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SED REC > Siliciclastics > Flashcards

Siliciclastics Flashcards

Sed Rec

1
Q

SILICICLASTIC SEDIMENTS COMPOSE THE FOLLOWING
ROCK TYPES:

A

 Breccia
 Conglomerate
 Sandstone
 Mudstone

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2
Q

MOST TERRIGENOUS GRAINS ARE RICH IN what?

A

QUARTZ

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3
Q

TRANSPORTATION TO THE DEPOSITIONAL SITE CAN OCCUR BY A VARIETY OF AGENTS SUCH AS:

A
  • WIND, WATER, GLACIER, GRAVITATION, ETC.
  • SOURCE AREA FOR SEDIMENTS ARE UPLAND
  • EX: MOUNTAIN REGIONS UNDERGOING UPLIFT ± EROSION IN LOWLAND AND COASTAL AREAS
  • FINAL SEDIMENT COMPOSITION (MINERALOGY) IS AFFECTED BY DISTANCE OF TRANSPORT AND
  • DIAGENETIC PROCESSES
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4
Q

**SEDIMENTARY PARTICLES REQUIRE ENERGY TO MOVE
1. High NRG depositional environments are the
2. Medium-size to fine grains are transported
3. As transport energy drops the size of the smallest particle
carried **

A
  1. largest grain sizes
  2. further away and laid down in lakes, deltas, and oceans
  3. drops proportionally
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5
Q

The Hjulstrom diagram tells us whether a river will do what?

A

erode, transport, or deposit
sediment

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6
Q

The Hjulstrom diagram can be used to reconstruct what?

A

Average water velocity based on grain size.

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7
Q

SEDIMENT TEXTURE: MORPHOLOGY

Morphology (particle shape) is defined by three related but different aspects of grains. What are these?

A
  • Form: refers to the overall configuration of particles and reflects variations in their proportions
  • Roundness: is a measure of the sharpness of grain corners (well-rounded to sharp/angular corners)
  • Surface texture: refers to small-scale, micro-relief markings such as pits, scratches, or ridges that occur on the surface of the grains.
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8
Q

SEDIMENT TEXTURE: FABRIC

What is Fabric?

A

a function of grain orientation and packing.

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9
Q

SEDIMENT TEXTURE: FABRIC

Orientation and grain packing controls what?

A

Bulk density, porosity, and permeability

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10
Q

SEDIMENT TEXTURE: FABRIC

Poorly sorted sediments tend to have what?

A

lower porosities and permeabilities than well-sorted sediments

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11
Q

MINERALOGY OF SILICICLASTIC SEDIMENTS

**SILICICLASTIC ROCKS ARE COMPOSED OF: **

A

CLASTS OF PRE-EXISTING ROCKS AND MINERALS, AND CHEMICAL CEMENTS

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12
Q

CLASTS CONSIST OF MAJOR AND ACCESSORY MINERALS, ROCK FRAGMENTS (LITHICS). WHAT ARE THE MAJOR MINERALS (>1-2%)?

A

Quartz, Feldspar, and chemical cements

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13
Q

CLASTS CONSIST OF MAJOR AND ACCESSORY MINERALS, ROCK FRAGMENTS (LITHICS). WHAT ARE THE ACCESSORY MINERALS?

(<1-2%)

A

Micas (muscovite & biotite) & heavy minerals,
Rock fragments

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14
Q

MINERALOGY OF SILICICLASTIC SEDIMENTS

Quartz

(makeup, origins, stability,etc)

A
  • up to 65% in sandstone and up to 30% in shales
  • mono- or polycrystalline aggregates
  • various origins: igneous, metamorphic (quartzite), chert
  • mechanically & chemical stable, thus abundant
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15
Q

MINERALOGY OF SILICICLASTIC SEDIMENTS

Feldspar

(makeup, origins, stability,etc)

A
  • 10%-15% in sandstone and up to 5% in shales;
  • potassium feldspar (orthoclase, microcline, sanidine)
  • plagioclase (albite to anorthite)
  • less stable, therefore weathers to clay minerals (kaolinite, montmorillonite, smectite, etc.)
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16
Q

MINERALOGY OF SILICICLASTIC SEDIMENTS

Micas + Heavy minerals

(makeup, origins, stability,etc)

A
  • stable non-opaque: zircon, rutile, anatase, tourmaline)
  • metastable non-opaque: amphiboles, garnet, pyroxene, chlorite, epidote, apatite, etc.
  • stable opaque: hematite & goethite
  • metastable non-opaque: magnetite, ilmenite
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17
Q

MINERALOGY OF SILICICLASTIC SEDIMENTS

Rock Fragments

(makeup, origins, stability,etc)

A
  • up to 10%-15%;
  • could be any igneous, metamorphic, or other sedimentary rocks
  • stability varies
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18
Q

MINERALOGY OF SILICICLASTIC SEDIMENTS

What are the chemical cements?

