Extension
0ftheintertongued
Dakota
SandstoneMancos
Shale
terminology
intothesouthern
ZuniBasin
T A B L E l - L o c n r t o N o F S E c r t o N S H o w No N F l c . 2 .
byStephen
C. Hook,Paleontologist,
NewMexico
Bureau
NM;
ol Minesand
Mineral
Resources,
Socorro,
WilliamA.
Cobban,
Paleontologist,
U.S Geological
Survey,
Denver,
C0;andEdwinR Landis,
Geologist,
U S Geological
Survey,
Denver,
C0
Since September1978, the U.S. Geological
Survey (USGS) and the New Mexico Bureau
of Mines and Mineral Resources have been
studying the geology and coal resourcesof the
Salt Lake coal field, Catron and Valencia
Counties. New Mexico. This work forms a
portion of the regional coal resource-assessment program of the Coal Exploratory Program of the USGS. As part of this study the
USGS is mapping four 7Vz-minute quadrangles (Moreno Hill, Rincon Hondo, Fence
Lake, and Fence Lake SW), and the New Mexico Bureau of Mines is mapping four lt/zminute quadrangles (Twentytwo Spring, Cantaralo Spring, The Dyke, and Cerro Prieto).
Mapping is nearly complete on the Moreno
Hill, Twentytwo Spring, Fence Lake SW, and
Cerro Prieto quadrangles; now a regional
stratigraphic framework that can be applied to
map units in these quadrangles must be
established.This paper shows how and why
the nomenclature applied to the intertongued
Dakota Sandstone-Mancos Shale sequenceof
the southeastern San Juan Basin can be extended into the southern Zuni Basin for use in
the Salt Lake coal field.
Correlation
The intertongued Dakota SandstoneMancos Shale rock sequenceis best developed
in well-exposed sections south of Laguna,
Valencia County, New Mexico (fig. l). Here,
Landis and others (1973) establishedthe principal reference section for this sequence(fig.
2, section 9; table l). From bottom to top
this sequence consists of the Oak Canyon
Member of the Dakota Sandstone,the Cubero
Tongue of the Dakota Sandstone, the Clay
Mesa Tongue of the Mancos Shale, the
PaguateTongue of the Dakota Sandstone,the
Whitewater Arroyo Tongue of the Mancos
Shale, and the Twowells Tongue of the
Dakota Sandstone. All but the upper two
tongues have their type sections in the Laguna
principal referencesequence(fig. 2, section9)
and were named by Landis and others (1973).
The upper two tongues, the Whitewater
Arroyo and the Twowells, with type sections
near the village of Two Wells, McKinley
County, New Mexico (fig.2, section l), were
named, respectively,by Owen (1966) and by
Pike (1947) and were classifiedas tonguesby
Dane and others( I 97 I ).
Landis and others (1973, fig. 3) demonstrated that the Paguate Tongue of the Dakota
Sandstonemergeswith the main body of the
Dakota Sandstone approximately 12 mi (19
km) west of Crants and that the Clay Mesa
A u g u s t1 9 8 0
New Mexico Geolog!
Tongue of the Mancos Shale wedgesout in the
main body of the Dakota Sandstone between
the Grants and Mount Powell areas (fig. l).
Consequently, tongues lower than Whitewater
Arroyo cannot be recognized in either the
Gallup or Two Wells area of the Zuni Basin.
However, fossils collected from the top of the
main body of the Dakota Sandstone at the
Two Wells section(Dane and others, l97l) indicate an age no older than that of the Paguate
at its type section(Landis and others, 1973).
l-Two Wells-outcrop section from Dane, Landis,
a n d C o b b a n ( 1 9 7 1 , p . 3 1 8 ) ; m e a s u r e di n N E %
sec.17, T. 12 N., R. 19 W., McKinleyCounty,
New Mexico
section measuredby C. H.
2-Atarque-outcrop
D a n e , E . R . L a n d i s , a n d W . A . C o b b a n i n s e c .2 4 ,
T . 6 N . , R . l 8 W . , V a l e n c i aC o u n t y , N e w M e x i c o
3 - T i g e r S t a t e N o . l - o i l t e s t d r i l l e d i n s e c .8 , T . 4
N . , R . l 7 W . , V a l e n c i aC o u n t y , N e w M e x i c o
4 - C l e a r y N o . I F e d e r a l - o i l t e s t d r i l l e d i n s e c .6 , T .
