environments where sediments deposits

1. Depositional Environments
And their Diagnostic Criteria

2. Group Members
Zain Ahmed
Faizan Sabir
Fahad Sultan
Haider Sikandar
Umer Shahid

3. Contents
Depositional Environment
How to identify them
Types of environments
Diagnostic criteria or Field recognition

4. Depositional Environment
Earth material is broken down by processes of
weathering and erosion, and is transported by the action
of wind, water, or ice, and/or by the force of gravity
A sedimentary environment has been defined as a “part
of the earth's surface which is physically, chemically
and biologically distinct from adjacent areas”
Physical characteristics and geographical location
determines the type of sediment that will be deposited

5. Cont.
 Layers of sediment have distinctive characteristics that
provide important information regarding the geologic history of
an area
 The characteristics that can be observed include its
Lithology
Sedimentary structures
Fossils

6. How to Identify
 The characteristics of a sedimentary rock that are affected by
its depositional environment are
Sedimentary Lithology (the minerals and texture of the rock)
 Sedimentary Structures
 Fossils
 Sedimentary rocks contain sedimentary structures that were
formed as the sediments were being deposited.
 Many sedimentary rocks also contain fossils, which are our
main source of information of the history of life on earth.

7. Cont.
 Sedimentary structures and fossils are best found and
examined in outcrops, where whole beds of sedimentary
rocks are exposed in their undisturbed geological setting.
 The structures and fossils in sedimentary rocks reveal what
was happening on the earth at the place and time the
sediments were being deposited.

8. Depositional Environments
 TerrestrialContinental: Deposited on land or in fresh water
 FluvialAlluvial
 Glacial
 EolianDesert
 Lacustrine
 Transitional: Deposited in an environment showing influence of both fresh
water or air and marine water.
 Deltaic
 Esturine
 Lagoonal

9. Types cont.
 Marine: Only influenced by sea water.
 Shallow marine clastic
 Carbonate shelfReefs
 Continental slope
 Deep marine

11. Fluvial
 River:
Confined water body moving downhill in channels
 Fluvial:
Processes associated with rivers and streams, deposits and landforms created by
them
 Fluvial processes:
 Motion of sediments
 Erosion
 deposition

12. Types
StraightBraided Rivers
Almost straight, less bends
Consists of network of small channels
Separated by temporary islands called
Bars
Occurs in river with high slope and
large Sediments load
Also typical in environments that
dramatically decrease in channel
depth and channel velocity

13. Cont.
Meandering Rivers
 A sinuous river with bends
 Forms as moving water erode stream at
outer banks(widens the valley)
 Deposition at the inner part of river
 Snaking pattern as stream meanders back
and forth
 Oxbow lakes forms as meander gets cut off
from main channel

14. Stages
Young
 High gradient, High velocity, Erosion, Tributaries, StraightBraided,
boulders mostly deposits
Mature
 Low Gradient, Erosion and Deposition, Meanders forms, Velocity
decreases
Old
 Very Low Gradient, Deposition, Low Velocity, Distributaries, Meanders

15. Depositions
Channel Lag:
 Boulders left at upstream in young age
Bars:
 Sediments deposition in rivers
Natural Levees:
 Elongated naturally occurring ridgeswalls of sediments which
regulates water levels
Flood Plain:
 Area of land adjacent to stream or river which experience flooding
during high discharge

16.  Concave convex oxbow lake

17. Cont.
 Crevasse Splay:
 Formed when river breaks natural levees and deposits sediments on floodplain

18. Alluvium
 Loose, unconsolidated(not cemented) soil or sediments
 Eroded and reshaped by water in some form
 Redeposited in a non-marine setting
Alluvial fan
 Fan or cone shaped deposits of sediments built up by streams
 Stream enters from high-land to low-land
 Typically found where canyons draining from mountain enters flat
area
 Poorly sorted material
 Caused by flash floods

20. Diagnostic criteria
 Absence of marine fossils (Typically Unfossiliferous)
 Presence of plant fossils
 Red beds (Oxidation)
 Scoured channels
 Unidirectional-flow
 Lamination, Cross-lamination, Ripple marks, Graded
beddings
Physical
 Grain size, angularity decrease from source to
mouth
 Sorting, sphericity, roundness increases from source
to mouth

21. AeolianDesert

22. Desert
 Desert areas cover about 20-25 percent of land surface
 Within latitudinal belts about 10-30 degrees north and south
 These areas have dry climate with low air pressure and low rainfall
( <25cm 10 inches )
 These dry areas are dominated by wind activity and covered by
sand
Wind Actions
Deflation -- the removal of loose, fine-grained particles by
the turbulent action of the wind
Abrasion -- the wearing down of surfaces by the grinding
action by windborne particles

23. Types of Dunes
 Traverse – these are perpendicular to the prevailing wind, and form a
wave like pattern
 Longitudinal (Seif) dunes – stretch parallel to the prevailing wind with
rounded or pointed tops. These can reach 300m in height and range up to
300km in length.

