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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
bedding and stratification
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
bedding forms change due to:
climate water depth velocity sediment source sediment supply
27
formation
depositional changes vary the stacking of rock features. unique packages over a region
28
ripple marks
small scale ridges and troughs sandy sediments **perpendicular to flow**
29
dunes
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
cross beds
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
turbidity currents and graded beds
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
mudcracks
polygonal dessication in wet mud alternating wet and dry terrestrial conditions scour marks: troughs eroded in soft mud by current flow
33
glacial deposition environments
due to movement of ice terrestrial ice carries and dumps grain size creates glacial till, poorly sorted
34
mountain stream deposition environments
terrestrial fast flowing water carries large clasts during flodos low flow: cobbles and boulders are immobile
35
alluvial fan
terrestrial sediments pile up at a mountain front drop in stream velocity creates cone-shaped wedge sediments become conglomerate and arkose FELDSPAR
36
sand dune deposition environments
wind-blown, well-sorted sand, aeolian deposition move according to winds, result in uniform sandstones with cross beds
37
river deposition environments
channelized sediment transport sand and gravel fill concave up channels deposition on nearby flood plains
38
deltas
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
coastal beach sand
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
shallow marine clastic deposit
finer sands, silts, muds deposited offshore where energy is low finer silts and muds turn into siltstones and mudstones
41
shallow water carbonate environments
sediments are carbonates, shells of organisms clear, free of clastic sediments blue water, coral reef
42
deep marine deposits
fines settle out far from land skeletons of. planktonic organisms make chalk or chert fine silt and clay lithify into shale
43
what is subsidence? what are basins?
subsidence: sinking of the land during sedimentation basins: where sediment accumulates. thicker surface
44
foreland basins
weight of mountain belt pushes down crust's surface
45
rift basins
down-dropped basin formed during rifting because of stretching and thinning of the continental crust. sediments fill troughs formed
46
intracontinental basins and passive margins basins
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
transgression
flooding due to sea-level rise. sediments belts sift landward
48
regression
sea level fall depositional belts shift seaward. tied to erosion

Geology (18 decks)

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