Clays and Clay Minerals. Vol. 48, No. 6, 693-698, 2000.

DETRITAL ORIGIN OF A S E D I M E N T A R Y FILL, L E C H U G U I L L A CAVE, G U A D A L U P E M O U N T A I N S , N E W MEXICO

ANNABELLE M. FOOS, l IRA D. SASOWSKY, 1 EDWARD J. LAROCK, 2 AND PATRICIAN. KAMBESIS 3

~Department of Geology, University of Akron, Akron, Ohio 44325-4101, USA 24148 E. 19th Ave., Denver, Colorado 80220, USA

3Cave Research Foundation, RR 1, Rutland, Illinois 61358-9801, USA

Abstraet--Lechuguil la Cave is a hypogene cave formed by oxidation of ascending hydrogen sulfide from the Delaware Basin. A unique sediment deposit with characteristics suggesting derivation from the land surface, some 285 m above, was investigated. At this location, the observed stratigraphy (oldest to youn- gest) was: bedrock floor (limestone), cave clouds (secondary calcite), calcite-cemented silstone, finely laminated clay, and calcite rafts. Grain-size analysis indicates that the laminated clay deposits are com- posed of 59-82% clay-size minerals. The major minerals of the clay were determined by X-ray diffraction analysis and consist of interstratified illite-smectite, kaolinite, iilite, goethite, and quartz. Scanning electron microscopy observations show that most of the clay deposit is composed of densely packed irregular- shaped clay-size flakes. One sample from the top of the deposit was detrital, containing well-rounded, silt-size particles.

Surface soils are probably the source of the clay minerals. The small amount of sand- and silt-size particles suggests that detrital particles were transported in suspension. The lack of endellite and alunite is evidence that the clays were emplaced after the sulfuric-acid dissolution stage of cave formation. Fossil evidence also suggests a previously existing link to the surface.

Key Words---Caves, Cave Sediments, Lechuguilla Cave.

I N T R O D U C T I O N

Lechugu i l l a Cave , wh ich is located in Car l sbad Cave rns Nat iona l Park, sou theas te rn N ew Mex ico (Figure 1), is the fifth longes t cave in the wor ld and the deepes t k n o w n cave in Nor th Amer ica , wi th a m a p p e d leng th o f ove r 160 km, and a vert ical range of 475 m. Since its d iscovery , Lechugu i l l a Cave has b e e n the focus o f n u m e r o u s geologic and b io logic studies, as wel l as ongo ing explorat ion. The cave is pe rhaps bes t k n o w n for its mine ra l decorat ions , such as the meter -s ize g y p s u m crys ta ls referred to as " g y p - sum chande l i e r s " .

Lechugu i l l a Cave is s i tuated on the wes te rn marg in of the P e r m i a n Basin , southeas t N ew Mexico , at the eas tern edge o f the Guada lupe Mounta ins . The area has a semiar id c l imate wi th an annua l prec ip i ta t ion of 36 c m (Pa lmer et al . , 1991). T he cave occurs mos t ly wi th in the Pe rmian Cap i t an Format ion , of the Capi tan R e e f Complex . The e leva t ion o f the cave en t rance is 1414 m above m e a n sea level (amsl) . The water table occurs at 955 m (Pa lmer e t al . , 1991), and the cave is p redominan t ly dry, wi th mos t wate r found in lower levels. The cave is o f h y p o g e n e origin, fo rmed by the mix ing of descend ing oxygen- r i ch meteor ic ground- waters , wi th ascending, sulfur-r ich bas ina l waters (Pa lmer et al . , 1991). Apparen t ly numerous phrea t ic ep isodes occurred. Po lyak e t al . (1998) de t e rmined the t iming of spe leogenes is at the 1230- and 1180-m ele- va t ions to be 5.7 and 5.2 Ma, respect ively.

