Lesson 3: Grain Shape and Fabric

Question 1

encompasses all aspects of the external morphology of particles

Answer 1

grain shape

Question 2

what are the 3 aspects of a particles external morphology

Answer 2

1. form
2. roundedness
3. surface texture

Question 3

refers to the overall morphology of the of the particles, 3D measure

Answer 3

form

Question 4

refers to the absence of sharp edges of the individual grains, commonly measured in 2D

Answer 4

roundedness

Question 5

refers to the overall shape of the particles approaching the shape of a sphere

Answer 5

sphericity

Question 6

refers to microrelief features on grains

Answer 6

surface texture

Question 7

example of surface texture features

Answer 7

scratches, pits, rills

Question 8

explain the implication of surface texture

Answer 8

these microrelief features usually tell much about the transportation history of sediments.

Question 9

what can change the texture of grains

Answer 9

• abrasion during transport
• cementation or diagenesis can change the form and roundness which ultimately affect surface texture

Question 10

explain the hierarchy of the 3 aspects of grain shape

Answer 10

1. form is first order
2. roundedness is superimposed on top making it 2nd order bc changes on form makes changes on roundedness
3. lastly surface texture is third order because it gets affected by both form and roundedness, but of course keeping in mind that they are independent parameters

Question 11

significance of grain shape analysis

Answer 11

provenance studies and environmental studies

Question 12

what are the 4 factors to be considered when interpreting the provenance of sediments based on shape

Answer 12

1. source of the parent rock
2. the erosion and transport mechanisms
3. the depositional setting and process (which affects the fabric)
4. the physical and chemical conditions of burial environment

Question 13

what are the 2 things to be considered when trying to study the parent rock when studying sediment sources

Answer 13

1. mineralogy
2. petrology

Question 14

when talking about grain shape, what type of sedimentary particles is this usually applied to?

Answer 14

siliciclastic particles

Question 15

significance of grain shapes that examines where it came from as well as the transport history

Answer 15

provenance studies

Question 16

significance of grain shape that examines the history of the end depositional environment

Answer 16

environmental studies

Question 17

explain how the depositional setting and processes affect fabric

Answer 17

even in depositional environments, there are still a lot of processes that could rework it, ultimately affecting the fabric of sedimentary rocks

Question 18

what are the physical and chemical conditions during burial diagenesis

Answer 18

this is when lithification occurs, the rocks are exposed in a half-baked metamorphic environment. still high pressure with fluids

Question 19

explain how sediment sources and parent rocks affect sediments

Answer 19

different tributaries have different types of rocks that produce different kinds of sediments, even the same mineral, but itf different environments, it could still be characterized

that’s why if they end up in the same depositional environment (mixing). meaning by examining particles in the same dep envi, you can still possibly identify the location of the parent rocks.

Question 20

what are the 3 main influences of erosional and transportation processes

Answer 20

1. sediment size and density
2. abrasion during transport
3. transportation agent

Question 21

what do we mean by depositional setting and processes

Answer 21

we mean the residual velocity from the transport agent orr the recurrence of a transport agent
-sorting
-reworking

Question 22

what do we mean by environmental studies of grain shape analysis

Answer 22

we mean the post lithification and diagenesis, because sedimentary rocks can be used for fingerprinting paleoenvironments

Question 23

how does sediment size affect transportation processes

Answer 23

well actually, depending on the current, the type of transportation agent and also the mineralogy and petrology of the rocks itself, but generally the heavier sediments are transported by stronger currents

Question 24

how does abrasion affect transport process

Answer 24

abrasion in suspended vs saltation, esp if hard minerals bounce, abrasion could round them out

Question 25

explain how type of transport agent can influence erosional and transportational process

Answer 25

the stronger agent can carry heavier sediments. ex. wind vs water in desert environments, water carries larger sized.

Question 26

what is the more significant agent in desert environments, water vs wind?

Answer 26

water, wind is prevalent but weak

Question 27

explain how depositional setting and processes affect sediments

Answer 27

-larger sediments upstream can get reworked because of recurrence of transpo agents, thus they become oriented to the direction of the current

-in beaches, finer sediments can get reworked bc of backwash and swash, rounding the sediments

thus reworking bc of transpo agent and depositional environment setting as well as also interaction with other sediments

Question 28

explain how sorting can tell the depositional environment

Answer 28

river
-upstream, high energy so bigger sized boulders
-downstream: finer
-delta: mixed because of meeting sa sea and river
-beach-finer bc of sea reworking

Question 29

explain environmental studies for grain shape analysis

Answer 29

tracing features tell much about the paleoenvironment, like fossils, and features that can reveal things about the depositional environement. ex. shell fossils, thus probs marine envi

Question 30

refers to the utilization of space among sediments, as well as the manner of arrangement or spacing of the solid particles

Answer 30

grain packing

Question 31

what are the 4 stages of maturity

Answer 31

immature, submature, mature, supermature

Question 32

describe immature grains based on clay content, sorting, roundedness and transport+reworking

Answer 32

more than 5% of clay, poorly sorted, poorly rounded, not undergone sufficient sediment transport and reworking

Question 33

describe submature grains based on clay content, sorting, roundedness and transport+reworking

Answer 33

low clay, not well sorted, not well rounded, undergone more transport and reworking

Question 34

describe mature grains based on clay content, sorting and roundedness

Answer 34

low clay, well sorted, not well rounded

Question 35

describe supermature grains based on clay content, sorting and roundedness

Answer 35

no clay, well sorted, well rounded

Question 36

3 things to consider about grain packing

Answer 36

1. Sediment size and sorting distribution
2. Particle shape and orientation
3. Degree of Diagenesis

Question 37

particle orientation may be a factor of 5 variables, what are they

Answer 37

1. nature of flow
2. bed slopes
3. flow velocity
4. particle size and shape
5. packing velocity

Question 38

explain the relationship of sorting and reworking

Answer 38

if the particles have been sufficiently reworked, they’d get well sorted

Question 39

5 kinds of packing

Answer 39

1. floating
2. point
3. long
4. concavo-convex
5. sutured

Question 40

what is the difference between tight packing in igneous, sedimentary and metamorphic rocks

Answer 40

sedimentary -in contact, no transition
metamorphic -with transition
igneous -individual crystals

Question 41

relationship of roundedness to transport velocity

Answer 41

the more angular, the more surface area, faster to travel

Question 42

can reworking happen in quieter depositional areas

Answer 42

yes, biological tho.