New Mexico Bureau of Mines & Mineral Resources Bulletin 117 Geology of Carlsbad Cavern and other caves in the Guadalupe Mountains, New Mexico and Texas

Cave deposits in Guadalupe caves are discussed using the classification scheme of Pettijohn (1957), whereby clastic deposits are described first, followed by the primary precipitates (gypsum and chert), mineral deposits (endellite-montmorillonite-palygorskite, sulfur, and carbonate speleothems related to speleogenesis problems), and biological deposits (bat guano and animal bones).

Clastic deposits

A clastic deposit is one which is composed of fragments of material. Clastic fragments in caves can be large (e.g. breakdown blocks), small (silt and sand particles), angular (breccia), or rounded (cobbles). The clastic deposits in Guadalupe caves are discussed in order of decreasing clast size, starting with breakdown and ending with mud.

Breakdown

Breakdown is bedrock which has fallen from the ceilings or walls to the floor of a cave. Breakdown pieces originating on cave ceilings often break along bedding planes (e.g. Seven Rivers Formation, Cottonwood Cave), and breakdown pieces originating along cave walls often exfoliate along vertical joints (e.g. the main corridor of Ogle Cave). The most common causes of breakdown collapse are: (1) loss of buoyancy and the drying out of rock directly after water recedes from a cave passage, (2) crystal-wedging of rock by crystalline material such as gypsum which forces bedding planes apart during a subaerial episode, and (3) earthquake tremors. The shape of breakdown pieces depends on whether the rock is bedded or not: breakdown in the bedded Seven Rivers Formation tends to be tabular, whereas in the massive Capitan reef it tends to be equant. Size of breakdown blocks varies from small, fist-size blocks up to blocks tens-of-meters high. The largest known piece of breakdown in any Guadalupe cave is Iceberg Rock in the Main Corridor of Carlsbad Cavern, which was estimated by Bullington (1968, p. 22) to be "170 feet in length and to weigh over 200,000 tons."

Breccia

Breccia is a clastic deposit which consists of angular fragments or clasts sometimes cemented together by matrix material, Breccia occurs in some Guadalupe caves, most notably in Virgin Cave and Carlsbad Cavern (Table 7), and it has also been observed in other caves including Cottonwood, Ogle, and New (M. Queen, pers. comm. 1984). The breccia is exposed in the bedrock walls and ceilings of cave passages, its clasts and matrix material having completely filled early-stage cavities in the rock which have been later truncated by the dissolution of the large cave passages.

TABLE 7—Breccia deposits in Guadalupe Caves.

Virgin Cave—Breccia deposits are displayed in cave walls and ceilings at the bottom of the first drop, all the way to the Four O'clock Staircase, and beyond to the Cavernacle. The breccia is composed of centimeter to 0.3 m long clasts cemented in a crystalline calcite or mudstone matrix. Many of these clasts appear to have been sheared in place. Virgin Cave is located near the contact of the backreef Seven Rivers and Queen(?) Formations with the Capitan Limestone reef facies. Almost the entire cave seems to be developed along a brecciated zone at or near this contact (Hill, 1984c).

Carlsbad Cavern—Breccia deposits in Carlsbad Cavern are also located primarily at or near the contact of backreef beds with the Capitan Limestone (Fig. 30). Queen (1981) recognized two joint-controlled trends of the breccia in Carlsbad Cavern which he noted as being continuous or parallel to breccia-filled clastic matrix and spar-filled joints in surface-bedrock exposures above the cave.

FIGURE 30—Distribution of breccia, Carlsbad Cavern (stippled areas). Queen (1981) and this study. (click on image for a PDF version)

One of the best breccia exposures in Carlsbad Cavern is in the north wall of the upper Guadalupe Room, near where blocky beds of the Yates Formation interfinger along the wall. In this occurrence breccia clasts, 0.3 m or more in length, are oriented at various angles in a fine-grained, tan to dark-gray mudstone matrix (Pl. 1A). Also in this area, breccia clasts of similar size occur in a matrix of crystalline calcite spar (Fig. 67).

Queen (1981) identified five breccia localities in the Appetite Hill-Iceberg Rock section of the Main Corridor. The breccia consists of abundant dark-gray, fine-grained clasts set in a dark carbonate and mudstone matrix composed of similar material as the clasts themselves. Mudstone clasts along with limestone clasts in a dark-orange matrix are present also along the Shortcut Route near Iceberg Rock. In other breccia occurrences at Iceberg Rock (along the trail climbing up Appetite Hill), individual clasts exist in the limestone not as cavity fillings, but as isolated, angular pieces of mudstone and limestone.

Cobble gravel

One of the most perplexing deposits in Carlsbad Cavern is the cobble gravel, rounded clasts which appear sporadically all the way from Bat Cave, down the Main Corridor, in Upper Devil's Den, down into Secondary Stream Passage, and—most dramatically of all—in Lower Cave, 150 m below the surface (Fig. 31). Only one other Guadalupe cave, Pink Fink Owlcove near Frank's Cave high in the escarpment above Black Canyon, is known to contain rounded clastic deposits. Description of the gravel in these two caves is summarized in Table 8.

FIGURE 31—Proposed travel route (arrows) of the cobble gravel down the Main Corridor, Secondary Stream Passage, and Lower Cave, Carlsbad Cavern. From Upper Devil's Den to the Green Clay Room the cobbles have almost as much vertical (90 m) as horizontal (120 m) extent.

TABLE 8—Cobble-gravel deposits in Guadalupe Caves.

Pink Fink Owlcove—This is a small cave about 15 m long, 9 m high, and 6 m wide, developed at the contact of the massive Capitan Limestone with its reef-talus member. Along a small ledge in the lower part of the chamber near the east wall is a lens of cemented gravel about 10 cm thick, both overlain and underlain by yellowish-tan silt. Many of the pebbles in the gravel are characterized by centers which are either hollow or filled with a dry moonmilk-like powder.

Carlsbad Cavern—Along the Main Corridor, near and in the boneyard maze that eventually leads to the Guadalupe Room, is an occurrence of pebble-cobble conglomerate overlain by laminated silt layered roughly parallel to the underlying horizontal bedrock surface. Pebble gravel can be seen packed into a ledge directly along the trail; if one follows the trail to where it turns abruptly, a "nest" of cobbles can be seen along a continuation of the ledge (Fig. 32). The gravel of the Main Corridor can be followed about 12 m into a maze of side passages in the wall, where cobbles and pebbles are overlain by, and mixed with, orange silt.

FIGURE 32—A "nest" of rounded cobbles exposed along the north wall of the Main Corridor, Carlsbad Cavern. Photo Ronal Kerbo.

The next appearance of cobbles is about 30 m down the Main Corridor in Upper Devil's Den, where the first cobbles encountered are located under a pile of huge breakdown to the left of the trail. These cobbles occur below a layer of orangish silt about 15 cm thick. Approximately 7 m further along the trail and directly next to it, cobbles can be seen included in the upper portion of a gypsum deposit.

In the Secondary Stream Passage, 60 m vertically below Upper Devil's Den, cobbles again appear abruptly under breakdown, near where the Secondary Stream Passage ascends up into Lower Devil's Den. Rounded limestone clasts in this passage are up to 45 cm in diameter; that is, a few of them are boulder-sized (>256 mm), but most are cobble- and pebble-sized. The cobbles continue intermittently along the Secondary Stream Passage all the way to the Lunch Room, where in places they are partly covered by floor flowstone, while in other places they can be seen filling solution pockets in the cave wall at floor level. The cobbles disappear again, equally as abruptly, where the Secondary Stream Passage joins with the Lunch Room.

The cobble gravel in Secondary Stream Passage is both overlain with silt and interbedded with it. Where the Secondary Stream Passage meets with the Lunch Room, orange silt is interbedded with lenses of lighter-colored, matrixed conglomerate. At this location the cobbles are mantled by laminated orange silt. At the Y-Junction, about 30 m into the Secondary Stream Passage from the Lunch Room, 0.6 m of orange silt is interbedded with 0.5 m of gravel in an orangish matrix. Orange silt once covered the exposed gravel to a depth of 1.5 m at this location, as is evidenced by the presence of orange silt in solution pockets up to 1.5 m above the present level of the cobble gravels, but this thick silt covering has been mostly eroded away. A shallow (0.3 m) trench dug at the Y-Junction revealed that most cobbles at this locality (ca 80%) do not directly touch one another; instead, the interstices between individual cobbles are filled with 3-4 cm of matrix material made up of semi-indurated pebble, sand, and silt. The larger cobbles make molds in the finer material if pried loose from the matrix.

The most extensive cobble-gravel deposits in Carlsbad Cavern occur in Lower Cave (Fig. 33) where they appear intermittently all the way from the Green Clay Room almost to Nicholson's Pit. The most peculiar aspect of the Lower Cave cobbles is their distribution: they do not seem to come from, or go, anywhere. The "upstream" limit of the cobbles is at the Green Clay Room where cobbles occur in a whirlpool-like floor depression about 1 m deep. The Green Clay Room continues on towards the Naturalist Room via a labyrinth of tight crawlways, but there is no evidence (such as cobbles hung-up in the crawlways) that the cobbles entered Lower Cave by this tortuous route. The "downstream" end of Lower Cave is no less an enigma. The cobbled "stream" channel abruptly ends about 30 m before Nicholson's Pit; yet, no cobbles fill the pit, as would be expected if the pit had antedated the cobbles.

FIGURE 33—Cobble gravel in the Junction Room, Lower Cave, Carlsbad Cavern. The cobbles are coated with a white carbonate crust. Photo Cyndi Mosch Seanor.

Bretz (1949) claimed to have traced the direction of "stream flow" in Lower Cave by noting the gradient of the passage and by the imbrication of the cobbles. However, most of the cobbles examined during the course of this study do not appear imbricated, the possible exceptions being five cobbles in the "cobblestone" floor at Nooges Realm. The average strike of the five cobbles is 56°, with a range of 37-79° and the cobbles imbricate 146° "upstream," not "downstream," in the direction of the 1-1.5° gradient of passage slope in lower Cave.

