GEOLOGY AND COAL RESOURCESOFTHE
LAKE
QUADRANGLE,
ATARQUE
CIBOLA COUNTY, NEW MEXICO
NEW MEXICO BUREAU O F MINES AND MINERALRESOURCES
OPEN-FILEREPORT
167
bY
O R I N J. ANDERSON
J u n e , 1982
( r e v i s e d 1, 9 8 3 )
Contents:
(1) D i s c u s s i o n of G e o l o g y and C o a lR e s o u r c e s
(attached)
( 2 ) G e o l o g i c map w i t h cross sesction
(accompanying)
T a b l e of C o n t e n t s
GEOLOGY
General
P.
S t u d y Area
P.
Structure
P.
Stratigraphy
P.
COAL RESOURCES
p. 22
REFERENCES
p. 23
Figures
1
-
Measured s e c t i o n of Zuni and Dakota SS.
p. 11
2
-
M e a s u r e d s e c t i o n of A t a r q u e and Moreno H i l l Fms.
p. 18
GEOLOGY
General
The Atarque Lake quadrangle l i e s i n t h e s o u t h w e s t e r n p a r t o f
t h e Z u n i Basin, a b r o a d ,s h a l l o ws t r u c t u r a le l e m e n tt h a te x t e n d s
southwestward from the Zuni Mountains of
c e n t r a l Arizona.
New Mexico i n t o e a s t -
A s such it l i e sn e a rt h es o u t h e a s t e r nm a r g i n
oftheColoradoPlateau.
is
The r e g i o n a ld i pi nt h es t u d ya r e a
very gently northeastward toward the Gallup
Sag which comprises
thenortheasternpartoftheBasin.Thereare,however,broad,
g e n t l e NW-SE t r e n d i n g f o l d s
d i p s , and a t l e a s t
which r e s u l t i n l o c a l
southwestward
up on t h e
twoabruptmonoclinalflexures,
n o r t h e a s ts i d e ,( o p p o s e dt or e g i o n a ld i p )t h a tc l e a r l yd e f i n et h e
NW-SE
structuralgrainofthearea,aswellas
minor f a u l t i n g .
These s t r u c t u r a l t r e n d s p a r a l l e l t h e a x i s o f t h e
Zuni
U p l i f t , b u t perhaps more i m p o r t a n t l y t h e y a p p e a r t o r e p r e s e n t
the southeastward extension of the structural axes that
around the southern
andKiven
(1975),
wrap
end of t h e D e f i a n c e U p l i f t , a s
shown by Davis
and t h e y a l s o a l i g n v e r y w e l l w i t h t h e
northwest-trendingdikesystemintheFence
quadrangle),Techado,
Lake
( t h e Dyke
Adams Diggings,andPietownareas.
Of t h e t h r e e s t r u c t u r a l f e a t u r e s
monoclines and f a u l t i n g
-
-
broadfolds,
monoclines are the most pronounced
s i g n i f i c a n tn o to n l yl o c a l l y ,
Kelley (1955) s t a t e d ," I n
mentioned
b u t i n a much broadercontext.
and
As
many r e s p e c t st h em o n o c l i n e sa r et h e
Most of
p r i n c i p a ls t r u c t u r a lf e a t u r e so ft h eC o l o r a d oP l a t e a u .
thedeformationhasoccurredalong
them."
T h e i rs i g n i f i c a n c e
is
tied to the concept of northeast-southwest horizontal compression
1
-~
~
of the Colorado Plateau during
the Laramide. As a response to
the regional compression, discrete, individual basement blocks
were uplifted by reverse
movements
fracture zones (Davis, 1978).
along
segments
of high-angle
These reverse faults produced
monoclinal folding in the overlying strata. Groupingsof these
monoclines, some of which
length,
which
have
when
been
attempted
related
Precambrian
may
to
basement
the
into
be
on
traced
the
over
100
basis
of similarity
fracture
a
for
miles
of
trends,
zones to
serve
subdivide
mosaic
of crustal
in
the
blocks.
The area under consideration is underlain (1)
by Cretaceous
sandstone and shales that may exceed 500 ft in thickness where
the Moreno Hill Formation (new name) is present,
( 2 ) highly cross
bedded eolian sandstoneof the
Jurassic
that
total
about
140 ft
in thickness, and ( 3 ) the Triassic shales, mudstones, siltstones,
and
sandstones
that
make
up
the
Chinle
Formation,
which
is
estimated to be 800 to 1000 ft thick in this area.
A 6 ft thick
flat
bedded
top
of
the Chinle Fm crops out at one locality and
represent
present
as
silty
sandstone
the
Rock
Point
a
much
thicker
and
sandy
Member
of the
unit
siltstone
Wingate
both
to
present
the
is
thought to
Sandstone
the
at
north
which
and
is
southeast.
In addition a1400 ft section of upper Paleozoic rocks
capped
by
the
San
Andres
locally as indicated by
Atarque Lake quadrangle.
an
Limestone
oil
test 10
occurs
in
the
subsurface
miles
to the north of
the
(Hole is in NE 1/4 sec. 5 , T 9N R 18W,
drilled in 1963 by Cities Service Oil
Co.; Maxwell and Nonini,
1977). This results in a cumulative sedimentary section of
approximately
2900
feet
overlying
2
the
Precambrian
basement
in
thoseareas
where t h e Moreno H i l l Formation i s p r e s e n t .
