sedimentary rocks. sedimentary petrology- what is it? study origin, occurrence, mineral comp. &...

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Sedimentary Rocks Sedimentary Rocks

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Sedimentary RocksSedimentary Rocks

Sedimentary Petrology- What is it?Sedimentary Petrology- What is it?

Study origin, occurrence, mineral Study origin, occurrence, mineral comp. & texture of sed rks.comp. & texture of sed rks.

Depositional environment usually not Depositional environment usually not emphasizedemphasized

Emphasize sed rocks– their Emphasize sed rocks– their description & classificationdescription & classification

Why study sedimentary rocks/sediments?

Sedimentary rocks make up only 7.9% of the Earth’s crust.

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66% of surface Earth covered by sediment or sedimentary rocks.

Humans interact with the Earth largely at or near its surface.

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On surface we…..Grow food on it.

Build structures on it. Take resources from [email protected]

At the same time we…..

Modify its physical and chemical properties so that it is no longer useable.

Important to understand properties of the sedimentary cover and have systematic methods for describing these properties.

Hide garbage and other waste material in it.

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More Reasons to Study Sed RocksMore Reasons to Study Sed Rocks

Sedimentary rocks-- Sedimentary rocks-- best evidence of best evidence of earth history earth history because:because:

Often contain fossils, Often contain fossils, properties to properties to establish establish environments, andenvironments, and

Often provide Often provide geologic age of geologic age of materials.materials.

Record Record sedimentological, sedimentological, chemical, fossil; chemical, fossil; evidence of changing evidence of changing tectonics & tectonics & paleoceanographypaleoceanography

Economic significanceEconomic significance Grand Canyon

Origin of SedimentsOrigin of Sediments

A. WeatheringA. Weathering ChemicalChemical MechanicalMechanical Weathering provides raw Weathering provides raw

materialsmaterials

ErosionErosion

Erosion is the displacement of solids Erosion is the displacement of solids ((soil, , mud, , rock, and so forth) by the , and so forth) by the agents of wind, water, ice, or agents of wind, water, ice, or movement in response to movement in response to gravity http://www.wordiq.com/http://www.wordiq.com/

1. Wind1. Wind

2. Water 2. Water

3. Ice3. Ice

DepositionDeposition

Where sediments accumulateWhere sediments accumulate EnvironmentsEnvironments

BeachesBeaches LakesLakes SlopesSlopes RiversRivers

Cementation/CompactionCementation/Compaction Sediment may be compactedSediment may be compacted Cement precipitates in voidsCement precipitates in voids

Extent Of Sedimentary Extent Of Sedimentary RocksRocks

Cover 66% cont. surface, much ocean Cover 66% cont. surface, much ocean floorfloor

Ig & met rocks unstable at surfaceIg & met rocks unstable at surface Form under dif. TP regimesForm under dif. TP regimes Surface= LTLP regimeSurface= LTLP regime Form in less O2, CO2, H2OForm in less O2, CO2, H2O

Minerals break downMinerals break down Form grains & claysForm grains & clays Break down due to weatheringBreak down due to weathering

Sedimentary RK Types & Sedimentary RK Types & LithologiesLithologies

Clastic/DetritalClastic/Detrital Formed of particles derived from Formed of particles derived from

pre-existing rkspre-existing rks Chemical precipitatesChemical precipitates

Precipitate from solutionPrecipitate from solution 95%=S.S, L.S, Mudrock95%=S.S, L.S, Mudrock Sandstone-20-25 %Sandstone-20-25 %

Form in high energy environmentForm in high energy environment Some in low energySome in low energy

Mud < .06mm; sand 2 - 0.06mmMud < .06mm; sand 2 - 0.06mm

Quartz Rich SandstoneQuartz Rich Sandstone

Quartz Rich Sandstone Quartz Rich Sandstone MicrophotographMicrophotograph

ArkoseArkose

ConglomerateConglomerate

BrecciaBreccia

Carbonate (COCarbonate (CO33)) Rocks Rocks

COCO33 rocks =10-15% of sed rocks rocks =10-15% of sed rocks CaCOCaCO33 (Arag/Calcite); CaMg (CO (Arag/Calcite); CaMg (CO33))22 (Dolomite) (Dolomite)

Also Siderite (FeCOAlso Siderite (FeCO33), Magnesite (MgCO), Magnesite (MgCO33)-rare)-rare

Most-hard parts of org.Most-hard parts of org. Deep HDeep H22O corrosiveO corrosive Most COMost CO33=shallow H=shallow H22OO

Transitional rocksTransitional rocks Coquina-SS or COCoquina-SS or CO33

Marl-COMarl-CO33 & clay & clay

CoquinaCoquina

MudrocksMudrocks Mudrocks 65%Mudrocks 65%

Most abundant-65% of sedimentary rocksMost abundant-65% of sedimentary rocks Not well studiedNot well studied

Common due to Ig/met rocksCommon due to Ig/met rocks Composed of 20% qtz & 80% other Composed of 20% qtz & 80% other

silicatessilicates Qtz stable others notQtz stable others not

Detrital contentDetrital content Qtz commonQtz common Minor feldsMinor felds Found low energy environmentFound low energy environment

Mudstone mostly silt/clayMudstone mostly silt/clay

HaliteHalite

CementationCementation

A. Rks get lithifiedA. Rks get lithified

B. Sed accumulation leads to B. Sed accumulation leads to compaction; porosity compaction; porosity

reducedreduced

C. Most common cements--SiOC. Most common cements--SiO22, , CaCOCaCO33, iron-oxide, iron-oxide

Thickness of Sedimentary rocksThickness of Sedimentary rocks

1.8km-continent., 0.3km-oceanic1.8km-continent., 0.3km-oceanic Difficult to measure-where does Difficult to measure-where does

meta beginmeta begin 20,000m in some basins20,000m in some basins

Major Settings for Sediment Major Settings for Sediment Accumulation—Sedimentary Accumulation—Sedimentary

BasinsBasins

Oceanic basinsOceanic basins Garben along cont. marginsGarben along cont. margins Arc-trench systemsArc-trench systems Suture belt basinsSuture belt basins Intracratonic basinIntracratonic basin

Oceanic BasinsOceanic Basins Coarser seds on Coarser seds on

continental continental marginmargin

Fine grained seds Fine grained seds in deep oceanin deep ocean

>4000m->4000m-generally no CO3 generally no CO3 seds.seds.