In general , caves are impac ted by surface s t reams and deve lop by ep igene (surface-re la ted) processes . In

contrast , hypogene caves rarely show signif icant ef- fects of surface waters unless e ros ion exposes the cave to a l low surficial ly der ived sed iments to enter the cave. In Lechugui l la , as in all of the h y p o g e n e caves of the Guada lupe Mounta ins , large ( > 1 m) connec - t ions to the surface are r a n d o m and not re la ted to spe- cific recharge points such as s inkholes . Un l ike o ther Guada lup ian caves, Lechugu i l l a has no t b e e n exten- s ively i nvaded by seepage water. A la teral ly extens ive , s i l ts tone caprock has p robab ly d iver ted wa te r away f rom the cave ( C u n n i n g h a m and Takahashi , 1992). Le- chugui l la is cons idered a pr is t ine cave sys tem wi th l imi ted input of a l loch thonous mater ia l ( C u n n i n g h a m e t al . , 1995)

A deposi t wi th in Lechugu i l l a Cave occurs wi th character is t ics typical of clastic, su r face-der ived sedi- ment . Severa l opt ions exis t for the source of this ma- terial: 1) The sed imen t was t ranspor ted in to the cave f rom a surface source; 2) d isso lu t ion o f l imes tone dur- ing spe leogenes is resul ted in l ibera t ion of t race con- st i tuents and accumula t ion of inso luble res idue; 3) the minera l s fo rmed dur ing speleogenes is by d iagenet ic reac t ion of exis t ing c lays wi th sulfuric g roundwate r ; or 4) the minera l s fo rmed by mic rob io log ic a l tera t ion of bed rock or o ther mater ials . To inves t iga te this ma- terial, we cons idered the texture by size analys is and clay fabric, and mine ra logy by X- ray diffract ion. We also inves t iga ted the deposi t in con tex t wi th the sur- round ing cave and wi th surficial features.

M E T H O D S

Twenty, 8 -cm a size samples were collected. The rel- a t ive amoun t s of sand, silt, and clay were d e t e r m i n e d

Copyright �9 2000, The Clay Minerals Society 693

694 Foos, Sasowsky, LaRock, and Kambesis Clays and Clay Minerals

Figure 1. Location of Lechuguilla Cave.

by cent r i fuge and s ieve analysis . Bu lk and clay min- e ra logy were de t e rmined wi th X- ray di f f ract ion (XRD) us ing CuKct rad ia t ion at 40 k V and 35 mA. The sam- ples were suspended in dist i l led water and the <2-1xm f rac t ion was separated, filtered, and t ransfer red onto a glass sl ide (Foos and Quick, 1988). Samples were air- dried, t reated wi th e thy lene-g lyco l vapor, sa turated wi th K +, and hea ted to 100, 300, 400, and 550~ The texture of the l amina ted clay deposi ts was obse rved by scann ing e lec t ron mic roscope (SEM).

R E S U L T S

Sample sites

The deposi ts are located in the southern par t of the cave in an area cal led De l ive rance Passage. The sam- ples were co l lec ted f rom the Ain t ry Room, located 2 k m into the cave at an e leva t ion of 1115 m amsl and 299 m be low the entrance. The land surface e leva t ion is - -1400 m ams l above the site, ind ica t ing 285 m of overburden .

The A i n t r y R o o m is up to 30 m wide and 7 m high. The cave walls cons is t of bed rock and secondary cal-

ci te coat ings. The floor is covered wi th thin, loose flakes of calci te ( "ca lc i t e r a f t s " ) that fo rmed w h e n the r o o m was part ial ly submerged . Rafts are fo rmed w h e n calci te c rys ta l l ized on pool surfaces as th in sheets, wh ich then sank to the b o t t o m of the pool w h e n they b e c a m e too heavy to float.

