SEDS: Sandstone Flashcards
the abundance of a particular mineral in a sedimentary rock is dependent on
availability, mechanical and chemical stability
quartz will likely be the only grain that will survive in this condition.
low relief and humid climate
unstable grains will survive in this area
high relief
Unstable grains are called
Labile grains
formed by the breakdown of pre-existing rocks by weathering and erosion, and from material that forms within the depositional environment.
Sand grains
2 types of breakdown products
detrital mineral grains, lithic fragments
Grains that form within the depositional environment are principally ___________
biogenic in origin
defined as a sedimentary rock with grains of these sizes.
Sandstone
Minerals that grow as crystals are called
Authigenic materials
Major Components of Sandstone
Detrital Minerals
Lithic Fragments
Biogenic particles
Authigenic materials – (Minerals that grow as crystals)
Matrix – Fine-grained material
types of lithic grains can be related to the plate tectonic setting of the provenance terrane and adjoining sedimentary basin
Rock Fragments
very useful in studies of the provenance of sandstone, but intravaginal lithics, which are commonly of mud and carbonate, are usually excluded.
Rock Fragments
________ rocks tend to break into individual grains
Plutonic rocks
most common mineral in sandstone; most stable of all minerals
Quartz
The average sandstone contains about ____ quartz
65%
Quartz in Sandstone is derived from
granitoid rocks, acid gneisses and schists
Why is K feldspare (ortoclase and microcline) are much more common in sand stone than plagioclase?
because K feldspar is chemically more stable and is more common in continental basement rocks.
Plagioclases are more common in sandstones derived from
uplifted oceanic and island-arc terranes
feldsp content is largely controlled by
rate of erosion and climate
Humid climates
promotes destruction of feldspars
in Arid environment
-fresh feldsp survive
___________ will produce some feldsp. grains in spite of a humid climate
Rapid erosion
The average percentage of feldspar in Sandstones
10-15%
The average percentage of feldspar in Arkoses
(commonly) reach up to 50%
common in the matrix of sandstones and coarse clastic.
Phyllosilicates
derived from many igneous rocks but are especially from metamorphic rocks.
Muscovite (more common) and biotite
both detrital and authigenic. Kaolinite, illite,
chlorite, smectites, and mixed-layer clays.
Clay
reflect source geology, climate, and weathering processes
Detrital clays
Study of ___________ gives indications of
provenance and of events in the source
area
Heavy Minerals
Metamorphic terranes
garnet,, epidote, and staurolite
Major changes in the source-area geology, such as the uplift and unroofing of a granite may be recorded in
Heavy min assemblage
iron potassium phyllosilicate (mica
group
Glauconite
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.
Chamosite
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.
Point counting
Counting ________ grains will accurately yield the proportion of each component.
250 to 300
graph used for the classification of Sandstone
Petti-john
Sandstones with at least 95% quartz grains
Quartz Aranite
the most compositionally mature, usually consisting of well-rounded and well-sorted grains so that textural maturity is also very high.
Quartz Arenite
in many cases, these are the products of extended periods of sediment reworking
quartz arenites
Why is climate a factor in the composition of Sandstones?
warm, humid climate will lead to the removal of many unstable grains.
factors that allow quartz to dominate in sandstones.
humid climate, low relief, and slow sedimentation
Many quartz grains in these arenites are
2nd cycle (derived from older sediments)
Quartz arenites produced by persistent waves or current reworking were deposited on
stable cratons and passive margins
sandstone that has >25% feldspar, much quartz, and some rock fragments
Arkose
Arkoses are derived from _________________ and vary from in situ weathering products to sandstones that have undergone long transport.
granites and gneisses
Arkoses are typically
poorly- to well-sorted, with very angular to subrounded grains
conditions that are favorable for feldspar to form Arkose
semi-arid and glacial climates, very rapid erosion, and High relief (despite of intense chem weathering)
Many arkoses were deposited in
fluvial environments
Lithic > Felds; These rocks range widely in composition (both grain types and chemistry), depending largely on the rock fragments present.
Litharenites
The immature composition of Litharenites implies
high rates of sediment production
followed by short transport distances
sandstone with a fine-grained matrix, which consists of an intergrowth of chlorite, sericite, and silt-sized grains of quartz and feldspar.
Graywackes
Origin of the matrix = “greywacke problem.”
(a) fine-grained sediment deposited along with the sand fraction, and
(b) diagenetic alteration of unstable rock
fragments.
Feldspar grains in Graywackes are chiefly
Na plag
Greywackes are ___________ in color
dark gray or black
