Sedimentary Petrology Oppo Exam 2 (excluding diagenesis)

Average heavy-mineral content of sandstone is about ____or less

1%

micas make up ___ of framework grains. they're mostly found in _____ and _____

2%; very fine sands; silts

quartz commonly takes up ____ of the common sandstone

2/3

quartz arenites facts:

90-95% quartz, well lithified, mature, hardly any matrix, a lot of overgrowths, most are multicycle deposits, and is mainly quartz because less stable minerals are weeded out through rough erosion/weathering practice

matrix size:

<0.03 mm

Lithic arenites facts:

<90% quartz, rock fragments exceeds feldspars; occur in fluvial deposits, deeper water depositional environment, and submarine basalts; fine to coarse grained, high matrix content makes it immature; silica overgrowth cement is abundant; can preserve organic material; 1st cycle sediments

arkose generally means

>1/4 feldspars

Feldspathic arenites facts:

>25% feldspar, 50-60% quartz. immature because they're typically young due to their instability, matrix at 15%, typically 1st cycle sediment, most common cement is carbonate, K-feld is most common, coarse grained, best preserved in cold/arid environments,

List parts in a Bouma unit from bottom to top:

A: massive sandstone, coarse to pebbly. Coarser one. B: parallel lamination in coarse-medium sand. Decreased sand size C: cross laminated rippled sandstone. Even more decreased sand size. Ripples that are climbing. D: laminated silts from tails of turbulence current (turbidite). Normal oceanic deposition. E: pelagic mud, structureless

Why do sandstones contain less than .1% of organic matter in them?

As soon as it deposits in an oxygenated environment, it begins to dismantle through oxidation.

Heavy minerals assumption in provenance: (2)

Assumption 1: each major source rock has a distinctive suite of heavy minerals (not always true) Assumption 2: all detrital assemblages accurately reflect originally present minerals in parent rocks. (almost impossible)

For Quartz provenance: cathodoluminescence shows fabric that show provenence. Volcanic quartz shows ____; plutonic quartz shows _____; metamorphic quartz shows _____;

CL zoning (alternating dark and light bands); spiders, rutile needles, repaired fractures; Mottled texture: light colored dots Shows incomplete recrystallization or annealing (cools down v slowly), Homogenous texture: Shows Recrystallization at high temperatures, Recrystallization: quartz dissolution of grain squished together by pressure, where they dissolve one into the other.

Quartz provenance: Volcanic quartz properties show that it

Doesn't contain so many vacuoles and is most of the time nearly water-clear

the ____ classification is your standard triangle with tail triangles on the feldspar and lithic respectively. one feldspar triangle and two lithic triangles

Folk

__________ (name) classification is based upon both the composition of framework grains and the abundance of matrix

Gilbert's

Potassium-sodium (alkali) feldspars are constituents of: (3)

Igneous rocks, pegmatites, many felsic and intermediate gneisses

Sand waves/dunes signals the _____ in ______ of ______.

Increase; strength; fluid

the _____ classification involves the lithic subarkose part in between feldspars, quartz, and lithic.

McBride

provenance interpretations are based on: (2)

Mineralogy/composition and Presence of directional features in the rocks

Orthoclase and microcline feldspars are constituents of: (2)

Plutonic felsic rocks and high-grade metamorphic rocks

List structures on upper bedding surfaces: (6)

Ripple marks, sand waves/dunes, Plane beds (primary current lineation), Mudcracks (desiccation/syneresis cracks), rain drop imprints, tracks & trails.

Opal is

SiO2 that contains a few percent water. It consists of mixtures of amorphous and crystalline silica

Detrital particles includes: (8)

Silica minerals Feldspars Coarse micas Clay minerals Heavy minerals Rock fragments Skeletal remains Organic matter

inverse/reverse grading:

Starts fine goes coarse

reactivation surfaces

System stops for whatever reason, a portion of ripple is removed and leaves an obvious downwards slope, when current reactivates, it'll continue on leaving the reactivation surface behind

terminology for distinguishing between strata and lamination: (7)

Very thickly bedded > 1m Thickly bedded- 30cm-1m Medium bedded- 10-30 cm Thinly bedded-3-10 cm Very thinly bedded- 1-3 cm Thickly laminated- .3-1cm Thinly laminated- <.3 cm

Plane beds, primary current lineation

Water just above the bed creates turbulence to erode/transport. lineation shows indication direction of the flow

Sedimentary structures are formed by: (4)

Weathering agents forms shape of structure, Gravity slumping or sediment loading that deforms sediments, Biogenic origin formed by burrowing/boring/browsing/sediment binding activities of organisms, Some types of bedding like laminated bedding of evaporites are generated by primary chemical precipitation processes

chalcedony is

a fibrous variety of quartz containing submicroscopic pores. "feathery"

