SEDIMENTOLOGY
SEDIMENTOLOGY
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Flow regime, sediment transport & deposition
Flow regime, sediment transport & deposition
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Sediment transport and deposition
Sediment transport and deposition
Transport modes in a turbulent fluid
" Traction (rolling over the bed surface)
" Saltation (jumping over the bed surface)
" Suspension (permanent transport within the fluid)
" Solution (chemical transport)
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Hjulstrom diagram
Hjulstrom diagram
Sediment transport and deposition - comment
Sediment transport and deposition - comment
" Fluid density and viscosity play a key role in determining which
particle sizes can be transported
" The amount of sediment transport is not only related to flow
velocity (or bed shear stress) and grain size, but also to:
" Grain density
" Grain shape
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BED FORMS AND 2. The flow regime concept:
BED FORMS AND 2. The flow regime concept:
SEDIMENTARY
SEDIMENTARY
STRUCTURES:
STRUCTURES:
... is the he result of experimental research
(processes and results)
(processes and results)
into fluid flows and their depositional
results
& relates flow energy with the deposited
bed forms and their internal structures
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'shooting flow'
Flume tank experiments
Flume tank experiments
Bedforms: antidunes
POJ
CIE REŻIMU
POJ
CIE REŻIMU
Bedforms:
planar bed (upper)
Current megaripples with megaripples-dunes
PRZEPA
YWU:
ripples small ripples on top without small ripples
PRZEPA
YWU:
Curved crest
Straight crest
Sed. structures: Parallel lamination Cross-lamination
Cross-lamination Cross-bedding with /cross-bedding
(= small-scale) (= large scale) parting lineation dipping upstream
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3. Current ripplemarks and dunes (bed forms)
3. Current ripplemarks and dunes (bed forms)
& their sedimentary structures:
& their sedimentary structures:
cross-lamination and cross-bedding
cross-lamination and cross-bedding
Features:
- asymmetrical bed forms: stoss side is gentle, lee
Lower flow regime
Lower flow regime
side : much steeper (up to 30 degr.)
- height: 0.5  3 cm; wave length 5-40 cm
- grain size: <0.7 mm (- structure: cross-lamination
Origin:
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Origin of cross lamination
Origin of cross lamination
Origin: key points:
in current ripplemark
in current ripplemark
- Stoss side (windward): grains rolled up the slope
- Temporary accumulation at the crest
Sedimentation
- Lee-side: grain avalanching (initiated when the
on the lee side:
slope reaches the angle of repose) & accumulation
grain avalanching.
of a lamina/bed inclined with regard to the
depositional surface (= horizontal bottom)
This way foresets originate
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Classification
Classification
SET
Slope of the foreset beds is a function of the
COSET
grain size of the sediments:
(= composite set)
" coarse sediments (sand and gravel) result in
The lower boundary of each set:
steep slopes
- is erosional
" fine sediments (fine sand and silt) result in
- its shape defines the type of
shallow slopes
cross-laminated
or cross-bedded set:
Sets:
1. Tabular - have planar bounding
surfaces
2. Trough - lower surfaces curved
or scoop-shaped and truncate the
underlying beds
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3. Wedge (a variety of tabular)
The shape of the crest defines the shape of the
Size classification: ripples vs. dunes
Size classification: ripples vs. dunes
lower boundary of the set  see classification 2-D & 3-D forms
(& frequency of occurrence)
(& frequency of occurrence)
Tabular - 2D
Crest straight
Trough  3D
Crest curved and
bedfrom height
decreases laterally
megaripples
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Climbing current ripples
Origin:
" Deposition out of traction associated with
Megaripplemarks
suspension
" Grain size: >0.2 mm (= >fine sand)
" The higher the intensity of deposition out of
suspension, the steeper the angle of climb
" Height usu up to a few dcm
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SAND WAVES : S. Francisco Bay (Golden
Backflow
Backflow
with formation of Gate)
with formation of
backflow ripples
backflow ripples
STOPPED HERE
STOPPED HERE
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Avalanches of sand grains
Aeolian dunes Barchan
Barchan
(sandy grain flows) down
the stoss side
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Atacama Desert, Chile
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Aeolian versus water-born cross
Aeolian versus water-born cross
bedding/lamination
bedding/lamination
Aeolian:
Steeper dips of foresets (high inter-granular friction of
dry sediment)
Inversely graded (dispersive pressure in dry sand
