Early diagenesis of High Plains Tertiary vitric and arkosic sandstone, Wyoming and Nebraska

Full text

SEPM
SPECIAL
PUBLICATION
No
26
P
40l
423
MARCH 1979
EARLY
DIAGENESIS
OF
HIGH
PLAIl
S
TERTIARY
VITRIC
AND
ARKOSIC
SANDSTONE
WYOMING
AND
NEBRASKA
K
O
STANLEY AND
L
V
BENSON
The
Ohio
State
University
Columbus
43210
and
The
University
of
California
Berkeley
94720
ABSTRACT
The
Cenozoic
High
Plains
sequence
is
a
semiarid
alluvial
and
eolian
complex
inwhich
low
temperature
diagenetic
processes
were
primarily
the
result
of
reactions
of
unconsolidated
sediment
and
dilute
aqueous
solutions
Post
depositional
modifications
of
arkosic
and
vitric
sandstone
include
intrastratal
alteration
and
dissolution
of
chemically
unstable
grains
and
the
precipitation
of
cement
in
pore
space
These
processes
however
have
only
slightly
altered
the
original
fabric
and
mineralogy
of
High
Plains
sandstone
although
chemically
unstable
heavy
minerals
and
volcanic
glass
are
abundant
Thermochemical
calculations
suggest
that
present
day
groundwater
is in
possible
equilibrium
with
calcite
montmorillonite
kaolinite
and
a
silica
phase
Cement
in
sandstone
is
commonly
montmorillonite but
can
be
calcite
opal
chert
and
rarely
clinoptilolite
Most
sandstone
is
friable
and
cemented
with
montmorillonite
Interspersed
in
this
sandstone
are
calcite
concretions
opal
and
chert
cemented
sandstone
occurs
sporadically
in
High
Plains
rocks
on
Cretaceous
shale
and
associated
with
old
land surfaces
in the
Tertiary
rocks
Commonly
the
order
of
precipitation
of
cement
is
calcite
montmorillonite
and
opal
All
cemented
sandstone
shows
some
dissolution
of
grain
surfaces
but
only
friable
sandstone
shows
extensive
intra
stratal
dissolution
of
grains
peripheral
alteration
of
pyroxene
and
amphibole
grains
and
hollow
montmorillonite
coatings
where
chemically
unstable
grains
were
dissolved
These
montmorillonite
coatings
are
up
to
100
micrometers
thick
and
consist
of
a
reticulate
arrangement
of
relatively
porous
clay
particles
oriented
normal
to
the
grain
s
surface
Most
of
the
cements
and
intrastratal
alteration
features
can
be
explained
by
pedogenic
processes
evaporative
concentration
of
groundwater
in
the
capillary
zone or
by
groundwater
reaction
with
sediment
I
INTRODUCTION
Incipient
diagenetic
alteration
of
the
Middle
and
Upper
Tertiary
High
Plains
sequence
Fig
I
demonstrates
that
vitric
and
arkosic
sandstone
can
persist
for
tens
of
millions
of
years
in
a
semiarid
eolian
alluvial
depositional
hydrologic
system
without
significant
modification
to
texture
fabric
or
composition
The
persistence
of
chemi
cally
unstable
grains
the
preservation
of
porosity
and
the
lack of
significant
amounts
of
cement
reflect
an
environmental
and
climatic
setting
that
strongly
inhibited
the
interaction
of
interstitial
fluids
and
sediment
That
this
sandstone
is
rich
in
chemically
unstable
grains
and
has
not
under
gone
significant
diagenetic
alteration
bears
direct
ly
on1our
thinking
about
the
evolution
of
porosity
and
authigenic
mineralogy
of
continental
sand
stones
which
is
of
consequence
to
the
exploration
for
economically
important
minerals
precipitated
or
trapped
in
the
rock
East
of
the
Rocky
Mountains
Cenozoic
conti
nental
deposits
occupy
a
similar
cratonic
setting
and
were
deposited
in
similar
environments
from
the
Texas
coastal
plain
northward
into
Canada
but
they
show
different
amounts
of
alteration
types
of
diagenetic
products
and
kinds
of
eco
nomic
mineral
resources
The
High
Plains
se
quence
east
of
the
Laramie
Range
in
Wyoming
and
Nebraska
represents
one
end
member
of
these
deposits
Other
sequences
in
Texas
New
Mexico
and
Kansas
show
more
extensive
grain
alteration
Copyright
@
1979
The
Society
of
Economic
Paleontologists
and
Mineralogists
cementation
and
concentration
of
uranium
ores
McBride
et
ai
1968
Walton
1975
Walker
1976
Berendsen
1977
Galloway
et
ai
1977
How
ever
unlike
many
other
sedimentary
basins
the
High
Plains
depositional
basin
provides
a
unique
opportunity
to
examine
early
diagenesis
of
vitric
and
arkosic
sandstones
in a
setting
where
many
components
of
the
depositional
diagenetic
system
have
remained
nearly
constant
The
most
impor
tant
of
these
components
are
hydrologic
lim
its
and
tectonic
framework
of
the
basin
types
of
sandstone
deposited
in
the
basin
environments
of
deposition
climate
and
pressure
temperature
history
The
importance
of
early
diagenesis
in
determin
ing
the
ultimate
compositional
and
textural
properties
of
continental
sandstone
sequences
has
been
stressed
by
Walker
1967 1976
for
arid
region
redbeds
and
by
Hay
1970 1976
and
others
for
alluvial
and
saline
alkaline
lake
deposits
Early
diagenetic
modifications
to
the
texture
fabric
and
composition
of
a
sandstone
are
important
factors
which
determine
the
ability
of
aclastic
reservoir
to
act
as
a
petroleum
sink
These
modi
fications
may
also
play
an
important
role
in
concentrating
ores
of
uranium
and
other
authigen
ic minerals
In
the
continental
facies
of
sedimen
tary
basins
the
early
phase
of
post
depositional
modification
is
commonly
a
consequence
of
chemical
reactions between
interstitial
fluids
and
sediment
at
low
temperatures
100
300
C
and
401

402
K
O
STANLEY
AND
L
V
BENSON
Eillill
Tertiary
rocks
Precambrian
rock
FIG
I
Distribution
of
Tertiary
rocks
in
mid
conti
nent
United
States
of
America
showing
the
location
of
the
High
Plains
sequence
heavy
lined
rectangle
in
relation
to
other
Tertiary
rock
units
in
the
Rocky
Mountains
plains
and
coastal
plain
pressures
about
I
bar
Relationships
between
sediment
composition
the
rate
of
movement
and
composition
of
interstitial
fluids
and
the
interac
tion
of
the
solid
and
fluid
phase
therefore
must
be
characterized
in
terms
of
different
tectonic
environmental
and
climatic
settings
in
order
to
generate
diagenetic
models
that
can
be
used
to
predict
the
timing
and
degree
of
alteration
In
addition
a
more
complete
understanding
of
mass
transfer in
the
diagenetic
system
is
necessary
to
generate
predictive
models
for
cements
and
po
rosity
distributions
based
on
sediment
composi
tion
and
textural
properties
Our
concern
in
this
paper
is
the
nature
and
variability
of
diagenetic
alterations
in
Oligocene
through
Pliocene
vitric
and
arkosic
alluvial
eolian
and
lacustrine
sand
stones
of
the
High
Plains
sequence
east
of
the
Laramie
Range
Fig
I
clay
silica
and
carbonate
mineral
equilibria
in
modern
groundwater
of
this
region
and
what
this
information
tells
us
about
the
reactions
of
fluids
and
sediment
in a
temperate
semiarid
grassland
plain
where
environmental
and
compositional
controls
on
diagenesis
can
be
eval
uated
DEPOSITIONAL
SYSTEM
The
depositional
system
responsible
for
ag
gradation
of
up
to
630
m
of
vitric
and
arkosic
sedimentary
rocks
east
of
the
Laramie
Range
Fig
Iwas
strongly
influenced
by
the
semiarid
climate
and
the
tectonic
stability
of
the
region
during
Oligocene
Miocene
and
Pliocene
time
The
flat
lying
post
orogenic
High
Plains
sequence
was
built
up
by
I
airfall
accumulation
of
pyroclastic
material
from
outside
of
the
hydrographic
basin
and
to
a
lesser
amount
by
2
supply
of
epiclastic
detritus
from
Precambrian
crystalline
rocks
and
Paleozoic
Mesozoic
sedimentary
rocks in
the
Laramie
and
Front
Ranges
and
Hartville
uplift
Stanley
1976
The
depositional
system
is
thus
an
eolian
fluvial
system
constructed
by
airfall
accumulation
of
vitric
detritus
with
I
smaller
contribution
by
streams
supplying
material
from
adjacent
mountains
and
includes
more
impor
tantly
2
the
reworking
of
sediment
by
streams
headed
on
the
plains
and
by
winds
blowing
across
the
plains
Fig
2
The
High
Plains
of
Nebraska
is
the
modern
expression
of
this
depositional
system
Today
this
region
is
characterized
by
major
rivers
flowing
eastward
from
the
Rocky
Mountains
that
are
separated
by
vast
expanses
EXTERNAL
SOURCE
INTERNAL
SOURCE
contemporaneous
volcanism
crystalline
rock in
tor
of
to
west
Laramie
and
Front
Ranges
and
Hartville
Uplift
1
PRIMARY
TRANSPORT
PRIMARY
TRANSPORT
i
Z
DEPOSITIONAL
SITE
Eolian
Flood
Dunes
I
LOIl tl
Plain
lo
SECONDARY
DEPOSIT1fNAL
liD
SECONDARY
DEPOSITIONAL
SITE
SITE
Sands
reworked
into
fluvial
t
Sands
reworked
into
dune
deposits
by
sh
twosh
and
by
wind
streoms
FIG
2
Schematic
flow
diagram
of
sources
and
de
positional
processes and sites
of
sandstone
of
the
High
Plains
sequence
east
of
the
Laramie
Range
in
Wyoming
and
Nebraska

