Surface Processes & Sediments Associate Professor John Worden DEC University of Southern Qld

Surface Processes & Surface Processes & SedimentsSediments

Associate Professor John Worden Associate Professor John Worden DECDEC

University of Southern QldUniversity of Southern Qld


Rock-forming Processes:Rock-forming Processes: IgneousIgneous, , SedimentarySedimentary, or , or MetamorphicMetamorphic.. Next examine Surface Processes which occur at 1A, 25Next examine Surface Processes which occur at 1A, 25oo C. C. Colliding, rotating, grinding & twisting plates Colliding, rotating, grinding & twisting plates generategenerate

tectonics tectonics which thrust upwhich thrust up Mountain Ranges. Mountain Ranges. As steadily as Mountains form, Erosion wears them down.As steadily as Mountains form, Erosion wears them down. Erosive agents - Wind, Water and Ice.Erosive agents - Wind, Water and Ice.

• Transport rock debris to depositional sitesTransport rock debris to depositional sites;;

• Accumulates as SedimenAccumulates as Sediment and,t and,

• Compacted, & Lithified to Sedimentary Rocks.Compacted, & Lithified to Sedimentary Rocks.

TimeTime is is recorded by Sedimentary Rocks. recorded by Sedimentary Rocks.


Principles & TermsPrinciples & Terms Sediments characterised by layers termed ‘Sediments characterised by layers termed ‘StrataStrata’.’. Discrete recognisable layers termed ‘Discrete recognisable layers termed ‘BedsBeds’, and these define ‘’, and these define ‘BeddingBedding’. ’. Depositional processes produce ‘Depositional processes produce ‘StratificationStratification, a record of changing , a record of changing

environmental conditions throughout time.environmental conditions throughout time. Law of Original HorizontalityLaw of Original Horizontality::

• States that sediments are deposited in Strata that are horizontal.States that sediments are deposited in Strata that are horizontal.

Principle of Stratigraphic SuperpositionPrinciple of Stratigraphic Superposition::• States that in any sequence of sedimentary strata,States that in any sequence of sedimentary strata,

““The oldest rock is at the bottom, and the youngest rockThe oldest rock is at the bottom, and the youngest rockon the top, of the sequenceon the top, of the sequence””. .


Conformable sequences consist of strata uniformly following Conformable sequences consist of strata uniformly following each other without interruption. However, breaks common.each other without interruption. However, breaks common.

Sedimentary record incomplete due to ‘Sedimentary record incomplete due to ‘UnconformitiesUnconformities’- ’- periods of non-depositionperiods of non-deposition or or erosion.erosion.

Three types of Unconformities-Three types of Unconformities- Non-conformityNon-conformity = Change in major classes of rock types, = Change in major classes of rock types, Angular unconformityAngular unconformity =Period of tectonism between rock types, =Period of tectonism between rock types, DisconformityDisconformity = Irregular = Irregular erosion erosion surface surface

separating two sedimentary layersseparating two sedimentary layers..

Unconformities are Unconformities are time gapstime gaps in in the the geol geologicalogical record. record.


Weathering:Weathering: The disintegration & decomposition of rock to produce ‘The disintegration & decomposition of rock to produce ‘RegolithRegolith’.’. Two typesTwo types of Weathering of Weathering: : PhysicalPhysical and and ChemicalChemical..

• Physical weathering reduces large masses to much smaller units thereby Physical weathering reduces large masses to much smaller units thereby increasing surface areas for chemical attack.increasing surface areas for chemical attack.

• Chemical & Biological Chemical & Biological weathering weathering convert mineral components to new convert mineral components to new components stable at 1A and 25components stable at 1A and 25oo C. C.

TheTheWeathering zone extends down as far as water & oxygen penetrate, Weathering zone extends down as far as water & oxygen penetrate, and and is is due to:due to:

• UnloadingUnloading of rock formations as exposed; of rock formations as exposed;

• PenetrationPenetration of soluble salts & later crystallisation; of soluble salts & later crystallisation;

• Water freezing & expansion as ‘Water freezing & expansion as ‘frost wedging’frost wedging’;;

• Plants wedgingPlants wedging rocks apart along cracks, and rocks apart along cracks, and

• Repeated bushfires causing unequal heating, expansion, and fracturing.Repeated bushfires causing unequal heating, expansion, and fracturing.


