Challenge the future Delft University of Technology M.E. Donselaar Fluvial deposits
Challenge the future
DelftUniversity ofTechnology
M.E. Donselaar
Fluvial deposits
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Sedimentary environments
•Continental: fluvial (braided, meandering)lacustrineaeolian
•Coastal: deltaslinear (clastic, carbonate)
•Marine: shelfdeep marine sandspelagic
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Fluvial deposits
•Morphology•Relation channel shape – sediment load•Fluvial architecture: Development in space and time•Braided rivers•Meandering rivers
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Morphology: River flow path
• Upstream part:- Erosion- Tributary pattern of channels
• Midstream part:- Sediment transport (bypassing)- Undivided flow path
• Downstream part:- Sedimentation- Distributary pattern of channels http://www.crescent.edu.sg/ipw/1999/29g9-river/featur2.gif
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Morphology: Example distributary pattern Mississippi River
http://bldgblog.blogspot.com/2008/02/prosthetic-delta.htmlhttp://bldgblog.blogspot.com/2008/02/prosthetic-delta.html
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River types
•Meandering•Braided•Straight•Anastomosing
Miall (1977)
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Relation morphology – sediment load
•Bed load•Suspended load•Mixed load
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•Development in space and time of river system by:• River switching within channel belt• Change of river flow path by avulsion• Accommodation development
Fluvial architecture
350 m
From: Steel (1993)
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Channel belt
•The total width of the area where fluvial deposits can be formed by lateral migration of a single river
channel belt
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River avulsion
•A channel belt is limited in time by avulsion•Avulsion: The process of river abandonment by
breakthrough of its levee, followed by a new river course
Smith et al. (1989)
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Reasons for avulsion - 1
•Breakthrough of river bank during peak flow:• Weak parts of river
bank• In bends
Columbia River, Canada - Crevasse splay. Photo taken by Univ. of Utrecht group. http://faculty.gg.uwyo.edu/heller.
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• New path is steeper, therefore more favorable for fluid flow:• Vertical aggradation of
channel floor within natural banks (levees)
• Compaction of area adjacent to the river (floodplain)
Reasons for avulsion - 2
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Avulsion types
www.geo.uu.nl/fg/palaeogeography/
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Multiple avulsions: Rhine river
www.geog.uu.nl/fg/palaeogeography/www.geog.uu.nl/fg/palaeogeography/
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Accommodation space
The space in a sedimentary basinwhere sediment accumulation can take place
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Interaction channel migration – accommodation development
•Horizontal component:• Fluvial channel switches within channel belt
•Vertical component:• Accommodation space added
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Avulsion vs. subsidence
•Fluvial sandstone connectivity function of (1) lateral migration within channel belt, (2) avulsion frequency, and (3) subsidence rate:
•Highest connectivity: Lateral migration + frequent avulsion within limited space + slow subsidence
•Lowest connectivity: High subsidence rate + frequent avulsion
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Labyrinth-type reservoirKS44
KS28 KS31 KS47KS27
Coal 45/2
Coal 45
Base sand
Coal 43/6
Coal 43/3
Coal 47
Coal 43/2
19 m
0 m
38 m
8 km
57 m
95 m
76 m
5 km
SE
argillaceous sandstone(< 30 % clay)
claystone(70-100% clay)
coaly claystone
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Braided rivers
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Braided rivers - characteristics
•Sandy or gravelly braided rivers•Multiple channels•High width-thickness ratio•High gradient•Low sinuosity•Fluctuating run-off•Bed load transport
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Morphology braided rivers: bar evolution
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Multiple channels
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Bar stabilisation
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Sedimentary analysis
•Geometry•Lithology•Sedimentary structures•Palaeo-current distribution•Fossils•Cores•Wireline logs
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Sedimentary analysis: Geometry
•Channel- & sheet geometry•Sand-on-sand contacts dominant, discontinuous
shale
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Geometry - 1
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Geometry - 2
clay layerclay layer
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Sedimentary analysis: Lithology
•Coarse sand, gravel•Fine grained sediment in abandoned channels•Diagenesis: red colour caused by oxidation of
organic matter
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Sedimentary analysis: Sedimentary structures
•Channel shape (pre-depositional)•Large scale cross bedding by bar growth•Imbricated pebbles
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Bar growth
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Sedimentary structures - 1
clayclay
X-X-bedded bedded bar frontbar front
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Sedimentary structures - 2
X-X-bedded bedded bar frontbar front
Sharp, Sharp, erosional erosional
basebase
Upward increase Upward increase of dip angleof dip angle
Small Small ripples ripples
migratinmigrating along g along the bar the bar frontfront
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Sedimentary analysis: Palaeocurrents
•Unimodal distribution•Low scatter
N
270o 90o
180o
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Sedimentary analysis: Fossils
