EPS 421 EPS 421 CLASTIC SEDIMENTARY ROCKSCLASTIC SEDIMENTARY ROCKS

Prof. Dr. Mahmoud A. M. ArefProf. Dr. Mahmoud A. M. Aref

Lecture 10: Classification of sandstones, Lecture 10: Classification of sandstones, Provenance and Tectonic SettingProvenance and Tectonic Setting

Department of Petroleum Geology & Sedimentology, Department of Petroleum Geology & Sedimentology, Faculty of Earth Sciences, Faculty of Earth Sciences, King Abdulaziz University, King Abdulaziz University,

Jeddah, Saudi ArabiaJeddah, Saudi Arabia

Framework

Matrix

Cement

PoresVoids Among The Above Components

Sand Grains That Are Made Up Crystals Of Two Or More Different Minerals. Sand (And Silt) Size Detrital Grains

Fine-grained (<0.03mm) Material That Are Associated With The Sand Grains. Silt And Clay Size Detrital Material

Material Precipitated Post-depositionally, During Burial. Cements Fill Pores And Replace Framework Grains

Four Major Components Of Sandstone

Classification of SandstonesMost sandstone classifications are based on the composition of the rock.

EPS 321 Lecture 10

FOUR COMPONENTS OF SANDSTONE

MATRIXFRAMEWORK

(QUARTZ)

FRAMEWORK(FELDSPAR)

CEMENT

PORE

Note different use of “matrix”by geologists and engineers

0.25 mm

1. Framework2. Matrix3. Cement4. Pores

Engineering“matrix”

Geologist’s Classification

EPS 321 Lecture 10

CLASSIFICATION OF SANDSTONESCLASSIFICATION OF SANDSTONESClassifications of sandstones are Classifications of sandstones are petrographicpetrographic, based on , based on microscopic studies and requiring approximate determinations microscopic studies and requiring approximate determinations of the modal composition. of the modal composition.

Most classifications use Most classifications use a triangular diagrama triangular diagram with end with end members of members of quartz (+ chert), feldsparquartz (+ chert), feldspar and and rock fragmentsrock fragments. The . The triangle is divided into various fields, and rocks with a modal triangle is divided into various fields, and rocks with a modal analysis falling within a particular field are given a particulaanalysis falling within a particular field are given a particular r name.name.

In this scheme, sandstones are divided into two major groups In this scheme, sandstones are divided into two major groups based on texture, that is whether the sandstones are based on texture, that is whether the sandstones are composed of grains only, the composed of grains only, the arenitesarenites, or contain more than , or contain more than 15% matrix15% matrix, forming the , forming the wackeswackes..

EPS 321 Lecture 10

EPS 321 Lecture 10

EPS 321 Lecture 10

Arenites GroupArenites GroupOf the arenites, the term Of the arenites, the term quartz arenitequartz arenite is applied to those with is applied to those with 95% or more quartz grains95% or more quartz grains, a rock, a rock--type formerly referred to as type formerly referred to as quartzite or quartzite or orthoquartziteorthoquartzite. .

Arkosic areniteArkosic arenite refers to an refers to an arenite with more than 25% feldspar, which arenite with more than 25% feldspar, which exceeds the rock fragments contentexceeds the rock fragments content, The , The arkosic arenitesarkosic arenites can be divided can be divided into into arkosesarkoses and and lithic arkoseslithic arkoses. .

LithareniteLitharenite is applied where is applied where the rock fragments content exceeds 25% and is the rock fragments content exceeds 25% and is greater than feldspargreater than feldspar. .

Specific names which have been applied to litharenite are Specific names which have been applied to litharenite are phyllarenitephyllarenite where where the the rock fragments are chiefly of shale or slaterock fragments are chiefly of shale or slate, and , and calclithitecalclithite where where the rock the rock fragments are of limestonefragments are of limestone..

Two rockTwo rock--types are transitional with quartz arenite are types are transitional with quartz arenite are subarkosesubarkose and and sublitharenitesublitharenite. .

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Wackes GroupWackes Group

The wackes are the transitional group between arenites and The wackes are the transitional group between arenites and mudrocks. The most familiar is the mudrocks. The most familiar is the greywackegreywacke..

