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geology > sedimentary rocks > Flashcards

sedimentary rocks Flashcards

1
Q

what is a sediment?

A

a collection of loose earth materials

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2
Q

how do sediments form?

A

when older bigger rocks break into smaller pieces
-when minerals in rock react with air/water to form new minerals
-minerals in rock dissolve in water and reprecipitate elsewhere
-animals extract dissolved mineral ions to build shells

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3
Q

what are minerals precipitated out of water called?

A

sedimentary minerals,
if loose, sediment
if together, rock

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4
Q

what is precipitation triggered by?

A

a change in conditions

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5
Q

what is weathering?

A

the process that creates sediments

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6
Q

what is physical weathering?

A

the physical breaking of big rocks into small rocks

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7
Q

what is chemical weathering?

A

alter minerals and rocks as they react with air and water
-produces new minerals and dissolved elements and compounds

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8
Q

what are the types of sediment texture?

A

crystalline
clastic

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9
Q

what is crystalline texture?

A

minerals precipitate out of solution

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10
Q

what is clastic texture?

A

broken pieces of earth material

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11
Q

what are compositions of chemical sediments?

A

iron bearing crystals/ residues
microcrystalline quartz
dolomite microcrystals
calcite crystals
halite crystals
gypsum crystals

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12
Q

what are biogenic sediment?

A

produced through biological activity
built out of dissolved minerals extracted from water

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13
Q

types of clastic sediment?

A

siliciclastic
bioclastic

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14
Q

what is siliciclastic?

A

consists of quartz and feldspar grain, rock fragments and clay

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15
Q

what is bioclastic?

A

fragments of transported skeletal material

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16
Q

what does source refer to?

A

the exposed rocks from which sediment forms

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17
Q

what happens to sediment once it has formed?

A

it can be picked up and transported through erosion

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18
Q

what are agents of erosion?

A

air, water, ice, gravity

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19
Q

erosion by gravity?

A

only solid clast moves
moves large and small clasts at the same time

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20
Q

erosion by air, water, ice?

A

pick up and move sediment
the more viscous, the more power to move clast

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21
Q

which erosion agent has the lowest viscosity?

A

air
only move small clasts

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22
Q

which erosion agent has the highest viscosity?

A

ice
moves small to large clasts

23
Q

how do clasts move from water and air?

A

rolling
saltation
traction
suspension if small

24
Q

how do clasts move in ice?

A

on top
trapped within

25
Q

how does speed affect erosion?

A

the faster it is, the more power it has to move a large range of clasts

26
Q

how are sediments deposited?

A

minerals form in situ from reaction with air/water and a rock
-precipitate out of solution when conditions change
-ions extracted from water to build shells/skeletons

27
Q

when is clastic sediment deposited?

A

when the agent of erosion loses its power to transport grains

28
Q

what causes agents of erosion to lose power?

A

a drop in velocity
a drop in viscosity

29
Q

what is the hjulstrom diagram?

A

predicts the critical velocities at which a given grain size can be picked up, moved and deposited by WATER

30
Q

why is clay so hard to erode?

A

because clay is platy and layered and it sticks to itself

31
Q

what are the main depositional environments?

A

continental
costal
marine

32
Q

what are features of sedimentary structures?

A

small
3D
form in sediment during or after deposition

33
Q

what is primary sedimentary structure?

A

structures form as sediment is deposited

34
Q

what is a strata?

A

most common primary sedimentary structure
horizontal layers of sediment

35
Q

what are beds?

A

layers bigger than 1cm

36
Q

what are laminations?

A

layers less than 1cm

37
Q

what is a graded bed?

A

when grains become more fine

38
Q

what is cross-bedding?

A

result of deposition on inclined surfaces, produced by flowing water or wind

39
Q

what are symmetrical ripples?

A

ripples with the same angle on both sides caused by bidirectional currents

40
Q

what are asymmetrical ripples?

A

ripples with one steep side one shallow side
caused by unidirectional cuurent

41
Q

what are imbricated pebbles?

A

overlapping flat pebbles due to flowing water pushing them over

42
Q

what are sole marks?

A

grooves or indents that form either from objects dragged across sediment or
back current eddies scour out patches in the sediment

43
Q

what is secondary sediment structure?

A

formed after the deposition

44
Q

how are mudcracks formed?

A

when water dries up and clay minerals contract

45
Q

what is bioturbation?

A

organisms pull up sediment and erase primary structure

46
Q

what is soft sediment deformation?

A

sediment is loaded onto waterlogged sediment
compression causes water to squeeze out, deforming the original bedding

47
Q

two types of lithification?

A

compaction
cementation

48
Q

what is lithification

A

the process that turns sediment to stone

49
Q

what is compaction

A

due to burial, reduces pore space by forcing grains together

50
Q

what is cementation?

A

precipitation of chemical sediments in-between clasts

51
Q

characteristics of siliciclastic composition?

A

distinguished by grain size and shape

52
Q

how are chemical sedimentary rocks distinguished?

A

crystal type

53
Q

how are bioclastic rocks distinguished?

A

composed of calcite organisms
grain size and shape
grain type

geology (15 decks)

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