biostratigraphy
conodont
Mississippian
Devonian-Lower
Upper
NewMexico
patterns,
southwestern
anddepositional
Arizona
andsoutheastern
of Geosciences'
Depaftment
E' Barrick,
andJames
NM88210,
Artesia,
Department,
andMinerals
Energy
NewMexico
Division,
Moore,
QilConservation
byDarrett
TX79409
Lubbock,
TechUniversity,
Texas
Introduction
Upper Devonian and Lower Mississippian
strata in southwestem New Mexico comprise more than 2fi) m of fine terrigenous
ilastics and marine carbonates. Although
excellent exposures exist in many of the
mountain ranges of New Mexico and adjacentArizona, the discontinuous outcrop pattem of Paleozoicrocks, a product of Mesozoic
and Cenozoic tectonics, has hindered accurate reconstruction of original depositional
patterns. This region has special paleogeographic significance, for here two different
Lower Mississippian carbonate shelves
(Lane, 1982;De Keyser, 1983;De Keyser et
al., 1985)and has been interpreted to extend
as far west as the Silver City area of New
Mexico (Fig. 1, BM). In southeasternArizona
a different combination of depositional factors produced a thick Mississippian carbon-
ate packagethat has been called the Escabrosa
Shelf (Gutschick and Sandberg, 1983)' The
EscabrosaShelf has been traced as far east
as the Klondike Hills, New Mexico (Armstrong, 1970),south of the supposedwestern
extent of the Lake Valley Shelf.
Becauseof apparent differencesin the lithologic successionbetween the Lake Valley
Shelf and the EscabrosaShelf, direct corre-
Mississippian sequence.
Recenl work on depositional patterns and
conodont faunas in Upper Devonian and
Lower Mississippian strata in southwestern
New Mexico prbvides a clearerpicture of the
timing of depositional events in the region
and reconstruction of paleogeographicfeatures. The focus of this work is a new interthe
pretation of the depositional sequence_in
Upper Devonian PerchaFormation and Lower
Mississippian EscabrosaGroup at,theMescal
Canyon- section in the Big Hatchet Mountaini. Conodont faunas obtained from the
Mescal Canyon section permit new,correlations from lhe EscabrosaShelf to the Lake
Valley Shelf.
Mescal CanYon section,
Big Hatchet Mountains
Previous studies
New Mexico, Armstrong (1962) presented
information on the shatigraphic distribution
Alsoin thisissue
RousseauHaynorFlower
(1913-1s88)
elementsin New
Rare-earth
Mexico
AbstractsfromNMGS1987
springmeeting
Service/News
Staffnotes
p.32
p. 33
p. 39
p. 46
p. 48
soon
Goming
FIGURE l--4eographic localitiesin southwestern New Mexico and adiacentArizona discussedin text.
Solid triangles indicate the locations of sections described in detaiL BL, Blue Mountain; BM, Bear
Mountain;"MC, Mescal Canyon. The approximate positions of the margins of the Lake Valley Shelf
and EscabrosaShelf relative to the Rancheria Basin are indicated in blue.
Laramidedeformationin south-central
New Mexico
Typeand referencesectionsof Lower
Cretaceousstrata
ChicosaLakeStatePark
Petroleumexplorationin NewMexico
in 1987
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L i m e s t o noer, g i l l o c e o u s
10, No.2,
May
1988
Editor:Carol A. Hjetlming
Draftiflg assistarce:Jean B. Mmdy
Publishedquarterly by
New Mexico Bureau of Mines and Mineral Resources
a division of New Msio lnstitute of Minint & ltdnolo6y
BOARD OF REGENTS
Ex Officio
Gany Carruthem, Gwemor of Nru Meico
Alan Morgan, Suryintendentof Publiclflstructiofl
Appointed
Lenton Malry, P/6., 1985 7997,Albuquerque
Robert O. Anderson, \rc. lTreas., 7987-1993, RosweII
Gilbert L- Cano, 1985 7989,Albu4uoque
Donald W. Morris, 19&37989,Ins Alamw
Steve Tores, 7967-1991,Smno
New Mexico Institute of Mining & Technology
Presid%t..
......
IaurenceH.lattman
New Mexico Buteau of Mines & Mineral Resources
D i r r t o r. .
.......
FrankE.Kottlowski
DeputyDircctor
.... JamesM.Robertson
Subrriptions: Issued quaiterl, Februart May' August,
November; subscription price 96.(X)/calendar
year.
EditorialMtter: Articles submitted for publi@tion should
be in the editor'shandsa minimum of five (5) months
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reviewed by at leasttwo people in the appropriatefield
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Publishedas publi domin, therelorereprcduciblewithout prmission. Sourcecredit reqwsted.
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,,I,.-
FIGURE 2-Stratigraphic column of Upper Devonian and Lower Mississippian strata at the Mescal
canyon section (NE1/asEr/+sec. 29, rc03, Rr5w) in the Big Hatchet Mounia'ins, New Meico. ,,older
.*it
primarily to PaPersby Armstrong and Mamei(1978a, 7978b)and Armstrong et al. (19g0).
Y"_.f 1 of imPortant
Kanges
conodont speciesare shown as are agesinferred from conodont diitribution.
May 1988 Nan Mexim Geology
GEOLOGV
o Science
andService
s's'=i€i
ffi
New AAexnc@
Volume
5-t.
