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11 Roci evaporitice. Mineralogie,
sistematica, petrogeneza.
12 Roci silicolitice. Mineralogie, sistematica,
petrogeneza.
• Definitie
• Mineralogie
• Sistematica si petrogeneza
Roci evaporitice:
Mineralogie: sulfati, cloruri si … cabonati
Principalele minerale evaporitice din grupele sulfatilor si clorurilor, Tucker (1991)
Minerale evaporitice marine Minerale evaporitice non-marine
halit NaCl halit, gips, anhidrit silvină KCl epsomit MgSO4 ∙7H2O
carnalit KMgCl3 ∙6H2O trona Na2CO3 ∙NaHCO3 ∙2H2O
kainit KMgClSO4 ∙3H2O mirabilit Na2SO4 ∙10H2O
anhidrit CaSO4 tenardit Na2SO4
gips CaSO4 ∙2H2O bloedit Na2SO4∙MgSO4∙4H2O
polihalit K2MgCa2(SO4)4 ∙2H2O gaylussit Na2CO3∙CaCO3 ∙5H2O
kieserit MgSO4∙H2O glauberit CaSO4 ∙Na2SO4
Definitie - roci formate prin precipitare chimica, in urma cresterii concentratiei
in saruri a solutiilor, prin evaporare
Criteriul mineralogic: • Depozite sulfatice (gips şi anhidrit) • Depozite salifere (halit şi săruri delicvescente)
Criteriul structural: • Evaporite laminate, ritmice (lamine alternante de gips-anhidrit sau gips/anhidrit cu nivele de calcit, halit, marne sau substanţă organică); • Evaporite nodulare alcătuite din anhidrit format diagenetic prin înlocuirea gipsului în mediile sabkha; • Evaporite clastice rezultate prin resedimentare sau brecifiere (brecia sării); • Evaporite masive (cele salifere).
Criteriul genetic: • Depozite primare (cele ritmice şi masive); marine si non-marine • Depozite secundare (diagenetice: anhidrite nodulare, gips porfirotopic şi fibros, alabastru, cute enterolitice).
Sistematica evaporitelor: criterii
Compozitia apei marine comparativ cu cea a apei raurilor (la o salinitate de 120 ppm)
Krauskoph (1979)
Precipitarea din solutii marine Ordinea precipitarii inversa solubilizarii: 4. Saruri de potasiu 3. Cloruri- Halit 2. Sulfati: Gips, Anhidrit 1. Carbonati
In Reading, (1996)
Clasificarea evaporitelor marine in functie de compozitia mineralogica
Mineral sau roca?
Boggs (2009)
Structuri si texturi sedimentare specifice pentru diverse medii depozitionale (dupa Kendall, 1984; Walker, 1992; Schreiber et al., 1976, Warren, 1989, in Boggs, 2009)
Medii depozitionale actuale, marine, costiere si continentale (Kendall 1984; Walker 1992; Warren 1989, in Boggs 2009)
Sistematica si petrogeneza
Modele evaporitice
Continental: salt pan
Marin
Costier-sabkha
Marin deschis (self, laguna barata intermitent)
Marin barat (self – abisal)
Continental si saline costiere. Bazine izolate
Costier-sabkha
Tucker, (1991)
Secvente tipice pt ciclurile sabkha. Au grosimi de ordinul metrilor si al zecilor de m.
Marin deschis (self, laguna barata intermitent)
Tucker, (1991)
Model asimetric
Tear-drop – Schmaltz (1969)
Marin barat (self – abisal)
Tucker, (1991)
Secventa ideala formata intr-un bazin barat initial adanc, cu realimentari periodice, Tucker, (1991)
Tucker, (1991)
Diageneza
Solubilizare
Recristalizare
Inlocuire
Precipitare in spatiul poros: ciment primar
Hidratare/deshidratare: gips/anhidrit
Evolutia diagenetica a sulfatilor. Schimbari mineralogice si texturale in timpul ingroparii si a exondarii (Tucker, 1991)
Distributia rocilor evaportitice
Laminated gypsum - folding due to expansion of anhydrite in changing to gypsum (Castile Fm. (Permian), NM).
Burdigalian, Romania evaporite nodulare(gips)
Burdigalian, Romania (cute enterolitice)
Badenian, Romania Evaporite clastice
• Definitie
• Mineralogie
• Sistematica si petrogeneza
Roci silicolitice:
Silicolitele sunt roci constituite din silice autigena de origine biogena sau chimica
Desi detin un procent scazut din volumul depozitelor exogene - 1% - ele au mare importanta deoarece se constituie in entitati petrografice reper putand fi utilizate cu succes pentru corelari litostratigrafice.
