(S1) Terrigenous Clastic Sediments: Gravel, Sand and Mud

Question 1

Define “detritus”

Answer 1

Clasts made of pre-existing rocks

Question 2

What is another name for detritus

Answer 2

Siliclastic Sediments

Question 3

Sandstones/Conglomerates make up __% of the sedimentary rocks in the geological records

Answer 3

20-25%

Question 4

Mudstone makes up __% of the sedimentary rocks in the geological record

Answer 4

60%

Question 5

How do we define the prefix of a conglomerate

Answer 5

The maximum size of clast found, eg pebble conglomerate

Question 6

What is the name of the grain-size scale used in sedstrat?

Answer 6

Wentworth Scale (Udden - Wentworth Grain-size Scale)

Question 7

What is the phi scale in the Wentworth scale?

Answer 7

A numerical representation, where Φ = -log2

Question 8

How many class devisions are there in the Wentworth Scale, and what are they?

Answer 8

Four: Gravel, Sand, Mud and Clay

Question 9

Why is -ve used on the phi scale?

Answer 9

Conventional to have grain-size on a graph decreasing from left to right

Question 10

Another name for consolidated gravel

Answer 10

Conglomerate, named according to dominant grain size

Question 11

What is a breccia?

Answer 11

Conglomerate with angular clasts

Question 12

What are the two forms of breccia?

Answer 12

Tectonic breccia and sedimentary breccia

Question 13

What is another name for a lithified mixture of rounded and angular clasts?

Answer 13

Breccio-conglomerate

Question 14

What is a monomict?

Answer 14

Gravel/Conglomerate made of all same material

Question 15

What is a polymict?

Answer 15

Gravel/Conglomerate made of many different types of material

Question 16

What is an oligomict?

Answer 16

Gravel/Conglomerate made of two or three different types of material

Question 17

How can we determine the source of the clasts in a conglomerate?

Answer 17

Comparison to surrounding bedrock

Question 18

What is the matrix?

Answer 18

Finer material in between clasts in a conglomerate

Question 19

What is a “sandy conglomerate” and a “muddy conglomerate”?

Answer 19

A conglomerate where >20% of the matrix is made of sand or mud respectively

Question 20

What is an “intra-formational conglomerate” and how does it form?

Answer 20

Clasts are same composition as matrix, formed from reworking of lithified sediment soon after deposition

Question 21

Define “clast supported” and “matrix supported”

Answer 21

Clast supported: clasts touching, matrix supported: clasts not touching

Question 22

In erosional processes, what kind of rocks form spheres?

Answer 22

Rocks with equally shaped fracture planes, which form cubic blocks, in turn eroding to spheres

Question 23

In erosional processes, what kind of rocks form oblate/discoid forms?

Answer 23

Lithologies which break into slabs, such as well bedded sandstone/limestone, clasts with one axis shorter than other two

Question 24

In erosional processes, what kind of rocks form rod/prolate forms?

Answer 24

Less common, from metamorphic rocks with strong linear fabrics

Question 25

In erosional processes, what kind of rocks form bladed?

Answer 25

Rocks with a mixture of strong linear fabrics and slab-like lithologies

Question 26

What is imbrication?

Answer 26

Where discoid clasts become preferentially orientated due to flow - e.g. dipping upstream

Question 27

What is paleoflow?

Answer 27

A bedform or indicator which gives an idea of which direction a sediment carrier (river, glacier etc) used to preferentially flow

Question 28

How does paleoflow differ in an elongated clast between glacial deposition and river deposition?

Answer 28

Glacial: long axis is parallel to flow River: long axis is perpendicular to flow

Question 29

What is an arenite?

Answer 29

Sandstone with less than 15% matrix

Question 30

What are detrital mineral grains?

Answer 30

Mineral grains from pre-existing rock broken down to sand-sized grains

Question 31

What are lithic fragments?

Answer 31

sand-sized pre-existing grains (Not Quartz or Feldspar)

Question 32

What is the most common mineral in sand/sandstone?

Answer 32

Quartz

Question 33

What mineral is absent from basic igneous?

Answer 33

Quartz

Question 34

What is the Moh's hardness of quartz?

Answer 34

7

Question 35

Why is the Moh's hardness of quartz relevant in sedstrat?

