UNIVERSITY OF SOUTH ALABAMA
402: Sedimentary Petrology
Lecture 14:
Siliciclastic Diagenesis
Instructor: Dr. Douglas W. Haywick
Last Time (online)
Immature siliciclastic sediment and sedimentary rocks
Pictorial overview
Alluvial fans
Braided rivers
Alluvial Fans
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
Chalk Board
Walker, R.G. and James, N.P., 1992. Facies Models. Response to Sea
Level Change.Geological Association of Canada, 409p.
Alluvial Fan Facies
Walker, R.G. and James, N.P., 1992. Facies Models. Response to Sea
Level Change.Geological Association of Canada, 409p.
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.
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.
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.
Braided Streams Facies
Gravel beds comprise the majority
of channel and bar facies, but sand
and mud are also common (flood
plain facies)
Walker, R.G. and James, N.P., 1992. Facies Models. Response to
Sea Level Change. Geological Association of Canada, 409p.
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
Diagenesis: all changes to sediment/sedimentary rock
from the time of deposition to the onset of
metamorphism.
Diagenesis
Deposition
Metamorphism
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.
Cementation
Cementation
Cementation: pore-filling minerals precipitated into
voids within sediment/sedimentary rocks.
Matrix versus Cement
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.
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.
Cementation
Cement
 Homogeneous
 Chemically pure
 Lines pores
 Specific fabrics
 Multiphased
 zoned
SEM
300 µm
cement
Quartz grain
Cementation
Cement
• Homogeneous
• Chemically pure
• Lines pores
• Specific fabrics
• Multiphased
• zoned
50 µm
PPL
Hematite cement Quartz cement
Cementation
Cement
• Homogeneous
• Chemically pure
• Lines pores
• Specific fabrics
• Multiphased
• zoned
SEM
300 µm
Quartz grain
Quartz overgrowth
cement
Cementation
Cements come in numerous fabrics
•Fibrous
•Bladed
•Acicular
•Pendant
•Concentric
•Poikilotopic
•Botryoidal
•Drusy
•Syntaxial
•Micritic
•Massive
•etc.
(McIlreath and Morrow, 1990)
Chalk board
Quartz
overgrowth
cement
https://www2.imperial.ac.uk/earthscienceandengineering/rocklibrary
Cementation
ppl
0.25 mm
Cementation
ppl
xn
glauconite
Cementation
ppl
xn
Cementation
ppl
xn
chalcedony
300 µm
Cementation
ppl
xn
opal
chalcedony
300 µm
Cement
Origins
XN
250 µm
Cement
Origins
 Cements precipitate from
pore waters (vadose and
phreatic zones)
Vadose
Phreatic
Cement
Origins
 Cements precipitate from
pore waters (vadose and
phreatic zones)
 Timing ranges from
synsedimentary to burial
Vadose
Phreatic
Cement
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
Vadose
Phreatic
Cement
Origins
 Cements can also be
precipitated directly on
(and below) the sea floor
Sea floor
Shallow Marine Phreatic
Deep Marine Phreatic
Carbonate Staining
Combination of potassium ferricyanide and Alizarin red-S
Red/Pink: distinguishes CaCO3
from other minerals
PPL
5 mm
Alteration/Mineral Replacement
Alteration/Mineral Replacement
Mineral Replacement: a change in composition from
one mineral to another (fabric preserving versus fabric destroying)
Plagioclase to calcite
(XN, 2 mm FOV)
Alteration/Mineral Replacement
Mineral Replacement: a change in composition from
one mineral to another (fabric preserving versus fabric destroying)
Plagioclase to sericite (muscovite)
(XN, 1 mm FOV)
http://www.union.edu/PUBLIC/GEODEPT/COURSES/petrology/ig_minerals/sericite1-X-40x.JPG
Upcoming Stuff
Assignment Due Date Changes
1) Write 4; Lit Review (due Thursday March 3rd)
2) Peer Review (due Friday March 4th )
3) Perdido Composite Section (due Friday March 11th Team Grade)
Lab Today
TS 3 Diagenesis thin section lab (due Thursday March 3rd )
Online Lecture
Moscow Land Tour (Lecture 15)
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.