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![Page 1: GE0-3112 Sedimentary processes and products Lecture 4. Sedimentary structures II – sediment massive flows Geoff Corner Department of Geology University.](https://reader031.fdocuments.us/reader031/viewer/2022020320/56649c805503460f949368f9/html5/thumbnails/1.jpg)
GE0-3112GE0-3112 Sedimentary processes and products Sedimentary processes and products
Lecture 4. Sedimentary structures II – sediment Lecture 4. Sedimentary structures II – sediment massive flowsmassive flows
Geoff CornerGeoff CornerDepartment of GeologyDepartment of GeologyUniversity of TromsøUniversity of Tromsø20062006
Literature:Literature:- Leeder 1999. Ch. 10, 11, 12. - Leeder 1999. Ch. 10, 11, 12. Cohesive sediments, sediment gravity flows and Cohesive sediments, sediment gravity flows and
deformation structures deformation structures
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ContentsContents
►4.1 Cohesive sediment transport and 4.1 Cohesive sediment transport and erosion.erosion.
►4.2 Sediment gravity flows4.2 Sediment gravity flows►4.3 Soft-sediment deformation4.3 Soft-sediment deformation
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4.1 Cohesive sediments4.1 Cohesive sediments
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Clay and cohesionClay and cohesion
►Atomic attractions between small clay Atomic attractions between small clay particles impart cohesive strength.particles impart cohesive strength.
►Positive-negative electrical charges Positive-negative electrical charges are ’amplified’ in suspensions in are ’amplified’ in suspensions in seawater a strong electrolyte) causing seawater a strong electrolyte) causing particle attraction (flocculation).particle attraction (flocculation).
►Flocculation is enhanced by organic Flocculation is enhanced by organic matter. matter.
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Cohesive bed processesCohesive bed processes
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Settling velocity vs. floc size and Settling velocity vs. floc size and sediment concentrationsediment concentration
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Cohesive bed erosionCohesive bed erosion
►Erosion may take the form Erosion may take the form of:of: direct particle-by-particle direct particle-by-particle
erosion where floc-floc bonds erosion where floc-floc bonds must be broken.must be broken.
erosion (re-entrainment) of erosion (re-entrainment) of freshly depsited water-rich freshly depsited water-rich suspension from the bed.suspension from the bed.
mass erosion due to failure mass erosion due to failure above a slide plane.above a slide plane.
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Erosional bedforms – flute Erosional bedforms – flute marksmarks
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4.2 Sediment gravity flows4.2 Sediment gravity flows
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Grain-flow avalanchesGrain-flow avalanches
►Movement by shear between grains Movement by shear between grains and against underlying surface.and against underlying surface.
► Interstitial fluid plays little part in the Interstitial fluid plays little part in the motion.motion.
►May involve boulder to sand size; also May involve boulder to sand size; also snow.snow.
►Low friction/high energyLow friction/high energy
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Avalanche depositsAvalanche deposits
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Fluidization and kinetic Fluidization and kinetic filteringfiltering
►Acoustic Acoustic fluidizationfluidization of high energy of high energy avalanches?avalanches?
►Kinetic filteringKinetic filtering (sorting) causes (sorting) causes inverse grading.inverse grading.
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Debris flowsDebris flows
►Extreme form of hyperconcentrated flow.Extreme form of hyperconcentrated flow.►Typically silt- to boulder-size particles Typically silt- to boulder-size particles
set in a matrix of clay-grade fines and set in a matrix of clay-grade fines and water.water.
► Involve transmission of both solid and Involve transmission of both solid and fluid stresses (excess pore pressure).fluid stresses (excess pore pressure).
►Excess pore pressure gives low shear Excess pore pressure gives low shear strength (low friction).strength (low friction).
►Density 1.8-2.3; velocity >10 m/s not Density 1.8-2.3; velocity >10 m/s not uncommon. uncommon.
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Debris-flow depositsDebris-flow deposits
►Plug flow gives no/little shear fabric or Plug flow gives no/little shear fabric or sorting.sorting.
►Traces of shear fabric may develop at Traces of shear fabric may develop at base and margins.base and margins.
►Plug flow leaves central channel bordered Plug flow leaves central channel bordered by high levees.by high levees.
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Debris-flow depositsDebris-flow deposits
►Surging may give weak stratification.Surging may give weak stratification.►Waning flow may give normal grading.Waning flow may give normal grading.►Kinetic filtering may give inverse Kinetic filtering may give inverse
grading.grading.
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Levees and lobesLevees and lobes
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Turbidity flowsTurbidity flows
►Cause by movement of density current Cause by movement of density current in water or air downslope.in water or air downslope.
►Triggered by:Triggered by: Evolve from slides/slumps.Evolve from slides/slumps. Hyperpycnal flows from rivers mouths.Hyperpycnal flows from rivers mouths. Longshore drift to submarine canyonsLongshore drift to submarine canyons (Pyroclastic flows; snow avalanches)(Pyroclastic flows; snow avalanches)
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TurbiditesTurbidites
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4.3 Soft-sediment 4.3 Soft-sediment deformationdeformation
►Liquefaction: change of state from Liquefaction: change of state from solid to liquid.solid to liquid.
►Pore pressure rather than grain Pore pressure rather than grain contacts supports the material.contacts supports the material.
►Caused by:Caused by: Shock (earthquake, tides, etc.)Shock (earthquake, tides, etc.) Fluid addition (fluidization).Fluid addition (fluidization).
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Deformation structuresDeformation structures
►Liquefaction structures:Liquefaction structures: Sand volcanoesSand volcanoes Convolute laminationConvolute lamination Pillar and dish structuresPillar and dish structures
►Slides and growth faultsSlides and growth faults►SlumpsSlumps►Skrinkage cracksSkrinkage cracks
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Sand volcanoesSand volcanoes
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Convolute laminationConvolute lamination
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Dish structuresDish structures
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Growth (listric) faultsGrowth (listric) faults
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SlumpsSlumps
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Further readingFurther reading