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    FACIES MODELS

    Sedimentology 340

    Pages 241-243

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    Previous Work

    Majority of the semester has been largelydescriptive, identifying; Lithology & mineralogy

    Sedimentary fabric and texture Sedimentary structures

    Scales of observation

    Now a Story to tell and puzzles to solve Sediments are products of sedimentary processes

    Snapshot of the environment of deposition

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    Sedimentary Facies

    Facies analysis

    The interpretation of rocks and sediments for the

    purpose of reconstructing the processes that were

    responsible for the original deposition

    Multi-pronged approach

    Physical

    Chemical

    Biological Lithofacies and Biofacies

    Example of sedimentary facies modal:

    Delta distributary channel

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    Pardon me, what are facies?

    In the field of geology, facies is often misusedand misunderstood

    AGI (1984) Definition: The aspect, appearance, and characteristics of a

    rock unit, usually reflecting the conditions of itsorigin; especially as differentiating it from adjacentor associated units Theimagecannot bedisplayed. Your computer may nothaveenough memory toopen theimage,or the imagemay havebeencorrupted.Restartyour computer,and then open thefileagain.If thered x stillappears,you may haveto deletetheimageandthen insertitagain.

    Facies!

    Refers to the lithologic and biologic

    characteristics of a sedimentary deposit

    imparted by the processes collectively

    operating in the depositional environment

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    Facies defined

    Deposits that evolve in a specific

    depositional environment are considered

    to be sedimentary facies Ex. Arid desert lakes/salt flats

    Bonneville Salt Flats, Utah

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    For this class and facies will be defined

    as

    A description of physical, chemical and

    biological properties of a sedimentary unit

    Main criteria in facies definition are:

    Lithology, sedimentary structures,paleontology, and sediment body geometry

    Facies defined

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    Sediment body geometry is the 3-D shape of deposit

    barrier island

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    Question?

    What are you looking at? How can you describe it in theframework of its depositional environment?

    ?

    This is a delta

    How do we know?

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    Delta

    Delta is at the end of a river and is the sedimentary

    record of deposition into deeper water

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    Nile Delta Example

    Modern examples are used

    to gather data on processes

    and deposits (cores)

    Facies model - a 3-D block

    diagram

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    Deltadepositional

    environment?

    Facies model 2-D vertical succession diagram

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    Depositional environments are generally composed of

    multiple subenvironments

    Ex. Delta Thus, we can expect that facies will vary throughout the

    environment to reflect the transition between

    subenvironments

    We must assume that adjacent facies represent adjacent

    environments

    So question was.how do we know ?

    Answer: facies associations

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    Delta components and facies

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    So how are they related?

    The association of certain facies near or adjacentto each other are characteristic of distinctdepositional environments

    Based on observations from modern

    environments of deposition and parallels topast environments

    By understanding these associations, we can

    generate facies models

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    General summary given to a depositional system

    2-D Vertical successions of sediment that

    represent facies relationships expected in thegeologic record

    3-D Block Diagrams

    4-D Models detailing sedimentary processes

    Facies Models

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    Facies that occur in comformable vertical successions of

    strata also occur in laterally adjacent environments

    Thus, facies boundaries may shift so that the deposits of an

    adjacent environment may lie directly atop those of a

    laterally related environment

    Walthers Law of Correlation of Facies

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    Takeaway Message:

    For any sedimentary package you can examine the faciesand their relationships to each other, apply a facies modeland assign a depositional environment

    So, what is this?

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    fluvial

    deltamarine

    Catskill Delta builds westward through time with sediment delivered by rivers

    Catskill Delta (Devonian)

    Regressive- sedimentscoarsen upwards

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    barrier island

    3-D Barrier Island Facies Model

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    The shoreline shiftslandward and fine grainedmarine sediments willoverly coarser beachsediments

    Environments are dependent on sediment supply,

    subsidence and changing sea levelTheimagecannot bedisplayed. Your computer may nothaveenough memory toopen theimage,or theimagemay havebeen corrupted.Restartyour computer,and then open thefile again.If thered x stillappears,you may haveto deletetheimageand then insertitagain.

    With rise in sea level ..

    Conditions (tectonics or climate) usuallychange with time

    Transgressivesediments fine upwards,

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    Transgressive and Regressive systems can beidentified by observing facies and lithologicalchanges in rock/sediment

    Transgressive sediments fine upwards,represent deeper water environments

    Regressive- sediments coarsen upwards,represents shallowing effect

    Facies

    Changes

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    What factors control the nature and distribution

    of facies?

    1. Sedimentary Processes

    2. Sediment Supply

    3. Climate

    4. Tectonics (subsidence or uplift)

    5. Sea level change

    Facies Distribution

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    What facies would you expect to find from this

    depositional environment?

    Fluvial Environment

    Meandering River

    Cross bedded sandstones

    Coarse gravel deposits

    Broad sheets of silty shale withroot casts and plant debris

    Isolated Shale bodies

    Beds of peat and coal

    Facies models help solve the puzzleof depositional environment

    Summary using an example