VITRIC
AND
ARKOSIC
SANDSTONES
of
eolian
dune
fields
and
loess
with
small
lakes
and
streams
These
major
rivers
are
fed
by
water
sheds
in
the
Rocky
Mountains
and
by
groundwa
ters
on
the
plains
Today
the
High
Plains
is
characterized
by
a
semiarid
temperate
continental
climate
with
variability
and
season
ability
of
precipitation
and
temperature
that
grade
eastward
to
a
subhumid
climate
Annual
precipitation
ranges
from
35
to
50
em
per
year
in
western
and
central
Nebraska
and
up
to
80
em
in
easternmost
Nebraska
Elder
1969
p
5
Natural
vegetation
of
this
region
is
a
mixed
prairie
grassland
on
featureless
prairie
between
streams
with
a
gallery
of
deciduous
trees
along
their
banks
Valleys
where
groundwater
is
within
reach
of
plant
roots
sustain
tall
grasses
whereas
valleys
and
hills
where
groundwater
is
beyond
the
reach
of
roots
support
stands
of
short
grasses
Elder
1969
Evidence from
fossil
grass
seeds
Elias
1942
Elias
and
Lugn
1939
fossil
trees
Wanless
1923
mammalian
faunas
Mat
thew
1901
Clark
et
ai
1967
Oligocene
and
Pliocene
caliche
profiles
Swineford
et
ai
1955
Lillengra
ven
1970
and
sediments
Lovering
1929
Stanley
1976
all suggest
that
a
semiarid
grassland
prevailed
during
deposition
of
the
High
Plains
sequence
In
addition
arid
conditions
are
suggested
during
deposition
of
the
upper
part
of
the
White
River
Group
and
the
lower
part
of
the
Arikaree
Group
by
extensive
sand
dune
and
massive
loesslike
deposits
mammalian
faunas
Schultz
and
Falkenbach
1968
and
the
absence
of
fossil
grasses
Geographic
and
textural
distribution
of
Oligo
cene
and
Miocene
eolian
and
alluvial
rocks
con
form
to
depositional
patterns
described
by
Garner
1959
for
sedimentation
under
arid
and
semiarid
climate
conditions
Fanglomerates
in
the
Oligo
cene
White
River
and
Oligocene
Miocene
Ari
karee
Groups
are
restricted
to
areas
adjacent
to
the
Laramie
Range
and
Hartville
uplift
More
than
20
km
from
the
mountains
small
and
volumet
rically
unimportant
coarse
grained
fluvial
sand
stone
composed
of
arkosic
detritus
is
intercalated
in
fine
grained
eolian
and
alluvial
material
which
is
in
large
part
pyroclastic
material
comprising
from
50
to
90
percent
of
the
sequence
Fig
2
Adjacent
to
the
Hartville
uplift
beds
of
Arikaree
vitric
arenite
abut
against
Precambrian
horn
blende
schist
with
little
contribution
from
the
uplift
and
only
local
and
sparse
breccias
composed
of
schist
are
intercalated
in
the
volcaniclastic
sand
stone
The
dominance
of
pyroclastic
detritus
re
quires
airfall
as
the
principal
mechanism
of
sedi
ment
supply
during
deposition
of
the
White
River
and
Arikaree
Groups
This
pattern
of
sedimentary
facies
requires
a
sufficient
volume
of
water to
periodically
carry
large
quantities
of
coarse
detri
tus
a
short
distance
from
the
mountains
as
well
403
as
sparse
vegetation
and
rainfall
on
the
plains
so
that
sand
dunes
and
loess
developed
away
from
the
mountains
Arkosic
material
in
the
Miocene
Pliocene
Ogallala
Group
reflects
a
regime
in
which
greater
material
was
supplied
from
the
Rocky
Mountains
but
pyroclastic
material
including
ash
falls
is
also
an
important
component
This
phase
of
sedimentation
reflects
a
time
of
regional
uplift
and
expansion
of
the
drainage
basin
that
drastical
ly
influenced
the
ability
of
streams
to
carry
detritus
away
from
the
mountains
Stanley
1971
1976
NORTHERN
HIGH
PLAINS
SEDIMENTARY
PETROLOGIC
PROVINCE
Tectonic
setting
and
stratigraphy
East
of
the
Laramie
Range
the
High
Plains
sequence
consists
of
a
wedge
of
Oligocene
through
Pliocene
fluvial
eolian
and
lacustrine
rocks
that
extends
several
hundred
kilometers
from
the
mountain
front
Fig
I
The
sequence
is
represented
by
the
Oligocene
White
River
Oligocene
Miocene Arikaree
Mio
cene
Hemingford
and
Miocene
Pliocene
Ogallala
Groups Stanley
1976
These
are
post
orogenic
sedimentary
rocks
subjected
only
to
epirogenic
movements
Stanley
1971
Stanley
and
Wayne
1972
In
eastern
Wyoming
and
adjoining
Nebras
ka
these rocks
rest
unconformably
on
gently
folded
Cretaceous
rocks
and
locally
on
a
late
Eocene
lateritic
paleosol
developed
on
Cretaceous
rocks
Pettyjohn
1966
Adjacent
to
the
moun
tains
they
abut
against
upturned
Paleozoic
and
Mesozoic
strata
and
rest
on
Precambrian
crystal
line
rocks
that
form
the
core
of
the
Laramie
and
Front
Ranges
and
Hartville
uplift
Darton
1899
1903
Darton
et
ai
1910
Denson
and
Botinelly
1949
Stratigraphic
evidence
indicates
that
the
relationship
of
the
sedimentary
basin
of
the
High
Plains
sequence
to
adjacent
uplifts
has
not
changed
greatly
either
physiographically
or
struc
turally
since
the
onset
of
continental
sedimenta
tion
during
the
earliest
Oligocene
Denson
and
Bergendahl
1961
Clark
et
ai
1967
Stanley
1971
Interpretation
of
the
stratigraphic
framework
of
the
High
Plains
sequence
and
of
the
strati
graphic
position
of
sandstone
sample
localities
is
based
on
published
geologic
maps
Stratigraphic
position
of
sandstone
sample
localities
is
based
on
published
geologic
maps
stratigraphic
sec
tions
and
land
mammal
ages
established
during
a
century
of
study
by
paleontologists
and
strati
graphers
Clark
et
ai
1967
Condra
and
Reed
1943
Darton
1899
1903
Darton
et
ai
1910
Elias
1942
Lugn
1939
McGrew
1963
I
967a
d
McGrew
1953
Schlaikjer
1935
Schultz
and
Stout
1955 1961
Vondra
et
ai
1969
Although
disagreements
exist
about
subdivision
of
the
High

404
K
O
STANLEY
AND
L
V
BENSON
Plains
sequence
the
major
lithostratigraphic
units
are
mapped
units
whose
biostratigraphic
range
isotopic
age
and
lithologic
boundaries
are
well
established
in
Nebraska
and
adjoining
Wyoming
Sandstone
composition
and
provenance
Sandstone
and
siltstone
in
the
High
Plains
se
quence
consists
of
pyroclastic
detritus derived
from
distant volcanic
eruptions
and
of
epiclastic
fragments
eroded
from
Precambrian
crystalline
rocks
Paleozoic
and
Mesozoic
sedimentary
rocks
and
Cenozoic
volcanic
rocks
exposed
in
the
Laramie
and
Front
Ranges
Hartville
uplift
and
Black
Hills
Wanless
1922 1923
Sato
and
Denson
1967
Stanley
1976
Modal
analyses
of
detrital
mineralogy
of
High
Plains
sandstones
indicate
that
it
is
immature
with
a
large
proportion
of
chemically
unstable
framework
constituents
angular
to
subangular
grains
poor
sorting
and
a
matrix
that
ranges
in
amount
from
a
trace
to
15
percent
Stanley
1976
All
sandstone
is
arkose
and
vitric
litharenite after
Folk
1968
and
these
compositions
also
characterize
siltstone
Four
distinct
natural
populations
of
detrital
minerals
are
recognized
in
the
High
Plains
se
quence
These
mineralogies
constitute
the
follow
ing
sandstone
petrofacies
which
are
independent
of
grain
size
and
biostratigraphic
position
I
volcaniclastic
sandstone
2
plagioclase
sand
stone
3
feldspathic
sandstone
and
4
rhyolite
bearing
feldspathic
sandstone
Table
I
Each
petrofacies
contains
a
unique
assemblage
of
light
and
heavy
minerals
and
lithic
fragments
which
can
be
related
to
a
specific
source
terrane
Stanley
1976
East
of
the
Laramie
Range
volcaniclastic
rocks
are
siltstone
mudrock
and
very
fine
grained
to
fine
grained
vitric
litharenite
which
together
comprise
the
main
body
of
the
rocks
of
the
Arikaree
Group
vitric
siltstone
and
mud
rock
dominate
the
White
River
Group
Table
2
These
lithologies
contain
40
to
80
percent
rhyolitic
shards
which
exhibit
bubble
wall
junctures
rod
shapes
or
are
pumiceous
Pyroclastic
material
was
probably
ejected
from
volcanoes
west
of
the
High
Plains
Similar
Middle
Tertiary
pyroclastic
rich
rocks
are common
in
the
Wind
River
basin
of
central
Wyoming
van
Houten
1957
and
in
Browns
Park
basin
in northwestern
Colorado
suggesting
a
volcanic
source
further
to
the
west
The
volcaniclastic
sandstone
of
the
High
Plains
and
in
the
intermontane
basins
to
the
west
were
deposited
contemporaneously
with
an
episode
of
immense
volcanic
activity
in
the
eastern
Great
Basin
of
Nevada
and
Utah
Armstrong
1968
which
is
the
most
likely
source
of
the
rhyolitic
glass
in
sandstone
and
ash
beds
The
source
of
major
constituents
in
the
plagio
clase
sandstone
petrofacies
shown
in
Table
I
is
the
Laramie
anorthosite
complex
in
the
central
Laramie
Range
where
norite
anorthosite
and
hypersthene
syenite
are
the
dominate
lithologies
Stanley
1976
Minerals
and
lithic
fragments
that
make up
the
feldspathic
sandstone
petrofacies
however
are
comparable
to
minerals in
granitic
TABLE
I
AVERAGES
MEANS
AND
STANDARD
DEVIATIONS
SQUARE
ROOT
OF
VARIANCE
OF
RESULTS
OF
POINT
COUNTS
ON
THIN
SECTIONS
OF
SANDSTONE
IN
THE
HIGH
PLAINS
SEQUENCE
AND
OF
SANDS
OF
MODERN
STREAMS
Modem
stream
sand
and
sandstone
of
Amphibole
High
Plains
Heavy
Petrofacies
sequence
N
Q
F
L
minerals
P F
V
L
Pyroxene
Chugwater
Creek
5
24
t
7
52
t
9
17
t
6 7
t
3 0 7
t
0 2 0 0 2
Plagioclase
Ogallala
Group
20 20
t
6
52
t
7
15
t
5
13
t3
0 8
t
0
1
00
1
sandstone
Arikaree
Group
83
27
t
6
57
t
10
II
t
4 5
t
2 0 7
t
0 2 0 0 3
White
River
Group
100
28
t
5
56
t
6
1O
t5
6
t
3 0 8
t
0 2 0 0 3
Feldspathic
Lodgepole
Creek
3
50
t
9
30
t
5
16
t
3 4
t
2
04
t
0
1
0
1
Arikaree
Group
30 50
t
8
23
t
10 14
t
5
13
t7
0 5
t
0
1
0
1
sandstone
White
River
Group
60 48
t
6
21
t
8
17
t
4
14
t
6 0 5
t
0
1
0
1
Rhyolite
North
Platte
River
4
58
t
10
24
t
5
17
t4
04
t
0
1
0
1 1
bearing
feldspathic
Ogallala
Group
50
51
t
6
23
t
4
20
t
3
6
t4
04
t
0 2
04
1
sandstone
Volcaniclastic
sandstone
Arikaree
Group
110
23
t
12 18
t
10
52
t
25
7
t4
04
t
0 2 0 8
1
Note
Procedures
of
modal
analyses
sample
localities
and
textural
properties
of
sandstone
are
reponed
by
Stanley
1976
N
is
the
number
of
thin sections
counted
Values
for
quartz
Q
Feldspar
Flithic and
granitic
fragments
L and
heavy
minerals
are
volumetric
percentages
of
the
total
framework
Values
of
P F V
IL
and
amphibole
pyroxene
are
decimal fractions
P is
plagioclase
V
is
volcanic lithic
fragments
or
pyroclastic
material