Two types are distinguished: Two types are distinguished: feldspathicfeldspathic and and lithic greywackelithic greywacke. .

The term The term arkosic wackearkosic wacke is used for is used for arkoses with a significant arkoses with a significant proportion of matrixproportion of matrix. .

Quartz wackesQuartz wackes, , not a common rocknot a common rock--type, are dominant quartz type, are dominant quartz plus some matrix.plus some matrix.

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Failure in the classification of sandstonesFailure in the classification of sandstonesThis classification is primarily concerned with the This classification is primarily concerned with the mineralogymineralogyof the sediment and presence or absence of a of the sediment and presence or absence of a matrixmatrix. .

It is independent of the It is independent of the depositional environmentdepositional environment, although , although some some lithologieslithologies are more common in certain environments.are more common in certain environments.

The nature of the The nature of the cementcement in arenites is not taken into account. in arenites is not taken into account.

With regard to fineWith regard to fine--grained interstitial material (grained interstitial material (matrixmatrix), a ), a basic feature of the wackes, there is often a problem of basic feature of the wackes, there is often a problem of originorigin. . Some is deposited along with the sediment grains, or could Some is deposited along with the sediment grains, or could be be authigenicauthigenic, a , a cementcement, and some a , and some a diagenetic alterationdiagenetic alterationproduct of unstable grains. The latter is particularly the case product of unstable grains. The latter is particularly the case with greywackes.with greywackes.

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Hybrid sandstonesHybrid sandstonesIn addition to terrigenous clastic sandstones, there are many In addition to terrigenous clastic sandstones, there are many hybrid hybrid sandstones.sandstones. These contain a nonThese contain a non--clastic component derived from within the clastic component derived from within the basin of deposition. basin of deposition. The three main types are The three main types are calcarenaceouscalcarenaceous, glauconitic and , glauconitic and phosphaticphosphaticsandstonessandstones. . In In glauconitic sandstonesglauconitic sandstones, the , the glauconiteglauconite occurs as sandoccurs as sand--sized pellets. sized pellets. With With phosphaticphosphatic sandstonessandstones, the phosphate may be present as a cement, , the phosphate may be present as a cement, nodules, coprolites or bone fragments.nodules, coprolites or bone fragments.Calcarenaceous sandstonesCalcarenaceous sandstones contain up to 50% CaCOcontain up to 50% CaCO33, present as , present as carbonate grains. The latter are chiefly ooids, often with quartcarbonate grains. The latter are chiefly ooids, often with quartz nuclei, and z nuclei, and carbonate skeletal fragments. Calcarenaceous sandstones are devecarbonate skeletal fragments. Calcarenaceous sandstones are developed in loped in carbonatecarbonate--producing areas where there is a large influx of terrigenous producing areas where there is a large influx of terrigenous clastics. They will often pass laterally into limestones or intoclastics. They will often pass laterally into limestones or into purer purer sandstones towards the source of the siliciclastic sediment. sandstones towards the source of the siliciclastic sediment. Terrigenous clastics cemented by calcite have been referred to aTerrigenous clastics cemented by calcite have been referred to as s calcareous sandstones.calcareous sandstones.

EPS 321 Lecture 10

Petrography and origin of principal sandstone typesPetrography and origin of principal sandstone typesThe four common types of sandstone are quartz arenite, arkose, The four common types of sandstone are quartz arenite, arkose, litharenite and greywacke. They are frequently typical of a partlitharenite and greywacke. They are frequently typical of a particular icular depositional environment, but because of the provenance control depositional environment, but because of the provenance control on on sandstone composition, they are not restricted to that particulasandstone composition, they are not restricted to that particular r depositional setting.depositional setting.

Four categories of sandstone as seen in thin section under the microscope.Diameter of field of view is about 4 mm.

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1. QUARTZ ARENITES1. QUARTZ ARENITES

Sandstones with at least 95% quartz grains are the Sandstones with at least 95% quartz grains are the most most compositionally maturecompositionally mature of all sandstones. In addition, they frequently of all sandstones. In addition, they frequently consist of wellconsist of well--rounded and wellrounded and well--sorted grains so that sorted grains so that textural textural maturity is maturity is alsoalso very highvery high. .

