26. Label the syncline and anticline
4.___________________(youngest)
3.____________________________
2 .____________________________
1. _____________________ (oldest)

30. Put these in sequence, and describe what happened…

33. Lab 42: Sequence of Events

38. Lab 43: Stratigraphy of Landscape Models
Folded Mountains Landscape (#7)
You are walking the outcrop along a valley and come to point 132 on the landscape model.
What is the type of rock on the valley floor? What is the rock type for the ridgelines on either side of you?  
Identify the relative ages of the bedrock of the valley and the two ridgelines. Justify your answer.

39. In terms of rock layers differing resistance to weathering, explain why this landscape is a series of parallel valleys and ridges.
Looking at the landscape model and the picture below, label the synclines and the the anticlines.

40. Determine the sequence of events that eventually produced this landscape (11 events).
11. _______________________________________Youngest
10. _______________________________________
9. _______________________________________
8. _______________________________________
7. _______________________________________
6. _______________________________________
5. _______________________________________
4. _______________________________________
3. _______________________________________
2. _______________________________________
1. _______________________________________ Oldest

41. Volcanism Landscape (#2)
a) Compare and contrast the stream drainage of this landscape to the previous landscape model.
b) The following questions refer to the portion of the landscape model below.
i) Using your ESRT, identify and label the types of rocks found in this picture.
ii) Identify the types of contact metamorphic rock that could be found, and label their location on the picture.

42. iii) Determine the sequence of events that eventually produced this landscape.

43. Domed Mountains (#3)
a) Using the portion of the model shown below, determine the sequence of events that produced this landscape.
b) In terms of weathering resistance, explain why the central region of this figure is considerably higher than the surrounding areas.

44. Fault Block Mountains (#3)
a) Determine the sequence of geological events which produced the portion of the landscape shown.
b) The erosional features are somewhat different in area 55 versus the larger range shown by 52. Describe the differences and give a reason for them.

45. List the events (be specific) needed to have the pattern of rock layers shown below in order from first (oldest) to last (youngest).
14._____________________________ (youngest)
13.______________________________________
12.______________________________________
11.______________________________________
10.______________________________________
9.______________________________________
8.______________________________________
7.______________________________________
6.______________________________________
5.______________________________________
4.______________________________________
3.______________________________________
2.______________________________________
1.________________________________(oldest)