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Geology > Sedimentary rocks > Flashcards

Sedimentary rocks Flashcards

1
Q

where are sedimentary rocks formed

A

at earth’s surface
cover underlying igneous or metamorphic rocks
upper part of crust

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2
Q

name the 4 types of sedimentary rocks

A

clastic
biochemical
organic
chemical
raw material provided by physical and chemical weathering

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3
Q

clastic sedimentary rocks

A

consist of detritus (loose clast) and cementing material

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4
Q

how are clastic sedimentary rocks created? WETDL

A

weathering
erosion
transportation
deposition
lithification

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5
Q

classification through clast size

A

diameter of fragments or grains
coarse to fine: boulder, cobble,pebble,sand,silt,clay
gravel = coarse
mud = fine

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6
Q

classification through clast composition

A

mineral makeup of sediments
tells story about original source rock

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7
Q

classification through shape

A

angularity: degree of edge or corner smoothness (fresh detritus)
sphericity: how much a clast resembles a sphere (increases with transport)

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8
Q

classification through sorting

A

unifority of grain size
well-sorted = nearly same grain size
poorly sorted = variety of sizes

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9
Q

classification through cement

A

different clastic sedimentary rocks have different cement
QUARTZ AND CALCITE (minerals) most common

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10
Q

Breccia

A

coarse clastic
angular rock fragments
deposited close to clast source

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11
Q

conglomerate

A

coarse
rounded rock clasts by flowing water
deposited further from source (eg. river channel)

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12
Q

arkose

A

coarse clastic
sand and gravel with lots of feldspar
feldspar indicated SHORT transport

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13
Q

sandstone

A

rock made of sand-sized particles. common in beach and dune setting. lots of quartz found in sandstones

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14
Q

fine clastics

A

deposited in quiet water settings
silt becomes siltstone
mud becomes mudstone or shale
lithification

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15
Q

biochemical sedimentary rocks

A

sediments derived from shells of living organisms
hard mineral skeletons accumulate after death

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16
Q

limestone

A

sedimentary rocks made of caco3
fossiliferous = visible fossil shells
micrite = fine carbonate mud
chalk = made up of plankton shells

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17
Q

chert

A

made of cryptocrystalline quartz
silica skeletons of some marine plankton
after burial, silica in bottom sediments dissolves
silica in pore fluids solidifies as a gel

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18
Q

organic sedimentary rocks

A

made of organic carbon
OIL SHALE: clay + organic material
COAL: altered remains of fossil vegetation. 50-90% carbon

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19
Q

chemical sedimentary rocks

A

minerals precipitated from water solution
crystalline texture

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20
Q

evaporites

A

rocks from evaporated sea or lake water
evaporation triggers deposition of chemical precipitates
halite and gypsum

21
Q

travertine

A

caco3 precipitated from ground water where it reaches the surface
CO2 expelled into the air causes caco3 to precipitate (thermal or caves)

22
Q

dolostone

A

limestone altered by Mg-rich fluids

23
Q

replacement chert

A

when other material is replaced by silica
flint
agate
petrified wood
FAP

24
Q

diagenesis

A

physical chemical and biological changes to sediment
as sediments are buried, p and t increase. lithification, chemical reactions, precipitation and dissolution can occur

25
Q

bedding and stratification

A

sedimentary rocks usually layered or stratified. planar, close to horizontal beds.
bedding plane boundary between two beds.
strata = several beds.
sequence of bed is bedding or stratification

26
Q

bedding forms change due to:

A

climate
water depth
velocity
sediment source
sediment supply

27
Q

formation

A

depositional changes vary the stacking of rock features. unique packages over a region

28
Q

ripple marks

A

small scale ridges and troughs
sandy sediments
perpendicular to flow

29
Q

dunes

A

similar to ripple marks but much larger
forms from water or wind transport of sand
streams and desert or beach
preserve internal cross beds

30
Q

cross beds

A

created by ripple and dune migration
sediment moves up gentle side of ripple or dune
sediment piles up then slips down steep face
slip face moves downcurrent

31
Q

turbidity currents and graded beds

A

turbidity current moves rapidly, carrying a mixture of coarse and fine sediments.
As the current slows down, larger and heavier particles settle first, creating the lower, coarser part of the graded bed.

32
Q

mudcracks

A

polygonal dessication in wet mud
alternating wet and dry terrestrial conditions
scour marks: troughs eroded in soft mud by current flow

33
Q

glacial deposition environments

A

due to movement of ice
terrestrial
ice carries and dumps grain size
creates glacial till, poorly sorted

34
Q

mountain stream deposition environments

A

terrestrial
fast flowing water carries large clasts during flodos
low flow: cobbles and boulders are immobile

35
Q

alluvial fan

A

terrestrial
sediments pile up at a mountain front
drop in stream velocity creates cone-shaped wedge
sediments become conglomerate and arkose FELDSPAR

36
Q

sand dune deposition environments

A

wind-blown, well-sorted sand, aeolian deposition
move according to winds, result in uniform sandstones with cross beds

37
Q

river deposition environments

A

channelized sediment transport
sand and gravel fill concave up channels
deposition on nearby flood plains

38
Q

deltas

A

sediments pile up where a river enters a lake
or where a river enters the sea. sediment dumped when velocity drops. grow over time. marine deltas more complicated than lake deltas

39
Q

coastal beach sand

A

marine
sand moves along coastline
Every wave brings in new sediments that form a ripple formation and it is preserved by pressure of water and of new sediments

40
Q

shallow marine clastic deposit

A

finer sands, silts, muds
deposited offshore where energy is low
finer silts and muds turn into siltstones and mudstones

41
Q

shallow water carbonate environments

A

sediments are carbonates, shells of organisms
clear, free of clastic sediments
blue water, coral reef

42
Q

deep marine deposits

A

fines settle out far from land
skeletons of. planktonic organisms make chalk or chert
fine silt and clay lithify into shale

43
Q

what is subsidence? what are basins?

A

subsidence: sinking of the land during sedimentation
basins: where sediment accumulates. thicker surface

44
Q

foreland basins

A

weight of mountain belt pushes down crust’s surface

45
Q

rift basins

A

down-dropped basin formed during rifting because of stretching and thinning of the continental crust. sediments fill troughs formed

46
Q

intracontinental basins and passive margins basins

A

intracontinental = interior of continent
passive margin = far from plate boundary at continental edge. Subsidence along a passive margin, mostly due to long-term accumulation of sediments on the continental shelf

47
Q

transgression

A

flooding due to sea-level rise. sediments belts sift landward

48
Q

regression

A

sea level fall
depositional belts shift seaward. tied to erosion

Geology (19 decks)

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