Transcript quartz arenites - Cal State LA

Mature Sandstones-Arenites
QUARTZ ARENITES
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Quartz Arenites
 Mistakenly referred to as orthoquartzites
 Quartz Arenite is accepted term
 Quartz arenite characteristics
►Generally white or pink; cemented with quartz
 Calcite cement also common
 Can get pressure solution between grains
►Thin blanket sands or very thick
►Monoxln qtz most common
►High proportion of undulatory quartz less common
►Can be cross bedded or contain ripple marks
►Generally sorted and rounded--end point of evolution
►May contain minor chert and heavy minerals
Quartz Arenite
Varieties
► Ist
cycle--more polyxln &
undulatory qtz, less rounded,
more feldspar, more diverse
heavy minerals
► Multi-cycle— well rounded,
sorted overgrowths
► Bimodality in some--selective
removal of fine sand or 2
sources
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Polycrystalline quartz
grain with sutured
crystal-crystal
boundaries. Such quartz
is classified as
a "unstable" grain. This
quartz is sourced from
low-grade
metamorphic rocks(You
ng, 1976).
Monocrystalline Quartz Grain
Origin
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Are supermature, sheet-like, mostly on margins of craton
Probably have eolian history
Look for bimodality
Beach depositional environment possible
Some are marine--marine fossils, interbedded with limestone &
dolomite
Most deposited in shallow marine environment,
May be trangressive sheet sands--Therefore shallow marine--clays
winnowed out
Conditions to form sands
i. removal of feldspars--weathering/transport
ii. removal of clay
iii. rounding of quartz
Beach Environment-Mussel Rock, CA
► High
Energy
► Usually well sorted
► Usually well rounded
► Lacks fines
Sinuous, barchanoidal transverse dunes on a transgressive dunefield
in an arid environment at Guerrero Negro, Baja California, Mexico
Photograph by Patrick Hesp http://www.geomorph.org/gal/mslattery/world.html
Navajo Sandstone
► Coconino
County, AZ
► Nearly pure quartz
► Note large scale cross
beds
USGS
St. Peters Sandstone
► Crossbedded
St. Peter
Sandstone in roadcut
along State Route 39,
near center of NW1/4
sec. 1, T. 4N., R. 5 E.
Iowa County,
Wisconsin
► Ordovician
USGS
► Freshly
exposed St.
Peter sandstone ,
U.S. Silica Quarry in
Pacific, MO.
http://www.rollanet.org/~conorw/cwome/article28,29,&30combined.htm
Ordovician Paleogeography
► Note
craton covered
by shallow seas
► Note demarcation of
equatore
► St Peters sandstone
deposited in these
shallow seas
► Cambrian
quartz
arenite of the Mt.
Simon and
Wonewoc Formation
is exposed along
bedding planes
► Deposited along a
sandy, equatorial
beach
www.uwsp.edu/.../hefferan/MosineeFossils.html
► Must
remove unstable minerals to be arenite
Quartz
Cementation
Two phases of cementation - This is a quartz
sandstone, seen under plain light. The quartz
grains have quartz overgrowths (labeled 'o'),
reflecting a first phase of cementation, and
then, later, a period of carbonate cementation
(c) seen as a brownish material filling the pore
space.
http://faculty.gg.uwyo.edu/heller/Sed%20Strat%20Class/SedStratL1/slideshow_1_16.htm
Calcite Cement
(Peter Kresan, from "Understanding Earth", Press & Siever)
“Immature” rocks
► (Mineralogically
unstable)
► Enriched in
feldspars and
► Unstable rock
fragments
Immature Siliciclastic Sediment
► Is
usually more diverse
► (mineralogy-wise) than
► mature sediment.
► Grains include:
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Plagioclase feldspar
Orthoclase
Microcline
Micas
Lithics
Quartz
General Arkose Description
► Typically
pink & coarse grained, may be
white, f.gr
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Polyxln quartz dominates
Feldspar usually k-spar (microcline)
Kaolinization of feldspars common
Angular and poor to moderate sorting
May have calcite cement and some matrix
Arkose
► Originally
--rock with qtz and feldspar
► Re-defined-- sandstone with >25% feldspar
 Feldspars from granite/gneiss source
► No
agreement on feldspar content
 25% usually cited
► Folk--subarkose
= 10-25% feldspar
Arkose – greater than 25% Felspar
► Usually compositionally immature to
submature
► Usually texturally submature
► Idicates rapid uplift, erosion, and
deposition for feldspars to survive
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Hand specimens Imature siliciclastic sandstones
(arkose - litharenite)
http://www.usouthal.edu/geology/haywick/GY402/402
-pp14.pdf
Arkose (basalt-derived)
Litharenite (igneous/sedimentaryderived)
Arkose (granite-derived)
Lithic Fragments
http://www.usouthal.edu/geology/haywick/GY402/402
-pp14.pdf
Lithic Fragments
http://www.usouthal.edu/geology/haywick/GY402/402
-pp14.pdf
Arkose
► Note
twinned plag
► Note interwoven
texture of kspar
► Rock has matrix.