FE=
I.T=
of macrofossil taxa in the EscabrosaGroup
in Mescal Canyon. In that publication, Armstrong proposed that the EscabrosaLimestone of Girty (1904)be elevated to group
status and divided into two formations. The
lower formation, the Keating Formation,
comprises a sequenceof encrinites and calcilutites that rests unconformably on Upper
Devonian units. The overlying Hachita Formation is a massive encrinite unit. The type
section for both formations is at Blue Mountain, in the Chiricahua Mountains of southeasternArizona (Fig. 1, BL). Eastward from
the Chiricahua Mountains, including the Big
Hatchet Mountains, the Keating Formation
was divided by Armstrong (1962)into two
members. Member A consistsof a basal unit
of coarse encrinite, 15 m thick at most sections, that is overlain by dark-gray limestoneswith minor amounts of nodular chert.
Member B comprisesthinlybedded dark-gray
limestone characterizedby significant quantities of chert occurring as lenticular and
nodular masses.
At the Mescal Canyon section in the Big
Hatchet Mountains, ihe base of Member A
of the Keating Formation was depicted as
resting unconformably on the argillaceous
carbonates of the Upper Devonian Portal
Formation (Armstrong, 1952, figs. 2 and 3,
plate in pocket). No preciselithologic boundary was describedor indicated, but the illushated faunal dishibutions (figs.2 and 3) show
that Mississippian fossils appear abruptly in
the section at a level approximately 175 m
below the top of the Keating Formation, or
near the prominent oolitic limestone shown
in Figure 2. Armstrong (1962) reviewed earlier arguments regarding the age of the Escabrosa Group, most of which assigned at least
the lower part to the Kinderhookian. Brachiopods and corals reported from Member A
of the Keating Formation at Mescal Canyon
by Armstrong (1962) included species that
characterize both Kinderhookian and Osagean strata elsewhere. Member B of the Keating Formation contained typical Osagean
forms.
Zeller (1955) provided the first detailed
lithologic description of the Devonian-Mississippian succession at Mescal Canyon.
Although he rejected the stratigraphic
nomenclature of Armstrong (1952)on the basis
of a lack of mappability, Zeller (1965) recognized three informal members of the Escabrosa Limestone. The upper member
corresponds to the Hachita Formation of
Armstrong and the middle member is the
cherty Member B of the Keating Formation.
The lower member of ZelIer, however.
extended nearly 50 m below the base of
Member A of the Keating Formation as used
by Armstrong (1962). Zeller could find no
lithologic evidence for an unconformity
between the Upper Devonian Percha Formation and the Mississippian Escabrosa
Limestone. He placed the base of the Escabrosa at the point where carbonates began
to dominate the section, just above a deeply
weathered dike that cuts the section. Lacking
any faunal evidence to the contrary, ZeIler
(1955) proposed that deposition may have
been continuous from the Late Devonian into
the Early Mississippian. Neither Armstrong
(1962) nor Zeller (1965) reported any diagnostic faunal elements from the interval that
lies between their respective bases of the
Escabrosa Group.
Kocurek (1977), during a study of the sedimentology of the Percha Formation in
southwestern New Meico, also failed to
detect any obvious break in deposition
between the Devonian and Mississippian at
the Mescal Canyon section. Kocurek arbitrarily chose the base of the oolitic limestone
used by Armstrong (1962) to mark the base
of the EscabrosaGroup as the level at which
to terminate his study, but Kocurek did not
attribute any special sedimentological significance to this occurrence.
Armstrong and Mamet (I978a) formally
named Armstrong's (1952) Member A and
Member B of the Keating Formation, the Bugle
and Witch members, respectivelv. The Mescal Canyon section was chosen to be the type
section for both members. Armstrong and
Mamet (1978a) described the Bugle Member
as a massively bedded bryozoan-echinoderm to ooid packstone and wackestone, and
argillaceous, crinoidal-bryozoan packstone
that rests with sharp contact on the yellowgray calcareous shale of the Box Member of
the Percha Formation. The base of the Bugle
Member (and Keating Formation) at the type
section was placed 35 m below where Armstrong (1962) had originally placed the base
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FIGURE 3-Composite
conodont zonation for
Upper Devonian through Lower Mississippian
strata as used in this report. Upper Devonian zones
are derived from Ziegler and Sandberg (1984), Kinderhookian zones from Sandberg et al. (1978), and
Osagean zones from Lane et al. (1980).
of the Keating Formation and 15 m above
the level where Zeller (1955)placedthe base
of the EscabrosaLimestone.Lessthan a meter
below the Bugle-Box contact a brachiopod
fauna had been obtained that was identified
by Dutro (in Armstrong and Mamet, t978a,
p. 92), who indicated that it was probably
middle Famennian (Late Devonian) and that
it had been described by Stainbrook (1947)
from the Box Member of the Perchaat other
localities. The Bugle Member was given a
late--early to early-middle Tournaisian age
(approximately the Kinderhookian-Osagean
boundary) basedon Armstrong's (1962)faunal
collections (now 30 to 50 m above the base
of the Bugle) and a microfossil assemblage
(foraminifera) of pre-Zone 7 age found by
Mamet 68 to 70 m above the base.
Conodont biostratigraphy
During the spring of 1983the authors, with
the assistanceof Thomas De Kevser,Marathon Oil Company,and SamThompson, New
Mexico Bureau of Mines and Mineral
Resources,redescribedthe Upper Devonian-Lower Mississippian successionat Mescal Canvon and sampled for conodonts.
Originaliy, the stratigraphicboundary proposedbyArmstrong and Mamet (1978a)was
used, but the conodont faunas obtained indicate that a reinterpretation of the sequence
is necessary (Fig. 2).