Soils:Soils: Equate to accumulated ‘Regolith’, which is composed of decomposed Equate to accumulated ‘Regolith’, which is composed of decomposed

products of rocks & minerals + organic matter.products of rocks & minerals + organic matter. Forms a succession of weathered zones termed ‘Horizons’.Forms a succession of weathered zones termed ‘Horizons’. Not strataNot strata, but comprise a , but comprise a soil profilesoil profile, which usually consists of:, which usually consists of:

• An organic-rich surface layer;An organic-rich surface layer;

• Upper Upper A horizonA horizon ( dark grey /black, depleted in clay, & enriched in organic M); ( dark grey /black, depleted in clay, & enriched in organic M);

• Middle Middle B horizonB horizon ( brown/ red, blocky, enriched in clay, & Fe-Al hydroxides); ( brown/ red, blocky, enriched in clay, & Fe-Al hydroxides);

• Possible Possible K horizonK horizon ( impregnated with Ca Carbonate); ( impregnated with Ca Carbonate);

• Underlying Underlying C horizonC horizon ( yellow/ brown, sl oxidised). ( yellow/ brown, sl oxidised).

Development dependent on :Development dependent on :• Climate, Vegetation cover, Soil organisms, RegolithClimate, Vegetation cover, Soil organisms, Regolith

composition, Topography, & Time. composition, Topography, & Time.


Erosion is the downslope movement of regolith/debris under Erosion is the downslope movement of regolith/debris under the the pull of gravity.pull of gravity. Termed ‘Termed ‘Mass Wasting’Mass Wasting’.. Influenced by composition, texture of regolith, amount of water/air Influenced by composition, texture of regolith, amount of water/air

mixed with debris, & steepness of slope. All influence velocity.mixed with debris, & steepness of slope. All influence velocity. Two general types: “Two general types: “Slope FailureSlope Failure” & “” & “Sediment FlowSediment Flow”.”. Slope failure is downslope movement of relatively coherent masses of Slope failure is downslope movement of relatively coherent masses of

rock or regolith slumping.rock or regolith slumping. Sediment flow is the downslope movement ofSediment flow is the downslope movement of

“Regolith”/ debris mixed with water + air.“Regolith”/ debris mixed with water + air. Landslides are examples of mass wasting.Landslides are examples of mass wasting. Once at bottom of slope, other agents transportOnce at bottom of slope, other agents transport

debris to lower elevations in the Landscape.debris to lower elevations in the Landscape.


Approx 30% of precipitation collects as ‘runoff’ in streams, Approx 30% of precipitation collects as ‘runoff’ in streams, which move downslope (stream flow).which move downslope (stream flow).

This transports debris particles & dissolved substances along This transports debris particles & dissolved substances along channels.channels.

Factors controlling channel flow include:Factors controlling channel flow include: Average Average wwidth & idth & ddepth;epth; Channel gradient;Channel gradient; Average Average vvelocity of waterelocity of water flow flow;; DischargeDischarge volume volume; and; and Total sTotal sedimenedimentt lload.oad.


Sediment LoadSediment Load ttransport moves in three ways:ransport moves in three ways: Coarse particles move along stream bed = ‘Coarse particles move along stream bed = ‘Bed load’Bed load’,, Fine particles move suspended in water = ‘Fine particles move suspended in water = ‘Suspended Load’Suspended Load’, &, & Material in solution = ‘Material in solution = ‘Dissolved load’Dissolved load’.. Bed load:Bed load:

• Moves by “Moves by “SaltationSaltation”- Sand -sized grains propelled into suspension, pulled ”- Sand -sized grains propelled into suspension, pulled down by gravity & returned to stream bed. Progressdown by gravity & returned to stream bed. Progress is is by short intermittent by short intermittent jumps along arcuate paths.jumps along arcuate paths.

Suspended Load:Suspended Load:• Silt and Clay particles moving in suspension,Silt and Clay particles moving in suspension,• Derived from fine-grained regolith,Derived from fine-grained regolith,• Particles settle when velocity of turbulent flow declines.Particles settle when velocity of turbulent flow declines.

Dissolved Load:Dissolved Load:• Bicarbonate, Ca, sulfate, Na, K, Mg, and Chloride ions. Bicarbonate, Ca, sulfate, Na, K, Mg, and Chloride ions.


