Lecture 3 - Clastic Sedimentary Rocks

Question 1

What are the four types of sedimentary rocks

Answer 1

Siliclastic, Biochemical, Chemicl, Volcanisclastic

Question 2

Whare a siliclastic rocks composed of?

Answer 2

These rocks are composed of preexsiting rocks that have been weathered.

Question 3

What do the classification schemes use to help classify the rocks

Answer 3

Grain size, Grain minarlogy, Grain Shape and the matrix

Question 4

Do you understand the sand, clay and silt matrix? The After Folk matrix 1974

Answer 4

;-)

Question 5

As grains are trasported what happens?

Answer 5

The grains become smaller and more rounded but thier spherericity may not change all that much.

Question 6

What does poorly sorted or well sorted indicate?

Answer 6

Poorly sorted grain size will be a low power enviroment such as a mass wasting where as well sorted would be a high energy enviroment such as rivers

Question 7

What factors controll the extent of sorting

Answer 7

Sediment Source, Grain size, Despoistional mechanism

Question 8

Explain the effect of sediment source as its effect on sorting

Answer 8

Weathning a more pure rocks such as sandstone will produce more consitant sediment that grainite

Question 9

Effect of grain size on sorting

Answer 9

The smaller sand size clasts are more easily transported and will therefore be sorted by rivers and wind etc

Question 10

Explain depositional mechanism on sorting

Answer 10

Rapid deposition and deposition in viscous mudflows will be poorly sorted. Reworking by wind and water will result in better sorted rocks

Question 11

What would a texturally immature rock have?

Answer 11

1) lots of matrix
2) poor sorting
3) angular grains

Question 12

What would a texturally mature rock have?

Answer 12

1) little matric
2) moderate to good sorting
3) subrounded to rounded grains

Question 13

What would a textually supreme rock have?

Answer 13

1) no matrix
2) amazing sorting
3) well rounded grains

Question 14

What does textually supreme rocks mean against textually immature?

Answer 14

supreme rocks will be an enviroment wehre ther was contuial sorting such as beach and textually immature will occour where there is minimal current activity

Question 15

What is primary porosity

Answer 15

Porosity of rock at time of deposition, although this can change later

Question 16

What can effect the primary porosity

Answer 16

Increase through dissolution and decreases through cementation

Question 17

Explain the resivour potential

Answer 17

A rock needs to be both porous and permeable to have as a resivour rock for oil, i.e sandstones which are often both.

Question 18

Factors of a conglomerates

Answer 18

Rounded clasts under 2mm

Question 19

factors of a breccias

Answer 19

Angular clasts under 2mm

Question 20

factors of a monomitic rock

Answer 20

Contains all pebbles of one type

Question 21

Factors of a polymitic rocks

Answer 21

is a rock that contrains more that one type of pebble

Question 22

What is a clast supported rock?

Answer 22

Pebbels touching each other and the void filled in with matrix

Question 23

What is a matrix suported rock?

Answer 23

Pebbles not touching each other but surpoted by a matix

Question 24

What can these conglomerates and breccias tell us?

Answer 24

1) Orogin of the sediment clasts
2) Enviroment of deposition
3) paleogeography
4) Techtonic setting

Question 25

An explaination about Arenties / Sandstones

Answer 25

Lithified equivlant to sand.
10-20% of the earths sed rocks
Pore spaces may be filled
Resivours of oil and petrolum
Building spaces
Resistant to weathing

Question 26

Fine grained clastics examples

Answer 26

Mud stone, Shale and mud

Question 27

Mud infomation

Answer 27

Clastic sedmiment with tiny grains, mainly clay and minerals. Found on rivers flood plains, etc

Question 28

Mudstone information

Answer 28

Equivalant of mud but in a rock. 50%ish of all sed sequences

Question 29

Shale Information

Answer 29

Sily and clay, break redily alonging bedding planes.

Question 30

Organic rich mudrocks are know as..

Answer 30

..Black shales

Question 31

Brief explanation of these black shales formation

Answer 31

1) Plankton live in the photic zone
2) Dead plankton sink through the water coloum
3) Organic matter (C) is oxididesed by bacteria using dissolved O2.
4) in normal situations not much reaches the ocean flloor.

Question 32

So what can increase the freqenecy of these black shales?

Answer 32

1) low 02 levels in seawater (preventing bacteria oxidising the co2)
2) High flux in organic matter (i.e a plankton boom)

Question 33

Past climate effects on black shales!

Answer 33

These were creators of the worlds largest oil supplies today, these anoxic ocean envoriments in the later creatacous. Deposition of these carbon rich rocks suched CO2 out of the atmpshere bring this super greenhouse period to a close.