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Mass Wasting Erosion Soils Weathering Weathering: the physical and chemical breakdown of rock – exposed to wind, water, ice, and living organisms Regolith: loose or broken rock layers resulting from weathering Regolith covers most of the earth. Soil: the upper-most layer of regolith that supports life Do “things” last for ever ? Consider : new concrete a 1955 Chevrolet Rocks can be broken down or chemically altered on the earth’s surface. Mechanical Weathering: Rocks are physically broken down by various surface processes into smaller parts without changing physical properties. Chemical Weathering: Rocks are altered from one form to a completely new form with a different set of physical properties. I weathering Discuss with a friend: 1. Describe the difference between mechanical and chemical weathering. 2. Give two examples of MW and CW you have observed. I will get an A on my exams and quizzes Mechanical Weathering – the breaking down of rocks How do we expose “more surface” area for chemical weathering to do its job ? Let’s show some surface Rock Less surface area More surface area Increased mechanical weathering accelerates chemical weathering. Types of Mechanical Weathering Processes Frost Wedging: repeated cycles of freezing and thawing Water rock rock Water Freezes (expands) pieces break off (watch for falling rock) Dominantly takes place in freezing / thawing areas Unloading – reduction of pressure from overlying rocks -- take the pressure off me. overlying rocks granite pluton granite pluton eroded and uplifted Frost Wedging – rocks are broken into plates and split apart. Exfoliation Dome – granite is “sheeting” from loss of pressure due to unloading processes. Types of Mechanical Weathering Processes Biological Activity – breaking down rocks through • animal burrowing • humans • plant roots Human intervention Animal burrowing Plant root weathering I mechanical weathering Discuss with a friend: 1. Why is MW important? 2. Briefly describe how frost wedging, unloading and biological activity contributes to mechanical weathering I will get an A on my exams and quizzes Chemical Weathering Rocks are chemically altered producing a new compound Why would a perfectly good rock want to change it’s appearance? STABILITY! Rocks require stability and achieve equilibrium with it’s surroundings •Most rocks are not chemically stable at the earth’s surface •Minerals (compositions) change to become stable at surface conditions What common agent can begin the process of chemical alteration????? •The Universal Solvent – WATER (H2O) How would we speed up the action of water? Rain + ????? What in the atmosphere is added to water to create a weak acid? H2O (rain) + CO2 (atmosphere) = H2CO3 (carbonic Acid) Let’s weather some granite with the natural acid H2CO3 Granite – the most abundant continental rock weathering the potassium feldspar (orthoclase) orthoclase carbonic acid water 2KAlSi2O8 + 2(H+ + HCO3) + H2O kaolinite clay Al2Si2O5(OH)4 + 2K + 2HCO3 + 4SiO2 Granite has been chemically weathered and broken down into individual grains. in solution Reduced to Clay I Chemical weathering Discuss with a friend: 1. What is the universal solvent? 2. How is carbonic acid naturally Produced? 3. How would you describe the “last” or most reduced material ----- the end product of chemical weathering? I will get an A on my exams and quizzes. Soil – product of weathering containing solids, liquids, and gas. What’s in your soil? CLAY Loam – dominant soil fraction Humus – partially decayed organic material CO2/Air – fills the soil voids Water – wets the soil SAND and carries high levels of dissolved substances SILT Soil Profiles: • horizons: a layer of soil with distinctive physical and chemical properties. • sequence of soil horizons from the surface to the underlying bedrock O- Organic matter (humus) A- Dark layer mixed with mineral and organic matter E- light-colored layer produced from removal of soluble material “leaching” B- accumulation of clay C- weathered parent rock O A E B C Factors that influence soil formation: • Parent Material: • residual regolith – soil forms emplace or “insitu” Soil forms and weathers emplace from parent material. • transported regolith – regolith that is moved by rivers, wind, and ice transported river transported deposits regolith on Mars Factors that influence soil