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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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concepts you will need to know for the exams
Concepts you will need to know for the exams
  • Weathering
  • Erosion
  • Transportation
  • Sorting
  • Angularity
  • Sedimentary environments,
  • Cross-bedding (sedimentary structures)
  • Bioturbation, bedding sequences, diagenesis
  • Classes of sediments and sedimentary rock:
  • -based on grain size
  • -based on chemical composition, e.g., carbonate rocks ("carbonates") and evaporitic rocks ("evaporites")
slide3

Lecture Outline

  • Sedimentary rocks
  • 2. Your sedimentary environment and Burial and diagenesis
  • 3. Interpretation of clastic texture
  • 4. Sedimentary structures
  • 5. Sedimentary Rock classification
1 sedimentary rocks
1. Sedimentary Rocks
  • Cover most of the land surface and seafloor
  • Your physical geography determines the dominant process at work in the sedimentary rock cycle
  • e.g. (1) Mountains => weathering and/or erosion
  • e.g., (2) Southern Louisiana =>
  • e.g., (3) offshore Louisiana =>
1 sedimentary rocks5
1. Sedimentary Rocks
  • Cover most of the land surface and seafloor
  • Your physical geography determines the dominant process at work in the sedimentary rock cycle
  • e.g. (1) Mountains => weathering and/or erosion
  • e.g., (2) Southern Louisiana => transportation or deposition or erosion
  • e.g., (3) offshore Louisiana =>
1 sedimentary rocks6
1. Sedimentary Rocks
  • Cover most of the land surface and seafloor
  • Your physical geography determines the dominant process at work in the sedimentary rock cycle
  • e.g. (1) Mountains => weathering and/or erosion
  • e.g., (2) Southern Louisiana => transportation or deposition or erosion
  • e.g., (3) offshore Louisiana => erosion or sedimentation
slide7

erosion

weathering

transportation

Erosion includes BOTH weathering and transportation

slide8

Sedimentary rocks are typically layered, (although layering is not diagnostic of only sedimentary rocks)

slide9

Lecture Outline

  • Sedimentary rocks; surface processes
  • 2. Your sedimentary environment and Burial and diagenesis
  • 3. Interpretation of clastic texture
  • 4. Sedimentary structures
  • 5. Sedimentary Rock classification
slide10

A sedimentary environment is a geographic location that has a peculiar combination of geological processes

walther s rule 1894

Walther’s Rule (1894)

“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….”

slide13

Bedding sequences---

are successions of rock ( in a vertical profile) that help geologists work out the past environment

where do you live
Where do you live?
  • What dominant sedimentary process is at work where you live?
slide17

If deposition is the dominant process, e.g., offshore Lousiana then rocks are in the process of being formed:

Diagnesis includes

(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.

slide21

DIAGENESIS

compaction

slide22

DIAGENESIS

compaction

dewatering

slide23

DIAGENESIS

compaction

dewatering

Cementation &

mineral changes

slide24

Lecture Outline

  • Sedimentary rocks; surface processes
  • 2. Your sedimentary environment and Burial and diagenesis
  • 3. Interpretation of clastic texture
  • 4. Sedimentary structures
  • 5. Chemical and biological classification
slide25
Geological FUZZY rulesfor determining degree of weathering and transport a rock or sediment has experienced respectively
slide28

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.

  • In a current of water or air, the larger and denser grains fall faster than the smaller grains. That is, for the same density, size determines settling velocity.
slide30

Lecture Outline

  • Sedimentary rocks; surface processes
  • 2. Your sedimentary environment and Burial and diagenesis
  • 3. Interpretation of clastic texture
  • 4. Sedimentary structures
  • 5. Chemical and biological classification
cross bedding
Cross-bedding

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.

slide37

Fossil example of the past activity of organisms mixing sediment --- an example of fossil BIOTURBATION

slide38

Lecture Outline

  • Sedimentary rocks; surface processes
  • 2. Your sedimentary environment and Burial and diagenesis
  • 3. Interpretation of clastic texture
  • 4. Sedimentary structures
  • 5. Sedimentary Rock classification
three types of sedimentary rocks
Three types of sedimentary Rocks
  • Clastic
  • Biochemical
  • Chemical
major classes of sediments and sedimentary rocks
Major Classes of sediments and sedimentary rocks

For clastic sedimentary rocks there is a classification scheme based on the SIZE of their clasts, (or rock fragments) that comprise them.

slide41

Clst size indicates ancient relative current velocity

weak

moderate

>=1.8 km/hr (strong currents)

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