Major u n c o n f o r m i t i e s i n t h e s e c t i o n o c c u r a t t h e s y s t e m i c
boundaries
-
t h eJ u r a s s i c / T r i a s s i c ,
and t h eC r e t a c e o u s / J u r a s s i c .
i s aneolian
The Upper J u r a s s i c ZuniSanndstone
on t h e Rock P o i n t Member of
fluvialunitdepositedunconformably
t h e WingateFormation.
and p a r t l y
The o v e r l y i n g DakotaSandstoneformsthe
basal Cretaceous rocks which consist of the nonmarine, marginal
marine, and marinesandstones
front of
and s h a l e s t h a t were deposited in
and immediately behind the shoreline of the advancing
Western I n t e r i o r Seaway.
I nt h i sa r e at h e
unconformably on t h e ZuniSandstone,
progressivelyolderrocks;inthe
Dakota r e s t s
b u t southward it r e s t s on
Zuni S a l t Lake a r e a t h e
Dakota
r e s t s on theChinleFormation.
Scattered remnants of the
areapresentthroughoutthearea
Creek on thesouthtoPinehaven
Upper Tertiary Bidahochi Formation
from t h e n o r t h s i d e o f C a r r i z o
on thenorth.
apron of alluvial material deposited along
fluvial axis in the
I t r e p r e s e n t s an
a northwest trending
upperreachesoftheancestral
ColoradoRiverdrainagebasin.IntheAtarque
formation consists of sandstones
Little
Lake a r e a t h e
and coarse conglomerate
largely of volcanic material derived for the
D a t i l , Mangas, and GalloMountainssouth
composed
most p a r t from t h e
and e a s t o f
Quemado, a s
w e l l a s some reworking of older coarse grained fluvial deposits
on t h e Zuni P l a t e a u and SantaRita
Mesa.
Northofthevillageof
Zuni and i n t h e P i n e h a v e n a r e a t h e p r e s e n c e o f g r a n i t i c d e b r i s i n
theFormationindicates
Mountains(Repenning,
a sourceareainthegranitecored
e t .a l . ,
1958).
3
Zuni
Study Area
Structure
The narrow,
l i n e a r zone of deformation that trends
northwestward through the southwestern corner of the Atarque
Lake
q u a d r a n g l e c a n b e t r a c e d f o r a d i s t a n c e o f a b o u t 1 5 m i l e s a n di s
t h e mostprominent
and s i g n i f i c a n tl o c a ls t r u c t u r a lf e a t u r e .
h a sb e e ni n t e r p r e t e da s
It
a f a u l t by v a r i o u s i n v e s t i g a t o r s ( s e e
Sears, 1925, p. 23) and i s shown a s a f a u l t on t h e Geologic Map
of New Mexico (Dane and Bachman, 1965),upthrown
on t h e e a s t
bringingTriassicChinleagainstCretaceousrocks.
investigationhas
The p r e s e n t
i s more than 100
shown, however, t h a t t h e r e
f e e t of Jurassic sandstone cropping out
i n a hogbacksequence
t h a t d i p s f r o m 140 t o 460 t o t h e s o u t h w e s t a n d d e f i n e s t h e z o n e
of maximum d e f o r m a t i o n : t h e d i p s d e c r e a s e r a p i d l y t o t h e
SW.
A t t h eb a s eo ft h e
Chinle Formation
-
a f a u l tc o n t a c t .
i s i n t e r p r e t e d as anabruptmonoclinal
h e r e i n named the Atarque Monocline, related to
anglereversefaultalong
i nt h e
a high
a northwesttrendingfracturepattern
Precambrianbasement
t h es o u t h e r n
the
The c o n t a c t w i t h t h eo v e r l y i n gJ u r a s s i c
i s a d e p o s i t i o n a lo n e ,n o t
T h e r e f o r e ,t h es t r u c t u r e
flexure
theupperpartof
and t h e Rock Point Member of the Wingate
Formationareexposed.
ZuniSandstone
hogbacksequence
NE and
(see c r o s ss e c t i o n
and westernpartofsec.10,
A-A'
on map).
In
T. 6N, R 19W, anabrupt
change in strikeofthemonocline fromN 750WtoNN 200Wtakes
place in
a very short distance:, one mile
t o the southeast of this
s t r i k e change t h e monocline i s buried under
doesnotappearagainas
a distinctfeature.
4
a basalt flow
and
The southwest-facingAtarqueMonocline
A s t h eu p p e r( a n t i c l i n a l )
r e g i o n a ld i p .
limb hasbeenerodedoff
a x i s of t h e f e a t u r e , a s
l i m b i s concealed,the
and thelower
i s opposed t o t h e
shown on t h e accompanying map, i s a r b i t r a r i l y p l a c e d a t o r n e a r
Z u n i Sandstone.
t h eb a s eo ft h e
convergeswith
The axisofthemonocline
a s y n c l i n a la x i st ot h es o u t h e a s t .T h i s
may
i s dying o u t i n t h a t d i r e c t i o n ,
indicatethestructure
the dips are not decreasing
b a s a l t flow.
McLelland,
however,
where t h e monoclinepassesunderthe
Haschke, and Robinson,
(1981)
have
indicated extensive faulting within
and s o u t h o f t h i s b a s a l t f l o w
on t h e Rincon Hondo quadrangle.
Othernotableaspectsofthemonoclineare
t h ep r e s e n c eo fc r o s sf o l d s .
more o r l e s s
The a x e so ft h e s ec r o s sf o l d sa r e
normal t o the monoclinal axis
across the monocline,
on theVenadito
i t s s i n u o s i t y and
and appear t o extend
b u t a r e much more i n e v i d e n c e t o t h e
west
Camp quadrangle(Anderson,1982a).Thesecross
folds probably represent deformation along basement fractures of
a d i v e r g e n tt r e n d .I nd i s c u s s i n gt h ec r o s sf o l d i n g
characteristic of the
ColoradoPlateau
stated that the inherent nature of
and s i n u o s i t y
monoc1ines;Davis
(1978)
basement f r a c t u r e zones
envisionedforthePlateau,coupledwiththerecurringnatureof
movements w i t h i n t h e s y s t e m
would t e n d t o f a v o r t h e
crossfoldinginthevicinityoffracture
Folds created
by movement along one fracture
t r a n s f o r m e di n t o
phenomenon of
zone i n t e r s e c t i o n s .
zone may be
domes, saddles,ordoublyplungingfoldsby
superposedorcontemporaneous
movement along a f r a c t u r e zone of
d i f f e r e n t strike.
