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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 misused

and misunderstood AGI (1984) Definition:

The aspect, appearance, and characteristics of arock unit, usually reflecting the conditions of its

origin; especially as differentiating it from adjacentor associated units

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 definedas

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 geometryis the 3-D shape of deposit

barrier island

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Question?

What are you looking at? How can you describe it in the

framework 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 model2-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 adjacent

to 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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3-D Block daigram

facies associations in adelta distributary

channel environment

4-D models

add

understandingof processes

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General summary given to a depositional system

2-D Vertical successions of sediment that

represent facies relationships expected in the

geologic 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 facies

and their relationships to each other, apply a facies modeland assign a depositional environment

So, what is this?

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fluvialdelta

marine

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 level

With rise in sea level ..

Conditions (tectonics or climate) usuallychange with time

Transgressivesediments fine upwards,

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Transgressiveand Regressivesystems can beidentified by observing facies and lithologicalchanges in rock/sediment

Transgressivesediments 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 Processes2. 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 thisdepositional environment?

Fluvial Environment

Meandering River

Cross bedded sandstones

Coarse gravel deposits Broad sheets of silty shale with

root casts and plant debris

Isolated Shale bodies

Beds of peat and coal

Facies models help solve the puzzleof depositional environment

Summaryusing an example