sedimentsary facies

1. •Sedimentary Facies is a body or packet of sedimentary rock with
features that distinguish it from other facies.
• Features used to separate facies are sediment composition (lithology),
grain size, texture, sedimentary structures, fossil content and colour.
•The characteristics of the rock unit come from the depositional
environment.
Facies
Depositional Environments
Concept of Sedimentary Facies

2. facies: the total textural, compositional and structural characteristics
of a sedimentary deposit resulting from physical, chemical
and biological processes and accumulated and modified in a
particular environment.
Facies can be described in terms of :
1. The sediment itself: (e.g. cross-bedded sandstone facies.
2. The depositional process (e.g. stream-flood facies)
3. The depositional environment (e.g. tidal-flat facies)

3. Limestone Shale Siltstone Sandstone
Reef Lagoon Near Shore Beach Environment
Facies
Lithofacies: A mappable subdivision of a stratigraphic unit that
can be distinguished by its lithology- texture, mineralogy,
grain size, and the depositional environment that produced it .
Example: gray cross-bedded fine-grained limestone rock
Facies Types
• Biofacies
– observations are based on fauna and flora present
– Ichnofacies focuses on trace fossils
– Examples
• echinoid and crinoids = biofacies
• burrows and tracks = ichnofacies

4. facies assemblage (association): collection of multiple facies
resulting from genetically related accumulation and modification.
EX: -lenticularly bedded stratified pebble conglomerate with
planar cross-stratified sandstone
-fluvial channel lithofacies assemblage
Turbidite Facies
Assemblage

5. depositional system: assemblage of multiple process-related
sedimentary facies assemblages, commonly identified by the
geography in which deposition occurs.
EX: nearshore depositional system, deep marine
depositional system.

6. •Facies sequences are recurring facies associations which occur in a
particular order due to the inherent temporal changes in depositional
conditions in particular depositional environments
Facies sequences

7. Factors controlling sedimentary Facies
1. Depositional processes:
• Sediments can be deposited by a wide range of processes including Wind,
streams, tidal currents, storm and turbidity currents, waves, in-situ growth
of animal skeleton as reefs, and the direct precipitation of minerals, as in
evaporites.
• They leave their record in the sediment in the form of sedimentary
structures and textures.
2. Tectonics framework
• It determines the depositional setting (e.g. stable craton, intracratonic basin
or rift, continental margin, ocean floor, trench and arc-related situation
• It includes rate of subsidence and uplift and volcanoes
• It controls sediment supply and organic productivity
3. Climates:
• It is a major factor in subaerial weathering and erosion which affect the
composition of terrigenous clastic sediments
• It is important in formation of some lithologies (evaporites and limestones).
4. Depositional environment

8. Depositional Environments
• Depositional environment is an area of the Earth’s surface
(geographic setting) where sediment is accumulating (deposited) as
a result of distinct physical, chemical and biological processes that
influence sediment deposition.
• Each setting is characterized by a particular combination of geologic
processes that controlled by: water type and depth (river, lake,
ocean); topography; biological activity; relation to plate tectonics.
• By studying present day
environments, geologist
can more easily interpret
the rock record along
the geologic time.
• The geologic setting
may change with time
(e.g. marine to
continental)

9. It can be determined by looking at
– Texture (grain size, shape and composition, etc..)
– Petrographic analyses (e.g., evaluate diagenesis)
– sedimentary structures
– fossils content,
– bed shape and vertical sequences within the sedimentary layers
How can determine the type of Depositional environment?
How can Depositional environment affect the Facies?
-Water depth, degree of agitation and salinity are import physical attributes of
subaqueous environments and these affect and control the living organisms or
forming the sediment.
- Chemical factors such as Eh and pH of water affect organisms and control
mineral precipitation.
-Shape and location of basin of deposition affect the composition, fossil
contents, and textures

10. Depositional Settings
• Continents: Desert, glacial, fluvial (rivers), lake, swamp, cave
• Mixed (Transition zone): Lagoon, river delta, beach, tidal flat
• Marine : Reefs, continental shelf, continental slope, deep water

12. Walther’s Law
Sedimentary environments that started out side-by-side
will end up overlapping one another over time due to
transgressions and regressions.
"Facies adjacent to one another in a continuous vertical
sequence also accumulated adjacent to one another laterally".
the vertical succession of facies reflects lateral changes in environment

13. • Applies only to a section with no unconformities.
•Applies to a section without rapid environmental change where non-
adjacent environments may replace one another.
•Gradational (vertical) transitions from one facies to another indicate original
adjacency and genetic relationship during formation.
•Sharp/erosional (vertical) contacts between facies provides NO evidence
of contemporaneous genetic relationship of depositional environments

