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Weathering and Erosion Formation of Sedimentary Rocks

Weathering and Erosion Formation of Sedimentary Rocks. Weathering – the physical breakdown ( disintegration ) and chemical alteration ( decomposition ) of rock at or near Earth’s surface Erosion – the physical removal of material by agents such as water, wind, ice, or gravity.

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Weathering and Erosion Formation of Sedimentary Rocks

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  1. Weathering and ErosionFormation of Sedimentary Rocks • Weathering – the physical breakdown (disintegration) and chemical alteration (decomposition) of rock at or near Earth’s surface • Erosion – the physical removal of material by agents such as water, wind, ice, or gravity

  2. Sediment: weathered material derived from pre-existing rocks Sedimentary rock: consolidated sediment (compacted, cemented) plus fossils

  3. Clastic sediments seen during fieldtrip

  4. Clastic sedimentary rocks seen during fieldtrip

  5. insoluable

  6. basalt (Mg,Fe)2SiO4 (Mg,Fe)SiO3 pyroxine H4SiO4 in solution Mg2+ in solution Fe (III) hydroxide (insoluble, rust) CaAl2Si2O8 Ca-feldspar and NaAlSi3O8 Na-Feldspar Ca+2 in solution Na+1 in solution Al2Si2O5(OH)4 (insoluble, “clay”)

  7. granite SiO2 quartz SiO2 (insoluble, “sand”) CaAl2Si2O8 Ca-feldspar; NaAlSi3O8 Na-Feldspar KAlSi3O8 K-Feldspar Ca+2 , Na+1, K+1 in solution Al2Si2O5(OH)4 (insoluble, “clay”) (Ca,Na)2(Mg,Fe,Al)5(Al,Si)8O22(OH)2 amphibole (and also mica) Mg+2, Ca+2 , Na+1 in solution Al2Si2O5(OH)4 (insoluble, “clay”) Fe (III) hydroxide (insoluble, rust)

  8. in quartz sand in clay in rust River sediments are consistent with the composition of the continental crust

  9. Effect of surface area on weathering

  10. Climateand Weathering

  11. Hot and wet favors chemical weathering

  12. Cold and snowy favors mechanial weathering

  13. Why erosion is important • Life in the sea depends on it to supply critical nutrients. • It is responsible for the salt content of the sea. • It is the source of the basic materials to form sedimentary rocks. • It continually reduces and shapes the surface of the land.

  14. Sea water Where’s the Cl come from? Why no silica?

  15. Mechanisms of Erosion

  16. Mass Wasting The often catastrophic (geologically rapid) movement of material on the Earth’s surface is referred to as mass wasting. Such features constitute the most widespread of the natural geological hazards. the Slumgullion earthflow/landslide, Hinsdale County, CO

  17. Nevado Huascaran, Peru, 1970 It began high in the mountains as an earthquake-induced avalanche of snow and ice, but picked up glacial sediment on its way. It hit the towns of Yungay and Ranrahirca, 18 km away, at around 150 km/hr. The former town was completely buried. An astounding 66,000 people were estimated dead as a result of this massive debris avalanche.

  18. Mudslides: Costa Rica, June, 2000 The June 27 slide killed 10. Six were killed in the same place in 1993 mudslides.

  19. landslides This is a typical landslide. Note that materials hold together in more-or-less singular blocks. As is common, when the slide blocks reach a lower slope, they break up (becoming a debris flow in this case). The La Conchita landslide, near Santa Barbara, CA, Spring, 1995.

  20. Glaciers (mechanical) weathering

  21. Freezing action

  22. Freezing action

  23. Frost wedging

  24. Joint-controlled weathering

  25. Roots (mechanical) weathering

  26. Root Wedging

  27. Chemical Weathering

  28. Chemical Weathering

  29. Differential Weathering and Erosioncreates topography Slowly weathered and eroded - high (Morningside Heights, Palisades, Ramapo Mountains) Quickly weathered and eroded - low (sediments beneath Hudson River and west of Palisades)

  30. Differential Weathering

  31. Differential Weathering

  32. Differential Weathering

  33. Differential Weathering

  34. Differential Weathering

  35. Resistant cap rock

  36. Clastic Sediments from “clast” … little piece Can be associated with rivers, glaciers, wind

  37. Clastic Sediments and Clastic Sedimentary Rocks A. Sediments B. Sedimentary Rocks

  38. Energy and Depositional Environment

  39. Coarse-Grained Sediments Conglomerates Breccias

  40. Tillite Brian J. Skinner

  41. Worldwide sediment yield of major drainage basins

  42. Where erosion occurs…elevationa factor…highermoreerosion

  43. Meaning of rate100 tons per sq km per year 100 tons Rock density about 2.5 tons per cubic meter so 100 tons is about 40 cubic meters (a cube 3.4 m on edge) 1 sq km is 1,000,000 sq meters Spread 40 cu meters over 1,000,000 sq meters and get a layer 40/1,000,000 = 0.00004 meters = 0.04 millimeters thick So in 100 years, wear away 4 mm 1000 m 1000 meters

  44. Rivers and Sediments

  45. Migrationof meandersleads tocross-bedding crossbed from fieldtrip

  46. Deltas

  47. Cross-section of Deltanote that delta grows (progrades) towards sea

  48. Hjulstrom Curve

  49. Hjulstrom Curve Pebbles and cobbles Pebbles and cobbles: hard to get moving, an hard to keep moving

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