How do grain size and shape, sorting, sphericity, and angularity change as sedim
ID: 288054 • Letter: H
Question
How do grain size and shape, sorting, sphericity, and angularity change as sediments move downstream? 3. 4. Describe the two different kinds of chert. How are they similar? How are they different? 5. Do all chemical sedimentary rocks have the same composition? What conditions produce evaporites? How does dolostone differ from limestone, and how does dolostone form? What are cross beds, and how do they form? How can you read the current direction from cross 6. 7. beds? 8. Describe how a turbidity current forms and moves. How does it produce graded bedding?Explanation / Answer
3 - Grain size will slowly become smaller as we go downstream, it changes from angular to rounded, thus becoming more spherical and get well sorted.
4- There are two types of chert- Replacement and Biochemical chert.
There similarity is that both are made of cryptocrystalline quartz, i.e, grains of quartz that can be seen only through extremely magnifying electron microscope.
Difference is that biochemical is directly made of cryptocrystalline quartz while Replacement chert is made when cryptocrystalline quartz replaces the calcite crystal within limestone.
5- No all chemical sedimentary rocks don't have same composition, they are of four types.
Condition that produces Evaporates are huge volume of water like oceans and seas.
6-Dolostone contains the mineral dolomite that comprises of Calcium as well as Magnesium in equal quantity, while limestone only comprises of Calcium carbonate.
Dolostone is formed due to reaction of Calcite to the groundwater magnesium.
7- Cross bed are the bedding planes that are inclined to some angle to the horizontal beds and they form due to the downstream migration of dunes or ripples.
The orientation of the bed indicates the wind direction during the time of deposition.
8- Turbidity current forms due to any tectonic activity and moves due to the presence of mud and sand on the continental shelf that are loosened by earthquake like activities.
When it moves down the slope it let the coarser grain to settle first and then finer at last , thus making a graded bedding pattern.
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