Sediment Routing: Weathering, Patterns, and Controls

1. Chapter 7: Sediment Routing This presentation contains illustrations from Allen and Allen (2005) And from Press, Siever, Grotzinger and Jordan 4th Edition (2003)

2. Sediment Routing • Weathering (in situ) • Chemical, Physical an Biological • Regolith • Sediment Yield • Patterns • Controls • Solute and Suspension • Modeling Landform Evolution • Relation between tectonics and sedimentation

3. erosion Weathering (in-situ) transportation Erosion includes BOTH weathering and transportation

4. Sediment Routing • Weathering (in situ) • Chemical, Physical an Biological • Regolith • Sediment Yield • Patterns • Computational Models • Controls • Solute and Suspension • Modeling Landform Evolution • Relation between tectonics and sedimentation

5. Regolith • Weathered layer between pristine bedrock and the land surface. • Main chemical agent is water. Water is moved by gravity (down) and capillarity effect (up)

6. Regolith Rate of regolith removal: –dH/dt by denudation (top) Thickness (H) of regolith depends on rate of bedrock decay: +dH/dt (bottom) H bedrock

7. Regolith Weathering rate decreases exponentially with depth H bedrock

8. Rate of weathering using Cosmogenic Radionuclide Dating P (concentration) y Berrylium 10 and Al 25 are produced (P) in situ by cosmogenic rays interacting with minerals P0 changes with latitude and altitude Y* (~50%) is about 0.5-0.7m bedrock

9. P (concentration ) of radionuclides is a measure of absolute time E P y bedrock See Perg et al., 2001 for details of the method

10. One General Rule of Weathering • Granites are composed of quartz (25%), micas and feldspars (other ~75%). • When weathering is intense and the source rock is average continental crust, a basin fill should contain sand, and clay in the same proportion (depending on climate)

11. (1) Product composition

14. World Weathering Patterns

15. Walther’s Law

20. Sediment Routing • Weathering (in situ) • Chemical, Physical an Biological • Regolith • Sediment Yield • Computational Models • Patterns • Controls • Solute and Suspension • Modeling Landform Evolution • Relation between tectonics and sedimentation

21. Run-off • Run-off (surface water flow) connects land and ocean water reservoirs and moves sediments • Precipitation = Evaporation + + Soil water change + + Groundwater change + + Run-off

22. Sediment Routing • Weathering (in situ) • Chemical, Physical an Biological • Regolith • Sediment Yield • Run-off • Computational Models • Patterns • Controls • Solute and Suspension • Modeling Landform Evolution • Relation between tectonics and sedimentation

23. Computational Models Denudation Rate or loss of elevation per unit of time and unit of area in a given catchment area can be calculated from know sediment exit rates from a catchment area: dh/dt = (1-porosity)/density * total sediment mass discharge /unit time and area (7.7) (elevation change) is proportional to sediments removed Sediment Yield = sediment mass/unit / catchment area time

24. Sediment Yield from artificial traps Amazon: 79mm/1000 yr NW Himalaya: 400 mm /1000 yr Nile: 45 mm/1000 yr Sediment Yield from preserved stratigraphy Bay of Bengal: 200 mm/1000 ky

25. Sediment Routing • Weathering (in situ) • Chemical, Physical an Biological • Regolith • Sediment Yield • Run-off • Computational Models • Patterns • Controls • Solute and Suspension • Modeling Landform Evolution • Relation between tectonics and sedimentation

26. Global Pattern of denudation rates

27. Sediment accumulation thicknesses

28. Chemical versus Mechanical Denudation Rates

29. Sediment Routing • Weathering (in situ) • Chemical, Physical an Biological • Regolith • Sediment Yield • Run-off • Patterns • Controls • Solute and Suspension • Modeling Landform Evolution • Relation between tectonics and sedimentation

30. Controls on Sediment Yield • Drainage Area and Tectonic Activity • Vegetative Cover • Precipitation • High vs. low relief