The cobble gravel of Lower Cave, unlike that of the Main Corridor and Secondary Stream Passage, is not interbedded with silt, but instead is overlain with orange silt in banks up to 7 m high. These two types of deposits, the gravel and the silt, are completely dissimilar: the cobble gravel contains rounded limestone cobbles up to 19.5 cm in diameter imbedded in a light-tan, well-indurated, and sometimes sparry matrix, whereas the orange silt consists of fine-grained, well-sorted, loosely consolidated material which does not contain a single cobble or pebble-sized clast. Furthermore, the contact between the two deposits is sharp, with the silt resting on top of an undulating cobble-gravel horizon. The contrast in composition between the two deposits and the sharp undulating contact between them suggest that an unconformity exists between the cobble gravel and silt in Lower Cave. The best localities to view this possible unconformity are along a loop-around side passage in the Junction Room (Pl. 1B) and in Nooges Realm; at the latter location, the undulate "cobblestone" can be traced underneath a 1 m high orange silt bank (Fig. 34).

FIGURE 34—Diagrammatic cross section of the trench made in Lower Cave, Carlsbad Cavern, showing a possible unconformity between the cobble gravel and orange silt. (click on image for a PDF version)

In order to study the possible unconformity, and also to investigate the cobble gravel at depth, a 0.3 m square, 1 m deep pit was dug in the silt and cobble gravel of Nooges Realm, Lower Cave (Fig. 34). Size, sphericity, roundness, and other parameters were ascertained for the cobble gravel excavated. The results for sieved samples of this gravel are shown in Table 9. The size data shows that the cobbles are flattened and disk-shaped according to Zingg's classification of shape (Krumbein and Sloss, 1963), with the average long axis of the cobbles more than twice as long as the short axis. According to the Power's roundness scale (Folk, 1968), the cobbles range from subangular to well-rounded. The cobbles in the "cobblestone" floor and in Level 1 of the pit are larger than those in Levels 2, 3, and 4, but below Level 1 there is no statistical difference in cobble size.

TABLE 9—Data on gravel excavated from a trench in Lower Cave, Carlsbad Cavern.

The cobble gravel exposed in the pit is heterogeneous, poorly sorted, and lacks internal stratification. Essentially, the gravel contains a chaotic size mixture of debris. The cobbles usually do not touch each other, but instead are matrix-supported. The matrix contains smaller particles of pebble, sand, and silt; it is light-colored and semi-indurated (i.e. the cobbles and pebbles can be dug out from the matrix with a knife but not with the fingers). Many of the cobbles in Lower Cave have fine-grained, moonmilk-like centers similar to those in Pink Fink Owlcove. Cobbles filled with this moonmilk-like substance can lie directly adjacent to completely crystalline limestone cobbles: both have the same outward appearance, but upon breaking the moonmilk-filled cobbles fall apart like talcum powder.

Almost all (99%) of the debris removed from the Lower Cave pit was composed of limestone with the exception of a few (1%) pieces of chert, iron-oxide fragments, and calcite spar. The chert fragments are angular, white or black, and vary in length from 1.5 mm to 12 mm (Table 9). Semi-rounded, thin pieces of iron oxide were found at all levels in the pit. These look as if they might have once been surface coatings over bedrock which broke off from the rock and then became semirounded. In Level 1 of the pit were found three pieces of spar, which may have once been part of a single rounded crystal.

Sand and silt

Compared with caves like Flint-Mammoth, Kentucky, which have kilometers of sediment-filled passages, the caves of the Guadalupe Mountains are relatively devoid of sediment. Where sand and silt do occur on cave floors, the source of these deposits can almost always be traced to nearby silty or sandy bedrock. Deposits which clearly display this relationship to bedrock units are: (1) Sand Passage, Carlsbad Cavern; (2) New Mexico Room, Carlsbad Cavern; (3) Bottomless Pit area, Carlsbad Cavern; (4) Sand Floor, Sand Cave; (5) Flat Floor Room, McKittrick Cave; (6) Green Lake Room, Endless Cave; and (7) Sand Slope, Cottonwood Cave. For the petrography of some of these deposits see Table 10. Carlsbad Cavern has the best exposures of fine-grained clastics; these are the only deposits that will be elaborated on. Clastic sediment lines the walls of parts of Left Hand Tunnel, covers the floor of a major part of Lower Cave, and occurs sporadically throughout the Big Room (Fig. 35).

FIGURE 35—Distribution of silt and sand in Carlsbad Cavern (stippled areas). (click on image for a PDF version)

TABLE 10—Petrographic description of some sand, silt, and mud deposits in Guadalupe Caves. Roundness according to Powers Scale, size classification after Folk (1968).

Left Hand Tunnel—Orange-silt banks up to 1.5 m high line sections of Left Hand Tunnel (Fig. 36). Many of these banks have been excavated for trail building, an activity which has exposed the slumped and layered nature of the silt. The silt banks are level along the walls on opposite sides of Left Hand Tunnel, but slump toward the middle of the passage wherever a canyon dissects the floor. The orange silt in Left Hand Tunnel appears and disappears in accordance with the appearance and disappearance of the reef-talus and reef-core facies (compare Figs. 18 and 35). Reef-talus sections are characterized by vertical canyons rather than horizontal mazes, by a lack of travertine deposits, by crude bedding planes which dip approximately 30° to the south, by fossiliferous (brachiopods, crinoids, fusulinid foraminifera) bedrock, and bypods of orange silt in the limestone and orange silt on the floor.

FIGURE 36—A silt bank, Left Hand Tunnel, Carlsbad Cavern. A carbonate crust extends outward over the layered silt where the silt has been excavated for trail construction. Photo Alan Hill.

Lower Cave—The most extensive deposits in Carlsbad Cavern are in Lower Cave, where flat-topped silt terraces and banks up to 7 m high line the passage walls (Fig. 37). The sediment directly overlies cobble gravel in many places along Lower Cave (Pl. 1B), and is itself overlain by subaerially formed crustal or dripstone deposits (Fig. 69).

FIGURE 37—Entrenched silt bank, Lower Cave, Carlsbad Cavern. Note the flatness of the bank. Photo Jeep Hardinge.

Dunham (1972) described the clastic material of Lower Cave as a reddish-tan gypsiferous silt containing particles coated with a hydrated ferric-iron oxide, and crystals of gypsum along with scarce fragments of quartz, dolomite, and calcite. Observations made during this study agree with those of Dunham: silt-sized, clay-coated quartz grains, and calcite and gypsum crystals comprise the bulk of the orange sediment of Lower Cave (Table 10). As elsewhere in the cave, the orange silt of Lower Cave contains no cobbles, pebbles, or montmorillonite-endellite clay.

DuChene (1972) collected samples of silt in Lower Cave (both below the Jumping Off Place and further down the passage near Stegosaurus Rock) and performed a statistical size analysis on them. The mean particle size of the sediment in Lower Cave is 4.65 phi units (0.04 mm), with a standard deviation of 0.158. Thus, the sediments of Lower Cave are a very well-sorted, coarse-grained silt. DuChene also determined a water-soluble-salt content of 2.5% for the water-soluble salts of sodium and magnesium, and a carbonate content of between 15% and 40% for the two collection sites, respectively. The 40% carbonate content for the Segosaurus Rock site is perhaps representative of the carbonate content in the upper parts of the sediment banks where they are covered with carbonate coralline crusts. The sediment near the Jumping Off Place, with a 15% carbonate content, was collected near a site of dripping water and, as such, has probably been leached of part of its carbonate content.

In some places in Lower Cave the silt displays a laminated texture highlighted by bands of lighter carbonate material between laminae. Three sets of bands are most pronounced, the sequence varying from place to place. There is a faint banding at 1 mm between laminae, more conspicuous bands 1-2 cm apart, and the lightest, most conspicuous bands 2-4 cm apart (Pl. 2A). Laminations are usually best preserved in sediment banks located under protected alcoves, but they also can be seen in silt banks within the largest passages in Lower Cave, such as at DuChene's Stegosaurus Rock collection site.

Like the sediment banks in Left Hand Tunnel, the tops of the Lower Cave banks are essentially level, both across the passage and all the way along the entire length of Lower Cave (Table 11). The original upper surface of the flat-topped terraces is difficult to determine because remnant patches of orange silt partially fill solution pockets in the limestone up to 1.5 m above the upper terrace level of the banks. This probably signifies that the silt has compacted since its initial deposition; thus, the sediment bank heights listed in Table 11 should be considered approximate values, varying as much as a meter or so, but not more, from the height of the originally deposited material.

TABLE 11—Sediment bank elevations, Lower Cave, Carlsbad Cavern.

The sediment banks in Lower Cave have been entrenched into erosional V's with slope angles of 30° or more (Fig. 37). A meandering pattern of downcutting is evident along a few segmented portions of Lower Cave, with the meanders confined by the walls of the cave. Downcutting continued throughout the entire silt horizon but stopped once the more competent, underlying cobble-gravel horizon was breached; indurated cobble gravel below the silt has not been downcut more than half a meter or so.

New Mexico Room—Along the east wall of the New Mexico Room are piles of clean white sand which represent residual sediment from the dissolution of light-colored, steeply dipping sandstone beds which comprise part of the east wall. The identity of these sandstone beds has been the subject of much debate. Black (1954) reported the occurrence of siliciclastic beds in the New Mexico Room which he interpreted as a possible basinward continuation of lower Yates sands. Moran (1955) speculated that the beds represented shelfward tongues of the sandstones of the Delaware Mountain Group (Bell Canyon Formation), possibly deposited on the basinward flank of an early reef. Candelaria (1982) thought that either interpretation was equivocal since neither of these sandstones is continuous enough to be traceable shelfward or basinward. This study favors Moran's contention that the sandstone beds in the New Mexico Room are part of the Bell Canyon Formation. It also favors Moran's definition of the Bell Canyon Formation; that is, that all sandstones on the basinward flank of the Capitan Limestone belong to the Bell Canyon. Evidence supporting a Bell Canyon origin for the New Mexico Room sandstone is:

(1) Strike and dip of beds in the New Mexico Room as measured by Moran (1955), Good (1957), and in this study are N70°E, 20-30°S; N65°E 33°S; and N62°E, 36°S respectively; i.e. the beds dip steeply toward the basin. In contrast to these measurements, backreef beds of the Artesia Group dip 3-4° toward the reef.