Sampl ing site 1 (Table 1) was an excava ted t rench on the floor. Sampl ing site 2 (Table 2) was a she l f --1 m above the floor, a t tached to the back and side walls of a smal l alcove, on the eas tern side of the room. At site 2, layers of l ight- and da rk -b rown l amina ted clays, capped by calci te rafts, occur on top of a she l f of l am- ina ted calcite-sil t . The exposure has a re la t ively fresh face, a l though it is unc lear w h y this is so. The th ick b a n d e d calci te-si l t ( layer 2K) shows a contac t rela- t ionsh ip wi th " c a v e c l o u d s " (mami l l a r i an structures) on the wal l at the south end of the shelf. Cave c louds are calci te coat ings that fo rm on walls or ce i l ings in subaqueous condi t ions . Depos i t ion of the calcif ied silt- s tone appears to post -date depos i t ion o f the cave clouds. The calci te-si l t is s imi lar to deposi ts descr ibed in Car l sbad Caverns (Hill, 1987) as calcif ied sil tstone. In Car l sbad Caverns , these deposi ts are over la in by calci te rafts, sugges t ing that the sequence is re la ted to regional shifts in wate r level wi th in the Guada lupe Mounta ins . The calci te s i l ts tone is c o m p o s e d of 80% calci te and 20% quartz silt. Hil l (1987) no ted that the s i l ts tone is found on up-fac ing surfaces, and at ele- va t ions b e t w een 1 1 1 5 - 1 1 5 0 m. The l l 1 5 - m value ma tches that of the deposi t in Lechugu i l l a Cave. The in te rbedded clay, calcite, and calci te rafts at site 2 (lay- ers 2J-2A) appear to represen t a semi -con t inuous de- posi t ional series charac ter ized by a l ternat ing clast ic sed imen t and calci te raf t fo rma t ion and deposi t ion.

Direc t cor re la t ion of the two sample sites is no t pos- sible. However , the uppe rmos t calc i te-raf t layer at site 2 (2A) is p robab ly roughly equiva len t wi th the top layer of rafts on the floor near site 2 and site 1 (1A). The th icker deposi t o f rafts at site 1 is cons i s ten t wi th the geomet ry of the room, and the effects of a decl in- ing water table. Likewise , the re la t ively th icker clay (and o ther raft) deposi ts at site 1 m a y reflect differ- ences in pos i t ion relat ive to the geomet ry of the room.

Table 1. Detailed description of site 1.

Thickness Unit (cm) Description

TOP 1A 7.7 1B 0.3 1C 74.4

1D 10.0 1E >25

BOTTOM

dusting of gray silty material calcite rafts gray clay massive to slightly laminated, dense, hard, medium-brown clay; with

"boxwork-like" calcite deposits that appeared to be infilling cracks within the clay (Samples IDS 293, 294, 295, 296, 297, 298, 299, 3OO)

extremely friable medium-brown clay (Samples IDS 301,302) weathered calcite rafts excavation became impractical; bedrock was not reached

Vol. 48. No. 6, 2000 695 Detrital origin of a sedimentary fill

Table 2. Detailed description of site 2.

Thickness Unit (cm) Description

TOP 2A 2.6 2B 1.3 2C 2.6 2D 0.3 2E 0.6 2F 0.3 2G 0.3 2H 0.3 21 10.3

2J 2.6 2K 20 to 51

92 BOTTOM

dusting of gray silty material loose calcite rafts (white and red) calcite layer red and silty calcite rafts white clay red rafts red cMcite rafts red/silty calcite white clay variably laminated, light to dark-brown, dry cracked

clay (Samples IDS 303, 304) punky clay/silt thick-banded calcite/silt air cave floor (rubble and rafts)

Grain-size analysis

The deposits are dominant ly composed of clay with minor amounts of fine sand and silt. These sediments (Table 3) contain an average of 9 wt. % sand, 21 wt. % silt, and 70 wt. % clay. The shelf deposit (site 2, IDS304) contained the greatest amount of clay (82 wt. %). The fine-grained nature of these deposits and small amount of sand-size particles suggest that the sediment was transported in suspension.

X-ray mineralogy

X R D analysis indicated that the samples consist of interstratified i l l i te-smecti te (I-S), kaolinite, illite, goe- thite, and quartz (Figures 2, 3, and 4). The swell ing clay (I-S) had a 0.142-nm reflection that increased to 0.170 nm after treatment with ethylene glycol, and col- lapsed to 0.100 nm after saturation with K + and heat- ing to 300~ The 00l reflections axe irrational indi- cating interstratifications. This clay was identified as i l l i te-smecti te with 3 0 - 4 0 % illite based on reflections at 0.552 and 0.88 nm (Moore and Reynolds, 1997). The d(060) of 0.1507 nm indicates the smectite com- ponent is dioctahedral and the I-S has a relat ively low concentrat ion of Mg and Fe. The occurrence of kao- linite was determined f rom basal reflections at 0.713 and 0.356 nm that were not affected by ethylene-gly- col t reatment or by heating to 400~ but these peaks disappeared after heating to 550~ Discrete illite was identified f rom the presence of periodic 00l reflections at 1.00, 0.50, and 0.33 nm, which did not change after

Table 3. Grain size analysis (wt. %).

