EOSC221

DIAGENESIS

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•  Introduc4onandDiagene4cZones•  SandstoneDiagenesis•  MudstoneDiagenesis

–  Marine–  NonMarine

•  CarbonateDiagenesis–  MajorProcesses–  Diagen4cEnvironments–  Dolomi4za4on

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LECTUREOUTLINE

•  Thetransforma4onofasedimentintoarock:•  Compac4on/recrystalliza4on/dissolu4on/authigenesis(growthof

newminerals)andcementa4on•  Importanteconomicallyintermsofporosity(Φ)andpermeability(K)

andintheforma4onofoil.

INTRODUCTION

hQp://www.earth.ox.ac.uk/~oesis/micro/medium/sandstone2_pm13-19.jpg

Porosityandpermeabilityofthissandstonehasbeengreatlyreducedbytheprecipita4onofcalcitecementinbetweenthe

porespaces

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Diagene+cZones:•  Differentdiagene4cprocesseswilloccuratdifferentdepthsofburial

andindifferentenvironments:marinevsterrestrial•  Differentsedimentswillbehavedifferentlyinthesezones

hQp://upload.wikimedia.org/wikipedia/commons/f/f2/Vadose_zone.gif

Phrea1cZone

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SANDSTONEDIAGENSIS

VadoseZonei.Clayinfiltra4onfromporewaters

ii.MineralSolu4on:pi[ngandetchingofunstablecomponents

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iii.GrowthofAuthigenicMinerals:IlliteandKaolinitethemostcommon

hQp://pubs.usgs.gov/dds/dds-033/USGS_3D/ssx_txt/figur27.htm

iv.Diagene4creddeningofsedimentsCausedbyinfiltra4onofhema4tea_erdeposi4onorthedissolu4onofunstablemineralsreleasingFetoformhema4te.

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Phrea+cZonei.  Con4nuedaltera4onanddissolu4onofgrainsii.  Mechanicalcompac4onofframeworkgrains–pressuresolu4onof

quartzgrains

hQp://en.wikipedia.org/wiki/File:Pressure_solu4on_sandstone.svg

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iii.Growthofcements:silicaandcalcite-  Silicao_enasquartz

overgrowthsinop4calcon4nuity

-  Calcitecanbebothanearlyoralatestagecement.

hQp://www.huntsearch.gla.ac.uk/cgi-bin/foxweb/huntsearch/DetailedResults.fwx?collec4on=geology&searchTerm=134394&browseMode=on

PPL

XPL

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MUDSTONEDIAGENSIS

MarineMudstoneDiagenesisZone1:0-0.5m

-  Uncompacted,highporosity-  oxicporewaters:bioturba4on-  Oxida4onoforganicsbyaerobicbacteriaformingCO2

-  Zone2:0.5–10m

-  Zoneofbacterialsulfatereduc4on-  Anoxiccondi4ons

2CHO+SO4

2-!2CO2+S2-+2H2O

Organicmaterial

Sulfatefrommarinewater

BacterialAc4vity

12C:mayformcalciteconcre4ons

S-mayformH2S

D.vulgaris

hQp://en.wikipedia.org/wiki/File:Dvulgaris_micrograph.JPG

Bioturba4on

hQp://pubs.usgs.gov/dds/dds-033/USGS_3D/ssx_gif/bss8038.gif

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Zone3:10–1000m-  ZoneofOrganicFermenta4on:nomoresulfatereduc4on

CH2O!CH4+CO2

-  Possibleforma4onofSiderite-  Expulsionofporewaterbycompac4on

Zone4:1–2.5km

-  BreakdownofremainingorganicmaQerbydecarboxyla4on

-  Moreporewaterexpelled

hQp://en.wikipedia.org/wiki/File:Decarboxyla4on_reac4on.png

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Zone5:2.5–7km

-  ZoneofHydrocarbongenera4on(about70–90°C)-  BreakdownofunstablemineralcomponentsreleasesH2O-  ReleaseofH2OexpelsSiO2,Mg2+,Fe2+andanygeneratedpetroleum-  Athighertempsgasratherthanliquidpetroleumproduced.

