Embed Size (px)
Citation preview
EOSC221
PART1:EVAPORITES(andothersediments)
PART2:SEDIMENTARYFACIES
1
• IntroducCon• EnvironmentsofDeposiCon
– Sabkha– BasinDeposits– Lakes
• ExampleEvaporiteDeposits• OtherSedimentaryrocks
– BandedIronFormaCons– Cherts– Coal– VolcaniclasCcs
• SedimentaryFacies
2
LECTUREOUTLINE
hNp://en.wikipedia.org/wiki/File:Sebkha_El_Melah_-_2001.jpg
• Minerals• WatersolublemineralsthatprecipitatefromsoluCon• CommonMinerals–mostderivedfromseawater
– Gypsum:CaSO4.H2O– Anhydrite:CaSO4
– Halite:NaCl
EVAPORITES:INTRODUCTION
hNp://en.wikipedia.org/wiki/File:Halite-249324.jpghNp://en.wikipedia.org/wiki/File:Anhydrite_HMNH1.jpghNp://en.wikipedia.org/wiki/File:SeleniteGypsumUSGOV.jpg
3Gypsum Anhydrite
Halite
4hNp://ngm.naConalgeographic.com/2008/11/crystal-giants/shea-text
giantgypsumcrystals(some11mlong)inMexico’sCuevadelosCristales
AbundanceandDistribu5on- 1%ofallPhanerozoic(542–0MA)rocks- MoreevaporiteproducConwhencontsgroupedaroundequator- Evaporiteshighlysoluble–rareinoutcrop–mostlysubsurface
TextbookFig.16.1
• Sabkha• SupraCdalenvironmentsalongaridcoastlines• Sabkhasbuildout‘prograde’OVERinterCdalsedimentsgivingthema
uniquesequenceoffaciesinsedimentarylogs.Goodexample:coastofPersianGulfintheUAE
EVAPORITEENVIRONMENTSOFDEPOSITION
6
OCEAN
EVAPORATION“mudcracked”HaliteCrust Gypsumand
Anhydrite
SalineGroundwaters
Stromatolitescommon
SupraCdal InterCdal
EVAPORATIVEPUMPINGINASABKHAENVIRONMENT
• Gypsumprecipitateddirectlyintosediments(alsodolomiCzaCon)• Gypsumasnodules/chickenwirestructures/enterolithictexture• MaygetanhydriteprecipitaCngfurtherlandwardratherthangypsum
hNp://www.soton.ac.uk/~imw/Visean-Evaporites.htmhNp://www.soton.ac.uk/~imw/Durlston-Bay-Lower-Purbeck.htm
• DeepBasins
• MostimportantgeologicalsourceofEXTENSIVEevaporiteformaCon• Nonreallyformingtoday.Twotypes:
– 1.Deepbasinsbarredbyabarrier:fault/CO3bank/reefetc– 2.Deepbasinswithoccasionalaccesstosea
8
Barrier“sill”
replenishment
OPENSEA
OPENSEA
Occasionalreplenishment
1.Deep,barredbasin
2.Deep,desiccatedbasin
precipitaCon
• Problem:Howdoyougetthick&variableevaporitedeposits?• SoluCon:Brinerefluxmodels
9
Barrier“sill”
Replenishmentofseawater
OPENSEA
Brinereflux
Brinesseeping
precipitaCon
• Basinalevaporitesonenlaminated• LaminaConsmayhaveawidelateralextent
10hNp://www.nps.gov/history/history/online_books/cave/446/sec3.htm
LaminatedEvaporites
Sediment Environment
Sedimentswithnormalmarinefauna OpenMarineBasin
Anhydrite&organic/carbonatelaminae
Haliteandanhydritelaminae
K&Mgsalts
Halitemassiveorlayered
AnoxicBasin
ShallowingbasinduetoevaporaCon
Salinelakes/Sabkha
subaerial
subaqu
eous
OVE
RALLdecreasingde
pthofwater
Increasin
gSalinity
12
3
4
5
6
OrganicrichdepositsCarbonatelaminae
• Lakes• Similarminerals(halite,anhydite,gypsum)butalsosomeunique
freshwaterprecipitatedminerals• Mineralogycanbeveryvariabledependingonlakechemistry• Twobroadcatergories
– Saltlakes:Halitedominated– BiNerlakes:sodiumcarbonateandsulfatedominated
hNp://en.wikipedia.org/wiki/File:Dead_Sea-12.jpg
TheDeadSea,asaltlake.11
hNp://en.wikipedia.org/wiki/File:Lakeside_of_Mono_Lake.jpg
MonoLakeCalifornia,abiNerlake.
