NRES 201 Lecture 4 Outline of Last Lecture I. Introduction to soil physical propertiesII. Soil colorIII. Soil textureIV. Soil structureV. Soil consistenceOutline of Current Lecture VI. Nature of soil genesisVII. Rocks, the basic ingredient of soilsVIII. Parent Materialsa. Residuumb. Colluviumc. Alluvium d. Marine sedimentsCurrent LectureHow soils form - natural process that occurs at the surface of the Earth- Going on between the geological materials and atmosphere- Soils are forming gradually over time- The parent material comes from rockFour soil forming processes:I. Transformationa. Chemical or physical changes in soil constituentsb. Destruction or synthesis c. Either produces something new or destroys something oldII. Translocationa. Movement between horizons or within a single horizon b. Water is the transporting agentIII. Additionsa. From external sourcesIV. Lossesa. To the external environment Igneous rocks - Originate from molten magma below the Earth's crust. Form by the cooling of volcanic lava and is very rich in minerals. Ex. Granite, Basalt, DioriteThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.Sedimentary rocks - Formed from igneous rocks. Sediments settle under water and recement and eventually form. They are the dominant form of rock. Ex. Sandstone, Limestone, ShaleMetamorphic rocks - Formed from igneous or sedimentary rocks under extreme temperature and pressure and there are an endless variety. Ex. Marble, Quartzite, SlateElemental composition: Oxygen and silicon are the most common elements because silicate minerals make up more than 90% of the Earth's crust.Parent Materials:- Formed by weathering, o Rocks disintegrated by: Temperature changes, erosive action of water, ice, and wind, plants and animalso Rocks decomposed by: Hydrolysis (a group of reactions where water splits and then takes part in some sort of chemical reaction) *very important process in weathering, Hydration (addition of water), Carbonation (addition of carbonate), Oxidation (removal of electrons), Dissolution (erosion/ also acidic water dissolution)- Potential for transport o Inorganic parent materials do not necessarily form in place. They may have transported from one site and deposited to another. Transporting agents have acted over long periodso Possible agents: Gravity, Flowing water, Glaciers, Windo Transport often leads to sorting by size- Importance to soil propertieso Texture: Course texture from sandstone Fine texture from shale Affects drainage and aerationo Soil reaction: (toward the issue of acidity and alkalinity) Alkalinity from limestone Acidity from sulfide - rich shale Affects natural vegetation and chemical weathering o Mineral composition Affects clay mineralogy and land use Soils are more fertile when there is a high content of minerals that supply:Calcium, Magnesium, Potassium Native vegetation shifts towards species having low fertility requirements:Kinds of Parent Materials: Residuum, Colluvium, Alluvium, Marine Sediment Residuum - Derived from rock that weathers in place and often the parents material for older soils. No transporting agent. You would find in the mountainous regions. Colluvium - Material moved by gravity and deposited at the base of steep slopes. It is unstable and prone to landslides and is variable in composition. Alluvium - Transported by flowing water. It is the stuff that is laid down near floodplains. Floodplain soils are nearly level and highly fertile. Alluvial soils are prone to flooding.Deposition can occur in - Deltas: Formed at the mouth of some rives, as sediments deposit from slow - movingwater. - Freshwater lakes: Known as lacustrine deposits. Analogous to delta formation. o Lacustrine soils are layered, fine textured, and poorly drained. Marine Sediment - Gradual accumulation of sediments carried by stream flow into oceans, estuaries and gulfs. A coastal plain builds up over time. - Acidification occurs during soil formation due to sulfide that is in these
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