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02 Sedimentary Rocks

02 Sedimentary Rocks - Chemical sediments precipated from...

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(B) Sedimentary Rocks Sedimentary rocks are those formed from sediments that are produced by weathering and erosion, transported and then deposited by the action of wind, water (rivers, waves or currents) or ice. Clastic (terrigeneous) sediments Broken-up fragments of preexisting rocks and minerals Rocks are classified based on size of grains: - Rudaceous: Conglomerate — rounded gravels (>2mm) Breccia — angular fragments (>2mm) Arenaeous: Sandstone — sand (0.06-2mm) Siltstone — silt (0.002-0.006mm) Argillaceous: Shale/Mudstone — clay (<0.002mm) Sorting is a measure of the range of grain sizes present Well-sorted: grains are all similar in size Poorly-sorted: wide variation in grain size
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Unformatted text preview: Chemical sediments: precipated from solution; evaporates & salt deposits Organic (biological) sediments • Diagensis is the process by which rocks are formed from sediments at low temperatures and pressures. It comprises a variety of processes as below: -Sediments pile atop other sediments Compaction of sediments under overburden pressure Sediments squeezed more tightly, pore space decreases and pore water squeezed out Cementation of sediments lead to formation of cohesive mass of rocks • Structures & features of sedimentary rocks: bedding, lamination (thin bedding) and stratum • Sedimentary environments (refer to notes)...
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