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