Module 9 Sedimentary Rocks · on Clast Size, Shape, Sorting, and Composition Close to source Far from source clast size large clasts small clasts clast shape angular clasts rounded

Module 9Module 9SedimentarySedimentary RocksRocks

Rocks formed from material derived from Rocks formed from material derived from preexisting rocks by preexisting rocks by surfacialsurfacial processes processes followed by followed by diagenesisdiagenesis

There are two main classes of sedimentary rocksThere are two main classes of sedimentary rocksClasticClastic ((detritaldetrital) sedimentary rocks) sedimentary rocksare formed from bits and pieces of previously are formed from bits and pieces of previously existing rocks, called existing rocks, called clastsclasts or detritusor detritusChemical sedimentary rocksChemical sedimentary rocksare formed in several waysare formed in several ways

By precipitation from aqueous solutionBy precipitation from aqueous solutionFrom plant materialFrom plant materialFrom animal materialFrom animal material

SEDIMENTARY ROCKSSEDIMENTARY ROCKS

Processes Leading to Formation of Processes Leading to Formation of Clastic Sedimentary RocksClastic Sedimentary Rocks

ClasticClastic Sedimentary RocksSedimentary Rocks

Weathering:Weathering: the processes that change rocksthe processes that change rocks’’ size and size and composition at or near Earthcomposition at or near Earth’’s surfaces surfaceErosion and Transportation:Erosion and Transportation: removal of rock particles removal of rock particles (clasts) from their source by water, wind, or glacial ice(clasts) from their source by water, wind, or glacial iceDeposition:Deposition: the settling of clasts on Earththe settling of clasts on Earth’’s surface as s surface as sediments, leads to formation of a sedimentary bedsediments, leads to formation of a sedimentary bedCompaction:Compaction: pressing together of clasts, squeezing out pressing together of clasts, squeezing out pore water, by pressure exerted by overlying bedspore water, by pressure exerted by overlying bedsLithificationLithification:: cementation of clasts together to form a cementation of clasts together to form a sedimentary rocksedimentary rockDiagenesisDiagenesis:: a process of conversion of unconsolidated a process of conversion of unconsolidated sediments to coherent sedimentary rockssediments to coherent sedimentary rocks

Formation of Metamorphic RocksFormation of Metamorphic RocksUplift and exposure

Weathering

Transportation

Deposition

Compaction andLithification

All rocks exposed All rocks exposed at earthat earth’’s surface s surface undergoundergo……

Rocks CycleRocks Cycle

Where do the sediments form?Where do the sediments form?

Tem

pera

ture

dec

reas

es

SiO

2of

liqu

id in

crea

ses

Olivine

Pyroxene

Amphibole

Biotite

Ca-rich

Na-rich

Ca-Na-rich

Na-Ca-rich

Quartz

Mus

covi

te

K-fe

ldsp

ar

Plag

iocl

ase

feld

spar

Dis

cont

inuo

us b

ranc

h

Con

tinuo

us b

ranc

h

BOWEN’S REACTION SERIES

Resistance of Minerals to WeatheringResistance of Minerals to Weathering

Most readilyto weathering

More resistant to weathering

Most resistant to weathering

Most resistant ofall to weathering

the effect of mineral compositionthe effect of mineral compositionon the resistance to weatheringon the resistance to weathering

Effect of Weathering, Gradient, Distance from SourceEffect of Weathering, Gradient, Distance from Source--Rock Rock on Clast Size, Shape, Sorting, and Compositionon Clast Size, Shape, Sorting, and Composition

Close to source Far from source

clast size large clasts small clasts

clast shape angular clasts rounded clasts

sorting poorly sorted sediments

well sorted sediments

composition rich in mafic mineralsand feldspar

quartz sands and clays

07_18.jpgEffect of Weathering, Gradient, Distance from SourceEffect of Weathering, Gradient, Distance from Source--Rock Rock on Clast Size, Shape, Sorting, and Compositionon Clast Size, Shape, Sorting, and Composition

Effects of Compaction, Cementation on SedimentsEffects of Compaction, Cementation on Sediments

On mudOn poorly-sorted

sediments

On well-sorted sediments

From sediments to sedimentary rocksFrom sediments to sedimentary rocks

clayclaysiltsiltsandsandgravelgravel

conglomerateconglomerate sandstonesandstone siltstonesiltstone claystoneclaystone

