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Challenge the future
DelftUniversity ofTechnology
M.E. Donselaar
Shelf deposits
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Sedimentary environments
Continental: fluvial (braided, meandering)
aeolian
lacustrine
Coastal: deltaslinear (clastic, carbonate)
Marine: shelf
deep marine sands
pelagic
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Outline
Introduction
Ocean circulation patterns
Shelf sedimentation
Examples tide-dominated shelf Reservoir analogue
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Definition shelf
The part of the sea bordered by:
The wave base
The shelf break (usually at 100-200 m water depth)
http://faculty.gg.uwyo.edu/heller/Sed%20Strat%20Class/SedStrat%207/SedStrat7.html
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Shelf types
Marginal (= peri-continental):
Shelf bordered by land on one
side, and the deep sea on the
other side
Epiric (= epi-continental):
Shelf bordered by land on
several sides
epiric
marginal
http://www.ruf.rice.edu/~feegi/coastal.html
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Factors that influence shelf sedimentation
Shape of the shelf
Type and intensity of the hydraulic regime
Amount and type of sediment supply
Sea level fluctuations Climate
Interaction sediment - fauna
Chemical factors
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Shape of the shelf
Wide shelf: large sediment storage capacity (largeaccommodation space). Trailing (passive) margins
Narrow shelf: low sediment storage capacity (smallaccommodation space).Active margins
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Plate margins
http://www.mc.maricopa.edu/academic/phy_sci/Geology/hernlund/
Active margin
passivemargins
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Active and passive plate margins
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Active margins narrow shelf
http://cache.eb.com/eb/image?id=4953&rendTypeId=4
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Passive margin wide shelf
http://www.utexas.edu/tmm/npl/mineralogy/Mineral_Genesis/PassiveMargin.jpg
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Hydraulic regime - 1
World wide circulation patterns caused by temperature andsalinity (=density) gradients
Tidal forces caused by gravity fields sun and moon
Meteorological currents
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Ocean circulation - 2
http://www.dkrz.de/dkrz/gallery/vis/ocean
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Ocean circulation - 3
Ocean currents (spiral eddies)
expand onto shelf
More spiral eddies:
http://www.navis.gr/meteo/ed
dies.htm
http://www.lpi.usra.edu/public
ations/slidesets/oceans/oceanviews/slide_01.html
http://www.navis.gr/meteo/eddies.htmhttp://www.navis.gr/meteo/eddies.htmhttp://www.lpi.usra.edu/publications/slidesets/oceans/oceanviews/slide_01.htmlhttp://www.lpi.usra.edu/publications/slidesets/oceans/oceanviews/slide_01.htmlhttp://www.lpi.usra.edu/publications/slidesets/oceans/oceanviews/slide_01.htmlhttp://www.lpi.usra.edu/publications/slidesets/oceans/oceanviews/slide_01.htmlhttp://www.lpi.usra.edu/publications/slidesets/oceans/oceanviews/slide_01.htmlhttp://www.lpi.usra.edu/publications/slidesets/oceans/oceanviews/slide_01.htmlhttp://www.navis.gr/meteo/eddies.htmhttp://www.navis.gr/meteo/eddies.htm8/10/2019 TA2910 08 - Shelf Sediments
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Meteorological currents
Air pressure gradients -> wind shear stress -> waves andcurrents
Animationhttp://www.weather.com/maps/maptype/satelliteworld/atlanticoceansatellite_large.html
http://www.weather.com/maps/maptype/satelliteworld/atlanticoceansatellite_large.htmlhttp://www.weather.com/maps/maptype/satelliteworld/atlanticoceansatellite_large.htmlhttp://www.weather.com/maps/maptype/satelliteworld/atlanticoceansatellite_large.htmlhttp://www.weather.com/maps/maptype/satelliteworld/atlanticoceansatellite_large.html8/10/2019 TA2910 08 - Shelf Sediments
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Hydraulic regime - 2
Wave dominated shelf: seasonal fluctuation of wave heightand current strength - sediment transport only duringstorms
Tide dominated shelf: strong bi-directional bottom currents- active sand transport, large bedforms
Ocean current dominated shelf: strong uni-directionalcurrents
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Amount and type of sediment supply
Relict sediment: Non-reworked sediment that was depositedon the shelf as fluvial or coastal sediment in a previous sealevel lowstand phase
Palimpsest sediment: Reworked fluvial or coastal sedimentfrom a previous sea level lowstand phase
Modern sediment: Sediment that was recently added to the
shelf: clay and silt (suspension from rivers, etc.)
sand (coastal source, seaward transport during storms)
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Sea level fluctuations
Influence the shelf accommodation space
Influence the type of sediment supply:
Low sea level: coarser sediment
High sea level : finer sediment
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Sediment supply
Sea level highstand: coarse
sediment trapped in estuaries,
only fine-grained suspended
sediment on shelf
Sea level lowstand: shelf is
(partly) exposed, coarse
sediment is transported ontothe shelf by rivers
Jervey (1988)
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Example tide-dominated shelf - 1
Strait of Dover: Convergence of
tidal currents, hence deep erosion
of sea bottom
North and south of Strait of Dover:
Flow expansion, hence gradual
decrease of current speed
Deposition of eroded sea bottom
sediment
Reading (1986)
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Example tide-dominated shelf - 2
Sedimentation succession at decreasing
current speed:
> 150 cm/s: furrows and gravel waves.
