1
2
Thesesedimentsweretransportedasflowsofmaterial,largelyquartz,feldspar,rock
(lithic)fragments,clayminerals,andmicaandvariousaccessoryminerals.ClasBc
sedimentsarefurthercategorizedbygrainsize(parBclediameter):gravel(>2mm
diameter),sand(1/16to2mmdiameter),andmud(clayis<1/256mmandsiltis
between1/16and1/256mm).
3
Rocksandmineralsareinequilibriumunderthespecificsetofphysicalandchemical
condiBonsinwhichtheyform.InnewcondiBonstheytendtomovetoanew
equilibriumstate.IRandMRformattemperatures(T)&pressures(P)higherthan
thoseatthesurfacewithlessfreeoxygen,CO2&water.Assuchtheserocksare
unstableatsurfaceT&PandwillchangeviaWEATHERINGintomineralsthatare
stableonthesurface.ThenetresultofthisequilibriumchangeistheformaBonofSR.
IRandMRasagrouparetypicallycomposedof20%quartzand80%othersilicates.
OnlyquartzisstableatsurfaceTandP.The80%“othersilicates”willundergo
equilibriumchangestoformsilicatesthatarestableatthesurface,mostlyclays.The
suscepBbilitytoweatheringwilldependon“howfaroutofequilibrium”theminerals
are.OlivineisprobablythemostsuscepBblefollowedbypyroxeneandsoon..Akind
ofreverseBowen’sreacBonseries.
ThiscanbeusedanesBmateofhowfarasedimenthasbeentransportedbeforeit
wasdeposited.Themineralsasedimentcontainsareremoved(tosomeextent)from
furtherweatheringbydeposiBon.SRrichinthehighTandPminerals(likeOlivine
andPyroxene)wouldbeconsideredtobemineralogically“immature”andprobably
hadnottravelledfarfromtheiroriginalsourcerock.Conversely,rocksrichinquartz
andnotmuchelseareconsideredtobemineralogically“mature”andmayhave
travelledalongdistancefromtheoriginalsourcerock.REMEMBERthisisjustarule
ofthumb–youcannotimplylongtransportdistanceandadistanceprovenancefor
allminerallogicallymatureSR.
4
TexturereferstothesizeandorientaBonofclasts/minerals.Thetextureofa
sedimentcanhaveimportantimplicaBonsforasedimentaryrocksdensity,porosity
orpermeability.INGENERALcoarsegrainedrockswillbeclosetothesourceofthe
parentsourcerock–REMEMBERTHISISAGENERALITY!
5
'Sphericity'isameasureofthedegreetowhichthegrainapproachesasphere.
Roundingreferstohowsmoothagrainis.Roundingofgrainswillincreasewith
transportofsedimentawayfromitssourceasthe“ruffedges”getabraded.
6
SorBngindicatesthedistribuBonofgrainsize.Poorlysortedindicatesthatthe
sedimentsizesaremixed(largevariance);whereaswellsortedindicatesthatthe
sedimentsizesaresimilar(lowvariance).ThedegreeofsorBngmayalsoindicatethe
energyand/orduraBonofdeposiBon–rapidlydepositedsedimentswilltendtobe
morepoorlysorted.Wellsortedrocksaregenerallyporous,whilepoorlysortedrocks
havelowporosity.SorBngisthedegreetowhichparBclesarethesamesize
7
This is a hypothetical diagram showing how two different source rocks may
produce different types of sandstone.
8
AconglomerateconsistsofindividualROUNDEDclasts(>2mm)withinafiner-grained
matrix.Breccias,consistofangularclasts.DiamicBtescanbecomposedofeither
angularorroundedclastsbutinamudmatrix(<30microns)
9
Itiscommontofind“basalconglomerates”atthebaseofsedimentarysequences
depositedduringmarinetransgressions(assealevelrisesandfloodsontotheland)
aboveanunconformity.
10
River(fluvial)depositsooencontainwellroundedandwellsortedconglomerates.
Clastsarecarriedas“bedload.”Maximumclastsizewillbeclosesttothe“source
rock”oftheconglomeratewithclasssizedecreasingdowntheriverscourseasthey
areabraded.Assuch,immatureriversystems(e.g.thoseinhighlandareas)tendto
havemoreconglomeriBcfacies.
