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) H
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 m
bedrock

9. P (concentration ) of radionuclides is a measure of absolute timey
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
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 ( 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 Evolution with 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 Evolution with thermochronometers

50. Apatite fission track analysis
X 200
X 1600

51. Apatite fission track analysis
X 1600
X 200
U(238) decay damages mineral structure. Above 100 C and over about 1 My the damage will anneal itself completely.
PAZ is the partial annealing zone C
Below 100 C track number acts as a geological clock. Track length is larger if the cooling is quick (lava flows)

52. Apatite fission track analysis
X 1600
X 200
If a geothermal gradient for an area is know, AFT analysis can provide information how long ago a sample passed through the PAZ. Several samples can be used to calculate rates of uplift (i.e., not denudation) from which denudation rates can be calculated.

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

56. Tectonic-Sedimentary model

58. Walther’s Law

59. Walther’s Law
Interpretation criteria
Mark erosional tops and bases
Identify sequence packages
Weight extrapolation

60. Walther’s Law