--
What i s t h e ZuniSandstoneToday
100 Years
A f t e rD u t t o n ? A Discussion andReview o f
J u r a s s i cS t r a t i g r a p h yi nW e s t - C e n t r a l
New Mexico
NEW MEXICO BUREAU OF MINES
AND MINERAL RESOURCES
OPEN-FILE REPORT 174
by
O r i n J. Anderson
New MexicoBureau o f MinesandMineralResources
1983
Contents
Introduction
Discussion
Todilto Limestone - Navajo Sandstone
San Rafael Group Defined
Glen CanyonGroup Defined
MorrisonFormation Subdivided
Cow SpringsSandstone
1956 Memorandum from C. H . Dane
Z u n i Sandstone Redefined
Summary
ReferencesCited
Figures
Fig. 1
Fig. 2
Fig. 3
Fig. 4
P.
P.
PP.
P.
p.
p.
p.
p.
1
3
5
8
9
14
17
22
26
p. 28
p. 30
Index map o f study area
Stratigraphic nomenclature and correlation chart1885 to present
Measured section at type locality of
Zuni Sandstone
(inside back cover)
Stratigraphiccross-section-Dakota and Z u n i sandstones,
showing southward t h i n n i n g of Z u n i Sandstone (inside
back cover)
WHAT IS THE ZUNI
SANDSTONE
TODAY -- 100 YEARS AFTER DUTTON?
A DISCUSSION AND REVIEW OF JURASSIC
STRATIGRAPHY
IN
WEST-CENTRAL NEW MEXICO
Introduction
The massivesequence(s)oflightcolored,cross
bedded sandstonesthat
underlie the Dakota Sandstone (Upper Cretaceous) i n west-central New Mexico
and northeasternArizona were f i r s t d e s c r i b e d and namedby
E. Dutton ofthe
U. S. Army Ordinance Corps.
Taylor and the Z u n i Plateau"(Dutton,
CaptainClarence
His r e p o r te n t i t l e d
"Mount
1885) contains an account of the
stratigraphy and s t r u c t u r e of those two areas and theimmediatelysurrounding
region(the
Zuni Plateau i s thepresent
day Z u n i u p l i f t ) .
In thereport
he described a "massive b r i g h t redsandstone"thatoverliesthe"basal
Triassediments"(thepresent
area; this u n i t henamed
day ChinleFormation)
i n theFort
Wingate
"provisionally" the Wingate Sandstone.
Overlyingthe Wingate Dutton recognized "a s e r i e s ofsandstones
sandy shales
ofFort
...... wonderfully bandedand
variegated i n color".
and
North
Wingate, New Mexico i t was described as "broken up i n t o a s e r i e s
of variegated beds of all.conceivable colors" whereasinthe
of "a nearly uniform creamy white color".
area i t was described as being
Dutton named a l l t h e s e
Z u n i Pueblo
beds the Z u n i Sandstones.
The type Wingate of Dutton (1885) i s now recognizedastheEntrada
Sandstone.
B u t thenomenclature
change d i d not come about a l l a t once;
t h e r e were severalinstallments.
a reviewofexisting
The f i r s t of thesetookplacefollowing
knowledge and additional field workby
Baker, Dane,
and Reeside (1947), who s t a t e d "this c l i f f forming sandstone which crops
out
....
i n thecliffsnorth
to the sandstone that
ofFort
i s calledEntradaover
and has below i t a t h i n zone ofred
t o be equivalenttothe
Wingate, New Mexico is thus equivalent
most of Utahand
Colorado,
s i l t y sand and s h a l e t h a t i s considered
Carmel formation".
Thus thetypelocality
of the
- 2Wingate was abandoned, butthetermWingate
o f t h e Glen Canyon Group.
was r e t a i n e d f o r t h e b a s a l s a n d s t o n e
The Glen Canyon Group was thenextended
into
theFortWingateareatoincludethelowerportionofDutton'soriginal
WingateSandstone.
The r e s u l t i n g d i v i s i o n
Canyon groupundivided,
was, i n ascendingorder,Glen
Carmel Formationequivalent,
and EntradaSandstone,
w i t h no t h i c k n e s s e s s p e c i f i e d .
During an investigation of ground water resources of the Navajo Country,
Harshbarger and others(1957)
measuredand
Wingate somewhat d i f f e r e n t l y .
o f Baker, Dane, andReeside
an u n d e r l y i n g 50 ft o f r e d s i l t y
r e f e r r e d t o asthe"medial
303 f t o f D u t t o n ' s
They consideredtheupper
o r i g i n a l Wingate t o be theEntradaSandstone
(1947),recognized
interpretedthesectionatFort
sandstonewhichthey
s i l t y member o f t h e E n t r a d a " ( r a t h e r t h a n
Carmel
e q u i v a l e n t ) and thendesignatedthebasal
359 ft o f t h e s e c t i o n
Member o f t h e WingateSandstone
Canyon group o f Baker, Dane, and
Reeside,1947).
(theGlen
The typesectionfortheLukachukai,theupper
theWingateSandstone,
was t h e v e r t i c a l c l i f f i n t h e
o f Lukachukai, Apache County,Arizona(Fig.
astheLukachukai
member o f
escarpmentnortheast
1).
It remained f o r Green (1974) t o p r o v i d e t h e f i n a l i n s t a l l m e n t i n t h e
nomenclature change.
H i sf i e l di n v e s t i g a t i o n si nt h eG a l l u p - G r a n t sa r e a
o f New M e x i c o r e v e a l e d t h a t t h e r e l a t i o n s h i p
oftheEntrada
Sandstoneand
the underlying Lukachukai
Sandstone was a comformable one.
o f theLukachukai.
named i t t h e I y a n b i t o
between t h e m e d i a l s i l t y
member
member o f t h e Wingate
The u n c o n f o r m i t y l a y r a t h e r a t t h e
base
Thus Green reassignedtheLukachukaitothebasalEntrada,
Member, andsuggestedtheunconformity
a t i t s base
representstheTriassic-Jurassicboundary.Withthegeneralacceptance
o f t h i s work,there
r
i s a t present,noWingateSandstone
a t F o r t Wingate.
Figure
I. Indexmapofstudyarea(modifiedfromHarshargerand
others. 19571
- 3The problemssurroundingthe"Zunisandstones"
confusing, andhave
more
n o t been r e s o l v e d t o t h e e x t e n t a s t h o s e o f t h e W i n g a t e .
The i n t e r v a l , o r p a r t s o f
itsoriginalcontext
WhiteSandstone
o fD u t t o na r ee v e n
it, representedbythetermZunisandstones
hasbeen
v a r i o u s l yc a l l e dt h e
member o ft h eM o r r i s o n ,
Cow Springs,Thoreau,
a t ZuniPueblo,thelowerpartofDutton'sZuni
EntradaSandstone.
Some o f t h e
McElmo,La
in
Plata,Navajo,
and Zuni.Also,
i s equivalenttothepresent
problemshavearisenbecauseJurassicrocks
i n west-central New Mexicoareisolatedfromequivalentrockselsewhere
on theColoradoPlateau,
lack of fossils
and l a t e r a l f a c i e s
change coupledwith
a distinct
have made r e g i o n a l c o r r e l a t i o n s v e r y d i f f i c u l t .
The purpose o f t h i s paper i s t o r e v i e w t h e
i n t h e ZuniBasin-Zuni
uplift(Fig.
1) areasinceDuttonand
theregionalcorrelationsofJurassicrocksthat
Stratigraphicdata
works o f t h e v a r i o u s i n v e s t i g a t o r s
t od i s c u s s
weresubsequentlyproposed.
on the Jurassic section obtained during geologic mapping
and c o a l r e s o u r c e s i n v e s t i g a t i o n s
i n theZuni-Atarqueareas
The emphasis i s i n t e n d e d t o be on theuppermost
i s presented.
ofDutton'sJura-Triasunits,
the "Zuni sandstones," but discussion of the lower part
isfrequentlynecessary
to clarify the evolution of the nomenclature for this area.
