Sedimentary Sedimentary PetrologyPetrologyGEO 333GEO 333

Lab (2)Lab (2)

Basic ClassificationBasic Classification

20092009

Mansour Al-HashimMansour Al-Hashim

Preview of Lab 1Preview of Lab 1

IntroductionIntroduction

Main minerals of sedimentary rocksMain minerals of sedimentary rocks

Objectives of Lab 2Objectives 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

Introduction to ClassificationIntroduction to Classification

1.1. A classification of rocks represents a A classification of rocks represents a theorytheory of of

how these rocks were formed, and how they relate how these rocks were formed, and how they relate

to each other.to each other.

2.2. Many classifications have been proposed for Many classifications have been proposed for

sedimentary rocks. sedimentary rocks.

3.3. Since 1950, more than 50 classifications of Since 1950, more than 50 classifications of

sandstones alone have been proposed. sandstones alone have been proposed.

4.4. No one classification is fully satisfactory. No one classification is fully satisfactory.

5.5. The type of classification depends on the purpose The type of classification depends on the purpose

of the study being conducted. of the study being conducted.

A Good ClassificationA Good Classification 1.1. Should be as inclusive as possible.Should be as inclusive as possible.

2.2. Includes as much variety as possible.Includes as much variety as possible.

3.3. Leaves only few or no orphan rocks. Leaves only few or no orphan rocks.

4.4. Dose not contain any internal Dose not contain any internal

contradictions.contradictions.

We will see several classification We will see several classification systems, ranging from basic to systems, ranging from basic to sophisticated.sophisticated.

Sedimentary Rock Sedimentary Rock ClassificationClassification

Sedimentary rocks are generally Sedimentary rocks are generally grouped into three main grouped into three main categories:categories:

a)a) Siliciclastic (clastic) rocksSiliciclastic (clastic) rocks

b)b) Chemical rocksChemical rocks

c)c) Biochemical rocksBiochemical rocks

Simple Classification of Sedimentary Rocks

Modified from Boggs (1992)

Clastic (terrigenous/detrital) Clastic (terrigenous/detrital)

Sedimentary RocksSedimentary Rocks 1.1. Derived from pre-existing rocks.Derived from pre-existing rocks.

2.2. Composed of physically derived components. Composed of physically derived components.

3.3. Sometimes referred to as Sometimes referred to as extrabasinalextrabasinal. .

4.4. Grains are mechanically durable and chemically Grains are mechanically durable and chemically stable. stable.

5.5. Clasts are made of quartz, feldspar, muscovite, Clasts are made of quartz, feldspar, muscovite, clay minerals, and rock fragments.clay minerals, and rock fragments.

6.6. Silica (SiOSilica (SiO22) is the major component. ) is the major component.

7.7. Classified based on texture (grain size).Classified based on texture (grain size).

8.8. Examples: breccia, conglomerate, sandstone, Examples: breccia, conglomerate, sandstone, siltstone, and shale. siltstone, and shale.

Basic Classification of Clastic Sedimentary Rocks

BrecciaBreccia

ConglomeConglomeraterate

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Chemical and Biochemical Chemical and Biochemical Sedimentary RocksSedimentary Rocks

1. Derived from precipitation of dissolved 1. Derived from precipitation of dissolved minerals in the solution.minerals in the solution.

a)a) Direct precipitation from seawater. The Direct precipitation from seawater. The result is result is Chemical RocksChemical Rocks. .

b)b) Organism extraction of the dissolved Organism extraction of the dissolved minerals from the sea. The result is minerals from the sea. The result is Biochemical RocksBiochemical Rocks. .

2. Classified based on the chemical composition.2. Classified based on the chemical composition.

3. Examples: limestone, chert, and chalk. 3. Examples: limestone, chert, and chalk.

Basic Classification of Chemical and Biochemical Sedimentary Rocks

ChertChert

Coquina Coquina

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Fundamental Constituents of Fundamental Constituents of Sedimentary RocksSedimentary Rocks

Sediments consist of three Sediments consist of three

components:components:

A.A. Terrigenous components Terrigenous components

B.B. Allochemical components Allochemical components

C.C. Orthochemical componentsOrthochemical components

They may be mixed in almost all They may be mixed in almost all

proportions.proportions.

