Sedimentary Sedimentary PetrologyPetrologyGEO 333GEO 333

Lab (3)Lab (3)Clastic Sedimentary RocksClastic Sedimentary Rocks

(Classification & Description)(Classification & Description)20092009

Mansour Al-HashimMansour Al-Hashim

Preview of Lab 2Preview of Lab 2

Classification in general Classification in general

Classification of sedimentary rocksClassification of sedimentary rocks

Clastic sedimentary rocksClastic sedimentary rocks

Chemical and biochemical Chemical and biochemical

sedimentary rockssedimentary rocks

Fundamental constituents of Fundamental constituents of

sedimentary rockssedimentary rocks

Objectives of Lab 3Objectives of Lab 3

Textures of sedimentary rocksTextures of sedimentary rocks Grain sizeGrain size Roundness and sortingRoundness and sorting MaturityMaturity ColorColor Cohesiveness (firmness)Cohesiveness (firmness) Mineral composition and sedimentary Mineral composition and sedimentary

structuresstructures Framework and matrixFramework and matrix Cements in sedimentary rocksCements in sedimentary rocks

Textures of Sedimentary Textures of Sedimentary RocksRocks

Sedimentary rocks may have Sedimentary rocks may have

1. Clastic (fragmental) texture1. Clastic (fragmental) texture Grains are stuck together. Grains are stuck together. Characteristic of clastic sedimentary rocks.Characteristic of clastic sedimentary rocks. Examples: sandstone and conglomerate.Examples: sandstone and conglomerate.

2. Non-clastic (crystalline) texture2. Non-clastic (crystalline) texture Interlocking crystals. Interlocking crystals. Characteristic of chemical sedimentary Characteristic of chemical sedimentary

rocks.rocks. Examples: limestone, dolomite, and chert.Examples: limestone, dolomite, and chert.

Clastic (fragmental) Clastic (fragmental) TextureTexture

From eos.ubc.caFrom eos.ubc.ca

Non-clastic (crystalline) Non-clastic (crystalline) TextureTexture

From eos.ubc.caFrom eos.ubc.ca

Grain Size (1)Grain Size (1)

Grain sizes can be determined by:Grain sizes can be determined by: Direct measurement with calipers or meter Direct measurement with calipers or meter

sticks. sticks.

For particles larger than several For particles larger than several centimeters. centimeters.

Screening and petrographic microscope. Screening and petrographic microscope.

For particles from 2 mm to about 1/16 mm.For particles from 2 mm to about 1/16 mm. Pipette or hydrometer (settling rates in Pipette or hydrometer (settling rates in

water)water)

For particles less than 1/16 mm.For particles less than 1/16 mm.

Grain Size (2)Grain Size (2)

Results of grain-size analysis can be Results of grain-size analysis can be

demonstrated as histograms, cumulative demonstrated as histograms, cumulative

curves, or frequency curves.curves, or frequency curves.

Many statistical parameters can be calculated Many statistical parameters can be calculated

(e.g., median, mean, skewness, kurtosis, etc.).(e.g., median, mean, skewness, kurtosis, etc.).

Used to characterize depositional processes Used to characterize depositional processes

and depositional environments.and depositional environments.

Udden-Wentworth grain-size scale is the most Udden-Wentworth grain-size scale is the most

widely used. widely used.

Wentworth grade scaleWentworth grade scale

Modified Modified Udden-Udden-

Wentworth Wentworth grain-size grain-size

Scale Scale

Simplified grain-size scaleSimplified grain-size scale

Roundness and Roundness and SortingSorting

Roundness Roundness (angularity) (angularity) Indicates how smooth or sharp the edges Indicates how smooth or sharp the edges

and corners of particles are. and corners of particles are. Usually measured with reference to a Usually measured with reference to a

comparative chart (the commonest is comparative chart (the commonest is Powers’ , 1953).Powers’ , 1953).

Sorting Sorting The degree of uniformity of grain sizes. The degree of uniformity of grain sizes.

Categories of roundnessCategories of roundness

From From Tucker (2001)Tucker (2001)

Degrees of sortingDegrees of sorting

From Compton (1962)From Compton (1962)

* Note the standard deviation values * Note the standard deviation values between classesbetween classes

Visual estimation of Visual estimation of sortingsorting

From Tucker (2001)From Tucker (2001)

MaturityMaturity Depends on how many cycles of erosion Depends on how many cycles of erosion

and redeposition the components of a rock and redeposition the components of a rock have undergone. have undergone.

There are two types of maturity:There are two types of maturity:

1.1. Compositional maturityCompositional maturity

Compositional maturity = quartz + chert / Compositional maturity = quartz + chert / feldspars + rock fragments.feldspars + rock fragments.

