Junaid Abdul Khaliq

Facies All the properties of a body of rock that allow

us to differentiate it from those above, below or laterally adjacent to it

Properties include› Lithology – rock type, including color, etc.› Composition – mineral content › Texture – grain size, sorting, roundness› Sedimentary structures› Fossils

Facies means aspect – same Latin root as “face” Overall appearance of a rock body Facies are the products of depositional

environments Examples:

› Planar laminated fine quartz arenite facies› Bioturbated, poorly sorted muddy skeletal limestone facies› Cross-stratified arkosic conglomerate facies› Stromatoporoid-tabulate coral reef facies

Facies Migration

Facies migrate through space and time Migration is in response to

environmental factors› Sediment supply› Sea level change› Subsidence

Facies become stacked during migration

A single facies is likely to be different ages in different locations

Facies Patterns Groups of facies commonly show

patterns Proximal Facies (near the source) tend

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

finer grained This pattern is displayed upstream and

down in rivers and onshore to offshore in coastal areas

Facies are arranged according to distribution of depositional environments

Concept of Sedimentary Facies

Sedimentary Facies (2 uses): 1. All characteristics of a rock unit, and• characteristics come from depositional environment, eg. “shelf facies”

2. Rocks that are subset of a group of rocks from an environment,

eg. “Rock A is a facies of Rock B.”

Facies

Depositional Environment(s)

Facies Example

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

A = Sandstone facies (beach environment)B = Shale facies (offshore marine environment)

C = Limestone facies (far from sources of terrigenous input)

Facies Change

Walther’s Law

Johannes Walther(1860-1937)

The Law of the Correlation (or Succession) of Facies of the German geologist Johannes Walther (1860–1937

Walther's Law of Facies, named after the geologist Johannes Walther, states that the vertical succession of facies reflects lateral changes in environment. Conversely, it states that when a depositional environment "migrates" laterally, sediments of one depositional environment come to lie on top of another.[3] A classic example of this law is the vertical stratigraphic succession that typifies marine trangressions and regressions. However, the law is not applicable where the contact between different lithologies is non-conformable (i.e. sedimentation was not continuous), or in instances of rapid environmental change where non-adjacent environments may replace one another.

http://faculty.weber.edu/bdattilo//fossils/notes/facies.html

Vertical/lateral variations in rock

Recognition of lateral variation› Because rocks are not constant through space,

you get a variation in lithology within one unit. Initially people didn’t recognize this-

› Thought Noah’s flood left layer cake layers of strata that extended to ends of Earth without change in lithology or thickness Began to trace beds

walked them looked at how the rocks between the boundaries changed realized fallacy of idea

› We retain layer cake to describe stacking pattern; not infinite nature

Walther's Law of Correlation of Facies

“Only those lithofacies which are a product of sedimentary environments found adjacent to one another in the modern can be occur superimposed in continuous, uninterrupted stratigraphic succession.”

Walther’s Law of Correlation of Facies

Relationship between vertical and lateral variations

The fact that there is lateral variation in facies leads to vertical variation in facies Walther’s Law of Correlation of Facies

Lateral variations are expressed in the vertical due to the succession of facies

the, facies boundaries may shift so that the deposits of an adjacent environment may lying directly at top those of a laterally related environment

EXPLINATION

Certain facies associations are common in the rock record.• For example, most clastic shoreline show a series of depositional environments that are progressively finer-grained in the offshore direction.

• There are facies belts of coarses sands, and silts and clays. If the relative sea level changes, deposits of these facies belts accumulate.• Three facies pattern are possible.

Explanation

In the other word the same section that is present vertically also present horizontal unless there is break in sedimentation.

A vertical change’s of facie’s with in a relatively conformable succession of genetically related strata.

EXP:

Facies show a transgressive pattern6. Walther’s Law when the sediment supply is overpower by a relative rise in sea level, or when the land subsides tectonically. Both cause the shoreline to move landward

Facies show a regression pattern7. Walther’s Law when the shoreline moves seaward due to an excess sediment supply from land, when the land is tectonically uplifted and the sea level retreats, or when there is a relative lowering of sea level.

This technique is known as become the part of sequence stratigraphy.

where sequence are regional co-relatable package of strata that record the local or regional changes in base level.

Walther’s Law Application

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 on› Distribution of environments› How environments migrated through space and time

Used as a basis to build facies maps or paleogeographic maps

Accurate time correlation of facies is essential Time lines provide framework for correlation

› Bio-events› Volcanic ashes› Other thin, unique lithologies or marker beds

The Law of the Correlation (or Succession) of Facies of the German geologist Johannes Walther (1860–1937used widely in the interpretation of sedimentary sections

Walther's Law is used to interpret the depositional setting of these parcels of sediment.

the application of Walther's Law have made this law a very POWERFUL tool and all sedimentary stratigraphers use it

An example of the application of Walther's Law can be seen in Coe et al's (2003) interpretation of the depositional setting of high frequency clastic parasequences from sections measured in the Book Cliff escarpment

Using this principle, a vertical succession, encountered say as drill core isretrieved, of sandstone over shale over limestone, can be read as regression(offlap), and a vertical succession of limestone over shale over sand, can beread as transgression (onlap) of an epeiric (continental shelf and interior,shallow) sea (Figure c15.1). Walther had originally applied his principle

for the correlation of facies to argue for the deepening of a

transgressive

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