sedimentary rocks Flashcards

1
Q

sediment

A

material weathered from pre-existing rocks

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2
Q

lithification

A

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

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3
Q

common example of sedimentary rock

A

quartz grains with calcite cement

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4
Q

5 groupings of sedimentary rocks

A
  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
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5
Q

order these in terms of clast size smallest first:

mudstone, conglomerate, sandstone

A
  1. mudstone
  2. sandstone
  3. conglomerate
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6
Q

what is a clue to transportation distance of clasts?

A

further transport distance = smaller and rounder clasts

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7
Q

3 categories to categorise clastic rocks

A
  1. compostition of clasts - quartz, feldspar, clays, etc
  2. presence of matrix
  3. type of cement
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8
Q

Breccia and conglomerate

A

a clastic sedimentary rock with large angular clasts in cement

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9
Q

mudstone vs shale

A

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

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10
Q

sandstone vs siltstone

A

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

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11
Q

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

A

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

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12
Q

coal

A

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

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13
Q

most common form of chemical sedimentary rocks and where they form

A

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

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14
Q

bedding in sedimentary rocks

A

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

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15
Q

what is grading?

A

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

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16
Q

main influence in stability of sedimentary rock slopes?

A

direction and ammount of bedding dip ( angle fro horizontal)

17
Q

what are dipping sedimentary rock sequuences susceptible too?

A

translational slides

18
Q

bedding planes are ….

A

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

19
Q

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

A

cement/matrix

20
Q

4 factors that influence compressive strength in sandstone

A
  1. porosity
  2. amount and type of matrix
  3. grain contacts (numbers and types)
  4. grain composition
21
Q

influence of pore waters on compressive strength

A

reduce compressive strength by 30-60%

22
Q

physical behaviour of shale/mudstone influenced by

A

mineral content

23
Q

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

A

FALSE, its the opposite my brother x.

24
Q

shale with low strength interbedded with stronger snadstones leads too…

A

instability of the rock mass

25
Q

greywacke sandstone

A

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

26
Q

greywacke argilite

A

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