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Petrologie sedimentara
An II
Inginerie Geologica si Geofizica
Lect. Dr. Relu D. Roban
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•Anastasiu N. , 1988, 1998- Petrologie sedimentara (Ed. Tehnica, Ed. Univ.)
•Anastasiu N. , 1988 - Rocile Sedimentare (T.U.B.)
•Anastasiu N. , C. Panaiotu, 1998 – Aplicatii practice (T.U.B.)
•BOGGS, S., JR., (2009). Petrology of sedimentary rocks (2nd ed.), Cambridge University Press, Cambridge, England. Hardback, 600 p.
•TUCKER, M. E., 1991. Sedimentary Petrology. An introduction to the origin of sedimentary rocks, 2nd edition, Blackewell Scientific Publication, 260 pp.
Bibliografie
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1 Introducere.
• Roca sedimentara. Sediment. Exogeneza.
• Factorii sedimentarii.
• Spatiul exogeneziei
• Procese depozitionale
• Procese postdepozitionale
• Metode de analiza specifice.
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1 Introducere.
Roca sedimentara. Sediment. Exogeneza.
Factorii sedimentarii.
Spatiul exogeneziei.
Procese depozitionale.
Procese postdepozitionale.
Metode de analiza specifice.
Patura sedimentara: - 5% din masa litosferei; - acopera 75% din arealul de uscat şi 95% din suprafata fundului oceanelor
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- fundamentala – stiintele Pamantului
- diagnosticarea rocilor sedimentare
- descifrarea genezei lor
Importanta:
Scop:
- aplicativa:
- resurse: nemetalifere, metalifere, energetice,
- sisteme petrolifere (roci sursa, rezervoare, ecrane
pentru hidrocarburi)
- acvifere
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1 Introducere.
Roca sedimentara. Sediment. Exogeneza.
Factorii sedimentarii.
Spatiul exogeneziei
Procese sedimentare.
Procese postdepozitionale.
Metode de analiza specifice.
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Roca sedimentara:
- formata la suprafata scoartei
- procese: mecanice, chimice, biotice
Roca:
- agregat mineral, natural
- compozitie, textura, structura
- r. magmatice, r. metamorfice, r. sedimentare
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Sediment vs roca sedimentara
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Stratifications obliques métriques dans les grès éoliens de la Formation de Navajo, Jurassique, Page, Arizona, USA.
http://www2.ulg.ac.be/geolsed/sedim/sedimentologie.htm
Sediment Duna actuala
Roca Duna fosila
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Gypsum nodules forming in Saudia Arabian Sabkha. http://www.oocities.org/earthhistory/grand3.htm
Alberta, Canada; extensive outcrops of Upper Jurassic gypsum http://www.geo.utexas.edu/faculty/marrett/photos/GaleanaEvap.jpg
Gips: sediment? roca?
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Eocen, Denver Colorado- arcoze (gresii feldspatice) - caolinitizate http://academic.emporia.edu/aberjame/struc_geo/rocky/rocky25.jpg
Caolinit: sediment?
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Cutting laterite bricks in Angadipuram, India http://en.wikipedia.org/wiki/Laterite
Laterite: sedimente?
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http://true-wild-life.blogspot.com/2011/02/coral.html
El Capitan reef: Guadalupe Mountains National Park, Texashttp://thestonescryout.com/flood_geology_challenges/guadalupe_mountains_national_park
Coral: sediment?
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Concluzie:
Sediment: depus, precipitat, neoformat sau bioconstruit in bazin Roca: sediment care a suferit procese diagenetice
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Exogeneza = totalitatea proceselor generate de factorii care acţionează asupra suprafeţei scoarţei terestre producând transformări ale acesteia şi generând noi produse (sedimentogeneza = sinonimie prin generalizare).
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1 Introducere.
Roca sedimentara. Sediment. Exogeneza.
Factorii sedimentarii.
Spatiul exogeneziei
Procese sedimentare .
Procese postdepozitionale.
Metode de analiza specifice.