31. Controls on Sediment Yield • Drainage Area, Tectonics

32. Low-relief vs. High relief Low relief: • erosion rates are limited by erosivity of transport processes, e.g. in dry environments this means availability of water but in LA this means how much sediment can be eroded from the Mississippi River Valley itself. High relief: • Erosion rates are held back by rock and soil strength. High relief assures availability of materials by rock falls, landslides. A high relief must be renewed bye.g., tectonic activity

33. Low-relief vs. High relief

34. Sediment Routing • Weathering (in situ) • Chemical, Physical an Biological • Regolith • Sediment Yield • Run-off • Patterns • Controls • Solute and Suspension • Modeling Landform Evolution • Relation between tectonics and sedimentation

35. Dissolved Solids • Run-off waters contain dissolved solid concentrations which depend on (1) precipitation, (2) weathering reactions in rocks and soil, and (3) the degree of evaporation. • Precipitation helps chemical weathering but steep slopes reduce the amount of time water is able to spend in the regolith. So, low-slope areas should produce more chemical weathering (General Rule) BUT that is not so in the Amazon, where most (85%) of solute comes from the Andes.

36. Concentrations • Arid areas have saltier waters and hence more dissolved solids e.g. Kazakhstan (1000-6000 mg/l) …… the Amazon has only 10 mg/l… but the Amazon takes 10% all river water so it may produce more dissolved compounds overall.

37. Precipitation, weathering rate and evaporation define water type High concentration of Na(+) through precipitation of CaCO3 Less weatheringlow concentration of Ca(2+) Colder climates- less dissolution

38. Observations • Principal cations in water are Ca(+2) • Principal anions are HC03 (-), S04 (2-) • Na (+) increases relative to Ca(+2) indicate that the Ca(2+) is precipitating out of solution • (80% dissolved load in rivers is made of Ca(2+), HC03 (-), S04 (2-), and SiO2) • Increase of Ca(2+) relative to Na(+) indicates greater chemical weathering, (because Ca is harder to dissolve and require more intense weathering to get into solution). • But composition reflects availability of ions in the source terrain.

39. Primary rock origins of solutes and their types

40. Observations • Most Na(+) and Ca(2+) ions come from weathering of secondary sources (salt and carbonates) • Dissolved SiO2 and K(+) come from silicates

41. Sediment Routing • Weathering • Chemical • Regolith • Sediment Yield • Patterns • Controls • Solute and Suspension • Modeling Landform Evolution • Relation between tectonics and sedimentation

44. Modeling Landform Evolution • Isostasy during denudation Height above sea-level (h) Future erosion (D) Sea-level hc Depth of compensation mantle

45. Modeling Landform Evolution • Isostasy during denudation Sea-level hc-D Depth of compensation mantle

46. Modeling Landform Evolution • Denudation removes material from the surface (drop in the head) • Rock is uplifted (from below because of isostasy) Change in elevation = rise of base – drop in head Surface rises to about 85% of its original height (P. 242)

47. Modeling Landform Evolution Mountain geometry • Planar geometry Height above sea-level = h - Height above sea-level = 2(h - ) Sea-level hc-D mantle

48. Modeling Landform Evolutionwith thermochronometers Apatite fission track analysis Below a certain temperature, natural damage tracks within apatite minerals do not heal. The number of tracks acts as a clock.

49. Modeling Landform Evolutionwith thermochronometers

50. Apatite fission track analysis X 200 X 1600 http://images.google.com/imgres?imgurl=http://faculty.plattsburgh.edu/mary.rodentice/images/research/apatite1.jpg&imgrefurl=http://faculty.plattsburgh.edu/mary.rodentice/research/Fission_Track.html&h=218&w=300&sz=19&hl=en&start=5&tbnid=urHg8C9toErWZM:&tbnh=84&tbnw=116&prev=/images%3Fq%3Dfission%2Btrack%26svnum%3D10%26hl%3Den%26lr%3D%26client%3Dfirefox-a%26rls%3Dorg.mozilla:en-US:official%26sa%3DG