Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Earth Systems 3209 Unit: 2 Historical Geology Reference: Chapters 6, 8; Appendix A & B

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Principles and Laws Used to Establish Relative Time Unit 2: Topic 2.2 Focus on...   Describing the various principles and demonstrating their use in relative dating. ex. Superposition, crosscutting relationships, etc…

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Relative Time Relative Dating Principles Include: 1.Principle (Law) of Superposition 2.Principle of Original Horizontality 3.Principle of Cross-Cutting Relationships 4.Principle of Inclusions 5.Unconformities - Angular Unconformity - Disconformity - Nonconformity Text Reference: pages

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Relative Dating Principles 1)Law of Superposition States that in any undisturbed sequence of sedimentary rocks, a sedimentary layer is older than the layers above it and younger than the layers below it.

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Relative Dating Principles 2)Principal of Original Horizontality States that most layers of sediment are deposited in a horizontal position. If rock layers are folded or inclined, then the layers must have been moved into that position by crustal disturbances.

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Relative Dating Principles 3) Law of Crosscutting Relationships States that an igneous rock or geologic feature is younger than the rocks it has intruded, or cuts across. Two examples of cross-cutting in this diagram: Igneous Dike cuts rock units A, B, & C. Fault cuts rock units A, B, C, D, & dike.

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Relative Dating Principles 4) Law of Included Fragments States that pieces of one rock found in another rock must be older than the rock in which they are found. Rock fragments from rock unit “D” is included in layer “E” above it.

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Relative Dating Principles 5)Unconformities Are buried eroded surfaces which represent gaps in geologic time. Unconformities form when land above sea level is eroded and sinks. Sediment is then deposited over the eroded surface. Three types of unconformities include; 1.Angular Unconformity 2.Disconformity 3.Nonconformity Text Reference: pages 222 & 223

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Relative Dating Principles - Unconformities Angular Unconformity:  Compressional forces causes layers to fold and uplift.  The folded layers are eroded and sink, where sediment buries the erosional surface.  Rock layers below the erosional surface are inclined and intersect rock layers above at an angle.

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Relative Dating Principles - Unconformities Disconformity:  Forms when rock layers above and below an erosional surface are arranged horizontally.

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Relative Dating Principles - Unconformities Nonconformity:  The eroded surface of metamorphic or plutonic igneous rocks are buried by younger sedimentary layers.

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador v Disconformity v Angular Unconformity v Nonconformity v Page 222 in Text Relative Dating Principles - Unconformities

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Discussion of Relative Dating Principles: 1.Law of Superposition 2.Principle of Original Horizontality 3.Principle of Cross Cutting Relationships 4.Principle of Inclusions 5.Unconformities - Angular Unconformity - Disconformity - Nonconformity

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Example 1: What principle tells us that the fossil brachiopod is older than the fossil gastropod in the rock section below? (A) catastrophism (B) correlation (C) superposition (D) uniformitarianism Reptile Brachiopod Fish Gastropod

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Example 2: Which is true about the relative ages of the layers below? (A) Layer 2 is younger than layer 1, but is older than layer 4. (B) Layer 2 is younger than layer 3, but is older than layer 1. (C) Layer 3 is older than layer 2, but is younger than layer 1. (D) Layer 3 is older than layer 4, but is younger than layer 2. Top Bottom

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Your Turn... Take the time and complete the following questions... (Solutions to follow) Questions: (i)Identify the geological principle which can be used to distinguish between the ages of rock layers X and Y. (ii)Explain your choice. X Y

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Solutions... Questions: (i)Identify the geological principle which can be used to distinguish between the ages of rock layers X and Y. (ii)Explain your choice. (i)The law of cross-cutting relationships is used to conclude that rock unit X is younger than rock unit Y. (ii)Any rock unit that cuts across another must be younger than the rock unit is cuts through. Since rock unit X cuts rock unit Y, it must be yoounger.

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Summary... Overview of Points covered: Relative Dating Principles Include: 1.Principle (Law) of Superposition 2.Principle of Original Horizontality 3.Principle of Cross-Cutting Relationships 4.Principle of Inclusions 5.Unconformities - Angular Unconformity - Disconformity - Nonconformity