Zone6:>7km-  Zoneofmetamorphism-  illite->Sericite->Muscovite(at300°C)-  Kaolinite->Dickite/Nacrite->Chlorite

(at200°C)

hQp://en.wikipedia.org/wiki/File:Chlorite_schist.jpg

ChloriteMicaSchist

Diagenesis-Metamorphism

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SulfateReduc4on

DETRITALINPUT

RED/BROWNCLAYS

BLACKPYRITICSHALES,CALCITE,

DOLOMITE,PHOSPHATES

SIDERITICMUDSTONES

OILandGASPROSPECT

$

Isburialratesufficientlyslowforextensive

genera8onandmigra8onofhydrocarbons?

Metamorphism

YES

NO

Isburialratesufficientlyslowfor

completeFe3+conversiontopyrite?

NO

YES

YES

Fermenta4onCH4CO2

NO

Isburialratesufficientlyslowforextensive

fermenta8onanddecarboxyla8on?

NO

Istherateofburialsoslowthatallorganiccarbonis

oxidizednearthesediment/waterinterface? YES

Isdeposi8onalwatermarine(SO42-rich)?

ZONE1

ZONE2

ZONE3-4

ZONE5

ZONE6

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YES

Non-MarineMudstoneDiagenesis-  NotsomuchSO4

2-

-  Sulfatereduc4onnotsignificant-  Tendtoproducesideriteinearlydiagenesis-  Sideriteconcre4onsmaybeafeatureoffreshwaterenvironments

hQp://www.ucmp.berkeley.edu/carboniferous/mazon.html

TheMazoncreek“Tullimonster”preservedinaSideritenodule 13

CARBONATEDIAGENESIS

Majorprocesses1)  Cementa4on:factors:CO2,Mg/Cara4o,CO3supply2)  Neomorphism:

•  Aggrading•  Calci4za4on

Aggrading

Calci8za8on

Spargrowinginmicrite

Shell

recrystallized:

internal

detaillost 14

3)  Dissolu4on4)  Compac4on5)  Dolomi4za4on:conversionfromCaCO3->CaMg(CO3)2 hQp://en.wikipedia.org/wiki/File:1_li_jiang_guilin_yangshuo_2011.jpg

Stylolites

hQp://en.wikipedia.org/wiki/File:7092_pieskovna_Dolinka_pri_Hradis4_pod_Vratnom_dolomit.JPG

Dolomite

hQp://en.wikipedia.org/wiki/File:Stylolites_mcr1.jpg

Guilin,China

hQp://en.wikipedia.org/wiki/File:Stylolite_oehrlikalk_1b.jpg

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Diagene+cEnvironmentsThreemainenvironments:Meteoric/Marine/Burial1)Meteoric:probablymoreimportantthanthemarinezonei.  UpperVadozezone:Zoneofinfiltra4on:acidicrainwatercausesdissolu4onof

highMgcalciteandAragoniteii.  LowerVadozezone:ZoneofPercola4on:recrystalliza4onofunstable

componentsandprecipita4onofmeniscuscements

hQp://sepmstrata.org/CarbonateDiagenesisGallery/CarbDiagenesisGallery.html hQp://en.wikipedia.org/wiki/File:GeopetalCarboniferousNV.jpg

Pendentforms

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OriginalaragoniteshellrecrystallizedtolowMgCalcite

iii.  Phrea4czone:Permanentwatersatura4on

- MoreLowMgCements- Ini4alphrea4ccementso_enIsopachous- Laterphrea4ccementstendtobecoarserblades- Syntaxialovergrowthsonsomegrains

SyntaxialovergrowthsIsopachous

coarserblades

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Isopachouscement

Meniscuscement

Pendentcement

Rain

METEORICVADOSE

METEORICPHREATIC

WaterTable

Poressaturatedwithwater

Airinpores

OceanOcean

MIXINGZONE MARINE

PHREATIC

18MARINE:MostlyAragonite/highMgcalcitecementsMETEORIC:LowMgcalcitecements

hQp://sepmstrata.org/CarbonatePar4cles/pages/164-Micri4za4on.html

-  Cementso_enaragonite/HighMgCalcite

-  Cangetsimilarisopachouscements(bladesandfibres)asinmeteoric

CretaceoushardgroundfromTexaswithencrus4ngoystersandbivalveborings.

