in
0riginofgypsum
deposits
Carlsbad
NewMexico
Gaverns,
surfacechannelswhere,uponcooling,gypsum
precipitated.
The gypsumof CarlsbadCavernsmusthave
beenderivedfrom a sulfideformed by microbial reductionof a sulfate.No other mechanism is known that could reasonablyaccount
byDouglas W. Kirkland, MobilResearch
TX
Dallas,
andDevelopment
Corporation,
for the unusualisotopicsignatureof the mass
of gypsumwithin the caverns.Microbial reacAbstract
which repdata are reportedin termsof d3oS,
tion leadsto enrichmentof sulfur-34in residresentsthe deviationof the S3o-td-S"ratio in
Gypsum within the Big Room of Carlsbad Cavual sulfate and to depletion,commonly subparts per thousand (o/o.) from the value
erns is greatly depleted in sulfur-34. This fact
stantial, of sulfur-34 in diageneticsulfide
precludes most previously hypothesized origins for
0.0450045,this value being the S34-to-Sil (Thodeand others, 1954;Jonesand Starkey,
the gypsum and indicates that microbial agents ratio of sulfur in a standardtroilite (FeS)in
1957).
played a part in its origin. The gypsum apparently
iron meteoritesfrom Canyon Diablo, Ariresulted from reaction of calcium carbonate with
zona; the deltaconventionindicatesthat sam- TABLE l-Suuun rsoropE VALUES
FoRcypsuM sAMsulfuric acid, which may have resulted from oxidaples; sample localities are shown in fig. l.
ples are enriched (positive d3oSvalues) or
tion of pyrite in sandstoneand siltstone of the Yates
depleted(negatived'nS values) in sulfur-34
o/o
Formation (a mechanism proposed by Jagnow,
d t'S
o
Samplenumber
with respectto the standard.l
1979). An alternate explanation is that ground water
1
8
.
9
1
Upper Permian marine evaporites from
bearing hydrogen sulfide moved from the Castile
-15.2
Formation into the phreatic zone of the cavern
westTexasand from other areasof the world
2
where the hydrogen sulfide was oxidized to yield
- 18.3
have d'nSvalueswith a mode of about + I I
3
elemental sulfur; with a lowering of the ground7"" (Thode and Monster, 1965;Holser and
-19.3
4
water table, the sulfur, in turn, was oxidized to
Kaplan, 1966;Claypooland others,1980);the
-22.0
5
sulfuric acid within the vadose zone.
range for Upper Permian marine evaporites
-15.0
6
worldwideis +9 7oo to + 13 o/o", n : 200
Introduction
(Claypooland others,fig. 5). Thus, the sulfur
Origin of gypsum
The sourceof large quantitiesof gypsum
isotopiccompositionof gypsumsamplesfrom
within Carlsbad Caverns and within some
Two
hypothesized
origins for the gypsum
the cave are markedly impoverishedin sulothercavesof the GuadalupeMountainsis not
Big
Room
deposits
of
the
of CarlsbadCaverns
fur-34as comparedto nearbybeddedgypsum
fully understood.Various origins have been units of Permian
age (Tansill, Yates,Castile, are in accord with the sulfur isotopic data
proposed(Bretz, 19491'Black, 1954; Good,
(table l). Both hypotheses
involvereactionof
and SaladoFormations).
1957;Moore, 1960;Bullington,1968;Palmer
calcium carbonate with sulfuric acid. Thls
A popular explanationfor the gypsumof
and others, 1977; Jagnow, 1979).Measure- the cavernshas beenthat it is derivedfrom
acid apparentlyresultedfrom eitheroxidation
pyrite (as proposedby Jagnow, 1979)or
ments of the sulfur isotopic compositionof bedded
marine evaporitesnearbyby dissolu- of
gypsumfrom CarlsbadCavernsindicatethat
from
oxidationof elementalsulfur.
tion, transportation, and reprecipitation
mostof thesehypothesized
originsareinvalid. (Bretz, 1949;Black,
The YatesFormationgradesinto and over1954;Bullington, 1968).
