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Sedimentary Petrology > Lesson 5: Sedimentary Structures > Flashcards

Lesson 5: Sedimentary Structures Flashcards

1
Q

why do we need to study sedimentary structures?

A
  1. textures of the sediments can give us a clue on:
    - depositional environment
    - provenance
  2. sedimentary structures can further elaborate or describe the manner of the transportation media:
    * Energy
    * Depth
    * Flow directions
    * Post-depositional events
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2
Q

9 kinds of bedding and bedforms

A
  1. bed
  2. laminae
  3. varves
  4. laminated beds
  5. graded bedding: normal, reverse
  6. massive beddings
  7. cross-bedding: tabular, trough
  8. flaser cross bedding
  9. lenticular bedding
  10. hummocky cross stratification
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3
Q

At least 1 cm thick, lenticular/tabular

A

beds

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4
Q

refers to those with lenses

A

lenticular beds

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5
Q

examples of resources commonly found with lenticular bedding

A

petroleum and coal resources (in swamps)

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6
Q

beds that are less than 1 cm thick

A

laminae

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7
Q

contact between beds is of erosional in nature

A

alamgamation surface, the beds (above and belown) between the surface are called amalgamation beds

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8
Q

what are amalgamation beds comparable to?

A

unconformities, diastem (period of nondeposition/erosion)

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9
Q

beds or laminae which features seasonal variation

A

varves

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10
Q

how to tell seasonal changes in varves

A

darker shades: organic matter; rainy season, deposited in wet conditions
lighter shades: dry season

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11
Q

For fine grained clastics and evaporites, results from suspension settling

A

laminated beds

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12
Q

explain laminated beds

A

more of settling action. if water carrying suspended solids and ions (esp in evaporites) becomes stagnant, the load will get deposited sa floor.

for larger particles like sandstones, mostly result of traction (bedload or bouncing)

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13
Q

“finering” upwards indicates:
- a sequence of a “sinking” basin
- turbidity currents

A

normal grading

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14
Q

explain normal grading for sinking basins

A

the floor of the basin is going down = particulate matter is slowly becoming finer

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15
Q

“coarsening” upwards (mud to conglomerate upwards) indicates:
- basin being filled with sediments, transitioning deep to shallow to subaerial environments (becoming shallower)

A

reverse grading

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16
Q

explain normal grading bc of turbidity currents

A

occurs between continental rise and slope, indicative of submarine landslides/canyons/currents

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17
Q

example of stratigraphic column that has a reverse grading

A

cagayan valley stratigraphic column (deep marine: finer; sands: fine, well-sorted sa beach depth; floodplains

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18
Q

bedding that has no internal structures, poor sorting, rare with coarser sediments, only really for finer sediments

A

massive beddings

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19
Q

what kind of deposits are mostly in massive beddings

A

finer deposits like sandstorm deposits or “loess”

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20
Q

structureless clay-sized silts (windblown sediments)

A

loess

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21
Q

the type of cross bedding depends on?

A

the initial surface

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22
Q

cross bedding is applicable to what other structures?

A

dunes and ripple marks

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23
Q

explain how cross bedding is formed

A

abrupt changes in wind/water direction and velocity causes carried sediments to get deposited in the lee side (steeper side) creating cross beds, while the stoss side (gentler slope) is getting eroded

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24
Q

flaser and lenticular bedding is related to what?

A

ripple marks

25
Q

fine sediments that partially or fully covers along the apex of a ripple marks, favoring sand being deposited over mud (high sand supply)

A

flaser cross beddings

26
Q

are more or less continuous beds, in favor of mud being deposited over sands (high mud supply)

A

lenticular bedding

27
Q

for flaser bedding, where does clay get deposited?

A

at the trough of sands

28
Q

Indicates continental shelf, and shoreface environments; continuous

A

hummocky cross stratification

29
Q

common thickness of hummocky cross stratification

A

15-20 cm

30
Q

what sometimes triggers hummocky bedding

A

sole marks

31
Q

most of the time forms transverse (parallel) to the laminar flowing current

A

ripple marks and dunes

32
Q

ripple marks or oscillation ripple is dependent on what 2 things?

A
  • flow velocity
  • flow direction
33
Q

explain the difference between current ripple and oscillation ripples

A

current ripples
- asymmetrical ripples (partial to one side bc of leeside and stoss side)
- oriented to one direction of current, one side stronger than other

oscillation ripples
- more symmetrical
- because of swash and backwash motion = oscillate

34
Q

poorly understood, however authors agree that these are fluid rich sediment beds undergoing deformation

A

convolute structures

35
Q

convolute structures are what kind of stratification?

A

irregular stratification

36
Q

explain formation of convolute structures

A

related to syn (or sine?) sedimentary structures, result of deformation during sediments still (mud or sands), not yet rocks

37
Q

3 types of convoluted structures based on time of formation

A

syn-depositional, meta-depositional, post-depositional

38
Q

type of convoluted structure in which the deposition and tectonic deformation occurred at the same time, that is why it’s chaotic

A

syn-depositional

39
Q

type of convoluted structure in which the tectonic deformation occurred right after deposition. there was not much settling that happened yet, then boom deformation

A

meta-depositional

40
Q

type of convoluted structure in which the tectonic deformation occurred after beds have been deposited and settled, ready to be lithified but then suddenly tectonism occurred.

A

post-depositional

41
Q

Commonly occurring on when mud is overlain by sandstone, and heavier sediments, where the mud sediments are reaching upwards owing to the weight of the heavier overlying sediments

A

flame structures

42
Q

do ball and pillow structures always occur with flame structures?

A

commonly, but not always, bc individual sand grains can form ball and pillow structures, but not necessarily flame structures

43
Q

Commonly are water escape structures

A

dish and pillar structures

44
Q

laterally extensive, some are impermeable, around 1 to 50cm

A

dish

45
Q

vertical to near vertical cross cutting columns, saturated with water

A

pillar

46
Q

related to sand boils, events of liquefaction

A

dish and pillar structures

47
Q

2 kinds Erosional Structures

A

channels
Scour and fill/cut and fill

48
Q

Sediment filled, U shaped or V shaped cross section that cut across previously formed beds or lamination,

A

channels

49
Q

resemble channels, however short and discontinuous
when river dries up and sediments fill the channel

A

Scour and fill/cut and fill

50
Q

example of Scour and fill/cut and fill

A

part of oxbow lake, meander scars, former dried up streams

51
Q

examples of biogenic structures

A

fossils -stromatolites

52
Q

organosedimentary structures formed largely by the trapping and binding activities of cyanobacteria

A

stromatolites

53
Q

blue green algae

A

cyanobacteria

54
Q

examples of bedding plane markings

A
  1. sole markings: bounce, brush, prod, roll, skip
  2. flute casts, groove casts
  3. current crescents
  4. rain drop imprints
  5. mudcracks
  6. rill marks
55
Q

casts of sediments covering bedding plane marks

A

flute casts

56
Q

larger, heavier sediments, obstruct the
path of fluid flow, protecting the sediments behind it

A

current crescents

57
Q

6 structures with secondary origin

A
  1. sand dikes and sills
  2. concretions
  3. nodules
  4. color banding or liesagang banding
  5. stylolites
  6. cone-in-cone structure
58
Q

refers to those cementing materials in between clasts

A

concretions

59
Q

rhythmic layering resulting from the oxidation of metals and fluid saturated form thin, closely spaced, commonly curved

A

color banding or liesagang banding

Sedimentary Petrology (11 decks)

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