Arkose
http://www.usouthal.edu/geology/haywick/GY402/402
-pp14.pdf
750 m
Arkose types
► Residual--in
situ disintegration of
granitic/gneissic rocks
► Arkosic Arenite--reworked by river/sea
 generally well sorted, matrix free, grains may
be rounded
Deposition
► Deposition
marine
in fluvial, lacustrine or transitional
 wedge-shaped (fan or apron) adjacent to uplifts
 thin and interbedded with lacustrine or marine
environment
► Arkoses
interbedded with marine/non-marine
 e.g. conglomerates, shales, limestones & evaporites
 .channels, plant fragments, trough cross-bedding =
fluvial env.
Alluvial Fans
► Fan-shaped
deposits
of siliciclastic
sediment deposited
at the base of
mountains
 Gravel to clay sized
 Angular to sub rounded
 immature
http://www.usouthal.edu/geology/haywick/GY402/402
-pp14.pdf
Alluvia Fans
􀂙 Best developed in arid
regions
􀂙 Best developed in
tectonically active areas
Lateral fining
From Walker, R.G. 1980. Facies Models. Geological Association of Canada
http://www.usouthal.edu/geology/haywick/GY402/402
-pp14.pdf
Braided Stream
► Note
meandering and
adjacent braided
stream
http://www.usouthal.edu/geology/haywick/GY402/402
-pp14.pdf
http://www.usouthal.edu/geology/haywick/GY402/402
-pp14.pdf
Origin
► Mostly
first cycle
► Plagioclase arkoses from volcanic source
► Need cold or arid climate for feldspar
preservation
 humid climate bad for feldspars
► D.
Need rapid uplift and erosion
 1. under these conditions, feldspar preservable
in humid climate
VI) Examples
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Devonian Old Red sandstone-England, Precambrian
Torridon sandstone-Scotland,
Silurian Clinton Fm-Pennsylvania
Old Red Sandstone, Siccar
Point
1778 Hutton studied outcrop
and recognized the great
expanse of geologic time
Near-vertical greywackes of
the Silurian Gala Group were
unconformably Overlain by
the younger, gently-dipping
sandstones of the DevonoCarboniferous Stratheden
Group (Upper Old Red
Sandstone)
http://www.hgs.org/en/articles/printview.asp?2399
Interpretations
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Tyee Formation
(Eocene, Oregon
Coast Range) - This
sandstone was deposited
late during an adjacent
orogeny and shows
evidence of a source
area that includes:
quartz (q); plagioclase
(f); potassium feldspar
(f(k) stained here to
straw yellow color);
muscovite (m); and
biotite (b) all of which
suggest that the source
area was granitic pluton
that contained micas,
The large Lv grain,
suggests that arc
volcanic rocks were also
exposed in the source
area
http://faculty.gg.uwyo.edu/heller/Sed%20Strat%20Class/SedStratL1/slideshow_1_12.htm
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Lookingglass Formation
(Eocene, Oregon Coast Range)
- This sandstone was deposited
below the Tyee Formation (last
slide) and shows a somewhat
different source area. These grains
include: quartz (q); feldsparlate
during an adjacent orogeny and
shows evidence of a source area
that includes: quartz (q);
plagioclase (f); many sedimentary
lithic grains (Ls, that are likely
from a shale source or a
phyllite/slate source) and several
heavy mineral grains (h). This
composition differs from the
volcanic arc derived Tyee
Formation, and suggests the
source area for this sandstone
involved rocks that were probably
laid down on the sea floor (shales)
and were later uplifted into an
active orogen. The heavy minerals
may indicate metamorphism in the
source area that would also be
consistent with orogeny.
http://faculty.gg.uwyo.edu/heller/Sed%20Strat%20Class/SedStratL1/slideshow_1_12.htm