24. Cont.
 Barchans – A curved, arc shaped sand mound with horns facing downwind
formed in arid regions.
 Parabolic – These are U-shaped mounds that form in the reverse direction of a
barchans. They consist of sand tails which may hold vegetation
 Blowout – These are most commonly found on beaches, and are
sandy depressions in a sand dune caused by the removal of sediments by wind

25. Cont.
 Star – These dunes are mounds that are subject to different wind directions,
forming their star-like pyramidal structure.

26. Erosional features
 Mountains eroded by wind actions

27. Depositional features
 Loess – This is the lightest material carried by the winds which form a so-called
blanket covering the existing land. This blanket is easily eroded and rain
penetrates through them rapidly
 Bajada – desert alluvial fan, broad surface area, fine grained

28. Diagnostic criteria
 Sand - Sandstone
 Well sorted- large scale
cross beds
 terrestrial reptile traces
 Vertebrates, pollen and
spores (fossils)
 Yellowish – brownish colour
sediments
 Hematite coating of grains

29. Lacustrine
Lake:
 Land locked water body having its own
drainage system
Environment:
 Still water in lakes permits very fine particles
(fine sand, silt, and clay) to settle out and to
form lacustrine deposits
 These deposits get exposed by elevation of
old lakebeds
 Lacustrine deposits are very well sorte
 Characterized by thin layers that reflect
annual deposition of sediments

30. Cont.
 These layers causes different flows in lake
 Flow are due to difference in density of water and material
 Overflow – in upper layer, fine particles
 Interflow – in between layers, medium size particles
 Underflow – at the bottom, coarse particles
 As water enters lake, currents are produced which is high
energy zone and fine particles remain suspended and move
away towards centre
 As energy gets low fine particles settles in middle of lake

31. Types:
On basis of Basin:
How each basin originates is where the
distinction between lacustrine deposit types
stem
 Rift graben - lakes are formed from
crustal stretching also known as rifting.
Sediment influx is typically dominated by
precipitation runoff and discharge through
channels migrating towards the
depression
 Oxbow lakes - form lacustrine deposits
from seasonal overbank flooding as well
as precipitation runoff which refills these
isolated basins with fresh water and new
sediments.

32. Cont.
 Glacial lakes - form when
terminal moraines block water
from escaping the newly carved
valley from glacial erosion. As the
glacier melts, the valley fills with
melt water that creates a glacial
lake.
 Crater lakes - can be meteoritic
or of the caldera variety. Crater
lakes sediments are provided from
precipitation runoff descending
their steep slopes

33. Lake Classification by Mixing
 Monomictic Lakes – one turnover per year
 Cold Monomictic Lakes – ice covered most of the year – turnover when lake
warms slightly during short ice free period in the summer (Arctic and high altitude
lakes)
 Warm Monomictic Lakes – no ice cover – warm and stratified for most of the
year, turnover in winter when surface cools (lower temperate region lakes)
 Dimictic Lakes – turnovers in spring and fall, ice covered in winter (temperate
regions)
 Amictic Lakes – always ice covered (Antarctica and Arctic regions, very high
altitude lakes)

34. Types on basis of oxygen
 Oligotrophic lakes – are
characterized by low nutrient values,
which limits the lake's ability to
support animal life, the water
remains clear.
 Eutrophic lakes – are
characterized by high nutrient
values, which allows
microorganisms and algae to grow
in large numbers, which then allows
animals that feed on those algae to
also be supported

35. Diagnostic criteria
 Lacustrine rocks appears circular to sub-
circular in map
 Fine sediments in middle
 Turbidites
 Rhythmic bedding ( showing seasoning )
 Natron, Trona ( salts )
 Fossils – Gastropods, Bivalves, Ostracods,
Green Algae ( charophytes )
 Lamination ( organic )
 Siderite ( Iron carbonate )

36. Glacial
 Ice is a major transport process.
Liquid water and wind can also
transport sediment in these
environments
 Wind transport is common when
there is little vegetation. Liquid water
transport occurs when the ice melts
 the high viscosity of ice makes all ice
transport of sediment laminar. grain
sizes are not sorted
 All of the sediment is transported
together, with the ice, and it is
deposited when the ice melts

