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Primary structures and facing directions

Primary structures and facing directions. Goal : To review and recognize different types of geologic contacts so that we can use them as markers of deformation. Quick review of Huttonian principals. Original horizontality Superposition Cross-cutting relationships Inclusion.

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Primary structures and facing directions

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  1. Primary structures and facing directions Goal: To review and recognize different types of geologic contacts so that we can use them as markers of deformation

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

  3. What are primary structures Structures formed during deposition or crystallization • Depositional, intrusive, or volcanic contacts • Sedimentary structures • Biogenic structures • Volcanic structures

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

  5. Flat-lying sedimentary contacts

  6. Intrusive contact

  7. Intrusive contacts

  8. Angular unconformity

  9. Angular unconformity

  10. Nonconformity

  11. Nonconformity

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

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

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

  15. Ginormous eolian cross-beds

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

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

  18. Graded beds: note sharp and gradual contacts

  19. Graded beds

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