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
10.
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
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
19.
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
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.
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
38.
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
40.
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 )
43.
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)
45.
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.
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
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