14. The facies within this
succession will represent
conformable deposits that
accumulated through time in
progressively shallower water
depths, and thus the vertical
succession through the
parasequence is:
-shallowing-upward,
-usually coarsening-upward, and
- as higher, younger sediments
are deposited under
progressively more proximal,
higher-energy conditions
Shallowing-upward cycle

15. The facies within this succession will
represent conformable deposits that
accumulated through time in
progressively deepnming water
depths, and thus the vertical
succession through the parasequence
is:
-deepening-upward,
-usually finning-upward, and
- as higher, younger sediments are
deposited under progressively more
deeper, lower-energy conditions
Deepening-upward cycle

16. Facies Analysis
• The interpretation of strata in terms of depositional
environments
• How?
– Recognize sedimentary environments
– Interpret rocks based on facies
– Rely heavily on facies associations
– Vertical
– Horizontal
– Can use idealized model to assist in analysis

18. • According to this classification, sandstones are divided into two major groups based
on texture (matrix content):
Sandstone Classification
The widely used classification is that presented by Pettijohn et al., (1973) and based
on Dott (1964). This classification is based on:
1. the mineralogy of the sediment (the three mineral components: Quartz plus chert,
feldspar, and lithic fragments (Q, F & R) and
2. presence or absence of a matrix (matrix content).
(a) matrix-poor sandstones, the arenites,
where the rocks are composed of grains only
or contain less than 15% matrix. Arenites are
texturally mature and clean sandstones. Their
lithification is due to cement precipitates in the
primary intergranular pores.
(b) matrix-rich sandstones, the wackes,
where the rocks contain 15-75% matrix.
Wackes are argillaceous, texturally immature,
or “dirty” sandstones.
• Each one of these two groups is subdivided into various rock-types based on
mineral composition.

19. • The percentage of quartz, feldspar and rock fragments allow the arenites and
wackes to be further subdivided.
Of the arenites, the term quartz arenite is applied to those with 95% or more
quartz grains. Arkosic arenite refers to an arenite with more than 25%
feldspar, which exceeds the rock fragments content, and litharenite is applied
where the rock fragments content 25% and is greater than feldspar. Other
transitional rock-types are present as arkose, lithic arkose, subarkose,…
The wackes are the
transitional group
between arenites and
mudrocks. They
include 1. greywacke
where two types are
distinguished:
feldspathic and lithic
greywacke, and 2.
quartz wacke, a rock-
type rich in quartz
with some matrix.
From Boggs, Principles of Sedimentology and Stratigraphy, 4th ed., Figure 5.5, p. 130

20. Quartz

21. Carbonate Rocks Constituents
I- Allochemical Particles (allochems)
– framework grains of a mechanically deposited limestone
– four main types:
- Skeletal grains (fossil and fossil fragments,
- Non-skeletal grains: Ooliths, Peloids, Intraclasts
•II. Orthochemical Particles (orthochems)
– matrix and cement that fill spaces, bind allochems together and lithify the
sediment Pores
Cement
Non-skeletal grains
Matrix
(<20 m)
Skeletal grains

22. 1. Intraclasts (rock fragments):
• formed, transported and redeposited within the basin
2. Ooliths: concentrically laminated carbonate structures, including:
• oolites -concentrically laminated structures,less than 2mm in
diameter, thought to be abiogenic in origin
• pisolites - same as oolites, but greater than 2mm in diameter
• oncolites - spheroidal stromatolites (> 1-2 cm)
3. Peloids:
• silt to fine grained sand sized carbonate particles with no distinctive
internal structure; most thought to be fecal pellets
4. Skeletal particles (bioclasts):
• whole microfossils, whole megafossils, broken shell fragments
– algae, forams, corals, bryozoans, brachiopods, gastropods,
pelecypods, ostracods, etc.

23. • Type I limestone, Sparry Allochemical rocks:
- allochems > 50%,
- spar cement > micrite mud
- 4 rock types
- more energetic environment, some sorting
• Type II limestone, Micritic Allochemical rocks:
– allochems >10%,
– micrite mud > spar cement
– 4 rock types
– lower energy environment, more poorly sorted
than Type I
• Type III limestone: Micrite
- allochems < 10%
- very low energy at the site of deposition
(carbonate mudrock)
• Type IV limestone “Biolithite”: Reef rock ,
- a separate categories were proposed for rocks
formed by organic growth
􀂄 Folk Classification (1959, 1962)

24. • Folk proposed a textural spectrum that incorporated textural parameters:
Mud component (matrix %), Sorting, Rounding and packing of grains
• Carbonate rocks with component grains coarser than sand size (>2 mm)
are differentiated as rudites, Oosparrudite, biomicrudite,…

25. • Dunham Classification
– Based on depositional Texture
• depositional texture recognizable or not recognized (crystalline)
• mud-bearing vs mud-free sediment
• Grain support vs mud support
• sediment deposited in calm vs agitated waters
• bound (biologically) (presence or absence of organic binding)