(2) Newell et al. (1953) and Grauten (1965) described the sandstone of the Bell Canyon Formation as a white, remarkably clean, homogeneous unit containing angular to well-sorted grains in the coarse-silt to fine-sand category. Moran (1955) found the light-tan to white sandstone of the New Mexico Room to be a coarse silt to sand, with over 50% of the particles in the very fine- to fine-sand category, and with negligible hydrocarbon content (0.015 mg/g). This study found the sandstone to be a clean, white, subarkosic (feldspar determined by the Mueller Process), homogeneous, fine-grained unit (Table 10). Where it is pure sand (99% sand, Table 27), it has a porosity and permeability of 28% and 61 millidarcies, respectively; if the carbonate content is greater and the sand content less (35% sand, Table 27), then the porosity and permeability is much lower (4.5% and 0.01 millidarcies, respectively). As is typical of Bell Canyon sands, porosity and permeability varies over short distances (about 5 m for the two collection sites in the New Mexico Room, Table 12).

TABLE 12—Porosity and permeability of bedrock, Carlsbad Cavern, and Bell Canyon Formation, Delaware Basin.

(3) The New Mexico Room is too low for the sandstone to be part of the silty and sandy Yates Formation. The lowermost Yates beds crop out at the top of the Guadalupe Room, almost 100 m higher than the New Mexico Room level (Fig. 17).

(4) The altitude of the Bell Canyon Formation in the basin 0.5 km south of Carlsbad Cavern is at about 740 m (2,470 ft) (Fig. 12). If Bell Canyon beds dip 10-30° at their intersection with the reef, as King (1942) stated and as the measured dips in the New Mexico Room indicate might be true, then the Bell Canyon sandstone could intersect the Capitan reef at about the Big Room-New Mexico Room level.

(5) The steeply dipping sandstone in the New Mexico Room is the site of sulfur mineralization. The fact that the sulfur occurs on the undersides of bedrock and gypsum speleothems is important because it indicates that the source of the sulfur (i.e. hydrogen-sulfide gas) may have come from below, or updip from the basin, along the clean, white, porous beds and into the cave. Moran (1955, p. 258) offered a similar opinion, but regarding oil rather than hydrogen-sulfide migration: "such sandstone tongues could serve as possibly conduits for oil from basin to porous reef. Lack of hydrocarbons may indicate that the sandstones have been effectively flushed, perhaps during the period of formation of Carlsbad Caverns."

Big Room—Sediment in the Big Room of Carlsbad Cavern differs significantly from sediment in other parts of the cave and also from sediment in other Guadalupe caves. Instead of being a homogeneous orange-tan color, the Big Room sediment varies from cream to brick-red to green, brown, ochre-yellow, and purple. In some places the deposits overlie montmorillonite-endellite clay and/or are interbedded with chert (Fig. 70).

The sand and silt in the Big Room have been previously described by Good (1957) and Queen (1981). Clay (montmorillonite-endellite) beds are usually overlain by silt and then by sand, but this trend is locally variable. Sand is commonly disseminated throughout the clay and silt, with the sand sometimes in layers of less than 1 cm thick and with each successive layer containing only minor amounts of other size fractions. The upper part of the sand unit is commonly quite pure and consists of very fine-grained, frosted or clear, angular to well-rounded quartz grains, with some of the grains containing black inclusions (Good, 1957).

Other silt deposits of the Big Room show a regular vertical succession of colors, from green and chocolate brown through red and orange to light-orange, yellow, and rarely light-purple (Queen, 1981). Specific colors may be missing at some locations, but the colors never change order. Brick-red silt occurs both on the floor of Bottomless Pit and at the Salt Flats. The Salt Flats silt shows crude to well-developed bedding parallel to the upper surface of the sediment mound except for near the top of the sediment bank where bedding has been highly deformed and folded (Pl. 2B).

A local type of silt deposit in the Big Room is the silt breccia, a 15 cm thick deposit composed of angular fragments of red, yellow, and tan silt and angular pieces of flowstone in a brown silt matrix. The silt breccia is located just to the right of the Texas Trail where it takes off from the main trail. The silt breccia partially underlies flowstone travertine (Fig. 70).

At the Bottomless Pit, along the west wall near the Breast of Venus, and also along the south wall between the Jumping Off Place and the Bottomless Pit, are white- to buff- to cream-colored sands (Fig. 38) that are similar in color, texture, and size distribution to the clean white sands of the New Mexico Room. The sand along the south wall and near the Breast of Venus occurs in semicircular, conical piles called "half cones" by Good (1957), "flowstone-covered alluvial sand cones" by Sanchez (1964), and "sand domes" by Bullington (1968). These white "quartz-sand half cones" of the Big Room are about 3 m high and 6 m in diameter, and abut directly up against the cave walls. The cone at the Breast of Venus is overlain by travertine flowstone, and, where the light-colored sediment has been excavated for trail building, a conical shell of flowstone has been left free standing. The sand of the cone is iron-stained along its upper part, near its contact with the flowstone.

FIGURE 38—Cream-colored silt underlying a gypsum block, Bottomless Pit, Big Room, Carlsbad Cavern. The silt directly overlies floor bedrock. Photo Ronal Kerbo.

The "sand" of the half cones is actually not pure sand but a mixture of coarse-grained silt and fine-grained sand, as are the other fine-grained clastic deposits in the cave (Table 10). The silt-sand is clean, well sorted, and according to Queen (1981) some of the clastic particles display beautiful quartz overgrowths.

The presence of the light-colored quartz-sand half cones in Carlsbad Cavern is most curious because this type of deposit is unknown in any other Guadalupe cave. Also, the half cones do not seem to be related to joints, bedding, sandstone dikes, or other such features in the wall limestone. In the Breast of Venus occurrence, the apex of the half cone corresponds to a hole in a section of wall directly above it. The sediment appears to have filtered down from above and through the hole, but if one climbs up onto the apex of the cone and looks straight up through the hole, one cannot trace the sand to any pertinent feature in the limestone ceiling. In the four south-wall occurrences, the apices of the cones do not correspond to any particular feature in the wall, not even to a hole along which the sand could have filtered down.

Like the clean, white sands in the New Mexico Room, the light-colored silt-sand at the Bottomless Pit and the quartz-sand half cones of the Big Room are thought to be part of the Bell Canyon Formation (Fig. 18).

(1) Strike and dip of the tilted beds at Bottomless Pit range between N60°E-N90°E and 20-50°S (for six readings; J. Roth, pers. comm. 1986).

(2) As with the New Mexico Room sands, the Big Room sands are too low to be part of the Yates Formation. Furthermore, the bedrock at Bottomless Pit differs compositionaily from Yates Formation outcrops. The Yates Formation in Sand Cave contains 0.08% silica, while the Bottomless Pit bedrock contains 2.8% silica (Table 26). The interfingering of the Yates Formation at the Auditorium, Carlsbad Cavern, contains 1.7% of insoluble residue, while the bedrock at Bottomless Pit contains 11.7% of insoluble residue (Table 27).

(3) While there are no bedding planes in the quartz-sand half cones, so that strike and dip cannot be measured, the sand is remarkably white, clean, and well sorted, like the light-colored sand of the Bell Canyon Formation. Good (1957) found the sand of the Big Room half cones to be similar to the sand of the New Mexico Room except for a higher percentage of larger grain sizes. Microscopic examination done during this study showed that the sand of the quartz-sand half cones near the Breast of Venus is nearly identical to that found in the New Mexico Room and at Bottomless Pit (Table 10).

(4) Jagnow (1977) and Queen (1981) were of the opinion that the quartz-sand half cones in the Big Room represent sand-filled fractures in the Capitan Limestone. This interpretation seems doubtful because sandstone fractures are nowhere to be found, The sand of the half cones does not crop out as thin, branching dikes according to either Hayes' (1964) or Dunham's (1972) descriptions. They are conical masses of slumped sand, and as Good (1957) noted, with gradational, not dike-like, contacts. In the two south end exposures of the Big Room, the half cones appear almost like sand balls or sand lenses in the wall which have slumped down into half-cone piles as the cave walls receded by dissolution.

(5) Sulfur occurs at the south end of the Big Room, very near the quartz sand half cones along the wall (see Sheet 2).

Calcified siltstone

Clastic deposits found only in Carlsbad Cavern are the thin-layered, orange-brown, variegated siltstones exposed in wall cavities or in pieces of breakdown on the floor and usually associated with overlying, well-indurated, cave rafts (Fig. 39). Queen (1981) named these deposits "granular flowstones" because they are banded like flowstone and are characterized by grains which reflect light. However, Queen's name is misleading because "flowstone" implies a secondary, subaerially formed, travertine deposit, and "granular" implies that detrital grains such as sand in the deposit reflect the light. Rather than being a flowstone or sandstone, the orange-brown deposit is actually a calcified siltstone with crystalline calcite cement comprising about 80% of the mass and with the remaining 20% composed of silt-sized debris with minor sand (Table 10). The calcite-cement crystal domains are what give the deposit its granular, sparkling texture. The siltstone is banded dark brown and orange, the darker color being caused by a relatively higher percentage of iron and manganese.

FIGURE 39—Indurated cave rafts directly overlying calcified silt stone, Guadalupe Room, Carlsbad Cavern. The siltstone is present on an up-facing surface, and where the surface starts to drop the siltstone pinches out (lower right). Photo Pete Lindsley.

The best localities of calcified siltstone are in the Guadalupe Room, Main Corridor, and Lower Devil's Den sections of Carlsbad Cavern (Table 13), and also in lower passages off the New Section. All of these localities are at or near the contact of backreef beds with the Capitan Limestone (Fig. 40). The calcified siltstone always rests on an upfacing surface (Fig. 39) and is usually overlain by cave rafts which have been well indurated and thickened with post-depositional calcite.

FIGURE 40—Distribution of the calcified siltstone—cave rafts, Carlsbad Cavern (stippled areas). Compare with distribution of breccia in Fig. 30. Queen (1981) and this study. (click on image for a PDF version)

TABLE 13—Calcified-siltstone—cave-raft deposits, Carlsbad Cavern.

In the Guadalupe Room, Lower Devil's Den, and New Section the sequence of calcified siltstone—cave rafts can be observed within small cavities, pockets, or alcoves in the bedrock which have been planed off concordant to the cave walls. In the Guadalupe Room and Lower Devil's Den areas siltstone-rafts are also found in floor breakdown, while in the Main Corridor (just beyond the tunnel before reaching the Green Lake Room) the deposits are in a mass of breakdown directly adjacent to the trail.