CementsCements are typically quartz overgrowths, but calcite is also are typically quartz overgrowths, but calcite is also common. Monocrystalline quartz grains dominate. Common heavy common. Monocrystalline quartz grains dominate. Common heavy minerals are tourmaline, zircon and minerals are tourmaline, zircon and ilmeniteilmenite..

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ARKOSESARKOSES--11Arkoses contain more than 25% feldspar, much quartz and some rocArkoses contain more than 25% feldspar, much quartz and some rock k fragments. Detrital micas are also present and some finefragments. Detrital micas are also present and some fine--grained matrix. grained matrix.

The feldspar is chiefly potassium feldspar and much of this is mThe feldspar is chiefly potassium feldspar and much of this is microcline. icrocline. The feldspar is usually fresh although some may be altered to kaThe feldspar is usually fresh although some may be altered to kaolinite and olinite and sericitesericite. .

Polycrystalline quartz and quartz/feldspar rock fragments are coPolycrystalline quartz and quartz/feldspar rock fragments are common. mmon.

Arkoses are typically red or pink, through the feldspar's color,Arkoses are typically red or pink, through the feldspar's color, but also but also through the presence of finely disseminated hematite, since manythrough the presence of finely disseminated hematite, since many arkoses arkoses occur in redoccur in red--bed sequences. bed sequences.

EPS 321 Lecture 10

ARKOSESARKOSES--22Arkose Arkose texturetexture is typically poorlyis typically poorly--sorted to wellsorted to well--sorted, with very sorted, with very angular to subangular to sub--rounded grains, the precise texture dependent rounded grains, the precise texture dependent on the degree of transportation. on the degree of transportation. GrainGrain--supported arkoses are cemented by calcite or quartz, supported arkoses are cemented by calcite or quartz, while others are cemented by a matrix, often containing much while others are cemented by a matrix, often containing much kaolinite. kaolinite.

EPS 321 Lecture 10

3. LITHARENITES3. LITHARENITESLitharenites are characterized by a rock fragment content which Litharenites are characterized by a rock fragment content which is in excess of is in excess of feldspar. feldspar. They range widely in composition, both in terms of mineralogy anThey range widely in composition, both in terms of mineralogy and chemistry, d chemistry, depending largely on the types of rock fragment present. These adepending largely on the types of rock fragment present. These are chiefly re chiefly fragments of mudrock and their low grade metamorphic equivalentsfragments of mudrock and their low grade metamorphic equivalents; other ; other components are flakes of mica, some feldspar and much quartz. components are flakes of mica, some feldspar and much quartz. There is little primary matrix, otherwise they are similar to grThere is little primary matrix, otherwise they are similar to greywackes in eywackes in composition and in fact they have been referred to as subgreywaccomposition and in fact they have been referred to as subgreywackes. kes. Cements are usually either calcite or quartz. Cements are usually either calcite or quartz.

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4. GREYWACKES 4. GREYWACKES As indicated by the name, greywackes are dark grey or black rockAs indicated by the name, greywackes are dark grey or black rocks, often s, often resembling dolerite resembling dolerite The characteristic feature of greywackes is the fineThe characteristic feature of greywackes is the fine--grained matrix, which grained matrix, which consists of an intergrowth of chlorite, consists of an intergrowth of chlorite, sericitesericite and siltand silt--sized grains of quartz sized grains of quartz and feldspar. and feldspar. Of the sand fraction, quartz dominates over rock fragments and fOf the sand fraction, quartz dominates over rock fragments and feldspar. Many eldspar. Many different rock fragments are usually present. Feldspar grains ardifferent rock fragments are usually present. Feldspar grains are chiefly e chiefly sodicsodicplagioclase and these are usually fresh in appearance. plagioclase and these are usually fresh in appearance. The The origin of the matrixorigin of the matrix has been referred to as the has been referred to as the 'greywacke problem'.'greywacke problem'. There There are two possibilities: fine grained sediment deposited along witare two possibilities: fine grained sediment deposited along with the sand h the sand fraction (fraction (primary originprimary origin), and diagenetic alteration of unstable rock fragments ), and diagenetic alteration of unstable rock fragments ((diagenetic origindiagenetic origin).).

