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HotE > Lecture 1 - Sediment and Sedimentary Rocks > Flashcards

Lecture 1 - Sediment and Sedimentary Rocks Flashcards

1
Q

what rocks are best for learning history

A

sedimentary rocks

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2
Q

what rocks are best for dating

A

igneous

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3
Q

metamorphic to extrusive igneous rocks

A

melting, magma, lava, consolidation

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4
Q

metamorphic to intrusive igneous rocks

A

melting, magma, crystallization

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5
Q

rocks to sediments

A

uplift and exposure, weathering, transportation, deposition

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6
Q

sediments to sedimentary rocks

A

lithification

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7
Q

ANY rock to metamorphic rock

A

metamorphism

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8
Q

what are sediments

A

loose solid particles formed by weathering or erosion of pre-existing rocks on the Earth’s surface, or by chemical precipitation from solution through organic or inorganic environments

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9
Q

unconsolidated sediment

A

sediment that is loosely arranged or unstratified and whose particles are not cemented together

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10
Q

3 types of particles

A

fragments (clasts) (eroded from pre-existing debris), skeletal debris (produced by organisms), crystals (precipitated by solution)

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11
Q

lithification process

A

compaction and cementation. the process that converts loose sediment into sedimentary rock

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12
Q

compaction

A

decrease in rock volume due to weight of overlying sediment

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13
Q

cementation

A

bind grains together with cement

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14
Q

common cementation molecules

A

carbonate (CaCO3) and silica (SiO2)

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15
Q

diagenesis

A

process of changing sedimentary rocks after lithification is termed

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16
Q

how can limestone go through diagenesis

A

the movement of MG-rich fluids through the rock. Mg substitutes for Ca ions in the rock to produce a carbonate rock called dolostone. The decreased rock volume forms vugs.
CaCO3 + Mg –> CaMg(CO3)2

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17
Q

vugs

A

voids of spaces in a rock

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18
Q

clastic sedimentary rocks

A

made from fragments of pre-existing rocks or organic particles such as shells and skeletal fragments (bioclastic)

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19
Q

siliciclastic (terrigenous clastic)

A

made from fragments of pre-existing rocks

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20
Q

what are chemical/biochemical and carbonaceous sediments made of

A

made from organic particles such as shells and skeletal fragments

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21
Q

what percentage of the earths surface is covered by sediments and sedimentary rocks

A

70%

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22
Q

what percentage of the volume of the earths crust is sediments and sedimentary rocks

A

5%

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23
Q

what are some interesting parts about sedimentary rocks

A
  • contain most of the worlds energy resources (fossil fuels)
  • hold most of the worlds subsurface aquifers
  • contain fossils that documents the history of the development of the earth
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24
Q

how are sediments and sedimentary rocks classified

A

clastic vs non-clastic

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25
Q

how are clastic sedimentary rocks classified

A

grain size, grain size distribution, grain shape

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26
Q

grain size

A

classification according to the grain size of the fragments they contain using a standardized scale like the Wentworth scale

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27
Q

what does the sediment gravel become

A

conglomerate

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28
Q

what does the sediment sand become

A

sandstone

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29
Q

what does the sediment silt become

A

siltstone

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30
Q

what does the sediment clay become

A

shale

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31
Q

chemical (non-clastic) sedimentary rocks

A

formed by direct precipitation of minerals from solution. commonly form in arid, tropical environments. “inorganic” limestones and cherts evaporite deposits.
ex. halite, gypsum

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32
Q

grain size distribution

A

sorting - organization according to grain size.

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33
Q

what can grain size distribution tell you

A

tell us the degree of transport and reworking such as wave action
very well-sorted will be far from the source with reworking and poorly sorted is close to the source with little reworking

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34
Q

grain shape

A

angularity/roundness of a rock

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35
Q

what can grain shape tell you

A

tell you about transport mechanisms. better rounding indicated more transport and reworking. ranges from very angular to well-rounded

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36
Q

how does sediment move

A

transported by water, wind, or ice as suspended load, bedload, or dissolved load

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37
Q

bedload

A

grains move in continuous or intermittent contact with the bed. rolling or jumping. coarse grained sediment

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38
Q

traction

A

rolling or dragging of grains in a bedload.

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39
Q

saltation

A

bounding or jumping of grains in a bedload. repeatedly picked up and dropped.

