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Geology Board Exam Day 2 > SEDS: Sandstone > Flashcards

SEDS: Sandstone Flashcards

1
Q

the abundance of a particular mineral in a sedimentary rock is dependent on

A

availability, mechanical and chemical stability

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2
Q

quartz will likely be the only grain that will survive in this condition.

A

low relief and humid climate

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3
Q

unstable grains will survive in this area

A

high relief

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4
Q

Unstable grains are called

A

Labile grains

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5
Q

formed by the breakdown of pre-existing rocks by weathering and erosion, and from material that forms within the depositional environment.

A

Sand grains

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6
Q

2 types of breakdown products

A

detrital mineral grains, lithic fragments

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7
Q

Grains that form within the depositional environment are principally ___________

A

biogenic in origin

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8
Q

defined as a sedimentary rock with grains of these sizes.

A

Sandstone

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9
Q

Minerals that grow as crystals are called

A

Authigenic materials

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10
Q

Major Components of Sandstone

A

Detrital Minerals
Lithic Fragments
Biogenic particles
Authigenic materials – (Minerals that grow as crystals)
Matrix – Fine-grained material

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11
Q

types of lithic grains can be related to the plate tectonic setting of the provenance terrane and adjoining sedimentary basin

A

Rock Fragments

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12
Q

very useful in studies of the provenance of sandstone, but intravaginal lithics, which are commonly of mud and carbonate, are usually excluded.

A

Rock Fragments

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13
Q

________ rocks tend to break into individual grains

A

Plutonic rocks

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14
Q

most common mineral in sandstone; most stable of all minerals

A

Quartz

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15
Q

The average sandstone contains about ____ quartz

A

65%

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16
Q

Quartz in Sandstone is derived from

A

granitoid rocks, acid gneisses and schists

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17
Q

Why is K feldspare (ortoclase and microcline) are much more common in sand stone than plagioclase?

A

because K feldspar is chemically more stable and is more common in continental basement rocks.

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18
Q

Plagioclases are more common in sandstones derived from

A

uplifted oceanic and island-arc terranes

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19
Q

feldsp content is largely controlled by

A

rate of erosion and climate

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20
Q

Humid climates

A

promotes destruction of feldspars

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21
Q

in Arid environment

A

-fresh feldsp survive

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22
Q

___________ will produce some feldsp. grains in spite of a humid climate

A

Rapid erosion

23
Q

The average percentage of feldspar in Sandstones

A

10-15%

24
Q

The average percentage of feldspar in Arkoses

A

(commonly) reach up to 50%

25
Q

common in the matrix of sandstones and coarse clastic.

A

Phyllosilicates

26
Q

derived from many igneous rocks but are especially from metamorphic rocks.

A

Muscovite (more common) and biotite

27
Q

both detrital and authigenic. Kaolinite, illite,
chlorite, smectites, and mixed-layer clays.

A

Clay

28
Q

reflect source geology, climate, and weathering processes

A

Detrital clays

29
Q

Study of ___________ gives indications of
provenance and of events in the source
area

A

Heavy Minerals

30
Q

Metamorphic terranes

A

garnet,, epidote, and staurolite

31
Q

Major changes in the source-area geology, such as the uplift and unroofing of a granite may be recorded in

A

Heavy min assemblage

32
Q

iron potassium phyllosilicate (mica
group

A

Glauconite

33
Q

the Fe2+ end member of the chlorite
group;

A hydrous aluminum silicate of iron, which is produced in an environment of low to moderate grade of metamorphosed iron deposits, as gray or black crystals in oolitic iron ore.

A

Chamosite

34
Q

a method whereby a thin section on a petrographic microscope is examined by stepping across the thin section at equal intervals and identifying the material (quartz, feldspars, rock fragments, or matrix) that lies immediately beneath the crosshairs.

A

Point counting

35
Q

Counting ________ grains will accurately yield the proportion of each component.

A

250 to 300

36
Q

graph used for the classification of Sandstone

A

Petti-john

37
Q

Sandstones with at least 95% quartz grains

A

Quartz Aranite

38
Q

the most compositionally mature, usually consisting of well-rounded and well-sorted grains so that textural maturity is also very high.

A

Quartz Arenite

39
Q

in many cases, these are the products of extended periods of sediment reworking

A

quartz arenites

40
Q

Why is climate a factor in the composition of Sandstones?

A

warm, humid climate will lead to the removal of many unstable grains.

41
Q

factors that allow quartz to dominate in sandstones.

A

humid climate, low relief, and slow sedimentation

42
Q

Many quartz grains in these arenites are

A

2nd cycle (derived from older sediments)

43
Q

Quartz arenites produced by persistent waves or current reworking were deposited on

A

stable cratons and passive margins

44
Q

sandstone that has >25% feldspar, much quartz, and some rock fragments

A

Arkose

45
Q

Arkoses are derived from _________________ and vary from in situ weathering products to sandstones that have undergone long transport.

A

granites and gneisses

46
Q

Arkoses are typically

A

poorly- to well-sorted, with very angular to subrounded grains

47
Q

conditions that are favorable for feldspar to form Arkose

A

semi-arid and glacial climates, very rapid erosion, and High relief (despite of intense chem weathering)

48
Q

Many arkoses were deposited in

A

fluvial environments

49
Q

Lithic > Felds; These rocks range widely in composition (both grain types and chemistry), depending largely on the rock fragments present.

A

Litharenites

50
Q

The immature composition of Litharenites implies

A

high rates of sediment production
followed by short transport distances

51
Q

sandstone with a fine-grained matrix, which consists of an intergrowth of chlorite, sericite, and silt-sized grains of quartz and feldspar.

A

Graywackes

52
Q

Origin of the matrix = “greywacke problem.”

A

(a) fine-grained sediment deposited along with the sand fraction, and

(b) diagenetic alteration of unstable rock
fragments.

53
Q

Feldspar grains in Graywackes are chiefly

A

Na plag

54
Q

Greywackes are ___________ in color

A

dark gray or black

Geology Board Exam Day 2 (17 decks)

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