37. Features
 Zone of Accumulation – is the area above the firn line, where
snowfall accumulates and exceeds the losses from ablation
 Zone of Ablation – area of a glacier or ice sheet below firn with a
net loss in ice mass due to melting
 Firn line – separates the accumulation zone from the ablation zone
 Firn – type of snow that has been left over from past seasons and
has been recrystallized into a substance denser than snow. It
is ice that is at an intermediate stage between snow and glacial ice
 Crevasses: cracks in glacier

39. Depositional Features
 Moraines – glacier deposition making land features
 Lateral: ridge of sediments along sides of glacier
 Medial: ridges formed in middle of glacier
 EndTerminal: ridges at the end ( last stop of glacier )
 Ground: thin sheet deposits
 Drumlin – spoon shaped sediment deposits formed due to
streams
 Esker – long sinuous deposition
 Kettle – small depression and cavity formed in bedrock due
to glacier movement

41. Erosional Features
 Cirques – Half Bowled
shaped valley formed by
glacial erosion
 Arête – Sharp long narrow
ridges at mountain tops
formed by glacial erosion
 Horn – sharpest and elevated
point of Arête

42. Diagnostic criteria
 Poorly sorted and unstratified deposits
 Striations
 Angular sediments with unspecific
origins
 Oxidising environment with few fossils
 Stromatolites ( fossils )

44. Delta
 When riverstream enters stillstanding
water body, sediments are deposited in
triangle shape
Major parts:
 Delta Plain: landward portion
 Sand size particles, distributaries
 Delta Front:
 Slightly grades into ocean, silt ( sand
and clay )
 Pro-Delta:
 Submerged into ocean, majority
clay(silt and sand also)

46. Delta Morphology
The shape of a delta is
influenced by sediment input,
wave energy, and tidal energy
River-dominated deltas –
occur in micro tidal settings
with limited wave energy,
river contribution > ocean
all three parts of delta
developed
 controlled by the water density
difference between the
inflowing river water and the
standing water on the basin

47. cont.
Tide-dominated deltas –
Deltas which undergo
strong tidal interaction
 ocean contribution > river
 resembles bird’s feet
 High tides and flood tides
confine sediment on the
delta plain and low tides
carry sediment seaward.
 Sediment supply is over
powered by strong tidal
currents so the delta
tends to be very small

48. Cont.
Wave-dominated deltas –
An open ocean basin accepts more
water input so potential for greater
wave energy, making wave-
dominated deltas
 High wave interference causes
conflicted or deflected river
mouths.
 Less influence from fluvial
sources
 Breaking waves cause
immediate mixing of fresh and
salt water. Typically, the fresh
water flow velocity decelerates
rapidly.

49. Diagnostic Criteria
 Majority sand size particles –
sandstone
 Cross-beddings, ripple marks,
laminations
 Yellowish-brownish colour
 Best reservoir
 Particle size decreases
towards ocean
 Forams, Brachiopods,
Pelecopods, leaves,
Gastropods (fresh + marine
water)

50. Estuary
 An partially enclosed
coastal body
of brackish water with
one or more rivers or
streams flowing into it,
and with a free
connection to the open
sea
 Less saline than lagoon
due to fresh water
 Inflows of sea and fresh
water provide nutrients,
so it is more productive

51. Lagoon
 A lagoon is a shallow
body of water separated
from a larger body of
water by barrier islands
or reefs
 little or no fresh water
inflow, and little or
no tidal flow
 More saline

52. Diagnostic Criteria
 Mostly Evaporates
 Thin beds of carbonates
 Salt pseudo-morphs

54. Marine
Only influenced by sea water
 Shallow marine clastic –
Regions near the mouths of rivers
are usually clastic dominated
because the critters that secrete
CaCO3 tend to have trouble living
in muddy water
 Carbonate shelf – Regions with
clear water shallow enough to be
penetrated by sunlight are often
dominated by the skeletons of
marine organisms

55. Cont.
 Continental slope –
Dominated by the
deposition of
submarine landslides
 Deep marine – Very
thin sediments formed
by the slow
accumulation of
skeletons ( Planktons
) and clasts ( clay )
dropped into the
ocean by wind

58. Conclusion
Help understand
 Paleo-climates
 Plate tectonics
 Find hydrocarbons and minerals

59. References:
 Applied Sedimentology by Richard C. Selley
 https://commons.wvc.edu/rdawes/g101ocl/basics/BscsTables/depenv.html#contine
ntal
 https://geo.libretexts.org/LibreTexts/UCD_GEL_109%3A_Sediments_and_Strata_(Su
mner)/Alluvial_Fans/Glacial_Environments
 https://www.geol.umd.edu/~jmerck/geol100/lectures/14.html