Mud

Dark-brown mud deposits have been found in many Guadalupe caves—Cottonwood, Endless, Little Sand, McKittrick, Spider, Three Fingers, Virgin, Cave Tree, Jurnigan, Madonna, and Vanishing River. In a side alcove of McKittrick Cave and in the Root Cellar Room of Three Fingers Cave, twig remnants can be picked out of the mud. In the Helictite Room of Spider Cave, leaves and fungus are associated with the mud and there is a light-brown mud line on helictite and flowstone decorations from a back-up of muddy water in the cave. The floor in the Mud Room of Cottonwood Cave is layered with a brown sticky mud of heavy-grease consistency (Boyer, 1964). A microscopic examination of this mud revealed tiny coagulated clumps of dark-brown, uncrystallized material (Table 10). In the Mud Crack Room of Endless Cave, the floor mud is semilaminated, with 1 cm thick lighter layers alternating with darker layers. No leaves or twigs were found in the Endless Cave mud, but fungus was observed growing on top of it. In one place the mud was measured to a depth of 0.3 m; in another place it was found to overlie a gypsum block. Major mud influxes have also occurred in the lower passage in the Cave of the Madonna and in the Mud Room-Grunge Hall and Thanksgiving Room-Deep Throat areas of Virgin Cave (D. Davis, pers. comm. 1984). The Virgin case is interesting because the mud evidently entered at an intermediate level; then a semifluid mudflow poured from the Thanksgiving Room down the Midterm side of the Four O'clock Staircase before reaching the lowest part of the cave. Hill (1984c) tried to correlate the occurrence of mud in Virgin Cave with a valley depression on the surface and speculated that the mud entered the cave via a brecciated zone along which both the depression and cave passages developed.

Gypsum blocks and rinds

Gypsum in Guadalupe caves occurs as (1) blocks and rinds, and (2) speleothems. Blocks and rinds are an alabaster-like, granular type of massive-gypsum deposit, whereas gypsum speleothems are secondary deposits such as stalactites, stalagmites, cave flowers, and selenite needles. Gypsum blocks occur as floor deposits up to 10 m in height (Fig. 41); most are segmented into sections and blocks, but some are continuous across sections of the cave floor. Gypsum rinds occur as wall deposits up to 1 m thick, which drape over bedrock or silt (Fig. 42). A description of the massive-gypsum deposits in Guadalupe caves is summarized in Table 14, and their location in Carlsbad Cavern is shown on Sheet 2 (in yellow).

FIGURE 41—A gypsum block with smooth, streamlined sides, Talcum Passage, Carlsbad Cavern. Photo Alan Hill.

FIGURE 42—A gypsum rind draped over bedrock, Left Hand Tunnel, Carlsbad Cavern. Photo Alan Hill.

Gypsum blocks and rinds are composed of massive-granular gypsum with individual crystals ca 1 mm long. Crystals larger than this are tabular and cover the outside surfaces of the blocks or rinds. The gypsum making up blocks and rinds can be porous and friable like talcum powder (e.g. the Big Room of Carlsbad Cavern) or it can be dense, hard, and compact (e.g. the McKittrick Hill caves). One attempt to drill a core into the gypsum blocks of the Big Room failed because it was like drilling into loose, uncompacted sugar. The gypsum making up blocks and rinds is white to light yellow except where it has been stained a darker yellow by bat guano or iron oxide. In Lower Devil's Den, Carlsbad Cavern, small segments of a few gypsum blocks are tinted a light mint green from traces of montmorillonite clay (C. M. Seanor and R. North, pers. comm. 1985).

Many gypsum blocks possess a crystalline crust sharply delineated from the main mass of more compacted and less crystalline gypsum. These "overgrowth crusts," as they are called, are up to 30 cm thick and are generally more white and porous than the underlying gypsum. Overgrowth crusts do not possess laminations and other textural features present in the blocks themselves, but occasionally a thin layer of overgrowth crust will highlight lamination ridges in the textured gypsum beneath it. Good examples of overgrowth crusts on gypsum blocks occur in the Big Room, Talcum Passage, and New Mexico Room of Carlsbad Cavern, and in the Balcony Room of Dry Cave. At the Jumping Off Place, Big Room, a 10-20 cm thick, coarse, porous overgrowth crust overlies the regular mass of gypsum (Queen, 1981). In the Talcum Passage and in the Balcony Room of Dry Cave, overgrowth crusts have slumped down along the vertical sides of gypsum blocks (Fig. 43).

FIGURE 43—An overgrowth crust (a) which slid down over an underlying gypsum block (b), Balcony, Dry Cave. The gypsum block directly overlies bedrock (c). Photo Alan Hill.

Spatial distribution

Gypsum blocks and rinds exist in caves throughout the Guadalupe Mountains. The lowest elevation at which this gypsum has been found is 1,080 m, in Lower Cave, Carlsbad Cavern, and the highest altitude is 2,073 m, in Wonderland, Cottonwood Cave. Gypsum blocks and rinds have been observed in Carlsbad, New, Cottonwood, Lechuguilla, Black, Hell Below, McKittrick, Dry, Sand, Endless, Little Sand, Virgin, Pink Panther, Three Fingers, and Spider Caves (Hill, 1973e). In Black Cave and New Cave only a few gypsum blocks have survived dissolution.

Within each cave, gypsum blocks and rinds display certain distributional trends. Gypsum deposits seem to be more sparsely distributed and/or more highly dissolved in long, linear passages such as Bat Cave, the Main Corridor, and Left Hand Tunnel of Carlsbad Cavern (Sheet 2); the Entrance Hall of Cottonwood Cave (Sheet 5); and the Expressway Passages of Endless and Dry Caves. Gypsum rinds are usually found in boneyard side passages; gypsum blocks usually reside on the floors of large rooms. As a rule, gypsum deposits are more abundant in middle cave levels than in upper and lower levels, a trend best demonstrated in the McKittrick Hill caves. The middle level (Middle Maze) of Endless Cave is choked with gypsum blocks 0.6-1.2 m high in a 1.2 m high passage, while the upper level (the Expressway) is nearly devoid of gypsum and the lower level (Lower Maze) has gypsum deposits 0.3-0.6 m high in a 2 m high passage. Gypsum once completely choked off the Middle Maze as evidenced by remnant gypsum pillars which reach from the cave floor to the ceiling (Fig. 44), and by gypsum blocks which have surfaces parallel to undulations in the ceiling bedrock (Fig. 45). In Cottonwood Cave, gypsum blocks occur at all levels in the Gypsum Passage, but primarily in the middle section intermediate between Wonderland and the lower Gypsum Passage. The lower Gypsum Passage contains many gypsum blocks, but most of these appear to have fallen from above; wherever a bedrock bridge has protected a low section from falling debris, gypsum blocks do not exist on the floor. In Carlsbad Cavern, massive gypsum blocks are rare above the Big Room-Talcum Passage level (Upper Devil's Den and the Music Room Balcony are the exceptions); also, gypsum is much less abundant at the Lower Cave level than at the Big Room level.

FIGURE 44—A remnant-gypsum pillar, Middle Maze, Endless Cave. Gypsum which once filled the passage has been dissolved away, leaving the pillar intact. Note how the angle of repose of the floor gypsum approximates the dip angle of bedding. A commode hole in the gypsum is an extension of a hole or holes in the floor limestone.

FIGURE 45—A compacted gypsum block, Middle Maze, Endless Cave. Gypsum once extended up to the ceiling, but compacted by a factor of about one-fourth during its solidification. A dissolution channel has been carved in the gypsum at middle left.

Where cave floors slope, such as in the McKittrick Hill caves, gypsum blocks lie at the approximate angle of floor repose. In McKittrick Cave, the slope of the floor gypsum mimics the dip of bedding except where vadose drippage has dissolved the gypsum away (Fig. 46). In Endless Cave, the slope of the floor gypsum approximates the passage dip even in areas where gypsum pillars extend from the floor to the ceiling (Fig. 44). In caves where the floor is roughly horizontal, as in the Big Room of Carlsbad Cavern, gypsum blocks may slope toward the center of a room. The slope, delineated by the top surface of the blocks, can be traced even where the blocks have been separated by erosion (Fig. 47). In Talcum Passage, Carlsbad Cavern, the gypsum blocks slope along the entire length of the passage, from a high of 7 m at the southern end of the passage to where the gypsum completely disappears at the northern end of the passage (R. Lipinski, written comm. 1984).

FIGURE 46—A gypsum block in relationship to dipping beds, McKittrick Cave. Water moves downdip along bedding planes until it encounters a vertical joint, whereupon it becomes diverted into the cave so as to form dripstone and to dissolve away the gypsum directly beneath the joint. Note that the angle of repose of the gypsum block approximates the dip angle of bedding.

FIGURE 47—Sloping gypsum blocks in the Salt Flats of the Big Room, Carlsbad Cavern. Note that the wall overhang corresponds to the maximum thickness of the block.

Another trend seen in some Guadalupe caves is that the height of gypsum blocks is approximately 10-30% the height of the passage in which the blocks reside. In the Big Room of Carlsbad Cavern for example, the blocks are 4.5-6.0 m high in a 45 m high passage. The McKittrick Hill caves have a gypsum/passage height ratio averaging ca 30%. Davis (1980) also noted this correlation between passage height and gypsum-block height.

At many localities, such as the Lower Maze, Endless Cave, and Lower Cave and Upper Devil's Den, Carlsbad Cavern, gypsum floor blocks are continuous with wall rinds, the gypsum thinning upwards along the wall as it grades from a block into a rind (Fig. 48). At other localities, such as Lower Cave and the Polar Regions, Carlsbad Cavern, gypsum blocks thin into rinds in the downward direction-along bedrock beneath floor blocks. Gypsum is only rarely attached to cave ceilings, one example of this being the archway ceiling of gypsum in the Gyp Joint of Hell Below Cave (Fig. 49) and another being the ceiling crustal rinds in Rim City and Windy City, Lechuguilla Cave (Table 14).

FIGURE 48—A gypsum block thinning upwards into a rind, Lower Maze, Endless Cave.

FIGURE 49—Archway of gypsum, Gyp Joint, Hell Below Cave. The passage may have been completely filled with gypsum before a solution channel formed in the gypsum. As the gypsum archway dried and compacted, it partly pulled away from the ceiling and walls. The gypsum is approximately 1.5 m thick, Photo Alan Hill.

TABLE 14—Gypsum blocks and rinds in Guadalupe Caves.

