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surfacechannels where, upon cooling, gypsum 0riginof gypsumdeposits in precipitated. The gypsumof CarlsbadCaverns must have beenderived from a sulfideformed by micro- CarlsbadGaverns, New bial reductionof a .No other mechan- byDouglas W.Kirkland, MobilResearch and Development Corporation, Dallas, TX ism is known that could reasonablyaccount for the unusualisotopic signature of the mass of gypsumwithin the caverns.Microbial reac- Abstract which rep- data are reportedin termsof d3oS, tion leadsto enrichmentof -34in resid- Gypsum within the Big Room of Carlsbad Cav- resentsthe deviationof the S3o-td-S"ratio in ual sulfateand to depletion,commonly sub- greatly parts per (o/o.) value erns is depleted in sulfur-34. This fact thousand from the stantial, of sulfur-34 in diageneticsulfide precludes previously most hypothesized origins for 0.0450045,this value being the S34-to-Sil (Thodeand others, 1954;Jones and Starkey, the gypsum and indicates that microbial agents ratio (FeS) of sulfur in a standardtroilite in 1957). played a part in its origin. The gypsum apparently iron meteoritesfrom Canyon Diablo, Ari- resulted from reaction of carbonate with zona;the deltaconvention indicates that sam- TABLE l-Suuun rsoropE VALUESFoR cypsuM sAM- , which may have resulted from oxida- ples (positive values) or ples; sample localitiesare shown in fig. l. tion of in sandstoneand siltstone the Yates are enriched d3oS of (negative Formation (a mechanism proposed by depleted d'nS values) in sulfur-34 t'S o/o Jagnow, Samplenumber d o 1979).An alternate explanation is that ground water with respectto thestandard.l bearing hydrogen moved from the Castile Upper Permian marine from 1 -18.9 Formation into the phreatic zone of the cavern westTexas and from other areasof the world 2 -15.2 where the was oxidized to yield have d'nSvalues with a mode of about + I I 3 - 18.3 ground- elemental sulfur; with a lowering of the 7"" (Thode and Monster, 1965;Holser and 4 -19.3 water table, the sulfur, in turn, was oxidized to Kaplan,1966; Claypool and others,1980); the 5 -22.0 sulfuric acid within the vadosezone. range for Upper Permian marine evaporites o/o", 6 -15.0 Introduction worldwideis +9 7oo to + 13 n : 200 (Claypooland others,fig. 5). Thus, the sulfur The sourceof large quantitiesof gypsum Origin of gypsum isotopiccomposition of gypsumsamples from within Carlsbad Caverns and within Two hypothesizedorigins for the gypsum some the are markedly impoverishedin sul- othercaves of theGuadalupe Mountains Big Room is not fur-34as comparedto nearbybedded gypsum depositsof the of CarlsbadCaverns fully understood.Various origins have been units of Permianage (Tansill, Yates, Castile, are in accord with the sulfur isotopic data proposed(Bretz, (table 19491'Black, 1954; Good, and SaladoFormations). l). Both hypothesesinvolve reaction of 1957;Moore, 1960;Bullington, with 1968;Palmer A popular explanationfor the gypsumof sulfuric acid. Thls 1977; from either and others, Jagnow, 1979).Measure- the cavernshas beenthat it is derivedfrom acidapparently resulted oxidation ments of the sulfur isotopic composition pyrite (as proposedby Jagnow, 1979) of beddedmarine evaporitesnearby by dissolu- of or gypsumfrom Carlsbad indicate Caverns that tion, transportation, and reprecipitation from oxidationof elementalsulfur. mostof thesehypothesized origins are invalid. Formationgrades into (Bretz, 1949;Black, 1954;Bullington, 1968). The Yates and over- vicinity The sulfur isotopicdata presentedin table I lies the Capitan Limestonein the of The gypsummasses (Hayes, preclude this possibility. The data also CarlsbadCaverns 1964,fig.27). Mi- Severalchambers within pyrite CarlsbadCaverns precludeGood's (1957)proposal that warm croscopicand disseminatedcrystals of contain gypsum; the greatestvolume pyrite occurs water within a shallow, calcium-sulfate- and large concretionsof occur within within the Big Room. In thischamber, Within tabular saturatedlake enteredthe cavethrough sub- theYates and siltstone. 3 km bodies of unstratifiedgypsum, 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 goethitepseudo- and with diametersranging from 2.5 cm to 30 morphsafter pyrite (Hayes,1964, p. 35). The cm, have formed by dripping water; some pyrite of the Yates, like most sedimentary largeblocks have lost more than 5090of their pyrite, probably resultedfrom diageneticreac- bulk by this action (Bretz, 1949).Those gyp- tions involving sulfate-reducing bacteria; sum blocksthat remainin the room usuallylie hencethe sulfur-34concentration of the pyrite in protectedalcoves or underoverhanging ceil- shouldbe impoverishedas comparedto Per- ings (Black, 1954),and locally the blocksare mianmarine gypsum and shouldbe of approx- I covered by flowstone and by stalagmites I imately the samemagnitude as the sulfur-34 (Bretz,1949; Good, 1957). ( concentrationof the gypsumdeposit of Carls- The gypsum massesof CarlsbadCaverns 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 CapitanLimestone would -with someblocks of gypsumdisplaying pet- result in