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• Factori terestri
Factorii sedimentarii
• Factori cosmici
Pamantul corp cosmic
Cicluri orbitale
P
T
activitate biotica
Litosfera Atmosfera Hidrosfera
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Factori cosmici
http://upload.wikimedia.org/wikipedia/commons/6/61/AxialTiltObliquity.png
• Miscare de revolutie: ~365 zile (365 zile, 6 ore, 9 min., 10 sec)
Consecinte: -succesiunea zilelor si a noptilor - efect Corriolis
Consecinte: - anotimpuri - inegalitatea zilelor si a noptilor
Pamantul corp cosmic:
• Forma:
• Inclinarea axei:
• Miscare de rotatie:
elipsoid de rotatie
(23,5 grade),
~24 ore (23 ore, 56 min., 4 sec)
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http://en.wikipedia.org/wiki/Milankovitch_cycles Cicluri orbitale: cicluri Milankovitch
•Excentricitatea (~ 100 000 ani) •Oblicitatea eclipticii (~ 40 000 ani) •Precesia (~20 000 ani)
Efecte: variatia cantitatii radiatiei solare si distributia inegala pe suprafata globului
Schimbari climatice
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Factori terestri • Litosfera: P, T, arii sursa, bazine de sedimentare
• Atmosfera: P, T, dinamica, clima
• Hidrosfera: P, T, dinamica
• Biosfera: diversitate specii, indivizi
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Temperatura • aerului (max: +58°C, min: -88°C), • în scoarţă (corelarea cu T. aerului: 5m - z. ecuatoriale, 20m - z. temperate, 100m – poli. - gradient geotermic ~1°C/33m dependent de tipul de crustă, situaţia tectonică; - 150-200°C - limita cu metamorfismul • în apă (max: 35°C, min: 0;-2°C) -anomalii locale (rift) efecte: densitatea apei, curenţi termoclini, reactivitate chimică.
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Presiunea
• atmosferică (1 kg/cm2= 1atm, ~1 Bar), variaţiile determină mişcarea aerului
(vânt)
• hidrostatică (1atm/100m), influenţează procesele chimice, mecanice, biotice
• litostatică (250 atm/km), determină compactări ale sedimentelor; 2,5-4 kb -
trecerea la metamorfism
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1 Introducere.
Roca sedimentara. Sediment. Exogeneza.
Factorii sedimentarii.
Spatiul exogeneziei.
Procese sedimentare – depozitionale
Procese postdepozitionale
Metode de analiza specifice.
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Arii sursa si bazine sedimentare
Arii sursa: - furnizeaza sedimente (claste) - extrabazinala/intrabazinala Se caracterizeaza prin: - structura geologica, - pozitie geografica - compozitie petrografica
Spatiul exogenezei- interferenta sferelor Pamantului (litosfera, atmosfera, hidrospera, atmosfera, biosfera)
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Clasificarea bazinelor funcţie de cadrul tectonic:
a) Tipul de litosferă: a1) continentală a2) oceanică a3) de tranziţie b) Poziţia faţă de limitele plăcilor litosferice b1) intracratonice sau intraplăci b2) margine de placă b2.1) divergent b2.2 ) convergent b2.3) falie transformantă
Bazine de sedimentare - Arii de acumulare a sedimentelor
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Litosfera: tectonica placilor
Ciclul Wilson după Allen şi Allen (2004)
Bazine de sedimentare – Ciclul Wilson Press and Siever (1978). (A) Extensiune- bazin oceanic nou format (Marea
Rosie) (B) Extensiune - bazin oceanic matur (Atlantic) (C) Initierea subductiei- consumul placii oceanice Pacific – vestul Anzilor (D) Coliziune- inchiderea finala – centuri montane
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Medii sedimentare
Continentale
• Glaciare
• Deşertice
• Conuri aluviale
• Fluviatile
• Lacustre
Tranziţie-Costiere:
• Litorale
• Deltaice
• Estuarine
Marine:
• Apa putin adanca
• Apa adanca
Clasificarea în funcţie de relaţia cu mediile sedimentare a) Bazine cu umpluturi sedimentare formate în medii continentale b) Bazine cu umpluturi sedimentare formate în medii tranziţionale c) Bazine cu umpluturi sedimentare formate în medii marine şi oceanice
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1 Introducere.
Roca sedimentara. Sediment. Exogeneza.
Factorii sedimentarii.
