NRES 201 Lecture 4 Outline of Last Lecture I Introduction to soil physical properties II Soil color III Soil texture IV Soil structure V Soil consistence Outline of Current Lecture VI Nature of soil genesis VII Rocks the basic ingredient of soils VIII Parent Materials a Residuum b Colluvium c Alluvium d Marine sediments Current Lecture How 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 rock Four soil forming processes I Transformation a Chemical or physical changes in soil constituents b Destruction or synthesis c Either produces something new or destroys something old II Translocation a Movement between horizons or within a single horizon b Water is the transporting agent III Additions a From external sources IV Losses a 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 Diorite These 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 Shale Metamorphic rocks Formed from igneous or sedimentary rocks under extreme temperature and pressure and there are an endless variety Ex Marble Quartzite Slate Elemental 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 animals o 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 periods o Possible agents Gravity Flowing water Glaciers Wind o Transport often leads to sorting by size Importance to soil properties o Texture Course texture from sandstone Fine texture from shale Affects drainage and aeration o 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 moving water 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 areas
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