Discussion
GunnisonGroup
F o l l o w i n gD u t t o n ' sd e s c r i p t i v ea c c o u n to ft h e" Z u n iP l a t e a u "c o u n t r y
i n 1885, a number o f i n v e s t i g a t o r s e i t h e r v i s i t e d t h e a r e a o r a t t e m p t e d
c o r r e l a t i o n sf r o mt h e i rs t u d ya r e a si n t ot h eZ u n ia r e a .C r o s s
(1905) suggestedthattheGunnison
theydividedinto
and Howe
Group ofsouthwesternColorado,which
a lowerunitcalledthe
La PlataSandstone
andan
upper
- 4one named the McElmo Formation, was equivalent to Dutton's
Z u n i sandstones
More s p e c i f i c a l l y , Cross and Howe were of the opinionthat
(Fig. 2).
La Plata which i n i t s typearea
the
i n the La Plata Mountains was a f r i a b l e ,
cross bedded, white or gray (locally orange to red), quartzose sandstone,
correlated w i t h Dutton's Zuni sandstone beds a t Navajo Church (1% miles
northof
Fort Wingate s t a t i o n , New Mexico).
Cross and Howe alsorecognized
a calcareous member, consisting locally of massive blue-gray limestone,
i n the upper halfof
partof
the remaining,overlying,
their La Platasandstone,with
the formation being " t h i n bedded shaly and inconspicuous."
McElmo Formation, being of a more variegated nature,
The
was correlated w i t h
the Morrison Formation on the basisofvertebrateremainsdescribed
(1901).
The MorrisonFormation
had been namedby
shales and sandstones so wellexposed
In a reconnaissancesurvey
i n the areaabout
f o r the nonmarine
Morrison, Colorado.
of northwest New Mexicoand
Darton (1910)appliedDutton'sstratigraphic
Triassic rocks at
Cross(1894)
by Riggs
northernArizona,
terms-Zuni and Wingate t o "the
the northern end of the Z u n i u p l i f t . "
One ofDarton's
measured sections i n t h a t l o c a l i t y shows the limestone bedsofthe
day Todilto Limestone forming the basalpartof
In a discussionof
Darton(1910
present
his Z u n i Sandstone section.
the Z u n i Pueblo, which i s south of the Todiltopinchout,
p. 48) stated "the Zuni Sandstone
i n c l i f f s o f uniformcreamy-white
.... is
or pale gray color, very
verymassive,appearing
different from
i t s (variegated)character on the north side of the Z u n i u p l i f t . " I t
appropriate to note that
the north side of the u p l i f t i s where the largely
eolian Zuni Sandstone(ofDutton)
begins tointertongue w i t h the Recapture
Member of the Morrison and i s overlain by the Westwater CanyonMember
the Morrison(Harshberger
is
and others,1957).
of
Darton a l s o observed t h a t
- 5Dutton's Wingate sandstone changed considerably between the Zuni Pueblo
the massive red c l i f f s just northofFort
area and the areaof
we nowknow
Wingate.
As
he was correlating the reddish brown, f l a t and t h i n l y bedded
s i l t y sandstone of the present Rock Point Member of the Wingate Sandstone
i n the Z u n i Pueblo area w i t h the massive,cross
Sandstone i n the Fort Wingate area.
andZuni
units t o be Triassic.
Darton (1910)considered
the upper part of
the lower part.
division into upper and lower p a r t s o r f o r
middleof
the age revision, b u t he d i d
the Zuni Sandstone,"southeastofGallup
the Todiltopinchout;
the Zuni and a
No reasons were s t a t e d f o r the
p. 46) the "suggestionof
mention(Darton,1910,
b o t h the Wingate
Darton (1915, sheet 15), however, indicated
a doubtfulCretaceous-Jurassicagefor
doubtfulJurassicagefor
bedded, present dayEntrada
i n the
an erosionalbreak
which i s just southof
the "break" represents the Todiltointerval
and thus
the section below i t i s equivalent to the present EntradaSandstone.
Todilto Limestone
-
Navajo Sandstone Terms Introduced
The next paper of significance to address
He retainedDutton's
area was Gregory (1917).
lower more reddish part of
the Jurassic rocks o f this
Wingate terminologyfor the
the section, b u t included i t a s the basal u n i t
of his La Plata Group, thereby establishing a correlation w i t h the La Plata
Sandstones(suggested
by Cross and Howe) ofsouthwesternColorado.
Gregory
then introduced the terms Todilto Limestone and Navajo Sandstone f o r the
middle and upper partsrespectively
of his La Plata Group.
of the Todilto Limestone was designated as Todilto Park,
The typelocality
McKinley County,
New Mexico, and t h a t of the Navajo Sandstone a s simply "the Navajo Country"
(see correlationchart,
Fig. 2).
-6-
The presenceof
a t h i n , c r y s t a l l i n e limestone u n i t (Gregory'sTodilto)
between two massivesandstones
had been noted a s e a r l y a s
saw this sequence a s somewhat
as well as by Darton (1910).Gregory(1917)
unique and hypothesized a correlation,through
section, to the section
1875 by Gilbert,
the southwesternColorado
exposed a t Navajo Mountain (30mileseast
Arizona on the Arizona-Utah l i n e ) where two massivesandstones,
ofPage,
a lower
redish one and a lighter colored upper one, were separated by up t o 200
f t of t h i n interbedded sandstone,shale,
Althoughproposed
and "limestoneconglomerate."
as only a "working field hypothesis"
this i s how and why
the name Wingate was introduced t o the northernArizona-southern
s e c t i o n .I t
remainstoday
a s the basalformationof
Utah s t r a t i g r a p h i c
the Glen Canyon Group,
even though a s pointed out i n the introductory remarks no Wingate Sandstone
i s present a t the originaltypelocalityofFort
Wingate, New Mexico ( t h a t
section now being recognized a s the Entrada).
The t h i n l y bedded, locally limy
u n i t separating the two massivesandstones
a t Navajo Mountain was eventuallyrecognizedasbeing
Todilto Limestoneof
lithologic character,
much older than the
New Mexico, aside from being of a t o t a l l y d i f f e r e n t
and wasnamed
the Kayenta Formation(Baker,
and Reeside, 1936) from exposures a t Kayenta, Arizona.Similarly
Sandstone, which is presentlyrecognizednorth
i s older than the strata overlying
Dane,
the Navajo
and west of Chinle, Arizona,
the Todiltoinnorthwest
New Mexico.
The Todilto and the overlying Summerville and Bluff.Formations would l a t e r
c o n s t i t u t e the upper partof
Gregory(1917)
the San Rafael Group.
further designated"all
the s t r a t a i n the Navajo Country
between the Dakota Sandstone and the Navajo Sandstone a s the McElmo Formation,
breaking up the Gunnison Group ofCross
and Howe (1905), b u t s t i l l recognizing
-7-
the correlation with the strata
Colorado.
To t h i s u n i t
exposedalong McElmo Creek i n southwestern
he assigned a J u r a s s i c ( ? ) age.
He acknowledged
some d i f f i c u l t y i n e s t a b l i s h i n g a Navajo-McElmo break i n mostareas
s t a t e d t h a t "iti s n o t p r a c t i c a b l e t o l o c a t e t h e c o n t a c t w i t h i n
of less than
100 f t and theboundaryhasaccordingly
base o f t h e l o w e s t s t r a t u m t h a t
o ft h e
McElmo Formation."
e a r l yi n v e s t i g a t o r s .
asthe
an e r r o r
been mapped a t t h e
shows f e a t u r e s u n m i s t a k a b l y c h a r a c t e r i s t i c
These "features"would
shales,argillaceoussandstones,
and
have t o be thevariegated
and marlsdescribedbyCross
It is now c l e a r t h a t
whatGregory
and o t h e r
(1917, p.61)designated
McElmo-Navajo contact at Navajo Church north of Fort Wingate (the
Dutton Plateau)
i s theRecapture Member-Cows Spring contact of Harshbarger
and o t h e r s (1957, p.