3 N., R. l6 W., Catron County, New Mexico
S-Huckleberry No. I Federal-oil test drilled in
s e c .l l , T 2 N . , R . 1 6 W . , C a t r o n C o u n t y , N e w
Mexico
6 - S p a n e l a n d H e i n z e N o . l - 9 6 1 7 - o i l t e s td r i l l e d i n
s e c . 2 7 ,T . 4 N . , R . l l W . , C a t r o nC o u n t y ,N e w
Mexico
7-D Cross Mountain-outcrop section measured
b y B . R o b i n s o ni n s e c s .8 , 2 1 , T . 3 N . , R . 8 W . ,
S o c o r r oC o u n t y , N e w M e x i c o
E-The Narrows-outcrop section from Landis,
Dane, and Cobban (1973, p. J36-J37) measured
i n s e c s .3 , 4 , T . 7 N . , R . l 0 W . , V a l e n c i aC o u n t y ,
New Mexico
section from Landis, Dane,
9-Laguna-outcrop
a n d C o b b a n ( 1 9 7 3 ,p . J 4 - J 8 ) m e a s u r e di n s e c s .2 0 ,
2 1 , T . l 0 N . , R . 5 W . , V a l e n c i aC o u n t y , N e w
Mexico
SANDOVAL
os
20-40 ft (6-12 m) above the top of the Twowells; the uppermost limestoneis calcarenite,
2-6 inches (5-15 cm) thick, composed of
inoceramid debris. ln the subsurface the
Bridge Creek equivalentproducesa distinctive
resistivedeflectionzone on electriclogs.
Throughout the area of west-centralNew
Mexico shown in figs. I and 2, we regard the
base of the Bridge Creek equivalent as an
i I
isochronous surface becausethis 6-inch (15vo.qa
"
c a r Ro N
i
cm)
thick limestone is lithologically distincSOCORRO
<l
tive, widespread,and easily recognizableand
roeo
roTo
0,".
becauseit carriesthe samevertically restricted
::"'
."
,u
"
molluscan fauna throughout its extent. This
FICURE l-lroex MApoF pARToF wEsr-cENTRALfauna includes the late Cenomanian amNew Mexrco showingthe locationsof outcrop monites Sciponoceras gracile (Shumard) and
(x) andoil tests(.Q)andline of sectionfor
sections
Metoicoceras gibbosum Hyatt, which are
fig.2.
restrictedto a vertical range of lessthan 10 ft
(3 m) of sectionin west-centralNew Mexico.
The Twowells Sandstone and Whitewater The datum line for fig. 2 was chosenat the top
Arroyo Shale can be traced physically from
of the Twowells becausethis surface is subparallel to the base of the Bridge Creek
their type sectionsto the vicinity of Atarque
(figs. I and 2). South of Atarque the Creta- equivalentand is easilyrecognizable.
ceous sequenceis covered by Tertiary basalts
Our interpretation of the thickness of the
for a distanceof 2 mi (3.2 km). South of this
Twowells in the Huckleberry No. I Federaloil
basalt cover, the Twowells can be recognized test(fig. 2, section5) differs significantlyfrom
on the basis of the stratigraphic interval those of Gadway (1959) and Foster (1964).
separatingit from the underlying main body
Both Gadway and Foster interpretedthis unit
of the Dakota Sandstone(fig. 2, sections3-6) as two sandstonesseparatedby a medial shale,
and the next overlying sandstone unit, the totaling 85 ft (25.9 m) in thickness (from a
Atarque Member of the MesaverdeFormation depth of 1,725ft to 1,810ft). Gadway referred
of Pike (194'7\.In addition the Mancos Shale this unit to the Tres Hermanos Sandstone:
tongue overlying the Twowells contains a
Foster considered it an unnamed sandstone in
distinctive50-ft ( I 5-m) thick sequenceof inter- the Mancos Shale. We have interpreted the
beddedlimestoneand calcareousshalenear its
basal 40-ft (12.2-m) sandstone of this interval
base. This limestone sequence is of late as the Twowells and the upper 45 ft (13.7 m) as
Greenhorn age and is equivalentto the Bridge the limestones, calcareous shales, and
Creek Limestone Member of the Greenhorn calcarenites of the overlying Bridge Creek
Formation (Cobban and Scott, 1972). The
equivalent.
baseof the Bridge Creek equivalentis a 6-inch
A marine sandstone,24 ft (7.3 m) thick,
(15-cm) thick, white- to orange-weathering, separated from the main body of the Dakota
concretionary limestonethat generallyoccurs Sandstoneby a marine shale, 50 ft (15.2 m)
G o l l u p - Z u n ic o o l f i e l d
t?