5
In the adjacent Venadito
associated with the monocline
Camp quadrangle the cross folding
and i t s a s s o c i a t e d d e p r e s s i o n on
t h e downwarped side has produced
a series of structural basins
and saddles.IntheAtarque
Lake q u a d r a n g l et h el a r g e s t
topographicfeatureproduced
by t h e c r o s s f o l d i n g
i s the west
f a c i n g mesa i n t h e S 1 / 2 s e c . 5 and t h e S E 1 / 4 s e c .
19W.
This mesa o f f e r st h eo n l ye x p o s u r e so ft h e
Tongue o f t h e
6, T 6N R
RioSalado
Mancos Shale on the quadrangle.
Mesa Colorado i n t h e n o r t h e a s t c o r n e r o f t h e q u a d r a n g l e d o e s
t o crossfolding;rather
notappeartoberelated
partofthesouthwest
predominant NW-SE
it r e p r e s e n t s a
limb of a s y n c l i n e t h a t p a r a l l e l s t h e
s t r u c t u r a lg r a i no ft h ea r e a .
The morphology
and r e l i e f on t h e mesa i t s e l f i s p a r t l y t h e r e s u l t o f l o c a l
v a r i a t i o ni nt h i c k n e s so ft h e
offoldaxes
ZuniSandstone.
The sinuousnature
is evidentinthisnortheastarea;theaxisofthe
synclinenortheastof
Mesa Colorado and t h e m o n o c l i n a l a x i s t o
t h es o u t h w e s ti ns e c s .1 3
b u t a r e of
and 14arebothcurved,
d i v e r g e n tt r e n d ,i n d i c a t i n gt h e ya r es e p a r a t es t r u c t u r e s .
F a u l t i n g on the quadrangle
is limited to the
minornorth-
south trending normal fault at the southwest corner of the
Colorado.Here
thewestblockhas
movedup30
Mesa
t o 40 f t r e l a t i v e
t o t h e e a s and
t
the middle shale unit of the Dakota Sandstone has
been juxtaposed against the upper marine sand unit of the east
The senseof
side.
movement a l o n g t h e f a u l t
i s easilyconfused
from a d i s t a n c e .
In addition minor faults are likely in the highly fractured
area in
the E 1/2 s e c 10, T 6N, R 19W where t h e s t r i k e o f t h e
6
AtarqueMonoclinechangesabruptly.
A 3 f tt h i c kl i g h tg r e e n i s h
graybentonitjr: clay found atone locality j u s t west ofthe road
i n t h e SE 1 / 4 SW 1 / 4 s e c l 0 p r e s e n t s a s t r a t i g r a p h i c p r o b l e m t h a t
i s included
i s p r o b a b l yr e l a t e dt of a u l t i n g .A l t h o u g ht h ec l a y
i n an area of Atarque Sandstone outcrops because of scale
l i m i t a t i o n s it i s u n l i k e l y t h a t
Outcrops a r e p o o r
it belongs in the Atarque.
and s t r u c t u r a l r e l a t i o n s h i p s
remain somewhat
uncertain at this locality.
Stratigraphy
Although the Chinle Formation
s t u d i e di nd e t a i l .
maroon,and
was mapped, t h i s u n i t was not
The upper p a r tc o n s i s t s
ofpurplishred,
graysiltstone,mudstone,claystone,
and t h i n
sandstonesthatareassignedtothePetrifiedForest
Stewart,Poole,
o ft h eC h i n l ea t
S t . Johns Ariz.
andWilson
( 1 9 7 2 ) described and measured s e c t i o n s
t w o n e a r b yl o c a l i t i e s .
A t one l o c a l i t y n o r t h o f
between 34042'N and 34046'N, t h e upper p a r to f
the Petrified Forest
Chinlesequencethat
Member i s 591 f e e t t h i c k w i t h i n
i s 827 f e e tt h i c k .
The thicknessoftheChinle
a total
A t t h eo t h e rl o c a l i t y ,
near Zuni, New Mexico, 178 f e e t o f P e t r i f i e d F o r e s t
present.
Member.
on theAtarque
quadrangle w a s n o t d e t e r m i n e d i n t h e p r e s e n t
e s t i m a t e d t o be 800 t o 1000 f t thick, based
Member i s
Lake
work, b u t i s
on breadth of outcrop
and i n f e r r e d d i p s on t h e u p p e r l i m b o f t h e m o n o c l i n e , a n d t h e
absenceof
San AndresLimestoneoutcrops.O'Sullivan
(1977)
showed t h e 400 m ( 1 3 2 0 f t ) i s o p a c h o f t h e C h i n l e p a s s i n a
g few
milestothenorthoftheAtarquearea;theChinle
thesouthinthisarea.
