15 Questions
What is the primary difference between detrital and chemical sedimentary rocks?
The way they are transported and deposited
What is the term for the process of creating both detrital and chemical sedimentary rocks?
Lithification
What is the primary cause of compaction in the formation of sedimentary rocks?
The weight of overlying layers
What is the role of minerals in the cementation process?
They precipitate in the pore spaces to form cement
What is the typical order of the lithification process?
Deposition, compaction, cementation
What is the term for the texture or pattern retained in a sedimentary rock that was formed by the process that deposited the original sediment?
Depositional feature
What type of rocks are formed from sediment, or detritus shed from pre-existing rocks?
Detrital sedimentary rocks
What determines the texture of a detrital sedimentary rock?
Grain size, grain sorting, and grain roundness
What is the term for the uniformity of grain size in a detrital sedimentary rock?
Grain sorting
What is the significance of the texture and composition of a detrital sedimentary rock?
It is the key to understanding the processes that deposited the sediments
What happens to the river's flow and energy when it exits the mountains?
It decreases, causing it to deposit large grains and transport smaller ones
What is the characteristic of the sedimentary rock formed from the remaining sediment deposited by the river when it meets the ocean?
Well-sorted, well-rounded particles
What is the primary difference between conglomerate and breccia sedimentary rocks?
The shape of the particles they contain
What is the process by which organic chemical sedimentary rocks are formed?
Organisms pulling compounds out of solution to create their shells or skeletal structures
What is the characteristic of micritic limestone formed in the ocean?
It has a very uniform composition
Study Notes
Sedimentary Rocks
- Sedimentary rocks are made of different components transported and deposited on the earth's surface.
Detrital vs Chemical Rocks
- Detrital or clastic sedimentary rocks form from the transportation and deposition of sediment and rock fragments.
- Chemical sedimentary rocks form from the transportation and precipitation of ions in a solution.
Lithification Process
- Lithification is the process of creating sedimentary rocks, containing three key steps: deposition, compaction, and cementation.
- Deposition: sediment and rock fragments are transported and deposited in a new location.
- Compaction: sediment is compressed by the weight of overlying material, causing grains to stick together.
- Cementation: minerals from surrounding water fill in spaces between grains, holding them together.
Depositional Features
- Depositional features are textures or patterns preserved in sedimentary rocks, providing clues to their formation environments.
- Examples of depositional features: ripple marks, sand dune cross-beds, mud cracks, and fossils.
Detrital Sedimentary Rocks
- Detrital sedimentary rocks form from sediment or detritus shed from pre-existing rocks.
- Also known as clastic sedimentary rocks, made of fragments of past rocks.
- Formed through erosion, transportation, and deposition of rock fragments.
Texture and Composition of Detrital Rocks
- Texture determined by grain size, sorting, and roundness.
- Grain size: clay, silt, sand, pebble, cobble, and boulder.
- Grain sorting: uniformity of grain size in the rock.
- Grain roundness: angular, subangular, subrounded, rounded, and well-rounded.
- Composition: uniformity in the composition of the rock's grains.
Common Detrital Sedimentary Rocks
- Shale or claystone: made up of well-sorted, clay-sized particles.
- Siltstone: made up of well-sorted, silt-sized particles.
- Sandstone: made up of sand-sized particles.
- Conglomerate: contains particles larger than sand, grains are sub-angular to rounded and can be very poorly to well-sorted.
- Breccia: contains particles larger than sand, grains are angular to sub-angular and usually very poorly sorted.
Chemical Sedimentary Rocks
- Form from grains that precipitate out of a water solution through organic or inorganic processes.
- Organic chemical rocks: formed from ocean organisms that pull compounds out of solution to create shells or skeletal structures (e.g., limestone and chert).
- Inorganic chemical rocks: formed when ions become oversaturated in a solution and precipitate as particles or mineral grains (e.g., micritic limestone, evaporite minerals like halite, gypsum, and anhydrite).
Learn about the two sub-types of sedimentary rocks, detrital or clastic and chemical rocks, and how they are formed through transportation and deposition of sediment and rock fragments or ions in a solution.
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