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Petrology of Sedimentary Rocks
G421P13, summer semester, 2/1 hours, 3-4th year
4. Evaporites, cherts, ironstones, phosphates
Karel MartínekInstitute of Geology and Palaeontology
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Evaporites
sea water chemistry, mineral succession of isothermic evaporation of sea water
typical sedimentary environment: subaqatic, subaerial - sabcha, shelf margin -lagoon, salina, isolated basin, playa
microstructures gypsum-anhydrite, halite, lacustrine evaporites
lateral and vertical distribution of facies driven by relative sea water level changes
diapirism
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four main stages of salt precipitation during isothermic sea water evaporation
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lacustrine evaporites
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anhydrite (large crystals and laths, high bir. colours) and microcrystalline gypsum nodules(low bir. colours)
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anhydrite (large prismatic crystals, high bir. colours) and microcrystalline gypsum nodules(low bir. colours)
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Cherts
mineralogy - opal A, opal CT, quartz
microstructures - euhedral, microquartz, megaquartz, chalcedonic quartz
sources, solubility
sed. environments – marine, lacustrine (alkaline lakes), spring cherts
diagenesis, silicification
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Ironstones
sources & transport Fe, eH-pH stability field Fe ox.-hox.
early diagenesis
glaukonygranular facies, impregnation, coatings; authigenic Fe glaukonitic smectite, early diag. Fe, K glaukonitic mica; driving mechanisms: abundance of Fe, K, balance between clastic input and washing, low sedimentation rate (103 - 106 let)
feromanganese nodules
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stages of glauconitization
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hematite ironstone
Crinoids, Bryozoans
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chamosite ironstoneooids
46berthierine, chamosite, siderite, goethite
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Phosphates
mineralogy (carbonate fluorapatite - CFA, frankolite, alophan)
distribution of present-day occurences
genetic models of marine phosphates - upwelling, islands, atols, sea mountains, guyots, epeiric seas
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Reading:
M.E.Tucker: Sedimentary petrology. 3rd ed. Blackwell, 2001.H. Blatt (1992): Sedimentary Petrology. Freeman &Co., New York.G.S.Odin a A.Matter (1981): De glauconiarum origine. Sedimenntology, 28, 611-641.C.R.Glenn and 15 others (1994): Phosphorus and phosphorites: Sedimentology and environments of formation. Eclogae Geol. Helv., 87, 3, 747-788.