7
is thinning to
As
previously
mentioned, 6a ft
thick
bed
of
reddish
brown,
flat bedded, silty sandstone is exposed at the base of
south
the
end of Mesa Colorado in sec
18 T 7N, R18W, resting on Chinle
Formation
mudstones
and
shales
with
no
apparent
break
in
deposition. It is considered to be the equivalentof the Rock
Point
Member
of
the
Wingate
Sandstone
described
by
Harshbarger,
Repenning, and Irwin, (1957,p. 8) as a pale reddish
brown silty
sandstone and sandy siltstone at the type locality near Rock
Point, Arizona. They further described it as a quiet water
deposit
that
-
Point Lagoon
accumulated
in
a
southward
plunging
- basin
Rock
fed by streams entering from the northeast, east,
of the lagoon
and southeast. An embayment at the eastern margin
is
shown
extending
across
the
New
Mexico
state
line
in
the
Zuni-
Atarque area.
Southeastward
from
the
Mesa
Colorado
exposure
the
Rock
Point
Member thickens before pinching out. An area
of excellent
exposures
de
Yeso
called
and
30 ft of the
Los
Fence
flat
Pilares
Lake
bedded
at
the
quadrangales
silty
boundary
is
sandstone
between
described
as
comformably
the
Mesita
having
nearl
overlying
the Chinle and overlain by the largely eolian Zuni Sandstone
(Anderson, 1982b).
The white, fine-grained, highly cross-bedded sandstone
comprising
the
uppermost
Jurassic
rocks
and
outcropping
in
monocline is considered to be the Zuni Sandstone. The Zuni
Sandstone, as redefined by Anderson (1983), consists
of the
undivided equivalents of the Entrada andCow Springs Sandstones.
et al, (1951),
The name Cow Springs was proposed by Harshbarger
8
the
Fig. 1
Measured section
Zuni Sandstoneand
Dakota Sandstone in
E+ NWk
sec.18, T 7N R 18w
scale
(ft.)
: . L
Pale 'yellowish brn to pale red. brn,
fn to med. gr. ss, with thin pebble cyl.
zones; burrowed bioturb. in low. part;
10 ft thick white& purple well indurated
s s in upper part overlain by erosional
surface with pebble cgl.
I-
Dakota
Sandstone
-
re. ~ u v ~ a ~
~
Lt gray & It. gray. brn, paludal shales, arenaceous
shales and siltstones, and carbonaceous clay; interbedded fn sandy siltst and silty clay in lower
part overlain'by carbonaceous zone;'
2 ft thick
burrowed
and
root
penetrated
sandstone
near
'
50
I
up
~
"
~
_I
2
I- I
&
paludal
Lt. brn to paleyell. brn up fn- low mediumgr
s s ; :trough cross bedding and channel scours;
clay galls in lower part.
75-
\
-
"
. ...
I
loo-.
aeolian
125-
150-
.Zuni
Sandstone
""
. ....
.:...:
_I
,.
::
"
1.75-
I
I
Fluvial
and
aeolian
.. .
Pinkish gray and grayish orange pink lower
.._.. fn grs s ; planar and .trough cross bedded
.......
.....
J:,:;::!,?.: except for ext&eme basal portion; thin
I con'glomeratic zones in fining upward
'i""'"'"'"
channel fill sequences
in middle and lower
";..---4--,I
Durrowea
bioturbated
-root
tube
-tj
. *.i..
A r i p p l e marks
,
.,
..:
.,
C a r b o n a c e o u s zon
- p.,y.
,.:-,
...
.
.
I
..
'Roc% Point Member .reddish brown silty
ss; flat bedded.
. .
for the greenish gray to light yellowish gray, fine grained,
cross
bedded
sandstone
that
weathers
to
grayish
white
rounded
cliffs. At the type section
4 miles east ofCow Springs,
Arizona, it is 342 ft thick and is unconformably overlain by the
Dakota Sandstone. Additional work by Harshbarger, et a1 (1957),
extended
theCow Springs
into
the
Zuni
Reservation
of
449
a
ft thick section at Black Rock was
New Mexico and
designated
terminology
asCow Springs
Sandstone,
unconformably
overlain
by
the Dakota Sandstone. On the Zuni Reservation and southward
it
becomes
difficult
underlying
to
Entrada
distinguish
snadstone
and
the
Cow
thus name
the
Springs
Zuni
from
the
Sandstone
(first used by Dutton, 1885) has been applied
to this interval by
Anderson (1983).
notch,
Basin
The Zuni sandstone, whichcommonly has a medial
maybe traced
quadrangle
in
to
outcrop
Mesa
southward
Colorado
on the
through
Atarque
although it thins considerably two
at localities
19W and sec 31T 8N R 18W.
southward
the
contact
-
the
Lake
Plumasano
quadrangle,
sec. 35 T 9N R
From the Lupton, Arizona area
between
Cow
the Springs
and
the
underlying
Entrada was reported by HarshbaFger, eta1 (1951) as
"unidentifiable."
Hackman and Olson (1977) used the term
Cow
Springs-Entrada (JCSe) for this interval in the Zuni area.
Northwest
Mesa
the
serve
to
of
the
Summerville
divide
study
and
area
the
the
Zuni.into its
toward
Bluff
Fort
Formation
component
Defiance
are
-
and
present
parts Entrada
Black
and
and
Cow Springs. Northward and northeastward near Todilto Park, the
upper part of the Zuni,i.e. Cow Springs, appears to intertongue
with the
westwater
Canyon
Member
10
of
the
Morrison
Formation
is
and
considered
tobe an eolian
deposit
contemporaneous
with
the
fluvial Morrison (Harshbarger, et.al.,1957, p. 50).
In the Atarque Lake area the "medial notch", which
is
thought
the
to
represent
the
break
between
Cow
Springs equivalent, is not as
the
Entrada
equivalent
and
well
defined as it is at
Zuni Pueblo. It can, however, be identified at the north endof
NW1/4
sec 6, T 7N R 18W, and to a lesser
Mesa Colorado in the
extent at the south end in sec 18,
7N RT 18W. At this southern
location
bedded
the
ledge
medial
break
is
represented 1 by
ft athick,
cross
forming
sandstone,
somewhat coarser grained than the
adjacent units (Fig.1).