VITRIC
AND
ARKOSIC
SANDSTONES
405
TABLE
2
DEPOSITlONAL
SYSTEM
OF
HIGH
PLAINS
SEQUENCE
Eolian
Stream
Channel
Flood
Plain
Deposits Deposits Deposits
EE E
Ogallala
S S S
D
S
C
Group
Arikaree C
S
C
CC
S
Group
White
River
C
S
S
CD
S
Group
E
External
source
of
sediment
volcanism
I
Internal
source
of
sediment
crystalline
rock
in
Laramie and
Front
Ranges
and
Hartville
uplift
D
Dominant
lithology
C
Common
lithology
S
Sparse
lithology
and
metamorphic
rocks in
the
Hartville
uplift
and
in
the
Laramie
and
Front
Ranges
Source
rocks
for
the
petrofacies
range
from
quartz
syenite
to
granodiorite
and
include
the
Sherman
batholith
south
of
the
Laramie
anorthosite
complex
and
metamorphic
rocks
of
amphibolite
facies
principally
hornblende
gneiss
and
schist
biotite
gneiss
and
quartz
feldspathic
gneiss
Denson
and
Botinelly
1949
Osterwald
and
Dean
1957
Smithson
and
Hodge
1972
The
rhyolite
bearing
feldspathic
sandstone
petrofacies
contains
con
stituents
derived
from
plutonic
and
metamorphic
rocks in
the
front
of
Laramie
Range
and
Tertiary
volcanic
fields
on
the
west
side
of
the
Front
Range
in
North
Park
basin
Colorado This
is
the
domi
nant
rock
type
in
the
Ogallala
Group
Table
2
DIAGENETIC
FEATURES
Fabric
Porosity
and
permeability
are
the
most
important
bulk
properties
of
potential
fluid
reservoirs
Post
depositional
chemical
and
me
chanical
alteration
of
rock
fabric
usually
reduces
porosity
and
permeability
but
can
enhance
these
properties
of
the
sediment
As
noted
by
Walker
1967
1976
the
fabrics
of
continental
sands
com
monly
are
significantly
altered
during
early
dia
genesis
The
fabric
of
sandstone
in
the
High
Plains
sequence
shows
no
stratigraphic
or
geographic
variations
and
detectable
modifications
of
origi
nal
depositional
fabric
are
restricted
to
porosity
reduction
by
cementation
minor
porosity
en
hancement
by
dissolution
of
chemically
unstable
detrital
grains
and
crushing
and
bending
of
some
mica
grains
at
grain
to
grain
contacts
The
volu
metric
percentage
of
cement
and
void
space
in
High
Plains
sandstones
determined
in
thin
sec
tion
ranges
from
25
to
42
percent
reflecting
the
very
loose
packing
that
developed
under
eolian
and
alluvial
conditions
of
deposition
Silica
and
calcite
cements
fill
most
intergranular
space
whereas
montmorillonite
and
or
zeolite
cements
that
volumetrically
range
up
to
27
percent
of
the
rock
seldom
fill
more
than
45
percent
of
the
intergranular
space
Scanning
electron
micro
scopy
indicates
that
these
cements
not
only
reduce
pore
space
but
also
inhibit
fluid
flow
through
the
sediment
by
reducing
the
size
and
number
of
interconnecting
holes
Thin
section
analysis
of
cement
free
sands
and
those
with
only
thin
less
than
10
microns
clay
and
zeolite
coatings
indicates
about
30
percent
porosity
nearly
all
of
which
is
intergranular
porosity
related
to
packing
of
grains Fig
3
Similar
porosities
were
obtained
by
thin
section
analysis
of
Quaternary
alluvial
sands
The
types
of
contacts
between
grains
in
sandstone
of
the
High
Plains
sequence
reflect
the
loose
packing
of
the
grains
and
the
lack
of
compaction
of
the
sediment
Fig
3
Taylor
1950
recognized
four
possible
types
of
grain
to
grain
contacts
for
sandstone
tangential
and
long
con
tacts
that
reflect
depositional
fabrics
and
packing
and
concavoconvex
and
sutured
contacts
that
reflect
pressure
solution at
grain
to
grain
contacts
during
more
intense
compaction
of
the
sand
with
burial
In
the
High
Plains
sequence
sandstone
fabrics
are
characteristically
tangential
and
long
grain
to
grain
contacts
Fig
3
Only
locally
are
biotite
grains
crushed
and
bent between
other
detrital
grains
Mudrock
glass
shards
and
car
bonate
grains
are
not
crushed
and
their
grain
to
grain
contacts
are
tangential
or
long
again
reflect
ing
the
dearth
of
compaction
alteration in
the
sediment
Fig
3
Aiteration
of
detritai
grains
Alteration
of
detrital
grains
in
the
High
Plain
sequence
and
in
overlying
Quaternary
sediments
is
related
I
to
weathering
with
formation
of
soils
Fig
4
and
2
to
intrastratal solution
Weathering
resulted
in
formation
of
soil
horizons
that
display
highly
variable
alteration
of
detrital
grains
and
mineral
associations
In
hardpan
calcrete
calcified
sand
and
surfaces
of
weathering
which
mayor
may
not
include
root
horizons detrital
grains
exhibit
the
most
intense
alteration
and
in
some
calcrete

406
K
O
STANLEY
AND
L
V
BENSON
FIG
3
Fine
grained
volcaniclastic
sandstone
of
the
basal
Arikaree
Group
from
Scotts
Bluff
Nebraska
showing
the
open
packing
and
porosity
that
are
common
in
sandstones
of
the
High
Plains
sequence
Sand
grains
are
coated
with
montmorillonite
cement 4
micrometers
thick
horizons
only
quartz
remains
of
the
original
detri
tal
modes
Caliche
and
root
horizons
show
calcite
replacement
of
feldspar
alteration
of
glass
to
montmorillonite
root
casts
filled
with
montmoril
lonite
fibrous
sepiolite
and
palygorskite
after
montmorillonite
in
Ogallala
profiles
and
variable
amounts
of
alteration
of
heavy
minerals
FIG
4
Paleosol
prof1le
in
upper
part
of
theArikaree
Group
near
Agate
Nebraska
showing
root
zone
devel
oped
in
alluvial
sandstone
below
an
ancient
land
surface
Pervasive
argillization
of
vitric
components
in
the
original
volcaniclastic
sandstone
characterize
the
root horizon
whereas
very
fme and fme
grained
vol
caniclastic
sandstone
below
the
root
horizon
is
coated
with
montmorillonite
r
I
r
Jj
j
I
J
L
1
I
II
IJ
FIG
5
Photomicrographs
of
calcite
cemented
pla
gioclase
sandstone
of
the
Ogallala
Group
adjacent
to
the
Laramie
Range
Anorthosite
complex
showing
the
lack
of
intrastratal
alteration
of
chemically
unstable
non
opaque
heavy
minerals
Top
Hypersthene
grain
showing
only
slight
oxidation
of
the
grain
surface
BOllom
Olivine
grains
0
with
iron
oxide
rims
and
fracture
fillings

VITRIC
AND
ARKOSIC
SANDSTONES
Intrastratal
solution
which
involves
the
dis
solution
of
grains during
early
diagenesis
is
more
uniform
and
resulted
in
a
general
sequence
in
the
kind
and
degree
of
alteration
Most
chemically
unstable
grains
in
High
Plains
sandstone
and
siltstone
indicate
incipient
intrastratal
solution
and
alteration
Fig
5 6
Olivine
grains
the
most
FIG
6
Photomicrographs
of
friable
plagioclase
sandstone
showing
intrastratal
alteration
and cement
types
of
sandstone
not
cemented
by
calcite
Top
Friable
sand
collected
adjacent
to
the
calcite cemented
sand
stone
shown
in
Figure
5
showing
intrastratal
alteration
of
hypersthene
and cement
which is
montmorillonite
dark
material
and
cIinoptiIolite
crystals
BOllom
White
River
Group
plagioclase
sandstone
near
Scotts
Bluff
Nebraska
with
unaltered
hornblende
adjacent
to
strongly
altered
hypersthene
all
grains
are
coated
with
a
thick
montmorillonite
cement
407
unstable
mineral
in
the
sandstones
exhibit
iron
oxide
rims
and
fracture
fillings
in
calcite
cemented
rocks but
are
otherwise
unaltered
Fig
5
This
early
calcite
cementation
of
sandstone
probably
inhibited
further
dissolution
and
alteration
Fig
5
Olivine
in
porous
and
friable
sand
however
is
altered
to
iddingsite
and
locally
the
grains
are
partly
or
wholly
removed
by
dissolution
The
only
other
mineral
to
show
extensive
alteration
is
hypersthene
which
is
the
principal
non
opaque
O
lmm
or
I
I
FIG
7
Scanning
electron
micrographs
of
mont
morillonite
cemented
sandstone
of
the
plagioclase
sand
stone
top
and
volcaniclastic
sandstone
bottom
petro
facies
showing
hollow
clay
coatings
where
detrital
grains
were
removed
by
intrastratal dissolution