68).BothGregory
bedded g r a y l i m e s t o n e s j u s t
and H a r s h b a r g e rr e f e r r e dt oi r r e g u l a r l y
above t h e c o n t a c t , w h i c h s t r o n g l y s u p p o r t s t h i s
i n t e r p r e t a t i o n .G r e g o r ya l s on o t e d
"one o r more u n c o n f o r m i t i e sw i t h i nt h e
McElmo, u s u a l l y a t nogreatdistancefrom
i t s base."
been recognized i n t h e l o w e r p a r t o f t h e R e c a p t u r e
recentworkers,suchas
Member i n t h i s areaby
Green (1974).
Inhisdiscussionofthesouthern
Gregory'snomenclature,butassignedthe
Rocky Mountains, Lee (1918)used
McElmo t o t h e Lower Cretaceous.
Darton(1922)likewiseadoptedtheGregorynomenclature
area,butreplacedthe
An unconformity has
i n t h e Zuni u p l i f t
McElmo w i t h t h e M o r r i s o n F o r m a t i o n t o t h e n o r t h e a s t
i n t h e Chama basin,RioArribaCounty,regardingthetwoformations
"atleastinpart."
presentas
as e q u i v a l e n t
He a l s o had theNavajoSandstoneasonlydoubtfully
a "chocolate brown sandstone", 150 f t t h i c k i n t h e Chama basin.
A t thepresenttimethissandyinterval
basalMorrisonFormation.Budding
i s considered t o be a p a r t o f t h e
and others(1960)describedthelower
-8-
member of the Morrison i n this area as an a l t e r n a t i n g sequenceofpale
chocolate, or
brown,
deep purple mudstone and white to pale gray siltstone that
ranges between 300and
400 f t i n thickness and t h a t rests on the Todilto
limestone or gypsum.
San Rafael Group Defined
Gilluly and Reeside (1928)expressed
t h a t the Wingate-Todilto-Navajosequence
some doubtaboutGregory’shypothesis
i n the northern Z u n i u p l i f t a r e a
correlated w i t h the Wingate-thin bedded limyinterval-Navajosequence
They d i d use the term Todiltowith
Navajo Mountain.
i n their stratigraphic descriptions across
a querry, however,
the San RafaelSwell
Utah; b u t f o r the section above the Navajo Sandstone andbelow
theyintroduced
age.
the term San Rafael Groupand
at
i n eastern
the Morrison
assigned i t an upper Jurassic
They then d i v i d e d the Group i n t o four formations which were named
Carmel, Entrada, Curtis, and Summerville i n ascending order, (see correlation
chart,Fig.
2).
Gregory andMoore,
The Carmel (this formation was
named
i n association w i t h
who were working simultaneously on theKaiparowitsPlateau,
b u t who d i d not p u b l i s h until 1931) was recognized i n the area as a shallow
o r r e s t r i c t e d marinedeposit w i t h limysandstones
i n the lowerpart,
upper part.
w i t h gypsum, anhydritenodules,
The Entrada, the most prominentof
massivesandstone
and shales, thinly
and minor s a l t i n the
the fourconsistedof
a
u n i t w i t h two major facies, clean and well sorted t o the
e a s t of the San Rafael Swell, finer grained and s i l t y t o the west.
named f o r exposures a t EntradaPointin
Swell.
bedded,
A massivesandstone
the northernpart
I t was
o f the San Rafael
above the Navajo Sandstone had heretoforenot
been recognized, and this wouldbe
ofimportance
i n latercorrelations into
-9-
the San Juan Basin of New Mexico.
Gilluly and ReesidecorrelatedtheEntrada
The Curtis
a t t h e time w i t h the Upper La Plata i n the Moab, Utah area.
Formation was described as a fine grained, glauconitic sandstone usually
i d e n t i f i a b l e by c o l o r a l o n e . I t
had a "peculiargreenish-graycolor
a l i g h t brown.
a fresh fracture" that weathers to
considered to be a shallowmarinedeposit
a s an equivalentoftheTodilto
andwould
on
Like the Carmel, i t was
l a t e r be established
Limestone i n northwest New Mexico.
The
Summervilleconsisted of even bedded red and whitesandstones andmaroon
shaleswith
some gypsiferous mudstone, andwasnamed
just southeast of the
on SummervillePoint,
the north end ofthe
GlenCanyon
from theexposures
head ofSummerville
Mash a t
San RafaelSwell.
Group Defined
With the growing confusion amongst the various investigators
i n correlating
the La Plata Group westward and southwestward from Colorado i n t o Utah and
Arizona,theterm
GlenCanyon
Group was introduced to include the massive
sandstones-Wingate and Navajo-so welldeveloped
f i r s t appeared i n Gilluly and Reeside(1928).
Gregory andMoore,
1931.
An unpublishedmanuscript
volume Darton (1928)recognizedthe
throughout northern New Mexicoand
f o r use i n New Mexico.
They, however; deferredto
referred t o by Gilluly and Reeside(1928).
of Gregory and Moorewas
In his "redbeds"
The term
i n t h e i r work on theKaiparowits
who had appliedtheterm
Plateau, b u t who d i d notpublishuntil
i n GlenCanyon.
consequently abandoned the term McElmo
The ageassignment
a comprehensive description of the
than 300 miles away)would
MorrisonFormation
remained Cretaceous ( ? ) , and
Morrison (the type area
wasnowmore
have t o awaitthe work of Gregory (1938).
shaley, argillaceous aspect of the
The
u n i t was noted a t most l o c a l i t i e s , b u t
- 10the sectionnorthofFort
thesandynatureof
mention.
W i t h respectto
Wingate againreceivedspecial
this area, Darton (1928, p. 38) s t a t e dt h a t
sandstone which had been classed as McElmoby
an "overlaponto
Gregory (1917)" m i g h t represent
a remnant of an oldersandstone."
The interpretationof
this i s t h a t Darton was referring t o the relationship of
a tongueof
Recapture Member of the Morrison to the underlying eolian sandstone
Cow SpringsSandstoneofHarshbarger
"the
the
(the
and others, 1957).
Darton retained the names Wingate, Todilto, and Navajo f o r the units
making up the section below the MorrisonFormation
i n the area north
of
the Z u n i u p l i f t , b u t correlated the Navajo Sandstone w i t h the basalpart
of the La PlataSandstone o f southwesternColorado(Darton,1928,
Although n o t e x p l i c i t l y s t a t e d
p. 35).
Darton thus no longer recognized the correlation
of the Todilto Limestone of New Mexico w i t h the calcareous member i n the
upper partof
Darton wouldbe
i n Utahwould
the La Plata Group, proposed by Gregory (1917).
In one sense
r i g h t a s the Navajo,Carmel,EntradaSandstonesequence
eventually be correlated w i t h the La PlataSandstone.
He,
however, a s d i d a l l his contemporaries, l e f t the Todiltotoo low i n the
section because of
i t s position below the "supposed Navajo Sandstone" a t
Fort Wingate; the Todilto would ultimately be correlated w i t h the calcareous
middle member of the La Plata Group.
Darton described the Navajo Sandstone i n the Zuni Pueblo and Inscription
Rock (El Morro) areas,southof
t h e Todiltopinchout,as
a massive white
and gray, i n p a r t red, sandstone, a t places u p t o 475 f t i n thickness, b u t
t h i n n i n g southward t o n o t more than 120 f t a t Atarque i n western Cibola
County.
