A brief over view about topic.

1. Sedimentary
Environments

2. Introduction
 The sedimentary environment is the specific depositional setting of a
particular sedimentary rock and is unique in terms of physical, chemical,
and biological characteristics.
 The physical features of a sedimentary environment include water depth
and the velocity and persistence of water.
 Chemical characteristics of an environment include the salinity
(proportion of dissolved salts), acidity or basicity (pH), oxidation potential
(Eh), pressure, and temperature.
 The biological characteristics are mainly the assemblage of fauna and
flora.

3. Classification
 All environments of deposition belong to one of three settings:
 Terrestrial/continental
 Coastal (or marginal marine)
 Marine.
 Sub environments, each with their own characteristic environmental
factors and sedimentary deposits, make up a sedimentary environment.

5. Terrestrial Environments
 Facies deposited in continental environment are dominantly siliciclastic
sediments.
 They characterized by general scarcity of fossils and complete absence
of marine fossils.
 Non siliciclastic sediments also occur in continental environment but they
are sub ordinate to siliciclastic sediments.
 Continental sedimentary rocks are less abundant overall than marine and
marginal marine rocks.

6. Fluvial Systems
 Desert areas to humid glacial regions.
 Two broad environmental settings:
 Alluvial fans
 River systems

7. Alluvial Fans
 Alluvial fans are deposits with fan shaped approximating a segment of a
cone and exhibiting convex-up cross sectional profile.
 Sediments are poorly sorted.
 Abundant gravel(>2mm) size detritus.
 Generally formed at the base of a mountain range.
 They occur both in sparsely vegetated arid and semiarid regions where
sediment supply is infrequent and in more humid areas where rainfall is
intense.

9.  Alluvial fans are classified into two types:
 Debris flow dominated fans
 Stream flow dominated fans
 Debris flow dominated fans:
 Poorly sorted
 Lacking sedimentary structures
 Impermeable and nonporous
 Stream flow dominated fans:
 Well sorted
 Sedimentary structures

10. River systems
 Channel Form:
 The channel form of rivers can be described in term of deviation of channel
from a straight path, the number of channels, the degree of channel sub
division by large bedforms(bars), braiding.
 Types:
 Meandering(single channel)
 Braided(multiple-channel)
 Anastomising

12.  Factors influencing the sinuosity:
 Magnitude and variability of stream discharge
 Channel slope
 Grain size of sediment
 Bed roughness
 The amount and kind of sediment load
 Stability of channel banks

13. Eolian Desert Systems
 Deserts are areas in which potential rates of evaporation greatly exceeds
rate of precipitation.
 They cover about 20-25 % of land surface.
 They have low rainfall approximately 25 mm/year.
 Deserts lies 10-30 degrees north and south of equator.
 They also lies in rain shadows of large mountain ranges.
 Large areas of desert environment may indeed be carpeted by eolian
sand(>125 km2=sand seas or ergs).

14. Transport and Depositional Process
 Vegetation is very sparse due to low rainfall.
 When rain comes, due to lack of vegetation it creates flash floods.
 Rain water move towards center of basin to create playas or inland
sabkhas.
 These playas and sabkhas become sites of carbonate and evaporate
minerals.
 Although, wind is the major agent of sediment transportation and
deposition.

15. Transport and Depositional Process
 Transported in 3 ways:
o Traction
o Saltation
o Suspension
 Traction and saltation is done by coarser sediment.
 Suspension is done by finer size particles.
 3 types of wind deposits:
 Loess
 Sand deposit
 Lag gravel

16. Wind deposits
 Loess:
 Accumulates far from source.
 Don’t have layers because particles are so fine.
 Sand deposit:
 Commonly well sorted.
 Lag deposits:
 Consisting of gravel size particles that are too longer to be transported by
wind and that form a deflation pavement.

