Lecture 6

Question 1

What are sedimentary rocks the products of?

Answer 1

Mechanical and chemical weathering.

Question 2

What percentage of Earth’s outer 16 km do sedimentary rocks account for?

Answer 2

Sedimentary rocks account for about 5% (by volume).

Question 3

What do sedimentary rocks contain evidence of?

Answer 3

Past environments.

Question 4

What information can sedimentary rocks provide?

Answer 4

Information about sediment transport.

Question 5

What do sedimentary rocks commonly contain?

Answer 5

Fossils.

Question 6

Why are sedimentary rocks economically important?

Answer 6

Contain coal, petroleum, natural gas, and sources of iron, aluminum, manganese, fertilizer, and construction materials.

Question 7

What is diagenesis? (IMPORTANT)

Answer 7

All the chemical, physical, and biologic changes that occur after sediments are deposited, but prior to metamorphism.

Question 8

Where does diagenesis occur? (IMPORTANT)

Answer 8

In the upper few kilometers of Earth’s crust at temperatures generally less than 200˚C.

Question 9

What does diagenesis include? (IMPORTANT)

Answer 9

Re-crystallization and lithification.

Question 10

What is lithification? (IMPORTANT)

Answer 10

The transformation of unconsolidated sediments into solid sedimentary rock through compaction and cementation.

Question 11

What are natural cements in lithification? (IMPORTANT)

Answer 11

Calcite, silica, and iron oxide.

Question 12

What is an environment of deposition?

Answer 12

A geographic setting where sediment is accumulating.

Question 13

What determines the nature of sediment in a depositional environment?

Answer 13

• Geographic setting
• Environmental conditions (grain size/shape/color)

Question 14

What principle is applied when studying present environments to understand ancient rocks?

Answer 14

Uniformitarianism.

Question 15

What is re-crystallization? (IMPORTANT)

Answer 15

Development of more stable minerals from less stable ones

Question 16

What are the three types of sedimentary environments?

Answer 16

Continental, transitional, and marine.

Question 17

What dominates sedimentary processes in continental environments?

Answer 17

Erosion and deposition associated with streams.

Question 18

What features can form in transitional environments?

Answer 18

• Tidal flats (quiet waters)
• beaches
• spits
• bars
• barrier islands
• lagoons,
• deltas (high energy waters).

Question 19

What types of sediments accumulate in shallow marine environments?

Answer 19

• Land-derived sediment
• skeletal debris
• coral reef accumulation.

Question 20

What characterizes deep marine environments?

Answer 20

• Tiny skeletons of organisms raining onto the seafloor
• Strong turbidity currents moving material.

Question 21

What can form lagoons ?

Answer 21

Sheltered, brackish water conditions

Question 22

When deltas forms ?

Answer 22

River velocity slows at river/sea interface = sediment deposited.

Question 23

What do lateral units of sedimentary rock reflect?

Answer 23

Changes in past environments.

Question 24

What causes the gradual transition between adjacent facies?

Answer 24

Sediments often accumulate adjacent to one another simultaneously, leading to merging.

Question 25

What are the three principal sources of sediment?

Answer 25

1) Mechanical/chemical weathering of existing rock (detrital sedimentary rocks). 2) Soluble material produced by chemical weathering (chemical sedimentary rocks). 3) Organic matter from once-living organisms (rich in carbon, e.g., plant remains in a swamp).

Question 26

What are the chief constituents of detrital sedimentary rocks?

Answer 26

Clay minerals, quartz, feldspars, and micas (referred to as siliciclastic sediment).

Question 27

What is the primary basis for distinguishing among types of detrital rocks?

Answer 27

Particle size, which also provides information about the depositional environment.

Question 28

How does current strength affect particle size?

Answer 28

Stronger currents carry larger particles.

Question 29

What particle size characterizes shale and mudrocks?

Answer 29

Clay to silt-sized particles.

Question 30

How does shale form?

Answer 30

Through gradual settling in quiet water, forming thin layers called laminae.

Question 31

What distinguishes shale, siltstone, and mudstone?

Answer 31

Shale exhibits fissility (splits into thin layers), siltstone does not, and mudstone breaks into chunks.

Question 32

What is the most common type of detrital sedimentary rock?

Answer 32

Shale.

Question 33

What particle size characterizes sandstone?

Answer 33

Sand-sized particles.

Question 34

How is sorting in sandstone described?

Answer 34

The degree of similarity in particle size, ranging from well-sorted to poorly sorted.

Question 35

What are the types of sandstone?

Answer 35

Quartz sandstone (most dominant), arkose, and wacke.

Question 36

What characterizes conglomerate rocks?

Answer 36

Rounded pebbles and cobbles of varying sizes.

Question 37

What does angular gravel indicate in breccia?

Answer 37

That the gravel did not travel far.

Question 38

How are chemical sedimentary rocks formed?

Answer 38

From chemical sediments carried in solution to lakes or seas.

Question 39

What is the most abundant chemical sedimentary rock?

Answer 39

Limestone.

Question 40

What are the types of limestone?

Answer 40

- Organic: Coral reefs, coquina, fossiliferous limestone, chalk. - Inorganic: Travertine (caves), oolitic limestone (spherical grains).

Question 41

What is dolostone composed of?

Answer 41

Calcium-magnesium carbonate (dolomite).

Question 42

What is chert composed of?

Answer 42

Microcrystalline silica (SiO2), with varieties including flint, jasper, and banded agate.

Question 43

What are evaporites?

Answer 43

Chemical precipitates formed by evaporation, including rock salt, gypsum, and sylvite.

Question 44

What are the types of coal in order of increasing formation temperature and pressure?

Answer 44

- Peat (partial decomposition in O2-poor environment). - Lignite (soft brown coal). - Bituminous coal (harder, blacker coal). - Anthracite (very hard, shiny black metamorphosed coal).

Question 45

Into what two groups are sedimentary rocks classified?

Answer 45

Detrital and chemical sedimentary rocks.

Question 46

What are the major texture subdivisions of sedimentary rocks?

Answer 46

- Clastic: Broken fragments and particles. - Bioclastic: Rocks with skeletal remains. - Non-clastic: Interlocking crystals, resembling igneous rocks.

Question 47

What do sedimentary structures provide?

Answer 47

Information useful in interpreting Earth’s history.

Question 48

What is bedding in sedimentary rocks?

Answer 48

Layers of sedimentary rock separated by bedding planes.

Question 49

What is cross-bedding?

Answer 49

Inclined layers of sedimentary rock.

Question 50

What is graded bedding?

Answer 50

Rapid deposition from water where coarse material settles first.

Question 51

What causes mud cracks?

Answer 51

Shrinkage upon exposure to air.

Question 52

What are ripple marks?

Answer 52

Small waves of sand formed by moving water.

Question 53

What is hummocky cross-stratification (HCS)?

Answer 53

Low-angle laminations with undulations formed by storms.