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Intro to ES > Sed Rx Lab > Flashcards

Sed Rx Lab Flashcards

1
Q

What are the three basic types of Sedimentary Rocks?

A

Clastic – Composed of transported rock and mineral grains that were weathered from pre-existing rock. (Qtz, feldspars, clays =common). Can contain fossils. Clasts = fragments

Chemical- Composed of minerals that grew at the site of deposition by precipitation from solution (water). (Calcite, gypsum, halite, hematite =common). Can contain fossils.

Biological- Composed mostly (or entirely) of fossils.

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2
Q

What is the main characteristic used to classify clastic sedimentary rocks?

A

Grain size

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3
Q

What are the two general types of weathering?

A
  • Physical Weathering
    Breaking of rock into pieces
    No new minerals created
    No minerals destroyed
  • Chemical Weathering
    Chemical reaction of rocks with air/water
    New minerals created
    Old minerals destroyed
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4
Q

What does physical weathering involve?

A

Breaking of rock into pieces without creating or destroying minerals

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5
Q

What is an example of physical weathering?

A

Frost wedging

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6
Q

What is chemical weathering?

A

Chemical reaction of rocks with air/water that creates new minerals

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7
Q

What is an example of chemical weathering?

A

Dissolution of halite in rainwater

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8
Q

What is the process of deposition in sedimentary rock formation?

A

Laying down of sediment carried by a transporting medium

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9
Q

What are clasts in sedimentary rocks?

A

Fragments of transported rock and mineral grains

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10
Q

What are the common minerals in clastic sedimentary rocks?

A
  • Quartz
  • Feldspar
  • Clays
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11
Q

What type of sedimentary rock is formed from the precipitation of minerals from solution?

A

Chemical sedimentary rock

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12
Q

What is the significance of Banded Iron Formations (BIFs)?

A

They record a time when early life began to generate oxygen

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13
Q

What is the main material in coal?

A

Compressed plant materials

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14
Q

What type of sedimentary rock is formed primarily from fossils?

A

Biological sedimentary rock

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15
Q

What is bedding in sedimentary rocks?

A

Layering that occurs due to changes in water velocity or sediment source

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16
Q

What are ripples in sedimentary structures?

A

Waves of sand formed by water or wind currents

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17
Q

Fill in the blank: Sedimentary rocks are comprised of material weathered from _______.

A

[pre-existing rock]

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18
Q

True or False: Sedimentary rocks can contain remnants of ancient organisms.

A

True

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19
Q

Clastic Sedimentary Rocks are formed through a series of processes such as….

A

(1) Weathering, (2) transportation, (3) deposition, (4) compaction, and (5) cementation. The last two steps are commonly referred to as “lithification”.

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20
Q

Describe abrasion

A

Scraping of a rock surface by friction between other rocks and sedimentary particles

Smooths and rounds clasts

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21
Q

Describe frost wedging

A

Repeated freezing and thawing of water
Expansion of ice creates outward force
Cracks are enlarged

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22
Q

Describe root wedging

A

Trees and plants take root in an existing crack in rock
As they grow, expanding roots forces the crack to open further

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23
Q

Describe chemical weathering porcess - dissolution

A

Some minerals are easily dissolved (i.e., halite )
Rainwater (slightly acidic due to dissolved CO2) and groundwater can gradually dissolve rocks that contain such minerals (e.g., calcite and limestone)

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24
Q

_____ topography features (or landscapes) are formed from the dissolution of soluble rock

A

Karst

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25
Q

How do you distinguish between breccia and conglomerate?

A

Conglomerate is composed of large (>2mm) grains/clasts that are round in shape, indicating grains were
transported considerable distances in fast flowing water. Breccia is composed of large, angular grains,
indicating grains underwent very little transport.

26
Q

How do you distinguish between sandstone and conglomerate?

A

Sandstone is composed of sand sized grains that are 0.06-2mm in size, whereas conglomerate is composed
of large grains that are >2mm in size. Both are generally rounded.

27
Q

How do you distinguish between a limestone and shale?

