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FoG > Seds > Flashcards

Seds Flashcards

1
Q

Ways that volume changes occur within fissures

A

1) frost weathering (H2O -> ice)
2) precipitate salts in fissures
3) biological (tree roots)

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2
Q

Types of physical weathering

A

1) pressure release
burial = pressure
then uplift = expand and break along planes of weakness

2) Insolation weathering
thermal expansion and contraction -> differential expansion between surface and middle creates stress

3) Hydration weathering
water absorbed and released by clay minerals, swelling and shrinking of rock

4) volume changes within fissures

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3
Q

methods of chemical weathering

A

1) acid hydrolysis
carbonic acid reacts with primary mineral to replace metal cation with H+ ion, forming hydrous mineral
e.g. acid hydrolysis of silicate minerals
carbonic aid + feldspar = hydrated aluminosilicate (+ metal ion + bicarbonate)

2) oxidation
metals lose e- and rust

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4
Q

methods of biochemical weathering

A

plant roots and bacteria produce organic acids which break down rocks
e.g. fungi penetrate and take nutrients directly from mineral

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5
Q

how does goldich’s weathering series relate to Bowens reaction series

A

as you do down Bowens reaction series, minerals become less susceptible to weathering, as were formed/are stable at conditions closer to those at the surface

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6
Q

4 categories of sediments/sedimentary rocks

A

1) clastic deposits
- particles from pre-existing rocks
2) biogenic/organic deposits
- resulting from biological materials/biologially mediated processes
3) chemical deposits
- precipitates from solution
4) volcaniclastic deposits
- products of volcanic eruption of breakdown of volcanic rocks

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7
Q

examples of each of the 4 types of sediments/sedimentary rocks

A

1) clastic depostis - breccia, sandstone, mudstone
2) biogenic - limestone, coal, CaCO3
3) chemical deposits - evaporite, BIF
4) volcaniclastic - tuff

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8
Q

difference between a matrix and a cement

A

matrix = fine grained granular
cement = precipitated out of fluid after deposition, crystalline

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9
Q

physical descriptors of clastic sediments

A
  • grain size + size distribution
  • grain morphology
  • grain packing (fabric)
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10
Q

what factors effect grain size distribution

A
  • nature of sediment source
  • efficiency of transport medium (only carry specific sizes, wind, water, glacier)
  • energy in deposition
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11
Q

what are patterns of grain morphology with distance transported

A
  • roundness = increase rapidly
  • size = slow decrease
  • sphericity = not much change
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12
Q

define textural maturity

A

immature = high matrix proportion, poorly sorted, angular grains

mature = less matrix, well sorted, rounded grains

high maturity = porous + permeable

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13
Q

what makes up clastic rocks

A

quartz
feldspars
lithic fragments
micas + clay minerals
heavy minerals (accessory grains)
other detrital (fossils)

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14
Q

characteristics of quartz in clastic rocks

A
  • v common, hard, no cleavage
  • derived from granite + gneiss
  • can be monocrystalline or polycrystalline
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15
Q

characteristics of feldspars important in clastic rocks

A
  • common, less hard than quartz, cleaved
  • chemically liable to be replaced by clay minerals = indicator of weathering intensity + environment
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16
Q

characteristics of lithic fragments important in clastic rocks

A
  • type depends on geology of source and durability
  • key in breccia, coarse sandstones
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17
Q

what is the pettijohn classification of sandstones

A

ternary diagram showing the relative proportion of quartz, feldspars, and lithic fragments in a rock

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18
Q

what is the importance of micas and clay minerals in clastic rocks

A
  • common in matrix
  • clay minerals small and fine grained
  • muscovite > biotite (stability)
  • matrix creates another scale on pettijohn classification (amount of matrix)
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19
Q

importance and characteristics of heavy minerals in clastic rocks

A
  • density > 2.85 g/cm^3
  • stable oxides and silicates
  • evidence for origin
    e.g. garnet = met, apatite = igneous
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20
Q

how does composition and texture evolve with maturity

A

composition:
unstable minerals (feldspar) -> stable + LFs -> entirely quartz

texture:
matrix, poor sorting, angular
-> decreasing matrix, increasingly sorted, increasingly rounded