gypsum,some of which might have rographicfeatures of the carbonatessuch as accumulatedwithin CarlsbadCaverns. A sim- pisolites,fossils, breccias, and primary pores. ilar origin has beenproposed for sulfate min- Jagnow(1979, p. 45), on the other hand, re- .aA erals within cavesof central Kentucky (Pohl ports that the gypsumaccumulated during a and , 1965). period of thousandsof yearsby precipitation Another origin for sulfuric acid is oxidation and sedimentationwithin pondedwaters. of elementalsulfur, a reaction that may have played a part in the formation of the gypsum Sulfur isotopicdata depositsof CarlsbadCaverns. Six samplesof gypsumwere obtained (with In Late Tertiaryand Holocenetimes, a mi- permission)from the Big Room (fig. l). The crobially aided reaction between hydrocar- -18.1 sampleshave an averaged"S value of FIGURE l-SnNlpr-e LocALtrrESln Brc Roov or bons and resulted in the partsper thousand( o/oo) and a rangeof - I 5.0 generation of great quantities of hydrogen o/oo Cnnlssnp CnvEnx$ dashedline is trail (after map to -22.0 "/"" (table l.) [Sulfur isotopic byJagnow,1979). sulfide within ground waters of the Castile

May 1982 Geology .-, 1980, Sulfur deposits in Ochoan rocks of the Gyp- (Davis 1970; Hinds Holser, W. T., and Kaplan, I. R , 1966, Isotope geochem- Formation and Kirkland, Plain, southeastern New Mexico and west : istry of sedimentary : Chemical Geology, v' I' p' sum 1970; Smith, 1978, 1980)' Guidebook 3lst field and Cunningham, 93-r 35 New Mexico Geological Society, 271-283 Hydrogen-sulfide-rich ground waters may Jagnow, D. H., 1979, Cavern development in the Guada- conference,P Wanless, R. K., and Wallouch, R ' 1954' have moved through breccia zones within the lupe Mountains: Albuquerque, Adobe Press (publication Thode, H. G., of native sulfur deposits from fractionation of Cave ResearchFoundation), 55 P The origin Castile (Anderson and others, 1972;Anderson et Cosmochimica Acta, v. 5' p. 286- G. 8., and Starkey, R. L., 1957, Fractionation of studies:Geochimica others, 1978), through fractures, and Jones, and stable isotopes of sulfur by microorganisms and their 298 and Monster, Jan, 1965, Sulfur-isotope geo- through solution channels for distances of role in deposition of native sulfur: Applied Microbiol- Thode, H. G., petroleum, evaporites, and ancient seas: several kilometers or more into the Capitan ogy,v.5,p.lll-ll8 chemistry of American Association of Petroleum Geologists, Mem' 4, Limestone, a major aquifer (Motts, 1968; Lindgren, Waldemar, 1933, deposits: New York, o Book ComPanY, 930 D-501-Jll Hiss, 1975),and henceinto a cavern system of McGraw-Hill P. Moore, G. W., 1960, Geology of Carlsbad Caverns, New were a part. which the early Carlsbad Caverns Mexico: National Speleological Society, Guidebook for Newbook on PorPhYrY Oxidation of hydrogen sulfide within the the 1960Convention, p. l0-17 phreatic zone of the caverns would result in Motts. W S., 1968, The control of ground-water occur- depositsPublished reef complex near and in accumulation of rence by lithofacies in the Guadalupian The University of Arizona Press recently an- precipitation of sulfur Mexico: Geological Society of America, Carlsbad, New nouncedpublication of a 580-pagebook Advances sulfur within the cave. With a decrease in Bull.,v.70, p. 1,737 geology oJ the porphyry copper deposits-soulh' elevation of the ground-water table, the ac- Palmer. A. N., Palmer, M. V., and Queen, J Nd'' 1977' in New Mexico westernNorth America, editedby SpencerR' Titley. cumulation of sulfur would be exposed to Speleogenesisin the Guadalupe Mountains, -gypsum replacement of carbonate by mixing: The cloth-boundbook, which sellsfor $35.fi)' pre- moist, oxidizing conditions. Oxygen, sulfur, Shelfield, International SpeleologicalCongress, Proc., p' sents findings of lecent geologic studies.Part one the bacterium and vadose water, aided by 333-336 containsinterpretations of manyaspects of oregen- Thiobacillus sp., would react to form sulfuric Pohl. E. R.. and White, W B., 1965, Sulfate - esisbased on field and laboratory studiesin accord- American acid. Transported into the phreatic zone by their origin in the central Kentucky : with advancesmade from 1960to 1980'while p. 1,461-l,465 ance this acid would dif- Mineralogist,v. 50, no. 9, part specificdeposits in detail. The descendingvadose waters, 1978, Sulfur deposits in Ochoan rocks of two describes Smith. A. R., the University of Arizona fuse and would react with the limestone wall southeasternNew Mexico and west Texas: New Mexico book is available from p' AZ 85722. rock to form gypsum. Bureau of Mines and Mineral Resources, Circ 159' Press,Box 3698,Tucson, Becauseof their elevation and their distance 7t-77 from the reef front, movement of hydrogen- sulfide-bearing waters into other of the Guadalupe Mountains in which gypsum has accumulated may be hydrodynamically im- probable. If so, Jagnow's (1979) explanation for the gypsum deposits of Carlsbad Caverns should receive additional support. Conceiv- ably, 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 unestab- lished. would be late.