Based on conodont faunas, the break
between the Devonian and Mississippian
Svstems at Mescal Canvon lies at the base of
the distinctive oolitic limestone originally used
by Armstrong (1962) to mark the base of the
Escabrosa Group. Below this oolitic horizon
are conodont faunas characterized by elements of Polygnathus semicostatusand "Icriodus"
raymonili. Both species are characteristic of
the Late Devonian (Famennian), but"l." raymondihas the shorter range (UppermostmarginifuaZone through the Middle expansaZone
of the standard conodont zonation, Sandberg and Dreesen, L9M, frg.3; Fig. 3 herein).
A sample from the base of the Escabrosa
Group as used by Armstrong and Mamet
(1978a; Fig. 2, herein) also contains Bispathodus costatusand B. aculeatus.The ranges of
both species begin in the Mddle expansaZone
and extend higher; B. aculeatus extends into
the Mississippian and B. costatus into the
Middle praesulcataZone, near the end of the
Devonian. The interval from the base of the
Escabrosa Group of Armstrong and Mamet
to the base of the oolitic limestone can be
assigned to the Middle expansaZone, indicating a late, but not latest Famennian age.
We recommend that this interval be designated informally as an upper limestone
member of the Percha Formation (Fig. 2).
Samples from underlying beds have yielded
less diagnostic Famennian conodonts.
Conodont faunas from the oolitic limestone and the overlying 55 m of coarse crinoidal packstones and grainstones of Unit 1
of the Bugle Member (Fig. 2) are characterizedby elements of Polygnathus communis, P.
inornatus, P. longiposticus, and P. symmetricus.
Two species of Siphonodella,S. obsoletaand S.
isosticha, occur in the lower two-thirds of this
interval. The co-occurrence of these two species permits this interval to be assigned to
the Early Mississippian, late Kinderhookian
isosticha-Upper crenulata Zone (Sandberg et
al.,1978; Fig. 3 herein). A substantial hiatus,
encompassing the latest Devonian and most
of the Kinderhookian exists at the base of the
oolitic limestone.
Dark-gray argillaceous wackestones rest
with sharp contact on the light-gray coarse
crinoidal carbonates at Mescal Canvon (Unit
2 of the Bugle Member, Fig. 2). Aithough a
sharp lithologic contact is present, no hiatus
can be identified from the conodont faunas.
Because a sample just above the contact
yielded a small fauna containing Siphonodella
isosticha, the base of the argillaceous wackestone belongs to the isosticha-Upper crenulata
Zone. A few meters higher appears a conodont fauna dominated by Polygnathus communis communis, and bearing P. c. carina,
Gnathoduspunctatus, and an early morphotype of G. cuneit'ormis(morphotype 1 of Lane
et al., 1980). This combination of species is
characteristic of the Lower typicus Zone (Lane
et al., 1980) and Faunal Unit 3 of Lane (1974,
1982), which are thought to be early Osagean
in age (Fig. 3).
Nao Merico Ceology
May 1988
The baseof the Witch Member. as defined
by Armstrongand Mamet(1978a),lies
at the
point where significant quantities of chert
occur as lenticular and nodular masses.As
so defined, the base of the Witch Member
can be placed about27 m above the base of
the argillaceouswackestonesof Unit 2 of the
Bugle Member. The conodont fauna from the
Iower part of the Witch Member is similar to
that of Unit 2 of the Bugle Member but has
somewhatgreaterdiversity and abundance.
Polygnathuscommunisstrongly dominates the
collections, and Pseudopoly
gnathusmultistriafas morpholype 1 and Gnathodusspeciesare
present. Although few short-ranging species
were recovered (Fig. 2), the cherty carbonatesassignedto the baseof the Witch Member by Armstrong and Mamet (l971a) appear
to lie within the Lower typicusZone.Samples
from higher in the Witch Member yielded
small conodont faunas dominated by p. communis, which lack diagnosticforms. Pseudopolygnathus
oxypageus,
which appearsat the
baseof the Upper typicusZone,-occursin the
middle of the Witch Member (Fig. 2).
No zonal diagnosticconodbnts were
obtained from the uppermost beds of the
Witch Member or the lower bedsof the overlying Hachita Formation. Armstrong and
Mamet (I978a) reported a foraminiferal
assemblageof Zone 7 (Osagean) from the
upper 4 m of the Witch Member at Mescal
Canyon. Armstrong and Mamet (1928a)did
n9t fi1{ diagnosticfossilsin the lower part
of the Hachita Formation, but the uppermost
20 m of the Hachita Formation w-eie interpreted to be late Meramecian in age on the
basis of foraminifera and brachiopods.
of the limestone member contains skeletal
wackestones in layers 3 to 5 cm thick, interbedded with yellow-brown to gray terrigenous mudstones. Higher in the section the
proportion of carbonates increases and skeletal packstones and grainstones become
common. A diverse fauna of pelmatozoans,
bryozoans, brachiopods, and ostracodes are
represented by their skeletal grains. Locally,
oolitic limestone and beds bearing intraclasts
of terrigenous mudstones occur. The uppermost beds of the upper carbonate member
are almost free of fine terrigenous clastics,
and skeletal grains, mostly pelmatozoan and
bryozoan debris, are badly broken and
abraded.