The lower portion ofthe
Zuni(be1owthe
medial notchor
break) contains scattered conglomeratic zones at the of
base
thin
channel fill sequences (Fig. 1).
chert
and
quartzite
pebble
It also contains a well rounded
conglomerate
that
is
well
exposed
in
the NE1/4 sec6, T 7N R 18W. The conglomerates represent
atypical facies for Entrada equivalent rocks, but fluvial facies
are not unknown in the Entrada. These conglomerates are probably
related to streams
traversed
this
northward
course
medial
silty
which
originated
area
of largely
toward
member
of
eolian
the
the
in
the
Mogollon
sedimentation
on
embayment
or
lagoon
Entrada
had
been
Highland
and
a
in
which
the
deposited
(Harshbarger and others,1957, p. 44-46).
Cretaceous rocks in the area consist in ascending of
order
the
main
body
Sandstone-Mancos
of
the
Shale
Dakota
sequence,
Sandstone,
the
Rio
an
intertongued
Salado
Dakota
Tongue
of the
Mancos (new name), the Atarque Sandstone (new name), and the
coal-bearing Moreno Hill Formation (new name). The rocks called
11
t h e mainbody
of the
Dakota Sandstone are the marine, marginal
marine, andnon-marinerockstha
Cretaceoussequence
makeup
i nw e s t - c e n t r a l
t h e lowest p a r t of t h e
New Mexico (Hook,Cobban,
Dakota i s comprisedof
Landis,1980).Inthestudyareathe
basalcross-bedded,fluvialsandstoneofvaryingthickness,
paludalshalesequencecontainingcarbonaceousshale
thin coal beds,
and marginalmarine
form theupper
2 5 f t of t h eu n i t( f i g .
locally in the
and
a
a
and very
and m a r i n e s a n d s t o n e s t h a t
1).
F o s s i l sc o l l e c t e d
upper marine sands include the bivalves Pycnodonte
c f . P. k e l l u m i andExogyra
l e v i s , and T u r i t e l l a s p, a n dv a r i o u s
"
othergastropods.
The Dakota i s o v e r l a i n by t h el o w e rp a r to f
t h e Mancos Shale,an18-foot-thickarenaceousshalethat
is
exposed only in the west-central portion of
the quadrangle:
elsewhere it i s coveredorunrecognizable.
This shaletongue
probably eqivalent to the Clay
is
Mesa Tongue which h a s a t y p e
s e c t i o n d e s i g n a t e d i n t h e Laguna, New M e x i c o a r e a ( a s d o m o s t o f
t h ei n t e r t o n g u e d
Cobban, 1973).
Dakota-Mancos units)(Landis,
Dane and
However, becauseofthepinchoutofanunderlying
sandstonetongue(theCubero)
a few milessouthwestof
Laguna,
t h e t e r m C l a y Mesa c a n n o t b e e x t e n d e d i n t o t h e s t u d y a r e aand
Mancos Shale'' i s used
hence the informal term "lower part of the
h e r e (Hook, Cobban, and Landis, 1980).
Overlying t h i s s h a l e
Sandstone; it c o n s i s t so f
i s t h e Paquate Tongue o f t h e
a 20-foot-thick,massive,cross-bedded,
coarsening upward s a n d s t o n e u n i t t h a t
zone a t t h e t o p
Dakota
commonly h a s a f o s s i l h a s h
composed a l m o s t e x c l u s i v e l y o f
Pynodonte c f . P. kellumi. Large
Exogyra l e v i s and
brown f e r r u g i n o u s / c a l c a r e o u s
concretions may also be present in the upper part. The tongue
characteristically
color,
but
near
weathersto a
the
Atarque
light
tan
or pale
Monocline
it
grayish
may
be
orange
reddish
brown.
Topographically, the Paguate is generally a small cliff former,
but outcrops are very restricted on this quadrangle. Northward
the unit merges with the main body of the Dakota, as the lower
part of the Mancos pinches out. Near the village Two
of Wells,
14 miles
due northof Zuni, at the type localities
of the
Twowells Tongue of the
Dakota
and
the
Whitewater
Arroyo
Tongue
of
the Mancos, the Paguate is not present as a lithologic unit
distinct from the main body
of the Dakota (Hook, Cobban, and
Landis, 1980 )
The
.
Whitewater
Arroyo
Tongue
of the
Mancos
Shale
overlies
the Paguate Tongue throughout the Zuni Basin. The name
was
proposed by Owen (1966) who applied it to a "well defined,
persistent
tongue
of
marine
shale
separating Twowells
the
(Tongue) from the rest
of the Dakota Sandstone in the
southwestern
area).
part
of
the
San
Juan
Basin"
(and
in
the
Gallup
Sa
A type section was designated in Whitewater Arroyo in
section17 o f T 12N, R 1 9 W near the village of Two Wells, where
it is 80 feet thick and described as a gray
to olive-gray, silty,
oyster-bearing shale. It does not crop out in the present study
area
but
it
consists
of an
estimated
55
feet
of
medium-to
dark-
gray fissile shale based
on outcrops in adjacent areas, and
contains the relatively large oyster Exogyra trigeri (Coqband) in
its
middle
portion;
also
very
near
the
middle
is
a
distinctive
white to orange-weathering 15-inch thick bentonite bed. Good
exposures of the
Whitewater
Arroyo
Tongue
and
the
bentonite
13
~
bed
occur
on
the
adjacent
Vennadito
Camp
quadrangle NE
in1/4
the
sec 30, T 7N, R 19W, where it is protected by a cover of
Twowells
Sandstone. The bentonite bed has also been recognized
18 miles
to the southwest on the Twentytwo Spring quadrangle, and
75 mi.
to the east on D-Cross Mountain where
it
mayonly
be 8 in. thick
(Hook, Cobban and Landis1980).
