Sedimentary Facies & Sea Level

Sedimentary Facies & Sea Level

Sedimentary Faciesand

Sea Level Changes

Sedimentary Facies:

• general appearance or aspects

of a rock (composition & texture).

Sedimentary Facies & Sea Level

Sedimentary Facies:

• original environment of deposition can be determined.

• used to describe vertical and lateral variations in strata.

Sedimentary Facies & Sea Level

Sedimentary Facies:

• facies transform laterally by

gradual changes in their properties

into different, adjacent facies.

Sedimentary Facies & Sea Level

Two types of facies

1). Lithofacies:

distinguishing characteristics are

. . . lithologic

Sedimentary Facies & Sea Level

Sedimentary Facies & Sea Level

sandstonefacies shale facies

Two types of facies

1). Lithofacies: can be degree of difference

Sedimentary Facies & Sea Level

limestone sandstonevs. vs.

fine grained limestone

coarse,

well sorted sandstone

Two types of facies

2). Biofacies:

differences in biological (fossil)

composition.

Sedimentary Facies & Sea Level

Two types of facies

2). Biofacies:

• can have different adjacent biofacies in the same lithology

• can be sensitive to small environmental differences

Sedimentary Facies & Sea Level

Sedimentary Facies & Sea Level

Foraminifera facies

Mississippi Delta

Sedimentary Facies & Sea Level

Changes in sea level

Transgression:

• Advance of sea over the land

Regression:

• Retreat of the sea from the land

Sedimentary Facies & Sea Level

Idealized gradation:

• Near shore = coarse sediment

- to -

• Off shore = fine sediment

- yielding to -

• Shelf carbonate deposition

Sedimentary Facies & Sea Level

Idealized gradation:

Sedimentary Facies & Sea Level

nearshore

offshore

continent

No sea level change:

Sedimentary Facies & Sea Level

nearshore

offshore

continent

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sediment through time

Sea level at Time A:

Sedimentary Facies & Sea Level

“the beach”

Sea level change: cross section

Sea level at Time B:

Sedimentary Facies & Sea Level

“the beach”

Sedimentary Facies & Sea Level

Transgression • facies shift on-shore

• resulting rock unit (sandstone) varies in age laterally

Shift from Time A to Time B:

Sedimentary Facies & Sea Level

“the beach”

“the beach”

Transgression • facies shift on-shore

• resulting rock unit (sandstone) varies in age laterally

Time A: on the beach

(sandstone)

Sedimentary Facies & Sea Level

Stand in one spotduring a transgression:

Time B: underwater (finer

sediment)

Sedimentary Facies & Sea Level

Stand in one spotduring a transgression:

Regression:

• facies shift off-shore

Sedimentary Facies & Sea Level

Regression:

• facies shift off-shore

Sedimentary Facies & Sea Level

“the beach”“the beach”

Time A Time B

Regression:

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

up section

Sedimentary Facies & Sea Level

Ls

Slt

Ss

fine

course

• In a vertical column,

facies become

progressively more

"on shore" (coarser)

up section.

Sedimentary Facies & Sea Level

Regression

Conglomerate

Sandstone

Siltstone

Limestone

erosion

• In a vertical column,

facies become

progressively more

"on shore" (coarser)

up section.

Sedimentary Facies & Sea Level

Regression

Conglomerate

Sandstone

Siltstone

Limestone

erosion

“deep”

“beach”

“land”

• In a vertical column,

facies become

progressively more

”off shore" (finer)

up section.

Sedimentary Facies & Sea Level

Transgression

Limestone

Siltstone

Sandstone

Conglomerate

erosion

• In a vertical column,

facies become

progressively more

”off shore" (finer)

up section.

Sedimentary Facies & Sea Level

Transgression

Limestone

Siltstone

Sandstone

Conglomerate

erosion

“deep”

“beach”

“land”

• A vertical sequence represents

facies that were once laterally

continuous

Sedimentary Facies & Sea Level

Walther’s Law

Limestone

Siltstone

Sandstone

vertical sequence

• A vertical sequence represents

facies that were once laterally

continuous

Sedimentary Facies & Sea Level

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.

Sedimentary Facies & Sea Level

Walther’s Law

Limestone

Sandstone

vertical sequence-1

Siltstone

vertical sequence-2

unconformity

• The relative sequence is more

important than absolute

completeness.

Sedimentary Facies & Sea Level

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

Sedimentary Facies & Sea Level

What cause a Transgression?

• Tectonic uplift

• Drop in sea level

• Over supply of sediment

Sedimentary Facies & Sea Level

What cause a Regression?

1. Continental Glaciation

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

Sedimentary Facies & Sea Level

Eustatic sea level change(world wide) - causes?

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1 meter rise

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2 meter rise

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6 meter rise

30 meter rise

100 meter rise

link to: USGS

2. Plate Tectonics

fast spreading rate = high sea level

slow = low sea level

(affects the shape of ocean

basins)

Sedimentary Facies & Sea Level

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.

Sedimentary Facies & Sea Level

Local sea level change