As particles move downstream, As particles move downstream, particle size decreasesparticle size decreases due to due to abrasion and impacts. Gravel in headwaters, sand & silt at abrasion and impacts. Gravel in headwaters, sand & silt at stream mouth.stream mouth.

Grains are progressively ‘rounded’ tending toward spherical Grains are progressively ‘rounded’ tending toward spherical shape. Degree of “rounding” indicates transport distance.shape. Degree of “rounding” indicates transport distance.

Grains are also ‘sorted’ by size or hydraulic equivalency.Grains are also ‘sorted’ by size or hydraulic equivalency. Therefore, detrital sediments demonstrate:Therefore, detrital sediments demonstrate:

Transport distance by degree of ‘Transport distance by degree of ‘roundingrounding’;’; Source rock type by Source rock type by sediment mineralogysediment mineralogy;; Type of transport agency by Type of transport agency by grain surface texturegrain surface texture;; Efficiency of transport by degree of ‘Efficiency of transport by degree of ‘sortingsorting’.’.


Water also exists as ice where T << 0Water also exists as ice where T << 0oo C. C. Precipitation falls as snow down to Precipitation falls as snow down to snowlinesnowline ( lower limit of perennial ( lower limit of perennial

snow).snow). Snow compacts, recrystallises to ice, and moves downslope as ‘Snow compacts, recrystallises to ice, and moves downslope as ‘GlacierGlacier’.’. Valley glaciers at high latitudes move from high to low altitude Valley glaciers at high latitudes move from high to low altitude

forming forming ‘F‘Fjordsjords’’, where they reach sea level., where they reach sea level. Ice sheet flows internally and by basal sliding in response to gravity.Ice sheet flows internally and by basal sliding in response to gravity. Glacier scrapes bedrock removing soils & regolith, plucks rocks, and Glacier scrapes bedrock removing soils & regolith, plucks rocks, and

grooves bedrock. Bedrock displays striations, etc.grooves bedrock. Bedrock displays striations, etc. Debris is transported by ice to depositional site:Debris is transported by ice to depositional site:

• Glacier terminus as Glacier terminus as terminal moraineterminal moraine..

• As As lateral moraineslateral moraines, icebergs, etc, icebergs, etc


Wind also transports sediment:Wind also transports sediment: Dominant in dry climate areas where no vegetation to retain regolith.Dominant in dry climate areas where no vegetation to retain regolith. Transported particles are mostly sand and finer grain sizes.Transported particles are mostly sand and finer grain sizes. Sand particles moved as high as 1 metre above surface by “Sand particles moved as high as 1 metre above surface by “saltationsaltation”.”. Form ‘Form ‘DunesDunes’ of different types when encounter obstructions.’ of different types when encounter obstructions.

• Sand grains move by saltation up windward slope of dune(~ 12Sand grains move by saltation up windward slope of dune(~ 12oo););

• Grains fall over slip face of dune ( ~ 33Grains fall over slip face of dune ( ~ 33oo) and come to rest.) and come to rest.

• Dune migrates downwind.Dune migrates downwind.

• Process of grain migration forms Process of grain migration forms ‘‘CCross beddingross bedding’’..

Silt and clay particles carried in suspension until:Silt and clay particles carried in suspension until:• Wind velocity decreases and particles settle to surface.Wind velocity decreases and particles settle to surface.

• Form deposits of ‘Form deposits of ‘LoessLoess’; uniformly blanket surface;’; uniformly blanket surface;

• Lack stratification, but can contain fossils, etc.Lack stratification, but can contain fossils, etc.


Deposition:Deposition: Sediment deposited when stream/ wind velocity decreases or ice melts.Sediment deposited when stream/ wind velocity decreases or ice melts. Turbulent flow ceases & coarse sediment deposits first, progressively Turbulent flow ceases & coarse sediment deposits first, progressively

followed by fines. Hence sediment sorted by relative grain size.followed by fines. Hence sediment sorted by relative grain size. Depositional sites occur from stream floodplain to Oceans.Depositional sites occur from stream floodplain to Oceans. Meandering streamsMeandering streams ( with large loop-like bends) in fine- grained ( with large loop-like bends) in fine- grained

alluvium & gentle gradients.alluvium & gentle gradients.• Erosion of outer bank of meander & deposition on inner bank.Erosion of outer bank of meander & deposition on inner bank.

• Produces ‘Produces ‘Point bars’Point bars’

• As stream erodes fine-grained silts, may cut off loop.As stream erodes fine-grained silts, may cut off loop.

