1. Introduction to sedimentary
environments
MAHBOOB AHMED

2.  Landscapes form and constantly change due to weathering and
sedimentation. The area where sediment accumulates and is later buried
by other sediment is known as its depositional environment.
 Depositional environments are often separated into three general types,
or settings: terrestrial (on land), marginal marine (coastal), and marine
(open ocean). Examples of each of these three regional depositional
settings are as follows:
 terrestrial-alluvial fans, glacial valleys, lakes.
 marginal marine- beaches, deltas, estuaries, tidal mud and sand flats.
 marine-coral reefs, continental slope and deep marine deposition.
 During deposition of sediments, physical structures form that are
indicative of the conditions that created them. These are known as
sedimentary structures. They may provide information about water
depth, current speed, environmental setting or a variety of other factors.
Among the more common of these are: bedding planes, beds, channels,
cross-beds, ripples, and mud cracks.

4. Continental/terrestrial depositional
environments
Continental environments Fluvial bed forms
Continental environments are those in
which sediments are deposited on land
or in fresh water.
Fluvial environments
In fluvial system sediments deposited by
Streams and rivers.
Fluvial deposits include cross-bedded
and rippled river sandstones and parallel
or cross-bedded floodplain contains
mudstones (siltstones and clay shales).

5. Braided and
meandering streams
Fluvial environments
include braided and
meandering river and
stream systems. River
channels, bars, levees, and
floodplains are parts of the
fluvial environment.
Channel deposits consist of
coarse, rounded gravel,
and sand. Bars are made of
sand or gravel. Levees are
made of fine sand or silt.
Floodplains are covered by
silt and clay.

6. Braided rivers
Rivers with a high proportion
of sediments , sand or gravel
in the
channel the flow is divided to
give the river a braided form.
The bars in a braided river
channel are exposed at low
flow stages.
The bars within the channel
may vary in shape lithology
and sizes.

7. Alluvial environments
Alluvial fans
Alluvial fans are fan shaped
deposits formed at the base
of mountains due to fast
flowing stream, which are
flattens, slows, and spreads
typically onto a flatter plain.
These are characterized by
poorly sorted, boulder and
gravel dominated, debris flow
conglomerates.

8. Deserts
environments
Aeolian
Deposited by wind in deserts
Deposits.
Usually contain vast areas
where sand is deposited in
dunes. Dune sands are cross-
bedded, well sorted, and well
rounded, without associated
gravel or clay.
Aeolian sandstones frequently
display large scale (1 to 3
meter) cross bed sets.

9. Lacustrine
environments
Sediments are deposited in
lack .
Lack deposits may be large or
small, shallow or deep, and
filled with terrigenous,
carbonate, or evaporitic
sediments.
Fine sediment and organic
matter settling in some lakes
produced laminated oil shales
and coal form.

10. Glacial environments
Sediments deposited by a
glacier.
Sediments which are
deposited by a Glacier are
poorly sorted ,angular
sediments .

11. Deltaic environments
Deltas are fan-shaped
deposits formed where a river
flows into a standing body of
water, such as a lake or sea .
Coarser sediment (sand)
tends to be deposited near
the mouth of the river; finer
sediment is carried seaward
and deposited in deeper
water.

13. Marginal marine
environments
Marginal marine
environments lies along the
boundary between
continental and marine
depositional
Environments.
A wide variety of sediments
including Conglomerates ,
sandstone s , shales
carbonates , and evaporites
can accumulate in these
various marginal marine
environments.

14. Beach and barrier
islands
These are shoreline deposits
exposed to wave energy and
dominated by sand with a
marine fauna.
Barrier islands are separated
from the mainland by a
lagoon. They are commonly
associated with tidal flats
deposits.

15. Lagoonal environments
Lagoons are coastal bodies of
water that have very limited
connection to the open
ocean.
Lagoons generally develop
along 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. Estaurine
environments
An estuary is the marine-
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 and seawater.
Sediment supply to the estuary
is from both river and marine
sources, and the processes that
transport and deposit this
sediment are a combination of
river and wave and/or tidal
processes.

17. Tidal flats
Tidal flat are formed when
mud is deposits 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
(either terrigenous or
carbonate) may be deposited
by a tidal flat.

19. Marine environments
Marine environments
are in the seas or
oceans. Marine
environments include
reefs, the continental
shelf, slope, rise, and
abyssal plain.
Continental shelf
The continental shelf
is the flooded edge of
the continent. It is
relatively flat (with a
slope of less than
0.1o), shallow (less
than 200 m or 600 ft
deep), and may be up
to hundreds of miles
wide. Continental
shelves are exposed
to waves, tides, and
currents, and are
covered by sand, silt,
mud, and gravel.

20. Reef deposits
Reef are wave-resistant,
mound-like structures made
of the calcareous skeletons of
organisms such as corals and
certain types of algae. Most
modern reefs are in warm,
clear, shallow, tropical seas,
between the latitudes of
30oN and 30oS of the
equator.

21. Continental slope
deposit
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 sediment,
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.
Continental slope and
continental rise are show deep
marine deposition.

23. Abyssal plain
Abyssal plain is the deep
ocean floor. It is basically flat,
and is covered by very fine-
grained sediment, consisting
primarily of clay and the shells
of microscopic organisms
(such as foraminifera,
radiolarians, and diatoms).
Abyssal plain sediments may
include chalk, diatomite, and
shale, deposited over the
basaltic ocean crust.