11
ThisisaprimarydeposiBonalfabricconsisBngofapreferredorientaBonofclasts
suchthattheyoverlaponeanotherinaconsistentfashion,ratherlikearunof
toppleddominoes.ImbricaBonisobservedinconglomeratesandsomevolcaniclasBc
deposits
12
Conglomeratescanbefoundinmatureriversbuttheytendtobeconfinedtothe
bopomofthechannelaspartofa“channelfill”deposit.Theseconglomeratesare
ooencalledpebblelags.
13
Alluvialfansareconeshapedbodiesofsedimentthatooenformatthepointofa
breakinslope,ooeninhighlandareas.Alluvialfansmaymergetogethertoform
largebraidplainstoformVERYthickdepositsof(onthewhole)clastsupported
conglomerates.
14
Glaciersooentransportalotofcoarse-grainedsedimentandmanydepositsare
ConglomeraBc.Tillitesareconglomeratesthatareooenfoundinglacial
environments.Theyarematrix-supportedandpoorlysorted.Thematrixisgenerally
fine-grainedcomposedofrockgroundbytheacBonoftheglacier.
15
ConglomeratesandBrecciasarecommonlydescribedbytheirclasttypes:
-Monomict–only1typeofclast
-Oligomict–afewdifferenttypesofclast
-Polymict–manydifferentclasttypes
Andalsoiftheyareclastsupported(moreclaststhanmatrix)ormatrixsupported
(morematrixthanclasts).
16
Quartzand/orfeldspararethemostcommonmineralsintheEarth'scrustandas
suchareooenthedominantcomponentofsandstones.Sandstonescandemonstrate
veryvariablecoloursincludingtan,brown,yellow,red,gray,pink,whiteandblack.
The3maincomponentsofsandstonesareGrains,MatrixandCement.
FrameworkGrainsarecomponents1/16-2mminsize.Themostcommonareare
quartzfollowedbyfeldsparandlithic(rock)fragments.Othercomponentsarecalled
accessorymineralgrainsandcanbeveryvariableincomposiBondependingonthe
rockthatwaserodedtoproducethesediment.
Matrixismaterial<30umthatliesinbetweenthegrainsandmaybedepositedalong
withthelargergrainsduringdeposiBon.Somematrixmayformwhenclaysform
betweengrainsduringdiagenesis,someBmesfromthealteraBonoffeldspars.
MineralCements“glue”grainstogether.Cementsareprecipitatedbetweenthe
grainsfollowingdeposiBonandburialofthesediment.Commoncementsarequartz
andcalcite.
17
OnebroadclassificaBonisbasedonthe%ofmatrixinasandstone.Anythingwith0
-15%matrixarearenites.15–75%areGreywackes.
18
TherearemanysandstoneclassificaBonschemes.MostusingtherelaBveporBonof
clasttypesandtheamountofmatrixpresentinthesediment.Theschemeof
Petjohnisshownhere.Beyond75%matrixsandstonespassintomudstones.
19
TherearemanysandstoneclassificaBonschemes.MostusingtherelaBveporBonof
clasttypesandtheamountofmatrixpresentinthesediment.Theschemeof
Petjohnisshownhere.Beyond75%matrixsandstonespassintomudstones.
20
21
22
23
1.Terrestrial(land)environments
-  Rivers(levees,pointbars,channelsands)
-  Alluvialfans
-  Glacialoutwash
-  Lakes
-  Deserts(sanddunesandergs)
2.Marineenvironments
-  Deltas
-  Beachandshorefacesands
-  Tidalflats
-  Offshorebarsandsandwaves
-  Stormdeposits(tempesBtes)
-  Turbidites(submarinechannelsandfans)
24
TheenvironmentofdeposiBonofasandstonewillhaveimportantimplicaBonsforits
possiblerangeofmaturiBes
25
AeoliansandstonesareooenverymatureasaresultoftheconBnualmovementof
sandbywindandgravity.Asaresultsandgrainsareooenverywellroundedand
spherical.Theyarealsogenerallyveryscratched(frosted)duetoabrasion.The
frequentlypossessathincoaBngofironoxideswhichinthinsecBonarereferredto
asironpellicles.
26
AnappreciaBonofsandstone(andcoarserclasBcs)composiBoniscommonlyusedin
thereconstrucBonoftectonicregimes.EachtectonicregimewillhaveparBcular
characterisBcsthatprovideacertainsetofsourcerocksandtransportregimeswhich
willinfluencethetypeandstyleofsandstonesbeingdeposited(seealsotherequired
readingfromthepreviouslecture).ThisQFLdiagramisaVERYcrudedemonstraBon
ofhowtherelaBveproporBonofthesegraincomponentsmaybeusedto
characterizecertaintectonicsetngs.