I t should be noted thatsouthof
SandstoneofDarton,
the Todiltopinchout
and ofGregory(1917),included
the Navajo
i n i t s lower portion
-11-
theequivalent of thepresentEntradaSandstone.
Darton reportedtheunderlying
Wingate a s t h i n n i n g from 280 f t t h i c k a t Zuni Pueblo t o not more than 40
f t a t Atarque(Darton,1928,
the Wingate wassomewhat
of Fort Wingate.
p. 144).
He alsonotedthatat
darker and l e s s massivethan
Z u n i and Atarque
i n the cliffs north
As i n his 1910 work, Oarton (1928)continued
what i s presentlyconsideredthe
Rock Point Member ofthe
t oc o r r e l a t e
Wingate i n the
Fort
Zuni-Atarque area w i t h the sandstone forming the red cliffs north of
Wingate (thepresentEntradaSandstone).
i n the absence of the Todilto, color
the lack of fossils
The miscorrelationpersisted
because
became the primary correlation tool;
was anotherdetriment.Correlationofthe
supposed
Navajo Sandstone a t Fort Wingate w i t h t h a t of Navajo Mountain was also largely
based on c o l o r a s t h e r e
Baker, Dane,and
wasno
"typical Todilto" present at the latter locality.
Reeside(1936)solved
by formally recognizing that the Todilto
was a younger u n i t than the thinly
comprisingtheinterval
Mountain.
Limestone o f northwest New Mexico
bedded, shaly, somewhat c a l c a r o u e s t r a t a
between the'wingate and Navajo Sandstone a t Navajo
They proposed the name Kayenta Formation f o r t h i s s h a l y
sandstoneinterval
Arizona.
some o f the correlation problems
and designated a typesection
The Kayentabecame
designatedasthe
one milenortheastof
the middle member of.the GlenCanyon
The sequenceofrocksoverlyingthe
and calcareous
GlenCanyonGrouphad
Kayenta,
Group.
previously been
San Rafael Group (Gilluly and Reeside, 1928) consisting
i n ascendingorder of the Carmel Formation, thedistinctiveEntradaSandstone,
the Curtis, and the Summerville Formations.Acceptablecorrelationscould
now bemade
acrossnorthernArizona
these two groupscontaining
MorrisonFormation.
and southern Utah w i t h reference to
seven formations,plus,locally,theoverlying
Correlationseastward
were s t i l l problematicalbecause
-12-
the 3000+ f t o f s t r a t a i n south-central Utah thinnedto
Colorado.Baker,
Reeside (1936)proposed
Dane,and
ofsouthwestColoradocorrelated
300-700 f t i n southwestern
t h a t the La PlataSandstone
w i t h the Navajo-Carmel-Entradasequence
and subsequently the term La Plata would be recommended f o r abandonment.
Correlations southward i n t o New Mexico remained a problem because f o r
considerabledistances the Glen CanyonGroup
andSan
Rafael Group a r e covered
and when theyreappear
some formations are missing and others have undergone
f a c i e s change.Baker,
Dane, and Reeside (1936) dispensed w i t h the San Rafael
Group e n t i r e l y i n northwest New Mexicoand
t o member.s of the lower partof
reduced the Todilto and Navajo
the MorrisonFormation.
In supportof
this
"the sum of the evidence i n hand shows t h a t both the Kayenta
they stated that
and the Navajo Formations, and indeed the whole San Rafael Group, t h i n out
southeastward
. ... and
scarcely enter New Mexico."
p. 17) "the massivesandstone
They also stated
t h a t rests upon the Wingate (present Entrada)
Lupton and upon the Todilto Limestone a t T o d i l t o Parkhas
a t Zuniand
designatedas
(1936,
the 'Navajo' by e a r l i e r workers.
The regionaldata
been
now i n
hand a s well a s the lithologic characters of the sandstone i t s e l f seem t o
the writers t o show d e f i n i t e l y t h a t the u n i t i s part of
the MorrisonFormation."
(They had recognizedthat
i n t o an eolian sand
facies).
The inclusionof
the Morrisongradedsouthward
the Todilto i n the Morrison wassomewhat
defencible b u t they stated that
developed,could
such diverse l i t h o l o g i e s , though l e s s well
be f o u n d elsewherein
of the Morrisonincluded
less
Morrisonagerocks.
Their d e f i n i t i o n
" a l l the Jurassiccontinentalsedimentsdeposited
subsequent t o the depositionofthe.San
Rafael Group".
recommended the abandonment of the name Zuni Sandstone!
Thus theystrongly
-13-
For themassivereddish
of theMorrison,
brown sandstoneunderlyingtheTodilto
Member
Baker, Dane, and Reeside retained the name Wingate Sandstone.
I t stood as the sole representative of
the GlenCanyonGroup
Even though i t d i d n o t s o l v ea l l
and was given a doubtfulJurassicage.
the correlation problems,norprovide
i n New Mexico
an adequatetreatment of the Morrison
Formation i n west-central New Mexico, t h e i r s was a significantpaper.
inclusionofthe
"Navajo" i n the lower Morrison had t h e b e n e f i c i a l e f f e c t
of removing the Navajo name from northwest New Mexicoand
lies above thetype
ideathatthetypeTodilto
chart(Baker,
Dane,and
hereinaspartof
The nomenclature
It' i s included
thevariousauthorstodate.
F i g . 2.
Gregory (1938) r e i t e r a t e d t h a t t h e r e
i n correlating Jurassic strata
t h a t" c o r r e l a t i o n s
Navajo.
prompting the
Reeside, 1936, t a b l e 8 ) provided an excellent summary
of t h e s t r a t i g r a p h i c termsof
were no p a r t i c u l a r d i f f i c u l t i e s
from southeastern Utah westward, b u t s t a t e d
southward have ledtounlikeconclusions."
the stratigraphic reassignment
tentative."
The
o f the Todilto to
He d i d , however, recognizethe
a younger position as "necessarily
Kayenta Formation tothewest,
b u t correlated i t w i t h the Todilto Limestone of New Mexicoand
calcareous member ofthe
w i t h the
La Plata Group i n southwesternColorado.Gregory
stated that "the great sandstone
beds o f the tentative Jurassic-Wingate,
Navajo, Entrada, and La'Plata-are so alike
color, and weatheringthat
He regarded
i n rangeofcomposition,structure,
hand specimens are practically indistinguishable,
and outcrops i n t h e f i e l d can be recognized w i t h certainty only where the
whole s e r i e s i s present."
He thus hung his c o r r e l a t i o n s on thelimestones
or calcareous members; the Todilto-La Plata correlation
n o t the Todilto-Kayenta.
would stand, b u t
- 14Gregory alsorecognized
some correlation of
New Mexico, as they b o t h l a y between
w i t h the Wingate (presentEntrada)of
the Chinle and the Morrison.
the La PlataSandstone
He assignedtheEntradaSandstone
Formations an upper Jurassicage
and the GlenCanyon
age, b u t w i t h the comment that paleontologic evidence
i n an older ageassignment
and Morrison
Group a Jurassic ( ? )
may ultimately result
f o r the GlenCanyon.
MorrisonFormationSubdivided
Gregory's greatest contribution
of the MorrisonFormation
and the division of
i n the 1938 paper was a description
i n the San.Juan'CountryofsouthwesternUtah,
the formationintofour,widelyrecognized
These were i n ascendingorder
members.
the BluffSandstone,RecaptureShale,
Canyon Sandstone, and the Brushy Basin Shale.
exposures a t the town ofBluff,Utah,
The Bluff wasnamed
Westwater
from
on the San Juan River, and the other
members took t h e i r names from drainage features northward from Bluff toward
the Abajo Mountains.