formation: • Climate – soil profiles differ around the world which is directly influenced by climate arid soils vs. tropical soils • Living organisms – a HUGE influence on soils Plants make organic matter. (humus) – animals mix the soil and recycle air and water. • Topography – the contour or “slope” of the land • Time – the longer the time the more mature a a soil becomes --- 1000’s of years Classification of soils Soil Taxonomy – Soil classification is based on physical/chemical properties of a soil profile, influenced by climate, living organisms, topography, and time. --- How many different soils are there? Six categories of soil classification: order sub-order great groups 12-orders sub groups family series Broadest Specific 19,000 -series 12-basic soil orders: Names of soils are derived from Latin/Greek. Latin = solum – soil Alfisols (High-Nutrient Soil) Andisols ((Volcanic Soil) Aridisols (Desert Soils) Entisols (New Soils) Gelisols (Permafrost Soils) Histosols (Organic Soils) Inceptisols (Young Soils) Mollisols (Prairie Soils) Oxisols (Tropical Forest Soils) Spodosols (Conifer Forest Soils) Ultisols (Low-Nutrient Soil) Verisols (Swelling Clay Soil) Distribution of Earth’s soils What soil type (order) characterizes the San Joaquin Valley? Alfisols I Sedimentary Rocks Discuss with a friend: 1. Draw a “typical” soil profile and identify the common horizons. 2. Identify at least 3 factors that influence soil formation. 3. Describe the difference between regolith and soil. I will get an A on my exams and quizzes. Sedimentary Rocks • Ig/met rocks represent 90-95% of the Earth’s crust. • Sediment and sedimentary rock make up 75% of the Earth’s surface • sediment covers the ocean floor --- except for mid-ocean ridges areas • sedimentary rock concentrated at the surface interacting with the atmosphere, hydrosphere, lithosphere, and biosphere Sediment/Sedimentary Rock Chapter-6 Sediment Compaction Cementation Weathering Transportation Sedimentary Rock Cycle Deposition Lithification Weathering Transportation Deposit Sediment Sediments are separated into 3-broad categories: • Detrital (clastic) sediments: inorganic grains or mineral fragments ranging in size from boulders to clay particles (flour size) • Chemical sediment: formed by the precipitation of minerals dissolved in lakes, rivers, or seawater environments • Biogenic (bioclastic) sediment: sediment composed of animal and plant remains or material precipitated by biological processes To be a sedimentary rock, it must be lithified. Lithification: processes by which sediment is transformed into sedimentary rock Sediment can be lithified in three common processes: Compaction: Overlying weight of the sediment “squeezes” and compresses pore spaces, which pushes particles together. A B A. loose, unconsolidated sediment with abundant pore space B. compacted, compressed sediment with reduced pore space Cementation: Pore water is expelled from voids, and rising water carries iron, calcium carbonate, and silica which precipitates as geological glue (cement) holding the grains. Grains are cemented together by three types of cements: •iron cement •calcium carbonate cement •silica cement Lithification processes Recrystallization: Overlying pressure causes less stable minerals to convert to more stable minerals, producing new substances that cement pre-existing grains. Overlying pressure Grain boundaries convert to more stable mineral compositions, “cementing” grains together. Detrital (Clastic) Sediment: Classification based on grain size lithified gravel sediment ranging from pea-sized to larger conglomerate >2mm lithified sand-sized particles (fine to coarse sandpaper) sandstone lithified finer particles – size of table salt finest sedimentary particles (flour-size) lithified 1/16 mm siltstone 1/256 mm shale Chemical Sediments and Sedimentary Rocks Chemical Sediment: sediment formed by the precipitation of minerals dissolved in a lake, river, or seawater Ca+2 +2 SO2-2 Ca SO2-2 Ca+2 Ca+2 SO2-2 Ca Ca+2 SO2-2 +2 . All surface water and groundwater contain dissolved ions, creating a venue for precipitation of chemical sediment. Ca+2 Precipitation of chemical rocks takes place in two ways: • Plants and animals alter the chemical balance of the water body (lake, ocean). Increasing amounts of calcium carbonate cause precipitation of limestone. • evaporation of chemically saturated water bodies Evaporation of chemically saturated water creates a chemical sedimentary rock (evaporite). Na+ Cl- Na+ Cl Cl + + Na Na ClEvaporation NaCl a lake containing sodium (Na+) and chlorine (Cl-)--free ions Lake water is evaporated, concentrating sodium and chloride ions (saturation). Sodium and chlorine combine to form halite (table salt). 