sedimentary rocks

Question 1

sediment

Answer 1

material weathered from pre-existing rocks

Question 2

lithification

Answer 2

process of converting sediment to sedimentary rocks

1. depostion forms pile of sediment with lots of pores
2. pile grows thicker and the weight compacts layers
3. grains cemented by remobilization of some minerals through pressure solution. Water moving through pores ppt. minerals

significant decrease in pore space, increase in strength

Question 3

common example of sedimentary rock

Answer 3

quartz grains with calcite cement

Question 4

5 groupings of sedimentary rocks

Answer 4

1. clastic - made of clasts (pieces of weathered mineral) e.g. sandstone
2. biogenic/bioclastic - made of particles originally from living organisms e.g. shells to limestone
3. organic - made of compressed and heated plant material e.g. coal
4. chemical - made from ppt. dissolved particles e.g. evaporite, ironstone
5. volcanicalstic - same as clastic but clasts are of volcanic origin

Question 5

order these in terms of clast size smallest first:

mudstone, conglomerate, sandstone

Answer 5

1. mudstone
2. sandstone
3. conglomerate

Question 6

what is a clue to transportation distance of clasts?

Answer 6

further transport distance = smaller and rounder clasts

Question 7

3 categories to categorise clastic rocks

Answer 7

1. compostition of clasts - quartz, feldspar, clays, etc
2. presence of matrix
3. type of cement

Question 8

Breccia and conglomerate

Answer 8

a clastic sedimentary rock with large angular clasts in cement

Question 9

mudstone vs shale

Answer 9

mudstone breaks into blocks, shale is fissle and breaks into thin layers along parallel planes

Question 10

sandstone vs siltstone

Answer 10

cant see clasts with naked eye in siltstone and sandstone feels grittier

Question 11

limestone is an example of a ________ sedimentary rock. explain formation

Answer 11

biogenic.
shells, ppt. of CaCO3 from water.
can look crystalline

Question 12

coal

Answer 12

organic.
forms from plant debris in swampy environments.
burial drives off volatile and compacts coal. Higher grade = fewer volatiles

Question 13

most common form of chemical sedimentary rocks and where they form

Answer 13

evaporites. e.g halite from salt rich water. form in VERY arid climates

Question 14

bedding in sedimentary rocks

Answer 14

layers of rock that have lithological, textural, or structural differences from layers above/below.
represent changes in environment

Question 15

what is grading?

Answer 15

beds with largest sediments on the bottom and smallest on the top, caused by dissipation of transport energy

Question 16

main influence in stability of sedimentary rock slopes?

Answer 16

direction and ammount of bedding dip ( angle fro horizontal)

Question 17

what are dipping sedimentary rock sequuences susceptible too?

Answer 17

translational slides

Question 18

bedding planes are ….

Answer 18

zones of weakness in sedimentary rock sequences e.g. roughness, water, clay

Question 19

sandstone will have less porosity if the amount of _______ increases.

Answer 19

cement/matrix

Question 20

4 factors that influence compressive strength in sandstone

Answer 20

1. porosity
2. amount and type of matrix
3. grain contacts (numbers and types)
4. grain composition

Question 21

influence of pore waters on compressive strength

Answer 21

reduce compressive strength by 30-60%

Question 22

physical behaviour of shale/mudstone influenced by

Answer 22

mineral content

Question 23

cemented shales are are weaker and less durable than compacted shales. TRUE/FALSE

Answer 23

FALSE, its the opposite my brother x.

Question 24

shale with low strength interbedded with stronger snadstones leads too…

Answer 24

instability of the rock mass

Question 25

greywacke sandstone

Answer 25

clastic, highly compacted sandstone. It is hard with white veins of quartz visible

Question 26

greywacke argilite

Answer 26

clastic, highly compacted mudstone. It is hard but no grains are visible. It has no engineering use.