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Sedimentary Rocks Terms to know Transportation – currents of wind and water and the movement of glaciers, transport particles downhill or downstream Deposition – (also called sedimentation) – sediment particles settle out as wind or water currents slow, or as glacier edges melt Terms to know – As layers of sediment accumulate, older deposited material is compacted and buried in the crust Burial – Physical and chemical changes, including pressure, heat and chemical reactions. Once this occurs, a new identity for the rock results Diagenesis Categories of Sedimentary Rock Clastic Chemical Organic Sedimentary Rocks •formed by the lithification of unconsolidated sediments. •lithification is a process of compaction and cementation The weight of overlying sediments causes sediments to be reduced in volume by 40% • There is also an increase press and temp • The heat causes some minerals to melt, like silica and calcite • these go into solution and fill spaces between remaining grains. • They then harden to form a glue or cement: cementation Clastic Rocks form from bits and pieces of other rocks Weathering and erosion by rivers, ice, wind and waves carry sediment down to the sea Major Classes of Clastic Sedimentary Rocks Conglomerate Coarse grain particles Boulder larger than 256mm About 10 inches Cobble 256-64mm about 2.5 inches Pebble 64-2mm about .08 inches Major Classes of Clastic Sedimentary Rocks Sandstone Medium particle size Sand 2 - .062 mm Major Classes of Clastic Sedimentary Rocks Siltstone Fine grained particles Silt .062 - .0039 mm Major Classes of Clastic Sedimentary Rocks Mudstone, Shale, Claystone Very fined Grained sediments Clay Finer than .0039 mm Clastic – classifications Sorting Particles that are close to the same size = well sorted beach Particles that are not the same size = poorly sorted River Clastic – classifications Shapes of Clastics Angular – particles have not traveled very far from the parent rock Rounded – rocks have traveled far from parent rock Clastic - Conglomerate Lithified equivalents of gravel (looks like gravel that is stuck together) Found in river beds and old drainage basins Roundness of clastics tell the story of travel Clastic - Sandstone Lithified equivalent of sand (looks like sand is stuck together Cross-bedding – layers of different colors Tells the story of paleocurrents Reveals the former stream, wind, or shallow marine water flows Clastic - Siltstone Lithified equivalent of silt (looks like silt is stuck together) Look similar to mudstone or very fine grained sandstone Clastic – Mudstone Muds are deposited by rivers and tides After a river has flooded its lowlands and the flood recedes, the current slows and the mud settles Deep ocean floor is covered by muds, due to weak or absent currents Clastic - Shale Shales are composed of silt and clay Have been known to contain large quantities of oily organic material (oil shale) Clastic - Claystone Either wind blown or water deposited Particles are the finest of all clastic sizes Dust settles after a wind storm Chemically- Formed Sedimentary Rocks Chemically- Formed sedimentary rocks are derived from minerals carried in solution into lakes and seas. Limestone Dolomite Travertine Gypsum Rock Salt Chert Chemical - Limestone Fine to coarse grained bedded rock Contains calcite (calcium carbonate) Fizzes with acid Chemical - Dolomite Fine to coarse grained bedded rock Contains dolomite (calcium, magnesium carbonate) Fizzes with acid Chemical – Travertine Found in caves – water passes through cave walls, pulls calcite out of rock and peculates onto the floor Contains calcite Fizzes with Acid Stalactites and Stalagmites Chemical - Gypsum It is formed by the evaporative deposition of gypsum from solution. commercially very important for the production of plaster of Paris and gypsum wallboard for house construction Chemical – Rock Salt This is the common name for the mineral "halite". table salt It is typically formed by the evaporation of salty water (such as sea water) dry lake beds, inland marginal seas, and enclosed bays and estuaries in arid regions Chemical – Chert Chert is composed mostly of the mineral chalcedony—silica, or quartz in crystals of submicroscopic size. forms in the deep sea where the tiny shells of siliceous organisms are concentrated, or where underground fluids replace sediments with silica Organic – Sedimentary Rock Organically-formed sedimentary rocks form from the remains of plants and animals Fossil Limestone Coal Coquina Organic – Fossil Limestone Fine to coarse grained bedded rock Contains calcium carbonate (fizzes w/acid) Often contains identifiable fossil shells -found in marine environments Organic - Coal Black to brown in color Contains compacted beds of peat and other organic debris Found in areas that at one time were heavily wooded Coquina Mostly consists of shells or fragments of shells It is a limestone – so it will fizz with acid Found in marine environments