sedrx - Rock Classifications Rock • Sedimentary...

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Unformatted text preview: Rock Classifications Rock • Sedimentary Sedimentary – – – detrital/siliciclastic sedimentary rocks carbonates other sedimentary rocks • • • • • • evaporites phosphates organic-rich rocks volcaniclastic rocks chert iron-rich rocks Sedimentary Rocks Sedimentary • Detrital/Siliciclastic Sedimentary Rocks – conglomerates & breccias – sandstones – mudstones • Carbonate Sedimentary Rocks – limestones – dolostones • Other Sedimentary Rocks – – – – – evaporites phosphates organic-rich sedimentary rocks cherts volcaniclastic rocks Detrital Sediments & Sedimentary Rocks Detrital gravel & conglomerate sand & sandstone clay, silt & mudstone Siliciclastic Sedimentary Rocks: Mudstones Siliciclastic • Mudstones – detrital (usually siliciclastic) sedimentary rocks with sediment finer detrital than sand than • Types – mudstones with dominant clay-sized particles • shale: fissile texture • claystone: homogeneous texture – mudstones with dominant silt-sized particles • siltstone: individual grains visible under a hand lens Siliciclastic Sedimentary Rocks: Mudstones • Minerals found in mudstones: Minerals – phyllosilicates /clays phyllosilicates • kaolinite: Al2Si2O5(OH)4 aluminosilicates (feldspars) • illite: KAl2((Al,Mg,Fe)Si3O10)(OH)2 muscovite • chlorite (Mg,Fe)3(Si,Al)4O10(OH)2·(Mg,Fe)3(OH)6 ironmagnesium silicates (Px, Hbl, Gt, Bio) • smectite: – montmorillonite: (Al, Mg)8(Si4O10)4(OH)8·12H2Ovolcanic ash – silt • • • quartz feldspars accessory minerals Kaolinite Kaolinite Siliciclastic Sedimentary Rocks: Sandstones • Sandstones – detrital (usually siliciclastic) sedimentary rocks with detrital sand-sized grains sand-sized • End-member Types – – – – quartzarenite: > 95% quartz arkose: <95% quartz, more feldspars than lithics litharenite: <95% quartz, more lithics than feldspars others • calcarenite: composed of sand-sized carbonate grains Siliciclastic Sedimentary Rocks: Sandstones • Common minerals found in sandstones – Quartz (Q) Quartz • monocrystalline (Qm) • polycrystalline (Qp) • chert (Ls) – Feldspars (F) • potassium feldspar (K) • plagioclase feldspar (P) – Lithic fragments (L) • sedimentary (Ls) • metasedimentary (Lm) • volcanic (Lv) volcanic – accessory minerals • • • • • • • zircon biotite & muscovite & chlorite hematite garnet sphene apatite corundum Quartz Quartz • SiO2 – – – – • • • • • polycrystalline polycrystalline monocrystalline cryptocrystalline/chert chalcedony conchoidal fracture no cleavage conchoidal translucent in hand sample vitreous luster hard (7-8) medium density: 2650 kg m-3 Quartz Quartz Feldspar Feldspar • Plagioclase Feldspars – (Na, Ca)AlSi3O8 – albite (Na) (also oligoclase, andesine) – anorthite (Ca) (also labradorite, bytownite) • Potassium Feldspars - KAlSi3O8 – – – • • • • • • orthoclase microcline sanidine (high-T, Na) two cleavages, blocky crystal habit opaque white/pink in hand sample twinning dull luster medium hard (6) 3 medium density: 2550 - 2760 kg m--3 Feldspar Feldspar Feldspar Feldspar Lithics Lithics Siliciclastic Sedimentary Rocks: Sandstones Quartzarenite Quartzarenite Arkose Arkose Litharenite Litharenite Siliciclastic Sedimentary Rocks: Sandstones Sediment (sand?) Maturity Sediment Sediment Maturity Sediment Coarse-grained Sedimentary Rocks Coarse-grained • Coarse-grained sedimentary rocks – detrital (usually siliciclastic) sedimentary rocks with detrital granule- (2 - 4 mm), pebble- (4 - 64 mm), cobble(64 - 256 mm) and boulder-sized (>256 mm) grains (64 • Types – conglomerate • variably rounded clasts, indicative of moderate transport – breccia • angular clasts, indicative of minimal transport Coarse-grained Sedimentary Rocks 20 cm 5 cm Coarse-grained Sedimentary Rocks 5m Coarse-grained Sedimentary Rocks Coarse-grained Sedimentary Rocks Coarse-grained Coarse-grained Sedimentary Rocks Coarse-grained Carbonate rocks are the product of the precipitation of calcium and/or precipitation magnesium carbonate from aqueous solutions. This precipitation can result from physical processes alone, but is more commonly mediated by organisms. organisms. Carbonate Mineralogy Carbonate • Aragonite – CaCO3 • Calcite – CaCO3 – – – stable in sea water & near surface crust Low-Magnesium Calcite High-Magnesium Calcite High-Magnesium • Dolomite – (CaMg)(CO3)2 – – – stable in sea water & near surface commonly secondary enigmatic primary formation Aragonite Aragonite Calcite Calcite Dolomite Dolomite Carbonate Components Carbonate • Classification & interpretation of carbonates Classification – Grain types – Grain packing or fabric – Sedimentary structures – Early diagenetic changes Early Carbonate Components Carbonate • orthochem: matrix – micrite: lime mud – sparite: crystalline carbonate • allochem: grains – skeletal – non-skeletal • pellets • ooids / coated grains • intraclasts Dunham’s Classification Dunham’s Folk’s Classification Folk’s ...
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This note was uploaded on 06/03/2011 for the course GEOL 201 taught by Professor Baruah during the Fall '10 term at South Carolina.

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