lies the Capitan Limestonein the vicinity of
The sulfur isotopicdata presentedin table I
The gypsummasses
preclude this possibility. The data also CarlsbadCaverns(Hayes,1964,fig.27). MiSeveralchamberswithin CarlsbadCaverns preclude
crystalsof pyrite
Good's (1957)proposal that warm croscopicand disseminated
pyrite occur within
contain gypsum; the greatestvolume occurs water within
a shallow, calcium-sulfate- and large concretionsof
within the Big Room. In this chamber,tabular
and siltstone.Within 3 km
saturatedlake enteredthe cavethrough sub- the Yatessandstone
bodies of unstratified gypsum, up to l0 m
of the Capitan Limestone,the siltstoneand
thick, are sporadically distributed (Cood,
sandstonebeds of the Yates locally contain
1957). Within the gypsum blocks, vertical
numerousnodules,up to approximately5 cm
tubes, some with lengthsin excessof 3.7 m
in diameter,of limonite or goethitepseudoand with diametersrangingfrom 2.5 cm to 30
morphsafter pyrite (Hayes,1964,p. 35). The
pyrite of the Yates, like most sedimentary
cm, have formed by dripping water; some
pyrite, probably resultedfrom diageneticreaclargeblockshavelost more than 5090of their
bulk by this action (Bretz, 1949).Those gyptions involving sulfate-reducing bacteria;
sum blocksthat remainin the room usuallylie
hencethe sulfur-34concentrationof the pyrite
in protectedalcovesor underoverhangingceilshould be impoverishedas comparedto Perings (Black, 1954),and locally the blocksare
mian marinegypsumand shouldbe of approxI
covered by flowstone and by stalagmites
imately the samemagnitudeas the sulfur-34
I
(Bretz,1949;Good, 1957).
(
concentrationof the gypsumdepositof CarlsThe gypsum massesof Carlsbad Caverns
bad Caverns(table l). Oxidationof the pyrite
are thoughtby Palmerand others(1977)to be
would generatesulfuric acid (Lindgren, 1933,
direct replacementof limestone-the Capitan
p. 60 and p. 829)and, subsequently,
reaction
Limestoneof LatePermian(Guadalupian)age
of the acid with the CapitanLimestonewould
-with someblocksof gypsumdisplayingpetresult in gypsum,someof which might have
rographicfeaturesof the carbonatessuch as
accumulatedwithin CarlsbadCaverns.A simpisolites,fossils,breccias,and primary pores.
ilar origin has beenproposedfor sulfate minJagnow(1979,p. 45), on the other hand, reerals within cavesof central Kentucky (Pohl
.aA
ports that the gypsumaccumulatedduring a
and white, 1965).
period of thousandsof yearsby precipitation
Another origin for sulfuric acid is oxidation
and sedimentation
within pondedwaters.
of elementalsulfur, a reaction that may have
played a part in the formation of the gypsum
Sulfur isotopicdata
depositsof CarlsbadCaverns.
Six samplesof gypsumwereobtained(with
In Late Tertiary and Holocenetimes,a mipermission)from the Big Room (fig. l). The
crobially aided reaction between hydrocarsampleshave an averaged"S value of -18.1 FIGURE l-SnNlpr-e LocALtrrESln Brc Roov or
bons and calcium sulfate resulted in the
partsper thousand( o/oo) and a rangeof - I 5.0
generation of great quantities of hydrogen
Cnnlssnp CnvEnx$ dashedline is trail (after map
o/ooto -22.0
"/"" (table l.) [Sulfur isotopic
byJagnow,1979).
sulfide within ground waters of the Castile
May 1982
New Mexico Geology
Formation (Davis and Kirkland, 1970; Hinds
and Cunningham, 1970; Smith, 1978, 1980)'
Hydrogen-sulfide-rich ground waters may
have moved through breccia zones within the
Castile (Anderson and others, 1972; Anderson
and others, 1978), through fractures, and
through solution channels for distances of
several kilometers or more into the Capitan
Limestone, a major aquifer (Motts, 1968;
Hiss, 1975), and hence into a cavern system of
which the early Carlsbad Caverns were a part.
Oxidation of hydrogen sulfide within the
phreatic zone of the caverns would result in
precipitation of sulfur and in accumulation of
sulfur within the cave. With a decrease in
elevation of the ground-water table, the accumulation of sulfur would be exposed to
moist, oxidizing conditions. Oxygen, sulfur,
and vadose water, aided by the bacterium
Thiobacillus sp., would react to form sulfuric
acid. Transported into the phreatic zone by
descendingvadose waters, this acid would diffuse and would react with the limestone wall
rock to form gypsum.