The
Twowells
Tongue
of the
Dakota
Sandstone
does
not
crop
out in the study area. It also may be seen on the adjacent
Venadito Camp quadrangle
where
it
is
about
30 feet thick and
consists of (1) a lower very fine-grained, flat-bedded sandstone
with
a few burrows; ( 2 ) a middle very fine
to fine-grained,
intensely burrowed and bioturbated sandstone, locally quite
friable; in at least one locality it has a flat-bedded,
undisturbed, well-cemented, ledge-forming sandstone near the top
of the bioturbated beds which in turn is overlain by a 10 ft
covered
interval
probably
composed
of
arenaceous
shale
or
interbedded very fine sandstone and siltstone;
(3) the upper part
is an upper fine- to medium-grained, planar cross-bedded unit,
generally 6 to 8 feet thick, containing clay clasts and, locally,
moderate concentrations of burrows including Ophiomorpha. Both
the
Twowells
represent
and
minor
the
Paguate
progradational
Tongues
events
are
in
here
the
considered
to
Dakota-Mancos
transgressive sequence.
The Rio SaladoTongueofthe Mancos Shale (new
represents
a
return
to open
marine
conditions
or
name)
an
interruption
in sediment supply following deposition
of the Twowells. It
consists of up to 240 feet
of
medium-gray
I
14
and
grayish-brown
shale, calcareous shale, and thin calcarenites, with
an
interbedded shale and very fine-grained sandstone sequence at the
top
where
name)
it
grades
into
the
overlying
Atarque
Sandstone
(new
.
The
name
Rio
and Cobban (1983).
between
Salado
Tongue
is
proposed
in
Hook,
Molenaar,
It is defined as the shale tongue lying
the Twowells Tongue of the
Dakota
Sandstone
and
the
Atarque Sandstone (the latter unit is also being defined by the
same authors) and is coextensive with these
two units.
The thin calcarenite and calcareous shale beds that occur
30
to 40 feet above the base of the Rio Salado in thi-s area
represent
the
equivalent
of the
Bridge
Creek
-
Limestone
Member
of
the Greenhorn Formation (Hook, Cobban, and Landis, 1980). The
beds may oftenbe recognized atadistance
yellow-weathering
calcarenites
stand
inoutcropbecause
out
in
contrast
to
the
the
typically gray Mancos Shale. They appear at only one locality
on
the map-the NE 1/4 sec
31, T 7N, R 19W. Deposition of these beds
is related to the very late Cenomanian (Greenhorn) transgressive
maximum, an
event
that
wasmarked
by
the
deposition
of
limestone
beds throughout most of the Western Innterior Seaway. These beds
form
important
marker
horizons
and
also
contain
the
guide
fossil
Pycnodonte newberryi (Stanton) in abundance or
at just below this
interval (Hook and Cobban, 1977).
P. newberryi was collected in
-
the NE 1/4 sec 31 and NW 1/4 sec 32 T 7N, R 19W and in the SW 1/4
sec 11 T 6N, R 19W. In the subsurface the Bridge Creek beds
may.
be recognized
by
the
distinctive
resistivity
the e-log, which is helpful in correlations.
kick
they
produce
on
L
About 100 feet above the Bridge Creek equivalent, limestone
concretions appear in the section; examples may be found in the
SE 114 sec 6 T 6N, R 19W.
Associated with the concretions are
ammonites
Mammites depressus, M. nodosoides,
the
Proplacenticeras
cummingsi, and Neoptychites cephalotus. Also found in
association
with
the
concretions
are
Ostrea
sp., Veniella
Baculitessp., Turritella sp. and
mortoni,
other
gastropods.
interbedded shale and sandstone sequence at the oftop
Rio
The
Salado
Tongue can be seen at the same 6 sec
locality.
The
Atarque
Sandstone
(new
name)
is
the
redefined
term
proposed in Hook, Molenaar, and Cobban
(1983) for the regressive
coastal
barrier
sandstone
unit
Tongue of the Mancos Shale and
regression
of
the
seaway
that
overlies
the
Rio
Salado
as
such marks the first major
following
the
Dakota-Mancos
transgression. As the shoreline had assumed a general NW-SE
trend
in
this
area
the
Atarque
prograded
northeastward
into
the
Mancos Seaway. It is a diachronous unit that becomes younger
to
the northeast. Throughout the Zuni Basin it
is a cli,ff-forming
unit and consistsof a lower flat-bedded sandstone, which appears
in
most
outcrops
as
the
first
massive
unit
overlying
the
transitional zone at the base, and coarsens upward from very
fine to fine grained; and an upper cross-bedded unit, generally
15 to 20 feet thick that is lower
to upper fine grained (see Fig.
2).
Only the upper cross bedded unit is well'exposed
on the
Atarque Lake quadrangle. Thesetwo units are similarto the
lower and upper shoreface units of Molenaar (1973).
shoreface
unit
is
thought
to have
16
been
deposited
The lower
offhsore
beyond
the
zone
where
wave
action
or
longshore
currents
effected
sedimentation. Deposition of the upper shoreface unit probably
took place in the zone where longshore currents were active.
Burrows, including Ophiomorpha, are
cammon in
bedded unit,
the
lower
and
are often present in the extreme
flat-
lower
andupper
parts of the cross-bedded unit.
