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This guide explores sediment and rock classification based on grain size and composition. Highlighting classification scales such as Udden-Wentworth and Krumbein's phi scale, it emphasizes how transport distance influences grain size and roundness. Better-sorted grains indicate longer transport distances. The guide discusses fabric and matrix presence, indicating depositional processes. Textural and compositional maturity are examined, with insights into cement types and their roles in lithification. Finally, it addresses sediment distribution in various depositional environments.
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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