Answer 35

Due to hardness, found in abundance in the sedimentary record: remains in tact for long periods/distances

Question 36

Aside from it's physical hardness, what other property does quartz possess, and why is it relevant in sedstrat?

Answer 36

Resistance to chemical breakdown - stable at earths surface

Question 37

Aside from quartz, what other mineral is common in most igneous rocks?

Answer 37

Feldspar

Question 38

What two important properties does feldspar possess relevant to the sedimentary record?

Answer 38

More susceptible to chemical and physical breakdown than quartz

Question 39

Where is feldspar most likely to be found in the sedimentary record? (Two possibilities)

Answer 39

Where transportation pathway is short and chemical weathering is not too intense

Question 40

What significant mineral to the sedimentary record is platy in shape?

Answer 40

Mica

Question 41

How is mica often found in the sedimentary record and why?

Answer 41

In bands: it's platy shape means that the settling of grains takes longer

Question 42

Most sandstones contain __% heavy minerals with densities of __ g cm-3

Answer 42

<1%, 2.85 g cm-3

Question 43

How can heavy minerals be separated from other sediments in a sample?

Answer 43

Placed into a liquid with a similar density as the majority of the grains (2.6-2.7 g cm-3)

Question 44

Why is it so useful to determine heavy minerals in a sedimentary sample?

Answer 44

Usually characteristic of a particular province

Question 45

Give five examples of heavy minerals which could be found within a sedimentary sample

Answer 45

Zircon, Tourmaline, Rutile, Apatite, Garnet

Question 46

Give four examples of misc. minerals which could be found within a sedimentary sample

Answer 46

Olivine, Pyroxene, Amphibole, Oxides of Iron

Question 47

What feature does the remaining misc. minerals found within a sedimentary sample usually have?

Answer 47

Readiness to chemical breakdown

Question 48

Give an example of a particularly resistant lithic fragment

Answer 48

Chert

Question 49

Aside from specific identified minerals, what are the other four potential components of a sedimentary sample?

Answer 49

Lithic fragments, Biogenic material, Authigenic material and Matrix

Question 50

Give two examples of biogenic material that could be found within a sandstone sample

Answer 50

CaCO3 - Shells | Wood/Seeds preserved in Sandstone

Question 51

What is an authigenic material?

Answer 51

Crystallised minerals which grow in depositional environments

Question 52

Give two prominent examples of authigenic minerals

Answer 52

Calcium carbonate - in supersaturated conditions | Glauconite - green iron silicate in shallow marine environments

Question 53

What would the typical matrix grain-size be for a sand/sandstone?

Answer 53

Silt/Clay

Question 54

What is the difference between matrix and cement?

Answer 54

Matrix is deposited with the larger grains, where as cement is chemically precipitated after deposition

Question 55

What is a micaceous sandstone, and when is it used?

Answer 55

Mica rich sandstone

Question 56

What is a calcareous sandstone, and when is it used?

Answer 56

Calcium Carbonate rich sandstone

Question 57

What is a ferruginous sandstone, and when is it used?

Answer 57

Iron rich sandstone

Question 58

What is the name of the classification scheme used in full petrographic analysis of a sand sized sedimentary sample?

Answer 58

Pettijohn Classification Scheme

Question 59

What shape could be used to describe the Pettijohn Classification Scheme?

Answer 59

Toblerone plot

Question 60

What is the name of a cross section found within the Pettijohn Classification Scheme?

Answer 60

QFL triangle

Question 61

What are the two steps in using the Pettijohn Classification Scheme?

Answer 61

1. Determine relative QFL abundance | 2. Determine matrix %

Question 62

What is a "wacke"?

Answer 62

Matrix of 15-75%

Question 63

How is a "mudstone" officially recognised in petrographic analysis?

Answer 63

A matrix of >75% within a sandstone/sand sample

Question 64

What is a "greywacke"?

Answer 64

Another name for a Feldspathic Wacke/Lithic Wacke

Question 65

What is the technical definition of a claystone?

Answer 65

>2/3rd of particles are clay sized

Question 66

What is the technical definition of a siltstone?

Answer 66

Majority of particles silt sized

Question 67

What is the name for a rock which has a mixture of minuscule particle sizes?