Mineralogie
•Opal – amorf
•Opal CT – criptocristalin (CT=crisobalit-tridimit)
•Cuart microcristalin, macrocristalin, calcedonie
Silice origine
biogena
(bio)chimica
diatomee radiolari o parte dintre spongieri
Izvoare – sintere Lacuri
fixarea silicei
variatia concentratiei si a pH-lui
Mineralogia scheletelor diverselor organisme. Cercurile umplute reprezintă minarale comune iar cele albe minerale mai puţin comune. După Lowenstam şi Weiner (1989); Flügel (2004).
Geometria
depozitului
Criteriul genetic
Depozitionale Postdepozitionale
Silicolite
stratiforme
Organogene:
Chimice:
Mecanice:
(hibride)
Diatomite
Radiolarite
Spongolite
Sintere
Gaize
Tufodiatomit
Jaspuri
Menilite
Silicolite
nodulare
Silexuri
Chaille-uri
Anastasiu, 1988
Photomicrograph showing moderately well-preserved radiolarians in chert from the Otter Point Formation (Jurassic), Oregon. Plane-polarized light. (Photograph courtesy of Robert Lent.)
Sperulitic (radial-fibrous) chalcedony cement (lower left corner) and microquartz (lower right corner) in a chert deposit from the Gunflint Formation (Precambrian), Ontario, Canada. Cross-polarized light. (From Maliva, R. G., A. H. Knoll, and B. M. Simonson, 2005, Secular changes in the Precambrian silica cycle: Insights from chert petrology: Geol. Soc. Am. Bull., 117, Fig. 4D, p. 840, reproduced by permission.)
Thin, well-bedded cherts in theMino Belt Group (Triassic), near Inuyama, Honshu, Japan.
Radiolarite – Strate de Tisaru, Carpatii Orinetali, Cretacic
Radiolarite tipice
Nodular chert in limestones of the Helena Formation (Precambrian), Glacier National Park, Montana. (From Boggs, S., Jr., 2006, Principles of Sedimentology and Stratigraphy, 4th edn.: Prentice-Hall, Upper Saddle River, NJ, Fig. 7.11, p. 210, reproduced by permission.)
Solubilitzarea si precipitarea silicei: T si pH
Solubilitatea silicei si a cuartului Rimstidt (1997) in functie de temperatura. Gunnarsson and Arnórsson (2000) Solubilitatea silicei si a cuartului
in functie de pH, in Boggs (2009)
Sursa silicei
Sursa silicei dizolvate in apa marina, Boggs, 2009
Diageneza- transformarea opalului
In Boggs, 2009
Schematic diagram showing major silica phases and their possible diagenetic transformations. Vertical dimension represents qualitative burial depth with associated increase in temperature and loss of porosity and permeability. Horizontal dimension represents qualitative water depth of the initial environment. In general, deep-sea siliceous oozes lie to the left of the diagram, whereas epicontinental deposits lie toward the right. Diagenetic path A represents silica initially deposited as opal-A (diatoms, radiolarians), which subsequently transforms to opal-CT and then microquartz by means of solution–reprecipitation steps. Path C represents early diagenetic cherts in which microquartz forms during shallow burial. B represents a possible pathway for chert formation under conditions intermediate between A and C. Megaquartz forms by metamorphic recrystallization of microquartz or by direct growth into voids (suggested by the “spike’) at any stage of burial. Fibrous silica can grow in vugs and fractures at all burial depths. (After Knauth, L. P., 1994, Petrogenesis of chert, in Heaney, P. J., C. T. Prewitt, and G.V. Gibbs (eds.), Silica: Physical Behavior, Geochemistry and Materials Applications: Mineralogical Society of America Reviews in Mineralogy 29, Fig. 4, p. 239, reproduced by permission.)
Cupluri Radiolarit - Argila dominant in baza
secventei pe 10m
Grosime cuplu: in teren 6 cm; decompactat 20 cm; factor
decompactare -2 argila, 5-radiolarit
Decompactate pt 7.6 m = 126 cupluri R/A – domina
radiolaritul sugereaza controlul productivitatii
Rate de sedimentare – comparativ un cuplu in 10-20ka
Compactat
10 cupluri/1m
Decompactat
4.8 cupluri/1m
In Boggs, 2009
Paleolatitude distribution of chert through time. [After Hein, J. R. and J. T. Parrish, 1987, Distribution of siliceous deposits in space and time, in Hein, J. R. (ed.), Siliceous Sedimentary Rock-Hosted Ores and Petroleum, Fig. 2–3, p. 17. Copyright 1987 by Van Nostrand Reinhold. All rights reserved.
Distribution of chert through time. [After Hein, J. R. and J. T. Parrish, 1987, Distribution of siliceous deposits in space and time, in Hein, J. R. (ed.), Siliceous Sedimentary Rock-Hosted Ores and Petroleum, Fig. 2–1, p. 15. Copyright 1987 by Van Nostrand Reinhold. All rights reserved.]