408
K
O
STANLEY
AND
L
V
BENSON
heavy
mineral
in
plagioclase
sandstone
and
occurs
in
trace
amounts
in
volcaniclastic
sand
stone
Fig
6
Hypersthene
grains
exhibit
only
etched
surfaces
or
thin
iron oxide
rims
in
calcite
cemented
plagioclase
and
volcaniclastic
sandstone
and
in
some
friable
volcaniclastic
sandstone
and
siltstone
Fig
5
In
many
friable
plagioclase
sandstones
however
hypersthene
grains
exhibit
peripheral
discoloration
produced
by
alteration
to
secondary
minerals
surfaces
intensely
etched
to
fragile
cockcomb
forms
and
dissolution
along
cleavage
planes
and
removal
of
material
within
the
grain
Fig
6
Locally
some
hypersthene
grains
are
almost
completely
removed
by
dissolu
tion
Fig
7
In
contrast
augite
amphibole
mica
and
other
heavy
minerals
are
little
altered
Discol
oration
of
grain
margins
and
etching
of
grain
surfaces
are
the
only
diagenetic
features
of
augite
and
amphibole
including
sandstones
where
hypersthene
is
extensively
altered
Fig
6
Feld
spar
is
commonly
fresh
although
more
calcic
varities
of
plagioclase
show variable
amounts
of
surface
etching
and
dissolution
Fig
8
The
quartz
is
unaltered
Of
the
lithic
fragments
in
sandstone
and
silt
stone
only
vitric
pyroclastic
material
shows
evi
dence
of
identifiable
alteration
Glass
shards
in
Oligocene
Miocene
and
Pliocene
sandstone
commonly
are
unaltered
and
appear
fresh
but
some
shards
are
porous
rounded
etched
and
pitted
by
dissolution
Fig
9
Shards
in
some
FIG
8
Clinoptilolite
crystals
on
labradorite
grain
that
partly
fill
pore
space
in
Ogallala
plagioclase
sand
stone
shown
in
Figure
6
Dissolution
of
the
feldspar
can
be
seen
in
the
scanning
electron
micrograph
below
the
zeolite
crystals
FIG
9
Top
Rhyolite
ash
from
Ogallala
Group
north
of
Sidney
Nebraska
showing
rhyolite
glass
shards
that
exhibit
evidence
of
only
minor
dissolution
BOllom
Rhyolitic
ash
from
the
Arikaree
Group
north
of
Scotts
bluff
Nebraska
showing
glass
shardthat
has
undergone
partial
dissolution
D
and
elsewhere
is
coated
by
montmorillonite
M
siltstones
have
undergone
argillation
or
have been
dissolved
and
as
noted
above
such
grain
localities
produce
minor
amounts
of
secondary
porosity
in
some
vitric
sandstone
and
siltstone
Fig
7
The
index
of
refraction
of
fresh
glass
is
between
1
49
and
1
53
values
which
are
similar
to
those
report
ed
by
Swineford
Frye
and
Leonard
1955
for
glass
in Miocene
and
Pliocene
ash
falls
in
Nebras
ka
and
Kansas The
indices
of
refraction
and
chemical
compositions
of
ash
falls
reported
by
Swineford
Frye
and
Leonard
1955
indicate
that
vitric
material
in
ash
sandstone
and
siltstone
is
similar
consisting
of
rhyolitic
glass
with
nearly
constant
water
content
of
about
five
percent
Slight
variations
in index
of
refraction
and
colora

VITRlC
AND
ARKOSIC
SANDSTONES
409
tion
of
large
shards
together
with
the
reported
high
water
content
for
the
rhyolitic
glass
imply
minor
hydration
of
Tertiary
vitric
material
What
is
notable
however
is
the
small
amount
of
post
depositional
alteration
of
rhyolitic
glass
even
though
this
material
is
a
major
component
in
the
sedimentary
sequence
Cement
Cenozoic
sediments
east
of
the
Laramie
Range
in
Wyoming
and
Nebraska
include
1
Quaternary
sands
silt
and
ashes
devoid
of
cement
2
upper
Eocene
through
Pliocene
alluvial
eolian
and
lacustrine
sandstone
silt
stone
and
volcanic
ashes
that
are
cemented
by
various
amounts
of
kaolinite
montmorillonite
calcite
clinoptilolite
or
silica
and
3
late
Oligo
cene
through
Pliocene
friable
uncemented
sand
silt
and
volcanic
ash
Although
cements
are
generally
absent
from
Quaternary
sediments
in
filtrated
clays
similar
to
those described
by
Walker
1976
are
pore
filling
material
in
some
dune
sands
and
in
addition calcite
cements
are
locally
asso
ciated
with
soil
profiles
in
eolian
alluvial
and
lacustrine
sediment
The
only
evidence
of
in
trastratal
alteration
in
Quaternary
sediment
is
dissolution
of
rhyolitic
glass
in
ash
beds and
locally
surface
etching
of
some
heavy
mineral
grains
in
sandstone Cenozoic
rocks
older
than
DIAGENETIC
MINERAL
B
II
Cal
iche
Silic
a
the
Oligocene
through
Pliocene
High
Plains
se
quence
form isolated
patches
of
sandstone
and
in northwestern
Nebraska
and
South
Dakota
a
late
Eocene
paleosol
is
developed
on
the
Creta
ceous
Pierre
Shale
below
the
unconformity
that
separates
the
High
Plains
sequence
from
older
rocks
Fig
10
Pettyjohn
1966
recognized
con
centrations
of
iron
and
alumina
in
the
upper
part
of
the
soil
profile
red
color
and
kaolinization
of
the
parent
material
believed
indicative
of
a
lateritic
soil
profile
formed
during
a
hot
and
wet
climatic
regime
Locally
in
western
South
Dako
ta
the
Eocene
paleosol
rests
on
sandstone
of
the
upper
Eocene
Slim
Buttes
Formation
which
is
characterized
by
feldspar
partly
altered
to
kaolinite
and
with
greenish
to
white
kaolin
cement
that
fills
intergranular
pore
space
Pettyjohn
1966
Clark
et
al
1967
Locally
in
Nebraska
kaolin
rich
sandstone
rests
on
Cretaceous
shale
and
is
over
lain
by
the
High
Plains
sequence
Fig
10
This
sandstone
contains
kaolin
cement
kaolinite
and
vermicular
kaolinite
crystals
replacing
feldspar
grains
and
shows
dissolution
of
quartz
grains
Fig
II
Consequently
the
sandstone
and
the
associated
Eocene
lateritic
paleosol
are
markedly
distinct
in
their
diagenetic
mineral
assemblage
from
the
younger
High
Plains
sequence
Fig
10
ASSEMBLAGES
rmm
Mlliill
III
Calcite
Zeoli
te
Cold
Ie
Kaolinite
Montmorillonite
Cretaceous
shale
chon
1
sandstone
Eocene
7
FIG
1O
Schematic
diagram
showing
stratigraphic
variations
in
diagenetic
mineral
assemblages
for
the
High
Plains
sequence
east
of
the
Laramie
Range
in
Wyoming
and
Nebraska

410
K
O
STANLEY
AND
L
V
BENSON
FIG
II
Photomicrograph
of
channel
sandstone
Eocene
east
of
Valentine
Nebraska
showing
detrital
quartz
grains
kaolin
cement
and
replacement
of
grains
and
large
vermicular
kaolinite
crystals
developed
authi
genically
after
deposition
This
sandstone
appears
to
pre
date
the
High
Plains
sequence
and
may
be
related
to
the Slim
Buttes
Formation
of
South
Dakota
They
must
represent
a
different
hydrochemical
system
operative
in
the
depositional
basin
before
the
Oligocene
Four
different
mineral
cements
occur
in
the
High
Plains
sequence
as
three
different
cement
assemblages
I
calcite
and
montmorillonite
with
only
local
trace
amounts
of
kaolinite
Figs
7
10
2
zeolite
and
montmorillonite
with
calcite
or
silica
and
3
silica
with
or
without
authigenic
fibrous
clays
sepiolite
or
palygorskite
In
addi
tion
silica
or
calcite
cement
is
locally
present
without
significant
amounts
of
other
diagenetic
minerals
Where
more
than
one
cement
phase
is
present
the
chronology
of
cement
precipitation
is
calcite
montmorillonite
silica
and
finally
zeo
lite
Fig
12
Late
calcite
or
silica
cement
also
may
be
locally
significant
Early
calcite
cement
forms
concretions
composed
of
sparry
calcite
pore
filling
of
large
up
to
2
cm
diameter
sand
calcite
crystals
That
these
concretions
formed
shortly
after
deposition
of
alluvial
and
eolian
sands
is
indicated
by
I
the
presence
of
water
worn
concretions
as
clasts
in
penecontemporaneous
fluvial
channels
a
relationship
first
described
by
Schultz
1941
and
by
2
the
paucity
of
intrastra
tal alteration
of
chemically
unstable minerals
e
g
olivine
and
hypersthene
within
concretions
Fig
5
The
absence
of
montmorillonite
kaolinite
silica
and
zeolite
pore
filling
cement
in
Quater
nary
alluvial
and
eolian
sediments
together
with
f
1
f
l
I
r
Q
Qlmm

VITRlC
AND
ARKOSIC
SANDSTONES
dissolution
of
grains
in
Quaternary
volcanic
ash
layers
suggests
that
these
cements
are
Tertiary
in
age
Stratigraphic
distributions
of
cement
types
imply
that
the
cements
except
for
late
calcite
and
silica
are
all
probably
related
to
the
early
post
depositional
history
of
fluids
of
each
rock
stratigraphic
unit
Fig
10
Opal
with
a
disordered
tridymite
or
cristobalite
structure
based
on
x
ray
diffraction
analysis
Mitchell
and
Tufts
1973
is
the
most
common
silica
cement
Fig
13
In
the
Ogallala
Group
friable
and
opal
cemented
sands
contain
fibrous
authigenetic
clay
minerals
that
impart
a
greenish
color
to
the
rocks X ray
diffraction
analysis
and
dispersive
Xray
analysis
with
scanning
electron
micr
oscopy
indicate
that
these
authigenic
clays
are
either
sepiolite
and
or
palygorskite
Frye
et
al
1974
report
this
mineral
association
below
calcrete
horizons in
the
Ogallala
Formation
of
New
Mexico
and
infer
it
to
be
related
to
alteration
of
montmorillonite
to
opal
and
fibrous
clay
by
pedogenic
processes
However
some
opal
ce
ments
in
the
Ogallala
and
in
the
White
River
and
Arikaree
Groups
of
Nebraska
and
Wyoming
do
not
occur
with
fibrous
clays
Fig
13
Pre
Ogallala
silica
cements
also
are
locally
crystalline
quartz
chert
and
or
chalcedony
that
mayor
may
not
occur
with
opal
The
only
zeolite
species
recognized
in
the
High
Plains
sequence
of
Wyoming
and
Nebraska
is
clinoptilolite
Fig
8
12
which
was
confirmed
by
x
ray
analysis
using
the
heat
treatment
method
described
by
Boles
1972
The
zeolite
was
found
in
coarse
friable
sandstone
of
the
plagioclase
sandstone
petrofacies growing
on
opal
and
mont
morillonite
coated
grains Fig
8
12
The
zeolite
occurs
in
the
lower
part
of
the
Ogallala
Group
a
relationship
also
noted
by
Frye
et
al
1974
for
heulandite
in
the
Ogallala
Formation
of
New
Mexico
and
in
White
River
Group
sandstones
below
the
Ogallala
The
zeolite
cement
is
progres
sively
more
abundant
toward
the
base
of
Ogallala
sandstone
beds and
is
rare
in
underlying
White
River
sandstone
This
relationship implies
that
zeolites
in
the
White
River
sandstone
may
reflect
percolation
of
waters
from
the
Ogallala
into
older
beds
Recently
the
Nebraska
State
Conservation
II
FIG
12
Top
Clinoptilolite
crystals
resting
on
an
earlier
phase
of
montmorillonite
cement
that
coats
grains
in
the
sandstone
Plagioclase
sandstone
from
the
Ogallala
Group
near
Farthing
Wyoming
Bottom
Clinoptilolite
crystals
resting
on
opal
cement
coating
sand
grains
White
River
Group
sandstone
below
the
Ogallala
Group
near
Farthing
Wyoming
The
zeolite
post
dates
the
formation
of
both the
montmorillonite
and
opal
cement
Samples
were
collected
within
a
distance
of
I
km
411
0
01
mm
FIG
B
Opal
cement
in
feldspathic
sandstone
of
theWhite
River
Group
near
Torrington
Wyoming
Top
feldspar
grain
showing
surface
etching
and
dissolution
with
authigenic
opal
tridymite
growing
in
pits
dissolved
in the
grain
Bottom
thick
coating
of
authigenic
opal
on
the
surface
of
a
quartz
grain
The
crystal
habit
of
the
surface
of
the
opal
cement
is
characteristic
of
tridymite
and
Survey
Division
of
the
University
of
Nebraska
has
also
identified
clinoptilolite
in
lacustrine
rocks
of
northwestern
Nebraska
perhaps
related
to
alkaline
lakes
Boellstorff
oral
communication
1976