Scour hollows up to 150 km long, 5 km
wide, 150 m deep ~ 100 cm/s: sand ribbons. Longitudinal
ridges parallel to flow. Up to 15 km
long, 200 m wide, 1 m high
~ 90 cm/s: barchan-like bedforms
~ 75-65 cm/s: sand waves. Straight-
crested large bedforms, crest
perpendicular to flow. 3-15 m high,
wave length 150-500 m
Reading (1986)
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Sandwave - example
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Tidal sand ridges - 1
Elongate ridges oriented
obliquely to tidal currents
Distribution related to
transgressive history of area
Do not follow sedimentation
succession (previous slides)
Up to 50 km long, 1-3 km wide
and 10-50 m high, spacing up
to 12 km Well-sorted, medium-fine sand
Reading (1986)
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Tidal sand ridges - 2
Are formed between mutually
evasive ebb and flood currents
(stage a)
Secondary cross shoal currents
deform straight crest line(stages band c)
Ebb and flood channels develop
in double curve (stage d)
Original tidal sand ridge breaks
up into three parallel ridges(stages eand f )
From: Caston (1972)
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Tidal sand ridges - 3
Active sand ridges:
Current speed > 50 cm/s
Sand waves superimposed on ridge
Asymmetrical in cross section, steep side up to 6o
Crest sharp to flattened (near sea surface)
Moribund sand ridges:
Current speed < 50 cm/s
Slope < 1o
Do not actively move Develop over sandy to muddy sea floor
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Eocene Brussels Sands
Fossil example of shallow-marine linear sand body deposits
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Tabular cross-bedded facies
(Houthuys, 1990)
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Sedimentary structures
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Transverse bar characteristics
Tabular cross bedding
Well-developed bottomsets
Set heights ~ 1m
Well-sorted fine to medium sand Glauconite coating
Iron oxide forms permeability baffles
Bioturbation restricted to low-energy parts bar
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Reservoir analogue
Shannon and Sussex Sandstones : producing linear sandridges
Additional reading:
http://pubs.usgs.gov/dds/1997/dds-
033/USGS_3D/ssx_txt/3dstart.htm
St ti h Sh d S
http://pubs.usgs.gov/dds/1997/dds-033/USGS_3D/ssx_txt/3dstart.htmhttp://pubs.usgs.gov/dds/1997/dds-033/USGS_3D/ssx_txt/3dstart.htmhttp://pubs.usgs.gov/dds/1997/dds-033/USGS_3D/ssx_txt/3dstart.htmhttp://pubs.usgs.gov/dds/1997/dds-033/USGS_3D/ssx_txt/3dstart.htmhttp://pubs.usgs.gov/dds/1997/dds-033/USGS_3D/ssx_txt/3dstart.htm8/10/2019 TA2910 08 - Shelf Sediments
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Stratigraphy Shannon and SussexSandstones
From: http://pubs.usgs.gov/dds/dds-033/USGS_3D/ssx_txt/geology.htm
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Powder River Basin - Shannon Sst
Reservoir potential:
Sand ridges develop on muddy
sea floor (source)
After formation of sand ridge:
covered with fine-grained marine
suspension sediment
Hence, permeable sand ridge
enveloped in impermeable mud
(Tillman & Martinsen, 1985)
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Shannon Sandstone - palaeogeography
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Shannon Sst at Hartzog Draw
(Tillman & Martinsen, 1985)
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Shannon Sst - Salt Creek area
Lower and upper unit separated by thin continuous shaleinterval
Total thickness ~ 50 m; length 45 km; width 1-4 km
(Tillman & Martinsen, 1985)
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Shannon lithofacies
Coarsening-upward sequence from:
Bioturbated marine shaley
sandstone at base, to
Large-scale trough cross-bedded
medium-grained sandstone at top
Porosity: 14.8% ave.
Permeability: 0.01-143 mD; ave.
16.3 mD
From: Ranganathan & Tye (1986)
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Sussex Sandstone
Elongate sand ridge
Sediment is transported by
smaller transverse bars
migrating obliquely over the
sand ridge surface
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Stacking of Sussex-B tidal sand ridges
http://pubs.usgs.gov/dds/dds-033/USGS_3D/ssx_txt/depomod.htm
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Sussex Sandstone
http://pubs.usgs.gov/dds/1997/dds-033/USGS_3D/ssx_txt/3dstart.htm
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Links http://msx4.pha.jhu.edu/ssip/asat_int/ocean.html
http://topex-www.jpl.nasa.gov/overview/why-study.html
http://msx4.pha.jhu.edu/ssip/asat_int/ocean.htmlhttp://topex-www.jpl.nasa.gov/overview/why-study.htmlhttp://topex-www.jpl.nasa.gov/overview/why-study.htmlhttp://topex-www.jpl.nasa.gov/overview/why-study.htmlhttp://topex-www.jpl.nasa.gov/overview/why-study.htmlhttp://topex-www.jpl.nasa.gov/overview/why-study.htmlhttp://topex-www.jpl.nasa.gov/overview/why-study.htmlhttp://msx4.pha.jhu.edu/ssip/asat_int/ocean.html8/10/2019 TA2910 08 - Shelf Sediments
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Compulsory reading
Chapter 11:
Section 11.4 Thermo-haline and geostrophic currents