Sediments and Sedimentary Rocks Chapter 5. Concepts you will need to know for the exams. Weathering Erosion Transportation Sorting Angularity Sedimentary environments, Cross-bedding (sedimentary structures) Bioturbation, bedding sequences, diagenesis
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Erosion includes BOTH weathering and transportation
Sedimentary rocks are typically layered, (although layering is not diagnostic of only sedimentary rocks)
A sedimentary environment is a geographic location that has a peculiar combination of geological processes
“The different (sedimentary) rocks (types) were formed beside each other in space, but in a crustal profile we see them lying on top of each other….”
are successions of rock ( in a vertical profile) that help geologists work out the past environment
If deposition is the dominant process, e.g., offshore Lousiana then rocks are in the process of being formed:
(1) compaction = volume loss (mechanical squeezing)
and is accompanied by dewatering (= water loss) (by chemical or physical means)
(2) changes in mineral composition (chemical process with heat and or fluids)
(3) cementation (physical)
If a sediment eventually becomes a rock we say it is lithified.
Sorting is a measure of how similar grain sizes are within a sediment or rock and tells us about the relative strength of the current before it dropped (deposited) it cargo.
(3) Angularity or roundness (antonym) is a measure of the distance of transportation
Cross-bedding: sets of bedded material within rock layers that are inclined at angles as large as 35 degrees from the horizontal. These latter indicate wind-blown conditions in either a desert or a beach.
Fossil example of the past activity of organisms mixing sediment --- an example of fossil BIOTURBATION
For clastic sedimentary rocks there is a classification scheme based on the SIZE of their clasts, (or rock fragments) that comprise them.
>=1.8 km/hr (strong currents)