Clastic Sedimentary RockClastic Sedimentary Rock’’s Textures Texture

TextureTexture::the relationship between the grains of mineralsthe relationship between the grains of mineralsforming a rockforming a rock

a.a. grain sizegrain sizeb.b. roundnessroundnessc.c. sortingsortingd.d. fabricfabrice.e. ffragmenragment, matrix, & cementt, matrix, & cement


a.a. Grain size:Grain size:•• Grain (Grain (particleparticle,, clastclast,, fragmentfragment) size) size is is primary primary

distinguishing factordistinguishing factor for clastic sedimentary for clastic sedimentary rocksrocks

•• Size means diameter of rockSize means diameter of rock’’s grainss grains

Clastic Sedimentary RockClastic Sedimentary Rock’’s Textures TextureSizeSize (mm)(mm) Sedimentary clastsSedimentary clasts Sedimentary rocksSedimentary rocks

>256>256128 128 –– 25625664 64 –– 12812832 32 –– 646416 16 –– 32328 8 –– 16164 4 –– 882 2 –– 441 1 –– 22

1/2 1/2 –– 111/4 1/4 –– 1/21/21/8 1/8 –– 1/41/41/16 1/16 –– 1/81/81/32 1/32 –– 1/161/161/64 1/64 –– 1/321/32

1/128 1/128 –– 1/641/641/256 1/256 –– 1/1281/128

<1/256<1/256

•• BoulderBoulder•• CobbleCobble•• CobbleCobble•• PebblePebble•• PebblePebble•• PebblePebble•• PebblePebble•• GranuleGranule•• SandSand•• SandSand•• SandSand•• SandSand•• SandSand•• SiltSilt•• SiltSilt•• SiltSilt•• SiltSilt•• ClayClay

•• ––•• CoarseCoarse--•• FineFine--•• Very coarseVery coarse--•• CoarseCoarse--•• FineFine--•• Very fineVery fine--•• ––•• Very coarseVery coarse--•• CoarseCoarse•• MediumMedium--•• Fine_Fine_•• Very fineVery fine•• Very coarseVery coarse--•• CoarseCoarse•• FineFine--•• Very fineVery fine•• ––

Conglomerate (predominantlyConglomerate (predominantlyrounded rounded clastsclasts))or or BrecciaBreccia (predominantly(predominantlyAngular Angular clastsclasts))

SandstoneSandstone

SiltstoneSiltstone

ClaystoneClaystone or Shaleor Shale

MudstoneMudstone

WentworthWentworth’’ ScaleScale


b. b. SphericitySphericity vsvs roundnessroundness•• SphericitySphericity is a degree of similarity to a ball is a degree of similarity to a ball

shapeshape•• Roundness is a degree of roundedness of the Roundness is a degree of roundedness of the

edges of a fragmentedges of a fragment

angularangular intermediateintermediate roundedrounded

High High sphericitysphericity

Low Low sphericitysphericity

RoundnessRoundness

Shapes of sand grains


c. Sortingc. Sorting•• Degree of similarity in particle sizeDegree of similarity in particle size


This quartz grains are:This quartz grains are:-well-sorted-well-rounded

d. Fabricd. Fabric•• Opened fabricOpened fabric•• Closed fabricClosed fabric


Closed fabricClosed fabric

Opened fabricOpened fabric


e. Fragments, matrix, cemente. Fragments, matrix, cement•• Fragments (Fragments (clastsclasts))•• MatrixMatrix•• CementCement

The Most Common Sedimentary CementsThe Most Common Sedimentary CementsClastic Sedimentary RockClastic Sedimentary Rock’’s Textures Texture

•• CalciteCalcite–– The most common cement present in marine sedimentary The most common cement present in marine sedimentary

rocksrocks–– Also common in sedimentary rocks formed from sediments Also common in sedimentary rocks formed from sediments

deposited in evaporite basinsdeposited in evaporite basins–– Calcite cemented sedimentary rocks give a positive acid Calcite cemented sedimentary rocks give a positive acid

test (will fizz when an acidic solution is dropped on them)test (will fizz when an acidic solution is dropped on them)