(makeup, origins, stability,etc)

A
  • Silicates (quartz, μquartz, opal, feldspars)
  • Carbonates (calcite)
  • Fe-oxide (hematite goethite)
  • Sulfates (gypsum, anhydrite, barite)
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19
Q

What is Breccia?

(sharpstone)

A
  • lithified rubble made up of angular clasts > 2 mm
  • Generally indicates clasts have not traveled far from their source or were transported by a non-fluid medium (e.g., gravity or glacial ice)
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20
Q

What is Conglomerate?

(roundstone)

A
  • lithified gravel made up of rounded to subrounded clasts > 2 mm
  • Rounded clasts may indicate considerable distance of transport from source
  • Rounding time varies with the lithology of the clast
  • EX: limestone clasts will become round a short distance from their source whereas quartzite will require much greater transport
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21
Q

BRECCIA AND CONGLOMERATE COMPOSITION

What makes up the particle composition?

A
  • mineral fragments (major components: Q, ; 5% or more);
  • mineral clasts (accessory constituents: garnet, Px, Amf, muscovite, zircon, Mgt*; <5%)
  • rock fragments: are typically the most abundant and interesting
  • They can be any variety of igneous (rhyolite), metamorphic (quartzite, slate, marble), or sedimentary rock (limestone)
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22
Q

BRECCIA AND CONGLOMERATE COMPOSITION

What is texture composition?

A
  • Interstitial space between framework grains can be empty (pores), filled with finer-grained
  • detrital matrix, occupied by cement, fluid (water or oil), or natural gas
  • breccia & conglomerate are best studied in the field
  • Difficult to use for stratigraphic correlations because of the lack of fossils
  • Texture and composition provide insights about provenance, depositional environment, paleogeography, and tectonic settings
23
Q

SILICICLASTIC ROCKS

Extraformational Source:

(where found, shape, framework, etc)

A
  • clasts are “exotic”(derived from outside the depositional basin from a distant source)
  • clasts are normally very well rounded and well sorted
  • framework clasts differ markedly from matrix in composition
24
Q

SILICICLASTIC ROCKS

Intraformational Source:

(where found, shape, framework, etc)

A
  • clasts are derived from within the depositional basin
  • clasts are eroded from the same sedimentary rock unit of which they are part
  • framework grains are identical with those of the matrix (e.g., mud clasts)
25
Q

ORTHOCONGLOMERATE IS FROM WHICH SOURCE?

A

Extraformational

26
Q

Characteristics of orthoconglomerate:

A
  • All clasts are in contact and support each other
  • Likely little to no matrix between clasts (open framework)
  • May have matrix of finer sediment between clasts (closed framework)**
27
Q

PARACONGLOMERATES ARE FROM WHICH SOURCE?

A

Extraformational

28
Q

Characteristics of Paraconglomerate:

A
  • Most clasts are not in contact (i.e., the matrix supports the clasts)
  • such conglomerates are typical for deposits of debris flow in which gravel size clasts were less abundant compared to the finer grain size
29
Q

What is a Diamictite?

A
  • a paraconglomerate composed of nonsorted-to-poorly sorted gravel-size grains suspended in a mud matrix
  • glacial origin: meltwater flow, moraines, or ice rafted sediments
30
Q

Orthoconglomerates can be oligomictic or polymictic. Describe each one.

A
  • Oligomictic: Clasts are made up of only one rock type. suggests source was either nearby or extended over a wide geographic area.
  • Polymictic: Clasts include several different rock types. Conglomerates include clasts from a broad-variety of source rocks, possibly derived over a wide geographic area or a smaller, but geologically more complex.
31
Q

What is Sandstone?

A

the indurated equivalent of unconsolidated sand

32
Q

Sandstones make up what percentage of Earth’s sedimentary rocks?

A

20-25%

33
Q

What is Sandstone classification based on?

A

the percentage of matrix and composition of sand framework grains
* Q, F, and lithics (L) (i.e. rock fragments)

34
Q

Arenites and wacke can be further subdivided using the QFL plot. What is the Q: F: L ratio?