EPS 321 Lecture 10

Genetic Implications of Sandstone Composition

a)Maturity of a sandstonei) Textural Maturityii) Compositional Maturity

b) Provenance of a sedimenti) Tectonic settingii) Climate

EPS 321 Lecture 10

EPS 321 Lecture 10

Provenance of a sediment

Provenance: where something originated.The Provenance of a sediment is determined by aspects of

composition that reflect the source rock and tectonic and climatic characteristics of the source area for the sediment.

i) Tectonic settingThe source rock of a sediment and the tectonic setting are

closely linked: the tectonic setting determines the relative abundance of different types of rock that is available for weathering and the production of clastic sediment.

e.g., An arkosic sandstone (rich in feldspars) would have a source area that is rich in granites.

EPS 321 Lecture 10

ii) ClimateClimate exerts a strong control on the type of weathering that takes place in the source area of a sediment; this, in turn, influences composition.

Cold, arid climate: predominantly physical weathering, producing abundant detrital grains (unaltered mineral grains and rock fragments).

Sandstones produced in such settings will be relatively immature, depending on the source rocks.

EPS 321 Lecture 10

Provenance & Tectonic setting of Quartz ArenitesProvenance & Tectonic setting of Quartz ArenitesIn many cases, quartz arenites are the product of extensive periIn many cases, quartz arenites are the product of extensive periods of ods of sediment reworking, so that all grains other than quartz have besediment reworking, so that all grains other than quartz have been broken en broken down. down.

The majority of the quartz grains are second cycle, derived fromThe majority of the quartz grains are second cycle, derived from prepre--existing existing sediments. Quartz arenites of this type, often deposited on shalsediments. Quartz arenites of this type, often deposited on shallowlow--marine marine shelves, with little tectonic movement and the basin subsides veshelves, with little tectonic movement and the basin subsides very slowly.ry slowly.

EPS 321 Lecture 10

Provenance Provenance & Tectonic setting & Tectonic setting of Arkosesof ArkosesArkoses are derived from granites and gneisses and vary from Arkoses are derived from granites and gneisses and vary from inin--situ weathering products, to stratified and crosssitu weathering products, to stratified and cross--bedded bedded arkoses where there has been substantial sediment transport.arkoses where there has been substantial sediment transport.

Arkoses are clearly derived from feldsparArkoses are clearly derived from feldspar--rich rocks but apart rich rocks but apart from an appropriate provenance geology, climate and source from an appropriate provenance geology, climate and source area relief are also important factors. area relief are also important factors. Under humid conditionsUnder humid conditions, , feldspars weather to clay mineralsfeldspars weather to clay minerals, so that , so that semisemi--arid and glacial arid and glacial climatesclimates favor arkose formation. If erosion is very rapid, favor arkose formation. If erosion is very rapid, however, i.e. the source area has a high relief, then arkoses however, i.e. the source area has a high relief, then arkoses can accumulate in spite of an adverse climate. Many arkoses can accumulate in spite of an adverse climate. Many arkoses were deposited in fluviatile environments.were deposited in fluviatile environments.

EPS 321 Lecture 10

Geologic environment in which an arkose wouldbe deposited.

EPS 321 Lecture 10

Provenance & Tectonic setting of Litharenites Provenance & Tectonic setting of Litharenites

Litharenites account for some 20 to 25% of all sandstones. Litharenites account for some 20 to 25% of all sandstones. Their Their immatureimmature composition implies high rates of sediment composition implies high rates of sediment production followed by short transport distances. Many production followed by short transport distances. Many fluviatile and deltaic sandstones are litharenites.fluviatile and deltaic sandstones are litharenites.

EPS 321 Lecture 10

Provenance & Tectonic settingProvenance & Tectonic setting of Greywackesof GreywackesMany greywackes were deposited by turbidity currents in basins oMany greywackes were deposited by turbidity currents in basins of various f various types, often off continental margins and in association with voltypes, often off continental margins and in association with volcanics.canics.Frequently greywackes are transported by masses of water highly charged with suspended sediment. Because of the suspended matter, the mass is denser than surrounding water and moves along the sloping sea floor or down submarine canyons as a turbidity current. Greywacke sediment characteristically accumulates in deep-sea fans at the base of the continental slope.