Trace elements abundances are given in ________

actual concentration units such as ppm

oscillatory zoning:

alternating dark/bright thin bands, Indicative of volcanic or hypabyssal origin

Climbing ripple cross lamination

angle of climb is bigger than the stoss side angle. Happens when there's a supercritical flow.

current ripple marks are____ because______

asymmetrical; current flows in the same direction

The principal source for detrital plagioclase is probably

basic and intermediate lavas, where it occurs as phenocrysts

horizontal bedding/lamination: determining sizes between bedding and lamination of strata

bedding >1cm; lamination <1cm

Organic material appears as ___________ under thin section

black/opaque or brownish translucent/transparent particle

Cathodoluminescence:

bombarding mineral with stream of high energy electrons in a scanning electron microscope to obtain emission of photons

progressive zoning:

broad wave of extinction, has no value in distinguishing between sources.

Detrital micas are ____ grained and derived mainly from ___ rocks. Also ____ (type if igneour rock)

coarse; metamorphic; granite

Feldspars are the most

common framework mineral in sands and sandstones after quartz

fewer rock fragments in _____ (quartz-rich) sandstones than in __________ sandstones. therefore, more rock fragments mean the sandstone is ____ in age.

compositionally mature; immature; young

Lee Side

crest drops low into trough

Examples of Ripple marks (5)

current ripple marks, wave-formed ripple marks, stoss side, lee side, increase in velocity results.

Rock fragments are

detrital particles made up of two or more mineral grains

authigenic minerals reflect conditions of the ________ environment

diagenetic

opal-CT is

disordered cristobalite/tridymite

sandstone classification types: (2)

epiclastic and volcaniclastic

climbing-ripple lamination is caused by a current ________ at the ___________part, and deposited more _______ at the ripples.

eroding; parallel (already deposited); sediment

Volcaniclastic deposits are those that are:

especially rich in volcanic debris, including glass, consist principally of pyroclastic materials derived through explosive volcanism

in making provenance interpretation of siliciclastic sedimentary rocks, the modal composition of detrital sediments faithfully reflects the composition of the source rocks

false

block faulted continental basements form ____ rich sandstones

feldspar

sandstones with >1/4 feldspar content is considered

feldspar rich

volcanic island arcs form more _____ and ____ rich sandstones

feldspar; lithic

predominance of sand cross laminated intervals and units. Less than 50% muddy matrix. More sand than mud. This bedding type is called

flaser bedding

Epiclastic deposits are formed from :

fragments of pre-existing rocks, composed mainly of silicate minerals and various kinds all 3 rock type fragments

epiclastic sandstones are identified by

framework grains

what are the geologist's 4 components of sandstones?

framework grains, matrix, cement, and pores

what are the 3 principle types of pyroclasts:

glassy fragments, crystals, and lithic fragments

graywacke is

gray, matrix rich sandstones

Coarse tail Normal Grading:

has fine grained in between the coarse grains, still has coarse going fine

Structures within bedding: (4)

horizontal bedding and lamination, cross bedding and cross lamination, graded bedding, slump folds/ convolute lamination

For Quartz provenance: cathodoluminescence shows colors that show provenence. Blue/violet = ____, red = ____, brown = _____, no color=_____, short lived blue or green = _____

igneous plutonic; volcanics only; metamorphic; authegenic; hydrothermal/pegmatitic

Tuffs are mixed origin. Comes through ______ processes and deposited through ________ processes.

igneous; sedimentary

Antidunes are ____, meaning the water surface elevation mimics the bed elevation. When wave ____, sediment is _____.

in phase; breaks; deposited

Properties with possible provenance significance for quartz:

inclusions undulatory extinction polycrystallinity nature of subgrain contacts grain shape or crystal shape trace-element composition cathodoluminescence properties

When current velocity is ________, it breaks up ____________________. ___________________________.

increased; intensity of a single ripple; straight line ripple turns into isolated parentheses shaped ripples

polycrystalline quartz (3 facts)

is extremely common in some sediments aggregates of two or more crystals can develop from monocrystalline quartz during metamorphism

Aggradation:

layering upwards

small lenses of sand in muddy beds are called

lenticular bedding

types of cross bedding and cross lamination: (5)

lenticular, flaser, wavy, hummocky, reactivation surfaces

Feldspars are ___ stable than quartz

less

Quartz inclusions have _______ in provenance significance

limited value

On the basis of particle composition, volcaniclastic sandstones classify as _________ (wackes) or ________

lithic arenites; feldspathic arenites

Unless authigenic minerals form quite early, while sediment is still very close to the depositional interface, they provide _____useful information about depositional conditions

little

skeletal remains in sandstones are_________, and important for interpreting the _____ and mainly important in _____ rocks

low in abundance; paleoenvironment; carbonate

Stoss side-

low in trough eases up to crest at top

list off some opaque heavy minerals:

magnetite, ilmenite, hematite and limonite, pyrite, and leucoxene

In sandstones, clay minerals are most common within _____

matrix

minerals involved are unstable, so they can be altered diagenetically to form _______

matrix

Amorphous opal (opal-A) is

metastable. its very small, packed, spherical masses and transforms in time to opal-CT.