Sand Silt Clay Sample # >50 Izm 50-2 ~m <2 ~m

IDS294 8 25 67 IDS298 11 30 59 IDS302 10 17 73 IDS304 8 10 82

treatment with ethylene glycol or heating to 550~ Characteristic peaks for goethite occurred at 0.418 and 0.269 nm. Quartz was observed in the bulk samples. The minerals alunite, hydrated halloysite (endellite), montmoril lonite , and palygorskite, which were ob- served in Lechugui l la by previous workers (DuChene, 1986; Cunningham et al., 1995; Polyak and Giiven, 1996), were not observed in these samples.

Scanning electron microscopy

SEM analysis indicates that the samples have the characteristics o f detrital sediment (Figure 5). Sample IDS 294, col lected at the top of a thick sequence of laminated clays, was clearly detrital, being composed of randomly oriented silt- and clay-size particles (Fig- ure 5a). Most of the finely laminated deposits axe clay- size material consisting o f densely packed irregular- shaped flakes with a random fabric. Random fabrics in clay deposits form either by bioturbation or depo- sition by flocculation (O 'Br ien and Slatt, 1990). Bio- turbation is unlikely in this setting. Thus, the clays

Q

"~ IS Q

. I K G K G K

IS illite-mlectite I illite K kaolinite G goethite Q quartz

, , i , , , , i , , ~ , u , , , , i , , , , i , , , , i , , , , i , , , , i , , , u

5 10 15 211 25 30 35 40 45 ~ CuKc~

Figure 2. Whole-rock XRD pattern of laminated clay de- posits from site 1 (IDS294) and site 2 (IDS304).

696 Foos, Sasowsky, LaRock, and Kambesis Clays and Clay Minerals

Figure 3.

1.70 nm IS

1.~ mn G

I

0.71 nm

I G K

ethylene glycol

~ K sat., 110 ~

j I illite K kaolinite

~ r 550 ~ G goelhite ' ' ' ' I , ' ' I ' ' ' t I ' ' ' ' I , t i , l ' ' ' r

5 10 15 20 25 30 35 ~ C u K ~

XRD patterns of oriented clay from site 1 (IDS294).

were deposited from suspension by flocculation. Floc- culation may have been promoted by the mixing of surface waters with standing water of a cave pool.

Dense structureless clay was the most common fea- ture observed (Figure 5c), The dense packing and lack of structure may be related to reorientation of the swelling illite-smectite that resulted from repeated wetting and drying. The lack of euhedral crystals and fine structures suggest the clay has undergone trans- port and was not precipitated in situ. Notably absent are tubular or rhombic structures, characteristic of hal- loysite or alunite. Minor post-depositional alteration of the deposits was observed. Rare detrital grains were replaced by iron hydroxides and a fibrous mineral, possibly illite. Fibrous material, similar to some of the features described by Cunningham et al. (1995) was also observed (Figure 5f). Cunningham et aL (1995) interpreted these features as representing bacterial or fungal filaments.

DISCUSSION AND CONCLUSIONS

Mixtures of clay, silt, and sand, and the SEM ob- servations indicate the sediments are detrital. How- ever, the sediments may have been transported to this site from elsewhere in the cave or accumulated from insoluble residue. The mineral assemblage (illite- smectite, kaolinite, illite, goethite, and quartz) is typ-

1.70 nm

V

\

V

V

/ 1.00 nm | l

[ - [ 0.71 run I|l I

5 10 15 20 25 30 35 ~ CuKc~

Figure 4. XRD patterns of ethylene-glycol treated, oriented- clay aggregates from sites 1 and 2.

