402: Sedimentary Petrology - University of South Alabama · 2017-02-17 · Diagenesis: all changes...
Transcript of 402: Sedimentary Petrology - University of South Alabama · 2017-02-17 · Diagenesis: all changes...
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402: Sedimentary Petrology
Lecture 14: Siliciclastic Diagenesis
Instructor: Dr. Douglas W. Haywick
UNIVERSITY OF SOUTH ALABAMA
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Last Time (online)
Immature siliciclastic sediment and sedimentary rocks
Pictorial overview
Alluvial fans
Braided rivers
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1 km
Alluvial Fans
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Alluvial Fans
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Best developed in arid regions
Best developed in tectonically active areas
From Walker, R.G. 1980. Facies Models. Geological Association of Canada
Lateral fining
Alluvial Fans
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Best developed in arid regions
Best developed in tectonically active areas
Formed primarily through the action of water flow, but there are also mass flow deposits
Debris flows, fluidized flow and “sieve” deposits
Alluvial Fans
Chalk Board
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Wal
ker,
R.G
. and
Jam
es, N
.P.,
1992
. Fac
ies
Mod
els.
Res
pons
e to
Sea
Le
vel C
hang
e.G
eolo
gica
l Ass
ocia
tion
of C
anad
a, 4
09p.
Alluvial Fan Facies
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Wal
ker,
R.G
. and
Jam
es, N
.P.,
1992
. Fac
ies
Mod
els.
Res
pons
e to
Sea
Le
vel C
hang
e.G
eolo
gica
l Ass
ocia
tion
of C
anad
a, 4
09p.
Alluvial Fan Facies
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Alluvial Fans - sed. sections
Nemec, W. and Steel, R.J., 1984. Alluvial and coastal conglomerates: their significant features and some comments on gravelly mass-flow deposits. In Koster, E.H. and Steel, R. eds), Sedimentology of Gravels and Conglomerates. Canadian Society of Petroleum Geologists Mem. 10, 1-31.
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Nemec, W. and Steel, R.J., 1984. Alluvial and coastal conglomerates: their significant features and some comments on gravelly mass-flow deposits. In Koster, E.H. and Steel, R. eds), Sedimentology of Gravels and Conglomerates. Canadian Society of Petroleum Geologists Mem. 10, 1-31.
Alluvial Fans - sed. sections
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Braided Streams Best developed in alluvial plains with “steep gradients” (1 to 3
degrees of slope); frequently in mountainous areas
http://www.ak.nrcs.usda.gov/technical/images/Braided%20River.jpg
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Braided Streams Facies
Walker, R.G. and James, N.P., 1992. Facies Models. Response to Sea Level Change. Geological Association of Canada, 409p.
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Walker, R.G. and James, N.P., 1992. Facies Models. Response to Sea Level Change. Geological Association of Canada, 409p.
Gravel beds comprise the majority of channel and bar facies, but sand and mud are also common (flood plain facies)
Braided Streams Facies
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Braided Stream –sed sections
Walker, R.G. and James, N.P., 1992. Facies Models. Response to Sea Level Change. Geological Association of Canada, 409p.
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Today’s Agenda
Siliciclastic Diagenesis
•Dia-what?
•Cementation
•Alteration/mineral replacement
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Diagenesis
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Diagenesis: all changes to sediment/sedimentary rock from the time of deposition to the onset of metamorphism.
Diagenesis Metamorphism
Deposition Chlorite
Diagenesis
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Diagenesis: all changes to sediment/sedimentary rock from the time of deposition to the onset of metamorphism.
•Burrowing •Boring •Encrustation
•Compaction •Cementation •Dissolution •Pressure solution
•Replacement •Recrystallization •Fracturing •Etc.
Diagenesis
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Cementation
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Cementation
Cementation: pore-filling minerals precipitated into voids within sediment/sedimentary rocks.
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Matrix: fine-grained* material deposited simultaneously with larger particles. Generally appears as darker-coloured detritus between grains
Cement: a chemical precipitate between grains formed from pore-water long after deposition.
Matrix versus Cement
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Cementation
Cementation: pore-filling minerals precipitated into voids within sediment/sedimentary rocks.
•Quartz •Chert •Chalcedony •Opal
•Hematite •Limonite •Phosphate •Clay •Glauconite
•Calcite •Aragonite •Mg-calcite •Dolomite •Siderite •Etc.
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Cement Homogeneous Chemically pure Lines pores Specific fabrics Multiphased zoned
300 µm SEM
Quartz grain cement
Cementation
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Cement • Homogeneous
• Chemically pure • Lines pores
• Specific fabrics • Multiphased
• zoned
50 µm PPL
Quartz cement Hematite cement
Cementation
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Cement • Homogeneous
• Chemically pure • Lines pores
• Specific fabrics • Multiphased
• zoned
300 µm SEM Quartz grain
Quartz overgrowth cement
Cementation
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Cementation
Cements come in numerous fabrics
•Fibrous •Bladed •Acicular •Pendant •Concentric •Poikilotopic
•Botryoidal •Drusy •Syntaxial •Micritic •Massive •etc.
Chalk board (McIlreath and Morrow, 1990)
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ppl
Cementation
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Quartz overgrowth
cement
0.25 mm
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ppl xn
glauconite
Cementation
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ppl xn
Cementation
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ppl xn
chalcedony
Cementation
300 µm
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ppl xn
chalcedony
Cementation
300 µm opal
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250 µm XN
Cement
Origins
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Cement
Phreatic
Vadose
Origins Cements precipitate from
pore waters (vadose and phreatic zones)
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Cement
Phreatic
Vadose
Origins Cements precipitate from
pore waters (vadose and phreatic zones)
Timing ranges from synsedimentary to burial
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Cement
Phreatic
Vadose
Origins Cements precipitate from
pore waters (vadose and phreatic zones)
Timing ranges from synsedimentary to burial
Cements give clues about water chemistry (pH, Eh, etc) and environment
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Cement
Origins Cements can also be
precipitated directly on (and below) the sea floor
Shallow Marine Phreatic
Sea floor
Deep Marine Phreatic
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Combination of potassium ferricyanide and Alizarin red-S
Carbonate Staining
Red/Pink: distinguishes CaCO3 from other minerals
5 mm PPL
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Alteration/Mineral Replacement
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Mineral Replacement: a change in composition from one mineral to another (fabric preserving versus fabric destroying)
Alteration/Mineral Replacement
Plagioclase to calcite
(XN, 2 mm FOV)
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Mineral Replacement: a change in composition from one mineral to another (fabric preserving versus fabric destroying)
Alteration/Mineral Replacement
Plagioclase to sericite (muscovite)
(XN, 1 mm FOV)
http://www.union.edu/PUBLIC/GEODEPT/COURSES/petrology/ig_minerals/sericite1-X-40x.JPG
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Upcoming Stuff Homework
1) Write 4; Lit Review (due Thursday Feb 23rd) 2) Peer Review (due Friday Feb 24th )
3) Grain Size project (due Thursday March 2nd ; Team Grade)
Lab Today TS 3 Diagenesis thin section lab (due Thursday Feb 23rd )
Online Lecture Nothing this week
Thursday Activity:
Activity 6-discussion on paper (Write 4 exercise )
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GY 402: Sedimentary Petrology
Lecture 14: Siliciclastic Diagenesis
Instructor: Dr. Doug Haywick [email protected]
This is a free open access lecture, but not for commercial purposes. For personal use only.