L4: Sedimentary Classification

Question 1

Clastic rocks

Answer 1

Clastic rocks are composed of fragments, or clasts, of pre-existing minerals and rock. A clast is a fragment of geological detritus, chunks and smaller grains of rock broken off other rocks by physical weathering.

Question 2

5 Physical Parameters for describing sedimentary rocks

Answer 2

Grain size
Sorting
Roundness
Sphericity/Shape
Fabric/Texture

+ Composition, colour, organic content

Question 3

Sediment grain size classification scheme

Answer 3

Udden-Wentworth scale

Question 4

Silt

Answer 4

0.0039mm - 0.0625mm

Question 5

Clay

Answer 5

smaller than silt

<0.0039mm

Question 6

Sand

Answer 6

0.0625mm - 1mm

Question 7

4 Coarse sediments in ascending order of size

Answer 7

granules
pebbles
cobbles
boulders

Question 8

3 fine sediments in descending order of size

Answer 8

Sand
Silt
Clay

Question 9

Argillite

Answer 9

Mudstone/Mudrock - Silt and Clay

Question 10

3 Methods of grain size analysis

Answer 10

Volume diametre
Sieving
Laser granulometry

Question 11

Sorting

Answer 11

Distribution of grain sizes in a rock

Well sorted is approx same grain size throughout

Question 12

Particle form

Answer 12

shape

roundness

Question 13

Roundness

Answer 13

measure of smoothness or angularity of sediments; whether they have been eroded smooth or are still jagged

Question 14

Sphericity

Answer 14

Shape or Elongation- the ratio between the surface area of a sediment and that of a sphere of the same volumne. How close the grain is to spherical

Question 15

Texture

Answer 15

Size, Sorting, and Grading i.e. as we go up to the grains get larger or smaller

Question 16

Clast and Matrix support

Answer 16

Clast - Rock fragments are in contact with one another and form a framework supporting one another
Matrix - Rocks not in contact and floating within a finer grain sediment

Question 17

Slate

Answer 17

Mudrock that splits easily along cleavage not bedding

Question 18

Shale

Answer 18

Oil industry/ US term - Mudrocks, usually those that split along bedding planes

Question 19

Mudrock

Answer 19

Siltstones

Mudstones

Question 20

Marl

Answer 20

Calcareous mudrock

Question 21

Intraformational conglomerates

Answer 21

Clasts from local lithologies and usually monomict

Question 22

Monomict

Answer 22

sedimentary rock composed of but a single mineral species.

Question 23

Extraformational conglomerates

Answer 23

Clasts from different lithologies than those locally

Question 24

Sandstone classification

Answer 24

Composition

Question 25

3 sandstone compositions in classification

Answer 25

Feldspar, Quartz, Other Rock Fragments/Lithics

Question 26

Arkose

Answer 26

Mostly Feldspar Sandstone

Question 27

Litharenite

Answer 27

Lithic based sandstone

Question 28

Quartz arenite

Answer 28

Sandstone - 95 or more % Quartz