sistematica rocilor sedimentare roci siliciclastice. • geneza
TRANSCRIPT
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2 Sistematica rocilor sedimentare
-principii de clasificare
Roci siliciclastice.
• Geneza clastelor
• Textura si structura
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criteriul chimic: • Roci siliciclastice (Terigene, detritice) • Roci carbonatice (Calcare si dolomite) • Roci silicolitice • Roci fosforitice • Roci ferilitice • Roci manganolitice • Roci alitice (Bauxite) criteriul genetic: • Roci evaporitice • Roci piroclastice criteriul mineralogic: • Roci argiloase
Sistematica rocilor sedimentare - principii de clasificare
Roci hibrid: tranzitii de la o categorie la alta Ex: • Marna (calcar-argila) • Tufit (tuf vulcanic-gresie) • Calcar cu elemente terigene (calcar –gresie)
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Rocilile siliciclastice Geneza clastelor
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Geneza clastelor
Procese mecanice (physical weathering)
Procese chimice (chemical weathering)
Procese biotice
Relaxare barica
Termoclastie
Crioclastie
Umectare-uscare
Haloclastie
Solubilizare (dizolvare)
Hidroliza-Hidratare
Oxidare
Bioturbatie
Excavatii (burows)
Sfredelire (borings)
Radacini
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Crioclastie - T 0°C, cicluri inghet-
dezghet, porozitate si permeabilitate
ridicata, rezistenta mecanica slaba
Termoclastie - variatii diurne 50-60°C,
minerale cu coeficienti de dilatare diferiti
Haloclastie - fluide interstitiale saline,
porozitate, precipitari, rezistenta
mecanica scazuta
Na2SO4·10H2O (Mirabilit)
Umectare-Uscare argile
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granite
bazalte roci sedimentare
Efecte- aparitia fisurilor
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Fisuri – cresterea suprafetei expuse agentilor exogeni
Expunerea muchiilor si colturilor proceselor de alterare – modificarea formei
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http://www.yosemite.ca.us/library/geologic_story_of_yosemite/images/43.jpg
Dobrogea de Nord Granitul de Pricopan
Gruss (produs al dezagregarii si alterarii granilelor)
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Rocilile siliciclastice
Textura clastelor (dimensiune si forma)
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Textura clastelor: dimensiunea si forma clastelor
Dimensiunea clastelor
Scara graulometrica
Metode analitice
Reprezentari grafice
Parametrii granulometrici
Denumirea distributiei granulometrice
Semnificatii genetice
Forma clastelor
Analiza formei:
clase morfometrice
parametri morfometrici
Analiza suprafezei (exosopie)
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Dimensiunea clastelor
Scara granulometrica: Udden (1914), Wentworth (1922)
Dimensiunea clastelor
Denumirea categoriilor granulometrice
rom. engl. (Shepard)
mm phi
-log2d(mm)
>256
64
4
2
<-8
-6
-2
-1
blocuri
galeţi
pietriş
rudit
(psefit)
boulders
cobbles
pebbles
granules
gravel
1
0.5
0.25
0.125
0.063
0
1
2
3
4
f.grosier
grosier
mediu
fin
f.fin
arenit
(psamit)
v.
coarse
coarse
medium
fine
v. fine
sand
0.031
0.016
0.008
0.004
5
6
7
8
grosier
mediu
fin
f.fin
silt
(aleurit)
coarse
medium
fine
v. fine
silt
<0.004 >8 lutit (pelit) clay
Analiza granulometrica: sitare, analiza laser
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P-P
)P-P(-)P-P(=K
1684
1684595Ascutimea (K)
Asimetria (Sk)
Md-M=Sk
Deviatia standard (σ)
Indice de clasticitate (C)
2
P-P= 1684
Modul (Mo)
Mediana (Md)
Inman (1952)
2
PPM 1684Media (Mz)
Parametrii granulometrici (optional)
P50
P1
Reprezentări ale datelor granulometrice
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Compton (1962)
Comparator vizual pentru estimarea sortării (abaterea standard)
2
P-P= 1684
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Nomenclatura distributiei granulometrice: diagrame ternare
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Forma clastelor Masurarea axelor
Cheel (2005)
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Riley Sphericity (ψR)
Parametrii formei
Rotunjime
Wadell’s Roundness (Rw)
unde :
r = razele cercurilor inscrise in colturi,
N=numarul colturilor
R=raza celui mai mare cerc inscripribil
1W
r rR
N R NR
Cheel (2005)
Sfericitate
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Comparator vizual al rotunjimii clastelor
Comparatorul vizual Power (1953) pentru estimarea rotunjimii dupa formula lui Wadell (Rw) (ρ reprezinta
transformarea logaritmica a lui Rw intr-un numar intreg) (din Cheel, 2005)
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Comparator vizual pentru estimarea simultana a indicilor de rotunjime si sfericitate
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Caractere
• genomorfice (primare) legate de geneza granulelor respective (suprafete de crestere, figuri de tensiune, concresteri, coroziuni primare)
• fenomorfice (secundare) dobândite în timpul sedimentogenezei (cratere de impact, santuri de zgâriere, depresiuni de coroziune chimica si dizolvare, anvelope de supracrestere, luciul suprafetei).