• Forms Forms ‘‘Oxbow lake’Oxbow lake’..

Braided streamsBraided streams form when debris load very high. form when debris load very high.• Stream divides into many channels & reunites often.Stream divides into many channels & reunites often.


Braided streams form ‘Braided streams form ‘Braid bars’Braid bars’ consisting of coarse debris. consisting of coarse debris. Such bars and channels are constantly re-worked by the stream.Such bars and channels are constantly re-worked by the stream.

Deposition at river mouths may form ‘Deposition at river mouths may form ‘Deltas’Deltas’, or be reworked , or be reworked by longshore currents into ‘by longshore currents into ‘spitsspits’, ’, ‘‘barsbars’’,,’barrier islands’’barrier islands’, etc., etc.

In all situations deposited sediment carries imprint of In all situations deposited sediment carries imprint of transporting processes in it’s texture, rounding, & degree of transporting processes in it’s texture, rounding, & degree of sorting.sorting.

Ice transport produces ill-sorted sediments.Ice transport produces ill-sorted sediments. Diverse grain size range;Diverse grain size range; Minimal degree of rounding;Minimal degree of rounding; Cosmopolitan range of sediment compositions; &Cosmopolitan range of sediment compositions; & Diverse types of resultant landform features.Diverse types of resultant landform features.


Lithification:Lithification: Sediment is ‘Sediment is ‘lithifiedlithified’ as it is buried by later sediments.’ as it is buried by later sediments. Formation water is expelled due to load pressure.Formation water is expelled due to load pressure. Compaction occurs as void space is reduced.Compaction occurs as void space is reduced. Grains frequently ‘Grains frequently ‘cementedcemented’ together by later mineral deposition in ’ together by later mineral deposition in

void space. Cementing agents include Calcite, Silica, Fe oxides, etc.void space. Cementing agents include Calcite, Silica, Fe oxides, etc. Resultant rock becomes ‘Resultant rock becomes ‘induratedindurated’ or hardened & strengthened with ’ or hardened & strengthened with

loss of ‘porosity’.loss of ‘porosity’.

Sediment generation is related to tectonics:Sediment generation is related to tectonics: Thickest sequences form near Mountain Belts.Thickest sequences form near Mountain Belts. These are typically ‘These are typically ‘immatureimmature’ sediments.’ sediments. Little tectonics means Little tectonics means maturemature sediments. sediments.


Sedimentary Rock PracticalSedimentary Rock Practical:: Important factors when describing & identifying rocks are:Important factors when describing & identifying rocks are:

TextureTexture- shape of fragments and their mutual arrangement;- shape of fragments and their mutual arrangement; RoundingRounding- degree of reduction towards spherical shape;- degree of reduction towards spherical shape; SortingSorting- tendency towards ‘unimodal’ or same grain size;- tendency towards ‘unimodal’ or same grain size; PorosityPorosity- percentage of void space in rock;- percentage of void space in rock; CementCement- nature and type of cement;- nature and type of cement; FissilityFissility- ability to split along bedding planes;- ability to split along bedding planes; FriabilityFriability- tendency to crumble;- tendency to crumble; Mineral CompositionMineral Composition- of fragments, grains,- of fragments, grains,

& matrix; & matrix; StructureStructure- bedding, cross bedding, joints, etc- bedding, cross bedding, joints, etc


Sedimentary Rocks:Sedimentary Rocks: Classified into two major groups- Detrital or Classified into two major groups- Detrital or ClasticClastic & & Non-clasticNon-clastic.. Clastic rocks subdivided on grain size basis into Coarse/ Medium/ Clastic rocks subdivided on grain size basis into Coarse/ Medium/

Fine;Fine; Coarse-grained further sub-divided on shape of fragments/grains into:Coarse-grained further sub-divided on shape of fragments/grains into:

• ConglomeratesConglomerates- with rounded grains;- with rounded grains;

• BrecciasBreccias- with angular grains or fragments.- with angular grains or fragments.

Medium-grained sub-divided on basis of degree of sorting & rounding Medium-grained sub-divided on basis of degree of sorting & rounding of grains into:of grains into:

• Sandstones / Sandstones / ArenitesArenites- well sorted, & well rounded;- well sorted, & well rounded;

• GreywackeGreywacke - poorly sorted, angular fragments. - poorly sorted, angular fragments.