The overall facies transition from the Box
Member to the top of the upper carbonate
member represents a gradual shift from a
low-energ'y environment ch aracteilzedby fine
terrigenous muds to a high-energy carbonate-shoal setting. Kocurek (1977) proposed
that this lithofacies transition was the result
of a change from a shallow-water lagoon and
tidal flat dominated by terrigenous muds to
an offshore carbonate platform. His arguments for a shallow-water origin for the Box
mudstones are based largely on the sequence
of sedimentary structures that charaiterize
the facies transition; however. manv-largely
of the
sedimentary structures provide
equivocal evidence. Regional stratigraphic
relations (e.g. Kottlowski, 1963) suggest that
the Box mudstones may have accumulated
in subtidal environmenis.
Conodont biofacies in the upper part of
the Percha Formation at Mescal Canyon do
not provide any clear indication of the depositional setting of the Percha mudstones.
No conodonts were recovered from carbonDepositional history
ate nodules in the Box Member. Sparse faunas
Three Upper Devonian and Lower Missischaracterized by small carminate elements
sippian depositional sequencescan be idenappear in the lower part of the upper limetified at the Mescal Canyon section: 1) an
stone member, associated with small indeU p p e r D e v o n i a n ( F a m i n n i a n ) s h o a l i n g terminate icriodids. Samples from the upper
two-thirds of the upper limestone member
lequence; 2) a Lower Mississippian (upper
Kinderhookian) sequenceof coirse-grairied are dominated by elements of Polygnathus
skeletal grainstonesthat rest unconformably
semrcostatusand "Icrioilus" raVmondiand lesser
on the Upper Devonian carbonates;3) air
numbers of P. communis,Biipathodusspecies,
Osageanshoaling sequencethat formed after
other species with carminate elemenls, and
a rapid submergence in the latest KinderApatogrnthus elements. This association is like
hookian.
that of the polygnathid-"icriodid"
biofacies
Upper Devonian shoaling sequence-At
of Sandberg and Dreesen (1984, frg.6). These
Mescal Canyon, the Box Membeiof the perauthors proposed that the polygnathidcha Formation comprisesunfossiliferous ter"icriodid"biofacies is typical of normal marine,
rigenous mudstonesthat contain occasional shaUow-water,outer-shelf environments. This
layers of carbonatenodules. Few skeletal interpretation applies well to the greater part
remains are apparent in the nodules; articof the upper limestone member of the Perulated ostracodesand sponge spiculesare
cha. Unfortunatelv, conodont faunas from
the most common components-. The frethe basal portion of the upper limestone
quency and thicknessof carbonateinterca- member lack conodont species that would
lations increase toward the top of the Box
indicate a deeper water environment (e.g.,
Member.
Palmatolepis species) or nearshore environThe base of the upper limestone member
ments (e.g., Pandorinellina or Clydngnathus
is placedwhere the proportion of carbonate species, Sandberg and Dreesen, t984).
beds abruptly predominatesover that of the
Upper Kinderhookian shallow-water carterrigenousmudstones.The boundary rec- bonate sequence-After a malor hiatus that
ognized here coincideswith the level at which
included most of Kinderhookian time, shalZeller (1965)placedhis baseof the Escabrosa low-water, high-energy environments again
Group, just above a deeply weathereddike
characterized the region. At the base of the
that cuts through the section.The lower part
sequence lies a prominent 3-m-thick oolitic
May 1988
Nru Mexico Ceology
grainstone that defines the basalpart of Unit
1 of the Bugle Member of the Keating Formation (Fig. 2). The basal oolite is overlain
by evenly bedded, coarse-grainedskeletal
packstonesand grainstones.Pelmatozoanand
bryozoan detrifus compose90Voof the grains,
and remains of corals, calcareousforminifera, ostracodes,and brachiopodsare present. Exceptfor the appearanceof algal-coated
grains near the top of the unit, there are no
obvious trends in composition or texture that
can be attributed to changesin environmental setting.
Conodont faunasfrom Unit 1 of the Bugle
Member are sparseand badly fragmented.
The predominance of robust elements of
Polygnathuslongiposticusand closely related
speciesis like that reported from similar highenergy carbonatesof late Kinderhookian age
(lower Andrecito Formation) in the San
Andres Mountains (De Keyser et al., 1985,
p.76.)
Osageanshoaling sequ€nce-Near the end
of the Kinderhookian an abrupt deepening
event occurred,and subtidalshelfsediments
spread over the shallow platform area. The
baseof an interval of 27 m of dark-gray argillaceous wackestones (Unit 2 of the Bugle
Member) rests with sharp contacton the lightgray, abraded skeletal grainstones of the
underlying depositionalsequence.The sparse
skeletaldebris is poorly sorted and moderately well preserved.Pelmatozoanand bryozoandetritus is common.Small,strucfureless
peloids, perhapsfecalpellets,are abundant.
The slope-forming dark-gray argillaceous
wackstones of Unit 2 of the Bugle grade
upward into cherty, cliff-forming dark-gray
carbonatesthat containa substantiallysmaller
proportion of fine terrigenous detritus, the
Witch Member. Elongate chert nodules oriented parallel to bedding are pervasive and
often coalesceinto thin discontinuous lavers
that break the thicker carbonate beds into
thin intercalations of chert and carbonate.
Skeletal wackestoneswith diverse fauna
characterize the lower 20 m of the Witch
Member. Pelmatozoan debris, brvozoan
remains, sponge spicules, ostracodes, and
brachiopods occur in nearly equal proportions. Twenty meters above the base of the
Witch Member a fossil-poor facies of ostracode carbonatemudstonesappears.Besides
ostracodes,sparsespongespiculesoccurwith
abundant peloids, like those found in the
carbonatesof Unit 2 of the Bugle Member.
