primary structures and facing directions
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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. - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: Primary structures and facing directions](https://reader036.vdocuments.us/reader036/viewer/2022081506/56813767550346895d9efb70/html5/thumbnails/1.jpg)
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
![Page 2: Primary structures and facing directions](https://reader036.vdocuments.us/reader036/viewer/2022081506/56813767550346895d9efb70/html5/thumbnails/2.jpg)
Quick review of Huttonian principals
• Original horizontality
• Superposition
• Cross-cutting relationships
• Inclusion
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What are primary structures
• Depositional, intrusive, or volcanic contacts• Sedimentary structures• Biogenic structures• Volcanic structures
Structures formed during deposition or crystallization
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Contacts as primary structures• Depositional or volcanic, conformable
• Intrusive
• Depositional or volcanic, unconformableDisconformity, Angular unconformity, Nonconformity
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Flat-lying sedimentary contacts
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Intrusive contact
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Intrusive contacts
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Angular unconformity
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Angular unconformity
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Nonconformity
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Nonconformity
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Primary structures: “Way-up indicators”
• Sedimentary
• Biogenic
• Volcanic
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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
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Cross beds: Note tangential contact at base and truncation at top
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Ginormous eolian cross-beds
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Ripples: Top of beds — can also have ripple casts
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Mud cracks: Tops of beds — can also have casts
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Graded beds: note sharp and gradual contacts
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Graded beds