ical of detrital sediments. The clay minerals probably did not accumulate as insoluble residue during cave formation or from condensation-corrosion residues, because the insoluble residue of the dolostone bedrock and condensation-corrosion residues are composed of illite and dickite (Polyak and (;riven, 2000). Surface soils are the most likely source of the clay minerals. The eolian-dust component of soils in the region is composed of kaolinite, illite, and smectite (Gile and Grossman, 1979). The illite-smectite may be formed by the pedogenic alteration of smectite in the surface soil horizons of arid regions (Allen and Hajek, 1989). Detrital cave-mud deposits have been observed in oth- er caves of the Guadalupe Mountains and their mineral assemblage (kaolinite, illite, and montmorillonite) is similar to this deposit in Lechuguilla (Polyak and Gti- ven, 2000). Because cave-authigenic clay minerals, in- cluding endellite, trioctahedral smectite, and palygor- skite were not observed in this deposit, and cave-form- ing sulfuric acid-bearing waters convert clay minerals to endellite and alunite (Polyak and Giiven, 1996) the clays were probably emplaced after the sulfuric-acid dissolution stage of cave formation.

Vol. 48, No. 6, 2000 Detrital origin of a sedimentary fill 697

Figure 5. SEM images of laminated clay deposits, a) Site 1, layer 1C, showing a random orientation of clay-size and well- rounded, silt-size particles (IDS294, scale bar = 10 p~m); b) site 2, layer 2I, showing a random orientation of clay-size particles and lack of silt-size material (IDS304, scale bar = 10 ~m); c) dense structureless sediment from site 1, layer 1C (IDS300; scale bar = 10 Ixm); d) an accumulation of iron hydroxides within the laminated clay from site 2, layer 21 (IDS304; scale bar = 10 ~xm); e) a detrital grain (possibly feldspar) replaced by a fibrous clay mineral (IDS298; scale bar = 2 I~m); f) either a fibrous clay mineral that was precipitated in s i tu or a bacterial/fungal filament (IDS300; scale bar = 5 ~m).

In add i t i on to t he s e d i m e n t cha rac te r i s t i c s , o t h e r da t a s u g g e s t a su r f ace sou rce fo r the c las t ic depos i t s f o u n d in the A i n t r y R o o m . Th i s po r t i on o f t he c a v e is ove r l a in b y Wa lnu t C a n y o n , s u g g e s t i n g d o w n w a r d wa-

ter s e e p a g e and t r anspo r t o f s e d i m e n t s f r o m the sur- face . H o w e v e r , the ve r t i ca l d i s t a n c e (280 m) is sub - s tant ia l . A p p a r e n t c las t i c d e p o s i t s o c c u r b e n e a t h sur- f ace c a n y o n s in o the r a reas in the cave . S u c h a reas

698 Foos, Sasowsky, LaRock, and Kambesis Clays and Clay Minerals

inc lude the Ove r the R a i n b o w sect ion at the end of the Wes te rn Borehole . In the Ou tback Area of the Fa r Eas te rn Maze , there is a subt le sheet o f mois ture wi th a th in venee r of sed imen t tha t is apparent ly be ing car- d e d d o w n a rift.

A semi-a r t i cu la ted ske le ton of a fossil r ingtai l cat (Bassar i scus as tutus) was found nea rby wi th in the cave ( C u n n i n g h a m and LaRock , 1991). A l though , the only en t rance to the cave is 2 k m f rom the site, this indi- cates tha t ano the r connec t ion to the surface was likely. I f not, the cat t raversed (in the dark) 2 k m and sur- v ived several ver t ical drops (--<50 m) to reach this por- t ion o f the cave via the present entrance. Ev idence of ano the r en t rance is suppor ted by radon levels (Cun- n i n g h a m and LaRock , 1991) that are cons is ten t ly low in a nea rby area o f the cave. Tempera ture and CO2 concen t ra t ions are 0.5~ and 0 .08% lower than cal- cula ted means for o ther parts of the Sou thwes t Branch of the cave, ind ica t ing f resh-ai r d i lu t ion nearby.

These resul ts sugges t a surface source for the lam- ina ted clay deposi ts . However , the data do not clearly p rove or d i sprove the ex is tence of a large-scale con- nec t ion wi th the surface dur ing the recent past. The bu lk of the mater ia l was p robab ly t ranspor ted in sus- pens ion by ground water. Connec t ions to the surface a l lowing the in t roduc t ion of clay- to si l t-size mater ia ls m a y be more p reva len t than p rev ious ly thought . The poss ib le in t roduc t ion o f organic mater ia l and o ther con t aminan t s to the microb io log ica l ecosys tem of Le- chugui l la Cave may indicate that the cave is not a c losed or pr is t ine system.

