1. Fluvial Sediments “As a young man, my fondest dream was to become a geographer. However, while working in the customs office I thought deeply about the matter and concluded it was far too difficult a subject. With some reluctance, I then turned to Physics as a substitute.” - Albert Einstein (unpublished letters) http://www.geocities.com/sogodbay/Images/SDK/Inecar03.jpg

2. 2 Main types: –Bedrock channels: –sediment transport capacity > sediment supply Types of rivers http:// www.fs.fed.us/eng/pubs/html/98771207/98771207.html

3. Types of rivers 2 Main types: –Alluvial channels Channels formed in and by sediment transport Sediment transport capacity <= sediment supply http://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/fluvial_systems/alluvial_landforms_page_1.html

4. What to rivers do? They.. –Erode material –Transport eroded material –Deposit transported eroded material -> sediments –Move in space over time

5. River erosion Leads to first few characteristics of fluvial sediments 1/ larger clasts than eolian sediments 2/ Not necessarily well sorted 3/ Often rounded movie

6. River transport Transported clasts dependent on flow “strength” “strength” proportional to density, flow velocity, flow depth, slope => deeper or faster or steeper flows can carry larger clasts Leads to next characteristics of fluvial sediments 4/ clast size can be an indication of river “strength”

7. River sediment deposition Sediments are deposited following change is river dynamics - If river slows down, shallows (slope and depth) -most dramatic example: Alluvial fans http://lang.sbsun.com/projects/fireflood/articles/alluvialfan.asp http://geology.about.com/library/bl/images/blalluvfan.htm

8. Types of alluvial rivers Straight: sinuosity (path length / length covered) < 1.3 Meandering -> side to side oscillations Braided: flow divides into more than one thread Anabranching: stable braid

9. Braided channels Virgin River [north fork] Zion National Park Compton (1985)

10. Meandering rivers “superelevation” Centrifugal force Hydrostatic pressure “Primary circulation”: “Secondary circulation”: Net Result: channel migration

12. Stratigraphic x-section

13. Channel x-section Idealized fluvial fining-upward sequence [Walker]

14. Summary 1/ larger clasts than eolian sediments 2/ Not necessarily well sorted 3/ Often rounded 4/ Clast size can be linked to channel “strength” Shinarump conglomerate

15. Example of alluvial fan conglomerate [fanglomerate] shed from the Sevier-Laramide uplifts Paleocene Echo Canyon conglomerate, Echo Canyon, Utah

16. Blocks of Shinarump, Coal Pits wash, Zion National Park

17. Triassic Chinle Formation [painted desert, mostly paleosols] overlain by Jurassic fluvial and eolian seds – ledge and cliff formers]

18. Lower Jurassic Moenave Fm. Zion National Park Ledge formers--fluvial channels and related facies Slope formers--paleosols

19. Eocene Claron Formation in Bryce National Park – mostly fluvial and floodplain

20. channel facies 

21. Shinarump Conglomerate member of the Triassic Chinle Formation [basal member]

23. Permian paleosols [soft, badlands topography, colorful] fluvial channel deposit [resistant cap, ledge former]

24. Shinarump conglomerate member of the Chinle Formation, Capitol Reef

25. Shinarump – cross-bedded coarse sandstone with some soft-sediment deformation

26. Shinarump conglomerate member of the Chinle Formation, outside Zion NP

27. Lower Jurassic Moenave Fm. Zion National Park

28. Lower Jurassic Moenave Formation, Zion National Park [trail above campground]

29. Lower Jurassic Moenave Fm. Zion National Park

30. Lower Jurassic Moenave Fm. Zion National Park

31. Lower Jurassic Moenave Fm. Zion National Park

32. Lower Jurassic Moenave Fm. Zion National Park