27
Around50%ofsedimentaryrocksinthegeologicrecordaremudrocks.Mudrocksare
themostcommonsedimentarydepositsonEarthprobablyasthisistheendproduct
oferosion.Ifamudrockcontainsclaygradematerialonlyonly(<65microns)=
claystone
Ifamudrockcontainssiltgradeonly=siltstone
Totellifamudstonecontainssiltymaterialyoucandothe“teethtest”–siltwillfeel
gripyontheteeth.
Mudrocksdon’tdemonstrateasmanyvariedsedimentarystructurebutmay
demonstratelaminaBons,mudcracksflamestructures(seepreviouslecture)and
fissility……
28
Burialpressuremayalignclaymineralsinthesedimentproducingaparallelfissility.A
mudstonethatsplitsintotheselayersparalleltobeddingiscalledashale.Fissilityin
mudrocksmaybeabsentasaresultofsomefeatureoftheoriginalsedimentorifthe
sedimentgetsmixedbytheburrowingacBonoforganisms(bioturbaBon).
29
Mudrockcolourisveryvariable:red,purple,brown,yellow,greenandgrey,and
blackwithgreysbeingthemostcommon.Ablackcolourmayindicatethepresence
ofsignificantamountsoforganiccarbonandpyrite.These“blackshales”indicatea
higherinputoforganicsrelaBvetotheamountofavailableoxygentooxidizethat
organiccarbonandareooenassociatedwiththeproducBonofH2Sandthe
formaBonofpyrite.Suchblackmudrocksareooendepositedinquiet,anoxic
condiBons(seelaterslides).
30
Whenironinamudrockbecomesoxidized(forexamplewhenanunconsolidated
sedimentisexposedtotheatmosphere)aredcolourcandevelop.
Whereorganicmaperdecomposesinamudrockinoxygenfree(reducing)
condiBons,inthepresenceofferriciron,agreencolouriscommon.Thegreen
colourisareflecBonofthesheetsilicatesinthemud(usuallygreen)withoutany
oxidizedironcomponent.
GreenReducBonspots/horizonsarecommoninredmudrocksprobablyreflecBng
thereducBonofferricironadjacenttoplantrootsorotherorganicmaterial.Green
lensesormoreextensivehorizonscouldindicateshalloworganicrichponds.
31
ThemajorityofEarth’smudisfoundinadiversityofoceanicenvironments.Erosion
andtransportofsedimentisasignificantsourceofmudbutsomeorganismscan
producemudaswell.
Riversareprobablythelargestsourceofmud,transporBnglargequanBBesoffine
grainedsedimenttotheoceanicshelf.Inpolarregionsglaciersmayalsodelivermud
totheoceans.Bothwindandexplosivevolcanismmayalsocontributetomuddy
sediments.Gravitywillooenmovesedimentpresentontheoceanicshelftodeeper
oceanicenvironments.
Marineshelf–typicallygrey,bioturbatedmudstones.Ooenpasslaterallyand
verBcallyinsandstonesand/orlimestones.
32
Nearshore-ExampleBdalflats/lagoons/deltas
OoendarkgreyreflecBnghighorganicinputintheseareas.Asasedimentary
environmenttheycanbeidenBfiedbytheflora/faunatheycontainandbyspecific
associaBonsoflithologyandsedimentarystructures.Mudcracksareacommon
feature.
MudrocksintheseenvironmentsareooenassociatedwithcoarseclasBcs
represenBngbeach/riverchanneldeposits.Brackish(marinedilutedwith
freshwater)/hypersaline(verysalty)condiBonsmayalsobecommonintheseareas
anddepositmudstones–ooendemonstrateareducedfossildiversity.
Aoerriversleaveadeltatoporanestuarytheymaystarttodepositmud.Thismay
beaidedbytheprocessofflocculaBonwherefinelydispersedsedimentinthewater
startstoclumptoformlargerparBclesthatstarttosepleoutofthewatercolumn.
Thisprocessoccurswhenfreshwatercontainingthefinesedimentmixeswitha
soluBoncontainingelectrolytes,e.g.,seawater.