T r ol Y € l l s
Dotil Mountoins cool field
678
Solt Loke coo I field
345
Tiqer
S l o l eN oI
Alorque
Cleory
N oI F e d
Huckleberry
N o . lF e d
-S"o o n e &
l H e r "n z e
lf. :S5" l
0 C r o s sM ' n .
-he
Nor'ows
S o nJ u o nB o s i n
9
L o gu n o
T w o w el sl
Tongue
I18OO.
Whilewoter
Arroyo
T on gu e
Poguoie
=-'
z6
Tongue
Cloy
Meso
Tongue
Zuni
Ss.
tr-Irll
j:-::
""
i 1
t-----l
fr==
ll--l
-" "" "" F : _ : l
l----F!
50n0sl0ne
p0rllyc0vered
30Troo
d e p t hl l r ) b e l o w
s u r t o c e( o r l t e s t s )
.ol
rn,onfo,rtry
Cubero
Tongue
2,too
Chinle
Fm,
I
u0
N o h o r i z o n t o ls c o l e
* o
=-'
Ook
Conyon
Member
Chinle
Fm.
Zuni
55
Morrison
I m.
".]
o-Lo
FIGURE 2-GeNenarrzgD GRAeHIcsEcrroNssHowrNc coRRELATToN
Dlxom SnNnsroNn-Mencos SHlr-E sequeNcr in the southern part
oF THEINTERToNGUTo
of west-central New Mexico. A tongue of Mancos Shale overlies the Twowells Tongue of the Dakota Sandstone. Both the Zuni Sandstone and Morrison
Formation are of Jurassic age; the Chinle Formation is of Triassic age. Precisegeographic locations of the sectionsare presentedin table 1; the line of section is shownon fis. l.
thick, is present in the Atarque section but is
not present to the north in either the Two
Wefls section (fie. 2, section l) or the Cliff
Dwellers Canyon section (fig. l) of Landis and
others (1973,p. J32, J33). This sandstonecan,
however, be correlated to the south with a 60ft (18.3-m) sandstonein the Tiger State No. I
wildcat (fig. 2, section3). From the Tiger State
well it can be correlated eastward through the
subsurface (fig. 2, sections 3-6) into a surface
section at D Cross Mountain (fig. 2, section
7). From D Cross Mountain the marine sandstone can be traced into the type section of the
Paguate Tongue of the Dakota Sandstone(fig.
2, section9).
Fossils collected from the top of this sandstone in the Perry Canyon area of the Twentytwo Spring quadrangle help substantiate this
correlation. These fossils include the ammonite Aconthoceras amphibolum Morrow,
which has been found only in the Paguate
Tongue in west-central New Mexico (Cobban,
1977a,b). In addition, an 8-inch (20-cm) thick
bentonite bed approximately 35 ft (10.7 m)
above the top of the Paguate Sandstone at D
Cross Mountain is apparently also present in a
similar stratigraphic position in Perry Canyon
(fig. l). We have attached considerable importance to this bentonite bed because l) bentonites more than 6 inches (15 cm) thick are
rare in the Dakota-Mancos sequencein westcentral New Mexico and 2) this bentonite is
approximately the same age as the marker or
"X" bentonite bed, which lies within the
Acanthoceros amphibolum Zone and has been
dated at 92.1 m.y. (Obradovich and Cobban,
t975).
South of Laguna the Clay Mesa Tongue of
the Mancos Shale is coextensive with the
underlying Cubero Tongue of the Dakota
Sandstone. The term "Clay Mesa Tongue,"
therefore, cannot be extended south of the
wedge-out point of the Cubero Tongue into
Age of the Dakota-Mancos sequence
Mancos Shalein secs.20 and2l, T. 9 N., R. 9
Fossils collected from the intertongued
W. (Maxwell , 1977), approximately 1l mi
Dakota-Mancos sequencewithin the area en(17.7 km) northeastof the Narrows measured
compassedby the sectionson fig. 2 indicate an
section (tig. 2, section 8). Accordingly, the
early Late Cretaceous age for the entire
informal term "lower part of the Mancos
sequence. The Twowells and Whitewater
Shale" (Landis and others, 1973, figs. 2,4\ rs Arroyo
Tongues are late Cenomanian,
used south of the wedge-out point of the
whereas the remainder of the member rank
Cubero Tongue. "Lower part" as used on fig.