Textural features

Textural features in the gypsum blocks and rinds of Guadalupe caves provide important clues to its origin, and also to its mode of coalescence and solidification. Such textural features are highly variable not only in gypsum deposits of different caves, but also within adjacent gypsum blocks in the same cave or even within the same gypsum block or rind over a distance of a few centimeters.

Laminations—Many of the gypsum blocks and rinds in Guadalupe caves display a laminated texture, but these are not obvious to the causal observer because one must look very closely to see them and because overgrowth crusts often hide them. Laminations in the cave gypsum represent a two-component system of colorless selenite alternating with opaque gypsum. Laminae are usually transparent white-translucent white, but in some caves, such as Cottonwood, the layering is a more visible white-gray. Despite their resemblance to the varves in the anhydrite beds of the Castile Formation in the Gypsum Plain, neither the white-gray couplets nor the transparent-translucent couplets contain calcite as do the gypsum-calcite varves of the Castile Formation. An attempt was made to drill into the gypsum blocks of the Big Room, Carlsbad Cavern, in order to correlate lamination sequences similarly to Anderson et al. (1972) in the Castile Formation of the Gypsum Plain. This attempt failed because the cave gypsum at this location has a sugar-like consistency, making the retrieval of a solid core impossible.

Examination of the cave-gypsum laminae in thin section revealed thicker (1 mm) transparent layers alternating with thinner (0.5 mm) opaque layers. One measured section displayed 12-15 laminae/cm. Pods of gypsum, reminiscent of nodular structures in the Castile Formation as described by Dean (1967; pl. 2E), distort some of the laminae, and often the laminae are not continuous but end abruptly. Laminated texture in the gypsum varies from equant in the more transparent layers to felty in the more opaque layers. The more felty-looking crystals show preferred alignment perpendicular to layering. In one thin section, a vertical array of large, lath-like gypsum crystals was superimposed upon the smaller, felted crystals, a texture which most likely represents a partial recrystallization of the gypsum.

Laminations in gypsum blocks and rinds are oriented roughly parallel to the surface against which the gypsum rests. Where a limestone wall or ledge is vertical, horizontal, inclined, or curved, the laminations are likewise disposed. In floor blocks, the laminations are usually horizontal or very gently inclined (Pl. 3A). In wall rinds, such as the 0.3-0.6 m thick rinds in the upper Gypsum Passage of Cottonwood Cave, the laminations are vertical or inclined parallel to the wall. In the area of Mirror Lake, Big Room, Carlsbad Cavern, gently tilted laminated layers of gypsum are overlain by horizontally laminated gypsum, looking like rock layers which have been separated by an angular unconformity. In the first trail arch at the Jumping Off Place, Big Room, tiny faults offset laminations in the gypsum.

Microfolding—Microfolded laminations are a common feature in the anhydrite of the Castile Formation of the Gypsum Plain (Kirkland and Anderson, 1970). The cave gypsum also sometimes displays a microfolded texture, best developed in the gypsum blocks of the Big Room, Carlsbad Cavern. Folding in the cave gypsum is not as tight, regular, or symmetrical as that in the anhydrite of the Castile Formation; it is more gentle and undulant (Pl. 3A). In rare instances, small faults occur at the microfold bends.

Slickensides—Slickensides can be seen in the gypsum blocks at the Jumping Off Place, Carlsbad Cavern, inside of the second of the two trail tunnels (Pl. 3B). They are grooved structures which occur at the contact of an overgrowth crust with the underlying gypsum mass. The grooves are not laminations nor do they appear to be mechanical cuts made while tunneling through the gypsum. The striations most closely resemble slickensides created where adjacent rocks have slid past each other. Two small patches of gypsum have slickenside surfaces: one patch is 8 cm long and 5 cm wide, and the other one (below and to the right of the first) is 10 cm long and 7 cm wide, In each case the striations are 1 mm or less apart and are inclined approximately 5-10° from the vertical.

Breccia—Small-scale breccia texture, consisting of jumbled masses of laminated angular fragments, occurs in the gypsum blocks of the Big Room, Carlsbad Cavern (Fig. 50). The breccia closely resembles the brecciated texture in the Castile Formation of the Gypsum Plain (see Dean, 1967, pl. 1G); however, unlike the breccia texture of the Castile Formation, the breccia in the cave gypsum does not seem to be related to microfolding. Breccia texture has been observed only in certain sections of the Big Room such as the Salt Flats, and then usually only in the upper part of the gypsum.

FIGURE 50—Breccia texture in a gypsum block near the Salt Flats, Big Room, Carlsbad Cavern. Note that the laminated breccia pieces are inclined at various angles in the gypsum. Photo Alan Hill.

Bedrock inclusions—Pieces of bedrock varying from 1 cm long fragments to large angular blocks are included within the cave gypsum. The bedrock inclusions are in various stages of replacement by gypsum: of five inclusions found in the gypsum blocks of the Big Room, Carlsbad Cavern, three still effervesce in acid (they are still limestone), whereas two do not react (they have altered to gypsum, at least on their surfaces). At one locality in the Big Room, two limestone pieces can be seen vertically arrayed in the gypsum as if they had fallen from a single point on the ceiling (Fig. 51).

FIGURE 51—Two limestone inclusions (a, b) vertically aligned in a gypsum block, Big Room, Carlsbad Cavern. These particular inclusions have not altered to gypsum, not even on their surfaces. Photo Ronal Kerbo.

In Cottonwood Cave, dolomite inclusions derived from the Seven Rivers Formation are in various stages of being replaced by gypsum. Some inclusions have totally altered to gypsum, some only have calcite veins remaining of their original bedrock mass, some are altered only around their edges, and others still remain unaltered dolomite. One inclusion in the gypsum of the upper Gypsum Passage consists of a dolomite core 10 cm in diameter, surrounded by a dark, 3-4 cm wide gypsum reaction rim (Fig. 52). A thin section made of one Cottonwood Cave inclusion revealed only gypsum crystals except for a few "ghost" calcite-spar crystals of high, but masked, birefringence.

FIGURE 52—Reaction rim of gypsum around a dolomite inclusion, upper Gypsum Passage, Cottonwood Cave. Dolomite has been replaced by gypsum in the reaction rim.

Inclusions within the gypsum have derived from nearby bedrock either as pieces fallen from the ceiling or pieces exfoliated from the wall. In the upper Gypsum Passage, Cottonwood Cave, inclusions are bedded pieces of dolomite corresponding in thickness to bedding in the Seven Rivers wallrock.

Included bat guano and bat bones—Pockets of orange to red material occur within some of the gypsum blocks of the Big Room and Talcum Passage, Carlsbad Cavern (Pl. 4A). This material is bat guano which has filtered down into the gypsum along cracks, dissolved sections, or drip tubes.

A partial bat skeleton (long bones and skull) has been found in a gypsum block near the trail, Bottomless Pit, Big Room, 4-5 cm down from the top of the gypsum. The bones look as if they fell into a drip hole or depression in the gypsum and then were covered over with a powdery mixture of gypsum and limestone.

Insoluble residue—The gypsum deposits of Guadalupe caves are almost devoid of insoluble residue. Two samples of gypsum, one from the Lower Maze of Endless Cave and one from near the Bottomless Pit, Carlsbad Cavern, were collected in order to determine their insoluble-residue content. The gypsum, when dissolved in 50% hydrochloric acid, produced a solution that was not even slightly discolored. However, tiny (0.05-0.1 mm) pieces of angular chert and quartz were identified in the gypsum from both localities; in addition, the Bottomless Pit sample contained black specks (of magnetite?). Insoluble residue in the Bottomless Pit sample was 0.01%, and in the Endless Cave sample it was <0.1% (Table 15). Hydrocarbon content of the gypsum, as determined from a carbon-tetrachloride extract, was only 0.5 ppm. The remarkable purity of the gypsum is also supported by the iron content as determined by whole-rock analyses. At four cave localities, the gypsum blocks had less or much less than 0.12% of ferric and 0.03% of ferrous iron (Table 26).

TABLE 15—Insoluble residue and hydrocarbon content of gypsum blocks, Guadalupe Caves.

There are a few exceptions to the general rule of residue-free gypsum. In the Pump Room of Carlsbad Cavern and in the Balcony Room of Dry Cave, the top surfaces of the gypsum are banded with orange layers (Pl. 4B). Microscopic examination of the layers revealed that the residue is a fine-grained silt. The silt layers are not necessarily laterally continuous; sometimes the layers disappear suddenly as if their deposition had not been originally continuous. Another occurrence of gypsum that contains silt is an eroded gypsum pillar at the end of the Expressway Passage, Dry Cave. The silt occurs as a 6 cm thick band or "belt" in the gypsum mass together with pieces of limestone (Pl. 5A). The orange silt and limestone pieces are believed to be clastic debris which slumped from a rear passage into the gypsum at the time of its deposition or consolidation.

Flow features—Egemeier (1981) compared the consistency of wet gypsum in the caves of the Big Horn Basin, Wyoming, to that of mud. Flow features in the cave gypsum of the Guadalupe Mountains attest to the fact that it also had a mud-like, semiplastic consistency when still wet. The overgrowth crusts in the Talcum Passage, Carlsbad Cavern, apparently have slid down over underlying gypsum; additionally, in the Talcum Passage, a lower section of a gypsum block looks like it crept down into cracks within the underlying limestone (Fig. 53). The gypsum of the Balcony in Dry Cave appears as if it flowed over the edge of the balcony limestone (Lindsley and Lindsley, 1978); also in Dry Cave, a spectacular cascade of pure-white crystalline gypsum approximately 2 m long plummets like a frozen alabaster waterfall into the Insane Rain Drain Trench Pit.

FIGURE 53—Lower part of a gypsum block in Talcum Passage, Carlsbad Cavern, that flowed down into a crack in the limestone and then solidified. The crack opens up and connects to the ceiling of Lower Cave, the floor of which is 30 m below. Photo Alan Hill.

Replacement features—Queen et al. (1977a) reported numerous replacement textures in the gypsum of the upper Gypsum Passage, Cottonwood Cave. These include pisolites, fossils, travertine, breccia, relict bedding, primary pores, and light/dark laminations. Also, dolomite clasts have been reported in various stages of replacement in the same gypsum (Fig. 52).