33
Hemipelagicmudrocks–Deep/distantmarinesetngs
Ooendarkgreybutcanbeavarietyofcolours.Redclaysmaybepresentinvery
distantmarinesetngs.TheseclaysrepresenttheaccumulaBonofwindblowndust
fromdistantconBnents.
Hemipelagicmudrocksarecommonlyassociatedwithpelagicfossils.Aclassic
examplearethegraptolites.Thesemarineorganismsfloatedingreatnumbers
throughthelowerPaleozoicoceans.Upontheirdeaththeywouldsinktotheocean
floorwheretheywouldaccumulate,parBcularlyindeeper,quietermarinesetngs.
ThiswidedistribuBon(andthefactthatmanyhaveveryshortgeologicalranges)
makesthemparBcularlyusefulinbiostraBgraphy(subdivision/correlaBonofstrata
usingfossils).
34
Alluvial(fluvial–river)valleyshaveaconstantsourceofrunningwater.During
floodingeventstheseenvironmentsmaydepositmudonafloodplane.Deltasare
ooencharacterizedbyveryslowmovingsluggishwaterandcanaccumulatemudin
infloodingeventsorinabandonedchannels.
35
LakescanbeamajorareaofmudrockdeposiBononland.Thecharacterofthe
mudrocksinthesesetngscanvaryconsiderablydependinguponlakechemistry,
climaBcandgeologicalsetngandorganicproducBvity.Innonglaciallakesrhythmic
laminaBonsalternaBngbetweenorganicrichandorganicpoorlaminaBon(onthe
mmscale)mayrepresentseasonalbloomsinphytoplankton.TheorganicproducBvity
insomeancientlakescanbesosignificantastoproducecommerciallyviableoil
shales.
Glaciallakesmaydemonstratevarves.HerelaminaBonsvaryfromCoarserclasBc(silt
–sand)depostedduringspringmelBng)tofinegrainedandsomeBmeorganicrich
materialdepositedfromsuspensionduringsummermonths.VariaBonsinvarves
havebeenusedinsomeancientlakestodeterminecyclicvariaBonsinclimate
thoughttobelinkedtovariaBonsintheEarth’sorbitandsolaroutput.
36
Organicrichmudrocksareanimportantresourceasasourceforpetroleum.
PetroleumformsataboutthreetosixkilometersbelowtheEarth'ssurface.IniBally
organicmaterialisconvertedintokerogenandastemperatureandpressure
increasestransformsintooil.Furtherincreasesintemperaturewillleadtothe
formaBonofgas.
Sulfidicblackshalescontainabundantorganicmaterialbutalsopyrite.Theyaregood
indicatorsofanoxicbopomwatersinamarinesetnggenerallyresulBngfrom
restrictedorreducedoceancirculaBonsuchastheBlackSea.
37
DuringthedecomposiBonoforganicmaperinanoxiccondiBonsbyanaerobicsulfate
reducingbacteria,sulfateionsarereduced.ThisgeneratesHydrogensulfide.AnyFe
ionspresentareprecipitatedasthemetalsulfide–pyrite.ThisreacBongenerally
occursinareasofslowsedimentaBonrate.
Alargescalemarineanoxiceventshasnotoccurredformillionsofyearsbut
significanteventshaveoccurredinthemoredistantpast.Andarelikelyassociated
withmassexBncBonevents.Theseoceanicanoxiceventsarestronglylinkedtoto
climatewarmingandgreenhousegaseswhichcausesstraBficaBonoftheoceanswith
verywarm(lessdense)surfacewatersthatactasa“lid”andreduce/stopoceanic
circulaBon.
38
SummaryofsomeoftheenvironmentsofdeposiBonofmudrocks.
39
Volcanoescanalsobesourcesofmudrocks.VolcanicashproducedbyerupBonsis
ooenalteredtoclaysformingbentonites.Thesewilldecreaseinthicknessawayfrom
thevolcanicsource.AstheymaysBllcontaindatable(byradiometrictechniques)
materialtheycanooenbeusedas“Bmemarkers”insedimentarysequences.
40
Finally,Loess-anaeoliansiltysedimenttransportedbythewind.Typicallyinthe20–
50umgrainsizerange,ooenlooselycementedbycalciumcarbonate.Commonly
homogeneousandporous.ExposuresofLoesscommonlyfracturetoformverBcal
bluffs.Insomepartsoftheworld(seeabove)thesedepositshavebeenusedtomake
cavedwellings.
41
42
43