•Oxidation of fossil remains: low preservation potential
•Lag deposits at channel base
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Subsurface characteristics
•Seismic: • Sharp top and basal reflection• Few or no internal reflectors
•Cores:• massive sand sequence with internal erosional surfaces
•Logs:• dipmeter: green pattern in shale, foreset dips of bars• gamma-ray: uniform sand sequence
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Well log expression - 1
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Well log expression - 20 9045
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Example: Caister Ss. - 1
4545
Example: Caister Ss. - 2
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Example: Caister Ss. - 3
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Meandering rivers
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Meandering rivers: Characteristics
•Single channel•Vegetated lowland•Stabile discharge•Low relief•Bed load, mixed load or suspension load
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Meandering rivers: Sub-environments
•Floodplain•Active channel•Abandoned channel•Crevasse splay
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floodplain
active channel
abandoned channel
http://www.jpl.nasa.gov/radar/sircxsar/sc-miss.gif
Meandering rivers: Sub-environments
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Meandering rivers: Floodplain
Area on both sides of the active channel
• Only flooded at peak run-off• Lithology: mainly silt & clay, fine sand: settles out of
suspension• Geometry: massive, sheet shape• Sedimentary structures: fine laminations, wave ripples,
shrinkage cracks• Palaeo-currents: none• Fossils: root horizons, coal
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Meandering rivers: Active channel
Single, non-branching channel
•Erosion in outer bend (cut bank) •Bordered by natural dikes (levees)•Sedimentation in inner bend (point bar)•Cause: helicoidal flow in bend
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Helicoidal flow - 1
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Helicoidal flow - 2
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point bar
cut bank
Helicoidal flow - 3
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Meandering rivers: Point bar accretion
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Levee development
http://craton.geol.brocku.ca/faculty/rc/teaching/1F90/index.html
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Levee break-through
•At peak run-off•Small, fan-shaped sediment bodies• Crevasse delta• Crevasse splay
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Crevasse splay
http://www.geo.uu.nl/fg/berendsen/pictures/photography/alaska/Crevasse.jpg
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Crevasse delta:Sedimentary structures & logs
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Crevasse splay:Sedimentary structures & logs
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Sedimentary analysis: Geometry of active channel deposits
•Lens- to sheet shaped geometry•‘Labyrinth-type’ stacking, continuous shale
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Lens-shaped channel
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Labyrinth-type reservoir - 1KS44
KS28 KS31 KS47KS27
Coal 45/2
Coal 45
Base sand
Coal 43/6
Coal 43/3
Coal 47
Coal 43/2
19 m
0 m
38 m
8 km
57 m
95 m
76 m
5 km
SE
argillaceous sandstone(< 30 % clay)
claystone(70-100% clay)
coaly claystone
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Labyrinth-type reservoir - 2
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Sedimentary analysis: Lithology
•Coarse sand, gravel at the base: lag deposit•Fining-upward sequence
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Lithology - 1
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Lithology - 2
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Sedimentary analysis: Sedimentary structures
•Channel shape (pre-depositional)•Cross bedding by point bar growth - 1: lateral
accretion•Cross bedding by point bar growth - 2: ripples
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Sedimentary structures - 1
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Lateral accretion Lateral accretion surfacessurfaces
Sedimentary structures - 2
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Sedimentary log of point bar
• Overbank mud and thin sand with soils and roots
• Fining-up point-bar succession
• Upward decrease of cross-bed set thickness ripple cross-lamination
• Lateral accretion surfaces oblique to cross beds
• Scoured case of channel with lag deposits
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Log expressionLateral Lateral
accretion accretion surfacessurfaces
Ripples climbing up Ripples climbing up the accretion the accretion
surfacesurface
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Sedimentary analysis: Palaeo-currents
•Unimodal distribution•Large scatter
N
90o270o
180o
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Sedimentary analysis: Fossils
•Oxidation of fossil remains: low preservation potential
•Lag deposits at channel base
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Oxbow lakes
•Cut bank erosion in opposing bends:
•Cut-off of entire meander bend
•Converted to oxbow lake
http://www.daviddarling.info/images/oxbow_lake.jpg
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Oxbow lake evolution
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Oxbow lake sediment
•After cut-off: Only receives water during peak run-off
•Organic carbon-rich clay sediment
http://www.panoramio.com/photo/39211485
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Links
•http://www.geog.uu.nl/fg/palaeogeography/•http://faculty.gg.uwyo.edu/heller/Sed%20Strat%20Cl
ass/Sedstrat4/sedlect_4.htm•http://www.virtual-geology.info/sedimentology/fluvial
.html
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Compulsory reading
•Chapter 9, Sections 9.1 – 9.4