The Atarque Sandstone, present usage, corresponds to the
Lower
Gallup,or
the
Atarque
Member
of
of Molenaar
Gallup,
the
(1973); he also, however, included the overlying nonmarine
carbonaceous shales, fluvial channel sandstones, and thin coal
beds in this member. The faunal evidence presented in Hook,
Molenaar, and Cobban (1983) points to a significant age
difference between the Atarque a,nd the Gallup. They recognize
the
Atarque
cycle
than
Gallup
by
as
having
been
the
Gallup
Sandstonne
Pescado
Tongue
of the
the
deposited
during
and
as
Mancos
an
being
earlier
separated
regressive
from
the
Shale.
The Pescado Tongue is not present in the study area. Its
southwesternmost
occurrence
is
some
10 miles
to
the
east
on the
Shoemaker Canyon Southeast quadrangle. Where present, the
Pescado Tongue separates the Gallup Sandstone from the (older)
(Hook, Molenaar, and Cobban,
redefined Tres Hermanos Formation
1983). The base of their Tres Hermanos is the regressive marine
sandstone
for
which
they
propose name
the Atarque
Sandstone
Member of the Tres Hermanos Formation. In their regional
stratigraphic
framework
southwestward or landward
landward
from
the
a
nomenclature
pinchout
pinchout
the
of
the
Atarque
change
exists
Pescado
is
the
Tongue;
raised
member to formation. Likewise the overlying nonmarine,
17
at
in
rank
from
'
75-
xncreasinq
grain sire
18
carbonaceous shales, fluvial channel sanstones, and thin coals
that
Molenaar (1973) included
in
the
Atarque
Member
of
the
Lower
Gallup, are currently recognized as a separate stratigraphic unit
that
must
also
undergo
the
nomenclature
change
at
the
landward
pinchout of the Pescado Tongue. The term proposed for that
nonmarine section in'Hook, Molenaar, and Cobban (1983) is the
Carthage
the
Member
Pescado
of
Tongue
the
is
Tres
Hermanos
present,
and
the
Formation
Moreno
in
Hill
the
area
Formation
wh
in
the area landward of the Pescado pinchout (McLelland, et.
al.,
1983).
The
Moreno
Hill
Formation,
as
defined
comprises
the
nonmarine carbonaceous shales, fluvial channel sandstones and
minor
thin
coals
that
overlie
the
Atarque
Sandstone
and
that
locally represent the youngest Cretaceous rocks. The
geographical
(the
is
area
Atarque
roughly
Mesaverde
in
the
Sandstone
indicated
Group
on
Zuni
and
by
the
Basin
Moreno
the
area
in
Hill
which two
these
new
Formation)
northwest
of Quemado
Geologic ofMapNew
Mexico
(Dane
names
may
be
mapped
applied
as
and
Bachman, 1965).
Most ofthe
MorenoHill
Formationhasbeen
erodedoff
inth
Atarque Lake quadrangle. Exposures of the remaining section are
limited to two areas in sec 5,
T 6N, R 19W. The basal 25 ft
consists of a cross bedded fluvial channel sandstone that rests
on the Atarque Sandstone (see Fig.2).
An overlying paludal
shale at this locality contains very thin coaly beds,
2 to 4
inches thick; this is the only coal occurrence
on the
quadrangle.
19
The light-gray and pinkish-ggay fluvial sandstones and
conglomerates
that
occur
largely
as
isolated
patches
and
remnants
unconformably overlying the Cretaceous, Jurassic, and Triassic
rocks are considered to
be part of the Bidahochi Formation. The
name Bidahochi was first proposed by Reagan (1924) for the
conglomerate
that
overlies
Cretaceous
rocks
in
the
Ganado,
Arizona area just eastof the Hopi Buttes volcanic field. Later
work by McCann (1938), Re.iche (1941) and Hack (1942) established
a
correlation
between
the
Bidahochi
and
the
Tertiary
sediments
of
the upper Little Colorado River drainage in the Zuni Basin.
Repenning and Irwin (1954) established a reference section for
the
Bidahochi15
Arizona
and
of the
east
miles
recognized
three
settlement
members,
a
of
Bidahochi,
lower
largely
lacustrine
member, a middle volcanic member, and an upper member. The Zuni
Basin
deposits
probably
correlate
In
the
present
study
exposed
but
for
most
unit
is
gentle
the
sandy
area
the
part
slopes
with
the
at
the
upper
formation
is
topographic
places
member.
locally
well
expression
of the
strewn
with
cobbles
or
boulders.
The
coarser
cobble-and
conglomerates
boulder-size
in
the
unit
fragments
of vesicular
are
composed
basalts,
of
basaltic
andesites, minor rhyolite and other volcanic rock, some
with
quartzite and chert and are well exposed in the vicinity of
the
Atarque Monocline. Quartzite, chert, and jasper comprise a much
larger
proportion
of
the
pebble
conglomerates
thando they
of the
coarser deposits: all have a calcareous cement. The sandstones
associated
with
the
conglomerates
20
are
white
to
very
light
gray,
medium to coarse grained, poorly sorted, rich in lithic fragments
including chert, and jasper, and are generally very friable. Low
angle
cross
beddingof highly
variable
directions
is common
a
feature. The clast lithologies suggest a source area to the
southeast in the Datil, Gallo, Mangas Mountains area and
deposition was along
A
finer
a
persistent
grained,
light
northwest
brown
to
trending
very
light
fluvial
grayish
axis.
brown,
highly friable sandstone occurs in the north and north central
parts of the quadrangle. These sandstones are not asociated with
to be
conglomerates, however, and tend
more
quartz
rich
than
those that are. They rest on the more gentle topography
developed on
exposed.
may
Chinle
Fm., but the base is nowhere well
It is for the most part a fluvial deposit, but there
be
aeolian
facies
near
theoftop
the
In the SE 1/4 SW 1/4 sec. 2 T
locally.
white
the
altered
tuff
was found
resting
remaining
section
7N 19W
R
a 2 5 ft thick
on
sandstone
of
the
Bidahochi Fm. An x-ray analysis ofthe tuff at the New Mexico
Bureau of
Minesand
Mineral
Resources
by
Robert
M. North
identified feldspar and kaolinite as the principal constituents.
