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Sediment/Rock Classification. Gravel. Sediments/rocks classified according to grain size & composition . What is size? Several scales proposed Udden-Wentworth is geometric (1,2,4,8,16) Krumbein = phi scale; phi=-log2S Present data graphically
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Sediment/Rock Classification Gravel • Sediments/rocks classified according to grain size & composition. • What is size? • Several scales proposed • Udden-Wentworth is geometric (1,2,4,8,16) • Krumbein = phi scale; phi=-log2S • Present data graphically • The greater the distance of transport the smaller the grain size. • Caution. Grain size may reflect what is available to be transported Sand Silt Clay
Grain Rounding • Roundness = curvature of corners of grains • Have angular to well-rounded • The rounder the grain, the greater the distance of transport • Rounded quartz grains imply many cycles of uplift, erosion, deposition • Beach and desert better rounded than river/glacial seds • Large grains round fastest
Grain Sorting • Measure of grain size distribution Indicate effectiveness of depositional medium in separating grains of diff sizes • Sorting depends on such factors as depositional mechanism, rk type • Poor sorting usually means limited transport • Better sorting usually means greater distance of transport • Rivers are good examples • Used to distinguish seds of dif. env.
Fabric • Fabric/grain alignment • may indicate bedding • Results from grain transport--e.g. wind, water • Lack of grain alignment also important
Matrix • Is finer material between grains • grains floating in matrix = matrix supported • grains in contact = framework/grain-supported • Lack of Matrix • probably removed by wind/water currents • Presence of matrix • reflects transport medium • e.g. debris flow
Textural Maturity • Immature = lots of matrix, poor sorting, angular grains • Mature = little matrix, mod-good sorting, well rounded • Supermature = no matrix, v. good sorting, well rounded • Provides clue to depositional process • persistent currents = more mature seds • immature seds = fluvial and glacial • more mature = desert, beach, shallow marine
Compositional Maturity • Compositionally mature = predominantly quartz • Unstable minerals removed during transport • B. Compositionally immature = labile constituents and quartz
Cement • Holds rock together--lithifies • could be clay, silica, calcium carbonate • clay looks like mud • quartz usually clear to white, harder than calcite • calcite
Depositional Environments and Grain Size • Low energy environments such as lakes and deep oceans consist of muds/clay • High energy environments such as rivers and beaches consist mostly of gravel and sand
Color of Mudrocks:Green-oygenated environmentBlack-Organic-rich, low oxygen
