Post on 29-Dec-2015
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.
rcheel@brocku.ca
66% of surface Earth covered by sediment or sedimentary rocks.
Humans interact with the Earth largely at or near its surface.
rcheel@brocku.ca
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.
rcheel@brocku.ca
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
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
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
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
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