From Folk (1974)

(A) Terrigenous components(A) Terrigenous components

Derived from erosion of areas Derived from erosion of areas outsideoutside the depositional basin. the depositional basin.

Brought to the basin as solids. Brought to the basin as solids.

Examples: quartz and feldspar sand, Examples: quartz and feldspar sand, heavy minerals, clay minerals, and heavy minerals, clay minerals, and chert and limestone clasts. chert and limestone clasts.

(B) Allochemical components(B) Allochemical components Greek: “allo” meaning different from normal.Greek: “allo” meaning different from normal.

Precipitated directly from solution Precipitated directly from solution withinwithin the depositional basin.the depositional basin.

Termed “allo” because they have been Termed “allo” because they have been moved as solids within the basin.moved as solids within the basin.

Examples: broken or intact shells, oolites, Examples: broken or intact shells, oolites, calcareous pellets, or fragments of calcareous pellets, or fragments of carbonate sediments.carbonate sediments.

(C) Orthochemical components(C) Orthochemical components

Greek: “ortho” meaning true. Greek: “ortho” meaning true.

Termed “ortho” because they are Termed “ortho” because they are produced chemically within the basin. produced chemically within the basin.

Examples: microcrystalline calcite or Examples: microcrystalline calcite or

dolomite ooze, some evaporites, and dolomite ooze, some evaporites, and cements in sandstones.cements in sandstones.

Notes Notes

Classes (B) and (C) are referred to Classes (B) and (C) are referred to as “chemical” constituents. as “chemical” constituents.

Classes (A) and (B) may be termed Classes (A) and (B) may be termed “fragmental”. “fragmental”.

Basic Classification of Basic Classification of Sedimentary Rocks (1)Sedimentary Rocks (1)

Sedimentary rocks are divided into five Sedimentary rocks are divided into five

classes based on proportions of the classes based on proportions of the

fundamental components:fundamental components:

1.1. T (Terrigenous Rocks)T (Terrigenous Rocks)

2.2. IA (Impure Allochemical Rocks)IA (Impure Allochemical Rocks)

3.3. IO (Impure Orthochemical Rocks)IO (Impure Orthochemical Rocks)

4.4. A (Allochemical Rocks) A (Allochemical Rocks)

5.5. O (Orthochemical Rocks)O (Orthochemical Rocks)

From Folk (1974)

Basic Classification of Basic Classification of Sedimentary Rocks (2)Sedimentary Rocks (2)

Terrigenous Rocks (T)Terrigenous Rocks (T)

Examples: mudrocks, sandstones, and Examples: mudrocks, sandstones, and

conglomerates.conglomerates.

Impure Allochemical Rocks (IA)Impure Allochemical Rocks (IA)

Examples: very fossiliferous shales; sandy Examples: very fossiliferous shales; sandy

fossiliferous or oolitic limestones.fossiliferous or oolitic limestones.

Impure Orthochemical Rocks (IO)Impure Orthochemical Rocks (IO)

Examples: clayey microcrystalline limestones.Examples: clayey microcrystalline limestones.

Basic Classification of Basic Classification of Sedimentary Rocks (3)Sedimentary Rocks (3)

Allochemical Rocks (A)Allochemical Rocks (A) Examples: fossiliferous, oolitic limestones Examples: fossiliferous, oolitic limestones

and dolomites.and dolomites.

Orthochemical Rocks (O)Orthochemical Rocks (O) Examples: limestone, dolomite, anhydrite, Examples: limestone, dolomite, anhydrite,

and chert.and chert.

Assignment (2)Assignment (2)

No.No. Rock Name Rock Name Origin (clastic, chemical, Origin (clastic, chemical, bio-chemical)bio-chemical)

References References

Journal of Geological Education, Journal of Geological Education,

1991,v.39,p.382.1991,v.39,p.382. Petrology of Sedimentary Rocks, Boggs, Petrology of Sedimentary Rocks, Boggs,

1992. 1992. Petrology of Sedimentary Rocks, Folk, Petrology of Sedimentary Rocks, Folk,

1974. 1974. csmres.jmu.educsmres.jmu.edu geology.com geology.com

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