Orthoclase and microcline appear to be by far the

most abundant potassium feldspars in sandstones

feldspar provenance is the _____ in telling source-rock lithology

most useful

metamorphic plagioclase is almost _______ zoned

never

Slumps/folds/convolute lamination:

not formed in place, shifted angles, tiny folds overlapping in cross section

Heavy minerals are divided into two groups on the basis of optical properties:

opaque, nonopaque

For antidunes, Sediment migrates on the ______ side of the dune. Eroded on the ____ side and deposited on the ____ side. this means they migrate ____.

opposite; lee; stoss; upstream

zoning of feldspars: (2)

oscillatory and progressive

Major elements are expressed as ________, and the abundances reported in ___________

oxides; weight percent of total oxides

the most important part of sandstones are their ____.

particle composition

textural inversion is

poor sorting and high rounding

particle composition of sandstones include:

porosity and framework grains

stable continental craton produces ___ rich sandstones

quartz

major petrographic divisions:

quartz arenites, feldspathic arenites, lithic arenites, and their respective wackes

The principal crystalline varieties of SiO2 are:

quartz, cristobalite (metastable), and tridymite (metastable)

recycled orogen produces more _____ and ____ rich sandstones

quartz; lithic

Hummocky/Swaley cross stratification

result of storms. hummocky- mounds, swales-valleys

Climbing-ripple lamination:

ripples succeed one another upward in such a manner that the crests of vertically succeeding ripples are out of phase and appear to be advancing or climbing in a down current direction

about 10-20% of the framework grains in average sandstones are:

rock fragments

Detrital micas are rarely ____. they're normally ___-round diagenetic minerals.

rounded; first

Recrystallization of quartz eventually turns it into

schistose

wave formed ripple marks are ____ and have ____. They're formed by ___

shallow marine ripple marks; symmetrical; formed by waves going out and back in.

secondary silica cementation is a fancy word for

silica overgrowths

Major elements of oxides: (8)

silicon, aluminum, iron, sodium/potassium, magnesium, titanium, phosphorous

Metamorphic rocks are more __________ and _________ with much less gradient. Potassium is nearly __________

sodium; calcium; nonexistent.

Plutonic rocks are more _______ and ______ rich with a smaller amount of __________.

sodium; calcium; potassium

list structures on lower bedding surfaces: (2)

sole marks, evaporite crystal molds

Authigenic:

something formed in the place where you find it

Normal grading:

start coarse then progressively goes fine

Antidunes occur in _____________ flow

supercritical flow

A weak asymmetrical current ripple stratification would look more _______, and a _________ one would be very mixed up and together

tabular; powerful/high energy;

Major element chemistry can provide info about ___________ of sandstone's accumulation

tectonic settling

rock fragments are ____ for determining provenance

terrible

some quartz arenites show ______. this is due to mixing of grains from many different sources.

textural inversion

why are sandstones a "restricted suite of minerals"?

the processes of chemical weathering and physical and chemical attack during transport, deposition, and burial gets rid of most particles.

Provenance is

the study of the location of the sediment source area

Apatite fission tracks:

thermochronology

Detrital constituents are defined as

those derived by mechanical and chemical disintegration of a parent rock

sole marks include:

tool marks - grooves, prods etc. groove casts- trails left behind from clasts moving with current scour marks - flutes, etc. load casts- billowy mud deposits

Epiclastic sandstone classification includes the ____ classification charts

triangle

Sand size volcaniclastic rocks formed by primary volcanic processes are called _______.

tuffs

quartz found in sandstones can be polyciclic, meaning:

undergo several cycles of diagenesis

Climbing-ripple lamination is where crests of _____ are _______ and appear to be ___________ in a current direction.. Looks like shadows from a light source at an angle.

vertically succeeding; out of phase; advancing/climbing down

plagioclase are constituents of:

volcanic, igneous, and metamorphic. presence of twinning indicates igneous

most epiclastic volcaniclastic sandstones are __________ rather than arenites

wackes

____ and ____ are the most effective weathering agents of quartz arenites

waves and wind

equal mix of small lenses of sand and muddy beds are called

wavy bedding

reliability of feldspar provenance heavily relies on

weathering, transportation (abrasion and impact), and diagenesis

whats used to date heavy minerals?

zircon

Sandstone = ___ sed. rocks in geologic record

¼