This fossil-poor faciesis 60 m thick and grades
upward into pelmatozoan and bryozoan
packstonesand grainstonesthat form the top
30 m of the Witch Member (Fig. 2). Skeletal
debris is well sorted and finely comminuted
in the uppermost beds, and carbonateintraclastsup to 10 mm in diameterare present.
Unit 2 of the BugleMember and the greater
part of the Witch Member represent deposition in quiet water, shallow subtidal environments. During the initial stage of
deposition, a moderate influx of fine terrigenous clastics produced argillaceous carbonates. When the influx of terrigenous
detritus decreased,clearerwater conditions
prevailed that permitted a relative abundance of sponges,whose siliceousspicules
were later mobilized by diagenetic fluids to
produce the characteristiccherts of the Witch
Member. A final shoalingevent is indicated
by the appearanceof packstonesand grainstones at the top of the Witch Member.
Conodont faunas from Unit 2 of the Bugle
Member and the Witch Member provide little
additional information about the environments of deposition becausethe paleoecologic distribution of early Osageanconodonts
remains unclear.Conodont diversity is low
(3-5 species) in the low-abundance faunas
from Unit 2 of the Bugle Member. Polygruthus communisdominates, and Gnathodus
punctatusoccursnear the base.Chauff (1983)
considered the association of abundant P
communis
with G. punctatus
on the Burlington
Shelf (Missouri-Illinois) to represent a nearshore shallow-water transgressivefauna.
However, G. punctatuswas recovered from
only shelf-margin sectionsin the SanAndres
Mountains (De Keyser et al., 1985).A maximum in diversity-(8 species)is attained at
the base of the Witch Member, where relatively abundant faunas are strongly dominated by P. communisand contain common
Pseudopolygnathus
and Gnathodusspecies.A
similar conodont associationoccurs in foreslope deposits on the eastern shelf margin
of the Deseret starved basin in Utah (Sandberg and Gutschick, L979; Gutschick and
Sandberg, 1983; Sandberg and Gutschick,
1984),but has been interpreted to be a shallow-water subtidal conodont biofaciesin the
midcontinent area (Chauff, 1983).Higher in
the Witch Member faunal diversity falls to a
few species(2-4), and P. communisremains
the dominant form to the top of the member.
Regional stratigraphic relations
Schumacher(1978)summarizedlithostratigraphic and biostratigraphic relations of
Upper Devonian strata in southeasternArizona. He recognized an upper Devonian
(Famennian) depositional complex consisting chiefly of yellow-gray to gray and black
shales and overlying carbonates.This interval rangesin age from the middle Famennian
trachyteraZone to possibly as high as the late
Famennian Middle expansaZone (Schumacher, 1978,fig" 2). The Box Member of the
Percha Shale of westem New Mexico was
assigned to this Famennian depositional
complex based on brachiopods (Stainbrook,
7947) and conodonts (Sandberg, 1976).
The upper limestone member of the Percha Formation at Mescal Canyon is similar
to Member4 of the PortalFormation(Sabins,
7957)in the Chiricahua Mountains of southeasternArizona (Fig. 1). Member 4 of the
Portal comprisesthick-bedded skeletalpackstonesand grainstonesthat may be as young
as the Middle elpensaZone. Similar shallowwater carbonatesoccur in the upper part of
the Devonian section in the intervening
Peloncillo Mountains of western New Mexico (Gillerman, 1958). Schumacher (1978)
traced these shallow-water carbonatesmore
than 100km farther west in Arizona, into the Keyseret al., 1985).This small outlier could
Mescal and Santa CatalinaMountains (Fig. r e p r e s e n t a f r a g m e n t o f a n u p p e r m o s t
1). In the most westem sections,the shales Devonian carbonateplatform that was hrgely
that underlie these carbonatesare gradually removed by erosion during the earliest Misreplacedby sandstones,suggestingincreas- sissippian.
ing proximity to a shorelinein this direction.
Armstrong and Mamet (1978b)and ArmComparableshallow-water, upper Famen- stronget al. (1980)presenteda seriesof cross
nian carbonatesmay extend slightly northsectionsand paleogeographicand lithofacies
east of the Big Hatchet Mountains. In the maps that depict Mississippian stratigraphic
Klondike Hills, the nodular Box Member of relationships in eastem Arizona and souththe Percha Formation is overlain by at least western New Mexico. Primary biostrati10 m of Upper Devoniancarbonatesthat are graphic control was provided through the
overlain by the base of the EscabrosaGroup use of the microfossil (largely foraminifera)
(Armstrong et al., 1980).Farthereast,in the zonation of Mamet althoughin someinstances
Florida Mountains, the Perchais represented conodonts and macrofossilzoneswere used.
only by dark shales.North of the Big Hatchet Basalstrata of the Keating Formation (Bugle
Mountains, in the Santa Rita area (Fig. 1), Member) of the EscabrosaGroup fall in the
the Box Member contains abundant carbon- pre-Zone 7 interval of Mamet's zonation,
ate nodules and layers that have yielded which is shown to be pre-Osageanin age
moderately diverse megafaunal collections (Armstrong and Mamet, 1978b;Armstrong
(Stainbrook,1947).
et al., 1980).