The BluffSandstone
Member would l a t e r be considered
a s a formation of the San Rafael Group (Craig, and others1955).
Additionalfieldstudies
w i t h C.B.
by Baker, Dane,and
Read of the U. S. GeologicalSurvey
Reeside and consultations
resultedinthepublication
of a revised correlationofJurassicformations(Baker,
1947) i n which the EntradaSandstone
New Mexico area.
cropsout
the sandstonethat
theEntrada
thecliffsnorthofFort
the s i l t y , f l a t bedded,sandstone
Colorado."
They
and shale zone underlying
the Carmel Formation.Unfortunately
thicknesses were specified for these
which
Wingate i s thus equivalentto
i s calledEntrada.over most of Utahand
t o be equivalentto
Reeside,
was recognized i n the FortWingate,
They concluded t h a t "the c l i f f formingsandstone
.... i n
alsoconsidered
Dane,and
no
new ( t o this a r e a ) s t r a t i g r a p h i c units.
i
I
- 15Although i t would l a t e r be determined t h a t the Carmel d i d n o t extend this
f a r southward, the recognition of the Entrada-Todiltosequence
a t Fort Wingate
I
established the correlation w i t h the San Rafael Group i n southeastern Utah.
The p o s s s i b i l i t y of the Entrada extending southward beyond theTodiltopinchout
and i n t o the Z u n i Pueblo area was not discussed, however.
The limestone and gypsum bedsof
evaporite deposits related to
a restricted portion of
sea and were subsequentlyexcluded
Dane,and
Reeside(1947)
the Todilto were acknowledged as being
the Upper Jurassic
from the MorrisonFormation.Baker,
d i d n o t recognize an overlyingSummerville-Bluff
sequence and a s a result ran i n t o d i f f i c u l t y i n attempting t o place an upper
limit on the San Rafael Group.
l o c a l i t y i n Utahhadbeen
massive,cross
However, the BluffSandstone
described(Gregory,1938)as
bedded sandstone,thatranges
A verysimilarsandstone
a tentativecorrelation.
a s "most probably a facies of
theTodiltolimestone
from 200 t o 350 f t thick.
by Baker, Dane,and
They insteadchoseto
the MorrisonFormation"
and gypsum beds be mademembers
generally accepted that
Reeside
refer t ot h e
sand
and proposed t h a t
of the Wanakah Formation
of the San Juan Mountain region i n southwesternColorado.
never grainedwidespreadusage
above the Todilto
and others, 1957) and perhapscould
have been designatedas the BluffSandstone
(1947)as
a white-light brown,
u n i t nearly 200 f t thickoccurs
i n the Fort Wingate section(Harshbarger
a t the type
The term Wanakah
i n New Mexico, although i t would l a t e r be
the Pony Express beds a t the base of the Wanakah
were equivalent to the Todilto Limestone.
In a discussionof
Baker, Dane,and
the areal extent of the "Todiltolimestone
Reeside(1947,
p. 1668) s t a t e d t h a t
unit"
the Todilto might now
be regarded a s a representative of the Curtis, o r perhapstheSummerville,
- 16and t h a t t h e y
Arizona.
had recognized i t a t Kayenta, Cow Springs, and Tuba City,
It r e m a i n su n c e r t a i na st ow h a tf a c i e so ft h eT o d i l t ot h e y
were
r e f e r r i n g , becauseno
limestoneoccurs
i n t h e s e c t i o n above theEntrada
a t t h e s el o c a l i t i e s .
The T o d i l t o has n o t been recognizedbysubsequent
workers i n thoseareas.
S i l v e r (1948)described
a sectionatthewestendof
30 mileswestofAlbuquerque,
a s e c t i o n .S i l v e r
butacknowledged
Mesa Gigante,
i n an area where Darton(1928)
hadmeasured
used t h e name Wingate f o r t h e E n t r a d a p a r t
i n a footnotethat
andReeside(1947)
i t hadbeen
t o be EntradaSandstone.
of Todilto in the section (mostly
of t h es e c t i o n ,
consideredbyBaker,
He recognizedabout
Dane,
100 f t
gypsum) and broke the overlying Morrison
Formation i n t o f o u r members a f t e r K e l l e y
and Wood (-1946).These
f o u r members
i n ascendingorderweretheBluffshale,Brown-Buffsandstone,Whitesandstone,
and theVariegatedshale
members w i t h t h o s e
member.
No attempt wasmade
t oc o r r e l a t et h e s e
named anddescribedbyGregory(1938)
b u t l a t e r workwoulddemonstratetheBuffshale
i n southeastUtah,
was t h e l o c a l r e p r e s e n t a t i v e
oftheSummervilleFormation,withtheBrown-buffsandstonebeingtheequivalent
o f t h e B l u f f Sandstone, t o g e t h e r f o r m i n g t h e u p p e r p a r t
Group.
The WhiteSandstone
was l a t e rd e s i g n a t e da st h eZ u n i
1976), o r Cow SpringsSandstonefurtherwest
mostimportantlythe
u n i t was recognizedas
o f t h e San Rafael
Sandstone(Maxwell,
intheGrants-Galluparea;
an e o l i a n sandstonepresent
alongthesouthernmarginofthebasinofMorrisondeposition.
The Variegated
shale member, which Silver described as grading southward into sandstone
would l a t e r be c o n s i d e r e d e q u i v a l e n t t o t h e B r u s h y B a s i n
Member o f the Morrison.
-17-
Cow Springs Sandstone
Working i n the Navajo CountryHarshbarger and others(1951)described
a grayish-white,massivesandstone,
w i t h large scale cross
bedding features,
capped by the Dakota Sandstone, from an exposure 4 miles east of
Arizona ( F i g . 1).
They proposed the name
Cow
Cow Springs,
SpringsSandstone
f o r the
unit and designated this s i t e a s the type locality.
A t the type locality
the Cow Springs is 342 f t thick(Harshbarger
others, 1951) and i s unconformably overlain by the darkercolored
Sandstone.
and
Dakota
I t may be distinguished from theunderlyingEntradaSandstone
on the basis of color,topographicexpression,grainsize,
and fines content.
The Entrada, a t l e a s t i n the upper part i s a cleaner, slightly coarser grained
sandstone that forms a bench below the lighter colored cliff forming-to
steep slope forming-Cow Springs Sandstone.Harshbarger
traced the u n i t southeastwardtoSteamboat,Arizona
and others (1951)
where i t thickened t o
420 f t and then correlated i t 60 miles further southeastward w i t h the 240
f t thickwhite-toverylightgraysandstonelying
Dakota Sandstones a t Lupton,Arizona.
between the Entrada and
Southward from this point toward
Black Rock, New Mexico, (immediatelyeastof
Z u n i Pueblo)they
found the
contact between the Cow Springs and Entrada t o become "practically unidentifiable."
Harshbarger and others (1951) alsorecognizedthatseveral
units gradedsouthward
and southwesterly into their Cow SpringsSandstone.
Included among these were the SummervilleFormation
of the San Rafael Groupand
and BluffSandstone
the Recapture Member of the Morrison.
more definitive work, Harshbarger and others(1957)described
gradation o r intertonguing more s p e c i f i c a l l y , n o t i n g t h a t
partof
upper Jurassic
In a
the southward
i n the southwestern
their area (the Navajo country) the entire interval between the
- 18Entrada and the Dakota i s composed ofthe
i n the area north
Cow Springs,whereasnortheastward
and lower members of
of GalluptheSummerville,Bluff,
the MorrisonFormation
relationships maybe
intertongue w i t h and replacethe
seen along the
Arizona-NewMexico
Cow Springs.
s t a t e l i n e northward
from Lupton t o T o d i l t o Park ( F i g . l ) , and i n theareanorthofFort
(Harshbarger and others, 1957, p. 50, 68).
relationships both suggest that the eolian
alongthesouthern
UpperSan
These
Wingate
The l i t h o l o g i c and s t r a t i g r a p h i c
Cow SpringsSandstoneaccumulated
and southwest margin of thebasinofdepositionofthe
Rafael Group and the MorrisonFormation
t o theseformations.
and i s e q u i v a l e n t ' i n p a r t
The main mass of the Cow Springs thus l i e s along a
northwest-southeast trending axis.