Replacement textures in the gypsum deposits of other Guadalupe caves are not nearly so pronounced. Of the numerous gypsum blocks examined in the Big Room, Carlsbad Cavern, only a few possible cases of replacement gypsum were found. The limestone inclusions mentioned previously have been, at least partially, replaced by gypsum on their surfaces. Gypsum laminations cross-cut limestone inclusions in one of the floor blocks of the Big Room, another possible indication of replacement (Fig. 54). A calcified fossil foraminifer was noted in one thin section made from a piece of a gypsum block taken from the Big Room; only a partial test was preserved, the rest apparently having been dissolved away. A thin (<1 cm), patchy crust of possible replacement-solution gypsum has been observed over limestone bedrock near the Bottomless Pit, Carlsbad Cavern. No replacement textures could be seen in this gypsum crust under microscopic examination. Other possible replacement features have been observed in the gypsum blocks of Glacier Bay, Lechuguilla Cave (Hill, 1986).

FIGURE 54—Possible replacement or recrystallized gypsum, Big Room, Carlsbad Cavern. Note that the rounded upper inclusion (a) is crosscut by lineations in the gypsum, whereas the lower inclusion (b) is not crosscut. Photo Alan Hill.

Recrystallization features—Much of the massive gypsum in Guadalupe caves is recrystallized, sometimes so severely as to completely obscure primary textures. Recrystallization is especially apparent in overgrowth crusts which are typically covered with tabular gypsum crystals 2-3 mm long and 1 mm thick. In Hell Below Cave, recrystallization has produced large crystal faces and perhaps even flower-like forms in the archway of gypsum in the Gyp Joint. Recrystallization may account for the lath-like gypsum laminae which were seen in thin section, and it may also be an alternative explanation for laminations which cross-cut inclusions (Fig. 54).

Dissolution features

In addition to textural features, gypsum deposits in Guadalupe caves exhibit a variety of dissolution features.

Drip tubes—Gypsum is a soluble material and dripping water readily dissolves vertical holes in blocks. Good (1957) first named such dripping water forms in gypsum "drip tubes," and they have been subsequently referred to as "drip-drill pits" or "drill holes." Drip tubes in gypsum are always vertical (if the gypsum has not been tilted subsequent to drilling). They are found beneath limestone pendants, joints, or stalactites where water drips into the cave, and they are usually vertically fluted due to slight positional changes in the overhanging drip (Figs. 55, 57). In rare instances, drip tubes can become filled with carbonate speleothems such as stalagmites; the dripping water first carves out the tube and then the stalagmite fills it (Fig. 56).

Where a drip tube extends entirely through a gypsum block, water drops splash onto the floor limestone and create a spray. The spray of water then dissolves the bottom of the gypsum block into a dome-shaped form concentric around the drip tube. Such "splash undercuts," can be observed in the gypsum blocks of the Polar Regions, Big Room, Carlsbad Cavern, where they are about 1 m in diameter (Figs. 55, 57).

FIGURE 55—A drip tube and splash undercut, Salt Flats, Big Room, Carlsbad Cavern. A drip tube forms where dripping water drills a vertical hole in the gypsum. A splash undercut forms where dripping water impacts the bedrock floor and then splashes in a radial pattern so as to create a circular zone of solution in the gypsum directly below the drip tube. The tube is vertically fluted due to slight shifts in the drip point. Photo Alan Hill.

FIGURE 56—Underside of a gypsum block, Big Room, Carlsbad Cavern, showing a stalagmite which has filled a drip tube in gypsum. Photo Alan Hill.

Commode holes—They resemble drip tubes in that, as viewed from above, they possess round to ellipsoidal holes, but they differ from drip holes in size, spatial configuration, and origin (Fig. 57). Typically, commode holes are of larger circumference than drip tubes, being about 15-100 cm in diameter; also, they are smooth on their insides and have overhanging upper lips or a rounded crown of gypsum partially rimming the hole. Commode holes also differ from drip tubes in that (1) they do not correspond to overhead limestone pendants, joints, or stalactites; (2) they are not necessarily vertical, but often have sloping insides; (3) they are never vertically fluted, but may be horizontally grooved; and (4) their position is a continuation of holes in the floor limestone (Figs. 44, 57). Commode holes are best developed in gypsum blocks that have been case-hardened on their outer surfaces, but still have granular and uncompacted interiors. The softer, interior gypsum is dissolved away preferentially between the case-hardened upper surface of gypsum and the underlying bedrock limestone.

FIGURE 57—A comparison of a commode hole and a drip tube, two dissolution features in gypsum. (click on image for a PDF version)

Commode holes have been identified in Glacier Bay, Lechuguilla Cave, the upper Gypsum Passage, Cottonwood Cave, the Big Room, Carlsbad Cavern, the Gyp Joint, Hell Below Cave, and the entrance area, Spider Cave, but they are best developed in the McKittrick Hill caves, especially in the Lower Maze, Endless Cave (Kunath, 1978). Many of the commode holes in Endless Cave have been modified by gypsum-rim speleothemic material along their tops, and this has caused them to assume bizarre shapes. The Commode of Endless Cave is the classic form of a compound commode hole-rim speleothem feature: the commode hole in this formation extends 1.5 m below floor level where it connects with a maze of small holes in the limestone, and the rim part of this formation projects about 1 m up and around the hole (Fig. 58). Commode holes are usually not vertical; the few vertical ones are called "post holes." Exceptionally large post-hole commodes occur in Glacier Bay, Lechuguilla Cave, and at the Polar Regions of the Big Room, Carlsbad Cavern. The largest of the Carlsbad ones, the "Giant's Commode," is 2 m wide and 2.5 m deep; the largest in Lechuguilla are 3 m wide and 10 m deep. In the upper Gypsum Passage, Cottonwood Cave, a post hole in a gypsum block has exposed an overgrowth crust and a partially replaced dolomite inclusion.

FIGURE 58—"The Commode," Lower Maze, Endless Cave. The 1.8 m tall caver is standing in a 1.5 m deep hole in bedrock which is a continuation of the commode hole. A rim of gypsum surrounds the caver's head. Photo Alan Hill.

Occasionally, commode holes can be found in other unconsolidated material, such as silt. In the Hall of the White Giant, Carlsbad Cavern, at the bottom of the first pit, is a post hole 0.2 m in diameter and 0.5 m deep in laminated silt. Other commode holes in the silt are not vertical, but wind their way through the silt like worm holes.

Streamlined surfaces—Many gypsum blocks exhibit extremely smooth, rounded surfaces, especially near pits or in areas where one cave level connects with another. Good examples of streamlined gypsum blocks can be seen in the Big Room of Carlsbad Cavern at the Bottomless Pit (Fig. 38), and next to the pits near the Jumping Off Place. In the Talcum Passage, Carlsbad Cavern, gypsum which is highly scoured along its bottom side completely obstructs a fissure (J. McLean, pers. comm. 1979). Also, many of the gypsum blocks in the Talcum Passage show a high degree of rounding (Fig. 41). Other notable examples of streamlined gypsum occur in the upper Gypsum Passage, Cottonwood Cave, where, like in the Talcum Passage, the undersides of many of the gypsum blocks are smooth and scoured-looking. In the Mud Crack Room, Endless Cave, gypsum blocks are truncated flush with the limestone against which they rest, and in the Expressway Passage, Dry Cave, a 1 m high gypsum pillar has been dissolved concordant with the walls and ceiling (Pl. 5A).

Scallops—In the lower Gypsum Passage, Cottonwood Cave, directly next to the floor gate, is a collapse block of gypsum containing scallop marks on its surface (Fig. 59).

FIGURE 59—Scallops in a gypsum block, lower Gypsum Passage, Cottonwood Cave. Photo Bob Trout.

Molds and casts—In the Alabaster Balcony, Virgin Cave, dissolution of a gypsum block has left an unusual form: a 0.6 m high tube of calcite 7.5 cm in diameter, which is a cast of a drip tube in gypsum (D. Davis, pers. comm. 1984). The cast formed like a conulite speleothem does in mud: calcite lined a drip tube in gypsum, and when the gypsum was removed by erosion, the more resistant calcite cast was left standing.

A possible mold of a gypsum block exists in the Crystal Springs Dome region of Carlsbad Cavern, where a flow stone cascade about 2 m² surrounds a pentagonal hole. This hole may possibly be a mold of a gypsum block which was dissolved away as the flowstone deposited over it.

Chert

Chert is a dense, cryptocrystalline, amorphous variety of quartz which displays conchoidal fracture. The only Guadalupe cave in which chert has been found is Carlsbad Cavern, and there it occurs as an up to 40 cm thick, gray to tan, chalcedonic chert interbedded with colorful silt deposits in a number of areas in the Big Room (Table 16).

TABLE 16—Chert deposits, Carlsbad Cavern.

The most impressive exposure of chert is in the area of the Salt Flats, Big Room, where 30-40 cm thick chert is interbedded with brick-red to ocher-yellow silt. The chert is not a continuous deposit in the silt but is lens-like, extending for about a meter or so, and then pinching out. Chert lenses are usually single deposits located near the top of a silt bank, but in one place in the Salt Flats' exposure, two lenses—one directly overlying the other but separated from it by about 5 cm of silt—can be seen between colorful silt layers. The silt bank of the Salt Flats has been excavated for trail building so that lenses of chert now lie on the floor where they were undermined of silt. One large piece of undermined chert, which has slid some distance toward the base of a silt bank and onto a gypsum block, displays a remarkable internal structure: three bands of finely laminated micritic chert, each 4-6 cm thick, are interbedded with three other, more porous, granular bands, each 6-9 cm thick (Pl. 5B). Other chert lenses also display this rhythmic sequence, but do not have as many bands. In all observed cases, a porous-chert band is at the bottom of a sequence, while a micritic layer is at the top. As seen in thin section, the porous layers display angular to well-rounded quartz grains 0.1-1 mm in diameter, contained in a matrix of chert. The micritic layers are composed of pure chert. Some minor calcite fills veins and pods in the porous layers, most usually in the zone between the micritic and porous sections.

Another important exposure of chert is in the Big Room along the Texas Trail next to a light fixture, where chert can be seen filling in polygonal cracks in the silt (Queen, 1981). Good exposures of chert showing stratigraphic relationship to other types of deposits in the Big Room also exist along the Texas Trail (near to the main trail) and under breakdown past the Salt Flats near the stalagmite called the Totem Pole (Fig. 70).

