Assignment #3 The relative age of rocks and geological events.

1. Assignment #3 The relative age of rocks and geological events. Unconformity The figure on the right is a geological cross-section showing the distribution of rocks, faults and unconformities. Modern land surface The uppermost surface is the modern land surface which is slowly undergoing erosion in response to processes at the earth’s surface. The geology shown in the cross-section is due to changing environmental conditions (related to rising and falling sea level and/or subsidence and uplift of the land surface) along with igneous intrusion and faulting. The sequence of events that led to the distribution shown can be determined using the basic principles covered in the lecture on relative time.

3. Principle of Erosional unconformities: unconformities are younger than the rocks that they affect. The following slides illustrate the sequence of events that would produce the geology shown in the geological cross-section on the first slide. They also tell you which of the principles is used to determine the relative order of events.

4. Deposition of sandstone Unconformity

5. Deposition of sandstone • Deposition of shale Unconformity Principle of superposition

6. Deposition of sandstone • Deposition of shale • Deposition of limestone Unconformity Principle of superposition

7. Deposition of sandstone • Deposition of shale • Deposition of limestone • Deposition of sandstone Unconformity Principle of superposition

8. Deposition of sandstone • Deposition of shale • Deposition of limestone • Deposition of sandstone • Tilting and uplift and/or falling sea level Unconformity Principle of original horizontality

9. Deposition of sandstone • Deposition of shale • Deposition of limestone • Deposition of sandstone • Tilting and uplift and/or falling sea level • Erosion forming an angular unconformity Unconformity Principle of erosional unconformities Assignment hint: Note that unconformities that are tilted, but parallel to underlying strata, formed prior to the event that caused the tilting.

10. Deposition of sandstone • Deposition of shale • Deposition of limestone • Deposition of sandstone • Tilting and uplift and/or falling sea level • Erosion forming an angular unconformity • Subsidence and/or sea level rise • Deposition of sandstone Unconformity Principle of superposition

11. Deposition of sandstone • Deposition of shale • Deposition of limestone • Deposition of sandstone • Tilting and uplift and/or falling sea level • Erosion forming an angular unconformity • Subsidence and/or sea level rise • Deposition of sandstone • Deposition of shale Unconformity Principle of superposition

12. Deposition of sandstone • Deposition of shale • Deposition of limestone • Deposition of sandstone • Tilting and uplift and/or falling sea level • Erosion forming an angular unconformity • Subsidence and/or sea level rise • Deposition of sandstone • Deposition of shale • Intrusion of granite Unconformity Principle of cross-cutting relationships

13. Deposition of sandstone • Deposition of shale • Deposition of limestone • Deposition of sandstone • Tilting and uplift and/or falling sea level • Erosion forming an angular unconformity • Subsidence and/or sea level rise • Deposition of sandstone • Deposition of shale • Intrusion of granite • Faulting Unconformity Principle of cross-cutting relationships

14. Deposition of sandstone • Deposition of shale • Deposition of limestone • Deposition of sandstone • Tilting and uplift and/or falling sea level • Erosion forming an angular unconformity • Subsidence and/or sea level rise • Deposition of sandstone • Deposition of shale • Intrusion of granite • Faulting • Uplift and/or falling sea level • Erosion forming a disconformity Unconformity Principle of erosional unconformities

15. Deposition of sandstone • Deposition of shale • Deposition of limestone • Deposition of sandstone • Tilting and uplift and/or falling sea level • Erosion forming an angular unconformity • Subsidence and/or sea level rise • Deposition of sandstone • Deposition of shale • Intrusion of granite • Faulting • Uplift and/or falling sea level • Erosion forming a disconformity • Subsidence and/or rising sea level • Deposition of limestone Unconformity Principle of superposition

16. Deposition of sandstone • Deposition of shale • Deposition of limestone • Deposition of sandstone • Tilting and uplift and/or falling sea level • Erosion forming an angular unconformity • Subsidence and/or sea level rise • Deposition of sandstone • Deposition of shale • Intrusion of granite • Faulting • Uplift and/or falling sea level • Erosion forming a disconformity • Subsidence and/or rising sea level • Deposition of limestone • Deposition of shale Unconformity Principle of superposition

17. Deposition of sandstone • Deposition of shale • Deposition of limestone • Deposition of sandstone • Tilting and uplift and/or falling sea level • Erosion forming an angular unconformity • Subsidence and/or sea level rise • Deposition of sandstone • Deposition of shale • Intrusion of granite • Faulting • Uplift and/or falling sea level • Erosion forming a disconformity • Subsidence and/or rising sea level • Deposition of limestone • Deposition of shale • Uplift and/or falling sea level • Formation of the modern land surface Modern land surface

18. Oldest • Deposition of sandstone H • Deposition of shale C • Deposition of limestone J • Deposition of sandstone I • Tilting and uplift and/or falling sea level • Erosion forming an angular unconformity G • Subsidence and/or sea level rise • Deposition of sandstone K • Deposition of shale L • Intrusion of granite E • Faulting D • Uplift and/or falling sea level • Erosion forming a disconformity B • Subsidence and/or rising sea level • Deposition of limestone A • Deposition of shale F • Uplift and/or falling sea level • Formation of the modern land surface Modern land surface Unconformity F B A L K G I Youngest J E C H In the assignment each lithological unit, fault, intrusion and unconformity is labeled with a letter. In your sequence of events you must include the letter associated with each as shown in the example above. D Note that even though units H, C, I, J, K and L are not laterally continuous due to faulting, the Principle of lateral continuity allows you to recognize that they are the same units in the same sequence on either side of the fault.