Eastward from Zuni-Black Rock, Harshbarger's Cow Springs interval can
be recognizedalongthesouthflankofthe
point i t i s s t i l l bounded by theEntrada
the lower contact wouldbe
Zuni U p l i f t a t E l Morro, a t which
and the Dakota Sandstonesalthough
difficulttoplace.Furthereastward
and on
Zuni U p l i f t Moench (1963) mapped a similar u n i t on
the other side of the
the Laguna Quadrangle astheBluffSandstone,overlyingtheSummerville
and overlain by theRecapture
Member of the MorrisonFormation.
Smith (1954) had designatedthesectionoverlyingtheTodilto
on the Thoreau Quadrangle (30 milesnorthwestofGrants,
Formation.
The lower partofthe
N.M.)
Summerville by
The upper p a r t was a lightercolored,cross
sandstone that wouldbe
variously referred to as Bluff,
Z u n i by l a t e r workers.
Smith (1959)extended
southward t o i n c l u d e t h e s e c t i o n a t I n s c r i p t i o n
southsideofthe
Zuni Uplift.
as the Thoreau
Thoreau was reddish brown, f l a t bedded,
and s i l t y and would l a t e r be considered equivalent to the
otherauthors.
Limestone
bedded, massive
Cow Springs, or
his Upper Thoreau Formation
Rock ( E l Morro), on the
-19-
of Grants, McKinley
In the Haystack Mountain area, 15 milesnorthwest
'Co. New Mexico, Thadenand
two sandstone units
Ostling(1967)recognized
between the Summerville and the MorrisonFormations.
"white and paleorange
u n i t " they mapped a s the BluffSandstone.
"moderate-orange-brown, fine grained,cross
the basis of
The upper
bedded eoliansandstone"they
mapped a s a tongue of the Cow SpringsSandstone.
twoon
The lower cross bedded,
a slight color contrast,
They distinguished the
more d i s t i n c t l y e o l i a n f e a t u r e s
and on the f a c t t h a t the Cow Springs wedged out i n the
i n the upperone,
north-central part
of their quadrangle map leaving the Recaptureshale
resting
on the BluffSandstone.
Allof
these authors whose works d e a l t w i t h Jurassic rocks of west-central
New Mexico had since Baker, Dane,and
open t o them.
Reeside (1947) a number ofoptions
They could (1) c o r r e l a t e s t r a t a above the Todilto(or
above
the Entrada further south) w i t h the Summervilleand/orBluffFormations
of the San Rafael Group, o r w i t h the lower members of the Morrison, a s was
being done on the western side of the San Juan Basin; ( 2 ) f o r the l i g h t
southward a t the expense of the
colored, eolian sandstones that developed
Upper San Rafael Groupand
lowerMorrisonFormationtheycould
use e x i s t i n g
or previously used names l i k e White sandstone member, Cow Springssandstone,
or Z u n i sandstone, or (3) introduce a new name.
difficult or impossible to correlate
recognizableformation
a s the choiceof
earlier (Baker,
Because i t i s extremely
the eolian facies northward i n t o a
i n the San Rafael Group, option number 2 emerged
most authors.
Dane,and
The name Z u n i , however, hadbeen
Reeside, 1936); even i f i t were t o be used a redefinition
would have been i n order as Dutton's original
usageof
the termincluded
the Todilto, Summerville, Bluff and MorrisonFormations,
ranged u p t o 1300 f t .
abandoned
Thus, authors tended toavoid
and the thickness
the name.
- 20No redefinition of the
Z u n i was forthcoming b u t i n 1957, Harshbarger
and o t h e r s , working southeastward from the Navajo Countryrecognized
in
the Lupton-Zuni areas the u n i t they had been c a l l i n g Cow Springs Sandstone
on Black Mesa.
I t had similarcolor,grainsize,crossbedding,
expression and occupiedthe
same s t r a t i g r a p h i cp o s i t i o n .
designated a 440 f t section 2 miles east of
p. 137)."
They accordingly
Zuni Pueblo as the Cow Springs
Cow Springs Sandstone
Sandstone, and acknowledged t h a t " i n some areas the
i s roughlyequivalenttothe
and topographic
Z u n i Sandstone as defined by Dutton (1885,
The Z u n i sectionturnedoutto
be one ofthethickersections
measured and the authors went on to state that "elsewhere the formation
is either transitional into
erosion has removedan
units w i t h which i t intertongues or pre-Dakota
appreciablethicknessof
it." They alsonotedthat
and on i n t o New
south of Lupton, which i s southoftheTodiltopinchout,
Mexico i t becomes i n c r e a s i n g l y d i f f i c u l t t o d i f f e r e n t i a t e t h e
the Cow Springs.
They did n o t discusstherocks
Entrada and
below the Cow Springs a t
the measured s e c t i o n e a s t of Z u n i , b u t Stewart,Poole,
andWilson
(1972)
working i n the same locality estimated 300 f t o f Entrada consisting of light
brown and verypaleorange,veryfinetofinegrainedsandstone.Stewart
and others also estimated another
Entrada(presumably
400 f t bf undescribed section above the
the Cow Springs) and measured 199 f t o f the Rock Point
Member of the lnlingate Sandstone below theEntrada.
Inasmuch a s i t i s d i f f i c u l t
t o g e t 900 f t of section exposed a t t h e i r measured l o c a l i t y , t h e Cow Springs
estimate i s probably somewhat h i g h .
has estimated the entire interval
to the base of the
w i t h this.
Stricker(personal
from the top of
communication,1982)
the Rock Point Member
Dakota t o be about 500 f t and the present author concurs
A medial color change t h a t commonly occurs a t a notch(depositional
-21-
break) t h a t i s noteverywhere
traceable (the Summerville-Todiltonotchof
some investigators) hasledto
the ideaof
the Entrada-Cow Springsbreak
a t this point.
A t the type locality of
the Cow SpringsSandstone,
no uncertaintyabout the baseofthe
f t thickgrayish
unit.
however, there i s
The present authornoted
a 28
red (10 R 4/2) t o p a l e reddish brown (10 R 5 / 4 ) , f l a t
bedded,
sandy s i l t s t o n e between the Entrada and the Cow Springs. Lithologically
i t doesnot
f i t w i t h e i t h e r the underlying or overlying sandstones,
the interval as only
Harshbargerand,others(1957)reported
and placed i t a t the baseof
23 f t thick
the Cow Springs a s a gradational u n i t between
I t i s not, however, gradational i n colororgrainsize
the two sandstones.
and shouldperhaps
but
be considered equivalent to
The Summerville which gradessouthward
the SummervilleFormation.
i n t o the Cow Springs, i s 108 f t thick
the Cow S p r i n g s type locality (Harshbarger
a t Marsh Pass 30 milesnortheastof
and others,1957).Thisinterpretation
would furtherstrengthenthecase
f o r two sandstones of d i s t i n c t l y different ages; an upper light colored,
eoliansandstone
and a lower, distinctly
older, commonly pale reddish brown-
moderate reddish brown, largelyeoliansandstone.
the two sandstoneshas
been questioned by Peterson(1974)
the upper lighter colored sandstone as
partof
the Entrada."
This relationshipof
"a thickbleached
who would interpret
zone i n the upper
Such an interpretation would seem unlikely i n view
oftheSummerville-likesediments
between the two sandstones a t the type
l o c a l i t y and a l s o because i n the Z u n i area the l i g h t e r , bleached color i s
a c h a r a c t e r i s t i c o f the lowersandnot
are often only superficial.
the upper.