units are middle Cenomanian (Cobban,
2 includes rocks of different time-equivalency 1977a,
b). Palynomorphs from the lower part
in different parts of west-central New Mexico.
of the Oak Canyon Member, originally reFor example, at the Narrows (fig. 2, section garded
as late Albian, are now considered to
8), the lower part of the Mancos Shale inbe Cenomanian in age (Cobban, 1971a).
cludes rocks laterally and temporally
The youngest fossils in the Dakota-Mancos
equivalent to the Clay Mesa Tongue of the
sequenceoccur in the Twowells. We have colMancos Shale, the Cubero Tongue of the
lected the oyster Pycnodonte newberryi (StanDakota Sandstone, and the upper part of the
ton) from the top of the Twowells in the
Oak Canyon Member of the Dakota Sand- northeast part of the Twentytwo Spring quadstone; whereas at Atarque (fig. 2, section 2), it
rangle. Pycnodonte newberryiranges from the
probably only includes rocks laterally
latest Cenomanian Sciponoceras gracile Zone
equivalent to the Clay Mesa Tongue. South of
into the overlying earliest Turonian PsellAtarque, the lower part of the Mancos Shale daspidoceras Zone in central and southwest
may include substantial thicknessesof sand- New Mexico (Hook and Cobban, 1977; Cobstone (fig. 2, sections 4, 5); detailed mapping
ban and Hook. 1979). In addition. we have
may indicate that these sandstones belong
collected the ammonite Pseudaspidoceras
more properly in the main body of the Dakota
from the top of the Twowells along the New
Sandstone. Fossils collected from the basal l0
Mexico-Arizona boundary in the Cottonft (3 m) of the lower part of the Mancos Shale wood Canyon area (fig. l). These occurrences
near Hayhurst Tank, Moreno Hill quadindicate that the top of the Twowells is becomrangle, include Pycnodonte cf. P. kellumi
ing younger to the southwest.
(Jones), Torrantoceras rototile Stephenson,
The oldest fossils in the Dakota-Mancos seand Acanthoceras aff . A. alvaradoense Morequence occur in the upper part of the Oak
man and indicate an age no older than that of
Canyon Member at Laguna and near the base
the basal part of the Clay Mesa Tongue at its
of the lower part of the Mancos Shale in the D
type section.
Cross Mountain area. These fossils generally
The rocks that are called main body of the
occur in ferruginous silty to sandy, limy conDakota Sandstone on fig. 2 are the marine,
cretionary beds and include 34 species of
marginal marine, and nonmarine rocks that
bivalves, ll species of gastropods, and five
make up the lowest part of the Cretaceous se- species of ammonites (Cobban, 1977a, b).
quence in west-central New Mexico and that
Many of these species have been recorded
cannot be included in one of the other named
IS
member-rank units in the sequence.
New Mexico Geology
August1980
from the WoodbineFormationof Texas.and
most have been recordedfrom the Thatcher
LimestoneMember of the GranerosShaleof
Colorado(Cobbanand Scott,1972).
southeast
This fauna will be referredto as the Thatcher
fauna and includesthe bivalvesInoceromus
eulessanus Stephenson, Plicatula arenaria
Meek, Pycnodonte cf. P. kellumi (Jones),
Exogyro columbella Meek, and Oslrea beloiti
Logan; the gastropod.Arrhoges modesta
(Cragin)?; and the ammonites Turrilites
aculus Passy, Calycoceras tarrantense
(Adkins), BorissiakocerascompressumCobban, and Johnsonites sulcatus Cobban
(Cobban,1977a,b). The Thatcherfauna is
middleCenomanianin ageand is the ".
oldest unquestionedCenomanianmegafossil
zonein the WesternInterior.
." (Cobban,
1 9 6 1p, . 7 3 8 ) .
The oldestCretaceousfossilsthat we have
collectedfrom the SaltLake coal field areaare
from the basall0 ft (3 m) of the lower part of
the MancosShalenearHayhurstTank. These
fossilsare late middleCenomanianin ageand
are younger than those from the Thatcher
level,but older than thosefrom the top of the
main body of the Dakota Sandstoneat the
Two Wellssection(fig. 2, sectionl).
must have been open to the east; it may,
however, have been considerablynarrower,
with a strongernortheasterlytrend than indicatedon fig. 3.
