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

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Preview of Lab 3 Textures of sedimentary rocks Textures of sedimentary rocks Grain size Grain size Roundness and sorting Roundness and sorting Maturity Maturity Color Color Cohesiveness (firmness) Cohesiveness (firmness) Mineral composition and sedimentary structures Mineral composition and sedimentary structures Framework and matrix Framework and matrix Cements in sedimentary rocks Cements in sedimentary rocks

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Objectives of Lab 4 Classification of sediments Classification of sediments Reading a ternary diagram Reading a ternary diagram Finding Clay : Silt Ratio Finding Clay : Silt Ratio Finding Mud : Sand Ratio Finding Mud : Sand Ratio

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Classification of Sediments (1) Classification of detrital sediments is based on particle size. Classification of detrital sediments is based on particle size. The major size categories are gravel, sand, and mud. The major size categories are gravel, sand, and mud. Boundaries between these categories are in accord with those of Udden-Wentworth grade scale. Boundaries between these categories are in accord with those of Udden-Wentworth grade scale.

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Classification of Sediments (2) The problem is that sediments are NOT always very well sorted. The problem is that sediments are NOT always very well sorted. There is always a spread of sizes around the mean size. There is always a spread of sizes around the mean size. So what does one do about naming mixed sediments?? So what does one do about naming mixed sediments?? For the sake of that purpose, various classifications have been proposed. For the sake of that purpose, various classifications have been proposed.

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Classifications of sediments that contain mixtures of size classes Figure by MIT OCW

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Classifications of sediments that contain mixtures of size classes Figure by MIT OCW

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Classifications of sediments that contain mixtures of size classes Figure by MIT OCW

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

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Reading a Ternary Diagram A ternary diagram is a triangle. A ternary diagram is a triangle. Each of its three apexes represents a specific component, such as gravel, sand, or mud. Each of its three apexes represents a specific component, such as gravel, sand, or mud. In the following example the apexes are labeled A, B, and C. In the following example the apexes are labeled A, B, and C.

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Composition A From csmres.jmu.edu

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Composition B From csmres.jmu.edu

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Composition C From csmres.jmu.edu

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A Complete Ternary Diagram From csmres.jmu.edu

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Example (1) What is the composition of the points 1-4 plotted on the diagram? From csmres.jmu.edu

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Solution Point 1 (60% A) (20% B) (20% C) = 100% Point 2 (25% A) (40% B) (35% C) = 100% Point 3 (10% A) (70% B) (20% C) = 100% Point 4 (0.0% A)(25% B) (75% C) = 100% Note: the total percentages of compositions that make up a specific sediment must be 100%.

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Notes In common practice, "A Scale", "B Scale", and "C Scale" are not always shown on the diagram. In common practice, "A Scale", "B Scale", and "C Scale" are not always shown on the diagram. Sometimes, these diagrams even lack the percent numbers. Sometimes, these diagrams even lack the percent numbers. Here, we will learn how to read such diagrams. Here, we will learn how to read such diagrams.

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From csmres.jmu.edu Can you read it now??

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Triangle (A) Folk (1954)

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Triangle (B) Folk (1954)

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Based on Folk (1954) Triangle (B)

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When do we use triangle A and B? Triangle (A): Sand, Silt, and Clay Sand, Silt, and Clay No Gravel No Gravel Clay : Silt Ratio Clay : Silt Ratio Triangle (B): Gravel, Sand, and Mud (Silt + Clay) Gravel, Sand, and Mud (Silt + Clay) Mud : Sand Ratio Mud : Sand Ratio

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Finding Clay : Silt Ratio Example (1) Sand= 25%, Silt= 25%, Clay= 50% Clay : Silt Clay : Silt 50 : : 25 50/25 : 25/25 50/25 : 25/25 2 : 1 2 : 1

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Finding Mud : Sand Ratio Example (2) Gravel= 10%, Sand= 80%, Mud= 10% Mud : Sand Mud : Sand 10 : : 80 10/10 : 80/10 10/10 : 80/10 1 : 8 1 : 8

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Assignment (4) Classify the following sediments using the ternary diagrams (A) or (B) Classify the following sediments using the ternary diagrams (A) or (B) Sediment 1 Gravel=70 %, Sand= 20 %, Mud= 10 % Sediment 2 Sand= 60 %, Clay= 40 %, Silt= 0 % Sediment 3 Gravel=30 %, Sand= 50 %, Mud= 20 % Sediment 4 Sand= 10 %, Clay= 15 %, Silt= 75 % Find the Mud : Sand or Clay : Silt for all the above cases. Find the Mud : Sand or Clay : Silt for all the above cases.

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References Long, D BGS detailed explanation of seabed sediment modified folk classification. Long, D BGS detailed explanation of seabed sediment modified folk classification. Folk, R.L., The distinction between grain size and mineral composition in sedimentary rock nomenclature. Journal of Geology 62 (4), Folk, R.L., The distinction between grain size and mineral composition in sedimentary rock nomenclature. Journal of Geology 62 (4), csmres.jmu.edu csmres.jmu.edu

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The End

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