Sphericity shows how much a particle deviated from a sphere o Oblate for grains

Sphericity shows how much a particle deviated from a

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Sphericity= shows how much a particle deviated from a sphere o Oblate= for grains with one large, one medium and one small dimension o Equant= for grains with three relatively equal dimensions o Bladed= for long and flat grain o Roller= for grains with one dimension considerably greater than the two others 11. Bedload vs suspended load o Bedload= movement along the bottom o Traction= rolling and sliding o Saltation= bouncing o Suspended load=movement in the fluid column 12. Grain size correlated to depositional environment o High energy environment to low energy: gravel, sand, silt, mud o Given certain fluvial energy, large grains move along the ground in traction motion; small grains are in suspension via turbulent eddies; intermediate sand grains move by saltation o With increased transport, average grain size decreases o Sorting becomes better with distance from source 13. Transportation mechanisms o Water: bedload figure o Gravity: the 4 types, what is a turbidite/turbidity current, Bouma Sequence 4 types: turbidity currents, debris flow, grain flow, fluidized flow Turbidity current= density current flows downslope because the suspension is heavier than the surrounding clear water Can be divided into head, neck, body, and tail From head to tail, turbulence greatly decreases at turbidity current head= rapid deposition; largest particles settle out of suspension first slower deposition in turbidity current body= deposit of bedload grains current tail very fine-grained particles deposited
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Turbidites= sedimentary rocks deposited form a turbidity current Bouma sequence= ideal sequence, most turbidities do not contain all of these 5 structural units Debris/Mud Flow= sediment/water mixture moving downslope Deserts, mountainous regions Grain Flow= “sand avalanches”, grains in the flow are kept in suspension by grain-to-grain collisions Common in Aeolian settings: desert and coastal sand dunes Fluidized flow= grains are kept in suspension from displaced fluid moving upward o Wind/aeolian and Glacial (we don’t go into detail- just know these are two additional modes of sediment transport) 14. Grain flow, Angle of repose o Grain flow= smaller grains are able to fall, or sieve downward, in between larger grains and settle out beneath them o Sediment gravity flow= the force of gravity causes movement of sediment/water mixtures because they have a higher density than their surroundings 15. Forces on a grain o Fluid lift force, fluid drag force, gravity force 16. Nature of deposition is characterized by o layers or beds, a variety of sediment structures, grain size grading, grain size sorting 17. Primary vs secondary structures o Primary sedimentary structures= formed during deposition Parallel layering, ripples o Secondary sedimentary structures= formed after deposition and before lithification Biogenic, chemical, and mechanical disruption (mudcracks, soft sediment deformation, burrows) 18. Law of original horizontality o Sedimentary material are deposited in horizontal layers 19. Beds/stratifications, bounding surfaces o
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