Endellite-montmorillonite-palygorskite

In Carlsbad Cavern and other caves of the Guadalupe Mountains, waxy, colorful (blue, blue-green, pure-white, and lavender) clay, and less waxy, soapy-feeling, colorful (gray-green, pink, brick-red, and brown) clay fills sponge-work pockets in the limestone or underlies clastic sediment. The waxy clay usually occurs as veins, pods, or stringers within the soapy-feeling clay, with a sharp color differentiation displayed by the two clay types.

Three minerals have been found to constitute these clay deposits: montmorillonite, (Na,Ca)_0.33(Al,Mg)₂ Si₄O₁₀(OH)₂·nH₂O; palygorskite (attapulgite), (Mg,Al)₂Si₄O₁₀(OH)·4H₂O; and endellite, Al₂Si₂O₃(OH)₄·2H₂O. Davis (1964a, b) reported that the soapy-feeling, gray-green deposits are composed of montmorillonite, with a minor amount of endellite. The pink deposits he found to be a mixture of roughly equal amounts of "attapulgite" and montmorillonite, ("Attapulgite" is an obsolete name for palygorskite; Fleischer, 1983.) At Davies' collection site in Lower Cave, Carlsbad Cavern, the pink "attapulgite"-rich clay directly overlies the gray-green montmorillonite clay, and both partially fill a phreatic solution pocket. The pink clay, which occurs in an exposed position in the pocket, has been hardened by calcite.

The montmorillonite clay is composed primarily of spherical aggregates ca 2.5-3.0 p.m in diameter plus a minor amount (<1%) of clay- and silt-size quartz. Trace amounts of feldspar, a fibrous mineral (possibly gypsum), and an extremely fine, black, opaque mineral (magnetite?) are present in the montmorillonite. The surface of one specimen had a brownish-red stain caused by the precipitation of iron minerals (limonite and some hematite) along a fracture.

The waxy clay mineral in Guadalupe caves is endellite. Endellite and its dehydration product, halloysite, are kaolinitic sheet-silicate minerals. Endellite is the stable mineral species under cave conditions of high humidity, but when removed from a cave to a less humid environment, it dehydrates rapidly and irreversibly to halloysite (Bates et al., 1950; Diamond and Bloor, 1970). Collected samples of the waxy mineral have been x-rayed and reported as the mineral halloysite by a number of investigators (Freisen, 1967; Davies and Moore, 1957; Davies, 1964a); however, since endellite is the actual mineral species in the caves, all such clay deposits are hereafter referred to as endellite.

Endellite and montmorillonite have been found primarily in Carlsbad Cavern (Sheet 2, green areas), but these minerals also occur in Cottonwood Cave, Endless Cave, and Dry Cave (Table 17). Bretz (1949) noted that the colorful clay deposits in Carlsbad Cavern have a vertical extent almost as great as the cave itself. The most extensive deposits in Carlsbad are in Lower Cave, where gray-green montmorillonite and, to a lesser extent, blue endellite fill sponge-work voids in the limestone (Pl. 6A). These clay deposits have dried, compacted, and cracked so that they are now sluffing out of the spongework and are piling up as talus debris on the cave floor.

TABLE 17—Endellite-montmorrillonite-palygorskite deposits in Guadalupe Caves.

Where endellite and montmorillonite occur together, the endellite forms veins, pods, nodules, and stringers within the surrounding montmorillonite matrix. For example, at the Top of the Cross, Big Room, and in the Mystery Room past the entrance to the Cable Slot, pure-white to light-blue, waxy endellite forms vein-like deposits between the limestone and surrounding brick-red clay matrix (Pl. 6B). Endellite-montmorillonite clay associations display various color combinations with the most usual being sky-blue or blue-green endellite in a matrix of gray-green montmorillonite, or pure-white endellite in an orange-red or brown matrix. Davies and Moore (1957, p. 24) reported: "white clay 6 in. to a foot thick in irregular beds consisting of nodules of the clay mineral endellite . . . in an orange red to brown clay bank in the New Mexico Room. On their outer surface is a layer of black angular quartz grains."

Sulfur

Elemental sulfur has been found in Lechuguilla Cave, Cottonwood Cave, and Carlsbad Cavern. In three of its six occurrences in these three caves, the sulfur is admixed with gypsum, and in three occurrences sulfur crystals directly coat bedrock and speleothems. The description of sulfur deposits in Guadalupe caves is summarized in Table 18.

TABLE 18—Native-sulfur deposits in Guadalupe Caves.

Two occurrences of sulfur exist in the lower Gypsum Passage of Cottonwood Cave, one near a large gypsum stalactite known as the Chandelier, and one about 80 m south of the Chandelier. Respectively, these two occurrences are: (1) a vein-like deposit 45 cm wide and 15 m long, in gypsum exposed along a ceiling joint (Davis, 1973; Pl. 7A); and (2) a crystalline deposit filling 1.2 m long and 0.3 m wide cavities within a gypsum block (Pl. 7B). In the vein-like occurrence near the Chandelier, the massive, dense, light-yellow sulfur sometimes projects out in relief from the gypsum in such a manner as to produce an almost stalactitic form. In the cavity occurrence, the gypsum block which encloses the crystalline, canary-yellow sulfur looks like it either slumped or fell into its present position on the floor. In both of these occurrences, the gypsum looks like it has been eroded away so as to expose the sulfur within it. A sample collected from the vein occurrence of sulfur was examined for the presence of sulfur bacteria. This examination proved negative; the sulfur had neither fossilized or living sulfur bacteria associated with it (D. Caldwell, pers. comm. 1980).

In Carlsbad Cavern, native sulfur is present in the Big Room, New Mexico Room, and in a side passage off of the Christmas Tree Room (Sheet 2, red dots). The Big Room sulfur is located at the Jumping Off Place, just past the second trail tunnel in a block of gypsum and about 2.5 m above the floor. The pale-yellow sulfur covers an area approximately 0.6 m high and 0.3 m wide, where it (1) resides on an overgrowth crust which lines a drip tube in the gypsum block, (2) occurs as a light covering on dense gypsum where the overgrowth crust has been eroded away, and (3) fills cracks separating the overgrowth crust and the more compacted underlying gypsum. The sulfur occurs on the underside of the cracks and surfaces.

The New Mexico Room sulfur is not admixed with gypsum, but rather directly coats limestone bedrock (Pl. 8A) and also subaerially formed gypsum flower and crustal speleothems (Pl. 8B). The sulfur crystals lightly cover the undersides or vertical faces of the bedrock or speleothems, but never the top sides.

The Christmas Tree Room sulfur directly overlies bedrock, crinkle blisters, and popcorn. It also coats, and fills the spaces between, indurated masses of stacked cave rafts. Where the crystals overlie bedrock, they usually occur on the undersides of dipping forereef beds or on projecting fins of limestone. The fins are covered with a thin (<1 mm), yellowish-brown, iron-rich, slaggy crust which directly underlies the sulfur crystals. Elsewhere on the bedrock surface, yellowish-brown "spots" occur with the sulfur crystals and are the same size as the crystals.

Speleothems

A speleothem is a secondary mineral deposit which has formed in a cave. Examples of speleothems are stalactites and stalagmites. Only those speleothem types that are related to speleogenesis problems are discussed in Part I; refer to Part II for a detailed discussion of all speleothem types that occur in Guadalupe caves.

Types related to speleogenesis

Spar—Dogtooth and nailhead spar line bedrock or fill solution cavities in the walls, ceilings, and floors of Guadalupe caves. Dogtooth spar consists of scalenohedrons of calcite and nailhead spar is a more blunted form of calcite consisting of combined flat rhombohedrons and prisms which display uneven-sided triangular patterns. Spar crystals are found in practically every cave in the Guadalupe Mountains, but the finest specimens occur in Carlsbad, Cottonwood, Three Fingers, Geode, Idono Crystal, Crystal, Virgin, Frank's, and Pink Fink Owlcove. The spar in Guadalupe caves can be very large (up to 50 cm in length), and some of it is colored (pale blue) or zoned (transparent centers overlain by an outer zone of milky calcite).

At least two spar episodes are clearly discernible in Guadalupe caves: (1) a spar matrix which fills the spaces between clasts in wall breccia (Fig. 67), and (2) large, well-developed spar crystals which protrude out from cavities or walls (Fig. 60). Large spar crystals are preserved in protected alcoves or spongework cavities. This relationship can best be seen in the Spar Room of the Secondary Stream Passage, Carlsbad Cavern, where large spar crystals occur in protected wall recesses, rounded and highly corroded spar occurs where the recesses open up into the Spar Room (Pl. 9A), and spar molds occur in the center of the room (Fig. 61). In a side passage off of Left Hand Tunnel, rounded and highly etched spar crystals, attached only by thin pieces of corroded limestone or crystalline calcite, project outward in relief from the wall.

FIGURE 60—Dogtooth-spar crystals, Guadalupe Room, Carlsbad Cavern. Photo Pete Lindsley.

FIGURE 61—Spar molds in limestone bedrock, Secondary Stream Passage, Carlsbad Cavern. Photo Ronal Kerbo.

In the Mystery Room, Carlsbad Cavern, nailhead spar predominates over dogtooth spar and occurs as columnar crystal linings overlying bedrock. In the Nailhead Spar Lining Room, at the very bottom of the Mystery Room, the crystal linings are 6-10 cm thick and are still in place except where a few sections have fallen to the floor, leaving a linoleum-like, triangular pattern imprinted on the bedrock. A large breakdown block in the middle of the Mystery Room (near the Mabel's Room Overlook) also displays the linoleum pattern, but the spar lining that once covered the breakdown has since been almost completely dissolved away.

Cave rafts—Thin planar deposits of calcite and aragonite which precipitate on the surface of a body of water. Cave rafts are a common speleothem type which form on the surfaces of many small cave pools (Pl. 13B). However, in Carlsbad Cavern this speleothem type takes on added significance because well-indurated cave rafts are found exposed in wall cavities where they overlie calcified siltstone (Fig. 39), and because huge conical piles of cave rafts (called cones) litter the floor in places such as the Balcony of the Lake of the Clouds Passage and the East Annex of the New Mexico Room. Three definable episodes of raft formation are displayed in Carlsbad Cavern: (1) Type 1 rafts, well-indurated deposits which are associated with underlying calcified siltstone and are truncated by the large cave passages; (2) Type 2 rafts, semiconsolidated rafts usually in the form of cave cones which occur in areas where the corrosion of speleothems and bedrock is pronounced; and (3) Type 3 rafts which can be seen floating on top of shallow cave pools or which have sunk to the floor of these pools. Type 1 and Type 2 cave rafts are believed related to speleogenesis problems and are discussed in this part of the paper. Type 3 rafts are discussed in Part II.