Red clays & Red clays & siliceous shells siliceous shells make up most of make up most of deep ocean deep ocean sedimentssediments

Rifted Continental Rifted Continental MarginMargin

Form when Form when continent rifted-continent rifted-get extensionget extension e.g S. America e.g S. America

rifted from Africarifted from Africa First get First get

volcanics & non-volcanics & non-marine seds.marine seds.

Periodic Periodic flooding-get flooding-get evaporitesevaporites

Then shallow to Then shallow to deep marine deep marine rocks with more rocks with more riftingrifting

Arc Trench Systems-Arc Trench Systems- Trench seds=TurbiditesTrench seds=Turbidites Forearc-overlie oceanic or transitional crustForearc-overlie oceanic or transitional crust

Volcanic seds & sed from pluton or uplifted trench/slope Volcanic seds & sed from pluton or uplifted trench/slope breakbreak

Great Valley=Forearc basinGreat Valley=Forearc basin Forearc=shelf, deltaic, terrestrialForearc=shelf, deltaic, terrestrial

Intra arcIntra arc Turbidites & volcani material from ArcTurbidites & volcani material from Arc

Retroarc basin=backarc basinRetroarc basin=backarc basin

Suture belt basinSuture belt basin

Form where Form where have cont-have cont-cont. cont. collisioncollision

Basins form Basins form in suture in suture zonezone

Seds=clastic Seds=clastic from erosion from erosion of continent.of continent.

Intracratonic BasinsIntracratonic Basins

Origin not well Origin not well understoodunderstood Downbowing next Downbowing next

to cont. marginto cont. margin Aborted cont. riftingAborted cont. rifting Local cooling of Local cooling of

asthenosphereasthenosphere Get cratonic seds.Get cratonic seds.

Mostly non-marine Mostly non-marine & shallow marine & shallow marine seds.-well roundedseds.-well rounded

Stop HereStop Here

III) III) Clastic/Detrital ComponentsClastic/Detrital Components

A Clays--sheet-like silicatesA Clays--sheet-like silicates

B QuartzB Quartz

C Feldspars--unstable--fast C Feldspars--unstable--fast erosion and depositionerosion and deposition

D Micas--unstable--fast erosion D Micas--unstable--fast erosion and depositionand deposition

IV) Size DistributionIV) Size Distribution

A. Know scaleA. Know scale

B. Provide info about depo. env.B. Provide info about depo. env.

C. Greater energy to transport C. Greater energy to transport larger particleslarger particles

D. Clays accumulate in quiet waterD. Clays accumulate in quiet water

V) Clastic Rk typesV) Clastic Rk types

A. Shale--clay and silt particlesA. Shale--clay and silt particles1. Particles are microscopic1. Particles are microscopic2. quiet water, non-turbulent 2. quiet water, non-turbulent

depositiondeposition3. Settle following flocculation3. Settle following flocculation4. Form laminae/massive beds4. Form laminae/massive beds5. Fissil=shale; non-fissil=mudstone5. Fissil=shale; non-fissil=mudstone6. Generally recessive6. Generally recessive

B. SandstoneB. Sandstone

1. Made of sand-sized grains1. Made of sand-sized grains

2. Deposited in a variety of 2. Deposited in a variety of environmentsenvironments

3. Sorted to poorly sorted3. Sorted to poorly sorted

4. Wind deposits better sorted than water-4. Wind deposits better sorted than water-tranported deposits?tranported deposits?

B. Sandstone B. Sandstone ContinuedContinued

5. Shape of grains--rounded to angular, 5. Shape of grains--rounded to angular, related to distance or time of transportrelated to distance or time of transport

6. Sandstone types6. Sandstone typesi. quartz arenitei. quartz areniteii. arkoseii. arkoseiii. graywackeiii. graywackeiv. lithic sandstoneiv. lithic sandstone

7. conglomerate/breccias7. conglomerate/brecciasi. good for provenancei. good for provenanceii. not transported farii. not transported far

VI) Chemical Sed RksVI) Chemical Sed Rks

A. Inorganic precipitatesA. Inorganic precipitatesB. Biochemical RksB. Biochemical RksC. LS most abundant chemical sed rkC. LS most abundant chemical sed rk

1. composed of calcite1. composed of calcite2. mostly marine2. mostly marine3. Corals= warm water, shallow 3. Corals= warm water, shallow

tropical environment; <30 lattropical environment; <30 lat

Other Chemical Sed RksOther Chemical Sed RksContinuedContinued

D. Rk typesD. Rk types

1. chalk1. chalk

2. travertine2. travertine

3. oolitic l.s3. oolitic l.s

E. DolomiteE. Dolomite

1. calcium magnesium carbonate1. calcium magnesium carbonate

2. Rks=dolostone2. Rks=dolostone

Chemical Sed Rks Chemical Sed Rks ContinuedContinued

F. ChertF. Chert1. composted of microcxline qtz1. composted of microcxline qtz2. nodules and layers, 2. nodules and layers,

biochemical rksbiochemical rks

G. EvaporitesG. EvaporitesHalite, GypsumHalite, Gypsum