•• HematiteHematite–– The cement present in red colored terrigenous (landThe cement present in red colored terrigenous (land--

derived) sedimentary rocks, very commonderived) sedimentary rocks, very common–– Hematite cemented rocks will not fizz when an acidic Hematite cemented rocks will not fizz when an acidic

solution is dropped on themsolution is dropped on them

•• SilicaSilica–– The cement present in terrigenous (landThe cement present in terrigenous (land--derived) derived)

sedimentary rocks that are not red, very commonsedimentary rocks that are not red, very common–– Silica cemented rocks will not fizz when an acidic solution is Silica cemented rocks will not fizz when an acidic solution is

dropped on themdropped on them

Clastic Sedimentary RockClastic Sedimentary Rock’’s Structures Structure

Sedimentary Beds and Bedding PlanesSedimentary Beds and Bedding PlanesBeds represent distinct sedimentary event, Beds represent distinct sedimentary event, times when deposition occurredtimes when deposition occurredBedding planes represent pauses between Bedding planes represent pauses between sedimentary events, times when deposition ceasedsedimentary events, times when deposition ceased

Beddingplane

Bed


Graded Sedimentary BedsGraded Sedimentary BedsForm in response to Form in response to decrease in energy decrease in energy during depositionduring depositionLarger, heavier clastsLarger, heavier clasts, , first pebbles then sand, first pebbles then sand, settle out first, in the settle out first, in the bottom of the bedbottom of the bedSmaller, lighter clastsSmaller, lighter clasts, , silt and finally clay, silt and finally clay, settle out last in the top settle out last in the top of the bedof the bed


Cross Beds Cross Beds Cross beds are Cross beds are deposited in response deposited in response to movement of a to movement of a currentcurrent

Cross beds are Cross beds are unidirectional if the unidirectional if the current was constant current was constant in directionin direction

Cross beds are biCross beds are bi--directional if the directional if the current was not current was not constant in directionconstant in direction

Note: these beds are Note: these beds are tilted

Current direction

tilted

Mud CracksMud CracksMud cracks form Mud cracks form when mud dries when mud dries upup

Their shape and Their shape and size may vary size may vary considerablyconsiderably

Mudcracks in fresh sediment

Mudcracks Mudcracks in a in a

sedimentary sedimentary rockrock


Clastic Sedimentary RockClastic Sedimentary Rock’’s Structures StructureRipple Marks Ripple Marks

Are formed in response to Are formed in response to movement of a currentmovement of a current

Symmetrical ripple marksSymmetrical ripple marksform if current is backform if current is back--andand--forth, biforth, bi--directionaldirectional

Asymmetrical ripple marksAsymmetrical ripple marksform if current is constant in form if current is constant in directiondirection

Asymmetrical ripple marks in fresh sediment

Symmetrical ripple marks preserved in mudstone

Raindrop Imprints and castsRaindrop Imprints and castsForm when big rain drops fall on mudForm when big rain drops fall on mudRaindrop imprintsRaindrop imprints are depressions formed on the are depressions formed on the bed upon which the raindrops fellbed upon which the raindrops fellRaindrop castsRaindrop casts are knobs formed on the bottom of are knobs formed on the bottom of the bed deposited on top of the bed upon which the the bed deposited on top of the bed upon which the raindrops fellraindrops fell

Raindrop imprints and mudcracks


Clastic Sedimentary RockClastic Sedimentary Rock’’s Structures StructureFossilsFossils

Are any evidence of life preserved in ancient rocksAre any evidence of life preserved in ancient rocksInclude bones, teeth, shells, molds and casts, Include bones, teeth, shells, molds and casts, petrified wood, impressions, footprints, etc.petrified wood, impressions, footprints, etc.

Chemical Sedimentary RocksChemical Sedimentary Rocks

Chemical Sedimentary RocksChemical Sedimentary Rocksderived from material carried derived from material carried in solutionin solution to to lakes/ seaslakes/ seasprecipitationprecipitation from solution to form from solution to form ““chemical sedimentschemical sediments””

by precipitation from aqueous solutionby precipitation from aqueous solutionfrom plant material from plant material from animal materialfrom animal material

Salt flats, UtahSalt flats, Utah


EvaporitesEvaporiteswater evaporates and water evaporates and dissolved stuff is dissolved stuff is depositeddepositedmostly marine rocks, mostly marine rocks, but some lakes/ playasbut some lakes/ playasSalt, gypsum, potashSalt, gypsum, potash

