facies gail
TRANSCRIPT
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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