At BearMountain, northwest of Si-lverCity,
Norby (1971) described conodont faunas
a conodont fauna that includes Palmatolepis from the EscabrosaGroup in Arizona that
perlobatapostera,P. gracilissigmoidalis,Polyg- more accuratelydate the base of the Missisnathus experplexus,and Pelelcysgnathus
incli- sippian succession.At Blue Mountain in the
natuswas recoveredfrom carbonatenodules Chiricahua Mountains, the type section of
in the upper 16 m of the Box Member (Fig. the EscabrosaGroup, the lower 20 m of the
4). This associationis characteristicof the late Bugle Member are coarse-grainedpelmatoFamennianLower and Middle exwnsaZones. zoan grainstonelike that found at the Mescal
The upper part of the Box at BearMountain Canyon section in the Big Hatchet Mounappearsto be approximately the sameage as tains. The basal three meters of the Bugle
the upper limestone member of the Percha Member bear a conodont fauna of latest Kinin the Big Hatchet Mountains. The Bear derhookian age (Siphonodella
isostichaand S.
M o u n t a i n c o n o d o n t f a u n a m o s t c l o s e l y obsoleta,
Norby, 1971,fig.5). The upper 30 m
resemblesthe polygnathid-icriodid biofacies of the Bugle Member at Blue Mountain conof Sandberg (1976) and is considered to be sist of dark-gray, fine-grained carbonatesthat
typical of the moderately shallow water con- contain only minor amounts of fine terrigenditions of the outer cratonic shelf, farther ous clastics. This upper interval is largely
offshore than the polygnathid-"icriodid"
barren of conodonts but includes one form,
conodont biofaciesthat is present in the Big Gnathoduscf. G. semiglaber,the illustrated
Hatchet Mountains. Farther east, near Santa specimens of which appear to be elements
Rita, Sandberg(1975)reported a comparable of G. punctatus(Norby, t971, pl.5, figs. 11
fauna associationfrom the Box Member.
and 15). Gnathoduspunctntusoccurs in the
From these sparse data, it is possible to
dark argillaceouscarbonatesof Unit 2 of the
reconstruct some aspectsof Late Devonian Bugle at Mescal Canyon, and the upper cardepositional history and paleogeographyin
bonates of the Bugle at Blue Mountain and
southwestern New Mexico. During the late Mescal Canyon appear to be the same age
Famennian (expansaZone?), the supply of
although slightly different lithofacies are
terrigenous clasticsinto the region decreased present in the two sections.Armstrong et al.
such that carbonate environments began to
(1980, fig. 5) indicate a similar correlation
develop. A shallow-water carbonate plat- based on macrofossil zones.
form area formed in eastern Arizona and
The conodont fauna of the Witch Member
extreme southwestern New Mexico. As best at Blue Mountain is shikingly similar to that
as can be determined, the edge of this platof the Witch Member at Mescal Canyon. At
form area ran approfmately north to south
the baseof the Witch Member at Blue Mounalong the western margin of New Mexico, tain (Norby, 1971), elements of Polygnathus
parallel to what later would be the margin
communisbecameabundant and lessernumof the EscabrosaShelf (Fig. 1). Eastward, bers of Pseudopolygnathus
multistriatus and
deeper water environmentsexisted,in which
Gnathodusspeciesare present. As is the case
nodular carbonates accumulated in domiat Mescal Canyon, the base of the Witch
nately terrigenous clastic environments. Member at Blue Mountain can be assigned
Whether or not a comparable uppennost to the Lower fgpicusZone.Higher in the Witch
Devonian carbonatecomplex existed in cen- Member, fewer conodonts occur, and the
tral New Mexico at this time is uncertain. At
sparse faunas continue to be dominated by
most sectionsthe Box Member of the Percha elementsof P.communis.
Formation is the youngest Devonian unit
Armstrong et al. (1980,fig. 7) illustrated
preserved (Bowsher, 1,967).However, at
how Mississippian strata of the Escabrosa
Rhodes Canyon in the San Andres MounShelf might be correlated with strata of the
tains, a 2.75-m unit of oolitic grainstone Lake Valley Shelf. Relatively little biostratiyielded a Polygruthus-Palmatolepis
graphic control for the lower units is indifauna that
is latest Devonian (expansa
Zone) in age (De
Nao Mexico Geology
May 1988
cated on their figure. Beds of the Andrecito
andAlamogordo Membersof the Lake Valley
Formation were shown to contain a pre-Zone
7 microfossilassemblage,
and the TierraBlanca
Member at Bear Mountain yielded a Zone 7
assemblage.However, considerablebiostratigraphic information for the Lake Valley Shelf
exists in the form of conodont faunas.
The Andrecito Member of the Lake Valley
Formation in the SacramentoMountains
(Lane, 1974, 1982), the San Andres Mountains (De Keyseret al., 1985),and the Cooke's
Range (Moore, 7984)ranges from the upper
part of the upper Kinderhookian isostichaUppet crenulataZoneinto the lower Osagean
Lower typicusZone. The Alamogordo Member contains conodont faunas of the Lower
typicusZoneinthe areascitedabovebut locally
ranges into the Upper typicusZone in some
sections in the southern part of the Sacramento Mountains (Lane, 1982).The carbonate mounds of the SacramentoMountains
are of an equivalent age, ranging from the
Lower typicusZone through the Upper typicusZone,and possiblyashigh as the middle
Osageananchoralis-latusZone (Lane, 1982).
Correlations based on conodonts between
the EscabrosaShelf and the Lake Valley Shelf
confirm most aspectsof the correlation proposed by Armstrong et al. (1980).The most
significant correlation is the apparent equivalenceof the lower part of the Witch Member
of the Keating Formation with the Alamogordo Member of the Lake Valley Formation.