avalanches: dry grain-flow  grain-to-grain collisions)
Water-born:
Lower dips of foresets (low inter-granular friction of
water-lubricated sediment)
Inverse grading absent (sorting in water-saturated
avalanches of sand grains)
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Sediment transport and deposition
Sediment transport and deposition
Plane beds and antidunes
" In coarse sands (>0.7 mm) lower-stage plane beds develop instead of current ripples
" At high (but still subcritical) flow velocities upper-stage plane beds
are formed in all sand grain sizes
Upper flow regime
Upper flow regime
" At still higher flow velocities (supercritical flow conditions, FrH"1 or higher)
antidunes are formed, characterized by bedform accretion in
an upstream direction
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Parting lineation: plane bed, upper flow regime Upper flow regime (supercritical flow): standing
Parting lineation: plane bed, upper flow regime
waves  here antidunes are formed
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Sediment transport and deposition by waves
Sediment transport and deposition by waves
Waves
REMEMBER:
REMEMBER:
DISTINGUISH BETWEEN THE BED FORMS AND
DISTINGUISH BETWEEN THE BED FORMS AND
" Waves are wind-generated oscillatory motions
SEDIMENTARY STRUCTURES
SEDIMENTARY STRUCTURES
of water
" Wave height is dependent on wind strength
" The depth to which the oscillatory motion due
to wave action extends is known as the
" eg.  a current ripplemark is a bed form
wave base
" Shallow water leads to breaking waves
" Its internal organisation of sediment:
" Wave ripples are distinct from current ripples
sedimentary structure = cross lamination
due to their symmetry and include low-
energy  rolling grain ripples and high-energy
 vortex ripples
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Sediment transport and deposition
Sediment transport and deposition
Waves
" Waves are wind-generated oscillatory motions of
water
" Wave height is dependent on wind strength
" The depth to which the oscillatory motion due to
wave action extends is known as the wave base;
shallow water leads to breaking waves
" Wave ripples are distinct from current ripples due to
their symmetry, and include low-energy  rolling grain
ripples and high-energy  vortex ripples
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swash &
oscillation waves translation waves
backwash
breakers
35 Animation wave ripples 36
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Wave ripplemarks
Wave ripplemarks
Internal structure of wave ripplemarks; Tumlin quarry Features:
(Gradzinski)
- symmetrical bed forms
- height: 0.5  3 cm
- grain size: <0.7 mm (- structure: composite lamination, bi-directional
------------------------------------------------------------
Important bathymetry indicator: are formed above
the wave base!!!!
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Sediment transport and deposition:
Sediment transport and deposition:
Interference ripples
Interference ripples
Tides
Tides
Tides result from the gravitational attraction of the
Moon and Sun on the Earth, combined with the
centrifugal force caused by movement of the Earth
around the center of mass of the Earth-Moon system
" Semi-diurnal (= every half-a-day) or diurnal tidal cycles
" Neap-spring tidal cycles
" Annual tidal cycles
Tide changes proceed via the following stages:
" Sea level rises over several hours, covering the intertidal zone:
flood tide.
" The water rises to its highest level, reaching high tide & stays at
this level (slack water).
" Sea level falls over several hours, revealing the intertidal
zone: ebb tide.
" The water stops falling, reaching low tide (slack water).
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Neap & spring cycles
Neap & spring cycles
Neap-spring tidal cycles are controlled by the position of
the Moon relative to the Sun and Earth
" Spring tides (meaning: 'rise'): when the Earth, Moon, and Sun
are all in a line (Full and New Moon Phases) the high tides
are MUCH higher than at other times
" In brief: high waters are higher than average, low waters are
lower than average
" Neap tides (unknown origin/meaning): when the Moon and Sun
are at right angles to each other the high tides are lower
than at other times
" In brief: Neaps result in less extreme tidal conditions
" There is about a seven-day interval between springs and
neaps
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Tidal currents (cont from here on 8/05)
Tidal currents (cont from here on 8/05)
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Tidal ranges around UK
Tidal ranges around UK
Herringbone cross stratification
Herringbone cross stratification
" Origin: deposition of current ripples or dunes by
the currents of alternating opposite flow directions
" Are characteristic for tidal conditions (tide-ebb-
& -...)