These colors, however,
-22-
In 1956 word reached C. H. Dane of the impending U. S. GeologicalSurvey
publication by Harshbarger and others i n which the Cow Springs Sandstone
would be recognized a s f a r e a s t a s t h e
Zuni-Black Rock area.
w i t h the following memorandum reprintedhere
Dane responded
w i t h permissionof
the U. S.
GeologicalSurvey.
March 8, 1956
TO:
Geologic Names Committee
Carle H. Dane
FROM:
SUBJECT:
Z u n i Sandstone
Reinstatementof
All the s t r a t a between the Wingate (now Entrada) and Dakota sandstones
Dutton (1885, Mt. Taylor and the Zuni Plateau,
were mappedby
(USGS
6th Ann. Rept. p. 137). The basal 2 t o 25 f e e t above the Wingate (now
Entrada), where i t was t h i n bedded limestone, was called by Gregory
the Todiltoformation and the overlyinglowerpartofthesandstone
unit was erroneously called
Navajo country).
partsof
Navajo by Gregory(1917,
Geology of the
The Todilto i s not present i n the western and southern
the Gallup-ZuniBasin.Baker,
Dane,and
Reeside (1936)recognized
Dutton's Zuni sandstone w i t h the Navajo
Gregory'smiscorrelationof
and corectly assigned the bulk of the Z u n i t o their Morrisonformation
a s asandstonefaciesof
Paper183),
the formation (see Figure 14, p. 51,Professional
b u t theyincluded
the Morrison.
the Todilto 1imestone a s a member of
The history is r a t h e r f u l l y documented on pp. 43-44
of the Baker, Dane and Reeside report.
i n the Black Mesa areaof
The comparablesandstone
facies
Arizona was l a t e r c a l l e d Cow Springssandstone
by Harshbarger.Subsequently
i t became c l e a r t h a t
the Baker, Dane,
Reesidereport"Morrisonsandstonefacies"includedequivalentsof
-23-
the upper p a r t of the San Rafael group of which -certainly the Todilto limestone,
theSummerville,
and t h e B l u f f s a n d s t o n e ( i f t h a t i s
now included i n the
and I believe i t i s ) arerepresentatives.Therefore,
San Rafaelgroup,
itisclearthattheonlyproperprocedure
i s t o r e s t o r e Z u n i sandstone
inDutton'soriginalusage.Ifthestratigraphicrelationships
fully understood,
i t wouldhavebeen
had been
highlyappropriateforHarshbarger
t o use Z u n i f o r what he termed Cow Springs sandstone i n the Black Mesa area.
In my opinion, this should have beendone
i n favorofalocalArizona
nogood
reason why
Cow
name.Once
b u t there are, of course,
arguments
i t was done, however, there was
Springs should have been permitted to jump e a s t of
the Defiance uplift into the
Arizona-NewMexico
borderarea;
and there i s
c e r t a i n l y no j u s t i f i c a t i o n f o r crow-hopping Cow Springs i n t o the Acoma Basin
f a r t h e re a s t .
l i k e Zuniby
( I might add thatthethoughtofreplacing
the tawdry commonplace Cow Springscurdles
an elegant name
my gizzard.
Imagine
the Enchanted Mesa, thefabulous E l Morro, "Acoma, the Sky City", and a l l
the other beautiful
rocks of the Land of Enchantment composed ofthe
Cow
Springs sandstone, Heaven f o r b i d ) On the New Mexico Geologic Map, I propose
t o use Z u n i sandstone i n the Gallup-Zuni and Acoma basins.
of the namewas
based on amisunderstandingofcorrelation.
The abandonment
I t should be
restored.
Carle H. Dane
Thememorandum,
which was nevercirculated,indicatedthat
Dane accepted
the correlation proposed by Harshbarger and found only the name
Cow
objectionable.
wasno
Springs
From Harshbarger's and others p o i n t of view, however, there
legitimate reason t o revive an abandoned name and "back c o r r e l a t e "
- 24he had
t h a t name (undefined) 120 miles to the original. type section that
named and described i n 1951.
connotation(suchas
I t i s unfortunatethat
a name with no geographic
the White Cliffs Sandstone) was not available to lessen
the objectiontoHarshbarger's
As per his memo,Dane
work.
d i d restore the name Zuni f o r use i n the Zuni-Acoma
of the restoration was n o t circulated
Basin, b u t an o f f i c i a l n o t i f i c a t i o n
by the U. S. GeologicalSurvey.Officialnotification
came ostensiblythrough
Keroher (1966) who updated the lexicon of geologic names.
however, contained no definition or redefinition
nor d i d the New Mexico stategeologic
The lexicon,
of the Z u n i Sandstone,
map (Dane andBachman,
1965).
appears the name Z u n i was being used in a d i f f e r e n t sense than that
It
ofDutton
(1885), b u t without a redefinition or a typesection.
Following the publicationof
the state geological map i n 1965 and the
lexicon i n 1966, variousinvestigators
began r e f e r r i n g t o the Z u n i asthe
equivalent of one of their mapped units.
wasby
One of the e a r l i e s t such usages
Thaden, Merrin and Raup (1967) and Thaden, Santos, and Raup (1967)
who mapped a 300-340 f t thick fine grainedcross-beddedsandstone
the SummervilleFormation
and the Recapture Member as the yellowsandstone
i n the Grants, New Mexico area.
had been called Bluff or
between
They s t a t e d t h a t
Z u n i bysome
the yellowsandstoneinterval
workers and t h a t i t maybe
a tongue
of the Cow SpringsSandstone.Diagrammaticallytheyindicatedasintertonguing
relationship between the Bluff and the yellowsandstone,
w i t h a tongueof
the Cow Springs coming i n from the west, and a l l units overlain by the Recapture
Member.
The Bluff and the yellowsandstoneinterval
way, w i t h minor colorchanges,to
can be tracedall
the FortWingate-Galluparea
and others (1957)described the sectionas
the
where Harshbarger
Cow Springs overlain by and inter-
-25-
tonguing w i t h the Recapture Member.
Other mapping i n the Grantsarea
Thaden and others(1967)hasalready
been discussed.
Hackman and Olson (1977)compiled
the geology of the Galluplo
by
x 20
quadrangle i n which they used the term Cow Springs-Entrada(afterHarshbarger
Further ,northwardthey
and others).
as a u n i t .
Greenand
Pierson(1977)
i n their San JuanBasin
arerecognizedseparately,
lumped the Cow Springs-Summerville
used the terms Cow Springs and Bluff
nomenclaturechart and s t a t e d t h a t where the two
the contact between them i s consideredto be
intertonguing and a r b i t r a r y .
units i n upper Jurassicrocksof
Green (1975) had e a r l i e r discussed paleodepositional
the Southern San JuanBasin
and included
the Bluff i n his Cow Springs Sandstone w i t h an unconformity i n the upper
part.
Lupe (1981)described the relationshipof
the lower partofthe
Morrison
t o the Bluff and Cow Springs a s a l a t e r a l f a c i e s change; he considered the
RecaptureShale
eolian facies
Mappingby
Member o f the Morrison t o have gone from a f l u v i a l t o an
southward.
Anderson (1982) i n the Atarquearea
i n i t i a l l y recognized
the Cow Springs Sandstone, b u t this had t o be revised w i t h the realization
t h a t the Cow SpringsSandstone d i d notinclude
ofthesection
the lower,Entradapart,
which i s now considered t o be present i n the area; the u n i t
i s now recognizedas the redefined Z u n i Sandstone.