EPS 321 Lecture 10

Sedimentary Rock Source area lithology Paleoclimate

Tectonic Activity Energy Levels Time

Quartz ss, well sorted, well rounded

Granite

Arkose, poorly sorted, poorly rounded

Granite

Quartz ss, angular, muddy, poorly sorted

Granite

Arkose, well sorted, well rounded

Granite

Litharenite, poorly sorted, no mud, angular

Basalt, Gabbro, Gneiss, other maficrock

Provenance & Tectonic settingProvenance & Tectonic setting of Sandstonesof Sandstones

EPS 321 Lecture 10

Basalt, Basalt, GabbroGabbro, , Gneiss,Gneiss,……

Litharenite, poorly Litharenite, poorly sorted, no mud, sorted, no mud, angularangular

GraniteGraniteArkose, well sorted, Arkose, well sorted, well roundedwell rounded

GraniteGraniteQuartz Quartz ssss, angular, , angular, muddy, poorly muddy, poorly sortedsorted

GraniteGraniteArkose, poorly Arkose, poorly sorted, poorly sorted, poorly roundedrounded

GraniteGraniteQuartz Quartz ssss, well , well sorted, well sorted, well roundedrounded

TimeTimeEnergy LevelsEnergy Levels

Tectonic Tectonic ActivityActivityPaleoclimatePaleoclimate

Source area Source area lithologylithology

Sedimentary RockSedimentary Rock

Humid

Humid

Arid

Arid

Arid or Temperate

Provenance & Tectonic settingProvenance & Tectonic setting of Sandstonesof Sandstones

EPS 321 Lecture 10

Basalt, Gneiss, other maficrock

Litharenite, poorly sorted, no mud, angular

GraniteArkose, well sorted, well rounded

GraniteQuartz ss, angular, muddy, poorly sorted

GraniteArkose, poorly sorted, poorly rounded

GraniteQuartz ss, well sorted, well rounded

TimeEnergy Levels

Tectonic ActivityPaleoclimate

Source area lithology

Sedimentary Rock

Humid

Humid

Arid

Arid

Arid or Temperate

Passive

Passive

Active

Active

Active

Provenance & Tectonic settingProvenance & Tectonic setting of Sandstonesof Sandstones

EPS 321 Lecture 10

Basalt, Gneiss, other maficrock

Litharenite, poorly sorted, no mud, angular

GraniteArkose, well sorted, well rounded

GraniteQuartz ss, angular, muddy, poorly sorted

GraniteArkose, poorly sorted, poorly rounded

GraniteQuartz ss, well sorted, well rounded

TimeEnergy Levels

Tectonic ActivityPaleoclimate

Source area lithology

Sedimentary Rock

Humid

Humid

Arid

Arid

Arid or Temperate

Passive

Passive

Active

Active

Active

High and consistent

Inconsistent

Inconsistent

High and consistent

Inconsistent

Provenance & Tectonic settingProvenance & Tectonic setting of Sandstonesof Sandstones

EPS 321 Lecture 10

Humid

Humid

Arid

Arid

Arid or Temperate

Basalt, Basalt, Gneiss, other Gneiss, other maficmafic rockrock

Litharenite, poorly Litharenite, poorly sorted, no mud, sorted, no mud, angularangular

GraniteGraniteArkose, well sorted, Arkose, well sorted, well roundedwell rounded

GraniteGraniteQuartz Quartz ssss, angular, , angular, muddy, poorly muddy, poorly sortedsorted

GraniteGraniteArkose, poorly Arkose, poorly sorted, poorly sorted, poorly roundedrounded

GraniteGraniteQuartz Quartz ssss, well , well sorted, well roundedsorted, well rounded

TimeTimeEnergy LevelsEnergy Levels

Tectonic Tectonic ActivityActivityPaleoclimatePaleoclimate

Source area Source area lithologylithology

Sedimentary RockSedimentary Rock

Passive

Passive

Active

Active

Active

Humid

Humid

Arid

Arid

Arid or Temperate

High and consistent

Inconsistent

Inconsistent

High and consistent

Inconsistent

Long

Long

Short

Short

Short

Provenance & Tectonic settingProvenance & Tectonic setting of Sandstonesof Sandstones

EPS 321 Lecture 10