Formation of Soil Resources1

Formation of Soil Resources1 - Summary of previous two...

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11/21/2002 ESM 203 - Weathering 1 1 ESM 203: Formation of Soil Resources Biogeochemical Role of the Lithosphere Jeff Dozier & Tom Dunne Fall 2007 2 Summary of previous two lectures square6 Global tectonic processes generate global patterns of rock types and landscape types (defined by their form and functioning) square6 Lithosphere reacts with atmosphere, hydrosphere, and biosphere square6 Incorporation of water into subducted sediments, tectonic and volcanic breakage and erosion of rocks, chemical reactions square6 Intensity of interaction varies with the type of geologic environment square6 Interactions most intense at plate margins 3 These interactions … square6 Sustain the nutrition of the biosphere, mainly through release of lithologic elements into solution in hydrosphere square6 Generate a water-holding soil that sustains primary production square6 Keep some ecosystems impoverished square6 Create some toxic hydrochemical and soil environments square6 Cause high rates of erosion and sedimentation square6 Margins of mountain belts and sedimentary basins (downwarps in Earth’s crust) square6 Major floodplains and deltas square6 Sedimentation stores rock minerals, carbon, and incorporated solutions square6 Modulates CO 2 content of the atmosphere and ocean over the long term (~10 4 yr) by incorporating CO 2 into weathered minerals 4 The effects result from a set of biogeochemical processes called weathering, defined as square6 Mechanical disintegration and chemical decomposition of rock minerals in situ near Earth’s surface (within ~1 km), and … square6 Short-distance translocation of the dissolved substances within the near-surface environment
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11/21/2002 ESM 203 - Weathering 2 5 General weathering“reaction” ‘Primary’ rock minerals + H 2 O, CO 2 , HNO 3 , O 2 , organic acids, ± changes in temperature and pressure Solutes (Na + , Ca 2+ , K + , Fe 2+ , Mg 2+ , Zn 2+ , etc.) Solid residuum ‘Secondary’ minerals separated into fragments (clay to gravel), coated with precipitates of amorphous oxides, storing cations and trace metals 6 General weathering“reaction” ‘Primary’ rock minerals + H 2 O, CO 2 , HNO 3 , O 2 , organic acids, ± changes in temperature and pressure Solutes (Na + , Ca 2+ , K + , Fe 2+ , Mg 2+ , Zn 2+ , etc. temporary storage in soils Solid residuum ‘Secondary’ minerals separated into fragments (clay to gravel), coated with precipitates of amorphous oxides, storing cations and trace metals To groundwater and streams (water quality) 7 Mechanical weathering square6 Unloading or pressure release square6 Crystal growth (salt or ice) square6 Create microfractures and joints in rocks that allow penetration of water 8 square6 Solution of carbonates , e.g.
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