A C K N O W L E D G M E N T S

We thank Carlsbad Caverns National Park for allowing ac- cess to the cave and permission to collect samples, and for providing copies of materials in the park files. In particular, the help of D. Pate, H. Burgess, and E Deckert is appreciated. J. Kennedy, M. Jancin, and M. Behn provided essential help with the field work. The National Speleological Society Re- search Advisory Committee provided a grant to support the field work. The Buchtel College of Arts and Sciences, Uni- versity of Akron provided additional support. T. Georgiadis provided assistance with SEM. Reviews by R. Hay and V. Polyak resulted in significant improvements to the manu- script.

R E F E R E N C E S

Allen, B.L. and Hajek, B.H. (1989) Mineral occurrence in soil environments. In Minerals in Soil Environments, 2nd edition, J.B. Dixon and S.B. Weed, eds., Soil Science So- ciety of America, Madison Wisconsin, 199-278.

Cunningham, K.I. and LaRock, E.J. (1991) Recognition of microclimate zones through radon mapping, Lechuguilla Cave, Carlsbad Caverns National Park, New Mexico. Health Physics, 61, 493-500.

Cunningham, K.I. and Takahashi, K.I. (1992) Evidence for petroleum-assisted speleogenesis, Lechuguilla Cave, Carls- bad Caverns National Park, New Mexico. In USGS Re- search on Energy Resources, 1992, L.M.H. Carter, ed., U.S. Geological Survey Circular 1074, Washington D.C., 16- 17.

Cunningham, K.I., Northrup, D.E., Pollastro, R.M., Wright, W.G., and LaRock, E.J. (1995) Bacteria, fungi and biokarst in Lechuguilla Cave, Carlsbad Caverns National Park, New Mexico. Environmental Geology, 25, 2-8.

DuChene, H.R. (1986) Lechuguilla Cave New Mexico, U.S.A. In Cave Minerals of the World, C.A. Hill, ed., Na- tional Speleological Society, Huntsville, Alabama, 343- 350.

Foos, A.M. and Quick, T.J. (1988) Preparation of oriented clay mounts with uniform thickness for XRD analysis. Journal of Sedimentary Petrology, 58, 759-760.

Gile, L.H. and Grossman, R.B. (1979) The Desert Project Soil Monograph. Doc. No. PB80-135304, National Tech- nology Information Service, Springfield, Virginia.

Hill, C.A. (1987) Geology of Carlsbad Cavern and Other Caves in the Guadalupe Mountains, New Mexico and Tex- as. New Mexico Bureau of Mines and Mineral Resources, Bulletin 117, Socorro, New Mexico, 150 pp.

Moore, D.M. and Reynolds, R.C. (1997) X-ray Diffraction and the Identification and Analysis of Clay Minerals. Ox- ford University Press, New York, 378 pp.

O'Brien, N.R. and Slatt, R.M. (1990) Argillaceous Rock At- las. Springer Verlag, New York, 141 pp.

Palmer, A.N., Palmer, M.V., and Davis, D.G. (1991) Geology and Origin of Lechuguilla Cave. In Lechuguilla-Jewel of the Underground, M.R. Taylor, ed., Speleo Projects, Basel, Switzerland, 22-31.

Polyak, V.J. and Gtiven, N. (1996) Alunite, nautroalunite and hydrated halloysite in Carlsbad Cavern and Lechuguilla Cave, New Mexico. Clay and Clay Minerals, 44, 843-850.

Polyak, V.J. and Giiven, N. (2000) Clays in caves of the Gua- dalupe Mountains, New Mexico. Journal of Cave and Karst Studies (in press).

Polyak, V.J., Mclntosh, W.C., Gtiven, N., and Provencio, E (1998) Age and origin of Carlsbad Cavern and related caves from 40-Ar/39-Ar of Alunite. Science, 279, 1919- 1922. E-mail of corresponding author: AFOOS@uakron.edu (Received 12 October 1999; accepted 9 July 2000; Ms.

384; A.E. Richard L. Hay)