Death Valley, CaliforniaDeath Valley, California

T&L Fig 6.12


ChertChertvery fine grained silicavery fine grained silicaalso called flint, jasper, also called flint, jasper, agateagatemost formed in oceanmost formed in oceanoccurs as layers (beds) occurs as layers (beds) & as irregular blobs in & as irregular blobs in limestonelimestonemarine creatures marine creatures remove silica from sea remove silica from sea water, make shellswater, make shells

AgateAgate

LimestoneLimestoneformed by marine organisms formed by marine organisms (corals, clams, algae)(corals, clams, algae)composed primarily of calcite composed primarily of calcite (calcium carbonate CaCO3)(calcium carbonate CaCO3)most abundant chemical most abundant chemical sedimentary rocksedimentary rock10% of all sedimentary rocks 10% of all sedimentary rocks (by volume)(by volume)some deposited directly out of some deposited directly out of ocean or other watersocean or other waters


Coral reefCoral reef

Coquina (rock of shell fragments)Coquina (rock of shell fragments)


Limestone MountainLimestone Mountain

Coal


CoalCoalburied and compacted plant materialburied and compacted plant materialdifferent kinds of coal, depending on formation different kinds of coal, depending on formation process process

peatpeat lignitelignite coalcoal anthraciteanthracite

Classification of Sedimentary RocksClassification of Sedimentary RocksC

last

icC

last

icSe

dim

enta

ry R

ocks

Sedi

men

tary

Roc

ksC

hem

ical

Che

mic

alSe

dim

enta

ry R

ocks

Sedi

men

tary

Roc

ks

ChertChert RadiolariteRadiolariteDiatomiteDiatomite

SILICASILICAPeatPeat

LigniteLigniteCoalCoal

AnthraciteAnthracite

CARBONACEOUSCARBONACEOUS

HaliteHaliteGypsumGypsum

AnhydriteAnhydrite

EVAPORITEEVAPORITE

OoliteOolite

Coral limestoneCoral limestoneDolomiteDolomiteCrystalline limestone Crystalline limestone

BioclasticBioclastic limestone limestone

Marl; Marl; ClasticClastic limestonelimestone((CalcaruditeCalcarudite, , CalcareniteCalcarenite, , CalcelutiteCalcelutite))

CARBONATECARBONATE

SILICATESILICATEBrecciaBreccia SiltstoneSiltstoneConglomerate Conglomerate ClaystoneClaystoneSandstone ShaleSandstone Shale

CLASTICCLASTIC

ANORGANICANORGANIC ORGANICORGANIC

Clastic Sedimentary Rocks:Clastic Sedimentary Rocks:MudstonesMudstones

Clastic Sedimentary Rocks: Clastic Sedimentary Rocks: SandstonesSandstones

Clastic Sedimentary Rocks: Clastic Sedimentary Rocks: ConglomeratesConglomerates

Clastic Sedimentary Rocks: Clastic Sedimentary Rocks: BrecciasBreccias

Chemical Sedimentary Rocks:Chemical Sedimentary Rocks:Formed by Precipitation from Aqueous SolutionFormed by Precipitation from Aqueous Solution

1. The Evaporites1. The Evaporites

a. Halite (NaCl)

b. Calcite (CaCO3)

c. Gypsum (CaSO4. H2O)

2. Precipitated Silica2. Precipitated Silica

Chert

Chemical Sedimentary Rocks:Formed from Plant Material

Chemical Sedimentary Rocks:Chemical Sedimentary Rocks:Formed from Plants Material: The CoalFormed from Plants Material: The Coal

Inundatedswamp or

marshBituminous coalBituminous coal

(soft coal)(soft coal)PeatPeat LigniteLignite

Coal seams in Mesa Verde National ParkCoal seams in Mesa Verde National Park Bituminous coalBituminous coal

Chemical Sedimentary Rocks:Chemical Sedimentary Rocks:Formed from Animal Material: The LimestonesFormed from Animal Material: The Limestones

1. Limestone (a limey mudstone)

All contain CaCOAll contain CaCO3 All will fizz in contact with acidAll will fizz in contact with acid3

2. Fossiliferous limestone

3. Coquina

4. Chalk

Documents

Module 9 Sedimentary Rocks · on Clast Size, Shape, Sorting, and Composition Close to source Far from source clast size large clasts small clasts clast shape angular clasts rounded