402: Sedimentary Petrology - University of South Alabama · 2017-02-17 · Diagenesis: all changes...

402: Sedimentary Petrology

Lecture 14: Siliciclastic Diagenesis

Instructor: Dr. Douglas W. Haywick

UNIVERSITY OF SOUTH ALABAMA

Last Time (online)

Immature siliciclastic sediment and sedimentary rocks

Pictorial overview

Alluvial fans

Braided rivers

1 km

Alluvial Fans

Alluvial Fans

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

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

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Alluvial Fan Facies

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Alluvial Fan Facies

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.

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

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

Braided Streams Facies

Walker, R.G. and James, N.P., 1992. Facies Models. Response to Sea Level Change. Geological Association of Canada, 409p.

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

Braided Stream –sed sections

Walker, R.G. and James, N.P., 1992. Facies Models. Response to Sea Level Change. Geological Association of Canada, 409p.

Today’s Agenda

Siliciclastic Diagenesis

•Dia-what?

•Cementation

•Alteration/mineral replacement

Diagenesis

Diagenesis: all changes to sediment/sedimentary rock from the time of deposition to the onset of metamorphism.

Diagenesis Metamorphism

Deposition Chlorite

Diagenesis

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

Cementation

Cementation

Cementation: pore-filling minerals precipitated into voids within sediment/sedimentary rocks.

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

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.

Cement Homogeneous Chemically pure Lines pores Specific fabrics Multiphased zoned

300 µm SEM

Quartz grain cement

Cementation

Cement • Homogeneous

• Chemically pure • Lines pores

• Specific fabrics • Multiphased

• zoned

50 µm PPL

Quartz cement Hematite cement

Cementation

Cement • Homogeneous

• Chemically pure • Lines pores

• Specific fabrics • Multiphased

• zoned

300 µm SEM Quartz grain

Quartz overgrowth cement

Cementation

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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Cementation

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Quartz overgrowth

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glauconite

Cementation

ppl xn

Cementation

ppl xn

chalcedony

Cementation

300 µm

ppl xn

chalcedony

Cementation

300 µm opal

250 µm XN

Cement

Origins

Cement

Phreatic

Vadose

Origins Cements precipitate from

pore waters (vadose and phreatic zones)

Cement

Phreatic

Vadose

Origins Cements precipitate from

pore waters (vadose and phreatic zones)

Timing ranges from synsedimentary to burial

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

Cement

Origins Cements can also be

precipitated directly on (and below) the sea floor

Shallow Marine Phreatic

Sea floor

Deep Marine Phreatic

Combination of potassium ferricyanide and Alizarin red-S

Carbonate Staining

Red/Pink: distinguishes CaCO3 from other minerals

5 mm PPL

Alteration/Mineral Replacement

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)

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

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 )

GY 402: Sedimentary Petrology

Lecture 14: Siliciclastic Diagenesis

Instructor: Dr. Doug Haywick dhaywick@southalabama.edu

This is a free open access lecture, but not for commercial purposes. For personal use only.