27 The Great Salt Lake, Utah (evaporite halite) As lake becomes saturated, density of water increases. Utah Chemical – sedimentary rocks that have been precipitated or are the result of evaporation Gypsum – evaporite CaSO4 Halite – evaporite NaCl Limestone-precipitated calcium carbonate Verities of Chert-SiO2 Biogenic Sediments and Biogenic Rocks: Biogenic sediment is composed of organic remains of plants and animals (bioclastic rocks). 30 • shell, bones, teeth, plant fragments, wood, roots Common Biogenic Rocks: • Limestone • most abundant biogenic sedimentary rock • composed of calcium carbonate CaCO3(calcite, dolostone, aragonite) • lithified shells, skeletal material • Chert • composed of silica SiO2 • precipitated silica shells (made by sea animals) that protect microscopic sea animals – Animals die, and silica shells sink, creating layers of chert beds on the ocean floor. “When the animal dies, it loses the chert off its back.” Biogenic (bio-clastic) rocks – result from animal and plant secretions -- The term “clastic” indicates that these rocks contain fossils or parts of plants, shells, compacted plant material Animal parts Cemented shell fragments Fossil Limestone Microscopic fossils 32 Coquina Chalk White Cliffs of Dover, England • made of microscopic hard parts of organisms • soft, porous material Common Biogenic Rocks 31 Peat to Coal • accumulated remains of terrestrial plants • with time and pressure ---- peat • continued pressure and lithification ------ coal Peat lithification metamorphism Anthracite coal Bituminous coal Inorganic (Chemical) Bio-clastic (Biochemical) Detrital sedimentary rocks the most common sedimentary type Sedimentary Rock Classification Chart Inorganic (Chemical) Sedimentary Rock Classification Summary Tree Sedimentary Rocks are divided into 3-classification categories: Clastic sediments Chemical sediments Bio-clastic (chemical) sediments formed by precipitation composed of inorganic grains classification based on distribution of grain sizes Conglomerate from plants and evaporation animals processes composed of “animal parts” Classification based on lack of grains and chemical composition Gypsum (CaSO4) Sandstone Siltstone Shale Halite (NaCl) Limestone (CaCO3) I Chemical weathering Discuss with a friend: 1. Briefly describe the textural differences between the 3 categories of sedimentary rock classification. I will get an A on my exams and quizzes. What do sedimentary rocks tell the earth scientist? These rock “layers” were deposited one layer at a time and lithified. strata The banded appearance is known as bedding or groups of layers called strata. The boundary between each stratum is called a bedding surface. By observing the sedimentary rock type (clastic, chemical, biogenic) and depositional patterns, an earth scientist can decipher the geologic history – like reading pages in a book. Sedimentary Environments: • accumulation of sediments characterized by physical and biological conditions • textural and compositional characteristics of sediment are “clues” that dictate the type of sedimentary environment. • Continental Sedimentary Environment • dominated by stream erosion/deposition • wind erosion producing dune landscapes (eolian environment) • characterized by playa deposits (evaporites) • glacial deposits – unsorted particles (clay to boulder size) • Marine Sedimentary Environment •Shallow marine (200m to surface) • boarders the worlds continents (continental shelf's) • sediment type dependent on water depth, climate • receives large quantities of continental sediment • warm climates – carbonate mud's dominant • cold climates – higher in silicate clasitc material • Deep marine • includes all the deep ocean floor • predominately fine particles “settling” on the ocean floor • Transitional Sedimentary Environment • shoreline represents the transition zone between continental and marine environments • beach, spits, barrier islands, delta type environments Transitional Continental Continental Continental Continental Continental Transitional Deep Marine Shallow Marine