A

The Q: F: L ratio is an index of compositional maturity, reflecting
the difference between sand with other soft, unstable rock
fragments and Fp

  • Q, F, L = quartz, feldspar, lithic major constituent (>5%); f, l = feldspar, lithic accessory abundance (<5%)
35
Q

DESCRIBE QUARTZ ARENITES

(texture, composition, color, size, etc)

A
  • Super mature texture and composition
  • Sedimentary structures = small, medium, and large scale cross stratifications
  • Aeolian quartz arenites are commonly red through the presence of finely disseminated hematite (Fe 2 O3 ) which coats grains
36
Q

What is the origin of Quartz Arenites?

A
  • First-cycle deposits derived from primary crystalline or metamorphic rocks
  • Product of multiple recycling of quartz grains from sedimentary rocks
37
Q

What is the depositional environment of Quartz Arenites?

A

Typical of, but not restricted to, high-energy shallow-marine environments and aeolian (wind-blown) sand-seas in desert

38
Q

DESCRIBE FELDSPATHIC ARENITES

(texture, composition, color, size, etc)

A
  • Less mature texturally and compositionally compare to Q-arenites
  • Bedding may range from structureless to parallel laminated or cross-bedded
  • White, gray, or pink color of Fp imparts a similar tint to Fp-arenites
39
Q

What is the depositional environment of Feldspathic Arenites?

A

Semi-arid and glacial climates favor Fp-arenites (arkoses) formation
(under humid conditions, Fp would weather to clay minerals)

40
Q

What is the origin of Feldspathic Arenites?

A

derived from granites and gneisses that were either weathered in situ
(little movement) or when stratified and cross-bedded implies
substantial sediment transport

41
Q

What is the occurrence of Feldspathic Arenites?

A

Cratonic or stable shelf settings, associated with conglomerates,
shallow-water Q-arenites or lithic arenites

42
Q

DESCRIBE LITHIC ARENITES

(texture, composition, color, size, etc)

A
  • Immature to sub-mature composition: Implies high rates of sediment production followed by short to moderate transport distances
  • Sedimentary structures = irregularly bedded, cross-stratified, ripple marks
  • Colors range from light gray, salt-and-pepper to medium, even dark gray
43
Q

What is the origin of Lithic Arenites?

A

Form under conditions favoring the production and deposition of large volumes of relatively unstable materials (mudrock, volcanic grains, muscovite, some Fp)

44
Q

What is the depositional environment of Lithic Arenites?

A

Characteristic of deltaic coastal plains, and may be deposited in nearshore marine environments, swamps, or marshes

45
Q

DESCRIBE WACKES

(matrix, sand fraction, structure, etc)

A
  • Hard, light to dark grey immature rocks as they are made of >15% matrix)
  • Matrix: Chlorite, sericite, and silt-sized grains of Q + Fp. Fine-grained sediment deposited along with the sand fraction or diagenesis
  • Sand fraction: Q&raquo_space; L, Fp
  • Sedimentary structures: sole structures, graded bedding, upward changes
    in grain size characteristics to turbidites
46
Q

What is the origin of Wackes?

BRUH..

A

Deposited by turbidity currents in deep water basins off continental margins,
in back-arc and fore-arc basins

47
Q

What is the occurrence of Wackes?

A

Dominant sandstone of the Archean, when nongranitic volcanic arcs were bordered by deep troughs

48
Q

What is cementation?

A

Involves μ-quartz, chalcedonic quartz and opaline silica
* carbonates may also be involved

49
Q

What is Authigenesis?

A

Is the process in which NEW mineral phases are crystallized in
the sediment following one of the three pathways.

50
Q

What are the three Authigenesis pathways?

A
  • Reactions involving phases already present in the sediment (rock)
  • Reaction between the primary sediment and other components introduced by circulating solutions
  • Through precipitation of materials introduced in the fluid phase
51
Q

What is Feldspar authegenesis?

A
  • When pore waters are rich in Na +, K+, Al 3+, and Si 4+
  • Hydrolysis & dissolution of metastable grains (volcanic ash) or transformation of plagioclase-Fp
52
Q

What is Clay authigenesis?

A
  • Illite & kaolinite are the most common authigenic clays in sandstones
  • Occur as clay rims (early diagenesis) and pore-filling cements (late diagenesis), reducing porosity & permeability
53
Q

DIAGENETIC ENVIRONMENTS

What is Early diagenesis?

A
  • Processes taking place from deposition and into the shallow burial realm
  • Time frame = 1,000 to 100,000 yrs
  • Depth = 1 to 100 m
54
Q

DIAGENETIC ENVIRONMENTS

What is Late diagenesis?

A
  • Processes affecting the sediments at deeper levels, during and after uplift
  • Time frame = million of years
  • Depth = 100 to 10,000 m

SED REC (3 decks)

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