In
their
discussion
of
the
lithology
and
depositional
features
of
the Upper Member of the Bidahochi Fm. Repenninget. al, (1958)
stated
the
Another
unit
containned
distinctive
a
few of
beds
white
facies
forms the resistant tops on
the
of
the
rhyolitic
Formation
is
ash.
present
and
mesas
in the E 1/2 sec 19 and the
NE 1/4 sec 30 T7N R19W. It is a dense, calcareous sandstone,
matrix and cement supported. A fresh surface is yellowish gray,
but
it
weathers
somewhat
darker;
thickness
varies
but
may
approach 2 0 ft in places; small root casts were noted at several
21
~~
horizons and localities. The,deposit maybe related to a shallow
impondment
monocline
formed
or
it
behind
may
be in
the
part
COAL
The
Atarque
Lake
hogback
created
pedogenic-a
by
caliche
the
truncated
caprock.
RESOURCES
quadrangle
encompasses
a
small
portion
of
the Salt Lake coal field. The field is essentially defined as
that area lying for the most part south of the North Plains
basalt flow andwest
underlain
by
the
of
Upper
the
continental
Cretaceous
divide,
Moreno
Hill
that
is
Formation
of
McLelland, et. al, (1982) (in preparation). In effect it
is
delineated on the State Geologic Map (Dane and Bachman, 1965) as
a Mesaverde Group outcrop area. A small portion
of the field,
however, lies northof the basalt flow: most of this "outlier" is
on
the
Venadito
Camp quadrangle
the west
trending
Monocline
miles
but
across
The
coal
a
the
flow
very
and
on
the
the
small
southwest
resources
in
northwest
portion
corner
of the
the
triangular
trending
extends
bounded
are
Lake
by
Atarque
eastwardfewfor
Atarque
quadrangle
area
a
quadrangle.
limited
to
the
Moreno Hill Fm. outcrops in this southwest corner and are
essentially nil. At the outcrop in the SE
1/4 NE 1/4 sec 5 , T 6N
R 19W several 4 inch thick coaly beds are present in a shale and
carbonaceous shale section resting
on the fluvial sandstones.
The
coal
bearing
sequence
as
noted
and
described
on
the
Venadito Camp quadrangle (Anderson, 1982a) is higher in the
section
and
has
been
eroded
22
off
here.
adjacent
REFERENCES
Anderson, Orin J..
1983, Preliminary reporton redefinition of
Zuni Sandstone, west-centralhiew Mexico:
New Mexico
Geology, vol. 5, no. 3 . , pp 56-59.
,
1982a, Geology and Coal Resources
of the Venadito
Camp Quadrangle, Cibola County, New Mexico: New Mexico
Bureau
,
of
Mines
and
Mineral
Resources
Open-file
report
163.
198213, Geology and Coal Resources
of the Mesita de
Yeso Quadrangle, Cibola County, New Mexico: New Mexico
Bureau of Mines and Mineral Resources Open-file 171 (in
preparation).
Dane, Carl H., and Bachman, GeorgeO., 1965, Geologic Map of New
Mexico: U.
S. Geol. Surv.
Davis, George H., 1978, Monocline fold pattern
of the Colorado
Plateau: Geological Society of America, Mem. 151.
Davis, George H., and Diven, Charles W.,
folds
in
Phanerozoic
rocks
of
the
1975, Structure map of
Colorado
Plateau
Tectonics
Province of Arizona: Office of Arid Lands Studies and the
Department of Geosciences, Univ. of Arizona.
Dutton, C. E., 1885, Mount
Taylorand the Zuni Plateau:
U. S.
Geol. Surv. 6th Annual Report, p. 105 (referenced in map
legend only).
Hack, J. T. 1942, Sedimentation and volcanism in the Hopi Buttes,
Arizona: Bull. Geol. Society of America, vol. 53.
Hackman, R. J., and Olson, A. B., 1977, Geology and structure of
the Gallup lo
X
20 quadrangle, New Mexico and Arizona: U.
S. Energy Research and Development Admin. Map 1981.
Harshbarger, J. W., Repenning, C. A., and Irwin, J. H., 1957.
Stratigraphy of
the
uppermost
rocks of the Navajo Country:
Triassic
and
the
Jurassic
U. S . Geol. Surv. prof.
paper
291.
Harshbarger, J. W., Repenning, C. A., and Jackson, R. L., 1951
Jurassic Stratigraphyof the Navajo Country:-in New Mexico
Geological Society Second Field Conference Guidebook,
1951,
pp. 9599.
Hook, S. C., and Cobban, W. A., 1977, Pycnodonte newberryi
"
(Stanton) common guide
Mexico:
fossil
in
the
Upper
CretaceousNewof
New Mexico Bureauof Mines and Mineral Resources
Annual Report 1976-77, pp. 4854.
Hook, S. C., and Cobban, W. A., and Landis, E. R., 1980,
Extension of
the
intertongued
Dakota
Sandstone
- Mancos
Shale Terminology into the Southern Zuni Basin: New Mexico
Geology, vol. 2, no. 3 .
Hook, S . C., Molenaar, C. M., and' Cobban, W. A., 1982 (in
preparation), Redefinition of the Cretaceous Tres Hermanos
Sandstone of Herrick (1900), west-central New Mexico: New
Mexico Bureau of Mines and Mineral Resources Circular
185.
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