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.]