Geologic Time, Unconformities and Relative Dating Uniformitarianism Appendix A.

12
Time, Unconformitie s and Relative Dating Uniformitarianism Appendix A

Transcript of Geologic Time, Unconformities and Relative Dating Uniformitarianism Appendix A.

Page 1: Geologic Time, Unconformities and Relative Dating Uniformitarianism Appendix A.

Geologic Time, Unconformities

and Relative Dating

Uniformitarianism

Appendix A

Page 2: Geologic Time, Unconformities and Relative Dating Uniformitarianism Appendix A.

Law of Original Horizontality, Law of Superposition

• All sedimentary rocks are deposited in an original, horizontal position (gravity)

• When undisturbed: Oldest rocks deposited first on bottom, youngest on top

Youngest

Oldest

Middle

Page 3: Geologic Time, Unconformities and Relative Dating Uniformitarianism Appendix A.

Cross Cutting Relations – 2 Types

• Whatever is doing the “cutting” is younger: Fault or intrusion

Page 4: Geologic Time, Unconformities and Relative Dating Uniformitarianism Appendix A.

Cross Cutting Relations: Faults

Page 5: Geologic Time, Unconformities and Relative Dating Uniformitarianism Appendix A.

Cross Cutting Relations: Faults• Faulting: An offset in rocks caused

by tectonic motions, mountain building, etc.

• Normal Fault: Tension– Headwall moves DOWN, footwall moves

UP

• Reverse Fault: Compression– Headwall moves UP, footwall moves down

• Thrust Fault: Low angle reverse fault

Page 6: Geologic Time, Unconformities and Relative Dating Uniformitarianism Appendix A.

Cross-Cutting Relationships: Igneous Intrusions

• NOTE: Contact Metamorphism

Page 7: Geologic Time, Unconformities and Relative Dating Uniformitarianism Appendix A.

Principle of Components

www.studyblue.com

Page 8: Geologic Time, Unconformities and Relative Dating Uniformitarianism Appendix A.

Unconformities – 3 Types• Unconformity – “missing time” in the rock

record

• A boundary (“Squiggly line”) separating two types of rocks; erosion or nondeposition

Erosion,

time passes

Original strata Deposition along erosional surface

Page 9: Geologic Time, Unconformities and Relative Dating Uniformitarianism Appendix A.

Nonconformity• Boundary separates younger sedimentary

rocks, from much older, underlying igneous or metamorphic rocks.

• Contact Metamorphism

Sed

Ig/Met

Page 10: Geologic Time, Unconformities and Relative Dating Uniformitarianism Appendix A.

Angular Unconformity

• The older strata below has been folded or tilted (usually steeper angle) due to tectonic motion

Sed

Sed

Page 11: Geologic Time, Unconformities and Relative Dating Uniformitarianism Appendix A.

Disconformity• The surface of “missing time” is parallel to

bedding in two sets of sed rocks

• Hardest unconformity to recognize in the field – how do you tell the surface is erosional and there really is missing time?

Sed

Sed

Page 12: Geologic Time, Unconformities and Relative Dating Uniformitarianism Appendix A.

Today’s lab

• Pages 34 to 42

• Complete Figures 2.11 to 2.22– Which event came first, second, etc– List type of unconformity (angular,

nonconformity, disconformity) and type of fault (normal or reverse)

• Remember: FOLDS, Unconformities, intrusions and deformation are events!