沉积岩石学(Sedimentary-Rocks)课件.ppt

1、Sedimentary Rocks 95% of the Earths volume is igneous and metamorphic rocks bu 75% of the Earths surface is covered by sediments or sedimentary rocks. Derived from pre-existing rocks: 1. detrital/clastic rocks: mineral grains or rock fragments (mechanical or biological weathering) 2. chemical: disso

2、lved & precipitated minerals (chemical weathering). Ex: granite: Quartz + Fs + Biotite Weathering: Mech/bio quartz sand clays Transport River, wind, ice Deposition Beach delta ocean lithification Cemented Rocksandstone shale Ex: granite: Qtz + Ca plag Fs + Biotite Weathering: Chem calcium Transport

3、solution in river Deposition ocean lithification precipitation Rock limestoneTerminology Precipitation: opposite of dissolve: aqueous to solid lithification: materials are compacted and/or cemented together to form rock. Rounded: angular fragments become rounded (& smaller) through abrasion as they

4、are transported Deposition: ice, wind, or water deposit/drop sediment in river bed, moraine, lake, beach, ocean, etc. Facies: a distinct sediment or rock type Sorting: process by which particles are separated according to size (& density) Clay with clay Sand with sand Gravel with gravelWater & wind

5、are excellent sorters, ice is poor Gravel SandSiltClayfaciesfaciesfacies facieshighlowriverEnergygravellake/oceandeltabeachsandsiltclaysorted Pore space = porosity = voids between particles Clay 80% sand 20% mixture 5%Well sorted Compaction: weight of overlying sediment compresses sediments, forces

6、water out and “glues”/lithifies mud siltstone & shale Cementation: weathered silica, calcite and iron oxides dissolved in water precipitate in pore spaces to cement/lithify particles together. Friable: rock is easily crumbled (like dry cake) Fissile: rock breaks easily along closely spaced parallel

7、lines Like cleavage in rockSedimentary Rocks 1. Detrital/Clastic 2. Chemical 3. Biochemical 1. Detrital/Clastic Detritus = solid particles or pre-existing rocks Clastic = composed of rock fragmentsSediment size description rock name Gravel 2mmrounded conglomerate gravelangular breccia gravel Sand 1/

8、16 2mm (mostly Qtz) sandstone Mud 1/16 mm silt siltstone silt & clay mudstone 1/256 mm clay claystone shale Sandstone = Sst: sandy Red sandstone: with lots of K Fs (pink Fs) = arkose sst Siltstone: gritty with wet mud smell Shale: greasy with wet mud smellSiltstone 2. Chemical: originate from substa

9、nces taken from solution from chemical weathering These chemicals are extracted from lake or ocean water via: i) precipitation (Ex; drying lake bed) Ii) organisms (coral reef) BUT this is a biochemical rock!Death Valley Salt FlatsDead SeaTexture Composition Rock NameVaries calcite CaCO3 limestone/Ls

10、tVaries dolomite CaMgCO3 dolostoneCrystalline gypsum CaSO4 rock gypsumCrystalline halite NaCl rock saltcarbonate Travertine: Lst that precipitates out of hotsprings but is rare Lst: most is biochemical Dolostone: forms from Lst that is altered in: i) very saline lagoons ii) where Lst has been uplift

11、ed above the water table and fresh water with Mg leeches through replacing the Ca Lst Dolostone CaCO3 CaMgCO3HCl Test!Barely fizzesFizz!Travertine Terraces in Turkey Evaporites: (rock gypsum and rock salt) precipitate from land-locked lakes and seas where the evaporation raises the salinity to the s

12、aturation point.Very salty waterevaporationGypsum & halite crystals Rock gypsum: white-pink-grey, massive or tabular crystals, H =2, white streak Rock salt = halite: colourless, cubic crystals, salty taste, H = 2-3 Silvite = KCl = potash: a fertilizer formed from evaporation on vast, shallow seas in

13、 SaskatchewanGypsumGypsum Thin section 3. BiochemicalTexture Composition Rock NameClastic- calcite CaCO3 limestone/Lstcrystalline chalk: microscopic coquina: shellsFine quartz chertFine- carbon C coal crumblyLimestone: accumulation of billions of skeletons of corals,shellfish,algae, etc. Originally

14、as aragonite which alters to calcite. Forms: Massive: shells broken and ground into powder before lithification Sugary = crystalline Coquina (KD)= cemented broken shells Chalk = soft, microscopic fossils HCl test!Chert: forms 2 ways:i) silica rich waters percolate up through earth replacing the Lst

15、in the form of nodules, a bulbous mass of chalcedony (“elephant man”)ii) organisms (sponges, diatoms) that use silica for skeletons die; the silica accumulates on the ocean floor to form bedded chert (usually grey).Flint = black chertJasper = red chertChert thin sectionRadiolariansRadiolariansCoal:

16、form in the processi) land plants accumulate in swamps, bogs low in pH and low in O2 to prevent bacterial decay of organic matter (OM).ii) The OM accumulates to form peat.iii) heat + time drives off the volatiles (H2, N2 & O2) leaving C to form coal Black, H = 1 3, SG = 1 (light)Go to Lab 6.1Go to 6.2 Notes