Earth Dynamics Class 4Weathering, Sediments, & Sedimentary Rocks Types of Sediments Classic Sediments are pre-exisiting rock fragments. Chemical sediments are dissolved minerals that recrystallize during evaporation. Biologic processes (bioclastic) can form both clastic and chemical sediments. Plankton use minerals to form their shells Cochena ? shell pieces compressed Transportation Erosion causes movement of sediment from source area and deposit to a new location Many particles are rounded during transportation. Particles that aren?t rounded = angular sediments = not transported very far. Sedimentary Processes Sediment sorting = sediments sorted by size = settling out of seawater. Poorly sorted = sediment deposited close to source. Deposition ? sediments come to rest, are deposited & horizontal layers form over time. Examples: Rivers, Lakes, Delta, Beach, Desert, Continental shelf, Ocean, Carbonate reef, tidal flat, submarine fan (marine landslide) Lithification ? Sediments deposited that over time have been deeply buried and covered/compacted. Crystallization of new mineral material that act as cement to bind the grains together. Minerals making up silt & clay tend to be flat. Fissle = have layers in which rocks can break. Silt vs. clay ? if tastes gritty like toothpaste = has silt / clay isn?t gritty Classification of sediment in size: Gravel > 2mm Conglomerate (rounded pebbles), Breccia (angular clasts)Sand 1/16-2mm Quartz Sandstone (color comes from cement), Arkose (contain angular fragments of potassium feldspar)Silt 1/256-1/16mm Siltstone, Mudstone, ShaleClay < 1/256 Claystone (fissle) Chemical Sedimentary RocksCalcite ? Limestone* Gypsum ? Rock GypsumDolomite ? Dolostone* Halite ? Rock SaltSiO2 ? Chert/Flint *react with HCl Organic Sedimentary RocksChalk (made of microscopic shells of foraminifera)Fossiliferous LimestoneCochenaCoal (deposited in a swamp) Sedimentary Structures Bedding Flat uniform horizontal (Grand Canyon) Cross bedding (produced by movement of sand by a current) Tangential (flatten out at bottom) ? flat part of bed going down Paleo-current direction Mud cracks Ripple Marks Assymetric ripples from crossbedding Symetric ripples from waves Fossils ? petrified wood ? NE Arizona ? quartz crystals from volcanic eruption.
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