gy 402: sedimentary petrology · gy 402: sedimentary petrology lecture 13: ... facies models....

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 dhaywick@southalabama.edu

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