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40
Q

suspended load

A

sediment carried in fluid without coming in contact with the bed. fine-grained sediment. deposited under low energy conditions

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41
Q

coarse-grained sediment

A

gravel and sand

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42
Q

fine-grained sediment

A

silt and clay

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43
Q

bedforms

A

topographic features on the bed. different bedforms develop as current velocities change, but can also depend on grain size. can be conserved in the rock record.

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44
Q

very low flow velocity bedform

A

plane bed

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45
Q

low flow velocity bedform

A

ripples

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46
Q

moderate flow velocity bedform

A

dunes

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47
Q

high flow velocity bedform

A

plane bed

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48
Q

what are flat bed bedforms preserved as

A

horizontal lamination

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49
Q

what are ripple bedforms preserved as

A

ripple X-lamination

50
Q

what are dune bedforms preserved as

A

cross bedding

51
Q

what does oscillating current result in

A

symmetrical ripples, with equal slopes on either side

52
Q

what does unidirectional current result in

A

asymmetrical ripples, with a gentler slope on thewindward and steeper slopes on the leeward face

53
Q

windward face angle

A

10-12 degrees

54
Q

leeward face angle

A

33-34 degrees

55
Q

wave base

A

depth at which water movement is negligible. is 1/2 wavelength. water molecules have circular orbits below waves that get smaller with depth

56
Q

fairweather wave base

A

depth beneath average daily waves

57
Q

storm wave base

A

depth beneath storm waves

58
Q

hummocky and swaley cross-stratified sands

A

formed under storm waves with water depths of 10-30m. indicate storm activity

59
Q

sediment gravity flows

A

density-driven currents of sediment downward that are triggered by slumping or failure of a slope

60
Q

grain size distribution of debris flows

A

poorly sorted

61
Q

sediment gravity flow of turbidites

A

turbidities become graded beds with more fine sediment upwards. this can be seen by looking at the x-axis of logs to see the decreasing pattern in grain size with decreasing depth. as size increases you see how the bigger grains settle to the bottom.

62
Q

graded beds

A

change in grain or clast size from bottom to top of the bed

63
Q

sediment gravity flow example

A

grand banks NFL earthquake and turbidity currents. the current could be recorded by when what cables broke on the sea floor

64
Q

turbidity current deposits

A

Normally graded beds are coarse at the base and fine at the top. Bouma sequence predicts distribution, there are sole marks on base, and the change in character is from proximal to distal. only happens in subaqueous settings

65
Q

Bouma sequence

A

A division - massive
B division - laminated
C division - rippled
D division - laminated
E division - massive silt/clay

66
Q

facies

A

a body of sediment or rock with a particular characteristic that distinguishes it from other rock bodies. it is descriptive and not interpretive, and the result gives the process of the event.

67
Q

how is paleoenvironmental information obtained from sediments and sedimentary rocks

A

interpretation of facies types according to depositional process to tell you about depositional environment

68
Q

depositional process

A

looking at individual facies. ex. sediment gravity flow, traction current, etc.

69
Q

depositional environment of facies

A

place and climate. looking at genetically related groups of facies. ex. coastline, lagoon, river, glacier, reef

70
Q

facies associations

A

groups of facies genetically related to one another. have some environmental significance. ex. shoreface sandstones and lagoonal deposits

71
Q

what is needed to determine a depositional environment

A

facies associations

72
Q

walthers law

A

facies sequences observed vertically are also found laterally. we see rocks in vertical sequence that were deposited beside each other at the same time
“Only those facies and facies areas can be superimposed primarily which can be observed beside each other at the present time” explains how the vertical stacking of facies relates to environments that were laterally connected in the past. environments change through the horizontal transition. there is a coarsening upward sequence, where deposits at the bottom are muddy bottom sets that transition to silty/sandy forests into delta front sands. it shows a sequence of migration of shoreline - shallowing upwards in a transition from one to the next.

73
Q

what is the vertical stacking of facies associated with

A

sea level change

74
Q

transgression

A

shoreline moves landward as relative sea levels rise.

75
Q

regression

A

shoreline moves seaward as relative sea levels lower. erosion of exposed surfaces can come with this.

76
Q

how does glaciation affect sea level change

A

global sea levels lower during glacial events. known as glacio-eustatic sea level lowering. ice leads to lower sea levels

77
Q

how does changes in sea floor spreading rates affect sea level

A

slow-spreading has a cool crust and low elevation, so no rises in sea level
fast spreading has a hot crust, high elevation, and displaces water onto land - transgression.
tectonic movements that lead to mountain building can also shift water nearby to the lower elevation area.