Fine-grained divided into:Fine-grained divided into:• ShaleShale- bedding visible & frequently fissile;- bedding visible & frequently fissile;

• MudstoneMudstone- bedding absent, non-fissile, often ‘blocky’.- bedding absent, non-fissile, often ‘blocky’.


Non-clastic or Non-clastic or ChemicalChemical Sedimentary rocks: Sedimentary rocks: Include Carbonates, Siliceous, Carbonaceous,Include Carbonates, Siliceous, Carbonaceous, Ferruginous Ferruginous & &

Evaporites.Evaporites. Carbonates are usually of two types;Carbonates are usually of two types;

• LimestonesLimestones- made up of calcite derived from shell fragments of organisms, - made up of calcite derived from shell fragments of organisms, direct precipitation from sea water or fresh water, and possibly “oolites”.direct precipitation from sea water or fresh water, and possibly “oolites”.

• DolomitesDolomites- generally converted limestones that have been re-crystallised by - generally converted limestones that have been re-crystallised by solutions to Ca-Mg carbonate.solutions to Ca-Mg carbonate.

Siliceous rocks form from siliceous skeletons of marine organisms Siliceous rocks form from siliceous skeletons of marine organisms which are later ‘lithified’ to “which are later ‘lithified’ to “chertscherts”. ”.

Carbonaceous rocks form from vegetation:Carbonaceous rocks form from vegetation:• Various types of Coal, Peat, & Organic-rich Shale.Various types of Coal, Peat, & Organic-rich Shale.

Evaporites are direct precipitates from seawater:Evaporites are direct precipitates from seawater:• Include Rock Salt (NaCl), Gypsum, and Anhydrite.Include Rock Salt (NaCl), Gypsum, and Anhydrite.• Rarer salts such Potash, etcRarer salts such Potash, etc


Depositional Environments:Depositional Environments: Sediments are products of Sediments are products of ProvenanceProvenance (Source region), (Source region), TransportTransport

history, & history, & Depositional EnvironmentDepositional Environment.. A hole in the ground is a necessary pre-requisite (Need Subsidence!).A hole in the ground is a necessary pre-requisite (Need Subsidence!). Depositional Environments have gradational boundaries.Depositional Environments have gradational boundaries. Sediments occur in distinct “Sediments occur in distinct “PackagesPackages” in a vertical section sense.” in a vertical section sense. In conformable sequences, only adjacent environment “packages” can In conformable sequences, only adjacent environment “packages” can

occur immediately overlying or underlying particular sediments.occur immediately overlying or underlying particular sediments. Results in superimposed sedimentary “Results in superimposed sedimentary “cyclescycles”.”. Examples: Examples:

• Fluvial/Alluvial; Deltaic; Coastal; Turbidite; etc.Fluvial/Alluvial; Deltaic; Coastal; Turbidite; etc.

• Consider only Fluvial & Deltaic Environments.Consider only Fluvial & Deltaic Environments.

• Point Bar deposits. Point Bar deposits.


Point Bar Sediments:Point Bar Sediments: Meandering stream deposits.Meandering stream deposits. Record ‘Record ‘fining upwards’fining upwards’ cycles of grain size in sediments, ie cycles of grain size in sediments, ie

• With each flood, deposition commences with gravel, grits , & coarse sands.With each flood, deposition commences with gravel, grits , & coarse sands.• As current slackens, sands become progressively finer-grained.As current slackens, sands become progressively finer-grained.• Sluggish current enables deposition of silt and clay layers.Sluggish current enables deposition of silt and clay layers.• Next flood repeats cycle.Next flood repeats cycle.• As river meanders over floodplain, deposits “packages” of gravelAs river meanders over floodplain, deposits “packages” of gravelsandsandclayclay

fining upwards cycles.fining upwards cycles. Deltaic sediments in contrast, “Deltaic sediments in contrast, “coarsen upwardscoarsen upwards”.”.

• Deeper water in front of delta is more distal from river.Deeper water in front of delta is more distal from river.• Results in deposition of fine-grained silts and clays.Results in deposition of fine-grained silts and clays.• As river advances, introduces fine sands, later coarserAs river advances, introduces fine sands, later coarser

sands and grits. = “sands and grits. = “Coarsening UpwardsCoarsening Upwards” cycles. ” cycles.

Documents

Surface Processes & Sediments Associate Professor John Worden DEC University of Southern Qld