1. You find a sediment that is well rounded, well sorted and the particles are s
ID: 153971 • Letter: 1
Question
1. You find a sediment that is well rounded, well sorted and the particles are small What is the mode of transport? (water or ice?) What is the distance from source? (near/medium/far) What is the energy of depositional environment? (high/low) 3 pts 2. You find a sediment that is poorly sorted, angular. What transported the sediment? 1 pt 3. What are three clues you could observe in a sedimentary rock that would indicate it was formed on land? 3 pts 4. Which image below is a nonconformity, disconformity, and angular unconformity? 3 ptsExplanation / Answer
1. a. Water.
Due to abrasion and hydraulic plucking water, water erodes the rocks and carry the materials with it. During transportation, abrasion (collision of the boulders, fragments with the bedrock and wall-rocks) and attrition (collision of the the fragments during transport) of materials carried by river takes place. Due to this, the particles becomes smaller and roundness increases of the particles. After a long distance, water deposits the fine grained sediment with higher sorting (sediments with similar grain size), higher roundness.
b. Far
When the sediment is fine grained, well sorted and well rounded, it means that the sediment is carried by river to a long distance because during this time, abrasion and attrition took place which reduces the size of particles and increases the roundness of particles.
c. Low.
Energy at the depositional environment is low. The energy of the river at the time of deposition is so low that it cannot carry the fine grains/particles further downstream and water flow become sluggish enough to deposit the sediment carried by it.
2. Glacier but water can also deposit poorly sorted and angular sediments.
The sediments deposited by glacier is characteristically poorly sorted and angular. The glacier erodes the bedrock and wall rock and carry the sediment within it and then at the end of the glacier where it melts, the glacier deposits all of the sediment carried by it. Thus, ultimately a coarse grained, poorly sorted (a chaotic mixture of angular boulder and fragment of varied sizes and fine grained silt is deposited by glacier) glacial till is formed by glacier.
Water can also form a poorly sorted, angular sedimentary deposit at the alluvial fans of rivers. When a river flows from a mountain to flat plain it experiences an abrupt slope break and due to which most of the sediments carried by the river is deposited (without much transportation). This results in formation of a poorly sorted, angular conglomerates in the alluvial fan.
3. Three clues-
a). Texture- Most of the sedimentary rocks formed on land are comprised of clastic texture. Clasts are broken fragments of rock which are physically transported by river. The clastic texture is characterised by Framework (which constitute the coarse grains of quartz, feldspar, rock fragments etc) and Pores (within these pores fine siliciclastic matrix or nonclastic cement are deposited).
b). Composition- Most of the clastic sedimentary rocks are siliciclastic rocks. Important minerals are quartz, feldspar and rock/lithic fragments are of granite, chert etc. Mud forms the matrix and calcite genrally forms the cement in pores.
c). Structure- The sediments during deposition forms various sedimentary structure like parting lineation on flat beds formed by high energy environment, cross-beds, ripple marks etc.
4.
A = Angular Unconformity.
In Angular Unconformity, the tilted beds or folded beds are overlain by flat horizontal beds and erosional surface exist between the two representing a period of non-deposition.
B= Disconformity.
In Disconformity, there is a erosional surface (representing a period of non-deposition) occur between older horizontal beds below and younger horizontal beds above the erosional surface.
C= Nonconformity.
In Nonconformity, a igneous body or a body of metamorphic rock is overlain by flat horizontal beds and an erosional surface (representing a period of non-deposition) seperates the igneous/metamorphic rock from the flat horizontal beds lying above it.
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