2.2. Textural maturityTextural maturity

Textural (structural) maturity = sorting and Textural (structural) maturity = sorting and roundness of sand-sized grains.roundness of sand-sized grains.

From Folk From Folk (1951)(1951)

Textural MaturityTextural Maturity

ColorColor

Organic matter, sulfides, and some iron Organic matter, sulfides, and some iron

oxides give rocks a dark color.oxides give rocks a dark color. Indicating deposition in a reducing Indicating deposition in a reducing

environment.environment.

Some iron oxides give rocks red or Some iron oxides give rocks red or

yellowish color.yellowish color. Indicating deposition in an oxidizing Indicating deposition in an oxidizing

environment.environment.

Color IndicationsColor Indications

Black - organic matter FeSBlack - organic matter FeS Yellowish - pyrite, markasite FeSYellowish - pyrite, markasite FeS22

Yellowish or bluish - sulphates, Yellowish or bluish - sulphates, carbonates, and chloridescarbonates, and chlorides

Yellowish to brownish - limonite, Yellowish to brownish - limonite, goethite FeO(OH)goethite FeO(OH)

Reddish - iron oxides FeO Reddish - iron oxides FeO

From eos.ubc.ca

Cohesiveness (firmness)Cohesiveness (firmness)

The degree to which the particles The degree to which the particles stick together.stick together.

Cohesiveness can be described as: Cohesiveness can be described as:

1.1. FragileFragile

2.2. Soft Soft

3.3. Intermediate Intermediate

4.4. Hard Hard

5.5. Very hard Very hard

Mineral CompositionMineral Composition The most common minerals in The most common minerals in

sedimentary rocks are:sedimentary rocks are:1.1. QuartzQuartz2.2. Clay mineralsClay minerals3.3. FeldsparsFeldspars4.4. Carbonates (calcite and dolomite)Carbonates (calcite and dolomite)5.5. Rock fragmentsRock fragments Small amounts of amphibole, Small amounts of amphibole,

pyroxene, and mica. pyroxene, and mica.

Sedimentary Sedimentary StructuresStructures

Some common sedimentary structures Some common sedimentary structures include:include:

1.1. Bedding (stratification)Bedding (stratification)2.2. Lamination Lamination 3.3. Graded BeddingGraded Bedding4.4. Cross-BeddingCross-Bedding5.5. Ripple MarksRipple Marks6.6. Mud CracksMud Cracks7.7. Raindrop Impressions Raindrop Impressions Nodules, concretions, geodes, and Nodules, concretions, geodes, and

Stromatolites.Stromatolites.

Framework and MatrixFramework and Matrix The grains in a sand-sized or coarser grained The grains in a sand-sized or coarser grained

sedimentary rock are known as the framework. sedimentary rock are known as the framework.

These grains are either: These grains are either:

1.1. In contact with each otherIn contact with each other

2.2. Surrounded by empty spaces Surrounded by empty spaces (pore spaces)(pore spaces)

3.3. Surrounded by finer grained sediment Surrounded by finer grained sediment

(matrix)(matrix)

4.4. Cemented together by a bonding material Cemented together by a bonding material

(cement)(cement)

Framework and Framework and MatrixMatrix

From Immenhauser (2002)From Immenhauser (2002)

Cements in Cements in Sedimentary RocksSedimentary Rocks

The most common cements in The most common cements in sedimentary rocks are: sedimentary rocks are:

1.1. Silica (quartz, opal, or chalcedony)Silica (quartz, opal, or chalcedony)

2.2. Carbonates (calcite, dolomite, or Carbonates (calcite, dolomite, or siderite)siderite)

3.3. Iron oxides (hematite)Iron oxides (hematite) Recognition of matrix and cement Recognition of matrix and cement

is not always possible in hand is not always possible in hand specimens.specimens.

Assignment 3Assignment 3

References References

Compton, 1962. Manual of field geology.Compton, 1962. Manual of field geology. Folk, 1974. Petrology of sedimentary rocks.Folk, 1974. Petrology of sedimentary rocks. Folk, 1951. Stages of textural maturity in Folk, 1951. Stages of textural maturity in

sedimentary rocks: Journal of Sedimentary sedimentary rocks: Journal of Sedimentary Petrology, v. 21.Petrology, v. 21.

Immenhauser, 2002. Sedimentology for master Immenhauser, 2002. Sedimentology for master students. students.

Tucker, 2001. Sedimentary petrology: an Tucker, 2001. Sedimentary petrology: an introduction to the origin of sedimentary rocks. introduction to the origin of sedimentary rocks. Blackwell Science, London, UK. Blackwell Science, London, UK.

eos.ubc.ca eos.ubc.ca

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