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 Classes of sediments and sedimentary rock: -based on grain size -based on chemical composition, e.g., carbonate rocks ("carbonates") and evaporitic rocks ("evaporites")

Lecture Outline Sedimentary rocks 4. Sedimentary structures 2. Your sedimentary environment and Burial Diagenesis 3. Interpretation of clastic texture 4. Sedimentary structures 5. Sedimentary Rock classification

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 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 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

erosion weathering transportation Erosion includes BOTH weathering and transportation

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

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

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

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….”

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

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

If deposition is the dominant process, e. g 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.

DIAGENESIS compaction

DIAGENESIS compaction dewatering

DIAGENESIS compaction dewatering Cementation & mineral changes

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

Geological FUZZY rules for determining degree of weathering and transport a rock or sediment has experienced respectively

(1) Product composition

(2) Degree of sorting

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.

(3) Angularity or roundness (antonym) is a measure of the distance of transportation

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: 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.

2 directions of fluid movement

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

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 Clastic Biochemical Chemical

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.

Clst size indicates ancient relative current velocity weak moderate >=1.8 km/hr (strong currents)

The End of Chapter 5