Geology: Sedimentary Rocks
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Describe the abundance of sedimentary rock and note why they are important?
Sedimentary Rocks contain evidence of past environments.
Coal is a sedimentary rock that provides an economic importance.
List/describe the processes involved in diagenesis.
Sediments are deposited and buried at shallow depths in the Earth's crust.
- Lithification occurs:
- Compaction - squeezes out water
- Cementation - Precipitation or addition of new minerals cements sediment particles
List/briefly describe the 3 general compositional types of sedimentary rocks.
Siliciclastic: composed of mineral particles formed by the weathering of silicate rocks.
Chemical: formed by the precipitation of dissolved material of chemical weathering
Biochemical: formed from mineral precipitation by organisms
List minerals commonly found in sedimentary rocks.
- Clay Minerals
- Shale(most common - made from compacted mud)
What is the texture of siliciclastic rocks and what texture features are used to identify these rocks? Give examples.
- Grain Sizes
- Grain Shape
- Well Rounded
- Grain Sorting
- Well Sorted
- Moderately Sorted
- Poorly Sorted
List/briefly describe the siliciclastic rocks we covered.
How does the velocity of wind/water currents affect sediment deposition?
What is the most common sedimentary rock?
Explain how chemical sedimentary rocks are formed.
Formed by the precipitation of dissolved material of chemical weathering
Give examples of chemical rocks and note minerals present in each.
- Limestone - Calcite
- Rock Gypsum - Gypsum
- Rock Salt - Halite
- Chert - Quartz
- Dolostone - Dolomite
Explain how biochemical sedimentary rocks are formed.
Formed from mineral precipitation by organisms
Give examples of biochemical rocks and note minerals present in each.
- Limestone - Calcite
- Chert - Microcrystalline Quartz
List/ describe several specific sedimentary environments and note the specific rocks formed in each.
- Built around rivers, lakes, deserts, glacial deposits, and alluvial fans
- Deltas, Beaches, Swamps, Bays
Give examples of how can we use sedimentary rocks to deduce past environmental conditions.
List, briefly describe, and discuss the importance of sedimentary structures (i.e. how can they be used to deduce transport medium or environmental conditions).
Cross-bedding - beds deposited by wind or water layered down at an angle
Graded-bedding - deep-sea sediments deposited by turbidity currents with particle sizes becoming finer upwards
Ripples - small ridges of sand or silt formed by water or wind currents
Mud Cracks - evaporated water leaving behind solid mud
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