Transcript Geology 12
Geology 12 Presents Sedimentary Rocks • 95% of the Earth’s volume is igneous and metamorphic rocks but 75% of the Earth’s 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: dissolved & precipitated minerals (chemical weathering). • Ex: granite: Quartz + Fs + Biotite • Weathering: Mech/bio quartz sand clays • Transport – River, wind, ice • Deposition – Beach delta ocean • lithification – • Rock Cemented sandstone shale Sedimentary Rocks • Ex: granite: Qtz + Ca plag’ Fs + Biotite • Weathering: Chem’ calcium • Transport – solution in river • Deposition – ocean • lithification – precipitation • Rock limestone Terminology • 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 are transported Rounding • 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 gravel Water & wind are excellent sorters, ice is poor Sorting high river gravel Energy beach sand low delta silt lake/ocean clay sorted • Gravel facies Sand facies Silt facies Clay facies • Pore space = porosity = voids between particles • Clay 80% sand 20% Well sorted mixture 5% Porosity • Compaction: weight of overlying sediment compresses sediments, forces 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 lines – Like cleavage in rock Fissile Sedimentary Rocks • 1. Detrital/Clastic • 2. Chemical • 3. Biochemical • 1. Detrital/Clastic – Detritus = solid particles or pre-existing rocks – Clastic = composed of rock fragments Sediment size description rock name • Gravel >2mm rounded conglomerate gravel angular breccia gravel • Sand 1/16 – 2mm (mostly Qtz) sandstone • Mud <1/16 mm silt siltstone silt & clay mudstone shale 1 < /256 mm clay claystone • 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 smell Siltstone • 2. Chemical: originate from substances 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 Flats Dead Sea Texture Composition Varies calcite CaCO3 Varies Rock Name limestone/Lst carbonate dolomite CaMgCO3 dolostone Crystalline gypsum CaSO4 Crystalline halite NaCl rock gypsum rock salt • 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 uplifted above the water table and fresh water with Mg leeches through replacing the Ca • Lst • CaCO3 Fizz!!! Dolostone CaMgCO3 HCl Test! Barely fizzes 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 saturation point. evaporation Very salty water Gypsum & 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 Saskatchewan Gypsum Gypsum Thin section • 3. Biochemical Texture Composition Clastic- calcite CaCO3 crystalline Rock Name limestone/Lst chalk: microscopic coquina: shells Fine Finecrumbly quartz carbon C chert coal Limestone: accumulation of billions of skeletons of corals,shellfi`sh,algae, etc. • Originally 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 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 chert Jasper = red chert Chert thin section Radiolarians Radiolarians Coal: form in the process i) 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) Do Lab 6.1 Do WS 6.1 Go to 6.2 Notes Go to Lab 6.1