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Sedimentary Petrology > Lesson 8: Mudrocks > Flashcards

Lesson 8: Mudrocks Flashcards

1
Q

define mudrocks in terms of composition

A

they have to be at least 50% silt or finer particles

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2
Q

describe mudrocks in terms of abundance

A
  • most abundant among sedimentary rocks
  • compromise 50% of stratigraphic record
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3
Q

mudstones vs siltstones vs shales

A

mudstones are massive, siltstones are more silt than clay, shales have fissility (they can easily split along planes)

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4
Q

what is the difference between conglomerates and mudstones in terms of erosional process, what is the implication?

A

unlike conglomerates with various agents for reworking, mudstone particles actually have little to no modification/reworking during erosion and transportation.
reason: they are mostly transported as suspended particles
effect: cannot be rounded by collision = they are mostly angular; maintained their crystal shape

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5
Q

3 main processes that affect the microfabric of mudrocks

A
  1. physiochemical processes
  2. burial diagenesis
  3. bioorganic processes
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6
Q

3 specific processes under physiochemical processes

A
  1. electrochemical
  2. thermochemical
  3. interface dynamics
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7
Q

2 specific processes under burial diagenesis

A
  1. mass gravity mechanisms
  2. cementation
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8
Q

3 specific processes under bioorganic processes

A
  1. biomechanical
  2. biophysical
  3. biochemical
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9
Q

refers to the bonding among minerals, the electromagnetic bonds

A

electrochemical processes

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10
Q

refers to how temperature affects the interaction between minerals and their ions

A

thermochemical processes

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11
Q

refers to how the overall environment affects mudstone formation

A

interface dynamics

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12
Q

refers to how overburden affects the formation of mudstones (compresses them)

A

mass gravity mechanisms

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13
Q

process mainly involving cementing minerals

A

cementation

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14
Q

differentiate burial diagenesis vs bioorganic proesses

A

burial diagenesis is more on lithification while bioorganic processes are more on biological aspects

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15
Q

an example of this process would be bioturbation (burrowing animals)

A

biomechanical processes

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16
Q

refers to when organic particles create new minerals

A

biochemical processes

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17
Q

specific example of biochemical processes affecting microfabric

A

when organic matter produces methane gas/natural gas which affects the overall make up of mudstones

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18
Q

property where splitting between roughly planar and parallel surfaces can occur (has parting)

A

fissility

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19
Q

what does fissility among shales favor?

A

favors the abundance of peptizing agents

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20
Q

explain peptizing agents

A

agents that orient mineral assemblages of rock

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21
Q

example of peptizing agent

A

organic matter (needs anoxic environment)

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22
Q

2 requirements for peptizing agents in the fissility of shales (high chance for shales to form)

A
  • organic matter are the main peptizing agents
  • anoxic environments favor the preservation of organic matter
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23
Q

why is it that organic matter needs to be preserved in anoxic environments?

A

because aerobic environments oxidizes the organic matter which will cause it to decay.

thus, no oxygen = no decay = preserved organic matter = fissility

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24
Q

enumerate entire mineralogy of lutites

A

silicate minerals:
- quartz
- feldspar
- zeolite

clay minerals:
- kaolinite
- smectite-illite-muscovite
- chlorite, corrensite, vermiculite
- sepiolite and attapulgite

oxides/hydroxides
- Fe-O
- gibbsite

carbonates:
- calcite
- dolomite
- siderite and ankerite

sulfites and sulfates

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25
Q

mineral composition of most coarse grained lutites (silty/siltstones)

A

silicate minerals:
- quartz
- feldspar
- zeolite

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26
Q

pyroclastic materials that have undergone low temperature alteration under seawater

A

zeolite

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27
Q

mineral composition of most fine grained lutites

A

clay minerals:
- kaolinite
- smectite-illite-muscovite
- chlorite, corrensite, vermiculite
- sepiolite and attapulgite

oxides/hydroxides
- gibbsite

28
Q

mineralogy of coatings

A

Fe-O

29
Q

example of coatings

A

Hematite -most common in shales
goethite or limonite -may be more common in modern muds

30
Q

weathering and oxidation products of iron minerals and gives color/pigmentation to the lutites

