1 / 24

Geology 3120 - Sedimentary Structures

Geology 3120 - Sedimentary Structures. Outline. Review the geologic history exercise from last time Contacts, primary structures, and secondary structures How to determine which “way is up”… Cross-bedding, graded-bedding, reverse graded-bedding

presley
Download Presentation

Geology 3120 - Sedimentary Structures

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Geology 3120 - Sedimentary Structures

  2. Outline • Review the geologic history exercise from last time • Contacts, primary structures, and secondary structures • How to determine which “way is up”… • Cross-bedding, graded-bedding, reverse graded-bedding • Determining way up using top surface features - ripples, mudcracks, raindrops, footprints • Determining way up using bottom surface features - load casts • Determining way up using features within rocks - geopetal, bioturbation, stromatolites, flame structures, pillow lavas

  3. Block model for exercise

  4. Geologic History • 12 Ma dike • 15 Ma dike • Normal fault • 20 Ma sed • 22 Ma sed • Erosion • Thrust fault • Folding • Layer B • 60 Ma sed • Layer G • 70 Ma sed • 80 Ma sed

  5. Contacts, Primary Structures & Secondary Structures • Contact - a boundary between rock units • Primary structure - structures that form during lithification • Secondary structure - structures that form after lithificaiton

  6. Contacts, Primary Structures & Secondary Structures • Contact - a boundary between rock units • Primary structure - structures that form during lithification • Secondary structure - structures that form after lithificaiton

  7. Which way is up? Today Option 1 Overturned syncline Option 2 “up side down” overturned anticline

  8. Cross-bedding Checkerboard Mesa, Zion National Park Younger Flow direction Y Concave up Older

  9. Graded bedding Younger Y Older • Decrease in depositional energy with sedimentation • Example: flood deposits, turbidity currents

  10. Graded bedding Younger Y Older • Decrease in depositional energy with sedimentation • Example: flood deposits, turbidity currents

  11. Reverse (Inverse) Graded Bedding Younger Y Older • Increase in depositional energy with sedimentation • Example: debris flows (a lot less common than normal graded beds)

  12. Ripple marks Y • Symmetric ripples indicate bi-modal current • Concave = up • Asymmetric ripples indicate unidirectional current

  13. Mud cracks • Desiccation of muddy sediments • Mud cracks 5 cm

  14. Raindrops Y • Limited to terrestrial sediments

  15. Footprints Y • Limited to terrestrial sediments

  16. Load casts • Protrusion of material into a layer below • Load casts indicate the base of a layer, not the top of a layer • Determining the current direction may be possible

  17. Geopetal Structures Y • A “natural” carpenter’s level Shell or cavity in the rock Matrix Infill material (I.e., calcite)

  18. Y Bioturbation • Habitation burrows • Feeding burrows • Movement

  19. Stromatolites Y • Sharks Bay, Australia • Cyanobacteria grow upward toward the surface

  20. Flame structures Y • Less dense material intrudes into material above • Caused by rapid loading of turbidite sands

  21. Pillow lava Y Upper curved surface “V “ notch

  22. References Slide 8 http://www.utahpictures.com/Checkerboard.html Slides 9-15, 17 Busch, R. M. and D. Tasa, Laboratory Manual in Physical Geology, 3rd. Ed., American Geological Institute and National Association of Geology Teachers, 260 p., 1990. Slide 18 http://www.discoverwest.com.au/hablin.html Slide 20 http://volcanoes.usgs.gov/Products/Pglossary/PillowLava.html http://volcanoes.usgs.gov/Products/Pglossary/ancientseq.html

More Related