Sedimentary Rocks Flashcards
What is a sediment
A collection of loose earth material (rocks, minerals, soil, fossils)
What are the different ways sediment can form? (4)
- When an older larger rock breaks into smaller pieces
- When a rock reacts with air or water and forms new minerals
- When a mineral dissolves in water and reprecipitates somewhere else
- When minerals dissolve in water and an animal extracts the ions to produce a shell
What is weathering
Describes the processes used to create sediments
What are the different types of weathering (2) and describe both
- Physical weather, breaking large rocks into smaller rocks
- chemical weathering, altering rocks or minerals with air or water producing new minerals and dissolved elements and compounds
Two commons types of sediment and what is there texture
- Clastic and has a clastic texture
- Chemical and has a crystalline texture
What is biogenic sediment and what type of sediment is it
sediment produced through biological activity and is a chemical sediment
What are the types of clastic sediments (2) and what does each mean
- Siliclastic, meaning it doesn’t come from dead things
- Bioclastic, meaning it comes from dead things
What is weathering and erosion, how do they differ
Weathering is how sediment is formed and erosion is how the sediment is picked up and transported
What are the agents for erosion (4)
- Air
- Gravity
- Ice
- Water
Clastic sediments are deposited when there is a drop in ______ of the medium in which it is traveling
Velocity
What are the main depositional environments (3)
- Continental
- Coastal
- Marine
What is the Hjulström diagram and what does it describe
It predicts at a specific velocity what size grains can be transported or entrained
What is the difference between entrainment and transportation
In entrainment, the sediment is fully suspended in the water and doesn’t touch the bottom. Whereas, in transportation the sediment is being pulled along with the current but is being dragged/bouncing along the bottom
In the Hjulström diagram it shows that clay is harder to entrain than grains that are much larger, why is that?
Because some clay is platy and the inter-particle forces hold the plates together (van der Waals and electrostatic forces)
What are the continental dispositional environments (6)
- Lake
- Desert
- Wetland
- Alluvian fan
- River
- Glacier
What are the coastal dispositional environments (5)
- Beach
- Delta
- Carbonate platform
- Barrier island
- Tidal wetland
What are the marine dispositional environments (2)
- Continental shelf
- Abyssal plain
What is a primary sedimentary structure and what are they (6) briefly explain each
Primary sedimentary structures are structures in a rock that was created at deposition
1. Stratas (roughly horizontal layers of sediment that have accumulated over time
2. Bed grading (a bed of sediment that is sorted by grain size, there are two types normal and reverse grading)
3. Cross-bedding (a bed that doesn’t run horizontally caused by ripples and dunes)
4. Ripples (ripples in the sediment caused by water running over the sediments, there are two types symmetrical and asymmetrical)
5. Imbricated pebbles (form when flat pebbles overlap because flowing water in rivers pushes over them causing them to point downstream)
6. Sole marks (grooves and indents that form either as an object is dragged across by a current, or caused by back-currents
What is a secondary sedimentary structure and what are they (3) brief explain each
A secondary sedimentary structure is a structure that forms after deposition
1. Mudcracks (when the water dries up causing the clay to contract)
2. Bioturbation (a result of animals burrowing into the ground)
3. Soft sediment deformation (occurs when sediment is loaded onto waterlogged sediments and compression may cause the water to squeeze out deforming the horizontal bedding)
What is lithification
Describes processes of turning sediment to stone
What are the types of lithification (2)
- Burial (due to burial)
- Cementation (precipitation of chemical sediments between clasts)
What are sedimentary rock types based on (2)
- Texture (clastic or crystalline)
- Composition (type of sediments its made of)
What are the types of sedimentary rocks)
- Siliciclastic rocks
- Chemical sedimentary rocks
- Bioclastic rocks
What are siliciclastic sedimentary rocks are distinguished by (2)
- Grain size and shape
- In sandstone, also identify grain type (relative proportion of quartz, feldspar, lithics and clay)
What are the types of siliciclastic sedimentary rocks from largest to smallest grain size (4)
- Breccia or conglomerate
- Sandstone
- Siltstone
- Shale or mudstone
Chemical sedimentary rocks are distinguished by (1)
Crystal type
What are the types of chemical sedimentary rocks (3)
- Travertine (non-biogenic carbonate)
- Rock salt
- Chert (microcrystalline quartz)
Bioclastic sedimentary rocks are distinguished by (2)
- Grain size and shape
- Grain type (chemical sediments like shells, or organic sediments like plants)
What are the types of bioclastic sedimentary rocks (4)
- Coquina (macroscopic shells)
- Chalk (microscopic shells)
- Chert (microcrystalline quartz)
- Coal (Plants)