Spatiul exogeneziei: Arii sursa si bazine de
sedimentare
Procese sedimentare – depozitionale
Procese postdepozitionale
Metode de analiza specifice
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Procese mecanice: (→ claste) • dezagregare, transportul si acumularea clastelor roci detritice (siliciclastite) • eruptii vulcanice explozive roci piroclastice Procese chimice: (→cristale) • alterarea rocilor preexistente (hidroliza, oxidare) scoarţa de alterare, roci reziduale (bauxite, laterite, argile-caolin) • reacţii chimice (dizolvări şi precipitări) carst, roci chimice (evaporite, calcare) Procese biotice (bioclaste, biomorfe) •biosecreţie, bioacretie, bioacumulare, bioconstrucţie roci organogene (calcare, silicolite, fosforite, ...)
Procese exogene si produse (particule sedimentare):
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Procese
fizico-mecanice
chimice
Procese biotice,
biochimice
Procese chimice
Siliciclastite
Piroclastite
Roci carbonatice
Silicolite
Fosforite
Dolomite
Evaporite
Ferilite
Bauxite
Manganolite
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Organizare stratala. Semnificatii genetice.
• Lamina • Strat • Cuplu • Set, coset • Secventa
• particulele sedimentare acumulate in bazine formeaza unitati depozitionale (strate)
Ierarhia este data de grosimea unitatilor si repetabilitate
Acumularea asociatiilor de unitati sedimentare sugereaza procese ciclice sau catastrofice
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Lamina Strat Set, coset Secventa
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Strat si lamina
Boogs Jr. (2006)
10 3 1 0,3 0,1
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Cupluri Gips/anhidrit si argila
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Quaternary, Ottawa, în Miall, note de curs
Large-scale planar crossbedding
Laminatie incrucisata la scara mica rezulata in urma actiunii curentilor unidirectionali
Stratificatie incrucisata la scara mare curenti unidirectionali
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Tipuri de secvente Semnificatii genetice
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Secventa fining up- umplutura de canal
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Secventa coarsening up- Delta progradanta
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Ciclu sedimentar Spatiul exogen: procese si limite
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1 Introducere.
Roca sedimentara. Sediment. Exogeneza.
Factorii sedimentarii.
Spatiul exogeneziei
Procese depozitionale
Procese postdepozitionale
Metode de analiza specifice
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DIAGENEZA - totalitatea proceselor de natura fizico-mecanica si chimica, care afecteaza postdepozitional sedimentele, transformându-le în roci, în timpul îngroparii progresive pâna la limita cu metamorfismul si în timpul exondarii si supunerii rocilor sedimentare factorilor exogeni pâna la limita cu alterarea.
Limitele termo-barice ( cu metamorfismul): ~ 200gC, 3-4kb
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Procese diagenetice:
Mecanice:
Chimice:
dizolvarea
precipitare chimica in pori
neomorfism (recristalizare)
inlocuire (metasomatoza)
dizolvarea sub presiune
compactarea
difuzia ionica
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Etapele diagenetice:
Sindiageneza (ingropare superficiala)
Mezodiageneza (ingropare profunda)
Epidiageneza (etapa de exondare)
Medii diagenetice:
continental
meteoric vados
meteoric freatic
marin freatic
ingroparea profunda
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1 Introducere.
Roca sedimentara. Sediment. Exogeneza.
Factorii sedimentarii.
Spatiul exogeneziei: Arii sursa si bazine de
sedimentare
Procese sedimentare – depozitionale
Procese postdepozitionale
Metode de analiza specifice
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• pe teren: diagnoza petrografica, identificarea structurilor
sedimentare, fotografiere, masuratori (grosimi, plane stratificatie,
directii paleocurenti), probare.
• in laborator: analize granulometrice, morfoscopice, plachete
lustruite, atac chimic diferentiat, colorare, amprente pe celuloid,
sectiuni subtiri, microscopie electronica, luminiscenta, analize RX,
izotopi (C, O), analize chimice
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Analiza proceselor sedimentare actuale
=> premiza a intelegerii proceselor sedimentare vechi si a formarii rocilor sedimentare
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Analiza sedimentologica la scara aflorimentului
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Analiza sedimentologica
la scara esantionului
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Analiza petrografica la
microscara
microscopie optica
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Analize la nanoscara
(microscopie electronica)