Type 1 rafts have been significantly widened by post-depositional calcite (an estimated 80% of their mass is post-depositional), and individual rafts have become cemented together with calcite so that they appear stacked like shingled plates (Fig. 39). These consolidated cave rafts usually directly overlie calcified siltstone without any other type of deposit intermediate in the sequence, and they are always the topmost deposit of a sequence, with either air space or subaerially formed travertine above the rafts. In their association with calcified siltstone, Type 1 cave rafts appear to have been packed into wall solution pockets before truncation by the large cave passages.

Type 2 rafts and cones of the Lake of the Clouds and East Annex areas also overlie silt, but both the silt and rafts are not well indurated. In the New Section, Carlsbad Cavern, the consolidation of floor rafts is more complete, but the silt underlying the rafts is not similarly indurated. In the Hall of the White Giant, at the bottom of the first pit, semi-indurated raft ledges 15-20 cm thick extend out from the wall, while laminated, non-indurated silt has compacted about 0.3 m beneath the ledges. Even lower in the New Section, raft bridges reportedly extend across the floor of the passage (D. Davis, pers. comm. 1984).

Popcorn—A type of knobular-shaped coralloid speleothem which decorates many cave passages in the Guadalupe Mountains. Usually this speleothem has no significance to speleogenesis problems, but in Hell Below Cave and Carlsbad Cavern "popcorn lines" cover walls and/or speleothems, lines which may possibly relate to speleogenesis events.

Moore (1960a) was the first to comment on the popcorn line in Carlsbad Cavern, and suggested that there might be a correlation between the level of the line and the tops of the gypsum blocks in the Big Room. Moore's suggestion has not been substantiated by recent leveling surveys (Table 19). The tops of the gypsum blocks at the Jumping Off Place in the Big Room are almost 6 m higher than the nearest popcorn line at the Temple of the Sun. It is probably just a coincidence that the gypsum blocks and popcorn line are nearly at the same elevation in the Big Room, since gypsum blocks exit in many other Guadalupe caves that do not have popcorn lines. Thrailkill (1965b) thought the line was an upper limit of a splash zone, while Jagnow (1977) thought it was a "waterline" corresponding to a past base level. Geologists M. Queen and J. McLean have informally hypothesized that air currents might be the cause of the line: dry-air currents moving into the cave could cause more evaporation and subsequent popcorn development near the floor, while more humid-air currents going out of the cave could be responsible for a lack of popcorn near the ceiling.

The popcorn line in Carlsbad Cavern is characterized by the following features:

(1) The line corresponds to a position of maximum passage width or "notch" in the passage, and it is marked by popcorn growth below the line, but not above it (Pl. 9B). The top of the line is not sharp; it is a zone 0.3-0.6 m thick.

(2) The line is nearly horizontal all the way along Left Hand Tunnel and the Big Room, with an average dip of only 1° that Jagnow (1979) ascribed to regional tilting subsequent to passage development.

(3) The line near the Green Lake Room is at exactly the same elevation as the line in the Big Room-Left Hand Tunnel (Table 19), even though the two localities are in different parts of the cave (Fig. 62).

TABLE 19—Comparison of altitudes of the tops of gypsum blocks and the popcorn line, Carlsbad Cavern.

FIGURE 62—Distribution of the popcorn line in Carlsbad Cavern. (click on image for a PDF version)

(4) In many places in the Left Hand Tunnel, Big Room, Secondary Stream Passage, and elsewhere, sprays of flat-bottomed popcorn (trays) occur below the line.

(5) The popcorn line is associated with pronounced corrosion: above the line speleothems and bedrock are highly corroded, whereas below the line they are not corroded.

(6) According to Jagnow (1979), the line disappears in the Big Room just south of the Hall of Giants, descending abruptly near the Temple of the Sun. Also, the line seems to "fall" into cross joints, with 30° dips over short distances (M. Queen, pers. comm. 1983).

(7) Except for the Green Lake area, the main popcorn line is not recorded at the Big Room level in other areas such as the New Mexico Room or Appetite Hill. Vague lines do occur in the Mystery Room and Lower Cave below the level of the Big Room.

(8) The popcorn of the popcorn line covers massive speleothems, both in the Lion's Tail area of the Big Room and in the Green Lake Room area of the cave.

(9) The line is not directly associated with pool speleothems such as rimstone, shelfstone, cave rafts, or subaqueous coralloids or coatings.

Rims—A cave rim is a projection of crystalline material on bedrock or speleothems which is smooth and scoured on the inside and rough and coralline on the outside. In Guadalupe caves, rims are composed of either carbonate (usually aragonite) or sulfate (gypsum) material. Sulfate rims line commode holes in gypsum blocks and these can build up around the commode hole so as to create bizarre shapes (Fig. 58). Carbonate rims line holes in bedrock or form as a continuation of a corroded area on speleothems (Fig. 63). They are another speleothem type associated with corrosion and late-stage speleogenesis events.

FIGURE 63—A carbonate rim on the flank of the Creeping Ear stalagmite, Lake of the Clouds Passage, Carlsbad Cavern. The banded area on the right is the corroded part of the stalagmite; the thin, white, crystalline shell to which the ruler is pointing is the rim. Both the stalagmite layers and the rim are corroded concordant with each other. Photo Cyndi Mosch Seanor.

Corrosion features

Many speleothems are severely corroded in sections of Carlsbad Cavern, Spider Cave, and Wind (Hicks) Cave. Chalk-white and flaky, they assume an almost ghostly appearance (Pl. 10A). In some cases, these speleothems have been corroded down to their very cores along with adjacent corrosion of cave walls and ceilings (Pl. 10B). The speleothems look almost as if they have been wind-eroded because they are planed off concordant with the bedrock (Palmer and Palmer, 1975; Hill, 1976c, 1979). Speleothems in Spider Cave are highly corroded in the Ghost Chambers, a series of rooms named for their "unearthly ... dead, chalk-like stalagmites and curtains" (Nymeyer, 1938, p. 40). Corrosion features are most dramatically represented in Carlsbad Cavern in the Left Hand Tunnel, Lake of the Clouds-Bell Cord Room-Bifrost Room area, Mystery Room, Taffy Hill, and East Annex and Balcony areas of the New Mexico Room. Corroded speleothems include stalactites, stalagmites, draperies, and "cloud" linings (Fig. 64). In sections of Carlsbad Cavern where speleothem corrosion is pronounced, and also in Spider and Wind (Hicks) Caves, two generations of speleothems are recognizable: (1) chalk-white, corroded speleothems which grew prior to corrosion, and (2) "normal," uncorroded speleothems which grew subsequent to corrosion (Pl. 11A). The first generation of speleothems is often corroded on one side and in a preferred direction (Fig. 63). In the Lake of the Clouds-Bell Cord Room-Bifrost Room area, the direction of corrosion consistently points towards the Lake of the Clouds (Fig. 93). In the upper part of the Mystery Room, the direction of corrosion faces the Cable Slot, not towards the lower chambers of the room (where speleothems are uncorroded).

FIGURE 64—Corroded cloud linings with exposed layers of black manganese, Balcony, Lake of the Clouds, Carlsbad Cavern. Photo Pete Lindsley.

Corroded stalagmites may be preferentially weathered along one side (Fig. 63), or they may possess hollow centers. A stalagmite and its hollow center form from the same drip point on the ceiling; the stalagmite formed from saturated water, the hollow center from undersaturated and corrosive water. Hollow-centered stalagmites of calcite and aragonite occur in the Big Room (along the trail) and in the Christmas Tree Room near the Lake of the Clouds Passage.

Bat guano

Carlsbad Cavern is world-famous for its bats. Allison (1937, p. 80) estimated that the cavern had a population of over 8.7 million bats, and compared an evening bat flight to "smoke pouring out from a volcano." The bats usually reside in Bat Cave (the upper level of Carlsbad), but isolated bats can also be seen in other parts of the cave and at any level, either live or mummified (Baker, 1963, Fig. 102). Likewise, bat guano is found at all levels in the cavern. The guano is in various stages of decay; it ranges from fresh, pungent droppings to material unrecognizable except by a chemical analysis (Table 20). Other Guadalupe caves that contain extensive bat-guano deposits are Dry Cave, McKittrick Hill; White Mule Cave, Big Canyon; and Ogle and New Caves, Slaughter Canyon, both of which were mined for guano in the 1930's and 1940's.

TABLE 20—Composition of bat guano in Carlsbad Cavern and New Cave.

Decayed bat guano closely resembles cave silt and much care must be taken to distinguish between these two types of deposits. In general, bat guano is more uncompacted and fluffy than clastic silt; one typically sinks down into guano but stands firm on silt. Bat bones are usually present in guano and absent in silt, but this is not a hard and fast rule because bats can fall into cave silt or bat guano can be mixed with large amounts of silt.

The bat guano of New Cave is unusual in that it has a high silica (silt) content (D. DesMarais, pers. comm. 1983). Also, bat bones in the guano-silt have a distribution which suggests that they have been water-washed (S. Altenbach, pers. comm. 1983). Heavier jaw bones and solid finger bones tend to be located deeper in the guano deposits, whereas lighter long bones and skull parts tend to be located near the top of the deposit.

Animal bones

Animal bones have been found in Carlsbad Cavern, Musk Ox Cave (Fig. 65), Dry Cave, Hermit's Cave, Burnet (Rocky Arroyo) Cave, Pratt Cave, Dust Cave, Upper Sloth Cave, Lower Sloth Cave, Pink Panther Cave, Dark Canyon Cave, and Williams Cave (Table 21). One of the most important of these paleontological finds is the ground sloth, Nothrotheriops shastensis, discovered in Lower Devil's Den, Carlsbad Cavern, in 1947 and then at another site in the cave (which has not been relocated) in 1959 (Hill and Gillette, 1985, 1987). Most of the sloth bone fragments that still remain in Lower Devil's Den are highly disturbed, but a few in-situ shards of bone on top of undisturbed silt occur in a 4-5 m radius around the site and look as if they might have been gently washed and water-laid. At the second site, the bones were covered by a thin coating of mud.

FIGURE 65—Bush-ox bones in Musk Ox Cave. Photo Ronal Kerbo.

TABLE 21—Paleontology of Guadalupe Caves.