Answer 67

Mudstone

Question 68

What is "fissility"?

Answer 68

A characteristic whereby a rock breaks predominantly in one plane

Question 69

Give an example of a fissile rock and the plane it usually breaks on

Answer 69

Shale - Parallel to bedding

Question 70

What is the difference between shale and slate?

Answer 70

Slate = metamorphic, breaks along the cleavage plane

Question 71

What is the most resistant mineral in silt/siltstone?

Answer 71

Quartz

Question 72

Aside from quartz, what other four minerals are often found in silt/siltstone?

Answer 72

Feldspar, Muscovite, Calcite, Iron Oxides

Question 73

What is "rock flour"?

Answer 73

Silt sized lithic fragments, usually from glacial erosion

Question 74

What type of energy environment is usually associated with silt/siltstone?

Answer 74

Low velocity/energy, still waters

Question 75

What grain size is loess usually associated with?

Answer 75

Silt/clay

Question 76

When in the geological record is loess usually most prominent?

Answer 76

Important during glacials

Question 77

Describe in one sentence how clay minerals form

Answer 77

Chemical products of feldspars and other silicates

Question 78

What is the name for the group of clay minerals with two layers?

Answer 78

Kandite Group

Question 79

What is the name for the group of clay minerals with three layers?

Answer 79

Smectite Group

Question 80

Under what conditions does Kaolinite usually form? (Environment, Bedrock lithologies)

Answer 80

Warm, humid environments where acidic waters leech bedrock lithologies such as granite

Question 81

Under what conditions does Montmorillonite usually form? (Environment, pH)

Answer 81

Moderate temperature conditions, neutral to alkaline pH or alkaline pH in arid conditions

Question 82

What clay group does Montmorillonite fall into?

Answer 82

Smectite Group

Question 83

What clay group does Kaolinite fall into?

Answer 83

Kandite Group

Question 84

What physical property does the Smectite Group have, and therefore what is another name for this group?

Answer 84

Swelling clays, due to their ability to absorb water within their structure

Question 85

Name the four most prominent clay types

Answer 85

Kaolinite, Montmorillonite, Illite, Chlorite

Question 86

Under what conditions does Illite usually form? (Environment, Leeching)

Answer 86

Temperate areas where leeching is limited

Question 87

Under what conditions does Chlorite usually form? (Groundwater, Environment)

Answer 87

Acidic groundwater conditions, arid climates

Question 88

What particular lithology does montmorillonite, illite and chlorite commonly form from?

Answer 88

Weathering of volcanic rocks, particularly volcanic glass

Question 89

What two properties make clay particles cohesive?

Answer 89

Electrostatic bonds between particles due to incomplete bonds, strong surface tension of smaller particles

Question 90

How does the cohesive property of clay lead to the formation of deltas?

Answer 90

1. Particles flocculate into smaller aggregates 2. Deposition is enhanced by saline and the fresh to saline transition 3. Cohesion keeps particles from becoming re-immobilised in regions of intermittent flow

Question 91

What are the five properties which define the texture of a terrigenous clastic rock

Answer 91

Clasts/Matrix, Sorting, Clast Roundedness (i.e. breccia), Clast Sphericity (i.e. parent feature, not feature of distance), Fabric (alignment)

Question 92

What is the main control of the shape of a pebble?

Answer 92

Shape of source bedrock, no amount of rounding will change fundamental directions

Question 93

What is the definition of "maturity" of a rock?

Answer 93

Extent of change compared to bedrock source

Question 94

Give an example where a sample may be compositionally immature but texturally mature?

Answer 94

Volcanic beach - unstable minerals still present in a high energy environment

Question 95

What are the properties of a texturally immature sandstone?

Answer 95

>15% mud (wacke)

Question 96

What are the properties of a texturally submature sandstone?

Answer 96

0.5)

Question 97

What are the properties of a texturally mature sandstone?

Answer 97

<0.5) | angular clasts

Question 98

What are the properties of a texturally supermature sandstone?

Answer 98

<0.5) | rounded clasts

Question 99

What does "labile" mean?

Answer 99

Less resistant

Question 100

Under what circumstances is a sandstone compositionally mature?

Answer 100

Is an arenite where the proportion of quartz is particularly high