SeboyetaBay expandedin three directions
(north, west, and south) until early late
Greenhorntime 0atestCenomanianto earliest
Turonian)whenit mergedwith the main body
of the Western Interior seaway.Limestone
bedswerethen depositedthroughoutmost of
the WesternInterior seaway.In west-central
New Mexico the base of theselimestonesis
generallywithin the lower 20-40ft (6-12m) of
the Mancos Shale tongue overlying the
Twowells.
By logical inference, SeboyetaBay expanded(transgressed)
into the southernZuni
Basinsoonerthan it did into the northernpart
becauseof a faster southwesterlytransgression rate. This explanationwould accountfor
of Cretaceous
the thicker and older sequence
rocks in the Salt Lake coal field areawithout
havingto invoke inter- and intra-formational
unconformitiesfor which we have no evidence.
Pike (1947)had come to a similar conclusion more than 30 yearsago. In the discussion
of his measuredsectionnear Atarque, Pike
FICURE 3-Mlp
op NEw MExrco AND sourHERN
(1947,p.36) notedthat thissection".
. difColonloo sttowtNc LocAltrlEs wne ne Tnnrcgpn
fers from thoseto the north in that it showsa
FAUNAHAs BEENcoLLEcrEo (x) and the approxBay
Seboyeta
imate position of the Late Cretaceous shoreline
considerablethickening of that part of the
The resultspresented
in this paperand sumMancosShalebelow the zoneof lPycnodontel
C--) during Thatcher time (Middle Cenomanian).
marizedgraphicallyin fig. 2 showthat thereis
of a thick
. and in the presence
newberryi.
a thicker sequence
of marinerocks below the
within this enlargedshale
massive
sandstone
TwowellsTonguein the southernpart of the
. The significanceof theserelasection.
Zuni Basin than in the northernpart. Fossils of Cenomanian age. As the bay enlarged,
is ratherimportantin that they seem
upward by marine tionships
collectedfrom theserocks indicate that the theseunits weresucceeded
to indicatean advanceof the seain this localbaseof this marine sequenceis older to the shaleand sandstonecontainingthe Thatcher
ity, perhapsin a local embayment,earlierthan
south,thus ruling out depositionalthickening fauna. Thesemarine beds merge northward
anywhereelse in the Mesa Verde-Atarque
as the only causativeagent.Theseresultsare and westwardwith the fluviatile sediments
tt
area.
incompatible with a northwest-southeast-typical of the main body of the Dakota Sandtrending Late Cretaceousshorelinethat ad- stone(Landisandothers,1973).
Summary
Fossilsdefinitelyof Thatcherage are presvancedlandwardin a generallysouthwesterly
nomenclatureapplied to
The
stratigraphic
directionand retreatedseawardin a generally e n ta s f a r w e s ta ss e c .3 1 ,T . 1 5N . , R . 1 2W . ,
McKinleyCounty,just westof the Thoreauto the intertonguedDakota Sandstone-Mancos
northeasterlydirection (Petersonand Kirk,
of the San Juan Basin can be
1977,p. l7l). Paleontologic
and stratigraphic Crownpointroad, wherethey arein sandstone Shalesequence
part into the southernZuni Basin
evidence indicates, however, that this 57 ft (17.4m) below the top of the main body extendedin
northwest-southeast-trending
shoreline was of the Dakota Sandstone.The northernmost for usein the Salt Lake coal field. The upper
established
in New MexicoduringlatestCeno- occurrenceis near Ojito Spring, Sandoval two tonguesof this sequence,the Twowells
manianand earliestTuroniantime (Hook and County, wherethe Thatcherfauna occurs5 ft and WhitewaterArroyo, can be tracedin surin the
Cobban, 1977, fig. l) and persistedthrough (1.5 m) abovethe main body of the Dakota. face sectionsfrom their type sections
just north of
Zuni
Basin
to
Atarque,
northern
middle Turonian time (Cobban and Hook,
To the south,a collectionl0 ft (3 m) abovethe
wherethe Cretaceous
1979, fig. 2) and late Turonian time (Hook
top of the main body of the DakotaSandstone the Salt Lake coal field,
Tertiary
sequence
is
covered
by
basalt.From
andCobban,1979,fig.4;1980,fig.6).
near D Cross Mountain, SocorroCounty, is
memberscan be correlatedinto
The marinerocks that includethe Thatcher the lastunquestionable
faunaof Thatcherage. Atarquethese
surfaceand subsurfacesectionsin the coal
fauna record the earliesttransgression
of the Southeastof D CrossMountain at Carthage,
Late Cretaceous
seawayinto New Mexicodurfossilscollectedfrom the baseof the Mancos field to the south.