• TheGulfCoastSaltBasinandtheOchoanSeriesDelawareBasin• Makenotes:page315–318–NOTEThisispotenCallyexaminable
EXAMPLEEVAPORITESDEPOSITS
12
Halite
TheJurassicGulfCoastSaltBasin.EvaporitesformintherinbasinsthatopenupintheearlyformaConoftheAtlanCcOcean
hNp://jan.ucc.nau.edu/~rcb7/namJ180.jpg
• BandedIronForma5ons• Commonaround1.8–2.5Billionyears• Bandsofironmineralsandchert• RelatedtoEarth’s“GreatOxygenaConEvent”
OTHERSEDIMENTS
Halite
hNp://de.wikipedia.org/w/index.php?Ctle=Datei:Karijini6.jpg&fileCmestamp=20070928204153
Karijini,Australia
13
hNp://en.wikipedia.org/wiki/File:MichiganBIF.jpg
• Chert• Microcrystallinesilica–conchoidalfracture• Mayoccurasnodulesorthickbandeddeposits• FormaCon:poorlyunderstood.
Halite
14
hNp://en.wikipedia.org/wiki/File:ChertUSGOVjpg.jpghNp://3dparks.wr.usgs.gov/goga/html/ribbonchert.html
• Coal• Concentratedplantmaterial• VolaCledrivenofftoformcoals• VerycommonintheCarboniferousoftheNorthernhemisphere
Halite
15
hNp://en.wikipedia.org/wiki/File:Sydney_Mines_Point_Aconi_Seam_038.JPG
• Volcaniclas5csediments• BlursthedefiniConbetweensedimentaryrocksandigneousrocks• Examples:
– Pyroclas)cs– Airbornfragmentedvolcanic
materialHalite
16PyroclasCcflowsMayonVolcano,Philippines,1984
hNp://en.wikipedia.org/wiki/File:PyroclasCc_Flow_St._Helens.jpg
hNp://en.wikipedia.org/wiki/File:PyroclasCc_flows_at_Mayon_Volcano.jpg
– Hyaloclas)tes– Brecciasthatformwhenhotvolcanicrocks
comeintocontactwithwater
Halite
17
hNp://en.wikipedia.org/wiki/File:Lava_enters_pacific.jpg
– Lahars– CoarsegrainedgenerallychaoCcdeposits– Movementofvolcanicmaterialdownflanksofavolcanointheformofaslurry
18
hNp://en.wikipedia.org/wiki/File:Armero_anermath_Marso.jpg
laharsfromtheNevadodelRuizerupConinColombiain1985
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
19
TERMS / NAMES DEFINITION
20
Facies: “part of a rock body that has characteristics from which we can infer the depositional environment.”
Sedimentary Facies
hNp://en.wikipedia.org/wiki/File:DryForkDome.jpg
hNp://en.wikipedia.org/wiki/File:Cliffs_of_Dover.jpg
• Faciesaredefinedby:sedimenttype,typeofsedimentarystructures(example:ripples)andsomeCmestheirfossilcontent
• SincedeposiConalenvironmentsgradelaterallyintootherenvironments-facieschangesareGRADUAL
hNp://en.wikipedia.org/wiki/File:RipplemarksCarmelFormaCon.jpg hNp://en.wikipedia.org/wiki/File:Logan_FormaCon_Cross_Bedding_Scour.jpg
hNp://en.wikipedia.org/wiki/File:Carmelo_FormaCon_at_Point_Lobos.jpg
hNp://en.wikipedia.org/wiki/File:Fossils_in_a_beach_wall.JPG
Turbulent (waves) “High Energy Environment”
RIVER INPUT
All clastic sediments have been deposited
All coarse sediments have been deposited
A coccolithophore: just one type of CaCO3 secreting planktonic
creature
Non clastic, biological sediment composed of CaCO3 “Low Energy Environment”
NOTE: this slope is greatly exaggerated
Consider this EXAMPLE of where sediment is being deposited……….
muds
sands
conglomerates
carbonates
i>clicker:WhichfactorsareresponsiblefortherelaCveposiConsofthesandstoneandshalefaciesinthisfigure?
