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Physical Properties of Sediments

Physical Properties of Sediments. SOURCES OF SEDIMENT 1. Crust a. nearly all sediments are derived from continental crust b. small fraction is from oceanic crust from volcanic ash c. rocks of the crust - 3 types

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Physical Properties of Sediments

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  1. Physical Properties of Sediments

  2. SOURCES OF SEDIMENT 1. Crust a. nearly all sediments are derived from continental crust b. small fraction is from oceanic crust from volcanic ash c. rocks of the crust - 3 types igneous rocks - formed by the crystallization of magma sedimentary rocks formed from sediments sedimentary rocks and sediments cover about 90% of all crust metamorphic rocks

  3. CLASSIFICATION • Physical properties -descriptive classification • Grain Size (or fossil size) (The most significant property) • i. nominal diameter • ii. sieve diameter • iii. Sedimentation diameter • iv. Standard diameter (fall diameter) • b. Composition (of the individual grains) • i. minerals • ii. Fossils • c. Particle Shape SF = c/√(a*b) • SF for sphere = 1 and 0.7 for natural sediments

  4. d. Specific Gravity and velocity i. gravity ranges from 2.6 to 2.8 ii. fall velocity of a grain with fall diameter an SG of 2.65 e. Cohesiveness (association between type and size) i. illite, kaolinite, and montomorillonite are the most minerals causing particles to stick together ii. No clear boundary between cohesive and not cohesive but clay is more cohesive than silt f. Gradation (variation in particle size with respect to direction) i. particle size ii. particle weight g. Sorting and packing i. Poor to well sorting ii. Cubic, tetragonal, and rohmbohedral h. Consolidation (process of compaction with time)

  5. 2. Genetic (based on their origin) a. Terrigenous - derived mainly from continents; most of these are found near continents i. materials eroded from the continents ii. volcanogenic--products of volcanoes iii. glacial- glaciers grind up rock b. Biogenous - produced by living organisms (mostly skeletal material produced by plankton i. calcareous- skeletal materials made of CaCO3 a) foraminifera (protozoans, forming calcite) b) coccolithophores (algae, forming calcite) c) pteropods (planktonic molluscs) d) benthic animals (e.g., corals, clams)

  6. ii. siliceous (skeletal materials made of opal) a) diatoms (algae) b) radiolarians (protozoans) iii. phosphatic - fish debris iv. organic matter (petroleum reserves) c. Hydrogenous (minor) - precipitated from seawater i. manganese nodules and crusts - mostly Fe oxides ii. hydrothermal - metal rich deposits iii. salts (evaporite deposits) d. Cosmogenous - sediments from outer space - very rare i. interplanetary dust constantly rains on the Earth ii. occasionally large asteroids or comets impact the Earth

  7. Porosity, Permeability, and Saturation

  8. Total and effective porosity of various sediments

  9. Permeability Permeability Is a measure of the capacity of a rock to transmit fluid It depends on Connected void, grain size, grain shape, and packing Darcy law κ = (Q/A) (u) (dL/p1-p2) Facts: Unit is L square Horizontal permeability Vertical permeability

  10. Common Diagenetic Changes in Sediments Process Results Depth Effect Compaction Mech rearrangement Shallow Reduce porosity of grains Cementation Intergranular calcite shallow Consolidation and silica overgrowths moderate Reduce Porosity Clay Precipit. Illite, Kaolinite coating same slight decrease in porosity Clay Dehyd. Loss water Moderate slight increase in porosity Dissolution Leaching of calcite Moderate Segnif. increase cement in porosity

  11. Saturation Saturation Is the amount of fluid in a rock It is a percentage of the pore space Porosity, permeability, and saturation can be measured in the lab and by tertiary methods.

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