A

Shale can be distinguished from limestone because it is always composed of very fine-grained compacted
clay sized, silicate minerals (<0.004mm) that are microscopic and too small to see with the naked eye. The
accumulation of clay in beds can form in thin layers (laminations) or thicker layers (bedding) that result in
shale to be fissile, meaning it has the tendency to easily split/break along these bedding planes. At a higher
level, shale is classified based on its mineral content, there is siliceous shale (contains mostly silicate
minerals), calcareous shale (contains calcite or dolomite), and even hematitic or limonitic shale that
contains iron minerals. We have learned that there are many minerals that can serve as cement in clastic
minerals. Shale can come in a variety of colors, and that will ultimately depend on the composition of the
grains, and of the cement that holds these particles together. Accordingly, shales are commonly subclassified on the basis of texture, mineralogical composition, type of cementation/cementing materials,
depositional environment, and organic matter content.

Limestone is a general name for a wide variety of sedimentary rocks that are composed primarily of
calcium carbonate. The grainsize in limestone can vary from very fine (microscopic) to visible, and
generally has clastic texture, but can be crystalline if formed chemically; or can be completely biogenic.
Since limestone is composed of carbonate minerals (like calcite and dolomite) it will ALWAYS react to HCl
acid. Note, if the limestone is composed predominantly of dolomite, then the rock will have to be
powdered (scratched) for the reaction to noticeably occur. Both shale and limestone can be fossiliferous
and easily scratched with a penny. Limestone also comes in a range of colors, like gray, white, yellow,
beige, brown, and even blue! these differences are due to the presence of minerals like hematite,
limonite, clay, or organic material like carbon which impose darker shades—these are also described as
impurities in rock

28
Q

How do you distinguish between gypsum and limestone?

A

Gypsum has a very low hardness and can be scratched with a fingernail. Limestone is noticeably harder
than gypsum ranking a 3-4 on the Mohs Hardness scale (with the exception of chalk which is also a
limestone—but is very soft and crumbly because it is composed of microscopic organisms with calcium
carbonate shells). Aside from chalk, other limestones can usually be scratched by a penny if composed of
calcite; and by a steel nail if composed of dolomite or aragonite. Limestone will always react to HCl acid,
gypsum does not react. Pure gypsum is white, but other mineral “impurities” may give a wide range of
colors to gypsum deposits.

29
Q

How do you distinguish between chalk and limestone?

A

Chalk is a form of limestone and it is composed of the shells of calcium-carbonate secreting, microscopic
organisms. Such organisms extract calcium carbonate from the seawater to make a protective shell. And
these shells eventually accumulate on the seafloor at moderate depths. This makes chalk very soft, porous
and crumbly with a very fine texture (because it’s composed of microscopic particles). Chalk is usually
white or light gray in color. Limestone is a general name for a wide-variety of sedimentary rocks that are
composed primarily of calcium carbonate. Limestone is slightly harder than chalk, can come in a variety
of colors and can form in many ways including through chemical precipitation (which will give it a
crystalline texture), biologically (bioclastic) as cemented fossil shells (i.e., coquina), and can also just be
clastic formed by clasts of cemented particles like ooids.

30
Q

How do you distinguish between chert and limestone?

A

Chert is composed of microcrystalline quartz generally formed through the accumulation and
recrystallization of silica-rich microscopic organisms. This means that chert typically looks massive
(homogenous in color with no clear grains), has a very hard hardness and breaks unevenly or fracture. The
“fossiliferous chert” sample in our rock trays is NOT TYPICAL of chert, and likely formed by the following
processes: replacement and permineralization. Replacement occurs when organic anatomical features
have been replicated /replaced by inorganic materials. Permineralization occurs when structures become
entombed within a mineral-filled matrix. Imagine—an original fossiliferous rock (made most likely of
fossils cemented by either calcite and/or mud which produces a fossiliferous limestone or mudstone),
that was LATER submerged in water with dissolved silica (i.e., silica-rich fluids). The original
minerals/materials were replaced and entombed by microcrystalline quartz that preserved the original
structures of the fossils(i.e., the shapes and anatomy of the spiraled snail shells), but CHANGED the overall
composition (i.e., chemical make-up). Limestone is made of carbonate minerals with a soft to
intermediate hardness and will always react to HCl acid, whereas chert will not. If the limestone is
composed mostly of dolomite, then the rock may have to be powdered (scratched) for the reaction to
visibly occur. Any minimal HCl reactions indicate that some of the original shell material is minimally
preserved. Long story short: chert is typically not made of large fossils and is more commonly composed
of microcrystalline quartz with a very fine-grained texture—and exhibits quartz properties like very
hardness and fracture! Unfortunately, it does NOT commonly look like the sample we have in our trays.