The base of each unit lies within the Lower
typicusZone, and the two units possesssimilar lithologic attributes. Both units comprise
dark-gray, cherty carbonate mudstones to
packstonesthat form cliffs to steep slopesin
outcrop. The widespread distribution of this
distinctive lithofaciesover both shelf regions
is probably a reflection of the regional Osagean hansgressiveevent that flooded most
of the North American uaton during Ear$
Mississippian time (Lane, 1982).The maximum of this transgressiveevent in the western United States was achieved during the
time represented by the ancharalis-latusZone,
in the middle Osagean(Sandberget al., 1983).
Interpretation of the more diverse lithofaciesrepresentedby stratabelow the WitchAlamogordo interval is more difficult. The
Andrecito Member of the Lake Valley Formation is equivalent in age to the Bugle
Member of the Keating Formation. The
Andrecito Member comprises a relatively
heterogeneousassociationof argillaceousgray
carbonates, typically mudstones to packstones and calcareousshalesand siltstones.
In contrast, the Bugle Member at Blue Mountain and MescalCanyon consistsof two lithofacies, a lower shallow-water pelmatozoan
grainstone and an upper deeper-waterinterval of carbonatemudstonesand wackestones
that are argillaceous at the Mescal Canyon
section. The lithologic sequence at Mescal
Canyon, where the slope-forming argillaceousbeds of the upper Buglegradeabruptly
into the ledge-forming cherty carbonatesof
the basal Witch Member, strongly resembles
the upper AndreciteAlamogordo sequence
May 1988 Nao MexicoGeology
L ok e E s c o Volley D T O S O
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FIGURE4-Stratigraphic column of Upper Devonian and Lower Mississippian strata at the BearMountain section (SE1/rsec. 17, T775, R15W) northwest of Silver City. "Lake Valley" and "Escabrosa"refer
to Lake Valley and EscabrosaShelf stratigraphic nomenclature, respectively.Rangesof important conodont speciesare shown as are agesinferred from conodont distribution.
on the Lake Valley Shelf. Locally,grainstones
do occur at the base of the Andrecito Member, such as at San Andres Canyon in the
SanAndres Mountains (De Keyseret al., 1985)
and south of Alamo Canyon in the Sacramento Mountains (Lane, 1982). In both
i n s t a n c e s , t h e b a s a l g r a i n s t o n e so f t h e
Andrecito occur near where the shelf margin
is more clearly indicated by the facies pattems in overlying units. The locationsof these
Osagean shelf margins are thought to have
been determined largely by topography
developed on the underlying Devonian surface (Lane 1982;De Keyser, 1983).It is conceivable that the existence of the basal
grainstonefaciesof the BugleMember is similarly related to the development and subsequent preservation of the upper Devonian
carbonate shelf that occupied southwestern
New Mexico and adjacent Arizona.
Becauseof the discontinuousoutcroPPattern, it is difficult to determine how strata of
the basal part of the Lake Valley Shelf might
Shelf.
have mergedinto strataof the Escabrosa
In south-central New Mexico, there is good
evidence that a starved-basinsetting existed
in the vicinity of the Florida Mountains during the Early Mississippian. There Kinderhookian and lower Osageanstrataare absent,
and the basal beds of the Mississippian carbonate section contain middle OsageanconZone) apparently
odonts (anchoralis-Iatus
transported off the edge of an adjacent carbonate shelf (Armstrong and Mamet, 1978b;
Moore, 1984).
To the northwest, in the Silver City area,
some
the sectionat BearMountain possesses
attributes of the strati$aphic successionsof
both the Lake Valley and EscabrosaShelves
(Fig. a). Resting unconformably on the nodular carbonates of the Box Member of the
Percha Formation is a 5-6-m unit of lightgray, wavy-bedded skeletalgrainstoneswith
intercalatedthin argilla6g6uslayers.Near the
base of the unit occur conodonts of the late
Kinderhookian isosficfta-Upperumulata 7nne.
Massivedark-graycarbonatewackestonesrest
with a knife-sharp contact on the lower
grainstone interval. The lower few meters of
the upper unit form a prominent ledge and
lack significant amounts of chert. Higher in
the section, chert becomesabundant and the
unit erodes into more of a slope exposure/
as illusrratedby Armstrong et al. (1980,fig.
7). Conodonts obtained from the lower 2 m
of the upper unit appearto representa Lower
typicusZone fauna although the collections
are not completelydiagnostic(Fig. a).
In their monographic work on the strata
of the take ValleyShelf,taudon and Bowsher
(1949)assigned the lower grainstone unit to
the Andrecito Member and the upper dark
carbonatesto the Alamogordo Member of the
Lake Valley Formation. Most subsequent
workers (e.9., Armstrong et al., 1980),have
followed this nomenclatural assignment.
However, the stratigraphic subdivisions of
the EscabrosaShelf can alsobe applied to the
BearMountain section.The lower grainstone
interval at BearMountain can be assignedto
Unit I of the Bugle Member of the Keating
Formation (Fig.a). The sharp contactbetween
the grainstones and the overlying dark carbonites at Bear Mountain is identical with
that found betweenUnits 1 and 2 of the Bugle
at the MescalCanyon sectionand could represent the same depositional event. Like the
contact at Mescal Canyon, this sharp lithoIogic contact separatesconodonts of the isosticha-lJppercrinulataZone from thoseof the
Lower typicusZone. Lithologically,the ledgeforming dark carbonatesat the base of the
upper unit at Bear Mountain more strongly
resemblethe upper Bugle Member at the Blue
Mountain section. The base of the Witch
Member of the Keating Formation can be
picked up at the level where abundant cherts
appear, approximately 20 m above the base,
asit was chosenat the Blue Mountain section
by Armstrong and Mamet (1978b).
