ch05 sedimentary rocks online notes

Concepts you will need to know for the • Cross-bedding sedimentary structures • Bioturbation, bedding sequences, diagenesis • • Classes of sediments and sedimentary rock: • -based on gra

Sediments and Sedimentary

Rocks Chapter 5

Concepts you will need to know for the

• 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")

sedimentary rock cycle

•e.g (1) Mountains => weathering and/or

erosion

•e.g., (2) Southern Louisiana =>

•e.g., (3) offshore Louisiana =>

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 =>

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

Sedimentary rocks are typically

layered, (although layering is not

diagnostic of only sedimentary rocks)

Lecture Outline

1 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 are successions of rock ( in

sequences -a verticsequences -al profile) thsequences -at 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., offshore Lousiana then rocks are in the

process of being formed:

(3) cementation (physical)cementation

If a sediment eventually becomes a rock we say it is lithified.lithified

DIAGENESIS

dewatering

DIAGENESIS

dewatering

Cementation &

mineral changes

DIAGENESIS

Lecture Outline

1 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

weathering and transport a

rock or sediment has experienced respectively

(1) Product composition

(2) Degree of sorting

•Sorting is a measure of Sorting how similar grain sizes how similarare 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 size

determines settling velocity.settling velocity

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

Lecture Outline

1 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

1 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

>=1.8 km/hr (strong currents)weak moderate

The End of Chapter 5