1. Describe and discuss what happens , and why , to clastic sediments during the
ID: 120700 • Letter: 1
Question
1. Describe and discuss what happens, and why, to clastic sediments during their transportation in a river? (if you can provide diagrams and illustration that would be great)
2. Clastic sediments are deposited when their transport medium looses energy and is no longer able to support the sediment load. When clastic sediments are deposited they commonly display one of three classic bedding/lamination textures that are representative of the evironment of deposition. SKETCH and DESCRIBE the three of the classic bedding/lamination textures that represent the evironment of deposition.
Explanation / Answer
1. Clastic sediments are generally composed of fragments, or clasts, of pre-existing minerals and rock. These are the smaller grains of rock broken off other rocks by physical weathering. Typically, rivers have a concave ‘longitudinal profile’. The characteristics and processes occurring in the river change downstream, as a result we find different landforms and deposition. From the river sources to river mouth the type of deposition you found are following:
Boulders-Cobbles-Pebbles-sand-silt-clay.
The sequence here you find is based on the size of the sediment. As you know, the force to move bigger volume will be bigger than the smaller one. Same apply here, Silt and clay due to its lesser size in samml volume transport more than the boulders- cobbles.
2. sedimentary structure in this case will depend on the direction of flow.
The follwing bedding are possible:
graded bedding, (If the particle size decreases upward, the bed is said to be normally graded; if the particle size increases upward, the bed is said to be reversely graded or inversely graded)
The following lamination are following:
Convolute lamination (characteristic of beds of fine sand, up to a meter thick, deposited rapidly by such events as turbidity currents )
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