At the present time, there is not sufficient
information availableto evaluate further the
lithologic successionof the Bear Mountain
section relative to the Lake Valley and Escabrosa sequences.Regardlessof the ProPer
applicationof shatigraphicnomenclature,the
Lower Mississippiansectionsin the Silver
City area, including Bear Mountain, appear
to represent the transitional area between the
Lake Valley and EscabrosaShelves.Only 30
km farther east, near SantaRita, a Lake Valley section is present that includes a more
typical development of the Andrecito Member at its base (Laudon and Bowsher, 1949,
fig. a!. The closest outcroP of the Keating
Formation of the EscabrosaGrouP lies more
than 100km to the southwest, in the Peloncillo Mountains (Armstrong et al., 1980,fig.
5). Unless additional lithofacies and biostratigraphic information can be obtained in this
region, the sections of the Bear Mountain
area mav be the onlv source of information
for making a detailed reconstruction of the
latest Kinderhookian and the earliest Osagean at the juncture of the two shelf regions.
AcxNowt-socMENTg-Theauthors wish to
thank Marathon Oil Company for providing
financial support for field work and processing of conodont samples.Thomas De
Keysei, Marathon Oil Company, originally
suggestedthis project and assistedthroughout the course of the proiect. Sam Thompson, III, New Mexico Bureauof Mines and
Mineral Resources,provided guidancein the
field in the Big Hatchet Mountains, shared
his extensive knowledge of New Mexico
geology, and reviewed the manuscript.
CharlesA. Sandberg,U.S. GeologicalSurvev. and H. Richard Lane, Amoco Production Company, provided substantive reviews
of the manuscript. Special thanks are due
Bart Boren. Mark Gilbert, Matt Parsley,and
Eric Yocum, who helped carry samplesfrom
the field for conodont processing.
References
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of the MississippianSystemin southwesternNew Mexico and adiacent southeasternArizona: New Mexico
Bureau of Mines and Mineral Resources,Memoir 8, 99
Armstrong, A. K., 1970,Mississippian stratigraPhyand
geology of the northwestern Part of the Klondike Hills:
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Armstrong, A. K., and Mamet. B. L., 7978a,The Bugle
and Witch Members of the Keating Fomation, EscabrosaGroup and the Mississippiannomenclaturein the
Big Hatchet Mountains, Hidalgo County, New Mexico:
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Armstrong, A. K., and Mamet, B. L',1978b, The Mississippian System of southwestem New Mexico and
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May 1988
Nan Mexico Ceology
Rousseau
HaynorFlower
(1913-1e88)
Rousseau Haynor Flower was born on
March 2l,l9l3 at the family home nearTroy,
New York. He was the son of FranklinRousseau and Ethna Haynor Flower. Rousseau
coming to New Mexico in 1951.
In 1951,Rousseaumarried Margaret(Peg)
and accepteda position as Stratigraphic
Geologistat the New Mexico Bureauof Mines
and Mineral Resourcesoffered to him by Dr.
EugeneCallaghan,then the Bureau'sdirector. His title was later changed to Senior
Paleontologist.Although technically retired
from the Bureau in March 1978, Rousseau
remained active to the end, despite a progressively frail constitution.
Rousseauwas an intemationally renowned
paleontologist.His interestin fossilstook him
to every continentexceptAfrica and Antarctica. He was known and respectedby
paleontologists wherever he went, and he
brought a great deal of distinction to New
Mexico Tech. His scientific accomplishments
are evident through his publications that
include almost 200 papers, many of them
cello. He entered Cornell University in 1930,
earning a tuition scholarshipand majoring
in entomology. He completed his undergraduate degree in 1934and an MA degree
in 1935under Dr. |. G. Needham.His thesis
dealt with the venation pattern of dragonfly
wings; a portion of the terminology he developed was incorporated in Needham and
Westfall's Dragonfliesof North America,published in 1955. Rousseau'sintroduction to
fossils came through a course in historical
geology that he took in his final undergraduate year, and he continued to study paleontology as a minor for his graduate degree.
He intended to complete a PhD in entomologt but a collectingtrip to the Gulf Coast
Tertiary in 1936altered the direction of his
important contributions to our understandcareer.
ing of New Mexico stratigraphy, fossil corals,
In 1936-37, Rousseau studied paleontol- graptolites, and other groups.
ogy at the University of Indiana under E. R.
Rousseau'slove of the opera and classical
Cummings, but family health concemsforced music is well known. For manv vearshe conhim to relurn to New York. In his free time
tributed reviews of musical prbductions to
he becameincreasinglyengrossedin the col- the Defensor Chieftain, Socorro's newspalection and study of-iossiliephalopods,and per. He had a love of literature and classital
he receivedencouragementfrom the distin- film as well.
guished paleontologist Rudolph Ruedemann. By 1938,Rousseau'sdear friend and
teacher Kenneth Caster managed to get him
support at the University of Cincinnati where
Rousseaucompletedhis PhD in June 1939.
His dissertation, Studv of the Pseudorthoceratidae, was later publiihed by the Paleontological Research'Institution.Rousseauwas
u n e m p l o y e d u n t i l S e p t e m b e r1 9 4 0 - t h e
effectsof the depressionwere stitl felt in the Donald of Syracuse,New York. It was my
sciences-when he became a curator at the
privilege to know Rousseaufor almost ten
University of Cincinnati. He held that posi- years; his kind will not soon be seen again
tion until 1944when he left to teachat Brvn
and we will all miss him.
Mawr. At year's end he becameAssistint
State Paleontologist,a position he held until
-Donald L. Wolberg