文本案例成果沉3lecture sed rocks

1、Sedimentary Rocks and environments“Second cycle”ROCK CYCLE2 major classes:1. Siliciclastic: composed of silicate particles eroded from pre-existing rock. 2. Chemical: inorganic or biochemical precipitatesSediment particles& ions in solution Synopsis of sedimentary environments.1) Siliciclastic rocks

2、: classified on basis of grain sizeShale/ mudstoneShale / mudstoneMaquoketa ShaleOrdovician90% quartz)Arkose(25% feldspar)Graywacke(lithic wacke) rock fragments feldspar, & clay50% quartzSandstone compositional classes: Compositional matureCompositional immatureTectonically passiveBeach, coastal pla

3、inActive tectonics, upliftedGranitic rxActive tectonics, upliftedVolcanic arcProportion of chemically unstable mineralsConglomerate2mm. Very high energy!River channel, Storm dominated beachBrecciaHigh energy but short transport distance, or transport medium incapable of rounding grainse.g. falling t

4、hrough air or glacial ice. Angular clastsTextural maturityfunction of: energy of environment / distance transport / mechanism of transportShape (rounding)Sorting of grains in sandstonesAngular Well RoundedPoorly sorted Well sortedHigh Textural maturity=well rounded, andWell sorted. Sorting (size ran

5、ge)Chemical sedimentary rocks: Inorganic and biochemical precipitates of ions from solutionEvaporitesHalite (NaCl), Potash (KCl), Gypsum CaSO4Inorganic salt precipitates evaporation. CarbonatesLimestone: CaCO3Dolostone: CaMg(CO3)2Predominantly Biochemical precipitates(organisms precipitate their she

6、lls)CarbonatesCarbonatesOolite- limestoneConcentrically coated grains CaCO3 like a beach of pearlsChertBiochemical silicaCoal Synopsis of sedimentary environments.Sedimentary EnvironmentsTalusRock fall: angular blocks (breccia)Alluvial fan; High gradient river emerges from mountainSuper high gradien

7、t riveremerges from mountains conglomerates compositionally immature, little mudBraided riverhigh gradient riverbraided channels, gravel bars conglomerates compositionally immature, little mudMeandering riverChannelFlood plainLower slope (gradient) down to coastal plain, sandy channel and muddy floo

8、d plain Greater mudAccumulation, Cohesive banks; Meandering morphologyCross bedded sandstone (channel)Asymmetrical ripples (channel)Mud cracks in flood plain depositsDeltaMeandering river system enters the seaDistributary channelInter-distributary bayLike the meandering river, but included influence

9、 of oceanPennsylvanian delta deposits, southern Illinois.Beach, typically quartz arenite, symmetrical ripples. Synopsis of sedimentary environments.Deep sea turbiditesSubmarine slope failure, generates turbid suspension of sedimentDriven down slope by gravity eventually settles out in deep sea. Grad

10、ed beddingOffshore carbonates, far from siliciclastic fluxCaicos platform,BahamasFlorida keysDesert dunes (Eolian), typically quartz areniteAncient dune deposits, large scale cross bedsLacustrine (Lake environment)Summary:1) Breakdown of a pre-existing rock through weathering and erosion will yield

11、particles and dissolved chemicals that will ultimately be deposited and lithified forming a sedimentary rock.2) There are two classes of sedimentary rocks: Siliciclastic (composed of silicate particles) and chemical (inorganic and biochemical precipitates). 3) Siliciclastic rocks include shale, silt

12、stone, sandstone (quartz sandstone, arkose, and graywacke), conglomerate and breccia. Chemical rocks include evaporites (salts), carbonates (limestone and dolostone), chert, and coal. 4) Mineral composition reflects compositional maturity (quartz sandstone being the most mature) which reflects tectonic setting. Sediment rounding and sorting reflects greater textural maturity (transport distance, transport medium, and energy). 5) Sedimentary structures such as r