Becauseof their elevation and their distance
from the reef front, movement of hydrogensulfide-bearing waters into other caves of the
Guadalupe Mountains in which gypsum has
accumulated may be hydrodynamically improbable. If so, Jagnow's (1979) explanation
for the gypsum deposits of Carlsbad Caverns
should receive additional support. Conceivably, pyrite within sandstone and siltstone of
the Yates originated during the hypothesized
influx of hydrogen-sulfide-bearing waters
from the Castile into the cavern systemsof the
Guadalupe Mountains. If this were true, the
diagenetic age of the pyrite, which is unestablished. would be late.
Holser, W. T., and Kaplan, I. R , 1966, Isotope geochemistry of sedimentary sulfates: Chemical Geology, v' I' p'
93-r35
Jagnow, D. H., 1979, Cavern development in the Guadalupe Mountains: Albuquerque, Adobe Press (publication
of Cave ResearchFoundation), 55 P
Jones, G. 8., and Starkey, R. L., 1957, Fractionation of
stable isotopes of sulfur by microorganisms and their
role in deposition of native sulfur: Applied Microbiolo g y , v . 5 , p .l l l - l l 8
Lindgren, Waldemar, 1933, Mineral deposits: New York,
McGraw-Hill Book ComPanY, 930 P.
Moore, G. W., 1960, Geology of Carlsbad Caverns, New
Mexico: National Speleological Society, Guidebook for
the 1960Convention, p. l0-17
Motts. W S., 1968, The control of ground-water occurrence by lithofacies in the Guadalupian reef complex near
Carlsbad, New Mexico: Geological Society of America,
B u l l . ,v . 7 0 , p . 1 , 7 3 7
Palmer. A. N., Palmer, M. V., and Queen, J Nd'' 1977'
Speleogenesisin the Guadalupe Mountains, New Mexico
-gypsum replacement of carbonate by brine mixing:
Shelfield, International SpeleologicalCongress, Proc., p'
333-336
Pohl. E. R.. and White, W B., 1965, Sulfate mineralstheir origin in the central Kentucky karst: American
M i n e r a l o g i s t ,v . 5 0 , n o . 9 , p . 1 , 4 6 1 - l , 4 6 5
Smith. A. R., 1978, Sulfur deposits in Ochoan rocks of
southeastern New Mexico and west Texas: New Mexico
Bureau of Mines and Mineral Resources, Circ 159' p'
7t-77
.-,
1980, Sulfur deposits in Ochoan rocks of the Gypsum Plain, southeastern New Mexico and west Texas:
New Mexico Geological Society, Guidebook 3lst field
conference, P 271-283
Thode, H. G., Wanless, R. K., and Wallouch, R ' 1954'
The origin of native sulfur deposits from fractionation
studies: Geochimica et Cosmochimica Acta, v. 5' p. 286298
Thode, H. G., and Monster, Jan, 1965, Sulfur-isotope geochemistry of petroleum, evaporites, and ancient seas:
American Association of Petroleum Geologists, Mem' 4,
o
D-501-Jll
copper
NewbookonPorPhYrY
deposits
Published
The University of Arizona Press recently announcedpublication of a 580-pagebook Advances
in geology oJ the porphyry copper deposits-soulh'
westernNorth America, editedby SpencerR' Titley.
The cloth-boundbook, which sellsfor $35.fi)' presents findings of lecent geologic studies.Part one
of ore genof manyaspects
containsinterpretations
esisbasedon field and laboratory studiesin accordmadefrom 1960to 1980'while
ancewith advances
part two describesspecificdepositsin detail. The
book is available from the University of Arizona
Press,Box 3698,Tucson,AZ 85722.