412
K
O
STANLEY
AND
L
V
BENSON
t
I
0
01
mm
LJ
tt
I
l4
4Ji
r
1
t
t
4
1
t
oj
i
ri5t
tI
ft
a
f
41
t
i
j
r
i
jJl
1Ii
4
c
a
7
ie
o
t
t
i
C
j
i
j
A
jt
3
it
i
C
I
l
tw
I
J
J1
J
jn
O
OOlmm
I
FIG
l4
Montmorillonite
coating
on
sand
grain
showing
the
fabric
of
authigenic
montmorillonite
Top
montmorillonite
coated
surface
of
asand
grain
Bottom
Cross
section
of
thicker
cement
coating
showing
mont
morillonite
cornflake
Iike
particles
that
increase
in
size
away
from
the
grain
surface
g
Montmorillonite
cement
in
High
Plains
sand
stone
and
siltstone
consists
of
coatings
on
grains
up
to
0
1
millimeters
thick
which
consist
of
a
reticulate
arrangement
of
relatively
porous
clay
Figs
7
14 15 16
Individual
particles
and
their
reticulate
arrangement
are
similar
to
montmoril
lonites
grown in
the
laboratory
by
Demirel
Erol
1
1
1
FIG
l5
Vitric
siltstone
of
the White
River
Group
at
Scotts
Bluff
Nebraska
showing
rhyolitic
glass
shards
with
development
of
montmorillonite
cement
Top
photomicrograph
of
vitric
siltstone
showing
bubble
wall
and
rod
shaped
shards
biotite
with
attached
glass
and
clay
filling
voids
between
grains
that
is
difficult
to
interpret
as
either
detrital
or
authigenic
in
thin
section
Bottom
scanning
electron
micrograph
of
the
above
sample
showing
that
clay
is
well
developed
authigenic
montmorillonite
growing
on
grain
surfaces
No
detrital
clay
is
present
although
size
analysis
of
this
samples
indicates
about
25
percent
clay
size
material

VITRlC
AND
ARKOSIC
SANDSTONES
and
Lohnes
1975
Individual
particles
in
the
coatings
are
up
to
4
micrometers
across
and
less
than
0
3
micrometers
thick
Most
coatings
are
less
than
4
micrometers
thick
and
are
made
up
of
one
layer
of
particles
arranged
normal
to
the
grain
surface
Fig
14
15
Thicker
cements
con
sist
of
more
randomly
oriented
particles
that
increase
in
size
away
from
the
grain
surface
FIG
l6
Intrastratally
altered
hypersthene
grain
from
sandstone
shown
in
Figure
6
from
theWhite
River
Group
Top
Hypersthene
grain
and
montmorillonite
cement
Bottom
Montmorillonite
filling
dissolved
parts
of
the
hypersthene
grain
Crystals
of
montmorillonite
are
oriented
normal
to
the
walls
of
the
dissolution
cavities
413
particle
size
ranges
from
0
5
micrometers
to
3
micrometers
across
Fig
7
16
The
identification
and
the
nature
of
interstratification
of
the
mont
morillonites
was
determined
from power
diffrac
tion
patterns
of
oriented
ethylene
glycol
treated
samples
Fig
17
microprobe
analyses
and
qual
itative
elemental
analyses
using
energy
dispersive
x
rays
on
the
scanning
electron
microscope
Fig
18
The
analyses
indicate
no
detectable
variation
in
montmorillonite
with
different
grain
sizes
of
sediment
depositional
settings
or
sandstone
pet
rofacies
All
montmorillonite
is
adioctahedral
alumino
silicate
with
variable
amounts
of
exchange
able ions
but
with
magnesium
calcium
and
iron
the
major
cations
Most
of
the
analyzed
montmorillonites
exhibited
x
ray
diffraction
profiles
like
that
shown
in
Figure
17
Only
a
few
samples
contain
kaolinite in
addition
to
mont
morillonite
By
comparison
with
x
ray
diffraction
profiles
reported
by
Reynolds
and
Hower
1970
the
amount
of
interstratification
in
the
montmoril
lonites
appear
to
be
small
with
greater
than
70
percent
montmorillonite
layers
in
the
interstrati
fied
clay
structure
Fig
17
001
w
I
Z
02
11
BAN
D
20
15 10
DEGREES
28
5
FIG
17
X
ray
diffraction
pattern
of
montmorillonite
cement
coating
sand
grains
in
the
High
Plains
sequence
The
interlocking
arrangement
of
clay
crystals
in the
cement
Fig
14
inhibits
good
preferential
alignment
of
the
clay
particles
in
oriented
power
preparations
for
x
ray
analysis
and
consequently
the
resulting
x
ray
diffraction
patterns
are
difficult
to
evaluate
in
terms
of
the
illite
mixed
layered
illite
montmorillonite
and
montmorillonite
patterns
described
by
Reynolds
and
Hower
1970
Nevertheless
sufficient
information
is
available
to
indicate
a
montmorillonite
with little
mixed
layering

414
K
O
STANLEY
AND
L
V
BENSON
N
MlI
AI
III i
K
C
I I I
F
Fe
I I
PLAGIOCLASE
SANDSTONE
VOLCANICLASTIC
SANDSTONE
FELDSPATHIC
SANDSTONE
FIG
IS
Qualitative
elemental
analyses
of
mont
morillonite
cement
in
the
plagioclase
volcaniclastic
and
feldspathic
sandstone
petrofacies
showing
the
peak
intensities
of
the
major
elements
in the montmorillonite
using
energy
dispersive
x
rays
on
the
Cambridge
Scan
ning
Electron
Microscope
I70
OOO
to
200 000
counts
were
made
so
that
peak
intensity
is
a
semiquantitative
estimate
of
abundance
PETROLOGIC
VARIATIONS
IN
DIAGENESIS
In
many
continental
and
marine
sedimentary
sequences
significant
differences
in
the
style
of
diagenetic
alteration
can
be
equated
with
texture
environment
of
deposition
and
or
composition
In
the
High
Plains
sequence
these
possible
con
trols
on
dissolution
and
cementation
can
be
eval
uated
for
asemiarid
climatic
regime
because
of
the
unique
association
in
which
eolian
alluvial
and
lacustrine
rocks
compose
the
plagioclase
volcaniclastic
and
feldspathic
sandstone
petrofa
cies
shown
in
Table
I
As
noted
previously
dissolution
is
selective
and
favors
specific
chemi
cally
unstable
detrital
grains
so
that
the
amount
of
dissolution in a
sandstone
can
be
related
to
composition
of
detrital
modes
The
plagioclase
sandstone
petrofacies
shows
the
most
grain
de
struction
with
varying
amounts
of
dissolution
and
alteration
of
olivine
hypersthene
and
labradorite
Fig
16
Volcaniclastic
sandstone
exhibits a
less
er
amount
of
dissolution
which
is
commonly
confined
to
removal
etching
and
pitting
of
rhyolitic
glass
and
rare
hypersthene
grains
Figs
7
16
Total
removal
of
glass
resulting
in
hollow
clay
coatings
Fig
7
appears
to
be
more
prevalent
in
vitric
siltstone than
in
sandstone
and
is
the
only
textural
influence
recognized
on
the
dissolu
tion
of
grains
in
the
sequence
Fig
15
Fe1d
spathic
sandstone
shows
the
least
amount
of
dis
solution
with
only
minor
surface
etching
of
feld
spar
and
amphibole
grains
In
general
the
amount
of
clay
and
or
zeolite
cement
in
sandstone
correlates
with
the
intensity
and
amount
of
intrastratal dissolution
of
grains
For
example
the
Ogallala
sandstone
petrofacies
adjacent
to
the
Laramie
Range
are
contempo
raneous
alluvial
rocks
whose
diagenetic
altera
tions exclusive
of
paleosol
horizons
are
marked
ly
different
Rhyolite
bearing
feldspathic
sand
stone
shows
only
minor
etching
of
grain
surfaces
and
no
clay
cements
whereas
plagioclase
sand
stone
only
a
few
kilometers
away
shows
extensive
alteration
of
hypersthene
and
olivine
minor
dis
solution
of
labradorite
and
montmorillonite
and
zeolite
pore
filling
cement
up
to
0
1
mm
thick
Similarly
grains
in Arikaree
eolian
dune
sand
stone
of
the
volcaniclastic
sandstone
petrofacies
east
of
Chugwater
Wyoming
exhibit
montmoril
lonite
coatings
that
commonly
are
less
than
4
micrometers
thick
Fig
7
whereas
similar
Ari
karee
dune
sandstone
of
the
plagioclase
sandstone
of
the
petrofacies
less
than
3
km
away
have
montmorillonite
coatings
from
10
to
100
microme
ters
thick
Fig
7
In
both
of
these
cases
and
indeed
in all
comparisons
where
the
environment
of
deposition
is
a
constant
composition
is
the
major
factor
that
controls
the
amount
of
dissolu
tion
and
cementation
Comparisons
of
rocks
deposited
in
different
environments
show
the
same
compositional
influence
but
differences
in
dissolution
and
cementation
in rocks
of
the
same
petrofacies
are
insignificant
The
only
exception
to
these
relations
is
zeolitic alteration
of
lacustrine
sandstone
that
is
presently
being
studied
by
workers
from
the
University
of
Nebraska
Con
servation
and
Survey
Division
Boellstorff
oral
communication
1976
where
alteration
is
proba
bly
related
to
saline
alkaline
lake
conditions
Montmorillonite
calcite
and
silica
are
the
most
common
cements
in
the
High
Plains
sequence
and
occur
in
all
sandstone
petrofacies
in
alluvial
eolian
and
lacustrine
rocks
and
in
siltstone
to
conglomeratic
sandstone
Kaolinite
occurs
only
with
montmorillonite
in
coarse
grained
sandstone
implying
a
textural
control
on
the
sparse
occur
rence
of
kaolinite in
the
High
Plains
sequence
As
noted
above
montmorillonite
shows
no
de
tectable
difference
in
the
amount
of
mixed
Iayer

