SEDIMENTARY

Question 1

What mode of deposition causes clay-y fine-grained sediments?

Answer 1

Long distance transportation and/or deposition in calm conditions

Question 2

What mode of deposition tends to cause coarse grained sediments?

Answer 2

Shorter transportation and/or deposition in turbulent conditions

Question 3

What is the difference between a cement and a matrix?

Answer 3

cements are later precipitated crystals, matrices are originally deposited mud

Question 4

Describe an immature sedimentary rock:

Answer 4

• Wide range of clast types
• Wide range of grain sizes, some often large.
• Very angular fragments

Question 5

Describe a mature sedimentary rock:

Answer 5

• Narrow range of clast types
• Narrow range of grain sizes; mostly small
• Rounded fragments/grains

Question 6

what 3 factors increase with maturity?

Answer 6

sorting, rounding, sphericy

Question 7

Describe freeze thaw weathering

Answer 7

Water expands by 9 per cent on
freezing, so fractures filled with water are prized further apart each time the water freezes until the fragment breaks off.

Question 8

Describe how heating and cooling f rocks can cause weathering:

Answer 8

Heating and cooling of rocks in desert

regions causes minerals to expand and contract at different rates until the rock eventually fractures. Not proven.

Question 9

Carbonation

Answer 9

Rainwater containing carbon dioxide (CO2) from the air and soil reacts with carbonates to form soluble hydrogen carbonates.

Question 10

Hydrolysis

Answer 10

Water reacts with minerals,particularly silicate minerals like feldspars,breaking them down.

Question 11

Hydration

Answer 11

The addition of water molecules to the atomic structures of minerals

Question 12

Oxidation

Answer 12

The addition of oxygen to the atomic structures of minerals or a similar chemical
change

Question 13

How does bacteria cause weathering?

Answer 13

Minerals decompose much more
quickly in the presence of bacteria; the
bacteria produce an acidic microenvironment
that allows them to remove elements directly
from minerals

Question 14

what do silicate rocks break down in to?

Answer 14

–quartz
–muscovite
–clay minerals
–soluble salts
–iron oxides
–resistant heavy minerals

Question 15

what is the best conditions for weathering?

Answer 15

warm humid climate

Question 16

what sedimentary rock is quartz most common in?

Answer 16

Sandstone

Question 17

why are feldspar less abundant in sedimentary rocks?

Answer 17

it is more easily decomposed

it has cleavage planes

Question 18

what does the presence of feldspar suggest?

Answer 18

low amounts of chemical weathering (i.e desert)

proximity to igneous source

Question 19

how are clays deposited?

Answer 19

suspension in water

Question 20

describe orthoquartzite:

Answer 20

-Pure quartz

Question 21

Describe arkoze

Answer 21

contains quartz and feldspar
f’spar are angular and may be twinned
may be orange due to orthoclase

Question 22

describe Greywake

Answer 22

Dark coloured, dense and well cemented

contains rock fragments, of dark mafic igneous rocks and clays.

Question 23

in what age are greywake most common?

Answer 23

Plagioclaisse

Question 24

in what environment is quartzite deposited?

Answer 24

–Very mature sediment: i.e. has had a lot of transport and weathering.
–Tends to be formed in a beach or desert setting

Question 25

what depositional environment is arkose typical of?

Answer 25

–Form in dry conditions as feldspar chemically weathers in wet
conditions.
–Often form close to granites from which the
f’spar is derived.

Question 26

In what environment is grywake depositioned?

Answer 26

–Mostly deep water: deposited from turbidity currents associated with tectonism in magmatic arc.

Question 27

Describe an aeolian sand

Answer 27

• pale fine sands
• well rounded well sorted
• wind-blasted and coated with heamotite
• may have f’spa
• large scale crossbeds
• few fossils (some bones and vertabrates)

Question 28

describe the process of abrasion

Answer 28

• pebbles colide together becoming smaller and more rounded

- Rivers with load scour away the bed and sides of the river.

Question 29

When is abrasion most effective?

Answer 29

at high speeds and if rock fragments are being carried

Question 30

describe rock corrosion and what is the best example of this?

Answer 30

Water dissolves certain minerals within the rock (solution). The best examples are limestones and evaporites

Question 31

What are the 3 ways loads can be transported by?

Answer 31

1) In solution
2) in suspension
3) by traction/saltation (when sand gravel and pebbles are temporarily lifted up by currents)

Question 32

where do pebbles occur?

Answer 32

high energy beaches

Question 33

where do clays occur?

Answer 33

lakes and deep water

Question 34

what minerals are present in fine fraction?

what minerals are present in coarse fraction?

Answer 34

• clays

- quartz and muscovite

Question 35

describe the process of flocculation

Answer 35

fine grains of clay gather together in water to form larger grains
larger grains sink to the bottom

Question 36

why and where does flocculation occur mostly?

Answer 36

sea water may cause flocculation, and is one of the reasons why sediments build up at deltas

Question 37

Precipitation:
what does it effect?
what conditions may be needed?

Answer 37

• salts and even silica

- raised salinity and higher temperature