References Anderson,R. Y., Dean,W. E., Kirkland,D. W , and Snider. H. I., 1972, Permian Castile varved se- R, Osbun quence, west Texas and New Mexico: Geological Society Phoro by Glenn ofAmerica, Bull., v.83, P 59-86 45 degreesdownward to the left from the Anderson.R. Y., Kietzke,K. K., and Rhodes,D. J ,1918' Socorro Peak, a well known landmark in central diagonally margins often form Development of dissolution breccias, northern Delaware New Mexico, is complex and interesting geologic- "M." Cauldron topographic unconformities. Basin, New Mexico and Texas: New Mexico Bureau of ally. The mountain block is uplifted along normal very large and abrupt erosional - Mines and Mineral Resources,Cir c. 159, p. 47 52 faults that separatethe low piedmont surfacesin the South of this unconformity, the cauldron-related of the ft thick' Black, T H., 1954, The origin and development foreground from the steep slopes of the mountain. rocks are thought to be more than 6,000 New Mexico Geological Society, Carlsbad Caverns: The most prominent features on the mountain are whereas they are only 800 ft thick above the Paleo- Guidebook 5th field conference,p. 136-142 Miocene-age rhyolite domes and flows that cap zoic rocks on Socorro Peak. Here, these rocks form Bretz, J. H., 1949, Carlsbad Caverns and other cavesof the northern ridge ending in the gentle slope and lower cliff between the bedded Guadalupe Block, New Mexico: Journal of Geology, v "M" Mountain and the (the pointed Paleozoic rocks and the big cliffs of well-indurated 57 p. 441 -463 steep cliffs, and form Strawberry Peak , rocks pinch out Bullington, N R., I968, Geology of the Carlsbad Caverns, hill at the right edgeof the photograph). Also promi- fanglomerates.The cauldron-related A detailed de- irl exploration: West Texas Geological nent are very well indurated Miocene alluvial fan within a short distance to the north. geology Socorro Society, Guidebook, p 20-23 and mudflow deposits that form the large vertically scription of the volcanic of the R., Sakai, Hi- Chamberlin Claypool, G. E'., Holser, W. T , Kaplan, I. striated cliffs just below the "M." Pennsylvanian Peak area has been presentedby R. M. toshi, and Zak, Israel, 1980, The age curves of sulfur Re- sedimentaryrocks of the Sandia and Madera Forma- in New Mexico Bureau of Mines and Mineral and oxygen isotopes in marine sulfate and their crop out further down the slope around the sources Open-file Rept. ll8 and in New Mexico mutual interpretation: Chemical Geology, v 28, p. tions nature Ceology, May 1981,v. 3, no.2. Severalmines pro- t99-260 prominent white area. Note the well-bedded veins in a fault block of Miocene Davis, J. B and Kirkland, D. W , l9?0, Native sulfur de- of theseoutcrops. Thesesedimentary rocks are trun- duced silver from mines position in the , Culberson County, cated on the south by the northeast topographic rhyolitic rocks during the late 1800's. These Texas: Economic Geology, v. 65, p 107-l2l margin of the Oligocene-ageSocorro cauldron (an were located in the small dark rounded hill above Good, J. M., 195?, Noncarbonate deposits of Carlsbad ash-flow cauldron similar to the young Valles caul- and to the left of the large white water tank. Speleological Society, Bull., v. 19, p. Caverns: National dron in northern New Mexico). This topographic -Glenn R. Osburn |-23 margin lies approximately in the gully that trends Hayes,P. T., 1964,Geology of theGuadalupe Mountains, GeologicalSurvey, Prof. Paper446, New Mexico:U.S. TO OUR READERS 69p. AN INVITATION Hinds, J. S., and Cunningham,R. R., 1970,Elemental With the photo and accompanyingdescription above, we woutdlike to inviteour readersto submittheir sulfur in Eddy County, New Mexico: U.S' Geological own work ro the Gsllery of Ctology, excellint quality black-and-whitephotographs of a geologicfeature or Survey,Circ.628, l3 p. geololic description(l-1Vz pagesin length)should be submittedto Marla D. ground-waterhydrol- areaand an accompanying Hiss, W. L , 1975,Stratigraphy and Giology, New Mexico Bureau of Mines and Mineral Resources, aquifer, southeasternNew Mexico Adkins-Heljeson,Editor, iew tlexico ogy of the Capitan wide selectionof photographsof New Mexico'sscenic and westernTexas: Ph.D thesis,University of Colorado Socorro.NM E7E0l.We look forward to seeinga (Boulder),396 p. geology.

New Mexico GeologY May 1982 2l