I
VITRlC
AND
ARKOSIC
SANDSTONES
ing
Qualitative
elemental
analysis
of
the
mont
morillonite
coating
suggests
some
minor
variations
in
the
exchangable
cations
of
the
clay
structure
depending
on
the
sandstone
composition
Fig
18
Counts
for
iron
sodium
potassium
and
calcium
which
are
crude
semiquantitative
estimates
of
abundance
arc
shown
in
Figure
18
by
peak
intensities
They
suggest
more
iron in
cements
of
the
plagioclase
sandstone
petrofacies
and
more
importantly
the
presence
of
sulfur
suggests
that
finely
disseminated
iron
sulfides
might
be
asso
ciated
with
the
montmorillonite
cement
in
these
rocks
The
high
iron
content
of
these
cements
also
could
reflect
derivation
of
the
clay
from
solution
and
alteration
of
iron
bearing
silicates
a
relationship
noted
by
Walker
Ribbe
and
Honea
1967
for
clay
which
repl
ces
hornblende
in
redbeds
of
Baja
California
Sodium
potassium
magnesium
and
calcium
also
seem
to
be
selec
tively
distributed
relative
to
sandstone
composi
tion
again suggesting
a
possible
control
on
clays
by
the
composition
of
the
sandstone
Although
textural
properties
and
environments
of
deposition
have
locally
affected
some
diage
netic
alterations
of
the
High
Plains
sequence
the
principal
factors
that
controlled
dissolution
and
cementation
is
the
mineralogic
composition
of
the
rocks
Nevertheless
cement
types
are
ubiquitous
and
only
changes
in
abundance
and
or
minor
changes
in
chemistry
can
be
equated
with
composition
STRONTIUM
IN THE
DIAGENETIC
SYSTEM
The
87Sr 86Sr
ratio
for
detrital
grains
in
sand
stone
and
for
their
parent
crystalline
source
rocks
of
the
High
Plains
depositional
basin
is
determined
by
the
composition
magmatic
history
and
age
of
these
materials
Continental
crust
is
enriched
in
87Sr
relative
to
the
mantle
and
therefore
rocks
formed
by melting
metasomatism
or
assimilation
of
continental
crustal
materials
will
have
a
higher
87Sr 86Sr
ratio
than
uncontaminated
rocks
derived
from
the
mantle
by
fractionation
Faure
and
Powell
1972
In
addition
the
87Sr
6Sr
ratio
is
determined
by
the
radioactive
decay
of
87Rb
to
87
Sr
so
that
older
rocks
will
have
a
higher
87
Sr
86Sr
ratio
than
younger
rocks
Where
a
considerable
difference
in
age
and
or
magmatic
history
can
be
ascribed
to
potential
source
materials
for
sandstone
the
relative
contribution
of
the
dif
ferent
sources
of
sand
grains
can
be
calculated
from
the
87Sr 86Sr
ratio
More
importantly
for
our
purpose
in
this
paper
the
87Sr 86Sr
ratio
of
interstitial
fluids
and
diagenetic
mineral
phases
in
sediment
should
be
controlled
by
the
87Sr 86Sr
ratio
of
ions
from
the
solids
that
were
dissolved
transported
and
precipitated
in
the
sediment
Therefore
the
isotopic composition
of
strontium
in
interstitial
fluids
can
be
regarded
as
a
mixture
415
of
different
isotopic
varieties
of
strontium
derived
from
weathering
and
or
intrastratal
dissolution
of
rocks
through
which
the
fluid
passed
Strontium
in
sandstone
of
the
High
Plains
sequence
is
from
three
potential
sources
I
Precambrian
crystal
line
rocks
of
the
cores
of
uplifts
and
detritus
derived
from
these rocks
in
sandstone
on
the
plains
2
late
Paleozoic
carbonate
rocks
on
the
eastern
flank
of
the
uplifts
and
3
Tertiary
airfall
rhyolitic
glass
in
sandstones
and
ash
layers
Precambrian
crystalline
rocks in
the
Front
Range
have been
studied
by
Hills
et
al
1968
and
Peterman
and
Hedge
1968
who
report
a
wide
range
of
87Sr 86Sr
ratios
of
from
0
7060
to
1
128
Late
Paleozoic
marine
carbonate
rocks
around
the
world
like
modern
ocean
waters
appear
to
be
isotopically
homogeneous
at
any
given
time
but
vary
with
time
the
late
Paleozoic
published
values
for
the
87Sr 86Sr
ratio
range
from
0
7070
to
0
7090
Peterman
Hedge
and
Tourtelot
1970
Rhyolitic
glass
in
Ogallala
ash
beds
on
the
High
Plains
has
a
strontium
isotopic
ratio
of
0
7143
Table
3
Strontium
isotopic
ratios
for
montmorillonite
calcite
and
zeolite
cements
in
sandstones
show
little
variation
and
range
from
0
7103
to
0
7113
although
these
cements
occur
in
plagioclase
feldspathic
and
volcaniclastic
sandstone Table
3
Strontium
in
these
cements
must
have been
equilibrated
with
strontium
in
the
interstitial
waters
when
cement
was
precipitated
The
slight
variation
in
87Sr 86Sr
ratios
of
cements
suggests
a
homogeneous
water
relative
to
strontium
The
TABLE
3
STRONTIUM
ISOTOPIC
COMPOSITION
FOR
DETRITAL
SANDSTONE
AND
CEMENT
IN
THE
HIGH
PLAINS
SEQUENCE
Feldspathic
Sandstone
Petrofacies
Calcite
cement
Sandstone
87Sr
86Sr
0
7112
0
7491
Plagioclase
Sandstone
Petrofacies
Calcite
cement
Zeolite
cement
Sandstone
0
7113
0
7110
0
7065
Sandstone
with
Components
of
both the
Feldspathic
and
Plagioclase
Sandstone
Petrofacies
Intercalated
in
rocks
of
the
volcaniclastic
sandstone
petrofacies
Montmorillonite
cement
0
7103
Sandstone
0
7103
Volcaniclastic
Sandstone
Petrofacies
Calcite
cement
Rhyolitic
glass
Ogallala
Group
age
7
m
y
0
7103
0
7143

416
K
O
STANLEY
AND
L
V
BENSON
dissimilarity
of
the
81Sr 86Sr
ratios
for
cement
and
sandstone
shown
on
Table
3
requires
a
hydro
chemical
system
in
which
solutes
in
pore
waters
were
not
controlled
locally
by
the
isotopic
composition
of
adjacent
sand
grains
A
homoge
neous
and
open
hydrochemical
system
is
indicated
with
water
moving
rapidly
through
large
volumes
of
sediment
or
rapid
diffusion
rates
relative
to
rates
of
precipitation
A
nearly
homogeneous
water
relative
to
strontium
isotopic
ratios
can
be
explained
by
relatively
rapid
mixing
of
strontium
from
different
sources
of
strontium
in
the
system
and
or
by
dissolution
oflarge
volumes
of
material
with
an
isotopic
composition
similar
to
that
of
the
water
Dissolution
and
mixing
of
strontium
from
Paleozoic
limestone
and
or
rocks
of
the
plagioclase
sandstone
petrofacies
with
strontium
from rocks
of
the
fe1dspathic
sandstone
petrofa
cies
is
one
possible
explanation
for
the
isotopic
composition
of
cements
Such
mixing
requires
that
most
of
the
strontium
was
derived
from
Paleozoic
limestone
C1Sr
86Sr
0
7070
or
rocks
of
the
plagioclase
sandstone
petrofacies
81
Sr
86Sr
0
7065
A
second
plausible
explanation
for
the
strontium
isotopic composition
of
cements
is
strontium
derivation from
rhyolitic
glass
which
has
an
isotopic composition
similar
to
that
of
the
cement
Table
3
However
vitric
material
con
tains
small
amounts
of
strontium
Fig
19
which
would
require
that
glass
dissolution
was
the
major
source
of
solutes
in
the
fluids
Analysis
of
stron
tium
and
rubidium
in
sandstone
and
rhyolitic
glass
shown
in
Figure
19
support
the
derivation
of
strontium
from
Precambrian
detritus
in
sandstone
and
not
from
rhyolitic
glass
Sandstone
contains
12
to
16
times
more
strontium
than
glass
and
the
amount
of
strontium
is
directly
proportional
to
the
amount
of
feldspar
particularly
plagioclase
in
the
sediment
so
that
dissolution
of
feldspar
is
believed
to
be
a
probable
important
source
of
strontium
in
the
hydrochemical
system
Fig
19
Available
information
cannot
be
used
to
discrimi
nate
between
these
possible
sources
of
strontium
but
it
does
indicate
that
strontium
in
cement
can
be
explained
by
a
hydrochemical
system
similar
to
that
of
today
in
which
rainwater
falls
on
the
plains
infiltrates
the
sediment
percolates
to
the
zone
of
saturation
and
moves
to
a
site
of
discharge
into
streams
or
lakes
Fig
20
INTERSTITIAL
WATER
AND
MINERAL
EQUILIBRIA
Hydrology
and
hydrochemistry
of
subsurface
water
Present
day
groundwater
and
its
move
ment
through
Tertiary
and
Quaternary
sediments
of
Nebraska
and
adjacent
Wyoming
is
perhaps
a
modern
analogue
of
the
ancient
hydrochemical
system
that
precipitated
cements
in
the
High
Plains
sequence
Figure
20
The
concentration
and
composition
of
these
groundwaters
is
a
func
60
PLAGIOCLASE
SAN
DSTONE
f
a
0
o
J
W
U
fO 8
Rb
O
1
F
Sr
30
FELDSPATHIC
SANDSTONE
o
45
Rb
0
1
F
Sr
0
SANDSTONE
O
4
Rb
2 4
F
Sr
z
w
a
w
0
o
R
b
7
S
r
500
STRONTIUM
ppm
1000
VOLCANIC
ASH
FIG
19
Plot
of
Strontium
concentration
against
percent
feldspar
Also
shown
are
the
correlation
between
sandstone
type
plagioclase
to
total
feldspar
ratio
P
j
F
and
the
rubidium
to
strontium
ratio
RbjSr
The
near
linear
correlation
between
feldspar
content
particularly
plagioclase
and
strontium
content
indicates
that
the
major
source
of
strontium
in the
sandstone
is the
feldspar
Pure
volcanic
glass
in
ash
beds
has
less
than
25
ppm
strontium
tion
of
rates
of
fluid
movement
in
the
sediment
coupled
with
the
kinetics
of
mineral
dissolution
and
cement
precipitation
These
processes
are
time
and
space
dependent
In
the
Sand
Hills
of
Nebraska
groundwaters
of
the
Elkhorn
River
drainage
basin
probably
exemplify
the
interaction
of
water
and
sediment
with
an
increase
in
dis
solved
solids
along
the
regional
hydrodynamic
gradient
west
to
east
and
with
depth
in
the
zone
of
saturation Bentall
1971
The
zone
of
satura
tion
in
the
Sand
Hills
and
in
Tertiary
rocks
in
western
Nebraska
is
commonly
within
30
m
of
the
surface
and
the
direction
of
groundwater
movement
is
toward
sites
of
discharge
at
the
land
surface
Fig
20
The
rate
of
lateral
movement
in
the
Sand
Hills
region
ranges
up
to
90
cm
per
day
in
major perched
and
shallow
aquifers
but
may
be
only
a
small
fraction
of
this
rate
in
deeper
or
less
porous
aquifers
Bentall
1971
The
frac
tion
of
precipitation
that
becomes
part
of
the
groundwater
system
is
highly
variable
In
areas
of
sand
or
friable
sandstone
the
fraction
of
pre
cipitation
that
infiltrates
the
soil
but
is
not
taken
up
by
plant
roots
or
returned
to
the
atmosphere

