Siliciclastics Flashcards
Sed Rec
1
Q
SILICICLASTIC SEDIMENTS COMPOSE THE FOLLOWING
ROCK TYPES:
A
Breccia
Conglomerate
Sandstone
Mudstone
2
Q
MOST TERRIGENOUS GRAINS ARE RICH IN what?
A
QUARTZ
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
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
- largest grain sizes
- further away and laid down in lakes, deltas, and oceans
- drops proportionally
5
Q
The Hjulstrom diagram tells us whether a river will do what?
A
erode, transport, or deposit
sediment
6
Q
The Hjulstrom diagram can be used to reconstruct what?
A
Average water velocity based on grain size.
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.
8
Q
SEDIMENT TEXTURE: FABRIC
What is Fabric?
A
a function of grain orientation and packing.
9
Q
SEDIMENT TEXTURE: FABRIC
Orientation and grain packing controls what?
A
Bulk density, porosity, and permeability
10
Q
SEDIMENT TEXTURE: FABRIC
Poorly sorted sediments tend to have what?
A
lower porosities and permeabilities than well-sorted sediments
11
Q
MINERALOGY OF SILICICLASTIC SEDIMENTS
**SILICICLASTIC ROCKS ARE COMPOSED OF: **
A
CLASTS OF PRE-EXISTING ROCKS AND MINERALS, AND CHEMICAL CEMENTS
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
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
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
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.)
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
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
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)
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)
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
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)
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
**ORTHOCONGLOMERATE IS FROM WHICH SOURCE?**
Extraformational
26
**Characteristics of orthoconglomerate:**
* 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
**PARACONGLOMERATES ARE FROM WHICH SOURCE?**
Extraformational
28
**Characteristics of Paraconglomerate:**
* 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
**What is a Diamictite?**
* 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
**Orthoconglomerates can be oligomictic or polymictic. Describe each one.**
* 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
**What is Sandstone?**
the indurated equivalent of unconsolidated sand
32
**Sandstones make up what percentage of Earth's sedimentary rocks?**
20-25%
33
**What is Sandstone classification based on?**
the percentage of matrix and composition of sand framework grains
* Q, F, and lithics (L) (i.e. rock fragments)
34
**Arenites and wacke can be further subdivided using the QFL plot. What is the Q: F: L ratio?**
The Q: F: L ratio is an index of compositional maturity, reflecting
the difference between sand with other soft, unstable rock
fragments and Fp
## Footnote
* Q, F, L = quartz, feldspar, lithic major constituent (>5%); f, l = feldspar, lithic accessory abundance (<5%)
35
**DESCRIBE QUARTZ ARENITES**
| (texture, composition, color, size, etc)
* 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
**What is the origin of Quartz Arenites?**
* First-cycle deposits derived from primary crystalline or metamorphic rocks
* Product of multiple recycling of quartz grains from sedimentary rocks
37
**What is the depositional environment of Quartz Arenites?**
Typical of, but not restricted to, high-energy shallow-marine environments and aeolian (wind-blown) sand-seas in desert
38
**DESCRIBE FELDSPATHIC ARENITES**
| (texture, composition, color, size, etc)
* 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
**What is the depositional environment of Feldspathic Arenites?**
Semi-arid and glacial climates favor Fp-arenites (arkoses) formation
(under humid conditions, Fp would weather to clay minerals)
40
**What is the origin of Feldspathic Arenites?**
derived from granites and gneisses that were either weathered in situ
(little movement) or when stratified and cross-bedded implies
substantial sediment transport
41
**What is the occurrence of Feldspathic Arenites?**
Cratonic or stable shelf settings, associated with conglomerates,
shallow-water Q-arenites or lithic arenites
42
**DESCRIBE LITHIC ARENITES**
| (texture, composition, color, size, etc)
* 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
**What is the origin of Lithic Arenites?**
Form under conditions favoring the production and deposition of large volumes of relatively unstable materials (mudrock, volcanic grains, muscovite, some Fp)
44
**What is the depositional environment of Lithic Arenites?**
Characteristic of deltaic coastal plains, and may be deposited in nearshore marine environments, swamps, or marshes
45
**DESCRIBE WACKES**
| (matrix, sand fraction, structure, etc)
* 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 >> L, Fp
* Sedimentary structures: sole structures, graded bedding, upward changes
in grain size characteristics to turbidites
46
**What is the origin of Wackes?**
| BRUH..
Deposited by turbidity currents in deep water basins off continental margins,
in back-arc and fore-arc basins
47
**What is the occurrence of Wackes?**
Dominant sandstone of the Archean, when nongranitic volcanic arcs were bordered by deep troughs
48
**What is cementation?**
Involves μ-quartz, chalcedonic quartz and opaline silica
* carbonates may also be involved
49
**What is Authigenesis?**
Is the process in which NEW mineral phases are crystallized in
the sediment following one of the three pathways.
50
**What are the three Authigenesis pathways?**
* 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
**What is Feldspar authegenesis?**
* 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
**What is Clay authigenesis?**
* 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
# DIAGENETIC ENVIRONMENTS
**What is Early diagenesis?**
* 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
# DIAGENETIC ENVIRONMENTS
**What is Late diagenesis?**
* Processes affecting the sediments at deeper levels, during and after uplift
* Time frame = million of years
* Depth = 100 to 10,000 m