An additional marine sandstonetongue,
ing middleCenomaniantime. Theserocksoc- Shalerevealan ageno older than that of the
separatedfrom the main body of the Dakota
cur over an areaof west-centralNew Mexico ClayMesaat its typesection.
by a marineshaletongue,is present
with a north-southextentof approximately75
Thus, only to the eastis therea possiblein- Sandstone
Atarque
at
and in the Salt Lake coal field, but
mi (l2l km) and an east-west
extentof slightly let from the main body of the WesternInterior
presentin the northernpart of the basin.
is
not
morethan that. This area,centeredroughlyon seaway.Unfortunately,we havenot collected
Mount Taylor, is hereincalledSeboyetaBay, the Thatcherfauna at the sectionsthat crop Paleontologicevidencefrom the Salt Lake
for the community of Seboyetain northeast out in the areawhereit might be present.We coal field indicatesthat the sandstonetongue
ValenciaCounty(fig. 3).
have not yet found a Thatcherlevelin a sec- is of the sameageasthe PaguateTongueat its
Initial Cretaceousdepositsin and around tion south of San Antonito, BernalilloCoun- type sectionand that the shaletongue is no
SeboyetaBay-the lower part of the Oak Can- ty; nor in a sectionatLamy, SantaFe County; older than the Clay Mesa Tongueat its type
section.The sandstonetongue can be correyon Memberand time-equivalent
rocks in the nor in an intermediatesectionbetweenthese
main body of the Dakota Sandstone-are two, at Rosario,west of Cerrillos, SantaFe lated throughsubsurfaceand surfacesections
fluvial conglomeratesand sandstones,folCounty. The regional stratigraphical and with the Paguateat its type sectionsouth of
lowed by dark marine shale containing paleontological results summarized above Laguna.The shaletongueis probablyequivahystrichospherids,
(continuedon p. 46)
dinoflagellates,
and spores absolutelycompel that an avenueto the sea
August1980
New Mexico Geology
of gas-filled cavities when the rock cooled.
East of Villa Hill, rocks exposed along the
paths are a typical cross section of volcanic
flows, showing flow basalt that is locally brecciated and contains small angular fragments
of the gravels onto which it was extruded.
To the north-northeast is Columbus. and in
the distance are the rugged Florida Mountains. On the eastern skyline, across the irrigated sandy Columbus Valley, the low
volcanic hills of the West Potrillo Mountains
stretch southward into northern Chihuahua.
Other volcanic hills and ranges lie to the south
amid sandy plains south of Palomas in northern Mexico. Underground water from ancient
rains, stored in sand and gravel underlying the
plains around Columbus, is now pumped to
irrigate the green fields that circle the town.
During past centuries the Mimbres River
(which rises in the Mogollon and Black Range
areas north of Santa Rita) has, during flood
stage, swept past Deming, rushed around the
north and east sidesof the Florida Mountains.
and passed east of Columbus into Mexico to
fill playas below Palomas.
To the southwest are the rugged peaks of
Sierra de Palomas in northern Chihuahua,
and on the western horizon is the sharp peak
of Big Hatchet Mountain in southwest New
Solntens oN LooKour erop Vtt-l,q Htll, March 10,
1916(courtesy New Mexico Historical Society)'
Dakota-Mancos
terminologY
kontinued
fromp. 44)
lent to the Clay Mesa Tongue, but that term
cannot be extended into the Salt Lake area
because of the pinchout of the underlying
Cubero Sandstone Tongue of the Dakota
Sandstone into Mancos Shale 30 mi (48 km)
southwest of the Laguna section. Consequently, the informal term "lower part of the
Mancos Shale" is applied to this unit. Similarly, the rocks that make up the lowest part
of the Cretaceous sequence in the southern
Zuni Basin cannot be included in one of
the other named member-rank units and are
simply referred to as the main body of the
Dakota Sandstone.
The Dakota-Mancos sequence in the Salt
bottom to
Lake coal field consists of-from
top-the Dakota Sandstone(main body), the
lower part of the Mancos Shale, the Paguate
Tongue of the Dakota Sandstone,the Whitewater Arroyo Tongue of the Mancos Shale,
and the Twowells Tongue of the Dakota Sandstone.