VITRlC
AND
ARKOSIC
SANDSTONES
SEMIARID
3I
c
yr
5t050cm
yr
Cl
Z
e
Ill
e
Ill
e
417
SUBHUMID
50
1060
cmiy
INCREASING
RAINFALL
AND
INFILTRATION
r
Cretaceous
shale
lkm
eIll
X
0
Ill
0
100
km
Ill
0
Z
QUATERNARY
SAND
DUNES
AND
ALLUVIUM
FIG
20
Schematic
diagram
of
the
present
day
High
Plains
east
of
the
Laramie
Range
showing
sedimentary
rock
sequences
and
the
circulation
of
hydrologic
system
by evaporation
is
up
to
25
percent
McGinness
1963
Bentall
1971
Keech
and
Bentall
1971
Rahn
and
Paul
1975
Where
clay
silt
or
caliche
are
the
surface material
little
or
no
water
is
infiltrated
to
the
zone
of
saturation
Rahn
and
Paul
1975
Much
of
the
discharge
from
the
zone
of
saturation in
Nebraska
is
due
to
evapotranspi
ration
in
places
where
the
water
table
is
within
the
reach
of
roots
the
remainder
occurs
as
seep
age
into
lakes
and
streams
and
constitutes
the
principal
regional
surface
water
source
Bentall
1971
Rahn
and
Paul
1975
This
hydrologic
system
is
a
consequence
of
the
regional
physiog
raphy
semiarid
climate
grassland
vegetation
and
sediment
types
factors
that
were
all
similar
during
the
deposition
of
the
High
Plains
sequence
Fig
20
Because
the
modern
ground
waters
are
dilute
solutions
with
a
short
residence
time
in
contact
with
sediment
before
discharge
into
streams
they
can
be
considered
as
precursors
of
interstitial
waters
from
which
cements
would
be
precipitated
Such
solutions
and
their
cement
phases
should
be
analogous
to
the
Tertiary
hydro
chemical
system
that
deposited
cements
in
the
pores
of
High
Plains
sequence
sandstone
For
several
decades
the
United
States
Geologi
cal
Survey
has
monitored
the
properties
and
dissolved
solids
in
surface
and
subsurface
waters
of
Nebraska
and
adjacent
Wyoming
Several
hundred
analyses
are
now
published
in
water
quality
reports
Wenzel
et
al
1946
Babcock
and
Visher
1952
Bradley
1956
Rapp
et
al
1957
Sniegocki
1959
Lowry
and
Crist
1967
Most
of
the
subsurface
water
data
are
from
wells
that
supply
potable
water to
ranches
and
towns
this
is
a
sample
bias
against
more
saline
waters
in
less
porous
rocks
In
addition
constraints
are
placed
on
the
significance
of
mineral
equilibria
and
saturation
calculation
for
these
waters
be
cause
many
properties
such
as
pH
were
mea
sured
in
the
laboratory
after
collection
Two
subsurface
water
masses
are
present
in
western
Nebraska
and
adjoining
Wyoming
Fig
21
I
sodium
bicarbonate
waters
that
charac
terize
Cretaceous
sandstone
and
shale
and
local
Iy
basal
sandstones
of
the
High
Plains
sequence

418
K
O
STANLEY
AND
L
V
BENSON
Ca
Mg
50
HC03
C03
CI
Ogallala
and
Arikaree
Groups
0
White
River
Group
Cretaceous
shale
FIG
21
Triangular
percentage
plots
showing
graphically
the
fields
of
present
day
well
waters
in
western
Nebraska
and
adjoining
Wyoming
in
terms
of
the
major
cations
and
anions
in
solut
on
and
the rock
unit
at the
bottom
of
the
well
Two
water
masses
have
been
recognized
in
southwestern
Nebraska
by
Smith
and
Souders
1975
calcium
bicarbonate waters
in
Arikaree
Ogallala
and
Quaternary
rocks
and sodium
bicarbonate
waters in
Cretaceous
sandstones
and
shales
and
some
basal
White
River rocks
A
mixture
of
these
waters
is
suggested
for
waters
in
some
White
River
rocks
and
2
calcium
bicarbonate
waters
in
the
High
Plains
sequence
and
Quaternary
sediments
Smith
and
Souders
1975
Dilute
sodium
bicarbonate
waters
contain
two
to
four
times
the
total
dissolved
solids
of
calcium
bicarbonate
waters
and
also
contain
more
chlorine
boron
iron
and
sulfate
Na
Smith
and
Souders
1975
Calcium
bicarbonate
waters
usually
contain
more
than
200
to
350
ppm
total
dissolved
solids
The
sodium
bicarbonate
waters
seem
to
reflect
movement
through
the
marine
Cretaceous
sandstones
and
shales
whereas calcium bicarbonate
waters
characterize
water
moving
through
Tertiary
continental
rocks
Mineral
equilibria
The
present
day
High
Plains
is
an
open
and
semi
confined
groundwater
flow
system
in
which
possible
mineral
equilibria
saturation and
precipitation
can
be
considered
in
terms
of
water
composition
data
reported
by
the
United
States
Geological
Survey
e
g
Wenzel
et
al
1946
Babcock
and
Visher
1952
Bradley
1956
Smith
and
Souders
1975
Previously
we
proposed
that
the
same
diagenetic
processes
have
been
taking
place
on
the
High
Plains
since
the
Eocene
or
during
the
past
37
million
years To
demonstrate
that
the
same
chemical
reactions
are
possible
today
the
mineral
equilibria
states
of
waters
from
113
wells
bottomed
in
White
River
Arikaree
or
Ogallala
rocks
have
been
calculated
with
respect
to
the
principal
authigenic
mineral
phases
The
thermodynamic
data
used
in
the
calculations
were
taken from
Aagaard
et
al
in
prep
Carbonate
mineral
equilibria
in
the
groundwa
ters
can
be
determined
by
comparison
of
mean
activity
products
of
mineral
species
in
the
aqueous
phase
with
their
solubility
products
and
by
the
scatter
of
water
data
on
the
activity
diagram
for
the
system
CaO
Mg
OH20
C02
For
the
High
Plains
ground
waters
analyzed
the
mean
activity
product
of
calcite
normalized
to
250
Cis
identical
to
the
solubility
product
of
calcite
of
10
85
It
appears
therefore
that
High
Plains
well
waters
are
in
general
equilibrium
with
calcite
the
perva
sive
carbonate
cement
in
the
High
Plains
se
quence
However
the
mean
activity
product
for
stoichiometric
dolomite
is
10
11
0
this
value
is
similar
to
the
mean
activity
value
of
10
16
9
reported
by
Langmuir
1971
for
groundwater
presumed
to
be
in
equilibrium
with
a
carbonate
terrain
This
indication
of
possible
equilibrium
with
both
carbonate
phases
is
also
suggested
by
the
distribution
of
water
composition
data
on
the
activity
diagram
for
the
system
CaO
MgO
H
20
CO2
Fig
22
The
data
shown
on
Figure
22
form
a
cluster
of
points
that
derme
a
linear
trend
that
is
parallel
to
the
calcite
dolomite
equilibrium
lines
Mineral
equilibria
in
the
multicomponent
alu
minosilicate
system
are
not
as
well
known
as
those
of
the
carbonate
system
and
therefore
saturation
and
equilibrium
are
more
difficult
to
predict
for
different
mineral
phases
With
respect
to
the
clay
system
conventional
activity
diagrams
such
as
those
published
by
Norton
1974
and
Tardy
1971
suggest
that
many well
waters
are
in
equilibrium
with
montmorillonite
Ca
or
Na
504

VITRlC
AND
ARKOSIC
SANDSTONES
montmorillonite
and
or
kaolinite
However
clay
mineral
crystalline
solutions
have
been
treated
in
these
activity
diagrams
as
if
they
are
pure
one
component
phases
or
as
if
they
are
solid
solutions
of
fixed
composition
The
lack
of
accurate
data
on
aluminum
species
in
the
aqueous
phase
prohib
its
the
explicit
calculation
of
activity
products
and
in
addition
clay
minerals
such
as
montmoril
lonite
and
illite
generally
occur
in
nature
as
crystalline
solid
solutions
and
not
as
pure
one
component
phases
Although
these
problems
are
by
necessity
partly
ignored
in construction
of
activity
diagrams
the
best
available
consideration
of
activities
for
clay
mineral
species
is
provided
by
ideal
site
theory
Helgeson
et
al in
prep
and
Benson
and
Aagaard
in
prep
have
applied
an
ideal
site
mixing
model
to
clay
minerals
which
allows
their
representation
as
solid
solutions
in
activity
space
Figure
23
is
atwo
dimensional
representation
of
the
system
K2
0
A12
03
Si02
H20
projected
through
an
aluminum
bearing
component
space
The
construction
and
inter
pretation
of
this
diagram
is
discussed
in detail
by
Benson
and
Aagaard
in
prep
The
composi
tions
of
the
113
well
waters
plotted
in
Figure
23 suggest
that
most
present
day
fluids
are
in
equilibrium
with
montmorillonite
Several
fluids
appear
to
be
in
equilibrium
with
kaolinite
and
a
few
fluids
are
inferred
to
be
in
equilibrium
with
a
mixed
layer
illite
montmorillonite
or
an
illite
phase
The
activity
of
aqueous
silica
ranges
from
about
10
3 8
to
10
3 0
This
range
of
values
is
15
II
14
OJ
oI13
cr
2
o
12
o
l
DOLOMITE
CALCITE
10
10
II
12 13
LOG
OCd
OH2
14
FIG
22
Activity
diagram
for
the
system
CaO
MgO
CO2
H
20
showing
the
plot
of
water
well
analyses
from
113
wells
in
Nebraska
and
adjacent
Wyoming
Water
analyses
are
shown
by
open
circles
419
8
0
7
0
6 0
0
O
5 0
O
r
1
4
0
I
GIBBSITE
1
e
g
3
0
1
I
I
PYROPHYLlITE
I
KAOLINITE
I
2
0
I
I
1
I
I
10
1
I
I
I
0
0
5
04 0 30
2
0
LOGo
Si02
FIG
23
Activity
diagram
for
the
aluminosilicate
system
showing
stability
fields
of
naturally
occuring
clay
mineral
groups
Mixed
layer
refers
to
illite
montmoril
lonite
solid
solutions
Also
shown
by
solid
dots
are
the
plots
of
water
analyses
of
113
shallow
wells
from
western
Nebraska
and eastern
Wyoming
that
indicate
equilibrium
with
montmorillonite
for
the
majority
of
well
waters
interpreted
to
indicate
equilibrium
with
a
silica
phase
of
variable
crystallinity
such
as
opal
CT
The
value
of
10
3 0
suggests
an
upper
activity
limit
buffered
by
the
solubility
of
j3
crystobalite
The
available
data
indicate
that
groundwaters
of
the
High
Plains
sequence
and
Quaternary
sediments
in
western
Nebraska
and
adjoining
Wyoming
are
in
equilibrium
with
observed
authi
genic
mineral
phases
This
suggests
that present
day diagenetic
processes
are
similar
to
past
pro
cesses
a
relationship
that
supports
a
persistent
depositional
hydrologic
history
for
the
deposi
tional
basin
in
the
middle
and
late Cenozoic
15
INTERPRETATIONS
AND
SUMMARY
Vitric
and
arkosic
sandstone
in
continental
facies
of
sedimentary
basins
are
generally
as
sumed
to
undergo
extensive
early
diagenetic
al
teration
of
fabric
and
composition
and
indeed
some
Tertiary
arid
and
subhumid
alluvial
se
quences
of
the
mid
continent do
show
great
amounts
of
alteration
of
chemically
unstable
grains
and
pervasive
cements
Walker
1967 1976
McBride
et
al
1968
Gallowayet
al
1977
The