18. Lacustrine environments
 Lakes cover about 1-2 percent of earth’s surface.
 Lake chemistry is sensitive to climatic conditions, making lake sediments
useful indicators of past climate.
 Lake sediments’ chemistry and mineralogy of wet and dry climates.
 Lake sediments can have economically important oil shales, coal, uranium
and evaporate minerals.
 2 types of lakes:
 Open lake
 Closed lake

19. How lakes are formed?
 By faulting and Rifting
 Glacial processes like ice scouring
 Volcanic activity
 Deflation by wind scour
 Fluvial activity

20. Varves
 Varves are thin alternating light and dark colored sediment layers.
 Thicker, light colored coarse grained laminae shows summer conditions.
 Thinner, finer grained , organic rich laminae form in winter months.

22. Paludal Environment
 HIGH amount of biological activity, so rocks of high organic content
 Mixed muds & coal/peat/lignite, with some fluvial sediments cutting
through organic-rich shale and sandstone or coal deposits with thin
stringers of siltstone and shale.
 Often associated with other environments (deltaic, fluvial, coastlines, etc.)
 Low energy
 Plant fossils are common in all stages of preservation.

24. Marginal Marine
Environments

25. Marginal marine environments

26. Classification
 Deltas
 Eustary
 Tidal flat
 Barrier island
 Lagoons

27. Deltas
 Deltas - form where rivers enter a standing body of water, slow down,
and deposit more sediment than can be removed by waves and currents.
 Although deltas also from in lakes, the largest deltas occur in the oceans.
 Many deltaic deposits resemble lake or shallow marine deposits at their
distal margins and fluvial deposits at their proximal margins.
 Deltas consist of a subaerial delta plain or delta-top (gradational
upstream to a floodplain, and a subaqueous delta front (delta-
slope and prodelta

29.  The delta slope is commonly 1-2° and consists of finer (usually silty) facies;
the most distal prodelta is dominated by even finer sediment.
 Fluvial dominated deltas:
 Jet: discharge of river
 Relationship between sediment laden inflowing water and receiving basin
influences shape of delta and sediment distribution.
 Types:
 Homopycnal deltas
 Hypopycnal deltas
 Hyperpycnal deltas

30.  Homopycnal deltas:
 Equal density
 Thorough mixing
 Abrupt deposition
 Common at the mouths of coarse grained rivers

32.  Hyperpycnal flow:
 River has high density than basin water
 Flows beneath the basin water
 Deposits on more gentle slopes of delta front

33. Hyperpycnal flow

34.  Hypopycnal flow :
 River outflow is less dense
 Flow outward on the top of the basin
 As horizontally oriented plane
 Fine sediments would be in suspension
 Generate a large active delta front area
 Most common type of delta flows.

35. Hypopycnal flow

37. Way of deposition

38. Beach and barrier island systems
 Mainland beaches are narrow accumulations of sand aligned parallel to
the shoreline and attached to the land.
 Barrier islands are similar to the mainland beaches but are separated
from the mainland beaches by lagoons, eustary or a marsh.
 Holocene beaches are more extensively studied because of their
recreational use, their accessibility, their economic potential(gold,
platinum, various minerals) and as erosion buffer between sea and the
land.

40. Eustarine Systems
 Eustary in a general sense are considered to be the lower portion of a
river open to the sea.
 The seaward portion of a drowned valley system which receive sediment
from both fluvial and marine sources which contains facies influenced by
tide, wave and fluvial processes.
 The estuary is considered to extent from the limit of tidal facies at it’s
head to the seaward side of coastal facies at it’s mouth.

42. Lagoonal Systems
 A lagoon is a shallow body of water separated from a larger body of
water by barrier islands or reefs.
 Lagoons run parallel to the coast which is opposite to eustary which is
perpendicular to the coast.
 Water may be fresh or saline.
 May be connected to river or not.
 Types:
 Atoll lagoons
 Coastal lagoons

45. Lagoons Types
 Atoll lagoons:
 A ring-shaped coral reef that encircles a lagoon partially or completely.
 Coral reefs grow upward while the islands subside.
 Depth may be >20m.
 Coastal lagoons:
 Form along gently sloping coasts where barrier islands or reefs can develop off-
shore, and the sea-level is rising relative to the land along the shore.
 Coastal lagoons do not form along steep or rocky coasts
 Due to the gentle slope of the coast, coastal lagoons are shallow.
 Coastal lagoons are usually connected to the open ocean by inlets between
barrier islands.
 Salinity varies.

