A2 sedimentary rocks student copy

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A2 Sedimentary Processes & Rocks Sedimentary Processes Weathering • Weathering • Types • Erosion • Products • Transportation • Rates • Deposition • Mineral Susceptibility • Diagenesis Sedimentary Environments • Marine – deep/shallow • Land – glacial/alluvial/desert • Transitional – delta/beach Maturity SEDIMENTARY ROCKS Sedimentary Structures • Bedding • Cross-bedding & graded bedding • Desiccation cracks • Ripple marks & sole marks • Textural maturity • Compositional maturity Sedimentary Rocks • Conglomerate & Breccia • Sandstones • Shale/siltstone/mudstone • Limestone/chalk/coal/halite/gypsum Fragmental Chemical & Biogenic How can sedimentary rocks be classified? Coarse >2 mm Medium 0.06 - mm Fine [...]... proportion of clay Maturity of Sedimentary Rocks Maturity of Sedimentary Rocks 1 mm Maturity of Sedimentary Rocks Texturally Immature • sub-rounded • poorly sorted • large grains Texturally Mature • well rounded • well sorted • small grain size Textural maturity describes ……… … the time and distance a sediment has been transported Maturity of Sedimentary Rocks Minerals in sedimentary rocks 1 Extent of chemical... Triangular Graphs ARKOSE Maturity of Sedimentary Rocks Minerals in sedimentary rocks 1 Extent of chemical weathering 2 Type & amount of transportation Sandstone – 70% quartz & 30% orthoclase feldspar What can you tell about the chemical weathering experienced by the original rock? Not much chemical weathering because feldspar unweathered Maturity of Sedimentary Rocks Compositionally Immature • undecomposed... G Rock Specimen B Rock Specimen G Maturity of Sedimentary Rocks What is Rock B? Rock Specimen B: Mineral 1 – quartz (~75%) Arkose • grey • glassy • not scratched by steel blade Mineral 2 – feldspar (~25%) • rectangular • white or pink • white powder Rock B is compositionally immature because there is a high proportion of feldspar Maturity of Sedimentary Rocks Rock Specimen G: • Minerals too small to... immediately oxidized to Fe 3+ and deposited as ferric oxide (rust) Quartzite – composed entirely of quartz & so has no mafic minerals Products of Weathering What sedimentary rocks would be formed? Products of Weathering What sedimentary rocks would be formed? Products of Weathering Original Mineral Feldspar KNaAlSiO Ferromagnesian FeMgSiO Muscovite mica KAlSiO Quartz SiO Calcite CaCO3 Chemical Weathering... leaving shattered fragments to accumulate on hill slopes? By physical weathering (frost shattering) – expansion of water on freezing in cracks & joints exerts pressure breaking rocks apart 2 How can quartz minerals be extricated from the rocks from which they are derived ? Physical weathering (frost shattering) may have shattered rock into smaller fragments which were then attacked by chemical weathering... minerals Compositionally Mature • quartz • clay minerals End products of chemical weathering Compositional maturity describes ……… … the amount of weathering a sediment has suffered Maturity of Sedimentary Rocks Examine Rock Specimen B by hand & hand lens: • There is more than 1 mineral present What minerals are they? What are their relative proportions in the rock? Explain how you made your identification
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