420
K
O
STANLEY
AND
L
V
BENSON
pastel
browns
and
greens
and
absence
of
hematite
cement
distinguish
the
High
Plains
sequence
from
arid
red
beds
of
the
Rio
Grande
Rift
2000
km
to
the
south in New
Mexico
Walker
1976
Color
of
the
High
Plains
sequence
is
similar
to
that
of
the
subhumid
Catahoula
Formation
of
south
Texas
3000
km
to
the
south
which
however
displays
more
extensive
alteration
of
grains
and
cementation
McBride
et
al
1968
The
semiarid
High
Plains
sequence
therefore
displays
some
of
the
same
gross
diagenetic
features
as
the
arid
and
subhumid
sequences
but
it
is
distinct
because
of
the
incipient
development
and
lack of
some
features
These
differences
between
rocks
depos
ited
in
different
climatic
settings
reflect
slightly
different
hydrochemical
systems
that
appear
in
turn
to
be
strongly
influenced
by
the
composition
of
the
sediment
the
amount
and
movement
of
interstitial
fluids
and
perhaps
vegetation
Post
depositional
changes
in
mineralogy
and
fabric
of
the
High
Plains
sequence
are
related
to
I
weathering
and
soil
forming
processes
thiil
operated during
deposition
of
the
stratigraphic
sequence
and
2
the
interaction
of
interstitial
fluids
of
open
and
semiconfined
ground
water
systems
with
sediment
Pedogenic
horizons
occur
throughout
the
High
Plains
sequence
but
cali
chi
fication
of
eolian
and
alluvial
sandstone
and
mudrock
are
most
common
in
the
Ogallala
Group
Pre
Ogallala
rocks
exhibit
soil
horizons
that
are
distinguished
by
surfaces
with
discoloration
pervasive
root
casts
and
abundant
clay
in
un
derlying
rocks
Fig
4
All
of
these
soil
profiles
are
characterized
by
calichification silicification
and
or
argillization
that
have
partly
or
wholly
destroyed
grains
rhyolitic
glass
altered
to
mont
morillonite
or
silica
opal
grains
replaced
by
silica
or
calcite
and
pore
space
filled
with
varying
amounts
of
cement
These
horizons
are
discon
tinuous
only
a
few
meters
thick
and
less
porous
than
underlying
or
overlying
rocks
The
lackof
alteration
of
sandstone
and
siltstone
between
paleosol
horizons
requires
that
these
sediments
have
persisted
for
long
intervals
of
time
in
the
zone
of
infiltration
and
capillary
assisted
evaporation
below
the
soil
horizon
and
above
the
zone
of
water
saturation
Preservation
of
vitric
siltstone
with
only
minor
hydration
and
dissolution
of
glass
requires
a
paucity
of
interstitial
fluids
that
could
react
with
unstable
mineral
species
and
just
as
importantly
dilute
waters
of
about
neutral
pH
The
grassland
vegetation
that
covered
areas
between
streams
and
lakes
may
have
played
an
important
role
in
this
diagenetic
system
by
I
reducing
the
infiltration
of
waters
to
the
water
table
through rapid
evapotranspiration
by
short
lived
annuals
and
by
2
lowering
the
pH
of
percolating
fluids
Diagenesis
of
sediment
in
the
zone
of
aeration
and
capillary
draw
of
interstitial
waters
probably
includes
formation
of
calcite
concretions
many
of
which
are
calcite
sand
crys
tals
several
centimeters
in
diameter
and
may
also
include
montmorillonite
coatings
precipitated
from
solutions
concentrated
by
the
evaporation
These
two
types
of
cement occur
in many
sand
stones
with
calcite
precipitated
before
montmoril
lonite
Calculations
of
cement
mineral
saturation
for
present
day
dilute
ground
waters
if
concen
trated
indicate
precipitation
of
a
similar
sequence
of
mineral
phases
Open
and
semi
confined
ground
water
flow
systems
in
sandstones
could
also
explain
petrographic
evidence
for
undersaturation
and
saturation
of
waters
dissolution
of
grains
zeolitization
and
formation
of
some
calcite
silica
and
clay
cements
Clinoptilolite
is
the
only
zeolite
species
we
recognized crystals
apparently
were
precipitated
on
sand
grains
already
coated
with
silica
or
montmorillonite
Fig
12
The
solution
from
which
clinoptilolite
was
precipitated
proba
bly
was
groundwater
of
alkaline
composition
formed
by
interaction
of
semiconfined
interstitial
water
and
chemically
unstable
grains
of
plagio
clase
and
or
volcaniclastic
sandstone
Unlike
many
continental
deposits
rich
in
ferro
magnesium
minerals alteration
of
sandstone
in
the
High
Plains
sequence
has
not
led
to
formation
of
iron oxide
cements
Present
day
groundwaters
commonly
contain
less
than
0 2
ppm
dissolved
iron
Smith
and
Sounders
1975
which
must
be
combined
in silicate
or
sulfide
authigenic
mineral
phases
or
removed
from
the
system
Montmoril
lonite
contains
iron
and
locally
in
some
cements
rich
in iron
sulfur
has
been
identified
which
suggests
the
possible
presence
of
iron
sulfide
minerals
The
interaction
of
interstitial
waters
and
sedi
ment
has
resulted
in
varying
amounts
of
intrastra
tal
alteration
of
the
most
chemically
unstable
grains
but
only
surface
etching
and
dissolution
of
amphiboles
rhyolitic
glass
micas
and
feld
spars
Dissolution
and
alteration
of
olivine
and
hypersthene
and
locally
glass
has
resulted
in
removal
of
some
grains
and
intensely
dissolved
cockscomb
features
of
others
Because
this
in
trastratal
alteration
is
mineralogically
selective
the
amount
of
post
depositional
alteration in
the
High
Plains
sequence
favors
specific
sandstone
petrofacies
shown
in
Table
I
Plagioclase
sand
stone
displays
the
most
intense
alteration
with
dissolution
and
alteration
of
olivine
and
hyper
sthene
and
etching
and
minor
dissolution
of
the
surface
of
labradorite
grains
Volcaniclastic sand
stone
shows
less
alteration
of
grains
with
only
minor
pitting
and
dissolution
of
the
surface
of
glass
amphibole
and
feldspars
and
locally
re
moval
of
glass
and
hypersthene
grains
Feldspath
ic
sandstones
show
the
least
alteration
with
only
surface
etching
of
grains Types
of
cements
pro

VITRlC
AND
ARKOSIC
SANDSTONES
duced
by
the
interaction
of
interstitial
waters
and
sediment
are
ubiquitous
and
their
presence
is
independent
of
sandstone
type
environment
of
deposition
and
fabric
and
texture
of
the
rock
The
amount
of
montmorillonite
cement
however
does
seem
to
correlate
with
the
amount
of
in
trastratal
alteration
of
the
sandstone
so
that
pla
gioclase
sandstone
tends
to
have
the
thickest
montmorillonite
coating
cement
on
grains
up
to
100
micrometers
whereas
volcaniclastic
sand
stone
commonly
has
a
thin
coating
less
than
4
micrometers
and
feldspathic
sandstone
only
sparce
and
thin
coatings
if
present
The
strontium
isotopic
composition
of
cements
reflects
either
I
the
isotopic composition
of
strontium
in
rhyolitic
glass
or
2
the
mixture
of
strontium
of
variable
isotopic composition
from
feldspathic
and
plagioclase
sandstones
and
Paleozoic
lime
stone
Strontium
in
the
system
is
probably
con
trolled
by
dissolution
of
feldspars
which
contain
the
most
strontium
but
also
could
reflect
dissolu
tion
of
large
volumes
of
glass
in
the
sediment
Preliminary
microprobe
analyses
of
the
mont
morillonite
coatings
suggest
that
the
major
ex
changeable
ions
in
this
authigenic
mineral
are
421
calcium iron
and
magnesium
cations
more
likely
were
derived
from dissolution
of
feldspar
and
heavy
minerals in
sandstone
than
from
rhyolitic
glass
The
available
data
suggest
that
ground
waters
of
the
High
Plains
and
Quaternary
sediments
in
central
and
western
Nebraska
and
adjoining
Wyoming
are
in
equilibrium
with
montmorillonite
kaolinite
illite
mixed
layer
illite
montmorillonite
opal
CT
calcite
and
possible
a
disordered
dolo
mite
Some
of
these
are
also
the
most
common
mineral
phases
found
as cement
in rocks
of
the
High
Plains
sequence
ACKNOWLEDGEMENTS
We
are
grateful
to
James
W
Collinson
and
Charles
H
Summerson
who
reviewed
an
earlier
version
of
the
manuscript
and
made
helpful
sug
gestions
for
improvement
Thanks
also
are
ex
tended
to
Theodore
R
Walker
for
his
helpful
discussion
of
diagenesis
while
in
the
field
with
Stanley
and
to
Gunter
Faure
who
determined
the
isotopic composition
of
High
Plain
sequence
sandstones
volcanic
ash
and
cements
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R
L
1968
Sevier
orogenic
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in
Nevada
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Utah
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429458
BABCOCK
H
MAND
VISHER
F
N
1952
Reconnaissance
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the
geology
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156
30
p
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RAY
1971
Water
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Anomalous
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1910
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EROL
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1961
Middle
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AND
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1949
Geology
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Hartville
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eastern
Wyoming
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1969
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Conservation
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60
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M
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176
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Late
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1907
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J
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1972
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1968
Petrology
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