UNIVERSITY OF SOUTH ALABAMA
GY 402: Sedimentary Petrology
Lecture 10:
Petrology of Mature Siliciclastic Sed. Rocks
Instructor: Dr. Douglas W. Haywick
Today’s Agenda
1. Recap major types of sediment & sedimentary rock
2. Recap important grain parameters
3. Cement versus matrix
4. Mature sediment/sedimentary rocks
Petrography Game Plan
Tuesday Lecture: petrographic parameters
Online Lecture (student recap): environments of
deposition
Tues/Thurs. Labs: representative samples (thin-sections
and hand specimens)
Major Sedimentary Rock Types*
* Examined in GY 402
Major Sedimentary Rock Types
Siliciclastic
Major Sedimentary Rock Types
Siliciclastic
Volcaniclastic
Major Sedimentary Rock Types
Siliciclastic
Volcaniclastic
Carbonates (evaporites/chemical, non-skeletal, skeletal)
Siliciclastic Sedimentary Rocks
Mature versus immature varieties…
… are best distinguished via QFR ternary plots
Siliciclastic Sedimentary Rocks
Q
Q = quartz
F = feldspars
R = lithic fragments
(includes chert)
F
R
Source: Blatt, H., Middleton, G and Murray, R., 1980: Origin of Sedimentary Rocks. Prentice Hill, 782 p.
Siliciclastic Sedimentary Rocks
Q
“Mature” rocks
(mineralogically stable)
Enriched in quartz and
clay minerals
F
R
Source: Blatt, H., Middleton, G and Murray, R., 1980: Origin of Sedimentary Rocks. Prentice Hill, 782 p.
Siliciclastic Sedimentary Rocks
Q
“Immature” rocks
(mineralogically unstable)
Enriched in feldspars and
unstable rock fragments
F
R
Source: Blatt, H., Middleton, G and Murray, R., 1980: Origin of Sedimentary Rocks. Prentice Hill, 782 p.
Important Parameters
Grain rounding
Important Parameters
Grain rounding
Immature
Mature
Increasing transport distance
Important Parameters
Grain sorting
Important Parameters
Grain sorting
Low energy
High energy
increasing energy of deposition
Important Parameters
Grain size
Important Parameters
Grain size
High energy
Low energy
Decreasing energy of deposition
Mature Siliciclastic Petrography
PPL
250 m
XN
250 m
Mature Siliciclastic Petrography
Quartz-rich (quartz arenites)
XN
250 m
Mature Siliciclastic Petrography
Quartz-rich (quartz arenites)
Generally well rounded grains
XN
250 m
Mature Siliciclastic Petrography
Quartz-rich (quartz arenites)
Generally well rounded grains
Poorly sorted to well sorted
XN
250 m
Mature Siliciclastic Petrography
Quartz-rich (quartz arenites)
Generally well rounded grains
Poorly sorted to well sorted
Gravel to clay sized grains
XN
250 m
Mature Siliciclastic Petrography
An important question….
XN
250 m
Mature Siliciclastic Petrography
An important question….
...What holds the rock together?
XN
250 m
Matrix versus Cement
Matrix versus Cement
Matrix: fine-grained* material deposited simultaneously with
larger particles. Generally appears as darker-coloured detritus
between grains
* This is a relative term. Matrix is material that is finer than the dominant
particle size comprising the sand/gravel sediment fraction.
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.
Matrix versus Cement
Matrix
 Heterogeneous
 Chemically impure
 Drapes over grains
 Predates cements
 Generally dark in color
XN
PPL
100 µm
Matrix versus Cement
Cement
 Homogeneous
 Chemically pure
 Lines pores
 Specific fabrics (acicular,
drusy, overgrowths etc.)
 Multiphased
 Zoned
50 µm
PPL
Hematite cement Quartz cement
Matrix versus Cement
Matrix
Cement
 Heterogeneous
 Homogeneous
 Chemically impure
 Chemically pure
 Drapes over grains*
 Lines pores*
 Predates cements
 Specific fabrics
 Generally dark in color*
 Multiphased
 Zoned
* Can be confusing
Hand specimens
Mature siliciclastic sandstones
(quartz arenite)
Liesengang banding, clay and iron
oxide cement
Quartz and chalcedony cement
4 cm
Limonite cement
Thin-section Photomicrographs
ppl
xn
750 m
monocrystalline quartz
Thin-section Photomicrographs
ppl
xn
cement
750 m
polycrystalline quartz
Thin-section Photomicrographs
xn
xn
1250 m
cement
Chert
sedimentary rock fragment
Thin-section Photomicrographs
Weakly cemented (friable)
ppl
xn
porosity
quartz
500 m
Thin-section Photomicrographs
Strongly cemented
ppl
xn
quartz
250 m
Thin-section Photomicrographs
Glauconite cement
ppl
xn
glauconite
250 m
Thin-section Photomicrographs
Chalcedony cement
ppl
xn
chalcedony
500 m
Thin-section Photomicrographs
Chalcedony cement
ppl
xn
chalcedony
500 m
Thin-section Photomicrographs
Quartz (overgrowth) cement
ppl
xn
Quartz overgrowth cement
125 m
Upcoming Stuff
Homework
1) Write 3 redo due today
2) Work on your group grain size project due Friday Feb 26th
This Week’s Lab
Open (grain size or thin-section petrography review)
Next Week:
1) Online paper Activity 4 and Midterm exam
2) Midterm exam issued Tuesday due Tuesday February 23rd
3) Thin-section analysis in labs
4) Embedded writing assignments begin in labs
(they are redo-able; the rest of the labs are NOT)
GY 402: Sedimentary Petrology
Lecture 11: Mature Siliciclastic Sedimentary
Rocks
Instructor: Dr. Doug Haywick
dhaywick@southalabama.edu
This is a free open access lecture, but not for commercial purposed.
For personal use only.