Lesson 8; Sediments and Sedimentary Rocks Flashcards
What are the differences between clastic, chemical, and biochemical sedimentary rocks?
Clastic/Detrital: Form from the breakdown of preexisting rock into smaller sediment
Chemical: Form from precipitated material that was once in solution (ions)
Biochemical: Precipitated first in the tissues of organisms, then deposited when the organism dies.
What is the Udden-Wentworth Grain Size Scale?
Determines how grain sizes are classified as gravel, sand, silt, or clay.
What are the 5 steps of clastic sedimentary rock formation?
- Weathering (Physical and Chemical)
- Erosion
- Transportation by gravity, wind, water, or ice
- Deposition
- Burial and Litification
Compare Arenite and Wacke.
arenite: clean sandstone (less than 15% slit and clay
wacke: sandstone with more than 15% slit and/or clay
Give some examples of clastic sedimentary rocks. (6)
- Conglomerate - abundant course-grain clasts, rounded, form in high-energy environments, and poorly sorted
- Breccia - abundant course-grain clasts, angular, travel a shorter distance, and poorly sorted
- Sandstone - forms in various environments, classified on the basis of texture and composition
- Mudrock/shale - brittle and forms gentle slopes; gradual settling of sediments in quiet water environments
- Slitstone - semi-quiet depositional environments, can be coarse or fine
Give some examples of Biochemical sedimentary rocks. (5)
- Fossiliferous limestone - Calcite precipitated by organisms into the form of shell/skeletal structure, accumulation of skeletal remains, very common in sedimentary rocks
- Coquina - composed of cemented fragments of shell material
- Chalk - soft, white, porous sedimentary rock, deep marine conditions from the gradual accumulation of tiny coccoliths shed from microorganisms coccolithophores
- Biochemical chert - tiny silica-secreting planktonic organisms accumulate on the seafloor.
- Coal - made from organic carbon, the remains of fossil plant matter.
Give some examples of chemical sedimentary rocks. (6)
- Travertine - groundwater containing dissolved calcium and bicarbonate ions can precipitate calcite
- Tufa - highly porous travertine that often forms from cooler water
- Oolitic limestone - composed of ooids in shallow marine water
- Dolostone - similar to limestone, but contains Mg in addition to Ca
- Evaporites - produce salt deposits as the concentration of solids increases due to water loss by evaporation.
- Chemical Chert - dissolved silica precipitates
What are the depositional environments of sedimentary rocks?
a geographic setting where sediment is accumulating
Three broad categories:
1. Continental
2. Transitional
3. Marine
What are the sedimentary structures? (4)
strata - layers of sedimentary rocks
Graded beds - sediment is deposited from a waning current
Cross-bedding - forms when sediment come to rest at an angle
Mud cracks - form when clay-rich sediments found in muds dry and shrink
The most abundant sedimentary rocks are _____.
Mudrocks/shales
A clay-sized sedimentary particle measures:
less than 1/256 mm
if an aggregate of sediment consists of particles that are all about the same size it is said to be:
well sorted
How does breccia differ from conglomerate?
Particles are more angular in breccia
____ forms under reasonably deep marine conditions from the gradual accumulation of minute calcite plates (coccoliths) shed from micro-organisms called coccolithophores.
Chalk
Which is best classified as a biochemical (organic) sedimentary rock?
a. Travertine that forms when calcium carbonate
precipitates from water flowing through a cave
b. Halite that forms when seawater evaporates
c. Oolitic limestone that forms when calcite precipitates in
spherical layers around a central fragment
d. Fossilferous limestone that is made of calcite extracted from seawater by marine organisms.
d. Fossilferous limestone that is made of calcite extracted from seawater by marine organisms
