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Surface Processes > W5 handout sedimentary rocks class notes > Flashcards

W5 handout sedimentary rocks class notes Flashcards

1
Q

three factors when looking at sedimentary rocks

A

source, slope, sink

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2
Q

source area

A 
factors such as 
composition of source area
climate
geological setting
influence how source material will respond to Earths reactive atmosphere
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3
Q

move down slope

A

Processes (wind, water, ice) serve to move weathered debris ( sediment) down slope until deposited

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4
Q

sink

A

sediment deposited in environment of accumulation or sink

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5
Q

Sedimentary Rocks make up

A

80% of rocks exposed on earth surface

layer of sedimentary rock relatively thin

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6
Q

stratified

A

sedimentary rocks are layered

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7
Q

beds or laminae

A

greater than 1 cm thick: beds

less than 1 cm: laminae

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8
Q

depositional unit means

A

accumulation of material > erosion

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9
Q

beds and laminae are seperated by

A

bedding or lamination planes

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10
Q

each surface represents

A

a change in conditions

ex change in source of material, particle size, energy of transporting agent

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11
Q

loss of recorded time

A

time is lost at bedding planes bcs erosion
bedding planes are all disconformities
major losses of time: unconformities

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12
Q

lithification

A

sediment is converted to sedimentary rock by lithification

processes: cementation and compaction

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13
Q

cementation

A

prcipitation of a chemical cement that binds the individual particles together
effective with coarser grained rocks

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14
Q

compaction

A

grains are forced together as a result of increased load pressure
more effective with finer clastic sedimentary rocks

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15
Q

Diagenesis

A

processes that act to modify the sediment and sedimentary rock after its buried
diagenesis may grade into metemorphism if temperature and pressure increase sufficiently

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16
Q

two broad cateegories of sedimentary rocks

A

clastic and chemical

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17
Q

clastic classified as

A

particles carried as solids by the slope agents

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18
Q

chemical classified as

A

ions transported in solution until they precipitate
such as limestomes (calcite and dolomite)
sulphates and salts

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19
Q

clastic bigger than sand sized

A

(bigger than 2mm)
conglomerates (rounded fragments)
breccia ( angular fragments)

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20
Q

clastic sand sized

A

(1/16 to 2mm)
quartz arenite- quartz is dominant component
arkose- feldspar is dominant componentt
litharenite- rock fragmeents are dominant component

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21
Q

clastic silt sized

A

1/256 to 1/16 mm)

silt stones

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22
Q

clastic clay sized material

A

(1/256 mm)
shale - rock is fissle, cleavage of clay minerals are parallel to each other, imparts a tendency to split into thin layers
mudstone- non fissle, cleavages not parallel,
rock has a blocky fracture

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23
Q

three major types of sedimentary rocks

A 
coarse clastics (conglomerates, breccias, sandstones) 
fine clastic ( shale and mudstone) 
chemical sedimentary rocks
24
Q

compositional maturity ( quartz)

A

the greater the amount of quartz in a coarse clastic sedimentary rock the higher the compositional maturity

25
Q

common minerals react to form clay if

A

climate conditions are favourable and source area is stable

26
Q

Sorting

A

set of processes that tend to concentrate particles of similar size

27
Q

quartz abrasion when transported

A

when quartz transported –> change in shape due to abrasion –> grains bang together –> sharp corners and rounded edges

28
Q

Feldspars abrasion when transported

A

Feldspars may cleave and retain angular shape when transported

29
Q

Supermature means

A

compositionally and tecturally mature

ex. rock consisting of clastic grains the same size, containing majorly well rounded quartz grains

30
Q

immature composition

A

mixture of sand sized angular quartz grains and clay minerals

31
Q

two types of maturity

A

mineralogical maturity

textual maturity

32
Q

mineralogical maturity

A

extent to which the unstable minerals have been destroyed by weathering

33
Q

textual maturity

A

measures the availability of persistent currents that are needed to produce sorting and rounding of quartz

34
Q

wind water and ice as producing mature sediments

A

wind and water produce mature sediments if slope agents are persistent
ice tends to be unselective, glacial deposits are characteristically poorly sorted and immature

35
Q

two other aspects of sedimentary rocks

A

porosity and permeability

36
Q

porosity

A

percent of open space in the rock

37
Q

permeability

A

extent to which the pores are interconnected so fluids can flow through the rock

38
Q

stored in rocks

A

hydrocarbons and other liwuids (water) stored in rocks that are porous and permeable
smth can be porpous but not permeable (ex. sponge)

39
Q

if permeability changes

A

fluids may be trapped in rock unit creating a reservoir

40
Q

cementation

A

reduced bot porosity and permeability of a coarse clastic rock

41
Q

shales and mudstone (permeability and porosity)

A

low permeability but moderate porsity

may form permeability barriers that prevent fluids from escaping from a reservoir

42
Q

aeolian grain marks

A 
wind transported (aeolian)  grains move through air and impact grains --> pits
pitting increases to give "frosted" look
43
Q

ripples, assymetric and symmetrical

A

ripples (beach area) cusp shaped ridges
location of ancient beaches so where marine met terrestrial environment
symmetry: back and forth of beach current (oscillation ripples)
assymetrical ripples: formed by streams etc with steep side pointing down slope and gentle side up slope

44
Q

cross beds as indicators

A

very thin beds and low velocity –> velocity increases –> some grains are picked up, carried in suspension slope agent –> grains inclined with respect to horizontal plane –> cross beds
cross beds record direction of transport
beds point down stream

45
Q

determine which side of bed was up

A

geopetal structures
oscillation ripple marks form on top of beds deposited along beach
coarsest grains in graded bde were deposited on bottom of bed

46
Q

lacustrine

A

sediment deposited in a lake

47
Q

sediment in transition zone between continent and ocean

A 
sediment can be transported to deep ocean however accumulation low
more accumulation in transition zone
deltas
beaches
barrier islands
48
Q

Pelagic component, 1 way of depositing sediment

A

volcano erupts –> ash transported –> eventually accumilates on ocean floor –> PLANKTON ETC. DIE AND SHEÖLS ACCUMULATE ON SEA FLOOR –> PELAGIC COMPONENT

49
Q

turbidity current, 2 way of depostitng sediment

A

Debris transported rapidly down slope by a turbidity current –> accumulatesat the foot of continental slope –> submarine fan
currentsc haracteristically develop along active continental margins where earthwuake and volcanic eruptions may trigger rapid underwater downslope movement of debris
trubdity currents scour out submarine canconcy, sediment fans out –> deposited as they exit canyon

50
Q

sediments in the deep ocean

A 
coarse sandstones (with fossils), clay minerals, shells of marine organisms
no calcium carbonate past 4000m, only accumulates in warmer, shallow water
51
Q

sediment at beach

A

continental sediment is coarsest
beach sediment is finer
well sorted, offshore material is even finer frained

52
Q

transgression of the marine environment over what had been a continental environment

A

relative rise in sea level resulting in n encroachment

53
Q

regression

A

relative drop in sea level resultimng in migration of continental environment over what had been the marine environment

54
Q

trans and regression caused by glaciers

A

short lives (1000yrs) gressions may be casued by glaciers
glaciers advance –> sea level lower
glaciers retreast –> sea level higher

55
Q

sea floor spreading leads to sea level rise

A

rapid sea floor spreading –> enlargement of mid ocean ridge –> increase in volume of ridge causes ocean water to enroach on land
if rate of spreading slows ridge occupies less volume and ocean water moves away from continent

Surface Processes (14 decks)

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