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Bedding types:
Association: Ripplemarks & mud
Association: Ripplemarks & mud
A. Flaser
NOTE:
a) Ripplemarks originate only in non-
B. Wavy
cohesive sediment (sand, coarse silt)
transported by traction
C. Lenticular
b) Muds are deposited out of suspension
only (being cohesive, cannot be
transported by traction)
D. Starved ripples
c) Therefore: interbeds of ripple cross
laminated sand and mud reflect
Sedimentary environment  most often tidal;
significant oscillations of the current
but also: fluvial  flood plain area
energy: traction  suspension (V~0 =
slack water)  traction  suspension -
(V~0 = slack water) & .
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Ocean currents Global system of winds
Ocean currents Global system of winds
Ocean currents
 Solar energy: variations in temperature
" The circulation of sea water in the world s oceans is driven by
wind and contrasts in density due to variable temperature and
 Coriolis effect: deflection of fluid flow in
salinity (thermohaline circulation), combined with the Coriolis
motion = winds (also water currents
effect
" Ocean currents transport clay and silt in suspension, and sand
 Major mountain ranges: deflection of
as bed load, and their effects are especially important in deep
winds
waters, where storms and tides are less important
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Four mechanisms supporting grains in sediment
Four mechanisms supporting grains in sediment
Gravity flows in general
Gravity flows in general
gravity flows
gravity flows
" Grain flow. Mechanism: (explain) Result: very well sorted sand
" Debris flow. Mechanism: (explain) Result: Poorly sorted, matrix-rich,
Two groups of flows generated by
massive or inversely-graded bed
" Liquefied flow. Mechanism: pore-fluid escape. Result: dish structures
gravity:
water escape pipes, sand volcanoes
" Turbidity current. Mechanism: turbulence. Result: normally-graded bed;
Bouma sequence
1. Fluid gravity flows  the motion of fluid powered
by gravity sets sediment grains in motion (e.g
rivers)
2. Sediment gravity flows: gravity sets sediment in
motion, which in turn sets the ambient fluid in
motion due to friction.
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Sediment transport and deposition (cont from
Sediment transport and deposition (cont from
Sediment transport and deposition
Sediment transport and deposition
here)
here)
Gravity flows Gravity flows
" Debris flows have a high (>50%) proportion of sediment to " Debris flows have a high (>50%) proportion of sediment to
water and can be both subaerial and subaqueous water and can be both subaerial and subaqueous
" Low Reynolds numbers " Low Reynolds numbers
" Turbidity currents have a higher proportion of water, are " Turbidity currents have a higher proportion of water, most
always subaqueous, and move due to density contrasts commonly are subaqueous, and move due to density contrasts
" Higher Reynolds numbers " Higher Reynolds numbers
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Autosuspension
Autosuspension
Motion Turbulence Suspension
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Newfoundland continental slope
Newfoundland continental slope
a part of
mud
remains
in
suspen-
Bouma sequeence
sion
intervals (Ta  Te)
after the
turbidity
current
V = 0
with sole marks
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Erosional structures Erosional structures
Erosional structures Erosional structures
" Small channel
" Channels
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Sole marks - origins
Sole marks - origins
Conditions of origin:
" Scour-and-fill
1. Bottom - covered with cohesive sediment (mud)
2. Erosion - caused by turbulence cells in, or objectes carried
by, turbidity current (shale clasts, wood fragments, fish
bones, itp.)
3. Sand deposition of the overlying bed  immediately after
erosion, preferably out of the same turbidity currrent that
caused erosion
Note  the erosional feature is a mold and the sole mark, which
we see at the base of the corresponding sandstone bed, is a
cast
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Bioturbations & trace fossils
Bioturbations & trace fossils
Other sedimentary structures
Other sedimentary structures
(ichnofossils)
(ichnofossils)
Resulting from liquefaction of sandy sediment:
" Sand volcanoes " Bioturbations (general term): Disturbances of
" Clastic dikes (sand dikes)
sediment by organisms
Deformational structures
Convolute lamination
" Preserved traces of activity of organisms
Recumbent folds
Traces of:
Slump folds
Slump beds
Resting, crawling, walking, feeding, hiding,
Load casts
burrowing, etc
Flame structures
Ball-and-pillow
" Traces of infauna: living within sediment
Dessication cracks (mud cracks)
" Traces of epifauna: living on sediment surface
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