Fasies n Deps Env

8/19/2019 Fasies n Deps Env

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Depositional

Environments,Facies, Facies

Models andPaleogeograpy


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DepositionalEnvironments

Sediments accumulate in some environment ofdeposition or depositional environments

These areas receive net deposition Erosion may occur, but deposition dominates Features of these depositional environments are

preserved in the rock record Examples:

Sediment texture

Sedimentary structures (formed by processes in theenvironment) Fossils of organisms that lived in the environment

Ancient environments can be reconstructedfrom the clues that are preserved in the

sedimentary rocks


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Classication! Continental " # Fluvial " Alluvial Fans, $raided

%tream

Meandering %tream

# &acustrine # Eolian

'! (ransisional )%horelines* " # &obate )Delta*

# &inear " Clastics

Mi+ Clastic

Carbonate

Carbonates

-! Marine " .eef

%helf

(urbidite Pelagic


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Facies All the properties of a body of rock that allo0

us to di1erentiate it from those above, belo0

or laterally ad2acent to it roperties include

!ithology " rock type, including color, etc# $omposition " mineral content Texture " grain si%e, sorting, roundness Sedimentary structures Fossils

Facies means aspect " same !atin root as &face' verall appearance of a rock body

Facies are the products of depositionalenvironments

Examples: lanar laminated ne *uart% arenite facies +ioturbated, poorly sorted muddy skeletal limestone facies $rossstratied arkosic conglomerate facies


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Facies and -epositionalEnvironments

• The facies concept refers to the sum ofcharacteristics of a sedimentary unit,commonly at a fairly small (cmm) scale

• !ithology

• .rain si%e

• Sedimentary structures

• $olor

•

$omposition• +iogenic content

• !ithofacies (physical and chemicalcharacteristics)

•+iofacies (macrofossil content)

•


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Facies and -epositionalEnvironments

• Facies analysis is the interpretation of strata interms of depositional environments (ordepositional systems), commonly based on a

0ide variety of observations• Facies associations constitute several facies

that occur in combination, and typically representone depositional environment (note that very fe0individual facies are diagnostic for one specic

setting1)• Facies successions (or facies se*uences) are

facies associations 0ith a characteristic verticalorder

•

3alther4s &a0 (2345) states that t0o di6erentfacies found superimposed on one another and


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http://www.gpc.edu/~pgore/geology/historical_lab/environmentchart.htm


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Facies Model

8n ideali%ed description of a facies

$onstructed from modernenvironments and ancient rocks

Serves as a 9orm for comparison

Frame0ork for observation

redictor of patterns


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Facies Patterns

.roups of facies commonly sho0patterns

Pro+imal Facies (near the source)

tend to be coarse grained Distal Facies (far from source) tend

to be ner grained

This pattern is displayed upstreamand do0n in rivers and onshore too6shore in coastal areas

Facies are arranged according to


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Transgressive and egressive systems can be identied byobserving facies and lithological

changes in rock;sediment

Transgressive " sediments ne

up0ards, represent deeper 0aterenvironments

egressive sediments coarsen

up0ards, represents shallo0ing

Facies $hanges


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Facies Migration

Facies migrate through space and time


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Walther’s Law

of the Correlation of Facies

Only works where there are no unconformities Only facies that were laterally adjacent during

deposition (result of laterally adjacent environments)can be stacked vertically

Vertical arrangement of facies gives us information : Distribution of environments How environments migrated through space and time

sed as a basis to build facies maps orpaleogeographic maps

!ccurate time correlation of facies is essential "ime lines provide framework for correlation

#io$events Volcanic ashes

Other thin% uni&ue lithologies or marker beds


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Representing Facies:Stratigraphic Sections


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Deltas

Marginal Marine Deposition


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Ganges Delta, India


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Mississippi Delta(partial), USA

Mi i i i D lt ( ti l)


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Mississippi Delta (partial),USA

Drowning!


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Niger Delta D Model


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Modern DeltaS"en#iron$ents

Documents

Fasies n Deps Env