Siliciclastic Sandstones Flashcards
(18 cards)
What are the different classifications of the Folk diagram?
The more mud, the more/less mature. The more quartz, the more/less mature.
less, more
T/F: Immature sandstone has no feldspar.
F, a lot of
What is Provenance?
All characteristics of a sediment or sedimentary rock source area, including source area composition, source area location (distance and direction) and source area relief. From French, provenire “to come forward”
Study this provenance diagram
Describe some qualities of quartz arenites
Over 90% quartz
Warm humid climates weather unstable grains more quickly such as feldspars and lithics leaving resistant quartz to dominate
Could be reworked (second gen) sedimentary rocks – look for abraded overgrowths (the inside space the grain can have coating of quartz)
Commonly form in stable cratons on passive margins (shores)
Describe some qualities of arkoses
- Common in rift basins, lots of feldspar bc less heavily weathered so show up in sandstone
- White feldspar can be mixed up with milky quartz
- Parent rocks granites and gneisses
- poorly sorted
- angular to subrounded grains
- semi arid and glacial climates or rapid erosion (bc feldspar breaks down with water)
- common in fluvial (river type) environments
Describe some qualities of lithic arenites
- authigenic clays - forming in situ, where you see the precipitation of minerals
What are the types of lithics?
Volcanic - forming at surface, rocks form and can be smaller grains than in underground plutons
Metamorphic (commonly phyllite and slate)
Sedimentary like chert
What are wackes?
Study these thin sections
What are some qualities of quartz cement?
Coats original grains
difficult to distinguish
can mask orginal grain shape
comes from pressure dissolution or biogenic origin (such as sponge spicules)
What are the different iron oxides?
hematite, goethite, limonite
What is authigenic?
Refers to material that is formed or generated in place, for example minerals that grow in place within a rock such as quartz and feldspar overgrowths that develop around transported grains after they are deposited.
What does high feldspar content in sandstone imply about source area climate?
Chemical weathering is not extensive
This is likely due to climate conditions and/or high source relief.
In what climate conditions is feldspar-rich debris typically produced?
Low precipitation in an arid setting or arctic climate
In arctic climates, precipitation occurs as snow and ice rather than as rain.
How does low precipitation affect feldspar content in sandstone?
It limits hydrolysis and produces feldspar-rich debris
Hydrolysis is a chemical weathering process that breaks down minerals.
Fill in the blank: High feldspar content in sandstone suggests that _______ is not extensive.
chemical weathering
