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Geology Exam 2
Sed and met rocks, mass mvmnt, water cycle, running water and ground water
| Topic | Material |
|---|---|
| Sedimentary Rocks | Sedimentary rocks are comprised of materials derived from previously existing rocks by weathering and erosion, and transported as solid particles or as ions in solution to accumulate at a depositional environment on the surface of the Earth. |
| Lithification | The accumulated sedimentary grains may become lithified by eliminating the pore spaces between grains as a result of the primary depositional process, compaction, or the addition of cement. |
| Classification of Sedimentary Rocks | Terrigenous or Siliciclastic rocks, Carbonate rocks, Chemical Precipitates, and Organic rocks. Texture and composition are the properties of sedimentary rocks used in simple field classifications. |
| Texture of Sedimentary Rocks | Texture in sedimentary rocks refers primarily to the size of the framework grains of the rock. Some sedimentary rocks may have a finer-grained matrix as well. |
| Particle Size 1 | The Wentworth scale is a logarithmic scale (to minimize the effects of size scaling) of particle diameter, with each defining limit differing from the next by a factor of 2. |
| Particle Size 2 | Major divisions separate Gravel, Sand, Silt, and Clay size particles at 2mm, 1/16mm, and 1/256mm respectively. |
| Field Identification | One can easily see whether particles are larger than 2 mm in diameter (gravel). As a simple rule of thumb, sand feels gritty to the touch, finer particles do not. Silt feels gritty between the teeth, clay does not. |
| Terrigenous or Siliclastic Rocks | Consist of silicate mineral grains transported to the depostional basin as solid particles. Composition of the grains is dominantly quartz and clay minerals and lesser amounts of feldspars, rock fragments, and other minerals. |
| Conglomerates and Sandstones | Grains are gravel size= conglomerate, or breccia if grains are very angular. Grains are sand=sandstone, quartz sandstone if there are few other minerals. signif. amount of feldspar=arkose. signif. amount of fine grained matrix= graywacke. |
| Mudrocks 1 | Finer grained rocks made up of silt or clay size particles. Mudrocks composed of silt= siltstones, or loess if they were deposited by the wind. If they are fissile (splitting apart easily along bedding plane surfaces=shale |
| Mudrocks 2 | Because of the small particle size, it is difficult to make distinctions among mudrocks. Color differences may indicate whether oxygen was readily available (red) or nearly depleted (black) at the site of deposition. |
| Carbonate Rocks 1 | composed primarily of one of the common carbonate minerals calcite (CaCO3) or dolomite (Ca,Mg CO3). In general, these rocks are called limestone and dolostone respectively. |
| Carbonate Rocks 2 | Calcium and magnesium are weathered from rocks and transported to a sedimentary basin in solution. There organisms extract the calcium from seawater to construct calcium carbonate. After death skeletal remains provide particles of all sizes |
| Carbonate Rocks 3 | Fine stoned LS= micrite. LS composed of spherical, sand-sized particles called ooids=oolitic limestone. LS made up of large shells and shell fragments=coquina. Coral reefs produce massive LS deposits as skeletons of coral colonies are cemented together. |
| Carbonate Rocks 4 | Dolomite does not appear to develop as a primary sediment. It forms as magnesium replaces some of the calcium in calcium carbonate sediments and rocks in certain arid environments, producing dolostone. |
| Chemical Precipitates 1 | Other minerals precipitated from solution within the depositional basin include silica, evaporites, phosphates, etc. Some marine organisms secrete hard parts of opaline silica. These skeletal remains accumulate and lithify to form chert. |
| Chemical Precipitates 2 | In some environments, usually associated with upwelling of water from the deep ocean basin, high concentrations of phosphates allows phosphatic organic remains to accumulate. |
| Evaporites | Gypsum, halite, and other evaporite sediments precipitate from hypersaline solutions concentrated by evaporation. Such conditions can occur in lakes or restricted marine basins intermittently connected to the sea, in arid environments. |
| Organic Sediments | Organic-rich sediments may accumulate in oxygen-poor environments to produce black shales or coals. Organic-rich shales may become a source for petroleum. Accumulations of woody plant remains form peat, and may become coal. |
| Coal 1 | As plant remains break down in an oxygen-poor environment, the hydrogen and oxygen of the organic compounds are lost, leaving only the carbon, coal. |
| Coal 2 | Progressively higher proportions of carbon characterize the ranks of coal from lignite to bituminous, and then anthracite. |
| Sedimentary Structures 1 | As sediment grains accumulate, they form layers called beds or laminae. Bedding is essentially horizontal overall and may be in detail. |
| Sedimentary Structures 2 | Features such as ripples or dunes that develop in the loose sediment may produce sedimentary structures such as cross lamination. Cross laminae are inclined in the direction of the current that formed the ripples. |
| Sedimentary Structures 3 | Other sedimentary structures, such as mudcracks, can provide other information about the depositional environment. |
| Sedimentary Environments 1 | Sediments can accumulate in a variety of environments that can be broadly classified as marine or non-marine. Some common non-marine environments include, streams & rivers, lakes, and eolian (wind deposited). |
| Sedimentary Environment 2 | Transitional environments such as deltas and beaches include both marine and non-marine parts. Marine environments include, shore environments, reefs, and the deep ocean . |
Created by:
ebrinklow
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