Sediments and Sedimentary Rocks Solidified Weathering Products Size Sorting The different minerals that form as weathering products have different characteristic grain sizes Un weathered material has largest grain size Quartz sand is 0 1 to 2 mm Clays are less than 0 001 mm 1 m Ca 2 Na 1 CO3 2 SO4 2 and Cl are dissolved Particle Sizes Particle Size Sediment Rock 25cm Boulder Conglomerate 6 25cm Cobble Conglomerate 2 60 mm Pebble Conglomerate 0 06 2 mm Sand Sandstone 4 60 m Silt Siltstone 4 m Clay Shale Size Sorting Gives Different Sedimentary Rocks Conglomerates are near source continental Sandstones are continental Eolian sandstones are desert deposits Alluvial sandstones are river deposits Shales are shallow marine salt water Limestones are also shallow marine Evaporites result from evaporation of seawater Conglomerates and Breccias Breccias are composed of coarse angular fragments Breccia fragments have not traveled far Conglomerates are composed of coarse rounded fragments Conglomerate fragments have traveled further Sandstones Arkose contains feldspar and is near source Fountain Formation Flatirons is made of arkose and conglomerates Eolian sandstones are desert wind deposits Commonly show cross bedding Alluvial sandstones are stream deposits Commonly have asymmetric ripples and channels Organic Sediments Swamp and bog deposits rich in organic matter lithify to form coal Peat is the first stage Lignite is peat that has begun to lithify Bituminous coal is an abundant energy source Anthracite is metamorphosed coal Petroleum and natural gas are also derived from organic sediments Shales and Mudstones Clay and silt can only be deposited in standing water Clays are layer silicates like mica and align Shale breaks along the layers and is said to be fissile Mudstones and siltstones are massive don t break along layers Limestone Limestone is made of calcite CaCO3 Most Phanerozoic limestones are biogenic formed by critters Seawater is saturated in calcium carbonate Calcite is more soluble in cold water than warm Dolomite is calcium magnesium carbonate CaMg CO3 2 Evaporites Evaporites are rocks deposited from evaporating seawater As seawater evaporates the sequence of minerals deposited is 1 calcite CaCO3 2 gypsum CaSO4 2H2O 3 halite salt NaCl 4 sylvite KCl Size Sorting Gives Different Sedimentary Rocks Conglomerates are near source continental Sandstones are continental Eolian sandstones are desert deposits Alluvial sandstones are river deposits Shales are shallow marine salt water Limestones are also shallow marine Evaporites result from evaporation of seawater
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