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GY 402: Sedimentary Petrology
Lecture 13: Immature Siliciclastic Sedimentary Environments
Alluvial Fans, Braided Streams
Instructor: Dr. Douglas W. Haywick
UNIVERSITY OF SOUTH ALABAMA
Last Time
1. Immature siliciclastic sediment
2. Immature siliciclastic sedimentary rocks
3. Point counting (for this or the next lab assignment)
Immature siliciclastic sediment and sedimentary rocks
Q
F R Source: Blatt, H., Middleton, G and Murray, R., 1980: Origin of Sedimentary Rocks. Prentice Hill, 782 p.
“Immature” rocks (mineralogically unstable)
Enriched in feldspars and unstable rock fragments
Siliciclastic Sedimentary Rocks
Important Grain Parameters
Grain Size (energy of deposition)
Rounding (degree of wear)
Sorting (energy of deposition)
Immature Siliciclastic Sediment
Is usually more diverse (mineralogy-wise) than mature sediment.
Grains include:
XN 250 μm
Plagioclase feldspar
Orthoclase
Microcline
Micas
Lithics
Quartz
Lithic Fragments
Lithic Fragments
ppl xn 750 m
Arkose
plagioclase
Thin-section Photomicrographs
Today’s Agenda Immature siliciclastic sediment and sedimentary rocks
Pictorial overview
Alluvial fans
Braided rivers
Alluvial Fans
1 km
1 km
Alluvial Fans
Alluvial Fans
Alluvial Fans
Fan head mid fan
Fan toe
Alluvial
plain
Alluvial Fans
Alluvial Fans
Alluvial Fans
wind
Alluvial Fans
Alluvial Fans
Alluvial Fans
Alluvial Fans
Alluvial Fans
Alluvial Fans
Alluvial Fans - view from the top
Alluvial Fans
Fan-shaped deposits of siliciclastic sediment deposited at the base of mountains Gravel to clay sized
Angular to sub rounded
immature
Best developed in arid regions
Alluvial Fans
Best developed in arid regions
Best developed in tectonically active areas
From Walker, R.G. 1980. Facies Models. Geological Association of Canada
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
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
Chalk Board
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
grav
el
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
sand
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
“mud
”
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
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
Debris flows
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
Channel deposits
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
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
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.
Interbedded gravel/ sand
beds
Alluvial Fans - sed. sections
Lenticular, scoured sediment bodies
Alluvial Fans - sed. sections
Braided Streams
Braided Streams
Meandering
Braided
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
Stream morphology
Walker, R.G. and James, N.P., 1992. Facies Models. Response to Sea Level Change.Geological Association of Canada, 409p.
Braided Anastomosing Meandering
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
Hei
n, F
.J. 1
984.
Dee
p-se
a an
d flu
vial
bra
ided
cha
nnel
con
glom
erat
es: a
com
paris
on o
f tw
o ca
se st
udie
s. In
Kos
ter,
E.H
. and
Ste
el, R
. eds
), Se
dim
ento
logy
of G
rave
ls a
nd
Con
glom
erat
es. C
anad
ian
Soci
ety
of P
etro
leum
Geo
logi
sts M
em. 1
0, 3
3-49
.
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.
GY 402: Sedimentary Petrology
Lecture 13: Alluvial Fans
Instructor: Dr. Doug Haywick [email protected]
This is a free open access lecture, but not for commercial purposes. For personal use only.