Dig ditch down in the soil to reveal soil profile layers horizons Top most A

Dig ditch down in the soil to reveal soil profile

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- Dig ditch down in the soil to reveal soil profile (layers – “horizons”) - Top most – A horizon – rich in humus, but has lost all “soluble” material. Contains clay, quartz - Next layer – B Horizon – little or no humus, but rich in iron oxides and soluble material from A horizon - Lowest – C Horizon – grading into decaying/broken bedrock - Climate and Soils - Different types of soils are formed form different starting rocks (igneous, sedimentary) under different climatic conditions - Where we have very hot, humid weather acting on rocks for long time (e.g. the tropics), resultant soils tend to be poor for agriculture - Supports lush vegetation initially, but “no lasting power.” People practice slash and burn tactics - Paleosols – ancient soils preserved in rock record (e.g. northern Arizona). Study of these unravels details of ancient climates. Thus paleosols indicate that little free oxygen was present in the atmosphere billions of years ago. - Human activity – building houses, shopping malls, highways, deforestation and causing acid rain – has speeded up weathering. Have also loaded soil in areas with salt, pesticides, toxic chemicals, that slowly leak into groundwater. - Raw material of sediments - In addition to soil, get sand, silt, clay, iron oxides ( detritus – broken grains) as major components going into detrital sediments formed elsewhere, Can be seen - Also have dissolved calcium bicarbonate and salt carried by running water, that on arrival at destination (lakes/oceans) can form biochemical sediments, Cannot be seen CHAPTER 5 Sediments and Sedimentary Rocks - Much of the earth’s surface (including sea floor) is covered by sediments. Mostly derived by weathering of rocks on continents. All processes occur at or close to earth’s surface (low temp and pressure) - Studying sediments and sedimentary rocks help us to understand Earth’s climate in the past, changes in weather processes - General Processes involved (in order): 1. Weathering of rocks 2. Erosion – removal of material formed by (1) above 3. Transport of materials – by rivers, glaciers, wind 4. Deposition – particles settle or precipitate out. Sediment formed 5. Burial – layers of sediment accumulate, compacting older layers 6. Diagenesis – pressure, heat, chemical reactions, “lithify” (harden) sediments to form sedimentary rocks - (1) and (2) yield both broken grains (detrital or clastic material) as well as dissolved material - Products in clastic part depends on starting rock type and intensity of weathering - Feldspar alter relatively easily to form clay minerals; if sediment contains feldspar, it denotes low amount of weathering
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- At highest weathering amounts, only quartz and clay minerals survive. Give rise to the two main types of clastic sedimentary rocks – sandstones (quartz dominant) and shales (clay dominant) - Biochemical sediments form from seawater – undissolved mineral remains of organisms, as well as minerals precipitate from sea water - Transportation - Most sediments are transported by water or air currents. Rivers play a major role. Strength of
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  • Spring '08
  • idontknow
  • Sedimentary rocks

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