Sedimentary Facies & Sea Level Sedimentary Facies and Sea Level Changes

Sedimentary Facies & Sea Level

Sedimentary Faciesand

Sea Level Changes

Sedimentary Facies:

• general appearance or aspects

of a rock (composition & texture).


Sedimentary Facies:

• original environment of deposition can be determined.

• used to describe vertical and lateral variations in strata.


Sedimentary Facies:

• facies transform laterally by

gradual changes in their properties

into different, adjacent facies.


Two types of facies

1). Lithofacies:

distinguishing characteristics are

. . . lithologic



sandstonefacies shale facies

Two types of facies

1). Lithofacies: can be degree of difference


limestone sandstonevs. vs.

fine grained limestone

coarse,

well sorted sandstone

Two types of facies

2). Biofacies:

differences in biological (fossil)

composition.


Two types of facies

2). Biofacies:

• can have different adjacent biofacies in the same lithology

• can be sensitive to small environmental differences



Foraminifera facies

Mississippi Delta


Changes in sea level

Transgression:

• Advance of sea over the land

Regression:

• Retreat of the sea from the land


Idealized gradation:

• Near shore = coarse sediment

- to -

• Off shore = fine sediment

- yielding to -

• Shelf carbonate deposition


Idealized gradation:


nearshore

offshore

continent

No sea level change:


nearshore

offshore

continent

http

://w

ww

.uh.

edu/

~jb

utle

r/ph

ysic

al/tr

ansr

eg.g

if

sediment through time

Sea level at Time A:


“the beach”

Sea level change: cross section

Sea level at Time B:


“the beach”


Transgression • facies shift on-shore

• resulting rock unit (sandstone) varies in age laterally

Shift from Time A to Time B:


“the beach”

“the beach”

Transgression • facies shift on-shore

• resulting rock unit (sandstone) varies in age laterally

Time A: on the beach

(sandstone)


Stand in one spotduring a transgression:

Time B: underwater (finer

sediment)


Stand in one spotduring a transgression:

Regression:

• facies shift off-shore


Regression:

• facies shift off-shore


“the beach”“the beach”

Time A Time B

Regression:

• in one place, facies become more “onshore” (= coarser)

up section


Ls

Slt

Ss

fine

course

• In a vertical column,

facies become

progressively more

"on shore" (coarser)

up section.


Regression

Conglomerate

Sandstone

Siltstone

Limestone

erosion


facies become

progressively more

"on shore" (coarser)

up section.


Regression

Conglomerate

Sandstone

Siltstone

Limestone

erosion

“deep”

“beach”

“land”


facies become

progressively more

”off shore" (finer)

up section.


Transgression

Limestone

Siltstone

Sandstone

Conglomerate

erosion


facies become

progressively more

”off shore" (finer)

up section.


Transgression

Limestone

Siltstone

Sandstone

Conglomerate

erosion

“deep”

“beach”

“land”

• A vertical sequence represents

facies that were once laterally

continuous


Walther’s Law

Limestone

Siltstone

Sandstone

vertical sequence

• A vertical sequence represents

facies that were once laterally

continuous


Walther’s Law

Limestone

Siltstone

Sandstone

vertical sequence

Lateral Distribution

Ls

Sh

Ss• A vertical sequence

represents facies that

were once laterally

continuous

Walther’s Law

Ls

Sh

Ss

“deep”

“beach”• A vertical sequence

represents facies that

were once laterally

continuous

Walther’s Law

• The relative sequence is more

important than absolute

completeness.


Walther’s Law

Limestone

Sandstone

vertical sequence-1

Siltstone

vertical sequence-2

unconformity

• The relative sequence is more

important than absolute

completeness.


Walther’s Law

Limestone

Sandstone

vertical sequence-1

Siltstone

vertical sequence-2

unconformity

Transgression Regression

“deep”

“beach”

“land”

“intermediate”

• Tectonic subsidence(sinking)

• Rise in sea level

• Erosion of shore line


What cause a Transgression?

• Tectonic uplift

• Drop in sea level

• Over supply of sediment


What cause a Regression?

1. Continental Glaciation

more ice = lower sea level (max. 200 meter change)


Eustatic sea level change(world wide) - causes?

http

://w

ww

.shi

ftin

gbas

elin

es.o

rg/b

log/

arch

ives

/000

430.

htm

l

1 meter rise

http

://w

ww

.shi

ftin

gbas

elin

es.o

rg/b

log/

arch

ives

/000

430.

htm

l

2 meter rise

http

://w

ww

.shi

ftin

gbas

elin

es.o

rg/b

log/

arch

ives

/000

430.

htm

l

6 meter rise

30 meter rise

100 meter rise

link to: USGS

http://pubs.usgs.gov/fs/fs2-00/

2. Plate Tectonics

fast spreading rate = high sea level

slow = low sea level

(affects the shape of ocean

basins)


Eustatic sea level change(world wide) - causes?

• transgression in one place while regression in another

• local mountain uplift or crustal subsidence

• very rapid influx of sedimentor erosion.


Local sea level change

Documents

Sedimentary Facies & Sea Level Sedimentary Facies and Sea Level Changes