31
Q

Explain why beds might vary in thickness and what this might imply about the environment in which these rocks formed.

A

The rate of deposition or sedimentation can cause beds may vary in thickness due to many
reasons including (but not limited to), (a) the density and size of sediments, (b) the energy of the geologic agent of erosion (i.e., water, wind, etc.), (c) changes in sediment source and (d) even weather/climate events. For example, changes in the velocity (current speed) of water and wind currents can cause beds/layers to be variable in thickness, where a more constant flow (i.e., stable and consistent environmental conditions) generally results in thicker beds. Remember that changes in velocity directly affects the size of clasts that can be transported at any given time too. Changes in environments can occur
as a result of sea level rise or fall (i.e., transgression and regressions). For ex., a beach/coastal environment (shallow, high energy) can later become an offshore environment (deep, low energy) due to rising sea
levels (transgression), and the resulting of changes in energy transport will reflect the type and rate of sediments that are deposited. In addition, weather phenomena such as storms and flooding can result in rapid erosion (i.e., at the coast) and re-deposition of sediments away from the source.

32
Q

Study this rock classification flow chart

A
33
Q

What are the four major types of sedimentary rocks?

A

Clastic Sedimentary Rocks
Chemical Sedimentary Rocks
Biochemical Sedimentary Rocks
Organic Sedimentary Rocks

34
Q

What is clastic sedimentation?

A

Clastic sedimentation occurs when particles of rock and minerals are transported by water, wind, or ice, and then deposited when the energy of the transporting medium is not enough to carry the particles further.

35
Q

What is the difference between biochemical and chemical sedimentation?

A

Biochemical Sedimentation: Occurs when living organisms extract ions from water to form shells or bones.

Chemical Sedimentation: Occurs when material dissolved in water chemically precipitates out to form sediments.

36
Q

What are the five processes involved in the formation of clastic sedimentary rocks?

A

Weathering
Erosion
Transportation
Deposition
Lithification (Diagenesis)

37
Q

What is lithification?

A

Lithification is the process by which loose sediment is transformed into solid rock. It involves compaction (pressing grains together) and cementation (minerals precipitate in pore spaces to bind grains).

38
Q

What factors are used to classify clastic sedimentary rocks?

A

Clastic sedimentary rocks are classified by grain size, shape, and composition.

39
Q

What are the sizes of clastic sediment particles?

A

Boulder: > 256 mm
Cobble: 64-256 mm
Pebble: 2-64 mm
Sand: 1/16 - 2 mm
Silt: 1/256 - 1/16 mm
Clay: < 1/256 mm

40
Q

What is sediment maturity?

A

Sediment maturity refers to how long the sediment has been transported. Texturally mature sediment is well sorted and rounded (as rounding increases with transport distance and time), while compositionally mature sediment consists of stable minerals like quartz.

41
Q

What is the composition of sandstones?

A

Sandstones are mostly composed of sand-sized particles, with quartz being the dominant mineral. Variants include Quartz arenite (almost pure quartz), Arkose (high feldspar content), and Lithic sandstone (mostly rock fragments)

42
Q

What are mudrocks, and how are they classified?

A

Mudrocks are fine-grained clastic rocks made of silt and clay. They are classified into:

Siltstone: Contains silt-sized particles.

Shale: Composed of clay-sized particles and tends to break into thin layers.

Mudstone: Similar to shale but does not break into thin layers.

43
Q

What is biochemical limestone?

A

calcite (CaCO3) is precipitated by organisms usually to form a shell or other skeletal structure. Accumulation of these skeletal remains results in a limestone. Sometimes the fossilized remains of the organism are preserved in the rock, other times recrystallization during lithification has destroyed the remains. Limestones are very common sedimentary rocks.

44
Q

What is coal, and how does it form?

A

Coal is an organic rock made from organic carbon that is the remains of fossil plant matter. It accumulates in lush tropical wetland settings and requires deposition in absence of Oxygen. It is high in carbon and can easily be burned to obtain energy.

