2. Sedimentary Environment
A depositional environment is a specific type of place
in which sediments are deposited, such as a stream
channel, a lake, or the bottom of the deep ocean. They
are sometimes called sedimentary environments
The layers of sediment that accumulate in each type of
depositional environment have distinctive
characteristics that provide important information
regarding the geologic history of an area
3. The characteristics that can be observed and measured
in a sedimentary rock to deduce its depositional
environment include its lithology (which is essentially
its rock type), its sedimentary structures, and any
fossils it may contain
4. WHY ARE DEPOSITIONAL ENVIRONMENTS
IMPORTANT?
Knowledge of depositional environments is important
for reconstructing earth history, understanding earth
processes, and helping humans survive and prosper
on earth
Reconstructing earth history
By analyzing a sedimentary rock, a geologist can
deduce what was happening on earth at the place
and time the sediment was originally being deposited
7. Alluvium
Alluvium is drived from Latin, alluvius, which means"to
wash against“
Alluvium is loose, unconsolidated (not cemented together
into a solid rock) soil or sediments, which has
been eroded, reshaped by water in some form, and
redeposited in a non-marine setting
Alluvium is typically made up of a variety of materials,
including fine particles of silt and clay and larger particles
of sand and gravel.
When this loose alluvial material is deposited or
cemented into a lithological unit, or lithified, it is called
an alluvial deposit
8. Aeolian
Aeolian processes, also spelled eolian or æolian,
pertain to wind activity in the study
of geology and weather and specifically to the wind's
ability to shape the surface of the Earth (or
other planets)
Winds may erode, transport, and deposit materials and
are effective agents in regions with sparse vegetation,
a lack of soil moisture and a large supply of
unconsolidated sediments
Although water is a much more powerful eroding
force than wind, aeolian processes are important in
arid environments such as deserts
9. Fluvial
Fluvial is a term used in and geology to refer to the
processes associated with rivers and streams and
the deposits and landforms created by them. When
the stream or rivers are associated with glaciers, ice
sheets, or ice caps, the term glaciofluvial or
fluvioglacial is used
Fluvial processes include the motion of
sediment and erosion or deposition on the river bed
10. Lake
A lake is an area of variable size filled with water, localized in
a basin, that is surrounded by land, apart from any river or other
outlet that serves to feed or drain the lake
Lakes lie on land and are not part of the ocean (except for sea
lochs in Scotland and Ireland), and therefore are distinct
from lagoons, and are also larger and deeper than ponds,
though there are no official or scientific definitions
Lakes can be contrasted with rivers or streams, which are usually
flowing. However most lakes are fed and drained by rivers and
streams
Natural lakes are generally found in mountainous areas, rift
zones, and areas with ongoing glaciation
Other lakes are found in endorheic basins or along the courses
of mature rivers
11. Lake
In some parts of the world there are many lakes
because of chaotic drainage patterns left over from the
last Ice Age
All lakes are temporary over geologic time scales, as
they will slowly fill in with sediments or spill out of the
basin containing them
13. Marginal Marine Sedimentry
Environment
Marginal marine environments lies along the boundary
between continetal and marine depositional
environments
A wide varity of sediments including Conglomerates,
Sand stones, Shales Carbonates and evaporites can
accumulate in these various marginal marine
environments
14. Beach & Barrier Islands
These are shoreline deposits exposed to wave energy
and dominated by sand with marine fauna
Barrier islands are separated from margined from the
mainland by a Lagoon
The are commonly associated with tidal flat deposits
15. Lagoon Environment
Lagoons are coastal bodies of water that have very
limited connection to the open ocean
Lagoons generally develop along the coasts where
there is a wave formed barrier and are largely
protected from the power of open ocean waves
A lagoonal succession is typically mudstone, often
organic rich with thin wave rippled sand beds
16. Estuarine Environments
An estuary is the margined influenced portion of a
drowned valley
A drowned valley is the seaward portion of a river
valley that becomes flooded with seawater when there
is a relative rise in sea level
They are regions of mixing of fresh water and seawater
Sediment supply to the estuary is from both river and
marine sources, and the processes that transport and
deposit sediments are a combination of river and wave
or tidal processes
17. Tidal Flats
Tidal flats are formed when mud is deposited by tides
or rivers
Tidal flats are the border of lagoons and estuarine
environments
Tidal flats are areas of low relief, cut by meandering
tidal channels
Laminated or rippled clay silt and fine sand may be
deposited by a tidal flat
18. Marine Environments
Marine environments are in the seas or oceans
Marine environments include reefs, the continental
shelf, slope, rise and abyssal plain
19. Continental Shelf
The continental shelf is flooded edge of the continent
It is relatively flat with a slope of less than 0.1*, shallow
less than 200m and may be up to hundreds of
kilometers wide
Continental shelves are exposed to waves tides and
currents and are covered by sand silt mud and gravel
20. Reef Deposits
Reefs are wave resistant, mound like structures made
of calcareous skeletons of organisms such as corals
and certain types of algae
Most modern reefs are in warm, clear, shallow, tropical
seas between latitudes of 30o N and 30o S of equator
21. Continental Slope Deposits
The continental slope are located seaward of the
continental shelf
The continental slope is the steep (5-25o) drop off at
the edge of the continent
The continental slope passes seaward into the
continental rise which has a more gradual slope
22. Continental Rise
Continental rise located between the continental slope
and the abyssal plain
The continental rise is the site of deposition of thick
accumulations of sediments much of which is in
submarine fans
Deposited by turbidity currents at the base of
continental rise
Turbidity current deposits are called turbidities are
characterized by graded bedding
23. Abyssal Plain
Abyssal plain is the deep ocean floor
It is basically flat, and is covered by very fine grained
sediments consisting primarily of microscopic
organisms e.g. radiolarians and diatoms
Abyssal plain sediments may include chalk diatomite
and shale deposited over basaltic oceanic crust