Seboyeta Bay, an east-west lobe of the
WesternInterior seawayabout 75 mi (l2l km)
long and wide, and roughly centered on
Mount Taylor, provides an explanation for
the thicker and older Dakota-Mancos sequence found in the southern Zuni Basin.
Seboyeta Bay formed in middle Cenomanian
time and expanded in a northerly, westerly,
and southerly direction until latest Cenomanian to earliestTuronian time, when it became
indistinguishable from the main body of the
Western Interior seaway. Deposition of
marine rocks occurred earlier in the Salt Lake
coal field than in the northern Zuni Basin
apparently because of a faster southwesterly
transgressionrate.
Acxrowr-eocunNrs-The
concept and
naming of SeboyetaBay originated with C. H.
Dane, E. R. Landis, and W. A. Cobban (unpublished manuscript, 1967) during the early
stagesof work that culminated in Landis and
others (1973). We gratefully acknowledge
Dane's contribution to this paper and to our
46
August1980
New Mexico Geologt
present understanding
of the Upper Cretaceous of New Mexico.
This paper was critically reviewed by M. E.
Maclachlan and C. H. Maxwell of the USGS,
Denver, and benefited from discussions with
C. M. Molenaar, USGS, Denver, and F. E.
Kottlowski, D. E. Tabet, S. J. Frost, and
C. T. Bolt, New Mexico Bureau of Mines and
Mineral Resources. The correlations of the
main body of the Dakota Sandstone at the
Narrows (fig. 2, section 8) are from C. H.
Maxwell. Funding for Hook was provided by
USGS Grant 14-08- 0001-C525 to the New
Mineral
Bureau
Mines
and
Mexico
of
Resources.
References
Cobban, W. A., 1961, The ammonite family
B i n n e y i t i d a eR e e s i d ei n t h e W e s t e r nI n t e r i o r o f t h e
U n i t e d S t a t e s :J o u r n a l o f P a l e o n t o l o g y ,v . 3 5 , n o '
4 , p . 7 3 7- 7 5 8 , 3 p l s . , 5 f i g s .
-.
1 9 7 ' 7 aF, o s s i lm o l l u s k s o f t h e D a k o t a s a n d stone and intertongued Mancos Shale of westcentral New Mexico: New Mexico Geological
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213-220,5 figs.
1977b. Characteristic marine molluscan
fossils from the Dakota Sandstone and intertongued Mancos Shale, west-centralNew Mexico:
U . S . G e o l o g i c a lS u r v e y , P r o f . P a p e r 1 0 0 9 ,7 4 p . ,
, figs.
21 pls.,4 tables7
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, em. 37, 5l p., 12
M i n e s a n d M i n e r a l R e s o u r c e sM
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Mexico. Sierra de Palomas' extension across
the Mexican-American border (15 mi to the
west) is the Carrizalillo Hills; the Cedar
Mountains form the low skyline ridges to the
west-northwest. Five miles to the northwest,
bold, jagged triple peaks of the three sisters
(Tres Hermanas Mountains) block distant
views in that direction.
Pancho Villa State Park is on the low edges
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from the Tres Hermanas Mountains. Pebbles,
cobbles, and boulders in the park were derived
from rock outcrops in those mountains; they
include fragments of quartz, feldspar, monzonite, rhyolite, latite, basalt, Iimestone,
chert, and andesite. Mines in the northwest
Tres Hermanas Mountains operated until the
1920's and produced about one-half million
dollars worth of zinc, lead, silver, gold, and
copper. Present-day outcrops of interest to
rock hounds contain Mexican onyx, calcite,
n
s p u r r i t e ,a n d d u m o r t i e r i t e .
F. E. Kottlowski(revised1980)
possibilities of Catron County, New Mexico: New
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f i e l d c o n f e r e n c ep, . 8 l - 8 4 , 2 f i g s .
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in Upper Cretaceousof New Mexico: New Mexico
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(Marcou)-common
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1977-78, p. 34-42, 5 figs.
, 1980, Some guide fossils in Upper
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1978-79, p. 38-49, 7 figs.
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M e x i c o : U . S . G e o l o g i c a lS u r v e y , B u l l . 1 3 7 2 - J , 4 4
p.,4 figs.
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P e t r o l e u m G e o l o g i s t s ,B u l l . , v . 5 0 ,
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tr