Morfoscopie
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A. Granul de nisip cuartos de plaja. Electron micrograph surface Norwich, Norfolk, England.
B. B. Detaliu. Sunt abundente formele in “V”-caracteristice pt. plajele de energie mare, (in Bogs, 2009).
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Imaturitate texturala
Energie ridicata, transport indelungat, eliminarea clastelor fine
Maturitate texturala
Lipsa prelucrarii prin transport, apropierea fata de sursa
Claste angulare
Sortare slaba
Claste rotunjite
Sortare buna
Maturitate texturala
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Rocilile siliciclastice
Structura sedimentelor si a rocilor sedimentare clastice
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Structuri sedimentare
ale suprafetelor de strat
top
baza
interne
Structuri sedimentare
erozionale
constructionale
Structuri sedimentare
depozitionale
postdepozitionale - deformationale
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Structurile sedimentare impreuna cu textura clastelor reflecta proclesele: - eroziune - transport
- acumulare
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Eroziune - efect combinat al factorilor:
• climatici (temperatura, umiditate, apa, vânturi),
• biotici (prezenta sau absenta vegetatiei)
• gravitationali
Eroziunea:
• apei la tarm - abraziune
• Vantului - coraziune
• Ghetii - exharatie
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Transportul
Factori
Agenti
Gravitatia
Contrast termic, baric, de densitate
aer
gheata
apa
Apa + sediment
Nr. lui Reynolds
Curgere laminara
Curgere turbulenta
Nr. lui Froud
Regim curgere subcritic (acumulare)
Regim curgere supracritic (eroziune)
Comportament mecanic
Curgere fluidala
Curgere plastica
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Tipuri de transport
In masa (gravitational)
Individual: • rulare, • tarare, • saltatie, • suspensie
• Curgere de fragmente • Curgere granulara • Curent turbiditic
Structuri organizate
Structuri organizate
Structuri neorganizate (masive)
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Acumularea clastelor
agradare
progradare
retrogradare
acretie laterala
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Structuri Structuri
Structuri Interpretare
Depozitionale Suprafete de strat Caneluri de eroziune Suprafata inf. Curent fluidal unidirectional
Urme de curent sau valuri Suprafata sup. Curent fluidal unidirectional, oscilator
Interne Masiva Transport in masa, subaerian, acvatic, nival
Granoclasare normala Curent fluidal unidirectional
Galeti imbricati Curent tractiv, fluidal, unidirectional, oscilator
Stralificatie/laminatie incrucisata
Curent fluidal acvatic, eolian unidirectional, oscilator
Laminatie/stratificatie paralela
Curent fluidal acvatic, eolian unidirectional
Postdepozitionale
Laminatie/stratificatie convoluta
Lichefiere, fluidizare
Bioturbatii Activitate biotica
Exemple de structuri sedimentare mecanice si biomecanice in roci siliciclastice
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caneluri de eroziune
http://serc.carleton.edu/images/NAGTWorkshops/sedimentary/images/sole_marks4.jpg
urme de lovire si zgariere
Caneluri de eroziune Suprafata inf. Curent fluidal unidirectional
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Urme de curent sau valuri Suprafata sup. Curent fluidal unidirectional, oscilator
ondulatii asimetrice, dune hidraulice
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Structura masiva Transport in masa, subaerian, acvatic, nival
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http://skeptic.smugmug.com/photos/206742562_a46Jg-L.jpg
Normally graded conglomerate layer with a muddy matrix, Cerro Toro Formation, Chile
Granoclasare normala Curent fluidal unidirectional
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Galeti imbricati Curent tractiv, fluidal, unidirectional, oscilator
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Stralificatie/laminatie incrucisata
Curent fluidal acvatic, eolian unidirectional, oscilator
Quaternary, Ottawa, în Miall, note de curs
Laminatie incrucisata la scara mica rezulata in urma actiunii curentilor unidirectionali
Stratificatie incrucisata la scara mare curenti unidirectionali
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Gresie cu laminatie orizontal paralela
Laminatie/stratificatie paralela
Curent fluidal acvatic, unidirectional
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Laminatie convoluta. Plaja -Quebec.
http://course1.winona.edu/csumma/images/sedstrux/convolute2.jpg
Laminatie/stratificatie convoluta
Lichefiere, fluidizare
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Structuri de bioturbatie: urme fosile Reflecta functiile comportamentale ale organismelor: hranire, locuire, deplasare, odihna
http://www.esd.ethz.ch/education/pyrenean/s14_trace_fossils.jpg?hires
Urme de deplasre si hrana - Santonian turbidites
Se pastreaza in interiorul sau suprafata stratelor
http://www.soton.ac.uk/~imw/jpg-Osmington/4OS-Diplocraterion-above.jpg
Urme de locuire si hrana
Bioturbatii Activitate biotica
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BOGGS, S., JR., (2009). Petrology of sedimentary rocks (2nd ed.), Cambridge University Press, Cambridge, England. Hardback, 600 p. CHEEL, R.J., (2005), Introduction to clastic sedimentology, Department of Earth Sciences, Brock University, Ontario, Canada, 124 p. FOLK, R. L., (1974), Petrology of Sedimentary Rocks, Hemphill ed., Austin, Texas.
Referinte bibliografice