Sedimentary Petrology GEO 333 Lab(4) Classification of Unconsolidated Sediments 2009 Mansour Al-Hashim.

Sedimentary Sedimentary PetrologyPetrologyGEO 333GEO 333

Lab(4)Lab(4)

Classification of Classification of Unconsolidated SedimentsUnconsolidated Sediments

2009 2009

Mansour Al-HashimMansour Al-Hashim

Preview of Lab 3Preview 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

Objectives of Lab 4Objectives of Lab 4

Classification of sediments Classification of sediments

Reading a ternary diagramReading a ternary diagram

Finding Clay : Silt RatioFinding Clay : Silt Ratio

Finding Mud : Sand RatioFinding Mud : Sand Ratio

Classification of Sediments Classification of Sediments (1)(1)

Classification of detrital sediments is Classification of detrital sediments is

based on particle size.based on particle size.

The major size categories are gravel, The major size categories are gravel,

sand, and mud.sand, and mud. Boundaries between these categories Boundaries between these categories

are in accord with those of Udden-are in accord with those of Udden-

Wentworth grade scale. Wentworth grade scale.

Classification of Sediments Classification of Sediments (2)(2)

The problem is that sediments are The problem is that sediments are NOT always very well sorted.NOT always very well sorted.

There is always a spread of sizes There is always a spread of sizes around the mean size.around the mean size.

So what does one do about naming So what does one do about naming mixed sediments?? mixed sediments??

For the sake of that purpose, various For the sake of that purpose, various classifications have been proposed. classifications have been proposed.

Classifications of sediments that contain mixtures of size classes

Figure by MIT OCW

Classifications of sediments that contain mixtures of size classes

Figure by MIT OCW

Classifications of sediments that contain mixtures of size classes

Figure by MIT OCW

From Long (2006), based on Folk (1954)

Reading a Ternary DiagramReading a Ternary Diagram

A ternary diagram is a triangle. A ternary diagram is a triangle. Each of its three apexes represents a Each of its three apexes represents a

specific component, such as gravel, specific component, such as gravel, sand, or mud.sand, or mud.

In the following example the apexes In the following example the apexes are labeled are labeled AA,, B B, and , and CC..

Composition A

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Composition B

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Composition C

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A Complete Ternary Diagram

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Example (1)• What is the composition of the points 1-4 plotted on the diagram?

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SolutionSolution

Point 1Point 1 (60% A) (20% B) (20% C) = 100% (60% A) (20% B) (20% C) = 100%

Point 2Point 2 (25% A) (40% B) (35% C) = 100% (25% A) (40% B) (35% C) = 100%

Point 3Point 3 (10% A) (70% B) (20% C) = 100% (10% A) (70% B) (20% C) = 100%

Point 4Point 4 (0.0% A)(25% B) (75% C) = 100% (0.0% A)(25% B) (75% C) = 100%

Note:Note: the total percentages of the total percentages of

compositions that make up a specific compositions that make up a specific

sediment must be 100%. sediment must be 100%.

NotesNotes

In common practice, "A Scale", "B Scale", In common practice, "A Scale", "B Scale", and "C Scale" are not always shown on the and "C Scale" are not always shown on the diagram.diagram.

Sometimes, these diagrams even lack the Sometimes, these diagrams even lack the percent numbers. percent numbers.

Here, we will learn how to read such Here, we will learn how to read such diagrams.diagrams.

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Can you read it Can you read it now??now??

Triangle (A)

Folk (1954)

Triangle (B)

Folk (1954)

Based on Folk (1954)

Triangle (B)

When do we use triangle A When do we use triangle A and B?and B?

Triangle (A):Triangle (A): Sand, Silt, and ClaySand, Silt, and Clay No GravelNo Gravel Clay : Silt RatioClay : Silt Ratio

Triangle (B):Triangle (B): Gravel, Sand, and Mud (Silt + Clay)Gravel, Sand, and Mud (Silt + Clay)

Mud : Sand RatioMud : Sand Ratio

Finding Clay : Silt RatioFinding Clay : Silt Ratio

Example (1)Example (1)

Sand= 25%, Silt= 25%, Clay= 50%Sand= 25%, Silt= 25%, Clay= 50%

Clay : SiltClay : Silt

50 : 2550 : 25

50/25 : 25/2550/25 : 25/25

2 : 12 : 1

Finding Mud : Sand RatioFinding Mud : Sand Ratio

Example (2)Example (2)

Gravel= 10%, Sand= 80%, Mud= 10%Gravel= 10%, Sand= 80%, Mud= 10%

Mud : SandMud : Sand

10 : 8010 : 80

10/10 : 80/1010/10 : 80/10

1 : 81 : 8

Assignment (4)Assignment (4) Classify the following sediments using the ternary diagrams Classify the following sediments using the ternary diagrams

(A) or (B)(A) or (B)

Sediment 1Sediment 1 Gravel= Gravel=7070 %, Sand= %, Sand= 20 20 %%, , Mud=Mud= 10 10 % %

Sediment 2Sediment 2 Sand= Sand= 6060 %, Clay= %, Clay= 4040 %, Silt= %, Silt= 00 % %

Sediment 3Sediment 3 Gravel= Gravel=3030 %, Sand= %, Sand= 5050 %, Mud= %, Mud= 2020 % %

Sediment 4Sediment 4 Sand= Sand= 1010 %, Clay= %, Clay= 1515 %, Silt= %, Silt= 7575 % %

Find theFind the Mud : Sand Mud : Sand oror Clay : SiltClay : Silt for all the above cases. for all the above cases.

References References

Long, D. 2006. BGS detailed explanation of Long, D. 2006. BGS detailed explanation of

seabed sediment modified folk classification.seabed sediment modified folk classification.

Folk, R.L., 1954. The distinction between grain Folk, R.L., 1954. The distinction between grain

size and mineral composition in sedimentary size and mineral composition in sedimentary

rock nomenclature. Journal of Geology 62 (4), rock nomenclature. Journal of Geology 62 (4),

344-359.344-359.

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The EndThe End