1. Primary structures and facing directions Goal: To begin to understand how to use primary structures as markers of deformation

2. Quick review of Huttonian principals Original horizontality Superposition Cross-cutting relationships Inclusion

3. What are primary structures Depositional, intrusive, or volcanic contacts — Bedding probably most useful Sedimentary structures Biogenic structures Volcanic structures Metamorphic features Structures that form during deposition or crystallization of the rock

4. Why do we care 1.Serve as markers of deformation 2.Can often be used to determine facing direction or “Which way is up” or “Way up” Upright beds Overturned beds

5. Contacts as primary structures Depositional or volcanic, conformable Intrusive Depositional or volcanic, unconformable Disconformity Angular unconformity Nonconformity

6. Flat-lying sedimentary contacts

7. Intrusive contact

9. Angular unconformity

11. Nonconformity

13. Primary structures: “Way-up indicators” Sedimentary Biogenic Volcanic

14. Cross beds: Note tangential contact at base and truncation at top

15. Ginormous eolian cross-beds

16. Cross-beds and erosional channel

17. Ripples: Top of beds — can also have ripple casts

18. Flute casts — On bottom of beds

19. Mud cracks: Tops of beds — can also have casts

20. Graded beds: note sharp and gradual contacts

21. Graded beds

22. Biogenic features Trace fossils Burrows and roots Stromatolites

23. Trace fossil: Footprints

24. Stromatolites

25. Volcanogenic features Pillow lavas Baked weathering surfaces

26. Pillow lavas

27. Why is it important to know facing direction? 1.Can help interpret complicated structures from isolated outcrops 2.Can serve as a predictive tool while mapping