References
D. W , and
R. Y., Dean,W. E., Kirkland,
Anderson,
Snider. H. I., 1972, Permian Castile varved evaporite sequence, west Texas and New Mexico: Geological Society
ofAmerica, Bull., v.83, P 59-86
A n d e r s o n . R . Y . , K i e t z k e , K . K . , a n d R h o d e s ,D . J , 1 9 1 8 '
Development of dissolution breccias, northern Delaware
Basin, New Mexico and Texas: New Mexico Bureau of
Mines and Mineral Resources,Cir c. 159, p. 47- 52
Black, T H., 1954, The origin and development of the
Carlsbad Caverns: New Mexico Geological Society,
Guidebook 5th field conference, p. 136-142
Bretz, J. H., 1949, Carlsbad Caverns and other cavesof the
Guadalupe Block, New Mexico: Journal of Geology, v
57 , p. 441 -463
Bullington, N R., I968, Geology of the Carlsbad Caverns,
irl Delaware Basin exploration: West Texas Geological
Society, Guidebook, p 20-23
Claypool, G. E'., Holser, W. T , Kaplan, I. R., Sakai, Hitoshi, and Zak, Israel, 1980, The age curves of sulfur
and oxygen isotopes in marine sulfate and their
mutual interpretation: Chemical Geology, v 28, p.
t99-260
Davis, J. B and Kirkland, D. W , l9?0, Native sulfur deposition in the Castile Formation, Culberson County,
Texas: Economic Geology, v. 65, p 107-l2l
Good, J. M., 195?, Noncarbonate deposits of Carlsbad
Caverns: National Speleological Society, Bull., v. 19, p.
|-23
Hayes,P. T., 1964,Geologyof the GuadalupeMountains,
New Mexico:U.S. GeologicalSurvey,Prof. Paper446,
69 p.
Hinds, J. S., and Cunningham,R. R., 1970,Elemental
sulfur in Eddy County, New Mexico: U.S' Geological
S u r v e yC, i r c . 6 2 8 l,3 p .
hydrolHiss, W. L , 1975,Stratigraphyand ground-water
New Mexico
ogy of the Capitan aquifer, southeastern
and westernTexas:Ph.D thesis,Universityof Colorado
(Boulder),396p.
Phoro by Glenn R, Osbun
Socorro Peak, a well known landmark in central
New Mexico, is complex and interesting geologically. The mountain block is uplifted along normal
faults that separatethe low piedmont surfacesin the
foreground from the steep slopes of the mountain.
The most prominent features on the mountain are
Miocene-age rhyolite domes and flows that cap
"M" Mountain and the northern ridge ending in
steep cliffs, and form Strawberry Peak (the pointed
hill at the right edge of the photograph). Also prominent are very well indurated Miocene alluvial fan
and mudflow deposits that form the large vertically
striated cliffs just below the "M." Pennsylvanian
sedimentaryrocks of the Sandia and Madera Formations crop out further down the slope around the
prominent white area. Note the well-bedded nature
of theseoutcrops. These sedimentary rocks are truncated on the south by the northeast topographic
margin of the Oligocene-ageSocorro cauldron (an
ash-flow cauldron similar to the young Valles cauldron in northern New Mexico). This topographic
margin lies approximately in the gully that trends
diagonally 45 degreesdownward to the left from the
"M." Cauldron topographic margins often form
very large and abrupt erosional unconformities.
South of this unconformity, the cauldron-related
rocks are thought to be more than 6,000 ft thick'
whereas they are only 800 ft thick above the Paleozoic rocks on Socorro Peak. Here, these rocks form
the gentle slope and lower cliff between the bedded
Paleozoic rocks and the big cliffs of well-indurated
fanglomerates.The cauldron-related rocks pinch out
within a short distance to the north. A detailed description of the volcanic geology of the Socorro
Peak area has been presentedby R. M. Chamberlin
in New Mexico Bureau of Mines and Mineral Resources Open-file Rept. ll8 and in New Mexico
C e o l o g y , M a y 1 9 8 1 ,v . 3 , n o . 2 . S e v e r a lm i n e s p r o duced silver from veins in a fault block of Miocene
rhyolitic rocks during the late 1800's. These mines
were located in the small dark rounded hill above
and to the left of the large white water tank.
-Glenn R. Osburn
AN INVITATION TO OUR READERS
descriptionabove,we woutd like to invite our readersto submittheir
With the photo and accompanying
own work ro the Gsllery of Ctology, excellint quality black-and-whitephotographsof a geologicfeatureor
geololic description(l-1Vz pagesin length)shouldbe submittedto Marla D.
areaand an accompanying
Adkins-Heljeson,Editor, iew tlexico Giology, New Mexico Bureau of Mines and Mineral Resources,
Socorro.NM E7E0l.We look forward to seeinga wide selectionof photographsof New Mexico'sscenic
geology.
New Mexico GeologY
May 1982
2l