A

coatings

31
Q

mineral composition of concretions/cement in lutites

A

carbonates:
- calcite
- dolomite
- siderite and ankerite

32
Q

what is gibbsite

A

an aluminum hydroxide clay

33
Q

what do sulfides indicate

A
  • reducing environment
  • post-deposition
34
Q

what do sulfates indicate

A

hypersaline environment

35
Q

example of sulfate in lutites

A

gypsum

36
Q

example of evaporites in lutites

A

halite, gypsum, potassium salts or sulfosalts

37
Q

other constituents found in lutites

A

apatite, volcanic glass, heavy minerals

38
Q

accumulated organic matter (phosphate oxide mineral)

A

apatite, ex. guano

39
Q

occurs along zeolite

A

volcanic glass

40
Q

rare occurrence in lutites

A

heavy minerals

41
Q

describe organic substances in lutites

A

discrete and structured

42
Q

examples of organic substances in lutites

A

vitrine and kerogen in oil shales

43
Q

particles from wood/plant materials

A

vitrine

44
Q

altered remains of microorganisms

A

kerogen

45
Q

how to classify lutites (bases)

A

there is no formal classification because there are a lot of ways to classify it:
- color
- abundance of minerals/organics
- particle size (mostly used)
- fabric/microstructures

46
Q

how to classify lutites based on color

A

red shale -associated with iron oxidation
black shale -a lot of organic matter within shale
green shale -anoxic environment with iron minerals
white siltstone -eroded away pyroclastic materials

47
Q

example of how the abundance of minerals/organics can be used to classify lutites

A
  • oil shale: bc a lot of oil, petroleum products preserved within shale)
  • argillaceous shale: because it is mainly composed of clay minerals (mud-sized doesn’t mean composed of clay/muddy minerals)
48
Q

example of how fabric/microstructures can be used to classify lutites

A
  • fossiliferous: if there are fossils
  • on the basis of fissility (see chart)
  • bedded siltstone: if the siltstone is bedded:”)
49
Q

why is it that lutites are the most common sedimentary rocks?

A
  • most are of marine origin
  • occurs in all ages: meaning at all times, there is always going to be a deep, basin-like area with gentle currents to make it possible for lutites to form, regardless if they would be preserved or not
50
Q

what is reflected in sedimentary records about lutites

A
  • high abundance of fine-grained material
  • erosional and efficiency of transport agents
51
Q

4 transport agents of lutites

A
  • wind
  • bottom currents
  • suspension transport mechanisms
  • turbidity currents
52
Q

expound about the transportation agents for lutites

A

if transportation agent is sufficient, it can carry sediments to portions where it can be preserved (deposited then eventually lithified)

53
Q

example of wind as a transport agent

A

sand from the sahara desert gets carried by wind to the amazon rain forest. thus the desert is feeding the forest

54
Q

discuss how bottom currents can be transport agents

A

if there are fine particles with bottom currents, it can carry the particles away from deposition area

55
Q

discuss how suspension transport mechanisms can be transport agents

A

finer sediments are usually transported through suspension because of their size

56
Q

discuss how turbidity currents can be transport agents

A

good transportation mechanism for silt and finer particles - bouma sequence, fining up

57
Q

3 different environments of lutites

A

fluvial, coastal and marine, eolian

58
Q

3 specific depositional areas under fluvial for lutites

A
  1. meandering rivers and anastomosing streams
  2. deltas
  3. estuary
59
Q

4 specific depositional areas under coastal and marine for lutites

A
  1. lagoons
  2. deep waters
  3. shelf and slope
  4. tidal flats
60
Q

example of sediments that make up lutites from eolian environments

A

loess deposits

61
Q

describe setting in meandering rivers and anastomosing streams

A
  • near final base level
  • water velocity becomes slow
  • calm river causes deposition in floodplain
62
Q

describe deltas and estuary

A
  • transition between rivers and seas
  • low energy environment
  • if silt/mud is still suspended by flowing water, coming to contact with standing water will suddenly decrease velocity and cause desposition
63
Q

describe setting in lagoons

A
  • enclosed areas from the sea
  • no deposition for a time in a year, but sediments from the sea eventually get deposited here
64
Q

T or F: lagoons are good hosts of mudstones (sulfate rich shales)

A

true

65
Q

Lutites found in deep waters and shelf slope

A

turbidites and deep marine shales

66
Q

describe tidal flat settings

A
  • platform areas that reveal if high or low tide
  • gentle environment
  • enough to form shales, thin layers or intercalation because of episodic high and low tides
67
Q

describe loess deposits

A

structureless (no internal structure within it)

Sedimentary Petrology (11 decks)

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