2)Marine-  Micri4za4onofgrainsonseafloor-  Cementa4on–forma4onofhardgrounds/beachrock-  Canpendentcementsinbeachrock

hQp://en.wikipedia.org/wiki/File:Cretaceous_hardground.jpg

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hQp://en.wikipedia.org/wiki/File:Reunion_Saint-Leu_Beachrock.JPGhQp://en.wikipedia.org/wiki/File:Reunion_Saint-Leu_Beachrock(detail).JPG

Beachrock

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3)  DeepBurial-  Cementsfillremainingporosity-  Calcitemadeavailablebyforma4onofstylolites-  Porositycandropfrom20–5%-  Tendtoferroan(ironrich)calcitecements(anoxicporewater)-  O_enmosaicinform-  Possibleaggradingneomorphism-patchesofsparinmicrite.

hQp://www.microscopy-uk.org.uk/mag/arzeb04/iwouslides.htmlhQp://www.earth.ox.ac.uk/~oesis/micro/medium/limestone-xpl_pm14-09.jpg

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Largerbladedlatervadoseorearlydeepburialcement

Deeperburial,oVenferroan

rich–equant“mosaic”crystals

Firstgenera1onvadosecement

Original

CarbonateGrain

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Dolomi+za+on-  Penecontemporaneous

-  altera4ontodolomitesoona_erdeposi4onofthelimestone-  2CaCO3+Mg2+->CaMg(CO3)2+Ca2+

-  Directprecipita4on-  Notrepeatedunderlabcondi4ons-  Ca2++Mg2++2CO3

2-->CaMg(CO3)2-  Deepburialdiagenesisandaltera4onoflimestone

TheDolomitesRange,Italy

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A.Penecontemporaneous

1)  Evaporite-BrineResidueModelI.  RefluxModel-  Gypsum(CaSO4)forma4onincreasesMg:Cara4o-  Resultantbrinesinksintosediment-  Problem:notobservedinnature

Supra4dal HighTide

OCEAN

MgDEPLETEDbrine

Dolomi4zedZone

MgRICHbrine

Seefigure15-34intextbook

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II.  Evapora4vePumping-  Sabkhaenvironment-  Evapora4ondrawsbrines

OCEAN

EVAPORATIONHaliteCrust Gypsumand

Anhydrite

SalineGroundwaters

Stromatolitescommon

Sabkha,Tunisia

hQp://en.wikipedia.org/wiki/File:Sebkha_El_Melah_-_2001.jpg

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2)  GroundwaterMixingModel-  Brackishwaterinzonewherefreshmixeswithsaltwater-  Mayproducecondi4onssuitablefordolomi4za4on-  Inallcasesdolomi4za4ono_enremovesordegradesoriginal

deposi4onalstructures/featuresRainfall

Meteoricporewaters

Marineporewaters

SeaLevel

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3)  SeawaterModel-  Tidaleffectsorrisingsealevelpumpseawaterthroughsediment-  Porescon4nuallyflushedwithfreshmarinewater-  Mginseawatermayallowfordolomi4za4on

Meteoricporewaters

Marineporewaters

RisingSeaLevel

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B.   DeepBurialDolomi1za1on

-  Majorityofdolomites–show“ghosttextures”-  Mustbealtera4onoforiginallimestones-  Probablyinindeepburialse[ngs-  Occursovermillionsofyears

DOLOMITEPEAK,ALBERTA

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GLOSSARY All lecture material is potentially examinable. It is up to you to know

unfamiliar terms / names / people. Use this space to create your own lecture glossary

TERMS / NAMES DEFINITION

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TERMS / NAMES DEFINITION

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