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Download Weathering - Bryn Mawr College
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Weathering • The process of natural decay • Changes that occur to rocks as a result of exposure to atmosphere and water Mass Wasting Erosion Minerals form in equilibrium Granite Peridotite Igneous and Metamorphic rocks most susceptible to weathering Physical Weathering Breakdown of rock into small fragments by physical processes without a change in chemical composition. Chemical Weathering Rocks are decomposed, the internal structure of minerals is destroyed, and new minerals are created. Chemical + Physical Weathering Fractures and Joints Other planes of weakness Sheeting The release of lithostatic pressure do to uplift or denudation Sheeting The release of lithostatic pressure do to uplift or denudation Ice Wedging Ice Wedging Biological Influences Spheroidal Weathering Differential Weathering Talus Chemical Weathering Chemical Weathering Dissolution A processes whereby a mineral passes completely into solution Chemical Weathering Dissolution Hydrolysis A chemical reaction wherein water breakdown other minerals Acidic Water Water that contains excess hydrogen ions (H+) Acid Hydrolysis Dissolution involving slightly acidic water. H2O + CO2 H+ + H2CO3 (Carbonic Acid) CaCO3 + H2CO3 (Calcite) (Carbonic Acid) Ca2+ + 2HCO3(Calcium bicarbonate) Acid Rain Clay Soil Acid Hydrolysis & Secondary Minerals Involves the formation of new minerals in addition to the dissolved ions. 2NaAlSi3O8 + 2H2CO3 + 9H2O (Na - Plagioclase) (Carbonic Acid) (Water) 2Na+ + 2HCO3- +Al2Si2O5(OH)4 (Dissolved components) (Clay) Oxidation Rusting – when Oxygen combines with Iron to form Irod Oxide 4Fe + 3O2 2Fe2O3 (Hematite) Oxidation Rusting – when Oxygen combines with Iron to form Irod Oxide 2H2O + 4O2 + FeS2 (Pyrite) 2H2SO4 + FeO(OH) (Sulfuric Acid) (Goethite) Things that influence the weathering of Rocks: •Mineral Composition •Rock Texture •Climate Granite Basalt Sandstone Limestone Regolith A blanket of loose debris that forms a cover over the landscape. Regolith A blanket of loose debris that forms a cover over the landscape. • cm to 100’s m • Function of:Rock Type Function of:Time Exposed Function of:Physiography Function of:Climate Uppermost layer of regolith - SOIL •Composed of: •Small Rock Fragments •New Minerals formed by Weathering •Decomposed Organic Matter Soil Soil Al and Fe are insoluble and thus accumulate in soils. •Bauxite (Al – rich mineral) Sedimentary Rocks Weathering Transport Erosion Deposition Depositional Environments Alluvial Shallow Marine Glacial Lacustrine Coastal Beach Deep Sea Fluvial Eolian Coastal Swamp Deltaic Fluvial Systems Alluvial - Fan Systems Eolian Systems Glacial Systems Lacustrine Systems Delta Systems Coastal Swamp -Lagoon Systems Shoreline Systems Reef Systems Shallow Marine Systems Deep-Marine System Biochemical and Chemical Sedimentary Rocks • Sediment formed during the growth of organisms such as algae, coral and vegetation • Formed as a product of inorganic chemical precipitation (lakes or shallow seas) Biochemical and Chemical Sedimentary Rocks Limestone – •Most abundant chemically precipitated rock •Primarily CaCO3 •Forms from both Biochemical and chemical processes Chalk – skeletal limestone in which fragments are from microcrystalline plants and animals Micrite – microcrystaline limestone that forms in quite water where CaCO3 is precipitated by algae. Foraminifera - Protozoan Coccolith Coquina – consists almost entirely of broken fragments of calcareous shells that are held together by a small amount of calcite cement Oolitic Limestone – composed of small semispherical grains of CaCO3 Travertine – Inorganic CaCO3 precipitated from natural springs and in caves. Stalactite Stalagmite Calcium Compensation Depth ~4500 m depth Average surface temperatures Dolostone – a carbonate rock composed of dolomite or magnesium CaCO3. Form as a result of: • Direct precipitation out of the water column • Reaction of limestone with magnesium rich groundwaters Chert – rock composed of microcrystalline quartz Flint (black) Jasper (red) Diatoms Radiolarian Organic compounds derived from living Organisms Hydrocarbons •Oil •Natural Gas Coal Evaporites –inorganic chemically precipitated rock •Salt (Halite) •Gypsum •Anhydrite Sedimentary Stratigraphy Strata / Beds Stratification Stratigraphy Bedding Planes Formation – Fundamental unit in stratigraphic classification. A body of rock identified by rock characteristics and stratigraphic position. Mappable at the Earth’s surface or subsurface Red Wall Ls Mauv Ls Bright Angle Shale Tapeats Ss Cross-Bedding Turbidity Currents Turbidity Currents Turbidity Currents Graded Bedding Bed Surface Markings Clues to past Environments Ripple marks Mud Cracks Mud Cracks Trace Fossils Trace Fossils Fossils Transgression & Regression Transgression & Regression Transgression & Regression