78
Q

how are carbonate sediments created

A

biological activity. carbonates are born not made, and the sediment producers change over time

79
Q

what percent of the sedimentary rock record is carbonate sediment

A

20-25%

80
Q

what percent of the worlds hydrocarbons are in carbonate sediments

A

50%

81
Q

what percent of N.A’s hydrocarbons are in carbonate sediments

A

20%

82
Q

what hydrocarbon is often used in construction

A

Limestone CaCO3

83
Q

what percent is limestone

A

> 50% calcite/aragonite

84
Q

what percent is dolostone

A

> 50% dolomite

85
Q

what is chalk composed of

A

it is veryfine grained and mostly composed of skeletal fragments of CaCO3 organisms. the grains are bioclasts and may be surrounded by mud matrix. it is a kind of mudstone

86
Q

how is paleontology used for carbonate sediments

A

it is important in classifying the carbonate depositional systems to understand the conditions in which organisms live

87
Q

what are limestones largely precipitated by

A

organisms like shells or skeletons

88
Q

how is carbonate sand and mud produced

A

disaggregated skeletons

89
Q

allochems

A

recognizable grains

90
Q

why are lime muds not usually shales

A

they don’t yield clay minerals

91
Q

examples of carbonate allochems

A
  • skeletal particles
  • ooids (coated grains)
  • stromatolites (coated grains)
  • peloids
  • intraclasts
92
Q

what rock do ooids make

A

oolite

93
Q

what are ooids

A

spherical coated grains <2mm in diameter

94
Q

how are stromatolites formed

A

formed by the photosynthetic cyanobacteria algae. the lamination formed by the vertical growth of bacterial filaments in daylight traps grains and horizontal growth at night that binds layers of sediment

95
Q

what are peloids

A

silt to sand-sized mudballs, round to pellet-shaped, mostly originate as fecal pellets from shrimp (450/day) and other lifeforms

96
Q

what are intraclasts

A

ripped-up clast that is typically mud

97
Q

how are carbonates classified

A

based on matrix content
- contains mud or lacks mud
- mud-supported or grain-supported

98
Q

what carbonate is identified as grains supporting one another and contains no mud

A

grainstone

99
Q

what carbonate is identified as grains supporting one another and contains mud

A

packstone

100
Q

what carbonate is identified as mud supported with less than 10 percent grains

A

mudstone

100
Q

what carbonate is identified as mud supported with more than 10 percent grains

A

wackestone

101
Q

what is the current big producer of carbonate

A

modern reefs. it is most productive in the reef and shallow platform

102
Q

subtidal factory

A

always underwater, reefs and lagoons

103
Q

intertidal

A

between tides, beach and tidal flats

104
Q

supratidal

A

above high tide, wet: algal marsh and arid: sabkha

105
Q

where do evaporites occur in tidal environments

A

the arid Sabkha area

106
Q

what conditions needed for coral reef growth

A

warm, clear, agitated water with plenty of sunlight. neat the equator. carbonates are good climate indicators as it was probably the same in the past

107
Q

temperature range for reefs

A

best between 25 and 29, but has to fall between 18 and 36

108
Q

what is chert

A

inorganic precipitation, microscopic siliceous fossils. it often occurs as ‘nodules’ within limestone or dolostone

109
Q

evaporites

A

evaporation of sea water, resulting in sediments such as halite, gypsum, and anhydrite

110
Q

where is lime-mud and sand made

A

lagoons

111
Q

where is reef sediment made

A

at the reef front

112
Q

how wide is the lagoon

A

0.1 - 2 km

113
Q

how wide is the reef core (reef front)

A

50 m

114
Q

how wide is the forereef slope

A

0.1-1km

115
Q

what can be said about the growth patters of reef builders

A

they are similar for corals, sponges, and stromatolites, which is an example of convergent evolution. zonation is also similar between builders

116
Q

how are fossils created

A
  • shells burried and preserved unaltered for <100 millions years. cavities are filled with silica, calcium carbonate, or iron, replacing any original substance with mineral matter and any soft tissues by carbon.
  • they can be preserved as molds, imprints, and casts in resin.
  • tracks, trails, burrows and borings preserved
117
Q

ichnology

A

study of trace fossils

118
Q

bioturbation

A

process of disturbing sediment

119
Q

two types of fossils

A

trace fossils and body fossils

120
Q

trace fossils

A

tracks, trails, burrows and borings preserved

121
Q

body fossils

A

remains of living things (bones). often these remains have undergone some alteration process

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