45
Q

Biochemical and Organic sediments and sedimentary rocks are those derived from living organisms. When the organism dies, the remains can accumulate to become sediment or sedimentary rock. Among the types of rock produced by this process are:

A

Biochemical Limestone

Biochemical Chert - Tiny silica secreting planktonic organism like Radiolaria and Diatoms can accumulate on the sea floor and recrystallize during lithification to form biochemical chert. The recrystallization results in a hard rock that is usually seen as thin beds (see figure 7.8a in your test).

Diatomite - When diatoms accumulate and do not undergo recrystallization, they form a white rock called diatomite as seen in the White Cliffs of Dover (see figure 7.22b in your text).

Coal

46
Q

What are the main types of sedimentary structures?

A

Stratification (Bedding)
Cross Bedding
Graded Bedding
Ripple Marks
Mudcracks
Sole Marks
Raindrop Marks
Fossils

47
Q

Groundwater containing dissolve Calcium and bicarbonate ions can precipitate calcite to form a chemically precipitated limestone, called ______________. This can occur in lakes, hot springs, and caves.

A

travertine

48
Q

Groundwater flowing through rock can precipitate SiO2 to replace minerals that were present. This produces a non-biogenic chert. There are many varsities of such chert that are given different names depending on their attributes, For example:

A

Flint – Black or gray from organic matter.

Jasper – Red or yellow from Fe oxides.

Petrified wood – Wood grain preserved by silica.

Agate – Concentrically layered rings

49
Q

A series of beds are referred to as ______.

A

strata

50
Q

A sequence of strata that is sufficiently unique to be recognized on a regional scale is termed a ____________.

A

formation

51
Q

What is Rhythmic Layering

A

Alternating parallel layers having different properties. Sometimes caused by seasonal changes in deposition (Varves). i.e. lake deposits wherein coarse sediment is deposited in summer months and fine sediment is deposited in the winter when the surface of the lake is frozen.

52
Q

Cross Bedding is

A

Sets of beds that are inclined relative to one another. The beds are inclined in the direction that the wind or water was moving at the time of deposition. Boundaries between sets of cross beds usually represent an erosional surface. Very common in beach deposits, sand dunes, and river deposited sediment.

53
Q

Graded Bedding is

A

As current velocity decreases, first the larger or more dense particles are deposited followed by smaller particles. This results in bedding showing a decrease in grain size from the bottom of the bed to the top of the bed. Sediment added as a pulse of turbid water. As pulse wanes, water loses velocity and sediments settle. Coarsest material settles first, medium next, then fine. Multiple graded-bed sequences called turbidites

54
Q

Non-sorted Sediment is

A

Sediment showing a mixture of grain sizes results from such things as rockfalls, debris flows, mudflows, and deposition from melting ice.

55
Q

Mudcracks are:

A

result from the drying out of wet sediment at the surface of the Earth. The cracks form due to shrinkage of the sediment as it dries. When present in rock, they indicate that the surface was exposed at the earth’s surface and then rapidly buried.

56
Q

Sole Marks are

A

Flutes are troughs eroded in soft sediment that can become filled with mud. Both the flutes and the resulting casts (called flute casts) can be preserved in rock.

57
Q

What is the difference between transgression and regression?

A

Transgression: Sea level rises, and the coast moves inland. Beach sand gets buried by marine sediments and the sea floor subsides due to the weight of the sediment. During a transgression, the beach sand forms an extensive layer, but does not all have the same age.

Regression: When sea level falls, the coast migrates seaward. This is called a Regression. The sedimentary sequence then repeats itself in a vertical sense as the sedimentary environment migrates back and forth.

58
Q

How does the color of sediment indicate environmental conditions?

A

Red sediment: Indicates an oxidizing environment (presence of iron oxides).

Black sediment: Indicates a reducing environment with abundant organic matter (e.g., peat, coal).

59
Q

What are the terrestrial non marine environments in which sed rx are divided.

A

Glacial

Alluvial fans

Sand Dunes

Mountain Streams

Lakes

Rivers

60
Q

What are the marine environments in which sed rx are divided.

A

Deltas

Coastal Beaches

Shallow Marine Clastics

Shallow Marine Carbonates

Deep Marine

61
Q

What is diagenesis?

A

Diagenesis refers to the processes that transform loose sediment into solid rock, including compaction, cementation, and mineral recrystallization.

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