1. Geologic and Rock Cycles, Fossils and Unconformities

2. 3 key events: deposition, uplift, erosion
The Geologic Cycle
3 key events: deposition, uplift, erosion
Sedimentation of beds A-D beneath the sea
Uplift above sea level and exposure of D to erosion
Continual erosion strips D away completely and exposes C to erosion
Subsidence below the sea and sedimentation of E over C; erosion surface of C preserved as an unconformity

3. Deposition or Sedimentation

4. Uplift

5. Erosion

6. Erosion by wind
Erosion by water

7. Geologic Cycle Cycle repeats over and over through geologic time
Forms Strata: layers of rock

9. h ^

10. The rock cycle explains how one type of rock can be transformed into another in nature.

11. Index Fossils
Use fossil layers to date rocks: index fossils

14. Fossils
Titanites

15. What is a Fossil?
Any evidence of past life, including remains, traces, imprints as well as life history artifacts.
Examples of artifacts include fossilized bird's nests, bee hives, etc

16. Mastodon at Wheaton College

17. How Fossils are Formed
About 67 million years ago -- A Tyrannosaurus rex died and its body was quickly covered by riverbed sand and mud.
Over time, pressure and some remineralization turned its bones to fossils.

18. Tully Monster; IL State Fossil
The Fossil Record
All of the fossils that have existed throughout life’s history, whether they have been found or not.
Tully Monster; IL State Fossil

19. Fossils Usually found in sedimentary rock
Sometimes in metamorphic rock
These are often distorted, hard to interpret
Upper layers - younger
Deeper layers – older

20. Principle of Fossil Succession
There is a unique, non-repeating pattern (history) of fossils through stratigraphic time.
All rocks containing fossils of the same species were deposited during the duration of that species on Earth.

21. Correlation by fossils
Correlation by fossils. Certain index fossils are keys to matching sedimentary strata in widely separated outcrops

22. Used in conjunction with radioisotope techniques to age rock layers

23. Unconformities
Unconformity: contact between layers of rock that should not touch; represents a gap in the fossil/geological record
Layers of sandstone over pink granite

25. Hutton's unconformity at Siccar Point Berwickshire, Scotland This was the very first (1789) example of an unconformity

26. Hutton's unconformity

27. Ordovician/Silurian unconformity in New York state

28. Nonconformity, Grand Canyon, Arizona
Nonconformity, Grand Canyon, Arizona. Nonconformities are types of unconformities in which sedimentary rock depositionally overlies metamorphic or intrusive igneous rock. In this photo, Cambrian sandstone overlies Proterozoic schist, with an age greater than 1.7 Ga--which means that the erosional surface between the two represents more than a billion years of geologic time!

29. Grey dolomite 500 myo Reddish rhyolite 1.5 byo
Description: Precambrian/Cambrian unconformity at the site of the Taum Sauk powerplant about 90 miles south of St. Louis, MO. The upper angled layer layer of grey dolomite is approximately 500 million years old. The reddish rhyolite on which the dolomite rests is approximately 1.5 billion years old. There is a billion years of geologic history missing in this picture.
Precambrian/Cambrian unconformity near St. Louis – 1 billion years is missing

30. Unconformities Disconformity: gap in geological record
Caused by long period of erosion between episodes of sedimentation
Or by faulting and uplift
Fossils in the two layers may be very different

32. Unconformities
Angular unconformity: younger strata overlie an erosion surface on tilted or folded rocks. Implies a specific sequence of events.
Nonconformity: contact with overlying sedimentary rocks on top of an erosion surface of plutonic or metamorphic rocks. Implies long-lived erosion prior to burial and re-deposition.

33. Angular Unconformity
Nonconformity

34. Upper Carboniferous and new red sandstones of the Triassic in Portugal – spectacular angular unconformity

35. Angular
Nonconformity

36. Angular Unconformity
Nonconformity

39. Great Lakes Lost Interval
Mesozoic Era
Very recent glacial sediments above ancient bedrock
Due to long period of erosion of uplifted sediments
Big gap in fossil record