i. Turbulenceofwaterii. Sizeofsedimentarygrainsiii. Biologyiv. Waterdepthv. Watertemperature
SandMud and Clay
Carbonate mud
River: input of sediment
ShorelineSea level
A. i.ii.iv.v.B. i.ii.iii.iv.C. i.ii.iv.D. iii.iv.v.E. iii.iv.
24
HOWEVER: Lets complicate things……
Plot sea level versus time:
Facies SHIFT through time due to changes in sea level
LOCAL and GLOBAL (Global = Eustatic)
Facies and Sea Level Change
hNp://en.wikipedia.org/wiki/File:Phanerozoic_Sea_Level.png
Key
Pebbles/GravelSandSiltCarbonate
mud
Increasing grain size
Existing land
surface
Sea LevelInput of sediment
Facies as Diachronous unitsDiachronus = “time crossing”
Example: with sea level rise
Shore line T1
NOTE TIME HORIZON T1
NOTE: Slope GREATLY exaggerated
Sea Level
Input of sedimentShore line
T2Shore line T1
Movement of shoreline: TRANSGRESSION
As Before: - sea level rises - facies migrate in the direction of the moving shoreline.
NOTE TIME HORIZON T2
Key
Pebbles/GravelSandSiltCarbonate
mud
Increasing grain size
Existing land
surface
Sea Level
Input of sediment
Shore line T2
Shore line T1
Shore line T3
- Sea level continues to rise.
Movement of shoreline: TRANSGRESSION
NOTE TIME HORIZON T3
Key
Pebbles/GravelSandSiltCarbonate
mud
Increasing grain size
Existing land
surface
Sea Level
Input of sediment
Shore line T2
Shore line T1
Shore line T3
Shore line Today
Movement of shoreline: TRANSGRESSION
Boundaries between different “sea floors”.. T1-T3
Effectively time horizons (red)
Boundaries between
different facies (yellow)
If we just correlated the same sediment TYPE (facies boundaries…. the yellow lines) we would be CROSS CUTTING the red time lines (T1, T2, T3)
Movement of shoreline: REGRESSION
facies
time
Key
Pebbles/GravelSandSiltCarbonate
mud
Increasing grain size
Existing land
surface
NOTE: Slope GREATLY exaggerated
i>clicker:OverallwhathasbeenhappeningtorelaCvesealevelasrepresentedbythisfigure?(assumefaciesboundariesareverCcal).
i. RelaCvesealevelisfallingii. RelaCvesealevelisrisingiii. Sedimentinputiskeepingpacewith
anysealevelchangeiv. Sedimentinputisnotkeepingpace
withsealevelchangev. RelaCvesealevelisconstant
SandMud and Clay
Carbonate mud
River: input of sediment
ShorelineSea level
A. i.iii.v.B. i.iv.C. ii.iv.D. i.iii.E. iii.v. 31
SO WHAT IS ALL THIS LEADING TO?
We know the following facts:
1. Facies reflect changing conditions of deposition across our planet. In our example, shallow high energy, near shore conditions are characterized by sand. Deeper, quieter conditions are characterized by finer grained sediments.
2. As conditions change (such as sea level) facies will appear to MIGRATE, “following” their particular environmental conditions.
3. Over time this will lead to patterns of facies as one facies MIGRATES OVER ANOTHER.
Walther’s Law
4. This means that when we recover a vertical succession of rock (like the one we used in our example) we can PREDICT the lateral equivalence of facies ……As we go from coarse, near-shore facies at the bottom of the core to off-shore, deeper water carbonate sediments at the top of the core, sea level (in this example) must have been RISING over time. silts sands Conglomerates
silts
sandscarbonates
carbonates
silts sandscarbonates pebbles
sands
silts
Carbon-ates
bottom
top
The uneven boundaries between the facies are an attempt to demonstrate that facies GRADE into each other just as environments grade into each other.
Conglomerates
Conglomerates
This is summed up in WALTHER’S LAW
“Facies that occur in a CONFORMABLE VERTICAL SUCCESSION of strata, were deposited in laterally adjacent depositional environments.”
and put another way……adjacent sedimentary environments (facies) will end up overlapping one another over time.
Sea level fall
Sea level rise
Shore lineBeach
sedimentsNear shore sediments
Off shore sediments
- Facies occur in ALL sedimentary environments - Do not just have to be in a marine environment to demonstrate migration and Walther’s Law
