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105_06-weathering-soil-sed_rx_part_2 - Chemical Weathering...

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Unformatted text preview: Chemical Weathering Hydrolysis Acids also change feldspars to clay Hydrogen ions (H+) replace potassium (K+) and the feldspars release silica, leaving clay minerals Hounds Tor, Dartmoor. Granite outcrop Factors in Weathering Climate Climate – Water and temperature Reaction Reaction 2X increase with each 10°C increase in temperature 10° Mineral resistance to weathering Time Time – More time = more weathering Organisms Organisms – Plants – Animals and Bacteria Mineralogy Mineralogy – Bowen’s Reaction Series 1 Effects of Weathering Effects of Weathering Rounded boulders = spheroidal spheroidal Rounded boulders spheroidal = spheroidal weathering weathering Effects of Weathering What is Soil and How Does it Form? Soil Soil is a mixture of weathered rock material, water, air, and organic matter Rounded boulders = spheroidal spheroidal weathering What is Soil and How Does it Form? The The Soil Profile – O horizon organic organic matter Factors controlling soil formation Parent Parent material – Grain size – Composition – A horizon top top soil, intense biological activity – B horizon subsoil, subsoil, zone of accumulation – C horizon little little organic matter, partially altered parent rock Climate Climate Topography Topography Vegetation Vegetation Time Time 2 Factors controlling soil formation Topography Topography Factors controlling soil formation Climate Climate and vegetation Reaction Reaction 2X increase with each 10°C increase in temperature 10° Soil erosion Soil erosion Destruction Destruction of rainforest or other vegetation cover increases erosion Sedimentary Rocks Rill erosion in Michigan field 3 Sedimentary Rocks Weathering Weathering Erosion Erosion Transportation Transportation (running water, wind, glacial ice) Deposition Deposition (in various environments such as rivers, deltas, beaches) Lithification Lithification (compaction, cementation) Sedimentary Rocks Sediment Sediment – Loose, solid particles Physical Physical and chemical products of weathering Sedimentary Sedimentary rock – Formed when sediment is lithified – Thin layer, barely 5% of the Earth’s crust – 75% of exposed rocks on Earth Sediment Size Sediment Transport Grain Grain size – Wind ⇒ fine grained (silt) – Ice ⇒ all sizes – Water ⇒ all sizes Particle Pebble Sand Silt Clay Size 2 - 64 mm Loose Sediment Gravel Sand Silt Clay Consolidated Rock Conglomerate or Breccia Sandstone Siltstone Claystone, Claystone, mudstone, and and shale 0.063 - 2 mm 0.004- 0.063 mm 0.004<0.004 mm Wind deposit Ice deposit Sediment Transport Driven Driven by pull of gravity – Water – Wind – Ice Sediment Transport 10 10 billion tons of detrital sediment is deposited into the world’s oceans annually 4 Sediment Transport Sediment Transport Grain Shape Abrasion and rounding angular SubSub-rounded Sediment Transport Grain Shape SubSub-rounded Limestone: 11 km Granite: 8585-335 km Rounded Sediment Transport Sorting Grains separated by size, shape, or density Wind: Wind: least viscous, well sorted sand Water: Water: intermediate viscosity, transports gravel Ice: Ice: high viscosity, typically poorly sorted Ice Wind Sediment deposition Sediment Sediment can be carried a considerable distance from its source, eventually eventually coming to rest in in a depositional environment – Continental – Transitional – Marine Lithification of Sediments How How does sediment turn into rock? – Compaction – Cementation – Crystallization All processes remove pore space between pore grains. 5 Lithification of Sediments Compaction Compaction – Reduces the volume of sediment Cementation of Rocks Cementation Cementation – Minerals precipitate between grains as groundwater moves through pore spaces Cementation of Rocks Pore space Calcite cement Shells Lithification of Rocks Crystallization Crystallization – Minerals precipitate from solution to form entire rock body. (Ex: Limestone) Photomicrograph Types of Sedimentary Rocks Clastic Clastic – Fragments of sedimentary, metamorphic, and igneous rocks cemented together Groups of Sedimentary Rocks Clastic Clastic – Consist of fragments of sedimentary, metamorphic, and igneous rocks – Pieces can have sizes from fistfistsize to barely visible: classification - names – Silicates There There are lots of them Resistance Resistance to weathering (quartz) Chemical Chemical (inorganic) – Precipitants from dissolved minerals Limestone, Limestone, Halite Biochemical Biochemical (organic) – Plants and animal shells or skeletons Coal Coal 6 Detrital Rocks Conglomerates Conglomerates – Grains are rounded Detrital Rocks Sandstone Sandstone – Silicate minerals – 0.64 – 2 mm – Quartz sandstone (Arenite) > 90% Quartz 90% Breccias Breccias – Grains are angular – Feldspathic sandstone (Arkose) ~ 25% Feldspar 25% ~ 75% Quartz 75% – Lithic sandstone (Graywacke) ~ 25% dark fragments (volcanic) 25% ~ 20-30 % Feldspar 20~ 45-65% Quartz 45- Detrital Rocks Siltstone Siltstone – Like mudstone, but grains barely visible Mudstone Mudstone - Shale – Clay minerals and mica – < 0.004 mm (not visible) – Low energy Lake, Lake, lagoon, floodplains, deep marine Shale exposure Chemical and biochemical sedimentary Rocks Consist Consist of ions and compounds released by chemical weathering – precipitated by chemical reactions (inorganic) or by – metabolism of organisms (organic) Chemical and biochemical sedimentary Rocks Inorganic Inorganic – Very fine grained – Limestones Calcite Calcite Bahamas Bahamas and Florida Caves Caves – Evaporates Halite Halite Gypsum Gypsum 7 Salt lake: formation of evaporites Salt lake: formation of evaporites 8 ...
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