Maxwell (1976) working i n the area east of Grants
was one of the earliest
t o map the reinstated-undefined Zuni Sandstonefollowingpublication
the stategeologic
map (1965).
colored eolian cross
Maxwellwas
abletodistinguish
of
a light
bedded sandstone from the underlyingBluffSandstone
i n the northernhalfof
he designated the Z u n i .
the Acoma Pueblo Quadrangle; this upper sandstone
He considered the Bluff t o be a f l u v i a t i l ed e p o s i t
-26-
a t this l o c a l i t y and the presence of numerous sandstonepipes
helps distinguish i t from the Z u n i (of Maxwell).
within i t
He noted t h a t the Z u n i
i s unconformably overlain by the Brushy Basin Member w i t h a f o s s i l s o i l
Thus the BrushyBasin
zone a tt h ec o n t a c t .
eoliansandstone
a t this l o c a l i t y , a s
of and therefore i s youngerthan
This i sc o n s i s t e n t w i t h the observation
by most workers that only the lower members of the
w i t h the eolianfacies
beingdeposited
was interrupted.
into
has been described a t o t h e r l o c a l i t i e s
(Silver, 1948) b u t rather has cut out part
the underlyingeoliansandstone.
doesnotgradesouthward
southward.
Morrison intertongue
By Brushy Basin time mostlyshale
was
and the sand supply for the eolian deposits t o the south
The Brushy Basin shaleoverlappedthe
Z u n i (of Maxwell)
as Morrison deposition came t o a close. 'A shortdistanceto
the south of
Maxwell's area the Brushy Basin member has been beveledoff
by pre-Dakota
erosionofgently
northward d i p p i n g s t r a t a and the Dakota Sandstone r e s t s
on the Z u n i Sandstone of Maxwell (see a l s o Maxwell, 1982).
Zuni SandstoneRedefined
The necessity of a redefinition of Zuni Sandstone can be explained
asfollows.
In i t s southern and -southwesternmost areastheeolian
Sandstone extends beyond thepinchout
marine and fluvial facies (Todilto
partof
Cow Springs
of the easily recognizable restricted
and SummervilleFormations)
of the upper
the San Rafael Group, and rests on theeolianEntradaSandstone.
In these areas, which include Z u n i Pueblo, i t i s somewhat d i f f i c u l t t o distinguish
the two eolian units,
b u t there i s commonly the color change and the notch.
The "Zuni sandstones" o f Dutton(and
d i d not distinguish the
the Navajo Sandstone of Gregory,1917)
two; Harshbarger and others(1951)(1957)
did distinguish
the two, although w i t h d i f f i c u l t y , and called only the upper one the Cow
-27-
SpringsSandstone.
and others(1951)
The point i s here made thatDutton's
Cow Springsarenotequivalent
elsewhere) and thatHarshbarger,
being t h e f i r s t t o r e c o g n i z e
Whether or not i t i s practicalfor
distinguish these
two eolian units
been traced into the
units a t Zuni Pueblo ( o r
and describe
the modern s t r a t i g r a p h i c framework has nomenclatorial
the inteval with respect to
priority.
Z u n i and Harshbarger's
the f i e l d geologist t o everywhere
i s doubtful, b u t they have nevertheless
Zuni area.
The present author i s recommending thefollowing:while
t h a t the i n - f i e l d d i s t i n c t i o n
i t is recognized
units-the Entrada
between the two largely eolian
name Zuni
and Cow Springs-will be d i f f i c u l t and notalwayspractical,the
Sandstoneshall
be applied to the undividedequivalentsoftheEntradaSandstone
and the Cow SpringsSandstonesouthof
i n theGallup
the Summerville-Todiltopinchouts
Sag-Zuni Basin area and eastward as appropriate into
Basin, (see correlationchart,Fig.2).
T h i s usagecorresponds
use of the term "Zuni sandstones" i n this areaonly.
the Acoma
totheoriginal
Northward and eastward
the Cow Springs Sandstone rests on younger San Rafael formations, the Summerville
and the Bluff, and i s more e a s i l y distinguished from them.
Although there
a r e problems l o c a l l y i n recognizing the Bluff and Cow Springs as separate
units, this doesnot
area.
the term Zuni outside the specified
j u s t i f y usageof
and the Acoma Sag the usageof
In the San JuanBasin
SpringsSandstoneoughttocontinue
i n the sense of Thadenand
Green (1975), Green and Pierson(1977)
The type locality of
the name
Cow
others(1966,67),
and Lupe (1981).
the.redefined Zuni Sandstone i s Taaiyalone Mesa
(Dowa Yalanne on the Zuni 7%'sheet) i n sec. 36 T. ID N., R. 19 W. and sec.
1 T. 9 N . , R. 19 W. ( F i g . 3 ) .
about two thirds ofthe
Here the Z u n i i s 490 f t thick w i t h the "notch"
way u p from the base.
Five milesnortheastward
- 28a yellowishgraytopale-olivegraypoorlysortedsandstonebeginstoappear
It is t h o u g h tb yt h ep r e s e n ta u t h o rt h a t
n e a rt h et o po ft h i ss e c t i o n .
Harshbarger and others(1957)recognizedthis
o f theWestwater
as thesouthernmostextent
Canyon Member oftheMorrisonFormation.Overlyingthe
Westwater Canyon i s a conspicuousbleached
downward f r o mt h eu n c o n f o r m i t ya tt h e
zone 20 t o 25 f b t h i c k e x t e n d i n g
base o f t h e
DakotaSandstone.
The
bleached zone i s widespread and appears t o be a Tongue o f t h e ZuniSandstone
t h a t has been thoroughly cementedand
induratedwithsilicaprobably
b yc a p i l l a r yw a t e r sp r i o rt od e p o s i t i o no ft h eD a k o t a
(personalcommunication)
has f o u n d t h a t b a r i t e
present in addition to the silica,
Sandstone.Maxwell
and k a o l i n i t e a r e commonly
and t h a t t h e o r i g i n o f t h e
withorganicrichwaterspercolating
emplaced
zone i s associated
downward fromtheDakotasandstone.
A s t r a t i g r a p h i cc r o s ss e c t i o nf r o mt h et y p el o c a l i t yo ft h eZ u n is a n d s t o n e
Los Pilares(Atarquearea)
southtoward
southwardthinning(Fig.
4).
shows thepronounced,thoughnonuniform,
This is due t ob o t hd e p o s i t i o n a lt h i n n i n g
and t o pre-Dakotabeveling.
Summary
Maxwell's usage o f t h e Zuni Sandstone followed that of
(1965) and is n o tc o n s i s t e n tw i t ht h e
Zunisandstone
area,where
Dane and Bachman
usage o fD u t t o n( 1 8 8 5 ) .D u t t o n ' s
was s t r a t i g r a p h i c a l l y most r e s t r i c t e d i n t h e ZuniPueblo
it was demonstratedbyHarshbarger
Poole, and Wilson(1972)
and others(1957)
t o be made up o f t h e E n t r a d a
and Stewart,
Sandstoneand
the
Cow Springs Sandstone, recognizable as two separate units only with difficulty.
The usage o f Zuni by Dane and Bachman (1965) on t h e s t a t e g e o l o g i c
undefined.
map remains
The usage recommended i n t h i s papercorrespondswithDutton's
-29-
usage only in the Zuni Pueblo area; here the Zuni is defined as encompassing
the undivided equivalentsof the Entrada Sandstone andthe Cow Springs Sandstone
and is recognized only inthe Gallup Sag-Zuni Basin area southof the pinchouts
of
the Todilto and Summerville Formationsand eastward as appropriate into
the Acoma Basin. At all other localities the upper part of the Zuni interval
would be recognized as Cow Springs, the lower part as Entrada. Maxwell's
Zuni Sandstone is equivalent toonly the upper partof the redefined Zuni
Sandstone, and thus is equivalent tothe Cow Springs Sandstone.
-30-
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