48. Tidal flats
 Tidal Flats: low-energy mud flats between low and high tide.
 They occur along open coasts of low relief and relatively low wave energy
or behind barriers on high energy coasts.
 They occur within eustaries, bays and backshores of barrier island complexes
and deltas as well as along open coasts.
 The tidal flat divided into 3 zones :
 Supratidal Zone, the zone is influenced by extreme tides. This zone will
evaporation and produce crystal salt. This zone also called Sabkha.
 Intertidal Zone, located on between high and low tide level. This zone occurs the
bedload and suspension load transportation.
 Subtidal Zone, is under the water when low tide level. Tide influence in this
environment is very important especially at tidal channels, where bedload
transport and deposition are dominant.

50. Marine Environments
 Marine environments include four depositional environments:
 Continental shelf
 Continental slope
 Continental rise
 Abyssal plain

51. Continental Shelf
 The continental shelf is an underwater landmass which extends from
a continent, resulting in an area of relatively shallow water known as
a shelf sea.
 The width of the continental shelf varies considerably.
 The average width of continental shelves is about 80 km (50 mi).
 The depth of the shelf also varies, but is generally limited to water
shallower than 150 m .
 The shelf usually ends at a point of increasing slope[7] (called the shelf
break).

52. Continental Shelf
 Sediments:
 The continental shelves are covered by terrigenous sediments.
 little of the sediment is from current rivers; some 60-70% of the sediment
on the world's shelves is relict sediment.
 Continental shelves are usually covered with a layer of sand, silts, and silty
muds.
 Their surfaces exhibit some relief, featuring small hills and ridges that
alternate with shallow depressions and valley like troughs.

54. Continental Slope
 Extends from shelf break and lower boundary is typically located at water
depths ranging from 1500 to 4000 m depth.
 They are comparatively narrow(10-100)km wide and dip seaward more
steeply than shelf.
 The transition from continental crust to oceanic crust usually occurs
below the continental slope.
 Mud dominates the continental slope. However, sand may also be found.
 The continental slopes are temporary sites for deposition of sediments.

55. Continental Slope
 The sediments get collected for a period of time until and unless the
structure becomes unstable.
 When the edge becomes unstable it sloughs off and forms
the continental slope.
 Sunlight does not penetrate these regions easily. Water pressures are
relatively high. The actual amount of sunlight that enters these water
bodies is mainly absorbed at the surface.
 About one-half of all continental slopes descend into deep-sea
trenches or shallower depressions, and most of the remainder terminate
in fans of marine sediment or in continental rises.

56. Continental Slope
 Beyond the shelf-slope break, the continental crust thins quickly, and
the rise lies partly on the continental crust and partly on the oceanic crust
of the deep sea.

57. Continental rise

58.  Continental rise, a major depositional regime in oceans made up of thick
sequences of continental material that accumulate between
the continental slope and the abyssal plain.
 Continental rises form as a result of three sedimentary processes:
 mass wasting
 the deposition from contour currents
 and the vertical settling of clastic and biogenic particles.

60.  3 types of deposits are there:
 Turbidites
 Contourites
 Biogenic particles

61. Abyssal Plain
 Abyssal plain, flat seafloor area at an abyssal depth (3,000 to 6,000 m)
 larger plains are hundreds of kilometres wide and thousands of kilometres
long.
 The plains are largest and most common in the Atlantic Ocean, less
common in the Indian Ocean.
 Horizontal silty, sandy, and even gravelly beds that are fractions of a
centimetre to several metres thick comprise 2 to 90 percent of abyssal-
plain sediment.
 The coarse layers are interbedded with homogeneous deposits of fine-
grained clay and the microscopic remains of organisms that inhabit the
waters overlying the abyssal plains.