21
Q

difference between conglomerates and breccia

A

conglomerate = rounded clasts
breccia = angular clases

22
Q

what is diagenesis

A

physical and chemical changes that alter the characteristics of a sediment after deposition
unconsolidated sediment -> consolidated rock

23
Q

how does packing change during diagenesis, and example with different grains

A

increase pressure by overlying sediments -> change packing to increase density -> decrease porosity

fluid expelled and volume is reduced
muds = very compressible due to layered structure
sand = compacted much less

24
Q

when are sutured contacts between grains seen

A

when grains fuse together due to temperature increase during diagenesis

25
Q

how does cementation occur

A
  • material dissolves at grain contacts
  • solution percolated through pore spaces
  • crystallise into cement
26
Q

what are common cements

A

silica
calcite

27
Q

name sediment transport media

A
  • water
  • air
  • ice
  • sed/water mixtures
  • gravity
28
Q

what are the 2 ways that fluids flow and what number defines this

A

laminar flow - in debris flow (high viscosity sed/water mixtures) and glaciers

turbulent flow - natural systems that transport sediments

Re (Reynolds no.):
high = turbulent flow
low = laminar flow

29
Q

what are the 4 categories of sedimentary structures

A

1) depositional
2) erosional
3) post depositional
4) biogenic

30
Q

difference between bedding and lamination

A

bedding > 1cm
lamination < 1cm

31
Q

what controls change in bedding/lamination

A
  • composition
  • size
  • shape
  • orientation
  • packing
    of deposited sediments
32
Q

what is the stoss side and lee side of an asymmetrical ripple

A

stoss = gentle slope, exposed, roll up
lee = steep, sheltered, fall down

33
Q

why are preserved unidirectional currents useful

A

indicator of palaeocurrent direction

34
Q

when are dunes created as opposed to ripples

A
  • higher mean flow velocity
  • larger grain size
35
Q

what structures do waves produce

A

symmetrical ripples by oscillatory motion, no net movement of grains

36
Q

examples of erosional sedimentary structures

A
  • scour marks
  • tool marks
37
Q

how are scour marks identified (erosional sedimentary structure)

A
  • flare downstream
  • created by turbulent eddies
  • cm scale on base of beds
38
Q

name and describe post depositional sedimentary structures

A
  • dewatering of sediment
  • deposition onto a slope - slumps
  • loading of higher density layer on lower density layer -> load balls, flame structures
39
Q

what are biogenic sedimentary structures

A
  • bioturbation
  • trace fossils
40
Q

what is a facies

A

a body of rock with specified characteristics that reflect the conditions under which it has formed

41
Q

what are classes/examples of major depositional environments

A

marine
- shallow, deep

terrestrial
- deserts, lakes, rivers

marginal
- deltas, estuaries

42
Q

describe the desert environment

A
  • low precipitation <250mm/yr
  • hot+cold arid regions
  • lack of water = susceptible to movement by wind
  • can have flash floods
43
Q

distribution/types of deserts

A

subtropical
- descending Hadley cell

rain shadow
- continental topography forces air upwards

coastal
- cool air over ocean wicks water from land

interior
- air loses moisture as crosses continental interior

polar
- air above 66º holds little moisture, wicks water from land

44
Q

characteristics of wind blown particles/deposits

A
  • very well rounded (saltation impacts)
  • frosted grains
  • well sorted (air small transport range)
  • compositionally mature (quartz + little matrix)
45
Q

3 stages of pettijohn classification of sandstones with increasing percent matrix

A

arenite
wacke
mudrock

46
Q

how to recognise deserts in the rock record

A
  • clean, quartz rich sandstones
  • large scale X-bedding
  • rare fossils
  • associated conglomerates from flash floods
47
Q

what are the types of sediments seen in lakes

A

clastic
- supplied by rivers

biochemical sedimentation
- carbonates through biological processes and chemical precipitation

organic production
- photosynthetic organisms

48
Q

how to recognise lakes in the rock record

A
  • diverse lithologies
  • ripples, cracks, stromatolites (near shore)
  • rhythmic laminations (deep)
  • fossils - non marine (anoxia preserved)
  • shallowing upward cycles
  • associated with fluvial facies
49
Q
A

FoG (7 decks)

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